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Kinetics investigation of direct natural gas conversion by oxidative coupling

of methane

Ali Farsi abc Ali Moradi a Sattar Ghader a Vahid Shadravan abc Zainuddin Abdul Manan c

a Department of Chemical Engineering Faculty of Engineering Shahid Bahonar University of Kerman Jomhori Blvd Kerman Iranb Young Researchers Society Shahid Bahonar University of Kerman Kerman Iranc Process Systems Engineering Centre (PROSPECT) Faculty of Chemical and Natural Resources Engineering Universiti Teknologi Malaysia UTM Skudai 81310 Johor Bahru

Johor Malaysia

a r t i c l e i n f o

Article history

Received 28 September 2010

Accepted 28 September 2010

Available online 10 November 2010

Keywords

Natural gas

Oxidative coupling of methane

Kinetics

a b s t r a c t

Since 1982 there has been much research on the Oxidative coupling of methane (OCM) process The main

obstacle for converting methane directly to more valuable products by heterogeneous catalysis is the low

selectivity at high conversions the products are more reactive than methane The main goal of this work

is to study the kinetics of OCM reaction and classi1047297es them We 1047297nd that with considering almost all

reaction steps of the other models reaction network of Stanch et al has the best accuracy in comparison

with the other models

2010 Elsevier BV All rights reserved

1 Introduction

Natural gas is a mixture of predominantly methane combined

with other hydrocarbons and non-hydrocarbons such as N2 CO2

and H2O (Goodwin and Hill 2009) In order to make an ef 1047297cient

utilization of natural gas we must consider transforming it into

more valuable chemicals Higher hydrocarbons are more useful for

chemical industries (Graf 2008) The geographical distribution of

methane (natural gas) is given in Fig 1 (BP Statistical Review of

World Energy 2007) It shows that Middle East (especially Iran)

has the most reserves of natural gas in the world at 2006 (BP

Statistical Review of World Energy 2007)

Considerable amountof research has been conducted to develop

various commercially viable processes for methane conversion via

the direct or indirect routes Compared to the indirect conversion

technologies that need the energy-intensive step of synthesis gasformation the direct route that converts methane into higher

hydrocarbons in one step by the oxidative coupling reactions(OCM)

is more economically attractive and consequently has been inten-

sively studied (Veser et al 2000 Paturzo et al 2003 Frade et al

2004 Lin and Zeng 1996 Lu et al 2000 Akin and Lin 2002)

Since 1982 there has been much research on the OCM process

(Takht Ravanchi et al 2009 Baerns et al 1989 Geerts 1990

Amenomiya 1990 Maitra 1993 Parkyns 1993 Couwenberg

1995) Considerable efforts have been placed on the development

of oxidative coupling of methane (OCM) catalysts in order to make

the product yields commercially feasible (Keller and Bhasin 1982

Otsuka et al 1987 Hutchings et al 1989 Lin et al 1994 Burch

et al 1988) OCM reaction is thermodynamically advantageous in

comparison with the direct coupling reaction of methane without

oxidant However no catalysts could reach the principal criteria for

industrial application of OCM (Xu and Lin 1999) It is quite dif 1047297cult

to obtain the coupling products in high yield because the oxidation

of coupling products to CO x proceeds more selectively than the

coupling reaction The limits of the process have been essentially

indicated (Gesser and Hunter 1998) The maximum yield obtained

so far is about 25 which means that the process is economically

unfeasible Recent studies have claimed that this may be overcomeby producing notonly ethylene but also electricity by making use of

the heat from the exothermic coupling reaction (Swanenberg

1998)

This work 1047297rst studies the former researches on the kinetics of

OCM reaction and classi1047297es them Investigation on the reactor

modeling and simulation is the next goal of the work in order to

1047297nd new methods which can have a good effect on the OCM view

The main goal of this work is to study the catalysts and nano-

catalysts performance in OCM reaction In this work about 80

various catalyst and nano-catalyst have been collected and their

main parameters such as method of preparation temperature of

Corresponding author Department of Chemical Engineering Faculty of Engi-

neering Shahid Bahonar University of Kerman Jomhori Blvd Kerman Iran

Tel thorn98 913 3875507

E-mail address alifarsigmailcom (A Farsi)

Contents lists available at ScienceDirect

Journal of Natural Gas Science and Engineering

j o u r n a l h o m e p a g e w w w e l s e v i e r c om l o c a t e j n g s e

1875-5100$ e see front matter 2010 Elsevier BV All rights reserved

doi101016jjngse201009003

Journal of Natural Gas Science and Engineering 2 (2010) 270e274

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reaction C2 yield and selectivity and catalyst test reactor andmethane conversion have been studied

