Highly Selective Conversion of Cellobiose and Cellulose to Hexitols

Apr 15, 2016 - View: ACS ActiveView PDF | PDF | PDF w/ Links | Full Text HTML. Citing Articles; Related Content. Citation data is made available by pa...
0 downloads 15 Views 1MB Size
Subscriber access provided by HOWARD UNIV

Article

Highly Selective Conversion of Cellobiose and Cellulose to Hexitols by Ru-Based Homogeneous Catalyst under Acidic Condition Guozhen Wang, Xuefeng Tan, Hui Lv, Mengmeng Zhao, Min Wu, Jinping Zhou, Xumu Zhang, and Lina Zhang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b00518 • Publication Date (Web): 15 Apr 2016 Downloaded from http://pubs.acs.org on April 19, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Industrial & Engineering Chemistry Research is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 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

Industrial & Engineering Chemistry Research

1

Highly Selective Conversion of Cellobiose and Cellulose to

2

Hexitols by Ru-Based Homogeneous Catalyst under Acidic

3

Condition

4

Guozhen Wang,† Xuefeng Tan,† Hui Lv,† Mengmeng Zhao,‡ Min Wu,‡ Jinping Zhou,

5



Xumu Zhang,*

,†

and Lina Zhang ,†

6 7 8 9 10



College of Chemistry and Molecular Sciences, Wuhan University, 430072, Wuhan,

China. ‡

Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, 100190,

Beijing, China

* To whom correspondence should be addressed. Phone: +86-27-87219274. Fax: +86-27-68754067.E-mail: [email protected], [email protected] (L. Zhang); [email protected] (X. Zhang).

ACS Paragon Plus Environment

Industrial & Engineering Chemistry Research

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

11

ABSTRACT:The catalytic transformation of the most abundant cellulose to valuable

12

platform chemicals is one of the significant issues to overcome the shortage of fossil

13

fuels. Herein, we reported the first example of Ru-based homogeneous catalyst for the

14

highly selective conversion of cellobiose and ball- milled cellulose to hexitols

15

(including sorbitol, mannitol and 1, 4-sorbitan) under an acidic condition with the

16

yield of 94.5 and 56.4%, respectively. The main features of this catalytic system were

17

the high conversion efficiency of biomass, mild reaction condition (100 C) and low

18

catalyst loading, which was 1/20 of the related Ru/C heterogeneous catalyst. This

19

work opened up a new avenue for the transformation of cellulose to hexitols under

20

mild conditions.

21

KEY WORDS: conversion of biomass, cellobiose, cellulose, hexitol, Ru-based

22

homogeneous catalyst

23

ACS Paragon Plus Environment

Page 2 of 33

Page 3 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

Industrial & Engineering Chemistry Research

24



25

To decrease the dependence on fossil fuels, much attention has been paid to develop

26

the ultraclean technologies such as hydrogen, wind, water and solar energy to resolve

27

the energy issue.1-4 However, no organic compounds are produced in these processes.

28

The conversion of renewable and sustainable biomass 5-6 is emerging as an important

29

strategy to produce valuable organic materials and platform c hemicals.7-12 Cellulose, a

30

linear polymer composed of glucose units linked by β-(1,4)-glycoside bonds, is the

31

most abundant and non-edible lignocellulosic biomass on earth. 13 The annual net yield

32

of photosynthesis production is 1.7 trillion tons for biomass, approximately 35–50%

33

of which, is cellulose.14

INTRODUCTION

34

It is noted that yet at present biorefineries are primarily concerned with the

35

efficient conversion of cellulose into fuels and chemicals. 15 To address this point, the

36

catalytic conversion of cellulose into organic monomers and platform chemicals has

37

attracted much attention, and many excellent results have been reported. 16-24 For

38

example, Fukuoka et al. studied the hydrolytic hydrogenation of cellulose into sorbitol

39

and mannitol over a series of supported metal catalysts with a sorbitol yield of 58%

40

by Ru/AC (AC = activated carbon) at 190 C in water.25 Zhang et al. developed a less

41

expensive Ni-promoted W2 C/AC hydrogenation catalyst for the transformation of

42

cellulose to ethylene glycol in aqueous system at 245 C.26 Tsubaki and co-workers

43

prepared Pt nanocatalysts loaded on the reduced graphene oxide (Pt/RGO) for the

44

selective hydrogenation of cellulose (or cellobiose) into sorbitol.27 The yield of

