EP3885470A1 - Method for producing alkaline metal alcaholates in a three-chamber electrolysis cell - Google Patents

Abstract

The present invention relates to a method for the electrochemical production of an alkali metal alcoholate solution. The process is carried out in an electrolysis cell which has three chambers, the middle chamber being separated from the cathode chamber by a solid electrolyte permeable to cations, e.g. NaSICON, and from the anode chamber by a diffusion barrier, e.g. a membrane selective for cations or anions.

Description

The present invention relates to a method for the electrochemical production of an alkali metal alcoholate solution. The process is carried out in an electrolysis cell which has three chambers, the middle chamber being separated from the cathode chamber by a solid electrolyte permeable to cations, e.g. NaSICON, and from the anode chamber by a diffusion barrier, e.g. a membrane selective for cations or anions.

1. Background of the invention

The electrochemical production of alkali metal alcoholate solutions is an important industrial process, for example in the DE 103 60 758 A1 , the US 2006/0226022 A1 and the WO 2005/059205 A1 is described. The principle of this process is an electrolysis cell in whose anode chamber the solution of an alkali salt, for example common salt or NaOH, and in whose cathode chamber the alcohol in question or a low-concentration alcoholic solution of the alkali alcoholate in question, for example sodium methoxide or sodium ethoxide, are located. The cathode chamber and the anode chamber are separated by a ceramic that conducts the alkali metal ion used, for example NaSICON or its analogues for potassium or lithium. When a current is applied, chlorine is produced at the anode - if a chloride salt of the alkali metal is used - and hydrogen and alcohol ions are produced at the cathode. The charge balance results from the fact that alkali metal ions migrate from the central chamber into the cathode chamber via the ceramic which is selective for them. The charge balance between the middle chamber and the anode chamber results from the migration of cations when using cation exchange membranes or the migration of anions when using anion exchange membranes or from 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 is reduced.

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 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 converted in a second step with electrolytically generated protons to glycerine and the respective alkali metal hydroxide.

The prior art therefore describes processes that are carried out in electrolysis cells with an ion-permeable layer, such as NaSiCON solid electrolytes. However, these solid electrolytes typically have the disadvantage that they are not long-term stable to aqueous acids. This is problematic insofar as the pH drops in the anode chamber during electrolysis due to oxidation processes (for example when halogens are produced by disproportionation or by the formation of oxygen). These acidic conditions attack the NaSICON solid electrolyte, so that the process cannot be used on an industrial scale. Various approaches have been described in the prior art to address this problem.

For example, three-chamber cells have been proposed in the prior art. Such are known in the electrodialysis field, 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 solid electrolyte such as NaSICON that is permeable to cations. In order to protect it from the acidic anolyte, solution from the cathode chamber, for example, is supplied to the central chamber. the US 2010/0044242 A1 also describes in Figure 6 that solution from the middle chamber can be mixed with solution from the anode chamber outside the chamber to obtain sodium hypochlorite.

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

So describes the U.S. 5,389,211 A a process for cleaning 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 middle chamber is used as a buffer chamber to prevent the purified alkoxide or hydroxide solution from the cathode chamber from mixing with the contaminated solution from the anode chamber.

the WO 2008/076327 A1 describes a process for the preparation of alkali metal alcoholates. A three-chamber cell is used, the middle chamber of which is filled with alkali metal alcoholate (see, for example, paragraphs [0008] and [0067] of WO 2008/076327 A1 ). As a result, the solid electrolyte separating the central chamber and the cathode chamber is protected from the solution in the anode chamber, which becomes more acidic during the electrolysis. However, this arrangement has the disadvantage that the alkali metal alcoholate solution is the desired product, but this is consumed as a buffer solution and continuously contaminated. Another disadvantage of 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 leads to a slowing down of the formation of the alcoholate.

The object of the present invention was therefore to provide an improved process for the electrolytic production of alkali metal alcoholate which ensures protection of the cation-conducting solid electrolyte from acid, but does not have the aforementioned disadvantages. In addition, the process should be distinguished by a more economical use of the starting materials compared to the prior art.

2. Brief description of the invention

A method has now surprisingly been found which achieves the object according to the invention.

