The lipase-catalyzed methyl esterification of the fatty acids present in canola oil deodorizer distillates (CODD) was studied by Ramamurthi et al. (1991).

CODD was esterified to methyl esters, using immobilized lipase Randozyme SP-382 as catalyst. Conversion of the FFA up to 96% was achieved without the use of vacuum or a dehydrating agent.

It was found that three variables, namely moisture content of the enzyme, reaction time and the amount of molecular sieves, did not exhibit any profound effect on the conversion rate. On the contrary, the ratio of the reactants had a significant effect on the conversion equilibrium and showed a high interaction effect along with the temperature. High conversion (>90%) was obtained at combinations of both high temperature (70°C) and low ratio of reactants (1.2) and for combinations of low temperature (50°C) and high ratio of reactants (2.0). It was observed that higher concentrations of enzymes could compensate the negative effect of increased temperature. The conversion of acylglycerols was not investigated in this study, since the esterification was considered as a preliminary step for the recovery of tocopherols and sterols.

Facioli and Barrera-Arellano (2001) investigated the enzymatic esterification of the FFA from SODD with ethanol using immobilized fungal lipase (LipozymeIM) as biocatalyst. SODD contained 47% FFA, 26% neutral oil and 26% unsaponifiable matter. The best conversion was above 88% with no tocopherol losses.

The esterification of S ODD with butanol, using Mucor miehei lipase as biocatalyst and SC-CO2, has been described by Nagesha et al. (2004). The feedstock was preliminary filtered in order to remove sediments and sterols and enzymatic hydrolyzed to FFA using immobilized lipase (Candida rugosa) in SC-CO2 reactor unit. Hydrolyzed SODD containing <88% FFA was further enzymatically esterified with M. miehei in presence of butanol, with a maximum yield of 95% FABE. The content of acylglycerols was not affected by esterification. The high content of residual glycerides (3%) present in the final FABE impeded its direct use as biodiesel.

Wang et al. (2006) described a process for simultaneous conversion of FFA (28%) and acylglycerols (60%) from SODD to alkyl esters using a mixture of two enzymes (3% Lipozyme TL IM and 2% Novozym 435) in the presence of tert — butanol as co-solvent. It was found that the negative effects on the enzyme stability caused by the excessive methanol ratio and by-product glycerol could be completely eliminated by using tert-butanol. The lipase activity remained stable after 120 cycles. The maximum yield of FAME (84%) was achieved with an increase of tert-butanol content up to 80% (based on the oil weight). However, a further increase of the solvent resulted in a decrease of the methyl esterification (ME) yield which was explained by the dilution effect on reactants.

Fine-porous silica gel and molecular sieves (3А) were found to be effective to improve biodiesel yield by controlling the water concentration formed as a by-product during the reaction. A conversion yield of 97% could be achieved when the 3А molecular sieves quantity was 10 times the maximal water weight (calculated from FFA) and 93% with less than 10 times silica gel as adsorbent. However, more than 10 times silica gel led to a decrease in the ME yield, which was explained by the reduced availability of methanol for the methanolysis due to its absorbance by silica.

Du et al. (2007) investigated the enzymatic esterification of SODD containing 28% FFA, 60% TAG and 6% tocopherols. The reaction was a lipase-mediated methanolysis using Novozym 435 as catalyst, at 40°C in a solvent-free medium. The enzyme kept its activity after being reused for 10 cycles, each cycle being 24 h. The highest biodiesel yield of 95% was achieved by adding tenfold molecular sieves (3А). The investigation of the lipase to methanol tolerance revealed that the lipase could maintain its stability and activity in the presence of methanol at even a three molar concentration. This tolerance was attributed to the presence of other compounds than TAG, namely FFA, sterols and tocopherols. A linear relationship between the FFA content and the lipase tolerance to methanol was observed but the presence of sterols and tocopherols showed no effect.