Catalytic Pyrolysis of Biomass-Derived Compounds - American

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Catalytic pyrolysis of biomass-derived compounds: Coking kinetics and formation network Shanshan Shao, Huiyan Zhang, Yun Wang, Rui Xiao, Lijun Heng, and Dekui Shen Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/ef5026505 • Publication Date (Web): 02 Feb 2015 Downloaded from http://pubs.acs.org on February 8, 2015

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Catalytic pyrolysis of biomass-derived compounds: Coking kinetics and formation network Shanshan Shao, Huiyan Zhang, Yun Wang, Rui Xiao,* Lijun Heng, Dekui Shen Key Laboratory of Energy Thermal Conversion and Control, Ministry of Education, Southeast University, Nanjing 210096, P.R. China

Abstract A deactivation study of ZSM-5 in heterogeneous catalysis during the pyrolysis of biomass-derived compound has been carried out. Experiments were performed in a gas-solid reactor with online weighting system at varied temperatures, weight hourly space velocities and partial pressures. Real-time catalyst weight monitoring during the catalytic conversion of furan as a main intermediate of biomass fast pyrolysis can be realized. Coke amount increased from 3.48% at temperature of 300 °C to 9.81% at 700 °C and then declined slightly at 800 °C. Catalyst weight increment included active carbon species confined in the catalysts and inert carbon species of large unsaturated carbon molecules, which were defined as active coke and inert coke respectively. Differentiation curves among displayed coke amount, active coke and inert coke were described. Active coke accumulated quickly at the early stage, meanwhile, inert coke was dominant for its suppression on the catalysis reaction at the later stage along with a slight decrease of active coke, namely, part of active coke was converted to inert species. An empirical and intrinsic model has been developed via an iterative process of model formulation, parameter estimation, and model validation with final correlation *Corresponding author. Tel: +86-25-83795726. Email address: [email protected]

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coefficient of 0.968. To determine the kinetic parameters, several supposed deactivation functions Φ were introduced to Arrhenius equation in temperature programmed reaction. Finally, a possible coking network was provided by introducing multilayer theory in which inert coke was supposed to be formed only on the surface of microporous catalyst layer by layer. Key words: ZSM-5; biomass; catalytic pyrolysis; coking kinetics; deactivation

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1. Introduction Biomass is a promising renewable energy for its abundance in nature and being considered friendly to the environment. Biomass fast pyrolysis liquid namely bio-oil can be stored for use as fuel or upgraded for chemicals.1-4 The high oxygen content of bio-oil prompts researchers to use catalysts in the pyrolysis for deoxygenation. However, catalysts addition brings new problems like coke deposition on their surfaces, which lead to much lower chemical yield when compared with its theoretical yield. 5, 6, 7

Generally, coke formation can be described as the result of polymerization, dehydration, decarboxylation, decarbonylation of three origins: anhydrosugars, furanic compounds and fragmented oxygenates and olefins in biomass pyrolysis process.8 Previous study indicates that coke composition is usually determined by working conditions like pyrolysis temperature, time on stream, et al. Coke formation containing aliphatics mainly involves condensation and rearrangement steps at a low reaction temperature (200 °C).9 Coke may block the catalyst pores or cover active sites, which will finally deactivates the catalysts. In the past decades, lots of study focused on the exploration of coke precursor and its transformation pathway to final deactivation species.10-13 Another carbon species accumulated in the early stage which is called “active coke” is also of great significance in the catalytic conversion of biomass derivates. Active coke plays the

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same role with “hydrocarbon pool” in MTO reactions.14,

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It is formed at the very

beginning with reagent fed in and then olefins released as clarified in the hydrocarbon pool mechanism. More importantly than all of that, active coke forms mainly in the pores of ZSM-5 used in our study, while inert coke only forms on the surface of ZSM-5 because of the diffusion limitation. It means that the average pore size (5 Å) is close to the size of a benzene molecule (5.8 Å).16 More attentions have also been paid to the influence of coke deposition on product distribution for its change of pore size and shape selectivity. A substantial part of study intended to build a kinetic model to predict coke content at a specified condition and to understand its relationship with product distribution.17-20