1. (a) ein Lösung L ₂ <113> umfassend den Alkohol ROH und bevorzugt umfassend mindestens ein Alkalimetallalkoholat XOR wird durch K _K <102> geleitet,
2. (b) eine neutrale oder alkalische, wässrige Lösung L ₃ <114> eines Salzes S umfassend X als Kation wird durch K _M <103>, dann über V _AM <112>, dann durch K _A <101> geleitet,
3. (c) zwischen E _A <104> und E _K <105> wird Spannung angelegt,

wodurch am Ablauf A _KK <109> die Lösung L ₁ <115> erhalten wird, wobei die Konzentration von XOR in L ₁ <115> höher ist als in L ₂ <113>,
und wodurch am Ablauf A _KA <106> eine wässrige Lösung L ₄ <116> von S erhalten wird, wobei die Konzentration von S in L ₄ <116> geringer ist als in L ₃ <114>,
wobei X ein Alkalimetallkation ist und R ein Alkylrest mit 1 bis 4 Kohlenstoffatomen ist.The method according to the invention is one for producing a solution L ₁ <115> of an alkali metal alcoholate XOR in alcohol ROH in an electrolysis cell E <100>,
wherein E <100> at least one anode chamber K _A <101>, at least one cathode chamber K _K <102> and at least one intermediate fluid chamber K _M <103> comprising,
where K _A <101> comprises an anodic electrode E _A <104> and a sequence A _KA <106>,
where K _K <102> comprises a cathodic electrode E _K <105>, an inlet Z _KK <107> and an outlet A _KK <109>,
where K _M <103> comprises an inlet Z _KM <108>, is separated from K _A <101> by a diffusion barrier D <110> and is separated from K _K <102> by an alkali-cation-conducting solid electrolyte F _K <111>,
where K _A <101> and K _M <103> are connected to one another by a connection V _AM <112>, through which liquid can be passed from K _M <103> to K _A <101>,
the method comprising the following concurrent steps (a), (b) and (c):

1. (a) a solution L ₂ <113> comprising the alcohol ROH and preferably comprising at least one alkali metal alcoholate XOR is passed through K _K <102>,
2. (b) a neutral or alkaline, aqueous solution L ₃ <114> of a salt S comprising X as a cation is passed through K _M <103>, then via V _AM <112>, then through K _A <101>,
3. (c) voltage is applied between E _A <104> and E _K <105>,

whereby the solution L ₁ <115> is obtained at the process A _KK <109>, the concentration of XOR in L ₁ <115> being higher than in L ₂ <113>,
and whereby an aqueous solution L ₄ <116> of S is obtained at the outlet A _KA <106>, the concentration of S in L ₄ <116> being lower than in L ₃ <114>,
where X is an alkali metal cation and R is an alkyl radical having 1 to 4 carbon atoms.

3. Illustrations

illustration 1 shows the method according to the invention on the basis of a three-chamber cell E <100> comprising a cathode chamber K _K <102>, an anode chamber K _A <101> and a central chamber K _M <103> lying in between. The three chambers are bounded by an outer wall <117> of the three-chamber cell E <100>. The cathode chamber K _K <102> is also separated from the central chamber K _M <103> by a NaSICON solid electrolyte F _K <111> which is selectively permeable to sodium ions. The central chamber K _M <103> is in turn separated from the anode chamber K _A <101> by a diffusion barrier D <110>. The NaSICON solid electrolyte F _K <111> and the diffusion barrier D <110> extend over the entire depth and height of the three-chamber cell E <100>.

A solution of sodium methoxide in methanol L ₂ <113> is passed through the cathode chamber K _{K <102>.} An aqueous solution of sodium chloride L ₃ <114> with pH 10.5 is fed into the middle chamber K _M <103> via the inlet Z _KM <108> in the same direction as the force of gravity. Is formed by the compound V _AM <112>, the <118> of the medium chamber K _M <103> and an inlet Z _KA <119> the anode chamber K _A between a sequence A _KM <101>, the middle chamber K _M <103 > connected to the anode chamber K _A <101>. Sodium chloride solution L ₃ <114> is passed through this connection V _AM <112> from the middle chamber K _M <103> into the anode chamber K _A <101>. When a voltage is applied, methanol is reduced to methanolate and H ₂ in the cathode chamber K _{K <102>.} Sodium ions diffuse from the middle chamber K _M <103> through the NaSICON solid electrolyte F _K <111> into the cathode chamber K _K <102>. Overall, this increases the concentration of sodium methoxide in the cathode chamber K _K <102>, as a result of which a methanolic solution of sodium methoxide L ₁ <115> is obtained, the concentration of sodium methoxide of which is higher than that of L ₂ <113>. In the anode chamber K _A <101>, chloride ions from L ₃ <114> are oxidized _{to Cl 2.}

Cl ₂ reacts acidic in aqueous solution. Due to the geometry of the three-chamber cell E <100> and the guidance of the aqueous solution L ₃ <114>, the acid-sensitive NaSICON solid electrolyte becomes <111> is protected from the increased acidity of the solution L ₄ <116> resulting in the anode chamber K _A <101> compared to L _{3 <114>.}

Figure 2 shows an embodiment of the method according to the invention, which is similar to that in illustration 1 shown corresponds. The only difference here is that the connection V _AM <112> from the central chamber K _M <103> into the anode chamber K _A <101> is formed by a perforation in the diffusion barrier D <110>.

