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In this study, modeling and optimization of Hydrothermal Carbonization (HTC) of Poultry litter were conducted to convert it into high-value materials. The aim was to understand the process and predict the effect of the influencing parameters on the product properties. The recovery of Inorganic Phosphorous (IP) and Carbon (C) was regarded as the model's response, although temperature and reaction time were thought to be important variables. Response Surface Methodology (RSM) was used along with temperature and time data sets ranging from 150 to 300C and 30–480 min, respectively, to identify the parameters influencing the response, three-dimensional networks, and optimization. Next, Multilayer Perceptron (MLP) and Radial Basis Function (RBF) were used to compare the results and improve the model fit. For these two neural networks, 7 neurons in two layers and 14 neurons in one layer were the ideal numbers. With fewer neurons and better accuracy and efficiency, the MLP model beat RBF with lower Mean Squared Error (MSE) values for both C (0.0015812 vs. 0.0037103) and IP (0.0014376 vs. 0.00623011) recovery and a higher R2 value (R2C recovery = 0.99742, R2IP recovery = 0.99816). These results demonstrate that MLP is a viable technique for maximizing resource recovery through HTC condition optimization, with potential uses in nutrient recycling and sustainable waste management. By examining the three-dimensional grids and obtained contours, it was found that temperature had a greater effect on the response, and the impact of time was more pronounced at lower temperatures. With increasing temperature and reaction time, C recovery decreased, while IP recovery increased. Furthermore, the optimal values for temperature and time were suggested to be 182.329 C and 427.746 min, respectively. The optimal product values under these conditions for C and IP recovery were obtained as 59.611 % and 29.114 mg/g, respectively.

The effects of reaction temperature, time, and medium on the properties of sludge hydrochar were experimentally studied. The results demonstrated that hydrothermal carbonization (HTC) treatment enhanced sludge dewatering and volume reduction, with a higher water removal rate (42.8%--53.3%) observed under acidic conditions compared to neutral conditions (28.9%--45.2%). Notably, the highest dehydration rate was achieved after HTC at 240°C for 1 hour. Increased reaction temperatures and longer reaction times led to reduced hydrochar yield due to enhanced dehydration and decarboxylation reactions. The H/C and O/C atomic ratios gradually decreased as a result. Furthermore, the regular and compact structure of sludge was disrupted to varying degrees following HTC treatment, resulting in the formation of holes and grooves that increased the specific surface area, pore volume, and pore size of the hydrochar produced. Specifically, hydrochar obtained from HTC at 220°C for 1 hour exhibited the highest specific surface area (129.98 m2/g) and pore volume (0.66 cm3/g). The composition and crystalline structure of hydrochar were primarily influenced by factors such as reaction medium > reaction temperature > reaction time. With the increase of HTC reaction temperature and residence time, the volatile content of hydrochar decreased while the fixed carbon and ash content increased. The main exothermic range during combustion of hydrochar occured between 250--550°C. [ABSTRACT FROM AUTHOR]

Four deciduous woody feedstocks (Casuarina equisetifolia L., Eucalyptus globulus, Wrightia tinctoria, and Neolamarika cadamba) were subjected to the Hydrothermal Carbonization (HTC) process inside a 50 mL stainless steel hydrothermal reactor at varying temperatures (180°C, 215°C, and 250°C), while keeping water-to-feedstock ratio (6:1 v/w%) and residence time (1.5 h) constant. The mass yield and energy yield of the resulting biomass were calculated as parameters for energy intensification. Characterization of the biomass, biochar, and bio-oil was conducted using elemental analysis, SEM, and GC-MS. Interestingly, the mass yield of biochar decreased with increasing temperature, but it significantly improved the energy densification ratio, with a minimum of 1.06 observed for Neolamarika cadamba biomass at 180°C and a maximum of 1.23 observed for Eucalyptus globulus biomass at 250°C. Moreover, detailed analysis of the bio-oil obtained at 250°C using GC-MS revealed the presence of a diverse range of fine chemicals, including benzyl, carboxylic acid, ester, methyl, phenol, pyrrole, nitro, and aliphatic hydrocarbons. These findings suggest that the HTC process can be optimized to tailor the production of specific value-added chemicals from lignocellulosic woody biomass. [ABSTRACT FROM AUTHOR]

Empty fruit bunches (EFBs) are waste from the palm oil production. It has a high potential for use as a renewable carbon resource. As it typically contains a high moisture content, it requires a moisture removal step prior to transformation into high-value products via thermochemical processes. Hydrothermal carbonization (HTC) is an effective method for converting moisture-rich biomass into carbon-based products. The feasibility of employing EFBs as a feedstock for the production of promising carbonaceous materials via HTC in a batched stirred tank reactor was investigated in this research. The parameters influencing the HTC’s product properties, including reaction temperatures ranging from 160 to 280 °C and reaction times ranging from 2 to 8 h, were examined. The mass ratio of dried EFBs to water content was kept constant at 1:10. The hydrochar properties were evaluated using ultimate analysis, proximate analysis, N2-physisorption, Scanning Electron Microscope (SEM), and Fourier Transform Infrared Spectroscopy analysis (FTIR). The carbon content and amount of fixed carbon increased with increasing reaction temperature. The well-developed hydrochar was produced at a temperature of 240 °C for 2 h, providing a carbon content of 70% and a fixed carbon of 35%, with a solid yield of 41%. The surface area of this hydrochar was 11.21 m2/g, the pore volume of 0.033 cm 3/g, and the pore diameter of 10.89 nm. This study showed the effective preparation of materials with high carbon content from moisture-rich agricultural wastes.

The characteristics of hydrothermal carbonization hydrochar derived from cattle manure including excrements and lignocellulosic biomass were analyzed. The effects of hydrothermal carbonization were evaluated by varying the reaction temperatures in the range of 180~240 °C. The hydrochars were evaluated with respect to their usefulness as renewable fuels via physicochemical analysis and pyrolysis processes. As reaction temperatures increased, the fractions of fixed carbon in proximate analyses, carbon elements in ultimate analyses, and higher heating values of hydrothermally carbonized biochars increased in correlation with the primary reactions of coalification. Various correlations were derived with the characteristics of hydrochars in order to be utilized for operating and designing HTC reactors for cattle manure. The correlation between the O/C and H/C ratios was deduced on the basis of a van Krevelen diagram. The interaction equation was represented with the increased fraction of HHV compared to the reaction temperature of hydrothermal carbonization. The ultimate correlation for the estimation of higher heating values was suggested for HTC hydrochars. Moreover, the pyrolysis characteristics and kinetic parameters of the cattle manure and hydrochar were deduced by utilizing a multi-step kinetic model scheme. As the HTC reaction temperature increased, the global activation energy and the pre-exponential factors of hydrochars decreased in the low-temperature section and increased in the high-temperature section. [ABSTRACT FROM AUTHOR]

