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Understanding the fate of nitrogen in food waste hydrothermal liquefaction.

Converting the chemical and biologically resistant structure of cellulosic biomass into useful products is a technological and economic challenge. The use of sustainable and efficient conversion technology sustainably has been gaining prominence. This work aimed to evaluate the integration of subcritical water hydrolysis (SWH) and enzymatic hydrolysis of sugarcane straw to obtain fermentable products and second-generation ethanol. SWH was conducted under semi-continuous conditions at 200 °C, 5 mL/min, and a 19-min retention time. Enzymatic hydrolysis using an enzyme blend produced simple sugars that were evaluated for fermentation using two strategies: (i) Saccharomyces cerevisiae SA-1; and (ii) co-culture of S. cerevisiae SA-1 and Scheffersomyces stipitis NRRLY-7124. Integrating subcritical water and enzymatic hydrolysis resulted in greater fermentable sugar yield (2.40 ± 0.01 g/L of xylose and 8.9 ± 0.6 g/L of glucose) than subcritical pre-treatment on its own. The co-culture fermentation strategy was more efficient than fermentation by S. cerevisiae on its own, resulting in 2.8 ± 0.3 g/L of ethanol. Subcritical water hydrolysis pre-treatment disrupted the lignocellulosic matrix, leading to increased enzymatic accessibility of cellulose, with minimal formation of degradation compounds, and with minimal waste formation. Future work can optimize the hydrolysis process to increase the yield of simple sugars, increase fermentation efficiency by controlling oxygen concentration and removing acetic acid, and consequently increase the yields of second-generation ethanol. more...

The use of nonaqueous solvents for conversion of biomass molecules into platform chemicals and fuels is hindered by a lack of solubility data and models. Accordingly, the solubility of the model ca... more...

Nickel (Ni)-impregnated metal oxide catalysts, Ni/CeZrOx, Ni/ZrO2, and Ni/CeO2, were investigated to maximize energy recovery and reduce char yield during catalytic hydrothermal liquefaction (CHTL) of food waste. Yields of char, biocrude, water soluble products, and gas were measured at 300 °C and 1 hour for both the parent oxides (CeZrOx, ZrO2, and CeO2) and the Ni-impregnated versions. Using Ni-based catalysts reduced the carbon-weighted char yield from 16–24% to 60%. Ni/ZrO2 and Ni/CeO2 show the greatest potential for controlling char growth and maximizing energy recovered from food waste. The crystalline structures of all three oxides were hydrothermally stable. Catalyst reuse tests indicate that the biocrude and char yields remained the same for the first and second use (within uncertainty) and that the catalyst retains its initial crystallinity and 93% of its initial Ni content. Molecular composition of biocrudes analyzed by the state-of-the-art analytical platforms (including GC-MS, GC × GC, FT-ICR MS, and 1H NMR) revealed minor differences in the chemical constituents of biocrudes obtained using different catalysts and provided some insight regarding reaction mechanism. more...

Increasing the stability of zeolites in liquid, near-critical, and supercritical water at temperatures greater than 200 °C is required for many important chemical processes, notably including hydro... more...

Industrial wastes and natural mixed oxide materials were evaluated as inexpensive heterogeneous catalysts for catalytic hydrothermal liquefaction (CHTL) of food wastes. Red mud and red clay achieve... more...

Food waste is an abundant and inexpensive resource for the production of renewable fuels. Biocrude yields obtained from hydrothermal liquefaction (HTL) of food waste can be boosted using hydroxyapatite (HAP) as an inexpensive and abundant catalyst. Combining HAP with an inexpensive homogeneous base increased biocrude yield from 14 ± 1 to 37 ± 3%, resulting in the recovery of 49 ± 2% of the energy contained in the food waste feed. Detailed product analysis revealed the importance of fatty-acid oligomerization during biocrude formation, highlighting the role of acid-base catalysts in promoting condensation reactions. Economic and environmental analysis found that the new technology has the potential to reduce US greenhouse gas emissions by 2.6% while producing renewable diesel with a minimum fuel selling price of $1.06/GGE. HAP can play a role in transforming food waste from a liability to a renewable fuel. more...

