An experimental/computational study of steric hindrance effects on CO2 absorption mechanism using nonaqueous/aqueous AMP

The reaction kinetics and molecular mechanisms of CO2 absorption using nonaqueous and aqueous amine solutions were analyzed by the stopped-flow technique and ab initio molecular dynamics (AIMD) simulations. Pseudo first-order rate constants (k0) of reactions between CO2 and amines were measured. A kinetic model was proposed to correlate the k0 to the amine concentration, and was proved to perform well for predicting the relationship between k0 and the amine concentration. The experimental results showed that AMP/MDEA only took part in the deprotonation of MEA-zwitterion in nonaqueous MEA+AMP/MEA+MDEA. In aqueous solutions, AMP can also react with CO2 through base-catalyzed hydration mechanism beside the zwitterion mechanism. The molecular mechanisms of CO2 absorption were also explored by AIMD simulations coupled with metadynamics sampling. The predicted free-energy barriers of key elementary reactions verified the kinetic model and demonstrated the different molecular mechanisms for the reaction between CO2 and AMP in nonaqueous and aqueous systems.

Secondary new particle formation initiated by sulfuric acid-amine nucleation in Beijing

<p>Secondary new particle formation is an important source of the number concentration of atmospheric aerosols. Despite relatively high coagulation sinks contributed by pre-existing aerosols, intensive new particle formation occurs frequently in polluted atmospheric environments such as in urban Beijing. Considering the measured concentrations of sulfuric acid and organic compounds, the contrast between the high coagulation sink and the frequent intensive NPF events in urban Beijing indicates an efficient nucleation mechanism. Based on long-term atmospheric measurements conducted at the campus of Beijing University of Chemical Technology, we show that sulfuric acid-amine nucleation is a governing mechanism to initiate new particle formation in urban Beijing. The molecular-level mechanism of sulfuric acid-amine nucleation, especially with low amine concentrations and high aerosol concentrations, are discussed. We present evidence for the existence of the missing amine molecules in the measured H<sub>2</sub>SO<sub>4</sub>-amine clusters. A neutral cluster needs to be ionized before it is detected by a mass spectrometer. Deprotonation or clustering with an additional reagent ion changes the stability of the original neutral cluster. Therefore, the amine molecules in neutral H<sub>2</sub>SO<sub>4</sub>-amine clusters may dissociate before detection. Combining measurements and cluster kinetic simulations, we show that although not directly detected, a considerable proportion of H<sub>2</sub>SO<sub>4</sub> monomers exist in the form of (H<sub>2</sub>SO<sub>4</sub>)<sub>1</sub>(amine)<sub>1</sub>, where the amine is most likely to be dimethylamine or trimethylamine. The evaporation rate of (H<sub>2</sub>SO<sub>4</sub>)<sub>1</sub>(amine)<sub>1</sub> is moderate and forming (H<sub>2</sub>SO<sub>4</sub>)<sub>1</sub>(amine)<sub>1</sub> is a critical step for H<sub>2</sub>SO<sub>4</sub>-amine nucleation. According to nucleation theory, (H<sub>2</sub>SO<sub>4</sub>)<sub>1</sub>(amine)<sub>1</sub> is the critical cluster at a low amine concentration, whereas H<sub>2</sub>SO<sub>4</sub>-amine nucleation may occur without a free energy barrier at a high amine concentration. The clustering between (H<sub>2</sub>SO<sub>4</sub>)<sub>1</sub>(amine)<sub>1</sub> and (H<sub>2</sub>SO<sub>4</sub>)<sub>n</sub>(amine)<sub>n</sub> is a major reaction pathway for the initial growth of H<sub>2</sub>SO<sub>4</sub>-amine clusters. These findings are supported by the measured H<sub>2</sub>SO<sub>4</sub> dimer concentration and its dependencies on amine concentrations and temperature in urban Beijing. Besides, the enhancement of cluster growth rate due to synergy between amines and ammonia are discussed.</p>

Optimization of MDEA-PZ Ratio and Concentration for CO2 Removal in Semi-Lean Membrane Contactor Process

