Exploration of the Strengthening Effect by Byproduct-Organic Acids on

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Exploration of the strengthening effect by byproductorganic acids on subcritical liquid hot water pretreatment Huisheng Lyu, Chunliu Lv, Xingfang Shi, Jiatao Liu, Fanmei Meng, and Minhua Zhang Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 06 Jun 2017 Downloaded from http://pubs.acs.org on June 6, 2017

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Exploration of the strengthening effect by byproduct-organic acids on subcritical liquid hot water pretreatment Huisheng LYU, Chunliu Lv, Xingfang Shi, Jiatao Liu, Fanmei Meng, Minhua Zhang* Key Laboratory for Green Chemical Technology of Ministry of Education, Tianjin University R&D Center for Petrochemical Technology, Tianjin 300072, China

Abstract: To improve the utilization of phragmites in biorefineries, the strengthening effect of byproduct-organic acids on the subcritical liquid hot water (SLHW) pretreatment was explored. The byproduct-organic acids were accumulated during the directly recycling of pretreated liquid, which could reduce water consumption. The byproduct-organic acids, including acetic acid and lactic acid, were used to strengthen the SLHW pretreatment of raw phragmites at different temperature (160-200°C) and time (20-90min) in the strengthening process. During the SLHW pretreatment, the high yield of C-5 sugars was 60.66% at the severity of 4.85 (200°C, 75min). However, the maximum C-5 sugars yield in the strengthening process was 85.01% at 180°C, for 50 min and with 2.106wt% byproduct-organic acids, which were obtained by the directly recycling of pretreated liquid for 3 times at 160°C and for 30min. Therefore, the full utilization of byproduct-organic acids could provide another economically feasible way to strengthen the SLHW pretreatment.

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Key words: subcritical liquid hot water pretreatment; byproduct-organic acids; lactic acid; pretreated liquid recycling; the strengthening effect; phragmites

1. INTRODUCTION Growing concerns over the environmental impact of fossil resource and its inevitable depletion have led to intense research on the development of renewable and sustainable biofuels from biomass.1,2 Lignocellulosic feedstocks, which have the potential to reduce the cost of producing ethanol owing to their competitive price, clean and large available quantities, offer a plausible alternative.3,4 The transformation of lignocellulosic biomass into fermentable sugars is the foremost stage promoting the development of a full-scale cellulosic-ethanol industry.5 The conversion of lignocellulosic material to fermentable sugars is, however, rather challenging due to the complex structure, which is mainly composed by cellulose, hemicellulose and lignin.6,7 Hemicellulose, which approximately makes up for 1/4-1/3 of lignocellulosic biomass, is primarily hydrolyzed into C-5sugars (xylose and arabinose).8 Most researchers have found that the efficient utilization of hemicellulose is a dominant factor in the feasibility of cellulosic ethanol production. Taking full advantage of C-5 sugars in lignocellulose could increase the output of ethanol by 25%. Therefore, the key condition in the utilization of lignocellulosic biomass is improving the C-5 sugars products. The components of lignocellulose are tightly connected by the various intermolecular hydrogen bonds and van der Waals forces as well as covalent bonds,


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hence, it is necessary to destroy the complex structure to increase the sugars production.9 Pretreatment can be an efficient way to alter the structure of the lignocellulosic biomass, making it more readily accessible to the enzyme and consequently improving the commercial viability of the process.10 In recent decades, numerous pretreatment methods with the aim of increasing fermentable sugars yields have been proposed, including dilute-acid pretreatment,11,12 alkaline pretreatment,13,14 and subcritical liquid hot water (SLHW) pretreatment.15 Pretreatment methods with adding chemicals, such as dilute acid and alkaline, are efficient but not cost-effective or environmental friendly.16 The sub critical water (SCW) is defined as hot water at a temperature ranging between 100°C and 374°C under high pressure to maintain water in a liquid state.17 In comparison with other pretreatment methods, the SLHW pretreatment is considered as an environmentally friendly approach, meanwhile avoiding the use of extra chemicals and corrosion of appliances.18 However, the mild process of the SLHW pretreatments would possibly lead to low yields of C-5sugars, thus investigating the strengthening process for SLHW pretreatment is of significant importance. The SLHW pretreatment is an auto-catalytic process, and lignocellulosic materials undergo hydrolysis reactions in the presence of hydronium ions, which are generated by water autoionization and act as catalysts.19, 20 Acetic acid and other organic acids generated from hemicellulose also facilitate this process.21 In addition, the formation of hydronium ions from byproduct-organic acids is more important than from water.10 Therefore, if the byproduct-organic acids can be fully utilized, it could


