EP4144888A1 - Method for producing alkaline metal alcaholates in an electrolysis cell - Google Patents

Abstract

The present invention relates to a method for producing an alkali metal alkoxide solution L ₁ in an electrolytic cell E which comprises at least one cathode chamber K _K , at least one anode chamber K _A and optionally a central chamber K _M located in between.

The interior I _KK of the cathode chamber K _K is separated by a partition wall W comprising at least one alkali cation-conducting solid electrolyte ceramic (= "AFK") F (e.g. NaSICON) from the interior I _KA of the anode chamber K _A or in cases where the electrolytic cell E has a Middle chamber K _M , separated from the inner space I _KM of the middle chamber K _M. F has the surface O _F and a part O _A/MK of this surface O _F contacts the inner space I _KM or the inner space I _KA directly, and a part O _KK of this surface O _F contacts the interior I _KK directly.

The surface O _A/MK and/or the surface O _KK comprises at least part of a surface O _{F Δ} . O _FΔ results from a pre-treatment step in which F is produced from an AFK F' with the surface O _F' .

For this purpose, the surface O _{F ′} is removed by etching with an etchant Ä AFK of F ′ , and the AFK F with the surface O _F comprising the surface O _FΔ formed by the etching is obtained.

Electrolysis to produce the alkali metal alkoxides with F instead of F' results in improved conductivity, which means that a lower voltage can be used at a constant current density.

Description

The present invention relates to a method for producing an alkali metal alkoxide solution L ₁ in an electrolytic cell E which comprises at least one cathode chamber K _K , at least one anode chamber K _A and optionally a middle chamber K _M located in between.

The interior I _KK of the cathode chamber K _K is separated by a partition W comprising at least one alkali cation-conducting solid electrolyte ceramic (= "AFK") F (e.g. NaSICON) from the interior I _KA of the anode chamber K _A or in cases where the electrolytic cell E is a middle chamber Includes K _M , separated from the interior I _KM of the middle chamber K _M . F has the surface O _F , and a part O _A/MK of this surface O _F contacts the interior space I _KM or the interior space I _KA directly, and a part O _KK of this surface O _F contacts the interior space I _KK directly.

The surface O _A/MK and/or the surface O _KK comprises at least part of a surface O _FΔ . O _FΔ results from a pre-treatment step in which F is produced from an AFK F' with the surface O _{F '} .

For this purpose, the surface O _{F ′} is removed by etching with an etchant Ä AFK from F′, and the AFK F with the surface O _F comprising the surface O _FΔ formed by the etching is obtained.

Electrolysis to produce the alkali metal alkoxides with F instead of F' results in improved conductivity, which means that a lower voltage can be used at a constant current density.

1. Background of the Invention

The electrochemical production of alkali metal alkoxide solutions is an important industrial process that is used, for example, in DE 103 60 758 A1 , the U.S. 2006/0226022 A1 and the WO 2005/059205 A1 is described. The principle of this process is reflected in an electrolytic cell in whose anode chamber there is a solution of an alkali salt, for example common salt or NaOH, and in whose cathode chamber there is the alcohol in question or a low-concentration alcoholic solution of the alkali metal alcoholate in question, for example sodium methoxide or sodium ethoxide. The cathode compartment and the anode compartment are separated by a ceramic which conducts the alkali metal ion used, for example NaSICON or an analog for potassium or lithium. When a current is applied, chlorine is formed at the anode - if a chloride salt of the alkali metal is used - and hydrogen and alcohol ions are formed at the cathode. The charge equalization takes place in that alkali metal ions from the central chamber into the cathode chamber via the ceramic that is selective for them hike. The charge equalization between the middle chamber and the anode chamber takes place through the migration of cations when using cation exchange membranes or the migration of anions when using anion exchange membranes or through the migration of both types of ions when using non-specific diffusion barriers. This increases the concentration of the alkali metal alcoholate in the cathode chamber and the concentration of the sodium ions in the anolyte decreases.

NaSICON solid electrolytes are also used in the electrochemical production of other compounds:
WO 2014/008410 A1 describes an electrolytic process for the production of elemental titanium or rare earths. This process is based on the fact that titanium chloride is formed from TiO ₂ and the corresponding acid, this reacts with sodium alcoholate to form titanium alcoholate and NaCl and is finally converted electrolytically to form elemental titanium and sodium alcoholate.

WO 2007/082092 A2 and WO 2009/059315 A1 describe processes for the production of biodiesel in which triglycerides are first converted into the corresponding alkali metal triglycerides with the aid of alcoholates electrolytically produced via NaSICON and in a second step are converted into glycerol and the respective alkali metal hydroxide with electrolytically produced protons.

A disadvantage of the electrolytic cells described in the prior art, however, is that the resistance of the solid electrolyte ceramics used therein is relatively high. As a result, the specific energy consumption of the electrolytically produced materials increases and the energy-specific data (current, voltage) of the cell also deteriorate. Eventually the whole process becomes economically unviable.

The object of the present invention was therefore to provide a process for preparing an alkali metal alkoxide solution in an electrolytic cell which does not have this disadvantage.

A further disadvantage of conventional electrolytic cells in this technical field results from the fact that the solid electrolyte is not stable over the long term with respect to aqueous acids. This is problematic insofar as the pH drops in the anode chamber during electrolysis as a result of oxidation processes (for example when halogens are produced by disproportionation or by oxygen formation). These acidic conditions attack the NaSICON solid electrolyte, so the process cannot be used on an industrial scale. Various approaches have been described in the prior art to address this problem.

Thus, three-chamber cells have been proposed in the prior art. Such are known in the field of electrodialysis, for example US 6,221,225 B1 .

WO 2012/048032 A2 and US 2010/0044242 A1 describe, for example, electrochemical processes for the production of sodium hypochlorite and similar chlorine compounds in such a three-chamber cell. The cathode chamber and the middle chamber of the cell are separated by a cation-permeable solid electrolyte such as NaSICON. In order to protect this from the acidic anolyte, the middle chamber is supplied with solution from the cathode chamber, for example. The US 2010/0044242 A1 also describes in Figure 6 that solution from the middle compartment can be mixed with solution from the anode compartment outside the compartment to obtain sodium hypochlorite.

Such cells have also been proposed in the prior art for the production or purification of alkali metal alkoxides.

That's how she describes it US 5,389,211A a process for the purification of alcoholate solutions in which a three-chamber cell is used, in which the chambers are separated from one another by cation-selective solid electrolytes or non-ionic partitions. The center compartment is used as a buffer compartment to prevent the purified alkoxide or hydroxide solution from the cathode compartment from mixing with the contaminated solution from the anode compartment.

The DE 42 33 191 A1 describes the electrolytic production of alcoholates from salts and alcoholates in multi-chamber cells and stacks of several cells.

The WO 2008/076327 A1 describes a process for preparing alkali metal alkoxides. A three-chamber cell is used, the middle chamber of which is filled with alkali metal alkoxide (see, for example, paragraphs [0008] and [0067] of WO 2008/076327 A1 ). This protects the solid electrolyte separating the middle chamber and the cathode chamber from the solution in the anode chamber, which becomes more acidic during the electrolysis. A similar arrangement is described in WO 2009/073062 A1 . However, this arrangement has the disadvantage that the alkali metal alkoxide solution, which is consumed as a buffer solution and is continuously contaminated, is the desired product. Another disadvantage of the in the WO 2008/076327 A1 The method described is that the formation of the alcoholate in the cathode chamber depends on the diffusion rate of the alkali metal ions through two membranes or solid electrolytes. This in turn slows down the formation of the alcoholate.

Another problem arises from the geometry of the three-chamber cell. In such a chamber, the central chamber is separated from the anode chamber by a diffusion barrier and from the cathode chamber by an ion-conducting ceramic. It occurs during electrolysis thus unavoidable for the formation of pH gradients and dead volumes. This can damage the ion-conducting ceramic and consequently increase the voltage requirement of the electrolysis and/or lead to breakage of the ceramic.

While this effect takes place throughout the electrolysis chamber, the drop in pH is particularly critical in the middle chamber, as this is bounded by the ion-conducting ceramic. Gases are usually formed at the anode and the cathode, so that there is at least a certain degree of mixing in these chambers. On the other hand, such mixing does not take place in the middle chamber, so that the pH gradient develops in it. This undesirable effect is amplified by the fact that the brine is generally pumped relatively slowly through the electrolytic cell.

A further object of the present invention was therefore to provide an improved process for the electrolytic production of alkali metal alkoxide. This should not have the aforementioned disadvantages and should in particular ensure improved protection of the solid electrolyte against the formation of the pH gradient and more economical use of the educts compared to the prior art.

2. Summary of the Invention

The objects according to the invention are achieved by the method according to claim 1.

3. Pictures

The figures show preferred embodiments of the method according to the invention.

3.1 Figures 1A to 1D

The figures 1 A (= " 1 A"), 1 B (= " 1 B"), 1 C (= " 1 C"), and 1 D (= " 1 D") illustrate steps (i) and (ii) of the method according to the invention.

Fig. 1A shows an alkali cation-conducting solid electrolyte ceramic F'<19>, as provided according to step (i). This has a surface O _{F '} <190>. For example, the surface O _{F '} <190> comprises two sub-areas, in Fig. 1A these are the opposite surfaces denoted by the references <191> and <192>, of which the rear <192> is covered.

The AFK F'<19> will, as in Fig 1B shown, arranged in a process chamber <90> opposite a nozzle <40> such that the surface portion <191> faces it while the surface portion <192> faces away from it.

Fig. 1C shows the step of contacting with the etchant Ä <30>, an aqueous acidic HCl solution (pH 5.5). Ä <30> is applied to the surface O _{F '} <190> with the nozzle <40>. As a result, AFK is removed as particle <185> from F'<19>.

This method step gives an AFK F <18> whose surface O _F <180> comprises a partial surface O _A/MK <181> facing the nozzle <40> and a partial surface O _KK <182> facing away from the nozzle <40> . O _A/MK <181> in turn comprises a partial area O _FΔ <183>, which was formed by etching AFK from F'<19>.

Optionally, an aqueous alkaline NaOH solution (pH 14) can then be sprayed on in order to neutralize the acidic aqueous solution and specifically end the etching process so that no further pieces of AFK <185> are removed from F'.

Fig. 1D shows the AFK F <18> obtained in this way. This has a surface O _F <180>. The surface O _F <180> includes the two partial areas O _A/MK <181> and O _KK <182>. F <18> corresponds to F'<19> or the surface O _F <180> corresponds to the surface O _{F '} <190> with the difference that O _A/MK <181> includes the partial area O _FΔ <183>. Due to this partial area O _FΔ <183>, S _MF , that is the mass-related specific surface area S _M of the AFK F <18>, is greater than S _{MF '} , that is the mass-related specific surface area S _M of the AFK F'<19>.

3.2 Figures 2A and 2B

The Figure 2A (= " 2 A") shows an embodiment not according to the invention based on an electrolytic cell E, which is a two-chamber cell.

The electrolytic cell E comprises a cathode chamber K _K <12> and an anode chamber K _A <11>.

The anode chamber K _A <11> comprises an anodic electrode E _A <113> in the interior I _KA <112>, an inlet Z _KK <110> and an outlet A _KA <111>.

The cathode chamber K _K <12> comprises a cathodic electrode E _K <123> in the interior I _KK <122>, an inlet Z _KK <120> and an outlet A _KK <121>.

The electrolytic cell E is delimited by an outer wall W _A <80>.

