Organic Solvent Nanofiltration Processes Research Articles

Integrated membrane process for pretreating and desolventizing hexane-soybean oil miscella – A pilot plant study

The study aimed to develop a membrane desolventizing technology for solvent recovery in vegetable oil extraction. Pretreatment of crude miscella is a prerequisite for an organic solvent nanofiltration (OSN) based desolventizing process. Solvent-resistant ultrafiltration (SRUF) membrane employed in micelle-enhanced ultrafiltration (MEUF) of hexane-crude soybean oil miscella displayed high phospholipids (PL) rejection (98.5 %) and productivity (∼28 L/m2/h), accompanied with a moderate oil rejection (∼22 %). The PL-rich retentate fraction was alkali-treated to recover the oil in the stream (8.8 %). This complementary pretreatment approach met the quality requirements and maximized the yield of treated oil (>98 %) while reducing the chemicals in the process. A subsequent two-stage desolventizing of MEUF-treated miscella with solvent-resistant nanofiltration (SRNF) membrane reduced the oil-in-permeate to 1.37 %, achieving the set recycling criteria (<2 %). The results obtained from the pilot scale study (batch size 40 kg of crude miscella) revealed that the MEUF met the pretreatment requirements, and the subsequent OSN process recovered ∼63 % of hexane through a non-thermal route for recycling in the extraction process. The pilot-scale evaluation demonstrated the technical feasibility of the proposed membrane desolventizing process employing indigenous spiral-wound SRUF and SRNF membrane modules.

Improving the Separation Properties of Polybenzimidazole Membranes by Adding Acetonitrile for Organic Solvent Nanofiltration.

In research on membranes, the addition of co-solvents to the polymer dope solution is a common method for tuning the morphology and separation performance. For organic solvent nanofiltration (OSN) applications, we synthesized polybenzimidazole (PBI) membranes with high separation properties and stability by adding acetonitrile (MeCN) to the dope solution, followed by crosslinking with dibromo-p-xylene. Accordingly, changes in the membrane structure and separation properties were investigated when MeCN was added. PBI/MeCN membranes with a dense and thick active layer and narrow finger-like macrovoids exhibited superior rejection properties in the ethanol solution compared with the pristine PBI membrane. After crosslinking, they displayed superior rejection properties (96.56% rejection of 366-g/mol polypropylene glycol). In addition, the membranes demonstrated stable permeances for various organic solvents, including acetone, methanol, ethanol, toluene, and isopropyl alcohol. Furthermore, to evaluate the feasibility of the modified PBI OSN membranes, ecamsule, a chemical product in the fine chemical industry, was recovered. Correspondingly, the efficient recovery of ecamsule from a toluene/methanol solution using the OSN process with PBI/MeCN membranes demonstrated their applicability in many fine chemical industries.

Enantioselective nanofiltration using predictive process modeling: Bridging the gap between materials development and process requirements

Organic solvent nanofiltration (OSN) is a low-energy alternative for continuous separations in the chemical industry. As the pharmaceutical sector increasingly turns toward continuous manufacturing, OSN could become a sustainable solution for chiral separations. Here we present the first comprehensive theoretical assessment of enantioselective OSN processes. Lumped dynamic models were developed for various system configurations, including structurally diverse nanofiltration cascades and single-stage separations with side-stream recycling and in situ racemization. Enantiomer excess and recovery characteristics of the different processes were assessed in terms of the solute rejection values of the enantiomer pairs. The general feasibility of stereochemical resolution using OSN processes is discussed in detail. Fundamental connections between rejection selectivity, permeance selectivity, and enantiomer excess limitations are revealed. Quantitative process performance examples are presented based on theoretical rejection scenarios and cases from the literature on chiral membranes. A model-based prediction tool can be found on www.osndatabase.com to aid researchers in connecting materials development results with early-stage process performance assessments.

Thin-Film Composite Membranes with a Carbon Nanotube Interlayer for Organic Solvent Nanofiltration.