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provide another economically feasible way to convert biomass to fermentable sugars. Using the byproduct-organic acids, which are accumulated by the directly recycling of pretreated liquid, as catalyst to pretreat new biomass could strengthen the SLHW pretreatment. Additionally, the byproduct-organic acids are firstly used to explore the strengthening effect on the SLHW pretreatment. Specifically, comparing to formic acid or acetic acid-catalyzed pretreatments,22,23 the direct recycling of pretreated liquid, which is rich in byproduct-organic acids, presents additional advantages of no extra added chemicals, and reduction of water consumption since further neutralization can be omitted and producing less wastewater. Phragmites, known as the common reed, have been considered as a potential lignocellulosic materials owing to their fast growth rate, easy adaptability to different environments and high productivity.24,25 Currently, more than 10 million hectares of phragmites have been harvested in the world and over 1.3 million hectares have been harvested in china.26 Additionally, phragmites have high biomass yields (which are estimated to range between 15 to 35 dry tons per hectare annually for aboveground biomass).27 Most of phragmites are generally used for livestock feed and paper making, which are not harvested, leading to a waste of resources and environmental pollution. However, phragmites are rich in cellulose and hemicellulose content, which is suitable for high value-added products manufacturing, such as ethanol. The main objective of the study was to explore the strengthening effect of SLHW pretreatment by the byproduct-organic acids produced from the directly recycling of pretreated liquid. During the SLHW pretreatment, it was found that the organic acids,


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including acetic acid and lactic acid, accumulated continuously as the number of recycling times increased. Then, the different concentrations of byproduct-organic acids were applied to pretreat the fresh phragmites so as to strengthen the SLHW pretreatment. The effect of strengthening conditions, such as temperature, time, and byproduct-organic acids, on the SLHW pretreatment were systematically investigated. Furthermore, the structural changes before and after pretreatments were characterized by scanning electron microscope (SEM) technology to further evaluate the impacts of the pretreatments on phragmites.

2. MATERIALS AND METHODS 2.1 Raw materials Phragmites used in the present work were obtained from Bio-energy and Bio-chemical Company. It was dried in natural environment to constant weight, and then was milled to powder. The particles in size of 40-60 mesh fraction were applied to all the experiments.

2.2 Pretreatment of phragmites The apparatus of SLHW pretreatment for phragmites was shown in Fig.1. The pressure of the reactor was maintained with nitrogen gas at 2.0Mpa and the magnetic agitator was operated at 300 rpm. Phragmites (20g, dried basis) and water were mixed in a 1000ml high-pressure reaction vessel (Parr 4843, Parr Instrument Company, USA) at 5% solids. The treatments were performed in triplicate at the design temperature (180ºC, 200ºC, 220ºC) and for the residence time (30-120min). Meanwhile, the pretreatments were denoted as P180-30, P200-30, P220-30 and so on. At the end of


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each run, the reactor was sealed, and the slurry was agitated until the reactor was cooled to room temperature. The cooled samples were then quickly separated into solid and liquid fraction by a Buchner funnel. The liquors were kept in the freezer for analysis and the solids were dried and kept in a climate cabinet at 25°C and 60% relative humidity.

2.3 The strengthened SLHW pretreatment The pretreated liquid part, which usually contained high concentration of byproduct-organic acids, was directly recycled to pretreat the fresh phragmites for strengthening the SLHW pretreatment process. Different concentrations of byproduct-organic acids were acquired at the different number of recycling times at 160 ºC and for 30min, which were regarded as the strengthening conditions in the paper. The amount of pretreated liquid after pretreating the raw material decreased as the number of recycling processes increased; therefore, only a small water was needed to add in order to maintain at 5% solids. Variables as temperature (160-200ºC), time (20-90min) and the concentrations of byproduct organic acids were investigated to evaluate the strengthening effect on SLHW pretreatment. The operating steps were the same as those described above. Moreover, the strengthening pretreatments were recorded as S160-20, S180-20, S200-20 and so on.

