(101f) Control of an Exothermic Reaction under Cryogenic Conditions by Direct Liquid Nitrogen Injection to a Glass on Stainless Steel Vessel

Maintaining cryogenic temperatures during exothermic reactions (lithiations, alklyations, carboxylations) is important in preventing thermal decomposition of reactive intermediates. In the typical pilot plant setting, this can be challenging given that existing jacket services may be unable to achieve or sustain the temperatures required to remove the heat generated in exothermic reactions at cryogenic conditions. Subsequently, the poor heat transfer rate results in impractically long reaction times and inevitably, lower product yield and quality. As a solution to this problem, a direct liquid nitrogen delivery system was designed for a 500 gallon glass on stainless steel reactor rated to -100ºC, and utilized for a series of lithiation and carboxylation reactions under cryogenic conditions. Liquid nitrogen was injected directly to the reaction mass during the exothermic reactions in order to meet the cooling duty while maintaining batch temperatures in the range of -70 to -80°C. Critical design considerations for this project included: liquid nitrogen pressure and pressure drop, liquid nitrogen flowrate, heat transfer coefficient measurements, maximum charge rate of the reactant CO2, jacket recirculation pump contributions to heat loss, vent sizing, as well as the location of the liquid nitrogen introduction into the reaction mass. The performance and design of this system will be discussed as well as other options for running similar types of chemistry at pilot plant scale using modular proprietary units that allow for more routine use of direct liquid nitrogen injection.