Coal-Based Carbons with Molecular Sieve Properties

Abstract

Naturally occurring and synthetic zeolites (1,2) find wide application in industry as molecular sieves. Some carbonaceous materials also show molecular sieve properties; however, their efficiencies and capacities are considerably lower compared with those of zeolites. Molecular sieve carbons can be obtained by coating activated carbons with thermosetting resins (3). Composite molecular sieves were obtained by heating precarbonized polyvinylidene chloride with certain binders (4). It has been found that the adsorption capacities of charcoals (4,5) depend on the accessibility of sorbate molecules, indicating molecular sieve action. Youssef (6, 7) has produced molecular-sieve carbons by carbonizing date pits and bagasse, in the presence and absence of zinc chloride, under controlled conditions. Carbon molecular sieves are used extensively in gas chromatography for the separation of permanent gases and light hydrocarbons. Carbon molecular sieves also find commercial application for the manufacture of pure hydrogen from hydrogen-rich gases such as coke-oven gas, and for the separation of air by the pressure-swing adsorption technique.