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 classification of the catalysts Preparation of the industrial catalyst Catalyst properties 2 RC ‐ 09121 ‐ RA HDT ‐ 09121_A ‐ DE16 ‐ Ver 1.0
Outline The chemical reaction: thermodynamics and kinetics Definition, role and classification of the catalysts Preparation of the industrial catalyst Catalyst properties 3 RC ‐ 09121 ‐ RA HDT ‐ 09121_A ‐ DE16 ‐ Ver 1.0 CHEMICAL REACTION THERMODYNAMIC KINETICS Feasibility of the Idea of rate reaction at T, P 4 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 Δ G = G final ‐ G initial = Δ H ‐ T Δ S Δ H: enthalpy of the reaction Δ S: entropy of the reaction It is essential to consider very early the thermodynamic aspect to determine whether the reaction is feasible or not 5 RC ‐ 09121 ‐ RA HDT ‐ 09121_A ‐ DE16 ‐ Ver 1.0 Thermodynamics Enthalpic and entropic balances for chemical reactions G = H ‐ T S G < 0: Total (combustion) H S G = 0; H > 0 Balanced and endothermic (Cracking reaction) G = 0; H < 0 (benzene hydrogenation) Balanced and exothermic Impossible G > 0 6 RC ‐ 09121 ‐ RA HDT ‐ 09121_A ‐ DE16 ‐ Ver 1.0
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 H H H H H H H H H H H C C C C C C C H H C C C C = C H + H C = C H + H 2 H H H H H H H H H H H H H H n = 1 n = 3 Reaction favored at low pressure 7 RC ‐ 09121 ‐ RA HDT ‐ 09121_A ‐ DE16 ‐ Ver 1.0 Thermodynamics DIMERIZATION H H H C = C H + H C = C H H C C = C C H H H H H H H H H n = 2 n = 1 Reaction favored at high pressure ISOMERIZATION H H H H H H3 C H H H H C C C C C H C C C H H H H H H H H H C 3 n = 1 n = 1 The reaction is not influenced by a variation of pressure 8 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: H > 0 reaction favored at high temperature ● Cracking ● Dimerization H < 0 reaction favored at low temperature ● Isomerization 9 RC ‐ 09121 ‐ RA HDT ‐ 09121_A ‐ DE16 ‐ Ver 1.0 Enthalpic balances Benzene hydrogenation Benzene + 3H 2 Cyclohexane ∆ Hf298 (kcal/mol) = +19.82 0 ‐ 29.43 ∆ Hf298 (kcal/mol) = ‐ 49.25 Hydrogenation = exothermic reaction Favored at low temperature 10 RC ‐ 09121 ‐ RA HDT ‐ 09121_A ‐ DE16 ‐ Ver 1.0
Enthalpic balances N ‐ Heptane aromatization N ‐ heptane Toluene + 4 H 2 ∆ Hf298 (kcal/mol) = ‐ 44.88 +11.95 0 ∆ H (kcal/mol) = +56.83 Aromatization = endothermic reaction Favored at high temperature 11 RC ‐ 09121 ‐ RA HDT ‐ 09121_A ‐ DE16 ‐ Ver 1.0 Enthalpic balances N ‐ Heptane hydrogenolysis N ‐ heptane + 3H 2 3 Ethane + 1 Methane ∆ Hf298 (kcal/mol) = ‐ 44.88 0 ‐ (20.24) ‐ 17.89 ∆ H (kcal/mol) ‐ 33.73 Hydrogenolysis = exothermic reaction Favored at low temperature 12 RC ‐ 09121 ‐ RA HDT ‐ 09121_A ‐ DE16 ‐ Ver 1.0
Enthalpic balances Desulfurization Thiophen (C 4 H 4 S) + 4H 2 Butane + H 2 S ∆ Hf298 (kcal/mol) = +27.66 0 ‐ 30.15 ‐ 4.82 ∆ H (kcal/mol) = ‐ 62.33 HDS = exothermic reaction Favored at low temperature 13 RC ‐ 09121 ‐ RA HDT ‐ 09121_A ‐ DE16 ‐ Ver 1.0 Example: n ‐ heptane dehydrocyclization 1. Write the equation of the reaction CH 3 H H H H H H H H C C C C C C C H 4 H 2 + H H H H H H H 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 The reaction is favored at low pressure ● H > 0 The reaction is favored at high temperature 14 RC ‐ 09121 ‐ RA HDT ‐ 09121_A ‐ DE16 ‐ Ver 1.0
n ‐ heptane dehydrocyclization 3. Check your answer on the figure at T = 480 ⁰ C % Tol = 50% for 35 bars and H 2 /HC = 4 % Tol = 92% for 18 bars at p = 35 bars % Tol = 50% for 480°C and H 2 /HC = 4 % Tol = 82% for 510°C The reaction is favored at low pressure and high temperature n ‐ heptane ‐ toluene equilibrium under hydrogen pressure 15 RC ‐ 09121 ‐ RA HDT ‐ 09121_A ‐ DE16 ‐ Ver 1.0 n ‐ heptane dehydrocyclization 4. The notion of H 2 /HC ratio, is very important because it allows to have access to the H 2 partial pressure Determine the H 2 partial pressure for a total pressure of 18 bars and H 2 /HC (molar) of 10 10.n HC n 10.n p = p H HC t H 10.n n 2 2 HC HC 10 10 p p 18 16.35b H t 11 11 2 16 RC ‐ 09121 ‐ RA HDT ‐ 09121_A ‐ DE16 ‐ Ver 1.0
Thermodynamics C 4 H 10 C 4 H 8 + H 2 Exo or endothermic reaction? Isobutane dehydrogenation - Thermodynamical equilibrium 1 500°C 0,9 520°C 0,8 540°C H 2 /iC4 = 1 0,7 560°C iC4 Conversion (%) 580°C 0,6 600°C 0,5 0,4 0,3 0,2 0,1 0 0 1 2 3 4 5 6 7 Pressure (atm) 17 RC ‐ 09121 ‐ RA HDT ‐ 09121_A ‐ DE16 ‐ Ver 1.0 Kinetics The aim of kinetics is to study the course of the chemical transformation versus time IDEA OF THE REACTION RATE [A] [B] V = k [A] for a 1 order reaction k = rate constant k = k o e ‐ Ea/RT (Arrhénius Law) E a = Activation energy Activation energy: energy to provide to the system to transform the reactants into products 18 RC ‐ 09121 ‐ RA HDT ‐ 09121_A ‐ DE16 ‐ Ver 1.0
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