Mechanism and Kinetic Modeling of Catalytic Upgrading of a Biomass

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Mechanism and kinetic modeling of catalytic upgrading of a biomass-derived raw gas: An application with ilmenite as catalyst Huong Ngoc Thuy Nguyen, Nicolas Berguerand, and Henrik Thunman Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b00650 • Publication Date (Web): 02 May 2016 Downloaded from http://pubs.acs.org on May 3, 2016

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Industrial & Engineering Chemistry Research

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Mechanism and kinetic modeling of catalytic

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upgrading of a biomass-derived raw gas: An

3

application with ilmenite as catalyst

4

Huong N.T. Nguyen,* Nicolas Berguerand, Henrik Thunman

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Division of Energy Technology, Department of Energy and Environment, Chalmers University

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of Technology, SE – 412 96 Gothenburg, Sweden

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KEYWORDS: Ilmenite, biomass, gasification, raw gas, catalytic gas cleaning, tar, light

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hydrocarbon, mechanism, kinetics

9

ABSTRACT

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A mechanism and kinetics to describe the catalytic upgrading of a biomass-derived raw gas is

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provided in this paper. The mechanism encompasses the principal trends in the evolution of tar

12

and light hydrocarbons. Using this mechanism and a pseudo-tar that represents tar and light

13

hydrocarbons formed in situ, a kinetic model is developed. The applicability of the kinetic model

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is demonstrated for a process-activated ilmenite. The experiments were conducted in a bench-

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scale, bubbling fluidized-bed reactor that was fed with a tar-rich raw gas stream from the 1

ACS Paragon Plus Environment


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Chalmers indirect biomass gasifier. The effects of the ilmenite on tar decomposition and total gas

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composition were evaluated at 800°C for three different gas-solid contact times. Combing the

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experimental results and the proposed kinetic model, the evolutionary profiles of the different tar

19

and light hydrocarbon groups can be evaluated in relation to the gas-solid contact time. The

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results form the basis of a process model for optimization and upscaling.

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1. INTRODUCTION

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Tar, which is present in biomass-derived raw gas and comprises a mixture of the condensable

23

organic compounds - in this work ranging from benzene to heavier compounds, is often the main

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source of problems in biomass gasification1,2. Tar condensation can result in the disruption of

25

downstream processes, thereby limiting direct uses of the raw gas. In addition, as the chemically

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stored energy in the tar may account for up to 15% of the energy content of the dry-ash-free

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biomass feedstock, which can significantly affect the cold gas efficiency of the process3. Thus,

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tar removal is not only a major challenge for process operation, but is also a crucial step in

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efforts to recover energy from the tar and thereby, increase process efficiency.

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Among the currently available methods for tar abatement, catalytic gas cleaning is particularly

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interesting1,4,5. This method enables the recovery of chemically stored energy in the tar instead of

32

the physical removal of condensed tar, which is the principle underlying e.g. wet cleaning

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methods. Moreover, the upgraded gas remains at a relatively high temperature and its

34

composition can be adjusted, representing potentially advantageous effects for downstream

35

syntheses, such as methanation6. Due to the inherently complex compositions of the raw gas and

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tar, the catalytic gas cleaning process involves a complicated pathway of simultaneous and 2


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consecutive reactions, in which other tar and light hydrocarbons (HC) can also be produced2,7.

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Consequently, it is difficult to propose a comprehensive mechanism and a kinetic model that

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describes the evolution of gas upgrading, which is essential for the scaling-up and optimization

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of the gasification process.

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In the literature, the kinetics of catalytic tar decomposition have been modeled using single-

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compound approaches or lumped models8. However, the tar in the raw gas contains hundreds of

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species with various molecular structures, which renders the single-compound approach

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insufficient for describing all tar species9,10. In contrast, the lump models consider all tar species

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that are present in the raw gas. In this approach, the tar is treated as a single-lump component,

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classified into two lumps that represent the more-reactive and the less-reactive tars, or divided

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into six groups based on differences in reactivity11-13. Furthermore, the various conversion paths

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taken by tar groups that possess different reactivities are partially taken into account13.

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Despite extensive studies being conducted and improvements being made to the kinetic

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modeling of catalytic tar degradation, some shortcomings remain. First, the facts that heavier tar

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components can be formed from lighter fractions and that the gas species can interact to form tar

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are not considered. Second, the roles of steam, H2, and CO2 as reforming/cracking agents are not

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adequately incorporated into the modeling. Furthermore, the above-discussed models focus

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solely on the tar, and only the major conversion pathways among tar species are taken into

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account. The evolution of light HC that is in this work referred to HC in the range of C1 to C5

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carbons is not included in the model, even though these components can be present in significant

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amounts in the raw gas and their reactions may make important contributions to the catalytic gas

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cleaning process14,15. 3



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The aims of this study were to: (i) formulate a reaction mechanism that would improve

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understanding of the principal evolutionary routes of the tar and light HC present in the raw gas;

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and (ii) further to develop a kinetic approach to catalytic gas cleaning. The catalyst that served as

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the basis for the kinetic model application was ilmenite fines collected from the Chalmers boiler

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during previous investigations, and hereinafter referred to as ‘process-activated ilmenite’15,16.

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This paper is organized as follows. Following the background introduction in Section 1 above,

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the theory regarding catalytic gas cleaning is summarized in Section 2, focusing on the reactions

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and products potentially associated with the process. In Section 3, a mechanism and kinetics

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describing the evolution of tar and light HC are respectively introduced in the first two sub-

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sections, and in the third sub-section the strategy to apply the kinetic model for process-activated

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ilmenite is presented. The next sections summarize experiments and results from model

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application i.e. the experimental set-up and procedures are described in Section 4 and the results

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obtained from applying the model are outlined in Section 5. Briefly, the catalytic activity of

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ilmenite was investigated at 800°C for three gas-solid contact times: 0.6, 0.8, and 1.1 s,

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respectively. The raw gas used in the experiments was produced in the Chalmers gasifier and

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contained a tar mixture with high fractions of secondary and tertiary compounds. By applying

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the kinetic approach and combining with the experimental results, kinetic data to formulate the

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time-dependent rate expressions were derived for different tar and light HC groups. Finally,

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general conclusions from the study are presented in Section 6.

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2. REACTIONS AND PRODUCTS OF CATALYTIC GAS CLEANING

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The catalytic gas cleaning concept involves the conversion of the tar in the raw gas into

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valuable gas components, such as CO, H2 and CH4, using catalysts. Various reactions can occur

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during the process, which consist of complete steam reforming-a reaction that produces only CO

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and H2, steam dealkylation, hydro-cracking, hydro-dealkylation, dry reforming, (thermal)

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cracking, carbon formation, methanation, and water-gas shift (WGS)7,17. In addition to the tar

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decompositions, the reforming/cracking reactions that involve light HC, which largely depend on

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the end-use of the raw gas, are of interest18. Moreover, equilibrium reactions have to be

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considered carefully, as they are essential for adjusting the reformed gas composition. The WGS

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reaction, for instance, is one of the dominant reactions in iron-based catalysis19-21.

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Figure 1. A simplified reaction scheme for a catalytic gas cleaning process.

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A simplified reaction scheme to describe the catalytic gas cleaning process is shown in Fig. 1.

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The scheme focuses on the reactions between tar/light HC and the steam, H2, and CO2, which are

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reforming/cracking agents for the complete steam reforming/steam dealkylation, hydro-

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cracking/hydro-dealkylation, and dry reforming of tar/light HC, respectively. It is noteworthy

94

that both thermal and catalytic effects affect the process and that the concentrations of CO*, H2*,

95

and CO2* in the reformed gas are adjusted by the WGS reaction.

