The application of trans-1,4-diaminocyclohexane as a bicarbonate formation rate promoter in CO2 capture

A sterically hindered diamine, trans-1,4-diaminocyclohexane (DACH), is studied as a bicarbonate formation promoter to enhance the CO2 absorption capacity of tertiary amine (N-methyl-N,N-diethanolamine, MDEA). Parallel studies using monoethanolamine (MEA) and 1,4-diaminobutane (DAB) are carried out to assess the influence of amine structure on the CO2 absorption rate. DACH, with cyclic structure, shows the highest initial CO2 absorption rate (1.904 × 10−2 mol CO2/L/min) and initial bicarbonate formation rate out of these three amines. The reasons have been explained in detail. Three mixed amine blends, MEA-MDEA, PZ-MDEA and DACH-MDEA, are also used to observe the advantages of DACH as a bicarbonate formation promoter. The CO2 absorption capacity, CO2 mass transfer coefficients and CO2 equilibrium loading are studied. Although the CO2 absorption rate is in the order of PZ-MDEA > DACH-MDEA > MEA-MDEA, DACH-MDEA blend has a higher concentration of bicarbonate and lower concentration of carbamate compared to PZ-MDEA blend. The highest bicarbonate formation enables DACH-MDEA blend to reduce the regeneration energy. The DACH-MDEA blend also shows the highest CO2 loading (0.576 mol CO2/mol amine) at low CO2 partial pressure. According to the investigation of corrosion behaviours of these three CO2-loaded amine blends, the corrosion rate is PZ-MDEA ≈ DACH-MDEA ≪ MEA-MDEA. All of the results indicate that the DACH diamine with cyclic structure is a promising promoter. This work investigates the effect of amine structural features on the CO2 absorption performance, which provides more knowledge to design efficient amine solvents for CO2 capture.