V. V. Teplyakov

Lab-scale bioreactor integrated with active membrane system for hydrogen production: experience and prospects

Abstract The development of new, low-energy consuming and clean technologies can include the utilization of organic wastes with the production of high-quality fuel gases (methane, hydrogen). This paper presents the results of organic wastes’ bioconversion into hydrogen and of the respective H 2 /CO 2 gas mixtures’ separation by using active membrane systems (membrane contactors) with moving liquid carriers. Rhodobacter capsulatus was used for lactate or low organic decomposition to H 2 -containing gas mixture and Thermohydrogenium kirishi was used for hydrogen production from glucose. Active membrane system was used for the separation of H 2 /CO 2 gas mixtures with the production of high-purity hydrogen. The possibility of integration of gas separating membrane systems with aerobic or anaerobic bioreactors are considered as well.

Improving gas separation properties of polymeric membranes based on glassy polymers by gas phase fluorination

The application area of existing gas separation membranes is limited by commercially available polymers for their preparation. In many cases the separation selectivity of these polymers is not sufficient for effective separation processes. One of the ways to improve the separation effectivity of existing membranes from glassy polymers is gas phase fluorination. It is very important to note that this method can be successfully used for modification of polymeric films, different types of membranes (flat sheet and hollow fiber) and membrane modules. The hollow fibers produced from Matrimid 5218 in Twente University and a flat-sheet membrane from polyvinylthrimethilsilane (PVTMS) produced in Russia were investigated. The treatment of samples by fluorination was carried out in closed reactor at 20–22 °C with gaseous mixtures of F2/He of different composition. A gas mixture of different concentrations (2–10 vol.% of F2) at 1 atm was used The time of fluorination was from 2 min to 265 min. The dependence of the structure of the PVTMS and Matrimid 5218 on gas phase fluorination by IR-spectroscopy and the influence of modification on membrane structure by SEM were studied. The productivity of He, CO2, N2 and CH4 through the membranes modified at different conditions of fluorination was measured, and it was shown that it is possible to achieve a significant increase of He/CH4, CO4/CH4 and He/N2 selectivity at high level He and CO2 productivity by this type of modification. Thus, modified membranes and membrane modules can be successfully used for separation of components of biogas in membrane contactors and selective membrane valves for extraction of He/Ne fraction from waste in the metallurgy industry and separation of natural gas components.

Evaluation of reproducible high flux silicalite-1 membranes: gas permeation and separation characterization

The permeation of helium, ethane, propane, n-butane, i-butane through a newly developed silicalite-1 membrane was performed using by a batch method and a Wicke–Kallenbach (WK) method. This membrane exhibits high flux properties and maintains a good separation selectivity. A procedure is outlined to interpret measured fluxes and estimate the various contributions of transport modes. The experimental fluxes of helium, ethane, propane and n-butane in the batch method could be divided into different parallel contributions, such as surface diffusion, activated gaseous diffusion and viscous flow. The permeation of helium was mostly governed by activated gaseous diffusion at 303–573 K. For adsorbing gases such as ethane, propane and n-butane, surface diffusion was dominant at temperatures up to 393 K. Their permeation mechanism shifted to activated gaseous diffusion with increasing temperature. In the WK method, both single component measurements and binary mixture separations using n-butane and i-butane were performed in the temperature range of 303–573 K. The selectivity for n-butane in a 1:1 mixture n-butane/i-butane was about 28 up to 400 K, which was higher than the ideal selectivity calculated from the single component measurements because of the competitive adsorption of the butanes. The selectivity of the membrane for n-butane/i-butane mixtures was highly dependent on feed composition and feed pressure.

Ceramic membranes modified with catalytic oxide films as ensembles of catalytic nanoreactors

Hybrid catalytic membrane systems have been produced by modifying porous ceramic membranes with metal oxide films. A two-layer cermet membrane consisting of a flexible stainless steel layer and an overlying porous TiO2 ceramic layer and a ceramic titanium carbide membrane are examined. The membrane surfaces have been modified by the alkoxide method using colloidal organic solutions of metal complex precursors. Producing a tetragonal single-phase ZrO2/Y2O3 coating on the cermet surface increases the abrasion strength of the ceramic layer. CO oxidation and the oxidative conversion of methane into synthesis gas and light hydrocarbons can be markedly intensified by modifying the membrane channels with Cu0.03Ti0.97O2±δ and La + Ce/MgO catalysts, respectively. A method has been developed for depositing, onto the geometrical surface of a membrane, a film of the new single-phase oxide P0.03Ti0.97O2±δ with an anatase structure and uniform pores of mean diameter 〈d〉 ∼ 2 nm. Blocks of zeolite-like silicalite can be formed on the surface of the phosphorus-titanium oxide film. The resulting hybrid membrane is characterized by an anisotropic permeability depending on the flow direction. This property has an effect on conversion and selectivity in the nonoxidative dehydrogenation of methanol.

In situ synthesis of novel ZIF-8 membranes on polymeric and inorganic supports

The fabrication of integrated ZIF-8 membranes via a direct in situ crystallization on a porous polyacrylonitrile material and a composite aluminum zirconate based support was performed for the first time. A novel free-seeding synthetic procedure was accomplished without an elevated temperature and autogeneous pressure. The proper choice of the support in combination with the appropriate synthesis procedure allowed for the preparation of phase-pure polycrystalline ZIF-8 membranes. The gas permeation experiments indicated that dense ZIF-8 selective layers, including a multi-layer coating, were perfectly grown on both the supports. Our results revealed a strong impact of the support on the gas separation characteristics of the resulting ZIF-8 membranes.

