Batch-to-Continuous transition in the specialty chemicals Industry: Impact of operational differences on the production of dispersants

Specialty chemicals are typically produced in large-volume batch reactors characterized by straightforward operation but limited efficiency. Process intensification via transition from batch to continuous operation offers the prospect of strong improvements over current state-of-the-art in energy intensity, process safety, capital cost, and physical footprint. The present study investigated the production of two dispersants to demonstrate the viability of batch-to-continuous transition for the specialty chemicals industry: Succinate ester dispersants, formed in a one-step addition reaction, and succinimide dispersants, formed via a two-step reaction with water as by-product. While the ester process showed identical dispersant yields in batch and continuous operation under identical conditions, the succinimide process produced significantly higher yields in the batch compared to the continuous reactor. This could be traced back to an operational difference between these processes: In the batch process, the by-product water is continuously removed from the reactive mixture while purging the reactor head space, rendering the dehydration step effectively irreversible. In contrast, to prevent steam-induced foaming, the continuous reactor is operated at high-enough pressure to maintain water in the liquid phase. This renders the dehydration step incomplete due to thermodynamic equilibrium limitations. However, the full succinimide product yield could be recovered via subsequent continuous drying using a thin film evaporator. This product was indistinguishable from the batch product and fulfilled commercial specifications. Finally, full reversible reaction kinetics were derived based on the continuous reactor operation. Comparison between batch operation results and reactor modeling predictions indicated that the slow apparent kinetics of the industrial batch process is the result of mass transfer limitations due to slow water evaporation, and not caused by limitations in the intrinsic reaction kinetics.