Research Article pubs.acs.org/journal/ascecg
Compositional and Structural Changes of Corn Cob Pretreated by Electron Beam Irradiation Xiaoya Guo,*,† Ting Zhang,† Sitao Shu,† Wei Zheng,‡ and Mintian Gao*,‡ †
Department of Chemical Engineering, Shanghai University, Shanghai 200444, China School of Life Sciences, Shanghai University, Shanghai 200444, China
‡
ABSTRACT: Effects of electron beam irradiation (EBI) on the content and structure of corn cob were evaluated in this study. Cellulose, hemicelluloses and lignin were separated and analyzed to investigate the structural changes in the pretreatment process. The results showed that EBI increased the removal of hemicellulose and lignin. Irradiation resulted in break and rearrangement between cellulose chains, the degree of polymerization (DP) of cellulose was reduced to the minimum (188) at 270 kGy, and part of cellulose was transformed from cellulose I to cellulose II. The thermal stability of the lignin extracted from pretreated corn cob decreased compared to that from raw sample. After the hydrolysis of the samples, the glucose yield and reducing sugar increased with the increasing irradiation dose and reached the maximum (44.3%) at 270 kGy after 48 h of enzymatic hydrolysis with an enzyme loading of 10 filter paper unit (FPU)/g of corn cob, which was 1.75 times of that of the untreated sample. The best yield of reducing sugar (267.9 mg/g corn cob) was obtained at 270 kGy after the hydrolysis with 2% sulfuric acid, which was 72.5% higher than the untreated sample. KEYWORDS: Lignocellulosic biomass, Electron beam irradiation, Cellulose, Hemicellulose, Lignin, Degree of polymerization, Hydrolysis
■
INTRODUCTION Energy is the main power of the development of social economy, so the exploration of new energy has become the first important task with the exhaustion of fossil energy. Because of its 30%−50% cellulose that could be hydrolyzed to glucose and fermented to bioethanol, lignocellulosic biomass has attracted more and more attention by the researchers all over the world. However, the structure of lignocelluloses is so complex and compact, the hemicellulose and cellulose are connected tightly by complex physical and morphological structures, forming the mainframe of plant cell walls.1 Besides, the lignin forms stable complexes with hemicellulose by strong covalent bond and hydrogen bond, thus making the cellulose wrapped and difficult to be hydrolyzed by cellulase or other chemical reagents, so the lignocelluloses biomass has to be pretreated to reduce the recalcitrance of the complex structure and improve the hydrolysis efficiency.1,2 Many chemical, physical and biological methods have been used to pretreat the biomass, such as oxidative delignification,3 acid and alkali hydrolysis,4,5 ionic liquid pretreatment,6,7 hydrothermal pretreatment,8 inorganic salt immersion,9,10 steam explosion,11 mechanical fragmentation12 and microbial degradation.13 These methods remove lignin or hemicellulose effectively and alter other features of the biomass, such as decrease of degree of polymerization or crystallinity of cellulose, increase of the surface area of the biomass that result in great increase in the ability of enzyme or other chemical reagents to reach cellulose and improve the hydrolysis efficiency.14−17 However, these pretreatment meth© 2016 American Chemical Society
ods are not applied in the industry due to some demerits or shortcomings such as high pressure, high energy, high demands for devices, and heavy pollution to the environment.1 In recent years, alternative methods such as electron beam and γ-ray irradiation have been introduced in to the degradation of lignocelluloses biomass such as wheat straw,2 switchgrass,15 pennisetum,18 giant reed,19 bagasse20 etc. The irradiation induces random chain scission in the lignocelluloses,21 decreases the DP or crystallinity of cellulose and removes parts of hemicellulose and lignin, which results in increases of the accessibility of the cellulose crystalline regions to reagents and improve of sugar yield after hydrolysis.15,18,22 EBI pretreatment shows some particular virtues, such as convenient operation (exposure to electron beam), mild conditions (atmosphere, room temperature, ordinary pressure), short treat time, low environmental impact. Using EBI pretreatment can also reduce the number of processing stages and decrease energy consumption. There have been some industrial scale EBI machines established in many countries, the EBI pretreatment of biomass with pre-existing EBI facilities will has no additional cost and will lift the utilization efficiency of the EBI machines. However, the changes in the three individual structural components, especially the structural changes of cellulose, lignin and hemicelluloses extracted from lignocelluReceived: July 29, 2016 Revised: October 11, 2016 Published: November 6, 2016 420
DOI: 10.1021/acssuschemeng.6b01793 ACS Sustainable Chem. Eng. 2017, 5, 420−425
Research Article
ACS Sustainable Chemistry & Engineering loses biomass exposed to EBI have not been discussed. Study on the changes in cellulose, hemicellulose and lignin during the EBI pretreatment is of interest because the amount of information obtained so far about the mechanism of radiolysis of lignocellulosic biomass is quite limited and further understanding on the irradiation effects is needed. In this study, we extracted cellulose, lignin and hemicelluloses and analyzed their compositional and structural changes after the corn cobs were exposed to EBI at 90, 180, 270 kGy.
