Low-temperature Hydrothermal Carbonization Research Articles

Macroscale properties and atomic-scale mechanisms of ash removal in low-temperature hydrothermal carbonization

Biogenic ash is a significant impediment to the utilization of agricultural residues in biofuel production. Such challenge can be addressed by various treatments, as demonstrated in this study on the experimental and computational mechanisms involved in the hydrothermal treatment (HT) of wheat straw. A combination of classical (all-atom) molecular dynamics simulations of cellulose carrying silica and calcium species, along with first principles quantum chemical calculations, indicates the dissociation of inorganics from the cellulose with increased HT temperature. This observation is confirmed by experimental evidence of effective ash removal by HT, showing at least 50% removal of sulfur, chlorine, potassium, and calcium, and 12.5% of silica, leading to a reduced total ash content (from 6.7% to 4.2%).Changes in structural features upon HT, such as surface cellular structure and porosity, were revealed, accompanied by an increased specific surface area (from 1.17 to 6.34 m2/g). Our simulations suggest that silica binds tightly to the hydrophobic face of cellulose at room temperature, but HT significantly reduces the binding free energy of association with both hydrophobic and hydrophilic surfaces. Most significantly, ash removal leads to an increased calorific value, rising from approximately 16 MJ/kg to about 19 MJ/kg, along with improved thermal behavior. The improved integration combustion index parameter S indicates that the combustion properties improve with ash removal efficiency. The proposed atomic-level mechanism behind the observed removal of inorganics during mild HT underscores the potential of such treatment in producing energy-dense wheat straw, a widely available agricultural residue.

Ionic liquid catalyzed low-temperature hydrothermal carbonization of sewage sludge to produce hydrochar with low heavy metal content and positive energy recovery

An ionic liquid (IL, [DMAPA]HSO4) was prepared to facilitate the removal of heavy metals by hydrothermal carbonization (HTC) in sewage sludge (SS) and to obtain a positive energy recovery (ER, (Energyoutput/Energyinput − 1) > 0). The results found that the removal efficiencies of the Fe, Mn, Zn, Co, and Cd from SS exceeded 75 % with positive ER (6 %) at 20 wt% IL dosage (IL:SS). IL promoted the HTC reactions of proteins and polysaccharides to produce fixed carbon and small molecule polymers. The process mainly relies on IL to catalyze the dehydration and graphitization of SS and to destroy the heavy metal binding sites such as carboxyl and hydroxyl groups. Additionally, IL aids in constructing the macropore structures in hydrochar, thereby facilitating the release of heavy metals and water during the HTC process. This discovery holds promise for removing heavy metals from SS by one-pot HTC processes with positive energy recovery.

Sustainable catalysts for esterification: Sulfonated carbon spheres from biomass waste using hydrothermal carbonization

