Improved process for depolymerization of polyethylene terephthalate

Abstract

The invention relates to a method for depolymerizing polyethylene terephthalate (= "PET"), in which PET is converted into bis (2-hydroxyethyl) terephthalate (= "BHET") in a mixture having ethylene glycol and an electrolytically produced alkali metal alkoxide, in particular lithium, sodium or potassium alkoxide. The method according to the invention is characterized in that a particularly high proportion of BHET is present in the cleavage products based on the undesired proportions of mono (2-hydroxyethyl) terephthalate (MHET) and terephthalate (TS) cleavage products. As a result, the process according to the invention provides a high yield of BHET, which can be directly used for new PET production. Thus, the invention also relates to a process for recovering PET in which BHET obtained in the process for depolymerizing PET is re-polymerized (optionally after further purification) to obtain PET.

Description

[0001] The present invention relates to a method for depolymerizing polyethylene terephthalate (= "PET"), in which PET is converted to bis(2-hydroxyethyl) terephthalate (= "BHET") in a mixture having ethylene glycol and an alkali metal alkoxide produced electrolytically, in particular lithium alkoxide, sodium alkoxide or potassium alkoxide.

[0002] The method according to the invention is characterized in that, based on the ratio of unwanted mono(2-hydroxyethyl) terephthalate (MHET) and terephthalate (TS) cleavage products, a particularly high proportion of BHET is present in the cleavage products. As a result, the method according to the invention provides a high yield of BHET, which can be directly used in new PET production.

[0003] Accordingly, the present invention also relates to a method for recycling PET, in which the BHET obtained in the method for depolymerizing PET (optionally after further purification) is polymerized again to obtain PET. Background Art

[0004] Polyethylene terephthalate (= "PET") is one of the most important plastics, which is used for textile fibers, as a film and as a material for plastic bottles. In 2007 alone, the amount used in plastic bottles was ~10 7 t (W. Caseri, Polyethylenterephthalate, RD-16-03258 (2009), in F. B. Dill, G. Eisenbrand, F. Faupel, B. Fugmann, T. Gamse, R. Matissek, G. Pohnert, A. Rühling, S. Schmidt, G. Sprenger, [Online], Stuttgart, Georg Thieme Verlag, January 2022).

[0005] Due to the persistence and amount of waste derived from PET, it constitutes one of the greatest environmental challenges at present. The solution to this problem lies in avoiding PET and the effective reuse of PET.

[0006] The prior art has proposed various PET cleavage methods.

[0007] GB784,248A describes the methanolysis of PET.

[0008] The hydrolysis method for PET depolymerization is described in JP2000 - 309663A, US4,355,175A, and T. Yoshioka, N. Okayama, A. Okuwaki, Ind. Eng. Chem. Res. 1998, 37, 336 - 340.

[0009] The reaction of PET with ethylene glycol is described in EP0723951 A1, US3,222,299A, WO2020 / 002999A2, S. R. Shukla, A. M. Harad, Journal of Applied Polymer Science 2005, 97, 513 - 517 (hereinafter referred to as "Shukla & Harad"), and N. D. Pingale, S. R. Shukla, European Polymer Journal 2008, 44, 4151 - 4156.

[0010] Shukla and Harad stated that the glycolysis of PET produces bis(2 - hydroxyethyl) terephthalate (= "BHET"). This cleavage product can be used simultaneously as a reactant for producing new PET. In contrast, specific by - products such as monoester mono(2 - hydroxyethyl) terephthalate (= "MHET") or free terephthalic acid or the corresponding carboxylate terephthalate (= "TS") are disadvantageous because these by - products cannot be directly used as reactants for producing new PET.

[0011] Therefore, there is an interest in methods for PET depolymerization in which the largest possible proportion of BHET is obtained in the cleavage products while the proportions of unwanted by - products such as MHET and TS should be minimized.

[0012] The problem solved by the present invention is to provide such a method. Summary of the Invention

[0013] Now, a method for solving the problem solved by the present invention has been surprisingly found.

[0014] The present invention relates to a method for depolymerizing polyethylene terephthalate PET, comprising the following steps:

[0015] (a) Generating an alkoxide M A or a solution L1<21> of M in an alcohol ROH;

[0016] where M A is an alkali metal cation, especially selected from lithium, potassium, sodium, preferably selected from potassium, sodium, and most preferably sodium,

[0017] and wherein R is an alkyl group having from 1 to 6, preferably from 1 to 5, more preferably from 1 to 4, even more preferably from 1 to 3 carbon atoms, and even more preferably R = methyl or ethyl, and most preferably R = methyl,

[0018] The electrolytic cell E<1> comprises:

[0019] - at least one anode chamber K A <11>, which has at least one inlet Z KA <110>, at least one outlet A KA <111> and an interior I A <113> containing an anodic electrode E KA <112>;

[0020] - at least one cathode chamber K K <12>, which has at least one inlet Z KK <120>, at least one outlet A KK <121> and an interior I K <123> containing a cathodic electrode E KK <122>;

[0021] - and optionally at least one inserted intermediate chamber K M <13>, which has at least one inlet Z KM <130>, at least one outlet A KM <131> and an interior I KM <132>;

[0022] wherein, I KA <112> and I KM <132> are separated from each other by a diffusion barrier D<14>, A KM <131> is connected to the inlet Z AM <15> by a connection V KA such that liquid can pass through the connection V AM <15> from I KM <132> to I KA <112>,

[0023] wherein

[0024] - in the case where the electrolytic cell E<1> does not contain the intermediate chamber K M <13>, I KA <112> and I KK <122> are separated from each other by a partition wall W<16>;

[0025] - When the electrolytic cell E<1> includes at least one intermediate chamber K M <13>, I KK <122> and I KM <132> are separated from each other by a partition wall W<16>;

[0026] Wherein the partition wall W<16> has a side S having a surface O KK <163> KK <161> and is located on the opposite side of the S KK <161> side and has a side S having a surface O A / MK <164> A / MK <162>, wherein the partition wall W<16> includes at least one alkali metal cation-conducting solid electrolyte ceramic F A <18>, such that the alkali metal cation-conducting solid electrolyte ceramic F A <18> included in the partition wall W<16> KK <163> is in direct contact with the interior I of the S KK <161> side KK <122>;

[0027] And wherein

[0028] - When the electrolytic cell E<1> does not include an intermediate chamber K M <13>, the alkali metal cation-conducting solid electrolyte ceramic F A <18> included in the partition wall W<16> A / MK <164> is in direct contact with the interior I of the S A / MK <162> side KA <112>;

[0029] - When the electrolytic cell E<1> includes at least one intermediate chamber K M <13>, the alkali metal cation-conducting solid electrolyte ceramic F A <18> included in the partition wall W<16> A / MK <164> is in direct contact with the interior I of the S A / MK <162> side KM <132>;

[0030] (α) Wherein, when the electrolytic cell E<1> does not include an intermediate chamber K M <13>, the following steps (α1), (α2), (α3) are carried out simultaneously in the electrolytic cell E<1>:

[0031] (α1) Guiding a solution L2<22> containing ROH through I KK <122>;

[0032] (α2) Feed the neutral or basic aqueous solution L3<23> of the salt S containing M A as the cation through I KA <112>;

[0033] (α3) Apply a voltage between E A <113> and E K <123>;

[0034] or

[0035] (β) wherein, when the electrolytic cell E<1> contains at least one intermediate chamber K M <13>, the following steps (β1), (β2), (β3) are carried out simultaneously in the electrolytic cell E<1>:

[0036] (β1) Feed the solution L2<22> containing ROH through I KK <122>;

[0037] (β2) Feed the neutral or basic aqueous solution L3<23> of the salt S containing M A as the cation through I KM <132>, then through V AM <15>, and finally through I KA <112>,

[0038] (β3) Apply a voltage between E A <113> and E K <123>,

[0039] which provides the solution L1<21> at the outlet A KK <121>, wherein the concentration of M A OR in L1<21> is higher than that in L2<22>;

[0040] and this provides the aqueous solution L4<24> of S at the outlet A KA <111>, wherein the concentration of S in L4<24> is lower than that in L3<23>;

[0041] (a*) Optionally, at least partially remove ROH from L1<21>, so as to obtain M A OR in solid form F* or as a solution L1* containing M A OR and ROH, wherein L1* has a reduced mass ratio of ROH compared to L1;

[0042] (b) Convert PET in the mixture to bis(2-hydroxyethyl) terephthalate BHET, the mixture comprising ethylene glycol and at least a portion of M comprised by L1<21>A OR, or if step (a*) is carried out, at least a part of M comprised by F* A OR or at least a part of M comprised by L1* A OR.

[0043] On the other hand, the present invention relates to a method for recycling PET, in which BHET obtained by the method according to the present invention for depolymerization is polymerized in step (ζ) to obtain PET.

[0044] Surprisingly, compared with the traditional method, it is found that the reaction of PET with M obtained by electrolysis in ethylene glycol produces lower proportions of unwanted MHET and TS by-products based on BHET. A OR The reaction produces lower proportions of unwanted MHET and TS by-products based on BHET. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1A and 1B

[0046] Figure 1A (=“ Figure 1A ”) shows the method of the present invention for producing a sodium methoxide solution L1<21> in an electrolytic cell E<1>. This includes a cathode chamber K K <12> and an anode chamber K A <11>.

[0047] The cathode chamber K K <12> includes a cathode electrode E KK <122> inside I K <123>, an inlet Z KK <120> and an outlet A KK <121>.

[0048] The anode chamber K A <11> includes an anode electrode E KA <112> inside I A <113>, an inlet Z KA <110> and an outlet A KA <111>.

[0049] The two chambers K A <11> and K K <12> are bounded by the outer wall W A <80> of a two-chamber cell E<1>. The inside I KK <122> is also separated from the inside I A <18> which consists of a sheet of NaSICON solid electrolyte ceramic F that selectively permeates sodium ions KA<112>Separation. NaSICON solid electrolyte ceramic F A <18>Extends over the entire depth and height of the two-chamber trough E<1>. The partition wall has two sides S KK <161>and S A / MK <162>, whose surfaces O KK <163>and O A / MK <164>contact the respective interiors I KK <122>or I KA <112>.

[0050] An aqueous sodium chloride solution L3<23>with a pH of 10.5 is introduced via the inlet Z KA <110>against the direction of gravity into the interior I KA <112>.

[0051] A 1 wt% solution of sodium methoxide in methanol L2<22>is guided via the inlet Z KK <120>into the interior I KK <122>.

[0052] Meanwhile, a voltage is applied between the cathode electrode E K <123>and the anode electrode E A <113>. This causes methanol in the electrolyte L2<22>to be reduced to methoxide and H2 (HOCH3 + e KK → CH3O - + 1 / 2H2) in the interior I - <122>. At the same time, sodium ions diffuse from the interior I KA <112>through the NaSICON solid electrolyte ceramic F A <18>into the interior I KK <122>. Overall, this increases the concentration of sodium methoxide in the interior I KK <122>, which provides a methanol solution L1<21>of sodium methoxide with an increased concentration of sodium methoxide compared to L2<22>(~20 wt% sodium methoxide in methanol) at the outlet A KK <121>.

[0053] In the interior I KA <112>, oxidation of chloride ions occurs to obtain molecular chlorine (Cl - → 1 / 2Cl2 + e - ). At the outlet A KA<111>, obtain aqueous solution L4 <24> with a reduced NaCl content compared to L3 <23>. According to the reaction Cl2 + H2O → HOCl + HCl, chlorine (Cl2) forms hypochlorous acid and hydrochloric acid in water, which undergoes an acidic reaction with further water molecules. The acidic destruction of the NaSICON solid electrolyte ceramic F A <18>.

[0054] Figure 1B (=" Figure 1B ) shows in the form of an electrolytic cell E<1> comprising an intermediate chamber K M <13> of a further embodiment of the method according to the invention. This three-chamber cell E<1> thus comprises a cathode chamber K K <12>, an anode chamber K A <11> and an inserted intermediate chamber K M <13>.

[0055] The cathode chamber K K <12> comprises a cathode electrode E KK <122> inside the interior I K <123>, an inlet Z KK <120> and an outlet A KK <121>.

[0056] The anode chamber K A <11> comprises an anode electrode E KA <112> inside the interior I A <113>, an inlet Z KA <110> and an outlet A KA <111>.

[0057] The intermediate chamber K M <13> comprises an interior I KM <132>, an inlet Z KM <130> and an outlet A KM <131>.

[0058] The interior I KA <112> is connected via a connection V AM <15> to the interior I KM <132>.

[0059] The three chambers are bounded by the outer wall W A <80> of the three-chamber cell E<1>. The interior I M <13> of the intermediate chamber K KM <132> is also separated by a partition wall W<16> which consists of a sheet of NaSICON solid electrolyte ceramic F that is selectively permeable to sodium ions Acomposed of <18> is separated from the cathode chamber K K inside I of <12> KK separated by the NaSICON solid electrolyte ceramic F of <122> A <18> extends over the entire depth and height of the three - chamber cell E<1>. The partition wall has S KK <161> and S A / MK <162> on both sides, whose surfaces O KK <163> and O A / MK <164> contact the respective inside I KK <122> or I KM <132>.

[0060] the interior I of the middle chamber K M <13> is thus additionally separated from the interior I of the anode chamber K KM <11> by the diffusion barrier D<14> A inside I of <11> KA <112>. The NaSICON solid electrolyte ceramic F A <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).

[0061] In the embodiment according to Figure 1B a connection V AM <15> is formed outside the electrolytic cell E<1>, especially formed by a tube or a hose, and the material thereof can be selected from rubber, metal, and plastic. The connection V AM <15> can guide the liquid from the interior I of the middle chamber K A <13> M inside I of <132> to the interior I of the anode chamber K KM <11> A inside I of <112> outside the outer wall W KA <80> of the three - chamber cell E<1>. The connection V AM <15> connects the outlet A KM <131> (which passes through the outer wall W of the electrolytic cell E<1> at the bottom of the middle chamber K M <13>) to the inlet Z A <110> (which passes through the outer wall W of the electrolytic cell E<1> at the bottom of the anode chamber K KA <11> A <80>). A <172>

[0062] An aqueous solution L3<23> of sodium chloride with a pH of 10.5 is introduced into the interior I of the middle chamber K along the direction of gravity via the inlet Z KM <130> M inside I ofKM In <132>. Connect V AM <15> connects the middle chamber K M The interior I of <13> KM <132> is connected to the anode chamber K A The interior I of <11> KA <112>. The sodium chloride solution L3 <23> from the interior I KM <132> is led through this connection V AM <15> to the interior I KM <112>.