Compared to the traditional chemical-crosslinking-based polymer, the porous polytetrafluoroethylene (PTFE) substrate is considered to be an excellent support for the fabrication of thin-film composite (TFC) organic solvent nanofiltration (OSN) membranes. However, the low surface energy and chemical inertness of PTFE membranes presented major challenges for fabricating a polyamide active layer on its surface via interfacial polymerization (IP). In this study, a triple-layered TFC OSN membrane was fabricated via IP, which consisted of a PA top layer on a carbon nanotube (CNT) interlayer covering the macroporous PTFE substrate. The defect-free formation and cross-linking degree of the PA layer can be improved by controlling the CNT deposition amount to achieve a good OSN performance. This new TFC OSN membrane exhibited a high dye rejection (the rejection of Bright blue B > 97%) and a moderate and stable methanol permeated flux of approximately 8.0 L m−2 h−1 bar−1. Moreover, this TFC OSN membrane also exhibited an excellent solvent resistance to various organic solvents and long-term stability during a continuous OSN process.

Mechanistic study of pH effect on organic solvent nanofiltration using carboxylated covalent organic framework as a modeling and experimental platform

Covalent organic framework (COF) membranes for organic solvent nanofiltration (OSN) have attracted growing interest due to their high stability, well-defined pore size, and controllable pore functionality. In aqueous nanofiltration processes, solution pH has a significant effect on membrane permeability, selectivity, and fouling. However, our understanding of pH effects on OSN processes is still limited. Here, we present experimental and reactive force field molecular dynamics (ReaxFF MD) simulation results on the effect of pH on OSN using a well-characterized carboxylated COF (C-COF) membrane. Filtration experimental and modeling results both demonstrate that pH changes can affect solvent permeance and solute rejection dramatically. Specifically, methanol permeance decreases with the increase of NaOH and HCl concentration, respectively. When Alcian Blue dye was used as the solute in methanol, the selectivity increased from 23% to 98% when changing the feed pH from 2.2 to 10.1, respectively. While ReaxFF MD results show that C-COF solvated pore size is only marginally affected by the pH of solution, methanol diffusion is affected by the size of methanol-solvated Na+ and Cl- ions, which increase with increasing Na+ and Cl- concentrations. Solution pH change also affected solute solvation layer thicknesses and C-COF pore charges, contributing to the significant AB dye selectivity increase with pH increase. To summarize, we have shown that dramatic changes in C-COF selectivity are not anomalous in OSN, but are instead controllable by varying feed solution pH to modify solvated solute radii and surface charge.

Biomimetic asymmetric structural polyamide OSN membranes fabricated via fluorinated polymeric networks regulated interfacial polymerization

Organic solvent nanofiltration (OSN) as a high-efficient membrane separation technology has play an important role in chemical industrial separation, clean energy production, and high-value resources recycling, etc. Inspired by the asymmetric biological structure of Desert beetle, herein a novel kind of polymeric OSN membranes with asymmetric structure have been fabricated via fluorinated polymeric networks (FPNs) regulated interfacial polymerization. The FPNs were formed with m-phenylenediamine (MPD), dopamine (DA) and 1H,1H,2H,2H-Perfluorodecane-thiol (PFDT) via the Michael addition and Schiff-base reaction. The FPNs tailored thin-film composite membrane (FPN-TFC) with biomimetic asymmetric structure, e.g., much hydrophilic looser front surface and much hydrophobic denser rear surface, exhibits an optimum ethanol permeance ~15.7 L m−2 h−1.MPa−1 and high rejection ~99.5% for Rose Bengal (RB) dye molecules (test with 0.05 g L−1 RB ethanol solution at 25 °C under 1.5 MPa), which is almost 6 times higher than that of the conventional TFC membranes. Moreover, there is a good stability for the FPN-TFC membrane tested with different polar solvents in long-term operation process. Therefore, this work provides a guidance for the development of advanced polymeric OSN membranes with both high solvent permeability and solute selectivity, as well as good stability in OSN process, which would have broad application prospects in chemical and other industrial fields.

