IMPROVED PROCESS FOR DEPOLYMERIZATION OF POLYETHYLENE TERETHELATE

Description

[0001] The present invention relates to a process for the depolymerization of polyethylene terephthalate (= "PET"), in which PET with sodium or potassium glycolate obtained by reactive distillation to form a mixture M 1 comprising bis-2-hydroxyethyl terephthalate (= "BETH"; CAS No.: 959-26-2) is implemented.

[0002] The method according to the invention is characterized by the fact that BET a particularly high proportion among the fission products in the mixture M 1 forms. As a result, the inventive method yields a high yield of BET, which is directly for the renewed PET -can be used in manufacturing.

[0003] The present invention therefore also relates to a method for recycling PET, in which the process for depolymerization of PET received BET, possibly after further cleaning M 1 , again PET is polymerized. Background of the invention

[0004] Polyethylene terephthalate (= "PET") Polyethylene is one of the most important plastics, used in textile fibers, films, and as a material for plastic bottles. In 2007 alone, the amount used in plastic bottles was approximately 10⁷ t (W. Caseri, Polyethylene Terephthalate, RD-16-03258 (2009) in F. Böckler, B. Dill, G. Eisenbrand, F. Faupel, B. Fugmann, T. Gamse, R. Matissek, G. Pohnert, A. Rühling, S. Schmidt, G. Sprenger, RÖMPP [Online], Stuttgart, Georg Thieme Verlag, January 2022).

[0005] Due to its durability and the on PET The sheer volume of waste generated represents one of the greatest environmental challenges of our time. The solution to this problem lies in waste prevention and efficient recycling. PET.

[0006] The prior art describes several methods for splitting PETproposed. GB 784,248 A describes the methanolysis of PET.

[0007] Hydrolytic processes for the depolymerization of PET JP 2000-309663 A, US 4,355,175 A and T. Yoshioka, N. Okayama, A. Okuwaki, Ind. Eng. Chem. Res. 1998, 37, 336 - 340.

[0008] The implementation of PET The process using glycol is described in EP 0723951 A1, US 3,222,299 A, WO 2020 / 002999 A2, by S.R. Shukla, A.M. Harad, Journal of Applied Polymer Science 2005, 97, 513-517 (hereinafter "Shukla & Harad") and by N.D. Pingale, S.R. Shukla, European Polymer Journal 2008, 44, 4151-4156. EP1457479A1 discloses a process for the synthesis and isolation of BHET from PET with NaOH in 1,2-ethylene glycol. EP1457479A1 does not disclose the use of reactive distillation for the preparation of a glycolyte.

[0009] Shukla & Harad describe that during PET glycolysis, bis-2-hydroxyethyl terephthalate (= "BETH")This fission product can simultaneously serve as a starting material for the production of new materials. PET s are used.

[0010] Therefore, there is an interest in methods for the depolymerization of PET, where the highest possible proportion of BET is obtained among the fission products.

[0011] The object of the present invention was to provide such a method. Kurzbeschreibung der Erfindung

[0012] A method has now been surprisingly found that solves the problem according to the invention.

[0013] The present invention relates to a process for the depolymerization of polyethylene terephthalate PET, comprehensively the following steps: (a) MA OH and glycol are reacted in a reactive distillation, resulting in a solution S AP(b) comprehensively glycol and MA glycolate are obtained, where MA is an alkali metal selected from sodium, potassium, preferably MA = sodium, (b) reaction of the solution S AP with PET to a mixture M 1 comprising bis-2-hydroxyethyl terephthalate ( = "BETH").

[0014] The preference is S AP in step (a) is obtained by a reactant current S AE1 comprising glycol with a reactant current S AE2 comprehensive MA OH in countercurrent flow in a reactivation column RR A to a raw product RP A comprehensively MA -glycolate, water, glycol, MA OH is reacted, whereby S AP at the lower end of RR A is extracted as a swamp product stream.

[0015] Optionally, at the top end of RR A a stream of vapors S AB Extensive water and, if necessary, glycol were removed.

[0016] In another aspect, the present invention relates to a method for recycling PET, in which in one step (ζ) the depolymerization obtained in the inventive process BET to PET is polymerized.

[0017] It was surprisingly found that during the implementation of the PET s with the one obtained by reactive distillation S AP a higher proportion of BET is obtained as in conventional methods, in which the alkaline alkali metal glycolate solution is obtained by mixing the glycol in the corresponding alkali metal hydroxide. Illustration

[0018] The figure shows a comparison of the salary of BET ("1"), 2-hydroxyethyl terephthalic acid ("MHET"; "2") and terephthalic acid ("TS"; "3") during depolymerization with sodium glycolate obtained according to the inventive process as well as with sodium glycolate obtained by conventional processes.

[0019] The bars with the hatching "\\\\\" show the respective content of BET, MET and TS in the reactor discharge during the depolymerization of PET according to the inventive example E1, in which the sodium glycolate used for depolymerization was obtained by reactive distillation.

[0020] The black bars show the respective salary of BET, MET and TS in the reactor discharge during the depolymerization of PET according to the comparative example V1, in which only glycol was used during depolymerization.

