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RESEARCH HIGHLIGHTS

Nature Reviews Chemistry | Published online 10 Jan 2018; doi:10.1038/s41570-017-0110

SUSTAINABILITY Sweet new route to Acrylonitrile is an important (for a process), the industrial-scale process with commodity chemical. It is used as a reaction produces some modifications to their initial The nitrilation precursor to , often as a by-product benchtop method. 3-HP would be reaction used for the production of carbon and is highly exothermic, such that extracted from a microbial cultiva- fibres. The high global demand it requires sophisticated process con- tion broth using . A reactive produces for acrylonitrile — over 6 million trol. We wanted to develop a method distillation affords ethyl acrylonitrile tonnes of it were produced last year that didn’t rely on fossil fuels and directly, is fed into the next step to in high yield — is only going to get higher, given address these issues.” produce acrylonitrile. In addition, using a cheap increasing interest in using carbon Previous attempts to use bio- the aminolysis reaction can be per- fibres in strong, lightweight products, based feedstocks have focused on formed using pure rather catalyst from such as vehicle components. the use of sugars derived from ligno- than ammonia diluted with . a bio-based The Sohio process — which cellulosic biomass, but have been It is predicted that a scaled process renewable converts propylene from crude oil relatively low yielding. “We were would produce acrylonitrile at a into acrylonitrile by ammoxidation inspired by earlier, mostly ignored, price similar to that which we pay starting over a bismuth -based reports that acids and esters could today, but with less price variation material catalyst — was originally developed be converted directly to over and lower greenhouse gas emissions in the 1950s. Now, writing in Science, acid catalysts,” explains Eric Karp, because the technology is Gregg Beckham and co-workers first author of the study, “this hadn’t independent of fossil fuels. (who are part of a US Department been applied to the synthesis of The next step is to scale up the of Energy-sponsored renewable acrylonitrile, but we knew we could process and use the acrylonitrile in carbon fiber consortium) describe a get 3-hydroxypropionic­ acid (3-HP) the production of polyacrylonitrile process for renewable acrylonitrile from microbial cultivation and knew and, ultimately, carbon fibre. “We production from microbial sugars. that it could be dehydrated easily.” need to compare the performance “We were keen to develop a new In industrial processes, esters are of bio-based carbon fibre with that of approach that could use renewable preferred to carboxylic acids as they petroleum-based carbon fibre,” feedstocks,” explains Beckham. are less corrosive and more volatile. explains Beckham. “We need to know “Besides being relatively low yielding Heating ethyl 3-hydroxypropionate whether and how impurities from with ammonia over a titania catalyst biomass affect the properties of the N O 2 eventually gives acrylonitrile. Ethyl carbon fibre compared to the industry EtOH HO O acrylate is the main product below standard.” Beckham and co-workers 230 °C, while acrylonitrile can be are also keen to investigate the pro- favoured by raising the temperature to duction of acrylonitrile from lactic 320 °C. It is proposed that ethyl 3-HP acid. The dehydration step is expected Dehydration is dehydrated first to , to be much more difficult than for TiO2 260°C followed by aminolysis to produce 3-HP, but it is easier to obtain. “Lactic and then a further de­­ acid is already used in the production hydration affords acrylonitrile. “The of biodegradable polylactic acid ,” he NH 2 nitrilation reaction produces acrylon­ says. ”Humanity has been making itrile in high yield using a cheap lactic acid for as long as we’ve been catalyst from a bio-based renewable making ethanol to drink, so we’re Nitrilation starting material,” says Karp. “The working on another new route to

TiO2 315°C process is endothermic, with only acrylonitrile again inspired by some and ethanol as by-products.” decades-old work.” The nitrilation reaction thus converts Stephen G. Davey the inherently oxygenated biomass + 2H O ORIGINAL ARTICLE Karp, E. M. et al. Renewable N 2 feedstock whereas ammoxidation acrylonitrile production. Science 358, 1307–1310 + OH requires a hydrocarbon substrate. (2017) Beckham and co-workers FURTHER READING Spevacek, J. A change is Adapted with permission from Karp, E. M. et al. gonna come. Nat. Rev. Chem. 1, 0008 (2017) (2017), AAAS. go on to propose a potential

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