Separation of linear, mono-methyl and di-methyl alkanes in the 5–7 carbon atom range by exploiting configurational entropy effects during sorption on silicalite-1
Abstract
We
have developed a novel concept for separating alkane mixtures, in the 5–7 carbon atom range, into three
separate fractions consisting of linear, mono-methyl and di-methyl alkanes by adsorption on silicalite. We make
use of the fact that with increased degree of branching, the “
packing efficiency” within the silicalite matrix
is significantly lower. This configurational entropy effect comes into play when the loading exceeds 4 molecules
per unit cell, when all the intersection sites are occupied, and results in the following hierarchy of sorption
strengths: linear alkanesmono-methyl alkanes
di-methyl alkanes. To demonstrate the feasibility of the
entropy-based separation concept we carried out configurational-bias monte carlo simulations for a variety
of binary, ternary and quaternary mixtures of alkanes, n-pentane (n-C5), 2-methylbutane (2MB), n-hexane
(n-C6), 2-methylpentane (2MP), 3-methylpentane (3MP), 2,2-dimethylbutane (22DMB), n-heptane (n-C7), 2-methylhexane (2MH), 2,2-dimethylpentane (22DMP). The entropy-driven separation concept has been verified, in part,
by comparison with the experimental
sorption
data of Santilli (J. Catal.,
1986, 99, 335) for the mixture n-C6–3MP–22DMB.