Effect of metal salts impregnation and microwave-assisted solvent pretreatment on selectivity of levoglucosenone and levoglucosan from vacuum pyrolysis of ashe juniper waste

Accepted Manuscript Title: Effect of metal salts impregnation and microwave-assisted solvent pretreatment on selectivity of Levoglucosenone and Levoglucosan from vacuum pyrolysis of Ashe juniper waste Authors: Julius Choi, Hyungseok Nam, Sergio C. Capareda PII: DOI: Reference:

S2213-3437(18)30721-8 https://doi.org/10.1016/j.jece.2018.11.041 JECE 2796

To appear in: Received date: Revised date: Accepted date:

2 August 2018 2 November 2018 18 November 2018

Please cite this article as: Choi J, Nam H, Capareda SC, Effect of metal salts impregnation and microwave-assisted solvent pretreatment on selectivity of Levoglucosenone and Levoglucosan from vacuum pyrolysis of Ashe juniper waste, Journal of Environmental Chemical Engineering (2018), https://doi.org/10.1016/j.jece.2018.11.041 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Effect of metal salts impregnation and microwave-assisted solvent pretreatment on selectivity of Levoglucosenone and Levoglucosan from vacuum pyrolysis of Ashe juniper waste

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Julius Choia,*, Hyungseok Namb and Sergio C. Caparedaa

Bio-Energy Test and Analysis Laboratory (BETA Lab), Department of Biological and Agricultural Engineering,

Texas A&M University, College Station, TX 77843, USA b

Greenhouse Gas Laboratory, Korea Institute of Energy Research, Daejeon, 34129, South Korea

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Corresponding author.

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E-mail addresses: [email protected] (J. Choi), [email protected] (S.C. Capareda)

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Abstract

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Levoglucosenone (LGO), furfural (FF) and levoglucosan are high value-added chemical components of bio-oil derived by thermal deconstruction of biomass. However, separation of these

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chemicals from bio-oil is challenging due to low selectivity. Impregnation of metal salts for catalytic pyrolysis or microwave treatment for altering chemical composition in biomass are

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potential methods to enhance selectivity of these high value-added chemicals. In the current study, Ashe juniper waste was pretreated with metal salts prior to vacuum pyrolysis and investigated the

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effects of metal salt type and its concentration on product yield and properties. The results showed that Levoglucosenone, which was attributed to dehydration of levoglucosan, was obtained only

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with the biomass pretreated with CuSO4 and ZnSO4. Metal salt type and concentration also affected the selectivity of levoglucosenone (LGO) and furfural (FF) by catalytic vacuum pyrolysis. Microwave-assisted organosolv treatment also affected biomass chemical composition, pyrolysis

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characteristics and promoted the selectivity of levoglucosan.

Keywords Catalytic pyrolysis, Bio-oil, Selectivity, Pretreatment, Characteristics

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1.

Introduction Pyrolysis is a thermochemical process to decompose organic compounds, such as biomass, at

elevated temperatures in the absence of oxygen. Using pyrolysis, biomass can be converted to syngas, bio-oil and biochar [1]. Syngas and bio-oil are considered major intermediate products that can be used to create alternatives to conventional fuels [1].

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Bio-oil is composed of hundreds of chemicals, including some high value added chemicals, e.g. levoglucosenone (LGO) [2], levoglucosan (LG) [3] and furfural (FF) [4], which can be recovered by separation processes such as distillation. For example, LGO can be used as a building block for pharmaceutical synthesis, such as (+)-chloriolide (antibiotic) and ras proteins activation inhibitors (anticancer drug); 1,6-hexanediol, widely used for polyester, polyamide, and polyurethane

production;

and

5-hydroxymethyldihydrofuranone

(5-HMF),

used

for

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pharmaceuticals, fuels, and nucleic acids. In addition, LG can be used as a carbon source for the

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fermentation process to produce itaconic acid [5] and bioethanol [6] as well as the synthesis of pesticides, growth regulators, macrolide antibiotics, etc [3]. Furthermore, FF can be used as a

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chemical feedstock for the production of furfuryl alcohol, furan, and biofuel [4]. Therefore, bio-

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oil is an excellent raw source to obtain specific value-added chemicals. However, recovery of these high value-added chemicals from bio-oils is technically

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challenging and generally uneconomical due to the compositional complexity and low

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concentration of each component in bio-oil. Therefore, the production rate and selectivity for the required chemicals must be improved for a successful commercialization. Catalytic selective pyrolysis is one method to produce high value-added chemicals with high production rate and

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selectivity from biomass.

