Patent Application
20240392451
The present invention relates to a process for producing an alkali metal alkoxide solution L1 in an electrolysis cell E comprising at least one cathode chamber KK, at least one anode chamber KA, and at least one interposed middle chamber KM.
The interior IKK of the cathode chamber KK is divided by a dividing wall W comprising at least one alkali metal cation-conducting solid-state electrolyte ceramic (=“ASC”) F (e.g. NaSICON) from the interior IKM of the middle chamber KM. F has the surface OF, and a portion OA/MK of this surface OF makes direct contact with the interior IKM, and a portion OKK of this surface OF makes direct contact with the interior IKK.
The surface OA/MK and/or the surface OKK comprises at least a portion of a surface OFA. OFA results from a pretreatment step in which F is produced from an ASC F′ having the surface OF′.
For this purpose, by etching the surface OF′ with an etchant T, ASC is removed from F′, and the ASC F is obtained with the surface OF comprising the surface OFA formed by the etching.
The electrolysis for production of the alkali metal alkoxides with F rather than F′ results in improved conductivity, which makes it possible to use a lower voltage at constant current density.
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, one disadvantage of the electrolysis cells described in the prior art is that the resistance of the solid-state electrolyte ceramics used therein is relatively high. This increases the specific energy consumption of the electrolytically produced materials, and there is also a deterioration in the energy-specific data (current, voltage) of the cell. Ultimately, the overall process becomes uneconomic.
It was accordingly an object of the present invention to provide a process for producing an alkali metal alkoxide solution in an electrolysis cell, which does not have this disadvantage.
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.
A further object of the present invention was accordingly that of providing an improved process for electrolytic production of alkali metal alkoxide. This is not to have the aforementioned disadvantages, and is 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 objects of the invention are achieved by the process according to Claim 1.
The figures show preferred embodiments of the process according to the invention.
The ASC F′ <19>, as shown in
This process step affords an ASC F <18>, the surface OF <180> of which has a part-surface OA/MK <181> facing the nozzle <40> and a part-surface OKK <182> facing away from the nozzle <40>. OA/MK <181> in turn comprises a subregion OFΔ <183> that has formed by virtue of removal of ASC from F′ <19> by means of etching.
Optionally, it is then possible to spray on an aqueous alkaline NaOH solution (pH 14) in order to neutralize the acidic aqueous solution and to end the etching operation in a controlled manner, such that no further pieces of ASC <185> are removed from F′.
This electrolysis cell comprises a cathode chamber KK <12> and an anode chamber KA <11>.
The anode chamber KA <11> comprises an anodic electrode EA <113> in the interior IKA <112>, an inlet ZKA <110> and an outlet AKA <111>.
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>.
This electrolysis cell is bounded by an outer wall WA <80>.
The interior IKK <122> is also divided from the interior IKA <112> by a dividing wall W <16> consisting of a sheet of an NaSICON solid-state electrolyte ceramic F′ <19> which is selectively permeable to sodium ions and has a surface OF′<190>. The NaSICON solid-state electrolyte ceramic F′ <19> extends over the entire depth and height of the two-chamber cell. The NaSICON solid-state electrolyte ceramic F′ <19> makes direct contact with the two interiors IKK <122> and IKA<112> via the part-surfaces <192> and <191>, such that sodium ions can be routed from one interior into the other through the NaSICON solid-state electrolyte ceramic F′ <19>. In
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 F <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 (CI-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) forms in water, according to the reaction Cl2+H2O→HOCl+HCl, hypochlorous acid and hydrochloric acid, which give an acidic reaction with further water molecules. The acidity damages the NaSICON solid-state electrolyte ceramic F′ <19>.
It show the process according to the invention in the form of an electrolysis cell E <1> which is a three-chamber cell.
The three-chamber electrolysis cell E <1> comprises a cathode chamber KK <12>, an anode chamber KA <11> and an interposed middle chamber KM <13>.
The anode chamber KA <11> comprises an anodic electrode EA <113> in the interior IKA <112>, an inlet ZKA <110> and an outlet AKA <111>.
