Patent Application
20240216889
Hydrogen chloride is used in the production of chlorides, fertilizers, and dyes, in electroplating, and in the photographic, textile, and rubber industries. Hydrogen chloride is typically produced by combining chlorine and hydrogen. The industrial production of hydrogen chloride is often integrated with the formation of chlorinated and fluorinated organic compounds, e.g., Teflon, Freon, and other CFCs, as well as chloroacetic acid and PVC.
Hydrogen chloride is also produced in large quantities in industry as a by-product of organic chlorination reactions.
Some of the hydrogen chloride obtained as by-product is decomposed back into chlorine and hydrogen by gas phase oxidation or electrochemical processes such as hydrochloric acid diaphragm electrolysis. These processes are all very energy intensive, use precious metal catalysts and require diaphragms or membranes during electrolysis.
Thus, it would be of an advantage to provide a method for separating HCl from industrial process gases that allows an easy and cost efficient separation of HCl.
It is in generally known that chlorides form with hydrogen chloride (HCl) poly(hydrogen chloride)chlorates(—I) of the type [Cat][Cl(HCl)n]. Examples are the symmetrical ammonium salts NR4 (R=Me, Et, Pr, Bu, Pen). The symmetrical tetrapentylammonium bichloride is the first to be described as a liquid. In addition, the [NMe3(C16H33)] and a few imidazolium-based bichlorides are known. However, the efficiency of these known compounds for absorbing HCl is not satisfying. Note, that a long alkyl chain can undergo chlorination reactions which might lead into decomposition of the material or modifies the properties of the compound, as shown for corresponding polychloride systems.
The amount of HCl absorbed by said compounds depends on different factors, such as temperature and corresponding partial pressure of the hydrogen chloride, as well as physical properties of the ionic compound. For example, the properties of the ionic compounds such as viscosities, conductivities, molar mass, etc. can be influenced by the choice and substitution of the cation, as shown for polychlorides (WO 2019215037 A1).
It was therefore an object underlying the proposed solution to provide a compound that shows an improved storage capability for HCl.
This object is solved by providing a storage medium for storing hydrogen chloride with the features as described herein and a method for separating and storing hydrogen chloride with features as described herein.
Accordingly, a storage medium for storing hydrogen chloride (HCl) comprising at least one ionic compound of the general formulae (I)
Viscosity was measured using a Ubbelohde viscosimeter for determination of the kinematic viscosity according DIN 51 562-2. The dynamic viscosity was calculated from the kinematic viscosity after determination of the density.
The ionic liquid compound of formulae (I) allows for a reversible absorption and storage of HCl from process gas. Another advantage is that hydrogen H2 can be released from compound (1) by electrolysis in an electrochemical process. Further storage of chlorine Cl2 in the ionic liquid is possible that can be used as Cl2 source for further synthetic applications, such as synthesis of phosgen (Voßnacker et al., Novel Synthetic Pathway for the Production of Phosgene, Science Advances 2021, 7, eabj5186).
The storage medium for HCl according to the solution comprises an ionic compound, in particular an ionic liquid, made of an asymmetrically substituted ammonium cation and poly(HCl)chloride anion. The cation is an ammonium cation that has at least two different alkyl moieties. The ammonium cation may have two, three or four different alkyl moieties, in particular lower alkyl moieties.
The ionic liquid according to the solution has a low viscosity, high electrical conductivity, low decomposition voltage, low molar mass. Furthermore, these compounds are easy to synthesize and can be produced in large quantities from very cheap chemicals.
Moreover, the ionic liquid can be decomposed into hydrogen and chlorine by electrolysis at a low cell voltage. Thus, the ionic liquid can be used as an anhydrous system to produce chlorine and hydrogen.
The ionic liquid of the storage system according to the solution has several advantages: the IL shows low corrosion; efficient storage of HCl with simultaneous purification of other impurities, since they are not absorbed by the ionic liquid; electrolysis shows significant gas evolution only at one electrode, thus easier separation of the resulting products is available; possible simpler cell design of the electrolysis; potential avoidance of diaphragms or membranes in the cell; carbon electrodes may be used instead of expensive precious metals as electrode material.
