• Energy Research

Membrane separation technology is rapidly emerging as an alternative to traditional gas separation processes, and increasingly challenging separations require a constant search for new and better-performing materials. This paper reports the gas separation performance of a poly (vinyl alcohol) (PVA) membrane blended with 53 wt% of the ionic liquid 1-ethyl-3-methyl-imidazolium dicyanamide ([EMIM][DCA]), known from our previous work as highly CO/H "reverse-selective" material, under different experimental conditions. The material properties of the solution-cast membranes are discussed and compared with the neat PVA polymer. Pure gas permeation measurements show a drastic increase of permeability for all gases (H, He, O, N, CH, and CO) compared to the neat polymer, with a change from diffusion-selective to sorption-selective behaviour. The gas permeability further increases over the temperature range from 25 °C to 55 °C and is accompanied by a decrease in selectivity for most gas pairs, in particular, CO/N and CO/CH, except for the H/CO gas pair. Mixed gas permeation measurements with the CO/CH mixture show a beneficial effect of humidity on permeability and selectivity. This is supported by vapour sorption measurements, which show the high affinity of the membrane for water vapour and the vapour of lower alcohols.

Biogas is a suitable alternative fuel if unwanted impurities are removed to avoid corrosion of the inner parts of an engine. A recent breakthrough in biogas purification showed that a thin hydrophilic composite membrane can create the selective water swollen barrier able to remove unwanted sour gases such as carbon dioxide and hydrogen sulphide owing to significantly higher water solubility of the latter in comparison to methane. This work presents the use of water-swollen membranes for the simultaneous removal of carbon dioxide, hydrogen sulphide and water vapour from agro-biogas. Up to 82 vol.% of carbon dioxide and 77 vol.% of hydrogen sulphide were successfully removed from the feed stream at a pressure of 220 kPa. The selection of the most suitable thin hydrophilic composite membrane based on the knowledge of its basic characteristics is discussed. SEM analysis showed that the surface of the best performing composites changed significantly upon swelling by water. It was found that a compact structure of the upper selective thin layer after the swelling by water is fundamental for obtaining a selective water-swollen membrane. The next key factor is a high porosity of the membrane support. A detailed comparison of various systems and their performance is presented. © 2014 Elsevier B.V. All rights reserved.

Leaking of volatile organic compounds (VOCs) from gasoline during its storage, handling and transportation constitutes a serious ecological problem seeing that VOCs are known as toxic, environmentally harmful and carcinogenic agents. Despite the fact that the lost amounts of mainly hydrocarbons during common operations in refineries or at fuel stations may seem negligible; in reality they reach hundreds of tons per year of valuable industrial products. All above mentioned facts are the reason why the separation of these compounds from air and their recycling is critically important. At the present time, VOCs removal from the air is realized by traditional cost-consuming technologies like adsorption or refrigeration and by ecological progressive high-efficiency membrane separations. Polymer membranes based on polydimethylsiloxane (PDMS) or polyether-block-amide (PEBA) currently belong to the group of polymers used for the preparation of composite separation membranes [1-4]. Some of their unfavourable limitations (lower chemical resistance, swelling) led researchers to test also other potentially utilisable polymers like polyvinylidene fluoride (PVDF), poly{1-trimythylsilyl-1-propyne} (PTMSP), high free volume amorphous glassy perfluoropolymers (Teflon AF) or cross-linked poly(amide-imide) polymers[2-4]. Hence, detailed knowledge of polymer structure-permeability relationship and polymer-penetrant interactions plays an important role in the development and potential industrial application of newly prepared membrane materials. Generally, the mass transport of VOCs in and through the polymer matrix is a complex process which depends on polymer properties (glassy/ rubbery state, orientation, porous/nonporous structure, symmetric/ asymmetric architecture etc.), penetrant properties (molecular size and shape, specific penetrant-penetrant or penetrant-polymer interactions) and also on external conditions (temperature, pressure, concentration gradient etc.). It is generally accepted that mass transport in dense polymer membranes takes place according to the well known solution-diffusion mechanism (SDM) [5]. For small, not-self-aggregative, low-sorbed molecules SDM is valid without any limitations. In other cases, especially for VOCs the solubility of the compound has a strong influence on the polymer behaviour (swelling, plasticization, chain flexibility, reorganisation of dynamic free volume elements) and, consequently, on diffusivity and permeability [1,5]. Therefore the concentration-dependence of transport parameters must be taken into account. In this chapter we shall give a survey of the VOCs transport in non-porous polymer membranes with special reference to the phenomenon of concentration-dependence of transport. © 2011 by Nova Science Publishers, Inc. All rights reserved.

