Improved method of depolymerization of polyethylene terephthalate

Abstract

This invention relates to a method for the depolymerization of polyethylene terephthalate (PET), wherein PET is reacted with sodium or potassium glycolate obtained by reactive distillation to provide a mixture M1 comprising bis(2-hydroxyethyl) terephthalate (BHET; CAS No.: 959-26-2). A key feature of this method is the formation of a particularly high proportion of BHET in the pyrolysis products of mixture M1. Therefore, this method provides a high yield of BHET, which can be directly used in new PET production. This invention also relates to a method for recycling PET, wherein BHET obtained by the depolymerization of PET is optionally further purified from M1 and then polymerized again to provide PET.

Description

An Improved Method for the Depolymerization of Polyethylene Terephthalate This invention relates to a polyethylene terephthalate (i.e., " The depolymerization method of PET, wherein... PET is reacted with sodium or potassium glycolate obtained via reactive distillation to provide bis(2-hydroxyethyl) terephthalate (i.e., " A mixture of "BHET" (CAS No.: 959-26-2). M 1. The technical feature of the method of the present invention lies in the mixture Among the cleavage products of M1, a particularly high proportion is formed. BHET. Therefore, the method of the present invention provides high yield. BHET, which can be directly used for new PET production. Therefore, this invention also relates to a recycling The PET method, wherein, via the The depolymerization method of PET BHET, casually in the After further purification, M1 is polymerized again to provide PET. Polyethylene terephthalate (i.e., " PET (Polyester Resin) is one of the most important plastics, used in textile fibers, films, and plastic bottles. In 2007 alone, the usage of plastic bottles was approximately 10... 7 W. Caseri, Polyethyenterephthalate, 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 the amount of PET-derived waste constitute one of the biggest environmental challenges today. The solution lies in avoiding the use of PET and effectively recycling it. PET. Previous techniques proposed various pyrolysis methods The PET method is described in GB 784,248A. Methods for methanol decomposition of PET. Depolymerization. Hydrolysis methods for PET are disclosed in JP 2000-309663A, US 4,355,175A, and T. Yoshioka, N. Okayama, A. Okuwaki, Ind. Eng. Chem. Res. 1998, 37, 336-340. The reaction of PET with ethylene glycol is revealed in EP 0723951 A1, US 3,222,299A, WO 2020 / 002999A2, by SR Shukla, AM Harad, Journal of Applied Polymer Science 2005, 97, 513-517 (“Shukla & Harad”) and ND Pingale, SR Shukla, European Polymer Journal 2008, 44, 4151-4156. Shukla & Harad pointed out... The glycolysis of PET results in bis(2-hydroxyethyl) terephthalate (i.e., " BHET This pyrolysis product can simultaneously serve as a new... Reactants in PET production. Therefore, there is a pair of depolymerizations. The PET method is of interest, in which the largest proportion can be obtained from the pyrolysis products. BHET. The problem that this invention aims to solve is to provide this method. Surprisingly, a method has now been discovered that can solve the problem that this invention seeks to address. This invention relates to a polyethylene terephthalate (PET) A method for depolymerizing PET includes the following steps: (a) converting M in reactive distillation A OR and ethylene glycol to obtain a mixture containing ethylene glycol and ethylene glycol M A Salt solution S AP M A M is an alkali metal selected from sodium and potassium. A Preferred to be sodium, wherein R is an alkyl group having 1 to 4 carbon atoms, particularly 1 to 3 carbon atoms, preferably 1 or 2 carbon atoms, and R is most preferably methyl, (b) making the solution S AP and PET reaction to provide bis(2-hydroxyethyl) terephthalate ( BHET) mixture M 1. Better place, S AP In step (a), by means of a reactive distillation column RR A The reaction stream containing ethylene glycol is used in the middle. S AE1 With M A OR reaction logistics S AE2 The reaction is carried out in countercurrent to provide ethylene glycol M. A Salt, ROH, ethylene glycol and M A Crude products of OR RP A And obtained, among which S AP It is in this RR A The bottom product stream extracted from the lower part. Randomly, in that RR A The upper part extracts a vapor stream containing ROH and with or without ethylene glycol. S AB . In another aspect, the present invention relates to a recycling Methods for obtaining PET, wherein the PET obtained via the depolymerization method of the present invention BHET aggregates in step (ζ) to provide PET. It has now been surprisingly discovered that PET and M via reactive distillation of alkoxide A OR S AP The reaction can provide a higher proportion than traditional methods. In conventional methods, alkaline ethylene glycol alkali metal salt solutions are obtained by mixing the ethylene glycol with the corresponding alkali metal hydroxide. It has now been surprisingly discovered that when sodium glycolate and potassium glycolate obtained by reactive distillation are used, The glycolysis of PET proceeds particularly efficiently. In the reactive distillation of this invention, the ethylene glycol salt is derived from the corresponding alkali metal alkoxide M. A OR is obtained by reacting it with ethylene glycol. It has now been observed that, compared to prior art methods using ethylene glycol to obtain ethylene glycol salts by dissolving alkali metal hydroxides in ethylene glycol, the method of the present invention can obtain a higher proportion of [unspecified substance] in the pyrolysis products. BHET. 1. Step (a): Reactive distillation to obtain the product containing ethylene glycol and ethylene glycol M. A Salt solution S AP In this invention, the method uses ethylene glycol and ethylene glycol M. A Salt solution S AP It is produced by reactive distillation from M A OR is obtained by the conversion of ethylene glycol. M A It is an alkali metal selected from sodium and potassium. M A Sodium is preferred. R is an alkyl group having 1 to 4 carbon atoms, preferably an alkyl group having 1 to 3 carbon atoms, more preferably methyl or ethyl, and most preferably methyl. The alkyl group having 1 to 4 carbon atoms is particularly selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, secondary butyl, and tertiary butyl, preferably selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, and tertiary butyl, and even more preferably selected from methyl, ethyl, isopropyl, and tertiary butyl. The alkyl group having 1 to 3 carbon atoms is particularly selected from methyl, ethyl, n-propyl, and isopropyl, preferably selected from methyl, ethyl, and isopropyl. Reactive distillation for the preparation of 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 preparation of active pharmaceutical or agrochemical components, and as catalysts in transesterification and amination reactions. Alkali metal alkoxides (MOR) # This system utilizes reactive distillation, typically in a countercurrent distillation column, where alkali metal hydroxides (MOHs) react with alcohols (R...). # Prepared by (OH), and removed according to the following reaction The water and distillate formed by the reaction <1>: MOH + R # OH ⇌ MOR # + H 2O. 