Theoretical Study of the Esterification of Carboxylic Acids with Glycerol in the Presence of Organic Calcium Salts

Esterification of carboxylic acids with glycerol is an important route to glycerides with potential applications in bio-based fuels and fuel additives, lubricants, emulsifiers, and specialty chemicals. Because glycerol contains three hydroxyl groups, esterification generally proceeds through a sequential reaction network in which monoacylglycerols can form diacylglycerols and, subsequently, triacylglycerols. Product distribution depends on catalyst properties and operating variables, including temperature, reactant ratio, water management, phase behaviour, and reaction time. This review examines the available evidence concerning organic calcium catalysts, with particular emphasis on calcium glycerate and calcium carboxylates. Published studies identify calcium glycerate as a promising catalyst for the esterification of oleic acid with glycerol and report acid conversion of approximately 58–86% after 10 hours under the conditions investigated. The reported induction period and differences in performance relative to calcium oleate suggest that catalyst effects, interfacial phenomena, and product-related changes in the reaction medium influence the observed kinetics. However, the evidence should be interpreted cautiously: structural studies of calcium glycerate and related calcium–glycerol compounds do not, by themselves, establish the identity of the active phase under esterification conditions. The literature on organic calcium salts is also considerably less developed than that on solid acids, zeolites, and enzyme catalysts, particularly with respect to catalyst reuse, deactivation, and scale-up. This review summarises the reaction network, discusses plausible catalytic and transport effects, compares calcium-containing systems with alternative catalytic platforms, and identifies the experiments needed to establish activity, selectivity, and process viability on a comparable basis.