Candida rugosa lipase was covalently immobilized on rice straw activated with glutaraldehyde using poly(ethylene glycol) (PEG) as the stabilizing agent. The effects of PEG molecular weight and enzyme loading were studied according to a full 2(2) factorial design. Higher immobilization yields (>70%) were attained when the lipase loading was 95 units/mg of dry support, independent of PEG molecular weight. All derivatives showed high hydrolytic and synthetic activities. This work provides preliminary results on the use of agricultural residues as a support matrix for immobilizing lipase and on the application of the resulting derivatives to butyl butyrate synthesis as a study model.

Heteropolyacids (HPA) with Keggin structures, such as H 3 PMo 12 O 40 (H 3 PMo), have been described as efficient catalysts in trans/esterification reactions due to their tolerance to water and free fatty acids contents, with particularly well-suited characteristics of high proton mobility and stability. The versatile array of HPA is considerably increased when such catalysts are supported onto solid matrices. In this sense, Al 2 O 3 was assessed as support for H 3 PMo to be used in trans/esterification reactions to produce biodiesel from high-acid feedstocks. The catalyst structure was characterized and applied on trans/ esterification reaction of acid oils using ethanol as acyl acceptor. A face centered composite design was employed to conduct the experimental design and results analysis, taking macaw palm oil as study model. The process achieved an optimum level of 99.8% ester content and 4.1 mm 2 s À1 viscosity under the following reaction conditions: 190 C reaction temperature, 50 : 1 ethanol-to-oil molar ratio and 13.0% catalyst concentration. Other tested feedstocks (fungal single cell oil and residual frying oil) were also tested promoting satisfactory results, though the parameters were found to be slightly outside the limits set by the USA (ASTM D6715) standard. The H 3 PMo/Al 2 O 3 catalyst presented good regeneration and can be reused for up to four reaction cycles and requires lower ethanol-to-oil ratio, temperature, and catalyst concentration in comparison with other data from the literature.

Niobium oxide impregnated with sodium (Na/Nb2O5) was used as a heterogeneous catalyst to produce biofuel from conventional raw materials, such as soybean oil and beef tallow, and non-conventional feedstocks, including andiroba, babassu, coconut, crambe, macaw palm, palm, palm kernel, and jatropha oils. The trials were performed at fixed conditions using 10% catalyst at 78.5 °C under stirring (600 rpm) for 5 h. On the basis of the results generated by gas and liquid chromatographies, high catalytic activity was found for all tested feedstocks, revealing yields higher than 95%. The purity of the ethyl esters was validated by thermogravimetric analysis and nuclear magnetic resonance. The Na/Nb2O5 catalyst performed efficiently, converting the fatty acids present in the lipid raw materials to the ethyl esters, and showed high stability in consecutive batches, generating products that meet the specificity of international standards. The heterogeneity of the catalyst was also confirmed by determining the sodium concentration in both biodiesel and the catalyst after consecutive batch runs.

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