2 Kinetics models for oxidative coupling of methane

Kinetics of OCM reaction to C2 hydrocarbons has been studied

extensively based on the various reaction mechanisms (Bistol1047297 et al

1992 Lehmann and Baerns 1992 Yaghobi et al 2008 Arutyunovet al 1997 Wolf 1992 Vereshchagin and Ross 1995 Couwenberg

et al 1996a Peil et al 1991 Zeng et al 2001 Amorebieta and

Colussi 1995) Indeed kinetics of OCM reaction is very compli-

cated in terms of proposed mechanism since it involves several

chemical species (Kao et al 1997 Su et al 2003 Couwenberg et al

1996b Xin et al 2008) Former research on the kinetics andor

mechanisms of the oxidative coupling of methane (OCM) was

reviewed and given in the following classi1047297cation

(A) Spectroscopic studies of O- species and the reaction with

methane

(B) Kinetic simulations of gaseous phase reactions

(C) Simultaneous kinetic simulation of gaseous phase and surface

reactions(D) Integrating kinetics of many radical reactions of single or

several reactions

(E) Focusing on surface kinetics of methane consumption

(F) Power rate law expression of C2 (ethane and ethylene) and C1

(CO and CO2) formation

Fig 1 Geographical distribution of proven natural gas reserves

Fig 2 The main pathways of the conversion of carbon-based compound ( Pyatnitsky

et al 1998) Scheme 1

A Farsi et al Journal of Natural Gas Science and Engineering 2 (2010) 270e 274 271

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21 Spectroscopic studies of O species and the reaction with

methane

The Lunsford Laboratory succeeded in producing O species on

oxide surface defects through the introduction of N2O O species

on an oxide surface were observed using electron paramagnetic

resonance (EPR) spectroscopy and were reactive with methane

even at room temperature They found for the1047297rst time that the O

species on MgO reacted with any alkane molecules in an equal

stoichiometry ratio The O abstracts a hydrogen atom from

methane to form methyl radicals which 1047297nally decompose to CO

and H2 at room temperature These studies provided the mecha-

nistic base for the OCM reaction (Aika and Lunsford 1977)

22 Kinetic simulations of gaseous phase reactions

The OCM reaction occurs without catalysts at high temperature

though the selectivity for C2 is poor The rate parameters of simple

gas phase reactions have been established and seen in many books

Theoretical simulations are possible using such parameters and

rather remarkable coincidence with the experimental results has

been obtained The selectivity for C2 molecules (ethane and

ethylene) is poor without a catalyst however these studies are

useful to evaluate the contribution of gas phase reactions to the

reaction with a catalyst especially under high temperatures and

pressure (Laidler 1965 Zanthoff and Baerns 1990 Geerts et al

1990)

Fig 3 Pairwise sum-of-square contours of rate constants j frac141 2 7 excluding k6 which was not adjusted but taken from the literature Each constant was varied in the range

01kilt

kilt

2ki the inner contour lines correspond to the minimum region at the con1047297

dence level of 90 (Wolf et al 2001)

A Farsi et al Journal of Natural Gas Science and Engineering 2 (2010) 270e 274272

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23 Simultaneous kinetic simulation of gaseous phase and surface

reactions

Gas phase reactions between methane and oxygen give theo-

retically and experimentally high COCO2 ratios as well as high H2

production compared to the reaction with a catalyst In addition to

the established gas phase (nearly 100) reactions eight steps are

proposed three steps for the activation of methane at the catalyst

surface supplying methyl radicals to the gas phase (oxygen activa-

tion methyl radical formation and water desorption) and 1047297ve

surface steps (methyl radical oxidation ethane oxidation formal-

dehyde oxidation CO oxidation and H2 oxidation) The eight rate

constants are successfully simulated to harmonize the total OCM

reaction Pyatnitsky et al (1998) showed the main pathway of the

conversion of carbon-based compounds in Fig 2 (Pyatnitsky et al

1998) They also calculated the yields through similar calculation

methods (Nelson and Cant1990 Kolts et al1991Asami et al1987

Labinger and Ott 1987)

