Fluid phase equilibria of (carbon dioxide plus a 1-alkanol plus an alkane)up to 100 MPa and T=393 K: cosolvency effect, miscibility windows, and holes in the critical surface

Phase equilibria phenomena such as cosolvency effects, miscibility windows, and non-critical (liquid + gas) (l.g.) holes in the critical surface in (c arbon dioxide + a 1-alkanol + an alkane) were studied up to 100 MPa. In continuation of experiments by Kordikowski and Schneider and Pohler et a l., carbon dioxide systems containing a 1-alkanol with m less than or equal to 10 and an alkane with n less than or equal to 16 (where m and n denote the number of carbon atoms in the alkyl chains of the 1-alkanol, or the alk ane, respectively) were investigated for large cosolvency effects. An isoth ermal cosolvency effect of 14 MPa has been found in (carbon dioxide + 1-oct anol + hexadecane) at T = 298 K with additional exhibition of large isobari c miscibility windows. Non-critical l.g. holes in the critical surface are also experimentally est ablished These l.g. holes in the critical surface, which have already been described as l.g. two-phase holes in the (liquid + liquid + gas) (l.l.g.) t hree-phase surface by Patton et al. and Peters et al., are now deduced from the occurrence of cosolvency effects when cosolvency lowers the critical s urface of a ternary system onto the l.l.g. three-phase surface. This can ul timately lead to a penetration of the l.l.g. three-phase surface by the cri tical surface with the exhibition of a, mostly closed-loop, critical end po int locus as the intersection line, surrounding a non-critical l.g. region. The relation between miscibility windows and holes in the critical surface is illustrated by the examination of systems exhibiting both miscibility wi ndows and holes such as (carbon dioxide + 1-heptanol + pentadecane) and (ca rbon dioxide + 1-decanol + tetradecane). (C) 2000 Academic Press.