CO2 Absorption Rate Research Articles

One-step synthesis of efficient manganese-based oxide catalyst for ultra-rapid CO2 absorption in MDEA solutions

The objective of this study is to develop a promising and feasible technique to significantly increase in the CO2 absorption rate of tertiary amine solutions. Here, for the first time, a manganese-based oxide (MnOx) with four different oxides, including Mn3O4, Mn2O3, MnOOH, and MnO2, is prepared using a one-step synthesis approach, and utilized to catalytically accelerate CO2 absorption in a typical tertiary amine, MDEA solution. The results reveal that the MnOx catalyst improves the CO2 absorption rate and amount as high as 360% and 132%, respectively. The MnOx also outperforms various single manganese-based oxides and their physical mixture, as well as most of the reported catalysts in terms of catalytic enhancement of CO2 absorption in the MDEA solution. The FT-IR analysis is used to confirm the catalytic promotion effect of CO2 absorption, and a catalytic mechanism is proposed. The remarkable catalytic enhancement effect of MnOx might primarily result from both plentiful basic sites and unsaturated Mn sites as well as the synergistic interaction between various oxides. Furthermore, the MnOx also has a favorable effect on CO2 desorption and exhibits outstanding recyclability. This work not only demonstrates a workable strategy for improving the CO2 absorption rate by incorporating a low-cost and high-efficiency solid base catalyst into tertiary amine solutions but also provides guidance for developing more effective catalysts to promote CO2 absorption.

CO2 capture and sequestration from a mixture of direct air and industrial exhaust gases using MDEA/PZ: Optimal design by process integration with organic rankine cycle

Achieving climate change targets requires a massive reduction in carbon dioxide emissions. According to the Paris agreement, this amount should be reached to 30 Gt/year CO2 reduction. Among different energy and environmental technologies, CO2 Capture and Storage (CCS) technologies are promising technologies to achieve those goals. Despite different technical, economical, and environmental CCS challenges, process development based on recent advances can significantly facilitate the CCS’s deployment. This study aims to simulate the absorption system of CO2 with Methyl-Diethanolamine (MDEA) and Piperazine (PZ) absorbents. In this study, three different scenarios have been considered for designing the parts of the absorption tower and air blower that have the highest energy consumption to achieve the highest amount of absorption, purity, and CO2 recovery. Compared results from the defined scenarios show that the use of an intercooler in the middle of the adsorption tower (Scenario 3) is the best design for the CO2 capture simulated process where the adsorption rate is 90.1%, the purity is 82.26 (mol%) and CO2 Recovered reaches 28.74 ton/hr. Since energy consumption in high CO2 absorption rate and purity is one of the main challenges of such technologies, this study also evaluates the combination of the organic Rankin cycle (ORC) with air blowers by three refrigerants R290, R227, and R124 to reduce energy in the carbon capture units. The results show that in this cycle, R290 has the highest power output against R227 and R124 refrigerants under the same conditions. Combining ORC with an air blower reduces the cooling load of the whole process to 104.85 MW and the total power consumption to 46.375 MW. Finally, this study concludes that using different designs and combinations, including ORC cycles in high-energy CCS processes, can also reduce the cost of energy required, and its deployment can help prevent climate change.

Research on technical route and economic calculation of solar assisted carbon capture system

This paper takes a 600MW supercritical unit as the research object, and studies the technical route and economic situation of solar photothermal system as the heat source of reboiler of carbon capture system. Taking Monoethanolamine (MEA) as the research object to analyse its desorption energy consumption characteristics, the calculation results show that the carbon capture and regeneration energy consumption of the system is 3.90Gj/t CO2, calculated by the CO2 absorption rate of 85%. Three technical routes of solar assisted carbon capture systems are proposed, and the main thermal economic indexes of the two methods, such as unit coal consumption and thermal efficiency, using the fifth stage extraction steam as an independent heat source and cooperating with the solar photothermal system, are calculated and compared respectively. Based on this, the influence of investment cost and collector area on CO2 emission reduction cost and coal consumption is analysed. The results show that after adding the solar thermal system, the coal consumption of the unit is reduced by 2.5g/(kw) compared with the pure steam extraction heating unit and the thermal efficiency is increased by 0.9%. The CO2 emission reduction cost has a positive correlation trend with the investment cost, and the unit coal consumption has a negative correlation trend with the increase of the collector area.