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 introduced countercurrently in a distillation column. This method is further described in substantially unchanged form in WO 01 / 42178 A1. The most important industrial alkali metal alkoxides are sodium and potassium alkoxides, especially methanol and ethanol salts. Many prior art techniques describe their synthesis methods, such as 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 some of them use an inducing agent, such as benzene. For example, 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 subjected to phase separation. 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 water in the condensate is separated with the aid of a membrane. In addition to alkali metal hydroxides, different alkali metal alkoxides (MORs) can also be used in the "conversion alcoholysis reaction". * By reactive distillation and reacting it with alcohol R # OH reaction to provide the required alkali metal alkoxide MOR # and alcohols R * OH. Typically this R * OH has a boiling point lower than R # Alcohols with OH radicals. Typically, methanol is used as an R... * OH and methoxy compounds are used as MOR * . For example, DE 2726491 A1, EP 0776995 or WO 2021 / 122702 A1 describe this transethanolation reaction. In a preferred embodiment of the method of the present invention, S AP In step (a), by means of a reactive distillation column RR A In the middle, the reactant stream containing ethylene glycol is made S AE1 With M A OR reaction logistics S AE2 The reaction is carried out in countercurrent to provide ethylene glycol M. A Salt, ROH, ethylene glycol, M A Crude products of OR RP A And obtained, among which S AP It is in this RR A The bottom product stream extracted from the lower part. Even better, in that RR A The upper part extracts a vapor stream containing ROH and with or without ethylene glycol. S AB . In this invention, a "reactive distillation column" is defined as a distillation column in which the reaction in step (a) of the method of this invention is carried out in at least some parts. It may also be simply referred to as a "reaction column". In a preferred embodiment of the method of the present invention, in this RR A The lower part extracts ethylene glycol and ethylene glycol M. A Bottom product stream of salt S AP In that RR A The upper part extracts a vapor stream containing ROH and with or without ethylene glycol. SAB . In this invention, "ethylene glycol" is understood to have the chemical formula HO-CH 2-CH Ethane-1,2-diol of 2-OH (CAS No. 107-21-1). In this invention, "ethylene glycol M" A Salt (M) A glycolate is understood to be a combination of ethylene glycol and M. A Salt. "Ethylene glycol M" A The term "salt" includes 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, optimally M A O-CH 2-CH 2-OH and M A O-CH 2-CH 2-OM A . M A It is an alkali metal selected from sodium and potassium, with sodium being preferred. The reaction stream S AE1 Contains ethylene glycol. In a preferred embodiment, S AE1 The mass percentage of ethylene glycol in the mixture is ≥95% by weight, and more preferably ≥99.5% by weight. S AE1 In other cases, it specifically contains water and diethylene glycol. In a preferred embodiment of the method of the present invention, the reactant stream is used as the reactant stream. S AE1 The ethylene glycol may also be commercial ethylene glycol, wherein the ethylene glycol mass percentage exceeds 99.5% by weight, and the water mass percentage is up to 0.03% by weight, and the diethylene glycol mass percentage is up to 0.05% by weight. In one specific embodiment of the present invention, the reaction stream S AE1 It is added to the reactive distillation column in vapor form. RR A . In a preferred alternative embodiment of the method of the present invention, prior to step (a), the ethylene glycol-based feedstock is introduced into the reactive distillation column. RR A The bottom and then the mixture is heated to boiling in step (a) in the reactive distillation column. RR A A constant reaction stream is produced. S AE1 If necessary, during step (a), proceed then in the reactive distillation column. RR A Add ethylene glycol to the bottom. The reaction stream S AE2 Includes M A OR. In a preferred embodiment, S AE2 Not just M A OR also includes at least one additional compound selected from ROH and ethylene glycol. Even more preferably, S AE2 Not just M A OR also includes ROH, in which case... S AE2 M A OR in an alcoholic solution in ROH. When the reaction stream S AE2 Includes M A OR and ROH, to form S AE2 Based on the total weight of the alcoholic solution in ROH, M AThe weight percentage of OR is particularly in the range of 5% to 75% by weight, preferably 10% to 40% by weight, more preferably 15% to 35% by weight, and even more preferably 21% to 30% by weight. When R is a methyl group, to form S AE2 Based on the total weight of the alcoholic solution in ROH, M A The weight percentage of OR is particularly in the range of 25% to 35% by weight, preferably 30% by weight. When R is ethyl, to form S AE2 Based on the total weight of the alcoholic solution in ROH, M A The mass percentage of OR is particularly in the range of 15% to 25% by weight, preferably 21% by weight. The reaction stream S AE2 Preferably, it contains a small amount of water, i.e., each case contains the reaction stream. S AE2 Based on total weight, the reaction stream S AE2 The proportion of water is preferably <1% by weight, more preferably <0.2% by weight, even more preferably <0.1% by weight, and even more preferably <0.01% by weight. Step (a) of the method of the present invention is preferably performed in a reactive distillation column (or "reaction column"). RR A In the process. The reactive distillation column RR A Preferably, it includes internal components. Suitable internal components are, for example, trays, structured packing, or unstructured packing. When this reactive distillation column... RR