Question

A process for the production of 1,3-butadiene results from the catalytic dehydrogenation at atmospheric pressure of 1-butene according to the reaction

C4H8(g) C4H6(g) + H2(g)

To suppress side reactions, the 1-butene feed stream is diluted with steam in the ratio of 10 moles of steam per mole of 1-butene. The reaction is carried out isothermally at 525oC, and at this temperature 33% of the 1-butene is converted to 1,3-butadiene. How much heat is transferred to the reactor per mole of entering 1- butene?

Answer 1

The production of 1,3 butadiene is done by the reaction

The reaction occurs at atmospheric pressure and 525°C isothermally

At T = 525°C

33% of 1- butene undergoes conversion

From handbook at T = 25°C , heat of formation values are taken

Hf(1-butene) = -0. 63 KJ/mol

Hf(1-3 Butadiene) = 108.8 KJ/mol

Hf(H2) = 0

∆H_r = ∆Hf _products - ∆Hf_reactants

∆H_r(25°C) = (108.8) -(-0.63) = 109.43 KJ/mol

According to kirchoffs law

∆H(525°C) = ∆H(25°C) + ∆Cp(525-25)

∆Cp = (nCp) _products -(nCp) _reactants

Cp is taken at average temperature of

(25+525) /2 = 275 °C = 548 K

From handbook

Cp(H₂) (g) = 29.288 J/mol °C

Cp(1, 3 Butadiene) (g) = 129.0116 J/mol°C

Cp(1-butene) (g) = 134.5512 J/mol°C

∆Cp = (129.0116+ 29.288) -(134.5512) =

23.7484 J/mol°C

∆H_r(525°C) = 109.43(1000) + (23.7484) (525-25)

∆H_r = 1213042 J/mol = 121.3042 KJ/mol

The reactor is isothermal

Heat of reaction should be added constantly maintain isothermal conditions

Basis : 1 mole butene

Conversion = 0.33

Q = ∆H_r(x)

Q = 0.33(121.3042) =

40.03038 KJ/(mol of 1-butene entering )

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