A new catalytic dehydration strategy by coupling chloride hydrate dehydration with water–gas shift reaction

Abstract

Thermal dehydration process is an indispensable unit operation involving most of the fields in industry. Driven by the imperious demands in energy consumption reduction and quality improvement, we developed a coupling catalytic dehydration strategy, in which the water in the chloride hydrate was directly used as the reactant to participate in water–gas shift reaction. The autocatalytic process is depended on the chemical reactivity of water interacted with the surrounding atoms in certain degree. The thermodynamic minimum temperatures of dehydration could be reduced significantly by coupling WGS reaction compared to the direct dehydration. With the guidance of thermodynamic calculation, an extremely challenging process of bischofite dehydration was performed experimentally. Study demonstrates that the residual crystallized water number was reduced to 0.64 by coupling WGS reaction at 433 K, while there is still 1.54 via the direct dehydration under the N2 atmosphere. Meanwhile, the amount of by-product MgOHCl is maintained at quite low level, which well solves the seesaw relationship between dehydration and hydrolysis side reaction in traditional process. Subsequently, the autocatalytic mechanism was revealed that CO reacted with the surficial OH group ligated with magnesium to product CO2 and H2, in which the formate species serve as active intermediate species. Furthermore, the universality of such novel strategy was revealed by coupling CaCl2·2H2O dehydration with WGS reaction.