Aqueous N-methyldiethanolamine Research Articles

Continuous biomethanation of flue gas-carbon dioxide using bio-integrated carbon capture and utilization

Biomethanation of carbon dioxide (CO2) from flue gas is a potential enabler of the green transition, particularly when integrated with the power-to-gas chain. However, challenges arise in achieving synthetic natural gas quality when utilizing CO2 from diluted carbon sources, and the high costs of CO2 separation using amine-based solutions make large-scale implementation unfeasible. We propose an innovative continuous biomethanation system that integrates carbon capture and CO2 stripping through microbial utilization, eliminating expenses with the stripper. Stable continuous biomethane production (83–92 % methane purity) was achieved from flue gas-CO2 using a biocompatible aqueous n-methyldiethanolamine (MDEA) solution (50 mmol/L) under mesophilic and hydrogen-limiting conditions. MDEA was found to be recalcitrant to biodegradation and could be reused after regeneration. Demonstrating the microbial ability to simultaneously strip and convert the captured CO2 and regenerate MDEA provides a new pathway for valorization of flue gas CO2.

Mixing γ-Al2O3, silica-ZIF-8 and activated carbon nanoparticles in aqueous N-methyldiethanolamine+sulfolane as a nanofluid for application on CO2 absorption

Mixing of Al2O3, superactive carbon (SAC), and Si-ZIF-8 nanoparticles in alkanol amine solvents with aqueous and hybrid context were used to study the absorption of carbon dioxide. Hybrid-based nanofluids composed of aqueous N- methyldiethanolamine (MDEA) + Sulfolane (SFL) + small amount of nano particles including-γ-Al2O3, Si-ZIF-8 and SAC in three concentrations levels, were prepared by weighting each components. The Zeta potential of suspensions was found thatγ-Al2O3, Si-ZIF-8 and super activated carbon is stable in aqueous solvents. Absorption measurements were performed using the static method at a temperature of T = 313.15 K, gas partial pressure ranges up to about 1.2 MPa, nanoparticle concentrations of 0.02 – 0.50 by weight percent, and fixed concentration of MDEA (40 wt%) and SFL (30 wt%). It was found that in the hybrid context (i.e., MDEA 40 wt% + SFL 30 wt%), the addition of γ-Al2O3 (0.1 wt%), Si-ZIF-8 (0.02 wt%) and SAC (0.1 wt%) has maximum effect on CO2 absorption. In aqueous context (i.e., MDEA 40 wt%), nanofluids used in the present study have no significant effect on CO2 capacity. The importance of the addition of SFL in nanofluids was discussed, and the experimental solubility data was modeled using Genetic Programming approach. Average absolute relative deviation (AARD), Coefficient of determination R2, as well as Root mean square error (RMSE) were 10.43% & 8.94%, 0.985 & 0.983, 0.051 & 0.054 for training and validating data, respectively. It is found that the determined parameters give satisfactory predictions in the modeling of the solubility.

Catalytic ozonation of N-methyldiethanolamine over mixed oxides derived from Mg/Fe-LDH.

The aim of this study was to evaluate the efficiency of catalytic ozonation to increase the degradation of aqueous N-methyldiethanolamine (MDEA) solutions, using two lamellar double hydroxides, namely MgxFe-LDH with x = Mg/Fe = 2, 3, were synthesized by the simple and rapid co-precipitation method. Then, the obtained materials were calcined at 400 °C for 6 h. The calcined products were respectively designated as HTcMg2Fe and HTcMg3Fe, and characterized by powder X-ray diffraction (XRD), N2 physisorption (BET), Fourier transform infrared spectra (FT-IR), and scanning electron microscopy (SEM). The powders produced were used in the ozonation reaction to remove MDEA from aqueous solutions. Experimental results showed that the highest MDEA removal efficiency is in the catalytic ozonation process. Under the optimal conditions for heterogeneous catalytic ozonation of MDEA: initial concentration of 4 Wt% MDEA, 30 °C, catalyst mass of 30 mg/100 ml solution, and contact time of 60 min. The results showed the highest percentage of COD removal, which was up to 80.76% for HTcMg2Fe higher than that of HTcMg3Fe 80.36%.

