(109b) Reactive Distillation Using External Side Reactors for Synthesis of Bio-Renewable Organic Acid Esters

Organic acid esters, produced from bio-based organic acids and alcohols, are truly bio-renewable, “green” chemicals that are promising replacements for halogenated and other petroleum-based solvents, lubricants, and plasticizers.  With current uncertainty regarding the future of ethanol and other alcohols as biofuels, and with the availability of organic acids via fermentation, there exists strong motivation to develop esters as viable commodity bio-chemicals to support and expand the existing bio-renewable infrastructure. 

Esters are advantageously produced using reactive distillation, where simultaneous reaction and separation take place in the same process unit.  The hardware design of standard reactive distillation columns exhibits challenges for slow chemical reactions where the reaction requirements of high liquid holdup and high catalyst mass must be present inside the reactive distillation column.  A similar situation arises when desirable reaction temperature inside the reactive distillation column is not in consonance with the distillation temperature or when side reactions occur.

In order to make the synthesis of esters economically competitive with their petroleum-based counterparts, in this study we have evaluated an alternative to the classical reactive distillation concept by using a conventional distillation column integrated with external side reactors. 

In this SBIR Phase I Project, we have developed and demonstrated advanced reactive distillation concepts of heat-integration with side reactors for esterification of citric acid with ethyl alcohol to produce tri-ethyl citrate (TEC), which is a good candidate for replacing phthalate-based plasticizers.  Phthalates have potential carcinogeneity and overall health concerns to the extent that they have been banned in Europe from use in children’s toys and human contact applications. The potential of TEC is currently limited by the lack of large-scale, energy efficient and economic production.

AspenPlus process analysis is performed based on the available kinetic data for esterification of citric acid with ethanol for an integration of pre-reactor as well as side reactors with fractionation column.  Heat integration is examined for energy efficiency and maintaining temperatures in side reactors for maximizing the catalyst utilization.  The concept of integrated reaction and distillation is validated by experiments using the reactive distillation facility at Michigan State University with a pre-reactor and one side reactor coupled to a distillation column.