Catalytic Upgrading of Fast Pyrolysis Products with Fe-, Zr-, and Co

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Catalytic Upgrading of Fast Pyrolysis Products with Fe, Zr, Co-modified Zeolites Based on Py-GC/MS Analysis Pan Li, Xu Chen, Xianhua Wang, Jingai Shao, Guiying Lin, Haiping Yang, Qing Yang, and Hanping Chen Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b03105 • Publication Date (Web): 13 Mar 2017 Downloaded from http://pubs.acs.org on March 23, 2017

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Catalytic Upgrading of Fast Pyrolysis Products with

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Fe, Zr, Co-modified Zeolites Based on Py-GC/MS

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Analysis

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Pan Lia, Xu Chena, Xianhua Wanga, Jingai Shao

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Yanga,b, Hanping Chena,b

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a

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Huazhong University of Science and Technology, Wuhan, Hubei, 430074, P. R. China.

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b

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Huazhong University of Science and Technology, Wuhan, Hubei, 430074, P. R. China.

a,b

*, Guiying Lin a, Haiping Yanga, Qing

State Key Laboratory of Coal Combustion, School of Energy and Power Engineering,

Department of New Energy Science and Engineering, School of Energy and Power Engineering,

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Abstract. To explore the influence of Fe, Zr, and Co-modified zeolites on bio-oil characteristics,

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the catalytic fast pyrolysis of cellulose combined with sawdust and cotton stalk was investigated

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using a pyrolyzer reactor. The results indicate that Fe loading zeolite favours naphthalene and 1-

13

methyl-naphthalene formation through catalytic deoxygenation and hydrocarbon formation. Zr

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modified zeolite enhances the contents of ketones and aromatics with higher benzene and p-

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xylene selectivity. Co leads to higher production of anhydrous sugars but suppresses the progress

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of aromatics evolution, whereas the selectivity of Co for toluene and p-xylene is the highest. A

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comprehensive reaction network is also proposed to describe the cellulose catalytic pyrolysis

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process. Considering the catalytic adaptability, catalytic pyrolysis of typical biomass samples

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with Fe/HZSM-5 was investigated. The total contents of aromatic hydrocarbons are in the

ACS Paragon Plus Environment

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following order: sawdust > cellulose > cotton stalk. The selectivity of naphthalene and 2-methyl-

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naphthalene in cellulose is the highest, while the selectivity of benzene and its derivatives in

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sawdust and cotton stalk are higher.

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Keywords.

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1. Introduction

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Compared with fossil fuels, biomass energy has attracted widespread attention due to its

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characteristics which were rich in resources, renewable, environmentally friendly and so on 1.

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Fast pyrolysis of biomass which could obtain the high value-added chemical raw materials or

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alternative products of fossil fuels was studied a lot 2, 3. While there are some negative properties

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associated with bio-oil during direct pyrolysis of biomass, such as high water and oxygen

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contents, strong causticity and worse thermal instability, so its quality promotion research is

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imperative 4. Catalytic fast pyrolysis (CFP) can convert biomass into aromatic hydrocarbons,

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including toluene, xylene, naphthalene and so on

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gasoline or chemical products, and is advantageous for optimizing the fuel characteristics and

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improving the stability.

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Many studies have focused on lots of catalysts to improve the bio-oil quality. Pattiya et al.

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found that ZSM-5 yielded the highest amount of aromatics in the derived bio-oil during the

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catalytic pyrolysis of cassava rhizome, as compared with the catalysts of Al-MCM-41, Al-MSU-

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F and MI-575. Lappas et al.

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ZSM-5 catalysts used a lab-scale fluid riser reactor, and found that with the catalysts addition the

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yields of water, gases, and char all increased, while the oxygen content of bio-oil had reduced.

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Carlson et al.

Catalysts, Cellulose, Py-GC/MS, Bio-oil, pyrolysis

9

8

5, 6

, which were the main raw materials for

7

carried out pine saw catalytic pyrolysis under the condition of

studied the catalytic fast pyrolysis of wood sawdust, and found that ZSM-5


2

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catalysts can improve the production of aromatics and olefins in bio-oil. There was a high

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amount (WHSV>10) of zeolite catalysts in most studies, but the specific product selectivity

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should be improved. Therefore metal-modified catalysts were desired for fast pyrolysis

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Zhang et al.

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(4.97%) and CO2 (13.8%) in metal-loaded catalysts. Jan et al.

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aromatic hydrocarbon could be further improved under the Pd/HZSM-5 catalysts than HZSM-5

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catalysts, and the increasing value was 44%. Iliopoulou et al.