Dairy manure, a significant source of phosphorus (P), can potentially cause environmental risk due to P runoff when dairy manure is directly applied to cropland. Thus, there is an increasing interest in mitigating P loss from manure prior to land applications. This study aimed to investigate the potential of hydrochar produced by hydrothermal carbonization (HTC) for P recycling from dairy manure with and without the addition of CaO, focusing on the plant bioavailability, stabilization, and transformation of P in the resultant hydrochar. Hydrochar was prepared under different temperatures (180-240°C). The effect of CaO addition (0-10% of raw manure on dry wt. basis) was also evaluated at 220°C. Results showed that water-soluble P (WSP), a key indicator of P runoff loss, was significantly reduced in hydrochar, particularly with CaO addition. In addition, the plant available P in hydrochar increased with HTC temperature increase till 220°C, which accounted for ∼90% of total P content, then decreased with temperatures higher than 220°C. The addition of CaO slightly reduced plant bioavailability when compared to hydrochar produced at 220°C without additive. The P fractionation and speciation analyses indicated the transformation of P into Ca-associated apatite P. Hydrochar produced at 220°C with 10% CaO addition resulted in a high P recovery (∼85%) and a reduced runoff risk by 97%. The results demonstrate the efficacy of P recycling through hydrochar produced from dairy manure through HTC, which offers a sustainable approach to managing dairy waste while mitigating the potential environmental risks of P runoff.

In recent years there has been an increase in the demand for environmentally friendly solutions to CO2 capture. Natural residues and eco-friendly solvents have been acknowledged as possible solutions. Loblolly pine (LP) has been favored due to its natural abundance and high pot-osity, Methods such as chemical activations have been a verified way in which to notably improve the porosity of LP, but often the chemical agent utilized. for example, potassium hydroxide (KOH), generates hazardous waste. Melainine is an activation agent that offers a greenei-alternative and with the addition of Deep Eutectic Solvents (DES). this study sought to favorably improve the properties of LP. Choline chloride-urea DES was used to pretreat LP and was then activated via hydrothermal carbonization (HTC). This was done at temperatures of 170,200, and 230°C, Samples were then chemically activated with either Melamine, KOH, or a combination of the two activation agents. The sample's surface area and porosity were then evaluated via the utilization of nitrogen (32) adsorption-desorption. To observe the crystallinity and thermographic composition of samples, X-ray powder diffraction, and thermographic analysis were used, respectively. The initial hypothesis indicated that samples super activated with both Melamine and KOH being most beneficial, but it was observed that the results suggested that Melamine was a superior activation agent, with DES pretreated hydrochars being the most beneficial when considering the success of (02 capture due to the increase of functionality in the ultraporous material. It was found that samples adsorbed C02 at values as high as 3.941 mmol/g. at 1 bar. [ABSTRACT FROM AUTHOR]

The search for sustainable municipal solid waste management in urban areas has become a dire need as the generated unprecedented volumes of waste eventually end up in landfills and emits greenhouse gas (GHG). To offer sustainable waste management in Dhaka, Bangladesh, the performance of incineration, anaerobic digestion, and hydrothermal carbonization (HTC) based Waste to Energy (WtE) processes were assessed and compared. The population and the GDP of Dhaka North City Corporation from 2015 to 2023 were used to estimate the MSW generation rate with an empirical multivariable linear regression model. In 2023 around 3600 tons/day of MSW was generated which was 35 % higher than in 2015. The IPCC decay models, ZODM, FODM, and modified triangular model (MTM) yielded 87.3, 41.3, and 38-k tonnes of CH 4 generation, respectively. The power generation from incineration-based plants can fall from 30 MW to 3 MW if the moisture content of MSW increases from 70 % to 90 %. Anaerobic digestion produces 34 MW of power. The Optimization of the HTC operating parameters was done and it demonstrates substantial energy potential (up to 65 MW with co-feeding of 420 tons/day of hydrochar with 426 tons/day of plastic from MSW) and GHG emission reduction (221.5 %) compared to landfilling. Additionally, HTC-derived wastewater presents an opportunity for nutrient recovery with 8.16 and 2.66, 0.3 tons/day of K, Na, and P reclamation potential, respectively. A comparison of different scenarios in plastic recycling in incineration and sensitivity analysis for three WtE schemes were conducted. Thus, the study provides a rigorous assessment of different pathways to offer a comprehensive framework for sustainable MSW management that contributes to a cleaner urban environment. • Over 9 years, the estimated increase of MSW generation in Dhaka city is by 35 %. • Up to 34 MW power can be obtained from anaerobic digestion of MSW. • Using 420 tons/day of MSW hydro-char, 65 MW of net power generation is possible. • 8.16, 2.66 and 0.3 tons/day of K, Na, and P are recoverable from HTC by-product. • HTC was found as a sustainable WtE process with remarkable GHG mitigation potential. [ABSTRACT FROM AUTHOR]

Spent coffee grounds (SCG) are industrial biowaste resulting from the coffee-brewing process, and they are often underutilized and end up in landfills, thereby leading to the emission of toxic gases and environmental damage. Hydrothermal carbonization (HTC) is an attractive approach to valorize wet biomass such as SCG to valuable bioproducts (i.e., hydrochar). Thus, in this work, the HTC of SCG was carried out in a 500 L stainless steel vessel at 150, 170, 190, 210, and 230 °C for 30 min, 60 min, 90 min, and 120 min and a feedstock to water weight ratio of 1:5, 1:10, and 1:15, and the use of the resulting hydrochar as a solid fuel was evaluated. The results showed that a high energy recovery (83.93%) and HHV (23.54 MJ/kg) of hydrochar was obtained at moderate conditions (150 °C, 30 min, and feedstock to water weight ratio of 1:5) when compared with conventional approaches such as torrefaction. Following this, the surface morphology, functionality, and combustion behavior of this hydrochar were characterized by SEM, FTIR, and TGA, respectively. In short, it can be concluded that HTC is an effective approach for producing solid fuel from SCG and the resulting hydrochar has the potential to be applied either in domestic heating or large-scale co-firing plants. [ABSTRACT FROM AUTHOR]

To produce hydrochar with less volatile matter (VM) and more fixed carbon (FC) to increase its stability, this study compared the hydrothermal carbonization (HTC) of hen (HM) and swine (SM) manures at typical HTC sub-critical temperature of 210 °C and slightly super-critical temperature of 400 °C. Physico-chemical properties such as proximate analysis; ultimate analysis; Brunauer–Emmett–Teller (BET) surface area; higher heating value (HHV); chemical oxygen demand (COD); and inorganic nutrients of hydrochar, gaseous, and liquid products were determined. As expected, both VM and yield decreased with temperature. The heats of HTC reactions were estimated to be exothermic, ranging from −5.7 to −8.6 MJ/kg. The FC approximately doubled, while VM significantly decreased with a yield of 42.7%, suggesting the high potential of producing more stable hydrochar via near-critical HTC (NCHTC) treatment of SM. Additional work is needed before recommendations on carbonization temperatures can be made. Specifically, there is a need to experimentally investigate how the chars produced from each carbonization condition influence plant growth and soil emissions. [ABSTRACT FROM AUTHOR]

