Regenerate CO₂ Absorption By PTFE Hollow Fiber Membranes Via A Membrane Flash Process

For the burning of fossil fuels in recent 100 years, the greenhouse effect becomes more serious. The CO₂ capture process was considered to be the most effective technology to control greenhouse effect. In the CO₂ capture technologies, membrane absorption process was considered to be the most feasible. During the membrane process, membrane material most has hydrophobic property. So PTFE material was ideal membrane material for membrane absorption process. In the CO₂ capture process, CO₂ desorption process ensured the recycle of absorbent.Currently thermal regeneration is main CO₂ desorption technology. It is not only cover a large area, but also etch apparatus. And it also cost a lot of energy. This seriously affects the development of CO₂ capture process. Therefore, the study of new CO₂ absorbent regeneration technology becomes more important for the CO₂ capture process. In this paper hydrophilic and hydrophobic PTFE membrane were used to study the technological parameter of the immersion membrane process of absorbing CO₂ and membrane flashing process of CO₂ absorbent regeneration.The main research work of this dissertation focuses on the following aspects:（1） Though the “extrusion-stretching-sintering” process preparing PTFE hollow fiber membrane, and modified its hydrophilic property. The microscopic surface morphology, pore size distribution and inside and the water contact angle of inside and outside membrane surface were tested for characterization of PTFE hollow fiber membranes.（2） The mixed gas flow rate, absorbent concentration, mixing speed of immersion membrane absorption process were studied.（3） The flashing temperature, flashing pressure, rich liquid flow rate, membrane module length,membrane packing density, pore size of membrane flashing process were studied via hydrophilic PTFE hollow fiber membrane.The experimental results show that as follow:（1） The pore size of PTFE hollow fiber membrane was control by stretch ratio, the water contact angle of PTFE hollow fiber membranes were near 115 °, and the water contact angle of hydrophilic PTFE hollow fiber membranes were near 80 °.（2） The smaller of mixed gas flow rate, the longer of gas and absorbent contact time. So the CO₂ absorption ratio is higher. Thehigher the concentration of absorbent, the faster of reaction rate between CO₂ and MEA. And the absorbent can load more CO₂, so the CO₂ absorption ratio and the CO₂ absorption capacity are higher. The faster of mixing speed, the faster of molecular movement. So the CO₂ absorption ratio and the CO₂ absorption capacity are higher.（3） The higher of the flashing temperature, the better of the thermal desorption. So the CO₂ desorption and desorption flux were larger. The higher of the flashing pressure, the lager of CO₂ partial pressure in the shell. And different of the the CO₂ partial pressure in the liquid and shell was smaller, so the CO₂ desorption and desorption flux were smaller. The larger of the rich liquid flow rate, the more cycles of the rich liquid. The heat loss became badly, thermal desorption became worse. So the CO₂ desorption and desorption flux were smaller. The longer of the membrane length, the greater of the membrane area, so the CO₂ desorption flux was smaller. When the membrane packing density is smaller than 10 %, the gap between the PTFE hollow fiber membranes were larger and the contact probability of permeate liquid was small. The rich liquid cycles were decreased with increasing the membrane packing density. So CO₂ desorption ratio was increased with increasing the membrane packing density. While the membrane packing density was larger than 10 %, the arrangement between PTFE hollow fiber membranes were closely. The probability of permeate liquid became larger liquid was increased, it increased the CO₂ mass transfer resistance. So CO₂ desorption ratio was decreased with increasing the membrane packing density.Because of membrane area was increased with increasing membrane packing density, so CO₂ desorption flux was decreased with increasing the membrane packing density. The volume of permeate liquid was increased with increasing the membrane pore size and the CO₂ mass transfer resistance and rich liquid permeation flux were increased. So CO₂ desorption ratio was decreased with increasing the membrane pore size and CO₂ desorption flux was increased with increasing the membrane pore size.