Chemical Absorption Of CO2 Research Articles

The influence of acoustic power on chemical absorption of CO2 using Slow Kinetic Solvent

Ultrasonic Irradiation (UI) is an emerging technology that is used to assist the CO2 absorption process. Even for the slow kinetic solvents without using any chemical promoter, high-frequency UI might enhance mass transfer during the absorption process. For this purpose, it is essential to study the performance of a high-frequency ultrasonic-assisted absorption system under varied operating conditions. The ultrasonic power is considered as one of the main parameters during the absorption of CO2. Thus, in this paper, the influence of ultrasonic power is presented using Methyl diethanolamine (MDEA) as a chemical solvent. The ultrasonic power has been varied from 0 to 15.3 W. The results tend to show a significant absorption rate enhancement for higher ultrasonic power. Moreover, they prove that the high-frequency ultrasonic absorption system has high potential to be utilized to enhance the absorption using promoter-free MDEA.

Characteristics of Carbonate Formation from Concentrated Seawater Using CO2 Chemical Absorption Methodology.

Carbon capture and storage is a popular CO2-reduction technology, and carbon capture and utilization (CCU) technology has been reported frequently over the years. However, CCU has certain disadvantages, including the requirement of high energy consumption processes such as mineral carbonation. In addition, stable metal sources are required to fix CO2. This study used concentrated seawater to supply metal ions. In addition, the selected 5 wt % amine solution changed CO2 into aqueous CO2 to reduce the additional energy required to form the metal carbonate under moderate conditions. As a result, precipitates were formed because of the reaction of carbonate radicals with metal ions in the seawater. These precipitates were analyzed by X-ray diffraction and field-emission scanning electron microscopy, and they were found to mostly consist of CaCO3 and NaCl. Furthermore, it was verified that the conversion solution maintained its CO2-loading capacity even after the solids and liquid were filtered twice. Therefore, the proposed method permits a substantial reuse of CO2 and waste seawater when sufficient metal ions are supplied. Therefore, methods to improve their purity will be developed in future studies.

Understanding the CO2 valorization to propylene carbonate catalyzed by 1-butyl-3-methylimidazolium amino acid ionic liquids

Nowadays, CO2 emission impacts on our life standards, revealing itself as one of the major environmental challenges of present century. One main strategy is to develop new technologies within integrated Carbon Capture and Utilization (CCU), to obtain valuable chemical products. The design of new systems able to efficiently retain CO2 and convert it at mild operating conditions is an important challenge. Ionic liquids (ILs) were demonstrated as multitask absorbents-catalysts in processes involving CO2 capture and cycloaddition reaction to obtain cyclic carbonates. In this work, the use of amino acid based ionic liquids (aa-ILs) is proposed to promote a sustainable catalytic process for CO2 valorization using propylene oxide (PO) to produce propylene carbonate (PC). Three aa-ILs were proposed in the study: 1-butyl-3-methylimidazolium glycinate ([bmim][GLY]), 1-butyl-3-methylimidazolium methioninate ([bmim][MET]), and 1-butyl-3-methylimidazolium prolinate ([bmim][PRO]). Computational calculations by DFT method reveals that the reaction firstly occurs through the PO ring opening by aa-IL catalyst, followed by CO2 nucleophilic addition, rather than direct CO2 activation. The carbonate formation using aa-IL catalysts was experimentally demonstrated by ATR-FTIR experiments at mild conditions (4 bar of initial pressure and 80–120 °C), obtaining PC yields ordered as [bmim][MET] > [bmim][GLY] > [bmim][PRO], same trend than their CO2 chemical absorption capacity. Further stirred tank reactor experiments were carried out to scale-up the process, confirming the suitability of aa-ILs as homogeneous catalyst for CO2 conversion to cyclic carbonates, with extremely low consumption (0.5% m/m).

Prediction of CO2 chemical absorption isotherms for ionic liquid design by DFT/COSMO-RS calculations

Ionic liquids with an aprotic heterocyclic anion (AHA-ILs) is a promising family of compounds to overcome the challenge of CO2 capture. In this work, a computational methodology has been developed to predict CO2 chemical absorption isotherms in AHA-ILs without the need of experimental data. This methodology combines DFT and COSMO-RS calculations allowing the design of new chemical absorbents for CO2 capture. The CO2 physical absorption equilibrium constants (Henry's law constants), chemical equilibrium constants and reaction enthalpies were reliably predicted by proposed computational approach, by means of comparison to available experimental data of 9 different AHA-ILs. Finally, 15 newly designed AHA-ILs were evaluated to demonstrate the flexibility of the DFT/COSMO-RS tool by predicting their CO2 absorption isotherms. The evaluated absorbents compromise very different behaviors: from physical absorption to reactions completely displaced toward products at very low CO2 partial pressure, emphasizing the extremely tunable character of AHA-ILs. Current results will definitively contribute to link molecular and processes scales in the research of new CO2 capture technology based on ILs.

