Aqueous MDEA Solutions Research Articles

Development of a selective sequential process for H2S enrichment and CO2 capture in aqueous MDEA solutions

The typical acid gas removal process can simultaneously remove acid gases from the raw gas using an aqueous MDEA solution. But it cannot further separate and capture hydrogen sulfide and carbon dioxide, and increases the burden on subsequent processing. Recovering carbon dioxide from that not only increases the H2S content in the acid gas, but also achieves the CO2 capture. To realize these, acid gas enrichment and carbon dioxide capture are integrated into the typical acid gas removal process. In this study, a novel selective sequential process in aqueous MDEA solutions is proposed for H2S enrichment and CO2 capture. And an optimization framework is proposed to optimize the parameters of the whole process, mainly to improve the efficiency of the column equipment. It is found that small diameter column is suitable for enhancing selectivity and large diameter column is suitable for maximizing productive capacity. To demonstrate the performance of the proposed process, the evaluation results, carbon sulfur ratio (3.81), return on investment (6.26) and carbon dioxide capture ratio (−0.63) are obtained from technical, economic and environmental evaluations. In comparison with the typical process, the novel process can achieve H2S enrichment and CO2 capture while remaining economically viable. This study presents a method for collaborative removal of H2S and CO2 in acid gas removal process. It is advantageous to reduce carbon dioxide emissions.

Amino acid-based ionic liquid as a promising CO2 sorption increasing agent by aqueous MDEA solution

The present study aims to enhance the efficiency of CO2 absorption by aqueous MDEA solutions and reduce the energy consumption of the process by designing combined absorbent systems. For this, a novel ionic liquid based on the amino acid glycine, known as bis(2-hydroxyethyl)dimethylammonium glycinate ([M2E2A][Gly]), was synthesized and investigated as a carbon dioxide sorbent. The composition was confirmed using 1H NMR. The sorption capacity of neat [M2E2A][Gly], its aqueous solutions and amine + IL aqueous mixtures was evaluated gravimetrically at different temperatures and concentrations of comprising components. The study observed an increase in both the sorption capacity and the rate of chemical reaction with carbon dioxide when using this compound as an additive. The H2O/MDEA/[M2E2A][Gly] absorbent (50/30/20 wt%) exhibited the highest sorption capacity of 2.98 mol CO2·kg-1solution. Furthermore, a mechanism of CO2 interaction with the H2O/MDEA/[M2E2A][Gly] absorbent was suggested and confirmed using FTIR spectroscopy. To assess the effect of the IL concentration on the absorbent’s viscosity behavior, studying rheological properties of absorbent with different contents of [M2E2A][Gly] were studied.

Zwitterionic "Solutions" for Reversible CO2 Capture.

The zwitterions resulting from the covalent attachment of 3- or 4-hydroxy benzene to the 1,3-dimethylimidazolium cation represent basic compounds (pKa of 8.68 and 8.99 in aqueous solutions, respectively) that chemisorb in aqueous solutions 0.58 mol/mol of carbon dioxide at 1.3 bar (absolute) and 40 °C. Equimolar amounts of chemisorbed CO2 in these solutions are obtained at 10 bar and 40 °C. Chemisorption takes place through the formation of bicarbonate in the aqueous solution using imidazolium-containing phenolate. CO2 is liberated by simple pressure relief and heating, regenerating the base. The enthalpy of absorption was estimated to be -38 kJ/mol, which is about 30 % lower than the enthalpy of industrially employed aqueous solutions of MDEA (estimated at -53 kJ/mol using the same experimental apparatus). The physisorption of CO2 becomes relevant at higher pressures (>10 bar) in these aqueous solutions. Combined physio- and chemisorption of up to 1.3 mol/mol at 40 bar and 40 °C can be attained with these aqueous zwitterionic solutions that are thermally stable and can be recycled at least 20 times.