Significance Plastic waste accumulating in the world's oceans forms massive “plastic islands” in the oceanic gyres. Removing the plastic offers an opportunity to restore our oceans to a more pristine state. To clean the gyres, ships must collect and store the plastic before transporting it to port, often thousands of kilometers away. Instead, ocean plastic waste can be converted into fuel shipboard, for example, using hydrothermal liquefaction (HTL), which depolymerizes plastics at high temperature (300 °C to 550 °C) and high pressure (250 bar to 300 bar). The resulting depolymerization products, termed “blue diesel,” have the potential for self-powered cleanup. The objective of this work is evaluating the thermodynamic feasibility of this scheme and its implications on cleanup., Collecting and removing ocean plastics can mitigate their environmental impacts; however, ocean cleanup will be a complex and energy-intensive operation that has not been fully evaluated. This work examines the thermodynamic feasibility and subsequent implications of hydrothermally converting this waste into a fuel to enable self-powered cleanup. A comprehensive probabilistic exergy analysis demonstrates that hydrothermal liquefaction has potential to generate sufficient energy to power both the process and the ship performing the cleanup. Self-powered cleanup reduces the number of roundtrips to port of a waste-laden ship, eliminating the need for fossil fuel use for most plastic concentrations. Several cleanup scenarios are modeled for the Great Pacific Garbage Patch (GPGP), corresponding to 230 t to 11,500 t of plastic removed yearly; the range corresponds to uncertainty in the surface concentration of plastics in the GPGP. Estimated cleanup times depends mainly on the number of booms that can be deployed in the GPGP without sacrificing collection efficiency. Self-powered cleanup may be a viable approach for removal of plastics from the ocean, and gaps in our understanding of GPGP characteristics should be addressed to reduce uncertainty. more...

Raman spectroscopy of network solids such as zeolites is critical for shedding light on collective vibrations of medium-range structures such as rings that exist in crystals and that form during crystallization processes. Despite this importance, assignments of Raman spectra are not completely understood, though it is often assumed that Raman bands can be assigned to individual rings. We report a systematic zeolite synthesis, spectroscopy, and periodic DFT study of several all-silica zeolites to test this assumption and to determine the fundamental structural motifs that explain Raman spectral features. We have discovered from normal-mode analysis that Raman bands can be assigned to tricyclic bridges-three zeolite rings that share a common Si-O-Si bridge. Furthermore, we have found that the vibrational frequency of a given Raman band can be correlated to the smallest ring of its tricyclic bridge and not to the ring that is actually vibrating. Finally, we have discovered a precise anticorrelation between Raman frequency and Si-O-Si angle. These discoveries open new ways to investigate structures of network materials made of corner-sharing tetrahedra and to study crystallization from amorphous gels where structural information is limited. more...

Surface free energy remains a fundamental material property to characterize the interfacial interactions between liquid and solid. Here, we developed a precise approach to determine surface energy by using contact angles of binary mixtures of water-dimethyl sulfoxide (DMSO), water-formamide, water-ethylene glycol, and water-glycerol and analyzed using the Owens-Wendt method. A mixing equation was developed to estimate liquid-dispersive surface tension (γL,mixd) and polar surface tension (γL,mixp) parameters for binary mixtures. To test the approach, two hydrophobic surfaces, flat polydimethylsiloxane (PDMS), and silane-derivatized glass were prepared and the contact angle of mixtures on the surfaces were obtained. Surface energy of PDMS determined by three binary mixtures agrees with that from pure solvents, but the uncertainty decreases to less than 13%; remarkably, the uncertainty drops to around 5% once we combined measured contact angles from all the mixtures, namely, water-DMSO, water-formamide, and water-ethylene glycol. Surface energies of silane-derivatized glass bearing ethyl (C2), hexyl (C6), and octadecyl (C18) alkyl chains were determined with water-formamide and water-glycerol mixtures. Measured contact angles fit the Owens-Wendt model, and surface energy value determined from different binary mixtures agree with each other within error. Contact angle measurement of liquid mixtures is a simple method for determination of surface energy that improves the precision of surface energy determined by measurements of multiple pure solvents. more...

