Physical and Chemical Lipase Adsorption on SBA-15. Effect of Different Interactions on Enzyme Loading and Catalytic Performance

Immobilization of Pseudomonas fluorescens lipase (Pfl) on the chemically modified, or unmodified, surface of SBA-15 mesoporous silica has been achieved. X-ray diffraction (XRD), transmission electron microscopy (TEM), and N2 physisorption are used to monitor the effect of surface functionalization on the structural and textural features of the SBA-15 silica support. The enzyme loading strongly depends on the type of enzyme-support interaction, the maximal loading of the chemisorbed lipase being about twice that of the physisorbed (502 and 256 mgprotein${{\rm g}{{- 1\hfill \atop {\rm support}\hfill}}}$ respectively). The resulting biocatalysts, regardless of the different loading, are tested with a hydrolytic catalytic assay. Despite the lower loading, the physically immobilized Pfl is more active than that which is chemically immobilized. Both biocatalysts are also active in a green process for biodiesel production, leading to almost full conversion of sunflower oil and ethanol into the corresponding ethyl esters after about 7 h at 30°C, atmospheric pressure, and in solvent-free conditions. Recycling experiments showed that the chemically immobilized Pfl was still active after twenty reaction cycles whereas the physically immobilized Pfl lost its activity after the tenth cycle