Citric acid is a very inexpensive and renewable raw material, nowadays used as a food additive. It can also be effectively converted into methacrylate, as discovered by researchers participating in the ACTION project. Methacrylate-based polymers have exceptional optical properties and can be used for a wide range of applications, from plexiglas, coatings and glues to optical conductive fibres.
BPM’s ACTION project focuses primarily on finding biobased building blocks for the production of industrial bulk chemicals. ‘It is not usually the chemistry is the limiting factor as biomass can be used to create almost anything,’ explains project leader Jacco van Haveren. ‘It is still mainly about minimizing production costs that currently determine whether a biobased variant would be of interest to industry.’
Most of the development work on biobased materials currently focuses on the use of polymers obtained by means of polycondensation chemistry. A well-known example of this is polylactic acid. However, many of the traditional plastics are based on polymers obtained through radical polymerisation. Alongside ethylene and propylene, important building blocks for these types of polymers are styrene, acrylic acid and methacrylic acid. To make such products more biobased, the project was initially based on a concept in which two of the building blocks could be made from biobased raw materials at the same time: styrene and acrylic acid from amino acids and acrylic acid and methacrylic acid from itaconic acid.
Although this concept was successful on a lab scale for the coproduction of styrene and acrylic acid, due to the high production costs involved, the manufacturing industry was not interested in scaling up. The research team subsequently decided to focus its research on the development of a biobased methacrylate. This widely-applicable raw material is related to acrylic acid, but PMMA polymer based on methacrylate has the exceptional optical property of being extremely transparent. One particularly interesting application of this material is in optical conductive fibres. These can replace copper-based electrical cables, such as those used for computers, thus making the ICT sector more sustainable.
After a thorough literature search, Van Haveren discovered a publication in which the authors explained how methacrylate could be produced from citric acid in supercritical water at 370 degrees. This production process was optimised by the research team who used a catalyst to enable the reaction to occur at lower temperatures and much more efficiently. This new process gave the team a relatively simple and efficient method for converting citric acid into methacrylate. It also provided cost benefits. Methacrylate costs around two thousand euros per tonne, while citric acid costs only five hundred euros per tonne. ‘This provides quite a considerable amount of financial leeway,’ says Van Haveren. ‘We can also reduce costs even further by producing citric acid from cheaper raw materials.’
‘It is mainly due to the efficiency and low costs of our process that it opens up very real opportunities for the manufacturing industry,’ explains Van Haveren. ‘We are therefore seeking companies that would be interested in further optimising the process and facilitating bulk production.’