Screening Solvents Based on Hansen Solubility Parameter Theory To

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Screening solvents based on Hansen solubility parameter theory to depolymerize lignocellulosic biomass efficiently under low temperature Quan Zhang, Xuesong Tan, Wen Wang, Qiang Yu, Qiong Wang, Changlin Miao, Ying Guo, Xinshu Zhuang, and Zhenhong Yuan ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.9b00494 • Publication Date (Web): 11 Apr 2019 Downloaded from http://pubs.acs.org on April 12, 2019

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ACS Sustainable Chemistry & Engineering

Screening solvents based on Hansen solubility parameter theory to depolymerize lignocellulosic biomass efficiently under low temperature Quan Zhang†,‡,§,┴, Xuesong Tan*,†,‡,§, Wen Wang†,‡,§, Qiang Yu†,‡,§, Qiong Wang

†,‡,§

, Changlin

†,‡,§

Miao

, Ying Guo†,‡,§, Xinshu Zhuang*,†,‡,§, Zhenhong Yuan†,‡,§,‖

†

Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 501640, China; ‡ CAS Key Laboratory of Renewable Energy, Guangzhou 501640, China; §Guangdong Provincial Key Laboratory of New and Renewable Energy Research and Development, Guangzhou 501640, China; ┴University of Chinese Academy of Sciences, Beijing 10049, China; ‖Collaborative Innovation Centre of Biomass Energy, Zhengzhou 450002, China * Corresponding author: Xin-shu Zhuang, E-mail: [email protected], Tel: 86-20-37029699, Guangzhou Institute of Energy Conversion, CAS, 2 Nengyuan Road, Wushan, Tianhe, Guangzhou 510640, China; Xuesong Tan, Email: [email protected], Tel: 86-20-37029690 , Guangzhou Institute of Energy Conversion, CAS, 2 Nengyuan Road, Wushan, Tianhe, Guangzhou 510640, China;

Abstract Ten solvents including water-soluble and water-insoluble solvents were first used to pretreat rice straw under a facile condition (110 ℃, 60 min). The results showed most of the hemicellulose was removed, and much of cellulose was held in solid residue. Based on Hansen solubility parameters (HSP) theory, the correlation between the relative energy difference (RED) of solvent system-lignin interactions and lignin removal was explored. Taking efficient enzymatic hydrolysis and ease fractionation of lignocellulosic biomass into account, biphase solvent 2-Phenoxyethanol (KL-EPH) was selected for further study. After that, effects of temperature, retention time, sulphuric acid loading and KL-EPH concentration on the degradation of rice straw were studied, and the results indicated that the condition of temperature 120 ℃, retention time 3 hours, sulphuric acid loading 0.1 M and KL-EPH concentration 50% was optimal. Under this condition, 90.17% of hemicellulose and 53.17% of lignin were removed from rice straw resulting in the residue enzymatic hydrolysis rate of 88%, and 66% of hemicellulose as xylose was present in the aqueous phase. Moreover, 33.55% of the precipitated solid (lignin rich) was collected from organic phase. The componential analysis suggested the lignin-rich residue mainly consisted of 78.68% of lignin, 8.26% of glucan and, 1.65% of xylan. The raw materials and residues were characterized by Scanning electron microscopy, Fourier transform infrared spectroscopy and XRD diffractions, and the results showed the remarkable removals of hemicellulose and lignin primarily contributed to the improved enzymatic hydrolysis of residue, based on these results. Keywords: Hansen solubility parameter, organic solvents, pretreatment, delignification, enzymatic hydrolysis Introduction 1 / 14

