Tài liệu Production of value added chemicals from rice straw

VIETNAM NATIONAL UNIVERSITY ± HO CHI MINH CITY HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY --------*------- LE MINH TAN PRODUCTION OF VALUE-ADDED CHEMICALS FROM RICE STRAW Major: Chemical engineering Code: 8520301 MASTER THESIS Ho Chi Minh, July - 2021 THIS RESEARCH WAS CONDUCTED AT HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY ± VNU-HCM Supervisor 1: Dr. Tran Tan Viet ................................................................. Supervisor 2: Assoc. Prof. Dr. Le Thi Kim Phung Reviewer 1: Dr. Tran Phuoc Nhat Uyen Reviewer 2: Dr. Pham Thi Hong Phuong The master thesis was defended at Ho Chi Minh city University of Technology, VNU-HCM, July 9th, 2021. (Online) The members of Assessment Committee including: 1. Assoc. Prof. Dr. Nguyen Quang Long - Chairman 2. Dr. Tran Phuoc Nhat Uyen - Reviewer 1 3. Dr. Pham Thi Hong Phuong - Reviewer 1 4. Dr. Nguyen Thi Le Lien - Committee 5. Dr. Dang Bao Trung - Secretary Confirmation of the Assessment Committee Chairman and the Head of Faculty after the thesis has been corrected (if any). Assessment Committee Chairman Assoc. Prof. Dr. Nguyen Quang Long Dean of Chemical Engineering Faculty Prof. Dr. Phan Thanh Son Nam VIETNAM NATIONAL UNIVERSITY - HCM SOCIALIST REPUBLIC OF VIETNAM HO CHI MINH CITY UNIVERSITY OF Independence - Freedom - Happiness TECHNOLOGY MASTER THESIS MISSIONS Full Name: LE MINH TAN Student¶V,' Date of Birth: 23/12/2997 Place of Birth: Tien Giang Major: Chemical engineering Code: 8520301 I. THESIS TITLE: PRODUCTION OF VALUE-ADDED CHEMICALS FROM RICE STRAW MISSIONS AND CONTENTS: - Production of lignin from rice straw through pre-treatment method. - Integration of delignification process, and bioethanol production for creating zerowaste biorefinery. - Conversion obtained lignin into bio-oil. - Evaluation of biorefinery approach, and creating the life cycle thinking of rice straw. II. DATE OF ASSIGNMENT: 22/02/2021 III. DATE OF COMPLETION: 05/12/2021 IV. SUPERVISORS: 1. Dr. Tran Tan Viet 2. Assoc. Prof. Dr. Le Thi Kim Phung Ho Chi Minh city, «/08/2021. SUPERVISORS Dr. Tran Tan Viet HEAD OF DEPARTMENT Assoc. Prof. Dr. Le Thi Kim Phung Assoc. Prof. Dr. Le Thi Kim Phung DEAN OF CHEMICAL ENGINEERING FACULTY Prof. Dr. Phan Thanh Son Nam ACKNOWLEDGEMENTS There are no proper words to convey my deep gratitude and respect for my thesis and research advisors, Dr. Tran Tan Viet and Assoc. Prof. Le Thi Kim Phung. They have inspired me to become an independent researcher and helped me realize the power of critical reasoning. They also demonstrated what a brilliant and hardworking scientist can accomplish. My sincere thanks must also go to my brilliants friends 3KL/ѭѫQ1in, ĈX{QJ who is always besides me from joyful moments to hard time, cheered me on, and celebrated each accomplishment. I will also never forget the sleepless nights in many coffee shops and the buffet parties. Additionally, I really appreciate with help of Dr. Tran Phuoc Nhat Uyen who JLYHPHPDQ\DGYLFHVIRUSXEOLVKHGSDSHUVLQP\PDVWHU¶VFRXUVH I am most grateful to the collaborators for giving me many memories in at RPTC. There is no way to express how much it meant to me to have been a member of RPTC. Last but not the least, I would like to express my gratitude to my family for their unfailing emotional support, unconditional trust, timely encouragement, and endless patience. I acknowledge the support of time and facilities from Ho Chi Minh City University of Technology (HCMUT), VNU-HCM for this study. Ho Chi Minh city, July-2021 Le Minh Tan ABSTRACT Rice straw, the main agricultural wastes from rice production, has great potential to be converted into value-added raw materials. In this study, the benefits of using rice straw in reducing the global dependency on fossil fuels and produce green chemicals were demonstrated by recovery process of high value material and integration of the process with bioethanol production for zero-waste biorefinery. First, the study developed a method to reduce the silica content in lignin from rice straw more effectively and selectively. The method is established by monitoring the precipitation behavior as well as the chemical structure of precipitate by singlestage acidification at different pH values of black liquor collected from the alkaline treatment of rice straw. The simple two-step acidification of the black liquor