Influence of different solvent and time of pre-treatment on commercial polymeric ultrafiltration membranes applied to non-aqueous solvent permeation (original) (raw)
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Separation and Purification Technology, 2010
The membrane technology application in the vegetable oil processing is associated to the hexane recovery from the miscella obtained during the extraction, degumming and subsequent refining stages, where the presence of the hexane results in higher permeate flux. However, the development of this technological alternative depends on membrane chemical stability. The objective of this work was to evaluate six flatsheet polymeric membranes in relation water affinity, permeability and flux of water, ethanol and hexane, with the purpose of characterizing their hydrophobic and hydrophilic profiles and resistance to hexane. The equipment used was a stirred cell. The following commercial flat membranes were used: 30 kDa and 50 kDa PVDF (polyvinylidene fluoride); 10 kDa PES (polyethersulfone); 0.05 m PC (polycarbonate); 0.05 m and 0.025 m CME (mixed cellulose esters). Membrane permeability with water, ethanol and hexane was evaluated in a laboratory unit at 4 bar, 200 rpm and 40 • C. Regarding flux rates with the tested solvents, the 50 kDa PVDF membrane revealed the highest permeability to water, two of the membranes were characterized as less hydrophilic (PC and PES) and the remaining ones were more hydrophobic. The membrane structural stability towards the hexane was verified by visual observation, filtering area variation (shortening or intumescence) and permeate flux assessments. The permeation with hexane was conducted for 12 h, at 1.5 bar, 200 rpm and 40 • C, with constant flux in all of the membranes during the experiment. Membranes untreated, submersed in hexane for 48 h and submitted to hexane permeation for 12 h were examined by scanning electron microscopy (SEM) in order to verify possible microscopic alterations. All the membranes were hexane-resistant, indicating that they are suitable for use with this solvent.
Characterization of polymeric membranes used in vegetable oil/organic solvents separation
Journal of Membrane Science, 2010
The characterization of commercial membranes used in the separation of refined soybean oil/n-butane and n-hexane mixtures was studied in this work using different commercial ultrafiltration membranes, with cut-offs ranging from 1 to 5 kDa. The membranes were used in the permeation of refined soybean oil/pressurized n-butane mixtures at 1:3 (w/w) and 1:1 (w/w) mass ratios in a continuous tangential flow module and in the permeation of soybean oil/n-hexane mixtures in a dead-end flow module. The membranes were characterized by DSC (differential scanning calorimetry), FTIR (Fourier transform spectroscopy), contact angle measurement (Goniometer), zeta potential and SEM-EDS (scanning electron microscopy with X-ray microanalysis) aiming to better understanding the phenomena involved in the permeation process. Some membranes did not show any measurable permeation flux for refined soybean oil/n-butane mixtures, which may be related to their low hydrophobicity. Contact angle and zeta potential measurements showed that the membrane surface hydrophilicity changes after permeation. FTIR spectra showed that the membranes were fouled with oil even after washing with solvent. Results obtained in this work showed that permeation caused few modifications on the surfaces of the tested membranes at the experimental conditions investigated. It is shown that these polymeric membranes can be used in the separation of vegetable oils/organic solvents effectively without degradations.
Journal of Membrane Science, 1983
Electron spin resonance technique was used to study the structure and transport of the asymmetric polyethersulfone (PES) membranes. 2,2,6,6-tetramethylpiperridinyloxy (TEMPO) free radical was used as a spin probe that was brought into the membrane either by ultrafiltration experiments with feed solutions involving TEMPO, or by blending TEMPO into casting solutions. Ultrafiltration experiments were further carried out with polyethylene oxide feed solutions with and without TEMPO. It was found that two types of radicals exist in studied PES membranes, one located in the membrane pore and the other, which diffused into the polymer matrix. Unlike cellulose acetate (CA) membranes, which are more hydrophilic and swollen by water, the second type of radicals in PES membranes could not be leached out even after 24 h immersion in water. It seems that both pores and the water channels through the swollen polymer matrix contribute to the transport of water in CA membranes. On the other hand, the transport of water in PES membranes is primarily through pores and the contribution of the little swollen polymer matrix is insignificant.