A When trays are included, suitable trays are bubble cap trays, valve trays, tunnel-cap trays, Thormann trays, cross-shaped bubble cap trays, or sieve trays. This applies to the reactive distillation column. RR AWhen using trays, it is preferable to select trays in which no more than 5% by weight, and more preferably less than 1% by weight, of liquid dripping through. The construction methods required to minimize liquid dripping are well known to those skilled in the art. In the case of valve trays, for example, a design with particularly tight shut-off valves can be selected. Reducing the number of valves can also increase the vapor velocity in the tray opening by up to twice the normally 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 for uniform liquid distribution. Step (a) of the method of the present invention can be performed continuously or in batches. It is preferred to perform it continuously. One specific embodiment of the present invention achieves "in a reactive distillation column" RR A This allows the reactants containing ethylene glycol to flow. S AE1 With M A OR reaction logistics S AE2 "Reaction in countercurrent", specifically by allowing at least a portion of the reaction stream containing ethylene glycol to react. S AE1 The feed point is located in this reactive distillation column RR A The middle is lower than the one containing M A OR reaction logistics S AE2 The location of the feed point. In an alternative preferred embodiment, "in a reactive distillation column" RR A In the middle, the reactant stream containing ethylene glycol is made S AE1 With M A OR reaction logistics S AE2 "Reaction in countercurrent" can also refer to the reaction stream containing at least a portion of the ethylene glycol. S AE1 The feed point is located in the reactive distillation column. RR A The middle is higher than the M A OR reaction logistics S AE2 This is achieved by determining the location of the feed point. In this specific embodiment, the reaction tower RR A Preferably, it includes at least two theoretical plates, particularly 15 to 40 theoretical plates, in the reactive stream. S AE1 The feed point and the reaction stream S AE2 Between the feed points. The reactive distillation column RR A The stripping column can be operated purely. Under these conditions, the reaction stream containing ethylene glycol... S AE1 It is introduced into the reaction tower in vapor form. RR A The area below. Arbitrarily, a portion of the reaction stream should contain ethylene glycol. S AE1 Added in vapor form to a concentration below M A OR reaction logistics S AE2 The location of the feed point, but still within the reaction tower. RR A The upper part or upper region. This can reduce the size of the reaction tower. RR A The dimensions of the area below. This refers to a portion of the reaction stream containing ethylene glycol. S AE1 Added to the reaction tower RR A When feeding into the upper or upper region, especially in vapor form, in each case, based on the total amount of ethylene glycol used, preferably only 10% to 70% by weight of the feed should be introduced into the reaction tower. RR A The lower portion, preferably 30% to 50% by weight, and the remaining portion, in a single stream or divided into multiple sub-streams, preferably 1 to 10 theoretical plates, more preferably 1 to 3 theoretical plates, are added in vapor form to a concentration below the M-value. A OR reaction logistics S AE2 The location of the feed point. In an alternative specific embodiment of step (a) of the method of the present invention, the following is achieved: "in a reactive distillation column..." RR A The reaction stream contains ethylene glycol. S AE1 and including M A OR reaction logistics S AE2 "Reaction in countercurrent", especially by means of this reactive distillation column RR A Ethylene glycol was present at the bottom, and the product containing M... A OR reaction logistics S AE2 The feed point is located above the bottom. In step (a) of the method of the present invention, then in the... RR A Heating ethylene glycol to boiling at the bottom produces a reaction stream containing ethylene glycol. S AE1 Then, guidance S AE1 and S AE2 They make each other go against the current. In the reactive distillation column RR A Then, the reaction stream containing ethylene glycol is allowed to flow. S AE1 With the inclusion of M A OR reaction logistics S AE2 The reaction provides ethylene glycol M A Salts and ROH, because this reaction is an equilibrium reaction, these products will be present in the presence of ethylene glycol and M. A OR in the mixture of reactants. Therefore, step (a) is provided in the reactive distillation column. RR A crude products RP A It contains more than just ethylene glycol M A Salts and ROH products, including ethylene glycol and M A OR. In RR A The lower part, then obtains and extracts ethylene glycol and ethylene glycol M. A Bottom product stream of salt SAP . In a preferred embodiment of the method of the present invention, in this RR A The upper part, preferably, is located in the tower. RR A At the top, extract the ROH stream, which may or may not contain ethylene glycol, i.e., as described above, "a vapor stream containing ROH and with or without ethylene glycol". S AB 。 If the vapor flow S AB If the mixture contains not only ROH but also ethylene glycol, the ethylene glycol can preferably be obtained by distillation, for example, in a distillation column. In this specific embodiment, at least a portion of the ethylene glycol obtained by distillation can be fed back into the reaction column. RR A As a reaction stream S AE1 . In a preferred embodiment, when S AB When it contains not only ROH but also ethylene glycol, S AB Guided to the distillation column RD A And in RD A Separated into at least one in RD A The vapor stream containing ROH extracted from the top S OA and at least one of them RD A The vapor stream containing ethylene glycol extracted from the bottom S UA . In the reaction stream S AE1 The amount of ethylene glycol contained therein is preferably chosen such that the ethylene glycol is also used as a component obtained from the bottom product stream. S AP The ethylene glycol M A The solvent of the salt. In the reaction stream S AE1 The optimal amount of ethylene glycol is chosen so that the desired concentration of ethylene glycol M is present at the bottom of the reaction tower. AThe salt solution, which is the extract containing ethylene glycol and ethylene glycol M, is... A Bottom product stream of salt S AP . In a preferred embodiment of the method of the present invention, and particularly in S AE2 