Patent Application
20240352606
The present invention relates, in a first aspect, to a dividing wall W suitable for use in an electrolysis cell E. The dividing wall W comprises a frame element R that forms an edge element RR and a separating element RT. The frame element R comprises two opposite parts R1 and R2, with at least two alkali metal cation-conducting solid-state ceramics FA and FB disposed therebetween. The separating element RT lies between the alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W and separates these from one another.
It is a feature of the invention that the two parts R1 and R2 are secured to one another by at least one securing element BR at the edge element RR and at least one securing element BT at the separating element RT.
Compared to the cases according to the prior art in which the dividing wall W encompasses the solid-state electrolyte in one piece, this arrangement is firstly more flexible since the individual ceramics have more degrees of freedom available in order to react to fluctuations in temperature, for example by shrinkage or expansion. This increases stability with respect to mechanical stresses in the ceramic. At the same time, the mechanical stability of the arrangement of the at least two solid-state electrolyte ceramics between the parts R1 and R2 is increased in that the parts R1 and R2 are secured to one another both at the edge element RR and at the separating element RT by at least one securing element BR or BT.
In a second aspect, the present invention relates to an electrolysis cell E encompassing a cathode chamber KK divided by the dividing wall W from the adjacent chamber, which is an anode chamber KA or a middle chamber KM of the electrolysis cell E.
In a third aspect, the present invention relates to a process for producing an alkali metal alkoxide solution in the electrolysis cell E according to the second aspect of the invention.
The electrochemical production of alkali metal alkoxide solutions is an important industrial process which is described, for example, in DE 103 60 758 A1, US 2006/0226022 A1 and WO 2005/059205 A1. The principle of these processes is reflected in an electrolysis cell in which the solution of an alkali metal salt, for example sodium chloride or NaOH, is present in the anode chamber, and the alcohol in question or an alcoholic solution with a low concentration of the alkali metal alkoxide in question, for example sodium methoxide or sodium ethoxide, is present in the cathode chamber. The cathode chamber and the anode chamber are separated by a ceramic that conducts the alkali metal ion used, for example NaSICON or an analogue for potassium or lithium. On application of a current, chlorine forms at the anode—when a chloride salt of the alkali metal is used—and hydrogen and alkoxide ions at the cathode. The charge is balanced in that alkali metal ions migrate from the middle chamber into the cathode chamber via the ceramic that is selective therefor. The balancing of charge between middle chamber and anode chamber results from the migration of cations when cation exchange membranes are used or the migration of anions when anion exchange membranes are used, or from migration of both ion types when non-specific diffusion barriers are used. This increases the concentration of the alkali metal alkoxide in the cathode chamber, and the concentration of the sodium ions in the anolyte is lowered.
NaSICON solid-state electrolytes are also used in the electrochemical production of other compounds:
WO 2014/008410 A1 describes an electrolytic process for producing elemental titanium or rare earths. The basis of this process is that titanium chloride is formed from TiO2 and the corresponding acid, and this is reacted with sodium alkoxide to give titanium alkoxide and NaCl and finally converted electrolytically to elemental titanium and sodium alkoxide.
WO 2007/082092 A2 and WO 2009/059315 A1 describe processes for producing biodiesel, in which, with the aid of alkoxides produced electrolytically by means of NaSICON, triglycerides are first converted to the corresponding alkali metal triglycerides and are reacted in a second step with electrolytically generated protons to give glycerol and the respective alkali metal hydroxide.
However, these solid-state electrolyte ceramics typically have some disadvantages. In the operation of the electrolysis cell, there will inevitably be fluctuations in temperature in the cell, which result in expansion or shrinkage of the solid-state electrolyte ceramic. Since these ceramics are brittle, this can lead to fracture of the ceramic.
This problem arises particularly in the constantly repeating startup and shutdown processes that are unavoidable in the operation of electrolysis. During the heating and cooling, there are expansion and shrinkage phases, which results in movement of the ceramic back and forth in the electrolysis cell. These movements, on account of the uncontrolled distribution of forces in the ceramic, can cause it to break.
This can result in losses of integrity that can lead to leakage of brine into alcohol or vice versa. As a result, the product of the electrolysis—the alkoxide solution—is watered down. In addition, the electrolysis cell itself can also lose integrity and leak.
It was therefore the object of the present invention to provide an electrolysis cell that does not have these disadvantages.
A further disadvantage of conventional electrolysis cells in this technical field arises from the fact that the solid-state electrolyte does not have long-term stability with respect to aqueous acids. This is problematic in that, during the electrolysis in the anode chamber, the pH falls as a result of oxidation processes (for example in the case of production of halogens by disproportionation or by oxygen formation). These acidic conditions attack the NaSICON solid-state electrolyte to such a degree that the process cannot be used on an industrial scale. In order to counter this problem, various approaches have been described in the prior art.
For instance, three-chamber cells have been proposed in the prior art. These are known in the field of electrodialysis, for example U.S. Pat. No. 6,221,225 B1.
WO 2012/048032 A2 and US 2010/0044242 A1 describe, for example, electrochemical processes for producing sodium hypochlorite and similar chlorine compounds in such a three-chamber cell. The cathode chamber and the middle chamber of the cell are separated here by a solid-state electrolyte permeable to cations, for example NaSICON. In order to protect this from the acidic anolyte, the middle chamber is supplied, for example, with solution from the cathode chamber. US 2010/0044242 A1 also describes, in
Such cells have also been proposed in the prior art for the production or purification of alkali metal alkoxides.
For instance, U.S. Pat. No. 5,389,211 A describes a process for purifying alkoxide solutions in which a three-chamber cell is used, in which the chambers are delimited from one another by cation-selective solid-state electrolytes or else nonionic dividing walls. The middle chamber is used as buffer chamber in order to prevent the purified alkoxide or hydroxide solution from the cathode chamber from mixing with the contaminated solution from the anode chamber.
DE 42 33 191 A1 describes the electrolytic recovery of alkoxides from salts and alkoxides in multichamber cells and stacks of multiple cells.
WO 2008/076327 A1 describes a process for producing alkali metal alkoxides. This uses a three-chamber cell, the middle chamber of which has been filled with alkali metal alkoxide (see, for example, paragraphs [0008] and [0067] of WO 2008/076327 A1). This protects the solid-state electrolyte separating the middle chamber and the cathode chamber from the solution present in the anode chamber, which becomes more acidic in the course of electrolysis. A similar arrangement is described by WO 2009/073062 A1. However, this arrangement has the disadvantage that the alkali metal alkoxide solution which is consumed as buffer solution and continuously contaminated is the desired product. A further disadvantage of the process described in WO 2008/076327 A1 is that the formation of the alkoxide in the cathode chamber depends on the diffusion rate of the alkali metal ions through two membranes or solid-state electrolytes. This in turn leads to slowing of the formation of the alkoxide.
A further problem results from the geometry of the three-chamber cell. The middle chamber in such a chamber is separated from the anode chamber by a diffusion barrier and from the cathode chamber by an ion-conducting ceramic. During the electrolysis, this results unavoidably in development of pH gradients and in dead volumes. This can damage the ion-conducting ceramic and, as a result, increase the voltage demand of the electrolysis and/or lead to fracture of the ceramic.
While this effect takes place throughout the electrolysis chamber, the drop in pH is particularly critical in the middle chamber since this is bounded by the ion-conducting ceramic. Gases are typically formed at the anode and the cathode, such that there is at least some degree of mixing in these chambers. By contrast, no such mixing takes place in the middle chamber, such that the pH gradient develops therein. This unwanted effect is enhanced by the fact that the brine is generally pumped relatively slowly through the electrolysis cell.
It was therefore a further object of the present invention to provide an improved process for electrolytic production of alkali metal alkoxides, and also an electrolysis cell especially suitable for such a process. These are not to have the aforementioned disadvantages, and are especially to assure improved protection of the solid-state electrolyte prior to the formation of the pH gradient and more sparing use of the reactants compared to the prior art.
The problem addressed by the invention is solved by a dividing wall W according to the first aspect of the invention. The dividing wall W <16> comprises one side SKK <161> having the surface OKK <163> and, opposite the side SKK <161>, a side SA/MK <162> having the surface OA/MK <164>.
The dividing wall W <16> also encompasses a frame element R <2> composed of two opposite parts R1 <201> and R2 <202>, with at least two alkali metal cation-conducting solid-state electrolyte ceramics FA <18> and FB <19> disposed therebetween.
At the same time, R1 <201> is directly contactable via the surface OKK <163>, and R2 <202> is directly contactable via the surface OA/MK <164>.
The frame element R <2> forms a frame element RR <20> and a separating element RT <17>, with the frame element RR <20> bounding, preferably fully surrounding, the surfaces OKK <163> and OA/MK <164>, and with the frame element RT <17> lying between the alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W <16> and dividing these from one another, such that the alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W <16> are directly contactable both via the surface OKK <163> and via the surface OA/MK <164>.
The dividing wall W <16> is characterized in that R1 <201> and R2 <202> are secured to one another by at least one securing element BR <91> at the edge element RR <20>, and R1 <201> and R2 <202> are secured to one another by at least one securing element BT <92> at the separating element RT <17>.
