Biodiesel Preparation From Transesterification Of Soybean Oil With Methanol By Solid Superacid Catalyst

Due to the increase in the price of the petroleum and the environmental concerns, biodiesel is becoming a developing area of high concern. Biodiesel is an environmentally friendly and renewable energy. In different types of catalyst for the production of biodiesel, solid acid catalysts are a promising catalyst. Solid acid catalysts offer several advantages over homogeneous acid catalysts. They are easily removed from the reaction medium, can be reused and avoid corrosion problems. They have more adaptability than the base catalysts when the feed oil (e.g., used deep-frying oils and non-edible oils ) has high acidity.In this paper, biodiesel was obtained through transesterification of soybean oil with methanol, using SO₄^2-/TiO₂-SiO₂ (catalyst A), SO₄^2-/SnO₂-SiO₂ (catalyst B), SO₄^2-/ Zr-SBA-15(catalyst C) as solid superacid catalysts, catalyst preparation factors and transesterification reaction factors were investigated. The catalyst's acidity was characterized by FT-IR and NH₃-TPD. The catalyst's recyclability was studied.(1) Spectral analysis of absorbing pyridine IR of the catalyst A showed that there were Lewis and Bronsted acid centers on the catalyst. NH₃-TPD curves showed that the catalyst A had superacidity. Among the catalyst A preparation factors, the calcined temperature is most important factor for formation of superacid. The catalyst A exhibited the highest activity for transesterification under the condition of Ti/Si mol ratio 1/3, the concentration of impregnating sulfuric acid solution over 1.0M, calcination at 450℃for 5h. The yield of methylesters reached over 90% at the most optimized reaction factor: 13:1 methanol/oil mole ratio, 1.0g catalyst/mol oil, reacted at 125℃for 3h.(2) The catalyst B also had Lewis and Bronsted acid centers, and had superacidity. The catalyst B was similar to the catalyst A in preparation factors. The catalyst B exhibited higher activity than the catalyst A and gave 90% ME yield at the most optimized reaction factor: 13:1 methanol/oil mole ratio, 1.0g catalyst/mol oil, reacted at 120℃for 3h.(3) The activity of the catalyst B was strongly reduced by the presence of water. The acitivity of the catalyst B was not affected by the presence of fatty acid. This fact shows that a variety of unrefined crude oil and non-edible oils could be transesterificated over the catalyst B with high efficiency. With the catalyst B both the esterification and tranesterification could be conducted in a single-operation.(4) The difference of catalytic activity for transesterification between SO₄^2-/ZrO₂, SO₄^2-/ZrO₂-SiO₂ and SO₄^2-/Zr-SBA-15 was studied. It could be concluded that the combination of the porous structure of mesoporous molecular sieves and the acid properties of superacids could obtain more prospective molecular superacid materials for tranesterification.(5) The study on catalyst's deactivity and regeneration showed that the spent catalyst was partly deactivated, because SO₄^2- were slowly leached out from the catalyst surface by methanol and activity sites were covered by oil and ME, that the used catalyst could be regenerated by calcined at 450℃, impregnated 1MH₂SO₄ solution for 30 min, filtered, dried, and re-calcined at 450℃.In a word, SO₄^2-/SnO₂-SiO₂ had the most activity among the three catalysts investigated in this study. It could catalyze both the esterification and tranesterification of oil at lower temperature (even at 100℃) in a single-operation. The used catalyst could be easily regenerated and the same activity could be obtained. SO₄^2-/SnO₂-SiO₂ are a promising solid acid catalyst for production of biodiesel from oil by transesterification reaction.