Improved method of depolymerization of polyethylene terephthalate

Abstract

This invention relates to polyethylene terephthalate (PET) Methods for depolymerization of PET, among which PET reacts with sodium or potassium glycolate, obtained by reactive distillation, to give a product containing bis(2-hydroxyethyl) terephthalate (= " A mixture of BHET M 1. The characteristic system of the method according to the present invention BHET in the mixture M The pyrolysis products in 1 have a particularly high proportion. Therefore, the method according to the invention provides a high yield. BHET, which can be directly used for new PET production. Therefore, the present invention also relates to a recycling The PET method, in which... Obtained by the depolymerization method of PET BHET casually from M After further purification in step 1, it is polymerized again to give PET.

Description

An Improved Method for the Depolymerization of Polyethylene Terephthalate This invention relates to polyethylene terephthalate (PET) PET The method of depolymerization of (”), in which PET reacts with sodium or potassium glycolate, obtained by reactive distillation, to give a product containing bis(2-hydroxyethyl) terephthalate (= " A mixture of "BHET" (CAS No.: 959-26-2). M 1. The characteristic system of the method according to the present invention BHET in the mixture The pyrolysis products in M1 constitute a particularly high proportion. Therefore, the method according to the invention provides a high yield of... BHET, which can be directly used for new PET production. This invention also relates to a recycling The PET method, in which... Obtained by the depolymerization method of PET BHET casually from M1 was further purified and then polymerized again to give PET. Polyethylene terephthalate (= " PET (Polyester Resin) is one of the most important plastics, used in textiles, as films, and as a material for plastic bottles. In 2007 alone, the usage of plastic bottles reached approximately 10... 7 Tons (W. Caseri, Polyethylenterephthalate, 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). because The persistence of PET and its origin The massive amounts of PET waste constitute one of the biggest environmental challenges today. The solution lies in how to avoid its use. PET and its effective reuse PET. Previous techniques proposed various pyrolysis methods PET method. GB 784,248 A Description Methanol decomposition of PET. for Hydrolysis methods for the depolymerization of PET are described in JP 2000-309663 A, US 4,355,175 A and T. Yoshioka, N. Okayama, A. Okuwaki, Ind. Eng. Chem. Res. 1998, 37, 336-340. The reaction between PET and ethylene glycol is described in EP 0723951 A1, US 3,222,299 A, WO 2020 / 002999 A2, and SR Shukla, AM Harad's Journal of Applied Polymer Science. 2005, 97, 513-517 (hereinafter referred to as "Shukla & Harad") and the European Polymer Journal of ND Pingale, SR Shukla 2008, 44, 4151-4156. Shukla & Harad points out that the glycolization of PET produces bis(2-hydroxyethyl) terephthalate (= " BHET). The pyrolysis product can also be used to produce new [products / products]. Reactants for PET. therefore The depolymerization method for PET is of interest, in which the maximum proportion of pyrolysis products is obtained. BHET. The problem that this invention aims to solve is by providing such a method. Surprisingly, a method has now been discovered that can solve the problem that this invention aims to address. This invention relates to a polyethylene terephthalate (PET). The method for depolymerizing PET includes the following steps: (a) converting M in reactive distillation A OH and ethylene glycol to obtain a mixture containing ethylene glycol and ethylene glycol M. A Salt solution S AP M A It is selected from alkali metals such as sodium and potassium, preferably M A =Sodium, (b)make the solution S AP and PET reaction to give a product containing bis(2-hydroxyethyl) terephthalate (= " A mixture of BHET M 1. Better place, S AP It is obtained in step (a) by allowing a reaction stream containing ethylene glycol to pass through. S AE1 With M A OH reaction stream S AE2 In reactive distillation columns RR A The countercurrent reaction is used to give a product containing ethylene glycol M. A Salt, water, ethylene glycol, M A Crude products of OH RP A , in S AP Tied in RR A The bottom product stream is extracted from the lower part. Randomly, a vapor stream containing water, or with or without ethylene glycol. S AB Tied in RR A The upper part was pulled out. In another instance, the invention relates to a recycling The PET method, wherein the depolymerization method according to the invention is used to obtain BHET aggregates in step (ζ) to give PET. It has been surprisingly discovered that... PET and those obtained through reactive distillation S AP The response provides a higher proportion than conventional methods. BHET, in this conventional method, obtains an alkaline ethylene glycol alkali metal salt solution by mixing ethylene glycol with the corresponding alkali metal hydroxide. It has now been surprisingly discovered that when using sodium glycolate or potassium glycolate, which have already been obtained through reactive distillation, The glycolysis of PET proceeds particularly efficiently. In the reactive distillation according to the present invention, the ethylene glycol salt is obtained by means of the corresponding alkali metal hydroxide M A The reaction of OH with ethylene glycol yields the product. It has now been observed that, compared to prior art methods using ethylene glycol salts obtained by dissolving alkali metal hydroxides in ethylene glycol, the method according to the invention yields a higher proportion of the product in the pyrolysis products. BHET. 1. Step (a): Reactive distillation to obtain a mixture containing ethylene glycol and ethylene glycol M. A Salt solution S AP According to the present invention, the method according to the present invention includes ethylene glycol and ethylene glycol M. A Salt solution S AP It is achieved through reactive distillation via M A It is obtained by the conversion of OH with ethylene glycol. M A It is an alkali metal selected from sodium and potassium. M A The preferred sodium series. Reactive distillation, used to prepare alkali metal alkoxides, is an important industrial process because alkali metal alkoxides are used as strong bases in the synthesis of many chemicals, such as in the production of active pharmaceutical ingredients or agrochemicals, and as catalysts in transesterification and amination reactions. Alkali metal alkoxides (MORs) are prepared by reactive distillation, typically in a countercurrent distillation column, from alkali metal hydroxides (MOHs) and alcohols (ROHs), and the resulting product is removed according to the following reaction. The water and distillate formed by the reaction of <1>: The principle of this method is described, for example, in US 2,877,274 A, in which an aqueous solution of an alkali metal hydroxide and gaseous methanol are carried out countercurrently in a distillation column. This method is further described in essentially unchanged form in WO 01 / 42178 A1. The most important alkali metal alkoxides in industry are sodium and potassium alkoxides, especially methanol and ethanol salts. Their synthesis has been described extensively in the prior art, for example in EP 1 997 794 A1, WO 2021 / 148174 A1 and WO 2021 / 148175 A1. Similar methods are described in GB 377,631 A and US 1,910,331 A, but they additionally use an introducing agent, such as benzene. Correspondingly, DE 96 89 03 C describes a method for the continuous preparation of alkali metal alkoxides in a reaction column, wherein a water-alcohol mixture drawn from the top of the column is condensed and then phase-separated. The aqueous phase is discarded, and the alcohol phase is returned to the top of the column along with fresh alcohol. EP 0 299 577 A2 describes a similar method in which the aqueous components in the condensate are separated by means of a membrane. In a preferred embodiment of the method according to the present invention, S AP It is obtained in step (a) by allowing a reaction stream containing ethylene glycol to pass through. S AE1 With M A OH reaction stream S AE2 In reactive distillation columns RR A The countercurrent reaction is used to give a product containing ethylene glycol M. A Salt, water, ethylene glycol, M A Crude products of OH RP A ,in S AP Tied in RR A The bottom product stream is extracted from the lower part. Even better, a vapor stream containing water, with or without ethylene glycol. S AB Tied in RR A The upper part was pulled out. According to the present invention, a "reactive distillation column" is defined as a distillation column in which at least a portion of the reaction in step (a) of the method according to the present invention is carried out. It may also be simply referred to as a "reaction column". In a preferred embodiment of the method according to the present invention, ethylene glycol and ethylene glycol M are included. A Bottom product stream of salt S AP Tied in RR A The lower part is extracted. A vapor stream containing water, with or without ethylene glycol. S AB Tied in RR A The upper part was pulled out. In the context of this invention, "ethylene glycol" is understood to mean having the chemical formula HO-CH 2-CH 2-OH (CAS No. 107-21-1) is ethylene-1,2-diol. In the context of this invention, "ethylene glycol M" A "Salt" is understood to refer to ethylene glycol and M. A Salt. The term "ethylene glycol M" is used. A Salt contains M A O-CH 2-CH 2-OH and M A O-CH 2-CH 2-OM A At least one of them, preferably at least M A O-CH 2-CH 2-OH, optimal geosystem M A O-CH 2-CH 2-OH and M A O-CH 2-CH 2-OM A . M A It is selected from alkali metals such as sodium and potassium, with sodium being preferred. Reaction logistics S AE1 It contains ethylene glycol. In a preferred embodiment, S AE1 The mass ratio of ethylene glycol in the solution is ≥95% by weight, more preferably ≥99.5% by weight. S AE1 It also includes, in particular, water and diethylene glycol. In a preferred embodiment of the method according to the present invention, it is used as a reaction stream. S AE1 The ethylene glycol may also be commercially available ethylene glycol having a mass percentage of more than 99.5% by weight of ethylene glycol and a mass percentage of at most 0.03% by weight of water and at most 0.05% by weight of diethylene glycol. In one embodiment of the invention, the reaction stream S AE1 It is added to the reactive distillation column in gaseous form. RR A middle. In an alternative preferred embodiment of the method according to the invention, ethylene glycol is fed into a reactive distillation column prior to step (a). RR A The bottom is then heated to boiling in step (a) in a reactive distillation column. RR A A constant reaction stream is produced. S AE1 If necessary, during the execution of step (a), in the reactive distillation column RR A Add ethylene glycol to the bottom. Reaction logistics S AE2 Includes M A OH. In a preferred embodiment, S AE2 Not only includes M A OH also contains at least one other compound selected from water and ethylene glycol. Even more preferably, S AE2 Not only includes M A OH also contains water, in this case S AE2 M A An aqueous solution of OH. When the reaction stream S AE2 Includes M A When OH and water are present, they form... S AE2 Based on the total weight of the aqueous solution, M A The mass percentage of OH is particularly in the range of 10% to 75% by weight, preferably 15% to 54% by weight, even better 30% to 53% by weight, and even better 40% to 52% by weight, and most preferably 50% by weight. Step (a) of the method according to the invention is preferably performed in a reactive distillation column (or "reaction column"). RR A In the process. reaction tower RR A Preferably, it contains internal components. Suitable internal components include, for example, trays, structured packing, or unstructured packing. When the reaction tower... RR A When using trays, suitable trays include bubble cap trays, valve trays, tunnel hood trays, Thormann trays, cross-slit bubble cap trays, or sieve trays. When the reaction column... RR A When using trays, it is preferable to select a liquid trickle through the corresponding tray at a rate of no more than 5% by weight, and more preferably less than 1% by weight. The construction method required to minimize the trickle-through of the liquid is well known to those skilled in the art. In the case of valve trays, for example, a particularly tight-closing valve design can be selected. Reducing the number of valves can also increase the vapor velocity in the tray openings to twice the generally established value. When using sieve trays, it is particularly advantageous to reduce the diameter of the tray openings while maintaining or even increasing the number of openings. When using structured or unstructured packings, structured packings are better in terms of uniform liquid distribution. Step (a) of the method according to the invention can be performed continuously or in batches. It is preferred to perform it continuously. In