Performance of Nanofiltration Membranes for Solvent Purification in the Oil Industry

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^®, STARMEM^TM122 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 STARMEM^TM122 and SOLSEP NF030306 with ethanol, iso-propanol and acetone. For example, considering a mixture with 30% edible oil in acetone, STARMEM^TM122 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.     

Solvent and pH resistance of surface crosslinked chitosan/poly(acrylonitrile) composite nanofiltration membranes

The resistance of novel surface crosslinked Chitosan/poly(acrylonitrile) (PAN) composite nanofiltration (NF) membranes to pH and organic solvents was studied with respect to the effects of crosslinking parameters, namely, glutaraldehyde concentration and crosslinking time. The pH resistance was determined by permeation of aqueous acidic (pH 2.5) and basic (pH 11) solutions as well as swelling studies in the pH range of 2.5–11. The solvent resistance was determined by swelling, immersion, and permeation studies with several industrially important organic solvents, namely methanol, ethanol, iso‐propanol, methyl ethyl ketone, ethyl acetate and hexane. It was observed that the crosslinked composite membranes maintain the permeate fluxes for test solvents for 2 h of continuous operation without any significant change in flux. SEM studies on membrane samples after immersion as well as permeation with the above‐mentioned solvents indicated that the membrane morphology was maintained. The results are explained in terms of solvent–membrane polar and hydrophobic interactions, using solubility parameters of membrane and solvents and dielectric constants of solvents. Pure water flux and polyethylene glycol transmission data indicated that at pH 2.5 and 11, the membrane stability increased with increasing glutaraldehyde concentration and was much better at pH 11 than at pH 2.5. All surface crosslinked membranes showed reduced swelling between pH 4–10. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1782–1793, 2000     

水溶性荧光染料溶液脱盐浓缩的纳滤实验研究

选用NTR7450和NF270两种纳滤膜对水溶性工业荧光染料原液进行分离，选择出透过通量大、除盐效果好和染料截留率高的纳滤膜，并对该染料溶液进行了脱盐和浓缩的间歇渗滤过程研究：在温度25℃和压力1.0MPa下，膜对染料截留率达到100％，最终料液中NaCl浓度从0.214mol／L降到0.0025mol／L,料液被浓缩了2．6倍。说明纳滤膜的间歇渗滤操作过程能够实现染料溶液的脱盐浓缩。     

Phase separation in polyetherimide/solvent/nonsolvent systems and membrane formation

Phase separation phenomena of polyetherimide (PEI)/solvent/nonsolvent systems were investigated by measuring their precipitation values over the temperature range from 20 to 50°C. The solvents used are N‐methyl‐2‐pyrrolidone (NMP), dimethylacetamide (DMAC), and dimethylformamide (DMF). Nine nonsolvents were employed including water, methanol, ethanol, 1‐propanol, 2‐propanol, acetic acid, propionic acid, ethylene glycol, and diethylene glycol. Based on the measured precipitation values, critical solubility parameters for PEI were calculated, and the partial solubility boundary for PEI was obtained in a two‐dimensional solubility parameter coordinate graph. The relationship between solvent strength and membrane structure was examined using PEI hollow‐fiber membranes prepared from binary polymer solutions containing NMP, DMAC, and DMF as solvents. Water was used both as internal and external coagulants. The cross‐sectional structure and gas permeation properties of these hollow fibers were examined. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1789–1796, 1999     

计算机辅助筛选分离联苯与4-联苯乙酮两种化合物的溶剂

引言 4-联苯乙酮是合成非甾体抗炎药联苯乙酸和液晶材料的重要精细化工中间体[1].以联苯为原料,在无水三氯化铝存在下,用乙酰氯或醋酐进行傅一克反应可合成4-联苯乙酮[2-3];反应结束后加入碎冰和盐酸水解,然后静置分层,分出油层,水层用二氯乙烷多次萃取;萃取物并入油层,减压蒸去溶剂后可得到4-联苯乙酮粗品;文献[4]以氯仿为萃取剂从水层中提取目的产物.     

Polymer solubility parameters determined from measurements in a single solvent

The solubility parameter of polyisobutylene has been determined from intrinsic viscosity measurements in a single solvent as a function of temperature. The change in solubility parameter of the solvent as a function of temperature was calculated form the equation \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{d{\rm}ln \delta s}}{{d{\rm}ln Vs}} = - \frac{{n + 1}}{2} $\end{document} where Vs, the molal volume, changes with temperature. The vlaue for the solubility parameter thus obtained compares well with values reported in the literature for intrinsic viscosity measurements in a series of solvents. Similar measurements were made with an ethylenepropylene copolymer. The solubility parameter of 87 mole % C₂ ethylene-propylene copolymer was determined to be 8.1-8.6 in either toluene or methylcyclohexane.     

