Hydrothermal Char Research Articles

Study on the characteristics of microwave pyrolysis of pine wood catalyzed by bimetallic catalysts prepared with microwave-assisted hydrothermal char

Bimetallic hydrothermal char catalysts (Co-Ni/MHC, Fe-Co/MHC, Fe-Ni/MHC) were prepared through ionic hydrothermal methods and microwave high-temperature activation. During catalyst preparation, different metals synergistically promoted the formation of ordered carbon structures such as carbon nanotubes and carbon microspheres, respectively. Serving both as microwave absorbers and catalysts for the microwave pyrolysis of pine wood, the bimetallic catalysts exhibited distinct advantageous characteristics. Fe-Ni/MHC exhibited excellent microwave absorption properties and was able to assist the PW to heat up rapidly at a rate of 6.17 °C/s, benefiting from which PW achieved a high bio-oil yield of 44.0 % in the microwave-assisted catalytic pyrolysis process. Using Co-Ni/MHC as a catalyst resulted in bio-oil with up to 42.7 % styrene content and had good catalytic effects on the formation of CO and H2. This study provides a scientific reference for the application of hydrothermal treatment and microwave-assisted pyrolysis in biomass pyrolysis technology.

Microwave-induced biomass pyrolysis coupled with hydrothermal char composites catalysis to selectively prepare phenols-rich liquid products

In this study, three types of hydrothermal char-supported metal nanoparticle composites (HCM-Fe, HCM-Co, and HCM-Ni) were prepared using pinewood as the raw material via an ion hydrothermal pretreatment followed by microwave heating method, which were then served as both catalysts and microwave absorbers to enhance the rapid pyrolysis of pine wood particles for the selective preparation of phenols-rich bio-oil. The combined effects of hydrothermal carbonization and microwave heating enriched the pore structure of the composite surface, yielding ordered carbon structures such as carbon microspheres, carbon nanotubes, and graphite layers. Also, metal nanoparticles were generated and uniformly anchored on the hydrothermal char matrix by the graphite layers. The three types of hydrothermal carbon-based catalysts exhibit excellent microwave absorption performance, facilitating rapid heating of pine particles at a rate as fast as 5.49 °C/s. Among these catalysts, HCM-Co demonstrates the best catalytic performance, efficiently promoting the cleavage of the β-O-4 bond in lignin and achieving a liquid product yield of 38.4 % at 500 °C. The resulting bio-oil is characterized by its richness in phenolic compounds, accounting for 54.9 % of its composition, and partial mitigation of acidity.

Preparation of hydrochar by one‐step hydrothermal carbonization with potassium ferrate‐assisted activation for the removal of tetracycline in water

AbstractBACKGROUNDWoody biomass has a low hydrothermal‐carbonization (HTC) degree and the hydrolysis process of some of its components is similar to that of saccharides. To improve the adsorption performance of wood‐chips hydrothermal char (hydrochar) for tetracycline in water, molasses and potassium ferrate (K2FeO4) were added to its HTC process; K2FeO4 catalyzed the carbonization of raw materials and the surface of wood chips and saccharides in molasses, along with the iron ions mutually polymerized, added more reactive‐oxygen functional groups to the hydrochar surface. The effects of K2FeO4 and molasses on the morphology, pore structure, surface oxygen‐containing functional groups, and tetracycline‐adsorption properties of hydrothermal carbon were investigated.RESULTSThe strong oxidizing properties of K2FeO4 promoted the hydrolysis of raw material. The modified hydrochar formed more oxygen‐containing functional groups and produced FeO bonds with an increased specific surface area. For the adsorption of tetracycline in water, the pseudo‐second‐order kinetic model and Freundlich isotherm were more consistent with the hydrochar‐adsorption process. The adsorption mechanism favored a combination of physical and chemical adsorption, with chemisorption being predominant. The maximum tetracycline‐adsorption capacity of HTC–0.15Fe was 119.7 mg g−1, which is significantly higher than that of unmodified hydrochar HTC‐C (56.4 mg g−1). Furthermore, molasses addition effectively improved the hydrochar structure, forming carbon‐coated iron‐core particles on its surface, which increased adsorption performance.CONCLUSIONK2FeO4‐catalyzed hydrochar produced from wood chips and sugarcane molasses is an effective adsorbent for tetracycline removal from water. This work provides innovative insights into the recycling and effective use of wood chips and molasses for environmental remediation and waste treatment. © 2023 Society of Chemical Industry (SCI).

