Organic Solvent Nanofiltration in Pharmaceutical Industry

Solvent-responsive covalent organic framework membranes for precise and tunable molecular sieving

Membrane-based nanofiltration has the potential to revolutionize the large-scale treatment of organic solvents in various applications. However, the widely used commercial membranes suffer from low permeability, narrow structural tunability, and limited chemical resistance. Here, we report a strategy for fabricating covalent organic framework (COF) membranes with solvent-responsive structural flexibility. The interlayer shifting of these COF membranes in polar organic solvents results in sub-nanopores with high selectivity. High rejection rates (>99%), high permeance (>15 kilogram meter-2 hour-1 bar-1), and excellent organic solvent resistance of these smart COF membranes are achieved for a diverse array of nanofiltration applications.

PEDOT:PSS Nanoparticle Membranes for Organic Solvent Nanofiltration

Recycling of valuable solutes and recovery of organic solvents via organic solvent nanofiltration (OSN) are important for sustainable development. However, the trade-off between solvent permeability and solute rejection hampers the application of OSN membranes. To address this issue, the poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) nanoparticle membrane with hierarchical pores is constructed for OSN via vacuum filtration. The small pores (the free volume of the polymer chain) charge for the solute rejection (high rejection efficiency for low molecule weight solute) and allow solvent passing while the large pores (the void between two PEDOT:PSS nanoparticles) promote the solvent transport. Owing to the lack of connectivity among the large pores, the fabricated PEDOT:PSS nanoparticle membrane enhanced solvent permeance while maintaining a high solute rejection efficiency. The optimized PEDOT:PSS membrane affords a MeOH permeance of 7.2 L m-2 h-1 bar-1 with over 90% rejection of organic dyes, food additives, and photocatalysts. Moreover, the rigidity of PEDOT endows the membrane with distinctive stability under high-pressure conditions. The membrane is used to recycle the valuable catalysts in a methanol solution for 150 h, maintaining good separation performance. Considering its high separation performance and stability, the proposed PEDOT:PSS membrane has great potential for industrial applications.

Self-standing membranes for separation: Achievements and opportunities

Supported membranes and mixed matrix membranes have a limitation of harming the mass transfer due to the incompatibility between the support layer or the matrix and the active components of the membrane. Self-standing membranes, which could structurally abandon the support layer, altogether avoid the adverse effect, thus greatly facilitating the transmembrane mass transfer process. However, the abandonment of the support layer also reduces the membrane's mechanical properties and formability. In this review, our emphasis will be on self-standing membranes within the realm of materials and separation engineering. We will explore the materials employed in the fabrication of self-standing membranes, highlighting their ability to simultaneously enhance membrane performance and promote self-standing characteristics. Additionally, we will delve into the diverse techniques utilized for crafting self-standing membranes, encompassing interfacial polymerization, filtration, solvent casting, Langmuir-Blodgett & layer-by-layer assembly, electrospinning, compression, etc. Throughout the discussion, the merits and drawbacks associated with each of these preparation methods were elucidated. We also provide a brief overview of the applications of self-standing membranes, including water purification, gas separation, organic solvent nanofiltration, electrochemistry, and membrane reactor, as well as a brief description of the general strategies for performance enhancement of self-standing membranes. Finally, the current status of self-standing membranes and the challenges they may encounter were discussed.

Fabrication of Coffee-Ring Nanostructured Membranes for Organic Solvent Nanofiltration

Organic solvent nanofiltration (OSN) plays important roles in pharmaceutical ingredients purification and solvent recovery. However, the low organic solvent permeance under cross-flow operation of OSN membrane hampers their industrial applications. Herein, we report the construction of coffee-ring structured membrane featuring high OSN permeance. A water-insoluble crystal monomer that dissolved in EtOH/H2O mixed solvent was designed to react with trimesoyl chloride via interfacial polymerization. Owing to the diffusion of EtOH to n-hexane, coffee-ring nanostructure on the support membrane appeared, which served as the template for construction of coffee-ring structured membrane. The optimal nanostructured membrane demonstrated 2.6-fold enhancement in the effective surface area with reduced membrane thickness. Resultantly, the membrane afforded a 2.7-fold enhancement in organic solvent permeance, e.g., ~13 LMH/bar for MeOH, without sacrificing the rejection ability. Moreover, due to the rigid monomer structure, the fabricated membrane shows distinctive running stability in active pharmaceutical ingredients purification and the ability for concentration of medicines.

