Citraconic Anhydride Storage & Tank Compatibility

Storing Citraconic Anhydride? Start Here

Citraconic anhydride (CAS 616-02-4, · C₅H₄O₃ · also called 2-methylmaleic anhydride or methylmaleic anhydride) is a clear, colorless to faintly yellow liquid that solidifies just below room temperature. It is the cyclic anhydride of citraconic acid and a close relative of maleic anhydride, used as a reactive intermediate and a comonomer in resins, copolymers, and specialty derivatives. Because it is an anhydride, it is hungry for water: it hydrolyzes on contact with moisture to the corresponding acid and is corrosive to skin, eyes, and the respiratory tract.

For tank selection the verdict is clear: citraconic anhydride is not a polyethylene chemical. Like other reactive organic anhydrides it swells, softens, and permeates polyethylene and most thermoplastics, and its acidic hydrolysis product attacks the wrong materials over time. Bulk citraconic anhydride is stored dry in stainless steel or glass-lined steel under an inert blanket — not in a poly tank. This page summarizes the verified identity, hazards, and correct materials of construction.

Why Polyethylene Tanks Are Not Suitable for Citraconic Anhydride

Rotationally molded HDPE and crosslinked (XLPE) tanks are outstanding for water, brines, and many aqueous acids and bases. Citraconic anhydride is a different class of chemical. It is a reactive, polar organic anhydride that behaves as an aggressive organic medium toward polyolefins: in contact with polyethylene it is absorbed into the polymer, causing swelling, softening, loss of mechanical strength, and permeation through the wall. There is no liner trick that turns a standard poly tank into an appropriate vessel for a reactive anhydride.

The chemistry compounds the problem. Citraconic anhydride is moisture-sensitive and slowly hydrolyzes to its acid form; that acidic product, plus the anhydride's own reactivity, makes for an aggressive, corrosive service that also liberates flammable hydrogen when it contacts bare metals in the presence of moisture, and it carries a bulk-polymerization hazard on overheating. Safe storage depends on a dry, sealed, inert-blanketed system built around stainless or glass-lined steel. For these reasons we rate polyethylene, polypropylene, and PVC/CPVC as Not Recommended (U) for citraconic anhydride and direct this product to custom stainless or glass-lined fabrication.

Get the right tank built: explore our custom stainless fabrication, compare alloys on 304 vs 316 stainless, and weigh the trade-offs in FRP vs steel vs poly. To scope a citraconic anhydride build with a dry inert blanket and sealed fittings, call 866-418-1777.

Material compatibility at a glance

Citraconic anhydride (2-methylmaleic anhydride) is a corrosive, moisture-sensitive reactive organic anhydride and a respiratory and skin sensitizer. As an anhydride it attacks and permeates polyethylene, so rotomolded HDPE/XLPE poly tanks are NOT suitable. The appropriate materials of construction are dry, sealed 316 stainless steel or glass-lined steel under an inert blanket; carbon steel and other bare metals are excluded because the anhydride (especially once it picks up moisture and hydrolyzes to an acid) corrodes metals and can liberate flammable hydrogen. Keep it dry and segregated from strong bases and oxidizers, and watch for a bulk-polymerization hazard on overheating.

Ratings: S suitable · C conditional / limited · U unsuitable. Verify against the cited resistance charts and your concentration/temperature before specifying.

The safety that actually matters

• Corrosive (H314 / H318): causes severe skin burns and serious eye damage. The SDS reports it caused severe rabbit-eye injury comparable to acetic acid; flush eyes and skin with water for at least 15 minutes and seek immediate medical aid.
• Sensitizer (H317 / H334): may cause an allergic skin reaction and may cause allergy, asthma, or breathing difficulties if inhaled; chronic exposure may cause asthma. Use supplied-air or appropriate respiratory protection per the SDS.
• Keep it dry: moisture-sensitive; hydrolyzes to its acid. Store under a dry inert (nitrogen) blanket in sealed, gasketed fittings to exclude humidity.
• Metal / hydrogen hazard: reacts with most metals in the presence of moisture, liberating flammable hydrogen gas. Exclude carbon steel and other bare reactive metals from wetted surfaces.
• Incompatibilities: keep segregated from strong bases/alkalies, strong oxidizers, and water; a bulk-polymerization and violent container-rupture hazard exists on fire or excessive heat.
• Always follow the manufacturer's Safety Data Sheet, OSHA requirements, and local fire code — this page is general guidance, not a substitute for the SDS or a qualified engineer.

Common questions

Can I store citraconic anhydride in a polyethylene tank?

No. Citraconic anhydride is a reactive organic anhydride that swells, softens, and permeates polyethylene (HDPE and XLPE) as well as polypropylene and PVC. There is no liner that makes a standard poly tank safe for it. Bulk citraconic anhydride belongs in dry, sealed stainless steel or glass-lined steel under an inert blanket.

What is the correct tank material for citraconic anhydride?

Dry 316 stainless steel or glass-lined steel, kept under a dry inert (nitrogen) blanket with sealed, gasketed fittings. Glass-lined steel is excellent for purity-critical service. Avoid carbon steel and other bare metals, because in the presence of moisture the anhydride and its acidic hydrolysis product corrode metals and can liberate flammable hydrogen.

Why is citraconic anhydride considered hazardous?

It is corrosive — it causes severe skin burns and serious eye damage — and it is both a skin and respiratory sensitizer that can trigger allergic reactions or asthma. It is moisture-sensitive and hydrolyzes to an acid, reacts with metals to release flammable hydrogen, and can undergo violent bulk polymerization if heated, potentially rupturing the container.

What materials and chemicals are incompatible with citraconic anhydride?

Avoid water and humidity (it hydrolyzes), most metals (especially carbon steel; reaction with moist metal releases hydrogen), strong bases/alkalies, and strong oxidizers. Keep it dry, sealed, blanketed, and segregated from these materials, and away from excess heat to control the polymerization hazard.