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Dissertation Abstract

Lignocellulose refinery process

with pretreatment using minimum amount of

biocompatible ionic liquid

最少量の低毒性イオン液体を用いた前処理にもとづいた

木質バイオマスリファイナリー

Graduate School of

Natural Science & Technology

Kanazawa University

Division of Natural System

Student ID No.

: 1524062010

Name

: Amaliyah Rohsari Indah Utami

Chief advisor

: Professor Kazuaki NINOMIYA

Date of Submission

: September 14

th

, 2018

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Abstract

This study developed the lignocellulose refinery process with pretreatment using minimum amount of biocompatible ionic liquid (IL). Pretreatment of bagasse was performed using choline acetate (ChOAc), as biocompatible IL, at different ionic liquid biomass ratio (w/w). The IL/biomass ratios of 0–3 were used. To employ a small amount of viscous ChOAc to all of the bagasse powder, the ChOAc aqueous solution was first mixed with bagasse powder, and the suspension was heated, which pretreated the biomass along with evaporation of water.

The experimental result of Chapter 1 of this dissertation showed that the minimum and sufficient IL/biomass ratio was found to be 1.5, which achieved cellulose and hemicellulose saccharification percentages of 95% and 93%, respectively, at low-loading (10 g/L) saccharification. Thus, the bagasse pretreated at the IL/biomass ratio of 1.5 was then applied to the following chapter.

Further, in Chapter 2 we performed an experimental of the recovery and reuse of ChOAc during repeated cycles of ChOAc-assisted bagasse pretreatment at the minimum and sufficient IL/biomass ratio of 1.5 (w/w) only. The ChOAc recovery percentage was 83% on average after 1–6 cycles of pretreatment. For pretreated bagasse obtained after 2–6 cycles of pretreatment, the cellulose, and hemicellulose saccharification percentages were about 83 and 70% on average, respectively, which corresponded to glucose and xylose concentrations of 48 and 16 g/L, respectively.

Moreover, Chapter 3 of this dissertation examined the co-fermentation efficiency of mixed sugars obtained from the saccharification of ChOAc IL-pretreated biomass with IL/biomass ratio of 1.5. The glucose and xylose concentrations were 56 g/L and 14 g/L, after 72 h of enzymatic saccharification at high-loading, which corresponded to cellulose and hemicellulose saccharification percentages of 95% and 65%, respectively. In the subsequent co-fermentation from a mixed sugar solution containing 27 g/L glucose and 7 g/L xylose, the ethanol concentration was 15 g/L at 24 h, which was 85% of the theoretical value for the sugar-based ethanol yield.

Furthermore, we succeeded to convert enzymatic lignin residue into lignin nanoparticle as a value-added product (Chapter 4). To accomplish the proposed of this study, two types of enzymatic lignin residue (IL-assisted pretreatment and diluted sulfuric acid-assisted pretreatment) were used. The hydroxyl group (OH) of IL-pretreated of lignin oligomer was higher than diluted sulfuric acid-assisted pretreatment, 5.89 mmol/g versus 4.97 mmol/g, respectively. The average of molecular weight of IL-assisted pretreatment of lignin oligomer was lower than diluted sulfuric acid-assisted pretreatment, 8.88×103 versus 10.5×103, respectively. The average particle size of the lignin nanoparticle dispersion liquid of IL-assisted pretreatment was smaller than diluted sulfuric acid-assisted pretreatment, 186 nm versus 373 nm, respectively.

This study effectively developed the lignocellulose refinery process with pretreatment using minimum amount of biocompatible ionic liquid (IL). Pretreatment at the minimum and sufficient IL/biomass ratio can contribute to reducing the costs of IL-assisted pretreatment processes.

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1

Lignocellulose refinery process

with pretreatment using minimum amount of

biocompatible ionic liquid

Introduction

In the lignocellulose refinery to get bioethanol as biofuel, there are three main processes: pretreatment, enzymatic saccharification, and fermentation. Recently, ionic liquid (IL)-assisted pretreatment has been gained attention in lignocellulose refinery due to their power for dissolving lignocellulosic biomass. However, the high cost and the toxicity of IL relies on this pretreatment technology. Therefore, the production of bioethanol from lignocellulosic biomass is lasting process and costly feasible. On the other hand, unfortunately, during most of the pretreatment process, lignin ends up as a residue. Therefore, to reduce price effect of IL and toxicity effect of IL, the main objectives of this research are followed. First, throughout the research, we used choline acetate (ChOAc) as a biocompatible IL in the completely of lignocellulosic refinery process without any residue such as enzymatic lignin residue and waste such as wastewater. Second, we investigated the minimum amount of IL used for pretreatment per unit biomass namely IL/biomass ratio on the pretreated bagasse with ChOAc-assisted pretreatment. Furthermore, we determined the following of specific objectives such as recovery and reuse of IL, saccharification, and co-fermentation, and lignin utilization.

