Amine-based Absorption Process Research Articles

Synthesis of core-shell magnetic mesoporous silica nanoparticles to disperse amine functionalities for post-combustion carbon dioxide capture

BackgroundPost-combustion capture technology appears a suitable approach to reduce the emission of CO2 by power plants. The use of solid sorbents would permit to overcome the limitations of the well-established liquid amine-based absorption process. In particular, mesoporous silica materials have been proposed as suitable sorbents especially if functionalized with amines. MethodsThe properties of as-synthesized (by using dodecylamine as synthesis amine) and calcined hexagonal mesoporous silica (HMS), impregnated or not with tetraethylenepentamine (TEPA), were studied. Magnetite (Fe3O4) nanoparticles were specifically used to obtain HMS core-shell nanoparticles in order to investigate the effect of the magnetite core on CO2 uptake capability. CO2 uptake measurements were carried out on all HMS and core-shell particles. Furthermore, Transmission Electron Microscopy (TEM) images, Fourier Transform Infrared (FTIR) spectra and N2 adsorption/desorption measurements allowed analyzing some important properties of the sorbent particles, such as particle aggregation, incorporation and dispersion of amines, surface area, pore volume and pore size distribution. Significant FindingsThe best performance in terms of chemical CO2 uptake was obtained on core-shell material, calcined and impregnated with TEPA (about 89 mg/g), but also the as prepared core-shell sample impregnated with TEPA seems promising since the synthesis dodecylamine sites can be activated during the impregnation process.

Pre-combustion CO2 capture using amine-based absorption process for blue H2 production from steam methane reformer

A novel pre-combustion CO2 capture process using methyl diethanolamine with piperazine (MDEA/PZ) was investigated for the production of blue H2 from a steam methane reformer (SMR). A sensitivity analysis was performed at various operating parameters (such as MDEA or PZ concentration, flash drum pressure, CO2 loading in a lean-amine solvent, and CO2 removal efficiency) using a validated rate-based model. The energy consumption to capture CO2 from SMR gas at 21 bar was evaluated, including the compression energy (up to 30 bar) for the dehydration of captured CO2. For 90% and 95% CO2 removal efficiency, reboiler duties were 1.318 GJ/tonCO2 and 1.364 GJ/tonCO2, and CO2 compression works were 11.673 kW/molCO2 and 11.615 kW/molCO2. The results indicated more than 40% lower reboiler duty than the energy consumption of conventional CO2 capture processes in post-combustion. Subsequently, artificial neural network model (ANN)-based optimization using the differential evolution method was performed. The developed ANN-based optimization suggested the possibility of additional 0.3 % reduction in the equivalent work at a low computational cost. The results indicated that the developed pre-combustion CO2 capture for a SMR was highly competitive in industrial applications. Moreover, the H2 mixture produced at 21 bar is beneficial for a H2 recovery unit because of no need for additional compression energy. Therefore, the MDEA/PZ-based absorption process can effectively contribute to centralized or semi-central blue H2 production from a SMR. This study provides a guideline for the feasible optimization and control of the CO2 absorption process at high feed pressures.

Pseudo counter-current turbulent fluidized bed process with sensible heat recovery for energy-efficient CO2 capture using an amine-functionalized solid sorbent

A fluidized bed adsorption (FLBA) process with internal heat integration is considered an energy-efficient method for large-scale CO2 capture. Herein, we propose a pseudo counter-current FLBA process for post-combustion CO2 capture as a proof-of-concept based on a rationally designed moving bed heat exchanger by incorporating the internal heat integration concept of the conventional amine scrubbing CO2 capture process. The proposed FLBA process consists of an adsorption bed, desorption bed, and moving bed heat exchangers for cooling and heating the solid sorbent. The design of the proposed FLBA process enables internal heat integration by recovering sensible heat from the cooling process. Furthermore, by installing multiple adsorption processes, the pseudo counter-current operation in the adsorption bed enhances the CO2 cyclic capacity of the amine-functionalized solid sorbent with high CO2 recovery. The proposed process complements the two weaknesses of FLBA, namely, large sensible heat and low cyclic capacity of the sorbent. The energy analysis, based on rigorous mathematical modeling, estimates that the energy demand of the optimized FLBA using SiO2/0.37 EB-PEI is approximately 258.6 kWh/t-CO2 with 45% sensible heat recovery. This low energy demand is comparable to that of the most mature amine-based absorption process (271 kWh/t-CO2) owing to the effect of internal heat integration, supporting the feasibility of the FLBA process for post-combustion CO2 capture.

