Method for improving color value of semi-gloss polyester chip recycled by chemical method

Abstract

The invention discloses a method for improving the color value of a semi-gloss polyester chip recycled by a chemical method, and belongs to the technical field of chips. Comprising the following steps: (1) adding DMT and EG, increasing the temperature of a kettle, and then adding an ester exchange catalyst to carry out ester exchange reaction; (2) heating the obtained BHET solution after the transesterification reaction, adding a stabilizer at 218-22DEG C, stirring for a period of time at 220-225 DEG C, adding a polymerization catalyst, a color correcting agent, a matting agent and a mixed toner, and continuously heating to distill redundant EG; (3) after distillation of EG is finished, carrying out two-stage vacuumizing treatment, and meanwhile, continuously increasing the temperature in the kettle until the polymerization reaction is finished; and (4) discharging, cooling, pelletizing and drying to obtain slices. According to the regenerated semi-gloss polyester chip prepared by the invention, the b value of the semi-gloss polyester chip is greatly improved on the basis of keeping the performance of the conventional regenerated semi-gloss polyester chip, and the regenerated semi-gloss polyester chip has a great effect on improving the whiteness of polyester fibers and the like.

Description

Technical Field

[0001] The invention relates to the technical field of polyester chips, and more specifically to a method for improving the color value of chemically recycled semi-gloss polyester chips. Background Art

[0002] The annual output of waste textiles in China exceeds 20 million tons, and the comprehensive utilization rate of waste textiles is only about 15%. Most old clothes are treated as garbage and eventually landfilled or incinerated. This not only causes a waste of energy but also has a certain impact on the environment. According to the calculation of the China National Textile and Apparel Council, if all waste textiles in my country can be recycled, it is equivalent to saving 24 million tons of crude oil and reducing 80 million tons of carbon dioxide emissions each year.

[0003] At present, physical, chemical and bio-based methods are used to degrade polyester textiles and bottle chips and synthesize them into products again, forming a recycling system. The chemical method is to decompose the macromolecular PET into small molecules through a depolymerization process, and then polymerize them to obtain polyester chips. Due to the complex source of raw materials for the chemical method, the color value of the chips produced by polymerization is poor. Although the yellow-green color of the chips can be corrected by colorants, it will also affect the L value while reducing the b value of the polyester chips, making it difficult to meet the color value requirements of downstream customers. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art and provide a method for improving the color value of chemically recycled semi-bright polyester chips. On the basis that the performance data of the recycled semi-bright polyester chips prepared by the method are basically consistent with the performance data before the improvement, the b value of the recycled semi-bright polyester chips is reduced to make them whiter, which has a certain effect on improving the whiteness of polyester fibers, saving process costs and resource waste. The present invention realizes the recycling of waste resources and improves the color value quality of recycled polyester products.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A method for improving the color value of chemically recycled semi-gloss polyester chips, comprising the following steps:

[0007] (1) DMT and EG prepared by chemical recycling are added into a polymerization reactor, and after the reactor temperature is raised, an ester exchange catalyst is added to carry out an ester exchange reaction, and methanol is precipitated as a reactant during the reaction;

[0008] (2) After the transesterification reaction, the BHET solution obtained by the transesterification reaction is heated continuously. When the temperature in the kettle reaches 218-222°C, a stabilizer is added, and the mixture is stirred for a period of time at a temperature of 220-225°C. Then, a polymerization catalyst, a positive color agent, a matting agent and a mixed toner are added, and the temperature is continued to be raised to distill out the excess EG;

[0009] (3) After the EG is distilled, two stages of vacuum treatment are performed, and the temperature in the reactor is continuously increased until the polymerization reaction is completed;

[0010] (4) After the polymerization reaction is completed, the polyester liquid in the polymerization kettle is discharged by nitrogen pressure, and after cooling, pelletizing and drying, chemically recycled semi-gloss polyester chips with improved color value are obtained.

[0011] The present invention is further configured such that, in step (1), the mass ratio of DMT, EG, and ester exchange catalyst is 750:(430-460):(10-15).

[0012] The present invention is further configured such that the transesterification catalyst is manganese acetate.

[0013] The present invention is further configured such that the kettle temperature is maintained at 160-165° C. when the transesterification catalyst is added.

