Electrostatic self-assembly is a simple, yet versatile and environmentally friendly technique. This technique has been widely used in different areas and recently it has also been used to make nano-structured separating layers for composite polyelectrolyte pervaporation membranes. Non-porous substrates are usually employed for electrostatic self-assembly depositions, but porous substrates have to be used for membrane applications because the composite membranes fabricated with non-porous substrates will have low permeation fluxes. When porous substrates were used to make composite membranes for pervaporation, it was reported that 60 double-layers were needed to get a membrane with suitable separation performance. The deposition of each double-layer needed about one hour, and the fabrication of reported self-assembled membranes with porous substrates was time-consuming and, from an industrial point of view, not practical. <br /><br /> The aim of this work was to make self-assembled composite membranes in a more practical way. The methodology used here is to find appropriate materials and suitable preparation conditions to make self-assembled composite membranes that have less than 10 self-assembled double layers but still have good performance for the dehydration of isopropyl alcohol (IPA)/ water mixtures by pervaporation. <br /><br /> A hydrolyzed polyacrylonitrile (PAN) ultrafiltration membrane is a permanently charged porous material. In this work, this porous material was, for the first time, used as a substrate for the fabrication of a composite self-assembled membrane. It was found that the hydrolyzed porous PAN membranes were good substrates for making self-assembled membranes for pervaporation. <br /><br /> In order to reduce the number of the depositions required for making composite membranes with suitable separation performance, a new deposition technique, concentration-changing deposition technique, has been developed. To obtain more extended conformations of polyelectrolytes to prevent them from going into the pores on a porous substrate, dilute deposition solutions were used for the first several depositions. After these first depositions, the pore size of the porous substrate had been reduced and more concentrated solutions (but still dilute solutions) could be used for the subsequent depositions. By using more concentrated deposition solutions, the number of the polyelectrolyte coils adsorbed by the charged substrate was increased and the thickness of each deposited layer was increased. In this way, the total number of deposition layers needed for a good membrane would be decreased. It has been proved in this work that the number of deposition layers in a composite membrane can be reduced by using the concentration-changing deposition technique. <br /><br /> By selecting appropriate materials and by selecting proper preparation conditions, composite polyelectrolyte membranes with less than 10 self-assembled double layers have been successfully fabricated. The obtained membranes had good performance for the dehydration of IPA/water mixtures by pervaporation. The lowest number of double layers in a composite membrane was 2 and this composite membrane had both a high flux and a high selectivity. It was also found that using polyelectrolytes with high molecular weights and a porous substrate with fine pores were the prerequisites for making composite polyelectrolyte membranes with less than 10 self-assembled double layers, while using a polyelectrolyte pair with high charge densities was the prerequisite for making composite membranes with a high selectivity. The successful fabrication of polyelectrolyte membranes with less than 10 double layers makes self-assembled membranes more practical because self-assembled composite membranes can be easily fabricated. <br /><br /> The data reproducibility and the stability of self-assembled composite membranes with less than 10 double layers have been discussed in this work. Random defects in the self-assembled separating layer and low repeatability of thickness in the first several deposition layers are believed to be the major reasons for the relatively low data reproducibility of single composite membranes, while the conformation change of adsorbed polyelectrolytes is one of the reasons for the flux reduction of composite membranes with less than 10 self-assembled double layers. Though the flux reproducibility of single membranes is barely acceptable (relative error about 25%), the average fluxes of several membranes made under the same conditions show good reproducibility. All composite membranes with less than 10 self-assembled double layers, from a structure point of view, were stable because the fluxes of polyelectrolyte membranes didn?t increase as time passed. <br /><br /> The separation performance of the self-assembled composite membranes developed in this work is not as good as it was originally expected, but it is still better than that of commercial poly(vinyl alcohol) (PVA) membranes for the dehydration of IPA/water mixtures, which indicates that new self-assembled composite membranes could be used for practical dehydration of IPA. The flux of the self-assembled composite membrane with 2 double layers was two times higher than that of reported self-assembled membrane in the literature when an IPA/water feed mixture with 10. 0 wt% of water was used at 60&deg;C. The composite membrane with 2 self-assembled double layers is a high performance membrane for IPA dehydration. <br /><br /> The formation of a single self-assembled layer on a non-porous substrate has been studied, but nothing has been reported about the formation of a self-assembled multilayer on a porous substrate. Based on the separation performance of different self-assembled composite membranes made from different materials and at different fabrication conditions, a two-stage process is proposed to explain the formation of a self-assembled multilayer on a porous substrate. Polyelectrolyte molecules, in the first stage, will deposit on the non-porous portion of the surface of a porous substrate while polyelectrolyte molecules will go into and fill the pores on the surface of a porous substrate to change a porous substrate into a "non-porous" substrate. In the second stage, polyelectrolyte molecules will deposit on a "non-porous substrate" to form a multilayer. This process can also be used to explain the formation of a multilayer on a non-porous substrate.

