(401ab) Carrier Saturation Phenomenon in Facilitated Transport Membrane for CO2 Separation from Low Concentration Sources

Authors: 
Wu, D., The Ohio State University
Han, Y., The Ohio State University
Ho, W. S. W., The Ohio State University
Amine-containing facilitated transport membranes exhibit superior CO2 separation performance because the CO2 transport is enhanced by the reversible reaction between CO2 and the active carrier, amine, incorporated in the membrane. Continuously increasing the CO2 partial pressure leads to the constant CO2 flux, which does not increase with CO2 partial pressure, i.e., the carrier saturation phenomenon. At the carrier saturation, all available carrier molecules have been reacted with the high pressure CO2. However, this carrier saturation phenomenon can be beneficial for CO2 capture from low CO2 concentration (~1% CO2) sources, e.g., the residual flue gas after the primary CO2 capture system (with 90% CO2 removal) and coal mine gas streams. For CO2 separation from low concentration sources, an improved membrane separation performance can be obtained. With reducing the CO2 concentration in the feed gas, both CO2 permeance and CO2/N2 selectivity increased. These were mainly due to more available amine carriers for CO2 molecular transport at lower CO2 concentration conditions. In this study of CO2 separation from low concentration feed, the membrane used consisted of polyvinylamine serving as the fixed-site carrier and piperazine glycinate acting as the mobile carrier. A CO2 permeance of 785 GPU (1 GPU = 10-6 cm3 (STP)·cm-2·s-1·cmHg-1) and a CO2/N2 selectivity of 150 were obtained with a feed of 20% CO2 and 80% N2 on a dry basis (16.6% CO2 and 66.2% N2 along with the saturation water vapor at 17.2%) at the typical flue gas temperature of 57°C. By reducing the CO2 concentration in the feed, a significant CO2 permeance increase was observed when the CO2 concentration was below 5%. For instance, the membrane showed a CO2 permeance of 950 GPU and a CO2/N2 selectivity of 190 with a feed of 1% CO2 and 99% N2 on a dry basis. The observed performance increase was due to the carrier saturation phenomenon as more carrier molecules were available for CO2 transport at a lower CO2 concentration. Additionally, it was found that the effect of SO2 was less significant when the CO2 concentration was low. The CO2 permeance dropped by approximately 2.5% with an introduction of 3 ppm SO2 in the feed gas of 20% CO2 and 80% N2 on a dry basis at 57°C. However, no performance reduction was observed after exposing the membrane to 3 ppm SO2 with the feed gas of 1% CO2 and 99% N2 on a dry basis at the same temperature. Therefore, the studied membrane can be applied for CO2 separation from low concentration sources with an exceptional separation performance.