Study On Non-porous Hollow Fiber Contactors For CO₂ Removal

Recently, the capture of carbon dioxide has gained an increasing attention. Naturalgas, refinery gas and coal gas generate huge quantity of CO₂ when they areemployed for industrial and domestic heating and other chemical processes.Emission of CO₂ from these processes is a potential cause of environmentalproblems such as global warming. Hence, the capture of CO₂ by varioustechniques has become a research focus in recent years. However, conventionaltechnologies for CO₂ capture such as column absorption and low-temperaturedistillation etc. are energy consuming and not easy to operate because of theflooding, foaming, channeling and entrainment problems. As a result, a hollowfiber membrane contactor, as a promising alternative, has won more and moreattention. This process offers several practical advantages including high interfacearea per unit contact volume, independent control of gas and liquid flow rates. Itcan effectively eliminate the problems of conventional technologies mentionedabove. Also it can be easily scaled up due to its modularity.Firstly, in the study, a hollow fiber contactor containing siliconerubber-polysulphone hollow fiber composite membranes was used for theabsorption of CO₂. The effects of various absorbents, liquid volumetric flowrate,liquid pressure, concentration of NaOH solution and gas pressure on theefficiency of CO2 absorption were investigated. The experimental results indicatedthat the chemical absorption had higher absorption efficiency than the physicalabsorption and the membrane resistance controlled the mass transfer accompaniedby chemical absorption. When 2×103mol·m-3NaOH solution was employed as theabsorbent, the overall mass transfer coefficient KG of CO2 approached to itspermeation rate through the membrane. Furthermore, a mathematical model of KGwas set up. It was well fit with the experimental results.In addition, in order to investigate the commercial application potential of ahollow fiber membrane contactor, a commercial asymmetric polyimide hollowfiber membrane module was modified and used as a contactor. The non-poroushollow fiber contactor performed a high ideal separation factor of 47 for CO2/N2separation. The bubbling and weeping problems were eliminated, and a stableoperation process was achieved.It is concluded that the non-porous hollow fiber membrane contactors used in thisstudy have potential ofapplication for CO2 removal.