Selective Oxidation of Selective Oxidation of hydrocarbonshydrocarbons

Part-1Part-1

Dr.K.R.KrishnamurthyDr.K.R.Krishnamurthy

National Centre for Catalysis Research (NCCR)National Centre for Catalysis Research (NCCR)

Indian Institute of TechnologyIndian Institute of Technology

Chennai-600036Chennai-600036

INDIAINDIA

10 th Orientation Course in Catalysis for Research Scholars28 th November to 16 th December,2009

Selective oxidation of Hydrocarbons- Part-1

Oxidation /ammoxidation of Propylene Epoxidation of Ethylene Oxychlorination of Ethylene

Chemical Industry- Products pattern

Chemicals- Intricately woven with our day to day life

Petrochemicals-37%Petrochemicals-37%

Major catalytic processes for Petrochemicals

RK Grasselli &JD. Burrington, Adv. Catalysis, 30, 133,1980

Important heterogeneous oxidation processes

RK Grasselli &JD. Burrington, Adv. Catalysis, 30, 133,1980

Oxidation & ammoxidation of Propylene

Scenario in feedstock for petrochemicals

RK Grasselli &JD. Burrington, Adv. Catalysis, 30, 133,1980

Current scenario reflects the predictions

1

2

3

4

5

Processes for manufacture of Acrylonitrile

JL.Callahan, RK.Grasselli, EC.Millberger & HA Strecker. Ind.Eng.Chem.,Proc.Res & Dev.9, 134 (1970)

Acrylonitrile- Fact fileAcrylonitrile- Fact file

Global production & Consumption 2008- 5.2 MMT Growth rate - 3% /yr Versatile chemical SOHIO’s Ammoxidation process Significant Landmark in History

of chemical industry

Allylic Oxidation processes

Oxidation/ Ammoxidation of Propylene – Key Process

RK Grasselli &JD. Burrington, Adv. Catalysis, 30, 133,1980

Selective oxidation /Ammoxidation of Propylene

Proceed through Mars- Krevelen mechanism Cyclic reduction- re-oxidation of the catalyst Catalyst systems contain binary/multi compoent metal oxides Bismuth molybdates (α-β-γ- phases ) most active & selective Facile reduction- re-oxidation capability Hydrocarbon gets activated and not oxygen

Redox Cycle for the catalyst

Surface reactions inselective oxidation/ Ammoxidation of propylene

Mechanism of Oxidation/Ammoxidation of Propylene

Experiments labeled with 14C

Labeling in 1-or 3- position results in acrolein with 14C scrambled in both positions Oxidation with 2- 14C Propylene did not lead to scrambling

Formation of allylic species from adsorbed propylene proposed as the first step

Sachtler WH & de Boer, NH, Proc.Inetrn Congr.Catal.3rd 1964,252(1965)

Mechanism of oxidation/ammoxidation of Propylene

α-Hydrogen abstraction leading to allylic species- rate determining step

CR Adams & JT Jennings,J.Catal.3,549,1964 HH.Voge, CD.Wagner & DP.Stevenson,J.Catalysis, 2, 58,1963

Role of Bi & Mo

Bi2O3 - Highly active but not selective

MoO3 - Highly selective but not that active

Bismuth molybdates- Active & Selective

On Bi2O3 propylene forms 1,5 Hexadiene / Benzene via allyl radical

On MoO3 Allyl iodide gets converted to acrolein

Bi-O sites – Abstraction of alpha Hydrogen & formation of allyl radical

Mo-O sites- Selective insertion of oxygen/nitrogen in allylic moiety

* Grzybowska B & Haber J & Janas J., J.catalysis, 49, 150 (1977)

Role of gas phase/lattice oxygen

Oxidation of propylene in the absence of gas phase oxygenParticipation of lattice oxygen in oxidation/ ammoxidationOxidation with 18O2 in gas phase & on 18O2 exchanged Bi-Mo

- Lattice oxygen gets incorporated in the product [CR.Adams, Proc.Intern Congr.Catal.3rd 1964,1,240 (1965) WH.Sachtler & NH deBoer, Proc.Itern Congr.Catal.3rd 1964,1,252 (1965)]

Lattice oxygen vacancies replenished by gas phase oxygen Facile internal diffusion of oxygen leads to oxygen insertion / replenishment

