Avaliação catalítica do NiO simples e sulfatado (NiO-SO4²-) aplicado na reação de transesterificação e esterificação etílica

Abstract

Literature has shown the increase use of catalyst based on simple and modified oxides in transesterification and esterification for biodiesel obtention; this is due mainly to its role and economic activity development. Regarding, the objective of the present work was to obtain a simply catalyst having nickel oxide (NiO) and sulfates (NiO-SO4^2-) by the polymeric precursors method, and in order to evaluate how different temperatures can influence in the crystallization and sulfation of the materials in transesterification/esterification process, temperatures of 600 and 700 ºC were used. This method evaluates the biodiesel production through transesterification reaction and simultaneous transesterification and esterification (TES). Synthesized nickel oxides were characterized by X-Ray Diffraction, Infrared Absorption Spectroscopy, Raman Spectroscopy and UV-vis Spectroscopy. Catalytic tests were conducted inside a parr reaction using commercial soybean and frying residual oils under the necessary condition for the reaction: molar ration ethanol/oil (6:1), catalyst percentage of 3% mass in a reaction time of 4h and temperature of 200 ºC. The X-Ray Diffraction analysis showed three well defined peaks resulting from the faced centered cubic structure of NiO, with spatial group Fm-3m, according crystallographic record (JCPDS Nº 00- 047-1049). For the Infrared spectrum region, it was observed the presence of characteristic bands of NiO and SO4^2- , the latter is present in the surface of the former; it is a sulfation efficiency indicator. Raman spectrum analysis showed longitudinal first and second mode order, transversal second order and the interaction between both; theses modes referred to NiO and the influence sulfates groups caused on them. In UV-vis spectroscopy region, bands for ligand-metal charge transfer (LMCT), octahedral Ni^2+ in simple NiO samples, and tetrahedral Ni^2+ were observed by disposition of sulfate groups. The tested catalysts showed an interesting catalytic activity for the production of biodiesel. With a conversion rate below 55% for soybean commercial and residual oil. For the catalyzed sample with calcinated NiO-SO4^-2 (600 ºC) the best efficiency was observed for the ethyl transesterification reaction of the commercial soybean oil viscosity reduction of 52,40%