Preparation And Kinetic Studies Of Biodiesel From Tung Oil By Two-step Catalyzed Process

The world is confronted with the double crises of energy depletion and environmental degradation. Finding the substitute energy resources actively that environmental friendly and renewable become to the focus all of the world, and among the numerous substitute fuels, the biodiesel is very improving one which has excellent performance. To develop biodiesel productions with food oil crops, which does not accord with the situation of our country. So the government supports and encourages developing and planting oilseed trees for biodiesel productions.In this work, a kind of inedible oil was used to produce biodiesel through a pre-esterification, trans-esterification two-step reaction process. In the pre-esterification reaction, free fatty acid (FFA) of tung oil was esterified with methanol catalyzed by the active carbon loaded with sulfuric acid (H₂SO₄/ AC) and the silica loaded with sulfuric acid (H₂SO₄/ SiO₂), hereby resulted in reduction of the acid value. In the followed trans-esterification reaction, the processed tung oil with methanol to produe biodiesel catalyzsed by potassium hydroxide. The effects of reaction temperature, reaction time, catalyst dosage, and mole ratioof methanol to tung oil on the reaction of pre-esterification were studied carefully. The results show that the optimum condition by H₂SO₄/ AC is: 1.5h of reaction time, 15:1 of mole ratio of methanol to tung oil, 90℃of reaction temperature, and 3% of catalyst. The optimum condition by H₂SO₄/SiO₂ is: 40min of reaction time, 15:1 of mole ratio of methanol to FFA, 65℃of reaction temperature, 0.8% of catalyst, and 1000rmp of stirring rate. The concentration of esterification was higher than 92.0% in the optimum condition by two catalysts. KOH was used to catalyze transesterification of glycerides in the tung oil to methyl esters. 97.8% of tung oil were transformed to biodiesel when 1.0% (w/w) of potassium hydroxide was added to the reaction mixtures containing the mole ration of methanol and oil with 6:1 and reached at 70℃for 50 minutes.Additionally, the kinetics of esterification and transesterification were also discussed. The controlling step of esterification kinetic and parameters in the kinetic equation were determined by measuring the conversion rate of free fatty acid (FFA) in tung oil under the conditions of different reaction temperatures and different methanol/FFA molar ratio in the existence of H₂SO₄/AC as catalyst. The result showed that the kinetic equation of esterification can describe the reaction process very well within the range of the experimental condition. The macro-kinetic equation of transesterification was obtained based on the transesterification mechanism in the existence of alkaline catalyst. The result showed that the esterification under 60℃and the mole ration of methanol and oil with 6:1, the apparent reaction order was 3.1, the rate constant was 2.133×10^-3(mol/L)^-2.1·min^-1, the reaction activation energy was 31.09 kJ·mol^-1, and the pre exponential faction was 1.958×105 L·mol^-1·min^-1.