다양한 고체산 촉매를 이용한 에스터화 반응과 전환 에스터화 반응 공정을 통한 바이오 디젤의 합성

Abstract

Abstract The production of biodiesel from low quality feedstocks, which are generally associated with high free fatty acid (FFA) contents, is a valuable alternative that would make the process more economical. The conventional alkali catalysts are not suitable while dealing with waste oils, FFAs and water contents can cause saponification leading to lower conversions and catalyst effectiveness. Hence, It is necessary to develop new and effective solid acid catalysts which are capable of catalyzing esterification and transesterification reactions simultaneously, important steps in biodiesel synthesis from waste oils, and have more tolerance against FFAs. In this dissertation, the use of Cs-doped heteropoly tungstate (CsHPW) has been studied for the biodiesel production in chapter 1 and 2. CsHPW exhibited high catalytic activity as well as better leaching stability in comparison to other solid acid catalysts, such as 20%HPW/ZrO2, 20%WO3/ZrO2, 20%HPW/γ-Al2O3, and 20%HPW/SiO2, when applied for the simultaneous esterification and transesterification of 10% oleic acid-soybean oil mixture. The catalyst was recoverable and reused without any significant activity loss. A maximum conversion of 90% was achieved at 200 °C and 10 h reaction time. To increase the reaction rates and to utilize highly insoluble feature of CsHPW, it was applied in the transesterification vii of used vegetable oil with supercritical methanol. The results showed that supercritical methanol compensated for the low reaction rate of solid acid catalytic transesterification, while the Cs-doped heteropoly acid catalyst mitigated the harsh operation conditions of the supercritical methanol process. The content of fatty acid methyl esters (FAME) reached 92% under the optimum reaction conditions of 260 °C, 20 MPa, a molar ratio of methanol to oil of 40, and a reaction time of 40 min in the presence of 3% catalyst. Titania-silica mixed metal oxide materials with a mesostructure were synthesized from relatively cheaper precursors i.e., titanium oxychloride and sodium silicate. The mesoporous titania-silica composite (TSC) was further used as a support material to synthesize novel solid acid catalysts for the biodiesel production. A series of 12-tungstophosphoric acid (HPW) immobilized on mesoporous TSC, with different HPW loadings from 5wt% to 50wt%, were prepared by impregnation method. The synthesized materials were characterized by BET, N2 adsorption isotherms, XRD, FT-IR, UV-visible spectroscopy, and SEM analysis. The utilization of these materials in the esterification of oleic acid showed that the 20%HPW/TSC was an active and stable catalyst which could be recycled for three consecutive runs without any considerable viii activity loss. The higher activity of this compound can be attributed to the higher surface area and better dispersion of the active material on the support surface. A sulfated titania-silica composite (S-TSC), with improved structural and catalytic properties, was synthesized through surface modification of mesoporous titania-silica composite using sulfuric acid. The synthesized materials were critically characterized with various characterization techniques. Further, the utilization of S-TSC for the esterification of oleic acid and transesterification of waste oil proved its effectiveness in the biodiesel synthesis.