Maleic Anhydride CAS 108-31-6
Chelora Chemicals supplies briquette, flake and molten maleic anhydride to unsaturated polyester resin, BDO, lubricant additive and agrochemical producers worldwide. Because MAN is corrosive and reacts vigorously with water, every consignment leaves with a batch-specific COA, the current SDS and full dangerous-goods documentation.
Also known as: MAN · MA · 2,5-Furandione · cis-Butenedioic anhydride · Maleic acid anhydride
Request a quotation
Price, lead time and a sample COA for Maleic Anhydride, usually within one working day. We ship worldwide.
Request a Quote Email the DeskDocumentation
- Batch-specific COA (purity, melting point, colour, iron)
- Safety Data Sheet (SDS)
- Transport and dangerous-goods documents
- Third-party inspection on request
- Certificate of origin
What is Maleic Anhydride?
Maleic anhydride is the cyclic anhydride of maleic acid, C₄H₂O₃, a white crystalline solid melting at about 53 °C with a sharp irritating odour. It is supplied as briquettes, flakes or molten liquid.
It is made by partial oxidation of n-butane over a vanadium phosphorus oxide catalyst, which has largely replaced the older benzene oxidation route on yield and emissions grounds.
Unsaturated polyester resins are the largest outlet, where the double bond in the maleate provides the crosslinking site that styrene later cures. 1,4-Butanediol, lubricant additives, agrochemicals and copolymers take the rest.
MAN reacts exothermically with water to maleic acid, which makes moisture exclusion a quality and a safety requirement rather than a preference.
Why Maleic Anhydride specifically
- An unsaturated anhydride. The ring opens readily with alcohols and amines while the double bond stays available for crosslinking.
- The UPR crosslink site. Maleate unsaturation in the polyester backbone is what styrene reacts with during cure.
- A Diels-Alder dienophile. Reacts with dienes to form cyclic adducts used in resins and additives.
- A BDO precursor. Hydrogenation gives 1,4-butanediol, THF and GBL.
How Maleic Anhydride is Manufactured
Maleic anhydride is made by partial oxidation of n-butane, with benzene oxidation now largely historical.
- n-Butane feed. Butane from LPG or natural gas liquids is mixed with air.
- Catalytic oxidation. Partial oxidation over a vanadium phosphorus oxide catalyst at about 400 °C in fixed bed, fluid bed or transport reactors.
- Recovery. The product is recovered by water absorption to maleic acid, or by solvent absorption which avoids the hydration step.
- Dehydration. Where the aqueous route is used, maleic acid is dehydrated back to the anhydride.
- Distillation. Vacuum distillation purifies the anhydride and removes colour bodies and heavies.
- Forming. The product is flaked, briquetted or kept molten for bulk dispatch.
Typical Commercial Specification
Figures below are representative of commercial maleic anhydride. Tell us the application and the form you can receive and we will confirm the matching specification.
| Parameter | Typical Value |
|---|---|
| Appearance | White briquettes, flakes or clear colourless molten liquid |
| Maleic anhydride purity | 99.5% min by weight |
| Crystallising point | 52.5 °C min |
| Maleic acid | To grade, typically 0.3% max |
| Colour (APHA, molten) | 20 max |
| Colour after heat test | To grade, typically 50 max |
| Iron | To grade, typically 2 ppm max |
| Ash | To grade, typically 20 ppm max |
| Fumaric acid | To grade, typically 0.2% max |
| Moisture | To grade, typically 0.1% max |
Physical & Chemical Properties
| Property | Value |
|---|---|
| Chemical formula | C₄H₂O₃ |
| Molecular weight | 98.06 g/mol |
| Appearance | White crystalline solid; clear liquid above 53 °C |
| Melting point | 52.8 °C |
| Boiling point | 202 °C |
| Flash point | About 102 °C (closed cup) |
| Density | 1.31 g/cm³ at 60 °C (molten) |
| Vapour pressure | About 0.02 kPa at 20 °C |
| Solubility in water | Reacts to form maleic acid |
| Sublimation | Sublimes readily; vapour deposits in cool sections |
| Dust explosion | Combustible dust requiring ignition control |
| Incompatibilities | Water, alkalis, amines, alcohols, oxidisers, alkali metals |
Behaviour in the process
MAN's reaction with water and its sublimation behaviour define most handling requirements:
- Reacts exothermically with water. Converts to maleic acid with heat release; moisture must be excluded from storage and transfer.
