1 Direct production of fiber recycling technology
The waste PET bottles and other packaging materials are collected, classified, purified, dried, and chemically degraded. Only necessary additives are added to the processing and granulation to achieve the spinning raw material quality standards. This regenerated polyester material can be made into staple fibers by melt spinning. It is further processed into textiles or non-wovens, fabrics such as geotextiles, needle-punched carpets, and automotive interior trim materials. Patagonia of the U.S. garment industry has produced outdoor sweatshirts made from fibres produced from recycled polyester bottles. Osaka's NemotoSangyo Co., Ltd. manufactures various carpets and women's clothing from raw materials for polyester bottles, and 20 pieces of 500ml polyester bottles can make one coat. Five 2l polyester bottles of recycled fibers can make 0.09m2 carpets, 35 pieces. The 2l PET bottle can be made into all the filler fibers used in a sleeping bag. Hearst Company of USA introduced a product called Trevira-II, which is a mixture of recycled polyester staple fiber and common ordinary polyester staple fiber. The company supplies 1.67detx and 2.5dtex to the Malden factory. With this specification, it is difficult to distinguish the pure fabric made from this mixed fiber with the pure new polyester fiber. Recently, it was reported that Pan Xiaolian, the State Key Laboratory of Modification of Fiber Materials of East China University, successfully tested polyester filaments with recycled PET bottles. The spinnability and dyeability of the polyester filaments have reached the requirements for textile dyeing.
2 Conversion to Production of Polyester Resin Raw Material Recovery Technology
This technology is to degrade polyester bottles into polyester raw materials or directly into monomers for polyester production. This area is relatively active and has relatively high economic returns.
2.1 Methanol alcoholysis
The principle of methanol alcoholysis is the alcoholysis of waste PET bottle in methanol solution to obtain DMT and EG. The process of alcoholysis is relatively simple, but the product purification is complex and the final product quality is low. For example, a patent on polyester recycling owned by DuPont is to add the crushed PET bottle material to the molten DMT. The reactor is heated to 180°C~200°C, and then the temperature is maintained for 60min~120min until it is poly. The ester bottle was completely dissolved and nitrogen was used during the reaction. The PET bottle is solubilized and hot filtered to remove insoluble impurities. The filtered polyester solution may (1) be sent to a solid phase polymerization apparatus to produce a resin having a higher intrinsic viscosity; and (2) methanolylated to give methanol terephthalate (DMT) and ethylene glycol (EC). DuPont's polyester recycling technology features recycled non-polyester waste polyesters, such as polyester and cotton blends, coated polyester film, beer bottles, and engineering plastics.
2.2 Hydrolysis
The principle of hydrolysis is to react the waste polyester bottle with water to degrade the polyester into terephthalic acid (PTA) and EG. The process also has post-separation issues. For example, Kobe Steel in Japan uses supercritical water to hydrolyze waste polyester into TPA and ethylene glycol. In this process, the solid PET is heated to the melting point (245°C) and then sent to the reactor along with the water for the hydrolysis reaction. The hydrolysis time is controlled, the hydrolysate is sent to the separator, the separator is at room temperature, and the PTA is from water. The phases were separated and ethylene glycol remained in the solution. When the hydrolysis temperature reached 350 °C and the time was 6 min, the recovery rate was the highest, and the purity of the recovered PTA was nearly 99%. This process needs to be performed at a high temperature, which brings difficulties to the operation.
2.3 Ethylene glycol alcoholysis
DuPont Co., Ltd. proposed that the principle of ethylene glycol alcoholysis is that waste PET bottles degrade in the presence of ethylene glycol to obtain ethylene terephthalate (BHET) and/or oligomers. This method is relatively low in cost because it is partially degraded. The specific alcoholysis process is as follows: waste polyester bottle material and excess ethylene glycol (molar ratio 1:4) at atmospheric pressure between 170 °C ~ 190 °C, the catalyst using acetate, etc., the reaction for 2.5h ~3.0h, PET depolymerizes into BHET and EG, filters impurities when the temperature is reduced to 100°C, then adds inhibitor, EG is distilled off under reduced pressure, and then BHET is dissolved in hot water to remove insolubles and oligomers, then cooled and crystallized. White needle-shaped BHET crystals were filtered. The high-purity BHET crystal obtained by the reaction can directly produce fiber-grade polyester. Under normal circumstances, the polyester factory adds a set of ethylene glycol depolymerization equipment on the basis of the original equipment, and then mixes the depolymerized product and the new monomer in proportion to directly produce fiber-grade polyester. Eastman Chemical developed the glycol alcoholysis process. In the Eastman process, ethylene glycol is added to the polyester bottle in a certain proportion and the reaction is carried out at 180° C. to 240° C. for 10 min to 4 h until the desired oligomer is obtained. The reaction mixture is dissolved in a solvent such as hot alcohols, esters, chlorinated hydrocarbons, ketones, etc., and then hot filtered to remove insoluble matter. The filtrate is cooled to obtain a product, and then the product can be sent to a polycondensation reaction section of a PET device to participate in the reaction. Fiber grade polyester. The Eastman process is characterized by: (1) Direct recovery of polyesters containing comonomers, such as polyesters containing isophthalic acid, 1,4-cyclohexanedimethanol or 2,6 naphthalene diacid monomers (2) Beer bottles and other beverage bottles that have been sprayed, compounded, and increased barrier layers can be treated directly; (3) Food grade resins can be produced.