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Co/ZSM-5 catalysts were more reactive to decreasing the organic phase products and increasing

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the gaseous products (mainly CO and C2H2), and showed a promising performance in reducting

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the oxygen content of bio-oil. T-Gopakumar et al. 15 reported that the yield of aromatic products

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increased more at the presence of Pt/ZSM-5 than HZSM-5 catalysts. However, it is essential to

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extensively study the pyrolytic behaviour of the polysaccharides in biomass to understand the

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reaction mechanism

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component of biomass structures, accounting for about 35% to 45% of biomass

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research has shown that the most significant contribution of cellulose is to produce bio-oil during

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the pyrolysis process 18. It is necessary to investigate cellulose pyrolysis bio-oil composition and

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characteristics under different catalytic conditions.

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Several previous studies have discussed the catalytic pyrolysis of cellulose to generate

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aromatized liquid oils. Carlson et al. 9 studied the catalytic fast pyrolysis of glucose with HZSM-

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5 and found that the maximum yield of the aromatics was 32%. Andrew et al.

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aromatic yield from glucose CFP went through the maximum and the ZSM-5 catalyst favoured

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the production of smaller mono-aromatics (benzene, toluene, xylene and so on).

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10, 11

.

reported that Fe/HZSM-5 catalysts brought the highest contents of naphthalene

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13

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reported that the yield of the

found that the Ni/ZSM-5 and

. Cellulose, a linear polymer of glucose, is the most abundant organic


19

17

. Previous

found that the

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Existing research mainly focused more on the effect of traditional zeolites during the cellulose

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pyrolysis. However, few studies have focused on the catalytic effects of metal-modified zeolites

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for cellulose pyrolysis, particularly different metal types and loading amounts. The fundamental

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catalytic effect of the modified zeolites were studied in our previous work

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played a good effect on the bio-oil upgrading, but the product formation mechanism, especially

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aromatic hydrocarbons, needed further exploration. Therefore, Fe, Zr, and Co were selected to

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prepare modified catalysts in the current study for catalytic fast pyrolysis of cellulose. The

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possible reaction path of cellulose conversion under Fe, Zr, Co-modified zeolites was explored.

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In addition, the selected catalyst was used for pyrolysis of sawdust and cotton stalk to investigate

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the adaptability of raw materials to enhance bio-oil production.

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2. Experimental situation

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2.1 Materials

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Microcrystalline cellulose purchased from the Sigma Company was used as a model compound

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of biomass materials in this study. Sawdust and cotton stalk collected from Wuhan, Hubei

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Province, China, were used as the raw biomass feedstock. The experimental biomass particle size

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was ranging from 0.15 mm to 0.25 mm. The sample was dried for 4 h at 105o C before each trial.

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Table 1 showed the basic analysis results. With regard to biomass, sawdust had a higher content

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of C (51.41 wt.%) and lower content of O (38.20 wt.%) in comparison with cotton stalk.

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However, the preparation of catalysts was mainly according to the literature

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catalysts were denoted as 2Fe/HZSM-5, 4Fe/HZSM-5, 6Fe/HZSM-5, 2Zr/HZSM-5, 4Zr/HZSM-

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5, 6Zr/HZSM-5, 2Co/HZSM-5, 4Co/HZSM-5 and 6Co/HZSM-5. All catalysts were kept in a dry

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environment to avoid water adsorption.

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2.2 Experimental Methods


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, and the catalysts

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, the obtained

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Fast pyrolysis under the catalysts with different amounts of metal loading was performed using a

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pyrolyzer (Py, CDS5250, CDS Company, USA) with direct connection to a gas chromatograph

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equipped with GC-MS spectrometry (HP7890 series GC with a HP 5975 Mass Selective

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Detector). The placement of the catalyst and biomass sample is shown in Figure 1. The operation

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parameters were as follows: The mass of feedstock and the catalyst (a layer) were 5.00 mg and

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2.50 mg, respectively. The selected temperature was 550 °C, the pyrolysis time was 10 s, and the

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heating rate was 20 °C/ms. The setting temperature of the gas transmission pipeline between the

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Py and GC-MS was 280 °C.

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2.3 Product/Catalyst characterization

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The main components of bio-oil were specified using a gas chromatograph–mass

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spectrometer(GC-MS; HP7890 series GC with an HP5975 MS Detector). Meanwhile, the phase

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composition was analysed via X-ray diffraction (XRD) (Panalytical Company, Netherlands), the

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acidity of the zeolite catalysts was analysed through the temperature programmed desorption

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(TPD) experiments (ChemiSorb 2720, Micromeritics Instrument Company, USA).and the

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porosity was analysed by the automatic adsorption equipment (ASAP2020, Micromeritics

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Instrument Company, USA). The specific experimental instruments and methods were

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introduced in our previous work 20.