[0021] The bars with the hatching " / / / / / " indicate the respective content of BET, MET and TS in the reactor discharge during the depolymerization of PET according to the comparative example V2, in which the sodium glycolate used for depolymerization was obtained by mixing NaOH and glycol in the reactor. Detailed description of the invention

[0022] It has now been surprisingly discovered that the glycolysis of PET The process is particularly efficient when sodium or potassium glycolate, obtained by reactive distillation, is used. In the reactive distillation according to the invention, the glycolate is obtained by reacting the corresponding alkali metal hydroxide MA OH with glycol. It has now been observed that, in the process according to the invention, compared to prior art processes in which glycolate obtained by dissolving the alkali metal hydroxides in glycol is used, a higher proportion of BET is obtained in the fission product. 1. Schritt (a): Reaktivdistillation zum Erhalt der Lösung S AP ompassend Glycol und MA -Glykolat

[0023] The solution used in the method according to the invention S AP Comprising glycol and MA glycolate, the product is obtained according to the invention by means of reactive distillation through the reaction of MA OH and glycol.

[0024] MA is an alkali metal selected from sodium and potassium. MA is predominantly sodium.

[0025] Reactive distillation for the production of alkali metal alkoxides is an important industrial process, as alkali metal alkoxides are used as strong bases in the synthesis of numerous chemicals, e.g. in the production of pharmaceutical or agrochemicals, and as catalysts in transesterification and amidation reactions.

[0026] Alkali metal alcoholates (MOR) are typically produced by reactive distillation in a countercurrent distillation column from alkali metal hydroxides (MOH) and alcohols (ROH), according to the following reaction. <1> The resulting reaction water is removed with the distillate.

[0027] Such a process principle is described, for example, in US 2,877,274 A, in which aqueous alkali metal hydroxide solution and gaseous methanol are operated countercurrently in a rectification column. This process, essentially unchanged, is described again in WO 01 / 42178 A1.

[0028] The most industrially important alkali metal alcoholates are those of sodium and potassium, and in particular the methylates and ethylates. Their synthesis is well described in the prior art, for example in EP 1 997 794 A1, WO 2021 / 148174 A1 and WO 2021 / 148175 A1.

[0029] Similar processes, in which an additional entraining agent, such as benzene, is used, are described in GB 377,631 A and US 1,910,331 A.

[0030] Accordingly, DE 96 89 03 C describes a process for the continuous production of alkali metal alcoholates in a reaction column, wherein the water-alcohol mixture drawn off at the top is condensed and subsequently subjected to phase separation. The aqueous phase is discarded, and the alcoholic phase, along with the fresh alcohol, is returned to the column at the top. A similar process is described in EP 0 299 577 A2, wherein the water separation in the condensate is carried out using a membrane.

[0031] In a preferred embodiment of the method according to the invention, S AP in step (a) by obtaining a reactant current S AE1 comprising glycol with a reactant current S AE2 comprehensive MA OH in countercurrent flow in a reactivation column RR A to a raw product RP A comprehensively MA glycolate, water, glycol, MA OH is reacted, with at the lower end of RR Aas swamp product stream S AP is taken from it.

[0032] Even more preferred is at the upper end of RR A a stream of vapors S AB Extensive water and, if necessary, glycol were removed.

[0033] According to the invention, a "reactive rectification column" is defined as a rectification column in which, at least in some parts, the reaction according to step (a) of the process according to the invention takes place. It can also be referred to as a "reaction column" for short.

[0034] According to the preferred embodiment of the method according to the invention, at the lower end of RR A a swamp product stream S AP Extensive glycol and MA glycolate were extracted. At the upper end of RR A A stream of vapors will form S AB Extensive water and, if necessary, glycol were removed.

[0035] For the purposes of this invention, "glycol" means 1,2-ethylenediol with the chemical formula HO-CH 2 -CH 2 -OH (CAS No. 107-21-1).

[0036] For the purposes of the invention, "MA glycolate" means the salt of glycol containing MA. The term "MA glycolate" includes at least one of MA O-CH₂-CH₂-OH and MA O-CH₂-CH₂-OM A, preferably at least MA O-CH₂-CH₂-OH, most preferably MA O-CH₂-CH₂-OH and MA O-CH₂-CH₂-OM A.

[0037] MA is an alkali metal selected from sodium, potassium, and is predominantly sodium.

[0038] The reactant current S AE1 includes glycol. In a preferred embodiment, the mass fraction of glycol is in S AE1 at ≥ 95 wt.%, even more preferably at ≥ 99.5 wt.%, wherein S AE1 otherwise contains, in particular, water and diethylene glycol.

[0039] The reactant current in the preferred embodiment of the method according to the invention S AE1The glycol used can also be commercially available glycol with a glycol mass fraction of more than 99.5 wt.% and a water mass fraction of up to 0.03 wt.%, up to 0.05 wt.% diethylene glycol.

[0040] The reactant current S AE1 In one embodiment of the present invention, the vapor is transferred to the reactivation column. RR A Admittedly.

[0041] In an alternative, preferred embodiment of the process according to the invention, glycol is added to the bottom of the reactivation column before step (a). RR A presented, and then heated to boiling in step (a), whereby in the reactive rectification column RR A a constant reactant current S AE1 is generated. If necessary, glycol is then added to the bottom of the reactivation column during step (a). RR A refilled.

[0042] The reactant current S AE2MA OH includes. In a preferred embodiment, it includes S AE2 In addition to MA OH, at least one other compound selected from water and glycol. Even more preferably, it comprises S AE2 besides MA OH water, then it is a matter of S AE2 to obtain an aqueous solution of MA OH.

