Mixed Gas Stream Research Articles

Novel hydrophobic hierarchical porous carbon from sewage sludge for the efficient capture of gaseous iodine

Finding an inexpensive and efficient porous adsorbent to capture the gaseous radioiodine generated during spent fuel reprocessing has been challenging. Herein, we present a design philosophy for waste control to develop porous carbon for gaseous iodine capture from sewage sludge waste. Among them, the novel in situ etching of polytetrafluoroethylene was employed to improve pore accessibility. The hazards of the conventional preparation of sludge-derived carbon using highly corrosive NaOH and HF solutions were overcome. Polytetrafluoroethylene etched porous carbon with large specific surface area (1103 m2/g), interconnected hierarchical porous structure, and excellent hydrophobicity (water contact angle 126.52°), providing efficient adsorption of gaseous iodine in hot (30–150 °C) and humid (50–96% relative humidity [RH]) environments. The iodine adsorption of hierarchical porous carbon was tested under static and dynamic conditions, and high records have been achieved. Notably, due to the structural advantage of hydrophobicity, a considerable dynamic adsorption capacity (1746.77 mg/g) was also maintained in a mixed iodine gas stream containing water vapor in a humid (50% RH) hot (75 °C) condition. This study is the first to use an in situ etching strategy for polytetrafluoroethylene, which opens a new avenue for converting sludge waste into low-cost porous carbon and provides an attractive option for capturing iodine in hot and humid environments.

Enhanced plasticization resistance of hollow fiber membranes for helium recovery from natural gas based on a novel thermally crosslinkable polyimide

Herein, we develop and investigate the performance of defect-free hollow fiber membranes (HFMs) based on a novel 6FDA-mPDA0.65-DABA0.3-TFMB0.05 copolyimide for helium separation from multi-component natural gas. The copolyimide is synthesized using a two-step condensation polymerization, and the hollow fiber membranes are fabricated using a dry-jet/wet-quench spinning approach. Thermal crosslinking of hollow fiber membranes is conducted to enhance plasticization resistance. The crosslinked membranes exhibit improved He selectivity (α(He/CH4) = 259) compared to the pristine hollow fiber membrane (α(He/CH4) = 210). Gas permeation tests are performed on the pristine and crosslinked hollow fiber membranes using pure-gas and mixed-gas at various pressures. The results demonstrate that the crosslinked membranes effectively resist plasticization even under high-pressure gas feeds containing CO2, light hydrocarbons, and heavy hydrocarbons. In contrast, the uncrosslinked membranes experience plasticization, dramatically decreasing selectivity. The findings provide valuable insights into the plasticization behavior of different impurity compounds in hollow fiber membranes and highlight the potential of thermal crosslinking as an effective strategy to improve the plasticization resistance of HFMs for He recovery. These defect-free and plasticization-resistant membranes hold promise for efficient He recovery from mixed-gas streams, offering a viable and energy-efficient alternative to traditional separation methods.

Microbial conversion of waste gases into single-cell protein

Climate change and food security are two of our most significant global challenges of our time. Conventional approaches for food production not only produce greenhouse gases but also require extensive land and water resources. An alternative is to use gas fermentation to convert greenhouse gases as feedstocks into microbial protein-rich biomass (single-cell protein). Aerobic methanotrophic (methane-oxidising) and hydrogenotrophic (hydrogen-oxidising) bacteria, which produce biomass using gases as their energy and carbon sources, are ideal candidates for single-cell protein production. However, multiple innovations are required for single-cell protein production to be economical and sustainable. Although current technologies rely on conversion of purified single gaseous substrates, the potential to directly use mixed gas streams from point sources remains reasonably unexplored. In addition, there is much potential to increase nutritional and commercial value of single-cell protein through synthetic biology. In this perspective, we discuss the principles, approaches, and outlook for gas fermentation technologies aiming to significantly reduce greenhouse gas emissions and enhance food security.