Wastes from recycled paper industry (WRP) was hydrothermally carbonized to remove impurities to produce alternative biofuel. The chlorine behaviors during hydrothermal carbonization (HTC) and the fuel properties of the generated hydrochar were evaluated. The degradation of lignocellulosic components improved free -OH bond and small free cellulosic fragments facilitating dechlorination. Meanwhile, dechlorination process stimulated degradation of biomass. The carbon content and density of WRP were improved by HTC resulting in high heating value increasing from 5044.40 MJ/m³ to 17,004.88 MJ/m³. Pollutants emission from hydrochar combustion would be effectively controlled because of the removal of sulfur and chlorine. Hydrochar enjoyed higher ignition temperature and average combustion rate while lower burnout temperature, indicating that the combustion range has been narrowed, thus improving the combustion efficiency. The increase of HTC temperature facilitated hydrochars combustion and reduce energy consumption during hydrochar combustion. Mild HTC operating conditions (220 °C for 90 min and 240 °C for 60 min) were supposed to effectively improve the combustion intensity with stability meanwhile reached the highest dechlorination efficiency. These results evidence the feasibility of converting WRP to clean biofuel via HTC. [ABSTRACT FROM AUTHOR]

Wastes from recycled paper industry (WRP) was hydrothermally carbonized to remove impurities to produce alternative biofuel. The chlorine behaviors during hydrothermal carbonization (HTC) and the fuel properties of the generated hydrochar were evaluated. The degradation of lignocellulosic components improved free -OH bond and small free cellulosic fragments facilitating dechlorination. Meanwhile, dechlorination process stimulated degradation of biomass. The carbon content and density of WRP were improved by HTC resulting in high heating value increasing from 5044.40 MJ/m3 to 17,004.88 MJ/m3. Pollutants emission from hydrochar combustion would be effectively controlled because of the removal of sulfur and chlorine. Hydrochar enjoyed higher ignition temperature and average combustion rate while lower burnout temperature, indicating that the combustion range has been narrowed, thus improving the combustion efficiency. The increase of HTC temperature facilitated hydrochars combustion and reduce energy consumption during hydrochar combustion. Mild HTC operating conditions (220 ℃ for 90 min and 240 ℃ for 60 min) were supposed to effectively improve the combustion intensity with stability meanwhile reached the highest dechlorination efficiency. These results evidence the feasibility of converting WRP to clean biofuel via HTC. [Display omitted] [ABSTRACT FROM AUTHOR]

Herein, mesoporous activated carbon (AC) was prepared through potassium hydroxide (KOH) activation of hydrochar derived from the hydrothermal carbonization (HTC) of chickpea stem (CS), and successfully applied to remove methylene blue (MB) dye from aqueous solutions in a batch system. The HTC-CSAC was prepared depending on different impregnation ratios (hydrochar:KOH, 50–150%), impregnation times (12–48 h), activation temperatures (400–600 ° C) and activation times (30–60 min). To define HTC-CSAC, various analytical techniques such as iodine adsorption number (IAN), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET) were used. In the removal process of MB by the best HTC-CSAC with a high IAN of 887 mg g−1 obtained under conditions including impregnation ratio of 70%, activation time of 45 min, activation temperature of 600 ° C and impregnation time of 24 h, the effects of adsorption parameters such as pH factor (2–10), adsorbent dosage (50–100 mg), initial MB concentration (40–80 mg/L) and contact time (90–180 min) were studied. Besides, a detailed evaluation of the adsorption mechanism for the removal of MB by HTC-CSAC was performed. The Langmuir model indicated the best isotherm data correlation, with a maximum monolayer adsorption capacity (Qmax) of 96.15 mg g−1. The adsorption isotherm findings demonstrated that the MB removal process is feasible, and that this process takes place through the physical interaction mechanism. Additionally, the HTC-CSAC adsorbent exhibited a high regeneration and reuse performance in MB removal. After five consecutive adsorption-desorption cycles, HTC-CSAC maintained the reuse efficiency of 77.86%. As a result, the prepared HTC-CSAC with a high BET surface area of 455 m2 g−1 and an average pore diameter of 105 Å could be recommended as a promising and reusable adsorbent in the treatment of synthetic dyes in wastewaters. Mesoporous activated carbon (AC) was prepared through KOH activation of hydrochar derived via hydrothermal carbonization (HTC) of chickpea stem (CS). The BET surface area and average pore diameter of HTC-CSAC were 455 m2 g−1 and 105 Å, respectively. The removal of MB dye by the best HTC-CSAC with a high IAN of 887 mg g−1, was studied using RSM optimization. The adsorption isotherm findings demonstrated that the MB removal process is feasible, and that this process takes place through the physical interaction mechanism. The HTC-CSAC adsorbent exhibited a high regeneration and reuse performance in MB removal. [ABSTRACT FROM AUTHOR]

The characteristics of hydrothermal carbonization hydrochar derived from cattle manure including excrements and lignocellulosic biomass were analyzed. The effects of hydrothermal carbonization were evaluated by varying the reaction temperatures in the range of 180~240 °C. The hydrochars were evaluated with respect to their usefulness as renewable fuels via physicochemical analysis and pyrolysis processes. As reaction temperatures increased, the fractions of fixed carbon in proximate analyses, carbon elements in ultimate analyses, and higher heating values of hydrothermally carbonized biochars increased in correlation with the primary reactions of coalification. Various correlations were derived with the characteristics of hydrochars in order to be utilized for operating and designing HTC reactors for cattle manure. The correlation between the O/C and H/C ratios was deduced on the basis of a van Krevelen diagram. The interaction equation was represented with the increased fraction of HHV compared to the reaction temperature of hydrothermal carbonization. The ultimate correlation for the estimation of higher heating values was suggested for HTC hydrochars. Moreover, the pyrolysis characteristics and kinetic parameters of the cattle manure and hydrochar were deduced by utilizing a multi-step kinetic model scheme. As the HTC reaction temperature increased, the global activation energy and the pre-exponential factors of hydrochars decreased in the low-temperature section and increased in the high-temperature section.