Preparation and Electrochemical Performance of Bio-Oil-Derived Hydrochar as a Supercapacitor Electrode Material.

The rapid consumption of fossil energy and the urgent demand for sustainable development have significantly promoted worldwide efforts to explore new technology for energy conversion and storage. Carbon-based supercapacitors have received increasing attention. The use of biomass and waste as a carbon precursor is environmentally friendly and economical. In this study, hydrothermal pretreatment was used to synthetize coke from bio-oil, which can create a honeycomb-like structure that is advantageous for electrolyte transport. Furthermore, hydrothermal pretreatment, which is low in temperature, can create a low graphitization degree which can make heteroatom introduction and activation easier. Then, urea and KOH were used for doping and activation, which can improve conductivity and capacitance. Compared with no heteroatom and activation hydrothermal char (HC) (58.3 F/g at 1 A/g), the prepared carbon material nitrogen doping activated hydrothermal carbon (NAHC1) had a good electrochemical performance of 225.4 F/g at 1 A/g. The specific capacitance of the prepared NAHC1 was improved by 3.8 times compared with that of HC.

The effect of microwave hydrothermal treatment on the combustion behavior of sewage sludge

In this study, the thermal behavior of microwave hydrothermal char of sewage sludge (MTC) was compared with dried sludge (DS) and char produced by electric hydrothermal treatment (ETC). The retention ratio of volatile matter in MTC was raised by 51.2% compared with in HTS, while their dewaterability by centrifugation were very close. The kinetic parameters of thermal disposal process of the DS and hydrochars were determined from TG analysis. It was found that the activation energy of combustion was reduced from 44.20 kJ/mol of DS to 47.29 kJ/mol for ETC. For MTC, the activation energy was slightly decreased (43.22 kJ/mol). In addition, the highest weight loss rate (0.49%/min) in combustion was also found for MTC. The evolution of gaseous nitrogen compounds was obtained by FTIR analyzer combined with TG. The results indicated that in devolatilization process, the emission of NH3, the main precursor of NOx in combustion, was postulated to higher temperature for MTC. In conclusion, MTC has a better combustion performance and a close dewaterability compared with to ETC. This study provided a new choice for the pre-treatment method of sewage sludge before combustion.

Production and characterization of adsorbents from a hydrothermal char by pyrolysis, carbon dioxide and steam activation

Production and characterization of adsorbents from a hydrothermal char by pyrolysis, carbon dioxide and steam activation

Preparation of sorbents derived from bamboo and bromine flame retardant for elemental mercury removal

This work showcases cost-effective elemental mercury capture strategy enabled by bamboo saw dust and bromine flame retardant (BFR) derived sorbent prepared by a novel hydrothermal-pyrolysis method. The hydrothermal treatment of bamboo and BFR blend was conducted in subcritical water resulting in a hydrothermal char. Subsequently, the hydrothermal char was pyrolyzed in nitrogen atmosphere leading to an improved pore architecture. The resulting biomaterials were proven highly effective for Hg removal. A thorough analysis of the physicochemical properties of the samples was conducted by means of BET, SEM, XRD, XPS and FT-IR. Key parameters such as bamboo/BFR ratio, hydrothermal temperatures and pyrolysis temperatures influence Hg0 removal capacity of our bio-sorbents. Overall, the optimal bamboo/BFR ratio, hydrothermal temperature and pyrolysis temperature are 2:1, 320 °C and 800 °C, respectively. Under these optimized conditions, a very promising elemental mercury removal efficiency of 99% is attained. The kinetics and mechanism of Hg0 removal are also proposed. The experimental data fit well with a pseudo-second-order model, indicating that Hg0 adsorption over sorbents was dominated by chemisorption. Our results indicate that the C–Br groups in sorbents provide active sites for oxidizing Hg0 into HgBr2.

