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gSAFT appplication areas

Polymers

The SAFT equation of state has been shown to accurately predict the effects of molecular weight, intermolecular association, and compressibility on the phase behaviour of mixtures containing solvents, monomers, and polymers.

Recent developments include the accurate prediction of the effects of multiple polar groups on the phase behaviour of polar copolymers, and the efficient and robust computation of phase equilibrium for polydispersed polymer solutions.

The explicit treatment of the chain-like nature of polymer molecules in SAFT provides a predictive capability for:

  • the direct relation between molecular and chain length
  • transferability relations for parameters of homologous series
  • polydispersity
  • gas absorption in polymer systems.

based on a continuum fluid model (as opposed to traditional lattice models). This approach naturally provides density and pressure dependence.

Examples

The following examples are described here:

  • Simultaneous description of absorption (vapour-liquid equilibrium, VLE) and cloud curves (liquid-liquid equilibrium, LLE) of light hydrocarbons in polyethylene (PE).
  • Enhanced absorption of ethylene in polyethylene polymer grain during gas phase polymerisation reactions
  • Aqueous solutions of polyethylene glycol (PEG).

Polyethylene polymers

SAFT representation of polyethylene and the shorter solvent molecule

Example: Simultaneous description of gas absorption (VLE) and cloud curves (LLE) in polyethylene polymers

This study applied SAFT techniques to determine the fluid phase behaviour of n-pentane and low density PE (LDPE, molecular weight 76 kg/mol for VLE and 108 kg/mol for LLE). Plots for the system are shown to the right.

 

Reference

P. Paricaud, A. Galindo, and G Jackson, Modeling the cloud curves and the solubility of gases in amorphous and semicrystalline polyethylene with the SAFT-VR approach and Flory theory of crystallization,Industrial and Engineering Chemistry Research, 43, 6871-6889 (2004).

Example: Enhanced absorption of ethylene in polyethylene grain during gas phase polymerisation reactions (courtesy of BP and Borealis)

This study demonstrated that  significantly enhanced activity in the reacting polymer grain could be achieved by replacing the inert pressurising gas nitrogen by pentane by increasing the absorption of ethene and but-1-ene. This is shown in the table below.

Absorption of ethylene in polyethylene grain

Study undertaken in conjunction with BP and Borealis

Prediction of the enhanced absorption of ethene and but-1-ene in the reacting polymer grain by successively replacing nitrogen by n-pentane

Experiments for enhanced activity in polyethylene manufacture

Solubility curves for the absorption of ethene and but-1-ene in the reacting polymer grain can be seen by clicking on the plots on the right. The Borstar process is shown below.

Borstar polyethylene process

Reference

A. J. Haslam, Ø. Moen, C. S. Adjiman, A. Galindo, and G. Jackson, Design of polyolefin reactor mixtures, Part II, Chapter 5 of Computer-Aided Chemical Engineering 22: Multiscale Modelling of Polymer Properties, Laso, M., and Perpète, E. A., Editors (ISBN 0-444-52187-9, Elsevier B. V, Amsterdam) 301-332 (2006).

Aqueous polymers

Study undertaken in conjunction with ICI / Akzo Nobel

SAFT representation of H2 and PEG molecules

Example: Closed-loops cloud curves of liquid-liquid immiscibility in systems of aqueous polymers (courtesy of ICI / Akzo Nobel)

The temperature-composition re-entrant regions of liquid-liquid equilibrium curves for the H2O – polyethylene glycol (PEG ) system are shown below:

Note the wide range of parameter space (pressure, temperature, and composition). The SAFT parameters determined for PEG are fully transferable for different molecular weights

G. N. I. Clark, A. Galindo, G. Jackson, S. Rogers, and A. N. Burgess, Modelling and understanding closed-loop liquid-liquid immiscibility in aqueous solutions of poly(ethylene glycol) using the SAFT-VR approach with transferable parameters, Macromolecules, 41, 6582-6595 (2008)