Simulation of Flash Separation in Polyethylene Industrial Processing: Comparison of SRK and SL Equations of State

Abstract

The Soave-Redlich-Kwong (SRK) and the Sanchez and Lacombe (SL) equations of state are applied to the flash simulation of polyethylene industrial separators, specifically low-density polyethylene (eight resins) and linear low-density polyethylene (25 resins). Three mixing rules are used in the SRK equation: van der Waals (VDW) one-fluid, Wong-Sandler, and LCVM (linear combination of the Vidal and Michelsen mixing rules). The latter two mixing rules incorporate the Bogdanic and Vidal activity coefficient model. All these models involve two adjustable parameters. The results indicate that SL is the best model to simulate the flash separation of polyethylene under industrial conditions.

Influence of α-Olefin Concentration and Length on the High-Pressure Phase Behavior of (α-Olefin + n-Hexane + LLDPE) Systems

“…Tork 19 found that 1-octene decreases phasetransition pressures in the (C 2 + C 8 + nC 6 + HDPE) system by about 0.07 MPa per wt % 1-octene in the solvent. Buchelli and Todd 5 and Costa et al 20 also report industrial operating data for the stream leaving the solution process's polymerization reactor, but they do not report the compositions of the phases. Phase behavior data, where the solvents contain 1-butene and/ or 1-octene, are also reported by Cameron 21 and Lonnqvist, 22 but these authors do not publish the compositions of the solvents nor do they characterize the polymers.…”

A Survey of Equations of State for Polymers

“…In general the equations of state using G E models are unable to describe high-pressure phase equilibria with the desired quality [65], thus have a more restricted application. On the other hand, their equations and mixing rules are simple, which facilitates their convergence and the obtaining of terms required for the calculation of other thermodynamic properties, e.g.…”

“…The SRK and the Sanchez and Lacombe (SL) equations of state were applied by Costa et al [65]- [66] to the flash simulation in a low-pressure separator (LPS) and also in a high-presure separator (HPS) in an industrial polyethylene facility (specifically, 8 low-density polyethylene resins and 25 linear low-density polyethylene resins were investigated). Three mixing rules were used in the SRK equation: van der Waals (vdW) one-fluid, Wong-Sandler and LCVM.…”

“…[3], [77]) and one using industrial plant data [65], a large number of SL EOS evaluations have been reported in the literature regarding liquid-liquid equilibrium.…”

Dynamic Multi‐Phase, Multi‐Zone Modeling of Flash Separators for Highly Viscous Polymerization Processes

“…It was found via the use of a SAFT EOS model that a shift in the phase transition type (i.e., from upper‐critical‐solution‐temperature (UCST) to upper‐lower‐critical‐solution‐temperature (U‐LCST)) could be observed with increasing the free VA content in the monomer–ethylene mixture. Costa et al, using the Soave–Redlich–Kwong (SRK) and the Sanchez and Lacombe (S–L) EOS, analyzed the equilibrium behavior of a number of LDPE and LLDPE industrial flash separators. They reported that the S–L EOS was the best model for analyzing the thermodynamic behavior of polyethylene–ethylene separation units under industrial conditions.…”