Figure 3 shows a diagram of the voltage curve of the electrolysis in a three-chamber cell according to the invention in comparison with a two-chamber cell. The measurement points of the comparative example are shown with triangles (▲), those of the example according to the invention with points (•). The x-axis shows the time in hours, while the y-axis shows the measured voltage in volts. The comparison shows that a constant voltage curve is obtained with the cell according to the invention, while the voltage increases rapidly in the two-chamber cell due to the destruction of the solid electrolyte.

4. Detailed description of the invention 4.1 Electric cell E.

The inventive process is in an electrolysis cell E, which comprises at least one anode chamber K _A, at least one cathode chamber K _K and at least one intermediate fluid chamber K _M is performed. This includes electrolysis cell E, which comprise more than one anode chamber K _A and / or cathode chamber K _K and / or fluid chamber K _M. Such electrolysis cells, in which these chambers are joined together in a modular manner, are for example in the DD 258 143 A3 , US 2006/0226022 A1 described.

The anode chamber K _A comprises an anodic electrode E _A. Any electrode familiar to the person skilled in the art that is stable under the conditions of the method according to the invention can be used as such anodic electrode E _A. Such are especially in WO 2014/008410 A1 , Paragraph [024] or DE 10360758 A1 , Paragraph [031]. This electrode E _A can consist of one layer or consist of several planar layers parallel to one another, 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 in particular platinum, which is supported 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. Further possible anode materials are in particular stainless steel, lead, graphite, Tungsten carbide, titanium diboride. E _A preferably comprises a titanium anode coated with ruthenium oxide / iridium oxide (RuO ₂ + IrO ₂ / Ti).

The cathode chamber K _K comprises a cathodic electrode E _K. Any electrode familiar to the person skilled in the art that is stable under the conditions can be considered as such cathodic electrode E _K. Such are especially 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 as “spheres”. 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.

The at least one middle chamber K _M is located between the anode chamber K _A and the cathode chamber K _K.

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

K _M is separated by a diffusion barrier of D K _A and separated by a cation-conducting solid electrolyte alkali F _K K _K.

Any material which is stable under the conditions of the method according to the invention and which prevents or slows the transfer of protons from the liquid in the anode chamber K _A into the central chamber K _M can be used as the diffusion barrier D.

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

The material for the nonionic partition is selected in particular from the group consisting of fabric, which is in particular textile fabric or metal fabric, glass, which is in particular sintered glass or glass frits, ceramics, in particular ceramic frits, membrane diaphragms.

If the diffusion barrier D is a “membrane permeable to specific ions”, this means according to the invention that the respective membrane favors the diffusion of certain ions through it over others. In particular, this means membranes which promote the diffusion through them of ions of a certain type of charge compared to oppositely charged ions. Even more preferably, membranes permeable to specific ions also favor the diffusion through them of certain ions with one type of charge as opposed to other ions of the same type of charge.

Accordingly, the diffusion barrier D is preferably an anion-conducting membrane or a cation-conducting membrane.

According to the invention, anion-conducting membranes are those which selectively conduct anions, preferably selectively certain anions. In other words, they favor the diffusion of anions through them over that of cations, in particular over protons, and even more preferably they also 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 certain cations. In other words, they favor the diffusion of cations through them over that of anions, more preferably they favor the diffusion of certain cations through them over the diffusion of other cations through them, even more preferably cations that are is not protons, even more preferably sodium cations, compared to protons.

“Favor 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 type X at a given temperature for the membrane in question is 10, preferably 100, preferably 1000 times higher as the diffusion coefficient of ion type Y for the membrane in question.

More preferably, it is in the D diffusion barrier to a anion-membrane, because this prevents particularly the diffusion of protons from the anode chamber K _A K _M into the central chamber.

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

Salt S is preferably a halide, sulfate, sulfite, nitrate, hydrogen carbonate 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, more preferably chloride, is preferably used as the anion-conducting membrane.

Anion-conducting membranes are described, for example, by MA Hickner, AM Herring, EB Coughlin, Journal of Polymer Science, Part B: Polymer Physics 2013, 51, 1727-1735 and CG Arges, V. Ramani, PN Pintauro, Electrochemical Society Interface 2010, 19, 31-35 , 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 ).

Accordingly, organic polymers, which are selected in particular from polyethylene, polybenzimidazoles, polyether ketones, polystyrene, polypropylene or fluorinated membranes such as polyperfluoroethylene, preferably polystyrene, are used as the anion-conducting membrane, these covalently bonded functional groups selected from -NH ₃ ⁺ , - NRH ₂ ⁺ , -NR ₃ ⁺ , = NR ⁺ ; -PR ₃ ⁺ , where R is alkyl groups with preferably 1 to 20 carbon atoms, or have other cationic groups. They preferably 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 which is selective for the cations comprised by the salt S. The diffusion barrier D is even more preferably an alkali-ion-conducting membrane, even more preferably a potassium- and / or sodium-ion-conducting membrane, most preferably a sodium ion-conducting membrane.

