Direct Liquefaction of Sawdust in Supercritical Alcohol over Ionic

Subscriber access provided by UNIV OF UTAH

Article

Direct liquefaction of sawdust in supercritical alcohol over ionic liquid nickel catalyst: Effect of solvents Qingyin Li, Dong Liu, Linhua Song, PINGPING WU, and Zifeng Yan Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/ef500634e • Publication Date (Web): 22 Sep 2014 Downloaded from http://pubs.acs.org on October 5, 2014

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 31

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

Direct liquefaction of sawdust in supercritical alcohol over ionic liquid nickel catalyst: Effect of solvents Qingyin Lia,b, Dong Liua1, Linhua Songb, Pingping Wua, Zifeng Yana2 a

State Key Laboratory of Heavy Oil Processing, PetroChina Key Laboratory of

Catalysis, China University of Petroleum, Qingdao 266580, China b

College of Science, China University of Petroleum, Qingdao 266580, China

Corresponding author, E-mail address: [email protected]; [email protected];

1

Corresponding author: Dong Liu (D. Liu), E-mail: [email protected]

2

Corresponding author: Zifeng Yan (Z. Yan), E-mail: [email protected], Fax: +86-532-86981295

ACS Paragon Plus Environment

Energy & Fuels

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

Abstract: The effect of different solvents on the hydro-liquefaction of sawdust with ionic liquid nickel catalyst was investigated. Subsequently, effects of different parameters on the liquefaction behavior of sawdust were explored with the suitable solvent. The optimized results with bio-oil yield of 58.51% were obtained using ethanol solvent at 320 oC and 10 min with solvent/biomass of 10 mL/g. The higher heating values of the bio-oil was 26.02 MJ·kg-1, which was higher than that of sawdust. According to the GC-MS analysis, the major compound in light oil was ethyl esters, and the components of heavy oil were mainly consisted of ethyl benzene other benzene derivatives.

Keywords: Solvent effect; Hydro-liquefaction; Bio-oil; Supercritical ethanol; Biomass


Page 2 of 31

Page 3 of 31

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

1. Introduction Considering the actual fossil fuel reserves and climate change, it is urgent to find alternative energy sources in terms of sustainable development. Biofuels, as a renewable energy resource, have drawn considerable attentions in the past decades.1 Compared with the first generation biofuels, 2nd generation fuels derived from lignocellulosic biomass were considered as a preferred solution.2 They are generally composed of lignin, cellulose and hemicellulose, which are not competing with human beings and animal’s food supplies.3Additionally, the fact is that CO2 emitted from the utilization of biofuels can be transformed into fuels through the photosynthesis of plants. The other advantages of lignocellulosic biomass include their abundant feedstock, availability and environment friendly due to their less sulfur and nitrogen contents.4

Thermo-chemical conversion processes have four options including combustion, gasification, pyrolysis and liquefaction.5.6Obviously, the higher temperature was required during the pyrolysis and gasification process, which could lead to undesired cross-linking reaction. However, less energy is required for the direct liquefaction method as it can be realized at a lower temperature. Furthermore, liquefaction process can move oxygen presented in the raw materials to obtain the bio-oil with a higher heating value (HHV) similar to that of petroleum (~40 kJ g-1).

Most importantly, implementation with additional reactants or atmospheres can be performed during the liquefaction process, where the products can be tailored by the


Energy & Fuels

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

market requirement, e.g., hydrogen or hydrogen donor solvent can be added to inhibit the coke formation and saturate the hydrocarbons. In the liquefaction of lignocellulose, the effect of different solvents was discussed. Beauchet and co-workers found that tetralin introduced as solvent could not only dissolve the biomass but also avoid the re-condensation of the intermediates during the liquefaction reaction.7 Li et al. revealed that1, 4-dioxane-water solvents have synergistic effects on the critical liquefaction of rice straw, resulted in improved decomposition performance of tubular structure of lignocellulose.8 The research on the effect of various solvents (water, acetone and ethanol) on the liquefaction of pinewood was studied, and the highest bio-oil yield could be obtained with employing ethanol.9 Xu et al. achieved the highest conversion of sawdust in the presence of glycerol and ethanol.10 Mazaheri et al. explored effects of different sub/supercritical solvents including methanol, ethanol, acetone and 1, 4-dioxane on the thermal decomposition of oil palm fruit press fiber (FPF),and found that1,4-dioxane performed well to degrade the biomass.11

As is known to all, the ionic liquid with strong hydrogen bond acceptor were used for the dissolution of biomass and/or its ingredients extensively,12 which can break effectively a dominant barrier for the development and utilization of sustainable lignocelluloses.13-14 Due to its excellent capability to dissolve natural biomass, it has attracted increasing attentions as the reaction medium for dissolution of biomass.15 The solubility of 10 wt% of microcrystalline cellulose could be obtained at 100 oC with 1-butyl -3-methylimidazolium chloride ([BMIM] Cl.16 It also was reported that the highest solubility of maple wood power was achieved in [AMIM] Cl and in


