Polyimide based mixed matrix nanofiltration membrane for refining palm oil

Abstract

The purification of vegetable oil is an important process to obtain purified vegetable oil for various applications. However, conventional processes in vegetable oil purification, such as deacidification, require a huge amount of energy which is not only costly, but also contributes to a high rate of carbon footprints. To improve the current state of purification, the capability of membrane technology in purifying vegetable oil was investigated. The main objective of this study is to investigate the potential of polyimide-based mixed matrix membrane (MMM) in refining palm oil by nanofiltration. To achieve the objective, preliminary investigations on the performance of commercially available membranes were made. Subsequently, polyimide-based MMM with different additives loadings were fabricated and characterized. Additionally, membrane transport models were used to describe and predict the membrane separation process and a suitable multistage configuration was also proposed. The structural and physical characteristics of the fabricated membranes were studied. The separation performances of the fabricated membranes were investigated by using a dead-end stirred cell and ethyl acetate as the diluting solvent for palm oil. From the membrane characterization, it was found that MMM with 0.5wt% of β-cyclodextrin functionalized multi-walled carbon nanotubes (βCD-fMWCNT) achieves the highest separation of palmitic acid from the feed diluted palm oil at 3.84 LMH/bar. The rejection of palmitic acid was found to be 60% and tocopherol, carotene and triglyceride at 94.43%, 98.74%, and 95.18% respectively. The membrane separation process was found to be best described by using the Solution-Diffusion model. Additionally, a theoretical study by using different multistage configurations found that the separation process can be further improved. The proposed multistage configuration was able to yield triglyceride with 99.28% purity with only 9.8% of oil loss in the purified permeate stream with a 41% of solvent recovery rate. Therefore, from this study, it is proven that membrane separation technology is a promising purification alternative and mixed matrix polyimide membrane has the potential in improving the conventional palm oil purification process.