A Comparative Parametric Study on Dynamic Biogenic Carbon of Harvested Wood Products: Biomass Rotation Period vs. Product Lifetime

Harvested wood products (HWPs) are a class of products that are recognized for their potential to mitigate climate warming: the absorption of CO2, which is necessary to the growth of their biomass feedstock, temporarily reduces the amount of CO2 present in the Earth’s atmosphere, effectively mitigating global warming. This study decided to look into the effect of changing two important parameters associated with HWPs: the rotation period of the biomass used for their raw material (effectively, the rate of CO2 absorption), and the length of their lifetime (effectively, the amount of time the captured carbon is stored within them in the form of embodied carbon). For this purpose, a carbon accounting calculator, Quantis’ Biogenic Carbon Footprint Calculator for Harvested Wood Products (BCFC-HWP), was employed. The Biogenic Global Warming Potential (GWPbio) metric, which was used by the BCFC-HWP to describe the climate impact of a wooden product’s embodied carbon, was analyzed for its evolution with respect to the two identified parameters. The results showed that while GWPbio followed a consistent decrease with respect to the product lifetime parameter, it showed a non-consistently evolving trend with respect to biomass rotation period i.e. first decreasing then increasing. This made the confrontation of both parameters’ effect complex mathematically, such that no clear-cut conclusions on the relative benefits of changing one parameter versus the other were made. Nonetheless, a valuable resolution was made based on the observations regarding the evolution of GWPbio with respect to the lifetime of an HWP: the results indicated that extending the lifetime of an HWP is an advantageous strategy in decreasing the climate effect of the considered product.

Dual-functionalized ionic liquid biphasic solvents with aqueous-lean for industrial carbon capture: Energy-saving and high efficiency

A novel, sustainable, dual-functionalized amino ionic liquid biphasic solvent of 3-(Dimethylamino)-1-propylamine-1,2,4-triazole/poly (ethylene glycol) dimethyl ether/water ([DMAPA][TZ]/NHD/water) was proposed for CO2 capture to reduce the consumption of regeneration energy. Experimental results showed that the CO2 absorption loading of the solvent was 1.95 mol CO2·L−1 solvent at a CO2 partial pressure of 15 kPa. The volume of the CO2-rich phase was 40 vol% of the total volume, with a loading of up to 4.65 mol CO2·L−1 solvent, accounting for approximately 95.4% of the blended CO2 loading in the solvent. The CO2-rich phase could be regenerated by 92.3% in 10 min at 373 K, without the presence of a lean phase. The regeneration efficiency of the solvent was maintained at 83% after 10 adsorption and desorption cycles. The reaction, regeneration, and phase-change mechanism were investigated using 13C NMR and phase composition analysis. CO2 reacted with [DMAPA][TZ] to form two kinds of carbamate during solubilization, and all carbamates could be further hydrolyzed to form HCO3− and CO32−. The solvent effect, phase-change behavior, and CO2 physical dissolution of NHD could promote the absorption and desorption rate and absorption capacity of CO2. The energy consumption for CO2 desorption could be reduced to 1.335 GJ·t−1 CO2, which was 67% lower than that of 30 wt% ethanolamine (3.99 GJ·t−1 CO2), given the lower heat of reaction, specific heat capacity, and solvent loss. Thus, this solvent presents a sustainable strategy for advancing carbon capture technologies.

Proposal and investigation of CO2 capture from fired heater flue gases to increase methanol production: A case study

In a petrochemical complex in Iran, for production of 209575 kg of MeOH/h, 154,712 kg/h of flue gas with a CO2 concentration of 10.74 mol% enter the atmosphere through a fired heater. The target of this study is to investigate the effect of using post-combustion CO2 capture technology to reduce carbon dioxide emissions and use it to increase methanol production. In order to, the proposed process was simulated and effect of three different solvents, including piperazine (PZ) 30 wt%, monoethanolamine (MEA) 30 wt%, and a blend of MEA 20 wt %+ PZ 10 wt % were investigated. This study investigated solvent regeneration energy, CO2 absorption rate, energy efficiency, and exergy efficiency of stripper column. Simulation results showed PZ with 93% energy efficiency, 55.45% exergy efficiency of stripper column, CO2 emission intensity equal to 0.01 tCO2/tMeOH and lowest solvent regeneration energy equal to 2.6 GJreb/tCO2 has better performance than the other two solvents. Also, the simulation results showed that blending CO2 output from PZ solvent with syngas increases methanol production by 7.8%. The techno-economic analysis also indicated proposed process is more profitable than original process.