Levoglucosenone is rarely produced by pyrolysis [2], and several catalytic pyrolysis methods

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have been proposed to increase LGO production rate and selectivity. Dobele et al. conducted catalytic pyrolysis with phosphoric acid-impregnated cellulose and biomass, producing maximum

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selectivity of 30% [7, 8]. Dobele et al. also investigated the effect of Fe3+ on the yield of LGO, of which maximum yield was 25.7%, derived from cellulose [9]. Branca et al. investigated acidcatalyzed pyrolysis of concorbs, producing 4.6% yield of LGO [10]. Solid acids such as sulfated ZrO2, sulfated TiO2, and sulfated TiO2/Fe2O3 were explored to improve LGO yield based on cellulose to 7.25% [11], 5.69% [11], and 15.4% [12], respectively. Xin et al. reported LGO

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selectivity up to 82.6% from cellulose impregnated with phosphoric acid using an evaporation method [2], and also showed that sulfates could increase LGO yield significantly. Metal salts and metal cation effects on LGO yield and selectivity has rarely been investigated. Particularly, the role of metal cations on LGO yield and selectivity should be confirmed by comparison between the effects from different metal sulfates. Therefore, the current study

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contributes the conversion of biomass waste used for remediation of contaminated soils, which is probably contaminated with metal salts, into high value-added products

Most research regarding the production of high value-added chemicals was conducted with cellulose rather than raw biomass, which consists of cellulose, hemicellulose, and lignin. Zheng et al. reported that lignin content affected the yield of levoglucosan [13]. Similarly, we think that the lignin content in biomass might also affect the yield and selectivity of LGO because dehydration

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of levoglucosan is one possible pathway to LGO during pyrolysis [14-16]. Therefore, the effect of

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biomass chemical composition, such as lignin content, on the selectivity and yield of compounds in bio-oil should be investigated.

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Microwave-assisted organosolv treatment (MSOT) is an efficient way to alter the chemical

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composition of biomass [13, 17, 18]. In this research, we applied MSOT using different solvents to investigate the effects on yield and composition of bio-oil.

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Ashe juniper is a native and rapidly expanded specie influencing production, composition, and

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structure of rangeland plant communities and hydrology of many areas. Management for Ashe juniper clearing using the hydraulic shears or a bulldozer might produce large quantities of waste [19]. However, Ashe juniper waste has high carbon content [20] and could be used as a renewable

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carbon source to produce high value added chemicals alternatives to fossil fuel derived chemicals. Nevertheless, to the best of our knowledge, there has been no study on the production of LGO, LG

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and FF from Ashe juniper waste. Therefore, the main objective of this research is to produce and improve LGO, LG and FF production selectivity by catalytic vacuum pyrolysis and alteration of

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the chemical composition of Ashe juniper waste. The specific objectives are (i) evaluating the effect of metal salts on yield and composition of products by vacuum pyrolysis, (ii) investigating the effect of metal salt type and concentration on yield of products and selectivity of compounds in bio-oil, (iii) determining the effect of metal cations on selectivity of LGO and FF, and (iv) investigating the effect of microwave-assisted treatment on the degradation properties of biomass and the chemical composition of bio-oil. 3

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Material and methods

2.1

Feed material Ashe juniper waste was crushed by a wiley mill using a 2 mm screen and stored in a zip-lock

bag at a room temperature. The samples were dried for two hours before pyrolysis. The volatility

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and fixed carbon and ash contents were determined following ASTM D3172. The elemental composition of Ashe juniper waste and mircrowave-treated sample was determined with an ultimate analyzer (a Vario MICRO elemental analyzer).

2.2

Microwave-assisted solvent treatment of Ashe juniper waste

Solvent mixture composed of ethanol, acetic acid, and water with sulfuric acid (50:50:50 v/v/v,

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0.1M H2SO4) was prepared. Ashe juniper waste was mixed with the mixture at 1:10 solid:liquid

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ratio (w/v) in a borosilicate round bottom glass flask. The mixture was solvothermally treated in a microwave oven at 350W for 10 min at 95°C. A condenser with 10°C water was installed for

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reflux. After the reaction, the mixture was filtered to collect insoluble residues. Insoluble residues

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were washed with the mixture then washed three times using deionized (DI) water. The washed

Metal salts impregnation

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samples were dried in an oven at 60°C for 24 h.

