Hydrochar Production Research Articles

Sugar, hydrochar and bio-oil production by sequential hydrothermal processing of corn cob

Hydrothermal liquefaction (HTL) is an alternative process for biomass conversion with promising outcomes and environmentally-friendly prospects. However, a gap in the intermediate bioproducts was found in the hydrolysis step of HTL after a careful investigation of the current state-of-the-art. This study investigated two routes of the hydrothermal conversion of corn cob through HTL and sequential processing, i.e. subcritical water hydrolysis (SWH) + HTL. The influence of SWH (230–260 °C) and HTL temperatures (300–350 °C), and volumetric flow rate (5–10 ml min−1) were evaluated. GC-MS and FTIR analysis were performed for bio-oil characterization. Results showed that lower SWH temperatures favored glucose and furfural production, while higher temperature favored xylose and hydroxymethylfurfural (HMF). Bio-oil produced by the sequential processing exhibited a high concentration of nitrogenous and oxygenated compounds. Hydrochar produced in both routes exhibited a similar higher heating value and elemental composition, although FTIR analysis revealed different functional groups.

Batch Process Operational Effects on Phosphorus Attainment in Hydrochar Produced by Hydrothermal Carbonization of Dairy Manure

Highlights Temperature ramp-up from 180°C to the pre-set processing temperature significantly affects total phosphorus attainment rate. The transition time of temperature ramp-up is crucial in assessing the change of TP attainment rate. Temperature cooling does not show significant effect on total phosphorus attainment rate. Abstract. As an alternative technology for phosphorus cycling, hydrochar produced from animal manure is a great vehicle to attain phosphorus from dairy manure and apply it back to cropland in an environmentally friendly manner. Hydrochar production by hydrothermal carbonization (HTC) greatly reduces the time to manage animal manure compared to traditional lagoon systems. Before being established as a practical technology for hydrochar production in continuous-flow operations, HTC in batch mode is the best way to systematically investigate and optimize the process conditions for high efficiencies. This study investigates specifically the effect of temperature ramp-up rates on the attainment of total phosphorus (TP) in hydrochar produced from dairy manure through batch-mode HTC operations. Experimental results revealed that the transition in temperature ramp-up greatly affected the TP attainment rate in hydrochar, depending on the pre-set processing temperatures and holding time. Statistical analysis confirms that such an effect is significant if the holding time is 30 min or less. This is due not only to the higher processing temperatures but also to the extra 5 to 15 minutes of processing time required for the ramp-up to the pre-set temperatures of 195°C to 255°C, at which point biomass decomposition has already occurred. It is concluded that the temperature ramp-up in batch HTC processes significantly affect the TP attainment rate in hydrochar produced from dairy manure. Before developing continuous-flow HTC systems, it is recommended that experimental results from batch operations be carefully interpreted. Keywords: Batch processes, Dairy manure, Hydrochar, Hydrothermal carbonization, Phosphorus.

Hydrochar an Innovative Solution for Sustainable Environmental Applications

Hydrochar is a carbon-rich material made from biomass using hydrothermal carbonization. It is gaining interest as a potential alternative to fossil fuels and soil amendment. However, hydrochar production requires careful management to minimize potential environmental issues such as feedstock availability, greenhouse gas emissions, water usage and contamination, waste management, and long-term impacts on soil quality and ecosystem health. Further research is necessary to optimize the production process and to understand its environmental impacts. Hydrochar has varied applications, including soil remediation, fuel source, and building material, but its production must be carefully managed to minimize negative environmental impacts. Proper management and optimization of hydrochar production can help to maximize its potential benefits while minimizing negative environmental impacts. Therefore, further research is crucial to optimize the hydrothermal carbonization process for different feedstocks and to better understand the long-term environmental impacts of hydrochar production and application

Production of hydrochars from Pinus caribaea for biosorption of methylene blue and tartrazine yellow dyes