Sulfonated catalysts derived from carbon spheres obtained from açai seeds (Euterpe oleracea) were synthesized using a hydrothermal carbonization method, followed by subsequent direct sulfonation. These solid acid catalysts, in the form of carbon spheres, were characterized through various techniques, including thermogravimetry, X-ray diffraction, infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy for elemental mapping (SEM-EDS), and Boehm titration. Two types of catalysts were produced through low-temperature hydrothermal carbonization. One catalyst underwent hydrothermal carbonization with the assistance of a catalyst, while the other was carbonized solely using water. The catalytic activity was assessed for up to the fifth reuse in the esterification reaction between oleic acid and methanol, employing 5% of the catalyst by mass, a 1-h reaction time at 100 °C, and a molar ratio of oleic acid to methanol at 1:12. The catalyst produced through hydrothermal carbonization in water demonstrated the best performance, with a conversion rate ranging from 91% to 88% over the five cycles, while the catalyst produced with the aid of a catalyst yielded conversion rates of 89%–82% over the same five cycles. Total acidity and sulfonic group acidity were calculated for each recycling of the aforementioned catalysts. As expected, catalytic activity was primarily influenced by the concentration of strong acid sites from the sulfonic groups, which decreased with each use of the catalyst. Scanning electron microscopy analysis confirmed that the removal of lignin from biomass residues increased the conversion of holocellulose into carbon spheres, and the functionalization with sulfuric acid did not disrupt the spherical structures of the catalysts. Thermogravimetric and differential thermogravimetric analyses showed that both hydrochars and catalysts possessed satisfactory thermal stability for use in sulfonation and esterification reactions, respectively. The TG-MS analysis allowed for the observation of the decomposition temperature of sulfur-containing gaseous emissions. FTIR and XPS confirmed the expected functional groups for hydrochars and biomass-derived catalysts. Moreover, XPS confirmed that the majority of sulfur present in the catalysts existed in the form of sulfonic groups. The optimization of reaction parameters, such as temperature, time, catalyst loading, and the molar ratio of oleic acid to methanol, was carried out using the catalyst with the best performance over the recycling cycles (91%–88%). By slightly increasing the values of these parameters in the esterification model reaction (5% catalyst by mass, 1-h reaction time at 100 °C, and a molar ratio of oleic acid to methanol of 1:12), oleic acid conversion between 89% and 93% was achieved. The utilization of açai seed-derived materials in this study showcases potential environmental benefits by reducing waste associated with açai seed commercialization. Additionally, these catalysts are considered green, as they are quick, cost-effective, and simple to produce, while exhibiting excellent catalytic activity and recyclability.

Low-temperature hydrothermal carbonization of activated carbon microsphere derived from microcrystalline cellulose as carbon dioxide (CO2) adsorbent

Activated carbon material produced by the low-temperature hydrothermal processes was needed to further decrease the production cost of CO2 adsorbent materials. In this study, we fabricated cellulose hydrochar microspheres (CHM) materials with a relatively low hydrothermal temperature (200 °C) with prolonged hydrothermal reaction time (48 h) using microcrystalline cellulose as a feedstock. The CHM is then further activated using a thermal and chemical agent. The activated carbon microsphere was then characterized using scanning electron microscopy (SEM), an X-ray diffractometer (XRD), and Fourier transforms infrared (FTIR) spectroscopy. The Brunauer–Emmett–Teller (BET) surface area (SBET) of the thermal activation (ACS) activated carbon was enhanced significantly with further chemical activation with KOH and NaOH, from 589 m2/g to 1334 m2/g and 2296 m2/g, respectively. Moreover, CHONS elemental analysis suggests that the chemical activation process enhances the surface functional group. Increasing textural properties and enrichment of the functional group of the ACS-NaOH and ACS-KOH samples gave a CO2 adsorption capacity up to 7.07 mmol/g after 300 min of contact. This finding enables the possibility of producing cellulose hydrochar microspheres using a low hydrothermal temperature that can be further activated to become CO2 adsorbent materials with great CO2 capture capabilities.

Development of Modified Mesoporous Carbon from Palm oil Biomass for Energy Storage Supercapacitor Application

Energy storage system research including battery and supercapacitor devices has been studied to increase efficiency, lower their cost and improve environmental friendliness. Supercapacitor (SC) device offers high transient response and power density which suitable for many applications. The electrodes in supercapacitor device usually produced from highly porous carbon materials. In this study, the modified mesoporous carbon was produced from Palm empty fruit bunch (EFB) biomass. The production of mesoporous carbon was done using a low-temperature hydrothermal carbonization process. The mesoporous carbon from EFB biomass has shown good properties in terms of high surface area and porosity. To improve the electrical conductivity of the carbon the modification by nitrogen doping with ammonium chloride and urea was studied. The effect of different nitrogen sources on surface area and pore properties were reported. The modified mesopore carbon was tested in a symmetrical swagelok supercapacitor cell to evaluate the specific capacitance and efficiency using galvanostatic charge-discharge method. The modified mesoporous carbon with urea doped exhibits the highest specific capacitance of 121 F g-1 at current loading of 0.1 A g-1 in an aqueous 1M H2SO4 electrolyte. The modified mesoporous carbon with urea doped has lower internal resistance due to nitrogen from urea enhance the electronic conductivity of the electrodes and thus increase the supercapacitor performance.

