Rise of the chemical plant

Date: 19-jun-2009
Author: Jon Evans

With all the fuss over liquid biofuels, the fact that plant biomass can also potentially be converted into a range of industrial chemicals is often forgotten. This is particularly surprising seeing as not only can the same production processes be used to generate liquid biofuels and industrial chemicals, but often the liquid biofuels and industrial chemicals are one and the same.

At the moment, most industrial chemicals, particularly plastics, are generated from petroleum. ‘Right now, about 5% of the world’s supply of petroleum is used to make feedstocks that are synthesised into commodity chemicals,’ says Jonathan Ellman, a chemistry professor at the University of California, Berkeley. ‘If these feedstocks can instead be made from biomass they become renewable and their production will no longer be a detriment to the environment.’

Indeed, a case can be made that converting plant biomass to chemicals may be a more efficient use of limited plant resources than converting them into biofuels. For biofuels such as ethanol and biodiesel are in many ways inferior to fossil fuels, whereas the chemicals produced from plant biomass should be direct replacements for petroleum-derived chemicals.

Furthermore, in response to the volatile oil price of the past few years, chemical companies are taking a growing interest in chemicals derived from plant biomass. In a report released at the end of last year, the UK market analyst firm Frost & Sullivan predicted that the global market for biorenewable chemicals would increase from $1.63 billion in 2008 to over $5 billion by 2015.

Ethanol, as well as being the world’s favourite biofuel, is already an industrial chemical, acting as a feedstock in the production of various other organic chemicals, such as diethyl ether. But scientists are working on ways to transform plant biomass into other chemical compounds that can act as both a liquid biofuel and a chemical feedstock. One of the most promising of these compounds is 5-hydroxymethylfurfural (HMF), which can act as a feedstock in the production of polyesters, including the polyethylene terephthalate used to make most plastic bottles, and synthetic diesel.

Over the past few years, a number of research groups have come up with various ways to produce HMF from glucose and fructose, and more recently from cellulose (see Biofuels of tomorrow). In 2007, scientists at the Pacific Northwest National Laboratory in Richland, Washington, led by Conrad Zhang, reported using the metal catalyst chromium chloride dissolved in an ionic liquid to convert glucose to HMF.

Ionic liquids are also able to break down cellulose and so Zhang and his colleagues wondered whether a variation of this method could produce HMF directly from cellulose. They managed to come up with such a method by simply dissolving small amounts of two metal catalysts – chromium chloride and copper chloride – into the ionic liquid, with this method able to convert 57% of the sugar content in cellulose into HMF in a single step. They reported this advance in a recent paper in Applied Catalysis A and also at a meeting of the North American Catalysis Society (NACS) at the beginning of June.

Other scientists are discovering that the major by-product of biodiesel production, glycerol, can also be converted into a range of useful chemicals. For instance, scientists at the US operations of the German chemical company Sud-Chemie have developed catalytic processes for converting glycerol into a wide range of industrial chemicals, including acetone and propanol. They also presented their work at the recent NACS meeting.

Most recently, Ellman and his colleagues at Berkeley developed an efficient way to convert glycerol into allyl alcohol, which is a major feedstock used in the production of pesticides, drugs and various polymers and organic chemicals. To do this, they simply mixed glycerol with formic acid, which gives bee venom its sting, at around 235°C.

Ordinarily, this reaction is not very productive, because it also produces a lot of unwanted compounds. But Ellman and his colleagues found that they could eliminate these unwanted compounds by passing a stream of nitrogen through the reaction mixture, improving the allyl alcohol yield by 80%.

Does all this indicate that plant biomass may soon have more to offer to the chemical sector than to the transport sector?

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