Lots of kinetic models have been built by researchers in the past years. Coke content/coking rate was firstly related to time on stream by Voorhies.21 Froment proposed that the deactivation mechanism should be in consideration, like the concentration of coke precursors.22 In another way, he added a deactivation function Φ in the coking kinetic model and several assumed equation of Φ were also given. A kinetic model used to describe the coke formation on the catalyst surface was based on the monolayer–multilayer coke growth model (MMCGM) which is a simple mechanistic model first proposed by Nam and Kittrell.23 The rate of coke formation on the catalyst surface is given by the sum of coke formation rates for monolayer coke on the surface of the catalyst and the simultaneous multilayer coke deposition rate. A

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kinetic model by Chen including the deactivating effect due to coke deposition has been developed to properly simulate the changes in activity and selectivity in the conversion of methanol to light olefins over SAPO-34 with the coke content in an oscillating microbalance reactor.24, 25 Similarly, Remero built a deactivation equation versus partial pressure of compositions (reactant and product), which helps predicting the evolution of cyclohexanol dehydrogenation with time on stream and space time for different feed compositions.26 Models above generally take coke source and its influence on catalytic reaction into consideration.

In the present work, the influence of operation parameters (pyrolysis temperature, weight hourly space velocity, partial pressure and time on stream) on coke formation during biomass-derivates catalytic pyrolysis was investigated in a gas-solid reactor with online weighting system and an empirical deactivation kinetic model was built. The study also focused on the separation of active coke and inert coke and discovered the transformation relationship between them. A reaction network of coke formation has been proposed based on the catalyst multilayer theory.

2. Experimental The ZSM-5 catalysts (SiO2/Al2O3=30, 0.08~0.15 mm) are commercially available from Zeolyst in USA. Catalysts were calcined in a muffle furnace at 600 °C for 2 hours at the beginning and stored in a drying container. A very small amount of moisture may be

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accumulated in the catalysts. The moisture will be deleted during the second calcination in the furnace with air for 1 hour at the specified temperature. Actually no obvious dehydration stage can be found, namely, the weight of sample before calcination can be regarded as the real sample weight directly. A mixture of furan and nitrogen (0.53% mole percentage) was prepared in a compressed gas cylinder. As boiling point of furan is 31 °C, the pipeline of feeding system must be kept up to 50 °C to make sure of no condensation.

All experiments were performed in a gas-solid reactor with in-situ weighting system as shown in Figure 1. It consisted of a weighting system and a reaction system. The weighting system has a precision of 0.001 mg. If not specified, 16 mg catalysts were loaded before each experiment. In an inert atmosphere of 20 ml/min nitrogen, the furnace was heated with a heating rate of 40 °C/min to the targeted temperature and then held steady for hours. Another 20 ml/min reaction gas above was fed in and the furan gas was heated to the targeted temperature instantaneously, thus, the heating rate should be much higher than 1 K/s. At the same time, data collection began.

To differentiate active coke and inert coke effectively, the catalytic conversion was stopped at some time point with 60 ml/min nitrogen sweeping active species of small molecules out of the reactor for one hour. With no feeding at the reaction temperature, the active coke has been released and converted to olefins and aromatics with nitrogen

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sweeping. So the sample includes original catalyst and inert coke only. When the furnace was rapidly cooled down to 20 °C, 40 ml/min air flowed in to combust coke with a heating rate of 20 °C/min from room temperature to 900 °C. The weight loss can be regarded as inert coke amount, and the difference between weight gain above and inert coke amount is just the weight of active coke. Data collection was done every 1 second automatically. In this study, coke content is defined as the proportion between coke weight and fresh catalyst loading. Also, all the experiments have been performed for three times and the final experimental values equal to the average value of three times.

