Maleic Anhydride CAS 108-31-6

Introduction to Maleic Anhydride

Maleic Anhydride is a versatile organic building block characterized by its highly reactive five-membered ring containing both an alkene double bond and an acid anhydride group. The global chemical industry consumes millions of tons annually, primarily as the backbone monomer for unsaturated polyester resins (UPR) used in fiberglass-reinforced plastics, artificial marble, and marine applications.

The primary processing advantage is its dual-reactivity: the anhydride ring opens readily for esterification, while the double bond enables free-radical copolymerization with styrene. The critical handling risk is its extreme hygroscopicity and corrosivity. Upon contact with ambient moisture, MA rapidly hydrolyzes into maleic acid, generating heat and causing severe caking. Furthermore, the hydrolyzed acid aggressively corrodes carbon steel equipment. Store strictly in moisture-proof, sealed packaging in a cool, dry warehouse.

Key Features of Maleic Anhydride

• Dual-functional reactivity. The acid anhydride group enables rapid esterification with polyols, while the alkene bond allows crosslinking with vinyl monomers like styrene during UPR curing.
• High thermal stability for melt processing. Can be safely melted and pumped at 60–70 °C (140–158 °F) for continuous reactor dosing without thermal degradation, provided the system is kept completely dry.
• Superior gloss and hardness in coatings. When incorporated into alkyd resins, it accelerates drying times and enhances the hardness, gloss, and chemical resistance of industrial paints and varnishes.
• Essential intermediate for advanced chemicals. Serves as the precursor for 1,4-butanediol (BDO), tetrahydrofuran (THF), and polyisobutylene succinic anhydride (PIBSA) ashless dispersants in engine oils.

Maleic Anhydride Chemical & Physical Properties

Applications of Maleic Anhydride

Unsaturated Polyester Resins (UPR): Accounts for over 50% of global consumption. Copolymerized with propylene glycol and styrene to produce FRP (fiberglass-reinforced plastics) for automotive parts, wind turbine blades, sanitary ware, and artificial stone countertops.

Alkyd Resins and Industrial Coatings: Reacted with glycerol and fatty acids to produce air-drying alkyd resins. The rigid maleate structure imparts fast drying, high gloss, and excellent adhesion to architectural paints and industrial primers.

Lubricant and Fuel Additives: Reacted via the “ene” reaction with high-molecular-weight polyisobutylene (PIB) to form PIBSA, which is further aminated to create ashless dispersants that keep soot and sludge suspended in modern engine oils.

Agricultural and Specialty Chemicals: Used to synthesize maleic hydrazide (a plant growth regulator) and as a modifier for rosin in paper sizing and adhesive tackifiers.

Storage & Safety Precautions for Maleic Anhydride

• Storage: Keep tightly sealed in original PE-lined bags in a cool, dry, and well-ventilated warehouse below 30 °C (86 °F). Protect strictly from moisture and water sources. Exposure to humidity causes hydrolysis into maleic acid, leading to irreversible caking and the formation of a highly corrosive environment that will degrade standard packaging and carbon steel storage bins.
• Safety: Classified as Corrosive (Class 8). Causes severe skin burns, serious eye damage, and respiratory tract irritation. Dust or vapors are lachrymatory. Mandatory PPE includes chemical-resistant gloves, a full face shield, and an N95/organic vapor respirator during manual bag slitting and reactor charging.
• Transport: Classified as Dangerous Goods. UN Number: 2215, Class 8 (Corrosive), Packing Group III. Ship in standard dry containers, but avoid prolonged exposure to extreme heat (above 50 °C / 122 °F) to prevent melting and resolidification into solid blocks inside the bags.
• QC note: Verify purity (≥ 99.5%) and melting point (52.8 °C / 127 °F) upon receipt. Inspect bags for signs of moisture ingress; if the flakes have turned into a sticky, crumbly mass with a sharp acidic odor, it indicates severe hydrolysis into maleic acid—reject the lot for UPR applications.

Maleic Anhydride FAQ

Q: How does Maleic Anhydride differ from Maleic Acid?

A: Maleic Anhydride is the water-free cyclic form, while Maleic Acid is the hydrolyzed diacid form. MA is the required feedstock for UPR and esterification reactions because it does not introduce water into the system, which would otherwise inhibit polycondensation and cause resin cloudiness.

Q: The flakes arrived fused into a solid block inside the bag. Is it ruined?

A: MA melts at 52.8 °C (127 °F). If container temperatures exceeded this during summer ocean transit, the flakes may have melted and resolidified into a solid mass. Chemically, it is still usable if carefully melted down in a reactor. However, if the block is sticky, crumbly, or shows signs of moisture ingress, it has hydrolyzed and must be rejected.

Q: Why is the Iron (Fe) content specification (≤ 1 ppm) so critical?

A: Trace iron ions catalyze the premature crosslinking (gelation) of unsaturated polyester resins during storage and cause severe yellowing/discoloration in final cured plastics and light-colored alkyd coatings. High-purity MA with strict iron control is mandatory for premium resin grades.