Method for regenerating catalyst for butadiene production

A method for regenerating a catalyst for butadiene production, conducted after the catalyst for butadiene production is used in oxidative dehydrogenation of butenes, for removing a coke-like substance in a reactor which is charged with the catalyst,

• the catalyst having a composition represented by following Formula 1 before being used in the oxidative dehydrogenation,
• Mo12BiaFebCocNidXe,YfZgOh (Formula 1)
• wherein X represents at least one alkali metal element selected from the group consisting of lithium, sodium, potassium, rubidium, and cesium, Y represents at least one alkaline earth metal element selected from the group consisting of magnesium, calcium, strontium, and barium, Z represents at least one element selected from the group consisting of lanthanum, cerium, praseodymium, neodymium, samarium, europium, antimony, tungsten, lead, zinc, cerium, and thallium, a, b, c, d, e, f, and g represent atomic ratios of the elements relative to Mo12, satisfying ranges of 0.2≤a≤2.0, 0.6<b<3.4, 5.0<c<8.0, 0<d<3.0, 0<e<0.5, 0≤f≤4.0, and 0≤g≤2.0, and h is a number that satisfies oxidation states of the other elements,
• wherein the method comprises:
• subjecting the reactor to gas treatment using first a gas which contains oxygen at a concentration over 0 vol % to not greater than 21 vol %;
• and
• subsequently, supplying, to the reactor, a second gas which contains water vapor at a concentration over 0 vol % to not greater than 42 vol % and oxygen at a concentration over 0 vol % to not greater than 21 vol %,
• wherein a temperature of a heat medium circulating in the reactor is in a range from not less than 200° C. to below 400° C., and the temperature of the heat medium circulating in the reactor is fixed from an end of the gas treatment until an end of the subsequent gas supplying, and
• wherein a water vapor content in the first gas and a water vapor content in the second gas are different.