A method for preparing a plasticizer of terephthalic acid di(2-ethyl)hexyl ester using waste polyethylene terephthalate

Abstract

The application discloses a method for preparing terephthalic acid di(2-ethyl)hexyl ester plasticizer by using waste polyethylene terephthalate, and belongs to the technical field of plasticizer preparation. The method uses waste polyethylene terephthalate and 2-ethylhexanol to carry out ester exchange reaction, obtains terephthalic acid di(2-ethyl)hexyl ester and ethylene glycol, and removes ethylene glycol by adding C8-C9 azeotrope in the reaction system. The method adds C8-C9 azeotrope in the reaction system, quickly removes EG, promotes the balance movement of waste PET in the ester exchange process, shortens the reaction time from 8-18 hours of the original process to 1-4 hours, greatly reduces the energy consumption, and strengthens the process intensification degree. Meanwhile, when the terephthalic acid di(2-ethyl)hexyl ester plasticizer is prepared by the method, the water washing process can be omitted in the EG separation step, so that the EG rectification in the later stage is carried out under water-free conditions, and the purification difficulty of EG is reduced.

Description

Technical Field

[0001] This invention belongs to the field of plasticizer preparation technology, and in particular relates to a method for preparing di(2-ethylhexyl) terephthalate plasticizer using waste polyethylene terephthalate. Background Technology

[0002] PET (polyethylene terephthalate) is widely used in the packaging industry, such as in beverage bottles, food packaging, daily chemical product packaging, polyester in the textile industry, industrial fibers, cable insulation in the electronics industry, and interior and plastic parts in the automotive industry. The large-scale application of polyester materials generates a significant amount of waste PET. Converting waste PET materials into the plasticizer DOTP is an important method for waste recycling.

[0003] DOTP (dioctyl terephthalate) plasticizer is known as a green plasticizer due to its advantages such as a higher boiling point, lower volatility, and lower dissolution rate than DOP (dioctyl phthalate). It can replace DOP in many plasticizer processing applications, and its market potential is gradually increasing.

[0004] Currently, there are two methods for producing DOTP: one is to directly esterify terephthalic acid with 2-ethylhexanol (2-EH); the other is to use waste PET and 2-ethylhexanol for transesterification under a catalyst to obtain DOTP and ethylene glycol (EG).

[0005] Currently, there are two routes for transesterification of waste PET: 1. Pure 2-ethylhexanol (2-EH) stripping method (e.g., CN101139293A): The traditional process uses excess 2-EH vapor to remove EG. However, since 2-EH and EG cannot form an azeotrope, and its boiling point (185℃) is lower than EG (197℃), the stripping efficiency is extremely low. To ensure the reaction rate, long-term high-temperature (>210℃) operation is often required, leading to product oxidation and yellowing, and a large amount of 2-EH is lost at the top of the column. In addition, after EG is removed by 2-EH, a one-step water washing method is required to separate EG, resulting in 2-EH being lost into the wastewater. After EG is dissolved in water, distillation is energy-intensive and costly. 2. Ionic liquid / supercritical method (e.g., CN105254503B, CN102617352A): Although the reaction rate is fast, the equipment is expensive, and the recovery of ionic liquid is difficult, making large-scale industrialization difficult. Summary of the Invention

[0006] To address the problems of excessive use of 2-EH, limited azeotropic carry-over capacity between 2-EH and EG, low EG removal rate, high reaction temperature, long reaction time, high product color, and high energy consumption in the existing transesterification process of waste PET and 2-ethylhexanol to prepare di(2-ethylhexyl) terephthalate plasticizer, this invention provides a method for preparing di(2-ethylhexyl) terephthalate plasticizer using waste polyethylene terephthalate. This invention enhances EG removal technology, shifting the equilibrium of the transesterification reaction of waste PET and 2-ethylhexanol to the right, significantly shortening the reaction time, improving conversion efficiency, reducing product color, and saving reaction steam.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A method for preparing di(2-ethylhexyl) terephthalate plasticizer using waste polyethylene terephthalate involves transesterifying waste polyethylene terephthalate with 2-ethylhexanol to obtain di(2-ethylhexyl) terephthalate and ethylene glycol, and removing ethylene glycol by adding a C8-C9 azeotropic agent to the reaction system.