Each 60 ml of 0.1, 0.2, and 0.4 M solution of ZnSO4, CuSO4, and NaCl, respectively, were prepared in DI water. 10 g of Ashe juniper was submerged in each solution. The mixtures were

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individually mixed on a rotary shaker at 200 rpm for 24 h. Then, the mixture was evaporated in

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the oven at 105°C for 24 h.

2.4

Vacuum pyrolysis for the production of oils

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Ashe juniper was pyrolyzed in a homemade vacuum pyrolysis machine as described previously

[20]. To investigate the effect of temperature and vacuum pressure on product yield and composition, 10 g of Ashe juniper waste was placed in a glass flask (Chemglass) inserted into an electrical furnace. The flask was connected to a condenser to collect the relatively heavy bio-oil (Fraction 1). The condenser was connected to a subsequent cold trap to collect the relatively light bio-oil (Fraction 2). The cold trap was connected to a mechanical vacuum pump. The system was 4

evacuated at 0.7 kPa. The reactor was heated to 450°C with a heating rate of 20°C/min controlled by PID controllers. The system was maintained at the final temperature, for 1 h, and then Fraction 1 and Fraction 2, and biochar were collected. The yield of each sample was calculated by weighing the various remainders after the vacuum

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pyrolysis. The total oil yields were calculated by summing Fraction 1 and Fraction 2 yields.

Fraction 1 yield (%) =

Fraction 1 weight × 100 Ashe juniper waste weight

Fraction 2 yield (%) =

Fraction 2 weight × 100 Ashe juniper waste weight

Biochar weight × 100 Ashe juniper waste weight

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Biochar yield (%) =

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To test the effects of metal impregnation and microwave-solvothermal treatment, 10 g of

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prepared samples were pyrolyzed at 0.7 kPa and 450°C. Biochar and oil were collected and yields

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were calculated as described above.

Oils analysis

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Chemical compositions of Fraction 2 were measured using GC-MS (A Shimadzu QP2010Plus)

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using helium as a carrier gas, and ZB5MS GC-MS (30 m × 0.25 mm × 0.25 µm thick) column. The column temperature program was set as follows: an injection temperature of 295°C; a column

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oven temperature of 45°C at the beginning and held for 5 min, then ramped to 330°C at the rate of 5°C/min and held for 5 min; a MS ion source temperature of 250°C, and an interface temperature

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of 320°C. The ion chromatographic peaks were identified according to NIST MS library 2.0 and peak area of identified products from different pyrolysis conditions was recorded. Average and standard deviation values of peak area were calculated. The relative selectivity were defined as the

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ratio of peak area for the specific product and peak area for total identified products to show the change of selectivity of taget product relative to the detected products in Fraction 2 [21, 22]. Relative selectivity (%) =

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Results and discussion 5

Specific peak area × 100 Total peak area

3.1

Effect of metal salts impregnation and microwave-assisted solvent pretreatment on product yield Fig. 1 shows the products yield derived from vacuum pyrolysis of samples as received, metal

salt impregnated and pretreated in the solvent using microwave. Microwave-assisted solvent pretreatment did not significantly affected the yield of biochar as compared to the result from raw

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sample. However, microwave-assisted solvent pretreatment increased the yield of Fraction 2 and decreased the yield of Fraction 1. Whereas, different metal salts affected product (biochar, Fraction 1 and Fraction 2) yields differently. Metal salt impregnation increased the yield of biochar compared to the yield without impregnation, with maximum biochar yield obtained from sodium chloride impregnated samples. This result is consistent with previous studies that have shown that metal cations promoted the formation of biochar [23, 24].

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The highest yield of Fraction 2 was obtained from vacuum pyrolysis of microwave-pretreated

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samples followed by ZnSO4-impregnated samples, raw samples, NaCl and CuSO4 impregnated samples in descending order. In contrast, Fraction 1 yield obtained from the metal salts

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impregnated samples and microwave solvent pretreated samples were lower than from non-

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impregnated sample. This observation was opposite to the trend shown in biochar production that the yield obtained from the impregnated sample was higher than the non-impregnated sample.