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Lignocellulosic biomass, due to its richness in reserves, low cost, easy getting and environmental friendliness, has been seen as a potential raw material for second-generation liquid biofuels today. To make this biorefinery feasible, increasing the conversion of lignocellulosic biomass to platform molecules such as furanic and sugars compounds was believed to be especially crucial 1. Lignocellulosic biomass primarily consists of cellulose, hemicellulose and lignin. Among them, cellulose is a high-polymerization (100-1000) and high-crystallinity biopolymer composed of Dglucose linked by 1,4-β-glycosidic bonds2. Hemicellulose with a lower degree of polymerization (100-200) compared with that of cellulose is mainly comprised of xylose and a few hexoses (e.g., Dglucose, D-mannose, D-galactose)3. Lignin, a three- dimensional natural polymer, is mainly derived from three monolignols, i.e., coniferyl alcohol, p-coumaryl alcohol, and sinapyl alcohol which are linked by carbon-carbon bonds or ester bonds (β-O-4)4. Further more, lignin and hemicellulose are crosslinked with each other through covalent bonds, which wrapps on the surface of cellulose. All this makes lignocellulosic biomass a strong resistant barrier to cellulase. It is, therefore, necessary to degrade lignocellulosic biomass. The removal of lignin increases the accessibility of cellulase to cellulose, thereby reducing the production cost of fiber ethanol. At the same time, effective pretreatment is also a prerequisite for the whole components application of lignocellulosic biomass5,6,7. Various methods, i.e., physical, chemical, physicochemical and biological pretreatment, until now, have been applied for liquid biofuels and high-value chemical products, which can be strategically divided into two categories2. One is hydrolyzing cellulose and hemicellulose, while reserving lignin in solid residue, which frequently applied in traditional biorefinery. The other is just degrading lignin and now used in lignin-first biorefinery 4,8. For the second category, organic solvents is a better choice to recovering lignin. After about 125 years of development, organosolv pulp has made great progress9,10. Lignin isolated via solvents method, compared to other methods, has higher purity as its core structures maintain constant and its molecular weight decreased as well as β-aryl ether linkages of the lignin are cleaved partially11. This is very beneficial for lignin-first biorefinery because condensation reactions among ether linkages will be drastically reduced during lignin being degraded through some methods, like Kraft pulping12. At present, the commonly used solvents are alcohol (e.g., Ethanol and Methanol), ketone (e.g., Acetone and Methyl ethyl ketone), organic acid (e.g., Formic acid and Acetic acid) and ester (e.g., Ethyl acetate and Butyl acetate)9,10,13,14. How to screen solvents is therefore worth researching because of to date, there being a large number of organic solvents. Hansen solubility parameters (HSP) theory which has taken into account three intermolecular forces (dispersion, polarity and hydrogen force) is reported to be able to describe the ability of a solvent to dissolve lignin.15. HSP indicated that the cohesive energy E roots in three major interactions, that is, dispersion, polarity and hydrogen bonding. Based on this standpoint, a solvent is characterized by these three parameters, called HSPs14. In this study, rice straw was firstly pretreated using ten solvents at a mild temperature. Then HSP theory was used as a tool to study the correlation between the relative energy difference of solvent system-lignin interactions and lignin removal. Subsequently, 2-Phenoxyethanol (KL-EPH) was selected for further study. Materials and methods Materials and solvents Rice straw was supplied from National Engineering Research Center of Plant Space Breeding, South China Agricultural University. Raw materials were first cut into several segments with a size of 2-5 cm using a hay cutter. Those segments were crushed into particles and then the particles were 2 / 14


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simultaneously filtered with two sieves of 20 and 60 meshes. Finally, the selected particles were oven dried at 105 ℃ overnight. Ethanol (EtOH), toluene and sulfuric acid were obtained from Sinopharm Chemical Reagent Beijing Co., Ltd. Tetrahydrofuran (THF), tetrahydrofurfuryl alcohol (THFA), 2Methyltetrahydrofuran (2-MeTHF), methyl isobutyl ketone (MIBK), cyclopentyl methyl ether (CPME), 2-Phenoxyethanol (KL-EPH) and γ-Butyrolactone (GBL) were all supplied by Shanghai Macklin Biochemical Co., Ltd. All solvents are of analytical grade. Solid-state cellulase was purchased from Jade Bio-technology Co., Ltd, and cellulase activity was 191.7 FPU/g. Solvents pretreatment and enzymatic hydrolysis Different pretreatment experiments with selected solvents were conducted with a temperature of 110 ℃, 60 min retention time, at liquid: solid ratio of 20:1 (V/W), sulphuric acid loading of 0.1 M (Total solution volume) and solvent: water ratio of 1: 1 (V/V). 2 g rice straw (dry weight, DW) was heated with acidified aqueous solvents in a 75 ml thick-wall pressure bottle. After 60-minute reaction time, the mixtures were cooled and then filtered with 40 ml glass sand funnels (G3). The solid residues were washed with the same solvent and water for at least three times and oven dried at 105 ℃ to constant weight. For biphasic systems, the organic phases were first separated from the aqueous phases by filtering. Then, the lignin was precipitated from the organic phase with dimethyl carbonate (DMC). The process was as follow. At room temperature, the organic phase was added to DMC with a ratio of 1:10 (V/V) and a retention time of 30 min. Then, The precipitated lignin was harvested from organic phase-DMC mixture by centrifugation (823×g, 10 min). Enzymatic digestion of the raw material and pretreated residues were conducted in citrate buffer (0.1 M, pH 4.8) with 2.5% solid loading. The cellulase loading was 20 FPU/g dry material. Subsequently, the mixtures were incubated at 50 ℃, 150 rpm for 72 h. An aliquot was withdrawn every 12 h. The glucose concentration was measured with high-performance liquid chromatography (HPLC, Waters 2498). All the experiments were conducted in duplicate. Hansen solubility parameter theory Hansen solubility parameter (δ) comprises dispersion force parameter (δd), polar force parameter (δp) and hydrogen force parameter (δh). δ was calculated as Eq. 1 and Eq. 216.