An intensified low-energy ultrasonic plug reactor for CO2 desorption from single and novel blended absorbents

Ultrasound as an efficient emerging technology for CO2 desorption enhancement has attracted great attention in recent years. In the present study, a mini-plug reactor was equipped with a 28 kHz ultrasound transducer and employed for CO2 stripping from different amine-based solutions. First, 30 wt% aqueous solutions of MEA, DEA, DIPA and MDEA were investigated under the effect of desorption temperature and flow rate of the solution. 26.4% energy saving and around 70% enhancement in desorption was reached for MEA at 55℃ using ultrasound irradiation. Some novel tri-solvent blends were also studied in the optimum temperature. Among four blended amine solutions, new aqueous solution of MEA+DIPA+AMP showed the maximum desorption rate of 84.2% and minimum regeneration energy of 2.7 MJ/kgCO2 using the designed ultrasound-equipped plug reactor. It was concluded that CO2 desorption from the MEA+DIPA+AMP blend could reduce required energy consumption by around 35% compared to 30 wt% MEA using conventional method. The present study provided an efficient intensified desorber as well as a kind of tri-solvent blend as a brilliant system for CO2 capture process at lower temperature than conventional.

Shape controlled ZIF-8 crystals for carbonic anhydrase immobilization to boost CO2 uptake into aqueous MDEA solution

Metal-organic frameworks (MOFs) have been extensively studied as candidate materials for enzyme immobilization over recent years. In this work, carbonic anhydrase was immobilized in ZIFs by “in situ” immobilization method. The growth state of ZIF-8 was adjusted by adjusting the ratio of Zn2+and 2-Hmim to obtain crystals with different morphologies (cubic-, dodecahedral- and leaf-shape). In addition, different surfactants (cationic surface-active agent, an-ionic surfactant, and non-ionic surface-active agent) were added as “shape-inducing agents” to further regulate the crystal shapes, thus affecting the activity of enzyme immobilization in ZIFs. Through CO2 absorption test, it was found that the thick leaf-shaped CA/ZIF-L-(PVP) induced by PVP had a higher relative activity (150%) than other shapes (cubic, dodecahedral, “burr puzzle” shape, “interpenetration leaves” shape, etc.) of immobilized enzymes. In addition, CA/ZIF-L-(PVP) exhibited excellent reusability and stability, which maintained a relative activity of 131% after 5 cycles, and remained approximately 99% relative activity after 15 days at 40 °C in MDEA solution.

Experimental investigation of waste tyres pyrolysis gas desulfurization through absorption in alkanolamines solutions

Pyrolysis of waste tyres produces harmful hydrogen sulfide and other mercaptan compounds as by-products. The current study is concerned with the purification of hydrogen-rich pyrolysis gas from hydrogen sulfide gas that is present in a great amount (up to 5.1% mol at 420 °C), and mercaptans that are also problematic impurities. The method proposed is absorption by alkanolamines which is one of the most economical methods applied in natural gas sweetening. However, it has not been adopted in waste tyre pyrolysis gas purification yet. Two organic absorbents were tested, diethanolamine (DEA), N-methyldiethanolamine (MDEA) as well as theirs blends, at various concentrations. The application of 30 wt% DEA in water reduced H2S emission by 98%. In turn, 40 wt% MDEA aqueous solutions reduced H2S emission by 97%. The best results were produced when 30 wt% DEA was mixed with 40 wt% of MDEA (1:1 vol ratio) which allowed a removal of 99% of H2S from the pyrolysis gas. Moreover, the maximum H2S emission was 7 ppm, and a level below 5 ppm was kept for 99% of experiments duration. Finally, the application of this mixture also reduced significantly the concentrations of other sulfur-containing compounds such as methyl mercaptan and carbonyl sulfide (a minimum of 98%), ethyl mercaptan (∼90%), and carbon disulphide (by more than 99%). Thus, aqueous solvent mixture of 30 wt% DEA with 40 wt% of MDEA (1:1 v/v) can be recommended as a potential desulfurization method for waste tyres pyrolysis gas.