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These trends were strongly related to various effects of metal salts on high molecular weight

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products, such as pyrolytic lignin, which is a major component of Fraction 1. Metal salts faciliate the secondary deomposition of the high-molecular-weight chemicals into light-molecular-weight chemicals or non-condensable gases [24] resulting in decreased yield of Fraction 1, but increased

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yield of Fraction 2 as observed for ZnSO4-impregnated samples. Metal salts also catalyze the repolymerization of volatiles during pyrolysis [24], resulting in increased biochar yield, as

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observed for impregnated samples. Therefore, selection of metal salt is important to control product yield.

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Biochar samples can be used for several applications. Pyrolysis of metal salt impregnated

samples is an efficient method to produce functionalized biochar suitable for adsorbents and catalysts [25]. These biochar samples contain high concentrations of certain metal elements, which can be regenerated by burning the biochar and employing as nutrient in fertilizer and synthesis of catalysts [26, 27].

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3.2

Effect of metal salt impregnation on the chemical composition of Fraction 2 Fig. 2 and Table 1 show the identified products within Fraction 2 produced from vacuum

pyrolysis of samples altered by the metal salt impregnation methods. FF and LGO were the major compounds for ZnSO4 and CuSO4 impregnated samples, and Glycoaldehyde dimethyl acetal, phenolic compounds, and 1,2-Cyclopentanedione were the major compounds derived from NaCl

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impregnated samples. shows that each Fraction 2 sample had different peak positions in ion chromatograms, which indicates the effect of impregnation on the change of chemical composition. Differences for major compounds were significant. Thus, metal salts are crucial factors to modify the selectivity of the target chemical, which is consistent with previous reports [28-31]. It is known that sulfate ions have a catalytic effect converting cellulose and hemicellulose into LGO and FF [2, 30, 32]; sulfate ions in ZnSO4 and CuSO4 probably catalyzed the conversion

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presumably affect LGO and FF production differently.

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of cellulose and hemicellulose in Ashe juniper to LGO and FF; and zinc and copper ions

To prove these assumptions, Ashe juniper impregnated with different concentrations of ZnSO4

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presented in the following sections.

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and CuSO4 by evaporation methods were pyrolyzed under the same condition. Results are

Metal sulfate concentration effects on production yield

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Fig. 3 shows that concentrations of different metal salts affected the yield of product differently. For ZnSO4 (Fig. 3a)), the yield of biochar increased, Fraction 1 decreased, and Fraction

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2 did not change significantly with increasing ZnSO4 concentration. As shown in Fig. 3b), the concentration of CuSO4 shows similar effects on the yield of products as ZnSO4. However, yields

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for biochar and Fraction 2 for CuSO4 are lower than ZnSO4 impregnated samples. This indicates that ZnSO4 catalyzed the secondary decomposition reaction and repolymerization to a greater

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extent than CuSO4. For the experiment, the same moles of ZnSO4 and CuSO4 were impregnated into Ashe juniper waste. Therefore, cation type is an important factor to control the yield of the products if the same concentration of sulfate is used.

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3.4

CuSO4 and ZnSO4 concentration effects on selectivity of furfural and levoglucosenone production Fig. 4 shows ion chromatograms for Fraction 2 derived from each sample. Table 2 lists the

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name of chemical compounds derived from each sample. Peak positions were consistent, indicating that ZnSO4 and CuSO4 concentration did not affect chemical composition. However, the peak intensities for FF and LGO increased with increasing concentration of both catalysts. Thus, it was confirmed that the concentration of catalysts affected the reaction rate, but did not change the reaction pathway. Fig. 5 shows that LGO selectivity increased from 22.0% to 25.2% with increasing CuSO4 concentrations four fold, and 15.0% to 27.2% for four fold increased ZnSO4

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concentration. While selectivity of FF increased from 15.4% to 18.73% as the concentration of

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CuSO4 increased, and from 19.6% to 25.8% with increasing ZnSO4. These results indicate that

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ZnSO4 had more significant effects on selectivity than CuSO4.

Effects of microwave-assisted solvent pretreatment effects on the characteristics of Ashe

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3.5

juniper waste

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We also investigated the effect of microwave-assisted solvent pretreatment on the vacuum

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pyrolysis of Ashe juniper waste. Table 4 shows the elemental composition of Ashe juniper waste with and without microwave-assisted solvent pretreatment. Carbon content decreased and oxygen content increased with the pretreatment compared to untreated Ashe juniper waste. This result is

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probably due to the removal of lignin content, which has the highest carbon and lowest oxygen content [13]. Microwave-assited pretreatment also increased O/C and H/C ratios of Ashe juniper

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waste.