The _interior I _KK <122> is also separated from the interior I _KA <112> separated. The NaSICON solid electrolyte ceramic F' <19> extends over the entire depth and height of the two-chamber cell E . The NaSICON solid electrolyte ceramic F' <19> contacts the two inner spaces I _KK <122> and I _KA <112> directly via the partial surfaces <192> and <191>, so that

Sodium ions can be conducted from one interior to the other through the NaSICON solid electrolyte ceramic F' <19>. In Figures 2 A and 2 B, the respective alkali cation-conducting solid electrolyte ceramic F' <19> or F <18> is arranged in the respective electrolytic cell in such a way that the darkened area in Figures 1 A or 1 D is visible in Figures 2 A and 2 B faces the viewer.

An aqueous solution of sodium chloride L ₃ <23> with pH 10.5 is added counter to gravity into the interior I _KA <112> via the inlet Z _KA <110>.

A solution of sodium methoxide in methanol L ₂ <22> is fed into the interior space I _KK <122> via the inlet Z _KK <120>.

A voltage is applied between the cathodic electrode E _K <123> and the anodic electrode E _A <113>. As a result, in the interior I _KK <122>, methanol in the electrolyte L ₂ <22> is reduced to methoxide and H ₂ (CH ₃ OH + e ^- → CH ₃ O ^- + ½ H ₂ ). Sodium ions diffuse from the interior I _KA <112> through the NaSICON solid electrolyte F <18> into the interior I _KK <122>. Overall, this increases the concentration of sodium methoxide in the interior I _KK <122>, as a result of which a methanolic solution of sodium methoxide L ₁ <21> is obtained, the concentration of sodium methoxide being higher than that of L ₂ <22>.

In the interior I _KA <112> the oxidation of chloride ions to molecular chlorine takes place (Cl ^- → ½ Cl ₂ + e ^- ). At the outflow A _KA <111>, an aqueous solution L ₄ <24> is obtained in which the NaCl content is reduced compared to L ₃ <23>. Chlorine gas Cl ₂ forms hypochlorous acid and hydrochloric acid in water according to the reaction Cl ₂ + H ₂ O → HOCl + HCl, which react acidically with other water molecules. The acidity damages the NaSICON solid electrolyte ceramic F' <19>.

Figure 2B (= " 2 B") shows an embodiment of the method according to the invention. The electrolytic cell E <1> corresponds to that in Fig. 2A shown arrangement with the difference that a NaSICON solid electrolyte ceramic F <18> with the surface O _F <180> pretreated with the method according to Figures 1 A to 1 D is used as the partition wall W <16>. F <18> has a partial surface O _KK <182> directly contacting the interior space I _KK <122> and a partial surface O _A/MK <181> directly contacting the interior space I _KA <112>. The NaSICON solid electrolyte F <18> is obtained from the NaSICON solid electrolyte F'<19> by the process shown in Figures 1 A to 1 D and, in contrast to F'<19>, has the partial area O _FΔ <183>, which has formed on the partial surface O _A/MK <181> as a result of the treatment in step (ii). As a result, the NaSICON solid electrolyte ceramic F <18> has a larger mass-related specific surface area S _MF than that ( S _MF' ) of the alkali cation-conducting solid electrolyte ceramic F'<19>. This leads to better conductivity, that is, to a Reducing the voltage at the same current during electrolysis, which leads to energy savings.

3.3 Figures 3A and 3B

The Figure 3A (= " 3 A") shows a further embodiment of the method according to the invention.

They show the method according to the invention using an electrolytic cell E<1>, which is a three-chamber cell.

The three-chamber electrolytic cell E <1> comprises a cathode chamber K _K <12>, an anode chamber K _A <11> and a middle chamber K _M <13> located therebetween.

The anode chamber K _A <11> comprises an anodic electrode E _A <113> in the interior I _KA <112>, an inlet Z _KK <110> and an outlet A _KA <111>.

The cathode chamber K _K <12> comprises a cathodic electrode E _K <123> in the interior I _KK <122>, an inlet Z _KK <120> and an outlet A _KK <121>.

The middle chamber K _M <13> comprises an interior space I _KM <132>, an inlet Z _KM <130> and an outlet A _KM <131>. The interior space I _KA <112> is connected to the interior space I _KM <132> via the connection V _AM <15>.

The electrolytic cell E <1> is delimited by an outer wall W _A <80>.

The interior I _KK <122> is also separated from the interior I KM <132> by a partition wall W <16>, which consists of a disk of a NaSICON solid electrolyte ceramic F <18> that is selectively permeable for sodium ions and has the surface _{O F} <180> separated. This has a partial surface O _KK <182> directly contacting the interior space I _KK <122> and a partial surface O _A/MK <181> directly contacting the interior space I _KM <132>. F <18> extends over the entire depth and height of the three-chamber cell E <1>. F <18> is obtained from the NaSICON solid electrolyte ceramic F'<19> by an etching process which corresponds to that shown in Figures 1A to 1D and, in contrast to F'<19>, has the partial region O _FΔ <183> , which has formed on the partial surface O _A/MK <181> as a result of method step (ii). In contrast to the in Figure 2B The NaSICON solid electrolyte ceramic F <18> shown is the surface O _FΔ <183> in the NaSICON solid electrolyte ceramic F <18> obtained by method step (ii). Figure 3A greater. In addition, not only the partial surface O _A/MK <181> but also partial surface O _KK <182> was treated in step (ii), which increases the mass-related specific surface S _MF even further. This more extensive processing is thus achieved by etching more extensively, and by processing F'<19> on both sides.

As a result, the NaSICON solid electrolyte F <18> has an even larger mass-related specific surface area S _MF than that ( S _MF' ) of the alkali cation-conducting solid electrolyte ceramic F'<19>. This leads to a further improvement in conductivity.

The NaSICON solid electrolyte ceramic F <18> contacts the two inner spaces I _KK <122> and I _KM <132> directly, so that sodium ions can be conducted from one inner space to the other through the NaSICON solid electrolyte ceramic F <18>.

The interior I _KM <132> of the middle chamber K _M <13> is additionally separated from the interior I _KA <112> of the anode chamber _KA <11> by a diffusion barrier D <14>. The NaSICON solid 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 Figure 3A the connection V _AM <15> is formed outside the electrolytic cell E <1>, in particular by a tube or hose, the material of which can be selected from rubber, metal or plastic. Through the connection V _AM <15>, liquid can be conducted from the interior I _KM <132> of the central chamber K _M <13> into the interior I _KA <112> of the anode chamber _KA <11> outside the three-chamber cell E <1>. The connection V _AM <15> connects an outlet A _KM <131>, which breaks through the outer wall _WA <80> of the electrolytic cell E <1> at the bottom of the central chamber K _M <13>, with an inlet Z _KA <110>, which breaks through the outer wall W _A <80> of the electrolytic cell E at the bottom of the anode chamber K _A <11>.

An aqueous solution of sodium chloride L ₃ <23> with pH 10.5 is added via the inlet Z _KM <130> in the same direction as gravity into the interior I _KM <132> of the central chamber K _M <13>. The interior space I _KM <132 is formed by the connection V _AM <15>, which is formed between the outlet A _KM <131> of the central chamber K _M <13> and an inlet Z _KA <110> of the anode chamber _KA <11>> of the middle chamber K _M <13> connected to the interior I _KA <112> of the anode chamber K _A <11>. Sodium chloride solution L ₃ <23> is conducted through this connection V _AM <15> from interior I _KM <132> to interior I _KA <112>.

A solution of sodium methoxide in methanol L ₂ <22> is fed into the interior space I _KK <122> via the inlet Z _KK <120>.

A voltage is applied between the cathodic electrode E _K <123> and the anodic electrode E _A <113>. As a result, in the interior I _KK <122>, methanol in the electrolyte L ₂ <22> is reduced to methoxide and H ₂ (CH ₃ OH + e ^- → CH ₃ O ^- + ½ H ₂ ). Sodium ions diffuse from the interior I _KM <132> of the middle chamber K _M <103> through the NaSICON solid electrolyte ceramic F <18> into the interior I _KK <122>. Overall, this increases the Concentration of sodium methoxide in the interior I _KK <122>, giving a methanolic solution of sodium methoxide L ₁ <21>, the concentration of sodium methoxide in which is increased compared to L ₂ <22>.

In the interior I _KA <112> the oxidation of chloride ions to molecular chlorine takes place (Cl ^- → ½ Cl ₂ + e ^- ). At the outflow A _KA <111>, an aqueous solution L ₄ <24> is obtained in which the NaCl content is reduced compared to L ₃ <23>. Chlorine gas Cl ₂ forms hypochlorous acid and hydrochloric acid in water according to the reaction Cl ₂ + H ₂ O → HOCl + HCl, which reacts acidically with other water molecules. The acidity would damage the NaSICON solid electrolyte ceramic F <18>, but is limited to the anode chamber K _A <11> by the arrangement in the three-chamber cell and is thus kept away from the NaSICON solid electrolyte ceramic F <18> in the electrolytic cell E <1>. This increases their lifespan considerably.

The Figure 3B (= " 3 B") shows a further embodiment of the method according to the invention. This is carried out in an electrolysis cell E <1>, which is of the type shown in Figure 3 A shown electrolytic cell corresponds to E <1> with the following difference:
The connection V _AM <15> from the interior I _KM <132> of the middle chamber K _M <13> to the interior I _KA <112> of the anode chamber K _A <11> is not outside, but through a perforation in the diffusion barrier D <14> formed within the electrolytic cell E <1>. This perforation can be introduced into the diffusion barrier D<14> subsequently (e.g. by stamping, drilling) or can already be present in the diffusion barrier D<14> from the outset due to the production thereof (eg in the case of textile fabrics such as filter cloths or metal fabrics).

As in the embodiment according to Figure 3A not only the partial surface O _A/MK <181>, but also partial surface O _KK <182> is treated, which further increases the mass-related specific surface area S _MF . However, O _FΔ <183> is smaller than in the embodiment according to FIG Figure 3A .

4. Detailed Description of the Invention 4.1 Step (i)

In step (i) of the method according to the invention, an alkali cation-conducting solid electrolyte ceramic (=“AFK”) F′ with the surface O _F′ is provided.

The AFK F′ provided in step (i) is subjected to step (ii) in the method according to the invention, and after step (ii) the AFK F with the surface O _F is obtained. Since F is essentially obtained from F' by removing a portion of AFK from F' in step (ii) to arrive at F, F' and F have essentially the same chemical structure.

Any solid electrolyte through which cations, in particular alkali cations, more preferably sodium cations, can be transported from I _AK to I _KK or from I _MK to I _KK can be used as the alkali cation-conducting solid electrolyte ceramic F', and in particular also F. Such solid electrolytes are known to those skilled in the art and, for example, in DE 10 2015 013 155 A1 , in the WO 2012/048032 A2 , paragraphs [0035], [0039], [0040], in the US 2010/0044242 A1 , paragraphs [0040], [0041], in which DE 10360758 A1 , paragraphs [014] to [025]. They are sold commercially under the names NaSICON, LiSICON, KSICON. A sodium ion conductive solid electrolyte ceramic F' is preferred, with this even more preferably having a NaSICON structure. NaSICON structures that can be used according to the invention are also, for example Anantharamulu N, Koteswara Rao K, Rambabu G, Vijaya Kumar B, Radha Velchuri, Vithal M, J Mater Sci 2011, 46, 2821-2837 described.

In a preferred embodiment, the alkali cation-conducting solid electrolyte ceramic F', and in particular also F, has a NaSICON structure of the formula M ^I _1+2w+x-y+z M ^II _w M ^III _x Zr ^IV _2-wxy M ^V _y (SiO ₄ ) _z (PO ₄ ) _3-z on.

M ^I is selected from Na ⁺ , Li ⁺ , preferably Na ⁺ .

