CO2 Separation Process Research Articles

Perovskite oxide based composite hollow fiber membrane for CO2 transport

Membrane technologies have been widely investigated for CO2 separation, especially inorganic membranes which could overcome the barrier of low melting point, and then been applied for combustion activities. Compared with molecular sieving membranes (MSMs), the mechanism during CO2 separation process on electrolyte membranes (EMs) is more complicated. Mixed ionic and electronic conductors, such as perovskite oxides, has been proved with superior activity than oxygen ion conductors because of the additional surface reaction path. To further demonstrate the applicability of perovskite oxides contained membrane for CO2 separation, in this work, CO2 transport via La0.6Sr0.4Co0.2Fe0.8O3-δ and carbonates composite membrane with hollow fiber microstructure was thoroughly investigated under various gas flow directions. This membrane presents the best permeability when CO2+N2 (feed gas) flows at shell side and He (sweep gas) flows at tube side in parallel model. In addition, it also presents excellent thermal shock resistance after six times rising and cooling operation with almost no performance degradation.

Hydrogen Production from Natural Gas Using an Iron‐Based Chemical Looping Technology: Process Modeling, Heat Integration, and Exergy Analysis

H2 production under a carbon‐constrained scenario attracts intensive research focus. Currently, the state‐of‐art H2 production technology with CO2 capture is the steam‐methane reforming (SMR) process with downstream CO2 sequestration. However, the need for combusting additional natural gas to supplement the endothermic heat for the reformer and the complexity of downstream H2 purification and CO2 separation processes make SMR less efficient and economical. As an alternative, an iron‐based three‐reactor chemical looping technology to convert natural gas to H2 (NTH) with 90% CO2 capture was designed and the process modeling was presented in previous publications. This work continues the study by focusing on the heat integration and exergy analysis of the process using ASPEN PLUS and ASPEN Energy Analyzer as simulation tools. Parametric studies of varying operating parameters are conducted, and the heat exchanger network of the NTH process is designed. Finally, the performance of the NTH process is compared with SMR, showing a 4.3% (percentage point) increase in the exergy efficiency.

IR Monitoring of Absorbent Composition and Degradation During Pilot Plant Operation

The monitoring of the absorbent during the operation of CO2 separation processes is a necessary and challenging task. The most common absorbent used is an aqueous amine solution. Traditional approa...

Molecular simulations of carbon-based materials for selected CO2 separation and water treatment processes

Carbon-based materials (e.g., activated carbons, carbon nanotubes, membranes) made of graphene or graphene-oxide structures are attractive and versatile materials. They are vital for a wide range of industries, due to their unique structural and chemical properties such as low density, high porosity, large surface area and stable mechanical properties, among others. The ability to experimentally control adsorbent structural features at the molecular level and recent progress made on modeling realistic carbon-structures and fluids force fields, enable building predictive models from molecular simulations for novel applications. This contribution is devoted to some recent advances and limitations faced in molecular simulation on carbonaceous materials, from building the model of the materials to their application in capturing and separating fluids by adsorption. An overview of recent examples on carbon dioxide capture and separation, and removal of compounds in water mixtures are presented as showcases to highlight the role of molecular simulations in these sustainable processes. Remaining challenges, perspectives and future directions are also provided.

Effect of Take-up Speed on the Fabrication of Cellulose Acetate Hollow Fibre Membrane in CO2 Separation from N2 and CH4

Over the past decades, hollow fibre membranes (HFMs) have attracted much interest of the researchers due to their extensive industrial usage in CO2 separation processes. In the current study, we have reported the effect of take-up speed on the fabrication of cellulose acetate (CA) HFMs in gas separation. The morphology of the resultant HFMs was examined by using field emission scanning electron microscopy (FESEM). The gas permeation results obtained in this work revealed that, when take-up speed increased from free fall to 12.2 m/min, CO2, N2 and CH4 permeances of the resultant CA HFM were reduced 55.68%, 87.25% and 82.00%, respectively. Meanwhile, gas pair selectivities were increased 146.18% and 247.76% respectively. These results were mainly due to the increment of polymer orientation and chain packing which suppressed the macro-voids in the HFMs and thus, the gas pair selectivities were improved. Furthermore, it was found that CA HFM spun at take-up speed of 12.2 m/min showed highest CO2/CH4 and CO2/N2 ideal selectivities of 3.9 and 3.6, respectively.