Investigation of foaming tendency of aqueous mixture of MDEA+IPAE for carbon dioxide absorption

This paper provides an experimental study on the foam behavior of aqueous solutions of MDEA and IPAE by the modified standard ASTM D892. The effect of different operating parameters, including temperature, amine concentration, and flow rate, in the range of 25–35 °C, 20–40 wt%, and 1–3 L/min, respectively, were studied using the response surface method. The physical properties of solutions such as viscosity, density, and surface tension were measured. At first, foam tests were performed only with MDEA, a conventional amine in gas purification, to obtain the effect of different operating conditions and their interactions on the foam volume and break time. A specific operating condition was selected based on obtained responses, and IPAE was added to MDEA. The mixture of MDEA and IPAE had better foam behavior than pure MDEA. Foam tests in the presence of formaldehyde and formic acid proved that IPAE acts as a defoamer even in the presence of impurities. A silicone antifoam was used, and there was no definite trend for foam volume, but with increasing antifoam concentration, the break time increases from 22.67 s to 150 s. Finally, 0.1 wt% antifoam was added to the combination of 15 wt% MDEA + 5 wt% IPAE + 1 wt% formaldehyde or formic acid to investigate its effect in the presence of impurities. The foam volume decreased by about 18 % in the formaldehyde-containing mixture, and the break time increased by about 61 %. Also, the foam volume was reduced by about 6 % in the formic acid mixture, and the break time increased significantly by 207 %.

CO2 absorption/desorption rates in aqueous DEEA/MDEA and sulfolane-contained hybrid solutions: effects of physical properties and reaction rate.

The rates of CO2 absorption into fresh and regenerated aqueous solutions of N,N-diethylethanolamine (DEEA), N-methyldiethanolamine (MDEA), and their mixture with sulfolane are investigated in a batch stirred cell reactor. The data are obtained in the temperature range of 293.15-313.15K, pressures up to 800kPa, and different concentrations of alkanolamines and sulfolane. The diffusion coefficients and Henry's law constants for all the solutions are obtained. The absorption rate of DEEA solutions increased by increasing component concentrations and pressure, but the effects of temperature on the absorption rates of hybrid and aqueous DEEA solutions are different. Comparison of absorption rates in aqueous and hybrid solutions under the same conditions can determine the role of sulfolane as the physical solvent. It has been found that sulfolane acts as an effective absorption activator in the hybrid DEEA solutions. However, in the MDEA solutions, in all experimental conditions except for high pressure ([Formula: see text] 400kPa) and certain MDEA concentration (20 wt%), sulfolane has a negative effect on the absorption rate. The absorption rates of regenerated aqueous DEEA solutions are in the range of 50.5-87.7% of fresh ones, while these values for the hybrid DEEA solution are in the range of 75-90.5%. These values for the aqueous and hybrid MDEA solutions are almost equal. Based on the values of Hatta number and enhancement factor, the CO2 absorption regime in the DEEA solutions is determined as the fast second-order reaction. The absorption rate can be interpreted considering the tradeoff between kinetics and thermodynamics of CO2 absorption in the aqueous and hybrid DEEA/MDEA solutions. The desorption rates in hybrid DEEA/MDEA solutions are higher than those in aqueous solutions.

A high efficient absorbent for the separation of H2S from low partial pressure coke oven gas.

To high efficiently remove H2S from low partial pressure coke oven gas (COG), a novel activator (tetramethylammonium arginine, [N1111][Arg]) was used to blend with N-methyldiethanolamine (MDEA) for the absorption of H2S. High concentrated [N1111][Arg]-MDEA aqueous solution was used as absorbent. Thermodynamic properties including absorption amount and H2S loading values were measured, then the kinetic apparent absorption rate was calculated based on the change of absorption amount with time. The removal efficiency of H2S in simulated COG was verified in tray towers. Compared with monoethanolamine (MEA)-MDEA and tetramethylammonium glycinate ([N1111][Gly])-MDEA aqueous solutions, [N1111][Arg]-MDEA aqueous solution takes advantages of higher absorption capacity, absorption rate and removal efficiency. Our results showed that the proposed absorbent has good industrial application prospect in coke oven gas desulfurization, because it achieved 100% removal of H2S in the tray tower containing only 4 sieve plates under high concentrated condition (water content < 45%), which may significantly decrease the energy consumption.

CO2 Heat of Absorption in Aqueous Solutions of MDEA and MDEA/Piperazine

In the present study, calorimetric measurements were conducted to determine CO2 behavior in aqueous solutions of 30 and 50 wt % N-methyl diethanolamine (MDEA) and 40 + 10 wt % MDEA–piperazine (PZ) ...

