Study On CO₂ Regeneration From Absorbent In Ptfe Hollow Fiber Membrane Contactor By Using Membrane Vacuum Regeneration Technology

It is well known that the gradually increased CO₂ emissions caused by human activities have resulted in the serious greenhouse effect and climate change. It is important for human life to control the CO₂ emissions effectively. Currently, several technologies have been selected to control CO₂ emissions, but CO₂ capture separation method still have many problems. The hollow fiber membrane module, which is a membrane gas separation efficiency, is extensively studied in recent years. It combines the advantages of membrane separation process and high selectivity in gas absorption technology. It is ideal for the absorption and separation of CO₂. In consideration of the membrane material selection, PTFE is an attractive membrane material due to its chemical resistance, great hydrophobicity and high mechanical strength. In this work, the PTFE follow fiber membranes were prepared through a cold pressing method including pushing, stretching and sintering. The PTFE follow fiber membranes were used for the membrane vacuum regeneration process to regenerate the CO₂ from the rich solution.（1） The PTFE hollow fiber membranes were prepared through “paste-extrusion- sintering”method, different kinds of PTFE hollow fiber membranes with different structures were made by changing extrusion head sizes and stretching ratios. The PTFE hollow fiber membrane surface morphology, pore size distribution, porosity and surface water contact angle of the inner and outer surfaces were also investigated.（2） The PTFE follow fiber membranes were used for the membrane vacuum regeneration process to regenerate the CO₂ from the rich solution. The MDEA-PZ complex amine solution was selected as absorbent. The effects of membrane structure（membrane wall thickness and membrane pore size） and membrane module structures（packing density and membrane length） on CO₂ regeneration flux and regeneration ratio were investigated.（3） The effects of key operating parameters（rich solution flow rate, regeneration temperature, regeneration pressure, CO₂ loading in rich solution, scavenging flow rate and the ratio of absorbent） on CO₂ regeneration flux and regeneration ratio were investigated.（4） The effects of molecular structures of absorbent（number of activated hydrogen atom in amine group,the steric hindrance effect, number of hydroxyl groups, number of amine groups, length of carbon chain and the position of hydroxyl groups） on CO₂ regeneration flux and regeneration ratio were investigated.The experimental results showed that as follows:（1） PTFE hollow fiber membrane had the asymmetric microporous structure. The average pore size of the PTFE membrane was between0.11⁰.2 μm, and the porosity of the PTFE membrane was up to 40%. The water contact angle of the surface of PTFE hollow fiber membranes are greater than 110°.（2） Increasing the membrane pore would improve regeneration performance. The increase in membrane thickness significantly reduced the regeneration performance. The membrane length and packing density reduction had the positive influence on the improvement of regeneration ratio, but would reduce the CO₂ regeneration flux.（3） The CO₂ regeneration flux and regeneration ratio increased with the increase of regeneration temperature, CO₂ loading, scavenging flow rate and concentration of MDEA. However, the regeneration pressure was negative to the regeneration flux and regeneration ratio. The regeneration ratio decreased and regeneration flux increased when the flow rate of rich solution increased. At the same time, vacuum membrane renewable energy reduced with the vacuum side pressure increased.（4） The CO₂ regeneration performance decreased with an increase of number of activated hydrogen atom in amine group. The CO₂ regeneration performance improved by increasing the steric hindrance effect, the number of the hydroxyl groups, the number of the amine groups and length of carbon chain. Furthermore, when the hydroxyl group was located on the α-C, it had the positive influence on the increase of CO₂ regeneration performance.