Katsuhide Murata

Basic study on a continuous flow reactor for thermal degradation of polymers

Abstract A continuous flow reactor for thermal degradation of polymer such as polyethylene (PE), polypropylene (PP) and polystyrene (PS) was operated at the feed rate of 0–1.5 kg h −1 in order to investigate the characteristics of the continuous flow operation and the thermal degradation behavior of polymers. Rate studies on thermal degradation of polymers were made at various temperatures and under a steady state. The activation energies, calculated on the basis of the rate of volatilization, were 221, 216 and 208 kJ mol −1 for thermal degradation of PE, PP and PS, respectively. These activation energies indicate that a chemical reaction takes a role of rate controlling step in this reactor system. By continuous flow operation, polymers were converted to the liquid product with high yield of 93.6–96.2, 96.1–99.1 and 99.9 wt.% for PE, PP and PS. The liquid products consisted of a wide spectrum of hydrocarbons distributed C 4 –C 30 . Thermal degradation by continuous flow operation is a suitable technique for converting plastic polymers into liquid hydrocarbons which could be used as feed stock materials. Based on the observed information, a macroscopic mechanism was proposed. The thermal degradation of polymers consists of two distinct reactions which simultaneously occur in the reactor. One is a random scission of links which causes a molecular weight reduction of the raw polymer, and the other is a chain-end scission of CC bonds, which causes the generation of the volatile product. The chain-end scission takes a place at the gas–liquid interface in the working reactor.

Thermal and catalytic degradation of structurally different types of polyethylene into fuel oil

The degradation of four different types of polyethylene (PE) namely high density PE (HDPE), low density PE (LDPE), linear low density PE (LLDPE), and cross-linked PE (XLPE) was carried out at 430 °C by batch operation using silica-alumina as a solid acid catalyst and thermally without any catalyst. For thermal degradation, both HDPE and XLPE produced a significant amount of wax-like compounds and the yields of liquid products (58–63 wt%) were lower than that of LDPE and LLDPE (76–77 wt%). LDPE and LLDPE produced a very small amount of wax-like compounds. Thus the structure of the degrading polymers influenced the product yields. The liquid products from thermal degradation were broadly distributed in the carbon fraction of n-C5 to n-C25 (boiling point range, 36–405 °C). With silica-alumina, all of the polyethylenes were converted to liquid products with high yields (77–83 wt%) and without any wax production. The liquid products were distributed in the range of n-C5 to n-C20 (mostly C5–C12). A solid acid catalyst indiscriminately degraded the various types of polyethylene into light fuel oil with an improved rate.

Catalytic degradation of polyethylene into fuel oil over mesoporous silica (KFS-16) catalyst

Abstract The thermal degradation of plastic polymers into fuel oil over mesoporous silica (KFS-16) catalyst has been investigated. The product yields, composition and degradation rate of polyethylene over KFS-16 were compared with those over solid acid catalyst (silica–alumina and zeolite) and non-catalytic thermal degradation. The initial rate of degradation of PE over KFS-16, which possesses no acid sites was as fast as that over silica–alumina (SA-1) and the yield of liquid products was higher. The composition of the liquid products of degradation over KFS-16 was different from that over SA-1 and similar to that of non-catalytic thermal degradation. SA-1 catalyst deactivated very rapidly due to coke deposition, whereas KFS-16 deactivated much more slowly. These findings over mesoporous silica suggest that the mesopores surrounded by the silica sheet may act as a flask for storing radical species for a long time and then long-lived radicals accelerate the degradation of plastics.

Thermal degradation of polyethylene mixed with poly(vinyl chloride) and poly(ethyleneterephthalate)

Thermal degradation of plastics such as polyethylene (PE), poly(vinylchloride) (PVC), poly(ethyleneterephthalate) (PET) and their mixtures (PE + PVC and PE + PET) was studied at 430 °C by batch operation to analyse the conversion of waste plastics into fuel oil. A visual inspection of the inside of the reactor was made and the macroscopic process of degradation was monitored. Products of degradation were classified into three groups: gases, liquids and residues in the reactor. The degradation of PE produced liquid products which consisted of C5-C25 fraction of hydrocarbons with a yield of 70 wt%. On the other hand, the degradation of PVC produced only 4.7 wt% liquid products which consisted of C5-C20 fraction of hydrocarbons and the degradation of PET produced no liquid products. The effect of mixing PVC and PET with PE on the yield and compositions of liquid products was investigated. The addition of either PVC or PET to PE decreased the overall liquid products yield; however, it promoted the degradation of PE into low molecular weight liquid hydrocarbon products.

Catalytic degradation of polyethylene and polypropylene into liquid hydrocarbons with mesoporous silica

Abstract The catalytic degradation of polyolefinic polymers such as polyethylene (PE) and polypropylene (PP) was carried out at atmospheric pressure by batch operation at 430 °C and 380 °C using non-acidic mesoporous silica catalyst (FSM). A comparison with non-catalytic thermal degradation and catalytic degradation using solid acid catalysis (silica-alumina, zeolite ZSM-5), silicalite, and silica-gel was made. Compared with thermal degradation, non-acidic FSM catalyst accelerated the initial rate of degradation, increased the liquid product yield and promoted degradation into lower molecular weight products. Silicalite and silica-gel had very negligible effects on polymer degradation. When the batch reaction was repeated four times using the same FSM catalyst, the extent of the decline in the degradation rate was lower for PE than PP. Compared with the solid acid catalyst, which turned completely black in the cases of both PE and PP, the deposition of coke on the used FSM catalyst was extremely slight. It seems likely that the catalytic effect of FSM for polyolefinic polymer degradation is related more to the hexagonal pore structure system of FSM.

Catalytic dechlorination of chloroorganic compounds from PVC-containing mixed plastic-derived oil

Abstract The dechlorination of chloroorganic compounds from PVC-containing mixed plastic-derived oil was studied over iron oxide and iron oxide-carbon composite catalysts. The catalysts are characterised by nitrogen adsorption and X-ray diffraction. The catalysts are deactivated initially due to the adsorption of HCl gas that is produced during the reaction. Continuous adsorption of HCl on iron oxide leads to the conversion of iron oxide to iron chloride. The catalysts’ deactivation was overcome by removing the reversible adsorbed HCl gas continuously, using He as a carrier gas.

Catalytic dehydrochlorination of chloro-organic compounds from PVC containing waste plastics derived fuel oil over FeCl2/SiO2 catalyst

A highly selective and stable FeCl2/SiO2 catalyst system was studied for the dehydrochlorination of various chloro-organic compounds from the fuel oil derived from polyvinyl chloride (PVC) containing waste plastics.