Low-temperature Hydrothermal Carbonization Research Articles

Low-Temperature Hydrothermal Carbonization of Fresh Pig Manure: Effects of Temperature on Characteristics of Hydrochars

AbstractThe impacts of temperature on the characteristics of hydrochars from pig manure (PM) following hydrothermal carbonization (HTC) at 140°C–220°C for 1 h were investigated. The total organic c...

Carbon Adsorbents from Sugarcane Bagasse Prepared through Hydrothermal Carbonization for Adsorption of Methylene Blue: Effect of Heat Treatment on Adsorption Efficiency

A carbon hydrochar material (BG-230) has successfully been prepared by conversion of sugarcane bagasse through low-temperature hydrothermal carbonization (HTC) at 230 °C. BG-230 was subsequently subjected to further thermal treatment at 400 °C for 1 hour under air (BG-230/400). Both resulting materials were characterized using specific surface area analysis (BET), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), elemental analysis (C, H, N, O) and X-ray photoelectron spectroscopy (XPS). The characterization results showed that BG-230 possesses a higher number of acidic-oxygen functionalities than BG-230/400, indicating that the thermal treatment at 400 °C under air removed those functionalities. The adsorption properties were evaluated by the removal of methylene blue (MB) from aqueous solutions. The adsorption capacity of MB was found to be higher for BG-230 (∼100 mg g-1) than that for BG-230/400 (∼25 mg g-1). The investigation into the adsorption performance of both prepared adsorbents suggests that the oxygen functional groups on the prepared carbon materials are responsible for the adsorption mechanism.

Utilization of Waste Biomass for the Synthesis of Functionalizable Support for Covalent Anchoring of Active Organo Catalyst

A single step synthetic procedure for carbon microspheres from agricultural waste residue (sugarcane bagasse) by low-temperature hydrothermal carbonization using oxalic acid as a hydrating/dehydrating agent is developed. The FTIR and XPS spectroscopy analysis indicates the presence of −OH, −COOH, and C═O functional groups on the surfaces of carbon spheres. These functional groups of the carbon spheres were utilized as a novel route to anchor 3-aminopropyl-triethoxysilane and 3-(2-aminoethylamino)propyl)-trimethoxysilane via condensation of triethoxy/trimethoxy silanes for the synthesis of organo base supported on carbon catalysts. The catalytic activity of the obtained supported organo-base catalyst was demonstrated for C–C bond forming (Henry) reaction. Among all prepared catalysts, 3-(2-aminoethylaminopropyl)-trimethoxysilane grafted in toluene showed high conversion (up to 100%) of aldehydes with excellent selectivity toward β-nitrostyrene. The catalyst was reused five times without losing significant ...

Hydrochars based on cigarette butts as a recycled material for the adsorption of pollutants

This paper reports the synthesis of hydrochair from cigarette butts (CBs) via low-temperature hydrothermal carbonization without using inert gas. The processing time and applicability of the material for removal of methylene blue (MB) was also examined. The proposed material exhibited significant capacity for adsorption in a basic environment, owing to excess OH− ions that enhanced the negative potential of the adsorbent surfaces, resulting in greater removal of MB. The amount of MB adsorbed on the activated samples was approximately three-times higher than on the non-activated coals. The obtained kinetic data were better fit with pseudo-second order and Elovich models. The Langmuir model best correlated with the equilibrium data suggesting that the adsorption of MB on the hydrochars occurred predominantly via chemisorption. The thermodynamic parameters indicated the spontaneity of the adsorption process of MB (ΔG° < 0) and its endothermic nature (ΔH° > 0). The positive entropy values (ΔS° > 0) indicated increasing irregularity at the solution-solid interfaces, demonstrating high affinity of adsorption owing to the effectiveness of adsorbent-adsorbate attraction forces. The CB-prepared hydrochars have great potential in applications aimed at the removal of organic pollutants from aqueous solutions.

Comparison study on fuel properties of hydrochars produced from corn stalk and corn stalk digestate

In this study, hydrothermal carbonization (HTC) was employed to upgrade the fuel quality of corn stalk digestate (CSD) ranged from 190 to 240 °C. Meanwhile, a comparison of corn stalk (CS) was investigated to explore the effects of anaerobic digestion (AD) on the fuel property and combustion behavior of hydrochars. The results showed that the HTC increased the carbon content and heating value of hydrochars while decreased the alkali and alkaline earth metals (AAEMs) content and hydrophilicity. Compared to CS, the CSD showed higher low-temperature HTC activity, but lower sensitivity to temperature changes. The improvement of fuel properties on CSD was limited with the HTC temperature increasing. The thermogravimetric analysis displayed the relative low temperature HTC (190 and 215 °C) improved the combustion of CSD, while 240 °C was appropriate for CS. FTIR and SEM analyses confirmed the aromatization and formations of spherical particles in CS hydrochars obtained at 240 °C, respectively, but was not observed in CSD hydrochars. The AD process weakened the pyrolysis-like reaction of cellulose in HTC. Considering the energy balance and engineering, 190 °C was recommend for the preparation of solid fuels from CSD and seemed to be more viable for the combination of AD and HTC.

