Phthalic anhydride cas, an organic chemistry compound, is mainly used for the production of PVC plasticizers, unsaturated polyester resins, alkyd resins, as well as dyes, coatings, pesticides, pharmaceuticals, instrument additives, and saccharin. It is an important organic chemical raw material. In PVC production, plasticizers account for more than 50% of the total usage, and the rapid development of the plastic industry has led to the increasing demand for phthalic anhydride cas and the rapid development of its production.
The earliest production of phthalic anhydride cas dates back to 1872, when a German company used naphthalene as raw material and chromium oxide for oxidation to produce phthalic anhydride cas. Later, it was changed to fuming sulfuric acid for oxidation, but the yield was very low, only 15%. Since 1917, the world has started to use vanadium oxide as a catalyst to produce phthalic anhydride cas from naphthalene, and the production of phthalic anhydride cas has gradually become industrialized and scaled, with two relatively mature processes of naphthalene method and ortho method developed successively.
The process flow is that purified air is compressed and preheated before entering the bottom of the fluidized bed reactor, and liquid naphthalene is sprayed in. The naphthalene is vaporized and mixed with air, and undergoes exothermic reactions through the fluidized catalyst layer to generate phthalic anhydride cas. The reactor is equipped with tube-type coolers, and water is used as a heat medium to remove the reaction heat. The reaction gas is separated by a three-stage cyclone separator, and the catalyst carried by the gas is separated and enters the liquid condenser, where 40%-60% of crude phthalic anhydride cas is condensed in liquid form. The gas then enters the switching condenser for further separation of crude phthalic anhydride cas. After pre-decomposition, the crude phthalic anhydride cas is subjected to rectification to obtain phthalic anhydride cas products. The tail gas is discharged after being washed, and the washing solution is diluted with water and discharged or sent to a catalytic incinerator.
In production, the process has been continuously improved. For example, the feeding method has been developed to atomize naphthalene, and the gas-solid separation uses highly efficient wear-resistant cyclone separators, etc. These improvements have not only greatly increased the production yield and quality of the products, but also greatly reduced the energy consumption of the naphthalene method. Due to the rapid development of the naphthalene fluidized bed method, most factories were still producing organic chemistry compounds using the naphthalene method in 1988, with naphthalene method accounting for 90% of the total production. With the development of the petroleum industry and the development of ortho method technology, the disadvantages of the naphthalene method became apparent: the supply of raw material tar naphthalene became increasingly tight and prices continued to rise, and the production capacity of a single reactor was relatively low, which inevitably led to high energy consumption of the naphthalene method. As naphthalene method production has not made great progress in reducing energy consumption, the impact of large quantities of low-priced ortho method phthalic anhydride cas has made the profit margin of the naphthalene method smaller and smaller. In order to improve their own economic benefits, many naphthalene method manufacturers began to carry out process improvements.
The specific process flow is that after filtration and purification, compressed and preheated air is mixed with vaporized ortho-xylene, and then enters the fixed bed reactor for exothermic reaction. The circulating molten salt outside the reaction tube removes the reaction heat and maintains the reaction temperature, and the reaction heat taken out by the molten salt is used to produce high-pressure steam.
The gas coming out of the reactor enters the switching condenser through the pre-cooler and condenses phthalic anhydride cas organic chemistry compounds on the fins. Then, hot oil is regularly introduced to melt the phthalic anhydride cas, which is then subjected to heat treatment and sent to the continuous rectification system to remove low-boiling-point and high-boiling-point impurities to obtain phthalic anhydride cas products. The tail gas from the switching condenser is discharged to the atmosphere after being washed in two stages. The circulating liquid containing organic acid with a concentration of 30% is sent to the phthalic anhydride cas recycling device or incinerator, or it can be recycled to produce maleic acid.
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