Material and Method

The material and experimental condition of this study were described in Figure 1. For the first process, we conducted pretreatment of bagasse by ChOAc aqueous solution associated with water evaporation. The IL/biomass ratios of 0-3 were used in the pretreatment. The pretreated bagasse/ChOAc aqueous mixture was heated at 110°C for 21 h. After heating, the bagasse pretreated/ChOAc mixture was washed and was then separated. Both the semi-wet pretreated bagasse and the ChOAc aqueous solution retrieved after pretreatment were retained. The precipitated wet bagasse was subjected to subsequent enzymatic saccharification, and the ChOAc aqueous solution recovered after pretreatment was used for the next cycle of pretreatment.

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2 Mixing Saccharification Fermentation Yeast Enzymatic lignin residue

ChOAc aq. solution recovered after Nth cycle of pretreatment (N = 1-6) Lignin nanoparticle

3. Fermentation

1. Pretreatment by using ChOAc and saccharificaton

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3

Result and Discussion

The summaries of the results are as follows. Chapter 1 in this dissertation examined the minimum and sufficient IL/biomass ratio for cholinium IL-assisted pretreatment of bagasse powder. The composition of bagasse pretreated at different IL/biomass ratios was displayed in Figure 2. The cellulose, hemicellulose, and lignin contents were approximately 40%, 20%, and 30%, respectively, irrespective of the IL/biomass ratio tested. The cellulose and hemicellulose saccharification percentages were 95% and 93%, respectively, at low-loading (10 g/L) saccharification (see Figure 3). Furthermore, the IL/biomass ratio of 1.5 was then applied to the following chapter.

As chapter 2 results, Figure 4 demonstrated the recovery and reuse of ChOAc during the repeated cycles of ChOAc-assisted bagasse pretreatment at the minimum IL/biomass ratio at 1.5, with supplementation of the ChOAc that was lost during the each cycles of pretreatment so as to maintain the efficiency of biomass pretreatment. The ChOAc recovery percentage was 83% on average for the aqueous solution obtained after 1st-6th cycles of pretreatment. Figure 5 shows the composition of pretreated bagasse obtained after Nth cycle of pretreatment, with or without supplementation of fresh ChOAc. There was almost no significant difference in the composition along with the cycle number of pretreatment N, irrespective of the case with or without supplementation of fresh ChOAc, although the values were fractionated. Subsequently, the cellulose and hemicellulose saccharification percentage were about 83% and 70%, respectively, for the pretreated bagasse obtained after 2nd-6th cycle of pretreatment, which corresponded to glucose and xylose concentrations of 48 g/L and 16 g/L (see Figure 6 (A) and (B)).

In the conversion into ethanol fermentation as Chapter 3 results, cellulose and hemicellulose of lignocellulosic biomass should be well converted into ethanol. Figure 7

investigated enzymatic saccharification from pretreated bagasse to glucose at high loading saccharification. The glucose and xylose concentrations were 56 g/L and 14 g/L after 72 h of enzymatic saccharification at high-loading, which corresponds to cellulose and hemicellulose saccharification of 95% and 65%, respectively. The mixed sugar solution was fermented into ethanol using yeast Saccharomyces cerevisiae YPH499XU to produce 15 g/L of ethanol. The initial glucose and xylose concentrations were 27 g/L and 7 g/L, respectively. The ethanol concentration was 15 g/L at 24 h, which was 85% of the theoretical sugar-based ethanol yield (see Figure 8).

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Figure 2 The content of cellulose (bottom of stacked bar), hemicellulose (middle of stacked bar), lignin (top of stacked bar) in bagasse pretreated with ChOAc at different IL/biomass ratios. The error bars indicate the standard deviation from three independent experiments.

