Research Article Cite This: ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
pubs.acs.org/journal/ascecg
Hydrothermal Liquefaction of Model Food Waste Biomolecules and Ternary Mixtures under Isothermal and Fast Conditions Akhila Gollakota and Phillip E. Savage* Department of Chemical Engineering, The Pennsylvania State University, 119 Greenberg Complex, University Park, Pennsylvania 16802, United States S Supporting Information *
ABSTRACT: We subjected potato starch, casein, and sunflower oil to both isothermal and fast hydrothermal liquefaction (HTL), both individually and as ternary mixtures in different proportions. Fast HTL (15 wt % biomass loading, 600 °C set-point temperature, 1 min) of sunflower oil produced the highest biocrude yield (91 wt %), followed by casein (23 wt %) and potato starch (19 wt %). Up to 21% of the phosphorus and 57% of the nitrogen in casein are distributed to the aqueous phase after fast HTL and can potentially be recovered as fertilizer for growing more food. Fast HTL (600 °C, 1 min) provided higher biocrude energy recoveries than did isothermal HTL (350 °C, 60 min) for all three feedstocks. Potato starch showed the greatest increase in energy recovery with fast (46%) vs isothermal (32%) HTL, and fast HTL of the ternary mixture rich in potato starch produced biocrude with the largest higher heating value (HHV) (42 MJ/kg). The results indicate that fast HTL is particularly beneficial for polysaccharides compared to the other biomolecules. Biocrude yields produced from fast HTL of ternary model mixtures were within two standard deviations of the yields estimated on the basis of individual biomolecules. The presence of pyrrolidines, pyrazines, fatty acid alkyl esters, and fatty acid amides indicate that chemical reactions occur between molecules derived from the different feedstocks during HTL of mixtures. KEYWORDS: Subcritical water, Supercritical water, Biocrude, Nutrient recovery, Biomass, Energy recovery
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INTRODUCTION The United Nations Food and Agriculture Organization estimates that each year approximately 1.3 billion tons of food is wasted globally.1 Food waste decomposes easily under ambient conditions, and disposal in improperly operated landfills can cause groundwater and soil contamination.2 Decomposition of food waste in landfills also emits methane, which is a 25 times more potent greenhouse gas than carbon dioxide over a 100-year time span. Food waste has been valorized using various methods such as extraction with solvents and supercritical fluids,3−5 production of sorbents,6 separating the nutritionally rich components of the waste,7,8 and biological processing routes including anaerobic digestion,9−11 composting,12,13 and fermentation to alcohols.14−17 The methods for producing fuels (anaerobic digestion and fermentation) employ microorganisms that are very sensitive to operating conditions (pH, temperature, etc.), and the processes require a long time.18 Thermochemical conversion processes including direct combustion, gasification, © XXXX American Chemical Society
or pyrolysis to produce bio-oils are much faster but work best with biomass with moisture content less than ∼30%.19 In this context, hydrothermal processes, which use thermochemical reactions in and with water at high temperatures and pressures, are promising routes as they work quickly and can directly use wet biomass and thus eliminate the energy-intensive drying needed for other thermochemical processes.20 Hydrothermal liquefaction (HTL) converts wet biomass into energy-dense biocrude that can then be upgraded and refined to distillate fuels. HTL takes advantage of the properties of hot, compressed liquid water at near critical conditions (Tc = 374.2 °C and Pc = 22.1 MPa). Notably, the dielectric constant and number and persistence of hydrogen bonds decrease as temperature increases, resulting in increased solvation of organic compounds.21 Furthermore, a higher ion product Received: March 26, 2018 Revised: May 4, 2018
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DOI: 10.1021/acssuschemeng.8b01368 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
Research Article
ACS Sustainable Chemistry & Engineering (KW) at these conditions results in a higher concentration of H+ and OH− ions, which accelerates acid- and base-catalyzed reactions such as hydrolysis and dehydration.21 Conventional HTL is performed isothermally for tens of minutes, and it has been established as a feasible process for valorizing a variety of agricultural and food processing wastes.22,23 Fast HTL, an emerging variation of this technology, employs rapid heating, nonisothermal conditions, and very short reaction times (tens of seconds) to convert wet biomass to biocrude.24 Studies on fast HTL of microalgae,24 macroalgae,25 corn stover,26 bacteria and yeast,27 soy protein isolate,28 bovine serum albumin (BSA),29 and sewage sludge30 have reported biocrude yields comparable to or exceeding those from isothermal HTL. These reports established the robustness of fast HTL for whole biomass, but apart from the few prior studies with proteins, its application to the major biochemical components of food waste remains unexplored. There have been no prior studies on fast HTL of polysaccharides, triglycerides, or well-defined mixtures containing these biochemical components. The abundance of food waste and the potential of fast HTL to produce high biocrude yields quickly motivated the present work. In this study, we subjected representative food waste biomolecules to both isothermal and fast HTL and quantified the gravimetric yields of the different product fractions, the quality of biocrude in terms of elemental composition and higher heating value (HHV), the energy recovery in the biocrude, and the recovery of phosphorus and nitrogen in the aqueous-phase products from fast HTL of casein. We also tentatively identified the most abundant molecular species in the different biocrudes. These results provide new understanding into how the principal biochemical components of food waste convert into different product fractions during fast HTL.
