| HS Code | |
| Productname | Adipic Acid |
| Iupacname | Hexanedioic acid |
| Chemicalformula | C6H10O4 |
| Molecularweight | 146.14 g/mol |
| Casregistrynumber | 124-04-9 |
| Ecnumber | 204-673-3 |
| Appearance | White crystalline powder |
| Odor | Odorless |
| Meltingpoint | 152.1 °C |
| Boilingpoint | 337.5 °C |
| Density | 1.36 g/cm³ |
| Solubilityinwater | 14 g/L at 20 °C |
| Pka1 | 4.43 |
| Pka2 | 5.41 |
| Flashpoint | 196 °C |
| Autoignitiontemperature | 420 °C |
As an accredited Adipic Acid factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Adipic Acid supplied in 25 kg multi-wall paper bags with polyethylene liners, palletized and shrink-wrapped for industrial transport. |
| Container Loading (20′ FCL) | Adipic Acid: 25 kg bags, palletized and shrink-wrapped, loaded into a 20′ FCL dry container with secure bracing. |
| Shipping | Adipic Acid is typically shipped as a non-hazardous, white crystalline solid in 25 kg bags, fiber drums, or bulk hopper/ISO containers. Transport by truck, rail, or sea requires a dry, cool, ventilated area away from strong alkalis and oxidizers. Standard freight documentation applies; no dangerous-goods placards are normally required. |
| Storage | Store adipic acid in a cool, dry, well-ventilated area away from heat, sparks, and open flames. Keep containers tightly closed, labeled, and upright to prevent moisture absorption and dust formation. Segregate from strong oxidizers, bases, and incompatible materials. Use secondary containment, avoid dust accumulation, and keep spill cleanup materials available. Follow local regulations and SDS recommendations. |
| Shelf Life | Adipic acid is stable for years if kept sealed in a cool, dry place, away from moisture and incompatible materials. |
Fiber-grade nylon 6,6 begins as an aqueous solution of the 1:1 adipic acid–hexamethylenediamine salt, commonly termed AH salt. A 50 wt% aqueous solution of AH salt at 25°C exhibits a pH of 7.6–8.0; deviations below 7.5 indicate excess dicarboxylic acid, while values above 8.2 indicate free diamine, both of which shift the final amine-to-carboxyl end-group ratio. For textile-grade continuous polymerization, the salt solution is concentrated to 60–80 wt% in an evaporator before entering a two-stage autoclave train. In the first stage, pressure is reduced from approximately 1.7 MPa to atmospheric pressure at 210–245°C, and in the second-stage vacuum finisher residual water is removed at 270–285°C under 60–80 kPa absolute vacuum to drive polycondensation. Relative viscosity in 90% formic acid is the primary process control parameter; textile filament targets 2.4–2.8, while high-tenacity tire cord and airbag yarn require values above 3.0 as measured per ASTM D789 and ISO 307:2019. Because water acts as a chain terminator, melt spinning of nylon 6,6 requires pre-drying to a moisture content below 0.2% using dehumidified air with a dew point of -30°C to -40°C. Production-scale twin-screw compounding for glass-reinforced engineering resin grades typically uses an L/D ratio of 40:1 with side-fed chopped glass, and barrel temperatures are held at 260–290°C to avoid thermal degradation. The end products span continuous filament, staple fiber, engineering resin pellets, and industrial monofilament; each conversion step is limited by thermal-oxidative sensitivity of the polyamide above 300°C, which requires nitrogen blanketing in the finisher and antioxidant packages based on hindered phenols or copper halide systems. AH salt storage is an additional boundary: the salt is hygroscopic, and prolonged exposure above 60% RH causes surface dissolution and caking in silos or hopper outlets.