■
Figure 2. Scheme for lignin separation from corn cob.
MATERIALS AND METHODS
then neutralized with 2% Ba(OH)2 solution. After neutralization, the mixture was centrifuged at 8000 rpm for 15 min to obtain supernatant; the supernatant was used for further analysis of reducing sugar.26 Analytical Methods. The cellulose, hemicellulose and lignin contents were measured with detergent extraction method according to Van Soest fiber analysis system.27 The methods for chemical analyses, including the DP of cellulose, calculation of cellulose recovery, hemicellulose and lignin removal rate, glucose yield determined by HPLC were described in our previous paper.1 The concentrations of reducing sugar after the dilute acid hydrolysis were determined by 3,5-dinitrosalicyclic acid (DNS) method.28 The reducing sugar concentrations were calculated as follows
Materials and Compositional Analysis. Corn cobs are one of the most popular agricultural wastes in China. For this study, corn cobs were obtained from Gaotang Technology Company, Ltd. (Shandong, China). Corn cobs were washed with distilled water to remove dust and dried at 105 °C for 2 h and subsequently milled to collect 1 mm pieces. The chemical composition analysis and detailed procedures were the same and provided in our previous study.1 All of the chemical reagents such as ethanol, benzene, sodium hypochlorite, potassium hydroxide, hydrochloric acid, etc. used in this experiment were analytical grade. Electron Beam Irradiation. The corn cobs were placed in a stainless steel tray, and the experiments were conducted by an electron accelerator (K-400, 400 kV, 1 mA, Ray Institute of Shanghai University) in open air under constant temperature and humidity at doses of 90, 180, 270 kGy; the untreated sample was used as control. Cellulose, Hemicelluloses and Lignin Separation. The scheme for cellulose and hemicellulose separation from corn cob is depicted in Figure 1, and the scheme for lignin is depicted in Figure 2. The
reducing sugar release (mg/g) =
reducing sugar in hydrolyate (mg) corn cob (g)
The structural changes of cellulose, hemicellulose and lignin extracted from corn cobs before and after the pretreatment were analyzed by an Avatar 370 FT-IR (Shanghai Thermo Fisher Scientific Co., Ltd.). 10 mg of pretreated corn cobs were pelleted with KBr, and the IR spectrum was recorded between 4000 and 400 cm−1 at 1 cm−1 resolution and 32 scans per sample.1 The crystalline nature of the cellulose extracted from raw and pretreated corn cob were examined using an X-ray diffractometer (18KW D/MAX2500 V+/PC, Japan) with the potential of 40 kV and current 250 mA. The diffraction spectra were collected using 2θ/θ mode from 4 to 50° with a step size of 0.02°. The TG-DSC analyzer (STA 499 TG-DTA/DSC) was used to analyze thermal properties of the lignin extracted from the corn cob before and after irradiation. The temperature ramping rate was 20 °C/ min from 30 to 700 °C in the nitrogen atmosphere.