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3. Results and discussion

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3.1 Catalyst characterization

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All catalysts were characterized through the three methods mentioned above. However, the

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characterization results of different types of metals with 4% loading amounts were selected for

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presentation in the paper.


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Figure 2(a) shows that the XRD patterns of all catalysts were essentially similar, consisting of

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obvious crystal diffraction peaks of HZSM-5 21, 22. However, the characteristic peaks of modified

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catalysts became weaker, which might demonstrate that there was some adverse impact of the

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metals on the structure of HZSM-5. And there was no characteristic diffraction peaks of the

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metals detected in the spectras, which mainly because the metallic components were dispersed

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on the inner and external surfaces of the zeolites.

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The results of the NH3-TPD experiments are presented in Figure 2(b). The results indicated that

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the signal of only a weak acidic center appeared at approximately 120 oC for HZSM-5, which

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was moved to about 150 oC for modified catalysts, and a signal of a strong acidic center at

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approximately 475 oC was obtained. These observations indicated that the catalyst acidity

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increased after the metal-modification progress, which could improve catalyst activity 23. While

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Fe showed better results than Zr and Co.

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As shown in Table 2, the BET surface area and pore volume of the modified catalysts were

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reduced slightly compared with those of HZSM-5 catalyst. This might be due to dispersion of the

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metal component on the surface or penetration into the pores. Besides, it might be related to the

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reaction between the metals and the zeolites, which could bring some damages to the pore

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structure

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m2·g-1.

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3.2 Catalytic pyrolysis of vapours with various Fe loading levels

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The chemical composition of the bio-oils under the effects of Fe loading catalysts is listed in

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Table 3. With non-catalysts, a wide range of oxygen-containing compounds were obtained and

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the yields were quite decentralized, except anhydrous sugars. Under HZSM-5 catalysts, there

24

. However, the BET surface areas of the catalysts were relatively large, about 300


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was a substantial reduction in oxygen-containing compounds and a significant increase in

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aromatic compounds. Compared with HZSM-5, the introduction of Fe brought a slight increase

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of acetic acid, hydroxyl acetaldehyde and 5-methyl-2-furancarboxaldehyde, and these aldehyde

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substances were unstable and were mainly intermediate products during pyrolysis progress. With

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respect to ketones, the contents of 1-hydroxy-2-propanone and 3,5-dihydroxy-2-methyl-4H-

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pyran-4-one were decreased under all kinds of catalysts, and even the latter achieved complete

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conversion. The yield of 1,2-cyclopentanedione decreased under HZSM-5 but was increased by

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Fe loading. The content of levoglucosenone was up to 5.62% under HZSM-5, and as the loading

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amounts of Fe increased, levoglucosenone contents decreased to 3.53%, which indicated that

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Fe/HZSM-5 facilitated the decomposition of levoglucosenone. Fe loading resulted in a

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significant decrease of the esters and alcohols, and certain types of these compounds were

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transformed completely, except for D-glucuronicacid gamma-lactone. There was an overall

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decrease of furan substances, including furfural and 5-hydroxymethylfurfural, under the

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catalysts. However, as Fe loading amounts increased from 0% (HZSM-5) to 6% (6Fe/ HSZM-5),

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the content of furfural increased from 2.63% to 3.66% and the content of 5-

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hydroxymethylfurfural decreased from 3.43% to 1.53%. This might be because Fe loading

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facilitated the removal of the hydroxyl-methyl group of 5-hydroxymethylfurfural to form

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furfural, which has been confirmed as an important precursor for aromatic hydrocarbons

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The contents of anhydrous sugars, which were the main products of cellulose pyrolysis with non-

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catalyst, decreased from 37.61% to 20.51% under 6Fe/HZSM-5, demonstrating that Fe

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incorporated into HZSM-5 was helpful for the transfer reaction of glucose substances. Moreover,

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Fe loading was beneficial to eliminating the carbohydrate-derived oxygenate molecules. As the

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Fe loading increased from 0% (HZSM-5) to 6% (6Fe/ HZSM-5), the hydrocarbon production


25, 26

.

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raised up from 21.09% to 35.03%. Fe loading could promote the generation of monocyclic

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aromatics as well as the cyclization reaction to obtain polycyclic aromatics. For instance, under

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6Fe/HZSM-5 catalyst, the contents of toluene, naphthalene, and 1-methyl-naphthalene were

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increased to 7.28%, 12.48%, and 5.86%, respectively.

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The product selectivity of aromatic hydrocarbons with different Fe loading is shown in Figure 3.