This novel research, presents the study of utilizing the wild almond shell as biomass waste to fabricate hydrochar using the hydrothermal carbonization (HTC) method based on a central composite design (CCD) with two independent variables (time and temperature) and three responses; productivity, higher heating value (HHV) and norfloxacin (NOR) adsorption capacity. The prepared hydrochar at 200 °C and 8 h was then employed to produce activated carbon (AC) by chemical-thermal activation technique. Hydrochar and AC were characterized using XRD, BET, SEM-EDX, Raman, and FTIR techniques. The pore development, resulting in a rise in the S BET (637.46 m2/g) value occurred after the activation process. Moreover, the results of XRD and Raman analyses revealed a decrease in graphitization degree. The adsorption of norfloxacin, methylene blue (MB), and sunset yellow (SY) by prepared hydrochar and AC were studied to assess the impact of the pH of the solution, initial concentration, temperature, and contact time. The maximum adsorption capacity for NOR, MB, and SY using hydrochar and AC were 85.37, 153.46, 93.35, and 384.1625, 556.465, 264.93 mg/g, respectively. The experimental data for the adsorption of NOR, MB, and SY using hydrochar and AC illustrated a good fit with the PSO model. Besides, the Langmuir and Freundlich models indicated better fitting with empirical data obtained for the adsorption of NOR, MB, and SY, respectively. Thermodynamic study outcomes validated the exothermicity and spontaneity of the adsorption process for both absorbents. This study presents a new opportunity to develop the circular economy by fabrication of sustainable adsorbents with high adsorption capacity for organic pollutants from biomass waste. [Display omitted] [ABSTRACT FROM AUTHOR]

The use of phytoremediation to remove metals of contaminated soils is an interesting technique that is usually limited by adverse physical and chemical properties of this type of soils. The addition of biochar produced from manure waste could improve soil properties due to its nutrient content, high cation exchange capacity or water holding capacity. However, the high water content of manure wastes precludes its pyrolysis treatment use for biochar production, without a previous drying step. Indeed, hydrothermal carbonization (HTC) of manure wastes could be an adequate treatment method as it takes place in water solution. The product obtained after HTC of biomass, named hydrochar, exhibits different physiochemical properties than biochar that could affect their potential application. The objective of the present work is to study the effect of chars obtained by pyrolysis or HTC of manure wastes in mining soil phytoremediation with Sinapis alba. Two selected mining soils (PORT and GAM) were treated with two manure biochars prepared at 450 °C (BMW450) and 600 °C (BMW600), two hydrochars prepared by HTC of manure at 190 °C (HWM190) and 240 °C (HMW240) and raw manure waste (MW) at a rate of 10% in mass. Later, different soil samples were incubated with or without Sinapis alba growth. Experimental results shown that properties of chars have a great influence on the efficiency of the use of Sinapis alba in the phytoremediation of mining soils. The addition of BMW600 and raw material (MW) increased the production of aerial and root biomass for GAM soil. For PORT soil, HMW190, two biochars and MW increases root and aerial biomass whereas HMW240 only produces an increment on aerial biomass. Addition of two hydrochars and MW had a positive effect on the biochemical soil activities and the highest microbial biomass carbon of GAM and PORT soil samples was observed after addition of HMW190. Finally, the addition of biochars and hydrochars could improve the phytoremediation of mining soils by Sinapis alba. However, the heavy metal uptake greatly depends on the type of soil, the amendment and the target metal. The accumulation of As, Pb and Zn in the aerial part of Sinapis alba was very low. However, Sinapis alba acts as accumulator for As in the presence of BMW600 and HMW190, for Zn after amendment with HM190 and for Pb after BMW600 addition to PORT soil. For GAM soil, only the addition of BMW450 and BM600 improves the capacity of accumulation of As in roots. [ABSTRACT FROM AUTHOR]

A remarkable number of scientific papers are available in the literature about the process of hydrothermal carbonization (HTC), also called wet or hydrous pyrolysis, applied to biomass substrates. However, the biggest share of it focuses on the characterization of HTC products obtained from different feedstocks. Only a few works are available on the process thermodynamics, particularly about the determination of the enthalpy change and the related heat release or absorption during HTC, which is a key parameter to understand the nature of the process and to evaluate the heat requirements for the design of industrial scale HTC plants. The present review summarizes the research carried out with the aim of assessing the process enthalpy for HTC. Two main approaches have been identified and described, and the research works are sorted into two categories: enthalpy calculation based on the direct application of the Hess's law and enthalpy evaluation based on differential heat measurement. The hypotheses and results obtained by the different authors are critically analysed and discussed, and directions for further research are proposed. [ABSTRACT FROM AUTHOR]

Iron-based industries are one of the main contributors to greenhouse gas (GHG) emissions. Partial substitution of fossil carbon with renewable biocarbon (biomass) into the blast furnace (BF) process can be a sustainable approach to mitigating GHG emissions from the ironmaking process. However, the main barriers of using biomass for this purpose are the inherent high alkaline and phosphorous contents in ash, resulting in fouling, slagging, and scaling on the BF surface. Furthermore, the carbon content of the biomass is considerably lower than coal. To address these barriers, this research proposed an innovative approach of combining two thermochemical conversion methods, namely hydrothermal carbonization (HTC) and slow pyrolysis, for converting biomass into suitable biocarbon for the ironmaking process. Miscanthus, which is one of the most abundant herbaceous biomass sources, was first treated by HTC to obtain the lowest possible ash content mainly due to reduction in alkali matter and phosphorous contents, and then subjected to slow pyrolysis to increase the carbon content. Design expert 11 was used to plan the number of the required experiments and to find the optimal condition for HTC and pyrolysis steps. It was found that the biocarbon obtained from HTC at 199 °C for 28 min and consecutively pyrolyzed at 400 °C for 30 min showed similar properties to pulverized coal injection (PCI) which is currently used in BFs due to its low ash content (0.19%) and high carbon content (79.67%).

Abstract This review aims at summarizing the literature for the coupling of the biological process of anaerobic digestion (AD) with one of three thermal processes: gasification (Gs), pyrolysis (Py), and hydrothermal carbonization (HTC). These thermal processes are investigated as pre and/or post treatments for AD, aiming at reducing its main drawbacks. The different cases are considered separately, based on the thermal treatment that is coupled with the AD process: AD-Gs, AD-Py, and AD-HTC. For each group, up to three sub-cases are discussed: the thermal treatment of the digestate, the use of char from the thermal treatment as stabilizer and enhancer in the AD reactor, and the AD of the aqueous products of the thermal treatment (this last case is not available with Gs). When possible, the result of the different researches for each configurations are grouped for comparison. Finally, an overview of the most promising future research investigations is given. Highlights • Biological and thermo-chemical processes towards the bio-refinery concept. • Anaerobic Digestion coupled with Gasification. • Anaerobic Digestion coupled with Pyrolysis. • Anaerobic Digestion coupled with Hydro-Thermal Carbonization. • Main challenges, points of interest and suggested future research focus. [ABSTRACT FROM AUTHOR]