 = d2   p2   h2

(1)

n

 mixture    iVi

(2)

i 1

Where δd, δp and δh are dispersion force parameter, polar force parameter and hydrogen force

parameter respectively. δmixture is δd, δp or δh of mixtures of which all parts are mutually soluble. δi and Vi are δd, δp or δh of a solvent which is a part of the mixture. To determine the dissolving capacity of solvents to lignin, the relative energy difference (RED) of lignin-solvent interactions was adopted. According to Eq. 3 and 4, RED is as follow. RED 

Ri R0

(3)

Ri2  4( ds2   dl2 ) 2  ( ps2   pl2 ) 2  ( hs2   hl2 ) 2

(4)

3 / 14



Where R0 is a constant related to lignin (R0=13.7). Ri is defined by Eq. 3. “s” and “l” refer to the solvents and lignin (δdl= 21.9 MPa1/2, δpl= 14.1 MPa1/2 and δhl= 16.9 MPa1/2) respectively. Analytical methods The chemical composition of rice straw was analysed following the method provided by the US National Renewable Energy Laboratory (NREL)17. The results showed that raw rice straw mainly consisted of 41.93±0.31% cellulose, 24.99±0.22% hemicellulose and 23.85±0.64% lignin (DW). The glucose and xylose were identified through HPLC (Waters 2695, Waters Technology Shanghai Co., Ltd, China) equipped with a sugar column of Shodex SH-1011 and 5 mM H2SO4 was employed as mobile phase with a flow rate of 0.5 ml/min at 50 ℃. Results and discussion Solvents pretreatment a 100

Cellulose removal Lignin removal Hemiellulose removal Glucose yield

90 80 70

b 90 85

60 50 40 30

Glucose yield=48.7956+0.7382 Lignin removal Adj. R2=0.7474

80

Glucose yield (%)

Percentage removal (%)

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

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75 70 65 60 55

20

50

10

45

0 L A GB THF

F TH

H EtO

ne te r BK HF PH PME MI olue MeT Wa KL-E C T 2-

Water soluble solvents

0

10

20

30

40

50

Lignin removal (%)

Water insoluble solvents

Fig. 1 a) lignin removal, sugar loss and glucose yield after enzymatic hydrolysis of the raw material and solid residues treated with different organic solvents, b) correlation between lignin removal and enzymatic hydrolysis of residues. (Temperatures of 110 ℃, retention time of 60 min, a liquid: solid ratio of 20:1, sulphuric acid loading of 0.1 M and a solvent: water ratio of 1: 1) To study the effects of ten solvents on rice straw depolymerisation and enzymatic hydrolysis, pretreatment with these water soluble and insoluble solvents at 110 ℃ was conducted. As shown in Fig.1a, cellulose loss treated with all solvents was less than 20%, which means more than 80% of cellulose could be recovered in solid residue for both water soluble solvents and water insoluble solvents. It will be beneficial to the downstream cellulose application. On the contrary, over 70% of hemicellulose was removed after pretreatment with all solvents. These two results indicated the organic solvents- water- H2SO4 system was mainly beneficial to keep cellulose in solid residue and remove of hemicellulose from lignocellulosic biomass. It is consistent with previous studies18,19,20 21. For lignin removal, we found, compared to water insoluble solvents, more lignin could be removed after being processed with water soluble solvents. Meanwhile, another interesting phenomenon is that glucose yield after enzymatic hydrolysis showed the same trend as lignin removal. The correlation between lignin removal and the effect of enzymatic hydrolysis was therefore investigated. Fitting lignin removal and effect of enzymatic hydrolysis in Fig.1b, we found more and more glucan was overall enzymatically hydrolyzed to glucose as lignin removal increased. This result was consistent with previous study22. Based on the above analysis, we could see most of the cellulose was held in 4 / 14