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As the Fe loading increasing, the selectivity of toluene and p-xylene decreased because their

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growth rates were lower than the growth of total hydrocarbon categories. In addition, the

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selectivity of benzene and indene changed slightly. 2-Methylindene appeared after the addition

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of 4Fe/HZSM-5, and its selectivity was relatively low. However, the selectivity of naphthalene

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and 1-methyl-naphthalene increased to 35.63% and 16.73%, respectively, as the amount of Fe

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loading increase. This demonstrated that Fe contributed the formation of naphthalene derivatives

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more than benzene derivatives based on zeolite catalysts. However, the changing rate was lower

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for the 4Fe/HZSM-5 as compared with the 6Fe/HZSM-5. Therefore, 4% may be the optimum

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loading amount.

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3.3 Catalytic pyrolysis of vapours with different Zr loading levels

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The catalytic effects of Zr loading were also considered. The liquid oils to which the catalysts

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were applied were complex but similar, so the liquid products were treated by category to

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simplify the analysis.The specific results is listed in Table 4.

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The acid content decreased further as Zr loading increased due to the addition of the HZSM-5

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catalyst, which is different from that with Fe loading. In addition, the production of aldehyde

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substances decreased further as Zr loading increased, and there was complete conversion with

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6Zr/HSZM-5. With respect to ketones, 1-hydroxy-2-propanone was not present under Zr/HZSM-


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5 catalysts, but the contents of 1,2-cyclopentanedione and 3,5-dihydroxy-2-methyl-4H-pyran-4-

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one increased as Zr loading increased compared with HZSM-5, and the yields of ketones was

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higher than Fe-modified zeolites. There was an apparent decrease in the contents of ester

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substances. As Zr loading increased from 0% (HZSM-5) to 6% (6Zr/HSZM-5), the content of D-

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glucuronicacid gamma-lactone decreased from 6.01% to 0.77%. In addition, as Zr loading

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increased, the contents of furans containing furfural and 5-hydroxymethylfurfural decreased, and

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even 5-hydroxymethylfurfural was not present under 6Zr/HZSM-5 catalyst. However, the

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contents of alcohols increased to 3.69% under the 2Zr/HZSM-5 catalyst, and the contents stayed

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nearly the same as Zr loading increased. The results demonstrated that Zr resulted in limited

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improvement in terms of alcoholic substances, which enhanced the stability of bio-oil

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alcohol contents decreased significantly under Fe-modified zeolites, as shown in Table 3. Sugar

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content decreased to 25.52% with 6Zr/HZSM-5, but there was no significant reduction as Zr

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loading increased from 2% to 6%. Furthermore, Zr did not enhance glucose substance transfer

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reaction as much as Fe-modified zeolites. However, the levoglucosenone and 1,6-anhydro-.beta.-

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D-glucofuranose yields under Zr-catalysts were relatively higher than under Fe-catalysts. Under

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Zr, aromatic hydrocarbons were also the primary products of the catalytic pyrolysis of bio-oil. As

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Zr loading increased, hydrocarbon production increased from 21.09% to 32.21%, a slightly lower

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maximum than under Fe loading. Except indene, the content of aromatic substances, including

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benzene, toluene, p-xylene, naphthalene and 1-methyl-naphthalene, increased to various degrees

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under Zr-modified zeolites.

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The product selectivity of aromatic hydrocarbons with different Zr loading amounts is shown in

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Figure 4. There was higher selectivity for toluene and naphthalene than for other hydrocarbons,

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and the sum of the two was approximately 60%. In contrast to the effects of Fe loading, the


27

. The

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selectivity of benzene and p-xylene increased as Zr loading increased. There was notable

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improvement in toluene selectivity, which increased to 28.06% under the 2Zr/HZSM-5 catalyst

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and was less affected by the amount of Zr loading. Moreover, the selectivity of naphthalene and

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1-methyl-naphthalene decreased to 28.44% and 10.40%, respectively, as Zr loading increased.

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The overall results for 4Zr/HZSM-5 and 6Zr/HZSM-5, shown in Figure 4, were relatively

204

similar, which was consistent with Table 4.

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3.4 Catalytic pyrolysis of vapours with different Co loading levels

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The catalytic effects of Co loading on pyrolysis progress were investigated, and Table 5 showed

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the bio-oil composition.

