Article pubs.acs.org/EF
Liquefaction of Macroalgae Enteromorpha prolifera in Sub-/ Supercritical Alcohols: Direct Production of Ester Compounds Dong Zhou, Shicheng Zhang,* Hongbo Fu, and Jianmin Chen* Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, People’s Republic of China ABSTRACT: The liquefaction of “green tide” macroalgae Enteromorpha prolifera in sub-/supercritical alcohols in a batch reactor had been investigated. Effects of the temperature and algae/solvent ratio on the liquefaction yields in methanol and ethanol were studied. The results showed that, under the conditions of the reaction time of 15 min and algae/solvent ratio set at 1:10, the macroalgae in methanol at 280 °C produced a bio-oil yield at 31.1 wt % of dry weight and the ethanol at 300 °C yielded bio-oil at 35.3 wt %. Different from bio-oils obtained by hydrothermal liquefaction of microalgae as well as macroalgae in our previous work, the bio-oils obtained by liquefaction of macroalgae in alcohols are mainly composed of ester compounds. A variety of fatty acid (C3−C22) esters (methyl or ethyl) in the bio-oils obtained in methanol and ethanol, respectively, were qualified by gas chromatography−mass spectrometry, and their relative contents are above 60% of the total area for each bio-oil. In addition, some N-containing compounds, sugars, fatty alcohols/ketones, and very few hydrocarbons were also qualified. Overall, bio-oils obtained in two alcohols are much similar to biodiesel on the composition. The elemental analysis of bio-oils indicated that biooils still have high oxygen contents. Moreover, the bio-oils are found to contain a considerable fraction of light components using thermogravimetric analysis (TGA), and the contents of low-boiling-point (bp < 350 °C) compounds are up to 70% of the weight for both bio-oils; therefore, it might help for the further separation and refining of bio-oils to produce fuels and chemicals.
1. INTRODUCTION Biomass, as a renewable resource, has received increasing attention in recent years because of the gradual depletion of fossil fuels available and the aim of reducing greenhouse gas emissions caused by the use of fossil fuels. Thus far, many efforts have been made to convert biomass to liquid fuels and chemicals by applying thermochemical conversion techniques, including pyrolysis, hydrothermal liquefaction, supercritical fluid technology, etc.1−4 Among these techniques, sub-/ supercritical fluids can covert biomass to liquid fuels in a quick and efficient way for their excellent solvent properties,5,6 which makes it a research focus in the field of bioenergy conversion. Algal biomass, including micro- and macroalgae (seaweeds), has been seen as promising feedstocks for biofuel production. Direct liquefaction of algae in sub-/supercritical water at 250− 380 °C can produce bio-oil of high quality, along with gas, solid char, and aqueous byproducts.7−18 However, the liquefaction of biomass using water as a solvent usually produced a relatively lower yield of water-insoluble oily products than that using other organic solvents, such as methanol, ethanol, 1-propanol, and acetone.19−24 Among all of these solvents, methanol and ethanol have low boiling points and much lower critical points than water. Moreover, the relatively high-molecular-weight products derived, such as cellulose and hemicellulose, are readily dissolved in these alcohols because of their lower dielectric constants when compared to that of water.25 All of these advantages have made methanol and ethanol promising solvents for the liquefaction of biomass. Until recently, there are only a few studies reporting the liquefaction of algae using alcohols. Zou et al.26 studied the liquefaction of microalgae Dunaliella tertiolecta in ethylene glycol at 120−200 °C with 2.4% sulfur acid as the catalyst and © 2012 American Chemical Society
