Tadashi Ikemura

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.

Kinetic study on the first stage during thermal degradation of polystyrene

Abstract The kinetic parameters of the first stage of polystyrene degradation have been investigated to elucidate the reaction mechanisms using the flow reactor system. The decrease in molecular weight of polystyrene was recorded at minute intervals over the temperature range 310°–390°C. Generally, the first and second stages were observed by thermogravimetric analysis (t.g.a.), however in the early stage of the degradation volatile yields of at least 5% occurred. Therefore, using t.g.a. analysis it is difficult to detect this earlier stage. It became evident that the first stage in the earlier part of the reaction could be detected by g.p.c. analysis. We have observed the hidden kinetic parameters of the nature of the first stage of the polystyrene degradation. The results indicate that the main chains were degraded randomly with the small quantitative volatile groups in the first stage and the rates of decrease in molecular weight in the first stage against reaction temperatures were evaluated as log k s = 12.0 − 41300/ RT .

Effect of molecular weight on formation of non-volatile oligomers by thermal degradation of polyisobutylene and its kinetic analysis

Abstract The formation of functional groups of non-volatile oligomers by the thermal degradation of polyisobutylene is characterized by a kinetic approach including intermolecular hydrogen abstraction of primary (p) and tertiary (t) terminal macroradicals (R p • and R t • ) and volatile small radicals (S • ), followed by β-scission. By assuming in the kinetic analysis that the reaction occurs competitively under a steady state regarding the on-chain macroradicals, various composition ratios for the functional groups can be represented in terms of the rates of respective hydrogen abstraction. The ratio between the tert-butyl endgroup (t-Bu) and the isopropyl endgroup (i-Pr), which corresponds to that between the abstraction rates of R p • and R t • , is expressed by the product of the rate constant ratio and the integrated macroradical concentration ratio (R p • ]/[R t • ]). The observed value of the ratio [ t-Bu ] [ i-Pr ] decreases with reaction time. This is induced by a decrease in the molecular weight ( M ) of the reaction medium. The molecular weight dependence ( M a ) of [ t-Bu ] [ i-Pr ] is expressed by that of R p bull; /[R t • ]. The value of exponent a was determined to be about 1.2 and 0.7 at 300 and 320°C, respectively, from the analysis of data at various reaction times. These values are roughly consistent with average values (1.0 and 0.9) of the same power-law exponent for the volatile oligomers. These results support the hypothesis that the concentrations of the respective radicals decrease in different ways.

Catalytic degradation of polystyrene in the presence of active charcoal

To obtain useful products from polystyrene degradation waste, the catalytic degradation of polystyrene over an active charcoal catalyst was carried out. By controlling the reaction conditions, the selective recovery of styrene dimer derivatives, a promising sourse of useful industrial additives, was investigated. Cis- and trans-l,3-diphenyl-2-butene. 1,3-diphenyl-1-butene and 1,3-diphenylbutane were detected as the main products. The yield of styrene dimer derivatives was about 15 wt.% of the total liquid products recovered. Also. selective recovery of the styrene dimer derivatives by the catalytic reaction of polystyrene in the presence of a catalyst was possible by controlling the contact time and activity of the catalyst.

Distribution of double bonds in thermally degraded polyisobutylene

Abstract The distribution of double bonds in thermally degraded polyisobutylene was determined quantitatively by using pulsed Fourier transform 1H n.m.r. spectroscopic analysis. The double bonds in the degraded polymer did not exist in the interior but at the terminal positions of the polymer chain. These olefins were of the terminal trisubstituted and terminal vinylidene types. The content of the former was much greater than that of the latter. This shows that radical chain transfer predominantly occurs at the methylene hydrogen rather than at the methyl groups of the polymer chain. The average number of double bonds per molecule, f, was greater than 1 and tended to be near 2. Thereby most of the degraded polyisobutylene was shown to have two terminal unsaturations per molecule.

Thermal stability of phthalic esters

Phthalic esters, as typical plasticizers for vinyl plastics, were thermally decomposed by a flow reactor system and their decomposition products were analyzed in detail. The thermal decomposition products were olefin, alcohol, hydrogen phthalate, benzoates with alkyl groups corresponding to these of the original phthalate esters and phthalic anhydride. We found from the main thermal decomposotion products-olefin, alcohol and hydrogen phthalate-that phthalic esters were thermally decomposed throughcis-elimination in the same way as in the general case for esters. In the presence of polyvinyl chloride (PVC), hydrochlorinated products were identified in the decomposition products. A good relationship was found between the amount of chloroalkanes produced and the reaction temperature. Thecis-elimination reaction of phthalic esters was found to be promoted by PVC.

Studies on the thermal decomposition of phthalate esters: VIII. Synthesis of bis(2-phenylhexyl) phthalate and thermal decomposition☆

Abstract In order to establish how phthalate esters are provided with heat stability, bis(2-phenylhexyl) phthalate (BPHP) containing side-chains with a phenyl group on each β-carbon atom was synthesized and its heat stability was compared with that of other phthalate esters. It was confirmed that BPHP is very resistant to heat.