Hydrothermal carbonization of soybean milk residue (okara) nutrient extraction and hydrochar fuel properties

VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY CAO THI THUY GIANG HYDROTHERMAL CARBONIZATION OF SOYBEAN MILK RESIDUE (OKARA): NUTRIENT EXTRACTION AND HYDROCHAR FUEL PROPERTIES MASTER'S THESIS VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY CAO THI THUY GIANG HYDROTHERMAL CARBONIZATION OF SOYBEAN MILK RESIDUE (OKARA): NUTRIENT EXTRACTION AND HYDROCHAR FUEL PROPERTIES MAJOR: ENVIRONMENTAL ENGINEERING CODE: 8520320.01 RESEARCH SUPERVISORS: Dr NGUYEN THI AN HANG Dr NGUYEN VIET HOAI Hanoi, 2021 ACKNOWLEDGMENTS After a period of conducting research, I have also completed the content of the thesis “Hydrothermal carbonization of soybean milk residue (okara): nutrient extraction and hydrochar fuel properties" The thesis was completed not only by the author's own efforts but also with the helps and active supports of many individuals and groups First of all, I would like to express my sincere and deep thanks to my Principal Supervisor Dr Nguyen Thi An Hang, who directly guided my thesis She gave me a lot of time and energy as well as many valuable ideas, corrected my thesis with specific comments Additionally, she always cared, encouraged and reminded me in a timely manner, thereby I could complete the thesis on schedule A special thank also goes to my Co-Supervisor Dr Nguyen Viet Hoai, for his valuable comments, concern, encouragment, and dedicated guidance for analysis of some hydrochar The second, I am also very grateful to Ms Nguyen Thi Xuyen, the assistant to Dr Nguyen Thi An Hang’s project, for supporting my experiment set-up and environmental parameters analysis In addition, I would like to thank the professors, officers and staffs of the Master’s Program in Environmental Engineering, Vietnam Japan University, Vietnam National University, Hanoi, who have wholeheartedly taught and helped me in my years in graduate school Last but not least, I would also like to express my sincere thanks to my family, friends, and fellow masters of the Master’s Program in Environmental Engineering – Batch for always encouraging, caring and helping me during my study and process thesis execution I acknowledge VJU’s JICA research fund (2021-2023 Principle investigator Dr Nguyen Thi An Hang) for financially supporting my thesis research Ha Noi, June 2021- Cao Thi Thuy Giang TABLE OF CONTENTS LIST OF TABLES i LIST OF FIGURES .ii LIST OF ABBREVIATIONS iii INTRODUCTION CHAPTER LITERATURE REVIEW 1.1 Hydrothermal Carbonization (HTC) 1.1.1 Fundamentals and advantages of HTC 1.1.2 Process parameters of HTC 1.1.3 Application of HTC 1.2 Nutrient extraction and recovery from agro-byproducts using HTC 11 1.2.1 Factors influencing nutrient extraction by HTC 11 1.2.2 Potential of axit humics (HA) and nutrient recovery from HTC water process 13 1.3 Fuel properties of agro-byproducts derived hydrochars 15 1.3.1 Evaluation of fuel properties of hydrochars 15 1.3.2 Factors influencing the fuel properties of hydrochars 16 1.3.3 Comparison between agro-byproducts derived hydrochars and other conventional fuels 17 1.4 Soybean milk residue (okara) as an agricultural by-product 19 CHAPTER MATERIALS AND METHODS 21 2.1 Materials 21 2.1.1 Soybean milk residue (okara) 21 2.2 Methods 22 2.2.1 HTC of okara 23 2.2.2 Axit humics and nutrient recovery from HTC process water 26 2.2.3 Fuel properties 27 2.3 Analytical methods and equipment 27 2.4 Statistical data analysis 28 CHAPTER RESULTS AND DISCUSSION 29 3.1 Extraction of nutrients from okara using HTC 29 3.1.1 Extraction of total phosphorus (TP) 29 3.1.2 Extraction of phosphate (PO43-) 33 3.1.3 Extraction of nitrogen as amonium (NH4+) 37 3.2 Nutrient and acid humic (HA) recovered from HTC process water 40 3.2.1 Potential of nutrients and humic substances in HTC process water 40 3.2.2 Recovery of axit humics and nutrients from HTC process water 42 3.2.3 Recovery of nutrients from HTC process water 45 3.3 Fuel properties of okara derived hydrochar 46 CHAPTER 4: CONCLUSION AND RECOMMENDATION 50 4.1 Conclusion 50 4.2 Recommendation 50 REFERENCES 51 APPENDICES 59 LIST OF TABLES Table 1.1 Evaluations of the state of different approaches for applications of HTC products 10 Table 1.2 Table of HHV values of hydrochar from different materials 17 Table 1.3 Table of ash content values of hydrochar from different materials 18 Table 1.4 Table of Fixed C values of hydrochar from different materials 18 Table 2.1 Methods for examination of parameters 27 Table 3.1 Values of some indicators of precipitation when changing the concentration of Fe 43 Table 3.2 Values