Two numbers on a drum of potassium octoate are both correct and look like they contradict each other.
The label reads 15% potassium. The drum holds roughly 70% catalyst.
The 15% is potassium metal by weight. The 70% is how much potassium 2-ethylhexanoate salt is actually dissolved in the glycol carrier.
For a rigid polyisocyanurate (PIR) foam formulator sizing a trimerization catalyst, knowing which of those two numbers the dosing math needs is the difference between hitting the isocyanurate target and missing it.
Potassium octoate earns that place through one reaction. It cyclotrimerizes isocyanate groups into isocyanurate rings, and its production route, grade label, and side jobs all follow from that.
What Potassium Octoate Is Chemically
Potassium octoate is potassium 2-ethylhexanoate, the potassium salt of 2-ethylhexanoic acid. Its formula is C8H15KO2, its molar mass 182.3 g/mol, and its CAS number 3164-85-0. In pure form it is a white, colorless solid that dissolves readily in organic solvents and can form a monohydrate.
Potassium octoate belongs to the metal-octoate salt family, the 2-ethylhexanoate salts used across catalysis, drying, and coatings.
The name carries a trap worth catching before you qualify a drum. Two different acids get sold as potassium octoate: the branched 2-ethylhexanoate (CAS 3164-85-0) and the straight-chain octanoate, also called caprylate (CAS 764-71-6).
The PIR catalyst grade is specifically the branched 2-ethylhexanoate. Supplier catalogs blur the two, with one listing 764-71-6, another 3164-85-0, and some vendor sheets calling the product caprylate outright.
Confirm the CAS number, not just the trade name. A grade label is a starting point for qualification, not a substitute for it.
How Potassium Octoate Catalyzes PIR Trimerization
Potassium octoate catalyzes the cyclotrimerization of isocyanate groups. Three isocyanate (-NCO) groups combine into a single, thermally stable isocyanurate ring.
That ring is the structural difference between a polyisocyanurate foam and a straight polyurethane. The isocyanurate network chars instead of melting, which carries PIR’s thermal and fire performance.
How the Trimerization Reaction Works
The potassium carboxylate does the work as a base. It activates an isocyanate group, an intermediate forms, cyclization closes the isocyanurate ring, and the catalyst regenerates for the next cycle.
Reported laboratory loadings sit around 3.2 pphp at an isocyanate index near 500, within a studied range of roughly 0.5 to 6 pphp. Raising the trimerization catalyst is reported to shorten cream, gel, and tack-free times, lift isocyanurate content, and lower thermal conductivity.
Against an amine-type trimerization catalyst, octoate is the slower, milder option. It runs longer cream and gel times and forms coarser cells, but handles more stably and shrugs off moisture better.
How Octoate Compares With Amine and Acetate Catalysts
The amine catalysts in the same formulation do a different job. They drive the gel (urethane) and blow (water-CO2) reactions, while potassium octoate drives the trimerization that builds the isocyanurate ring. A PIR system runs both, at an isocyanate index well above 100.
Where a tin catalyst like stannous octoate pushes the urethane gel reaction, potassium octoate pushes ring formation.
Potassium octoate also rarely works alone. Its usual partner, potassium acetate, is not a competitor but the other trimerization salt in the blend, ratio-tuned rather than swapped.
| Trait | Potassium octoate | Potassium acetate |
|---|---|---|
| Carrier | Diethylene glycol | Water-miscible glycol or alcohol |
| Color added | Yellow-orange | Lower |
| Ring-forming onset | Milder, slower | Higher efficiency (reported) |
Blending lets a formulator dial reactivity between octoate’s later onset and acetate’s faster ring formation without touching anything else in the system. Swapping one for the other in a running formulation changes carrier and color load at once, so re-check the cure profile before you do it.
How Potassium Octoate Is Made and Why It Ships in DEG
Potassium octoate is made by neutralizing 2-ethylhexanoic acid with a potassium base, then diluting the salt in a diethylene glycol (DEG) carrier for catalyst use. The core reaction is a plain acid-base neutralization: 2-ethylhexanoic acid plus potassium hydroxide gives potassium 2-ethylhexanoate and water.