one embodiment of the present invention, a reaction stream containing ethylene glycol is achieved. S AE1 With M AOH reaction stream S AE2 In reactive distillation columns RR A "Central countercurrent reaction", specifically, it relies on a reactant stream containing at least a portion of ethylene glycol. S AE1 The feed point is located in the reaction tower. RR A Includes M A OH reaction stream S AE2 Below the feed point. In this embodiment, the reaction tower RR A Better in response logistics S AE1 Feed point and reaction stream S AE2 There are at least two, and in particular 15 to 40, theoretical plates between the feed points. reaction tower RR A It can be operated using a pure stripping tower. In that case, the reaction stream contains ethylene glycol. S AE1 It is introduced into the reaction tower in the form of steam. RR A In the lower region. Randomly, a portion of the reaction stream containing ethylene glycol is... S AE1 Added in vapor form to the solution M containing alkali metal hydroxide A OH reaction stream S AE2 Below the feed point, but still within the reaction tower. RR A The upper part or upper region. This allows for the reduction of the reaction tower. RR A The dimensions of the lower region. When a portion of the reaction stream contains ethylene glycol. S AE1 (especially in vapor form) attached to the reaction tower RR A When added to the upper part or upper region, it is preferable to feed only 10% to 70% by weight, more preferably 30% to 50% by weight (in each case, based on the total amount of ethylene glycol used) into the reaction tower. RR A The lower part, while the remaining part is added in the form of steam in a single stream or divided into multiple sub-streams (preferably 1 to 10 theoretical plates, more preferably 1 to 3 theoretical plates) to the part containing M. A OH reaction stream S AE2 Below the feed point. In an alternative embodiment of step (a) of the method according to the invention, a reaction stream containing ethylene glycol is achieved. S AE1 With M A OH reaction stream S AE2 In reactive distillation columns RR A "Countercurrent reaction", in particular, it relies on the presence of ethylene glycol in the reactive distillation column. RR A Bottom and contains M A OH reaction stream S AE2 The feed point is located above the bottom. During step (a) of the method according to the invention, ethylene glycol is then added... RR A The bottom is heated to boiling and a reaction stream containing ethylene glycol is produced. S AE1 Then guide S AE1 and S AE2 To make each other flow against the current. In the reaction tower RR A Next, the reaction stream containing ethylene glycol will be... S AE1 With M A OH reaction stream S AE2 Based on the above reaction <1> (where "ROH" stands for "ethylene glycol") reaction, to give ethylene glycol M A Salt and H 2O, since this reaction is an equilibrium reaction, these products are related to ethylene glycol and M. AThe OH reactants are present in the mixture. Therefore, step (a) occurs in the reaction tower. RR A Crude products are provided in the middle RP A It not only contains ethylene glycol M A Salts and aquatic products, and also contains ethylene glycol and M A OH. exist RR A The lower part, then obtains and extracts ethylene glycol and ethylene glycol M. A Bottom product stream of salt S AP . exist RR A The upper part, preferably in RR A At the top of the tower, in a preferred embodiment of the method according to the invention, a stream of water, which may or may not contain ethylene glycol, is extracted, referred to above as "a vapor stream containing water, with or without ethylene glycol". S AB 。 If the vapor flow S AB The mixture contains not only water but also ethylene glycol, which is preferably obtained, for example, by distillation in a distillation column. In this embodiment, at least a portion of the ethylene glycol obtained by distillation can be used as a reaction stream. S AE1 Feed back to the reaction tower RR A middle. In a preferred embodiment, when S AB When it contains not only water but also ethylene glycol, it is directed to a distillation column. RD A In, and in RD A Separation into at least one vapor stream containing water S OA Its relationship is RD A The upper part is extracted, along with at least one stream containing ethylene glycol. S UA Its relationship is RD AThe lower part was pulled out. Better choice of reaction logistics S AE1 The amount of ethylene glycol included in the product stream is such that the ethylene glycol is simultaneously used as a component in the bottom product stream. S AP Ethylene glycol M obtained A Solvent for salts. Preferred reaction streams. S AE1 The amount of ethylene glycol in the solution is such that it comprises ethylene glycol and ethylene glycol M. A Bottom product stream of salt S AP The extracted ethylene glycol M A The salt solution is present at the bottom of the reaction tower at the desired concentration. In a preferred embodiment of the method according to the present invention, particularly S AE2 Not only includes M A When OH also contains water, it is used as a reaction stream. S AE1 The total weight (mass; unit: kg) of ethylene glycol and the reactants used as reactants S AE2 M A The ratio of the total weight (mass; unit: kg) of OH is 1:1 to 50:1, more preferably 2:1 to 40:1, even more preferably 3:1 to 30:1, and even more preferably 5:1 to 10:1. The reaction tower in a preferred embodiment of the method according to the present invention RR A The operation is performed with or without reflux, but it is preferable to operate with reflux. "With reflux" refers to the presence of reflux in the corresponding tower (especially the reaction tower). RR A The upper part of the stream is extracted containing water, or vapor with or without ethylene glycol. S AB It was not completely removed. Therefore, the associated vapor flow... S AB At least a portion, preferably a portion, of the feed is returned to the corresponding tower as reflux feed, especially to the reaction tower. RR AIn the case of establishing such a backflow, the better backflow coefficient is 0.01 to 1, the better coefficient is 0.02 to 0.9, the better coefficient is 0.03 to 0.34, the best coefficient is 0.04 to 0.27, the very best coefficient is 0.05 to 0.24, and the best coefficient is 0.2. The reflux ratio is generally understood, and in the context of this invention, to be the ratio of the mass flow rate (kg / h) removed from the corresponding column in liquid or gas form to the mass flow rate (kg / h) returned to the column in liquid form (reflux). Reflux can be established by