■
RESULTS AND DISCUSSION Effect of Irradiation on the Compositional Changes. To investigate the effect of irradiation dose on the content of major components, corn cobs were treated with EBI at 0, 90, 180 and 270 kGy. Figure 3 shows that hemicellulose and lignin
Figure 1. Scheme for cellulose and hemicellulose separation from corn cob. separated cellulose and lignin were then dried at 105 °C for 2 h and the hemicellulose at 60 °C for 24 h for further analysis.1,23−25 Enzymatic Hydrolysis. 10 FPU of acremonium cellulase was used to hydrolyze the pretreated corn cobs (1 g) to investigate the hydrolysis rate in in 50 mM citrate buffer (pH 5) at 10% (w/v) substrate consistency in triplicate following the NREL standard procedures.24 The specific hydrolysis procedures and calculation methods of glucose yield were the same as our previous research.1 Dilute Acid Hydrolysis. Dilute acid hydrolysis was carried out in a 250 mL Erlenmeyer flask; 1 g of pretreated corn cob was suspended in 2% (v/v) of sulfuric acid solutions and incubated at 121 °C at a constant solid-to-liquid ratio of 1:20 (g/mL) for 15 min. After the hydrolysis, the hydrolysates were cooled to room temperature and
Figure 3. Effect of irradiation dose on the content of major components. 421
DOI: 10.1021/acssuschemeng.6b01793 ACS Sustainable Chem. Eng. 2017, 5, 420−425
Research Article
ACS Sustainable Chemistry & Engineering effectively removed during EBI pretreatment. The removal rate increased with the increase of irradiation dose. Moreover, the cellulose recovery changed insignificantly. It may be explained that absorbed energy in irradiation process destroyed the monomeric units of hemicellulose and lignin, but did not destroy the structure of cellulose monomeric units. In cellulose molecules, absorbed energy induced break and chain scission reaction, which result in depolymerization of the molecules. The highest hemicellulose removal (35.8%) and lignin removal (26.7%) were achieved at 270 kGy. This could be ascribed to the cleavage and depolymerization of macromolecules into small molecule volatile organic compounds or soluble fractions.2,16 In fact, many researchers have reported irradiation was an efficient method to pretreat lignocellulose biomass for bioethanol. For example, Ke-qin Wang reported cellulose, hemicellulose and lignin for irradiation pretreated rice straw were much more greatly degraded compared with steam explosion pretreated samples and the relative content of glucose was significantly enhanced from 6.58% to 47.44%.22 K. Karthika also demonstrated electron beam irradiation of hybrid grass resulted in great removal of hemicellulose and decrease of crystallinity of cellulose.18 However, they did not extract the cellulose, hemicellulose and lignin from biomass and determinate their structural changes after pretreatment by irradiation. Characterization of Cellulose. Effect of irradiation on degree of polymerization (DP) of cellulose is depicted in Figure 4. The figure shows that the irradiation resulted in great
Figure 5. XRD spectra of cellulose extracted from untreated and pretreated corn cobs.
untreated sample to 21.7° for that after irradiation at 270 kGy, and the peak intensity at 34° became weaker. A new peak at 20.2° appeared for the sample after irradiation, which showed that EBI resulted in the break and rearrangement between cellulose chains, leading to the transform of parts of cellulose I to cellulose II with the decrease of DP of cellulose. The FTIR spectra of the cellulose extracted from raw and pretreated corn cobs are depicted in Figure 6. It confirms the
Figure 4. Effect of irradiation dose on DP of extracted cellulose.
decrease of DP of cellulose, and the DP decreased with the increase of dose and reached the minimum value of 188 at 270 kGy. It may be demonstrated that irradiation resulted in break and chain scission of cellulose molecules, and higher doses gave more energy to the chain scission. Low polymers could be hydrolyzed more conveniently and efficiently for the cellulase or other chemical reagents. The crystallinity of cellulose extracted from corn cob before and after pretreatment was extensively investigated by XRD analysis. As is shown in Figure 5, the peak at 2θ 22° corresponds to 002 plane of cellulose, and another peak at 20° is assigned to the diffraction plane 101 of cellulose II. The peak at 34° is ascribed to 1/4 of the length of one cellobiose unit and arises from ordering along the fiber direction.29 The crystalline peak of 002 plane decreased from 22.2° for the cellulose from
Figure 6. FTIR spectra of cellulose extracted from raw and pretreated corn cobs: (a) untreated, (b) irradiated at 90 kGy, (c) irratiated at 180 kGy and (d) irratiated at 270 kGy.