Evaluation of performance improvements through application of anisotropic foam packings in rotating packed beds

Constantly increasing interest in HIGEE technology and rotating packed beds require detailed investigations of the mass transfer and hydrodynamic performance. Classical isotropic single block packings constitute the most applied and investigated packings for absorption and stripping processes. Yet, the large geometric surface area which is offered by these packings can hardly be exploited to the full extent due to the constant change in gas and liquid loads along the radius of the annular packings. In order to overcome these limitations and extend the operating range and mass transfer performance of foam packings, the current study presents a detailed comparison of isotropic and anisotropic packings. The conducted pressure drop and mass transfer experiments, based on chemical absorption of CO2 with aqueous sodium hydroxide, illustrate the improved performance that can be expected from anisotropic packings, while dedicated gamma-ray computed tomography provides further insight into the improved liquid distribution for this kind of packings.

Energy Performance of CO2 Capture Processes: Interaction Between Process Design and Solvent

Implementation of amine-based post-combustion CO2 capture on power plants would lead to large penalties on the electric production. Researches focus either on the improvement of process flow scheme to maximize exergy integration or on characterization of new promising solvents to reduce this energy consumption. However, both aspects are often taken into account separately whereas they should be studied simultaneously since the energy efficiency of process modifications also depends on the considered solvent. In order to highlight this point, several schemes based on modifications proposed in literature are investigated for several classes of amine-based solvents and the total energy consumption is determined by a rigorous phenomenological model coupled with an optimization algorithm. Simulation results confirms that the efficiency of process modifications depends on the considered solvent since process improvements make use of the solvent specific properties, in particular the differences between thermodynamic and kinetic properties. General understandings are given on the relative efficiency of process modifications according to measurable solvent properties. Carbon dioxide capture and geological storage is foreseen to be one of the solutions to reduce the atmospheric emissions of fossil-fired power plants. Among the different technologies, post-combustion chemical absorption in amine-based solvents is the most mature at this stage of development. However, the energy consumption of such processes implies a large penalty on the power plant efficiency. The reference configuration used for chemical absorption of CO2 is a conventional absorption/desorption loop operating with monoethanolamine (MEA) where the CO2 is separated from the flue gas by chemical absorption in the solvent and the solvent is thermally regenerated in a stripper, sensible heat being exchanged in an economizer between the hot lean solvent and the cold rich solvent. The released CO2 is then compressed up to 110 bars at supercritical state for transportation and storage. For this base case, the energy requirement leads to a loss of around 11 %-pts in terms of power plant efficiency. In order to reduce this penalty, researches focus either on the improvement of process flow scheme to maximize heat integration or on characterization of new promising solvents. This work intends to emphasize the interaction between solvent properties and optimal process design and how both solvent characterization and process design should be carried out simultaneously, since the energy performance of a process modification is deeply dependent of the chosen solvent. In order to highlight this point, several schemes based on modifications proposed in literature are investigated for two classes of amine-based solvents. For each process flow scheme associated with each solvent, the operating parameters are optimized with respect to the total energy consumption with a dedicated algorithm using rigorous thermodynamic and rate-based models, which are mandatory for a proper representation of all limiting phenomena. By this means, the potential of each configuration is determined in terms of total energy penalty on the power plant.

Process intensification of CO2 absorption using a 3D printed intensified packing device

AbstractThis study presents a first of its kind demonstration of successful enhancement of CO2 chemical absorption, under selected conditions, using a process intensification approach. A multifunctional device that integrates contact of phases and heat exchange has been developed, characterized, and tested. Heat transfer analysis has demonstrated the efficacy of the device as a heat exchanger, and mass transfer results have shown substantial improvement in the uptake of CO2 under a range of operating conditions.