Page 4 of 31

Page 5 of 31

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

[BMIM] Cl.17Especially, as the green chemicals, the application of ionic liquid in the biomass liquefaction was favored due to less cost, low vapor pressure, effective dissolution ability and reduced viscosity.18 Additionally, the metal ion in ionic liquid was proved to be a good catalyst for efficient conversion of lignocellulose. Recently, it is reported that metal ion in ionic liquid catalyst plays an essential role in enhancing yield of 5-hydroxymethylfurfural and furfural from microcrystalline.19Besides, the application of Ni based catalyst in direct liquefaction has been studied in the previous paper.7, 20In our study, ionic liquid nickel catalyst, consisted of [BMIM] Br and NiCl2, was utilized in the direct liquefaction process. The [BMIM] Br was selected because of its simple preparation procedures and good dissolution for biomass.

To the best of our knowledge, there are few studied carried out to investigate how these solvents affect the liquefaction behavior of sawdust with ionic liquid nickel catalyst. In this study, to understand the role of solvent in the direct liquefaction of sawdust, effects of various solvents including methanol, ethanol, propanol, acetone, i-propanol and i-butanol on the yield and distribution of products were studied. The suitable solvent was chose to explore the influence of reaction time, temperature, solvent/biomass(S/B) and particle size of biomass on the liquefaction behavior of sawdust. The bio-oils were characterized by gas chromatography-mass spectrometry (GC-MS), elemental analysis (EA). Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilized to characterize the raw material and solid residue.


Energy & Fuels

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

2.

Experimental Section

2.1. Material and Methods. The sawdust from wood industry was washed for 3 times, followed by drying at 105 oC for 15h. The dried lignocellulosic materials were ground with a high-speed rotary cutting mill, and then sieve to the required meshes. The ionic liquid [BMIM] Br was synthesized in our previous work.21All other chemicals, such as acetone and ethanol, were purchased from Sinopharm Chemical Reagent Co., Ltd. The high-pressure micro-autoclave was made in the lab. The illustration of autoclave is shown in Figure 1.

Figure 1.Schematic diagram of the micro-autoclave.

The chemical compositions (cellulose, hemicellulose, lignin, extractives and ash) were determined with Van Soest method.22The elemental compositions (C, H and N)


Page 6 of 31

Page 7 of 31

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

were analyzed by an elemental analyzer (Vario EL Ⅲ). The content of oxygen was estimated by difference. The Higher Heating Value (HHV) was calculated according to the Dulong formula.23, 24

HHV (MJ/kg) =338.2wt %(C) +1442.8(wt. %(H)-wt. %(O)/8)

(1)

The analysis results of chemical and elemental composition are shown in Table 1.

Table 1. Chemical and elemental compositions of sawdust.

Elemental composition (wt. %)

Chemical composition (wt. %)

C

47.68

cellulose

48.27

H

6.30

hemicellulose

19.50

N

0.45

lignin

19.80

O

45.57

extractives

11.40

ash

0.97

HHV/MJ kg-1

17.00

2.2. Experimental Procedures and Product Separation. In a typical run, the reactor was charged with 1g sawdust, 10 ml various solvents, 1wt. % [BMIM] Br and 300µg/g Ni-based catalyst. Then the reactor was sealed and displaced by pure hydrogen for three times. Subsequently, the reactor was pressurized to 4.0MPa, and heated up to the desired temperature and maintained for the desired time. After the reaction, it was cooled to room temperature in a cooling water bath immediately. The gaseous product was vented, and the mixtures (liquid and solid products) inside were filtered through a pre-weighed filter paper, and the remaining residue was rinsed with ethanol and acetone until the elution become colorless, respectively. Then the “solid


Energy & Fuels

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 8 of 31

residue” (SR) and filter paper was dried at 110oC overnight before weighing. The ethanol was evaporated to remove the solvent, and the resulting product was defined as “light oil” (LO). Subsequently, the collected liquid was defined as “heavy oil” (HO) after the acetone was evaporated. The specific procedures are showed in Figure 2. The yields and conversion of products are defined as follows: Yield of light oil =

mass of light oil ×100% mass of sawdust

(2)

Yield of heavy oil =

mass of heavy oil ×100% mass of sawdust

(3)

mass of residue ×100% mass of sawdust

(4)

Yield of residue=

Conversion of sawdust=

mass of sawdust-mass of residue ×100% mass of sawdust

Yield of gasa =100%-yield of bio-oil-yield of residue a

(5) (6)

The yield of gas showed in the calculation formulae represented the yield of

evaporated hydrocarbons, water and gaseous products. All the yield and conversion were calculated based on a dry raw material introduced into the reactor.

Figure 2. Products separation and analysis.


