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Methods for Preparation of Phthalic Anhydride


1. Introduction to phthalic anhydride


Phthalic anhydride, abbreviated as 1,3-isobenzofurandione, is a white solid, an important raw material in the chemical industry, especially used in the manufacture of plasticizers.


2. Preparation method of phthalic anhydride


The production of phthalic anhydride has two process routes: o-benzene oxidation and naphthalene oxidation.


Phthalic anhydride ortho-benzene oxidation method: The industrial production method generally uses vanadium pentoxide as the main vanadium catalyst for the gas phase oxidation of o-xylene. A ring-shaped carrier is used to prepare the catalyst. This new type of catalyst can reduce the deep oxidation reaction caused by internal diffusion, thereby improving the yield, selectivity and catalyst load of phthalic anhydride. The reactor mostly adopts a tube fixed bed.


Phthalic anhydride naphthalene oxidation method: the naphthalene oxidation reaction occurs at the α position, and under mild conditions, naphthalene is oxidized to produce quinone. Under strong conditions, naphthalene is oxidized to produce phthalic anhydride. Side reactions generate naphthoquinone, maleic anhydride, etc. The catalyst used is also a vanadium-based catalyst. The process is similar to that of o-xylene oxidation.


There are two types of reactors for phthalic anhydride naphthalene oxidation: tubular fixed bed and fluidized bed. The reaction heat of the fluidized bed reactor is removed by the cooling pipe in the reactor. The particle size of the fluidized bed catalyst requires a suitable range, usually 40-300μm. The advantage of using a fluidized bed is that the reactor can be operated at a relatively uniform temperature and a higher raw material-air ratio, and the product is easier to capture.


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