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Commercially available polymeric membrane materials may also show their potential for CO2 capture by the association of the membrane process with other separation techniques in a hybrid system. In the current study, PRISM PA1020/Air Products and UBE UMS-A5 modules with membrane formed of modified polysulfone and polyimide, respectively, were assessed as a second stage in the hybrid vacuum swing adsorption (VSA)&ndash, membrane process developed in our laboratory. For this purpose, the module permeances of CO2, N2, and O2 at different temperatures were determined, and the separation of CO2/N2 and CO2/N2/O2 mixtures was investigated in an experimental setup. An appropriate mathematical model was also developed and validated based on experimental data. It was found that both modules can provide CO2-rich gas of the purity of &gt, 95% with virtually the same recovery (40.7&minus, 63.6% for maximum carbon dioxide content in permeate) when fed with pre-enriched effluent from the VSA unit. It was also found that this level of purity and recovery was reached at a low feed to permeate the pressure ratio (2&minus, 2.5) in both modules. In addition, both modules reveal stable separation performance, and thus, their applicability in a hybrid system depends on investment outlays and will be the subject of optimization investigations, which will be supported by the model presented and validated in this study.

Experimental adsorption isotherms of carbon dioxide, nitrogen and oxygen at 293, 313 and 333 K over a zeolite molecular sieve 13X Grace are presented. The data were used in the simulations of the hybrid VSA-membrane process for carbon dioxide capture from flue gas as presented in a related article entitled "The performance of a hybrid VSA-membrane process for the capture of CO2 from flue gas" [1]. A representative sample of ZSM 13X Grace (149.7 mg) was prepared using the Microscal Spinning Riffler. Adsorption equilibria were determined by a gravimetric method, which uses a microbalance IGA003, Hiden Isochema Ltd., UK at temperatures of 293, 313 and 333 K. Every adsorption isotherm was started at 0 bar. For CO2 the equilibrium concentration reaches 3.755-4.857 mol kg-1 at the maximum pressure of 1 bar. In the case of N2 and O2 the equilibrium concentration reaches, respectively, 0.721-1.255 mol kg-1 and 0.299-0.531 mol kg-1 at the maximum pressure of 5 bar. Data may be reused in any adsorptive CO2/N2/O2 separation process which uses ZMS 13X as an adsorbent.

Over the last decade, membrane-based CO2 capture using ionic liquids (ILs) has been demonstrated as a promising technology. However, elaborative synthesis of monomers and long-term instability of IL-based composite membranes have so far limited their industrial relevance. In this paper, novel membranes are introduced for CO2 separation using poly(ionic liquids) (PILs) based on polyvinylbenzyl chloride (PVBC). Three PIL-based membranes were prepared as thin-film composites (TFC) by solvent casting with subsequent sealing. They were tested for the CO2 removal from synthetic flue gas. An ammonium-derivatised PVBC-analogue was prepared as a first PIL-type by polymerisation of an IL monomer, whereas two other PILs, respectively with hydroxyethyl ammonium and pyrrolidinium cations, were obtained using a modification of commercial PVBC. Introduction of bis(trifluoromethylsulfonyl) imide (Tf2N) anions was accomplished by metathesis. A thorough characterisation of the material structure, composition, membrane morphology and gas separation properties demonstrates that the presence of hydroxyl groups in the polycation enhanced the interaction with CO2 molecules. The mixed-gas selectivity increases with the higher positive charge on the cation species (hydroxyethyl-dimethylammonium > trimethylammonium > pyrrolidinium). More importantly, experiments performed in humidified conditions particularly revealed a doubled CO2 permeance and a 20-30% increased selectivity in comparison to dry conditions. These developments are spurring the application of PIL-based TFC membranes for CO2 capture from flue gas streams.