Microwave-assisted biodiesel production using –SO3H functionalized heterogeneous catalyst derived from a lignin-rich biomass

The synthesis of biodiesel from renewable resources has immense potential as a sustainable and cost-effective energy alternative. In this work, a reusable –SO3H functionalized heterogeneous catalyst that has a total acid density of 2.06 mmol/g was prepared from walnut (Juglans regia) shell powder by low-temperature hydrothermal carbonization (WNS-SO3H). Walnut shell (WNS) contains more lignin (50.3%), which shows great resistance toward moisture. The prepared catalyst was employed for the effective conversion of oleic acid to methyl oleate by a microwave-assisted esterification reaction. The EDS analysis revealed the significant presence of sulfur (4.76 wt%), oxygen (51.24 wt%), and carbon (44 wt%) content. The results of the XPS analysis confirm the bonding of C–S, C–C, C=C, C–O, and C=O. Meanwhile, the presence of –SO3H (the responsible factor for the esterification of oleic acid) was confirmed by FTIR analysis. Under the optimized conditions (9 wt% catalyst loading, 1:16 oleic acid to methanol molar ratio, 60 min reaction time, and 85 °C temperature), the conversion of oleic acid to biodiesel was found to be 99.01 ± 0.3%. The obtained methyl oleate was characterized by employing 13C and 1H nuclear magnetic spectroscopy. The conversion yield and chemical composition of methyl oleate were confirmed by gas chromatography analysis. In conclusion, it can be a sustainable catalyst because the catalyst preparation controls the agro-waste, a great conversion is achieved due to the high lignin content, and the catalyst was reusable for five effective reaction cycles.

Investigation of charge storage in admixture of dextrose derived interconnected carbon spheres and micro-sized silicon

This work reports the investigations and electrochemical properties of a material, prepared by micro-sized Si (mSi) (upto 50 μm) which were partially coated with upto ~7 μm sized carbon microspheres (CS). The mixture of mSi enwrapped with CS ([email protected]) was fabricated using a low temperature and facile hydrothermal carbonization (HTC) of dextrose. XRD and Raman study revealed an amorphous phase due to carbon/SiO2 and a highly disordered nanocrystalline graphite respectively. Also, FTIR suggested the SiO bending and symmetric stretching of linear SiOSi. The electrochemical investigation with three cell assembly of fabricated [email protected] as an electrode material for supercapacitor application exhibited a maximum specific capacitance of 278.79 F g−1 at 5 mV s−1 scan rate which is around 7 times as calculated for pristine mSi powder. In [email protected], conducting, amorphous and nano crystalline carbon combined with mSi exhibited enhanced specific capacitance and a low equivalent series resistance (ESR). mSi served as anchor and contributed to enhancing specific capacitance and providing 2 V voltage window. This work opens the possibility of designing energy materials with the waste Si and pseudocapacitive materials.

Cotton-Based Activated Carbon Fiber with High Specific Surface Area Prepared by Low-Temperature Hydrothermal Carbonization with Urea Enhancement

The traditional preparation method of activated carbon fiber is high-temperature carbonization and activation. In this experiment, cotton-based activated carbon fiber was prepared by urea-enhanced low-temperature hydrothermal carbonization and activation method. A specific surface area of 2304.8 m2/g of activated carbon fiber prepared by low-temperature hydrothermal carbonization with urea enhancement was the maximum reported using biomass as a raw material, which was higher than that of activated carbon fibers prepared by other biomass raw materials. X-ray photoelectron spectroscopy and elemental analysis studies have shown that the form of N transformed and decomposed during the high-temperature process, leading to the separation of C–N. Thermogravimetry mass spectrometry characterization analysis found that K2CO3 of low-temperature hydrothermal-assisted KOH activation may fully react with the N-containing group produced during the carbonization process to generate NH3, which lead to the formation of more pore structures in the carbon materials. The adsorption capacity of activated carbon fiber activated by hydrothermal-assisted KOH for iodine could reach up to 2254.8 mg/g. This process provides a new idea for the preparation of high-performance activated carbon fibers.

