Issues related to the purity of gas in methanol synthesis
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There is a question: Why is the indicator for the purity of the gas in methanol synthesis set at (H2—CO2)/(CO+CO2) = 2.1, rather than H2/CO = 1.0? Is there a difference between the two? This post was last edited by tomy120 on 2009-3-18 07:28]
(1) CO + 2H2 → CH3OH + Q (2) CO2 + 3H2 → CH3OH + H2O + Q These are the equations for the main synthesis reactions
CO2 + H2 = CO + H2O; a certain amount of H2 is consumed as a result of the reaction between the previously existing CO and the CO that is produced in this process. Last edited by tomy120 on 2009-3-18 07:27.]
Can someone be more specific? The person upstairs didn’t explain it clearly enough!
From a reflective perspective, the comparison theory appears somewhat theoretical; in simple terms, two hydrogen atoms and one carbon monoxide molecule combine to form methanol, while three hydrogen atoms and one carbon dioxide molecule combine to form methanol with an additional water molecule – meaning that one more hydrogen atom is consumed in the latter case.
This 2.1 is based on the chemical reaction equation, but it cannot be achieved in actual production, or it might even exceed that value!
In fact, the main reactions involved in synthesis are these two; the hydrogen-to-carbon ratio required for complete reaction is 2, with a slight excess of hydrogen being used to alkylate the olefins present in the upstream syngas. (1) CO + 2H2 → CH3OH + Q (2) CO2 + 3H2 → CH3OH + H2O + Q
A hydrogen-to-carbon ratio of H2/CO=1 is too low; it is not the optimal ratio for methanol synthesis. In the synthesis, the theoretical ratio of hydrogen to CO is 2, while that of CO2 is 3. An excess of reactants in the reaction facilitates its progression to the right.
Since there are inert gases in the fresh gas, the system needs to be vented. The hydrogen content in the vent gas is much higher than that of CO; therefore, it will be slightly above 2.0 as per theory. The amount to be controlled depends on hydrogen recovery and the inert gas content in the fresh gas.