Graphene‐Based Advanced Membrane Applications in Organic Solvent Nanofiltration

AbstractOwing to the increasing need to mitigate excessive organic solvent waste, the efficient separation and recovery of organic solvents have received major research attention in recent years. The membrane‐based organic solvent nanofiltration (OSN) process has demonstrated its feasibility in addressing this problem with low energy costs, compared to conventional separation techniques, such as adsorption, liquid–liquid extraction, and solvent evaporation. Recently, membranes made of 2D graphene‐based materials have shown great promise because they attain high solvent flux and solute rejection using easy processing methods. Thus, this paper focuses on state‐of‐the‐art studies of graphene‐based membranes used in OSN processes, which include syntheses, characterizations, performance evaluations, membrane fouling, and simulation studies, in combination with the development of the “upper‐bound” line to indicate the performance of graphene‐based membranes. In this paper, critical challenges involved in the development of graphene‐based membranes are also focused on and discussed to map out the future directions of these membranes in industrial OSN processes. In addition to OSN, this paper pertains to a broader audience in other separation processes, particularly in the fields of gas separation and water treatment.

Progress and Perspectives on Ceramic Membranes for Solvent Recovery.

With the increase in demand for commodities in the world, it is advisable to conserve resources. In the case of liquid wastes generated from pharmaceutical and petroleum industries, an unconventional solution is provided for the regeneration of solvents. However, this solvent recovery can be carried out using various efficient methods. Recently, Mixed Matrix Membranes (MMM) obtained by the addition of nanoparticles into a polymer matrix as reinforcements, or using a material with a well-defined inorganic network as a membrane like zeolite, silica based, Zeolite imidazolate frameworks (ZIFs) and Metal organic frameworks (MOFs), were explored for a solvent recovery process. These membranes possess characteristics such as high selectivity, flux and stability at various environmental conditions for the solvent recovery process. In this review, we have covered the polymer, nanocomposites, and ceramic membranes for solvent recovery through the pervaporation and organic solvent nanofiltration processes. The key challenges faced by the materials such as MOFs, zeolite, silica, zeolite and ZIFs when they are fabricated (through in situ synthesis or secondary growth process) as membranes and separation of solvents to explore for the solvent recovery process are reviewed.

Exploiting the electrical conductivity of poly-acid doped polyaniline membranes with enhanced durability for organic solvent nanofiltration

We have developed stable organic solvent nanofiltration (OSN) membranes that are electrically conductive. These membranes overcome key issues with current tuneable membranes: molecular weight cut off (MWCO) limited to the UF-range and lack of filtration stability. Polyaniline (PANI) was in-situ doped by poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA) using chemical oxidative polymerization that leads to formation of interpolymer complex. The PANI-PAMPSA membranes were prepared by phase inversion method and the pore sizes were shrunk by annealing the membranes at temperatures lower than the crosslinking temperature. The membranes were systematically evaluated using visual and chemical analysis and in-filtration experiments. The developed membranes were solvent stable, reusable, had a denser structure and lower MWCO and there was no thermal crosslinking as seen by IR. The solvent permeance obtained were: 0.46, 0.60 and 0.74 Lm−2h−1bar−1 for acetone, 2-propanol and methanol respectively, with MWCO below 300 Da and 266 Da for methanol. For the tuneability investigation, when applying an electrical potential (20 V) in a custom-made cross-flow membrane cell, an increase in MWCO and permeance (10.4% and 55.6%, respectively) was observed. These results show that this simple in-situ doping method with heat treatment can produce promising and stable PANI membranes, for OSN processes in different solvents, with the distinctive feature of in-situ performance control by applying external electrical potential.

Can the variance in membrane performance influence the design of organic solvent nanofiltration processes?

