Separation Of Organic Mixtures Research Articles

Microwave-assisted design of nanoporous graphene membrane for ultrafast and switchable organic solvent nanofiltration

Layered two-dimensional materials can potentially be utilized for organic solvent nanofiltration (OSN) membrane fabrication owing to their precise molecular sieving by the interlayer structure and excellent stability in harsh conditions. Nevertheless, the extensive tortuosity of nanochannels and bulky solvent molecules impede rapid permeability. Herein, nanoporous graphene (NG) with a high density of sp2 carbon domain was synthesized via sequential thermal pore activation of graphene oxide (GO) and microwave-assisted reduction. Due to the smooth sp2 carbon domain surfaces and dense nanopores, the microwave-treated nanoporous graphene membrane exhibited ultrafast organic solvent permeance (e.g., IPA: 2278 LMH/bar) with excellent stability under practical cross-flow conditions. Furthermore, the membrane molecular weight cut-off (MWCO) is switchable from 500 Da size of molecule to sub-nanometer-size molecules depending on the solvent type, and this switching occurs spontaneously with solvent change. These properties indicate feasibility of multiple (both binary and ternary) organic mixture separation using a single membrane. The nanochannel structure effect on solvent transport is also investigated using computation calculations.

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.

Liquid-Liquid Equilibrium Data for the System N-Octane + Toluene + DES at 293.15 and 313.15 K and Atmospheric Pressure

Deep eutectic solvents (DESs) are promising alternative for ionic liquids due to their low cost and sustainability. Considerable attention is paid on the ability of DES to replace ionic liquids in the separation of organic liquid mixtures via extraction. In this sense, it is important to determine the physicochemical parameters of liquid-liquid equilibrium for the industrially significant mixtures and deep eutectic solvents. In the present work a mixture of n-octane, toluene and DES based on choline chloride and malonic acid was studied at 293.15, 313.15 K and atmospheric pressure. Tie-lines were obtained and ability of deep eutectic solvents to separate aliphatic-aromatic mixture was analyzed. Experimental liquid-liquid equilibrium data were fit with the NRTL model, and interaction parameters of components were obtained and discussed.

A Morphological Study of Poly (Vinylidene Fluoride) Pvdf Membranes: In Perspective of Membrane Pervaporation Process

Membrane separation plays an important role in chemical industry (Prabhat et al. 2011). Pervaporation is one of the most promising membrane separation processes which is used in a wide range of applications such as separation of organic mixtures and dehydration of solvents. This study investigated the effect of polymer concentration on the morphology of pervaporation membrane, where polyvinylidene fluoride (PVDF) was chosen as the base polymeric material while phase inversion method was employed as a technique to prepare an asymmetric PVDF membrane. The polymer concentration in dope solution was varied from 16 to 20wt% and the prepared membranes were characterized in terms of its structure, porosity, contact angle, and pore size. Five PVDF membrane samples were prepared (without any post-treatment) with polymer concentration of 16, 17, 18, 19, and 20wt% respectively. Depending on permeating component, two main areas of pervaporation processes can be identified: hydrophobic and hydrophilic and consequently two types of membranes could be observed: hydrophobic and hydrophilic membranes. From the results, it was found that the increase in polymer concentration has produced membranes with low pore size and porosity and as a result, high contact angle (low hydrophilicity).The highest contact angle of 83º was found for membrane with highest polymer concentration of 20wt% with the lowest pore size and porosity of (0.4156µm and 65%) respectively. The lowest contact angle of 76º was found for membrane with the lowest polymer concentration of 16wt% with the highest pore size and porosity (0.8671µm and78%) respectively.