BACKGROUND Carbon is the raw material for many commercial products; conventionally their production is from non‐renewable sources such as petroleum coke, pitch and coal. Recently carbon has been obtained from bioresources because of their renewability and high lignocellulosic content. This article details the synthesis of carbon microspheres from rubber wood, which is one of the largest commodity plants, via hydrothermal carbonization (hydrothermal rubber wood carbon; HTRW carbon) and evaluation of their characteristics. RESULTS: Two sets of carbon were synthesized: (i) in the first set, excess of water (20–40 × weight of biomass) was used in the hydrothermal process at 180–260 °C for 3–9 h; and (ii) in the second set, water ratio was 25–35 × weight of biomass and the hydrothermal carbonization (HTC) reaction temperature was fixed at 260 °C. The H/C and O/C ratios of starting rubber wood were ∼1.78 and ∼0.85, respectively, which upon processing through the first strategy resulted in H/C ∼0.78 and O/C ∼0.29; thereby suggesting increased condensation under HTC. On the other hand, the carbonization process was accelerated by water when the temperature was maintained at 260 °C; Fourier transform infrared (FTIR) studies show that this carbon has a different chemical structure from the starting rubber wood. Scanning electron microscopy (SEM) images showed that HTRW carbon was in the form of microspheres (size ∼1.5–5 µm). CONCLUSION: HTRW carbon with carbon content as high as 68% was developed from rubber wood biomass by hydrothermal processing of a mixture containing 35 times more water than the solid raw biomass at a temperature of 260 °C for 7 h. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract The mesophilic anaerobic co-digestion of the liquid fraction from hydrothermal carbonization (LFHTC) of dewatered waste activated sludge with primary sewage sludge (PSS) has been studied. Mixtures of different composition (25, 50 and 75% of LFHTC on a chemical oxygen demand (COD) basis), as well as the individual substrates, have been tested using two inocula (flocculent (FS) and granular (GS) sludges). Methane production decreased as the LFHTC/PSS ratio increased, which can be related to the presence of recalcitrant compounds in the LFHTC, such as alkenes, phenolics, and other oxygen- and nitrogen-bearing aromatics hard-to-degrade through anaerobic digestion. Methane yield reached 248 ± 11 mL CH 4 STP/g COD added with the GS inoculum and 25% LFHTC. A 74 and a 30% increase of methane production was achieved in the 25% LFHTC runs respect to the obtained in the similar experiments with 100% LFHTC, using the FS and GS inocula, respectively. In those late runs, the COD was reduced more than 86%, with a negligible concentration of total volatile fatty acids. With both inocula, total Kjeldahl nitrogen hydrolysis increased as the LFHTC to PSS mixture ratio decreased, reaching values higher than 79% at the end of the experiments. Methane yield values fitted well the first-order, Cone and Weibull kinetic models for both inocula. Significant differences in the kinetic constant values, ranging from 0.100 to 0.168 d−1 and 0.059–0.068 d−1, were found with the FS and GS inocula, respectively. The results obtained support the potential integration of HTC of dewatered waste activated sludge in wastewater treatment plants. Graphical abstract Image 1 Highlights • Valorization of waste activated sludge by HTC + anaerobic co-digestion is studied. • Experiments with three LFHTC/PSS ratios and two inocula were performed. • High COD removal and CH 4 yield with negligible volatile acid concentration were reached. • Anaerobic co-digestion of LFHTC to PSS mixture ratios of 25% is a feasible option. • Cumulative methane yield were adequately fitted by first-order, Cone and Weibull equations. [ABSTRACT FROM AUTHOR]

Wheat bran is a massive by-product from agro-industry, which is a sustainable raw material to make carbon material (CM). This work addresses wheat bran as a possible source for leather tanning agents to enlarge its industrial applications. Firstly, wheat bran was extracted with water and further modified with a hydrothermal carbonization (HTC). The UV–vis spectra, the FTIR spectra and the fluorescence phenomena were recorded to speculate the effects of HTC on the components in the bran extract solutions in terms of the reaction time (1 h, 3 h, 5 h and 7 h) at 170 ℃ and the reaction temperature (150 ℃, 170 ℃ and 190 ℃) at 5 h. Secondly, the bran-based CM was directly used to tan pickled pigskins without purification according to a normal leather processing procedure. The maximum rise in shrinkage temperatures of pigskins reached to 27 ℃ after tanning with bran CM. Scanning electron microscope images and atomic force microscope images revealed that bran-based CM penetrated into the collagen fibers to loosen and dilate fibers and then further provide stable crosslinking, resulting in firm and delicately grained surfaces. These results demonstrated that bran-based CM was an effective and environmentally-friendly tanning agent. [Display omitted] • Bran carbon materials (CMs) were prepared with hydrothermal carbonization (HTC). • Bran granules ruptured and more reactive substances went into the solution after HTC. • CMs had strong UV absorption in 200–400 nm and apparent fluorescence at 365 nm. • CMs brought higher shrinkage temperature (TS) and TS increment reached to about 27 ℃. • CMs penetrated into collagen fibers to loosen, dilate and crosslink collagen. [ABSTRACT FROM AUTHOR]

Activated carbon was produced by chemical activation of hydrothermally carbonized (HTC) banana empty fruit bunch (BEFB), using phosphoric acid (H3PO4) as the activating agent. The activation process was optimized using a Box-Behnken factorial design (BBD), with an outcome of 17 different experiments under the predefined conditions. Three different parameters (activation temperature (x1), activation time (x2), and the concentration of activating acid (x3)) were analyzed with respect to their influence on maximum adsorption percentage for divalent cations, Pb(II) (Y1) and Zn(II) (Y2), and carbon yield (Y3). All process parameters had strong positive effects on adsorption capacity up to a certain limit. The specific surface area of the hydrochar (HTC) was enhanced substantially after the activation process. Scanning electron microscopy (SEM) revealed that the morphology of the BEFB-based char changed noticeably after the acid impregnation and activation process. The Langmuir maximum monolayer adsorption capacity for Pb (II) and Zn (II) cations was 74.62 mg/g and 77.51 mg/g, respectively. Equilibrium isotherm data were in agreement with the Langmuir model. Thermodynamic characterization revealed that the equilibrium system was endothermic and spontaneous.

Phenol and p-nitrophenol (PNP) are priority pollutants widely present in wastewater. Developing superior or low-cost sorbents for their removal would be of great benefit. Here, corncob residues (CCR) were converted to hydrochars via hydrothermal carbonization (HTC) and further upgraded to carbon materials by thermal activation in an N2 atmosphere. The influence of HTC conditions including the temperature, residence time, and CCR/water weight ratio on the material properties and their performance for removing phenol and PNP from water were investigated and compared with those that were obtained from pyrochar (directly pyrolyzed CCR). Hydrochars showed lower adsorption capacities for phenols than pyrochar. The initial hydrothermal treatment at 220 °C and 2 h resulted in an improved porosity and 4- to 5-fold higher adsorption capacities for phenol and PNP compared with the pyrochar. However, hydrochars prepared at 250 °C or with a prolonged residence time (4 and 6 h) could not be upgraded to high performance carbon materials by thermal activation. The adsorption isotherms of both phenols on the best performance material were well correlated by the Sips model.

