Chlorine is one of the most abundant naturally occurring chemical elements, playing an important and significant role in the manufacturing of thousands of products we depend on every day.
A pale green gas at normal temperature and pressure, chlorine is highly reactive and not found as a gas in nature. Instead, it appears as naturally occurring organochlorine compounds and salts.
Liquid chlorine is a clear amber-coloured mobile fluid and about one-and-one-half times the weight of water.
It evaporates extremely rapidly when spilled, one volume of liquid forming 460 volumes of gas and as a result, a liquid chlorine leak may be extremely hazardous as the quantity of chlorine given out is many times greater than that from a gaseous leak.
There are more than 2,000 naturally-occurring chlorine-based compounds. For more than 100 years now, industry has exploited this highly-reactive chemical produced from one of nature’s most plentiful and inexhaustible minerals – common salt.
Today, chlorine is used in a vast range of processes to create thousands of often indispensable products that serve our everyday needs at work, home and play.
More than 95% of world chlorine production is achieved using the chlor-alkali process. This process applies a direct electric current to a brine (water and salt) solution to produce chlorine and hydrogen gas and sodium hydroxide, or caustic soda solution.
Chlorine is produced and collected at the negatively charged electrode, cathode and hydrogen and caustic soda are produced and collected at the anode.
There are three main electrolytic production technologies used in the chlor-alkali industry – the diaphragm cell, mercury cell and membrane cell. Each technology incorporates a different way of keeping chlorine separated from hydrogen and caustic soda.
Globally in 2005, the Chlor-Alkali industry met a demand of more than 49 million tonnes of chlorine, with China representing 22% of that global demand.
The industry is operating at approximately 88% of capacity, but that will increase in the coming years as new demand is expected to exceed new capacity.
In Europe, chlorine production climbed to a new high in 2007 with a total of 10.7 million tonnes. This represents a 2.9% increase on the 10.4 million tonnes produced in 2006. Capacity utilisation rates in 2007 averaged 84.5% compared with 82.8% in 2006.
Germany remained Europe’s largest chlorine producer in 2007, accounting for 43.5% of European production, followed by Belgium/The Netherlands with 14.4%. France dropped to fourth position with 11.4%, surrendering its third-placed position to the UK/ Austria /Switzerland /Finland /Sweden/Norway with 12.3%.
Together these top four regions are thought to have accounted for more than 80% of total 2007 European chlorine production (Figure 2).
Production cost of chlorine is dependent on energy prices and most producers have passed these escalating costs onto the consumers, however with recent dropping in fuel prices, costs are likely to be moderated to some extent.
Natural gas is the prime fuel used to generate electricity for chlor-alkali cells, and electricity is the largest single cost component in chlorine production. Electricity accounts for 56% of the manufacturing costs of a typical diaphragm plant when gas rates are $5.5 million/Btu.
Applications – A world of uses
Although we may not realise it, chlorine is one of the most important building blocks of modern industry. Whether present in the final product, or used in an intermediate process and absent from the final product, chlorine is essential to producing countless items that we rely on everyday without a passing thought.
It is used in the manufacture of many different products including polyvinyl chloride (PVC), organic and inorganic chemicals, agrochemicals and pharmaceuticals, as well as chemicals crucial for our essential water treatment and sterilisation processes.
The main end-use product of chlorine is PVC, via the intermediates ethylene dichloride (EDC) and vinyl chloride monomer (VCM). PVC consumption is mainly influenced by the construction industry and hence, demand correlates closely with economic growth.
Chlorinated organic chemicals account for a large proportion of chlorine demand, but this sector has in fact seen slow or negative growth in many regions. One exception is phosgene which has been growing due to the increased production of polycarbonates and isocyanates used in polyurethanes.
In the inorganic chemicals category, chlorine is used in the manufacture of many diverse chemicals such as titanium dioxide, sodium and calcium hypochlorites and hydrogen chloride.
About 85% of all pharmaceuticals contain, or are manufactured, using chlorine, while it is also involved in the production of over 95% of crop protection chemicals.
Chlorine molecule is present in Dow Biocides that are used to prevent the spread of Bird Flu and generally, chlorine is involved in over 50% of all commercial chemistry, even if it is not present in the final molecule.
Health and safety
The health effects resulting from most chlorine exposures begin within seconds to minutes. The severity of the signs and symptoms caused by chlorine will vary according to amount, route and duration of exposure.
Most chlorine exposures occur via inhalation. Low level exposures to chlorine in air will cause eye/skin/airway irritation, sore throat and cough.
Chlorine’s odour provides adequate early warning of its presence, but also causes olfactory fatigue or adaptation, reducing awareness of one’s prolonged exposure at low concentrations. At higher levels of exposure, signs and symptoms may progress to chest tightness, wheezing, dyspnea, and bronchospasm.
Severe exposures may result in noncardiogenic pulmonary edema, which may be delayed for several hours.
Asia would appear to be the main demand driver in the medium term as its growth demand is expected to be strong as a result of China & India. The main growth is from the vinyl’s sector where the construction of acetylene-based PVC plants has fuelled growth of the local chlor-alkali industry.
Chlorine capacity in Northeast Asia is expected to double from 15 million tonnes in 2001 to 31 million tonnes by 2011. In the same period, China will raise its share of chlorine capacity from 53% to almost three-quarters of total Northeast Asian capacity.
China’s chlorine demand grew at more than its GDP which averaged 10% per year from 2001 to 2006. However, China’s chlorine demand is expected to moderate towards the end of the decade as the global economy slows down.