at pilot-scale by sulfuric acid 20 w/v% is applied to recover lignin at pH 9 and silica at pH 3 and gives a percentage of silica removal as high as 94.38%. Next, a pilot-scale biorefinery, whose bioethanol production from rice straw was an integrated recovery system for lignin, silica, and nutrient recovery was continuously developed. The recovery yield of silica and lignin from the black liquor of alkaline pretreatment was up to 96%, and the lignin purity reached 79% without the existence of carbohydrate fiber. After the recovery, the final liquid waste mainly contained inorganic matters and has a potential to be reused in the acidification step. The distillation residue was a nitrogen source for simultaneous saccharification and fermentation equivalent to corn steep liquor with the final ethanol concentration of 1.6 wt.% in 160 hours. The material flow indicated that more valued products produced by the simple method increase the profits of this process. Also, the energy efficiency of the process was 0.53 that demonstrated the process's economy and sustainability. Additionally, silica derived rice husk was used to synthesize ZSM-5 and Ni/ZSM-5 to catalyze for hydro processing of rice straw lignin for the first time. The results show the high yield of bio-oil of 24.4 wt% and phenolic content of 41.2 wt.% when using Ni/ZSM-5. Finally, the full life cycle thinking of rice residues was also argued in this study. 7Ï07Ҳ7 5ѫPUҥOj mӝt phӃ phҭm chtnh trong quiWUuQKVҧQ[XҩWO~DJҥRYj FyQKLӅXWLӅP QăQJFKX\ӇQKyDWKjQKQJX\rQOLӋX FyJLiWUӏcao7URQJQJKLrQFӭXQj\ FiFVҧQ SKҭPFyJLiWUӏFDRÿѭӧFWұQGөQJWKXKRLRJWӯUѫPUҥÿӗQJWKӡLTXiWUuQKWKXKӗL Qj\FNJQJÿѭӧFQJKLrQFӭXNӃWKӧSYӟLTX\WUuQKVҧQ[XҩWELRHWKDQROWӯUѫPUҥYӟL PөFWLrXWҥRUDPӝWTX\WUuQKNK{QJ[ҧWKҧLĈҫXWLrQQJKLrQFӭXÿmSKiWWULӇQPӝW SKѭѫQJSKiSÿӇJLҧPKjPOѭӧQJVLOLFDWURQJOLJQLQWӯUѫPUҥPӝWFiFKKLӋXTXҧYj FyFKӑQOӑFKѫQ3KѭѫQJSKiSÿѭӧFWKLӃWOұSEҵQJFiFKWKHRG}Lquá trình NӃWWӫD, VӵWKD\ÿәL FҩXWU~FKyDKӑFFӫD FiFNӃWWӫD NӃWWӫDEҵQJFiFKD[LWKyD GӏFKÿHQ thu ÿѭӧFWӯ TXiWUuQK[ӱOêNLӅPFӫDUѫPUҥ ӣFiFJLiWUӏS+NKiFQKDX .ӃWTXҧFKR WKҩ\TXiWUuQKD[LWKyDKDLEѭӟFUѭӧXÿHQEҵQJD[LWVXOIXULFWKtFKKӧSÿӇWKX KӗL silica và lignin OҫQOѭӧWӣS+YjS+YjFKRSKҫQWUăPORҥLEӓVLOLFDFDRWӟL  7LӃS WKeo, TX\ WUuQK WLӃS WөF ÿѭӧF Pӣ UӝQJ VҧQ [XҩW WKHR TX\ P{ SLORW, WURQJÿyTX\WUuQKQj\FNJQJÿѭӧFQJKLrQFӭXYӟLTX\WUuQKVҧQ[XҩWELRHWKDQROӣ TX\P{SLORWÿӇ[ӱOêGzQJFKҩWWKҧLGӏFKÿHQ.ӃWTXҧFKRWKҩ\KLӋXVXҩWWKXKӗL VLOLFD Yj OLJQLQ Wӯ GӏFK ÿHQ OrQ ÿӃQ  Yj ÿӝ WLQK NKLӃW FӫD OLJQLQ ÿҥW  và NK{QJFyVӵWӗQWҥLVӧLFDUERK\GUDWH trong lignin. 6DXNKLWKXKӗLFKҩWWKҧLOӓQJ Wӯ TX\ WUuQK WKX KӗL FKӫ \ӃX FKӭD FiF FKҩW Y{ Fѫ Yj Fy NKҧ QăQJ ÿѭӧF WiL Vӱ GөQJ WURQJEѭӟFD[LWKyD1JRjLUDKLӋXVXҩWsӱ dөng QăQJOѭӧQJFӫDTX\WUuQKOj WăQJVRYӟLTX\WUuQKFNJFKӭQJWӓWtQKNLQKWӃYjWtQKEӅQYӳQJFӫDTX\WUuQK PӟL Qj\. Ngoài ra, 6LOLFD ÿѭӧF FKLӃW [XҩW Wӯ WUR WUҩX ÿѭӧF Vӱ GөQJ ÿӇ WәQJ KӧS ZSM-5 và Ni/ZSM-5 làm xúc tác cho quá trình cKX\ӇQKyDlignin thành biocrude. .ӃWTXҧFKRWKҩ\QăQJVXҩWFӫDGҫXVLQKKӑF WKXÿѭӧF OjYjKjPOѭӧQJcác KӧS FKҩW phenolic là 41.2% kKL Vӱ GөQJ xúc tác Ni/ZSM- &XӕL FQJ YLӋF [k\ GӵQJ Yj ÿiQK JLi WKHR ÿӏQK KѭӟQJ NLQK WӃ WXҫQ KRjQ FNJQJ ÿѭӧF EjQ OXұQ WURQJ QJKLrQFӭXQj\ DECLERATION I hereby declare that the thesis has been composed by myself and that the work has not be submitted for any other degree or professional qualification. I confirm that the work submitted is my own, except where work which has formed part of jointly-authored publications has been included. My contribution and those of the other authors to this work have been explicitly indicated below. I confirm that appropriate credit has been given within this thesis where reference has been made to the work of others. A part of the work presented in this thesis was my publication, which was previously published in Scientific Report as ³The novel method to reduce the silica content in lignin recovered from black liquor originating from rice straw´ DQG LQ Clean Technologies and Environmental policy as ³Sustainable bioethanol and value-added chemicals production from paddy residues at pilot scale´ The Author Le Minh Tan July 2021 i CONTENTS CONTENTS ............................................................................................................... i LIST OF TABLES .................................................................................................... v LIST OF ABBREVIATIONS ................................................................................. vi CHAPTER 1. PREFACE ......................................................................................... 