CO2 Separation from Flue Gases by Adsorption

This paper deals with gas separation by adsorption processes. The key objective is to investigate the adsorption suitability for Post-combustion Carbon Dioxide (CO2) Capture (PCC). Adsorption is a promising technology suitable for a high volume of diluted gas processing. Unlike commercialised amine-based absorption processes, adsorption seems to require less energy for sorbent regeneration and extends the sorbent lifetime. Two common industrial methods utilizing a difference in adsorption equilibrium of the gas components were investigated: 1) Pressure Swing Adsorption (PSA) including Vacuum Swing Adsorption (VSA), 2) Temperature Swing Adsorption (TSA). A comparison of their energy consumption, suitability for industrial use with consideration of Carbon Capture and Storage standards is evaluated. A complex mathematical model for the adsorption step of the fixed bed adsorber was proposed and solved by the structural programming. Three adsorbent materials: Mg-MOF-74, UTSA-16, and Zeolite 13X were evaluated based on their CO2 adsorption capacity, selectivity, and market availability. Zeolite 13X was further explored. As a benchmark case, a medium-sized natural gas cogeneration unit was used to study the potential of VSA unit. The lower limit of CO2 capture efficiency in simulations was 75 %. The results presented in this paper suggest that adsorption can be a feasible CO2 capture solution for a low-carbon emission power generation technologies. Optimal parameters for the adsorption step and column configuration are proposed.

Economic evaluation for four different solid sorbent processes with heat integration for energy-efficient CO2 capture based on PEI-silica sorbent

An amine-functionalized solid sorbent-based process with heat integration is considered an energy-efficient method for large-scale CO2 capture. Herein, we propose a techno-economic analysis (TEA) of four different solid sorbent processes for post-combustion CO2 capture with internal heat integration as an alternative to the conventional amine scrubbing process. Our proposed processes are fluidized bed adsorption, fixed bed adsorption, moving bed adsorption, and rapid thermal swing adsorption and involve continuous adsorption, heating, desorption, and cooling. In addition, the four processes use an amine-functionalized solid sorbent, SiO2/0.37 EB-PEI, which was transformed into powder, pellet, and hollow fiber to reflect the characteristics of each process. The proposed processes enable internal heat integration by recovering sensible heat from the cooling process and further enhance the CO2 cyclic capacity of amine-functionalized solid sorbents with high CO2 recovery by performing adsorption heat removal. Most importantly, our TEA based on rigorous mathematical modeling revealed that the CO2 capture cost of the four solid sorbent-based processes was approximately 48.1–75.2 $/t-CO2, with a 45%–58% sensible heat recovery. Such a low CO2 capture cost is comparable to that of the most mature amine-based absorption process (62.8 $/t-CO2), owing to a combination of internal heat integration and enhanced CO2 cyclic capacity. The results support the feasibility of four solid sorbent-based processes for post-combustion CO2 capture.

Core-shell magnetic ZIF-8@Fe3O4-carbonic anhydrase biocatalyst for promoting CO2 absorption into MDEA solution

Tertiary amine-based absorption process possesses high absorption capacity and low heat duty for CO2 capture. However, its slow CO2 absorption rate retards its industrial application. This work developed a core-shell magnetic ZIF-8@Fe3O4-carbonic anhydrase composite to promote CO2 absorption into tertiary amine, e.g., diethanolamine (MDEA) due to its easy recovery from the solution. The catalytic performance of CA@ZIF-8@Fe3O4 that had three particle sizes were investigated. Experimental results revealed that the obtained CA@ZIF-8@Fe3O4 can achieve the relative activity as high as 95.2 % compared with the free counterparts. Large particle size of ZIF-8@Fe3O4 was beneficial to activity but adverse to loading. Magnetic analysis shows that the developed CA@ZIF-8@Fe3O4 possessed remarkable magnetic response which made recycling more convenient.

