Generation of biofuels by slow pyrolysis of palm empty fruit bunches: Optimization of process variables and characterization of physical-chemical products

Abstract Residues of the palm oil agro-industry (palm empty fruit bunches - EFB) were pyrolysed to produce biofuels. Effects of several parameters on the slow pyrolysis process were evaluated using the central compound rotational design (DCCR) for modelling and optimization the process conditions aiming the maximum yield of bio-oil. After pyrolisis and using various approaches the products were characterized with emphasis on bio-oil. The response surface methodology and desirability function indicate that the temperature was the most influential parameter in regard to the liquid yield, in which the optimum pyrolysis conditions were: temperature of 628.2 °C and N2 flow rate of 0.259 L/min. The empirical relationships for the bio-gas, bio-oil, and bio-char were carried out from a second-order polynomial equation adequately describing the nonlinear behaviour of the experimental data with a precision of approximately 85%. Gas chromatography-mass spectrometry (GC-MS) and Fourier Transformer infrared (FTIR) analysis shows that bio-oil has a high content of oxygenated compounds with four main components: hexadecanoic acid methyl ester (25.57 area%), nonane (12.51 area%), n-hexadecanoic acid (10.66 area%) and phenol (10.13 area%). Moreover, high-performance thin-layer chromatography (HPTLC) analysis showed the bio-oil is very promising for biodiesel-based automotive additives preventing oxidation of the bis-allylic methylene groups and the consequent generation of free radicals. Biochar showed low yield (27.52%) but good energy capacity, with a calorific value of 19.27 MJ/kg. Regarding to gases production, CO2 and CH4 are the main compounds observed in optimized conditions suggestion its use like raw material in the energy production.