FLOW CHEMISTRY batches caused by cleaning, setup and changeovers can limit overall productivity.
Integrated processes
The integration of flow and batch chemistry into a single process can deliver synergistic benefits in terms of flexibility, efficiency, and safety. However, this hybrid approach introduces its own set of challenges.
The inherent differences in process dynamics-flow being continuous and steady-state, batch being time-dependent and cyclical – require careful synchronisation. For example, aligning flow rates with the timing of batch operations like quenching, extraction or purification can be difficult and may result in process bottlenecks or equipment underutilisation.
Material handling at the interface between continuous and batch steps adds another layer of complexity.
Transferring intermediates between units often requires buffer vessels or surge tanks to decouple flow rates and ensure stable operation. This introduces additional concerns related to mixing, pressure balancing, contamination and cleaning. Control systems for hybrid processes must coordinate disparate operating philosophies, requiring sophisticated integration of sensors, analytics and automation.
Hybrid approach
Arxada has developed various large-scale continuous processes with flexible batch and semi-batch assets at its site at Visp, Switzerland. One example of this integration is the company’ s ketene and diketene technology network. Ketene( Figure 1, 1), a highly reactive and shortlived intermediate, is produced continuously through the pyrolysis of acetic acid at high temperatures.
The nature of this reaction requires rapid and efficient heat removal after the formation of ketene to prevent its reversion to acetic acid. This is achieved via a continuous process set-up, while also ensuring immediate downstream utilisation due to ketene’ s instability. Ketene can be converted into acetic anhydride( 2) in a subsequent continuous step or used directly in fast, clean acetylation reactions that produce minimal by-products.
Diketene is formed by the dimerisation of ketene( 3), which also proceeds in a continuous process to ensure stability and safety. Although diketene can be stored temporarily, it is generally processed further on-site. The availability of ketene enables the production of valuable intermediates such as lactones( 4) and acetoacetates( 5), many of which are best produced in continuous flow due to their reactivity and sensitivity.
SEP / OCT 2025 SPECCHEMONLINE. COM
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