The potential of pervaporation for separation of acetic acid and water mixtures using polyphenylsulfone membranes

Conventional pervaporation (PV) membranes usually have limited resistance to acetic acid (HAc), particularly in high pressure and temperature conditions, resulting in a cumbersome water-acetic acid separation. When acetic acid is to be recycled in process conditions in a hybrid pervaporation approach, the PV membrane may experience these conditions of high temperatures and pressures. This study explores the potential of dehydrating acetic acid using pervaporation with novel polyphenylsulfone (PPSU) membranes. These membranes were tested for PV dehydration of mixtures of acetic acid-water with 80 and 90. wt.% acetic acid in the temperature range between 30 and 80 °C. In addition to that, an experimental study of membrane stability was performed at high concentration of HAc and high temperatures. It was found that a higher polymer concentration does not necessary yield a better separation factor: PPSU-based membranes with 27.5wt.% of the polymer (PPSU-27.5) were similar to 30wt.% (PPSU-30) in terms of overall performance, considering both flux and separation factor. Although the total flux of PPSU-27.5 (∼0.12-0.83kg/m 2h) is lower than PPSU-25 (∼0.24-1.48kg/m 2h) the average separation factor can be higher than for the PPSU-30 membrane. For example, in 90wt.% HAc, the separation factor is 8.4 for PPSU-27.5 and 5.7 for PPSU-30. The swelling degree (DS) was found to decrease with feed temperature, while an increase of the selectivity and flux was observed. The activation energy of permeability (E p) shows that PPSU membranes have negative E p values. This indicates that the membrane partial permeabilities decrease with increasing temperature. With the enrichment of acetic acid on the feed side of the membrane, the degree of swelling, flux and separation factor all increase. Regarding on the membrane stability tests, the PPSU membranes showed promising results at tested conditions

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®, 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 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-2h and 70%, respectively. For the same conditions, SOLSEP NF030306 exhibited a flux of 4.8 L m-2h with 78% rejection, which shows the potential application of nanofiltration membranes in the oil industry

Considerations on the use of nanofiltration for solvent purification in the oil industry

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Performance of solvent resistant nanofiltration membranes for purification of residual solvent in the pharmaceutical industry: Experiments and simulation

This study explores the possibility of developing a sustainable extraction method for use in pharmaceutical production, based on purification with membrane processes. Two types of commercial polymeric organic solvent nanofiltration membranes (StarMem122 and DuraMem150) were selected and tested for their abilities to recover the solvent from a pharmaceutical/solvent mixture (5, 10, 50 mg L -1). Five different pharmaceutical compounds have been selected in this work, namely: Imatinib mesylate, Riluzole, Donepezil HCl, Atenolol and Alprazolam. Solvents tested in the experiment were those used in the manufacturing process, i.e., methanol, ethanol, iso-propanol and ethyl acetate. An acceptable performance (rejection over 90%) was obtained for DuraMem150 in all tested pharmaceutical and solvent mixtures except for iso-propanol. No flux was observed for iso-propanol over the DuraMem150 due to its high viscosity. No separation was observed by using StarMem122 for Imatinib mesylate in iso-propanol (over 80%). Commercially available solvent resistant nanofiltration (SRNF) membranes (StarMem™122 and DuraMem™150) show promising performances as alternative tools to traditional separation units such as distillation columns for the recovery of solvents. Furthermore, to evaluate the potential of SRNF as a substitution for traditional solvent recovery, a model was developed for nanofiltration membrane units and implemented in a common process simulation software (Aspen Plus). These models were based on the pore flow mechanism and describe a single membrane module. A membrane module is not available in Aspen Plus and in its Model Library. In this study, this shortcoming was overcome through implementation of the NF membrane module within the Aspen Custom Modeler link to Aspen Plus. The model has been tested for two model solutes (Disperse orange 3 and Disperse red 19) since the pharmaceutical physical properties are not included in the Aspen Properties Database. The results presented here confirm the value of the Aspen Custom Modeler as a simulation tool for the use of NF as a novel and sustainable tool in pharmaceutical manufacturing

Polyvinylidene fluoride dense membrane for the pervaporation of methyl acetate-methanol mixtures

