Production of diacylglycerols by esterification of oleic acid with glycerol catalyzed by diatomite loaded SO₄²⁻/TiO₂

A new and efficient technique is described for the production of diacylglycerols (DAGs) by the esterification of oleic acid with glycerol catalyzed by diatomite-loaded SO₄²⁻/TiO₂. DAGs show some potential health benefits compared to triacylglycerols, and also can be used to produce the novel industrial plasticizer epoxy fatty acid methyl ester in material science. Diatomite-loaded SO₄²⁻/TiO₂ catalyst was prepared and characterized, and the selected conditions for the synthesis of DAGs were determined to be: reaction time = 6.0 h, temperature = 210 °C, catalyst loading = 0.1% of the oleic acid weight, and mass ratio of oleic acid to glycerol = 2:1. Under these conditions, DAGs yield reached 59.6% with a purity of 69.6% after a one-stage molecular distillation. Diatomite-loaded SO₄²⁻/TiO₂ as a solid catalyst could be recycled and reused with high catalytic efficiency. Under the same conditions, diatomite-loaded SO₄²⁻/TiO₂ showed a better catalytic performance than the commercial solid acid SO₄²⁻/ZrO₂-Al₂O₃. Based on this, a two-step reaction method for the production of DAGs was performed and provided a yield similar to the one-step method (58.3% vs. 59.6%), but with a shorter reaction time (4 h vs. 6 h). It is concluded that a two-step reaction method could be a better alternative to the one-step production of DAGs in the presence of diatomite-loaded SO₄²⁻/TiO₂.