Carbon dioxide capture by solvent absorption using amino acids: A review

The emission of large amounts of carbon dioxide is of major concern with regard to increasing the risk of climate change. Carbon capture, utilisation and storage (CCUS) has been proposed as an important pathway for slowing the rate of these emissions. Solvent absorption of CO_2 using amino acid solvents has drawn much attention over the last few years due to advantages including their ionic nature, low evaporation rate, low toxicity, high absorption rate and high biodegradation potential, compared to traditional amine solvents. In this review, recent progress on the absorption kinetics of amino acids is summarised, and the engineering potential of using amino acids as carbon capture solvents is discussed. The reaction orders between amino acids and carbon dioxide are typ- ically between 1 and 2. Glycine exhibits a reaction order of 1, whilst, by comparison, lysine, proline and sarcosine have the largest reaction constants with carbon dioxide which is much larger than that of the benchmark solvent monoethanolamine (MEA). Ionic strength, p H and cations such as sodium and potassium have been shown to be important factors influencing the reactivity of amino acids. Corrosivity and reactivity with impurities such as SOx and NOxare not considered to be significant problems for amino acids solvents. The precipitation of CO_2 loaded amino acid salts is thought to be a good pathway for increasing CO_2loading capacity and cutting desorption energy costs if well-controlled. It is recommended that more detailed research on amino acid degradation and overall process energy costs is conducted. Overall, amino acid solvents are recognised as promising potential solvents for car- bon dioxide capture.

Modelling of a post-combustion carbon dioxide capture absorber using potassium carbonate solvent in Aspen Custom Modeller

The process models for an equilibrium CO_2 absorber and a rate based CO_2 absorber using potassium carbonate(K2 CO3) solvents were developed in Aspen Custom Modeller(ACM) to remove CO_2 from a flue gas. The process model utilised the Electrolyte Non-Random Two Liquid(ENRTL) thermodynamic model and various packing correlations. The results from the ACM equilibrium model shows good agreement with an inbuilt Aspen Plus?model when using the same input conditions. By further introducing a Murphree efficiency which is related to mass transfer and packing hydraulics, the equilibrium model can validate the experimental results from a pilot plant within a deviation of 10%. A more rigorous rate based model included mass and energy flux across the interface and the enhancement effect resulting from chemical reactions. The rate based model was validated using experimental data from pilot plants and was shown to predict the results to within 10%. A parametric sensitivity analysis showed that inlet flue gas flowrate and K2 CO3 concentration in the lean solvent has significant impact on CO_2 recovery. Although both models can provide reasonable predictions based on pilot plant results, the rate based model is more advanced as it can explain mass and heat transfer, transport phenomena and chemical reactions occurring inside the absorber without introducing an empirical Murphree efficiency.

Precipitation study of CO2-loaded glycinate solution with the introduction of ethanol as an antisolvent

Focused beam reflectance measurement(FBRM)and 13C nuclear magnetic resonance(13C NMR)analysis were used to study the precipitation process of CO2-loaded potassium glycinate(KGLY)solutions at different CO2 loadings,during the addition of ethanol as an antisolvent at a rate of 10 mL·min−1.The volume ratio of ethanol added to the KGLY solution(3.0 mol·L−1,340 mL)ranged from 0 to 3.0.Three solid-liquid-liquid phases were formed during the precipitation process.The FBRM results showed that the number of particles formed increased with CO2 loading and ethanol addition for CO2-unsaturated KGLY solutions,whilst for CO2-saturated KGLY solution it first increased then decreased to a stable value with ethanol addition.13C NMR spectroscopic analysis showed that the crystals precipitated from the CO2-unsaturated KGLY solutions consisted of glycine only,and the quantity crystallised increased with CO2 loading and ethanol addition.However,a complex mixture containing glycine,carbamate and potassium bicarbonate was precipitated from CO2-saturated KGLY solution with the maximum precipitation percentages of 94.3%,31.4%and 89.6%,respectively,at the ethanol volume fractions of 1.6,2.5 and 2.3.