Adsorption breakthrough and cycling stability of carbon dioxide separation from CO2/N2/H2O mixture under ambient conditions using 13X and Mg-MOF-74

Carbon dioxide and storage is an efficient method to reduce the emitted CO2 from the burning of fossil fuels. Zeolite-based materials are conventional adsorbents used to adsorb some gasses involving carbon dioxide. Mg-MOF-74 is an eminent reticular material among adsorbents due to its good CO2 capacity at low pressures (10–20 kPa). In this study, an experimentally validated model is used to report the H2O effect on CO2 separation using 13X and Mg-MOF-74 under ambient conditions. A computational model has been developed using ANSYS Fluent program linked by user-define-function (written in C). The adsorption breakthrough results show that a humid CO2/N2 mixture, under 300 K, 86% RH, 101.3 kPa, could slightly reduce the CO2 adsorption capacity by about 0.05% and 6% for 13X and Mg-MOF-74, respectively (at CO2 adsorption breakthrough saturation). Regardless of these reductions, Mg-MOF-74 has better adsorption capacity, even under humid ambient conditions, by about 5.77 mmol/g in a comparison to 2.27 mmol/g for 13X, respectively.Cycling stability over more than 90 cycles is also simulated; and shows that, a dehydration process is recommended to be carried out before the CO2 separation process for efficient energy consumption and sustainable adsorbents. The total recyclable amounts of adsorbed CO2 are about 0.94 and 3.07 mmol/g for 13X and Mg-MOF-74, respectively, under 101.3 kPa adsorption, 2 kPa desorption, 86% relative humidity, and 298 K. The cyclic CO2 separation is found to be a robust method more than the breakthrough separation to evaluate the real adsorption capacities.

Performance of Mixed Matrix Membranes Containing Porous Two-Dimensional (2D) and Three-Dimensional (3D) Fillers for CO2 Separation: A Review

Application of conventional polymeric membranes in CO2 separation processes are limited by the existing trade-off between permeability and selectivity represented by the renowned upper bound. Addition of porous nanofillers in polymeric membranes is a promising approach to transcend the upper bound, owing to their superior separation capabilities. Porous nanofillers entice increased attention over nonporous counterparts due to their inherent CO2 uptake capacities and secondary transport pathways when added to polymer matrices. Infinite possibilities of tuning the porous architecture of these nanofillers also facilitate simultaneous enhancement of permeability, selectivity and stability features of the membrane conveniently heading in the direction towards industrial realization. This review focuses on presenting a complete synopsis of inherent capacities of several porous nanofillers, like metal organic frameworks (MOFs), Zeolites, and porous organic frameworks (POFs) and the effects on their addition to polymeric membranes. Gas permeation performances of select hybrids with these three-dimensional (3D) fillers and porous nanosheets have been summarized and discussed with respect to each type. Consequently, the benefits and shortcomings of each class of materials have been outlined and future research directions concerning the hybrids with 3D fillers have been suggested.

Thermodynamic analysis of polygeneration systems based on catalytic hydropyrolysis for the production of bio-oil and fuels

Novel polygeneration concepts based on catalytic hydropyrolysis and hydrodeoxygenation are presented and compared via process simulation and thermodynamic analysis. These systems process and convert biomass into high-quality bio-oil and fuels such as synthetic natural gas (SNG), molecular hydrogen (H2) and methanol (MeOH). Twelve system layouts were evaluated and compared with regards to their energy demands and performances. Detailed thermodynamic models were developed, considering the different technological alternatives for the valorisation of bio-char, removal of carbon dioxide, fuel upgrading and water electrolysis, as well as the opportunities for energy integration. The results show that the standard system, which produces only bio-oil, reaches an energy efficiency of 61% (LHV). This value can be increased by 7–28%-points when co-producing SNG, 10–21%-points when producing H2, and 10–19%-points when producing MeOH. The highest values are achieved by co-production of SNG as light hydrocarbons are produced in the hydropyrolysis, and limited processing is therefore required to reach the desired product quality. High system efficiencies are possible mainly because of the high efficiency of the core hydropyrolysis process. Carbon conversion efficiencies are highest when generating SNG or MeOH and reach a maximum when electrolysis and char gasification are implemented (98% and 95%). The performance of these polygeneration systems is strongly impacted by the type of CO2-separation process and electrolyser - these processes have a strong influence on the power and heating demands, as well as on the potential energy savings and waste heat valorisation.

Modeling Amorphous Microporous Polymers for CO2 Capture and Separations.

This review concentrates on the advances of atomistic molecular simulations to design and evaluate amorphous microporous polymeric materials for CO2 capture and separations. A description of atomistic molecular simulations is provided, including simulation techniques, structural generation approaches, relaxation and equilibration methodologies, and considerations needed for validation of simulated samples. The review provides general guidelines and a comprehensive update of the recent literature (since 2007) to promote the acceleration of the discovery and screening of amorphous microporous polymers for CO2 capture and separation processes.