[0063] A solution L2 <22> of sodium methoxide in methanol of ~1 wt% is led via the inlet Z KK <120> to the interior I KK <122>.

[0064] Meanwhile, a voltage is applied between the cathode electrode E K <123> and the anode electrode E A <113>. This causes methanol in the electrolyte L2 <22> in the interior I KK <122> to be reduced to methoxide and H2 (CH3OH + e - → CH3O - + 1 / 2H2). Meanwhile, sodium ions diffuse from the interior I M <103> of the middle chamber K KM <132> through the NaSICON solid electrolyte ceramic F A <18> to the interior I KK <122>. Overall, this increases the concentration of sodium methoxide in the interior I KK <122>, which provides, at the outlet A KK <121>, a methanol solution L1 <21> of sodium methoxide having an elevated concentration of sodium methoxide compared to L2 <22> (sodium methoxide in methanol of ~20 wt%).

[0065] In the interior I KA <112>, oxidation of chloride ions occurs to give molecular chlorine (Cl - → 1 / 2Cl2 + e - ). At the outlet A KA <111>, an aqueous solution L4 <24> is obtained, the NaCl content of which is reduced compared to L3 <23>. According to the reaction Cl2 + H2O → HOCl + HCl, chlorine gas (Cl2) forms hypochlorous acid and hydrochloric acid in water, which provides an acidic reaction with further water molecules. The acidity would damage the NaSICON solid electrolyte ceramic F A <18>, but the acidity is confined to the anode chamber K by the configuration in the three - chamber cellA <11>, and thus is kept away from the NaSICON solid electrolyte ceramic F in the electrolytic cell E<1> A <18>. This significantly increases its service life.

[0066] Figure 2A and 2B

[0067] Figure 2A (=" Figure 2A ") shows the preferred partition wall W<16>. This contains two NaSICON solid electrolyte ceramics F A <18> and F B <19>, which are separated from each other by the separation group T<17> and each is fixed to the separation component T<17> in a gapless manner. The separation component T<17> has a cuboid geometry, and on its opposite sides, F A <18> and F B <19> are fixed in a gapless manner (e.g., by an adhesive).

[0068] Has a side S with surface O KK <163> located in the drawing plane, while the side S with surface O KK <161> A / MK <164> located behind the drawing plane and is invisible in A / MK Figure 2A it.

[0069] Figure 2B (=" Figure 2B ") shows another embodiment of the preferred partition wall W<16>. This contains four NaSICON solid electrolyte ceramics F A <18>, F B <19>, F C <28>, F D <29>, which are separated from each other by the separation component T<17> and each is fixed to the separation component T<17> in a gapless manner. The separation component T<17> has a cross shape, and on its opposite sides, F A <18>, F B <19>, F C <28> and F D <29> are fixed.

[0070] Has a side S with surface O KK <163> located in the drawing plane, while the side S with surface O KK <161> A / MK <164> located behind the drawing plane and is invisible in A / MK Figure 2B it.​​

[0071] Figures 3A to 3C

[0072] Figure 3A (= " Figure 3A ) is shown in Figure 2A and 2B in the detailed view indicated by the dashed circle. As described, for example by an adhesive, the solid electrolyte ceramics F A <18> and F B <19> are fixed to the separation component T<17>.

[0073] Figure 3B (= " Figure 3B ) illustrates a further embodiment of the preferred partition wall W. Here, the separation component T<17> has two concave recesses (grooves) into which the two solid electrolyte ceramics F A <18> and F B <19> are adapted. For this purpose, the shape of the edges of the solid electrolyte ceramics F A <18> and F B <19> can be adjusted mechanically accordingly. Additionally, a seal Di<40> is used, which is mounted, for example using an adhesive, on the separation component T<17> and each of the solid electrolyte ceramics F A <18> or F B <19>. The separation component T<17> can here be composed of two or more parts <171> and <172>, which can be fixed to each other as indicated by the dashed line in Figure 3B . In the case of a suitable geometry and fit of the edge shape of the solid electrolyte ceramics F A <18> and F B <19>, the solid electrolyte ceramics can be clamped between the two parts <171> and <172>, which further improves the connection stability of the separation component T<17> / ceramic F A <18> or F B <19> and the integrity of the partition wall W<16>.

[0074] Figure 3C (= " Figure 3C ) illustrates a further embodiment of the preferred partition wall W. This corresponds to what is described in Figure 3B , except that the recesses (grooves) in the separation component T<17> (into which the two solid electrolyte ceramics F A <18> and F B <19> are adapted) are not concave, but conical.

[0075] Figures 4A to 4D

[0076] Figure 4A (= " Figure 4A ) to a further embodiment of the preferred dividing wall W<16> for 4D display.

[0077] In Figure 4A the dividing wall W<16> shown corresponds to the dividing wall W<16> shown in Figure 2A except that it further includes a frame component R<20>. This completely covers all surfaces of the dividing wall W<16> except for O KK <163> and O A / MK <164>. The frame component R<20> is not in one-piece form with the separating component T<17>.

[0078] Figure 4B (= " Figure 4B ) shows a further embodiment of the preferred dividing wall W<16>. This corresponds to the embodiment shown in Figure 4A except that it includes two frame components R<20> bounded by the upper and lower surfaces of the dividing wall W<16>.

[0079] Figure 4C (= " Figure 4C ) shows a further embodiment of the preferred dividing wall W<16>. In Figure 4C the dividing wall W<16> shown corresponds to the dividing wall W<16> shown in Figure 2B except that it further includes a frame component R<20>. This completely covers all surfaces of the dividing wall W<16> except for O KK <163> and O A / MK <164>. The frame component R<20> is not in one-piece form with the separating component T<17>.

[0080] Figure 4D (= " Figure 4D ) shows a further embodiment of the preferred dividing wall W<16>. This corresponds to the embodiment shown in Figure 4C except that it includes two frame components R<20> bounded by the upper and lower surfaces of the dividing wall W<16>.

[0081] Figure 5A And 5B

[0082] Figure 5A (= " Figure 5A ) shows the electrolytic cell E<1> in a preferred embodiment according to the method of the present invention. This corresponds to the electrolytic cell shown in Figure 1A except that the dividing wall W<16> separates the cathode chamber K KInner I of <12> KK <122> and the anode chamber K A Inner I of <11> KA <112> is separated. The partition wall is the one shown in Figure 2A and 2B as shown therein.

[0083] Figure 5B (= “ Figure 5B ”) is shown in the electrolytic cell E<1> in a preferred embodiment of the method according to the invention. This corresponds to the electrolytic cell shown in Figure 1A except that the partition wall W<16> separates the cathode chamber K K Inner I of <12> KK <122> from the anode chamber K A Inner I of <11> KA <112>. The partition wall W<16> is the one shown in Figures 4A to 4D as shown therein. The frame assembly R<20> forms part of the outer wall W A <80> such that the solid electrolyte ceramic contained in the partition wall W<16> is protected from the pressure that would act on it via the partition wall W<16> if it were part of the partition wall W<16>. Furthermore, the solid electrolyte ceramic is thus fully used for separating the inner I KK <122> from I KA <112> within the electrolytic cell E<1> because it is not partially covered by the outer wall.

[0084] Figure 6A and 6B

[0085] Figure 6A (= “ Figure 6A ”) shows the method according to the invention corresponding to the electrolytic cell E<1> shown in Figure 1B except that the difference from the electrolytic cell of Figure 1B is that the connection V M Inner I of <13> KM <132> to the anode chamber K A Inner I of <11> KA <112> is formed by a plurality of perforations in the diffusion barrier D<14>. These perforations can subsequently be punched into the diffusion barrier D<14> or may be present therein from the start because of the process for producing the diffusion barrier D<14> (for example in the case of a textile fabric such as a filter cloth or a wire mesh). In this embodiment, the totality of these perforations constitutes the connection V AM <15>, through which connection V AM <15>, the electrolyte can flow from the inner I AM <15>KM <132> is led to the interior I KA of <112>.

[0086] Figure 6B (=" Figure 6B ) shows a further embodiment of the method according to the invention in the form of an electrolytic cell E<1>. This corresponds to the electrolytic cell E<1> shown in Figure 1B , with the difference that the connection V M from the interior I of the intermediate chamber K KM <132> to the interior I of the anode chamber K A <11> KA <112> AM <15> is formed by the gap formed between the diffusion barrier D<14> and the outer wall W A <80>. The gap can be set up by arranging the originally impermeable diffusion barrier D<14> in the electrolytic cell E<1> such that it does not completely separate the interior I of the intermediate chamber K M <132> KM from the interior I of the anode chamber K A <11> KA <112>, but instead leaves a gap as the connection V AM <15>.

[0087] Figure 7A and 7B

[0088] Figure 7A (=" Figure 7A ) shows a further embodiment of the preferred partition wall W<16>. This comprises four NaSICON solid electrolyte ceramics F A <18>, F B <19>, F C <28> and F D <29>, which are separated from each other by a separating component T<17> comprising two halves <171> and <172>. The partition wall W<16> also comprises a frame component R<20> which also consists of two halves <201> and <202>.

[0089] The partition wall W<16> consists of two parts which can be folded up, where the half <171> of the separating component T<17> and the half <201> of the frame component R<20> are in one-piece form, and the half <172> of the separating component T<17> and the half <202> of the frame component R<20> are in one-piece form. These two parts can optionally be connected to each other via a hinge <50> and can be locked in place via a lock <60> in the folded-up state.

[0090] Four NaSICON solid electrolyte ceramics F A <18>, F B <19>, F C <28> and F D <29> are sandwiched between these halves, and in each case a ring that functions as a seal Di<40> for sealing is used.

[0091] Figure 7A The left - hand side of the figure shows the side S of the partition wall W<16> having a surface O KK <163> KK <161> front view. The ring that functions as a seal Di<40> is shown by a dashed outline. The right - hand side of the figure shows a side view of the partition wall W<16>.

[0092] Figure 7B (=“ Figure 7B ”) shows a further embodiment of the preferred partition wall W<16>. This corresponds to the embodiment described in Figure 7A except that it contains nine NaSICON solid electrolyte ceramics F A <18>, F B <19>, F C <28>, F D <29>, F E <30>, F F <31>, F G <32>, F H <33>, F I <34>. DETAILED DESCRIPTION OF THE INVENTION

[0094] It has been observed that in the method according to the invention, a higher proportion of BHET is obtained in the cleavage product compared to the prior - art method in which an alkali metal alkoxide M A OR in an alcohol ROH obtained by dissolving the corresponding alkali metal hydroxide M A OH in the alcohol ROH is used.

[0095] 1. Step (a): Electrolysis to obtain a solution L1 containing ROH and M A OR

[0096] According to the invention, a solution L1 containing ROH and M A OR used in the method according to the invention is obtained electrolytically in an electrolytic cell E<1>.

[0097] “Ethylene glycol” in the context of the present invention is understood to mean ethylene - 1,2 - diol (CAS No. 107 - 21 - 1) having the chemical formula HO - CH2 - CH2 - OH.

[0098] R is an alkyl group having 1 to 6 carbon atoms, especially an alkyl group having 1 to 5 carbon atoms, preferably an alkyl group having 1 to 4 carbon atoms, and more preferably an alkyl group having 1 to 3 carbon atoms. More preferably, R is selected from ethyl and methyl. Most preferably, R = methyl.

[0099] According to the present invention, the alkyl group having 1 to 6 carbon atoms is especially selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 3,3-dimethylbutyl, 1-ethylbutyl, 2-ethylbutyl, 1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethyl-1-methylpropyl, and 1-ethyl-2-methylpropyl, preferably selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, and n-hexyl, and even more preferably selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, n-pentyl, and n-hexyl.

[0100] In the context of the present invention, the alkyl group having 1 to 5 carbon atoms is especially selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, and 1-ethylpropyl, preferably selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, and n-pentyl, and more preferably selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, and n-pentyl.

[0101] In the context of the present invention, the alkyl group having 1 to 4 carbon atoms is especially selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, and tert-butyl, preferably selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, and tert-butyl, and more preferably selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, and n-butyl.

[0102] In the context of the present invention, the alkyl group having 1 to 3 carbon atoms is especially selected from the group consisting of methyl, ethyl, n-propyl, and isopropyl, preferably selected from the group consisting of methyl, ethyl, and isopropyl.

[0103] M Ais an alkali metal cation, especially selected from lithium, sodium, potassium, and preferably selected from sodium, potassium. Most preferably, the alkali metal cation is sodium.

[0104] 1.1 Electrolytic cell E

[0105] M used in step (b) of the process according to the invention or optionally in step (a*) A OR solution L1 of <21> in ROH is prepared in electrolytic cell E in step (a) of the process according to the invention.

[0106] Electrolytic cell E comprises at least one anode chamber K A and at least one cathode chamber K K , and optionally at least one inserted intermediate chamber K M . This also includes an electrolytic cell E having more than one anode chamber K A and / or cathode chamber K K and / or intermediate chamber K M . Such an electrolytic cell, in which these chambers are connected to each other in a modular form, is described, for example, in DD 258143A3 and US2006 / 0226022A1.

[0107] In a preferred embodiment, electrolytic cell E comprises an anode chamber K A and a cathode chamber K K , and an optionally present inserted intermediate chamber K M .

[0108] Electrolytic cell E typically has an outer wall W A . Outer wall W A is especially made of a material selected from the group consisting of steel (preferably rubberized steel), plastics (especially from (thermosetting poly dicyclopentadiene), PVC (polyvinyl chloride), PVC-C (post-chlorinated polyvinyl chloride), PVDF (polyvinylidene fluoride)). W A can especially be perforated for inlets and outlets. Then inside W A is the at least one anode chamber K A , the at least one cathode chamber K K , and in the embodiment where electrolytic cell E comprises one, the at least one inserted intermediate chamber K M .

