MAH is commercially supplied as a solid in three main forms:

• Flakes: The most common form - thin white flakes pressed from solidified molten MAH; easy to dissolve; may absorb moisture and cake during storage; packaged in 25 kg paper/PE bags or 500–1,000 kg big bags
• Briquettes / pellets: Compressed solid blocks; slower dissolving but lower dust generation; used where dust control is a priority
• Molten bulk: For very large industrial users (UPR manufacturers processing hundreds of tonnes per month) - MAH is delivered as a hot liquid by insulated tanker and stored in heated tanks above 60 °C; eliminates melting step at site

For most industrial applications, solid MAH must be melted before use. Key parameters:

• Melt at 60–70 °C - above the melting point (52.8 °C) to ensure complete liquefaction; avoid temperatures above 90–100 °C unnecessarily to prevent premature hydrolysis by ambient moisture
• Heated vessels required - stainless steel (316L preferred) or glass-lined reactors with steam or electric heat tracing
• Nitrogen atmosphere recommended - reduces moisture ingress and prevents surface oxidation / colour development during extended melt hold
• Dust precautions for flake handling - MAH dust is a serious inhalation and eye irritant; enclosed handling, dust extraction, and P3 respirators required for flake loading operations

The single largest MAH application. UPR is produced by polycondensation of MAH (and sometimes phthalic anhydride) with glycols; the resulting polyester contains reactive C=C bonds that crosslink with styrene to give hard, durable thermosets. Used in fibreglass-reinforced composites for marine, construction, automotive, and wind energy applications.

MAH hydrolyses with water to give maleic acid; maleic acid isomerises thermally or catalytically to fumaric acid. Both diacids serve as food acidulants (E296, E297), polymer monomers, and pharmaceutical intermediates. Fumaric acid is also used in psoriasis treatment. The MAH → maleic acid → fumaric acid cascade is a key downstream chemical route.

Styrene-maleic anhydride (SMA) copolymers are used in engineering thermoplastics, paper sizing, and detergent builders. Poly(ethylene-alt-maleic anhydride), poly(isobutylene-alt-maleic anhydride), and vinyl ether copolymers serve in dispersants, scale inhibitors, and biomedical polymers. This segment has been growing rapidly due to applications in EV battery binders and advanced coatings.

MAH is used as a reactive modifier in alkyd resin synthesis - it introduces additional double bond functionality and can replace part of the phthalic anhydride component. Maleate esters (dibutyl maleate, dioctyl maleate) serve as plasticiser intermediates and reactive modifiers. MAH-modified rosin esters are used in printing ink varnishes and adhesive tackifiers.

MAH can be grafted onto polyolefins (PP, PE, EPDM) via reactive extrusion to introduce anhydride functionality. MAH-g-PP and MAH-g-PE are the most widely used compatibilisers in polymer blends and composites - they enable adhesion between incompatible polymers (e.g., glass fibres and PP matrix, PA6 and polyolefin blends) by reacting with amine and hydroxyl groups on the polar polymer.

Poly(maleic acid) and poly(maleic anhydride-co-acrylic acid) are powerful scale inhibitors and dispersants in industrial water systems. They inhibit calcium carbonate and calcium sulphate scale formation in cooling towers, boilers, and desalination membranes by a threshold effect and crystal modification mechanism. The MAH content imparts good thermal stability and high anionic charge density.

High styrene/MAH ratio SMA (3:1) is a rigid engineering thermoplastic with heat deflection temperature above 100°C and excellent dimensional stability. Used in automotive interior components, electrical housings, and consumer appliances where heat resistance above standard polystyrene is required. SMA thermoplastics are produced by companies including Polyscope and Ineos Styrolution.

SMA in ammonium salt form (solubilised with ammonia) is an effective paper sizing agent. Applied in the size press or coating formulation, SMA improves ink holdout, water resistance, and surface strength of printing papers and packaging grades. The anhydride groups react with cellulose hydroxyl groups to provide covalent bonding to the fibre. Growing demand from coated paper and specialty packaging.

Hydrolysed SMA (SMA-diacid form) has strong sequestrant and dispersant properties. Used in laundry detergent formulations as a phosphate replacement co-builder, in industrial cleaners, and as a dispersant for pigments and mineral slurries. The 1:1 alternating SMA copolymer is particularly effective for calcium carbonate and calcium phosphate scale inhibition in detergent applications.

In alkyd resin synthesis, MAH can partially substitute for phthalic anhydride to introduce additional crosslinking potential through the maleate double bond. MAH-modified alkyds have faster drying and better hardness development than pure phthalic alkyds. MAH also reacts with rosin (abietic acid) via Diels-Alder addition to produce maleated rosin - a hardened, acid-modified tackifier used in hot-melt adhesives, printing inks, and pressure-sensitive adhesives.

