No abstract

Coprocessing behavior of mixtures of high density polyethylene ͑HDPE͒ and deoiled cakes of Jatropha and Karanja was studied by thermogravimetric analyses under dynamic conditions in the presence of nitrogen atmosphere and compared with those of individual materials. Experiments were carried out in the temperature range of ambient temperature to 900°C at two heating rates ͑5 and 20°C / min͒. Kinetic studies indicated activation energies for HDPE decomposition to be 235 and 258 kJ/mol at heating rates of 5 and 20°C / min, respectively. Values of activation energy for pyrolysis of cakes of Jatropha and Karanj and those for cake-HDPE mixtures varied with the rate of heating as well as with the three temperature ranges. This variation has been explained based on the materials' decomposition behavior. Reduction in activation energy for decomposition of the mixtures implies synergetic effects to be existing when two materials are coprocessed together.

Thermal degradation behavior of mixtures of rice bran (RB) and high density polyethylene (HDPE) was investigated by thermo-gravimetric analyses (TGA) under dynamic conditions in nitrogen atmosphere and was compared with that of individual materials. Experiments were carried out in the range of ambient temperature to 900 o C at two heating rates (5 and 20 o C per minute). Kinetic analysis indicated that activation energy for pyrolysis of RB, HDPE and those for RB-HDPE mixtures varied with rate of heating as well as with the three temperature ranges. This variation has been explained on the materials' decomposition behavior. Maximum difference between experimental and theoretical mass loss (∆m) was 26% at 475 o C and 34% at 489 o C at the heating rates of 5 and 20 o C per minute, respectively. These maxima indicate stronger interactions at corresponding temperature between RB and HDPE during copyrolysis. Reduction in activation energy for pyrolysis, lower temperatures at which rate of decomposition is highest, and negligible quantity of the residue suggest a synergism between thermal degradation of RB and HDPE.

Three plastics, high density polyethylene (HDPE), polypropylene (PP) and polystyrene (PS), were individually co-pyrolysed with deoiled cake of jatropha (JC) at 400 and 450°C in a batch reactor in the presence of nitrogen under atmospheric pressure to produce modified liquid fractions. At higher temperature (450°C), the yield of liquid fractions by the pyrolysis of plastics (HDPE, PP and PS) alone was found to increase by 11, 12.5 and 11% for HDPE, PP and PS, respectively. Furthermore, the gaseous fraction increased by 1.3 to 2.6% while the residue generation reduced by 12.3 to 15.1%. In comparison with only plastics pyrolysis, the yield of the liquid fraction improved by 2.0 to 4.9% for their co-pyrolysis with JC. Gas chromatography-mass spectrometry analyses demonstrated that the co-processing afforded a reduction of paraffin and olefins in the liquid fractions for all of the experiments. This reduction was found to be in the order of PS > PP > HDPE. Furthermore, the proportion of oxygenates in the liquid product increased in the order of PP > HDPE > PS. Physical characteristics such as oxygenates, water contents, acid values and viscosity increased during the co-pyrolysis of plastics and JC in contrast to the liquid fractions obtained from the pyrolysis of pure plastics. Furthermore, co-pyrolysis offered a reduction in calorific values.

Various technological methods are being developed to overcome the drawback of plastics, namely, their non-biodegradability. Conversion of waste plastics into fuels is one of the best means of conserving valuable petroleum resources in addition to protecting the environment by limiting the volume of non-degradable waste. Catalytic—rather than thermal—decomposition of plastics allows higher selectivity of products in the boiling point range of liquid fuels, for example, diesel and gasoline. In this context, an attempt has been made to review the relevant literature dealing with catalytic decomposition of waste plastics into liquid fuels. The paper also addresses the effects of different properties of catalysts, for example pore system, pore size, crystal size, Si/Al ratio of zeolites, and acidities, on product distribution.