2.4 Analytical methods The chemical components of phragmites were determined according to the standard Laboratory Analytical Procedures (LAP) for biomass analysis provided by the National Renewable Energy Laboratory (NREL). The sugars in the hydrolysate


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were identified based on NREL LAP. The sugars were determined by HPLC (AGILENT-1100, Agilent Technologies Inc., USA) using a ZorBax-SB-NH2 column coupled with a refractive index detector. The mobile phase was 4 mm H2SO4 at a flow rate of 0.6 mL/min, with a column temperature of 40°C. The concentrations of 5-hydroxymethyl furfural (HMF), furfural, acetic acid and lactic acid were determined by gas chromatography−mass spectroscopy (GC−MS, Agilent 6980-5973N, Tianjin, China) in a HP-INNOWAX column. C-5 sugars yield and cellulosic loss in the pretreated liquid were used to evaluate the pretreatment, demonstrated as Eq. (1,2). Generally, the “severity factor” were calculated to combine the effect of multiple pretreatment parameters, such as temperature and time.21 Meanwhile, the severity factor (logR0) was used to compare and evaluate the effect of the SLHW pretreatment in the study, which was defined as the following formula (3). − 5 =

(/)× ! " # $% &%###'% (/) ×(

#&'% (/)×.

,- , =

! " # &%###'% (/) ×/( "

× 100%

× 100%

6((

0,1, = 0,[ 3( 45 ( 7.9 )］

(1) (2) (3)

Where t(min) was the pretreated time, and T(°C) represented the pretreated temperature.

2.5 SEM analysis The microstructures of raw and pretreated phragmites were analyzed by SEM (Nanosem430, FEI Company, USA). The specific parameters of SEM were the acceleration voltage 0.1-30KV, step of 1KV, the magnification of 12 times, the


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resolution of 1 nm and metal film thickness 5-10nm. Meanwhile the range of sample stage movement was 50mm in the X, Y direction, 30mm in the Z direction.

3. RESULTS AND DISCUSSION 3.1 The SLHW pretreatment With the application of co-utilization C-5 and C-6 sugars, the research on C-5 sugars from hemicellulose was quite necessary.3 Hemicellulose, which approximately accounted for 1/3 of phragmites, was mainly decomposed into C-5 sugars. The SLHW experiment was designed as Table.1 and the LogR0 varied in the range of (3.83-5.61) according to Eq. (3). During the SLHW pretreatment, the change of C-5 (xylose and arabinose) and C-6 (glucose) sugars and byproduct-organic acids in pretreated liquid at different conditions were shown in the Fig.2. From the Fig.2 (a), the yield of C-5 sugars all first increased and then decreased with the increase of pretreated time at the different temperature. That indicated that the production rate of C-5 sugars became lower than the degradation rate, leading to the decrease of the C-5 sugars. The maximum C-5 sugars yield of 60.66% was obtained at 200°C and for 75min. The cellulosic loss increased with the increase of temperature and time. Compared with C-5sugars yield, the cellulosic loss was lower in pretreated liquid. The results indicated that the majority of cellulose could not be destroyed under the pretreated conditions, which had a better for the recovery of glucose in pretreated solid. During the pretreatments, the hemicellulose was partially acetylated and the acetyl ester bonds were hydrolyzed to produce acetic acid. The lactic acid was


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generated from the xylose degradation. From the Fig.2(b), not only acetic acid but also lactic acid were identified as byproducts in the pretreated liquid. The concentrations of acetic acid and lactic acid displayed an increase trend as the severity factor rose from 3.83 to 5.61. The lactic acid concentration was lower than that of acetic acid at different conditions, but it was getting close to the concentration of acetic acid with the increase of severity factor. However, when the yield of C-5 sugars reached the higher value, the concentration of acetic acid and lactic acid were still relatively low. Although the SLHW pretreatment method showed promising results in C-5 sugar yield (60.66%), there was still room for improvement, and it was necessary to strengthen the utilization of hemicellulose. The presence of byproduct-organic acids in pretreated liquid, such as acetic acid and lactic acid, could accelerate the acidic environment of the pretreatment system. Therefore, the next step was mainly to investigate the effect of byproduct-organic acids on SLHW pretreatment.