Utilization of an innovative sono-microreactor for CO2 stripping from aqueous methyldiethanolamine solution

In the present study, a novel designed ultrasound-equipped microchannel reactor has been used to improve the CO2 desorption process from aqueous N-methyldiethanolamine (MDEA) solutions. CO2 desorption rate for a microreactor without ultrasound irradiation was compared with an ultrasound-equipped one at various temperatures, flow rates, and ultrasound powers. The results revealed that ultrasound vibrations could facilitate CO2 desorption and cause a significant increase in the rate of that through generation of cavitation bubbles and turbulence. Evaluation of energy and mass transfer characteristics was performed; 37.8% energy saving and 144.2% increase in mass transfer coefficient was obtained using ultrasound at its maximum power compared to microreactor without ultrasound irradiation. Also, comparisons between the designed sono-microreactor and conventional methods for CO2 desorption were performed in terms of desorption energy consumption and mass transfer coefficient, indicating 40.9% energy saving compared to 30 wt% MEA benchmark process and 160 times increase in mass transfer coefficient. Due to its high performance in terms of energy saving and mass transfer enhancement compared to the conventional method, the newly designed sono-microreactor can be introduced as a highly efficient technique for solvent regeneration.

Equilibrium solubility measurement of carbon dioxide in hybrid solvents of aqueous N-methyldiethanolamine blended with 1-Methyl-3-octyl-imidazolium tetrafluoroborate ionic liquid at high pressures

Solubility of CO2 in the hybrid solvents composed of aqueous N-methyldiethanolamine (MDEA) blended with 1-methyl-3-octyl-imidazolium tetrafluoroborate ([Omim][BF4]) ionic liquid (IL) was measured at temperatures from (298.15–343.15 K) and pressures of (0.2–4 MPa). The experimental trials were performed in a static high pressure equilibrium cell to determine the CO2 absorption capacity of novel absorbent solutions based on the isochoric saturation technique. The experimental data showed that, by rising the concentration of IL in the absorbent solutions’, the mole fraction of dissolved CO2 gas enhances gradually. Absorption capacity of these aqueous solutions was assessed and compared with pure ILs and alkanolamine solvents, which indicates the solutions studied in this research as better hybrid solvents in terms of CO2 loading. Furthermore, a semi empirical model is used to correlate the solubility data of this work, which presents a good agreement with an absolute average deviation (AAD %) of below 1%.

Application of ePC_SAFT-MB EoS in prediction of VLE for CO2+MDEA+H2O ternary and H2O+MDEA+CO2-CH4 quaternary mixtures

The present study aims to implement an electrolyte EoS developed in our previous work [A. Raeispour Shirazi, M. N. Lotfollahi, Fluid Phase Equilib., 502 (2019) 112289] to model the vapor-liquid equilibria (VLE) of CO2 solubility in aqueous N-methyldiethanolamine (MDEA) solution (CO2+MDEA+H2O ternary mixture) as well as H2O+MDEA+CO2-CH4 quaternary mixture. The proposed electrolyte PC-SAFT+MSA+Born equation of state ((ePC_SAFT-MB) consists of PC-SAFT equation of state, the mean spherical approximation (MSA) term and the Born term. First, an appropriate association scheme for water is specified via performing VLE calculations for H2O-CO2 binary mixture and without any adjustment in binary interaction parameter (BIP). By determining the proper association scheme for water (4C), the BIPs of H2O-CO2, MDEA-CH4 and CH4-H2O binary mixtures are adjusted with binary VLE experimental data. In what follows, the nonelectrolyte PC-SAFT EoS is applied considering the obtained BIPs to predict 162 selected data points of bubble pressure for H2O-MDEA-CO2 ternary system in a wide range of temperature (298-413 K), MDEA concentration (18.7-48.8 wt.%) and CO2 loading (0.0001-1.5). The average absolute relative deviation (AAD%) for the calculation results is obtained 25.9%. In order to consider the ions interactions in the solution and to improve the precision of calculations, Born and MSA contributions are added to PC-SAFT EoS. By adjusting two BIPs (kMDEAH+−−CO2and kMDEAH+−HCO3−) and without any readjustment of other BIPs, the AAD% is obtained 15.3%. Finally, the obtained BIPs between the molecular and ionic species for proposed ePC_SAFT-MB EoS are employed to predict the VLE of H2O-MDEA-CO2-CH4 quaternary mixture without any readjustment in BIPs. For this case, the AAD% of 28.05% indicates the reliability of proposed ePC_SAFT-MB EoS for the prediction of H2O-MDEA-CO2-CH4 quaternary VLE results.

