| The biggest advantage of biofuels is renewable and zero emission compared with traditional fossil fuels.Waste vegetable oil is one of the main raw materials for biofuel production.Thermal cracking of waste vegetable oil obtain renewable hydrocarbon fuel with large quantity of noncondensible gas byproduct rich in hydrogen.Meanwhile waste plastics which is known as white pollution produce low liquid fuel during thermal cracking due to coking since not enough hydrogen supply.Therefore co-pyrolysis of waste vegetable oil and waste polyethylene plastics was investigated in the present work.This study focused on production of high quality renewable hydrocarbon fuels through catalytic pyrolysis of waste vegetable oil and polyethylene with the Zr2O3/Al2O3/TiO2 polycrystalline ceramic foam as catalyst.Solid,liquid and gas products are analyzed with GC-MS?FT-IR and GC.This study also investigated the effect of pyrolysis temperature,time,ratio of catalyst and material on the liquid yield and the distribution of product components and developed the possible reaction mechanism of co-pyrolisis of waste vegetable oil and polyethylene.The catalyst was also characterized and the optimal conditions of co-pyrolysis of waste vegetable oil and polyethylene were obtained through the Box-Behnken experiment design.It should provide some scientific guidances for preparation high quality renewable hydrocarbon fuels from co-pyrolysis of waste vegetable oil and polyethylene and reduce the bottleneck of making high quality renewable hydrocarbon fuels in China.Following are the effect of different pyrolysis conditions on the production of the renewable hydrocarbon fuels in the process of co-pyrolysis of waste vegetable oil and polyethylene:(1)The liquid yield was increased first and then decreased as the increase of pyrolysis temperature,the optimal temperature is 43?.The content of alkanes were 74.47%,olefins were 0.85%,arenes were 19.85%,and little oxygenated chemicals were found in the pyrolytic liquid.(2)The optimal retention time was 40 min.The content of straight-chain alkanes were continuously decreased from 95.15%at 20 min to 59.49%at 60 min,while cycloalkanes,olefins,arenes were increased at the same time in the pyrolytic liquid.The content of oxygenated chemicals was also increased slightly at the same time.(3)The optimum catalyst addition ratio was 15%.The content of straight-chain alkanes increased from 64.93%to 97.85%when catalyst addition ratio increased from 0%to 15%and slightly decline to 92.04%at 20%addition ratio.The content of cycloalkanes decreased gradually.The content of arenes changed little when catalyst addition ratio is less than 10%,but reduced rapidly when more than 10%.(4)The content of straight-chain alkanes was almost 97.85%in the pyrolytic liquid when the ratio of waste vegetable oil and polyethylene was 1:1.(5)The Zr2O3/Al2O3/TiO2 foam ceramic catalyst was characterized.Both Lewis acid site and Bronsted acid site existed in the catalyst.There were a lot of pore structure observed both on surface and internal of the catalyst after calcination through the environmental scanning electron microscope.The pores were irregular and the corrugation of pores greatly increased the catalyst surface area.The liquid product and gas product obtained from the pyrolysis of different systems were also analyzed in order to understand the possible reaction mechanism.Abundant H2,CH4 and part of CO,CO2 were found in the gas product.The results show that glyceryl of the vegetable oil may serve as the main hydrogen source,and provided hydrogen in the co-pyrolysis.Pyrolysis reaction mechanism of the polyethylene belonged to the free radical reactions with irregular fracture,cracking of waste oil and oxygen removal was mainly by means of acyl oxygen bond cleavage(i.e.decarbonylation),and accompanied by decarboxylation reaction.Through analysis of liquid product through elemental analyzer,and calculation of the calorific value of pyrolytic oil,the heating value was found to be around 41.2MJ/kg which is similar to the#0 diesel.Comparison of pyrolytic oil and#0 diesel,it was found that the alkane content in the pyrolytic oil was far more than that of#0 diesel.Finally,we obtained the regression equation from the Box-Behnken experimental design to be:Y%=65.14+2.51 A+0.57B+0.2C+0.24AB-0.68AC-0.5BC-1.46A2-0.69B2-0.69C2.The determine factor on the liquid yield in the co-pyrolysis of waste oil and polyethylene was in the order of pyrolysis temperature>pyrolysis time>addition proportion of catalyst.Response surface optimization experiment gave the optimum conditions as:pyrolysis temperature of 450 ?,reaction time of 45 min,catalyst addition proportion of about 15%. |
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