M ^II is a divalent metal cation, preferably selected from Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ²⁺ , Co ²⁺ , Ni ²⁺ , more preferably selected from Co ²⁺ , Ni ²⁺ .

M ^III is a trivalent metal cation, preferably selected from Al ³⁺ , Ga ³⁺ , Sc ³⁺ , La ³⁺ , Y ³⁺ , Gd ³⁺ , Sm ³⁺ , Lu ³⁺ , Fe ³⁺ , Cr ³⁺ , more preferably selected from Sc ³⁺ , La ³⁺ , Y ³⁺ , Gd ³⁺ , Sm ³⁺ , particularly preferably selected from Sc ³⁺ , Y ³⁺ , La ³⁺ .

M ^V is a pentavalent metal cation, preferably selected from V ⁵⁺ , Nb ⁵⁺ , Ta ⁵⁺ .

The Roman indices I, II, III, IV, V indicate the oxidation numbers in which the respective metal cations are present.

w, x, y, z are real numbers, where 0 ≤ x < 2, 0 ≤ y < 2, 0 ≤ w < 2, 0 ≤ z < 3, and where w, x, y, z are so chosen become that 1 + 2w + x - y + z ≥ 0 and 2 - w - x - y ≥ 0.

According to the invention, the NaSICON structure more preferably has a structure of the formula Na( _{1 +v} )Zr ₂ Si _v P _(3−v) O ₁₂ , where v is a real number for which 0≦v≦3 applies. Most preferably v = 2.4

In a preferred embodiment of the method according to the invention, the solid electrolyte ceramics F′ and F which conduct alkali cations have the same structure. 4.2 Step (ii)

In step (ii) of the method according to the invention, part of the alkali cation-conducting solid electrolyte ceramic F' is removed by etching the surface O _{F '} with an etchant Ä.

The etchant A is preferably an acidic aqueous solution.

As a result, an alkali cation-conducting solid electrolyte ceramic F with the surface O _F is obtained, the surface O _F differing from the surface O F in at least a partial area O _{FΔ and} the surface O _F comprising the surfaces O _{A / MK} and O _KK , where O _A/MK and/or O _KK comprise at least part of O _FΔ .

4.2.1 Etching the surface O _{F '} with an etchant Ä

"Etching the surface O _{F '} with an etchant Ä" can be carried out using any method familiar to the person skilled in the art.

Agents familiar to the person skilled in the art can be used as etchant A (also referred to as “pickling agent” or “etchant liquid”). In particular, an acid or an oxidizing liquid is used as the etchant Ä.

An aqueous, acidic solution is particularly preferably used as the etchant A. These are particularly suitable because of the easy handling of such solutions and because of the acid sensitivity of the AFK.

In step (ii), part of F' is removed by the etching process AFK.

The extent to which AFK is removed from F' can be controlled by those skilled in the art through the choice of etchant λ and the time that F' is exposed to it. In the preferred embodiment, where the etchant, λ is an acidic aqueous solution, this can be controlled, for example, via the pH of this acidic aqueous solution.

"Acidic aqueous solution" means 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, more preferably <1.0, more preferably <0.5.

In another preferred embodiment, the pH of the aqueous acidic solution is then in the range 0.5 to 6.9, more preferably in the range 0.5 to 6.0, even more preferably in the range 1.0 to 5.5, more preferably in the range 1.0 to 5.0, more preferably in the range 1.0 to 4.0, more preferably in the range 1.0 to 3.0.

The temperature of the etchant A 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 in particular a solution of an acid selected from the group of inorganic acids and organic acids, preferably selected from the group of inorganic acids.

Typical organic acids are formic acid, acetic acid, trifluoroacetic acid.

The acid is preferably selected from the group consisting of H ₂ SO ₄ , HNO ₃ , methanesulfonic acid, hydrogen halides, in particular HCl, HBr. HCl, H ₂ SO ₄ are particularly preferred.

The duration over which the surface O _{F '} is etched with the etchant A, in particular the acidic aqueous solution, is in particular >1 min, preferably more than 30 min, preferably more than 60 min, even more preferably more than 120 min.

The etching of the surface O _{F '} with the etchant Ä, in particular the acidic aqueous solution, can be carried out by contacting the surface O _{F '} with the etchant Ä, for example by completely or partially immersing AFK F' in the etchant Ä or by complete or partial spraying of F' with the etchant Ä.

When etching the surface O _{F '} with the etchant Ä according to step (ii), the entire surface O _{F '} can be treated. This is possible, for example, by first etching a part of the surface O _{F '} in a first sub-step, in particular making contact with Ä and removing AFK from this part of the surface O _{F '} , and then in a second sub-step that in the first sub-step uncontacted side of F' is contacted with Ä and AFK is removed there. In this embodiment, the entire surface O _{F '} is treated according to step (ii) and the surface O _F of the obtained AFK F is completely different from O _{F '} , ie O _F and O _FΔ are identical.

Alternatively and preferably, only part of the surface O _{F ′} can also be treated in step (ii). This is possible, for example, by only making contact with A on a part of the surface O _{F '} of F and AFK being removed only on this part of the surface O _{F '} . In addition, part of the surface O _{F ′} can also be covered with a template, so that only part of the surface O _{F ′} is removed from that in step (ii). In this case, an AFK F will be obtained, whose surface O _F is still partially identical to the surface O _{F '} of F' and differs in part O _FΔ from O _{F '} .

In the embodiment of the present invention, in which only a part of the surface O _{F '} is treated in step (ii) and the surface O _F of the obtained AFK F is not completely but only partially different from O _{F '} , the shape of is O _FΔ , as long as O _FΔ is only at least partially encompassed by O _A/MK and/or O _KK , not further limited. For example , O _FΔ can form a contiguous subregion on the surface O _F . Alternatively, O _FΔ can be formed by several unconnected partial areas on the surface O _F so that their shape is reminiscent of the shape of the black spots (corresponds to O _FΔ ) on the white coat (corresponds to O _F ) of the dog breed "Dalmatian".

If the entire surface O _{F '} is treated according to step (ii), the surface O _F of the resulting AFK F differs completely from O _{F '} , ie O _F and O _FΔ are identical.

It is preferred that the surface O _{F '} of the AFK F' is treated in step (ii) in such a way that the area O _FΔ formed by the etching in the resulting AFK F comprises at least one of the surface parts O _{A / MK} and O _KK , preferably includes both. It is very particularly preferred that the part O _FΔ of the surface O _F formed by etching coincides with at least one of the parts O _A/MK , O _KK ( O _FΔ = O _A/MK or O _FΔ = O _KK ). More preferably, the part O _FΔ of the surface O _F formed by etching coincides with both parts O _A/MK , O _KK ( O _FΔ = O _A/MK + O _KK ).

The etching process in step (ii) of the method according to the invention can be terminated in that the etchant Ä is removed from the surface O _F of F, for example by washing it off with water.

In a preferred embodiment of step (ii) of the method according to the invention, the etching of the surface O _{F '} with the etchant Ä is terminated in that after the etching of the surface O _{F '} with the etchant Ä the surface O _F of the alkali cation-conducting solid electrolyte ceramic F with a neutral (pH 7) or alkaline (pH > 7) aqueous solution is contacted.

An alkaline aqueous solution is preferably used, which preferably has a pH in the range from 7.1 to 14.0, more preferably in the range from 8.0 to 14.0, even more preferably in the range from 9.0 to 14.0, even more preferably in the range from 10.0 to 14.0, even more preferably in the range from 11.0 to 14.0 , more preferably in the range 12.0 to 14.0, even more preferably in the range 13.0 to 14.0, even more preferably in the range 13.5 to 14.0.

This stops the caustic effect of the etchant Ä on the AFK.

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 more preferably at > 13.0, even more preferably at > 13.5.

The aqueous alkaline solution is in particular an aqueous solution of a base selected from the group consisting of inorganic bases, in particular alkali metal hydroxides, preferably NaOH, KOH.

The termination of the etching process in the preferred embodiment of step (ii) can be done by contacting the AFK F with the aqueous alkaline solution, for example by completely or partially immersing AFK F in the aqueous alkaline solution or by fully or partially spraying F with the aqueous alkaline solution can be carried out.

Subsequent to step (ii), i.e. after part of the alkali cation-conducting solid electrolyte ceramic F' has been removed by etching the surface O _{F '} with an etchant Ä, the etching of the surface O _{F '} with the etchant Ä being preferably ended in that after etching the surface O _{F '} with the etchant Ä the surface O _F of the alkali cation-conducting solid electrolyte ceramic F was contacted with a neutral (pH 7) or alkaline (pH > 7) aqueous solution, an AFK F with the surface O _F is then obtained . This is then placed in the electrolytic cell E in step (iii).

In a preferred embodiment of the present invention, step (ii) precedes step (iii) and electrolytic process steps (iv-a) or (iv-β) and thus takes place outside an electrolytic cell E.

In this preferred embodiment, the AFK F' is not subjected to step (iii) and (iv-a) or (iv-β) while carrying out step (ii).

Accordingly, preferably not the AFK F′, but only the AFK F obtained after step (ii) according to step (iii) is arranged in an electrolysis cell E and subjected to step (iv-a) or (iv-β).

4.2.2 Increase in the mass-related specific surface

The surprising advantage of the present invention is that through step (ii) an AFK F is obtained, compared to the in step (ii) used AFK F 'when used in the Electrolytic cell E according to step (iii) and step (iv-a) or (iv-β) has a higher conductivity.

In particular, it applies that S _{MF '} < S _MF , where S _{MF '} is the mass-related specific surface area S _M of the alkali cation-conducting solid electrolyte ceramic F' before step (ii) is carried out and where S _MF is the mass-related specific surface area S _M of the alkali cation-conducting solid electrolyte ceramic F after it has been carried out of step (ii). This means that the mass-related specific surface area S _M of the AFK F' subjected to step (ii) increases during the performance of step (ii) from S _MF' to S _MF in the AFK F obtained.

The mass-related specific surface S _M means the surface A that a material has per mass m ( S _M = A/m, unit m ² /kg).

The comparison of the mass-related specific surfaces S _MF' and S _MF , ie the examination of the condition whether S _MF' < S _MF , can be determined using methods known to those skilled in the art for measuring the BET (Brunauer-Emmett-Teller) surface area, as long as both AFK F and F' are measured under the same conditions. Even if the ratio of the two parameters S _MF' and S _MF is determined under different measurement conditions, the ratio S _MF / S _MF' measured under certain measurement conditions will essentially be the same as the ratio S _MF / S _MF' measured under other measurement conditions.

In particular, within the scope of the present invention, the mass-related specific surface areas are carried out via BET measurements according to ISO 9277:2010 with N ₂ (purity 99.99% by volume) as the adsorbent at 77.35 K.

Device: Quantachrome NOVA 2200e, Quantachrome Instruments.

Sample preparation: degassing of the sample at 60 °C at 1 Pa. The evaluation is carried out in particular using the static volumetric method (according to point 6.3.1 of the ISO 9277:2010 standard).

In a preferred embodiment of the present invention, the following applies to the ratio S _{MF '} and S _MF , ie the quotient S _MF / S _{MF '} :
S _MF / S _MF' ≥ 1.01, preferably S _MF / S _MF' ≥ 1.1, preferably S _MF / S _MF' ≥ 1.5, preferably _S MF / S _MF' ≥ 2.0, preferably S _MF / S _MF' ≥ 3.0, preferably S _MF / S _MF' ≥ 5.0, preferably S _MF / S _MF' ≥ 10, more preferably S _MF / S _MF' ≥ 20, more preferably S _MF / S MF' ≥ 50, more preferably S _MF / S _{MF' ≥} 100, more preferably S _MF / S _MF' ≥ 150, more preferably S _MF / S _MF' ≥ 200, more preferably S _MF / S _MF' ≥ 500, more preferably S _MF / S _MF' ≥ 1000.