3.2 The strengthening pretreatment During the SLHW pretreatment, in one side, there were a large of byproduct-organic acids in the pretreated liquid. On the other hand, the presence of organic acids could strengthen the process for promoting hemicellulose hydrolysis. If the byproduct-organic acids could be fully taken advantage of, it could provide another economically feasible way to strengthen the process and tackle the problem of water consumption in the SLHW pretreatment. 3.2.1 The strengthening conditions To make full use of byproduct-organic acids, the pretreated liquid was directly


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recycled to treat the fresh material in order to obtain the different concentration of organic acids, as shown in the Table.2. The lactic acid concentration continuously increased from 0.031g/L to 0.371g/L as the number of recycling times increased from 1 to 5. The concentrations of acetic acid were greater than those of lactic acid at different strengthening conditions. Meanwhile, the concentrations of lactic acid and acetic acid both increased slowly as the number of recycling times from 3 to 5, which may be due to the presence of large amounts of lactic acid and acetic acid also inhibited the hemicellulose hydrolysis. The different concentrations of byproduct-organic acids in the pretreated liquid were used to pretreated raw phragmites at different temperature (160-200°C) and time (20-90min). The different recycling liquids, assumed that the various components kept constant, were used to strengthen the SLHW pretreatment. 3.2.2 Effect of the strengthening conditions on C-5 sugars The effects of byproduct-organic acids concentration, pretreated temperature and time on C-5 sugars yield were shown in Fig.3. The C-5 sugars yield all showed first increase and then decrease trends at different conditions. Meanwhile, the pretreated time, which was required to reach the optimal C-5 sugars yield, gradually decreased as the pretreated temperature increased. From the Fig. 3(a), the maximum C-5 sugars yield was obtained at 60min. At 180°C, the optimal time was 50min, which was 10min longer than that at 200°C. Overall, our results were in agreement with the observations reported by other researchers that increasing reaction temperature could reduce the reaction time. Furthermore, the different concentrations of


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byproduct-organic acids had different effects on the strengthening process. From the Fig.3(b), when the pretreated time was 50min, the C-5 sugars yield improved from 67.02% to 85.01% with the byproduct-organic acids concentrations increasing from 0.362wt% to 2.106wt%, whereas the C-5 sugars yield reduced by increasing the byproduct-organic acids from 2.106wt% to 3.870wt%. Compared with the acid-catalyzed liquid hot water pretreatment, there was a similar trend for xylose yield, which was observed by Y. Benjamin.27 The possible reason was that polysaccharide dissolution was a process promoted by H+ and increasing H+ concentrations could accelerate the hydrolysis rate of hemicellulose. Besides, the co-presence of acetic acid and lactic acid may have the synergistic effect to promote the maximum hydrolysis of hemicellulose. Therefore, using byproduct-organic acids could effectively strengthen SLHW pretreatment for increasing C-5 sugars yield. The decline of C-5 sugars in the hydrolysate could be attributed to the degradation of C-5 sugars into furfural and other small degradation products at more severe pretreatment conditions.28 Based on the investigations, the optimal condition for the strengthening pretreatment was determined, namely pretreated temperature of 180°C, byproduct-organic acids of 2.106wt% and time of 50 min. Under the optimal condition, the C-5 sugars yield could reach 85.01%, which was greater 24.35% than that at suitable condition in the SLHW pretreatment. Regarding the production of C-5 sugars, the use of byproduct-organic acids exhibited a better result. The SLHW pretreatment technology would be strengthened by the direct recycling of the pretreated liquid, which contained a lot of byproduct-organic acids. Additionally, the


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strengthening process also achieved an additional effect at a much lower temperature and time, offering an alternative for energy efficiency. 3.2.3 Effect of the strengthening conditions on cellulosic loss The effect of the strengthening conditions (byproduct-organic acids, temperature and time) on the cellulosic loss were shown in the Fig.4. Compared with C-5 sugars yield, the cellulosic loss was lower and increased slightly with increasing of byproduct-organic acids. It was probably due to that cellulose equipped the stronger thermal stability and it was difficult to degrade under the experimental pretreatment conditions. The cellulosic loss was less than 5% at the optimal condition of 180 ºC, 50 min and 2.106wt% byproduct-organic acids. Meanwhile, the cellulosic loss at 200°C was a little higher compared with that at 160°C and 180°C. The higher temperature would promote cellulose degradation to glucose, which would in turn lead to the cellulosic loss in pretreatment and reduce the glucose yield in the enzymatic hydrolysis. In a word, the use of byproduct-organic acids in the SLHW pretreatment could effectively promote hemicellulose decomposition and inhibit the loss of cellulose. The results were in consistent with the founding by Wan et al, in which cellulose recovery was nearly up to 100% after a hot water pretreatment for soybean straw.29 3.2.4 Effect of the strengthening conditions on organic acids The change of degradation products, organic acids, at different conditions were displayed in the Fig.5. The concentrations of organic acids showed a rising trend on the whole range of variables, namely temperature, time and byproduct-organic acids.