CO2 Reactive Absorption into an Aqueous Blended MDEA and TMS Solution: Experimental and Modeling

In this research, the significant environmental process of CO2 capture is investigated into an aqueous blended MDEA + TMS solution using a stirrer reactor experimentally and numerically. The experiments were designed based on the response surface methodology (RSM) under operating conditions of a pressure range of 2–8 bar, a temperature range of 20–70 °C, MDEA, and TMS concentration range of 10–20 wt%. The results indicated that by enhancing the initial pressure from 3.5 to 8 bar, the equilibrium CO2 loading increases by 17.8%. Based on RSM and central composite design method, the maximum values of CO2 loading and absorption percentages were 0.308% and 72.73%, respectively, at appropriate conditions of the temperature of 32.5 °C, the pressure of 3.5 bar, and MDEA and TMS concentrations of 12.5 wt%. A new relation for CO2 loading was correlated with a correlation coefficient of 0.994, as a function of studied independent variables.

CO2 absorption/desorption in aqueous DEEA/MDEA and their hybrid solutions with sulfolane

CO2 absorption capacities in aqueous and hybrid solutions were investigated by applying a batch reactor under intermediate pressures up to 800 kPa. Tertiary alkanolamine of diethyl ethanol amine (DEEA), N-methyl di ethanol amine (MDEA), and physical solvent of sulfolane were used. Utilizing DEEA and sulfolane in the current research is considered as the first attempt to take the advantages of both chemical and physical solvents in CO2 capturing. The absorption capacities were increased by increasing the reactant concentration, pressure, and by decreasing the temperature. A higher absorption capacity was observed for the aqueous DEEA solution compared to the other solutions except in high pressures, in which the DEEA hybrid solution represented a higher capacity. Regeneration of the solutions by desorption at 80 °C revealed the effective role of the physical solvent (sulfolane) that yields higher regeneration efficiencies of absorption capacities for the hybrid solutions. The regeneration efficiencies of absorption capacity of the hybrid DEEA solution were in the range of 88.1%–99.1% while those efficiencies for the aqueous DEEA solution were in the range of 50–83.1%. These values for the hybrid and aqueous MDEA solutions were 93.4–98.8% and 85.5–94.2%, respectively. In conclusion, adding sulfolane to the aqueous DEEA solution significantly improved the absorption capacity of the regenerated solution.

Polyethyleneimine functionalized graphene oxide/methyldiethanolamine nanofluid: Preparation, characterization, and investigation of CO2 absorption

Polyethyleneimine(PEI) functionalized graphene oxide was synthesized and completely described by SEM, FTIR, TGA, EDX, XRD, BET and XPS analysis to identify the structure. Then, the as-prepared GO and PEI-GO was dispersed in a 40 wt% aqueous MDEA solution to obtain an amine-based nanofluid. The prepared nanofluid was examined by zeta potential analysis to examine the stability of the solution in the presence of nanoparticles. Absorption experiments were carried out at 303.15, 313.15, 323.15 and 333.15 K and a pressure range of 100–2300 kPa. When 0.1 and 0.2 wt% GO was added to the amine solution, the CO2 absorption capacity was improved up to 9.1% and 10.4%, respectively. The CO2 absorption capacity of the solution in the presence of PEI-GO showed an enhancement rate of 15%. Comparison of the experimental data verified that the addition of PEI-GO greatly affected the CO2 absorption capacity enhancement relative to the addition of GO. Experimental data showed that raising the temperature negatively affect the CO2 absorption rate while higher absorption capacities were observed with increasing the CO2 partial pressure. The increase in partial pressure was the predominant effect compared with temperature.