Page 9 of 31

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

2.3. Characterization. FT-IR analysis was performed on a Nicolet 6700 FT-IR spectrometer to determine the functional groups. Gas chromatography-mass spectrometry (GC-MS) was performed on a Trace GC-MS system with an Agilent model DB-35MS column (30m×0.25mm×0.25µm) to analyze the composition of the liquid products. The compounds were identified with the NIST library of mass spectra. The crystalline phases of samples were determined by XRD measurement on a Rigaku D/MAX-IIIC X-ray diffractometer with a scanning speed of 4° min-1, using Cu Kα radiation (λ=1.936 Å) and a filament current of 40 mA. Scanning electron microscopy (SEM) was conducted using an S-4800 high-resolution analytical field emission scanning electron microscope with an operating voltage of 5.0 kV.

3. Results and Discussion

3.1. Effect of Solvent Types. The product yields and distributions with different solvents are illustrated in Figure 3. Effect of solvents (methanol, ethanol, propanol, acetone, i-propanol and i-butanol) on the hydro-liquefaction of sawdust was investigated. It can be seen that liquefaction of sawdust highly depends on types of solvents. Among these tested solvents, the highest bio-oil yield of 53.74% was obtained when methanol was used. The bio-oil yields obtained with employing ethanol, propanol, acetone, i-propanol and i-butanol are 42.96%, 38.04%, 45.09%, 42.77% and 40.04%, respectively. It was reported that free radical reaction and the ionic reactions including nucleophilic, electrophilic and elimination reactions


Energy & Fuels

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

occurred in the reactor.25Obviously, these reactions mostly are relevant to the polarity of reaction system. The differences in conversion and bio-oil yield obtained from various solvents may be related to polarity of solvents. Therefore, it can be deduced that higher conversion and bio-oil yield were achieved in the solvents with higher polarity. The dipole moment of methanol, ethanol, propanol, i-propanol and i-butanol are about 1.70, 1.69, 1.68, 1.6 and 1.66D, thus among these solvents, methanol was the most effective on the conversion of sawdust under the identical experimental conditions.

Figure 3. Effect of solvent types on the product yield at 320 oC for 30 min with solvent/biomass ratio of 10:1.

However, it is very interesting to note that, in spite of the highest dipole moment (2.88D) of acetone, the highest yield of bio-oil was not achieved as expected. It is not explained universally the differences in the conversion of sawdust due to the


Page 10 of 31

Page 11 of 31

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

differences in polarity of solvents. As is known to all, these physical properties of the supercritical solvents are pressure or temperature-dependent. Thus, the reaction performance in different solvents probably changed with the temperature or pressure. The interactions between solvents and sawdust could be enhanced as the activity of solvent increased.11 Therefore, one possible reason is that the polarity of supercritical acetone under reaction condition will be different from that of acetone at the ambient condition. Besides, the influence of solvents on the conversion and bio-oil yield was different due to different biomass species. Duan et al. have investigated the effect of solvents on the chemical conversion of Chlorella pyrenoidosa, and found that the bio-oil yield in acetone was higher than that of produced in methanol and ethanol.26It can be explained that the component and structure of sawdust was totally different from that of microalgae, and thus lead to different results.

Although the bio-oil yield observed in methanol was higher than that produced in other solvents, in view of economic and environmental perspective, ethanol seems to be an optimal choice. On the one hand, methanol is a poisonous chemical, and ethanol is non-toxic and environmentally benign solvent. On the other hand, ethanol is cheap and sustainable, which can be derived from the fermentation of biomass as the desired production.27Additionally, according to the GC-MS results, the ethanol acts as solvent as well as reactant in the liquefaction process, which can facilitate effectively conversion of sawdust.

3.2. Effect of temperature. The higher temperature ranging from 280 to 360 oC were


Energy & Fuels

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

tested for direct liquefaction of sawdust to produce bio-oil. The experimental results are shown in Figure 4.

The results clearly displayed that the yield of gaseous product was increased obviously from 280 to 360 oC, whereas the yield of solid residue was declined sharply. The bio-oil yield increased from 41.04% to 42.96% as the temperature increased from 300 to 320 oC. When the temperature exceeded 320 oC, the yield of bio-oil was gradually decreased with the elevated temperature. On the contrary, the trend of gaseous yield showed the opposite direction, which may be attributed to further thermal cracking of bio-oil. These findings were consistent with the results from the conversion of Dunaliella tertiolectra for bio-oil.27

Figure 4. Effect of temperature on the product yield for 30 min with solvent/biomass ratio of 10:1.


Page 12 of 31

Page 13 of 31

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

The main reaction was thermal cracking of sawdust as the elevated temperature was conducive to the liquefaction. However, higher temperature also could promote further decomposition of bio-oil or intermediate.

