Properties Of Hydrochar Research Articles

Biochars and hydrochars prepared by pyrolysis and hydrothermal carbonisation of pig manure

Pyrolysis of organic wastes for biochar preparation has been proved as a useful way of waste management. However, the elevated water content of some organic wastes precludes its use without a drying step before pyrolysis treatment. For this reason, hydrothermal carbonization (HTC) of wet biomass could be an inexpensive alternative management method. The main objective of the present work is to compare the properties of biochars and hydrochars obtained from thermal treatment of pig manure. Biochars were prepared at 300 °C (BPM300), 450 °C (BPM450) and 600 °C (BPM600) and hydrochars were obtained using a pig manure solution (ratio 30:70) that was heated at 200 °C (HPM200), 220 °C (HPM220) and 240 °C (HPM240) during 2 h. Characterization of biochar and hydrochar samples showed that pyrolysis led to chars with more aromatic structures and high thermal stability while HTC process originated chars with more aliphatic structures. HPM220 and HPM240 showed the highest values of field capacity water content and available water probably due to their higher O/C ratios and the macroporosity development in the range from 200 to 30,000 nm. These results suggested that HTC could be an interesting method to obtain soil growing media or green roof materials with adequate hydrophysical properties.

What is the influence of the nitrogen-containing composition during hydrothermal carbonization of biomass? A new perspective from mimic feedstock

The influence of nitrogen-containing composition during hydrothermal carbonization of biomass was investigated. Representative chemicals, protein, glycine, (NH4)2SO4, NH4Cl, and NaNO3, were used as nitrogen-containing species and glucose was used as model carbohydrate. The hydrochar yield, nitrogen distribution, and hydrochar properties were assessed. High ratio of glycine, (NH4)2SO4 and NH4Cl decreased hydrochar yield, conversely protein and NaNO3. The nitrogen content in hydrochar depended on the nitrogen-containing species and mass ratio in biomass, with 5 g glycine (260 °C and 2 h) having the highest value (9.20%). Especially, high (NH4)2SO4 and NH4Cl ratio increased of H/C and O/C of hydrochar at 180 °C, while protein and glycine mainly decreased O/C. However, all hydrochar had high degree of carbonization at 260 °C. Thermally unstable components appeared when protein and NH4Cl were added into the reaction mixture and more NH4Cl and NaNO3 decreased the maximum mass loss rate during pyrolysis.

Physicochemical, structural and combustion characterization of food waste hydrochar obtained by hydrothermal carbonization

A solid carbon-rich product hydrochar, was prepared using hydrothermal carbonisation of food waste at temperatures of 200, 250 and 300 °C. To acquire detailed insight into physicochemical and structural properties, hydrochar samples were characterised using a range of techniques. The carbon content and higher heating value of food waste increased considerably from 39 to 73% and 15 to 31 MJ/kg corresponding to the heating temperature. The blends of hydrochar and coal prepared in three different ratios (5%, 10% and 15%) exhibited different thermal behaviour. The overall results of co-combustion study showed that the activation energy of hydrochar samples decreased from 56.78 KJ/mol to 29.80 KJ/mol with increase in temperature. Hydrochar prepared at 300 °C with coal blending ratio of 10% exhibited the lowest activation energy of 19.45 KJ/mol. Additionally thermal gravimetric analysis of the samples showed that high temperature carbonization can increase the combustion properties of hydrochar.

Co-hydrothermal carbonization of lignocellulosic biomass and swine manure: Hydrochar properties and heavy metal transformation behavior

Co-hydrothermal carbonization (HTC) of lignocellulosic biomass and swine manure (SM) was conducted, and the hydrochar properties and transformation behavior of heavy metals (HMs) were investigated in this study. The results showed that co-HTC with lignocellulosic biomass promoted the dehydration of SM and enhanced the aromatization of the hydrochar. Compared to the hydrochar from SM, the carbon content, higher heating value and energy yield of the hydrochar from co-HTC were significantly increased, reaching the maximum of 57.05%, 24.20 kJ/kg and 80.17%, respectively. Significant synergy occurred between lignocellulosic biomass and SM during co-HTC and different lignocellulosic biomass exhibited similar influence on the synergy. Additionally, the concentration and bioavailability of HMs in the hydrochar from co-HTC were decreased in comparison to SM. These findings suggested that co-HTC with lignocellulosic biomass offered an effective approach to convert SM into clean solid fuel with remarkably improved fuel properties.