[0008] Furthermore, the specific preparation process of the method for preparing di(2-ethylhexyl) terephthalate plasticizer using waste polyethylene terephthalate includes the following steps: adding waste polyethylene terephthalate, 2-ethylhexanol and C8-C9 azeotropic agent to a reaction vessel, adding a catalyst after heating, continuing to heat the reaction to obtain azeotropic vapor, condensing the azeotropic vapor and allowing it to naturally separate into layers to obtain ethylene glycol and C8-C9 azeotropic agent, returning the C8-C9 azeotropic agent to the reaction vessel, stopping the reaction when the amount of ethylene glycol obtained reaches the theoretical amount, then recovering the C8-C9 azeotropic agent and unreacted 2-ethylhexanol from the reaction vessel, and purifying the obtained crude di(2-ethylhexyl) terephthalate.

[0009] This invention introduces a C8-C9 azeotropic agent into the reaction system. The C8-C9 azeotropic agent will form an azeotrope with EG (ethylene glycol), increasing the vapor pressure of EG. By removing the azeotropic vapors of the C8-C9 azeotropic agent and EG, the mixture is separated in the water separator of the reactor, and EG is separated in the lower layer. This enhances the removal of EG and shifts the reaction equilibrium to the right, thereby significantly shortening the reaction time and improving the reaction efficiency.

[0010] Furthermore, the content of polyethylene terephthalate in the waste polyethylene terephthalate is 85 wt.%.

[0011] Further, the C8-C9 azeotropic agent includes one or more of m-xylene, o-xylene, p-xylene, ethylbenzene, 1,2,3-trimethylbenzene, 1,3,5-trimethylbenzene, 1,2,4-trimethylbenzene, cumene, 2-ethyltoluene, 3-ethyltoluene, and 4-ethyltoluene; the catalyst includes one or more of isopropyl titanate, butyl titanate, zinc acetate, and titanium dioxide.

[0012] Furthermore, the C8-C9 azeotropic agent is selected from 1,2,4-trimethylbenzene.

[0013] C8-C9 solvents can form an azeotrope with ethylene glycol. Among them, trimethylbenzene has a high boiling point, which is more conducive to increasing the reaction temperature and shortening the reaction time, while 1,2,4-trimethylbenzene is the cheapest, which helps to reduce costs.

[0014] Further, the mass ratio of the waste polyethylene terephthalate to 2-ethylhexanol is 1:(1-2); the mass ratio of the waste polyethylene terephthalate to C8-C9 azeotropic agent is 1:(0.1-0.15); and the mass ratio of the waste polyethylene terephthalate to the catalyst is 1:(0.005-0.02).

[0015] Furthermore, the temperature increase is to 160-180℃.

[0016] Furthermore, the time from adding the catalyst after heating to stopping the reaction is 1-4 hours.

[0017] Compared with the prior art, the present invention has the following advantages and technical effects: This invention provides a method for preparing di(2-ethylhexyl) terephthalate plasticizer from waste polyethylene terephthalate (PET). By adding a C8-C9 azeotropic agent to the reaction system, EG is rapidly removed, promoting the equilibrium shift of waste PET during transesterification. This reduces the reaction time from the original 8-18 hours to 1-4 hours, significantly lowering energy consumption and enhancing process efficiency. Furthermore, the method eliminates the need for water washing during EG separation, allowing subsequent EG distillation to be carried out under anhydrous conditions, thus reducing the difficulty of EG purification. Detailed Implementation

[0018] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0019] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0020] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0021] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0022] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0023] This invention provides a method for preparing di(2-ethylhexyl) terephthalate plasticizer using waste polyethylene terephthalate. The method involves transesterifying waste polyethylene terephthalate with 2-ethylhexanol to obtain di(2-ethylhexyl) terephthalate and ethylene glycol. Ethyl glycol is removed by adding a C8-C9 azeotropic agent to the reaction system. The preparation method provided by this invention can shorten the reaction time, improve reaction efficiency, reduce steam energy consumption, and obtain a low-color DOTP plasticizer. The specific preparation process includes the following steps: waste polyethylene terephthalate, 2-ethylhexanol and C8-C9 azeotropic agent are added to the reaction vessel, a catalyst is added after heating, and the reaction is continued to obtain azeotropic vapor. The azeotropic vapor is condensed and naturally separated to obtain ethylene glycol and C8-C9 azeotropic agent. The C8-C9 azeotropic agent is returned to the reaction vessel. When the amount of ethylene glycol obtained reaches the theoretical amount, the reaction is stopped. Then, the C8-C9 azeotropic agent and unreacted 2-ethylhexanol in the reaction vessel are recovered. The obtained crude product di(2-ethylhexyl) terephthalate is purified.