45

sorbitol from cellobiose was 91.5% and from cellulose was 58.9%, respectively. Sels

46

et al. studied the bifunctional Ru/H-USY catalysts for the conversion of cellulose in

47

hot liquid water, and up to 95% hexitol yield could be obtained.24 As a result of the

48

difficulty in the cellulose conversion, these systems were carried out under harsh

ACS Paragon Plus Environment

Industrial & Engineering Chemistry Research

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 4 of 33

49

conditions (e.g., 200–500 C, 30–100 atm H2 ) with relatively large amount of

50

heterogeneous catalysts.28 It was worth noting that environmental- friendly

51

homogeneous catalysts usually exhibited higher catalytic efficiency under mild

52

reaction condition. One case was the reduction of aldehydes and ketones to alcohols

53

using a Ru-diamine-diphosphine catalytic, which has been extensively studied by

54

Noyori and others.29-30 However, most of the efficiently catalytic reaction for the

55

reduction of carbonyls worked under the basic condition, which was unfavourable for

56

the hydrolysis of hemiacetals in β-1, 4-glycosidic bonds. These catalysts could also be

57

easily deactivated by multi- functional groups, such as amino and hydroxyl groups.

58

For the hydrogenation of cellulose to hexitols, it may be highly desirable for an

59

acid-assisted

60

homogeneous catalyst in the conversion of cellulose to hexitols has never been

61

reported. An effort should be made to develop a worthwhile homogeneous catalytic

62

hydrogenation system, which is capable of efficiently and selectively transforming

63

cellulose into hexitols with low catalyst loading under mild condition.

and

multi- functional

group-tolerant

catalyst.

However,

such

64

In our previous work, an easily available ruthenium (II) catalyst, 31 which was

65

coded as Ru1 (chemical structure is shown in Scheme 1), has been synthesized as a

66

new compound for the catalytic hydrogenation of various aldehydes including glucose

67

with excellent performance. As the rate-determining step for the hydrogenation of

68

various aldehydes, Ru1 displayed high chemoselectivity in the presence of C=C bond

69

and ketone group. Different from the situation in the hydrogenation of aldehydes, acid

70

is essential for the cleavage of the glycosidic bond between the glucose units in

71

cellobiose or cellulose. So the acidic medium was selected for the conversion of

72

biomass. Herein, a novel homogeneous ruthenium catalyst/H2 SO 4 system for the

73

hydrolysis and hydrogenation of cellobiose and cellulose to hexitols was studied. To

ACS Paragon Plus Environment

Page 5 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

Industrial & Engineering Chemistry Research

74

achieve a high chemo-selectivity, the mild reaction condition (100 C) was used for

75

the transformation of cellulose to hexitols. The catalytic transformation of the most

76

abundant cellulose to valuable platform chemicals is very important to solve the

77

shortage of fossil fuels.

78 79



EXPERIMENTAL SECTION

80

Materials. Raw cellulose (cotton linter pulp) was supplied by Hubei Chemical

81

Fiber Co. Ltd. China. To decrease the molecular weight and the crystallinity of the

82

raw cellulose, ball- milling experiments were performed in batches of 10 g cellulose

83

using several ZrO 2 balls (mass of 1.8 kg and the diameter of 2 cm) in a 2000 mL ZrO 2

84

bottle for 30 h to obtain the ball- milled cellulose. The rolling speed was set at 540

85

rpm. Cellobiose, H2 SO4 and BaCO 3 were of analytical grade and were purchased from

86

Aladdin. Ru/C (5% Ru) and Pd/C (10% Pd) were purchased from Sigma-Adrich. All

87

the chemical reagents were used without pretreatment.

88

Catalyst Ru1 was synthesized according to our previous method.31 To screen out

89

the best catalyst, another two catalysts, coded as Ru2 and Ru3 (chemical structure are

90

also shown in Scheme 1), were prepared according to the references. 32-33 The catalysts

91

inc luding Ru1, Ru2 and Ru3 were used in the homogeneous catalytic

92

hydrogenation system of cellobiose and cellulose.