3. Results 3.1. Elimination of the influence of diffusion To obtain accurate data for determination of intrinsic coke formation kinetics, it was necessary to perform experiments in the absence of external and internal diffusion limitations. Catalyst particles of different sizes were used to investigate internal diffusion limitations. Feed flow rates were also varied over a wide range keeping weight hourly space velocity (WHSV) constant to investigate external diffusion limitations.

To eliminate the external diffusion limitations, experiments were conducted in which the size of the catalyst pellet was kept constant and the catalyst loading was varied over a range while keeping WHSV constant at 1.13 h-1. If coke content was unaffected by

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varying furan flow rate at constant WHSV, it can be concluded that the reaction was independent of the external diffusion of the fluid outside the catalyst pellet. The results of these experiments are shown in Figure 2 indicating that WHSV of 1.13 h-1 was enough to ignore the influence of external diffusion limitation.

In order to eliminate internal diffusion limitations, experiments should be performed using different sizes of catalyst pellets at a feed flow rate where external diffusion limitations were eliminated. Related study indicates that catalyst diameter size of 0.08~0.15 mm is enough to eliminate internal diffusion.25

3.2. Effect of pyrolysis temperature on coke deposition Coke deposition over the catalyst during the reaction is a crucial factor leading to the deactivation of catalyst. The deactivation of catalyst depends closely on the reaction temperature and time on stream. Figure 3 shows the coke content with time on stream at a pyrolysis temperature range from room temperature to 800 °C. In addition, accumulated coke content as a function of pyrolysis temperature is also obtained in Figure 4. Coking behavior at room temperature indicated that furan was a very active species which is easy to absorb on ZSM-5 and form some organic species inside. Irrespective of 20 °C, total coke content as shown in Figure 4 increased from 3.4% at pyrolysis temperature of 300 °C to 9.8% at 700 °C and then decreased slightly at 800 °C. In a specified temperature range, higher temperature resulted in higher coke deposition.

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This is in consistent with the results reported for methanol conversion on SAPO-34 to olefins.27 In a view of reaction process, coke content tended to be steady with increasing time on stream. The time it took to be steady was defined as Ts. It became longer when pyrolysis temperature was higher. However, an interesting phenomenon was observed that coke content at 800 °C increased linearly to a constant value. Namely, the pyrolysis temperature of 700 °C is a particular point for furan catalytic conversion.

Pyrolysis temperature has a dominant influence on the coke species as we can see from the color of catalyst. Deactivated catalyst appeared brick-red at room temperature, turned pale gray at 500 °C and finally presented as black color at 800 °C. The colors of catalysts at different temperatures showed the different chemical composition of coke species which was in consistent with catalyst combustion experiment in oxygen atmosphere in previous work.16

3.3. Effect of WHSV on coke deposition Besides pyrolysis temperature, WHSV was also considered to understand its effect on coking behavior. At temperature of 600 °C, WHSV was varied by changing catalyst amount. Figure 5 shows the coke content as a function of time on stream at different WHSVs. Except for WHSV of 0.64 h-1, total coke content was not very sensitive to WHSV, and a closer analysis showed that higher space velocities resulted in a higher coking rate which may be attributed to a higher conversion of furan, and it is in good

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agreement with the study by Holmen.25, 27 But great difference can be found from the view point of Ts. Large WHSV led to short Ts, namely, short time was needed to reach steady state at high WHSV. The increase of WHSV enhanced coking rate which is in agreement with Chen and Qi et al.27,

28

Keeping furan flow rate constant, WHSV

increasement offered large furan molecule concentration per active site in the catalyst. At first, a higher WHSV means a lower catalyst loading accompanied by a larger coke content per milligram of catalysts. And Ts becomes lower with enough furan fed in. However, WHSV of 1.81 h-1 may give much lower contact time between furan and catalyst compared with 1.13 h-1 along with a longer Ts.

