Insight into the Chemical Complexity of Soluble Portions from

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Insight into the Chemical Complexity of Soluble Portions from Cornstalk Methanolysis Hong-Lei Yan, Zhi-Min Zong, Zhan-Ku Li, Jiao Kong, QuanXi Zheng, Mei-Xia Zhao, Yan Li, and Xian-Yong Wei Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.5b02962 • Publication Date (Web): 16 Mar 2016 Downloaded from http://pubs.acs.org on April 1, 2016

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Insight into the Chemical Complexity of Soluble Portions from Cornstalk Methanolysis Hong-Lei Yana, Zhi-Min Zonga *, Zhan-Ku Lia, Jiao Konga, Quan-Xi Zhenga, Mei-Xia Zhaoa, Yan Lib, Xian-Yong Weia a

Key Laboratory of Coal Processing and Efficient Utilization, Ministry of Education, China

University of Mining & Technology, Xuzhou 221116, Jiangsu, China b

The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington

State University, Pullman, WA 99164, USA Abstract: Cornstalk was subjected to methanolysis in the presence of NaOH at 220–320 oC to afford soluble portions (SPs) 1–5 (SP1–SP5) and inextractable portion (IEP). The maximum total yield (ca. 51%) of SPs was acquired at 300 oC with the same mass of NaOH and cornstalk. Under the same conditions, SP1 has the highest yield, followed by SP5 and SP2. The relatively volatile and less polar species in the resulting portions were identified with a gas chromatograph/mass spectrometer (GC/MS). The polar species in SP1, SP2, and SP5 were further analyzed with a negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer (FTICRMS). The analysis with GC/MS shows that phenolic compounds and alcohols are the dominant group components in SP1 and SP2, respectively, while the predominant compounds in esterified SP3–SP5 and IEP are esters. According to analysis with FTICRMS, thousands of compounds were detected in SP1, SP2, and SP5. Most of the compounds are On (n = 1–10) class species with double bond equivalent (DBE) values of 1–14 and carbon atom numbers of 5–35. The most abundant class species in SP1, SP2, and SP5 are O3, O3, and O8, respectively. SP1 and SP2 are rich in O2–O4 class species with DBE values of 5–8, which may be attributed to lignin-derived compounds. Different from SP1 and SP2, SP5 has relatively high contents of O5–O10 class species, corresponding to various acidic species. In addition, N1On (n = 0–8) class species with DBE values of 3–14 were also identified, which should contain a pyrrole ring as the parent structure. ACS Paragon Plus Environment

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1. INTRODUCTION With its environmental friendliness and great abundance, biomass, such as agricultural wastes, forestry residues, and wood, is considered as a potential alternative resource for the sustainable supply of fuels and chemicals.1,2 Cornstalk is an common agricultural waste and its annual yield in China is ca. 130 Mt.3 During harvest seasons, burning cornstalk to ensure normal farming in China results in not only wasting resources but also serious environmental pollution.4 As an efficient conversion technology, biomass liquefaction in supercritical solvents has been extensively investigated.5-9 Regardless of its toxicity, methanol as solvent used for liquefaction has great potentials due to its low cost as well as alkylation and hydrogen-donating abilities.10-12 Xue et al. investigated biomass liquefaction in the presence of alkali, such as NaOH and KOH. They found that the alkali species could promote biomass conversion, suppress char formation, and increase liquid yield.13-16 Liquids from biomass liquefaction in supercritical solvents exhibit a better quality with good flow ability and relatively high calorific value than bio-oils from biomass pyrolysis.17-19 However, they still cannot be directly used as vehicle fuels and the lack of knowledge on their compositional complexity makes them difficult to be upgraded. Therefore, understanding the liquid compositions in detail is necessary for their upgrading to second-generation biofuels or using them to obtain chemicals. Multiple characterization tools, such as elemental analyzer,20,21 Fourier transform infrared spectrometer,22,23 gas chromatograph/mass spectrometer (GC/MS),24,25 and Fourier transform ion cyclotron resonance mass spectrometer (FTICRMS),26,27 have been used for obtaining compositional information on biomass-derived liquids (BDLs). GC/MS is usually limited to relatively volatile, thermally stable, and less polar species. With ultrahigh resolving power and mass accuracy, FTICRMS equipped with electrospray ionization (ESI) proved to be powerful for

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identifying a large number of polar species in petroleum,28,29 coal-derived liquids,30,31 and BDLs.32,33 Thus, combination of GC/MS and FTICRMS may provide a promising and effective way for fully understanding molecular compositions of BDLs. In the present work, cornstalk was subjected to methanolysis in the presence of NaOH to afford soluble portions (SPs) 1–5 (SP1–SP5) and inextractable portion (IEP). The resulting portions were characterized with GC/MS and ESI FTICRMS to obtain insight into chemical complexity of the SPs. 2. EXPERIMENTAL 2.1. Materials. The cornstalk was collected from Hutubi County, Xinjiang Uygur Autonomous Region, China. The sample pretreatment and analyses regarding elemental and group composition of the sample were described elsewhere.34 NaOH, methanol, petroleum ether (PE), carbon disulfide (CDS), and ethoxyethane (EOE) used in the experiments are commercially purchased analytical regents and all the organic solvents were distilled prior to use. 2.2. Methanolysis Procedure and Product Separation. As Figure 1 shows, cornstalk, NaOH, and methanol (30 mL) were put into a 100 mL stainless-steel, magnetically stirred autoclave. After replacing air with N2, the autoclave was heated to a described temperature (220–320 oC) and maintained at that temperature for 0.5 h. Then, the autoclave was cooled to ambient temperature and the reaction mixture was taken out and separated into filtrate and filter cake by filtration. After removing methanol, the solute in the filtrate was sequentially extracted with PE and EOE to afford SP1 and SP2 and inextractable portion 2 (IEP2). Then IEP2 was acidified to pH 2–3 followed by sequential extraction with PE, CDS, and EOE and subsequent solvent evaporation to acquire SP3– SP5 and the final IEP. The yields of each SP (YSP) and IEP (YIEP) were calculated as the mass ratio of the SP (mSP) and IEP (mIEP) to cornstalk on a dry and ash-free basis, respectively; i.e., YSP =