In the context of pervaporative separation of methyl acetate-methanol binary mixtures, polyvinylidene fluoride (PVDF) pervaporation membranes were prepared in order to selectively separate methyl acetate by pervaporation.The PVDF membranes were compared to chlorinated polypropylene and polyvinyl alcohol dense membranes (developed for the same application) by pervaporation of a quaternary equimolar methyl acetate-methanol-. n-butyl acetate-. n-butanol reference feed. PVDF membranes resulted in a permeate richer in methyl acetate than the corresponding quaternary feed, and in a selectivity methyl acetate/methanol higher than one for the same mixture. Chlorinated polypropylene and polyvinyl alcohol membranes gave a permeate richer of both methanol and methyl acetate than the corresponding feed and were thus not applicable during the extensive study on the binary methyl acetate-methanol mixture.These preliminary results performances were also assessed with the Hansen solubility parameters theory, which resulted inadequate for predicting the behavior of the two glassy-state and the rubbery-state (PVDF) polymeric membranes during pervaporation.Thus, pervaporation of methyl acetate-methanol binary mixtures by PVDF membranes was studied experimentally using feed concentrations in the range 11-78mol% methyl acetate, and temperatures in the range 30-44°C, resulting in separation factors methyl acetate/methanol above 1 (up to 2.1 at 11mol% methyl acetate in the feed), in the whole feed concentration range. High total fluxes up to 35kgm-2h-1 (at 78mol% methyl acetate and 44°C) were also observed.Interestingly, when removing the contribution of the driving force to the separation, for concentrations below 60. mol% methyl acetate in the feed the membrane was selective for methanol, while for higher concentrations it was selective for methyl acetate (values up to 1.44).This work shows that methyl acetate selective membranes (starting from the improvement of PVDF membranes) are realistic and can be employed in order to concentrate low content methyl acetate-methanol industrial waste streams

Novel polyphenylsulfone membrane for potential use in solvent nanofiltration

In this work, the preparation of nanofiltration flat sheet membranes based on polyphenylsulfone (PPSU) was investigated. A synthesis method based on phase inversion with three different compositions of PPSU (17wt.%, 21wt.% and 25wt.%) in dimethylacetamide (DMA), N-methyl-2-pyrrolidone (NMP) and a mixture of dimethylformamide (DMF) and NMP was employed. Scanning electron microscopy (SEM) was used to investigate the morphological characteristics and the structure of the membranes, which were found to have a typical asymmetric structure with a dense skin top layer and a porous substructure. The pore size was estimated by measuring the permeation rate of N2 when different pressures are applied, ranging from 15nm to 40nm, depending on the manufacturing method. An increasing amount of macro-voids was observed in the membrane substructure when the polymer concentration is decreased. The performance of the prepared membranes has been tested by the measure of methanol permeability and the rejection of a dissolved dye (Rose Bengal). The methanol permeability decreases with increasing polymer concentration while the rejection of Rose Bengal (RB) increases. In addition, the impact of ethyl acetate, n-hexane, toluene, diethyl ether, iso-propanol and acetone on the membranes was investigated by measuring the flux of methanol and rejection of RB before and after solvent exposure. The membranes were visually stable in most of the solvents except acetone and toluene. The performance of the membranes changed dramatically for ethyl acetate and diethyl ether while iso-propanol had a minor effect and complete stability was observed with n-hexane

Comparison between exergy and energy analysis for biodiesel production

This study investigates the exergy concept for use in chemical engineering applications, and compares the energy and exergy methodology for the production process of biodiesel. A process for biodiesel production was suggested and simulated in view of the energy and exergy analysis. A method was developed to implement the exergy concept in Aspen Plus 7.3. A comparison between the energy and the exergy approach reveals that the concepts have similarities but also some differences. In the exergy study, the reaction section has the largest losses whereas in the energy study separation steps are the most important. An optimization, using both concepts, was carried out using the same parameters. The optimized results were different depending on the objective function. It was concluded that exergy analysis is crucial during the design or redesign step in order to investigate thermodynamic efficiencies in each part of the process

Purification of biodiesel using a membrane contactor: Liquid-liquid extraction

The use of biodiesel in engines requires a high purity (99.65 wt.%), which is to be obtained by the removal of a large water amount and a large number of distillation steps. Membrane extraction was studied as a more efficient and environmentally friendly process to purify a synthetic biodiesel stream composed of methyl esters from rapeseed oil, methanol and glycerol. The potential of several flat sheet membranes to remove impurities was evaluated. All hydrophobic membranes showed breakthrough pressure values higher than 0.5 bar. A PTFE membrane from Sterlitech was selected due to its high chemical resistance against biodiesel. The effect of the concentration of solutes and of the flow rate on the flux was investigated. The overall mass transfer coefficient was calculated and compared with experimentally observed values, which are in the range of 3.5-7 E-03 (cm/min) for methanol. Thus, this membrane technique allows purifying biodiesel, suggesting its potential in industrial applications