Preparation Of Biodiesel And Refining Of Its Byproduct Of Glycerol

Biodiesel is a clean fuel using vegetable and animal oil as raw material, which can be directly used in compression-ignition engine and acts as the substitute of diesel oil. Because it's a retainable, bio-degradative and innoxious energy resource with high flash point, it aroused worldwide interest. In this research, alkali-catalysis and acid-catalysis were applied to prepare biodiesel from palm oils and palmitic acids respectively.Potassium hydroxide was used to catalyze transesterification of glycerides fi'om the palm oil to methyl esters. It was found that the highest conversion was achieved when the mole ratio of methanol to glycerides was 4:1 with addition of 1.2% of potassium hydroxide (w/w) and reacted at 60℃for 1h, under these reaction conditions, 99.85% of methyl esterification product was obtained. Ferric sulfate and sulfuric acid was used to catalyze the conversion of palmitic acid to methyl esters. The optimal technology for ferric sulfate-catalysis was that 2% of ferric sulfate (w/w) was added to the reaction mixtures containing methanol to palmitic acids with 10:1 (in molar rate) and reacted at 95℃for 4 hours. The optimal technology for sulfuric acid-catalysis was that 2% of sulfuric acid (w/w) was added to the reaction mixtures containing methanol to palmitic acids with 8:1 (in molar rate) and reacted at 85℃for lh. It was found that 98% ofpalmitic acid was transferred to methyl esters and the acid value decreased from 200 mg KOH/g to less than 4.0mgKOH/g by the two catalysis methods.Inorganic ceramic membrane filtration with membrane aperture size of 0.1μm and 0.2μm and 0.6μm respectively was investigated to remove soap from alkali-catalyzed biodiesel. It was found that, under the inlet pressure 0.26MPa and outlet pressure 0.06MPa, the residual soap and free glycerol were decreased to 0.07%(wt) and 0.01%(wt) respectively, and 99.14% of potassium was removed when 0.1μm membrane aperture was used.Glycerol was purified by three steps, neutralization (phosphoric acid), ethanol crystallization and molecular distillation. Semi-products of glycerol with purity of 75.77% was obtained by centrifugation at 3000r/rain after the products were reacted with phosphoric acid at 70~C for 1 h. When ethanol was added to the semi-products with final concentration of 25% and kept at 20~C for 40 min, 92% of the salt was removed by crystallization. The products could be further purified by molecular distillation. Glycerol with purity of 99.5% was obtained by molecular distillation when the distillation temperature, pressure and rotation speed were kept at 110℃, 30Pa and 246rpm respectively.Vegetable oils contain undersaturated fatty acids, which are easy to suffer from oxidation when exposure to oxygen. The antioxidants of BHA and BHT and TBHQ were used to test their preservative effect on biodiesel by POV value testing method and AOM method respectively. In POV value testing method, 100ppm, 200ppm and 300ppm of the antioxidants mixing with biodiesel were kept at 30℃and 60℃respectively for 35 days and it was shown that the antioxidant capacity ofantioxidants for biodiesel was TBHQ＞BHT＞BHA according their POV values. In AOM method, 1000ppm, 2000ppm and 3000ppm mixing with biodiesel were kept at 110-130℃with air flux 10L/h, their shelf life was determined by a 743 Rancimat. The results showed that the longest shelf-life was respectively achieved at the concentration of 1000ppm for BHA (2.2 years), 2000ppm for BHT (2.30 years), and 2000ppm for TBHQ (2.41years) in biodiesel prepared from waste cooking oil. While for biodiesel prepared from feed oil, the longest shelf-life was respectively achieved at the concentration of 1000ppm BHA (4.45 years), 3000ppm BHT (1.62 years), 2000ppm TBHQ (1.88 years).