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How fracking is upending the chemical industry : Nature News Comment

How fracking is upending the chemical industry : Nature News Comment

Jeff J Mitchell/Getty

A ship carrying US shale gas, the Ineos Insight, approaches port in Scotland in September 2016.

As the Ineos Intrepid cruised slowly through the sapphire waters of Norway's Frierfjord, chaperone tugboats sprayed jets into the sky to herald her arrival. In giant refrigerated tanks below decks, the ship carried 27,500 cubic metres of liquid ethane — enough to fill 11 Olympic swimming pools. Intrepid also brought a message, painted in giant capital letters along her side: “SHALE GAS FOR PROGRESS”.

The vessel's arrival in March 2016 brought the first ever shipment of shale gas from the United States to Europe — and marked the start of a burgeoning business. More of these 180-metre-long 'Dragon'-class vessels have followed in her wake, forming a 'virtual pipeline' for ethane across the Atlantic Ocean. This gas, which is extracted from the ground through the hydraulic fracturing of shale deposits, isn't destined to fuel power stations or domestic stoves. Instead, it will be transformed into the chemical building blocks needed to make a panoply of products, including plastics, clothes, adhesives and medicines.

Intrepid's voyage is a striking demonstration of how cheap US shale gas is reshaping the chemical industry and changing the origin of countless manufactured objects. For decades, the industry's raw ingredients have mostly come from crude oil. Chemical plants break down long hydrocarbon molecules in crude to produce a smorgasbord of smaller molecules, such as ethene, propene and benzene — all important precursors to polymers.

But shale gas, which is composed mainly of methane, ethane and propane, is turning that pathway on its head. The abundance of the gas has slashed the costs of these molecules. As a result, some are now usurping large hydrocarbons as the preferred starting point for industrial synthesis.

This shift from oil to gas brings enormous opportunities. According to the American Chemistry Council, a trade group based in Washington DC, the shale boom has attracted about US$160 billion in investment from the US chemical industry since 2011, and will help to create half a million jobs in plastics manufacturing over the coming decade. But it also poses huge challenges. Some of the main techniques that are used to turn the components of shale gas into more valuable compounds — processes generally known as upgrading — are decades-old, dirty and energy-intensive. And they rarely produce the same mix of chemicals as conventional oil-based routes, which means that some relatively minor, yet valuable, chemicals such as butadiene, an ingredient of synthetic rubber, are becoming scarcer.

These challenges are driving an intensive research effort, spanning industry and academia, to develop catalysts and reactors that can transmute small hydrocarbons in cleaner, cheaper and more efficient ways.

“We could totally redesign our chemical plants.”

Translating that research into commercial production will depend on the finely balanced economics of a changeable market. It will also require a reliable supply of gas. The US Energy Information Administration predicts that natural-gas extraction in the United States will continue to grow until at least 2040, but that might be too optimistic (see Nature 516, 2830; 2014). Meanwhile, concerns that fracking can contaminate groundwater — along with the broader climate implications of extracting fossil fuels — continue to dog the technology. If the glut does persist, however, it could usher in technologies that would form the foundations of a much more sustainable chemical industry. “We could totally redesign our chemical plants,” says Bert Weckhuysen, a chemist at Utrecht University in the Netherlands.

The ethane revolution

Shale gas is extracted from kilometres below ground, and typically contains about 70–95% methane, less than 15% ethane and less than 5% propane. After traces of oil, water and other impurities are cleaned out, the gas is chilled so that ethane and propane can be separated in liquid form, leaving methane behind.

Although ethane makes up a small proportion of shale gas, it has so far had the biggest impact on the chemical industry. That's because chemists can easily use it to make ethene, also known as ethylene. Ethene is used to make various types of polyethylene and the precursors to other plastics, such as polyvinyl chloride (PVC) and polystyrene. So voracious is the world's appetite for these plastics that the chemical industry produces roughly 150 million tonnes of ethene every year, more than any other chemical building block.

Most processes in the chemical industry use catalysts. But ethene can be produced simply by steam cracking ethane or larger hydrocarbons. First developed in the 1920s, steam cracking is a blunt, energy-intensive process that requires little more than water and 850 °C temperatures. “You basically just heat the snot out of it,” says Jeffrey Plotkin, an industry analyst at IHS Markit in New York City. “The heart and soul of the thing is this gigantic furnace, that's where all the chemistry happens.”

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