Reaction Conditions Influencing the Formation of Propylene Oxide and Aldehydes when Propylene is Oxidized under Pressure

Abstract

Oxidation of propylene with small amount of oxygen was carried out under pressure in a pyrex tube as reactor by varying the conditions of reaction. The oxidation products were mainly acetaldehyde, propylene oxide, and acrolein along with various gaseous products as reported in the case of stainless steel U tube. The optimum reaction conditions for the maximum yields of epoxide and C2-C3 aldehydes were influenced by temperature, pressure, space velocity, and oxygen content in the feed gas. Optimum pressure existed for reaction when other conditions were kept constant. The oxidation reaction was incomplete when the pressure was below the optimum, and the yields of epoxide and C2-C3 aldehydes decreased at pressures above the optimum. The carbon distribution of propylene to propylene oxide, acetaldehyde, and acrolein decreased with increase in pressure, and those of carbon monoxide, carbon dioxide, methane and ethylene were almost constant at pressures above the optimum, while those of liquid product and C4 hydrocarbons increased with increase in pressure. Increase in oxygen concentration resulted in a decrease of optimum pressure, and the contents of epoxide and C2-C3 aldehydes in the product gas at the optimum pressure increased with increase in oxygen concentration up to 24%. Carbon distribution of propylene to epoxide and C2-C3 aldehydes, however, decreased with higher oxygen concentration but those of combustion and decomposition products increased. When high purity propylene was used, the yields of epoxide and C2-C3 aldehydes increased but the carbon distribution of propylene to various products was little influenced because of increase in the quantity of propylene reacting. When residence time was increased at constant temperature and pressure, the yields of epoxide and aldehydes suddenly increased after a period of time, which is considered to be induction period, and began decreasing slowly. Liquid product was inferred to be C5 aldehyde. The mechanism of propylene autoxidation was discussed also.