The fine particulate matter (PM) emissions from the use of two types of Fischer-Tropsch aviation fuels and their 50:50 blends with military JP-8 were quantified as part of the first Alternative Aviation Fuel Experiment (AAFEX). Measurements were made at 30-m downstream of a CFM56–2C1 engine for PM mass and number, particle size distribution, black carbon (BC), and volatile PM (sulfate + organics) using selected on-line instrumentation. The PM number emission index (EI(N)) ranged from ~ 2 × 10(15) to 7 × 10(16) particles/kg fuel burned depending on fuel flow, fuel composition, and sampling temperature with the magnitude of the emissions inversely correlated to fuel flow. The PM mass emissions (EI(M)) measured in the study varied from ~ 5 to 680 mg/kg fuel again depending on fuel flow, fuel type, and sampling temperature with a characteristic U-shaped curve of EI(M) with respect to fuel flow observed from the data. At low fuel flow (corresponding to low engine power), particle number and volume size distributions contained a single mode whereas at higher engine power, a bi-modal distribution was observed. The BC emissions varied from ~ 3 to 415 mg/kg fuel depending on fuel type and were found to exponentially increase with engine power (fuel flow). The volatile PM varied with sample temperature, fuel type, and increasing fuel flow within the range of EIs from ~ 0.4 to 11 mg/kg fuel with the highest values being at low fuel flow. Finally, the use of the two neat alternative fuels reduced the EI(N) by a median value of 70–73% and the EI(M) by ~ 94% as compared to JP-8 across all power conditions tested. more...

Chemical modification and microwave activation are cost-effective and eco-friendly engineering methods to improve biochar’s physicochemical and adsorption performance. Therefore, a series of biochars samples was produced by pyrolysis at 500 °C in the presence of phosphoric acid (H3PO4) without and with microwave (MW) irradiation of the raw tea waste (RTW). Effect of acid and MW activation on the characteristics of biochar was compared with biochars produced from pyrolysis of RTW at 300, 500, 700, and 900 °C. Pyrolysis in the presence of H3PO4 promoted the formation of oxygen-containing functional groups and increased the surface area of the biochar product (931 m2 g–1 compared with 13.6 m2 g–1). Compared with biochars obtained from acid-assisted pyrolysis, MW activation nearly doubled the measured surface area (1763 m2 g–1) by the formation of a micropore structure and required seconds instead of hours to perform. Heavy metal adsorption capacities observed for the acid-activated chars were comparable to biochar samples produced in the temperature range of 500–900 °C, but acid-promoted activation required much lower temperatures, and the effects of activation depended on the metal, the solution pH, and the activation treatment. Specifically, acid promotion increased Cu and Cd sorption capacity, attributable to the increased surface area and increased surface densities of oxygen functional groups (C = O and OH). The results of ternary-metal adsorption results demonstrated the competitive adsorption between three metals, and the affinity sequence of biochar produced at 900 °C (BC900) was found as Pb(II) > Cd(II) > Cu(II). However, the metal affinity sequence of BC900 to single metal is Pb(II) > Cu(II) > Cd(II). FTIR and SEM–EDS results revealed that Pb(II) had the same adsorption sites with Cu(II), but Pb(II) has a greater affinity than Cu(II). Kinetic measurements and spectroscopic analysis indicated that Pb, Cu, and Cd form chemical complexes on the surface. These results provide new insight on the utilization of tea wastes for heavy metal removal from aqueous streams. more...