- Sublimes readily. Vapour deposits crystals in vent lines and cool headspaces, which can block them.
- Melts at 53 °C. Molten handling is straightforward but needs tracing; solid handling needs dust control.
- Corrosive in the presence of moisture. Maleic acid formed from moisture attacks carbon steel; stainless is preferred.
MAN Grades and Alternative Anhydrides
Maleic anhydride is bought by form and by colour grade, with the application deciding both.
| Material | Origin / type | When it is the right choice |
|---|---|---|
| Briquette maleic anhydride | Solid, low dust | UPR producers and users handling solids |
| Flake maleic anhydride | Solid, easier to meter | Smaller users and specialty applications |
| Molten maleic anhydride | Bulk heated supply | Large UPR and BDO plants with heated receiving |
| Phthalic anhydride | Aromatic anhydride, CAS 85-44-9 | Saturated acid in UPR; no crosslinking unsaturation |
| Fumaric acid | The trans isomer, CAS 110-17-8 | UPR where higher reactivity and heat resistance are wanted |
Stated plainly: in unsaturated polyester resins maleic anhydride provides the unsaturation and phthalic anhydride provides the backbone, so they are partners rather than alternatives. Fumaric acid substitutes for maleic where higher cure reactivity justifies the cost.
Industries We Supply Maleic Anhydride To
MAN reaches composites, engineering chemicals, lubricants and agriculture.
Where Maleic Anhydride is Used
Unsaturated polyester resins take the largest share, with 1,4-butanediol the second largest and growing outlet.
In unsaturated polyester resins
Maleic anhydride is condensed with glycols and phthalic anhydride to build a polyester chain carrying maleate double bonds. During cure, styrene copolymerises across those double bonds to form the crosslinked network. The maleic to phthalic ratio sets the crosslink density and therefore the stiffness, heat resistance and brittleness of the finished composite.
Handling solid and molten forms
Briquettes minimise dust and are the common solid form; flake is easier to meter but dustier. Molten supply suits large plants with heated receiving, avoiding melting energy and dust entirely, but needs traced lines and attention to sublimation in vents. All forms require moisture exclusion, because water converts anhydride to acid with heat release.
Need a specific grade, purity and packing format?
Tell us the grade, the form you can receive and the colour grade your resin requires, the packing format you can receive and the annual quantity. We will come back with a price, a lead time, a sample COA and the full documentation set.
Quality Control & Testing
Every lot is released against a batch-specific Certificate of Analysis, with maleic acid content and colour reported alongside purity because both indicate how well the material has been protected.
- Maleic anhydride purity and crystallising point — confirming identity and bulk quality.
- Maleic acid content — the direct indicator of moisture exposure.
- Colour, molten and after heat test — predicting resin appearance and thermal stability.
- Iron and ash — measured because metals affect resin colour and catalyse degradation.
- Fumaric acid — reported as the isomerisation by-product.
- Moisture — confirming the lot has been kept dry in transit.
Common Process Problems & Likely Causes
When maleic anhydride causes trouble, it is usually moisture, colour, sublimation or dust. This table is the shortcut our technical desk works through before anyone opens a complaint file.
| Symptom | Likely cause | What to check |
|---|---|---|
| Material caked or melting point high | Moisture converting anhydride to maleic acid | Maleic acid figure and container integrity |
| Resin colour poor | Colour bodies or iron in the anhydride | Colour, heat test and iron results |
| Blocked vent lines on molten storage | Sublimation and recrystallisation in cool sections | Vent tracing and cleaning schedule |
| Resin cure reactivity low | Maleic acid consuming active anhydride, or fumaric isomerisation | Maleic acid and fumaric acid figures |
| Corrosion in storage or lines | Moisture plus maleic acid attacking carbon steel | Moisture figure and material of construction |
| Dust during solid handling | Flake attrition in conveying | Form selection — briquettes reduce dust — and extraction |
Packaging, Storage & Shipping
- Standard packing. 25 kg bags, drums and jumbo bags for briquettes and flakes; heated ISO tanks and road tankers for molten product.
