Experimental and Mathematical Modelling of Factors Influencing Carbon Dioxide Absorption into the Aqueous Solution of Monoethanolamine and 1-Butyl-3-methylimidazolium Dibutylphosphate Using Response Surface Methodology (RSM)

This paper investigated the solubility of carbon dioxide (CO₂) in an aqueous solution of monoethanolamine (MEA) and 1-butyl-3-methylimidazolium dibutylphosphate ((BMIM)(DBP)) ionic liquid (IL) hybrid solvents. Aqueous solutions of MEA-(BMIM)(DBP) hybrid solvents containing different concentrations of (BMIM)(DBP) were prepared to exploit the amine’s reactive nature, combined with the IL’s non-volatile nature for CO₂ absorption. Response surface methodology (RSM) based on central composite design (CCD) was used to design the CO₂ solubility experiments and to investigate the effects of three independent factors on the solubility of CO₂ in the aqueous MEA-(BMIM)(DBP) hybrid solvent. The three independent factors were the concentration of (BMIM)(DBP) (0–20 wt.%), temperature (30 °C–60 °C) and pressure of CO₂ (2–30 bar). The experimental data were fitted to a quadratic model with a coefficient of determination (R²) value of 0.9791. The accuracy of the developed model was confirmed through additional experiments where the experimental values were found to be within the 95% confidence interval. From the RSM-generated model, the optimum conditions for CO₂ absorption in aqueous 30 wt% MEA-(BMIM)(DBP) were 20 wt% of (BMIM)(DBP), a temperature of 41.1 °C and a pressure of 30 bar.     

Amine functionalised metal organic frameworks (MOFs) as adsorbents for carbon dioxide

Three different porous metal organic framework (MOF) materials have been prepared with and without uncoordinated amine functionalities inside the pores. The materials have been characterized and tested as adsorbents for carbon dioxide. At 298 K the materials adsorb significant amount of carbon dioxide, the amine functionalised adsorbents having the highest CO₂ adsorption capacities, the best adsorbing around 14 wt% CO₂ at 1.0 atm CO₂ pressure. At 25 atm CO₂ pressure, up to 60 wt% CO₂ can be adsorbed. At high pressures the CO₂ uptake is mostly dependent on the available surface area and pore volume of the material in question. For one of the iso-structural MOF pairs the introduction of amine functionality increases the differential adsorption enthalpy (from isosteric method) from 30 to around 50 kJ/mole at low CO₂ pressures, while the adsorption enthalpies reach the same level at increase pressures. The high pressure experimental results indicate that MOF based solid adsorbents can have a potential for use in pressure swing adsorption of carbon dioxide at elevated pressures.     

Evaluation of CO2 adsorption capacity of solid sorbents

The CO₂ adsorption capacity of the low-cost solid sorbents of waste tire char (TC) and chicken waste char (CW) was compared with commercial active carbon (AC) and 5 ? zeolite (ZA) using thermogravimetric analysis (TG), pressurized TG, and differential scanning calorimetry (DSC). The sorbents were degassed in a TG up to 150 °C to release all gases on the surface of the sample, then cooled down to the designed temperature for adsorption. TG results indicated that the CO₂ adsorption capacity of TC was higher than that of CW, but lower than those of AC and ZA. The maximum adsorption rate of TC at 50 °C was 0.61% min⁻¹, lower than that of AC, but higher than that of CW, 0.44% min⁻¹. The maximum adsorption rate of ZA at 50 °C was 3.1% min⁻¹. When the pressure was over 4 bar, the adsorption rate of ZA was lower than that of TC and AC. At 30 bar, the total CO₂ uptake of TC was 20 wt%, higher than that of CW and ZA but lower than that of AC. The temperature, nitrogen concentration, and water content also influenced the CO₂ adsorption capacity of sorbents to some extent. DSC results showed that adsorption was an exothermic process. The heat of CO₂ adsorption per mole of CO₂ of TC at 50 °C was 24 kJ mol⁻¹ while the ZA had the largest heat of adsorption at 38 kJ mol⁻¹. Comparing the characteristics of TC and CW, TC may be a promising sorbent for removal of CO₂.     