Viscosity Measurement and Correlation of Unloaded and CO2-Loaded Aqueous Solutions of N-Methyldiethanolamine + 2-Amino-2-methyl-1-propanol

This work contributes to new and complementary experimental viscosity data for blended amine mixtures of aqueous N-methyldiethanolamine + 2-amino-2-methyl-1-propanol (MDEA + AMP) solutions with and without CO2 at different temperatures and mass fractions. For the unloaded MDEA + AMP solutions, measurements were conducted with total amine mass fractions ranging from 0.30 to 0.60. In the case of CO2-loaded aqueous MDEA + AMP solutions, experiments were performed at CO2 loadings ranging from 0.11 to 0.80. Proposed correlations were used to represent viscosity at the unloaded and CO2-loaded solutions within experimental uncertainty.

Modeling H2S solubility in aqueous N-methyldiethanolamine solution using a new ePC_SAFT-MB equation of state

Perturbed chain statistical associating fluid theory (PC-SAFT) equation of state (EoS), mean spherical approximation (MSA) term and Born term are combined and proposed as a new electrolyte equation of state (ePC_SAFT-MB EoS) to model the solubility of H2S in aqueous N-methyldiethanolamine (MDEA) solutions in a wide range of temperature, pressure, MDEA concentration, and H2S loading. In order to find the best association schemes (2B, 3B and 4C) for H2O, MDEA and H2S in PC-SAFT EoS, different association schemes are considered for each one of the components in the wide range of temperature and pure parameters are determined. The binary interaction parameters (BIP) for H2O + H2S and MDEA + H2O binary systems are adjusted in the VLE calculation for different association schemes. The best result with minimum average absolute relative deviation percent (AAD%) of 2.21 and 2.72 are obtained with considering the 4C, 4C and 3B association schemes for MDEA, water and H2S, respectively. By using the obtained BIPs, 277 data points of the bubble pressure for H2O + MDEA + H2S system are predicted by PC-SAFT EoS with the AAD% of 25.5. To improve the accuracy of PC-SAFT EoS, the Born and MSA terms are added to PC-SAFT EoS. The BIPs between the ion-ion and molecules-ions are adjusted by the bubble pressure calculation algorithm using 277 experimental data points. Very good results with the AAD% of 18.6 are obtained by adjusting the binary parameters (MDEAH+−MDEA,MDEAH+−H2O,MDEAH+–H2S and MDEAH+−HS−) in H2O + MDEA + H2S ternary system. Finally, to investigate the predictive ability of the proposed ePC_SAFT-MB EoS, it is employed to model the selected 44 solubility data points of H2O + MDEA + H2S system without further adjustment for model parameters. The value of AADs% is obtained about 30.0 for the H2 S partial pressure, which shows the predictive ability of the proposed model.