[0109] 1.1.1 Cathode chamber K K

[0110] The at least one cathode chamber K K has at least one inlet Z KK , at least one outlet A KK , and an interior I K containing a cathode electrode EKK 。

[0111] If the electrolytic cell E does not include an intermediate chamber K M , then the interior I A of the anode chamber K KA is separated from the interior I K of the cathode chamber K KK by a partition wall W. If the electrolytic cell E includes at least one intermediate chamber K M , then the interior I K of the cathode chamber K KK is separated from the interior I M of the intermediate chamber K KM by a partition wall W. The partition wall W and its configuration in the electrolytic cell E are further described below (section 1.1.4).

[0112] 1.1.1.1 Cathode electrode E K

[0113] The cathode chamber K K includes an interior I KK , which thus includes the cathode electrode E K . Such a useful cathode electrode E K is any electrode familiar to those skilled in the art that is stable under the conditions of step (a) of the method according to the invention. These are described in particular in paragraph

[025] of WO2014 / 008410A1 or paragraph

[030] of DE 10360758A1. This electrode E K is optionally selected from the group consisting of mesh wool, three-dimensional matrix structures, and "balls". The cathode electrode E K especially includes a material selected from the group consisting of steel, nickel, copper, platinum, platinumized metals, palladium, palladium on carbon, titanium, and more preferably from the group consisting of steel and nickel. E K Preferably includes steel, and even more preferably VA steel (= stainless steel).

[0114] In an embodiment of the electrolytic cell E (wherein it includes an intermediate chamber K M ), the intermediate chamber K M is located between the anode chamber K A and the cathode chamber K K .

[0115] 1.1.1.2 Inlet Z KK and outlet A KK

[0116] The cathode chamber K K also includes at least one inlet Z KK and at least one outlet A KK . This enables a liquid (such as solution L2) to be added to the cathode chamber K KInternal I KK , and capable of removing the liquid present therein (eg solution L1). Inlet Z KK and Exit A KK Here, the liquid is made to flow through the cathode chamber K K Internal I KK When the cathode electrode E K Connected to cathode chamber K by contact K This is to be used as the solution L2 of alcohol ROH, optionally also containing alkali metal alcoholate M A OR, is guided through the cathode chamber K K Internal I KK When implementing step (a) of the method according to the present invention, at outlet A KK Prerequisites for obtaining solution L1.

[0117] Entrance Z KK and Exit A KK The connection to the electrolysis cell E can be made by methods known to those skilled in the art, for example by means of holes in the outer wall and corresponding connections (valves) which simplify the introduction and discharge of liquids.

[0118] 1.1.2 Anode chamber K A

[0119] The at least one anode chamber K A Has at least one entrance Z KA , at least one exit A KA , and comprising an anode electrode E A Internal I KA .

[0120] If the electrolytic cell E contains an intermediate chamber K M , anode chamber K A Internal I KA Then it passes through the diffusion barrier D and the intermediate chamber K M Internal I KM Separation.

[0121] If the electrolytic cell E does not contain the intermediate chamber K M , the interior of the anode chamber K I KA Then through the partition wall W and the cathode chamber K K Internal I KK Separation.

[0122] 1.1.2.1 Anode electrode E A

[0123] Anode chamber K A Contains internal I KA , which thus comprises an anode electrode E A Such useful anode electrode E AAny electrode that is stable under the conditions of step (a) of the method according to the invention and is familiar to those skilled in the art. These are described in particular in paragraph

[024] of WO2014 / 008410A1 or paragraph

[031] of DE 10360758A1. This electrode E A can consist of a single layer or of a plurality of planar layers parallel to each other that can each be perforated or unfolded. The anode electrode E A in particular comprises a material selected from the group consisting of ruthenium oxide, iridium oxide, nickel, cobalt, nickel tungstate, nickel titanate, noble metals (such as in particular platinum) supported on a carrier such as titanium or (an iron / nickel / cobalt alloy, where the respective components are preferably as follows: 54% by mass of iron, 29% by mass of nickel, 17% by mass of cobalt). Further possible anode materials are in particular stainless steel, lead, graphite, tungsten carbide, titanium diboride. Preferably, the anode electrode E A comprises a titanium anode coated with ruthenium oxide / iridium oxide (RuO2+IrO2 / Ti).

[0124] 1.1.2.2 Inlet Z KA and outlet A KA

[0125] The anode chamber K K also comprises an inlet Z KA and an outlet A KA . This enables a liquid (such as solution L3) to be added to the interior I A of the cathode chamber K KA , and enables the liquid present therein (such as solution L4) to be removed. The inlet Z KA and the outlet A KA are here connected to the anode chamber K in such a way that the liquid comes into contact with the anode electrode E A when flowing through the interior I KA of the anode chamber K A . This is a prerequisite for obtaining solution L4 at the outlet A A in the implementation of step (a) of the method according to the invention when the solution L3 of the salt S is passed through the interior I A of the anode chamber K KA . KA

[0126] Inlet Z KA and outlet A KA can be connected to the electrolytic cell E by methods known to those skilled in the art, for example by means of holes in the outer wall and corresponding connections (valves) that facilitate the introduction and discharge of the liquid. In a particular embodiment in which the electrolytic cell E comprises an intermediate chamber K M the inlet Z KA ​It may also be present in the electrolytic cell, for example, in the form of perforations in the diffusion barrier D.

[0127] 1.1.3 Optional intermediate chamber K M

[0128] The electrolytic cell E used in step (a) of the method according to the invention optionally has at least one intermediate chamber K M . The optional intermediate chamber K M is located between the cathode chamber K K and the anode chamber K A . It contains at least one inlet Z KM , at least one outlet A KM and an interior I KM .

[0129] If the electrolytic cell E contains an intermediate chamber K M , the interior I A of the anode chamber K KA is separated from the interior I M of the intermediate chamber K KM by a diffusion barrier D. In that case, A KM is also connected to the inlet Z AM by a connection V KA [[ID=4)), such that liquid can be guided from I KM through the connection V AM to I KA .

[0130] 1.1.3.1 Diffusion barrier D

[0131] The interior I M of the optional intermediate chamber K KM is separated from the interior I A of the anode chamber K KA by a diffusion barrier D and from the interior I K of the cathode chamber K KK by a partition wall W.

[0132] The material used for the diffusion barrier D can be any material that is stable under the conditions of step (a) of the method according to the invention and that prevents or slows down the transfer of protons from the liquid present in the interior I A of the anode chamber K KA to the interior I M of the optional intermediate chamber K KM .

[0133] The diffusion barrier D used is in particular a non-ion-specific partition wall or a membrane permeable to specific ions. The diffusion barrier D is preferably a non-ion-specific partition wall.

[0134] The material of the partition wall for non-specific ions is particularly selected from the group consisting of fabrics (especially textile fabrics or metal braids), glass (especially sintered glass or frit), ceramics (especially ceramic materials), and diaphragms, and more preferably is a textile fabric or a metal braid, and particularly preferably is a textile fabric. The textile fabric preferably contains plastics, and more preferably plastics selected from PVC, PVC-C, polyvinyl ether ("PVE"), and polytetrafluoroethylene ("PTFE").

[0135] If the diffusion barrier D is a "membrane permeable to specific ions", according to the present invention, this means that each membrane promotes the diffusion of particular ions through the membrane over other ions. More particularly, this means that the membrane promotes the diffusion of ions of a particular charge type through the membrane over ions of the opposite charge. Even more preferably, the membrane permeable to specific ions also promotes the diffusion of particular ions of one charge type through the membrane over other ions of the same charge type.

[0136] 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.

[0137] According to the present invention, anion-conducting membranes are those that selectively conduct anions, preferably selectively conduct particular anions. In other words, they promote the diffusion of anions through the membrane over the diffusion of cations through the membrane, especially over protons; even more preferably, they additionally promote the diffusion of particular anions through the membrane over the diffusion of other anions through the membrane.

[0138] According to the present invention, cation-conducting membranes are those that selectively conduct cations, preferably selectively conduct particular cations. In other words, they promote the diffusion of cations through the membrane over the diffusion of anions through the membrane; even more preferably, they additionally promote the diffusion of particular cations through the membrane over the diffusion of other cations through the membrane, still more preferably, non-proton cations, and more preferably, the diffusion of sodium cations through the membrane is better than that of protons.

[0139] More particularly, "promoting the diffusion of particular ions X over other ions Y" means that at a given temperature, the diffusion coefficient (unit: m 2 / s) of ion type X for the membrane in question is 10 times higher, preferably 100 times higher, preferably 1000 times higher than the diffusion coefficient of ion type Y for the membrane in question.

[0140] If the diffusion barrier D is a "membrane permeable to specific ions", it is preferably an anion-conducting membrane because this particularly effectively prevents protons from diffusing from the anode chamber K A to the intermediate chamber K M in.

[0141] The anion-conducting membrane used is in particular a membrane selective for the anions comprised by salt S. Such membranes are known and available to the person skilled in the art. According to the invention, salt S comprises M A as a cation.

[0142] Salt S is preferably a halide, sulfate, sulfite, nitrate, hydrogencarbonate or carbonate of M A and even more preferably a halide.

[0143] Halides are fluorides, chlorides, bromides, iodides. The most preferred halide is chloride.

[0144] The anion-conducting membrane used is preferably a membrane selective for halides (preferably chloride).

[0145] The anion-conducting membrane is described, for example, via M.A. Hickner, A.M. Herring, E.B. Coughlin, Journal of Polymer Science, Part B: Polymer Physics 2013, 51, 1727 - 1735, via C.G. Arges, V. Ramani, P.N. Pintauro, Electrochemical Society Interface 2010, 19, 31 - 35, in WO2007 / 048712A2, and via page 181 of the textbook Elektrochemische Verfahrenstechnik: Grundlagen, Reaktionstechnik, Prozessoptimierung [Electrochemical Engineering: Fundamentals, Reaction Technology, Process Optimization], 1st Edition (8 October 2003) by Volkmar M. Schmidt.

[0146] Even more preferably, the anion-conducting membrane used is thus an organic polymer, in particular selected from polyethylene, polybenzimidazole, polyether ketone, polystyrene, polypropylene and fluorinated membranes such as polytetrafluoroethylene, preferably polystyrene, wherein these have covalently bonded functional groups selected from -NH3 + , -NRH2 + , -NR3 + , =NR + , -PR3 + wherein R is preferably an alkyl group having 1 to 20 carbon atoms, or other cationic groups. It preferably has covalently bonded functional groups selected from -NH3 + , -NRH2+ and -NR3 + , more preferably selected from -NH3 + and -NR3 + , even more preferably -NR3 + covalently bonded functional groups.

[0147] When the diffusion barrier D is a cation-conducting membrane, it is particularly selective for M A (i.e., the cations contained in the salt S). Even more preferably, the diffusion barrier D is an alkali metal cation-conducting membrane, even more preferably a potassium and / or sodium ion-conducting membrane, and most preferably a sodium ion-conducting membrane.

[0148] Cation-conducting membranes are described, for example, on page 181 of the textbook by Volkmar M. Schmidt, Elektrochemische Verfahrenstechnik: Grundlagen, Reaktionstechnik, Prozessoptimierung, 1st edition (October 8, 2003).

[0149] Even more preferably, the cation-conducting membrane used is thus an organic polymer, particularly selected from polyethylene, polybenzimidazole, polyether ketone, polystyrene, polypropylene, and fluorinated membranes such as polyvinylidene fluoride, preferably polystyrene and polyvinylidene fluoride, where these carry covalently bonded functional groups selected from -SO3 - , -COO - , -PO3 2- and -PO2H - , preferably -SO3 - (described in DE10 2010062804A1, US 4,831,146).

[0150] This can be, for example, sulfonated polyvinylidene fluoride (having CAS number: 31175-20-9 ). These are known to those skilled in the art, for example, from paragraph

[058] of WO 2008 / 076327A1, paragraph

[0042] of US 2010 / 0044242A1, or US2016 / 0204459A1, and are commercially available under F, etc. Membranes are described, for example, by S.A. Mareev, D.Yu. Butylskii, N.D. Pismenskaya, C. Larchet, L. Dammak, V.V. Nikonenko, Journal of Membrane Science 2018, 563, 768-776.

[0151] If a cation-conducting membrane is used as the diffusion barrier D, this can be, for example, a polymer functionalized via sulfonic acid groups, in particular one having the formula P NAFION where n and m can independently be integers from 1 to 10 6 , preferably integers from 10 to 10 5 , more preferably 10 2 to 10 4 of the integer.

[0152]

[0153] 1.1.3.2 Inlet Z KM and outlet A KM

[0154] The optional intermediate chamber K M also includes an inlet Z KM and an outlet A KM . This enables a liquid (such as solution L3) to be added to the interior I M of the intermediate chamber K KM , and enables the liquid (such as solution L3) present therein to be transferred to the interior I A of the anode chamber K KA .

[0155] Inlet Z KM and outlet A KM can be connected to the electrolytic cell E by methods known to those skilled in the art, such as by means of holes in the outer wall and corresponding connections (valves) that facilitate the introduction and discharge of the liquid. Outlet A KM can also be within the electrolytic cell, for example in the form of perforations in the diffusion barrier D.

[0156] 1.1.3.3 Connection V AM

[0157] In the electrolytic cell E used in step (a) of the method according to the invention, outlet A KM is connected to inlet Z AM in such a way that the liquid can be led from I KM through connection V AM to I KA via connection V KA .

[0158] Connection V AM can be formed inside and / or outside the electrolytic cell E and is preferably formed inside the electrolytic cell.

[0159] 1) If connection V AMIt is formed inside the electrolytic cell E, which is preferably formed by at least one perforation in the diffusion barrier D. This embodiment is preferred especially when the diffusion barrier D used is a partition wall that is not specific to ions, especially a metal woven fabric or a textile fabric. This serves as the function of the diffusion barrier D, and due to the woven nature, it has perforations and gaps that serve as the function of the connection V from the beginning. AM and gaps.