Enhanced mass transfer and reduced pressure drop in a compound rotating zigzag bed

A rotating zigzag bed (RZB) had achieved the commercial application of Higee in continuous distillation processes, and then a compound rotating zigzag bed (CRZB) was developed from the RZB. The CRZB rotor was composed of a disk layer including several perforated concentric circular ripple disks fixed on a perforated rotating ring at the inner part of the rotor and several coupled rotational-stationary baffles at the outer part of the rotor. And a stationary four-arm liquid distributor was located at the eye of the CRZB rotor. The effective interfacial area (ae) and local liquid-side mass transfer coefficient (kL) of the CRZB rotor were measured by experiments of a chemical absorption of CO2 in NaOH solution, and the local gas-side mass transfer coefficient (kG) of the CRZB rotor was measured by experiments of a stripping of ethanol from an ethanol-water mixture by air. The gas pressure drop across the CRZB was measured with air-water system. Effects of gas flow rate, liquid flow rate and rotational speed on these mass transfer parameters and gas pressure drop were investigated. The stationary four-arm liquid distributor led to stronger end effect of the CRZB rotor than that of the RZB rotor. The end effect of the CRZB rotor had significant effect on the ae and kL of the rotor. The ae of the CRZB rotor was much higher than that of the RZB rotor because the total space in the disk layer of the CRZB rotor served as mass transfer zones and the CRZB rotor had stronger end effect than the RZB rotor. The local volumetric liquid- and gas-side mass transfer coefficients (kLae and kGae) of the CRZB rotor reached 2.3 times higher than those of the RZB rotor at a higher liquid flow rate and a rotational speed of 1200 rpm. The gas pressure drop across the CRZB was lower than that across the RZB, because the coupled rotational-stationary baffles were abandoned at the inner part of the CRZB rotor, which reduced the gas flow resistance and led to a lower pressure drop compared to the RZB. Thus, mass transfer was enhanced and gas pressure drop was reduced in the CRZB compared to the RZB, which showed the CRZB had excellent potential as a representative of the second-generation RZB for commercial applications.

Numerical simulation of CO2 chemical absorption in a gas-liquid bubble column using the space-time CESE method

Abstract In this study, numerical simulation of the removal process of CO2 using aqueous solutions of piperazine (PZ) in a bubble column has been done. The main focus of this work is to investigate the applicability of the space-time conservation element and solution element (CESE) method for the numerical solution of the coupling of hydrodynamics, mass transfer and chemical reactions. The reactive absorption process has been investigated by means of experiments and numerical simulation. A two-dimensional computational fluid dynamics (CFD) model in the Eulerian framework has been used to describe the gas-liquid system. To obtain the numerical solution, the CESE method based on a uniform rectangular mesh has been implemented by developing a computer code. Experimental study and CFD simulations have been carried out at different conditions of CO2 partial pressure (20 and 36 kPa) and solution concentration (0.1, 0.3 and 0.5 M). The simulation results were in reasonable agreement of 5.226 % and 4.575 % with the experimental values for gas holdup and mass transfer flux, respectively. The comparisons prove that the CESE method can be considered as a proper numerical method for the simulation of complex multiphase flows due to its simplicity, accuracy and low computational costs.

CO2 chemical absorption from fluid catalytic cracking unit flue gases of Abadan Oil Refinery in Iran, using diethanolamine solvent.

The Fluid Catalytic Cracking Unit process converts heavy vacuum gas oil into more valuable products in the presence of zeolite catalyst at 520°C and 2.5bar. The coke is burned off with air in the regenerator tower at 700°C and 230ton/h of flue gases are produced. The flue gases consist of CO2 (12.7% mole), N2 (66.2% mole), H2O (19.2% mole), O2 (1.7% mole), and SO2 (0.2% mole). In this study, the chemical absorption of CO2 in an absorption and desorption pilot plant was investigated and this process was simulated by Aspen Hysys. The pilot plant used has an absorber tower of 15cm in diameter and a stripper tower of 10cm. The towers were filled up to 1.5m with 3-mm Raschig ring packing. A concentration of 30wt% diethanolamine (DEA) solvent is used for CO2 absorption. Absorption was carried out at 1.1bar, solvent temperature of 40°C, flue gas temperature of 60°C, and liquid to gas ratio (L/G = 3.7). Amine regeneration was carried out at 125°C and 1.9bar. The CO2 absorption efficiency in the pilot plant was obtained 96% and in Aspen Hysys simulation its 95%. The CO2 recovery efficiency in the stripper tower obtained 95% and CO2 purity is 94.6%. The overall efficiency of the chemical absorption with this process is 92%, and the regeneration energy in the stripper tower is 2.52 GJ/ton-co2. With this method, 1003ton/day CO2 is captured from the FCCU flue gases and preventing emission to the atmosphere.

Reversible Chemical Absorption of CO2 in Polyethylenimine Supported by Low-Viscous Tetrabutylphosphonium 2-Fluorophenolate

Traditional amine solutions for CO2 capture are associated with many defects such as sacrificed CO2 capacities and high volatility. Herein, a new type of mixed solvent was constructed by diluting p...