Microwave-assisted synthesis of biodiesel by a green carbon-based heterogeneous catalyst derived from areca nut husk by one-pot hydrothermal carbonization

In this study, we have synthesized a solid acid catalyst by areca nut husk using low temperature hydrothermal carbonization method. The fabricated catalyst has enhanced sulfonic actives sites (3.12%) and high acid density (1.88 mmol g−1) due to –SO3H, which are used significantly for effective biodiesel synthesis at low temperatures. The chemical composition and morphology of the catalyst is determined by various techniques, such as Fourier transform infrared (FTIR), powder X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Scanning electron microscope (SEM), Energy disruptive spectroscopy (EDS), Mapping, Thermogravimetric analysis (TGA), CHNS analyzer, Transmission electron microscopy (TEM), particle size analyzer, and X-ray photoelectron spectroscopy (XPS). Acid–base back titration method was used to determine the acid density of the synthesized material. In the presence of the as-fabricated catalyst, the conversion of oleic acid (OA) to methyl oleate reached 96.4% in 60 min under optimized conditions (1:25 Oleic acid: methanol ratio, 80 °C, 60 min, 9 wt% catalyst dosage) and observed low activation energy of 45.377 kJ mol−1. The presence of the porous structure and sulfonic groups of the catalyst contributes to the high activity of the catalyst. The biodiesel synthesis was confirmed by gas-chromatography mass spectrometer (GC–MS) and Nuclear magnetic resonance (NMR). The reusability of the catalyst was examined up to four consecutive cycles, yielding a high 85% transformation of OA to methyl oleate on the fourth catalytic cycle.

Improving Kraft Pulp Mill Energy Efficiency through Low-Temperature Hydrothermal Carbonization of Biological Sludge

Of the various waste and side streams created in a kraft pulp mill, the biological sludges from the wastewater treatment plant are some of the most problematic to handle. Incineration is becoming a common solution as landfilling is no longer permitted by legislation in many countries, but this is also problematic due to the high moisture content, poor drying characteristics, and high ash content in the solids. This study evaluates the technical potential of mild hydrothermal carbonization (HTC) at 160 °C for 3 h to improve the energy efficiency of on-site incineration as a biosludge handling method. HTC treatment transforms wet organic substrates into a hydrophobic carbonaceous material (hydrochar). The heating value and elemental composition of both the sludge and the hydrochar product were analyzed. Based on this, a hydrothermal carbonization model developed earlier was adjusted for the feedstock, and process integration modelling performed to evaluate the performance impact on the power and heat generation at the mill. The results indicate that if the alternative is combustion in the power boiler, HTC pre-treatment could allow a significant increase in power generation. If the sludge is combusted in the recovery boiler, a practice often avoided in order to not introduce non-process elements to the chemical recovery cycle but sometimes necessary due to, e.g., absence of a power boiler, a much smaller increase is obtained. The increase is smallest if the freed evaporator plant capacity cannot be utilized for increasing the firing liquor dry solids content.

Low-temperature hydrothermal carbonization of pectin enabled by high pressure

Pectin is an important component of biomass waste widely existing in the plant cell wall. Hydrothermal carbonization of pectin can produce carbon materials for energy storage, adsorption, and catalysis. However, pressure is generally the self-generated pressure in the hydrothermal reaction, which changes with temperature during the heating process. The independent effect of pressure on the hydrothermal reaction of pectin is unclear and has not been investigated before, especially the effect of high pressure at a low temperature. In this study, by performing the hydrothermal treatment of pectin under different pressures (up to 20 MPa) at a fixed temperature of 200 °C, we found that high pressure could effectively promote carbonization. To understand the mechanism of pressure effect on hydrochar properties, the produced hydrochars were characterized by elemental analysis, scanning electron microscopy (SEM), N2 adsorption/desorption, Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), while pyrolysis and combustion behaviors were analyzed using the thermogravimetric analyzer (TGA). The mechanism of high pressure was cleaving the hydroxyl groups, ester carbonyl groups, and aliphatic structures with the process of dehydration and decarboxylation. More aromatic structures were formed in hydrochars with higher carbon content, resulting in a structure with better thermal stability. Carbon spheres with a larger diameter could be formed under higher pressure. The promoting effect was strongest in the range of 2–8 MPa and weaker under higher pressures (8–20 MPa). Future studies may improve the degree of hydrothermal carbonization of pectin by applying an appropriate high pressure.