occurrence of structural changes after pretreatment. However, the spectra did not show formation of any new peaks, which proved that the basic composition units of cellulose (glucose and cellobiose) were not destroyed in the EBI pretreatment. The absorbance band at 3445 cm−1 presented the O−H stretching of the hydrogen bonds.30 However, the absorbance band at 2896 cm−1 was attributed to the C−H or CH2 stretching vibration.16 Decrease of IR bands at 1429, 1511 and 1645 cm−1 belonging to the aromatic skeletal vibration and C−O stretching in conjugation to aromatic ring, respectively, of lignin were observed in the cellulose extracted from treated 422
DOI: 10.1021/acssuschemeng.6b01793 ACS Sustainable Chem. Eng. 2017, 5, 420−425
Research Article
ACS Sustainable Chemistry & Engineering corn cob,31−33 which showed the EBI pretreatment scattered the lignocellulose structure and removed lignin effectively. The absorbance at 1164 cm−1 indicated the presence of arabinosyl side chains.26 The absorption peak at 1374 cm−1 was attributed to C−H deformation (symmetric) of cellulose.16 The peak at 895 cm−1 corresponds to the glycosidic C1−H deformation with ring vibration contribution, which is a characteristic of βglycosidic linkages between glucose in cellulose.23 The increase of the peak at 895 cm−1 indicated that the crystallinity of cellulose reduced after the irradiation, which can lead to significant increase of the hydrolysis rate.18 Characterization of Hemicellulose. FTIR spectra of hemicellulose fraction are shown in Figure 7. The IR peaks at
Figure 8. FTIR spectra of lignin extracted from raw and pretreated corn cobs: (a) untreated, (b) irradiated at 90 kGy, (c) irratiated at 180 kGy and (d) irratiated at 270 kGy.
stretching indicating hydroxylcinnamates were usually esterified with lignin or hemicellulose.23 The peak at 1249 cm−1 was associated with aromatic CO stretching in guaiacyl and syringl units, and the peak at 1029 cm−1 corresponded to C H in plane deformation in guaiacyl units.35,36 The increased peak at 1029 cm−1 could be demonstrated that the guaiacyl units increased after irradiation pretreatment. The intensity of peaks at 1249 and 833 cm−1 were mildly reduced after pretreatment indicating that the syringl units were destroyed partly during the pretreatment. Pretreated lignin had higher intensity in 2935 and 3371 cm−1, which correspond to the C H vibration of aliphatic carbon and OH stretching respectively,38 than untreated sample indicating that lignin depolymerized to some extent and more terminal groups revealed. Another important peak at 890 cm−1 associated with β anomers or β-linked glucose polymer showed the existence of cellulose in the extracted lignin from pretreated corn cob.1 The IR bands in profile of 180 kGy are similar to that of 270 kGy, whereas the profile of 90 kGy is a little different. The intensity of peaks at 833 and 1029 cm−1 are higher than that of other three profiles. These two peaks are characteristic of CH out plane deformation in aromatic ring and CH in plane deformation in guaiacyl unit, respectively. The increase may be due to the fact that the irradiation at 90 kGy reduced, to an extent, the recalcitrance of the complex and compact structure of lignocellulosic biomass, and destroyed the covalent bond and hydrogen bond between the lignin and hemicellulose. On the other hand, the energy absorbed by the sample was not high enough to degrade the lignin sharply. Scatter of ligniocellulosic structure leads to high content of pure lignin in the separated lignin, especially guaiacyl and syringl units. However, the lignin was damaged at higher irradiation dose and many degradation products exist in the pretreated corn cob, which result in the decrease of the lignin purity in the separated lignin. Thermal analysis was performed and the TG and DTG curves of lignin extracted from raw and pretreated corn cobs are illustrated in Figure 9. The pyrolysis process can mainly be divided into three stages. The first stage was between 30 and 160 °C, at which the weight loss was mainly due to the evaporation of moisture. The second stage at 160−300 °C was due to the pyrolysis or fragmentation of the side chains of lignin, during which the C−H, C−O bonds or the remained
Figure 7. FTIR spectra of hemicellulose extracted from raw and pretreated corn cobs: (a) untreated, (b) irradiated at 90 kGy, (c) irratiated at 180 kGy and (d) irratiated at 270 kGy.
