Coproduction of Furfural and Easily Hydrolyzable Residue from Sugar

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Co-production of furfural and easily hydrolysable residue from sugarcane bagasse in MTHF/aqueous biphasic system: influence of acid species, NaCl addition and MTHF Xing-kang Li, Zhen Fang, Jia Luo, and Tong-chao Su ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b01847 • Publication Date (Web): 30 Aug 2016 Downloaded from http://pubs.acs.org on August 31, 2016

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ACS Sustainable Chemistry & Engineering

1

Co-production of furfural and easily hydrolysable residue from sugarcane bagasse in MTHF/aqueous

2

biphasic system: influence of acid species, NaCl addition and MTHF

3

Xing-kang Lia,c, Zhen Fangb*, a, Jia Luo a, Tong-chao Sua

4 5 a

6

Key Laboratory of Tropical Plant Resources and Sustainable Use, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, 88 Xuefulu, Kunming, Yunnan Province 650223, China

7 8 9

b

Biomass Group, College of Engineering, Nanjing Agricultural University, 40 Dianjiangtai Road, Nanjing, Jiangsu 210031, China

10 11 12

c

University of Chinese Academy of Sciences, 19A Yuquan Road, Beijing 100049, China

13 14 15

*Author for correspondence

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Zhen Fang ([email protected])

17

Web: http://biomass-group.njau.edu.cn/

18 19

Emails:

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Xing-kang Li: [email protected]

21

Jia Luo: [email protected]

22

Tong-chao Su: [email protected]

23

1

ACS Paragon Plus Environment


Abstract

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In order to develop a process for the simultaneous production of furfural and easily hydrolysable

3

cellulose, the degradation of sugarcane bagasse in single aqueous and 2-methyltetrahydrofuran

4

(MTHF)/aqueous AlCl3 biphasic system was studied. In single aqueous system, influence of acid species

5

(FeCl3, HCl and AlCl3) on furfural production and cellulose degradation was investigated at 150 oC. FeCl3

6

and HCl promoted furfural production from hemicellulose but with severe cellulose degradation. AlCl3

7

decreased cellulose degradation with considerable furfural yield and high glucan content in solid residues.

8

The role of NaCl in furfural production and cellulose decomposition was also investigated in single aqueous

9

system using different acid as catalyst. Adding NaCl significantly promoted furfural yield without catalyst

10

but also accelerated cellulose decomposition when FeCl3 or HCl was used as catalyst. In AlCl3-catalyzed

11

system, NaCl had less influence on residue yield and its composition, although NaCl also promoted furfural

12

production. The influence of MTHF on furfural yield, residue composition and enzymatic hydrolysis of

13

residue was also studied. Under the best conditions (0.45 g bagasse, 9 mL MTHF, 9 mL water, 0.1 M AlCl3,

14

150 oC, 45 min and 10 wt% NaCl), 58.6% furfural was obtained while more than 90% of cellulose was

15

remained in the residue. The organic phase was separated from the aqueous phase directly by decantation.

16

After reuse of organic phase for 3 cycles, 11.5 g/L furfural was obtained. The catalyst-containing aqueous

17

phase could be reused directly after decantation of the organic phase without loss of activity. The obtained

18

residue was easy to be hydrolyzed and produced 89.3% glucose yield after 96-h enzymatic hydrolysis at low

19

cellulase loading (30 FPU of cellulase /g glucan).

20 21

Key words: furfural; glucose; bagasse; hydrolysis; 2-methyltetrahydrofuran/aqueous; AlCl3; NaCl

22 23

2


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Introduction

2

Dwindling reserve of fossil resources and environmental concern associated with fossil fuel application

3

spur research on the conversion of lignocellulosic biomass to renewable fuels and chemicals 1-2. Furfural is a

4

platform chemical that has potential to produce biofuels and attracts much attention from academia and

5

industry 3. It is produced from pentose (e.g., xylose and arabinose) in hemicellulose that occupies 20-30 wt%

6

of typical terrestrial biomass such as wood. Cellulose，accounting for another 30-50 wt% biomass, is

7

normally hydrolyzed to fermentable sugars for bioethanol

8

surrounded by hemicellulose and protected by lignin. Pretreatment of lignocellulosic biomass is required to

9

remove hemicellulose and lignin and make cellulose highly accessible to catalysts or cellulases 6. A chemical

10

method that could efficiently convert hemicellulose to furfural and simultaneously produce

11

cellulose-enriched residue is encouraged as it remarkably promotes the economics of biorefinery process 7.

12

However, few studies have focused on the co-production of furfural and cellulose-enriched residue.

4-5

. In lignocellulosic biomass, cellulose is

13 14

Nowadays, most industrial production of furfural is adapted from the Quaker Oats process started in

15

1921 8 that uses strong mineral acids such as H2SO4 as catalyst and is operated at high temperature (> 150

16

o

17

moderate Lewis and Brönsted acidity in water. Lewis acidity catalyzes the isomerization of xylose to

18

xylulose and Brönsted acidity catalyzes the dehydration of xylulose into furfural

19

Lewis and Brönsted acidity enables furfural formation under mild conditions that may avoid severe

20

decomposition of cellulose. It is found that AlCl3 can reduce the active energy of xylan degradation in

21

orgnosolv pulping process 11.

C) causing complete degradation of cellulose 4. Some metal chlorides (e.g., AlCl3 and CrCl3) have both

9-10

. The combination of

22 23

Normally, furfural is produced with very low yield from the reactions of lignocelluloses in single 12

24

aqueous system

. But, adding salts such as NaCl can significantly influence Brönsted acid-catalyzed

25

furfural production from xylose in both single aqueous system 13-14 and organic/aqueous biphasic system 15.

26

However, the role of NaCl in Lewis acid-catalyzed furfural production from actual biomass has not been

3



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studied. Adding NaCl also improves 5-hydroxymethylfurfural (HMF) production from glucose over AlCl3

2

catalyst 16, and accelerates cellulose degradation in aqueous organic acid solution 17 and subcritical water 18.

3

Therefore, new methods that avoid the degradation of cellulose during furfural production over Lewis acid

4

catalyst in NaCl solutions are required to develop.

5 6

Adding organic solvent considerably promotes furfural yield by reactive extraction, while the optional

7

organic solvents could be ethanol, methanol, γ-valerolactone, tetrahydrofuran, 2-methyltetrahydrofuran

8

(MTHF), and alkylphenols 15, 19-20. Among these solvents, MTHF deserves particular attention due to its high

9

immiscibility with water, stability under acidic environment and easy recycle (boiling point about 80 oC) 21. 22

and SnCl4

23

10

FeCl3 - NaCl

catalyzed furfural production in MTHF/water biphasic system with the

11

assistance of NaCl was studied. Furfural was efficiently extracted into MTHF, with its yield promoted from

12

34-50% to 54-78%. After reaction, the MTHF phase rich in furfural was separated from the aqueous phase

13

containing catalyst easily by decantation. Furfural could be purified after distillation of MTHF and the

14

aqueous phase was reused without the loss of activity.22 However, these studies use pure xylose and xylan or

15

hemicellulose hydrolysate as substrate rather than actual lignocelluloses that may have different furfural

16

yields

17

greatly restrains the activity of cellulases by competitive adsorption during cellulose saccharification

18

One-step fractionation of biomass in aqueous oxalic acid/MTHF biphasic system provided cellulose with

19

similar enzymatic digestibility to Avicel cellulose

20

phase and soluble sugars were reserved in aqueous phase (mainly from hemicellulose) as byproducts

21

simultaneously.

