Studies of Distribution Characteristics of Inorganic Elements during the

Mar 29, 2016 - ... Yang Sun, and Rundong Li. College of Energy and Environment, Shenyang Aerospace University, Key Laboratory of Clean Energy, Liaonin...
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Studies of Distribution Characteristics of Inorganic Elements during the Liquefaction Process of Cornstalk Tianhua Yang, Weidan Wang, Xingping Kai, Bingshuo Li, Yang Sun, and Rundong Li* College of Energy and Environment, Shenyang Aerospace University, Key Laboratory of Clean Energy, Liaoning Province, Shenyang 110136, P.R. China ABSTRACT: Liquefaction of cornstalk for producing bio-oil was conducted with different solvents (water, ethanol, and acetone) at temperatures of 280, 320, and 360 °C. The distribution characteristics of the inorganic elements K, Na, Mg, Ca, Al, and Fe during liquefaction were studied. The results demonstrated that liquefaction temperature and solvent clearly affected the distribution. The inorganic elements distributed mainly into biochars (>60.0 wt %) with acetone and ethanol as solvent, with less than 26 wt % into the bio-oils; however, K and Na distributed mainly into aqueous phases with water as solvent, and Ca, Al, and Fe distributed mainly into biochars, with less than 31 wt % into the bio-oils. Increasing liquefaction temperature (320 to 360 °C) reduced the contents of inorganic elements in bio-oils. In addition, ICP-OES showed that the concentrations of inorganic elements in bio-oils were very high and also affected significantly by liquefaction temperature and solvent. The concentrations of K, Na, Mg, and Al in bio-oil obtained from water were higher than those obtained from acetone and ethanol; however, the concentrations of Ca and Fe in bio-oil obtained from acetone were higher than those obtained from water and ethanol. It was suggested that the bio-oil should be pretreated before utilization.

1. INTRODUCTION The rapid development of the economy and the increasing population have led to a dramatic increase in the consumption of fossil fuels; thus, seeking alternatives to fossil energy has become an interesting topic in recent years.1,2 Biomass is increasingly favored due to its advantages, such as renewability, environmental friendliness, and rich reserves.3,4 To date, biomass has been transformed into biofuel by various methods, such as biochemical and thermochemical conversion.3,5 Among these methods, thermochemical conversion is the best choice for producing biofuel because of its brief conversion process. Thermochemical conversion primarily involves pyrolysis, liquefaction, and gasification;6,7 among these processes, pyrolysis and liquefaction are the major methods for producing bio-oil. Pyrolysis is a high-temperature and anoxic thermochemical conversion process during which biomass is heated to gain gaseous product and bio-oil.8 Subsupercritical liquefaction is a high-pressure and low-temperature process during which biomass is broken down into fragments of small molecules in water or organic solvents (such as acetone and ethanol) and then the small molecule products undergo a series of complex chemical reactions such as condensation and reunion to produce bio-oil.9,10 However, compared to pyrolysis, liquefaction consumes less energy, and the bio-oil from the liquefaction process has a higher calorific value, higher yield, and lower oxygen content;11−13 thus, utilizing liquefaction technology for producing bio-oil has become a focus of research. However, inorganics in biomass have migration and transformation abilities during the liquefaction process, which can be transformed into the bio-oil. In addition, inorganics significantly affect the refinement and utilization of the bio-oil. For example, the existence of alkaline and alkaline earth metal, i.e. K, Na and Mg, Ca contributed to the deactivation of catalyst in the refinery process, the corrosion of mechanical equipment, and the formation of ash during the combustion of fuel.14,15 In © XXXX American Chemical Society