installing a condenser at the top of the corresponding tower. Specifically, for this purpose, the condenser... K RRA Installed in the reaction tower RR A Above. In the condenser K RRA In the middle, steam flow S AB At least part of the condensate is condensed and fed back to the corresponding column, especially back to the reaction column. RR A middle. In the reaction tower RR A In embodiments where reflux is established, it is used as a reaction stream in a preferred embodiment of the method according to the present invention. S AE2 M A OH can also be mixed at least partially with the reflux stream, and the resulting mixture can thus be supplied to the reaction tower. RR A . In a preferred embodiment of the method according to the invention, step (a) is carried out, particularly under distillation conditions with ethylene glycol reflux. Step (a) is performed, particularly at temperatures ranging from 80°C to 197°C, more preferably from 100°C to 197°C, and even more preferably from 120°C to 140°C, and at absolute pressures ranging from 0.01 bar to 1 bar, more preferably from 0.05 bar to 1 bar, even more preferably from 0.05 bar to 0.15 bar, and even more preferably from 0.05 bar to 0.10 bar. In a preferred embodiment, the reaction tower RR A It includes at least one evaporator, which is particularly selected from intermediate evaporators. V ZA and bottom evaporator V SA Reaction tower RR A More preferably includes at least one bottom evaporator V SA . According to the present invention, an "intermediate evaporator" V Z This refers to the evaporator located above the bottom of the corresponding column, especially in reaction columns. RR A Above the bottom (in this case, they are referred to as " V ZA (or distillation column) RD A The evaporator above the bottom, which is used in the preferred embodiment and is described in further detail below (here they are referred to as ""). V ZRD ").exist RR A In this case, the evaporator is particularly effective at evaporating crude products. RP A The crude product is produced by side flow. S ZAA It was pulled out of the tower. According to the present invention, a "bottom evaporator" V S This refers to heating the evaporator at the bottom of the corresponding column, especially the reaction column. RR A Bottom or distillation column RD A The bottom, which is used in the preferred embodiment and is described in further detail below (in this case, they are referred to as "the bottom"), V SRD "or" V SRD' ").exist RR A In this case, the evaporator evaporates at least a portion of the bottom product stream. S AP .exist RD A In this case, the evaporator especially evaporates the bottom product stream. S UA or part of S UA , SUA1 . Evaporators are typically located outside the corresponding reaction tower or distillation tower. Suitable evaporators for use as intermediate and bottom evaporators include, for example, natural circulation evaporators, forced circulation evaporators, forced circulation rapid evaporators, kettle evaporators, falling-film evaporators, or thin-film evaporators. In the case of natural circulation and forced circulation evaporators, the heat exchanger used is typically a shell-and-tube or plate device. When using a shell-and-tube exchanger, the heat carrier flows through the tubes while the mixture to be evaporated flows around the tubes, or the heat carrier flows around the tubes while the mixture to be evaporated flows through the tubes. In the case of a falling-film evaporator, the mixture to be evaporated is generally introduced as a thin film onto the inside of the tubes and heated from the outside. Compared to falling-film evaporators, thin-film evaporators additionally include a rotor with a scraper that distributes the liquid to be evaporated onto the inner wall of the tubes to form a thin film. In addition to the listed evaporator types, any other desired evaporator types known to those skilled in the art and applicable to distillation columns may be used. In a preferred embodiment of the method according to the present invention, ethylene glycol and ethylene glycol M are included. A Salt S AP Tied to the reaction tower RR A The bottom product stream is extracted from the lower part. Preferably, the reaction tower RR A Includes at least one bottom evaporator V SA Then some bottom product stream S AP Ethylene glycol is partially removed through and from this bottom evaporator, compared to S AP Provides ethylene glycol M with an improved mass ratio A Bottom product stream of salt S AP* . In particular, in the method according to the invention, if at least some bottom product streams are used S AP Through at least one bottom evaporator V SA And at least partially remove ethylene glycol from it, then S AP ,or S AP* With the ability to respond to all situations S AP Ethylene glycol M, by total mass, ranges from 1% to 50% by weight, more preferably from 5% to 35% by weight, even more preferably from 15% to 35% by weight, and most preferably from 20% to 35% by weight. A The mass ratio of salt to ethylene glycol. by S AP Total mass S AP / S AP* The mass ratio of residual water in the best-case system is <1% by weight, <0.8% by weight, and <0.5% by weight in the even better-case system. by S AP Total mass S AP / S AP* Middle reactant M A The mass ratio of OH is preferably <1% by weight, preferably <0.8% by weight, and even more preferably <0.5% by weight. In one or even a preferred embodiment of the method according to the invention, a vapor stream comprising water, with or without ethylene glycol is used. S AB Tied in RR A The upper part is extracted. 2. In the distillation column R DA Steam flow in the middle S AB Distillation (preferably) In another preferred embodiment, when the vapor flow S AB When it contains water and ethylene glycol, it is directed to a distillation column. RD A In, and in RD A Separation into at least one vapor stream containing water S OA Its relationship is RD AThe upper part is extracted, along with at least one stream containing ethylene glycol. S UA Its relationship is RD A The lower part was pulled out. "At least one type of vapor stream containing water" S OA Its relationship is RD A The phrase "the upper part was pulled out" should be understood as meaning that in RD A The steam obtained at the top can be extracted from one or more steam streams there. "At least one stream containing ethylene glycol" S UA Its relationship is RD A The phrase "the lower part was pulled out" should be understood as meaning that in RD A The ethylene glycol obtained from the lower part can be drawn out in one or more streams there. Steam flow S