Production of aromatic hydrocarbons through catalytic pyrolysis of 5-Hydroxymethylfurfural from biomass

Bioresource Technology 147 (2013) 37–42

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Production of aromatic hydrocarbons through catalytic pyrolysis of 5-Hydroxymethylfurfural from biomass Yan Zhao, Tao Pan, Yong Zuo, Qing-Xiang Guo ⇑, Yao Fu ⇑ Anhui Province Key Laboratory of Biomass Clean Energy, Department of Chemistry, University of Science and Technology of China, Hefei 230026, People’s Republic of China

h i g h l i g h t s  A novel method for the production of aromatic hydrocarbons from biomass-derived HMF.  The carbon yield of aromatic hydrocarbons was 48.99%, and the selectivity of toluene was over 46%.  Four zeolites were screened and HZSM-5 exhibits robustness for high tolerance to 5-HMF.  The carbon yield of aromatic hydrocarbons was stable in five recycle catalytic runs.

a r t i c l e

i n f o

Article history: Received 18 May 2013 Received in revised form 12 July 2013 Accepted 16 July 2013 Available online 20 July 2013 Keywords: HMF Catalytic pyrolysis Zeolites Aromatic hydrocarbons

a b s t r a c t Catalytic pyrolysis of 5-Hydroxymethylfurfural (HMF) was conducted on a fixed bed reactor at atmospheric pressure. HMF could be converted into aromatic hydrocarbons through catalytic pyrolysis. The catalysts and reaction conditions were both critical in maximizing the aromatic hydrocarbons selectivity. Four catalysts, b-zeolite, HZSM-5, Ga/HZSM and In/HZSM were tested in this study. HZSM-5 (Si/Al = 50) was found to be the most effective catalyst in both reactivity and selectivity among these catalysts. Under the reaction temperature of 600 °C, the highest carbon yield of 48.99% of aromatic hydrocarbons was achieved from catalytic pyrolysis HMF with HZSM-5 (Si/Al = 50) as catalyst. Moreover, the HZSM-5 (Si/ Al = 50) catalyst was recycled for five times without shown deactivation of the catalyst. Ó 2013 Published by Elsevier Ltd.

1. Introduction The rapid consumption of fossil resources and increasing the amount of carbon dioxide in the atmosphere require innovative strategies for the sustainable production of fuels from renewable raw materials. Biomass is the most abundant renewable source (Wyman et al., 2005; Shen and Wyman, 2011) and adequate availability for large scale sustainable production of liquid fuels (Huber et al., 2006; Leshkov et al., 2006; Corma et al., 2007; Singh et al., 2010). Biomass has been processed in diverse ways to make bioethanol and biodiesel as first generation of biofuels. However, their feedstocks were from sugar, starch and vegetable oils, which induce compete with food. Therefore, the production of liquid fuel from renewable biomass to achieve was great importance. In this regard, a large number of studies have been performed to identify interest⇑ Corresponding author. Address: No. 96, JinZhai Road, Baohe District, Hefei 230026, Anhui Province, People’s Republic of China. Tel.: +86 551 63607476; fax: +86 551 63606689. E-mail addresses: [email protected] (Q.-X. Guo), [email protected] (Y. Fu). 0960-8524/$ - see front matter Ó 2013 Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.biortech.2013.07.068

ing biomass derivatives to be used as platform chemicals for the chemical industry. A platform chemical HMF could be converted into liquid fuels (Huber et al., 2005). HMF was a key intermediate of a biobased chemical industry as well (Mehdi et al., 2008), so the efficient production of HMF from biomass was great important. In 2006, Dumesic and co-workers developed a process for the selective dehydration of fructose to HMF that operated at high fructose concentrations with achieved high yield (80% HMF selectivity at 90% fructose conversion) (Leshkov et al., 2006). Zhao et al., (2007) reported catalytic conversion of sugars giving high yield (70%) to HMF. More recently, Binder and Raines (2009) reported production of HMF in a single step from untreated lignocelluloses biomass. However, HMF suffered from several limitations for directly used as liquid transportation fuel, such as the high water solubility, easy decomposition and the relatively low energy density compared to petroleum-derived fuels. Therefore, studies have been conducted to convert HMF to hydrocarbons with higher molecule weight, which have similar properties to gasoline, diesel and jet fuel. One of the most studied HMF conversion methods was the acid catalyzed dehydration leading to levulinic acid and formic