Poly(ether-b-amide) (Pebax11657)/polyacrylonitrile (PAN) composite hollow fiber membranes for a potential use in CO2/CH4 separation were prepared by a new continuous coating method, referred to as cross-flow filtration. This technique allows to obtain the simultaneous coating of a large number of fibers, facilitating the scale-up. The dense layer was deposited in the lumen of the fibers allowing the coating of all the fibers in a single step. The coating on the inner surface of the fibers avoids the negative effects such as sticking or accidental mechanical damages occurring in the case of external coating. The membrane preparation was optimized by modulating different parameters. The optimal range of viscosity and concentration of the polymer solution to obtain a selective homogeneous Pebax1 layer was identified. The presence of the Pebax11657 dense layer was confirmed by IR spectroscopy and the morphology of the composite membranes was observed by SEM analysis. The gas separation performance of the membrane modules was determined by single gas permeation measurements. A preliminary optimization yielded membranes with PCO2 = 5x 103 (m3m2 h1 bar1), aCO2=CH4 = 18 equal to that of the neat dense polymer. The PEBAX1/PAN hollow fibers modules are potentially useful for application in the purification of biogas.

Abstract: This work presents a case study, aimed at biogas upgrading with simultaneous purification of methane and CO2. The study was performed on industrial plant of biogas production constructed by Tecno Project Industriale Srl. It has a biomass treatment capacity of 400.000 ton/year and can treat 6250 m3/h of biogas1. The objective was to evaluate the feasibility of biogas upgrading to distribution grid quality biomethane via different steps, including CO2/CH4 separation by polymer membranes. Fig. 1. Three-stage of membrane modules for CO2/CH4 separation connected to CO2 recovery unit. The innovative aspect is the final purification of CO2 from useless by-product to a food-grade quality gas for the food and beverage industry. The chemical purity of different process streams was analysed by a certified laboratory and was compared with the guidelines of the European Industrial Gases Association and the International Society of Beverage Technologists (EIGA /ISBT)2. With a purity of 96.3 vol%, methane respects the purity requirement for the household network. With a purity of 99.9 vol% the CO2 proves to be chemically and microbiologically suitable for food-grade applications, closing the CO2 loop of Biogas production. References 1 E. Esposito et al., World Acad. Sci. Eng. Technol. Int. Sci. Index, Chem. Mol. Eng., 2017, 4, 2153. 2 European Industrial Gases Association, 2008, 13.

