Membranes for CO2 capture - report on pilot plant tests

Although the main part of the world has now accepted the fact that the global climate change is due to human activities, we will not be able to switch gear and only go for “green energy” without fossil fuels for still many decades. One way of contributing to combat the climate change is hence to capture the CO2 from fossil fuel flue gases, and either find ways to utilize the CO2 or sequestrate it in aquifers or depleted oil fields, while we slowly develop a “green way of living”. Membranes will for sure represent one of the emerging technologies to be used for CO2 capture. Today there are a few pilot installations around the world using different types of membranes, to demonstrate and learn the best way of optimize such a capture plant – in Norway there are two of such kind; one at a cement factory in Brevik in South Norway and one at a test center at Tiller in Trondheim. At the cement plant the CO2 concentration in the flue gas can be close to 20 vol%, while at the Tiller plant there is a possibility to vary the CO2 concentration over a range of 8 – 12vol%. At the cement plant the flue gas contains quite a few unwanted components, while at Tiller the flue gas is relatively “clean”. The type of membrane installed at these two sites is hollow fiber modules where the support fiber is polysulfone (PSf) and the coated mebrane is a polyvinylamine (PVAm). The technique for applying the coating is not straight forward, and an efficient flue gas separation depends strongly on a successful coating procedure. Going from lab tests using a few cm2 up to several m2 of a commercial scale module is extremely challenging. The tests are being performed with 2 or 3 modules in parallel or series, but not yet as a complete two-stage process. Based on obtained results, a full scale process will be simulated. Preliminary results using only one stage at Tiller are already documenting an encouraging 58% CO2 in permeate from 7% CO2 in feed line. The PVAm membrane is based on facilitated transport of the CO2 through the membrane, which means that water needs to be handled in the separation process – this has again a large influence on the engineering design of the process and process operation parameters. The presentation will highlight and report some results and challenges from these two tests sites. Acknowledgement The GASSNOVA projects 229949 and 249036 are highly recognized for contributions from the CLIMIT-Demo program in the Norwegian Research Council, Air Products and Chemicals, Inc. (USA), Air Products AS (Norway), Alberta Funders (Canada), Statoil ASA, NORCEM (Heidelberg Cement), SINTEF Materials and Chemistry, DNV GL (The Netherlands)

Effect of water interactions on Polyvinylamine at different pH for Membrane gas separation

Polyvinylamine (PVAm) is a linear polyelectrolyte type of polymer which is water-soluble with highest contents of primary amine. It has been attractive in different fields such as: biomedical applications [1], encapsulation [2], oil recovery [3], and primarily it has extensively been used as a fixed-site–carrier polyvinylamine membrane for carbon dioxide separation and capture. A thin selective layer on polysulfone support for CO2 Separation membranes[4, 5] has been successfully used in composite flat sheet and hollow fiber membranes. The amine group plays the role as the carrier of the gas, increasing the transport performance of the membrane by chemical and physical forces. PVAm composite membrane in dry condition will separate according to solution-diffusion mechanism only. It was however documented by Kim et al. in 2004 [4] that by allowing the membrane to be exposed gas with high relative humidity, the separation performance increased exponentially[4-6]. Through these efforts, it is needed to develop a greater understanding of the relationships between the structure and the interfacial properties of PVAm – water surface. The degree of hydrophilicity manipulation of a given surface necessarily requires understanding the micro-scale principles that, in turn, control the macro-scale surface wetting behavior. See Fig. 1. Please click Additional Files below to see the full abstract

Two-stage membrane cascades for post-combustion CO2 capture using facilitated transport membranes: Importance on sequence of membrane types

The use of membrane module performance data obtained in industrially-relevant environment as the basis in process simulation can lead to a more realistic prediction of a CO2 capture system. In this work, we report the use of two classes of industrially validated membranes, i.e., hybrid facilitated transport membranes (HFTMs), which are characterized by higher permeances and lower selectivity, and the fixed site carrier (FSC) polyvinylamine (PVAm) membrane, which is characterized by lower permeance and higher selectivity relative to each other, to study the potential of these membranes in two-stage configurations for post-combustion CO2 capture applications. Two-stage cascades with and without recycle streams were simulated for a target CO2 recovery of >80% and purity of 80–99.5%. Recycle systems were found to contribute in reaching high purity targets of CO2 >90% at the fixed recovery of 90%. The positioning of membranes with different properties in different stages was found to influence the performance of the system significantly. Processes employing HFTMs in the first stage coupled with a PVAm membrane in the second stage performed best with the lowest total energy/membrane area requirement and recycle ratio for a target of 90% recovery and >90% purity of CO2. The process employing HFTMs in both stages outperformed all other cases in terms of membrane area required. The case employing PVAm membranes in both stages performs at its optimum only at a lower purity requirement (<90%). This study reveals the importance of using an optimized combination of membranes with different separation capabilities at different stages.publishedVersio

Enhanced CO2/H2 separation by GO and PVA-GO embedded PVAm nanocomposite membranes