Solubility of CO2 in 3-amino-1-propanol and in N-methyldiethanolamine aqueous solutions: Experimental investigation and correlation using the CPA equation of state

The solubility of CO2 in 1.3M and 2M aqueous N-methyldiethanolamine (MDEA) and 3-amino-1-propanol (MPA) solutions was experimentally measured at 298, 313, 323 and 333 K, using a pressure decay method. Since only limited experimental data exist in literature for MPA aqueous systems, the results of this study were compared with literature data mainly for 2M MDEA solutions, showing satisfactory agreement. The obtained new experimental data were used to parameterize the Cubic-plus-Association (CPA) equation of state using a pseudo chemical reaction approach, i.e. to account for chemical interactions as very strong specific intermolecular interactions, which is a crude approximation, but is necessary for applying equation of state models. It was found that the model satisfactorily describes the experimental data using six or four binary parameters for the CO2-MPA or CO2-MDEA interactions, respectively, which, however, are less than the number of adjustable parameters in similar literature models.

Study of Various Aqueous and Non-Aqueous Amine Blends for Hydrogen Sulfide Removal from Natural Gas

Various novel amine solutions both in aqueous and non-aqueous [monoethylene glycol (MEG)/triethylene glycol(TEG)] forms have been studied for hydrogen sulfide (H2S) absorption. The study was conducted in a custom build experimental setup at temperatures relevant to subsea operation conditions and atmospheric pressure. Liquid phase absorbed H2S, and amine concentrations were measured analytically to calculate H2S loading (mole of H2S/mole of amine). Maximum achieved H2S loadings as the function of pKa, gas partial pressure, temperature and amine concentration are presented. Effects of solvent type on absorbed H2S have also been discussed. Several new solvents showed higher H2S loading as compared to aqueous N-Methyldiethanolamine (MDEA) solution which is the current industrial benchmark compound for selective H2S removal in natural gas sweetening process.

Modified nonelectrolyte Wilson-NRF: A new model for strong and weak electrolyte solutions

In this work, the nonelectrolyte Wilson-NRF model has been modified and a new model composed of a modified nonelectrolyte Wilson-NRF (m-Wilson-NRF) equation and the Pitzer-Debye-Hückel equation has been used to represent thermodynamics properties of strong and weak electrolyte solutions. In the first attempt, the present model is applied to correlate activity coefficients of various aqueous solutions of salt at 25 °C and 1 bar as strong electrolyte systems. Also, the osmotic coefficients of the binary and ternary electrolyte solutions are well predicted using the present model. In following, as weak electrolyte systems the solubility of acid gases such as CO2 and H2S in aqueous N-methyldiethanolamine (MDEA) solutions have been represented by the new model in a wide range of temperature, MDEA concentration and partial pressures of acid gases. Comparisons between the results of the new model with other electrolyte models confirm the good capability of the new equation for strong and weak electrolyte solutions.

Kinetic modeling on ionic liquid mediated bi-liquid phase transfer catalyzed synthesis of bis-(2-phenylethyl) sulfide with H2S-rich methyldiethanolamine

A kinetic investigation was carried out on the utilization of H2S for the synthesis of bis-(2-phenylethyl) sulfide (PES) using ionic liquid catalyst trihexyltetradecylphosphonium chloride as a phase transfer catalyst. The method involved the absorption of H2S into aqueous N-methyldiethanolamine (MDEA) which is followed by reaction of this aqueous H2S-laden MDEA with organic reactant 2-bromoethylbenzene (2-BEB) to yield PES under liquid–liquid (L–L) phase transfer catalytic condition. The effect of various reaction parameters on the conversion of 2-BEB was studied and the product selectivity was found as 100%. A suitable reaction mechanism involving the possible paths of product formation was proposed. A novel mathematical model was developed to explain the experimental findings. This method will be helpful in overcoming the cost of disposal of organic solvents which have been used often in multiphase organic synthesis.

