Production of fatty nitriles from fatty acids: fundamentals and alternative production routes
On November 23rd 2023, Carola Raffel successfully defended her PhD thesis 'Production of fatty nitriles from fatty acids: fundamentals and alternative production routes'
Combatting climate change means the chemical industry needs to change majorly, while still producing the same quality and quantity of goods. If we imagine the whole palette of chemical products as a tree, the products we use daily are at the top of the tree, its leaves; pharmaceuticals, cosmetics, plastic, and many more. They are made from different types of chemicals, the tree's branches, which are all coming from the same tree trunk, representing a few base chemicals. These base chemicals are made from the roots of the tree, which traditionally have been petroleum based feedstocks. The challenge is now to switch the chemical tree's roots - to source the feedstock from renewable resources, no longer from oil and gas. An example for a base chemical where this is possible are fatty nitriles. They are produced from fatty acids, which can be directly sourced from plant or animal fats and oils. The reaction has been carried out industrially since the 1930s, but little is known about the fundamentals of the reaction, which makes further intensification difficult. Traditionally, fatty acid is contacted with an excess of ammonia to produce fatty amide and water. The fatty amide dehydrates to the fatty nitrile.
The first chapter of the thesis gives a short overview over the topic. The second chapter dives into the thermodynamics and kinetics of the reaction, showing the the first reaction from fatty acid to fatty amide is comparatively quick and governed by an equilibrium between acid and amide, while the second reaction from amide to nitrile is comparatively slow. Therefore we study the amide dehydration to nitrile in more depth in chapter 3, highlighting the reaction mechanism coordinated by dimer formation and the effect of water on both the equilibrium and the intrinsic kinetics. Chapter 4 presents an inline-analysis technique to follow the formation of amide in the reactor, as well as the side reaction of acid and ammonia to the ammonium salt. The inline-analysis technique allows to gather a high quantity of data, which can be used to study subtle changes such as the formation of different dimers, for which we found evidence. Now we turn towards an alternative production route for fatty nitriles from fatty acids; the traditional reaction pathway requires ammonia, which is toxic and can be difficult to use. Alternatively, fatty nitriles can be produced via transnitrilation, where fatty acid and a cheaply available nitrile exchange functional groups. The equilibrium of this reaction is studied in chapter 5, showing that its equilibrium constant of unity is temperature independent as the reaction is stochastic. This is applied to the transnitrilation of fatty acid and acetonitrile in a microflow reactor, studying the kinetics in chapter 6. Chapter 7 draws the main conclusions of the thesis and gives an outlook on further research.
The traditional reaction is governed by a set of equilibrium reactions, whose kinetics, thermodynamics and mechanism were determined in this thesis, which can be used for intensification. To avoid the use of ammonia completely, transnitrilation is an alternative production route, and with the information on equilibrium and kinetics presented in this thesis, can also be simulated for intensification. Intensification of the traditional or alternative production route of fatty nitriles can make the production of the base chemical fatty nitrile in the "trunk" of the chemical tree more energy-efficient and sustainable.
Title of PhD thesis: Production of fatty nitriles from fatty acids: fundamentals and alternative production routes. Supervisors: Prof. John van der Schaaf and Prof. Fausto Gallucci.