found that the bio-oil was mainly composed of fatty acid methyl ester and fatty acid hydroxyethyl ester with a long chain from C14 to C18. Huang et al.27 obtained bio-oil with a yield up to 45.3% by liquefaction of a high-protein microalga Spinlina in sub-/supercritical ethanol at 280−380 °C. Yang et al.28 produced a high yield (∼72%) of bio-oil from microalgae Dunaliella salina in ethanol under moderate conditions (200 °C, 2 MPa, and 60 min) with Reny-Ni as the catalyst, and the dominant compounds of bio-oil were found to be esters and glycerin. The bio-oils obtained in these studies are somewhat like the biodiesel on the components. The conventional method to produce biodiesel from microalgae is by lipid extraction with solvent and then transesterification of lipids with methanol/ethanol. This process requires a microalga of high lipid content, but the efficient extraction of algal lipids is still a challenge. Another shortcoming of the conventional method is that catalysts (acid/base) are necessary but difficult to recover, and a large volume of wastewater and other solid wastes are also produced. To overcome these problems, Levine et al.29 developed a catalyst-free, two-step approach to synthesize biodiesel involving the hydrolysis of a lipid-rich microalga to wet fatty-acid-rich solids and subsequent esterification with supercritical ethanol. Using the two-step method, 80−90% lipids were separated and the crude biodiesel and fatty acid ethyl ester (FAEE) yields are as high as 100 and 66%, respectively. This method separates algal lipids by hydrolysis in subcritical water; however, for other low-lipid algae, especially macroalgae, it has an obvious limitation, requiring an alga of high lipid content. Aresta et al.30 have even Received: December 15, 2011 Revised: February 27, 2012 Published: February 28, 2012 2342
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Table 1. Characteristics of E. prolifera ultimate analysis (wt %)a
proximate analysis (wt %) VM
b
FC
42.35
a
c
ash
19.54
C
30.10
H
28.75 5.22 inorganic composition of the ash (wt %)a
N
Od
H/C
3.65
32.28
2.18
Na
K
Mg
Ca
Al
Fe
Ni
Ti
Cl
Br
S
P
Si
31.5
9.64
9.05
2.02
4.19
1.32
0.13
0.10
27.1
0.44
6.24
1.27
7.04
All measured on a dry basis. bVM = volatile matter. cFC = fixed carbon. dO (wt %) = 100 − (ash + C + H + N) (wt %).
employed two techniques, supercritical carbon dioxide (scCO2) and thermochemical liquefaction at 250−395 °C, to extract fatty acids from a green macroalgae Chaetomorpha linum and then transesterification to produce biodiesel. Although the thermochemical liquefaction was more efficient, the yield of biodiesel fuel was still very low. To our knowledge, thus far, there are no studies about the liquefaction of macroalgae using alcohols as solvents to produce biodiesel fuel. It is important to explore the production of biofuels or synthesis of value-added chemicals from macroalgae via onestep liquefaction in alcohols, which may help to develop a new path for the use of macroalgae. In the present study, liquefaction of the “green tide” macroalgae Enteromorpha prolifera using sub-/supercritical methanol and ethanol in a batch reactor was investigated. Effects of two alcohols, temperature, and algae/solvent ratio on the liquefaction yields were studied, and the characterization of bio-oils and solid residues were analyzed using elemental analysis, Fourier transform infrared (FTIR) spectroscopy, gas chromatography−mass spectrometry (GC−MS), and thermogravimetric analysis (TGA).
