Hydrogenation of non-polar Fraction of Bio-oil from Co-pyrolysis of Corn Cobs and Polypropylene for Bio-diesel Production

Bio-diesel was synthesized by hydrogenating the non-polar fraction of the bio-oil produced from the co-pyrolysis between corncobs and polypropylene. Co-pyrolysis of corn cobs and polypropylene was conducted in a stirred tank reactor at heating rate of 5°C/min and maximum temperature of 500°C to attain synergetic effect in non-polar fraction yield where polypropylene served as a hydrogen donor and oxygen sequester so that the oxygenate content in the biofuel product reduced. Stirred tank reactor configuration allowed phase separation between non-polar and polar (oxygenate) compounds in the bio-oil. Hydrogenation reaction of the separated non-polar phase, which contained alkenes, was carried out in a pressured stirred tank reactor using a NiMo/C catalyst in order to reduce the alkene content in the bio-oil. The aim of the present work is to reduce the alkene content in the separated non-polar fraction of bio-oil by catalytic hydrogenation to obtain biofuel with low alkene content and viscosity approaching to that of diesel fuel. To quantify effect of the pressure on the alkene composition, the experiment was done at H2 initial pressures of 4, 7, 10, and 13 bar and at corresponding saturation temperatures of octane. The biofuel products were characterized using GC-MS, LC-MS, FTIR spectroscopy, H-NMR, Higher heating values (HHV) and viscometer for comparison with those of commercial diesel fuel. Analysis of the lower molecular weight fractions of biofuels by GC-MS found that the hydrogenation reactor at pressures at 4 and 7 bar produced biofuels with predominant hydrocarbon contents of cycloalkanes and alkanes, while that at 10 and 13 bar produced biofuels with predominant contents of alkanes and alkenes. In comparison, diesel fuel contains mostly alkanes and aromatics. However, analysis over the whole content of bio-oil by H-NMR found that different pressures of reactor hydrogenation did not reduce alkene compositions in biofuels appreciably from alkene composition in bio-oil feed. In comparison, diesel fuel contained mostly alkanes with aromatic composition about 4% and no alkene content. Various data suggest that alkene content in the biofuels be reduced to approach their viscosity to that of diesel fuel. Modification of the hydrogenation reactor is required by improving convective momentum of hydrogen gas into the bio-oil to enhance contact of solid catalyst, hydrogen gas and bio-oil.