Eco-efficient separation of mono- and di-chloroacetic acid by thermally coupled extractive distillation

Owing to its high reactivity, monochloroacetic acid (MCA) is an essential intermediate that is used in manufacturing a wide variety of chemicals. The industrial process for MCA production is highly energy and capital intensive, requiring additional costly purification steps by hydrogenation and crystallisation to remove the dichloroacetic acid (DCA) impurities. That is required in practice because conventional distillation is unfeasible for the separation of such close boiling components mixtures.
This paper proposes an innovative eco-efficient process for MCA-DCA separation, based on extractive distillation in fully thermally coupled system – a dividing-wall column (DWC) or equivalent side-rectifier configuration – using a new effective solvent (diethylene glycol dipentylether, DGDP). The design was optimized by performing sensitivity analysis and varying key operating and design parameters, aiming to reduce the costs and carbon footprint. The study proves by rigorous simulations that separating MCADCA by an extractive DWC (or thermally coupled) is a feasible more efficient, controllable, economic and sustainable alternative. The results show that over 28% savings in operating cost, 28% reduction in carbon footprint (with energy use of 1.2 MJ/kg MCA), 19% less capital cost and 24.5% lower total annual cost are possible as compared to a conventional extractive distillation – solvent recovery system.