Application of a Burkholderia cepacia lipase-immobilized silica monolith to batch and continuous biodiesel production with a stoichiometric mixture of methanol and crude Jatropha oil

Abstract

Background: The enzymatic production of biodiesel through alcoholysis of triglycerides has become more attractive because it shows potential in overcoming the drawbacks of chemical processes. In this study, we investigate the production of biodiesel from crude, non-edible Jatropha oil and methanol to characterize Burkholderia cepacia lipase immobilized in an n-butyl-substituted hydrophobic silica monolith. We also evaluate the performance of a lipase-immobilized silica monolith bioreactor in the continuous production of biodiesel.

Results: The Jatropha oil used contained 18% free fatty acids, which is problematic in a base-catalyzed process. In the lipase-catalyzed reaction, the presence of free fatty acids made the reaction mixture homogeneous and allowed bioconversion to proceed to 90% biodiesel yield after a 12 hour reaction time. The optimal molar ratio of methanol to oil was 3.3 to 3.5 parts methanol to one part oil, with water content of 0.6% (w/w). Further experiments revealed that B. cepacia lipase immobilized in hydrophobic silicates was sufficiently tolerant to methanol, and glycerol adsorbed on the support disturbed the reaction to some extent in the present reaction system. The continuous production of biodiesel was performed at steady state using a lipase-immobilized silica monolith bioreactor loaded with 1.67 g of lipase. The yield of 95% was reached at a flow rate of 0.6 mL/h, although the performance of the continuous bioreactor was somewhat below that predicted from the batch reactor. The bioreactor was operated successfully for almost 50 days with 80% retention of the initial yield.

Conclusions: The presence of free fatty acids originally contained in Jatropha oil improved the reaction efficiency of the biodiesel production. A combination of B. cepacia lipase and its immobilization support, n-butyl-substituted silica monolith, was effective in the production of biodiesel. This procedure is easily applicable to the design of a continuous flow-through bioreactor system.

Figure 1

Comparison of the production rate of biodiesel from different oil feedstocks. Jatropha oil and methanol (closed circles), rapeseed oil and methanol (closed squares), rapeseed oil, 18% oleic acid and methanol (closed triangles), and Jatropha oil and methanol with non-immobilized lipase (closed diamonds). Methanol:oil molar ratio, 3:1; water content, 0.6% (w/w).

Figure 2

Effect of water content on biodiesel yield. After 0.5 hours (closed gray bars), after 12 hours (open circles) and after 24 hours (closed gray circles). Methanol:oil molar ratio, 3:1.

Figure 3

Effect of methanol:oil molar ratio on the production rate of biodiesel. 1:1 (open circles), 3:1 (closed circles), 4:1 (closed triangles), 5:1 (closed squares), and 6:1 (closed diamonds). Water content, 0.6% (w/w).

Figure 4

Effect of washing of used immobilized lipase during its repeated use. First reaction (open circles), second reaction after washing with acetone (open squares), second reaction after washing with ter-butanol (open diamonds), second reaction without washing (closed circles). Methanol:oil molar ratio, 3:1; water content, 0.6% (w/w).

Figure 5

Effect of the addition of silica gel on biodiesel yield. After 0.5 hours (closed gray bars), after 12 hours (open circles) and after 24 hours (closed gray circles). Methanol:oil molar ratio, (a) 3:1; (b) 3.3:1; and (c) 3.5:1. Water content, 0.6% (w/w).

Figure 6

Schematic representation of a flow-through silica monolith bioreactor system. (1) Reservoir for substrate solution, (2) semi-micro HPLC pump, (3) lipase-immobilized silica monolith bioreactor (10 mm × 10 cm or 30 cm), and (4) receiver for product solution.

Figure 7

Steady state yields of biodiesel in the lipase-immobilized silica monolith bioreactor. The yields are shown as a function of W/v (mass of lipase divided by flow rate of substrate solution). The substrate solution, composed of methanol and oil at 3:1 molar ratio and 0.6% (w/w) water, was fed continuously at constant flow rates between 0.6 mL/h and 30 mL/h to the bioreactor (10 mm × 30 cm) loaded with 4.92 g silica monolith containing 1.67 g lipase.

Figure 8

Operational stability of the lipase-immobilized silica monolith bioreactor in the continuous production of biodiesel. The substrate solution, composed of methanol and oil at 3:1 molar ratio and 0.6% (w/w) water, was fed continuously at a constant flow rate of 0.06 mL/h to the bioreactor (10 mm × 10 cm) loaded with 1.87 g silica monolith containing 0.63 g lipase.