Experimental and Computational Evaluation of Heavy Metal Cation Adsorption for Molecular Design of Hydrothermal Char

A model hydrochar was synthesized from glucose at 180 °C and its Cu(II) sorption capacity was studied experimentally and computationally as an example of molecular-level adsorbent design. The sorption capacity of the glucose hydrochar was less than detection limits (3 mg g−1) and increased significantly with simple alkali treatments with hydroxide and carbonate salts of K and Na. Sorption capacity depended on the salt used for alkali treatment, with hydroxides leading to greater improvement than carbonates and K+ more than Na+. Subsequent zeta potential and infrared spectroscopy analysis implicated the importance of electrostatic interactions in Cu(II) sorption to the hydrochar surface. Computational modeling using Density Functional Theory (DFT) rationalized the binding as electrostatic interactions with carboxylate groups; similarly, DFT calculations were consistent with the finding that K+ was more effective than Na+ at activating the hydrochar. Based on this finding, custom-synthesized hydrochars were synthesized from glucose-acrylic acid and glucose-vinyl sulfonic acid precursors, with subsequent improvements in Cu(II) adsorption capacity. The performance of these hydrochars was compared with ion exchange resins, with the finding that Cu(II)-binding site stoichiometry is superior in the hydrochars compared with the resins, offering potential for future improvements in hydrochar design.

Nanoporous Carbon from Water Hyacinth Via Hydrothermal Carbonization

Nanoporous carbon materials have been successfully synthesized from water hyacinth via hydrothermal carbonization (HTC). This research was studied the effect of hydrothermal temperature from 160 - 200 °C and reaction time for 4 - 24 h. Afterwards, carbonization was carried out at the temperature of 600 - 900 °C for 2 h in N2 atmosphere for developing porosity and even removing contaminants of hydrothermal char to obtain the porous carbon. The physico-chemical properties of nanoporous carbon materials were comprehensively characterized through Scanning electron microscope (SEM), Fourier transforms infrared spectroscopy (FT-IR), CHN elemental analysis, X-ray diffraction (XRD) and BET analysis. The adsorption capacity and carbon content of nanoporous carbon materials from water hyacinth were increased with increased hydrothermal carbonization temperature and time. Performing HTC at 200 °C for 12 h. Is the optimum condition to synthesis of precursor materials for good adsorbent.

Influence of the Mineral Content on the Emissivity of Hydrothermal Char

AbstractThe influence of minerals on solid fuel conversion is an important topic and has so far been addressed focusing mainly on the catalytic effects. Here, the impact of iron oxide on the emissivity of burning char particles was investigated. Synthetic, hydrothermally carbonized char was doped with SiO2 or with a mixture of SiO2 and Fe2O3. The sample was then exposed to an oxy‐fuel atmosphere in a laboratory reactor. An established pyrometer/infrared (IR) spectrometer setup was used to measure the size, temperature, and IR radiation of single burning particles. Based on these measurements, the spectral and total emissivity in the near‐IR (1.25–2.25 μm) and the total emissivity in the mid‐IR region (2.4–5.5 μm) were calculated. The results show that the iron content directly influences the emissivity of char during combustion.

Granular Activated Carbon from Grape Seeds Hydrothermal Char

A two-stage conversion process for the production of a valuable product from biomass waste, i.e., grape seeds activated carbon (GSAC) was investigated. Such process involved hydrothermal carbonization (HTC) of grape seeds, followed by chemical activation with potassium hydroxide (KOH). Different HTC temperatures (THTC = 180–250 °C), as well as different KOH:hydrochar ratios (R = 0.25:1–1:1), were explored. The samples that were obtained from both stages of the biomass conversion process were analyzed in terms of textural characterization (apparent total and micro-pore surface areas, total and micro-pore volumes, pore size distribution), proximate and ultimate compositions, thermal stability, surface morphology (via SEM), and surface chemistry characterization (via FTIR). Overall yields of approximately 35% were achieved, which are comparable to those obtained with the state-of-art one-stage process. In a wide range of operating conditions, the higher THTC and R, the higher was the surface area of the GSAC, which was maximal (above 1000 m2/g) for THTC = 250 °C and R = 0.5. At such optimal conditions, around 90% of the total porosity was due to micro-pores. Such a trend was not fulfilled at the most severe operating conditions (THTC = 250 °C; R = 1), which resulted in larger pore size, causing surface area reduction. A proper selection of the process parameters of both the process stages gives great opportunities of tuning and optimizing the overall process. The produced GSACs showed a remarkable thermal stability, and their surface appeared rather free of functional groups.