The aim of this work was to develop innovative membranes able to separate carbon dioxide and eventually other undesirable compounds from raw biogas. Such membranes should be stable in an aggressive environment and resistant to humidity present in biogas. Therefore, three completely different types of membranes were investigated in this work, namely a supported ionic liquid membrane, a water condensing membrane [1] and a water-swollen thin film composite membrane [2]. This work deals mainly with a model mixture, but raw biogas taken from a sewage plant was used to complete the results of the work. Biogas is produced by anaerobic digestion of organic waste, and consists mainly of methane, carbon dioxide, and a small amount of corrosive gases (water vapor, hydrogen sulfide, ammonia, and mercaptanes). The methane present gives biogas the potential to become an alternative source to classical fuels. Unfortunately, the composition of biogas, typically 50-70 vol% methane and 30-50 vol% carbon dioxide, depends on its origin and on the season. Consequently, it is most commonly used in ancillary combined heat and power plants connected to biogas sources, such as farms or sewage plants, where a change in the composition of biogas is not a problem. For use as a fuel, the best source of biogas is that produced in sewage plants, because it has generally the highest methane content and it is easily accessible. Many different methods have been studied to purify biogas to engine-fuel quality. Water scrubbing, polyethylene glycol scrubbing, or molecular sieves are used to remove carbon dioxide. Pressure-swing absorption is also very common. Hydrogen sulfide, which is problematic because of its corrosive effect, is captured on impregnated active coal or by absorption. Membrane separation represents the latest approach to biogas purification. Polymeric membranes made of silicone rubber [3] and cellulose acetate have already been described [4]. Polyimide membranes [5,6] are very popular and polyether block amide membranes have also been tested [7]. Most of these membranes are effective for CH4/CO2 separation, but the majority cannot be used for biogas purification because they are damaged by aggressive gases. Nevertheless, they have already been applied for inert gases [8]. A promising novel class of gas separation membranes is represented by ionic liquid membranes. Their main advantages are high fluxes through the membranes and a very good selectivity [9]. Many different ionic liquids have been used to separate methane from carbon dioxide [10-11] and their effectiveness has been proved. However, ionic liquids appear to be too expensive for biogas treatment on an industrial scale. Recently we have proposed a new method of membrane separation, using a so-called "condensing-liquid membrane" [1]. This type of membrane has a significant advantage over the usual liquid membrane. Unwanted and toxic gases are removed from its continuously refreshed surface with condensed water to avoid contamination of the perm-selective membrane; furthermore, condensed water passing through the membrane ensures selectivity of the whole separation. The method is in fact based on a liquid (water in this case), condensing on a hydrophilic membrane as a result of the temperature difference of the membrane and the water-saturated biogas feed. The feed gas mixture is saturated by water vapor. The membrane has to be cool enough to make the liquid condense on the surface. Various operational conditions were followed and their effect on the separation of methane from unwanted gases was monitored. Another type of membrane based on a similar principle is the swollen hydrophilic thin film composite membrane. The condensing water on the membrane or on the swollen hydrophilic thin film composite membrane creates a separation barrier, which separates polar gasses (CO2, H2S) and CH4 from biogas on the basis of their higher solubility in water. In order to achieve spontaneous condensation of water, the membrane temperature must be below the dew point of the biogas feed. The contact of the membrane surface with water causes swelling of the polyamide thin film in the case of composite membranes. During the impregnation, the porous support is also saturated with water, but this water tends to evaporate during the experiment. Thus, the membrane has to be cooled down enough to make the liquid condense on its surface. A binary mixture was used to see the performance of the membrane treated by the new method. The upstream pressure was kept at 500kPa to achieve the highest possible permeation flux (within apparatus limits).. Preliminary tests revealed that the permeation fluxes of methane and carbon dioxide in raw biogas increase with increasing temperature. At a pressure difference of 400kPa on the reverse osmosis membrane (a swollen skin layer on a dry support) is possible to obtain from raw biogas even more than 95 vol. % of CH4 in retentate stream (Fig. 1.). Fig. 1. Dependence of CH4 and CO2 concentration in retentate during raw biogas separation with water condensing on reverse osmosis membrane. The two plateaus correspond to partial and complete wetting of the membrane surface, where the highest selectivity is reached in the completely wetted membrane. In conclusion we propose a new effective method for upgrading of raw biogas to the same quality as that of fuel standard natural gas, based on membrane separation processes. In our single stage method with a temperature below the dew point of the raw biogas feed, condensing water on the swollen hydrophilic thin film composite reverse osmosis membrane promotes the formation of a very thin selective water layer. The significant difference in solubility and permeability of methane and of raw biogas impurities (carbon dioxide, hydrogen sulfide) in and through the water layer results in an effective CO2/CH4 separation. The presented work represents an innovative approach to enable relatively inexpensive production of biomethane from sewage biogas. All our data were compared with the supported ionic liquid membrane and with literature data in Robeson plot. References 1.M. Poloncarzová, J. Vejrazka, V. Veselý, P. Izák, Angewandte Chemie Int. Ed., 50 (2011) 669-671. 2.M. Kárászová, J. Vejrazka, V. Veselý, K. Friess, A. Randová, V. Hejtmánek, L. Brabec, P. Izák, Sep. Pur., in press. 3.F. Wu, L. Li, X. Zhihong, T. Shujuan, Z. Zhibing, Chem. Eng. J. 2006, 117, 51-59. 4.H. M. Ettouney, G. Al-Enezi, S. E. M. Hamam, R. Hughest, Gas Sep. Purif. 1994, 8, 31-38. 5.J. Zhang, J. Lu,W. Liu, Q. Xue, Thin Solid Films 1999, 340, 106-109. 6.J. D. Wind, D. R. Paul, W. J. Koros, J. Membr. Sci. 2004, 228, 227-236. 7.S. Sridhar, R. Suryamurali, B. Smitha, T. Aminabhavi, Colloids Surf. A 2007, 297, 267-274. 8.F. F. Krull, C. Fritzmann, J. Membr. Sci. 2008, 325, 509-519. 9.A. Corti, D. Fiaschi, L. Lombardi, Energy 2004, 29, 2025-2043. 10.X. Hua, T. Jianbin, A. Blasig, S. Youqing, M. Radosz, J. Membr. Sci. 2006, 281, 130-138. 11.J. E. Bara, C. J. Gabriel, E. S. Hatakeyamaa, T. K. Carlisle, J. Membr. Sci. 2008, 321, 3-7. 12.P. Scovazzo, D. Havard, M. McShea, S. Mixon, D. Morgan, J. Membr. Sci. 2009, 327, 41-48.

