Fig. 6

Schematic overview of the proposed main conversions that occurred during continuous methanol-based elongation of propionate (Pro) and simultaneous propionate and acetate (Pro&Ac) elongation at 309 K. The four scenarios represent the steady-states in the propionate elongation reactor at pH 5.8 (a) and pH 5.5 (b) and in the simultaneous propionate and acetate elongation reactor with 250 (c) and 400 (d) mM methanol in the reactor influent. The conversions with dashed arrows are proposed to maintain the electron balance. The main reactions are indicated with thicker arrows. For simplicity, only the productivities of the compounds with a value higher than 5 mmol/L/day are shown. The reaction equations and Gibbs free energy of the numbered conversions can be found in Additional file 1