Plant-wide MPC control scheme for CO2 absorption/stripping system

Abstract The high contents of CO2 in natural gas processing industries cause various issues in the operation, and it is essential to reduce the amount of CO2 using amine-based absorption processes. An efficient and flexible control strategy is highly desirable for CO2 removal in CO2 absorption/stripping system. The excellent performance of Model Predictive Control (MPC) in setpoint tracking and disturbance rejection scenarios could make it a better option for the flexible controllability of a CO2 absorption/stripping plant. MPC performance depends significantly on the accuracy of the identified mathematical model of the plant. The state-space model is believed as the better option for MPC as it represents the plant model with true dynamics. Therefore, this study is focused on the design of the 2 × 2 MPC control strategy in MATLAB® MPC Designer Toolbox using 2nd order continuous-time state-space model. The main aim of this study is to develop a plant-wide control scheme based on MPC for the natural gas absorption/striping system. Step changes in the CO2 composition of sweet gas (±5%) and stripper temperature (±15%) have been introduced in the absorption/stripping simulation model. The results show that the MPC controller has achieved the new setpoint of CO2 composition within 0.5 sec in the setpoint tracking scenario. Similarly, the MPC controller has been able to reject the disturbances successfully introduced as ± 15% step change in stripper temperature within 7.5 sec. Hence, the performance of the MPC controller using the state-space model at higher step changes is adequate with no peak, closer to the setpoint, and no overshoot in the output.

Selection of efficient absorbent for CO2 capture from gases containing low CO2

Amine-based absorption processes are widely used in natural gas processing, but recently they have been considered for CO2 capture from flue gas emitted from thermal power plants. The main issue of amine used in the CO2 capture process is the high cost of solvent regeneration. So, this issue can be solved by using efficient amine absorbent. The amine type absorbents employed in the experimentation were an aqueous blend of 2-(Diethylamino)ethanol (DEEA) with different types of diamine activators such as piperazine (PZ), 2-(2-aminoethylamino)ethanol (AEEA), hexamethylenediamine (HMDA), ethylenediamine (EDA), and 3-(Dimethylamino)-1-propylamine (DMAPA). An absorption experiment was performed to evaluate the CO2 absorption performance in terms of CO2 loading, absorption capacity, and absorption rate. The experiment was performed to assess the CO2 desorption performance in terms of desorption capacity, desorption rate, cyclic capacity, and regeneration efficiency. From the results of absorption-desorption and comparison with benchmark amine absorbent MEA, the aqueous blend of DEEA and HMDA indicated the best performance for CO2 capture applications among all the tested amine blends.

Rapid thermal swing adsorption process in multi-beds scale with sensible heat recovery for continuous energy-efficient CO2 capture

Abstract A rapid thermal swing adsorption (RTSA) process with heat integration is considered to be an energy-efficient method for large-scale CO2 capture. Herein, we propose a new heat-integrated RTSA process for post-combustion CO2 capture as a proof-of-concept based on rationally designed multi-fixed beds by incorporating the internal heat integration concept of the moving bed adsorption process. Our proposed RTSA process consists of multiple beds, each of which undergoes four sequential processes, including adsorption, heating, desorption, and cooling in a continuous cyclic mode. Also, the switching time of adsorption/desorption process is determined by CO2 adsorption/desorption kinetics while that of the heating/cooling process is determined by the heat transfer rate. Our unique RTSA design enables internal heat integration by recovering sensible heat from the cooling process. Furthermore, it can enhance the CO2 cyclic capacity of hollow fiber sorbents with high CO2 recovery by performing multiple adsorption processes simultaneously. Most importantly, our economic analysis based on experiments and rigorous mathematical modeling revealed that the energy demand of the optimized RTSA process is estimated to be approximately 272 kWh/t-CO2 with 58% sensible heat recovery. Such low energy penalty is comparable to that of the most mature amine-based absorption process (271 kWh/t-CO2) due to a combination of internal heat integration and enhanced CO2 cyclic capacity, supporting the feasibility of a RTSA process for post-combustion CO2 capture.

Kinetics, Thermodynamics, and Mechanism of a Novel Biphasic Solvent for CO2 Capture from Flue Gas.