Cation-conducting membranes are described, for example, on page 181 of the textbook by Volkmar M. Schmidt Electrochemical process engineering: Fundamentals, reaction engineering, process optimization, 1st edition (October 8, 2003 ).

Accordingly, organic polymers, which are selected in particular from polyethylene, polybenzimidazoles, polyether ketones, polystyrene, polypropylene or fluorinated membranes such as polyperfluoroethylene, preferably polystyrene, polyperfluoroethylene, are used as the cation-conducting membrane, 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 ) wear.

This can, for example, be a sulfonated polyperfluoroethylene (Nafion ® with CAS number: 31175-20-9). These are known to the person skilled in the art, for example, from WO 2008/076327 A1 , Paragraph [058], US 2010/0044242 A1 , Paragraph [0042] or the US 2016/0204459 A1 known and under the Trade names Nafion ®, Aciplex ® F, Flemion ®, Neosepta ®, Ultrex ®, PC-SK ® are available. Neosepta® membranes are described by, for example 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, for example, be a polymer functionalized with sulfonic acid groups, in particular of the following formula P _NAFION , where n and m are, independently of one another, 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 .

Any solid electrolyte which can transport cations, in particular alkali cations, more preferably sodium cations, from the central chamber K _M into the cathode chamber K _K can be used as the solid electrolyte F _{K which conducts alkali cations.} Such solid electrolytes are known to the person skilled in the art and, for example, in the 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 the DE 10360758 A1 , Paragraphs [014] to [025]. They are sold commercially under the names NaSICON, LiSICON, KSICON. A solid electrolyte F _K which conducts sodium ions is preferred, this even more preferably having a NaSICON structure. NaSICON structures that can be used according to the invention are also described, for example, by N. Anantharamulu, K. Koteswara Rao, G. Rambabu, B. Vijaya Kumar, Velchuri Radha, M. Vithal, J Mater Sci 2011, 46, 2821-2837 .

NaSICON preferably 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 .

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 chosen in this way that 1 + 2w + x - y + z ≥ 0 and 2 - w - x - y ≥ 0.

According to the invention, NaSICON even 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 applies
The cathode chamber K _K also includes an inlet Z _KK and an outlet A _KK , which makes it possible to _add liquid, such as solution L ₂ , to the cathode chamber K K and to add liquid located therein, such as solution L ₁ remove. The inlet Z _KK and the outlet A _KK are attached to the cathode chamber K _K in such a way that the solution contacts the cathodic electrode E _K when it flows through the cathode chamber K _K. This is the prerequisite that when the method according to the invention is carried out at the outlet A _KK, the solution L _{1 is} obtained when the solution L _{2 of} an alkali metal alcoholate XOR in the alcohol ROH is passed through K _K.

The anode chamber K _A also includes an outlet A _KA , which makes it possible to remove liquid located in the anode chamber K _A , for example the aqueous solution L _4. In addition, the central chamber K _M includes an inlet Z _KM , while K _A and K _M are connected to one another by a connection V _AM. As a result, a solution L ₃ can be added to K _M and this can then be passed through K _M , and via V _AM into the anode chamber K _A , then passed through this K _A. V _AM and the drain A _KA are attached to the anode chamber K _A in such a way that the solution L ₃ contacts the anodic electrode E _{A as it flows} through the anode chamber K _A. This is the prerequisite that when the method according to the invention is carried out at the outlet A _KA, the aqueous solution L _{4 is} obtained when the solution L _{3 is} first passed through K _M , then V _AM , then K _A.

Inlets Z _KK , Z _KM , Z _KA and outlets A _KK , A _KA , A _KM can be attached to the electrolysis cell by methods known to those skilled in the art.

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

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.

If the connection V _{AM is formed} outside the electrolytic cell E , it is preferably formed by a connection of K _M and K _A extending outside the electrolytic cell E , in particular by the fact that in the central chamber K _M an outlet A _KM through the outer wall W _{A is} preferred at the bottom of the middle chamber K _M , with the inlet Z _KM being more preferably at the top of the middle chamber K _M , and in the anode chamber K _A an inlet Z _KA through the outer wall W _A , preferably at the bottom of the anode chamber K _A , is formed, and these are connected by a line, for example a pipe or a hose, which preferably comprises a material selected from rubber, plastic. The drain A _KA is then even more preferred at the top of the anode chamber K _A.

"Drain A _KM at the bottom of the central chamber K _M " means that the drain A _KM is attached to the electrolytic cell E in such a way that the solution L ₃ leaves the central chamber K _{M in the} same direction as the force of gravity.

“Inlet Z _KA at the bottom of the anode chamber K _A ” means 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 against gravity.

