Siavash Darvishmanesh

Mechanisms of solute rejection in solvent resistant nanofiltration: the effect of solvent on solute rejection.

The separation performance of solvent resistant nanofiltration (SRNF) membranes was studied in a systematic way to elucidate the complex mechanisms involved in rejection of solutes. Rejection of three dyes (Sudan II, Sudan Black, Sudan 408) from common organic solvents (methanol, ethanol, acetone, methyl ethyl ketone, toluene and n-hexane) through a polyimide based SRNF membrane, STARMEM™122, was studied. It was found that the rejection of the STARMEM™122 membrane was lower than that indicated by the manufacturer. The experimental observations for Sudan II were not promising for the rejection study as they were lower than expected. Sudan Black and Sudan 408, which are larger solutes than Sudan II, provided more interesting insights. The effects of the solvent on the membrane and solute were studied separately. A higher permeation rate of ketones and alcohols was observed, while permeabilities of non-polar solvents were low which shows that this membrane shows higher affinity toward semi-polar solvents (alcohols, ketones). The effect of the solvent on the solutes rejection, based on the results for Sudan Black and Sudan 408, was studied for solvents in the same chemical groups, since the membrane showed a similar separation performance for solvents with similar functional groups (e.g. alcohols). The effect of solvent on solute molecular size was investigated by using simulation with Molecular Dynamics. It was shown that the effective size of a molecule is dependent on the solvent due to solvation and hydration of the solute by the solvent. The size of the solute in the solvent belonging to a similar family was studied separately. It was clear that the rejection was influenced by molecular size of the solute in the same group of solvents. A surprising negative rejection of solutes was achieved for n-hexane. Although solutes in n-hexane have higher volume compared to those in other solvents, the affinity between the solute and membrane increases the solute permeation in the presence of n-hexane. The affinity of solvent and solute for the membrane was investigated by means of solubility parameters for solvents within the same chemical family. In two different systems including two different solvents and one solute (Sudan Black and methanol, Sudan Black and ethanol), lower rejection (in this case for Sudan Black and methanol) was achieved when the solutes have higher affinity toward the solvent. Finally, it was found that in a system comprising the solvent, solute and membrane, interactions between solvent and membrane have much more effect on separation than solvent-solute interactions.

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.

Physicochemical characterization of transport in nanosized membrane structures.

The understanding of polymer-solvent interactions is highly important for the development of tailored membrane manufacturing procedures and for the prediction of membrane performance from transport mechanisms. This study examines the permeation performance of organic solvents through state-of-the-art polyimide membranes (STARMEM, Membrane Extraction Technology Ltd.). Solvents are systematically selected to allow investigation of the effects of key physicochemical transport parameters by keeping constant all other parameters thought to be relevant. The effect of the solubility parameter, polarity (dielectric constant), surface tension, and viscosity are studied in detail. Dead-end permeation experiments are carried out at 20 bar with STARMEM 122 and STARMEM 240 membranes. Results for the selected solvents show higher permeation rates for ketones over alcohols and aromatics as well as for acids. It is suggested that the viscosity and polarity have a greater influence than the other parameters. The effect of solvent molar volume is also investigated. Transport of solvents with high molar volume, independent of their polarity and compatibility with the membrane material, is slower in all cases than for solvents with smaller molar volume. The solubility parameter does not show any significant effect on transport phenomena.

Physicochemical characterization of solute retention in solvent resistant nanofiltration: the effect of solute size, polarity, dipole moment, and solubility parameter.

Growing interest in nanofiltration for solvent purification requires a fundamental understanding of the physicochemical mechanisms of solute retention in organic solvent nanofiltration. In this study, the retention of a similar series of azo dyes with approximately similar molar mass (around 350 Da) by four nanofiltration membranes was studied. The membranes used are commercially available polymeric nanofiltration membranes with molecular weight cutoff between 150 and 300 Da (DuraMem150, StarMem122, NF270 and Desal-Dk). In order to correlate the retention with the size of the molecules, which is assumed to be one of the main factors that determines the retention, use was made of different parameters for the molecular size: molar mass, the Stokes diameter, the equivalent molar diameter, and the cavity surface in methanol and ethanol. All parameters were calculated by using molecular dynamics simulations. For each size parameter, the correlation with retention in nanofiltration experiments was calculated. For the StarMem122 membrane, zero retentions were observed due to the swelling of the membrane and pore size enlargement in methanol and ethanol. For the three other membranes, a fairly good correlation of the retention with the size could only be observed if the size difference between compounds is sufficiently large. Two other factors were studied by using molecular dynamics, i.e., the polarity of the molecule and the electron density of the molecule. The importance of these factors depends on the structure of the molecule as well as the functional groups of the polymer. A very good correlation has been observed for retention of dyes versus their dipole moment. Finally, the effect of solubility parameters of dyes on their retention did not show any significant effect.

Solubility and absorption rate enhancement of CO2 in K2CO3

ABSTRACT The influence of addition of 2-(1-piperazinyl)-ethylamine (as a promoter) on the solubility and absorption rate of carbon dioxide (CO2) in aqueous potassium carbonate solution (as a main solvent) was investigated experimentally, using a vapor liquid equilibrium (VLE) equipment in temperatures from 303.15 to 323.15 K and CO2 initial partial pressures between 25 and 75 kPa. The experimental data showed that the addition of 2-(1-piperazinyl)-ethylamine to potassium carbonate solution results in a significant enhancement in the solubility and absorption rate of CO2. The response surface methodology was applied to explore the relationship between independent parameters on the CO2 loading capacity of blended solution.

Mass Transport through Nanostructured Membranes: Towards a Predictive Tool

This study proposes a new mechanism to understand the transport of solvents through nanostructured membranes from a fundamental point of view. The findings are used to develop readily applicable mathematical models to predict solvent fluxes and solute rejections through solvent resistant membranes used for nanofiltration. The new model was developed based on a pore-flow type of transport. New parameters found to be of fundamental importance were introduced to the equation, i.e., the affinity of the solute and the solvent for the membrane expressed as the hydrogen-bonding contribution of the solubility parameter for the solute, solvent and membrane. A graphical map was constructed to predict the solute rejection based on the hydrogen-bonding contribution of the solubility parameter. The model was evaluated with performance data from the literature. Both the solvent flux and the solute rejection calculated with the new approach were similar to values reported in the literature.