Depolymerization technology

The commercial potential for recycling post-consumer PET is not limited by lack of depolymerizing technology. Many options are available with varying degrees of capital intensity. The technologies most probable to provide satisfactory quality product, suitable for reuse in food packaging, are likely to cost US 1.00/kg or more and require capacities of over 20000 annual tonnes. 

Glycolysis is claimed to be somewhat less cosdy than methan olysis (33). Depolymerization is not taken completely to monomers (34). Rather, recovered PET is depolymerized to low molecular weight oligomers. Contaminants are removed using proprietary technology. The oligomers are then fed to a melt polymerization vessel in which PET is produced. 

Interest in solution inhibition resist systems is not limited to photoresist technology. Systems that are sensitive to electron-beam irradiation have also been of active interest. While conventional positive photoresists may be used for e-beam applications (31,32), they exhibit poor sensitivity and alternatives are desirable. Bowden, et al, at AT T Bell Laboratories, developed a novel, novolac-poly(2-methyl-l-pentene sulfone) (PMPS) composite resist, NPR (Figure 9) (33,34). PMPS, which acts as a dissolution inhibitor for the novolac resin, undergoes spontaneous depolymerization upon irradiation (35). Subsequent vaporization facilitates aqueous base removal of the exposed regions. Resist systems based on this chemistry have also been reported by other workers (36,37). 

Because all depolymerization processes will generate waste that may be classified as hazardous waste or at least chemical waste, it will always be economically preferable to separate as much non-PET material from the PET material as is practical. Traditional bottle washing procedures can produce used bottle flake that is clean enough to be used to make more bottles or somewhat less clean and less expensive material. Technologies have been proposed to dissolve the polyester scrap in appropriate solvents to separate PET from other materials such as cotton fiber or magnetic tape components [19]. 

One critical issue is the evaluation alternative. In the case of methanolysis, the alternatives are to make DMT and EG by depolymerization or secure materials from traditional petrochemical sources. For hydrolysis, the alternatives are TPA and EG by depolymerization or from traditional sources. For both technologies, the amount of copolymerizing isophthalate and/or 1,4-cyclohexane dimethanol is likely to be too little to justify the cost of recovery. For the various forms of glycolysis and the methanolysis/BHET hybrid, the alternative is the BHET and BHET-like materials made by the combination of a terephthalate and isophthalate plus EG and various glycols. Market prices exist for TPA and EG. BHET is not an item of commerce, and so the value must be imputed from the market price for TPA (the modern terephthaloyl) and EG, plus a conversion cost. 

Hammel, K. E. Moen, M. A. (1991). Depolymerization of a synthetic lignin in vitro by lignin peroxidase. Enzyme Microbial Technology, 13, 15-18. 

Thermo-Depolymerization Process, LLC CHANGING WORLD TECHNOLOGIES INC Think Green WASTE MANAGEMENT INC Thomas H. Lee Partners L.P. HAWKE YE HOLDINGS INC... 

Funaoka M, Shibata M, Kako T Abe I (1988) Structure of highly condensed lignins and their depolymerization by phenolation Proc Cellucon 88 Japan, Nov 28-Dec 1 Kyoto, Japan, The Society of Fiber Science and Technology Kyoto, Japan, p 160... 

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