Identifying the reducing capacity of biomass derived hydrochar with different post-treatment methods

In this study, hydrochar was prepared from wheat straw (WS) and Spartina alterniflora (SA) biomass by hydrothermal carbonization, and further treated with HCl and NaOH washing, HNO3 oxidization and low temperature thermal heating. The reducing capacity (RC) of sample was quantified by I2 titration to explore how these modification methods affected the redox properties of hydrochar. The results indicated HNO3 and thermal oxidization increased the RC of hydrochar by 2–5 folds while NaOH washing had the negative effect on samples' RC. By analyzing the excitation-emission matrix (EEM) fluorescence of alkaline extraction solution of sample, humic acid like substances generated from various methods were identified as one of the major sources for electron donating. HNO3 oxidization could significantly increase the RC in hydrochar, which was likely resulting from the generation of alkali-soluble small molecule organic compounds. However, excessive oxidation by nitric acid with prolonged duration led to the gradual decrease in hydrochar's RC. Heating treatment caused a significant increase in the content of redox-active oxygen-containing functional groups and persistent free radicals (PFRs) in hydrochar. Even though both could donate electrons in the redox reaction with I2, the former was considered a greater contributor for the RC of hydrochar. From this study, the origin of RC of hydrochar can be identified as: oxygen-containing functionality, humic-like matter and PFRs. By employing different modification methods, the RC of hydrochar could be tuned by regulating the above sources. This study provided fundamental knowledges and simple routes to manipulate the redox properties of hydrochar for different environmental applications.

Optimization of the conventional hydrothermal carbonization to produce hydrochar from fish waste

Fish waste disposal is a major cause for concern for the seafood processing industries. Fish processing generates enormous quantities of waste as almost 45% of the live weight of fish is regarded as waste. Current ways of managing fish waste involves dumping in oceans, landfills, or treating them with already established strategies. Dumping these wastes without any form of treatment is far from being environmental friendly. Current utilization strategies suffer from disadvantages such as incomplete utilization of solid and liquid wastes or generation of new waste effluents that needs further processing. Therefore, there is a need to find an alternate/supplemental method of seafood utilization. Previously, we have reported the use of microwave hydrothermal carbonization (MHTC) to carbonize fish waste to hydrochar. Here, a conventional heating method such as a custom autoclave reactor is reported that could also be used to carbonize fish waste to hydrochar. Upon response surface design optimization, it was found that a maximal yield of hydrochar (~ 35%) can be achieved at a holding temperature of 180 °C and at a holding time of 120 min. We have also characterized the elemental, proximate, energy, and surface properties of hydrochar produced by conventional hydrothermal carbonization (CHTC). It was found that the quality of the hydrochar produced by MHTC is largely comparable to CHTC. This further proves that HTC could be employed to generate energy from non-lignocellulosic wastes such as fish waste while getting rid of the waste in an eco-friendly manner.

Correlations between hydrochar properties and chemical constitution of orange peel waste during hydrothermal carbonization

For efficient hydrothermal treatment of biomass, this study aims to figure out the correlations between complex chemical constitution of orange peel (OraPeel) as typical bio-waste and the physicochemical structure of its derived hydrochar, which could be utilized to adjust hydrochar properties for specific applications (e.g., adsorbent, fuel) by regulating respective proportions of each component in bio-waste. Cellulose, hemicellulose and lignin were used as the control variables of feedstocks composition in this work. After hydrothermal process, lignin added feedstock produced more hydrochar, which contained rougher surface with nearly doubled BET areas and more benzene rings. Hemicellulose-aided hydrochar possessed higher density of carbonaceous microspheres and richer hydroxyl. This char was simultaneously covered by more esters or lactones with more aromatic oxygen-containing groups inside. Similar to hemicellulose, cellulose improved the formation of diverse oxygenous groups but reduced the size of microspheres on hydrochar.

Removal of methylene blue from aqueous solution by modified bamboo hydrochar

Four hydrochars (labeled as HC, AHC, MHC, and MAHC, respectively) were prepared by hydrothermal carbonization of bamboo with and without chlorane or followed by NaOH modification. Various techniques were adopted to characterize the physicochemical properties of hydrochars and the removal of methylene blue (MB) by these hydrochars from aqueous solution was investigated. The MB adsorption isotherm and kinetic onto MAHC and MHC can be preferably interpreted by Langmuir adsorption mode and the pseudo-second-order model, respectively. Thermodynamic parameters implied that adsorption was a spontaneous and exothermic process. The adsorption capacity of MAHC was 655.76 mg g−1, which was 2–3 times compared to that of MHC (268.93 mg g−1) at 303 K. The high adsorption capacity of MAHC for MB suggests that hydrothermal carbonization in acidic medium followed by alkaline treatment has the potential application to produce efficient MB adsorbents used in wastewater treatment.