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 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 electrolysis cell E <1> is bounded by an outer wall WA <80>.
The interior IKK <122> is also divided from the interior IKM<132> by a dividing wall W <16> consisting of a sheet of an NaSICON solid-state electrolyte ceramic F <18> which is selectively permeable to sodium ions and has the surface OF <180>. This surface has a part-surface OKK<182> that makes direct contact with the interior IKK <122> and a part-surface OA/MK <181> that makes direct contact with the interior IKM<132>. F <18> extends over the entire depth and height of the three-chamber cell E <1>. F <18> is obtained by an etching method corresponding to that shown in
As a result, the NaSICON solid-state electrolyte F <18> has an even greater mass-based specific surface area SMF than that (SMF′) of the alkali metal cation-conducting solid-state electrolyte ceramic F′ <19>. This leads to a further improvement in conductivity.
The NaSICON solid-state electrolyte ceramic F <18> makes direct contact with the two interiors IKK<122> and IKM<132>, such that sodium ions can be routed from one interior into the other through the NaSICON solid-state electrolyte ceramic F <18>.
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 ceramic F <18> and the diffusion barrier D <14> extend over the entire depth and height of the three-chamber cell E <1>. 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 <13>. The connection VAM <15> formed between the 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 <11> 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 <103> through the NaSICON solid-state electrolyte F <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) forms in water, according to the reaction Cl2+H2O→HOCl+HCl, hypochlorous acid and hydrochloric acid, which give an acidic reaction with further water molecules. The acidity would damage the NaSICON solid-state electrolyte ceramic F <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 ceramic F <18> in the electrolysis cell E <1>. This considerably increases the lifetime thereof.
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 introduced into the diffusion barrier D <14> subsequently (for instance by stamping, drilling) or may already have been present therein from the outset on account of the production of the diffusion barrier D <14> (for example in the case of textile fabrics such as filter cloths or metal weaves).
As in the embodiment according to
In step (i) of the process according to the invention, an alkali metal cation-conducting solid-state electrolyte ceramic (=“ASC”) F′ having the surface OF′ is provided.
The ASC F′ provided in step (i) is subjected to step (ii) in the process according to the invention and, after step (ii), the ASC F is obtained with the surface OF. Since F is essentially obtained from F′ by removing a portion of ASC from F′ in step (ii) in order to arrive at F, F′ and F have essentially the same chemical structure.
A useful alkali metal cation-conducting solid-state electrolyte ceramic F′, and especially also F, is any solid-state electrolyte by which cations, especially alkali metal cations, even more preferably sodium cations, can be transported from IKM into IKK. 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 ceramic F′ 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, the alkali metal cation-conducting solid-state electrolyte ceramic F′, and especially also F, has an NaSICON structure of the formula
MI1+2w+x−y+zMIIwMIIIxZrIV2−w−x−yMVy(SiO4)z(PO4)3−z.
MI here is selected from Na+, Li+, preferably Na+.
MII here is a divalent metal cation, preferably selected from Mg2+, Ca2+, Sr2+, Ba2+, Co2+, Ni2+, more preferably selected from Co2+, Ni2+.
MIII here is a trivalent metal cation, preferably selected from Al3+, Ga3+, Sc3+, La3+, Y3+, Gd3+, Sm3+, Lu3+, Fe3+, Cr3+, more preferably selected from Sc3+, La3+, Y3+, Gd3+, Sm3+, especially preferably selected from Sc3+, Y3+, La3+.
MV here is a pentavalent metal cation, preferably selected from V5+, Nb5+, Ta5+.
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 process according to the invention, the alkali metal cation-conducting solid-state electrolyte ceramics F′ and F have the same structure.
In step (ii) of the process according to the invention, a portion of the alkali metal cation-conducting solid-state electrolyte ceramic F′ is removed by etching the surface OF with an etchant T.
The etchant T is preferably an acidic aqueous solution.
