METHOD FOR MEASURING PROPYLENE OXIDE SELECTIVITY

PROBLEM TO BE SOLVED: To provide a method for measuring a precise propylene oxide selectivity and a method for optimizing the propylene oxide selectivity to maintain an optimum reaction condition.SOLUTION: In the production method of propylene oxide in which a reactant gas flow containing propylene and oxygen is supplied to a reaction tower containing a catalyst and a generated gas flow containing propylene oxide is discharged from the reaction tower, the method for measuring propylene oxide selectivity includes the steps of: (I) determining at least two concentrations of propylene, oxygen, propylene oxide, carbon and water in the reactant gas by measuring absorption rates of infrared ray or near infrared ray in the reactant gas flow or the sample of the reactant gas flow and analyzing a composition of the reactant gas flow ; (II) determining the concentration of the compound from the measurement of absorption rates of infrared ray or near infrared ray; and (III) calculating the propylene oxide selectivity from the concentrations obtained in the step (I) and the step (II).