Process for converting poly (ethylene terephthalate) to terephthalic acid

Abstract

The process for converting poly (ethylene terephthalate) to terephthalic acid comprises: a glycolysis step in which poly (ethylene terephthalate) is reacted with ethylene glycol in the presence of a specific catalyst; a hydrolysis step in which the product of the glycolysis step is reacted with an alkali metal hydroxide to produce an alkali metal salt of terephthalic acid; and an acidification step in which the product of the hydrolysis step is acidified to produce a precipitate containing terephthalic acid. Each step of the process can be carried out at ambient pressure or near ambient pressure, and the process produces terephthalic acid in high yield and high purity.

Description

Background Art

[0001] Poly(ethylene terephthalate) (PET) is the most common recycled plastic. There are many methods for converting poly(ethylene terephthalate) into its component monomers, ethylene glycol and terephthalic acid (or terephthalate esters), so that they can be reused. Some methods utilize glycolysis with ethylene glycol to produce bis(hydroxyethyl) terephthalate and additional ethylene glycol. See, e.g., S. Ugduler et al., “Towards closed-loop recycling of multilayer and coloured PET plastic waste by alkaline hydrolysis,” Green Chemistry, 2020, Vol. 22, pp. 5376-5394 (Table 2, cited from R. Lopez-Fonseca et al., “A kinetic study of the depolymerization of poly(ethylene terephthalate) by phase transfer catalysed alkaline hydrolysis,” Journal of Chemical Technology and Biotechnology, 2009, Vol. 84, pp. 92-99). However, such methods do not approach complete depolymerization of PET within a reasonable time, or require high pressure and / or high temperature to do so. Other methods utilize base-catalyzed hydrolysis to produce ethylene glycol and salts of terephthalic acid. See, e.g., J. Harvie et al., U.S. Patent No. 5,886,057, issued March 23, 1999; and S. Ugduler et al., “Towards closed-loop recycling of multilayer and coloured PET plastic waste by alkaline hydrolysis,” Green Chemistry, 2020, Vol. 22, pp. 5376-5394. But such methods require high pressure or organic solvents other than ethylene glycol. There are also other methods that utilize a combination of glycolysis and hydrolysis. See, e.g., J. Harvie et al., U.S. Patent No. 5,886,057, issued March 23, 1999; and Czechoslovakian Patent of Sirek et al., No. CZ 299244B6, published May 28, 2008. However, these methods also require high pressure and / or high temperature in the glycolysis, hydrolysis, or combined glycolysis / hydrolysis steps. Accordingly, there is a need for a method for depolymerizing PET to terephthalic acid in high yield, which is carried out at a temperature below the melting point of poly(ethylene terephthalate) of 260 °C and at ambient pressure or near ambient pressure.Preferably, the method will also avoid using organic solvents other than ethylene glycol. SUMMARY OF THE INVENTION

[0002] One embodiment is a method for converting poly(ethylene terephthalate) to terephthalic acid, comprising: reacting poly(ethylene terephthalate) with ethylene glycol in the presence of a catalyst at a temperature of 150 to 230 °C and an absolute pressure of 90 to 200 kPa for a time effective to produce a first reaction mixture comprising at least partially depolymerized poly(ethylene terephthalate); wherein the catalyst is selected from the group consisting of acetates of copper, aluminum, tin, nickel, iron, lead, manganese, titanium, and antimony; chloride and bromide salts of copper, aluminum, tin, nickel, iron, lead, manganese, zinc, titanium, and antimony; ionic liquids composed of cations and anions, wherein the cations are 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1-octyl-3-methylimidazolium, 1-decyl-3-methylimidazolium, 1-dodecyl-3-methylimidazolium, 1-butyl-2,3-dimethylimidazolium, 1,3-bis(N,N-dimethylaminoethyl)-2-methylimidazolium, 4-methyl-N-butyl-pyridinium, N-octylpyridinium, tetraethylammonium, or tetrabutylammonium, and the anions are tetrafluoroborate (BF 4 - ), hexafluorophosphate (PF 6 - ), bis(trifluoromethanesulfonyl)amide (CF 3 SO 2 ), trifluoromethanesulfonate, dicyanamide, hydrogen sulfate (HSO 2 N - ), ethyl sulfate (CH 4 - ), CH 3 CH 2 SO 4 - ), or tetrachloroferrate (FeCl 4 - ); (C 1 -C 6) - alkoxides; hydrotalcite; zeolite; montmorillonite; lipase; and combinations thereof; adding an alkali metal hydroxide to a first reaction mixture to produce a second reaction mixture, and maintaining the second reaction mixture at a temperature of 35 to 100 °C and an absolute pressure of 90 to 200 kPa for a time effective to produce a third reaction mixture comprising an alkali metal salt of ethylene glycol and terephthalic acid; optionally, contacting the third reaction mixture with a decolorizing agent insoluble in the third reaction mixture to produce a fourth reaction mixture, and filtering the fourth reaction mixture to produce a filtrate; and adding an aqueous solution of an inorganic acid to the filtrate or the third reaction mixture to prepare a fifth reaction mixture comprising a precipitate containing terephthalic acid.

[0003] This embodiment and other embodiments are described in detail below. Detailed Description

[0004] The inventors have determined that a high yield of high-purity terephthalic acid is produced by a method comprising a glycolysis step carried out in the presence of a specific catalyst, followed by a hydrolysis step and an acidification step, each step being carried out at ambient pressure or near ambient pressure. According to this method, it is possible to avoid using organic solvents other than ethylene glycol.