The physical basis for solvent flow in organic solvent nanofiltration

Organic solvent nanofiltration (OSN) is an emerging membrane technology that could revolutionize chemical separations in numerous vital industries. Despite its significance, there remains a lack of fundamental understanding of solvent transport mechanisms in OSN membranes. Here, we use an extended Flory-Rehner theory, nonequilibrium molecular dynamic simulations, and organic solvent transport experiments to demonstrate that solvent flow in OSN membranes is driven by a pressure gradient. We show that solvent molecules migrate as clusters through interconnected pathways within the membrane pore structure, challenging the widely accepted diffusion-based view of solvent transport in OSN. We further reveal that solvent permeance is dependent on solvent affinity to the OSN membrane, which, in turn, controls the membrane pore structure. Our fundamental insights lay the scientific groundwork for the development of next-generation OSN membranes.

Organic Solvent Nanofiltration in Pharmaceutical Applications

Separation and purification in organic solvents are indispensable procedures in pharmaceutical manufacturing. However, they still heavily rely on the conventional separation technologies of distillation and chromatography, resulting in high energy and massive solvent consumption. As an alternative, organic solvent nanofiltration (OSN) offers the benefits of low energy consumption, low solid waste generation, and easy scale-up and incorporation into continuous processes. Thus, there is a growing interest in employing membrane technology in the pharmaceutical area to improve process sustainability and energy efficiency. This Review comprehensively summarizes the recent progress (especially the last 10 years) of organic solvent nanofiltration and its applications in the pharmaceutical industry, including the concentration and purification of active pharmaceutical ingredients, homogeneous catalyst recovery, solvent exchange and recovery, and OSN-assisted peptide/oligonucleotide synthesis. Furthermore, the challenges and future perspectives of membrane technology in pharmaceutical applications are discussed in detail.

Ultrathin organosiloxane membrane for precision organic solvent nanofiltration

Promising advances in membrane technology can lead to energy-saving and eco-friendly solutions in industrial sectors. This work demonstrates a highly selective membrane with ultrathin and highly interconnected organosiloxane polymer nanolayers by initiated chemical vapor deposition to effectively separate solutes within the molecular weight range of 150-300 g mol-1. We optimize the poly(1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane) membrane by adjusting both the thickness of the selective layer and the pore sizes of its support membranes. Notably, the 29 nm selective layer imparts a uniformly narrow molecular sieving property, providing a record-high solute-solute selectivity of 39.88 for different-sized solutes. Furthermore, a solute-solute selectivity of 11.04 was demonstrated using the real-world active pharmaceutical ingredient mixture of Acyclovir and Valacyclovir, key components for Herpes virus treatment, despite their molecular weight difference of less than 100 g mol-1. The highly interconnected membrane is expected to meet rigorous requirements for high-standard active pharmaceutical ingredient separation.

Enhancing the water permeability of composite NF membranes through the incorporation of organic ions in the aqueous phase

Composite nanofiltration (NF) membranes prepared using interfacial polymerization (IP) have gained significant attention in the field of wastewater treatment. In this study, sodium camphor sulfonate (CSA-Na) and tetraethylammonium chloride (TEAC) were employed as aqueous phase additives to regulate the diffusion of piperazine (PIP) molecules through electrostatic interactions. The dissociated CSA-Na and TEAC in the aqueous solution formed an organic structure at a certain concentration, restricting the interfacial transport behavior of PIP monomers. The results show that when the content of CSA-Na is 2% w/v, TEAC is 3.9% w/v, that is, the material dosage ratio is 1 : 3, and the NF membrane shows the best performance, with a water flux of 55.61 L m-2 h-1 (test pressure is 0.5 MPa), and MgSO4 rejection rate of more than 98%.

Tailor-made β-ketoenamine-linked covalent organic polymer nanofilms for precise molecular sieving

The membranes that accurately separate solutes with close molecular weights in harsh solvents are of crucial importance for the development of highly-precise organic solvent nanofiltration (OSN). The physicochemical structures of the membrane need to be rationally designed to achieve this goal, such as customized crosslinked networks, thickness, and pore size. Herein, we synthesize a type of covalent organic polymer (COP) nanofilms with tailor-made thickness and pore structure using a cyclic deposition strategy for precise molecular sieving. By elaborately designing monomer structures and controlling deposition cycle numbers, the COP nanofilms linked by robust β-ketoenamine blocks were endowed with sub-nanometer micropores and a linearly tunable thickness of 10-40 nm. The composite membranes integrating COP nanofilms exhibited adjustable solvent permeance. The membranes further demonstrated steep and finely-regulated rejection curves within the molecular weight range of 200 to 400 Da, where the difference value was as low as 40 Da. The efficient purification and concentration of the antibacterial drug and its intermediate was well achieved. Therefore, the exploited COP nanofilms markedly facilitate the application of microporous organic polymers for precise molecular separation in OSN.