In a second aspect, the present invention relates to an electrolysis cell E <1> comprising
In a third aspect, the present invention relates to a process for producing a solution L1 of an alkali metal alkoxide XOR in the alcohol ROH, where X is an alkali metal cation and R is an alkyl radical having 1 to 4 carbon atoms,
The cathode chamber KK <12> comprises a cathodic electrode EK <123> in the interior IKK <122>, an inlet ZKK <120> and an outlet AKK <121>.
The anode chamber KA <11> comprises an anodic electrode EA <113> in the interior IKA <112>, an inlet ZKK <110> and an outlet AKA <111>.
The two chambers are bounded by an outer wall <80> of the two-chamber cell E. The interior IKK <122> is also divided from the interior IKA <112> by a dividing wall consisting of a sheet of a NaSICON solid-state electrolyte FA <18> which is selectively permeable to sodium ions. The NaSICON solid-state electrolyte FA <18> extends over the entire depth and height of the two-chamber cell E. The dividing wall has two sides SKK <161> and SA/MK <162>, the surfaces OKK <163> and OA/MK <164> of which contact the respective interior IKK <122> or IKA <112>.
An aqueous solution of sodium chloride L3 <23> with pH 10.5 is introduced via the inlet ZKA <110>, counter to the direction of gravity, into the interior IKA <112>.
A solution of sodium methoxide in methanol L2 <22> is routed into the interior IKK <122> via the inlet ZKK <120>.
At the same time, a voltage is applied between the cathodic electrode EK <123> and the anodic electrode EA <113>. This results in reduction of methanol in the electrolyte L2 <22> to give methoxide and H2 in the interior IKK <122> (CH3OH+e−→CH3O−+½ H2). At the same time, sodium ions diffuse from the interior IKA <112> through the NaSICON solid-state electrolyte FK <18> into the interior IKK <122>. Overall, this increases the concentration of sodium methoxide in the interior IKK <122>, which affords a methanolic solution of sodium methoxide L1 <21> having an elevated sodium methoxide concentration compared to L2 <22>.
In the interior IKA <112>, the oxidation of chloride ions takes place to give molecular chlorine (Cl−→½ Cl2+e−). In the outlet AKA <111>, an aqueous solution L4 <24> is obtained, in which the content of NaCl is reduced compared to L3 <23>. Chlorine gas (Cl2) in water, according to the reaction Cl2+H2O→HOCl+HCl, forms hypochlorous acid and hydrochloric acid, which give an acidic reaction with further water molecules. The acidity damages the NaSICON solid-state electrolyte FA <18>.
The cathode chamber KK <12> comprises a cathodic electrode EK <123> in the interior IKK <122>, an inlet ZKK <120> and an outlet AKK <121>.
The anode chamber KA <11> comprises an anodic electrode EA <113> in the interior IKA <112>, an inlet ZKK <110> and an outlet AKA <111>.
The middle chamber KM <13> comprises an interior IKM <132>, an inlet ZKM <130> and an outlet AKM <131>.
The interior IKA <112> is connected to the interior IKM <132> via the connection VAM <15>.
The three chambers are bounded by an outer wall <80> of the three-chamber cell E. The interior IKM <132> of the middle chamber KM <13> is also divided from the interior IKA <122> of the cathode chamber KK <12> by a dividing wall consisting of a sheet of a NaSICON solid-state electrolyte FA <18> which is selectively permeable to sodium ions. The NaSICON solid-state electrolyte FA <18> extends over the entire depth and height of the three-chamber cell E. The dividing wall has two sides SKK <161> and SA/MK <162>, the surfaces OKK <163> and OA/MK <164> of which contact the respective interior IKK <122> or IKM <132>.
The interior IKM <132> of the middle chamber KM <13> is additionally divided in turn from the interior IKA <112> of the anode chamber KA <11> by a diffusion barrier D <14>. The NaSICON solid-state electrolyte FA <18> and the diffusion barrier D <14> extend over the entire depth and height of the three-chamber cell E. The diffusion barrier D <14> is a cation exchange membrane (sulfonated PTFE).
In the embodiment according to
An aqueous solution of sodium chloride L3 <23> with pH 10.5 is introduced via the inlet ZKM <130>, in the direction of gravity, into the interior IKM <132> of the middle chamber KM. The connection VAM <15> formed between an outlet AKM <131> from the middle chamber KM <13> and an inlet ZKA <110> to the anode chamber KA <11> connects the interior IKM <132> of the middle chamber KM <13> to the interior IKA <112> of the anode chamber KA <11>. Sodium chloride solution L3 <23> is routed through this connection VAM <15> from the interior IKM <132> into the interior IKA <112>. A solution of sodium methoxide in methanol L2 <22> is routed into the interior IKK <122> via the inlet ZKK <120>.
At the same time, a voltage is applied between the cathodic electrode EK <123> and the anodic electrode EA <113>. This results in reduction of methanol in the electrolyte L2 <22> to give methoxide and H2 in the interior IKK <122> (CH3OH+e−→CH3O−+½ H2). At the same time, sodium ions diffuse from the interior IKM <132> of the middle chamber KM <13> through the NaSICON solid-state electrolyte FA <18> into the interior IKK <122>. Overall, this increases the concentration of sodium methoxide in the interior IKK <122>, which affords a methanolic solution of sodium methoxide L1 <21> having an elevated sodium methoxide concentration compared to L2 <22>.
In the interior IKA <112>, the oxidation of chloride ions takes place to give molecular chlorine (Cl−→½ Cl2+e−). At the outlet AKA <111>, an aqueous solution L4 <24> is obtained, in which the content of NaCl is reduced compared to L3 <23>. Chlorine gas (Cl2) in water, according to the reaction Cl2+H2O→HOCl+HCl, forms hypochlorous acid and hydrochloric acid, which give an acidic reaction with further water molecules. The acidity would damage the NaSICON solid-state electrolyte FA <18>, but is restricted to the anode chamber KA <11> by the arrangement in the three-chamber cell, and hence kept away from the NaSICON solid-state electrolyte FK <18> in the electrolysis cell E. This considerably increases the lifetime thereof.
The dividing wall W <16> comprises two NaSICON solid-state electrolyte ceramics FA <18> and FB <19> disposed between a frame element R <2>. The frame element R <2> comprises two parts R1 <201> and R2 <202>, between which the ceramics FA <18> and FB <19> are disposed. The frame element R <2> here forms an edge element RR <20> and a separating element RT <17>. The separating element RT <17> lies between the NaSICON solid-state electrolyte ceramics FA <18> and FB <19> and separates these from one another. The separating element RT <17> is the part of the frame element R <2> shown in shaded form in
In
In the cross section QRT <166>, the two solid-state electrolyte ceramics FA <18> and FB <19> are disposed between the two frame parts R1 <201> and R2 <202> which form the separating element RT <17> here. They are secured to one another by a screw as securing element BT <92> and clamp the solid-state electrolyte ceramics FA <18> and FB <19> between them, preferably with provision of a seal Di <40>.
In this case, in the embodiment according to
In the embodiment according to
1. The connection VAM <15> from the interior IKM <132> of the middle chamber KM <13> to the interior IKA <112> of the anode chamber KA <11> is formed not outside the electrolysis cell E <1>, but rather inside through a perforation in the diffusion barrier D <14>. This perforation may be made in the diffusion barrier D <14> or may already have been present therein from the outset in the production of the diffusion barrier D <14> (for example in the case of textile fabrics such as filter cloths or metal weaves).
2. In the embodiment according to
The separating element RT <17> is the part of the frame element R <2> shown in shaded form in
This comprises four NaSICON solid-state electrolyte ceramics FA <18>, FB <19>, FC <28> and FD <29>, which are disposed between two halves R1 <201> and R2 <202> of a frame element R <2>. The frame element R <2> here forms an edge element RR <20> and a separating element RT <17>. The separating element RT <17> is cross-shaped and lies between the NaSICON solid-state electrolyte ceramics FA <18>, FB <19>, FC <28> and FD <29>, and separates these from one another. The separating element RT <17> is the part of the frame element R <2> shown in shaded form in
The present invention relates in a first aspect to a dividing wall W. This is especially suitable as a dividing wall in an electrolysis cell, especially an electrolysis cell E.
In one aspect, the present invention thus also relates to an electrolysis cell comprising the dividing wall W, especially an electrolysis cell E comprising the dividing wall W.
The dividing wall W comprises at least two alkali metal cation-conducting solid-state electrolyte ceramics (“alkali metal cation-conducting solid-state electrolyte ceramic” is abbreviated hereinafter as “ASC”) FA and FB, separated from one another by a separating element RT.
The dividing wall W comprises two sides SKK and SA/MK that are opposite one another, meaning that side SA/MK is opposite side SKK (and vice versa). The two sides SKK and SA/MK especially comprise planes that are essentially parallel to one another.
The geometry of the dividing wall W is otherwise subject to no further restriction, and may be matched in particular to the cross section of the electrolysis cell E in which it is used. For example, it may have the geometry of a cuboid and hence have a rectangular cross section, or the geometry of a frustocone or cylinder and accordingly a circular cross section.