Reactive extrusion of polypropylene (PP) or polyethylene (PE) with small amounts (0.5–2 wt%) of MAH and a free-radical initiator (peroxide) generates MAH-grafted polyolefins (MAH-g-PP, MAH-g-PE). The pendant anhydride groups react with amines and hydroxyl groups on incompatible polymers or reinforcing fillers, enabling:

• Glass fibre / PP composite adhesion (tie-layer)
• PA6 / PP alloy compatibilisation for engineering plastics
• Adhesion promotion in multilayer packaging films
• Wood-plastic composite (WPC) coupling agent

Poly(maleic acid) (HPMA) and its copolymers are the most thermally stable organic scale inhibitors available for industrial water treatment. Key advantages over polyacrylate-based inhibitors:

• Effective up to 250°C in high-pressure boiler systems
• Inhibits CaCO₃, CaSO₄, BaSO₄, and iron oxide deposition
• Performs well at high calcium hardness (Ca²⁺ > 500 ppm)
• Compatible with chlorine, bromine, and non-oxidising biocides
• Used in reverse osmosis antiscalant formulations, cooling tower treatment, and oilfield produced water treatment

• Food acidulant (E296) - beverages, jams
• Malic acid precursor (via enzymatic hydration)
• Pharmaceutical synthesis intermediate
• Textile treatment (anti-crease)
• Copolymer monomer (water-soluble polymers)

• Food acidulant (E297) - baking powder, beverages
• Pharmaceutical - psoriasis treatment (dimethyl fumarate / Tecfidera®)
• UPR co-monomer (improves water resistance vs maleate)
• Animal feed supplement (rumen methane reduction)
• Polyester resin modifier

Maleic anhydride and maleic acid are distinct chemicals with different CAS numbers (108-31-6 vs 110-16-7), different molecular weights (98 vs 116), and different reactivity profiles. Maleic anhydride is the anhydrous form; maleic acid is the diprotic acid formed by hydrolysis. They are not interchangeable in resin or polymer synthesis - always specify which form you require and verify CAS number on the COA.

Global MAH capacity exceeds 4 million MT/year. China is the dominant producer, accounting for approximately 60–65% of world capacity, primarily based on n-butane oxidation (vapor-phase catalytic oxidation over V₂O₅/MoO₃ catalysts). Major non-Chinese producers include Lanxess, Huntsman, Bartek, and Polynt in Europe and the Americas. Chinese-origin MAH is 30–50% cheaper than Western-origin at comparable purity.

• 25 kg bags: Standard; most common for small–medium users; palletised
• 500 kg / 1,000 kg big bags (FIBC): Economical for ≥5 MT orders; requires FIBC discharger for controlled unloading
• Molten bulk ISO tank: For large UPR manufacturers; heated tank with steam tracing; most economical ≥20 MT
• IMDG classification: Class 4.1 (Flammable solid), PG III - DG for all transport modes; DGD required

• COA per batch - purity, colour (APHA), maleic acid content, Fe, crystallisation point
• GHS SDS - 16-section; confirm corrosive (Cat.1 skin), sensitiser classification; Section 14 Class 4.1
• REACH OR letter (EU buyers)
• TSCA positive certification (US buyers)
• DGD - Class 4.1, PG III, UN 2215
• Certificate of Origin

Q1: What is maleic anhydride used for?

Maleic anhydride (CAS 108-31-6) is an industrial chemical intermediate used in five main application sectors: (1) Unsaturated polyester resins (UPR) - the largest use, approximately 40–50% of global MAH consumption; MAH reacts with glycols to form a polyester containing reactive double bonds that crosslink with styrene to produce fibreglass composites for boats, construction panels, and wind turbine blades; (2) Maleic and fumaric acid production - MAH hydrolyses to maleic acid, which isomerises to fumaric acid; both are used as food acidulants and pharmaceutical intermediates; (3) Styrene-maleic anhydride (SMA) copolymers - engineering thermoplastics, paper sizing agents, and detergent co-builders; (4) Maleic anhydride-grafted polymers (MAH-g-PP/PE) - compatibilisers for glass-filled composites and polymer alloys; (5) Water treatment polymers - poly(maleic acid) and copolymers as scale inhibitors in cooling towers and boilers. The common thread is MAH's reactive anhydride ring and activated C=C double bond, which make it an exceptionally versatile building block.

Q2: What is the melting point of maleic anhydride?