24 Integrating kinetics of many radical reactions of single or

several reactions

The feature of these studies is the use of a small number of elemental steps to explain the reaction performance in the low

conversionregionIn a lotof researchesit is assumedthatthe reaction

is composed of several steps such as oxidation of methane (to

produce methyl radicals or to complete oxidation) recombination of

methyl radicals and oxidation of methyl radicals In some researches

it is assumed that the oxidation of methane occurs in the gas phase

on the surface either by parallel reactions or by a series of reactions

The advantages of these kinetic models are the ease of analysis so

that data can be accumulated and compared with many other cases

(Iwamatsu and Aika 1989 Sinev et al 1988 Miro et al 1990

Lehmann and Baerns 1992 Agarwal et al 1990 Wolf and Moros

1997 Wolf et al 1998) Wolf et al (2001) showed the potential of

steady state analysis in predicting rate of surface reaction and steady

state surface coverages depending on solid phase properties for theoxidative coupling of methane over CaOCeO2 mixed oxides They

proposed a kinetics model on the forthcoming reaction Scheme 1

However any analysis of relationships between kinetic param-

eters and catalyst properties can be reliable only on the basis of

information that contains an assessment of parameter signi1047297cance

and correlation They showed their analysis for CaOCeO2 in Fig 3

(Wolf et al 2001) The contour lines in Fig 3 are functions of the

kinetic constants changed in the pair The contour lines indicate

constant levels of residual values which correspond to deviations

between experimental kinetic data and those predicted by the

kinetic model In general such linear correlations indicate fast

equilibration of the corresponding reaction steps

25 Focusing on surface kinetics of methane consumption

Research that has used simpler kinetic treatments than in the

above category has been presented where the rate of methane

consumption is the main concern Most of these studies were pub-

lishedat theearlier stage of OCMresearch Theanalysisis simplistic

however the relationship of C2 selectivity to the chemical nature of

the catalyst is not the main concern (Efstathiou et al 1993 Otsuka

and Jinno 1986 Amorebieta and Colussi 1988 Roos et al 1989)

26 Power rate law expression of C 2 (ethane and ethylene) and C 1(CO and CO 2) formation

This is a typical style of reaction engineering which is simplistic

and can be easily applied to process design This could be the most

practical approach when the best catalyst is selected (Ali Emesh

and Amenomiya 1986 Santamaria et al 1991 Al-Zahrani 2001

Yaghobi and Ghoreishy 2008)

Al-Zahrani (2001) used the two-phase theory which considers

the 1047298uidized bed reactor to consist of a bubble phase and a dense

phase He assumed that the dense phase is perfectly mixed and

uniform in temperature The ideal gas law applies to the gas phase

in both phases He used a simple triangular network as follows-

Scheme 2

Stansch et al (1997) proposed a various reaction scheme for

description of the network of primary reactions for oxidative

coupling of methane They validated their model by comparing it

with its corresponding experimental model by using 135 experi-ments They concluded that the measured conversions of methane

and oxygen were predicted with an average relative error of less

than 22 for integral data

Daneshpayeh et al (2009) modeled Kinetics of oxidative

coupling of methane over MnNa2WO4SiO2 Catalyst using exper-

imental data of a micro catalytic 1047297xed bed reactor and the genetic

algorithm as parameter estimation method In order to choose the

best OCM reaction network for developing a comprehensive kinetic

model over this catalyst 1047297ve OCM reaction networks were

compared such as Stansch et al over La2O3CaO (model 1) (Stansch

et al 1997) Sohrabi et al over CaTiO3 (model 2) (Sohrabi et al

1996) Lacombe et al over La2O3 (model 3) (Lacombe et al 1995)

Olsbye et al over BaCO3La2On(CO3)3n (ngt 15) (model 4) (Olsbye

et al 1992) and Traykova et al over La2O3MgO (model 5)(Traykova et al 1998) and shown the Stoichiometric equations of

