Industrial Catalysis Lecture for Makrokierunek. Nikodem Kuźnik

Transcription

1 Industrial Catalysis Lecture for Makrokierunek Nikodem Kuźnik

2 Lecture 1 Scope of the lecture Role of catalysis in industrial chemistry, chemical lab and life History of catalysis the biggest inventors, discoveries, improvements Characteristic concepts for catalysis: activity, selectivity and lifetime Definition of catalyst, thermodynamic and kinetic approach How does a catalyst work? Types of catalysis: homogeneous, heterogeneous, autocatalysis, inhibition Few example of catalysis

3 Role of catalysis Catalysts are big business. The chemical industry depends upon catalysts. We depend upon the chemical industry for our 21st century life style. We depend on catalysts. Moreover, most of the chemical reactions in nature are biocatalytic reactions.

4 History of catalysis - Over 2000 BC enzymatic (biocatalytic) production of alcohol Catalytic (Pt) oxidation of SO 2 to SO 3 to produce H 2 SO Catalytic (Ni) hydrogenation of olefins (P. Sabatier, J. B. Sendérens) Catalytic synthesis of ammonia (F. Haber & C.Bosch) : First commercial operation o f Platforming Process reforming - Early 1950s: commercial synthesis for zeolites : Catalyst system for polymerizing ethylene at low temperature and pressure - Nobel Prize awarded to Ziegler in : "Beginning" of catalyst characterizations using instruments : Olefin metathesis announced : Startup by Monsanto of the world's first biodegradable detergents : Auto Exhaust Treatment system accepted by Chrysler s: beginning of enantioselective catalysis

5 Role of catalysis 80% of processes in the chemical industry use catalysts. Wolrd catalyst demant in 2010 was 15 milliard ( ) dollars. Growth in catalyst sales is increasing at between 5% and 10% per year. Turnover in industries using catalysts was about 14 trillion ( ) dollars which is equal to the gross domestic product of USA (2010). The conversion of coal or natural gas to anything uses a catalyst.

6 What do they do for the chemical industry? Catalysts have an enormous impact on the chemical industry because they: enable reactions to take place make processes more efficient a 0.5% to 1% increase in selectivity can lead to a up to 1 million dollar increase in operating profit make processes environmentally friendly.

7 Definition of a catalyst A catalyst is a substance that accelerates the rate of a chemical reaction, at some temperature, but without itself being transformed or consumed by the reaction. A catalyst participates in the reaction but is neither a chemical reactant nor a chemical product. Catalysts provide an alternative pathway with a lower activation energy, for a reaction to proceed.

8 Characteristic concepts for catalysis activity selectivity lifetime

9 Activity How fast reaction proceeds in the presence of the catalyst Theory Reaction rate Rate constant k Activation energy E a

10 Impact of catalyst on chemical reaction thermodynamic approach E Reactants E * cat E * Products k Reaction course Ae E * /RT

11 Impact of catalyst on chemical reaction kinetic model and thermodynamic approach

12 Practice in industry Activity Conversion under const. reaction conditions Space velocity for given constant conditions Space velocity = V 0 m cat m 3 kg 1 s 1 V 0 volume flow rate, m cat catalyst mass Space-time-yield (SPY) STY = Desired product quantity Catalyst volume time (mol L 1 1 ) Temperature required for given conversion

13 Activity, lifetime Turnover frequency (TOF) TOF = TOF = volumetri rate of reaction number of centers volume (s 1 ) moles of convertet substrate time moles of catalyst (s 1 ) Typical catalyst s -1, enzymes s -1 Turnover number (TON) TON = TOF [time -1 ] litefime of the catalyst [time] Typical industrial catalyst

14 Autocatalysis A single chemical reaction is said to have undergone autocatalysis, or be autocatalytic, if the reaction product is itself the catalyst for that reaction.

15 Autocatalysis Oxidation of oxalic acid with potassium permanganate: 2MnO 4- (aq ) + 5H 2 C 2 O 4 (aq ) + 6H 3 O + (aq ) 2Mn 2+ (aq ) + 10CO 2 (aq ) + 14 H 2 O KMnO 4 is added. Source: J.Chem.Edu. MnSO 4 is added to the solution on the right. It catalyzes the reduction of KMnO 4 to colorless Mn 2+. The other solution's reaction rate eventually increases as it forms Mn 2+, which subsequently autocatalyzes its own formation.

16 Inhibition An Inhibitor is a material (substance) which is added to some system in order to retard certain chemical reaction(s). For example, 2,6-di-tert-butyl-p-cresol may be added to tetrahydrofuran to prevent potentially dangerous polymerization. Inhibitors are often added to chemicals which tend to undergo self-induced free-radical polymerization.

17 Types of catalysis Heterogeneous, when catalyst is in separate phase Homogeneous, when all reactants and catalyst are in the same phase

18 Classification of Catalysts Catalysts Homogeneous Catalyst Heterogenized Homogeneous catalysts Heterogeneous catalysts Acid/base catalysts Transition metal compounds Biocatalysts (enzymes) Bulk catalysts Supported catalysts

19 How does a catalyst work? Intermediate compounds Adsorption H 3 C CH 3 H H [Rh] C H 3 CH 2 [Rh] H H [Rh] H H [Rh] H H H H H H H H H

20 Examples of catalytic reactions H 3 O + /OH - The experimentally determined rate law is of first order with respect to the concentration of the reagent, but the rate constant also depends upon the ph : The ph-dependence can be quantified as follows : k obs = k 0 + k H [H + ] + k OH [OH - ] In this example, catalysis is performed either by H 3 O +, or by OH -, as is often the case in such hydrolysis reactions.

21 Examples of catalytic reactions Hydrogenation of C=C