Potassium Hydroxide (KOH)

About This Product

Potassium hydroxide, KOH, caustic potash, CAS number 1310-58-3, is supplied as white flakes or pellets at 90 percent minimum, which is the standard commercial strength. The balance is largely water, and the assay is quoted on that basis rather than treated as an impurity. A biodiesel plant can catalyse transesterification with either sodium or potassium hydroxide, and the choice is usually made on what happens downstream rather than in the reactor. KOH dissolves in methanol faster and more completely than NaOH, which matters when methoxide is made up batchwise, and its soaps and salts are more soluble, so the glycerine phase separates cleanly and lines are less prone to blocking with precipitated sodium salts. The crude glycerine it leaves carries potassium rather than sodium, and potassium salts, after acidulation largely potassium sulfate or phosphate, are a saleable fertiliser where the sodium equivalent is a disposal problem. Set against that, KOH costs more per tonne and has a higher molar mass, so a plant needs roughly 1.4 times the weight of NaOH for the same molar catalyst charge. Feedstock free fatty acid content still governs everything: above about 2 percent FFA, base catalysis saponifies rather than transesterifies, and an acid pre-esterification step is needed whichever hydroxide is used. It is used to make potassium methoxide for biodiesel transesterification, to neutralise free fatty acids in feedstock pretreatment, for pH control in washing and effluent, and in the potassium-salt fertiliser route for crude glycerine. Bio Green Fuels supplies potassium hydroxide at 90 percent minimum as white flakes or pellets in 25 kg bags or jumbo bags. It is UN 1813, Class 8, corrosive to skin and eyes, and releases heat on dissolution; handle to the safety data sheet.