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reactor temperature profiles at all the sand bath set-point temperatures used in this work are shown in Figure S1. The loaded reactors were sealed and sonicated for 20 min in a Fisher Scientific digital ultrasonic bath cleaner (CPX1800) to promote better mixing of the reactor contents. The reactors, along with the proxy reactor were placed in a Techne IFB-51 sand bath preheated to the desired set-point temperature. “Isothermal” HTL involved reactors being at the sand bath set-point temperature for >20 min. “Fast” HTL involved reactors being removed from the sand bath well before reaching the set-point temperature. For example, the reaction mixture for fast HTL at a 600 °C set point reached just 399 °C after 1 min. The goal of fast HTL is for the reactor contents to experience a high heating rate throughout the entire (short) reaction time (e.g., 1 min). After reaching the required holding time, the reactors were removed from the sand bath and quenched in an ice−water bath for 10 min. The external surfaces of the reactors were thoroughly dried and allowed to equilibrate to room temperature for 2 h. Product Recovery. The difference in the mass of the reactor before and after opening was recorded and taken to be the mass of the gas produced. The remaining HTL products were recovered by emptying the contents of the reactor entirely into a 30 mL glass syringe fitted with an Advantec 25 mm steel syringe membrane holder consisting of a glass fiber filter (Type A/E, Pall Laboratory). The interior of each reactor and the cap were then washed with 10 mL of DCM followed by 10 mL of DI water, each in small aliquots and emptied into the glass syringe. After the contents in the syringe were pushed through, all the solids were collected in the membrane filter. The liquid products were collected in centrifuge tubes, and the multiphase mixture in these tubes was centrifuged at 6000 rcf for 10 min. The separated aqueous and DCM phases were then each carefully transferred via Pasteur pipets to their own respective preweighed test tubes. Biocrude was recovered by flowing N2 over the DCM phase at 40 °C with a Labcono RapidEvap Vertex Evaporator for >6 h until the test tube masses changed by less than 0.5 mg. The membrane filter with solid-phase products was dried for ∼12 h in an oven at 70 °C, and then, we determined the solids mass. Analytical Chemistry. The gravimetric yields of the different product fractions were calculated as the mass recovered divided by the mass of the model compound loaded into the reactor. The aqueousphase product yield was evaluated as the difference between the sum of the other products yields and unity. All HTL experiments were done in triplicate, and the product yields are reported as the average of three trials and uncertainties as standard deviations. Gas chromatography (GC) with a thermal conductivity detector (TCD) (Shimadzu GC-2014) was used for qualitative analysis of the gas in the reactor headspace. A 2 m, 1 mm inner diameter column packed with 100/200 mesh ShinCarbon ST was used to separate the gaseous components in the mixture. Argon (10 mL/min) was the carrier gas for the analysis. The temperature of the injection port was 130 °C. The column temperature was initially held at 30 °C for 5 min and then increased to 240 °C at a rate of 8 °C min−1. The final temperature of the column was held at 240 °C for 1 min. The biocrude was analyzed with a Shimadzu GC-MS QP-2010 Ultra equipped with a 0.25 mm inner diameter Agilent DB-5MS column (30 m × 0.25 μm). The injection port temperature was 310 °C. The temperature program consisted of a 2 min soak at 40 °C followed by a ramp at 5 °C min−1 to 250 °C. The molecular species in the biocrude were tentatively identified by comparing their mass spectra against the NIST mass spectral library. Elemental (C, H, N, S) analysis was performed on the biocrude samples and the model compounds using a CEInstruments (Thermo Electron Corp) Elemental Analyzer EA 1110 equipped with a TCD. The O content was determined by difference. Select aqueous-phase samples obtained after HTL of casein were quantified for total nitrogen (TN) using dry combustion analysis and total phosphorus (TP) using EPA 3050B (acid digestion)34 and EPA 6010 (inductively coupled plasma-atomic emission spectrometry (ICP-AES)).35
MATERIALS AND METHODS