“Inlet Z _KM at the top of the middle chamber K _M ” means that the inlet Z _KM is attached to the electrolytic cell E in such a way that the solution L ₃ enters the middle chamber K _{M in the} same direction as the force of gravity.

"Drain A _KA at the top of the anode chamber K _A " means that the drain 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 gravity.

This embodiment is particularly advantageous and therefore preferred when the outlet A _{KM is formed} by the outer wall W _A at the bottom of the central chamber K _M and the inlet Z _{KA is formed} by the outer wall W _A at the bottom of the anode chamber K _A. By this arrangement, it is separate ₃ particularly simple manner resulting in the central chamber K _M gases through the gas outlet G of L, while the gases formed in the anode chamber K _A L _4, the anode chamber K _A left and may then be further separated.

Accordingly, the direction of flow from L ₃ in K _{M is} opposite or in the same direction, preferably opposite to the direction of flow from L ₃ in K _A , depending on how the connection V _{AM is} attached to the electrolytic cell E. The direction of flow from L ₃ in K _M is preferably in the same direction as the force of gravity.

In a preferred embodiment of the present invention, connection V _{AM is arranged} between central chamber K _M and anode chamber K _{A in} such a way that at least part of the aqueous

Solution L ₃ , more preferably the entire aqueous solution L ₃ , the central chamber K _M and the anode chamber K _A flows completely through.

If the connection V _AM <112> is formed outside the electrolysis cell E <100>, this can be ensured in particular by the fact that Z _KM <108> and A _KM <118> on opposite sides of the outer wall W _A <117> of the central chamber K. _M <103> are arranged (i.e. Z _KM <108> on the bottom and A _KM <118> on the top of the electrolytic cell E <100> or vice versa) and Z _KA <119> and A _KA <106> on opposite sides of the outer wall W _A <117> of the anode chamber K _A <101> is arranged (that is, Z _KA <119> on the bottom and A _KA <106> on the top of the electrolytic cell E <100> or vice versa), as in particular in FIG illustration 1 is shown. Due to this geometry, L ₃ <114> must flow through the two chambers K _M <103> and K _A <101>. Z _KA <119> and Z _KM <108> can be formed on the same side of the electrolytic cell E <100>, A _KM <118> and A _KA <106> then also being formed automatically on the same side of the electrolytic cell E <100> are. Alternatively, as in illustration 1 shown, Z _KA <119> and Z _KM <108> be formed on opposite sides of the electrolytic cell E <100>, A _KM <118> and A _KA <106> then also being formed automatically on opposite sides of the electrolytic cell E <100> are.

If the connection V _AM <112> is formed within the electrolytic cell E <100>, this can be ensured in particular by the fact that one side (“side A”) of the electrolytic cell E <100>, which is the top or the Bottom of the electrolytic cell E <100>, preferably as in Figure 2 is the upper side, the inlet Z _KM <108> and the outlet A _KA <106> comprises and the diffusion barrier D <110>, starting from this side A, extends into the electrolysis cell <100>, but not all the way to that of the Side A opposite side ("side B") of the electrolytic cell E <100>, which is then the bottom or the top of the electrolytic cell E <100>, extends and thereby 50% or more of the height of the three-chamber cell E <100>, more preferably 60% to 99% of the height of the three-chamber cell E <100>, even more preferably 70% to 95% of the height of the three-chamber cell E <100>, even more preferably 80% to 90% of the height of the three-chamber cell E <100> , even more preferably spans 85% of the height of the three-chamber cell E <100>. Because the diffusion barrier D <110> does not touch the B side of the three-chamber cell E <100>, a gap is created between the diffusion barrier D <110> and the outer wall W _{A of} the B side of the three-chamber cell E <100>. The gap is then the connection V _AM <112>. 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 <104>, which leads to the formation of acids.

According to the invention, the “bottom of the electrolysis cell E” is the side of the electrolysis cell E through which a solution (eg L ₃ <114> at A _KM <118> in illustration 1 ) exits the electrolysis cell E in the same direction as gravity or the side of the electrolysis cell E through which a solution (e.g. L ₂ <113> at Z _KK <107> in Figures 1 and 2 and L ₃ <114> at A _KA <119> in illustration 1 ) is fed to the electrolytic cell E against gravity.

According to the invention, “top of the electrolytic cell E” is the side of the electrolytic cell E through which a solution (eg L ₄ <116> for A _KA <106> and L ₁ <115> for A _KK <109> in Figures 1 and 2) is opposite gravity exits the electrolysis cell E or the side of the electrolysis cell E through which a solution (e.g. L ₃ <114> at Z _KM <108> in Figures 1 and 2) is fed to the electrolysis cell E in the same direction as the force of gravity.

4.2 Process steps according to the invention

The method according to the invention comprises the following steps (a), (b) and (c), which are carried out simultaneously.