There two competitive reactions existed during the liquefaction process. On the one hand, the liquid products undergo reactions including cyclization, re-condensation and re-polymerization that ultimately formed residue solid. The decomposition of bio-oil can produce gaseous products. These two main factors may cause decrease of bio-oil yield. On the other hand, the decomposition of solids and condensation of gases can increase the yield of bio-oil.9 The similar results were obtained from liquefaction of rice husk for bio-oil.28 It can be deduced that the first reaction was dominant when the temperature beyond the critical point. The decomposition of bio-oil may be the main process, resulted in the liquid yield decreased and gas yield increased.

3.3. Effect of residence time.


Energy & Fuels

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

Figure 5. Effect of reaction time on the product yield at 320 oC with solvent/biomass ratio of 10:1.

To investigate the effect of reaction time on the hydro-liquefaction of sawdust, the reaction was conducted at 320 oC and S/B ratio of 10/1 mL/g by varying the holding time from 10 to 50 min. The reaction results are shown in the Figure 5.

It is obvious that the residence time had a significant effect on the product yield under the reaction conditions. The shortest residence time rendered the highest bio-oil yield. The bio-oil yield decreased from 58.51 to 36.85 % as the reaction time increased from 10 to 50 min. Along with the reaction time prolonged, a remarkable decrease of bio-oil yield was observed, which may be due to the further decomposition of bio-oil. The large molecules in bio-oil took place the hydrocracking reaction, and then converted to more volatile component.26 The gaseous yield increased with increasing time as the bio-oil yield decreased. As inferred from the Figure 5, the yield of solid residue slightly decreased as increasing time from 10 to 50 min. On the one hand, the residue yield may increase due to the re-polymerization/re-condensation of intermediates. Interestingly, on the other hand, the secondary reaction took place when the reaction time was prolonged, at which the solids can decompose to lighter fragments. It is speculated that the influence of reaction time on the latter reaction outweigh the former one based on our results. Some previous reports related to liquefaction of biomass showed that the shorter time was beneficial for conversion of biomass to produce bio-oil effectively.29, 30


Page 14 of 31

Page 15 of 31

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

3.4. Effect of solvent/biomass ratio. As is shown in Figure 6, influence of solvent/biomass ratio on the product yield and conversion rate was investigated by varying the amount of ethanol from 4 to 12 ml.

The yield of solid residue decreased continuously with increasing S/B ratio as the sufficient solvent prevented the re-condensation/re-polymerization of intermediates and then inhibited the forming of residue. The bio-oil yield increased with increasing ethanol amount firstly, and then decreased at the concentration higher than 10/1 mL/g, at which the highest bio-oil yield was found to be 42.96%.

Figure 6. Effect of solvent/ biomass on the product yield at 320 oC and 30 min Clearly, a higher solvent/biomass ratio favors conversion of sawdust, lead to higher bio-oil yield and lower solid residue yield. Regarding the conditions with a lower ethanol/biomass ratio, a higher biomass concentration prevailed throughout the process. Therefore, the sawdust and ethanol could not form a well-mixed suspension


Energy & Fuels

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

in the reactor, which weakened the function of solvent and limited the solvolysis of sawdust, and thus it could lead to a higher residue yield and lower bio-oil yield. Another possible reason is that the lower ethanol concentration could not dissolve well the intermediates with high molecular weight, resulted in occurrence of the cross-linked or reverse reaction during the liquefaction process. When the S/B ratio was greater than 10 mL/g, the corresponding bio-oil yield showed a decrease trend. Recent study also showed the similar trend that excessive amount of solvent could prevent the liquefaction of rice husk in ethanol-water system.28

3.5. Effect of Particle Size.

Figure 7. Effect of particle size on the product yield at 320 oC with solvent/biomass ratio of 10:1

The direct liquefaction process in the study is a tri-phase system including gas, solid


Page 16 of 31

Page 17 of 31

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

and liquid phases. Therefore, the mass transfer and diffusion are very crucial to the reaction. Four various meshes (20, 40, 60 and 80 mm) sawdust particles were tested in the liquefaction of sawdust. As shown in Figure 7, the particle sizes have little influence on the yield of solid residue, gaseous products and bio-oil. This is probably due to the characteristic of supercritical solvents that render a good heat and mass transfers and overcome the energy transfer limitation.4 Furthermore, the well-mixed suspension in the reactor also enhanced biomass conversion and weakened the role of particle size. Therefore, the parameter of particle size is less significant on the product yield and conversion. It should be noted that the pretreatment of sawdust towards to desired particle sizes is time-consuming and cost-ineffective. However, larger sawdust particle could also not mixed with solvents well, thus in the work the particle size of 60 mm is selected.

3.6. GC-MS analysis of bio-oil. The GC-MS analysis was carried out to identify the components of bio-oil from the hydro-liquefaction of sawdust. The identification of the main compounds was performed using a NIST mass spectral database.

3.6.1. Light oil

Table 2. GC-MS analysis of light oil.

No.

RT(min)

Name of compound

Relative content (wt. %)

1

5.67

Acetic acid

0.26

2

6.51

2-Pentanol

0.20

3

7.4

Hydroxyacetic acid ethyl ester

14.19


Energy & Fuels

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 18 of 31

No.