[0005] Thus, one embodiment is a method for converting poly(ethylene terephthalate) to terephthalic acid, comprising: reacting poly(ethylene terephthalate) with ethylene glycol in the presence of a catalyst at a temperature of 150 to 230 °C and an absolute pressure of 90 to 200 kPa for a time effective to produce a first reaction mixture comprising at least partially depolymerized poly(ethylene terephthalate); wherein the catalyst is selected from the group consisting of acetates of copper, aluminum, tin, nickel, iron, lead, manganese, titanium, and antimony; chloride and bromide salts of copper, aluminum, tin, nickel, iron, lead, manganese, zinc, titanium, and antimony; ionic liquids composed of a cation and an anion, wherein the cation is 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1-octyl-3-methylimidazolium, 1-decyl-3-methylimidazolium, 1-dodecyl-3-methylimidazolium, 1-butyl-2,3-dimethylimidazolium, 1,3-bis(N,N-dimethylaminoethyl)-2-methylimidazolium, 4-methyl-N-butyl-pyridinium, N-octylpyridinium, tetraethylammonium, or tetrabutylammonium, and the anion is tetrafluoroborate (BF 4 - )、hexafluorophosphate (PF 6 - )、bis(trifluoromethanesulfonyl)amideate ((CF 3 SO 2 ) 2 N - )、trifluoromethanesulfonate, dicyanamide, hydrogen sulfate (HSO 4- ), ethyl sulfate group (CH 3 CH 2 SO 4 - ), or tetrachloroferrate (FeCl 4 - ); alkoxides of copper, aluminum, tin, nickel, iron, lead, manganese, zinc, titanium, or antimony (C 1 -C 6 ); hydrotalcite; zeolite; montmorillonite; lipase; and combinations thereof; adding an alkali metal hydroxide to the first reaction mixture to produce a second reaction mixture, and maintaining the second reaction mixture at a temperature of 35 to 100 °C and an absolute pressure of 90 to 200 kPa for a time effective to produce a third reaction mixture containing an alkali metal salt of ethylene glycol and terephthalic acid; optionally, contacting the third reaction mixture with a decolorizing agent insoluble in the third reaction mixture to produce a fourth reaction mixture, and filtering the fourth reaction mixture to produce a filtrate; and adding an aqueous solution of an inorganic acid to the filtrate or the third reaction mixture to prepare a fifth reaction mixture containing a precipitate of terephthalic acid-containing material.

[0006] The method includes a glycolysis step in which poly(ethylene terephthalate) is reacted with ethylene glycol in the presence of a catalyst to effect at least partial depolymerization of the poly(ethylene terephthalate). The poly(ethylene terephthalate) starting material is preferably recycled poly(ethylene terephthalate) from domestic and / or industrial sources. The poly(ethylene terephthalate) can be transparent or colored. In some embodiments, the recycled poly(ethylene terephthalate) is rinsed with water, a dilute aqueous alkali solution, or both prior to the glycolysis step. In some embodiments, prior to the glycolysis step, the poly(ethylene terephthalate) is shredded to produce irregularly shaped flakes having a major dimension of 0.05 to 5 cm, or 0.1 to 2 cm as determined by optical microscopy. In a very specific embodiment of the pretreatment, the poly(ethylene terephthalate) starting material is a recycled poly(ethylene terephthalate) bottle from which any separable markers have been removed, then the bottles are washed with water and then with a dilute aqueous alkali solution prior to cutting into flakes having a major dimension of 0.05 to 5 cm or 0.1 to 2 cm as determined by optical microscopy, and the flakes are washed with water prior to use in the glycolysis step.

[0007] In the glycolysis step, poly(ethylene terephthalate) reacts with ethylene glycol in the presence of a catalyst. In some embodiments, the reaction of poly(ethylene terephthalate) with ethylene glycol includes reacting 1 to 3 moles of ethylene glycol per mole of ethylene terephthalate unit in poly(ethylene terephthalate). In other words, in poly(ethylene terephthalate), the molar ratio of ethylene glycol to ethylene terephthalate units can be from 1:1 to 3:1. Within this range, the molar ratio of ethylene glycol to ethylene terephthalate units in poly(ethylene terephthalate) can be from 1.5:1 to 3:1, or from 1.5:1 to 2.5:1.

[0008] The catalyst for the glycolysis step is selected from the group consisting of: acetates of copper, aluminum, tin, nickel, iron, lead, manganese, titanium, and antimony; chloride and bromide salts of copper, aluminum, tin, nickel, iron, lead, manganese, zinc, titanium, and antimony; ionic liquids composed of a cation and an anion, where the cation is 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1-octyl-3-methylimidazolium, 1-decyl-3-methylimidazolium, 1-dodecyl-3-methylimidazolium, 1-butyl-2,3-dimethylimidazolium, 1,3-bis(N,N-dimethylaminoethyl)-2-methylimidazolium, 4-methyl-N-butyl-pyridinium, N-octylpyridinium, tetraethylammonium, or tetrabutylammonium, and the anion is tetrafluoroborate (BF 4 - ), hexafluorophosphate (PF 6 - ), bis(trifluoromethanesulfonyl)amide (CF 3 SO 2 ), trifluoromethanesulfonate, dicyanamide, hydrogen sulfate (HSO 2 N - ), ethyl sulfate (CH 4 - ), ethylsulfate (CH 3 CH 2 SO 4 - ), or tetrachloroferrate (FeCl 4 - ); alkoxides of copper, aluminum, tin, nickel, iron, lead, manganese, zinc, titanium, or antimony (C 1 -C 6 ); hydrotalcite; zeolite; montmorillonite; lipase; and combinations thereof.

[0009] In some embodiments, the catalyst is selected from the group consisting of: chromium acetate (Cr 2 (O 2 CCH 3 ) 4 ; CAS Registry No. 14976-80-8), magnesium chloride (MgCl2 , CAS Registry Number 7786-30-3), magnesium bromide (MgBr 2 , CAS Registry Number 7789-48-2), calcium chloride (CaCl 2 , CAS Registry Number 10043-52-4), strontium chloride (SrCl 2 , CAS Registry Number 10025-70-4), zinc chloride (ZnCl 2 , CAS Registry Number 7646-85-7), zinc bromide (ZnBr 2 , CAS Registry Number 7699-45-8), stannous chloride (SnCl 2 , CAS Registry Number 7772-99-8), aluminum chloride (AlCl 3 , CAS Registry Number 7446-70-0), iron(III) chloride (FeCl 3 , CAS Registry Number 7705-08-0), cobalt(II) chloride (CoCl 2 , CAS Registry Number 7646-79-9), 1-butyl-3-methylimidazolium bromide (CAS Registry Number 85100-77-2), 1-butyl-3-methylimidazolium chloride (CAS Registry Number 79917-90-1), 1-butyl-3-methylimidazolium acetate (CAS Registry Number 284049-75-8), titanium(IV) isopropoxide (Ti(OCH(CH 3 )) 2 )) 4 , CAS Registry Number 546-68-9), titanium(IV) isobutoxide (Ti(OCH 2 C(CH 3 )) 2 )) 4 , CAS Registry Number 5593-70-4), aluminum isopropoxide (Al(OCH(CH 3 )) 2 )) 3 , CAS Registry Number 555-31-7), magnesium aluminum isopropoxide (Mg[Al(OCH(CH 3 )) 2 )) 4 ) 2 , CAS Registry Number 69207-83-6), tin(IV) isopropoxide (Sn(OCH(CH 3 )) 2 )) 4 , CAS Registry Number 546-68-9), antimony(III) isopropoxide (Sb(OCH(CH 3 )) 2 )) 3 , CAS Registry Number 18770-47-3), basic magnesium aluminum carbonate (Mg 6 Al 2(CO 3 )(OH) 16 .4H 2 O, CAS Registry Number 11097-59-9), zeolite ZSM-5 (Na n Al n Si 96- n O 192 .16H 2 O (0 ≤ n ≤ 27); CAS Registry Number 1318-02-1), montmorillonite K10 (CAS Registry Number 1318-93-0), lipase (CAS Registry Number 9001-62-1), and combinations thereof.