This affords an alkali metal cation-conducting solid-state electrolyte ceramic F with the surface OF, where the surface OF differs from the surface OF′ in at least one subregion OFΔ, and where the surface OF comprises the surfaces OA/MK and OKK, where OA/MK and/or OKK comprise at least a portion of OFΔ, and where in particular OA/MK and OKK comprise at least a portion of OFΔ.
4.2.1 Etching of the Surface OF′ with an Etchant T
“Etching of the surface OF with an etchant T” can be effected by any method familiar to the person skilled in the art.
Etchants T (also referred to as “mordant” or “etching fluid”) used may be agents familiar to the person skilled in the art. More particularly, the etchant T used is an acid or an oxidizing liquid.
The etchant T used is more preferably an aqueous acidic solution. These are particularly suitable on account of the ease of handling of such solutions and on account of the acid sensitivity of the ASCs.
In step (ii), the etching operation partly removes ASC from F′.
The extent to which ASC is removed from F can be controlled by the person skilled in the art via the selection of etchant T and via the time for which it is allowed to act on F′. In the preferred embodiment, in which the etchant T is an acidic aqueous solution, this can be controlled, for example, via the pH of this acidic aqueous solution.
What is meant by “acidic aqueous solution” is that the pH of this solution is <pH 7.
The pH of the aqueous acidic solution is then preferably <6.9, more preferably <6.5, even more preferably <6.0, even more preferably <5.6, even more preferably <5.0, even more preferably <4.0, even more preferably <2.0, even more preferably <1.0, even more preferably <0.5.
In another preferred embodiment, the pH of the aqueous acidic solution is then in the range of 0.5 to 6.9, more preferably in the range of 0.5 to 6.0, even more preferably in the range of 1.0 to 5.5, even more preferably in the range of 1.0 to 5.0, even more preferably in the range of 1.0 to 4.0, even more preferably in the range of 1.0 to 3.0.
The temperature of the etchant T in step (ii) is preferably 10° C. to 90° C., preferably 30° C. to 70° C., more preferably 40° C. to 60° C.
The aqueous acidic solution is especially a solution of an acid selected from the group of inorganic acids and organic acids, preferably selected from the group of the inorganic acids.
Typical organic acids are formic acid, acetic acid, trifluoroacetic acid.
The acid is preferably selected from the group consisting of H2SO4, HNO3, methanesulfonic acid, hydrohalic acids, especially HCl, HBr. Particular preference is given to HCl, H2SO4.
The duration over which the surface OF′ is etched with the etchant T, especially the acidic aqueous solution, is especially >1 min, preferably more than 30 min, preferably more than 60 min, even more preferably more than 120 min.
The etching of the surface OF′ with the etchant T, especially the acidic aqueous solution, can be conducted by contacting the surface OF′ with the etchant T, for example by immersing ASC F′ completely or partially in the etchant T, or by completely or partly spraying F′ with the etchant T.
In the etching of the surface OF′ with the etchant T in step (ii), it is possible to treat the entire surface OF′. This is possible in that, for example, a portion of the surface OF′ is first etched in a first sub-step, especially contacted with T, and ASC is removed in this part of the surface OF′, and then, in a second sub-step, the side of F′ that has not been contacted in the first sub-step is contacted with T and ASC is removed there. In this embodiment, the entire surface OF′ is treated in step (ii), and the surface OF of the resultant ASC F differs completely from OF′, meaning that OF and OFΔ are identical.
Alternatively and preferably, in step (ii), it is also possible to treat just part of the surface OF′. This is possible, for example, in that just a portion of the surface OF′ of F is contacted with T, and ASC is removed only in this part of the surface OF′. In addition, a portion of the surface OF′ may also be covered with a template, such that just part of the surface OF′ of the is removed in step (ii). In this case, an ASC F is obtained, the surface OF of which is still partly identical to the surface OF′ of F′ and differs from OF′ in the portion OFΔ.
In the embodiment of the present invention in which just a portion of the surface OF′ is treated in step (ii) and the surface OF of the ASC F obtained does not differ completely, but differs only partly, from OF′, the shape of OFΔ, if OFΔ is encompassed only at least partly by OA/MK and/or OKK, is subject to no further restriction. For example, OFΔ may form a coherent subregion on the surface OF. Alternatively, OFΔ may be formed by multiple unconnected subregions on the surface OF, such that the shape thereof is reminiscent of the shape of the black spots (which would correspond to OFΔ) on the white coat (which would correspond to OF) of the Dalmatian breed of dog.