Polyester polyols prepared from adipic acid and short-chain diols such as ethylene glycol, diethylene glycol, 1,4-butanediol, or neopentyl glycol serve as the soft-segment precursor for thermoplastic polyurethane and castable polyurethane elastomers. Condensation in a 200–230°C stirred stainless steel reactor is driven by nitrogen sparging and a final vacuum stage below 50 mbar, with a tetraalkyl titanate or organotin catalyst at 0.05–0.2 wt% of the total charge. Termination is controlled by acid value and hydroxyl value rather than by molecular weight alone; for a linear poly(ethylene adipate) diol with a number-average molecular weight of 2,000 g/mol, the calculated hydroxyl value is 56.1 mg KOH/g, and for 1,000 g/mol the value is 112.2 mg KOH/g. Acid value for elastomer-grade polyester diols is normally held below 1.0 mg KOH/g because residual carboxyl groups catalyse ester hydrolysis and alter isocyanate reactivity. Water content must be reduced below 0.05% before reaction with 4,4'-diphenylmethane diisocyanate; otherwise dissolved water consumes isocyanate and generates carbon dioxide, producing bubbles in cast elastomers. In polyester-based TPU, the adipate segment provides high tensile strength and oil resistance under dynamic load, but hydrolytic stability is the limiting operational boundary; continuous exposure to water above 70°C causes ester scission and measurable tensile-strength loss within 500–1,000 hours in accelerated ageing. Therefore, polyester polyols derived from adipic acid are selected for oil-resistant seals, hydraulic hoses, cable jackets, and industrial rollers, while polyether polyols are preferred for high-humidity immersion service. Analytical control follows ASTM D4274-21 for hydroxyl number and ASTM D4662-20 for acid number, with moisture determined by Karl Fischer titration according to ASTM E203. On production lines, acid value excursions are most often traced to insufficient vacuum during the final polycondensation stage or to diol loss through the partial condenser, which shifts the stoichiometric balance and changes the hydroxyl value of the finished batch.
In unsaturated polyester resin synthesis, adipic acid is introduced as a partial replacement for phthalic anhydride or isophthalic acid to increase the flexibility of the cured thermoset and reduce the exotherm in thick-section castings. Typical flexible resin formulations operate with a dicarboxylic acid fraction containing 5–20 mol% adipic acid; the remainder is usually maleic anhydride, phthalic anhydride, or isophthalic acid. The condensation reaction with propylene glycol at a glycol-to-diacid molar ratio of 1.05–1.10 is carried out at 180–220°C under an inert gas sparge, with water removed either by a xylene azeotropic column or by a partial condenser with vacuum. Process termination is based on acid value; a typical laminating resin is terminated at 15–35 mg KOH/g according to ISO 2114, then cooled and thinned with styrene monomer to a solids content of 60–70 wt%. Increasing adipic acid content reduces the glass transition temperature and elastic modulus of the cured casting, but it also increases water absorption and reduces the heat deflection temperature; formulations exceeding 20 mol% adipic acid often require post-cure above 80°C to reach acceptable Barcol hardness. The resin is catalysed with a methyl ethyl ketone peroxide or cobalt naphthenate system, and gel time is measured by ISO 584 using a cure bath at 25°C. End uses include cast polymer concrete, artificial marble, flexible putty, marine gelcoat repair compounds, and low-profile automotive body panels. Production-scale batch variance occurs primarily because styrene loss during thinning alters final viscosity; closed reactors with cooling capacity below 25°C are required to prevent premature polymerization during monomer addition.