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In Fig. 1, a pseudo-tar with the formula of CHm On is introduced, which represents all the tar

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and light HC produced in situ. It must be emphasized that after the formation CHm On continues

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the reforming/cracking cycle. Indeed, relatively stable tar/light HC can also be formed during

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catalytic gas cleaning7,14,19. Methane, which is one of the most stable species of light HC due to

100

the sp3 hybridization in its molecular structure, can be produced via the destruction of tar and

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other light HC with or without the presence of catalysts17,19,22. Benzene and naphthalene, which

102

are the most stable tar components, were shown to increase considerably when e.g. ilmenite

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catalyst was used at 800°C for secondary gas cleaning17. This was attributed to the molecular

104

structures of the original tar species in the raw gas. Indeed, phenols, 1-ring aromatic and 2-ring

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aromatic compounds were stripped off their hydroxy and alkyl groups to form benzene and

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naphthalene. Thus, tar molecules are primarily fragmented at the chemical bonds that have lower

107

bond-dissociation energy (BDE)23-26. More precisely, tar molecules are more readily destroyed at

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their carbon-hetero atom bonds, such as C-O, and at the C-C bonds between the aromatic rings

109

and side chains. The pure aromatic rings are the most difficult to break owing to the high BDEs

110

of the C-H and C=C bonds27-29. Finally, the formation of larger tar molecules was noted, in

111

addition to the relatively lighter tar species or light HC7,10,19,30. The growth of molecules was also

112

observed during the pyrolysis of biomass tar and steam cracking of HC in the petroleum refinery,

113

and this effect was attributed to reactions between two HC free radicals or between one HC free

114

radical and one HC molecule23,26,31,32.

115 116

3. MECHANISM AND KINETICS OF THE CATALYTIC EVOLUTION OF TAR AND LIGHT HYDROCARBONS

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3.1. Mechanism underlying the destruction of tar and light hydrocarbons

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For the inert thermal cracking of crude oil and pyrolysis of biomass tar, the free radical

119

mechanism is well-described24,26,32. This mechanism has also been applied by several authors to

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the catalytic decomposition of dedicated tar components, despite the presence of heterogeneous

121

gas-solid phases33,34. These applications of the free radical mechanism to the heterogeneous

122

catalysis could be due to the fact that comparable products were observed in decomposing

123

tar/HC under the influence of inert thermal and catalytic effects1,25,26.

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The basis of the free radical mechanism is that free radicals produced from parent molecules

125

act as the principal reactive factors in chain reactions. These reactions consist of: (i) initiation, in

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which two free radicals are generated by breaking chemical bonds in the parent molecules; (ii)

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propagation, in which the generated radicals react further with other molecules or self-

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decompose to form a new molecule and a new radical, or the radicals combine with unsaturated

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compounds to form larger radicals; and (iii) termination, whereby two radicals react with each

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other to form a molecule.

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In the present study, a mechanism based on reactive intermediates is proposed to describe the

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catalytic evolution of tar and light HC. This mechanism reflects the free radical mechanism.

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However, the general term ‘reactive intermediate’ is preferred instead of ‘free radical’, since the

134

heterogeneous gas-solid phases exist. The following sub-sections present the main assumptions

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supporting the mechanism, the dissociation of reforming/cracking agents, and finally, the

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evolution of tar/light HC species.

137

3.1.1. Assumptions for the reactive intermediates 7



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To describe the gradual destruction and evolution of tar/light HC species in gas cleaning

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processes and to formulate further the kinetic equations, the following assumptions are made

140

regarding the reactive intermediates.

141



The reactive intermediates are either free radicals in the gas phase or other

142

intermediates that form and react further on the catalyst surface. In the case of free

143

radicals, they can be created in the gas phase by the thermal effect or on the catalyst

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surface by the catalytic effect, and they are then desorbed to the gas phase, which is

145

accelerated at high temperature.35,36

146



For the dissociation that occurs on the catalyst surface, different molecules need

147

different types and number of active sites35. The concentration of active sites on the

148

catalyst surface is assumed to be at equilibrium.

149



Tar/light HC molecules are first converted into reactive intermediates, and it is only in

150

this state that they can react further21,34,37,38. Note that tar/light HC reactive

151

intermediates can be generated by self-dissociation of the tar/light HC molecule, as

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well as through the interactions between tar/light HC molecules and other

153

intermediates. In addition, the rate of formation of reactive intermediates is mainly

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dependent upon the temperature, catalyst, and original molecule.

155



The elementary reactions in which the tar/light HC reactive intermediates are initially

156

generated from the parent molecules are the rate-determining steps, and the subsequent

157

steps will be in quasi-equilibrium26,38,39.

8


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It should be noted that the two former assumptions apply to reactive intermediates produced

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from tar/light HC and from reforming/cracking agents, and the two latter assumptions refer

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exclusively to the tar/light HC intermediates.

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3.1.2. Dissociation of reforming/cracking agents

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The reactive intermediates that result from the dissociations of reforming/cracking agents

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facilitate the conversion of tar/light HC. For instance, hydrogen intermediates H* produced from

164

the dissociation of steam and H2 facilitate the initial destruction of tar/light HC molecules22,26,40.

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Furthermore, oxygen intermediates O* formed through the dissociation of steam and CO2 react

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with the tar/light HC intermediates to produce CO, and thereafter to produce CO2 via the WGS

167

reaction21,41.

168

The dissociation of steam and H2 takes place in reversible steps, forming OH*, H*, and O*

169

reactive intermediates39,41,42. However, OH* continues to dissociate to H* and O*. Thus, the

170

overall dissociations follow elementary reactions (1) and (2):

171

H2 O ⇆ 2H* + O*

(1)

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H2 ⇆ 2H*

(2)

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For CO2 dissociation, two mechanisms are generally proposed in the literature39,41; see

174

elementary reactions (3) and (4). Here, it is assumed that CO2 disscociation only follows reaction

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(3). This is mainly to reduce the computation effort for estimating the concentration of hydrogen

176

intermediate H*, which is presented in Section 3.2.

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CO2 ⇆ CO+ O*

(3)

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CO2 + H* ⇆ CO + OH*

(4) 9



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The dissociations of steam, H2, and CO2 are interrelated, as they are elementary steps in the

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regenerative mechanism applied for the WGS reaction at high temperature20,43. The

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performances of steam, H2, and CO2 dissociations can vary, and they depend heavily on the

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related thermodynamics and catalysts. Comparing the BDEs, the dissocation of steam and H2 is

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more thermodynamically favorable than that of CO228.

184

3.1.3. Evolution of tar and light hydrocarbons

185

The gradual evolution of tar/light HC is typically described simply as follows. Note that the

186

symbols C with subscripts indicate tar/light HC, the symbols C* with subscripts indicate tar/light

187

HC reactive intermediates, and the subscript letters represent the number of carbons in the

188

molecules or reactive intermediates.

189 190 191



Tar/light HC molecule self-dissociation:

Cx → C*x' + C*x−x' 

192

C*x' is H* if 𝑥 ′ = 0

(5)

Interaction between tar/light HC molecule and reactive intermediates (atom or group transfer):

193

Cx + H* → C*x − f + Cf

Cf is H2 if f = 0 (atom transfer)

(6)

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Cx + C*x' → C*x + x' − j + Cj

C*x + x' − j is H* if 𝑥 + 𝑥′ − 𝑗 = 0

(7)

195 196 197 198 199



Addition of unsaturated HC to reactive intermediates:

C*x' + Cq → C*x' + q 

(8)

Decomposition of tar/light HC intermediates:

C*x' → Cx'' + C*x' − x'' 

Cq is unsaturated HC

C*x' − x'' is H* if 𝑥′ − 𝑥′′ = 0

(9)

Termination: 10


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200

C*x' + H* → Cx'

(10)

201

C*x' + C*u → Cx' + u

(11)

202

Tar/light HC molecules in the raw gas are initially converted into reactive intermediates in

203

elementary reactions (5), (6) and (7). More precisely, the tar/light HC molecules can be self-

204

dissociated in reaction (5). The conversion of the tar/light HC molecules into reactive

205

intermediates can also be triggered by interactions with the hydrogen intermediate H* in reaction

206

(6) or with tar/HC reactive intermediates in reaction (7). After formation, the tar/HC reactive

207

intermediates can react with unsaturated HC to form larger intermediates in elementary reaction

208

(8) or they can be decomposed to form smaller species in elementary reaction (9). In the

209

termination step, two reactive intermediates interact to form new molecules. Note that reaction

210

(5) is reversible and this is accounted for in the termination step.