An activated carbon manufacturing process from winemaking waste is analyzed. In that way, vine shoots conversion is studied as a basis for plant designing, and mass and energy balances of hydrothermal carbonization and physical activation are fulfilled. To develop an energy-integrated plant, a network of heat exchangers is allocated to recover heat waste, and a cogeneration cycle is designed to provide electricity and remaining heat process demands. Furthermore, thermoeconomic analysis is applied to determine the thermodynamic efficiency and the economic viability of the plant. Energy balance indicates that heat exchangers energy integration covers 48.9% of the overall demands by crossing hot and cold streams and recovering heat from residual flue gas. On the other hand, the exergy costs analysis identifies combustion of pruning wood as the main source of exergy destruction, confirming the suitability of the integration to improve the thermodynamic performance. Attending to economic costs analysis, production scale and vineyard pruning wood price are identified as a critical parameter on process profitability. With a scale of 2.5 ton/h of pruning wood carbonization, a break-event point to compete with activated carbons from biomass origin is reached. Nevertheless, cost of pruning wood is identified as another important economic parameter, pointing out the suitability of wet methods such as hydrothermal carbonization (HTC) to treat them as received form the harvest and to contribute to cutting down its prices.

Hydrothermal carbonization (HTC) reactor systems used to convert wet organic wastes into value-added hydrochar are generally classified in the literature as liquid water-based (HTC) or vapor-based (VTC). However, the distinction between the two is often ambiguous. In this paper, we present a methodological approach to analyze process conditions for hydrothermal systems. First, we theoretically developed models for predicting reactor pressure, volume fraction of liquid water and water distribution between phases as a function of temperature. The reactor pressure model predicted the measured pressure reasonably well. We also demonstrated the importance of predicting the condition at which the reactor system enters the subcooled compression liquid region to avoid the danger of explosion. To help understand water–feedstock interactions, we defined a new solid content parameter %S(T) based on the liquid water in physical contact with feedstock, which changes with temperature due to changes in the water distribution. Using these models, we then compared the process conditions of seven different HTC/VTC cases reported in the literature. This study illustrates that a large range of conditions need to be considered before applying the label VTC or HTC. These tools can help in designing experiments to compare systems and understand results in future HTC research.

Porous carbon materials are currently subjected to strong research efforts mainly due to their excellent performances in energy storage devices. A sustainable process to obtain them is hydrothermal carbonization (HTC), in which the decomposition of biomass precursors generates solid products called hydrochars, together with liquid and gaseous products. Hydrochars have a high C content and are rich with oxygen-containing functional groups, which is important for subsequent activation. Orange pomace and orange peels are considered wastes and then have been investigated as possible feedstocks for hydrochars production. On the contrary, orange juice was treated by HTC only to obtain carbon quantum dots. In the present study, pure orange juice was hydrothermally carbonized and the resulting hydrochar was filtered and washed, and graphitized/activated by KOH in nitrogen atmosphere at 800 °C. The resulting material was studied by transmission and scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and nitrogen sorption isotherms. We found porous microspheres with some degree of graphitization and high nitrogen content, a specific surface of 1725 m2/g, and a pore size distribution that make them good candidates for supercapacitor electrodes.

To optimize the energy yield (EY) of food waste (FW) via hydrothermal carbonization (HTC), a response surface method was applied. Hydrochars and spent liquor were further conducted to evaluate their characterization and anaerobic digestion potential. Results found that optimal parameters for HTC of FW were suggested as temperature of 260 °C, reaction time of 4 h and moisture of 80%, with higher EY of 66.1%. Higher heating value, good combustion quality, lower H/C and O/C ratios indicated that hydrochar could be utilized as a safe solid fuel. Biochemical methane potential (BMP) experiment showed that spent liquor and hydrochars could be used as feedstocks for anaerobic digestion. Interestingly, hydrochars added in the spent liquor could promote the specific methane yield, which was 2.53 times higher than no addition of hydrochars. The finding of this study could provide useful information for HTC of FW and the utilization of hydrochars and spent liquor. [ABSTRACT FROM AUTHOR]

This research deals with the effect of the temperature on the physical, thermal, electrochemical, and adsorption properties of the carbon micro-spheres using hydrothermal carbonization (HTC). Until recently, limited research has been conducted regarding the effects of delignification during the HTC process of biomass residues especially Dimocarpus longan. In this regard, lignin was first extracted fromthe lingo-cellulosic waste of Longan fruit peel (Dimocarpus longan). The holocellulose (HC) separated from lignin and raw biomass substrates (Longan fruit exocarp/peel powder, LFP) were carbonized at different temperatures using water as the green catalyst. Hydrothermal carbonization (HTC) was performed for both of the samples (LFP and HC) at 200 °C, 250 °C, and 300 °C for 24 h each. The surface morphological structures, the porosity, and the Brunauer-Emmett-Teller (BET) surface area of the prepared micro-spherical carbon were determined. The BET surface areas obtained for HC-based carbon samples were lower than that of the raw LFP based carbon samples. The carbon obtained was characterized using ultimate and proximate analyses. The surface morphological features and phase transformation of the synthesized micro-spherical carbon was characterized by a field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) analysis. The results demonstrated that the extraction of lignin could significantly alter the end properties of the synthesized carbon sample. The carbon spheres derived from LFP showed a higher carbon content than the HC-based carbon. The absence of lignin in the holo-cellulose (HC) made it easy to disintegrate in comparison to the raw, LFP-based carbon samples during the HTC process. The carbonaceous samples (LFP-300 and HC-300) prepared at 300 °C were selected and their adsorption performance for Pb (II) cations was observed using Langmuir, Freundlich, and Temkin linear isotherm models. At 30 °C, the equilibrium data followed the Langmuir isotherm model more than the Freundlich and Temkin model for both the LFP-300 sample and the HC-300 sample. The potential of the synthesized carbon microspheres were further analyzed by thermodynamic characterizations of the adsorption equilibrium system. [ABSTRACT FROM AUTHOR]