Characterization of carbon fibers from Thai horse manure via hydrothermal carbonization

Carbon fibers from biomass have been successfully prepared via hydrothermal-carbonization and activated in air atmosphere for catalyst supporter. In this research, we study the effect of temperature (160-200 °C) and residence time (4-24 h) to pretreat the initial carbon precursor in terms of chemical properties (i.e. carbon content, surface functional group) including the physical properties such as porosity and total surface areas. Afterwards, carbonization was obtained at the temperature of 300 °C for 2h for developing the porosity and even removing the contaminants of hydrothermal char to reach the carbon fiber. Nevertheless, carbon fiber was characterized. Scanning electron microscopy (SEM) and Functional Transform Infrared spectroscopy (FTIR) were employed to characterize physical morphology and functional group on the surface, respectively.

Structural analysis of hydrothermal char and its models by density functional theory simulation of vibrational spectroscopy

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 Kekulé 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.

Applications of subcritical and supercritical water conditions for extraction, hydrolysis, gasification, and carbonization of biomass: a critical review

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.

Spectroscopic tracking of mechanochemical reactivity and modification of a hydrothermal char

A glucose hydrothermal char (HTC) was synthesized and ball milled to break chemical bonds, generate defects, and form new chemical structures.

Removal of copper (II) and phenol from aqueous solution using porous carbons derived from hydrothermal chars

The feasibility of hydrothermal char (HTC), a byproduct from biomass hydrothermal liquefaction for bio-oil production, as raw material for preparation of porous carbons was investigated in the present study. The resultant HTC-derived porous carbons were characterized and utilized as adsorbents for copper (II) and phenol removal from aqueous solution. Compared with porous carbons using pyrolytic char as precursor, the HTC-derived porous carbons exhibited unique textural features, e.g., narrow pore size distribution, high surface area and large pore size. In addition, FT-IR analysis confirmed that substantial amount of ketene groups existed on the surface of the HTC-derived porous carbons. As the adsorbents, the copper (II) adsorption onto HTC-derived carbons was strongly affected by the pH value of the solution in comparison with phenol adsorption. The carbons derived from pinewood and rice husk HTC exhibited high adsorption capacity of 83.88 and 39.30 mg/g for phenol and 25.18 and 22.62 mg/g for copper (II), respectively. The adsorption data for copper (II) and phenol onto the carbon adsorbents could be well described by Langmuir and Freundlich models. In comparison with pinewood sawdust HTC-derived carbon, the adsorption onto rice husk HTC-derived carbon preferentially followed Freundlich model due to the presence of silica on the surface.

Characterization and application of chars produced from pinewood pyrolysis and hydrothermal treatment

Two types of pinewood chars, hydrothermal char (H300) and pyrolytic char (P700) from biomass-to-energy conversion were characterized and used as adsorbent for the copper removal from aqueous solution. The result showed that the pinewood underwent a deeper carbonization during pyrolysis process and more activated sites available and stable carbon–oxygen complex existed after hydrothermal treatment. Comparing with raw pinewood, hydrothermal treatment increased 95% total oxygen-containing groups (carboxylic, lactone and phenolic group) while 56% oxygen-containing groups decreased after pyrolysis process. SEM analysis indicated that both hydrothermal and pyrolytic processes developed rough surface with new cavities on the chars, and the BET surface area were 21 and 29 m 2/g for H300 and P700, respectively. Although H300 had lower surface area, its adsorption capacity for copper was much higher than P700 since ion-exchange reaction was the predominant removal mechanism by H300, while physical adsorption dominated by P700. The adsorption data could be well described by Langmuir isotherm model for copper onto both H300 and P700.