reaction network models in Table 1

They concluded that both experimental and statistical analysis

con1047297rm that the reaction network of Stansch et al (Stansch et al

1997) has the best accuracy compared to other models They

stated that this model considers almost all reaction steps of other

models including heterogeneous and homogeneous primary and

consecutive reactions

Scheme 2

Table 1

Stoichiometric equations of reaction network models

Reaction Model 1 Model 2 Model 3 Model 4 Model 5

2CH4 thorn05O2 C2H6 thornH2O U U U U U

CH4 thornO2 COthornH2O thornH2 U U

CH4 thorn15O2 COthorn2H2O U U

CH4 thorn2O2 CO2 thorn 2H2O U U U U

2CH4 thornO2 C2H4 thorn2H2O U

COthorn05O2 CO2 U U

C2H6 thorn05O2 C2H4 thornH2O U U U

C2H6 thornO2 2COthorn 3H2 U

C2H6 thorn25O2 2COthorn 3H2O U

C2H6 thorn35O2 2CO2 thorn3H2O U U

C2H6C2H4 thornH2 U U U


C2H4 thorn2O22COthorn 2H2O U U

C2H4 thorn3O22CO2 thorn2H2O U

C2H4 thorn2H2O2COthorn 4H2 U

CO2 thornH2 COthornH2O U U

COthornH2O CO2 thornH2 U U


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3 Concluding remarks

1 The main obstacle for converting methane directly to more

valuable products by heterogeneous catalysis is the low selec-

tivity at high conversions the products are more reactive than

methane

2 The simulation of the oxidative coupling of methane taking

into account surface processes demonstrated that the yield of

ethane can be increased in the range of short contact time by

optimizing the ratio of methane-to-oxygen partial pressure at

the reactor inlet as well as by non-steady state

3 Considering almost all reaction steps of the other models

reaction network of Stanch et al has the best accuracy in

compare with the other models

References

Agarwal SK Migone RA Marcelin G 1990 J Catal 123 228Aika K Lunsford JH 1977 J Phys Chem 81 1393Akin FT Lin YS 2002 AIChE J 48 2298Ali Emesh IT Amenomiya Y 1986 J Phys Chem 90 4785Al-Zahrani SM 2001 Catal Today 64 217Amenomiya Y 1990 Catal Rev Sci Eng 32 163Amorebieta VT Colussi AJ 1988 J Phys Chem 92 4576Amorebieta VT Colussi AJ 1995 J Am Chem Soc 117 3856Arutyunov VS Basevich VYa Vedeneev AI 1997 Stud Surf Sci Catal 107 351Asami K Shikada T Fujimoto K Tominaga H 1987 Ind Eng Chem Res 26

2348Baerns M van der Wiele K Ross JRH 1989 Catal Today 4 471Bistol1047297 M Fornasari G Molinari M Palmery S Dente M Ranzi E 1992 Chem

Eng Sci 47 2647BP statistical review of world energy httpwwwinvestiscombp_acc_iastat_

review_06htdocsreportsreport_11html 2007Burch R Squire GD Tsang SC 1988 Appl Catal 43 105Couwenberg PM Chen Q Marin GB 1996a Ind Eng Chem Res 35 415Couwenberg PM Chen Q Marin GB 1996b Ind Eng Chem Res 35 3999Couwenberg P M PhD dissertation Technical University of Eindhoven Eind-

hoven 1995Daneshpayeh M Khodadadi AA Mostou1047297 N Mortazavi Y Sotudeh-

Gharebagh R Talebizadeh A 2009 Fuel Process Technol 90 403Efstathiou AM Boudouvas D Vamvouka N Verykios XE 1993 J Catal 140 1Frade JR Kharton VV Yaremchenko A Naumovich E 2004 J Power Sources

130 77Geerts JWMH Chen Q van Kasteren JMN van der Wiele K 1990 Catal Today

6 519Geerts J W M H PhD dissertation Technical University Eindhoven 1990

Gesser HD Hunter NR 1998 Catal Today 42 183Goodwin ARH Hill JA 2009 J Chem Eng Data 54 2758Graf PO PhD dissertation University of Twente 2008 ISBN 978-90-365-2778-1Hutchings GJ Scurrell MS Woodhouse JR 1989 Catal Today 4 371Iwamatsu E Aika K 1989 J Catal 117 416Kao YK Lei L Lin L 1997 Ind Eng Chem Res 36 3583Keller GE Bhasin MM 1982 J Catal 73 9Kolts J H Kimble J B Porter R ACS Meeting 1991Labinger JA Ott KC 1987 J Phys Chem 91 2682Lacombe S Durjanova Z Mleczko L Mirodatos C 1995 Chem Eng Technol