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Compared with other catalysts, such as HZSM-5, Fe/HZSM-5, and Zr/HZSM-5, the categories of

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oxygenated compounds were further decreased under Co-modified zeolites. As mentioned above,

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acetic acid might undergo two competitive conversion pathways. The introduction of increased

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Co loading could promote the decarbonylation reaction to form gaseous products and restrain the

212

secondary reaction of glucopyranose substances to form acetic acid, since the percentage of 1,6-

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anhydro-.beta.-D-glucopyranose increased from 18.96% under 2Co/HZSM-5 to 24.15% under

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6Co/HZSM-5. Therefore, acetic acid did not appear in the bio-oil under Co-modified zeolites, a

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different result from that for Fe/HZSM-5 and Zr/HZSM-5. Between 2Co/HZSM-5 and

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6Co/HZSM-5, the contents of aldehydes decreased, and in some cases were even absent. Next,

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the contents of ketones were reduced to approximately 1% with 6Co/HZSM-5. Simultaneously,

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the content of esters, derived from D-glucuronicacid gamma-lactone, decreased as Co loading

219

increased. The contents of furans was relatively high and stable (nearly 7%) under Co-modified

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zeolites, which again was different from that for Fe- and Zr- modified zeolites, which decreased

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contents of furans significantly. As to alcohols, increasing Co loading from 2% to 6% reduced


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the content of glycidol, and 4-methyl-cyclohexanol did not appear. However, Co loading caused

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significant changes in the content of anhydrous sugars, with the contents increasing to 37.23%.

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This was far greater than for Fe- and Zr- modified zeolites, under which, for instance, the

225

contents of 1,6-anhydro-.beta.-D-glucopyranose and 1,6-anhydro-.beta.-D-glucofuranose were

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24.15% and 6.13%, respectively. The overall contents and categories of aromatic hydrocarbons

227

decreased when Co loading increased, but the contents of toluene and p-xylene were higher than

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under HZSM-5 and there were lower contents of other aromatics, such as naphthalene and 1-

229

methyl-naphthalene. The specific product selectivity of aromatic hydrocarbons is shown in

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Figure 5.

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Though Co loading caused a slight decline in the content of aromatic hydrocarbons, the

232

selectivity of toluene and p-xylene increased to 45.28% and 29.77%, respectively under the

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6Co/HZSM-5 catalyst. This was significantly higher than under the other catalysts. In contrast,

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the selectivity of naphthalene and 1-methyl-naphthalene decreased, in the case of naphthalene

235

dropping from 32.48% to 14.72%. Benzene selectivity was reduced to 7.73% under 2Co/HZSM-

236

5, and then disappeared as Co loading increased. Only four kinds of aromatic hydrocarbons were

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detected under the catalytic effects of 6Co/HZSM-5: toluene, p-xylene, naphthalene and 1-

238

methyl-naphthalene. All the results indicated that Co-modified zeolites could promote the

239

simplification of aromatic hydrocarbons.

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Combining the above results with the results of previous studies

241

network for cellulose catalytic pyrolysis was proposed (Figure 6). Anhydrous sugars, aromatics

242

and furans were the main products of the pyrolysis process.


28-30

, a comprehensive reaction

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It has been reported that cellulose, which exists in crystalline form, is first thermally decomposed

244

into vapours. These oligosaccharides were obtained, with different degrees of polymerization 31.

245

The oligosaccharides are produced primarily mainly through two pyrolysis reactions as shown in

246

Figure 6(a1 and a2)

247

bonds, as seen in Figure 6(a1), and other intermediates are obtained by opening the chain

248

structure, as seen in Figure 6(a2). Anhydrous sugars are formed through some protonation and

249

deprotonation reactions and dehydrations, as seen in Figure 6(b1) 33. Based on the results, it can

250

be inferred that Co loading enhanced reactions a1 and b1, but that Fe and Zr loading decreased

251

the yields of anhydrous sugars. The open chain structure undergoes several dehydroxylation (b2)

252

and aromatization (b3) reactions to form furans and monocyclic aromatics, while BTX (benzene,

253

toluene and xylene) can also be generated through the deoxidation and intermolecular hydrogen

254

transfer reaction (b3’)34. However, the Fe- and Zr- modified catalysts may promote the certain

255

reactions during the pyrolysis progress, such as b2, b3 and b3’, that increase hydrocarbon yields,

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and therefore Zr loading primarily promoted the generation of benzene and its derivatives, while

257

Fe loading could also promote additional reactions of the benzene ring (c1), resulting in higher

258

contents of naphthalene and its derivatives. Moreover, the use of Co-modified zeolites lowered

259

yields of aromatics.

260

3.5 Catalytic pyrolysis of different materials

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During the chemical components of bio-oil from the catalytic pyrolysis, aromatic substances are

262

considered the most useful to the high-value utilization

263

catalytic process more than other catalysts. Considering the amount of Fe loading and the results

264

shown in Table 3, 4Fe/HZSM-5 was selected as the catalyst for biomass pyrolysis of materials

32

. Glucosan substances are formed through the cleavage of the glycosidic

35

. Fe-modified zeolites enhanced the


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265

containing cellulose, sawdust and cotton stalk. Table 6 lists the distribution of different materials

266

under the catalytic effects of 4Fe/HZSM-5 for aromatic hydrocarbons.

