Shamsuddin Ilias

Flux Enhancement in Cross-Flow Membrane Filtration by Flow Reversal: A Case Study on Ultrafiltration of BSA

Fouling problems are perhaps the single most important reason for relatively slow acceptance of ultrafiltration in many areas of chemical and biological processing. To overcome the losses in permeate flux associated with concentration polarization and fouling, in cross-flow membrane filtration, we investigated the concept of flow reversal as a method to enhance membrane flux in ultrafiltration. Conceptually, flow reversal prevents the formation of stable hydrodynamic and concentration boundary layers at or near the membrane surface. Furthermore, periodic reversal of the flow direction of the feed stream at the membrane surface results in prevention and mitigation of membrane fouling. Consequently, these advantages are expected to enhance membrane flux significantly. BSA is a well-studied model solute in membrane filtration known for its fouling and concentration polarization capabilities. Laboratory-scale tests on a hollow-fiber ultrafiltration membrane module using bovine serum albumin (BSA) solution as feed show that under flow reversal conditions, the permeate flux is significantly enhanced when compared with the conventional unidirectional flow. The flux enhancement is dramatic (by an order of magnitude) with increased feed concentration and operating transmembrane pressure.

Effect of Viscosity on Membrane Fluxes in Cross-Flow Ultrafiltration

Abstract For practical applications of ultrafiltration (UF), an estimation of membrane fluxes under various operational conditions is very important. This study analyzed concentration polarization (CP) as a coupled transport problem with concentration-dependent solute viscosity. Besides the effects of variable viscosity, the model includes the effects of solute osmotic pressure, solute rejection at the membrane surface, and the axial pressure drop. This provides a fundamental understanding of the effects of various operating parameters on concentration polarization and transmembrane flux. A finite-difference solution of the transport equations is presented to model the concentration polarization in a thin-channel UF system. Simulation results for ultrafiltration of Dextran T-70 show that concentration-dependent solute viscosity adversely affects the transmembrane flux and needs to be carefully considered in modeling concentration polarization in membrane filtration.

Steam Reforming of Methanol in a Pd-Composite Membrane Reactor

Palladium-based membranes are being studied for simultaneous production and separation of H2 from reforming reactions in a single-unit operation by equilibrium shift. In this work a Pd-composite membrane in tubular configuration as fuel reformer was used to study the steam reforming of methanol (SRM) over Zn/Ni catalyst on Al2O3 support. The Pd-composite membrane was fabricated by depositing thin Pd film on microporous stainless steel (MPSS) support by surfactant induced electroless plating (SIEP) method. The effects of steam to methanol molar feed ratio (S/M), temperature, and catalyst time factor on methanol conversion, H2- and CO-selectivity were studied for the SRM in the membrane reactor. A two-dimensional, pseudo-homogeneous membrane-reactor model for the SRM reactions was developed to study the membrane reactor performance. Experimental results show that a significant enhancement of methanol conversion is achievable in H2-selective Pd-MPSS membrane reactor by equilibrium shift. The S/M ratio has marginal effect on methanol conversion, and at high S/M ratio, steam acts as diluent. The temperature has a greater effect on methanol conversion and with increased catalyst time factor, methanol conversion increased to some extent. The CO-selectivity was sensitive to temperature and to a lesser extent to the S/M ratio. On the contrary, H2-selectivity was insensitive to both temperature and S/M ratio. The trends observed in this experimental SRM in Pd-MPSS membrane reactor were in good agreement with a 2-D pseudo-homogeneous SRM membrane reactor model.

Characterization of Pd-Composite Membrane Fabricated by Surfactant Induced Electroless Plating (SIEP): Effect of Grain Size on Hydrogen Permeability

