The World in a Barrel

IN 2016 the world consumed 96 million barrels of oil every day.  They all started out as algae or plankton, with the odd dinosaur thrown in for good measure.  Dead and buried, this ancient life was transformed into a suite of molecules made up of chains and rings of carbon with hydrogen stuck to them, and thus, prosaically known, as hydrocarbons.  (They have some sulphur in them, too; it’s a pain.)

Hydrocarbons, which sometimes seep to the surface unbidden, have been used for millennia. They can be set alight to frighten your enemy’s cavalry, or slathered into the seams between the planks of your ship’s hull.  Today they power a global economy and can be used to make almost anything.

Using oxygen to burn up hydrocarbons liberates lots of energy. It also creates water, which doesn’t matter much, and carbon dioxide, which does.  Oil accounts for 35% of industrial CO2 emissions.

Different hydrocarbons are used to fuel different things.  The shorter the carbon chain, the more easily a fuel is vapourised, and in turn burned.  A little molecule like butane—four carbons long—is good for a cigarette lighter; a ship’s engine may use something 10 times longer.

Every barrel of crude oil contains a mix of all these molecules.  Refineries sort them out, exploiting the fact that they vapourise at different temperatures to separate them by distillation. But even “light” crude—the short-chain-rich sort the industry likes best—contains more of the long chains than anyone needs.  So refiners use clever chemistry (“fluid catalytic cracking”) and brute-force heat (“coking”) to break some long molecules into shorter ones.

Distillation and cracking also produce plenty of small molecules containing just two or three carbons; these form the basis for the petrochemical industry, which uses them either for their own properties or as the building blocks for all manner of plastics, fibres and pharmaceuticals.  The global market for these is some $680bn: more than a third as big as the $1.6trn oil market

All this takes a lot of energy: most refineries use between five and ten percent of the energy in the crude that passes through them.  In years to come that might change.  Practitioners of “synthetic biology” are learning to genetically engineer microbes that can synthesise the building blocks of petrochemicals—and indeed the chemicals themselves.  In the future, the refinery may well fall prey to the descendants of its long-dead reason for being: algae.

The Economist December 19, 2017