How is the hydrogen-to-carbon ratio in methanol synthesis calculated?
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The hydrogen-to-carbon ratio of the fresh gas used in methanol synthesis is very important, but when we were learning*, we only knew to plug the parameters into formulas to calculate it: H2/CO2/CO, CO2=? ? But what I want to know is how this formula was derived; I hope experts can give some guidance
Currently, methanol in industry is synthesized from CO, CO2, and hydrogen through a gas-solid phase catalytic reaction under pressure. It is currently recognized that three reactions occur in the synthesis of methanol from syngas: CO + 2H2 = CH3OH (1), CO2 + 3H2 = CH3OH + H2O (2), and CO + H2O = CO2 + H2 (3). These three reactions proceed at different rates, with reaction (1) being faster and reaction (2) being slower. The transformation/inverse transformation reactions are also not reactions that reach equilibrium instantaneously; their forward and reverse directions are often influenced by the amount of water produced in reaction (2). At the same time, there are also minor side reactions that produce high-carbon hydrocarbons and alcohols with more than 2 carbon atoms. Considering only reaction (1), the stoichiometry is n (H2)/n (CO) = 2; considering only reaction (2), the stoichiometry is n (H2)/n (CO2) = 3 ； The two reactions coexist, with a stoichiometric ratio of n (H2－CO2)/n (CO+CO2) = 2 (R value). The stoichiometric ratio n (H2－CO2)/n (CO＋CO2) = 2 applies to feed gases with any CO/CO2 ratio. Regardless of the number of forward or reverse reaction transformations that occur during the process, the gas stoichiometric value (R) remains unaffected by the system. During the methanol synthesis reaction, regardless of the respective conversion rates of CO and CO2, the hydrogen-to-carbon ratio in the residual gas remains constant. By appropriately taking into account the formation of side reactions, the hydrogen content can be increased slightly to n (H2－CO2)/ n (CO+CO2) = 2.05–2.1. Therefore, the raw material gas for methanol synthesis requires an n (H2－CO2)/ n (CO+CO2) ratio of around 2.1.
Practice has shown that the composition at the maximum reaction rate is not the stoichiometric composition, but rather the optimal hydrogen-to-carbon ratio determined by the kinetic equation.
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What was said upstairs is very detailed; I’ve learned it.