of precipitation at the optimal P extraction conditions 44 Table 3.3 Values of precipitation at the optimal N extraction conditions 44 Table 3.4 The value of ultimate analysis of hydrochar 47 Table 3.5 The value of proximate analysis of hydrochar 48 Table 3.6 Comparison table of HHV values of hydrochar from different materials 49 i LIST OF FIGURES Figure 1.1 Okara as a by-product of the tofu and soymilk production processes 20 Figure 1.2 Image of fresh soybean by-product (okara) 20 Figure 2.1 Tofu business household 21 Figure 2.2 Soybean milk residue (okara) raw 21 Figure 2.3 Soybean milk residue (okara) after preparation process 22 Figure 2.4 Experimental diagram 23 Figure 2.5 Vacuum filtration apparatus 24 Figure 2.6 Hydrochar after drying until unchanged weight 25 Figure 2.7 Images of apparatus used in this study 28 Figure 3.1 Effect of the solvent categories 29 Figure 3.2 Effect of the solvent concentration 30 Figure 3.3 Effect of the HTC temperature 31 Figure 3.4 Effect of the HTC time 32 Figure 3.5 Effect of the solvent categories 33 Figure 3.6 Effect of the solvent concentration 34 Figure 3.7 Effect of the HTC temperature 35 Figure 3.8 Effect of HTC time 36 Figure 3.9 Effect of the solvent categories 37 Figure 3.10 Effect of the solvent concentration 38 Figure 3.11 Effect of the HTC temperature 39 Figure 3.12 Effect of the HTC time 40 Figure 3.13 Concentrations of PO43- and NH4+ in the HTC process water 41 Figure 3.14 Precipitation from recovery humic acid and phosphorus process 44 Figure 3.15 The concentration of N in the solution in the condensate when change the condition of experiments 45 Figure 3.16 The images of ultimate analysis of hydrochar 47 ii LIST OF ABBREVIATIONS BET: Brunauer–Emmett–Teller COD: Chemical oxygen demand FC: Fixed carbon HA: Humic acid HHV: Higher heating value HTC: Hydrothermal carbonization N: Nitrogen P: Phosphorous TCVN: Vietnam standard TN: Total nitrogen TP: Total phosphorous VM: Volatile matter iii INTRODUCTION In the food processing, besides the process of creating quality products, the recovery of waste by-products is very necessary Besides being meaningful in terms of environmental protection, the treatment of waste by-products will bring economic benefits to businesses One of the by-products of the food industry is soybean milk residues (okara) Okara is the main by-product obtained after processing soybeans into soy milk Our country has favorable natural conditions and farmers' agricultural experience, so the planted area and soybean yield are quite high over the years According to the Food and Agriculture Organization of the United Nations (FAO), by 2009, soybean area increased to 98.8 million hectares, production reached 222.3 million tons, yield 22.49 quintals/ha, most concentrated in America (76.0%), followed by Asia (20.6%) In Vietnam, the General Statistics Office of Vietnam and the Ministry of Agriculture and Rural Development reported that in 2014, the soybean growing area reached 120 thousand hectares with the total output was 176.4 thousand tons Along with the growing area and production of soybeans, the amount of soybean residue obtained in soy milk production is also expected to increase Currently, a large amount of soybeans is used to produce soy milk In our country, there are big soy milk brands such as Vinasoy, Vinamilk, Tribeco With a capacity of 120 million liters per year at Vinasoy factory (Quang Ngai) and 90 million liters per year at Vinasoy factory (Bac Ninh), experts say: Vinasoy is leading the production capacity of dairy products soy bean The total amount of soybean residue (okara) discharged annually in two factories of Vinasoy alone can reach more than 20 thousand tons/year Okara contains a large amount of nutrients (phosphorus), protein, glucide, fat and fiber However, okara does not last long at room temperature (less than days) and even under refrigeration due to easy decomposition This can cause odors and pollute the environment Therefore, handling okara is very necessary On the one hand, this treatment will help reduce solid waste into the environment On the other hand, it contributes to the creation of useful materials (biochar, soil improvement nutrients, etc) In addition, the treatment of soybean milk residues also helps bring economic benefits to enterprises Hydrothermal carbonization (HTC) is a developing but promising innovation for the treatment of waste biomass as well as agricultural residues with high moisture (Burguete et al., 2016; He et al., 2015; Yao et al., 2016) The HTC is efficient in nitrogen (N) recovery through change of organic-N into ammonium-N (He et al., 2015; Huang