Electrostatic self-assembly is a simple, yet versatile and environmentally friendly technique. This technique has been widely used in different areas and recently it has also been used to make nano-structured separating layers for composite polyelectrolyte pervaporation membranes. Non-porous substrates are usually employed for electrostatic self-assembly depositions, but porous substrates have to be used for membrane applications because the composite membranes fabricated with non-porous substrates will have low permeation fluxes. When porous substrates were used to make composite membranes for pervaporation, it was reported that 60 double-layers were needed to get a membrane with suitable separation performance. The deposition of each double-layer needed about one hour, and the fabrication of reported self-assembled membranes with porous substrates was time-consuming and, from an industrial point of view, not practical. <br /><br /> The aim of this work was to make self-assembled composite membranes in a more practical way. The methodology used here is to find appropriate materials and suitable preparation conditions to make self-assembled composite membranes that have less than 10 self-assembled double layers but still have good performance for the dehydration of isopropyl alcohol (IPA)/ water mixtures by pervaporation. <br /><br /> A hydrolyzed polyacrylonitrile (PAN) ultrafiltration membrane is a permanently charged porous material. In this work, this porous material was, for the first time, used as a substrate for the fabrication of a composite self-assembled membrane. It was found that the hydrolyzed porous PAN membranes were good substrates for making self-assembled membranes for pervaporation. <br /><br /> In order to reduce the number of the depositions required for making composite membranes with suitable separation performance, a new deposition technique, concentration-changing deposition technique, has been developed. To obtain more extended conformations of polyelectrolytes to prevent them from going into the pores on a porous substrate, dilute deposition solutions were used for the first several depositions. After these first depositions, the pore size of the porous substrate had been reduced and more concentrated solutions (but still dilute solutions) could be used for the subsequent depositions. By using more concentrated deposition solutions, the number of the polyelectrolyte coils adsorbed by the charged substrate was increased and the thickness of each deposited layer was increased. In this way, the total number of deposition layers needed for a good membrane would be decreased. It has been proved in this work that the number of deposition layers in a composite membrane can be reduced by using the concentration-changing deposition technique. <br /><br /> By selecting appropriate materials and by selecting proper preparation conditions, composite polyelectrolyte membranes with less than 10 self-assembled double layers have been successfully fabricated. The obtained membranes had good performance for the dehydration of IPA/water mixtures by pervaporation. The lowest number of double layers in a composite membrane was 2 and this composite membrane had both a high flux and a high selectivity. It was also found that using polyelectrolytes with high molecular weights and a porous substrate with fine pores were the prerequisites for making composite polyelectrolyte membranes with less than 10 self-assembled double layers, while using a polyelectrolyte pair with high charge densities was the prerequisite for making composite membranes with a high selectivity. The successful fabrication of polyelectrolyte membranes with less than 10 double layers makes self-assembled membranes more practical because self-assembled composite membranes can be easily fabricated. <br /><br /> The data reproducibility and the stability of self-assembled composite membranes with less than 10 double layers have been discussed in this work. Random defects in the self-assembled separating layer and low repeatability of thickness in the first several deposition layers are believed to be the major reasons for the relatively low data reproducibility of single composite membranes, while the conformation change of adsorbed polyelectrolytes is one of the reasons for the flux reduction of composite membranes with less than 10 self-assembled double layers. Though the flux reproducibility of single membranes is barely acceptable (relative error about 25%), the average fluxes of several membranes made under the same conditions show good reproducibility. All composite membranes with less than 10 self-assembled double layers, from a structure point of view, were stable because the fluxes of polyelectrolyte membranes didn?t increase as time passed. <br /><br /> The separation performance of the self-assembled composite membranes developed in this work is not as good as it was originally expected, but it is still better than that of commercial poly(vinyl alcohol) (PVA) membranes for the dehydration of IPA/water mixtures, which indicates that new self-assembled composite membranes could be used for practical dehydration of IPA. The flux of the self-assembled composite membrane with 2 double layers was two times higher than that of reported self-assembled membrane in the literature when an IPA/water feed mixture with 10. 0 wt% of water was used at 60&deg;C. The composite membrane with 2 self-assembled double layers is a high performance membrane for IPA dehydration. <br /><br /> The formation of a single self-assembled layer on a non-porous substrate has been studied, but nothing has been reported about the formation of a self-assembled multilayer on a porous substrate. Based on the separation performance of different self-assembled composite membranes made from different materials and at different fabrication conditions, a two-stage process is proposed to explain the formation of a self-assembled multilayer on a porous substrate. Polyelectrolyte molecules, in the first stage, will deposit on the non-porous portion of the surface of a porous substrate while polyelectrolyte molecules will go into and fill the pores on the surface of a porous substrate to change a porous substrate into a "non-porous" substrate. In the second stage, polyelectrolyte molecules will deposit on a "non-porous substrate" to form a multilayer. This process can also be used to explain the formation of a multilayer on a non-porous substrate.