Thermogravimetric (TG) and differential thermogravimetric (DTG) analyses were performed

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for the characterization of pyrolysis characteristics of raw Ashe juniper and microwave-assisted pretreated Ashe juniper waste, as shown in Fig. 6. As shown in Fig. 6a and 6b), TG and DTG curves show that microwave-assisted pretreatment shifted the peak of main decomposition stages to higher temperature. This observation is probably attributed to partial removal of lignin and extractable ash [13], which catalyze the pyrolysis reaction over the microwave treatment. It is known that the typical decomposition temperatures [33] for hemicellulose, cellulose, and lignin 8

are 220°C to 315°C, 315°C to 400°C, and 160°C to 900°C, respectively. Samples pretreated in the solvent using microwave also exhibited a narrower range of decomposition temperature compared to Ashe juniper waste without any pretreatment as shown in Fig. 6a). Thus, this result means the microwave-assisted solvent pretreatment changed the chemical composition of Ashe juniper

glycerol pretreatment of a corncob [13].

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waste. Furthermore, this observation is consistent with the result regarding microwave-assisted

Effect of microwave-assisted solvent pretreatment on chemical composition in fraction 2 and selectivity of levoglucosan and phenolic compounds

As shown in Fig. 7a), the peak intensity for levoglucosan increased after microwave-assisted solvent pretreatment. Based on peak area, we calculated the relative selectivity of levoglucosan

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and phenolic compounds. The selectivity of levoglucosan increased from 5.9% to 53% after

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microwave pretreatment of samples in the mixture, whereas, selectivity of phenolic compounds decreased from 20% to 5% as seen in Fig. 7b) and c). Since phenolic compounds are derived from

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lignin, this result suggests that microwave-assisted solvent pretreatment partially removed lignin,

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which is consistent with elemental analysis result in section 3.5 and the decreased yield of Fraction 1 as shown in Fig. 1. It is known that levoglucosan is a precursor for LGO production during

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pyrolysis [16, 32, 34]. Therefore, it is expected that the impregnation of either ZnSO4 or CuSO4

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will improve selectivity of LGO due to the increased the selectivity to levoglucosan after

Conclusion

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4.

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microwave-assisted solvent pretreatment.

The impreganation of metal salt on biomass before pyrolysis varied the product yield, chemical

composition of bio-oil and selectivity of target chemicals. Among the metal salts, only the metal

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sulfate impregnated biomass over pyrolysis showed the LGO chemical, which was not produced from vacuum pyrolysis with raw and NaCl impregnated Ashe juniper waste. Therefore, metal sulfate inclusion during the pyrolysis reaction should lead a positive effect on the selectivity of LGO and FF. However, the cation played a different effect on the selectivity of LGO and FF; ZnSO4 had more significant effect than CuSO4. Biochar produced from metal-impregnated biomass has potential as functional biochar for adsorbents and catalysts. On the other hand, 9

microwave solvothermal pretreatment enhanced the selectivity of the levoglucosan from Ashe juniper waste. The combination of metal salt impregnation and microwave-assisted solvent pretreatment is a promising method to achieve the optimum selectivity of LGO.

Acknowledgements

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The authors acknowledge the facilities, and the scientific and financial assistance of the Bio

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Energy Testing and Analysis Laboratory and AgriLife Research at Texas A&M University.

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Fig. 1. Yield of a) Fraction 1, b) Fraction 2, and c) biochar from vacuum pyrolysis of samples as

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received, pretreated by microwave and impregnated by metal salts.