Effect of silver(I) ion reduction on the selectivity of olefins, paraffins, and aromatic compounds by gas chromatographic stationary phases consisting of silver(I) salts in ionic liquids

The olefin/paraffin selectivity offered by ionic liquid (IL) stationary phases can be enhanced through the addition of silver(I) ion, which is well-known to undergo selective complexation with unsaturated compounds. However, such stationary phases often suffer from the loss of chromatographic selectivity as silver(I) ion can be reduced to elemental silver. To maintain the separation performance of silver(I) ion/IL stationary phases, an understanding of factors and conditions that promote the reduction of silver(I) ion is needed. In this study, capillary gas chromatography columns featuring a stationary phase consisting of the 1-decyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([C10MIM+][NTf2−]) IL impregnated with [Ag+][NTf2−] were examined to investigate the effects of temperature, hydrogen content in exposure gas stream, and time of heating/exposure events on olefin selectivity. Retention factors of representative analytes, such as C6 olefins and paraffins as well as aromatic compounds, were measured after subjecting the columns to the aforementioned conditions, followed by an evaluation of selectivity factors over time. Selectivity factors of olefins and aromatic compounds were observed to decrease significantly when the stationary phases were heated to temperatures higher than 110°C as well as being subjected to mixed gas streams containing greater than 50 mol% of hydrogen. As constant column heating temperatures were applied under exposure gas mixtures containing hydrogen and nitrogen, a gradual decrease in analyte selectivity factors was observed under prolonged periods of time. However, application of a ternary gas mixture comprised of 25/50/25 mol% hydrogen/nitrogen/methane resulted in an increase in the 3-hexyne/cis-2-hexene selectivity when measured at 120°C for 60 h, due to a smaller decrease in the retention factor of 3-hexyne compared to cis-2-hexene.

Biomass generation and heterologous isoprenoid milking from engineered microalgae grown in anaerobic membrane bioreactor effluent

Wastewater (WW) treatment in anaerobic membrane bioreactors (AnMBR) is considered more sustainable than in aerobic reactors. However, outputs from AnMBR are a mixed methane and carbon dioxide gas stream as well as ammonium- (N) and phosphate- (P) containing waters. Using AnMBR outputs as inputs for photoautotrophic algal cultivation can strip the CO2 while removing N and P from effluent which feed algal biomass generation. Recent advances in algal engineering have generated strains that produce high-value side products concomitant with biomass, although only shown in heavily domesticated, lab-adapted strains. Here, it was investigated whether engineered Chlamydomonas reinhardtii could be grown directly in AnMBR effluent with CO2 concentrations found in AnMBR off-gas. The strain was found to proliferate over bacteria in the non-sterile effluent, consume N and P to levels that meet general discharge or reuse limits, and tolerate cultivation in modelled (extreme) outdoor environmental conditions prevalent along the central Red Sea coast. In addition to ∼2.4 g CDW L–1 biomass production in 96 h, a high-value heterologous sesquiterpene co-product could be obtained from ‘milking’ up to 837 µg L–1 culture in 96 h. This is the first demonstration of a combined bio-process that employs a heavily engineered algal strain to enhance the product generation potentials from AnMBR effluent treatment. This study shows it is possible to convert waste into value through use of engineered algae while also improving wastewater treatment economics through co-product generation.

Deconvoluting the Combined Effects of Gas Composition and Temperature on Olefin Selectivity for Separations Using Silver(I) Ions in Ionic Liquids.