3.4. Effect of partial pressure on coke deposition Varied partial pressures of furan were realized by changing flow rate of pure nitrogen to investigate the influence of partial pressure on coke deposition. Keeping WHSV of 1.13 h-1 and pyrolysis temperature of 600 °C, total coke content increased to 9.32% at partial pressure of 1.34 Torr and then decreased slightly as shown in Figure 6. As referred in the literature, the conversion and the coke deposition increased with increasing partial pressure of reagent. The increase of partial pressure was accompanied with the coke precursor concentration increasing; nevertheless, extra furan gas was blown out of thermogravimetric analyzer at low partial pressure which led to the decrease of coke content.20, 25, 27

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In general, once the reaction conditions are determined, namely reactor type, reaction temperature and WHSV et al. are constant, coke content is only a function of time on stream. It is in consistent with the coking change rules in FCC reaction by Voorhies.21

3.5. Differentiation curve of catalyst weight increment Real-time weight increment of catalysts includes furan adsorbate, active organic species (active coke) and inert coke deposited on catalysts. Furan absorbed on ZSM-5 and is soon converted at the pyrolysis temperature higher than 300 °C. Therefore, the weight gain of furan adsorbate can be neglected. Catalyst weight gain actually includes active coke and inert coke, and how to separate them efficiently and to understand the roles they are playing should be solved urgently.29

Differentiation curves of deactivated catalysts at five reaction time points at pyrolysis temperature of 600 °C, WHSV of 1.13 h-1, partial pressure of 1.68 Torr are given in Figure 7. It can be found that total coke amount almost kept constant after reaction time of 180 min, which meant that furan catalytic conversion had reached chemical equilibrium state. At the early stage (before 120 min), active coke rapidly accumulated and coking rate was relatively high. An inert coke rapid accumulation period appeared at the time range of 120~180 min in which active coke amount decreased slightly. That is, part of active coke was converted to inert coke of large molecules.30, 31 Inert coke is

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the dominant species, part of which was formed at early stage and the others originated from active coke conversion. It led to ZSM-5 final deactivation gradually.

3.6. Coke deposition in the temperature-programmed furan catalytic conversion Heating rate is a key factor in biomass catalytic fast pyrolysis and it has remarkable impact on product distribution as well as catalyst deactivation.32 Comparison study was performed of furan catalytic conversion with heating rates of 2.5 °C/min and 5 °C/min. Catalyst weight gain curves and coking rate curves are shown in Figure 8. In the figures, great differences appeared on TG and DTG curves with two heating rates. We can see that two platforms corresponding to 320~380 °C and 590~605 °C existed in the weight gain curves when the heating rate was 2.5 °C/min. If heating rate was 5 °C/min, TG curve was smooth indicating that coking rate increased steadily as shown in Figure 8(a).

Figure 8(b) gives DTG curves of ZSM-5 in furan catalytic conversion with heating rate of 2.5 °C/min and 5 °C/min. At heating rate of 2.5 °C/min, we can find extreme values of coking rate at low temperature of 149 °C & 246 °C and high temperature of 489 °C & 700 °C. A higher heating rate of 5 °C/min intensified the temperature gap which had an influence on the reaction at the gas-solid interface. It can be concluded that coking formation at pyrolysis temperature higher than 700 °C will be suppressed. The coking rate kept at a relative high level which meant that ZSM-5 still had strong activity for furan catalytic conversion. And the difference of coke content between the two curves in

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Figure 8 indicated that the catalytic conversion had not reached a steady state.

4. Discussion 4.1. Kinetic model of furan catalytic conversion network Technical parameters like reaction temperature, WHSV, partial pressure and time on stream have great influence on coke formation. The correlation considering only one or two key parameters is limited in practical use since lots of factors impact on coke formation. Now coke content in catalyst is correlated with all parameters above and a function revealing the relevance among them is built. It can help predicting average coke amount at a specified condition using the association model including all technical parameters.