Wool-Based Carbon Fiber/MoS2 Composite Prepared by Low-Temperature Catalytic Hydrothermal Method and Its Application in the Field of Gas Sensors.

Under the background of the Paris Agreement on reducing greenhouse gases, waste wools were converted into wool carbon fiber (WCF) and WCF–MoS2 composites by low-temperature catalytic hydrothermal carbonization. Their structures and gas-sensing performances were studied for the first time. Due to the existence of heterojunctions, the responses of the WCF–MoS2 composite to the five analytes were 3–400 times those of MoS2 and 2–11 times those of WCF. Interestingly, because of the N, P, and S elements contained in wools, the WCF prepared by the hydrothermal method was realized the doping of N, P, and S, which caused the sensing curves of WCF to have different shapes for different analytes. This characteristic was also well demonstrated by the WCF–MoS2 composite, which inspired us to realize the discriminative detection only by a single WCF–MoS2 sensor and image recognition technology. What’s more, the WCF–MoS2 composite also showed a high sensitivity, a high selectivity, and a rapid response to NH3. The response time and the recovery time to 3 ppm NH3 were about 16 and 5 s, respectively. The detection of limit of WCF–MoS2 for NH3 was 19.1 ppb. This work provides a new idea for the development of sensors and the resource utilization of wool waste.

Single-Step Hydrothermal Synthesis of Biochar from H3PO4-Activated Lettuce Waste for Efficient Adsorption of Cd(II) in Aqueous Solution.

Developing an ideal and cheap adsorbent for adsorbing heavy metals from aqueous solution has been urgently need. In this study, a novel, effective and low-cost method was developed to prepare the biochar from lettuce waste with H3PO4 as an acidic activation agent at a low-temperature (circa 200 °C) hydrothermal carbonization process. A batch adsorption experiment demonstrated that the biochar reaches the adsorption equilibrium within 30 min, and the optimal adsorption capacity of Cd(II) is 195.8 mg∙g−1 at solution pH 6.0, which is significantly improved from circa 20.5 mg∙g−1 of the original biochar without activator. The fitting results of the prepared biochar adsorption data conform to the pseudo-second-order kinetic model (PSO) and the Sips isotherm model, and the Cd(II) adsorption is a spontaneous and exothermic process. The hypothetical adsorption mechanism is mainly composed of ion exchange, electrostatic attraction, and surface complexation. This work offers a novel and low-temperature strategy to produce cheap and promising carbon-based adsorbents from organic vegetation wastes for removing heavy metals in aquatic environment efficiently.

Thermally activated mango peels hydrochar for fixed-bed continuous flow decontamination of Pb(II) ions from aqueous solution

Thermally activated hydrochars prepared from mango peels have been tested for continuous removal of lead ions from contaminated drinking water for possible use in point-of-use candle-type water filters. The hydrochar was obtained using low-temperature hydrothermal carbonization, which was activated at various temperatures to produce activated hydrochars. The materials have been characterized physicochemically according to ASTM standards for activated carbons. The structure and morphology were studied by FTIR, XRD, SEM and nitrogen adsorption porosimetry. The results obtained showed that hydrochar activated at 400 °C (ACH 400) was promising for the elimination of lead with a obtained equilibrium absorption capacity of 38.31 mg/g at the optimized height parameters of bed (2.4 cm), flow rate (12 mL/min) and lead concentration (100 mg/L). The results of the experimental breakthrough curves given by adsorption process were successfully fitted by kinetic models according to Adams–Bohart, Thomas and Yoon–Nelson in their linearized forms. The Thomas and Yoon-Nelson data provided a better correlation with the prediction of the breakthrough curve data with high R2 values, showing a good agreement between the breakthrough curves and the experimental data points. ACH 400 is a suitable sorbent in place of activated carbon for a continuous system and can be applied for large-scale treatment for the removal of lead from water samples.