addition, iron element can also accelerate the oxidative decomposition of fuel,16,17 thereby reducing its storage stability. Moreover, the existence of nonmetallic elements also has a negative influence on fuel. Silicon easily forms on the oxide precipitation during the fuel combustion process, causing equipment abrasion, and phosphorus can lead to environmental pollution and catalyst deactivation.18,19 Therefore, in addition to considering the yield and chemical component of the bio-oil,20,21 the distribution and migration of the inorganic element also should be subjects of focus during the biomass liquefaction process for producing bio-oil. However, the toxicological effect of heavy metals makes them a hot topic in current research. Leng et al.22 studied the migration and transformation of heavy metals, such as Pb, Zn, Cu, and Ni, during the liquefaction process of sewage sludge, indicating that more than 90% of heavy metals distributed into the biochar, with less than 10% being distributed into the biooil, and the content of heavy metals in bio-oil increased with the increase of temperature. Yuan et al.23 assessed the ecotoxicity and bioavailability of the residue from the liquefaction of sewage sludge and found that heavy metals such as Pb, Zn, Cu, Cd, Cr, and Ni were distributed mainly into the residue (>70%); in addition, the introduction of catalyst reduced the content of heavy metals in the residue and changed the forms of heavy metals. By studying the bio-oil from the liquefaction of Camellia oleifera cake, Chen et al.24 reported the concentration and content of heavy metals (Zn, Cu, Cd, Ni, Fe, Mn, Cr) in bio-oil, finding that heavy metals were concentrated mainly in biochar and less in bio-oil. Furthermore, it was indicated that temperature and solvent affected the content of Received: January 13, 2016 Revised: March 17, 2016

A

DOI: 10.1021/acs.energyfuels.6b00096 Energy Fuels XXXX, XXX, XXX−XXX

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Energy & Fuels Table 1. Proximate and Element Analysis of the Cornstalks Ultimate analysis (wt %)a Item

C

H

Cornstalk

41.44

5.31

Total a

N

Proximate analysis (wt %)a b

S

O

M

0.84 0.14 52.27 5.45 Total concentrations of inorganic elements (mg/kg)a

A

V

FC

5.84

74.55

14.16

K

Na

Mg

Ca

Al

Fe

5279.67

463

3210.07

2217.4

494.37

283.05

On a dry basis. bBy difference.

Figure 1. Separation and collection processes of products. screening with a particle diameter of less than 50 meshes. The element composition of cornstalks was measured by the organic trace element analyzer (FLASH2000, Thermo). The proximate analysis of cornstalks was achieved by Standard Test Methods for Analysis of Wood Fuels (ASTM E870-82). The concentration of major inorganic elements (i.e., K, Na, Mg, Ca, Al, and Fe) was determined in terms of the Solid Biofuels-Determination of major elements (DD CES/TS 15290:2006). All results are shown in Table 1. The deionized water was prepared for the experiment. The nitric acid, hydrogen peroxide, hydrofluoric acid, and boric acid used for pretreatment were of guaranteed reagent quality, and their concentrations are 65, 30, 40, and 4 wt %, respectively. The ethanol and acetone were of analytical grade. A single-element standard solution and multielement standard solution were used as the standard stock solution for inductively coupled plasma-atomic emission spectrometry (ICP-OES, PerkinElmer Analyst 8300, US). All reagents were purchased from Merck (Darmstadt, Germany). 2.2. Liquefaction of cornstalks and products separation. The liquefaction of cornstalks was conducted in a 500 mL batch autoclave (KCFD05-30, China). In each experiment, 15 g of cornstalk powders and 150 mL of solvent (water, ethanol, or acetone) were loaded into the autoclave. The autoclave was then heated to the required temperature (280, 320, or 360 °C) for 60 min by a PID temperature controller. After the reaction, the autoclave was cooled to 25 °C by cooling water and then the vent valve was opened to vent the gas. After that, the autoclave was opened to obtain the solid/liquid

heavy metals in bio-oil, and the bio-oil obtained by liquefaction with ethanol as the solvent contained lower heavy metal content. In summary, heavy metals were mainly concentrated in biochar during the biomass liquefaction process. However, in addition to heavy metals, the other inorganic elements in biomass, especially from lignocellulosic biomass, such as K, Na, Mg, and Ca, also affect the quality of liquefaction products; furthermore, research on the distribution and migration of other inorganic elements during the lignocellulosic materials liquefaction has thus far been very rare. As we all known, lignocellulosic materials contain large amounts of alkaline and alkaline earth metals, which can be transformed into the bio-oil during the liquefaction process, and thus have a negative influence on the refinement and application of bio-oil. In this work, liquefaction of cornstalk was conducted at different temperatures with various solvents, aimed to realize the effects of temperature and solvent on the distribution of inorganic elements such as K, Na, Mg, Ca, Al, and Fe in the liquefaction products.

