Polyvinyl alcohol-crosslinked polyvinylidene fluoride hollow fiber membrances for crude palm oil refining

Abstract

Over recent years, there has been an explosive growth of interest in the development of alternative approaches for crude palm oil (CPO) refining. During a typical refinery process, free fatty acid (FFA) is one of the key impurities that need to be reduced if not completely removed from CPO in order to minimize their detrimental effects on the oil quality. Polyvinylidene fluoride (PVDF) membrane shows great potential in removing FFA from CPO owing to its hydrophobic properties, high mechanical strength and good thermal stability. However, low concentration of FFA in CPO, which is normally ranging from 3 to 5%, has hindered the capability of the membranes to separate the trace amount of FFA from the bulk. Thus, modification of PVDF membrane is essential to enhance the interaction between the membrane surface and FFA molecules to facilitate efficient FFA removal. In order to achieve this purpose in the present study, the outer surface of PVDF hollow fiber membranes was crosslinked with polyvinyl alcohol (PVA). Glutaraldehyde was used as a crosslinking agent to avoid the PVA dissolution. Morphological change was observed on the membrane surface with longer immersion time during the crosslinking process. The contact angle was significantly reduced in proportional to the concentration of PVA used for the crosslinking, addition of catalyst which is hydrochloric acid as well as the immersion time, which indicates the enhanced surface hydrophilicity. Additionally, the average roughness of the crosslinked PVDF membranes increased with the increasing of PVA concentration. The results obtained showed that the PVDF hollow fiber crosslinked with 100 ppm PVA exhibited the highest FFA rejection of 5.93% after 3 hours of operation. In addition, the membrane also capable of removing phosphorus content as high as 90% rejection as well as partial reduction of its colour intensity. This study served as the first attempt of CPO deacidification through membrane system without the addition of any chemical during the filtration process.