Silver(I) ions have the propensity of undergoing reduction to form metallic silver within olefin/paraffin separation systems when they are subjected to hydrogen at elevated temperatures. Ionic liquids (ILs) are versatile solvents known for their low vapor pressure, high thermal stability, and structural tunability and have been shown to minimize hydrogen-induced reduction of silver(I) ions when employed as solvents. In the development of robust separation platforms that employ silver(I) ions, it is essential to deploy reliable approaches capable of measuring and assessing the factors that lower the overall separation performance. In this study, silver(I) ions dissolved in an imidazolium-based IL are subjected to mixed gas streams composed of hydrogen, nitrogen, and methane under varying temperatures. Using inverse gas chromatography, a total of 44 columns with stationary phases containing four different concentrations of silver(I) bis[(trifluoromethyl)sulfonyl]imide ([Ag+][NTf2 -]) dissolved in the 1-decyl-3-methylimidazolium ([C10MIM+]) [NTf2 -] IL were used to measure partition coefficients of olefins and paraffins, as well as aromatics, esters, and ketones. Upon exposing the stationary phases to mixed gases at elevated temperatures, olefin partitioning between the silver(I) ion pseudophase and the two other phases (i.e., carrier gas and IL stationary phase) was observed to decrease over time, while partitioning between the IL stationary phase and carrier gas remained unchanged. It was found that exposure gases composed of 5.0 to 85.0 mol % hydrogen and temperatures ranging from 95 to 130 °C resulted in a remarkable acceleration of silver(I) ion reduction and an approximate 36.4-61.3% decrease in olefin partitioning between the silver(I) ion pseudophase and both the carrier gas and IL stationary phase after 60 h. While binary mixtures of hydrogen and nitrogen resulted in a continuous decrease in silver(I) ion-olefin complexation capability, a ternary gas mixture produced varied silver(I) ion reduction kinetics.

Renewable biomethane production from biogas upgrading via membrane separation: Experimental analysis and multistep configuration design

In this work, we studied the upgrading of a mixed gas stream having a typical biogas composition by membrane gas separation with the aim of producing a purified biomethane stream. A polyetherimide/polyimide (PEI-PI) membrane module with an area of 1500 cm2 was used to evaluate the mass transport properties and the influence of water vapour and H2S on the separation performance. CO2 permeance was depleted by the presence of CH4 contrarily to this latter, whose permeation was enhanced by CO2. The permeances of both CO2 and CH4 were significantly affected by the presence of water vapour, showing a reduction of about 24–27% with respect to dry gas. Long-term analysis lasted about 650 days, showed an overall permeance variation of about 23% for N2 and 14% for CO2.The experimental permeance and selectivity values measured in wet conditions were used to simulate a multistep membrane system able to purify a “clean” biogas stream up to 98% of methane. It was found that the increasing number of steps from 3 to 7 allows a significant saving of membrane area, paired to an increment of CH4 recovery and CO2 purity.

Research and Performance Evaluation on Selective Absorption of H2S from Gas Mixtures by Using Secondary Alkanolamines

Exploring new solvents for efficient acid gas removal is one of the most attractive topics in industrial gas purification. Herein, using 2-tertiarybutylamino-2-ethoxyethanol as an absorbent in a packed column at atmospheric pressure was examined for selective absorption of H2S from mixed gas streams. In the present work, the acid gas load, H2S absorption selectivity, acid gas removal ratio, amine solution regeneration performance, and corrosion performance were investigated through evaluating experiments absorbing H2S and CO2 by using methyldiethanolamine and 2-tertiarybutylamino-2-ethoxyethanol. The experimental results illustrate that the H2S absorption selective factors were 3.88 and 15.81 by using 40% methyldiethanolamine and 40% 2-tertiarybutylamino-2-ethoxyethanol at 40 °C, respectively, showing that 2-tertiarybutylamino-2-ethoxyethanol is an efficient solvent for selective H2S removal, even better than methyldiethanolamine. Based on the consideration of cost, we added 5% TBEE to 35% MDEA to form a blended aqueous solvent. To our satisfaction, the blended amine solvent obtained a 99.79% H2S removal rate and a 22.68% CO2 co-absorption rate, while using the methyldiethanolamine alone achieved a 98.33% H2S removal rate and a 23.52% CO2 co-absorption rate; the blended solvent showed better H2S absorption efficiency and selectivity. Taken together, this work provides valuable information for a promising alkanolamine for acid gas removal, and the preliminary study has found that the aqueous blend of methyldiethanolamine and 2-tertiarybutylamino-2-ethoxyethanol is an efficient solvent for selective H2S removal, which not only extends the application field for sterically hindered amines, but also opens up new opportunities in blended solvent design.