Wood is one of the most abundant renewable resources in the world. However, large volumes of waste are generated in the losses and cuts of wood saws, being an important environmental problem. This work aims to evaluate the production of hydrochar from wood residues of Pinus caribaea combined with acid-base treatment for application as dyes Methylene Blue (MB) and Tartrazine Yellow (TAR). Hydrocarbonization was carried out at 200 or 240 ..C for 12 or 24 h, in acidic or basic medium. The pHZPC of the hydrocarbons obtained in acidic medium was between 2.66-4.12 and 4.46-5.76 for those processed in basic medium. The pseudo-secondorder model (PSO) better fitted the adsorption of MB and TAR on Pinus in natura and on hydrochar. In addition, the Sips model was considered the most suitable for MB (qmax= 132.1 mg g-1 for PIN and 149.0 mg g-1 for PIN-200-24-B) and Toth for TAR (qmax= 18.14 mg g-1 for PIN and 23.01 mg g-1 for PIN-200-24-B adsorption isotherms). Therefore, the hydrocarbonization of waste generated from the wood industry in acidic and basic environments has great potential for the treatment of materials such as biosorbents, thus promoting greater sustainability in this sector.

Hybrid Hydrothermal Carbonization and Ultrasound Technology on Oil Palm Biomass for Hydrochar Production

AbstractThe hybrid hydrothermal carbonization and ultrasound technology (HHTC‐Us) efficiently utilizes the function of both ultrasounds‐assisted and hydrothermal carbonization for hydrochar production. The HHTC‐Us of oil palm residues plays an essential role in hydrochar production. Hydrochar is a carbon‐rich material potentially produced from oil palm biomass, which has gained great interest due to its unique properties. Four main topics were highlighted: the production of crude palm oil and impacted biomass residue generation, properties and potential values of oil palm biomass conversion as hydrochar, hybrid hydrothermal carbonization reaction routes, and processing parameters that affect the HHTC‐Us technology. The review elucidates the promising production process or modification of hydrochar from oil palm biomass residues through hybrid technology. The technology potentially enhanced sustainability, creating challenges and new opportunities.

Conversion of sewage sludge from industrial wastewater treatment to solid fuel through hydrothermal carbonization process

Sludge is the unwanted solid waste produced during the treatment of industrial wastewater. The hydrothermal carbonization process (HTC) can be used to convert sewage sludge into a coal-like solid fuel. The effects of solid-to-liquid ratio and feed water pH on the physicochemical properties of hydrochars were investigated. According to the results, hydrothermal treatment enhanced the fuel characteristics of hydrochar with a high HHV and fixed carbon. Adding 0.8 M acetic acid resulted in the highest rate of energy recovery at 96.98 %. The observed H/C and O/C atomic ratios of HTC-0.4AA have been lowered to levels comparable to lignite coal. ICP-OES confirmed the presence of the metal in the hydrochar product. Examining the thermogravity analysis of raw materials and hydrochars with a TGA analyzer was then used to determine the combustion kinetics. In addition, combustion characteristics indicate that HTC improves the S combustibility index.

Green synthesis of a novel eco-friendly hydrochar from Pomegranate peels loaded with iron nanoparticles for the removal of copper ions and methylene blue from aqueous solutions

