Entrainer-enhanced reactive distillation

This paper presents a novel approach in reactive distillation (RD) processes, the use of a Mass Separation Agent (entrainer). This technique enables to overcome limitations due to distillation boundaries, and increase the degrees of freedom in design. As application the catalytic esterification of fatty acids with light alcohols C2–C4 is studied. In a standard RD device a supplementary separation step is needed for recovery and recycle of the alcohol that distillates in top with the water product. The problem can be solved elegantly by making use of an internally recycled entrainer. This should fulfil the following conditions: form minimum-boiler ternary heterogeneous azeotrope, allow quantitative water removal by L–L separation or steam stripping, and give acceptable impurity in the final product. Moreover, the entrainer enhances the reaction rate, by higher reactant concentration in the reaction space, and offers better protection of catalyst against deactivation. The paper discusses in more detail the conceptual design of a process for the esterification of lauric acid with 1-propanol and sulphated zirconia as catalyst. The following aspects are investigated: chemical and phase equilibrium, entrainer selection, kinetic design and optimisation. Minimum and maximum entrainer ratios have been identified. The use of entrainer leads to 50% reduction in the amount of catalyst.