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Purifying mixtures without using heat would lower global energy use, emissions and pollution - and open up new routes to resources, say David S. Sholl and Ryan P. Lively.
Most industrial chemists spend their days separating the components of large quantities of chemical mixtures into pure or purer forms. The processes involved, such as distillation, account for 10-15% of the world's energy consumption1,2.
Methods to purify chemicals that are more energy efficient could, if applied to the US petroleum, chemical and paper manufacturing sectors alone, save 100 million tonnes of carbon dioxide emissions and US$4 billion in energy costs annually3 (see 'Cutting costs'). Other methods would enable new sources of materials to be exploited, by extracting metals from seawater, for example.
Unfortunately, alternatives to distillation, such as separating molecules according to their chemical properties or size, are underdeveloped or expensive to scale up. Engineers in industry and academia need to develop better and cheaper membranes and other ways to separate mixtures of chemicals that do not rely on heat.
Here, we highlight seven chemical separation processes that, if improved, would reap great global benefits. Our list is not exhaustive; almost all commercial chemicals arise from a separation process that could be improved.
SEVEN SEPARATIONS
Hydrocarbons from crude oil. The main ingredients for manufacturing fossil fuels, plastics and polymers are hydrocarbons. Each day, refineries around the world process around 90 million barrels of crude oil - roughly 2 litres for every person on the planet. Most do so using atmospheric distillation, which consumes about 230 gigawatts (GW) per year globally3, equivalent to the total energy consumption of the United Kingdom in 2014 or about half that of Texas. In a typical refinery, 200,000 barrels per day of crude oil are heated in 50-metretall columns to liberate thousands of compounds according to their boiling points. Light gases emerge at the cool top (at around 20 °C); progressively heavier fluids leave at lower and hotter points (up to 400 °C).
Finding an alternative to distillation is difficult because crude oil contains many complex molecules, some with high vis- "A major cosities, and myriad hurdle is contaminants, includ- scaling up ing sulfur compounds membranes." and metals such as mercury and nickel. It is feasible in principle to separate...