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Y. Zhao et al. / Bioresource Technology 147 (2013) 37–42

acid as the main products. Formic acid could be used in the transfer hydrogenation of levulinic acid to g-valerolactone (GVL) (Deng et al., 2009, 2010; Du et al., 2011). However, GVL yet had several problems, for example, the high water solubility and the relatively low energy density, and cannot be directly used as transportation fuel (Bond et al., 2010). Serrano-Ruiz et al. reported the conversion of GVL to 5-nonanone, which has similar properties compared with diesel fuel (Serrano-Ruiz et al., 2010). Lange et al. reported a strategy for the production of alkyl valeric esters fuel components (Lange et al., 2010). Bond Bond et al. (2010) have reported that aqueous solutions of GVL can be converted to liquid alkenes in the molecular weight range appropriate for transportation fuels through an integrated catalytic system. A novel method for the production of aromatic hydrocarbons from HMF through a single step has been reported in this manuscript. Aromatic hydrocarbons were important platform molecules for the development of high-value-added fine chemicals and also can provide the basic feedstocks for the petrochemical industry (Bi et al., 2013; Zakzeski et al., 2010). Since this work provided an alternative strategy for the production of aromatic hydrocarbons from biomass-derived HMF. Different zeolite catalysts and reaction conditions have been tested for the conversion of HMF to aromatic hydrocarbons. Several reaction conditions, i.e., temperature, nitrogen flow rate, feed rate, catalyst and catalyst regeneration were tested in this manuscript for catalytic pyrolysis of HMF. By decreasing the oxygen content and increasing the carbon chain length, the energy density of the aromatics product was significantly increased compared with HMF. 2. Methods 2.1. Materials 5-Hydroxymethylfurfural (HMF, CAS: 67-47-0), 5-methylfuran2-carbaldehyde (5-MF, CAS: 620-02-0), Ga (NO3)3 and In (NO3)3 were purchased from Aladdin Reagent Co. Ltd. 2,5-dimethylfuran (DMF, CAS: 625-86-5) and furan-2,5-dicarbaldehyde (DFF, CAS: 820-85-5) were purchased from TCI Reagent Co. Ltd. These reagents were used without further purification. ZSM-5 and b-zeolite were provided by the catalyst plant of Nankai University. HZSM-5 was purchased from Fuxu zeolite Co. Ltd. Analytical reagents such as methanol, benzene, toluene, o/p/m-xylene, naphthalene and 1-methylnaphthalene (MNP) were purchased from Sinopharm Chemical Reagent Company Limited in China (Shanghai, China). 2.2. Experimental setups and procedures Ga/HZSM-5 and In/HZSM-5 were synthesized according to the method described elsewhere (Chen et al., 2012) . Ga/HZSM and In/HZSM catalysts were prepared by ion exchange, where 1 g of HZSM-5 (SiO2/Al2O3 = 50) was refluxed in 100 mL of aqueous solution of Ga(NO3)3 and In(NO3)3 (0.01 mol) at 70 °C for 12 h. After ion exchange, the solution was dried at 110 °C. Both of the remained powders were calcined under air at 550 °C. The metal Ga and In contents of the catalysts respectively 0.61 wt% and 1.05 wt%. The typical properties of the catalysts were listed in Table 1. Pyrolysis of HMF was carried out in a tubular reactor (1 cm i.d.) made of quartz glass. In Fig. 1, before the reaction, 1.0 g zeolite was loaded in the heating zone with quartz wool. During the pyrolysis, HMF was fed into the heating zone by an autosampler (1.6 g/h) and purged with nitrogen (10 ml/min). The productions were condensed and collected in a liquid nitrogen trap. The gas productions were collected with a gasbag. For catalyst regeneration, air (100 ml/min) was used to remove the coke at 600 °C.