24

. MTHF also effectively removes lignin, the third abundant component in raw lignocelluloses that 25

.

26

. In this process, lignin was extracted into the organic

22 23

In this study, sugarcane bagasse, one of the commonly used biomass in furfural industry 7, was chosen

24

as raw material for one-pot production of furfural and cellulose-enriched residue using AlCl3, FeCl3 and HCl

25

as catalysts. The influences of AlCl3, NaCl and MTHF on furfural yield and enzymatic accessibility to

26

residue were studied (Scheme 1).

27

Experimental Section 4


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Materials

2

Bagasse was purchased from Dehong Liangheliliang biological food Ltd. (Yunnan). It was air-dried,

3

milled and passed through a 20-mesh sieve (< 0.85 mm). It was air-dried in oven (WFO-710, EYELA,

4

Tokyo Rikakikai Co., Ltd.) again at 105 oC for 4 h before use. Its composition was determined with two

5

repetitions according to the National Renewable Energy Laboratory (NREL) procedure

6

38.3±1.0 glucan, 20.4±1.5 xylan, 3.1±0.4 arabinan, 3.0±0.2 manan, 22.5±0.9 lignin, 2.1±0.2 ash and 8.4±0.3

7

extractives. Detailed analytical procedure was described in previous work

8

Avicel PH101 was purchased from Sigma-Aldrich (Shanghai). MTHF (> 99%), HMF (> 99%), furfural (>

9

99.5%), cellubiose (> 99%), D-(+)-glucose (> 99.5%), D-(+)-xylose (99%), L-(+)-arabinose (> 99%) and

10

D-mannose (> 99%) were bought from Aladdin Factory Co., Ltd. (Shanghai). AlCl3·6H2O(> 99%) and

11

FeCl3·6H2O(> 99%) were from Xilong Chemical Factory Co., Ltd. (Shantou, Guangdong). Concentrated

12

HCl (36-38%) was bought from Shandian Medicine Co., Ltd (Kunming, Yunnan). Cellulase (Celluclast

13

1.5L® from Trichoderma reesei ATCC 26921, >700 Ug-1) and β-glucosidase (Novozyme 188 from

14

Aspergillus niger) were purchased from Sigma-Aldrich (Shanghai). The activities of cellulase and

15

β-glucosidase were 88.8 FPU/mL and 514 cellobiase unit (CBU)/mL, respectively, determined by the

16

method established by Ghose et al 29.

17

Acid-catalyzed reactions and analysis of the filtrate

27

with (wt%)

28

. Microcrystalline cellulose

18

Acid-catalyzed reactions of bagasse were carried out in a microwave reactor (Monowave 300, Anton

19

Paar, Graz, Austria). For a typical reaction, 0.3 g dried bagasse, appropriate amount of chlorides [e.g., 0.217

20

g AlCl3·6H2O (0.1 M) and 0.9 g NaCl (10 wt%)], 9 mL aqueous solution and 9 mL MTHF were added into a

21

30 mL quartz tube with a magnetic stir bar stirring at 600 rpm. The tube with sample was heated by

22

microwave irradiation to 130-170 oC (5.6-13.1 bar) within 3 min for 30 min reaction. After reaction, the tube

23

was cooled down to 40 oC within 5-10 min by pressurized air. Product mixture was taken out from the tube

24

and filtered through a 0.22 µm membrane. Deionized water was used to wash the residue and dilute the

25

filtrate to 150 mL in a homogeneous phase (MTHF and water were miscible). The filtrate was analyzed by

26

HPLC (LC-20A, Shimadzu) equipped with Bio-Rad Aminex® HPX-87H column, and 50 mM H2SO4 was

27

used as mobile phase at flow rate of 0.6 mL min-1. Oven temperature was set at 60 oC. Furfural and HMF 5



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1

were determined by UV detector at 284 nm, while pentose and hexose in aqueous product were determined

2

by refractive index (RI) detector. Standard calibrated curves for these products were determined with five

3

points (0.05, 0.1, 0.2, 0.4 and 0.8 mg/mL, R2 > 0.999) 28. The yields of furfural, HMF, glucose and xylose

4

were defined as their weights in the filtrate divided by their weight equivalents contained in bagasse 19:

5

Furfural yield (wt %) = (furfural weight in filtrate)/(pentosan weight in bagasse×1.375)×100%

(1)

6

HMF yield (wt %) = (HMF weight in filtrate)/(hexosan weight in bagasse×1.286)×100%

(2)

7

Glucose yield (wt %) = (glucose weight in filtrate)/(glucan weight in bagasse×0.90)×100%

(3)

8

Xylose yield (wt %) = (xylose weight in filtrate)/(xylan weight in bagasse×0.88)×100%

(4)

9

Residue yield (wt %) = (weight of recovered residue)/(weight of bagasse)×100%

(5)

10

Under these definitions, theoretical yield of all products were 100%.

11

CSF (combined severity factor) used in this study is defined as:

12

CSF = log{t·exp[(TH-100)/14.75]}-pH

13

Where, t is the reaction time of treatment in minutes, TH the reaction temperature in oC and pH is the

14 15

(6)

acidity of the aqueous solution before reaction.30 All the experiments were repeated 2 times except specially mentioned and the errors were 0.1-4.3%

16

for furfural, 0.8-8.0% for HMF, 0-6.3% for glucose, 0.3-5.8% for xylose, and 0.5-3.4% for residue,

17

respectively.

18

Solvent separation and recycle

19

MTHF was insoluble in water, two phases were formed after MTHF was added to aqueous AlCl3.

20

Adding NaCl decreased MTHF solubility in aqueous phase further. So, the liquid product was centrifuged at

21

3000 rpm (relative centrifugal force of 2013) for 5 min in a refrigerated centrifuge (TG18G-Ⅱ, Kaida

22

Scientific Instrument Co., Ltd., Hunan). Then the MTHF phase (about 8.5 mL) was drawn out directly by 5

23

mL syringe, the salt-containing aqueous phase was separated from the residue by filtration with 0.2 µm filter

24

membrane and be reused directly. Several runs were done to obtain enough used organic/aqeous phase. To

25

examine reusability of organic phase, 9 mL used MTHF was added to 9 mL of fresh aqueous phase.

26

Similarly, 9 mL used aqueous phase was added to 9 mL fresh MTHF to test the reusability of aqueous phase.

