What is phthalic anhydride?
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Phthalic anhydride (PA) is a toxic, colorless solid that dissolves in alcohol and carbon disulfide. Phthalic anhydride is an important chemical. It is a versatile intermediate in organic chemistry and is a toxic crystalline compound.
Phthalic anhydride is also used in the manufacture of phthaleins, dyes and resins, emollients and insecticides.
Dust from this substance is irritating and allergenic for the respiratory system. The resulting dust is also dangerous to the eyes. PA reacts with water. Its vapor, especially hot water, reacts quickly to produce and eliminate phthalic acid. Therefore, they should be kept away from them.
PA is currently produced by the oxidation of naphthalene or ortho xylene in the gaseous phase in air flow with vanadium pentoxide and titanium dioxide. This reaction is exothermic and maleic anhydride is also produced as a by-product. By heating phthalic anhydride, acid is also obtained.
Application of “phthalic anhydride”:
The primary use of PA is as a chemical mediator in the production of softeners from polyvinyl chloride. One of the applications of phthalic anhydride is in the production of polyester resins and other minor applications in the production of alkyd resins.
It is also used in paints and varnishes. Insect repellents and polyester urethane polyethylenes are other uses of PA.
One of the major uses of phthalic anhydride is in unsaturated polyester resins. They are usually mixed with glass fibers to produce fiberglass-reinforced plastics.
This material is used in the production of key resins based on solvent coatings for architectural applications, machinery, furniture and equipment. Other uses include phthalic anhydride in the production of detergents, herbicides and insecticides.
Phthalic anhydride is used in the synthesis of plasticizers, alkyd resins and polyunsaturated resins. Derivatives of this substance are phthalate esters, which are the main agents of softeners such as DIDP, DOP, BBP and DINP.
These compounds are the main emollients for polyvinyl chloride resins. It is mostly used in the production of plastic ropes, garden hoses and home appliances.
Production process of phthalic anhydride (PA)
Phthalic anhydride was first produced by the oxidation of naphthalene in concentrated sulfuric acid in the presence of mercury sulfate. This pathway was later replaced by the presence of vanadium oxide catalyst with naphthalene catalytic vapor phase oxidation.
Today, naphthalene raw materials have generally been replaced by orthoxylene. Naphthalene currently supplies only 16% of the raw materials needed. In the United States, all production is currently done through orthoxylene, and only coopers have the ability to change primary sources. In Europe, more manufacturers are able to use naphthalene.
In the orthoxylene-based process, a mixture of air and orthoxylene with a weight ratio of 20: 1 is transferred to a reactor containing vanadium pentoxide with a titanium dioxide-antimony trioxide catalyst. Alternative catalysts include molybdenum trioxide and calcium oxide or manganese oxides. The reaction is performed at a temperature of 375-425 ° C and a pressure below 1 bar.
The effluent gases are cooled and recovered by re-sublimation before entering the switch condensers where the pa accumulates as a solid on the walls. Purification involves vacuum distillation and the product is stored in melt or in a bag as a shell.
Process technology has changed a bit, although the catalysts last three years longer and their efficiency has improved. A development in this area has been the reduction of the weight ratio of air to orthoxylene to 9.5: 1, which reduces capital costs and energy savings.
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