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From the Fig.5 (a)-(c), the lactic acid concentration gradually increased over time at lower temperatures, whereas it first increased and then decreased at 200°C. With the increase of byproduct-organic acids concentrations, the lactic acid concentration gradually increased at 160°C, which was a little different from the results of pretreatment at 180°C and 200°C. The phenomenon may probable due to the stability of lactic acid at a low temperature. Under severer pretreatment conditions, lactic acid could be degraded into acetaldehyde, CO, H2O and other small degradation products. In addition, the presence of lactic acid also inhibited the production of more lactic acid from hemicellulose. As shown as Fig.5 (d)-(f), the change of acetic acid at different conditions was similar to that of lactic acid. However, the acetic acid concentrations were greater than those of lactic acid at the different conditions. As the pretreated temperature and byproduct-organic acids increase, the concentrations of lactic acid were approaching to the concentrations of acetic acid. 3.2.5 Effect of the strengthening conditions on byproducts The sugars yield based on the amount of raw material was not the unique measure. The hydrolysates from pretreatment contained not only fermentable sugars, but also a wide variety of degradation products, such as furfural and HMF. Furfural and HMF were generated from dehydration of C-5 sugars and C-6 sugars, respectively.30 Besides, they were considered to be the most potential inhibitors on downstream microbial processes and thus reducing the overall efficiency for bioconversion of lignocellulosics to ethanol. The changes of furfural and HMF at different conditions were displayed in the Fig.6. As shown in Fig.6(a)-(c), the


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concentration of furfural all displayed an increase trend with the increase of byproduct-organic acids, temperature and time. At low byproduct-organic acid concentrations (0.362-1.082wt%), the HMF concentration increased over time. However, when the organic acid concentrations was higher (2.106-3.870wt%), the HMF concentration first increased and then decreased after reaching a maximum value as the pretreated time increased (see as Fig.6(d)-(f)). That was indicated that HMF could degrade into other small molecules at the most severe pretreated conditions. Under the optimal conditions (180°C, 50min, 2.106wt% of byproduct-organic acids), the concentrations of furfural and HMF were nearly 33.2g/kg and 5.9g/kg, respectively. The furfural and HMF concentrations that significantly inhibit microorganisms are 2g/L and 5g/L, respectively.31 Therefore, furfural and HMF did not inhibit yeast growth and ethanol fermentation in our study. High concentrations of furfural and HMF, namely 5.22 ± 0.01g/L and 0.28 ± 0.03g/L, were obtained when a sequential dilute acid and alkali pretreatment was applied to the hydrolysis of corn stover.31 To sum up, the use of byproduct-organic acids in the SLHW pretreatment process had more advantages than the other acid-catalyzed pretreatment methods due to the limited number of inhibiting byproducts.

3.3 The analysis of mass balance During the SLHW pretreatment, the maximum concentration of C-5 sugars was obtained at the severity of 4.85 (200°C, 75min). At the same time, the optimal condition was acquired at the severity of 4.05 (180°C, 50min, 2.106wt% byproduct-organic acids) at the strengthening process for SLHW pretreatment. The


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process mass balances of the SLHW pretreatment and the strengthened SLHW process were developed as displayed in Fig7. Compared with the Fig7.(a) and Fig7.(b), the yield of the pretreated solid decrease from 12.224g to 11.778g and the yield liquid fraction increased from 6.936g to 7.838g in the strengthened process. In addition, the cellulose production, in the strengthened process, was 3.53% higher than that in the SLHW pretreatment. Pretreatment with byproduct-organic acids, produced from the directly recycling of pretreated liquid, turned to be effective in the hydrolysis of hemicellulose, meanwhile producing very highly digestible remaining cellulose. Using of byproduct-organic acids to strengthen the SLHW pretreatment remains a promising method for realizing the maximum utilization of C-5 and C-6 sugars.

3.4 SEM characterization The residual solids were tested using SEM to visually evaluate the effects of the SLHW pretreatment and the strengthening process. As shown in Fig.8(a), the untreated phragmites exhibited a smooth and ridged surface structure. In contrast, in Fig.8(b) and (c), structure breakdown and some cracks in pretreated phragmites were identified under the two suitable conditions, indicating that the pretreatments destroyed the compact structure of phragmites. The degree of damage to phragmites gradually increased along with the severity of pretreatment conditions. From the Fig.8(c), the pretreated phragmites exhibited rough, cracks and even signs of structural breakdown. Our observations implied that the strengthening process destroyed the dense structure in favor of the enzyme accessibility.