It can be seen obviously that there is a non-linear relationship between coke content in ZSM-5 catalysts and reaction time. Taking data under the following condition, pyrolysis temperature of 500 °C, WHSV of 1.13 h-1, partial pressure of 1.68 Torr for example, mathematic correlation is performed between coke amount and time on stream. The fitting data proves that coke amount was in proportion to power series of reaction time, namely, C~tn, and the correlation coefficient reaches 0.9963. It is worth noting that coke data at room temperature is not involved in modeling.

A model is proposed as follows to fit experimental data.

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C  a  exp(b / T )  W m  P n  t c

（1）

Where a, b, c, m, n are constants, C is coke amount per milligram of catalyst, T is pyrolysis temperature, W is the weight hourly space velocity and P is the partial pressure of furan vapor.

The estimation of the parameters of the kinetic model has been carried out as shown in Table

1

by

the

nonlinear

least-squares

routine

in

MATLAB

using

the

Levenberg-Marquardt method. The optimum function is given in equation 2. n

S   (Ci,exp  Ci,cal )

2

（2）

i 1

Correlation coefficient is 0.9688. Figure 9 shows the comparison between experimental and predicted coke amount in the kinetic model. It can be seen from Figure 9 and error analysis that model equation (1) has good linear dependence and data dispersity. Actually, this coking kinetic model is of limited use because of restricted reaction conditions like catalyst loading and flow rate of carrier gas. Further study on coke deposition is necessary in fixed bed or fluidized bed reactor to collect in-situ coke amount.

4.2. Parameters determination in Arrhenius equation Arrhenius kinetic study is an important tool to predict the ease or complexity of coke formation and to understand the mechanism of coking reactions, which is of great

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meaning to technique development and application of biomass catalytic conversion. Heating rate has great impact on kinetic parameter determination of biomass pyrolysis.

Coke formation in biomass catalytic pyrolysis involves a complex series of reaction like dehydration, dehydrogenation, hydrogen transfer et al. This study uses the simplified style of Coats-Redfem integral model to analyze the kinetics based on TG curves of different heating rates. Froment proposed a classical coking rate function, dC/dt=k·Φ, and Φ is a deactivation function which was supposed to depend on coke content. Several empirical correlations are put forward in Table 2. α is supposed to be 1. And Arrhenius

formula

is

plugged

into

the

coking

rate

equation,

namely,

dC/dt=Aexp(-E/RT)·Φ. We use Coats-Redfem method to fit model as follows, where G(C)=∫ΦdC, β=dT/dt. For general reaction and activation energy value, E/RT>>1, so ln[AR/βE·(1-2RT/E)] can be regarded as constant. E and A can be obtained from slope in linear regression ln[G(C)/T2]—1/T.

Kinetic parameters are estimated in Table 2 for the TG curve with heating rate of 2.5 °C/min and 5 °C/min. In the view of correlation index R, we can conclude that deactivation function Φ=1/(1+αC)2 works well. The data indicates that heating rate has no remarkable effect on activation energy, however the increasing of heating rate is accompanied with the raise of pre-exponential factor.

4.3. Coking network

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TGA experiments with air were also performed to study chemical characteristics of spent catalysts as shown in Figure 10. In particular, coke deposition corresponding to inert part after time on stream of 40 min, 80 min, 120 min, 180 min and 240 min showed very different combustion performances. The amount of inert coke was determined by the above method. TG curve of spent catalyst presented small amounts of weight loss at low temperature and main weight loss happened at temperature higher than 400 °C, which can be obtained from DTG curves. DTG curve can be divided in to two peaks at reaction time of 40 min. The first peak appeared at the range of 200~400 °C and the summit was at 334 °C, while the second peak appeared at the range of 400~900 °C and the summit was at 618 °C. A new peak appeared at 422 °C for the catalyst after the reaction of 80 min and the low temperature peak and high temperature peak corresponded to 297 °C and 628 °C respectively. Therefore, inert coke deposited on catalyst contained two types standing for coke species of different molecular size. Coke combustion rate at high temperature showed the largest value for the catalyst after reaction time of 240 min, which can be attributed to its high coke amount and limited temperature range. Overall, the summit of low temperature peak tended to lower temperature with reaction processing forward, while the summit of high temperature peak tended to higher temperature, which indicated that the reaction process forward was not only accompanied by accumulation of coke amount but also change of coke composition.

