March 3 - 5,1999, Karlsruhe, Germany - FZK

GVC GVC^*+\
GVC-Fachausschuß „High Pressure Chemical Engineering", March 3-5, Karlsruhe, Germany, 1999 FZK
: K j r 99^)
The Influence of Inert Gases on the High-Pressure Phase
Equilibria of Copolymer-Comonomer Mixtures
G. Luft*, M. Kinzl
Technische Universität Darmstadt, Institut fur Chemische Technologie,
Petersenstraße 20, D-64287 Darmstadt, Germany
Email: luft@bc methane > nitrogen > carbon dioxide.
Except methane, the alkanes did not act as antisolvents. Ethane did not have an observable effect on the phase
behaviour, whereas the addition of propane and especially n-butane resulted in a reduction of cloud point pressures.
Introduction
Highly compressed supercritical ethylene is known
as a good solvent for organic compounds. Several
industrial processes, such as the polymerization of
ethylene, take advantage of the solubility of polymers
and copolymers in this medium [1]. The chain
molecules formed during the reaction are dissolved
in the monomer mixture. They can easily be separated
from the reactants by depressurizing.
Whereas the influence of liquid comonomers like
vinyl acetate or 1-hexene on the phase behaviour of
polymer-ethylene and copolymer-ethylene systems
has been investigated in detail [2,3,4,5], only few
studies on the addition of inert compounds have
been published [6,7]. The experimental data reported
so far have been determined in a very narrow
range of conditions.
This work contributes to the understanding of the
impact of anorganic gases and alkanes on the phase
equilibria of copolymer-monomer mixtures at technical
conditions. Nitrogen, carbon dioxide, helium
and alkanes like methane, ethane, propane and nbutane
were added to solutions of poly-(ethylene-co-
1-hexene) (EH) and poly(ethylene-co-vinyl acetate)
(EVA) in mixtures of the monomers.
Using two different high-pressure autoclaves we systematically
measured cloud point pressures and coexistence
curves of these quasi-quaternary systems
in dependence on temperature and mixture composition.
15
Materials and Methods
The copolymers were supplied by the Exxon Corporation,
Houston, TX. The data are listed in Tables
1 and 2.
copolymer
number average MW
weight average MW
polydispersity
incorporated vinyl acetate
melt index (463 K, 2.16 kp)
EVA-copolymer
61900 g/mol
167000 g/mol
2.70
27.5 wt%
l.Og/lOmin
Table 1. Data of Poly(ethylene-co-vinyl acetate)
copolymer
number average MW
weight average MW
polydispersity
incorporated 1-hexene
EH-copolymer
60000 g/mol
129000 g/mol
2.15
16.1 wt%
Table 2. Data of Poly(ethylene-co-1-hexene)
The purities and sources of the inert compounds and
the comonomers vinyl acetate and 1-hexene are given
in Table 3.