Optionally, the dividing wall W may also have the geometry of a cuboid with rounded corners or bulges which may in turn have holes. The dividing wall W then has bulges (“rabbit's ears”) by which the dividing wall W can be fixed to electrolysis cells, or else the two frame parts R1 and R2 of the dividing wall W can be fixed to one another.
The side SKK of the dividing wall W has the surface OKK, and the side SA/MK of the dividing wall W has the surface OA/MK.
The dividing wall W encompasses a frame element R. This comprises two opposite parts, preferably halves, R1 and R2, with at least two alkali metal cation-conducting solid-state ceramics FA and FB disposed therebetween. R1 is directly contactable via the surface OKK; R2 is directly contactable via the surface OA/MK.
The frame element R forms a frame element RR and a separating element RT, with the frame element RR bounding and preferably fully surrounding the surfaces OKK and OA/MK, and with the frame element RT lying between alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W and separating these from one another,
What is meant by the feature “dividing wall” is that the dividing wall W is liquid-tight. This means that the ASCs and the frame element R gaplessly adjoin one another. Thus, no gaps exist between frame element R and the ASCs encompassed by the dividing wall W, through which aqueous solution, alcoholic solution, alcohol or water could flow from the SKK side to the SA/MK side or vice versa.
If there are two or more pairs of opposite sides via the surfaces of which the alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W and the respective part R1 or R2 are directly contactable, the pair of opposite sides referred to as SKK and SA/MK in the context of the invention is preferably that pair which encompasses the greatest surface areas OKK and OA/MK. If the surface areas encompassed by two pairs of opposite sides are the same, the person skilled in the art can select one pair as SKK and SA/MK with surfaces OKK and OA/MK.
Among dividing walls W where there are two or more pairs of opposite sides via the surfaces of which the alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W and the respective part R1 or R2 are directly contactable, preference is given to the dividing walls W where the surface areas encompassed by the respective pair of opposite sides are different, in which case the pair of opposite sides referred to as SKK and SA/MK in the context of the invention is that which encompasses the greatest surface areas OKK and OA/MK.
The dividing wall W according to the first aspect of the present invention also includes embodiments in which the dividing wall W comprises more than two ASCs, for example four or nine or twelve ASCs.
In the dividing wall W, all ASCs encompassed by the dividing wall W are separated from one another by the separating element RT of the frame element R, meaning that no ASC directly adjoins another ASC, that is without a frame element R being in between.
The dividing wall W is further characterized in that the ASCs encompassed by the dividing wall W are directly contactable both via the surface OKK and via the surface OA/MK.
What is meant by “directly contactable” with regard to the ASCs encompassed by the dividing wall W is that some of the surfaces OKK and OA/MK are formed by the surface of the ASCs encompassed by the dividing wall W, meaning that the ASCs encompassed by the dividing wall W are directly accessible at the two surfaces OKK and OA/MK, such that they can be wetted at the two surfaces OKK and OA/MK, for example, with aqueous solution, alcoholic solution, alcohol or water.
What this means for the arrangement of the ASCs in the dividing wall W is that, for each ASC encompassed by the dividing wall W, there is a route from the surface OKK on the side SKK to the surface OA/MK on the side SA/MK that leads completely through the respective ASC.
The two frame elements R1 and R2 are directly contactable via the surfaces OKK and OA/MK.
What is meant by “directly contactable” with regard to the frame part R1 encompassed by the dividing wall W is that part of the surface OKK is formed by the surface of the frame part R1, meaning that the frame part R1 is directly accessible at the surface OKK, such that it can be wetted at the surface OKK, for example, with aqueous solution, alcoholic solution, alcohol or water.
What is meant by “directly contactable” with regard to the frame part R2 encompassed by the dividing wall W is that part of the surface OA/MK is formed by the surface of the frame part R2, meaning that the frame part R2 is directly accessible at the surface OA/MK, such that it can be wetted at the surface OA/MK, for example, with aqueous solution, alcoholic solution, alcohol or water.
What this means more particularly for the arrangement of the frame element R in the dividing wall W is that there is a route from the surface OKK on the side SKK to the surface OA/MK on the side SA/MK that leads through the R1 part and then through the R2 part (and possibly through a seal Di), but not through an ASC.
In a preferred embodiment of the dividing wall W in the first aspect of the invention, 50% to 95%, more preferably 60% to 90%, even more preferably 70% to 85%, of the surface OKK is formed by the ASCs encompassed by the dividing wall W, with the rest of the surface OKK even more preferably being formed by the frame part R1.
In a preferred embodiment of the dividing wall W in the first aspect of the invention, 50% to 95%, more preferably 60% to 90%, even more preferably 70% to 85%, of the surface OA/MK is also formed by the ASCs encompassed by the dividing wall W, with the rest of the surface OA/MK even more preferably being formed by the frame part R2.
In a preferred embodiment, the dividing wall W, especially between frame element R and the ASCs, comprises a seal Di (shown, for example, in
The seal Di especially comprises a material selected from the group consisting of elastomers, adhesives, preferably elastomers.
A useful elastomer is especially rubber, preferably ethylene-propylene-diene rubber (“EPDM”), fluoropolymer rubber (“FPM”), perfluoropolymer rubber (“FFPM”), or acrylonitrile-butadiene rubber (“NBR”).
The seal Di is preferably selected such that it is compressed when the two frame parts R1 and R2 are secured to one another and the ASCs are arranged between the two frame parts R1 and R2. This further increases the integrity of the dividing wall W.
In a preferred embodiment, the dividing wall W comprises at least four ASCs FA, FB, FC and FD, and even more preferably comprises exactly four ASCs FA, FB, FC and FD.
In a further preferred embodiment, the dividing wall W comprises at least nine ASCs FA, FB, FC, FD, FE, FF, FG, FH and FI, and even more preferably comprises exactly nine ASCs FA, FB, FC, FD, FE, FF, FG, FH and FI.
In a further preferred embodiment, the dividing wall W comprises at least twelve ASCs FA, FB, FC, FD, FE, FF, FG, FH, FI, FJ, FK and FL, and even more preferably comprises exactly twelve ASCs FA, FB, FC, FD, FE, FF, FG, FH, FI, FJ, FK and FL.
This inventive arrangement of at least two ASCs alongside one another in the dividing wall W, compared to the conventional dividing walls in the prior art electrolysis cells, results in a further direction of spread for the ASCs in the event of the fluctuations in temperature that arise in the operation of the electrolysis cell. In the prior art electrolysis cells, the NaSICON sheets that function as dividing walls are framed by the outer walls of the electrolysis cell or by solid plastic frames. It is not possible in this way to dissipate the mechanical stresses that occur in the event of expansion within the NaSICON, which can lead to fracture of the ceramic.
By contrast, the individual ASCs within the dividing wall W in the first aspect of the invention adjoin the separating element RT, and, in the case of the ASCs at the edge of the surfaces OKK and OA/MK, also adjoin the frame element RR, which leads to advantageous effects, both of which increase the long-term stability of the ASC:
As a result, the tendency to fracture is distinctly reduced for the “divided” ASCs in the dividing wall W compared to the use of one sheet.
The frame element R comprises two opposite parts R1 and R2, with the at least two alkali metal cation-conducting solid-state ceramics FA and FB encompassed by the dividing wall W disposed therebetween. This arrangement can be effected in any manner familiar to the person skilled in the art. In a particular embodiment, the two parts R1 and R2 clamp the ASCs between them, preferably using a seal Di that additionally stabilizes the ASCs in the frame element R. In another preferred embodiment, the ASCs are bonded to the two frame parts R1 and R2. Adhesives KI used for the purpose may be any of the adhesives familiar to the person skilled in the art that are stable under the conditions of the electrolysis. Preferred KIs include at least one substance selected from epoxy resins, phenolic resins.
The dividing wall W may have a hinge by which the two parts R1 and R2 of the frame element R can be opened and closed.
The frame element R especially comprises a material selected from the group consisting of plastic, glass, wood. More preferably, the frame element R comprises plastic.
Even more preferably, the plastic is one selected from the group consisting of polypropylene, polystyrene, polyvinylchloride.
In a preferred embodiment, a seal Di is provided between frame element R and the ASCs encompassed by the dividing wall W. This improves the liquid-tightness of the dividing wall W.
The frame element R forms an edge element RR and a separating element RT.
Separating element RT refers to that region of the frame element R that lies between at least two ASCs and separates these from one another. The separating element RT as a region of the frame element R is formed by the two parts R1 and R2.
A suitable separating element RT which is formed by the frame element R is any body by means of which the respective ASCs can be arranged separately from one another. The ASCs here gaplessly adjoin the separating element RT in order not to impair the function of the dividing wall W which, in the electrolysis cell E, is to divide the cathode chamber in a liquid-tight manner from the adjacent middle chamber or anode chamber.
The shape of the separating element RT can be chosen by the person skilled in the art, especially depending on the number and shape of the ASCs encompassed by the dividing wall W.
If the dividing wall W comprises two or three ASCs, for example, these may each be separated by a land disposed between the ASCs as a separating element RT (see, for example,
If the dividing wall W comprises four or more ASCs, these may be separated by a separating element RT in the form of a cross (see
It is preferable that the dividing wall W comprises at least four ASCs, and even more preferable that the separating element RT is then in the form of a cross or grid, since all three dimensions are then fully available to the ASCs for thermal expansion/shrinkage.