2. MATERIALS AND METHODS 2.1. Materials. Macroalgae E. prolifera used in this study was produced from the Yellow Sea coast in Zhejiang Province. After impurities in the algae were manually removed and sea salts on the surface of algae were washed, the raw material was dried at 60 °C for 12 h and then milled to 50−100 meshes for liquefaction. The ash content of macroalgae was measured at 550 °C, and the volatile matter and fixed carbon were determined by means of TGA. The C, H, and N contents in the macroalgae was measured by elemental analyzer Vario EL III. The composition of the ash was measured by X-ray fluorescence (XRF) using a S4 EXPLORER X-ray spectrometer. The analysis results are shown in Table 1. The reaction solvents, namely, methanol and ethanol (analytical grade), were purchased from Sinopharm Chemical Reagent Co., Ltd. and used as received. 2.2. Liquefaction and Product Separation. The experiments were carried out in a 250 mL GSH-0.25 zirconium cylindrical autoclave, and the scheme of equipment was illustrated in our previous work.15 In a typical experimental run, 10 g of E. prolifera powder and 100 mL of methanol or ethanol were loaded in the autoclave. Then, the autoclave was sealed firmly, and the residue air inside was removed by purging with N2 for 5 min. After that, the autoclave was pressurized to 2.0 MPa with N2 to prevent drastic boiling of solvents during the liquefaction process. The reaction was started by heating the autoclave with stirring at 150 rpm. When the autoclave was heated to the desired temperature, it was held for 15 min and then cooled with running water to room temperature. After the reaction, the gas was vented to the fume hood. The reaction mixture was carefully transferred into a beaker, and the autoclave inside was further rinsed with 100 mL of reaction solvent (methanol or ethanol) for 2 or 3 times and then filtrated. The separation of liquefaction products is depicted in Figure 1. The solvent was removed under reduced pressure in a rotary evaporator at 62 °C for methanol and at 72 °C for ethanol, and the liquid fraction
Figure 1. Separation of liquefaction products. remained was called “raw oil”. The alcohol-insoluble residues were dried at 105 °C for 6 h and then weighed. The raw oil was added with 100 mL of CH2Cl2 [high-performance liquid chromatography (HPLC) grade] and then filtrated to remove the ash, and the ash was also weighed. The bio-oil was obtained by removing CH2Cl2 in a rotary evaporator under reduced pressure at 40 °C. The overall alcohol-insoluble residues and ash were called the solid residue (SR). The experimental errors for the liquefaction yields are lower than 5% by three duplicate runs at the same conditions. The yields of bio-oil, SR, gas, and water were calculated to the feed as follows:
bio‐oil (wt %) =
SR (wt %) =
Wbio‐oil × 100% Walgae
WSR × 100% Walgae
gas + water (wt %) = 1 −
Wbio‐oil + WSR × 100% Walgae
(1)
(2)
(3)
Because the yield of gas and water is obtained by difference, it should be noted that this fraction also includes those volatiles lost during the separation and collection of products. 2.3. Product Analysis. The elemental compositions of bio-oils and residues were analyzed by elemental analyzer Vario EL III. The higher heating value (HHV) of bio-oils was calculated using Mott and 2343
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Spooner’s31 formula: HHV (MJ/kg) = 0.3361C + 1.419H − (0.1532 − 0.0007O)O + 0.0942S (O > 15%). FTIR spectroscopic analysis of raw material E. prolifera and bio-oils was performed by Thermo Nicolet Nexus 470 over a range of 400− 4000 cm−1. All measurements were carried out by means of KBr plates. GC−MS analysis of bio-oil was carried out using Thermo Focus DSQ with a HP-5 ms column (5% phenyl−95% dimethylpolysiloxane, 30 m × 0.25 mm × 0.25 μm), and helium was used as the carrier gas at a flow rate of 1.5 mL/min. A total of 1 μL of dichloromethane solution of bio-oil (0.2 g/10 mL CH2Cl2) was injected into the column in a splitless mode. The injector temperature was set at 280 °C. The temperature program was 3 min at 40 °C and then at 5 °C/min to 300 °C. Compounds were identified using the National Institute of Standards and Technology (NIST) 05 library of mass spectra. TGAs of bio-oils were performed with a Perkin-Elmer Pyris 1 TGA in a nitrogen atmosphere (purity of 99.99%). Bio-oil samples were heated from 25 to 750 °C with a heating rate of 10 °C/min. The gas flow rate was 20 mL/min.
