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Membrane technology for glycerin purification
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posted on 15.02.2017by Mah, Shee Keat
Recently, the worldwide market value of glycerin has proliferated owing to its major role as an active ingredient in food, cosmetic and personal care product. The rapid growth of biodiesel industries in the past decade has emerged as a reliable source of glycerin in significant amount. Glycerin is produced as a by-product from transesterification process in the biodiesel production, accounting up to 12 % of the total biodiesel production capacity. In general, the crude glycerin effluent oftentimes encompasses glycerin in a concentration range of 3 – 60 wt%. A series of separation and purification processes are normally practiced to purify the crude glycerin into 99 wt% purified glycerin. These include evaporation, vacuum distillation and product refinement processes such as ion exchange and bleaching. The capital and operating cost of these processes are high and usually involve the use of chemicals.
In this regard, the potential of utilizing membrane technology in purifying crude glycerin solution is interminable. Membrane technology is a chemical-free process. At the same time, it possesses advantageous characteristics such as environmental friendly and operation simplicity. To date, there is limited study reported on the application of membrane technology in glycerin purification process.
The main aim of this project was to investigate the feasibility of membrane technology in glycerin purification. In the present study, crude glycerin purification processes were carried out through ultrafiltration for removal of palm oil and fatty acids, further removal of palm oil using nanofiltration, water extraction using reverse osmosis and dehydration of glycerin using pervaporation.
The first stage of this study demonstrated that ultrafiltration was capable of removing palm oil and oleic acid from glycerin solution with the highest rejection of 87.00 and 98.59 %, respectively. Next, data fitting of Hermia’s model showed that cake layer formation was the most consistent fouling mechanism during ultrafiltration process. Besides, multistage Hermia’s model offered a more comprehensive description of the overall fouling mechanism, which indicated the transition period of fouling from standard blocking to cake layer formation.
Following ultrafiltration, the optimization of operating parameters using central composite rotatable design in a nanofiltration process revealed that 40 oC, 60 bar and 1 L/min contributed to the best performance of nanofiltration, with 97.55 % of glycerin permeation and 265.64 kg/m2.h of permeate flux recorded. Palm oil rejection of above 99 % was evident at the optimum condition in a steady state nanofiltration. In reverse osmosis, TFC-HR membrane yielded the highest glycerin rejection of 99.81 % along with the permeate flux of 11.86 kg/m2.h using crossflow configuration. Finally, HybSi pervaporation membrane was successfully dehydrating glycerin solution up to 99 wt% with the permeate flux and permeance water content of 13.63 kg/m2.h and 98 wt%, respectively.