Moving to renewables

25 March 2020

Renewable feedstock is central to the chemical industry’s goal of sustainability. However, balancing the costs of new chemicals with those of fossil-based ones can make the shift a slow process.

25 March 2020

Malic acid, a naturally occurring chemical first isolated from apples, is a platform chemical which has a wide number of uses. Its main application is in the food and beverage industry, where up to 90% of the malic acid produced is used. It has application as a taste enhancer in products such as sweets, soft drinks and bakery products, it is labelled as E296. It is also used as a buffering and chelating agent in personal care and cleaning formulations, as well as having application in pharmaceutical sector where, for example, it is used as a compound in the migraine drug almotriptan malate. Further new applications could include low transition temperature mixtures and polymer production. The chemical is produced in almost all continents with the global production capacity said to stand at 80 000 to 100 000 tonne per year.

The feedstock for producing malic acid is n-butane. Research published in the Journal of Chemical Technology and Biotechnology indicates that there are a number of renewable substrates that can be used to produce malic acid via microbial action. However, using renewable feedstock comes with a number of challenges. These include process impurities, along with the heterogeneous nature and availability of the renewable feedstock. This means that currently, malic acid production based on renewable resources is still not able to compete with the well established, low priced chemical production methods. However, ongoing research is also investigating the use of inexpensive industrial side-streams or waste for producing malic acid, with crude glycerol an interesting prospect.

Renewable substrates that have been investigated include glucose, but this has proved to be an expensive route. Materials derived from crop and forest waste as well as miscanthus, Jerusalem artichoke, and sweet potato, species which can be cultivated on barren poor quality soil, are interesting prospects for renewable malic acid.

Researchers conclude that while there has been much investigation into the upstream processing of biotechnological malic acid production, literature about scale-up and downstream processing is still scarce.

‘Given the already existing market demand, bio-based [enzymatic]-malic acid can be directly incorporated into existing value-chains completely replacing fossil-based [chemical]-malic acid. Therefore, despite all challenges which still need to be addressed, [enzymatic]-malic acid can become an important platform in the bio-based economy,’ the researchers said.

Journal of Chemical Technology & Biotechnology DOI: 10.1002/jctb.6269

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