In an embodiment of the present storage medium a, b=1, 2 or 3, and c=0, 1 in the ionic compound of general formula (I).
In a further embodiment of the present storage medium the ionic compound of general formula (I) is selected from [NEt3Me][Cl(HCl)n], [NEt2Me2][Cl(HCl)n], [NEtMe3][Cl(HCl)n], [NBuEt2Me][Cl(HCl)n], [NPr3Me][Cl(HCl)n], [NBu2Me2][Cl(HCl)n], [NBu3Me][Cl(HCl)n, with n being 1-6, preferably 1-4. It is to be understood that n can be any possible number between 1 and 6, preferably between 1 and 4. There is an equilibrium between different [Cl(HCl)n]− (n=1-4) species in the liquid.
In a preferred embodiment of the present storage medium the ionic compound of general formula (I) is selected from [NEt3Me][Cl(HCl)n], [NEt2Me2][Cl(HCl)n], [NEtMe3][Cl(HCl)n], with n being 1-6, preferably 1-4.
In still a further embodiment of the present storage medium the ionic compound of general formula (I) contains (in the loaded state) at least 0.3 g HCl/g ionic compound, preferably at least 0.4 g HCl/g ionic compound, more preferably at least 0.5 g HCl/g ionic compound. Thus, the storage capacity by mass may be between 0.3 and 1 g HCl/g ionic compound, preferably between 0.4 and 0.8 g HCl/g ionic compound, more preferably between 0.5 and 0.7 g HCl/g ionic compound. The storage capacity was determined as follows: A defined amount of chloride salt was loaded into a Schlenk flask. The chloride salt was loaded with HCl as described in the Example 1 and 2. The amount of HCl stored on the chloride salt was determined by weighing.
The storage capacity by amount of substance may be at least 1.5 mol/mol ionic compound, preferably at least 2.0 mol/mol ionic compound, more preferably at least 2.5 mol/mol ionic compound. The range of storage capacity by amount of substance may be between 1.5 and 3 mol/mol ionic compound, preferably between 2.0 and 2.8 mol/mol ionic compound, more preferably between 2.2 and 2.6 mol/mol ionic compound.
Furthermore, the present storage medium has a conductivity of at least 20 mS/cm (20° C.), preferably at least 30 mS/cm, more preferably at least 40 mS/cm, even more preferably at least 50 mS/cm. The conductivity was determined using a SevenCompact S230 Conductivity meter from Mettler Toledo.
The density of the present storage medium may be in a range between 0.5 and 1.5 kg/L, preferably between 0.8 and 1.2 kg/L, more preferably between 0.9 and 1.1 kg/L. Densities are determined by using a Schlenk tube with a volume scale in which a defined volume of the substance is weighted.
In an embodiment of the present storage medium a hydrogen H2 development is detectable at at least 1 V, preferably at least 0.8 V, more preferably at least 0.5 V, such as in the range of 1-1.5 V, preferably in the range of 1-1.2 V.
As mentioned, the storage medium according to the solution may be used for separating of HCl from process gas and/or for reversible absorption and storage of HCl from process gas.
This is done in a method for separating and storing hydrogen chloride HCl from HCl containing gas, in particular HCl containing process gas,
In an embodiment of the present method the ionic compound of general formula (II) is selected from [NEt3Me][Cl], [NEt2Me2][Cl], [NEtMe3][Cl], [NBuEt2Me][Cl], [NPr3Me][Cl], [NBu2Me2][Cl], preferably from [NEt3Me][Cl], [NEt2Me2][Cl], [NEtMe3][Cl].
As mentioned previously, the hydrogen chloride stored in the ionic compound of general formulae (I) of the storage medium may be released form said compound if needed.
In an embodiment the hydrogen chloride HCl stored in the ionic compound of general formulae (I) is split into hydrogen H2 and chlorine Cl2 by electrolysis, specifically by applying a cell voltage of at least 1 V, preferably at least 0.8 V, more preferably at least 0.5 V, such as in the range of 1-1.5 V, preferably in the range of 1-1.2 V.
