Yumiko Ishihara

Catalytic decomposition of polyethylene using a tubular flow reactor system

Abstract Catalytic decomposition of polyethylene (PE) was carried out with a flow reactor (370 mm × 27 mm) and a batch reactor, and the results were compared to clarify the polymer decomposition process during gasification. The decomposition of PE was not found to occur directly from polymer and oligomer chain ends but from the liquid fraction ( MW = 200–400 ). In the presence of a catalyst, conversion to gas at 430 °C in the flow reactor was 72.0 wt%, while in non-catalytic thermal degradation, it was 7.0 wt%. The catalytic decomposition of PE occurred by the following process, in which the concentration of gasification precursors and their backbone branchings are fundamental factors: polymer → thermally decomposed oligomer → catalytically decomposed low molecular weight components (gasification precursor, liquid fraction) → gas.

Catalytic degradation of polystyrene in the presence of aluminum chloride catalyst

The authors have been engaged in studies on the bulk catalytic degradation of various polymers in the presence of solid catalysts. This paper reports the results of bulk degradation of polystyrene in the presence of aluminum chloride carried out at 50°C for 1 to 4 h. The only volatile degradation product was benzene over the entire course of reaction. The molecular weight of the polymer decreased linearly with reaction time down to Mn = 5·3 × 103 (after 4 h). A linear relationship was also observed between the decrease in molecular weight and the decrease in the content of phenyl groups. Stepwise changes in polymer structure were found to take place, which were ascribed to the formation of the indane skeleton in the main chain. Based on these results, combined with the result of an experiment using a model compound (1,3,5-triphenylhexane), a reaction mechanism was proposed which postulates (1) elimination of phenyl groups induced by the addition of protons (initiation step), (2) decomposition of the resulting polymeric carbonium ions through β-scission accompanied by a drop in molecular weight and (3) change in polymer main chain structure, reactions (2) and (3) proceeding competitively.

Mechanism for gas formation in polyethylene catalytic decomposition

Abstract Gas formation mechanisms were studied in detail to find means for the selective recovery of specific components through catalytic gasification of polyethylene. Isobutene and butanes were obtained, respectively, by β-scission from chain-end tertiary carbonium ions and by the hydrogenation of butene. The selective recovery of isobutane was possible by controlling reaction conditions such as temperature, reactor shape and, particularly, the exit temperature for gaseous products.

Mechanism of gas formation in catalytic decomposition of polypropylene

The catalytic decomposition of polypropylene was studied. The production of gas precursors was found essential to decomposition. Attempts were made to elucidate the gas formation mechanism. The most important elementary reaction is the intramolecular rearrangement of chain-end secondary carbonium ions in the liquid fraction to inner tertiary carbon atoms; the C9 fraction was produced by β-scission of the rearranged ions. The C4 and C5 fractions were subsequently obtained by the decomposition of the C9 fraction.

Thermal Decomposition Products of Phthalates with Poly(vinyl chloride) and Their Mutagenicity

The thermal decomposition of phthalate alone and with poly(vinyl chloride) (PVC) was carried out under a nitrogen atmosphere in a 4-necked separable flask. The thermal decomposition of phthalate in the presence of PVC began at 150°, about 100°C lower than the decomposition of phthalate alone. The formation of octyl chloride indicated an interaction reaction between phthalate and PVC. From the analysis of the composition of commercially plasticized PVC sheet (film and board), the phthalates (dibutyl phthalate, dihexyl phthalate) and di(2-ethylhexyl) phthalate), 2-ethyl-1-hexanol, phthalic anhydride, and 2-ethylhexyl hydrogen phthalate were identified. The mutagenicities of these decomposition products were higher than those of phthalic diesters (phthalates).

Novel Method for Polystyrene Reactions at Low Temperature

Thermal decomposition reactions of polystyrene using a new heating medium were carried out by a batch system at 190∼280 °C to clarify the manner in which decomposition is initiated. Polystyrene obtained from a commercial source and low molecular weight compounds obtained from the thermal decomposition were analyzed by GC, GPC, IR,13C-NMR and GC-MS. The main chain underwent virtually no change by heat application. Polystyrene underwent decomposition below its molding temperature and the major decomposition products were 2,4,6-triphenyl-1-hexene (trimer), 2,4-diphenyl-1-butene (dimer) and styrene (monomer). Ethylbenzene, propylbenzene, naphthalene, benzaldehyde, biphenyl and 1,3-diphenylpropane were detected as minor products. This paper presents a new method for examining the decomposition of polystyrene at low temperature into volatile low molecular weight compounds.