Enhancement of CO2 solubility in a mixture of 40 wt% aqueous N-Methyldiethanolamine solution and diethylenetriamine functionalized graphene oxide

Graphene oxide functionalized by diethylenetriamine (DETA) was prepared and characterized with SEM, XRD, BET, TGA and IR spectroscopy techniques to find out its morphology, crystalline building, porous structure, thermal stability and functional groups. The CO2 solubility in 40 wt% aqueous amine solution, 40 wt% aqueous amine solution +0.1 wt% GO, and 40 wt% aqueous amine solution +0.1 wt% DETA-GO is determined. The solubility measurements were performed at three temperature (303.15, 313.15 and 323.15 K) and CO2 partial pressures up to 2200 kPa. Addition of GO and DETA-GO to MDEA (N-Methyldiethanolamine) solution enhanced the CO2 adsorption capacity of the aqueous amine solution up to 7.5% and 12.5%, respectively. Increasing CO2 partial pressure and decreasing temperature enhanced the CO2 solubility.

High-pressure absorption study of CO2 in aqueous N-methyldiethanolamine (MDEA) and MDEA-piperazine (PZ)-1-butyl-3-methylimidazolium trifluoromethanesulfonate [bmim][OTf] hybrid solvents

In present study, high pressure CO2 absorption performance of aqueous N-methyldiethanolamine (MDEA) and its hybrid solvents with anhydrous perazine (PZ) and ionic liquid (IL) 1-butyl-3-methylimidazolium trifluoromethanesulfonate [bmim][OTf] were investigated. The absorption performance of hybrid solvents were carried out to investigate CO2 loading capacity (mol of CO2/mol of solvent), and apparent absorption rate (CO2 capture efficiency, overall rate constant). The CO2 loading capacity of aqueous MDEA and its hybrid solvents were experimentally investigated for a wide range of compositions between pressure ranges of 2 to 50bar and at three different temperatures (303.15, 313.15, and 333.15K). Furthermore, apparent absorption rate performance of hybrid solvents were determined at 303.15K temperature and 2bar pressure. The effect of temperature, CO2 partial pressure, and ionic liquid (IL) concentrations on CO2 loading of aqueous IL-amines hybrid solvents were also investigated. The results indicated that CO2 loading of hybrid solvents were increased with increase in CO2 partial pressure and IL concentration (up to 10wt%), further increased concentration of IL suppressed CO2 loading capacity. The CO2 loading capacity of hybrid solvents were also reduced with rise in system's temperature. The addition of IL and anhydrous PZ significantly enhanced CO2 capture efficiency (nCO2) and overall absorption rate constant (k) of aqueous MDEA solvent.

Rate-Based Modeling of CO2 Absorption into Piperazine-Activated Aqueous N -Methyldiethanolamine Solution: Kinetic and Mass Transfer Analysis

A comprehensive two-dimensional mathematical model based on surface renewal theory has been developed to analyze the CO2 absorption into piperazine (PZ)-activated aqueous N-methyldiethanolamine (MDEA) solvent by taking into account the structured packed bed column hydraulics, mass transfer resistances, and chemical reactions. The modeling results have been validated with the experimental data reported in the literature, and they have been found to be in good agreement with the experimental results. The effects of amine concentration, liquid temperature, initial CO2 partial pressure, liquid flow rate, and CO2 loading on the mass transfer performance have been evaluated in terms of overall mass transfer coefficient (KGav). The overall mass transfer coefficient and absorption flux of CO2 into aqueous MDEA+PZ blended solution have been calculated over the CO2 partial pressure range of 4–16 kPa, temperature range of 298–333 K, and solvent concentration of 1–3 M. To evaluate the performance of different solvents on separation process, some common industrial chemical absorbents including monoethanolamine (MEA), diethanolamine (DEA), triethylamine (TEA), MDEA and PZ were compared with a MDEA+PZ blended solution. The results indicate that CO2 absorption reaction with PZ is faster than that with MDEA, but also adding small amounts of PZ as a promoter to MDEA solvents improves significantly the absorption rate. The results show that CO2 absorption reaction with the MDEA+PZ blended solution is faster than that with TEA and MDEA, also comparable with DEA, but slower than those with MEA and PZ. The modeling results illustrate that the KGav enhances with increasing the solvent concentration, liquid temperature, and liquid flow rate, but reduces with increasing the CO2 loading and initial CO2 partial pressure. In addition, the reaction kinetics in terms of enhancement factor was found to decrease as the CO2 loading enhances and increase as the operating temperature rises.