[0010] In some embodiments, the catalyst is selected from the group consisting of magnesium chloride, titanium isopropoxide, 1-butyl-3-methylimidazolium bromide, magnesium aluminum basic carbonate, ZSM-5, montmorillonite K10, and combinations thereof.

[0011] In some embodiments, the catalyst is magnesium chloride (MgCl 2 , CAS Registry Number 7786-30-3).

[0012] In some embodiments, the catalyst is titanium isopropoxide (Ti(OCH(CH 3 ) 2 ) 4 , CAS Registry Number 546-68-9).

[0013] In some embodiments, the catalyst is titanium isobutoxide (Ti(OCH 2 C(CH 3 ) 2 ) 4 , CAS Registry Number 5593-70-4).

[0014] In some embodiments, the catalyst is montmorillonite K10 (CAS Registry Number 1318-93-0).

[0015] In some embodiments, the catalyst is zeolite ZSM-5 (Na n Al n Si 96-n O 192 .16H 2 O (0 ≤ n ≤ 27); CAS Registry Number 1318-02-1).

[0016] In some embodiments, the reaction of poly(ethylene terephthalate) with ethylene glycol in the presence of a catalyst comprises reacting 100 parts by weight of poly(ethylene terephthalate) in the presence of 0.025 to 10 parts by weight of a catalyst. In the range of 0.025 to 10 parts by weight, the amount of the catalyst can be 0.05 to 8 parts by weight, or 0.05 to 0.6 parts by weight per 100 parts by weight of poly(ethylene terephthalate).

[0017] In some embodiments, the reaction of poly(ethylene terephthalate) with ethylene glycol in the presence of a catalyst comprises reacting 100 parts by weight of poly(ethylene terephthalate) in the presence of 0.025 to 0.4 parts by weight of a catalyst. In the range of 0.025 to 0.4 parts by weight, the amount of the catalyst can be 0.05 to 0.2 parts by weight, or 0.05 to 0.15 parts by weight per 100 parts by weight of poly(ethylene terephthalate).

[0018] The reaction of poly(ethylene terephthalate) with ethylene glycol is carried out in the presence of a catalyst at a temperature of 150 to 230 °C. Within this range, the temperature can be 150 to 210 °C, 160 to 200 °C, or 170 to 200 °C, or 180 to 230 °C, or 180 to 200 °C, or 185 to 200 °C. The reaction is carried out at an absolute pressure of 90 to 200 kPa. Within this range, the absolute pressure can be 90 to 150 kPa, or 90 to 110 kPa. An important advantage of the method of the present invention is that the glycolysis step can be carried out at or near ambient pressure. The reaction proceeds for a time to effectively produce a first reaction mixture comprising at least partially depolymerized poly(ethylene terephthalate). The degree of depolymerization can be determined by analyzing the first reaction mixture by gel permeation chromatography using a polystyrene standard to determine the weight average molecular weight of the partially depolymerized poly(ethylene terephthalate). In some embodiments, the at least partially depolymerized poly(ethylene terephthalate) has a weight average molecular weight of 500 to 10,000 g / mol as determined by gel permeation chromatography using a polystyrene standard. In the range of 500 to 10,000 g / mol, the weight average molecular weight of the at least partially depolymerized poly(ethylene terephthalate) can be 500 to 5,000 g / mol, or 500 to 2,000 g / mol. These values can be compared to the weight average molecular weight of the poly(ethylene terephthalate) starting material (typically about 60,000 g / mol) and the molecular weight of the fully glycolyzed product (bis(hydroxyethyl) terephthalate) (about 254 g / mol).

[0019] In some embodiments, the glycolysis reaction proceeds for 1.5 to 20 hours. Within this range, the glycolysis reaction time can be 1.5 to 15 hours, 1.5 to 12 hours, 1 to 6 hours, or 1.5 to 6 hours, or 2 to 5 hours.

[0020] In a very specific embodiment of the glycolysis step, the reaction of polyethylene terephthalate with ethylene glycol is carried out in the presence of a catalyst for a time of 1.5 to 20 hours at a temperature of 180 to 230 °C and an absolute pressure of 90 to 110 kPa.

[0021] In another very specific embodiment of the glycolysis step, the reaction of polyethylene terephthalate with ethylene glycol is carried out in the presence of a catalyst for a time of 1.5 to 6 hours at a temperature of 180 to 230 °C and an absolute pressure of 90 to 110 kPa.

[0022] In some embodiments, the glycolysis step involves little or no hydrolysis. Specifically, in these embodiments, the reaction of polyethylene terephthalate with ethylene glycol in the presence of a catalyst is carried out in the presence of 0 to 1 part by weight of water based on 100 parts by weight of polyethylene terephthalate. Within the range of 0 to 1 part by weight, the amount of water can be 0 to 0.5 part by weight, or 0 to 0.1 part by weight, or zero parts by weight / 100 parts by weight of polyethylene terephthalate.