Metal Oxides Enhance the Absorption Performance of N-Methyldiethanolamine Solution during the Carbon Dioxide Capture Process.

Fly ash from coal-fired power plants can enter chemical absorbents along with flue gas. Silica and metal oxides are the main components of fly ash. To explore the effect of the metal oxides on absorbents, we analyzed the integrated CO2 absorption-desorption process using N-methyldiethanolamine (MDEA) as the standard and an amine absorbent after adding different metal oxides. The effects of each metal oxide on CO2 capture by the MDEA solution, including CO2 reaction heat, absorption rate, cyclic loading, and carbonation rate, were assessed. It was found that supplementation with appropriate calcium oxide and magnesium oxide proportions accelerates the CO2 absorption rate and shortens the saturation time of the MDEA solution by 9%-17%. Magnesium oxide and calcium oxide were precipitated as carbonates during absorption. The CO2 reaction heat of the MDEA solution increased by 95% after adding magnesium oxide, thereby significantly increasing the energy consumption of the desorption process. On the basis of the experimental studies, the increase in CO2 absorption rate by MDEA after adding MgO and CaO may be mediated through two different mechanisms.

Performance improvement of waste oyster-shell powder–cement binary system via carbonation curing

The dumping of significant amounts of industrial waste oyster shells causes marine pollution and economic loss. Grinding and processing waste oyster shells into oyster shell powder (OSP) to substitute a portion of cement can potentially reduce marine pollution and greenhouse gas emissions. Herein, 0, 15, and 30% OSP were added to cement and cured by employing different methods with and without CO2. The dilution effect of the OSP reduced the heat of hydration. The compressive strength and electrical resistivity of all the mixtures increased after carbonation curing compared to the seal cured specimens. The CO2 absorption contents and rate of carbonation increased with an increase in the OSP content. During carbonation curing, OSP contributes to the carbonation of the cement material, forming large amounts of carbonation products (calcite, aragonite, and vaterite). The precipitation of carbonation products acts as a pore filler, significantly increasing the mixture's performance more than seal curing. Therefore, OSP has significant potential as a replacement material for cement via carbonation curing, and its promising CO2 capture and storage capacities provide a viable solution for greenhouse gas reduction.

Reduction of energy consumption in post-combustion carbon capture process via amine-functionalized metal-organic frameworks

In this study, CO2 capture performance of ethylenediamine-functionalized Mg-MOF-74 (EDMOF-74) suspended in 30 wt% monoethanolamine (MEA) aqueous solution is analyzed. A CO2 absorption experiment was performed in a bubble column reactor based on EDMOF-74 concentrations of 0.005, 0.01, 0.05, and 0.1 wt% for different ethylenediamine loadings. It shows that EDMOF-74/30 wt% MEA mixtures improve CO2 absorption performance by a maximum of 7.18 % as compared with the base fluid. Subsequent experiment based on large-volume feed gas reveals a less volatile CO2 absorption rate. By adding EDMOF-74 to the 30 wt% MEA aqueous solution in a cyclic CO2 absorption experiment to evaluate its industrial application, an increase in durability is indicated, which implies a reduction in energy consumption during CO2 regeneration. A feasibility study on the reduction of CO2 regeneration energy was investigated in terms of the results of cyclic experiment and the facility status of Boryeong power plant. The CO2 regeneration energy can be reduced by 13.64 %, which corresponds to a decrease of 484,233 MWht/year for 1 unit of the Boryeong power plant. The abovementioned approach is expected to compensate for the disadvantages of MEA in the industrial CO2 capture process, i.e., low CO2 capacity and high CO2 regeneration energy input.