2. EXPERIMENTAL SECTION 2.1. Materials and reagents. Cornstalks were obtained from Shenyang, Liaoning Province, China. The cornstalks were dried in an oven at 105 °C for 24 h followed by smashing into powders and B

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washed solution was filtered by a vacuum filtration apparatus with a 0.45 μm filter membrane and diluted to 50 mL for measurement. 2.3.2. Pretreatment of biochar. The pretreatment of biochar involved the production of ash and wet digestion. The process of producing ash was conducted according to the method specified in Standard Test Method for Ash in Biomass (ASTM E1755-01). However, the wet digestion of ash was carried out according to DD CEN/TS 15290:2006, and the digestion solution was filtered by a vacuum filtration apparatus with a 0.45 μm filter membrane and diluted to 50 mL for measurement. 2.3.3. Wet digestion of aqueous phase. Because the aqueous phase contains a small amount of organic matter, such as ketones, organic acids, and alcohols,26 the aqueous phase should be pretreated to meet the requirement of ICP-OES. The organic matter of the aqueous phase was decomposed by wet digestion. In each test, 2 mL of sample, 3 mL of concentrated nitric acid and 2 mL of hydrogen peroxide were loaded into the Teflon crucible. The Teflon crucible was then heated on the electric hot plate for 1 h. The Teflon crucible was cooled slightly, and 3 mL of hydrogen peroxide was later added to the Teflon crucible for heating sequentially until the solution was clear and transparent. The temperature of the electric hot plate was increased to remove the acid until its volume was approximately 1 mL. The Teflon crucible was cooled to room temperature and then washed three times with water. In the end, the washed solution was filtered by a vacuum filtration apparatus with a 0.45 μm filter membrane and diluted to 50 mL for measurement. 2.4. Measurement methods and instruments. The concentrations of K, Na, Mg, Ca, Al, and Fe in bio-oil, biochar and aqueous phase were analyzed by ICP-OES. The major operating parameters are shown in Table 3.

products. The liquid and solid products in the autoclave were collected by a beaker (Beaker 1). The wall and cooling pipes of the autoclave were then washed with 150 mL of acetone and 100 mL of ethanol, and the washed organic solutions and other solid products were collected in another beaker (Beaker 2). With water as solvent, the products in Beaker 1 were filtered by a vacuum filtration apparatus with a 0.45 μm filter membrane to obtain the solid and aqueous phase, and then the solid and products in Beaker 2 were filtered to obtain organic filtrate. The organic filtrate was evaporated by a rotavapor at 85 °C to remove the organic solvents, and then the remaining liquid product was biooil. The solids were dried to obtain biochar. With acetone or ethanol as solvent, the products in Beaker 1 and Beaker 2 were filtered to obtain organic filtrate. The organic filtrate was evaporated to obtain bio-oil, and solids were dried to obtain biochar. The separation and collection processes are detailed in Figure 1. The blue line in Figure 1 represented the separation process with water as solvent; however, the red line represented the separation process with ethanol (or acetone) as solvent. The abbreviations of the liquefaction experiment are shown in Table 2.