[0023] In addition to the glycolysis step, the method includes a hydrolysis step after the glycolysis step. The hydrolysis step can be carried out immediately after the glycolysis step, or the hydrolysis step can be carried out after one or more intermediate steps between the glycolysis step and the hydrolysis step. In the hydrolysis step, an alkali metal hydroxide is added to the first reaction mixture to produce a second reaction mixture, and the second reaction mixture is maintained at a temperature of 35 to 100 °C and an absolute pressure of 90 to 200 kPa for a time effective to produce a third reaction mixture comprising an alkali metal salt of ethylene glycol and terephthalic acid. Within the range of 35 to 100 °C, the temperature of the hydrolysis step can be 35 to 90 °C, or 35 to 70 °C, or 35 to 60 °C, or 40 to 90 °C, or 40 to 70 °C, or 40 to 60 °C. Within the range of 90 to 200 kPa, the absolute pressure of the hydrolysis step can be 90 to 150 kPa, or 90 to 110 kPa. Suitable alkali metal hydroxides include lithium hydroxide, sodium hydroxide, potassium hydroxide, and combinations thereof. In some embodiments, the alkali metal hydroxide includes sodium hydroxide. In some embodiments, adding the alkali metal hydroxide to the first reaction mixture includes adding 2 to 5 moles of the alkali metal hydroxide based on 1 mole of ethylene terephthalate units in the poly(ethylene terephthalate) starting material. Within this range, based on 1 mole of ethylene terephthalate units in the poly(ethylene terephthalate), the number of moles of the alkali metal hydroxide can be 2 to 4 moles, or 2.5 to 3.5 moles. The hydrolysis step is carried out for a time effective to produce a third reaction mixture comprising an alkali metal salt of ethylene glycol and terephthalic acid. In some embodiments, the hydrolysis step reaction time is 0.25 to 4 hours, or 0.5 to 2 hours, or 0.5 to 1.5 hours. In a very specific embodiment of the hydrolysis step, the second reaction mixture is maintained at a temperature of 35 to 60 °C and a pressure of 90 to 110 kPa for a time of 0.5 to 2 hours to produce the third reaction mixture.

[0024] The method optionally includes a decolorization step, which is particularly useful when the poly(ethylene terephthalate) starting material includes a colored material (e.g., a colored poly(ethylene terephthalate) bottle). The decolorization step includes contacting a third reaction mixture with a decolorizing agent that is insoluble in the third reaction mixture to produce a fourth reaction mixture, and filtering the fourth reaction mixture to produce a filtrate. Suitable decolorizing agents include activated carbon, alumina, silica, and combinations thereof. In some embodiments, the decolorizing agent comprises activated carbon. In some embodiments, the decolorizing agent is used in an amount of 1 to 100 parts by weight / 100 parts by weight of poly(ethylene terephthalate). Within this range, the amount of the decolorizing agent can be 2 to 50 parts by weight, or 5 to 20 parts by weight / 100 parts by weight of the poly(ethylene terephthalate) starting material. In a very specific embodiment of the decolorization step, the second reaction mixture is contacted with 5 to 20 parts by weight of activated carbon / 100 parts by weight of poly(ethylene terephthalate).

[0025] In addition to the glycolysis step, the hydrolysis step, and the optional decolorization step, the method includes an acidification step. In the acidification step, an aqueous solution of an inorganic acid is added to the filtrate (if the decolorization step is carried out) or to the third reaction mixture (if the decolorization step is not carried out) to produce a fifth reaction mixture containing a precipitate of terephthalic acid. Suitable inorganic acids include hydrochloric acid, sulfuric acid, and combinations thereof. In some embodiments, the inorganic acid includes hydrochloric acid. The amount of the inorganic acid is used in an amount effective to reduce the pH of the solution to which it is added to a value less than or equal to 2 (the pKa values of terephthalic acid are about 3.5 and 4.8). Within this limitation, the amount of the inorganic acid used can be an amount effective to reduce the pH of the solution to which it is added to a value of 1 to 2, or 1.5 to 2.

[0026] The method may optionally further include separating a precipitate from the fifth reaction mixture. In some embodiments, the method further includes filtering the fifth reaction mixture to separate the precipitate, washing the separated precipitate, and drying the washed and separated precipitate. A terephthalic acid yield of greater than 90 mole %, and in some cases greater than 95 mole %, can be achieved, where the mole percentage values are based on the number of moles of ethylene terephthalate units in the poly(ethylene terephthalate) starting material. In some embodiments, based on the number of moles of ethylene terephthalate units in the poly(ethylene terephthalate) starting material, the yield of separated terephthalic acid is 92 to 98 mole %, or 93 to 97 mole %. Based on 100% of the total peak area in the 254 nm absorption chromatogram from high performance liquid chromatography, the purity of the separated terephthalic acid can be greater than 99.5%. In some embodiments, based on 100% of the total peak area in the 254 nm absorption chromatogram from high performance liquid chromatography, the purity of the separated terephthalic acid is 95 to 99.7%, or 98 to 99.7%, or 99 to 99.7%. The only significant impurity in the separated terephthalic acid is isophthalic acid, which is typically present in small amounts as a comonomer with terephthalic acid in the poly(ethylene terephthalate) starting material. Based on 100% of the total peak area in the 254 nm absorption chromatogram from high performance liquid chromatography, isophthalic acid is typically present in an amount less than or equal to 0.5%.

[0027] In some embodiments of the method, ethylene glycol is separated from the first reaction mixture before adding the alkali metal hydroxide to the first reaction mixture. In some embodiments of the method, ethylene glycol is not separated from the first reaction mixture before adding the alkali metal hydroxide to the first reaction mixture. In other embodiments, ethylene glycol is separated from the filtrate (if a decolorization step is performed) or the fifth reaction mixture (if a decolorization step is not performed).

[0028] In some embodiments, the method excludes a transesterification reaction between the glycolysis step and the hydrolysis step. In some embodiments, the method does not use organic solvents other than ethylene glycol (e.g., it does not use ethanol). In some embodiments, the method does not use aromatic hydrocarbon solvents.

[0029] In a very specific embodiment of the method, the reaction of poly(ethylene terephthalate) with ethylene glycol includes reacting 100 parts by weight of poly(ethylene terephthalate) with 50 to 80 parts by weight of ethylene glycol; the reaction of poly(ethylene terephthalate) with ethylene glycol in the presence of a catalyst includes reacting 100 parts by weight of poly(ethylene terephthalate) in the presence of 0.025 to 0.4 parts by weight of a catalyst selected from the group consisting of titanium(IV) isopropoxide, titanium(IV) isobutoxide, and combinations thereof; the reaction of poly(ethylene terephthalate) with ethylene glycol in the presence of a catalyst is carried out at a temperature of 180 to 230 °C and an absolute pressure of 90 to 110 kPa for a time of 1.5 to 6 hours; the reaction of poly(ethylene terephthalate) with ethylene glycol in the presence of a catalyst is carried out in the presence of 0 to 0.1 parts by weight of water, based on 100 parts by weight of poly(ethylene terephthalate); adding an alkali metal hydroxide to the first reaction mixture includes adding 1.5 to 5 moles of alkali metal hydroxide based on 1 mole of ethylene terephthalate units in the poly(ethylene terephthalate); and maintaining the second reaction mixture at a temperature of 35 to 60 °C and a pressure of 90 to 110 kPa for a time of 0.5 to 2 hours to produce a third reaction mixture.