RT(min)

Name of compound


4

7.9

2-Hydroxy-propionic acid ethyl ester

8.53

5

10.33

2-Furanmethanol

0.11

6

10.47

2-Hydroxy-butyric acid ethyl ester

1.99

7

10.73

2-Methoxy-1,3-dioxolane

0.37

8

11.63

2-Hydroxy-3-methyl-butyric acid ethyl ester

0.16

9

12.63

2,2-Diethoxy-ethanol

0.23

10

13.02

Phenol

2.59

11

13.31

2-Ethoxytetrahydrofuran

0.17

12

14.19

3-Methyl-cyclopentane-1,2-dione

0.68

13

14.34

Furan-2-carboxylic acid ethyl ester

0.24

14

14.53

4-Oxo-pentanoic acid ethyl ester

0.88

15

14.83

Pantolactone

21.03

16

15.03

2-Methyl-4-oxo-pentanoic acid ethyl ester

0.1

17

15.12

4-Methoxy-phenol

1.38

18

15.82

3-Ethyl-2-hydroxy-cyclopent-2-enone

0.61

19

15.98

3-Hydroxy-butyric acid butyl ester

0.48

20

16.18

2-Methyl-succinic acid diethyl ester

0.46

21

16.36

Succinic acid diethyl ester

2.46

22

16.68

2-Ethyl-malonic acid diethyl ester

0.59

23

16.8

2-Methoxy-6-methyl-phenol

0.32

24

17.1

2,5-Diethoxy-tetrahydro-furan

0.63

25

17.23

2,3-Dimethyl-octan-3-ol

1.41

26

17.4

2-Hydroxy-3-methyl-succinic acid diethyl ester

0.18

27

17.54

Pentanedioic acid diethyl ester

1.38

28

17.71

4-Ethyl-2-methoxy-phenol

1.94

29

18.06

5-Methyl-3-propyl-hexanoic acid methyl ester

4.48

30

18.35

Dec-2-enoic acid ethyl ester

1.03

31

18.51

2,6-Dimethoxy-phenol

12.69


Page 19 of 31

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

No.

RT(min)

Name of compound


32

18.75

2,3-Dimethoxy-phenol

0.28

33

18.98

2-Ethyl-2-propyl-hexan-1-ol

0.73

34

19.25

2-Methoxy-4-propenyl-phenol

4.73

35

19.5

2,3,4,5-Tetrahydroxy-hexanal

1.67

36

19.71

1,2,3-Trimethoxy-5-methyl-benzene

2.53

37

19.97

1-(4-Hydroxy-3-methoxy-phenyl)-propan-2-one

0.37

38

20.23

3,4-Diethyl-hexa-2,4-dienedioic acid dimethyl ester

5.12

39

20.5

(4-Hydroxy-3-methoxy-phenyl)-oxo-acetic acid

0.42

40

20.87

4-Allyl-2,6-dimethoxy-phenol

1.21

41

21.12

3-(4-Hydroxy-3-methoxy-phenyl)-propionic acid 0.18 ethyl ester 42

21.38

1-(2,6-Dihydroxy-4-methoxy-phenyl)-butan-1-one

0.24

43

21.65

Benzo[1,3]dioxol-5-yl-phenyl-methanone

0.25

44

21.89

Diphenyl-acetic acid ethyl ester

0.14

45

22.22

Hexadecanoic acid ethyl ester

0.39

3.6.2 Heavy oil

Table 3. GC-MS analysis of heavy oil.

No

RT (min)

Name of compound


1

5.61

Toluene

0.26

2

7.09

2-Pentanone, 4-hydroxy-4-methyl-

0.79

3

7.35

o-Xylene

8.38

4

7.61

Ethylbenzene

78.9

5

7.91

Cyclohexane

0.09

6

8.01

Cyclopentane, 1,3-dimethyl-, trans-

0.09

7

8.08

Cyclohexane, ethyl-

0.09


Energy & Fuels

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 20 of 31

8

8.3

p-Xylene

7.07

9

9.38

Cyclohexane, propyl-

0.79

10

10.29

Benzene, 1,2,3-trimethyl-

0.09

11

10.57

Benzene, propyl-

0.18

12

10.76

Benzene, 1-ethyl-2-methyl-

2.09

13

13.04

Phenol

0.09

14

14.82

Pentane, 2,2,3-trimethyl-

0.09

15

16.81

Heptane, 2,6-dimethyl-

0.18

16

17.08

Octane, 2-methyl-

0.09

17

17.27

Heptane, 3,4,5-trimethyl-

0.18

18

17.55

Nonane, 4-methyl-

0.09

The relative percent area for each compound identified was defined by the percentage of the chromatographic area of the compound out of the total area. The percent area values illustrated in the table only represent the relative content of compound in the bio-oil that can pass through the GC column.

