Method for preparing DOTP (dioctyl terephthalate) from PET (polyethylene terephthalate) waste plastics

Abstract

The invention relates to a method for preparing DOTP (dioctyl terephthalate) by using PET (polyethylene terephthalate) waste plastics, which comprises the following steps: (1) mixing metal salt with imidazolium ionic liquid, and stirring at 60-80 DEG C for reaction to obtain a composite catalyst; (2) mixing the PET waste plastics, isooctanol and a composite catalyst for reaction to obtain a mixed solution; and (3) cooling and filtering the mixed solution, mixing the filtrate with deionized water, standing for layering, carrying out reduced pressure distillation on an upper organic phase to obtain a crude product, and purifying to obtain the final DOTP. The DOTP is prepared by taking the PET waste plastic as the raw material through the one-step method, and the method has the advantages of high product yield and purity, short reaction time, good repeated use stability of the catalyst and the like.

Description

Technical Field

[0001] This invention belongs to the field of waste plastic degradation and recycling technology, specifically relating to a method for preparing DOTP using PET waste plastic. Background Technology

[0002] Dioctyl terephthalate (DOTP) is a high-performance plasticizer with excellent insulation properties, low volatility, heat resistance, cold resistance, pull-out resistance, flexibility, and good compatibility with PVC resin. It is widely used as a plasticizer for PVC plastics and synthetic rubber, a coating additive, a lubricant for precision instruments, a paper softener, cable materials, and in the production of artificial leather films. Furthermore, because it does not contain phthalates and is not within the scope of phthalate-containing plasticizers restricted by the EU and other countries, it is a relatively high-performance, environmentally friendly plasticizer, increasingly attracting the attention of researchers.

[0003] Currently, there are two main methods for producing DOTP: one is the direct esterification method, which involves the direct esterification of terephthalic acid (PTA) and octanol under the action of a catalyst; the other is the transesterification method, which involves the transesterification reaction of dimethyl terephthalate (DMT) and octanol under the action of a catalyst. Of these two methods, the raw materials PTA and DMT are relatively expensive, and the processes are complex, resulting in higher production costs.

[0004] Polyethylene terephthalate (PET) plastic is one of the most widely used plastics in the world today, extensively used in beverage bottles, disposable food packaging, medical and health products, clothing and textiles, and electronics. It is estimated that global PET production is approximately 74 million tons per year. This results in a large amount of PET waste, accounting for about 8% of the world's solid waste by weight and 12% by volume. Meanwhile, the stable physicochemical properties of waste PET make it difficult to degrade in the natural environment, and landfilling and incineration severely pollute ecosystems. Therefore, the recycling of waste PET is urgent. Currently, PET recycling is mainly mechanical, but this process leads to PET chain breakage and a reduction in molecular weight, affecting the performance and quality of recycled plastics, resulting in only downgraded utilization and limited recycling cycles. Chemical recycling methods, mainly including glycolysis, hydrolysis, and ammonolysis, can degrade PET into monomers or low-molecular-weight intermediates through reactions, which can then be repolymerized into PET plastics or used to prepare high-value-added chemicals such as plasticizers and unsaturated polyesters, thereby achieving the recycling of waste PET plastics. Therefore, this has become a current research hotspot.

[0005] CN113801621A discloses a method for preparing a flame-retardant waterborne polyurethane adhesive based on the alcoholysis products of waste PET. First, waste PET is alcoholyzed to obtain diethylene terephthalate (BHET). Then, diisocyanate, polyester polyol and catalyst are mixed and heated to react. After cooling to 60-80℃, diethylene terephthalate, hydrophilic chain extender, crosslinking agent and phosphorus-containing compound are added to finally obtain the flame-retardant waterborne polyurethane adhesive.

[0006] CN117736402A discloses a method for preparing highly conductive elastomers from waste PET alcoholysis products. First, waste PET is alcoholyzed, then the alcoholysis products undergo a prepolymerization reaction in the presence of lithium difluoromethane yellow imide, and finally a chain extender is added to obtain a conductive elastomer.