[0030] In some embodiments, the method further includes separating a precipitate from the fifth reaction mixture and using the separated precipitate in the reaction to form a product selected from the group consisting of dimethyl terephthalate, dioctyl terephthalate, bis(2-hydroxyethyl) terephthalate, poly(ethylene terephthalate), glycol-modified poly(ethylene terephthalate), poly(butylene terephthalate), poly(butylene adipate-co-terephthalate), poly(trimethylene terephthalate), poly(cyclohexylene dimethylene terephthalate), glycol-modified poly(cyclohexylene dimethylene terephthalate), poly(cyclohexylene dimethylene terephthalate-co-isophthalate cyclohexylene dimethyl ester), poly(terephthalamide), poly(ethylene terephthalamide), poly(butylene terephthalamide), poly(terephthaloyl-2-methylpentylenediamine), and poly(p-phenylenediamine terephthalamide).

[0031] All ranges disclosed herein include the endpoints, and the endpoints can be combined independently of each other. Each range disclosed herein constitutes a disclosure of any point or sub-range located within the disclosed range.

[0032] The present invention includes at least the following aspects.

[0033] Aspect 1: A method for converting poly(ethylene terephthalate) into terephthalic acid, comprising: reacting poly(ethylene terephthalate) with ethylene glycol at a temperature of 150 to 230 °C and an absolute pressure of 90 to 200 kPa in the presence of a catalyst for a time effective to produce a first reaction mixture comprising at least partially depolymerized poly(ethylene terephthalate); wherein the catalyst is selected from the group consisting of acetates of copper, aluminum, tin, nickel, iron, lead, manganese, titanium, and antimony; chloride and bromide salts of copper, aluminum, tin, nickel, iron, lead, manganese, zinc, titanium, and antimony; ionic liquids composed of cations and anions, wherein the cation is 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1-octyl-3-methylimidazolium, 1-decyl-3-methylimidazolium, 1-dodecyl-3-methylimidazolium, 1-butyl-2,3-dimethylimidazolium, 1,3-bis(N,N-dimethylaminoethyl)-2-methylimidazolium, 4-methyl-N-butyl-pyridinium, N-octylpyridinium, tetraethylammonium, or tetrabutylammonium, and the anion is tetrafluoroborate, hexafluorophosphate, bis(trifluoromethanesulfonyl)amide, trifluoromethanesulfonate, dicyanamide, bisulfate, ethyl sulfate, or tetrachloroferrate; (C 1 -C 6 )-alcoholates of copper, aluminum, tin, nickel, iron, lead, manganese, zinc, titanium, or antimony; hydrotalcite; zeolite; montmorillonite; lipase; and combinations thereof; adding an alkali metal hydroxide to the first reaction mixture to produce a second reaction mixture, and holding the second reaction mixture at a temperature of 35 to 100 °C and an absolute pressure of 90 to 200 kPa for a time effective to produce a third reaction mixture comprising ethylene glycol and an alkali metal salt of terephthalic acid; optionally, contacting the third reaction mixture with a decolorizing agent insoluble in the third reaction mixture to produce a fourth reaction mixture, and filtering the fourth reaction mixture to produce a filtrate; and adding an aqueous solution of an inorganic acid to the filtrate or the third reaction mixture to prepare a fifth reaction mixture comprising a precipitate containing terephthalic acid.

[0034] Aspect 2: The method according to Aspect 1, wherein the catalyst is selected from the group consisting of chromium acetate, magnesium chloride, magnesium bromide, calcium chloride, strontium chloride, zinc chloride, zinc bromide, stannous chloride, aluminum chloride, iron chloride, cobalt chloride, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium acetate, titanium(IV) isopropoxide, titanium(IV) isobutoxide, aluminum(III) isopropoxide, aluminum magnesium isopropoxide, tin(IV) isopropoxide, antimony(III) isopropoxide, basic magnesium aluminum carbonate, montmorillonite K10, ZSM-5 (zeolite), lipase, and combinations thereof.

[0035] Aspect 3: The method according to aspect 1 or 2, wherein the catalyst is selected from the group consisting of magnesium chloride, titanium(IV) isopropoxide, titanium(IV) isobutoxide, montmorillonite K10, ZSM-5, and combinations thereof.

[0036] Aspect 4: The method according to aspect 1, wherein the catalyst is magnesium chloride.

[0037] Aspect 5: The method according to aspect 1, wherein the catalyst is titanium(IV) isopropoxide.

[0038] Aspect 6: The method according to aspect 1, wherein the catalyst is titanium(IV) isobutoxide.

[0039] Aspect 7: The method according to aspect 1, wherein the catalyst is montmorillonite K10.

[0040] Aspect 8: The method according to aspect 1, wherein the catalyst is zeolite ZSM-5.

[0041] Aspect 9: The method according to any one of aspects 1-8, wherein the reaction of poly(ethylene terephthalate) with ethylene glycol in the presence of a catalyst comprises reacting 100 parts by weight of poly(ethylene terephthalate) in the presence of 0.025 to 0.4 parts by weight of the catalyst.

[0042] Aspect 10: The method according to any one of aspects 1-9, wherein the reaction of poly(ethylene terephthalate) with ethylene glycol in the presence of a catalyst is carried out at a temperature of 180 to 230 °C and an absolute pressure of 90 to 110 kPa for a time of 1.5 to 20 hours.

[0043] Aspect 11: The method according to any one of aspects 1-9, wherein the reaction of poly(ethylene terephthalate) with ethylene glycol in the presence of a catalyst is carried out at a temperature of 180 to 230 °C and an absolute pressure of 90 to 110 kPa for a time of 1.5 to 6 hours.

[0044] Aspect 12: The method according to any one of aspects 1-11, wherein at least partially depolymerized poly(ethylene terephthalate) has a weight average molecular weight of 500 to 10,000 g / mol as determined by gel permeation chromatography using polystyrene standards.

[0045] Aspect 13: The method according to any one of aspects 1-12, wherein the reaction of poly(ethylene terephthalate) with ethylene glycol in the presence of a catalyst is carried out in the presence of 0 to 1 part by weight of water based on 100 parts by weight of poly(ethylene terephthalate).

[0046] Aspect 14: The method according to any one of Aspects 1 - 13, wherein adding the alkali metal hydroxide to the first reaction mixture comprises adding 2 to 5 moles of the alkali metal hydroxide based on 1 mole of ethylene terephthalate units in the poly(ethylene terephthalate).

