A steam of 100mol/s ethanol(C 2 H 5 OH) vapor at 400 o C and 1 atm is fed to an

Question

A steam of 100mol/s ethanol(C2H5OH) vapor at 400oC 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:

Cp,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.

Explanation / Answer

(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:

?Hrx=?H0f,H2+?H0f,CH3CHO-?H0f,C2H5OH

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

General energy balance equation

?H=x*?Hrx+?nhout-?nhin

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

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