Biomolecules and Solvents. Sunflower seed oil (Spectrum Chemical Mfg. Corp.), potato starch (VWR), and micellar casein (77% protein, NutraBio) served as model compounds for lipid, polysaccharide, and protein, respectively. Potato starch was chosen as it is completely soluble in water at room temperature31 and is an abundant carbohydrate in food waste.32 Sunflower oil is widely used in cooking, and ∼10 million ton/year of waste cooking oil is produced in the USA.33 Casein is a family of phosphoproteins found in milk and is representative of dairy waste. Deionized (DI) water prepared with Direct-Q3 UV-R EMD Millipore was used as the reaction medium and for recovering aqueous-phase products from the batch reactors. Dichloromethane (DCM) (HR-GC grade, EMD Millipore) was used for recovering biocrude from the reactors. HTL Procedure. HTL experiments were carried out in 316 stainless-steel batch reactors (∼4.1 mL internal volume) assembled with one 1/2 in. Swagelok port connector and two Swagelok caps. To enable gas analysis, some reactors were fitted with a high-pressure (30,000 psi) valve (High Pressure Equipment Co.) with 8.5 in. of 1/8 in. stainless steel tubing (0.028 in. wall thickness). The gas valve assembly added 0.5 mL to the reactor volume. The reactors were loaded such that each contained 15 wt % model compound(s). The water loading was such that the water would expand to occupy 95% of the reactor volume for experiments at subcritical sand bath set-point temperatures or provide a density of 0.5 g cm−3 at 400 °C for reactions at supercritical sand bath set-point temperatures. A proxy reactor was constructed and loaded with DI water similar to the HTL reactors, but it also included an Omega 1/8 in. K-type thermocouple to measure the internal temperature of the reactors. The temperature profiles of the proxy reactor were recorded with an Omega UWBT-TC-UST-NA data logger every 1 s. The B
DOI: 10.1021/acssuschemeng.8b01368 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
Research Article
ACS Sustainable Chemistry & Engineering
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and reported solids yield of 40 wt %.42 Thus, the present solids yields from isothermal HTL of potato starch are consistent with previous work done at similar biomass loadings. In contrast with isothermal HTL of potato starch, all of the fast HTL conditions resulted in very low solids yield (30 wt % yield of solids (insoluble in both DCM and water), some of which adhered to the reactor wall. The literature indicates that at these longer holding times, secondary reactions including oligomerization or condensation of the newly formed compounds result in the formation of char.40,41 Teri et al. estimated a solids yield as high as 30 wt % for HTL of corn starch at 350 °C and 30 min.36 Biller et al. reported 20 wt % solids yield after isothermal HTL of starch at 350 °C and 60 min.37 Déniel et al. performed isothermal HTL of monosaccharides (glucose and xylose) at 300 °C and 60 min
Figure 2. Temporal variation of product fraction yields for fast HTL of potato starch at a set-point temperature of 600 °C. C
DOI: 10.1021/acssuschemeng.8b01368 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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ACS Sustainable Chemistry & Engineering
Figure 4 shows yields of different product fractions in 15 s intervals for the fast HTL of the casein feedstock at a set-point
sand bath. Potato starch was completely soluble in water, and none of the initial material could be extracted by DCM. The solids yield was 95%. Starch is a biopolymer with 10%−35% linear chain αamylose (1,4-linked glucose chain) and 65%−90% branched chain α-amylopectin (basic repeat units of 1,4-linked glucose with branches of 1,6-linked glucose). The most abundant biocrude products identified in the total ion chromatogram from HTL of starch were 2-cyclopenten-1-one and other cyclic ketones, substituted phenols (cresols, butylated hydroxytoluene), indanones, and furans. Starch rapidly hydrolyzes to monosaccharides at subcritical conditions (180−250 °C, 15 min),22,55 and these then form aldehydes, ketones, and phenolic compounds by condensation and dehydration.20,38 Further, Catallo et al. reported the formation of unsaturated cyclic products including cyclopentenones via Diels−Alder addition and aromatization of alkenes and diene fragments from glucose in hydrothermal treatment at 400 °C.56 Indanones found in the biocrude could be a result of condensation of furfurals.57 Hydrothermal conversion of protein proceeds with hydrolytic decomposition into peptides, amino acids, and secondary amines.28 Depending on their structure (−R group), amino acids undergo secondary reactions including decarboxylation, deamination, dehydration, and oligomerization under hydrothermal conditions.55 Deamination is the key denitrogenation pathway, and decarboxylation is the main deoxygenation pathway.58 The abundant biocrude compounds from HTL of casein are phenols, amides, indoles, cyclodipeptides (diketopiperazines), five-membered lactams, pyrroles, and piperidines. Styrene and phenyl ethyl alcohol were also identified. The literature provides precedence for these compounds being in the biocrude from HTL of proteins. Changi et al. identified styrene and phenylethanol as the products from decarbox-