et al., 2016), at the same time it make possible the conversion of organic-P into inorganic-P, it is efficient in P recovery when HTC condition is acidic (Dai et al., 2015) Okara is a by-product from soybean, which is a nutritious agricultural product Therefore, the potential to recover nutrients from okara is very large In order for the nutrient recovery process to achieve maximum efficiency, it is necessary to study to find the optimal extraction conditions To achieve that, it is necessary to investigate the factors affecting the extraction process by testing the nutrient recovery method In addition, besides liquid phase, HTC also generates the solid product known as hydrochar, so its energy potential needs to be assessed value (NH4)2SO4 obtained at the optimum condition of phosphorus recovery Besides, at optimal N extraction conditions, with a condensation time of minutes, ammonium sulfate solution with N concentration: 1026.7 mg/L is obtained 3.3 Fuel properties of okara derived hydrochar Biomass is a valuable and plentiful resource in the globe; annual production was eight times that of global fossil energy demand Because of its low sulfur content, ability to trap carbon dioxide, and ability to regenerate, biomass is a promising biofuel for replacing fossil fuels in the future However, in recent decades, the majority of biomass has been burned directly as a fuel Biomass is classified as a low-fuel because of its high moisture content, hygroscopic feather, low energy value, high volatile content, and high oxygen content Therefore, it is necessary to improve the fuel value of the biomass There are a number of ways to increase the fuel value of biomass, one of which is to convert it to biochar Biochar has a number of advantages over biomass feedstock, including a high carbon content, high energy density, refractory nature, and the ability to reduce greenhouse gas emissions The conversion of biomass to biochar (hydrochar) via a hydrothermal carbonization process with subcritical water has become a hot issue in recent years In this study, fuel characteristics such as higher heating value (HHV), proximate analyses and ultimate analyses are discussed Many efforts have been paid on the effects of holding time and temperature of HTC on the elemental composition of resulting hydrochar These previous results showed that, on many occasions, C content in hydrochar was increased with increase of time or temperature, whereas O and H contents in hydrochar showed a reverse trend to C content, and N and S contents were not strongly influenced by HTC time or temperature (Yang et al., 2015) Regarding to the values of ultimate analysis, the effect of various hydrothermal carbonization settings on the elemental contents of hydrochar is shown in Table 3.4 The initial okara included 51.33 percent carbon and 48.67 percent oxygen, respectively When okara were treated at 170 and 200 degrees Celsius for extended periods of time, the carbon content rose as well With an increase in hydrothermal carbonization temperature and a large decrease in oxygen content, the carbon content of hydrochar increased from 51.33 to 80.79 percent Meanwhile, at 200 °C for hours, the oxygen content was reduced to 4.73 percent The low oxygen 46 content was caused by the degradation of hemicellulose and cellulose, both of which had a high oxygen concentration at the time of treatment These results are in the same line with the results from research of Nizamuddin et al.(2016) Table 3.4 The value of ultimate analysis of hydrochar C (%) O (%) S (%) Al (%) Sample 1: H2SO4 0.3M, 170 oC, 6h 75.46 23.49 1.05 Sample 2: H2SO4 0.3M, 200 oC, 8h 80.79 18.76 0.24 0.21 Figure 3.16 The images of ultimate analysis of hydrochar 47 Table 3.5 The value of proximate analysis of hydrochar Sample HHV Ash content Volatile matter (MJ/kg) (%) (%) 23.48 2.68 73.02 24.3 24.15 3.51 60.95 35.54 Fixed C (%) 1: H2SO4 0.3M, 170 oC, 6h Sample 2: H2SO4 0.3M, o 200 C, 8h Furthermore, Table 3.5 indicates about the values also the trends of proximate parameters It can be seen clearly that as the hydrothermal carbonization temperature increased, the ash content, HHVs, fixed C rise while volatile matters decline (Table 3.5) The hydrothermal carbonization process caused dehydration, decarbonation, and demethanation, which resulted in these effects The ash content, fixed C increase 0.83 % and 11,27 %, respectively In contrast, the volatile of hydrochar from HTC drop from 73.02 % to 60.95 % This trend is supported by (Kambo and Dutta, 2015), who propose that when changing the temperature and time of HTC process, in particularly, when increasing these