As illustrated in table 2, the major compounds in the light oil were ethyl ester (64.01%), phenol and derivatives (25.14%), ether (3.7%), alcohol (2.68%) and some minor species (aldehyde and carboxylic acid).

The ethyl esters, as the dominant category, are produced following the proposed approaches. Ethanol, acting as reactant, can react with acids to form ester. Additionally, the ethanol is considered as hydrogen donor solvent, which reacted via the hydride transfer of their α hydrogen.

The previous literatures showed that phenol compounds and derivatives, such as


Page 21 of 31

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

4-methoxy-phenol and 4-ethyl-2-methoxy-phenol, were possibly derived from the degradation of lignin component in the sawdust because the derived phenol compounds have similar structure with lignin monomer.31Besides,the decomposition of furfural and its derivatives can also contribute to the production of phenolic compounds.1

The supercritical ethanol can be regarded as the weak acid. During the acid-catalyzed process, dehydration and depolymerization of cellulose and hemicellulose took place, along with the generation of the monosaccharide. Subsequently, the monosaccharide could react with ethanol towards the formation of furan derivatives and acids.32

In terms of the heavy oil, according to GC-MS results, the major compounds identified in the heavy oil were ethyl benzene, xylene and its derivatives. This may be resulted from the decomposition of lignin monomer with subsequent stabilization with hydrogen radicals from hydrogen and ethanol. It can be explained that the species of compound were less than that of light oil, due to some high molecular and non-volatile compounds that were unable to be detected through GC-MS existed. Besides, most oxy-compounds may be transferred to light oil when ethanol was used as extractant.

3.7. Characterization of Solid Residue

3.7.1 FTIR analysis.


Energy & Fuels

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

Figure 8. FTIR spectrum of sawdust and solid residue collected under different solvents

The Fourier transform infrared spectroscopy (FTIR) spectrum for the raw material and residue collected at different solvents are illustrated in Figure 8. The similar IR adsorptions of solid residue are displayed in despite of various solvents, suggesting that similar chemical structures of liquefied products.

The band at 3433cm-1is assigned to the adsorption of typical hydroxyl group, which was caused by the combination and overlap of aliphatic and aromatic O-H stretching from the phenolic compounds. The bands between 2973 and 2921cm-1are due to symmetrical and asymmetrical C-H stretching vibrations of methyl and methylene groups. Besides, the band at 1379cm-1representing the C-H stretching vibration indicates that alkanes are included in the residue. The absorption peak at 1740cm-1 in


Page 22 of 31

Page 23 of 31

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

the sawdust represents the -C=O stretching vibration, which is the characterization adsorption of ketone, aldehyde and ester group. However, the disappearance of peaks corresponding to carbonyl group in the solid residue may be due to the alcoholysis of hemicellulose.

The band at 1621cm-1 is contributed to the benzene backbone C=C stretching vibration of lignin. The broad adsorption from 1421 to 1629cm-1 belongs to the aryl group. Meanwhile, the adsorption peaks between 880 and 670cm-1also indicate the existence of aromatic ring, which are from the out-of-plane vibrations of methyl or other alkyl constituents on the aromatic group. Adsorption peaks at 1050 and 1089 cm-1 are identified as O-H bending vibration and C-O-C stretching vibration, respectively, which belong to the characteristic groups of cellulose. It is shown that the adsorption peak at 784 cm-1disappeared in the residue, which attributed to the formation of the acid and alcohol condensation and aromatic substitution type of three adjacent hydrogen atom, respectively.33

3.7.2. XRD analysis.


Energy & Fuels

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

Figure 9. XRD patterns of sawdust and residues obtained under different solvents.

It is clear that quantitative determination of the relative crystallinity of cellulose in the biomass is difficult because the hemicellulose and lignin with complicate structures are included. The X-ray characterization of the crystallinity index is the best option to explore the influence on biomass crystallinity. Figure 9 shows the change of crystalline structure of raw materials after the liquefaction reaction.

The X-ray diffraction pattern of sawdust shows three distinct peaks at 2θ = 14.9°,16.5° and 22.2°, which are characteristic peaks of cellulose, corresponding to the (11 0 ), (110) and (200) planes of cellulose.34,35 However, these characteristic peaks (2θ=16.5° and 22.2°) in the residues obtained with employing different solvents disappeared, while the diffraction peak corresponding to cellulose ( 11 0 ) was still existed. These strongly support that the crystal structure of cellulose in the sawdust was destroyed.