Influences of SO2 contamination in long term supercritical CO2 treatment on the physical and structural characteristics of the Zululand Basin caprock and reservoir core samples

Understanding the mineral and microstructure changes in sandstone samples during supercritical CO2 gas treatment is an important aspect of geological CO2 sequestration. To gain insight into the effects of SO2 contamination in CO2 in South Africa, two core samples extracted from the reservoir lateral seal (ZC) and Cenomanian sandstone aquifer (ZG) within the Zululand Basin were studied. The samples were treated with CO2 and CO2/SO2 gas streams at typical reservoir temperature and pressures (10 MPa and 316 K, and 17,5 MPa and 346 K) under supercritical conditions. High pressure Parr reactors were used for storing the rock-gas-water mixtures for up to two months using a water:rock ratio of 23:1. Tests were conducted using pure CO2 and a 99% by weight (wt.) CO2 and 1% (wt.) SO2 mixed gas stream. Due to the prohibitive costs associated with CO2 purification, the knowledge of the consequences of key impurities relevant to geological sequestration is critical. Pre-and post- CO2/CO2–SO2 treatment characterisation was conducted using X-ray Diffraction (XRD) Analyses, Fourier transform infrared spectroscopy (FTIR), and low-pressure gas adsorption (LPGA). Varying mineral alterations were observed in the CO2 treated samples, mainly comprising of calcite, plagioclase and smectite dissolution and the precipitation of quartz, plagioclase, calcite and smectite. Dissolution pores and pore clogging were observed and increased microstructure heterogeneity was reported. Increases in the adsorption capacity, surface area and pore volume were observed in all samples. After treatment with CO2–SO2 gas mixture, increases in mineral reactivity were observed in the ZC sample along with gypsum precipitation, indicating potential improvement in the lateral seal's self-sealing capacity. The introduction of SO2 lead to the increase in quartz and plagioclase precipitation and increased dissolution of smectite and stilbite in the ZG sample. The study presents a novel investigation of the changes expected to take place during CO2 injection in sandstone basins.

Separation of isoprene from biologically-derived gas streams

ABSTRACT Renewable organic precursors, including olefinic compounds such as isoprene, have attracted interest from the polymer and pharmaceutical industries. Biologically-derived processes can generate these target compounds; however, their gaseous product streams are complex mixtures of condensable organic vapors (COVs), water vapor, carbon dioxide (CO2), and/or nitrogen (N2). Because COVs, CO2 and water vapor are known to alter polymer membranes, mixed gas separations data at ambient and elevated temperatures are limited. This study focused on two classes of polymer membranes, glassy [polyetherimide (Ultem®)] and a rubbery [polydimethylsiloxane (PDMS)] with results indicating that isoprene separation is possible in humidified gas environment (2–4 vol% water). Gas permeabilities of these membranes did not noticeably change in the presence of humidity; however, the selectivity of these membranes was significantly lower compared to their performance under dry conditions. The role of water vapor in gas transport was derived from the energy of activation of permeation (Ep) for PDMS and Ultem® from 30–80°C in humidified mixed gas streams. For both polymers, Ep data shows a slight decrease in selectivity with the other gases (hydrogen, N2, CO2, and methane) at elevated temperatures in the presence of water vapor. Thus, these COVs separations are feasible with polymer membranes in the presence of humidified gas streams, even in the case of glassy and rubbery membranes in series.

Selective carbon-based adsorbents for carbon dioxide capture from mixed gas streams and catalytic hydrogenation of CO2 into renewable energy source: A review

The rise in the temperature contributing to global warming is attributed to the increased human-generated greenhouse gas emission in the ambient atmosphere. In this paper, firstly, a comprehensive overview of the capture technologies is presented, highlighting the post-combustion capture technology as one of the promising CO2 mitigation strategies. The performance of activated carbon, amine-functionalized and metal-oxide impregnated materials prepared from renewable precursors as the acknowledged adsorbents are well assessed and presented systematically. Conversion of CO2 is proposed as a sustainable practice to substitute for dwindling fossil fuels. A strong emphasis is put on the conversion of CO2 into value-added chemicals like higher hydrocarbons via series of catalytic-hydrogenation reactions. The specific aim of this study is to assist researchers by providing a holistic overview of different aspects of carbon-based adsorbents for post-combustion capture instead of the current-state-of art technology and enhancing the pathways for CO2 valorization to clean and renewable end-products.