Efficient Low Temperature Hydrothermal Carbonization of Chinese Reed for Biochar with High Energy Density

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 from 200 °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 Electron Microscope (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.

Functionalized hydrothermal carbon derived from waste pomelo peel as solid-phase extractant for the removal of uranyl from aqueous solution.

To develop a high-performance solid-phase extractant for the separation of uranyl f, pomelo peel, a kind of waste biomass, has been employed as carbon source to prepare carbonaceous matrix through low-temperature hydrothermal carbonization (200°C, 24h). After being oxidized by Hummers method, the prepared hydrothermal carbon matrix was functionalized with carboxyl and phenolic hydroxyl groups (1.75mmolg-1). The relevant characterizations and batch studies had demonstrated that the obtained carbon material possessed excellent affinity toward uranyl (436.4mgg-1) and the sorption process was a spontaneous, endothermic and rapid chemisorption. The selective sorption of U(VI) from the simulated nuclear effluent demonstrated that the sorbent displayed a desirable selectivity (56.14% at pH=4.5) for the U(VI) ions over the other 11 competitive cations from the simulated industrial nuclear effluent. The proposed synthetic strategy in the present work had turned out to be effective and practical, which provides a novel approach to prepare functional materials for the recovery and separation of uranyl or other heavy metals from aqueous environment.

Consecutive preparation of hydrochar catalyst functionalized in situ with sulfonic groups for efficient cellulose hydrolysis

Hydrochars in situ functionalized with –SO3H groups were generated from kenaf core via a low-temperature hydrothermal carbonization process of 105 °C with a consecutive catalysis of H2SO4. The micro-morphology of the hydrochars was strongly affected by the sulfuric acid concentration. Sphere-like particles with size varying between 200 nm and 1 μm were obtained when the acid concentration was 52 wt%. Acid density of the hydrochar increased with the H2SO4 concentration increasing. The presence of considerable acidic groups of –SO3H, –COOH, and –OH on the surface of hydrochars was evidenced by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. The hydrochar obtained can be used directly for effective catalytic hydrolysis of cellulose without any post-modification. This study proposed a promising sustainable and cost-effective route for facile production of acidic hydrochar from crude plant with tunable properties.

Magnetic carbon composites with a hierarchical structure for adsorption of tetracycline, prepared from sugarcane bagasse via hydrothermal carbonization coupled with simple heat treatment process

Sugarcane bagasse, an agricultural waste, was successfully converted into novel magnetic carbon composites by low temperature hydrothermal carbonization at 230°C for 24h, followed by heat treatment at 400°C for only 1h in air. Effects of NaOH and iron loading on the chemical properties of the composites were studied. In addition, various techniques were employed to investigate the physicochemical properties of the composites. Adsorption kinetics and isotherms were investigated with tetracycline (TC) for the magnetic composites. The magnetic carbon composite exhibited 48.35mg/g maximum adsorption capacity and was highly stable chemically and mechanically, with also good magnetic properties. The adsorption of TC by the magnetic adsorbent was mainly attributed to H-bonds and π-π interactions. The results indicate that waste sugarcane bagasse from the sugar industries can be efficiently transformed to a magnetic adsorbent for TC removal via a facile environmentally friendly method.

Gasification characteristics of hydrochar and pyrochar derived from sewage sludge

Two types of the biochars, pyrochar and hydrochar derived from low temperature pyrolysis (LTP) and hydrothermal carbonization (HTC) of sewage sludge were prepared and characterized. Their gasification properties were further experimentally evaluated. The results showed that the hydrochar was more hydrophobic than the pyrochar. The hydrochar was rich in nitrogen-containing functional groups and increased nickel, iron, alkali and alkaline earth metallic species compared to the raw sludge and pyrochar. It enhanced the interactions between the carbon surface and hydrogen bonding as well as gasification reactivity of the hydrochar, thus resulting in a higher hydrogen concentration and yield than the pyrochar under identical conditions. Additionally, the hydrochar had a more porous structure on the surface, facilitating the pores better accessible for condensable hydrocarbon molecules and thus improved the gas production and gasification efficiency. Although the energy recovery efficiency of LTP-gasification method was higher than that of HTC-gasification approach, the total energy consumption during the HTC pretreatment combined with subsequent gasification was lower than the energy evolved in the corresponding product gas in most gasification conditions. This study demonstrates that the integration of HTC pretreatment and subsequent gasification has promising potential for hydrogen-rich syngas production from sewage sludge.