Different Strategies for Accelerated CO2 Absorption in Packed Columns by Application of the Biocatalyst Carbonic Anhydrase

Within this work, the combination of an energetically favorable aqueous N-Methyldiethanolamine (MDEA) solution and the enzyme carbonic anhydrase is investigated in a packed column pilot plant. The use of aqueous MDEA solution for CO2 separation is already known from natural gas applications, for which an increased driving force due to the higher partial pressures of CO2 overcompensates reaction kinetic limitations. The objective of the addition of carbonic anhydrase is to countervail the loss of separation efficiency caused by the lower driving force in CO2 capture from power plant flue gases. Hence, carbonic anhydrase acts as a key to harness the energetic advantage of these solvent systems. However, application of the enzyme also poses restrictions on the process. Especially compliance with the enzyme stability limits is challenging for desorption, which is generally performed at high temperatures.In order to determine an optimal implementation of the enzyme into the process the current work presents different strategies how to apply CA as a biocatalyst in reactive absorption processes and shows how absorption efficiency is influenced. For introducing the enzyme to a packed column two approaches are investigated in this study. The simplest way of application is to dissolve the enzyme in the solvent. This allows the enzyme to work exactly where the reaction kinetic limitation can be found, in the liquid boundary layer. However, due to the temperature sensitivity of the enzyme an additional enzyme recovery step prior to the desorber might be necessary if desorption is to be performed at high temperatures. The immobilization of the enzyme inside the absorption column presents an alternative to prevent this additional separation, but may cause additional mass transfer limitations at the solid particles in which the enzyme is immobilized. The immobilization and the necessity of a suitable packing in which the enzyme particles can be filled, also makes this strategy more complicated but allows placing the enzyme at a location of most suitable process conditions in the column. But most importantly it completely avoids that the enzymes experience high temperature in the desorber. Systematic investigations of the influence of specific liquid load, liquid inlet temperature, MDEA-concentration and enzyme immobilization on absorption performance are conducted. Dissolved enzyme showed a nearly three times higher absorption performance than the immobilized enzyme under equivalent operating conditions, however the immobilized enzyme concentration used was effectively 50 times lower, meaning the result is actually quite promising for immobilized CA. From the investigated operating conditions, a liquid inlet temperature of 20°C, a MDEA concentration of 30wt.-% and a liquid flow rate of 24 m3 m-2 h-1 showed the best absorption performance with the dissolved enzyme. The measured absorption rate was 7.57 times higher than without enzyme added.

On the estimation of viscosities and densities of CO2-loaded MDEA, MDEA + AMP, MDEA + DIPA, MDEA + MEA, and MDEA + DEA aqueous solutions

As noteworthy properties of amine aqueous solutions, the densities and viscosities of aqueous N-Methyldiethanolamine (MDEA) solutions and mixtures of MDEA with 2-Amino-2-methyl-1-propanol (AMP), Diisopropanolamine (DIPA), Monoethanolamine (MEA), and Diethanolamine (DEA) were estimated under CO2 gas loading using Adaptive Neuro-Fuzzy Inference System (ANFIS), Multi-Layer Perceptron Artificial Neural Network (MLPANN), Support Vector Machine (SVM), and Least Square Support Vector Machine (LSSVM). The density and viscosity were estimated as a function of temperature, CO2 loading, pressure, and molecular weight of mixtures. In this regard, the actual data points were collected from the literature. Genetic Algorithm (GA) was employed to determine hyper variables of the LSSVM approach and Levenberg–Marquardt algorithm was employed to optimize bias and weight values of the ANN model. In addition, Particle Swarm Optimization algorithm (PSO) was used to determine membership parameters of the ANFIS approach and related parameters of the SVM were optimized using GA. The developed tools can be of massive value for chemical engineers and chemists to have a quick check of the densities and viscosities of the aforementioned amine solutions. Results obtained from the proposed models are in satisfactory agreement with actual data. According to statistical analyses, while the obtained values of Mean Squared Error (MSE) and R-squared (R2) for estimating densities of amine solutions are 0.000011 and 0.9938, 0.000013 and 0.9937, 0.000009 and 0.9953, 0.000001 and 0.9993 for the ANN, ANFIS, SVM, and LSSVM models respectively, these values obtained 0.079 and 0.994, 0.113 and 0.9911, 0.0634 and 0.9971, 0.0079 and 0.9996 for estimating the viscosities of amine-based solutions.