93

General Procedure for the Hydrolysis/Hydrogenation Reaction. In a typical

94

reaction, the desired amount of cellobiose or cellulose, catalyst, H2 SO 4 , water and

95

iso-propanol were placed into a 100 mL stainless steel autoclave. The autoclave was

96

purged by three cycles of pressurization/evacuating with N 2 , and then by three

97

cycles of pressurization/venting with H2 (10 atm) before pressurized with H2 (50

98

atm). The reaction mixture was stirred at a given temperature in an oil bath for the

ACS Paragon Plus Environment

Industrial & Engineering Chemistry Research

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 6 of 33

99

desired time. After reaction, the mixture was cooled to room temperature and the

100

products were centrifuged. The resultant solution was neutralized with BaCO 3 and

101

analysed by the high-performance liquid chromatography [HPLC; Agilent 1100 Series,

102

refractive index detector (RID), Hi-Plex Ca column (300 × 7.7 mm), the mobile phase:

103

ultra-pure water, the flow rate: 1.0 mL min-1 , column temperature: 80 C]. The

104

conversion of cellobiose was determined by HPLC. The conversion of cellulose was

105

calculated by the weight difference before and after the reaction. 34 The yield of each

106

product was calculated as follows:35

107

Yield  %  =

100%   mols of carbon in each product  mols of carbon in charged cellulose or cellobiose

(1)

108

Characterizations. The morphology of cellulose was observed using scanning

109

electron microscopy (SEM) with a field emission scanning electron microscopy

110

(FESEM, Zeiss, SIGMA), with an accelerating voltage of 5 kV. The samples were

111

coated with Au for the SEM observation.

112

Solid-state

13 C

NMR spectra of the raw cellulose and the ball- milled cellulose 13 C

113

were recorded on a BRUKER 500WC spectrometer. It was operated at a

114

frequency of 125.88 MHz using the combined technique s of magic angle spinning

115

(MAS) and cross-polarization. The spinning speed was set at 10 kHz for all samples.

116

The contact time, acquisition time and recycle delay were 2 ms, 8 ms and 4s,

117

respectively. A typical number of 10000 scans were acquired for each spectrum.

118

X-ray diffraction (XRD) patterns were measured with a WAXD diffractometer

119

(D8-Advance, Bruker, USA). The diffracted intensity of Cu Kα radiation (λ =

120

0.15405 nm) was operated at 40 kV and 30 mA. The samples were measured in the 2θ

121

region from 10 to 50°with a scanning rate of 2°/min. The crystallinity index (Icr) of

122

cellulose was indicated on each curve and calculated as follows 36

ACS Paragon Plus Environment

Page 7 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

123

Industrial & Engineering Chemistry Research

ICr = (I002 -Iam)/I002 ×100

(2)

124

where I002 was the diffraction intensity of the crystalline plane (002) of cellulose at 2θ

125

= 22.6°, and Iam was the intensity of the amorphous peak (2θ =18°), respectively.

126

The intrinsic viscosity ([η]) of cellulose in LiOH/urea aqueous solution was

127

measured at 25 °C by using an Ubbelohde capillary viscometer. The original

128

concentration of cellulose was 3×10−3 gmL-1 . The viscosity molecular weight of

129

cellulose was calculated according to the Mark-Houwink equation.37

130

[η] = 3.72×10-2 Mw0.77 mLg-1

(3)

131 132 133

 RESULTS AND DISCUSSION Hydrogenolysis of Cellobiose.

Cellobiose, a glucose dimer connected by one

134

glycosidic bond, is the simplest model molecule of cellulose. 38 It was selected as the

135

model substrate for the degradation of cellulose. 27,

136

photographs of the products of the hydrolytic hydrogenation from cellobiose and

137

cellulose. Obviously, the conversion of cellulose and cellobiose into hexitols by

138

homogeneous catalyst under the optimal conditions (0.1 mol% Ru1, 0.5 mol·L-1

139

H2 SO 4 , 50 atm H2 , 100 C, 16 h for cellobiose and 0.2 mol% Ru1, 1.5 mol·L-1 H2 SO4 ,

140

50 atm H2 , 100 C, 20 h for cellulose) was successfully realized. Clear and transparent

141

solution was obtained from cellobiose (Figure 1a), whereas brown and transparent

142

supernatant liquid was obtained from cellulose (Figure 1b). Figure 1c performs the

143

HPLC profiles for the hydrolytic hydrogenation products from cellobiose and

144

cellulose by using Ru1 catalyst under the optimal hydrogenation conditions. It was

145

interesting that there was only three major kinds of product (glucose, sorbitol and 1,

146

4-sorbitan) generated in the cellobiose and cellulose systems. Trace amount of

147

by-products mainly including 5- hydroxymethylfurfural (5-HMF) has been detected

39-41

ACS Paragon Plus Environment

Figure 1a and b show the

Industrial & Engineering Chemistry Research

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

148

which was partially contributed to the discoloration of the supernatant from cellulose.

