The Properties and Uses of the Phthalic Anhydride

1. Introduction to the phthalic anhydride

The phthalic anhydride is also known as the phthalic acid anhydride; 1,2-benzenedicarboxylic acid an-hydride; 1,2-benzenedicarboxylic anhydride; 1,3-isobenzofurandione; 1,3-phthalandione, etc. Abbreviation: PA. Chinese name: 邻苯二甲酸酐，苯酐，邻苯二酸酐，酞酐. The molecular formula is C8H4O3 and the molecular weight is 148.12. The CAS number is 85-44-9. It is one of the types of compounds in organic chemistry.

2. The properties of phthalic anhydride

Physical and chemical properties: It is a white solid scaly crystalline powder or white needle-like crystals with a melting point of 130 to 131℃, relative density of 1.53, and boiling point of 284 to 295℃, which is easy to sublime. The flash point (closed cup) is 152°C. The auto-ignition temperature is 570°C. The explosive limit of the mixture in the air is 1.7% to 10.5%. The vapor pressure (20°C) is 0.2Pa. Phthalic anhydride is slightly soluble in water (6g/L), easily soluble in hot water and hydrolyzed to the phthalic acid and soluble in ethanol, benzene and pyridine.

According to the quality standard of phthalic anhydride (GB/T 15336-2006), the purity of premium and first-class phthalic anhydride is ≧99.5%, the free acid content is ≦0.2% and 0.3%, respectively, and the crystallization point is 130.5°C and 130.3°C, respectively. The purity of qualified products is ≧99.0%.

3. Characteristics and uses of phthalic anhydride

Phthalic acid anhydride is mainly used to produce plasticizers, unsaturated polyester resins, alkyd resins, saturated polyester polyols, and also used to produce anthraquinone and its derivatives (dyes), isatoic anhydride and phthalocyanine dyes (coatings, ink pigments), halogenated acid anhydrides (reactive flame retardants and flame retardant intermediates), polyetherimide resins, medicines, pesticides, saccharin and other products. Phthalic anhydride applications are very extensive.

In the polyurethane industry, phthalic anhydride is mainly used to synthesize aromatic polyester polyols. This type of polyester polyols can be used in rigid polyurethane foams, as well as in polyurethane adhesives and coatings. In addition, phthalate plasticizers are also used in polyurethane products in small amounts.