The development trend and problems of PET recyclin

2022-07-31
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Development trend and problems of PET recycling at home and abroad (II)

development trend of PET recycling and problems faced by China's Recycled PET industry

long term degradation problems:

if mechanical recycling is legalized, since the IV value of recycled PET is reduced by about 0.07dl/g every time it is extruded, in the long run, the sample cutting, measurement and experiment should be carried out continuously, and its degradation is more serious. In fact, if a PET bottle contains 50% recycled materials, after secondary processing, 50% of the materials have experienced two thermal histories. After three processing, 25% of the materials have experienced three thermal histories. After four processing, 12.5% of the materials have experienced four thermal histories, and the IV value has decreased by about 38%

The decrease of

iv value was accompanied by the decrease of mechanical properties and the production of a large number of carboxyl end groups (COOH). These disadvantages make the chemical recovery method more and more concerned, although the chemical method is more expensive

the second is chemical recovery (or corrosion method)

the chemical reagents that can be used to degrade pet mainly include water (hydrolysis), methanol (alcoholysis), ethylene glycol or diethylene glycol (glycolysis) and butanediol. In the process of hydrolysis and transesterification, a catalyst is usually used for various physiological reasons. The degraded monomer or oligomer is purified and copolymerized with ethylene glycol to form pure PET. The process route is as follows:

note: DMT dimethyl terephthalate; TPA terephthalic acid; BHET - ethylene terephthalate; Eg - ethylene glycol; MeOH - methanol

now, the process characteristics of the processing plant for recycling waste PET bottles through glycolysis hydrolysis composite treatment are described as follows:

the main advantages of the chemical recovery method

can be recycled indefinitely, and relatively pure PET raw materials (TPA, eg, etc.) can be obtained

disadvantages of chemical dissolution method:

although it can be used in contact with food, due to economic reasons, chemical recycled PET has not been commercialized. Its high price comes from the price of raw materials, investment and operating costs

in addition to TPA and eg, recycled PET contains a large number of comonomers. These increase the development of key brands and output the experimental reports and platform construction support monomers that meet the standard requirements, which increases the chemical heterogeneity of recycled materials

since chemically recovered pet cannot produce intermediate products at competitive prices, it is mainly used in applications where the content of recycled materials should reach a certain minimum value as stipulated by legislation

in order to make the pet degradation equipment economically viable, at least 1.5*104t of raw materials should be supplied every year. The minimum volume of raw materials varies with the technology used

due to the high investment cost of chemical recovery of pet, at present, the international mainstream pet recovery method is mainly mechanical method

development status and trend of PET recycling technology

development status of mechanical PET recycling technology

at present, some European manufacturers have launched a fully automatic waste PET bottle chip cleaning production line with a capacity of 4000kg/h, with an investment of 10000 euros/set. The product quality can meet the following standards

table-3 quality index of cleaned PET film given by a European manufacturer

type

project

index

particle size

humidity

quality

color classification

material loss

hdpe/pp bottle cap

pe, pp

paper

binder

organic matter

metal

none

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