Production of Chemicals
- Ammonia and Urea Production (PDF 55 kb)
Urea (NH2CONH2) is of great importance to the agriculture industry as a nitrogen-rich fertiliser. In Kapuni natural gas field in Taranaki, Petrochem manufacture ammonia and convert the majority of it into urea. The remainder is sold for industrial use.
This article describes the synthesis of ammonia from natural gas and air, and the synthesis of urea from this ammonia and carbon dioxide at Kapuni, Taranaki. The urea solution is then concentrated to give 99.6% by wieight of molten urea, and granulated for use as fertiliser and chemical feedstock.
- The Manufacture of Sulfuric
Acid and Superphosphate (PDF 132 kb)
This article describes the manufacture of sulfuric acid from sulfur, and the production of superphosphate by reacting it with insoluble phosphate rock.
Superphosphate is the fertiliser most commonly used in New Zealand to ensure that soil has a sufficiently high phosphorous content. It is manufactured from the reaction between sulfuric acid and 'phosphate rock' (rock rich in the mineral fluorapatite, Ca5(PO4)3F).
- Hydrofluorosilicic acid
and Water Fluoridation (PDF 54 kb)
This article describes how silicon tetrafluoride is obtained as a by-product of superphosphate manufacture and converted into hydrofluorosilicic acid for water fluoridation.
Water fluoridation is an important preventative measure carried out in much of the western world. It results in some of the hydroxyapatite, Ca5(PO4)3OH, of which human tooth enamel is made being replaced by fluoroapatite, Ca5(PO4)3F - a substance significantly more resistant to decay.
To protect the teeth of the population, water is often fluoridated. This is usually done with one of three fluorine-containing chemicals (sodium fluoride, sodium fluorosilicate and hydrofluorosilicic acid), but this article focuses on hydrofluorosilicic acid as that is the chemical most commonly used in New Zealand for this purpose.
Hydrofluorosilicic acid manufacture can be viewed as a two-step process, although in reality it is carried out in four steps to ensure that the right concentration of acid is obtained.
- Oxygen - Pressure Swing
Adsorption (PDF 34 kb)
Oxygen needs to be produced in large volumes for many applications. Perhaps the commonest of these are in medicine and in the pulp and paper industry. There are two methods used for doing this: cryogenic and pressure swing adsorption.
Pressure swing adsorption, which is outlined in this article, is most useful for small applications such as oxygen production in the home for asthma sufferers. This article describes how oxygen is obtained from air by passing the air over a zeolite which adsorbs the nitrogen.
- The Manufacture of Hydrogen
Peroxide (PDF 33 kb)
This article describes the production of hydrogen peroxide from dioxygen and dihydrogen using an anthroquinone as a carrier for the hydrogen.
Hydrogen peroxide (H2O2) is a weakly acidic, colourless liquid, miscible with water in all proportions. It is the simplest peroxide (molecules containing two oxygen atoms covalently bonded to one another) and is commercially available in aqueous solution over a wide concentration range.
The main uses of hydrogen peroxide are in the preparation of other peroxides and as an oxidising agent.
The manufacturing process involves the catalysis of the reaction of H2 (obtained from processing Maui Gas) with atmospheric O2 to give H2O2. Anthraquinone (Q) is used as an H2 carrier.
- The Manufacture of Aluminium
Sulfate (PDF 57 kb)
This article describes the manufacture of aluminium sulfate, alum, for use in the paper industry and in water purification.
Aluminium sulfate, Al2(SO4)3, is widely used by industry in New Zealand . Its most common applications are in the pulp and paper industry and in the purification of water.
In both these instances alum is used as a source of Al3+, a highly charged ionic species. Negative particles, such as those which discolour our raw water supplies, are attracted to this cation, react with it and then precipitate out of solution as ionic solids.
- Soluble Sodium Silicate
Manufacture (PDF 26 kb)
This article describes the manufacture of soluble sodium silicates, water glass, for uses in the paper and detergent industries.
Soluble sodium silicates (waterglass) are liquids containing dissolved glass which have some water like properties. They are widely used in industry as sealants, binders, deflocculants, emulsifiers and buffers.
Their most common applications in New Zealand are in the pulp and paper industry (where they improve the brightness and efficiency of peroxide bleaching) and the detergent industry, in which they improve the action of the detergent and lower the viscosity of liquid soaps etc. Sodium silicates are produced in a two or three step process, depending on the desired end products of the waterglass.
- The Salt Recovery Process (PDF 79 kb)
This article describes the production of salt from sea water at Lake Grassmere in Marlborough and the purification of the sodium chloride at Mt Maunganui.
Much of New Zealand 's salt needs are provided for from salt purified from the sea at Lake Grassmere, some of which is further refined at Mt. Maunganui . This salt has many uses in industry and agriculture, as well as being used for water softening, in the production of pharmaceuticals and other chemicals, and of course in food.
In New Zealand salt is initially purified by the solar process, and then is sometimes further purified by the vacuum process for applications where a high purity is required.
- Chromium Sulfate Tanning
Powder (PDF 50 kb)
This article describes the production of chromium(III) sulfate by reduction of sodium dichromate by sulfur dioxide. It is used in the tanning of leather.
Chromium sulfate is the most important ingredient used in the tanning of leather, and hence is of great significance to New Zealand . It is manufactured from the simple reduction of
Cr(VI) to Cr(III) by the addition of an excess of sulphur dioxide
Na2Cr2O7 + 3SO2 + H2O --> Cr2(SO4)2(OH)2 + Na2SO4
This reaction is carried out in a steam-heated vessel, and then the excess SO2 is removed in a second reaction tower. Finally, the liquid product is spray-dried to form a powder which is then bagged and sold.
- The Production of Phenoxy
Herbicides (PDF 79 kb)
This article describes the manufacture of phenoxy herbicides in New Plymouth by Dow Agrosciences up to 1988 when production was discontinued because of environmental concerns.
Phenoxy herbicides were of great significance in New Zealand because of their strength and selectivity. They include a group of herbicides consisting of a benzyl ether, of which the best known are 2,4,5-T and 2,4-D. This article focuses on 2,4-D and the herbicide formulations made from it.
- Industrial Gases (PDF
This article describes the production of acetylene (from calcium carbide), hydrogen (by electrolysis of water), carbon dioxide (from Kapuni natural gas), and nitrogen, oxygen and argon (from air) by fractional distillation.