Journal of Membrane Science, 2015
The aim of this study was to evaluate the influence of different solvent and time conditionings in the permeation of n-hexane and oil/n-hexane solutions through several reverse osmosis (ORAK-Osmonics, BW30-Dow Filmtec) and nanofiltration (NF270-Dow Filmtec, NP030-Microdyn Nadir) polymeric membranes. The study of the influence of membrane conditioning on the n-hexane flux was carried out using different solvents (n-hexane, ethanol, npropanol, iso-propanol and butanol) as pretreating agents in different time intervals. Membrane performance was tested by measuring n-hexane fluxes and rejections of dissolved castor oil. The conditioning with ethanol increased n-hexane fluxes in the polyamide membranes ORAK, NF270 and BW30, while the polyethersulfone membrane NP030 did not present any increase in permeability. An increase in contact angle after membrane conditioning was detected, as well as a reduction in free surface energy. This suggests that pretreatment steps alter the surface hydrophilic character. Salt rejections for all the membranes decreased after the pretreatments and permeation with n-hexane for 8 h. These rejections dropped from 87-99% to 72-77 % for membranes NF270, NP030 and BW30; and from 99% to 88 % for ORAK, which showed better stability to solvent exposure. For castor oil, the highest retention was 60 % for reverse osmosis membrane ORAK. The results obtained in this work with commercial RO and NF membranes, normally used in aqueous solutions operations, indicate that most of these membranes do not present adequate stability towards non-aqueous solvents.
Journal of Food Engineering, 2015
Macauba is a Brazilian palm tree with high edible oil productivity and of great interest to many applications. In the oil extraction process, solvent recovery is one point of major concern, due to its high energy consumption and oil quality losses. Those drawbacks can be partially overcome by integration of membrane technology to the usual solvent distillation step. The present work tested four ultrafiltration (UF) and one nanofiltration (NF) membrane (Microdyn-Nadir) on the solvent recovery of synthetic mixtures of macauba oil and n-hexane. Membranes were pre-treated before use with different solvents in specific time lengths, according to preliminary studies. The membrane performance was evaluated by permeate flux and oil retention. Macauba (pulp and kernel) oil was evaluated by determinations of acidity, peroxide value and fatty acid profile. Membranes showed usual flux behaviour, compatible with other studies concerning oil/solvent mixtures permeation, although its values were quite above the expected. Best results for retention (>30%) are related to the membranes with lower molar mass cut-off (MMCO), and the best balance between permeate flux and oil retention was found for the NF membrane (12.4 g m À2 h À1 , 34.7%).
Performance of Nanofiltration Membranes for Solvent Purification in the Oil Industry
Journal of The American Oil Chemists Society
The extraction stage of edible oil in the oil industry is commonly performed by using toxic solvents (e.g. hexane) and processes with high energy consumption (e.g. distillation, evaporation) to recover the solvent, which represents around 70–75 wt% in the oil–solvent mixture. In this paper, a membrane-based extraction method using nanofiltration (NF) membranes is presented. Commercial nanofiltration membranes made of different polymers (Desal-DK-polyamide NF from GE-osmonics®, NF30 polyethersulfone NF from Nadir®, STARMEMTM122 polyimide from MET® and SOLSEP NF030306 silicone base polymer SOLESP®) were selected and tested to recover the solvent from soybean oil/solvent (10–20–30% w/w oil) mixtures at various separation pressures and constant temperature in a dead-end filtration set up. The selection of the solvent was made in order to compare solvents obtainable from renewable resources, such as ethanol, iso-propanol and acetone, with solvents traditionally used in the industry (i.e. cyclohexane and n-hexane). The structural stability of the membranes towards the different solvents used in this work was verified visually, by the variation of the membrane area and by means of permeate flux assessments. Desal-DK and NF30 showed poor filtration performance and even visible defects after exposure to acetone but a good performance was obtained for the nanofiltration membranes STARMEMTM122 and SOLSEP NF030306 with ethanol, iso-propanol and acetone. For example, considering a mixture with 30% edible oil in acetone, STARMEMTM122 shows a flux and oil rejection of 16.8 L m−2 h and 70%, respectively. For the same conditions, SOLSEP NF030306 exhibited a flux of 4.8 L m−2 h with 78% rejection, which shows the potential application of nanofiltration membranes in the oil industry.
