Research Article
Kumar S, Ghaly AE and Broo
Abstract
The effectiveness of enzymatic transesterification of animal fat using the experimental enzyme catalyst NS88001 with no solvent was studied. The effects of oil:alcohol molar ratio (1:1, 1:2, 1:3, 1:4 and 1:5), reaction temperature (35, 40, 45 and 50°C) and reaction time (4, 8, 12 and 16 h) on the biodiesel yield were evaluated. The highest biodiesel yield was obtained at the 1:4 molar ratios. No reactions were observed with the 1:1 and 1:2 (oil:alcohol) molar ratios and increasing the oil:alcohol molar ratio above 1:4 decreased the biodiesel conversion yield. The rate of conversion of fatty acid esters increased with increases in the reaction time. The reaction proceeded slowly at the beginning and then increased rapidly due to the initial mixing and dispersion of alcohol into the oil substrate and activation of enzyme. After dispersion of alcohol, the enzyme rapidly interacted with fatty acids esters giving a maximum conversion yield. Increasing the reaction time from 4 to 16 h increased the conversion yield of biodiesel by 114.95-65.59%. The interactions between enzyme polymer surface and substrate appears to be dependent on reaction temperature due to hydrogen bonding and ionic interactions which play an important role in maintaining the thermostability of lipase in the system. The optimum reaction temperature for the experimental enzyme catalyst (NS88001) in the solvent free system was 45°C. Increasing the reaction temperature from 40 to 45°C increased the biodiesel conversion yield while higher temperatures above 45°C denatured the specific structure of enzymes and resulted in decreased methyl esters formation. The activity of experimental enzyme catalyst NS88001 in the presence of methanol without solvent at the optimum conditions (a reaction temperature of 45°C, an oil:alcohol molar ratio of 1:4 and a reaction time of 16 h) remind relatively constant for 10 cycles and then decreased gradually reaching zero after 50 cycles.