[0043] If the reactant current S AE2 If MA OH and water are included, the mass fraction of MA OH, based on the total weight of the aqueous solution, which S AE2 forms, in particular in the range of 10 to 75 wt.%, preferably from 15 to 54 wt.%, more preferably from 30 to 53 wt.%, even more preferably 40 to 52 wt.% and most preferably 50 wt.%.

[0044] Step (a) of the process according to the invention is preferably carried out in a reactivation column (or "reaction column") RR A carried out.

[0045] Preferably the reaction column contains RR AInternals. Suitable internals include, for example, trays, structured packings, or unstructured packings. When the reaction column RR A If the reaction column contains trays, then bubble-cap trays, valve trays, tunnel trays, Thormann trays, cross-slotted bubble-cap trays, or sieve trays are suitable. RR AIf the system contains trays, trays are preferably selected in which a maximum of 5% by weight, and preferably less than 1% by weight, of the liquid passes through the respective trays. The design measures required to minimize liquid percolation are familiar to those skilled in the art. For example, particularly tightly sealing valve designs are selected for valve trays. Furthermore, by reducing the number of valves, the vapor velocity in the tray openings can be doubled to the value that is usually set. When using sieve trays, it is particularly advantageous to reduce the diameters of the tray openings and to maintain or even increase the number of openings.

[0046] When using structured or unstructured packings, structured packings are preferred with regard to the uniform distribution of the liquid.

[0047] Step (a) of the method according to the invention can be carried out either continuously or discontinuously. Preferably, it is carried out continuously.

[0048] "Conversion of a reactant current S AE1 comprising glycol with a reactant current S AE2 comprehensive MA OH in countercurrent flow in a reactivation column "RR A" In an embodiment according to the invention, this is ensured in particular by the fact that the inlet point of at least a part of the reactant current S AE1 comprehensive glycol at the reaction column RR A below the point where the reactant current enters the building S AE2 comprehensive MA OH is located.

[0049] The reaction column RR A In this embodiment, preferably at least 2, in particular 15 to 40 theoretical stages are included between the point where the reactant current enters the circuit. S AE1 and the point where the reactant current enters the building S AE2.

[0050] The reaction column RR AIt can be operated as a pure stripping column. Then, in the lower section of the reaction column... RR A The reactant current is vaporous. S AE1 Extensive glycol was added.

[0051] Optionally, a portion of the efflux current is S AE1 Comprehensive glycol, although below the point where the reactant stream enters the site. S AE2 comprehensive alkali hydroxide MA OH, but nevertheless at the top end or in the area of ​​the top end of the reaction column RR A added in vapor form. This allows for the dimensions in the lower section of the reaction column to be adjusted. RR A will be reduced. If part of the reactant current S AE1 comprehensive glycol at the top end or in the area of ​​the top end of the reaction column RR A If the glycol is added in vapor form, preferably only a partial amount of 10 to 70 wt.%, preferably 30 to 50 wt.% (in each case based on the total amount of glycol used) is added at the lower end of the reaction column. RR Afed in and the remaining subset distributed in a single stream or across several substreams, preferably 1 to 10 theoretical stages, particularly preferably 1 to 3 theoretical stages below the feed point of the reactant stream. S AE2 MA OH was added in vapor form.

[0052] In an alternative embodiment of step (a) of the method according to the invention, "conversion of a reactant current S AE1 comprising glycol with a reactant current S AE2 comprehensive MA OH in countercurrent flow in a reactivation column "RR A" This is ensured in particular by the fact that glycol is present in the sump of the reactivation column. RR A is located and the point of entry of the reactant current S AE2 comprising MA OH above the sump. During step (a) of the process according to the invention, glycol is then added to the sump of RR A heated to boiling and a reactant current S AE1 Comprehensive glycol production. S AE1 and S AE2 are then directed in opposite directions.

[0053] In the reaction column RR A The reactant current then continues S AE1 comprehensive glycol with the reactant current S AE2 comprehensive MA OH according to the reaction described above <1> (in which "ROH" then stands for "glycol") to MA glycolate and H₂O, whereby, since this is an equilibrium reaction, these products are present in mixture with the reactants glycol and MA OH. Therefore, in step (a) a crude product is RP A in the reaction column RR A received, which includes not only the products MA glycolate and water, but also glycol and MA OH.

[0054] At the lower end of RR A One then obtains and extracts the swamp product stream S AP comprehensive glycol and MA glycolate.

[0055] At the top end of R.R.A., preferably at the column head of R.R.A.,In a preferred embodiment of the inventive method, a water stream, optionally containing glycol, is extracted, referred to above as "vapor stream". S AB "comprehensive water and, if necessary, glycol".

[0056] Does the vapor stream contain S AB In addition to water, glycol is also obtained, preferably by distillation, for example in a rectification column. At least a portion of the glycol obtained during distillation can be used in this embodiment of the reaction column. RR A as reactant current S AE1 be reintroduced.

[0057] In a preferred embodiment S A B , if it contains glycol in addition to water, into a rectification column R.D.A. guided and in R.D.A. in at least one stream of vapors S O A comprehensive water, which is located at the upper end of R.D.A. is extracted, and at least one current S U A comprehensive glycol, which is at the lower end of R.D.A. It is extracted and separated.