Table 1 Typical properties of the catalysts.

a

Entry

Catalyst

BET surface area/m2/g

Average pore diameter/nm

Si/Al

1 2 3 4 5 6

b-Zeolite ZSM-5 HZSM-5 (1) HZSM-5 (2) Ga/HZSM-5 In/HZSM-5

63 420 375a 350a 293 255

0.7a 0.5a 0.5a 0.5a 0.5a 0.5a

50a 50a 63a 50a 50 50

Provided by the manufacturers.

The absolute mole HMF was detected by HPLC with an error within ±2.27%. The absolute moles of most of liquid components such as benzene, toluene, o/p/m-xylene, naphthalene and 1-methylnaphthalene were determined by the calibrated GC–MS peak area with the standard samples (error within ±2.18%). For solid product analysis, the solid residues after each experiment were immediately removed from the heating zone and cooled to room temperature in a N2 flow. The solid residue in each experiment was weighed (±2.55%). The HMF conversion (Eq. (A.1)), overall carbon yields (Y (C-mol%)) of the gas, solid aromatic and oxygenates products, carbon yield (Yl (C-mol%)) of a specific product, and aromatic selectivity (S (C-mol%)) were calculated based on Eqs. (A.2) – (A.6): Moles of HMF reacted  100% Moles of HMF fed in Carbon moles in gas or solid products Yðgas and solid productsÞ ¼  100% Carbon moles of HMF fed in Carbon moles in aromatic YðAromaticÞ ¼  100% Carbon moles of HMF fed in Carbon moles in oxygenates  100% YðOxygenatesÞ ¼ Carbon moles of HMF fed in Carbon moles in a product Y1ðC-molÞ% ¼  100% Carbon moles of HMF fed in Carbon moles in a product SðC-molÞ% ¼  100% Carbon moles in all liquid products

Conversion of HMF ¼

ðA:1Þ ðA:2Þ ðA:3Þ ðA:4Þ ðA:5Þ ðA:6Þ

2.3. Analytical determination Nitrogen adsorption/desorption isotherms was measured by a Micromeritics ASAP 2020 analyzer. The surface area was determined using Barrett–Emmet–Taller (BET) method. The metal Ga and In contents of the catalysts were measured by an inductively coupled plasma atomic emission spectroscopy (ICPAES, Thermo-Jarrell ASH-Atom Scan Advantage). The concentration of HMF was detected by HPLC using external standard method. HPLC was performed with a Hitachi L-2000 HPLC system equipped with two L-2130 pumps and an L-2455 photodiode array detector. Liquid samples were analyzed by a GC–MS (Thermo Trace GC Ultra with a PolarisQ ion trap mass spectrometer) equipped with a TR-35MS capillary column (30 m  0.25 mm  25 lm). Split injection is performed at a split ratio of 50 using helium (99.999%) as carrier gas. Gas product was collected by a gasbag and analyzed with GC equipped with a thermal conductivity detector (TCD). The yield of gaseous products were measured by weight difference (weight of gas = weight of feed  weight of liquid  weight of coke). The components were determined by the external standard method using calibration gas. 3. Results and discussion 3.1. Catalytic pyrolysis of HMF HMF was entered into the fixed-bed reactor and generated HMF vapor. In this process, the HMF vapor enter the catalysts pores

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Y. Zhao et al. / Bioresource Technology 147 (2013) 37–42

Fig. 1. Schematic diagram of the experimental apparatus for the catalytic pyrolysis of HMF.