From wasted sludge to valuable biochar by low temperature hydrothermal carbonization treatment: Insight into the surface characteristics

In this study, the hydrothermal carbonization (HTC) technology at low temperature was applied to convert the wasted sludge into biochar, by establishing the correlation between the operation conditions and biochar characteristics. The contents of C, H, O, N and S, and the values of (O + N)/C and O/C in biochar were negatively correlated to the temperature, retention time and initial pH conditions. This implies that increasing temperature and retention time are beneficial for sludge dewatering and reduction. The maximum high heating value of biochar at 15.21 MJ/kg was achieved, which is similar to the cellulosic biochar and lignite surface known as the primary renewable fuel. The typical macromolecules such as proteins and lipids still existed on the biochar surface after low temperature HTC treatment. Decreasing the initial pH enforced the protonation effect and structural stability of the organic macromolecules in sludge, resulting in a diverse morphology with more compact microspheres on the biochar surface. Particularly, the catalytic ability to generate the carbon-centered persistent radicals was enhanced with g-factor at 2.01138–1.98428. In terms of environmental safety, the detected concentrations of heavy metals (Zn, Pb, Cu and Al) during the secondary dissolution of biochar were below 0.25 mg/L, indicating the low leaching risk for the land application. In addition, some humic acid and fulvic acid analogues were also detected in the secondary dissolution liquid, which can facilitate the redox reaction in soil microenvironment. In sum, this study confirmed that the low temperature HTC is a feasible method for sludge treatment and resource recovery.

Low-Temperature Synthesis of Magnetic Carbonaceous Materials Coated with Nanosilica for Rapid Adsorption of Methylene Blue.

This work reports the synthesis of nanosilica-coated magnetic carbonaceous adsorbents (MCA@SiO2) using low-temperature hydrothermal carbonization technique (HCT) and the feasibility to utilize it for methylene blue (MB) adsorption. Initially, a carbon precursor (CP) was synthesized from corn starch under saline conditions at 453 K via HCT followed by the magnetization of CP again via HCT at 453 K. Subsequently, MCA was coated with silica nanoparticles. MCA and MCA@SiO2 were characterized using X-ray diffraction, Fourier transform infrared, scanning electron microscopy/energy-dispersive spectroscopy, transmission electron microscopy, and Brunauer–Emmett–Teller (BET) N2 adsorption–desorption isotherms. The BET surface area of MCA and MCA@SiO2 were found to be 118 and 276 m2 g–1, respectively. Adsorption of MB onto MCA@SiO2 was performed using batch adsorption studies and in the optimum condition, MCA@SiO2 showed 99% adsorption efficiency with 0.5 g L–1 of MCA@SiO2 at pH 7. Adsorption isotherm studies predicted that MB adsorption onto MCA@SiO2 was homogeneous monolayer adsorption, which was best described using a Langmuir model with the maximum adsorption capacity of 516.9 mg g–1 at 25 °C. During adsorption kinetics, a rapid dye removal was observed which followed pseudo-first- as well as pseudo-second-order models, which suggested that MB dye molecules were adsorbed onto MCA@SiO2 via both ion exchange as well as the chemisorption process. The endothermic and spontaneous nature of the adsorption of MB onto MCA@SiO2 was established by thermodynamics studies. Mechanism of dye diffusion was collectively governed by intraparticle diffusion and film diffusion processes. Furthermore, MB was also selectively adsorbed from its mixture with an anionic dye, that is, methyl orange. Column adsorption studies showed that approximately 500 mL of MB having 50 mg L–1 concentration can be treated with 0.5 g L–1 of MCA@SiO2. Furthermore, MCA@SiO2 was repeatedly used for 20 cycles of adsorption–desorption of MB. Therefore, MCA@SiO2 can be effectively utilized in cationic dye-contaminated wastewater remediation applications.

