The model reaction chosen to investigate in-line catalyst recovery was the same alkylation reaction optimized by Wen et al., albeit with a different substrate (dimethyl maleate). The starting material was changed to avoid any UV-vis absorbance of the substrate and product in the same wavelength range of the TBADT peak, thus enabling determination of the TBADT concentration from the measurement of UV-vis spectra of the retentate and permeate streams obtained during filtration experiments. The validity of the previously identified optimal reaction conditions was confirmed by varying the catalyst loading, the number of cyclohexane equivalents, and the residence time of the reaction involving the new substrate (Tables in Supplementary Information).