The effect of liquid viscosity and modeling of mass transfer in gas–liquid slug flow in a rectangular microchannel

AbstractBoth chemical (by adding 0.05 M NaOH) and physical absorption of CO2 into aqueous glycerol solutions with viscosity up to 45.6 mPa·s in a microchannel are investigated. The concentration distribution pattern, absorption time, and mass transfer coefficient are analyzed and discussed. A new concentration distribution pattern is observed with the lowest concentration locating at the channel center. It is shown for the first time that presents a positive relationship with liquid viscosity, which is explained by the essential role of the mass exchange between the liquid film and bulk liquid slug. This mass exchange may lead to a rise in k L when increasing the liquid viscosity under some cases in chemical absorption. A mass transfer model is successfully applied to predict the bubble size evolution in physical absorption. The model also shows about 10–46% of the mass transfer contribution from liquid films before saturation.

CO2 absorption intensification using novel DEAB amine-based nanofluids of CNT and SiO2 in membrane contactor

Recent developments in nanotechnology have a great impact to improve the mass transfer in gas-liquid systems. The effect of nanoparticles was taken into account considering Grazing effect and Brownian motion as main phenomena of mass transfer enhancement in nanofluids. In the present study, a sensitivity analysis was performed to evaluate the influence of nanoparticles on the CO2 absorption inside a hollow fiber membrane contactor (HFMC). The distilled water and chemical system of 4-diethylamino-2-butanol (DEAB)-water nanofluid for CO2 absorption was studied. The considered drops were nanofluids containing carbon nanotube (CNT) and nanosilica (SiO2). A rigorous two-dimensional mathematical model for CO2 absorption from a N2/CO2 gas mixture was developed. The predicted results indicated that the injection of nanoparticles to distilled water and DEAB amine solution improves the CO2 absorption efficiency. Nanofluid of CNT represented better separation performance than nanosilica. Also, the CO2 absorption efficiency of nanofluids was enhanced with the increasing amine and nanoparticle concentration, liquid flow rate and also, decreasing the gas flow rate. Although increasing the liquid temperature decreased the physical absorption of CO2, it enhanced the chemical absorption of CO2 due to improvement of the reaction rates and diffusion coefficients.

Design of carbonic anhydrase with improved thermostability for CO2 capture via molecular simulations

Chemical absorption of CO2 is the most widely used method to capture CO2. However, high cost and slow CO2 absorption rate severely hinder its commercial utilization. Human carbonic anhydrase II (hCA II) having rapid hydratase reaction rate can potentially overcome these obstacles but being highly unstable against harsh process conditions. To enhance thermostability, a novel CA was developed based on molecular simulations. Substituting residue Leu204 with Lys has a comparable hydratase activity as the wild type (WT) hCA II, 1.98 × 106 s−1 for kcat and 2.36 × 108 M−1s−1 for kcat/Km. Importantly, the replacement of L204 K results in higher temperature resistance with 100 % retention at 45 °C and around 50 % at 55 °C while WT totally inactivates at 45 °C. Furthermore, L204 K is able to maintain its activity in the presence of anions and EDTA. The robustness and efficiency of this novel CA make it a competitive candidate for CO2 capture.

Experimental investigation of effective gas-liquid specific interfacial area in a rotor-stator reactor

This work aimed to experimentally determine the effective gas-liquid specific interfacial area (ae) in a countercurrent flow rotor-stator reactor (RSR) by chemical absorption of CO2 into NaOH solution. The effects of different operating parameters such as rotation speed, liquid volumetric flow rate and gas volumetric flow rate on ae were investigated. Results indicate that higher rotation speed, gas and liquid volumetric flow rates favor larger ae. A correlation to predict ae of gas-liquid phases in RSR is also established, and the predicted values are in agreement with the experimental data with deviations within 5 %.

Current status of CO2 chemical absorption research applied to CCS: Towards full deployment at industrial scale

This work provides a wide overview of the state-of-art of the CO2 chemical absorption applied to Carbon Capture and Storage (CCS) technology. The objective is not only to provide the current status of the technology and the research and development activities carried out towards its deployment in the CCS field, but also to identify the future directions and knowledge gaps. A summary of the conventional solvents used for acid gas removal and novel solvent formulations specifically adapted to new challenges such as fossil-fuels power plants and industrial processes was reported. Novel configurations from the conventional CO2 absorption-desorption layout were summarized and their impact on the operational performance and the reboiler duty was further evaluated. Novel opportunities offered by CO2 concentrated flue gas derived from partial oxy-combustion were further discussed in the final section. A large review of the published data from pilot plants has been done to facilitate the final comparison between the current status of post-combustion and novel partial oxy-combustion configurations. Demonstration plants currently available and the commercial solutions proposed by the most important companies were briefly described. CCS pilot plants via chemical absorption have been executed in last decades reaching several CO2 capture capacities up to 80 t CO2/day. Commercial scale plants have been recently developed, being US and China the countries which lead the investment funds. The most important commercial scale demo plants, namely Boundary Dam and Petra Nova, were also described. Nevertheless, there were still many countries which need to bet for CCS at large scale.