895, 1042, 1167, 1256, 1420, 1461, 2882 and 3387 cm−1 were typical characteristic of hemicellulose. The peaks at 1042 and 1167 cm−1 were ascribed to arabinoxylans.34,23 The absorption around 1256 cm−1 was attributed to C−O stretching. The peak at 1645 cm−1 was assigned to H2O absorbed.16 The intensity of peaks at 895, 1042, 1167, 1256 and 1420 cm−1 increased implying the content of arabinoxylans and acetyl group increased in hemicellulose extracted from the pretreated corn cob, which was probably due to the depolymerization of hemicellulose during the pretreatment. No peak at 837, 1507 and 1604 cm−1 corresponding to lignin23,32 was found, implying that lignin was not exist in the separated hemicellulose. Characterization of Lignin. FTIR spectra of lignin extracted from corn cobs are shown in Figure 8. As shown in Figure 8, the peaks at 2935, 1716, 1600, 1511, 1463, 1425, 1330, 1249, 1164, 1029 and 835 cm−1 are typical spectra for lignin.35 The existence of these peaks indicated the basic structure of lignin was not damaged greatly during the irradiation and extraction process.23,32,36,37 Although the IR band at 1511 cm−1, which was ascribed to the CC aromatic skeleton, decreased gradually with the increasing irradiation dose indicating that the samples absorbed more energy at high irradiation dose, which promoted the damage of aromatic skeleton. The presence of syringl aromatic units was detected by peaks at 833 and 1330 cm−1, presenting the characteristic of CH deformations and CO stretching, respectively.34,35 The significant peak at 1716 cm−1 was ascribed to CO 423
DOI: 10.1021/acssuschemeng.6b01793 ACS Sustainable Chem. Eng. 2017, 5, 420−425
Research Article
ACS Sustainable Chemistry & Engineering
Figure 11: the reducing sugar yield increased with the irradiation dose and reached its best 267.9 mg/g corn cob at
Figure 9. TG and DTG curves of lignin extracted from raw and pretreated corn cobs.
Figure 11. Effect of irradiation dose on reducing sugar yield of acid hydrolysis of corn cob.
hemicellulose and cellulose in lignin were pyrolyzed into some volatile gas. The last stage was from 300 to 600 °C, which arose from the degradation of the main part of lignin, such as the pyrolysis or gasification of aromatic ring or alkyl groups.32 In general, the lignin was greatly degraded between 160 and 600 °C, and the maximum weight loss temperatures at the second and third stage were 285 and 325 °C, respectively, for the raw sample. However, the first maximum weight shifted to 270 °C for the pretreated one, which illustrated that lignin was destroyed partly during the pretreatment, the amount of side chains and lignin degradation products increased and the bond energy of side chains might decrease. When the heating temperature was over 600 °C, the degradation rate slowed down and the final 29% of solid residues were left for the pretreated samples, which was a little lower than that 33.5% of the raw sample. These data showed the thermal stability of the lignin decreased after irradiation by electron beam. Hydrolysis of Corn Cobs. The glucose released after the enzymatic hydrolysis of the biomass samples exposed to different doses of EBI is given in Figure 10. The glucose yield increased with the extension of hydrolysis time, and the glucose yield increased with the increasing of irradiation dose. The largest glucose yield 44.3% was achieved when the dose was increased to 270 kGy at 48 h of enzymatic hydrolysis, which was 1.75 times of that 25.3% of the untreated sample. A great improvement was also seen for the reducing sugar yield from
270 kGy after 2% sulfuric acid hydrolysis, which was 72.5% higher than the control. Hence, irradiation pretreatment broke the complex and compact structure of lignocellulose biomass, removed lignin partly and improved the hydrolysis efficiency.