[0160] 2) Especially when the diffusion barrier D used is a membrane that is permeable to specific ions, the following-described embodiment is preferred: In this embodiment, the connection V AM is formed outside the electrolytic cell E, preferably formed by the connection of A KM and Z KA that extends outside the electrolytic cell E, especially: formed from the inside I M of the intermediate chamber K KM through the outer wall W A of the outlet A KM , preferably at the bottom of the intermediate chamber K M , the inlet Z KM more preferably at the top of the intermediate chamber K M , and formed by the outer wall W A entering the internal I A of the anode chamber K KA of the inlet Z KA , preferably at the bottom of the anode chamber K A , and these inlets and outlets are connected by pipelines, such as pipes or hoses (preferably made of materials selected from rubber and plastics). Then the outlet A KA is more preferably at the top of the anode chamber K A .

[0161] "The outlet A M at the bottom of the intermediate chamber K KM " means: The outlet A KM is connected to the electrolytic cell E in such a way that the solution L3 leaves the intermediate chamber K M along the direction of gravity.

[0162] "The inlet Z A at the bottom of the anode chamber K KA " means: The inlet Z KA is connected to the electrolytic cell E in such a way that the solution L3 enters the anode chamber K A against the direction of gravity.

[0163] "The inlet Z M at the top of the intermediate chamber K KM " means: The inlet Z KM is connected to the electrolytic cell E in such a way that the solution L3 enters the intermediate chamber K M along the direction of gravity.

[0164] “At the top of the anode chamber K A the outlet A KA ” means that the outlet A KA is installed on the electrolytic cell E in such a way that the solution L4 leaves the anode chamber K A against the direction of gravity.

[0165] When the outlet A KM is formed at the bottom of the intermediate chamber K M by the outer wall W A and the inlet Z KA is formed at the bottom of the anode chamber K A by the outer wall W A this embodiment is particularly advantageous and thus preferred. This configuration makes it possible in a particularly simple way to remove the gas formed in the anode chamber K A and L4 from the anode chamber K A in order to separate them further. Figure 1B Figure 30 shows such an embodiment.

[0166] When the connection V AM is formed outside the electrolytic cell E, Z KM and A KM are in particular arranged at opposite ends of the outer wall W M of the intermediate chamber K A (i.e. for example Z KM at the bottom of the electrolytic cell E and A KM at the top of the electrolytic cell E, or vice versa) and Z KA and A KA are arranged at opposite ends of the outer wall W A of the anode chamber K A (i.e. Z KA at the bottom of the electrolytic cell E and A KA at the top of the electrolytic cell E, or vice versa), as shown more particularly in Figure 1B Figure 61. By virtue of this geometry, L3 has to flow through two chambers K M and K A . Here, Z KA and Z KM can be formed on the same side of the electrolytic cell E, in which case A KM and A KA are also automatically formed on the same side of the electrolytic cell E. Or, as in the embodiment shown in Figure 1B Figure 75, Z KA and Z KM can be formed on opposite sides of the electrolytic cell E, in which case then A KM and A KA are also automatically formed on opposite sides of the electrolytic cell E.

[0167] 3) When connecting V AM is formed within electrolytic cell E, this can be ensured in particular as follows: One side of electrolytic cell E ("side A", which is the top or bottom of electrolytic cell E, preferably the top as shown in Figure 6B contains inlet Z KM and outlet A KA , and diffusion barrier D extends from this side ("side A") into electrolytic cell E, but does not reach completely to the side of electrolytic cell E opposite to side A ("side B", which is then the bottom or top of electrolytic cell E), and at the same time covers 50% or more of the height of three-chamber cell E, preferably 60% to 99% of the height of three-chamber cell E, more preferably 70% to 95% of the height of three-chamber cell E, even more preferably 80% to 90% of the height of three-chamber cell E, still more preferably 85% of the height of three-chamber cell E. Since diffusion barrier D does not contact the outer wall W A of side B of three-chamber cell E, a gap is formed between diffusion barrier D and outer wall W AM of side B of three-chamber cell E. In that case, the gap is connection V M and K A . By virtue of this geometric configuration, L3 must flow completely through two chambers K

[0168] These embodiments best ensure that the aqueous salt solution L3 flows past the acid-sensitive solid electrolyte before it comes into contact with the anode electrode E A (which results in the formation of acid).

[0169] According to the present invention, "the bottom of electrolytic cell E" is the side of electrolytic cell E through which a solution (such as L3 in the case of Figure 1B A in KM ) leaves electrolytic cell E in the same direction as the direction of gravity, or the side of electrolytic cell E through which a solution (such as L2 in the case of Z in Figure 1A , 1B , 5A, 5B, 6A and 6B, and L3 in the case of Z in KK and Figure 1A , 1B , 5A and 5B) is supplied to electrolytic cell E in the opposite direction of gravity. KA

[0170] According to the present invention, "the top of electrolytic cell E" is the side of electrolytic cell E through which a solution (such as L4 in the case of A in Figure 1A , 1B , 5A, 5B, 6A and 6B, and L1 in the case of A in KA ) leaves electrolytic cell E in the opposite direction of gravity, or the side of electrolytic cell E through which a solution (such as KK ) is supplied to electrolytic cell E in the opposite direction of gravity. Figure 1B ​, 6A and Z in 6B KM In the case of L3), it is supplied to the side of the electrolytic cell E in the same direction as gravity.

[0171] 1.1.3.4 Intermediate chamber K M Further embodiments

[0172] In a preferred embodiment of the electrolytic cell E, the interior I KM also comprises at least one additional feature selected from:

[0173] 1) Established internal components that cause turbulence in the electrolyte L3;

[0174] 2) Stirring equipment;

[0175] 3) Via an additional inlet at the bottom of the intermediate chamber and an additional outlet at the top of the intermediate chamber, an inert gas (such as nitrogen or a noble gas) is additionally introduced. When the salt S is a carbonate or bicarbonate, using this additional outlet, it is also possible to remove any gas formed from I KM such as CO2.

[0176] By virtue of these additional preferred embodiments 1), 2) and 3), vortices and turbulence are formed in the electrolyte L3 as the electrolyte L3 flows through I KM This additionally hinders the formation of a pH gradient in the intermediate chamber and thus prevents damage to the ASC due to too low a pH. This increases the service life of the ASC.

[0177] 1.1.4 Partition wall W

[0178] The electrolytic cell E used in step (a) of the method according to the invention comprises a partition wall W. The partition wall W comprises at least one alkali metal cation-conducting solid electrolyte ceramic F A . In a preferred embodiment, the partition wall W consists of the alkali metal cation-conducting solid electrolyte ceramic F A .

[0179] In an alternative preferred embodiment of the present invention, the partition wall W comprises at least two alkali metal cation-conducting solid electrolyte ceramics (hereinafter simply referred to as "ASC") F A and F B , which are optionally separated from each other by a separating component T.

[0180] The partition wall W has two sides S KK and S A / MK , which means that side S A / MK is the opposite side of S KK (and vice versa). The two sides S KKand S A / MK Particularly, it includes planes that are substantially parallel to each other.

[0181] In addition, the geometry of the partition wall W is not subject to other restrictions and can be particularly matched to the cross-section of the electrolytic cell E in which the partition wall W is used. For example, it can have a cuboid geometry and thus have a rectangular cross-section, or a frustocone or cylindrical geometry and thus have a circular cross-section.

[0182] Optionally, the partition wall W can also have a cuboid geometry with rounded corners or protrusions, which can thus have holes. Then the partition wall W has protrusions ("rabbit ears"), whereby the partition wall W can be fixed to the electrolytic cell, or the frame members of the partition wall W can be fixed to each other.

[0183] The side S of the partition wall W KK has a surface O KK , and the side S of the partition wall W A / MK has a surface O A / MK .

[0184] The feature "partition wall" means that the partition wall W is liquid-tight. Therefore, there are no gaps through which an aqueous solution, an alcohol solution, an alcohol, or water can flow from side S KK to side S A / MK or vice versa. In the case where the partition wall W contains at least two alkali metal cation-conducting solid electrolyte ceramics F A and F B and an optional separation component T, this means that F A and F B and at least one separation component T (if present) are contiguous to each other without gaps.

[0185] In the electrolytic cell E in step (a) of the method according to the invention, the available partition walls W also cover embodiments in which the partition wall W contains more than two ASCs (for example, four or nine or twelve ASCs), where the ASCs are either directly contiguous to each other or separated from each other by a separation component T.

[0186] However, when the ASCs are directly contiguous to each other, this requires precise fitting of the separately contiguous ASCs to avoid forming gaps between them through which an aqueous liquid or water or alcohol ROH or an alcohol solution can flow from side S KK to side S A / MK . Therefore, it is advantageous and preferably that: when the partition wall W contains more than one ASC, all the ASCs contained in the partition wall W are separated from each other by at least one separation component T in the partition wall W, which means that no ASC is directly contiguous to any other ASC, i.e., without a separation component T between them.

[0187] A further feature of the dividing wall W is that the ASC F contained in the dividing wall W A via surface O KK and via surface O A / MK can both be in direct contact. In embodiments where the dividing wall W contains at least two ASC F A 、F B it is preferably the case that all the ASC contained in the dividing wall W via surface O KK and via surface O A / MK can both be in direct contact.

[0188] "Can be in direct contact" in relation to the ASC contained in the dividing wall W means that at least some of surface O KK and O A / MK are formed by the surfaces of the ASC contained in the dividing wall W, meaning that the ASC contained in the dividing wall W is directly accessible at the two surfaces O KK and surface O A / MK such that the ASC can be wetted at the two surfaces O KK and O A / MK with, for example, an aqueous solution, an alcohol solution, an alcohol ROH or water.

[0189] Regarding the configuration of the ASC in the dividing wall W, this means that for each ASC contained in the dividing wall W, there is a path that completely passes through each ASC from the surface O KK on side S KK to the surface O A / MK on side S A / MK of each ASC.

[0190] When the dividing wall W has at least one separation component T, at least one separation component T is also typically in direct contact via at least part of surface O KK and via at least part of surface O A / MK both.

[0191] "Can be in direct contact" in relation to the at least one separation component T optionally contained in the dividing wall W means that parts of surface O KK and O A / MK are formed by the surface of the separation component T, meaning that the separation component T is directly accessible at the two surfaces O KK and O A / MK such that the separation component T can be wetted at the two surfaces O KK and O A / MK with, for example, an aqueous solution, an alcohol solution, an alcohol or water.

[0192] Regarding the configuration of the optional separation component T in the dividing wall W, it particularly means that for the separation component T optionally covered by the dividing wall W, there is a path from side SKK The surface O KK to the side S A / MK The surface O A / MK through the separation component T and optionally through the seal Di, but not through the ASC pathway.

[0193] In a preferred embodiment of the partition wall W, the surface O A / MK At least 50%, more preferably at least 60%, even more preferably at least 70%, and even more preferably at least 85% is formed by the ASC contained in the partition wall W.

[0194] In a preferred embodiment of the partition wall W, the surface O KK At least 50%, more preferably at least 60%, even more preferably at least 70%, and even more preferably at least 85% is formed by the ASC contained in the partition wall W.

[0195] In an embodiment where the partition wall W has more than one ASC, in particular, the surface O KK 50% to 99%, more preferably 60% to 96%, even more preferably 70% to 92%, and even more preferably 85% to 90% is formed by the ASC contained in the partition wall W, while the surface O KK The remainder is even more preferably formed by the separation component T and optionally the frame component R. At the same time, in an embodiment where the partition wall W has more than one ASC, in particular, the surface O A / MK 50% to 99%, more preferably 60% to 96%, even more preferably 70% to 92%, and even more preferably 85% to 90% is formed by the ASC contained in the partition wall W, while the surface O A / MK The remainder is even more preferably formed by the separation component T and optionally the frame component R.

[0196] In a preferred embodiment, the partition wall W<16> contains an alkali metal cation-conducting solid electrolyte ceramic F A and optionally the frame component R. Even more preferably, the partition wall W<16> consists of the alkali metal cation-conducting solid electrolyte ceramic F A composed.

[0197] In another preferred embodiment, the partition wall W contains at least four ASCs F A 、F B 、F C and F D , and even more preferably contains exactly four ASCs F A 、F B 、F C and F D .

[0198] In a further preferred embodiment, the dividing wall W comprises at least nine ASC F A 、F B 、F C 、F D 、F E 、F F 、F G 、F H and F I and, even more preferably, comprises exactly nine ASC F A 、F B 、F C 、F D 、F E 、F F 、F G 、F H and F I .

[0199] In a further preferred embodiment, the dividing wall W comprises at least twelve ASC F A 、F B 、F C 、F D 、F E 、F F 、F G 、F H 、F I 、F J 、F K and F L and, even more preferably, comprises exactly twelve ASC F A 、F B 、F C 、F D 、F E 、F F 、F G 、F H 、F I 、F J 、F K and F L .

[0200] The configuration of at least two ASCs side by side with each other in the dividing wall W has advantages over the configuration of just one ASC, i.e., in the case of temperature variations occurring during the operation of the electrolytic cell, for the further spreading direction of the ASCs. The NaSICON sheet that functions as the dividing wall is located in the electrolytic cell bounded by the outer wall of the electrolytic cell or a solid plastic frame. It is not possible to dissipate the mechanical stress that occurs in the case of expansion within the NaSICON, which can lead to ceramic rupture.

[0201] In contrast, each ASC within the dividing wall W preferably abuts the separation component T, which results in two beneficial effects that enhance the long-term stability of the ASC:

[0202] - Each ASC has a further available degree of freedom, namely the dimension in which it can expand. Expansion not only in the z-direction (i.e., beyond the thickness of the ceramic sheet perpendicular to the plane of the dividing wall W), but also in the x- and / or y-directions is now possible, i.e., the horizontal and vertical directions within the plane of the dividing wall W. When the ASC, for example as a solid sheet, spans the cross-section of the electrolytic cell and abuts the solid wall of the electrolytic cell, this expansion direction does not exist or is at least significantly restricted.