where they were simultaneously converted into aromatic hydrocarbons, carbon monoxide, carbon dioxide, water, and coke. Inside the zeolite catalyst, the HMF vapor undergoes a series of decarbonylation, isomerization and oligomerization reactions. The challenge for the selective production of aromatic hydrocarbons was to minimize the formation of gas and coke. The overall stoichiometry for the conversion of HMF into toluene, CO, and H2O was shown in Eq. (B.1). The maximum theoretical yield of toluene from HMF was 63.64% carbon yield, when CO and H2O were produced as by-products:

C6 H6 O3 ! 18=33C7 H8 þ 72=33CO þ 25=33H2 O

ðB:1Þ

Table 2 Catalytic pyrolysis of HMF at various temperatures. Entry

1 2 3 4

60

ðC:1Þ

The H/Ceff ratio of petroleum-derived feeds ranges from slightly over 2 (for liquid alkanes) to 1 (for benzene). The H/Ceff ratio of HMF (C6H6O3) was H/Ceff = 0 < 1. The H/Ceff ratio of toluene (C7H8) was H/Ceff = 8/7 > 1. 3.2. Effects of temperature on HMF conversion

50

Selectivity(%)

H=Ceff

Conversion (%)

Coke (%)a

Gas (%)a

Yield (%)a Aromatic

Oxygenatesb

500 550 600 650

68.92 71.06 81.19 88.63

17.04 17.88 8.70 7.76

54.87 53.74 44.79 70.97

4.53 11.38 34.24 14.18

23.56 17.00 12.73 7.09

Reaction conditions: catalyst HZSM-5 (2) 1.0 g; HMF 2.0 g (velocity 2 ml/h); N2 20 ml/min. a Carbon yield%. b DMF, 5-MF, DFF.

Chen and co-workers have defined the effective hydrogen-tocarbon ratio (H/Ceff) as shown in Eq. (C.1) (Chen et al., 1986). (H, C, and O correspond to the number of atoms of hydrogen, carbon, and oxygen, respectively):

H  2O ¼ C

Temperature (°C)

500 550 600 650

40

30

20

Temperature was a significant effect on HMF conversion. The reactions were carried out in the zeolite catalysts bed at a reaction temperature of 500–650 °C. Table 2 showed the product selectivity for HMF conversion as a factor of temperature. The conversion of HMF improved dramatically from 68.92% to 88.63% as the reaction temperature was raised from 500 to 650 °C. Generally, the highest yield was obtained at 600 °C for aromatic hydrocarbons (34.24% carbon yield). However, the yield of aromatic hydrocarbons started to decline at 600–650 °C, because at such temperatures aromatic hydrocarbons were also likely to undergo pyrolysis leading to more gas products. The coke selectivity decreased with increasing temperature. As shown in Fig. 2, Benzene, toluene and xylene had higher selectivity in catalytic pyrolysis HMF at higher temperatures. Oxygenates, such as 2,5-dimethylfuran (DMF), 5-methylfurfural (5-MF) and diformylfuran (DFF), had been found only three productions in catalytic pyrolysis of HMF, and selectivity of these were decreased with raised temperature. The main products were CO, CO2 and gas alkenes in gas, and the selectivity of gas were increased significantly with the increase of temperature. 3.3. Effect of nitrogen flow rate HMF was fed into the heating zone by an autosampler and the HMF vapor purged with nitrogen at different flow rates. This work

10

0 Benzene Toluene Xylene Naphtal

MNP

DMF

5-MF

DFF

Aromatics

Fig. 2. Product distribution of the catalytic pyrolysis of HMF with different temperature.

has investigated the influence of sweeper gas flow rates (from 5 to 100 ml/min) on the conversion of HMF in the catalytic pyrolysis. Table 3 showed the distribution of the products with different nitrogen flow rates. Results for these measurements shown that reduced the nitrogen flow rate increased the conversion of HMF. Table 3 showed that the highest conversion (87.07%) at lowest nitrogen flow rate (5 ml/min) with the yield of aromatic hydrocarbons 25.71%. But the highest yields of aromatic hydrocarbons were 43.25% at 10 ml/min flow rates of nitrogen. The yield of gas was increased with decreasing nitrogen flow rate. Their formation was probably due to continued pyrolysis from aromatics or oxygenates. Fig. 3 showed the selectivity of liquid products from catalytic pyrolysis of HMF with different flow rate of N2. The major products were benzene, toluene and xylene in catalytic pyrolysis of HMF

