The Pre-esterification Of Jatropha Curcas L. Oil Containing High Free Fatty Acid

Biodiesel is a good substitute of conventional fossil diesel and it is environmental benign and renewable. Biodiesel contains a series of mono-alkyl esters of long chain fatty acids, which are obtained by the transesterification of vegetable oils or animal fats with short carbon alcohol like methanol. The cost of biodiesel is directly decided by the price of raw materials. Finding a cheap oil resource is important for the commercial application of biodiesel.Jatropha curcas L. oil is a potential cheap material of biodiesel, but it contains high content of free fatty acids. In this work, the Jatropha curcas L. oil was used to produce biodiesel through a two-step routine involving pre-esterification and trans-esterification reaction process. The free fatty acids contained in oil feedstock were firstly converted to esters by esterification with methanol in presence of sulfuric acid in the pre-esterification reaction, and then the glycerides were converted to esters in the following transesterification with methanol in presence of KOH catalyst.Both pre-esterification and transesterification of Jatropha curcas L. oil were systematically investigated. The reaction parameters including methanol amount, acid value, water and phospholipids contents were tested. The results showed that a high acid value of oil may result in serious emulsification in transesterification and therefore it is important to reduce the acid value of Jatropha curcas L. oil under 1.5mg KOH/g in the pre-esterification section. Jatropha curcas L. oil with an acid value of 20 mg KOH/g reacted with methanol at 70℃for 2 hours using 1% H₂SO₄ and 12% methanol, can reduce its acid value below 1.5mg KOH/g that met the requirement of the following transesterification section. The fatty acid conversion increased with the increase of mole ratio of methanol/FFA until the ratio reached 10. Water contained in raw Jatropha curcas L. oil sharply decreased the conversion of pre-esterification. Even though the phospholipids did not affect the conversion of pre-esterification, it is better to be controlled below 1% in order to prevent the emulsification in following separation process.The effects of water on the kinetics and equilibrium of pre-esterificaion were specially concerned in this work. At about 50℃-70℃, if [H⁺] was kept constant, it can also be expressed as: r_FFA=k₀ exp(-E/(RT))C_FFA. For a dry raw oil without water, the apparent activation energy was about 31.5 KJ/mol and the apparent rate constant was 1.29×10²min^-1. When the oil contained 3.0% water, the apparent activation energy increased to 45.3KJ/mol, and the apparent rate constant was 3.17×10⁴min^-. Water in oil not only reduced the concentration of catalyst, reaction rate.