纳滤膜的电解质截留率及其带电特性

根据浓差极化模型和非平衡热力学模型，对４种纳滤膜（ＮＦ４０膜、ＮＴＲ７４５０膜、Ｄｅｓａｌ５膜和Ｇ２０膜）在不同浓度（１０～５００ｍｏｌ／ｍ３）的电解质（ＮａＣｌ）溶液体系的透过实验数据进行回归计算，求得膜的反射系数和溶质透过系数。根据ＴｅｏｒｅｌＭｅｙｅｒＳｉｅｖｅｒｓ模型从膜的反射系数估算这些纳滤膜的有效电荷密度并对其进行了电解质浓度的经验关联。结果讨论同时证明了ＴｅｏｒｅｌＭｅｙｅｒＳｉｅｖｅｒｓ模型适用于纳滤膜的带电特性评价     

A study of sorption/desorption and diffusion of substituted aromatic probe molecules into semi interpenetrating polymer network of polyurethane/polymethyl methacrylate

The sorption-desorption-resorption-redesorption experiments have been conducted to evaluate the transport behaviour of polyethylene glycol (PEG) based polyurethane/polymethyl methacrylate (PU/PMMA, 50/50) semi interpenetrating polymer network (SIPN) with aromatic probe molecules. Molecular migration depends on the nature of the organic solvent, membrane-solvent interaction, temperature, solubility parameter, molecular volume and free volume available within the polymer matrix. The transport parameters like sorption (S), diffusion (D) and permeation (P) coefficients have been calculated for IPN-aromatic probe molecule systems. Sorption and diffusion results measured at different temperatures viz. 20, 40 and 60 °C are found to follow Fickian mechanism. The liquid concentration profiles in the membranes during sorption and resorption processes have been simulated by solving Fick's diffusion equations and by using numerical method. Equilibrium swelling results have been used to measure the molecular mass between cross links, degree of cross linking and cross link density using Flory-Rehner theory. It is found that the mass uptake values decreased with increase in cross link density during polymer-solvent interactions. The estimated Arrhenius activation energy for diffusion (E_D) and permeation (E_P) are indicative of nature of liquid and their interaction with membrane. Thermodynamic parameters like change in entropy (ΔS) and enthalpy (ΔH) have been calculated using van't Hoffs equation. The rate of evaporation of liquids have been calculated for desorption and redesorption runs, and these results depend on volatility of solvents.     

Pebax membrane for CO2/CH4 separation: Effects of various solvents on morphology and performance

In this study, the effects of different solvents on the morphology and permeation of poly(ether‐block‐amide) (Pebax‐1657) membranes were investigated. Pebax membranes were fabricated via a solution casting method with five different solvents, that is, N,N‐dimethyl formamide (DMF), N,N‐dimethyl acetamide (DMAc), N‐methyl‐2‐pyrrolidone (NMP), formic acid, and a mixture of ethanol (EtOH) with water (H₂O). Cross‐sectional scanning electron microscopy analysis of the membranes was performed to investigate the morphology of the prepared membranes. X‐ray diffraction and Fourier transform infrared analysis were also carried out to characterize the membranes. The interactions of the polymer and various solvents were evaluated with Hansen solubility parameters. Permeation experiments for CO₂ and CH₄ gases were performed to study the effects of the solvents on the permeation properties of the membranes. The solvent properties, such as the molar volume, boiling point, and solubility parameters, were investigated as were the membranes characteristics, such as the crystallinity, d‐spacing, and fractional free volume. The results obtained from the experiments show that the CO₂ permeability for the membranes prepared with different solvents followed this order: NMP > DMF > Formic acid > DMAc > H₂O/EtOH mixture. With increasing molar volume, the gas permeability increased for all of the membranes, except for DMAc, which showed a lower permeability because of its highly crystalline structure. DMF showed a higher CO₂/CH₄ ideal selectivity compared to the other membranes and, consequently, could be introduced as the best solvent from all aspects for the Pebax‐1657 membrane. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44531.     

Hydrophilic/hydrophobic IPN membranes for the pervaporation of ethanol-water mixture

Summary Pervaporation of ethanol-water mixture was examined on IPN membranes composed of hydrophilic polyurethane(PU) and hydrophobia polystyrene(PS). The IPN membranes showed preferential pervaporation of water over ethanol and revealed high permeation rate. As the content of hydrophobic PS was increased, the permeation rate decreased while the separation factor increased, indicating that the PS domains suppressed the swelling of the PU phase and reduced the plasticizing effect. The average diffusion coefficient, computed from the permeation rate and solubility, was highly dependent on the viscosity and concentration of the permeant in the membrane.     