Not only includes M A OR also includes ROH cases, as a reaction stream S AE1 The total weight (mass; unit: kg) of ethylene glycol as a reactant stream S AE2 M A The ratio of the total weight (mass; unit: kg) of OR 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 13.5:1. In a preferred embodiment of the method of the present invention, the reaction tower RR A It operates with or without backflow, but it is better to operate with backflow. "Backflow" refers to the fact that the residue was not completely removed from the corresponding tower (specifically, the reaction tower). RR A The vapor stream extracted from the upper part contains ROH and may or may not contain ethylene glycol. S AB Therefore, at least a portion (preferably a portion) of the corresponding vapor flow S AB It is returned as reflux feed to the corresponding tower, specifically for the reaction tower. RR A In the case of reflux, the reflux 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 very particularly preferably 0.05 to 0.24, with the best being 0.2. The reflux ratio is commonly known, and in the context of this invention, it refers to the ratio of the mass flow rate (kg / h) removed from the corresponding column in liquid or gaseous form to the mass flow rate (kg / h) returned to the column in liquid form (reflux). Reflux can be established by a condenser located at the top of the corresponding tower. To achieve this, in particular, the condenser... K RRA Configured in this reaction tower RR A Above. In the condenser K RRA In the middle, the steam flow S AB For at least partial condensation and feed return to the corresponding tower, especially the reaction tower RR A . In a specific embodiment, in this reaction tower RR A Establishing a reflux, in a preferred embodiment of the method of the present invention, is used as the reaction stream. S AE2 The M A OR can also be at least partially mixed 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 of the present invention, step (a) is particularly carried out under distillation conditions with ethylene glycol reflux. Step (a) is particularly performed at a temperature range of 80°C to 197°C, preferably 100°C to 197°C, more preferably 120°C to 140°C, and at a pressure range of 0.01 bar absolute pressure to 1 bar absolute pressure, preferably 0.05 bar absolute pressure to 1 bar absolute pressure, more preferably 0.05 bar absolute pressure to 0.15 bar absolute pressure, and more preferably 0.05 bar absolute pressure to 0.10 bar absolute pressure. 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 The reaction tower RR A Preferably, it includes at least one bottom evaporator. V SA . In this invention, the "intermediate evaporator" V Z This refers to the evaporator above the bottom of the corresponding tower, especially in the reaction tower. RR A The evaporator above the bottom (in this case, it is considered " V ZA(or a distillation column used in a preferred embodiment, as described in further detail below) RD A The evaporator above the bottom (in this case, it is considered as " V ZRD ").exist RR A In this case, the evaporator specifically evaporates the crude product. RP A ， It is based on lateral flow S ZAA The form is extracted from the tower. In this invention, the "bottom evaporator" V S This refers to the evaporator at the bottom of the corresponding column, especially the reactive distillation column. RR A The bottom of the distillation column, or the distillation column used in a preferred embodiment and described in further detail below. RD A The bottom (in this case, it is considered as " V SRD "or" V SRD’ ").exist RR A In this case, the evaporator specifically evaporates at least a portion of the bottom product stream. S AP .exist RD A In this case, the evaporator specifically evaporates the bottom product stream. S UA or part of S UA , S UA1 . Evaporators are typically located outside the corresponding reactive distillation or rectification column. Suitable evaporators for use as intermediate and bottom evaporators include, for example, natural circulation evaporators, forced circulation evaporators, forced circulation flash evaporators, kettle evaporators, falling film evaporators, or thin-film evaporators. In the case of natural circulation and forced circulation evaporators, the heat exchanger typically used for the evaporator is a shell-and-tube or plate type device. When using a shell-and-tube exchanger, the heat carrier flows through the tubes, accompanied by the mixture to be evaporated flowing around the tubes, or the heat carrier flows around the tubes, accompanied by the mixture to be evaporated flowing through the tubes. In the case of a falling film evaporator, the mixture to be evaporated is typically introduced into the interior of the tubes in the form of a thin film, and the tubes are heated externally. Unlike falling film evaporators, thin-film evaporators additionally include a rotor with scrapers that disperses the liquid to be evaporated to form a thin film on the inner wall of the tubes. In addition to the evaporator types described above, any other evaporator types known to those skilled in the art and suitable for use in distillation columns may be used. In a preferred embodiment of the method of the present invention, ethylene glycol and ethylene glycol M are included. A Salt S AP It is located in the reaction tower RR A The lower part is extracted as the bottom product stream. The reaction tower RR A Preferably, it includes at least one bottom evaporator. V SA Then some of the bottom product flow S AP Through the bottom evaporator V SA And remove the bottom product stream S AP The portion of ethylene glycol thus provides more than S AP Ethylene glycol M with a high mass ratio A Bottom product stream of salt S AP* . In particular, in the method of the present invention, if at least one bottom evaporator is used... V SA At least some of them flowed from the bottom product stream. S AP By passing through and removing the bottom product stream S AP The middle portion of ethylene glycol, in each case, is... S AP Based on total mass, S AP or S AP* Ethylene glycol M A The mass percentage of salt in ethylene glycol ranges from 1 wt% to 50 wt%, preferably from 5 wt% to 35 wt%, more preferably from 15 wt% to 35 wt%, and most preferably from 20 wt% to 35 wt%. Should S AP / S AP* The mass ratio of ROH in the medium is based on S AP Based on total mass, preferably <1% by weight, more preferably <0.8% by weight, and even more preferably <0.5% by weight. Should S AP / S AP* The mass ratio of greywater is based on S AP Based on total mass, preferably <1% by weight, more preferably <0.8% by