The separating element RT here is especially shaped in such a way that the respective ASC can be fitted or clamped into the separating element. This can already be implemented in a corresponding manner in the production of the dividing wall W.
The separating element RT preferably comprises a material selected from the group consisting of plastic, glass, and wood. More preferably, the separating element RT comprises plastic.
Even more preferably, the plastic is one selected from the group consisting of polypropylene, polystyrene, polyvinylchloride (“PVC”). PVC also includes post-chlorinated polyvinylchloride (“PVC-C”).
The frame element R forms not only the separating element RT but also an edge element RR. The edge element RR as a region of the frame element R is formed by the two parts R1 and R2. The edge element RR (as distinct from the separating element RT) is that region of the frame element R which is not disposed between the alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W, i.e. does not separate these from one another.
The edge element RR bounds the surfaces OKK and OA/MK at least partly, preferably completely. What this means is more particularly: The edge element RR surrounds the surfaces OKK and OA/MK at least partly, preferably completely.
The edge element RR here may or may not be part of the surfaces OKK and OA/MK. The edge element RR is preferably part of the surfaces OKK and OA/MK.
The edge element RR is especially directly contactable or not directly contactable via the surfaces OKK and OA/MK.
The edge element RR is preferably directly contactable via the surfaces OKK and OA/MK. In this preferred embodiment, the edge element RR as part of R1 is directly contactable via the surface OKK, and as part of R2 is directly contactable via the surface OA/MK.
The edge element RR preferably comprises a material selected from the group consisting of plastic, glass, wood. More preferably, the edge element RR comprises plastic.
Even more preferably, the plastic is one selected from the group consisting of polypropylene, polystyrene, polyvinylchloride (“PVC”). PVC also includes post-chlorinated polyvinylchloride (“PVC-C”).
In a further preferred embodiment, the edge element RR and the separating element RT comprise the same material, and both even more preferably comprise plastic, which is even more preferably selected from polypropylene, polystyrene, polyvinylchloride, PVC-C.
In a preferred embodiment, at least part of the separating element RT is formed in one piece with at least part of the frame element RR. What this means more particularly is that at least part of the separating element RT merges into the edge element RR.
The embodiment of an edge element RR has the further advantage that it functions as part of the outer wall in the electrolysis cell E. This part of the dividing wall W does not make contact with the solutions in the respective interior IKK, IKA or IKM, and it would therefore be a waste to form this part of the dividing wall W with a solid-state electrolyte ceramic. In addition, the part of the dividing wall W which is clamped between the outer wall or forms part thereof is subjected to forces that the brittle solid-state electrolyte ceramic might not withstand. Instead, a fracture-resistant and cheaper material is thus selected for the frame element R.
4.1.2 Securing Elements BR and BT
The dividing wall W in the first aspect of the invention is characterized in that R1 and R2 are secured to one another by at least one securing element BR at the edge element RR, and R1 and R2 are secured to one another by at least one securing element BT at the separating element RT.
What is meant by “at the edge element RR” in this context is “in the region of the edge element RR”.
What is meant by “at the separating element RT” in this context is “in the region of the separating element RT”.
Suitable securing elements BR and BT are all means familiar to the person skilled in the art for securing the two frame parts R1 and R2 to one another.
These securing elements BR and BT are especially selected from hinges, clamps, nails, screws, hooks, preferably from screws, hooks, most preferably hooks.
The securing elements BR and BT may be made from a material familiar to the person skilled in the art.
They preferably comprise a material selected from the group consisting of plastic, glass, wood. Particular preference is given to plastic.
Even more preferably, the plastic is one selected from the group consisting of polypropylene, polystyrene, polyvinylchloride, PVC-C.
Even more preferably, the at least one securing element BR and the at least one securing element BT are each in the form of mutually engaging hooks BH. In the state secured to one another, these hooks especially then span the dividing wall W.
For this purpose, as BT, mutually opposing pairs of hooks BH are advantageously each formed on the mutually facing sides of the two frame parts R1 and R2 in the region of the separating element RT, and these engage with one another, preferably reversibly, on arrangement of the ASCs between the frame parts R1 and R2. It will be apparent that, for this embodiment, the edge element RR must be directly contactable via the surfaces OKK and OA/MK.
For this purpose, as BR, mutually opposing pairs of hooks BH are advantageously each formed on the mutually facing sides of the two frame parts R1 and R2 in the region of the edge element RR, and these engage reversibly with one another on arrangement of the ASCs between the frame parts R1 and R2.
“Mutually facing sides of the two frame parts R1 and R2” relates to the sides of the two frame parts the surface of which is not directly contactable via the surface OKK in the case of R1, and the surface of which is not directly contactable via the surface OA/MK in the case of R2. These are especially the surfaces R1 and R2 that make contact with the ASCs and/or the seal Di in the dividing wall W.
The securing means BR and BT, especially the hooks, are preferably in one-piece form with at least one of the parts R1 and R2 (
In another preferred embodiment, the at least one securing element BR and the at least one securing element BT are each in the form of mutually engaging hooks BH.
In a preferred embodiment, hooks BH are formed on both frame parts R1 and R2 in the region of the separating element RT and in the region of the edge element RR in such a way that they engage when the ASCs are arranged between the frame parts R1 and R2 and hence secure the frame parts R1 and R2 to one another. Even more preferably, this is reversible, meaning that the hooks BH can be detached from one another. This can be achieved, for example, in that the hooks are designed so as to be movable with respect to one another.
The mounting of the securing means BR and BT both on the edge element RR and on the separating element RT surprisingly improves the stability of the dividing wall W. The use of securing means in the region not just of the edge element RR but also of the separating element RT makes it possible to introduce compression forces not just at the outer corners but over the entire area of the frame element R.
A useful alkali metal cation-conducting solid-state electrolyte ceramic FA, FB etc. encompassed by the dividing wall W is any solid-state electrolyte through which cations, especially alkali metal cations, even more preferably sodium cations, can be transported from the SA/MK side to the SKK side. Such solid-state electrolytes are known to the person skilled in the art and are described, for example, in DE 10 2015 013 155 A1, in WO 2012/048032 A2, paragraphs [0035], [0039], [0040], in US 2010/0044242 A1, paragraphs [0040], [0041], in DE 10360758 A1, paragraphs [014] to [025]. They are sold commercially under the NaSICON, LiSICON, KSICON name. A sodium ion-conducting solid-state electrolyte is preferred, and this even more preferably has an NaSICON structure. NaSICON structures usable in accordance with the invention are also described, for example, by N. Anantharamulu, K. Koteswara Rao, G. Rambabu, B. Vijaya Kumar, Velchuri Radha, M. Vithal, J Mater Sci 2011, 46, 2821-2837.
In a preferred embodiment of the dividing wall W, the alkali metal cation-conducting solid-state ceramics encompassed by the dividing wall W independently have an NaSICON structure of the FORMULA MI1+2w+x−y+z MIIw MIIIx ZRIV2−w−x−y MVY (SiO4)z (PO4)3−z.
The Roman indices I, II, III, IV, V indicate the oxidation numbers in which the respective metal cations exist.
Even more preferably in accordance with the invention, the NaSICON structure has a structure of the formula Na(1+v)Zr2SivP(3−v)O12 where v is a real number for which 0 ≤v≤3. Most preferably, v=2.4.
In a preferred embodiment of the dividing wall W according to the first aspect of the invention, the ASCs encompassed by the dividing wall W have the same structure.
The dividing wall W can be produced by methods known to the person skilled in the art.
For example, the ASCs encompassed by the dividing wall W may be inserted into an appropriate casting mould, optionally with seals, and the frame element R may be cast by means of liquid plastic and then left to solidify (injection-moulding method). In the course of solidification, this then surrounds the ASCs. The securing elements BT and BR may be provided in one casting by a suitable shape on the frame element R (and are then in one-piece form therewith). In this embodiment, mutually engaging hooks BH in particular are suitable as securing means.
Alternatively, the frame element R or the frame parts R1 and R2 are cast separately. The securing elements BT and BR may be provided in one casting by a suitable shape on the frame element R (and are then in one-piece form therewith). In this embodiment, mutually engaging hooks BH in particular are suitable as securing means.
Alternatively, the ASCs, optionally with the seal Di, can be arranged between the frame parts R1 and R2, and then the securing elements BT and BR can be attached. Suitable examples for this purpose are screws or nails that are driven through suitable cutouts in the frame parts R1 and R2 and secure these to one another.
The dividing wall W in the first aspect of the invention is suitable as a dividing wall in an electrolysis cell E.
In a second aspect, the present invention therefore relates to an electrolysis cell E comprising
The electrolysis cell E in the second aspect of the invention comprises at least one anode chamber KA and at least one cathode chamber KK, and optionally at least one interposed middle chamber KM. This also includes electrolysis cells E having more than one anode chamber KA and/or cathode chamber KK and/or middle chamber KM. Such electrolysis cells in which these chambers are joined to one another in the form of modules are described, for example, in DD 258 143 A3 and US 2006/0226022 A1.