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A new way called multilayer theory is used to describe the coke accumulation on the catalyst. Firstly, it is confirmed that inert coke deposition only happens on the surface for ZSM-5 catalyst in this study for its spatial diffusion limitation to channels.33 Coke is thought to accumulate layer by layer especially inert coke. Active species also played an important role in co-reaction with inert coke on the monolayer. Figure 11 is a schematic diagram of coke formation from the viewpoint of a catalyst particle. In the first 120 min, we can find that active coke rapidly accumulated and a few inert coke forms in this period, while active coke were transformed gradually and amount of inert coke grows accompanied with molecular size enlargement in the later stage. The total amount of inert coke is always higher than that of active coke. Actually, inert coke has little influence on furan diffusion into channels for not blocking pores on the surface before reaction time of 120 min. Generally speaking, active coke accumulation period should promote catalysis reaction itself. Nevertheless, after a certain point, active carbon species are converted to inert species of large molecules and inert coke vast accumulation decides its dominant negative role on the surface of microporous catalyst.

5. Conclusion Coking data were obtained during furan conversion over ZSM-5 catalyst in a gas-solid reactor with in-situ weighting system by varying pyrolysis temperature, WHSV, partial pressure and reaction time. Coke amount increased to an inflection point of 9.81 % at 700 °C. It tended to a constant value with the increasing of WHSV and it increased to

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9.32% at partial pressure of 1.34 Torr and then decreased slightly. A simple empirical model, in which the above reaction parameters were considered, was developed to describe the coke content with time on stream. Temperature-programmed furan catalytic conversion with heating rate of 2.5 °C/min and 5 °C/min was performed to determine kinetic parameters introducing several supposed deactivation functions. Total coke was separated into active coke and inert coke successfully based on their role in catalytic reaction. The results show that active coke accumulated at the early stage and then was partially converted into inert coke which led to the dominating and negative role at the late stage. Finally, inert coke is supposed to accumulate layer by layer on the surface of microporous catalyst, while active coke functions both in the pores and on the monolayer of catalysts.

Acknowledgements This work is financially supported by the National Natural Science Foundation of China (Grant No. 51306036 and 51476035), the Major Research Plan of National Natural Science Foundation of China (Grant 91334205), and the National Basic Research Program of China (973 Program) (Grant 2012CB215306).

References (1) Czernik, S.; Bridgwater, A. V. Overview of applications of biomass fast pyrolysis oil. Energy Fuels 2004, 18, 590-598.

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coke deposition in the catalytic fast pyrolysis of biomass Derivates. Energy Fuels 2014, 28, 52-57. (10) Schmidt, F.; Hoffmann, C.; Giordanino, F.; Bordiga, S.; Simon, P.; Carrillo-Cabrera, W.; Kaskel, S. Coke location in microporous and hierarchical ZSM-5 and the impact on the MTH reaction. J. Catal. 2013, 307, 238-245. (11) De Lucas, A.; Canizares, P.; Durán, A. Improving deactivation behaviour of HZSM-5 catalysts. Appl. Catal. A: Gen. 2001, 206, 87-93. (12) Li, J.; Li, X. Y.; Zhou, G. Q.; Wang, W.; Wang, C. W.; Komarneni, S.; Wang, Y. J. Catalytic fast pyrolysis of biomass with mesoporous ZSM-5 zeolites prepared by desilication with NaOH solutions. Appl. Catal. A: Gen. 2014, 470, 115-122. (13) Song, Y. Q.; Li, H. B.; Guo, Z. J.; Zhu, X. X.; Liu, S. L.; Niu, X. L.; Xu, L. Y. Effect of variations in acid properties of HZSM-5 on the coking behavior and reaction stability in butene aromatization. Appl. Catal. A: Gen. 2005, 292, 162-170. (14) White, J. L. Methanol-to-hydrocarbon chemistry: The carbon pool (r)evolution. Catal. Sci. Tech. 2011, 1, 1630-1635. (15) Johansson, R.; Hruby, S. L.; Rass-Hansen, J.; Christensen, C. H. The hydrocarbon pool in ethanol-to-gasoline over HZSM-5 catalysts. Catal. Lett. 2009, 127, 1-6. (16) Shao, S. S.; Zhang, H. Y.; Heng, L. J.; Luo, M. M.; Xiao, R.; Shen, D. K. Catalytic conversion of biomass derivates over acid dealuminated ZSM-5. Ind. Eng. Chem. Res. 2014, 53, 15871–15878. (17) Froment, G. F. Kinetic modeling of hydrocarbon processing and the effect of

