With in-flow techniques rapidly gaining traction over the past two decades, the scope and viability of flow chemistry processes have increased dramatically (2) As well as enabling unique control over reaction parameters (such as increased temperature control or higher temperature and pressure operating windows), flow chemistry intrinsically aligns itself with Green Chemistry principles such as increased safety and efficiency (3). Dr. Russell Taylor and Samuel Raynes used the H.E.L FlowCAT to develop a process for the production of acetaldehyde from bioethanol in a flow process.
Acetaldehyde is an important precursor for the manufacture of a variety of higher-value compounds, including pyridine derivatives, pentaerythritol, and butanol (4). Acetaldehyde is typically produced industrially via the Wacker process, whereby ethylene is oxidized using a PdCl2/CuCl2 catalyst system, typically giving a 95% acetaldehyde yield at 110 °C and 10 bar. However, the process requires substantial infrastructure investment and predominantly utilizes non-renewable carbon source feedstocks. With the global market for acetaldehyde predicted to grow to around 1.8 billion USD by 2022, a viable method for producing acetaldehyde from renewable feedstocks is desirable (5).
In this study, the H.E.L FlowCAT benchtop flow reactor was used to help develop an in-flow process for the synthesis of acetaldehyde using bioethanol as a feedstock. Bioethanol is produced in large quantities worldwide, with the USA producing bioethanol in excess from the fermentation of corn (6). Direct conversion of bioethanol to acetaldehyde, therefore, represents a more sustainable route to the synthesis of higher-value acetaldehyde derivatives (Figure 1).
The FlowCAT provides an all-in-one flow reactor solution that is optimized for high-pressure catalyst applications. In this study, the FlowCAT provided the necessary flexibility to quickly and easily trial a number of catalysts. Precise control over reaction parameters such as inlet temperature and pressure and reactor temperature enabled optimization of the process for a chosen catalyst, while connection of the FlowCAT’s outlet to a GC-MS-BID enabled real-time analysis of effluent.