The electrolysis cell E in the second aspect of the invention, in a preferred embodiment, comprises an anode chamber KA and a cathode chamber KK, and optionally an interposed middle chamber KM.
The electrolysis cell E typically has an outer wall WA. The outer wall WA is especially made from a material selected from the group consisting of steel, preferably rubberized steel, plastic, especially from Telene® (thermoset polydicyclopentadiene), PVC (polyvinylchloride), PVC-C (post-chlorinated polyvinylchloride), PVDF (polyvinylidenefluoride). WA may especially be perforated for inlets and outlets. Within WA are then the at least one anode chamber KA, the at least one cathode chamber KK and, In the embodiments in which the electrolysis cell E comprises one, the at least one interposed middle chamber KM.
The cathode chamber KK has at least one inlet ZKK, at least one outlet AKK, and an interior IKK comprising a cathodic electrode EK.
The interior IKK of the cathode chamber KK is divided from the interior IKA of the anode chamber KA by the dividing wall W in the first aspect of the invention, if the electrolysis cell E does not comprise a middle chamber KM. The interior IKK of the cathode chamber KK is divided from the interior IKM of the middle chamber KM by the dividing wall W in the first aspect of the invention, if the electrolysis cell E comprises at least one middle chamber KM.
The cathode chamber KK comprises an interior IKK which in turn comprises a cathodic electrode EK. A useful cathodic electrode EK of this kind is any electrode familiar to the person skilled in the art that is stable under the conditions of the process according to the invention in the third aspect of the invention. These are described, in particular, in WO 2014/008410 A1, paragraph [025] or DE 10360758 A1, paragraph [030]. This electrode EK may be selected from the group consisting of mesh wool, three-dimensional matrix structure and “balls”. The cathodic electrode EK especially comprises a material selected from the group consisting of steel, nickel, copper, platinum, platinized metals, palladium, carbon-supported palladium, titanium. Preferably, EK comprises nickel.
In the embodiments of the electrolysis cell E according to the second aspect of the invention in which it comprises a middle chamber KM, this is between the anode chamber KA and the cathode chamber KK.
4.2.1.2 Inlet ZKK and Outlet AKK The cathode chamber KK also encompasses an inlet ZKK and an outlet AKK. This enables addition of liquid, for example the solution L2, to the interior IKK of the cathode chamber KK, and removal of liquid present therein, for example the solution L1. The inlet ZKK and the outlet AKK are attached here to the cathode chamber KK in such a way that the liquid comes into contact with the cathodic electrode EK as it flows through the interior IKK of the cathode chamber KK. This is the prerequisite for the solution L1 to be obtained at the outlet AKK in the performance of the process according to the invention in the third aspect of the invention when the solution L2 of an alkali metal alkoxide XOR in the alcohol ROH is routed through the interior IKK of the cathode chamber KK.
The inlet ZKK and the outlet AKK may be attached to the electrolysis cell E by methods known to the person skilled in the art, for example by means of holes in the outer wall and corresponding connections (valves) that simplify the introduction and discharge of liquid.
The anode chamber KA has at least one inlet ZKA, at least one outlet AKA, and an interior IKA comprising an anodic electrode EA.
The interior IKA of the anode chamber KA, if the electrolysis cell E comprises a middle chamber KM, is divided from the interior IKM of the middle chamber KM by a diffusion barrier D.
If electrolysis cell E does not comprise a middle chamber KM, the interior IKA of the anode chamber K is divided from the interior IKK of the cathode chamber KK by the dividing wall W.
The anode chamber KA comprises an interior IKA which in turn comprises an anodic electrode EA. A useful anodic electrode EA of this kind is any electrode familiar to the person skilled in the art that is stable under the conditions of the process according to the invention in the third aspect of the invention. These are described, in particular, in WO 2014/008410 A1, paragraph [024] or DE 10360758 A1, paragraph [031]. This electrode EA may consist of one layer or consist of multiple planar layers parallel to one another that may each be perforated or expanded. The anodic electrode EA especially comprises a material selected from the group consisting of ruthenium oxide, iridium oxide, nickel, cobalt, nickel tungstate, nickel titanate, precious metals such as, in particular, platinum, supported on a support such as titanium or Kovar® (an iron/nickel/cobalt alloy in which the individual components are preferably as follows: 54% by mass of iron, 29% by mass of nickel, 17% by mass of cobalt). Further possible anode materials are especially stainless steel, lead, graphite, tungsten carbide, titanium diboride. Preferably, the anodic electrode EA comprises a titanium anode coated with ruthenium oxide/iridium oxide (RuO2+IrO2/Ti).
4.2.2.2 Inlet ZKA and Outlet AKA
The anode chamber KK also encompasses an inlet ZKA and an outlet AKA. This enables addition of liquid, for example the solution L3, to the interior IKA of the cathode chamber KA, and removal of liquid present therein, for example the solution L4. The inlet ZKA and the outlet AKA are attached here to the anode chamber KA in such a way that the liquid comes into contact with the anodic electrode EA as it flows through the interior IKA of the anode chamber KA. This is a prerequisite for the solution L4 to be obtained at the outlet AKA in the performance of the process according to the invention in the third aspect of the invention when the solution L3 of a salt S is routed through the interior IKA of the cathode chamber KA.
The inlet ZKA and the outlet AKA may be attached to the electrolysis cell E by methods known to the person skilled in the art, for example by means of holes in the outer wall and corresponding connections (valves) that simplify the introduction and discharge of liquid. The inlet ZKA, in particular embodiments in which the electrolysis cell E comprises a middle chamber KM, may also be within the electrolysis cell, for example in the form of a perforation in the diffusion barrier D.
The electrolysis cell E in the second aspect of the invention preferably has a middle chamber KM. The optional middle chamber KM lies between cathode chamber and KK anode chamber KA. It comprises at least one inlet ZKM, at least one outlet AKM and an interior IKM.
The interior IKA of the anode chamber KA, if the electrolysis cell E comprises a middle chamber KM, is divided from the interior IKM of the middle chamber KM by a diffusion barrier D. AKM is then also connected to the inlet ZKA by a connection VAM, such that liquid can be guided from IKM into IKA through the connection VAM.
The interior IKM of the optional middle chamber KM is divided from the interior IKA of the anode chamber KA by a diffusion barrier D and divided from the interior IKK of the cathode chamber KK by the dividing wall W.
The material used for the diffusion barrier D may be any which is stable under the conditions of the process according to the invention in the third aspect of the invention and prevents or slows the transfer of protons from the liquid present in the interior IKA of the anode chamber KA to the interior IKM of the optional middle chamber KM.
The diffusion barrier D used is especially a non-ion-specific dividing wall or a membrane permeable to specific ions. The diffusion barrier D is preferably a non-ion-specific dividing wall.
The material of the non-ion-specific dividing wall is especially selected from the group consisting of fabric, which is especially textile fabric or metal weave, glass, which is especially sintered glass or glass frits, ceramic, especially ceramic frits, membrane diaphragms, and is more preferably a textile fabric or metal weave, especially preferably a textile fabric. The textile fabric preferably comprises plastic, more preferably a plastic selected from PVC, PVC-C, polyvinylether (“PVE”), polytetrafluoroethylene (“PTFE”).
If the diffusion barrier D is a “membrane permeable to specific ions”, what this means in accordance with the invention is that the respective membrane promotes the diffusion of particular ions therethrough over other ions. More particularly, what this means is membranes that promote the diffusion therethrough of ions of a particular charge type over ions of the opposite charge. Even more preferably, membranes permeable to specific ions also promote the diffusion of particular ions of one charge type over other ions of the same charge type therethrough.
If the diffusion barrier D is a “membrane permeable to specific ions”, the diffusion barrier D is especially an anion-conducting membrane or a cation-conducting membrane.
According to the invention, anion-conducting membranes are those that selectively conduct anions, preferably selectively conduct particular anions. In other words, they promote the diffusion of anions therethrough over that of cations, especially over protons; even more preferably, they additionally promote the diffusion of particular anions therethrough over the diffusion of other anions therethrough.
According to the invention, cation-conducting membranes are those that selectively conduct cations, preferably selectively conduct particular cations. In other words, they promote the diffusion of cations therethrough over that of anions; even more preferably, they additionally promote the diffusion of particular cations therethrough over the diffusion of other cations therethrough, more preferably still that of cations that are not protons, more preferably sodium cations, over protons.
What is meant more particularly by “promote the diffusion of particular ions X over the diffusion of other ions Y” is that the coefficient of diffusion (unit: m2/s) of ion type X at a given temperature for the membrane in question is higher by a factor of 10, preferably 100, preferably 1000, than the coefficient of diffusion of ion type Y for the membrane in question.
If the diffusion barrier D is a “membrane permeable to specific ions”, it is preferably an anion-conducting membrane since this particularly efficiently prevents the diffusion of protons from the anode chamber KA into the middle chamber KM.
The anion-conducting membrane used is especially one selective for the anions encompassed by the salt S. Such membranes are known to and can be used by the person skilled in the art.
The salt S is preferably a halide, sulfate, sulfite, nitrate, hydrogencarbonate or carbonate of X, even more preferably a halide.