1 1.1. Study Background ............................................................................................. 1 1.2. Research aims and Objectives .......................................................................... 2 1.3 Outline of thesis .................................................................................................. 2 CHAPTER 2. LITERATURE REVIEW ............................................................... 3 2.1. Rice straw ± a potential lignocellulose biomass overview .............................. 3 2.1.1. Lignocellulosic biomass ............................................................................... 3 2.1.2. Rice straw ..................................................................................................... 6 2.2. Rice straw- based biorefinery ........................................................................... 7 2.3. Production of rice straw lignin ......................................................................... 9 2.4. Conversion of straw lignin into bio-oil .......................................................... 11 2.5. Circular bioeconomy ....................................................................................... 12 CHAPTER 3. MATERIALS AND METHODS .................................................. 14 3.1. Chemicals and Materials ................................................................................ 14 3.2. Experiments ..................................................................................................... 14 3.2.1. Rice straw pretreatment.............................................................................. 14 3.2.2. Insight the precipitation behavior of black liquor in different pH values .. 14 3.2.3. Lignin recovery by 2-step acidification ..................................................... 15 3.2.4. Synthesis Ni/ZSM-5 from rice husk silica ................................................. 15 3.2.5. Conversion of rice straw lignin into bio-oil ............................................... 16 ii 3.3. Characterization and analysis ....................................................................... 17 3.3.1. Lignin characterization............................................................................... 17 3.3.2. Catalyst characterization ............................................................................ 17 3.3.3. Bio-oil characterization .............................................................................. 18 CHAPTER 4. RESULTS AND DISCUSSIONS .................................................. 20 4.1. Lignin recovery with lower silica effects ....................................................... 20 4.1.1. Rice straw composition .............................................................................. 20 4.1.2. Insight the precipitation behavior of black liquor in different pH values .. 20 4.1.3. Two-step acidification method for lignin and silica recovery. .................. 27 4.2. Hydroprocessing of lignin ............................................................................... 31 4.2.1. Catalyst characterization ............................................................................ 31 4.2.2. Catalytic hydroprocessing of lignin ........................................................... 35 4.2.3. Products analysis ........................................................................................ 36 4.3. Scale-up into pilot scale and integrated with bioethanol production process...................................................................................................................... 40 4.3.1. Production of lignin in pilot scale .............................................................. 40 4.3.2. Integrated with the bioethanol production process .................................... 44 4.4. Circular bioeconomy analysis. ....................................................................... 47 CHAPER 5. CONCLUSION AND FUTURE WORKS...................................... 51 LIST OF PUBLICATION ..................................................................................... 53 REFERENCES ....................................................................................................... 54 SHORT CURRICULUM VITAE ......................................................................... 