Study on the Viscosities of MDEA-Amino Acid Ionic Liquid Aqueous Solutions

The viscosities of 1-butyl-3-methylimidazolium glycine ([Bmim][Gly])-N-methyldiethanolamine (MDEA), tetramethyl amine glycine ([N1111] [Gly])-MDEA and l-butyl-3-methyl-imidazolium lysine ([Bmim][Lys])-MDEA aqueous solutions were respectively measured by using the NDJ-5S digital rotational viscometer. The temperatures ranged from 303.2K to 323.2K. The mass fractions of MDEA and amino acid ionic liquids (AAILs) respectively ranged from 0.30 to 0.45 and 0.05 to 0.15. The Weiland equation was used to correlate and predict the viscosities of [Bmim][Gly]-MDEA, [N1111] [Gly]-MDEA and [Bmim][Lys]-MDEA aqueous solutions. The temperature and mass fraction dependences of the viscosity of MDEA-AAIL aqueous solutions were demonstrated on the basis of experiments and calculations.

Correlation and prediction of H2S and mixture of CO2 + H2S solubility in aqueous MDEA solutions using electrolyte modified HKM plus association EoS

In this study, the electrolyte mHKM Plus Association (emHKM-CPA) EoS is applied to correlate H2S solubility in MDEA aqueous solutions at different conditions including temperatures between 298 and 413 K and pressures up to 50 bar. Moreover, weight percent range of MDEA is up to 50. The mHKM and the Wertheim association terms in addition to MSA theory together with the Born terms are the four sections of the model. More than 302 experimental data utilized. Implementing a reactive bubble point pressure calculation technique, liquid phase concentrations and then bubble pressure and vapor phase compositions are calculated. The obtained overall AAD% is 13.33 that illustrates so better performance in comparison with the other models present in the literature.Furthermore, 25 experimental data used to predict the simultaneous solubility of CO2 and H2S. The AADs% for CO2 and H2S partial pressures obtained 32.64 and 22.99, respectively. Moreover, some thermal properties of the present components and mixtures are predicted.As the results show, emHKM-CPA shows very good performance in both correlation and prediction of acid gas solubility.

Absorption characteristics and kinetics of CO2 capture into N-methyldiethanolamine aqueous solution catalyzed by the immobilized carbonic anhydrase

Carbonic anhydrase (CA) is the most effective CO2 hydratase catalyst, but the poor storage stability and repeatability of CA limit its development. Therefore, CA was immobilized on the epoxy magnetic composite microspheres to enhance the CO2 absorption into N-methyldiethanolamine (MDEA) aqueous solution in this work. In the presence of immobilized CA, the CO2 absorption rate of MDEA solution (10 wt%) (0.63 mmol·min−1) was greatly improved by almost 40%, and their reaction equilibrium time was shortened from 150 min to 90 min compared with that into MDEA solution. The results indicated that the absorption of CO2 into MDEA solution had been significantly enhanced by using CA. After the 7th reuse recycle, the activity of the immobilized CA was still closed to its initial value at 313.15 K. Moreover, enzyme catalytic kinetics of immobilized CA was investigated using the p-nitrophenyl acetate (p-NPA) as substrate. The values of Michaelis–Menten constant (Km) and the maximum velocity (Vmax) of the immobilized CA were calculated to be 27.61 mmol/L and 20.14 × 10−3 mmol·min−1·mL−1, respectively. Besides, the kinetics of CO2 reaction into MDEA with or without CA were also compared. The results showed that CO2 absorption into CA/MDEA aqueous solution obeyed the pseudo first order regime and the second order kinetics rate constant (k2) was calculated to be 929 m3·kmol−1·s−1, which was twice higher than that of MDEA aqueous solution without immobilized CA (k2=414 m3·kmol−1·s−1) at 313.15 K.

Implementation of electrolyte CPA EoS to model solubility of CO2 and CO2 + H2S mixtures in aqueous MDEA solutions

