Aplicação de membranas poliméricas incorporadas com cortiça para purificação de biodiesel produzido a partir de óleo residual

Abstract

The growing interest in sustainable technologies has increasingly driven the production of biofuels such as biodiesel. However, the conventional purification step in biodiesel production requires high water consumption and generates large volumes of effluent, causing significant environmental impact. In this context, alternative purification processes, such as membrane separation, have been investigated. Therefore, this study aimed to develop polymeric membranes incorporated with cork residue and apply them to biodiesel purification. The polymeric membranes were prepared by the phase inversion technique using polyethersulfone as the polymer, polyvinylpyrrolidone as the copolymer, dimethylacetamide as the solvent, and cork as an additive. Membranes were produced with the addition of 0.2, 0.5, and 1% cork, as well as a membrane without additive for comparison. These membranes were employed in a dead-end filtration module and characterized in terms of hydraulic permeability, contact angle, swelling degree, thermal properties, and morphology. Two purification processes were performed: one with the reaction mixture, previously rotaryevaporated, obtained from ethylic alkaline transesterification of waste cottonseed oil, and another with the ester-rich light phase obtained after rotary evaporation of the reaction mixture and preliminary phase decantation. In the filtration of the reaction mixture, the addition of acidified water to the feed was investigated at concentrations of 1, 5, and 10%, under 1 bar. The effect of membrane composition under the same conditions was also evaluated, and, finally, serial filtration was performed with two new membranes of the same composition at 1 bar, selecting the one that exhibited the best performance in heavy-phase retention. For the light phase, the addition of acidified water (1, 5, and 10%) at 1 bar was also tested. Furthermore, the influence of membrane composition was analyzed at 1 bar, and, using the membrane with the highest glycerol retention, the effect of pressure was assessed at 0.5 and 2 bar. Membrane characterization results indicated typical ultrafiltration features, with hydrophobic surfaces. For the reaction mixture, the membrane containing 0.5% cork achieved the highest heavy-phase retention (53.33%) and was employed in serial filtration, reaching a total retention of 76.67%, demonstrating the effectiveness of this strategy. For the light phase, the membrane containing 1% cork showed the best performance, resulting in 91.75% retention and a free glycerol content in the permeate of 0.008%. The pressure effect was also evaluated, and at 0.5 bar the highest glycerol retention (93.62%) and the lowest free glycerol fraction (0.006%) were obtained. In addition, the membranes were able to retain soaps present in both the reaction mixture and the light phase. Soap retention is essential, since these compounds hinder phase separation and reduce flux, compromising the quality of purified biodiesel. A fouling study was also carried out, showing that membranes used for light-phase filtration recovered more than 90% of the initial flux after cleaning, whereas those used for the reaction mixture underwent irreversible degradation and flux increase associated with damage to the porous structure. Finally, analyses showed that almost all properties of the biodiesel produced met the ANP specifications for commercialization. Compared with glycerol retention by the membranes, the conventional water-washing route generated a large amount of wastewater and did not promote efficient phase separation due to the high concentration of soaps. Thus, biodiesel purification using cork-incorporated membranes proves to be a feasible and environmentally favorable alternative to water washing. Keywords: Membrane separation;