Use of hydroxyapatite as a support in the immobilization of Thermomyces lanuginosus lipase for application in the production of biodiesel using a by-product as lipid raw material

Abstract

The use of new materials in the field of biofuel production has been represented as a step in the development of remarkable catalysts. The use of lipases in the production of biodiesel is often seen as a cost-limiting step, as the operating expenses in recovering such catalysts can lead to unfeasible market expectations. In this study, hydroxyapatite (HAp) particles were evaluated as a support to immobilize commercial lipase, following application in ethyl ester synthesis. First, hydroxyapatite was synthesized through the co-precipitation method at constant pH and selected as a support to be used in enzyme immobilization. The characterization of the biocatalyst support materials produced was carried out using DRX, BET, FTIR, TGA, and SEM analysis. The lipase from Thermomyces lanuginosus was then immobilized in the matrices, and, subsequently, there was transesterification of the vegetable oil deodorization distillate (VODD). The biodiesel samples generated showed that they were within commercial standards, achieving ester conversion greater than 96.5%. Other properties such as density (0.87 g.cm^-3) and viscosity (4.36 mm².s^-1) meet the specifications required by ASTM to be used as a biofuel. In the experiment planning technique, the results revealed an experimental trend and a defined behavior: a higher lipase loading in the immobilization and the use of temperatures in the range of 40-50 °C favor high conversions of ethyl esters. Thus, this confirms that the enzymatic chemical catalyst was able to form the main fatty acid esters even using a residual lipid raw material.

Keywords: Biodiesel; Hydroxyapatite; Lipase; Transesterification.

Fig. 1

X-ray diffractogram of the hydroxyapatite support (HAp)

Fig. 2

FTIR spectrum of the hydroxyapatite support (HAp)

Fig. 3

Hydroxyapatite (HAp) support TG curve

Fig. 4

SEM micrographs of hydroxyapatite support (HAp)

Fig. 5

SEM micrographs of Thermomyces lanuginosus lipase immobilized on hydroxyapatite (HAp)

Fig. 6

Hydrolysis activity in relation to the Michaelis–Menten kinetic model in TL immobilized on HAp

Fig. 7

Profile of formation of ethyl esters as a function of the reaction time of transesterification of commercial soybean oil using hydroxyapatite as chemical catalyst, without calcination and calcined at 500 °C

Fig. 8

Initial rate of transesterification using different lipid feedstocks (VODD and soybean oil) with ethanol catalyzed by TL lipase immobilized on HAp particles

Fig. 9

Effects of the independent variables studied, X₁ = lipase loading in immobilization (% wt) and X₂ = temperature (°C) and their interactions on the conversion to ethyl esters (%) to a 95% confidence level (p < 0.05)

Fig. 10

Response surface for the effects of the lipase loading in immobilization and temperature variables for the formation of methyl esters

Fig. 11

Profile of ethyl esters formation as a function of the reaction time of the transesterification of VODD using TL lipase immobilized on HAp as catalyst under conditions estimated by factorial design: catalyst concentration 100% (0.50 g/1 g of support) and temperature of 45 °C