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4. CONCLUSIONS The byproduct-organic acids (lactic acid and acetic acid), accumulated by the direct recycling of pretreated liquid, were used to pretreat raw phragmites, which strengthened the SLHW pretreatment. Compared with the SLHW pretreatment, the byproduct-organic acids of 2.106wt%, which was obtained by the directly recycling of pretreated liquid for 3 times, was the optimal strengthening condition reducing 10% on the pretreated temperature, saving 33.33% on pretreated time, and increasing C-5 sugars yield 40.14%. Meanwhile, the degradation products concentration levels were lower than the levels that significantly inhibit the growth of fermenting microorganisms. The byproduct-organic acids strengthened SLHW pretreatments, in one side, could increase the utilization of biomass and increase the economic benefits. On the other hand, the method could provide an effective guidance to reduce water consumption in SLHW pretreatment process.

Acknowledgement The authors gratefully acknowledge the financial support provided by Tianjin University. AUTHOR INFORMATION Corresponding Author * Minhua Zhang Phone/Fax: +86-22-27406119

E-mail: [email protected]


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Notes The authors declare no competing financial interest. Present Addresses Key Laboratory for Green Chemical Technology of Ministry of Education, Tianjin University R&D Center for Petrochemical Technology, Tianjin 300072, China.

ABBREVIATIONS SLHW, subcritical liquid hot water; HMF, hydroxymethyl furfural; SEM, scanning electron microscope.


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9:1-16. (10) Dehghani M, Karimi K, Sadeghi M. Pretreatment of Rice Straw for the Improvement of Biogas Production. Energy & Fuels, 2015, 29:3770-3775. (11) Yang Y, Sharma-Shivappa R, et al. Dilute Acid Pretreatment of Oven-dried Switchgrass Germplasms for Bioethanol Production. Energy & Fuels. 2009, 23:3759-3766. (12) Martin C, Garcia A, et al. Combination of water extraction with dilute-sulphuric acid pretreatment for enhancing the enzymatic hydrolysis of Jatropha curcas shells. Ind Crop Prod, 2015, 64:233-241. (13) Bali G, Meng X, et al. The effect of alkaline pretreatment methods on cellulose structure and accessibility. ChemSusChem, 2015, 8:275–279. (14）Pang Y Z, Liu Y P, et al. Improving Biodegradability and Biogas Production of Corn Stover through Sodium Hydroxide Solid State Pretreatment. Energy & Fuels, 2008, 22:2761-2766. (15) Lin R, Cheng J, et al. Subcritical water hydrolysis of rice straw for reducing sugar production with focus on degradation by-products and kinetic analysis. Bioresour Technol, 2015, 186:8-14. (16) Shen Z, Jin C, et al. Pretreatment of corn stover with acidic electrolyzed water and FeCl3 leads to enhanced enzymatic hydrolysis. Cellulose, 2014, 21:3383-3394. (17) Prado J M, Forster-Carneiro T, et al. Obtaining sugars from coconut husk, defatted grape seed, and pressed palm fiber by hydrolysis with subcritical water. J Supercrit Fluid, 2014, 89:89-98.


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(18) Tangkhavanich B, Kobayashi T and Adachi S. Properties of rice straw extract after subcritical water treatment. Biosci Biotechnol Biochem, 2012, 76:1146–1149. (19) Garrote G, Dominguez H. Hydrothermal processing of lignocellulosic materials. Eur J Wood Prod, 1999, 57:191-202. (20) Ruiz H A, Fernandes B D, et al. Hydrothermal processing, as an alternative for upgrading agriculture residues and marine biomass according to the biorefinery concept: A review. Renew Sust Energ Rev, 2013, 21:35-51. (21) Kim Y, Kreke T, et al. Severity factor coefficients for subcritical liquid hot water pretreatment of hardwood chips. Biotechnology & Bioengineering, 2014, 111:254-263. (22) Yong Sun, Lu Lin, et al. Hydrolysis of Cotton Fiber Cellulose in Formic Acid. Energy& Fuels, 2007, 21, 2386-2389. (23) Xu J, Thomsen M H, Thomsen A B. Enzymatic hydrolysis and fermentability of corn stover pretreated by lactic acid and/or acetic acid. Journal of Biotechnology, 2009, 139:300. (24) Lemons e S C F, Schirmer M A, et al. Potential of giant reed (Arundo donax L) for second generation ethanol production. Electronic Journal of Biotechnology. 2015, 18:10-15. (25) Szijarto N, Kadar Z, et al. Pretreatment of reed by wet oxidation and subsequent utilization of the pretreated fibers for ethanol production. Appl Biochem Biotechnol, 2009, 155:386-396. (26) Ge X M, Xu F Q, et al. Giant reed: a competitive energy crop in comparison with miscanthus. Renew Sust Energ Rev. 2016, 54:350-362.