If the entire surface OF′ is treated in step (ii), the surface OF of the resultant ASC F differs completely from OF′, meaning that OF and OFΔ are identical.
It is preferable that the surface OF′ of the ASC F′ is treated in step (ii) such that the area OFΔ formed by etching in the resulting ASC F comprises at least one of the surface portions OA/MK and OKK, and preferably comprises both. It is very particularly preferable that the part OFA of the surface OF formed by etching coincides with at least one of the parts OA/MK, OKK (OFΔ=OA/MK or OFΔ=OKK). It is even more preferable that the part OFA of the surface OF formed by etching coincides with both parts OA/MK, OKK (OFΔ=OA/MK+OKK).
The etching operation in step (ii) of the process according to the invention can be ended when the etchant T is removed from the surface OF of F, for example by washing it off with water.
In a preferred embodiment of step (ii) of the process according to the invention, the etching of the surface OF′ with the etchant T is ended by, after the etching of the surface OF′ with the etchant T, contacting the surface OF of the alkali metal cation-conducting solid-state electrolyte ceramic F with a neutral (pH 7) or alkaline (pH >7) aqueous solution.
Preference is given to using an alkaline aqueous solution that preferably has a pH in the range of 7.1 to 14.0, more preferably in the range of 8.0 to 14.0, even more preferably in the range of 9.0 to 14.0, even more preferably in the range of 10.0 to 14.0, even more preferably in the range of 11.0 to 14.0, even more preferably in the range of 12.0 to 14.0, even more preferably in the range of 13.0 to 14.0, even more preferably in the range of 13.5 to 14.0.
This stops the etching effect of the etchant T on the ASC.
The pH of the aqueous alkaline solution is preferably >7.1, more preferably >7.5, even more preferably >8.0, even more preferably >9.0, even more preferably >10.0, even more preferably >11.0, even more preferably >12.0, even more preferably >13.0, even more preferably >13.5.
The aqueous alkaline solution is especially an aqueous solution of a base selected from the group consisting of inorganic bases, especially alkali metal hydroxides, preferably NaOH, KOH.
The ending of the etching operation in the preferred embodiment of step (ii) can be accomplished by contacting the ASC F with the aqueous alkaline solution, for example by complete or partial immersion of ASC F in the aqueous alkaline solution or by complete or partial spraying of F with the aqueous alkaline solution.
After step (ii), i.e. once a portion of the alkali metal cation-conducting solid-state electrolyte ceramic F has been removed by etching the surface OF′ with an etchant T, the etching of the surface OF′ with the etchant T preferably having been ended by, after the etching of the surface OF′ with the etchant T, contacting the surface OF of the alkali metal cation-conducting solid-state electrolyte ceramic F with a neutral (pH 7) or alkaline (pH >7), an ASC F with the surface OF is then obtained. This is then disposed in the electrolysis cell E in step (iii).
In a preferred embodiment of the present invention, step (ii) is preceded by step (iii) and the electrolytic process step (iv-β), and thus takes place outside an electrolysis cell E.
In this preferred embodiment, the ASC F′ is not subjected to step (iii) and (iv-β) during the performance of step (ii).
Accordingly, it is preferably not the ASC F′ that is disposed in an electrolysis cell E and subjected to step (iv-β), but rather the ASC F according to step (iii) that has been obtained after step (ii).
The surprising advantage of the present invention is that step (ii) affords an ASC F having higher conductivity compared to the ASC F′ used in step (ii) when used in the electrolysis cell E according to step (iii) and step (iv-β).
More particularly, SMF′<SMF, where SMF′ is the mass-based specific surface area SM of the alkali metal cation-conducting solid-state electrolyte ceramic F′ before performance of step (ii) and where SMF is the mass-based specific surface area SM of the alkali metal cation-conducting solid-state electrolyte ceramic F after performance of step (ii). This means that the mass-based specific surface area SM of the ASC F subjected to step (ii) is increased during the performance of step (ii) from SMF′ to SMF in the ASC F obtained.