This study developed a novel eco-friendly and cost-effective bioadsorbent by synthesizing iron nanoparticles loaded onto hydrochar (FeNPs@HC). Pomegranate peels were used as feedstock for hydrochar (HC) production. The production of FeNPs@HC was done by hydrothermal carbonization process using the black solution of iron nanoparticles as a hydrothermal carbonization media. The FeNPs@HC was characterized using FTIR, Transmission electron microscope (TEM), Zeta potential techniques, X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area, SEM with EDX analysis, and Thermal analysis. The mean particle size of FeNPs and HC were ∼28 and 196 nm, respectively. The batch experiments like initial concentration, contact time, solution temperature, adsorbent dosage, and pH on the adsorption capacity of the bioadsorbent for Cu (II) and MB were examined and determined. Maximum sorption capacity (qm) of Cu (II) and MB was 95.24 and 278 mg g−1. Different adsorption isotherms and kinetics models have been used for evaluating the adsorption process. The R2 value obtained by Langmuir isotherm was the highest for Cu(II) = 0.997, while the R2 value obtained by Freundlich isotherm is the highest for MB = 0.9957. The thermodynamic parameters have been determined for the adsorption process. The ΔG0 values are negative, referring to the adsorption processes being spontaneous. The reusability of FeNPs@HC for removal Cu(II) and MB has been tested in four cycles and showed a good removal efficiency. The FeNPs@HC was successfully applied to actual wastewater samples.

In-situ production of magnetic char via rapid subcritical hydrothermal carbonisation of paunch waste

The conventional hydrothermal carbonisation (HTC) is mainly tied to the high capital investment of the reactor and low product quality. In a novel approach, the rapid subcritical HTC of paunch waste (at 240 °C for only 5 min) was proposed to enhance the quality of products and their utilisation via in-situ production of magnetic hydrochar. Magnetite nanoparticles were found on the surface of hydrochar with size of 10–20 nm and crystal lattice spacing of 0.25 nm, XRD characteristic peaks of magnetite, and strong FTIR peak at 580 cm−1 assigned to Fe-O stretching in the crystalline lattice of magnetite. Magnetic hydrochar could adsorb Congo Red at a capacity of 59.9 mg g−1. An organic-rich process water with a high COD of 43 g L−1 was co-generated along with magnetic hydrochar and assumed to be anaerobically digested. The estimated theoretical methane yield was found sufficient to run the HTC plant in an energy-neutral mode. After developing a process model in Aspen plus, the discounted cash flow analysis revealed a net present value of US$13.04 MM for 30 years of operation, which can increase to $34.79 MM if the iron precursors are sourced from locally available iron-rich sludge.

Catalytic wet torrefaction of lignocellulosic biomass: An overview with emphasis on fuel application

Wet torrefaction (WT), also named hydrothermal carbonisation (HTC), has been regarded as one of the highly studied thermochemical process pathways for biomass-to-solid fuel conversion in the last decade (2012–2021). Catalysts have been added in the WT or HTC of lignocellulosic biomass for various applications (i.e. solid fuel synthesis, carbon material synthesis, pre-treatment, sugar production, ash content removal, and the study of reaction kinetics). Regardless, there is no review on the addition of catalysts in WT to produce hydrochar as fuel, specifically on the role of catalysts in the formation of ‘secondary deposits’, which refers to deposits that have been observed on the hydrochar. This review discusses the fundamentals of WT and how the lignocellulosic biomass components in various biomass, operating process parameters, and catalysts affect the fuel properties of the hydrochar product. For catalytic WT and HTC, relevant studies in different yet interrelated applications are overviewed, where insights are given based on the effect of catalyst addition on the properties of hydrochar and the promotion of ‘secondary deposits’. The ‘secondary deposits’ established in carbon material synthesis studies can reveal the relationship between catalyst addition and formation. On top of that, it also serves as a complimentary knowledge to enhance the understanding of how these deposits can be used to increase the higher heating value of the hydrochar, which is lacking in the existing hydrochar synthesis studies. Therefore, the aim of this review is to provide insights into the addition of catalysts for the synthesis of hydrochar for fuel application.