In another preferred embodiment of the present invention, the quotient S _MF / S _MF' 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 of 3.0 to 400, more preferably in the range of 5.0 to 300, more preferably in the range of 15 to 250, more preferably in the range of 180 to 220.

4.3 Step (iii)

In step (iii) of the process according to the invention, the AFK F obtained in step (ii) is arranged in an electrolysis cell E.

4.3.1 Electrolytic cell E

The electrolytic cell E comprises at least one anode chamber K _A and at least one cathode chamber K _K and optionally at least one intermediate chamber K _M . This also includes electrolytic cells E which have more than one anode chamber K _A and/or more than one cathode chamber K _K and/or more than one middle chamber K _M . Such electrolytic cells, in which these chambers are joined together in a modular manner, are, for example, in DD 258 143 A3 and the U.S. 2006/0226022 A1 described.

In a preferred embodiment of the invention, the electrolytic cell E comprises an anode chamber K _A and a cathode chamber K _K and optionally a middle chamber K _M located in between.

The electrolytic cell E usually has an outer wall W _A . The outer wall W _A is in particular made of a material selected from the group consisting of steel, preferably rubberized steel, plastic, in particular Telene ^® (thermosetting polydicyclopentadiene), PVC (polyvinyl chloride), PVC-C (post-chlorinated polyvinyl chloride), PVDF (polyvinylidene fluoride ) is selected. W _A can be perforated in particular for inlets and outlets. Within W _A then lie the at least one anode chamber K _A , the at least one cathode chamber K _K and, in the embodiments in which the electrolytic cell E comprises such, the at least one intermediate chamber K _M .

4.3.1.1 Cathode chamber K _K

The cathode chamber K _K has at least one inlet Z _KK , at least one outlet A _KK and an interior space I _KK , which includes a cathodic electrode E _K .

The interior I _KK of the cathode chamber K _K is separated by the partition W from the interior I _KA of the anode chamber K _A if the electrolytic cell E does not include a central chamber K _M .

The partition W includes the alkali cation-conducting solid electrolyte ceramic F, and F then directly contacts the interior I _KK via the surface O _KK and the interior I _KA via the surface O _A/MK .

The interior I _KK of the cathode chamber K _K is separated by the partition W from the interior I _KM of the middle chamber K _M if the electrolytic cell E comprises at least one middle chamber K _M .

The partition W includes the alkali cation-conducting solid electrolyte ceramic F, and F then directly contacts the interior I _KK via the surface O _KK and the interior I _KM via the surface O _A/MK .

4.3.1.1.1 Partition W

The partition wall W includes the alkali cation-conducting solid electrolyte ceramic F. The feature "partition wall" means that the partition wall W is liquid-tight. This means in particular that the alkali cation-conducting solid electrolyte ceramic F enclosed by the partition wall completely separates the interior I _KK and the interior I _KM or the interior I _KK and the interior I _KA from one another, or comprises several alkali cation-conducting solid electrolyte ceramics which, for example, adjoin one another without gaps.

In any case, there are no gaps in the partition W through which aqueous solution, alcoholic solution, alcohol or water could flow from I _KK to I _AK or from I _KK to I _MK or vice versa.

"Direct contact" means for the arrangement of the alkali cation-conducting solid electrolyte ceramics in the partition wall W and in the electrolytic cell E as well as for the surfaces O _KK and O _A/MK that there is an imaginary path from I _KK to I _AK or from I _KK to I _MK , which leads completely from I _KK via O _KK through F to O _A/MK and finally in I _AK or I _MK .

It is preferred that at least 1% of the surface O _A/MK is formed by O _FΔ and/or, in particular and, at least 1% of the surface O _KK is formed by O _FΔ .

Even more preferably, at least 10% of the surface area O _A/MK is formed by O _FΔ and/or, in particular and, at least 10% of the surface area O _KK is formed by O _FΔ .

Even more preferably, at least 25% of the surface area O _A/MK is formed by O _FΔ and/or, in particular and, at least 25% of the surface area O _KK is formed by O _FΔ .

Even more preferably, at least 40% of the surface area O _A/MK is formed by O _FΔ and/or, in particular and, at least 40% of the surface area O _KK is formed by O _FΔ .

Even more preferably, at least 50% of the surface O _A/MK is formed by O _FΔ and/or, in particular and, at least 50% of the surface O _KK is formed by O _FΔ .

Even more preferably, at least 60% of the surface O _A/MK is formed by O _FΔ and/or, in particular and, at least 60% of the surface O _KK is formed by O _FΔ .

Even more preferably, at least 70% of the surface area O _A/MK is formed by O _FΔ and/or, in particular and, at least 70% of the surface area O _KK is formed by O _FΔ .

Even more preferably, at least 80% of the surface area O _A/MK is formed by O _FΔ and/or, in particular and, at least 80% of the surface area O _KK is formed by O _FΔ .

Even more preferably, at least 90% of the surface O _A/MK is formed by O _FΔ and/or, in particular and, at least 90% of the surface O _KK is formed by O _FΔ .

Even more preferably, 100% of the surface O _A/MK is formed by O _FΔ and/or, in particular and, 100% of the surface O _KK is formed by O _FΔ .

This is advantageous because the surface of F treated according to the invention, which takes part in the method according to the invention [steps (iv-a) or (iv-β)], ie through which the ion flow takes place during the electrolysis, is particularly large.

4.3.1.1.2 Cathodic electrode E _K

The cathode chamber K _K includes an interior space I _KK , which in turn includes a cathodic electrode E _K . Any electrode familiar to a person skilled in the art that is stable under the conditions of the method according to the invention can be used as such a cathodic electrode E _K . Such are in particular in WO 2014/008410 A1 , paragraph [025] or DE 10360758 A1 , paragraph [030]. This electrode E _K can be selected from the group consisting of mesh wool, three-dimensional matrix structure or "balls". The cathodic electrode E _K comprises in particular a material which is selected from the group consisting of steel, nickel, copper, platinum, platinized metals, palladium, palladium supported on carbon, titanium. E _K preferably comprises nickel.

4.3.1.1.3 Inlet Z _KK and outlet A _KK

The cathode chamber K _K also includes an inlet Z _KK and an outlet A _KK . This makes it possible to add liquid, such as solution L ₂ , to the inner space I _KK of the cathode chamber K _K and to remove liquid, such as solution L ₁ , located therein. The inlet Z _KK and the outlet A _KK are attached to the cathode chamber K _K that the liquid flowing through the interior I _KK of the cathode chamber K _K the cathodic Electrode E _K contacted. This is the prerequisite for the solution L ₁ being obtained at the outlet A _KK when the process according to the invention is carried out when the solution L ₂ of an alkali metal alcoholate XOR in the alcohol ROH is passed through the interior I _KK of the cathode chamber K _K .

The inlet Z _KK and the outlet A _KK can be attached to the electrolytic cell E by methods known to those skilled in the art, for example through bores in the outer wall W _A and corresponding connections (valves) that simplify the introduction and removal of liquid.

4.3.1.2 Anode chamber K _A

The anode chamber K _A has at least one inlet Z _KA , at least one outlet A _KA and an interior space I _KA , which includes an anodic electrode E _A .

The interior space I _KA of the anode chamber K _A is separated from the interior space I _KM of the center chamber K _M by a diffusion barrier D if the electrolytic cell E includes a central chamber K _M .

If the electrolytic cell E does not include a middle chamber K _M , the interior space I _KA of the anode chamber K is separated by the partition wall W from the interior space I _KK of the cathode chamber K _K .

4.3.1.2.1 Anodic Electrode E _A

The anode chamber K _A includes an interior space I _KA , which in turn includes an anodic electrode E _A . Any electrode familiar to a person skilled in the art that is stable under the conditions of the method according to the third aspect of the invention can be used as such an anodic electrode E _A . Such are in particular in WO 2014/008410 A1 , paragraph [024] or DE 10360758 A1 , paragraph [031]. This electrode E _A can consist of one layer or of several planar, mutually parallel layers, each of which can be perforated or expanded. The anodic electrode E _A comprises in particular a material which is selected from the group consisting of ruthenium oxide, iridium oxide, nickel, cobalt, nickel tungstate, nickel titanate, noble metals such as platinum in particular, which is deposited on a carrier such as titanium or ^Kovar® (an iron/nickel/ Cobalt alloy, in which the individual proportions are preferably as follows: 54% by mass iron, 29% by mass nickel, 17% by mass cobalt) is supported. Other possible anode materials are, in particular, stainless steel, lead, graphite, tungsten carbide, titanium diboride. The anodic electrode E _A preferably comprises a titanium anode (RuO ₂ +IrO ₂ /Ti) coated with ruthenium oxide/iridium oxide.

4.3.1.2.2 Inlet Z _KA and outlet A _KA

The anode chamber K _A also includes an inlet Z _KA and an outlet A _KA . This makes it possible to add liquid, such as solution L ₃ , to the interior space I _KA of the anode chamber K _A and to remove liquid, such as solution L ₄ , located therein. The inlet Z _KA and the outlet A _KA are attached to the anode chamber K _A in such a way that the liquid makes contact with the anodic electrode E _A as it flows through the interior space I _KA of the anode chamber K _A . This is the prerequisite for the solution L ₄ being obtained at the outlet A _KA when the method according to the invention is carried out if the solution L ₃ of a salt S is passed through the interior space I _KA of the anode chamber _KA .

The inlet Z _KA and the outlet A _KA can be attached to the electrolytic cell E by methods known to those skilled in the art, eg through bores in the outer wall W _A and corresponding connections (valves) that simplify the introduction and removal of liquid. In certain embodiments in which the electrolytic cell E comprises a central chamber K _M , the inflow Z _KA can also lie within the electrolytic cell, for example as a perforation in the diffusion barrier D .

4.3.1.3 Optional center chamber K _M

The electrolytic cell E preferably has a central chamber K _M . The optional middle chamber K _M is located between the cathode chamber K _K and the anode chamber K _A .

The interior space I _KA of the anode chamber K _A is separated from the interior space I _KM of the center chamber K _M by a diffusion barrier D if the electrolytic cell E includes a central chamber K _M . A _KM is then also connected to the inlet Z _KA by a connection V _AM , so that liquid can be conducted from I _KM into I _KA through the connection V _AM .

4.3.1.3.1 Diffusion barrier D

The interior I _KM of the optional central chamber K _M is separated from the interior I _KA of the anode chamber K _A by a diffusion barrier D and from the interior I _KK of the cathode chamber K _K by the partition wall W.

Any material which is stable under the conditions of the method according to the invention and which prevents or slows down the transfer of protons from the liquid in the interior I _KA of the anode chamber K _A to the interior I _KM of the optional middle chamber K _M can be used for the diffusion barrier D.

In particular, a non-ion-specific dividing wall or a membrane permeable to specific ions is used as the diffusion barrier D. The diffusion barrier D is preferably a non-ion-specific partition.

The material of the non-ion-specific partition wall is in particular selected from the group consisting of fabric, in particular textile fabric or metal fabric, glass, in particular sintered glass or glass frits, ceramic, in particular ceramic frits, membrane diaphragms, and is selected particularly preferably a textile fabric or metal fabric, particularly preferably a textile fabric. The textile fabric preferably comprises plastic, more preferably a plastic selected from PVC, PVC-C, polyvinyl ether ("PVE"), polytetrafluoroethylene ("PTFE").