Halides are fluorides, chlorides, bromides, iodides. The most preferred halide is chloride.
The anion-conducting membrane used is preferably one selective for halides, preferably chloride.
Anion-conducting membranes are described, for example, by M. A. Hickner, A. M. Herring, E. B. Coughlin, Journal of Polymer Science, Part B: Polymer Physics 2013, 51, 1727-1735, by C. G. Arges, V. Ramani, P. N. Pintauro, Electrochemical Society Interface 2010, 19, 31-35, in WO 2007/048712 A2, and on page 181 of the textbook by Volkmar M. Schmidt, Elektrochemische Verfahrenstechnik: Grundlagen, Reaktionstechnik, Prozessoptimierung [Electrochemical Engineering: Fundamentals, Reaction Technology, Process Optimization], 1st edition (8 Oct. 2003).
Even more preferably, anion-conducting membranes used are accordingly organic polymers that are especially selected from polyethylene, polybenzimidazoles, polyether ketones, polystyrene, polypropylene and fluorinated membranes such as polyperfluoroethylene, preferably polystyrene, where these have covalently bonded functional groups selected from —NH3+, —NRH2+, —NR3+, ═NR+; —PR3+, where R is alkyl groups having preferably 1 to 20 carbon atoms, or other cationic groups. They preferably have covalently bonded functional groups selected from —NH3+, —NRH2+ and —NR3+, more preferably selected from —NH3+ and —NR3+, even more preferably —NR3+.
If the diffusion barrier D is a cation-conducting membrane, it is especially a membrane selective for the cations encompassed by the salt S. Even more preferably, the diffusion barrier D is an alkali metal cation-conducting membrane, even more preferably a potassium and/or sodium ion-conducting membrane, most preferably a sodium ion-conducting membrane.
Cation-conducting membranes are described, for example, on page 181 of the textbook by Volkmar M. Schmidt, Elektrochemische Verfahrenstechnik: Grundlagen, Reaktionstechnik, Prozessoptimierung, 1st edition (8 Oct. 2003).
Even more preferably, cation-conducting membranes used are accordingly organic polymers that are especially selected from polyethylene, polybenzimidazoles, polyether ketones, polystyrene, polypropylene and fluorinated membranes such as polyperfluoroethylene, preferably polystyrene and polyperfluoroethylene, where these bear covalently bonded functional groups selected from —SO3−, —COO−, —PO32− and —PO2H−, preferably —SO3− (described in DE 10 2010 062 804 A1, U.S. Pat. No. 4,831,146).
This may be, for example, a sulfonated polyperfluoroethylene (Nafion® with CAS number: 31175-20-9). These are known to the person skilled in the art, for example from WO 2008/076327 A1, paragraph [058], US 2010/0044242 A1, paragraph [0042] or US 2016/0204459 A1, and are commercially available under the Nafion®, Aciplex® F, Flemion®, Neosepta®, Ultrex®, PC—SK® trade names. Neosepta® membranes are described, for example, by S. A. Mareev, D. Yu. Butylskii, N. D. Pismenskaya, C. Larchet, L. Dammak, V. V. Nikonenko, Journal of Membrane Science 2018, 563, 768-776.
If a cation-conducting membrane is used as diffusion barrier D, this may, for example, be a polymer functionalized with sulfonic acid groups, especially of the formula PNAFION below, where n and m may independently be a whole number from 1 to 106, preferably a whole number from 10 to 105, more preferably a whole number from 102 to 104.
4.2.3.2 Inlet ZKM and Outlet AKM
The optional middle chamber KM also encompasses an inlet ZKM and an outlet AKM. This enables addition of liquid, for example the solution L3, to the interior IKM of the middle chamber KM, and transfer of liquid present therein, for example the solution L3, to the anode chamber KA.
The inlet ZKM and the outlet AKM may be attached to the electrolysis cell E by methods known to the person skilled in the art, for example by means of holes in the outer wall and corresponding connections (valves) that simplify the introduction and discharge of liquid. The outlet AKM may also be within the electrolysis cell, for example in the form of a perforation in the diffusion barrier D.
In the electrolysis cell E according to the second aspect of the invention, the outlet AKM is connected to the inlet ZKA by a connection VAM in such a way that liquid can be guided from IKM into IKA through the connection VAM.
The connection VAM may be formed within the electrolysis cell E and/or outside the electrolysis cell E, and is preferably formed within the electrolysis cell.
1) If the connection VAM is formed within the electrolysis cell E, it is preferably formed by at least one perforation in the diffusion barrier D. This embodiment is preferred especially when the diffusion barrier D used is a non-ion-specific dividing wall, especially a metal weave or textile fabric. This functions as a diffusion barrier D and, on account of the weave properties, has perforations and gaps from the outset that function as connection VAM.
2) The embodiment described hereinafter is preferred especially when the diffusion barrier D used is a membrane permeable to specific ions: In this embodiment, the connection VAM is formed outside the electrolysis cell E, preferably formed by a connection of AKM and ZKA that runs outside the electrolysis cell E, especially in that an outlet AKM through the outer wall WA is formed from the interior of the middle chamber IKM, preferably at the base of the middle chamber KM, the inlet ZKM more preferably being at the top end of the middle chamber KM, and an inlet ZKA through the outer wall WA is formed in the interior IKA of the anode chamber KA, preferably at the base of the anode chamber KA, and these are connected by a conduit, for example a pipe or a hose, preferably comprising a material selected from rubber and plastic. The outlet AKA is then more preferably at the top end of the anode chamber KA.
“Outlet AKM at the base of the middle chamber KM” means that the outlet AKM is attached to the electrolysis cell E in such a way that the solution L3 leaves the middle chamber KM in the direction of gravity.
“Inlet ZKA at the base of the anode chamber KA” means that the inlet ZKA is attached to the electrolysis cell E in such a way that the solution L3 enters the anode chamber KA counter to gravity.
“Inlet ZKM at the top end of the middle chamber KM” means that the inlet ZKM is attached to the electrolysis cell E in such a way that the solution L3 enters the middle chamber KM in the direction of gravity.
“Outlet AKA at the top end of the anode chamber KA” means that the outlet AKA is mounted on the electrolysis cell E in such a way that the solution L4 leaves the anode chamber KA counter to gravity.
This embodiment is particularly advantageous and therefore preferred when the outlet AKM is formed by the outer wall WA at the base of the middle chamber KM, and the inlet ZKA by the outer wall WA at the base of the anode chamber KA. This arrangement makes it possible in a particularly simple manner to remove gases formed in the anode chamber KA from the anode chamber KA with L4, in order to separate them further.
When the connection VAM is formed outside the electrolysis cell E, ZKM and AKM are especially arranged at opposite ends of the outer wall WA of the middle chamber KM (i.e., for example, ZKM at the base and AKM at the top end of the electrolysis cell E or vice versa) and ZKA and AKA are arranged at opposite ends of the outer wall WA of the anode chamber KA (i.e. ZKA at the base and AKA at the top end of the electrolysis cell E or vice versa), as shown more particularly in
3) When the connection VAM is formed within the electrolysis cell E, this may especially be ensured in that one side (“side A”) of the electrolysis cell E, which is the top end or the base of the electrolysis cell E, preferably the top end as shown in
These embodiments best ensure that the aqueous salt solution L3 flows past the acid-sensitive solid-state electrolyte before it comes into contact with the anodic electrode EA, which results in the formation of acids.
According to the invention, “base of the electrolysis cell E” is the side of the electrolysis cell E through which a solution (e.g. LU in the case of AKM in
According to the invention, “top end of the electrolysis cell E” is the side of the electrolysis cell E through which a solution (e.g. L4 in the case of AKA and L1 in the case of AKK in
The dividing wall W is arranged in the electrolysis cell E in such a way that the alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W, and preferably also the frame element R, directly contact the interior IKK on the side SKK via the surface OKK.
This means that the dividing wall W is arranged within the electrolysis cell E such that, when the interior IKK on the side SKK side is completely filled with solution L4, the solution L4, via the surface OKK, then makes contact with all alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W, and preferably also the frame element R via part R1, such that ions (e.g. alkali metal ions such as sodium, lithium) from all ASCs encompassed by the dividing wall W can enter the solution L4.
In addition, the dividing wall W, in the embodiments in which the electrolysis cell E does not comprise a middle chamber KM, is arranged in the electrolysis cell E such that the alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W, and preferably also the frame element R, make direct contact with the interior IKA on the side SA/MK via the surface OA/MK.
What this means is as follows: in the embodiments in which the electrolysis cell E does not comprise a middle chamber KM, the dividing wall W adjoins the interior IKA of the anode chamber KA. In these embodiments, the dividing wall W is arranged within the electrolysis cell E such that, when the interior IKA on the side SAM/K is completely filled with solution L3, the solution L3, via the surface OA/MK, then makes contact with all alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W, and preferably also the frame element R via part R2, such that ions (e.g. alkali metal ions such as sodium, lithium) from the solution L3 can enter any ASC encompassed by the dividing wall W.
In addition, the dividing wall W, in the cases in which the electrolysis cell E comprises at least one middle chamber KM, is arranged in the electrolysis cell E such that the alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W, and especially also the frame element R, make direct contact with the interior IKM on the side SA/MK via the surface OA/MK.
