Study of a biodiesel batch production from degummed soybean oil

Abstract

The use of renewable resources as replacement for petroleum-derived chemicals is gaining importance. This is mainly due to the serious pollution problems with increasing fuel prices increase and the scarcity of fossil resources. In Spain, the “Plan de energías renovables 2011 – 2020” has been carried out to improve the difficult situation that the biodiesel industry is experiencing in our country, due to according to the European directive, from 2020, 20% of the energy consumed should be renewable. One of the most widely used type of biofuels is biodiesel and it can be obtained from vegetable oils. One of the most common is soybean oil. The production process is split in three different stages: degumming, transesterification and purification. Usually, plant for large productions operate continuously. Nevertheless, if the production is not very high, the possibility of working in discontinuous (per batches) the transesterification stage can be considered. Hence, the final project’s goal is to consider the viability of working in discontinuous the transesterification stage, for a production plant of refined biodiesel (without impurities) of 30,000 tonnes per year. In transesterification stage, the soybean oil is converted to biodiesel, using methanol excess as a reactant and sodium methoxide as catalyst. Biodiesel and glycerin, are the products of the reaction, which are separated by gravity. Due to the reaction is an equilibrium reaction, the glycerine must be removed in order to force the reaction to the right to obtain more product. Therefore, the transesterification step will consist of two vessels and two settlers. A batch size of 20,500 kg of refined biodiesel (RB) has been chosen, corresponding to 21,000 kg of non-refined biodiesel (NRB). From this value and the physical-chemical product properties have been dimensioned the main equipment. Also, the block and process diagrams have been made with their corresponding mass balance. The necessary pumps, valves and pipes have been chosen, as well as the automation and control system that is presented in the corresponding in the P&ID. Block and process diagram and P&ID have been drawn with AutoCad. Moreover, it has been estimated the times of each equipment that it should be carried out, as well as, the period of occupation of the equipment. Working in two campaigns with overlapping, batch time and cycle time have been determined. In this case, the batch time is 7.5 (BT = 7.5 h) and the cycle time is 3 hours (CT = 3h). Different scheduling strategies of the transesterification batch production have been proposed. The most convenient has been the weekly production of 31 or 32 batches, in two campaigns of 15 and 16 batches, the first one, and 15 and 17 batches, the second one. In addition, even if the purification stage and the recovery methanol excess operates continuously without disruption, the transesterification stage will work only 5 days per week, with 3 shifts per day, without working the weekends. Working with two campaigns per week, necessarily involves an intermediate shutdown, which it will be used for cleaning work and maintenance. Moreover, this shutdown has been programmed in such a way that it takes place coinciding with the central shift of the plant.