Methane (ch4) and oxygen (o2) react to form formaldehyde (ch2o) (reaction #1), with a competing side reaction (#2) in which methane and oxygen form carbon dioxide (co2):
ch4(v) + o2(g) -> ch2o(v) + h2o(l) (reaction #1)
ch4(v) + 2o2(g) -> co2(g) + 2h2o(l) (reaction #2)
a fresh feed of an equimolar gas mixture of ch4 and o2 is combined with a recycle stream and fed to a reactor. the single-pass conversion of ch4 is 30% and the selectivity of ch2o over co2 is 4.5. the exiting products are sent to a condenser in which all of the ch2o and h2o are condensed. the vapor stream exiting the condenser is split into two streams: one stream is recycled and combined with the fresh feed prior to entering the reactor, while the other stream is purged. the purge stream exits the process at a rate of 55 scmh and is composed of 50 mol% ch4, 25 mol% o2, and the balance co2.
a) draw and fully label a flow diagram for this process.
b) based on this information, do you need to assume a basis? explain briefly.
c) assume that the purge stream is at 200°c and 15 atm. calculate the actual volumetric flow rate of this gas stream (in m3 /h) assuming ideal gas behavior.
d) for the conditions in part (c), prove that the ideal gas law is inaccurate. which equation of state would be better to use: (i) srk equation of state or (ii) compressibility factor with kay’s rule? explain briefly.
e) given the composition of the purge stream (50 mol% ch4, 25 mol% o2, and the balance co2), calculate the mass fraction of each component. molecular weight of ch4 = 16 g/mol, molecular weight of o2 = 32 g/mol, and molecular weight of co2 = 44 g/mol.