weight, and even more preferably <0.5% by weight. Should S AP / S AP* Middle reactant M A The mass ratio of OR, in order to S AP Based on total mass, preferably <1% by weight, more preferably <0.8% by weight, even more preferably <0.5% by weight, and even more preferably <0.005% by weight. Should S AE1 The mass ratio of greywater is based on S AE1 Based on total mass, preferably <1% by weight, more preferably <0.8% by weight, even more preferably <0.1% by weight, and even more preferably <0.005% by weight. exist S AE2 The mass ratio of greywater is based on S AE2 Based on total mass, preferably <1% by weight, more preferably <0.8% by weight, even more preferably <0.1% by weight, and even more preferably <0.005% by weight. In an even more preferred embodiment of the method of the present invention, in this RR A The upper part extracts a vapor stream containing ROH and with or without ethylene glycol. S AB 2. (Preferably) in a distillation column R DA Medium-distillation vapor flow S AB In another preferred embodiment, when the steam flow S AB When it contains ROH and ethylene glycol, it is guided to the distillation column. RD A And in RD A Separate into at least one in RD A The vapor stream containing ROH extracted from the top S OA and at least one in RD A The vapor stream containing ethylene glycol extracted from the bottom S UA . "At least one in" RD A The vapor stream containing ROH extracted from the top S OA "Should be understood as referring to in" RD A The steam obtained from the upper part can be from one or more steam streams. RD A Pull out the upper part. "At least one in" RD A The vapor stream containing ethylene glycol extracted from the bottom S UA "Should be understood as referring to in" RD A The ethylene glycol obtained from the lower part can be obtained from one or more streams. RD A Pull out the lower part. The vapor flow S AB It can be guided to the distillation column via one or more feed points. RD A In a specific embodiment of the present invention, the steam flow S AB Two or more separate streams are directed to the distillation column. R DA When the feed point of the individual vapor stream is actually in the distillation column RD A It is advantageous to be at the same altitude. In a preferred embodiment of the method of the present invention, when the steam flow S AB When it contains ROH and ethylene glycol, it is in a distillation column. RD A Separation into RD A The vapor stream containing ROH extracted from the top S OA and in RD A The vapor stream containing ethylene glycol extracted from the bottom S UA . Another term for the "upper part of a distillation column" is "head." Another term for the "lower part of a distillation column" is "bottom" or "foot." This distillation column... RD A Any distillation column familiar to those skilled in this technique can be used. The distillation column RD A Preferably, internal components are included. Suitable internal components include, for example, trays, structured packing, or unstructured packing. Typical trays used are bubble cap trays, sieve trays, valve trays, tunnel-cap trays, or slotted trays. Unstructured packing is typically a bed of randomly packed elements. Typical randomly packed elements used are Raschig rings, Pall rings, Berl saddles, or Intalox packing. ® (saddles). Structured fillers are, for example, Sulzer Mellapack. ® Product name seller. In addition to the aforementioned internal components, other suitable internal components familiar to those skilled in the art may also be used. Superior internal components result in a low specific pressure drop per theoretical column. Structured packing and randomly packed elements exhibit, for example, a significantly lower theoretical pressure drop than trays. This is advantageous for the distillation column. RD A The pressure drop is kept as low as possible, thus keeping the mechanical power of the compressor and the temperature of the ethanol / ROH mixture to be evaporated at a low level. When the distillation column RD A When structured or unstructured packing is included, it can be in the form of separate or continuous packing. Typically, however, at least two packings are provided, one of which is in the steam flow. S AB Above the feed point and a packing material in the steam flow S AB Below the feed point. A packing material is provided in this steam flow. S AB Above the feed point and providing two or more trays in the vapor flow S AB Below the feed point is also feasible. If unstructured packing is used, such as random packing, the random packing element is typically configured on a suitable support grid (e.g., a sieve plate or mesh plate). In this preferred embodiment, then in the distillation column RD A The upper part extracts at least one vapor stream containing ROH. S OA This steam flow S OA The preferred mass fraction of ROH in the sample is ≥99% by weight, more preferably ≥99.6% by weight, and even more preferably ≥99.9% by weight, with the remainder being ethylene glycol. In this preferred embodiment, the distillation column RD A At least one stream containing ethylene glycol was extracted from the lower part. S UA It preferably contains <1% by weight, more preferably ≤5000 ppm by weight, even more preferably ≤1000 ppm by weight, and most preferably ≤100 ppm by weight. As should be specifically understood from the content of this invention, from this distillation column RD A At least one vapor stream containing ROH is extracted from the top. S OAThis refers to the distillation column RD A At least one vapor flow is extracted from the top of the internal components in the form of a top flow or a side flow. S OA . As should be specifically understood from the content of this invention, from this distillation column RD A At least one vapor stream containing ethylene glycol is extracted from the bottom. S UA This means that at least one vapor stream S UA It is drawn out as a bottom flow or in this distillation column RD A The lower tray is removed. The distillation column RD A It operates with or without backflow, but preferably with backflow. "Recirculation" should be understood as referring to the flow from that distillation column. RD A The steam stream extracted from the top S OA It is not completely discharged, but partially condensed and returned to the corresponding distillation column. RD A When a reflux is established, the reflux 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 very particularly preferably 0.05 to 0.24, with the best being 0.2. Reflux can be achieved through this distillation column RD A Top-mounted condenser K RD Established. This corresponds to the vapor flow. S OA In the condenser K RD The middle portion condenses and returns to the distillation column. RD A 3. Step (b): PET and solution S AP reaction In step (b) of the method of the present invention, the product obtained from step (a) contains ethylene glycol and ethylene glycol M. A The salt solution S AP and PET reaction to provide containing BHET Mixture M 1. 