Characterization of asymmetric membranes of cellulose acetate from biomass: Newspaper and mango seed

Asymmetric membranes may be used in a broad range of applications such as reverse osmosis, hemodialysis and separation of organic mixtures. In this paper, asymmetric membranes were produced using cellulose acetate (CA) from biomass: newspaper and mango seed. The degree of substitution of CA was 2.65 ± 0.07. Different formulations were used to prepare the CA membranes: CA/dichloromethane/water with and without magnesium perchlorate. The asymmetry of the membranes was characterized by scanning electron microscopy (SEM). Membranes produced with magnesium perchlorate presented higher water vapor flux than those produced without this salt. This difference is due to pore formation in the membrane skin when using magnesium perchlorate. Membrane substructure showed to be a determining factor in ion diffusion experiments. The coefficient of ion diffusion for the membrane of cellulose acetate from mango seed was 1.82 × 10 −8 cm 2 s −1 while for the membrane of cellulose acetate from newspaper was 7.43 × 10 −8 cm 2 s −1 which similar to the value reported in the literature for commercial CA (8.46 × 10 −8 cm 2 s −1).

Separation of organic mixtures by pervaporation using crosslinked and filled rubber membranes

Natural rubber (NR) and poly(styrene-co-butadiene) rubber (SBR) were crosslinked chemically with sulfur and accelerator by efficient vulcanization. These were then compounded for physical crosslinking with high abrasion carbon black filler (grade N330) with three different doses, i.e. 5, 10 and 20 phr to obtain three filled membranes from each of these two rubbers (NR-5, NR-10 and NR-20 and SBR-5, SBR-10 and SBR-20). These six filled rubber membranes were used for pervaporative separation of toluene–methanol mixtures up to 11 wt% of toluene in feed. It has been found that with increase in filler doses from membrane-5 to membrane-20, the selectivities and mechanical properties of the membranes increase. All of these membranes showed reasonably good range of flux (20.814 g/m 2 h for SBR-5 to 10.26 g/m 2 h for NR-20) and separation factor (286.4 for NR-5 to 183.7 for SBR-5) for 0.55 wt% of toluene in feed. Among these membranes NR-20 and SBR-20 with highest crosslink density showed maximum separation factor for toluene along with good flux. It has also been found that for comparable crosslink density NR membranes showed better separation factor than SBR membranes.

Separation of organic mixtures by pervaporation using crosslinked rubber membranes

Natural rubber (NR) and poly(styrene-co-butadiene) rubber (SBR) has been crosslinked with sulfur and accelerator with three different doses of varied accelerator to sulfur ratios to obtain three crosslinked membranes from each of these two rubbers (NR-1, NR-2 and NR-3 and SBR-1, SBR-2 and SBR-3). These six rubber membranes were used for pervaporative separation of toluene–methanol mixture up to 10 wt% of toluene in feed. It has been found that with increase in accelerator to sulfur ratio from membrane-3 to membrane-1, the vulcanization system shifts from conventional to efficient system resulting in higher degree of crosslink density and permeation selectivity. All of these membranes showed reasonably good range of flux (45.26 gm/m 2 h for NR-3 to 12.0 gm/m 2 h for SBR-1) and separation factor (162 for SBR-1 to 35.12 for NR-3) for 0.55 wt% of toluene in feed. Among these membranes NR-1 and SBR-1 with highest crosslink density showed maximum separation factor for toluene along with good flux. It has also been found that for comparable crosslink density SBR membranes showed better separation factor than NR membranes.

Novel high performance photo-graft composite membranes for separation of organic liquids by pervaporation

A new application of the ‘pore filling’ concept yielded high-performance composite membranes for the selective pervaporation (PV) separation of organic mixtures. Asymmetric polyacrylonitrile (PAN) membranes (average pore sizes of 7 or 12 nm) were used as matrix for polymeric PV separation phases which were in situ prepared by heterogeneous photoinitiated graft copolymerization. By this means, defect-free and stable layers were synthesized from various moderately hydrophilic (meth)acrylates, e.g. poly(ethylene glycol) (meth)acrylates. The impact of (meth)acrylate side-group functionality (hydrophilicity, size) and preparation parameters (monomer concentration, UV irradiation time) was analyzed using PV methanol removal from less polar hydrocarbons (cyclohexane or MTBE) as example. High selectivities ( α methanol/cyclohexane ⩽ 2000) and extraordinarily high permeate fluxes ( J ⩽ 8 kg/m 2 h) were achieved. Major reasons for the excellent performance were the small effective PV barrier thickness (< 1 μm; determined by the thickness of the selective layer of the matrix membrane) and the fixation of the graft polymer (covalent anchoring, suppressed swelling) in a matrix (PAN) which is not swollen under PV conditions. Due to the functionalization principle, a great variety of thin-layer composite membranes can be prepared, ‘tuning’ the PV selectivity by functionality of the graft polymer, thus providing possibilities to efficiently solve various PV separation problems.