Study on Benzylamine(BZA) and Aminoethylpiperazine(AEP) Mixed Absorbent on Ship-Based Carbon Capture

To find suitable absorbents for ship-based carbon capture, the absorption and desorption properties of four mixed aqueous amines based on BZA were investigated, and the results indicated that BZA-AEP had the best absorption and desorption performance. Then, the absorption and desorption properties of different mole ratios of BZA-AEP were tested. The results showed that the average CO2 absorption rate had the highest value at the mole ratio of BZA to AEP of three. The average CO2 desorption rate had the maximum value at the mole ratio of BZA to AEP of one. Three fitted models of the absorption and desorption performance of BZA-AEP based on the test data were obtained. The p-values of all three models were less than 0.0001. Considering the performance and material cost, the BZA-AEP mole ratio of 1.5 is more appropriate for ship carbon capture. Compared with MEA, the average CO2 absorption rate increased by 48%, the CO2 desorption capacity increased by 120%, and the average CO2 desorption rate increased by 161%.

Activated Carbon Produced from the Hydrothermal Treatment of Glucose with KOH Activation for Catalytic Absorption of CO2 in a BEA-AMP Bi-Solvent Blend.

The amine-based postcombustion CO2 capture (PCC) process involves absorption of CO2 into a solvent and then regenerating the solvent to produce CO2. In this study, the effect of an activated carbon (AC) catalyst, synthesized through hydrothermal treatment and furnace activation on CO2 absorption in a 4M BEA/AMP amine blend, was evaluated and compared with that of a KMgO/CNTs (1:4) catalyst. The physical and chemical properties of AC were investigated with a scanning electron microscope (SEM), CO2 temperature-programmed desorption (CO2-TPD), Brunauer-Emmett-Teller (BET), powder X-ray diffraction (XRD), and thermogravimetric analyzer (TGA) and compared with the KMgO/CNTs (1:4) catalyst. The results showed that when compared against noncatalytic CO2 absorption, AC enhanced the linear rate of CO2 absorption by 33.3%, while for KMgO/CNTs, it was reported as 25.5%. The relatively higher surface area, combined with the higher number and strength of basic sites of AC relative to the KMgO/CNTs (1:4) catalyst, provided effective basic reaction sites for CO2 absorption, thereby enhancing the rate of CO2 absorption into the amine. AC was also relatively easier to synthesize which would provide a good replacement for the CNT-based catalyst which has carcinogenic tendencies.

Investigation on the Performance of CO2 Absorption in Ceramic Hollow-Fiber Gas/Liquid Membrane Contactors.

The absorption efficiencies of CO2 in ceramic hollow-fiber membrane contactors using monoethanolamine (MEA) absorbent under both cocurrent- and countercurrent-flow operations were investigated theoretically and experimentally; various MEA absorbent flow rates, CO2 feed flow rates, and inlet CO2 concentrations were used as parameters. Theoretical predictions of the CO2 absorption flux were analyzed by developing the mathematical formulations based on Happel's free surface model in terms of mass transfer resistances in series. The experiments of the CO2 absorption were conducted by using alumina (Al2O3) hollow-fiber membranes to confirm the accuracy of the theoretical predictions. The simplified expression of the Sherwood number was formulated to calculate the mass transfer coefficient of the CO2 absorption incorporating experimental data. The data were obtained numerically using the fourth-order Runge-Kutta method to predict the concentration distribution and absorption rate enhancement under various fiber packing configurations accomplished by the CO2/N2 stream passing through the fiber cells. The operations of the hollow-fiber membrane contactor encapsulating N = 7 fiber cells and N = 19 fiber cells of different packing densities were fabricated in this work to examine the device performance. The accuracy derivation between experimental results and theoretical predictions for cocurrent- and countercurrent-flow operations were 1.31×10-2≤E≤4.35×10-2 and 3.90×10-3≤E≤2.43×10-2, respectively. A maximum of 965.5% CO2 absorption rate enhancement was found in the module with embedding multiple fiber cells compared with that in the device with inserting single-fiber cell. Implementing more fiber cells offers an inexpensive method of improving the absorption efficiency, and thus the operations of the ceramic hollow-fiber membrane contactor with implementing more fiber cells propose a low-priced design to improve the absorption rate enhancement. The higher overall CO2 absorption rate was achieved in countercurrent-flow operations than that in cocurrent-flow operations.

