The potential for use of cellulose triacetate membranes in post combustion capture

Abstract

Cellulose triacetate (CTA) membranes occupy much of the gas separation market in natural gas processing. With a high CO 2 /N 2 selectivity, this material may also be prospective for post-combustion carbon capture, if the permeance can be optimised. In capture applications, the impacts of liquid water condensate of variable pH, SO x and NO x on the gas separation performance are of critical interest to ensure maximum membrane lifetime. In this work, dense CTA membranes were aged in pH solutions of 3, 7 and 13 for a total of 60 days. It was found that the plasticisation of the CTA membrane when aged in pH 3 and pH 7 solutions enhanced the permeability of CO 2 and N 2 by over 30% with little impact on CO 2 /N 2 selectivity. Conversely, the membrane aged at pH 13 failed due to hydrolysis reactions. The membrane was selective for SO 2 over CO 2 with a SO 2 permeability of 20 Barrer. Conversely, NO did not readily permeate, so that the permeate composition was below the level of detection. CTA membranes stored in SO 2 /N 2 and pure N 2 for a 120 day period at 22 o C were relatively stable, with a slight loss in permeability due to membrane aging. Conversely, a significant loss in permeability was observed when these membranes were exposed to 0.74 kPa of NO for the same period. The performance loss appeared to relate to reaction of alcohol groups within the cellulose acetate structure with trace levels of NO 2 in the gas mixture. The results highlight the possibility for use of CTA membranes in postcombustion capture, if the active layer thickness can be reduced to enhance gas flux.

The impact of ethylene glycol and hydrogen sulphide on the performance of cellulose triacetate membranes in natural gas sweetening

“…Again, the deviation may be due to differences in both degree of acetylation and operating pressures. Gas permeability generally falls with time due to the densification of membrane matrix as observed in Figure 8a and in other studies [21,56,59,60]. As observed in section 3.2.2, the changes in free volume impact most the penetrant of larger kinetic diameter (CH 4 ) [21,56,59].…”

“…A variable volume constant pressure (VVCP) gas permeation apparatus was utilised to measure the permeability of gas mixtures through CTA membranes across the pressure range from 100 to 900 kPa gauge and temperature range from 22 to 80 o C. The gas permeation setup has been reported in previous studies [6,20,21]. The H 2 S mixed gas (1000ppm H 2 S in balance N 2 , Coregas Australia) was fed into the feed side of the permeation cell with stage cut less than 0.2%.…”

“…For measuring the permeability of individual gases (He (99.99% purity, Coregas Australia), CH 4 (99.9% purity, Coregas Australia) and CO 2 (99.5% purity, BOC Australia), a constant volume -variable pressure (CVVP) gas permeation apparatus was used. The gas permeation rig was operated at 35 o C and the setup was also as reported in previous studies [21,22]. The membrane with an effective area of 10.75 cm 2 was installed into the permeation cell and placed under a vacuum overnight prior to the gas permeation measurement.…”

Effects of industrial gas impurities on the performance of mixed matrix membranes

“…The membrane density (ρ) was determined based on the Archimedean principle using an analytical balance (Mettler Toledo AB204-5) at room temperature (23 ± 1°C) [9,37].…”

“…However, industrial gas streams are not the pure component mixtures tested in laboratories, but can contain water vapor, hydrocarbons, aromatic compounds, and acid gases as major impurities [8]. Flue gas streams in post-combustion capture applications are typically saturated with water and contain 200-5000 ppm sulphur oxide (SOx) and 150-300 ppm (NOx), with nitric oxide (NO) the major component and less than 10 ppm nitrogen dioxide (NO2) [9]. The use of flue gas desulfurization can reduce these concentrations to <10 ppm SOx and remove 90% of the NOx [10], but such processes are not always used, particularly in Australia and China.…”