Hybrid techniques, which combine standard separation methods, are being developed in an attempt to overcome some limitations (especially high energy demands) associated with standalone absorptive, adsorptive or membrane processes for CO2 capture from flue gases. The hybrid system developed in our laboratory, which includes a four-column VSA (vacuum swing adsorption) unit followed by a membrane stage has been theoretically investigated in this paper in order to assess its performance. The adsorbers are packed with ZMS 13X Grace and the membrane stage is based on the Air Products PRISM module with the membrane area of 1575–2250 m2. It was concluded that such a system is flexible enough to improve the capture of carbon dioxide both in terms of energy consumption and adsorbent productivity in comparison with standalone VSA or membrane systems. At the same time it assures high CO2 purity (>95 vol. %) and recovery (85–95 %). It was found that the specific energy consumption in the system analyzed does not exceed 2 MJe kgCO2−1 and may be lowered to the level of 1.54–1.56 MJe kgCO2−1 by properly choosing the VSA cycle step time and/or the area of the membrane stage. At the same time a possibility to increase the adsorbent productivity in the VSA unit to as high as 1.8 t m−3 day−1 along with ways for a simultaneous improvement of the process throughput and the energy usage have been shown while maintaining acceptable carbon dioxide purity and recovery.

The removal of carbon dioxide from flue gas streams can be carried out using standard separation techniques, such as adsorption or membrane separation. However, due to the low CO2 concentrations (below 20 vol.%), the adequate purity and recovery of CO2 in the product can usually be achieved by using two-stage systems, in which the high recovery is commonly obtained by minimizing CO2 content in the gas leaving stage 1 and recycling the CO2 that remains after stage 2 to the inlet of the installation. The hybrid technique is an alternative to the two-stage adsorptive or membrane systems, both simpler and, potentially, more economical. In the hybrid process, proposed in this paper stage one includes a four-column VSA (vacuum swing adsorption) unit, whereas stage two is a membrane module. Extensive experiments were performed in a demonstration hybrid installation processing 5–10 m3 (STP)/h of dry flue gas showing the possibility to increase CO2 content from the initial 12 vol.% to over 95 vol.% with a 100% recovery over a wide range of the operating parameters. The experimental energy consumption (in excess of 4.1 MJ/kg of CO2 removed) can be reduced, for higher capacities, to a value as low as 1.7 MJ/kg of CO2, and thus, lower than that for a number of one- and two-stage adsorption processes. The detailed investigation of the hybrid technique, so far inadequately explored in the context of CO2 capture from flue gas, has provided a wealth of data that shows the principal directions in which further studies should proceed.

The majority of commercial membrane units for large-scale natural gas sweetening are based on cellulose acetate (CA). However, the low selectivity and risk for and plasticisation affect adversely the performance of CA-based systems. Herein, we present a new class of CA-derived poly(ionic liquid) (PIL) as a thin film composite (TFC) membrane for CO2 separations. CA is modified with pyrrolidinium cations through alkylation of butyl chloride, substituting the hydroxyl group in the polymer backbone, and further anion exchange to bis(trifluoromethylsulfonyl)imide, P[CA][Tf2N]. The synthesised PIL material properties are extensively studied. The CO2 separation performance of the newly synthesised materials is evaluated by gravimetric gas sorption experiments, single gas time-lag experiments on thick membranes, and mixed-gas separation experiments on TFC membranes. The results are compared to the parent material (CA) as well as a reference PIL (poly(diallyldimethyl ammonium) bis(trifluoromethylsulfonyl)imide (P[DADMA][Tf2N])). The ideal CO2/N2 sorption selectivity of P[CA][Tf2N] is constant up to 10 bar. The single gas transport measurements in P[CA][Tf2N] reveal improved ideal CO2 selectivity for the CO2/N2 gas pair and increased CO2 permeability for the CO2/CH4 gas pair compared to the reference PIL. Mixed-gas permeation tests demonstrated that P[CA][Tf2N]-based membranes with a 5 µm thick selective layer has a two-fold higher CO2 flux compared to conventional CA. These results present CA modification into PILs as a successful approach promoting the higher permeate flows and improved process stability in a wide range of concentrations and pressures of CO2/N2 and CO2/CH4 gas mixtures.