211

11



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Figure 2. Simplified reaction network and product distribution for tar/light HC conversion.

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The evolution of tar/light HC during catalytic gas cleaning is summarized in Fig. 2. Among the

214

elementary steps, the initial bond cleavage, whereby the original tar/light HC molecules undergo

215

initial break-down, is slower than the subsequent steps. It is assumed that once the C*1

216

intermediates are produced after gradual fragmentation following reaction (9), they can react

217

with available oxidizing agents to produce CO, and thereafter to produce CO2 via the WGS

218

reaction5,21,26,41. It should be noted that these oxidizing agents can be steam and CO2 or their

219

dissociated forms, e.g., reactive intermediate O*.

220

From the proposed elementary steps, the trend of in situ formation of smaller or larger tar/light

221

HC molecules at a certain operational temperature can be predicted, based on the raw gas

222

composition and the given catalyst. More specifically, this trend largely depends on the ratio of

223

the number of hydrogen intermediates H* to the number of tar/light HC intermediates. If this

224

ratio is relatively high, the probability that H* will collide and react with other tar/light HC

225

intermediates to produce smaller molecules is higher than the probability of reactions between

226

the tar/light HC intermediates. In contrast, a low ratio indicates a high probability to form larger

227

intermediates or larger molecules through reactions, e.g., (8) and (11).

228

3.2. Kinetic modeling for the prediction of reformed gas composition

229

The kinetic modeling of the time-dependent evolution of tar and light HC is described in this

230

section and is derived from the mechanism presented previously. A direct application of the

231

kinetic model is to predict the compositions of the reformed gases obtained for various gas-solid

232

contact times. 12


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233

To take into account the differences in reactivity, the tar in the raw gas is divided into six

234

groups (denoted C1–C6) as follows: phenolic and oxygen-containing compounds (C1); benzene

235

(C2); 1-ring compounds (C3) (benzene is not included in C3); naphthalene (C4); 2-ring

236

compounds (C5) (naphthalene is not included in C5); and 3-ring and larger compounds (C6). The

237

general tar formulas Cxi Hyi Ozi with specific values of 𝑥𝑖 , 𝑦𝑖 and 𝑧𝑖 for each tar group Ci are

238

defined based on the tar composition of the raw gas. In the same way, light HC are categorized

239

into group C7, which consists of HC in the range of C2 to C5 carbons, and the methane group

240

(C8). The general formula Cxi Hyi for group C7 is defined based on the raw gas composition.

241

As earlier shown in Fig. 1, all tar/light HC produced in situ is represented by the pseudo-tar

242

CHm On . Here, the values of 𝑚 and 𝑛 in CHm On are derived from the contents of carbon,

243

hydrogen, and oxygen in the reformed gas, excluding CO, CO2 and H2. The formation and

244

distribution of the pseudo-tar CHm On are summarized in Fig. 3.

245 246

Figure 3. Formation and distribution of pseudo-tar CHm On .

13



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247

As shown in Fig. 3, CHm On can be produced from the destruction of all tar/light HC groups. In

248

addition, CHm On can be formed from the gas species CO and H2, according to reaction (12), in

249

which the methanation reaction is also included.

250

CO + (1 + 0.5m − n)H2 → CHm On + (1 − n)H2 O

(12)

251

Immediately after its formation, CHm On is distributed to all the tar and light HC groups Ci with

252

the distribution coefficient 𝑝𝑖 , which is given by reaction (13): CHm On → 𝑝𝑖 Cxi Hyi Ozi

253

In situ tar/light HC formation

(13)

254

The values of the coefficient 𝑝𝑖 satisfy the carbon balance in reaction (13). Moreover, their

255

value ranges can be estimated based on the composition and molecular structures of the original

256

tar/light HC species in the raw gas.

257

As the rate-determining steps are defined, namely elementary reactions (5), (6) and (7), the rate

258

expression for the time-dependent conversion of tar/light HC group Ci can be written as follows,

259

for which S, 𝑋𝐶 ∗ and 𝑋𝐻 ∗ will be defined further. It should be noted that for unsaturated HC

260

molecules, they may undergo elementary reaction (8) to be converted into reactive intermediates,

261

however, this can be taken into account through elementary reaction (7) to form the rate equation

262

for the corresponding group Ci.

263

𝑑𝑋𝐶𝑖 𝑑𝑋𝐶𝑖 (5) 𝑑𝑋𝐶𝑖 (6) 𝑑𝑋𝐶𝑖 (7) =− − − + 𝑝𝑖 𝑆 𝑑𝑡 𝑑𝑡 𝑑𝑡 𝑑𝑡

264

= −𝑘𝑖5 𝑋𝐶𝑖 − 𝑘𝑖6 𝑋𝐶𝑖 𝑋𝐻 ∗ − 𝑘𝑖7 𝑋𝐶𝑖 𝑋𝐶 ∗ + 𝑝𝑖 𝑆

265

where,

266

𝑋𝐶𝑖 is the mole fraction of tar/light HC group Ci [-];

267

𝑋𝐻 ∗ is the mole fraction of hydrogen intermediate H*[-];

(14)

14


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268

𝑋𝐶 ∗ is the mole fraction of tar/light HC intermediate C* [-];

269

𝑝𝑖 is the distribution coefficient in reaction (13) for tar/light HC group Ci [-];

270

𝑆 is the total rate of CHm On formation [s −1 ]; and

271

𝑘𝑖5 , 𝑘𝑖6 , 𝑘𝑖7 are the pseudo-kinetic rate constants of elementary reactions (5), (6) and (7),

272

respectively, with respect to group Ci [s−1 ].

273

As shown in Fig. 3, the total rate 𝑆 of CHm On formation has to take into account the

274

productions of CHm On from the destruction of tar/light HC and from the gas species CO and H2.

275

To enable the estimation of 𝑆, the relative productions of CHm On and CO from the destruction

276

of original tar/light HC has to be known. Therefore, the parameter wi (0 ≤ 𝑤𝑖 ≤ 𝑥𝑖 ) which

277

represents the number of carbon in a tar/light HC molecule Cxi Hyi Ozi converted into CHm On is

278

introduced. Note that wi values depend on the actual catalyst used and other process conditions

279

such as operating temperature. Finally, the total rate 𝑆 is estimated following Eqn. (15), in which

280

𝑆𝑔𝑎𝑠 is the rate of CHm On formation from CO and H2 via reaction (12).