Study on the composite gravel preparation and the synergistic absorption of CO2 by fly ash of CFB boiler

The cooperative treatment of fly ash and fuel gas of coal-fired plants is a promising way. In this study, circulating fluidized bed fly ash (CFBFA), gypsum, Portland Cement (PC) and water were mixed and pelleted, with carbonation curing by fuel gas to prepare the composite gravel. Experimental results showed that CSH gel and ettringite were the main hydration products and calcite was the main carbonation product. The highest strength of the composite gravel reached 11.11 MPa at 28d which was positively related to the absorption rate of CO2, and the CO2 absorption rate reached 4.789 %. Both hydration and carbonation reactions contributed positively to strength. The carbonation process caused a higher Si 2p binding energy, and the addition of gypsum led to a higher binding energy of Ca 2p. The addition of gypsum increased the porosity and main pore diameter. The porosity and main pore diameter determined the strength of composite gravel. It was observed that gypsum acted as a catalyst to promote the formation of hydration products and carbonation products. This study provided a theoretical support for the preparation of composite gravel which was a substitute for river sand and natural gravel.

Experimental investigation of carbon dioxide absorption by amine-based nanofluids containing two-dimensional hexagonal boron nitride nanostructures

In this research, the influence of the two-dimensional hexagonal boron nitride nanostructures (hBNNs) upon the process of carbon dioxide (CO2) absorption into the aqueous solution of methyl diethanolamine (MDEA) was investigated. The absorption tests were performed using the pressure drop technique in a stirred thermostatic reaction chamber. The hBNNs were synthesized through the sonication-assisted hydrolysis method and characterized by FTIR, XRD, FESEM, EDX, and TGA techniques. After synthesis and characterization, the nanostructures were dispersed in an aqueous MDEA solution at different concentrations via ultrasonication and without surfactants. The stability of the nanodispersions was measured by the zeta potential analysis. The effect of hBNNs loading, MDEA concentration in the base fluid, and amount of nanofluid on the absorption process was also studied. The results revealed that the addition of hBNNs into the base fluids up to a concentration of 0.025 wt% improves the initial CO2 absorption rate and the total amount of absorbed CO2, yet, by further increasing the concentration, the mentioned values are decreased. According to the absorption measurements, for the 5 wt% aqueous solution of MDEA containing 0.025 wt% hBNNs, the highest enhancement of the initial CO2 absorption rate and the total absorbed CO2 into the nanofluid were 5.1 and 3.98%, respectively. The results also indicated that higher MDEA concentrations weaken the enhancement effect of the nanofluids. Furthermore, it was observed that the effect of the nanofluids on the absorption process is independent of their amount. According to the experiments, hBNNs could be reused for at least five consecutive cycles, without a significant drop in the nanofluid efficiency. The results of this study indicated that the use of the two-dimensional hBNNs at very low concentrations improved the CO2 absorption process.

Statistical Optimization of Carbon Dioxide Capture Performance by Tri-Solvent System of MEA-DEA-PZ from the Stored Gas Reservoir

Aims/Objective: The current study evaluates the effectiveness of a blended tri-solvent system composed of monoethanolamine (MEA), diethanolamine (DEA), and piperazine (PZ) for removing the carbon dioxide (CO2) from the stored gas reservoir. The developed system is intended to be both environmentally benign and productive. Methods: The CO2 absorption was carried out for the total solvent (5, 10, and 15% v/v), during the course of three temperature ranges (20, 25, and 30°C) while maintaining the reservoir pressure of 1.5, 2, and 2.5 bar. The fraction of DEA: MEA has been restricted to 0.2, 0.5, and 0.8, with simultaneous loading of anhydrous PZ ranging from 0 to 2 gm. and agitation speed for step intervals of 300, 600, and 900 rpm. For the purpose of investigating the synergetic effects of the process parameters on the rapid absorption of CO2 (ξ) and the initial CO2 absorption rate (ε0), Box-Behnken Design (BBD) of response surface methodology (RSM) has been exploited. The design of experiments (DoE) assisted artificial neural network (ANN) and metaheuristic approach of hybridising ANN-whale optimization algorithm (WOA) was also developed and utilised to train and test the developed model. Three optimization models based on RSM, DoE-WOA and ANN-WOA were compared. Under the optimized operating conditions pertaining to DoE, DoE-WOA and DoE-ANN-WOA, (ε0 = 3.340, 3.460 3.513 gm./min-250 mL) and (ξ = 17.114, 18.069, 18.145 gm./250 mL) were obtained. Results: The hybridised DoE-ANN-WOA shows promising results in correlation with the experimental outcomes having error % for ε0 & ξ of 0.790 & 1.31. Conclusion: The DoE-ANN-WOA tends to be selected to predict the optimal absorption conditions as compared to other optimization techniques used in current article.