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the solid residue and a large amount of hemicellulose in lignocellulosic materials could be readily hydrolyzed using the organic solvents- water- H2SO4 system. The most remarkable lignin removals of 47.80% and 26.30%, and enzymatic hydrolysis of 84.49% and 71.19% were obtained with the water insoluble solvent, THF, and the water insoluble solvent, KL-EPH, respectively. Thus, removing as much lignin as possible will be significant not only for improving enzymatic hydrolysis, but also for fractionating lignocellulosic biomass. Lignin removal based on Hansen solubility parameters theory To screen efficient solvents for delignification, Hansen solubility parameters theory was introduced. Then, ten solvents system were used to study the correlation between RED and lignin removal based on HSP theory. The RED and Hansen solubility parameters of all solvents were listed in Table 1. Table 1 The RED and Hansen solubility parameters of ten solvents CAS No.

Solvents

Hansen solubility parameters/MPa1/2

96-48-0

GBL

δd 19.0

δp 16.6

δh 7.4

0.9074

97-99-4

THFA

δd 17.8

δp 8.2

δh 10.2

1.0366

109-99-9

THF

δd 16.8

δp 5.7

δh 8.0

1.0600

64-17-5

EtOH

δd 15.8

δp 8.8

δh 19.4

1.3729

7732-18-5

water

δd 15.5

δp 16.0

δh 42.3

2.0808

122-99-6

KL-EPH

δd 17.0

δp 7.2

δh 12.3

0.9371

5614-37-9

CPME

δd 16.7

δp 4.3

δh 4.3

1.3906

108-10-1

MIBK

δd 15.1

δp 6.1

δh 4.1

1.4830

108-88-3

Toluene

δd 18.0

δp 1.4

δh 2.0

1.5383

96-47-9

2-MeTHF

δd 16.9

δp 5.0

δh 4.3

1.3490

REDa

a. For water soluble solvents, RED is the relative energy difference of solvent system- lignin (50% solvent: 50% water) interactions. For water insoluble solvents, RED is the relative energy difference of solvent - lignin interactions. 55 50 45

Lignin removal (%)

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 Lignin removal=77.8966-35.9244 RED Adj. R =0.8432 2 Lignin removal=50.2702-25.0747 RED Adj. R =0.7986

40 35

Water soluble solvents Water insoluble solvents

30 25 20 15 10 5 0 0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

RED

Fig. 2 Correlation between RED of solvent system-lignin interaction and lignin removal In Fig.2, the results showed the overall lignin removal decreased with the increase RED. According to Hansen solubility parameters theory, RED1 indicates solvent can hardly dissolve lignin. RED=1, that is to say, only part of lignin can be dissolved in solvent16. In a word, smaller RED value corresponds to stronger 5 / 14



dissolving capacity to lignin. These solvents with high solubility to lignin can continuously dissolve degraded lignin until the solution reaches saturation. Hence, the solvents with RED1. It is consistent with our results although high lignin removals were obtained after THFA system (RED=1.0366) and THF system (RED=1.0600) treatment. This is primarily due to the difference of lignin parameters between the lignin in rice straw and the model lignin used to calculate RED in this study. On the other hand, we also found the correlation between RED of water soluble solvent system-lignin and lignin removal was more closer than that between RED of water insoluble solvent system-lignin and lignin removal. This is mainly due to the water solubility of solvents being higher at 110 ℃ than at room temperature and poorer process of mass transfer, which will have a certain degree of influence on the calculation of the RED value23. On the basis of the above results and analyses, we can conclude that Hansen soluble parameter theory is a valid tool to screen organic solvents which can efficiently depolymerize lignocellulosic biomass. Among all of the above solvents, significant lignin removal and enzymatic hydrolysis of rice straw can be obtained after treatment with THF system. However, considering fractionation of lignocellulosic biomass, biphase solvent system has more potential than monophasic system24,25,26. KL-EPH is consequently a better choice and will be further studied to support the above conclusion and simultaneously evaluate the application potential of KL-EPH. 3.3 Processing rice straw with KL-EPH system a