[0203] - Compared with an equally sized dividing wall consisting of only one ASC, dividing into multiple small ASCs has the effect that the absolute term of the stress occurring within the smaller ASCs is also smaller and can be dissipated more quickly, and thus it is impossible to quickly accumulate to a stress that causes the ASC to rupture.

[0204] As a result, compared with using a single sheet, the tendency of the "divided" ASC in the dividing wall W to rupture is significantly reduced.

[0205] 1.1.4.1 Alkaline Metal Cation-Conducting Solid Electrolyte Ceramics "ASC"

[0206] The useful alkaline metal cation-conducting solid electrolyte ceramics F contained in the dividing wall W A 、F B etc. are any solid electrolytes through which cations (especially alkaline metal cations, even more preferably sodium cations) can be transported from side S A / MK to side S KK . Such solid electrolytes are known to those skilled in the art and are described, for example, in paragraphs

[0035] ,

[0039] ,

[0040] of DE 10 2015013155A1, WO 2012 / 048032A2, paragraphs

[0040] ,

[0041] of US2010 / 0044242A1, and paragraphs

[014] to

[025] of DE10360758A1. They are commercially sold under the names NaSICON, LiSICON, KSICON. Sodium ion-conducting solid electrolytes are preferred, and this is even more preferably of the NaSICON structure. The NaSICON structure available according to the present invention is 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.

[0207] In a preferred embodiment of the dividing wall W, the dividing wall W contains an alkali metal cation-conducting solid electrolyte ceramic, and in particular ASC F A , independently has the formula M I 1+2w+x-y+z M II w M III x Zr IV 2-w-x-y M V y (SiO4) z (PO4) 3-z of the NaSICON structure.

[0208] M I is selected from Na + , Li + , preferably Na + .

[0209] 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+ .

[0210] 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+ , especially selected from Sc 3+ , Y 3+ , La 3+ .

[0211] M V is a pentavalent metal cation, preferably selected from V 5+ , Nb 5+ , Ta5+ 。

[0212] Roman numerals I, II, III, IV, and V indicate the oxidation numbers of the respective metal cations present therein.

[0213] w, x, y, and z are real numbers, where 0 ≤ x < 2, 0 ≤ y < 2, 0 ≤ w < 2, 0 ≤ z < 3, and w, x, y, and z are selected such that 1 + 2w + x - y + z ≥ 0 and 2 - w - x - y ≥ 0.

[0214] Even more preferably according to the present invention, the NaSICON structure has the formula Na (1+v) Zr2Si v P (3-v) O 12 where v is a real number, where 0 ≤ v ≤ 3. Most preferably, v = 2.4.

[0215] In a preferred embodiment of the partition wall W (which contains at least two ASC F A , F B ), all the ASC contained in the partition wall W have the same structure.

[0216] 1.1.4.2 Separation component T

[0217] In an embodiment of the partition wall W of the present invention (which contains at least two ASC F A , F B ), the partition wall W preferably contains a separation component T. In that case, according to the present invention, the separation component T separates at least two alkali metal cation-conducting solid electrolyte ceramics F A and F B contained in the partition wall W, which means that it is inserted between at least two alkali metal cation-conducting solid electrolyte ceramics F A and F B contained in the partition wall W.

[0218] A suitable separation component T preferably covered by the partition wall W is any object that can be used as a means to separately dispose the respective ASC. The ASC are contiguous to the separation component T without gaps so as not to disrupt the function of the partition wall, which liquid-tightly separates the cathode chamber from an adjacent intermediate chamber or anode chamber in the electrolytic cell E.

[0219] The shape of the separation component T can be selected by those skilled in the art according to the number of ASC contained in the partition wall W in the preferred embodiment.

[0220] For example, if the partition wall W contains two or three ASC, these can be separated from each other by a land provided as the separation component T between the ASC.

[0221] If the dividing wall W contains four or more ASCs, these can be separated by a separating component T in the form of a cross or a grid.

[0222] In an embodiment of the dividing wall W of the present invention, where it contains at least two ASCs F A 、F B ), it is particularly preferred that the dividing wall W contains at least four ASCs, and even more preferably, the separating component T is in the form of a cross or a grid in that case, because this ensures that all three dimensions are fully available to the ASCs for thermal expansion / contraction.

[0223] The separating component T can here consist of a single piece. In that case, the ASCs are fixed to the separating component T without gaps, for example by means known to the person skilled in the art, such as by means of an adhesive, which is preferably an epoxy resin or a phenolic resin. Alternatively or additionally, the separating component T can also be shaped such that each ASC can be adapted or clipped into the separating component. This can already be implemented in a corresponding manner during the manufacture of the dividing wall W.

[0224] In a preferred embodiment in which the dividing wall W encompasses the separating component, this particularly includes a seal Di ( Figure 3B 、 3C ) between the separating component T and the ASC. This ensures in a particularly effective manner that the dividing wall W is liquid-tight. The seal Di can be selected by the person skilled in the art for each ASC or each separating component T.

[0225] The seal Di particularly includes a material selected from the group consisting of elastomers, adhesives, preferably elastomers.

[0226] Useful elastomers are in particular rubbers, preferably ethylene-propylene-diene rubber (“EPDM”), fluoropolymer rubber (“FPM”), perfluoropolymer rubber (“FFPM”), acrylonitrile-butadiene rubber (“NBR”).

[0227] In a further preferred embodiment, the separating component T includes at least two parts T1 and T2, which can be fixed to each other and thus clamp the ASC therebetween.

[0228] In this embodiment, it is then particularly preferred to install the seal Di between the separating component T and the ASC to ensure liquid-tightness.

[0229] The separating component T preferably includes a material selected from the group consisting of plastics, glass, wood. More preferably, the separating component T consists of plastic. Even more preferably, the plastic is a plastic selected from the group consisting of polypropylene, polystyrene, polyvinyl chloride, post-chlorinated polyvinyl chloride (“PVC-C”).

[0230] 1.1.4.3 Framework component R

[0231] In a further preferred embodiment, the dividing wall W further comprises a framework component R. The framework component R differs from the separating component T in that it is not arranged between the alkali metal cation-conducting solid electrolyte ceramics comprised in the dividing wall W, i.e., it does not separate them from each other. Surface O KK and O A / MK are at least partly and in particular bounded by the framework component R, and surface O KK and O A / MK are preferably completely bounded by the framework component R. This more particularly means that the framework component R at least partly and preferably completely surrounds surface O KK and O A / MK .

[0232] The framework component R may or may not be part of surface O KK and O A / MK . The framework component R is preferably part of surface O KK and O A / MK .

[0233] The framework component R is in particular either directly contactable or non-directly contactable via surface O KK and O A / MK , and is preferably directly contactable.

[0234] "Non-directly contactable" in relation to the framework component R optionally comprised in the dividing wall W means that the framework component R forms at least part of the surface of only those sides of the dividing wall W that are not sides S KK and S A / MK . More particularly, in that case the framework component R forms at least 1%, more preferably at least 25%, more preferably at least 50%, and even more preferably 100% of the surface area of those sides of the dividing wall W that are not sides S KK and S A / MK .

[0235] "Directly contactable" in relation to the framework component R optionally comprised in the dividing wall W means that the parts of surface O KK and O A / MK are formed by the surface of the framework component R, which means that the framework component R comprised in the dividing wall W is directly accessible at the two surfaces O KK and O A / MK such that the framework component R can be wetted at the two surfaces O KK and O A / MK with, for example, an aqueous solution, an alcoholic solution, an alcohol or water.

[0236] With regard to the configuration of the framework component R in the dividing wall W, it means that then there is a line from at side SKK the surface O KK to the side S A / MK the surface O A / MK a path completely through the frame assembly R.

[0237] This includes the following embodiments:

[0238] - the surface O KK and O A / MK portions of the edges are formed by the frame assembly R (as shown in Figure 4B , 4D shown);

[0239] - the surface O KK and O A / MK the edges are completely formed by the frame assembly R (as shown in Figure 4A , 4C , 7A, 7B shown).

[0240] Here, the frame assembly R may additionally also form at least part of the surface of those sides of the partition wall W that are not the side S KK and S A / MK More particularly, the frame assembly R forms at least 1%, more preferably at least 25%, more preferably at least 50%, and even more preferably 100% of the surface area of those sides of the partition wall W that are not the side S KK and S A / MK

[0241] Figure 4B Figure 4D and

[0242] KK and S A / MK Figure 4A Figure 4C

[0243] and

[0244] KK and S A / MK

[0243] The frame assembly R is made of a material selected from the group consisting of plastic, glass, and wood. More preferably, the frame assembly R is made of plastic. Even more preferably, the plastic is a plastic selected from the group consisting of polypropylene, polystyrene, polyvinyl chloride, and PVC-C.

[0244] In a further preferred embodiment, when the partition wall W includes the separation component T and the frame assembly R, the frame assembly R and the separation component T are made of the same material, and even more preferably both are made of plastic, which is even more preferably selected from polypropylene, polystyrene, polyvinyl chloride, and PVC-C. ​

[0245] The frame component R can here consist of a single piece. In that case, the ASC is fixed to the frame component R without gaps, for example by means known to a person skilled in the art, such as by means of an adhesive (for which epoxy resins and phenolic resins are particularly suitable). Alternatively or additionally, the frame component R can also be shaped such that the individual ASCs can be adapted or clipped into the frame component R.

[0246] This also means that in which the partition wall W contains at least two ASCs F A 、F B 、at least one separating component T and a frame component R in a preferred embodiment, the ASC, the at least one separating component T and the frame component R are adjacent to each other without gaps. Thus, there is no gap between the separating component T, the frame component R and the ASC contained in the partition wall W through which the alcohol ROH, the alcohol solution, the aqueous solution or water can flow from side S KK to side S A / MK or vice versa.

[0247] Furthermore, especially when the partition wall W contains at least two ASCs F A 、F B 、a frame component R and at least one separating component T, and the frame component R and the at least one separating component T are at least partly in one-piece form, the frame component R can consist of at least two parts which are fixed to each other and clamp the ASC therebetween. For example, the partition wall W can then have a hinge by means of which the two parts of the frame component R can be opened and closed. Additionally, the partition wall W can then have a lock ( Figure 7A ) by means of which the two parts of the frame component R can be locked in place in the closed state.

[0248] In the closed state, the ASC and, if the separating component T is not already in one-piece form with the frame component R, the separating component T can then be clamped between the two parts of the frame component R. In this embodiment, a seal is then installed between the separating component T and the ASC or between the frame component R and the ASC to ensure liquid tightness.

[0249] In a preferred embodiment, when the partition wall W contains at least two ASCs F A 、F B 、a frame component R and at least one separating component T, at least part of the separating component T is in one-piece form with at least part of the frame component R. This more particularly means that in that case at least part of the separating component T is incorporated into the frame component R.

[0250] Preferably, then the at least one separating component T and the frame component R are in one-piece form.

[0251] The embodiment of the frame component R has the advantage that it can function as part of the outer wall in the assembly of the electrolytic cell E. This part of the partition wall W does not come into contact with the solution in each of the interiors I KK 、I KA or I KM and thus it is wasteful to use at least one solid electrolyte ceramic F A for this part. Additionally, the part of the partition wall W that is sandwiched between the outer walls or forms part of them is subjected to pressure, which makes the brittle solid electrolyte ceramic F A unsuitable. Instead, a material that is crack-resistant and cheaper is thus chosen for the frame R.

[0252] 1.1.4.4 Production of the partition wall W

[0253] The partition wall W can be manufactured by methods known to those skilled in the art.

[0254] In one embodiment of the method according to the invention, the partition wall W used can be an ASC F that is cut or formed by methods known to those skilled in the art A .

[0255] If the partition wall W contains the frame component R or at least one separating component T, the ASC contained in the partition wall (optionally together with a seal) can be placed in a casting mold, and the separating component can be cast using liquid plastic and then left to solidify (injection molding method). During the solidification process, this will then surround the ASC.

[0256] Alternatively, the separating component T is cast separately (or in parts) and then fixed to the at least two ASCs in a gapless manner (e.g., by adhesion).

[0257] 1.1.4.5 Configuration of the partition wall W in the electrolytic cell E

[0258] 1) Configure the partition wall W in the electrolytic cell E in such a way that the alkali metal cation-conducting solid electrolyte ceramic F A contained in the partition wall W is in direct contact with the interior I KK on the side S KK via the surface O KK .

[0259] When the partition wall W contains at least two ASCs F A 、F B 、at least one separating component T and optionally the frame component R, configure the partition wall W in the electrolytic cell E such that the alkali metal cation-conducting solid electrolyte ceramics F A and F B contained in the partition wall W, and preferably also the separating component T, are in contact with the side S KK via the surface OKK Inner I KK Make direct contact.

[0260] This means that the partition wall W is arranged in the electrolytic cell E such that when the side S KK Inner I KK is completely filled with the solution L2, then the solution L2 passes through the surface O KK and makes contact with at least the alkali metal cation-conducting solid electrolyte ceramic F A contained in the partition wall W, such that ions (e.g., alkali metal ions such as sodium, lithium, potassium) can pass from F A into the solution L2.

[0261] When the partition wall W contains at least two ASC F A 、F B 、at least one separation component T and optionally a frame component R, this means that the partition wall W is arranged in the electrolytic cell E such that when the side S KK Inner I KK is completely filled with the solution L2, then the solution L2 passes through the surface O KK and makes contact with at least the two alkali metal cation-conducting solid electrolyte ceramics F A and F B contained in the partition wall W, and preferably also makes contact with the separation component T, such that ions (e.g., alkali metal ions such as sodium, lithium, potassium) can pass from F A and F B into the solution L2.

[0262] 2) Additionally, in an embodiment where the electrolytic cell E does not contain an intermediate chamber K M the partition wall W is arranged in the electrolytic cell E such that the alkali metal cation-conducting solid electrolyte ceramic F A contained in the partition wall W makes direct contact with the inner I A / MK on the side S A / MK through the surface O KA

[0263] When the partition wall W contains at least two ASC F A 、F B 、at least one separation component T and optionally a frame component R, and when the electrolytic cell E does not contain an intermediate chamber K M this means that the partition wall W is arranged in the electrolytic cell E such that the alkali metal cation-conducting solid electrolyte ceramic contained in the partition wall W, and preferably also the separation component T, makes direct contact with the inner I A / MK on the side S A / MK through the surface O KA

[0264] ​​This means the following: in an embodiment in which the electrolytic cell E does not include an intermediate chamber K M the partition wall W is contiguous with the interior I A of the anode chamber K KA .