Journal of Materials Science, 2020
The study covers the fundamental relationships between the nature of aprotic polar solvents [N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF) and dimethylsulfoxide (DMSO)] used for casting solution preparation and the structure and performance of poly (amide-imide) (PAI) ultrafiltration membranes. It was found that the distinctive feature of the ternary systems PAI-poly(ethylene glycol) (PEG-400, M n = 400 g mol-1) solvent is gel formation upon the increase in PEG-400 concentration in the solution. The PEG-400 addition to the casting solution was shown to increase pure water flux of the PAI membranes prepared from the casting solutions in different solvents. However, different patterns of the change of pure water flux when gel point is exceeded in PAI-PEG-400-solvent system were revealed. The PAI membranes obtained from the ternary systems PAI-PEG-400-solvent were found to combine high pure water flux at P = 0.1 MPa (130 L m-2 h-1 for DMSO, 120 L m-2 h-1 for DMA and 70 L m-2 h-1 for NMP) and high poly(vinylpyrrolidone) (PVP) rejection coefficients: 98-99% for PVP with M n = 40000 g mol-1 and 86-95% for PVP with M n = 10000 g mol-1. SEM studies reveal the significant difference in the PAI membrane structure when different solvents are used for casting solution preparation. The structure of the membranes obtained from 20 wt% PAI solutions in NMP and DMA consists of the thin selective layer supported by substructure pierced by elongated macrovoids. Meanwhile, when DMSO and DMF are used as solvents the addition of PEG-400 yields the suppression of macrovoid formation and anisotropic sponge-like membrane structure is obtained.
Journal of Membrane Science, 2012
High free volume polymers are characterized by much higher permeability and diffusivity for gases and vapors than commodity polymers. Polymers of intrinsic microporosity (PIMs), an important member of this class of polymers, are only soluble in a few solvents. This gives reason to expect stability in many solvents and an application in organic solvent nanofiltration (OSN) may be feasible. Thin film composite membranes of PIM-1 and PIM copolymers were developed on a polyacrylonitrile (PAN) porous support. For control of swelling, a simple, technically realizable method of cross-linking was produced by blending the PIM with polyethyleneimine, coating to give thin film composites (TFCs) and thermally or chemically cross-linking the separation layer on the supporting membrane. The TFCs were tested in OSN with the solvents n-heptane, toluene, chloroform, tetrahydrofuran, and alcohols, and compared to similarly crosslinked poly(trimethylsilyl propyne) TFCs and state of the art industrial Starmem TM 240 membranes. Better retention, a steeper retention curve and much higher fluxes were detected for the newly developed PIM TFC membranes.
Journal of Membrane Science, 2022
Hypercrosslinked polymer (HCP) additives were successfully incorporated into two polymer matrices: glassy polymer with intrinsic microporosity comprising ethanoanthracene and Tröger's base (PIM-EA-TB) as well as rubbery polydimethylsiloxane (PDMS), forming thin-film nanocomposite (TFN) membranes for organic solvent nanofiltration (OSN) applications. The thermal stability and surface morphology of TFN membranes were characterized by TGA and SEM. OSN results showed that HCP additives increased the alcohol permeances for both kinds of membranes as it provided extra pathways for alcohol molecules to transport through the membranes. Particularly, the PIM-EA-TB membrane gained above 32% improvement on methanol and ethanol permeances after loading of 5 wt.% HCP, whilst maintaining a rejection of 92% for Rose Bengal. Moreover, the physical aging of PIM-EA-TB membrane was retarded by HCP additives and the swelling of the PDMS membrane in non-polar solvents was reduced. In small quantities, the HCP nanoparticles proved to be effective additives to improve the OSN performances for both glassy and rubbery polymer membranes.