[0007] CN112521279A discloses a method for producing the environmentally friendly plasticizer DOTP. The method includes: processing recycled waste PET plastic, crushing it into granules, adding it to a NaOH methanol solution, reacting it under the action of a quaternary ammonium salt phase transfer catalyst, then adding a strong acid for neutralization to obtain terephthalic acid (PTA). PTA is then added to an esterification reactor for esterification to produce crude dioctyl terephthalate (DOTP). After filtering out impurities, the crude DOTP is fed into a distillation vessel to remove excess octyl alcohol. The crude DOTP is then condensed and added to a neutralization reactor. The neutralized DOTP is then heated for dehydration. The dehydrated material is then poured into a decolorization reactor to remove pigments and visible flocculent impurities from the crude ester. Finally, after filtering out activated carbon and impurities, qualified DOTP product is obtained.

[0008] The aforementioned patents employ a two-step method, both of which require the use of specific catalysts and solvents to first obtain BHET or PTA that meet the usage requirements. Otherwise, excessive impurities in the product will affect the preparation of subsequent products and the quality of the final product.

[0009] CN102603532A discloses a method for preparing plasticizer terephthalate esters via the catalytic alcoholysis reaction of waste polyester PET. The method uses a dual-acidic ionic liquid composed of alkyl sulfonic acid-functionalized acidic quaternary ammonium salt cations and Lewis acidic inorganic anions as a catalyst. Under conditions of a molar ratio of waste PET structural units to C2-C10 alkyl alcohols of 1:2.1 to 1:5, a mass ratio of waste PET to ionic liquid of 10:1 to 10:5, a reaction temperature of 80-220℃, and a reaction time of 5-14 hours, terephthalate esters are prepared, and ethylene glycol is recovered. However, the reagents used in the preparation of this catalyst are not widely available and are difficult to obtain, increasing the difficulty of recycling.

[0010] In summary, existing methods for preparing chemicals through PET alcoholysis suffer from drawbacks such as generally low product yields, excessively long reaction times, high temperatures, complex processes and separation steps, and poor catalyst reusability. Furthermore, the availability and ease of preparation of the catalyst, in addition to its catalytic performance, significantly impact its industrial application. Summary of the Invention

[0011] To address the shortcomings of existing technologies, this invention provides a method for preparing DOTP from waste PET plastics. This invention uses waste PET plastics as raw material to produce DOTP in a one-step process, offering advantages such as high product yield and purity, short reaction time, and good stability of the catalyst for repeated use.

[0012] This invention provides a method for preparing DOTP from waste PET plastics, comprising the following:

[0013] (1) Mix metal salt with imidazole ionic liquid and stir the reaction at 60-80℃ to obtain composite catalyst;

[0014] (2) PET waste plastic, isooctyl alcohol and composite catalyst are mixed and reacted to obtain a mixture;

[0015] (3) Cool and filter the mixture, mix the filtrate with deionized water, let it stand to separate into layers, and obtain the crude product by vacuum distillation of the upper organic phase, and then purify it to obtain the final DOTP.

[0016] In this invention, the metal salt mentioned in step (1) is one or more of zinc acetate, zinc chloride, manganese chloride, ferric chloride, etc., preferably zinc acetate.

[0017] In this invention, the imidazole ionic liquid in step (1) is at least one of 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) and 1-butyl-3-methylimidazolium bromide ([Bmim]Br), preferably [Bmim]Cl.

[0018] In this invention, the molar ratio of the metal salt to the imidazole ionic liquid in step (1) is 1:1-8. The reaction is carried out at 60-80℃ with a stirring rate of 300-800 rpm for 4-8 hours.

[0019] In this invention, the PET waste plastic mentioned in step (2) can be selected from one or more of waste PET bottle flakes, PET fibers, PET films, etc. Furthermore, the PET waste plastic is washed, dried, and cut before use, and its size is generally less than 10 mm.