The development of organic solvent nanofiltration (OSN) membranes has been a continuous effort during the past decade. Several groups generated and published experimental results and simulations with either tailor-made membranes or industrial products. The published data space is diverse, with a single publication often focusing on a certain membrane only, a group of specific solutes only, on the effect of solvent only. A comprehensive comparison of all of these is still lacking. An analysis on the reliability of quantified transport parameters is missing, in particular when different analysis methods and different membrane systems are used. The technology is in its incubation phase with a need for reliable data and measurement standards to ground the process design on reliable membrane transport properties. This study uses an unprecedented extensive standard experimental procedure to measure separation characteristics of polymer membranes for the separation of organic solutes from organic solvents.For a variety of different solvents, solutes and membranes, flux and retention measurements are rigorously characterized by round robin tests at different labs using different analytical systems. This extensive collaborative study evaluates for the first time which fluctuations in results occur under comparable conditions of lab-scale experiments at different locations and which influence these have on the design of OSN processes.Utilizing the variance in the membrane transport data, a process design study and optimization is presented. For the first time ever, we report how variance in membrane transport properties can influence the process design ranging from a simple single stage system for values for the upper transport limits, to a two stage system with a permeate recirculation for mean values, to a complex three stage system for the lower limits.

Sorption and Nanofiltration Characteristics of PIM-1 Material in Polar and Non-Polar Solvents

The affinity of polar extractants (propylene carbonate, dimethylsulfoxide, dimethylformamide, triethylene glycol and dimethylacetamide) and benzene, toluene, p-xylene and m-xylene (so-called BTX fraction) for PIM-1 material was evaluated. The mass-transfer coefficients of selected solvents were determined in organic solvent nanofiltration process. All solvents showed a good affinity toward PIM-1 polymer; while the large values of sorption and PIM-1 swelling degree were in the case of benzene (1.63 g/g, 192%), toluene (1.72 g/g, 186%) and xylenes (1.61–1.76 g/g, 147–170%); while these values for selected polar solvents were in the range of 1.09–1.48 g/g and 83–108%, respectively. The values of sorption and swelling degree were successfully correlated with Hansen’s solubility parameters. Values of permeability coefficients of nonpolar solvents through PIM-1 membranes were 1.5–5.5 times higher than those for polar solvents. With increasing affinity of the solvent toward polymer, the values of the permeability coefficients also increased.

The potential of organic solvent nanofiltration processes for oleochemical industry

Abstract Pressure-driven membrane separation processes bare the promise to significantly reduce energy requirements and operational cost compared to classical thermal separation processes. The ability of organic solvent nanofiltration (OSN) to operate at mild temperatures makes it especially interesting for oleochemical processes, such as the refinement of non-edible oils or waste oils. In this study, the potential of OSN for solvent recovery and deacidification is investigated by means of a model-based process analysis. On the basis of optimized membrane cascade configurations the OSN process is compared to the conventional reference process in terms of energy requirements and costs to judge on the competitiveness. It is shown that the energy demand for the recovery of extraction solvents can be reduced by more than 70% using an OSN-assisted evaporation process. While the operating costs are significantly reduced, the investment costs are increased in comparison to a classical evaporation process. The process analysis also shows that OSN is a promising alternative for deacidification of various low-quality oils using multi-stage membrane cascades. Optimal process design allows to upgrade the triglycerides to the necessary purity, e.g. for processing them in biodiesel production, while the free fatty acids are recovered as valuable by-product that enhance the profitability. Hence, OSN constitutes a valuable processing technology that can be integrated into upstream separation and recovery processes of the oleochemical industry.

