Solid Acid Catalysts For Preparing Biodiesel With Jatropha Curcas L. Oil

Petroleum crisis and environmental pollution accelerated the development of renewable and environmentally friendly alternative energy sources like biodiesel. However, the expensive cost of biodiesel restricts its usage and comercialized. Decreasing the cost of its raw material is effective means to decrease the cost of biodiesel. Low cost feedstocks such as Jatropha curccas L. oil and used frying oil usually contain a great deal of free fatty acids (FFA), which influences the transesterification via alkali catalylic method and its subsequent separating process. The acidic catalylic esterification of FFA with lower alcohols such as methanol is commonly used to reduce the acid value of a high acid value feedstock. Conventional liquid acid catalysts cause not only more side reaction, but also device erosion and vast acidic waste water emission, resulting in environment problems. Using solid acid catalyst to replace liquid acid catalyst is an environmentally benign technology as it is easy to be recovered and separated from product.A variety of solid acid catalysts were screened in the pre-esterification of FFA in high acid value Jatropha curccas L. oil with methanol. The results show that ST- II solid acid prepared by directly calcining cheap metatitanic acid, has the highest activity. Upon this catalyst, the preparation conditions and reaction parameters were systemically investigated. Calcination temperature of the catalyst greatly affects the activity, and, on the contrary, the calcination time exhibited less effect on the activity. A optimal preparing condition is calcining for 2 hours at 500℃. And the optimal conditions for the pre-esterification of FFA in high acid value Jatropha curccas L. oil with methanol are: 90℃, 4 wt.% solid acid catalyst, a molar ratio of methanol to FFA 20:1 and reaction time 2h. The conversion of FFA is higher than 97%. For the pre-esterification of FFA in high acid value Jatropha curccas L. oil with methanol, the acid site in H₀ between -12.70 and -8.2 over solid catalyst is corresponding to the its catalytic activity.The ST- II solid acid catalyst was characterised by using XRD, TG, BET and S content determination techniques. The results illustrated that the strong acid site increased and the weak acid site decreased with the calcination temperature in preparing ST- II solid acid. Since the surface sulfate decomposed and desorbed at higher calcination temperature, the amount and strength of acid site deceased sharply, which induced the decreasing of the pre-esterification activity of the ST- II solid acid. The pre-esterification activity of ST- II solid acid also decreased with the decreasing of specific surface, pore volume and sulfur content and the increasing of TiO₂ crystallization as calcination temperature increased. FTIR studies suggested that ST-II solid acid possessed pyrosulfate structure, which converted to protonic acidic sites when the catalyst absorbed water. The ST- II solid acid catalyzed esterification proceeds through a reaction routine of protonating fatty acid, nucleophilic addition with methanol and deprotonating.Stability studies of ST- II solid acid indicate that the deactivation was mainly caused by both the loss of active species in polar solvent and the effect of absorbing organic compounds on surface. Resulfuration and calcination in oxygen are possibly effective way to recover the activity of the ST- II solid acid.