In-situ deep eutectic solvent enhance hydrothermal carbonization of garden waste for methylene blue removal

Modification of hydrochar requires either toxic chemicals or high temperature during the hydrothermal carbonization process, which are the main shortcomings for industrial upgrading and cleaner production of hydrochar. Herein, a novel green catalyst formed by in-situ deep eutectic solvent (DES, i.e. ChCl-H2O) and inorganic salt (FeCl3) was developed to prepare hydrochars derived from garden waste under low temperature for removing methylene blue (MB). The effects of key operational parameters including different temperatures (160 °C–260 °C), reacting time (3–9 h) on hydrochars performance were firstly evaluated. It was found that the adsorption capacity of hydrochar on MB reached its highest value of 169.19 mg/g at the optimal temperature of 180 °C for 5 h. Subsequent adsorption kinetics study showed that the obtained data fitted better to the pseudo-second-order kinetics. The results indicated that DES and inorganic salts could be used to effectively prepare hydrochar in hydrothermal carbonization process.

Conversion of empty fruit bunches (EFBs) by hydrothermal carbonization towards hydrochar production

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

Simultaneous production of nutritional compounds and hydrochar from Chlorella pyrenoidosa via hydrothermal process

Hydrothermal process is an eco-friendly method for simultaneously extracting antioxidant compounds and producing hydrochar. This study examined the simultaneous production of nutritional compounds and hydrochar from Chlorella pyrenoidosa via a hydrothermal process. The experiments were conducted using a batch reactor at varying temperatures (160, 180, and 200 °C) and holding times (10, 20, and 30 min). The results revealed that phenolic contents, antioxidant activity, and hydrochar production were strongly affected by both temperature and time. The highest total phenolic content (1.70 ± 0.16 mg/g) and antioxidant activity (94.2 ± 1.8 %) were found in process water at 200 °C with a holding time of 20 min. Under these conditions, a hydrochar yield of 30.79 % was obtained. Intriguingly, the hydrochar obtained at 200 °C exhibited higher heating values (24.93–28.32 MJ kg−1) than typical sub-bituminous coals, giving it potential for use as a solid fuel.

Co-hydrothermal carbonization of corn stover and food waste: Characterization of hydrochar, synergistic effects, and combustion characteristic analysis

Hydrochar was prepared via the co-hydrothermal carbonization (Co-HTC) method using corn stover (CS) and food waste (FW) as materials, and the influences of the synergistic effect of Co-HTC on fuel performances and combustion behavior were analyzed. Characterization of hydrochar was conducted using elemental analysis, industrial analysis, SEM, BET, XRD, and FTIR. The outcomes indicated that the higher heating values (HHVs) of hydrochar increased, the atomic ratios of H/C and O/C decreased, the fuel ratios ranged from 0.33 to 0.57, and the average pore diameter decreased when the FW ratio was increased. The synergistic effect of Co-HTC of CS and FW improved hydrochar yield, energy yield, organics retention, and C capture efficiency. Thermogravimetric and kinetic analysis showed that Co-HTC improves the combustion characteristics of hydrochar. Thus, production of hydrochar via Co-HTC of CS and FW provides some guidance for the resourcing and reducing solid organic waste, and offers a promising direction for renewable energy production.

Effects of sewage sludge hydrochar on emissions of the climate-relevant trace gases N2O and CO2 from loamy sand soil

This work explores the effects of amending a loamy sand soil with hydrochars having different physicochemcial characteristics. The effects of different hydrochars on emissions of the greenhouse gases nitrous oxide (N2O) and carbon dioxide (CO2) were investigated together with the relationship between the hydrochar's mineral nitrogen content and the soil microbial biomass. Soil samples were amended with eleven different hydrochars and feedstocks having different carbon and nitrogen contents at application rates of 5 t ha−1 and 25 t ha−1. Microbial immobilization was the main mineral nitrogen sink in soil following hydrochar application. Moreover, the processing conditions applied during hydrochar production (i.e., the pyrolysis temperature and residence time) had significant effects on N2O and CO2 emissions: treatment with incubated hydrochars yielded significantly lower N2O emissions than treatment with non-carbonized feedstocks, particularly at the highest level of hydrochar application (25 t ha−1). Further analysis revealed that increasing the process temperature and residence time during hdyrochar production significantly increased the final product's total organic carbon content but reduced its content of hot water extractable carbon. Hydrochars produced with higher process temperatures and longer residence times therefore yielded lower CO2 emissions during a 44-day incubation experiment than raw feedstocks or hydrochars produced under less severe conditions. Hydrochars formed from sewage sludge at high process temperatures and with long residence times are thus promising soil additives for reducing GHG emissions.

