Speciality Chemicals Magazine MAY / JUN 2022 | Page 64

Spinning disc reactors intensify mixing , heat and mass transfer through formation of thin films under centrifugal force shear
For example , if a reaction is known to be very fast , rapid mixing of the reactants at molecular scale is of the utmost importance to allow the reaction to proceed at its inherent rate . The engineer or chemist should then be able to select from devices that have been characterised as high-speed mixers . Similarly , if a reaction between two compounds is known to release a large amount of heat , a reactor with capabilities for high heat transfer rates should be chosen . Therefore , PI application is a knowledgebased methodology , which relies on extensive process information and equipment characteristics being available .
Catalyst discovery
Precious metal catalysts , such as those based on palladium , platinum , ruthenium , iridium , or even silver or gold , often have inherently high activity and selectivity . They displaced commonly available base metal catalysts , such as copper , iron , nickel and zinc , from industrial processes over the course of the 20th century . As a result , precious metals have also found their way into green and biorefining chemistries , often with ambiguous claims regarding the sustainability of the processes . Because of this , a new trend towards base metals and sustainable catalysis has been emerging over the last couple of decades to address issues with precious metals . To guarantee the sustainability of the process at all levels , it is essential to replace precious and scarce metals with more sustainable alternatives . This will help to prevent problems related with high and fluctuating costs , and with material scarcity , making biorefining more viable and a more competitive alternative to fossilbased processes . It is also necessary to avoid precious metals associated with unethical supply chains that resort to conflict , slave and / or child labour . ( It should be noted that the conflict metals group also includes some base metals , such as cobalt .) Finally , it is essential to minimise toxicity hazards in precious metals , which also affect some base metals , particularly cobalt , nickel and cadmium . Research into the replacement of precious metal catalysis has focussed mostly on two areas . In the first ,
researchers have been working to understand the catalytic mechanisms and devise strategies to make base metal catalysts work harder , to match or even supersede the performance of precious metal catalysts . This is often achieved through judicious selection of alternative ligands in homogenous metal complexes , the addition of promoters and stabilisers to base metal catalysts , or using alternative materials , such as zeolites , polyoxometales or carbides . Catalyst discovery and screening can be accelerated with the aid of high-throughput and machine learning methods . In the second area , researchers have been investigating novel formulation and synthesis methods , where metal crystallite structures can be prepared and deposited in controlled ways to achieve the required catalytic effects . However , further work is still necessary to find simplified ways to achieve complex effects , and to ensure that formulation and synthesis methods for the most exquisite , but ultimately efficient , catalysts are scalable and transferable to industrial practice .
64 SPECIALITY CHEMICALS MAGAZINE ESTABLISHED 1981