[GW.Kelks J.Cat.19, 232,(1970); T.Otsubo et.al J.Catal.36,240,1975]

Terminal Mo-O bond with double bond character responsible for selective oxidation- IR absorption band at 990-1000 cm-1

[F.Trifiro et.al J Catal.19,21(1970)]

Two types of lattice oxygen in Bi-Mo-O- Selective & Non selective [RK.Grasselli & DD.Suresh, J Catal.25, 273,(1972)]

Loss of selectivity related to disappearance of terminal Mo-O bond- IR study

(TSR Prasada Rao,KR Krishnamurthy & PG.Menon, Proc.Intrn Conf “ Chemistry & uses of Molybdenum, Michigan, p.132,1979)

Crystal structure of Bismuth Molybdate

Layered structurehelps in facileOxygen diffusion

Shear structure of Bismuth molybdate

Mo-O- Corner shared Oh On loss of oxygen

edge shared Oh formed Shear structure imparts

Structural stability Amenable to redox cycles Partial reduction tempers

M-O bond strength - Criterion for selectivity

Features of selective oxidation catalysts

Selection of appropriate redox-couple- redox potentialSuitable electronic configuration - Partially filled orbitals - Alpha H abstraction - Full orbitals - Olefin adsn. , O/N insertion

Typical commercial catalyst formulations

Desirable catalyst characteristics

Hydrogen abstraction

Labile lattice oxygen

O/N insertion

Redox stability

Layered structure/Shear structure

Matrix stabilization

Typical redox process – Phase stability is the key

RK.Grasselli, Appl.Catal.15, 127,1985

TSR.Prasada Rao & KR.Krishnamurthy, J.Catalysis,95,209,1985

Model for multi-component molybdate catalysts

Role of different phasesBi-Mo - Activity & SelectivityFe-Mo - Facilitate re-oxidation of Bi & MoCo,Ni-Mo - Hold excess MoO3 in bulk molybdate phase - Ensure structural stabilityK,Cs - Moderate Mo-O bond strength, acidity,

Fe3+phase

Fe2+ phase

Seven principles/Seven pillars for selective oxidation

Lattice oxygen,

Metal–oxygen bond strength,

Host structure,

Redox characteristics

Multi-functionality of active sites,

Site isolation,

Phase co-operation

RK Grasselli, Topics in Catalysis, 21,79,2002

Burrington, JD, Kartisek,CT,& Grasselli,RK J.Catalysis, 63, 235,(1980)

Selective oxidation / ammoxidation of Propylene

Surface transformations

Selective oxidation of Propylene- Mechanism

Selective ammoxidation of Propylene -Mechanism

Selective Oxidation/ammoxidation of Propylene

Epoxidation of Ethylene

Epoxidation of ethylene - Fact file

First patented in 1931 Process developed by Union Carbide in1938 Currently 3 major processes - DOW, SHELL & Scientific Design Catalyst- Ag/α-alumina with alkali promoters Temperature 200-280°C; Pressure - ~ 15- 20 bar Organic chlorides (ppm level) as moderators Reactions

C2H4 + 1/2O2 -> C2H4O C2H4O + 2 1/2O2 -> 2CO2 + 2H2O

C2H4 + 3O2 -> 2CO2 + 2H2O Per pass conversion -10-20 % EO Selectivity 80- 90 % Global production -19 Mill.MTA

(SRI Report- 2008)

Best example of Specificity - catalyst (Ag) & reactant ( Ethylene)

Utilization of Ethylene Oxide

71%

7%

9%

5%8%

MEG

Higher glycols

Ethoxylates

Ethanolamine

Others

Epoxidation of ethylene - Reaction Scheme

Selective Epoxidation – 100 % atom efficient reaction

Epoxidation of ethylene - EO selectivity

6 C2H4 + 6O2- → 6 C2H4O + 6 O-

C2H4 + 6O- → 2 CO2 + 2H2OMaximum theoretical selectivity- 6/7 = 85.7 %

AssumptionsO2

- Selective oxidationO- - Non selective oxidation - No recombinationCl- - Retards O- formationAlkali/Alkaline earth - Form Peroxy linkages - Retard Ag sintering Selective oxidation

Non- selective oxidation

WMH Sachtler et. al.,Catal. Rev. Sci. Eng, 10,1,(1974)&23,127(1981); Proc. Int. CongrCatal.5 th, 929 (1973)

EO selectivity > 86 % realizedin lab & commercial scale !!!