The separation characteristics of binary alcohol-water mixtures were studied overa wide range of feed concentration and temperature using polymeric and zeoliticpervaporation membranes. For the hydrophilic PVA membrane, the total flux (at 55 0C)for the ethanol-water system decreased from 0.45 to 0.05 kg/m2/hr as the feed ethanolconcentration was increased from 30 to 95 wt. %. The separation factor (water/ethanol)was found to increase by about 100 times for the same range of concentration. TheUNIQUAC theory was used to predict the activity of binary alcohol-water mixtures in thePVA membrane. The UNIQUAC theory successfully takes into account the nonidealitiespresent in the alcohol/water-PVA membrane system. The transport of waterand alcohol species through the PVA membrane was modeled using the UNIQUACtheory in conjunction with the conventional activity driving force model. Using themodel and the experimental pervaporation data, the diffusivity correlations andconcentration profiles for various species through the membrane were developed. Basedon the developed diffusivity correlations, the water and alcohol fluxes through the PVAmembrane were predicted at 80 ??C.Experiments were also conducted on the water selective zeolite (type NaA)membrane using various alcohol-water mixtures and with dimethylformamide-watermixture over a wide range of temperatures (25 to 70 ??C) and solvent concentrations (0 -100 wt. %). The total flux for the ethanol-water mixture was found to decrease from 2 to0.05 kg/m2/hr at 60 ??C as the feed ethanol concentration was increased from 0 to 100 wt.%. Both, the water to ethanol and water to isopropanol separation factors were observedto lie between 1000 and 5000 over a wide range of solvent concentrations. The Maxwell-Stefan theory was used to model the permeation of water through zeolite NaAmembranes. The precise micropore structure of the zeolite cage helps in a partialmolecular sieving of the large solvent molecules leading to high separation factors. Thezeolite membrane active layer may contain certain non-zeolitic interstitial pores withpreferential water sorption. A high degree of hydrophilicity of the zeolite membrane issuggested from a pure water sorption value of 0.6 gm/gm zeolite. The detailedinterpretation of this result, however, requires consideration of both true zeoliticmicrocavity uptake as well as interstitially held water between crystallites. The use ofpervaporation for volume reduction and solvent recovery applications in thepharmaceutical industry has been demonstrated.