[0014] The present invention is further configured such that, in step (1), the transesterification reaction starts at 175-185° C. and methanol is precipitated, and the transesterification reaction pressure is normal pressure; the transesterification reaction reaches an end point when the methanol distillation volume reaches 300 ml.

[0015] The present invention is further configured such that the mass ratio of the polymerization catalyst, stabilizer, positive color agent, matting agent, mixed colorant in step (2) to the DMT in step (1) is (17-22): (0.4-0.8): (0.3-0.7): (9-13): (0.13-0.18): 750.

[0016] The present invention is further configured as follows: in step (2), the stabilizer is trimethyl phosphate; the polymerization catalyst is antimony ethylene glycol; the positive color agent is cobalt acetate; the matting agent is titanium dioxide; the mixed colorant is a mixed solution of phosphate, colorant, EG and silane coupling agent, wherein the colorant is a combination of solvent red and solvent blue.

[0017] The present invention is further configured as follows: phosphate ester, colorant, EG and silane coupling agent are stirred and mixed at a mass ratio of 4:20:100:1 at 80-120°C to obtain a mixed toner; the mass ratio of solvent red to solvent blue in the toner is 1:2-3.5, and the silane coupling agent is one of KH550, KH560 and n-dodecyltrimethoxysilane.

[0018] The present invention is further configured such that, in step (2), the temperature is raised to 230-240° C. for EG distillation, and the EG distillation time is 20-40 minutes.

[0019] The present invention is further configured such that, in step (3), the temperature is raised to 242-245°C and low vacuum is started, and the low vacuum time is controlled to be 40 minutes. After the kettle temperature rises to 267-270°C, high vacuum is started to be drawn to 5-10Pa, the final temperature of the polymerization reaction is controlled at 285-287°C, and the total reaction time of the polymerization reaction is 1.5-2 hours.

[0020] In summary, the present invention has the following beneficial effects:

[0021] PET chips are prepared by the DMT method using high-quality DMT, a chemically recycled product, as raw material. Through process improvement and the addition of a small amount of phosphate ester, silane coupling agent and mixed colorant, the b value of the chips is reduced while the L value is less affected, which helps to improve the whiteness of the fiber and reduce resource waste. The mixture of phosphate ester, colorant and silane coupling agent has a synergistic effect and can improve the temperature resistance of the chips. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] The method for improving the color value of chemically recycled semi-gloss polyester chips of the present invention comprises the following steps:

[0024] (1) DMT and EG prepared by chemical recycling are added into a polymerization reactor, and the reactor temperature is raised to 160-165° C., and then an ester exchange catalyst (preferably manganese acetate) is added, and then the temperature is raised to 175-185° C. and an ester exchange reaction is carried out under normal pressure. During the reaction, methanol is precipitated as a reactant. When the amount of methanol distilled reaches 300 ml, the ester exchange reaction reaches an end point;

[0025] The DMT prepared by chemical recycling is obtained by existing technology, see steps ① to ⑦ of Example 1 of the patent "A production process for antimony-free recycled polyester chips" (application number CN201811226519.6) for details.

[0026] (2) After the transesterification reaction, the BHET solution obtained by the transesterification reaction is heated continuously. When the temperature in the kettle reaches 218-222°C, a stabilizer is added. The mixture is stirred for a period of time (20-30 minutes) at a temperature in the kettle of 220-225°C. Then, a polymerization catalyst, a positive color agent, a matting agent and a mixed toner are added. The temperature is then continued to be raised to 230-240°C to distill out the excess EG. The EG distillation time is 20-40 minutes.

[0027] The mass ratio of DMT, EG, ester exchange catalyst in step (1) to polymerization catalyst, stabilizer, positive color agent, matting agent, mixed colorant in step (2) is 750: (430-460): (10-15): (17-22): (0.4-0.8): (0.3-0.7): (9-13): (0.13-0.18).

[0028] The stabilizer is preferably trimethyl phosphate; the polymerization catalyst is preferably antimony ethylene glycol; the positive color agent is preferably cobalt acetate; and the matting agent is preferably titanium dioxide.

