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IMPORTANT PETROCHEMICAL PROCESSES

L. PETROVSABIC Chair in Catalysis

Chemical and Materials Engineering DepartmentCollege of Engineering, King Abdulaziz University, Jeddah

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OXIDATION PROCESSES

There are two types of oxidation processes of organic compounds:

1. Processes of total oxidation

2. Processes of selective oxidation

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Total oxidation of organic compounds

Oxidation of organic compounds are irreversible exothermic reactions

Catalysts for total oxidation

Metal catalysts: Pt, Pd, Rh, CuOxide catalysts: NiO, MnO2, Co3O4, Fe2O2

Oxidizing agentsMolecular oxygen, ozone, hydrogen peroxide, 40-60% HNO3, permanganates, bichromates, chromium trioxide, transition metal odxides

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Total oxidation of Volatile Organic Compounds (VOC)

Hydrocarbons - oil refining and petrochemical industry, pharmaceutical industry, natural gas, organic fuels, transportation, chemical industry;Aromatic compounds - paints, adhesives, liquid fuels, combustion products, textiles, plastics, insulations, disinfectants, transportation, chemical industry;Alcohols - aerosols, paints, cosmetics, pharmaceutical industry, food industry;Ketones – adhesives, lacquers, varnisherers;Ethers – resins, paints;Halogen containing hydrocarbons – chemical industry, refrigerators, cleaners; pesticidesSulphur containing hydrocarbons – oil fractions, chemical industry; Nitrogen containing hydrocarbons - oil fractions, chemical industry;

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Selective (Partial) oxidation of organic compounds

Two thirds of high-value organic chemical intermediates contain oxygen functional groups: aldehydes, anhydrides, nitriles, organic acids, epoxides, ketones, and alcohols.

The total volume of produced intermediates is 215 million tons per year worth of roughly 100 billion $ US.

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1. Oxidation without rupture of the carbon chaina) CH3CH2CH2CH3 + O2 = CH3CH2COCH3 + H2Ob) CH2=CHCH3 + 0.5O2 = CH2=CHCHO + H2O

2. Oxidation at the double bonda) RCH=CH2 + 0.5O2 = RCOCH3b) RCH=CH2 + 0.5O2 + H2O = RCHOH-CH2OHc) CH2=CH2 + 0.5O2 = CH2OCH2

3. Destructive oxidation with breaking of C-C bondsa) CH3CH2CH2CH3 + 2.5O2 = 2CH3COOH + H2Ob) RCH=CHR’ + 2O2 = RCOOH + R’COOH

4. Oxidative couplinga) CH2=CH2 + CH3COOH + 0.5O2 = CH2=CH-O-C=OCH3b) 2RSH + 0.5O2 = RSSR+ H2Oc) RCH3 +NH3 +1.5O2 = RCN +3H2O

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Oxidation of organic compounds are irreversible exothermic reactions

Oxidizing agentsMolecular oxygen, ozone, hydrogen peroxide, 40-60% HNO3, permanganates, bichromates, chromium trioxide, transition metal odxides.

Catalysts : Metals: Cu, Ag, Pt, Pd; Oxides: CuO+Cu2O, V2O5, Co2O3Mixed oxides: Bi2O3.MoO3, CoO.WO3

Mechanisms1) With participation of ion-radicals containing oxygenAg-O-O. + C2H4 = Ag-O-O-C2H4

. = Ag-O. + C2H4O

2) Via redox cyclea) CH2=CH-CH3 + 2KO = CH2=CH-CHO + 2Kb) 2K + O2 = 2KO

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Processes

1. Selective oxidation of methanol to formaldehydeIntermediate in copolymerization that produce urea, phenolic and melamine resins, desifectants, intermediate for organic synthesisCH3OH + 0.5O2 = HCHO + H2O ∆H = -155.2 kJ/mol

2. Selective oxidation of ethylene to ethylene oxideIntermediate in manufacturing of ethylene glycol, polyols, surfactants, polymersCH2=CH2 + 0.5O2 = CH2CH2O ∆H = -105.0 kJ/molCH2=CH2 + 3O2 = 2CO2 + 2H2O ∆H = -1326.0 kJ/mol

3. Ammoxidation of propylene to acrylonitrileIntermediate for production of acrylic fibers, synthetic rubber (ABS), plastics and resins.CH2=CHCH3 + NH3 +1.5O2 = CH2=CHCN + 3H2O ∆H = -515.0 kJ/mol

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4. Selective oxidation of propene to acrolein and acrylic acidAcrolein is used for production of alllyl alcohol and acrylic acid

