INFLUENCE OF SOME HETEROGENEOUS CATALYSTS ON PYROLYTIC CONVERSION OF MODEL POLYPROPYLENE AND HIGH DENSITY POLYETHYLENE INTO FUEL LIKE PRODUCTS

Abstract

Because of the limitations of petroleum products in terms of their high prices, scarce supplies, and the reality of petroleum depletion, emphasis must be on finding cheap, abundant & environmentally friendly alternative resources. Throughout the world, many steps are being taken in this direction to find alternatives to petroleum based fuels. Several substitute candidates including liquids from coal, biomass, spent lubricants, waste plastics, tyres, etc. are the focus of researchers in the past few decades to get fuel having properties similar to petroleum based oils. Among these, waste plastics are the promising one to get not only fuel like products to valorize petroleum and petrochemicals, but also to get rid of the disposal issues in a more environmental friendly way. The present work was aimed at catalytically converting two commonly used polyolefins i.e. PP and HDPE in a fixed-bed reactor over original and metal supported heterogeneous catalysts into useful products with emphasis on high conversion to liquid products that could be used as fuels or feed-stock in chemical industries. Four catalys systems i.e. original and metal impregnated titanates (BaTiO 3 ), prebaked clay (PBCs), bentonite clay (BCs) and activated carbon (ACs) were used to identify their potential as catalysts in conversion of PP and HDPE to liquid products with interest in gasoline and light gas oil fractions. All the laboratory prepared catalysts were calcined prior to use and characterized by using SEM, EDS, SAA, XRD and surface acidity measurements. The pyrolysis reactions were carried out in a steel made micro reactor under nitrogen environment. Preliminary experiments were performed in the temperature range of 250-400 °C in order to optimize the temperature. Time optimization study was also performed. The optimum temperature and time were decided on the basis of highest wt% yield of the liquid products.The effect of catalyst type and concentration on total conversion and conversions to liquid, gas and coke/residue was next studied. The optimum catalyst and its concentration in case of four catalysts systems were also decided on the basis of highest wt% yield of the liquid product. viiThe llquid products derived from both polyolefins in thermal and catalyzed runs in highest yields were subjected to compositional analyses by FTIR and GC-MS in order to study the carbon range and hydrocarbon group types distributions. The results indicated that polyolefins (both PP and HDPE) were converted more meaningfully into useful liquid products through catalytic route compared to thermal route. The catalytic activities of the various catalysts were toward formation of C 6 -C 12 C- range products in case of PP and C 13 -C 16 , and C 21 -C 30 range hydrocarbons in case of HDPE. Compared to thermal runs, the derived liquids were mostly comprised of paraffinic and olefinic hydrocarbons. Some of the catalysts used caused the formation of naphtenic hydrocarbons.Formation of oxygenates and aromatics were not observed. The standard fuel oil analyses developed for petroleum based fuels were applied to crude/lump liquids as well as their distillate fractions.The results indicated that the lump liquid pyrolysates derived from both thermal and catalytic degradation met the fuel grade criteria and may be used as feed stock to refineries or petrochemical industries. The fuel qualities of the distillate fractions (b.pt. 65-180 °C) closely matched with the gasoline and kerosene range hydrocarbons. On the other hands, the fuel characteristics of the distillates fractions (b.pt. 180-250 °C) showed that these fractions can be used as blends to marketable premium fuel products particularly gasoline & light gas oil.