LECTURE 3 REACTION EVALUATIONS

LECTURE 3 REACTION EVALUATIONS

CONVERSION, EFFICIENCY, YEILDThe conversion of ethylene to ethanol is given by:

CH2=CH2 + H2O CH3CH2OHIf in an acid catalyzed reaction, 6.000 moles of ethylene and 10.000 moles of water were fed to a reactor and the reactor effluent contained 0.244 mole of ethanol 0.9750 moles of water and 5.748 moles of ethylene then:

Conversion of ethylene is:

The efficiency of the process, selectivity of the catalyst is x 100 = 97.0%

The yeild of ethanol based upon ethylene converted is x 100 = 97.0%

The yeild of ethanol based on ethylene charged is x 100 = 4.07%

ACADEMIC vs INDUSTRIALThere are large number of commercially important processes that are based upon familiar reactions in textbooks:The reduction of nitrobenzene to aniline:

NO2+ 3H2

300oC, Cu catalystNH2 + 2H2O

the manufacture of aspirin

OH

C

O

OH

+ acetic anhydride

OC

O

H3C

C

O

OH

+ acetic acid

The manufacture of magnesium metal MgCl2 electrolysis Mg (s) + Cl2

The production f calcium hydroxide from limestones:CaCO3 heat CaO + CO2

CaO + H2O Ca(OH)2

EVALUATION OF A REACTION:Suppose we are given a task of producing ethyl amine. We might want to consider the following reactions:1. CH3CH2Cl + NH3 → CH3CH2NH2 + HCl 2. CH3C≡N + 2H2 → CH3CH2NH2 3. CH3CH2NO2 + 3H2 → CH3CH2NH2 + 2H2O

4. CH3C(=O)H + NH2OH + H2 → CH3CH2NH2 +

2H2O 5. CH3C(=O)H + NH3 + H2 → CH3CH2NH2 + H2O 6. CH3CH2OH + NH3 → CH3CH2NH2 + 2H2O 7. CH2=CH2 + NH3 → CH3CH2NH2 8. CH3-CH3 + 1/2N2 + 1/2H2 → CH3CH2NH2

What factors must be considered when selecting which (if any) of the reactions is most suitable?

ECONOMIC FEASIBILITY:To asses comparative economic potential among the various possible reactions for producing ethyl amine, must estimate the difference in market value between reactants and products. At first approximation, assume1) 100% yeild2) No costs for solvents or catalysis3) No value for by-products

costs, costs, costs

Chemical Value ($/kg)acetaldehyde 0.068acetonitrile 0.254ammonia 0.068Ethane 0.041ethanol 0.114

ethylamine 0.438Ethyl chloride 0.084

ethylene 0.231hydrogen 0.039

hydroxylamine 0.568nitroethane 0.404

nitrogen 0.009

for reaction 1 CH3CH2Cl + NH3 → CH3CH2NH2 + HCl 64.5 amu 17.0 amu 45.1amu 53.5 amu64.5 kg 17.0 kg 45.1 kg 53.5 kgTo produce a kg of EA, requires 1.43 kg of ethyl chloride at a cost of $0.118 plus 0.354 kg of ammonia at a cost of 0.052. Thus the total cost for the reactants is $0.170 to produce 1 kg of AE which has a market value of $0.439Difference $0.439-0.170 = $0.269 (for utilities, equipment depreciation, labor, etc) marketing cost + profits.

economic feasibilityReactions /RM RM Cost Market

value DiffCH3CH2Cl + NH3 0.170 +0.269CH3CN + 2H2 0.235 +0.204CH3CH2NO2 + 3H2 0.678 -0.234CH3CHO + NH2OH + 2H2O

1.102 -0.926

CH3CHO + NH3 + H2 0.094 +0.344CH3CH2OH + NH3 0.141 +0.297CH2=CH2 + NH3 0.170 +0.269CH3CH3 + 1/2N2 + 1/2H2 0.031 +0.408

Processes based on nitrotroethane and hydroxylamine are not economically feasible

Process based on acetaldehyde or ethanol has raw material has cost advantage over processes using ethyl chloride or ethylene

A process using ethane would have the lowest raw material cost

THERMODYNAMIC FEASIBILITYAs an example of this type of calculations let us consider the dissociation of Ethyl Choride:

CH3CH2Cl CH2=CH2 + HCl

THERMODYNAMIC DATA:At 298 K

CH2CH2Cl CH2=CH2 HCl∆H -26.70 12.50 -22.06∆G -14.34 16.28 -22.07S 65.93 52.45 44.64

At 1000 K∆H -30.43 9.21 -2.56∆G 18.60 28.85 -24.28S 93.80 72.07 53.25

278 K 1000 K∆Hrxn +17.14 +17.08∆Grxn +7.86 -14.43∆Srxn +31.15 +31.52

An indication of the thermodynamic feasibility of a reaction is given both by the magnitude and sign of ∆Grxn

Change in Free Energy Indication

∆G is - promising

Small +∆G Worthy of further investigation

Large +∆G Possible at unusual conditions

SELECTED THERMODYNAMIC DATA, ∆Gf

Substance 298 K 1000 KCH2=CH2 16.28 28.25CH3-CH3 -7.87 26.13CH3CH2NH2 8.91 60.96CH3CH2-OH -40.22 1.98NH3 -3.86 14.85H2O -54.64 -46.04H2 0 0N2 0 0

For the following reaction: CH3-CH3 + 1/2N2 + 1/2H2 → CH3CH2NH2

∆Grxn = ∑ ∆Gproducts - ∑ ∆Greactants ∆G298 = ∆G1000 =

For the following reactionCH3CH2OH + NH3 → CH3CH2NH2 + 2H2O∆Grxn = ∑ ∆Gproducts - ∑ ∆Greactants

∆G298 = ∆G1000 =

For the reaction,CH2=CH2 + NH3 → CH3CH2NH2

∆Grxn = ∑ ∆Gproducts - ∑ ∆Greactants ∆G298 = ∆G1000 =

For the following reaction: CH3-CH3 + 1/2N2 + 1/2H2 → CH3CH2NH2

∆Grxn = ∑ ∆Gproducts - ∑ ∆Greactants ∆G298 = +16.78 kcal/mol ∆G1000 = + 34.83 kcal/mol

For the following reactionCH3CH2OH + NH3 → CH3CH2NH2 + 2H2O∆Grxn = ∑ ∆Gproducts - ∑ ∆Greactants

∆G298 = -1.65 kcal/mol ∆G1000 = -1.91 kcal/mol

For the reaction,CH2=CH2 + NH3 → CH3CH2NH2

∆Grxn = ∑ ∆Gproducts - ∑ ∆Greactants ∆G298 = -3.51 kcal/mol ∆G1000 = +17.86 kcal/mol

OTHER FACTORS By-products Side reactions RM and product handling Etc.