Properties of Hydrochar as Function of Feedstock, Reaction Conditions and Post-Treatment

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.

Towards Biochar and Hydrochar Engineering—Influence of Process Conditions on Surface Physical and Chemical Properties, Thermal Stability, Nutrient Availability, Toxicity and Wettability

The impact of conversion process parameters in pyrolysis (maximum temperature, inert gas flow rate) and hydrothermal carbonization (maximum temperature, residence time and post-washing) on biochar and hydrochar properties is investigated. Pine wood (PW) and corn digestate (CD), with low and high inorganic species content respectively, are used as feedstock. CD biochars show lower H/C ratios, thermal recalcitrance and total specific surface area than PW biochars, but higher mesoporosity. CD and PW biochars present higher naphthalene and phenanthrene contents, respectively, which may indicate different reaction pathways. High temperatures (>500 °C) lead to lower PAH (polycyclic aromatic hydrocarbons) content (<12 mg/kg) and higher specific surface area. With increasing process severity the biochars carbon content is also enhanced, as well as the thermal stability. High inert gas flow rates increase the microporosity and wettability of biochars. In hydrochars the high inorganic content favor decarboxylation over dehydration reactions. Hydrochars show mainly mesoporosity, with a higher pore volume but generally lower specific surface area than biochars. Biochars present negligible availability of NO 3 − and NH 4 + , irrespective of the nitrogen content of the feedstock. For hydrochars, a potential increase in availability of NO 3 − , NH 4 + , PO 4 3 − , and K + with respect to the feedstock is possible. The results from this work can be applied to “engineer” appropriate biochars with respect to soil demands and certification requirements.

Conventional Hydrothermal Carbonization of Shrimp Waste

Shrimp is among the most consumed seafood across the world. Shrimp-processing operations generate enormous quantities of waste. Current strategies of shrimp waste management and the current utilization strategies suffer from several disadvantages, especially from being not environmentally friendly. This warrants alternate methods to completely utilize shrimp waste. Previously, we have shown that microwave hydrothermal carbonization (MHTC) can be used to treat shrimp waste to produce hydrochar. In this study, conventional hydrothermal carbonization (CHTC) using a customized autoclave reactor was performed to treat shrimp waste. Upon using response surface design, it was found that at a holding temperature of 186 °C and a time of 120 min, a maximal hydrochar yield of ∼29% was achieved. Furthermore, characterization results of elemental, proximate, energy, and surface properties of CHTC shrimp waste hydrochar were found to be comparable to that of the MHTC hydrochar from shrimp waste. In addition, the hydroc...

Spent coffee enhanced biomethane potential via an integrated hydrothermal carbonization-anaerobic digestion process

This study reports the implications of using spent coffee hydrochar as substrate for anaerobic digestion (AD) processes. Three different spent coffee hydrochars produced at 180, 220 and 250 °C, 1 h residence time, were investigated for their biomethane potential in AD process inoculated with cow manure. Spent coffee hydrochars were characterized in terms of ultimate, proximate and higher heating value (HHV), and their theoretical bio-methane yield evaluated using Boyle-Buswell equation and compared to the experimental values. The results were then analyzed using the modified Gompertz equation to determine the main AD evolution parameters. Different hydrochar properties were related to AD process performances. AD of spent coffee hydrochars produced at 180 °C showed the highest biomethane production rate (46 mL CH4/gVS.d), a biomethane potential of 491 mL/gVS (AD lasting 25 days), and a biomethane gas daily composition of about 70%.

