Degradation of polystyrene in supercritical n-Hexane
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Degradation of Polystyrene in Supercritical n-Hexane Gyou-Cheol Hwang, Jung-Hwan Choi, Seong-Youl Bae ~ and Hidehiro Kumazawa *
Department of Chemical Engineering, l-tanyang University, Ansan, Kyunggi-do 425-791, Korea *Department of Chemical Process Engineering, Toyama University, 3190Gofuku, Toyama 930-8555, Japan (Received 25 ~;eptember 200t 9 accepted 11 October 20011
Abstract-Degradation of polystyrene was carried out in supercritical n-hexane under reaction temperature ranging li'om 330 r to 390 "C, pressure ranging from 30 bar to 70 bar and reaction duration of 9{) rain. -thc conversion of polyst? rene increa~,,cdwith rising temperature mid pressure. The degradation per~brmance was influenced by the temperature rather than applied pressure. Polystyrene rapidly degraded in 30 rain after reaching a prescribed temperature ranging fi'om 350 "C to 39()'V. At a prescribed temperature of 390 "C, the degree of dcgradation was higher than 90%. The degradation reaction was examined experimentally at a relati,,.cly low temperature of 330 "C. The degradation of pc@styrene by using supcrcrit[c-al n-hcxane has been lbund to be more cffecti~,e compared tt~ general pyrolysis (thermal degradation). Among the selectMty of liquid products, that of a single aromatic ring group like" st}rene at 39(1 "'C increased up to 65% in 90 rain. It was ft~und t'rom the analysis by a gel permeation chromatograph ((}PC). that high molecular-weight compounds decreased but oligomers increased with rising temperature. Ke? words: Degradation. Polys~ rene, Supercritical n~Hcxane, Pyrolysis carbon products of shorter carbon chain and a higher ratio of l-alkene/n-alkane than those yielded through general thermolysis, Chert et al. [1995] decomposed natuiaI rubber using supercritical water and carbon dioxide at 380 "C and 276 bar. Joung et al. [1999, 2001] re-ported seven types of solvents like toluene and cyclohexane: and selected solvents that are most appropriate to waste tire processing, At the conditions of 300~ 10 MPa and a reaction time of I hr, cyclohexane decomposed waste tires into lower molecular weight substances. Supercritical toluene also gave a similar result. Hwang et at, [2001] used supercritical acetone in the degradation ofPE, PP and their mixture. Lee et aL [19981 used supercritical teWahydrofuran in decomposing cis-polyisoprene rubber, and got products of narrow distribution. Also they determined an appropriate pressure for the decomposition. In case of thermolysis of PS, monomers of PS are gained because the main chain tends to be cut. Carniti et al. [1995] reported that the yield rate ofoil through the themlolysis of PS was about 80%, whereas the yield of gaseous products was less than 10%. Yang and Shibasaki [1998] reported the de m~adation mechanism of PS thermolysis. Hwang et al. [ [9991 used supereritical acetone in decomposing waste PS. The total conversion of waste PS, composition of the decomposed products and the yield of monomer for various solvent densities were determined. In this study, the degradation of waste po
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