Waste contributes to environmental, health, economic, and climate problems. Yet waste is not inevitable, but rather a consequence of perception. Organizing physical, biological, and social scientists, engineers, and economists around the theme of waste elimination will reap a harvest of clean energy, a more natural environment, better health outcomes at lower costs, and a more equitable society. The price of action will be high; the price of inaction will be even greater. more...

The objective of this work was to produce C-5 sugars from the hydrolysis of the spent grains of the brewery. The total sugar recovery and formation of by-products were evaluated as a function of the reaction temperature (140, 160, 180 and 210 °C), flow rate (10 and 20 mL min–1) and the solvent/feed ratio (S/F: 64, 80 and 112). The total carbohydrate yields were dependent on the hydrolysis temperature. Arabinose was the main product, followed by xylose and the arabinose yield increased with increasing the S/F ratio and the flow rate. Yields of furfural were sensitive to flow rate. The hemicellulose content of the residual solids was reduced by approximately 90% after hydrolysis, with the parallel formation of carbonyl and carbonized species. The effects of flow rate on the efficiency of converting hemicellulose into simple sugars were complex, suggesting roles for the formation of autocatalytic acids. more...

Mechanical decrystallization and water-promoted recrystallization of cellulose were studied to understand the effects of cellulose crystallinity on reaction engineering models of its acid-catalyzed hydrolysis. Microcrystalline cellulose was ball-milled for different periods of time, which decreased its crystallinity and increased the glucose yield obtained from acid hydrolysis treatment. Crystallinity increased after acid hydrolysis treatment, which has previously been explained in terms of rapid hydrolysis of amorphous cellulose, despite conflicting evidence of solvent promoted recrystallization. To elucidate the mechanism, decrystallized samples were subjected to various non-hydrolyzing treatments involving water exposure. Interestingly, all non-hydrolyzing hydrothermal treatments resulted in recovery of crystallinity, including a treatment consisting of heat-up and quenching that was selected as a way to estimate the crystallinity at the onset of hydrolysis. Therefore, the proposed mechanism involving rapid hydrolysis of amorphous cellulose must be incomplete, since the recrystallization rate of amorphous cellulose is greater than the hydrolysis rate. Several techniques (solid-state nuclear magnetic resonance, X-ray diffraction, and Raman spectroscopy) were used to establish that water contact promotes conversion of amorphous cellulose to a mixture of crystalline cellulose I and cellulose II. Crystallite size may also be reduced by the decrystallization-recrystallization treatment. Ethanolysis was used to confirm that the reactivity of the cellulose I/cellulose II mixture is distinct from that of truly amorphous cellulose. These results strongly point to a revised, more realistic model of hydrolysis of mechanically decrystallized cellulose, involving recrystallization and hydrolysis of the cellulose I/cellulose II mixture. more...

Zeolites have recently attracted attention for upgrading renewable resources in the presence of liquid water phases; however, the stability of zeolites in the presence of liquid-phase water is not completely understood. Accordingly, the stability of the ZSM-5 framework and its acid sites was studied in the presence of water at temperatures ranging from 250 to 450 °C and at pressures sufficient to maintain a liquid or liquid-like state (25 MPa). Treated samples were analyzed for framework degradation and Al content and coordination using a variety of complementary techniques, including X-ray diffraction, electron microscopy, N2 sorption, 27Al and 29Si NMR spectroscopy, and several different types of infrared spectroscopy. These analyses indicate that the ZSM-5 framework retains >80% crystallinity at all conditions, and that 300–400 °C are the most aggressive. Decrystallization appears to initiate primarily at crystal surfaces and share many characteristics in common with alkali promoted desilication. Liquid water treatment promotes ZSM-5 dealumination, following a mechanism analogous to that observed under steaming conditions: initiation by Al–O hydrolysis, Al migration to the surface, and finally deposition as extra framework Al or possibly complete dissolution under some conditions. As with the framework, dealumination is most aggressive at 300–400 °C. Several models were evaluated to capture the non-Arrhenius effect of temperature on decrystallization and dealumination, the most successful of which included temperature dependent values of the water auto-ionization constant. These results can help interpretation of previous studies on ZSM-5 catalysis in hot liquid water and suggest future approaches to extend catalyst lifetime. more...

