A method for improving the color value of semi-dull polyester chips by chemical recycling

Abstract

The present invention discloses a method for improving the color value of chemically recycled semi-gloss polyester chips, belonging to the technical field of chips. The method comprises the following steps: (1) adding DMT and EG, raising the kettle temperature, and then adding an ester exchange catalyst to carry out an ester exchange reaction; (2) heating the resulting BHET solution after the ester exchange reaction, adding a stabilizer at 218-222°C, stirring at 220-225°C for a period of time, then adding a polymerization catalyst, a positive color agent, a matting agent, and a mixed colorant, and then continuing to heat and distill out excess EG; (3) after the EG distillation is completed, performing a two-stage vacuum treatment while continuously raising the kettle temperature until the polymerization reaction is completed; (4) discharging, cooling, pelletizing, and drying to obtain chips. The regenerated semi-gloss polyester chips prepared by the present invention retain the performance of conventional regenerated semi-gloss polyester chips, while significantly improving the b value of the semi-gloss polyester chips, and have a significant effect on improving the whiteness of polyester fibers.

Description

Technical Field

[0001] The present invention relates to the technical field of polyester chips, and more specifically, to a method for improving the color value of chemically recycled semi-dull 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 finally landfilled or incinerated as garbage. This not only causes 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 China can be recycled, it is equivalent to saving 24 million tons of crude oil and reducing 80 million tons of carbon dioxide emissions annually.

[0003] Textiles, bottle chips, etc. made of polyester have currently been degraded and recycled into products through physical, chemical, and bio-based methods, forming a recycling system. The chemical method decomposes macromolecular PET into small molecules through a depolymerization process and then polymerizes to obtain polyester chips. Due to the complex source of chemical raw materials, the color value of the polymerized chips is poor. Although the yellow-green of the chips can be corrected by a toner, 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 above-mentioned deficiencies of the prior art and provide a method for improving the color value of chemically recycled semi-dull polyester chips. On the basis that the performance data of the recycled semi-dull polyester chips prepared by this method are basically the same as the performance data before improvement, the b value of the recycled semi-dull polyester chips is reduced to make them whiter, which has a certain improvement effect on the whiteness of polyester fibers, saves process costs and resource waste. The present invention realizes the recycling of waste resources and improves the color value quality of recycled polyester products at the same time.

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

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

[0007] (1) Put DMT and EG prepared by chemical recycling into a polymerization reactor, raise the temperature of the reactor, and then add a transesterification catalyst to carry out a transesterification reaction. Methanol, the reactant, is precipitated during the reaction;

[0008] (2) Continuously heat the BHET solution obtained from the transesterification reaction after the transesterification reaction. When the temperature in the kettle reaches 218 - 222 °C, add a stabilizer, stir for a period of time at a kettle temperature of 220 - 225 °C, then add a polymerization catalyst, a colorant, a matting agent, and a mixed color toner, and then continue to heat up to distill out the excess EG;

[0009] (3) After the distillation of EG is completed, perform two-stage vacuum pumping treatment while continuously raising the temperature in the kettle until the polymerization reaction ends;

[0010] (4) After the polymerization reaction ends, discharge the polyester liquid in the polymerization kettle by means of nitrogen pressurization, and obtain chemically recycled semi-dull polyester chips with improved color value after cooling, pelletizing, and drying.

[0011] The present invention is further configured such that in step (1), the mass ratio of DMT, EG, and the transesterification 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 when adding the transesterification catalyst is maintained at 160 - 165 °C.

[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; when the methanol distillate reaches 300 ml, the transesterification reaction reaches the end point.

[0015] The present invention is further configured such that in step (2), the mass ratio of the polymerization catalyst, stabilizer, colorant, matting agent, mixed color toner to 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 such that in step (2), the stabilizer is trimethyl phosphate; the polymerization catalyst is antimony glycolate; the colorant is cobalt acetate; the matting agent is titanium dioxide; the mixed color toner is a mixed solution of phosphate ester, color toner, EG, and silane coupling agent, wherein the color toner is a composition of solvent red and solvent blue.