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Y. Zhao et al. / Bioresource Technology 147 (2013) 37–42

Table 3 Catalytic pyrolysis of HMF with different nitrogen flow rate. Entry

1 2 3 4 5

Table 4 Carbon yield as a function of Feed rate for catalytic pyrolysis of HMF.

N2 (ml/ min)

Conversion (%)

Coke (%)a

Gas (%)a

Yield (%)a Aromatic

Oxygenates

100 50 20 10 5

62.97 66.35 81.19 84.08 87.07

4.38 5.82 8.70 6.38 4.59

55.41 57.86 44.79 40.30 63.18

29.22 29.05 34.24 43.25 25.71

10.98 7.27 12.73 10.61 6.52

Entry b

Reaction conditions: reaction temperature 600 °C; catalyst HZSM-5 (2) 1.0 g; HMF 2.0 g (velocity 2 ml/h). a Carbon yield%. b DMF, 5-MF, DFF.

40

5ml 10ml 20ml 50ml 100ml

35

Selectivity(%)

30 25 20 15 10 5 0 Benzene Toluene Xylene Naphtal

MNP

DMF

5-MF

DFF

Aromatics

Fig. 3. Product distribution of the catalytic pyrolysis of HMF with different nitrogen flow rate.

at HZSM-5 (2) as catalyst, and toluene as the dominant product with a selectivity of 36.85% at 5 ml/min flow rate of N2. 3.4. Effect of feed rate Table 4 shown the product selectivity for catalytic pyrolysis of HMF with HZSM-5 (2) as a function of the feed rate. The conversion of HMF was increase as the feed rate decrease. When the feed rate was decreased to 0.4 g/h, the conversion was elevated to 97.68%. The coke yield increased and the yield of aromatic hydrocarbons and oxygenates decreased as the feed rate decreased. The maximum carbon yield of aromatic hydrocarbons (48.99%) and the lowest coke yield (6.20%) were obtained at the feed rate 1.6 ml/h (as shown in Table 4). Assuming that the products of the cracking reaction were toluene, CO and H2O, the theoretical molar carbon yield of toluene from HMF is about 63.64% (Eq. (B.1)). The aromatic hydrocarbons from catalytic pyrolysis of HMF were mainly composed of benzene, toluene, xylene, naphthalene, and toluene had the highest selectivity of (42.66%) in aromatic hydrocarbons. 3.5. Catalysts-to-HMF ratio In addition to appropriate feed rate, the catalyst to HMF ratio was another factor for produced more aromatic hydrocarbons in catalytic pyrolysis of HMF. Table 5 shown the yield of productions for catalytic fast pyrolysis of HMF with HZSM-5 (2) as a function of the catalyst-to-HMF. The conversion of HMF was raised up with increase the amount of catalyst-to-feed ratio at using 1 g HZSM-5 (2) as catalyst for catalytic pyrolysis HMF. The conversion of

1 2 3 4 5

HMF (g/ h)

Conversion (%)

Coke (%)a

Gas (%)a

Yield (%)a Aromatic

Oxygenatesb

2.0 1.6 1.2 0.8 0.4

84.08 95.72 96.18 96.78 97.68

6.38 6.20 8.40 9.18 9.77

40.30 33.94 42.62 47.92 58.34

43.25 48.99 39.40 33.23 24.21

10.61 10.87 9.58 9.67 7.68

Reaction conditions: reaction temperature 600 °C; catalyst HZSM-5 (2) 1.0 g; HMF 2.0 g; N2 10 ml/min. a Carbon yield%. b DMF, 5-MF, DFF.