ZSM-5, HY, and β zeolites were tested for cracking supercritical dodecane (SCD) in the presence and absence of supercritical water (SCW). A key experimental advantage of operating at supercritical conditions is that SCW and SCD are completely miscible, eliminating uncertainty introduced by liquid-liquid mass transport. As expected, all three zeolites were active in the absence of SCW, resulting in 70–80% dodecane conversion after 2 h at 400 °C. In the presence of SCW, only ZSM-5 retained activity, with a measured dodecane conversion of approximately 35%. Post-reaction characterization of the zeolites indicated that only ZSM-5 retained crystallinity, suggesting that access to acid sites decreases when the Y and β zeolites decrystallize. Although ZSM-5 retained crystallinity after exposure to the SCD/SCW reaction mixture, its BAS density decreased by >95% and its micropore area decreased by 80%. Interestingly, while the SCW environment decreases ZSM-5 activity, the reduction is not consistent with the magnitude of the reduction in BAS or micropore area. The apparent contradiction suggested that some material other than ZSM-5 may play the role of catalyst and extensive tests were performed to verify that acid sites on ZSM-5 remained catalytically active in the presence of SCW. Catalyst reuse experiments indicated that ZSM-5 can be reused in SCW. Additional tests with Na-ZSM-5, silicalite, alumina, coke, silicic acid, Al(NO3)3, HNO3, and the supernatant liquid recovered after reaction failed to identify any material other than ZSM-5 that could act as a catalyst. Therefore, ZSM-5 must act as an acid catalyst, even in the presence of SCW and despite loss of many of its acid sites. In contrast, HY and β do not. This work helps guide future work on the use of zeolites in the presence of liquid water and dense supercritical water phases. more...

Successful Food-energy-water (FEW) nexus projects will be more likely to succeed if a transdisciplinary approach is used. Ecological modernization (ecological technology) policies and practices, and sustainable supply chains influence the FEW nexus from a commerce and industry perspective. Taking these perspectives and considering their intertwined linkages is important for advancing research and adoption of FEW nexus efforts. This paper provides an overview of these perspectives and interlinkages. A biosolids case study is used to exemplify the complexities and interactions of these four thematic perspectives: the FEW nexus, transdisciplinarity, ecological modernization, and sustainable supply chains. An integrative multi-level analysis scheme is used to analyze interrelationships. This analysis and the case study help to identify a series of research opportunities to further this nascent field. Research opportunities include methodological developments, attitudinal and social concerns, performance indicator systems, and meta-social evolutions in technology and policy. more...

This study assessed the subcritical water hydrolysis (SWH) of poultry feathers to recover amino acids. Experiments were conducted in a semi-continuous flow-through subcritical reactor (110 mL), which was operated over a range of temperatures (210–250 °C) and water flow rates (5–15 mL min–1), combined through a 22 central composite design, at constant feed (10 g) and pressure (15 MPa). The results demonstrated that non-essential and essential amino acids were obtained from SWH of poultry feathers. The highest hydrolysis temperature resulted in the highest concentrations of valine, methionine, tryptophan, phenylalanine, isoleucine, leucine, and lysine. Otherwise, threonine, histidine, and arginine were obtained more effectively at lower temperatures. The response surface methodology was adopted to identify the best conditions for amino acid production, and it was possible to identify the ranges of temperatures and water flow rates to be used to recover specific amino acids. This study allowed concluding that SWH is a promising eco-friendly technology to recover amino acids from protein-rich wastes. more...

Supercritical water assisted aromatization (SCWA) using ZSM-5 was examined for conversion of dodecane and an atmospheric distillate into benzene, toluene, ethyl benzene, and xylene (BTEX) products. When compared with observations made in the absence of water, addition of 15 wt% or less water resulted in several benefits, including enhanced dodecane conversion rate, decreased formation of coke and coke precursors, and increased BTEX yields, retention of crystallinity (>90%), and retention of Bronsted acid site (BAS) density (60%). In contrast, addition of ≥ 25 wt% water resulted in reduced dodecane cracking rate, reduced aromatic production, decreased crystallinity ( more...