3 Direct recovery of fine chemical products
This technology refers to the conversion of waste PET bottles into other fine chemical products through degradation, transesterification, esterification, condensation, and other reactions. For example, TBI of France uses waste polyester bottles to produce aromatic polyester polyols (APP). The new plant has been put into production. The project has invested 530,000 U.S. dollars and has a production capacity of 15,000 t/a. The factory directly produces aromatic polyester polyols from PET waste bottles. The specific process is the alcoholysis of a large number of flattened PET waste polyester bottles into low-viscosity aromatic polyester polyols. The viscosity of the aromatic polyester polyol is 700 MPa·s, wherein the mass fraction of the small molecule free glycol is less than 5%, and it has good storage stability. This aromatic polyester polyol can be used for the production of flame-retardant polyisocyanurate hard foam panels for construction, and can also be used for the production of insulation products, polyurethane sound insulation materials, foam sealing materials, waterproof coatings and waterproof membranes. It is said that TBI's alcoholysis process is not affected by the color of PET bottles. This advantage is very important. Because there is no practical method for separating colored bottles and transparent bottles in the industry, the green or brown polyester bottles are on the rise, and manual delivery of bottles has increased recycling costs.
Shao Jianxin of Weifang Medical College used alcohol waste and polycondensation of waste PET bottles and polyols to synthesize a wide range of high-performance, 1730 polyester insulation paints. The specific steps are as follows: 120 grams of ethylene glycol, 78 grams of glycerol and 0.48 grams of zinc acetate were added to a three-necked flask, heated to 215°C with stirring, and 309 grams of waste polyester bottle material was then added in portions. When the waste polyester material is completely dissolved and the temperature rises to 240°C, the time is counted and the alcoholysis is controlled for 7h to 7.5h. The reflux apparatus was changed to a vacuum distillation apparatus, 0.42 g of antimony trioxide was added, and vacuum condensation was conducted at 245°C±1°C. When the degree of vacuum reached 93.33 kPa, the ethylene glycol was basically steamed and the polycondensation reaction was also completed. Near the end point, keep warm for 40 minutes. At 180° C., 0.48 g of tributyl phosphate was added, 420 g of cresol was added, and the mixture was stirred and dissolved for 2 h. When the temperature drops below 120°C, 270 g of xylene and 15 g of n-butyl phthalate are pre-mixed and slowly added to the three-vial bottle under stirring. The mixture is stirred for 1 h and adjusted to the viscosity with xylene to obtain a finished product. The technical features are simple process, convenient operation and significant benefits.
Ren Yanqiang and others of the School of Materials Science and Engineering of Beijing University of Chemical Technology used polyester bottle waste and dimer acid polyester diol for transesterification to obtain a flexible and rigid polyester diol with good solubility. , To open up new ways to prepare polyurethane coatings. The specific process is as follows: a certain amount of dimer acid is mixed with the catalyst, slowly heated to 135° C. under nitrogen protection, and kept for 4 hours. Then cooled to 120 ° C, decompression separation of by-product water and excess glycol, until no liquid extraction, cooling to room temperature. The above-mentioned dimer acid polyester diol/PET waste/catalyst was mixed in a certain proportion, heated to 150° C. under nitrogen protection, reacted for 8 hours, cooled to 110° C., and vacuum was used until there was no more distillate. The resulting polyester diol can be used as the solid content of the polyurethane coating. According to the data, it is reported that waste PET bottles can also be depolymerized, synthesized into polyester powder coatings, unsaturated polyester, polyester hot-melt adhesives and other fine chemical products. These polyester recycling products can be used in a batch reactor. By changing the operating conditions, such as temperature increase and temperature decrease, pressurization and pressure increase, products suitable for market requirements can be obtained. So the cost of the product is greatly reduced. This recycling technology is very suitable for SMEs, and the added value of the products is generally high.
The waste polyester bottle recycling industry is a new industry that emerged with the rise of polyester bottle packaging materials. However, the users of polyester bottles are scattered and varied, and collection is very difficult, resulting in high recycling costs, and often the cost of recycling is higher than the cost of producing polyesters. This makes recycling industries difficult to turn into profitable industries. The waste polyester bottles must be recycled. This is related to the major problems of the reuse of resources and environmental protection, and it is related to the sustainability of the national economy. How can we resolve this contradiction? Only by strengthening research on polyester depolymerization technology, and promoting the continuous progress of depolymerization technology, the polyester recycling technology can keep up with the trend of world economic development and contribute to the harmonious development of human society.