Molten Carbonate Fuel Cells for Retrofitting Postcombustion CO2 Capture in Coal and Natural Gas Power Plants

The state-of-the-art conventional technology for postcombustion capture of CO2 from fossil-fueled power plants is based on chemical solvents, which requires substantial energy consumption for regeneration. A promising alternative, available in the near future, is the application of molten carbonate fuel cells (MCFC) for CO2 separation from postcombustion flue gases. Previous studies related to this technology showed both high efficiency and high carbon capture rates, especially when the fuel cell is thermally integrated in the flue gas path of a natural gas-fired combined cycle or an integrated gasification combined cycle plant. This work compares the application of MCFC-based CO2 separation process to pulverized coal fired steam cycles (PCC) and natural gas combined cycles (NGCC) as a “retrofit” to the original power plant. Mass and energy balances are calculated through detailed models for both power plants, with fuel cell behavior simulated using a 0D model calibrated against manufacturers' specifications and based on experimental measurements, specifically carried out to support this study. The resulting analysis includes a comparison of the energy efficiency and CO2 separation efficiency as well as an economic comparison of the cost of CO2 avoided (CCA) under several economic scenarios. The proposed configurations reveal promising performance, exhibiting very competitive efficiency and economic metrics in comparison with conventional CO2 capture technologies. Application as a MCFC retrofit yields a very limited (<3%) decrease in efficiency for both power plants (PCC and NGCC), a strong reduction (>80%) in CO2 emission and a competitive cost for CO2 avoided (25–40 €/ton).

Synthesis and characterization of poly(amide-imide)s derived from a new ortho-functional unsymmetrical dicarboxylic acid

Herein, we report a new diacid monomer containing an imide ring and a methoxy pendant group, 3-trimellitimido-4-methoxybenzoic acid TMBA, for the preparation of poly(amide-imide)s.

Numerical Investigations of CO2 Sorption and Recovery Process from Wet Flue Gas by Using K2CO3/Al2O3 in a Fixed Bed

Fixed-bed sorption technology is a promising option for separating CO2 from flue gas, and potassium-based Al2O3 (K2CO3/Al2O3) is a potential sorbent in the presence of H2O. This paper studies the stepwise reaction mechanism of CO2/H2O sorption on K2CO3/Al2O3, and the expressions of sorption equilibrium and kinetics are proposed and verified by experimental data. A comprehensive set of mathematical models of separation and recovery CO2 from wet flue gas in a fixed bed of K2CO3/Al2O3 is established. The CO2 separation and recovery process from wet flue gas in the fixed bed are numerically studied. Detailed results of H2O/CO2 sorption and desorption in the fixed bed during pressure/vacuum swing cycles are revealed, and the optimum operating parameters are suggested. Results show that carbon dioxide recovery can be further enhanced using a vacuum temperature swing adsorption (VTSA) process or by adding a pre-wetting step before sorption process.

Energy Consumption and Exergy Analysis of MEA-Based and Hydrate-Based CO2 Separation

Carbon capture and storage (CCS) is regarded as the most efficient approach in handling the global warming crisis. MEA-based CO2 capture is a well-developed chemical absorption method with a long period of industrial application. A novel hydrate-based gas separation (HBGS) method, with a wide range of advantages, has recently received special attention from researchers. In this study, two different CO2 separation processes were simulated utilizing Aspen Plus software. The feasibility of both processes was validated, and the process energy consumption and exergy loss were also compared at the same flue gas condition. Some efforts have also been made to investigate the effects of different operation parameters on the process energy efficiency. Results show that the first law efficiency of the MEA-based CO2 separation system is 88.19% and the second law efficiency of the system is 38.32%, while the corresponding values of the hydrate-based separation system are 74.15% and 38.85%, respectively. Cooling of the...

