Question

A steam of 100mol/s ethanol(C₂H₅OH) vapor at 400^oC and 1 atm is fed to an adiabatic reator. The ethanol is reacted to produce acetaldehyde (CH₃CHO) vapor and hydrogen (H₂) gas.After a conversion of 30% the products exit from the reactor at 1atm.It is given that the heat capacity of acetaldehyde,in kJ/(mol.^oC) is given as below:

C_p,CH3CHO=50.48X10^-3+13.26x10^-5T-8.049x10^-8T²+23.8X10^-12T³

i)Express the molar flowrate and specific enthalpy for all substances in the inlet-outlet enthalpy table.

ii)Show the stoichiometric equation for the reaction in the reactor.

iii)Calculate the molar flowrate of ethanol,acetaldehyde and hydrogen separately,which exits from the reactor after reaction.

iv)By determining the standard heat of reaction,estimate the temperature of the product stream.

Answer 1

(i)

Inlet:

C2H5OH= 100 mol/s

30% conversion

Outlet:

CH3CHO=0.3*100=30 mol/s

H2=30 mol/s

Remaining C2H5OH=100-30=70 mol/s

From appendix

Heat of formation at 400⁰C

?H⁰f,C2H5OH=-235.31 kJ/mol

?H⁰f,CH3CHO=-166.2 kJ/mol

?H⁰f,H2=0

(ii)

C2H5OH---------->CH3CHO+H2

(iii)

Ethanol=70 mol/s

CH3CHO=30 mol/s

H2=30 mol/s

(iv)

The standard heat of reaction is calculated from the heats of formation as follows:

?H_rx=?H⁰_f,H2+?H⁰_f,CH3CHO-?H⁰_f,C2H5OH

?H_rx=0-166.2-(-235.31)=69.11 kJ/mol

General energy balance equation

?H=x*?H_rx+?nh_out-?nh_in

At 25 C

Cp,H2=29 kj/mol C

Cp,C2H5OH=78 kj/mol c

Cp,CH3CHO=96 kj/mol C

Open system, adiabatic process, no change in potential and kinetic energy.

So

?H=0

h=nCp?T

So

0=30*69.11+70*78*(T2-25)+30*96*(T2-25)+30*29(T2-25)-100*78(400-25)

So

T2=117.5 C