H2C=CHCH3 + O2 = H2C=CHCHO +H2O ∆H = -341.0 kJ/mol

5. Selective oxidation of acrolein to acrylic acidAcrylic acid is a monomer for acrylic esters used in production of textiles, carpeting, paints

H2C=CHCHO +0.5O2 = H2C=CHCOOH ∆H = -254.0 kJ/mol

6. Selective oxidation of n-butane to maleic anhydrideMaleic anhydride is a monomer for production of unsaturated polyester resins used for reinforced fiber glass products

C4H8 +3.5O2 = C4H2O3 + 4H2O ∆H = -1260.0 kJ/mol

7. Selective oxidation of o-xylene to phtalic anhydride

C8H10 +2.5O2 = C8H6O3 + 2H2O

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Negative factors influencing the present practice of oxidation reactions

1. Costly feedstocks;2. Hazardous, corrosive reactants and products;3. Low selectivities causing process inefficiences, byproduct waste,

difficult separation and disposal problems;4. Energy intensive and energy-inefficient process design;5. Marginally-save, high-risk operations;6. Multistep processing, which adds to the complexity and expence of

production.

Common misperceptions

1. Selective oxidation technologies are mature;2. Weak economical and technical drivers for innovations

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Future trends

1. The use of oxidation processes will probably enjoy continued modest

grows of about 3% over next five years.

2. The use of inexpensive or renewable feedstocks;

3. Substantial improvement of catalytic activity, selectivity and stability;

4. To introduce new technologies with minimized number of processing

steps;

5. To introduce new more effective and selective oxidants;

6. To introduce new technologies operating at less severe, energy

intensive, process conditions

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HYDROGENATION-DEHYDROGENATION REACTIONS

Hydrogenation catalytic processes

Selective, catalytic hydrogenation of functional groups contained in organic molecules is one of most useful, versatile and environmentally-acceptable reaction routes available for organic synthesis.

This important area of catalytic chemistry is foundation of numerous industrial hydrogenation processes for production of:

1. Fine chemicals, 2. Intermediates for pharmaceutical industry, 3. Monomers for various polymers,

Hydrogenation catalytic processes are used to produce about 20 % of fine chemicals and pharmaceutical products.

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Used Catalysts:

- Supported noble metals: Pt, Pd, Rh, Ru, Re, Pt-Re

- Supported transition metals: Ni, Co, Fe, Cu, Mo

- Catalyst supports: γ-Al2O3, SiO2, TiO2, Activated Carbon, zeolites, kieselguhr

- Raney type metal catalyst: Ni, Cu-Ni

- Oxide catalysts: Cr2O3, Ga2O3

- Sulfides catalysts: MoS2/Al2O3, WS2/Al2O3, NiS/Al2O3, CoS/Al2O3

Reactors used:

Liquid phase reactions: batch reactors, stirred tank reactors, slurry reactorsGas phase reactions: tubular reactors, multitray fixed bed reactors, moving bed reactors

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Important Hydrogenation Processes1. Hydrogenation of alkenes to alkanes and alkadienes or alkynes to alkenes

1.1. Hydrogenation of alkenes to alkanes – hydrogenation of ethylene, propylene.

R-CH=CH-R’ + H2 =R-CH2-CH2-R’

1.2. Hydrogenation of alkadienes – pentadiene, cyclopentadiene, butadiene.Hydrogenation of by products in the production of ethylene by steam cracking of naphta.

R-CH=CH-CH=CH-R’ = R-CH=CH-CH-CH-R’+ H2 = R-CH-CH-CH-CH-R’

1.3. Hydrogenation of alkynes to alkenes – acetylene in light alkene feeds

HC≡HC + H2 = CH2=CH2

R-C≡CH + H2 = R-CH=CH2

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2. Hydrogenation of aromatics and nitroaromatics.2.1. Hydrogenation of aromatics – benzene, terephtalic acid purification Hydrogenation of 4-carboxybenzaldehyde acid to toluic acid.

p-COOH-C6H4-CHO + H2 + = p-COOH-C6H4-CH3

2.2. Hydrogenation of nitroaromatics.Hydrogenation of nitrobenzene.

C6H5NO2 + 3H2 = C6H5NH2 +H2O

2.3. Reductive alkylation of nitroaromatics

A-NH-A-NH2 + CH3-CO-CH2-R = A-NH-A-NH-C(CH3)H-CH2-R

2.4. Hydrogenation of nitriles to amines

RCH2C≡N+H2 = RCH2CH2NH2

2.5. Reduction of aldehydes to alcohols

CH2=CH-CH2-CHO + 2H2 = CH3-CH2-CH2-CH2-OHCH2=CH-CH2-CHO + H2 = CH3-CH2-CH2-CHO

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Dehydrogenation catalytic reactions

Dehydrogenation reactions find wide application in production of hydrogen, alkenes, polymers, and oxygenates i.e. production of light (C3-C4) alkenes, (C4-C8) alkenes for detergents, polypropylene, styrene, aldehydes and ketones etc.

