Avoids use of corrosive chemicals
nylon production generates large quantities of corrosive by-products. Now, a team of two British scientists has developed an environment friendly method to make caprolactam, which is the precursor of nylon.
An important textile and industrial fibre, nylon is a polymer (chain) of caprolactam and is used to make a variety of products including automative parts, sporting goods and packaging materials. Its current global demand is estimated at 4 million tonnes.
Conventionally, caprolactam is synthesised through a complex process from an organic compound called cyclohexanone, which is converted into its corresponding oxime, followed by a molecular rearrangement. The method has one major drawback: it produces immense quantities of unwanted ammonium sulphate -- as much as 2.3 kilogramme for every kg of caprolactam. Ammonium sulphate is used as a fertiliser in sulphur-deficient soils, but it has a small market. The nylon-manufacturing process also entails use of highly active reagents, such as sulphuric acid, that are highly corrosive.
The new process of producing caprolactam developed by John Meurig Thomas from the department of materials science and Robert Raja from the department of chemistry of the University of Cambridge is far simpler and does not require use of corrosive chemicals. An offshoot of the team's 15-year-long research in solid-state chemistry, the method uses a cleverly designed catalyst with tiny pores to produce caprolactam from a reaction between ammonia and air at a temperature of 80 degree Celsius. The method is described in the September 27, 2005 issue of the Proceedings of the National Academy of Sciences (Vol 102, No 39) .
The peculiarity of the catalyst -- aluminophosphate -- is that it can simultaneously hasten two types of chemical reactions, one independent of the other, occurring at two different types of sites. One set of sites is created by replacing some aluminium molecules with cobalt, manganese or iron molecules, and the other by replacing some phosphate molecules by either silicon or magnesium molecules. The former set of sites helps generate hydroxylamine from ammonia and air. Subsequently, hydroxylamine is mixed with cyclohexanone to form the intermediate oxime. It's here the second set of sites come into play, aiding oxime molecules to rearrange to form caprolactam.
"We're proud of the fact that we've been able to tackle an environmentally harmful process using genuinely benign reagents and catalysts. This new method is simple, solvent-free and minimises production and disposal costs," says Thomas in a press release brought out by the university.
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