CO2 Absorption in Mixed Aqueous Solution of MDEA and Cholinium Glycinate

A new mixed solvent system that consists of cholinium glycinate ([Cho][Gly]) and aqueous N-methyldiethanolamine (MDEA) solution was developed in this work to serve as CO2 absorbent. The equilibrium absorption was carried out to investigate the effect of solution composition, pressure, and temperature on CO2 absorption performance. The effect of CO2 absorption on the viscosity of the aqueous solutions was studied, and the regeneration efficiency of the aqueous solutions was also investigated. The results showed that the CO2 absorption loading decreased with increasing [Cho][Gly] concentration and temperature, and the absorption loading strongly depended on CO2 partial pressure. The reactivity of MDEA was significantly enhanced with the addition of [Cho][Gly]. The aqueous solution with (10 wt % [Cho][Gly] + 20 wt % MDEA) showed an optimal CO2 absorption and high regeneration efficiency. Furthermore, the CO2 absorption mechanism in the aqueous [Cho][Gly]-MDEA solution was explored by 13C nuclear magnetic res...

Thermophysical properties of aqueous N-methyldiethanolamine (MDEA) and ionic liquids 1-butyl-3-methylimidazolium trifluoromethanesulfonate [bmim][OTf], 1-butyl-3-methylimidazolium acetate [bmim][Ac] hybrid solvents for CO2 capture

In this research work, thermophysical properties such as density, refractive index, surface tension, and viscosity of aqueous N-methyldiethanolamine (MDEA) and 1-butyl-3-methylimmidazolium trifluoromethanesulfonate [bmim][OTf], 1-butyl-3-methylimmidazolium acetate [bmim][Ac] hybrid solvents were investigated. All thermophysical properties were investigated at an atmospheric pressure, between the temperature ranges of 298.15 to 343.15K with an interval of 5K. In all samples, the concentration of MDEA was kept constant at 30wt%, while the concentration of the ionic liquids was varied between 5–20wt%. Experimental investigation demonstrated that the thermophysical properties were mainly dependent on the temperature and the concentration of the ionic liquids. All thermophysical properties were decreased with increase in temperature of the system. An increasing trend was observed in density, refractive index, and viscosity data with the increase in the concentration of the ionic liquids. The surface tension data for all samples under investigated was found to be in decreasing order with the increase in the concentration of the ionic liquids. It was also noticed that the use of two different ionic liquids has a different impact on the thermophysical properties of the hybrid solvents. Empirical correlations were used to correlate the experimental data of all the properties as a function of temperature and concentration of both the components (IL and amine). The correlated data were found to be in good agreement with the experimental data at all concentrations.

Thermodynamic modelling of acid gas removal from natural gas using the Extended UNIQUAC model

Thermodynamics of natural gas sweetening process needs to be known for proper design of natural gas treating plants. Absorption with aqueous N-Methyldiethanolamine is currently the most commonly used process for removal of acid gas (CO2 and H2S) impurities from natural gas. Model parameters for the Extended UNIQUAC model have already been determined by the same authors to calculate single acid gas solubility in aqueous MDEA. In this study, the model is further extended to estimate solubility of CO2 and H2S and their mixture in aqueous MDEA at high pressures with methane as a makeup gas.