Biolubricant production from castor oil in a magnetically stabilized fluidized bed reactor using lipase immobilized on Fe3O4 nanoparticles

Abstract

Candida rugosa lipase was covalently immobilized onto functionalized magnetic nanoparticles (MNPs), and the particles were structurally characterized by TEM, XRD, FTIR, and VSM analyses. The MNPs-immobilized lipase (MNPs-IL) possessed a specific activity of 2.4U/mg protein when the protein loading and immobilization efficiency were 38mg protein/g MNPs and 95%, respectively. The enzymatic conversion of castor oil to biolubricant in a magnetically stabilized fluidized bed reactor (MSFBR) was studied. The performance of MNPs-IL in the reactor was affected by the magnetic field strength and liquid flow rate. The effect of other reaction variables, such as enzyme amount, substrate molar ratio, and temperature, were also determined. A 96.9% methyl ester yield was obtained after 24h reaction under the optimum conditions. The biocatalysis was modeled with reference to the ping-pong bi-bi mechanism and considering substrate inhibition, and the following kinetic parameters were obtained: Vmax=6.64mmol/Lmin, Km,oil=219.16mmol/L, Km,methanol=881.34mmol/L, Ki,oil=1305.74mmol/L, and Ki,methanol=623.15mmol/L. The data were statistically analyzed, and the adequacy of the suggested model was confirmed. In a reusability test of the MNPs-IL in the MSFBR, 87% of the initial activity was retained after eight consecutive runs.