Question

provide me step by step solution.this is 20 marks question , the question ask to do pfd process flow diagram for formaldehyde production plant using catalytic oxidation of methanol .the main equipment of pfd is mixer, reactor and separator . Unreacted reactants will be recycled but 20% of methanol from the unreacted reactants will be sent to product stream as stabilizer. then state any basis calculation and solve the material balance when overall conversion of methanol is within 80-90 % . The ratio on the amount of feed reactants fixed accordingly before enter the reactor.

Answer 1

The reaction occuring is

Here the fresh feed

is methanol and pure oxygen

I am doing for case of methanol and pure oxygen as feed

Basis :

100 mol/min methanol

The PFD for the process is given below

Overall conversion of methanol is fixed at 90%

Methanol in P

= 100(1-0.90) = 10 mol/min

Formaldehyde in product if overall conversion = 90% according to stiochometry = 100(0.90)

= 90 mol/min

H2O in product according to stiochometry 100(0.90) = 90 mol/min

No oxygen is in product and all of oxygen is consumed

Product analysis

Component	mol/min	mol%	M.W(g/mol)	mass(g/min)
HCHO	90	47.36	30	2700
H2O	90	47.36	18	1620
CH3OH	10	5.263	32	320
Total	190	100		4640

Overall mass is conserved

So

Mass flowrate of F = mass flowrate of P

M. W of methanol = 32 g/mol

M. W of oxygen = 32 g/mol

Average molecular weight of feed = 32 g/mol

Mass flowrate of F = mass flowrate of P =

4640 g/h

Molar flowrate = 4640/32 =145 mol/h

Feed analysis

Component	mol/min	mol%	M.W(g/mol)	mass(g/min)
CH3OH	100	68.965	32	3200
O2	45	31.034	32	1440
Total	145	100		4640

Methanol in product is 20% of total methanol unreacted

Methanol unreacted = (10) /0.20= 50 mol/min

Methanol recycled = 50-10= 40 mol/min

Reactor inlet analysis

Component	mol/min	mol%
CH3OH	100+40 = 140	75.67
O2	45	24.32
Total	185	100

Reactor outlet analysis

Component	mol/min	mol%
Methanol	50	21.739
H2O	90	39.13
HCHO	90	39.13
Total	230	100

Single pass conversion of methane =

((140-50) /140) (100) = 0.6428 = 64.28%

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