281

𝑆 = 𝑆𝑔𝑎𝑠 + ∑𝑖 𝑤𝑖 (𝑘𝑖5 𝑋𝐶𝑖 + 𝑘𝑖6 𝑋𝐶𝑖 𝑋𝐻 ∗ + 𝑘𝑖7 𝑋𝐶𝑖 𝑋𝐶 ∗ )

282

The maximum rate of tar/light HC intermediate C* formation can be estimated from

283 284

(15)

elementary reaction (5) as follows: 𝑑𝑋𝐶∗ 𝑑𝑡

= 2 ∑𝑖 𝑘𝑖5 𝑋𝐶𝑖

(16)

285

For a characteristic time-step ∆𝜏, the mole fraction 𝑋𝐶𝑖 in Eqn. (16) can be considered as

286

constant. Furthermore, the concentration of reactive intermediates can be assumed to be constant

287

throughout the reactions as the reactive intermediates are much more reactive than the original

288

molecules 29. Therefore, Eqn. (16) can be integrated to give: 15



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289 290 291 292

𝑋𝐶 ∗ = 2∆𝜏 ∑𝑖 𝑘𝑖5 𝑋𝐶𝑖

Page 16 of 43

(17)

′ By using 𝑋𝐶 ∗ from Eqn. (17) and further introducing 𝑘𝑖7 to replace the term 𝑘𝑖7 . ∆𝜏, Eqn. (14)

can be re-written as follows: 𝑑𝑋𝐶𝑖

′ = −𝑘𝑖5 𝑋𝐶𝑖 − 𝑘𝑖6 𝑋𝐶𝑖 𝑋𝐻 ∗ − 2𝑘𝑖7 𝑋𝐶𝑖 ∑𝑖 𝑘𝑖5 𝑋𝐶𝑖 + 𝑝𝑖 𝑆

𝑑𝑡

(18)

293

The rate expression for the mole fraction of H* versus time is presented in Eqn. (19) below, in

294

which 𝑘𝑓,𝐻2 𝑂 , 𝑘𝑏,𝐻2 𝑂 , 𝑘𝑓,𝐻2 and 𝑘𝑏,𝐻2 are the pseudo-rate constants in the reversible dissociation

295

steps (1) and (2) for steam and H2, respectively.

296

𝑑𝑋𝐻∗ 𝑑𝑡

= 2𝑘𝑓,𝐻2 𝑂 𝑋𝐻2 𝑂 − 𝑘𝑏,𝐻2 𝑂 𝑋𝐻2 ∗ 𝑋𝑂∗ + 2𝑘𝑓,𝐻2 𝑋𝐻2 − 𝑘𝑏,𝐻2 𝑋𝐻2 ∗

(19)

297

To estimate the mole fraction of hydrogen intermediate H*for incorporation into Eqn. (18), two

298

cases are considered that differ with respect to the gas-solid contact time and the catalyst in use:

299

(i) steam and H2 dissociate insignificantly; and (ii) steam and H2 dissociate significantly and

300

reach equilibrium. In the latter case, the WGS reaction is also at equilibrium. For a given

301

temperature and gas composition, the time length required for elementary reactions (1), (2) and

302

(3) to reach equilibrium depends on the catalyst used.

303

For the case in which steam and H2 dissociate insignificantly, the approximation already

304

applied for the tar/light HC intermediates C* is used to estimate the mole fraction of hydrogen

305

intermediate H*. Note that the backwards reactions in reactions (1) and (2) are considered to be

306

′ slow, as compared with the forward reactions. Finally, using 𝑘𝑖6 to replace the term 𝑘𝑖6 . ∆𝜏, Eqn.

307

(18) becomes:

308

𝑑𝑋𝐶𝑖 𝑑𝑡

′ ′ = −𝑘𝑖5 𝑋𝐶𝑖 − 2𝑘𝑖6 𝑋𝐶𝑖 [𝑘𝑓,𝐻2 𝑂 𝑋𝐻2 𝑂 + 𝑘𝑓,𝐻2 𝑋𝐻2 ] − 2𝑘𝑖7 𝑋𝐶𝑖 ∑𝑖 𝑘𝑖5 𝑋𝐶𝑖 + 𝑝𝑖 𝑆

(20)

16


Page 17 of 43

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309

In the case that steam and H2 dissociate significantly and reach equilibrium, the mole fraction

310

of H* is derived from the expression of the equilibrium constant 𝐾𝐻2 for elementary reaction (2).

311

Eqn. (18) is further adapted as follows, in which the equilibrium constant 𝐾𝐻2 is already

312

′′ incorporated into the pseudo-rate constant 𝑘𝑖6 :

313

𝑑𝑋𝐶𝑖 𝑑𝑡

′′ ′ = −𝑘𝑖5 𝑋𝐶𝑖 − 𝑘𝑖6 𝑋𝐶𝑖 𝑋𝐻0.5 − 2𝑘𝑖7 𝑋𝐶𝑖 ∑𝑖 𝑘𝑖5 𝑋𝐶𝑖 + 𝑝𝑖 𝑆 2

(21)

314

Finally, the estimation of the mole fractions for gas species CO, H2 and CO2 has to be

315

performed in relation to the quantity of CHm On , and it takes into account the dry reforming,

316

hydro-cracking/hydro-dealkylation, and WGS reaction. Note that CO and H2 are initially

317

produced from the reforming/cracking reactions, and that CO further reacts in the WGS to

318

produce CO221. Moreover, CO2 and H2 are also consumed during dry reforming and hydro-

319

cracking /hydro-dealkylation, respectively.

320

3.3. Model application for process-activated ilmenite

321

To demonstrate the applicability of the kinetic approach presented above, calculations were

322

performed for process-activated ilmenite. This ilmenite had previously been activated during a

323

time-on-stream of approximately 1 day in the Chalmers boiler, which was operated at about

324

900°C44,45. The ilmenite fraction used in the current study had a grain size in the range of 45–90

325

µm. Ilmenite was selected as it is naturally occurring, inexpensive compared to synthetic

326

materials, attrition-resistant, and it possesses proven catalytic activity, making it a promising

327

catalyst for gas cleaning applications3,17,46,47.

328

Ilmenite facilitates the dissociation of steam, H2 and CO2. Indeed, ilmenite contains iron that is

329

known to chemisorb these reforming/cracking agents35,41,42,48,49. Moreover, ilmenite is known for 17



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Page 18 of 43

330

its significant catalytic effect on the WGS reaction14,19,46. Therefore, the rate expressions for the

331

conversion of tar/light HC during ilmenite catalysis can be described using Eqn. (21). In the

332

present study, the aggregate mole fraction of CO plus CO2 on the one side, and the combined

333

mole fraction of H2 plus steam on the other side were estimated. This was necessary due to the

334

lack of available kinetic data regarding ilmenite catalysis. Moreover, the focus of this model

335

demonstration was exclusively on tar and light HC. The model calculations were performed

336

under the following assumptions:

337



338 339

thermodynamic equilibrium for the raw gas mixture; 

Steam accounted for 60 vol.% of the raw gas, and the consumption of steam in each experiment was estimated from the hydrogen balance15;

340 341

The value for the mole fraction of H2 used in Eqn. (21) was estimated at the



The estimated value ranges for the rate constants for tar/light HC groups were derived

342

from experimental results in which a continuous stirred-tank reactor was assumed.

343

However, for benzene, naphthalene, and methane, the estimated value ranges for the

344

rate constants were derived from other studies19,50;

345



environment and therefore, it was not considered19,51;

346 347 348

Carbon deposition on the ilmenite particles was negligible in the excess steam



The formation of CHm On from CO and H2 was ignored under the conditions used in this study, i.e., 𝑆𝑔𝑎𝑠 = 0 19;

18


Page 19 of 43

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349




While the values of 𝑝𝑖 most likely change as the tar and light HC gradually evolve, to

350

simplify the calculations, these values were assumed to remain constant during the

351

evolution of tar and light HC in relation to gas-solid contact time;

352



thermal effect at 800°C17;

353 354



In the raw gas and reformed gas, HC in the range of C4–C5 carbons were neglected. Thus, group C7 consisted of only C2-3Hy14,15,52; and

355 356

For the destruction of tar and light HC, the effect of catalysis was greater than the



Unknown tars refer to compounds identified in the Gas Chromatograph-Flame

357

Ionization Detector (GC-FID) analysis but at very low levels, and thus not included in

358

the standard tar compounds predefined in the GC-FID method. Additionally, these

359

unknown tars were assigned to the most plausible known tar groups based on their

360

retention times in the GC-FID chromatograms.