18 216Laidler KJ 1965 Chemical Kinetics second ed McGraw-Hill IncLehmann L Baerns M 1992 J Catal 135 467Lin YS Zeng Y 1996 J Catal 164 220Lin T Ling ZJ Lin L 1994 Appl Catal A Gen 115 243Lu Y Dixon A Mose WR Ma YH 2000 Chem Eng Sci 55 4901Maitra AM 1993 Appl Catal A Gen 104 11Miro EE Santamaria JM Wolf EE 1990 J Catal 124 465Nelson PF Cant NW 1990 J Phys Chem 94 3756Olsbye U Desgrandchamps G Jens KJ Kolboe S 1992 Catal Today 13 209Otsuka K Liu Q Hatano M Morikawa A 1987 Chem Lett 16 1835Otsuka K Jinno K 1986 Inorg Chem Acta 121 237Parkyns ND 1993 Catal Today 18 385Paturzo L Gallucci F Basile A Vitulli G Pertici P 2003 Catal Today 82 57Peil KP Goodwin JG Marcelin G 1991 J Catal 132 556Pyatnitsky YuI Ilchenko NI Pavlenko MV 1998 Catal Today 42 233RoosAJ KorfSJ Veehof RHJvan Ommen JGRoss JRH1989 ApplCatal 52131Santamaria JM Miro EE Wolf EE 1991 Ind Eng Chem Res 30 1157Sinev MYu Korchak VN Krylov OV 1988 Kint Catal 28 1188Sohrabi M Dabir B Eskandari A Golpasha RD 1996 J Chem Technol

Biotechnol 67 15Stansch Z Mleczko L Baerns M 1997 Ind Eng Chem Res 36 2568Su YS Ying JK Green WH 2003 J Catal 218 321Swanenberg GMJM August 1998 Eindhoven University of Technology

EindhovenTakht Ravanchi M Kaghazchi T Kargari M 2009 Desalination 235 199Traykova M Davidova N Tsaih JS Weiss AH 1998 Appl Catal A Gen 169 237Vereshchagin SN Ross JRH 1995 Catal Today 24 285Veser G Frauhammer J Friedle U 2000 Catal Today 61 55Wolf D Moros R 1997 Chem Eng Sci 52 1189Wolf D Slinko M Kurkina E Baerns M 1998 Appl Catal A Gen 166 47Wolf D Heber M Grunert W Muhler M 2001 J Catal 199 92Wolf EE 1992 Methane Conversion by Oxidative Processes Fundamental and

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8102019 1-s20-S1875510010000727-main


reaction C2 yield and selectivity and catalyst test reactor andmethane conversion have been studied

2 Kinetics models for oxidative coupling of methane

Kinetics of OCM reaction to C2 hydrocarbons has been studied

extensively based on the various reaction mechanisms (Bistol1047297 et al

1992 Lehmann and Baerns 1992 Yaghobi et al 2008 Arutyunovet al 1997 Wolf 1992 Vereshchagin and Ross 1995 Couwenberg

et al 1996a Peil et al 1991 Zeng et al 2001 Amorebieta and

Colussi 1995) Indeed kinetics of OCM reaction is very compli-

cated in terms of proposed mechanism since it involves several

chemical species (Kao et al 1997 Su et al 2003 Couwenberg et al

1996b Xin et al 2008) Former research on the kinetics andor

mechanisms of the oxidative coupling of methane (OCM) was

reviewed and given in the following classi1047297cation

(A) Spectroscopic studies of O- species and the reaction with

methane

(B) Kinetic simulations of gaseous phase reactions

(C) Simultaneous kinetic simulation of gaseous phase and surface

reactions(D) Integrating kinetics of many radical reactions of single or

several reactions

(E) Focusing on surface kinetics of methane consumption

(F) Power rate law expression of C2 (ethane and ethylene) and C1

(CO and CO2) formation

Fig 1 Geographical distribution of proven natural gas reserves

Fig 2 The main pathways of the conversion of carbon-based compound ( Pyatnitsky

et al 1998) Scheme 1


8102019 1-s20-S1875510010000727-main



methane






















1990)


01kilt

kilt




8102019 1-s20-S1875510010000727-main



reactions

















several reactions













































Scheme 2

























Scheme 2

Table 1








COthorn05O2 CO2 U U













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methane









References
















8102019 1-s20-S1875510010000727-main



methane






















1990)


01kilt

kilt




8102019 1-s20-S1875510010000727-main



reactions

















several reactions













































Scheme 2

























Scheme 2

Table 1








COthorn05O2 CO2 U U













8102019 1-s20-S1875510010000727-main






methane









References
















8102019 1-s20-S1875510010000727-main



reactions

















several reactions













































Scheme 2

























Scheme 2

Table 1








COthorn05O2 CO2 U U













8102019 1-s20-S1875510010000727-main






methane









References
















8102019 1-s20-S1875510010000727-main






methane









References
















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