[0058] The amount of the reactant current S AE1 The glycol included is preferably selected such that it simultaneously serves as a solvent for the product contained in the bottoms stream. S AP The obtained MA glycolate is used. Preferably, the amount of glycol in the reactant stream is S AE1 chosen so that the desired concentration of the MA glycolate solution is present in the bottom of the reaction column, which is used as the bottom product stream. S AP Comprehensive glycol and MA glycolate are extracted.

[0059] In a preferred embodiment of the method according to the invention, and particularly in cases where S AE2 In addition to MA OH, which also includes water, the ratio of the total weight (mass; unit: kg) to the reactant current is S AE1 Glycol used as a reactant current, to the total weight (mass; unit: kg). S AE2MA OH used 1 : 1 to 50 : 1, preferred 2 : 1 to 40 : 1, even more preferred 3 : 1 to 30 : 1, still more preferred 5 : 1 to 10 : 1.

[0060] The reaction column RR A In the preferred embodiment of the method according to the invention, it is operated with or without, preferably with, return flow.

[0061] "With reflux" means that the liquid at the top of the respective column, especially the reaction column, is... R.R.A., extracted vapor stream S AB The water and, if applicable, glycol are not completely removed. The relevant vapor stream S AB Therefore, at least partially, preferably partially, it is returned as reflux from the respective column, in particular the reaction column. R.R.A.,supplied. In cases where such a return flow is set, the return ratio is preferably 0.01 to 1, more preferably 0.02 to 0.9, even more preferably 0.03 to 0.34, particularly preferably 0.04 to 0.27 and most particularly preferably 0.05 to 0.24, most preferably 0.2.

[0062] A reflux ratio is generally understood, and within the meaning of this invention, to be the ratio of the proportion of the mass flow (kg / h) withdrawn from the column that is discharged in liquid or gaseous form to the proportion of this mass flow (kg / h) that is returned to the column in liquid form (reflux). A reflux can be achieved by installing a condenser at the top of the respective column. For this purpose, a condenser is installed, in particular, on the reaction column. RR A a capacitor K RRA attached to the capacitor K RRA will the Brünn stream S ABat least partially condensed and the respective column, in particular the reaction column RR A reintroduced.

[0063] In the embodiment in which the reaction column RR A When a return flow is set, the current used in the preferred embodiment of the inventive method can be called the reactant current. S AE2 The MA OH used should also be at least partially mixed with the reflux stream and the resulting mixture should thus enter the reaction column. RR A be supplied.

[0064] In a preferred embodiment of the method according to the invention, step (a) is carried out in particular under distillation conditions in which glycol refluxes.

[0065] Step (a) is carried out in particular at a temperature in the range of 80 °C to 197 °C, preferably 100 °C to 197 °C, more preferably 120 °C to 140 °C, and at a pressure of 0.01 bar abs. to 1 bar abs., preferably in the range of 0.05 bar abs. to 1 bar abs., more preferably in the range of 0.05 bar abs. to 0.15 bar abs., more preferably in the range of 0.05 bar abs. to 0.10 bar abs.

[0066] The reaction column RR A In a more preferred embodiment, it comprises at least one evaporator, which in particular consists of intermediate evaporators. V Z A and sump evaporators V US is selected. The reaction column RR A preferably includes at least one sump evaporator V SA.

[0067] As an "intermediate evaporator" VZ According to the invention, evaporators are defined as those located above the bottom of the respective column, in particular above the bottom of the reaction column. RR A (then as "V ZA"designated) or the rectification column used in the preferred embodiment and described in more detail below. R.D.A. (then as "V ZRD" (designated) are located. In the case of RR A In them, especially raw product RP A evaporates, which flows from the column as a side stream S ZAA is taken from it.

[0068] As a "swamp evaporator" VS According to the invention, evaporators are defined as those that remove the bottom of the respective column, in particular the bottom of the reaction column. RR A or the sump of the rectification column used in the preferred embodiment and described in more detail below R.D.A. (then as "V SRD" or "V SRD" (designated) to heat. In the case of RR A In particular, at least a portion of the swamp product stream is contained within them. S AP evaporates. In the case of RD A In particular, swamp product stream is contained in them US or part of USA , USA1 , evaporates.

[0069] An evaporator is usually located outside the respective reaction column or rectification column.

[0070] Suitable evaporators that can be used as intermediate and sump evaporators include natural circulation evaporators, forced circulation evaporators, forced circulation evaporators with expansion, boiler evaporators, falling film evaporators, and thin-film evaporators. In natural and forced circulation evaporators, a tube bundle or plate heat exchanger is typically used. When using a tube bundle heat exchanger, the heat transfer fluid can either flow through the tubes and the mixture to be evaporated flows around the tubes, or the heat transfer fluid can flow around the tubes and the mixture to be evaporated flows through the tubes. In a falling film evaporator, the mixture to be evaporated is typically added as a thin film on the inside of a tube, and the tube is heated from the outside.Unlike a falling film evaporator, a thin film evaporator also includes a rotor with wipers that distributes the liquid to be evaporated onto the inner wall of the tube to form a thin film.

[0071] In addition to those mentioned, any other type of evaporator known to experts that is suitable for use on a rectification column can also be used.

[0072] In the preferred embodiment of the process according to the invention, at the lower end of the reaction column RR AS AP Comprehensive glycol and MA glycolate were extracted as bottoms product stream.

