Abstract: This invention is related to a shell-and-tube type reactor provided with reaction tubes packed with a catalyst and adapted to circulate a heat medium to the fluid outside the tubes and is characterized by a method introducing a gas into the catalyst beds so as to retain the relative humidity of the catalyst in the range of more than 40% while elevating the temperature of the reactor thereby starting up the reactor. This method prevents the catalyst from degradation of activity due to absorption of moisture, exalts the service life of the catalyst, and permits stable production of methacrylic acid.

Abstract: The present invention has for its object to provide a production method of a pyromellitic anhydride which is not only conducive to an increased catalyst life and, hence, an enhanced operating rate of a plant (reduced downtime) and a reduction in catalyst cost but also conducive to reductions in byproducts and, hence, savings in the cost of after-treatments such as collection and purification. A production method of a pyromellitic anhydride comprising a step for catalytic gas-phase oxidation of a starting mixture gas consisting of a tetraalkylbenzene and/or a trialkylbenzaldehyde and a molecular oxygen-containing gas in a fixed-bed type reactor having a catalyst bed wherein the production method of a pyromellitic anhydride is carried out under the condition that the moisture content of said starting mixture gas to be introduced into the catalyst bed is not more than 2 volume %.

Abstract: This invention is related to a shell-and-tube type reactor provided with reaction tubes packed with a catalyst and adapted to circulate a heat medium to the fluid outside the tubes and is characterized by a method introducing a gas into the catalyst beds so as to retain the relative humidity of the catalyst in the range of more than 40% while elevating the temperature of the reactor thereby starting up the reactor. This method prevents the catalyst from degradation of activity due to absorption of moisture, exalts the service life of the catalyst, and permits stable production of methacrylic acid.

Abstract: The present invention has for its object to provide a production method of a pyromellitic anhydride which is not only conducive to an increased catalyst life and, hence, an enhanced operating rate of a plant (reduced downtime) and a reduction in catalyst cost but also conducive to reductions in byproducts and, hence, savings in the cost of after-treatments such as collection and purification.