Carbon Dioxide Absorption into Aqueous Ammonia in a Hollow Fiber Membrane Contactor

Abstract

Chemical absorption has been considered as a promising technology for carbon dioxide (CO2) capture from different industrial waste gases. However, this technology has not been widely commercialized due to its high capital and operational costs, especially the cost for solvent regeneration. Studies have been focused on developing more efficient gas/liquid contactors or superior solvents that require less energy for regeneration. Aqueous ammonia (NH3) has been recently studied as a CO2 absorption solvent in many traditional gas/liquid contactors due to its lower cost and low energy requirement for solvent regeneration compared to traditional amine solutions. Since membrane contactors offer more advantages than traditional gas/liquid contactors, it could be more efficient and economic to capture CO2 using aqueous ammonia as a solvent in a membrane contactor. However, little research has been reported in this field. The main objective of this research is to investigate the CO2 absorption performance of aqueous ammonia in a hollow fiber membrane contactor. In order to achieve this research goal, a number of lab-scale CO2 absorption experiments were conducted using aqueous ammonia and monoethanolamine (MEA) as absorption solvents in a membrane contactor fitted with polytetrafluoroethylene (PTFE) hollow fiber membranes at ambient temperatures. The CO2 absorption performance was evaluated in terms of the volumetric overall mass transfer coefficient (KGav) under different operating parameters. The absorption performance of aqueous ammonia was compared to that of MEA solvent under the same experimental conditions. The longterm membrane stability was evaluated by continuously running the CO2 absorption experiments using aqueous ammonia as a solvent for up to ten hours.