AB It can be guided to the distillation column via one or more feed points. RD A In the middle. Within it, steam flows. S AB It is directed to the distillation column in two or more separate streams. R DA In an embodiment of the present invention, when the feed point of an individual stream is in the distillation column RD A It is advantageous when the upper systems are at substantially the same height. In a preferred embodiment of the method according to the present invention, when the steam flow S AB When it contains water and ethylene glycol, it is placed in a distillation column. RD A Separation into a vapor stream containing water S OA Its relationship is RD A The upper part was extracted, along with a stream containing ethylene glycol. S UA Its relationship is RD A The lower part was pulled out. Another term for "the upper part of a distillation column" is "the top (head)". Another term for "the lower part of a distillation column" is "bottom" or "the very bottom (foot)". The distillation column used RD A It can refer to any distillation column known to a person of ordinary knowledge in the relevant technical field. Distillation column RD A Preferably, it contains internal components. Suitable internal components include, for example, trays, unstructured packing, or structured packing. The trays used are typically bubble cap trays, sieve trays, valve trays, tunnel hood trays, or slotted trays. Unstructured packing is usually random packing elements. The random packing elements used are typically Raschig rings, Pall rings, Berl saddles, or Intalox saddles. ® (saddle). Structured filler systems, such as those marketed under the trade name Sulzer Mellapack. ® The filler material is for sale. In addition to the mentioned internals, other suitable internals are known to those skilled in the art and are equally usable. Superior internals exhibit a low specific pressure drop per theoretical plate. For example, structured packing and random packing elements have significantly lower pressure drops per theoretical plate than trays. This offers the following advantages for distillation columns. RD A The pressure drop is kept as low as possible, and thus the mechanical power of the compressor and the temperature of the ethylene glycol / water mixture to be evaporated are kept low. When the distillation column RD A When structured or unstructured packing is used, these packings can be separate or exist as continuous packing. However, generally at least two types of packing are provided, one of which is used in the steam flow... S AB Above the feed point, another type of packing is in the steam flow. S AB Below the feed point. It can also be located in the steam flow. S AB A packing is provided above the feed point and in the steam flow S AB Two or more trays are provided below the feed point. If unstructured packing, such as random packing, is used, the random packing elements are typically placed on a suitable support grid (e.g., sieves or mesh). In this preferred embodiment, the at least one vapor stream containing water S OA Then it was tied to the distillation column RD A The upper part was extracted. The steam flow... S OA The preferred mass fraction of water is ≥96.0 wt%, more preferably ≥99.6 wt%, and even more preferably ≥99.9 wt%, with the remainder being ethylene glycol. In this preferred embodiment RD A The lower part is extracted from at least one flow containing ethylene glycol. S UA It may preferably include <1% by weight, more preferably ≤5000 ppm by weight, even more preferably ≤1000 ppm by weight, and more preferably ≤100 ppm by weight of water. In the distillation column RD A At least one vapor stream containing water is extracted from the top. S OA In the context of this invention, it should be specifically understood that it refers to at least one vapor flow. S OA It is used in the distillation column as top flow or side flow. RD A The upper part of the inner part was pulled out. In the distillation column RD A At least one stream containing ethylene glycol was extracted from the bottom. S UA In the context of this invention, it should be specifically understood that it refers to at least one flow. S UA It is drawn out from the bottom stream or in the distillation column RD A The lower tray was removed. Distillation column RD A The operation is performed with or without reflux, but it is preferable to operate with reflux. "There is reflux" should be understood as referring to the situation in the distillation column. RD A The steam stream extracted from the upper part S OA Instead of being completely discharged, some of the condensate was condensed and returned to the corresponding distillation column. RD AIn the case of establishing such a backflow, the better backflow coefficient is 0.01 to 1, the better coefficient is 0.02 to 0.9, the better coefficient is 0.03 to 0.34, the best coefficient is 0.04 to 0.27 and the very best coefficient is 0.05 to 0.24, and the best coefficient is 0.2. It can be achieved by using a distillation column RD A Condenser installed on top K RD To establish a reflux. Corresponding to the vapor flow. S OA In the condenser K RD The middle portion is condensed and returned to the distillation column. RD A 3. Step (b): PET and solution S AP reaction In step (b) of the method according to the present invention, the solution obtained in step (a) S AP It contains ethylene glycol and ethylene glycol M. A Salt, and PET reaction to give inclusion BHET Mixture M1.3.1 PET starting materials In step (b) of the method according to the present invention PET can be any material that must be depolymerized. PET. Generally speaking, this type PET is found in the form of waste, especially in households, industry, or agriculture. In one embodiment of the method according to the present invention, the polymer to be depolymerized PET is therefore mixed with other plastics, especially at least one plastic selected from polyethylene ("PE") and polyvinyl chloride ("PVC"). When it comes from plastic waste... This is the general case when PET is to be depolymerized in the method according to the invention. In this embodiment, prior to step (b) of the method according to the invention, PET can be at least partially separated from other plastics, preferably through sorting. In one embodiment of the method according to the present invention, PET undergoes at least one pretreatment step. This preprocessing step is described, for example, in DE 10032899 C2. According to the present invention, The PET undergoes at least one pretreatment step selected from chemical pretreatment step and pulverization step