65 iii LIST OF FIGURES Figure 1.1. The scientific idea of this study. .............................................................. 2 Figure 2.1. The structure of lignocellulose biomass. ................................................. 4 Figure 2.2. Three type of lignin monomers: (A) p-coumaryl alcohol (hydroxyphenyl unit), (B) coniferyl alcohol (guaiacyl units), and (C) sinapyl alcohol (syringyl unit) 5 Figure 2.3. Burning rice straw in field (a) and Using rice straw for animal feeds (b). .................................................................................................................................... 6 Figure 2.4. The biorefinery in Vietnam. ..................................................................... 8 Figure 3.1. Schematic representation of the process of recovery of lignin and silica from rice straw. ......................................................................................................... 15 Figure 4.1. Mass of total precipitate, ash, and non-ash in the black liquors. ........... 21 Figure 4.2. The color variation of the precipitate (a) and the filtrates of black liquors (b) at different pH values from 1 to 10. .................................................................... 22 Figure 4.3. FTIR and XRD spectrums of the precipitate from pH 10 to pH 6 (a,c) and from pH 5 to pH 1 (b,d). .................................................................................... 24 Figure 4.4. TG analysis of the precipitates from pH 10 to 5 (a) and from pH 4 to 1 (b).............................................................................................................................. 26 Figure 4.5. The recovery yield of lignin and silica, the ash content of lignin in difference processes .................................................................................................. 28 Figure 4.6. FTIR (a) and XRD (b) spectrums of lignin in a two-steps process. ...... 29 Figure 4.7. The recovery yield, the purity, and the silica content of lignin in several concentrations of NaOH. .......................................................................................... 30 Figure 4.8. The XRD diffractograms of ZSM-5 and Ni/ZSM-5 (a), SEM micrographs of ZSM-5 (b) and Ni/ZSM-5 (d) and the TPD-Br of ZSM-5 and Ni/ZSM-5 (c). ........................................................................................................... 32 Figure 4. 9. The BET isotherms of ZSM-5 and Ni/ZSM-5. ..................................... 34 iv Figure 4. 10. The SEM of ZSM-5 (a,c) and Ni/ZSM-5 (b,d) in different magnification ............................................................................................................ 35 Figure 4.11. FTIR spectra of bio-oil obtained from catalytic hydroprocessing of rice straw lignin with a various catalyst (a) Ni/ZSM-5, (b) ZSM-5, (c) no catalyst, (d) raw lignin. Reaction condition of lignin (2g), n-hexane (80 mL), solid catalyst (0.5 g), temperature (325oC), reaction time (2h), 60 bar H2. ........................................... 37 Figure 4.12. The composition of bio-oil obtained from catalytic hydroprocessing of rice straw lignin with Ni/ZSM-5 and ZSM-5. Reaction condition of lignin (2g), nhexane (80 mL), solid catalyst (0.5 g), temperature (325oC), reaction time (2h), 60 bar H2. ....................................................................................................................... 38 Figure 4.13. The FTIR spectrum of obtained lignin and silica on a pilot scale. ...... 42 Figure 4.14. The thermogram of silica and lignin (a) and the photograph of silica (b) and lignin (c) on a pilot scale. .................................................................................. 43 Figure 4.15. The SEM of silica (a,b) and lignin (c,d) at smaller (a,c) and higher (b,d) magnification. ........................................................................................................... 44 Figure 4.16. The energy balance of the new sustainable process............................. 46 Figure 4.17. Paddy residues-biorefinery based circular bioeconomy. ..................... 49 Figure 4.18. The mass estimation of bioconversion of rice straw and rice husk in biorefinery concept. .................................................................................................. 