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 (K _Ga_v). 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 K _Ga_v 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.     

Enthalpy of absorption and limit of solubility of CO2 in aqueous solutions of 2-amino-2-hydroxymethyl-1,3-propanediol, 2-[2-(dimethyl-amino)ethoxy] ethanol,and 3-dimethyl-amino-1-propanol at T = (313.15 and 353.15) K and pressures up to 2 MPa

In order to study the influence of amine structure on absorption of carbon dioxide, enthalpies of solution of CO₂ in 2.50 mol · L^?1 aqueous solutions of 2-amino-2-hydroxymethyl-1,3-propanediol (THAM), 2-[2-(dimethyl-amino)ethoxy] ethanol (DMAEOE), and 3-dimethyl-amino-1-propanol (DMAP) were measured. The enthalpies of solution are determined as function of gas loading charge (moles of CO₂/mole of amine), at temperatures (313.15 and 353.15) K, and pressures range from (0.5 to 2) MPa. Measurements were carried out using a flow calorimetric technique. CO₂ solubilities in the aqueous solutions of amine are derived from calorimetric data. Molar volumes of aqueous amine solutions required to handle calorimetric data were determined at 303.15 K using a vibrating tube densimeter. Experimental enthalpies of solution are discussed on the basis of amines alkalinity.     

Gas solubility of CO2 in aqueous solutions of N-methyldiethanolamine and diethanolamine with 2-amino-2-methyl-1-propanol

Gas solubility of carbon dioxide in an aqueous solution of 32.5 wt.% N-methyldiethanolamine and 12.5 wt.% diethanolamine with 4, 6, and 10 wt.% 2-amino-2-methyl-1-propanol has been measured, at 313.15, 343.15, and 393.15 K, over a range of pressure from 3 to 2000 kPa, using a chromatographic method for analysis of the liquid phase. The results of the gas solubility are given as the partial pressure of CO₂ against its mole ratio α (mol CO₂/mol alkanolamine) and its mole fraction at each temperature studied. The solubility of CO₂ in all the systems studied decreases with an increase in temperature and increases with an increase in the partial pressure of CO₂ at a given temperature and it is a function of the concentration of the mixture of alkanolamines in solution. The enthalpy of solution of CO₂ has been calculated from the experimental solubility data.     

Biogas upgrading with novel cellulose nano-crystals and polyvinyl amine nanocomposite membranes

A novel crystalline nano cellulose (CNC) and polyvinyl amine (PVAm) based nanocomposite membranes were synthesized and evaluated for biogas upgrading. Different concentrations of CNC was incorporated in 3 wt % PVAm solution on commercial polysulfone (PSf) sheet using dip coating method. The effect of feed pressure (5, 10 and 15 bar) was investigated for the CO₂/CH₄ separation. The incorporation of CNC increased the crystallinity of membranes. The thickness of selective layer enhanced to 2.16 μm from 1.5 μm with increasing concentration of CNC. However, degree of swelling reduced from 75.88% to 68.93 with CNC concentration at 1.5 wt%. The best results were shown by PVAm membrane with 1 wt % CNC concentration i.e. CO₂ permeance of 0.0216 m³(STP)/m².bar.hr and selectivity (CO₂/CH₄) of 41.The permeance decreased approximately 1.8 folds for PVAm/1CNC membrane with the increase in pressure from 5 to 15 bar. However, selectivity dropped from 41 to 39 for formulated membranes.     