Abstract The electrolyte version of SRK plus association equation of state (eSRK-CPA EoS) was employed to correlate CO2 solubility in MDEA aqueous solutions. The applied model comprises the classic form of CPA EoS including SRK EoS plus Wertheim association term in addition to MSA theory and Born terms so that the two last terms are responsible for the long-range interactions. A reaction-containing bubble pressure computation technique comprising two nested loops was utilized to model the systems. The internal loop, calculates the liquid phase concentrations via reaction, mass and charge balance equation solving, whereas, the vapor phase concentrations will be obtained in the external one. 470 experimental data were used to correlate binary subsystems and the H2O + MDEA + CO2 ternary system. Since, there not exist any binary VLE data for MDEA + CO2 subsystem, two fitting scenarios were applied. At the first scenario, the binary interaction parameter was assumed equal to zero, while, in second approach the parameter was obtained through ternary system correlation. Both scenarios show very good accuracy in that the Absolute Average Deviation percentages (AAD) obtained were 19.12% and 18.85%, respectively. Also, to show the efficiency of the used model, a comparison between our results and those of the best-known models was made. Finally, having model parameters for H2S solubility from our previous work [A. Afsharpour, Petroleum Science and Technology 35 (3) (2017) 292-298], simultaneous solubility of CO2 + H2S mixtures in MDEA solutions was predicted using the eSRK-CPA EoS with no new optimizable parameters. As the results show, the applied model has a good performance for correlation and prediction of acid gas solubility in a wide range of pressures, temperatures, acid gas loadings, and MDEA concentrations.

Absorption of carbon dioxide in aqueous MDEA solution coupling dust suppression under atomization

ABSTRACTLarge amounts of CO2 and dust particles coming from power plant flue need to be captured and removed before flue is discharged into the air. In present work, absorption of carbon dioxide in aqueous N-methylidiethanolamine (MDEA) solution coupling dust suppression has been studied in an atomization absorption column, with MDEA concentrations ranging from 0.1 to 0.5mol/L, and with atomization frequencies ranging from 50 to 80 HZ. The obtained experimental results show that absorption rate of CO2 in aqueous MDEA solution can be enhanced when the absorption process couples a dust suppression one under the condition of atomization. The reason for it is attributed to the adsorption of droplets on the solid particles which restrains the amount of entrainment and makes more droplets contact with gas so as to increase effective mass transfer area, thus resulting in the increase of CO2 absorption rate. The range of obtained enhancement factor is from 1.1 to 1.7. Mass transfer enhancement factor increases with the increase of MDEA concentration and atomization frequency at a certain range. Effective mass transfer areas and entrainment ratios suppressed have been calculated based on theoretic research. The results calculated agree with our experimental phenomena, and support the enhancement mass transfer mechanism proposed.

Polarization behavior of carbon steel in the CO2-[N1111][Lys]-MDEA aqueous solutions

Polarization behavior of carbon steel in the CO2 absorption process using tetramethylammoniumlysinate ([N1111][Lys]) promoted N-methyldiethanolamine (MDEA) aqueous solutions as absorbents was investigated at the temperatures ranging from 303.2K to 323.2K. The mass fractions of MDEA and [N1111][Lys] respectively ranged from 0.3 to 0.4 and 0 to 0.15. The effects of temperature and mass fractions of [N1111][Lys] on the polarization behavior were elucidated.

CO2 removal in tray tower by using AAILs activated MDEA aqueous solution

A tray tower was designed to verify the absorption performance of CO2 in 1-butyl-3-methylimidazolium glycinate ([Bmim][Gly]), 1-butyl-3-methylimidazolium lysinate ([Bmim][Lys]) and tetramethylammonium glycinate ([N1111][Gly]) activated MDEA (N-methyldiethanolamine) aqueous solutions. The simulated flue gas was composed of 15% (mole fraction) CO2 and 85% N2 and the experiments were performed at 313.2 K. To find a suitable absorbent composition, the mass fractions of MDEA and amino acid ionic liquids (AAILs) respectively ranged from 0.200 to 0.400 and 0.025 to 0.100. The removal efficiency of CO2 (ηCO2) and the overall volumetric mass transfer coefficient (KGav) were determined. The effects of absorbent composition (w), absorbent flow rate (L), gas flow rate (G) and plate number (Np) on ηCO2 and KGav were demonstrated. Our results showed that, when activated by AAILs, MDEA aqueous solution was able to absorb CO2 in tray tower efficiently, and both ηCO2 and KGav were significantly increased, e.g., in the case of wMDEA = 0.200, ηCO2 and KGav were increased from 43.48% to 95.55% and from 0.0069 (kmol m−3 h−1·kPa−1) to 0.0350 (kmol m−3 h−1·kPa−1), respectively, when w[N1111][Gly] was changed from 0 to 0.100, indicating AAILs activated MDEA aqueous solution is of great potential for industrial application in CO2 capture process.