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CONVERSION, EFFICIENCY, YEILD The conversion of ethylene to ethanol is given by: CH2=CH2 + H2O CH3CH2OH If 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 INDUSTRIAL There are large number of commercially important processes that are based upon familiar reactions in textbooks: The reduction of nitrobenzene to aniline:
The manufacture of magnesium metal MgCl2electrolysis 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, assume • 100% yeild • No costs for solvents or catalysis • No value for by-products
for reaction 1 CH3CH2Cl + NH3→ CH3CH2NH2 + HCl 64.5 amu 17.0 amu45.1amu 53.5 amu 64.5 kg 17.0 kg 45.1 kg 53.5 kg To 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 $0.439 Difference $0.439-0.170 = $0.269 (for utilities, equipment depreciation, labor, etc) marketing cost + profits.
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 FEASIBILITY As an example of this type of calculations let us consider the dissociation of Ethyl Choride: CH3CH2Cl CH2=CH2 + HCl
An indication of the thermodynamic feasibility of a reaction is given both by the magnitude and sign of ∆Grxn
For the following reaction: CH3-CH3+ 1/2N2 + 1/2H2 → CH3CH2NH2 ∆Grxn = ∑ ∆Gproducts - ∑ ∆Greactants ∆G298 = ∆G1000 =
For the following reaction CH3CH2OH + 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 reaction CH3CH2OH + 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.