Chapter 4, Problem 4.67P

Methane and oxygen react in the presence of a catalyst to form formaldehyde. In a parallel reaction, methane is oxidized to carbon dioxide and water:

CH4 + Cb -> HCHO + H₂O

CH4 + 202 -* CO2 + 2H₂O

The teed to the reactor contains equimolar amounts of methane and oxygen. Assume a basis of 1 (X) mol feed/s.

1. Draw and label a flowchart. Use a degree-of-freedom analysis based on extents of reaction to determine how many process variable values must be specified for the remaining variable values to be calculated.
2. Use Equation 4.6-7 to derive expressions for the product stream component flow rates in terms of the two extents of reaction. £1 and ^₂.
3. The fractional conversion of methane is 0.900 and the fractional yield of formaldehyde is 0.855. Calculate the molar composition of the reactor output stream and the selectivity of formaldehyde production relative to carbon dioxide production.
4. A classmate of yours makes the following observation: “Ifyou add the stoichiometric equations far the two reactions, you get the balanced equation
2CH ₄ + 3O ₂ - HCHO + CO ₂ + 3H ₂O

The reactor output must therefore contain one mole of CO2 for every mole of HCHO, so the selectivity' of formaldehyde to carbon dioxide must be 1.0. Doing it the way the book said to do it, I got a different selectivity. Which way is right, and why is the other way wrong?" What is your response?