Experimental study of CO2 chemical absorption kinetics by a thermomorphic lipophilic biphasic solvent

Chemical absorption is a frequently used post-combustion process that separates CO2 from gaseous compounds of the flue gases with the use of specific solvents for which the main drawback is their cost of regeneration. In order to overcome this problem, the new Thermomorphic Lipophilic Biphasic solvents are here studied. The limited solubility of the Lipophilic amines in water offers a new degree of freedom while optimizing the global process: it is in fact possible to carry out the absorption with an initial biphasic solvent (organic, aqueous) that evolves towards a mono-phase solvent after a certain amount of CO2 is absorbed. This work aims at assessing experimentally the CO2 absorption kinetic into a Lipophilic amine based solvent, namely 3 M 1:3 DPA (dipropylamine) + DMCA (dimetylcyclohexylamine) + water using a Lewis Cell type reactor. Activation energy values obtained by the Arrhenius law show similar values for those of benchmark amines and the selected solvent seems to require less energy to start the chemical reaction.

Chemical Absorption of CO2 Enhanced by Nanoparticles Using a Membrane Contactor: Modeling and Simulation.

In the present work, membrane resistance was estimated and analyzed, and the results showed that total membrane resistance increased sharply when membrane pores were wetted. For further study, a two-dimensional (2D) mathematical model was developed to predict the chemical absorption of CO2 in aqueous methyldiethanolamine (MDEA)-based carbon nanotubes (CNTs) in a hollow fiber membrane (HFM) contactor. The membrane was divided into wet and dry regions, and equations were developed and solved using finite element method in COSMOL. The results revealed that the existence of solid nanoparticles enhanced CO2 removal rate. The variables with more significant influence were liquid flow rate and concentration of nanoparticles. Furthermore, there was a good match between experimental and modeling results, with the modeling estimates almost coinciding with experimental data. Solvent enhanced by solid nanoparticles significantly improved the separation performance of the membrane contactor. There was around 20% increase in CO2 removal when 0.5 wt% CNT was added to 5 wt% aqueous MDEA.

An experiment and model of ceramic (alumina) hollow fiber membrane contactors for chemical absorption of CO2 in aqueous monoethanolamine (MEA) solutions

The chemical absorption of CO2 in a monoethanolamine (MEA) solution by a ceramic hollow fiber membrane contactor (HFMC) was investigated experimentally and numerically to obtain the best compromise between the mass transfer coefficient and structural characteristics such as membrane pore size and porosity. The mathematical model derived is based on the three resistances in the resistance-in-series model. The accuracy of the numerical simulation was verified quantitatively by the experimental data obtained in this study. A good agreement between experimental and computational results was found with an average absolute deviation (AAD) between observed data and predicted values of 2.86%. In addition, the effects of the operating condition (i.e., gas and liquid flow rates) on the mass transfer coefficients for ceramic HFMC systems were also studied, revealing that the membrane and gas-phase mass transfer resistances were dominant factors in the overall mass transfer. In conclusion, the present study suggests that the membrane structure plays a very important role in the optimization of HFMC performance. In fact, the best results were obtained with an intermediate range of the pore size between 102 and 104 nm, corresponding to the best compromise between performance (i.e., overall mass transfer coefficient) and applicability (i.e., breakthrough pressure).

Energy Analysis of Physical Absorption and Chemical Absorption of CO2 in Ionic Liquids

CO2 solubility in ionic liquids (ILs) is measured extensively to develop IL‐based technology for CO2 capture. Herein, the choline‐ and acetate‐based ILs are selected as the studied physical and chemical absorbents for CO2 capture, respectively. The CO2 solubilities in choline‐ and acetate‐based ILs are thermodynamically modeled. The ILs consumed for CO2 absorption and the energy demands for the ILs regeneration are calculated and compared with those of the conventional imidazolium‐based ILs. The results show that the three choline‐based ILs are not energy saving in the pressure‐swing process. In the temperature‐swing process, the energy demand for CO2 absorption by using acetate‐based ILs reveals that the chemical absorption‐based ILs are the absorbent with lower energy demands compared with the physical absorption‐based ILs.