CHEMICAL DEPOLYMERISATION

This paper discusses in depth advanced technologies for recycled materials from solid waste streams. Chemical depolymerisation, thermal depolymerisation, pyrolytic liquefaction, pyrolytic gasification, partial oxidation, and feedstock compatibility are all explained. The economic feasibility of the methods are considered. 

Chemical depolymerisation of P(3HB) to generate methyl esters of (R)-3HB have been performed by acidic alcoholysis using sulfuric acid [244] and hydrochloric acid [245], whereby the latter method proved to be more effective. 

Recently, PHA are also gaining much attention as a source of enantiomerically pure compounds although this possibility was realised almost a decade ago [231,232], Due to the specificity of the PHA synthase, biosynthesised PHA only contain the (R)-isomers of 3-hydroxyacids. Close to 150 different monomer constituents of PHA have been identified to date and therefore various enantiomerically pure compounds can theoretically be obtained by depolymerising the polymers. The depolymerisation can be performed either by chemical or biological methods. Chemical depolymerisation of P[3HB] to generate methyl esters of (R)-3HB have been performed by acidic alcoholysis using sulfuric acid [232] and hydrochloric acid [233], whereby the latter method proved to be more effective. 

The main types of feedstock recycling processes can be summarised as chemical depolymerisation, gasification and partial oxidation, thermal degradation, catalytic cracking and reforming, and hydrogenation [852663]. The current advanced thermal treatments are as follows [a.372]. 

Thermal stability is largely concerned with chemical reactivity which may involve oxygen, u.v. radiation or depolymerisation reactions. The presence of weak links and the possibility of chain reactions involving polymer chains may lead to polymers having lower thermal stability than predicted from studies of low molecular weight analogues. 

Recycling can include chemical recycling. This involves plastics waste being processed chemically, either by cracking or depolymerisation, to... 

A number of cracking/depolymerisation processes are currently operating commercially. These include the Texaco gasification process and the BP Chemicals polymer cracking process. Both have been operating since the mid 1990s. 

The effect of incorporating p-hydroxybenzoic acid (I) into the structures of various unsaturated polyesters synthesised from polyethylene terephthalate (PET) waste depolymerised by glycolysis at three different diethylene glycol (DEG) ratios with Mn acetate as transesterification catalyst, was studied. Copolyesters of PET modified using various I mole ratios showed excellent mechanical and chemical properties because of their liquid crystalline behaviour. The oligoesters obtained from the twelve modified unsaturated polyesters (MUP) were reacted with I and maleic anhydride, with variation of the I ratio with a view to determining the effect on mechanical... 

The technical advantages of the chemical recycling of PETP bottles are discussed, and some developments in depolymerisation processes are examined. Particular attention is paid to glycolysis, hydrolysis and solvolysis processes respectively developed by TBl, Tredi and Eastman Chemical. 

Eastman Chemical is starting a pilot depolymerisation plant that it hopes ean provide a eost-effeetive solution for some new hard-to-reeyele PETP bottles. In the laboratory, the proeess has been able to handle all the different eoloured PETP and all the barrier layers that have been tested. The proeess produees food-grade material. 

This fall, the closed-loop Evergreen Nylon Recycling plant will start up in the US, a joint venture of DSM Chemicals North America and AlliedSignal. The facility will recover 45,000 m.t./year of caprolactam by depolymerising the fibres from 100,000 m.t./year of discarded nylon-6 carpets. Meanwhile in Germany, Lurgi is building the Polyamid 2000 AG facility. It will process 120,000 m.t./year of carpet waste and recover 10,000 m.t./ year of caprolactam from nylon-6 carpets and 13,000 m.t./ year of nylon-6-6 from nylon-6-6 carpets. 

Researchers at AECI s Research and development Department have developed a novel microwave depolymerisation process for the thermal decomposition of polymethyl methacrylate and the recovery of the monomer methyl methacrylate. This comprehensive article supplies a detailed explanation and examination of the process which has been patented in South Afriea. The microwave technology provides a purer produet which will simplify downstream processing and reduee effluent volume and chemical consumption. 

ICI Acrylics activities in chemical recycling of acrylics is discussed. The company is offering a take-back service for scrap PMMA which it chemically recycles back into MMA. Together with Mitsubishi Rayon, it has established a joint venture to develop more efficient depolymerisation... 

Chemical Marketing Reporter 252, No.26, 29th Dee. 1997, p.1/8 DEPOLYMERISATION GETS THE NOD AS ROUTE TO LOW-COST FEEDSTOCK Brand T... 

Large companies are taking a closer look at depolymerising nylon, polyester and PU produets that would otherwise end up in landfills. The most reeent project is a worldscale faeility to be built by DSM Chemicals North America and AlliedSignal that will produce about 100 million pounds of caprolactam per year by depolymerising nylon 6. The faeility will remove about 200 million pounds of earpet from landfills annually. DuPont says it has a proeess, ammonolysis, that ean depolymerise a combination of nylon 6 and 66. 

Polymers with hetero-atoms in the chain are suitable for chemical recycling of waste materials. In addition to depolymerisation (nylon 6) and solvolysis (nylon 6,6, PETP, PU) the degradation of aliphatic polyamides with dicarboxylic acids, diamines and cyclic anhydrides, especially trimellitic anhydride, becomes more and more important. The utilisation of the obtained fragments is described. 

Techniques for the chemical recycling of plastics into monomers and petrochemical feedstocks are described, including chemical and thermal depolymerisation, pyrolytic liquefaction, pyrolytic gasification and partial oxidation. BRITISH PETROLEUM CO.PLC... 

For the purpose of the identification and quantification of additives (broadly defined) in polymeric materials extraction and dissolution methods are favoured (Sections 3.3-3.7). However, additives are also made accessible analytically by digestion of the sample matrix (cf. Section 8.2). Such wet chemical techniques, that remove the sample matrix first, are often limited to mg amounts because of pressure build-up in destruction vessels. Another reactive extraction approach to facilitate additive analysis is depolymerisation by acid hydrolysis or saponification, sometimes under pressure. This is then frequently followed by chemical methods such as titrimetry or photometry for final identification and quantification. 

It has an excellent outdoor life period and good strength. It is amorphous because of the presence of bulky side groups in the molecules. It is resistant to many chemicals but soluble in organic solvents like ketones, chlorinated hydrocarbons and esters. It can be thermally depolymerised to give back the entire quantity of monomer. 

It is obtained as fragments of commercial grade heparin which is produced by chemical or enzymatic depolymerisation. It contains less pentasaccharide sequences with a high affinity for antithrombin III. 

Uchiyama, V. et al., Chemical change involved in the oxidative reductive depolymerisation of hyaluronic acid, J. Biol. Chem., 265, 7753, 1990. 

Class 4 any class 1 to 3 material which had been chemically reprocessed by depolymerisation into monomers or oligomers from which, after purification, a new polymer has been regenerated. 

The oldest method of using biomass to create energy is direct combustion, which has been used for thousands of years. Other thermochemical techniques which can be used for the production of chemicals from biomass usually involve depolymerisation at elevated temperatures and pressures. Among these are gasification, pyrolysis, liquefaction and acid hydrolysis. 

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