If the diffusion barrier D is a “membrane that is permeable to specific ions”, this means according to the invention that the respective membrane favors the diffusion of certain ions through it compared to other ions. In particular, this means membranes that favor the diffusion through them of ions of a certain type of charge compared to oppositely charged ions. More preferably, specific ion permeable membranes also favor the diffusion of certain ions having one charge type through them over other ions of the same charge type.

If the diffusion barrier D is a “membrane permeable to specific ions”, the diffusion barrier D is in particular an anion-conducting membrane or a cation-conducting membrane.

According to the invention, anion-conducting membranes are those which selectively conduct anions, preferably selectively specific anions. In other words, they favor the diffusion of anions through them over that of cations, especially over protons, more preferably they additionally favor the diffusion of certain anions through them over the diffusion of other anions through them.

According to the invention, cation-conducting membranes are those which selectively conduct cations, preferably selectively specific cations. In other words, they favor the diffusion of cations through them over that of anions, more preferably they additionally favor the diffusion of certain cations through them over the diffusion of other cations through them, much more preferably cations where there is are not protons, more preferably sodium cations, over protons.

"Favour the diffusion of certain ions X over the diffusion of other ions Y" means in particular that the diffusion coefficient (unit m ² /s) of the ion species X at a given Temperature for the membrane in question by a factor of 10, preferably 100, preferably 1000 higher than the diffusion coefficient of the ionic species Y for the membrane in question.

If the diffusion barrier D is a “membrane that is permeable to specific ions”, it is preferably an anion-conducting membrane because this prevents the diffusion of protons from the anode chamber K _A into the middle chamber K _M particularly well.

In particular, a membrane which is selective for the anions comprised by the salt S is used as the anion-conducting membrane. Such membranes are known to those skilled in the art and can be used by them.

The salt S is preferably a halide, sulfate, sulfite, nitrate, bicarbonate or carbonate of X, more preferably a halide.

Halides are fluorides, chlorides, bromides, iodides. The most preferred halide is chloride.

A membrane selective for halides, preferably chloride, is preferably used as the anion-conducting membrane.

Anion-conducting membranes are for example by MA Hickner, AM Herring, EB Coughlin, Journal of Polymer Science, Part B: Polymer Physics 2013, 51, 1727-1735 , by CG Arges, V Ramani, PN Pintauro, Electrochemical Society Interface 2010, 19, 31-35 ,
in WO 2007/048712 A2 as well as on Page 181 of the textbook by Volkmar M. Schmidt Electrochemical Process Engineering: Fundamentals, Reaction Engineering, Process Optimization, 1st edition (October 8, 2003 ) described.

Organic polymers, which are selected in particular from polyethylene, polybenzimidazoles, polyetherketones, polystyrene, polypropylene or fluorinated membranes such as polyperfluoroethylene, preferably polystyrene, are therefore even more preferably used as anion-conducting membrane, with these covalently bonded functional groups selected from -NH ₃ ⁺ , - NRH ₂ ⁺ , -NR ₃ ⁺ , =NR ⁺ ;-PR ₃ ⁺ , where R is an alkyl group preferably having 1 to 20 carbon atoms, or other cationic groups. Preferably they have covalently bonded functional groups selected from -NH ₃ ⁺ , -NRH ₂ ⁺ , -NR ₃ ⁺ , more preferably selected from -NH ₃ ⁺ , -NR ₃ ⁺ , even more preferably -NR ₃ ⁺ .

If the diffusion barrier D is a cation-conducting membrane, it is in particular a membrane that is selective for the cations comprised by the salt S. The diffusion barrier D is even more preferably an alkali 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, in Page 181 of the textbook by Volkmar M. Schmidt Electrochemical Process Engineering: Fundamentals, Reaction Engineering, Process Optimization, 1st edition (October 8, 2003 ).

Accordingly, organic polymers, which are selected in particular from polyethylene, polybenzimidazoles, polyetherketones, polystyrene, polypropylene or fluorinated membranes such as polyperfluoroethylene, preferably polystyrene, polyperfluoroethylene, are even more preferably used as the cation-conducting membrane, with these covalently bonded functional groups selected from -SO ₃ ^- , -COO ^- , -PO ₃ ^2- , -PO ₂ H ^- , preferably -SO ₃ ^- , (described in DE 10 2010 062 804 A1 , U.S. 4,831,146 ) carry.

This can be, for example, a sulfonated polyperfluoroethylene ( ^Nafion® with CAS number: 31175-20-9). These are the expert, for example, from WO 2008/076327 A1 , paragraph [058], US 2010/0044242 A1 , paragraph [0042] or the U.S. 2016/0204459 A1 known and commercially available under the trade names ^Nafion® , ^Aciplex® F, ^Flemion® , ^Neosepta® , ^Ultrex® , PC- ^SK® . Neosepta ^® membranes are described, for example, by SA Mareev, D.Yu. Butylskii, ND Pismenskaya, C Larchet, L Dammak, VV Nikonenko, Journal of Membrane Science 2018, 563, 768-776 .

If a cation-conducting membrane is used as the diffusion barrier D, this can be, for example, a polymer functionalized with sulfonic acid groups, in particular of the following formula P _NAFION , where n and m independently of one another are an integer from 1 to 10 ⁶ , more preferably an integer from 10 to 10 ⁵ , more preferably is an integer from 10 ² to 10 ⁴ .

4.3.1.3.2 Inlet Z _KM and outlet A _KM

The optional middle chamber K _M also includes an inlet Z _KM and an outlet A _KM . This makes it possible to add liquid, such as solution L ₃ , to the interior space I _KM of the middle chamber K _M , and to transfer liquid therein, such as solution L ₃ , to the anode chamber K _A .

The inlet Z _KM and the outlet A _KM can be attached to the electrolytic cell E by methods known to those skilled in the art, for example through bores in the outer wall W _A and corresponding connections (valves) that simplify the introduction and removal of liquid. The drain A _KM can also be within the electrolytic cell, for example as a perforation in the diffusion barrier D.

4.3.1.3.3 Connection V _AM

In the electrolytic cell E, the outlet A _KM is connected to the inlet Z _KA by a connection V _AM in such a way that liquid can be conducted from I _KM into I _KA through the connection V _AM ,

1. 1) Ist die Verbindung V_AM innerhalb der Elektrolysezelle E ausgebildet, wird sie bevorzugt durch mindestens eine Perforation in der Diffusionsbarriere D gebildet. Diese Ausführungsform ist insbesondere dann bevorzugt, wenn als Diffusionsbarriere D eine nicht ionenspezifische Trennwand, insbesondere ein Metallgewebe oder textiles Gewebe eingesetzt wird. Dieses fungiert als Diffusionsbarriere D und weist aufgrund der Webeigenschaften von vorneherein Perforationen und Lücken auf, die als Verbindung V_AM fungieren.
2. 2) Die folgend beschriebene Ausführungsform ist insbesondere dann bevorzugt, wenn als Diffusionsbarriere D eine für spezifische Ionen durchlässige Membran eingesetzt wird: In dieser Ausführungsform ist die Verbindung V_AM außerhalb der Elektrolysezelle E ausgebildet, wobei sie bevorzugt durch eine außerhalb der Elektrolysezelle E verlaufende Verbindung von A_KM und Z_KA gebildet wird, insbesondere dadurch, dass vom Innenraum der Mittelkammer I_KM ein Ablauf A_KM , bevorzugt am Boden der Mittelkammer K_M , wobei noch bevorzugter der Zulauf Z_KM an der Oberseite O_EM der Mittelkammer K_M ist, gebildet wird, und ein Zulauf Z_KA in den Innenraum I_KA der Anodenkammer K_A , bevorzugt am Boden der Anodenkammer K_A , gebildet wird, und diese durch eine Leitung, beispielsweise ein Rohr oder ein Schlauch, der bevorzugt ein Material ausgewählt aus Gummi, Kunststoff umfasst, verbunden sind. Dies ist insbesondere deshalb vorteilhaft, da der Ablauf A_KA erfindungsgemäß an der Oberseite O_EA der Anodenkammer K_A ausgebildet.

The connection V _AM can be formed inside the electrolytic cell E and/or outside the electrolytic cell E, and is preferably formed inside the electrolytic cell.

1. 1) If the connection V _AM is formed within the electrolytic cell E, it is preferably formed by at least one perforation in the diffusion barrier D. This embodiment is particularly preferred when a non-ion-specific dividing wall, in particular a metal fabric or textile fabric, is used as the diffusion barrier D. This acts as a diffusion barrier D and, due to the weaving properties, has perforations and gaps from the outset, which act as a connection V _AM .
2. 2) The embodiment described below is particularly preferred when a membrane permeable to specific ions is used as the diffusion barrier D: In this embodiment, the connection V _AM is formed outside the electrolytic cell E, and it is preferably formed by a connection running outside of the electrolytic cell E A _KM and Z _KA is formed, in particular in that an outlet A _KM is formed from the interior of the middle chamber I _KM , preferably at the bottom of the middle chamber K _M , with the inlet Z _KM even more preferably being at the top O _EM of the middle chamber K _M and an inlet Z _KA into the interior I _KA of the anode chamber K _A , preferably at the bottom of the anode chamber K _A , is formed, and this through a line, for example a pipe or hose, which is preferably a material selected from rubber, plastic includes, are connected. This is particularly advantageous because the outlet A _KA is formed according to the invention on the upper side O _EA of the anode chamber K _A .

"Outflow A _KM at the bottom of the middle chamber K _M " means in particular that the outflow A _KM is attached to the electrolytic cell E in such a way that the solution L ₃ leaves the middle chamber K _M in the same direction as gravity.

"Inlet Z _KA at the bottom of the anode chamber K _A " means in particular that the inlet Z _KA is attached to the electrolytic cell E in such a way that the solution L ₃ enters the anode chamber K _A counter to the force of gravity.

"Feed Z _KM at the top O _EM of the central chamber K _M " means in particular that the feed Z _KM is attached to the electrolytic cell E such that the solution L ₃ enters the central chamber K _M in the same direction as gravity.

"Outflow A _KA on the top O _EA of the anode chamber K _A " means in particular that the outflow A _KA is attached to the electrolytic cell E in such a way that the solution L ₄ leaves the anode chamber K _A against the force of gravity.

This embodiment is particularly advantageous and therefore preferred if the outlet A _KM is formed through the base of the central chamber K _M and the inlet Z _KA is formed through the base of the anode chamber K _A . This arrangement makes it particularly easy to discharge gases formed in the anode chamber K _A with L ₄ from the anode chamber K _A in order to then separate them further.

If the connection V _AM is formed outside the electrolytic cell E, in particular Z _KM and A _KM are arranged on opposite sides of the outer wall W _A of the central chamber K _M (i.e. Z _KM on the bottom and A _KM on the top O _EM of the electrolytic cell E or vice versa) and Z _KA and A _KA are arranged on opposite sides of the outer wall W _A of the anode chamber K _A (i.e. Z _KA on the bottom and A _KA on the top O _EA of the electrolytic cell E), as is particularly the case in Figure 3A is shown. Due to this geometry , L ₃ must flow through the two chambers K _M and K _A . In this case, Z _KA and Z _KM can be formed on the same side of the electrolytic cell E, with A _KM and A _KA then automatically also being formed on the same side of the electrolytic cell E. Alternatively, Z _KA and Z _KM can be formed on opposite sides of the electrolytic cell E, with A _KM and A _KA then automatically also being formed on opposite sides of the electrolytic cell E.
3) If the connection V _AM is formed inside the electrolytic cell E, this can be ensured in particular by having one side ("side A") of the electrolytic cell E, which is the top O _E , the inlet Z _KM and comprises the outlet A _KA and the diffusion barrier D extends from this side ("side A") into the electrolytic cell E, but not all the way to the side A opposite ("side B") of the electrolytic cell E, where it then it is the bottom of the electrolytic cell E, and it is 50% or more of the height of the three-chamber cell E, more preferably 60% to 99% of the height of the three-chamber cell E, even 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, even more preferably 85% of the height of the three-chamber cell E spans. The fact that the diffusion barrier D does not touch side B of the three-chamber cell E creates a gap between the diffusion barrier D and the container B _E on side B of the three-chamber cell E. The gap is then the connection V _AM . Due to this geometry , L ₃ must flow completely through the two chambers K _M and K _A .