100

90 80

80



b

Cellulose removal Hemiellulose removal Lignin removal

90

70 60 50 40 30 20

70


60 50 40 30 20 10

10 0 60

70

80

90

100

110

120

130

140

0

150

0

1

2

3

Temperature (℃ )

d 90

80

80


70


60 50

4

5

6

7

8

9

60

70

80

90

Time (h)

c 90


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

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40 30 20

70 60


50 40 30 20

10

10

0.0

0.1

0.2

0.3

0.4

0.5

0

10

20

H2SO4 concentration (mol/l)

30

40

50

KL-EPH concentration (%)

Fig. 3 Effects of temperature, retention time, sulphuric acid loading and KL-EPH concentration on the degradation of rice straw (a. Temperatures of 70 ℃-150 ℃, retention time of 3 h, sulphuric acid loading of 0.1 M and KL-EPH concentration of 50%; b. Temperatures of 110 ℃, retention time of 1-9 h, sulphuric acid loading of 0.1 M and KL-EPH concentration of 50%; c. Temperatures of 110 ℃, 6 / 14


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retention time of 3 h, sulphuric acid loading of 0.05-0.5 M and KL-EPH concentration of 50%; d. Temperatures of 110 ℃, retention time of 3 h, sulphuric acid loading of 0.1 M and KL-EPH concentration of 10%-90%) To improve depolymerisation of rice straw, effects of temperature, retention time, sulphuric acid loading and KL-EPH concentration on the degradation of rice straw were firstly investigated (Fig.3). In general, the results demonstrated temperature had the most significant impact on cellulose, hemicellulose and lignin removals, following by retention time. Increasing sulphuric acid loading from 0.05 M to 0.1 M resulted in a negative effect of cellulose recovery, whereas better hemicellulose and lignin removals. In contrast, sulphuric acid loading ranging from 0.1 to 0.5 M, had an insignificant increase in depolymerization of rice straw. The result indicated more than 0.1 M of sulphuric acid loading was excessive, and acid loading of 0.1 M was consequently selected. In Fig.3d, acidity of KL-EPH-water system was varied due to different concentration of KL-EPH. Therefor, using the result in Fig3c as a control, we fortunately found KL-EPH concentration chiefly played the key role in removing hemicellulose and lignin. Moreover, Increasing temperature from 130 ℃ to 150 ℃ or extending retention time from 3 hours to 9 hours, lignin removals were surprisingly decreased (Fig.3a, 3b). After analyzing scanning electron microscopy (SEM) images, interesting, we found that there were many particles on the surfaces of residue processed at 110 ℃ for 9 hours (Fig.4b) and 150 ℃ for 3 hours (Fig.4e). This discovery was similar to that reported in Koo’s study27. Furthermore, high temperatures or/and long time during degradation of lignocellulose will result in irreversible condensation of lignin12. Based on these reports and results, we supposed these particles to be condensed lignin. In any case, it is inadvisable to process lignocellulosic biomass using high temperature or/and long time. According to the results in Fig.3, the retention time of 3 hours, the sulphuric acid loading of 0.1 M and the KL-EPH concentration of 50% were considered to be the optimized condition. As to temperature, 85.63% of cellulose can be kept in residue after treatment at 110 ℃ (Fig.3a). But only 76.98% of hemicellulose and 36.54% of lignin were removed. In contrast, 92.43% of hemicellulose and 60.51% of lignin were depolymerized raising temperature from 110 ℃ to 130 ℃, which were increased by 20.07% and 65.59%, respectively. However, 20.14% of cellulose loss in residue was hardly accepted, compared to that at 110 ℃. Accordingly, we added a temperature point between 110 ℃ and 130 ℃. That is, 120 ℃ with a retention time of 3 hours, a sulphuric acid loading of 0.1 M and 50% KL-EPH concentration.

