In a chemical industry full of amazing materials, one of the most underrated is potassium hydroxide (KOH).
Also called lye or caustic potash, potassium hydroxide is considered to be a very basic chemical. It is typically white, water soluble, odourless, corrosive to metals, non-combustible, with a pH of 13.5, and is usually supplied in the form of powder, pellets, or flakes.
So far, so unspectacular.
But what gives KOH its true worth is that is a staple industrial chemical for the manufacture of so many different products.
KOH is used in the manufacture of soap, biodiesel, textiles, batteries, fuel cells, paints, cleaners, and much more. In fact, there are few rooms in the world where potassium hydroxide has not been involved.
But what exactly is potassium hydroxide and what makes it so useful?
Potassium hydroxide is typically formed electrolytically from potassium chloride (2KCl + 2H2O → 2KOH + Cl2↑ + H2↑). It is a deliquescent/hygroscopic solid (in that it extracts moisture from the air), but it becomes a very versatile product when applied to the manufacture of chemicals, such as cleaning products or petroleum refining. For example, it is widely used to purify gas by helping to remove sulfur compounds.
It is a highly sought-after chemical product largely because it is such a strong alkali. This means that when it is placed in an acidic solution potassium hydroxide adds hydroxide ions (OH–), takes up the hydrogen ions (H+) through deprotonation and, consequently, regulates pH. It is a chemical reaction which, as the American National Standards Institute (ANSI) explains, “… benefits industrial manufacturing and processing …” Noting that in, “agriculture it can help with raising the pH of acidic soils, and [in] the water industry … it is ideal to secure a neutral pH for potable and other clean water supplies.”
Additionally, potassium hydroxide is also a precursor to other potassium compounds, and can be used in food to adjust pH, as a stabilizer, and as a thickening agent.
It has a major use in the production of paint and varnish removers, and is also used in electroplating, lithography, and also as an electrolyte in alkaline batteries.
Liquid drain cleaners can contain as much as 36% potassium hydroxide.
In fact, perhaps its largest function is the role it plays in the production of soap.
Potassium Hydroxide for Use in the Industrial Manufacture of Soap
Potassium hydroxide is an excellent raw material for making soap. However, to do so it must be combined with surfactants and other sources of alkalinity before being dissolved in water. This highly alkaline solution (or solid) is able to remove a multitude of contaminants from a wide variety of surfaces.
It does this by lowering the surface tension of the solution and separating the contaminants from the surface to form an emulsion. At this point, because the surfactants are soluble in water (hydrophilic) as well as soluble in oil (hydrophobic), they create an oil-water emulsion that is easily rinsed away.
Manufacturers have to be wary however, as the cleaning power of potassium hydroxide is so effective. Consequently, its concentration in any cleaning product should be varied according to the surface being cleaned.
For example, steel, cast iron, and stainless-steel surfaces can handle concentrations of KOH that are much higher than would be recommended for relatively ‘soft’ alloy surfaces, such as brass, copper, and aluminium.
Inside of a chemical industry worth $5 trillion per year, the benefits and practical uses of a basic chemical like potassium hydroxide are largely overlooked. However, to live a world without it would be to live with inferior batteries, a less efficient petroleum industry, less colourful textiles, lower crop production, and less flavoursome food.
And, as a major input chemical in the production of soap, without KOH the world would simply be a much dirtier place.