The main issue related to the deployment of the amine-based absorption process for CO2 capture from flue gas is its intensive energy penalty. Therefore, this study screened a novel biphasic solvent, comprising a primary amine e.g., triethylenetetramine (TETA) and a tertiary amine e.g., N, N-dimethylcyclohexylamine (DMCA), to reduce the energy consumption. The TETA-DMCA blend exhibited high cyclic capacity of CO2 absorption, favorable phase separation behavior, and low regeneration heat. Kinetic analysis showed that the gas- and liquid-side mass transfer resistances were comparable in the lean solution of TETA-DMCA at 40 °C, whereas the liquid-side mass transfer resistance became dominant in the rich solution. The rate of CO2 absorption into TETA-DMCA (4 M, 1:3) solution was comparable to 5 M benchmark monoethanolamine (MEA) solution. Based on a preliminary estimation, the regeneration heat with TETA-DMCA could be reduced by approximately 40% compared with that of MEA. 13C NMR analysis revealed that the CO2 absorption into TETA-DMCA was initiated by the reaction between CO2 and TETA via the zwitterion mechanism, and DMCA served as a CO2 sinker to regenerate TETA, resulting in the transfer of DMCA from the upper to lower phase. The proposed TETA-DMCA solvent may be a suitable candidate for CO2 capture.

Evaluating the Feasibility of a TSA Process Based on Steam Stripping in Combination with Structured Carbon Adsorbents To Capture CO2 from a Coal Power Plant

The present work evaluates the feasibility to capture at least 85% of the CO2 emitted by an advanced supercritical pulverized coal power plant of 800 MWe, delivering a CO2 product with a purity of 95% (dry basis) or higher, using an adsorption-based postcombustion capture process based on carbon honeycomb monoliths regenerated by steam stripping. Process performance has been evaluated through the dynamic simulation of the cyclic adsorption process. The fixed bed adsorption model, which was validated against experimental results, is based on the mass, momentum, and energy conservation equations, and it accounts for competitive adsorption between the three main flue gas components: N2, CO2, and H2O. The evaluated TSA process meets the targets for the capture rate and product purity, with a heat duty of 3.59 MJ kg–1 CO2, which is close to the specific reboiler duty of the benchmark amine-based absorption process. Materials and process development will lead to lower duties. A sensitivity analysis was carried ...

Application of a Chilled Ammonia-based Process for CO2 Capture to Cement Plants

The chilled ammonia process (CAP) is considered one of the most promising alternatives to amine-based absorption processes for post-combustion carbon capture applied to power plants. This work provides an insight on the CAP adaptations required to meet the conditions found in the flue gas emitted in cement plants, where CO2 generation is inherent to the manufacturing process. A rate-based model has been validated to simulate the CO2 absorber of the CAP for cement plant-like flue gas composition in order to obtain the Murphree efficiencies to be used in full CAP simulations in Aspen Plus. A preliminary minimum exergy need of 0.92 MJ/kgCO2 has been found for the CAP applied to the cement plant case making use of an optimization algorithm and capturing 85.2% of the emitted CO2. Higher temperatures (> 45°C) are found in the CO2 absorber of the CAP when applied to cement plant-like flue gas conditions in comparison to the power plant case (< 40°C), requiring a lower pumparound temperature in order to control the ammonia slip in the CO2-depleted flue gas exiting the column.

Experimental study of carbon dioxide absorption into aqueous ammonia with a hollow fiber membrane contactor

The aqueous ammonia process is a promising CO2 capture technology for post-combustion flue gas treatment. The most attractive advantage of this technology is a relative low cost of solvent regeneration compared to traditional amine solutions. In this work, the absorption of CO2 into aqueous ammonia was experimentally studied in a gas/liquid contactor fitted with hollow fiber PTFE membranes at ambient temperature. The absorption performance was evaluated in terms of KGav. Experimental results indicated aqueous ammonia can absorb CO2 in a hollow fiber membrane contactor over a wide range of experimental conditions. The value of KG ranged from 1.06 × 10−4 to 2.89 × 10−4m/s. The impacts of operating parameters including CO2 partial pressure, liquid flow rate, ammonia concentration and inletCO2 solution loading were evaluated. The parametric impacts are similar to those of traditional amine-based absorption processes. Although the reactivity of aqueous ammonia is moderately lower than MEA, the KGav value of aqueous ammonia is the same order of magnitude as that of MEA under the same operating conditions. As the liquid flow rate increases aqueous ammonia can achieve a performance comparable to MEA solvent. Long-term stability tests showed the absorption performance of aqueous ammonia remained constant in the first hour and then gradually decreased over time. Precipitation of ammonium salts was observed on the membrane surface of the shell side, which caused membrane fouling and may facilitate membrane wetting.