Hydrothermal carbonization of sawdust with the bio-oil of same origin impacts evolution of structures of hydrochar

The high tendency towards polymerization is a bottle-neck issue in upgrading of bio-oil, which, however, is highly desirable in co-hydrothermal carbonization (HTC) of biomass with bio-oil for enhancing production of hydrochar. In this study, co-HTC of bio-oil of the same origin with poplar sawdust was conducted at 180 to 260 °C. The results showed that the HTC in a water medium containing 10% bio-oil could enhanced the yield of hydrochar by ca. 36% at 220 or 260 °C through the cross-polymerization of the sugar-derived furans and ketones/aldehydes as well as the phenolics in bio-oil with the sawdust-derived organics. Furans/sugars in bio-oil showed much more contribution to the increase of hydrochar yield than the phenolics like guaiacol. The highly reactive organics in bio-oil even could react with the crystal region of cellulose at 180 °C, and affected property of hydrochar at especially the higher temperatures by promoting deoxygenation, enhancing carbonization, eliminating polar functionalities like -OH, retaining C=O for continued polymerization, etc. The co-existence of aliphatic organics and phenolics in bio-oil renders the simultaneous formation of highly volatile fraction and aromatic structures in the hydrochar. These created the carbon-rich hydrochar with higher crystallinity, lower hydrophilicity and improved comprehensive combustion index.

In-depth study of the sulfur migration and transformation during hydrothermal carbonization of sewage sludge

This study investigated the effect of temperature on sulfur transformation behavior during the hydrothermal carbonization of raw sludge, water washed sludge and the corresponding filtrate solution at 110–235 °C. The different sulfur species in the various products were determined, primarily focusing on the sulfur species present in the aqueous product. At 110 °C, 31.9% of sulfur migrated to the aqueous product, primarily in the form of sulfone-S and sulfoxide-S. As the temperature increased to 160 °C, the hydrolysis of aliphatic-S and aromatic-S was enhanced, and the former species further transformed to other organic-S or SO42-S in the aqueous product. High temperature is beneficial to the formation of sulfate-S and thiophene-S/aromatic-S in the aqueous and hydrochar products, along with the release of H2S and CH3SH. This caused a retention of only 29.2% sulfur (i.e., sulfate-S) in the hydrochar at 235 °C, with a large amount of sulfur migrating to the aqueous product (51.1%), followed by the gas product (9.1%). Among all the sulfur species in raw sludge, aliphatic-S was the most thermally unstable. SO42-S and sulfur-containing gas were primarily formed from the decomposition of water-insoluble aliphatic-S, while part of thiophene-S/aromatic-S in aqueous products was generated from water-soluble sulfone-S and sulfoxide-S at high temperatures of ≥160 °C. The results indicate that 210 °C is the optimal temperature for preparing of sludge-based fuel during hydrothermal carbonization, and water washing pre-treatment is a good strategy for enhancing the removal of sulfur in hydrochar and reducing the release of sulfur-containing odorous gas.

Production of Hydrochars from Lignocellulosic Biomass with and without Boric Acid

AbstractHydrothermal carbonization (HTC) is an important thermochemical process where biomass is converted into coal‐like solid products known as hydrochars. The HTC process is performed in hot‐compressed water under self‐generated pressures. In this work, the HTC of acorn shells was conducted at various temperatures and reaction times with and without boric acid (H3BO3). A high degree of carbonization occurred at 250 °C in non‐catalytic and catalytic 4‐h runs. Hydrochars obtained from non‐catalytic and catalytic runs at 250 °C consisted of spherically carbon particles with diameters ranging from 303 nm to 3.27 μm. Carbon spheres at 200 and 225 °C for 2 h were not observed. The yield and carbon content of the hydrochars were slightly increased by reuse of the process water in thermal runs without catalysts.

