Polystyrene devolatilization, two solvents (Sanchez-Lacombe)

A solution-polymerized polystyrene (100 kg/mol) carried in toluene and benzene, flashed at 480 K and 0.2 atm to strip the solvent — the multi-solvent case the Flory-Huggins package cannot take (one polymer, one solvent) and the reason the Sanchez-Lacombe lattice-fluid equation of state is in the tree. Characteristic parameters are the published ones: polystyrene T* 735 K, P* 357 MPa, rho* 1105 kg/m3; toluene 543 K, 402 MPa, 966 kg/m3; benzene 523 K, 444 MPa, 994 kg/m3 (Sanchez & Lacombe, J. Phys. Chem. 80 (1976) 2352 and Macromolecules 11 (1978) 1145), with the segment number r from M P*/(R T* rho*). What it computes: 94% of the feed moles leave overhead as solvent vapour and the melt retains 0.16 wt% residual solvent — read it on mass, not moles, since a 100 kg/mol chain is one mole against 0.09 kg/mol solvents. No binary k_ij (none is published for this pair); a single equilibrium stage, no diffusion-limited devolatilization kinetics.