Simultaneously to the release of hydrogen and chlorine the compound of general formulae (II) is obtained. Compound of formulae (II) may be recycled for reuse as HCl storage medium.
In a further embodiment the chlorine Cl2 released and obtained during electrolysis is (immediately) stored, in particular in the ionic compound of general formulae (II), providing an ionic compound of general formulae (III)
The storage of chlorine from chlorine containing gases is described for example in WO 2019/215037 A1.
The solution is now explained in more detail by means of examples with reference to the figures.
Accordingly, 2 molecules HCl are absorbed by [NEt3Me]Cl providing [NEt3Me][Cl(HCl)2]. When applying a voltage of about 1-1.2 V to [NEt3Me][Cl(HCl)2] the hydrogen chloride HCl stored in the ionic compound is split into hydrogen H2 and chlorine Cl2.
The chlorine Cl2 released and obtained during electrolysis is (immediately) stored as [NEt3Me][Cl—Cl—Cl] and subsequently released.
Simultaneously to the release of hydrogen and chlorine [NEt3Me]Cl is obtained that is recycled for reuse as HCl storage medium.
In the larger context of
[NEt3Me]Cl (36.2 g, 239 mmol) were dried at 150° C. for 1 hour to remove residual moisture. The dry salt was placed in a flask which was evacuated. Hydrogen chloride gas was introduced into the flask (18.5 g, 507 mmol, 2.12 equiv.) until the system retains a constant pressure of 950 mbar. A low viscous, colorless liquid, which stores 0.51 g HCl per g storage medium, is obtained.
The obtained compound can be described as [NEt3Me][Cl(HCl)2.16] which means there are 2.16 equivalents of HCl per Chloride. There is an equilibrium between different [Cl(HCl)n]− (n=1-4) species in the liquid. This was demonstrated for comparable [F(HF)n]− systems using NMR spectroscopy. The most stable [Cl(HCl)n] species is the [ClHCl]− anion of which also a molecular structure in the solid state was obtained.
Properties of [NEt3Me][Cl(HCl)2.16] were determined: Conductivity: 62.6 mS/cm at 25° C.; Viscosity: 12 mPa s, Density: 1.03 g/mL.
[NEt3Me][Cl(HCl)2.16] was characterized by current-voltage (CV) experiments (see Diagram of
Characterization of the gas phase via UV/Vis showed the formation of chlorine (see diagram of
1H NMR spectra of the remaining IL showed the signals for the cation and ClHCl (see diagram of
[NMePr3]Cl (1.52 g, 7.72 mmol) were dried at 150° C. for 1 hour to remove residual moisture. Hydrogen chloride was added to the system (0.757 g, 20.8 mmol, 2.69 equiv.). A low viscous, colorless liquid, which stores 0.50 g HCl per g storage medium, is obtained.
Further studies on [NR3Me][Cl(HCl)n] systems were performed and the following storage capacities, densities, dynamic viscosities and conductivities were determined. The samples of the loaded system were prepared as described above for [NEt3Me]Cl.
[a]Storage capacity by amount of substance is equal to the amount of substance of HCl which can be stored on 1 mol of the chloride salt.
[b]Storage capacity by mass is equal to the mass of HCl which can be stored on 1 kg of the chloride salt.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21192129.1 | Aug 2021 | EP | regional |
This application is a National Phase patent application of International Patent Application Number PCT/EP2022/072594, filed on Aug. 11, 2022, which claims priority of European Patent Application Number 21 192 129.1, filed on Aug. 19, 2021. The disclosure relates to a storage medium for storing hydrogen chloride, the use of such a storage medium for separating of HCl from process gas and/or for reversible absorption and storage of HCl from process gas; a method for separating and storing hydrogen chloride HCl from HCl containing gas, and a method for releasing hydrogen and chlorine from the storage medium.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/072594 | 8/11/2022 | WO |