Highly reproducible high-flux silicalite-1 membranes: optimization of silicalite-1 membrane preparation

Abstract Silicalite-1 membranes were prepared on a TiO 2 coated porous stainless steel support. Different thicknesses of the membranes were achieved by changing the synthesis temperature. Increasing the crystallization temperature resulted in the formation of a monolith-type layer, which is close to a perfect microporous phase (without pores between crystals forming the layer). The silicalite-1 membranes were characterized by permeation measurements using single gases and a mixture of n -butane and i -butane in a Wicke–Kallenbach set-up. A direct relationship between the membrane thickness and the selectivity of n -butane to iso-butane was observed; the selectivity improved with an increase in the membrane thickness. The improvement in the selectivity was correlated with decreasing the intercrystalline spaces between the crystals forming the membrane. The best performing membranes were synthesized in the temperature range of 453–463 K. The competitive adsorption of the butanes at 303 K was governing the separation properties of the membranes. The selectivity for n -butane in a 50:50 n -butane/iso-butane mixture was as high as 55, and the flux equal to 2.75 mmol/m 2 per s (WK method at 101 kPa, 303 K). The ideal selectivities, calculated from the single component measurements towards n -butane, were between 33–48 and n -butane fluxes between 7–12 mmol/m 2 per s (WK method at 101 kPa, 303 K). Small variations in the selectivity performance of the membranes synthesized under the same conditions show that the optimized preparation method was highly reproducible.

Investigations on the peculiar permeation properties of volatile organic compounds and permanent gases through PTMSP

Abstract In contrast to common glassy polymers, poly(1-trimethylsilyl-1-propyne) (PTMSP), a high free volume glassy polymer, shows a preferable permeation of large condensable organic vapors in comparison to permanent gases. In order to investigate this phenomenon, a systematic permeability study over a large activity range has been performed on PTMSP with three types of volatile organic compounds (VOCs) as diffusing probes: toluene, dimethylketone and dichloromethane. PTMSP was synthesized with different catalytic systems (Nb or Ta based) able to induce controlled sub-molecular cis–trans structures. Whereas dimethylketone and dichloromethane permeability can be correctly described by a classical dual-mode equation, a peculiar bell shaped pattern was obtained for toluene, with a minimum permeability located at an activity value around a=0.3–0.4. In that case, only a dual-mode expression taking into account a concentration dependent diffusion coefficient can account for the results. On the other hand some apparent conflicting data recorded from PTMSP brand new films were related to the microstructure of the polymer main chain thanks to 13 C NMR spectroscopy analysis showing importance of cis- and trans-forms of the main chain of PTMSP. cis-Structure is more flexible and can be responsible for the creation of a higher density physical network (HDN) in polymeric matrix; conversely, trans-structure is more rigid and can provide lower density physical network (LDN). The higher permeability recorded for several probes through PTMSP synthesized with TaCl5/Al(i-Bu)3 catalytic system compared to those of NbCl5 based polymer can be explained by the geometric difference of the macromolecule networks.

Asymmetric Effects in Catalytic Membranes

A catalytic membrane hybrid system based on a cermet membrane with a channel size 〈d〉 of ∼0.12 μm has been produced using sol-gel processing. A layer of a superfine methanol conversion catalyst with the composition Cr2O3 · Al2O3 · ZnO has been formed on the inner surface of the channels, and a thin oxide coating of composition P0.03Ti0.97O2 ± δ with a homogeneous porous structure and 〈d〉 ∼ 2 nm has been formed on the geometric membrane surface. The methanol conversion rate and the gas permeability of the membrane depend considerably on the methanol vapor and gas (H2, He, CO2, Ar, CH4) flow directions. When methanol vapor diffuses toward the mesoporous layer, the catalytic activity is one order of magnitude higher and the gas permeability coefficients are 3–8 times lower than in the case of the reverse flow of the gaseous molecules. The temperature dependence of the gas permeability taking into account the possible types of mass transfer in porous solids suggests that, when the gases move toward the mesoporous coating consisting of phosphorus-modified titanium oxide, surface flow and activated diffusion dominate, whereas the reverse gas motion is dominated by free molecular flow.

Separation of gas mixtures in unsteady-state conditions

Abstract The prospects for the application of unsteady-state boundary conditions at the membrane inlet for increasing the selectivity of gas separation are discussed in this paper. The phenomena occurring upon passage of a concentration pulse and two-gas-component penetrant concentration waves through the membrane have been investigated. It has been shown that pulsed supply of the mixture to be separated at the membrane inlet increases the separation coefficients by a factor of several orders owing to differences in the diffusion coefficients of the gas mixture components in the membrane. Sinusoidal boundary conditions at the membrane inlet allow filtration of the amplitude of the total output oscillations from the signal of the component with a low diffusion coefficient (in this case the membrane acts as a frequency filter), which can be employed for increasing the selectivity of the sensors. The proposed techniques are exemplified by separation of the He/CO 2 gas mixture on a polymeric polyvinyltrimethylsilane (PVTMS) membrane.

Integrated membrane systems for gas separation in biotechnology: potential and prospects

Integrated non-porous membrane systems were applied for microbial combustible gas separation processes. Methane/CO2 mixtures of various concentrations from methane fermentation processes (biogas) were separated using a membrane-separation complex of permabsorber type into individual components of technical grade (more than 95% purity). In experiments with three-component mixtures, using a selective membrane valve with various liquid carriers, all the gases of interest (H2, CH4 and CO2) were obtained at greater than 90% purity in one separation step. The perspectives for the further application of non-porous membrane separating devices for various gaseous mixtures from different microbial processes are discussed.