The reduction of CO2 emission into the atmosphere as a result of human activity is one of the most important environmental challenges to face in the next decennia. Emission of CO2, related to the use of fossil fuels, is believed to be one of the main causes of global warming and climate change. In this scenario, the production of biomethane from organic waste, as a renewable energy source, is one of the most promising strategies to reduce fossil fuel consumption and greenhouse gas emission. Unfortunately, biogas upgrading still produces the greenhouse gas CO2 as a waste product. Therefore, this work presents a case study on biogas upgrading, aimed at the simultaneous purification of methane and CO2 via different steps, including CO2/methane separation by polymeric membranes. The original objective of the project was the biogas upgrading to distribution grid quality methane, but the innovative aspect of this case study is the further purification of the captured CO2, transforming it from a useless by-product to a pure gas with food-grade quality, suitable for commercial application in the food and beverage industry. The study was performed on a pilot plant constructed by Tecno Project Industriale Srl (TPI) Italy. This is a model of one of the largest biogas production and purification plants. The full-scale anaerobic digestion plant (Montello Spa, North Italy), has a digestive capacity of 400.000 ton of biomass/year and can treat 6.250 m3/hour of biogas from FORSU (organic fraction of solid urban waste). The entire upgrading process consists of a number of purifications steps: 1.Dehydration of the raw biogas by condensation. 2.Removal of trace impurities such as H2S via absorption. 3.Separation of CO2 and methane via a membrane separation process 4.Removal of trace impurities from CO2. The gas separation with polymeric membranes guarantees complete simultaneous removal of microorganisms. The chemical purity of the different process streams was analysed by a certified laboratory and was compared with the guidelines of the European Industrial Gases Association and the International Society of Beverage Technologists (EIGA/ISBT) for CO2 used in the food industry. The microbiological purity was compared with the limit values defined in the European Collaborative Action. With a purity of 96-99 vol%, the purified methane respects the legal requirements for the household network. At the same time, the CO2 reaches a purity of >98.1% before, and 99.9% after the final distillation process. According to the EIGA/ISBT guidelines, the CO2 proves to be chemically and microbiologically sufficiently pure to be suitable for food-grade applications.

Food production, preservation, distribution and organic food waste deposal, consume a considerable amount of energy and contribute to the total CO2 emission [1]. This associated to the use of traditional fossil fuel energies are the main cause of environmental pollution, greenhouse gas emissions and global warming. In this contest it's necessary to reduce the CO2 emission, making the food chain more sustainable trough the use of renewable energy. The biogas obtained from the anaerobic digestion of biomass based on the organic wastes of food is one of the most promising alternative energy. The biogas upgrading still produces the greenhouse gas CO2 as waste product. This work presents a case study, aimed at biogas upgrading with simultaneous purification of methane, CO2 and concomitant re-use of CO2 in the food industry. The objective was to evaluate the feasibility of biogas upgrading to distribution grid quality methane, via different purification steps, including CO2/CH4 separation by polymeric membranes. The innovative aspect is the further purification of CO2 from a useless by-product to a food-grade quality gas for commercial application in the food and beverage industry. The chemical purity of gas streams was compared with the guidelines of the European Industrial Gases Association and the International Society of Beverage Technologists (EIGA /ISBT) for CO2 used in the food industry. The microbiological purity was compared with the limit values defined in the European Collaborative Action [3,4]. The chemical and microbiological analysis of CO2 was proved to be suitable for food-grade applications. References: 1. I.E. Grossmann, Comput. Chem. Eng. 29 (2004) 29-39 2. P. Roy, J. Food Eng. 90 (2009) 1-10 3. P. Carrer et al., Science of the total environment, 270 (2001) 1-3. 4.EIGA_Spezifikationen