Design and Control of the Acetone Process via Dehydrogenation of 2-Propanol

Abstract

Acetone is produced via several alternative processes, one of which is the dehydrogenation of 2-propanol (IPA). The endothermic gas-phase reaction converts IPA to acetone and hydrogen. The process consists of a vaporizer, heated tubular reactor, flash tank, absorber, and two distillation columns. The liquid fresh feed is a mixture of IPA and water. It is combined with a small IPA/water recycle stream, vaporized, and fed into the vapor-phase reactor, which is heated by high-temperature molten salt. Reactor effluent is cooled and fed to a flash tank. The gas from the tank contains most of the hydrogen but also some acetone. This gas is fed to an absorber in which a water stream is used to recover acetone. The liquids streams from the base of the absorber and the flash tank are fed to the first distillation column, which produces high-purity acetone out the top. There is also a vapor vent stream leaving the reflux drum of this column to remove the small amount of hydrogen dissolved in the feed. The second distillation column produces a high-purity water bottoms and a distillate with a composition near the IPA/water azeotrope, which is recycled back to the vaporizer. There are a number of interacting design optimization variables in this process, which illustrate some interesting design trade-offs. Removing the hydrogen without losing too much product acetone is the main challenge. Losses can occur in both the absorber off-gas and the column vent. Raising absorber pressure decreases off-gas losses but increases vent losses. Raising absorber pressure has several other effects. It raises the vaporizer pressure, which raises the required temperature and cost of the vaporizer heat source. It adversely affects kinetics because the reaction is nonequimolar and conversion decreases with increasing pressure. A higher reactor temperature is required to achieve the desired conversion. The purpose of this paper is to develop the economically optimum design considering capital costs, energy costs, and raw material costs and then to develop a plantwide control structure capable of effectively handling large disturbances in production rate.