The melting point of maleic anhydride is 52.8 °C (127 °F). This is the most commercially important physical property of MAH because it means the material is a solid at normal room temperature (20–25 °C) but becomes a mobile liquid when heated above 52.8 °C. For industrial processing - UPR synthesis, SMA polymerisation, esterification reactions - maleic anhydride must first be melted in heated vessels or received as molten material in heated ISO tanks. Storage of solid MAH (flakes or briquettes) must avoid heat sources above 50 °C to prevent caking and partial melting. The crystallisation point (≥52.5 °C for commercial grade) is used as a quality control parameter - suppression of the crystallisation point below 52 °C indicates contamination with maleic acid (from hydrolysis by moisture) or fumaric acid, both of which act as freezing point depressants.

Q3: What is the formula and molecular weight of maleic anhydride?

The molecular formula of maleic anhydride is C₄H₂O₃ and the molecular weight is 98.06 g/mol. The IUPAC name is 2,5-furandione, reflecting its structure as a five-membered lactone ring (furan-2,5-dione). The structure contains: two carbonyl groups (C=O) at positions 2 and 5 of the ring; one bridging oxygen atom; and one carbon-carbon double bond (C=C) between positions 3 and 4, with one hydrogen on each of these carbons (cis configuration). The molecular weight of 98.06 g/mol is low for an industrial chemical, meaning that per gram of MAH, you get approximately 10 millimoles of reactive anhydride functionality - unusually high molar reactivity. For comparison: phthalic anhydride (MW 148 g/mol) provides about 6.8 mmol/g; maleic anhydride (98 g/mol) provides 10.2 mmol/g. This high molar content per gram is one reason MAH is such a cost-effective building block.

Q4: What is the difference between maleic anhydride and maleic acid?

Maleic anhydride (CAS 108-31-6, MW 98, C₄H₂O₃) and maleic acid (CAS 110-16-7, MW 116, C₄H₄O₄) are structurally related but chemically distinct. Maleic anhydride is the cyclic anhydride - the two carboxylic acid groups are joined by a shared oxygen to form a five-membered ring, eliminating one molecule of water. Maleic acid is the open-chain dicarboxylic acid formed when MAH reacts with water: MAH + H₂O → maleic acid. The key practical differences: (1) MAH is a solid at room temperature (mp 52.8°C); maleic acid melts at 138°C but is typically used as a solution; (2) MAH is more reactive for polymer synthesis because the anhydride ring opens faster and more cleanly than diacid esterification; (3) MAH is the industrial starting material; maleic acid is a downstream derivative; (4) MAH cannot be made directly from maleic acid under normal conditions (ring closure requires high temperature and elimination of water). They are not substitutable in UPR synthesis - specify which form your process requires and verify the CAS number on the COA.

Q5: How is maleic anhydride produced industrially?

Maleic anhydride is produced industrially by two main routes - both involve catalytic vapour-phase oxidation: (1) n-Butane oxidation (dominant route, ~85% of global production): n-Butane is oxidised with air over a vanadium-phosphorus-oxide (VPO) catalyst at 350–450°C in a fixed-bed or fluidised-bed reactor. The selective oxidation converts n-C₄H₁₀ to C₄H₂O₃ + 4H₂O in one step. The butane route is preferred because: butane is cheaper than benzene; the reaction is more selective; CO₂ by-product is lower; and the process generates fewer environmental concerns than benzene; (2) Benzene oxidation (legacy route, ~15% of global capacity, mainly older plants in China/India): Benzene is oxidised with air over V₂O₅/MoO₃ catalysts at 350–450°C. Produces MAH with slightly higher yield per pass but is more expensive due to benzene feedstock cost and benzene handling regulations. Chinese producers are progressively switching from benzene to butane routes as older plants are upgraded. The product (molten MAH) is absorbed in circulating solvent or water, then recovered and purified by distillation to the final solid or molten specification.

Q6: How can I buy maleic anhydride from China?

Sinolook Chemical supplies maleic anhydride (CAS 108-31-6) to customers in Europe, the Middle East, South and Southeast Asia, and the Americas. We supply standard grade (purity ≥99.0%, APHA ≤30 molten) and premium grade (≥99.5%, APHA ≤10) in 25 kg bags, 500 kg / 1,000 kg big bags, and by arrangement as molten bulk in heated ISO tanks for large UPR manufacturers. MAH is classified as a Class 4.1 flammable solid DG (UN 2215) - all shipments come with full DG documentation (DGD, CPC), REACH OR letter for EU buyers, TSCA positive certification for US buyers, and a batch COA with purity, colour, maleic acid content, and crystallisation point. Contact us at: WhatsApp 0086 18150362095 · WeChat/Tel 0086 13400715622 · Email sales@sinolookchem.com. We provide CIF quotations to your port within 24 hours of enquiry.