What this means is as follows: in the embodiments in which the electrolysis cell E comprises at least one middle chamber KM, the dividing wall W adjoins the interior IKM of the middle chamber KM. In these embodiments, the dividing wall W is arranged within the electrolysis cell E such that, when the interior IKM on the side SAM/K is completely filled with solution L3, the solution L3, via the surface OA/MK, then makes contact with all alkali metal cation-conducting solid-state electrolyte ceramics encompassed by the dividing wall W, and preferably also the frame element R via part R2, such that ions (e.g. alkali metal ions such as sodium, lithium) from the solution L3 can enter any ASC encompassed by the dividing wall W.
In a preferred embodiment of the electrolysis cell E in the second aspect of the invention, at least 50%, especially at least 70%, preferably at least 90%, most preferably 100%, of the portion of the surface OKK which is formed by ASCs makes contact with the interior IKK.
In a preferred embodiment of the electrolysis cell E without a middle chamber in the second aspect of the invention, at least 50%, especially at least 70%, preferably at least 90%, most preferably 100%, of the portion of the surface OA/MK which is formed by ASCs makes contact with the interior IKA.
In a preferred embodiment of the electrolysis cell E with at least one middle chamber in the second aspect of the invention, at least 50%, especially at least 70%, preferably at least 90%, most preferably 100%, of the portion of the surface OA/MK which is formed by ASCs makes contact with the interior IKM.
The present invention relates, in a third aspect, to a process for producing a solution L1 of an alkali metal alkoxide XOR in the alcohol ROH, where X is an alkali metal cation and R is an alkyl radical having 1 to 4 carbon atoms. The process according to the third aspect of the invention is conducted in an electrolysis cell E in the second aspect of the invention.
X is preferably selected from the group consisting of Li+, K+, Na+, more preferably from the group consisting of K+, Na+. Most preferably, X=Na+.
R is preferably selected from the group consisting of n-propyl, iso-propyl, ethyl and methyl, more preferably from the group consisting of ethyl and methyl. R is most preferably methyl. 4.3.1 Process according to the invention in an electrolysis cell E without a middle chamber KMIn the cases in which the electrolysis cell E does not comprise a middle chamber KM, the steps (α1), (α2), (α3) that proceed simultaneously are conducted.
In step (α1), a solution L2 comprising the alcohol ROH, preferably comprising an alkali metal alkoxide XOR and alcohol ROH, is routed through KK.
Solution L2 is preferably free of water. What is meant in accordance with the invention by “free of water” is that the weight of water in solution L2 based on the weight of the alcohol ROH in solution L2 (mass ratio) is ≤1:10, more preferably ≤1:20, even more preferably ≤1:100, even more preferably ≤0.5:100.
If solution L2 comprises XOR, the proportion by mass of XOR in solution L2, based on the overall solution L2, is especially >0% to 30% by weight, preferably 5% to 20% by weight, more preferably 10% to 20% by weight, more preferably 10% to 15% by weight, most preferably 13% to 14% by weight, at the very most preferably 13% by weight.
If solution L2 comprises XOR, the mass ratio of XOR to alcohol ROH in solution L2 is especially in the range of 1:100 to 1:5, more preferably in the range of 1:25 to 3:20, even more preferably in the range of 1:12 to 1:8, even more preferably 1:10.
In step (α2), a neutral or alkaline, aqueous solution L3 of a salt S comprising X as cation is routed through KA.
The salt S is preferably a halide, sulfate, sulfite, nitrate, hydrogencarbonate or carbonate of X, even more preferably a halide.
Halides are fluorides, chlorides, bromides, iodides. The most preferred halide is chloride.
The pH of the aqueous solution L3 is >7.0, preferably in the range of 7 to 12, more preferably in the range of 8 to 11, even more preferably 10 to 11, most preferably 10.5.
The proportion by mass of salt S in solution L3 is preferably in the range of >0% to 20% by weight, preferably 1% to 20% by weight, more preferably 5% to 20% by weight, even more preferably 10% to 20% by weight, most preferably 20% by weight, based on the overall solution L3.
In step (α3), a voltage is then applied between EA and EK.
This results in transfer of current from the charge source to the anode, transfer of charge via ions to the cathode and ultimately transfer of current back to the charge source. The charge source is known to the person skilled in the art and is typically a rectifier that converts alternating current to direct current and can generate particular voltages via voltage transformers.
This in turn has the following consequences:
In step (α3) of the process according to the third aspect the invention, in particular, such a voltage is applied that such a current flows such that the current density (=ratio of the current supplied to the electrolysis cell to the area of the solid-state electrolyte in contact with the anolyte present in the anode chamber KA) is in the range from 10 to 8000 Nm2, more preferably in the range from 100 to 2000 Nm2, even more preferably in the range from 300 to 800 Nm2, and even more preferably is 494 Nm2. This can be determined in a standard manner by the person skilled in the art. The area of the solid-state electrolyte in contact with the anolyte present in the anode chamber KA is especially 0.00001 to 10 m2, preferably 0.0001 to 2.5 m2, more preferably 0.0002 to 0.15 m2, even more preferably 2.83 cm2.
It will be apparent that step (α3) of the process according to the third aspect of the invention is conducted when the chamber KA is at least partly laden with L3 and KK is at least partly laden with L2, such that both L3 and L2 come into contact with the ASCs encompassed by the dividing wall W and especially also come into contact with the frame element R.
The fact that transfer of charge takes place between EA and EK in step (α3) implies that KK and KA are simultaneously laden with L2 and L3 respectively, such that they cover the electrodes EA and EK to such an extent that the circuit is complete.
This is the case especially when a liquid stream of L3 is routed continuously through KA and a liquid stream of L2 through KK, and the liquid stream of L3 covers electrode EA and the liquid stream of L2 covers electrode EK at least partly, preferably completely.
In a further preferred embodiment, the process according to the third aspect of the invention is performed continuously, i.e. step (α1) and step (α2) are performed continuously, while applying voltage as per step (α3).
After performance of step (α3), solution L1 is obtained at the outlet AKK, wherein the concentration of XOR in L1 is higher than in L2. If L2 already comprised XOR, the concentration of XOR in L1 is preferably 1.01 to 2.2 times, more preferably 1.04 to 1.8 times, even more preferably 1.077 to 1.4 times, even more preferably 1.077 to 1.08 times, higher than in L2, most preferably 1.077 times higher than in L2, where the proportion by mass of XOR in L1 and in L2 is more preferably in the range from 10% to 20% by weight, even more preferably 13% to 14% by weight.
An aqueous solution L4 of S is obtained at the outlet AKA, with a lower concentration of S in L4 than in L3.
The concentration of the cation X in the aqueous solution L3 is preferably in the range of 3.5 to 5 mol/l, more preferably 4 mol/l. The concentration of the cation X in the aqueous solution L4 is more preferably 0.5 mol/l lower than that of the aqueous solution L3 used in each case.
More particularly, steps (α1) to (α3) of the process according to the third aspect of the invention are conducted at a temperature of 20° C. to 70° C., preferably 35° C. to 65° C., more preferably 35° C. to 60° C., even more preferably 35° C. to 50° C., and that a pressure of 0.5 bar to 1.5 bar, preferably 0.9 bar to 1.1 bar, more preferably 1.0 bar.
In the course of performance of steps (α1) to (α3) according to the third aspect of the process according to the invention, hydrogen is typically formed in the cathode chamber KK, which can be removed from the cell together with solution L1 via outlet AKK. The mixture of hydrogen and solution L1 can then, in a particular embodiment of the present invention, be separated by methods known to the person skilled in the art. When the alkali metal compound used is a halide, especially chloride, it is possible for chlorine or another halogen gas to form in the anode chamber KA, and this can be removed from the cell together with solution L4 via outlet AKK. In addition, it is also possible for oxygen or/and carbon dioxide to form, which can likewise be removed. The mixture of chlorine, oxygen and/or CO2 and solution L4 can then, in a particular embodiment of the present invention, be separated by methods known to the person skilled in the art. It is then likewise possible, after the chlorine, oxygen and/or CO2 gases have been separated from solution L4, to separate these by methods known to the person skilled in the art.
4.3.2 Process According to the Invention in an Electrolysis Cell E with a Middle Chamber KM
In the cases in which the electrolysis cell E comprises at least one middle chamber KM, the steps (β1), (β2), (β3) that proceed simultaneously are conducted.
It is preferable that the electrolysis cell E comprises at least one middle chamber KM, and then the steps (β1), (β2), (β3) that proceed simultaneously are conducted.
In step (β1), a solution L2 comprising the alcohol ROH, preferably comprising an alkali metal alkoxide XOR and alcohol ROH, is routed through KK.
Solution L2 is preferably free of water. What is meant in accordance with the invention by “free of water” is that the weight of water in solution L2 based on the weight of the alcohol ROH in solution L2 (mass ratio) is ≤1:10, more preferably ≤1:20, even more preferably ≤1:100, even more preferably ≤0.5:100.