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Fig. 2. Ion chromatograms of Fraction 2 from vacuum pyrolysis of Ashe juniper waste as received

and impregnated by metal salts detected by GC/MS. The peaks numbers correspond to chemical

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compounds listed in Table 1

15

SC RI PT

Fig. 3. Yield of products from vacuum pyrolysis of samples impregnated with a) ZnSO4 and b)

A

CC

EP

TE

D

M

A

N

U

CuSO4 at different concentrations

16

SC RI PT

U

Fig. 4. Ion chromatograms of Fraction 2 derived from vacuum pyrolysis of samples impregnated with a)

N

ZnSO4 and b) CuSO4 at different concentrations. The peaks numbers correspond to chemical compounds

A

CC

EP

TE

D

M

A

listed in Table 2

17

SC RI PT U N A M D TE EP

Fig. 5. Selectivity of LGO and FF in Fraction 2 derived from vacuum pyrolysis of samples

A

CC

impregnated with ZnSO4 and CuSO4 at different concentration: a), b) LGO; c), d) FF

18

SC RI PT U

N

Fig. 6. a) DTG and b) TGA of Ashe juniper wastes as received and pretreated in the mixture of

A

CC

EP

TE

D

M

A

H2O, acetic acid, ethanol and sulfuric acid using microwave

19

SC RI PT

U

Fig. 7. a) Ion chromatograms of Fraction 2 from vacuum pyrolysis of Ashe juniper waste as received and pretreated, b) Selectivity of levoglucosan and c) phenolic groups for samples as

N

received and pretreated using microwave in the mixture of H2O, acetic acid, ethanol and sulfuric acid.

A

CC

EP

TE

D

M

A

The peaks numbers correspond to chemical compounds listed in Table 3

20

Table 1. The list of chemical compounds in Fraction 2 from vacuum pyrolysis of Ashe Juniper waste as received and impregnated by metal salts

A

N

U

SC RI PT

Compounds 1-Nitro-2-propanone Furfural 2-Cyclopenten-1-one, 2-methylNot identified 2-Cyclopenten-1-one, 2-hydroxy-3-methylPhenol, 2-methoxyPhenol, 2-methoxy-3-methylCreosol not identified 1,6-Anhydro-.bete.-d-talopyranose 4-Hydroxy-2-methoxybenaldehyde Phenol, 2-methoxy-4-propylLevoglucosan 4-Hydroxy-2-methoxycinnamaldehyde Glycoaldehyde dimethyl acetal Not identified Not identified Levoglucosenone 1,4:3,6-Dianhydro-alpha-d-glucopyranose Not identified Not identified Not identified Not identified Not identified 2,2-Dimethoxypropionamide 2-Propanone, 1-(acetyloxy)tert-Butyldimethylsilanol Cyclopentanone 1,2-Cyclopentanedione Hexanal dimethyl acetal

A M D TE EP

CC

Number 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

21

Table 2. The list of chemical compounds in Fraction 2 from vacuum pyrolysis of Ashe Juniper waste impregnated with ZnSO4 and CuSO4 Compounds Glycoaldehyde dimethyl acetal Furfural Not identified Not identified Phenol methoxy Levoglucosenone Cresol 1,4:3,6-dianhydro-alpha-d-glucopyranose Not identified Not identified Not identified Levoglucosan Ethane, 1,1,2,2-tetramethoxy Pentanoic acid, 4-oxo, methyl ester Not identified Not identified

A

CC

EP

TE

D

M

A

N

U

SC RI PT

Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

22

Table 3. The list of chemical compounds in Fraction 2 from vacuum pyrolysis of Ashe Juniper waste as received and pretreated Compounds 1-Nitro-2-propanone Furfural 2-Cyclopenten-1-one, 2-methylOxazolidine, 2,2-diethyl-3-methyl2-Cyclopenten-1-one, 2-hydroxy-3-methylPhenol, 2-methoxyPhenol, 2-methoxy-3-methylCreosol Not identified 1,6-Anhydro-.bete.-d-talopyranose 4-Hydroxy-2-methoxybenaldehyde Phenol, 2-methoxy-4-propylLevoglucosan 4-Hydroxy-2-methoxycinnamaldehyde Not identified D-Allose 1,6-Anhydro-.alpha.-d-galactofuranose

A

CC

EP

TE

D

M

A

N

U

SC RI PT

Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

23

Table 4. Elemental analysis and H/C, O/C, and S/C molar ratio Elemental analysisa (wt %) H

N

O

S

H/C

O/C

A

48.6±0.4

6.66±0.07

0.11±0.01

44.6±0.4

0

1.62±0.00

0.69±0.02

B

46.5±0.3

6.38±0.02

0.11±0.00

47.0±0.3

0

1.65±0.01

0.76±0.01

SC RI PT

C

A: Raw Ashe juniper waste and B: Ashe juniper waste pretreated in the mixture of H2O, acetic

A

CC

EP

TE

D

M

A

N

U

acid, ethanol and sulfuric acid under microwave

24