6


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1

Also, 5 mL of used organic/aqeous phase after each recycle were diluted to 150 mL using deionized water to

2

determine products concentration in both phases and calculate partition efficient as follows:

3 4

Partition coefficient = (product concentration in organic phase)/ (product concentration in aqueous phase)

(7)

5

Haan et al. reported separation of furfural from a liquid aqueous phase comprising furfural and organic

6

acids.31 However, in this study, after the removal of MTHF by vacuum rotary evaporator (RE-52AA, Yarong

7

biological and chemical instrument factory, Shanghai) at 30 oC for about 30 min, products in MTHF phase

8

from R-Al-Na-MTHF reaction system (MTHF/AlCl3-NaCl aqueous solution at 150 oC for 45 min) were

9

dissolved in CDCl3 for

10

13

C NMR analysis on Avance III 600 spectrometer (600 MHz, Bruker BioSpin

GmbH, Karlsruher, Germany) at 22 oC.

11

The solid residue was washed with 30 mL distilled water for 3 times and dried in a freeze-drier

12

(PDU-1200, EYELA, Tokyo Rikakikai Co., Ltd.) for 48 h for weight (residue yield) and composition

13

determination (the same method for raw bagasse), and subsequent enzymatic hydrolysis.

14

Characterization of bagasse and residues

15

SEM (ZEISS EVO LS10, Cambridge, UK) operated at 10 keV was used to observe the morphology of

16

solid samples. FT-IR measurement was performed on Nicolet is10 spectrometer (Madison, WI) with a

17

resolution of 4 cm-1 at 500-4000 cm-1.

18

Enzymatic hydrolysis of residue

19

Enzymatic hydrolysis was carried out in 20 mL glass vials containing 2500 µL 0.1 M citrate buffer, 50 µL

20

2% sodium azide, 75 mg solid residue, 5-30 FPU of cellulase and 20 CBU of β-glucosidase. Deionized

21

water was supplemented to bring the total volume of reaction solution to 5000 µL in the vials. Temperature

22

was kept at 50 oC and rotation rate at 150 rpm for hydrolysis in a thermostat incubator (SPH-100B, Shanghai

23

Shiping laboratory equipment Co., Ltd.). During hydrolysis, 200 µL sample was taken out of the vials by a 1

24

mL pipettor at 3, 6, 12, 24 and 96 h for glucose and cellubiose analysis by LC-20A HPLC equipped with RI

25

detector, using the same conditions as the above analysis for the sugars. Glucose yield (wt%) was defined as

26

follows:

27

Glucose yield (wt%) = 0.90×(glucose weight in hydrolysate)/(glucan weight in residue)×100% 7



(8)

1

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2 3

Results and Discussion

4

Furfural production from bagasse using different acids as catalysts

5

Time evolution of furfural production from bagasse (about 0.3 g) was studied in 9 mL aqueous phase at

6

150 oC using different chloride salts as catalyst (Fig. 1). Fixed moles of AlCl3 (0.1 M, pH = 3.4), FeCl3 (0.1

7

M, pH = 1.6) and HCl (0.3 M, pH = 0.52) were used to keep the concentration of chloride ion same for

8

different reactions. Furfural yields of 49.2% and 54.8% were obtained at 90 min with FeCl3 and at 45 min

9

with HCl, respectively. Surprisingly, AlCl3 gave furfural yield of 35.5% at 30 min, much lower than those

10

with FeCl3 and HCl. However, severe degradation of cellulose was observed using FeCl3 or HCl as catalyst,

11

with glucose yield of more than 20%. This was attributed to their strong Brönsted acidity for long reaction

12

time.

13

As CSF used for furfural production was much higher than that for hemicellulose removal and

14

lignocellulose pretreatment, so when furfural yield reached the peak value hemicellulose removal procedure

15

has already finished. Thus furfural production from lignocellulose in one-pot often led to severe

16

decomposition of cellulose. To obtain high yield of furfural and high recovery of cellulose in residue

17

simultaneously, both furfural yield and degradation products of cellulose such as glucose and HMF should

18

be monitored. In FeCl3-catalyzed system, the yield of furfural increased from 26.3% to 49.2% as time was

19

prolonged from 45 to 90 min, and changed slightly within 47.2-49.2% as time rose further to 180 min (Fig.

20

1a). The yield of xylose was 53.9% at 45 min, but gradually dipped to 10.1% at 180 min. The yields of

21

glucose and HMF at 90 min were 19.9% and 1.0%, respectively, and rose to 25.5% and 1.6% at 120 min.

22

In HCl-catalyzed system, the yield of furfural increased from 18.3% to 54.8% as time was prolonged

23

from 5 to 45 min, but remarkably decreased to 44.5% at 120 min (Fig. 1b). The yield of xylose sharply

24

jumped from 73.3% to 6.5% as time increased from 5 to 75 min, while the yields of glucose and HMF were

25

21.3% and 1.3% at 45 min, and 29.8% and 1.8% at 90 min, respectively.

26

In AlCl3-catalyzed system, the yield of furfural increased from 13.0% to 35.5% as time was prolonged 8


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1

from 5 to 30 min, and slightly declined to 31.6% at 75 min (Fig. 1c). Simultaneously, the yield of xylose

2

remarkably decreased from 38.9% to 5.1% as time increased from 5 to 30 min, and decreased further to

3

1.2% at 75 min. The yields of glucose and HMF at 30 min were 0.7% and 5.6%, respectively. AlCl3

4

seriously catalyzed the degradation of glucose to HMF, which made glucose yield much lower than HMF

5

yield.

6

When the highest furfural yield was obtained, CSF were 1.8, 2.6 and -0.45, respectively for FeCl3, HCl

7

and AlCl3 catalyzed reaction systems. In comparison, CSF applied for acid-assisted lignocellulose

8

pretreatment varied from 1.0 to 2.0.30, 32 Although CSF for FeCl3-catalzyed furfural production was similar

9

to traditional acid-assisted pretreatment, it did cause severe degradation of cellulose, suggesting that

10

appropriate CSF may be different when different acid species were used as catalysts.33 When HCl was used

11

as catalyst, CSF was much higher than that for pretreatment and also caused severe degradation of cellulose,

12

in agreement with phenomena found in industrial production of furfural. Very interesting result was found

13

when AlCl3 was used as catalyst. AlCl3 facilitated hemicellulose removal and furfural formation even at low

14

CSF of -0.45. In summary, AlCl3 was more suitable to co-produce furfural and cellulosic residue from

15

bagasse, because it had three advantages: i) considerable furfural yield but the least degradation of cellulose

16

(yield ratio of glucose to furfural was 0.02 for AlCl3, 0.58 for FeCl3 and 0.39 for HCl at 45 min); ii) the

17

shortest time for the completion of furfural production (30 min vs. 90 min for FeCl3 and 45 min for HCl); iii)

18

moderate pH (3.4) circumstance than FeCl3 (1.6) and HCl (0.52).

19

Role of NaCl in furfural production in AlCl3 system

20

NaCl was found to significantly increase furfural yield from xylose in Bronsted-acid-catalyzed

21

reactions 14, however, the influence of NaCl on furfural production with Lewis acid has not been studied yet.