361

Finally, the rate expressions for the conversions of tar/light HC groups were solved by

362

integration, with the initial condition being the raw gas composition, i.e. at a gas-solid contact

363

time equal to zero. During the calculation procedure, values of the parameters 𝑝𝑖 , 𝑤𝑖 and rate

364

constants 𝑘𝑖 were randomly generated within the predefined value ranges, as previously

365

mentioned. Moreover, the sums of squares of deviations between the calculated values and

366

experimental values for the mole fractions of tar/light HC groups at three different gas-solid

367

contact times were calculated and compared with predefined tolerances as criteria for the

368

convergence of the iteration loop. In all, the evolutionary profiles of the different tar/light HC

369

groups in relation to the gas-solid contact time were obtained.

370

4. EXPERIMENTAL SECTION 19



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371

Page 20 of 43

4.1. Experimental set-up

372

The experimental set-up is presented in Fig. 4. The main part is the reforming reactor. This is a

373

bench-scale, bubbling fluidized-bed reactor operated in batch mode. The reactor has an inner

374

diameter of 55 mm and has a height of 379 mm, as measured from the porous plate to the reactor

375

outlet. The reactor is composed of the high-chromium austenitic stainless steel RA 253 MA. In

376

all, five pressure taps and three thermocouples are connected to the reactor. The pressures are

377

measured as the pressure differences between two taps or between one tap and the atmosphere.

378

The heat required for the reactor is supplied externally by a heating oven.

379 380

Figure 4. Schematic of the experimental set-up. 20


Page 21 of 43

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381

The batch of catalyst can be subjected to air, nitrogen or raw gas. For operation with raw gas, a

382

slipstream of raw gas is extracted from the Chalmers gasifier and supplied to the reactor. During

383

raw gas operation, the high temperature valve in Fig. 4 is opened and the raw gas flowing to the

384

reactor is controlled by a diaphragm valve and a pump downstream of the reactor. The gas enters

385

the reactor through a wind box and is distributed through a porous plate, to reduce the pressure

386

fluctuation and ensure even distribution of the gas. Before entering the reactor, a trace stream of

387

He is added to the raw gas, so as to derive the flow rate of the reformed gas exiting the reactor.

388

As the line from the gasifier to the reactor is heated to approximately 350°C to prevent tar

389

condensation, the actual flow rate of the raw gas entering the reactor is calculated based on the

390

conservation of the inert nitrogen throughout the reactor, rather than being measured using

391

conventional apparatuses.

392

Downstream of the reactor, a tar sampling port for Solid Phase Adsorption (SPA) is available.

393

The SPA method involves dual-layer Solid Phase Extraction columns (Supelclean ENVI-

394

Carb/NH2 SPE tube; Sigma-Aldrich). The procedures for extracting, preserving, and eluting the

395

SPA samples and for sample analysis by GC-FID are described elsewhere53.

396

The gas conditioning system downstream of the SPA sampling port is described in detail

397

elsewhere17. This system is used for condensing steam and removing the tar remaining in the

398

reformed gas. After the conditioning step, the permanent gas composition is analyzed online

399

using the Rosemount NGA 2000 Multi-Component gas analyzer and a micro-GC.

400

A parallel raw gas sampling line from the gasifier is used to compare the inlet and outlet

401

streams of the reforming reactor (see Fig. 4). The raw gas sampling system is operated for one

21



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Page 22 of 43

402

hour to yield the tar and dry gas compositions of the raw gas. This period of time coincides with

403

the duration of the raw gas operation of the reforming reactor.

404

4.2. Experimental procedure

405

In the typical reforming experiment, a certain amount of ilmenite was placed in the empty

406

reforming reactor under the ambient condition. Air was introduced into the reactor as the

407

fluidizing medium. The heating sequence was initiated, and the reactor was heated to 800°C,

408

which was the temperature used in the reforming experiments. The gas concentrations in the off-

409

gas were monitored online using the NGA analyzer. Air was introduced into the reactor until the

410

concentration of oxygen stabilized at approximately 21 vol.%, so as to remove any carbon

411

deposits on the ilmenite particles. The air flow was then decreased in a step-wise manner and

412

replaced by inert nitrogen until no oxygen was detected at the outlet. The high-temperature valve

413

was then opened, the nitrogen flow was decreased in a step-wise manner, and the raw gas flow

414

was increased progressively until the nitrogen was entirely replaced. The raw gas operation

415

lasted for 60–80 minutes, depending on the experimental conditions used, and this was followed

416

by an inert period during which the nitrogen was increased in steps until no CO or CO2 or CH4

417

was detected at the outlet.

22


Page 23 of 43

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418 419

Figure 5. Different fluidizing media used in the experiment, and compositions of the resulting

420

outlet gases (dry basis).

421 422

Figure 6. Molar concentrations of CO and CO2 (dry basis) in the outlet gas during raw gas

423

operation.

23



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Page 24 of 43

424

Figure 5 shows the different fluidizing media used and the resulting outlet gas compositions

425

during the course of a typical experiment. Fig. 6 focuses on the CO and CO2 concentrations in

426

the gas that left the reactor, and shows the time-points at which the dry gas composition and tar

427

were sampled. During the raw gas phase, some of the raw gas was initially combusted, since

428

there was available oxygen on the oxidized ilmenite particles. After the oxygen was consumed,

429

the ilmenite particles were fully reduced and were prone to act as catalysts, as evidenced by the

430

stable concentrations of CO and CO2 exiting the reactor.

431

4.3. Operating conditions

432

The primary parameter in the present investigation was the gas-solid contact time, which was

433

varied by changing either the raw gas flow rate or the quantity of ilmenite particles. The gas-

434

solid contact time was estimated following the formula used by Lind et al.14, and the calculated

435

values are given in Table 1. For these calculations, the bed voidage, which represented the void

436

fraction in the bubbling fluidized bed as a whole, was estimated using the simple two-phase

437

model and assuming a fixed bubble diameter of 15 mm54. Note that the total gas flows entering

438

and leaving the reactor increased due to the presence of He in the gas streams, and this reduced

439

the gas-solid contact time. The operating conditions for the gasifier and for the reforming

440

experiments with ilmenite are also presented in Table 1. Further details of the Chalmers indirect

441

gasifier are available elsewhere15.

442

Table 1. Operating conditions for the gasifier and for the reforming experiments. Gasifier Bed material

Silica sand 24


Page 25 of 43

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Temperature (°C)

~820

Fuel

Wood pellets

Fuel flow rate (kg/h)

~293

Steam flow rate for fluidization in

~160

the gasifier (kg/h)

443 444

Reforming experiments

Exp. 1

Exp. 2

Exp. 3

Ilmenite amount (g)

300

300

200

Raw gas flow rate (wet) (Ln/min)

3.1

2.1

0.9

He tracing (Ln/min)

0.3

0.3

0.24

Flow rate of air/nitrogen (Ln/min)

1.5

1.5

1.2

Temperature (°C)

800

800

800

Gas-solid contact time (s)

0.6

0.8

1.1

5. RESULTS AND DISCUSSION 5.1. Prediction of the reformed gas composition

445

Using the tar composition of the raw gas, the general formulas for the tar/light HC groups from

446

C1 to C8 were determined (Table 2). The formula for the pseudo-tar CHm On was derived as

447

CH2.82 , with the value 𝑛 for oxygen being negligible.

448

Table 2. Tar/light HC groups in the C1–C8 range with general formulas. Group

General formula

Components in group

C1: phenolic and oxygen-containing compounds

C6.77 H6.41 O1

phenol ; o/p-cresol; 1/2-naphtol ; 2,3-benzofuran; dibenzofuran; xanthene

C2: benzene

C 6 H6

benzene 25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

C3: 1-ring compounds

C7.18 H8.19

toluene; o/p-xylene; styrene; methylstyrene

C4: naphthalene

C10 H8

naphthalene

C5: 2-ring compounds

C9.79 H8.71

1,2-dihydronaphthalene; 1/2methylnaphthalene; biphenyl; indene

C6: ≥3-ring compounds

C13.33 H9.22

acenaphthylene; fluorene; phenanthrene; anthracene; fluoranthene; pyrene; chrysene

C7: light C2.05 H4.20 hydrocarbons C2-3Hy

C2H2; C2H4; C2H6; C3H6

C8: methane

Methane

CH4

Page 26 of 43

449

It should be noted that although the operating conditions of the gasifier were kept constant

450

throughout the experimental campaign, the composition of the raw gas varied slightly. Thus, the

451

average values for the permanent gas and tar compositions were used in the calculations.