Rapeseed hull oil as a source for phytosterols and their separation by organic solvent nanofiltration

Hulling of rapeseed leads to hulls as an additional valuable by‐product of rapeseed oil production, containing remarkable concentrations of phytosterols and tocopherols compared to the concentrations in the entire seed and double‐pressed kernel. It was shown that the content of these substances in hull oil is significantly higher than in the entire seed. In particular, the sterol concentration with 3% is remarkably high. Another characteristic of hull oil is the high concentration of alpha‐tocopherol. Therefore, the hull oil can be an interesting source for sterols and tocopherols, which are used as health promoting additives in food industry. The nanofiltration with organic solvent resistant membranes was tested for the enrichment of these substances. The experiments were performed in a dead‐end cell at pressures up to 20 bar at ambient temperature using n‐hexane and n‐heptane as solvents. Fluxes of pure solvent and solutions of triglycerides and sterols were determined. Rejections of sterols and triglycerides were measured in binary (solvent‐sterol or solvent‐oil) and ternary (solvent‐sterol‐oil) solute solvent systems. A five‐fold increase in sterol concentration in the solvent free permeate was possible with a single nanofiltration step. After removal of the solvent from the permeate, sterol crystallization was observed. Further investigations have to be done to optimize membrane separation and coupling with a crystallization of sterols.Practical applications: The hull fraction of rapeseed can be used as a source for phytosterols and tocopherols which are both food additives. Thus, in addition to the advantages with respect to the quality of the oil and protein, hulling leads to additional valuable products, which are oil fractions rich in sterols and tocopherols. The feasibility of an organic solvent nanofiltration process for the separation between unsaponifiables and oil is demonstrated.Rapeseed hull oil has a remarkably high content of alpha‐tocopherol and sterols. It was shown that organic solvent nanofiltration is a process, which can be used for a partial separation of sterols and triglycerides. An enrichment by a factor of five is possible, leading to oils with such a high sterol concentration that crystallization occurred.

Cyclic Peptide Formation in Reduced Solvent Volumes via In-Line Solvent Recycling by Organic Solvent Nanofiltration

Cyclic peptides have found numerous and wide ranging applications that include drug molecules, nanomaterials, and chiral chromatography stationary phases. However, in the crucial cyclization step, high dilution conditions are often required, resulting in large volumes of solvent being consumed to prepare relatively small quantities of product. This paper demonstrates the synthesis of a cyclic nonapeptide with in-line solvent recycling via organic solvent nanofiltration (OSN) resulting in a significant reduction in the solvent load of the reaction and concomitant improvement in process mass intensification (PMI). The membrane was used to remove the reaction product from the reaction vessel, as the cyclic peptide product shows limited stability in the presence of an excess of reaction reagent. In comparison to the standard batch reaction, no loss in yield or product purity was observed for the OSN process tested. The proof-of-concept study outlined in this paper was performed on a real active pharmaceutical...

Graphene oxide membranes on ceramic hollow fibers – Microstructural stability and nanofiltration performance

Graphene oxide (GO) membranes have demonstrated great potential in liquid filtration. With the aim of real applications, GO membranes in a hollow fiber shape are of particular interest because of the high-efficiency and easy-assembly features at the module level. We report here that GO membranes on ceramic hollow fiber substrates are unstable at the dry state, mainly due to the drying-related shrinkage. And we demonstrate that these GO hollow fiber membranes can be stabilized by keeping them wet after initial controlled formation of the membranes. The GO hollow fiber membranes show higher permeation fluxes of acetone and methanol than most commercial membranes, and reject molecules larger than 300Da, showing a great potential in the use of value-added organic solvent nanofiltration processes.

Separation of different metathesis Grubbs-type catalysts using organic solvent nanofiltration

Abstract In this paper, the challenge of separating and re-using homogeneous catalysts from their post-reaction mixture in the field of metathesis is addressed using organic solvent nanofiltration (OSN). A coupled reaction–separation process was applied for the metathesis reaction of 1-octene to 7-tetradecene and ethene. Five different Grubbs-type catalysts and the STARMEM™ series of OSN membranes were used. It was found that the STARMEM™ 228 membrane successfully separates the different catalysts from their post-reaction mixtures to below 9 ppm. The coupled reaction–separation and recycling process also increased the turnover number from 1400 for a single pass reaction to 5500 for the overall consecutive reaction–separation steps of four cycles. The OSN process was further characterized for mixtures of 1-octene, 1-tetradecene and 7-tetradecene by varying operating pressures and solvent concentration.