Phase behavior of β-d galactose pentaacetate–carbon dioxide binary system

Phase behavior of β-d galactose pentaacetate–carbon dioxide binary system is investigated by dew-point and bubble-point measurements conducted in a high pressure variable volume sapphire cell. The phase envelope for solutions of β-d galactose pentaacetate in supercritical CO₂ is obtained for β-d galactose pentaacetate concentrations between 2 and 26 wt%, and for the temperature range of 308–323 K. The system exhibits lower critical solution temperature (LCST) behavior and high solubility of β-d galactose pentaacetate is observed. The densities of the system are also measured, and liquid-like densities (near 1 g/cm³) are observed for single-phase solutions of β-d galactose pentaacetate in supercritical CO₂ at concentrations of 18 wt% and higher. Viscosity is measured for solutions of 18 and 25 wt% β-d galactose pentaacetate in the single-phase region at 313 K and 17 MPa and the viscosity values, 0.095 and 0.103 cp, respectively, are similar in magnitude to the viscosity of pure carbon dioxide.     

A synthesis of porous activated carbon materials derived from vitamin B9 base for CO2 capture and conversion

CO₂ capture and conversion are still a favorable way to reduce CO₂ in the atmosphere. Herein, we have developed an environmentally friendly, low energy consumption porous activated carbon from vitamin B9 carbonaceous material for CO₂ capture and conversion materials. It is demonstrated that the KOH/vitamin B9 carbonaceous material impregnation ratio of 2 is the optimum condition for obtaining porous activated carbons with high specific surface area of 1903 m²g^-1, micropore surface area of 710 m²g^-1, total pore volume of 1.05 cm³g^-1 and micropore volume of 0.38 cm³g^-1. Among all the porous activated carbons prepared, the porous activated carbon synthesized with the KOH/vitamin B9 carbonaceous material impregnation ratio of 2 registers the most excellent CO₂ capture for 5.41 mmolg^?1 at 0 °C/1 bar and 3.66 mmolg^?1 at 25 °C/1 bar. They can also effectively catalyze the cycloaddition of CO₂ and epoxides under mild conditions (1 bar, 100 °C and 8 h) with a yield of 89–94%. The synthesized porous carbon materials from vitamin B9 is a promising candidate material for CO₂ capture and fixation.     

(Vapour + liquid) equilibria (VLE) of CO2 in aqueous solutions of 2-amino-2-methyl-1-propanol: New data and modelling using eNRTL-equation

This work presents new experimental results for carbon dioxide (CO₂) solubility in aqueous 2-amino-2-methyl-1-propanol (AMP) over the temperature range of (298 to 328) K and CO₂ partial pressure of about (0.4 to 1500) kPa. The concentrations of the aqueous AMP lie within the range of (2.2 to 4.9) mol · dm^?3. A thermodynamic model based on electrolyte non-random two-liquid (eNRTL) theory has been developed to correlate and predict the (vapour + liquid) equilibrium (VLE) of CO₂ in aqueous AMP. The model predictions have been in good agreement with the experimental data of CO₂ solubility in aqueous blends of this work as well as those reported in the literature. The current model can also predict speciation, heat of absorption, enthalpy of CO₂ loaded aqueous AMP, pH of the loaded solution, and AMP volatility.     

Adsorption of CO2 on nitrogen-enriched activated carbon and zeolite 13X

Adsorption may be a potentially attractive alternative to capturing CO₂ from stationary sources in the context of Carbon Capture and Sequestration (CCS) technologies. Activated carbon and zeolites are state-of-art adsorbents which may be used for CO₂ adsorption, however physisorption alone tends to be insignificant at high temperatures. In the present work, commercial adsorbents have been impregnated with monoethanolamine (MEA) and triethanolamine (TEA) in order to investigate the effect of the modified surface chemistry on CO₂ adsorption, especially above room temperature. Adsorption isotherms for CO₂, N₂ and CH₄ were measured in a gravimetrically system in the pressure range of UHV to 10 bar, at 298 and 348 K for activated carbon and zeolite 13X supports. The adsorbed concentration of CO₂ was significantly higher than those of CH₄ and N₂ for both adsorbents in the whole pressure range studied, zeolite 13X showing a remarkable affinity for CO₂ at very low pressures. However, at 348 K, the adsorbed concentration of CO₂ decreases significantly. The supports impregnated with concentrated amine solutions and dried in air suffered a detrimental effect on the textural properties, although CO₂ uptake became much less susceptible to temperature increase. Impregnations carried out with dilute solution followed by drying in inert atmosphere yielded materials with very similar textural characteristics as compared to the parent support. CO₂ isotherms in such materials showed a significant change with similar capacities at 348 K as compared to the original support at 298 K in the case of activated carbons. The impregnated zeolite showed a decrease in adsorbed phase concentration in low pressures for a given temperature, but the adsorbed amount also seemed to be less affected by temperature. These results are promising and indicate that CO₂ adsorption may be enhanced despite high process temperatures (e.g. 348 K), if convenient impregnation and drying methods are applied.     