Table 5 Distribution of production species as a function of catalyst-to-HMF ratio for catalytic pyrolysis HMF used HZSM-5 (2) as catalyst. Entry

1

2

3

4

5

6

7b

HMF (g)/cat (g) Temperature (°C) N2 (ml/min) Conversion

0.5/1 600 10 100

1/1 600 10 100

1.5/1 600 10 95.97

2/1 600 10 95.72

2/2 600 10 100

1/2 600 10 100

2/1 600 10 96.12

Overall carbon selectivity (%) Gas 69.08 Coke 6.32 Aromatic 24.60 Oxygenatesa 0 a Aromatic + oxygenates 24.60

59.55 7.89 32.09 0.48 32.56

44.67 5.69 48.10 1.55 49.64

33.94 6.20 48.99 10.87 59.86

54.65 7.73 37.11 0.51 37.62

63.09 5.74 31.04 0.13 31.17

37.31 6.95 48.89 3.52 52.41

Aromatic carbon selectivity Benzene Toluene Xylene Naphtal MNP Other aromatics

1.01 14.85 5.37 4.18 3.33 3.35

0.94 17.29 7.78 4.84 6.39 10.84

1.76 20.90 2.86 4.81 7.67 10.99

1.38 16.80 5.83 5.59 5.09 2.41

1.30 13.57 4.48 5.73 4.78 1.18

1.81 21.79 10.73 5.67 3.30 5.59

/ 0.35 1.19

2.96 3.64 4.27

/ 0.51 /

/ 0.13 /

0.31 2.23 0.98

17.50 18.24 4.14 2.73 2.05

16.47 12.09 2.08 0.98 2.33

19.91 22.13 2.10 4.38 6.13

21.52 30.00 4.45 1.20 5.92

11.38 11.02 6.14 2.86 5.92

Oxygenates DMF 5-MF DFF

a

(%) 0.85 10.60 3.86 4.68 3.54 1.07

carbon selectivity (%) / / / 0.48 / /

Gas carbon selectivity (%) CH4 CO CO2 C2 C3

26.51 29.13 2.59 4.42 6.43

21.77 20.87 7.67 3.61 5.62

‘‘/’’ Trace amounts. a DMF, 5-MF, DFF. b 80 wt% HMF aqueous solution as feed.

HMF was 100% at high catalyst-to-HMF ratio (1/0.5), and also obtained the highest selectivity of aromatic hydrocarbons (100%) at this reaction conditions. The yield of aromatic hydrocarbons was raised as the catalyst-to-HMF ratio decreases. The selectivity of aromatic hydrocarbons was a strong function of the catalyst-toHMF ratio as shown in Table 5. Decreasing the catalyst to feed ratio slightly improve the carbon yield for benzene, toluene, and methylnaphthalene. Trace amounts of aromatic hydrocarbons, styrene, methylstyrene, ethylbenzene, trimethylbenzene, benzofuran, indane had been detected in catalytic pyrolysis of HMF. Table 5 shown oxygenates selectivity were increases as the catalyst-toHMF ratio decreases. These thermally stable oxygenates were intermediates in the production of aromatics (Carlson et al., 2009). The gas products were analyzed with GC equipped with a thermal conductivity detector (TCD), and main products included CH4, CO and CO2. Catalytic pyrolysis HMF was conducted using 2 g HZSM-5 (2) as catalyst (As shown in Table 5 entry 5 and 6). The height of catalyst bed would be increased when added the

41

Y. Zhao et al. / Bioresource Technology 147 (2013) 37–42 Table 6 Catalytic pyrolysis of HMF with different catalysts. Blank

b-Zeolite

ZSM-5

HZSM-5 (2)

HZSM-5 (1)

