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| Stages of Crude oil refining Courtesy Wikipedia . |
A report analysing the energy expenditure in the US Petroleum Industry, hints that if we could cut down the energy incurred for chemical separations, possible saving of 420 TBtu per year could be achieved. Fractionation of crude oil, separation of alkenes and alkanes, separation of isomers of benzene derivatives - all these are essential yet tricky downstream operations Because the components are so similar in their chemical and physical properties, as of now fractional distillation is the only effective answer. Professors David Sholl and Ryan Lively (School of Chemical and Biomolecular Engg, Georgia Institute of Technology, Atlanta Georgia, USA) reiterate that " Purifying mixtures without using heat would lower global energy use, emissions and pollution and open up new routes to resources."
Sholl and Lively suggest that we re-evaluate alternate technologies such as adsorption, crystallisation and membrane separation. Of course they are aware that thermal processes can't be avoided altogether but even a partial substitution can cut down the energy cost and reduce pollution substantially. For example petroleum cracking yields a mixture of paraffins. Ethylene, a gaseous olefin which polymerises to yield polyethylene, (or polythene as it is commonly called ) must be isolated from this mixture. The current process of separating the components of the paraffin gas mixture involves first liquifying the gaseous mixture then subjecting the liquid to cryogenic distillation under high pressure at ultra low temperatures. Could we avoid this intermediate liquefaction/distillation step? If so a lot of energy can be saved. Perhaps a two step process could be adopted: in the first step carbon membranes separate the hydrocarbon mixture into individual streams of 99.9% purity at ambient temperature and moderate pressure and the second step adopts cryogenic distillation to achieve higher purity.
Sholl and Lively list seven processes which would yield huge energy savings if alternate smarter methods can be devised.
1. Hydrocarbons from crude oil
2. Uranium from seawater
3. Alkenes from alkanes
4. Greenhouse gases from dilute emissions
5. Rare-earth metals from ores
6. Benzene derivatives from each other
7. Trace contaminants from water
Scientists and engineers need to think out of the box
Sholl and Lively suggest that we re-evaluate alternate technologies such as adsorption, crystallisation and membrane separation. Of course they are aware that thermal processes can't be avoided altogether but even a partial substitution can cut down the energy cost and reduce pollution substantially. For example petroleum cracking yields a mixture of paraffins. Ethylene, a gaseous olefin which polymerises to yield polyethylene, (or polythene as it is commonly called ) must be isolated from this mixture. The current process of separating the components of the paraffin gas mixture involves first liquifying the gaseous mixture then subjecting the liquid to cryogenic distillation under high pressure at ultra low temperatures. Could we avoid this intermediate liquefaction/distillation step? If so a lot of energy can be saved. Perhaps a two step process could be adopted: in the first step carbon membranes separate the hydrocarbon mixture into individual streams of 99.9% purity at ambient temperature and moderate pressure and the second step adopts cryogenic distillation to achieve higher purity.
Sholl and Lively list seven processes which would yield huge energy savings if alternate smarter methods can be devised.
1. Hydrocarbons from crude oil
2. Uranium from seawater
3. Alkenes from alkanes
4. Greenhouse gases from dilute emissions
5. Rare-earth metals from ores
6. Benzene derivatives from each other
7. Trace contaminants from water
Scientists and engineers need to think out of the box
Tailpiece:
Folklore tells the story of a little princess who was harassed by the wicked queen, her stepmother. The little girl had to sort out a hillock high mixture of grains into separate heaps, that too before sunset. An army of ants came to her rescue and finished the job neat and clean before the timeline ended.
If only life were a fairy tale!
REFERENCES
1. Seven chemical separations to change the world: Sholl and Lively, Nature 28 April 2016, vol. 532, pages 435-7