Bis(2-ethylhexyl) adipate, commonly designated DOA, is the reference adipate ester for plasticized PVC compounds requiring flexural performance below -30°C without the regulatory burden associated with low-molecular-weight phthalates. DOA is produced by direct esterification of adipic acid with 2-ethylhexanol under acid catalysis, typically p-toluenesulfonic acid or tetrabutyl titanate, with azeotropic removal of water using toluene or cyclohexane. The finished ester is neutralized, washed, steam-stripped, and dried to an acid value below 0.1 mg KOH/g, a moisture content below 0.1%, and a platinum-cobalt colour below 30. In flexible PVC compounding, DOA is added at 20–60 phr; at 50 phr loading in a suspension PVC with a K-value of 70, the compound retains flexibility at temperatures where general-purpose phthalate-stabilized compounds stiffen. Compatibility limits are determined by exudation testing under compression per ASTM D3291, and plasticizer volatility is measured by activated-carbon volatile loss according to ASTM D1203. For food-contact PVC gaskets used in jar closures, the use of DOA is controlled under EU Regulation (EU) No 10/2011, where bis(2-ethylhexyl) adipate carries a specific migration limit of 18 mg/kg; the converter must verify migration under the intended food simulant and time-temperature condition. Diisodecyl adipate and diisononyl adipate extend the application range to lower volatility and higher molecular weight, but the trade-off is higher viscosity and a slightly higher low-temperature modulus. DOA is a primary plasticizer in cold-flexible PVC film, refrigerator gaskets, low-temperature cable compounds, and synthetic leather, while its migration tendency makes it unsuitable for direct styrenic or polycarbonate contact unless barrier layers are used.
In dry beverage and gelatin dessert powders, the low hygroscopicity of adipic acid maintains free flow while delivering a buffered acid profile; the material is listed as E 355 in the European Union and is affirmed as generally recognized as safe in the United States under 21 CFR 184.1009. Adipic acid has two dissociation steps with pK a1 4.42 and pK a2 5.41, which creates a buffering plateau at pH 3.0–4.0, less sour than citric acid at equivalent molar concentration. This property allows partial replacement of citric acid in citrus-flavoured dry mixes where citric acid monohydrate absorbs moisture and causes bridging in hoppers. In leavening systems, the stoichiometric reaction of 100 g adipic acid with 114.9 g sodium bicarbonate releases 2 mol carbon dioxide per mole of adipic acid; however, the reaction is slowed in dry batter by the limited water phase, so the particle size of the acidulant determines the rate of gas evolution during baking. Adipic acid is added at the dry-blending stage before a final sieving pass through a 500 µm screen to reduce agglomerates. Food-grade adipic acid must meet the FCC monograph requirement for assay not less than 99.5% on the dried basis, with a water content not exceeding 0.2% and a melting point of 151–153°C. A further operational boundary is solubility: adipic acid dissolves at approximately 1.4 g/100 mL at 15°C, which limits its use in cold-filled clear beverages unless hot preparation or partial sodium salt formation is used. Dry blends containing sodium bicarbonate must be kept below 45% relative humidity in the packaging line because condensation initiates premature CO2 release. The Joint FAO/WHO Expert Committee on Food Additives established an acceptable daily intake of 0–5 mg/kg body weight for adipic acid; products formulated for direct consumption require label consistency with EU Regulation (EC) No 1333/2008. End products include powdered tea drinks, gelatin desserts, acidified candy powders, and encapsulated bakery leavening systems.
For hydroxy-functional saturated polyester resins used in coil and powder coatings, adipic acid is incorporated to lower the glass transition temperature and increase the flexibility of the crosslinked film without external plasticizers. In a typical coil-coating polyester, adipic acid replaces 5–15 mol% of the aromatic dicarboxylic acid fraction; the majority aromatic acid is usually terephthalic acid or isophthalic acid, and the polyol side is built around neopentyl glycol with a small amount of trimethylolpropane for branching. The melt condensation is run at 230–250°C under a nitrogen sweep until the acid value drops below 5 mg KOH/g and the hydroxyl value reaches 20–60 mg KOH/g; then the resin is cut in aromatic solvent and n-butanol for coil coating application. The resin is crosslinked with a methylated melamine-formaldehyde resin at 15–25 wt% on resin solids, catalysed by p-toluenesulfonic acid blocked with an amine. Formability is evaluated after curing by zero-T bend and impact tests according to ASTM D4145 and ASTM D2794; coatings on 0.5 mm galvanized steel are expected to survive a 9 J reverse impact without cracking. Adipic acid levels above 15 mol% reduce hardness, acid-etch resistance, and humidity resistance; therefore, outdoor-durable coil coatings usually retain aromatic dicarboxylic acids as the majority fraction. For hydroxyl-functional powder coatings, adipic acid is used at low levels to improve flow and levelling before crosslinking with blocked isocyanates; the powder resin acid value is maintained below 3 mg KOH/g and the glass transition temperature above 55°C to prevent sintering during storage at 25–30°C. End products include pre-painted architectural panels, domestic appliance top coats, automotive interior trim films, and outdoor furniture powder coatings.