50 v LIST OF TABLES Table 4.1. The composition of rice straw and black liquor ...................................... 20 Table 4. 2. FTIR frequency range and functional groups present in the sample. .... 25 Table 4.3. The BET analysis of ZSM-5 and Ni/ZSM-5 ........................................... 33 Table 4.4. The product yield of catalytic hydroprocessing of lignin at reaction condition of 2g lignin, n-hexane (80 mL), solid catalyst (0.5 g), temperature (325oC), reaction time (2h), 60 bar H2. .................................................................... 36 Table 4. 5. The Compounds identified in liquid products of depolymerization of rice straw lignin with ZSM-5 and Ni/ZSM-5. ................................................................. 40 Table 4.6. Results of lignin and silica recovery on different scales. ........................ 41 vi LIST OF ABBREVIATIONS EtOH MS FTIR Ethanol mass spectrometry Fourier-Transform inferred spectroscopy GC Gas chromatography HDO Hydrodeoxygenation HPLC High performance liquid chromatography IRRI International Rice Research Institute SEM Scanning Electron Microscopy TGA Thermogravimetric analysis XRD X-ray powder diffraction XRF X-ray fluorescence HCMUT Ho Chi Minh City University of Technology Approx. Approximately 1 CHAPTER 1. PREFACE 1.1. Study Background In recent years, the utilization of lignocellulosic biomass as a renewable source for energy and chemical platforms has been investigated by scientists all over the world [1]. Lignin is one of the most potential renewable and sustainable energy resources which is present in a huge amount of agricultural waste such as maize, rice straw, corn stover, sugarcane bagasse, etc [2, 3]. Amongst them, rice straw accounts for the highest proportion of nearly 50 million tons generated annually in Vietnam, especially in the Mekong delta. However, most of the rice straw is burned resulting in huge emissions of harmful gasses such as NOx, CO, CO«. Therefore, lignin recovery from rice straw not only prepares a high calorific bio-fuel but also reduces their negative impacts on the environment [4±6]. Rice straw contains a significant amount of silica, which originates from the soil and enters the roots of the rice plant as mono-silicic acid, Si(OH)4. Evaporation and transpiration of water in the plant condense the monomeric Si(OH)4 species to their saturation point, thus leading to the polymerization into insoluble polysilicon acid [7, 8]. Furthermore, the appearance of linkages among components was also confirmed: Lignin associates with polysaccharides, especially hemicellulose, via covalent bonds to form lignin-carbohydrate complexes. Likewise, silica is hypothesized to have interaction with cellulose and lignin [9, 10]. The recalcitrant structure of lignocellulosic biomass inhibits bio-refineries such as the fermentation of cellulose for bioethanol, conversion of lignin into value-added chemicals. A lot of silica reduction methods were released but some require harsh conditions or special equipment and others are not efficient [9, 11, 12]. Moreover, there are several desilication methods conducted in mill conditions giving good results, however, this method was not reported about lignin recovery or removing both lignin and silica for gaining cellulose and hemicellulose [13±15]. Keywords: lignin, bioethanol, circular bioeconomy, biooil, conversion. 2 1.2. Research aims and Objectives The main objectives of this research were to study the valorization of the rice straw following the biorefinery concept with the main idea shown in Figure 1.1. The specific objectives were: - Recovery of lignin from rice straw after pre-treatment. - Integration of delignification process, and bioethanol production toward a zero-waste biorefinery. - Conversion of obtained lignin into biocrude. - Evaluation of biorefinery approach and the life cycle of rice straw. Figure 1.1. The scientific idea of this study. 