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mSP/mcornstalk, daf and YIEP = mIEP/ mcornstalk, daf. 2.3. Analytical Methods. SP3–SP5 and IEP were esterified with CH2N2 before analysis with GC/MS. SP1, SP2, and esterified SP3–SP5 and IEP were analyzed with an Agilent 7890/5975 GC/MS. The column temperature was programmed from 60 to 240 oC at a rate of 3 oC/min, then raised to 300 oC at a rate of 10 oC/min and held at that temperature for 5 min. The compounds were identified by comparing mass spectra with NIST11 library data. The detailed information on GC/MS was described elsewhere.35 SP1, SP2, and SP5 were further analyzed with a 9.4 T Bruker apex-ultra ESI FTICRMS in negative-ion mode. Data processing was performed according to our recent investigation.36 3. RESULTS AND DISCUSSION 3.1. Effects of Temperature and NaOH/Cornstalk Ratio on the SP Yields. As demonstrated in Figure 2, the total SP yield markedly increased up to ca. 51% with raising temperature from 220 to 300 oC and slightly decreased with further raising temperature, while increasing NaOH/cornstalk ratio monotonously increased the total SP yield. The results suggest that temperature and NaOH play crucial roles during cornstalk methanolysis. SP1 and SP5 have much higher yield than other three SPs regardless of reaction conditions, implying that methanol-soluble portion from cornstalk methanolysis are mainly extractable in PE before acidification and subsequently soluble in EOE after acidification. SP1 yield significantly increased with raising temperature, while increasing NaOH/cornstalk ratio increased SP1 yield up to ca. 25%. Interestingly, SP5 yield decreased with raising temperature but increased with increasing NaOH/cornstalk ratio. Compared with our previous study,34 the total yield of SPs from cornstalk methanolysis increases ca. 15% in the presence of NaOH. The yield of IEP is less than 1%, indicating that most of the methanol-soluble portion from cornstalk methanolysis are extractable by the selected solvents. In


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this study, the SPs acquired at 300 oC with NaOH/cornstalk ratio of 1 g/g were selected to analyze with GC/MS and FTICRMS. 3.2. Analysis with GC/MS. In total, 412 organic species were identified in the SPs and IEP. They can be classified into hydrocarbons (HCs), alcohols, phenolic compounds (PCs), ethers, ketones, carboxylic acids (CAs), esters, nitrogen-containing organic compounds (NCOCs), and others, as illustrated in Tables 1–4, Figures S1–S6, and Tables S1–S8 (see the Supporting information). As Figures 3 and 4 demonstrate, PCs and alcohols are dominant group components in SP1 and SP2, respectively, whereas no PC and negligible alcohols were detected in esterified SP3– SP5 and IEP. Esters are the most abundant compounds in esterified SP3–SP5 and IEP. As shown in Figure 3 and Table 1, most of the detected PCs in SP1 are alkylphenols with carbon number from 1 to 4 in side chain and mesitol is the most abundant. Guaiacols and syringols are predominant PCs in SP from cornstalk methanolysis without NaOH,34 while only a small amount of guaiacols and no syringols were detected in SP1 and SP2. The fact suggests that alkali promotes the breakage of Car– O bonds in lignin during biomass methanolysis, which is consistent with Miller’s report.37 PCs are important industrial chemicals and can be obtained from coals through pyrolysis and liquefaction.38,39 The high relative content of PCs in SP1 indicates that biomass methanolysis could be another feasible approach for producing PCs. Esters can be classified into methyl alkanoates (Table 2), dimethyl alkanedioates (Table 3), aromatic esters (Table 4) and other esters (Table S6). Methyl alkanoates and aromatic esters are the main esters in esterified SP3 and dimethyl alkanedioates are the dominant esters in esterified SP4, SP5, and IEP. In total, 14 CAs were identified in SP1 and SP2, whereas no CA was identified in esterified SP3–SP5 and IEP. Esters detected in esterified SP3–SP5 and IEP should correspond to CAs in SP3–SP5 and IEP. Most of the CAs are important fine chemicals. For example, palmitic acid and stearic acid are widely used in


