Quaternary recycling process

Recycling processes for plastics can be classified in a variety of ways. One categorization differentiates between primary, secondary, tertiary, and sometimes quaternary recycling. 

Secondary or mechanical recycling processes differ from tertiary or feedstock recycling and quaternary or energy recovery processes principally in the potential to retain some of the energy used from plastics production, and in general terms provide for financially advantageous options. 

Data relating to the nature and quantities of plastics wastes arising from industrial processes and municipal refuse have been reviewed [1,2], together with a consideration of the economics and appropriateness of primary, secondary, tertiary and quaternary recycling respectively. 

Processes that do not rely on the melting of plastic recyclate relate to large scale predominantly tertiary and quaternary recycling. Thermoset matrix composites recycling also falls within this description, and the principal recycling routes for thermoset matrix composites are outlined below. 

Tertiary or quaternary recycling, (recovery of chemicals or energy), should only be considered when other types of recycling are not economically or technologically feasible. In tertiary recycling, waste plastics are converted to either monomers or fuels or petrochemical feedstocks. Conversion to monomers by solvolytic methods is feasible for condensation polymers but often requires pure polymer streams. Sorting and cleaning of the waste stream increases the cost of the process. 

Quaternary recycling The process of recovering energy from waste plastics by incineration [21]. 

Manufacture. For the commercial production of DPXN (di-/)-xylylene) (3), two principal synthetic routes have been used the direct pyrolysis of -xylene (4, X = Y = H) and the 1,6-Hofmaim elimination of ammonium (HNR3 ) from a quaternary ammonium hydroxide (4, X = H, Y = NR3 ). Most of the routes to DPX share a common strategy PX is generated at a controlled rate in a dilute medium, so that its conversion to dimer is favored over the conversion to polymer. The polymer by-product is of no value because it can neither be recycled nor processed into a commercially useful form. Its formation is minimised by careful attention to process engineering. The chemistry of the direct pyrolysis route is shown in equation 1 ... 

The reaction of the quaternary compound (16) with carbon nucleophiles results in attack at sulfur leading to an open-chain intermediate that recyclizes to ring-expanded compounds (79TL1281). Reaction of (16) with one equivalent of cyanide ion proceeds according to Scheme 4 to produce (17) in high yield. When an excess of cyanide ion is employed, (17) reacts further to form 80% of a compound whose structure is represented by either (18) or (19). The reaction of (16) with methyl propiolate anion produces (20) via a similar process. 

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