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Mass Spectrometry Analysis of Sugar and Anhydro-sugar Oligomers from Biomass Thermochemical Processing Yun Yu, Bing Song, Yu Long, and Hongwei Wu Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b01843 • Publication Date (Web): 31 Aug 2016 Downloaded from http://pubs.acs.org on September 5, 2016
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Mass Spectrometry Analysis of Sugar and Anhydro-sugar Oligomers from Biomass Thermochemical Processing Yun Yu *, Bing Song, Yu Long and Hongwei Wu *
Department of Chemical Engineering, Curtin University, GPO Box U1987, Perth WA 6845, Australia
*
Corresponding
Authors.
Fax:
+61-8-92662681
(Y.
Yu
and
H.
Wu);
Email
addresses:
[email protected] (Y. Yu);
[email protected] (H. Wu).
Submitted to Energy & Fuels as a rapid communication
Abstract. Sugar and anhydro-sugar oligomers are important reaction intermediates produced in various biomass thermochemical processes. This study reports the mass spectrometry analysis of sugar and anhydrosugar oligomers produced from hydrothermal processing and pyrolysis using high performance anion exchange chromatography with pulsed amperometric detection and mass spectrometry (HPAEC-PAD-MS). The results confirm that the conventional method to assign the degrees of polymerization (DPs) of sugar and anhydro-sugar oligomers according to the sequence of oligomer in the chromatogram is suitable. This study also successfully identifies the formation of the isomers of glucose oligomers from cellulose conversion in hot-compressed water, revealing new insights into the underlying reaction mechanism. Keywords: biomass conversion, sugar oligomer; anhydro-sugar oligomer; HPAEC-PAD-MS
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Introduction 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
Biomass has received increasing attentions as a renewable feedstock for the production of bioenergy, biofuels and biochemicals.1-3 Lignocellulosic biomass consists of three major polymers including cellulose, hemicellulose and lignin.4 Biomass thermochemical processing produces various intermediate products including oligomers and/or monomers.5-10 For example, biomass hydrothermal processing produces a series of sugar oligomers as primary products.11,12 Biomass pyrolysis proceeds through a molten intermediate5,8,13 that mainly consists of sugar or anhydro-sugar oligomers.14,15 Understanding on the composition of those oligomers is essential to revealing the underlying reaction mechanisms. However, the analysis of sugar and anhydro-sugar oligomers is challenging, considering the wide range of degree of polymerization (DP) and the limited availability of standards. Recently, high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) has been widely used for the analysis of carbohydrates.11,16 It can separate both sugar and anhydro-sugar oligomers with high sensitivities and the oligomers with DP up to 5 can also be identified using standards. As the standards for oligomers with DP>5 are unavailable, the conventional method to assign the DP is according to the sequence of oligomer in the chromatogram.11,16 Therefore, this study employs HPAEC-PAD with simultaneous mass spectrometry, i.e., HPAEC-PAD-MS, to analyse sugar and anhydro-sugar oligomers produced in various themochemical processes.15,16 It is also shown that HPAEC-PAD-MS can detect the formation of the isomers of sugar oligomers during cellulose conversion in HCW, which is reported as the first time in the field.
Experimental Samples from two biomass thermochemical processes were considered. One was produced from cellulose conversion in hot-compressed water (HCW) at 270 °C using a semi-continuous reactor system (with details given elsewhere16). This system allows the minimization of secondary reactions of liquid products and facilitates the investigation into the primary reactions. The other is the water-soluble intermediate sample extracted from the char that was produced from cellulose fast pyrolysis at 250 °C in a drop-tube/fixed-bed quartz reactor (with details given elsewhere15). Both samples were subjected to simultaneous PAD and MS analysis using an HPAEC-PAD-MS system, following a method developed elsewhere.17 As shown in Figure 1, the HPAEC-PAD-MS system consists of a Thermo Scientific Dionex ICS-5000 ion chromatography (IC) system equipped with a Thermo Scientific MSQ system. The analysis uses sodium hydroxide and sodium acetate as eluents. Depending on the purpose of analysis, different IC columns (i.e., Dionex CarboPac PA20 and PA200 analytic columns) have been employed to separate the sugar and anhydro-sugar oligomers in the liquid sample. After separation, the flow was split into two streams for simultaneous PAD and MS analyses. Because high-pH eluents are not compatible with MS, a suppressor was installed as in-line desalter to reduce the pH of the stream. Depending on the eluent concentration, different regeneration currents were set for the Page 2 of 8 ACS Paragon Plus Environment
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suppressor. For efficient ionization of the sugar and anhydro-sugar oligomers in the sample, a 0.5 mM LiCl 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
solution was also fed into the stream at a flow rate of 0.05 mL min-1 before the stream was delivered into the electrospray ionization (ESI) interface for MS analysis. The data acquisition and analysis were controlled by Dionex Chromeleon chromatography data system.