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foods, cosmetic, surfactants, and lubricant. Succinic acid is a precursor for synthesizing many important industrial products, such as 1,4-butanediol, tetrahydrofuran, polyamides, polyesters, and biodegradable plastics.40,41 Benzoic acid and phthalic acid are important feedstocks for pharmaceuticals and plasticizer, respectively.42 3.3. Analysis with FTICRMS. As shown in Figure 5, the molecular masses of SP1, SP2, and SP5 range from m/z 100 to 500 and the average molecular masses of SP1, SP2, and SP5 are m/z 334, 324, and 286, respectively. Most of the species in SP1 and SP2 center between m/z 300 and 400, while SP5 has much wider molecular mass distribution than SP1 and SP2. The insert in Figure 5 shows that closely spaced isobaric species can be clearly resolved. On the basis of the accurate mass and isotopic mass ratio, each mass spectral peak in Figure 5 was assigned to a unique elemental composition. The negative-ion ESI FTICRMS resolved ca. 1800, 1800, and 1000 species in SP1, SP2, and SP5, respectively. As reported for similar analysis in our previous study,31 each compositionally distinct component can be assigned to a definite “class” and “type” based on its heteroatom number and double bond equivalent (DBE, i.e., rings plus double bonds) value. For example, each N1O1 class species has one nitrogen atom and one oxygen atom in addition to carbon and hydrogen atoms. The compounds with odd masses in mass spectra of SP1, SP2, and SP5 are O1– O10 class species with DBE values of 1–14 and carbon atom numbers (CANs) of 5–35, while those with even masses are N1O0–N1O8 class species with DBE values of 3–14 and CANs of 10–30. For class analysis, relative content of each class species is defined as the sum of magnitudes of all the species in a given class divided by the sum of magnitudes of all the identified peaks (excluding the isotopic peaks) in the mass spectrum. As Figure 6 exhibits, On (n = 1–10) class species are the most abundant. SP1 and SP2 have the highest relative abundance of O3 class species, while the relative abundance of O7–O10 class species is less than 1%. The most abundant class species in SP5 is O8


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class. In addition, different from SP1 and SP2 with relatively high contents of O2–O4 class species, SP5 has relatively high contents of O5–O10 class species. The highest relative contents of N1On in SP1, SP2, and SP5 are N1O4, N1O4, and N1O5 class species, respectively. 3.4. Kendrick Mass Defect (KMD) Analysis. As a commonly used data interpretation approach for the analysis with FTICRMS, KMD assigns compounds in complex mixtures to molecular formulae with various homologous series.43 Each horizontal row having identical KMD represents a homologous series of species with the same number of heteroatoms (N, O, and S) and DBE values, but different alkylation degrees in the x-axis. As illustrated in Figure 7, all the homologous series for the O2–O8 class species have their unique and different KMD values to each other and the KMD values increase with increasing oxygen atom number for the homologous series with the same DBE value in different classes. For example, O8 class species with DBE = 3 have a higher KMD value than O4 class species with the same DBE value. Many rows are displayed in Figure 7, showing that the types of oxygen-containing compounds detected are diverse. Once a few single charged ions for each On class have been assigned to specific formulae, molecular formula assignments of other members in each class can be achieved based on KMD values. 3.5. DBE versus CAN for the On Class Species. DBE is an important structural parameter using in the analysis with FTICRMS. It can reveal the structural features of organic species detected. To obtain detailed information on various class species in SP1, SP2, and SP5, iso-abundance plots were built by correlating DBE and CAN distribution of the species, as displayed in Figures 8–11. The On class species in SP1, SP2, and SP5 mainly have DBE values of 1– 14 and CANs of 5–35. Most of the O1 class species in SP1 have a DBE range of 4–14 and CAN range of 10–30. The species with DBE = 4 in the O1 class species should be alkylphenols with CANs from 14 to 21,


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corresponding to CANs of alkyl side chains from 8 to 15. The species with high intensity in the O1 class have DBE values of 5–8. The increase of 1 DBE value leads to a double bond or an aliphatic ring introduced into a structure. An addition of benzene ring to the existing structure results in 4 DBE value increment. Thus, the O1 class species with DBE = 5 and 8 could be cyclohexylphenols and biphenylols, respectively. The O2 class species with DBE < 4 should be attributed to alkanoic acids (DBE = 1), alkenoic acids (DBE = 2), and alkadienoic acids (DBE = 3) since they exhibit sufficient acidity to be ionized during negative-ion ESI process. The O3 class species may contain different oxygen-containing functional groups, such as hydroxy, carboxy, methoxy, and carbonyl groups. Among the O3 class species, hydroxyalkanoic or methoxyalkanoic acids (DBE = 1) and oxoalkanoic acids (DBE = 2) may be present in SP1 and SP2. According to a previous report,44 the O4–O8 class species with DBE < 4 are mostly “sugaric compounds”, such as derivates or polymers of levoglucosan, anhydropentose, deoxypentopyranose, and glucal. The O2–O4 class species with DBE ≥ 4 in SP1 and SP2 should be the 3 general lignin-derived monomeric phenylpropane units, including p-coumaryl, coniferyl, and sinapyl structures, as the parent structures. The lignin-derived monomers have DBE = 5 and CAN = 9–11.45 The O2–O4 class species with DBE = 5–8 are abundant in SP1 and SP2 (Figures 6, 8, and 9), suggesting that lignin-derived compounds, especially lignin-derived monomers, are the main On class species in SP1 and SP2. Compared with SP1 and SP2, the On class species in SP5 have narrower DBE range (centered within 2–6), as illustrated in Figure 10. Since a series of dimethyl alkanedioates (Table 3) and dimethyl benzenedicarboxylates (Table 4) in esterified SP5 were confirmed by analysis with GC/MS, the O4 class species with DBE = 2 and 6 in SP5 should be ascribed to alkanedioic acids and benzenedicarboxylic acids, respectively. Alkanedioic acids with CANs of 5–25 dominate in the O4 class species. As demonstrated in Figure 6, large amounts of O5–O10 class species were identified in


