Exploring more sustainable routes to acrylate monomer manufacture

Acrylic based monomers are used to create a wide range of organic polymers with applications from false nails to lighting panels and from lightweight, scratch-proof laptop screens to viewing windows in aquariums and submarines. Petrochemicals have been the predominant feedstock for these monomers since their introduction, but moves to make the industry “cleaner” and “greener” have led to a growing interest in renewable resources. Exploiting such resources for bulk plastic manufacture is the focus of this project. This thesis describes the hydrothermal conversion of di- and tricarboxylic acids into acrylic acid and methacrylic acid. In order to produce these chemicals via sustainable routes, the di- and tri-carboxylic acid precursors used in this work are all available from biomass or from known biological processes that convert biomass into useful precursors. Previous work in this area has focussed on the production of methacrylic acid from itaconic acid and its isomers or from citramalic acid. However, the first section of this thesis investigates the production of acrylic acid from malic acid. Malic acid is readily available from biomass sources and can produce acrylic acid after decarboxylation and dehydration akin to the previously reported route from citramalic acid to methacrylic acid. However, significant levels of by-products and unselective extractions meant we were unable to present an industrially viable route that could compete with current processes. The focus of the project then returned to the production of methacrylic acid. Fermentation of sugar molasses using Aspergillus terreus yields itaconic acid. This acid can then be used in the continuous production of methacrylic acid in high temperature water (>200 °C), at elevated pressure (>2000 psi) in the presence of sodium hydroxide. Our research looks at the stability of methacrylic acid under these reaction conditions, showing the hydration to 2-hydroxyisobutyric acid and decomposition to acetone. By investigating the effect of temperature and residence time on the stability of methacrylic acid and 2 hydroxyisobutyric acid, it is suggested that reactions do not exceed 260°C and have a residence time shorter than 360 s. Finally, this thesis describes a proposed new process for methacrylic acid production to include the recycling of a sodium hydroxide catalyst. Subsequent acidification of reaction exit solutions releases free methacrylic acid that can be extracted with a suitable organic solvent. Previous work in this area demonstrated this process with the use of sulfuric acid to release free methacrylic acid and yield the free acid as well as aqueous sodium sulfate waste. However, by using an acidic precursor, such as itaconic acid, to acidify the exit solution, methacrylic acid can be extracted and the remaining aqueous solution can be cycled through the continuous flow equipment, recycling the base catalyst as sodium itaconate. This process is demonstrated up to 20 cycles, and collected methacrylic acid has been esterified and polymerised to yield a sample of poly(methyl methacrylate), demonstrating proof of the concept behind our new process as a route to bulk plastic manufacture from renewable resources