Table 1 Possible pathways from literature and the calculation of the Gibbs free energy changes for caproic acid formation

Equation (1)

3Ethanol + 4H₂ + 2H⁺→Caproate + 4H₂O

\(\Delta G_{r}^{0\prime }\) = − 96.71 kJ/mol

[31]

Equation (2)

Butyrate + Ethanol + 2H₂ + H⁺→ Caproate + 2H₂O

\(\Delta G_{r}^{0\prime }\) = − 48.41 kJ/mol

Equation (3)

Butyrate + 2CO₂ + 6H₂ → Caproate + 4H₂O

\(\Delta G_{r}^{0\prime }\) = − 143.29 kJ/mol

Equation (4)

Ethanol + H₂O → Acetate + 2H₂ + H⁺

\(\Delta G_{r}^{0\prime }\) = 9.65 kJ/mol

[5]

Equation (5)

4Ethanol + 4Acetate → 4Butyrate + 4H₂O

\(\Delta G_{r}^{0\prime }\) = − 38.65 kJ/mol

Equation (6)

Ethanol + Butyrate → Caproate + H₂O

\(\Delta G_{r}^{0\prime }\) = − 38.76 kJ/mol

Equation (7)

Lactate + H₂O → Acetate + 2H₂ + CO₂

\(\Delta G_{r}^{0\prime }\) = − 6.9 kJ/mol

[18]

Equation (8)

Lactate + Acetate + H⁺ → Butyrate + H₂O + CO₂

\(\Delta G_{r}^{0\prime }\) = − 97.5 kJ/mol

Equation (9)

Lactate + Butyrate + H⁺ → Caproate + H₂O + CO₂

\(\Delta G_{r}^{0\prime }\) = − 80.9 kJ/mol