increasing temperature but the bio-oil yield changes slightly, ranging from 28.3 to 31.2 wt %. The yield of gas and water rises with the temperature, while a slight increase is observed when above 280 °C. In Figure 2b, the SR yield of macroalgae liquefaction in ethanol decreases with the temperature and ranges from 52.4 to 39.0 wt %, while the bio-oil yield shows a significant increase from 220 to 320 °C, with a bio-oil yield ranging from 22.1 to 36.5 wt %. However, the yield of gas and water appears as an “abnormal” downward trend on the whole, which is very different from the change of that in methanol, as shown in Figure 2a. This phenomenon may possibly explain that methanol or ethanol had reacted with the algal material to form those bio-oil compounds, because the molecular weight of ethanol is about 1.5 times that of methanol, thus resulting in a much higher increase rate for the bio-oil yield in ethanol. For two cases (e.g., liquefaction in sub-/supercritical methanol and ethanol, respectively), the yields of bio-oil and SR in both methanol and ethanol begin to rise when beyond their critical temperatures. In addition, an interesting point is that the yields of bio-oil and SR in methanol appear to level off when the temperature rises beyond 240 °C, while the SR yield in ethanol decreased and the bio-oil yield increased with the temperature. According to Alenezi et al.,32 Pinarat,33 and Changi et al.,34,35 the esterification of free fatty acid (as a model compound) in sub-/supercritical alcohol is influenced by several factors, such as chemical equilibrium or phase equilibrium effects and kinetic effects. The reaction took place in a liquid phase at subcritical temperatures, and at supercritical temperatures, a single vapor or supercritical fluid phase was formed. With the increase of the temperature, the equilibrium conversion is gradually being approached. These experimental results showed that esterification of free fatty acid in methanol or ethanol has displayed different reaction kinetics because of the physicochemical properties of the alcohols, and the changing of the reaction temperature as well as pressure can significantly affect the conversion yield. Thus, it could help to understand the different conversion trends of macroalgae E. prolifera in methanol and ethanol. The macroalgae E. prolifera has a low content of lipids but contains a large fraction of carbohydrates, that is, water-soluble polysaccharides and cellulose, and its depolymerization is highly dependent upon the liquefaction temperature. Previous studies have demonstrated that the decomposition of biomass, such as cellulose and lignin, usually starts above 200 °C and the conversion process tends to complete with an increasing temperature.36,37 It is evident that bio-oil yield in subcritical methanol is higher than that in subcritical ethanol probably because of the higher polarity and dielectric constant of methanol than those of ethanol,25 while the bio-oil yield in supercritical ethanol is higher than that in supercritical methanol. Because alcohols have involved reactions during the liquefaction process and the molecular weight of ethanol is much larger than that of methanol, it leads to a higher increase rate of bio-oil yields in ethanol than that in methanol. With the further increase of the temperature, the conversion of the algae−alcohol mixture is gradually approaching equilibrium and the bio-oil yield tends toward “stabilization”. However, the higher the liquefaction temperature, the higher the reaction pressure, and operation at such conditions is not conducive to the life of the reactor. Meanwhile, some target compounds, such as long-chain fatty acid esters, tend to decompose at higher temperatures.38 Considering the conversion yield as well as the energy input and life of the reactor, the liquefaction of
3. RESULTS AND DISCUSSION 3.1. Effects of the Temperature on the Liquefaction Yields in Methanol and Ethanol. The liquefaction yields of macroalgae E. prolifera in (a) methanol at 220−300 °C and (b) ethanol at 220−320 °C with a reaction time of 15 min are presented in Figure 2. For the liquefaction in methanol (Figure 2a), the SR yield decreases from 50.5 to 41.1 wt % with an
Figure 2. Effects of the temperature on the liquefaction yields in (a) methanol and (b) ethanol. 2344