[0017] The present invention is further configured such that the phosphate ester, color toner, EG, and silane coupling agent are stirred and mixed at a mass ratio of 4:20:100:1 under the condition of 80 - 120 °C to obtain a mixed color toner; the mass ratio of solvent red and solvent blue in the color 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 to start pumping low vacuum, the low vacuum pumping time is controlled for 40 min, after the kettle temperature rises to 267 - 270 °C, start pumping high vacuum to 5 - 10 Pa, 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] Using high-quality DMT recycled by chemical method as raw material, preparing PET chips by DMT method, through process improvement and adding a small amount of phosphate ester, silane coupling agent and mixed toner, the purpose of reducing the b value of the chips while having a small impact on the L value is achieved, which helps to improve the whiteness of the fibers and also reduces resource waste; and the mixture of phosphate ester, toner and silane coupling agent plays a synergistic role, which can improve the temperature resistance of the chips. Specific embodiments

[0022] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

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

[0024] (1) Put DMT and EG prepared by chemical recycling into the polymerization reactor, raise the kettle temperature to 160 - 165 °C, then add an ester exchange catalyst (preferably manganese acetate), and then raise the temperature to 175 - 185 °C for ester exchange reaction under normal pressure. During the reaction, the reactant methanol is precipitated. When the methanol distillate reaches 300 ml, the ester exchange reaction reaches the end point;

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

[0026] (2) Continuously heat the BHET solution obtained from the transesterification reaction after the transesterification reaction. When the temperature in the kettle reaches 218 - 222 °C, add a stabilizer. Stir for a period of time (20 - 30 min) at a temperature of 220 - 225 °C in the kettle, then add a polymerization catalyst, a colorant, a matting agent, and a mixed toner, and then continue to heat up 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, and the transesterification catalyst in step (1) to the polymerization catalyst, stabilizer, colorant, matting agent, and mixed toner 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 glycolate; the colorant is preferably cobalt acetate; the matting agent is preferably titanium dioxide.

[0029] The mixed toner is a mixture of phosphate ester, toner, EG, and silane coupling agent (prepared by stirring and mixing at 80 - 120 °C). The mass ratio of phosphate ester, toner, EG, and silane coupling agent is preferably 4:20:100:1, where 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. The phosphate ester can improve the dispersion effect of the toner, increase the heat resistance of the chips, and reduce the thermal degradation and oxidation phenomena during the reaction; the addition of the coupling agent can improve the compatibility and adhesion effect between the toner and the polyester; the addition of the toner can effectively improve the b value of the chemically recycled semi-dull polyester chips.

[0030] (3) After the EG distillation is completed, perform two-stage vacuum pumping treatment while continuously increasing the temperature in the kettle until the polymerization reaction ends; among them, start pumping low vacuum when the temperature rises to 242 - 245 °C, control the low vacuum pumping time to be 40 min. After the kettle temperature rises to 267 - 270 °C, start pumping high vacuum to 5 - 10 Pa. 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 ends, discharge the polyester liquid in the polymerization kettle by means of nitrogen pressurization (the nitrogen pressurization pressure is 0.1 - 0.15 MPa), and obtain chemically recycled semi-dull polyester chips with improved color value after cooling, pelletizing, and drying.

[0032] The preferred embodiments are as follows:

[0033] Example 1

[0034] (1) Charge the DMT and EG prepared by chemical recycling regeneration, gradually heat up to 160 °C, put manganese acetate into the polymerization kettle through the feed port, continue to heat up until the temperature in the kettle reaches 185 °C, and the transesterification reaction starts. Methanol, the reactant, is precipitated during the reaction. When the distillate amount of methanol reaches 300 ml, the transesterification reaction reaches the end point.

[0035] (2) Continuously heat up the BHET solution obtained from the transesterification reaction in the polymerization kettle. When the temperature in the kettle reaches 220 °C, add trimethyl phosphate, the stabilizer, into the polymerization kettle. Stir for 20 min at a temperature of 220 - 225 °C in the kettle, then add ethylene glycol antimonide, the polymerization catalyst, cobalt acetate, the colorant, titanium dioxide, the delustering agent, and the mixed color toner. Then continue to heat up until the temperature in the kettle reaches 235 °C, and start to distill the excess EG. The distillation time is 25 min.

[0036] The mass ratio of the DMT, EG, and transesterification catalyst added in step (1) to the stabilizer, polymerization catalyst, colorant, delustering agent, and mixed color toner added in step (2) is 750:447.5:12:0.6:19:0.5:11:0.16; the mixed color toner is prepared by stirring and mixing trimethyl phosphate, color toner, EG, and KH560 at 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 color toner is 1:2.7.

[0037] (3) After the distillation of EG ends, perform two-stage vacuum pumping treatment, and at the same time continuously increase the temperature in the kettle until the polymerization reaction ends; among them, start pumping low vacuum when the temperature rises to 242 °C, control the low vacuum pumping time to be 40 min, start pumping high vacuum after the kettle temperature rises to 267 °C, and finally reach a high vacuum state of 5.5 Pa. The final temperature of the polymerization reaction is 285 °C, and the total reaction time of the polymerization reaction is 1.2 hours.

