Imobilização de lipase em hidróxido duplo lamelar obtido a partir de resíduos ácidos de decapagem e aplicação na hidrólise de óleos de fritura

Abstract

The use of industrial waste pickling acid (WPA) for the production of layered double hydroxides (LDH) is a relevant alternative for reducing raw material costs and making the LDH production process more sustainable. Layered double hydroxides (LDH) belong to a category of synthetic clays that are similar to cationic clay minerals and have anion exchange properties. They are suitable for enzyme immobilization because they are relatively affordable, have various compositions, low toxicity and high surface area. Considering the concern with the disposal of industrial waste and analyzing the catalysis potential of lipases immobilized in LDHs, this work proposes the immobilization, characterization and application of lipases from Burkholderia lata in a layered double hydroxide (LDH) formed by zinc, iron and aluminum containing chloride, obtained from waste pickling acid (WPA) that arises when removing iron oxide layers from the surface of raw steel. For the enzyme immobilization process (LDH-Lip), by physical adsorption, an efficiency of 71% (24 h) and retention of activity after immobilization of 193% were observed. Regarding the characterization, scanning electron microscopy (SEM) showed that after immobilization, the LDH maintained the lamellar structure with less grouped morphology, in relation to LDH without enzyme, and presence of sharp crystallites. For the thermogravimetric analysis (TGA), greater stability was noted for LDH-Lip in relation to free lipase. It was observed that for the analysis of LDH-Lip by X-ray diffraction (X-RD) there was a loss of crystallinity of the material, maintaining the reference diffraction peaks practically in the same positions. The FTIR spectra were very similar for LDH before and after immobilization. LDH-Lip showed high stability at acidic pHs (pH 4.0 to 5.0), with residual activity close to 90%, and was stable at 40°C. Regarding storage stability at 4°C, the immobilized enzyme did not lose activity for 30 days, with a reduction of approximately 15% after 60 days. Free lipase and LDH-Lip were applied in hydrolysis reactions of used vegetable oils (frying oil) for the production of free fatty acids. The highest amounts of free fatty acids, 959 and 133 mol, were obtained at 55°C and 100 U, for free lipase and after immobilization, respectively. It is concluded that the immobilization of lipase in LDH, obtained from WPA, can be an alternative for the application of advanced materials (LDH) in the production of heterogeneous biocatalysts, thus contributing to the sustainability of chemical processes.