452

Furthermore, the flow rate of the dry raw gas entering the reactor was calculated using the total

453

carbon in the reformed gas that exited the reactor to ensure that the carbon balance was fulfilled.

454

This was done because the carbon balance across the reactor in which the flow rate of the raw

455

gas was estimated based on nitrogen conservation reached approximately 98%.

26


Page 27 of 43

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456

457 458

Figure 7a-b. Predicted (lines) and measured (markers) reformed gas compositions.

459

Figure 7a-b shows a typical result from the model for the predicted gas composition at a

460

contact time of up to 1.1 s. The calculated data are in good agreement with the experimental

461

results for all the tar and light HC groups, which suggests that the proposed mechanism and

462

kinetic model sufficiently capture the main features of the catalytic gas cleaning process. The 27



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Page 28 of 43

463

model reveals that lower mole factions of tar groups C1, C3, C5, and C6 are achieved as the

464

contact time increases. The destruction of groups C1, C3, C5, and C6 produces C2: benzene and

465

C4: naphthalene, which results in increases in the mole fractions of these two groups (see Fig.

466

7a). For the light HC C2-3Hy, there is a considerable decrease in its concentration (see Fig. 7b).

467

However, a very small increase in the methane level is noted. In addition, Table 3 summarizes

468

the calculated data used to derive the rate expression for each tar/light HC group.

469

Table 3. Calculated data to derive the rate expressions for the conversion of tar/light HC groups. Group

𝑘𝑖5

′′ 𝑘𝑖6

′ 𝑘𝑖7

Formation and distribution of CHm On 𝑤𝑖 /𝑥𝑖

𝑝𝑖

C1

1.73

3.57

1.47

0.84

0

C2

0.12

0.90

0.83

0.16

0.0735

C3

2.02

2.61

1.36

0.78

0.0277

C4

0.94

1.20

0.21

0.44

0.0217

C5

3.30

2.07

0.54

0.78

0.0079

C6

0.20

1.37

0.75

0.81

0

C7

~0

0.004

0.027

0.53

0.0016

C8

0.49

0.83

0.26

0

0.0625

470

28


Page 29 of 43

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471

472 473

Figure 8a-b. Semi-log plots for reformed gas compositions at longer gas-solid contact times.

474

Figure 8a-b shows the reformed gas composition at a gas-solid contact time of up to 20 s using

475

the same source data as presented in Table 3. To validate the model prediction, this would

476

require additional experimental data at longer contact times than those in this present work. From

477

the contact time of approximately 5 s, one could expect full conversion of phenolic and oxygen29



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Page 30 of 43

478

containing compounds (C1), 1-ring compounds (C3), 2-ring compounds (C5), and 3-ring and

479

larger compounds (C6). Naphthalene (C4) requires a longer contact time, approximately 6 s, to

480

be completely removed. Benzene (C2), which is the most abundant tar group in the reformed gas,

481

requires a significantly longer contact time (approximately 12 s) to be eliminated completely. For

482

the light HC, the C2-3Hy group is nearly completely removed at a contact time of around 3 s,

483

while the methane fraction remains nearly constant. The model suggests that ilmenite is not a

484

suitable catalyst for the removal of benzene and methane, especially at 800°C. To eliminate to a

485

sufficient level these stable components, higher operating temperatures and/or more efficient

486

catalysts, such as nickel-based materials, are probably needed.

487

The numerical data from the model calculation reveal that the initial destruction of tar/light HC

488

molecules triggered by the interaction of these molecules with the tar/light HC reactive

489

intermediates is negligible, as compared with the total effect of the self-dissociation and the

490

dissociation facilitated by the hydrogen intermediate H*. Therefore, the third term in Eqn. (21)

491

can be neglected. Moreover, the initial bond cleavage facilitated by H* is the most important

492

mechanism, even for the destruction of methane, benzene, and 3-ring and larger compounds.

493

Thus, the role of H* in facilitating the initial cleavage of the chemical bonds in tar/light HC

494

molecules is confirmed.

495

5.2. Conversion network for tar and light hydrocarbon groups

496

It was assumed that the pseudo-tar CH2.82 lumped together all the tar and light HC formed in

497

situ and that it was distributed to all groups in the form of the source terms 𝑝𝑖 𝑆. Therefore,

30


Page 31 of 43

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498

conversion pathways among the different groups need to be further defined and incorporated into

499

the model if conversions from one group to other groups are expected.

500

A conversion network among the tar and light HC groups is presented in Fig. 9. It is suggested

501

based on the composition of the permanent gas and tar analysis results obtained from the

502

experimental section and the results obtained from the modeling evaluation.

503 504

Figure 9. A conversion network for the tar and light HC groups with: C1, phenolic and oxygen-

505

containing compounds; C2, benzene; C3, 1-ring compounds; C4, naphthalene; C5, 2-ring

506

compounds; C6, 3-ring and larger compounds; C7, C2-3Hy; C8, methane.

507

Figure 9 takes only into account the conversion routes in that the heavier tar/light HC groups

508

produce the lighter ones. The formation of relatively heavier tar/HC molecules is neglected, as

509

the raw gas contained a high steam content and ilmenite facilitates steam dissociation. Light HC,

510

i.e., C2-3Hy and methane, can be produced from all tar groups, and the destruction of C2-3Hy can

511

result in the formation of the lighter HC methane. Moreover, the conversion routes, which

512

produce naphthalene, benzene and methane, and are represented by the thicker lines in Fig. 9, are

513

identified as among the most important pathways. Finally, the coefficients for the contributions

514

of the different tar/light HC groups to the in situ formation of group Ci are summarized in Table

515

4. 31



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Page 32 of 43

516

Table 4. Coefficients for the contributions of the different tar/light HC groups to in situ

517

formation of group Ci. Group

518

Contribution of different groups to in situ formation of group Ci C1

C2

C3

C4

C5

C6

C7

C8

C1

-

0

0

0

0

0

0

0

C2

0.76

-

3.71

1.07

0.15

1.44

0

0

C3

1.53

0

-

0.83

2.23

0.77

0

0

C4

0.40

0

0

-

1.35

2.89

0

0

C5

0.14

0

0

0

-

1.38

0

0

C6

0

0

0

0

0

-

0

0

C7

0.004

0.012

0.029

0.0012

0.037

0.0007

-

0

C8

0.57

0.019

1.01

0.30

2.11

0.67

0.10

-

5.3. Approach used for full-model development

519

The proposed kinetic approach has great potential for predicting the evolution of tar and light

520

HC. The model has the advantage over others in that the entire tar species in the raw gas

521

encompassing different reactivities, the main reaction routes, and the important roles of

522

reforming/cracking agents are considered. However, further investigations are needed to refine

523

the model:

524



The relative quantities of CO and tar/light HC formed in situ from the destruction of

525

tar/light HC, i.e., the ratio wi/𝑥𝑖 in Table 3 should be estimated through

526

experimentation; 32


Page 33 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

527




The decomposition of single tar components and mixtures thereof under similar

528

experimental conditions should be investigated; this is also to confirm the conversion

529

pathways in Fig. 9, and to derive the formula CHm On for the pseudo-tar and the

530

coefficients 𝑝𝑖 in pseudo-reaction (13) more accurately;

531



Experiments with longer gas-solid contact times than those achieved in the experiments

532

carried out in the present study are required to validate the model prediction (Fig. 8a-b).