[0047] Aspect 15: The method according to any one of Aspects 1 - 14, wherein the second reaction mixture is maintained for a time of 0.5 to 2 hours at a temperature of 35 to 60 °C and a pressure of 90 to 110 kPa to produce a third reaction mixture.

[0048] Aspect 16: The method according to any one of Aspects 1 - 15, comprising contacting the second reaction mixture with a decolorizing agent.

[0049] Aspect 17: The method according to Aspect 16, wherein contacting the second reaction mixture with the decolorizing agent comprises contacting the second reaction mixture with 5 to 20 parts by weight of activated carbon per 100 parts by weight of poly(ethylene terephthalate).

[0050] Aspect 18: The method according to any one of Aspects 1 - 17, wherein the reaction of poly(ethylene terephthalate) with ethylene glycol comprises: reacting 100 parts by weight of poly(ethylene terephthalate) with 50 to 80 parts by weight of ethylene glycol; the reaction of poly(ethylene terephthalate) with ethylene glycol in the presence of a catalyst comprises reacting 100 parts by weight of poly(ethylene terephthalate) in the presence of 0.025 to 0.4 parts by weight of a catalyst selected from the group consisting of titanium(IV) isopropoxide, titanium(IV) isobutoxide, and combinations thereof; reacting poly(ethylene terephthalate) with ethylene glycol in the presence of a catalyst at a temperature of 180 to 230 °C and an absolute pressure of 90 to 110 kPa for a time of 1.5 to 6 hours; the reaction of poly(ethylene terephthalate) with ethylene glycol in the presence of a catalyst is carried out in the presence of 0 to 0.1 parts by weight of water based on 100 parts by weight of poly(ethylene terephthalate); adding the alkali metal hydroxide to the first reaction mixture comprises adding 1.5 to 5 moles of the alkali metal hydroxide based on 1 mole of ethylene terephthalate units in the poly(ethylene terephthalate); and maintaining the second reaction mixture for a time of 0.5 to 2 hours at a temperature of 35 to 60 °C and a pressure of 90 to 110 kPa to produce a third reaction mixture.

[0051] Aspect 19: The method according to any one of Aspects 1 - 18, further comprising separating a precipitate from the fifth reaction mixture.

[0052] Aspect 20: The method according to aspect 19 further comprises using the separated precipitate in the reaction to form a product selected from the group consisting of dimethyl terephthalate, dioctyl terephthalate, bis(2-hydroxyethyl) terephthalate, poly(ethylene terephthalate), glycol-modified poly(ethylene terephthalate), poly(butylene terephthalate), poly(butylene adipate-co-butylene terephthalate), poly(propylene terephthalate), poly(cyclohexanedimethylene terephthalate), glycol-modified poly(cyclohexanedimethylene terephthalate), poly(cyclohexanedimethylene terephthalate-co-cyclohexanedimethylene isophthalate), poly(hexamethylene terephthalamide), poly(ethylene terephthalamide), poly(butylene terephthalamide), poly(2-methylpentamethylene terephthalamide), and poly(p-phenylene terephthalamide).

[0053] The invention is further illustrated by the following non-limiting examples.

[0054] Examples

[0055] The materials used in these examples are summarized in Table 1. Poly(ethylene terephthalate) (PET) was provided in the form of flakes that were derived from a process that began with recycled PET bottles and included removing the necks and printed labels from the bottles, washing the remaining bottle portions with water, crushing the bottle portions into irregularly shaped flakes having a major dimension of about 5 millimeters, washing the flakes with dilute base, subsequently washing the flakes with hot water, and drying the flakes.

[0056] Table 1

[0057]

[0058] In the following examples, "yield" refers to the yield of terephthalic acid based on the number of moles of terephthalate units in the poly(ethylene terephthalate) starting material. Specifically,

[0059]

[0060] "Purity" refers to the purity of the separated terephthalic acid product relative to a terephthalic acid standard as determined by the following high performance liquid chromatography (HPLC). An accurately weighed sample of about 25 milligrams of the separated terephthalic acid was taken. The separated terephthalic acid sample was added to a 25 milliliter volumetric flask and 20 milliliters of dimethyl sulfoxide was added. The resulting suspension was sonicated for 10 minutes to produce a homogeneous solution, and additional dimethyl sulfoxide was added to form a 25 milliliter solution. Two microliters of the solution was injected into the high performance liquid chromatograph, and all the peak areas (product and impurity peaks) in the product sample were integrated and compared to a blank sample (dimethyl sulfoxide). The HPLC conditions are summarized below.

[0061]

[0062] The purity is calculated as follows.

[0063]

[0064] All peak areas are at 254 nm.

[0065] "APHA" refers to the color of a liquid determined by the platinum-cobalt color test in accordance with ASTM D1209-05(2019). A color standard with an APHA value of 500 is prepared in accordance with ASTM D1209-05(2019). Specifically, 124.5 mg of potassium chloroplatinate (K 2 PtCl 6 ) and 100.0 mg of cobalt chloride (CoCl 2 .6H 2 O) are added to a 100 mL volumetric flask, and then 10 mL of 12N hydrochloric acid is added. Deionized water is used to dilute the resulting solution to 100 mL. The test solution contains 10 wt% of separated terephthalic acid in dimethyl sulfoxide. A blank solution of dimethyl sulfoxide is also analyzed, and its APHA value (typically 4 - 5 units) is subtracted from the APHA value of the test sample.

[0066] Example 1

[0067] Poly(ethylene terephthalate) fragments (100 g) are combined with ethylene glycol (65 g) in a three-necked round-bottom flask equipped with a top-mounted stirrer and a water-cooled condenser. Magnesium chloride catalyst (0.1 g) is added to the flask, and the resulting mixture is heated to 200 °C and held at this temperature for 10 hours. The glycolysis step converts the insoluble PET fragments into soluble oligomers that are more easily hydrolyzed in the subsequent hydrolysis step. After 10 hours, the reaction mixture is cooled to 50 °C with stirring, then 54 g of a 2 wt% sodium hydroxide solution is added to the flask, and stirring is continued at 50 °C for 1 hour. The hydrolysis step converts the PET oligomers into ethylene glycol and disodium terephthalate. Then activated carbon (10 g) is added to the flask, and the resulting mixture is stirred at 50 °C for 1 hour. After that, the mixture is filtered to remove the activated carbon. Then an aqueous hydrochloric acid solution (20 wt%) is added to the filtrate until the pH is less than 2, resulting in the formation of a precipitate. The precipitate is filtered, washed with approximately 750 g of water, and dried at room temperature while pulling air through the filtrate, and then dried in a vacuum oven at 100 °C for 10 hours. Yield = 81%, purity = 99.79%, and APHA color value = 38.