The mass-based specific surface area SM means the surface area A possessed by a material per unit mass m (SM=A/m, unit: m2/kg).
The comparison of the mass-based specific surface areas SMF′ and SMF, i.e. the testing of the condition whether SMF′<SMF, can be determined by methods known to the person skilled in the art for measuring the BET (Brunauer-Emmett-Teller) surface area, provided that both ASCs F and F′ are measured under the same conditions. Even if the ratio of the two parameters SMF′ and SMF is determined under different measurement conditions, the ratio SMF/SMF′ measured under particular measurement conditions will essentially be the same as the ratio SMF/SMF′ measured under different measurement conditions.
More particularly, in the context of the present invention, the mass-based specific surface areas are carried out via BET measurements to ISO 9277:2010 with N2 (purity 99.99% by volume) as adsorbent at 77.35 K.
Instrument: Quantachrome NOVA 2200e, Quantachrome Instruments.
Sample preparation: degassing of the sample at 60° C. at 1 Pa. The evaluation is especially undertaken via the static volumetric method (according to point 6.3.1 of standard ISO 9277:2010).
In respect of the ratio of SMF′ and SMF, i.e. the quotient SMF/SMF′, the following applies in a preferred embodiment of the present invention:
SMF/SMF′≥1.01, preferably SMF/SMF′≥1.1, preferably SMF/SMF′≥1.5, preferably SMF/SMF′≥2.0, preferably SMF/SMF′≥3.0, preferably SMF/SMF′≥5.0, preferably SMF/SMF′≥10, more preferably SMF/SMF′≥20, more preferably SMF/SMF′≥50, more preferably SMF/SMF′≥100, more preferably SMF/SMF′≥150, more preferably SMF/SMF′≥200, more preferably SMF/SMF′≥500, more preferably SMF/SMF′≥1000.
In another preferred embodiment of the present invention, the quotient SMF/SMF′ is in the range from 1.01 to 1000, preferably in the range from 1.1 to 800, more preferably in the range from 1.5 to 600, more preferably in the range from 2.0 to 500, more preferably in the range from 3.0 to 400, more preferably in the range from 5.0 to 300, more preferably in the range from 15 to 250, more preferably in the range from 180 to 220.
4.3 Step (iii)
In step (iii) of the process according to the invention, the ASC F obtained in step (ii) is disposed in an electrolysis cell E.
The electrolysis cell E comprises at least one anode chamber KA and at least one cathode chamber KK, and at least one interposed middle chamber KM. This also includes electrolysis cells E having more than one anode chamber KA and/or more than one cathode chamber KK and/or more than one 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 a preferred embodiment, comprises an anode chamber KA and a cathode chamber KK, and 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 selected 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 IKM of the middle chamber KM by the dividing wall W.
The dividing wall W comprises the alkali metal cation-conducting solid-state electrolyte ceramic F, and F makes direct contact with the interior IKK via the surface OKK and with the interior IKM via the surface OA/MK.
The dividing wall W comprises the alkali metal cation-conducting solid-state electrolyte ceramic F. What is meant by the feature “dividing wall” is that the dividing wall W is liquid-tight. What this means more particularly is that the alkali metal cation-conducting solid-state electrolyte ceramic F encompassed by the dividing wall divides the interior IKK and the interior IKM completely from one another, or comprises multiple alkali metal cation-conducting solid-state electrolyte ceramics which join one another, for example in a gapless manner.
There at least exist no gaps in the dividing wall W through which aqueous solution, alcoholic solution, alcohol or water could flow from IKK into IKM or vice versa.
What is meant by “makes direct contact” in respect of the arrangement of the alkali metal cation-conducting solid-state electrolyte ceramics in the dividing wall W and in the electrolysis cell E and in respect of the surfaces OKK and OA/MK is that there is a theoretical pathway from IKK into IKM that leads completely from IKK via OKK through F to OA/MK and ultimately into IKM.