22

The effect of NaCl on furfural production from bagasse with different catalysts was studied in 9 mL aqueous

23

phase at 150 oC (Fig. 2). In FeCl3-catalyzed reaction at 150 oC for 90 min (Fig. 2a), furfural yield slightly

24

increased from 49.2% to 52.5% as NaCl increased from 0 to 10 wt%, but decreased to 46.2-47.2% when

25

NaCl exceeded 10 wt%. However, the yield of xylose substantially decreased from 25.6% to 5.1% as NaCl

26

increased from 0 to 20 wt%. Cellulose degradation was also promoted when NaCl increased to 20 wt%, with

27

the yields of glucose and HMF increasing from 19.9% and 0.9% to 29.4% and 3.0%, respectively. 9



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Page 10 of 33

1

In HCl-catalyzed reaction at 150 oC for 45 min, NaCl with less than 10 wt% showed slightly influence

2

on furfural production with furfural yield of 54.8-56.6% (Fig. 2b). But, when NaCl increased from 10 to 20

3

wt%, furfural yield remarkably decreased from 55.9% to 35.6%. Simultaneously, the degradation of xylose

4

was substantially accelerated. Xylose yield decreased from 24.0% to 7.8% when NaCl increased from 0 to 5

5

wt%. Marcotullio et al.13 proposed that Cl- anion could promote the formation of 1,2-enediol, an

6

intermediate from xylose dehydration. The yields of glucose and HMF were also promoted from 21.3% and

7

1.3% to 30.1% and 2.4%, respectively when NaCl increased to 10 wt%.

8

In AlCl3-catalyzed system at 150 oC for 30 min, with NaCl increasing from 0 to 20 wt%, furfural yield

9

almost linearly rose from 35.5% to 56.3%, while xylose yield slightly declined from 5.1% to 3.1% (Fig. 2c).

10

It demonstrated that adding NaCl significantly improved furfural production from xylose but relieved the

11

degradation of furfural. When 20 wt% NaCl was added, furfural yield of 56.3% was achieved, which was

12

comparable to the optimized furfural yields obtained using FeCl3 (52.5% at 150 oC for 90 min in aqueous

13

solution containing 0.1 M FeCl3 and 10 wt% NaCl) or HCl (56.6% at 150 oC for 45 min in aqueous solution

14

containing 0.3 M HCl and 10 wt% NaCl). More importantly, both glucose and HMF yields from the

15

degradation of cellulose were not stimulated by NaCl.

16

In summary, furfural yields in FeCl3 or HCl-catalyzed system at 150 oC declined remarkably as NaCl

17

exceeded 10 wt%, but the degradation of cellulose was promoted. However, in AlCl3-catalyzed system,

18

furfural production was significantly enhanced by adding NaCl without serious degradation of cellulose as

19

both glucose and HMF yields were still low (< 2% glucose yield and about 7% HMF yield).

20

Role of MTHF and furfural production in MTHF/aqueous AlCl3 biphasic system

21

Addition of organic solvent could benefit furfural production

20

by reactive extraction, while MTHF

22

efficiently promoted furfural yield catalyzed by FeCl322 or SnCl423. Production of furfural from bagasse was

23

studied in MTHF/aqueous AlCl3 biphasic system (volume ratio of 1:1) at 130-170 oC (Scheme 1). The

24

influence of temperature, time, AlCl3 concentration and NaCl usage on the yields of furfural, HMF and

25

residue in MTHF/aqueous AlCl3 biphasic solution was studied by single-factor experiment (Fig. 3).

26

Under the fixed conditions (60 min and 0.1 M AlCl3 without NaCl), temperature increasing from 130 to 10


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1

150 oC significantly promoted the yields of both furfural and HMF from 8.7% and 1.1% to 45.8% and 6.6%,

2

respectively, while both yields kept almost constant until 170 oC (Fig. 3a). Cellulose in lignocellulosic

3

materials contains both crystalline and amorphous parts. Hydrolysis of amorphous cellulose could be easily

4

achieved at low temperature of 150 oC, but the degradation of crystalline cellulose needs much severer

5

conditions (e.g., > 160 oC)

6

degradation of amorphous cellulose. On the other hand, the yield of solid residue continuously decreased

7

from 62.7% to 39.9% with temperature growing from 130 to 170 oC. The selected temperature was 150 oC.

17, 34

. So, the increase of HMF yield with temperature was mainly from the

8

Under the fixed conditions (150 oC and 0.1 M AlCl3 without NaCl), reaction time prolonging from 15 to

9

45 min significantly promoted the yields of both furfural and HMF from 25.7% and 3.2% to 46.0% and

10

6.3%, respectively, and changed little until 75 min (Fig. 3b). The yield of solid residue decreased from

11

64.3% to 53.8% with time increasing from 15 to 45 min, and changed slightly until 75 min. The selected

12

time was 45 min.

13

Under the fixed conditions (150 oC and 45 min without NaCl), AlCl3 concentration increasing from 0.03

14

to 0.1 M significantly promoted furfural yield from 31.9% to 46.0%, but excessive AlCl3 slightly influenced

15

furfural yield (Fig. 3c). The yields of HMF and solid residue were slightly affected by the variation of AlCl3

16

concentration. So, 0.1 M AlCl3 was selected as the optimized concentration.

17

The influence of NaCl on furfural yield was optimized at 150 oC with 0.1 M AlCl3 for 45 min (Fig. 3d).

18

NaCl increasing from 5 to 10 wt% promoted furfural yield greatly by 24% (from 48.2% to 60.0%), while

19

NaCl concentration < 5 wt% or >10 wt% had slight influence on furfural yield. The highest furfural yield

20

(62.2%) was obtained at 20 wt% NaCl, which was comparable to the results (furfural yield of 55-66%)

21

obtained from different lignocellulosic biomass in microwave-assisted tetrahydrofuran/aqueous saturated

22

NaCl system at 160 oC for 60 min in previous studies 9. High NaCl concentration in aqueous solution had

23

slight effects on the variation of HMF and residue yields. Concentration of 10 wt% NaCl was selected as

24

best value.

25

The influence of MTHF and NaCl was studied at 150 oC for 45 min using 0.1 M AlCl3 (Table 1). The

26

total volume of reaction liquor (including aqueous and organic phases) was adjusted to 18 mL to keep the

27

liquid/biomass ratio fixed (0.45 g bagasse). Table 1 lists different systems with results and reaction 11



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Page 12 of 33

1

conditions: R-Al (18 mL 0.1 M AlCl3 aqueous solution at 150 oC for 45 min, where R means reaction),

2

R-Al-Na (18 mL water with 0.1 M AlCl3 and 10 wt% NaCl), R-Al-MTHF (9 mL MTHF and 9 mL water

3

with 0.1 M AlCl3), and R-Al-Na-MTHF (9 mL MTHF and 9 mL water with 0.1 M AlCl3 and 10 wt% NaCl).

4

In AlCl3-catalyzed reaction without NaCl, adding MTHF significantly promoted furfural yield from 30.6%

5

to 43.6% (Table 1, R-Al vs. R-Al-MTHF) because the reactive extraction of furfural into MTHF phase

6

reduced the degradation of furfural in aqueous phase. The concentration of furfural in MTHF phase was 6.3

7

times that in aqueous phase. Similarly, in AlCl3-catalyzed reaction with 10 wt% NaCl, furfural yield grew

8

from 50.0% to 58.6% as MTHF was added (Table 1, R-Al-Na vs. R-Al-Na-MTHF). Simultaneously, the

9

yield of solid residue decreased from 62.6-63.0% to 54.7-54.9% with slight growth of HMF yield.