267

There were significant differences among the different materials (Table 6). Due to the relatively

268

complex component structures, biomass presented a more complicated distribution than

269

cellulose. The main components of cellulose pyrolysis bio-oil were benzene (3.48%), toluene

270

(7.15%), p-xylene (4.64%), naphthalene (11.96%), and 2-methyl-naphthalene (5.57%). The

271

contents of naphthalene and 2-methyl-naphthalene were the highest among these materials. And

272

they are the primary raw materials to produce plasticizers and fibre dyeing assistants

273

simplified and centralized composition distribution was beneficial to further fractionation and

274

purification. As to sawdust, catalytic pyrolysis under 4Fe/HZSM-5 yielded a wider range of

275

aromatic hydrocarbons. The primary products were benzene (6.36%), toluene (8.22%), p-xylene

276

(4.75%), naphthalene (7.58%) and 2-methyl-naphthalene (4.89%). The contents of benzene and

277

its derivatives were the highest among the three materials. Usually, benzene could be used as a

278

basic material to produce rubber, fibre, detergents, pesticides, and other industrial products

279

The BTX (benzene, toluene, p-xylene) compounds in sawdust were higher than single

280

component pyrolysis, which may be related to the component composition of biomass, since the

281

lignin was able to be transformed into benzene derivatives under zeolites catalysts

282

aromatic hydrocarbons distribution of cotton stalk was similar to sawdust, but contents of the

283

primary components were relatively lower. Overall, the 4Fe/HZSM-5 catalyst was effective in

284

generating aromatics during biomass pyrolysis, with total contents yielded in the following

285

order: sawdust (37.55%) > cellulose (34.13%) > cotton stalk (27.68%).


36

38, 39

. The

37

.

. The

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Page 14 of 31

286

The main industrial contribution of cellulose is to produce bio-oil during the pyrolysis process.

287

Therefore, there are some similarities in the distribution of aromatic hydrocarbons and selectivity

288

between sawdust, cotton stalk and cellulose, such as high yields of toluene and naphthalene in

289

their respective products and that PAHs were not detected. These main aromatic hydrocarbons

290

could be obtained through certain reactions, such as b2, b3 and b3’ (Figure 6), which were

291

promoted by the 4Fe/HZSM-5 catalysts. However, as seen in Table 6, the content and selectivity

292

of naphthalene derivatives in biomass pyrolysis were lower than those of cellulose pyrolysis. It

293

can be speculated that other components in biomass might affect addition reactions of the

294

benzene ring (c1) (Figure 6), since there were different composition properties 40, such as that the

295

interaction of components of biomass and biomass originated ash could also impact pyrolysis

296

reactions

297

4Fe/HZSM-5 enhanced the generation of aromatic hydrocarbons in cellulose pyrolysis, as well

298

as in sawdust and cotton stalk.

299

4. Conclusions

300

Catalytic effects of the Fe, Zr, Co-modified zeolites on bio-oil characteristics based on cellulose

301

pyrolysis were investigated. To study the bio-oil characteristics of different biomass (cellulose,

302

sawdust, and cotton stalk), 4Fe/HZSM-5 was selected. The major conclusions are summarized as

303

follows:

304

1) Compared to HZSM-5, the Fe-, Zr-, and Co- modified catalysts exhibited improved

305

characteristics, including better particle size distribution, stronger acidity, as well as minor

306

structural variations.

307

2) HZSM-5 catalysts were beneficial in improving bio-oil composition. Furthermore, Fe loading

308

was in favor of the deoxygenation and hydrocarbon generation, and the selectivity of

41, 42

. Further study is needed to improve the understanding on this. Moreover,


14

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naphthalene and 1-methyl-naphthalene were enhanced. Increasing the Zr loading brought an

310

increase in the contents of ketones and aromatics, and the selectivity of benzene and p-xylene

311

were increased. Increasing the Co loading led to a decrease in aromatics but an increase in

312

anhydrous sugars, while the selectivity of toluene and p-xylene were the highest.

313

3) With the use of 4Fe/HZSM-5, the total contents of aromatic hydrocarbons were all relatively

314

high and in the following order: sawdust > cellulose > cotton stalk. There was higher selectivity

315

of naphthalene and 2-methyl-naphthalene in cellulose, while the selectivity of benzene and its

316

derivatives in sawdust and cotton stalk were higher.

