Crude glycerol utilisation in monolaurin production using immobilised Rhizomucor miehei lipase: Optimisation and thermodynamics study

Abstract

The significant growth of biodiesel industry causes an excessive production of crude glycerol in Malaysia's market, especially being as one of the global biggest producers and exporters of palm oil. The ability of crude glycerol being reused as a substrate to produce monolaurin has been the main focus while catalysing the production efficiency using Lipozyme RM IM, a commercial immobilised Rhizomucor miehei lipase in a solvent-free system. Optimal reaction conditions obtained were 8:1 molar ratio of crude glycerol to lauric acid, temperature 47°C, and lipase loading 1 wt% of lauric acid. Over 82% lauric acid conversion with 56 mol% monolaurin yields was achieved within 8 hr. Using Arrhenius equation and transition-state theory, thermodynamic studies on monolaurin synthesis under the optimum conditions were performed. Energy of activation (Ea) and energy of deactivation (Ed) were found to be 89.5 kJ mol-1 and 110.7 kJ mol-1, respectively, suggesting that higher energy was required for enzyme irreversible denaturation to occur. Values of enthalpy (86.90≤ΔH≤86.84kJ mol-1 entropy(0.29≤ΔS≤0.28kJ mol K-1)and Gibbs free energy(-2.53≤ΔG≤-5.22 kJ mol-1) of the esterification were also determined.