10

The results of NaCl influence in Table 1 were in accordance with the results in Fig. 2c. Adding 10 wt%

11

NaCl in aqueous AlCl3 solution resulted in furfural yield greatly increasing from 30.6% to 50.0%, while the

12

yield of residue changed little (Table 1, R-Al vs. R-Al-Na). In MTHF/aqueous AlCl3 solution (Table 1,

13

R-Al-MTHF vs. R-Al-Na-MTHF), NaCl improved furfural yield from 43.6% to 58.6% with almost constant

14

residue yield of 54.7% because of the enhanced partition coefficient of furfural in organic phase (Table 1,

15

R-Al-MTHF vs. R-Al-Na-MTHF) 4. On the other hand, HMF formation was also promoted by NaCl,

16

especially in aqueous solution.

17

In summary, to simultaneously achieve high furfural and cellulosic residue yields, the suggested

18

conditions for bagasse conversion in MTHF/aqueous AlCl3 biphasic system were 150 oC, 45 min, 0.1 M

19

AlCl3 and 10 wt% NaCl with furfural yield of 60.0% and residue yield of 53.9%.These conditions were

20

further used for the following optimization of solid loading.

21

Influence of solid loading and solvent recycle on furfural production

22

In practical process, relatively high ratio of solid biomass to reaction solvent was always required to

23

achieve better economics, although it might affect the efficiency of mass and heat transfer. Here, the

24

influence of solid loading on furfural yield was tested in MTHF/AlCl3 aqueous solution at 150 oC for 45 min

25

(Table 2). Other conditions were 9 mL MTHF, 9 mL aqueous solution, magnetic stirring rate of 600 rpm, 0.1

26

M AlCl3 and 10 wt% NaCl. When bagasse loading increased from 0.3 to 0.6 g, the yield of furfural

27

remarkably decreased from 60.0% to 54.0%, while residue yield increased from 53.9% to 57.2%. Increased 12


Page 13 of 33

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1

bagasse loading led to higher furfural concentration both in the organic phase and in the acidic aqueous

2

phase. Exposure of furfural to acidic aqueous phase accelerated furfural degradation to humins. Polymeric

3

soluble lignin also greatly affected furfural yield.35

4

Organic and aqueous phases were recycled 2 times (Table 3). Increasing concentration of furfural in the

5

spent MTHF decreased the efficiency of furfural production in next recycle. Furfural yield decreased from

6

58.6% to 55.6% and 53.8% for the first and second recycle. However, high furfural concentration of 11.5 g

7

L-1 (>1 wt%, based on the mass of organic solvent) was realized in MTHF phase after 2 recycles, which

8

benefited the post-treatment of organic products. The recycle of aqueous phase containing residual sugars

9

from the latest reaction slightly promoted the furfural yield in the next reaction. Furfural yields were

10

enhanced from 58.6% to 60.8% and 61.2% with the first and second recycle of aqueous phase. HMF yield

11

remarkably increased from 7.9% to 9.9% and 11.1% respectively for the first and second recycle of aqueous

12

solution.

13

Influence of MTHF and NaCl on the composition and structure of residues

14

Besides high furfural yield, it is important to obtain high cellulose yield that has good structure for

15

easily enzymatic hydrolysis. Table 4 showed the glucan and xylan contents in solid residues as well as lignin

16

content and residue yields after different reactions under the same conditions in Table 1 (150 oC, 45 min, 0.1

17

M AlCl3), while the conditions for MTHF extraction were 0.45 g bagasse, 18 mL MTHF, 150 oC and 45 min.

18

After reaction in aqueous AlCl3 or aqueous AlCl3-NaCl solution, xylan content in residues from R-Al and

19

R-Al-Na systems was sharply reduced from 20.4% to 3.5% and 2.8%, respectively. Glucan content

20

remarkably increased from 38.3% to 52.1-53.3% because hemicellulose and extractives were removed from

21

solid residues. Adding MTHF did not influence the degradation and removal of hemicellulose. However,

22

glucan content in residues from R-Al-MTHF and R-Al-Na-MTHF rose further to 63.2-64.1%, indicating

23

other chemical compositions such as lignin in raw bagasse were removed by MTHF. Nuclear magnetic

24

resonance (NMR) analysis of the organic phase after reaction in MTHF/aqueous AlCl3-NaCl solution

25

(R-Al-Na-MTHF) demonstrated that some aromatic products were indeed extracted by MTHF (Fig. 4). For

26

subsequent enzymatic hydrolysis, the removal of lignin and other impurities in bagasse might be more

27

important than the reduction of cellulose crystallinity. The crystalline structure of cellulose only hindered the 13



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Page 14 of 33

1

contact of cellulosic substrate with enzyme molecules, and retarded the efficiency of enzymatic hydrolysis.

2

However, competitive adsorption by lignin and other impurities might result in irreversible damage of

3

enzymes

4

hemicellulose or lignin from bagasse to increase cellulose concentration in the residues. So, the combination

5

of MTHF and aqueous AlCl3 corporately removed hemicellulose and lignin to yield cellulose-enriched

6

residue. On the other hand, 10 wt% NaCl in aqueous AlCl3 or MTHF/aqueous AlCl3 solution showed less

7

influence on the variation of residue composition (Table 4), although the furfural production was promoted

8

(50.0-58.6% with NaCl vs. 30.6-43.6% without NaCl in Table 4). In conclusion, reaction of bagasse in

9

MTHF/AlCl3-NaCl aqueous solution produced not only high furfural yield of 58.6%, but also lead to high

10

25

. Extraction of bagasse by MTHF without the assistance of AlCl3 could hardly remove

glucan content of 63.7% in the residue (residue yield 54.7%).

11

Scanning electron microscopy (SEM) images (Fig. 5) showed that after treatment with aqueous AlCl3 or

12

MTHF/aqueous AlCl3 solution, the surface of residues became neater with fewer deposits on the parallel

13

cellulosic microfibers, because of the removal of hemicellulose and lignin. Fourier transform-infrared

14

spectroscopy (FT-IR, Fig. 6) illustrated that all samples had absorptions at 3410-3460 and 2896-2905

15

cm-1corresponding to the stretching of -OH group and C-H bonds of alkyl group, respectively 36. Based on

16

the reference 37, the band around 1715 cm-1 was from carbonyl and carboxyl stretching. The bands at 1605

17

and 1512 cm-1 were from the skeletal and stretching vibration of benzene rings. Absorptions at 1370-1205

18

cm-1 were mainly from the bending of C-H or O-H bonding in polysaccharides, including cellulose and

19

hemicellulose, those absorptions at 1160-1030 cm-1 were from the bending of C-O or C-O-C linkages in

20

polysaccharides36. It could be concluded that after reaction in aqueous AlCl3 or MTHF/aqueous AlCl3

21

solution, the carbonyl and carboxyl stretching at 1715 cm-1 for the solid residues became weaker, proving

22

the removal of hemicellulose (mainly containing acetyl group)38. Simultaneously, absorptions at 1370-1205

23

and 1160-1030 cm-1 were remarkably strengthened, indicating the substantial increase of polysaccharides in

24

the solid residues after reactions38.