1.3 Outline of thesis This work is split into two sections: a theoretical section (which includes a literature review) and an experimental section. In Chapter 2. Literature Review, the theoretical portion is discussed. This section contains a literature analysis of the raw material as well as relevant chemical techniques for understanding the new biorefinery approach and this study. The experimental part of the thesis is described in chapter 3. Material and Method, and discusses planning of experiments. The results from the experiments, and finally, conclusions and future work are presented in chapter 4. Results and Discussion, and chapter 5. Conclusion and Future Work. 3 CHAPTER 2. LITERATURE REVIEW 2.1. Rice straw ± a potential lignocellulose biomass overview 2.1.1. Lignocellulosic biomass Lignocellulose biomass, also known as lignocellulose, is the most abundant biorenewable substance on the planet [16], created by the photosynthesis process from atmospheric CO2 and water. It is a complex matrix consisting primarily of polysaccharides, phenolic polymers, and proteins that is an integral component of plant woody cell walls. As seen in Figure 2.1, LCB has a complex spatial structure in which cellulose (a carbohydrate polymer) is wrapped by a thick structure made up of hemicellulose (another carbohydrate polymer) and lignin (an aromatic polymer). Cellulose molecules are arranged in crystalline regions in regular coils, or in amorphous regions in random geometry. Hemicellulose and lignin shield the microfibrils of cellulose polymers, which are connected by hydrogen and van der Waals bonds. Carbohydrates, the main ingredient of cellulose and hemicellulose, account for about 70% of the dry weight of lignocellulose biomass and are the source of virtually all of the most promising bio-based building blocks and chemical intermediates, regardless of the conversion technologies used (biological or thermochemical). Lignin, which accounts for around 25% of the weight of lignocellulose biomass, is by far the most essential natural source of aromatics, apart from being a strong solid biofuel. Because of this structure, lignocellulose can play an important role in the energy industry, as it can be used to produce a variety of energy products, including solid (briquettes), liquid (bioethanol and biodiesel), and gas (biogas and bio-H2) [17]. 4 Figure 2.1. The structure of lignocellulose biomass [18]. Cellulose is a compound composed of polysaccharides, that consists of an open chain of D-JOXFRVH PROHFXOHV FRXSOHG WKURXJK ȕ-(1-4) glycosidic bonds with the formula (C6H10O5)n (Fig 2.1). Cellulose is that the commonest organic compound material on the market. Cotton fiber is containing 90% of cellulose content, wood is 40%-50%, and dried hemp is containing close to 57% [19, 20]. High amounts of cellulose contained in pulp and cotton for economic use. cellulose is usually accustomed to yield composition boards and paper-type materials. A prospective characteristic of cellulose is crystallinity. Cellulose is converted into an amorphous solid at conditions of 25 MPa pressure and temperature of 320°C. Many environmentfriendly biofuels may be derived from conversions of cellulosic materials, such as agricultural residues and energy crops. Hemicellulose is a branched heteropolymer containing close to 500-3000 sugar units [21]. It consists of several sugar units, with a prevalence of monosaccharide parts (xylose and arabinose) beside hexoses (mannose, glucose, galactose, and rhamnose) 5 and acetylated sugars. Hemicellulose cross-links with either cellulose or lignin, strengthening the semipermeable membrane (Figure 2.1). Though hemicelluloses are widely available, their utilization is harder compared to cellulose, due to their structural diversity, and the complex mechanism of the enzymatic hydrolysis of pentose sugar units. However, hemicelluloses supply a lot of prospects for regioselective chemical and accelerator modifications compared to cellulose, thanks to the variability in sugar constituents, glycosidic linkages, and structure of glycosyl aspect chains still as 2 reactive hydroxyl group teams at the carbohydrate continuance unit. Lignin is that the third major element of LCB, having a polymeric complicated structure, which is responsible for some of the structural materials in the particular types of tissues of vascular plants and some algae [22]. It is an inevitable a part of plant semipermeable membrane, particularly in bark and wood. Lignin shows rigidity and hard quality because of the cross-linked synthetic polymers in its structure. It's primarily amorphous (noncrystalline). It is a branched long-chain compound created of 3 varieties of monomers (Figure 2.2.), like primarily three-dimensional compound of 4-propenyl phenol (hydroxyphenyl unit or p-coumaryl alcohol), 4-propenyl-2-methoxy phenol (guaiacyl units or coniferyl alcohol), and 4-propenyl-2.5-dimethoxyl