Abstract
We entrapped lipase from Pseudomonas cepacia in polyallylamine-mediated biomimetic silica, and then applied entrapped lipase to the synthesis of biodiesel with soybean oil or waste cooking oil as a feedstock. The effects of reaction temperature, substrate molar ratio (methanol/oil) and n-hexane content (w/w of oil) were evaluated using response surface methodology (RSM) combined with Box-Behnken design. The optimal reaction conditions for soybean oil were 43.6 °C, substrate molar ratio of 4.3%, and 75% n-hexane. The predicted and experimental values of biodiesel conversion were 79% and 76%, respectively. The optimal reaction conditions for waste cooking oil were 43.3 °C, substrate molar ratio of 5%, and 38% n-hexane. The predicted and experimental values of conversion were 68% and 67%, respectively. The conversion efficiency remained the same even after 1-month storage of entrapped lipase at 4 °C or room temperature.
Highlights
The search for alternative fuels has drawn immense amount of attention during the past decade because of the inevitable depletion of fossil fuels
After removing the n-hexane using a rotary evaporator, content of fatty acid methyl esters (FAME), kinematic viscosity at 40 °C, and density at 15 °C of the biodiesel synthesized from waste cooking oil were 72.3% ± 0.01% (w/w), 6.67 ± 0.04 mm2/s, and 883 ± 3 kg/m3 (N = 3), respectively
The density was within the specified range of 860 to 900 kg/m3. These results clearly indicate the current conversion of the waste cooking oil needs to be increased in order to improve the properties of the biodiesel
Summary
The search for alternative fuels has drawn immense amount of attention during the past decade because of the inevitable depletion of fossil fuels. The alkali-catalyzed process has the advantages of short reaction time, high yield, and low cost for the catalysts. Biomimetic silica, which mainly mimics the cell wall formation of diatoms, has been applied to entrap a variety of biomolecules and inorganic materials [26] It can be formed in vitro by mixing silicic acid with silaffin peptides derived from diatom Cylindrotheca fusiformis such as R5. (H2N-SSKKSGSYSGSKGSKRRIL-COOH) or their synthetic counterparts in the presence of phosphate [27] Polymers such as poly-L-lysine and polyallylamine structurally resembling the biological templates have been reported to catalyze silicification [28]. Such immobilization technique offers advantages such as mild reaction condition, rapid kinetics, excellent stability, and ease of operation [26]. We evaluated the reusability and the storage stability of entrapped enzyme
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