Table 2. Abbreviations of Liquefaction Experiment Abbreviations AO1,AO2,AO3 EO1,EO2,EO3 WO1,WO2,WO3 AC1,AC2,AC3 EC1,EC2,EC3 WC1,WC2,WC3 WA1,WA2,WA3 A1,A2,A3 E1,E2,E3 W1,W2,W3

Instruction bio-oils from acetone at temperatures of 280, 320, and 360 °C, respectively bio-oils from ethanol at temperatures of 280, 320, and 360 °C, respectively bio-oils from water at temperatures of 280, 320, and 360 °C, respectively biochars from acetone at temperatures of 280, 320, and 360 °C, respectively biochars from ethanol at temperatures of 280, 320, and 360 °C, respectively biochars from water at temperatures of 280, 320, and 360 °C, respectively aqueous phases produced at temperatures of 280, 320, and 360 °C, respectively acetone runs at temperatures of 280, 320, and 360 °C, respectively ethanol runs at temperatures of 280, 320, and 360 °C, respectively water runs at temperatures of 280, 320, and 360 °C, respectively

Table 3. Major Operating Parameters of ICP-OES Parameter

Value

Rf power generator (W) Plasma gas flow (L/min) Assistant gas flow (L/min) Peristaltic pump flow (mL/min) Atomizer flow (L/min) Flush time of sample (s) Reading delay (s)

1500 8 0.2 1 0.7 30 40

The water content of bio-oil was determined as Standard Test Method for Water in Crude Oils (ASTM D4928-12) using a Karl Fischer moisture titrator (Metrohm). The total acid number (TAN) of bio-oil was measured according to Standard Test Method for Acid Number of Petroleum Products (ASTM D644-09a) using an acidity meter (Metrohm). The analytical methods of the data were defined as follows. m Yield1 = bio ‐ oil × 100% mcorn (1)

2.3. Pretreatment of liquefaction products. Bio-oil, biochar, and aqueous phase should be pretreated to satisfy the requirement of ICP-OES. The experimental vessels used for pretreatment of liquefaction products were steeped in 5 wt % nitric acid solution for 24 h, washed three times with water, and dried in an oven at 105 °C for use. 2.3.1. Wet digestion of bio-oil. Wet digestion was performed by using oxidant agents in the liquid (such as HNO3 or H2O2) to digest the sample for obtaining an aqueous solution suitable for analysis using a variety of instruments.25 In each test, 0.5 g of bio-oil and 15 mL of concentrated nitric acid were mixed in a 100 mL Erlenmeyer flask, which was covered by a funnel overnight. The next day, the Erlenmeyer flask with the funnel was heated on the electric hot plate until the volume of the concentrated nitric acid in the Erlenmeyer flask was approximately 5 mL. The Erlenmeyer flask was then cooled slightly, after which 5 mL of concentrated nitric acid and 5 mL of hydrogen peroxide were added to the Erlenmeyer flask to be heated by the electric hot plate sequentially. The hydrogen peroxide was gradually added to the Erlenmeyer flask during the heating process until the solution was clear and transparent. The Erlenmeyer flask was then covered by the funnel again, and the temperature of the electric hot plate was increased to remove the acid until the volume was approximately 1 mL. The Erlenmeyer flask was cooled to room temperature and then washed three times with 1 wt % nitric acid solution. In the end, the

Yield 2 =

mbio ‐ char × 100% mcorn

(2)

Yield3 = 100% − Yield1 − Yield 2 P1 =

Cbio ‐ oil × Yield1 × 100% Ccorn

(4)

P2 =

Cbio ‐ char × Yield 2 × 100% Ccorn

(5)

P3 =

Caqueous phase × Vaqueous phase Ccorn × mcorn

P 4 = 100% − P1 − P 2 − P 3 C

(3)

× 100%

(6) (7)

DOI: 10.1021/acs.energyfuels.6b00096 Energy Fuels XXXX, XXX, XXX−XXX

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Energy & Fuels where mcorn, mbio‑oil, and mbiochar were the weights of cornstalk, bio-oil, and biochar, respectively, g; Yield1 and Yield2 were the yields of bio-oil and biochar, respectively, wt %; Yield3 was the yields of gas with acetone (ethanol) as solvent; however, with water as solvent Yield3 was the yields of gas and water-solution organic products (WSOs) in the aqueous phase, wt %; Ccorn, Cbio‑oil, Cbiochar, and Caqueous phase were the total concentrations of K, Na, Mg, Ca, Al, and Fe in cornstalk, bio-oil, biochar, and the aqueous phase, respectively, mg/kg; P1, P2, and P3 were the portions of K, Na, Mg, Ca, Al, and Fe distributed to bio-oil, biochar, and the aqueous phase, respectively, wt %; P4 represented the loss portion of K, Na, Mg, Ca, Al, and Fe and the portion in gas products, wt %; Vaqueous phase was the volume of the aqueous phase.