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catalyst deactivation by coke formation. Catal. Rev. 2008, 50, 1-18. (18) Chen, J. R.; Li, J. Z.; Wei, Y. X.; Yuan, C. Y.; Li, B.; Xu, S. T.; Zhou, Y.; Wang, J. B.; Zhang, M. Z.; Liu, Z. M. Spatial confinement effects of cage-type SAPO molecular sieves on product distribution and coke formation in methanol-to-olefin reaction. Catal. Commun. 2014, 46, 36-40. (19) Hong, L.; Benxian, S. Characterization of coke deposited from cracking of cottonseed oil over zeolite catalyst and deactivation kinetics of coke deposition. Energy Sources Part A 2010, 32, 1159-1166. (20) Chen, D.; Moljord, K.; Fuglerud, T.; Holmen, A. The effect of crystal size of SAPO-34 on the selectivity and deactivation of the MTO reaction. Microporous Mesoporous Mat. 1999, 29, 191-203. (21) Voorhies Jr, A. Carbon formation in catalytic cracking. Ind. Eng. Chem. 1945, 37, 318-322. (22) Froment, G. F. Modeling of catalyst deactivation. Appl. Catal. A: Gen. 2001, 212, 117-128. (23) Niknaddaf, S.; Soltani, M.; Farjoo, A.; Khorasheh, F. Modeling of coke formation and catalyst deactivation in propane dehydrogenation over a commercial Pt-Sn/γ-Al2O3 catalyst. Petrol. Sci. Technol. 2013, 31, 2451-2462. (24) Grønvold, A.; Rebo, H. P.; Moljord, K.; Holmen, A. Catalyst deactivation studied by conventional and oscillating microbalance reactors. Appl. Catal. A: Gen. 1996, 137, L1-L8.

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(25) Chen, D.; Grønvold, A.; Moljord, K.; Holmen, A. Methanol conversion to light olefins over SAPO-34: Reaction network and deactivation kinetics. Ind. Eng. Chem. Res. 2007, 46, 4116-4123. (26) Simón, E.; Rosas, J. M.; Santos, A.; Romero, A. Coke formation in copper catalyst during cyclohexanol dehydrogenation: Kinetic deactivation model and catalyst characterization. Chem. Eng. J. 2013, 214, 119-128. (27) Chen, D.; Rebo, H.P.; Grønvold, A.; Moljord, K.; Holmen, A. Methanol conversion to light olefins over SAPO-34: kinetic modeling of coke formation. Microporous Mesporous Mater. 2000, 35-36: 121-135. (28) Qi, G.Z.; Xie, Z.K.; Yang, W.M.; Zhong, S.Q.; Liu, H.X.; Zhang, C.F.; Chen, Q.L. Fuel Process. Technol. 2007, 88: 437-441. (29) Wei, Y. X.; Zhang, D. Z.; Chang, F. X.; Liu, Z. M. Direct observation of induction period of MTO process with consecutive pulse reaction system. Catal. Commun. 2007, 8, 2248-2252. (30) Olsbye, U.; Bjørgen, M.; Svelle, S.; Lillerud, K.; Kolboe, S. Mechanistic insight into the methanol-to-hydrocarbons reaction. Catal. Today 2005, 106, 108-111. (31) Arstad, B.; Kolboe, S. Methanol-to-hydrocarbons reaction over SAPO-34. Molecules confined in the catalyst cavities at short time on stream. Catal. Lett. 2001, 71, 209-212. (32) Cecilia, J. A.; Infantes-Molina, A.; Rodríguez-Castellón, E.; Jiménez-López, A.; Oyama, S. T. Oxygen-removal of dibenzofuran as a model compound in biomass