A transport model for the absorption of mixed solvents in glassy polymer membrane

Transport model for mixed solvents in glassy polymer membrane is rare in literature. In our previous work, a new experimental method has been developed and absorption kinetic curves for two mixed solvent systems (ethanol/1,2-dichloroethane and ethanol/ethyl acetate) in polyurethane (PU) membrane at have been measured. In this work, based on Liu et al.'s transport model for single solvent/polymer membrane system, a transport model for the absorption of mixed solvents in glassy polymer membrane is established. Three model parameters in this model can be obtained by correlating the experimental data of the corresponding single solvent/polymer membrane systems; the other three should be determined by correlating the experimental data of mixed solvents/polymer membrane system. The effect of model parameters on diffusion is studied by numerical simulation. The correlated results agree well with the experimental absorption curves. The model has the ability to predict the transport phenomena of mixed solvents in polymer membrane.     

Impact of Organic Solvents on Physicochemical Properties of Nanofiltration and Reverse‐Osmosis Membranes

Polymeric membranes subjected to the permeation of n‐hexane were characterized and the influence of pretreatment with ethanol on the properties of the membranes was studied to assess membrane performance and stability. The results suggest that the selectivity of the membrane depends not only on the pore size, but also to a great extent on the interaction between solvent and polymer. An increase in membrane roughness and contact angle was observed for all membranes after pretreatment with ethanol and n‐hexane permeation. Moreover, the surface free energy decreased after solvents exposure, indicating an increase in membrane surface hydrophobicity and polymer swelling. The studied membranes show feasibility of use for the recovery of solvents, if suitable process parameters are selected.     

Comparative studies on the effects of casting solvent on physico‐chemical and gas transport properties of dense polysulfone membrane used for CO2/CH4 separation

The effects of casting solvents on the physico–chemical and transport properties of polysulfone membranes were investigated. Comparative analysis of the properties of membranes prepared from a new solvent (diethylene glycol dimethyether, DEG) and other commonly used solvents (1‐methyl‐2‐pyrrolidone, N,N‐dimethylacetamide, dimethyl sulfoxide and N,N‐dimethylformamide) were performed using gas permeation, X‐ray diffraction, scanning electron microscopy, thermogravimetric, and Fourier transform infrared spectroscopy analyses. The degree of polymer–solvent interaction was evaluated using the solvent molar volume, and Hansen and Flory–Huggins parameters. Membrane prepared from DEG displayed a relatively higher permeability of 29.08 barrer and CO₂/CH₄ selectivity of 23.12 compared to membranes prepared from other solvents. This improved performance was attributed to the better interaction between the DEG solvent and polysulfone than other solvents that were considered. DEG has the highest molar volume of 142.280 cm³/mol and the lowest Flory–Huggins parameter of 0.129. Thus a thorough evaluation of polymer–solvent interaction is very crucial in preparing membranes with optimum performance. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42205.     

低分子量中性溶质体系的纳滤膜的透过特性

根据浓差极化模型和非平衡热力学模型,对４种品牌的纳滤膜（ＮＦ４０膜、ＮＴＲ７４５０膜、Ｄｅｓａｌ５膜和Ｇ２０膜）在醇类和糖类中性溶质体系的透过实验数据进行回归计算,求得膜定数（即膜的反射系数和溶质透过系数）,再由这些膜定数结果根据细孔模型估算了４种品牌的纳滤膜的细孔结构参数,这４种膜的细孔半径范围在０．４～０．８ｎｍ。结果讨论表明细孔模型适用于纳滤膜的结构评价。     

Membrane processing of crude vegetable oils: Pilot plant scale remoyal of solvent from oil miscellas

The recovery of solvents used in the extraction step of edible oil processing is required for economical, environmental, and safety considerations. The miscella (mixture of extracted oil and solvent) exits the extractor at 70 to 75 wt% solvent content. Currently, the solvent is recovered by distillation. This paper reports the results of a study on separation of vegetable oils from commercial extraction solvents using various types of Reverse Osmosis (RO) and Ultrafiltration (UF) membranes. Solvent permeation rates and separation performances of various RO and UF membranes were determined by using ethanol, isopropyl alcohol and hexane as the solvents. One membrane exhibited a flux of 200 GFD (ethanol) with 1% oil remaining in the permeate. However, hexane rapidly deteriorated all but one of the membranes tested. The membrane that was compatible with hexane had a low flux and unacceptably low oil retention. Industrial-scale membranes were also evaluated in pilot plant trials. A hexane separation was attempted with a hollow-fiber membrane unit, and it was noted that the pores of the fibers swelled almost closed. Some of the commercially available membranes selectively removed solvent (ethanol or isopropanol) from the edible oil miscellas with reasonable flow rates. The research reported has shown that membranes manufactured from polyamide were the least affected by hexane. Fluxes achieved during solvent-oil separations were increased by increases in either temperature or pressure and decreased by increases in oil concentration in the feed. The processing temperature affected the percentage of oil in solution in either ethanol or isopropanol as well as the viscosity of the feed. Both of these factors in turn influenced the flux achieved. Approximately 2 trillion Btu/yr could be saved using a hybrid membrane system to recover solvents used in the extraction step of crude oil production. Studies to date report marginal success. The development of hexane-resistant membranes may make this application viable.     