149

And the yield of 5-HMF in all samples were less than 0.1%. These results indicated

150

that the Ru-based homogeneous catalyst had highly selectivity on the conversion of

151

cellobiose and cellulose with high hexitol yield. It was worth noting that there was no

152

mannitol generated in our homogeneous catalytic system, confirmed by HPLC

153

profiles compared with the retention time of standards. This suggested that no

154

epimerization of sorbitol occurred.

155

The catalyst loading (catalyst/substrate mol%) played an important role in the

156

hydrogenation of cellobiose. As listed in Table 1, when the catalyst loading increased

157

from 0.01 to 0.1 mol%, the yields of sorbitol and 1, 4-sorbitan remarkably increased

158

since the produced glucose was immediately converted into sorbitol. Once the catalyst

159

loading was higher than 0.1 mol%, the yield of hexitol hardly changed. Because the

160

catalyst reached up to saturation and almost equal amounts of sorbitol had been

161

generated. More sorbitol had time to convert into 1, 4-sorbitan with higher catalyst

162

loading. Therefore, 0.1 mol% catalyst loading was chosen for the hydrogenation of

163

cellobiose. The results of cellobiose degradation at different H2 SO 4 concentration are

164

shown in Figure 2. It was revealed that the hydrolysis of cellobiose strongly depended

165

on the acid concentration, and 0.5 mol·L-1 H2 SO4 was the optimal condition. Initially,

166

increasing the acid concentration could promote the cleavage of the β-(1, 4)- glycoside

167

bond to produce more hexitols. When the acid concentration was too high, the sorbitol

168

could be dehydrated to form a significant amount of 1, 4-sorbitan. Interestingly,

169

cellobiose could be converted into sorbitol with high selectivity by three

170

homogeneous catalysts (Ru1-Ru3), as shown in Figure 3. And Ru1 displayed higher

171

catalytic activity than Ru/C when using identical amount of Ru in the same conditions.

172

When the catalyst loading of Ru1 was 1/20 of Ru/C, almost the same yield of hexitols

ACS Paragon Plus Environment

Page 8 of 33

Page 9 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

Industrial & Engineering Chemistry Research

173

was obtained, as listed in Table 2. As shown in Figure 3, with the same loading of

174

catalyst (Ru or Pd: 0.1 mol %), the hexitol yield was as follows: Ru1 > Ru2 > Ru/C >

175

Ru3> Pd/C. Higher hexitol yield of Ru1 was as a result of the higher hydrogenation

176

catalytic activity of Ru1. Once the glucose produced under the acidic condition, it

177

was immediately converted into sorbitol with Ru1. The highest glucose yield was

178

obtained when the Pd/C catalyst was used. It indicated that Pd/C performed the lowest

179

hydrogenation activity for the produced glucose under the same conditions. The

180

phosphine ligand of Ru1-Ru3 played an important role in the catalysts activity. The

181

bidentate phosphine ligands, e.g. DPPP (Ru1) and BINAP (Ru2), were better than a

182

monophosphine ligand, e.g. PPh3 (Ru3). Additionally, the more electron-rich of Ru1

183

performed better than Ru2. It was found that no hexitol generated in the

184

hydrogenation reaction in the absence of catalyst (Table 2, entry 3). The cellobiose

185

was almost converted into glucose, but could not be further transformed into sorbitol

186

as a result of the absence of ruthenium catalyst. Generally, the trace amount of

187

homogeneous Ru-based catalysts was not recovered in organic synthesis which can

188

avoid the complicated recovery process in industry. Similar to this situation, for the

189

first employment of homogeneous Ru-based catalysts in the conversion of cellobiose

190

and cellulose, we didn’t recover these catalysts.

191

Effects of the Ball-Milling on Morphology and Structure of Cellulose. To

192

increase the accessibility and the reaction activity of the cellulose hydrogenation,

193

ball- milling was used for the cellulose pretreatment.42-45 Figure 4 shows the

194

photographs and SEM images of cellulose before and after the ball- milling.

195

Obviously, the raw cellulose retained fibrous shape with 10 μm width and 100-200

196

μm length, whereas the ball- milled cellulose changed to small particles with