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derived bio-oil on nickel phosphide catalysts: Role of phosphorus. Appl. Catal. B: Environ. 2013, 136, 140-149. (33) Zhang, H. Y.; Luo, M. M.; Xiao, R.; Shao, S. S.; Jin, B. S.; Xiao, G. M.; Zhao, M.; Liang, J. Y. Catalytic conversion of biomass pyrolysis-derived compounds with chemical liquid deposition (CLD) modified ZSM-5. Bioresource Technol. 2014, 155, 57-62.

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Table captions Table 1 Computational value of parameters in the model Table 2 Deactivation kinetic parameters with different heating rates

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Energy & Fuels

Table 1 Computational value of parameters in the model Parameters

a

b

c

m

n

Values

0.1897

-11.1430

0.6431

0.3814

0.6431

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Table 2 Deactivation kinetic parameters with different heating rates Heating rate (°C/min)

2.5

5.0

Deactivation function

E(KJ/mol)

A(min-1)

R

Φ=exp(-αC)

26.25

54.80

0.9712

Φ=1-αC

8.80

6.97E-4

0.8792

Φ=(1-αC)2

8.95

7.36E-4

0.8839

Φ=1/(1+αC)

14.42

0.81

0.9645

Φ=1/(1+αC)2

20.94

11.11

0.9873

Φ=1/(1+αC)

14.65

1.71

0.9645

Φ=1/(1+αC)2

21.11

23.08

0.9880

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Energy & Fuels

Figure captions Figure 1 Schematic diagram of thermogravimetric analyzer Figure 2 Mass change of ZSM-5 with different catalysts loadings Figure 3 Coke amount as a function of time on stream at several pyrolysis temperatures Figure 4 Influence of pyrolysis temperature on total coke amount Figure 5 Effect of WHSV on coke deposition over ZSM-5 in the catalytic conversion of furan Figure 6 Coke content as a function of time on stream at different partial pressures Figure 7 Differentiation of active coke and inert coke with the impel of reaction process Figure 8 Influence of heating rate on coke deposition in the catalytic conversion of furan (a) TG curve and (b) DTG curve Figure 9 Comparison between model computational coke content and experimental value Figure 10 Regeneration of spent catalyst with different reaction times (a)TG curve and (b)DTG curve Figure 11 Diagram of coke formation from the perspective of a catalyst particle

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Figure 1 Schematic diagram of thermogravimetric analyzer

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Energy & Fuels

Figure 2 Mass change of ZSM-5 with different catalysts loadings

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Figure 3 Coke amount as a function of time on stream at several pyrolysis temperatures

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Figure 4 Influence of pyrolysis temperature on total coke amount

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Energy & Fuels

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Figure 5 Effect of WHSV on coke deposition over ZSM-5 in the catalytic conversion of furan

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Energy & Fuels

Figure 6 Coke content as a function of time on stream at different partial pressures

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Figure 7 Differentiation of active coke and inert coke with the reaction time

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Energy & Fuels

(a)

(b)

Figure 8 Influence of heating rate on coke deposition in the catalytic conversion of furan (a) TG curve and (b) DTG curve

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Energy & Fuels

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Figure 9 Comparison between model computational coke content and experimental value

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(a)

(b)

Figure 10 Regeneration of spent catalyst with different reaction times (a)TG curve and (b)DTG curve

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Energy & Fuels

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Figure 11 Diagram of coke formation from the perspective of a catalyst particle

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Catalytic Pyrolysis of Biomass-Derived Compounds - American

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