When dialkyl adipates are formulated into synthetic lubricant base stocks, the processing boundary changes from PVC compatibility to thermal-oxidative stability and viscosity index control. Diisodecyl adipate and bis(2-ethylhexyl) adipate are blended into Group V synthetic ester base stocks for low-temperature hydraulic fluids and compressor lubricants where mineral oil fails at pour point. The esterification process is similar to the plasticizer route, but the finished ester is subjected to aggressive wiped-film evaporation to remove light alcohol and partial ester fractions, achieving a hydroxyl value below 5 mg KOH/g and a water content below 100 mg/kg. In low-temperature hydraulic fluid development, an adipate ester content of 20–50 wt% may lower pour point below -50°C, but published data for this specific configuration is limited; blend-specific cloud point and pour point must be confirmed by ASTM D97. Biodegradability claims for adipate esters require verification against the specific product data under OECD 301B ready biodegradability testing because isomer distribution and chemical oxygen demand affect the result. The operational boundary is thermal stability: dialkyl adipates begin to degrade in continuous service above 150°C without antioxidant addition, so they are limited to compressor or hydraulic applications with bulk oil temperatures below 120°C unless synthetic antioxidant packages are present. End products include refrigerator compressor lubricants, low-temperature hydraulic oils, and biodegradable metalworking fluid esters; however, if the target application demands oxidative stability above 160°C, polyol esters are preferred because of their greater thermal-oxidative resistance.
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Adipic acid, CAS 124-04-9, EINECS 204-673-3, is a linear six-carbon saturated dicarboxylic acid with the molecular formula HOOC(CH2)4COOH and molar mass 146.14 g/mol. Industrial material is supplied as white crystalline powder or fine granular solid with a typical bulk density of 0.80–0.90 g/cm³; particle-size distribution is controlled by screen residue on 0.500 mm, 0.150 mm, and 0.075 mm sieves. Polymerisation-grade certificate-of-analysis boundaries include purity ≥99.8% (w/w) by alkalimetric titration, melting range 151–153 °C by differential scanning calorimetry at 10 K/min, water content ≤0.20 wt%, ash ≤5 mg/kg, iron ≤0.5 mg/kg, and methanolic colour ≤5 APHA. Food-grade material is controlled in the United States under 21 CFR 184.1009 and in the European Union under Regulation (EC) No 1333/2008 Annex II as E355; reported food-grade assay is ≥99.7% with residue on ignition ≤0.01% and arsenic ≤1 mg/kg. No universal model-number system exists across suppliers; grade codes are supplier-specific, so cross-supplier qualification is performed against certificate-of-analysis parameters rather than the product name. Published aqueous solubility at 15 °C is 14.4 g/L, rising to more than 1,000 g/L near the normal boiling point. The dominant industrial route is nitric acid oxidation of a cyclohexanol/cyclohexanone mixture; the crude product contains glutaric acid and succinic acid, which are removed by crystallisation. Bio-based adipic acid produced from fermentation-derived muconic acid is chemically identical, but carbon-14 analysis under ASTM D6866-20 can distinguish fossil-derived from bio-derived material for sustainable sourcing verification.