Ultrathin Polyamide Nanofilms with Controlled Microporosity for Enhanced Solvent Permeation

Organic solvent nanofiltration (OSN) technology shows reduced energy consumption by almost 90% with great potential in achieving low-carbon separation applications. Polyamide nanofilms with controlled intrinsic and extrinsic structures (e.g., thickness and porosity) are important for achieving such a goal but are technically challenging. Herein, ultrathin polyamide nanofilms with controlled microporosity and morphology were synthesized via a molecular layer deposition method for OSN. The key is that the polyamide synthesis is controlled in a homogenous organic phase, rather than an interface, not only involving no monomer kinetic diffusion but also broadening the applicability of amine monomers. The particular nonplanar and rigid amine monomers were superbly used to increase microporosity and the nanofilm was linearly controlled at the nanometer scale to decrease thickness. The composite membrane with the polyamide nanofilms as separation layers displayed highly superior performance to current counterparts. The ethanol and methanol permeances were up to 5.5 and 14.6 L m^-2 h^-1 bar^-1, respectively, but the molecular weight cutoff was tailored as low as 300 Da. Such separation performance remained almost unchanged during a long-term operation. This work demonstrates a promising alternative that could synergistically control the physicochemical structures of ultrathin selective layers to fabricate high-performance OSN membranes for efficient separations.

The roles of artificial intelligence techniques for increasing the prediction performance of important parameters and their optimization in membrane processes: A systematic review

Membrane-based separation processes has been recently of significant global interest compared to other conventional separation approaches due to possessing undeniable advantages like superior performance, environmentally-benign nature and simplicity of application. Computational simulation of fluids has shown its undeniable role in modeling and simulation of numerous physical/chemical phenomena including chemical engineering, chemical reaction, aerodynamics, drug delivery and plasma physics. Definition of fluids can be occurred using the Navier-Stokes equations, but solving the equations remains an important challenge. In membrane-based separation processes, true perception of fluid's manner through disparate membrane modules is an important concern, which has been significantly limited applying numerical/computational procedures such s computational fluid dynamics (CFD). Despite this noteworthy advantage, the optimization of membrane processes using CFD is time-consuming and expensive. Therefore, combination of artificial intelligence (AI) and CFD can result in the creation of a promising hybrid model to accurately predict the model results and appropriately optimize membrane processes and phase separation. This paper aims to provide a comprehensive overview about the advantages of commonly-employed ML-based techniques in combination with the CFD to intelligently increase the optimization accuracy and predict mass transfer and the unfavorable events (i.e., fouling) in various membrane processes. To reach this objective, four principal strategies of AI including SL, USL, SSL and ANN were explained and their advantages/disadvantages were discussed. Then after, prevalent ML-based algorithm for membrane-based separation processes. Finally, the application potential of AI techniques in different membrane processes (i.e., fouling control, desalination and wastewater treatment) were presented.

Microporous Matrimid/PIM-1 Thin Film Composite Membranes with Narrow Pore Size Distribution used for Molecular Separation in Organic Solvents

Polymers of intrinsic microporosity (PIMs) are a class of microporous organic materials that contain interconnected pores of less than 2 nm in diameter. Such materials are of great potential used in membranes for molecular separation, such as drug fractionation in pharmaceutical industry. However, the PIMs membranes are often susceptible to low separation selectivity toward different molecules due to their wide pore size distribution. Herein, a linear polyimide, Matrimid, is incorporated with PIM-1 (a typical member of PIMs) by solution blending, and the blends are dip-coated onto a polyimide P84 support membrane to prepare thin-film composite (TFC) membranes to control pore size distribution while keep high microporosity. The component miscibility, pore characteristics, and molecular separation performances of the Matrimid/PIM-1 TFC membranes are investigated in detail. The Matrimid and PIM-1 are partially miscible due to their similar Hansen solubility parameters. The Matrimid endows the selective layers (coatings) with narrower pore size distribution due to more compact chain packing. The prepared Matrimid/PIM-1 TFC membranes show high selectivity for separation of riboflavin (80% of retention) and isatin (only 5% of retention). The developed membranes exhibit great potential for separating molecules with different molecular weights.

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.

