Considerations on the Use of Nanofiltration for Solvent Purification in the Oil Industry

Abstract

Dear Editor,We wish to reply to the comments made on our paper ''Performance of nanofiltration membranes for solvent purification in the oil industry'', by S. Darvishmanesh, T. Robberecht, J. Degrëve, and B. Van der Bruggen and published in J Am Oil Chem Soc 88, 1255-1261 (2011) [1] by Albert Dijkstra [2]. We are very pleased that the paper invoked discussion, which should be the objective of all scientific research. Nevertheless, it is clear that the discussion in the letter to the editor by Albert Dijkstra is rather subjective and based on a difference in opinion arising from his experience in the oil industry in comparison with the paper's objectives.He raised the issue of energy consumption. We claimed that conventional solvent recovery by distillation consumes about 50% of the total energy in edible oil extraction. In our paper, we stated that nanofiltration requires much less energy than distillation. Dijkstra believes that we overestimated the energy savings because most of this energy is supplied by the vapors leaving the desolventizer/toaster and thus there is little net energy saving. This may be true but is not relevant to our study, in which a comparison of technologies is made without taking into account the overall energy balance. His comment assumes that part of the heat that is supplied is waste heat and should therefore not be taken into account, or in other words, to paraphrase George Orwell (in his book Animal Farm) with some adaptation, all energy is equal but some energy is less equal than the rest.The analysis ignores the efforts currently being made on usage of waste heat, which may turn waste heat into a valuable resource. Moreover, technologies become available that produce significantly less waste heat so that this heat may not be available for distillation in a later stage. In view of this trend, it seems inappropriate to make a difference between different sources of energy. This is also a matter of opinion, but it cannot be denied that utilizing low grade thermal energy is more and more necessary [3].However, the proposal of membrane filtration as an alternative for distillation is indeed not optimal. A combination of membrane filtration and distillation as an alternative for the combination of a desolventizer/toaster and classical distillation might be even more advantageous and should be investigated, in view of suggested advantages of hybrid processes [4].Regarding the use of isopropanol, it is not at all straightforward to consider a heating and cooling cycle more energy efficient than a pressurization and depressurization cycle. Much depends on the way these technologies are implemented. A heating and cooling cycle can be operated most efficiently by integrating heat pump technology. Yet it is not at all clear this is technically feasible or economically viable. Moreover, the application of heat pump technology in industry is mostly an emerging field [5]. On the contrary, a pressure recovery device can be used to recover the applied pressure during nanofiltration. These devices ...

Membrane technology for vegetable oil processing—Current status and future prospects

“…This is due to the fact that membrane desolventizing is accomplished without a phase change, thus, saving the energy otherwise required to meet the latent heat during thermal evaporation. However, the net energy savings in an industrial plant had been a point of debate among researchers (Dijkstra, 2012; Darvishmanesh et al., 2012).…”

Recent Advances in Polymeric Solvent‐Resistant Nanofiltration Membranes

“…Sheth et al 165 claimed that precompacting commercial MPF-50 or MPF-60 with used solvents at operational pressures and temperatures is necessary to remove erythromycin because precompaction increased the rejection of erythromycin by SRNF membranes, which reduced the loss of erythromycin and increased the purification efficiency. Shi et al 166 fabricated a type of PI membrane to concentrate spiramycin 220 (n-alkanes in toluene) [168][169][170][171][173][174][175]180,182,184,[190][191][192]195,197 Starmem TM 228 280 (n-alkanes in toluene) 169,179,184,196 Starmem TM 240 400 (n-alkanes in toluene) [171][172][173][174][175]180,182,184,185,189,196,197 Puramem TM extracts and recover the used solvent (butyl acetate). They indicated that the permeability of the spiramycin solution was significantly affected by the operating conditions, although the rejection of spiramycin (higher than 99%) was not influenced.…”

“…As NF has two unique features as talked before, it has been widely applied in many fields, especially in the removal of hazardous contaminates from waste water . Most recently, the separation and purification of active molecules in organic medium by NF membranes (called SRNF membranes) has attracted significant attention because unlike conventional distillation, this process is athermal . The SRNF membranes can potentially be used in the pharmaceutical manufacturing industry, catalysis recovery processes, the concentration of biologically active compounds in food technology, the recovery of ion liquids, the purification of fuels and solvents, refining technologies, and many other fields .…”