Molecular Vs Atomic adsorbed Oxygen – Key for selectivity

Continuous improvements in selectivity

Epoxidation of ethylene- Surface species & reactivity

No adsorption of ethylene on clean Ag surface

Ethylene adsorbs on Ag surface with

pre-sorbed Oxygen

O2- unstable beyond 170 K

EO formed with atomic O- - in-situ IR & TPRS studies

( EL Force & AT Bell, J.Catal,44,175, (1976)

Sub-surface Oss oxygen essential for EO formation

Oss influences the nature of Oads

Cl- decreases Oads but weakens its binding to Ag

Alkali facilitates adsorption of O2 & ethylene

[ RA.van Santen et.al, J.Catal. 98, 530,(1986);

AW.Czanderna, J. Vac.Sci.Technolgy, 14,408,(1977)] Surface species identified

Comprehensive picture of surface species

Epoxidation of ethylene - Reaction pathways

Strength & nature of adsorbed oxygen holds the key 2 different Oads species besides subsurface oxygen Reactivity of oxygen species governs the selectivity

Elelctrophillic attack /insertion of Oxygen → Selective oxidation

Nucleophillic attack of Oxygen → Non selective oxidation

RA.van Santen &PCE Kuipers, Adv.Catal. 35, 265,1987

Reaction paths in line with observed higher selectivity

Epoxidation of ethylene - Transition state

RA. Van Santen & HPCE Kuipers, Adv.Catalysis, 35,265,1987

Ethylene adsorbed on oxygenated Ag surface

Electrophillic attack by Oads on Ethylene leads to EO ( Case a)

Cl- weakens Ag-O bond & helps in Formation of EO (Case c)

Strongly bound bridged Oads attacks C-H bond leading to non-selective Oxidation ( Case b)

Non-selective oxidation proceeds via isomerization of EO to acetaldehyde which further undergoes oxidation to CO2 & H2O

Epoxidation of ethylene- Surface transformations

J.Greeley & M Mavrikakis, J.Pys.Chem. C, 111, 7992,2007S.Linic & MA.Barteau, JACS,124,310,2002; 125,4034,2003S.Linic, H.Piao,K.Adib & MA.Barteau, Angew.Chem.Intl.Ed.,43,2918,2004

Based on DFT , TPD & HREELS studiesSimilar intermediates in epoxidation of butadiene

A new approach to surface transformations

Ethyene epoxidation- Reactivity of Surface species

Reactivity of oxametallacycle governs selectivity

Epoxidation of Ethylene- Why only Silver & Ethylene?

Bond strength & nature of adsorbed oxygen

Governed by Oss & Clads

No stable oxide under reaction conditions

Inability to activate C-H bond

Other noble metals activate C-H bond

Oxametallacycles on other metals are more stable

Butadiene forms epoxide- 3,4 epoxy 1-butene

Propylene does not form epoxide due to

- facile formation of allylic species

- its high reactivity for further oxidation

Oxychlorination of Ethylene

Ethylene Oxychlorination

Production of Ethylene Di Chloride (EDC) for VCM

Ethylene Oxychlorination- VCM production

EDC- Precursor for VCM

Ethylene Oxychlorination- Source for EDC

Ethylene Oxychlorination

Ethylene Oxychlorination- Major route for VCM

Alternative routes for VCM

VCM Production-Feedstocks

82%

18%

Ethylene Acetylene

Global VCM capacity- 42.7 MMTA (2008) ( Nexant Report)