Pilot test of water-lean solvent of 2-(ethylamino) ethanol, 1-methyl-2-pyrrolidinone, and water for post-combustion CO2 capture

Water-lean solvent for post-combustion CO2 capture is promising to significantly reduce regeneration energy. It hasn’t been put into commercial application due to unsolved challenges including water balance issue, increased viscosity, and high volatility. Even though numerous water-lean solvents were developed in laboratory, rare of them were tested in pilot scale. Water-lean solvent of 2-(ethylamino) ethanol (EMEA) dissolving into 1-methyl-2-pyrrolidinone (NMP) and water was tested in a CO2 capture pilot with flue gas rate of 280 m3/h. Effects of liquid/gas ratio and reboiler steam rate on CO2 removal efficiency, regeneration energy, lean/rich heat exchanger performance, and volatile amine emission were investigated. Water-lean EMEA achieved CO2 removal efficiency greater than 90 % and the lowest regeneration energy of 2.3 GJ/tCO2, which is 43 % lower than that of 5 M MEA. Water-lean EMEA showed significantly reduced latent heat, greater CO2 capacity, and lower reaction heat (secondary amino) than aqueous MEA and amine blends. It was found that water-lean EMEA regeneration in stripper had extremely lower lean loading (0.1–0.5 mol CO2/L) than aqueous MEA and amine blends, which enables a faster CO2 absorption rate in absorber and a greater CO2 capacity, but also causes larger volatile amine emission. Volatile amine emission after water wash was 110–380 mg/m3. 13C NMR spectrum suggested amine carbamate dominated CO2 absorption products. Due to that increased viscosity decreases heat transfer coefficient (h), lean/rich heat exchanger temperature difference (ΔT) for water-lean EMEA (6.5–7.5℃) was greater than MEA (3.5-5℃) and amine blends (5-6℃), yet smaller than biphasic solvent (8-9℃). A negative power (-0.614) function relation between h and viscosity was fitted and can be further used to normalize sensible heat.

Performance comparation of MEA and EDA in electrochemically-mediated amine regeneration for CO2 capture

Electrochemically-mediated amine regeneration (EMAR) for CO2 capture was recently developed as a promising substitute for conventional amine-based CO2 capture by avoiding the amine thermal regeneration process. A suitable solvent is significant for the overall performance and the scale-up of the EMAR system. However, there is currently a lack of comprehensive solvent comparison methods. In this work, a systematic comparison was conducted to elucidate the absorption and desorption behavior of the most discussed monoethanolamine (MEA) and ethylenediamine (EDA) in the EMAR process. Firstly, the CO2 absorption performance was compared by considering the CO2 absorption capacity, absorption rate, and coordination ability separately. Subsequently, the performance of absorbents was compared from the perspective of thermodynamics. Results indicated that the complex of Cu(II)-EDA shows higher stability which means it is more competitive than MEA in releasing the absorbed CO2 in the EMAR process. Then, the electrochemical behaviors comparison of MEA and EDA shows that the electrochemical reactions in EDA solvent are simpler and easier to occur, but the poor diffusion performance of reactive ions in EDA hinders its scale-up application. Finally, the CO2 desorption performance in MEA and EDA was carefully studied. A competitive and practically instructive desorption energy consumption of 42.4 kJe/mol CO2 with 300 A/m2 current density was obtained in EDA solvent. Overall, compared with MEA, EDA is more recommended to be used as an absorbent in the EMAR system.