- Moisture exclusion. Critical. Water converts anhydride to maleic acid exothermically. Keep containers sealed and systems dry.
- Temperature control. Hold molten product at 60 to 70 °C. Above 80 °C colour development accelerates.
- Nitrogen blanketing. Standard for molten storage to exclude moisture and prevent colour development.
- Material compatibility. Stainless steel preferred; carbon steel corrodes once moisture and maleic acid are present.
- Segregation. Keep strictly apart from water, alkalis, amines, alcohols and oxidisers — all react vigorously.
- Shelf life. Typically 12 months for sealed solid product in dry storage; molten should be used promptly.
- Transport classification. UN 2215, maleic anhydride, Class 8 corrosive, packing group III.
Hazards & Safe Handling
Maleic anhydride is corrosive, a respiratory sensitiser and reacts exothermically with water. Dust and vapour exposure are both significant, and sensitised workers can react at very low concentrations.
- Corrosivity. Causes severe skin burns and serious eye damage, both as solid dust and as molten liquid.
- Respiratory sensitisation. A recognised respiratory sensitiser; once sensitised, workers can react asthmatically at very low concentrations.
- Water reactivity. Reacts exothermically with water to maleic acid. Avoid water in firefighting on bulk material where possible.
- Occupational exposure. Limits are low, commonly around 0.1 ppm as an 8-hour average; confirm the limit in your jurisdiction.
- Combustible dust. Solid forms generate explosible dust; use earthed, enclosed conveying with extraction.
- Hot liquid. Molten MAN above 60 °C causes thermal and chemical burns together.
- PPE. Chemical-resistant gloves, goggles and face shield, with respiratory protection for dust or vapour exposure.
- Environment. Harmful to aquatic life and lowers pH; contain spills and prevent entry to drains.
Regulatory & Compliance Notes
Maleic anhydride is regulated as a corrosive substance and a respiratory sensitiser. The notes below are orientation rather than legal advice.
- GHS classification. Acute toxicity Category 4, skin corrosion Category 1B, respiratory and skin sensitisation Category 1 and STOT SE Category 3.
- Dangerous goods transport. UN 2215, Class 8 corrosive, PG III. ADR, IMDG, IATA and DOT rules apply; molten shipments carry elevated temperature declarations.
- Occupational health surveillance. Respiratory sensitisation means health surveillance is commonly required for exposed workers.
- Dust explosion regulation. Solid handling systems fall under ATEX, NFPA or equivalent combustible dust requirements.
- REACH and inventories. Registered under EU REACH and listed on the major chemical inventories.
- Food chain uses. Where MAN feeds fumaric or malic acid production, food-grade documentation applies downstream.
We Supply Maleic Anhydride Worldwide
Chelora Chemicals is a supplier and export partner, not a single-plant trader. We ship Maleic Anhydride from India and from partner sources to customers across Asia, Europe, the Middle East, Africa, and North and South America, handling the export documentation, transport paperwork and freight so the material arrives ready to use.
- Incoterms. EXW, FOB, CIF, CFR and DAP quoted to suit your purchasing terms and freight arrangements.
- Ports. Regular shipments through Nhava Sheva (JNPT) and Mundra, with other ports arranged where routing and cargo rules allow.
- Documentation. Commercial invoice, packing list, certificate of origin, COA, SDS and the transport declaration issued as a complete set.
- Flexible volumes. From a pallet of bagged briquettes up to repeat bulk shipments on a supply contract.
- Supply continuity. Because we are independent of any one producer, a plant turnaround or a shipping disruption at one source does not have to become your stock-out.
Buying Maleic Anhydride from Chelora
We are an independent sourcing and supply partner. For maleic anhydride that means settling three things at enquiry: the form you can receive — briquette, flake or molten — the colour grade your resin needs, and the moisture exclusion your storage can maintain.
- Documentation on every lot. Batch-specific COA (purity, melting point, colour, iron), plus SDS and the full transport paperwork.
- Analysis before commitment. Representative analysis shared ahead of a commercial order so your lab can qualify the material.
- Quantities. From a pallet of bagged briquettes through to full bulk shipments on contract supply.