The beneficial impacts of functional groups of CNT on structure and gas separation properties of PEBA mixed matrix membranes

Incompatibility between filler and polymer chains accompanied by particle agglomeration has a detrimental effect on the performance of mixed matrix membranes (MMMs). To obviate intermolecular forces of different additives, functional groups (-COOH, –NCO, and –NH₂) were grafted on the surface of multi-walled carbon nanotubes (MWCNTs) which were then incorporated as fillers in the poly(ether-block-amide) (PEBA) polymeric matrix in the range of 0.1–1 wt% loading. CO₂ permeability and ideal CO₂/N₂ and CO₂/CH₄ selectivity of MMMs was compared with the neat membrane, and the results revealed favorable enhancement and surpassed CO₂/N₂ Robeson's upper bound under 4–10 bar in the range of 15–55 °C. Mixed gas separation performance of MMMs, which is of vital importance in industrial applications, was also investigated. The results indicate that MWCNT-NCO created superior grafts with the polymer chains, and MMMs with this additive had a better gas separation performance with high mechanical and thermal stability.     

Synthesis of nitrogen doped activated carbon/polyaniline material for CO2 adsorption

The equilibrium adsorption isotherms of carbon dioxide and nitrogen on the nitrogen doped activated carbon (NAC) prepared by the chemical activation of a pine cone‐based char/polyaniline composite were measured using a volumetric technique. CO₂ and N₂ adsorption experiments were done at three different temperatures (298, 308, and 318 K) and pressures up to 16 bar, and correlated with the Langmuir, Freundlich, and Sips models. The Sips isotherm model presented the best fit to the experimental data. The N‐doped adsorbent showed CO₂ and N₂ adsorption capacity of 3.96 mmol·g⁻¹ and 0.86 mmol·g⁻¹, respectively, at 298 K and 1 bar. The selectivity predicted by ideal adsorbed solution theory (IAST) model was achieved 47.17 for NAC at 1 bar and y_N2 = 0.85 which is a composition similar to flue gas. The results showed that NAC adsorbent has a high CO₂‐over‐N₂ selectivity in a binary mixture. The relatively fast sorption rate of CO₂ on NAC compared to N₂ indicates the stronger affinity between CO₂ and amine groups. The isosteric heat of adsorption of CO₂ by the NAC demonstrated the physico‐chemical adsorption of CO₂ on the adsorbent surface. These data showed that prepared NAC could be successfully applied in separation of CO₂ from N₂.     

Solubility of semi-fluorinated and nonfluorinated alkyl dichlorobenzoates in supercritical CO2

Isopleths and solution densities, from ∼25 to 100 °C, are reported for mixtures of CO₂ with semi-fluorinated and nonfluorinated propyl, butyl, octyl, and decyl 2,5-dichlorobenzoates. The maxima in the pressure–composition (P–x) isotherms for the alkyl 2,5-dichlorobenzoates range from 70 to 600 bar and the maxima increase with increasing alkyl chain length at each temperature. When the alkyl side chains are semi-fluorinated, the P–x maxima range from 60 to 175 bar over the same temperature range as with the nonfluorinated analogs. The P–x maxima of the semi-fluorinated 2,5-dichlorobenzoates in CO₂, first decrease as the benzoate alkyl chain is increased from propyl to butyl, but then increase as the alkyl chain length is further increased from butyl to octyl to decyl, although the differences in the maxima at a given temperature between these four semi-fluorinated benzoates are not as great as that observed with the nonfluorinated analogs. Also, the alkyl 2,5-dichlorobenzoate–CO₂ mixtures exhibit three-phase, liquid–liquid–vapor (LLV), equilibria near the vapor pressure curve and critical point of CO₂ whereas three phases are not observed for the semi-fluorinated analogs.     

