Optimal design and operation of semi-batch reactive distillation for methyl lactate synthesis with fixed product demand

Abstract

Abstract Esterification of lactic acid is a well-known process producing a number of industrially important chemical products such as alky esters, alkyl t-butyl ethers. However, the synthesis of methyl lactate (ML) using batch or semi-batch reactive distillation (SBRD) was not widely considered in the past. Here, the design and operating parameters of SBRD process are optimised while maximising the profit under fixed product demand and strict purity specification. Methanol is fed continuously to improve the conversion of lactic acid. For a given product demand, the profitability is used as the performance measure which is maximized while a number of design (vapour load) and operating parameters (reflux ratio and feed rate) are optimized using model based techniques via gPROMS software. Sensitivity of the operating and utility costs as well as the raw materials prices on the design and operation are discussed. The reboiler is initially fed to the full capacity and an additional constraint is added into the optimisation problem to avoid overloading of still pot (reboiler) at any time of the operation due to continuous feeding of methanol. The control variables (reflux ratio, the methanol feed rate) are treated as a piecewise constant over batch time.