Page 24 of 31

Page 25 of 31

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

The distinct weakened signals of cellulose in the residues revealed that direct liquefaction reaction of sawdust took place. Meanwhile, these also suggest that the crystallization/graphitization reaction of carbon occurred in the liquefaction process. The similar results of crystallization of carbon have been observed in some previous studies on the preparation of pyrolysis of coal.36

3.7.3 SEM analysis.

Figure 10. SEM images of sawdust and solid residue

The morphological structure change of sawdust will be a good index to investigate the conversion of sawdust. The SEM images of raw material and solid residue obtained under the optimal condition are shown in the Figure 10A-D. As shown in Figure 10A and B, structures of sawdust particle are observed with an organized and smooth surface, and a group of solid cells is bounded together, which


Energy & Fuels

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 26 of 31

appear an apparent stripe clearly. However, structures of liquefied product in the Figure 10C and D exhibit a rough and loose surface, which is distinctly different from the original structures. It can be explained that the cellulose skeleton was totally vanished under harsh condition. The fiber bundles was thermal cracked into irregular granules, indicating the liquefaction reaction occurred completely as the raw sawdust structure was destroyed.

3.8. Elemental analysis.

Table 4. Elemental analysis of the bio-oil, residue and sawdust

Properties

Bio-oil Light oil

Heavy oil

Sawdust

Residue

C/wt%

58.77±0.01

70.41±0.02

47.68±0.08

51.46±0.01

H/wt%

8.28±0.02

5.66±0.04

6.30±0.00

4.41±0.00

Oa/wt%

32.17±0.02

22.89±0.06

45.57±0.08

43.40±0.04

N/wt%

0.78±0.01

1.04±0.00

0.45±0.00

0.73±0.03

Heating values/MJ kg-1

26.02±0.04

27.85±0.07

17.00±0.04

15.94±0.01

H/C

1.69±0.04

0.96±0.007

1.58±0.002

1.03±0.0002

O/C

0.41±0.0006 0.24±0.0007 0.81±0.002

0.63±0.0007

a

Caculated by difference and neglected the sulfur content

Table 4 presents the elemental analysis of bio-oil, solid residue and sawdust. Compared with raw material, the light oil includes a higher carbon and hydrogen content and a lower oxygen content, resulted in the increase of heating values (17.00 to 26.02MJ·kg-1). It can be deduced that the hydrocracking and hydrogenation


Page 27 of 31

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

reaction occurred during the hydro-liquefaction process. In comparison between light oil and heavy oil, the H/C ratio of light oil is much higher than that of heavy oil. These results may be attributed to the fact that the components in the light oil contain less aromatic compounds, in other words, the unsaturated degree of heavy oil is higher than that of light oil, which is consistent with results from GC-MS. However, the O/C ratio in heavy oil is lower than that of light oil because the main components of light oil are oxy-compounds, and the dominant ones in heavy oil are aromatic compounds.

4. Conclusion In this study, sawdust was effectively liquefied with different tested solvents including methanol, ethanol, propanol, acetone, i-propanol and i-butanol. Some key conclusions are summarized below: (1) In terms of bio-oil yield and environmental perspective, ethanol was studied as the suitable solvent in the hydro-liquefaction of sawdust. (2) The yields of bio-oil increased markedly as the temperature increased from 300 to 320 o

C, but the bio-oil yield dropped continuously when the temperature was increased

further to 360 oC. These results suggested that the highest bio-oil yield could be obtained at 320 oC. (3) The maximum bio-oil yield was achieved from sawdust liquefaction at the shortest reaction time of 10 min with employing ethanol as the reaction medium. (4) The solvent/biomass ratio of 10 mL/g was found to be the optimized condition for hydroliquefaction of sawdust to produce the bio-oil using ethanol. (5) The influence of particle sized on the product yields and distribution


Energy & Fuels

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

could be neglected in the liquefaction process. (5) The GC-MS characterization clarified that light fraction was mainly composed of ethyl ester, phenol and phenol derivatives. However, the components of heavy oil were mainly ethyl benzene xylene and its derivatives. (6) The FTIR, XRD and SEM measurement for solid residue from hydroliquefaction of sawdust revealed that the liquefaction reaction of sawdust took place at 320 oC and 10 min with 10 mL/g using ethanol solvent. (7) According to elemental analysis, the obtained light oil had higher heating value than that of sawdust.

Acknowledgment This work has been financially supported by the Key Joint Foundation of PetroChina and Natural Science Foundation of China (No. U1362202), the PetroChina key programs on oil refinery catalysts (2010E-1908, 2010E-1903) and National Natural Science Foundation of China (21176259).