[0265] In these embodiments, the partition wall W is then arranged within the electrolytic cell E such that when the interior I A / MK of the side S KA is completely filled with the solution L3, then the solution L3 contacts at least the alkali metal cation-conducting solid electrolyte ceramic F A / MK comprised by the partition wall W via the surface O A such that ions (such as alkali metal ions such as sodium, lithium, potassium) can enter the ASCF A from the solution L4

[0266] When the partition wall W comprises at least two ASC F A , F B , at least one separation component T and optionally a frame component R, then this means that the partition wall W is arranged in the electrolytic cell E such that when the interior I A / MK of the side S KA is completely filled with the solution L3, then the solution L3 contacts at least the two alkali metal cation-conducting solid electrolyte ceramics F A / MK and F A comprised by the partition wall W via the surface O B and preferably also contacts the separation component T such that ions (such as alkali metal ions such as sodium, lithium) can enter the ASC F A and F B from the solution L3

[0267] 3) Further, in the case where the electrolytic cell E includes at least one intermediate chamber K M the partition wall W is arranged in the electrolytic cell E such that the alkali metal cation-conducting solid electrolyte ceramic F A comprised by the partition wall W contacts directly the interior I A / MK of the side S A / MK via the surface O KM .

[0268] When the partition wall W comprises at least two ASC F A , F B , at least one separation component T and optionally a frame component R and when the electrolytic cell E includes at least one intermediate chamber K M this means that the partition wall W is arranged in the electrolytic cell E such that the alkali metal cation-conducting solid electrolyte ceramic comprised by the partition wall W, and preferably also the separation component T, contact the interior I A / MK of the side S A / MKInternal I KM is in direct contact.

[0269] This means the following: In embodiments in which the electrolytic cell E comprises at least one intermediate chamber K M the partition wall W is contiguous with the interior I M of the intermediate chamber K KM is contiguous.

[0270] In these embodiments, the partition wall W is then arranged within the electrolytic cell E such that when the side S A / MK is completely filled with the solution L3, the solution L3 then contacts at least the alkali metal cation-conducting solid electrolyte ceramic F KM comprised by the partition wall W via the surface O A / MK such that ions (such as alkali metal ions such as sodium, lithium, potassium) can enter the ASCF A from the solution L3. A

[0271] When the partition wall W comprises at least two ASCs F A , F B , at least one separating component T and optionally a framework component R, this then means: The partition wall W is arranged in the electrolytic cell E such that when the side S A / MK is completely filled with the solution L3, the solution L3 then contacts at least the two alkali metal cation-conducting solid electrolyte ceramics F KM comprised by the partition wall W via the surface O A / MK and preferably also contacts the separating component T such that ions (such as alkali metal ions such as sodium, lithium) can enter the ASCs F A and F B from the solution L3. A and F B

[0272] In a preferred embodiment of the electrolytic cell E, at least 50%, in particular at least 70%, preferably at least 90%, most preferably 100% of the part of the surface O KK formed by the ASC is in contact with the interior I KK

[0273] In a preferred embodiment of the electrolytic cell E without an intermediate chamber, at least 50%, in particular at least 70%, preferably at least 90%, most preferably 100% of the part of the surface O A / MK formed by the ASC is in contact with the interior I KA

[0274] In a preferred embodiment of the electrolytic cell E with at least one intermediate chamber, the surface O A / MK ​​​​At least 50%, in particular at least 70%, preferably at least 90%, most preferably 100% of the part formed by ASC is in contact with the interior I KM Contact.

[0275] 1.2 According to step (a) of the method of the present invention

[0276] According to step (a) of the method of the present invention regarding the production of alkoxide M A OR a solution L1 in ROH, wherein M A Is an alkali metal cation, and wherein R is an alkyl group having 1 to 6 carbon atoms. The method is carried out in an electrolytic cell E.

[0277] M A Is preferably selected from the group consisting of Li + 、K + 、Na + More preferably, it is selected from the group consisting of K + 、Na + Most preferably, M A = Na + .

[0278] R is preferably an alkyl group having 1 to 5, more preferably 1 to 4, even more preferably 1 to 3 carbon atoms, and even more preferably R = methyl or ethyl, most preferably R = methyl.

[0279] 1.2.1 The method according to the present invention in an electrolytic cell E without an intermediate chamber K M In the case where the electrolytic cell E does not contain an intermediate chamber K

[0280] Steps (α1), (α2), and (α3) are carried out simultaneously. M In the case where the electrolytic cell E does not contain an intermediate chamber K

[0281] 1.2.1.1 Step (α1)

[0282] In step (α1), a solution L2 containing ROH (preferably containing alkali metal alkoxide M A OR and ROH) is passed through I KK .

[0283] Solution L2 preferably does not contain water. "Without water" according to the present invention means that the weight of water in solution L2 based on the weight of all alcohols ROH in solution L2 (mass ratio) is ≤ 1:10, more preferably ≤ 1:20, even more preferably ≤ 1:100, even more preferably ≤ 0.5:100, even more preferably ≤ 1:1000, even more preferably ≤ 1:10000.

[0284] If solution L2 contains M A OR, M in solution L2A OR is based on the mass ratio of the entire solution L2, especially > 0 wt% to 30 wt%, preferably 0.1 wt% to 20 wt%, more preferably 0.2 wt% to 10 wt%, more preferably 0.5 wt% to 5 wt%, most preferably 0.7 wt% to 2 wt%, and most preferably 1 wt%.

[0285] If the solution L2 contains M A OR, M in the solution L2 A OR the mass ratio of M to ROH is especially in the range of 1:1000 to 1:5, more preferably in the range of 1:250 to 3:20, even more preferably in the range of 1:120 to 1:8, and even more preferably 1:100.

[0286] 1.2.1.2 Step (α2)

[0287] In step (α2), a neutral or basic aqueous solution L3 of a salt S containing M A as a cation is passed through I KA .

[0288] The salt S is preferably a halide, sulfate, sulfite, nitrate, bicarbonate or carbonate of M A , and even more preferably a halide.

[0289] The halide is fluoride, chloride, bromide, iodide. The most preferred halide is chloride.

[0290] The pH of the aqueous solution L3 is ≥ 7.0, preferably in the range of 7 to 12, more preferably in the range of 8 to 11, even more preferably 10 to 11, and most preferably 10.5.

[0291] The mass ratio of the salt S in the solution L3 based on the entire solution L3 is preferably in the range of > 0 wt% to 20 wt%, preferably 1 wt% to 20 wt%, more preferably 5 wt% to 20 wt%, even more preferably 10 wt% to 20 wt%, and most preferably 20 wt%.

[0292] 1.2.1.3 Step (α3)

[0293] In step (α3), then a voltage is applied between E A and E K .

[0294] This causes the current to transfer from the charge source to the anode, the charge to transfer to the cathode via ions and finally the current to transfer 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 a specific voltage via a transformer.

[0295] This thus has the following consequences:

[0296] Solution L1 is obtained at outlet A KK and the concentration of M A is higher in L1 than in L2,

[0297] An aqueous solution L4 of S is obtained at outlet A KA and the concentration of S is lower in L4 than in L3.

[0298] In step (α3) of the process according to the invention, in particular, such a voltage is applied that such a current flows that the current density (= ratio of the current supplied to the electrolytic cell to the area of the solid electrolyte in contact with the anolyte present in I KA is in the range from 10 to 8000 A / m 2 and more preferably in the range from 100 to 2000 A / m 2 and even more preferably in the range from 300 to 800 A / m 2 and even more preferably 494 A / m 2 . This can be determined by a person skilled in the art in a standard manner. The area of the solid electrolyte in contact with the anolyte present in the interior I A of the anode chamber K KA is in particular from 0.00001 to 10 m 2 and preferably from 0.0001 to 2.5 m 2 and more preferably from 0.0002 to 0.15 m 2 and even more preferably 2.83 cm 2 .

[0299] It is evident that step (α3) of the process according to the invention takes place when the interior I A of the anode chamber K KA is at least partially filled with L3 and the interior I K of the cathode chamber K KK is at least partially filled with L2, such that both L3 and L2 are in contact with the ASC contained in the partition wall W and in particular also with the separation assembly T when the partition wall W contains a separation assembly.

[0300] In step (α3), the fact that charge transfer occurs between E A and E K implies that I KK and I KA simultaneously and respectively carry L2 and L3 to such an extent that they cover the electrodes E K / E A to complete the circuit.

[0301] Especially when the liquid flow of L3 is continuously guided through I KA and the liquid flow of L2 passes through I KK , the liquid flow of L3 at least partially, preferably completely, covers the electrode E A and the liquid flow of L2 at least partially, preferably completely, covers the electrode E K This is especially the case when

[0302] In a further preferred embodiment, the method according to the invention is carried out continuously, i.e. steps (α1) and (α2) are carried out continuously and a voltage is applied in accordance with step (α3) simultaneously.

[0303] After carrying out step (α3), at the outlet A KK a solution L1, M A is obtained, and the concentration of M A OR in L1 is higher than in L2. If L2 already contains M A OR, the concentration of M A OR in L1 is preferably 1.01 to 200.2 times higher than in L2, more preferably 5.04 to 100.8 times higher, even more preferably 10.077 to 50.4 times higher, even more preferably 18.077 to 20.08 times higher, and most preferably 20.00 times higher than in L2, where the mass ratio of M

[0304] OR in L1 and in L2 is more preferably in the range of 0.1 wt% to 50 wt%, even more preferably 1 wt% to 20 wt%. KA an aqueous solution L4 of S is obtained at the outlet A, and the concentration of S in L4 is lower than in L3.

[0305] The cation M A in the aqueous solution L3 is preferably in the range of 0.5 to 5 mol / l, more preferably 1 mol / l. In each case, the concentration of the cation M A in the aqueous solution L4 is more preferably 0.5 mol / l lower than in the aqueous solution L3 used.

[0306] More particularly, steps (α1) to (α3) according to the invention are carried out at a temperature of 20 °C to 110 °C, preferably 50 °C to 105 °C, more preferably 80 °C to 99 °C, even more preferably 90 °C to 95 °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.

[0307] During the implementation of steps (α1) to (α3) of the method according to the invention, hydrogen is typically formed in I KK which can be discharged via the outlet A KK, removed from the tank together with solution L1. Then the mixture of hydrogen and solution L1 can be separated by methods known to those skilled in the art in a particular embodiment of the present invention. When the alkali metal used is a halide (especially chloride), chlorine gas or other halogen gases may be formed in I KA and this can be removed from the tank via outlet A together with solution L4 KK In addition, oxygen and / or carbon dioxide may also be formed, which can be removed in the same way. Then the mixture of chlorine, oxygen and / or CO2 and solution L4 can be separated by methods known to those skilled in the art in a particular embodiment of the present invention. Then it is possible to separate these in the same way after the chlorine, oxygen and / or CO2 gases have been separated from solution L4, by methods known to those skilled in the art.

[0308] 1.2.2 In the electrolytic cell E with an intermediate chamber K M The method according to the invention

[0309] In which the electrolytic cell E comprises at least one intermediate chamber K M the steps (β1), (β2), (β3) are carried out simultaneously.

[0310] Preferably: the electrolytic cell E comprises at least one intermediate chamber K M and then the steps (β1), (β2), (β3) are carried out simultaneously.

[0311] 1.2.2.1 Step (β1)

[0312] In step (β1), a solution L2 containing ROH (preferably containing an alkali metal alkoxide M A OR and ROH) is passed through I KK .

[0313] Solution L2 is preferably water-free. "Water-free" according to the invention means that the weight of water in solution L2 is ≤ 1:10, more preferably ≤ 1:20, even more preferably ≤ 1:100, even more preferably ≤ 0.5:100, based on the weight of all alcohols ROH in solution L2 (mass ratio).

[0314] If solution L2 contains M A OR, the M A OR in solution L2 is especially > 0 wt% to 30 wt%, preferably 0.1 wt% to 20 wt%, more preferably 0.2 wt% to 20 wt%, more preferably 0.5 wt% to 5 wt%, most preferably 0.7 wt% to 2 wt%, and most preferably 1 wt%, based on the mass of the entire solution L2.

[0315] If solution L2 contains M AOR, M in solution L2 A The mass ratio of OR to ROH is especially in the range of 1:1000 to 1:5, more preferably in the range of 1:250 to 3:20, even more preferably in the range of 1:120 to 1:8, and even more preferably 1:100.

[0316] Step (β2) of 1.2.2.2

[0317] In step (β2), a neutral or basic aqueous solution L3 containing salt S with M as the cation is passed through I A , then via V KM , and then through I AM . KA

[0318] Salt S is preferably a halide, sulfate, sulfite, nitrate, bicarbonate or carbonate of M A , and even more preferably a halide.

[0319] Halides are fluorides, chlorides, bromides, iodides. The most preferred halide is chloride.

[0320] The pH of the aqueous solution L3 is ≥7.0, preferably in the range of 7 to 12, more preferably in the range of 8 to 11, even more preferably 10 to 11, and most preferably 10.5.

[0321] The mass proportion of salt S in solution L3 based on the entire solution L3 is preferably in the range of >0 wt% to 20 wt%, preferably 1 wt% to 20 wt%, more preferably 5 wt% to 20 wt%, even more preferably 10 wt% to 20 wt%, and most preferably 20 wt%.

[0322] Step (β3) of 1.2.2.3

[0323] In step (β3), a voltage is then applied between E A and E K .

[0324] This causes the current to transfer from the charge source to the anode, the charge to transfer to the cathode via ions, and finally the current to transfer 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 a specific voltage via a transformer.

[0325] This thus has the following result:

[0326] Solution L1 is obtained at outlet A KK , and the concentration of M A OR in L1 is higher than that in L2,

[0327] ​The aqueous solution L4 of S exits at outlet A KA is obtained, and the concentration of S in L4 is lower than in L3.

