(382b) Process Intensification in the Synthesis of Tributyl Citrate: Pilot Scale Validation

Over the few last decades, bio based plasticizers have been their market share due to the generalized toxicity concern from phthalate esters and other traditional plasticizers. Tributyl citrate (TBC) may be synthesized from citric acid and n-butanol in presence of an acid catalyst. Current production process is highly energy intensive due to its semi-batch configuration and the excess of butanol used at the reaction stage which must be recovered downstream.

The present work evaluated the production of TBC via reactive distillation and other intensifies configurations to increase energy and mass efficiency and furthermore profitability. The thermodynamic model to describe the non-ideal behavior of the reactive system has been regressed from liquid-liquid, solid-liquid , and vapor-liquid experimental equilibria of binary and ternary mixtures. The kinetic model has been regressed from experiments with homogeneous and heterogeneous catalysts. The conceptual design has been carried out using reactive residue curve maps with the introduction of the substitution degree to visualize multicomponent mixtures on a 2D color-scale. Pilot experimental evaluation was carried out in a 7m tall 3” wide stainless steel reactive distillation column available in our laboratory with structured packing similar to KATAPAK SP-11 with Amberlyst 70 as catalyst in the reactive section and 1” nutter rings in the stripping and recovery sections. The experimental pressure was 74kPa, the atmospheric pressure in Bogota, Colombia. Variables of study during the pilot experimentation include: reflux ratio, reactive mixture feed, use of pure butanol in a side stream, use of azeotropic grade over dehydrated butanol, and the use of prereactor. Pilot plant data were reconciled to develop a robust model for process up-scaling. An industrial process was modelled and optimized for a production capacity of 1000Ton/yr with a natured inspired algorithm. Results from optimization indicate a citric acid conversion>99.9%, selectivity towards TBC >90%, energy savings of 27% and cost reduction of 13% over the conventional process.