These embodiments best ensure that the aqueous salt solution L ₃ flows past the acid-sensitive solid electrolyte before it comes into contact with the anodic electrode E _A , as a result of which acids are formed.

"Bottom of the electrolytic cell E" is, according to the invention, the side of the electrolytic cell E through which a solution (e.g. L ₃ at A _KM in Figure 3A) in the same direction as gravity exits the electrolytic cell E or the side of the electrolytic cell E through which a solution (e.g. L ₂ at Z _KK in Figures 2 A, 3 A and 3 B and L ₃ at A _KA in Figures 2 A, 2 B and 3 A) of the electrolytic cell E is fed against gravity.

According to the invention, "top O _E of the electrolytic cell E" is the side of the electrolytic cell E through which a solution (e.g. L ₄ at A _KA and L ₁ at A _KK in all figures) escapes from the electrolytic cell E against the force of gravity or the side of the Electrolytic cell E, through which a solution (eg L ₃ at Z _KM in Figures 3 A and 3 B) is fed to the electrolytic cell E in the same direction as gravity.

4.3.1.4 Arrangement of the partition wall W in the electrolytic cell E

The dividing wall W is arranged in the electrolytic cell E in such a way that the solid electrolyte ceramic F, which conducts alkali cations and is enclosed by the dividing wall W, makes direct contact with the interior space I _KK via the surface O _KK .

This means that the dividing wall W is arranged in the electrolytic cell E in such a way that when the interior space I _KK is completely filled with solution L ₂ , the solution L ₂ contacts the surface O _KK of the alkali cation-conducting solid electrolyte ceramic F enclosed by the dividing wall W ( ie wetted), so that ions (eg alkali metal ions such as sodium, lithium) from the alkali cation-conducting solid electrolyte ceramic F, which is surrounded by the partition W, can enter the solution L ₂ via the surface O _KK .

In addition, in the embodiments in which the electrolytic cell E does not include a central chamber K _M , the dividing wall W is arranged in the electrolytic cell E in such a way that the solid electrolyte ceramic F, which is included in the dividing wall W and which conducts alkali cations, makes direct contact with the interior space I _KA via the surface O _A/MK .

This means the following: in the embodiments in which the electrolytic cell E does not include a central chamber K _M , the partition wall W borders on the interior space I _KA of the anode chamber K _A .

In these embodiments, the dividing wall W is arranged in the electrolytic cell E in such a way that when the interior I _KA is completely filled with solution L ₃ , the solution L ₃ then covers the surface O _{A / MK} of the alkali cation-conducting solid electrolyte ceramic F surrounded by the dividing wall W contacted (ie wetted), so that ions (eg alkali metal ions such as sodium, lithium) from the solution L ₃ can enter the alkali cation-conducting solid electrolyte ceramic F, which is covered by the partition W, via the surface O _{A / MK} .

In addition, in cases where the electrolytic cell E comprises at least one central chamber K _M , the partition W is arranged in the electrolytic cell E in such a way that the solid electrolyte ceramic F, which conducts alkali cations, is contained in the partition W, the interior space I _KM over the surface O _A/MK directly contacted.

This means the following: in the embodiments in which the electrolytic cell E comprises at least one central chamber K _M , the partition wall W borders on the interior space I _KM of the central chamber K _M .

In these embodiments, the dividing wall W is arranged in the electrolytic cell E in such a way that when the interior space I _KM is completely filled with solution L ₃ , the solution L ₃ then covers the surface O _A/MK of the alkali cation-conducting solid electrolyte ceramic F surrounded by the dividing wall W contacted (ie wetted), so that ions (eg alkali metal ions such as sodium, lithium) from the solution L ₃ can enter the alkali cation-conducting solid electrolyte ceramic F, which is covered by the partition W, via the surface O _{A / MK} .

4.4 Process steps according to the invention

The present invention relates to a process for preparing a solution L ₁ 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 carried out in an electrolytic cell E.

Preferably X is 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, methyl, more preferably selected from the group consisting of ethyl, methyl. Most preferably R is methyl.

4.4.1 Process steps in an electrolytic cell E without a central chamber KM

In the cases in which the electrolytic cell E does not include a middle chamber K _M , the steps (α1), (α2), (α3) running simultaneously are carried out.

4.4.1.1 Step (α1)

In step (α1), a solution L ₂ comprising the alcohol ROH, preferably comprising an alkali metal alkoxide XOR and alcohol ROH, is passed through I _KK . In cases where O _KK comprises at least part of O _FΔ , the solution L ₂ contacts the surface O _FΔ directly. In particular, the solution L ₂ then contacts the entire surface O _FΔ encompassed by O _KK directly.

This means that in the cases where O _KK covers the whole surface O _FΔ , L ₂ directly contacts at least a part of the surface O _FΔ , and in the cases where O _KK covers only a part of the surface O _FΔ , L ₂ directly contacts at least part of the part of the surface O _FΔ comprised by O _KK .

This means preferably that in the cases where O _KK covers the whole surface O _FΔ , L ₂ contacts the whole surface O _FΔ directly, and in the cases where O _KK covers only part of the surface O _FΔ , L ₂ directly contacts the entire part of the surface O _FΔ encompassed by O _KK .

The solution L ₂ is preferably free of water. According to the invention, “free of water” means that the weight of the water in the solution L ₂ based on the weight of the alcohol ROH in the solution L ₂ (mass ratio) is ≦1:10, more preferably ≦1:20, even more preferably ≦1:100 , more preferably ≤ 0.5:100.

If the solution L ₂ comprises XOR, the mass fraction of XOR in the solution L ₂ , based on the entire solution L ₂ , is in particular >0 to 30% by weight, preferably 5 to 20% by weight, even more preferably at 10 to 20% by weight, more preferably at 10 to 15% by weight, most preferably at 13 to 14% by weight, most preferably at 13% by weight.

If the solution L ₂ includes XOR, the mass ratio of XOR to alcohol ROH in the solution L ₂ is in particular in the range from 1:100 to 1:5, more preferably in the range from 1:25 to 3:20, even more preferably in the range 1:12 to 1:8, more preferably at 1:10.

4.2.1.2 Step (α2)

In step (α2), a neutral or alkaline, aqueous solution L ₃ of a salt S comprising X as a cation is passed through I _KA . In cases where O _A/MK comprises at least part of O _FΔ , the solution L ₃ contacts the surface O _FΔ directly. In particular, the solution L ₃ then directly contacts the entire surface O _FΔ encompassed by O _A/MK .

This means that in the cases where O _A/MK encompasses the whole surface O _FΔ , L ₃ contacts at least part of the surface O _FΔ directly, and in the cases where O _A/MK only comprises a portion of the surface O _FΔ , L ₃ directly contacts at least a portion of the portion of the surface O _FΔ comprised by O _A/MK .

This means preferably that in cases where O _A/MK encompasses the whole surface O _FΔ , L ₃ contacts the whole surface O _FΔ directly, and in cases where O _A/MK only a part of the surface O _FΔ comprises, L ₃ directly contacts the entire part of the surface O _FΔ comprised by O _A/MK .

The salt S is preferably a halide, sulfate, sulfite, nitrate, bicarbonate or carbonate of X, more preferably a halide.

Halides are fluorides, chlorides, bromides, iodides. The most preferred halide is chloride.

The pH of the aqueous solution L ₃ is ≧7.0, preferably in the range from 7 to 12, more preferably in the range from 8 to 11, even more preferably from 10 to 11, most preferably at 10.5.

The mass fraction of the salt S in the solution L ₃ is preferably in the range > 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 at 20% by weight, based on the total solution L ₃ .

4.2.1.3 step (α3)

In step (α3), a voltage is then applied between E _A and E _K .

This leads to a current transport from the charge source to the anode, to a charge transport via ions to the cathode and finally to a current transport back to the charge source. The charge source is known to those skilled in the art and is typically a rectifier that converts alternating current into direct current and can generate certain voltages via voltage converters.

• am Ablauf A_KK wird die Lösung L₁ erhalten, wobei die Konzentration von XOR in L₁ höher ist als in L₂,
• am Ablauf A_KA wird eine wässrige Lösung L₄ von S erhalten, wobei die Konzentration von S in L₄ geringer ist als in L₃ .

This in turn has the following consequences:

• at the outlet A _KK the solution L ₁ is obtained, the concentration of XOR in L ₁ being higher than in L ₂ ,
• at the outlet A _KA an aqueous solution L ₄ of S is obtained, the concentration of S in L ₄ being lower than in L ₃ .

In step (α3) of the method, such a voltage is applied in particular that a current flows such that the current density (= ratio of the current flowing to the electrolytic cell to the Area of the solid electrolyte that contacts the anolyte in the interior I _KA ) is in the range from 10 to 8000 A/m ² , more preferably in the range from 100 to 2000 A/m ² , even more preferably in the range from 300 to 800 A/m ² , more preferably 494 A/m ² . This can be determined by a person skilled in the art by default. The area of the solid electrolyte that contacts the anolyte in the interior I _KA is in particular 0.00001 to 10 m ² , preferably 0.0001 to 2.5 m ² , more preferably 0.0002 to 0.15 m ² , even more preferably 2.83 cm ² .

It is preferred that both O _A/MK and O _KK comprise part of the surface O _FΔ . Step (α3) of the method is then even more preferably carried out if the interior space I _KA is at least loaded with L ₃ and the interior space I _KK is loaded with L ₂ at least to the extent that L ₃ and L ₂ Partition W covered surface O _FΔ of the alkali cation-conducting solid electrolyte ceramic F contact directly. This is preferred because the surface O _FΔ obtained by the treatment in step (ii) takes part within both surfaces O _{A / MK} and O _KK in the electrolysis process and the advantageous properties of the alkali cation-conducting solid electrolyte ceramic F, which result in an increase in conductivity and thereby reflect an increase in current at the same voltage, have a particularly positive effect.

The fact that charge transport takes place between E _A and E _K in step (a3) implies that I _KK and I _KA are loaded simultaneously with L ₂ and L ₃ , respectively, in such a way that they extend the electrodes E _A and E _K so far cover that the circuit is closed.

This is particularly the case when a liquid flow is continuously passed from L ₃ through I _KA and a liquid flow from L ₂ through I _KK and the liquid flow from L ₃ passes the electrode E _A and the liquid flow from L ₂ passes the electrode E _K at least partially , preferably completely covered.

In a further preferred embodiment, the method is carried out continuously, ie step (α1) and step (α2) are carried out continuously and voltage is applied in accordance with step (α3).

After step (α3) has been carried out, the solution L ₁ is obtained at the outlet A _KK , the concentration of XOR in L ₁ being higher than in L ₂ . If L ₂ already comprised XOR, the concentration of XOR in L ₁ is preferably 1.01 to 2.2 fold, more preferably 1.04 to 1.8 fold, even more preferably 1077 to 1.4 fold, even more preferably 1077 to 1077 fold 1.08-fold higher than in L ₂ , most preferably 1,077-fold higher than in L ₂ , more preferably with the mass fraction of XOR in L ₁ and in L ₂ being in the range 10 to 20% by weight, even more preferably 13 to 14% by weight.