[0024] In some preferred embodiments of the present invention, the C8-C9 azeotropic agent includes one or more of m-xylene, o-xylene, p-xylene, ethylbenzene, 1,2,3-trimethylbenzene, 1,3,5-trimethylbenzene, 1,2,4-trimethylbenzene, cumene, 2-ethyltoluene, 3-ethyltoluene, and 4-ethyltoluene; the catalyst includes one or more of isopropyl titanate, butyl titanate, zinc acetate, and titanium dioxide. Exemplarily, the C8-C9 azeotropic agent is selected from 1,2,4-trimethylbenzene or xylene.

[0025] In some preferred embodiments of the present invention, the mass ratio of the waste polyethylene terephthalate to 2-ethylhexanol is 1:(1-2); for example, the mass ratio of the waste polyethylene terephthalate to 2-ethylhexanol is 1:1 or 1:2.

[0026] The mass ratio of the waste polyethylene terephthalate to the C8-C9 azeotropic agent is 1:(0.1-0.15); for example, the mass ratio of the waste polyethylene terephthalate to the C8-C9 azeotropic agent is 1:0.1 or 1:0.15.

[0027] The mass ratio of the waste polyethylene terephthalate to the catalyst is 1:(0.005-0.02). For example, the mass ratio of the waste polyethylene terephthalate to the catalyst is 1:0.005 or 1:0.02.

[0028] In some preferred embodiments of the present invention, the temperature rise is to 160-180°C, for example, the temperature rise is to 160°C or 180°C.

[0029] In some preferred embodiments of the present invention, the time from adding the catalyst after heating to stopping the reaction is 1-4 hours. For example, the time from adding the catalyst after heating to stopping the reaction is 1 hour, 2 hours or 4 hours.

[0030] To facilitate understanding, the following explanations will first cover several technical terms.

[0031] This invention employs the platinum-cobalt colorimetric method to evaluate the color intensity of the prepared di(2-ethylhexyl) terephthalate. The measurement principle is as follows: 1 mg / mL of platinum chloroplatinic acid is dissolved in water to form a standard solution, and its colorimetric value is defined as 500. By diluting this standard solution, a series of standard color levels from 0 to 500 can be obtained. The closer the color of the tested sample is to a certain standard color level, the higher its colorimetric value. In the quality indicators of chemical products (especially the plasticizer DOTP), a lower colorimetric value indicates a lighter product color and higher quality.

[0032] Unless otherwise specified, all materials used in this invention are commercially available products.

[0033] In the examples and comparative examples, the content of polyethylene terephthalate in the waste polyethylene terephthalate was 85 wt.%.

[0034] Example 1 At 5m 3 1000 kg of granulated waste PET, 1000 kg of 2-EH (2-ethylhexanol), and 100 kg of 1,2,4-trimethylbenzene were added to a reactor (equipped with a water separator). The temperature was raised to 180°C, and 5 kg of tetrabutyl titanate was added. The reaction was continued under heating (the temperature was controlled by the amount of EG produced, the same below). The azeotropic vapors of 1,2,4-trimethylbenzene and EG were obtained by condensation through the water separator and naturally separated into layers. The lower layer of EG was separated, and the upper layer of 1,2,4-trimethylbenzene was returned to the reactor. After 2 hours, a total of 274 kg of EG was obtained. The reaction was stopped, and the 1,2,4-trimethylbenzene and unreacted 2-EH in the reactor were distilled off under reduced pressure. The 1,2,4-trimethylbenzene and 2-EH were recycled. The crude product DOTP (di(2-ethylhexyl) terephthalate) obtained in the reactor was transferred to a vacuum distillation vessel equipped with activated carbon. The product DOTP was obtained by high-vacuum distillation. 1691 kg, with a yield of 98% based on pure PET, and a color (platinum-cobalt) number of 42.

