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Conversion of Biomass into Acrylonitrile, a Key Precursor for Carbon Fiber Manufacture

Published on 2018-02-07. Author : SpecialChem

TAGS:  Biobased Solutions      Polymer Reinforcement    

From cars and bicycles to airplanes and space shuttles, manufacturers around the world are trying to make these vehicles lighter, which helps lower fuel use and lessen the environmental footprint.

Conversion of Lignocellulosic Biomass into a Bio-based Chemical

National Renewable Energy Laboratory (NREL), and an interdisciplinary team reported the results of experimental and computational investigations on the conversion of lignocellulosic biomass into a bio-based chemical called acrylonitrile, the key precursor to manufacturing carbon fiber.

The catalytic reactor for converting chemical intermediates into acrylonitrile.

Acrlyonitrile is a large commodity chemical, and it's made today through a complex petroleum-based process at the industrial scale. Propylene, which is derived from oil or natural gas, is mixed with ammonia, oxygen, and a complex catalyst. The reaction generates high amounts of heat and hydrogen cyanide, a toxic by-product. The catalyst used to make acrylonitrile today is also quite complex and expensive, and researchers still do not fully understand its mechanism.

One way that cars, bicycles, airplanes and other modes of transportation have become lighter over the last several decades is by using carbon fiber composites. Carbon fiber is five-times stronger than steel, twice as stiff, and substantially lighter, making it the ideal manufacturing material for many parts.

"That's where our study comes in," Beckham said. "Acrylonitrile prices have witnessed large fluctuations in the past, which has in turn led to lower adoption rates for carbon fibers for making cars and planes lighter weight. If you can stabilize the acrylonitrile price by providing a new feedstock from which to make acrylonitrile, in this case renewably-sourced sugars from lignocellulosic biomass, we might be able to make carbon fiber cheaper and more widely adopted for everyday transportation applications."

Acrylonitrile from Plant Waste Material

To develop new ideas to make acrylonitrile manufacturing from renewable feedstocks, the Department of Energy (DOE) solicited a proposal several years ago that asked: Is it possible to make acrylonitrile from plant waste material? These materials include corn stover, wheat straw, rice straw, wood chips, etc. They're basically the inedible part of the plant that can be broken down into sugars, which can then be converted to a large array of bio-based products for everyday use, such as fuels like ethanol or other chemicals.

"If we could do this in an economically viable way, it could potentially decouple the acrylonitrile price from petroleum and offer a green carbon fiber alternative to using fossil fuels," Beckham said.

Multiple Advantages over the Petroleum-based Process

NREL team working on sustainable process for creating acrylonitrile
and carbon fibers from renewable biomass.

Beckham and the team moved forward to develop a different process. The NREL process takes sugars derived from waste plant materials and converts those to an intermediate called 3-hydroxypropionic acid (3-HP). The team then used a simple catalyst and new chemistry, dubbed nitrilation, to convert 3-HP to acrylonitrile at high yields.

The catalyst used for the nitrilation chemistry is about three times less expensive than the catalyst used in the petroleum-based process and it's a simpler process. The chemistry is endothermic so it doesn't produce excess heat, and unlike the petroleum-based process, it doesn't produce the toxic byproduct hydrogen cyanide. Rather, the bio-based process only produces water and alcohol as its byproducts.

From a green chemistry perspective, the bio-based acrylonitrile production process has multiple advantages over the petroleum-based process that is being used today. "That's the crux of the study," Beckham said.

Next Steps

  • There's a large community of chemists, biologists and chemical engineers who are developing ways to make everyday chemicals and materials from plant waste materials instead of petroleum.
  • Researchers have tried to do this before with acrylonitrile. But no one has been as successful in the context of developing high yielding processes with possible commercial potential for this particular product.
  • With their new discovery, the team hopes this work makes the transition into industry sooner rather than later.
  • The immediate next step is scaling the process up to produce 50 kilograms of acrylonitrile. 
  • The researchers are working with several companies including a catalyst company to produce the necessary catalyst for pilot-scale operation; an agriculture company to help scale up the biology to produce 3-HP from sugars; a research institute to scale the separations and catalytic process; a carbon fiber company to produce carbon fibers from the bio-based acrylonitrile; and a car manufacturer to test the mechanical properties of the resulting composites.

"We'll be doing more fundamental research as well," Beckham said. "Beyond scaling acrylonitrile production, we are also excited about is using this powerful, robust chemistry to make other everyday materials that people can use from bio-based resources. There are lots of applications for nitriles out there — applications we've not yet discovered."

Source: TACC
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