Patent benchmark: methyl lactate synthesis (CN104628563A)

Real patent replication, not an invented process: CN104628563A's acid-catalyzed lactate-ester route -- lactic acid esterified with excess methanol, then purified by vacuum distillation -- reproduced here as a continuous flowsheet. The patent's own worked methyl-lactate example reports 98.8% esterification conversion and 99.6% product purity at 120 degC/3h. This flowsheet's reactor conversion is set directly to the patent's reported 98.8% (not fitted); the vacuum column (0.2 atm, matching the patent's vacuum-distillation purification step) then splits the methanol and reaction water off the ester completely -- zero methyl lactate leaves overhead -- and delivers 97.8 mol% methyl lactate in the bottoms at 389.9 K.

The property method is the whole story here, exactly as it was on the sulfolane extractive column. Written on Peng-Robinson, this example did not converge at all: every pair in a methanol / water / lactic-acid / methyl-lactate mixture is hydrogen-bonding, which van der Waals mixing cannot represent, and the column returned a partial profile carrying 2.60 mol/s of methyl lactate out of a column fed 1.98 -- 32% more product than the reactor made, a 0.26 component-balance residual. (That wrong profile is where this example's previously-published 98.75% purity was read from; the number was retracted at the test level and is now corrected here.) A plain activity model cannot be used either, for a data reason rather than a physics one: neither lactic acid nor methyl lactate carries a regressed ideal-gas-Cp correlation, and the gamma-phi enthalpy path raises on that where a cubic quietly falls back to a corresponding-states estimate. PSRK is a cubic whose mixing is driven by UNIFAC, so it has both -- and it converges to a 2.7e-06 component-balance residual, with methyl lactate and lactic acid each leaving in exactly the amount the reactor made.

Honesty note: the 2.2 mol% of the product that is not methyl lactate is arithmetic, not an unconverged residual, and it splits cleanly in two. 1.19 points of it is unreacted lactic acid, and that part is structural -- at the patent's own 98.8% conversion 1.2% of the feed acid survives, and lactic acid boils above methyl lactate (505 K vs 418 K), so it leaves with the product in the bottoms. No lights-removal column rejects it at any stage count; the patent's 99.6% needs a second product column or an acid recycle, and this flowsheet has neither. The other 0.99 points is the deliberate light-cut margin: methanol plus reaction water is exactly 0.800 of the feed, and this column takes 0.798, leaving 1% of the light cut in the bottoms rather than specifying a perfect split no finite column can deliver. Raising the stage count does not move either number -- 10 and 12 stages were both measured and return the same 97.82%, because the ester/lights split is already complete at 8. See the Patent Benchmarks docs page for the full validation table and citation.