[0068] Example 2

[0069] In a three-necked round-bottom flask equipped with a top-mounted stirrer and a water-cooled condenser, poly(ethylene terephthalate) chips (100 g) were combined with ethylene glycol (65 g). Titanium(IV) isopropoxide catalyst (0.1 g) was added to the flask, and the resulting mixture was heated to 190 °C and maintained at this temperature for 3 hours. After 3 hours, the reaction mixture was cooled to 50 °C with stirring, then 54 g of a 2 wt% sodium hydroxide solution was added to the flask, and stirring was continued at 50 °C for 1 hour. The hydrolysis step converted the PET oligomers into ethylene glycol and disodium terephthalate. Then activated carbon (10 g) was added to the flask, and the resulting mixture was stirred at 50 °C for 1 hour. After that, the mixture was filtered to remove the activated carbon. Then an aqueous hydrochloric acid solution (20 wt%) was added to the filtrate until the pH was less than 2, resulting in the formation of a precipitate. The precipitate was filtered, washed with about 750 g of water, and dried at room temperature while pulling air through the filtrate, and then dried in a vacuum oven at 100 °C for 10 hours. Yield = 81%, purity = 99.83%, and APHA color value = 30.

[0070] Example 3

[0071] In a three-necked round-bottom flask equipped with a top-mounted stirrer and a water-cooled condenser, poly(ethylene terephthalate) chips (100 g) were combined with ethylene glycol (65 g). Titanium(IV) isobutoxide (0.1 g) was added to the flask, and the resulting mixture was heated to 190 °C and maintained at this temperature for 3 hours. After 3 hours, the reaction mixture was cooled to 50 °C with stirring, then 54 g of a 2 wt% sodium hydroxide solution was added to the flask, and stirring was continued at 50 °C for 1 hour. The hydrolysis step converted the PET oligomers into ethylene glycol and disodium terephthalate. Then activated carbon (10 g) was added to the flask, and the resulting mixture was stirred at 50 °C for 1 hour. After that, the mixture was filtered to remove the activated carbon. Then an aqueous hydrochloric acid solution (20 wt%) was added to the filtrate until the pH was less than 2, resulting in the formation of a precipitate. The precipitate was filtered, washed with about 750 g of water, and dried at room temperature while pulling air through the filtrate, and then dried in a vacuum oven at 100 °C for 10 hours. Yield = 81%, purity = 99.84%, APHA color value = 34.

[0072] Example 4

[0073] Poly(ethylene terephthalate) fragments (100 g) were combined with ethylene glycol (65 g) in a three-necked round-bottom flask equipped with a top-mounted stirrer and a water-cooled condenser. Montmorillonite K10 (MMT-K10) catalyst (5.0 g) was added to the flask, and the resulting mixture was heated to 200 °C and maintained at this temperature for 10 hours. After 10 hours, the reaction mixture was cooled to 50 °C with stirring, then 54 g of 2 wt% sodium hydroxide solution was added to the flask, and stirring was continued at 50 °C for 1 hour. The resulting solution was filtered to remove MMT-K-10, then activated carbon (10 g) was added to the flask, and the resulting mixture was stirred at 50 °C for 1 hour. After that, the mixture was filtered to remove the activated carbon. Then aqueous hydrochloric acid solution (20 wt%) was added to the filtrate until the pH was less than 2, resulting in the formation of a precipitate. The precipitate was filtered, washed with about 750 g of water, dried at room temperature while drawing air through the filtrate, and then dried in a vacuum oven at 100 °C for 10 hours. Yield = 81%, purity = 99.84%, APHA color value = 34.

[0074] Example 5

[0075] Poly(ethylene terephthalate) fragments (100 g) were combined with ethylene glycol (65 g) in a three-necked round-bottom flask equipped with a top-mounted stirrer and a water-cooled condenser. ZSM-5 catalyst (5.0 g) was added to the flask, and the resulting mixture was heated to 200 °C and maintained at this temperature for 10 hours. After 10 hours, the reaction mixture was cooled to 50 °C with stirring, then 54 g of 2 wt% sodium hydroxide solution was added to the flask, and stirring was continued at 50 °C for 1 hour. The resulting solution was filtered to remove ZSM-5, then activated carbon (10 g) was added to the flask, and the resulting mixture was stirred at 50 °C for 1 hour. After that, the mixture was filtered to remove the activated carbon. Then aqueous hydrochloric acid solution (20 wt%) was added to the filtrate until the pH was less than 2, resulting in the formation of a precipitate. The precipitate was filtered, washed with about 750 g of water, and dried at room temperature while drawing air through the filtrate, and then dried in a vacuum oven at 100 °C for 10 hours. Yield = 81%, purity = 99.89%, APHA color value = 34.

[0076] All ranges disclosed herein include the endpoints, and the endpoints can be combined independently of each other. Each range disclosed herein constitutes the disclosure of any point or sub-range located within the disclosed range.

Claims

1. A method for converting poly(ethylene terephthalate) into terephthalic acid, comprising: The time for reacting polyethylene terephthalate with ethylene glycol in the presence of a catalyst at a temperature of 150 to 230 °C and an absolute pressure of 90 to 200 kPa to effectively produce a first reaction mixture comprising at least partially depolymerized polyethylene terephthalate; wherein the catalyst is selected from the group consisting of acetates of copper, aluminum, tin, nickel, iron, lead, manganese, titanium, and antimony; chloride and bromide salts of copper, aluminum, tin, nickel, iron, lead, manganese, zinc, titanium, and antimony; ionic liquids composed of cations and anions, wherein the cations are 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1-octyl-3-methylimidazolium, 1-decyl-3-methylimidazolium, 1-dodecyl-3-methylimidazolium, 1-butyl-2,3-dimethylimidazolium, 1,3-bis(N,N-dimethylaminoethyl)-2-methylimidazolium, 4-methyl-N-butyl-pyridinium, N-octylpyridinium, tetraethylammonium, or tetrabutylammonium, and the anions are tetrafluoroborate, hexafluorophosphate, bis(trifluoromethanesulfonyl)amide, trifluoromethanesulfonate, dicyanamide, hydrogen sulfate, ethyl sulfate, or tetrachloroferrate; (C 1 -C 6 )-alcoholates of copper, aluminum, tin, nickel, iron, lead, manganese, zinc, titanium, or antimony; hydrotalcite; zeolite; montmorillonite; lipase; and combinations thereof; adding an alkali metal hydroxide to the first reaction mixture to produce a second reaction mixture, and maintaining the second reaction mixture at a temperature of 35 to 100 °C and an absolute pressure of 90 to 200 kPa for a time effective to produce a third reaction mixture comprising an alkali metal salt of ethylene glycol and terephthalic acid; optionally, contacting the third reaction mixture with a decolorizing agent insoluble in the third reaction mixture to produce a fourth reaction mixture, and filtering the fourth reaction mixture to produce a filtrate; and adding an aqueous solution of an inorganic acid to the filtrate or the third reaction mixture to prepare a fifth reaction mixture comprising a precipitate containing terephthalic acid.