In this work, mechanochemical pretreatment of Bambusa vulgaris is evalu-ated for waste-free production of renewable sugars for subsequent fermen-tation. After a 60 min mechanochemical pretreatment followed by enzyme hydrolysis at 50 °C, 62% of the available carbohydrate can be recovered as fermentable sugars, primarily in the form of glucose and xylose. Structural and chemical analysis finds that mechanochemical pretreatment increases accessible surface area and amorphizes the crystalline cellulose present in bamboo, both of which increase reactivity. The experimental results are then used for a systems-level analysis of ethanol production in Nigeria. The energy required for mechanochemical pretreatment is estimated to be 0.5–5.6 MJ per kg of bamboo; this energy can be provided by solar power, while still satis-fying existing needs for stationary power. Ethanol production on marginal land alone is projected to be sufficient to replace nearly 80% of Nigeria's current gasoline usage while reserving sufficient land area for solar power generation to meet current electricity needs, meaning that bamboo cultiva-tion followed by mechanochemical pretreatment can play an important role for utilizing locally available resources without generation of new chemical wastes.N. B. Ekwe, M. V. Tyufekchiev, G. A. Tompsett, H. O. LeClerc, E. R. Belden, M. T. TimkoDepartment of Chemical EngineeringWorcester Polytechnic Institute100 Institute Road Worcester, MA 01609, USAE-mail: mttimko@wpi.eduN. B. Ekwe, A. A. Salifu, E. O. Onche, W. O. SoboyejoDepartment of Materials Science and EngineeringAfrican University of Science and Technology (AUST)Abuja, NigeriaN. B. EkweDepartment of Chemical EngineeringUniversity of AbujaAbuja, NigeriaThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adsu.202100286.A. A. Salifu, W. O. SoboyejoDepartment of Biomedical EngineeringWorcester Polytechnic Institute60 Prescott StreetGateway Park Life Sciences and Bioengineering CenterWorcester, MA 01609, USAA. A. Salifu, W. O. SoboyejoMechanical Engineering Department and Materials Science and Engineering ProgramWorcester Polytechnic Institute100 Institute RoadWorcester, MA 01609, USAA. AtesDepartment of Chemical EngineeringEngineering FacultySivas Cumhuriyet UniversitySivas 58140, TurkeyK. Schmidt-Rohr, S. Yuan, Z. ZhengDepartment of ChemistryBrandeis University415 South Street, Waltham, MA 02453, USAAdv. Sustainable Syst.2022, 6, 2100286 more...

Arabian Heavy crude oil was fractionated into distillate and vacuum residue fractions. The vacuum residue fraction was treated with supercritical water (SCW) at 450°C in a batch reactor for 15 to 90 minutes. The main products were gas, coke, and upgraded vacuum residue; the upgraded residue consisted of gasoline, diesel, and vacuum gas oil range components. The molecular composition of gas and upgraded vacuum residue was analyzed using gas chromatography (GC, GC×GC). SCW treatment converted higher carbon number aliphatics (≥ C[subscript 21]) and long chain (≥ C[subscript 5]) alkyl aromatic compounds into C[subscript 1]-C[subscript 20] aliphatics, C[subscript 1]-C[subscript 10] alkylaromatics and multi-ringed species. The concentrations of gasoline and diesel range compounds were greater in the upgraded product, compared to the feed. A first-order, five lump reaction network was developed to fit the yields of gas, coke, diesel and gasoline range components obtained from SCW upgrading of vacuum residue. Distillation of crude oil followed by SCW treatment of the heavy fraction approximately doubled the yield of chemicals, gasoline, and diesel, while forming significantly less coke than conventional upgrading methods. more...