Newly developed ceramic membranes for dehydration and separation of organic mixtures by pervaporation

Polymeric pervaporation membranes sometimes show great variety in performance when they are alternately used for different solvent mixtures. In addition, membrane stability in time is a problem in case of some solvents. Therefore, newly developed ceramic silica membranes with a “dense” top layer were tested for pervaporation. In dehydration of the lower alcohols methanol, ethanol and 2-propanol selectivities of 400, 200 and 600, respectively, were found at water concentrations of about 2 w/w% in the feed. Fluxes were 50, 150 and 160 g/m 2/h, respectively. At higher water concentrations in the feed selectivities decreased and fluxes increased. Especially methanol selectivity decreased drastically at water concentrations above 5 w/w%. Fluxes increased significantly with water concentrations above 5 w/w% in the 2-propanol/water case. The overall performances were comparable with those found with commercially available polymeric membranes. The performance of the ceramic membrane did not decrease noticeably during an experimental period of three months, although a wide range of alcohols were tested with changing water concentrations. Also periodic changes to the system methanol/MTBE did not decrease the performance for dehydration. Methanol could be recovered from MTBE with selectivities of about 19 and fluxes of 41 g/m 2/h with 9 w/w% methanol in the feed. Activated diffusive transport through micropores is the suggested separation mechanism for this membrane.

Inclusion Compounds ? possibility of their combination and use in different branches of chemistry

Hofmann-type and related compounds, a natural zeolitic material of the clinoptilolite type, and cyclodextrins have been studied. Different products, useful in the separation of organic mixtures, used with fertilizers and insecticides in agrochemistry, perfumes, and in the detoxication of raw materials, have been prepared by combinations of the inclusion compounds studied. In the Hofmann-type compounds and cyclodextrins the original guest is substituted; in the zeolite the original sorbate, as well as some part of the zeolitic host is substituted. The physical mixtures of the starting materials differed from the products in their thermal, spectral and diffractographic characteristics. Field test results and other supporting evidence are added.

Predictability of transport equations for pervaporation on the basis of pore-flow mechanism

In this paper a transport model for pervaporation based on the pore-flow mechanism was tested by examining whether it could describe main features observed in pervaporation experiments. The pervaporation systems used for the above test include mixtures of ethanol/n-heptane, methanol/ethanol, 2-propanol/water and cyclohexane/benzene. Membrane polymeric materials such as cellulose, cellulose diacetate-triacetate blend, polyamide, polyethylene and poly(γ-methyl- l-glutamate) are also included in this study. Membranes are either asymmetric or homogeneous but not of composite nature. Separation of organic mixtures by vapor permeation was also discussed in relation to pervaporation.

Separation of organic mixtures by sequential gas‐liquid chromatography

AbstractA new sequential continuous chromatographic refiner (SCCR‐2) for high temperature production scale G.L.C. (gas‐liquid chromatographic) separations is described. In this equipment the counter‐current movement between the gas and liquid phase is simulated by sequencing a system of inlet and outlet port functions around twelve static 2.54 cm internal diameter and 61 cm long stainless steel columns. The versatility of the equipment has been demonstrated by the separation of equivolume mixtures of the halocarbons arklone P/genklene P, methylchloroacetate/ethyl lactate and ethyl caprate/ethyl laurate at temperatures of 60°, 105° and 160°C respectively. Throughputs between 21–75 cm3h−1 have been explored with product purities in excess of 99.8% achieved under certain process conditions.