Due to the low CO 2 concentrations in flue gases (below 20vol.%), the adequate recovery and purity of carbon dioxide in the product can only be achieved by using two-stage adsorptive or membrane systems. In these systems, the high recovery is commonly obtained by minimising CO 2 content in the gas leaving stage 1 and recycling the CO 2 that remains after stage 2 to the inlet of the installation. The hybrid technique is an obvious extension of the two -stage adsorptive or membrane process. However, there are a number of problems that have to be tackled before such a system becomes practically attractive. One of these problems is the sequence in which the two sections (adsorption and membrane separation) are incorporated into the complete installation. Preliminary studies show that, in the case of flue gas purification, the adsorptive section based on pressure swing adsorption (PSA) should come first. In the present paper results of detailed numerical simulations are presented for the arrangement proposed. A demonstration installation processing around 10 m 3 (STP)/h of the flue gas is briefly described.

Gas from coal gasification contains less hydrogen than from other syngas production methods. An attractive option is its further hydrogen enrichment for pure hydrogen production in a membrane reactor (MR) by water gas shift (WGS). The goal of the present study was to analyse MR fed with coal derived gas. Simulations for feasible membrane permeation parameters revealed that to get high conversion above 90% a relatively high S/C should be applied. Moreover, hydrogen recovery is in this case low (below 30%) so for hydrogen production an additional H2 separation after the MR should have been applied. The paper also shows that a clear advantage of counter- over co-current flow configuration in MR appears only for low pressure in the reaction zone. The realistic feasible Pd–Cu–Ni membrane parameters result in a rather large membrane area, thus possible heat exchange between the reaction and permeation zone can have important influences on temperature profiles in the MR. This cooling effect could lessen excessive temperature increase in the reaction zone. Results for other than single step MR configurations are also presented in the paper. It is stated in conclusion that future successful application of MRs for coal-derived gas depends on development of not only new catalysts with adequately wide operational temperature range, but also membranes with a high enough permeability. © 2010 Published by Elsevier B.V.

Mathematical model of a membrane reactor for the water-gas-shift (WGS) reaction and results of simula- tion studies are presented. The physicochemical phenomena and brief description of the model are given. Due to the fact that membranes for CO2 separation exhibit poor selectivity at the elevated temperature range (indispensable for the desired activity of WGS catalysts), the simulations were carried out only for H2 selective membranes, containing Pd or its alloys. Comparison of the conventional two-stage WGS reactor with the membrane reactor revealed that operating temperature range of the catalyst used in the membrane reactor unit has to be much wider than that in conventional industrial reactors with separate high- and low temperature catalyst stages and with cooling in between. Thus, the research of new cata- lysts should accompany development of the membrane reactor technology. Simulations discussed in the present paper were focused on processing the gas derived from the coal gasification plant. Some results of mathematical simulations are presented. They reveal that under some conditions the membrane reactor technology can be promising for the hydrogen production from the coal-derived gas. © 2010 Elsevier B.V. All rights reserved.

To carry out a comparative assessment of a recently proposed idea of using thermal flow-reversal reactors (TFRR) for mine ventilation air, the results for the catalytic flow-reversal reactor (CFRR) investigated within the European Project (2003) are briefly presented. Next, experimental investigations of thermal combustion are presented in this paper. These consisted of the kinetic study of homogeneous combustion in the pelletized bed and in the monolith. Kinetic equations for the two cases are derived and discussed. Experimental autothermal reverse-flow operation in a laboratory setup was performed. Due to the high heat capacity of the wall and insulation of the pelletized bed reactor, with considerable heat losses to the surroundings, autothermal operation was successful only in the monolithic reactor. It is finally concluded that the thermal combustion can be competitive compared with the catalytic oxidation.

In a recent paper (Warmuzinski, 2002) a simple analytical formula has been developed to measure energy savings resulting from the pressure equalization step. The formula enables the energy consumption factor to be calculated using basic operating parameters of the system. However, although the approach proposed can be used in conjunction with other guidelines to assess the impact of the pressure equalization step on the overall energy requirements of a PSA (pressure swing adsorption) process, it is based on the assumption that the PE pressure can be calculated as either arithmetic or geometric (Banerjee, Narayankhedkar, Sukhatme, 1990, 1992) mean of P H and P L . This, obviously, is a rough approximation that impairs the generality of the analysis. Therefore, in this study a more realistic approach is proposed to calculating the intermediate pressure in PSA systems. This approach is the compared with the present authors' own experimental data. Although the experiments were not originally designed to verify the analysis, it is shown that the more rigorous formula provides a much better approximation of P I than the geometric mean of P H and P L .