[0020] In this invention, the mass ratio of isooctanol to PET waste plastic in step (2) is 2-8:1, preferably 3-5:1. The mass ratio of the composite catalyst to PET waste plastic is 0.1-1:1, preferably 0.4-0.6:1.

[0021] In this invention, it is further preferred that chloroform is added to the reaction system, and the mass ratio of chloroform to PET waste plastic is 0.5-1.5:1.

[0022] In this invention, the reaction temperature in step (2) is 170-210℃, preferably 180-200℃, the reaction time is 1-7h, preferably 3-5h, the reaction pressure is 1-2atm, and the stirring rate is 500-1500rpm.

[0023] In this invention, step (3) involves cooling the mixture to room temperature and filtering it using methods such as vacuum filtration or pressure filtration. The filtrate is mixed with deionized water at a volume ratio of 1:3-15, preferably 1:5-8. After standing and separating the layers, the upper organic phase is distilled under reduced pressure at 140-200℃ and 0.001-0.002MPa for 2-5 hours to obtain the crude product. The crude product is then desorbed by reduced pressure distillation to remove chloroform and isooctyl alcohol, which are then reused in step (2).

[0024] In this invention, after step (3) of settling and layering, the lower aqueous phase mainly contains catalyst, ethylene glycol, etc. Water and ethylene glycol are removed by vacuum distillation, and the obtained composite catalyst is recovered for recycling. Vacuum distillation is carried out at 50-60℃ and 0.003-0.0035MPa for 2-6 hours to obtain ethylene glycol.

[0025] In this invention, the crude product in step (3) can be purified by first using a decolorizing agent such as activated carbon at 60-100℃ for 2-4 hours; then further purification is carried out using a SiO2 chromatographic column to obtain the final DOTP product.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) This invention uses PET waste plastic and isooctanol as raw materials to prepare DOTP in one step in the presence of a composite catalyst. Metal ions can interact with the C=O bond in the PET ester group, thereby enhancing the electrophilicity of the carbonyl carbon and making it easier for isooctanol to nucleophilically attack the carbonyl group in the PET polyester. Ionic liquid can help remove the -OH of isooctanol, thereby enhancing its electronegativity. Through the synergistic effect of the two, the yield of DOTP is improved, the reaction time is shortened, and the catalyst is easy to separate and recover, and has stable performance for repeated use.

[0028] (2) Adding chloroform to the system, together with the composite catalyst, can further shorten the reaction time and reduce the reaction temperature, so that the reaction can be carried out under mild conditions and reduce the difficulty of preparation.

[0029] (3) DOTP can be prepared in one step using PET waste plastic. The preparation process is simple, the product is easy to separate and purify, the production cost of DOTP is reduced, and waste can be reused. This is in line with the development concept of circular economy and green environmental protection and is easy to promote and apply in industry. Specific implementation methods

[0030] The technical solution and its effects of the present invention will be described in detail below with reference to specific embodiments. The embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following embodiments.

[0031] Unless otherwise specified, the experimental methods used in the following examples are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following examples were purchased from conventional biochemical reagent stores.

[0032] In this invention, the preparation method of [Bmim]Cl is as follows: Chlorobutane and 1-methylimidazole in a molar ratio of 1.2:1 are added to a round-bottom flask equipped with a reflux condenser. The mixture is magnetically stirred and refluxed at 70°C for 48-72 hours to remove the top layer of unreacted material. Acetone is then added and thoroughly mixed. The culture flask is then frozen in a refrigerator for 24 hours to form [Bmim]Cl crystals. The liquid phase containing unreacted material and acetone is decanted, and fresh acetone is added. This step is repeated twice. After a third decantation of acetone, the remaining acetone is evaporated using a rotary evaporator to obtain the product [Bmim]Cl, which is then vacuum dried at 70°C for 48 hours. The preparation of [Bmim]Br involves replacing bromobutane with chlorobutane, and the process is similar.

[0033] PET conversion rate = (initial PET addition amount - mass of PET remaining after degradation) / initial PET addition mass × 100%.