At outlet A _KA an aqueous solution L ₄ of S is obtained, the concentration of S in L ₄ being lower than in L ₃ .

The concentration of the cation X in the aqueous solution L ₃ is preferably in the range from 3.5 to 5 mol/l, more preferably 4 mol/l. The concentration of the cation X in the aqueous solution L ₄ is more preferably 0.5 mol/l lower than that of the aqueous solution L ₃ used in each case.

In particular, steps (α1) to (α3) of the process are carried out 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 a pressure of 0.5 bar to 1.5 bar, preferably 0.9 bar to 1.1 bar, more preferably 1.0 bar.

When carrying out steps (α1) to (α3) of the method, hydrogen is typically produced in the interior I _KK of the cathode chamber K _K , which hydrogen can be removed from the cell via the outlet A _KK together with the solution L ₁ . In a particular embodiment of the present invention, the mixture of hydrogen and solution L ₁ can then be separated by methods known to those skilled in the art. In the interior I _KA of the anode chamber K _A , if the alkali metal compound used is a halide, in particular chloride, chlorine or another halogen gas can form, which can be removed from the cell via the outlet A _KK together with the solution L ₄ . In addition, oxygen and/or carbon dioxide can also be formed, which can also be removed. In a particular embodiment of the present invention, the mixture of chlorine, oxygen and/or CO ₂ and solution L ₄ can then be separated by methods known to those skilled in the art. Likewise, after the gases chlorine, oxygen and/or CO ₂ have been separated from the solution L ₄ , these can be separated from one another by methods known to those skilled in the art.

4.4.2 Process steps in an electrolytic cell E with a central chamber K _M

In cases in which the electrolytic cell E comprises at least one central chamber K _M , steps (β1), (β2), (β3) are carried out simultaneously.

It is preferred that the electrolytic cell E comprises at least one middle chamber K _M , and then the steps (β1), (β2), (β3) running simultaneously are carried out.

4.4.2.1 Step (β1)

In step (β1), a solution L ₂ comprising the alcohol ROH, preferably comprising an alkali metal alkoxide XOR and alcohol ROH, is passed through I _KK . In cases where O _KK comprises at least part of O _FΔ , the solution L ₂ contacts the surface O _FΔ directly. In particular, the solution L ₂ then contacts the entire surface O _FΔ encompassed by O _KK directly.

This means that in the cases where O _KK covers the whole surface O _FΔ , L ₂ directly contacts at least part of the surface O _FΔ , and in the cases where O _KK only part of the Surface O _FΔ includes, L ₂ at least a part of the part of the surface O _KK covered by O _FΔ contacted directly.

This means preferably that in the cases where O _KK covers the whole surface O _FΔ , L ₂ contacts the whole surface O _FΔ directly, and in the cases where O _KK covers only part of the surface O _FΔ , L ₂ directly contacts the entire part of the surface O _FΔ encompassed by O _KK .

The solution L ₂ is preferably free of water. According to the invention, “free of water” means that the weight of the water in the solution L ₂ based on the weight of the alcohol ROH in the solution L ₂ (mass ratio) is ≦1:10, more preferably ≦1:20, even more preferably ≦1:100 , more preferably ≤ 0.5:100.

If the solution L ₂ comprises XOR, the mass fraction of XOR in the solution L ₂ , based on the entire solution L ₂ , is in particular >0 to 30% by weight, preferably 5 to 20% by weight, even more preferably at 10 to 20% by weight, more preferably at 10 to 15% by weight, most preferably at 13 to 14% by weight, most preferably at 13% by weight.

If the solution L ₂ includes XOR, the mass ratio of XOR to alcohol ROH in the solution L ₂ is in particular in the range from 1:100 to 1:5, more preferably in the range from 1:25 to 3:20, even more preferably in the range 1:12 to 1:8, more preferably at 1:10.

4.4.2.2 Step (β2)

In step (β2), a neutral or alkaline aqueous solution L ₃ of a salt S comprising X as a cation is passed through I _KM , then over V _AM , then through I _KA . In cases where O _A/MK comprises at least part of O _FΔ , the solution L ₃ contacts the surface O _FΔ directly. In particular, the solution L ₃ then directly contacts the entire surface O _FΔ encompassed by O _A/MK .

This means that in cases where O _A/MK encompasses the whole surface O _FΔ , L ₃ directly contacts at least part of the surface O _FΔ , and in cases where O _A/MK only part of the surface O _FΔ , L ₃ directly contacts at least part of the part of the surface O _FΔ comprised by O _A/MK .

This means preferably that in cases where O _A/MK encompasses the whole surface O _FΔ , L ₃ contacts the whole surface O _FΔ directly, and in cases where O _A/MK only a part of the surface O _FΔ comprises, L ₃ directly contacts the entire part of the surface O _FΔ comprised by O _A/MK .

The salt S is preferably a halide, sulfate, sulfite, nitrate, bicarbonate or carbonate of X, more preferably a halide.

Halides are fluorides, chlorides, bromides, iodides. The most preferred halide is chloride.

The pH of the aqueous solution L ₃ is ≧7.0, preferably in the range from 7 to 12, more preferably in the range from 8 to 11, even more preferably from 10 to 11, most preferably at 10.5.

The mass fraction of the salt S in the solution L ₃ is preferably in the range > 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 at 20% by weight, based on the total solution L ₃ .

4.4.2.3 Step (β3)

In step (β3), a voltage is then applied between E _A and E _K .

This leads to a current transport from the charge source to the anode, to a charge transport via ions to the cathode and finally to a current transport back to the charge source. The charge source is known to those skilled in the art and is typically a rectifier that converts alternating current into direct current and can generate certain voltages via voltage converters.

• am Ablauf A_KK wird die Lösung L₁ erhalten, wobei die Konzentration von XOR in L₁ höher ist als in L₂,
• am Ablauf A_KA wird eine wässrige Lösung L₄ von S erhalten, wobei die Konzentration von S in L₄ geringer ist als in L₃ .

This in turn has the following consequences:

• at the outlet A _KK the solution L ₁ is obtained, the concentration of XOR in L ₁ being higher than in L ₂ ,
• at the outlet A _KA an aqueous solution L ₄ of S is obtained, the concentration of S in L ₄ being lower than in L ₃ .

In step (β3) of the method, such a voltage is applied in particular that a current flows such that the current density (= ratio of the current flowing to the electrolytic cell to the area of the solid electrolyte that contacts the anolyte I _KM located in the interior) is in the range of 10 to 8000 A/m ² , more preferably in the range of 100 to 2000 A/m ² , even more preferably in the range of 300 to 800 A/m ² , even more preferably 494 A/m ² . This can be determined by a person skilled in the art by default. The area of the solid electrolyte that contacts the anolyte in the interior I _KM of the middle chamber K _M is in particular 0.00001 to 10 m ² , preferably 0.0001 to 2.5 m ² , more preferably 0.0002 to 0.15 m ² , even more preferably 2.83 cm ² .

It is preferred that both O _A/MK and O _KK comprise part of the surface O _FΔ . Step (β3) of the method is then even more preferably carried out when the interior space I _KM is at least loaded with L ₃ and the interior space I _KK is loaded with L ₂ at least to the extent that L ₃ and L ₂ Partition W covered surface O _FΔ of the alkali cation-conducting solid electrolyte ceramic F contact directly. This is preferred because the surface O _FΔ obtained by the treatment in step (ii) takes part within both surfaces O _{A / MK} and O _KK in the electrolysis process and the advantageous properties of the alkali cation-conducting solid electrolyte ceramic F, which result in an increase in conductivity and thereby reflect an increase in current at the same voltage, have a particularly positive effect.

The fact that charge transport takes place between E _A and E _K in step (β3) implies that I _KK , I _KM and I _KA are simultaneously charged with L ₂ and L ₃ , respectively, in such a way that they connect the electrodes E _A and E Cover _K so far that the circuit is closed.

This is particularly the case when a liquid stream is continuously passed from L ₃ through I _KM , V _AM and I _KA and a liquid stream from L ₂ through I _KK and the liquid stream from L ₃ passes the electrode E _A and the liquid stream from L ₂ the electrode E _K at least partially, preferably completely covered.

In a further preferred embodiment, the process is carried out continuously, ie step (β1) and step (β2) are carried out continuously and voltage is applied in accordance with step (β3).

After step (β3) has been carried out, the solution L ₁ is obtained at the outlet A _KK , the concentration of XOR in L ₁ being higher than in L ₂ . If L ₂ already comprised XOR, the concentration of XOR in L ₁ is preferably 1.01 to 2.2 fold, more preferably 1.04 to 1.8 fold, even more preferably 1077 to 1.4 fold, even more preferably 1077 to 1077 fold 1.08-fold higher than in L ₂ , most preferably 1,077-fold higher than in L ₂ , more preferably with the mass fraction of XOR in L ₁ and in L ₂ being in the range 10 to 20% by weight, even more preferably 13 to 14% by weight.

At outlet A _KA an aqueous solution L ₄ of S is obtained, the concentration of S in L ₄ being lower than in L ₃ .

The concentration of the cation X in the aqueous solution L ₃ is preferably in the range from 3.5 to 5 mol/l, more preferably 4 mol/l. The concentration of the cation X in the aqueous solution L ₄ is more preferably 0.5 mol/l lower than that of the aqueous solution L ₃ used in each case. In particular, steps (β1) to (β3) of the process are carried out 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 a pressure of 0.5 bar to 1.5 bar, preferably 0.9 bar to 1.1 bar, more preferably 1.0 bar.

When carrying out steps (β1) to (β3) of the method, hydrogen is typically produced in the interior I _KK of the cathode chamber K _K , which hydrogen can be discharged from the cell together with the solution L ₁ via the outlet A _KK . In a particular embodiment of the present invention, the mixture of hydrogen and solution L ₁ can then be separated by methods known to those skilled in the art. In the interior I _KA of the anode chamber K _A , if the alkali metal compound used is a halide, in particular chloride, chlorine or another halogen gas can form, which can be removed from the cell via the outlet A _KK together with the solution L ₄ . In addition, oxygen and/or carbon dioxide can also be formed, which can also be removed. In a particular embodiment of the present invention, the mixture of chlorine, oxygen and/or CO ₂ and solution L ₄ can then be separated by methods known to those skilled in the art. Likewise, after the gases chlorine, oxygen and/or CO ₂ have been separated from the solution L ₄ , these can be separated from one another by methods known to those skilled in the art.

4.4.2.4 Additional advantages of steps (β1) to (β3)

Carrying out steps (β1) to (β3) brings other surprising advantages which were not to be expected in the light of the prior art. Steps (β1) to (β3) of the method according to the invention protect the acid-labile solid electrolyte from corrosion without having to sacrifice alcoholate solution from the cathode space as a buffer solution, as in the prior art. These process steps are therefore more efficient than those in

WO 2008/076327 A1 described procedure in which the product solution is used for the middle chamber, which reduces the overall turnover.

5. Examples 5.1 Comparative example 1

Sodium methylate (NM) was produced via a cathodic process, with 20% by weight NaCl solution (in water) being fed into the anode chamber and 10% by weight methanolic NM solution being fed into the cathode chamber. The electrolytic cell consisted of three chambers, as in Figure 3A shown.

The connection between the middle and anode chamber was made by a hose that was attached to the bottom of the electrolytic cell. The anode compartment and middle compartment were separated by a 33 cm ² cation exchange membrane (Asahi Kasei, sulfonic acid groups on polymer). The cathodes and middle chamber were separated by a ceramic of the NaSICON type with an area of 33 cm ² . The ceramic had a chemical composition of the formula Na _3.4 Zr _2.0 Si _2.4 P _0.6 O ₁₂ .

