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EghtesadOnline: Caustic soda, or sodium hydroxide, is one of the most important chemicals manufactured. Sodium hydroxide, also known as Caustic Soda is a highly caustic metallic base. It is a white solid available in pellets, flakes, granules, and as a 50% saturated solution. Sodium hydroxide is soluble in water, ethanol and methanol. This alkali is deliquescent and readily absorbs moisture and carbon dioxide in air.

Caustic is consumed in large quantities in the manufacture of:

• Rayon

• Explosives

• Soap

• Paper

• Petroleum Refining

Caustic soda flakes is the strongest alkali and it is commonly produced in various grades of purity. Much of the total production of high grade caustic soda utilized by rayon industry and also textile industry for mercerization of cotton, bleaching and dyeing processes.

Caustic soda is one of the main products from soda ash and is frequently made in the soda ash plant.

1. Chemical: Lime Soda Process

2. Electrochemical: Chloro Alkali Process

  • Mercury Cell Process
  • Diaphragm Cell Process
  • Membrane Cell Process


Chemical Process: Lime Soda Process


• Previously made by Causticization of soda ash with lime

• Na2CO3 + Ca(OH)2 → 2 NaOH + CaCO3

• Only 10% NaOH solution obtained

Lime Soda Process

• Fresh lime, make-up lime is fed along with some of the soda ash solution to a combination

classifier-slaker. Milk of lime is formed.

• Grit is removed from the slurry by the classifier.

• The soda solution is causticized with a slight excess of lime in three agitators in series.

• The sludge in the bottom of the first thickener is pumped with a diaphragm pump to the second


• In 2nd thickner, filtrate and water are added. The overflow from this thickener is used as a weak liquor to make up the original soda solution.

• The sludge from the second thickener is filtered on and washed.

• The filtrate is returned to the second thickener.

• The cake is calcined in the limekiln.


Caustic Soda Market

Caustic soda is also the only commodity chemical whose price can swing by a factor of fifteen on the spot market - from $30 to $500 per ton. Even late last year it was as low as $80 recovering just a few months later to $200. To buy caustic soda you should consider it is a product that whilst not directly influenced by environmental issues, is closely linked however to the outlook for chlorine which is sensitive to the environmental debate. However its importance is not so much the demand for caustic in Asia, but the influence it has on the trade in chlorine chemicals by caustic soda suppliers, notably EDC, VCM and PVC. The imbalance in demand creates an opportunity for an Australian chloralkali producer using competitive energy. Caustic soda is co-produced with chlorine by electrolysis in the ratio of 1.1 tonnes of caustic soda for every 1.0 tonne of chlorine. More than 95 per cent of all chloralkali production is based on the electrolysis of brine using one of three types of technology. In Europe, typical of an industrialised region, about 60 per cent of production is by the mercury cell, about 30 per cent by the diaphragm cell 10 per cent by the newer membrane technology cell. Worldwide the membrane cell technology represents about 20 per cent of production and nearly all new investment in chloralkali production. There are some 500 major chloralkali producers worldwide with a nameplate capacity of 45 million tonnes of caustic of which one-third is produced by theUnited States as a competitive centre.


Of the 42 million tonnes per year of caustic soda produced, 16 per cent or 7 million tonnes per year is traded, of which 80 per cent is from the USA and Europe. Around 94 per cent of trade is in the liquid form - typically 50 per cent solid. Of the liquid trade, some 2 million tonnes per year is through deep sea ports and 5 million tonnes per year across borders. Nearly all the deep sea transport of caustic is for the alumina industries.


The solid form of caustic soda typically attracts a premium of between $100 per tonne and $200 per tonne over the liquid form (dry basis). The markets for the solid form are principally developing countries with infrastructure inadequate to handle the more difficult liquid. With improving infrastructure, the larger markets such as China and the CIS are shrinking leaving Algeria, Cuba and Africa as major destinations for solid caustic. Indonesia is now the only major user in Asia.

Being more expensive, world trade in the solid form of caustic is only about 400 000 tonnes per year and declining by around 8 per cent per year. About 225 000 tonnes, representing one-half the trade in the solid form, is supplied by Europe with the balance by Latin America, South Africa and India.


For the very large liquid caustic soda market, trade is predominantly for the production of alumina most notably for Australia, which takes nearly one-half of deep sea trade, but also for Brazil, Venezuela, Surinam, Jamaica and Guinea. Other large importers, reflecting regional chloralkali imbalances, are Korea and Colombia.


As a generalisation, the Asian market is unable to absorb all the caustic soda it could produce to be self sufficient in chlorine. It has to import chlorine chemicals with a deficiency that is growing. Accordingly, many Asian countries are exporters of caustic with higher power costs in a sense partly offset by the need for chlorine chemicals, notably PVC. Relatively high power costs restrain caustic exports to modest levels and generally at below home market levels to be competitive against the lower cost US and Saudi Arabian producers.

The single largest destination for caustic soda trade is Australia that requires 1 million tonnes per year for its alumina industry. Currently supplied by Japan, Saudi Arabia, Europe and the USA, Australia will therefore be the major target, for any new producer in Asia. If a new chloralkali plant is established, it could influence the world market and trade in caustic and chlorine.


methanol carbon dioxide SODA