Characterization of functionalized ionic liquids for a new quasi-isothermal chemical biogas upgrading process

Abstract In this work, a new CO2 separation process using ionic liquid solvents is proposed. The approach focusses not only on improving the applied solvents or their CO2 absorption chemistry, but also on adapting the separation process itself for exploiting the advantages of ionic liquids. This is achieved by adjusting the operating temperatures of the absorption and the regeneration columns of the upgrading process to the same moderate temperature level and operating the desorption of CO2 under moderate vacuum instead of applying high grade heat from an external source. In this article, the proposed CO2 separation process is described in detail and the results of the development and characterization of appropriate ionic liquid solvents for applying the process to biogas upgrading are presented. The characterization section includes measurements on thermal and chemical stability, physical and chemical CO2 solubility, physical CH4 solubility, effective and intrinsic absorption kinetics, heat of reaction and various additional material properties of ionic liquid solvents. Physical gas solubility is examined for Room Temperature Ionic Liquids with [NTf2], [Tf], [DCA] and [TCM] anions with imidazolium cations in a wide temperature range of 25–125 °C. The applied short chain [Tf] and [TCM] based RTIL feature a high selectivity concerning physical solubility of CO2 and CH4. Furthermore, the applied chemically functionalized IL (CFIL) show almost the double chemical CO2 loading capacity than conventional amines. The measurements on absorption kinetics show that the absorption of CO2 in the applied IL solvent in the desired temperature range is about as fast as when aqueous DEA is applied. Based on the derived experimental results, an energetic evaluation of the process is carried out indicating that the proposed process enables considerable potentials for energetic savings, forming the basis for being close to economic feasibility within relatively short payback periods.

Cooperative CO2 Absorption Isotherms from a Bifunctional Guanidine and Bifunctional Alcohol.

Designing new liquids for CO2 absorption is a challenge in CO2 removal. Here, achieving low regeneration energies while keeping high selectivity and large capacity are current challenges. Recent cooperative metal–organic frameworks have shown the potential to address many of these challenges. However, many absorbent systems and designs rely on liquid capture agents. We present herein a liquid absorption system which exhibits cooperative CO2 absorption isotherms. Upon introduction, CO2 uptake is initially suppressed, followed by an abrupt increase in absorption. The liquid consists of a bifunctional guanidine and bifunctional alcohol, which, when dissolved in bis(2-methoxyethyl) ether, forms a secondary viscous phase within seconds in response to increases in CO2. The precipitation of this second viscous phase drives CO2 absorption from the gas phase. The isotherm of the bifunctional system differs starkly from the analogous monofunctional system, which exhibits limited CO2 uptake across the same pressure range. In our system, CO2 absorption is strongly solvent dependent. In DMSO, both systems exhibit hyperbolic isotherms and no precipitation occurs. Subsequent 1H NMR experiments confirmed the formation of distinct alkylcarbonate species having either one or two molecules of CO2 bound. The solvent and structure relationships derived from these results can be used to tailor new liquid absorption systems to the conditions of a given CO2 separation process.

Crystal morphology-based kinetic study of carbon dioxide-hydrogen-tetra-n-butyl ammonium bromide hydrates formation in a static system

Hydrate based CO2 separation process is affected by many factors which mainly includes additive concentration, gas-liquid volume ratio and operating conditions. The most of the investigations on the CO2 hydrate-based separation in the previous work were carried out around the kinetics and thermodynamics of the hydrate formation along with the CO2 separation efficiency. However, few studies focus on the morphology of hydrate though the difference of the morphologies directly leads to the difference of the CO2 separation efficiency. In this work, the morphology along with the kinetics of the hydrate-based CO2 separation from CO2/H2 (40%/60%) is carried out in the presence of tetra-n-butyl ammonium bromide (TBAB) of 0.29 mol%. The results indicate, firstly, TBAB hydrate formation and TBAB/gas mixture hydrate formation were two independent processes. Secondly, the different operating conditions resulted in different hydrate morphologies. Thirdly, the consumption of CO2 in low pressure (<2.5 MPa) was controlled by the driving force, while that was controlled by the formed hydrate layer in the gas-liquid interface in the relatively high pressure especially for the initial pressure ≥4.5 MPa.

Post combustion CO2 capture in power plant using low temperature steam upgraded by double absorption heat transformer

In CO2 capture retrofit unit of existing coal-fired power plants, energy level mismatch between extraction steam from turbines and CO2 regeneration process always results in large exergy destruction and low thermal efficiency. Thus, a new CO2 capture system driven by double absorption heat transformer is proposed. Through the absorption heat transformer, low-temperature steam is upgraded into a higher energy level to match the temperature of CO2 regeneration. Also, flue gas heat is partly recovered to preheat the circulating water from CO2 capture process to further decrease system energy penalty. Aspen Plus 11.0 is used to simulate the system and parameters of key processes are validated by experimental values. It is shown that with 90% CO2 capture, the thermal efficiency of the power plant with proposed CO2 capture system is enhanced by 1.25 percentage points compared with traditional method. And the efficiency enhancement of the proposed system has a trend of increase first and then decrease with CO2 capture rate growth. For a 350MW coal-fired power plant, the optimum CO2 capture rate is 53.65% and the corresponding efficiency enhancement is 2.06 percentage points. Exergy analysis shows that the exergy destruction in CO2 separation and steam condensation process can decrease by 49.5% in the proposed system, and thereby the exergy efficiency is 1.85 percentage points higher than the conventional method. Furthermore, the cost of CO2 avoided and cost of electricity of the proposed system will be reduced by 10.7 $/t-CO2 and 1.9 $/MWh, respectively.

