Comparative analysis of immobilized biocatalyst: study of process variables in trans-esterification reaction

This study deals with an experimental investigation into the trans-esterification behavior of two biocatalysts produced by different immobilization techniques of the same lipase from Pseudomonas cepacia. Biocatalysts catalyzed trans-esterification of commercial frying oil. It was verified that no enzyme leaching occurs and stepwise addition of ethanol is needed to improve the process performance. When stoichiometric ethanol has been added completely at the beginning of the reaction, percent mass fraction of esters reached 33% after 9 h and 52% after 30 h. Instead, when ethanol has been added in steps, ester production gradually increased at any time. Moreover, different amounts of biocatalyst were added to the reaction system and it was found that it is not necessary to add more than 3% of biocatalyst with respect to the oil mass to avoid inhibition. The immobilization method influences the reaction progress and the intermediate-glyceride profiles were analyzed. Results showed that the two biocatalysts have the same affinity towards triglycerides, but the covalently immobilized lipase (epobond P. cepacia) has a lower affinity towards diglycerides and monoglycerides and, in general, a lower activity than the absorbed lipase (lipo P. cepacia).

A review on variation in crude glycerol composition, bio-valorization of crude and purified glycerol as carbon source for lipid production

Crude glycerol (CG) is a by-product formed during the trans-esterification reaction for biodiesel production. Although crude glycerol is considered a waste stream of the biodiesel industry, it can replace expensive carbon substrates required for lipid production by oleaginous micro-organisms. However, crude glycerol has several impurities, such as methanol, soap, triglycerides, fatty acids, salts and metals, which are created during the trans-esterification process and may affect the cellular metabolism involved in lipid synthesis. This review aims to critically present a variation in crude glycerol composition depending on trans-esterification process and impact of impurities present in the crude glycerol on the cell growth and lipid accumulation by oleaginous microbes. This study also draws comparison between purified and crude glycerol for lipid production. Several techniques for crude glycerol purification (chemical treatment, thermal treatment, membrane technology, ion-exchange chromatography and adsorption) have been presented and discussed with reference to cost and environmental effects.

Pseudomonas sp. BUP6 produces a thermotolerant alkaline lipase with trans-esterification efficiency in producing biodiesel

The present study describes the characteristics of a thermotolerant and alkaline lipase secreted by Pseudomonas sp. BUP6, a novel rumen bacterium isolated from Malabari goat, and its trans-esterification efficiency in producing biodiesel from used cooking oil (UCO). The extracellular lipase was purified to homogeneity (35.8 times purified with 14.8% yield) employing (NH₄)₂SO₄ salt precipitation and Sephadex G-100 chromatography. The apparent molecular weight of this lipase on SDS-PAGE was 35 kDa, the identity of which was further confirmed by MALDI-TOF/MS. The purified lipase was found stable at a pH range of 7-9 with the maximum activity (707 U/ml) at pH 8.2; and was active at the temperature ranging from 35 to 50 °C with the optimum at 45 °C (891 U/ml). Triton X-100 and EDTA had no effect on the activity of lipase; whereas SDS, Tween-80 and β-mercaptoethanol inhibited its activity significantly. Moreover, Ca²⁺ (1.0 mM) enhanced the activity of lipase (1428 U/ml) by 206% vis-à-vis initial activity; while Zn²⁺, Fe²⁺ and Cu²⁺ decreased the activity significantly. Using para-nitrophenyl palmitate as substrate, the K_m (11.6 mM) and V_max [668.9 μmol/(min/mg)] of the purified lipase were also determined. Crude lipase was used for analyzing its trans-esterification efficiency with used cooking oil and methanol which resulted in the worthy yield of fatty acid methyl esters, FAME (45%) at 37 °C, indicating its prospects in biodiesel industry. Thus, the lipase secreted by the rumen bacterium, Pseudomonas sp. BUP6, offers great potentials to be used in various industries including the production of biodiesel by trans-esterification.

Development of direct conversion method for microalgal biodiesel production using wet biomass of Nannochloropsis salina

In this work, the effects of several factors, such as temperature, reaction time, and solvent and acid quantity on in situ transesterification yield of wet Nannochloropsis salina were investigated. Under equivalent total solvent volume to biomass ratio, pure alcohol showed higher yield compared to alcohol-chloroform solvent. For esterifying 200 mg of wet cells, 2 ml of methanol and 1 ml of ethanol was sufficient to complete in situ transesterification. Under temperatures of 105 °C or higher, 2.5% and 5% concentrations of sulfuric acid was able to successfully convert more than 90% of lipid within 30 min when methanol and ethanol was used as solvents respectively. Also, it was verified that the optimal condition found in small-scale experiments is applicable to larger scale using 2 L scale reactor as well.