The effect of excess water on the hydrothermal carbonization of anise waste from ouzo production on Lesvos island

Beverage and food production industries are playing a major role in the local economy of Lesvos Island, with ouzo production being - by far-the most prominent one. In the framework of this present study, anise waste from ouzo production were sampled and valorized by means of hydrothermal carbonization (HTC) for the production of hydrochars. The novelty of this study is the examination of the products quality for different excess water percentages in the hydrothermal reactor. In addition, the hydrothermal treatment of anise waste is a novel and unique application. On the one hand, the analysis included the assessment of the chemical oxygen demand (COD), the total phenolic content (TPC), the pH and the conductivity of the HTC liquors. On the other hand, the higher heating value (HHV), the mass yield and the phytotoxicity were assessed for the produced hydrochars. The COD and TPC fluctuated for moderating conditions of temperature and excess water. On the one hand, reduced excess of water increased the mass yield and the HHV, while it reduced the pH values of hydrochars. On the other hand, all hydrochars had low germination index values, which is an indicator that the use of hydrochar as soil amendment is problematic and should be further investigated.

Green algae to green fuels: Syngas and hydrochar production from Ulva lactuca via sub-critical water gasification

Biomass-derived energy is gaining more attention due to environmental issues and increasing energy demand. To ensure the sustainability of fossil energy substitution using biomass, diversification of sources, including marine organisms, is vital. Among various types of marine biomass discussed in the literature, the utilization of green algae Ulva lactuca for energy generation is still rare globally. Therefore, this study aims to investigate the potential of green fuel (syngas and hydrochar) production from U. lactuca (Chlorophyta) via sub-critical water gasification (SbWG). The experiments were conducted using a batch reactor at varying temperatures (300, 350, and 400 °C), reaction times (30, 60, and 90 min), and feedstock concentrations (1 and 5 wt%). The effect of temperature on gas composition was examined in detail. The results revealed that increasing temperature from 300 to 400 °C leads to an increase in the H2 content significantly from 2.21 % to 8.09 % within 90 min. However, increasing feedstock concentration from 1 to 5 wt% reduces the H2 fraction due to suppression of the steam reforming and water-gas shift reactions. Based on the ultimate analysis, the high severity of operating conditions leads to lower O/C and H/C atomic ratios owing to dehydration and decarboxylation reactions. It was confirmed by scanning electron microscope (SEM) analysis that more void structures existed in hydrochar than the algal feedstock. The SbWG process at varying temperatures and times can increase the energy contents of U. lactuca by over 47 %. Intriguingly, hydrochar obtained at 400 °C exhibited higher HHVs (i.e., 21.75–22.93 MJ kg−1) than typical low-ranked coals, making hydrochar more potential to be used as solid fuels. Finally, a reaction model was deduced, and the decomposition of U. lactuca was confirmed to follow the Arrhenius behavior.

Environmental implications, potential value, and future of food-waste anaerobic digestate management: A review.

Globally, the valorisation of food waste into digestate through the process of anaerobic digestion is becoming increasingly popular. As a result, a large amount of food-waste digestate will need to be properly utilised. The utilisation of anaerobic digestion for fertiliser and alternative uses is essential to obtain a circular bioeconomy. The review aims to examine the environmental management of food-waste digestate, the value of digestate as a fertiliser and soil conditioner, and the emerging uses and improvements for post-anaerobic digestion reuse of digestate. Odour emissions, contaminants in food waste, emission and leaching of nutrients into the environment, and the regulations, policies, and voluntary initiatives of anaerobic digestion are evaluated in the review. Food-waste digestate can provide essential nutrients, carbon, and bio-stimulants to soils and increase yield. