Development of cesium-incorporated carbon membranes for CO 2 separation under humid conditions

Abstract

Cesium-incorporated carbon membranes were developed to overcome the problem of separation performance decline under humid conditions. A cardo-type polyimide was chosen as the precursor for the carbon membranes. Cesium carbonate (Cs 2CO 3) was chosen as a Cs source and blended with precursor solution. Carbonization was conducted at 600 °C for 3 h under a nitrogen atmosphere. Analyses by atomic absorption spectrometry, inductively coupled plasma mass spectrometry and electron probe microanalysis revealed that Cs was incorporated into the carbon membranes uniformly and that the concentration of the incorporated Cs could be controlled by the concentration of Cs 2CO 3 in the precursor. The separation performance was evaluated using a CO 2/N 2 gas mixture with controlled relative humidity at 40 °C at atmospheric pressure. The original carbon membrane without Cs had a lower CO 2 permeance and CO 2/N 2 separation factor under humid conditions than it did under dry conditions. On the other hand, Cs-incorporated carbon membranes had a higher CO 2 permeance and separation factor under humid conditions. The CO 2 permeance ( Q C O 2 ) and separation factor ( α C O 2 / N 2 ) using a CO 2/N 2 gas mixture (CO 2/N 2 = 5/95%) at 100% relative humidity (RH%) for Cs-incorporated carbon membranes (Cs 2CO 3 concentration in precursor: 1.4 wt%) were ca. 2.2 × 10 −10 m 3 (STP) m −2 s −1 Pa −1 and 44, respectively, and were greater than values for the original carbon membrane ( Q C O 2 = 2.4 × 10 − 11 m 3 ( STP ) m − 2 s − 1 P a − 1 , α C O 2 / N 2 = 11 ) . It was revealed by a water vapor sorption experiment and nanopermporometry, that carbon pores became more hydrophilic and that the pore size distribution was shifted to larger pore size by the incorporation of Cs into the carbon membranes. It was suggested that the change in pore size distribution and the pore surface properties played an important role in improving CO 2 separation performance under humid conditions.