| Biodiesel was environment-friendly renewable and easy-to-biodegradable. It is produced by transesterification of soybean oil, rapeseed oil and other animal or plant oil with methanol in the presence of homogeneous and heterogeneous catalyst. Traditional biodiesel production technologies of homogeneous catalysts had deficiencies, such as difficult to separate catalysts and bring about some environmental problems. So the research focus on the heterogeneous catalyst in recent years. Common heterogeneous catalysts can be divided into solid acid catalyst and solid base catalyst. The solid base catalyst was higher catalytic activity so could short the reaction time. And the reaction conditions were mild too.Coal fly ash is discharged from industrial waste of coal-fried power plant. It mostly contains SiO2 and Al2O3 with adsorption and ion-exchange properties. Therefore, fly ash can serve as a good catalyst carrier. The main catalyst carrier concludes alumina, calcium oxide, magnesium oxide, silica, titanium dioxide, zeolite and so on. Catalysts with fly ash as carrier were not applied widely.A series of solid base catalysts with fly ash as carrier were prepared by impregnation and applied into the biodiesel production. Chose alkali metal and alkaline earth metal hydroxide, nitrate, carbonate, acetate, hydrazine as the precursor loaded on fly ash. The catalyst which has the highest activity was obtained, and its base strength and the total alkali content (H≥35) was determinate. The catalyst was also analyzed and characterized by SEM, IR and XRD. Orthogonal analysis can optimize the best preparation conditions for the highest activity of the catalyst.The results showed that the catalyst with NaOH and NaNO3 loaded on fly ash has the highest activity. The optimum conditions for catalyst preparation were obtained as follows: NaOH content of 20%, NaNO3 content of 20%, the catalyst calcination temperature of 270℃and the calcination time of 4h. The optimum reaction conditions for the transesterification between cottonseed oil and methanol were determined as methanol/oil mole ratio of 10:1, catalyst dosage(catalyst/oil) of 1.2%, reaction time of 80min and reaction temperature of 70℃. The base catalyst exhibits excellent catalytic activity and the conversion of biodiesel production reaches over 98.75% under the optimum reaction conditions. After the catalyst was used repeatedly four times, the activity decreased less. The characterization showed that the catalyst had active sites. The highest base strength (H- )of the base catalyst reaches over 43, and the basicity is 5.12mmol/g. Using fly ash as a carrier of biodiesel catalyst reflects the recycling of waste, reduces the environmental pressure, eases the energy crisis. Therefore, this study has great practical and economic value. |
