Thermal swing membrane based method for CO2 capture from flue gas

Carbon dioxide, a greenhouse gas and a major contributor to global warming, is released in large amounts by flue gases. To limit climate change, such CO2 emissions have to be reduced, CO2 captured and sequestered. Conventional monoethanolamine (MEA)-based absorption techniques are costly due to high capital cost and high energy consumption since the absorbent has to be regenerated at a high temperature ~ 120°C. A temperature swing membrane absorption (TSMAB) process was described by Mulukutla et al. (2015) using a novel membrane contactor, novel absorbents and a cyclic process. In this device, the absorbent is on the shell side of a membrane device containing two commingled sets of hollow fiber membranes. One set consists of porous hydrophobic hollow fibers through which the feed gas at 25-50°C comes in for a while and CO2 from this feed gas gets absorbed in the shell-side absorbent. After sometime when the absorbent gets saturated with CO2 and CO2 breaks through the other end of the membrane device, CO2-containing feed gas introduction is stopped. The membrane device has another set of solid essentially impermeable hollow fibers through the bore of which hot water is then passed for some time at a temperature ~ 80-95°C to desorb the absorbed CO2 from the absorbent into the bore of the porous hollow fibers. This purified CO2 stream is taken out for some time. Once the desorption process is over, the TSMAB cycle is initiated again with the CO2-containing feed gas coming in. The device and absorbent used by Mulukutla et al. (2015) had many deficiencies. The absorbent had a very high viscosity; the thickness of the absorbent in between the two sets of hollow fibers was very high since only a few fibers were used; further the porous hollow fibers had a very large diameter (OD/ID, 925/691 μm). In this research, porous hollow fibers have much smaller OD/ID, 300/240 μm. The fibers were well packed in the device so that the film thickness for absorption was small and saturating it was quickly achieved. Further the viscosity of the absorbent namely, a very concentrated aqueous solution of N-Methyldiethanolamine (MDEA), is much lower than that of dendrimer-ionic liquid combination used by Mulukutla et al. (2015). This thesis has studied the behavior of such a device and its performance in a cyclic process of CO2 absorption and desorption