3.1 PET Starting materials Step (b) of the method of the present invention is used. PET can be used for any material that must be depolymerized. PET. Typically, this type PET appears as waste, especially household, industrial, or agricultural waste. In one specific embodiment of the method of the present invention, therefore the polymer to be depolymerized PET refers to a mixture of other plastics, particularly at least one selected from polyethylene (PE) and polyvinyl chloride (PVC). Typically, this occurs when the method of the present invention depolymerizes PET from plastic waste. In this specific embodiment, prior to step (b) of the method of the present invention, the PET is at least partially separated from the other plastics, particularly by sorting. In one specific embodiment of the method of the present invention, the PET undergoes at least one pretreatment step. Such preprocessing steps can be described, for example, in DE 10032899 C2. In this invention, prior to step (b), the PET undergoes at least one pretreatment step selected from chemical pretreatment steps and pulverization steps. In PET is the case in a mixture containing other plastics, prior to its use in step (b). PET is preferably subjected to at least one pretreatment step selected from at least partially separating it from other plastics (preferably by sorting), chemical pretreatment step, and pulverization step. In PET refers to the case where it 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. This chemical pretreatment step is specifically a cleaning step. Such a cleaning step helps remove any impurities, particularly food residues, cosmetic residues, and / or bodily secretions (e.g., blood, semen, feces), before performing step (b). These impurities can reduce the reaction efficiency of step (b) and / or thus degrade the obtained product. The purity of BHET. In this chemical pretreatment step, particularly the cleaning step, the waste is specifically heated in the cleaning solution to a temperature of 30°C to 99°C, preferably 50°C to 90°C, and more preferably 70°C to 85°C. Typical cleaning solutions are those 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 for the chemical pretreatment step (especially the cleaning step) is particularly 1 minute to 12 hours, preferably 10 minutes to 6 hours, more preferably 30 minutes to 2 hours, even more preferably 45 to 90 minutes, and most preferably 60 minutes. The chemical pretreatment steps, especially the cleaning steps, are used to treat the... After PET, the aqueous solution will be separated, for example by filtration, and the washed solution... PET is preferably rinsed with water at least once to remove any residue from the rinsing solution. Then dry the resulting product. PET waste is dried, particularly in a drying chamber. The drying temperature range here is specifically 30°C to 120°C, preferably 50°C to 100°C, more preferably 60°C to 90°C, and most preferably 80°C. The pulverization step is beneficial for increasing the amount of material available for reaction step (b). The surface area of ​​PET increases the reaction efficiency of step (b). This pulverization can be carried out in apparatus familiar to those skilled in the art, such as a pulverizer or shredder. In another specific embodiment of the method of the present invention, before performing step (b), the PET can be decolorized or dyed in a controlled manner. This can be done using methods familiar to those skilled in the art, such as decolorization with hydrogen peroxide or dyeing with dyes. 3.2 Reaction conditions Should PET and ethylene glycol and ethylene glycol M A Salt solution S AP The reaction provides a mixture The reaction of M1 can be carried out under conditions familiar to those skilled in this technique. Preferably, the reaction in step (b) is carried out until at most one time point. t b At this point, the method used in step (b) At least in PET P is 10%, which is better than at least P is 20%, or better yet at least P is 25%, better than at least P is 30%, or better yet at least P is 40%, better than at least P is 50%, or better yet at least P is 60%, better than at least P is 70%, better than at least P is 80, better at least P is 90%, better than at least P is 95%, or even better. P is 99% converted. The percentage P is calculated using the following formula: P= (n TA + n MHET + n BHET ) / n PET 。 Where, n PET For use in step (b) The following structures in PET ( The molar quantity of the repeating unit of Ξ): n TA From the start of step (b) until that point in time is reached. t b The formation in step (b) TA's molar quantity. MHET From the start of step (b) until that point in time is reached. t b The formation in step (b) The molar quantity of MHET. BHET From the start of step (b) until that point in time is reached. t b The formation in step (b) BHET's molar volume. This compound BHET , MHET , The structure of TA is as follows: " MHET It also includes the carboxylate salts corresponding to the structures shown. "TA" also includes the monocarboxylic acid salt and dicarboxylic acid salt corresponding to the structure shown. The reaction in step (b) is carried out at a temperature of at least 100°C, preferably in the range of ≥100°C to ≤197°C, more preferably in the range of ≥130°C to ≤197°C, more preferably in the range of ≥150°C to ≤197°C, 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, it is ethylene glycol reflux, meaning that ethylene glycol evaporates from the reaction, condenses, and then returns to the reaction. This reflux can be established by methods familiar to those skilled in the art, such as a distillation apparatus. To be used in this method Based on the total weight of PET, the ethylene glycol M used in this method A The 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 apparatus used to perform the reaction in step (b) is familiar to those skilled in the art. After step (b) of the method of the present invention is completed, a mixture is obtained. M1, where BHET's molar value (n) BHET )right MHET and Total amount of TA (n) MHET +n TA The molar ratio η ranges from 1:1 to 1000:1, preferably from 2:1 to 500:100, more preferably from 4:1 to 300:1, even more preferably from 10:1 to 100:1, even more preferably from 13:1 to 60:1, and even more preferably from 13:1 to 24:1. η = n BHET / (n MHET +n TA ) 3.3 Best steps (c) In the preferred additional step (c), BHET is at least in part composed of M1 is separated. Even more preferably, this is done by crystallization and / or distillation. Even more preferably, in step (c)... BHET is... M1 is filtered out and then crystallized. 