■
CONCLUSIONS The corn cobs were exposed to electron beam irradiation at the doses of 90, 180 and 270 kGy, and the irradiation increased the removal of hemicellulose and lignin, whereas the cellulose recovery did not change drastically. The structural analysis showed the characteristic peaks of cellulose and hemicellulose in extracted cellulose and hemicellulose from the pretreated corn cobs were more prominent than that from untreated sample. Besides, irradiation resulted in break and rearrangement of cellulose chains, the DP of cellulose was greatly reduced and reached its minimum value of 188 with parts of cellulose was transformed from cellulose I to cellulose II when the irradiation dose increased to 270 kGy. The thermal stability of lignin extracted from pretreated corn cob was also decreased compared to that from untreated sample. The glucose and reducing sugar yield in the hydrolysis of pretreated corn cobs were greatly improved. The largest glucose yield of 44.3% was achieved when the dose was increased to 270 kGy after 48 h of enzymatic hydrolysis by acemonium cellulase (10 FPU/g of corn cob), which was 1.75 times of that of untreated sample. The best reducing sugar yield 267.9 mg/g corn cob were also obtained at 270 kGy after 2% sulfuric acid hydrolysis, which was 72.5% higher than that of the untreated sample.
■
AUTHOR INFORMATION
Corresponding Authors
*Xiaoya Guo. Phone: 86-21-66137491. Fax: 86-21-66137725. E-mail:
[email protected]. *Mintian Gao. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work was supported by National Natural Science Foundation of China (No. 21571127) and Program for
Figure 10. Effect of irradiation dose on glucose yield of enzymatic hydrolysis of corn cob. 424
DOI: 10.1021/acssuschemeng.6b01793 ACS Sustainable Chem. Eng. 2017, 5, 420−425
Research Article
ACS Sustainable Chemistry & Engineering
(18) Karthika, K.; Arun, A. B.; Rekha, P. D. Enzymatic hydrolysis and characterization of lignocellulosic biomass exposed to electron beam irradiation. Carbohydr. Polym. 2012, 90, 1038−1045. (19) Li, Q.; Li, X.; Jiang, Y.; Xiong, X.; Hu, Q.; Tan, Xi.; Wang, K.; Su, X. Analysis of degradation products and structural characterization of giant reed and Chinese silvergrass pretreated by 60Co-γ irradiation. Ind. Crops Prod. 2016, 83, 307−315. (20) Kumakura, M.; Kaetsu, I. Effect of radiation pretreatment of bagasse on enzymatic and acid hydrolysis. Biomass 1983, 3, 199−208. (21) Driscoll, M.; Stipanovic, A.; Winter, W.; Cheng, K.; Manning, M.; Spiese, J.; Galloway, R. A.; Cleland, M. R. Electron beam irradiation of cellulose. Radiat. Phys. Chem. 2009, 78, 539−542. (22) Wang, K.; Xiong, X.; Chen, J.; Chen, L.; Su, X.; Liu, Y. Comparison of gamma irradiation and steam explosion pretreatment for ethanol production from agricultural residues. Biomass Bioenergy 2012, 46, 301−308. (23) Zhang, P.; Dong, S.; Ma, H.; Zhang, B.; Wang, Y.; Hu, X. Fractionation of corn stover into cellulose, hemicellulose and lignin using a series of ionic liquids. Ind. Crops Prod. 2015, 76, 688−696. (24) Resch, M. G.; Baker, J. O.; Decker, S. R. Low Solids Enzymatic Saccharification of Lignocellulosic Biomass: Laboratory Analytical Procedure (LAP); Technical Report NREL/TP-5100-63351; National Renewable Energy Laboratory: Golden, CO, 2015. (25) Sun, R.; Hughes, S. Fractional extraction and physico-chemical characterization of hemicelluloses and cellulose from sugar beet pulp. Carbohydr. Polym. 