Carbon molecular sieves from bituminous coal by controlled coke deposition

Abstract

Carbon molecular sieves (CMS) and zeolites are widely used as microporous sieving solids for gas and liquid separations. However, due to hydrophobicity, better thermal stability and neutrality in both acidic and alkaline media, CMSs have definite advantages over zeolites. In the present work, an effort has been made to develop suitable process conditions for synthesizing CMSs from the locally available bituminous coal. The coal was crushed, milled and agglomerated with sulfate pulp waste liquor (SPWL) or coal-tar pitch (CTP) as the binders and then carbonized in nitrogen atmosphere at 800°C for about 60 minutes. In order to narrow down the pore mouth sizes, acetylene and benzene were each cracked separately at 800°C to facilitate the deposition of coke on the char. Acetylene and benzene were cracked for 3 to 10 minutes and 10 to 30 minutes, respectively. Acetylene cracked samples did not show good separation, probably because of over-coking in deeper locations. In contrast, benzene cracked samples were found to be highly suitable for CO 2-CH 4 separation. The best result (i.e., uptake ratio of 39.9) was obtained for feed benzene entrainment in N 2 of 1.27 × 10 −4 g/ml, cracking time of 30 minutes and this ratio was more than 10 times that of non-cocked sample. CMS samples produced using SPWL as binder showed poor O 2 N 2 uptake ratios throughout (1 to 1.5), whereas samples with CTP as binder showed far more encouraging results, the best uptake ratio being 5.5 for benzene-nitrogen feed stream containing 3.508 × 10 −4 g/ml benzene and 5 minutes cracking time. This ratio is about 5.5 times more than that of uncoked sample.