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Pumping Potassium hydroxide-caustic potash

Potassium hydroxide, aka ‘Caustic Potash’ is a strongly alkaline base that is commonly supplied in pellet form. The pellets are readily dissolved in water, producing a strong exothermic reaction. Similar in characteristics to sodium hydroxide, potassium hydroxide is used in similar industries, however in different applications, mainly due to the cost and solubility.

Potassium hydroxide is very corrosive and damaging to human tissue and respiratory tract.

Applications

  • Potassium hydroxide is used primarily as a precursor to potassium salt compounds such as in the production of potassium phosphate, used in fertilizers.
  • For soaps and hair removal products - Potassium hydroxide is favoured in the production of ‘soft’ soaps.
  • Manufacture of biodiesel
  • In the production of alkaline batteries, potassium hydroxide is preferred as an electrolyte as the potassium solution is more conductive than that of sodium hydroxide.
  • Used in refineries as a caustic treatment to react with organic acids and sulphur compounds to improve the colour and odour of petroleum

Pumping considerations

Potassium hydroxide has many of the same characteristics as sodium hydroxide. Certainly they are both strongly caustic and corrosive and must be controlled in close proximity to the workforce and equipment.

The S.G. can vary greatly as the concentration increases; from 1 at 1% to 1.5 at 50%. Molten potassium hydroxide has a fairly high freezing point and should the process line be in an exposed area and the fluid sit in the pump for a length of time, it may freeze. Handling the fluid at a higher temperature can increase the corrosive nature of potassium hydroxide exponentially.

Residue will crystallize when exposed to the air.

It is strongly recommended to use a leak-free pumping solution, such as a mag drive centrifugal pump. The Verdermag range of pumps has been used to handle potassium hydroxide. The pump is highly suited to pumping caustic solutions as it will not leak. The mag drive working principle eliminates the need for mechanical seals so there is no abrasive wear from a working part on a containment seal. This has several benefits for the process: No risk of leakage associated with mechanical seals so there is no downtime, risk to employees, clean-up costs and documentation of a ‘release to atmosphere’.

Both metallic and non-metallic models can be specified, depending on the concentration and temperature. SS316L and 304L steel alloys are chemically resistant at ambient; however as the temperature increases it is advisable to specify either Hastelloy if a metallic material is required, or ideally an ETFE/PTFE lined pump. PTFE or Viton o-rings are recommended, natural rubber and Buna-N are acceptable.

Avoid aluminium, copper, brass and bronze based alloys as this will react with potassium hydroxide to liberate hydrogen gas into the system.

In higher concentrations, the impeller will require trimming to accommodate the higher S.G.

Where a more flexible solution is required, or compressed air is preferred, a double diaphragm pump is an ideal solution. With a wide range of compatible materials, an air diaphragm pump provides exceptional chemical resistance with the robust pumping method required in some premises, particularly when emptying smaller containers. 

AODD pumps are available in 100% pure virgin PTFE/PE construction for pumping hazardous fluids such as potassium hydroxide, particularly at higher temperatures. 

For the dosing of potassium hydroxide, a peristaltic pump can provide accurate flows at proportional or constant rates. It is recommended specifying an EPDM hose and either high grade stainless steel flanges or PP inserts.