The differentiation between polymerisation-grade and food-grade material appears mainly in trace-metal, ash, and residue-on-ignition limits, because polymerisation catalysts and melt-phase polyamide quality are sensitive to iron and non-volatile residues. The table below lists representative certificate-of-analysis boundaries from published supplier data; individual lot data may be tighter.
| Parameter | Polymerisation-grade | Food-grade | Test basis |
|---|---|---|---|
| Assay, dry basis | ≥99.8% | ≥99.7% | Alkalimetric titration |
| Water content | ≤0.20 wt% | ≤0.20 wt% | Karl Fischer titration |
| Ash | ≤5 mg/kg | ≤100 mg/kg | Ignition at 800 °C |
| Iron | ≤0.5 mg/kg | not routinely specified | ICP-OES |
| Colour in methanol | ≤5 APHA | ≤10 APHA | Visual or photometric |
| Heavy metals as Pb | not routinely specified | ≤10 mg/kg | Food Chemicals Codex method |
For fibre-grade polyamide production the iron limit is not merely cosmetic. Soluble iron in the melt phase reduces colour stability and can participate in redox side reactions that shift the end-group balance, so polymerisation-grade material is qualified by lot-based spectrochemical data rather than by total purity alone.
In continuous polyamide 66 polymerisation, adipic acid is first dissolved with hexamethylenediamine in demineralised water to form the 1:1 nylon salt; the salt solution is usually maintained at 50–60 wt% and pH 7.6–8.2. A deviation of ±0.3 mol% from the stoichiometric acid–amine ratio changes the end-group balance and lowers the molecular weight ceiling measured as viscosity number under ISO 307. The salt is concentrated and polymerised in two-stage equipment at 210–280 °C; below 210 °C conversion rate becomes the bottleneck, while sustained operation above 285 °C increases nitrogenous volatile formation and gel content. Textile-grade relative viscosity is typically 2.4–2.7; industrial-yarn grades run 3.0–3.3 in sulfuric acid solution. The low ash and iron specifications of polymerisation-grade adipic acid are therefore linked directly to stable melt spinning and downstream drawing. In fibre-grade production, insoluble char particles above 10 µm increase spinneret pack changes and draw-line breaks; in resin-grade production, moisture in the acid feed must still be controlled to avoid hydrolysis of the polyamide during melt processing.
For polyester polyol production, adipic acid is reacted with excess glycol—commonly 1,4-butanediol, diethylene glycol, or mixed glycols—under nitrogen at 180–230 °C. The diacid-to-glycol molar ratio is typically 1:1.10 to 1:1.25, producing hydroxyl numbers of 50–60 mg KOH/g measured according to ISO 14900-1. Esterification is monitored by acid value; discharge is normally below 2 mg KOH/g. Water removal is performed through a packed column with top temperature 95–105 °C. The critical processing fault is sublimation of adipic acid into vent lines and condenser internals; overhead surfaces below 120 °C accumulate crystalline deposits, raising back-pressure and causing batch-to-batch hydroxyl-number drift. Heated overhead lines and condensate returns kept above 120 °C reduce this failure mode. Operation above 235 °C increases colour and branching, while operation below 170 °C gives insufficient esterification rate for standard batch cycles. In semi-continuous plants, the diacid addition profile is set to keep top temperature below 105 °C and to avoid separator flooding. Final polyester polyols for cast elastomer or flexible foam systems are dried to water contents below 0.05 wt% before reaction with isocyanate; residual moisture above 0.08 wt% can generate carbon dioxide and reduce Shore A hardness under ISO 868.
Conversion to di-2-ethylhexyl adipate, commonly DEHA, is a major non-polyamide application. Esterification with 2-ethylhexanol proceeds under acid catalysis; after neutralisation the residual acid value is controlled at ≤0.1 mg KOH/g, and residual alcohol is reduced to ≤100 mg/kg for low-volatile-loss plasticiser performance. DEHA produces lower low-temperature stiffening than ortho-phthalate esters because the linear adipate backbone increases molecular mobility; comparative stiffness is characterised under ASTM D1043-16. In flexible PVC, DEHA is typically used at 20–35 phr, but published data for drop-in substitution ratios across all plastisol and calendering formulations is limited; formulation-specific fusion and Shore D hardness under ISO 868 must be confirmed. The higher water extraction of DEHA compared with polymeric plasticisers is an operational boundary in humid applications.