This work presents a detailed structure–activity analysis of a polymeric solid acid catalyst used in cellulose hydrolysis. In contrast to previous work, our studies show that the high catalytic act... more...

Density Functional Theory (DFT) and experimental measurements were used to develop a systematic method for interpreting the Raman spectra of hydrothermal char (hydrochar). Average band locations, relative intensities, and their trends relative to structural features were determined for the G, D, and Kekule bands. When combined with several other less prominent vibrational modes, including vibrations associated with aromatic, ether, alkyl, and carbonyl bonds, the calculated average locations reproduced all major features of hydrochar Raman spectra. Two model structures were found that could reproduce the main features of the hydrochar Raman spectrum and its elemental analysis: 1) a structure consisting of arene domains comprised of 6–8 rings connected via aliphatic chains or 2) a furan/arene structure consisting primarily of single furans and 2 or 3ring arenes. NMR confirmed that the furan/arene ratio of glucose hydrochar is approximately 1:1, consistent with the furan/arene structure supported by Raman spectra. This work establishes an interpretation method for hydrochar Raman spectra and reconciles the main features of hydrochar structures determined using Raman spectroscopy with those based on other methods. more...

Subcritical water has potential as an environmentally friendly solvent for applications including hydrolysis, liquefaction, extraction, and carbonization. Here, we report hydrolysis of sugarcane straw, an abundant byproduct of sugar production, in a semi-continuous reactor at reaction temperatures ranging from 190 to 260 °C and at operating pressures of 9 and 16 MPa. The target hydrolysis products were total reducing sugars. The main products of sugarcane straw hydrolysis were glucose, xylose, arabinose, and galactose in addition to 5- hydroxymethylfurfural and furfural as minor byproducts. Fourier transform infrared spectroscopy and thermogravimetric analysis provided additional information on the surface and bulk composition of the residual biomass. Char was present on samples treated at temperatures equal to and greater than 190 °C. Samples treated at 260 °C contained approximately 20 wt% char, yet retained substantial hemicellulose and cellulose content. Hydrolysis temperature of 200 °C provided the greatest TRS yield while minimizing char formation. more...

This review summarizes the recent essential aspects of subcritical and supercritical water technology applied tothe extraction, hydrolysis, carbonization, and gasification processes. These are clean and fast technologies which do not need pretreatment, require less reaction time, generate less corrosion and residues, do not usetoxic solvents, and reduce the synthesis of degradation byproducts. The equipment design, process parameters, and types of biomass used for subcritical and supercritical water process are presented. The benefits of catalysis to improve process efficiency are addressed. Bioactive compounds, reducing sugars, hydrogen, biodiesel, and hydrothermal char are the final products of subcritical and supercritical water processes. The present review also revisits advances of the research trends in the development of subcriticaland supercritical water process technologies. more...

peer-reviewed The full text of this article will not be available in ULIR until the embargo expires on the 27/03/2022 Torrefaction or hydrothermal carbonization processes were compared for conversion of olive pulp into metallurgical reducing agent. The dependence of yield, CO2 reactivity, and mechanical properties to reaction time and heat treatment temperature was investigated. Hydrochar yield increased with increasing residence time and the maximum solid yield was observed for a residence time of 15 h. On the other hand, CO2 reactivity slightly decreased with increasing heat treatment temperature at a residence time of 2 h. Notably, the CO2 reactivity of hydrochar was less than that of olive pulp char produced by torrefaction, approximating that of carbon-based reducing agents derived from non-renewable resources. An additional heat treatment improved hydrochar pellet durability to greater than 95%, whereas stable torrefied char pellets could not be produced under any set of conditions. Hydrothermal carbonization is superior to torrefaction for production of renewable reducing agents with reactivity and mechanical properties comparable to those afforded by reducing agents from non-renewable sources. more...