polarity of the liquefaction solvent. Generally speaking, highpolarity liquefaction solvent was conducive to accelerating the conversion of the sample30,12,31 and improving the bio-oil yield. As shown in Figure 2, the yields of bio-oils obtained from acetone were higher than those of bio-oils obtained from water or ethanol because the dipole moments of acetone, ethanol, and water are 2.9, 1.7, and 1.8 D,12 respectively. The higher dipole moment of acetone accelerated the conversion of cornstalk during the liquefaction process to obtain more bio-oil.24 In addition, Figure 2 shows that the yields of bio-oils obtained from water decreased considerably faster than those of bio-oils obtained from acetone or ethanol as the liquefaction temperature increased from 320 to 360 °C. A possible reasons for this result was that acetone and ethanol could react with the intermediately decomposed cornstalk during the liquefaction process to produce bio-oil, and the decomposition and condensation reactions of intermediate cornstalk were prevented, resulting in the lower decomposition rate of biooil. However, the effects of liquefaction solvent on biochar yield were different from those of bio-oil. The higher-polarity solvent resulted in a lower yield of biochar or a higher conversion rate of cornstalk. As shown in Figure 2, the yields of biochars obtained from acetone were less than those of biochars obtained from water or ethanol. 3.2. Concentrations of inorganic elements in products from the liquefaction of cornstalk. 3.2.1. Concentrations of inorganic elements in bio-oils. Figure 3(a−c) shows the concentrations of K, Na, Mg, Ca, Al, and Fe in biooils. As shown in Figure 3(a−c), the liquefaction solvent had an influence on the concentrations of K, Na, Mg, Ca, Al, and Fe in bio-oils. The concentrations of K, Na, Mg, and Al in bio-oils obtained from water were higher than those in bio-oils obtained from acetone or ethanol. Possible causes of the result were that inorganic elements K, Na, Mg, and Al may exist in bio-oil, mainly in the form of water-soluble metal salts (such as chloride),32 and the water contents of bio-oils obtained from water were also considerably higher than those of bio-oils obtained from acetone and ethanol (as shown in Table 4). However, compared to bio-oils obtained from water or ethanol, the concentrations of Ca and Fe in bio-oils obtained from acetone were higher, which was because the inorganic elements Ca and Fe may easily combine with acid oxy-compounds (such as phenols and organic acid) of bio-oil to generate the oilsoluble metal salts existing in bio-oil and because the higher total acid number of bio-oil (as shown in Table 4) led to higher concentrations of oil-soluble metal salts.33,34 In addition, the liquefaction temperature also obviously affected the concentrations of K, Na, Mg, Ca, Al, and Fe in biooils. Figure 3(a) shows that the concentrations of K, Na, Mg, Ca, Al, and Fe in bio-oils obtained from acetone increased to the peak values 901.17, 201.13, 241.23, 435.53, 363.00, and 518.55 mg/kg, respectively, when the liquefaction temperature increased from 280 to 320 °C. Moreover, as the liquefaction temperature increased to 360 °C, the concentrations of K, Na, Mg, Ca, Al, and Fe began to decrease, among which the concentrations of K, Mg, and Al decreased more sharply. The results were mainly caused by the variation of total acid number and water content in bio-oils obtained from acetone (as shown in Table 4). The concentration variation tendency affected by the liquefaction temperature of K and Al in bio-oils obtained from ethanol was similar to those in bio-oils obtained from acetone. As shown in Figure 3(b), at 320 °C, the concentrations of K and Al reached maximum values of

3. RESULTS AND DISCUSSION 3.1. Analysis of products yield. 3.1.1. Effects of liquefaction temperature on the yield. Figure 2 shows the