If solution L2 comprises XOR, the proportion by mass of XOR in solution L2, based on the overall solution L2, is especially >0% to 30% by weight, preferably 5% to 20% by weight, more preferably 10% to 20% by weight, more preferably 10% to 15% by weight, most preferably 13% to 14% by weight, at the very most preferably 13% by weight.
If solution L2 comprises XOR, the mass ratio of XOR to alcohol ROH in solution L2 is especially in the range of 1:100 to 1:5, more preferably in the range of 1:25 to 3:20, even more preferably in the range of 1:12 to 1:8, even more preferably 1:10.
In step (β2), a neutral or alkaline aqueous solution L3 of a salt S comprising X as cation is routed through KM, then via VAM, then through KA.
The salt S is preferably a halide, sulfate, sulfite, nitrate, hydrogencarbonate or carbonate of X, even more preferably a halide.
Halides are fluorides, chlorides, bromides, iodides. The most preferred halide is chloride.
The pH of the aqueous solution L3 is >7.0, preferably in the range of 7 to 12, more preferably in the range of 8 to 11, even more preferably 10 to 11, most preferably 10.5.
The proportion by mass of salt S in solution L3 is preferably in the range of >0% to 20% by weight, preferably 1% to 20% by weight, more preferably 5% to 20% by weight, even more preferably 10% to 20% by weight, most preferably 20% by weight, based on the overall solution L3.
In step (β3), a voltage is then applied between EA and EK.
This results in transfer of current from the charge source to the anode, transfer of charge via ions to the cathode and ultimately transfer of current back to the charge source. The charge source is known to the person skilled in the art and is typically a rectifier that converts alternating current to direct current and can generate particular voltages via voltage transformers.
This in turn has the following consequences:
In step (β3) of the process according to the third aspect the invention, in particular, such a voltage is applied that such a current flows such that the current density (=ratio of the current supplied to the electrolysis cell to the area of the solid-state electrolyte in contact with the anolyte present in the middle chamber KM) is in the range from 10 to 8000 Nm2, more preferably in the range from 100 to 2000 Nm2, even more preferably in the range from 300 to 800 Nm2, and even more preferably is 494 Nm2. This can be determined in a standard manner by the person skilled in the art. The area of the solid-state electrolyte in contact with the anolyte present in the middle chamber KM is especially 0.00001 to 10 m2, preferably 0.0001 to 2.5 m2, more preferably 0.0002 to 0.15 m2, even more preferably 2.83 cm2.
It will be apparent that step (β3) of the process according to the third aspect of the invention is conducted when the two chambers KM and KA are at least partly laden with L3, and KK is at least partly laden with L2, such that both L3 and L2 come into contact with the solid-state electrolytes encompassed by the dividing wall W and especially also come into contact with the frame element R.
The fact that transfer of charge takes place between EA and EK in step (β3) implies that KK, KM and KA are simultaneously laden with L2 and L3 such that they cover the electrodes EA and EK to such an extent that the circuit is complete.
This is the case especially when a liquid stream of L3 is routed continuously through KM, VAM and KA and a liquid stream of L2 through KK, and the liquid stream of L3 covers electrode EA and the liquid stream of L2 covers electrode EK at least partly, preferably completely.
In a further preferred embodiment, the process according to the third aspect of the invention is performed continuously, i.e. step (β1) and step (β2) are performed continuously, while applying voltage as per step (β3).
After performance of step (β3), solution L1 is obtained at the outlet AKK, wherein the concentration of XOR in L1 is higher than in L2. If L2 already comprised XOR, the concentration of XOR in L1 is preferably 1.01 to 2.2 times, more preferably 1.04 to 1.8 times, even more preferably 1.077 to 1.4 times, even more preferably 1.077 to 1.08 times, higher than in L2, most preferably 1.077 times higher than in L2, where the proportion by mass of XOR in L1 and in L2 is more preferably in the range from 10% to 20% by weight, even more preferably 13% to 14% by weight.
An aqueous solution L4 of S is obtained at the outlet AKA, with a lower concentration of S in L4 than in L3.
The concentration of the cation X in the aqueous solution L3 is preferably in the range of 3.5 to 5 mol/l, more preferably 4 mol/l. The concentration of the cation X in the aqueous solution L4 is more preferably 0.5 mol/l lower than that of the aqueous solution L3 used in each case.
More particularly, steps (β1) to (β3) of the process according to the third aspect of the invention are conducted at a temperature of 20° C. to 70° C., preferably 35° C. to 65° C., more preferably 35° C. to 60° C., even more preferably 35° C. to 50° C., and at a pressure of 0.5 bar to 1.5 bar, preferably 0.9 bar to 1.1 bar, more preferably 1.0 bar.
In the course of performance of steps (β1) to (β3) according to the third aspect of the process according to the invention, hydrogen is typically formed in the cathode chamber KK, which can be removed from the cell together with solution L1 via outlet AKK. The mixture of hydrogen and solution L1 can then, in a particular embodiment of the present invention, be separated by methods known to the person skilled in the art. When the alkali metal compound used is a halide, especially chloride, it is possible for chlorine or another halogen gas to form in the anode chamber KA, and this can be removed from the cell together with solution L4 via outlet AKK. In addition, it is also possible for oxygen or/and carbon dioxide to form, which can likewise be removed. The mixture of chlorine, oxygen and/or CO2 and solution L4 can then, in a particular embodiment of the present invention, be separated by methods known to the person skilled in the art. It is then likewise possible, after the chlorine, oxygen and/or CO2 gases have been separated from solution L4, to separate these by methods known to the person skilled in the art.
This performance of steps (β1) to (β3) brings further surprising advantages that were not to be expected in the light of the prior art. Steps (β1) to (β3) of the process according to the invention protect the acid-labile solid-state electrolyte from corrosion without, as in the prior art, having to sacrifice alkoxide solution from the cathode space as buffer solution. Thus, the process according to the invention is more efficient than the procedure described in WO 2008/076327 A1, in which the product solution is used for the middle chamber, which reduces the overall conversion.
Sodium methoxide (SM) was produced via a cathodic process, with supply of 20% by weight NaCl solution (in water) in the anode chamber and of 10% by weight methanolic SM solution in the cathode chamber. The electrolysis cell consisted of three chambers that corresponded to those shown in
The anolyte was transferred through the middle chamber into the anode chamber. The flow rate of the anolyte was 1 I/h, that of the catholyte was 90 ml/h, and a current of 0.14 A was applied. The temperature was 35° C. The electrolysis was conducted for 500 hours at a constant voltage of 5 V. It was observed that a pH gradient developed in the middle chamber over a prolonged period, which is attributable to the migration of the ions to the electrodes in the course of the electrolysis and the spread of the protons formed in further reactions at the anode. This local increase in pH is undesirable since it can attack the solid-state electrolyte and can lead to corrosion and fracture of the solid-state electrolyte specifically in the case of very long periods of operation.
In addition, there is expansion and shrinkage of the NaSICON ceramic on account of the heating and cooling effects when the electrolysis cell is repeatedly started up and shut down. In addition, the NaSICON membrane may be displaced within the cell. This is problematic since the tendency of the ceramic to fracture is enhanced and can lead to leakage of electrolyte from the middle chamber into the cathode chamber, which waters down the electrolysis product. In addition, this can lead to leaks in the outer wall of the cell, which leads to leakage of electrolyte to the outside.
Comparative Example 1 was repeated with a two-chamber cell comprising just one anode chamber and one cathode chamber, with the anode chamber separated from the cathode chamber by the ceramic of the NaSICON type (
Comparative Example 1 is repeated using an electrolysis cell according to
This arrangement reduces the extent of the expansion and shrinkage processes, which contributes to the service life of the ceramic and results in a cleaner product solution since the leakage is prevented.
Comparative Example 2 is repeated using an electrolysis cell according to
This arrangement reduces the extent of the expansion and shrinkage processes, which contributes to the service life of the ceramic and results in a cleaner product solution since the leakage is prevented. However, it is observed that the frame R is flexible in the region of the separating element RT, and hence the stability of the dividing wall W in this region is low.
Comparative Example 3 is repeated, with attachment of a securing element BT <92> (mutually engaging hooks) in the region of the separating element RT. This distributes compression forces over the entire surface of the respective side of the dividing wall, which increases the stability of the dividing wall.
The alleviation of the tensions within the solid-state electrolyte ceramics in the expansion and shrinkage processes which result from the repeated electrolysis cycles leads to an extension of the lifetime of the electrolysis chamber. In the execution according to Inventive Examples 1 and 2, these effects are reduced, which increases the stability of the solid-state electrolyte.
In addition, by comparison with Comparative Example 3, the stability of the dividing wall W is increased by homogeneous distribution of the compression forces exerted by the frame element on the ceramics in the dividing wall, by providing a securing element BT in the region of the separating element RT.
The use of a three-chamber cell according to the invention in the process according to the invention also prevents the corrosion of the solid-state electrolyte, and at the same time there is no need to sacrifice alkali metal alkoxide product for the middle chamber and the voltage is kept constant. These advantages that are already apparent from the comparison of the two Comparative Examples 1 and 2 underline the surprising effect of an electrolysis cell according to the invention comprising at least one middle chamber and the process conducted therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21188434.1 | Jul 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/070127 | 7/19/2022 | WO |
