Speciality Chemicals Magazine MAY / JUN 2022 | Page 63

GREEN CHEMISTRY
for example , HMC can make up to 30 % of lignocellulosic biomass . The concentration and purification of diluted flows are challenging due to the complexity of the matrices , solvent removal costs and the sensitivity of many biomass compounds to hightemperature separation processes . The reliance on expensive precious metal catalyst technologies to guarantee efficient conversion of biomass feedstock into functionalised platform biorenewable chemicals exacerbates the issue . Unlike hydrocarbon-based streams , the high degree of functionalisation of the biorenewable products is frequently associated with a higher reactivity and weaker stability of these species , which require prompt separation and isolation , creating further obstacles .
Multicell reactors allow high-pressure and temperature screening of catalysts
Process intensification
Process intensification ( PI ) technologies for the purification and catalytic conversion of biorefining streams can contribute to a reduction of plant equipment footprints , energy consumption and safety inventories by orders of magnitude , while also enhancing yields and process rates . Miniaturisation has long been a driving principle of PI and has led to significant developments in microreactors and other thin-film technologies . Working with small volumes in miniaturised structures has a great beneficial impact on molecular scale processes , allowing faster transfer of heat , mass and momentum across significantly shorter distances . Hence reactions can be sped up .
More uniformity in concentration and temperature can also be expected in these smaller volumes compared to the larger bulk volumes used in conventional equipment , improving the control of target products formation . The PI toolbox is focused on three distinct strands of innovative development strategies around technology , processes and materials ( Figure 1 ), all of which provide opportunities for miniaturised devices to be implemented . Technology development typically includes novel reactor or separator designs , such as rotating packed beds , spinning disc technology or oscillatory flows , along with structured surfaces for enhanced contact between process streams . Innovation in processing can often be achieved by shifting the mode of operating from batch to continuous , where reduction in equipment footprint and all other associated benefits are often realised . Designing equipment that incorporates multiple functionalities where , for instance , reaction and separation steps can be performed in tandem , is another popular method for implementing PI . Membrane reactors have received considerable attention . Innovation through material development ensures optimal integration of the chemistry with the process . That is the case when using nanomaterials , heterogeneous catalysts or adsorbents that are specifically tailored for optimal interactions with streams in intensified flow fields or adapted for immobilisation in structured equipment . Ideally all three strands should be combined in a given application for maximum impact on process efficiency . In practice , applying process intensification involves a matchmaking exercise between the requirements of a process at all scales ( molecular / microscale , mesoscale / millimetre and macroscale / equipment ) and the equipment and process capabilities available to the engineer and the chemist .
MAY / JUN 2022 SPECCHEMONLINE . COM
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