Modeling of CO2 solubility and carbamate concentration in DEA,MDEA and their mixtures using the Deshmukh–Mather model

The equilibrium of CO₂ and carbamate concentration data for the absorption of CO₂ in aqueous solutions of single and mixed amines was analyzed using the Deshmukh–Mather model. Data on CO₂ loading in aqueous solutions of DEA and MDEA and their mixtures at various temperature (303–323 K) and CO₂ partial pressure (0.09–100 kPa) together with carbamate concentrations in case of DEA and its mixtures with MDEA were fitted simultaneously to generate the different interaction parameters required to calculate the activity coefficients in the model. Using the generated interaction parameters, the model was applied to correlate the CO₂ loading in solutions of DEA and MDEA and their mixtures reported in the literature as well as those obtained in our laboratory and was found to be able to give a good estimation of CO₂ loading and carbamate concentration over a wide range of operating conditions in both single and mixed amine solutions.     

Study on the effect of process parameters on CO2/CH4 binary gas separation performance over NH2-MIL-53(Al)/cellulose acetate hollow fiber mixed matrix membrane

The aim of current work is to study the interaction of process parameters including, temperature, CO₂ feed composition and feed pressure were towards CO₂ separation from CO₂/CH₄ binary gas mixture over hollow fiber mixed matrix membrane using design of experiment (DoE) approach. The hollow fiber mixed matrix membrane (HFMMM) containing NH₂-MIL-53(Al) filler and cellulose acetate polymer was successfully spun and fibers with outer diameter of approximately 250–290 nm were obtained. The separation results revealed that the increment of temperature from 30 °C to 50 °C reduced the CO₂/CH₄ separation factor while, increasing feed pressure from 3 bar to 15 and increment of CO₂ feed composition from 15 to 42.5 vol% increased the separation factor of HFMMM. The DoE results showed that the feed pressure was the most significant process parameter that intensely affected the CH₄ permeance, CO₂ permeance and CO₂/CH₄ separation factor. Based on the experimental results obtained, maximum CO₂ permeance of 3.82 GPU was achieved at feed pressure of 3 bar, temperature of 50 °C and CO₂ feed composition of 70 vol%. Meanwhile, minimum CH₄ permeance of 0.01 GPU was obtained at feed pressure of 15 bar and temperature of 30 °C and CO₂ feed composition of 70 vol%. Besides, maximum CO₂/CH₄ separation factor of 14.4 was achieved at feed pressure of 15 bar and temperature of 30 °C and CO₂ feed composition of 15 vol%. Overall, the study on the interaction between separation processes parameters using central composite design (CCD) coupled with response surface methodology (RSM) possesses significant importance prior to the application of NH₂-MIL-53(Al)/Cellulose Acetate HFMMM at industrial scale of natural gas purification.     

High pressure phase behavior and modeling of CO2–propyl acrylate and CO2–propyl methacrylate systems

