Immobilization of lipase on iron nanoparticles and kinetic characterization for bio-oil esterification
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Date
2016-07
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G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Abstract
Agro-waste is a promising source of renewable energy. It can be converted to bio-oil by pyrolysis, but due to many limitations, its use as a fuel is not feasible. Corrosiveness, due to presence of acids is one of the limitation. Esterification is an upgrading method to neutralize the acidity. Chemical catalysts have been utilized for esterification but did not have desired results. Lipases can perform esterification/transesterification reactions. Immobilization can be an efficient method to overcome the limitation of free-lipase catalyzed reactions. In the present study, commercial Aspergillus niger lipase (EC 3.1.1.3) was effectively immobilized on iron nanoparticles via glutaraldehyde linkage. Iron nanoparticles were synthesized by coprecipitation of Fe²
⁺ and Fe³
⁺ under nitrogen protection in ammonia solution (25%). These particles were subsequently amine functionalized by using 3aminopropyltriethoxysilane (APTES). The binding of lipase to magnetic particles was confirmed by Fourier transform infrared (FT-IR) spectra and TEM. Further, the characterization of bare iron nanoparticles and enzyme bound iron nanoparticles was done by TEM and SEM. Esterification reaction was carried using lauric acid and 1propanol as substrate. A comparative study of the kinetic parameters, determining their Km, Vmax, optimum pH and temperature for free and immobilized lipase was done. It was observed that Km and Vmax for immobilized lipase (175.5 mM , 0.983 mM/min) was higher than the free lipase (121.2 mM, 0.669 mM/min). Also, the optimum pH and temperature for immobilized lipase (50 ⁰ C) was higher than free lipase (45 ⁰ C). The Kcat value for free enzyme was 2.67 min-1 while for immobilized enzyme was 3.92 min-1. The catalytic efficiency of free lipase was found to be 0.2207 mMmin-1 while of immobilized lipase was 0.224 mMmin-1. Esterification of bio-oil samples, obtained from wheat straw and sugarcane dried leaves was carried out. By determining the acid value of bio-oil samples before and after esterification, a significant change in acid value was observed. However, by GC-MS analysis significant esterification was seen in some samples while in others it was nonsignificant.
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