Conversion of Natural Tannin to Hydrothermal and Graphene-Like Carbons Studied by Wide-Angle X-ray Scattering.

The atomic structure of carbon materials prepared from natural tannin by two different techniques, high-temperature pyrolysis and low-temperature hydrothermal carbonization, was studied by wide-angle X-ray scattering. The obtained diffraction data were converted to the real space representation in the form of pair distribution functions. The X-ray photoelectron spectroscopy measurements provided information about the chemical state of carbon in tannin-based materials that was used to construct final structural models of the investigated samples. The results of the experimental data in both reciprocal and real spaces were compared with computer simulations based on the PM7 semiempirical quantum chemical method. Using the collected detailed information, structural models of the tannin-based carbons were proposed. The characteristics of the investigated materials at the atomic level were discussed in relation to their preparation method. The rearrangement of the tannin molecular structure and its transformation to graphene-like structure was described. The structure of tannin-based carbons pyrolyzed at 900 °C exhibited coherently scattering domains about 20 Å in size, consisting of two defected atomic layers and resembling a graphene-like arrangement.

Direct synthesis of carbon-based microtubes by hydrothermal carbonization of microorganism cells

Streptomyces sporoverrucosus dwc-3, a type of microbial biomass was used to prepare carbon-based microtubes (CMTs) due to their natural micro-tubular structure. After low temperature hydrothermal carbonization at 180°C, CMTs with a diameter of 400–500nm and a wall thickness of about 50nm was obtained. It was demonstrated that the intrinsic biologic tissue of the soft biomass could also be well inherited during the formation process of CMTs. Electrochemical evaluations in 0.5M Na2SO4+0.1M H2SO4 solution at room temperature showed that the prepared CMTs exhibited high electrocatalytic activity for hydrogen evolution reaction. The significant outcomes in this work showed a novel approach to fabricate CMTs that can be used as non-metal electrocatalysts for hydrogen evolution reaction by using low temperature hydrothermal carbonization method.

Hydrothermal preparation of highly porous carbon spheres from hemp (Cannabis sativa L.) stem hemicellulose for use in energy-related applications

This work provides a new route for high-value-added utilization of hemicellulose extracted from agricultural crops. Hemp stem hemicellulose is chosen as precursor to prepare well-shaped carbon spheres with large surface area of up to 3062m2g−1 by an improved low-temperature hydrothermal carbonization method and KOH activation. A pre-carbonization strategy before activation is also employed to keep activated carbons in perfectly spherical morphology even at a high KOH/carbon ratio 5/1. The influence of KOH/carbon ratio on the structure, surface chemistry and application performance is systematically investigated. Due to abundant micropores and ample oxygen functionalities, the samples can achieve a high capacitance of 318Fg−1 as electrode material in supercapacitors. The plentiful micropores also lead to excellent CO2 and CH4 adsorption capacities at ambient pressure and 0°C. Hemicellulose-derived activated carbon spheres should be potentially sustainable materials applied in energy and environmental areas.

하수슬러지의 Biochar특성을 이용한 토양내 중금속 제거 연구

This study proposed a low temperature hydrothermal carbonization to treat and recycle sewage sludge and determined the optimal conditions for the biochar production. The physical and chemical properties of biochar were analyzed and its sorption capacity for heavy metals was evaluated. To produce biochar, 50 g of sewage sludge was heated at 220, 230, and <TEX>$240^{\circ}C$</TEX> for 1, 2, 3, 5, 8, and 10 hours in a reactor. The optimal conditions to produce biochar was <TEX>$230^{\circ}C$</TEX> and 8 hours. Sorption capacity tests were conducted for arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), zinc (Zn) and nickel (Ni). Among them, lead was shown the highest heavy metal adsorption efficiency of biochar, followed by copper, cadmium, zinc, and nickel, but arsenic was hardly adsorbed overall.

Hydrothermal preparation of carbon nanosheets and their supercapacitive behavior

Deflated-balloon-like and crumpled carbon nanosheets were prepared via a low-temperature hydrothermal carbonization of glucose at the two-phase interfaces. A low amount of glucose and a high amount of sodium dodecyl sulfate were found to be propitious to the formation of graphitic carbon nanosheets with low thickness. Their applications as supercapacitive materials were demonstrated.