Toluene removal from 1-butanol solvent (modified UNIFAC, Dortmund)

A recovered 1-butanol solvent contaminated with 5 mol% toluene, redistilled to send the toluene overhead: 24 stages, reflux 3, an 8% distillate. There is no fitted toluene/1-butanol binary, so this runs on modified UNIFAC (Dortmund) — the variant that cuts infinite-dilution error from 42% to 16% in this tree, and a dilute contaminant in a solvent is exactly the infinite-dilution regime. The toluene/butanol azeotrope at 68 mol% toluene caps the overhead: it comes out at 39% toluene rather than pure, with 2.1% left in the bottoms — 62% of the contaminant removed per pass. The two variants agree on the azeotrope (67.6% against original UNIFAC's 67.7%) and differ where the toluene is dilute: original UNIFAC removes 67% on the same column, so the model choice is worth five points of recovery here.