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SP5. Such species almost cannot be eluted during analysis with GC/MS due to their high polarity. In the O5 and O6 class species, hydroxyalkanedioic or methoxyalkanedioic acids (DBE = 2), oxoalkanedioic or alkanetricarboxylic acids (DBE = 3), and hydroxybenzenedicarboxylic or methoxybenzenedicarboxylic acids (DBE = 6) are predominant. The species with highest intensity in the O7, O8, and O9 classes have DBE values of 5, 6, and 6, respectively. However, owing to the complexity of isomers, determining the structural compositions of these species is very difficult. 3.6. DBE versus CAN for the N1On Class Species. In all the N1On class species, pyrroles are the typical nitrogen compounds that can be efficiently ionized via deprotonation in negative-ion mode.46,47 The increase of 3 DBE units results in the addition of a fused aromatic ring. Hence, pyrroles, indoles, and carbazoles should be the N1On class species with DBE = 3, 6, and 9, respectively. As Figure 11 displays, no species with DBE < 3 were detected, implying that all the N1On class species are aromatics. Oxygen atoms in the N1On class species may be present in alkoxy, furan, hydroxy, carboxy, and carbonyl groups. Factually, it is difficult to speculate with high reliability the molecular structures of the species with 2 or more oxygen atoms based on DBE values alone because all the pyrrole-, hydroxy-, and carboxy-containing compounds can be ionized in negative-ion mode. 4. CONCLUSIONS Temperature and NaOH play crucial roles in cornstalk methanolysis and the highest total SP yield reaches to ca. 51% at 300 oC with the same mass of NaOH and cornstalk. According to analysis with GC/MS, PCs and alcohols are the dominant group components in SP1 and SP2, respectively. Esters are the most abundant compounds in esterified SP3–SP5 and IEP, while no ester was identified in SP1. No PC and negligible alcohols were detected in esterified SP3–SP5 and IEP. Numerous oxygen- and nitrogen-containing compounds were detected with FTICRMS, suggesting


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the chemical complexity of SPs from cornstalk methanolysis. The broadband mass spectra of SP1, SP2 and SP5 exhibit that the molecular mass distributions range from m/z 100 to 500. The identified compounds in SP1, SP2, and SP5 include On (n = 1–10) and N1On (n = 0–8) class species, in which On class species with DBE values of 1–14 and CANs of 5–35 are predominant. Both SP1 and SP2 have the highest relative abundance of O3 class species, while O8 class species are the most abundant in SP5. The O2–O4 class species with DBE values of 5–8 are abundant in SP1 and SP2, which could be lignin-derived compounds. AUTHOR INFORMATION Corresponding Author *Telephone: +86 (516) 83884399 (Z.-M.Z.). E-mail: [email protected] (Z.-M. Z.). Notes The authors declare no competing financial interest. ACKNOWLEDGEMENTS This work was subsidized by National Basic Research Program of China (Grant 2012CB215302), the Program of University in Jiangsu Province for Graduate Student’s Innovation in Science Research (Grant KYLX_1397), and a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions. ASSOCIATED CONTENT Supporting Information Total ion chromatograms of SP1, SP2, and esterified SP3–SP5 and IEP (Figures S1–S6), and corresponding table lists of group components detected (Tables S1–S8). This information is available free of charge via the Internet at http://pubs.acs.org. NOMENCLATURE ACS Paragon Plus Environment

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BDLs

biomass-derived liquids

CAs

carboxylic acids

CAN

carbon atom number

CDS

carbon disulfide

DBE

double bond equivalent

EOE

ethoxyethane

ESI

electrospray ionization

FTICRMS

Fourier transform ion cyclotron resonance mass spectrometer

GC/MS

gas chromatograph/mass spectrometer

HCs

hydrocarbons

IEP

inextractable portion

KMD

Kendrick mass defect

N1On

species which contain one nitrogen atom and n oxygen atoms

NCOCs

nitrogen-containing organic compounds

On

species which contain n oxygen atoms

PCs

phenolic compounds

PE

petroleum ether

SP

soluble portion

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256-264. (22) Tang, S. R.; Zong, Z. M.; Zhou, L.; Zhao, W.; Li, X. B.; Peng, Y. L.; Xie, R. L.; Chen, X. F.; Gu, W. T.; Wei, X. Y. Renew. Energy 2010, 35 (5), 946-951. (23) Aysu, T.; Küçük, M. M. J. Supercrit. Fluids 2013, 83, 104-123. (24) Yip, J.; Chen, M.; Szeto, Y. S.; Yan, S. Bioresour. Technol. 2009, 100 (24), 6674-6678. (25) Yang, H. M.; Zhao, W.; Wang, Y. G.; Liu, D.; Zhao, J.; Fan, X.; Zong, Z. M.; Lu, Y.; Wei, X. Y. Energy Fuels 2013, 27 (1), 596-598. (26) Jarvis, J. M.; McKenna, A. M.; Hilten, R. N.; Das, K. C.; Rodgers, R. P.; Marshall, A. G. Energy Fuels 2012, 26 (6), 3810-3815. (27) Sudasinghe, N.; Dungan, B.; Lammers, P.; Albrecht, K.; Elliott, D.; Hallen, R.; Schaub, T. Fuel 2014, 119, 47-56. (28) Ruddy, B. M.; Huettel, M.; Kostka, J. E.; Lobodin, V. V.; Bythell, B. J.; McKenna, A. M.; Aeppli, C.; Reddy, C. M.; Nelson, R. K.; Marshall, A. G. Energy Fuels 2014, 28 (6), 4043-4050. (29) Klein, G. C.; Rodgers, R. P.; Marshall, A. G. Fuel 2006, 85 (14-15), 2071-2080. (30) Liu, F. J.; Wei, X. Y.; Zhu, Y.; Wang, Y. G.; Li, P.; Fan, X.; Zhao, Y. P.; Zong, Z. M.; Zhao, W.; Wei, Y. B. Fuel 2013, 111, 211-215. (31) Li, Z. K.; Zong, Z. M.; Yan, H. L.; Wang, Y. G.; Ni, H. X.; Wei, X. Y.; Li, Y. H. Fuel Process. Technol. 2014, 128, 297-302. (32) Liu, Y.; Shi, Q.; Zhang, Y. H.; He, Y. L.; Chung, K. H.; Zhao, S. Q.; Xu, C. M. Energy Fuels 2012, 26 (7), 4532-4539. (33) Tessarolo, N. S.; Silva, R. C.; Vanini, G.; Pinho, A.; Romão, W.; de Castro, E. V. R.; Azevedo, D. A. Microchem. J. 2014, 117, 68-76. (34) Zhu, W. W.; Zong, Z. M.; Yan, H. L.; Zhao, Y. P.; Lu, Y.; Wei, X. Y.; Zhang, D. K. Fuel