Elucidation of Operating Parameters Influencing the Ultrasonic-Assisted Absorption of Bulk CO2 Using Unpromoted and Promoted Methyldiethanolamine

Various acid gas sweetening processes can be used to separate CO2 from natural gas. As one of the most matured and widely utilized gas sweetening processes, absorption has been continuously improved to meet the stringent separation requirement. Ultrasonic irradiation has recently been introduced as an alternative technique to intensify the absorption process. Nevertheless, further studies are still needed to mature this new technique, particularly using slow kinetic absorbents possessing high inherent CO2 absorption capacity. Moreover, performing experimental studies using blended solvents in the high-frequency ultrasonic-assisted absorption system has also introduced a new idea in this field. This experimental study presents the CO2 absorption into aqueous solutions of methyldiethanolamine (MDEA) and piperazine (PZ)-promoted MDEA in an ultrasonic-assisted batch reactor. The influences of various operating parameters on CO2 absorption performance were evaluated in both promoted and unpromoted conditions. The parameters of the experiments included ultrasonic power at a frequency of 1.7 MHz, absorbent concentration, temperature, and CO2 partial pressure. Based on the results, ultrasonic power was found to be the most critical factor influencing the CO2 absorption rate. Moreover, the potential of the high-frequency ultrasonic-assisted CO2 absorption reactor was further elucidated via comparison with the conventional stirring and silent conditions under identical operating conditions. The highest CO2 absorption rate was achieved at an ultrasonic power of 12.36 W, a temperature of 70 °C, a CO2 partial pressure of 10 bar, an absorbent concentration of 50 wt %, and a promoter concentration of 5 wt %. In addition, the CO2 absorption rate in the high-frequency ultrasonic-assisted reactor using the MDEA absorbent was 28 and 52 times higher compared to stirring and silent conditions, respectively. The CO2 absorption rate enhancement was approximately 17 and 54 times higher for the PZ-MDEA.

Bipolar membrane electrodialysis combined with ozone oxidation wet scrubbing to remove SO2 and NOx from flue gas and achieve CO2 mineralization

This study proposed a new process based on bipolar membrane electrodialysis (BMED) for the one-stop simultaneous removal of SO2 and NOx and mineralization of CO2 from flue gas. The process could be divided into two simultaneous aspects: the mineralization of CO2 into calcium carbonate using calcium ions in seawater; meanwhile, and the removal of SO2 and NOx by wet scrubbing. During this process, the OH– generated by the bipolar membrane was used as an absorbent, and ozone (O3) was used as an oxidizer for NO in the flue gas. It was found that at higher current density, the absorption rate of CO2 could be enhanced, but the calcium and magnesium were precipitated in the form of carbonate at the same time, and the product was no longer pure calcium carbonate product, thus reducing the purity and added value of the product. Enhancing the liquid flow rate could reduce the membrane surface resistance, thus effectively decreasing the energy consumption of the system. The increase of SO2 concentration and n (O3/NO) could significantly improve the NOx removal efficiency, however, higher SO2 concentration would consume more OH– and inhibit CO2 absorption. Under the optimal conditions, the average CO2 absorption rate, decalcification rate, and denitrification rate were 53. 57%, 92.56%, and 87. 61%, respectively, and the desulfurization rate was close to 100%. Given the high energy consumption in the decalcification process and the problem that the by-product was calcium carbonate with mixed crystal form, the experiment was optimized. The electrodialysis process could produce aragonite-type calcium carbonate, which was utilized as crystal seed to ensure the purity of subsequent by-products. Especially, the energy consumption was effectively reduced by utilizing the accumulation of carbonate and bicarbonate in the mother fluid of the electrodialysis process through the self-crystallization process of calcium carbonate induced by crystal seed to shorten the time of the electrodialysis process.

Physiology of the forage cactus cultivate Opuntia stricta (Haw.) Haw under different irrigation frequencies in the Semiarid

The objective of this work was to evaluate the physiological variables of the cultivar Opuntia stricta (Haw.) Haw in the first cycle and in the regrowth, under different frequencies of drip irrigation, cultivated in the Agreste da Paraíba mesoregion. Therefore, a randomized block design was used, with 2 treatments (irrigation frequencies) and 4 replications (blocks), with each treatment repeated 3 times within the block (triplicate) totaling 24 experimental plots. For physiological variables, data were evaluated by analysis of variance (ANOVA) and means compared by t test at 5% probability using SAS ® (2002). The present study shows that the stress of environmental conditions had a greater impact on the frequency of irrigation every 28 days, since the forage cactus irrigated every 7 days had the highest internal concentration of CO2; CO2 absorption rate; instant efficiency in water use; intrinsic efficiency of water use; instantaneous carboxylation efficiency, both in the first cycle and in the regrowth period. Respiratory rate and stomatal conductance did not differ between irrigation frequencies for both cycles, showing the good adaptation of the cultivar to the semiarid region.