317

Author Information

318

*Corresponding author: Jingai Shao.

319

E-mail address: [email protected].

320

Tel.: 086+027-87542417

321

Fax: 086+027-87545526

322

Author Contributions

323

The manuscript was written through contributions of all authors.

324

Acknowledgment

325

The research project was financially supported by the National Basic Research Program of China

326

(2013CB228102), the National Natural Science Foundation of China (No. 51506071, No.

327

51376075 and No. 51576087), the Foundation of State Key Laboratory of Coal Combustion

328

(FSKLCCB1405) and the Fundamental Research Funds for the Central Universities.


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Page 16 of 31

329

The authors are grateful for the technical support of the Analytical and Testing Centre of

330

Huazhong University of Science and Technology (http://atc.hust.edu.cn).

331

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Page 20 of 31

448 449

Figure 1. The placement of the catalyst and feedstock in the quartz filler tube

450


20

Page 21 of 31

15000 4Co/HZSM-5 10000 5000 15000 4Zr//HZSM-5 10000 5000 15000 4Fe/HZSM-5 10000 5000 15000

HZSM-5

10000 5000 10

15

20

25

30 2θ/

35

40

45

50

ο

451 452

(a)

0.008

HZSM-5 4Fe/HZSM-5 4Zr/HZSM-5 4Co/HZSM-5

0.006

TCD signal

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

Energy & Fuels

0.004

0.002

0.000 100

453 454 455

200

300

400

500

600

Temperature/℃

(b) Figure 2. Characterization of catalysts through XRD (a) and TPD (b)

456


21

Energy & Fuels

40

Selectivity / %

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 22 of 31

HZSM-5 2Fe/HZSM-5 4Fe/HZSM-5 6Fe/HZSM-5

30

20

10

0

457 458

e e e e ne ne ne den linden thalen thalen yle nze Tolue n X I e y p B ph aph eth Na yl-n 2 -M h t e 1-M

Figure 3. Product selectivity of aromatic hydrocarbons with different loading amounts of Fe

459


22

Page 23 of 31

460

40

HZSM-5 2Zr/HZSM-5 4Zr/HZSM-5 6Zr/HZSM-5

30

Selectivity / %

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

Energy & Fuels

20

10

0

ne nze Be

461 462

e ne uen yle Tol p-X

e Ind

ne

e e len len tha tha h h p p Na l-na thy e M 1-

Figure 4. Product selectivity of aromatic hydrocarbons with different loading amounts of Zr

463


23

Energy & Fuels

50 HZSM-5 2Co/HZSM-5 4Co/HZSM-5 6Co/HZSM-5

40

Selectivity / %

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 24 of 31

30

20

10

0 Be

464 465

ne nze

To

lu e

ne

p-X

n yle

e

e Ind

ne N

th ap h

al e

eth 1- M

ne

yl-n

th aph

al e

ne

Figure 5. Product selectivity of aromatic hydrocarbons with different loading amounts of Co

466


24

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Energy & Fuels

467

468 469

Figure 6. A comprehensive reaction network for cellulose catalytic pyrolysis

470


25

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Page 26 of 31

471 472

Table 1. Basic analysis results of biomass Proximate analysis

Ultimate analysis

Components analysis

(wt.%)

(wt.%)

(wt.%)

Samples

Fixed Ash Volatile

Hemi C

H

O*

N

S

Cellulose

Carbon

473

Lignin cellulose

Cellulose (d)

0.00

95.50

4.50

42.70

6.20 51.00 0.03

0.05

--

--

--

Sawdust (d)

4.03

82.06

13.91 51.41

6.04 38.20 0.29

0.02

45.14

22.69

27.65

Cotton stalk (d) 3.16

79.96

16.88 47.43

6.65 41.31 1.10

0.36

55.21

19.07

18.74

O* is obtained by the subtraction method.

474


26

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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

475

Energy & Fuels

Table 2. The pore structure parameters of catalysts Types

BET surface area／m2·g-1

Pore volume ／cm3·g-1

Pore diameter /nm

HZSM-5

314.83

0.19

0.55

4Fe/HZSM-5

298.39

0.17

0.52

4Zr/HZSM-5

295.42

0.16

0.49

4Co/HZSM-5

301.73

0.17

0.51

476


27

Energy & Fuels

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477

Page 28 of 31

Table.3 Chemical composition of bio-oils with different loading amounts of Fe Peak area percentage (%) Types