[0035] Example 2 At 5m 3 1000 kg of granulated waste PET, 1000 kg of 2-EH, and 100 kg of p-xylene were added to a reactor (equipped with a water separator). The temperature was raised to 160°C, and 5 kg of isopropyl titanate was added. The reaction was continued under heating. The azeotropic vapors of p-xylene and EG were condensed through the water separator and naturally separated into layers. The lower layer of EG was separated, and the upper layer of p-xylene was returned to the reactor. After 4 hours, a total of 270 kg of EG was obtained. The reaction was stopped, and the xylene and unreacted 2-EH in the reactor were distilled off under reduced pressure. The 1,2,4-trimethylbenzene and 2-EH were recycled. The crude DOTP obtained in the reactor was transferred to a vacuum distillation vessel equipped with activated carbon. 1670 kg of DOTP was distilled off under high vacuum, with a yield of 97% based on pure PET. Its color (platinum-cobalt) number was 38.

[0036] Example 3 At 5m 31000 kg of granulated waste PET, 1000 kg of 2-EH, and 150 kg of 1,2,4-trimethylbenzene were added to a reactor (equipped with a water separator). The temperature was raised to 180°C, and 5 kg of tetrabutyl titanate was added. The reaction was continued under heating. The azeotropic vapors of 1,2,4-trimethylbenzene and EG were condensed through the water separator and naturally separated into layers. The lower layer of EG was separated, and the upper layer of 1,2,4-trimethylbenzene was returned to the reactor. After 1 hour, a total of 275 kg of EG was obtained. The reaction was stopped, and the 1,2,4-trimethylbenzene and unreacted 2-EH in the reactor were distilled off under reduced pressure. The 1,2,4-trimethylbenzene and 2-EH were recycled. The crude DOTP obtained in the reactor was transferred to a vacuum distillation vessel equipped with activated carbon. 1699 kg of DOTP was distilled off under high vacuum, with a yield of 98.5% based on pure PET and a color (platinum-cobalt) number of 40.

[0037] Example 4 At 5m 3 1000 kg of granulated waste PET, 2000 kg of 2-EH and 100 kg of 1,2,4-trimethylbenzene were added to a reactor (equipped with a water separator). The temperature was raised to 180°C, and 5 kg of tetrabutyl titanate was added. The reaction was continued under heating. The azeotropic vapors of 1,2,4-trimethylbenzene and EG were condensed through the water separator and naturally separated into layers. The lower layer of EG was separated, and the upper layer of 1,2,4-trimethylbenzene was returned to the reactor. After 1 hour, a total of 268 kg of EG was obtained. The reaction was stopped, and the 1,2,4-trimethylbenzene and unreacted 2-EH in the reactor were distilled off under reduced pressure. The 1,2,4-trimethylbenzene and 2-EH were recycled. The crude DOTP obtained in the reactor was transferred to a vacuum distillation vessel equipped with activated carbon. 1656 kg of DOTP was distilled off under high vacuum, with a yield of 96.0% based on pure PET and a color (platinum-cobalt) number of 39.

[0038] Example 5 At 5m 3 1000 kg of granulated waste PET, 1000 kg of 2-EH, and 150 kg of 1,2,4-trimethylbenzene were added to a reactor (equipped with a water separator). The temperature was raised to 180°C, and 20 kg of tetrabutyl titanate was added. The reaction was continued under heating. The azeotropic vapors of 1,2,4-trimethylbenzene and EG were condensed through the water separator and naturally separated into layers. The lower layer of EG was separated, and the upper layer of 1,2,4-trimethylbenzene was returned to the reactor. After 1 hour, a total of 270 kg of EG was obtained. The reaction was stopped, and the 1,2,4-trimethylbenzene and unreacted 2-EH in the reactor were distilled off under reduced pressure. The 1,2,4-trimethylbenzene and 2-EH were recycled. The crude DOTP obtained in the reactor was transferred to a vacuum distillation vessel equipped with activated carbon. 1680 kg of DOTP was distilled off under high vacuum, with a yield of 97.4% based on pure PET and a color (platinum-cobalt) number of 42.

