A novel, simple, compact, efficient system based on a unit operation of bubble stripping was developed for intensive methanol (MeOH) removal from crude biodiesel (BDF) which was synthesized by potassium hydroxide-catalyzed transesterification reaction of triacylglycerol (TAG) with MeOH. As TAG both rapeseed oil and used cooking oil were tested. In the system, gas was supplied by a gas pump through a gas bubbler into the crude biodiesel, then the exit gas containing MeOH vapor passed through a condenser (0°C) and the condensed MeOH was collected in a vessel. MeOH-free gas from the condenser returned into the inlet of the gas pump, thus gas was circulated in a closed system. After the intensive MeOH removal by the bubble stripping, insoluble sediment always appeared in the biodiesel so that it was removed by centrifugation. As a final step, trace amounts of potassium (K) and free glycerol were removed by adsorbent treatment. MeOH, K, free glycerol, fatty acid methyl ester, and water contents, acid, and iodine values and oxidation stability of the purified biodiesel cleared the specifications of EN 14214 Standard. The proposed dry process consisting of the three steps will be applicable to an industrial production of high-quality biodiesel.
Practical applications: Bubble stripping that has been developed in this study is simple but very effective to remove almost completely residual methanol from the crude biodiesel. Compared with the conventional wet process, the dry process that authors' have proposed has no necessity of washing water, hence no waste water treatment. Elimination of sediment after the intensive residual MeOH removal by the bubble stripping before the final adsorption step will make it possible to decrease significantly the amount of the adsorbent (kg) required per kg of the crude biodiesel or to prolong the life span of its packed bed column, resulting in the cost reduction of the biodiesel production. The proposed dry process consisting of the three steps will be applicable to an industrial production of high-quality biodiesel.