(76g) Prediction of the Solubility of Ethylene in Polyethylene Using Molecular Simulations at the Operating Conditions of LDPE Polymerization Process Equipment
AIChE Annual Meeting
Monday, November 9, 2015 - 10:30am to 10:50am
The Solubility Of Ethylene In Polyethylene Using Molecular Simulations At The
Operating Conditions Of LDPE Polymerization Process Equipment
Gondu*, Jhumpa Adhikari**
of Chemical Engineering, IIT Bombay
(e-mail: *sudheer7g@ iitb.ac.in, ** email@example.com)
The aim of the
present work is to study the fluid phase behavior of ethylene and polyethylene
mixtures by employing molecular simulations and theoretical methods such as
equation of state (EOS) modeling (perturbed-chain statistical associating fluid
theory, PC-SAFT, and SAFT) [1, 2]. Thermodynamic properties (such as
vapor-liquid equilibria data) are necessary for the design and optimization of
the separators, downstream of the polymerization reactor; in the high pressure
process for low density polyethylene (LDPE) production. The vapor-liquid
equilibria (VLE) data reported in literature at the operating conditions of the
high pressure separator (HPS) and the low pressure separator (LPS) are limited.
In this work, molecular simulations have been employed to generate the
necessary data in conjunction with the Nath, Escobedo and de Pablo (NERD) force
field [3, 4]. We have used the Hybrid Monte Carlo (HMC) and the Gibbs Ensemble
Monte Carlo (GEMC-NPT) techniques  to determine the VLE of the
ethylene-polyethylene mixtures. First, we have performed the simulations at the
conditions reported by Nath et al.  and observed that our results are in
reasonable agreement with the literature data . This has been followed by
molecular simulations at the operating conditions of the HPS and LPS. The
solubility data from our simulations have also been compared with that
estimated from traditionally employed EOS for polymer systems, viz., PC-SAFT and
SAFT. It has been observed that ethylene content in the polymer rich phase
increases with pressure at constant temperature at both the HPS and LPS
operating conditions; this is consistent with the trend reported by Bogdanovic
. In the entire temperature and pressure range of the operating conditions
of the separators, the SAFT estimates are higher than the corresponding values
determined from our simulations; while PC-SAFT predictions show lower
solubilites as compared to molecular simulation predictions. The VLE data
estimated by all the three methods have been used in sizing the HPS and LPS.
The volume of the HPS computed from molecular simulation generated data is
lower than that calculated using either SAFT or PC-SAFT predictions. However,
for the LPS, the volume calculated from molecular simulation data is
significantly higher than that from SAFT and PC-SAFT.
 Gross J., and Sadowski, G., 2001,
?Perturbed-Chain SAFT: An Equation of State Based on a Perturbation Theory for
Chain Molecules?, Ind. Eng. Chem. Res., 40, 1244-1260.
 Huang, S.H. and Radosz, M., 1991,?Equation of
State for Small, Large, Polydisperse,and Associating Molecules: Extension to
Fluid Mixtures?, Ind. Eng. Chem. Res., 30,1994-2005.
 Nath, S.K., Escobedo, F.A., de Pablo, J.J. and Patramai, I.,
1998,? Simulation of Vapor-Liquid Equilibria for Alkane Mixtures?, Ind. Eng.
Chem. Res., 37, 3195-3202.
 Nath, S.K., Banaszak, B.J. and de Pablo, J. J. ?Simulation of
Ternary Mixtures of Ethylene, 1-Hexene, and Polyethylene?, Macromolecules, 2001,
 Bogdanovic, V., 1985,? Industrial Aspects of Phase Separation In
Ethylene-Polyethylene System at Pressures of 15-30 MPa?, Ind. Eng. Chem.
Process Des. Dev., 24, 576-581.