Polycrystalline palladium (Pd) was deposited on micro-porous stainless steel (MPSS) substrate using a suitable surfactant of various concentrations in the electroless plating process. The micro-structural characterization was carried out using Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and X-ray diffraction (XRD). The concentrations of the surfactant were chosen as a function of critical micelle concentration (CMC) in order to elucidate the interaction of the surfactant in solid-liquid and solid-gas interface during grain coarsening. It appears that during electro-crystallization, the driving force between the newly formed crystallite and the originally coarsed grains depends on the relative size and crystalline configuration of the newly formed crystallite. This crystallite on the other hand is affected by the localized over potential, the presence of active nucleating particles, and the texture of MPSS surface and operating conditions. The size of the newly formed grain is smaller when the concentration of the surface-active agents is relatively higher. It suggests that the surfactant active polar group inherently participates in the reaction/deposition process and effectively activates the process of grain nucleation and agglomeration in electro-crystallization. The membranes of different grain sizes were fabricated in the presence of the cationic surfactant DTAB (dodecyltrimethyiammonium bromide) of various concentrations. DTAB concentration is expressed in critical micelle concentration (CM), which ranged from CMC × ½ to CMC × 4. Fabricated membranes of different grain size and distribution were also studied for hydrogen permeability and selectivity. Results show that membranes with agglomerated grains (higher grain size) possess relatively higher permeability and selectivity.

Membrane Bioreactor Model for Removal of Organics from Wastewater

Abstract The persistence of trace organics in wastewater effluent is a major environmental concern. Possible use of fixed microbial films in wastewater treatment processes is currently an active area of research that may be able to address many of these problems. In the waste effluent, the persistence of trace organics is attributed, in part, to the inability of microbial populations to extract energy from dilute environments at a rate fast enough to sustain themselves. To address this problem, a novel wastewater treatment scheme is considered. On the basis of previous hollow fiber biomass growth studies, we believe that an anaerobic biofilm supported by hollow fibers could achieve greater biomass density than a film grown on traditional impermeable supports. This in turn could lead to improved substrate removal efficiency in a reactor of a given volume. Using this concept, we developed a mathematical model to test the potential of hollow fiber membrane reactors for biodegradation of acetate solution. A c...

Thermal stability study of Pd-composite membrane fabricated by surfactant induced electroless plating (SIEP)

ABSTRACT Over the years, several different methods have been developed by modifying the conventional electroless plating (CEP) technique to fabricate dense thin Pd composite membranes with high H2 permselectivity. In this study, Pd composite membranes on macroporous stainless steel substrate (MPSS) were fabricated using CEP and novel surfactant induced electroless plating (SIEP) methods. The structural characteristics of CEP and SIEP fabricated Pd membranes were investigated before and after the heat treatment using SEM, XRD, EDS, and AFM techniques. The H2 permselectivity performance of the SIEP membranes was compared with that of CEP at different temperatures and trans-membrane pressures in the range of 523-823 K and 20-100 psi, respectively. The long-term thermal stability test of SIEP fabricated membranes was carried out on two different membranes, fabricated on MPSS substrates with and without oxide layer at 15 psi trans-membrane pressure and thermal cycling of 573-723-573 K. The microstructure analysis revealed that SIEP membranes have finer grains and diffused grain boundaries resulting in uniform, smooth, continuous, and pinhole free Pd-film. The SIEP membrane showed eight-fold higher H2 flux (1.7172 mol/m2/s) and four-fold higher H2 selectivity (~148) at 823 K and 100 psi trans-membrane pressure, compared to CEP membrane. Pd/MPSS membrane subjected to test for long-term performance and thermal cycling showed stable performance up to 1200 h while maintaining infinite H2 selectivity. Interestingly, although the thickness of Pd/oxi-MPSS (13.49 µm) membrane was higher than that of Pd/MPSS (11.6 µm) membrane, the H2 flux of Pd/oxi-MPSS membrane was two times higher than that of Pd/MPSS, attributed to the effective action of oxide layer as diffusion barrier.