Membrane technology for CO2/H2 separation, especially when using CO2-selective membranes to keep H2 on the high-pressure retentate side, has been considered promising and energy-efficient for further H2 transport and utilization. This work prepared and optimized a CO2-selective membrane based on polyvinylamine (PVAm) with embedded graphene oxide (GO) and grafted GO for CO2/H2 separation. The facilitated transport effect of PVAm enhances CO2 transport, while the GO-based 2D nanosheets bring in a barrier effect to compensate for the high H2 diffusivity. The GO-modified surface with higher CO2 affinity also provides additional CO2 sorption sites. The membranes’ chemical structure, thermal stability, and morphology were characterized. The effects of GO and PVA-GO in the PVAm matrix and optimal loadings of GO or PVA-GO were investigated. Introducing GO into PVAm significantly increased CO2 permeance with a slight increase in CO2/H2 selectivity. While by adding 0.5 wt% PVA-GO, CO2/H2 selectivity significantly increased from 10 to 22. The selective layer thickness also greatly affects CO2/H2 separation. By increasing the coating layer thickness to approx. 11 μm, the CO2/H2 selectivity substantially increased. The separation performances of the studied membrane are far above the current CO2/H2 upper bound.publishedVersio

Development and modification of glass membranes for aggreessive gas separations

Chlorine as a chemical is widespread in industry and found in a great variety of processes ranging from water purification to plastic production. In this thesis, a magnesium production factory was chosen as an example because it involved both chlorine - air separation and hydrogen –hydrogen chloride separation. Previously, various types of membrane materials have been tested out for their applicability in the chosen process. The materials previously tested either lacked sufficient membrane performance or sufficient membrane stability. As an attempt to improve both the membrane performance and stability, glass membranes are used in this thesis. Glass membranes are prepared from a borosilicate glass, via a phase separation followed by an acid leaching route. By choosing the appropriate phase separation temperature and acid to glass ratio, the membrane can be produced with an average pore diameter of 2 nm (or 4 nm). However, the 2 nm average pore size is still too large to separate gases with separation selectivities beyond the selectivities predicted from Knudsen diffusion theory. If the pores are narrowed, the selectivity may be raised while the flux hopefully is maintained. The narrowing of the pores was done by a silane coupling to the surface OH-groups on the glass. The silane coupling agent is of the dimethylacyl-chlorosilane type, where the length of the acyl chain varies from 1 carbon up to 18 carbons. Glass fibres are also tested in this work, which are produced without phase separation and their average pore size is smaller than the surface-modified glasses. To be able to compare the performance of the various membranes, permeance measurements are performed and these measurements are evaluated by the separation power (product of the selectivity and the permeability of the fastest permeating compound). Because of the harsh chlorine or hydrogen chloride environment, to which the membranes are exposed in this work, the membrane stability is at least as important s factor as the perm-selectivities. To evaluate this, both short- and longterm aggressive gas exposures are performed using a special designed durability chamber. From the combination of the perm-selectivities and the durability tests, the following conclusions may be drawn (evaluated at 30°C and 1 bar): Firstly, the pure glasses have a relatively poor stability (for chlorine gas) and the perm-selectivity is too low (for both separations in question). Secondly, the C8 and C12 modified glass membranes have a relatively satisfactory perm- selectivity for chlorine separation, but the durability in chlorine is poor. Thirdly, the long-chained C18 modified glass membrane has a relatively satisfactory perm-selectivity but a fair to low chlorine stability. If the C18 membrane is applied in the hydrogen chlorine separation the perm-selectivity is a bit low, but the stability is sufficient. However, this membrane is the best choice for a low temperature HCl selective membrane. Finally, to improve the chlorine stability, a perfluorinated version of a C1 modification is tried out. This membrane has excellent chlorine stability, and the perm-selectivity is fair. This membrane is the best choice for a chlorine selective membrane. The stability of the fibres is comparable to that found for the pure glass tubes. However, the permeabilities in the glass fibres are several orders of magnitude lower than for the glass tubes. The pore size in the fibre is so narrow that separation occurs according to a molecular sieving mechanism. The mounting of the fibres into a labsized module is tricky and the permeabilities are at the border of detection, so the results obtained here should only serve as trends

Screening Cellulose Spinning Parameters for Fabrication of Novel Carbon Hollow Fiber Membranes for Gas Separation

Novel carbon hollow fiber membranes (CHFMs) have been, for the first time, prepared from cellulose precursors directly spun with a cellulose/(1-ethyl-3-methylimidazolium acetate (EmimAc) + dimethyl sulfoxide (DMSO)) system. The spinning parameters such as air gap, dope and bore flow, bore fluid composition, and take-up speed are investigated by a factorial design method to screen hollow fiber precursors. All the precursors were carbonized using the same controlled protocol, and the prepared CHFMs show good performance that are above the Robeson upper bounds of CO2/CH4 and O2/N2. The best obtained CHFMs shows a CO2 permeability of 239 barrer and a CO2/CH4 selectivity of 186 from single gas permeation measurement. The CHFM shows attractive CO2/CH4 selectivities of 75 and 50 from 10% CO2/90% CH4 permeation tests at 25 °C with a feed pressure of 28 bar, and at 60 °C with 8 bar, respectively. Thus, the developed cellulose-based CHFMs show potential for gas separation.acceptedVersio