The influence of solvent type on the viscosity of concentrated polymer solutions

The viscosity of concentrated (17.5 g/dl) solutions of cellulose acetate in 11 single solvents and in four binary solvent mixtures was related to a thermodynamic measure of solvent power. In single solvents, the specific viscosity varied from 4600 in dimethyl sulfoxide to 78,000 in diacetone alcohol, with the specific viscosity increasing with decreasing abolute value of the partial molar free energy of dilution. This behavior can be accounted for by the hypothesis that the number of chain entanglements increases with decreasing solvent power. In solvent mixtures, the specific viscosity often attains a minimum value at a composition where the average solubility parameter locus is near the center of the solubility region of the polymer.     

Pervaporation of dilute alcoholic mixtures using PDMS membrane

Pervaporation (PV) of methanol/water and ethanol/water mixtures through PDMS membrane was investigated using a PV cell (in laboratory scale). PDMS membrane is a well-known hydrophobic membrane for removing organics from aqueous mixtures. Experimental results were obtained at different initial alcohol (methanol and ethanol) concentrations (0.3-3 wt%) and temperatures (30-). Recirculation flow rate was kept constant at a value of 15.6 l/h. Average permeation flux (j), separation factor (α) and activation energy of permeation (E_P) were calculated. Separation factor of PDMS membrane for methanol was greater than that for ethanol. Total flux for methanol/water and ethanol/water mixtures was observed to vary from 0.37 to 0.56 and 0.52 to 0.90 at , respectively, as alcohol concentration changed from 0.3 to 3 wt%. Separation of alcohols depends on both their selective sorption in polymeric membrane and their diffusivity. The most important observation was that separation factor of methanol/water mixtures is greater than that of ethanol/water mixtures and it is because of different molecular size of alcohols. Different behavior of alcohol/water mixtures can also be explained in the entire concentration range studied using relative values of solubility parameters of the alcohols. It can be due to the fact that activation energy of alcohol permeation increases as solubility parameter difference between alcohol and membrane increases.     

Designing Absorption Processes with Aqueous Diglycolamine

2‐(2‐Aminoexthoxy)ethanol or diglycolamine (DGA) is a CO₂ absorption solvent that is suitable to treat natural gas, flue gas, and biogas or landfill gas. Equilibrium CO₂ solubility in concentrated aqueous DGA solvents with varying molality was measured under absorption and desorption conditions at different temperatures. Viscosity and surface tension of the solvent before absorption, after absorption, and after desorption were determined. With increasing DGA molality, CO₂ loading remained constant until the number of moles of DGA exceeded the number of moles of water. For a given DGA molality, with higher CO₂ loading, viscosity increased exponentially and surface tension rose with a power of two.     

Concentration of biologically active compounds extracted from Sideritis ssp. L. by nanofiltration

In the present study experimental results on the nanofiltration of ethanolic extracts from Sideritis ssp. L. are reported, regarding polyphenols and flavonoids concentration and solvent reuse. Three membranes, resistant to organic solvents, have been used: Starmem™ 240 (polyimide), Duramem™ 300 and Duramem™ 500 (both of them modified polyimide). The dependence of the membrane rejection on its MWCO is presented. The separation of flavonoids from phenols with lower molecular weight is found possible at MWCO > 400 Da. A decrease of the flux is observed at permeate to feed volume ratio of about 0.58, thus indicating the existence of a critical concentration, independent of the feed volume and MWCO of the membranes used. The membrane behaviour during nanofiltration has been characterised by ESEM and ATR-FTIR.Concentrations of active compounds up to 3-4 times higher have been obtained in the retentates. The extracts concentrated by nanofiltration preserve their high antioxidant activity. Further dilution of the retentates displays a logarithmic concentration dependence of the radical scavenging activity. The experiments have proved the possibility for permeate use for extraction instead of ethanol, thus essentially reducing the volume of the solvent.