al. conducted fast HTL of soy protein isolate and observed 80% N in the aqueous-phase products at 30 s and 59% as the holding time approached 60 s.28 Figure 7(b) shows that just 21% of the phosphorus from casein partitioned into the aqueous phase in 15 s. The remaining phosphorus could have partitioned to the biocrude and/or the solids.49 As the reaction conditions became more severe, less than 10% of the casein phosphorus was recovered in the aqueous phase. That milder reaction conditions favor retention of phosphorus in the aqueous phase has been observed previously for HTL of other protein-rich biomass.49,50 Additionally, the P recoveries reported here are similar to the recoveries obtained after fast HTL of Nannochloropsis sp. at 350 and 450 °C for a holding time of 1 min.51 They are lower, however, than those in previous isothermal HTL studies that used microalgae (C. Vulgaris, Nannochloropsis sp.) and chicken manure as feedstocks.49,52 HTL converts most of the feedstock phosphorus into free phosphate.49,53 This phosphate could combine with calcium, when present in the feedstock, and depending on what other species are in solution form precipitates that take phosphorus out of the aqueous phase.52,54 Differences in the HTL solution compositions and the Ca content of the feedstocks might account for these different results regarding P recovery in the aqueous phase after HTL. The amount of P partitioned to the aqueous phase is highest at the mildest condition whereas the amount of N distributed to the aqueous phase is highest at a more severe condition (45 s). Also, N and P recovery in the aqueous phase are both lowest at the condition (60 s) where the biocrude yield was highest. These outcomes show some of the trade-offs that exist in HTL as one cannot simultaneously maximize biocrude production and N and P recovery in the aqueous phase. HTL of Mixtures. Fast HTL of ternary mixtures was investigated to elucidate the influence of hydrothermal reactions for one biochemical component on the reactions of the other components. We selected a set-point temperature of 600 °C for a holding time of 1 min as this reaction condition produced the highest biocrude yields from the individual feedstocks. Figure 8 shows the biocrude yields (vertical bars) obtained from fast HTL of four different mixtures of casein (C), potato starch (PS), and sunflower oil (SO). The blue triangles represent the mass-averaged biocrude yields calculated for each mixture based on experimental yields for each individual model compound at the same reaction condition.
Figure 8. Experimental (vertical bars) and mass-averaged (discrete points) biocrude yields from fast HTL of ternary mixtures at 600 °C (set point), 1 min. G
DOI: 10.1021/acssuschemeng.8b01368 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
Research Article
ACS Sustainable Chemistry & Engineering
point temperature examined (600 °C) led to the partitioning of 21% of the casein phosphorus into the aqueous phase within 15 s. The P content in the aqueous phase decreased as the reaction severity increased. The trend for N was different, as a maximum of 57% of the casein nitrogen partitioned to the aqueous phase in 45 s and then decreased as the reaction severity increased. Aqueous-phase recovery of phosphorus is favored by mild liquefaction conditions, and that of nitrogen is favored by moderate liquefaction conditions. High biocrude yields and energy recovery are favored by more severe HTL conditions. It appears that one cannot simultaneously maximize N recovery, P recovery, and energy recovery. Rather there are trade-offs that must be considered. The HHVs for the biocrude produced by fast HTL of the biomolecules at a 600 °C set point for 1 min were higher than those of the biocrudes produced from isothermal HTL for 30 min. Thus, fast HTL provided both higher-quality biocrude and greater energy recovery in the biocrude than did isothermal HTL and did so with a much shorter reaction time. The energy recovery from potato starch showed the largest difference for fast vs isothermal HTL, suggesting that fast HTL is especially beneficial for valorizing polysaccharides. Though the yields of biocrude from fast HTL of ternary mixtures of the model compounds were in general agreement with the mass-averaged biocrude yields from fast HTL of the individual biomolecules, analysis of the molecules in the biocrude revealed that reactions did occur between molecules derived from different feedstocks in the mixture. Fast HTL of the equimass mixture produced biocrude with the highest energy recovery, and the mixture rich in potato starch produced biocrude with the largest HHV (∼42 MJ/kg). This result again points to polysaccharides being better processed via fast, rather than isothermal, HTL. Given these encouraging results from model biochemical components, we view fast HTL as an effective process to convert food waste into energy-dense biocrude.