factors, the HHV values and percentage of carbon will rise In the fact that, when the temperature was raised from 170 to 200 degrees Celsius, the HHV of hydrochar increased from 23.48 to 24.15 MJ/kg At 170 and 200 oC, respectively, the HHV was continually raised during the extended treatment Nizamuddin et al (2016) also proposed that the lower hydrogen and carbon contents were, the lower HHV of fuels were Comparing to other HHV values of some conventional fuels, it can be seen that HHV value of okara is smaller than that of some conventional fuels Table 3.6 shows that, HHV value of okara also slightly lower than those of some conventional fuels: coal (30 MJ / kg), fuel oil (43 MJ / kg), diesel oil (45.7 MJ/ kg) Besides, they were compatible with lignite char (31.3 MJ/kg) and charcoal (34.4 MJ/kg) However, on the contrary, when make a comparison between HHV value of okara and HHV value of other agro-waste derived hydrochars, there is a fact that HHV value of okara is clearly 48 higher From the table 3.6, most of HHV value of agro- waste are smaller than 20 MJ/kg Meanwhile, HHV value of okara at the optimal of extraction phosphorus and nitrogen are 23.48 MJ/kg, 24.15 MJ/kg, respectively Besides, hydrochars from okara had substantially greater HHVs than methanol (22.7 MJ/kg) Table 3.6 Comparison table of HHV values of hydrochar from different materials Number Type of hydrochar HHV (MJ/kg) Author, Year Corn stover 16.2 Fueres, 2010 Eucalyptus sawdust 16.69 Sevilla, 2011 Barely straw 17.34 Sevilla, 2011 Coconut fiber 18.4 Liu, 2013 Maize sillage 22.3 Mumme, 2011 Okara 23.48 This study Fuel oil 42.9 Wei Yang, 2014 Diesel oil 45.7 Wei Yang, 2014 In short, from the results of fuel properties, the carbon content and HHVs of hydrochar were between 75.46- 80.79 % and 23.48- 24.15 MJ/kg, respectively Although HHV value of okara slightly lower than those of some conventional fuel, this higher than that of other agro-waste derived hydrochars According to these findings, hydrothermal carbonization of biomass could be a viable method for producing energydense hydrochars from biomass and hydrochar of okara has the great potential for energy recovering 49 CHAPTER 4: CONCLUSION AND RECOMMENDATION 4.1 Conclusion The optimal conditions for P extraction from okara was H2SO4 0.3M, 170oC, h The HTC process solution had composition of 207.8 mg P/L and 472.9 mg N/L The extracted P amount accounted for 90.5 % of the total P content in the pristine okara The optimal conditions for N extraction was H2SO4 0.3M, 200 oC, h The HTC process was characterized by the composition of 188.8 mg P/L and 718.8 mg N/L The extracted P amount represented 70.8 % of the total P content in the pristine okara HA and P contents in the HTC process solution were recovered as the solid products whereas N was recovered as (NH4)2SO4 liquid At the optimal P extraction conditions, the recovery percentages of HA and P were 82 and 99.9%, respectively; the HA and P contents in the recovered solid product were 4.62 and 0.08%, respectively At the optimal N extraction conditions, the recovery percentages of HA and P were 85 and 99.9%, respectively; the HA and P contents in the recovered solid product were 4.64 and 0.09%, respectively N concentrations in the recovered liquids were 554.9 and 1026.7 mg N/L for the optimal P and N extraction conditions, respectively Okara-derived hydrochar demonstrated higher HHV than other agro-waste derived hydrochars but slightly lower as compared to conventional fuels 4.2 Recommendation At optimal extraction conditions, the extracted HA and nutrient contents in the HTC process water were relatively high Though the recovery percentages of HA and P from HTC process water were high, their contents in the recovered solid product were still low This resulted from utilizing a big amount of FeCl3 in an attempt to recovery a majority of HA in the HTC process water Since high Fe content in the recovered solid product may have undesirable effects on crop’s growth, it is recommended to seek for alternative method that can successfully recover HA in advance, thus enabling the recovery of 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soybean milk residue (okara): nutrient extraction and hydrochar fuel properties" ... HANOI VIETNAM JAPAN UNIVERSITY CAO THI THUY GIANG HYDROTHERMAL CARBONIZATION OF SOYBEAN MILK RESIDUE (OKARA): NUTRIENT EXTRACTION AND HYDROCHAR FUEL PROPERTIES MAJOR: ENVIRONMENTAL ENGINEERING CODE:... by-product of the tofu and soymilk production processes Figure 1.2 Image of fresh soybean by-product (okara) 20 CHAPTER MATERIALS AND METHODS 2.1 Materials 2.1.1 Soybean milk residue (okara) a)