Ga/HZSM

In/HZSM

HMF/cat Temperature (°C) N2 (ml/min) Conversion

/ 600 10 48.92

2/1 600 10 85.78

2/1 600 10 90.17

2/1 600 10 95.72

2/1 600 10 90.29

2/1 600 10 94.15

2/1 600 10 90.69

Overall carbon selectivity (%) Gas Coke Aromatic Oxygenatesa Aromatic + Oxygenatesa

16.30 13.20 4.18 66.32 70.50

55.68 16.75 6.85 23.60 30.45

53.72 11.71 12.62 23.94 36.56

33.94 6.20 48.99 10.87 59.86

48.94 9.17 30.28 11.61 41.89

33.82 8.81 36.05 21.32 57.37

37.66 9.62 33.57 19.15 52.72

Aromatica carbon selectivity (%) Benzene Toluene Xylene Naphtal MNP Other aromatics

0.03 0.37 0.88 0.58 0.56 1.76

0.04 0.81 1.24 0.34 7.81 2.38

0.58 8.28 3.92 2.79 5.20 5.65

1.76 20.90 2.86 4.81 7.67 10.99

0.62 8.82 5.17 2.41 4.47 8.79

0.66 10.04 5.68 5.04 2.14 12.49

0.36 5.02 5.64 1.70 10.38 10.47

Oxygenates carbon selectivity (%) DMF 5-MF DFF

1.47 31.10 33.75

0.38 7.57 15.99

0.66 6.85 11.85

2.96 3.64 4.27

0.48 7.19 3.94

0.75 11.66 8.91

0.96 10.61 7.58

Gas carbon selectivity (%) CH4 CO CO2 C2 C3

4.12 3.12 1.47 0.87 6.72

2.25 21.10 19.87 6.51 5.96

14.42 34.15 2.32 1.32 1.52

10.47 18.09 2.08 0.98 2.33

17.97 21.00 4.62 1.32 4.03

16.69 13.29 2.94 0.60 0.30

13.60 21.22 1.40 1.19 0.25

‘‘/ ’’ trace amounts. a DMF, 5-MF, DFF.

The appropriate catalyst selection was essential for high aromatic hydrocarbons selectivity. Four kinds of catalysts, b-zeolite ZSM-5, HZSM-5, Ga/HZSM-5 and In/HZSM-5 were tested in this study. Table 1 shown typical properties of ZSM-5, HZSM-5, Ga/ HZSM-5 and In/HZSM-5. The pore structures and BET surface area of the catalysts were quite different in nature. Table 6 was showing catalytic pyrolysis of HMF with these catalysts. In the blank experiment, the conversion of HMF was extremely low (48.92%), and the carbon yield of aromatic hydrocarbons was lowest (4.18% carbon yield). Table 6 was also shown catalytic pyrolysis of HMF with b-

100

60

50

Coke Gas Aromatic Oxygenates

80

40 60 30 40 20

Conversion(%)

3.6. Catalyst selection

Zeolite catalyst. In catalytic pyrolysis, the HMF vapors could be adsorbed on the catalyst surface, and have to diffuse into the pores for catalytic reforming. (Gopakumar et al., 2011; Stefanidis et al., 2011). In catalytic pyrolysis of HMF with b-zeolite as catalyst, conversion of 85.78% could be obtained with he yield of aromatic hydrocarbons was only 6.85%. The conversion of HMF was increase upto 90.17% in catalytic pyrolysis of HMF with ZSM-5 as catalyst, and the yield of aromatic hydrocarbons was raised 12.62%. b-zeolite has intersecting channels similar to ZSM-5, has a pore diameter of 0.7 nm, which is larger than the pore diameter of ZSM-5 (Xia et al., 2003). The results suggested that shape-selective catalysis played an essential role in the catalytic pyrolysis of HMF. HZSM5 and ZSM-5 have the same pore structures, but different numbers