Before being placed in the cell, the NaSICON ceramic used in Comparative Example 1 was cut from the same block together with another ceramic of the same dimensions.

The anolyte was transferred to the anode compartment through the middle compartment. The flow rate of the anolyte was 1 l/h, that of the catholyte was 1 l/h. The temperature was 60°C.

The voltage was changed in a range from 0 to 8 V and the current was recorded.

It was also observed that a pH gradient formed in the middle chamber over a longer period of time, which can be attributed to the migration of the ions to the electrodes in the course of the electrolysis and the propagation of the protons formed at the anode in subsequent reactions. This local increase in the pH value is undesirable since it can attack the solid electrolyte and can lead to corrosion and breakage of the solid electrolyte, especially over very long running times.

5.2 Comparative example 2

Comparative example 1 is repeated with a two-chamber cell comprising only an anode and a cathode chamber, the anode chamber being separated from the cathode chamber by the ceramic of the NaSICON type. The arrangement corresponds to that in Figure 2 A shown. Thus, this electrolytic cell does not contain a center chamber.

This is reflected in even more rapid corrosion of the ceramic compared to Comparative Example 1, which leads to a faster increase in the voltage curve if the electrolysis is to be operated at a constant current intensity over a defined time.

5.3 Example 1 according to the invention

Comparative example 1 is repeated.

To do this, the other NaSICON ceramic 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 MH ₂ SO ₄ at 60° C. for 2 hours. The solution is gently mixed with a stirrer. The plate is then rinsed with water and placed in an NaOH bath (20% by weight).

Alternatively, the ceramic can also be built directly into the electrolytic cell, which is then operated with NaOH as the anolyte for 4 hours.

The mass-related specific surface of the NaSICON ceramic increases by a factor of ~ 200.

Thereafter, the electrolysis process of Comparative Example 1 is repeated, with the surfaces formed on the ceramic contacting the interiors of the cathode and center chambers.

It is found that with the same current intensity as in Comparative Example 1, a significantly lower voltage has to be applied over the duration of the electrolysis.

5.4 Example 2 according to the invention

Comparative example 2 is repeated using an electrolytic cell in which the solid electrolyte ceramic treated in accordance with example 1 according to the invention is used. Here, too, a voltage that is significantly lower than that in comparative example 2 is required for the same current intensity.

5.5 Outcome

The etching of the NaSICON ceramic and the exposure of the surfaces resulting from the treatment on the interior spaces of the anode chamber or middle chamber and the cathode chamber surprisingly increase the conductivity of the solid electrolyte.

The use of the three-chamber cell in the method of the invention also prevents corrosion of the solid electrolyte while at the same time not sacrificing an alkali metal alkoxide product for the center chamber and keeping the voltage constant. These advantages, which can already be seen from the comparison of the two comparative examples 1 and 2, underline the surprising effect of using the electrolytic cell comprising at least one middle chamber in the process according to the invention.

6. Reference marks in the figures

component abbreviation Reference marks in figures electrolytic cell E <1> anode chamber K _A <11> Intake Z _KA <110> Sequence A _KA <111> inner space I _KA <112> anodic electrode E _A <113> cathode chamber K _K <12> Intake Z _KK <120> Sequence A _KK <121> inner space I _KK <122> cathodic electrode E _K <123> center chamber K _M <13> Intake Z _KM <130> Sequence _AKM <131> inner space I _KM <132> diffusion barrier D <14> Connection _VAM <15> partition wall W <16> Solid electrolyte ceramic after step (ii) f <18> atomized particles of the solid electrolyte ceramic F <185> surface of F O _F <180> Section of O _F which in the electrolytic cell E directly contacts the interior I _KM of the middle chamber K _M or the interior I _KA of the anode chamber K _{A OA/MK} <181> Section of O _F that contacts the interior I _KK of the cathode chamber K _K in the electrolytic cell E directly O _KK <182> Portion of O _F formed by etching in step (ii) of the method according to the invention; O _F differs from O _F' through this sub-area O _FΔ <183> solid electrolyte ceramic before step (ii) F' <19> surface of F' O _F' <190> Part of O _F' <191> Part of O _F' <192> Alkali metal alkoxide XOR in alcohol ROH _L1 <21> Solution comprising the alcohol ROH _L2 <22> neutral or alkaline, aqueous solution of a salt S comprising X as a cation _L3 <23> aqueous solution of S, where [ S ] _L4 < [ S ] _L3 . _L4 <24> caustic Ä <30> jet <40> outer wall _WA <80> Process chamber for etching treatment <90>

Claims (15)

Process for preparing a solution L ₁ <21> of an alkali metal alkoxide XOR in the alcohol ROH in an electrolytic cell E <1>, where X is an alkali metal cation and R is an alkyl radical having 1 to 4 carbon atoms,
comprising the following steps: (i) an alkali cation-conducting solid electrolyte ceramic F' <19> with the surface O _F' <190> is provided; (ii) a part of the alkali cation conductive solid electrolyte ceramic F' <19> is removed by etching the surface O _F' <190> with an etchant λ <30>, thereby obtaining an alkali cation conductive solid electrolyte ceramic F <18> with the surface O _F <180> where the surface O _F <180> differs from the surface O _F' <190> in at least one partial area O _FΔ <183>,
and wherein the surface O _F <180> comprises the surfaces O _A/MK <181> and O _KK <182>, where O _A/MK <181> and/or O _KK <182> at least a portion of O _FΔ <183 > include (iii) and the alkali cation-conducting solid electrolyte ceramic F <18> in an electrolytic cell E <1>, which comprises at least one anode chamber K _A <11>, at least one cathode chamber K _K <12> and optionally at least one intermediate chamber K _M <13> ,
wherein the at least one anode chamber K _A <11> - at least one inlet Z _KA <110>, - at least one sequence A _KA <111>, - and an interior space I _KA <112> with an anodic electrode E _A <113>, wherein the at least one cathode chamber K _K <12> - at least one inlet Z _KK <120>, - at least one sequence A _KK <121>, - and an interior space I _KK <122> with a cathodic electrode E _K <123>, and where in the cases where the electrolytic cell E <1> comprises at least one central chamber K _M <13>, this - at least one inlet Z _KM <130>, - at least one sequence A _KM <131>, - and an interior space I _KM <132> includes,
and in which case I _KA <112> and I _KM <132> are separated from one another by a diffusion barrier D <14>, and A _KM <131> is connected to the inlet Z _KA <110> by a connection V _AM <15>, so that liquid can be conducted from I _KM <132> to I _KA <112> through the connection V _AM <15>, is arranged so that in cases where the electrolytic cell E <1> does not include a middle chamber K _M <13>, I _KA <112> and I _KK <122> are separated from one another by a partition wall W <16> comprising the alkali cation-conducting solid electrolyte ceramic F <18> , where F <18> directly contacts the interior I _KK <122> via the surface O _KK <182> and the interior I _KA <112> via the surface O _A/MK <181>, in cases where the electrolytic cell E <1> comprises at least one central chamber K _M <13>, I _KK <122> and I _KM <132> are separated from one another by a partition wall W <16> comprising the alkali cation-conducting solid electrolyte ceramic F <18> where F <18> directly contacts the interior I _KK <122> via the surface O _KK <182> and the interior I _KM <132> via the surface O _A/MK <181>, (iv-α) and then, in cases where the electrolytic cell E <1> does not include a central chamber K _M <13>, the following steps (α1), (α2), (α3) are carried out simultaneously: (α1) a solution L ₂ <22> comprising the alcohol ROH is passed through I _KK <122>, whereby if O _KK <182> comprises at least part of O _FΔ <183>, the solution L ₂ <22> die surface O _FΔ <183> directly contacts, (α2) a neutral or alkaline aqueous solution L ₃ <23> of a salt S comprising X as a cation is passed through I _KA <112>, where if O _A/MK <181> at least a part of O _FΔ <183> the solution L ₃ <23> directly contacts the surface O _FΔ <183>, (α3) voltage is applied between E _A <113> and E _K <123>, (iv-β) and in those cases in which the electrolytic cell E <1> comprises at least one central chamber K _M <13>, the following steps (β1), (β2), (β3) are carried out simultaneously: (β1) a solution L ₂ <22> comprising the alcohol ROH is passed through I _KK <122>, where if O _KK <182> comprises at least part of O _FΔ <183>, the solution L ₂ <22> the surface O _FΔ <183> directly contacts, (β2) a neutral or alkaline aqueous solution L ₃ <23> of a salt S comprising X as a cation is passed through I _KM <132>, then through V _AM <15>, then through I _KA <112>, where if O _A/MK <181> comprises at least part of O _FΔ <183>, the solution L ₃ <23> directly contacts the surface O _FΔ <183>, (β3) voltage is applied between E _A <113> and E _K <123>, whereby the solution L ₁ <21> is obtained at the outlet A _KK <121>, the concentration of XOR in L ₁ <21> being higher than in L ₂ <22>,
and whereby an aqueous solution L ₄ <24> of S is obtained at outlet A _KA <111>, the concentration of S in L ₄ <24> being lower than that in L ₃ <23>. Method according to claim 1, wherein the following applies: S _{MF '} < S _MF , where S _{MF '} is the mass-related specific surface area S _M of the alkali cation-conducting solid electrolyte ceramic F' before step (ii) is carried out and S _MF is the mass-related specific surface area S _M of the alkali cation-conducting Solid electrolyte ceramic F after performing step (ii). Method according to claim 2, wherein the quotient S _MF / S _MF' ≥ 1.01. Method according to any one of claims 1 to 3, wherein at least 1% of the surface area O _A/MK <181> is formed by O _FΔ <183> and/or at least 1% of the surface area O _KK <182> is formed by O _FΔ <183> become. The method according to any one of claims 1 to 4, wherein the alkali cation-conductive solid electrolyte ceramic F' <19> has a structure of the formula:

M ^I _1+2w+x-y+z M ^II _w M ^III _x Zr ^IV _2-wxy M ^V _y (SiO ₄ ) _z (PO ₄ ) _3-z

having, where M ^I is selected from Na ⁺ , Li ⁺ , M ^II is a divalent metal cation, M ^III is a trivalent metal cation, M ^V is a pentavalent metal cation, the Roman indices I, II, III, IV, V indicate the oxidation numbers in which the respective metal cations are present,
and w, x, y, z are real numbers, where 0 ≤ x < 2, 0 ≤ y < 2, 0 ≤ w < 2, 0 ≤ z < 3, and w, x, y, z so be chosen such that 1 + 2w + x - y + z ≥ 0 and 2 - w - x - y ≥ 0. A method according to any one of claims 1 to 5, wherein X is selected from the group consisting of Li ⁺ , Na ⁺ , K ⁺ . A method according to claim 6, wherein X = Na ⁺ . A method according to any one of claims 1 to 7, wherein S is a halide, sulfate, sulfite, nitrate, bicarbonate or carbonate of X. A method according to claim 8, wherein S is a chloride of X. A method according to any one of claims 1 to 9, wherein R is selected from the group consisting of methyl, ethyl. A method according to claim 10, wherein R = methyl. A method according to any one of claims 1 to 11, wherein the electrolytic cell E <1> does not comprise a central chamber K _M <13>. The method according to any one of claims 1 to 11, wherein the electrolytic cell E <1> comprises at least one central chamber K _M <13>. The method of claim 13, wherein the connection V _AM <15> is formed within the electrolytic cell E <1>. The method according to claim 13, wherein the connection V _AM <15> is formed outside the electrolytic cell E <1>.

Images