Stoichiometric number for syngas

One of the most important ways to describe the quality of synthesis gas is by using the stoichiometric number, this number respresents the hypothetical ratio of hydrogen to carbonmonoxide. It easy to see that if you want to synthesize methanol from hydrogen and carbonmonoxide the molar ratio should  be 2 to 1 repectivily. It’s harder to see how close the actual syngas (that also includes CO2) is to this desired molacular ratio of 2.

Therefor industry can up with a way to describe a mixutre of H2, CO and CO2 as if it where only H2 and CO. Since CO2 can be converted to CO via the water-gas-shift reaction, CO2 can be expressed as being CO by subtraction the amount of hydrogen thats needed for the shift reaction (this equals the CO2 concetration since CO2 and H2 react one on on to form CO).

SNnumber

For methanol synthesis the ratio of  hydrogen to carbon monoxide should be optimal at Sn equals 2. At Sn equals two all the hydrogen is consumed in hydrogenation of carbonmonoxide and noting is left. Below a graph is showing that what concentrations of the various components can be to achieve Sn equals 2. As can be seen there are two limitting situations at hydrogen concentrations of 66.7 and 75%.

 SN2

Fitting with mathematica

MathematicaThis video will show you how to solve different parameters for a ratelaw.