2. The method according to claim 1, wherein the catalyst is selected from the group consisting of: chromium acetate, magnesium chloride, magnesium bromide, calcium chloride, strontium chloride, zinc chloride, zinc bromide, stannous chloride, aluminum chloride, iron chloride, cobalt chloride, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium acetate, titanium(IV) isopropoxide, titanium(IV) isobutoxide, aluminum(III) isopropoxide, aluminum magnesium isopropoxide, tin(IV) isopropoxide, antimony(III) isopropoxide, basic magnesium aluminum carbonate, montmorillonite K10, ZSM-5 (zeolite), lipase, and combinations thereof.

3. The method according to claim 1 or 2, wherein the catalyst is selected from the group consisting of: magnesium chloride, titanium(IV) isopropoxide, titanium(IV) isobutoxide, montmorillonite K10, ZSM-5, and combinations thereof.

4. The method according to claim 1, wherein the catalyst is titanium(IV) isopropoxide.

5. The method according to claim 1, wherein the catalyst is titanium(IV) isobutoxide.

6. The method according to claim 1, wherein the catalyst is magnesium chloride.

7. The method according to claim 1, wherein the catalyst is montmorillonite K10.

8. The method according to claim 1, wherein the catalyst is ZSM-5.

9. The method according to any one of claims 1-8, wherein reacting poly(ethylene terephthalate) with ethylene glycol in the presence of a catalyst comprises reacting 100 parts by weight of poly(ethylene terephthalate) in the presence of 0.025 to 0.4 parts by weight of the catalyst.

10. The method according to any one of claims 1-9, wherein reacting poly(ethylene terephthalate) with ethylene glycol in the presence of a catalyst is carried out at a temperature of 180 to 230 °C and an absolute pressure of 90 to 110 kPa for a time of 1.5 to 20 hours.

11. The method according to any one of claims 1-9, wherein reacting poly(ethylene terephthalate) with ethylene glycol in the presence of a catalyst is carried out at a temperature of 180 to 230 °C and an absolute pressure of 90 to 110 kPa for a time of 1.5 to 6 hours.

12. The method according to any one of claims 1-11, wherein the at least partially depolymerized poly(ethylene terephthalate) has a weight-average molecular weight of 500 to 10,000 g / mol as determined by gel permeation chromatography using polystyrene standards.

13. The method according to any one of claims 1-12, wherein reacting the poly(ethylene terephthalate) with ethylene glycol in the presence of a catalyst is carried out in the presence of 0 to 1 part by weight of water based on 100 parts by weight of the poly(ethylene terephthalate).

14. The method according to any one of claims 1-13, wherein adding the alkali metal hydroxide to the first reaction mixture comprises adding 2 to 5 moles of the alkali metal hydroxide per mole of ethylene terephthalate units in the poly(ethylene terephthalate).

15. The method according to any one of claims 1-14, wherein the second reaction mixture is maintained for a period of 0.5 to 2 hours at a temperature of 35 to 60 °C and a pressure of 90 to 110 kPa to produce the third reaction mixture.

16. The method according to any one of claims 1-15, the method comprising contacting the second reaction mixture with a decolorizing agent.

17. The method according to claim 16, wherein contacting the second reaction mixture with a decolorizing agent comprises contacting the second reaction mixture with 5 to 20 parts by weight of activated carbon per 100 parts by weight of the poly(ethylene terephthalate).

18. The method according to any one of claims 1-17, wherein reacting the poly(ethylene terephthalate) with ethylene glycol comprises reacting 100 parts by weight of the poly(ethylene terephthalate) with 50 to 80 parts by weight of ethylene glycol; reacting the poly(ethylene terephthalate) with ethylene glycol in the presence of a catalyst comprises reacting 100 parts by weight of the poly(ethylene terephthalate) in the presence of 0.025 to 0.4 part by weight of a catalyst selected from the group consisting of titanium(IV) isopropoxide, titanium(IV) isobutoxide, and combinations thereof; reacting the poly(ethylene terephthalate) with ethylene glycol in the presence of a catalyst is carried out for a period of 1.5 to 6 hours at a temperature of 180 to 230 °C and an absolute pressure of 90 to 110 kPa; reacting the poly(ethylene terephthalate) with ethylene glycol in the presence of a catalyst is carried out in the presence of 0 to 0.1 part by weight of water based on 100 parts by weight of the poly(ethylene terephthalate); adding the alkali metal hydroxide to the first reaction mixture comprises adding 1.5 to 5 moles of the alkali metal hydroxide per mole of ethylene terephthalate units in the poly(ethylene terephthalate); and the second reaction mixture is maintained for a period of 0.5 to 2 hours at a temperature of 35 to 60 °C and a pressure of 90 to 110 kPa to produce the third reaction mixture.

19. The method according to any one of claims 1-18, the method further comprising separating the precipitate from the fifth reaction mixture.

20. The method according to claim 19, wherein the method further comprises using the separated precipitate in a reaction to form a product selected from the group consisting of dimethyl terephthalate, dioctyl terephthalate, bis(2-hydroxyethyl) terephthalate, poly(ethylene terephthalate), glycol-modified poly(ethylene terephthalate), poly(butylene terephthalate), poly(butylene adipate-co-butylene terephthalate), poly(propylene terephthalate), poly(cyclohexylene dimethylene terephthalate), glycol-modified poly(cyclohexylene dimethylene terephthalate), poly(cyclohexylene dimethylene terephthalate-co-cyclohexylene dimethylene isophthalate), poly(hexamethylene terephthalamide), poly(ethylene terephthalamide), poly(butylene terephthalamide), poly(2-methylpentamethylene terephthalamide), and poly(p-phenylene terephthalamide).

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