25

Enzymatic digestibility of residues

26

Enzymatic hydrolysis of bagasse and residues after different reactions was carried out with low

27

cellulase loading of 10 FPU (filter paper unit) (Fig. 7). Cellulose in raw bagasse was hard to be hydrolyzed, 14


Page 15 of 33

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1

with low glucose yield of 16.2% obtained after 96-h reaction, similar to previous studies (8.6-19.3% for 72-h

2

enzymatic hydrolysis)39-40. At initial stage (< 6 h), glucose was released rapidly from all substrates, and

3

significantly slowed down until 96 h 40. After reaction in AlCl3 aqueous solution (R-Al system), the residue

4

yielded high glucose yield of 48.1% after 96-h hydrolysis, mainly due to the removal of hemicellulose.

5

Adding NaCl in R-Al system suppressed glucose yield to 43.6% after 96 h. The negative effect of NaCl on

6

enzymatic digestibility of residues was caused by: i) acceleration of pseudo-lignin formation via the

7

condensation of furfural with high concentration 41-42, and ii) more recalcitrant structure of lignin in the raw

8

material formed during the chemical degradation reaction

9

system further improved the enzymatic hydrolysis of residue, with glucose yield enhanced to 58.4% after 96

10

h. MTHF effectively removed lignin, which relieved physical barrier and non-productive bonding of lignin

11

to cellulases, and increased glucan content in the pretreated residue. Lignin content in residue decreased

12

from 36.1% to 26.7 when MTHF was added. However, this glucose yield was still lower (58.4% vs. 81.0%)

13

than that from enzymatic hydrolysis of Avicel PH101 cellulose, which might be attributed to high lignin

14

content in residues that inhibited enzymatic hydrolysis of cellulose. Adsorption of cellulases by lignin

15

decelerated cellulose degradation

16

organosolv method, this glucose yield was also lower. Agnihotri et al.46 reported almost complete conversion

17

of cellulose for bagasse pretreated at 210 oC for 90 min in 50:50 (v/v) % ethanol:water media using pH 3.5

18

formic acid as catalyst. Considering that higher enzymes loading applied in their study (30 FPU of cellulase,

19

32 pNPGU of β-glucosidase per gram of cellulose), we investigated the influence of different cellulase

20

dosage on the enzymatic hydrolysis of residue. Increasing cellulase loading often improved enzymatic

21

hydrolysis rate

22

increased from 45.4% to 58.4%, 68.8% and 89.3%, respectively after 96-h digestion (Fig. 8), indicating that

23

high cellulase dosage provided more active sites for the enzymatic hydrolysis of cellulosic substrates. Pan et

24

al.

25

enzyme loading was higher (40 FPU/g glucan) in their study.

26

Conclusion

48

47

43-44

. Adding MTHF in AlCl3-NaCl-catalyzed

45

. As compared with other studies where bagasse was pretreated with

. When cellulase loading increased from 5 to 10, 15 and 30 FPU, glucose yield sharply

obtained about 90% glucose yield for softwood residue with similar residual lignin (27.4%), although

15



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Page 16 of 33

1

Conversion of bagasse in aqueous solution with FeCl3 and HCl benefited furfural production from

2

hemicellulose but degraded cellulose seriously. Using AlCl3 replacing FeCl3 and HCl achieved lower

3

furfural yield of 35.5% with less cellulose decomposition (glucose yield of 0.7% and HMF yield of 5.5%).

4

Adding NaCl remarkably promoted furfural production by 34.4-63.4% in AlCl3-catalyzed system with less

5

influence on the variation of residue composition. The introduction of MTHF increased furfural yield by

6

17.2-42.5% and glucan content in residue to 63.7%. Under the best conditions (9 mL MTHF, 9 mL water,

7

0.1 M AlCl3, 150 oC, 45 min and 10 wt% NaCl), furfural yield of 58.6% was obtained while more than 90%

8

of glucan was maintained in the residue. Both organic and aqueous phases were recycled 2 times, with

9

furfural yield of 53.8% for the second recycle of organic phase and 61.2% for the second recycle of aqueous

10

phases. Enzymatic hydrolysis of cellulosic residue was also remarkably enhanced with the highest glucose

11

yield of 58.4% at 50 oC for 96 h [10 FPU of cellulase and 20 CBU (cellubiase unit) of β-glucosidase], 3.6

12

times of that from raw bagasse. After cycles, the organic phase was decanted and distilled to separate

13

furfural and lignin and got purified MTHF. Lignin and furfural concentrations in the aqueous phase were low,

14

they tended to solubilize in the organic phase. After many cycles, the aqueous phase could be purified by

15

extraction with organic phase.

16

Acknowledgements

17 18

The authors wish to acknowledge the financial support from Nanjing Agricultural University (68Q-0603), and the Yunnan Provincial Government (Baiming Haiwai Gaocengci Rencai Jihua).