In step (a) a solution L ₂ comprising the alcohol ROH, preferably comprising an alkali metal alcoholate XOR in the alcohol ROH, is passed through K _K. X is an alkali metal cation and R is an alkyl radical with 1 to 4 carbon atoms.

X is preferably selected from the group consisting of Li ⁺ , K ⁺ , Na ⁺ , more preferably from the group consisting of K ⁺ , Na ⁺ . Most preferably X = Na ⁺ .

R is preferably selected from the group consisting of n- propyl, iso- propyl, ethyl, methyl, more preferably selected from the group consisting of ethyl, methyl. Most preferably R is methyl.

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) 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 comprises XOR, the mass ratio of XOR to alcohol ROH in solution L _{2 is} in particular in the range 1: 100 to 1: 5, more preferably in the range 1:25 to 3:20, even more preferably in the range 1:12 up to 1: 8, more preferably 1:10.

In step (b) a neutral or alkaline aqueous solution L _{3 of} a salt S comprising X as a cation is passed through K _M , then through V _AM , then through K _A.

The salt S is described above. The pH of the aqueous solution L ₃ is 7.0, preferably in the range 7 to 12, more preferably in the range 8 to 11, even more preferably 10 to 11, most preferably 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 .

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

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

• am Ablauf A _KK <109> wird die Lösung L ₁ <115> erhalten, wobei die Konzentration von XOR in L ₁ <115> höher ist als in L ₂ <113>,
• am Ablauf A _KA <106> wird eine wässrige Lösung L ₄ <116> von S erhalten, wobei die Konzentration von S in L ₄ <116> geringer ist als in L ₃ <114>.

This in turn leads to the following consequences:

• at the process A _KK <109> the solution L ₁ <115> is obtained, whereby the concentration of XOR in L ₁ <115> is higher than in L ₂ <113>,
• an aqueous solution L ₄ <116> of S is obtained at the outlet A _KA <106>, the concentration of S in L ₄ <116> being lower than in L ₃ <114>.

In the method according to the invention, in particular, such a voltage is applied that such a current flows, so that the current density (= ratio of the current flowing to the electrolytic cell to the area of the solid electrolyte that contacts the anolyte located in the central chamber K _M ) 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 as standard by a person skilled in the art. The area of the solid electrolyte that contacts the anolyte located in the central 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 goes without saying that step (c) is carried out in the process according to the invention when both chambers K _M and K _{A are} at least partially loaded with L ₃ and K _{K is} at least partially loaded with L _2.

The fact that a charge transport takes place between E _A and E _K in step (c) implies that K _K , K _M and K _{A are} simultaneously charged with L ₂ and L _{3 in} such a way that they the electrodes E _A and E _{Cover K to the} extent that the electrical circuit is closed.

This is particularly the case when a liquid flow from L _{3 is} continuously passed through K _M , V _AM and K _A and a liquid flow from L _{2 is passed} through K _K and the liquid flow from L ₃ passes the electrode E _A and the liquid flow from L ₂ the electrode E _{K is} at least partially, preferably completely covered.

In a further preferred embodiment, the process according to the invention is carried out continuously, that is to say step (a) and step (b) are carried out continuously and voltage is applied in accordance with step (c).

After step (c) 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 from 1.01 to 2.2 times, more preferably from 1.04 to 1.8 times, even more preferably from 1.077 to 1.4 times, even more preferably from 1.077 to 1.08 times higher than in L ₂ , most preferably 1.077 times higher than in L ₂ , the mass fraction of XOR in L ₁ and in L ₂ in the range from 10 to 20% by weight, even more preferred 13 to 14% by weight.

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 .

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, the process according to the invention is 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 up to 1.5 bar, preferably 0.9 bar to 1.1 bar, more preferably 1.0 bar.

When the method according to the invention is carried out, hydrogen is typically produced in the cathode chamber K _K , which can be discharged from the cell together with the solution L ₁ via the outlet A _KK. The mixture of hydrogen and solution L ₁ can then in a particular embodiment of the present invention are separated by methods known to those skilled in the art. In the anode chamber K _A , if the alkali metal compound used is a halide, in particular chloride, chlorine or another halogen gas can arise, which can be discharged from the cell together with the solution L ₄ via the outlet A _KK. In addition, oxygen and / or carbon dioxide can also arise, 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 the person skilled in the art. In the same way, after the gases chlorine, oxygen and / or CO _{2 have been separated off} from solution L _4, these can then be separated from one another by methods known to those skilled in the art.

These results were surprising and not to be expected in the light of the prior art. The method according to the invention protects 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. The method according to the invention is thus more efficient than that in WO 2008/076327 A1 described procedure, in which the product solution is used for the middle chamber, which reduces the total turnover.