SEPARATION OF HYDROGEN AND CARBON DIOXIDE USING A NOVEL MEMBRANE REACTOR IN ADVANCED FOSSIL ENERGY CONVERSION PROCESS

Inorganic membrane reactors offer the possibility of combining reaction and separation in a single operation at high temperatures to overcome the equilibrium limitations experienced in conventional reactor configurations. Such attractive features can be advantageously utilized in a number of potential commercial opportunities, which include dehydrogenation, hydrogenation, oxidative dehydrogenation, oxidation and catalytic decomposition reactions. However, to be cost effective, significant technological advances and improvements will be required to solve several key issues which include: (a) permselective thin solid film, (b) thermal, chemical and mechanical stability of the film at high temperatures, and (c) reactor engineering and module development in relation to the development of effective seals at high temperature and high pressure. In this project, we are working on the development and application of palladium and palladium-silver alloy thin-film composite membranes in membrane reactor-separator configuration for simultaneous production and separation of hydrogen and carbon dioxide at high temperature. From our research on Pd-composite membrane, we have demonstrated that the new membrane has significantly higher hydrogen flux with very high perm-selectivity than any of the membranes commercially available. The steam reforming of methane by equilibrium shift in Pd-composite membrane reactor is being studied to demonstrate the potential application this new development. To have better understanding of the membrane reactor, during this reporting period, we developed a two-dimensional pseudo-homogeneous reactor model for steam reforming of methane by equilibrium shift in a tubular membrane reactor. In numerical solution of the reactor model equations, numerical difficulties were encountered and we seeking alternative solution techniques to overcome the problem.

Bimetallic nanocatalysts in mesoporous silica for steam reforming reactions to produce H2 for fuel cells

Bimetallic nanocatalysts in ordered MCM-41 mesoporous silica have been synthesized using a one-pot hydrothermal procedure. The catalysts have been characterized using N2 adsorption–desorption isotherms, X-ray diffraction, highresolution transmission electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric-differential scanning calorimetry techniques. The mesoporous silica support showed surface area of about 974 m 2 /g and average pore size of 2.8 nm while upon metal encapsulation they decreased to 775 m 2 /g and 2.16 nm, respectively. While the small angle XRD studies confirmed the ordered structure of the silica, the HRTEM studies show uniform distribution of the metallic nanoparticles in mesoporous silica. Initial studies of the bimetallic nanocatalysts showed excellent activity for methanol conversion (~97% for Pd-Co/MCM-41 vs ~ 40% for Co/MCM-41) and selectivity to hydrogen (~95% for Pd–Co/MCM-41 vs 81% for Co/MCM-41), compared to the MCM-41containing only Pd or Co metal. This result suggested a synergistic interaction between the bimetallic nanocatalysts which resulted in a high methanol conversion and superior selectivity compared to the catalysts containing

Solubilization of TX-100™ and PEG-PPG-PEG in Liquid Carbon Dioxide

Carbon dioxide (CO2) at the subcritical, near-critical, and supercritical states has been found to be a powerful solvent with tunable characteristics. It is currently considered an alternative solvent to the conventional organic solvents and has attracted numerous industrial activities (processes). However, CO2 has been limited in its application due to challenges with dissolving polar macromolecules, which limits its applications. This article presents the solubilization of surfactant; octylphenol ethylene oxide (TX-100™) and poly(ethylene glycol)-block-poly (propylene glycol)-block-poly (ethylene glycol) (PEG-PPG-PEG) in liquid carbon dioxide. The TX-100™ is solubilized in the liquid CO2 in a programmable phase equilibrium analyzer at varying temperatures and pressures. The emulsion characteristics as well as the water capacity of TX-100™ and PEG-PPGPEG each in liquid CO2 is predicted by using ethyl acetate as substituted solvent. For PEG-PPG-PEG and TX-100™ emulsion systems, microemulsion form at water-to-surfactant volume ratios of less than 1.0 and 1.2 with their corresponding liquid CO2 volume of greater or equal to 94% and 94.6%, respectively.

Ultrafiltration of W/CO2 Microemulsions in Ceramic Membranes

Abstract Water‐in‐CO2 (W/CO2) reverse microemulsions stabilized with 1100 Da poly(ethylene glycol)‐poly(propylene glycol)‐poly(ethylene glycol) block copolymer were recovered using an ultrafiltration ceramic membrane in a custom high‐pressure cross‐flow separation unit. Viscosity‐corrected liquid CO2 flux (298 K) through the membrane was investigated as a function of time and surfactant concentration to determine the cake layer mass transfer resistance. Rapid CO2 flux decline was observed with increasing surfactant concentration, denoting cake layer buildup on the membrane surface. For instance, at 0.09 and 0.55 wt% surfactant, the ratio of cake resistance to membrane resistance was 0.4 and 3.8, respectively. Based on our previous work, the reverse‐micelles retain their aqueous core and are not altered during filtration. Ultimately, inorganic membrane separations can reduce energy consumption associated with compression/expansion cycles typically used in CO2‐based processes.