ylation of phenylalanine in HTW.55 Here, α-alanine, β-alanine, and glycine form diketopiperazines via dehydration/cyclization of dipeptides.59,60 Déniel et al. studied the hydrothermal reactions of glutamic acid (most abundant amino acid in casein) and observed 5-membered lactams including 2pyrrolidinone and 1-propyl-2-pyrrolidinone.42 Teri et al. reported phenol, pyrrolidinone, piperidine, and indole as major products from isothermal HTL of soy protein, and Sheehan et al. observed similar groups of products after HTL of BSA.29,36 Thus, the results here for casein are consistent with prior work. The hydrothermal reaction paths for triglycerides are relatively simple, and the kinetics and mechanisms of ester hydrolysis are well understood.55 Hydrolysis of triglycerides to diglycerides is the first step, followed by hydrolysis of diglycerides to monoglycerides, and finally, the monoglycerides are hydrolyzed to glycerol. With each step, one fatty acid molecule is generated.61 The biocrude from HTL of triglycerides consists of fatty acids and products formed from secondary reactions among these compounds.55 The compounds identified in this work from the HTL of sunflower oil are palmitic acid, linoleic acid, oleic acid, stearic acid, pentadecanoic acid, undecanoic acid, n-decanoic acid, heptanal, 1-octene, and 9,12-octadecadien-1-ol, (Z,Z)−. Palmitic acid, linoleic acid, oleic acid, and stearic acid, observed here, are the constituent fatty acids in sunflower oil.62 In addition to the compounds present from HTL of each feedstock alone, HTL of the ternary mixture produced fatty acid alkyl esters and fatty acid amides. The latter compounds may be formed by the condensation reaction between fatty acids from triglycerides and ammonia from amino acids in proteins.63 The presence of these molecular species in the biocrude from HTL of the mixture confirms the occurrence of interactions between individual components from different biomolecules. We also identified Maillard reaction products including pyrrolidines and pyrazines. There are multiple reports suggesting the formation of Maillard products between sugars and amino acids or amines (formed by amino acid decomposition) under hydrothermal conditions.36,38,64−67 These compounds are very stable, even in supercritical water.58
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ASSOCIATED CONTENT
S Supporting Information *
CONCLUSIONS This study provides the first account of fast HTL for a polysaccharide, a triglyceride, and ternary mixtures of biochemical components. Fast HTL at a set-point temperature of 600 °C for just 1 min always provided higher biocrude yields than did isothermal HTL for 30 min. The highest biocrude yields from sunflower oil (91 wt %), casein (23 wt %), and potato starch (19 wt %) were from fast HTL at this condition. This ability of fast HTL to convert more of the most recalcitrant biochemical component (polysaccharide) into biocrude is an important finding and indicates that fast HTL of polysaccharides is worthy of additional research. The biomass loading (wt %) affects biocrude yields from isothermal HTL of polysaccharides. HTL of potato starch at 290 °C for 30 min using a 2 wt % biomass loading resulted in a higher biocrude yield of 12.7 ± 1.7 wt % than did HTL with a 15 wt % loading at the same condition (4.9 ± 1.4 wt % yield). The reasons for this effect and the influence of this process variable on outcomes for fast HTL are topics for further study. The protein component in food waste can be processed via fast HTL to recover both energy (biocrude) and nutrients to grow more food (aqueous-phase N and P). The highest set-
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.8b01368. Figure S1: Temperature profiles of proxy reactor at sand bath set-point temperatures of (a) 290, 350 °C − isothermal HTL and (b) 450, 500, 550, and 600 °C − fast HTL Figure S2: HHV of feed and biocrude (left axis) and energy recovery in biocrude (right axis) from fast HTL (600 °C, 1 min) of different ternary mixtures. (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Akhila Gollakota: 0000-0002-1281-3979 Phillip E. Savage: 0000-0002-7902-3744 Notes
The authors declare no competing financial interest. H
DOI: 10.1021/acssuschemeng.8b01368 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
Research Article
