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A World of Sulfur

Published by
World Fertilizer,

AK Tyagi, Nuberg EPC, India, takes a detailed look at the production of sulfur and provides a case study on a plant installation in Egypt.

Sulfuric acid is one of the most important mineral acids that has a lot of applications in the chemical industry. It is a viscous liquid that is colourless, odourless, and soluble in water. Its solubility in water releases a lot of heat in a reaction that is highly exothermic. Sulfuric acid occurs naturally as sulfide minerals in rocks. However, dilute forms of sulfuric acids occurs naturally in the atmosphere following the oxidation of sulfur dioxide in the presence of atmospheric moisture. Following the huge applications of sulfuric acid, it is required in huge quantities. Hence, sulfuric acid is manufactured commercially by the reaction of sulfur trioxide in the presence of water in a process known as the contact process. Generally, the processes involved in the manufacture of sulfuric acid have undergone a series of evolutions. In the 18th century, the contact process was developed by Rudolf Messel and Peregrine Phillips. Initially, the process utilised a more expensive platinum metal as a catalyst. However, it was then replaced by a much cheaper vanadium oxide catalyst which is still in use today. Currently, it is not out of place to say that there is a positive correlation between the level of a nation’s development and its demand for sulfuric acid; several countries are keying into this.

Global production and market overview of sulfuric acid

The sole time the demand for sulfuric acid witnessed a dive was during the global economic crisis in 2009. However, there was an upward trend between 2010 and 2012. Currently, the global production of sulfuric acid stands at more than 270 million t and this figure is expected to increase. So far, there are five countries that rank as the leading producers of this chemical. Leading the chart is China, whose production output stands at more than 74 million t. The US sits second with more than 37 million t, India produces 16 million t, Russia accounts for 14 million t, and Morocco produces 7 million t of the world output. Generally, these five countries account for approximately 61.5% of the global production of sulfuric acid. Currently, the fertilizer industry consumes more than 55% of the world output. At this rate, there is no doubt that the need for sulfuric acid cannot be overemphasised. In 2016, the global sulfuric market was valued at US$10.1 billion. It is estimated that this figure will reach US$15 billion by 2025. Likewise, it is anticipated that the global demand is rising exponentially, while there is a need for an increase in production to meet this demand.

Grades of sulfuric acid

It is practically impossible to get 100% sulfuric acid, therefore, depending on the method of production, there are several grades of sulfuric acid. In most cases, the concentration of sulfuric acid produced is usually 98% following the loss of sulfur trioxide during the production process. This is the most stable form of sulfuric acid. Other grades include the following:

  • 10% sulfuric acid (dilute sulfuric acid).
  • 29 – 32% sulfuric acid.
  • 62 – 70% (chamber acid/fertilizer acid).
  • 78 – 80% (tower or glover acid).
  • 98% (concentrated sulfuric acid).

    Sulfuric acid production in India

    India is one of the major producers of sulfuric acid in the world. As already mentioned, there is a positive correlation between the level of consumption of sulfuric acid in a country and its per capita income. So far, India utilises the majority of its sulfuric acid in the production of fertilizers. The process involves the acidulation of rock phosphates, as well as the production of ammonium sulfate. Other industrial applications include petroleum refining, steelworks, and other inorganic chemicals. Currently, there are more than 65 sulfuric acid plants spread across India. The major raw materials used in the manufacture of sulfuric acid include elemental sulfur, hydrogen sulfide, pyrites, etc. Nearly all factories in India rely heavily on elemental sulfur as the major source of raw material.

    Production of sulfuric acid

    There have been evolutions in the methods for the production of sulfuric acid, however, there are two major processes for its commercial production. There is the lead chamber process and the contact process. Irrespective of the difference in the processes, the manufacture of sulfuric acid is generally based on the following principles:

    • The extraction of pure elemental sulfur from its ore.
    • The conversion of elemental sulfur into sulfur dioxide in the presence of oxygen.
    • The conversion of sulfur dioxide into sulfur trioxide.
    • The conversion of sulfur trioxide into sulfuric acid.

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