[0034] DOTP yield = (mass of DOTP obtained / molecular weight of DOTP) / (mass of PET / molecular weight of PET) × 100%.

[0035] Example 1

[0036] Zinc acetate and [Bmim]Cl were mixed at a molar ratio of 1:4 and stirred at 70℃ and 500 rpm for 6 h to obtain the [Bmim]Cl-(CH3COO)2Zn composite catalyst.

[0037] Before use, the collected PET plastic bottles were washed, dried, and cut into small pieces less than 10 mm in size. 5 g of PET bottle pieces, 20 g of isooctanol, and 2.5 g of composite catalyst were mixed and reacted at 190 °C, 1 atm, and 500 rpm for 4 hours to obtain a mixture.

[0038] The mixture was cooled to room temperature and filtered. The filtrate was mixed with deionized water at a volume ratio of 1:5, and allowed to stand for separation. The upper organic phase was distilled under reduced pressure at 180℃ and 0.001 MPa for 3 hours to recover chloroform and isooctyl alcohol for reuse. Activated carbon was added to the crude product, and it was decolorized at 80℃ for 2 hours. After cooling and filtration to remove the activated carbon, the product was further purified using a SiO2 column to obtain the final product DOTP. The lower phase was distilled under reduced pressure at 50℃ and 0.003 MPa for 3 hours to remove water and ethylene glycol, yielding a composite catalyst for recycling.

[0039] Testing showed that the conversion rate of PET was 97.3% and the yield of DOTP was 92.2%. After the composite catalyst was recycled 5 times, the conversion rate of PET remained above 96.1% and the yield of DOTP remained above 91%.

[0040] Example 2

[0041] Similar to Example 1, except that: manganese chloride was used as the metal salt, [Bmim]Br was used as the ionic liquid, and the composite catalyst was obtained by stirring at 80°C and 500 rpm for 4 hours. The mixture was prepared by reacting at 195°C for 4 hours.

[0042] Testing showed that the conversion rate of PET was 96.5% and the yield of DOTP was 91.6%. After the composite catalyst was recycled five times, the conversion rate of PET remained above 95.2% and the yield of DOTP remained above 90%.

[0043] Example 3

[0044] Same as Example 1, except that: ferric chloride was used as the metal salt, and [Bmim]Cl and [Bmim]Br were used as the ionic liquids in a volume ratio of 1:1. The mixture was stirred at 60°C and 500 rpm for 8 hours to obtain the composite catalyst. The mixture was prepared by reacting at 200°C for 4 hours.

[0045] Testing showed that the conversion rate of PET was 96.4% and the yield of DOTP was 91.9%. After the composite catalyst was recycled five times, the conversion rate of PET remained above 95% and the yield of DOTP remained above 90.9%.

[0046] Example 4

[0047] Same as Example 1, except that chloroform was added to the reaction system, with a mass ratio of chloroform to PET waste plastic of 1:1. The mixture was prepared by reacting at 180°C for 3 hours.

[0048] Testing showed that the conversion rate of PET was 99.9% and the yield of DOTP was 93.4%. After the composite catalyst was recycled 5 times, the conversion rate of PET remained above 97.2% and the yield of DOTP remained above 92.0%.

[0049] Example 5

[0050] Same as Example 3, except that chloroform was added to the reaction system, with a mass ratio of chloroform to PET waste plastic of 1.5:1. The mixture was prepared by reacting at 185°C for 3 hours.

[0051] Testing showed that the conversion rate of PET was 98.1% and the yield of DOTP was 93.1%. After the composite catalyst was recycled 5 times, the conversion rate of PET remained above 96.3% and the yield of DOTP remained above 91.7%.

[0052] Comparative Example 1

[0053] Similar to Example 1, except that the composite catalyst is a mixture of metal salt and ionic liquid. The mixture was prepared by reacting at 215°C for 4 hours.