[0328] In step (β3) according to the invention, in particular, a voltage is applied such that a current flows, the current density (= the ratio of the current supplied to the electrolytic cell to the area of the solid electrolyte in contact with the anolyte present in I KM is in the range of 10 to 8000 A / m 2 and more preferably in the range of 100 to 2000 A / m 2 and even more preferably in the range of 300 to 800 A / m 2 and even more preferably 494 A / m 2 . This can be determined by a person skilled in the art in a standard manner. The area of the solid electrolyte in contact with the anolyte present in the intermediate chamber K M is in particular 0.00001 to 10 m 2 and preferably 0.0001 to 2.5 m 2 and more preferably 0.0002 to 0.15 m 2 and even more preferably 2.83 cm 2 .

[0329] It is evident that step (β3) of the method according to the invention is carried out when the interiors I M and K A of two chambers K KA and I KM are at least partially filled with L3 and the interior I KK is at least partially filled with L2, such that both L3 and L2 are in contact with the solid electrolyte contained in the partition wall W and, in particular, also in contact with the separation assembly T when the partition wall W includes a separation assembly.

[0330] In step (β3), the fact that charge transfer occurs between E A and E K implies that I KK , I KM and I KA are simultaneously filled with L2 and L3 respectively to such an extent that they cover the electrodes E K / E A to complete the circuit.

[0331] In particular, when the liquid flow of L3 is continuously guided through I KM , V AM and I KA and the liquid flow of L2 through I KK , the liquid flow of L3 at least partially, preferably completely, covers the electrodes E AAnd the liquid flow of L2 at least partially, preferably completely, covers the electrode E K This is even more the case when

[0332] In a further preferred embodiment, the method according to the invention is carried out continuously, i.e. steps (β1) and (β2) are carried out continuously and the voltage is applied in accordance with step (β3) simultaneously.

[0333] After carrying out step (β3), at the outlet A KK Solution L1, M is obtained A The concentration of OR in L1 is higher than that in L2. If L2 already contains M A OR, M A The concentration of OR in L1 is preferably 1.01 to 200.2 times higher than that in L2, more preferably 5.04 to 100.80 times higher, even more preferably 10.077 to 50.40 times higher, even more preferably 18.077 to 20.08 times higher, and most preferably 20.00 times higher than that in L2, where M A The mass ratio of OR in L1 and in L2 is more preferably in the range of 0.1 wt% to 50 wt%, even more preferably 1 wt% to 20 wt%.

[0334] The aqueous solution L4 of S is obtained at the outlet A KA and the concentration of S in L4 is lower than that in L3.

[0335] The cation M A The concentration of the cation M in the aqueous solution L3 is preferably in the range of 0.5 to 5 mol / l, more preferably 1 mol / l. In each case, the cation M A The concentration of the cation M in the aqueous solution L4 is more preferably 0.5 mol / l lower than that in the aqueous solution L3 used.

[0336] More particularly, steps (β1) to (β3) according to the invention are carried out at a temperature of 20 °C to 110 °C, preferably 50 °C to 105 °C, more preferably 80 °C to 99 °C, even more preferably 90 °C to 95 °C, and at a pressure of 0.5 bar to 1.5 bar, preferably 0.9 bar to 1.1 bar, more preferably 1.0 bar.

[0337] During the implementation of steps (β1) to (β3) of the method according to the invention, hydrogen is typically formed in the cathode chamber I KK and it can be removed from the cell via the outlet A KK together with the solution L1. Then the mixture of hydrogen and the solution L1 can be separated by methods known to those skilled in the art in a particular embodiment of the present invention. When the alkali metal used is a halide (especially chloride), chlorine or other halogen gases may be present in I KAformed therein and this can be removed via outlet A together with solution L4 KK from the cell. Additionally, oxygen and / or carbon dioxide may also be formed and can be removed likewise. Then, in a particular embodiment of the present invention, the mixture of chlorine gas, oxygen and / or CO2 and solution L4 can be separated by methods known to those skilled in the art. Then, likewise, these may be separated by methods known to those skilled in the art after the chlorine gas, oxygen and / or CO2 gas has been separated from solution L4.

[0338] 1.2.2.4 Additional advantages of steps (β1) to (β3)

[0339] Performing steps (β1) to (β3) brings further unexpected advantages. According to steps (β1) to (β3) of the method of the present invention, acid-labile solid electrolytes are protected from corrosion without the need to sacrifice an alkoxide solution from the cathode space as a buffer solution as in the prior art. Thus, the method according to the present invention is more efficient than the procedure described in WO 2008 / 076327A1 (where the product solution is used in the intermediate chamber, which reduces the overall conversion rate).

[0340] 2. Optional step (a*): Removal of ROH from L1

[0341] In an alternative embodiment of the method according to the present invention, in optional step (a*), ROH can be at least partially removed from L1<21>, which gives a solution L1* containing M A OR and ROH (where L1* has a reduced mass proportion of ROH compared to L1<21>), or gives M in solid form F* A OR, either one.

[0342] Whether this preferred embodiment (a*) gives solution L1* or solid state substance F* depends on whether ROH is partially or substantially completely removed from L1<21>.

[0343] In optional step (a*), the at least partial removal of ROH from L1<21> can be carried out by methods known to those skilled in the art, for example by means of distillation equipment known to those skilled in the art.

[0344] In a preferred embodiment, if ROH is substantially completely removed from L1<21>, this can be carried out, for example, in a distillation apparatus known to those skilled in the art. In that case, M A OR is obtained in solid form F*.

[0345] 3. Step b): Conversion of PET

[0346] In step (b) of the process according to the invention, (b) PET is converted to bis(2-hydroxyethyl) terephthalate BHET in a mixture comprising ethylene glycol and at least part of the M comprised by L1<21> A OR, or if step (a*) is carried out, at least part of the M comprised by F* A OR or at least part of the M comprised by L1* A OR.

[0347] In other words, this means that: in step (b), PET is converted to BHET in a mixture comprising ethylene glycol and at least part of the M comprised by L1<21> A OR.

[0348] In an embodiment of the invention in which step (a*) is carried out, PET is converted to BHET in step (b) in a mixture comprising ethylene glycol and at least part of the M comprised by F* A OR, or PET is converted to BHET in step (b) in a mixture comprising ethylene glycol and at least part of the M comprised by L1* A OR.

[0349] 3.1 PET starting material

[0350] The PET used in step (b) of the process according to the invention can be any PET that has to be depolymerized. Typically, such PET is present as waste, especially in the home, in industry, in the health sector (e.g. hospitals, doctors' surgeries) or in agriculture.

[0351] In one embodiment of the process according to the invention, the PET to be depolymerized is thus in a mixture with other plastics, especially at least one plastic selected from polyethylene ("PE"), polyvinyl chloride ("PVC"). This is typically the case when PET from plastic waste is to be depolymerized in the process according to the invention. In this embodiment, the PET is at least partially separated from the other plastics, preferably by sorting, before being subjected to step (b) of the process according to the invention.

[0352] In one embodiment of the process according to the invention, the PET is subjected to at least one pretreatment step.

[0353] Such a pretreatment step is described, for example, in DE 10032899 C2.

[0354] According to the invention, before being used in step (b), the PET is subjected to at least one pretreatment step selected from chemical pretreatment steps, comminution steps.

[0355] In the case where PET is in a mixture with other plastics, prior to being used in step (b), it is preferably subjected to at least one pretreatment step selected from at least partial separation from other plastics (preferably by sorting), a chemical pretreatment step, and a comminution step.

[0356] In the case where PET is in a mixture with other plastics, it is more preferably first at least partially separated from other plastics, then subjected to at least one chemical pretreatment and finally comminuted.

[0357] The chemical pretreatment step is in particular a cleaning step. Such a cleaning step has the advantage that, prior to carrying out step (b), any impurities are removed, in particular food residues, cosmetic residues and / or body secretions (such as blood, semen, excrement). Such impurities can reduce the efficiency of the reaction in step (b) and / or deteriorate the purity of the BHET obtained thereby.

[0358] In the chemical pretreatment step, in particular in the cleaning step, the waste is heated in a cleaning solution especially at a temperature in the range from 30 °C to 99 °C, preferably in the range from 50 °C to 90 °C, more preferably in the range from 70 °C to 85 °C.

[0359] Typical cleaning solutions are familiar to those skilled in the art and are preferably selected from:

[0360] - an aqueous solution of a surfactant (preferably a non-ionic surfactant);

[0361] - an aqueous solution of an alkali metal hydroxide or an alkaline earth metal hydroxide, preferably an aqueous solution of NaOH.

[0362] In the chemical pretreatment step, in particular in the cleaning step, the treatment time is especially in the range from 1 minute to 12 hours, preferably in the range from 10 minutes to 6 hours, more preferably in the range from 30 minutes to 2 hours, even more preferably in the range from 45 to 90 minutes, most preferably 60 minutes.

[0363] After treating PET by a chemical step, in particular a cleaning step, the aqueous solution is separated off, for example by filtration, and the clean PET is preferably washed with water at least once to remove residues of the cleaning solution.

[0364] The PET waste obtained thereby is then dried, in particular in a drying oven. The temperature for drying is especially in the range from 30 to 120 °C, preferably in the range from 50 °C to 100 °C, more preferably in the range from 60 °C to 90 °C, most preferably 80 °C.

[0365] The comminution step has the advantage that it increases the surface area of the PET available for the reaction in step (b). This increases the reaction rate of the reaction in step (b). Comminution can be carried out in equipment known to those skilled in the art (such as a shredder or a cutting machine).

[0366] In a further embodiment of the process according to the invention, before subjecting the PET to step (b), it is decolorized or colored in a controlled manner. These can be carried out by methods known to those skilled in the art, such as decolorization with hydrogen peroxide or dyeing with dyes.

[0367] 3.2 Conversion conditions in step (b)

[0368] In step (b) of the process according to the invention, the PET is converted into BHET in a mixture which comprises ethylene glycol and at least part of the M comprised by L1<21> A OR, or if step (a*) is carried out, at least part of the M comprised by F* A OR or at least part of the M comprised by L1* A OR.

[0369] It is evident that "the PET is converted into BHET in a mixture which comprises ethylene glycol and at least part of the M comprised by L1<21> A OR, or if step (a*) is carried out, at least part of the M comprised by F* A OR or at least part of the M comprised by L1* A OR" means that step (b) is carried out in a mixture which comprises: PET, ethylene glycol and at least part of the M obtained in step (a) or step (a*) (if this step (a*) is carried out) A OR.

[0370] In the conversion of step (b), the M A OR the alkoxide anion which functions as a catalyst, the PET is formally transesterified with ethylene glycol at the internal ester bond [see structure (Ξ) shown below].

[0371] Without being bound by any particular theory, the mechanism of the cleavage of PET into BHET first involves the nucleophilic attack of the alkoxide anion RO - on the ester bond and the cleavage of the polymer PET, which results in the formation of an intermediate of the ester of terephthalic acid units with the alcohol ROH, followed by the transesterification of this ester with ethylene glycol. This is schematically shown below for the ester bond of PET:

[0372]

[0373] "M obtained in step (a) in the form of solution L1" A OR, or when performing step (a*), M obtained in step (a*) in the form of solution L1* or in the form of solid state material F* A OR" is abbreviated according to the present invention as "M obtained in step (a) or step (a*)" A OR".

[0374] Step (b) of the method according to the present invention can be carried out in any manner familiar to those skilled in the art. Typically, in step (b), the components PET, ethylene glycol, and M obtained in step (a) or step (a*) are mixed in any order A OR, and the reaction conditions for the cleavage of PET into BHET are established in step (b).

[0375] In particular, in step (b), PET is mixed with ethylene glycol and at least a part of M obtained in step (a) or step (a*) A OR to obtain a mixture M1 containing PET, ethylene glycol, and M A OR, and in the mixture M1, PET reacts at least partially with ethylene glycol and M A OR to obtain bis(2-hydroxyethyl) terephthalate BHET. After step (b) has ended, this preferably results in a mixture M2 with or without MHET and with or without TS, which contains BHET, and which particularly additionally contains ethylene glycol, M A OR, and any unreacted PET.

[0376] In a preferred embodiment of step (b), one or two of the three components selected from PET, ethylene glycol, and M obtained in step (a) or step (a*) are first fed, reaction conditions are established therein, and then the other components are finally added. Then, immediately after adding the last component, a mixture M1 is obtained, in which, since the reaction conditions have been established, PET is immediately cleaved into BHET in step (b), and at the end of step (b), a mixture M2 with or without MHET and with or without TS is obtained, which contains BHET, and which particularly additionally contains ethylene glycol, M A OR, and any unreacted PET. A OR, and any unreacted PET.

[0377] In a further alternative embodiment of step (b), which is particularly implemented in a continuous process scheme, at least one, preferably two, and preferably all three of the components selected from PET, ethylene glycol, and M obtained in step (a) or step (a*) are added to a mixture containing PET, ethylene glycol, and M obtained in step (a) or step (a*) A OR, and preferably all three are added to a mixture containing PET, ethylene glycol, and M obtained in step (a) or step (a*) AIn the mixture M1 of OR and BHET, this means that the conversion of PET to BHET in step (b) is carried out in this mixture M1 during the addition of at least one of the three components of PET, ethylene glycol, and M obtained in step (a) or step (a*). When adding the components PET, ethylene glycol, and M obtained in step (a) or step (a*) to this mixture M1 A and in the case of at least two of OR, these components are added especially separately from each other. After step (b) has ended, this preferably gives a mixture M2 with or without MHET and with or without TS, which contains BHET and which especially additionally contains ethylene glycol, M A OR, and any unreacted PET. A

[0378] The reaction in step (b) is especially carried out at a temperature of at least 100 °C, preferably in the range of 100 °C to 197 °C, more preferably in the range of 130 °C to 197 °C, more preferably in the range of 150 °C to 197 °C, more preferably in the range of 175 °C to 197 °C.