Figure 2. Yields of products from liquefaction of cornstalk; Yield1, the yield of bio-oil; Yield2, the yield of biochar; Yield3, the yield of gas (acetone and ethanol as solvent) or the yield of gas and water-solution organics in aqueous phase (water as solvent).

yields of bio-oil, biochars, gas, and WSOs at liquefaction temperatures of 280, 320, and 360 °C. According to Figure 2, the yields of bio-oils produced from acetone, ethanol, and water runs increased as the liquefaction temperature increased from 280 to 320 °C. At 320 °C, the yields of bio-oils reached peak values of 35.10, 29.60, and 30.83 wt %, respectively. As the liquefaction temperature increased to 360 °C, the bio-oil yields gradually decreased; conversely, the yields of gas and WSOs gradually increased. A similar trend was also observed by Zhu et al.,27 who concluded that the yield of bio-oil increased as the liquefaction temperature increased from 280 to 300 °C and then decreased at 320 °C. This indicated that excessive liquefaction temperature had a negative effect on the yield of bio-oil; when the liquefaction temperature increased, the gas product began to form through cracking reactions of the biooil.28 The yields of biochars produced from acetone, ethanol, and water runs gradually decreased with the increase of liquefaction temperature. The same results were achieved by Liu et al.29 When the liquefaction temperature was 360 °C, the yields of biochars reached the minimum values 18.68, 27.68, and 26.42 wt %, respectively. This illustrated that higher liquefaction temperature favored the conversion of cornstalk. 3.1.2. Effects of liquefaction solvent on the yield. In addition to temperature, liquefaction solvent was also an important factor affecting the yield. However, the effects of liquefaction solvent on the yield mainly depended on the D

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Figure 3. Concentrations of K, Na, Mg, Ca, Al, and Fe in bio-oils: (a) liquefaction with acetone as the solvent; (b) liquefaction with ethanol as the solvent; (c) liquefaction with water as the solvent.

tions of K, Mg, and Al in bio-oils obtained from water. The concentrations of K, Mg, and Al reached maximum values at 320 °C, whereas the concentrations declined sharply as the liquefaction temperature increased to 360 °C, which may be related to the water content of bio-oils obtained from water (as shown in Table 4). However, at the same time, the concentrations of Ca, Fe, and Na varied relatively stably. In conclusion, choosing a suitable liquefaction temperature could effectively decrease the concentrations of inorganic elements in bio-oils. 3.2.2. Concentrations of inorganic elements in biochars and aqueous phases. As the important byproduct from liquefaction of biomass, biochar had attracted many researchers. Biochar was used in many applications, such as soil remediation,35 fixing carbon,36 and adsorbing the pollutants.37 In addition, biochar also can be regarded as fuel to provide energy. However, the inorganic elements K, Na, Mg, Ca, Al, and Fe in biochars might have an obvious effect on the

Table 4. Total Acid Number and Water Content of Bio-Oils Bio-oils

Total acid number (mgKOH/g)

Moisture content (wt %)

AO1 AO2 AO3 WO1 WO2 WO3 EO1 EO2 EO3

90.55 97.43 80.26 71.99 58.38 53.39 28.20 13.13 16.97

0.66 1.74 0.47 12.50 16.75 10.16 2.03 1.91 0.90

1480.50 and 171.00 mg/kg, respectively. However, the concentrations of Na, Mg, Ca, and Fe achieved a peak value at 280 °C, because the total acid number and water content of bio-oil (EO1) also achieved the peak value at 280 °C (as shown in Table 4). According to Figure 3(c), it was found that the liquefaction temperature significantly affected the concentra-

Table 5. Concentrations of K, Na, Mg, Ca, Al, and Fe in Bio-chars Biochar AC1 AC2 AC3 EC1 EC2 EC3 WC1 WC2 WC3