Easing of frequency gaps in carbon monoxide formation with argon diluents in carbon dioxide dielectric barrier discharge

The transformation of carbon dioxide (CO2) to carbon monoxide (CO) employing atmospheric pressure dielectric barrier discharge (DBD) cold plasma in Ar mixed CO2 systems is reported. This work is aimed to re-utilize CO2 in the form of CO, which is well accepted as industrial gas and also has many manufacturing applications. Under the study, Ar mixed CO2 gas stream is used to investigate the effective conditions for achieving low to high CO yields using a coaxial cylindrical single dielectric (SD) (consisting of one Pyrex and one bare copper surfaces) DBD reactor. The CO as DBD outlet product and leftover CO2 are analyzed online with gas chromatograph-flame ionization detector after their successive separation with a suitable GC column and methanation using Ni-catalyzed methaniser. The experiments are carried out at a fixed gas flow of 110 ml/min (translating gas residence time (GRT) = 3.2 s) with applied electric field and working frequency variations. The resulting contour plots (generated using electric fields, frequency and CO yields) indicate that the mixing of 90% Ar in CO2 system exhibits substantial reduction of frequency gaps in CO formation. Nevertheless, the frequency gaps are more prominent in low/negligible Ar mixed CO2 systems. It is also noticed that the lower electric fields are adequate to generate CO in Ar mixed CO2 systems in contrast to pristine CO2 system. Both Ar mixing as well as electric field inputs are responsible to easy/lessen the frequency gaps.

In Situ Investigation of CO2 Separation in Macrocyclic and Porous Ionic Liquids

With the continued rise in atmospheric CO2 levels and the potential impact on climate, carbon capture and storage has gained prominence as a potential technological solution to reduce CO2 emissions, resulting in increased interest in advanced materials to facilitate the removal of CO2 from energy-related emissions. While a number of approaches have been explored to separate CO2 from mixed streams, ionic liquids are promising materials due to their negligible vapor pressure, high thermal stability, and the ability to tune physicochemical properties such as CO2 solubility. The incorporation of free volume into ionic liquids through appropriate development of bulky cation/anion pairs or through the creation of porous ionic liquids can impact both gas transport and solubility. Macrocyclic ionic liquids where the bulky cation consists of a nitrogen heterocycle connected by ether linkages can selectively remove CO2 from mixed gas streams and offer a potential avenue for CO2 capture. Porous ionic liquids are emerging materials that combine the attributes of porous materials within a nonvolatile liquid matrix. Permanent porosity is incorporated into the ionic liquid by adding a framework material (zeolitic imidazolate framework) where the cations and anions are too large to diffuse into the host. We investigated the selective absorption of CO2 in both macrocyclic and porous ionic liquids and examined the effect of porosity on CO2 sorption capacity and gas transport. Relevant physical and chemical properties of these unique materials such as solubility, density, viscosity and structure were measured. In addition, analysis of the vibrational modes of both the ionic liquid and the CO2 through in situ attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) measurements was used to better understand the mechanisms of CO2 interaction with the ionic liquids and the impact on solubility and transport. Moreover, we find that certain of these ionic liquids exhibit a unique binding and release of CO2 which could open new avenues for CO2 capture and storage.

Novel Porous Organic Polymer for the Concurrent and Selective Removal of Hydrogen Sulfide and Carbon Dioxide from Natural Gas Streams.

