Automated pH and conductivity conditioning using feedback control to support a two-step continuous purification process

Integrated continuous flow method with dual feedback-based controls for online analysis and process control

The concept of an integrated automated continuous flow method with dual feedback controls is presented for diluting a stock solution to provide a solution of a given concentration. The one control is used for the online process monitoring by a feedback-based flow ratiometry, where the product (the diluted liquid) is titrated through the rapid bidirectional scan of the product/reagent flow ratio. The feedback control limits the scanning to the necessary range to increase the analytical throughput. The other control is used for the process control to output the product with a preset concentration. The merging ratio of the stock solution and a solvent (diluent) is changed based on the information from the online analysis. The concept was verified by applying it to producing 0.1 mol dm^-3 CH₃COOH. When the stock concentration was changed from 0.1 (reference concentration) to 0.3 and then 0.2 mol dm^-3, the system searched for the suitable merging ratio and converged the output concentration to the reference value within 7.43 min with a relative error below 1.05%. The mean throughput rate of the process analysis was 11.2 titrations min^-1. Successful results were also obtained for the 0.1 mol dm^-3 HCl production. The present concept could be the basis for process control with reduced wasteful output and effluent treatment with eco-friendly treated water discharge, resulting in the contribution to SDGs' goals of 6 (Clean water and sanitation), 9 (Industry, innovation and infrastructure), and 14 (Life below water).