C CATA LYSTS S IN P PETRO O REF FINING G P PROC CESSES S 016 - - PDF document

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C CATA LYSTS S IN P PETRO O REF FINING G P PROC CESSES S 016 D Decem mber 20 Applied Catalysis RC 09121 RA HDT 09121_A DE16 Ver 1.0 Outline The chemical reaction: thermodynamics and kinetics Definition, role and

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C P

D

CATA PROC

Decem

LYSTS CESSES

mber 20

S IN P S

016 PETRO O‐REF FINING G

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Applied Catalysis

RC ‐ 09121 ‐ RA HDT ‐ 09121_A ‐ DE16 ‐ Ver 1.0

Outline

RC ‐ 09121 ‐ RA HDT ‐ 09121_A ‐ DE16 ‐ Ver 1.0

The chemical reaction: thermodynamics and kinetics Definition, role and classification of the catalysts Preparation of the industrial catalyst Catalyst properties

SLIDE 3

Outline

RC ‐ 09121 ‐ RA HDT ‐ 09121_A ‐ DE16 ‐ Ver 1.0

The chemical reaction: thermodynamics and kinetics Definition, role and classification of the catalysts Preparation of the industrial catalyst Catalyst properties

CHEMICAL REACTION

THERMODYNAMIC Feasibility of the reaction at T, P KINETICS Idea of rate

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RC ‐ 09121 ‐ RA HDT ‐ 09121_A ‐ DE16 ‐ Ver 1.0

Thermodynamics

Thermodynamics is the science of initial and final states It allows to predict the spontaneous evolution of a system, knowing the thermodynamical values ΔG = Gfinal ‐ Ginitial = ΔH ‐ TΔS

ΔH: enthalpy of the reaction ΔS: entropy of the reaction

It is essential to consider very early the thermodynamic aspect to determine whether the reaction is feasible or not

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Thermodynamics

Enthalpic and entropic balances for chemical reactions

Impossible G > 0 G < 0: Total (combustion)

H S G = 0; H > 0 (Cracking reaction) G = 0; H < 0 (benzene hydrogenation) G = H ‐ TS

Balanced and endothermic Balanced and exothermic

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Thermodynamics

Evolution of a reaction with the pressure If there is a decrease of the number of moles, the reaction is favored by an increase of pressure (and vice versa) Examples: CRACKING n = 1 n = 3  Reaction favored at low pressure

2 H H H H + C = C H + H H H H H H H H H C = C C C C H H H H H H H H H H H H H H H H C C C C C C C H

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Thermodynamics

DIMERIZATION n = 2 n = 1  Reaction favored at high pressure ISOMERIZATION n = 1 n = 1  The reaction is not influenced by a variation of pressure

H C = C H H H + H C = C H H H H C C = C C H H H H H H H H H H H C C C H H H H H H H H H H H C C C C C H H H C H3 C 3 H

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RC ‐ 09121 ‐ RA HDT ‐ 09121_A ‐ DE16 ‐ Ver 1.0

Thermodynamics

Evolution of a reaction with the temperature An endothermic reaction is favored at high temperature An exothermic reaction is favored at low temperature Examples:

Cracking

H > 0  reaction favored at high temperature

Dimerization

H < 0  reaction favored at low temperature

Isomerization

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Enthalpic balances

Benzene hydrogenation

Benzene + 3H2 Cyclohexane ∆Hf298 (kcal/mol) = +19.82 ‐29.43 ∆Hf298 (kcal/mol) = ‐49.25

Hydrogenation = exothermic reaction  Favored at low temperature

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Enthalpic balances

N‐Heptane aromatization

N‐heptane Toluene + 4 H2 ∆Hf298 (kcal/mol) = ‐44.88 +11.95 ∆H (kcal/mol) = +56.83

Aromatization = endothermic reaction  Favored at high temperature

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Enthalpic balances

N‐Heptane hydrogenolysis

N‐heptane + 3H2  3 Ethane + 1 Methane ∆Hf298 (kcal/mol) = ‐44.88 ‐(20.24) ‐17.89 ∆H (kcal/mol) ‐33.73

Hydrogenolysis = exothermic reaction  Favored at low temperature

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Enthalpic balances

Desulfurization

Thiophen (C4H4S) + 4H2 Butane + H2S ∆Hf298 (kcal/mol) = +27.66 ‐30.15 ‐4.82 ∆H (kcal/mol) = ‐62.33

HDS = exothermic reaction  Favored at low temperature

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Example: n‐heptane dehydrocyclization

1. Write the equation of the reaction
2. The reaction is endothermic (H = 250 kJ/mol)

What is the influence of temperature and pressure on the evolution of this reaction?

The number of moles increases
H > 0

 The reaction is favored at low pressure  The reaction is favored at high temperature

H H H H H H H H H H H H H H H C C C C C C C H CH 3 + 4 H 2

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n‐heptane dehydrocyclization

3. Check your answer on the figure

at T = 480⁰C % Tol = 50% for 35 bars and H2/HC = 4 % Tol = 92% for 18 bars at p = 35 bars % Tol = 50% for 480°C and H2/HC = 4 % Tol = 82% for 510°C

 The reaction is favored at low pressure and high temperature

n‐heptane‐toluene equilibrium under hydrogen pressure

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n‐heptane dehydrocyclization

4. The notion of H2/HC ratio, is very important because it allows to have access

to the H2 partial pressure

Determine the H2 partial pressure for a total pressure of 18 bars and H2/HC (molar) of 10

2 H p = t p HC n HC 10.n HC 10.n HC 10.n 2 H n    

16.35b 18 11 10 t p 11 10 2 H p     

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Thermodynamics

Isobutane dehydrogenation - Thermodynamical equilibrium 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 1 2 3 4 5 6 7 Pressure (atm) iC4 Conversion (%) 500°C 520°C 540°C 560°C 580°C 600°C H2/iC4 = 1

C4H10 C4H8 + H2

Exo or endothermic reaction?

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Kinetics

The aim of kinetics is to study the course

f the chemical transformation versus time

IDEA OF THE REACTION RATE [A]  [B] V = k [A] for a 1 order reaction k = rate constant k = ko e‐Ea/RT (Arrhénius Law) Ea= Activation energy Activation energy: energy to provide to the system to transform the reactants into products