Library/ID

NonCatalyst

Acids Aldehydes

Ketones

Furans

Alcohols

Sugars

Aromatics

4Fe /

6Fe/

HSZM-5

HSZM-5

HSZM-5

3.93

1.74

1.92

2.21

2.14

Hydroxyl acetaldehyde

5.57

1.32

2.16

2.64

2.56

1.56

--

--

0.95

0.92

1-Hydroxy-2-propanone

1.23

0.79

0.54

0.67

0.42

1,2-Cyclopentanedione

1.11

0.45

0.73

1.06

1.01

2.42

--

--

--

--

Propanoic acid, 2-oxo-,methyl ester

0.68

--

--

--

--

Pentanoic acid,1-methylpropyl ester

1.22

0.87

--

--

--

D-Glucuronicacid.gamma.-lactone

7.46

6.01

2.15

1.63

1.44

Furfural

3.74

2.63

3.21

3.17

3.66

5-Hydroxymethylfurfural

4.55

3.43

2.35

2.02

1.53

Glycidol

0.42

0.81

--

--

--

4-Methyl-cyclohexanol

0.65

1.31

--

--

--

Levoglucosenone

2.88

5.62

4.44

3.76

3.53

4.02

3.31

1.82

1.85

1.22

1,6-Anhydro-.beta.-D-glucopyranose

26.47

17.38

15.93

13.52

13.45

1,6-Anhydro-.beta.-D-glucofuranose

4.24

5.14

4.02

2.17

1.31

Benzene

--

2.53

3.17

3.48

3.66

Toluene

--

5.09

6.94

7.15

7.28

p-Xylene

--

3.21

4.25

4.64

4.43

Indene

--

0.45

0.54

0.71

0.75

--

--

--

0.62

0.57

Naphthalene

--

6.85

9.94

11.96

12.48

1-Methyl-naphthalene

--

2.96

4.63

5.57

5.86

5-Methyl-2-furancarboxaldehyde

3,5-Dihydroxy-2-methyl

1,4:3,6-Dianhydro-.alpha. Anhydrous

2Fe/

Acetic acid

-4H-pyran-4-one

Esters

HZSM-5

-d-glucopyranose

2-Methylindene

478 479 480 481 ACS Paragon Plus Environment

28

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482

Energy & Fuels

Table 4. Chemical composition of bio-oils with different loading amounts of Zr Peak area percentage (%) Types

2Zr/

4Zr/

6Zr/

HSZM-5

HSZM-5

HSZM-5

1.74

1.27

0.67

0.72

7.13

1.32

1.23

1.04

--

Ketones

4.76

1.24

1.52

2.06

2.50

Esters

9.36

6.88

2.60

1.37

0.77

Furans

8.29

6.06

5.39

3.50

1.69

Alcohols

1.07

2.12

3.69

3.96

3.89

37.61

31.45

27.27

25.71

25.52

--

21.09

27.94

31.15

32.21

Non-Catalyst

HZSM-5

Acids

3.93

Aldehydes

Anhydrous Sugars Aromatics

483


29

Energy & Fuels

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484

Page 30 of 31

Table 5. Chemical composition of bio-oils with different loading amounts of Co Peak area percentage (%) Types

2Co/

4Co/

6Co/

HSZM-5

HSZM-5

HSZM-5

1.74

--

--

--

7.13

1.32

1.07

0.89

--

Ketones

4.76

1.24

1.29

0.93

0.88

Esters

9.36

6.88

4.32

2.44

2.12

Furans

8.29

6.06

6.64

6.81

6.95

Alcohols

1.07

2.12

1.28

0.83

--

37.61

31.45

32.48

36.01

37.23

--

21.09

20.82

17.04

15.15

Non-Catalyst

HZSM-5

Acids

3.93

Aldehydes

Anhydrous Sugars Aromatics

485


30

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486

Energy & Fuels

Table 6. Aromatic hydrocarbons distribution of different materials Peak area percentage (%) Aromatic hydrocarbons

Formula Cellulose

Sawdust

Cotton stalk

Benzene

C 6H 6

3.48

6.36

3.34

Toluene

C 7H 8

7.15

8.22

6.97

Styrene

C 8H 8

--

1.27

0.28

Ethylbenzene

C8H10

--

0.71

0.43

p-Xylene

C8H10

4.64

4.75

5.33

Indene

C 9H 8

0.71

0.92

0.72

Allylbenzene

C9H10

--

0.45

0.63

Naphthalene

C10H8

11.96

7.58

4.89

2-Methylindene

C10H10

0.62

0.95

0.86

2-Methyl-naphthalene

C11H10

5.57

4.89

3.21

2,6-Dimethyl-naphthalene

C12H12

--

0.68

0.49

1-Ethyl-naphthalene

C12H12

--

0.77

0.53

487 488


31

Catalytic Upgrading of Fast Pyrolysis Products with Fe-, Zr-, and Co

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