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Spirulina, and their results showed that the solid/liquid (S/L) ratio had little effect on the residue yields. The role of methanol and ethanol in the liquefaction is not only as solvents but also as hydrogen donors that can promote the formation of bio-oil, and an excess amount of solvent, to a certain extent, can inhibit the repolymerization or secondary decomposition of bio-oil. When the amount of solvent is increased, that is, the algae/solvent ratio is decreased, the promotion effects of the solvent on bio-oil are enhanced; therefore, the yields of bio-oil increase with the decrease of the algae/solvent ratios. On the basis of a consideration of the liquefaction yields, costs, and use of the reactor volume, the algae/solvent ratio of 1:10 is favorable for the liquefaction of macroalgae E. prolifera in both methanol and ethanol. 3.3.1. Analysis of Bio-oils. Elemental Compositions of Bio-oils. The elemental compositions of bio-oils obtained in methanol and ethanol at various temperatures are shown in Table 2. It can be seen that the carbon, hydrogen, and nitrogen contents have greatly increased in comparison to that of the raw material, as shown in Table 1. The carbon contents in biooils obtained in methanol are 53−60 wt %, and the HHVs of bio-oils are around 22−27 MJ/kg, while the carbon contents and HHVs of bio-oils obtained in ethanol are higher, at 55−63 wt % and 25−31 MJ/kg, respectively. For two bio-oils, the carbon contents and HHVs increase with the temperature; however, it is clear that the bio-oils still have high oxygen contents because of the introduction of oxygen-containing groups during the liquefaction process. The bio-oils also have relatively higher N content (7−9 wt %) than that of algal feedstock (3.65 wt %; see Table 1). As a result, to produce transportation fuels, the deoxygenation and denitrogenation of bio-oils are needed. 3.3.2. FTIR Characterization of Bio-oils. The FTIR spectra of raw material and bio-oils are shown in Figure 4. It can be seen that the spectra of bio-oils obtained in methanol at 280 °C and ethanol at 300 °C (spectra b and c of Figure 4) are similar. The O−H stretching vibrations at 3400 cm−1 in spectrum a of Figure 4 indicate the presence of polysaccharides and proteins in raw material. The absorption at around 3300 cm−1 for biooils (spectra b and c of Figure 4) might be from O−H or N−H stretching vibrations.39 The absorbance peaks in 2855−2965 cm−1 are ascribed to C−H stretching vibrations of CH3 and CH2. The absorption at 1738, 1704, and 1674 cm−1 in
macroalgae E. prolifera in a reaction time of 15 min is favorable at 280 °C in methanol and at 300 °C in ethanol, along with biooil yields at 31.1 and 35.3 wt %, respectively. 3.2. Effects of the Algae/Solvent Ratio on the Liquefaction Yields in Methanol and Ethanol. The algae/solvent ratio was defined as the percentage of the mass of macroalgae E. prolifera (10 g) to the volume of solvent (mL). The effects of the algae/solvent ratio (g/mL) on the conversion of macroalgae E. prolifera in (a) methanol at 280 °C and (b) ethanol at 300 °C are depicted in Figure 3. Results show that
Figure 3. Effects of the algae/solvent ratio on the liquefaction yields in (a) methanol at 280 °C and (b) ethanol at 300 °C.
bio-oil yields in two alcohols increase with the decrease of the algae/solvent ratio from 1:5 to 1:10 and the yields of bio-oil (panels a and b of Figure 3) range from 21.8 to 31.1 wt % and from 28.5 to 35.3 wt %, respectively. However, a slight change for the SR yield is observed at the algae/solvent ratio from 1:5 to 1:10, and the SR yield in methanol and ethanol is from 40.1 to 41.6 wt % and from 45.5 to 42.0 wt %, respectively. These results are similar to the study by Huang et al.,27 using ethanol as the liquefaction medium to produce bio-oil from microalgae Table 2. Elemental Analyses of Bio-oils
elemental compositions (wt %) solvent
temperature (°C)
C
H
N
Oa
H/C
HHV (MJ/kg)
220 240 260 280 300
53.72 55.49 57.18 58.29 59.50
6.27 6.78 7.15 7.04 7.14
7.79 6.90 8.87 7.38 7.99
32.22 30.83 26.80 26.29 25.37
1.40 1.47 1.50 1.45 1.44
22.74 24.21 25.76 26.04 26.69
220 240 260 280 300 320
55.56 57.72 57.73 60.43 62.81 62.87
7.56 8.03 7.67 9.01 8.75 8.55
6.86 6.99 7.61 7.45 7.95 7.71
30.02 27.26 26.99 23.11 20.49 20.87
1.63 1.67 1.59 1.79 1.67 1.63
25.43 27.14 26.66 29.93 30.68 30.37
methanol
ethanol
a
By difference. 2345
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Figure 4. FTIR spectra of raw material (a) and bio-oils obtained in (b) methanol at 280 °C and (c) ethanol at 300 °C.
