Equilibrium Solubility of CO2 in Alkanolamines

AbstractEquilibrium solubility of CO2 were measured in aqueous solutions of Monoethanolamine (MEA) and N,N-diethylethanolamine (DEEA). Equilibrium cells are generally used for these measurements. In this study, the equilibrium data were measured from the calorimetry. For this purpose a reaction calorimeter (model CPA 122 from ChemiSens AB, Sweden) was used. The advantage of this method is being the measurement of both heats of absorption and equilibrium solubility data of CO2 at the same time. The measurements were performed for 30 mass % MEA and 5M DEEA solutions as a function of CO2 loading at three different temperatures 40, 80 and 120oC. The measured 30 mass % MEA and 5M DEEA data were compared with the literature data obtained from different equilibrium cells which validated the use of calorimeters for equilibrium solubility measurements

Heat of Absorption of CO2 in Aqueous Solutions of DEEA, MAPA and their Mixture

AbstractA reaction calorimeter was used to measure the differential heat of absorption of CO2 in phase change solvents as a function of temperature, CO2 loading and solvent composition. The measurements were taken for aqueous solutions of 2-(diethylamino)ethanol (DEEA), 3-(methylamino)propylamine (MAPA) and their mixture. The tested compositions were 5M DEEA, 2M MAPA and their mixture, 5M DEEA + 2M MAPA which gives two liquid phases on reacting with CO2. Experimental measurements were also carried out for 30% MEA used as a base case. The measurements were taken isothermally at three different temperatures 40, 80 and 120°C at a CO2 feed pressure of 600kPa. In single aqueous amine solutions, heat of absorption increases with increase in temperature and depends on thetype of amine used. DEEA, a tertiary amine, has lower heat of absorption compared to MAPA being a diamine with primary and secondary amine functional groups. For amine mixtures, heat of absorption is a function of CO2 loading and temperature. The heat of absorption against CO2 loading depends on the composition of the amines in the mixture. All the measured data in this work were compared with 30% MEA at absorption (40°C) and desorption (120°C) conditions

Aerosol growth in CO2 absorption with MEA, modelling and comparison with experimental results

A new and improved aerosol model has been developed and tested against experimental data. An e-NRTL equilibrium model for MEA was extended to cover sulphuric acid containing droplets and validated against new eboulliometer data in this work. The droplet model predicts emissions without demister installed in the absorber, within ± 20% and with demister, 30-80% of the measured emissions. The model predicts well the change in emissions from NG-based to coal-based exhaust. Under conditions reported in this work, the droplet number concentration was found to have a small effect on predicted emissions because of more MEA gas-phase depletion with high droplet concentrations and slower growth. The effects counteract each other. With significant MEA depletion in the gas phase, the emissions are largely determined by the mass transfer rate from the bulk liquid. The initial droplet sulphuric acid concentration had a minor effect on the outlet droplet size distribution. The effect on MEA emissions was significant: the emissions went up with increased initial sulphuric acid concentration. The effect of sulphuric acid was stronger for low inlet gas CO2 concentration (NG) than for coal-based exhaust. The increase in emissions is believed to be caused by the increase in overall driving force for MEA between bulk liquid phase and droplets. The log-normal model does not catch small inlet droplet sizes in the range below 20-30nm. These droplet sizes hardly grow in the absorber and water wash and in the total emissions, these droplets have a negligible impact on emissions.publishedVersio

Absorption of Carbon Dioxide in Aqueous Solutions of N-methyldiethanolamine Mixtures