Natural gas sweetening currently requires multistep, complex separation processes to remove the acid gas contaminants, carbon dioxide and hydrogen sulfide. In addition to being widely recognized as energy inefficient and cost-intensive, the effectiveness of this conventional process also suffers considerably because of limitations of the sorbent materials it employs. Herein, we report a new porous organic polymer, termed KFUPM-5, that is demonstrated to be effective in the concurrent separation of both hydrogen sulfide and carbon dioxide from a mixed gas stream at ambient conditions. To understand the ability of KFUPM-5 to selectively capture these gas molecules, we performed both pure-component thermodynamic and mixed gas kinetic adsorption studies and correlated these results with theoretical molecular simulations. Our results show that the underlying polar backbone of KFUPM-5 provides favorable adsorption sites for the selective capture of these gas molecules. The outcome of this work lends credence to the prospect that, for the first time, porous organic polymers can serve as sorbents for industrial natural gas sweetening processes.

Selectively capturing carbon dioxide from mixed gas streams using a new microporous organic copolymer

Abstract A novel crosslinked microporous polymer was synthesized via a modified acid-catalyzed Friedel-Crafts polycondensation reaction. By virtue of the rigid and polarizable monomers (aniline and pyrrole), the polymer, termed KFUPM-4, was proven permanently porous (Brunauer-Emmett-Teller surface area = 650 m2 g−1) with a high CO2 capacity (33 cm3 g−1 at 760 Torr and 298 K) and selectivity (CO2:CH4 selectivity = 15:1 at 298 K). As a result of these properties, KFUPM-4 was subjected to breakthrough measurements, whereby the material's ability to selectively capture CO2 under dynamic conditions from both dry and wet mixed gas streams was clearly demonstrated.

An overview on trace CO2 removal by advanced physisorbent materials

This review paper focuses on various gas processing technologies and materials that efficiently capture trace levels of carbon dioxide (CO2). Fundamental separation mechanisms such as absorption, adsorption, and distillation technology are presented. Liquid amine-based carbon capture (C-capture) technologies have been in existence for over half a century, however, liquid amine capture relies upon chemical reactions and is energy-intensive. Liquid amines are thus not economically viable for broad deployment and offer little room for innovation. Innovative C-capture technologies must improve both the environmental footprint and cost-effectiveness. As a promising alternative, physisorbents have many advantages including considerably lower regeneration energy. Generally, existing classes of physisorbent materials, such as metal-organic frameworks (MOFs) and zeolites are selective toward C-capture. However, their selectivity is currently not high enough to remove trace levels (e.g., ~1%) of CO2 from various natural gas process streams. This review summarizes the current advancements in physisorbent materials for CO2 capture. Here, key performance parameters needed to select the most suitable candidate are highlighted. Furthermore, this review discusses the scope for the development of better performing CO2 selective physisorbents from both environmental and economic perspectives. In addition, hybrid ultra microporous materials (HUMs), characterized mainly by ultra-micro pores (<0.7 nm), are discussed in reference to C-capture. Various characteristics of HUMs result in high selectivity and applicability in difficult separations such as the gas sweetening and C-capture from complex humid mixed gas streams.

Adsorbents and adsorption models for capture of Kr and Xe gas mixtures in fixed-bed columns

Off-gases produced during the reprocessing of used nuclear fuel (UNF) include 129I2, 3HHO, 14CO2, 85Kr, and 135Xe, which are volatilized out into the off-gas. In order to meet regulatory requirements for reprocessing plant emissions, these gases must be captured and removed from the off-gas stream prior to off-gas emission. Of particular interest are the noble gases, Kr and Xe, which can be fairly difficult to remove from the off-gas due to their low chemical reactivity. Thus, this work is focused on utilizing engineered adsorbents, AgZ-PAN and HZ-PAN, to capture Kr and Xe from a mixed-gas stream at relatively low temperatures (191–295 K) and various flow rates (50–2000 mL/min). Isothermal data for Kr and Xe on each adsorbent are analyzed to produce the Langmuir parameters needed to model the mixture adsorption capacities at relevant temperatures using the Extended Langmuir model. Those parameters are then incorporated into a fixed-bed adsorption model developed in this work using the Mulitphysics Object-Oriented Simulation Environment (MOOSE). That model is used to simulate breakthrough times for Kr and Xe in packed columns of AgZ-PAN and HZ-PAN, ranging in length from 6 to 20 in., at relevant temperatures and flow rates. Breakthrough times varied from nearly instantaneous for Kr in AgZ-PAN to 30 h for Xe in HZ-PAN. After the developed model was validated by comparisons with experimental breakthrough data, the model framework was used to simulate the performance of multiple fixed-bed columns connected in series.