1998, 36, 293−299. (26) Ramadoss, G.; Muthukumar, K. Influence of dual salt on the pretreatment of sugarcane bagasse with hydrogen peroxide for bioethanol production. Chem. Eng. J. 2015, 260, 178−187. (27) Goering, H. K.; Vansoest, P. J. Forage fiber analyses. In Agriculture Handbook; Agricultural Research Services: Department of Agriculture: Washington, DC, 1970. (28) Miller, G. L. Use of dinitrosalicylic acid reagent for determination of reducing sugar. Anal. Chem. 1959, 31, 426−428. (29) Nishiyama, Y.; Langan, P.; Chanzy, H. Crystal structure and hydrogen-bonding system in cellulose Iβ from synchrotron X-ray and neutron fiber diffraction. J. Am. Chem. Soc. 2002, 124, 9074−9082. (30) Lateef, H.; Grimes, S.; Kewcharoenwong, P.; Feinberg, B. Separation and recovery of cellulose and lignin using ionic liquids: a process for recovery from paper-based waste. J. Chem. Technol. Biotechnol. 2009, 84, 1818−1827. (31) Hoareau, W.; Trindade, W. G.; Siegmund, B.; Castellan, A.; Frollini, E. Sugar cane bagasse and curaua lignins oxidized by chilorine dioxide and reacted with furfuryl alcohol: chararcterization and stability. Polym. Degrad. Stab. 2004, 86, 567−576. (32) Su, Y.; Du, R.; Guo, H.; Cao, M.; Wu, Q.; Su, R.; Qi, W.; He, Z. Fractional pretreatment of lignocellulose by alkaline hydrogen peroxide: Characterization of its major components. Food Bioprod. Process. 2015, 94, 322−330. (33) Thangavelu, S. K.; Ahmed, A. S.; Ani, F. N. Bioethanol production from sago pith waste using microwave hydrothermal hydrolysis accelerated by carbon dioxide. Appl. Energy 2014, 128, 277−283. (34) Xue, B.; Wen, J.; Xu, F.; Sun, R. Structural characterization of hemicelluloses fractionated by graded ethanol precipitation from Pinus yunnanensis. Carbohydr. Res. 2012, 352, 159−165. (35) Ghaffar, S. H.; Fan, M. Structural analysis for lignin characteristics in biomass straw. Biomass Bioenergy 2013, 57, 264−279. (36) Medina, J. D. C.; Woiciechowski, A.; Filho, A. Z.; Noseda, M. D.; Kaur, B. S.; Soccol, C. R. Lignin preparation from oil palm empty fruit bunches by sequential acid/alkaline treatment − A biorefinery approach. Bioresour. Technol. 2015, 194, 172−178. (37) Watkins, D.; Nuruddin, M.; Hosur, M.; Tcherbi-Narteh, A.; Jeelani, S. Extraction and characterization of lignin from different biomass resources. J. Mater. Res. Technol. 2015, 4, 26−32. (38) Liu, Q.; Wang, S.; Zheng, Y.; Luo, Z.; Cen, K. Mechanism study of wood lignin pyrolysis by using TG-FTIR analysis. J. Anal. Appl. Pyrolysis 2008, 82, 170−177.
Innovative Research Team of Shanghai University (No. IRT13078).