Carbon Molecular Sieve Membranes for Hydrogen Purification from a Steam Methane Reforming Process

Asymmetric carbon molecular sieve (CMS) membranes prepared from cellulose hollow fiber precursors were investigated for H2/CO2 separation in this work. The prepared carbon membrane shows excellent separation performance with H2 permeance of 111 GPU and an H2/CO2 selectivity of 36.9 at 10 bar and 110 °C dry mixed gas. This membrane demonstrates high stability under a humidified gas condition at 90 °C and the pressure of up to 14 bar. A two-stage carbon membrane system was evaluated to be techno-economically feasible to produce high-purity H2 (>99.5 vol%) by HYSYS simulation, and the minimum specific H2 purification cost of 0.012 $/Nm3 H2 produced was achieved under the optimal operating condition. Sensitivity analysis on the H2 loss and H2 purity indicates that such membrane is still less cost-effective to achieve ultrapure hydrogen (e.g., >99.8 vol%) unless the higher operating temperatures for carbon membrane systems are applied

Techno-economic evaluation of helium recovery from natural gas; A comparison between inorganic and polymeric membrane technology

Natural gas produced at high pressure (50-70 bar) is the only industrial source of helium (He). A membrane separation process may offer a more efficient production system with smaller footprint and lower operational cost than conventional cryogenic system. Inorganic membranes with high mechanical strength are known to exhibit good stability at high pressure. In this work, two inorganic membranes, porous silica and carbon molecular sieve (CMS) were studied by simulation for their applicability in the He recovery process and compared against a Matrimid polymeric membrane. An in-house developed membrane simulation model (Chembrane) interfaced with Aspen HYSYS was used to simulate the membrane area and energy requirement for the He separation process. He was separated directly from a mixture containing methane (CH4) and 1-5 mole% He in the feed stream, and natural gas containing 1-5 mole% of He in a mixture of CH4 and N2. These streams were considered at 70 bar pressure and 25 °C. Single and two-stage membrane separation processes with and without recycle stream were simulated to achieve 97 mole % purity and 90% recovery of He. The simulation results showed that all three membranes can achieve required purity and recovery in a two-stage separation process. However, a recycle is required while using Matrimid membrane which adds cost and complexity to the system. The highest net present value (NPV) for silica, CMS, and Matrimid membrane was $M 2.5, 2, and 1.75 respectively when 5% He is present in feed gas and 15 years of plant life is considered

Preparation of Carbon Molecular Sieve Membranes with Remarkable CO2/CH4 Selectivity for High-pressure Natural Gas Sweetening

Carbon hollow fiber membranes (CHFMs) were fabricated based on cellulose hollow fiber precursors spun from a cellulose/ionic liquid system. By a thermal treatment on the precursors using a preheating process before carbonization, the micropores of the prepared CHFMs were tightened and thus resulting in highly selective carbon molecular sieve (CMS) membranes. By increasing the drying temperature from RT to 140 ◦C, the cellulose hollow fiber precursors show a substantial shrinkage, which results in a reduction of average pore size of the derived CHFMs from 6 to 4.9 Å. Although the narrowed micropore size causes the decrease of gas diffusion coefficient, stronger resistance to the larger gas molecules, such as CH4, eventually results in an ultra-high CO2/ CH4 ideal selectivity of 917 tested at 2 bar for CHFM-140C due to the simultaneously enhanced diffusion and sorption selectivity. The CHFM-140C was further tested with a 10 mol%CO2/90 mol%CH4 mixed gas at 60 ◦C and feed pressure ranging from 10 to 50 bar. The obtained remarkable CO2/CH4 separation factor of 131 at 50 bar and good stability make these carbon membranes great potential candidates for CO2 removal from high- pressure natural gas.publishedVersio

Carbon membranes for oxygen enriched air – Part I: Synthesis, performance and preventive regeneration

Chemisorption of oxygen on the active sites of carbon layers limits the use of carbon membranes in air separation application. A novel online electrical regeneration method was applied to prevent the active sites on carbon surface to be reacting with O2 while the membrane was in operation. This method reduced the aging effect and the membrane showed relative stable performance with only 20% loss in O2 permeability and 28% increase in O2/N2 selectivity, over the period of 135 days using various feeds containing H2S, n-Hexane and CO2-CH4 gas. The carbon membranes reported here were produced at the pilot-scale facility by the carbonization of regenerated cellulose under optimized conditions to achieve good air separation properties. The permeation properties of the membranes were tested by single gas separation experiments at 5 bar feed pressure (50 mbar permeate) and temperature range 20–68 °C. It was observed that O2 permeability is increasing exponentially with increase in operating temperature without significant loss in the O2/N2 selectivity. The O2 permeability of 10 Barrer (1 Barrer = 2.736E − 09 m3(STP)m/m2 bar h) with O2/N2 selectivity of 19 was achieved at 68 °C. Thermal (80 °C), chemical (propylene) and online-electrical (10 V DC) regeneration approaches were studied to lessen the aging effect on carbon membranes