A simple, fast, sustainable, and scalable strategy to prepare nanoporous materials based on poly(ionic liquid)s (PILs) is presented. The synthetic strategy relies on the radical polymerization of crosslinker-type ionic liquid (IL) monomers in the presence of an analogous IL, which acts as a porogenic solvent. This IL can be extracted easily after polymerization and recycled for further use. The great advantages of this synthetic approach are the atom-efficiency and lack of waste. The effects of different monomer/porogen ratios on the specific surface area, porosity, and pore size have been investigated. Finally, the potential of the materials as CO2 sorbents has been evaluated.

Air contaminated with volatile organic compounds (VOCs) is associated with a number of industrial processes. The purification of these air streams based on conventional techniques, such as combustion, condensation or adsorption is usually uneconomical. Environmental considerations require, however, that this problem should be dealt with as efficiently as possible. Therefore, the use of hybrid systems is analysed that include membrane separation and condensation or, alternatively, membrane separation followed by combustion.

The mathematical model of nonisothermal multicomponent pressure swing adsorption, developed in Part I of this study (K. Warmuzinski, M. Tanczyk, Chem. Eng. Proc., 36 (1997) 89–99) is validated based on experimental data concerning the separation of CH 4 and H 2 on activated carbon and the production of hydrogen on zeolite 5A. For a wide range of the various operating parameters, the measured values of the purity and recovery of the products, together with the concentration and temperature profiles during a PSA cycle are compared with those predicted by the model. In all cases a satisfactory agreement is found between theory and experiment.

A general model of multicomponent pressure swing adsorption (PSA) is presented which describes the operation of multi-column PSA installations. The individual columns can be packed with one or two layers of different adsorbents. All the basic steps of modern PSA cycles are taken into account. The operation of a large-scale PSA installation is analysed using a hydrogen purification plant as a test case

The paper deals with the cellular convection resulting from the parallel mass transfer of two components. It is shown that the case analysed cannot be regarded as fully equivalent to that of the simultaneous mass and heat transport due to the effect of the phenomena occurring in the Gibbs dividing layer.

The paper presents a model of surface phenomena accompanying the absorption of carbon dioxide into aqueous solutions of monoethanolamine. The model is based on the assumption that the cellular convection is driven by surface tension gradients, induced in turn by infinitesimally small perturbations of concentration. The model derived makes it possible to study in detail certain characteristics of the process of chemical absorption. Thus, the probability of oscillatory modes occurring in the system is analysed, the dimensions of the convective cells are evaluated and the gas—liquid contact time necessary for the instability to appear is determined. The quantitative conclusions are compared with the relevant experimental data concerning the absorption of CO 2 into monoethanolamine in both wetted-wall and packed columns.

A model of cellular convection during absorption accompanied by chemical reaction has been extended to include non-zero time constants. Based on the model a numerical analysis has been carried out to test the validity of the principle of exchange of stabilities in the system considered. It has been found that, unlike in cases of pure mass transfer, oscillatory modes may appear in systems where absorption is coupled with chemical reaction.

Publisher Summary This chapter illustrates that a number of research organizations have focused their programs upon the abatement of greenhouse gases (GHG), including methane. Methane emissions, apart from the adverse environmental impact, lead to considerable losses of the valuable fuel. The utilization of methane becomes even more important in view of the ever-decreasing reserves of primary energy sources. The chapter deals with two techniques for the utilization of coal-related methane emissions in Poland. An analysis is carried out of the enrichment of coal bed methane via adsorptive separation to produce gas that can be used commercially in natural gas networks. It is found that a two-stage pressure swing adsorption system can yield the gas containing more than 90% of methane. Also, economic feasibility is studied for an alternative utilization option, namely, the combustion of ventilation air methane in existing boilers. Conditions are derived that determine the upper limit of the distance at which the transportation of ventilation air remains an economically viable solution.