Hydrothermal carbonization of Miscanthus × giganteus: Structural and fuel properties of hydrochars and organic profile with the ecotoxicological assessment of the liquid phase

In this study, hydrothermal carbonization (HTC) was employed for thermochemical conversion of energy crop Miscanthus × giganteus GREEF et DEU. The effect of process temperatures, in the range between 180 and 220 °C, on the relevant characteristics of the obtained products, hydrochars and process waters, was investigated. The obtained results showed that the HTC promotes fuel properties and energy density of the solids regarding the feedstock. Furthermore, temperature governs the lowering of the volatiles, ash, and moisture in hydrochars, making its potential use as solid fuels more beneficial than the miscanthus. FT-IR spectroscopy and thermal analysis confirmed degradation of hemicellulose at temperatures above 200 °C, and an increase of the total content of cellulose and lignin in the hydrochars. In general, hydrochar obtained at 220 °C exhibited the best combustion characteristics and is, therefore, the most suitable for use as a solid biofuel. However, in the residual liquids, some amounts of fluorene, phenanthrene, fluoranthene, and pyrene were detected. The polluting potential, visible through the growth of TOC, COD and BOD values, of the analyzed process waters, increases with the rise in carbonization temperature. The TOC values (5.8–9.9 gC L−1) were on average lower than those reported for organic wastewaters (>10 gC L−1). The proportion of hydrocarbons in the process water increases with the increase in the carbonization temperature from 2.92 to 20.9%. Consequently, bioassays with Vibrio fischeri showed a relatively high toxicity of the liquid phase, where a concentration of about 1% was causing bacteria inhibition of 50%.

Effect of acid-assisted hydrothermal carbonization (HTC) process of tree branches using nitric acid on cadmium adsorption

Application of acid in HTC process has been confirmed to have effect on hydrochar properties related to its adsorption capacity. Woody materials (tree branches) were used to investigate the relation of nitric acid addition in HTC process on the hydrochar surface properties and its adsorption mechanism toward cadmium in water solution. Tree branches were processed at 200-260 °C mixed with water and nitric acid (HNO3) at ratio 0-50% to hydrochar mass and held for holding time of 30, 105 and 180 minutes. Batch adsorption test was conducted by mixing the hydrochars with cadmium solution at 100 ppm and shaken for 24 hours at room temperature. The BET surface area, oxygen functional group (OFG) and the exchanged cations were analysed to investigate the effect of HTC process condition, nitric acid addition, and adsorption mechanism of cadmium. Tree branches treated at 200°C for 30 minutes and acid ratio of 50% showed the best adsorption result. Analysis on the surface properties also showed the best condition for cadmium adsorption. Thus hydrothermal treatment condition at low temperature, short time and high acid ratio usage could be effective in removing cadmium from water. The cadmium adsorption by cation exchange interaction might be the major adsorption mechanism as shown by consistency of trend of the exchanged cation concentration with cadmium adsorption capacit

A novel pyro-hydrochar via sequential carbonization of biomass waste: Preparation, characterization and adsorption capacity

Comprehensive utilization of agricultural biomass waste, such as biochar, is a hot spot in recent years. In order to keep high chemical stability, large specific surface area, and rich oxygenated functional groups of carbonized product, a novel rich-carbon material ‘pyro-hydrochar’ was proposed firstly via sequential carbonization of biomass wastes. In the present study, the pyro-hydrochar was derived from the corn straw and corncob by consecutive hydrothermal carbonization under 200 °C and then pyrolysis at the temperatures of 350–650 °C. The physicochemical properties of biochar, hydrochar and pyro-hydrochar were compared by multi-analysis including the characterization by elemental composition, BET, FTIR, XPS, SEM, chemical oxidation method by K2Cr2O7 and H2O2. The results showed the pyro-hydrochar is a newly developed rich carbon material with large specific surface area, rich functional groups, high aromatization degree and strong chemical oxidation stability. Specifically, the stable carbon-rich pyro-hydrochar indicates the strong capacity of potential carbon sequestration. Additionally, the biochar, hydrochar and pyro-hydrochar could show different adsorption performance on the representative contaminants like atrazine, Cd2+ and Cr(VI). It suggested the pyro-hydrochar with rich oxygenated functional groups and large specific surface area could be a new candidate of economic adsorbent, and it also indicated the important practical value for further modification and development of pyro-hydrochar derived from biomass wastes.

Influences of feedstock type and process variables on hydrochar properties

In this study, the effect of process variables, such as temperature, biomass:water ratio and reaction time, in hydrothermal carbonization (HTC) has been studied for different type biomasses. Response surface methodology was used to study the influence of each factors as well as their combined interactive effect on the mass yield and energy density of hydrochars. The results showed that the temperature and time were significant factors effecting the mass yield and energy densification ratio in HTC of the sunflower stalk and algae, whereas temperature was only significant factor in HTC of poultry litter. The biomass:water ratio was found insignificant for all tested biomasses. In addition, the fuel properties of hydrochars were compared with the properties of biochar derived from torrefaction at 300 °C. The results showed that for all tested biomass, the biochars had lower volatile matter and fixed carbon than hydrochars.

