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Nylon was the first synthetic polymer to be produced on a commercial scale. Since it was synthesized by DuPont in 1935, Nylon has been deployed in a wide range of commercial applications. First used as toothbrush bristles, it has gone on to make its mark in areas as diverse as clothing, transport, military equipment and even aerospace. In spite of the advent of a large number of new materials, Nylon continues to be popular for a wide range of commercial applications; almost 4 million tons of the material is produced around the world every year.
Like many other important petrochemical and polymer products in common commercial use today, Nylon precursors are manufactured by liquid-phase oxidation of hydrocarbon feedstock in the presence of a catalyst. Intermediates from cyclohexane oxidation are processed further, to create Nylon fibres.
Picture Credit: Ashish Unnarkat
While this method has been in continuous use since the dawn of the Nylon industry to the present day, it is not a particularly efficient process; the Nylon fibres yielded weigh less than 5% of the weight of the feedstock. Moreover, the Cobalt salts that catalyse the reaction are completely consumed. Although efforts have been going on to find a better way to manufacture Nylon, not much headway has been made so far. More than fifty years of research and development hasn’t yielded any significant improvement in the conversion rate.
Until now, that is. At the IITB-Monash Research Academy in Mumbai, Research Scholar Ashish Unnarkat has made significant breakthroughs in improving the efficiency of the manufacturing process for Nylon. Working under the guidance of Prof. Tam Sridhar, Prof. Huanting Wang, Prof. S. M. Mahajani and Prof. A. K. Suresh, Ashish had to overcome severe constraints relating to safety and analytical accuracy.
The former was entailed by the very nature of the conversion process, which involves very high temperatures and pressures. In order to ensure the safety of the personnel involved and the facilities used, strict safety measures were implemented and processes were adhered to without deviations.
The latter arose because, while the conversion rate is less than 5%, the margin of error in the analytical instruments used in gas chromatography ranges from 2% to 3%. To overcome this challenge, Ashish and his team developed an analytical instrument that works on the complete conversion of oxygenates and computing the conversion on the basis of absorbed CO2. The instrument resulted in less than a percent error.
As mentioned earlier, the prevalent manufacturing process uses cobalt in homogeneous form as a catalyst. The catalyst is used up in the process, as a result of which it needs to be constantly and continuously replenished. In order to reduce the expense that this gives rise to, Ashish chose to develop heterogeneous alternatives to the homogeneous Cobalt in prevalent use.
Picture Credit: Ashish Unnarkat
Heterogeneous catalysts can be reused and give almost identical results as their homogeneous counterparts. Transition metals are known to be good for the oxidation reactions. So the target was to synthesize the heterogeneous catalyst utilizing the transitional metal as oxides or on supports that gives good performance for the reaction.
Since Cobalt is the catalyst that has conventionally been used by the industry in homogenous form, it was decided to work on improving the same so that it should be readily acceptable and replaceable with the industry. The IITB-Monash team were able to synthesize heterogeneous catalyst Cobalt and Molybdenum that gave better conversion rates and selectivity compared to the homogeneous catalyst.
The manufacturing process for Nylon starts with the oxidation of Cyclohexane to yield cyclohexanol and cyclohexanone. These are the starting materials in the preparation of adipic acid and caprolactam, which are used in the manufacture of nylon polymers.
Conventional oxidation of the feed stock using cobalt salt as catalyst achieves cyclohexane conversions lower than 5%, and yields cyclohexanol and cyclohexanone up to 80-85%. Ashish and his team, however, achieved conversion rates of 92%, using improved processes and new catalytic material. This increase would, naturally, also be reflected in the final yield of Nylon.
As Ashish points out, the project will significantly impact energy, environment and economy.
1. Any improvement in the yield from the manufacturing process will help in reducing the energy required to produce the same amount of product and, consequentially, the carbon footprint.
2. Being heterogeneous, the catalyst can be re-used. This will help in reducing catalyst usage.
3. All of the above ultimately benefits the industry; reduction in operation cost / mass of product, energy savings, material and utilities savings.
4. Cost of the polymer will reduce and products made from Nylon will become more accessible to the common man.
IITB-Monash Research Academy is a Joint Venture between IIT Bombay and Monash University. Research scholars study for a dually-badged PhD from both institutions, and enrich their research and build collaborative relationships by spending time in Australia and India over the course of their degree. Established in 2008, IITB-Monash Research Academy aims to enhance scientific collaborations between Australia and India.
Research scholar: Ashish Prabhudas Unnarkat
Project title: Catalytic and Reaction Engineering Studies on Organic Liquid Phase Oxidations
Supervisors: Prof. Tam Sridhar, Prof. Huanting Wang, Prof. S. M. Mahajani, Prof. A. K. Suresh
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