phenol (sinapyl alcohol or syringyl unit) [20]. Figure 2.2. Three type of lignin monomers: (A) p-coumaryl alcohol (hydroxyphenyl unit), (B) coniferyl alcohol (guaiacyl units), and (C) sinapyl alcohol (syringyl unit) 6 2.1.2. Rice straw Rice straw, a residual byproduct of rice production at harvest, is one of abundant lignocellulosic biomass in the world. Annual rice straw production is in the ranges of 100±140, 330±470, and 370±520 million t/year in Southeast Asia (SEA), the whole of Asia, and over the world, respectively [23]. In Vietnam, rice straw accounts for the highest proportion of nearly 50 million tons generated annually, especially in the Mekong delta. However, currently, most of the rice straw is burned (Figure 2.3) resulting in huge emissions of harmful gasses such as NOx, CO, CO«. Therefore, utilizing this material for production of bio-based products is an eco-friendly solution in context of climate changes. Figure 2.3. Burning rice straw in field (a) and Using rice straw for animal feeds (b). The biomass component in rice straw is mainly composed of 38% cellulose, 25% hemicellulose, and 12% lignin which are associated together to form a highly rigid network. More recently, energy crops are raw materials used for the production of second-generation biofuels as they offer high biomass productivity. Straw has a long history as an energy source: for many centuries, straw has been the most widely used raw material to burn fire. From the middle of the 20th century, problems rose from pollution and the exhaustion of fossil fuels has increased the demand of biomass for the production of energy [24]. More recently, second-generation biofuels were developed, based on the conversion of LCB components to liquid fuels. Secondgeneration biofuels allow the utilization of the entire plants, such as woody crops, agricultural residues, or waste, as well as dedicated non-food energy crops grown on 7 marginal land, thus allowing a dramatic increase of the productivity. With a million tons of rice straw being wasted into the environment, rice straw is promising as a new feedstock for value-added chemicals such as renewable energy or material production [25]. 2.2. Rice straw- based biorefinery Biorefineries could be the most promising means of creating a sustainable biobased economy because of their undeniable benefits [26]. Biorefinery cleanly produces various fuels, power, or heat that contribute to human energy needs; also generates various chemical commodities and bioproducts in an environmentally sustainable manner by utilizing local agricultural residues and municipal wastes feedstocks, thus reducing disposal problems [27]. Local agricultural residues used as biorefinery feedstocks are derived from lignocellulose-rich biomass resources, including wood, straw, grasses,... Biorefineries have been significantly advanced significantly towards fractionating lignocellulose to its major constituents in the past decade [27±29]. These constituents have been studied to process continuously into a range of products and energy using different process configurations with zero-waste generation to create more economically feasible biorefineries [30]. Recently, biorefineries have been significantly studied towards fractionating lignocellulose to its major constituents [29], then being processed continuously into a range of products and energy using different process configurations with zero-waste generation to create more economically feasible biorefineries [30]. Paddy field-based biorefineries have gained much attention in recent years [31]. Large rice-producing countries have adopted research strategies to develop small-scale biorefineries utilizing crop residues integrated with sustainable management of local agriculture [32]. Several pilot-scale plants have been made available, followed by R&D activities to develop fully-fledged systems as [33±36]. Paddy straw-based biorefinery systems could be based on a biochemical operation mode, including pretreatment/delignification, hydrolysis, and fermentation of cellulosic fractions into ethanol or other value-added products [30]. Pretreatment is the most crucial challenge of the biorefinery development to enrich cellulosic components for hydrolysis and fermentation into ethanol because of stability and structural toughness to the cell walls of the rice straw. This robustness is attributable to the cross-