Question

The gas that comes out of a gasoline stabilizer has the following composition by volume: C₃H₈ 8%, CH₄ 78%, C₂H₆ 10%, and C₄H₁₀ 4%. This gas that comes out at 90 ° F and 16 psi of absolute pressure is supplied at the rate of 70,000 ft³ / h to a gas conversion plant, where the following reactions take place:

CnH2n + 2 + n H2O n CO + (2n + 1) H2

CO + H2O CO2 + H2.

CnH2n + 2 gases are converted to 95% and 90% of CO that also reacts, depending on the reactions. Make a process diagram and calculate:

a) Average molecular weight of the gas coming out of stabilizer.

b) Weight of the gas supplied to the conversion plant in lb / h.

c) Weight of the H2 that leaves the converter plate in lb / h.

d) Composition in volume of the gases that leave the converter plant.

Thank you!

Answer 1

Feed composition

C_{​​​​​​3}​​H₈    - 8%

CH​​_{​​​​​4} -  78%

C_{​​​​​​2} H_​​6. -  10%

C_{​​​​​​4} H_{​​​​​​10} - 4%

M.W of propane = 3(12)+(8)= 44

M.W of methane = 12+4 = 16

M.W of ethane = 2(12)+6 = 30

M.W of butane = 4(12)+10 = 58

M.W(avg)= 44(0.08)+ 16(0.78)+ 30(0.10) + 58(0.04)= 21.32

B)

V = 70000 ft^{​​​​​3}/h = 1982.1792 m^{​​​​​​3}/h

T = 90°F = 32.22°C = 305.372 K

P = 16 psi

1 psi = 6894.757 Pa

16 psi = 110316.112 Pa

n = PV/(RT)

n = (110316.112×1982.1792)/(8.314×305.372)

n = 86127.658 mol/h = 86.12765 Kmol/h

Feed analysis

Component	mol%	Kmol/h	M.W(Kg/Kmol)	kg/h.
Propane	8	6.8902	44	303.168
Methane	78	67.1795	16	1074.872
Ethane	10	8.6127	30	258.381
Butane	4	3.4451	58	199.8158
Total	100	86.12765		1836.2368

Mass flow rate of gas = 1836.2368 Kg/h

1 Kg = 2.205 lb

Mass flow rate of gas = 4048.9021 lb/h

C)

The reactions occurring are

Conversion is 95%

Conversion of CO - 90%

Moles of H2 produced

= (6.8902((2×3)+1) + 67.1795((2×1)+1)+ 8.6127((2×4)+1)+ 3.4451 ((2×2)+1)))(0.95)= 327.2842 Kmol/h

M.w of H2 = 2 Kg/Kmol

Mass of H2 produced = 327.2842(2)=

654.5684 Kg/h

1 Kg = 2.205 lb

Mass of H2 produced = 654.5684(2.205)= 1443.323 lb/h

Moles of CO produced =( 6.8902(3)+ 67.1795(1)+8.6127(2) + 3.4451(4))(0.95)= 112.9131 Kmol/h

90% of CO reacts

D)

Composition of outlet gases

mol% = vol%

Component	Kmol/h	mol%
Propane	6.8902(0.05)= 0.34451	0.0775
Methane	(67.1795)0.05)= 3.3589	0.7562
Ethane	8.6127(0.05)= 0.430635	0.0969
Butane	3.4451(0.05)= 0.17225	0.03878
CO	11.2913	2.542
CO2	101.6217	22.879
H2	327.2842	73.686
Total	444.158	100

Please upvote if helpful