Results and Discussion Liquid sample from cellulose conversion in HCW Figure 2 presents the analysis of the liquid sample from cellulose conversion in HCW by HPAEC-PAD-MS. A wide range of glucose oligomers can be detected by PAD analysis and the first 5 peaks in the PAD chromatogram are identified as the glucose oligomers with DP of 1-5 using pure standards.16 Other peaks with higher retention times were assigned as high-DP glucose oligomers, with the DP assigned according to the sequence of oligomer shown in the chromatogram – a conventional method for DP assignment in previous studies.11,16 In this work, the PAD results were compared with the selected ion monitoring (SIM) scans at different m/z ratios (see Table 1) for sugar oligomers in Figure 2. The SIM scans indeed match well with the position of glucose oligomers with DP up to 8 (m/z 1321) in the PAD chromatogram. The SIM scans of higher-DP glucose oligomers were not possible due to the low concentrations of those oligomers in the sample. Although being less sensitive than the PAD analysis, the MS analysis confirms that the conventional method to assign the DP of sugar oligomer based on the sequence of oligomer in the PAD chromatogram is suitable. It was reported12 that the glucose yield of the liquid sample after post-hydrolysis is ~80%, suggesting that some derivatives of glucose oligomers are present in the primary product from cellulose conversion in HCW. To obtain further information on the sugar derivatives, the liquid sample was further analysed using CarboPac PA20 column to achieve the separation of the low-molecular-weight compounds. As shown in Figure 3, the SIM scans of both m/z 205 (DP = 1) and m/z 349 (DP = 2) show three well-separated peaks, which match well with three peaks in the PAD chromatogram. Although the SIM scan of m/z 511 (DP = 3) only show two peaks, it is clear that the first peak of the SIM scan includes two compounds which are not well separated. Also, two peaks can be found for the SIM scan of m/z 673 (DP = 4). Further efforts were then taken to separate the peaks of high-DP glucose oligomers by optimising eluent concentration, and at least two peaks can be identified for DP up to 8. In previous studies on cellobiose decomposition in HCW,18,19 it was reported that isomerization reactions play important roles in producing two cellobiose isomers (glucosyl-fructose and glucosyl-mannose) as major primary products. The current results in Figure 3 show that similar isomers also exist for each glucose oligomer during cellulose decomposition in HCW. The IC chromatogram was then compared with the standards of glucose isomers (i.e., fructose and mannose) and cellobiose isomers (i.e., glucosyl-fructose and glucosyl-mannose). It is confirmed that the two additional Page 3 of 8 ACS Paragon Plus Environment
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peaks close to glucose are indeed fructose and mannose, and the peaks close to cellobiose are indeed 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
glucosyl-fructose and glucosyl-mannose, respectively. This new finding strongly suggests that the isomers of glucose oligomers are present in the primary liquid product from cellulose conversion in HCW, providing some new insights into the reaction mechanism. Similar as those for cellobiose decomposition, isomerization reactions also play an important role during cellulose decomposition in HCW. It should be noted that the secondary reactions have been minimized in the semi-continuous reactor system, those isomers are unlikely to be produced from the secondary decomposition of glucose oligomers in the aqueous phase. Rather, those isomers are directly produced from cellulose as primary products. Therefore, isomerization reactions can take place in the solid phase during cellulose decomposition in HCW, leading to in situ structural changes in cellulose as reported in our previous study.20