[0029] The mixed toner is a mixture of phosphate, toner, EG and silane coupling agent (prepared by stirring and mixing at 80-120°C), the mass ratio of phosphate, toner, EG and silane coupling agent is preferably 4:20:100:1, wherein the toner is a composition of solvent red and solvent blue (the mass ratio of solvent red and solvent blue is preferably 1:2-3.5); the silane coupling agent is one of KH550, KH560 and n-dodecyltrimethoxysilane. Phosphate can improve the dispersion effect of toner, increase the temperature resistance of slices, and reduce thermal degradation and oxidation during the reaction process; the addition of coupling agent can improve the compatibility and bonding effect between toner and polyester; the addition of toner can effectively improve the b value of chemically regenerated semi-gloss polyester slices.

[0030] (3) After the distillation of EG is completed, two-stage vacuum treatment is carried out, and the temperature in the kettle is continuously raised until the polymerization reaction is completed; wherein, low vacuum is started when the temperature is raised to 242-245°C, and the low vacuum time is controlled to be 40 minutes. After the kettle temperature rises to 267-270°C, high vacuum is started to be drawn to 5-10Pa. The final temperature of the polymerization reaction is controlled at 285-287°C, and the total reaction time of the polymerization reaction is 1.5-2 hours.

[0031] (4) After the polymerization reaction is completed, the polyester liquid in the polymerization kettle is discharged by nitrogen pressurization (nitrogen pressurization pressure is 0.1-0.15MPa), and after cooling, pelletizing and drying, chemically recycled semi-gloss polyester chips with improved color value are obtained.

[0032] The preferred embodiments are as follows:

[0033] Example 1

[0034] (1) DMT and EG prepared by chemical recycling are added, the temperature is gradually raised to 160° C., manganese acetate is added into the polymerization reactor through the feed port, and the temperature is continued to be raised until the temperature inside the reactor reaches 185° C., and an ester exchange reaction begins. During the reaction, reactant methanol is precipitated. When the amount of methanol distilled reaches 300 ml, the ester exchange reaction reaches the end point;

[0035] (2) The BHET solution obtained by the ester exchange reaction was heated continuously in the polymerization kettle. When the temperature in the kettle reached 220°C, trimethyl phosphate as a stabilizer was added to the polymerization kettle. The mixture was stirred for 20 min at a temperature of 220-225°C. Then, the polymerization catalyst ethylene glycol antimony, the positive color agent cobalt acetate, the matting agent titanium dioxide and the mixed colorant were added. The temperature was then continued to be raised until the temperature in the kettle reached 235°C. Then, the excess EG was distilled for 25 min.

[0036] The mass ratio of DMT, EG, ester exchange catalyst added in step (1) to the stabilizer, polymerization catalyst, positive color agent, matting agent, and mixed toner added in step (2) is 750:447.5:12:0.6:19:0.5:11:0.16; the mixed toner is prepared by stirring and mixing trimethyl phosphate, toner, EG and KH560 in a mass ratio of 4:20:100:1 at 80-120° C., and the mass ratio of solvent red 24 to solvent blue 36 in the toner is 1:2.7.

[0037] (3) After the distillation of EG was completed, two stages of vacuuming were performed, and the temperature in the kettle was continuously raised until the polymerization reaction was completed; wherein, low vacuum was started when the temperature was raised to 242°C, and the low vacuum time was controlled to be 40 min. After the kettle temperature rose to 267°C, high vacuum was started, and finally a high vacuum state of 5.5 Pa was reached. The final temperature of the polymerization reaction was 285°C, and the total reaction time of the polymerization reaction was 1.2 hours.

[0038] (4) After the polymerization reaction is completed, nitrogen is used to pressurize the reactor to 0.1 MPa, and then the polyester liquid in the polymerization reactor is discharged. After cooling, pelletizing and drying, chemically recycled semi-gloss polyester chips with improved color value are obtained.

[0039] Example 2

[0040] The chips were produced according to the method of Example 1, except that in step (1), the mixed toner and the ester exchange catalyst were added together, the mass ratio of the mixed toner to the ester exchange catalyst was 0.3:12, and the polymerization reaction time in step (3) was 2 hours.

[0041] Comparative Example 1

[0042] The chips were produced according to the method of Example 1, except that only toner (Solvent Red 24, Solvent Blue 36) and trimethyl phosphate were added to the mixed toner in step (2).

