A Novel Cost-Efficient Tributyl Citrate Production Process

Abstract

Phthalates are the most widely used plasticizers in the polymers industry; however, their toxicity and environmental impacts have led to their ban in various applications. This has driven the search for more sustainable alternatives, including biobased citrate esters, especially tributyl citrate (TBC) and its acetylated form. TBC is typically produced by refined citric acid (CA) esterification with 1-butanol (BuOH). However, the high energy and materials-intensive downstream purification of fermentation-derived CA involves high production costs, thus limiting the widespread adoption of TBC as a plasticizer. This work presents an innovative approach for TBC production using calcium citrate as feedstock instead of pure CA. The process involves a simultaneous acidification-esterification stage and further hydration of calcium sulfate, thus reducing costs by avoiding multiple CA refining steps. The approach proceeds via a solid-solid-liquid reaction of calcium citrate with sulfuric acid in butanol, releasing CA, which is simultaneously esterified to form TBC. The resultant calcium sulfate aids in water removal to enhance esterification conversion. Based upon experimentally validated models and rigorous simulations, the proposed approach was evaluated, and it exhibited significant reductions in processing times and operating costs, with savings of at least 46% in utilities compared to traditional TBC production. The novel approach was found suitable and promising for industrial deployment.