Water-soluble intermediate sample from cellulose pyrolysis Biomass pyrolysis proceeds through a molten intermediate state,8 which evaporates or further decomposes into more volatile compounds in the liquid intermediate phase. Therefore, the intermediates are important precursors of volatiles, and greatly determine the composition of volatiles from pyrolysis. However, the identification of the intermediates from biomass pyrolysis is challenging, due to the complicated chemical composition. The water-soluble intermediates can be extracted from chars produced from cellulose pyrolysis at various temperatures and it was reported that various sugar and anhydro-sugar oligomers are present in the water-soluble intermediates.15 This study further employs HPAEC-PAD-MS for analysing the watersoluble intermediate sample extracted from char produced from cellulose pyrolysis at 250 °C. Figure 4a compares the PAD chromatogram with the SIM scans for sugar oligomers. The sugar oligomers with DP up to 7 can be clearly identified, with the detection of high-DP sugar oligomers being difficult due to the low concentration of those oligomers. Similarly, the anhydro-sugar oligomers with DPs up to 8 can be clearly identified by MS analysis (see Figure 4b). Therefore, with the combination of PAD and MS, the DP of different peaks can be easily assigned for both sugar and anhydro-sugar oligomers. The MS results further confirm that the conventional method for assigning the DPs of oligomers according to the sequence of the oligomers in the PAD chromatogram is applicable for both sugar and anhydro-sugar oligomers. It is also plausible to use a liquid sample from cellulose hydrothermal processing in HCW as a standard for sugar oligomers – an approach taken in a previous work.15
Conclusions The study demonstrates that the sugar and anhydro-sugar oligomers, which are important reaction intermediates produced from various biomass thermochemical processes, can be successfully analysed using HPAEC-PAD-MS. The results confirm that the conventional method for assigning the DPs of oligomers Page 4 of 8 ACS Paragon Plus Environment
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according to the sequence of the oligomers in the PAD chromatogram is applicable for both sugar and 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
anhydro-sugar oligomers. As the first time in the field, this study also detects the isomers of glucose oligomers in the primary liquid products from cellulose conversion in HCW, providing new insights into the cellulose decomposition mechanism in HCW.
Acknowledgement The authors are grateful to the partial support from the Australian Research Council via its Discovery Project Scheme. Bing Song also sincerely acknowledges the Curtin Strategic International Research Scholarship (CSIRS) received for supporting his PhD study.
References (1) Parikka, M., Biomass Bioenerg. 2004, 27, 613-620. (2) Ragauskas, A. J.; Williams, C. K.; Davison, B. H.; Britovsek, G.; Cairney, J.; Eckert, C. A.; Frederick Jr., W. J.; Hallett, J. P.; Leak, D. J.; Liotta, C. L.; Mielenz, J. R.; Murphy, R.; Templer, R.; Tschaplinski, T., Science 2006, 311, 484-489. (3) Vispute, T. P.; Zhang, H.; Sanna, A.; Xiao, R.; Huber, G. W., Science 2010, 330, 1222-1227. (4) Yu, Y.; Lou, X.; Wu, H., Energy Fuels 2008, 22, 46-60. (5) Boutin, O.; Ferrer, M.; Lédé, J., J. Anal. Appl. Pyrolysis 1998, 47, 13-31. (6) Chaiwat, W.; Hasegawa, I.; Tani, T.; Sunagawa, K.; Mae, K., Energy & Fuels 2009, 23, 5765-5772. (7) Dufour, A.; Castro-Díaz, M.; Marchal, P.; Brosse, N.; Olcese, R.; Bouroukba, M.; Snape, C., Energy Fuels 2012, 26, 6432-6441. (8) Lédé, J., J. Anal. Appl. Pyrolysis 2012, 94, 17-32. (9) Cantero, D. A.; Dolores Bermejo, M.; José Cocero, M., Bioresour. Technol. 2013, 135, 697-703. (10) Tolonen, L. K.; Juvonen, M.; Niemelä, K.; Mikkelson, A.; Tenkanen, M.; Sixta, H., Carbohydr. Res. 2015, 401, 16-23. (11) Yang, B.; Wyman, C. E., Bioresour. Technol. 2008, 99, 5756-5762. (12) Yu, Y.; Wu, H., Energy Fuels 2010, 24, 1963–1971. (13) Dauenhauer, P. J.; Colby, J. L.; Balonek, C. M.; Suszynski, W. J.; Schmidt, L. D., Green Chem. 2009, 11, 1555-1561. (14) Piskorz, J.; Majerski, P.; Radlein, D.; Vladars-Usas, A.; Scott, D. S., J. Anal. Appl. Pyrolysis 2000, 56, 145-166. (15) Yu, Y.; Liu, D.; Wu, H., Energy Fuels 2012, 26, 7331-7339. (16) Yu, Y.; Wu, H., Ind. Eng. Chem. Res. 2009, 48, 10682-10690. (17) Bruggink, C.; Maurer, R.; Herrmann, H.; Cavalli, S.; Hoefler, F., J. Chromatogr. A 2005, 1085, 104-109. (18) Yu, Y.; Shafie, Z. M.; Wu, H., Ind. Eng. Chem. Res. 2013, 52, 17006-17014. (19) Mohd Shafie, Z.; Yu, Y.; Wu, H., Ind. Eng. Chem. Res. 2014, 53, 14607-14616. (20) Yu, Y.; Wu, H., Ind. Eng. Chem. Res. 2010, 49, 3919-3925.