Energy & Fuels

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Process. Technol. 2014, 117, 1-7. (35) Yan, H. L.; Zong, Z. M.; Zhu, W. W.; Li, Z. K.; Wang, Y. G.; Wei, Z. H.; Li, Y.; Wei, X. Y. Energy Fuels 2015, 29 (5), 3104-3110. (36) Yan, H. L.; Zong, Z. M.; Li, Z. K.; Wei, X. Y. Fuel 2015, 160, 596-604. (37) Miller, J. E.; Evans, L.; Littlewolf, A.; Trudell, D. E. Fuel 1999, 78 (11), 1363-1366. (38) Mochida, I.; Okuma, O.; Yoon, S. H. Chem. Rev. 2014, 114 (3), 1637-1672. (39) Kong, J.; Zhao, R. F.; Bai, Y. H.; Li, G. L.; Zhang, C.; Li, F. Fuel Process. Technol. 2014, 127, 41-46. (40) Song, H.; Lee, S. Y. Enzyme Microb. Technol. 2006, 39 (3), 352-361. (41) Besson, M.; Gallezot, P.; Pinel, C. Chem. Rev. 2014, 114 (3), 1827-1870. (42) Li, Z. K.; Wei, X. Y.; Yan, H. L.; Wang, Y. G.; Kong, J.; Zong, Z. M. Energy Fuels 2015, 29, 6869-6886. (43) Hughey, C. A.; Hendrickson, C. L.; Rodgers, R. P.; Marshall, A. G. Anal. Chem. 2001, 73 (19), 4676-4681. (44) Smith, E. A.; Park, S.; Klein, A. T.; Lee, Y. J. Energy Fuels 2012, 26 (6), 3796-3802. (45) Li, C.; Zhao, X.; Wang, A.; Huber, G. W.; Zhang, T. Chem. Rev. 2015, 115 (21), 11559-11624. (46) Li, Z. K.; Wei, X. Y.; Yan, H. L.; Zong, Z. M. Fuel 2015, 153, 176-182. (47) Tong, J. H.; Liu, J. G.; Han, X. X.; Wang, S.; Jiang, X. M. Fuel 2013, 104, 365-371.


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Page 15 of 30

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

Energy & Fuels

Table 1. PCs Detected in SP1 and SP2 according to Analysis with GC/MS. relative content (%) peak PC SP1 SP2 phenol 0.16 0.78 110 o-cresol 0.56 149 p-cresol 0.75 0.40 165 2,6-xylenol 0.82 177 5-methylguaiacol 2.32 178 2,4-xylenol 2.74 0.92 197 2,5-xylenol 0.55 199 4-methylguaiacol 3.11 202 4-ethylphenol 1.36 1.10 208 3,5-xylenol 0.71 213 2-ethyl-6-cresol 0.67 222 5-isopropyl-2-cresol 1.83 223 mesitol 13.83 1.18 225 3-ethyl-5-cresol 0.49 234 2,3,6-trimethylphenol 1.70 239 4-isopropylphenol 3.14 1.14 240 3-ethyl-6-cresol 0.96 242 2-acetyl-4,5-xylenol 1.05 247 2,3,5-trimethylphenol 0.62 251 2,4,5-trimethylphenol 1.92 254 thymol 2.15 0.32 262 4-isopropyl-3-cresol 6.37 1.17 270 2,3,5,6-tetramethylphenol 0.55 274 2-(tert-butyl)-4-cresol 0.44 278 5-isopropyl-3-cresol 0.48 279 4-methoxymesitol 1.01 289 3-isopropyl-2-cresol 0.38 290 4-(tert-butyl)-2-cresol 0.60 292 3-(tert-butyl)-5-cresol 0.62 294 2,3,4,6-tetramethylphenol 0.43 297 2,4,5,6-tetramethylphenol 4.48 299 2-(tert-butyl)quinol 0.60 301 4-(tert-butyl)guaiacol 0.25 322 3-(tert-butyl)guaiacol 0.32 323 3-(tert-butyl)-4-methoxyphenol 0.86 324 4-(methoxymethyl)-2,6-xylenol 0.59 325 4-isopropyl-2-cresol 0.36 326 4-(3-methylbut-2-enyl)phenol 0.30 336 4-formyl-3,5-xylenol 0.31 337 2-(tert-butyl)-4,6-xylenol 0.29 338 6-(tert-butyl)guaiacol 0.54 347 2-(tert-butyl)-4-methoxyphenol 0.66 350