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(27) Benjamin Y, Cheng H , et al. Optimization of dilute sulfuric acid pretreatment to maximize combined sugar yield from sugarcane bagasse for ethanol production. Appl Biochem and Biotech, 2014, 172:610-30. (28) Rafiqul I, Sakinah AM. Design of process parameters for the production of xylose from wood sawdust. Chem Eng Res Des, 2012, 90:1307–1312. (29) Wan C and Li Y. Effect of hot water extraction and liquid hot water pretreatment on the fungal degradation of biomass feedstocks. Bioresour Technol, 2011, 102:9788-93 (30) Imman S, Arnthong J, et al. Autohydrolysis of tropical agricultural residues by compressed liquid hot water pretreatment. Appl Biochem Biotechnol, 2013, 170:1982-95. (31) Zhang H, Xu S and Wu S. Enhancement of enzymatic saccharification of sugarcane bagasse by liquid hot water pretreatment. Bioresour Technol, 2013, 143:391-396.


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Table of Contents Graphic and Synopsis Table1. Experimental conditions for the SLHW pretreatment The pretreated

Pretreated temperature

Pretreated time

sign

/°C

/min

LogR0 P180-30

30

3.83

P180-45

45

4.01

P180-60

60

4.13

75

4.23

P180-90

90

4.31

P180-105

105

4.38

P180-120

120

4.43

P200-30

30

4.42

P200-45

45

4.60

P200-60

60

4.72

75

4.82

P200-90

90

4.90

P200-105

105

4.97

P200-120

120

5.02

P220-30

30

5.01

P220-45

45

5.19

P220-60

60

5.31

75

5.41

P220-90

90

5.49

P220-105

105

5.55

P220-120

120

5.61

P180-75

P200-75

P220-75

180

200

220


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Table.2 Composition of the strengthening conditions with different recycling times Strengthening conditions

Organic acids a

Lactic

Acetic

acid

Acid/

/g/L

g/L

/wt%

C-5sugars

C-6 sugars

Furfural

HMF

/g/L

/g/L

/g/L

/g/L

Log(R0)=3.83 (180°C,30min)

a

1

0.362

0.031

0.150

1.531

0.005

0.040

0.000

2

1.082

0.085

0.456

3.125

0.012

0.095

0.000

3

2.106

0.154

0.899

4.236

0.059

0.168

0.002

4

3.060

0.296

1.234

4.981

0.091

0.315

0.007

5

3.870

0.371

1.564

5.110

0.102

0.542

0.010

: lactic acid and acetic acid


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Fig. 1. Experimental apparatus for the pretreatments


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Yield of C-5 sugars (%)

8.00

C-6 sugar, 180°C C-6 sugar, 200°C 7.00 C-6 sugar, 220°C

C-5 sugars, 180°C C-5 sugars, 200°C C-5 sugars, 220°C

6.00

50.00

5.00 40.00 4.00 30.00 3.00 20.00

Cellulosic loss (%)

70.00

60.00

2.00

10.00

1.00 0.00

0.00 30

45

60

75

90

105

120

40.00 35.00

6.00

Lactic acid acetic acid 5.50

Log(R0) 30.00

5.00 25.00 20.00

4.50

Log (R0)

(b)

Pretreated time (min)

Concentration of organic acids (g/kg raw material)

15.00 4.00 10.00 3.50 5.00 0.00

3.00

P1 80 P1 -30 80 P1 -45 80 P1 -60 80 P1 -75 80 P1 -9 80 0 P1 -10 80 5 P2 120 00 P2 -30 00 P2 -45 00 P2 -60 00 P2 -75 0 P2 0-9 00 0 P2 -10 00 5 P2 120 20 P2 -30 20 P2 -45 20 P2 -60 20 P2 -75 2 P2 0-9 20 0 P2 -10 20 5 -1 20