■
REFERENCES
(1) Guo, X.; Shu, S.; Zhang, W.; Wang, E.; Hao, J. Synergetic degradation of corn cob with inorganic salt (or hydrogen peroxide) and electron beam irradiation. ACS Sustainable Chem. Eng. 2016, 4, 1099−1105. (2) Yang, C.; Shen, Z.; Yu, G.; Wang, J. Effect and after effect of γ radiation pretreatment on enzymatic hydrolysis of wheat straw. Bioresour. Technol. 2008, 99, 6240−6245. (3) Gierer, J.; Yang, E.; Reitberger, T. On the significance of the superoxide radical in oxidative delignification, studied with 4-tButylsyringol and 4-t-Butylguaiacol. Part I. The Mechanism of aromatic ring opening. Holzforschung 1994, 48, 405−414. (4) Lee, Y. Y.; Iyer, P.; Torget, R. W. Dilute-acid hydrolysis of lignocellulosic biomass. Adv. Biochem. Eng./Biotechnol. 1999, 65, 93− 115. (5) Kumar, P.; Barrett, D. M.; Delwiche, M. J.; Stroeve, P. Methods for pretreatment of lignocellulosic biomass for efficient hydrolysis and biofuel production. Ind. Eng. Chem. Res. 2009, 48, 3713−3729. (6) Raj, T.; Gaur, R.; Dixit, P.; Gupta, R. P.; Kagdiyal, V.; Kumar, R.; Tuli, D. K. Ionic liquid pretreatment of biomass for sugars production: Driving factors with a plausible mechanism for higher enzymatic digestibility. Carbohydr. Polym. 2016, 149, 369−381. (7) Uja; Nakamoto, A.; Goto, M.; Tokuhara, W.; Noritake, Y.; Katahira, S.; Ishida, N.; Nakashima, K.; Ogino, C.; Kamiya, N.; Shoda, Y. Short time ionic liquids pretreatment on lignocellulosic biomass to enhance enzymatic saccharification. Bioresour. Technol. 2012, 103, 446−452. (8) Petersen, M. Ø.; Larsen, J.; Thomsen, M. H. Optimization of hydrothermal pretreatment of wheat straw for production of bioethanol at low water consumption without addition of chemicals. Biomass Bioenergy 2009, 33, 834−840. (9) Kang, K. E.; Park, D. H.; Jeong, G. T. Effects of inorganic salts on pretreatment of Miscanthus straw. Bioresour. Technol. 2013, 132, 160− 165. (10) Yu, Q.; Zhuang, X.; Yuan, Z.; Qi, W.; Wang, Q.; Tan, X. The effect of metal salts on the decomposition of sweet sorghum bagasse in flow-through liquid hot water. Bioresour. Technol. 2011, 102, 3445− 3450. (11) Zhao, X.; Moates, G. K.; Wilson, D. R.; Ghogare, R. J.; Coleman, M. J.; Waldron, K. W. Steam explosion pretreatment and enzymatic saccharification of duckweed (Lemna minor) biomass. Biomass Bioenergy 2015, 72, 206−215. (12) Barakat, A.; Monlau, F.; Solhy, A.; Carrere, H. Mechanical dissociation and fragmentation of lignocellulosic biomass: Effect of initial moisture, biochemical and structural proprieties on energy requirement. Appl. Energy 2015, 142, 240−246. (13) Keller, F. A.; Hamilton, J. E.; Nguyen, Q. A. Microbial pretreatment of biomass: Potential for reducing severity of thermochemical biomass pretreatment. Appl. Biochem. Biotechnol. 2003, 105, 27−41. (14) Tóth, T.; Borsa, J.; Takács, E. Effect of preswelling on radiation degradation of cotton cellulose. Radiat. Phys. Chem. 2003, 67, 513− 515. (15) Sundar, S.; Bergey, N. S.; Salamanca-Cardona, L.; Stipanovic, A.; Driscoll, M. Electron beam pretreatment of switchgrass to enhance enzymatic hydrolysis to produce sugars for biofuels. Carbohydr. Polym. 2014, 100, 195−201. (16) Karthika, K.; Arun, A. B.; Melo, J. S.; Mittal, K. C.; Kumar, M.; Rekha, P. D. Hydrolysis of acid and alkali presoaked lignocellulosic biomass exposed to electron beam irradiation. Bioresour. Technol. 2013, 129, 646−649. (17) Yoon, M.; Choi, J. I.; Lee, J. W.; Park, D. H. Improvement of saccharification process for bioethanol production from Undaria sp. by gamma irradiation. Radiat. Phys. Chem. 2012, 81, 999−1002. 425
DOI: 10.1021/acssuschemeng.6b01793 ACS Sustainable Chem. Eng. 2017, 5, 420−425