4. Recovery PET process The mixture from the method of the present invention M1 obtained BHET is preferably polymerized in the process of recovering polyethylene terephthalate in step (ζ). PET. This polymerization process is known to those skilled in the art as "condensation polymerization," and is described, for example, in EP 0 723 951 A1 and in Chapter 2, "Poly (Ethylene Terephthalate) Polymerization - Mechanism, Catalysis, Kinetics, Mass Transfer and Reactor Design," on page 92 of Th. Rieckmann and S. Völker's "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." Specifically, for this purpose, in step (ζ) in the presence of a catalyst BHET aggregation back PET, in which the catalyst is specifically selected from the group composed of antimony compounds, preferably Sb 2O 3. Preferably, in step (ζ) BHET aggregates into The PET reaction is carried out at least at the boiling point of ethylene glycol. Specifically, during the polymerization in step (ζ), ethylene glycol is removed from the reaction mixture to shift the reaction equilibrium towards the polymer. PET side. More preferably, in step (ζ) BHET aggregates into The PET reaction is carried out at the boiling point of ethylene glycol. Even more preferably, in this case, during the polymerization in step (ζ), ethylene glycol is removed from the reaction mixture to shift the reaction equilibrium towards the polymer. PET side. This is achieved, in particular, by distillation at a pressure < 1 bar (preferably 0.1 mbar) and at a temperature where ethylene glycol boils simultaneously at the corresponding pressure. [Example] 1. Embodiment of the Invention E1: 1.1 Ethylene glycol solution for preparing sodium glycolate by reactive distillation The following apparatus is used as the distillation unit: The distillation unit uses a reservoir or a heated 2.5-liter jacketed container with a temperature sensor and a vacuum-sealed stirrer at the bottom. Above this is a 25 cm column (stripping section) with multifill packing and a silver mirror. A dropping funnel is used above the aforementioned column to meter the addition of sodium methoxide ("NaOMe"). Above this metering point is another column (rectification section) for separating ethylene glycol and methanol vapors. The reflux ratio is established by a vapor distributor at the top of this column, and the distillate is collected in a round-bottom flask. This round-bottom flask can be separated and displaced from the distillation system by a pressure-equalizing dropping funnel. In the rectification section, a reflux condenser with a vacuum connector is attached, thereby evacuating the entire unit. The vacuum is generated by a vane pump connected to the distillation unit via two condensation traps and a protective bottle. The pressure of the distillation unit is measured in the protective bottle (Büchi vacuum controller), where ventilation is also possible. To ensure uniform temperature in the reactor / tower and for insulation purposes, the bottom reservoir and the tower with multifill packing are completely surrounded by aluminum foil. The bottom feedstock, ethylene glycol, and the entire apparatus are evaporated to 50 mbar. The bottom product is then heated to boiling temperature to establish reflux from the rectification section. Subsequently, NaOMe (30% by weight in methanol solution) is metered in using a dropping funnel. The metering rate is chosen to ensure that the NaOMe methanol solution does not reach the bottom (approximately 2 ml / min). The added / formed methanol is separated from ethylene glycol by distillation in this rectification section and collected in the round-bottom flask. The reflux ratio is 5:1 (5 parts reflux, 1 part distillate). The amount distilled off must correspond at least to the amount of newly added methanol. After distillation, the sodium glycolate in the bottoms is subjected to a further 2 hours of continuous distillation (to remove methanol present in this rectification section under constant vacuum and temperature to prevent backflow to the bottom). After the experiment was completed and cooled, the bottom was opened by the outlet valve and approximately 20% by weight of the sodium glycol solution in ethylene glycol was removed. 1.2 Using an ethylene glycol solution derived from sodium glycolate through reactive distillation PET Depolymerization In the method of this invention, 100 g of initial feed is used. PET and 800 g of ethylene glycol were added to an autoclave. The solution was then heated to 150°C with stirring. Once the temperature reached 150°C, 19.5 g of a 20% sodium glycol solution (equivalent to 0.046 mol) from reactive distillation in ethylene glycol was added. The reaction was carried out for five hours, and the reactor output was analyzed after cooling. The analysis was performed using a gas chromatograph. BHET(1) and 2-hydroxyethyl terephthalate ( MHET) (2) and terephthalic acid ( The conversion result of TA)(3). 2. Comparative Example V1: In the comparative test, the initial material of 100 g... PET and 800 g of ethylene glycol were added to an autoclave. The solution was then heated to 150°C with stirring. The reaction was carried out for five hours, and the reactor output was analyzed after cooling. The analysis was performed using a gas chromatograph. BHET(1) and MHET(2) and The conversion result of TA(3). 3. Comparative Examples V2: In the comparative test, the initial material of 100 g... PET and 800 g of ethylene glycol were added to an autoclave. The solution was then heated to 150°C with stirring. Once the temperature reached 150°C, 3.7 g of a 50% by weight NaOH aqueous solution (equivalent to 0.046 mol) was added. The reaction was carried out for five hours, and the reactor output was analyzed after cooling. The analysis was performed using a gas chromatograph. BHET(1) and MHET(2) and 4. Results of the transformation of TA(3). Comparative embodiments of the invention E1 and Comparative Examples V1、 V2 depolymerization products BHET MHET and The TA content indicates that a higher proportion can be obtained by depolymerization of a sodium glycol solution obtained through reactive distillation. BHET. This is advantageous because it results in more products, and these can be directly converted into new products during the polycondensation reaction. PET products.

