The most studied molten carbonate-direct lignin fuel cell (MC-LFC) or molten carbonate-direct carbon fuel cell (MC-DCFC) prototypes are those which are fed by fossil fuel. Substituting these fossilized fuels in the MC-DCFC operation with lignin, which is a bio-based carbon, may make this system more efficient, clean, and sustainable. The manipulation module (Mixture) and the computational module (Equilib) of the FactSage package were used to simulate two systems that can represent the anodic compartment of a direct carbon fuel cell based on MC-DCFC. The first system includes lignin and a mixture of molten carbonate (Li2CO3-Na2CO3-Cs2CO3). The second system uses also lignin and a mixture of molten carbonate (Li2CO3-Na2CO3-Cs2CO3) and CO2 gas was also added. The results show the formation of mixed gases in the anodic compartment which are composed of H2, CO, CO2, CH4, and H2O. The relative concentration of each of the species of this mixed gas has an impact on the efficiency of the MC-DCFC. How the relative concentration of these gases in this electrolyte can impact the performance parameters of the MC-DCFC is systematically analyzed. If the operating conditions of the fuel cell are optimized to get a gas composition of mainly CO2 with low amounts of H2, CO, CH4, and H2O in the anode compartment of the MC-DCFC, this will help to improve the conversion efficiency of lignin fuel in the MC-DCFC.