spectrum b of Figure 4 and at 1731 and 1675 cm−1 in spectrum c of Figure 4 is ascribed to CO vibrations possibly from ketones and esters.39−41 The absorption peaks at 1455 and 1377 cm−1 (spectra b and c of Figure 4) are ascribed to the CH3 and CH2 vibrations from aromatics and their derivates. The C−O stretching vibrations between 1200 and 1276 cm−1 (spectra b and c of Figure 4) indicate the presence of fats and esters in bio-oils.26,40,41 In addition, the absorbance peaks appearing in the band from 650 to 900 cm−1 are ascribed to the C−H bending vibrations from aromatics. On the basis of the FTIR characterization of bio-oils, it can be inferred that Ncontaining compounds, ketones, esters, and compounds with aromatic structures could exist in the bio-oils. 3.3.3. GC−MS Analysis of Bio-oils. Bio-oil produced by liquefaction of macroalgae E. prolifera in methanol and ethanol is a dark brown viscous liquid and shows good flow characteristics at room temperature of around 25 °C. The compounds in both bio-oils were analyzed by GC−MS. Tables 3 and 4 list the analysis results of bio-oils obtained in methanol at 280 °C and ethanol at 300 °C, respectively. The relative contents of compounds identified take up about 85% of the total area for each bio-oil. It can be seen that bio-oils obtained in alcohols are mainly composed of fatty acid esters, Ncontaining compounds, carbohydrates, hydrocarbons, and fatty alcohols/ketones. The fatty acid esters (C3−C22), that is, none N-containing methyl/ethyl esters, are the most abundant compounds in the bio-oils, and among these compounds, hexadecanoic-acid-formed esters, which are hexadecanoic acid methyl ester [retention time (RT) = 21.91 min, in Table 3] and hexadecanoic acid ethyl ester (RT = 21.27 min, in Table 4), have the highest relative contents, accounting for 31.86 and 37.10% of the total area, respectively. The N-containing compounds, such as amino acids, indole, indolizine, are mainly from the decomposition of proteins. Pyrazines, pyridines,
pyridones, and their derivatives are typical products from the Maillard reaction of amines with sugars.42,43 Also, some Ncontaining esters, such as L-proline, 1-methyl-5-oxo-, methyl ester (RT = 14.44 min, in Table 3) were identified, and they are possibly generated from the reactions of amino acids with alcohols. The identification of carbohydrates in both bio-oils, including xylopyranoside and glucopyranoside, is believed to derive from the decomposition of the polysaccharides and cellulose. However, very few hydrocarbons (500
a
33.21 36.85
18.93 16.77
10.86 8.30
4.63 2.75
2.87 3.51
10.55 10.91
5.99 12.54
sample 1 (wt %) sample 2b (wt %) a
Bio-oil obtained by liquefaction of macroalgae in methanol at 280 °C. bBio-oil obtained by liquefaction of macroalgae in ethanol at 300 °C.
°C in a nitrogen atmosphere. The bio-oils were heated from 25 to 750 °C under an inert atmosphere, resulting in a mass loss of about 90 wt %. As seen in Figure 6, the weight loss of bio-oils in both TG curves are observed to transform from a high rate to a low rate at the point around 250 °C. The DTG curves for both bio-oils show that the maximum weight loss rate of both biooils appears at around 150 °C. The most weight loss for both bio-oils occurring below 300 °C is 60−70 wt %. Overall, the TG/DTG characterizations of bio-oils indicate that the bio-oils contain a large distillable fraction at low temperatures. Table 6 lists the boiling point distribution of bio-oils obtained in methanol and ethanol. It can be seen that the bio-oils have a large fraction at distillation temperatures lower than 200 °C, accounting for 52.14 and 53.12 wt %, respectively, much higher than those of bio-oils obtained by hydrothermal liquefaction of the brown macroalgae L. saccharina.17 Moreover, the results indicate that bio-oils still contain a certain amount of high-boiling-point compounds that could not be analyzed by GC−MS. For two bio-oils (obtained in methanol/ethanol), the light fraction with a boiling point point < 350 °C takes up 70.5 and 68.18 wt % of the total, respectively, and indicates that both bio-oils are favorable for further separation and refining to produce fuels and chemicals. 3.4. Analysis of Solid Residues. Table 7 presents the elemental compositions (C, H, and N) of solid residues
supercritical state display better a solvent function than that of water at low temperatures and can enhance the conversion of macroalgae and promote the formation of bio-oil.
