Relationship Between The Properties Of Adsorption/Desorption And The Pore Structure Of Polyethylenimine/Carbon Xerogel CO₂ Adsorption Adsorbent

It’s essential to stickly control CO₂ concentration in confined spaces, such as submarine, space shuffle and spacecraft. Focused on the relationship between the properties of adsorption/desorption and the pore structure of polyethylenimine （PEI）/carbon xerogel, carbon xerogel material used for capturing CO₂ in confined spaces was studied in this thesis.Using Na2CO3 （C） as conditioner, carbon xerogels with different pore structure were prepared with resorcinol （R） and formaldehyde （F）. The average pore diameter （APD） of the carbon xerogels was in the range of 15.3 to 424.4 nm, and the BET surface areas （BET S）,367.58 to 461.51 m2/g. PEI/carbon xerogel CO₂ adsorbents were obtained by impregnating PEI （MW600） on the carbon xerogel support. Experimental investigations were carried out for the adsorption of 0.4% （vol） CO₂ on PEI/carbon xerogel adsorbents in fixed bed reactor and desorption of CO₂ both in fixed bed reactor and thermogravimetric/vacuum device.In the fixed bed reactor, the results of the adsorption experiment showed that the adsorption capacities of CO₂ on the 16% PEI/carbon xerogel adsorbents at 20℃ were in the range of 42.544 to 49.431 mg/g for the adsorbents with APD of 17.5 to 50 nm, 50 to 79.7 nm, BET S was 81.72 to 35.15 m2/g,35.15 to 18.55 m2/g （mesopore, meso-macropore）, and in the range of 16.807 to 21.724 mg/g when APD was 168.2 to 525.3 nm, BET S was 10.88 to 4.36 m2/g （macropore）.The influences of PEI loadings on adsorption capacities of the adsorbents were different for the adsorbents with different pore sizes. In the experimental range, with the increasing PEI loading, adsorption capacities for mesopore adsorbents decreased after an initial increase, adsorption capacities for meso-macropore adsorbents increased constantly, adsorption capacities for macropore adsorbents adsorbents increased, but not much. In addition, the pore size of the PEI/carbon xerogel adsorbent affected the rate of adsorption of CO₂. It was found that the average CO₂ adsorption rate of the adsorbent with mesopore or meso-macropore was greater than that of macropore adsorbents and the adsorbents with different pore structure showed different kinetics of adsorption characteristics, indicating that the adsorption mechanism varied with the pore size of the adsorbent.Under 30℃ and 36℃, desorption performance of PEI/carbon xerogel adsorbents were investigated on thermogravimetric/vacuum device. It was found that the pore size of the PEI/carbon xerogel adsorbent affected the rate of desorption of CO₂. The average CO₂ desorption rate of the adsorbent with mesopore or meso-macropore was smaller than that of macropore adsorbents, and the adsorbents with different pore structure showed different kinetics of desorption characteristics, indicating that the desorption mechanism varied with the pore size of the adsorbent.Comprehensive comparison of adsorption capacity, adsorption and desorption rates, R/C=1000 adsorbent is one of the best absorbents among those prepared since it not only showed good adsorption performance, but also was relatively easy for the desorption of CO₂. Kinetics of desorption of CO₂ on the adsorbent was investigated both in fixed bed reactor and thermogravimetric/vacuum device. The desorption activation energy （Ed） of nitrogen purging in fixed bed was 73.59 kJ/mol, Ed of vacuum isothermal desorption was 95.22 kJ/mol, while Ed of vacuum thermal swing desorption was 34.18 kJ/mol. The results show that the diffusion has the most profound effect on vacuum-isothermal-desorption process.