Hydrochloric Acid Manufacture
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Hydrochloric Acid manufacture began as far back as the Middle Ages when it was used by alchemists who were searching for the philosopher's stone, which was a mythical substance of great legend supposedly able to turn ordinary metal into gold.
Later, Eurpoean scientists used Hydrochlorioc Acid in their research but it was not until the Industrial Revolution that Hydrochloric Acid manufacture developed into large-scale production. Today, Hydrochloric Acid manufacture can be used as a measure of the industrial development of a nation, with the more industrialised countries producing greater volumes of Hydrochloric Acid than those countries with little or no industrialisation. Globally, the annual Hydrochloric Acid manufacture stands at over 20 million tonnes.
In its purest form Hydrochloric Acid is a gas but when Hydrogen Chloride is mixed with water, it forms the solution which is commonly known as Hydrochloric Acid, Muriatic Acid or HCl. The word 'Muriatic' means 'pertaining to brine' and this reflects the origins of Hydrochloric Acid manufacture when it was first produced by mixing common Salt with Vitriol (Sulphuric Acid) to produce Hydrochloric Acid.
In its strongest form, a prefix of 'fuming' is often used, to produce Fuming Hydrochloric Acid, Fuming Muriatic Acid and Fuming HCl, the word 'fuming' referring to the white fumes which are apparent in strong concentrations of the product. Essentially, however, all these materials are the same product with simply a variation in concentration. Fuming Hydrochloric Acid is a concentration of between 36% and 40%. Production above 40% is not realistic as the product evaporates. More dilute solutions can be obtained by mixing Hydrochloric Acid with water to produce concentrations to the desired strength.
Hydrochloric Acid is generally referred to as HCl but this is actually the formula for Hydrogen Chloride, a colourless gas at room temperature. When exposed to the atmosphere it produces white fumes of Hydrochloric Acid, due to moisture in the air.
Solutions of Hydrochloric Acid are manufactured by dissolving the Hydrogen Chloride in water. Several methods of generating Hydrogen Chloride are available and large scale production is usually connected to manufacture of other chemicals.
Commercially, Hydrochloric Acid solutions are produced up to approximately 38%, above this the evaporation rate is very high meaning that extra storage precautions are needed. The majority of Hydrogen Chloride gas produced is used for Hydrochloric Acid production.
The various methods of manufacture include:-
Direct Synthesis
This process is carried out in an HCl oven or HCl burner which firstly involves electrolysing brine (a solution of Sodium Chloride in water) to produce Chlorine Cl2, Sodium Hydroxide and Hydrogen. Secondly, the Chlorine and Hydrogen are reacted to produce Hydrogen Chloride,
Cl2 + H2 = 2HCl
Organic Synthesis
The majority of Hydrochloric Acid production is linked to the manufacture of chlorinated or fluorinated organic compounds. Chlorine gas is reacted with the organic compound which results in a Hydrogen atom being replaced by a Chlorine. This Hydrogen then reacts with the other Chlorine atom from the Cl2 molecule to form HCl,
R - H + Cl2 = R - Cl + HCl
The Hydrogen Chloride can either be captured and re-used in the process or dissolved in water to produce Hydrochloric Acid solution. The process can be summarised as follows:-
After leaving the chlorination process, a gas stream including HCl, passes into an absorption column where the HCl is absorbed into a weak solutionof Hydrochloric Acid. Chlorination gases now removed of HCl can be re-used in the process. The gas stream continues to a final scrubber which removes any remaining HCl before venting to the atmosphere.
Laboratory Methods
Sulphuric Acid can be reacted with Sodium Chloride.
2NaCl + H2SO4 = Na2SO4 + 2HCl
Chloride compounds are also hydrolysed by the addition of water to produce Hydrogen Chloride gas which is converted to Hydrochloric Acid on addition of more water, e.g. Phosphorous Pentachloride.
PCl5 + H2O = POCl3 + 2HCl
Hydrochloric Acid solutions can be dehydrated with Sulphuric Acid or Anhydrous Calcium Chloride to produce Hydrogen Chloride gas. The apparatus is called a HCl generator.
Thermal Decomposition
Hydrated metal chlorides produced from metal treatment processes can undergo thermal decomposition to produce HCl.
2FeCl3 + 6H2O = Fe2O3 + 3H2O + 6HCl
Incineration Process
This involves combustion of chlorinated organic waste, for example
C4H6Cl2 + 5O2 = 4CO2 + 2H2O + 2HCl
Hydrochloric Acid is used in a whole variety of industrial processes from food manufacturing, PVC production and steel manufacturing. It is used in the preparation of food and for the canning process and is also used to make corn syrup for soft drinks. The steel industry uses Hydrochloric Acid to remove rust from metal, a process known as 'pickling'. Hydrochloric Acid can be found in dilute form in many household cleaning products, from drain cleaner to over cleaner. Hydrochloric Acid is also used for swimming pool maintenance.
In all concentrations, Hydrochloric Acid carries potential risks and care should be taken when handling or working with the product. Personal Protective Equipment (PPE) should always be worn and full details of requirements can be found under the relevant Hydrochloric Acid Safety and Hydrochloric Acid Hazards pages of this website.
Government legislation controls the way in which Hydrochloric Acid is packed, labelled and transported and again, full details of these requirements can be found on the pages entitled Hydrochloric Acid packaging, Hydrochloric Acid Labelling and Transporting Hydrochloric Acid.
http://www.hydrochloric-acid.co.uk/hydrochloric-acid-manufacture | Saved Friday, February 12th, 2010 - 5:46 AM