Estudo da purificação de biodiesel utilizando membranas poliméricas e farelo de semente de maracujá como biossorvente

Abstract

Biodiesel is a biofuel obtained industrially by transesterification. After separation of biodiesel and glycerol (co-product) by decantation, water washing is used in order to ensure the quality of biodiesel as biofuel. However, this method requires a high volume of water to perform the proper purification of biodiesel, and consequently a high amount of effluent is generated. Considering this environmental impact, the objective of this work was to evaluate the process of separation by polymeric membrane and the adsorption with passion fruit seed meal, both in isolation and in a sequential process, as substitutes for water washing in biodiesel purification. The membrane purification process was carried out in a perpendicular filtration module, filtering the reaction mixture, without the previous settling step, and also the esterrich phase obtained after phase separation. Five polymeric membranes were used, two commercial: mixed cellulose ester membrane (M1) and regenerated cellulose membrane (M2), and three manufactured by the phase inversion technique (M3, M4 and M5). Among the membranes produced, one was incorporated with passion fruit seed meal (M4) and the other with sisal fiber (M5). In the adsorption process, the passion fruit seed meal was previously characterized by particle size distribution, PCZ, TGA, FTIR, surface area and SEM/EDS before being evaluated as biosorbent in the removal of free glycerol from biodiesel. The membrane separation and adsorption processes were also evaluated sequentially in the purification of biodiesel using the best conditions previously determined in each process. In the separation and purification step of the reaction mixture, the best result in terms of glycerol phase retention was obtained with the M2 membrane, at 1 bar pressure and with the addition of 10% acidified water to the mixture, reducing the amount of glycerol from 31.5% in the feed to 0.025% in the permeate. In the purification of the ester-rich phase, the M5 membrane was able to remove 93.4% free glycerol from the feed, while the membrane functionalized with passion fruit seed meal removed three times more glycerol than the M1 membrane. With adsorption, using 40 g L-1 of the biosorbent, at 45°C, for 90 minutes, a maximum glycerol removal of 72.2% was obtained. The isotherms presented a characteristic profile of cooperative adsorption, and the Freundlich and Weber and Morris models best represented the adsorption on meal. Finally, with the combined process of membrane separation and adsorption, it was possible to reduce the free glycerol content of the permeate from 0.025% to 0.008%, meeting the maximum limit imposed by the legislation (0.02%). With the results obtained, it was concluded that the integrated process of separation with polymeric membrane and adsorption could replace the decantation and aqueous washing processes employed industrially, and consequently reduce water consumption, besides eliminating the effluent treatment step.