19 20

References

21 22 23 24 25 26 27 28 29 30 31 32

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by a Magnetic Carbonaceous Acid with Microwave. Scientific Reports 2015, 5, 17538. (29) Ghose, T. K. Measurement of cellulase activities. Pure Appl. Chem. 1987, 59 (2), 257-268. (30) Lee, J. W.; Jeffries, T. W. Efficiencies of acid catalysts in the hydrolysis of lignocellulosic biomass over a range of combined severity factors. Bioresour. Technol. 2011, 102 (10), 5884-5890. (31) Haan, J. P. Process for separating furfural from a liquid aqueous phase comprising furfural and one or more organic acids. WO2011161141 A1, 20111229, 2011. (32) Pedersen, M.; Vikso-Nielsen, A.; Meyer, A. S. Monosaccharide yields and lignin removal from wheat straw in response to catalyst type and pH during mild thermal pretreatment. Process Biochem. 2010, 45 (7), 1181-1186. (33) Pedersen, M.; Meyer, A. S. Lignocellulose pretreatment severity - relating pH to biomatrix opening. New Biotechnol. 2010, 27 (6), 739-750. (34) Lai, D. M.; Deng, L.; Li, J.; Liao, B.; Guo, Q. X.; Fu, Y. Hydrolysis of cellulose into glucose by magnetic solid acid. Chemsuschem 2011, 4 (1), 55-58. (35) Dussan, K.; Girisuta, B.; Lopes, M.; Leahy, J. J.; Hayes, M. H. B. Effects of Soluble Lignin on the Formic Acid-Catalyzed Formation of Furfural: A Case Study for the Upgrading of Hemicellulose. Chemsuschem 2016, 9 (5), 492-504. (36) Bu, L. X.; Xing, Y.; Yu, H. L.; Gao, Y. X.; Jiang, J. X. Comparative study of sulfite pretreatments for robust enzymatic saccharification of corn cob residue. Biotechnology for Biofuels 2012, 5, 87. (37) Kaparaju, P.; Felby, C. Characterization of lignin during oxidative and hydrothermal pretreatment processes of wheat straw and corn stover. Bioresour. Technol. 2010, 101 (9), 3175-3181. (38) Nadji, H.; Diouf, P. N.; Benaboura, A.; Bedard, Y.; Riedl, B.; Stevanovic, T. Comparative study of lignins isolated from Alfa grass (Stipa tenacissima L.). Bioresour. Technol. 2009, 100 (14), 3585-3592. (39) Jiang, L. Q.; Fang, Z.; Li, X. K.; Luo, J.; Fan, S. P. Combination of dilute acid and ionic liquid pretreatments of sugarcane bagasse for glucose by enzymatic hydrolysis. Process Biochem. 2013, 48 (12), 1942-1946. (40) Zhang, Z. Y.; Wong, H. H.; Albertson, P. L.; Harrison, M. D.; Doherty, W. O. S.; O'Hara, I. M. Effects of glycerol on enzymatic hydrolysis and ethanol production using sugarcane bagasse pretreated by acidified glycerol solution. Bioresour. Technol. 2015, 192, 367-373. (41) Hu, F.; Jung, S.; Ragauskas, A. Pseudo-lignin formation and its impact on enzymatic hydrolysis. Bioresour. Technol. 2012, 117, 7-12. (42) Hu, F.; Ragauskas, A. Suppression of pseudo-lignin formation under dilute acid pretreatment conditions. Rsc Advances 2014, 4 (9), 4317-4323. (43) Pu, Y. Q.; Hu, F.; Huang, F.; Davison, B. H.; Ragauskas, A. J. Assessing the molecular structure basis for biomass recalcitrance during dilute acid and hydrothermal pretreatments. Biotechnology for Biofuels 2013, 6 (1), 1-13. (44) Zeng, Y. N.; Zhao, S.; Yang, S. H.; Ding, S. Y. Lignin plays a negative role in the biochemical process for producing lignocellulosic biofuels. Curr. Opin. Biotechnol. 2014, 27, 38-45. (45) Lee, S. H.; Doherty, T. V.; Linhardt, R. J.; Dordick, J. S. Ionic liquid-mediated selective extraction of lignin from wood leading to enhanced enzymatic cellulose hydrolysis. Biotechnol. Bioeng. 2009, 102 (5), 1368-1376. (46) Agnihotri, S.; Johnsen, I. A.; Boe, M. S.; Oyaas, K.; Moe, S. Ethanol organosolv pretreatment of softwood (Picea abies) and sugarcane bagasse for biofuel and biorefinery applications. Wood Sci. Technol. 2015, 49 (5), 881-896. (47) Jin, S. G.; Zhang, G. M.; Zhang, P. Y.; Li, F.; Fan, S. Y.; Li, J. Thermo-chemical pretreatment and enzymatic hydrolysis for enhancing saccharification of catalpa sawdust. Bioresour. Technol. 2016, 205, 34-39. (48) Pan, X. J.; Arato, C.; Gilkes, N.; Gregg, D.; Mabee, W.; Pye, K.; Xiao, Z. Z.; Zhang, X.; Saddler, J. Biorefining of softwoods using ethanol organosolv pulping: Preliminary evaluation of process streams for manufacture of fuel-grade ethanol and co-products. Biotechnol. Bioeng. 2005, 90 (4), 473-481.

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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


1

Scheme caption

2

Scheme 1 Furfural and cellulosic residue production from xylan catalyzed by Lewis acid/Bronsted acid.

3 4

Figure captions

5

Fig. 1 Furfural production vs. time from raw bagasse in aqueous solution with (a) 0.1 M FeCl3, (b) 0.3 M HCl and (c) 0.1 M AlCl3 (0.3 g bagasse, 9 mL aqueous solution and magnetic stirring rate of 600 rpm at 150 o C; ◇ xylose; □ glucose; △ furfural; ○ HMF).

6 7 8 9 10 11

Fig. 2 Influence of NaCl on the degradation of raw bagasse in aqueous phase with (a) 0.1 M FeCl3, (b) 0.3 M HCl and (c) 0.1 M AlCl3 (0.3 g bagasse, 9 mL aqueous solution and magnetic stirring rate of 600 rpm at 150 oC; ◇ xylose; □ glucose; △ furfural; ○ HMF).

12

15

Fig. 3 Furfural, HMF and residue yields changed with (a) temperature, (b) time, (c) AlCl3 concentration and (d) NaCl concentration (0.3 g bagasse, 9 mL MTHF, 9 mL aqueous solution, magnetic stirring rate of 600 rpm; × residue; △ furfural; ○ HMF).

16 17 18

Fig.4 13C NMR spectra of organic phase after reaction from R-Al-Na-MTHF system (600 MHz, CDCl3 and 22 oC).

13 14

19 20 21 22 23 24

Fig. 5 SEM images of original bagasse and residues after reactions. Fig. 6 FT-IR spectra of bagasse and residues after reactions (a: wavenumber at 400-4000 cm-1; b: wavenumber at 800-2000 cm-1)36

25 26

Fig. 7 Enzymatic hydrolysis of cellulosic residues (75 mg solid residue, 10 FPU cellulase, 20 CBU β-glucosidase, 50 oC and rotation rate of 150 rpm).

27 28 29 30

Fig. 8 Influence of cellulase loading on glucose yield from residue R-Al-Na-MTHF (75 mg solid residue,20 CBU β-glucosidase, 50 oC and rotation rate of 150 rpm).

31 32 33 34 35 36 37 38

Table captions Table 1 Influence of NaCl and MTHF on the yields of furfural, HMF and residue. Table 2 Influence of solid loading on furfural yield in MTHF/aqueous AlCl3 system. Table 3 Recycle of organic and aqueous phases in MTHF/aqueous AlCl3 system.

39 40

Table 4 Residue yields and glucan contents in residues after reactions.

19



1 21 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 2 22 3 23 4 24 5 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

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Table 1 Influence of NaCl and MTHF on the yields of furfural and HMF Reaction condition [a] Reaction system [a]

Product yield (%)

Partition coefficient [b]

AlCl3

NaCl

MTHF

HMF

Furfural

Org(Furfural)/ Aq(Furfural)

Org(HMF)/ Aq(HMF)

R-Al

18 mL 0.1 M

-

-

4.3±0.2

30.6±0.3

-

-

R-Al-Na

18 mL 0.1 M

10 wt%

-

7.0±0.3

50.0±0.6

-

-

R-Al-MTHF

9 mL 0.1 M

-

9 mL

6.1±0.1

43.6±0.3

6.3±0.4

1.4±0.1

R-Al-Na-MTHF

9 mL 0.1 M

10 wt%

9 mL

7.9±0.1

58.6±0.5

8.7±0.3

2.2±0.1

[a]

R-Al: AlCl3 aqueous solution; R-Al-Na: AlCl3 and NaCl; R-Al-MTHF: MTHF and water with AlCl3; R-Al-Na-MTHF: MTHF and water with AlCl3 and NaCl (0.45 g bagasse, 150 oC, 45 min and stirring rate of 600 rpm). [b] Partition coefficient was defined as product concentration in organic phase divided by that in aqueous phase.