It is preferable that at least 1% of the surface OA/MK is formed by OFΔ and/or, especially and, at least 1% of the surface OKK by OFΔ.
Even more preferably, at least 10% of the surface OA/MK is formed by OFΔ and/or, especially and, at least 10% of the surface OKK by OFΔ.
Even more preferably, at least 25% of the surface OA/MK is formed by OFΔ and/or, especially and, at least 25% of the surface OKK by OFΔ.
Even more preferably, at least 40% of the surface OA/MK is formed by OFΔ and/or, especially and, at least 40% of the surface OKK by OFΔ.
Even more preferably, at least 50% of the surface OA/MK is formed by OFΔ and/or, especially and, at least 50% of the surface OKK by OFΔ.
Even more preferably, at least 60% of the surface OA/MK is formed by OFΔ and/or, especially and, at least 60% of the surface OKK by OFΔ.
Even more preferably, at least 70% of the surface OA/MK is formed by OFΔ and/or, especially and, at least 70% of the surface OKK by OFΔ.
Even more preferably, at least 80% of the surface OA/MK is formed by OFΔ and/or, especially and, at least 80% of the surface OKK by OFΔ.
Even more preferably, at least 90% of the surface OA/MK is formed by OFΔ and/or, especially and, at least 90% of the surface OKK by OFΔ.
Even more preferably, 100% of the surface OA/MK is formed by OFΔ and/or, especially and, 100% of the surface OKK by OFΔ.
This is advantageous since, as a result, the surface of F that has been treated in accordance with the invention and takes part in the process according to the invention [step (iv-β)], i.e. through which the ion flow takes place in the electrolysis, is particularly large.
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. 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.
4.3.1.1.3 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 a prerequisite for the solution L1 to be obtained at the outlet AKK in the performance of the process according to 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 WA 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 is divided from the interior IKM of the middle chamber KM by a diffusion barrier D.
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. 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).
4.3.1.2.2 Inlet ZKA and Outlet AKA
The anode chamber KA 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 anode 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 when the solution L3 of a salt S is routed through the interior IKA of the anode 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 WA and corresponding connections (valves) that simplify the introduction and discharge of liquid. The inlet ZKA, in particular embodiments, may also be within the electrolysis cell, for example in the form of a perforation in the diffusion barrier D.
The electrolysis cell E has at least one middle chamber KM. The middle chamber KM lies between cathode chamber KK and anode chamber KA.
The interior IKA of the anode chamber KA 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 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 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
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
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.
4.3.1.3.2 Inlet ZKM and Outlet AKM
The 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 WA 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, 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 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 OEM of the middle chamber KM, and an inlet ZKA 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. This is advantageous especially since the outlet AKA, according to the invention, is formed at the top end OEA of the anode chamber KA.
What is more particularly meant by “outlet AKM at the base of the middle chamber KM” is 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.
What is more particularly meant by “inlet ZKA at the base of the anode chamber KA” is 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.
What is more particularly meant by “inlet ZKM at the top end OEM of the middle chamber KM” is 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.
What is more particularly meant by “outlet AKA at the top end OEA of the anode chamber KA” is that the outlet AKA is attached to 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 base of the middle chamber KM, and the inlet ZKA by 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 then 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 OEM 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 OEA of the electrolysis cell E), as shown more particularly in
3) When the connection VAM is formed within the electrolysis cell E, this may especially be implemented in that one side (“side A”) of the electrolysis cell E, which is the top end OE, comprises the inlet ZKM and the outlet AKA, and the diffusion barrier D extends proceeding from this side (“side A”) into the electrolysis cell E, but does not quite reach up to the opposite side (“side B”) of the electrolysis cell E from side A, which is then the base of the electrolysis cell E, and at the same time covers 50% or more of the height of the three-chamber cell E, preferably 60% to 99% of the height of the three-chamber cell E, more preferably 70% to 95% of the height of the three-chamber cell E, even more preferably 80% to 90% of the height of the three-chamber cell E, more preferably still 85% of the height of the three-chamber cell E. Because the diffusion barrier D does not touch side B of the three-chamber cell E, a gap thus arises between diffusion barrier D and the vessel BE on side B of the three-chamber cell E. In that case, the gap is the connection VAM. By virtue of this geometry, L3 must flow completely through the two chambers KM and KA.