before being used in step (b). exist When PET is mixed with other plastics, PET preferably undergoes at least one pretreatment step selected from at least partial separation from other plastics (preferably by sorting), chemical pretreatment step, and pulverization step before being used in step (b). exist When PET is mixed with other plastics, PET is preferably first separated from other plastics, at least partially, then subjected to at least one chemical pretreatment, and finally crushed. Chemical pretreatment steps, especially washing steps, are important. The advantage of this washing step is that it removes any impurities, particularly food residues, cosmetic residues, and / or bodily secretions (e.g., blood, semen, feces), before step (b). Such impurities can reduce the efficiency of the reaction in step (b) and / or affect the resulting product. The purity of BHET deteriorated. In the chemical pretreatment step (especially the washing step), the waste is heated in the washing solution at a temperature of 30°C to 99°C, preferably 50°C to 90°C, and more preferably 70°C to 85°C. Typical washing solutions are familiar to those skilled in the art and are preferably selected from: - aqueous solutions of surfactants, preferably aqueous solutions of nonionic surfactants; - aqueous solutions of alkali metal hydroxides or alkaline earth metal hydroxides, preferably aqueous solutions of NaOH. The processing time in the chemical pretreatment step (especially the washing step) is particularly 1 minute to 12 hours, preferably 10 minutes to 6 hours, even better 30 minutes to 2 hours, and even better 45 minutes to 90 minutes, with the best being 60 minutes. Processed by chemical pretreatment steps (especially washing steps) After PET, the aqueous solution is separated, for example by filtration, and preferably washed with water. PET should be applied at least once to remove any residue from the washing solution. Then obtain PET waste is dried, especially in a drying box. The temperature used for drying is particularly in the range of 30 to 120°C, preferably 50 to 100°C, more preferably 60 to 90°C, and most preferably 80°C. The advantage of the pulverizing step is that it can be used for the reaction in step (b). The surface area of ​​PET increases. This increases the reaction rate in step (b). The pulverization can be carried out in equipment known to those skilled in the art, such as a shredder or cutter. In another embodiment of the method according to the invention, PET is decolorized or colored in a controlled manner before undergoing step (b). This can be done by methods known to those skilled in the art, such as decolorization with hydrogen peroxide or dyeing with dye. 3.2 Reaction Conditions PET and ethylene glycol and ethylene glycol M A Salt solution S AP To give a mixture The reaction of M1 can be carried out under conditions familiar to those generally knowledgeable in the relevant technical field. Preferably, the reaction in step (b) is carried out until at most one juncture. t b At least at that point in time 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 better, at least P=99% is used in step (b) PET has been converted. that percentage P is calculated using the following formula: n here PET The one used in step (b) The following structures in PET ( The molar quantity of the repeating unit: n TA In step (b), from the start of step (b) to the latest time point... t b The formed TA's molar volume. n MHET In step (b), from the start of step (b) to the latest time point... t b The formed The molar quantity of MHET. n BHET In step (b), from the start of step (b) to the latest time point... t b The formed BHET's molar volume. compound BHET MHET The structure of TA is as follows: " "MHET" also covers the corresponding carboxylate of the structure shown. " "TA" also covers the corresponding monocarboxylic acid salts and dicarboxylic acid salts of the structures shown. The reaction in step (b) is carried out, particularly 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, and even more preferably in the range of ≥175°C to ≤197°C. The reaction in step (b) is preferably carried out at the boiling temperature of ethylene glycol. Even more preferably, the ethylene glycol is refluxed, meaning 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, such as in a distillation apparatus. The method used The total weight of PET, and the amount of ethylene glycol M used in the method. AThe total weight of salt is particularly in the range of 0.1 wt% to 100 wt%, preferably in the range of 0.5 wt% to 80 wt%, more preferably in the range of 1.0 wt% to 50 wt%, more preferably in the range of 1.5 wt% to 25 wt%, more preferably in the range of 2.0 wt% to 10 wt%, more preferably in the range of 2.5 wt% to 6.0 wt%, more preferably in the range of 3.5 wt% to 5.0 wt%, and most preferably 3.9 wt%. The reaction in step (b) can be carried out using an apparatus familiar to those skilled in the art. After step (b) of the method according to the invention is completed, a mixture is obtained. M1, where BHET's molar quantity (n BHET )and MHET and The total amount of moles of TA (n) MHET + n TA The molar ratio η is in the range of 1:1 to 1000:1, preferably 2:1 to 500:100, even better 4:1 to 300:1, even better 10:1 to 100:1, even better 13:1 to 60:1, and even better 13:1 to 24:1. 3.3 Preferred procedure (c) In a preferred alternative step (c), BHET is at least partially related to M1 separation. This is even more preferably carried out by crystallization and / or distillation. Even more preferably, in step (c) BHET Group Filtered from M1, then crystallized. 4. Recycling PET procedure In the mixture according to the method of the present invention Obtained in M1 BHET is preferably polymerized in step (ζ) of the method for recovering polyethylene terephthalate. PET. Those skilled in the art refer to this polymerization as "polycondensation" and it is described, for example, in EP 0 723 951 A1 and in Chapter 2, 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", Th. Rieckmann and S. Völker's "Poly (Ethylene Terephthalate) Polymerization - Mechanism, Catalysis, Kinetics, Mass Transfer and Reactor Design". Specifically, for this purpose, BHET polymerizes in the presence of a catalyst in step (ζ) and returns to its original state. PET, wherein the catalyst is particularly selected from the group consisting of antimony compounds, preferably Sb 2O 3. Preferably, in step (ζ) BHET Polymer The reaction of PET is carried out at least at the boiling temperature of ethylene glycol. Specifically, during polymerization in step (ζ), ethylene glycol is