[0073] It is preferred that the reaction column RR A at least one sump evaporator V SA exhibits, via the swamp product stream S AP then partially conducted and glycol partially removed from it, resulting in a bottom product stream S AP* with an opposite S APAn increased mass fraction of MA glycolate is obtained.

[0074] In particular, the inventive method S AP or, if at least one sump evaporator V SA is used, through which the sump product stream S AP is at least partially conveyed and glycol is at least partially removed from it, S AP* , a mass fraction of MA glycolate in glycol in the range of 1 to 50 wt.%, preferably 5 to 35 wt.%, more preferably 15 to 35 wt.%, most preferably 20 to 35 wt.%, in each case based on the total mass of S AP .

[0075] The mass fraction of residual water in S AP or S AP* The percentage is preferably < 1 wt.%, preferably < 0.8 wt.%, more preferably < 0.5 wt.%, based on the total mass of S AP .

[0076] The mass fraction of reactant MA OH in S AP or S AP*The percentage is preferably < 1 wt.%, preferably < 0.8 wt.%, more preferably < 0.5 wt.%, based on the total mass of S AP .

[0077] In a more preferred embodiment of the method according to the invention, at the upper end of RR A a stream of vapors S AB Extensive water and, if necessary, glycol were removed. 2. Rectification des Brüdenstroms S AB in a Rectification column R DA (provided)

[0078] The Brünen Stream S AB In a further preferred embodiment, when it comprises water and glycol, it is placed in a rectification column. RD A guided and in RD A in at least one stream of vapors S OA comprehensive water, which is located at the upper end of RD A is extracted, and at least one current US comprehensive glycol, which is at the lower end of RD A It is extracted and separated.

[0079] "At least one stream of condensation S OAcomprehensive water, which is located at the upper end of RD A "is taken" means that the brothers, who are at the top of RD A is obtained, where it can be extracted as one or more streams of vapor.

[0080] "At least one electricity US comprehensive glycol, which is at the lower end of RD A "is extracted" means that glycol, which is at the lower end of RD A is obtained, where one or more streams can be extracted.

[0081] The Brünen Stream S AB This can involve entering the rectification column via one or more inlets. RD A are directed. In the embodiments of the present invention, in which the vapor stream S AB as two or more separate streams into the rectification column R DA If the flow is directed, it is advantageous if the inlets of the individual streams are essentially at the same height on the rectification column. RD A lay.

[0082] In a preferred embodiment of the method according to the invention, the vapor stream S AB , when it includes water and glycol, in a rectification column RD A into a stream of vapors S OA comprehensive water, which is located at the upper end of RD A is extracted, and a current US comprehensive glycol, which is at the lower end of RD A It is extracted and separated.

[0083] Another term for "top end of a rectification column" is "head".

[0084] Another term for "lower end of a rectification column" is "swamp" or "foot".

[0085] As a rectification column RD A Any rectification column known to a person skilled in the art can be used.

[0086] Preferably, the rectification column contains RD AInternal components. Suitable internal components include, for example, trays, unstructured packings, or structured packings. Common trays used are bubble-cap trays, sieve trays, valve trays, tunnel trays, or slotted trays. Unstructured packings are generally loose fills. Common fill materials include Raschig rings, Pall rings, Berl saddles, or Intalox® saddles. Structured packings are marketed, for example, under the trade name Mellapack® by Sulzer. In addition to the internal components mentioned, other suitable internal components are known to those skilled in the art and can also be used.

[0087] Preferred internals exhibit a low specific pressure drop per theoretical separation stage. Structured packings and fills, for example, have a significantly lower pressure drop per theoretical separation stage than trays. This has the advantage that the pressure drop in the rectification column is lower. RD Aso that the mechanical power of the compressor and the temperature of the glycol / water mixture to be evaporated remain as low as possible.

[0088] If in the rectification column RD A Whether structured or unstructured packings are present, these may be divided or a continuous packing may be present. However, at least two packings are usually provided, one packing above the point where the vapor stream enters. S AB and a package below the point where the vapor stream enters the building S AB . It can also be a package above the point where the vapor stream enters the building. S AB and several floors below the inlet of the Brüden stream S AB This is provided for. If an unstructured packing is used, for example a filler packing, the filler particles usually rest on a suitable support grid (e.g. sieve tray or grid tray).

[0089] In this preferred embodiment, the at least one vapor stream is then S OA comprehensive water at the top end of the rectification column RD A extracted. The preferred mass fraction of water in this vapor stream. S OA is ≥ 96.0 wt.%, preferably ≥ 99.6 wt.%, even more preferably ≥ 99.9 wt.%, the remainder being in particular glycol.

[0090] At the lower end of RD A In this preferred embodiment, at least one current is used. US comprehensively glycol is removed, which preferably contains < 1 wt.%, more preferably ≤ 5000 wt.ppm, even more preferably ≤ 1000 wt.ppm, more preferably ≤ 100 wt.ppm water.

[0091] The extraction of at least one vapor stream S OA comprehensive water at the head of the rectification column RD A In the context of the present invention, this means in particular that the at least one vapor stream S OAas a headstream or as a side draw-off above the internals in the rectification column RD A is taken from it.

[0092] The withdrawal of at least one current US comprehensive glycol at the bottom of the rectification column RD A In the context of the present invention, this means in particular that the at least one current US as a swamp stream or at the bottom of the rectification column RD A is taken from it.

[0093] The rectification column RD A It is operated with or without, preferably with, return flow.