ACS Sustainable Chemistry & Engineering
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(23) Déniel, M.; Haarlemmer, G.; Roubaud, A.; Weiss-Hortala, E.; Fages, J. Energy valorisation of food processing residues and model compounds by hydrothermal liquefaction. Renewable Sustainable Energy Rev. 2016, 54, 1632−1652. (24) Faeth, J. L.; Valdez, P. J.; Savage, P. E. Fast Hydrothermal Liquefaction of Nannochloropsis sp. To Produce Biocrude. Energy Fuels 2013, 27 (3), 1391−1398. (25) Bach, Q.-V.; Sillero, M. V.; Tran, K.-Q.; Skjermo, J. Fast hydrothermal liquefaction of a Norwegian macro-alga: screening tests. Algal Res. 2014, 6, 271−276. (26) Zhang, B.; von Keitz, M.; Valentas, K. Thermal effects on hydrothermal biomass liquefaction. Appl. Biochem. Biotechnol. 2008, 147 (1−3), 143−150. (27) Valdez, P. J.; Nelson, M. C.; Faeth, J. L.; Wang, H. Y.; Lin, X. N.; Savage, P. E. Hydrothermal liquefaction of bacteria and yeast monocultures. Energy Fuels 2014, 28 (1), 67−75. (28) Sheehan, J. D.; Savage, P. E. Products, Pathways, and Kinetics for the Fast Hydrothermal Liquefaction of Soy Protein Isolate. ACS Sustainable Chem. Eng. 2016, 4 (12), 6931−6939. (29) Sheehan, J. D.; Savage, P. E. Molecular and Lumped Products from Hydrothermal Liquefaction of Bovine Serum Albumin. ACS Sustainable Chem. Eng. 2017, 5 (5), 10967−10975. (30) Qian, L.; Wang, S.; Savage, P. E. Hydrothermal liquefaction of sewage sludge under isothermal and fast conditions. Bioresour. Technol. 2017, 232, 27−34. (31) Posmanik, R.; Cantero, D. A.; Malkani, A.; Sills, D. L.; Tester, J. W. Biomass conversion to bio-oil using sub-critical water: Study of model compounds for food processing waste. J. Supercrit. Fluids 2017, 119, 26−35. (32) Li, F.; Liu, L.; An, Y.; He, W.; Themelis, N. J.; Li, G. Hydrothermal liquefaction of three kinds of starches into reducing sugars. J. Cleaner Prod. 2016, 112, 1049−1054. (33) Gui, M. M.; Lee, K.; Bhatia, S. Feasibility of edible oil vs. nonedible oil vs. waste edible oil as biodiesel feedstock. Energy 2008, 33 (11), 1646−1653. (34) Edgell, K. SW-846 Method 3050B: Acid Digestion of Sediments, Sludges, and Soils; U.S. Environmental Protection Agency, Environmental Monitoring Systems Laboratory, 1989. (35) SW-846 Method 6010D: Inductively Coupled Plasma-Optical Emission Spectrometry, July 2014. U.S. Environmental Protection Agency. https://www.epa.gov/sites/production/files/2015-12/ documents/6010d.pdf (assessed May 2018). (36) Teri, G.; Luo, L.; Savage, P. E. Hydrothermal Treatment of Protein, Polysaccharide, and Lipids Alone and in Mixtures. Energy Fuels 2014, 28 (12), 7501−7509. (37) Biller, P.; Ross, A. B. Potential yields and properties of oil from the hydrothermal liquefaction of microalgae with different biochemical content. Bioresour. Technol. 2011, 102 (1), 215−25. (38) Yang, W.; Li, X.; Li, Z.; Tong, C.; Feng, L. Understanding lowlipid algae hydrothermal liquefaction characteristics and pathways through hydrothermal liquefaction of algal major components: Crude polysaccharides, crude proteins and their binary mixtures. Bioresour. Technol. 2015, 196, 99−108. (39) Yin, S.; Tan, Z. Hydrothermal liquefaction of cellulose to bio-oil under acidic, neutral and alkaline conditions. Appl. Energy 2012, 92, 234−239. (40) Qu, Y.; Wei, X.; Zhong, C. Experimental study on the direct liquefaction of Cunninghamia lanceolata in water. Energy 2003, 28 (7), 597−606. (41) Akhtar, J.; Amin, N. A. S. A review on process conditions for optimum bio-oil yield in hydrothermal liquefaction of biomass. Renewable Sustainable Energy Rev. 2011, 15 (3), 1615−1624. (42) Déniel, M.; Haarlemmer, G.; Roubaud, A.; Weiss-Hortala, E.; Fages, J. Hydrothermal liquefaction of blackcurrant pomace and model molecules: understanding of reaction mechanisms. Sustain. Energy Fuels 2017, 1 (3), 555−582. (43) Promdej, C.; Matsumura, Y. Temperature effect on hydrothermal decomposition of glucose in sub-and supercritical water. Ind. Eng. Chem. Res. 2011, 50 (14), 8492−8497.
REFERENCES