C2H4 + Cl2 → C2H4Cl2

C2H4Cl2 → C2H3Cl + HCl

C2H4 + 2HCl + ½O2 → C2H4Cl2 + H2O

C2H4 + Cl2 → C2H4Cl22 C2H4Cl2 → 2 C2H3Cl + 2 HCl

C2H4 + 2HCl + ½O2 → C2H4Cl2 + H2Ooverall,

2 C2H4 + Cl2 + ½O2 → 2 C2H3Cl + H2O

Ethylene Oxychlorination –Relevance to VCMProcess steps for VCM

Direct chlorination to EDC

Thermal cracking of EDC

Oxychlorination of ethylene

Overall process for VCM

Oxychlorination ensures Complete utilization of Chlorine

Ethylene Oxychlorination- Reaction mechanism

Follows redox pathway – CuCl2 / Cu2Cl2

Elementary steps

C2H4 + 2CuCl2 C2H4Cl2 + 2CuCl2CuCl + ½ O2 Cu2OCl2Cu2OCl2+ 2HCl 2CuCl2 + H2O

Unique role of CuCl2 lattice & redox character

Ethylene oxychlorination- Catalyst characteristics

CuCl2- KCl/ Alumina- + Rare earth oxide promoters

Active phases identified – CuCl2, K CuCl3, Cu (OH) Cl, Cu aluminate

Cu hydroxy chlorides bound to alumina

R.Vetrivel, K.Seshan,KR Krishnamurthy & TSR Prasada Rao, Bull.Mat.Sci.,9,75,1987G.Lambert,et.al., J.Catalysis,189, 91 &105 2000KR.Krishnamurthy et.al, Ind J,Chem.,35A,331,1996

Phase transformations in Catalyst during oxychlorination

GC.Pandey, KV.Rao, SK.Mehtha, K.R.Krishnamurthy,DT.Goakak &PK.Bhattacharya, Ind.J.Chemistry, 35A, 331, 1996

Characterization of Ethylene Oxychlorination catalysts

Characterization of Ethylene Oxychlorination catalysts

Sample From DRS

(x 103cm-1)

Wt / Wt, % Cu/K Ratio

Phases identified

Cu K

CB-1 19.80 2.74 1.56 2.30 CuCl2 [3Cu(OH)2],

CuOHCI

CB-2 17.85 6.00 1.56 2.30 CuCl2 [3Cu(OH)2]

CB-3 17.54 8.66 0.98 5.45 CuCl2 [3Cu(OH)2],

KCI

CB-4 18.87 6.13 2.07 1.82 CuCl2 [3Cu(OH)2] CuOHCI

CB-5 17.54 8.76 0.90 6.00 CuCl2 [3Cu(OH)2]

Crystalline phase identified in oxychlorination catalysts of different compositions by X-ray powder diffractometry

Ethylene Oxychlorination catalyst- XPS study

Fresh catalyst contains Cu2+ and Cu+ statesSpent catalyst shell has Cu in both oxidation statesSpent catalyst core shows only Cu+ state

Structural & electronic changes across catalyst geometry

R.Vetrivel, K.Seshan,KR Krishnamurthy & TSR Prasada Rao, Bull.Mat.Sci.,9,75,1987

No Potassium in the core

XPS data on Oxychlorination catalystsXPS data on Oxychlorination catalysts

Ethylene oxychlorination catalyst- TPR study

TPR profiles indicate presence of Cu 2+ & Cu+ states in fresh & spent shellCatalyst & only Cu+ in spent core section- Confirms XPS dataR.Vetrivel, KV.rao, K.Seshan,KR Krishnamurthy & TSR.Prasada Rao,Proc.9 th Intern. Congr. Catal. Calgery, Canada, 1766,1988

XPS & TPR indicate slow re-oxidation of Cu+ in core part

Ethylene oxychlorination catalyst- TPO study

TPO profiles indicate the presence of Cu+ in fresh catalystR.Vetrivel, KV.rao, K.Seshan,KR Krishnamurthy & TSR.Prasada Rao,Proc.9 th Intern. Congr. Catal. Calgery,Canada,1766,1988

Ethylene oxychlorination catalyst- TPO study

Difference in re-oxidation rates- Core-Sphere & Core-PowderR.Vetrivel, KV.rao, K.Seshan,KR Krishnamurthy & TSR.Prasada Rao,Proc.9 th Intern. Congr. Catal. Calgery, Canada,1766,1988

Spherical shape detrimental – Retards re-oxidation of Cu

Ethylene oxychlorination catalyst – Further developments

Studies indicate that re-oxidation of Cu+ to Cu2+ is the limiting step Observations supported by G.Lamberti et.al

(J.Catalysis, 189,91 & 105 (2000), 202,279(2001) 205,375 (2002) Angew.Chem.Intl Ed., 41,2341(2002)

All further commercial formulations changed the shape- -Spherical to Annular ring – Racsig ring

Developments are towards increasing catalyst life