[0094] "With reflux" means that the rectification column at the top is returned to its original state. RD A extracted vapor stream S OA It is not completely removed, but partially condensed and returned to the respective rectification column. RD Ais supplied. In cases where such a return flow is set, the return ratio is preferably 0.01 to 1, more preferably 0.02 to 0.9, even more preferably 0.03 to 0.34, particularly preferably 0.04 to 0.27 and most particularly preferably 0.05 to 0.24, most preferably 0.2.

[0095] A reflux can be set by adjusting the head of the rectification column. RD A a capacitor K RD is attached to the capacitor K RD The respective stream of vapors will be S OA partially condensed and the rectification column RD A reintroduced. 3. Step (b): Conversion of PET with the solution S AP

[0096] In step (b) of the method according to the invention, the solution obtained in step (a) is S AP comprehensive glycol and MA glycolate with HOW MANY to a mixture M 1 comprehensive BHET implemented. 3.1 PET Output Material

[0097] As HOW MANY,which is used in step (b) of the method according to the invention, can be any HOW MANY which must be depolymerized. Typically, such HOW MANY as waste, especially in households, industry or agriculture.

[0098] In one embodiment of the process according to the invention, the material to be depolymerized is located HOW MANY in a mixture with other plastics, in particular at least one plastic selected from polyethylene ("PE") or polyvinyl chloride ("PVC"). This is typically the case when, in the process according to the invention, HOW MANY is to be depolymerized from plastic waste. In this embodiment, the HOW MANY at least partially separated from the other plastics, preferably by sorting, before being subjected to step (b) of the inventive method.

[0099] In one embodiment of the method according to the invention, the HOW MANY exposed to at least one pretreatment step.

[0100] Such pretreatment steps are described, for example, in DE 10032899 C2.

[0101] According to the invention, the HOW MANY at least one pretreatment step selected from a chemical pretreatment step, a comminution step, is subjected to before it is used in step (b).

[0102] In cases where the HOW MANY when present in a mixture with other plastics HOW MANY preferably subjected to at least one pretreatment step selected from at least partial separation from other plastics, preferably by sorting, chemical pretreatment step, comminution step, before being used in step (b).

[0103] In cases where the HOW MANY when present in a mixture with other plastics HOW MANYpreferably first separated at least partially from other plastics, then chemically pretreated at least once and finally crushed.

[0104] The chemical pretreatment step is primarily a washing step. Such a washing step has the advantage of removing any impurities, particularly food residues, cosmetic residues, and / or bodily secretions (e.g., blood, semen, feces), before step (b) is carried out. Such impurities could reduce the efficiency of the reaction in step (b) and / or the purity of the resulting product. BHET worsen.

[0105] In the chemical pretreatment step, in particular the washing step, the waste is heated, in particular in a washing solution, at a temperature of 30 °C to 99 °C, preferably 50 °C to 90 °C, more preferably 70 °C to 85 °C.

[0106] Typical washing solutions are familiar to the professional and are preferably selected from: Aqueous solution of a surfactant, preferably a non-ionic surfactant; aqueous solution of an alkali metal hydroxide or alkaline earth metal hydroxide; preferably aqueous NaOH.

[0107] The treatment time of the chemical pretreatment step, in particular the washing step, is preferably 1 min to 12 h, more preferably 10 min to 6 h, more preferably 30 min to 2 h, more preferably 45 to 90 min, most preferably 60 min.

[0108] After the treatment of HOW MANY In the chemical pretreatment step, especially the washing step, the aqueous solution is separated, e.g. by filtration, and the purified HOW MANY Preferably washed at least once with water to remove any residue of the washing solution.

[0109] The resulting PET waste is then dried, in particular in a drying oven. The drying temperature is preferably in the range of 30 to 120 °C, more preferably 50 to 100 °C, more preferably 60 to 90 °C, and most preferably 80 °C.

[0110] The comminution step has the advantage that the surface area available for the reaction in step (b) is reduced. HOW MANY The reaction rate in step (b) is increased. This increases the reaction rate of the conversion. The comminution can be carried out in apparatus known to those skilled in the art, for example a shredder or a cutting mill.

[0111] In a further embodiment of the method according to the invention, the HOW MANY, Before being subjected to step (b), it is decolorized or selectively colored. This can be done using methods known to those skilled in the art, e.g. decolorization with hydrogen peroxide or coloring with a dye. 3.2 Conversion Terms

[0112] The implementation of the HOW MANY with a solution S AP comprehensive glycol and MA glycolate to a mixture M 1 This can then be done under conditions familiar to the expert.

[0113] Implementation in step (b) is preferred as long as, i.e., until a certain point in time. tb , carried out until at least P = 10%, preferably at least P = 20%, preferably at least P = 25%, preferably at least P = 30%, preferably at least P = 40%, preferably at least P = 50%, preferably at least P = 60%, preferably at least P = 70%, preferably at least P = 80%, preferably at least P = 90%, preferably at least P = 95%, or even more preferably at least P = 99% of the amount used in step (b) HOW MANY have implemented it.

[0114] This percentage P is calculated according to the following formula: P = n TS + n MHET + n BHET / n PET .

[0115] This involves n HOW MANY the amount of substance in the number of repeating units of the following structure (Ξ) in the one used in step (b) HOW MANY: n TS is the amount of substance at TS, which from the beginning of step (b) until the time tb formed in step (b).