(1) Gustavsson, J.; Cederberg, C.; Sonesson, U.; Otterdijk, R. v.; Meybeck, A. Global Food Losses and Food Waste − Extent, Causes and Prevention; FAO, 2011.. (2) Lee, D. H.; Behera, S. K.; Kim, J. W.; Park, H.-S. Methane production potential of leachate generated from Korean food waste recycling facilities: a lab-scale study. Waste Manage. 2009, 29 (2), 876−882. (3) Viganó, J.; Machado, A. P. d. F.; Martínez, J. Sub- and supercritical fluid technology applied to food waste processing. J. Supercrit. Fluids 2015, 96, 272−286. (4) Vardanega, R.; Prado, J. M.; Meireles, M. A. A. Adding value to agri-food residues by means of supercritical technology. J. Supercrit. Fluids 2015, 96, 217−227. (5) Wang, X.; Chen, Q.; Lü, X. Pectin extracted from apple pomace and citrus peel by subcritical water. Food Hydrocolloids 2014, 38, 129− 137. (6) Grycova, B.; Pryszcz, A.; Lestinsky, P.; Chamradova, K. Preparation and characterization of sorbents from food waste. Green Process. Synth. 2017, 6 (3), 287−293. (7) Tu, Y.; Huang, J.; Xu, P.; Wu, X.; Yang, L.; Peng, Z. Subcritical Water Hydrolysis Treatment of Waste Biomass for Nutrient Extraction. BioResources 2016, 11 (2), 5389−5403. (8) Banik, S.; Nag, D.; Debnath, S. Utilization of pineapple leaf agrowaste for extraction of fibre and the residual biomass for vermicomposting. Indian J. Fibre Text. Res. 2011, 172−177. (9) Holm-Nielsen, J. B.; Al Seadi, T.; Oleskowicz-Popiel, P. The future of anaerobic digestion and biogas utilization. Bioresour. Technol. 2009, 100 (22), 5478−5484. (10) Li, Y.; Park, S. Y.; Zhu, J. Solid-state anaerobic digestion for methane production from organic waste. Renewable Sustainable Energy Rev. 2011, 15 (1), 821−826. (11) Bouallagui, H.; Touhami, Y.; Cheikh, R. B.; Hamdi, M. Bioreactor performance in anaerobic digestion of fruit and vegetable wastes. Process Biochem. 2005, 40 (3), 989−995. (12) Sundberg, C. Food Waste Composting − Effects of Heat, Acids and Size; Report 254; Swedish University of Agricultural Sciences, Department of Agricultural Engineering: Uppsala, Sweden, 2003. (13) Saer, A.; Lansing, S.; Davitt, N. H.; Graves, R. E. Life cycle assessment of a food waste composting system: environmental impact hotspots. J. Cleaner Prod. 2013, 52, 234−244. (14) Kim, J. K.; Oh, B. R.; Shin, H.-J.; Eom, C.-Y.; Kim, S. W. Statistical optimization of enzymatic saccharification and ethanol fermentation using food waste. Process Biochem. 2008, 43 (11), 1308− 1312. (15) Kim, J. H.; Lee, J. C.; Pak, D. Feasibility of producing ethanol from food waste. Waste Manage. 2011, 31 (9), 2121−2125. (16) Hammond, J. B.; Egg, R.; Diggins, D.; Coble, C. G. Alcohol from bananas. Bioresour. Technol. 1996, 56 (1), 125−130. (17) Arapoglou, D.; Varzakas, T.; Vlyssides, A.; Israilides, C. Ethanol production from potato peel waste (PPW). Waste Manage. 2010, 30 (10), 1898−1902. (18) Pham, T. P. T.; Kaushik, R.; Parshetti, G. K.; Mahmood, R.; Balasubramanian, R. Food waste-to-energy conversion technologies: current status and future directions. Waste Manage. 2015, 38, 399− 408. (19) Grycová, B.; Koutník, I.; Pryszcz, A. Pyrolysis process for the treatment of food waste. Bioresour. Technol. 2016, 218, 1203−1207. (20) Peterson, A. A.; Vogel, F.; Lachance, R. P.; Fröling, M.; Antal, J. M.; Tester, J. W. Thermochemical biofuel production in hydrothermal media: A review of sub- and supercritical water technologies. Energy Environ. Sci. 2008, 1 (1), 32. (21) Akiya, N.; Savage, P. E. Roles of water for chemical reactions in high-temperature water. Chem. Rev. 2002, 102 (8), 2725−2750. (22) Pavlovic, I.; Knez, Z.; Skerget, M. Hydrothermal reactions of agricultural and food processing wastes in sub- and supercritical water: a review of fundamentals, mechanisms, and state of research. J. Agric. Food Chem. 2013, 61 (34), 8003−25. I
DOI: 10.1021/acssuschemeng.8b01368 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
Research Article
ACS Sustainable Chemistry & Engineering
glycine interactions in high-temperature, high-pressure water. Ind. Eng. Chem. Res. 2010, 49 (5), 2107−2117. (65) Bailey, R. G.; Ames, J. M.; Mann, J. Identification of new heterocyclic nitrogen compounds from glucose-lysine and xyloselysine Maillard model systems. J. Agric. Food Chem. 2000, 48 (12), 6240−6246. (66) Zhang, C.; Tang, X.; Sheng, L.; Yang, X. Enhancing the performance of Co-hydrothermal liquefaction for mixed algae strains by the Maillard reaction. Green Chem. 2016, 18 (8), 2542−2553. (67) Hadhoum, L.; Balistrou, M.; Burnens, G.; Loubar, K.; Tazerout, M. Hydrothermal liquefaction of oil mill wastewater for bio-oil production in subcritical conditions. Bioresour. Technol. 2016, 218, 9− 17.