Preferred embodiments of the invention

illustration 1 shows a preferred embodiment of the invention in a three-chamber cell E <100>. This comprises a cathode chamber K _K <102>, a central chamber K _M <103> and an anode chamber K _A <101>. The anode chamber K _A <101> and the central chamber K _M <103> are separated from one another by an anion exchange membrane extending over the entire cross section of the three-chamber cell E <100> as a diffusion barrier D <110>. The cathode chamber K _K <102> and the central chamber K _M <103> are separated from one another by a permeable solid electrolyte (NaSICON) <111> which is selective for sodium ions and extends over the entire cross section of the three-chamber cell E <100>. The cathode chamber K _K <102> comprises a cathodic electrode E _K <105>, an inlet Z _KK <107> and an outlet A _KK <109>.

The anode chamber K _A <101> comprises an anodic electrode E _A <104> and a drain A _KA <106> and is connected to the central chamber K _M <103> via the connection V _AM <112>. The middle chamber K _M <103> also includes an inlet Z _KM <108>. In the embodiment according to illustration 1 the connection V _AM <112> is formed outside the electrolytic cell E <100>, in particular by a tube or hose, the material of which can be selected from rubber, metal or plastic, with which liquid from the central chamber K _M <103> in the anode chamber K _A <101> can be conducted outside the outer wall W _A <117> of the three-chamber cell E <100>. The connection V _AM <112> connects an outlet A _KM <118>, which breaks through the outer wall W _A <117> of the electrolysis cell E <100> at the bottom of the central chamber K _M <103>, with an inlet Z _KA <119>, which at the bottom of the anode chamber K _A <101> breaks through the outer wall W _A <117> of the electrolytic cell E <100>.

An electrolyte L ₂ <113> is fed into the cathode chamber K _K <102> via the inlet Z _KK <107>. The electrolyte L ₂ <113> comprises methanol; a methanolic solution of sodium methoxide L ₂ <113> is preferably used as the electrolyte L _{2 <113>.}

At the same time, an aqueous NaCl solution L ₃ <114> with a pH of 10.5 is introduced into the central chamber K _M <103> via the inlet Z _{KM <108>.} This flows through the central chamber K _M <103> and the connection V _AM <112> into the anode chamber K _A <101>.

A voltage is applied between the cathodic electrode E _K <105> and the anodic electrode E _A <104>. As a result, methanol in the electrolyte L ₂ <113> is _{reduced to methanolate and H 2} in the cathode chamber K _K <102> (CH ₃ OH + e ^- → CH ₃ O ^- + ½ H ₂ ). In the anode chamber K _A <101> the oxidation of chloride ions to molecular chlorine takes place (Cl ^- → ½ Cl ₂ + e ^- ). Chlorine gas Cl ₂ forms in water according to the reaction Cl ₂ + H ₂ O → HOCl + HCl hypochlorous acid and hydrochloric acid, which react acidic with other water molecules. The acidity damages the NaSICON solid electrolyte <111>, but is affected by the Arrangement in the anode chamber K _A <101> and thus kept away from the NaSICON solid electrolyte F _K <111> in the electrolysis cell E <100>. This increases its service life considerably.

Sodium ions diffuse from the middle chamber K _M <103> through the NaSICON solid electrolyte <111> into the cathode chamber K _K <102>. Overall, this increases the concentration of sodium methoxide in the cathode chamber K _K <102>, as a result of which a methanolic solution of sodium methoxide L ₁ <115> is obtained, the concentration of sodium methoxide of which is increased compared to L ₂ <113>. Due to the geometry of the three-chamber cell E <100> and the inventive guidance of the aqueous solution L ₃ <114>, the acid-sensitive NaSICON solid electrolyte <111> becomes the resulting in the anode chamber K _A <101> before the increased acidity compared to L _{3 <114>} Solution L ₄ <116> protected.

In the Figure 2 The embodiment of the present invention shown corresponds to that in FIG illustration 1 shown. The only difference is that the connection V _AM <112> within the electrolysis cell E <100> is designed in such a way that the diffusion barrier D <110> does not extend over the entire cross section of the three-chamber cell E <100>. The connection V _AM <112> from the central chamber K _M <103> into the anode chamber K _A <101> is thereby formed by a gap in the diffusion barrier D <110>. In further preferred embodiments of the present invention, diffusion barriers D <110> with more than one gap can also be used, so that the connection V _AM <112> between central chamber K _M <103> and anode chamber K _A <101> passes through several gaps trains.

Examples Inventive example

Sodium methylate (NM) was produced using 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 illustration 1 shown, with the anolyte being transferred through the middle chamber into the anode chamber. The connection between the central and anode chambers is established by a hose that is attached to the bottom of the electrolysis cell. The anode chamber and the middle chamber were separated by a 2.83 cm ² anion exchange membrane (Tokuyama AMX, ammonium groups on polymer). The cathode and central chamber were separated by a ceramic of the NaSICON type with an area of 2.83 cm ² . The ceramic has a chemical composition of the formula Na _3.4 Zr _2.0 Si _2.4 P _0.6 O ₁₂ . The flow rate of the anolyte and that of the catholyte were each 90 mL / h, and a current of 0.14 A was applied. The temperature was 35 ° C. The voltage curve (in V) over time (in hours) is in Figure 3 shown (●).

