Amine-based absorbents selection for CO_2 membrane vacuum regeneration technology by combined absorption-desorption analysis

摘要

A novel membrane vacuum regeneration (MVR) technology was developed to achieve lower regeneration energy demand for CO_2 absorption process. Sixteen different amine-based absorbents including primary, secondary, tertiary amines, polyamines, diamines, and sterically hindered amines were analyzed by combined absorption-desorption screening experiments for selecting the most effective absorbents for CO_2 membrane vacuum regeneration (MVR) technology. The CO_2 absorption experiments were conducted in a hollow fiber membrane contactor (HFMC) at 25°C and 12.5kPa CO_2 partial pressure. The CO_2 rich solvent was regenerated at 75°C and 20kPa regeneration pressure by using the MVR technology. The chain length, number of functional groups, side chain, and number of hydroxyl groups of amines were investigated to get a better understanding on the effects of the structure in the MVR process. The results show that the tertiary amines have greater regeneration performances than the primary amines, but the CO_2 absorption rates of the tertiary amines are worse than the primary amines. For the polyamines, the absorption performance of polyamines can be improved by increasing the number of amine groups while the MVR performance of the polyamines can be reduced. Steric hindered amines exhibited greater MVR performances. In addition, amines with steric hindrance effect caused by the substitution of hydroxyl group or methyl group to amine group in structure has also shown good performance in the MVR process for CO_2 desorption. The overall performance of amine-based absorbents was also investigated by an absorption-desorption characters analysis. It shows triethylenetetramine (TETA) and N-methyldiethanolamine (MDEA) have great average CO_2 absorption rates and relatively high cyclic capacities per mole absorbent, and ethylenediamine (EDA) is considered to be the promising absorbent as cyclic capacity in mol CO_2/kg absorbent. Diethanolamine (DEA) and 2-Amino-2-methyl-1-propanol (AMP) are found to have the best overall performances in terms of CO_2 absorption rate at lean loading and cyclic capacity in mol CO_2/mol absorbent. In terms of overall performance, MDEA is mostly recommended for using in MVR process. Sweeping steam can significantly improve MVR performance in most selected absorbents except AMP and 2-amino-2-hydroxymethyl-1,3- propanediol (THAM) absorbents which present the potential to reduce the regeneration energy demand by operating without sweeping steam. The study also finds that MVR shows better regeneration performance as compared to traditional thermal regeneration process at the same regeneration temperature.