This study deals with polyvinylamine (PVAm)-poly(vinyl alcohol) (PVA) based composite membranes incorporated with carbon nanotubes (CNTs) and molecular amines (e.g., piperazine (PZ), triethanolamine (TEA), N-methyldiethanolamine (MDEA), PZ/TEA and PZ/MDEA blends, diethylenetriamine (DETA) and triethylenetetramine (TETA)) for CO2 separation, solvent dehydration by pervaporation, and hydrogen purification. The effects of the parameters involved in the procedure of membrane formation and operating conditions on the membrane performance were investigated. Composite membranes comprising of a skin layer of PVAm-PVA incorporated with CNTs and a microporous polysulfone substrate were developed for CO2 separation from flue gas and dehydration of ethylene glycol by pervaporation. The membranes were characterized with Fourier transform infrared (FTIR), Raman spectroscopy, X-ray diffraction (XRD), contact angle measurement and water sorption uptake, using dense films of PVAm-PVA/CNTs, to determine the effects of CNTs on the intermolecular interactions, degree of crystallinity, surface hydrophilicity, and degrees of swelling of the membranes. For CO2/N2 separation, adding CNTs in the membrane was shown to enhance CO2 permeance while retaining a similar CO2/N2 selectivity; a CO2 permeance of 18.5 GPU and a CO2/N2 ideal selectivity of 64 were obtained at 0.6 MPa feed pressure. For pervaporative dehydration of ethylene glycol, the incorporation of CNTs into the membrane was shown to increase both the permeation flux and separation factor, and at 70??? a permeation flux of 146 g/(m2.h) and a separation factor of 1160 were achieved at 1 wt% water in feed using a PVAm-PVA/CNT composite membrane containing 2 wt% MWNTs. Novel facilitated transport membranes containing both PVAm as fixed carriers and various molecular amines as mobile carriers were fabricated and used for CO2 separation from N2 and H2, as well as CO2 separation from ethanol fermentation off gas. For membranes containing a single amine (i.e., PZ, DETA or TETA), the CO2 permeance increased with an increase in the amine content in the membrane until the amine content is sufficiently high, beyond which a further increase in the amine content would decrease the membrane performance. The facilitation in CO2 transport was more significant with membranes containing mixed amines (e.g., PZ/TEA and PZ/MDEA). Among all the molecular amines tested, TETA was shown to be most effective in facilitating CO2 transport in terms of CO2/N2 permselectivity. Using a PVAm-PVA/TETA composite membrane with a TETA to polymer (i.e., PVAm plus PVA) mass ratio of 150/100, a CO2 permeance of 22.6 GPU and a CO2/N2 selectivity of 86.5 were obtained at 0.6 MPa feed pressure for the removal of CO2 from flue gas, a CO2 permeance of 23.3 GPU and a CO2/H2 selectivity of 28.5 were obtained at 0.6 MPa feed pressure for CO2 separation from H2, a water vapor permeance of 16700 GPU was obtained at 25??? and 2.5 mol% water vapor concentration in the feed for dehydration of ethanol fermentation off gas.

Ethanol production through biomass fermentation is one of the major technologies available to produce liquid fuel from renewable energy sources. A major problem associated with the production of ethanol through fermentation remains the inhibition of the yeast Saccharomyces cerevisiae by the produced ethanol. Currently high water dilution rates are used to keep the ethanol concentrations in the fermentation broth at low concentrations, resulting in low yields and increased downstream processing to remove the excess water. Yeast strains that have a high tolerance for ethanol have been isolated but the time and cost associated with doing so poses a challenge. The fermentation process can be combined with pervaporation, thereby continuously removing ethanol while it is being formed. In this study a mathematical model for ethanol fermentation with yeast, Saccharomyces cerevisiae, coupled with pervaporation was developed. The fermentation of glucose was optimised in the first part of the study and experimental data were obtained to find a kinetic model for fermentation. It was found that an optimum ethanol yield can be obtained with an initial glucose concentration of 15wt%, a yeast concentration of 10 g.L–1, and a pH between 3.5 and 6. The maximum ethanol yield obtained in this study was 0.441g.g–1 (86% of the theoretical maximum) using 15wt% glucose, 10g/L yeast and a pH of 3.5. Two kinetic models for fermentation were developed based on the Monod model. The substrate–limiting model, predicted fermentation very accurately when the initial glucose concentration was below 20wt%. The second model, the substrate–inhibition model, predicted fermentation very well when high initial glucose concentrations were used but at low glucose concentrations, the substrate–limiting model was more accurate. The parameters for both models were determined by non–linear regression using the simplex optimisation method combined with the Runge–Kutta method. The PERVAP®4060 membrane was identified as a suitable membrane in this study. The effect of the ethanol content in the feed as well as the influence of the glucose content was investigated. The total pervaporation flux varied with ethanol content of the feed and the highest total flux of 0.853 kg/m2h was obtained at a feed with 20wt% ethanol. The addition of glucose had almost no effect on the ethanol flux but it lowered the water flux, thereby increasing the enrichment factor of the membrane. The mass transport through the PERVAP®4060 membrane was modelled using the solution–diffusion model and Greenlaw’s model for diffusion coefficients was used. The limiting diffusion coefficient (Di0) and plasticisation coefficients (Bij) were determined by using the Nelder–Mead simplex optimisation method. The theoretical values predicted with the model showed good agreement with the measured experimental values with R2 values above 0.998. In the third part of this investigation, the kinetic model developed for fermentation was combined with the transport model developed for pervaporation. The combined kinetic model was compared to experimental data and it was found that it could accurately predict fermentation when coupled with pervaporation. This model can be used to describe and better understand the process when fermentation is coupled with pervaporation. / Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2012.

