Recycling pyrolyses

The boiling flask is charged with 2-acetoxycyclohexanone and heated to reflux. The pyrolysis column, which is packed with glass beads and electrically heated to 500 with the Nichrome wire, cracks a portion of the ester then the cyclohexenone, acetic acid, and unreacted acetate pass into the fractionating column. The products are collected by distillation and the unreacted acetate is continuously returned to the boiling flask through the pyrolysis column bypass. The vapor trap, which is merely a U-shaped portion of the bypass for the pyrolysis column, soon fills with liquid and prevents distillation around the pyrolysis chamber. The yield of 2-cyclohexenone with this apparatus exceeds 90%. 

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Thermoset plastics have also been pyrolysed with a view to obtain chemicals for recycling into the petrochemical industry. Pyrolysis of a polyester/styrene copolymer resin composite produced a wax which consisted of 96 wt% of phthalic anhydride and an oil composed of 26 wt% styrene. The phthalic anhydride is used as a modifying agent in polyester resin manufacture and can also be used as a cross-linking agent for epoxy resins. Phthalic anhydride is a characteristic early degradation product of unsaturated thermoset polyesters derived from orf/io-phthalic acid [56, 57]. Kaminsky et al. [9] investigated the pyrolysis of polyester at 768°C in a fiuidized-bed reactor and reported 18.1 wt% conversion to benzene. 

Pyrolysis could be considered as an nnsnitable way of recycling for polyurethanes because the liquid product is extremely viscous and can solidify over time [41]. The main reason of the severe instability of polynrethane pyrolysate is the reactivity of the diisocyanate component, the regained polynrethane-forming reactant. The other component of thermoplastic polyurethanes is either a polyether or a polyester which could lead to stable pyrolysis liquid if the reactive diisocyanate is eliminated from it. 

U. Arena and Mastellone M. L., The role of some process variables in the operation of fluidized bed pyrolyser of plastic wastes. Polymer Recycling, 6, 35-41 (2001). 

M. Hamm, Stoffliches Recycling von Shredderleichtgut durch Pyrolyse im Drehrohrofen, PhD Thesis, GHS-Essen, 1993. 

PET from post-consumer soft-drink bottles was cut into small pieces and batches of this raw material ( 40 g) were pyrolysed in a first step at 400 °C, under nitrogen atmosphere, in a 35 mm internal diameter vertical quartz reactor. Then, a second heat treatment was performed, at 725 °C for 2 hours. The distribution of the final products of the pyrolysis process was approximately 58% of gaseous compounds (CO, CO2 and a complex mixture of hydrocarbons), 20% of a yellow crystal solid that condensed in the upper part of the reactor, and 22% of a black solid residue (i.e., char, denoted as P) with a glassy sheen, retrieved from the bottom of the reactor. The characterisation of the yellow crystal solid revealed that terephthalic acid was the principal component, which can be recycled for PET synthesis. 

Cortplex integrated operation of three subsystems rotating cone pyrolyser, bubbling bed char combustor, and riser for sand recycling. 

Energy in the char and gas averaged 77% of the gross calorific value of the feedstock. In these experiments, energy to pyrolyse the feedstock was supplied by propane. About 100 MJ were required to heat the kiln to 870 K. Another 121 MJ/h were required to maintain this temperature and 189 MJ/h were required to maintain a temperature of 1170 K. About 90% of this heat was lost in the exhaust and in an actual system most could be recovered for process heating. Calculations were made to predict thermal efficiencies of a self-sustaining system where a portion of the product is recycled and combusted to provide process heat thermal efficiencies of about 65% were predicted. 

Another alternative to recycling is pyrolysis [6], While the idea of material resource recovery is attt ctive, a mixed-feed stock generally yields a pyrolysate of complex nature. Oie has but to remember the coal pyrolysis attempts of a generation ago to appreciate the difficulty of making effective use of a mixture of hundreds of chemical intem ates. 

In the current state of the technology, the production capacity of a two-cell pyrolysis furnace is ahout 40,000 t/year of ethylene. Thus a 400,000 t/year steam cracker comprises ten furnaces on naphtha and one or two used to pyrolyse recycled ethane. One or two spare furnaces (10 to 15 per cent of the theoretical production capacity) are also normally provided, in order to compensate for the production deficit due to decoking operations. 

A Belestrini. Traitment des matieres plastiques et du caoutchouc par pyrolyse. Paper presented at Seminar on Recycling of High Polymeric Wastes, Dresden, Sept. 17-23, 1978. 

The catalyst mixture is supported on alumina or silica and is either packed into a tubular reactor or used in a fluidized bed. Reaction conditions are 200-350°C and 0.2-1 MPa (2-10 atmospheres) and high yields of ethylene dichloride are obtained. The ethylene dichloride is then pyrolysed as described previously (and the hydrogen chloride produced is recycled). 

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