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LIST OF TABLES 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
Table 1. Mass to charge (m/z) ratios of different sugar and anhydro-sugar oligomers Sugar oligomers Anhydro-sugar oligomers DP m/z ion DP m/z ion 1 205 [C1+H2O+Li]+ 1 187 [AC1+H2O+Li]+ 2 349 [C2+ Li]+ 2 331 [AC2+ Li]+ + 3 511 [C3+ Li] 3 493 [AC3+ Li]+ 4 655 [AC4+ Li]+ 4 673 [C4+ Li]+ + 5 835 [C5+ Li] 5 817 [AC5+ Li]+ + 6 979 [AC6+ Li]+ 6 997 [C6+ Li] + 7 1159 [C7+ Li] 7 1141 [AC7+ Li]+ 8 1321 [C8+ Li]+ 8 1303 [AC8+ Li]+ Note: C1−C8 are sugar oligomers (or isomers) with DPs of 1−7; AC1−AC8 are anhydro-sugar oligomers with DPs of 1−8.
LIST OF FIGURES
Cell
PAD
Splitter Gradient Pump
Guard Column
Column Desalter
Eluent 1
Eluent 2
MS
Pump Autosampler
Pump
Water
0.5 mM LiCl
Figure 1. Schematic diagram of the HPAEC-PAD-MS system.
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Intensity (a.u.)
205 m/z
349 m/z 511 m/z 673 m/z 835 m/z 997 m/z 1159 m/z 1321 m/z
PAD
0
2
4
6
8
10 12 14 16 18 20 Retention Time (min)
22
24
26
28
30
Figure 2. HPAEC-PAD-MS analysis of a liquid sample from cellulose decomposition in HCW at 270 °C. Column: Dionex CarboPac PA200 analytic column; eluents: 20−225 mM sodium acetate and 100 mM NaOH over 30 min at a flow rate of 0.5 mL min-1; suppressor: Dionex AERS 500 (4 mm); suppressor current: 186 mA; MS detection mode: ESI positive; probe temperature: 450 °C; cone voltage: 75 V; needle voltage: 3.5 kV.
205 m/z 349 m/z
Intensity (a.u.)
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511 m/z 673m/z PAD
0
20
40
60
80
100
120
Retention Time (min) Figure 3. HPAEC-PAD-MS analysis of a liquid sample from cellulose decomposition in HCW at 270 °C. Column: Dionex CarboPac PA20 analytic column; eluents: 5 mM NaOH for the first 10 min, 5−60 mM NaOH over the following 30 min, and 60−100 mM NaOH over the following 80 min at a flow rate of 0.5 mL min-1; suppressor: Dionex AERS 500 (4 mm); suppressor current: 186 mA; MS detection mode: ESI positive; probe temperature: 450 °C; cone voltage: 75 V; needle voltage: 3.5 kV.
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(a)
Intensity (a.u.)
205 m/z
349 m/z
511 m/z 673 m/z 835 m/z 997 m/z 1159 m/z PAD
0
2
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8 10 12 14 Retention Time (min)
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(b) 331 m/z 493 m/z
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655 m/z 817 m/z 979 m/z 1141 m/z 1303 m/z
PAD
0
2
4
6
8 10 12 14 Retention Time (min)
16
18
20
Figure 4. HPAEC-PAD-MS analysis of a water-soluble intermediate sample extracted from char produced from cellulose pyrolysis at 250 °C. (a) SIM scans of sugar oligomers; (b) SIM scans of anhydro-sugar oligomers. Column: Dionex CarboPac PA200 analytic column; eluents: 20−225 mM sodium acetate and 100 mM NaOH over 30 min at a flow rate of 0.5 mL min-1; suppressor: Dionex AERS 500 (4 mm); suppressor current: 186 mA; MS detection mode: ESI positive; probe temperature: 450 °C; cone voltage: 75 V; needle voltage: 3.5 kV.
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