- Grade matching. Briquette, flake or molten maleic anhydride to the purity, colour and maleic acid limits your resin or hydrogenation process requires.
- Inspection. Independent third-party inspection available at loading when the contract requires it.
- Related products. Phthalic Anhydride, Mono Propylene Glycol, Styrene Monomer and other feedstocks alongside Maleic Anhydride from one supplier.
How ordering works
- Send the enquiry. Product, grade or purity, quantity, destination port and the Incoterm you buy on. If you have a spec sheet, attach it — it saves a round trip.
- We quote. Price, lead time, packing format and a sample COA, normally within one working day.
- Qualify the supply. For first orders or critical applications, we share the analysis and handling documentation so your technical and safety teams can sign off before you commit.
- Confirm the order. Proforma invoice issued; payment terms agreed against the volume and the relationship.
- Allocation and QC. Material allocated and released against a batch-specific COA, with an independent inspection where the contract calls for it.
- Ship and document. Filled, labelled and loaded with the full export document set, and tracked through to arrival.
Maleic Anhydride — Common Questions
The questions our technical desk is asked most often about Maleic Anhydride. If yours isn't here, call or email and you will reach someone who knows the chemistry.
What is the CAS number of maleic anhydride?
The CAS number for maleic anhydride is 108-31-6, and its EC number is 203-571-6. Its molecular formula is C₄H₂O₃ with a molecular weight of 98.06 g/mol, and it is classified under HS code 2917.14.
What is maleic anhydride used for?
Mainly for unsaturated polyester resins, where it supplies the crosslinking unsaturation. It also feeds 1,4-butanediol, THF and GBL production, lubricant additive dispersants, agrochemicals, copolymers and fumaric and malic acid.
Do you supply maleic anhydride worldwide?
Yes. Chelora Chemicals supplies and exports maleic anhydride worldwide — across Asia Pacific, Europe, the Middle East, Africa and the Americas, as well as throughout India, in briquette, flake and molten form.
How is maleic anhydride manufactured?
By partial oxidation of n-butane over a vanadium phosphorus oxide catalyst at about 400 °C, followed by water or solvent absorption, dehydration where needed, and vacuum distillation. The older benzene oxidation route is now largely historical.
Why does moisture matter so much?
Because water converts maleic anhydride to maleic acid exothermically. The acid raises melting point, causes caking, consumes active anhydride in the resin reaction and corrodes carbon steel equipment.
What form should I buy — briquette, flake or molten?
Briquettes minimise dust and suit most solid handling; flake is easier to meter but dustier; molten suits large plants with heated receiving and avoids melting energy and dust entirely. All three need moisture exclusion.
Is maleic anhydride hazardous?
Yes. It is corrosive, causing severe skin burns and eye damage, and it is a respiratory sensitiser — once sensitised, workers can react asthmatically at very low concentrations. It also reacts exothermically with water.
What are the UN number and transport class?
UN 2215, maleic anhydride, Class 8 corrosive, packing group III. ADR, IMDG, IATA and DOT rules apply, with elevated temperature declarations for molten shipments.
How should maleic anhydride be stored?
Solid forms in sealed containers in dry, covered storage; molten at 60 to 70 °C in nitrogen-blanketed, traced stainless tanks with dry nitrogen, strictly away from water, alkalis, amines and alcohols.
What is the difference between maleic and phthalic anhydride in resins?
Maleic anhydride carries a double bond that styrene crosslinks during cure, so it provides the reactivity. Phthalic anhydride is saturated and forms the backbone. They are used together, with the ratio setting the resin's stiffness and heat resistance.
Why do vent lines block on molten MAN storage?
Because maleic anhydride sublimes readily, and the vapour recrystallises in any cool section of a vent line. Tracing and periodic cleaning are part of normal operation on molten storage.
What packing sizes and order quantities are available?
25 kg bags, drums and jumbo bags for solid forms, and heated ISO tank containers or road tankers for molten product. Orders run from a pallet of bagged briquettes up to repeat bulk shipments on contract supply.
Ready to source Maleic Anhydride?
Send us your specification, grade and annual volume. You will get a price, a realistic lead time and a sample COA from someone who understands what the material has to do in your process — delivered anywhere in the world.