Thermodynamic assessment of the swing adsorption reactor cluster (SARC) concept for post-combustion CO2 capture

This paper presents the novel swing adsorption reactor cluster (SARC) for post combustion CO2 capture. The SARC concept consists of a cluster of bubbling/turbulent multistage fluidized bed reactors which dynamically cycle a solid sorbent between carbonation and regeneration. A synergistic combination of vacuum swing through a vacuum pump and temperature swing through a heat pump is employed to ensure high process efficiency. The base case SARC configuration imposed an energy penalty of 9.64%-points on a conventional coal-fired power plant, which is in line with advanced amine-based absorption processes. Sensitivity analyses showed that significant potential for further improvements (∼1.5%-points) exist through mechanisms such as an increase in the number of reactor stages, further reductions in regeneration pressure and optimization of the cycle length. Additional efficiency improvements can also be traded for increased reactor footprint. However, future sorbent material selection studies especially for this novel process hold the largest potential for further efficiency improvements. The SARC concept is well suited to retrofitting purposes due to limited integration with the steam cycle, and the simple standalone reactor design will simplify future scale-up efforts. The concept is therefore recommended for further study.

Rational design of temperature swing adsorption cycles for post-combustion CO2 capture

The design of temperature swing adsorption (TSA) cycles aimed at recovering the heavy product at high purity is investigated by model-based design and applied to the capture of CO2 from flue gases. This model based design strategy and an extensive parametric analysis enables gaining an understanding of how individual steps within TSA cycles affect the achievable purity and recovery of the CO2 product. This insight is used to evaluate three novel TSA cycle configurations by assessing them based on their productivity and energy consumption. The influence of heat integration, cycle scheduling and an external drying step on the performance of the cycles is systematically evaluated. This detailed analysis reveals the importance of the cycle configuration and provides a basis to rationally design TSA cycles for post-combustion CO2 capture. Using a commercial zeolite 13X adsorbent our novel TSA cycle design achieves for the first time CO2 capture and storage specifications (96% CO2 purity and 90% recovery) with moderate heating temperatures of up to 420K while avoiding the use of compression or vacuum. The specific energy consumption and productivity of this cycle are similar to amine-based absorption processes. The obtained results demonstrate the feasibility of TSA based processes for post-combustion CO2 capture applications, and the presented methodology can be used to evaluate and quantify possible improvements provided by using novel technology elements such as alternative materials.

Identifying Optimal Zeolitic Sorbents for Sweetening of Highly Sour Natural Gas.

Raw natural gas is a complex mixture comprising methane, ethane, other hydrocarbons, hydrogen sulfide, carbon dioxide, nitrogen, and water. For sour gas fields, selective and energy-efficient removal of H2 S is one of the crucial challenges facing the natural-gas industry. Separation using nanoporous materials, such as zeolites, can be an alternative to energy-intensive amine-based absorption processes. Herein, the adsorption of binary H2 S/CH4 and H2 S/C2 H6 mixtures in the all-silica forms of 386 zeolitic frameworks is investigated using Monte Carlo simulations. Adsorption of a five-component mixture is utilized to evaluate the performance of the 16 most promising materials under close-to-real conditions. It is found that depending on the fractions of CH4 , C2 H6 , and CO2 , different sorbents allow for optimal H2 S removal and hydrocarbon recovery.

Monte Carlo Simulations Probing the Adsorptive Separation of Hydrogen Sulfide/Methane Mixtures Using All-Silica Zeolites.

Selective removal of hydrogen sulfide (H2S) from sour natural gas mixtures is one of the key challenges facing the natural gas industry. Adsorption and pervaporation processes utilizing nanoporous materials, such as zeolites, can be alternatives to highly energy-intensive amine-based absorption processes. In this work, the adsorption behavior of binary mixtures containing H2S and methane (CH4) in seven different all-silica zeolite frameworks (CHA, DDR, FER, IFR, MFI, MOR, and MWW) is investigated using Gibbs ensemble Monte Carlo simulations at two temperatures (298 and 343 K) and pressures ranging from 1 to 50 bar. The simulations demonstrate high selectivities that, with the exception of MOR, increase with increasing H2S concentration due to favorable sorbate-sorbate interactions. The simulations indicate significant inaccuracies of predictions using unary adsorption data and ideal adsorbed solution theory. In addition, the adsorption of binary H2S/H2O mixtures in MFI is considered to probe whether the presence of H2S induces coadsorption and reduces the hydrophobic character of all-silica zeolites. The simulations show preferential adsorption of H2S from moist gases with a selectivity of about 18 over H2O.