Page 28 of 31

Page 29 of 31

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

References 1. Yang, J.; Dai, G.H.; Ma, L.Y.; Jia, L.M.; Wu, J.; Wang, X. H. Renew. Sust.Energ. Rev.2013, 18, 478-485. 2. Sims, R.H.; Mabee, W.; Saddler, J.N.; Taylor, M. Bioresour. Technol. 2010, 101, 1570-1580. 3. Gan, J.; Yuan, W.Q. Appl. Energy. 2013, 103, 350-357. 4. Akhtar, J.; Amin, N.A.S. Renew. Sust.Energ. Rev. 2011, 15, 1615-1624. 5. Rezzoug, S.A.; Capart, R. Energy Convers. Manage. 2003, 44, 781-792. 6. Lee, J.Biotechnol. 1997, 83, 37-46. 7. Beauchet, R.; Pinard, L.; Kpogbemabou, D.; Laduranty, D.; Lemee, L.; Lemberton, J.L.; Bataille, F.; Magnoux, M.; Amibles, A.; Barbier, J.Bioresour. Technol. 2011, 102, 6200-6207. 8. Li, H.; Yuan, X.; Zeng, G.; Tong, J.; Yan, Y.; Cao, H.; Wang, L.; Cheng, M.; Zhang, J.; Yang, D. Fuel Process. Technol. 2009, 90, 657-663. 9. Liu, Z.; Zhang, F.S. Energy Convers. Manage. 2008, 49, 3498-3504. 10. Xu, J.; Jiang, J.; Dai, W.; Xu, Y. Process Saf. Environ. Prot. 2012, 90, 333-338. 11. Mazaheri, H.; Lee, K.T.; Bhatia, S.; Mohamed, A.R. Bioresour.Technol. 2010, 101, 7641-7. 12. Zakrzewska, M.E.; Bogel-Lukasik, E.; Bogel-Lukasik, R. Energy & Fuels. 2010, 124, 4974-4975. 13. Klaas, M.R.G.; Schone, H. ChemSusChem. 2009, 2, 127-128. 14. Zhang, Y.G.; Chan, J.Y.G. Energy Environ. Sci. 2010, 3, 408-417.


Energy & Fuels

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

15. Fort, D.A.; Remsing, R.C.; Swatloski, R.P.; Moyna, P.; Moyna, G.; Rogers, R.D. Green Chem. 2007, 9, 63-69. 16. Swatloski, R.P.; Spear, S.K.; Holbrey, J.D.; Rogers, R.D. J. Am. Chem.Soc. 2002, 124, 4974-4975 17. Lee, S.H.; Doherty, T.V.; Linhardt, J.S. Biotechnol. Bioeng. 2009, 102, 1368-1376. 18. Rogers, R.D.; Seddon, K. Science. 2003, 302, 792-793. 19. Tao, F.R.; Song, H.L,; Chou, L.J. J MolCatal A: Chem. 2012, 357, 11-18. 20. Yang, C.; Jia, L.; Chen, C.; Liu, G.; Fang, W. Bioresour. Technol. 2011, 102, 4580-4. 21. He, A.Z.; Wang, K.; Liu, H.G.; Yuan, L.; Zhang, Y. Advances in Fine Petrochemicals. 2009,10,22-24. (in Chinese) 22. Van Soet, P.J.; J. Ass.Offic.Agr. Chem. 1963, 46, 829-835. 23. Zhong, C.; Wei, X. Energy. 2004, 29, 1731-1741. 24. Huang, H.; Yuan, X.; Zeng, G.; Wang, J.; Li, H.; Zhou, C.; Pei, X.; You, Q.; Chen, L. Fuel Process. Technol. 2011, 92, 147-153. 25. Kabyemela, B. M.; Adschiri, T.; Malaluan, R. M.; Arai, K.; Ohzeki, H. Ind. Eng. Chem.Res. 1997, 36, 5063-5067. 26. Duan, P.; Jin, B.; Xu, Y.; Yang, Y.; Bai, X.; Wang, F.; Zhang, L.; Miao, J. Bioresour. Technol. 2013, 133, 197-205. 27. Chen, Y.; Wu, Y.; Zhang, P.; Hua, D.; Yang, M.; Li, C.; Chen, Z.; Liu, J. Bioresour. Technol. 2012, 124, 190-8. 28. Liu, Y.; Yuan, X.Z.; Huang, H.J.; Wang, X.L.; Wang, H.; Zeng, G.M. Fuel Process.


Page 30 of 31

Page 31 of 31

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

Technol. 2013, 112, 93-99. 29. Qu, Y.; Wei, X.; Zhong, C. Energy. 2003, 28, 597-606. 30. Akalin, M.K.; Tekin, K.; Karagoz, S. Bioresour.Technol. 2012, 110, 682-7. 31. Chumpoo, J.; Prasassarakich, P. Energy & Fuels. 2010, 24, 2071-2077. 32. Peterson, A.A.; Vogel, F.; Lachance, R.P.; Fröling, M.; Antal, J.M.J.; Tester, J.W. Energ. Environ. Sci. 2008, 1, 32-65. 33. Sun, P.Q.; Heng, M.X.; Sun, S.H.; Chen, J.W. Energy Convers. Manage. 2011, 52, 924-933. 34. Ishikawa, A.; Kuga, S.; Okano, T. Polymer. 1998, 39, 1875-1878. 35. Borysiak, S.; Doczekalska, B. Fibre Text East Eur. 2005, 13, 87-89. 36. Tsubouchi, N.; Xu, C.B.; Ohtsuka, Y. Energy & Fuels. 2003, 17, 1119-1125.


Direct Liquefaction of Sawdust in Supercritical Alcohol over Ionic

Recommend Documents