[0038] (4) After the polymerization reaction ends, pressurize with nitrogen until the pressure in the kettle is 0.1 MPa, then discharge the polyester liquid in the polymerization kettle, and obtain the chemically recycled semi-dull polyester chips with improved color value after cooling, pelletizing, and drying.

[0039] Example 2

[0040] Produce chips according to the method of Example 1, the difference is that: in step (1), add the mixed color toner together with the transesterification catalyst, and the mass ratio of the mixed color toner to the transesterification catalyst is 0.3:12, and the polymerization reaction time in step (3) is 2 h.

[0041] Comparative Example 1

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

[0043] Comparative Example 2

[0044] The slices are produced by the method of Example 1, except that only silane coupling agent and trimethyl phosphate are added to the mixed toner in step (2).

[0045] Comparative Example 3

[0046] The slices are produced by the method of Example 1, except that only silane coupling agent and toner are added to the mixed toner in step (2).

[0047] The performances of the slices obtained in each example and comparative example are shown in Table 1.

[0048] Table 1

[0049]

[0050]

[0051] The above are only the preferred embodiments of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions within the idea of the present invention belong to the protection scope of the present invention. It should be noted that for those of ordinary skill in the art, several improvements and refinements made without departing from the principle of the present invention should also be regarded as within the protection scope of the present invention.

Claims

1. A method for improving the color value of semi-dull polyester chips recycled by chemical method, characterized in that: It includes the following steps: (1) Put DMT and EG prepared by chemical recycling regeneration into the polymerization reactor. After raising the temperature of the reactor, add a transesterification catalyst to carry out transesterification reaction, and methanol, the reactant, will precipitate during the reaction; (2) After the transesterification reaction, continuously heat the BHET solution obtained from the transesterification reaction. When the temperature in the reactor reaches 218 - 222 °C, add a stabilizer, stir for a period of time at a temperature of 220 - 225 °C in the reactor, then add a polymerization catalyst, a color fixative, a matting agent, and a mixed toner, and then continue to heat up to distill out the excess EG; (3) After the distillation of EG is completed, carry out two-stage vacuum pumping treatment, and at the same time continuously raise the temperature in the reactor until the polymerization reaction ends; (4) After the polymerization reaction ends, discharge the polyester liquid in the polymerization kettle by means of nitrogen pressurization, and after cooling, pelletizing, and drying, obtain chemically recycled semi-gloss polyester chips with improved color value; In step (2), the mass ratio of the polymerization catalyst, stabilizer, color fixative, matting agent, mixed toner to DMT in step (1) is (17 - 22):(0.4 - 0.8):(0.3 - 0.7):(9 - 13):(0.13 - 0.18):750; In step (2), the stabilizer is trimethyl phosphate; the polymerization catalyst is antimony glycolate; the color fixative is cobalt acetate; the matting agent is titanium dioxide; the mixed toner is a mixed solution of phosphate ester, toner, EG, and silane coupling agent, where the toner is a composition of solvent red and solvent blue; mix the phosphate ester, toner, EG, and silane coupling agent according to a mass ratio of 4:20:100:1 and stir and mix at 80 - 120 °C to obtain the mixed toner; the mass ratio of solvent red and solvent blue in the toner is 1:2 - 3.5, and the silane coupling agent is one of KH550, KH560, and n-dodecyltrimethoxysilane.

2. The method for improving the color value of semi-dull polyester chips by chemical recycling 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 semi-dull polyester chips by chemical recycling according to claim 1, characterized in that: The transesterification catalyst is manganese acetate.

4. The method for improving the color value of semi-dull polyester chips by chemical recycling according to claim 1, characterized in that: The temperature of the reactor when adding the transesterification catalyst is maintained at 160 - 165 °C.

5. The method for improving the color value of semi-dull polyester chips by chemical recycling according to claim 1, characterized in that: In step (1), the transesterification reaction starts and methanol precipitates at 175 - 185 °C, and the transesterification reaction pressure is normal pressure; the transesterification reaction reaches the end point when the methanol distillate volume reaches 300 ml.

6. The method for improving the color value of semi - dull polyester chips by chemical recycling according to claim 1, characterized in that: In step (2), heat up to 230 - 240 °C for EG distillation, and the EG distillation time is 20 - 40 minutes.

7. A method for improving the color value of semi-dull polyester chips by chemical recycling according to claim 1, characterized in that: In step (3), heat up to 242 - 245 °C to start pumping low vacuum, control the low vacuum pumping time to be 40 min, and start pumping high vacuum to 5 - 10 Pa after the reactor temperature rises to 267 - 270 °C. 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.

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