20


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1 21 3 2 4 5 6 7 8 9 10 11 12 13 14 3 15 4 16 17 5 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


Table 2 Influence of solid loading on furfural yield in MTHF/aqueous AlCl3 system Product yield (%) [a] Bagasse loading (g)

[a]

HMF

Furfural

Residue

0.3

8.6±0.3

60.0±0.4

53.9±0.4

0.45

7.9±0.1

58.6±0.5

54.7±2.5

0.6

7.4±0.5

54.0±0.8

57.2±1.0

o

9 mL MTHF, 9 mL aqueous solution, 150 C, 45 min, magnetic stirring rate of 600 rpm, 0.1 M AlCl3 and 10 wt% NaCl.

21



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Table 3 Recycle of organic and aqueous phases [a] in MTHF/aqueous AlCl3 system Product yield in MTHF phase (%)

Furfural concentration in organic phase (gL-1)

HMF

Furfural

Fresh MTHF

7.9±0.1

58.6±0.5

4.4±0.2

Recycle 1

7.3±0.3

55.6±0.5

8.0±0.1

Recycle 2

6.5±0.3

53.8±0.7

11.5±0.4

Fresh aqueous

7.9±0.1

58.6±0.5

-

Recycle 1

9.9±0.6

60.8±0.8

-

Recycle 2

11.1±0.4

61.2±1.5

-

[a]

Spent MTHF containing high concentration of furfural from the latest reaction was directly used in next recycle without any pretreatment. Spent aqueous solution containing residual sugars from the latest reaction was directly used in the next reaction without supplement of AlCl3 and NaCl, but another 0.45 g bagasse was added (0.45 g bagasse, 9 mL MTHF, 9 mL aqueous solution, 150 oC, 45 min, magnetic stirring rate of 600 rpm, 0.1 M AlCl3, and 10 wt% NaCl).

22


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1 21 3 2 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 3 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


Table 4 Residue yields and glucan contents in residues after reactions Residue composition (wt%) Reaction systems Raw Bagasse MTHF extraction

Glucan

Xylan

lignin

Residue yield (wt%)

38.3±1.0

20.4±1.5

22.5±0.9

-

40.4±0.8

21.2±2.0

23.4±1.2

94.8±0.2

Reaction conditions 0.45 g bagasse, 18 mL MTHF, 150 oC, 45 min o

R-Al

0.45 g bagasse, 18 mL water, 0.1 M AlCl3, 150 C, 45 min

53.3±0.5

3.45±0.3

35.2±0.6

63.0±1.0

R-Al-Na

0.45 g bagasse, 18 mL water, 0.1 M AlCl3, 10 wt% NaCl, 150 oC, 45 min

52.1±0.7

2.8±0.2

36.1±1.0

62.6±0.9

R-Al-MTHF

0.45 g bagasse, 9 mL MTHF, 9 mL water, 0.1 M AlCl3, 150 oC, 45 min

62.5±0.7

2.6±0.2

25.2±1.4

54.9±0.7

R-Al-Na-MTHF

0.45 g bagasse, 9 mL MTHF, 9 mL water, 0.1 M AlCl3, 10 wt% NaCl, 150 oC, 45 min

63.7±0.4

3.2±0.2

26.7±0.7

54.7±2.5

23



Sugarcane Bagasse Lignin Cellulose Hemicellulose

Glucose

MTHF

Lignin

Filtration

Enzymatic hydrolysis

+

Reuse of aqueous phase

Aqueous AlCl3+NaCl decantation

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 33

cellulose-enriched Furfural/lignin in MTHF residue in aqueous phase Cellulose-enriched residue

Scheme 1


Page 25 of 33

(a)

80 Yield (%)

60

Temp.: 150 oC FeCl3 conc.: 0.1 M

40 20

0 30

60

90 120 Time (min)

150

Temp.: 150 oC HCl conc.: 0.3 M

(b)

60 40 20 0

180

80 Yield (%)

Yield (%)

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

80


0

30

60 90 Time (min)

Temp.: 150 oC AlCl3 conc.: 0.1 M

(c)

60 40 20

0 0 Fig. 1

20

40 60 Time (min)


80

120


80

(a)

40 20

Temp.: 150 oC Time: 45 min HCl conc.: 0.3 M

(b)

60 Yield (%)

60

80

Temp.: 150 oC Time: 90 min FeCl3 conc.: 0.1 M

40 20 0

0 0

5 10 15 NaCl Concentration (%) (c)

80 Yield (%)

Yield (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 33

60

0

20

5 10 15 NaCl Concentration (%)

Temp.: 150 oC Time: 30 min AlCl3 conc.: 0.1 M

40 20 0 0

Fig. 2

5 10 15 NaCl concentration (%) ACS Paragon Plus Environment

20

20

Page 27 of 33

80

80

(a)

60

40

Time: 60 min AlCl3 conc.: 0.1 M NaCl conc.: 0 wt%

20

Yield (%)

Yield (%)

(b)

60 40

Temp.: 150 o C AlCl3 conc.: 0.1 M NaCl conc.: 0 wt%

20

0

0 130

140 150 160 Temperature (oC)

15

170 80

(c)

60 40

Temp.: 150 o C Time: 60 min NaCl conc.: 0 wt%

20

Yield (%)

80 Yield(%)

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


30

45 60 Time (min)

75

(d)

60 Temp.: 150 oC Time: 60 min AlCl3 conc.: 0.1

40

20 0 0

0 0.03

Fig. 3

0.07 0.1 0.135 AlCl3 concentration(M)

0.17


5 10 15 NaCl concentration (wt%)

20


Intensity

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

Fig. 4


Page 28 of 33

Page 29 of 33

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

(a) Bagasse

10 μm


(b) R-Al

10 μm

(c) R-Al-Na

(d) R-Al-Na-MTHF

10 μm

10 μm

Fig. 5



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

Fig. 6


Page 30 of 33

Page 31 of 33

100 Glucose yield (%)

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


Bagasse R-Al-Na

Avicel R-Al-Na-MTHF

R-Al

80 60 40 20 0 0

Fig. 7

20

40 60 Time (h) ACS Paragon Plus Environment

80

100


100

Glucose yield (%)

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

80 5 FPU

60

10 FPU 15 FPU

40

30 FPU

20 0 0

20

40

60 Time (h)

Fig. 8

Page 32 of 33


80

100

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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


Title: Co-production of furfural and easily hydrolysable residue from sugarcane bagasse in MTHF/aqueous biphasic system: influence of acid species, NaCl addition and MTHF Authors: Xing-kang Li, Zhen Fang, Jia Luo, Tong-chao Su

Coproduction of furfural (58.6% yield) and cellulose-enriched residue (>90% glucan recovered) with 89.3% glucose yield in MTHF/aqueous AlCl3 system


Coproduction of Furfural and Easily Hydrolyzable Residue from Sugar

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