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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(a)

Page 25 of 31

Pretreated conditions

Fig. 2 Production of C-5 and C-6 sugars (a) and byproduct-organic acids (b) in the pretreated liquid


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90.00 80.00 70.00 60.00

0.362wt% 1.082wt% 2.106wt% 3.060wt% 3.870wt%

organic acids organic acids organic acids organic acids organic acids

(a)

50.00 40.00 30.00 20.00 10.00

Yield of C-5 sugars (%)

0.00 90.00

(b)

80.00 70.00 60.00 50.00 40.00 30.00 20.00 10.00 0.00 70.00

(c)

60.00 50.00 40.00 30.00 20.00 10.00

090 S2 0

S2 0

080

070 S2 0

060 S2 0

050 S2 0

040 S2 0

S2 0

030

020

0.00

S2 0

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

Page 26 of 31

Pretreated conditions

Fig. 3 The yield of C-5 sugars in the pretreated liquid at different conditions (a) 160°C, (b) 180°C, (c) 200°C


Page 27 of 31

6.00 5.00 4.00

(a)

0.362wt% organic acids 1.082wt% organic acids 2.106wt% organic acids 3.060wt% organic acids 3.870wt% organic acids

3.00 2.00 1.00

Cellulosic loss (%)

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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0.00 6.00

(b)

5.00 4.00 3.00 2.00 1.00 0.00 8.00

(c)

7.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00 20

30

40

50

60

70

80

90


Fig. 4 Cellulosic loss in pretreated liquid at different conditions (a) 160°C, (b) 180°C, (c) 200°C


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14.00

35.00

0.362wt% organic acids 1.082wt% organic acids 2.106wt% organic acids 3.060wt% organic acids 3.870wt% organic acids

12.00 10.00

(a)

(d)

30.00 25.00

8.00

4.00 2.00 0.00

(b)

30.00 25.00 20.00 15.00 10.00 5.00 0.00

(c)

30.00 25.00

Concentration of acetic acid (g/kg phragmites)

20.00

6.00

Concentration of lactic aicd (g/kg phragmites)

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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15.00 10.00 5.00 0.00 70.00

(e)

60.00 50.00 40.00 30.00 20.00 10.00 0.00 70.00

(f)

60.00 50.00

20.00 40.00 15.00

30.00

10.00

20.00

5.00

10.00 0.00

0.00 20

30

40

50

60

70

80

90

20


30

40

50

60

70

80


Fig. 5 The concentrations of organic acids at different conditions (a) lactic acid at 160°C, (b) lactic acid at 180°C, (c) lactic acid at 200°C (d) acetic acid at 160°C (e) acetic acid at 180 °C (f) acetic acid at 200°C


90

Page 29 of 31

8.00

70.00 0.362wt% organic acids 1.082wt% organic acids 2.106wt% organic acids 3.060wt% organic acids 3.870wt% organic acids

60.00 50.00

(a)

(d) 6.00

40.00 4.00 30.00 20.00

2.00

10.00 0.00 90.00

(b)

80.00 70.00 60.00 50.00 40.00 30.00 20.00 10.00 0.00 90.00

(c)

80.00 70.00

Concentration of HMF (g/kg phragmites)

Concentration of furfural (g/kg phragmites)

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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0.00 10.00

(e)

8.00

6.00

4.00

2.00

0.00 10.00

(f)

8.00

60.00 6.00

50.00 40.00

4.00 30.00 20.00

2.00

10.00 0.00

0.00 20

30

40

50

60

70

80

90

20

30


40

50

60

70

80

90


Fig. 6 The concentrations of byproducts at different conditions (a) furfural at 160°C, (b) furfural at 180°C, (c) furfural at 200°C (d) HMF at 160°C (e) HMF at 180 °C (f) HMF at 200°C


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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

Fig7. The process mass balance analysis of the products at the different conditions (a) The SLHW pretreatment at the severity of 4.85, (b) The strengthened SLHW pretreatment at the severity of 4.05, 2.106wt% byproduct-organic acid


Page 30 of 31

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Fig.8 SEM images of pretreated phramites: (a) raw phragmites (b) 200°C, 75min (c) 180°C, 50min and with 2.106wt% byproduct-organic acids


Exploration of the Strengthening Effect by Byproduct-Organic Acids on

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