533

This is also required to elucidate the destruction of stable components, particularly

534

naphthalene, benzene, and methane, during ilmenite catalysis; and

535



Studies of thermal effects are necessary if temperatures higher than 800°C are used.

536

The model that is under development is applicable to catalysts other than ilmenite. Depending

537

on the catalyst and the operating conditions, the current model can be adapted with specific

538

features. As examples: (i) carbon deposits and soot can be designated as tar groups and thereby,

539

they can be included in the calculation; (ii) methanation and other Fischer-Tropsch reactions

540

between CO and H2 to form CHm On can be incorporated into the calculation by specifying the

541

rate Sgas in Eqn. (15); and (iii) the individual mole fractions of CO, H2, and CO2 in the reformed

542

gas can be predicted if the kinetic data for the WGS reaction and the relative efficiencies of the

543

different reforming/cracking reactions triggered by steam, H2, and CO2 are available for the

544

studied catalysts.

545

6. CONCLUSIONS

546

In this paper, we propose a mechanism based on reactive intermediates to describe the

547

principal trends in the catalytic evolution of tar and light hydrocarbons in a raw gas from 33



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Page 34 of 43

548

biomass gasification. Furthermore, a kinetic model is developed using the proposed mechanism

549

and a pseudo-tar that represents tar and light hydrocarbons formed in situ. Finally, the

550

mechanism and kinetic approach are applied for process-activated ilmenite. The experiments

551

with ilmenite were conducted in a bench-scale bubbling fluidized bed reactor that was operated

552

at 800°C and fed with a raw gas stream from the Chalmers gasifier. Three gas-solids contact

553

times, 0.6 s, 0.8 s, and 1.1 s, were investigated. From the obtained results, the following

554

conclusions are drawn:

555



Applying the mechanism and kinetic approach for process-activated ilmenite

556

successfully explains the evolution of different tar and light hydrocarbon groups as a

557

function of gas-solid contact time.

558 559



A conversion network for tar and light hydrocarbon groups is proposed, although this needs to be verified in more specific experiments.

560

AUTHOR INFORMATION

561

Corresponding Author

562

*E-mail: [email protected]. Tel: + 46 (0) 31 772 14 45

34


Page 35 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

563


ACKNOWLEDGMENTS

564

This work was made possible by financial support from E.On and the Swedish Gasification

565

Centre (SFC). Operation of the gasifier was supported by Göteborg Energi, Metso, Akademiska

566

Hus, and the Swedish Energy Agency (Energimyndigheten). The authors thank research

567

engineers Rustan Hvitt, Jessica Bohwalli, and Johannes Öhlin for their valuable help with the

568

experimental equipment.

569

ABBREVIATIONS

570

HC, light hydrocarbons

571

WGS, water-gas shift (reaction)

572

BDE, bond-dissociation energy

573

GC-FID, Gas chromatograph-Flame ionization detector

574

SPA, Solid phase adsorption

575

REFERENCES

576

(1) Milne, T. A.; Evans, R. J.; Abatzoglou, N. Biomass Gasifier “Tars”: Their Nature,

577

Formation, and Conversion; National Renewable Energy Laboratory: Golden, Colorado, United

578

States, 1998. 35



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

579 580

Page 36 of 43

(2) Torresa, W.; Pansarea, S. S.; Goodwin, J. G. Hot Gas Removal of Tars, Ammonia, and Hydrogen Sulfide from Biomass Gasification Gas. Catal. Rev. 2007, 49, 407-456.

581

(3) Larsson, A.; Israelsson, M.; Lind, F.; Seemann, M.; Thunman, H. Using Ilmenite To

582

Reduce the Tar Yield in a Dual Fluidized Bed Gasification System. Energy Fuels 2014, 28,

583

2632-2644.

584 585 586 587

(4) Dayton, D. A Review of the Literature on Catalytic Biomass Tar Destruction; National Renewable Energy Laboratory: Golden, Colorado, United States, 2002. (5) Yung, M. M.; Jablonski, W. S.; Magrini-Bair, K. A. Review of catalytic conditioning of biomass-derived syngas. Energy Fuels 2009, 23, 1874-1887.

588

(6) Kopyscinski, J.; Schildhauer, T. J.; Biollaz, S. M. A. Production of synthetic natural gas

589

(SNG) from coal and dry biomass-A technology review from 1950 to 2009. Fuel 2010, 89, 1763-

590

1783.

591 592 593 594

(7) Simell, P. A.; Hepola, J. O.; Krause, A. O. I. Effects of gasification gas components on tar and ammonia decomposition over hot gas cleanup catalysts. Fuel 1997, 76, 1117-1127. (8) Li, C.; Suzuki, K. Tar property, analysis, reforming mechanism and model for biomass gasification-An overview. Renew. Sustainable Energy Rev. 2009, 13, 594-604.

595

(9) Świerczyński, D.; Libs, S.; Courson, C.; Kiennemann, A. Steam reforming of tar from a

596

biomass gasification process over Ni/olivine catalyst using toluene as a model compound. Appl.

597

Catal., B 2007, 74, 211-222. 36


Page 37 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


598

(10) Devi, L.; Ptasinski, K. J.; Janssen, F. J. J. G. Pretreated olivine as tar removal catalyst for

599

biomass gasifiers: investigation using naphthalene as model biomass tar. Fuel Process. Technol.

600

2005, 86, 707-730.

601

(11) Corella, J.; Narváez, I.; Orío, A. In Criteria for selection of dolomites and catalysts for tar

602

elimination from gasification gas; kinetic constants, VTT Symposium 163, Finland, 1996; pp

603

177-184.

604 605

(12) Corella, J.; Toledo, J. M.; Aznar, M.-P. Improving the Modeling of the Kinetics of the Catalytic Tar Elimination in Biomass Gasification. Ind. Eng. Chem. Res. 2002, 41, 3351-3356.

606

(13) Corella, J.; Caballero, M. A.; Aznar, M.-P.; Brage, C. Two Advanced Models for the

607

Kinetics of the Variation of the Tar Composition in Its Catalytic Elimination in Biomass

608

Gasification. Ind. Eng. Chem. Res. 2003, 42, 3001-3011.

609 610

(14) Lind, F.; Berguerand, N.; Seemann, M.; Thunman, H. Ilmenite and Nickel as Catalysts for Upgrading of Raw Gas Derived from Biomass Gasification. Energy Fuels 2013, 27, 997-1007.

611

(15) Larsson, A.; Seemann, M.; Neves, D.; Thunman, H. Evaluation of Performance of

612

Industrial-Scale Dual Fluidized Bed Gasifiers Using the Chalmers 2–4-MWth Gasifier. Energy

613

Fuels 2013, 27, 6665-6680.

614

(16) Thunman, H.; Lind, F.; Breitholtz, C.; Berguerand, N.; Seemann, M. Using an oxygen-

615

carrier as bed material for combustion of biomass in a 12-MWth circulating fluidized-bed boiler.

616

Fuel 2013, 113, 300-309.

37



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 43

617

(17) Lind, F.; Seemann, M.; Thunman, H. Continuous Catalytic Tar Reforming of Biomass

618

Derived Raw Gas with Simultaneous Catalyst Regeneration. Ind. Eng. Chem. Res. 2011, 50,

619

11553-11562.

620 621

(18) E4Tech Review of Technologies for Gasification of Biomass and Wastes; NNFCC project 09/008; National Non-Food Crops Centre: United Kingdom, 2009.

622

(19) Nguyen, H. N. T.; Berguerand, N.; Schwebel, G. L.; Thunman, H. Effect of

623

reforming/cracking reactions on carbonaceous products of catalytic gas cleaning using ilmenite.

624

To be submitted.

625

(20) Ratnasamy, C.; Wagner, J. P. Water Gas Shift Catalysis. Catal. Rev. 2009, 51, 325-440.