K (mg/g) 18.79 18.83 22.70 11.74 13.21 14.98 0.45 0.44 0.35

± ± ± ± ± ± ± ± ±

0.24 0.36 0.03 0.05 0.20 0.25 0.003 0.005 0.04

Na (mg/g) 1.32 1.48 1.81 1.02 1.11 1.28 0.13 0.12 0.32

± ± ± ± ± ± ± ± ±

0.07 0.08 0.005 0.03 0.05 0.03 0.013 0.03 0.04

Mg (mg/g) 11.49 12.89 16.51 8.34 9.56 11.40 2.70 3.55 4.53

± ± ± ± ± ± ± ± ±

0.34 0.26 0.30 0.21 0.02 0.21 0.07 0.06 0.05 E

Ca (mg/g) 7.60 8.68 10.49 6.01 6.42 7.49 5.72 6.39 6.59

± ± ± ± ± ± ± ± ±

0.12 0.13 0.06 0.20 0.23 0.16 0.17 0.12 0.14

Al (mg/g) 1.43 1.28 2.04 1.22 1.29 1.58 1.15 1.08 1.28

± ± ± ± ± ± ± ± ±

0.08 0.05 0.09 0.04 0.01 0.004 0.04 0.03 0.01

Fe (mg/g) 0.59 0.39 0.49 0.63 0.75 0.89 0.71 0.92 0.98

± ± ± ± ± ± ± ± ±

0.04 0.01 0.02 0.002 0.001 0.018 0.02 0.01 0.02

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Energy & Fuels Table 6. Concentrations of K, Na, Mg, Ca, Al, and Fe in Aqueous Phases and the Volumes of Aqueous Phasesa Conc of inorganic elements in aqueous phases (mg/L)

a

Item

Volume (mL)

K

Na

Mg

Ca

Al

Fe

WA1 WA2 WA3

130 ± 2 125 ± 1 127 ± 2

514.8 ± 6.26 502.1 ± 16.52 524.9 ± 1.28

30.0 ± 0.69 29.9 ± 1.14 24.6 ± 0.79

238.6 ± 1.67 181.5 ± 4.14 160.5 ± 9.34

33.6 ± 1.06 31.1 ± 1.05 48.8 ± 1.01

1.508 ± 0.88 0.325 ± 0.04 3.860 ± 0.58

54 wt %), with less than 3 wt % K and 18 wt % Na observed in the biochars. This indicated that K and Na existed in mainly water-solution form during the liquefaction process. Compared to Figures 4(a) and 4(b), the P1 of K and Na in bio-oils obtained from water was higher. This result was possibly caused by the higher concentrations of K and Na bio-oils obtained from water. In addition, at 320 °C, the P1 of K and Na in bio-oils reached peak values of 17.66 and 24.04 wt %, respectively; then, P1 decreased along with increasing temperature to 360 °C. The inorganic elements Ca, Al, and Fe distributed mainly into biochars (P2 > 62.6 wt %), with less than 18.6 wt % measured in aqueous phases, which showed that Ca, Al, and Fe were mainly non-water-solution existence forms during the liquefaction process. The P1 of Ca and Fe in bio-oils was lower than that obtained from acetone because of the effects of the yields and total acid numbers of bio-oil; moreover, the P1 decreased gradually as the temperature increased from 280 to 360 °C. Figure 4(c) showed that inorganic element Mg distributed mainly into aqueous phases (P3 > 42.3 wt %) and biochars (P2 > 27.0 wt %). The P1 of Mg in bio-oils was less than 14.44 wt %, and the P1 increased to its peak value as the temperature increased to 320 °C; then, the P1 began to decrease as the temperature increased. By comparing Figure 4(a) to Figure 4(b), it was found that the P1 values of Mg in bio-oils were higher than those obtained from acetone or ethanol because Mg in the bio-oils obtained from water had higher concentrations.

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AUTHOR INFORMATION

Corresponding Author

*Phone: (86) 024-89728889. Fax: (86) 024-89724558. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors acknowledge research grant support by the National Natural Science Foundation of China (No. 51576135), and the Joint Funds of the Natural Science Foundation of Liaoning Province, China (No. 2013024019).

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DOI: 10.1021/acs.energyfuels.6b00096 Energy Fuels XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.energyfuels.6b00096 Energy Fuels XXXX, XXX, XXX−XXX