Claims

1. A method for depolymerizing polyethylene terephthalate (PET), comprising the steps of: (a) converting MAOR and ethylene glycol in reactive distillation to obtain a solution SAP comprising ethylene glycol and ethylene glycol MA salt, wherein MA is an alkali metal selected from sodium and potassium, and wherein R is an alkyl group having 1 to 4 carbon atoms; and (b) reacting the solution SAP with PET to provide a mixture M1 comprising 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 MAOR in countercurrent in a reactive distillation column RRA to provide crude product RPA containing ethylene glycol MA salt, ROH, ethylene glycol, and MAOR, wherein SAP is the bottom product stream drawn from the lower part of the RRA.

3. The method of claim 2, wherein a vapor stream SAB containing ROH and having or not having ethylene glycol is extracted from the upper part of the RRA.

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

5. The method of Request 1, wherein step (b) is performed until at least 10% of the P in the PET used in step (b) has been converted.

6. As in Request 1, wherein the ROH content in SAP is <1 wt%.

7. The method of claim 1, wherein step (b) is performed at the boiling temperature of the ethylene glycol.

8. The method of claim 1, wherein 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 claim 1, wherein the method further comprises step (c), wherein BHET is at least partially separated from M1.

10. The method of claim 9, wherein in step (c) the BHET at least partially separated from M1 is crystallized and / or distilled.

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

12. A method for recovering polyethylene terephthalate (PET), wherein BHET is obtained by any one of claims 1 to 11, and the obtained BHET 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 reaction 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.