In the present study, the influence of substrate pre-treatment (grinding and sieving) on batch anaerobic digestion of the organic fraction of municipal solid waste (OFMSW) was first assessed, then followed by co-digestion experiments with the liquid fraction from hydrothermal carbonization (LFHTC) of dewatered sewage sludge (DSS). The methane yield of batch anaerobic digestion after grinding and sieving (20 mm diameter) the OFMSW was considerably higher (453 mL CH 4 STP g −1 VS added ) than that of untreated OFMSW (285 mL CH 4 STP g −1 VS added ). The modified Gompertz model adequately predicted process performance. The maximum methane production rate, R m , for ground and sieved OFMSW was 2.4 times higher than that of untreated OFMSW. The anaerobic co-digestion of different mixtures of OFMSW and LFHTC of DSS did not increase the methane yield above that of the anaerobic digestion of OFMSW alone, and no synergistic effects were observed. However, the co-digestion of both wastes at a ratio of 75% OFMSW-25% LFHTC provides a practical waste management option. The experimental results were adequately fitted to a first-order kinetic model showing a kinetic constant virtually independent of the percentage of LFHTC (0.52–0.56 d −1 ) and decreasing slightly for 100% LFHTC (0.44 d −1 ). [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) is a promising technology to convert wet biomass into carbon-rich materials. Until now, the chemical processes occurring and their influence on the product properties are not well understood. Therefore, a target-oriented production of materials with defined properties is difficult, if not impossible. Here, model compounds such as cellulose and lignin, as well as different definite biomasses such as straw and beech wood are converted by hydrothermal carbonization. Following this, thermogravimetic (TGA) and FTIR measurements are used to get information about chemical structure and thermal properties of the related hydrochars. Some of the isolated materials are thermally post-treated (490 °C and 700 °C) and analyzed. The results show that at "mild" HTC conversion, the cellulose part in a lignocellulose matrix is not completely carbonized and there is still cellulose present. Thermal post-treatment makes the properties of product materials more similar and shows complete carbonization with increase aromatic cross-linking, proven by TGA and FTIR results. [ABSTRACT FROM AUTHOR]

[Display omitted] • New Pt/TiO 2 /Ti 2 Fe 2 O 7 nanocomposite based-sugarcane bagasse waste was synthesized by hydrothermal technique for the first time. • IT was characterized and confirmed by different recent techniques like FEEM, EDX, HRTEM, FTIR, and DRS. • Iτ ισ αππλιεδ ιο degrade the toluene gas pollutant under solar irradiation. • It has a high degradation performance for toluene gas pollutant reached up to 95%. • This new nanophotocatalyst could be used as a promising catalyst treatment technique in different fields. An eco-friendly and economical hydrothermal carbonization route is applied to prepare Pt-C hard template from sugarcane bagasse agro-waste, and then synthesize new Pt/TiO 2 /Ti 2 Fe 2 O 7 nanocomposites. Pt-C was prepared by utilizing the sugarcane bagasse. Spheres of Pt-C were obtained by hydrothermal technique at 180 °C for 6 h. TiO 2 nanoparticles with mixed anatase/rutile phases were synthesized by calcination at 700 °C and confirmed by XRD patterns. The elemental composition and surface morphology of Pt/TiO 2 /Ti 2 Fe 2 O 7 nanocomposite were evaluated by using FEEM equipped with EDX. The particle size and shape were determined by HRTEM. FTIR analysis was also performed and the diffuse reflection spectrum (DRS) was carried out. N 2 adsorption was utilized to establish the textural characters. The results of photocatalytic test exhibited that the percentage of degradation efficiency of toluene using Pt/C and Pt/TiO 2 was 23% and 25%, respectively, as compared to ˃ 95% for Pt/TiO 2 /Ti 2 Fe 2 O 7 under visible light, almost 4 times enhancement. [ABSTRACT FROM AUTHOR]

In many countries, sewage sludge is directly used for energy and agricultural purposes after dewatering or digestion and dewatering. In recent years, there has been a growing interest in additional upstream hydrothermal carbonization (HTC), which could lead to higher yields in the energetic and agricultural use. Twelve energetic and agricultural valorization concepts of sewage sludge are defined and assessed for Germany to investigate whether the integration of HTC will have a positive effect on the greenhouse gas (GHG) emissions. The study shows that the higher expenses within the HTC process cannot be compensated by additional energy production and agricultural yields. However, the optimization of the HTC process chain through integrated sewage sludge digestion and process water recirculation leads to significant reductions in GHG emissions of the HTC concepts. Subsequently, nearly the same results can be achieved when compared to the direct energetic use of sewage sludge; in the agricultural valorization, the optimized HTC concept would be even the best concept if the direct use of sewage sludge will no longer be permitted in Germany from 2029/2032. Nevertheless, the agricultural valorization concepts are not generally advantageous when compared to the energetic valorization concepts, as it is shown for two concepts.

Olive trimmings (OT) were used as feedstock for an in-depth experimental study on the reaction kinetics controlling hydrothermal carbonization (HTC). OT were hydrothermally carbonized for a residence time τ of up to 8 h at temperatures between 180 and 250 °C to systematically investigate the chemical and energy properties changes of hydrochars during HTC. Additional experiments at 120 and 150 °C at τ = 0 h were carried out to analyze the heat-up transient phase required to reach the HTC set-point temperature. Furthermore, an original HTC reaction kinetics model was developed. The HTC reaction pathway was described through a lumped model, in which biomass is converted into solid (distinguished between primary and secondary char), liquid, and gaseous products. The kinetics model, written in MATLABTM, was used in best fitting routines with HTC experimental data obtained using OT and two other agro-wastes previously tested: grape marc and Opuntia Ficus Indica. The HTC kinetics model effectively predicts carbon distribution among HTC products versus time with the thermal transient phase included; it represents an effective tool for R&D in the HTC field. Importantly, both modeling and experimental data suggest that already during the heat-up phase, biomass greatly carbonizes, in particular at the highest temperature tested of 250 °C.

Hydrothermal carbonization (HTC), as an environmental friendly process, presents wide potential applicability for converting biomass to biochar with high energy density. Reed, a major energy crop, was converted by a HTC process in a batch reactor at 200-280 °C for 0.5 to 4 h. Biochar mass yield changed from 66.7% to 19.2% and high heating value (HHV) from 20.0 kJ/g to 28.3 kJ/g, respectively, by increasing the carbonization temperature from200 °C to 280 °C and decreasing the residence time from 2 h to 1 h. The Fourier Transform infrared spectroscopy (FTIR), X-ray Diffraction (XRD), and Scanning ElectronMicroscope (SEM) results indicated the lignocellulosic crosslink structure of reed is broken and biochar having a high energy density is obtained with the increase of temperature. The microcrystal features of reed are destroyed and biochar contained mainly lignin fractions. The HTC of biocrude is carried out at 200-280 °C for 2.0 h and the results showed that the obtained biochar has uniform particles filled with carbon microspheres. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) has become an accepted means of converting a wide variety of lignocellulosic feedstocks into solid hydrochars, which have improved physical and chemical properties compared to raw biomass. To date, HTC applications have involved batch or semi-continuous process systems, which has limited their economic viability. The work presented here describes a fully-continuous HTC process, made possible by use of a specially modified twin-screw extruder (TSE). The reaction time within this fast HTC (FHTC) reactor system is very short (20–30 sec) as compared to a typical batch reactor. Therefore, the concept of reaction ‘severity factor’ is used when comparing the FHTC products with those produced in other reactor systems. While solid hydrochar produced in the FHTC system has different physical properties than hydrochar from batch reactor systems, these materials exhibit similar energy densification and pelletization behavior, when produced under comparable severity conditions. However, total hydrochar yields are considerably higher from the FHTC reactor compared to batch reactor systems. This is a consequence of the de-pressurization process in the FHTC system, whereby most water-soluble organic products are retained in the hydrochar, rather than exiting the process in a separate aqueous product stream. FHTC treatment of loblolly pine at a severity factor of 5.3 (290 °C) produced a hydrochar yield of nearly 85% (based on dry feedstock mass). Condensation of the flashed vapor products provided a relatively clean water stream, containing only 1.2% organics – primarily furfural and acetic acid. Recovery of these organics and recycling of the condensed water would further improve the cost-effectiveness of FHTC operations. [ABSTRACT FROM AUTHOR]