Membrane contactor has garnered interest in the recent decade due to its advantages. This study looks at optimisation of the amine concentration, comprising of methyldiethanolamine (MDEA) with piperazine (PZ) in membrane contactor to remove CO2 from 25mol% down to 6.5mol%. 37 experiments were carried out and the results were analysed through response surface analysis. Model is found to be significant with R2 of 0.9854. Based on contour plot produced, there exists a trade-off between amine concentration and viscosity that greatly impacts the performance. For better overall evaluation, the amine regeneration side is considered by running process simulation through gPROMS to obtain data on expected hydrocarbon co-absorption and amine regeneration energy required. The optimum amine is found to be at 45wt% concentration and MDEA-to-PZ ratio of 0.047 where the process would meet outlet spec whilst minimising amine regeneration duty and the amine rich loading.

Effect of Various Parameters on the Thermal Stability and Corrosion of CO2-Loaded Tertiary Amine Blends

In this study, the thermal stability and corrosivity of various CO2-loaded tertiary amine blends in both aqueous and non-aqueous form in stainless steel cylinders were studied for combined acid gas and water removal. The thermal stability was measured from the remaining amine concentration and the corrosivity was measured from the amount of various metals in blends using titration and inductively coupled plasma mass spectrometry (ICP-MS), respectively. The experimental data were used to calculate the rate constants of amine group loss. The developed model represented the experimental data very well. Solvent change from H2O to triethylene glycol (TEG) in blends decreased the thermal stability and vice versa for corrosivity. The amine stability was increased when contact with stainless steel was reduced. An increase in the amine concentration or CO2 loading at constant temperature decreased the thermal stability and vice versa for corrosivity.

Theoretical Study of CO2 Absorption into Novel Reactive 1DMA2P Solvent in Split-flow Absorber-stripper Unit: Mass Transfer Performance and Kinetic Analysis

In the present study, the mass transfer performance of CO2 absorption into 1-dimethylamino-2-propanol (1DMA2P) as a novel amino alcohol solvent has been theoretically investigated in a split-flow absorber-stripper unit. The mass transfer performance has been presented in terms of CO2 absorption flux and overall mass transfer coefficient (KGav) by simultaneous considering of chemical reactions and mass transfer phenomenon. The developed comprehensive mathematical model has been validated based on related experimental data in literature. The impact of main operation parameters including liquid feed temperature, amine concentration, liquid velocity and CO2 loading were evaluated. The presented results indicated that increasing the liquid feed temperature, amine concentration and liquid flow rate improves the overall mass transfer coefficient. Also, the CO2 absorption performance of conventional and alternative amines such as monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), methyldiethanolamine (MDEA), piperazine (PZ), 4-(diethylamino)-2-butanol (DEAB) and 1DMA2P have been investigated and compared in order to provide guidelines about effective screening of solvents. The modeling results indicated that the KGav for CO2 absorption into different solution can be ranked as follows: PZ>MEA>DEA>DEAB>1DMA2P>MDEA>TEA.

Optimization of Post Combustion CO2 Capture from a Combined-Cycle Gas Turbine Power Plant via Taguchi Design of Experiment

The potential of carbon capture and storage to provide a low carbon fossil-fueled power generation sector that complements the continuously growing renewable sector is becoming ever more apparent. An optimization of a post combustion capture unit employing the solvent monoethanolamine (MEA) was carried out using a Taguchi design of experiment to mitigate the parasitic energy demands of the system. An equilibrium-based approach was employed in Aspen Plus to simulate 90% capture of the CO2 emitted from a 600 MW natural gas combined-cycle gas turbine power plant. The effects of varying the inlet flue gas temperature, absorber column operating pressure, amount of exhaust gas recycle, and amine concentration were evaluated using signal to noise ratios and analysis of variance. The optimum levels that minimized the specific energy requirements were a: flue gas temperature = 50 °C; absorber pressure = 1 bar; exhaust gas recirculation = 20% and; amine concentration = 35 wt%, with a relative importance of: amine concentration > absorber column pressure > exhaust gas recirculation > flue gas temperature. This configuration gave a total capture unit energy requirement of 5.05 GJ/tonneCO2, with an energy requirement in the reboiler of 3.94 GJ/tonneCO2. All the studied factors except the flue gas temperature, demonstrated a statistically significant association to the response.