Energy & Fuels

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 2. Methyl Alkanoates Detected in SP2 and Esterified SP3–SP5 and IEP Analysis with GC/MS. relative content (%) peak methyl alkanoate SP2 SP3 SP4 methyl 2-hydroxypropanoate 15 methyl 2-methoxyacetate 18 methyl 2-methoxypropanoate 31 methyl 2-hydroxybutanoate 43 methyl 3-hydroxybutanoate 0.14 44 methyl 2-methylbut-2-enoate 0.02 53 methyl 2-methylpentanoate 0.05 55 methyl 3-methylpentanoate 0.11 66 methyl 3-methoxy-2-methylpropanoate 68 methyl 4-methylpentanoate 0.14 70 methyl 2-hydroxy-3-methylbutanoate 0.75 72 methyl 2-methoxy-3-methylbutanoate 0.19 83 methyl hexanoate 0.11 84 methyl 2-hydroxypentanoate 86 methyl 3-methylbut-2-enoate 89 methyl 4-methoxybutanoate 0.40 92 methyl 2,4-dimethylpent-4-enoate 0.05 95 methyl 1-methyl-3-oxocyclopentanecarboxylate 0.25 102 methyl 2,4-dimethylpent-3-enoate 0.14 104 methyl 2-methylhex-3-enoate 0.10 105 methyl 4-oxopentanoate 112 methyl 5-methylhexanoate 0.08 113 methyl 2-hydroxy-4-methylpentanoate 0.20 114 methyl 2-hydroxy-3-methylpentanoate 121 methyl hept-2-enoate 0.16 122 methyl 3-methylcyclopentanecarboxylate 0.07 133 methyl heptanoate 0.27 135 methyl 2-methylhept-2-enoate 0.24 137 methyl 5-methoxypentanoate 1.09 145 methyl 3-methylhept-2-enoate 0.18 150 methyl 2-methylheptanoate 0.07 154 methyl cyclohexanecarboxylate 0.04 155 methyl cyclohex-3-enecarboxylate 0.14 164 methyl 6-methylheptanoate 0.27 168 methyl hex-2-enoate 0.37 171 methyl 3-oxocyclohexanecarboxylate 0.06 181 methyl octanoate 0.64 182 methyl hept-5-enoate 0.37 188 methyl 2-methyl-3-oxobutanoate 0.46 189 methyl 5-hydroxy-2-methylhex-3-enoate 190 methyl cyclohex-1-enecarboxylate 0.24 195 methyl 3,4-dimethylcyclopent-3-enecarboxylate 0.54 201 ACS Paragon Plus Environment

Page 16 of 30

according to

SP5 1.18 0.67 1.11 2.63

IEP

0.13 3.35 0.19

0.88

0.29 1.07 0.68

0.03

0.03

0.17

0.29

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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

Energy & Fuels

Table 2. Methyl Alkanoates Detected in SP2 and Esterified SP3–SP5 and IEP according to Analysis with GC/MS (Continued). relative content (%) peak methyl alkanoate SP2 SP3 SP4 SP5 IEP methyl 4-methylcyclohex-3-enecarboxylate 0.17 205 methyl 3,4-dimethylcyclopent-2-enecarboxylate 0.20 206 methyl 8-hydroxyoctanoate 0.29 216 methyl 3-methyl-4-methylenecyclopentane carboxylate 0.20 218 methyl 3,4-dimethylcyclopent-2-enecarboxylate 0.50 221 methyl nonanoate 0.34 232 methyl decanoate 0.29 281 methyl 1-methylcyclopent-2-enecarboxylate 1.18 0.18 291 methyl undecanoate 0.33 321 methyl dodecanoate 0.61 351 methyl tetradecanoate 1.15 374 methyl 9-methyltetradecanoate 0.19 383 methyl pentadecanoate 0.62 384 methyl 14-methylpentadecanoate 0.15 389 methyl hexadec-11-enoate 0.36 391 methyl palmitate 0.40 16.35 0.96 392 methyl heptadecanoate 0.57 398 methyl octadec-9-enoate 2.39 399 methyl octadec-8-enoate 1.39 400 methyl stearate 6.21 0.96 401 methyl nonadecanoate 0.21 403 methyl icosanoate 1.10 0.93 406 methyl henicosanoate 0.34 0.37 407 methyl docosanoate 1.24 2.08 410 methyl tricosanoate 0.55 1.03 411 methyl tetracosanoate 1.42 2.95 412