Carbon dioxide (CO2) is one of the greenhouse gases (GHG) that has contributed to the global warming problem. Carbon dioxide is produced in large quantity from coal-fired power plants, iron and steel production, cement production, chemical and petrochemical industries, natural gas purification, and transportation. Some efforts to reduce the CO2 emissions to the atmosphere are then required. Amine-based absorption may be an option for post-combustion capture. The objective of this study is to measure the effect of promoter addition as well as MDEA concentration for the CO2 absorption into the aqueous solutions of MDEA to improve its performances, i.e. increasing the absorption rate and the absorption capacity. Absorption of CO2 in aqueous solutions of MDEA mixtures were measured at 40 °C in a bubble tank reactor. The systems tested were the mixtures of 30 wt% MDEA with 5 and 10 wt% BEA and the mixtures of 40 and 50 wt% MDEA with 6 wt% AEEA. It was found that for MDEA-BEA-H2O mixtures, the higher the promoter concentraation the higher the CO2 absorption rate, while for the MDEA-AEEA-H2O mixtures, the higher the MDEA concentration the lower the CO2 absorption rate

Understanding Carbamate Formation Reaction Thermochemistry of Amino Acids as Solvents for Postcombustion CO2 Capture

The carbamate stability constant for a data set of 10 amino acids, having potential for being postcombustion CO2 capture (PCC) solvents, has been calculated using various implicit and explicit solvation shell models. This work also includes an extensive study of gas-phase free energy and enthalpy for the amino acid carbamate formation reaction with the Hartree Fock method, density functional methods [B3LYP/6-311++G(d,p)], and composite methods (G3MP2B3, G3MP2, CBS-QB3, and G4MP2). Ideal PCC solvent properties require finding a profitable tradeoff between various thermodynamic and system optimization parameters. Benchmark gaseous-phase and solution-phase thermodynamic properties given in this work can help in making informed decisions when choosing promising PCC solvents. The temperature dependency of the carbamate stability constant of amino acids is predicted using PCM and SM8T implicit solvation models. PCC is a temperature swing absorption–desorption process, and the high-temperature sensitivity of the ln KcAmCOO– value is of vital importance in attaining cost-efficient processes

Effect of water wash on mist and aerosol formation in absorption column

Environmental issues regarding solvent emissions can hamper the realization of state of the art post combustion CO2 capture (PCCC). These emissions stem from the emitted flue gas from which CO2 has been recovered and are due to volatile solvent in gas form and solvent carrying aerosols, either formed in the absorption column or carried over from an up-stream unit and contaminated by solvent in the absorber. The issue of aerosol-based emissions has only recently been reported for a PCCC process and very little information is available in this area. It is therefore important to understand and characterize the mechanisms of aerosol formation and growth so that appropriate actions can be taken in reducing the total amine emissions. From the literature and common practice, it is known that the use of a water wash section in a CO2 capture column can reduce the total amine emissions from these plants. This is mainly a reduction in gaseous solvent content whereas emissions caused by aerosols may not be removed. Moreover, typical demisting equipment has low efficiency when the droplets or particles are in the range 0.1–3 µ. It is thus very important to be able to predict the behavior of these aerosols passing through a water wash section. In this study, we focus on the effect of water wash on aerosol composition and growth. It is found that water wash systems help in reducing both gaseous and aerosol-born amine emission. Aerosol droplets grow extensively in the water wash section because of water condensation and this may simplify subsequent removal in a demister. Droplet growth is found to be highly sensitive to gas phase amine depletion or content increase caused by high droplet number concentrations. Variations in operating parameters of the absorber and water wash columns were found to have effect on droplet growth and emission levels

CO2 absorption with membrane contactors vs. packed absorbers-Challenges and opportunities in post combustion capture and natural gas sweetening

The present work presents a case study where membrane contactors are compared with absorption towers for post combustion CO2 capture and for natural gas sweetening. Simulations are performed using a absorber model which has been validated with experiments in a membrane contactor setup. The design of the membrane contactors is made with emphasis on the constraints in gas and liquid side pressure drop and size limitations of membrane modules, in addition to the common design criteria for industrial absorbers. Results show that absorber size may potentially be reduced by 75%, given that liquid is flowing on the shell side of the membrane units. Natural gas sweetening is a more viable option than post combustion capture due to the potentially large gas side pressure drop and the need for many membrane units in parallel in the latter case