Reference procedures describe adding roughly 50% aqueous KOH to the acid over about two hours, letting the exotherm climb from ambient to near 45 C under cooling. The finished solution carries around 1% water.
The feedstock is the anchor of the whole route. This can be sourced against 2-ethylhexanoic acid (CAS 149-57-5), the same branched C8 acid behind every metal octoate.
Neat potassium octoate is a solid, and a solid is a poor way to meter a catalyst. Dissolving it to a concentrated solution in diethylene glycol gives a pumpable, dust-free liquid that disperses evenly into the polyol side and doses to spec.
The carrier is not inert background in the dosing math. It is most of what sits in the drum.
How to Read a Potassium Octoate Grade Label
The percentage on a potassium octoate grade label is potassium metal by weight, not the amount of catalyst salt in the drum. A grade sold as 15% K in DEG holds about 70% actual potassium 2-ethylhexanoate by weight; the 15% counts only the potassium atoms.
The arithmetic behind that is fixed. Pure potassium 2-ethylhexanoate is only 21.4% potassium by weight, because the 39.1 mass of the potassium atom is a small share of the 182.3 molar mass. A solution assaying 15% potassium therefore carries about 70% salt, the balance being the DEG carrier.
Umicore states its VALIREX K 15 DEG grade at 71 wt% concentration, and PIR literature describes commercial octoate as a roughly 70% solution in diethylene glycol. The computed figure and the datasheet agree.
| Марка | K metal | Carrier | Вязкость | Вода |
|---|---|---|---|---|
| VALIREX K 15 DEG (Umicore) | 15% | DEG | ~5000 mPa.s, RT | 4% |
| 15% Potassium Hex-Cem (Borchers) | 14.9-15.2% | DEG | 3000-6000 mPa.s, 20 C | 3.0-4.5% |
The two brands list the same 15% K in DEG grade through different test standards, which is why their viscosity windows do not line up.
For dosing, the 70% salt figure is the number that governs the calculation. Size the catalyst on potassium 2-ethylhexanoate content, and a grade change that holds 15% K while shifting carrier or water spec will not surprise your cream time.
Be wary of vendor tables quoting 18 to 22% active potassium. Those describe a salt-content grade, not the 15% metal-assay datasheet, and mixing the two conventions is exactly how a dosing number goes wrong. The COA number you dose against is the salt content, not the metal assay printed on the drum.
Where Potassium Octoate Is Used Beyond PIR Foam
Potassium octoate has two roles outside PIR foam. It works as a co-accelerator in unsaturated polyester gelcoats and as a corrosion-inhibitor component in some coolant packages.
Co-Accelerator in Polyester Gelcoats
In unsaturated polyester resins and gelcoats, potassium octoate works as a co-catalyst that boosts cobalt performance and cuts the color the cured composite picks up. It lets the cobalt octoate drier reach the same cure at a lower cobalt level. Cobalt in these systems typically runs 0.005 to 0.020% as metal.
A reformulation trend runs alongside this role. Umicore now offers 2-EHA-free potassium grades, its VALIKAT K line, introduced to address toxicity concerns around 2-ethylhexanoic acid and its metal salts while keeping the same cobalt-boost and color-reduction function.
Corrosion Inhibitor in Coolants
Potassium 2-ethylhexanoate also appears in some antifreeze and coolant formulations as a corrosion inhibitor, where the carboxylate protects metal surfaces rather than catalyzing a reaction. That role is chemically unrelated to trimerization, and it should not drive a grade choice made for PIR foam.
What This Means for Your Formulation
Buy potassium octoate on two numbers, not one. The CAS 3164-85-0 confirms you have the branched 2-ethylhexanoate that actually catalyzes trimerization, and the salt content behind the metal assay is what your dosing keys on.
The trimerization job is the whole reason the drum exists. The isocyanurate ring it builds is what earns PIR its char and fire performance, and the DEG carrier, the 15% label, and the gelcoat crossover all follow from that one reaction.
Read the grade right and potassium octoate stops being a mystery liquid. It becomes a spec you can qualify, substitute, and defend.