Review on Liquid-Liquid Separation by Membrane Filtration

Liquid-liquid separation is crucial in the present circumstances. Substitution of the conventional types of separation like distillation and pervaporation is mandatory due to the high energy requirement of the two. The separation of organic mixtures has a huge potential in industries such as pharmaceutical, fine chemicals, fuels, textile, papers, and fertilizers. Membrane-affiliated separations are one of the prime techniques for liquid-liquid separations. Organic solvent nanofiltration, solvent-resistant nanofiltration, and ultrafiltration are a few methods through which organic liquid-liquid separation can be attained. Implementation of such a technology in chemical industries reduces the time consumption and is cost efficient. Even though a lot of research has been done, attention is needed in the field of organic-liquid separation aided by membranes. In this review, various membranes used for organic mixture separations such as polar-nonpolar, polar-polar, and nonpolar-nonpolar are discussed with a focus on membrane materials, additives, separation theory, separation type, experimental setup, fouling mitigation, surface modification, and major challenges. The review also offers insights and probable solutions for existing problems and also discusses the scope of research to be undertaken in the future.

Microporous polymer adsorptive membranes with high processing capacity for molecular separation

Trade-off between permeability and nanometer-level selectivity is an inherent shortcoming of membrane-based separation of molecules, while most highly porous materials with high adsorption capacity lack solution processability and stability for achieving adsorption-based molecule separation. We hereby report a hydrophilic amidoxime modified polymer of intrinsic microporosity (AOPIM-1) as a membrane adsorption material to selectively adsorb and separate small organic molecules from water with ultrahigh processing capacity. The membrane adsorption capacity for Rhodamine B reaches 26.114 g m⁻², 10–1000 times higher than previously reported adsorptive membranes. Meanwhile, the membrane achieves >99.9% removal of various nano-sized organic molecules with water flux 2 orders of magnitude higher than typical pressure-driven membranes of similar rejections. This work confirms the feasibility of microporous polymers for membrane adsorption with high capacity, and provides the possibility of adsorptive membranes for molecular separation.

Trade-off between permeability and nanometer-level selectivity is an inherent shortcoming of membrane-based separation of molecules. Here, the authors report a membrane adsorption material based on hydrophilic amidoxime modified polymer of intrinsic microporosity to selectively adsorb and separate small organic molecules from water with ultrahigh processing capacity

Liquid-Phase Peptide Synthesis (LPPS): A Third Wave for the Preparation of Peptides

Since the last century, peptides have gained wide acceptance as drugs, with almost 100 already in the market and a large number in the pipeline. In this context, peptide synthesis has grown massively as a stringent field for pharmaceuticals around the globe. Three methodologies, namely, classical solution peptide synthesis (CSPS), solid-phase peptide synthesis (SPPS), and liquid-phase peptide synthesis (LPPS), have made significant contributions to the field. This review provides a comprehensive and integrated vision of LPPS as the third wave for peptide synthesis. LPPS combines the advantages of CSPS and SPPS, where peptide elongation is carried out in solution and the growing peptide chain is supported on a soluble tag, which confers characteristic properties. LPPS protocols allow the large-scale production of peptides and reduce the use of excess reagents and solvents, thus meeting the principles of green chemistry. In this review, tags associated with LPPS are broadly discussed under the following headings: polydisperse polyethylene glycol (PEG), membrane-enhanced peptide synthesis (MEPS), fluorous technology, ionic liquids (ILs), PolyCarbon, hydrophobic polymers, and group-assisted purification (GAP). It also highlights the signature accomplishments of LPPS tags and the limitations of the same.

A Superstructure Based Optimization Approach for Regeneration Reuse of Water Network: Optimal Design of a Detailed Nanofiltration Regenerator Network

Increasing freshwater costs and environmental concerns have necessitated the adoption of strategies for reducing freshwater consumption and effluent water discharge in chemical processes. Regeneration technologies increase opportunities for water reuse and recycle, and nanofiltration has emerged as a competitive wastewater regeneration technology. However, the optimal design of nanofiltration networks has not been extensively investigated. This study presents a framework for the optimal design and synthesis of multicontaminant nanofiltration membrane regenerator networks for application in water minimization problems. Mathematical optimization technique is developed based on a superstructure containing all system components and streams, incorporating nanofiltration units, pumps, and energy recovery devices. A linear approach and the modified Spiegler-Kedem model are explored in modelling the nanofiltration, and the steric-hindrance pore model is used to characterize the membrane. The objective of the optimization is to simultaneously minimize the water consumption and the total annual cost of the network. Furthermore, the optimal size, configuration, membrane properties and operating conditions of the equipment are determined. The applicability of the model is illustrated using a case study of an integrated pulp and paper plant. It was found that detailed models with customized modules are more useful when compared to the linear “black box” approach and approaches using fixed module specifications. The customized, detailed design of the regenerator network increased freshwater savings by 24% when compared to a black-box model, 31% when compared to a detailed model with fixed module specifications and 41% when compared to a reuse-recycle system with no regeneration. Similarly, cost savings of 38, 35 and 36% respectively were obtained. A trade-off was noted between the energy costs and the other components of the objective function since more energy was required to facilitate the reduction of water consumption and capital requirements.