[0116] n MHET is the amount of substance at MHET, which from the beginning of step (b) until the time tb formed in step (b).

[0117] n BHET is the amount of substance at BHET, which from the beginning of step (b) until the time tb formed in step (b).

[0118] The structures of the connections BHET, MHET, TS are as follows:

[0119] "MHET." This also includes the corresponding carboxylate of the structure shown.

[0120] " TS " also includes the corresponding mono- and dicarboxylate of the structure shown.

[0121] The conversion in step (b) is carried out in particular at a temperature of at least 100 °C, preferably at a temperature in the range of ≥ 100 °C to ≤ 197 °C, more preferably at a temperature in the range of ≥ 130 °C to ≤ 197 °C, more preferably at a temperature in the range of ≥ 150 °C to ≤ 197 °C, more preferably at a temperature in the range of ≥ 175 °C to ≤ 197 °C.

[0122] The reaction in step (b) is preferably carried out at the boiling point of the glycol. Even more preferably, the glycol is refluxed, i.e., glycol is evaporated from the reaction, condensed, and then returned to the reaction. This refluxation can be controlled using methods familiar to those skilled in the art, for example, in a distillation apparatus.

[0123] The total weight of the MA glycolate used in the process, in relation to the total weight of the material used in the process HOW MANY The concentration is particularly in the range of 0.1 to 100 wt.%, preferably in the range of 0.5 to 80 wt.%, more preferably in the range of 1.0 to 50 wt.%, more preferably in the range of 1.5 to 25 wt.%, more preferably in the range of 2.0 to 10 wt.%, more preferably in the range of 2.5 to 6.0 wt.%, particularly preferably at 3.5 to 5.0 wt.%, most preferably at 3.9 wt.%.

[0124] The implementation in step (b) can be carried out using equipment familiar to the professional.

[0125] After completion of step (b) of the inventive method, a mixture M 1 obtained, in which the molar ratio η of the amount of substance of BHET (n BHET ) to the sum of the amounts of substance of MHET and TS (n MHET + n TS) in the range of 1 : 1 to 1000 : 1, preferably 2 : 1 to 500 : 100, more preferred 4 : 1 to 300 : 1, even more preferred 10 : 1 to 100 : 1, even more preferred 13 : 1 to 60 : 1, even more preferred 13 : 1 to 24 : 1. η = n BHET / n MHET + n TS 3.3 Carrier Step (c)

[0126] In a preferred further step (c) BHET at least partially from M 1 separated. This is preferably done by crystallization and / or distillation. Even more preferably BHET in step (c) from M 1 filtered and then crystallized. 4. Methods for recycling HOW MANY

[0127] The mixture in the process according to the invention M 1 received BHET is preferably used in a process for recycling polyethylene terephthalate in one step (ζ) to HOW MANY polymerized.

[0128] This polymerization is known to those skilled in the art as "polycondensation" and is described, for example, in EP 0 723 951 A1 and by Th. Rieckmann and S. Völker 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 TE Long, 2003, John Wiley & Sons, Ltd ISBN: 0-471-49856-4".

[0129] In particular, this will be done BHET in step (ζ) in the presence of catalysts, in particular catalysts selected from the group consisting of antimony compounds, preferably Sb₂O₃, to be again HOW MANY polymerized.

[0130] The polymerization of is preferred BHET to HOW MANYStep (ζ) is carried out at least at the boiling point of the glycol. In particular, during the polymerization in step (ζ), glycol is removed from the reaction mixture to shift the reaction equilibrium towards the polymer. HOW MANY to postpone.

[0131] The polymerization of is preferred BHET to HOW MANY Step (ζ) is carried out at the boiling point of the glycol. Even more preferably, during the polymerization in step (ζ), glycol is removed from the reaction mixture to shift the reaction equilibrium towards the polymer. HOW MANY to postpone.

[0132] This is achieved in particular by distillation at a pressure < 1 bar, preferably 0.1 mbar, at the simultaneous boiling point of the glycol at the respective pressure. Examples 1. Inventive example E1: 1.1 Recovery of Glycolytic Sodium Glycol Reduction by Reactive Distillation

[0133] The following apparatus was used as a distillation apparatus:The distillation apparatus used a heated 2.5 L double-jacketed vessel with a temperature sensor and vacuum-tight stirrer as the receiving vessel or sump. Above this was a 25 cm column with multifill packing and a silver mirror (removal section). NaOH was added above the column using a dropping funnel. Above the addition was another column for separating ethylene glycol and water vapor (refining section). A vapor divider in the upper part of the column allowed for the adjustment of the reflux ratio, with the distillate being collected in a round-bottom flask. The round-bottom flask could be disconnected and replaced from the distillation system via a pressure-equalizing dropping funnel. A reflux condenser with vacuum connections was attached to the refining section, allowing for the evacuation of the entire apparatus.The vacuum was generated by a rotary vane pump, which was connected to the distillation apparatus via two cold traps and a safety bottle. The pressure in the distillation apparatus was measured at the safety bottle (Büchi vacuum controller), where venting was also possible. The sump and the column with the multifill packing were completely wrapped in aluminum foil for insulation to ensure a constant temperature in the reactor / column.

[0134] Ethylene glycol was placed in the sump, and the entire apparatus was evacuated to 50 mbar. The sump was then heated to boiling point, causing reflux from the rectifier section. Subsequently, sodium hydroxide solution (50 wt% in water) was added using a dropping funnel. The dosing rate was chosen so that the sodium hydroxide solution did not reach the sump (approximately 2 mL / min).