[0379] The reaction in step (b) is preferably carried out at the boiling point temperature of ethylene glycol. Even more preferably, the ethylene glycol is refluxed, which means that the ethylene glycol evaporates from the reaction, condenses, and then returns to the reaction. This reflux can be established by means familiar to those skilled in the art (for example, in a distillation apparatus).

[0380] This embodiment is especially advantageous when M A OR is added to the mixture in step (b) as a solution in ROH (i.e., especially in the form of L1 or L1*), because the excess alcohol ROH (which has a lower boiling point than ethylene glycol) will then evaporate from the mixture. This additionally reduces the occurrence of by-products.

[0381] Preferably, the reaction in step (b) is carried out until (i.e., up to) the moment t b at which moment t b at least P = 10%, preferably at least P = 20%, more preferably at least P = 25%, more preferably at least P = 30%, more preferably at least P = 40%, more preferably at least P = 50%, more preferably at least P = 60%, more preferably at least P = 70%, more preferably at least P = 80%, more preferably at least P = 90%, more preferably at least P = 95%, and even more preferably at least P = 99% of the PET used in step (b) has been converted.

[0382] This percentage P is calculated by the following formula:

[0383] P = (n TS + n MHET + n BHET ) / n PET .

[0384] n PET is the molar amount of the repeating unit of the following structure (Ξ) in the PET used in step (b):

[0385]

[0386] n TS is the molar amount of the TS formed in step (b) from the start of step (b) until time t b .

[0387] n MHET is the molar amount of the MHET formed in step (b) from the start of step (b) until time t b .

[0388] n BHET is the molar amount of the BHET formed in step (b) from the start of step (b) until time t b .

[0389] The structures of the compounds BHET, MHET, and TS are as follows:

[0390]

[0391] "MHET" also encompasses the corresponding carboxylic acid esters of the structures shown.

[0392] "TS" also encompasses the corresponding monocarboxylic acid esters and dicarboxylic acid esters of the structures shown.

[0393] The total weight of M A OR used in step (b) of the process according to the invention is based on the total weight of the PET used in step (b) of the process according to the invention, in particular in the range from 0.1% to 100% by weight, preferably in the range from 0.5% to 80% by weight, more preferably in the range from 1.0% to 50% by weight, more preferably in the range from 1.5% to 25% by weight, more preferably in the range from 2.0% to 10% by weight, more preferably in the range from 2.5% to 6.0% by weight, more preferably from 3.5% to 5.0% by weight, most preferably 3.9% by weight.

[0394] The ratio of the weight of ethylene glycol [unit: kg] used in step (b) of the process according to the invention to the weight of PET [unit: kg] used in step (b) of the process according to the invention, in particular, is in the range of 1:1 to 100:1, preferably in the range of 2:1 to 50:1, more preferably in the range of 3:1 to 40:1, more preferably in the range of 4:1 to 30:1, more preferably in the range of 5:1 to 20:1, more preferably in the range of 6:1 to 10:1, more preferably 7:1 to 9:1, and most preferably 8:1.

[0395] The reaction in step (b) can be carried out using equipment familiar to those skilled in the art.

[0396] After step (b) of the process according to the invention has ended, in the mixture obtained after step (b), the molar amount of BHET (n BHET ) to the sum of the molar amounts of MHET and TS (n MHET + n TS ) of the molar ratio η is preferably in the range of 1:1 to 1000:1, preferably 2:1 to 500:1, more preferably 4:1 to 300:1, even more preferably 10:1 to 100:1, still more preferably 11:1 to 60:1, still more preferably 13:1 to 24:1. In a particularly preferred embodiment, in the mixture obtained after step (b), the molar amount of TS is not measurable, i.e., = 0.

[0397] η = n BHET / (n MHET + n TA )

[0398] 3.3 Preferred step (c)

[0399] In a further preferred step (c), BHET is at least partially separated from the mixture obtained after step (b) has ended, in particular mixture M2. This is even more preferably carried out by crystallization and / or distillation. Even more preferably, in step (c), BHET is filtered out from the mixture obtained after step (b) has ended and then crystallized.

[0400] 4. Method for recycling PET

[0401] In the method for recycling polyethylene terephthalate, in step (ζ), the BHET obtained in mixture M1 in the process according to the invention is preferably polymerized into PET.

[0402] This polymerization is "polycondensation" known to those skilled in the art and is described, for example, in EP 0723951A1 and by Th. Rieckmann and S. Described in Chapter 2, "Poly(Ethylene Terephthalate) Polymerization - Mechanism, Catalysis, Kinetics, Mass Transfer and Reactor Design", on page 92 of the book "Modern Polyesters: Chemistry and Technology of Polyesters and Copolyesters. Edited by J. Scheirs and T. E. Long, 2003, John Wiley & Sons, Ltd ISBN: 0 - 471 - 49856 - 4".

[0403] In particular, for this purpose, in step (ζ), BHET is polymerized back to PET in the presence of a catalyst, the catalyst being especially selected from the group consisting of antimony compounds, preferably Sb2O3.

[0404] Preferably, the polymerization of BHET to PET in step (ζ) is carried out at least at the boiling temperature of ethylene glycol. In particular, during the polymerization in step (ζ), ethylene glycol is removed from the reaction mixture in order to shift the reaction equilibrium to the polymer PET side.

[0405] More preferably, the polymerization of BHET to PET in step (ζ) is carried out at the boiling temperature of ethylene glycol. Even more preferably, in that case, during the polymerization in step (ζ), ethylene glycol is removed from the reaction mixture to shift the reaction equilibrium to the polymer PET side.

[0406] This is achieved in particular by distillation at a pressure of < 1 bar, preferably 0.1 mbar and at the simultaneous boiling temperature of ethylene glycol at the corresponding pressure. Examples

[0407] 1. Invention Example E1:

[0408] A methanol solution of 20% sodium methoxide was obtained by the method described in the invention example of EP 3885470A1.

[0409] In the process according to the invention, the autoclave is initially charged with 150 g of PET together with 1200 g of ethylene glycol. The solution is then heated to 175 °C while stirring. As soon as the temperature reaches 175 °C, 12.3 g of a 20% solution of sodium methoxide from electrolysis in methanol (corresponding to 0.046 moles (mol) of NaOCH3) are added. The reaction is carried out over a period of twelve hours and the output of the reactor after cooling is analyzed. The conversion obtained is determined by gas chromatography. The amounts of the minor components mono(2-hydroxyethyl) terephthalate (= "MHET") and terephthalic acid (= "TS") relative to the major product BHET formed are determined.

[0410] 2. Comparative Example V2:

[0411] Depolymerization of PET with a conventionally produced methanol solution of sodium methoxide

[0412] In a comparative experiment, the autoclave is initially charged with 150 g of PET together with 1200 g of ethylene glycol. The solution is then heated to 175 °C while stirring. As soon as the temperature reaches 175 °C, 1.8 g of solid NaOH in 7.3 g of methanol (corresponding to 0.046 mol of sodium methoxide) are added. The reaction is carried out over a period of five hours and the output of the reactor after cooling is analyzed. The amounts of the minor components MHET and TS relative to the major product BHET formed are determined.

[0413] 3. Results

[0414] Comparison of the contents of BHET, MHET and TA in the depolymerization products in inventive Example E1 and comparative Example V1 shows that the use of a methanol solution of sodium methoxide obtained by electrolysis for depolymerization results in a lower proportion, based on BHET, of the unwanted MHET and TS by-products. This is advantageous since proportionally more cleavage products are obtained which can be directly converted into new PET products in polycondensation.

[0415] Reference signs in the figures

[0416]

[0417] *) "[...]": Square brackets indicate the concentration of the substance in brackets in the solution specified by the subscript after the right bracket.

Claims

1. A method for depolymerizing polyethylene terephthalate (PET), comprising the following steps: (a) Production of alkoxide M in electrolytic cell E<1> A OR a solution L1<21> in an alcohol ROH, where M A is an alkali metal cation and where R is an alkyl group having 1 to 6 carbon atoms, and the electrolytic cell E<1> comprises - at least one anode chamber K A <11>, which has at least one inlet Z KA <110>, at least one outlet A KA <111>, and an interior I A <113> containing an anode electrode E KA <112> - At least one cathode chamber K K <12>, which has at least one inlet Z KK <120>, at least one outlet A KK <121>, and an interior I K <123> that contains a cathode electrode E KK <122> - and at least one optionally inserted intermediate chamber K M <13>, which has at least one inlet Z KM <130>, at least one outlet A KM <131> and an interior I KM <132> wherein I KA <112> and I KM <132> are then separated from each other by a diffusion barrier D<14>, A KM <131> is connected to the inlet Z AM <15> via a connection V KA <110> such that liquid can flow from I KM <132> through the connection V AM <15> to I KA <112>. wherein - where the electrolytic cell E<1> does not include an intermediate chamber K M in the case of <13>, I KA <112> and I KK <122> are separated from each other by a partition wall W<16> - in which the electrolytic cell E<1> comprises at least one intermediate chamber K M in the case of <13>, I KK <122> and I KM <132> are separated from each other by a partition wall W<16> wherein the partition wall W<16> has a side S having a surface O KK <163> KK <161> and a side S on the opposite side of the side S KK <161> and having a surface O A / MK <164> A / MK <162>, wherein the partition wall W<16> contains at least one alkali metal cation-conducting solid electrolyte ceramic F A <18> in the following manner: the alkali metal cation-conducting solid electrolyte ceramic F A <18> contained in the partition wall W<16> KK <163> is in direct contact with the interior I KK <161> on the side S KK <122>. and wherein - where the electrolytic cell E<1> does not include an intermediate chamber K M <13>, the alkali metal cation-conducting solid electrolyte ceramic F A <18> via the surface O A / MK <164> and at the side S A / MK <162> of the interior I KA <112> is in direct contact - wherein the electrolytic cell E<1> includes at least one intermediate chamber K M In the case of <13>, the alkali metal cation-conducting solid electrolyte ceramic F A <18> via the surface O A / MK <164> and the side S A / MK <162> of the interior I KM <132> is in direct contact (α) Among them, in the electrolytic cell E<1>, when it does not include the intermediate chamber K M <13>, the following steps (α1), (α2), and (α3) that are implemented simultaneously are executed: (α1) Guide the solution L2<22> containing ROH through I KK <122>, (α2) A neutral or basic aqueous solution L3<23> containing a salt S with M A as the cation is passed through I KA <112>, (α3) at E A between <113> and E K apply a voltage between <123> or (β) Among them, in the electrolytic cell E<1>, when it contains at least one intermediate chamber K M <13>, the following steps (β1), (β2), and (β3) are simultaneously implemented: (β1) Guide the solution L2<22> containing ROH through I KK <122>, (β2) A neutral or basic aqueous solution L3<23> containing salt S with M as the cation is passed through I A <132>, and then via V KM <15>, and then through I AM <112>, KA ​ (β3) between E A <113> and E K apply a voltage between <123> This is at the outlet A KK <121> provides the solution L1<21>, M A The concentration of OR is higher in L1<21> than in L2<22>, and at the outlet A KA <111> provides an aqueous solution L4 of S <24>, the concentration of S in L4 <24> being lower than in L3 <23>; (a*) Optionally, at least partially remove ROH from L1<21> such that M A OR is obtained in solid form F* or as a solution L1* containing M A OR and ROH, wherein L1* has a reduced mass proportion of ROH compared to L1<21>. (b) Convert PET to bis(2-hydroxyethyl) terephthalate BHET in the mixture, the mixture comprising ethylene glycol and at least a portion of the M comprised by L1<21> A OR, or if step (a*) is carried out, at least a portion of the M comprised by F* A OR or at least a portion of the M comprised by L1* A OR.

2. The method according to claim 1, wherein the alkali metal cation-conducting solid electrolyte ceramic F A <18> has the formula M I 1+2w+x-y+z M II w M III x Zr IV 2-w-x-y M V y (SiO4) z (PO4) 3-z of the structure, where M I is selected from Na + and Li + , M II is a divalent metal cation, M III is a trivalent metal cation, M V is a pentavalent metal cation, the Roman numerals I, II, III, IV, V indicate the oxidation number of the corresponding metal cations present, and w, x, y, z are real numbers, where 0 ≤ x < 2, 0 ≤ y < 2, 0 ≤ w < 2, 0 ≤ z < 3, and wherein w, x, y, z are selected such that 1 + 2w + x - y + z ≥ 0 and 2 - w - x - y ≥ 0.

3. The method according to claim 1 or 2, wherein the electrolytic cell E<1> does not include an intermediate chamber K M <13>.

4. The method according to claim 1 or 2, wherein The electrolytic cell E<1> includes at least one intermediate chamber K M <13>.

5. The method according to any one of claims 1 to 4, wherein M A is selected from lithium, potassium, and sodium.

6. The method according to any one of claims 1 to 5, wherein step (b) is carried out until at least P = 10% of the PET used in step (b) has been converted.

7. The method according to any one of claims 1 to 6, wherein step (b) is carried out at the boiling point temperature of ethylene glycol.

8. The method according to any one of claims 1 to 7, wherein in step (b), a sufficient amount of M A OR solution is used such that, based on the total weight of the PET used in step (b), the total weight of M A OR used in step (b) is in the range of 0.1% by weight to 100% by weight.

9. The method according to any one of claims 1 to 8, wherein in a further step (c), BHET is at least partially separated from the mixture obtained after the end of step (b).

10. The method according to claim 9, wherein at least partial separation of BHET in step (c) is carried out by crystallization and / or distillation.

11. The method according to any one of claims 1 to 10, wherein the PET is subjected to at least one pretreatment step selected from chemical pretreatment steps and comminution steps before being used in step (b).

12. A method for recycling polyethylene terephthalate, wherein BHET is obtained by the method according to any one of claims 1 to 11, and the thus obtained BHET is polymerized into PET in step (ζ).

13. The method according to claim 12, wherein, The polymerization of BHET to PET in step (ζ) is carried out at least at the boiling point temperature of ethylene glycol.

14. The method according to claim 12 or 13, wherein the polymerization in step (ζ) is carried out in the presence of a catalyst.

15. The method according to claim 14, wherein the catalyst is selected from antimony compounds.

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