Evaluating the effects of CO2 capture benchmarks on efficiency and costs of membrane systems for post-combustion capture: A parametric simulation study

Membrane separation is considered to be the most promising alternative to chemical absorption for decarbonizing fossil fuel power generating systems. However, the implementation of a membrane system has several implications for the energy and economic performances of power plants. Indeed, membrane systems allow for the non-negligible reduction of power plant capacity, which can negatively affect its efficiency. This aspect, combined with the additional capital and operating expenses, is also responsible for an increase in the electricity generation costs.Currently, the majority of studies neglected to investigate the influence of CO2 separation targets on costs, thus limiting their investigation to the case of geological storage or enhanced oil recovery (EOR) that mean CO2 purity levels after compression higher than 95%. But for certain valorization aims, like CO2 hydrogenation or solar thermochemical conversion, lower CO2 quality standards may be sufficient; to the best of our knowledge there is currently no study allowing to know the cost of CO2 capture in this unusual framework.The aim of this paper was to analyze the effects of CO2 purity targets on the energy requirement for the separation and compression operations and costs of membrane systems, considering as a study case the recovery of CO2 from flue gases of a coal-fired power plant and using a Polyactive membrane. The CO2 separation process was first investigated by exploring several membrane system concepts. Then, by focusing on dual-stage configurations, the entire carbon capture and storage (CCS) chain was analyzed. From an energy view point, the study quantified the impact of CO2 capture retrofit intervention on the power plant’s net efficiency and the extent of CO2 emissions reduction. Besides, the economic analysis allowed for an evaluation of the specific cost of the CO2 capture and the mitigation cost with or without credits for EOR. Finally, an energy and economic comparison was made with the CO2 capture based on chemical scrubbing.With a CO2 separation cost of 20÷33 $/tonne, a single stage membrane system with feed compression and permeate vacuum pumping represents the most interesting option to be used in combination with CO2 recycling technologies requiring a medium-low CO2 purity level (70÷80%). Simulation results also revealed that dual stage membrane systems envisaged are economically competitive compared to amine absorption processes in the case of geological storage, involving a cost of CO2 capture of 36÷41 $/tonne.

Design of energy-saving carbon dioxide separation process using fluidized bed

Carbon dioxide capture and storage technology has attracted recent attention for the mitigation of CO2 emissions; however, to facilitate its commercial implementation, its capture cost should be further decreased. This research proposes an innovative energy-saving process using chemical absorption by a solid in a circulating fluidized bed. In this process, the reaction heat that accompanies absorption is successfully supplied through a heat pump to achieve thermal decomposition in a regenerator, thereby leading to recirculation of all process heat. Absorption and fluidization experiments were conducted to determine the separation performance. An energy balance of the proposed process was simulated using the experimental data with a commercial process simulator. The simulation results indicate that the proposed CO2 separation process has large energy-saving potential when compared with conventional approaches.

Energy Penalty of a Single Stage Gas Permeation Process for CO2 Capture in Post-combustion: A Rigorous Parametric Analysis of Temperature, Humidity and Membrane Performances

Over the last decade, membrane separation processes have attracted considerable research attention. This is due to their potential for lowering the costs of post-combustion CO2 capture compared with the more established technologies, which are based on the use of chemical solvents. It is well known that the performance of membrane-based CO2 capture is related to several factors, including flue gas composition, membrane material and system design. Membrane working temperature is one of the operating parameters that have several implications on the CO2 separation process. However, surprisingly, this key operating variable has not been investigated in detail. It not only influences the intrinsic membrane properties and the feed composition, but also indirectly affects the energy behavior of the whole capture system. Hence, the resulting outcome cannot be intuitively deduced. This work aims to study the effect of membrane operating temperature on a CO2 capture process, which is operated by means of a single stage unit with feed compression and permeate vacuum pumping. The flue gas from a coal-fired power plant is considered, and the variation in separation performances and energy expenses is evaluated with respect to two types of polymeric membranes, which have different gas separation properties (permeability, selectivity).This study reveals that an increase in the membrane operating temperature negatively affects CO2 permeate purity and power consumption to drive the separation process. In addition, the influence on area requirement is strictly related to the type of membrane material.