[0043] Comparative Example 2

[0044] Chips were produced in the same manner as in Example 1, except that only a silane coupling agent and trimethyl phosphate were added to the mixed toner in step (2).

[0045] Comparative Example 3

[0046] The chips were produced in the same manner as in Example 1, except that only the silane coupling agent and the toner were added to the mixed toner in step (2).

[0047] The slice performances obtained in each embodiment and comparative example are shown in Table 1.

[0048] Table 1

[0049]

[0050]

[0051] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for improving the color value of chemically recycled semi-gloss polyester chips, characterized in that: The following steps are involved: (1) DMT and EG prepared by chemical recycling are added into a polymerization reactor, and after the reactor temperature is raised, an ester exchange catalyst is added to carry out an ester exchange reaction, and methanol is precipitated as a reactant during the reaction; (2) After the transesterification reaction, the BHET solution obtained by the transesterification reaction is heated continuously. When the temperature in the kettle reaches 218-222°C, a stabilizer is added, and the mixture is stirred for a period of time at a temperature of 220-225°C. Then, a polymerization catalyst, a positive color agent, a matting agent and a mixed toner are added, and the temperature is continued to be raised to distill out the excess EG; (3) After the EG is distilled, two stages of vacuum treatment are performed, and the temperature in the reactor is continuously increased until the polymerization reaction is completed; (4) After the polymerization reaction is completed, the polyester liquid in the polymerization kettle is discharged by nitrogen pressure, and after cooling, pelletizing and drying, chemically recycled semi-gloss polyester chips with improved color value are obtained.

2. A method for improving the color value of chemically recycled semi-gloss polyester chips according to claim 1, characterized in that: In step (1), the mass ratio of DMT, EG and transesterification catalyst is 750:(430-460):(10-15).

3. The method for improving the color value of chemically recycled semi-gloss polyester chips according to claim 1, characterized in that: The transesterification catalyst is manganese acetate.

4. The method for improving the color value of chemically recycled semi-gloss polyester chips according to claim 1, characterized in that: The kettle temperature was maintained at 160-165°C when the transesterification catalyst was added.

5. The method for improving the color value of chemically recycled semi-gloss polyester chips according to claim 1, characterized in that: In step (1), the transesterification reaction starts at 175-185° C. and methanol is precipitated. The transesterification reaction pressure is normal pressure. When the methanol distillation volume reaches 300 ml, the transesterification reaction reaches the end point.

6. The method for improving the color value of chemically recycled semi-gloss polyester chips according to claim 1, characterized in that: The mass ratio of the polymerization catalyst, stabilizer, positive color agent, matting agent, mixed colorant in step (2) to DMT in step (1) is (17-22): (0.4-0.8): (0.3-0.7): (9-13): (0.13-0.18):

750.

7. The method for improving the color value of chemically recycled semi-gloss polyester chips according to claim 1, characterized in that: In step (2), the stabilizer is trimethyl phosphate; the polymerization catalyst is antimony ethylene glycol; the positive color agent is cobalt acetate; the matting agent is titanium dioxide; the mixed toner is a mixed solution of phosphate, toner, EG and silane coupling agent, wherein the toner is a combination of solvent red and solvent blue.

8. A method for improving the color value of chemically recycled semi-gloss polyester chips according to claim 7, characterized in that: Phosphate, toner, EG and silane coupling agent are stirred and mixed at a mass ratio of 4:20:100:1 at 80-120° C. to obtain a mixed toner; the mass ratio of solvent red to solvent blue in the toner is 1:2-3.5, and the silane coupling agent is one of KH550, KH560 and n-dodecyltrimethoxysilane.

9. The method for improving the color value of chemically recycled semi-gloss polyester chips according to claim 1, characterized in that: In step (2), the temperature is raised to 230-240° C. for EG distillation, and the EG distillation time is 20-40 minutes.

10. The method for improving the color value of chemically recycled semi-gloss polyester chips according to claim 1, characterized in that: In step (3), the temperature is raised to 242-245°C and low vacuum is started. The low vacuum time is controlled to be 40 minutes. After the kettle temperature rises to 267-270°C, high vacuum is started to be drawn to 5-10Pa. The final temperature of the polymerization reaction is controlled at 285-287°C. The total reaction time of the polymerization reaction is 1.5-2 hours.

Images