Incorporation of an ionic liquid into a midblock-sulfonated multiblock polymer for CO2 capture

In the present work, hybrid block ionomer/ionic liquid (IL) membranes containing up to 40 wt% IL are prepared by incorporating 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) into a midblock-sulfonated pentablock polymer (Nexar) that behaves as a thermoplastic elastomer. Various analytical techniques, including thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR) spectroscopy, small-angle X-ray scattering (SAXS), and water sorption have been employed to characterize the resultant membrane materials. Single- and mixed-gas permeation tests have been performed at different relative humidity conditions to evaluate membrane gas-separation performance and interrogate the molecular transport of CO2 through these membranes. Addition of IL to Nexar systematically enhances CO2 permeability through membranes in the dry state. Introduction of water vapor into the gas feed further promotes CO2 transport, yielding a maximum permeability of 194 Barrers and a maximum CO2/N2 selectivity of 128 under different test conditions. These results confirm that humidified Nexar/IL hybrid membranes constitute promising candidates for the selective removal, and subsequent capture, of CO2 from mixed gas streams to reduce the environmental contamination largely responsible for global climate change.

Studies on the utilization of post-distillation liquid from Solvay process to carbon dioxide capture and storage

In this work, a method of precipitated calcium carbonate production from the post-distillation liquid created in the Solvay process and waste carbon dioxide was proposed and investigated. Precipitation was carried out in a model solution of calcium chloride containing ammonia at various molar ratios in relation to Ca2+ ions, while gaseous carbon dioxide was supplied to the reactor as a pure gas or as a mixture with air. It was assumed that the reaction was completed when the pH of the reaction mixture reached the value of 7. To characterize precipitated calcium carbonate particles, its size and crystalline form were determined. It was possible to utilize above 80% of calcium ions from a model post-distillation liquid and above 80% of carbon dioxide from a mixed air-CO2 gas stream using the one-stage precipitation process since the conditions of precipitation were controlled. Calcium carbonate in vaterite form produced in this process can be also a valuable product.

Improved gas transport properties of cellulose acetate via sub-Tg acid-catalyzed silanation

Cellulose acetate (CA) remains one of the few polymers to be commercialized for use in industrial CO2/CH4 gas separations, despite the fact that other polymeric materials, such as polymers of intrinsic microporosity and thermally rearranged polymers, have demonstrated higher gas separation performance. The availability of this renewable polymer, in addition to its high inherent selectivities and facile processing, make CA a preferred candidate for industrial applications. This study describes a modification for fabricating improved CA membranes through acid-catalyzed silanation of dense CA films. Processing advantages include using neat CA films and a reaction temperature well below the glass transition temperature of CA. In addition, the resulting modified CA membranes exhibit substantially higher gas permeabilities for both pure and mixed gas feeds. In comparing neat CA to modified CA, CO2 permeability increases from 4.6 to 24.5 Barrer in 100 psi pure gas feeds and from 2.7 to 12.7 Barrer in 800 psi mixed gas feeds. The crosslinking present in the modified CA also increases plasticization resistance in high pressure mixed gas streams, which causes modified CA's CO2/CH4 selectivity to increase from 25.3 at 200 psi to 26.1 at 800 psi, whereas neat CA's CO2/CH4 selectivity markedly drops from 35.9 at 200 psi to 28.8 at 800 psi. TGA and gel fractions, as well as FTIR NMR and SEM/EDS, confirm that this acid-catalyzed silanation reaction both silanates and crosslinks the membrane.