| Summary: | 博士 === 國立成功大學 === 化學工程學系 === 106 === A study of biodiesel production via transesterification of triglycerides, such as triolein, in excess methanol in presence of zeolite catalysts was carried out. Various zeolite frameworks, including HY, MCM-22 and Beta, were synthesized and modified, mainly with alkali ion exchange processes, to render satisfactory catalysis in transesterification at a temperature lower than 65°C.
Zeolite MCM-22 and zeolite HY (CBV-780) could not effectively catalyze the transesterification of triolein without prior proper surface modifications. For example, a conversion efficiency of triolein to biodiesel near 16.3% and ca. 90% was obtained with the use of zeolite MCM-22 after a 90-h reaction and with zeolite HY after a 40-h reaction. In contrast, the conversion yields were much improved with Na+ ion-exchange to the surface of the aforementioned zeolite catalysts. For example, the yields of triolein to biodiesel reached 98% and 99% within a 5.5-hour reaction, respectively, using the NaOH-treated HY and MCM-22 catalysts, even though these NaOH-treated catalysts became amorphous and suffered a loss of the Brunauer-Emmett-Teller (BET) surface area. No saponification was observed using these NaOH-treated catalysts. The process parameters of the ion-exchange process to activate Zeolite HY catalysts, including the temperature, the process time, the pH value, as well as the concentrations and sources of the Na+ cations (NaOH, NaCl and Na2SO4), on the conversion yield of triolein to biodiesel were investigated accordingly. As a result, a high conversion yield of triglycerides to biodiesel at 97.3% was obtained at 65°C.
Zeolite Beta with a high Si/Al ratio as a heterogeneous catalyst in the transesterification of triolein for biodiesel production was synthesized hydrothermally in fluoride media. The prepared Zeolite Beta was subsequently treated with dilute NaOH solutions to obtain better catalysis in the transesterification reaction. A conversion efficiency of over 90% could be attained within an hour of the reflux reaction. Moreover, these Na-treated zeolite catalysts still exhibit acceptable durability and good catalysis in the transesterification reaction after nine consecutive cycles.
The main mechanism on the catalysis of these surface-modified zeolites is inferred from the alkali active sites on the surface of zeolites based on the surface characterization of the catalysts mainly through the use ofwith solid-state NMR, Porosimetry, and other instruments. During the transesterification reaction, sodium cations existing in the cages and the defect sites of the NaOH-treated Zeolite Beta can be supplied to the surface of the catalysts and, thus, enhance the catalysis.
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