Auburn UniversityRobert Kline

1/19/12

Chemistry

Thermodynamics

Flowsheet Development

What are esters?

ReactionsCarboxylic Acid + Alcohol Ester + Water

R O C R’O

CH3COOH + CH3(CH2)3OH CH3COO(CH2)3CH3 + H2O

Equilibrium Limited

Catalysts• Typically acid catalyzed• Homogeneous (sulfuric acid)• Heterogenous (amberlyst resins)

Ester Keq (@ 363 K)

Equimolar Equilibrium Conversion

Methyl Acetate 16.8 80%

Ethyl Acetate 3.5 65%

Isopropyl Acetate 8.7 75%

Butyl Acetate 10.9 77%

Pentyl Acetate 1.6 56%

Nonideal liquids• This is a chemical system rather than a

hydrocarbon or petrochemical one Significant liquid phase noidealities

can exist• Azeotropes• Liquid-Liquid Behavior

Satiiiii PxPy

Binary data from Horsely’s Azeotropic data, reprinted in Reactive Distillation Design and Control by Luyben and Yu

Azeotrope Temperature (C ) Mole Fraction TypeBuOH/BuOAc/H2O 89.4 0.11/0.13/0.754 Heterogenous

BuOAc/H2O 90.2 0.278/0.722 HeterogenousBuOH/H2O 92.7 0.248/0.752 Heterogenous

BuOH/BuOAc 116.2 0.73/0.27 Homogenous

Vapor Phase Association

HR C OO

H O C RO

H O C RO

HR C OO

H O C RO

Vapor Phase Association• In the vapor phase carboxylic acids can

form weakly bound dimers & trimers• This has an impact on vapor phase density,

fugacity, and enthalpy

Satiiiii PxPy

What are your thermodynamic model choices?• Liquid phase nonideality capable of

modeling 2 liquid phases NTRL UNIQUAC UNIFAQ

• Vapor phase dimerization Hayden O’Connell Nothnagel

Chemistry Issues• Equlibrium limited• Solid or homogenous catalyst

Thermodynamic Issues• Azeotropes• Liquid-Liquid Equilibria

Reaction SeparationRaw

Materials

Recycles

Products

Wastes

Reaction Section CSTR(s) PFR Feed ratios (which RM is easier

to recover?) Catalyst introduction & recovery

Separation Section How can raw materials be

recovered? Can LLE be exploited?

(extractors/decanters/reflux decanters)

What sequence should the separation be done?

Reaction&

SeparationSeparation

RawMaterials

Recycles

Products

Wastes

Rxn & Separation Section Multistage reactor + separator Reactor in a reboiler Reactive distillation Catalyst introduction & recovery

Separation Section How can raw materials be

recovered? Can LLE be exploited?

(extractors/decanters/reflux decanters)

What sequence should the separation be done?