When technical requirements exclude ortho-phthalate plasticisers, adipate esters are compared with citrate, sebacate, and terephthalate systems. The six-carbon adipic acid itself yields esters with lower intrinsic viscosity and higher volatility than sebacate esters, which carry a ten-carbon chain; however, adipate esters show better PVC solvency than azelates in plastisol fusion, as measured by minimum fusion temperature on a torque rheometer. In flexible PVC compounds, direct replacement is not stoichiometric: plasticiser loading is commonly adjusted upward to compensate for lower plasticising efficiency, and dry-blend handling requires cooled mixer settings below 60 °C to prevent early additive absorption. REACH registration dossiers list end-use exposure scenarios for the specific ester CAS number; formulators must verify food-contact clearance such as 21 CFR 175.105 or 177.2600 before use in packaging or article-contact applications.
Food-grade adipic acid is used as acidulant E355 in dry beverage bases, gelatin desserts, and chemical leavening systems. Its acidification profile differs from citric acid because the first acid dissociation constant pKa1 is 4.44, compared with 3.13 for citric acid, producing a less sharp initial pH drop in aqueous solution. In chemical leavening, reaction with sodium bicarbonate is controlled by the dissolution rate of the acid; therefore the crystalline particle-size distribution is specified by residue on 0.150 mm and 0.075 mm sieves. Regulatory status in the United States appears in 21 CFR 184.1009; European Union food-additive use appears in Regulation (EC) No 1333/2008 Annex II as E355. At high pH, the adipate dianion may precipitate as insoluble calcium salts, which limits its use in hard-water systems and requires buffering in liquid formulations.
For bulk handling, adipic acid dust forms combustible organic dust clouds; equipment should be grounded, and dust extraction should be designed to avoid explosive concentrations. Minimum ignition energy is reported in safety data sheets but varies with particle size and moisture. Storage in silos or closed bags at 10–30 °C prevents caking, and the product is stable under normal conditions. Prolonged heating above 265 °C causes decarboxylation to cyclopentanone and carbon dioxide; this is an operational limit for melt processing and for dryers. In downstream plants where hot-air dryers above 120 °C are used to pre-dry material, stagnant zones must be avoided because local overheating can produce odorous decomposition products and reduce assay.
Compared with other saturated linear dicarboxylic acids used in polycondensation, adipic acid occupies an intermediate position between the shorter-chain succinic acid and the longer-chain azelaic or sebacic acids. The following physical constants are representative values from published safety data sheets and supplier specifications.
| Acid | Chain length | Molar mass (g/mol) | Melting range (°C) | pKa1 | pKa2 |
|---|---|---|---|---|---|
| Succinic acid | C4 | 118.09 | 185–188 | 4.21 | 5.64 |
| Glutaric acid | C5 | 132.12 | 95–99 | 4.32 | 5.42 |
| Adipic acid | C6 | 146.14 | 151–153 | 4.44 | 5.44 |
| Azelaic acid | C9 | 188.22 | 106–108 | 4.54 | 5.52 |
| Sebacic acid | C10 | 202.25 | 131–134 | 4.59 | 5.59 |
Adipic acid differs from succinic acid in crystal packing, reflected in a lower melting range despite higher molecular weight, because the additional methylene units reduce crystal lattice energy. Compared with sebacic acid, adipic acid provides higher ester-group density in polyester polyols, which raises tensile modulus and Shore A hardness under ISO 868, while sebacate systems show lower glass-transition temperatures and better low-temperature flexibility. In polyamide condensation, adipic acid with hexamethylenediamine yields nylon 66, whereas sebacic acid with hexamethylenediamine yields nylon 6,10, which absorbs less moisture and has lower modulus; selection between them is therefore governed by the required balance of mechanical stiffness, water uptake, and low-temperature behaviour rather than by purity considerations alone.