Energy & Fuels

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 3. Dimethyl Alkanedioates Detected in Esterified SP3–SP5 and IEP according to Analysis with GC/MS. relative content (%) Peak dimethyl alkanedioate SP3 SP4 SP5 IEP 2.20 12.90 13.41 139 dimethyl succinate 0.24 7.51 19.58 18.91 157 dimethyl 2-methylsuccinate 0.12 1.07 1.23 173 dimethyl 2,3-dimethylsuccinate 2.06 1.60 183 dimethyl 2-isopropylmalonate dimethyl 2,2-dimethylsuccinate 2.16 185 2.45 10.30 7.90 192 dimethyl glutarate 0.16 2.33 2.41 2.03 198 dimethyl 2-ethylsuccinate 1.63 3.16 2.08 210 dimethyl 3-methylglutarate 0.53 7.41 9.01 6.20 212 dimethyl 2-methylglutarate 0.03 1.56 0.65 214 dimethyl 2,4-dimethylglutarate 1.27 0.51 220 dimethyl 2-methylhexanedioate 2.04 0.76 1.24 226 dimethyl 2,4-dimethylglutarate 0.34 0.15 229 dimethyl 2-isopropylsuccinate 0.72 0.23 231 dimethyl 2,2-dimethylglutarate 0.61 0.20 236 dimethyl 3-methylhexanedioate 0.16 2.91 1.15 238 dimethyl 2-ethyl-3-methylsuccinate 0.60 1.28 1.44 241 dimethyl adipate 1.45 0.56 246 dimethyl 2-ethylglutarate 0.53 257 dimethyl 3-ethyl-3-methylsuccinate 1.06 266 dimethyl cyclopentane-1,2-dicarboxylate 0.16 268 dimethyl cyclopentane-1,3-dicarboxylate 0.70 0.12 280 dimethyl 4-methylcyclopentane-1,3-dicarboxylate 0.05 282 dimethyl 2-methylcyclopentane-1,3-dicarboxylate 0.48 0.06 283 dimethyl 2-propylglutarate 0.23 284 dimethyl cyclohexane-1,4-dicarboxylate 0.07 285 methyl 5-(1-methoxy-1-oxopropan-2-yl)-2,3-dimethylcyclopentanecarboxylate 0.44 0.04 286 methyl 5-(1-methoxy-1-oxopropan-2-yl)-2,2-dimethylcyclopentanecarboxylate 0.28 287 dimethyl heptanedioate 0.10 288 dimethyl cyclohexane-1,3-dicarboxylate 0.31 2.05 300 dimethyl 2-methoxyhexanedioate 1.24 302 dimethyl 2-methylheptanedioate 0.94 0.05 305 dimethyl 4-methylcyclopentane-1,2-dicarboxylate 0.12 309 dimethyl cyclohexane-1,2-dicarboxylate 0.16 311 dimethyl 3-methylheptanedioate 0.46 315 dimethyl 2,4-dimethylheptanedioate 0.85 0.29 332 dimethyl octanedioate 0.52 339 dimethyl 2-methyloctanedioate 0.29 5.52 0.59 356 dimethyl nonanedioate 0.30 359 dimethyl 2-methylnonanedioate 0.77 368 dimethyl 3-methylnonanedioate 0.48 378 dimethyl decanedioate ACS Paragon Plus Environment

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Page 19 of 30

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

Energy & Fuels

Table 4. Aromatic Esters Detected in SP2 and Esterified SP3–SP5 and IEP according to Analysis with GC/MS. relative content (%) peak aromatic ester SP2 SP3 SP4 SP5 IEP methyl benzoate 2.47 0.23 172 methyl 2-methylbenzoate 0.28 215 methyl 3-methylbenzoate 7.01 227 methyl 4-methylbenzoate 1.55 230 methyl 2-ethylbenzoate 0.15 243 methyl 3-phenylpropanoate 1.83 2.33 258 methyl 2,4-dimethylbenzoate 0.44 265 methyl 3,4-dimethylbenzoate 0.33 271 methyl 3,5-dimethylbenzoate 1.63 273 methyl 2,4-dimethylbenzoate 4.44 277 methyl 4-ethylbenzoate 1.88 293 methyl 4-isopropylbenzoate 0.35 295 methyl 3-isopropylbenzoate 0.36 303 methyl 4-phenylbutanoate 0.26 306 methyl 2,4,5-trimethylbenzoate 1.39 313 methyl 3-(3-hydroxyphenyl)acrylate 0.29 317 methyl 2,4,6-trimethylbenzoate 0.22 320 methyl 3-methoxy-4-methylbenzoate 0.89 327 methyl 3,4,5-trimethylbenzoate 0.57 330 dimethyl phthalate 0.10 1.71 334 methyl 2,4,5,6-tetramethylbenzoate 0.35 341 methyl 2,3,5,6-tetramethylbenzoate 0.65 342 dimethyl terephthalate 1.44 0.13 1.30 0.15 346 dimethyl isophthalate 0.48 1.13 0.17 349 methyl 3-veratroleacrylate 2.08 353 dimethyl 4-methylphthalate 0.58 0.11 358 dimethyl 4-methylisophthalate 0.34 364 methyl 3-(4-methoxyphenyl)butanoate 0.40 365 dimethyl 3-methylphthalate 0.87 367 methyl 3-(2-methoxyphenyl)butanoate 0.70 372 methyl 2-(4-isobutylphenyl)propanoate 0.61 376 methyl 9-(2-propylphenyl)nonanoate 0.33 402


Energy & Fuels

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 20 of 30

cornstalk, NaOH, and methanol methanolysis at 220-320 oC gaseous products

liquid/solid mixture filtration

filter cake

filtrate

methanol evaporation extraction with PE SP1

IEP1 extraction with EOE

SP2

IEP2 acidification extraction with PE

SP3

IEP3 extraction with CDS

SP4

IEP4 extraction with EOE

SP5

IEP

Figure 1. Procedure for cornstalk methanolysis and subsequent treatments.