removed from the reaction mixture to allow the reaction to reach equilibrium with the polymer. PET side movement. More preferably, in step (ζ) BHET Polymer The reaction of PET is carried out at the boiling temperature of ethylene glycol. Even more preferably, in this case, during polymerization in step (ζ), ethylene glycol is removed from the reaction mixture to allow the reaction equilibrium to shift towards the polymer. PET side movement. This is achieved, in particular, by distillation at a pressure of <1 bar, preferably 0.1 mbar, at a temperature at which ethylene glycol simultaneously boils. Example 1. Example of the Invention E1: 1.1 Preparation of sodium glycol solution by reactive distillation The following equipment is used as distillation equipment: The storage container or bottom of the distillation apparatus is a heated 2.5 L jacketed vessel equipped with a temperature sensor and a vacuum-sealed stirrer. Above is a 25 cm column with multifill packing and a silver mirror (stripping section). NaOH is metered in at the top of the column using a dropping funnel. Above the metering point is another column used to separate ethylene glycol and water vapor (rectification section). A reflux ratio is established using a vapor distributor at the top of the column, and the distillate is collected in a round-bottom flask. The round-bottom flask can be separated from and replaced by the distillation system via a pressure-equalizing dropping funnel. In the rectification section, a reflux condenser with a vacuum connector is attached, allowing the entire apparatus to be evacuated. The vacuum is generated by a rotary vane pump connected to the distillation apparatus via two cold traps and a protective bottle. The pressure in the distillation apparatus is measured in the protective bottle (Büchi vacuum controller), which can also be vented. The bottom reservoir and the tower with multifill packing are completely surrounded by aluminum foil for insulation to ensure uniform temperature throughout the reactor / tower. The bottom was initially filled with ethylene glycol, and the entire apparatus was evacuated to 50 mbar. The bottom mixture was then heated to boiling temperature to establish reflux from the rectification section. A sodium hydroxide solution (50% by weight in water) was then metered in using a dropping funnel. A metering rate was chosen such that the sodium hydroxide solution did not reach the bottom (approximately 2 mL / min). The added / formed water is separated from ethylene glycol by distillation in the rectification section and collected in a round-bottom flask. The reflux ratio is 5:1 (5 parts reflux, 1 part distillate). The amount distilled must correspond at least to the amount of water added. After removing the distillate, the sodium glycolate in the bottoms is allowed to undergo further distillation for approximately 2 hours. Water present in the rectification section is removed under constant vacuum and temperature to prevent backflow to the bottoms. After the experiment was completed and cooled, approximately 20% by weight of the sodium glycol solution was removed from the ethylene glycol solution by opening the outlet valve. 1.2 Depolymerization was performed using the ethylene glycol solution of sodium glycol obtained from reactive distillation. PET In the method according to the present invention, the autoclave is initially filled with 100 g of... PET was added along with 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 a 20% sodium glycolate solution (corresponding to 0.046 mol) from reactive distillation in ethylene glycol was added. The reaction proceeded for five hours, and the reactor output was analyzed after cooling. The conversion rate was determined by gas chromatography. BHET(1) and 2-hydroxyethyl terephthalate (= " The conversion rates of MHET (2) and terephthalic acid (TA) (3) are shown in the figure (relative to...). Repeating units used in PET ( ) (Indicated by percentage; a bar chart with a shaded line "\\\\\\" from top left to bottom right). 2. Comparative Example V1: In the comparative experiment, the autoclave was initially filled with 100 g of... PET was added along with 800 g of ethylene glycol. The solution was then heated to 150°C with stirring. The reaction proceeded for five hours, and the reactor output was analyzed after cooling. BHET(1) and The product conversion rate of MHET(2) and The conversion rate of TA(3) is shown in the figure (black, "■"). 3. Comparative Example V2: In the comparative experiment, the autoclave was initially filled with 100 g of... PET was added along with 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 a 50% by weight NaOH aqueous solution (corresponding to 0.046 mol) was added. The reaction proceeded for five hours, and the reactor output was analyzed after cooling. BHET(1) and The conversion rate obtained from MHET(2) and The conversion rate obtained from TA(3) is shown in the figure (a bar chart marked with shaded lines " / / / " from the upper right to the lower left). 4. Results Examples of the present invention E1 and Comparative Examples V1、 V2 depolymerization products BHET MHET and The comparison of TA content shows that the depolymerization of ethylene glycol solution containing sodium glycolate obtained by reactive distillation provides a higher concentration of TA. BHET ratio. This is advantageous because it allows for the acquisition of more product, which can be directly converted into new products during condensation polymerization. PET products. [Figure 1] illustrates the depolymerization of sodium glycolate obtained by the method according to the present invention and sodium glycolate obtained by conventional methods. BHET ("1"), 2-hydroxyethyl terephthalate (" MHET”; "2") and terephthalic acid (" Comparison of the content of TS ("3") and TS ("3") A bar chart with shaded lines "\\\\\" illustrates an example according to the present invention. E1 The reactor output of PET depolymerization BHET MHET and The specific content of TS, in this example, is obtained by reactive distillation using sodium glycolate for depolymerization. The black bar chart shows the comparison examples. V1 The reactor output of PET depolymerization BHET MHET and The specific amount of TS, in this example, is only used for depolymerization with ethylene glycol. The bar chart with shaded lines " / / / / / " shows the comparison example. V2 The reactor output of PET depolymerization BHET MHET and The specific content of TS, in this example, is obtained by mixing NaOH and ethylene glycol in a reactor using sodium glycol for depolymerization.