Ethanol production through biomass fermentation is one of the major technologies available to produce liquid fuel from renewable energy sources. A major problem associated with the production of ethanol through fermentation remains the inhibition of the yeast Saccharomyces cerevisiae by the produced ethanol. Currently high water dilution rates are used to keep the ethanol concentrations in the fermentation broth at low concentrations, resulting in low yields and increased downstream processing to remove the excess water. Yeast strains that have a high tolerance for ethanol have been isolated but the time and cost associated with doing so poses a challenge. The fermentation process can be combined with pervaporation, thereby continuously removing ethanol while it is being formed. In this study a mathematical model for ethanol fermentation with yeast, Saccharomyces cerevisiae, coupled with pervaporation was developed. The fermentation of glucose was optimised in the first part of the study and experimental data were obtained to find a kinetic model for fermentation. It was found that an optimum ethanol yield can be obtained with an initial glucose concentration of 15wt%, a yeast concentration of 10 g.L–1, and a pH between 3.5 and 6. The maximum ethanol yield obtained in this study was 0.441g.g–1 (86% of the theoretical maximum) using 15wt% glucose, 10g/L yeast and a pH of 3.5. Two kinetic models for fermentation were developed based on the Monod model. The substrate–limiting model, predicted fermentation very accurately when the initial glucose concentration was below 20wt%. The second model, the substrate–inhibition model, predicted fermentation very well when high initial glucose concentrations were used but at low glucose concentrations, the substrate–limiting model was more accurate. The parameters for both models were determined by non–linear regression using the simplex optimisation method combined with the Runge–Kutta method. The PERVAP®4060 membrane was identified as a suitable membrane in this study. The effect of the ethanol content in the feed as well as the influence of the glucose content was investigated. The total pervaporation flux varied with ethanol content of the feed and the highest total flux of 0.853 kg/m2h was obtained at a feed with 20wt% ethanol. The addition of glucose had almost no effect on the ethanol flux but it lowered the water flux, thereby increasing the enrichment factor of the membrane. The mass transport through the PERVAP®4060 membrane was modelled using the solution–diffusion model and Greenlaw’s model for diffusion coefficients was used. The limiting diffusion coefficient (Di0) and plasticisation coefficients (Bij) were determined by using the Nelder–Mead simplex optimisation method. The theoretical values predicted with the model showed good agreement with the measured experimental values with R2 values above 0.998. In the third part of this investigation, the kinetic model developed for fermentation was combined with the transport model developed for pervaporation. The combined kinetic model was compared to experimental data and it was found that it could accurately predict fermentation when coupled with pervaporation. This model can be used to describe and better understand the process when fermentation is coupled with pervaporation. / Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2012.

Stuttgart, Univ., Diss., 2007.

Zugl.: Dortmund, Techn. University, Diss., 2008.

Techn. Universiẗat, Diss., 2001--Berlin.

Th. doct.-ing.--Nancy, I.N.P.L., 1982.