Figure 3 The saccharification percentage at low-loading (10 g/L) for bagasse pretreated with ChOAc at different IL/biomass ratios. The error bars indicate the standard deviation from three independent experiments.

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Cycle number of pretreatment,

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Figure 4 The ChOAc recovery percentages for the aqueous solution obtained after the Nth cycle of pretreatment, where N = 0 indicates the initial ChOAc aqueous solution (30 g/L). The bagasse was pretreated with ChOAc at an IL/biomass ratio of 1.5. Cycle number of pretreatment N = 1–6. Open bars: control pretreatment without supplementation of fresh ChOAc, filled bars: pretreatment with supplementation of fresh ChOAc. Light blue indicates the supplemented portion of fresh ChOAc (to 30 g/L) for the next cycle of pretreatment.

Figure 5 The composition (cellulose, hemicellulose, lignin, and the others from the bottom). UT indicates untreated bagasse. The bagasse was pretreated with ChOAc at an IL/biomass ratio of 1.5. Cycle number of pretreatment N = 1–6. Open bars: control pretreatment without supplementation of fresh ChOAc, filled bars: pretreatment with supplementation of fresh ChOAc.

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(A) (B)

Figure 6 (A) The cellulose saccharification percentages, and (B) hemicellulose saccharification percentages for the pretreated bagasse obtained after the Nth cycle of pretreatment. UT indicates untreated bagasse. The saccharification percentages were determined at 72 h of enzymatic saccharification of the bagasse at high loading (100 g/L). The bagasse was pretreated with ChOAc at an IL/biomass ratio of 1.5. Cycle number of pretreatment N = 1–6. Open bars: control pretreatment without supplementation of fresh ChOAc, filled bars: pretreatment with supplementation of fresh ChOAc.

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Figure 7 The glucose and xylose concentrations during enzymatic saccharification at high-loading (100 g/L) of pretreated bagasse with ChOAc at the IL/biomass ratio of 1.5. The error bars indicate the standard deviation from three independent experiments.

Figure 8 The reaction time of sugar and ethanol concentrations during subsequent fermentation. The bagasse pretreated with ChOAc at different IL/biomass ratios. The error bars indicate the standard deviation from three independent experiments.

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8

As mentioned in the Figure 1, we performed not only to complete the lignocellulose refinery into bioethanol production but also to utilize enzymatic lignin residue. To obtain lignin nanoparticle, in the Chapter 4, we conducted the fractionation of enzymatic lignin residues with organic solvent and nanofabrication of lignin oligomer method. To accomplish the proposed of this study, two types of enzymatic lignin residue (IL-assisted pretreatment and diluted sulfuric acid-assisted pretreatment) were used. Furthermore, the synthesized of lignin nanoparticles are analyzed dimensionally and morphologically.

Figure 9 shows the lignin oligomer dispersion by photo and SEM results. The lignin particles of about 10μm were observed in both IL-assisted pretreatment and diluted-acid pretreatment. Figure 10 and Figure 11 show the average particle size of the lignin nanoparticle dispersion liquid of IL-assisted pretreatment was smaller than dilute acid pretreatment, 186μm versus 373μm, respectively.

Ionic liquid pretreatment Diluted sulfuric acid

Lignin Oligomer Lignin Nanoparticles Lignin Oligomer Lignin Nanoparticles Lignin Oligomer, Lignin Nanoparticles Dispersion (1g-Lignin/L) SEM 600nm 600nm 600nm 600nm

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Figure 10 The average particle size of the lignin nanoparticle dispersion liquid of IL-assisted pretreatment.

Figure 11 The average particle size of the lignin nanoparticle dispersion liquid of diluted sulfuric acid-assisted pretreatment.

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10

Conclusion

This study successfully developed the lignocellulose refinery process with pretreatment using minimum amount of biocompatible ionic liquid (IL). Pretreatment at the minimum and sufficient IL/biomass ratio can contribute to reducing the costs of IL-assisted pretreatment processes. These are accomplished by (1) the using of choline acetate (ChOAC) as a biocompatible IL, (2) the reduction of IL and (3) the IL aqueous solution recovered after pretreatment and washing can be reused for the next cycles of pretreatment, without an additional water evaporation step. It can be concluded that the method suggested in this study is an economical alternative for biomass pretreatment in lignocellulose refinery.

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References

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