These embodiments best assure 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. L3 in the case of AKM in
According to the invention, “top end OE of the electrolysis cell E” is the end 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 all figures) exits from the electrolysis cell E counter to gravity, or the end of the electrolysis cell E through which a solution (e.g. L3 in the case of ZKM in
The dividing wall W is arranged in the electrolysis cell E such that the alkali metal cation-conducting solid-state electrolyte ceramic F encompassed by the dividing wall W makes direct contact with the interior IKK via the surface OKK.
This means that the dividing wall W is arranged in the electrolysis cell E such that, when the interior IKK is completely filled with solution L2, the solution L2 contacts (i.e. wets) the surface OKK of the alkali metal cation-conducting solid-state electrolyte ceramic F encompassed by the dividing wall W, such that ions (e.g. alkali metal ions such as sodium, lithium) can enter the solution L2 from the alkali metal cation-conducting solid-state electrolyte ceramic F encompassed by the dividing wall W via the surface OKK.
In addition, the dividing wall W is arranged in the electrolysis cell E such that the alkali metal cation-conducting solid-state electrolyte ceramic F encompassed by the dividing wall W makes direct contact with the interior IKM via the surface OA/MK.
What this means is as follows: the electrolysis cell E comprises at least one middle chamber KM, and the dividing wall W adjoins the interior IKM of the middle chamber KM.
The dividing wall W is arranged in the electrolysis cell E such that, when the interior IKM is completely filled with solution L3, the solution L3 contacts (i.e. wets) the surface OA/MK of the alkali metal cation-conducting solid-state electrolyte ceramic F encompassed by the dividing wall W, such that ions (e.g. alkali metal ions such as sodium, lithium) from the solution L3 can enter the alkali metal cation-conducting solid-state electrolyte ceramic F encompassed by the dividing wall W via the surface OA/MK.
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 process is conducted in an electrolysis cell E.
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.
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 IKK. In the cases in which OKK encompasses at least a portion of OFA, the solution L2 makes direct contact here with the surface OFA. More particularly, the solution L2 then makes direct contact with the entire surface OFA encompassed by OKK.
This means that, in the cases in which OKK encompasses the entire surface OFA, L2 makes direct contact with at least part of the surface OFA, and, in the cases in which OKK encompasses only part of the surface OFA, L2 makes direct contact with at least part of the surface OFA encompassed by OKK.
This preferably means that, in the cases in which OKK encompasses the entire surface OFA, L2 makes direct contact with the whole surface OFA, and, in the cases in which OKK encompasses only part of the surface OFA, L2 makes direct contact with the whole part of the surface OFA encompassed by OKK.
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 IKM, then via VAM, then through IKA. In the cases in which OA/MK encompasses at least a portion of OFA, the solution L3 makes direct contact here with the surface OFA. More particularly, the solution L3 then makes direct contact with the entire surface OFA encompassed by OA/MK.
This means that, in the cases in which OA/MK encompasses the entire surface OFA, L3 makes direct contact with at least part of the surface OFA, and, in the cases in which OA/MK encompasses only part of the surface OFA, L3 makes direct contact with at least part of the surface OFA encompassed by OA/MK.
This preferably means that, in the cases in which OA/MK encompasses the entire surface OFA, L3 makes direct contact with the whole surface OFA, and, in the cases in which OA/MK encompasses only part of the surface OFA, L3 makes direct contact with the whole part of the surface OFA encompassed by OA/MK.
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:
the solution L1 is obtained at the outlet AKK with a higher concentration of XOR in L1 than in L2, an aqueous solution L4 of S is obtained at the outlet AKA, with a lower concentration of S in L4 than in L3.