Comparative example

The process was repeated with a two-chamber cell comprising only one anode and one cathode chamber, the anode chamber being separated from the cathode chamber by the ceramic of the NaSICON type. Thus this electrolytic cell did not contain a central compartment. This is reflected in faster corrosion of the ceramic compared to the inventive example, which leads to a rapid increase in the stress curve, see FIG Figure 3 , (▲).

Result

The use of a three-chamber cell as in the method according to the invention prevents corrosion of the solid electrolyte, while at the same time no alkali alcoholate product has to be sacrificed for the middle chamber.

Claims (15)

Process for the production of a solution L ₁ <115> of an alkali metal alcoholate XOR in alcohol ROH in an electrolysis cell E <100>,
wherein E <100> at least one anode chamber K _A <101>, at least one cathode chamber K _K <102> and at least one intermediate fluid chamber K _M <103> comprising,
where K _A <101> comprises an anodic electrode E _A <104> and a sequence A _KA <106>,
where K _K <102> comprises a cathodic electrode E _K <105>, an inlet Z _KK <107> and an outlet A _KK <109>,
where K _M <103> comprises an inlet Z _KM <108>, is separated from K _A <101> by a diffusion barrier D <110> and is separated from K _K <102> by an alkali-cation-conducting solid electrolyte F _K <111>,
where K _M <103> and K _A <101> are connected to one another by a connection V _AM <112>, through which liquid can be passed from K _M <103> to K _A <101>,
the method comprising the following concurrent steps (a), (b) and (c): (a) a solution L ₂ <113> comprising the alcohol ROH and preferably additionally comprising at least one alkali metal alcoholate XOR is passed through K _K <102>, (b) a neutral or alkaline, aqueous solution L ₃ <114> of a salt S comprising X as a cation is passed through K _M , then via V _AM , then through K _A <101>, (c) voltage is applied between E _A <104> and E _K <105>, whereby the solution L ₁ <115> is obtained at the process A _KK <109>, the concentration of XOR in L ₁ <115> being higher than in L ₂ <113>,
and whereby an aqueous solution L ₄ <116> of S is obtained at the outlet A _KA <106>, the concentration of S in L ₄ <116> being lower than in L ₃ <114>,
where X is an alkali metal cation and R is an alkyl radical having 1 to 4 carbon atoms. The method of claim 1, wherein X is selected from the group consisting of Li ⁺ , Na ⁺ , K ⁺ . The method of claim 1 or 2, wherein S is a halide, sulfate, sulfite, nitrate, bicarbonate, or carbonate of X. A method according to any one of claims 1 to 3, wherein R is selected from the group consisting of methyl, ethyl. Method according to one of Claims 1 to 4, wherein the diffusion barrier D <110> is selected from the group consisting of cation-conducting, anion-conducting membranes. The method according to claim 5, wherein the diffusion barrier D <110> is a sodium cation conductive membrane. Method according to one of Claims 1 to 6, wherein the direction of flow of L ₃ <114> in the central chamber K _M <103> is opposite to the direction of flow of L ₃ <114> in the anode chamber K _A <101>. Method according to one of Claims 1 to 7, the connection V _AM <112> being formed inside and / or outside the electrolysis cell E <100>. Method according to one of Claims 1 to 8, wherein the connection V _AM <112> between central chamber K _M <103> and anode chamber K _A <101> is arranged in such a way that at least part of the aqueous solution L ₃ <114> the central chamber K. _M <103> and the anode chamber K _A <101> flows completely through. Method according to one of Claims 1 to 9, wherein the solid electrolyte F _K <111> which conducts alkali ions 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 ,
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 where w, x, y, z are chosen such that 1 + 2w + x - y + z ≥ 0 and 2 - w - x - y ≥ 0 applies. Method according to one of Claims 1 to 10, wherein L ₂ <113> comprises the alcohol ROH and an alkali metal alcoholate XOR. The method according to claim 11, wherein the mass ratio of XOR to alcohol ROH in L ₂ <113> is in the range 1: 100 to 1: 5. The method according to claim 11 or 12, wherein the concentration of XOR in L ₁ <115> is 1.01 to 2.2 times higher than in L ₂ <113>. The method according to any one of claims 1 to 13, wherein the concentration of X in L ₃ <114> is in the range from 3.5 to 5 mol / l. Process according to one of Claims 1 to 14, which is carried out at a temperature of 20 to 70 ° C and a pressure of 0.5 to 1.5 bar.

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