Efficient cellulose depolymerization is a major bottleneck for economical production of second-generation biofuels. In this work, crystalline cellulose was subjected to sequential ball milling and ethanolysis as a mild and selective depolymerization approach. Ball milling and ethanolysis resulted in 38±1 % cellulose conversion, with 24 % ethyl-glucopyranoside as the main identified and quantified product and negligible side reaction of the ethanol solvent to form diethyl ether. In comparison, ethanolysis of the original cellulose resulted in only 3±1 % conversion. Additional soluble products from cellulose ethanolysis included carbohydrate isomers and oligomers, differing from the products obtained from hydrolysis. X-ray diffraction and nuclear magnetic resonance spectroscopy revealed increased crystallinity post-reaction, retarding further depolymerization. Hot liquid water extracted soluble oligomers from the ethanolyzed cellulose, suggesting formation of a nanoscale barrier of crystalline cellulose that traps soluble products during ethanolysis. Use of cellulose-swelling co-solvents and repeated mechanical decrystallization both proved effective at increasing cellulose conversion and soluble product yields. Repeated ball milling and ethanolysis resulted in 62±1 % cellulose conversion. Ethanolysis of decrystallized cellulose has potential for rapid ( more...

A detailed reaction network is proposed for the pyrolysis and desulfurization of hexyl sulfide in the presence or absence of both supercritical water (SCW) and hexadecane, but without any added H2 or catalyst, for T = 400–450 °C. The new kinetic model is developed using the Reaction Mechanism Generator (RMG) software where most of the rate coefficients are derived from quantum chemical calculations. We previously reported that pentane, carbon monoxide and carbon dioxide are major products of hexyl sulfide desulfurization in SCW, but not in the anhydrous pyrolysis of hexyl sulfide. The observation of CO and CO2 in the reaction products indicates that water effectively acts as a hydrogen source; presumably this assists in sulfur reduction to H2S. Kinetic parameters for several of the important reactions are calculated using transition state theory and quantum chemical calculations at the CBS-QB3 level of theory and then further refined using CCSD(T)-F12//cc-pVTZ-F12 single point energies. Predictions from the new kinetic model agree with factor-of-2 accuracy with new and previously published experimental data for hexyl sulfide conversion and for yields of most major products, either neat or in a hexadecane solvent, both in the presence and absence of SCW. Flux analysis was then used to identify the most important reaction steps, and sensitivity analysis was used to propose reactions that should be studied further in the future to decrease the model's uncertainty. This study establishes the molecular role of water as diluent, hydrogen bond donor, and reductant in the decomposition of hexyl sulfide. Future work to add molecular weight growth pathways to the model would lead to a more complete mechanism, resulting in improved predictions of product yields. more...

Macauba husks are inedible lignocellulosic wastes obtained after extracting oil from the fruit for biodiesel production. The objective of this study was to valorize macauba husks through subcritical water hydrolysis (SWH) pretreatment followed by anaerobic digestion (PT+AD) in comparison to a control reactor (CR). The semi-continuous parameters were: 10 g of dried husk; flow rate of 10 mL/min at 200 °C and 14 MPa and for a total reaction time of 40 min. For AD, mesophilic conditions (35 °C) were kept for both experimental trials. For the PT+AD experiment, digestion was performed for 38 days and for 39 days for the CR experiment. The chemical oxygen demand (COD) removal for the PT+AD reactor was 48% and 43% for CR, indicating the pretreatment improved digestibility of the organic feed. Similarly, the CH4 yield per unit of COD for 590 mL CH4/g COD for the PT+AD experiment compared with 57 mL CH4/g COD for the CR experiment. The corresponding biogas yield was 161% greater than in the PT+AD experiment compared with the CR. Energy analysis revealed a corresponding benefit from SWH for production of heat and power, and several recommendations were made for decreasing the heat required by SWH to make the process self-sufficient. Macauba cultivation has promise as an energy crop that can be grown locally in Brazil and similar tropical locations for co-production of biodiesel from the extracted oil and biogas from the husks, thereby avoiding greenhouse gas emissions by replacement of traditional fossil sources. more...