Method for producing liquid fuel and liquid fuel synthesis system

A method of producing a liquid fuel, comprising:

• causing a raw material gas containing at least a carbon oxide and hydrogen to flow into a reactor storing a catalyst;
• and
• producing the liquid fuel from the raw material gas through a conversion reaction in the presence of the catalyst,
• wherein the raw material gas further contains an inert gas,
• wherein the liquid fuel contains methanol,
• wherein an approximate straight line produced by subjecting points plotted on the basis of results of thermodynamic equilibrium calculation, which is performed on the conversion reaction at 200° C. and 4 MPa (G) when a ratio of a concentration of carbon monoxide (CO) to a concentration of carbon dioxide (CO2) in the carbon oxide in the raw material gas and a ratio of a concentration of the inert gas (Inert) to a concentration of the carbon dioxide (CO2) in the raw material gas are changed, against an X-axis indicating a ratio “(Inert+CO)/CO2” in the raw material gas and a Y-axis indicating a product “(ratio of suppressed heating value)×(ratio of obtained combustion energy increase)” to linear approximation (Y=ax+b) has a gradient “a” of 1.4 or less,
• wherein the plotting is performed on a total of 18 pieces of data when an Inert/CO2 ratio is changed in a range of from 0 to 1.6 in increments of 0.1, and when the Inert/CO2 ratio is 0.05 for a case in which the raw material gas having each CO/CO2 ratio is used, and
• wherein the ratio of the suppressed heating value and the ratio of the obtained combustion energy increase are values calculated from the following respective equations:
• ratio of f suppressed heating value=(heating value calculated under reference condition-heating value calculated when each raw material gas is used)/heating value calculated under reference condition;
• and
• ratio of obtained combustion energy increase=(combustion energy of produced methanol calculated when each raw material gas is used-combustion energy of produced methanol calculated under reference condition)/combustion energy of produced methanol calculated under reference condition, where
• the reference condition is a case in which a raw material gas containing only carbon dioxide and hydrogen at a ratio “CO2/H2” of ⅓ is used, and
• the combustion energy of the produced methanol is a value calculated from an “equation:
• combustion energy of produced methanol=production amount of methanol×higher heating value of methanol.”