(21b) Epoxidation of Soybean Oil at Maximum Heat Removal and Single Addition of All Reactants

Epoxidized soybean oil is largely used especially in the PVC (polyvinyl chloride) industry as a co-stabilizer and a secondary plasticizer, with a worldwide production of more than 2,000 kt/yr. The application of this material as a plasticizer and building block for other bio-based chemicals has been growing significantly in the past years, mainly due to better quality of the epoxidized products and improved competitiveness (cost) over petroleum based traditional materials.

The epoxidation of vegetable oils is a well know reaction, with patent applications as early as 1940s, but current industrial processes still rely on technologies that are limited primarily by the heat removal capacity of the equipment, since the reaction is highly exothermic. The most commonly used industrial process employs lengthy batch reactions (more than 8 hours total time), with temperature controlled by the gradual addition of hydrogen peroxide, resulting in significantly high investments to obtain products with specified quality, in addition to several safety concerns.  The reaction occurs in two liquid phases, with mass transfer between phases. The reaction studies have always simplified the internal reactions and mass transfers, determining kinetics and heat generation of the combined reaction.  The literature presented very little data to clarify potential optimizations and debottlenecking of the processes, in order to maximize conversion, reduce reaction times, and improve the operation safety.

Literature has also covered the use of various catalysts and complexing agents, seeking better conversion results. The industry, however has adopted the simplified process that employs no catalysts, with formic acid as the preferred choice, due to its reactivity and cost effectiveness, considering optimized quantities and separations processes.  The use of the most common catalysts and solvents also results in undesired oxirane cleavage. 

The reaction is highly exothermic and temperature control is fundamental to prevent reaction runaway.  In industrial use, a batch process is employed, where performic acid is generated “in situ” by the addition of hydrogen peroxide to vigorously mixed oil and formic acid.  Hydrogen peroxide is added gradually as the key means to maintain proper temperature control.

In this work, the reaction was carried out under a highly effective heat removal system and the way of feeding the reactants were changed to analyze the trade-off between reaction rate and heat transfer to keep the temperature under control. Experiments were performed with different numbers of shot additions of reactants to assess the temperature increase and the heat transfer capacity of the reactor. The results obtained provided a better understanding of the kinetic and transport phenomena variables of the epoxidation reaction under maximum heat removal conditions.  A preliminary model of the reaction allows an easier comparison of experimental data with simulated results, providing the bases for a more accurate model, which could enable the design of a continuous, safer and more efficient reaction system.