Claims

1. A method for depolymerizing polyethylene terephthalate (PET), comprising the following steps: (a) converting MAOH and ethylene glycol in reactive distillation to obtain a solution SAP containing ethylene glycol and ethylene glycol MA salt, wherein MA is selected from alkali metals such as sodium and potassium; (b) reacting the solution SAP with PET to give a mixture M1 containing bis(2-hydroxyethyl) terephthalate (BHET).

2. The method of claim 1, wherein SAP is obtained in step (a) by reacting a reaction stream SAE1 containing ethylene glycol and a reaction stream SAE2 containing MAOH in a reactive distillation column RRA to give crude product RPA containing ethylene glycol MA salt, water, ethylene glycol, and MAOH, wherein SAP is a bottom product stream drawn from the lower part of the RRA.

3. The method of claim 2, wherein a vapor stream of water, with or without ethylene glycol, is drawn from the upper part of the RRA.

4. The method of claim 3, wherein the SAB, comprising water and ethylene glycol, is directed into a distillation column RDA and separated in the RDA into at least one vapor stream SOA containing water, which is drawn from the upper part of the RDA, and at least one stream SUA containing ethylene glycol, which is drawn from the lower part of the RDA.

5. The method of claim 1, wherein step (b) is performed until at least P = 10% of the PET used in step (b) has been converted, wherein the percentage P is calculated by the following formula: , wherein nPET is the molar amount of repeating units of the following structures () in the PET used in step (b): , nTA is the molar amount of TA terephthalate formed in step (b), nMHET is the molar amount of MHET mono(2-hydroxyethyl) terephthalate formed in step (b), and nBHET is the molar amount of BHET formed in step (b).

6. The method of any one of requests 1 to 5, wherein the water content in the SAP is <1 wt%.

7. The method of any one of claims 1 to 5, wherein step (b) is carried out at the boiling temperature of the ethylene glycol.

8. The method of any one of claims 1 to 5, wherein a sufficient amount of SAP is used in step (b) such that the total weight of the ethylene glycol MA salt used in step (b) is in the range of 0.1% by weight to 100% by weight based on the total weight of the PET used in step (b).

9. The method of any of claims 1 to 5, further comprising step (c), wherein BHET is at least partially separated from M1.

10. The method of claim 9, wherein in step (c) the separation of BHET at least partially from M1 is achieved by crystallization and / or distillation.

11. The method of any one of claims 1 to 5, wherein the PET undergoes at least one pretreatment step selected from chemical pretreatment step and pulverization step prior to step (b).

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

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

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

15. The method of claim 14, wherein the catalyst is selected from the group consisting of antimony compounds.

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