[0039] Comparative Example 1 At 5m 3 1000 kg of granulated waste PET and 2000 kg of 2-EH were added to a reactor (equipped with a water separator). The temperature was raised to 180°C, and 5 kg of tetrabutyl titanate was added. The reaction was continued under heating. The mixture of EG and 2-EH was continuously separated by the water separator and sent to a water washing device. The upper layer of 2-EH was returned to the reactor, and the lower layer was washed with water to obtain EG. After 8 hours, 258 kg of EG was obtained. The reaction was stopped, and the unreacted 2-EH was distilled off. The crude DOTP obtained in the reactor was transferred to a vacuum distillation vessel, and 1650 kg of DOTP was distilled off under high vacuum. The yield was 95.6% based on pure PET, and its color (platinum-cobalt) number was 62.

[0040] Comparing Examples 1-3 and Comparative Example 1, it can be seen that the method for preparing di(2-ethylhexyl) terephthalate plasticizer using waste polyethylene terephthalate provided by the present invention has a short reaction time, with the optimal reaction time being 1 hour. Furthermore, the EG removal process using the method provided by the present invention eliminates the need for a water washing and separation step. Due to the short reaction time, the final product DOTP has a short residence time at high temperature, reducing the degree of oxidation. The color number of the final product DOTP is lower than that of the DOTP obtained in Comparative Example 1, indicating higher product purity. Simultaneously, the short reaction time significantly saves steam.

[0041] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing di(2-ethylhexyl) terephthalate plasticizer from waste polyethylene terephthalate, characterized in that, Waste polyethylene terephthalate was subjected to transesterification with 2-ethylhexanol to obtain di(2-ethylhexyl) terephthalate and ethylene glycol. Ethyl glycol was removed by adding a C8-C9 azeotropic agent to the reaction system.

2. The method for preparing di(2-ethylhexyl) terephthalate plasticizer from waste polyethylene terephthalate according to claim 1, characterized in that, The specific preparation process includes the following steps: waste polyethylene terephthalate, 2-ethylhexanol and C8-C9 azeotropic agent are added to the reaction vessel, a catalyst is added after heating, and the reaction is continued to obtain azeotropic vapor. The azeotropic vapor is condensed and naturally separated to obtain ethylene glycol and C8-C9 azeotropic agent. The C8-C9 azeotropic agent is returned to the reaction vessel. When the amount of ethylene glycol obtained reaches the theoretical amount, the reaction is stopped. Then, the C8-C9 azeotropic agent and unreacted 2-ethylhexanol in the reaction vessel are recovered. The obtained crude product di(2-ethylhexyl) terephthalate is purified.

3. The method for preparing di(2-ethylhexyl) terephthalate plasticizer from waste polyethylene terephthalate according to claim 2, characterized in that, The waste polyethylene terephthalate contains 85 wt.% polyethylene terephthalate.

4. The method for preparing di(2-ethylhexyl) terephthalate plasticizer using waste polyethylene terephthalate according to claim 2, characterized in that, The C8-C9 azeotropic agent includes one or more of m-xylene, o-xylene, p-xylene, ethylbenzene, 1,2,3-trimethylbenzene, 1,3,5-trimethylbenzene, 1,2,4-trimethylbenzene, cumene, 2-ethyltoluene, 3-ethyltoluene, and 4-ethyltoluene; the catalyst includes one or more of isopropyl titanate, butyl titanate, zinc acetate, and titanium dioxide.

5. The method for preparing di(2-ethylhexyl) terephthalate plasticizer from waste polyethylene terephthalate according to claim 3, characterized in that, The C8-C9 azeotropic agent is selected from 1,2,4-trimethylbenzene.

6. The method for preparing di(2-ethylhexyl) terephthalate plasticizer from waste polyethylene terephthalate according to claim 2, characterized in that, The mass ratio of the waste polyethylene terephthalate to 2-ethylhexanol is 1:(1-2). The mass ratio of the waste polyethylene terephthalate to the C8-C9 azeotropic agent is 1:(0.1-0.15). The mass ratio of the waste polyethylene terephthalate to the catalyst is 1:(0.005-0.02).

7. The method for preparing di(2-ethylhexyl) terephthalate plasticizer using waste polyethylene terephthalate according to claim 2, characterized in that, The temperature increase refers to raising the temperature to 160-180℃.

8. The method for preparing di(2-ethylhexyl) terephthalate plasticizer from waste polyethylene terephthalate according to claim 2, characterized in that, The time from adding the catalyst after heating to stopping the reaction is 1-4 hours.