4. CONCLUSION In this study, liquefaction of macroalgae E. prolifera in sub-/ supercritical methanol (220−300 °C) and ethanol (220−320 °C) was carried out in a batch reactor. The experimental results showed that the liquefaction temperature has significant effects on the bio-oil yields and methanol and ethanol under a supercritical state have exhibited outstanding fluid characteristics. Under the relative optimized liquefaction conditions, the highest yield of bio-oil obtained in each alcohol has exceeded 30 wt %. Bio-oils produced from macroalgae E. prolifera in alcohols are composed of fatty acid (C3−C22) esters, Ncontaining compounds, sugars, fatty alcohols/ketones, and hydrocarbons. The fatty acid esters (methyl or ethyl), depending upon the liquefaction alcohol used, are dominant in each bio-oil. The bio-oils produced from macroalgae E. prolifera in alcohols are different from those bio-oils obtained by liquefaction of micro- or macroalgae in water but much similar to biodiesel on the composition. TGA was performed to have a further understanding of the characteristics of bio-oils from a perspective of industrial processing. With this method, the bio-oils obtained in methanol and ethanol are found to contain a large fraction of low-boiling-point (bp < 350 °C) compounds, both of which are around 70 wt %; thus, it is favorable for further separation and refining of bio-oils.
Table 7. Elemental Analysis of Solid Residues
■
elemental analysis (wt %) condition
temperature (°C)
C
H
N
H/C
220 240 260 280 300
21.74 20.58 19.28 17.43 19.01
3.47 2.97 2.25 1.87 2.29
2.59 2.37 2.33 2.06 1.70
1.92 1.73 1.40 1.29 1.45
220 240 260 280 300 320
18.88 18.45 16.73 15.72 13.59 12.90
1.50 2.39 1.83 1.68 1.19 1.03
2.85 2.63 2.21 2.05 1.49 1.31
0.95 1.55 1.31 1.28 1.05 0.96
methanol
AUTHOR INFORMATION
Corresponding Author
*Telephone: +86-21-65642297. Fax: +86-21-65642080. E-mail:
[email protected] (S.Z.);
[email protected] (J.C.). Notes
The authors declare no competing financial interest.
■
ethanol
ACKNOWLEDGMENTS The authors are thankful for the financial support from the 10th Graduate Innovation Fund Program from Fudan University and the Shanghai Science and Technology Committee.
■
REFERENCES
(1) Bridgwater, A. V. Chem. Eng. J. 2003, 91, 87−102. (2) Mohan, D.; Pittman, C. U.; Steele, P. H. Energy Fuels 2006, 20 (3), 848−889. (3) Goyal, H. B.; Seal, D.; Saxena, R. C. Renewable Sustainable Energy Rev. 2008, 12, 504−517. (4) Zhang, L. H.; Xu, C.; Champagne, P. Energy Convers. Manage. 2010, 51 (5), 969−982. (5) Peterson, A. A.; Vogel, F.; Lachance, R. P.; Fröling, M.; Antal, M. J.; Tester, J. W. Energy Environ. Sci. 2008, 1, 32−65. (6) Wen, D. S.; Jiang, H.; Zhang, K. Prog. Nat. Sci. 2009, 19, 273− 284. (7) Dote, Y.; Sawayama, S.; Inoue, S.; Minowa, T.; Yokoyama, S. Y. Fuel 1994, 73 (12), 1855−1857.
obtained in methanol and ethanol at various temperatures. The carbon content of residues obtained in methanol ranges from 19.01 to 21.74 wt %, while that of residues obtained in ethanol ranges from 12.90 to 18.88 wt %. The C, H, and N contents and the C/H ratio of the two kinds of residues gradually decrease with the increasing reaction temperature. The carbon contents of residues obtained in methanol and ethanol are much lower than those of raw material (28.75 wt %, in Table 1), and also, these are much lower than those of residues obtained from hydrothermal liquefaction of brown macroalgae L. saccharina.17 It is indicated that monohydric alcohols under a 2350
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Energy & Fuels
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dx.doi.org/10.1021/ef201966w | Energy Fuels 2012, 26, 2342−2351