Hydrochar-derived activated carbon from sugar cane bagasse employing hydrothermal carbonization and steam activation for syrup decolorization

Activated carbon (AC) was produced from sugarcane bagasse using hydrothermal carbonization (HTC) and steam activation for syrup decolorization. The HTC temperature was 180–240 °C over 30–90 min of holding time and the steam activation temperature was 700–900 °C at 1 h. Results showed that dry-basis AC yield was in the range of 10.4–27.1%. The maximum Brunauer–Emmett–Teller (BET) surface area of the product was 390 m2/g. The average pore size of the AC was 2.2 to 2.5 nm with total pore volume of 0.1–0.25 cm3/g. Decolorization tests showed that the AC produced from low-temperature HTC had better decolorization performance with maximum removal rates of 63.4% and 74% in batch-type and fixed-bed, continuous-flow decolorization, respectively. International Commission for Uniform Methods of Sugar Analysis (ICUMSA) unit reduction of the produced AC was about 62%. This study shows that the AC produced can be used for low-cost preliminary syrup decolorization in sugar mills, offering circular utilization of agricultural residues.

Low Temperature Hydrothermal Synthesis of Biochar from Green Algae and Its Combustion Performance

The low temperature hydrothermal carbonization reaction of green algae was studied by combining with the low temperature hydrothermal carbonization technology. The hydrothermal carbon was prepared in the temperature range of 180?C - 240?C. The experimental results had been characterized in detail by oxygen bomb calorimeter, synchronous thermal analyzer and infrared spectrum analysis. The effects of reaction time, reaction temperature and salt concentration on hydrothermal carbonization and combustion were analyzed by studying the experimental conditions under the optimal calorific value. Results showed that algal carbonized, diversity and continental wooden biomass combustion process, and algae in the low temperature hydrothermal carbonization reaction of calorific value significantly increase, and comprehensive consideration of low temperature hydrothermal carbonization algae biomass to improve its calorific value is the best solution to time, salt concentration control in 8 - 10 h, around 0.05%, the reaction temperature is slightly greater than 240?C. It provides a reference for the further research in the field of clean biomass and is of great significance for the development of algal biomass combustion function.

One-pot synthesis of two-dimensional multilayered graphitic carbon nanosheets by low-temperature hydrothermal carbonization using the in situ formed copper as a template and catalyst.

Two-dimensional (2D) multilayered graphitic carbon nanosheets are prepared via a facile, green, and mild method of one-pot hydrothermal carbonization at a temperature below 300 °C. Copper with a 2D structure is formed in situ and serves as both a template and catalyst. The obtained multilayered carbon nanosheets exhibit well-defined shapes and a radius-to-thickness ratio as high as 104, with monolayer thickness as small as 2.86 nm.

Black yet green: Sulfonic acid functionalized carbon as an efficent catalyst for highly selective isomerization of α-pinene oxide to trans-carveol

In this study, an inexpensive, high yielding, and environmentally benign bifunctional acid-base catalyst is prepared using a simple low-temperature hydrothermal carbonization method from a fishery bio-waste, chitosan as a carbon source and sulfuric acid, as _SO3H source. The successful formation of _SO3H group grafted carbon was confirmed by various physiochemical characterization methods such as powder XRD, FTIR, RAMAN, FESEM, EDAX, HRTEM, and XPS. Under the optimized reaction conditions, the bio-derived sulfonated hydrothermal carbon catalyst showed excellent performance for the isomerization of α-pinene oxide to trans-carveol (85% yield) at 160 °C in 1.5 h. The product selectivity was influenced mainly by the type of solvent used for the isomerization. No leaching of the sulfonated groups was observed even after five cycles without any significant loss in conversion and selectivity.