In step (β3) of the process, in particular, such a voltage is applied that such a current flows 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 interior IKM) is in the range from 10 to 8000 A/m2, more preferably in the range from 100 to 2000 A/m2, even more preferably in the range from 300 to 800 A/m2, and even more preferably is 494 A/m2. 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 interior IKM of 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 is preferable that both OA/MK and OKK encompass part of the surface OFA. Step (β3) of the process is more preferably performed when the interior IKM is laden with L3 and the interior IKK with L2 at least to such an extent that L3 and L2 make direct contact with the surface OFA of the alkali metal cation-conducting solid-state electrolyte ceramic F encompassed by the dividing wall W. This is preferable since, as a result, the surface OFA obtained as a result of the treatment in step (ii) within the two surfaces OA/MK and OKK takes part in the electrolysis process, and the advantageous properties of the alkali metal cation-conducting solid-state electrolyte ceramic F, which are manifested in an increase in conductivity and hence an increase in current density at the same voltage, have a particularly positive effect.
The fact that transfer of charge takes place between EA and EK in step (β3) implies that IKK, IKM and IKA 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 IKM, VAM and IKA and a liquid stream of L2 through IKK, 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 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/1 lower than that of the aqueous solution L3 used in each case.
More particularly, steps (β1) to (β3) of the process 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) of the process, hydrogen is typically formed in the interior IKK of cathode chamber KK, which can be removed from the cell together with solution L1 via the 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 interior IKA of 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 from one another 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, these process steps are 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. This electrolysis cell consisted of three chambers, as shown in
The connection between middle chamber and anode chamber was established by a hose mounted at the base of the electrolysis cell. The anode chamber and middle chamber were separated by a 33 cm2 cation exchange membrane (Asahi Kasei, sulfonic acid groups on polymer). Cathode chamber and middle chamber were separated by a ceramic of the NaSICON type with an area of 33 cm2. The ceramic had a chemical composition of the formula Na3.4Zr2.0Si2.4P0.6O12.
The NaSICON ceramic used in Comparative Example 1, before being disposed within the cell, was cut with a further ceramic of equal dimensions from the same block.
The anolyte was transferred through the middle chamber into the anode chamber. The flow rate of the anolyte was 1 l/h, and that of the catholyte 1 l/h. The temperature was 60° C.
The voltage was varied within a range from 0 to 8 V while recording the current.
It was also 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.
Comparative Example 1 is 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. The arrangement corresponds to that shown in
This is reflected in even faster corrosion of the ceramic compared to Comparative Example 1, which leads to a more rapid rise in the voltage curve when the electrolysis is to be conducted at constant current over a defined period of time.
Comparative Example 1 is repeated.
For this purpose, the other NaSICON ceramic that was cut from the same block as that used in Comparative Example 1 is subjected to an etching process as follows:
The ceramic is first placed in 2 M H2SO4 at 60° C. for 2 hours. In the course of this, the solution is mixed gently with the aid of a stirrer. Subsequently, the sheet is rinsed with water and introduced into an NaOH bath (20% by weight).
Alternatively, the ceramic can also be installed directly into the electrolysis cell, which is then operated with NaOH as anolyte for 4 h.
This increases the mass-based specific surface area of the NaSICON ceramic by a factor of ˜200.
Thereafter, the electrolysis process according to Comparative Example 1 is repeated, with the surfaces that form on the ceramic in contact with the interiors of the cathode chamber and middle chamber.
It is found that a significantly lower voltage has to be applied over the duration of the electrolysis at the same current as in Comparative Example 1.
Comparative Example 2 is repeated using an electrolysis cell in which the solid-state electrolyte ceramic treated according to Inventive Example 1 is used. Here too, a significant reduction in voltage compared to Comparative Example 2 is necessary at the same current.
The etching of the NaSICON ceramic and the exposure of the surfaces that result from the treatment in the interiors of the anode chamber or middle chamber and the cathode chamber surprisingly increases the conductivity of the solid-state electrolyte.
The use of the three-chamber cell 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 the use of the electrolysis cell comprising at least one middle chamber in the process according to the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21195064.7 | Sep 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/073149 | 8/19/2022 | WO |