[0135] The added or generated water was separated from the ethylene glycol by distillation in the rectifier section and collected in a round-bottom flask. The reflux ratio was 5:1 (5 parts reflux, 1 part distillate). The distilled volume had to be at least equal to the added volume of water. After distillation, the sodium ethylene glycolate was redistilled in the sump for approximately 2 hours. Maintaining constant vacuum and temperature, the water present in the rectifier section was removed to prevent reflux into the sump.

[0136] After completion and cooling of the experiment, the sump was opened via a drain valve and approximately 20 wt% solution of sodium glycolate in ethylene glycol was removed. 1.2 Depolymerization HOW MANY with glycolic sodium glycolate solution from reactive distillation

[0137] In the process according to the invention, 100 g were used. HOW MANYThe solution was placed in an autoclave containing 800 g of ethylene glycol. The solution was then heated to 150 °C with stirring. Once the temperature of 150 °C was reached, 19.5 g of 20% sodium glycolate solution in ethylene glycol (corresponding to 0.046 mol) from the reactive distillation were added. The reaction was carried out for five hours, and the reactor discharge was analyzed after cooling. The conversion was determined by gas chromatography. BHET (1) and 2-hydroxyethyl terephthalic acid (= "MHET") (2) and terephthalic acid (= " TS (3) is shown in the figure (in % in relation to the repetition unit used). (Ξ) the HOW MANY s; striped bar from top left to bottom right: "\\\\\\"). 2. Comparative example V1:

[0138] In a comparative experiment, 100 g were used. HOW MANYThe solution was placed in an autoclave containing 800 g of ethylene glycol. The solution was then heated to 150 °C while stirring. The reaction was carried out for five hours, and the reactor output was examined after cooling. The conversion of BHET (1) and MHET (2) TS (3) is shown in the figure (black, "▪"). 3. Comparison Example Q2:

[0139] In a comparative experiment, 100 g were used. HOW MANY The solution was placed in an autoclave containing 800 g of ethylene glycol. The solution was then heated to 150 °C with stirring. Once the temperature of 150 °C was reached, 3.7 g of 50 wt% NaOH solution in water (corresponding to 0.046 mol) were added. The reaction was carried out for five hours, and the reactor output was examined after cooling. The conversion obtained was... BHET (1) and MHET (2) TS (3) is shown in the figure (from top right → bottom left striped bar: " / / / / "). 4. Expertise

[0140] Comparing salaries to BHET, MHET and TS in the depolymerized product in the inventive example E1 and the comparative examples V1, V2 shows that a higher proportion of depolymerization occurs when using the glycolic sodium glycolate solution obtained by reactive distillation. BHET This is advantageous because it makes more product available, which can be directly used in a polycondensation reaction to form a new product. HOW MANY can be implemented.

Claims

1. Method of depolymerization of polyethylene terephthalate PET, comprising the following steps: (a) converting MAOH and glycol in a reactive distillation to obtain a solution SAP comprising glycol and MA glycolate, where MA is an alkali metal selected from sodium, potassium, (b) reacting the solution SAP with PET to give a mixture M1 comprising bis-2-hydroxyethyl terephthalate BHET.

2. Method according to Claim 1, wherein SAP is obtained in step (a) by reacting a reactant stream SAE1 comprising glycol with a reactant stream SAE2 comprising MAOH in countercurrent in a reactive rectification column RRA to give a crude product RPA comprising MA glycolate, water, glycol, MAOH, wherein SAP is withdrawn as bottom product stream at the lower end of RRA.

3. Method according to Claim 2, wherein a vapour stream SAB comprising water, with or without glycol, is withdrawn at the upper end of RRA.

4. Method according to Claim 3, wherein SAB comprises water and glycol, is directed into a rectification column RDA and is separated in RDA into at least one vapour stream SOA comprising water which is withdrawn at the upper end of RDA, and at least one stream SUA comprising glycol which is withdrawn at the lower end of RDA.

5. Method according to any of Claims 1 to 4, wherein step (b) is conducted until at least P = 10% of the PET used in step (b) has been converted.

6. Method according to any of Claims 1 to 5, wherein the content of water in SAP is < 1% by weight.

7. Method according to any of Claims 1 to 6, wherein step (b) is performed at the boiling temperature of the glycol.

8. Method according to any of Claims 1 to 7, wherein a sufficient amount of SAP is used in step (b) that the total weight of the MA glycolate used in step (b), based on the total weight of the PET used in step (b), is in the range from 0.1% to 100% by weight.

9. Method according to any of Claims 1 to 8, wherein BHET is at least partly separated from M1 in a further step (c).

10. Method according to Claim 9, wherein the at least partial separation of BHET from M1 in step (c) is effected by crystallization and / or distillation.

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

12. Method of recycling polyethylene terephthalate PET, in which BHET is obtained by a method according to any of Claims 1 to 11 and the BHET thus obtained is polymerized to PET in a step (ζ).

13. Method according to Claim 12, wherein the polymerization of BHET to PET in step (ζ) is conducted at at least the boiling temperature of the glycol.

14. Method according to Claim 12 or 13, wherein the polymerization in step (ζ) is performed in the presence of a catalyst.

15. Method according to Claim 14, wherein the catalyst is selected from the group consisting of antimony compounds.