A method for producing conjugated diolefins, for example, 1,3-butadiene and isoprene, corresponding to monoolefins having four or more carbon atoms, such as n-butene and isopentene, by the catalytic oxidative dehydrogenation reactions of these monoolefins in contact with molecular oxygen is well known. A large number of catalysts used in the above oxidative dehydrogenation reactions are proposed.
The important reactions in the chemical industry are heterogeneous reactions involving two phases, such as gas-solid. For example, ammonia synthesis, ethylene oxide synthesis, and the catalytic cracking of petroleum are known as heterogeneous reactions industrially using oxide catalysts.
Reaction methods in which oxide catalysts are used include a fixed bed, a fluidized bed, and a moving bed. Among these, the fixed bed reaction method is often industrially used, making the most of the advantage of being able to increase reaction yield since the gas flow state is similar to an extrusion flow. However, the fixed bed reaction method has low heat transfer properties, and can be said to be unsuitable for exothermic reactions and endothermic reactions, which require heat removal and heating. Particularly, when the fixed bed reaction method is applied to an intense exothermic reaction, such as an oxidation reaction, the temperature increases suddenly to make control difficult, and the reaction may get out of control. A further problem is that the catalyst is damaged by such a sudden temperature increase, and deteriorates early. For example, an oxidative dehydrogenation reaction in which 1,3-butadiene is synthesized from butene is an exothermic reaction with about 30 kcal/mol.
The fluidized bed reaction method is characterized in that catalyst particles flow intensely in a reactor. Because of such a characteristic, an advantage is that (1) during a reaction when the heat transfer properties are high and the reaction involving large heat generation or heat absorption, the temperature in the reactor can be kept substantially uniform, and excessive progress of the reaction can be suppressed. A further advantage is that (2) local accumulation of energy is suppressed, and thus, a raw material gas within the explosion range can be reacted, and the raw material concentration can be increased to improve productivity. Therefore, the fluidized bed reaction method is a reaction method suitable for the oxidative dehydrogenation reactions of hydrocarbons involving intense heat generation.
Patent Literature 1 describes applying the fluidized bed reaction method to the production of a conjugated diolefin. In addition, Patent Literature 2 describes a method for producing butadiene with the amount of carbon contained in a catalyst controlled in a specific range.
In addition, when conjugated diolefins, for example, 1,3-butadiene and isoprene, corresponding to monoolefins having four or more carbon atoms are produced by the catalytic oxidative dehydrogenation reactions of these monoolefins and molecular oxygen, organic matter adheres to the catalyst by the progress of the operation, and the amount of carbon on the catalyst increases. If this amount of carbon increases too much, the crushing of the catalyst, the deterioration of flowability, a decrease in the selectivity of the conjugated diolefins, and the like are caused, and it is difficult to stably produce the conjugated diolefins from the corresponding monoolefins. Therefore, it is necessary to provide a catalyst regeneration step in order to remove carbon adhering to the catalyst. Patent Literature 3 describes a method for regenerating a catalyst that has been used in such production of butadiene.