Hydrothermal pretreatment of bamboo sawdust using microwave irradiation

In the present study, the effect of temperature and residence time during microwave hydrothermal pretreatment (MHT) on hydrochar properties and pyrolysis behaviors was investigated. Experimental results indicated that higher heating value (HHV) and fixed carbon content gradually increased with increased pretreatment severity. Obvious reduction of oxygen content was found under MHT at 230°C-15min and 210°C-35min. Although lower mass yield was observed under severe conditions, corresponding energy yield was relatively higher. Crystallinity indexes of hydrochar demonstrated an upward trend with increased residence time. Unlike hydroxyl group, dissociation of acetyls was more favorable under prolonged residence time rather than increased temperature. Peaks in thermogravimetric and derivative thermogravimetric curves shifted to higher temperature region under severe conditions, indicating better thermal stability. Py-GC/MS analysis suggested that acids content was decreased but sugars increased with increased MHT severity. Moreover, compared to temperature, residence time was mainly responsible for acetic acid formation.

Demethanation Trend of Hydrochar Induced by Organic Solvent Washing and Its Influence on Hydrochar Activation.

Hydrochar derived from hydrothermal carbonization (HTC) has been recognized as a promising carbonaceous material for environmental remediation. Organic solvents are widely used to extract bio-oil from hydrochar after HTC, but the effects of solvent extraction on hydrochar characteristics have not been investigated. This study comprehensively analyzed the effects of different washing times and solvent types on the hydrochar properties. The results indicate that the mass loss of hydrochar by tetrahydrofuran washing occurred mainly in the first 90 min, and the loss ratios of elements followed a descending order of H > C > O, resulting in a decrease in the H/C atomic ratio and an increase in the O/C atomic ratio. The use of various solvents for washing brought about hydrochar loss ratios in a descending order of petroleum ether < dichloromethane < acetone < tetrahydrofuran. The results from the Van Krevelen diagram and Fourier transform infrared, 13C nuclear magnetic resonance, and X-ray photoelectron spectroscopies further confirmed that demethanation controlled this washing process. Most importantly, the surface area of hydrochar increased after bio-oil removal via washing, which promoted the surface area development for hydrochar-derived magnetic carbon composites, but to some extent decreased the microporosity. Additionally, hydrochar washing by organic solvent has important implications for the global carbon cycle and its remediation application.

Impact of HTC reaction conditions on the hydrochar properties and CO2 gasification properties of spent grains

The impact of residence time and temperature during hydrothermal carbonization (HTC) on hydrochar properties and CO2 gasification properties has been studied for brewers' spent grain (BSG), treated at temperatures from 180°C to 280°C and residence times from 0.5 to 12hours. Lower heating values (LHV) of the hydrochars are found to increase to values of bituminous coal and anthracite as reaction severity increases. Temperature is found to have a greater influence on the LHV of the hydrochar than residence time. Mass and energy yields decrease with increasing reaction severity. With higher reaction severity decreased molar O/C and H/C ratios as well as decreased volatile contents and increased fixed carbon contents are observed. The influence of residence time is more pronounced for the formation of fixed carbon, main carbonization reactions occur for a reaction severity greater than 180°C and 0.5hours. Char reactivity is found to decrease with increasing carbonization reaction severity with a strong influence of both residence time and temperature due to the formation of fixed carbon in the hydrochar. Activation energies are decreased with increased carbonization temperature but only mildly affected by residence time. Hereby the catalytic influence of ash compounds has to be further determined.

Properties of Animal-Manure-Based Hydrochars and Predictions Using Published Models

In order to fully utilize hydrothermal carbonization (HTC) to produce value-added hydrochars from animal manures, it is important to understand how process conditions (e.g., temperature, reaction time, solids concentration) influence product characteristics. The effect of process conditions on the extent of carbonization, solid yield, energy density, and combustion characteristics of the hydrochars, as well as the fate of carbon and nitrogen in the three phase process was investigated for swine solids and poultry litter. While hydrothermal treatment increased the percentage of fixed carbon in the solids compared to the original feedstock, increasing the reaction time 5-fold did not increase the percentage of fixed carbon in the hydrochars. Increasing the temperature had an inverse effect on solid yield and, to a lesser extent, energy content. Three different published statistical models in the literature were evaluated for their ability to predict hydrochar properties, based on feedstock properties and pr...