Styrene, from thermal degradation

C, and styrene production was also more by 11 wt% in the case of waste expanded polystyrene. Oil yield increased from 24 to 98 wt% with increase in reaction temperature from 350 to 480 °C, while styrene selectivity, which was about 76 wt% up to 450 °C, decreased sharply to 49 wt% at 480 °C. This decrease in styrene selectivity takes place with increase in styrene dimer formation from 4 to 10 wt% and production of other chemicals. Also the production of toluene, ethylbenzene and methylstyrene decreased with the same rise in pyrolysis temperature. Thermal degradation of PS was reported to have started with random initiation to form polymer radicals, the main products being styrene and its corresponding dimers and trimers. These results were comparable with studies reported elsewhere on oil yield of 99 wt% with 60 wt% styrene monomer and 25 wt% for other aromatics. Another work has reported on recovery of 58 wt% styrene from thermal degradation of PS at 350 °C after a time of 60 min [a.379]. Furthermore, oil yields of 82 wt% with 70 wt% styrene selectivity and 77 wt% styrene recovery at 580 °C have been reported [a.380]. 

Polystyrene - Thermal degradation is the simplest of the current techniques used to recover feedstock chemicals from styrene-based polymers and has therefore been studied extensively. Investigations of the product distributions from thermal degradation of polystyrene have mainly focused on liquid products. It has been observed that the yield and the composition of liquid products vary strongly with temperature and the reactor configuration,... 

Carniti et al. examined the product distributions evolved when polystyrene was reacted in batch mode at temperatures of 623 and 673 K up to 120 min in the presence of HY and REY zeolites. The catalyst concentration was 10 wt% for all runs. The product selectivities for these two catalysts were similar and markedly different from thermal degradation. The yields of benzene and ethylbenzene increased, and the yield of styrene decreased to zero with the addition of the catalyst. Selected product yields from the more comprehensive table provided by Carniti et al are summarized in Table 5. Values for a silica-alumina catalyst with a Si02/Al203 ratio of 6.5 are also included for comparison. 

R. Balart, L. Sanchez, J. L6pez, and A. Jimenez, Kinetic analysis of thermal degradation of recycled polycarbonate/acrylonitrile-butadi-ene-styrene mixtures from waste electric and electronic equipment,... 

Copolymers of itaconic esters with butadiene have not yet been used technically. On the other hand, acrylonitrile containing copolymers with other components have been studied from several points of view. Standard Oil Co. has claimed a terpolymer of isobutylene, butadiene, and acrylonitrile, and BASF a similar product of butadiene, acrylonitrile, and styrene. The films from these combinations are said to have high flexibility and cold resistance. However, all butadiene containing copolymers are not light fast. Copolymers of butadiene, acrylonitrile, and unsaturated dicarboxylic esters are suggested for plasticizing PVC, but they must be thermally degraded before they are combined with the polymer. 

This chapter summarizes efforts aimed at removing styrene monomer from PS to low levels, i.e. <200 ppm. Also discussed is the current state of understanding regarding the mechanism of monomer regeneration by thermal degradation of PS during fabrication. 

All of tl products l,3 triphenylbenzene, 1,3-diphenylpropane, 1,3,5-triphenylpen-tane, ethylbenzMie, methylben2 ne, and styrene are volatile products of thermal degradation of polystyrene This kind of intramolecular cyclization is not likely to be important in thermal degradation of poly(methyl methacrylate) and poly(a-methylstyrene), because the reactive site is linked to two bulky substituents which restrict the rotation of the terminal carbon atom containing the unpaired electron and thus prevent it from coming into proper orientation to attack the other carbon atoms in the chain. 

The pyrolysis process for waste recycling is frequently done at larger scale than analytical pyrolysis. However, analytical pyrolysis studies are performed independently for the understanding and the optimization of such processes [10,16-19]. Also, model mixtures can be used in parallel with real samples. For example, the comparison of thermal degradation products from real municipal waste plastic and model mixed plastics can help understand the compounds generated in waste incinerators. In one such study [20], analytical pyrolysis of real municipal plastic waste obtained from Sapporo, Japan and model mixed plastics was carried out at 430 °C in atmospheric pressure by batch operation. The chlorinated hydrocarbons found in degradation liquid products of poly(ethylene)/poly(propylene)/ poly(styrene)/poly(vinyl chloride) and other polymeric mixtures were monitored. It was determined that the presence of poly(ethylene terephthalate), in addition to chlorinated plastics in the waste, facilitates... 

Figure 1.40. Chain scission (given as number of scissions, S, per number-average molecule) during thermal degradation of poly(styrene) polymerized anionically (a), M = 2.3x10, or by free-radical initiation (b), M — 1.5x 10. Adapted from McNeill (1989).

Figure 4.20 First-order plots of the monomers formed in the thermal degradation at 500 °C of PMMA, PS and alternating PMMAS copolymer 1 O methyl methacrylate from PMMA, styrene from PS, methyl methacrylate from PMMAS, styrene from PMMAS.

Jeschke G, Schlick S (2006) Spatial distribution of stabilizer-derived nitroxide radicals during thermal degradation of poly(acrylonitrile-butadiene-styrene) copolymers a unified picture from pulsed ELDOR and ESR imaging. Phys Chem Chem Phys 8 4095 103... 

They found that thermal degradation of poly(4- -alkyl styrenes) followed mainly a free radical depolymerisation mechanism. The main product is a monomer similar to unsubstituted PS, i.e., 59% to 92% monomer from poly(4-n alkyl styrenes) ranging from 136,500-737,000 and = 37,000-99,000. The amoxmts of this monomer decrease with increasing length of alkyl sidechain from hexyl to decyl. This behaviour is connected with the stability of monomer under isothermal pyrolysis conditions at 600 °C. 

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