626

(21) Rostrup-Nielsen, J. R. Catalytic Steam Reforming. In Catalysis, Anderson, J. R.; Boudart,

627 628 629 630 631

M., Eds.; Springer Berlin Heidelberg: 1984; Vol. 5, pp 1-117. (22) Taralas, G.; Kontominas, M. G.; Kakatsios, X. Modeling the Thermal Destruction of Toluene (C7H8) as Tar-Related Species for Fuel Gas Cleanup. Energy Fuels 2003, 17, 329-337. (23) Kinoshita, C. M.; Wang, Y.; Zhou, J. Tar formation under different biomass gasification conditions. J. Anal. Appl. Pyrolysis 1994, 29, 169-181.

632

(24) de Klerk, A. Cracking. In Fischer-Tropsch Refining, Wiley: 2011; pp 407-440.

633

(25) Duprez, D. Selective steam reforming of aromatic compounds on metal catalysts. Appl.

634

Catal., A 1992, 82, 111-157.

38


Page 39 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

635 636 637 638 639


(26) Vreugdenhil, B. J.; Zwart, R. W. R. Tar formation in pyrolysis and gasification; Energy Research Centre of the Netherlands: The Netherlands, 2009. (27) Blanksby, S. J.; Ellison, G. B. Bond Dissociation Energies of Organic Molecules. Acc. Chem. Res. 2003, 36, 255-263. (28) Dean, J. A. Properties of atoms, radicals, and bonds. In Lange's handbook of chemistry, 15

640

ed.; McGraw-Hill: 1999.

641

(29) Carey, F. A.; Sundberg, R. J. Advanced Organic Chemistry. Part A: Structure and

642

Mechanisms 5ed.; Springer: New York, 2007.

643 644 645 646 647 648

(30) Sarıoğlan, A. Tar removal on dolomite and steam reforming catalyst: Benzene, toluene and xylene reforming. Int. J. Hydrogen Energy 2012, 37, 8133-8142. (31) Morf, P.; Hasler, P.; Nussbaumer, T. Mechanisms and kinetics of homogeneous secondary reactions of tar from continuous pyrolysis of wood chips. Fuel 2002, 81, 843-853. (32) Wittcoff, H. A.; Reuben, B. G.; Plotkin, J. S. Chemicals from Natural Gas and Petroleum. In Industrial Organic Chemicals, John Wiley & Sons, Inc.: 2012; pp 93-138.

649

(33) Taralas, G. Modeling the influence of mineral rocks, active in different hot gas

650

conditioning systems and technologies, on the production of light α-olefins. Can. J. Chem. Eng.

651

1999, 77, 1205-1214.

39



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 40 of 43

652

(34) Aldén, H.; Björkman, E.; Carlsson, M.; Waldheim, L. Catalytic Cracking of Naphthalene

653

on Dolomite. In Advances in Thermochemical Biomass Conversion, Bridgwater, A. V., Ed.;

654

Springer Netherlands: 1993; pp 216-232.

655 656 657 658 659 660 661 662

(35) Murzin, D.; Salmi, T. Heterogeneous catalytic kinetics. In Catalytic Kinetics, Elsevier Science: Amsterdam, 2005; pp 225-284. (36) Ismagilov, Z. R.; Pak, S. N. Study of elementary reactions of free radicals formed on oxide and platinum containing catalysts. Catal. Lett. 1992, 15, 353-362. (37) Golombok, M. Steam Hydrocarbon Cracking and Reforming. J. Chem. Educ. 2004, 81, 228. (38) Tamhankar, S. S.; Tsuchiya, K.; Riggs, J. B. Catalytic cracking of benzene on iron oxidesilica: catalyst activity and reaction mechanism. Appl. Catal. 1985, 16, 103-121.

663

(39) Wei, J.; Iglesia, E. Isotopic and kinetic assessment of the mechanism of methane

664

reforming and decomposition reactions on supported iridium catalysts. Phys. Chem. Chem. Phys

665

2004, 6, 3754-3759.

666 667 668 669

(40) Robaugh, D.; Tsang, W. Mechanism and rate of hydrogen atom attack on toluene at high temperatures. J. Phys. Chem 1986, 90, 4159-4163. (41) Shah, Y. T.; Gardner, T. H. Dry Reforming of Hydrocarbon Feedstocks. Catal. Rev. 2014, 56, 476-536.

40


Page 41 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

670 671 672 673


(42) Henderson, M. A. The interaction of water with solid surfaces: fundamental aspects revisited. Surf. Sci. Rep. 2002, 46, 1-308. (43) Smith, R. J. B.; Loganathan, M.; Shantha Murthy, S. A Review of the Water Gas Shift Reaction Kinetics. Int. J. Chem. React. Eng. 2010, 8.

674

(44) Berdugo Vilches, T.; Thunman, H. Experimental Investigation of Volatiles-Bed Contact

675

in a 2-4 MWth Bubbling Bed Reactor of a Dual Fluidized Bed Gasifier. Energy Fuels 2015, 29,

676

6456-6464.

677 678

(45) Nguyen, H. N. T.; Berguerand, N.; Thunman, H. In Process activated ilmenite as catalyst for cleaning of biomass producer gas iSGA-4, Vienna, Austria, 2014.

679

(46) Min, Z.; Asadullah, M.; Yimsiri, P.; Zhang, S.; Wu, H.; Li, C.-Z. Catalytic reforming of

680

tar during gasification. Part I. Steam reforming of biomass tar using ilmenite as a catalyst. Fuel

681

2011, 90, 1847-1854.

682 683

(47) Leion, H.; Lyngfelt, A.; Johansson, M.; Jerndal, E.; Mattisson, T. The use of ilmenite as an oxygen carrier in chemical-looping combustion. Chem. Eng. Res. Des. 2008, 86, 1017-1026.

684

(48) van der Laan, G. P.; Beenackers, A. A. C. M. Intrinsic kinetics of the gas–solid Fischer–

685

Tropsch and water gas shift reactions over a precipitated iron catalyst. Appl. Catal., A 2000, 193,

686

39-53.

41



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 42 of 43

687

(49) Zou, C.; van Duin, A. T.; Sorescu, D. Theoretical Investigation of Hydrogen Adsorption

688

and Dissociation on Iron and Iron Carbide Surfaces Using the ReaxFF Reactive Force Field

689

Method. Top. Catal. 2012, 55, 391-401.

690 691

(50) Boroson, M. L.; Howard, J. B.; Longwell, J. P.; Peters, W. A. Product yields and kinetics from the vapor phase cracking of wood pyrolysis tars. AlChE J. 1989, 35, 120-128.

692

(51) Keller, M.; Leion, H.; Mattisson, T.; Thunman, H. Investigation of Natural and Synthetic

693

Bed Materials for Their Utilization in Chemical Looping Reforming for Tar Elimination in

694

Biomass-Derived Gasification Gas. Energy Fuels 2014, 28, 3833-3840.

695

(52) Israelsson, M.; Larsson, A.; Thunman, H. Online Measurement of Elemental Yields,

696

Oxygen Transport, Condensable Compounds, and Heating Values in Gasification Systems.

697

Energy Fuels 2014, 28, 5892-5901.

698

(53) Israelsson, M.; Seemann, M.; Thunman, H. Assessment of the Solid-Phase Adsorption

699

Method for Sampling Biomass-Derived Tar in Industrial Environments. Energy Fuels 2013, 27,

700

7569-7578.

701

(54) Kunii, D.; Levenspiel, O. Bubbling Fluidized Beds. In Fluidization Engineering (Second

702

Edition), Levenspiel, D. K., Ed.; Butterworth-Heinemann: Boston, 1991; pp 137-164.

703

For Table of Contents Only

42


Page 43 of 43

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704

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Mechanism and Kinetic Modeling of Catalytic Upgrading of a Biomass

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