The demand for basic chemicals like acrylonitrile, oxo alcohols, ethylene and propylene oxides are rapidly growing and as a result the dehydrogenation of lower alkanes is a rapidly expanding business.

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Characteristics of the dehydrogenation processes

1. Dehydrogenation is endothermic process. Thus equilibrium extent and reaction rate are favored at high temperatures and at a low pressure because the volume of reaction products exceeds that of reactants.2. Removal of H2 from the products improves the equilibrium extent and reaction rate of dehydrogenation3. Gas phase dehydrogenation is favored by low partial pressures of the reactants.4. Dehydrogenation catalysts are less sensitive than hydrogenation catalysts to poisons 5. Costly, difficult separation and recycling of unconverted hydrocarbons at low degree of conversion.6. Supplying sufficient heat without overheating.7. Rapid deactivation by coke formation.8. Irreversible deactivation due to phase transformation, sintering and volatilization of the catalyst components of the catalysts at high temperatures.9. High energy consumption to achieved sub-ambient pressure and high temperatures.

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Used Catalysts:

- Supported noble metals: Pt, Pd, Rh, Ru, Re, Pt-Re - Supported transition metals: Ni, Co, Fe, Cu, Mo- Catalyst supports: γ-Al2O3, SiO2, TiO2, zeolites, kieselguhr- Raney type metal catalyst: Ni, Cu-Ni- Oxide catalysts: Cr2O3, Fe2O3, Al2O3-Cr2O3, Fe2O3-K2CO3-Cr2O3, Ca3Ni(PO4)3-

Cr2O3Reactors used:

Gas phase reactions: tubular reactors, multitray fixed bed reactors, moving bed reactors, fluidized bed

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Important Industrial Dehydrogenation Processes

1. Preparation of butadiene by dehydrogenation of n-butane and n-butenes

Annual world production is over 8 mil. t/year

1.1. Two steps process

1. CH3CH2CH2CH3 = CH3CH2CH=CH2 + H2, at 560 - 600oCAl2O3-Cr2O3 catalyst, in fluidized bed reactor, xbutene = 30 – 34 %

2. CH3CH2CH=CH2 = CH2=CH-CH=CH2 +H2, at 600 – 660oCFe2O3-K2CO3-Cr2O3 or Ca3Ni(PO4)3-Cr2O3 catalystsin adiabatic reactor, n-butenes : steam = 1 : 10, xbutadiene = 33 – 40 %

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1.2. One step Houdry process

CH3CH2CH2CH3 = CH2=CH-CH=CH2 + 2H2 at 620 – 700oC

Cr2O3 supported on Al2O3 catalyst, eight parallel adiabatic reactorsworking cycle: reaction 5 -10 min, catalyst regeneration 10 – 20 min xbutadiene = 60 %

New process - Cr2O3 supported on Al2O3 catalyst, in fluidized bedat 550 -600oC, xbutadiene = 90 %

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2. Dehydrogenation of i-pentane to isoprene

Annual world production of over 1 mil. t/year

Two steps process

1. CH3-CH(CH3)-CH2-CH3 = monoolefins C5H10 + H2 at 530 – 610oC

Cr2O3 supported on Al2O3 catalyst, in fluidized bed reactor, xi-pentene = 28-33 %

2. monoolefins C5H10 = CH2=C(CH3)-CH=CH2 + H2 at 550 – 650oC

Ca3Ni(PO4)3-Cr2O3 catalyst xi-pentene = 28-33 %

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3. Dehydrogenation of ethylbenzene to styrene.

It is the largest catalytic dehydrogenation process. The world annual production is over 21 mil. t/year

C6H5-CH2-CH3 = C6H5-CH=CH2 + H2

Catalyst Fe2O3-Cr2O3-KOH

To different reactors are used:

Adiabatic: at 580 - 650oC, EB : steam = 1 : 10 -15

Isothermal tubular: 580 -610oC

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4. Oxidative dehydrogenation of n-butenes

n-C4H8 + ½O2 = C4H6 + H2O at 350 – 450oC i-C5H10 + ½O = i-C5H8 + H2O

Catalysts: Fe2O3-ZnO-Cr2O3 or Ca3Ni(PO4)3-Cr2O3

butene : O2 : H2O = 1 : 1 : 10 - 30

Selectivity over 90%, xbutadiene = 50 – 70 %