Herein, the valorization of vegetable and fruit waste was assessed via hydrothermal carbonization (HTC) and anaerobic digestion (AD) in terms of product characterization and energy requirements. HTC was conducted at reaction temperatures between 150 ºC and 190 ºC, and residence times between 20 min and 40 min. The increase in the process severity resulted in hydrochars with higher carbon contents and higher energy densification ratios. AD was performed in two different ways. i.e., batch and semi-continuous reactions. From the batch experiments a methane yield of 300 L CH 4 /kg VS was obtained, while for the semi-continuous, the average specific methane production estimated (for HRTs from 75 to 50 days) was 213 ± 32 L CH 4 /kg VS. To estimate the energy requirements, mass and energy balances were performed considering the basic stages of each process to obtain a suitable biofuel material. In this sense, it was concluded that for this specific waste, AD was a more suitable process with a positive energy net balance. On the contrary, HTC presented a negative energy net balance being required 1.29 MJ/kg of fresh food waste. A combined HTC-AD treatment may be an efficient method to take advantage of both technologies leading to higher energy efficiencies and other valuable products. [Display omitted] • A carbon-rich solid product is obtained from HTC of fruit and vegetable waste. • The higher the severity of the HTC, the better the fuel properties of the hydrochars. • The energy recovered by HTC is higher than that of AD (923 MJ vs. 867.1 MJ). • Batch and semi-continuous anaerobic digestion experiments were performed. • AD presented a positive energy balance, while HTC showed negative outputs. [ABSTRACT FROM AUTHOR]

Hydrochar is a very interesting product from agricultural and food production residues. Unfortunately, severe conditions for complete conversion of lignocellulosic biomass is necessary, especially compared to the conversion of sugar compounds. The goal of this work is to improve the conversion of internal carbohydrates by application of a two-steps process, by acid addition and slightly higher water content. A set of experiments at different temperatures (180, 200, and 220 °C), reaction times (2 and 4 h), and moisture contents (80% and 90%) was performed to characterize the solid (high heating value (HHV), elemental) and liquid product phase. Afterwards, acid addition for a catalyzed hydrolysis reaction during hydrothermal carbonization (HTC) and a two-steps reaction (180 and 220 °C) were tested. As expected, a higher temperature leads to higher C content of the hydrochar and a higher fixed carbon (FC) content. The same effect was found with the addition of acids at lower temperatures. In the two-steps reaction, a primary hydrolysis step increases the conversion of internal carbohydrates. Higher water content has no significant effect, except for increasing the solubility of ash components.

Peat moss and miscanthus were hydrothermally carbonized (HTC) either individually or co-processed in a different ratio to produce hydrochar. The hydrochar and pelletized hydrochar were then characterized to determine if hydrochar can be used as an alternative to coal to produce bioenergy from existing coal-fired power plants in Ontario that have already been shut down. The properties of carbonized biomass (either hydrochar or pellets) reveal that fuel grade hydrochar can be produced from peat moss or from the blend of peat moss and miscanthus (agricultural biomass/energy crops). Hydrochar either produced from peat moss or from the blend of peat moss and miscanthus was observed to be hydrophobic and porous compared to raw peat moss or raw miscanthus. The combustion indices of carbonized biomass confirmed that it can be combusted or co-combusted to produce bioenergy and can avoid slagging, fouling, and agglomeration problems of the bioenergy industry. The results of this study revealed that HTC is a promising option for producing solid biofuel from undervalued biomass, especially from high moisture biomass. Co-processing of peat moss with rural biomass, a relatively novel idea which can be a potential solution to heat and power for the rural communities/agri-industry that are not connected with national grids and alleviate their waste management problems. In addition, the hydrochar can also be used to run some of the existing coal-fired power plants that have already been shut down in Ontario without interrupting investment and employment.

This research deals with the effect of the temperature on the physical, thermal, electrochemical, and adsorption properties of the carbon micro-spheres using hydrothermal carbonization (HTC). Until recently, limited research has been conducted regarding the effects of delignification during the HTC process of biomass residues especially Dimocarpus longan. In this regard, lignin was first extracted from the lingo-cellulosic waste of Longan fruit peel (Dimocarpus longan). The holocellulose (HC) separated from lignin and raw biomass substrates (Longan fruit exocarp/peel powder, LFP) were carbonized at different temperatures using water as the green catalyst. Hydrothermal carbonization (HTC) was performed for both of the samples (LFP and HC) at 200 °C, 250 °C, and 300 °C for 24 h each. The surface morphological structures, the porosity, and the Brunauer-Emmett-Teller (BET) surface area of the prepared micro-spherical carbon were determined. The BET surface areas obtained for HC-based carbon samples were lower than that of the raw LFP based carbon samples. The carbon obtained was characterized using ultimate and proximate analyses. The surface morphological features and phase transformation of the synthesized micro-spherical carbon was characterized by a field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) analysis. The results demonstrated that the extraction of lignin could significantly alter the end properties of the synthesized carbon sample. The carbon spheres derived from LFP showed a higher carbon content than the HC-based carbon. The absence of lignin in the holo-cellulose (HC) made it easy to disintegrate in comparison to the raw, LFP-based carbon samples during the HTC process. The carbonaceous samples (LFP-300 and HC-300) prepared at 300 °C were selected and their adsorption performance for Pb (II) cations was observed using Langmuir, Freundlich, and Temkin linear isotherm models. At 30 °C, the equilibrium data followed the Langmuir isotherm model more than the Freundlich and Temkin model for both the LFP-300 sample and the HC-300 sample. The potential of the synthesized carbon microspheres were further analyzed by thermodynamic characterizations of the adsorption equilibrium system.