Novel shortcut estimation method for regeneration energy of amine solvents in an absorption-based carbon capture process.

Among various CO2 capture processes, the aqueous amine-based absorption process is considered the most promising for near-term deployment. However, the performance evaluation of newly developed solvents still requires complex and time-consuming procedures, such as pilot plant tests or the development of a rigorous simulator. Absence of accurate and simple calculation methods for the energy performance at an early stage of process development has lengthened and increased expense of the development of economically feasible CO2 capture processes. In this paper, a novel but simple method to reliably calculate the regeneration energy in a standard amine-based carbon capture process is proposed. Careful examination of stripper behaviors and exploitation of energy balance equations around the stripper allowed for calculation of the regeneration energy using only vapor-liquid equilibrium and caloric data. Reliability of the proposed method was confirmed by comparing to rigorous simulations for two well-known solvents, monoethanolamine (MEA) and piperazine (PZ). The proposed method can predict the regeneration energy at various operating conditions with greater simplicity, greater speed, and higher accuracy than those proposed in previous studies. This enables faster and more precise screening of various solvents and faster optimization of process variables and can eventually accelerate the development of economically deployable CO2 capture processes.

Optimization during the process synthesis: enabling the oxidative coupling of methane by minimizing the energy required for the carbon dioxide removal

Optimization is scarcely ever carried out during process synthesis. Nonetheless, this contribution shows that optimization at the design stage can be vital to make new process concepts economically feasible and open up new, cleaner production paths. Herein, a hybrid separation system for the carbon dioxide removal from product gas of the oxidative coupling of methane is investigated. The combination of a polyimide and a polyethylene oxide membrane as well as an amine-based absorption process is investigated, modeled, and subsequently optimized to minimize the required energy while keeping the loss of the reaction product at a minimum. By means of process optimization at the synthesis stage process configurations are discovered, which allows for the realization of an alternative process concept to improve greenhouse gas emission reduction. Furthermore, new reaction paths towards the synthesis of longer hydrocarbons based on natural or bio gas are enabled.

Sensitivity of amine-based CO2 capture cost: The influences of CO2 concentration in flue gas and utility cost fluctuations

The amine-based absorption process is the preferred technique to capture CO2 from flue gas. However, the cost of CO2 capture using an amine-based absorption process is considered high due to the solvent regeneration step. Therefore, in order to make this process a viable option for CO2 capture, its cost, especially its operating cost, must be reduced. This paper presents the results of a systematic sensitivity analysis, which covers the effects of CO2 concentration in flue gas and utility cost fluctuations on the optimum amine-based CO2 capture cost. The paper aims to determine whether the operating conditions of an existing CO2 capture plant can be changed to offset the effects of CO2 concentration in flue gas and utility cost fluctuations in order to yield the same or lower CO2 capture cost as the original plant design. It also provides an understanding of how the optimum CO2 capture cost changes with these fluctuations. The considered utility costs are the prices of amine solvent(s), electricity, process water, cooling water, and low pressure saturated steam. The response surface technique, coupled with the steepest descent method, is utilized to search for the direction of lower CO2 capture cost. The final result obtained from this methodology consists of the optimum operating conditions of the process with the minimum CO2 capture cost. The studied solvents are monoethanolamine (MEA) and diglycolamine (DGA), and diethanolamine–triethanolamine mixture (DEA–TEA). The results show that changes in the CO2 concentration in flue gas have the highest impact on the optimum CO2 capture cost of an existing plant when compared with the remaining parameters. For all solvents, the optimum CO2 capture cost shows an inversely proportional relationship to the CO2 concentration in flue gas. The optimum cost decreases by around 29–33% as the CO2 concentration increases by 50%, and the cost increases by around 86–104% as the CO2 concentration decreases by 50% when compared to the base case. The fluctuations in the utility costs do not exhibit a significant impact on the minimum CO2 capture cost.