(44) Dote, Y.; Inoue, S.; Ogi, T.; Yokoyama, S.-y. Studies on the direct liquefaction of protein-contained biomass: the distribution of nitrogen in the products. Biomass Bioenergy 1996, 11 (6), 491−498. (45) Luo, L.; Sheehan, J. D.; Dai, L.; Savage, P. E. Products and kinetics for isothermal hydrothermal liquefaction of soy protein concentrate. ACS Sustainable Chem. Eng. 2016, 4 (5), 2725−2733. (46) Powell, T.; Bowra, S.; Cooper, H. J. Subcritical Water Processing of Proteins: An Alternative to Enzymatic Digestion? Anal. Chem. 2016, 88 (12), 6425−6432. (47) Speight, J. G. Handbook of Petroleum Product Analysis; John Wiley & Sons, 2015. (48) Garcia Alba, L.; Torri, C.; Fabbri, D.; Kersten, S. R. A.; Brilman, D. W. F. Microalgae growth on the aqueous phase from Hydrothermal Liquefaction of the same microalgae. Chem. Eng. J. 2013, 228, 214− 223. (49) Valdez, P. J.; Nelson, M. C.; Wang, H. Y.; Lin, X. N.; Savage, P. E. Hydrothermal liquefaction of Nannochloropsis sp.: Systematic study of process variables and analysis of the product fractions. Biomass Bioenergy 2012, 46, 317−331. (50) Biller, P.; Ross, A. B.; Skill, S. C.; Lea-Langton, A.; Balasundaram, B.; Hall, C.; Riley, R.; Llewellyn, C. A. Nutrient recycling of aqueous phase for microalgae cultivation from the hydrothermal liquefaction process. Algal Res. 2012, 1 (1), 70−76. (51) Jiang, J.; Savage, P. E. Metals and Other Elements in Biocrude from Fast and Isothermal Hydrothermal Liquefaction of Microalgae. Energy Fuels 2018, 32, 4118. (52) Ekpo, U.; Ross, A.; Camargo-Valero, M.; Williams, P. A comparison of product yields and inorganic content in process streams following thermal hydrolysis and hydrothermal processing of microalgae, manure and digestate. Bioresour. Technol. 2016, 200, 951−960. (53) Garcia Alba, L.; Torri, C.; Samorì, C.; van der Spek, J.; Fabbri, D.; Kersten, S. R.; Brilman, D. W. Hydrothermal treatment (HTT) of microalgae: evaluation of the process as conversion method in an algae biorefinery concept. Energy Fuels 2012, 26 (1), 642−657. (54) Yu, G.; Zhang, Y.; Guo, B.; Funk, T.; Schideman, L. Nutrient flows and quality of bio-crude oil produced via catalytic hydrothermal liquefaction of low-lipid microalgae. BioEnergy Res. 2014, 7 (4), 1317− 1328. (55) Changi, S. M.; Faeth, J. L.; Mo, N.; Savage, P. E. Hydrothermal Reactions of Biomolecules Relevant for Microalgae Liquefaction. Ind. Eng. Chem. Res. 2015, 54 (47), 11733−11758. (56) Catallo, W. J.; Shupe, T. F.; Comeaux, J. L.; Junk, T. Transformation of glucose to volatile and semi-volatile products in hydrothermal (HT) systems. Biomass Bioenergy 2010, 34 (1), 1−13. (57) Madsen, R. B.; Zhang, H.; Biller, P.; Goldstein, A. H.; Glasius, M. Characterizing Semivolatile Organic Compounds of Biocrude from Hydrothermal Liquefaction of Biomass. Energy Fuels 2017, 31 (4), 4122−4134. (58) Guo, Y.; Yeh, T.; Song, W.; Xu, D.; Wang, S. A review of bio-oil production from hydrothermal liquefaction of algae. Renewable Sustainable Energy Rev. 2015, 48, 776−790. (59) Cox, J. S.; Seward, T. M. The reaction kinetics of alanine and glycine under hydrothermal conditions. Geochim. Cosmochim. Acta 2007, 71 (9), 2264−2284. (60) Klingler, D.; Berg, J.; Vogel, H. Hydrothermal reactions of alanine and glycine in sub-and supercritical water. J. Supercrit. Fluids 2007, 43 (1), 112−119. (61) Alenezi, R.; Leeke, G. A.; Santos, R. C. D.; Khan, A. R. Hydrolysis kinetics of sunflower oil under subcritical water conditions. Chem. Eng. Res. Des. 2009, 87 (6), 867−873. (62) Jamieson, G. S.; Baughman, W. F. The chemical composition of sunflower-seed oil. J. Am. Chem. Soc. 1922, 44 (12), 2952−2957. (63) Chiaberge, S.; Leonardis, I.; Fiorani, T.; Bianchi, G.; Cesti, P.; Bosetti, A.; Crucianelli, M.; Reale, S.; De Angelis, F. Amides in bio-oil by hydrothermal liquefaction of organic wastes: a mass spectrometric study of the thermochemical reaction products of binary mixtures of amino acids and fatty acids. Energy Fuels 2013, 27 (9), 5287−5297. (64) Peterson, A. A.; Lachance, R. P.; Tester, J. W. Kinetic evidence of the Maillard reaction in hydrothermal biomass processing: glucose− J
DOI: 10.1021/acssuschemeng.8b01368 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
