The RTD profiles of the CSTR cascade were obtained using the pulse injection method (Fig. 2). The carrier phase was deionized (DI) water, and the tracer was methylene blue. In-line UV-Vis spectroscopy (light source: Ocean Optics, Inc., DH-2000-BAL; spectrometer: Ocean Optics, Inc., HR2000+) was used to determine the concentration profiles of the tracer at the inlet and outlet. A six-way valve (IDEX Health & Science LLC., MXP7900-000) combined with LabVIEW control enabled automatic pulse injection and data collection.

Fig. 2 Scheme of the residence time distribution measurement using in-line UV-Vis to record concentration profiles at the inlet and outlet.

Procedure for predicting reaction conversions in the CSTR cascade

The scheme of the setup is shown in Fig. S1 (see the ESI†). Reagents for the Diels–Alder reaction (Scheme 1), isoprene and maleic acid anhydride, were prepared in the DMF solvent. The concentration of isoprene solution was 1.0 M and the concentration of maleic acid anhydride solution was 1.5 M. Two HPLC pumps (AZURA P 4.1S) were used to deliver reagent solutions into the reactor. Mineral wool was used to insulate the reactor in order to minimize the temperature gradient through the reactor wall. A thermocouple was placed between two reactor units to measure the reaction temperature. The product sample was diluted using ethyl acetate (1 : 20) and cooled down to 0 °C in an ice bath in order to quench the reaction. Conversions were measured by gas chromatography (Agilent 6890).

Scheme 1 The Diels–Alder reaction of isoprene and maleic acid anhydride.