Selectivity(%)

quantity of catalyst in the same tubular reactor. The conversion of HMF was increase significantly as the height of catalyst bed extend. The conversion of HMF was upto 100% at high catalyst-toHMF ratio (2/1). However, the yields of aromatic hydrocarbons and gas were 31.04% and 63.09% from catalytic pyrolysis HMF. HMF was water soluble and the high water solubility, the influence of water content was discussion in this work. As shown in entry 7 (Table 5), an 80 wt% HMF aqueous solution was used in this experiment. By applying aqueous solution of HMF, the conversion of HMF (96.12%) was higher than the direct catalytic pyrolysis of HMF. When use 80 wt% HMF aqueous solution as feed at the same conditions to catalytic pyrolysis, the HMF feed rate (1.6 ml/h0.8) was smaller than the experiment in entry 4 (the HMF feed rate 1.6 ml/h). At this time, the feed rate was decreased to 1.28 g/h and the conversion of HMF regular meets with the result in Table 4. The selectivity for aromatic hydrocarbons was not changed (the aromatic hydrocarbons yield was 48.89%), whereas the selectivity of Xylene (the yield from 2.86% to 10.73%) increased. The result suggested that HZSM-5 (2) was also applied catalytic pyrolysis aqueous solution of HMF for the production of aromatic hydrocarbons.

20

10

0

0 1

2

3

4

5

Run Fig. 4. Products distributions of at 600 °C in recycle catalytic runs. (Reaction conditions: reaction temperature 600 °C; catalyst HZSM-5 (2) 1.0 g; HMF 2.0 g (velocity 1.6 ml/h); N2 10 ml/min).

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Y. Zhao et al. / Bioresource Technology 147 (2013) 37–42 100

Benzene Toluene Xylene Naphtal MNP DMF 5-MF DFF other aromatics

90

Selectivity(%)

80 70 60 50 40 30 20 10 0 1

2

3

4

5

Run Fig. 5. Aromatic selectivity for catalytic pyrolysis of HMF in catalyst cycle.

of acid sites (Carlson et al., 2009; Hilten et al., 2011). The highest aromatic hydrocarbons yields (48.99% carbon yield) and least amount of coke (6.20% carbon yield) were obtained in catalytic pyrolysis of HMF with HZSM-5 (2) as catalyst. Ga/HZSM and In/ HZSM catalysts were tested in this work. The conversion of HMF was similar to HZSM-5 (2) catalyst, but the aromatic hydrocarbons selectivity was low. 3.7. Catalyst regeneration With regard to the conversion of HMF to aromatic hydrocarbons, catalyst stability tests shown in Fig. 4. HZSM-5 (2) regeneration test was carried out at 600 °C. After the experiment of pyrolysis, some coke was formed on the surface of the catalyst. The catalyst effectively can be regenerated in an air stream at 600 °C. Several recycles of the catalyst did not show deactivation of the catalyst. The conversion of HMF was similar to first run. The change in the yield of coke was not obvious, but the yield of gas increases from 33.94% to 41.85%. The yield of aromatic hydrocarbons was not clear changed in the Fig 4. As shown in Fig. 5, the selectivity for benzene was not changed, whereas the selectivity of toluene (selectivity from 34.92% to 38.44%) increased slightly in five runs. These results suggested that HZSM-5 (2) was stable for the production of aromatic hydrocarbons. 4. Conclusions In summary, this work has demonstrated that the HMF can be transformed into aromatic hydrocarbons through catalytic pyrolysis. Four zeolites, b-zeolite, HZSM-5, Ga/HZSM and In/HZSM was examined in order to obtained high yield of aromatic hydrocarbons at catalytic pyrolysis of HMF. The effects of reaction temperatures, feed rate and catalysts on the main pyrolytic products are analyzed. Under optimized conditions, HMF generated aromatic hydrocarbons in 48.99% carbon yield at 600 °C. HZSM-5 (Si/ Al = 50) was most effective for catalytic pyrolysis of HMF, and catalyst active sites was stable. Acknowledgements

of

The authors are grateful to the National Basic Research Program China (2013CB228103, 2012CB215306), NSFC(21172209),

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