Page 21 of 30

SP1

SP2

SP3

SP4

SP5

IEP

total

50

Yield (wt%)

40

30

20

10

0 220

240

260 280 Temperature (oC)

300

320

0.46 0.64 0.82 NaOH/cornstalk ratio (g/g)

1.00

50

40 Yield (wt%)

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

Energy & Fuels

30

20

10

0 0.10

0.28

Figure 2. Effects of temperature and NaOH/cornstalk ratio on yields of SPs.


Energy & Fuels 100

SP1

80 OH

OH

60

OH

40

OH

OH

OH

20 0 100

SP2

80 60

HO OH

HO HO

40 HO

20

O O

O

40 O

20

O

O

O

O

O

O

O

O

O

0 100

SP4

O O

80

O O

O

O

60

O O

O

O

methyl docosanoate

O

methyl icosanoate

60

SP3

methyl stearate

methyl palmitate

80

methyl tetracosanoate

OH OH

0 100

Relative abundance (%)

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 22 of 30

O O

O

40

O

O

20 0 100

O

O O

O

O

SP5

O

80 O

60

O

O

O O

40

O

HO

HO

O

O O

O

20 0 100

IEP

80 60 40 20 0 5

10

15

20

25

30

35 40 45 Retention time (min)

50

55

60

Figure 3. Total ion chromatograms of SP1, SP2, and esterified SP3–SP5 and IEP. ACS Paragon Plus Environment

65

70

Page 23 of 30

100

80

others NCOCs

Relative content (%)

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

Energy & Fuels

esters 60

CAs ketones ethers

40

PCs alcohols HCs

20

0

SP1

SP2

SP3

SP4

SP5

IEP

Figure 4. Distribution of group components in SP1, SP2, and esterified SP3–SP5 and IEP according to analysis with GC/MS.


Energy & Fuels

[C19H23O3][C13H15O8]

299.05

-

[C18H19O4][C15H23O6][C14H19O7]-

299.10

[C20H27O2]-

[C16H27O5][C17H31O4]-

299.15

299.20

[C18H35O3]-

299.25

299.30

100 SP1

80 60 40 20

Relative abundance (%)

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 30

0 100 SP2

80 60 40 20 0 100

SP5

80 60 40 20 0 100

200

300 m/z

400

500

Figure 5. Broadband mass spectra of SP1, SP2, and SP5 from analysis with negative-ion ESI FTICRMS and mass scale-expanded segments (insert) at m/z 299.


Page 25 of 30

1

2

3

4

5

6

7

8

9

10

11

12

13

14

28 SP1 24 20 16 12 8 4 0 45 SP2 Relative content (%)

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

Energy & Fuels

36 27 18 9 0 SP5

20 16 12 8 4 0 O1

O2

O3

O4

O5

O6 O7 O8 O9 O10 N1O0 N1O1 N1O2 N1O3 N1O4 N1O5 N1O6 N1O7 N1O8 Oxygen- and nitrogen-containing species

Figure 6. Distributions of On and N1On class species in SP1, SP2, and SP5 according to analysis with negative-ion ESI FTICRMS.


Energy & Fuels

0.35 SP1

O2 O3

0.30

O4 O5 O6

0.25

O6 (9 DBE)

KMD

O5 (9 DBE) 0.20

O4 (9 DBE) O3 (9 DBE) O2 (9 DBE)

0.15

0.10

0.05 0.35

0.30

KMD

0.25

O2 O3

SP2

O4 O5 O6 O6 (6 DBE)

0.20

O5 (6 DBE) O4 (6 DBE)

0.15

O3 (6 DBE) O2 (6 DBE)

0.10

0.05 0.35 O4 0.30

0.25 KMD

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

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SP5

O5 O6 O7 O8 O8 (3 DBE)

0.20

O7 (3 DBE) O6 (3 DBE)

0.15

O5 (3 DBE) O4 (3 DBE)

0.10

0.05 100

200

300 400 Nominal Kendrick mass

500

600

Figure 7. KMD versus nominal Kendrick mass plots for different On class species in SP1, SP2, and SP5. ACS Paragon Plus Environment

Page 27 of 30

15

12

DBE

9 6 3 O1

O2

O3

O4

O5

O6

0 15

12 9 DBE

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

Energy & Fuels

6

3 0 5

10

15

20 CAN

25

30

35 5

10

15

20 CAN

25

30

35 5

10

15

Figure 8. Iso-abundance plots of DBE versus CAN distributions of O1–O6 class species in SP1.


20 CAN

25

30

35

Energy & Fuels

15

12

DBE

9 6 3 O2

O3

O4

O5

O6

O7

0 15 12

9 DBE

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

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6

3 0 5

10

15

20 CAN

25

30

35 5

10

15

20 CAN

25

30

35 5

10

15



20 CAN

25

30

35

Page 29 of 30

15

12

DBE

9 6 3 O4

O5

O6

O7

O8

O9

0 15 12

9 DBE

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

Energy & Fuels

6

3 0 5

10

15

20 CAN

25

30

35 5

10

15

20 CAN

25

30

35 5

10

15



20 CAN

25

30

35

Energy & Fuels

15 SP1

SP2

SP5

N1O4

N1O4

N1O5

12

9 DBE

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

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6

3 0 5

10

15

20 CAN

25

30

35 5

10

15

20 CAN

25

30

35 5

10

15

20 CAN

Figure 11. Iso-abundance plots of DBE versus CAN distributions of major N1On class species in SP1, SP2, and SP5.


25

30

35

Insight into the Chemical Complexity of Soluble Portions from

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