7 / 14



Fig. 4 Surface morphology of raw materials and residues.(a. rice straw; b. residue treated for 9 h; c. residue treated at 120 ℃; d. precipitated residue; e. residue at 150 ℃) 1.6 1.4

Rice straw Treated at 120℃ Precipitated residue 3346

1245 1060

2902

1.2

Transmittance

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

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1.0 0.8 0.6 835

0.4 0.2 0.0 4000

1514

3500

3000

2500

2000

1463

1500

1124

1000

500

Wavenumbers (cm-1)

Fig. 5 FTIR spectrums of rice straw and residues After treatment at 120 ℃, 12.66% of cellulose, 90.17% of hemicellulose and 53.17% of lignin were removed from rice straw (Fig. 3a). These results were much higher than those obtained with 2MeTHF or MIBK system at similar temperature, summarized in Table 228,29,30. Then, 33.55% of precipitated residue (based on lignin weight) was obtained from organic phase. Afterward, the components of the precipitated residue was measured by the US National Renewable Energy Laboratory (NREL) method17. The results of SEM image showed the morphology of precipitated residue looked like unconsolidated fragments as opposed to that of the residue treated at 120 ℃(Fig.4c, 8 / 14


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4d). FTIR spectrums, as shown in Fig. 5, revealed bands at 3346 cm-1 and 2902 cm-1 were assigned to OH stretching of lignin and polysaccharides (cellulose and hemicelluloses)31. According to the results of componential analysis, most of the hemicellulose in residue treated at 120 ℃ and precipitated residue were removed. It indicated these two increased bands should be assigned to OH stretching of lignin. The peaks at 1245 cm-1 and 1060 cm-1 were assigned to the stretching of CO bonds which is characteristic of hemicellulose and lignin, and CO stretching in cellulose, respectively32. The significant decrease of the intensity of the peak from the treated residue at 1245 cm-1 indicated the hydrolysis of hemicellulose or/and lignin, which was consistent with the result of componential analysis. The increased intensity of the peak from the precipitated residue at 1245 cm1 suggested the hydrolysis of hemicellulose. In other words, this peak was mainly related to lignin in the precipitated residue, compared with rice straw and the residue treated at 120 ℃. The increased intensity of the peak at 1060 cm-1 showed more cellulose in the residue treated at 120 ℃, compared with rice straw. The absence of the peak at 1060 cm-1 revealed there was little cellulose in the precipitated residue. Meanwhile, the peaks at 1514 cm-1, 1463 cm-1, 1124 cm-1 and 835 cm-1 were only observed in the precipitated residue. These bands were assigned to the C=C stretching of the lignin aromatic ring, aromatic ring vibrations of lignin, syringyl ring breathing and benzene ring CH bending of lignin, respectively32,33,34. The result suggested the precipitated residue mainly consisted of lignin. Table 2 Work found in the literatures on organosolv pretreatment System

Material

KLEPH-

Rice straw

Reaction

Cellulose

Hemicellulose

Lignin

Cellulase

condition

recovery

removal

removal

yield

loadinga

120

87.34%

90.17%

53.17%

88.06%

20 FPU/g

℃,

180 min

water-

Glucose

(72 h)

Reference Current study

H2SO4 MIBK-

Beechwood

℃,

83.8%

96.6%

49.4%

-

48.40%

23.91%

60 min

water-H2SO4 MTHF-

175

bamboo

120

℃,

8.4 mg/g

28

10 FPU/g

29

10 FPU/g

29

10 FPU/g

29

17 FPU/g

30

17 FPU/g

30

(48 h)

20 min

water-oxalic

29.30% 20.46% (96 h)

acid MTHF-

bamboo

140

℃,

-

~85%

~35%

20 min

water-oxalic

~50 (96 h)

acid MTHF-

bamboo

water-oxalic

180

℃,

-

99.31%

56.48%

20 min

92.89% (96 h)

acid MIBK-

Eucalyptus

160

water-formic

grandis

90 min

MTHF-

Eucalyptus

180

water-formic

grandis

30 min

℃,

31.48%

99.74%

74.33%

Screening Solvents Based on Hansen Solubility Parameter Theory To

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