High pressure phase behavior are obtained for CO₂–propyl acrylate system at 40, 60, 80, 100 and 120 °C and pressure up to 161 bar and for CO₂–propyl methacrylate systems at 40, 60, 80, 100 and 120 °C and pressure up to 166 bar. The solubility of propyl acrylate and propyl methacrylate for the CO₂–propyl acrylate and CO₂–propyl methacrylate systems increases as the temperature increases at constant pressure. The CO₂–propyl acrylate and CO₂–propyl methacrylate systems have continuous critical mixture curves that exhibit maximums in pressure at temperatures between the critical temperatures of CO₂ and propyl acrylate or propyl methacrylate. The CO₂–propyl acrylate and CO₂–propyl methacrylate systems exhibit type-I phase behavior with a continuous mixture critical curve.The experimental results for CO₂–propyl acrylate and CO₂–propyl methacrylate systems are modeled using both the statistical associating fluid theory (SAFT) and Peng–Robinson equations of state. A good fit of the data are obtained with SAFT using two adjustable parameters for CO₂–propyl acrylate and CO₂–propyl methacrylate systems and Peng–Robinson equation using one and two adjustable parameter for CO₂–propyl acrylate and CO₂–propyl methacrylate system.     

The co-solubility of 2-ethylhexanoic acid and some liquid alcohols in supercritical carbon dioxide

The co-solubility in supercritical carbon dioxide of 1-butanol, 1-pentanol, 2-ethyl-1-hexanol, or 1-decanol in the presence of 2-ethylhexanoic acid in the pressure range of 100–180 bar and at 313 or 323 K was measured. The solubility of these alcohols in the presence of 2-ethylhexanoic acid is lower than in the systems alcohol + CO₂ and remains nearly constant in the pressure range of 120–180 bar, with the exception of 1-decanol. The lower selectivities in the ternary systems are explained by strong intermolecular hydrogen bonding between alcohol molecules and 2-ethylhexanoic acid molecules. The FT-IR spectra of mixtures of alcohols and 2-ethylhexanoic acid at a 1:1 mole ratio in the liquid CCl₄ confirmed this conclusion.     

Equilibrium solubility of carbon dioxide in the amine solvent system of (triethanolamine + piperazine + water)

In this study, a new set of data for the equilibrium solubility of carbon dioxide in the amine solvent system that consists of triethanolamine (TEA), piperazine (PZ), and water is presented. Equilibrium solubility values were obtained at T = (313.2, 333.2, and 353.2) K and pressures up to 153 kPa using the vapour-recirculation equilibrium cell. The TEA concentrations in the considered ternary (solvent) mixture were (2 and 3) kmol · m^?3 and those of PZ’s were (0.5, 1.0, and 1.5) kmol · m^?3. The solubility data (CO₂ loading in the amine solution) obtained were correlated as a function of CO₂ partial pressure, system temperature, and amine composition via the modified Kent–Eisenberg model. Results showed that the model applied is generally satisfactory in representing the CO₂ absorption into mixed aqueous solutions of TEA and PZ.     

High performance of PES-GNs MMMs for gas separation and selectivity

In this study, graphene nanosheets (GNs) were incorporated into polyethersulfone (PES) by phase inversion approach for preparing PES-GNs mixed matrix membranes (MMMs). To investigate the impact of filler content on membrane surface morphology, thermal stability, chemical composition, porosity and mechanical properties, MMMs were constructed with various GNs loadings (0.01, 0.02, 0.03, and 0.04 wt%). ?The performance of prepared MMMs was tested for separation and selectivity of CO₂, N₂, H₂ and CH₄ gases at various pressures from 1 to 6 bar and temperature varying from 20 to 60 °C. It was observed that, compared to the pristine PES membrane, the prepared MMMs significantly improved the gas separation and selectivity performance with adequate mechanical stability. The permeability of CO₂, N₂, H₂ and CH₄ for the PES + 0.04 wt% GNs increases from 9 to 2246, 11 to 2235, 9 to 7151, and 3 to 4176 Barrer respectively, as compared with pure PES membrane at 1 bar and 20 °C due to improving the membrane absorption and porosity. In addition, by increasing the pressure, the permeability and selectivity of CO₂, N₂, H₂ and CH₄ are increased due to the increased driving force for the transport of gas via membranes. Furthermore, the permeability of CO₂, N₂, H₂ and CH₄ increased by increasing the temperature from 20 to 60 °C due to the plasticization in the membranes and the improvement in polymer chain movement. This result proved that the prepared membranes can be used for gas separation applications.