[0054] Testing revealed that the PET conversion rate was 94.6%, and the DOTP yield was 81.8%. After the composite catalyst was recycled five times, the PET conversion rate dropped to 91.3%, and the DOTP yield fell below 80%.

[0055] Comparative Example 2

[0056] Similar to Example 4, except that the composite catalyst was directly a mixture of metal salt, ionic liquid, and chloroform. The mixture was prepared by reacting at 210°C for 4 hours.

[0057] Testing revealed that the PET conversion rate was 95.3%, and the DOTP yield was 82.9%. After the composite catalyst was recycled five times, the PET conversion rate dropped to 92.6%, and the DOTP yield fell below 81.5%.

Claims

1. A method for preparing DOTP from waste PET plastic, characterized in that... The following contents are included: (1) Mixing metal salt with imidazole ionic liquid and stirring at 60-80℃ to obtain composite catalyst; (2) Mixing PET waste plastic, isooctanol and composite catalyst to obtain mixed liquid; (3) Cooling and filtering the mixed liquid, mixing the filtrate with deionized water, letting it stand to separate into layers, obtaining crude product by vacuum distillation of the upper organic phase, and then purifying it to obtain final DOTP.

2. The method according to claim 1, characterized in that: The metal salt mentioned in step (1) is one or more of zinc acetate, zinc chloride, manganese chloride, and ferric chloride, preferably zinc acetate.

3. The method according to claim 1, characterized in that: The imidazole ionic liquid mentioned in step (1) is at least one of 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) and 1-butyl-3-methylimidazolium bromide ([Bmim]Br), preferably [Bmim]Cl.

4. The method according to claim 1, 2 or 3, characterized in that: The molar ratio of the metal salt to the imidazole ionic liquid in step (1) is 1:1-8.

5. The method according to claim 1, characterized in that: Step (1) The reaction is stirred at 300-800 rpm at 60-80℃ for 4-8 hours.

6. The method according to claim 1, characterized in that: The PET waste plastic mentioned in step (2) is selected from one or more of waste PET bottle flakes, PET fibers, and PET films; preferably, it is washed, dried, and cut before use, and the size is less than 10mm.

7. The method according to claim 1 or 6, characterized in that: In step (2), the mass ratio of isooctyl alcohol to PET waste plastic is 2-8:1, preferably 3-5:

1.

8. The method according to claim 1 or 6, characterized in that: In step (2), the mass ratio of the composite catalyst to PET waste plastic is 0.1-1:1, preferably 0.4-0.6:

1.

9. The method according to claim 1, characterized in that: Step (2) Add chloroform to the reaction system. The mass ratio of chloroform to PET waste plastic is 0.5-1.5:

1.

10. The method according to claim 1 or 9, characterized in that: The reaction temperature in step (2) is 170-210℃, preferably 180-200℃, and the reaction time is 1-7h, preferably 3-5h; the reaction pressure is 1-2atm; and the stirring rate is 500-1500 rpm.

11. The method according to claim 1, characterized in that: Step (3) Cool the mixture to room temperature and filter it by suction filtration and pressure filtration. Mix the filtrate with deionized water at a volume ratio of 1:3-15, preferably 1:5-8. After standing and separating the layers, distill the upper organic phase under reduced pressure at 140-200℃ and 0.001-0.002MPa for 2-5 hours to obtain the crude product. Remove chloroform and isooctyl alcohol from the crude product by reduced pressure distillation and reuse it in step (2).

12. The method according to claim 1, characterized in that: After step (3) is allowed to stand and separate into layers, the lower aqueous phase mainly contains catalyst and ethylene glycol. Water and ethylene glycol are removed by vacuum distillation, and the obtained composite catalyst is recovered for recycling. Vacuum distillation is carried out at 50-60℃ and 0.003-0.0035MPa for 2-6 hours to obtain ethylene glycol.

13. The method according to claim 1, characterized in that: The crude product in step (3) is first decolorized with activated carbon at 60-100℃ for 2-4 hours; then it can be further purified with a SiO2 chromatographic column to obtain the final DOTP product.