Highly Efficient One-Step Protein Immobilization on Polymer Membranes Supported by Response Surface Methodology

Immobilization of proteins by covalent coupling to polymeric materials offers numerous excellent advantages for various applications, however, it is usually limited by coupling strategies, which are often too expensive or complex. In this study, an electron-beam-based process for covalent coupling of the model protein bovine serum albumin (BSA) onto polyvinylidene fluoride (PVDF) flat sheet membranes was investigated. Immobilization can be performed in a clean, fast, and continuous mode of operation without any additional chemicals involved. Using the Design of Experiments (DoE) approach, nine process factors were investigated for their influence on graft yield and homogeneity. The parameters could be reduced to only four highly significant factors: BSA concentration, impregnation method, impregnation time, and electron beam irradiation dose. Subsequently, optimization of the process was performed using the Response Surface Methodology (RSM). A one-step method was developed, resulting in a high BSA grafting yield of 955 mg m−2 and a relative standard deviation of 3.6%. High efficiency was demonstrated by reusing the impregnation solution five times consecutively without reducing the final BSA grafting yield. Comprehensive characterization was conducted by X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and measurements of zeta potential, contact angle and surface free energy, as well as filtration performance. In addition, mechanical properties and morphology were examined using mercury porosimetry, tensile testing, and scanning electron microscopy (SEM).

Thermally Induced Silane Dehydrocoupling: Hydrophobic and Oleophilic Filter Paper Preparation for Water Separation and Removal from Organic Solvents

Organic solvents with high purity are essential in various fields such as optical, electronic, pharmaceutical, and chemical areas to prevent low-quality products or undesired side-products. Constructing methods to remove impurities such as water residue in organic solvents has been a significant challenge. Within this article, we report for the first time a new method for the preparation of hydrophobic and oleophilic filter paper (named OCFP), based on thermally induced silane dehydrocoupling between cellulose-based filter paper and octadecylsilane. We comprehensively characterized OCFP using various characterization techniques (FTIR, XPS, XRD, and EDS). OCFP showed super-hydrophobic and oleophilic properties as well as remarkable water separation and removal efficiency (>93%) in various organic solvents with sustained reusability. In addition, the analytical results both before and after filtration of an NMR solvent using OCFP indicated that OCFP has an excellent solvent drying efficiency. This work presents a new strategy for the development of super-hydrophobic cellulose-based filter paper, which has great potential for solvent drying and water separation.

Recovery of Valuable Solutes from Organic Solvent/Water Mixtures via Direct Contact Membrane Distillation (DCMD) as a Non-Heated Process

Recently, the demand for the recovery of valuable solutes from organic solvents/water mixtures has increased in various fields. Furthermore, due to the abundance of heat-sensitive valuable solutes, the demand for non-heated concentration technologies has increased. In this study, the direct contact membrane distillation (DCMD) using hydrophobic polyvinylidene difluoride (PVDF) hollow fiber membranes was investigated to confirm the possibility of recovering valuable solutes from organic solvents/water mixtures as a non-heated process. The DCMD with 1000 ppm NaCl aqueous solution achieved 0.8 kg/m²·h of vapor flux and >99.9% of NaCl retention, even at feed and coolant temperatures of 25 and 10 °C, respectively. Furthermore, when DCMD was conducted under various conditions, including feed temperatures of 25, 35 and 45 °C, and organic solvent concentration of 15, 30 and 50 wt%, using ethanol/water and acetonitrile/water mixtures containing 1000 ppm NaCl. A surfactant was also used as a valuable solute, in addition to NaCl. As a result, it was found that the total vapor flux increased with increasing temperature and concentration of organic solvents, as the partial vapor pressure of the organic solvents increased. Additionally, no solute leaked under any condition, even when the surfactant was used as a valuable solute.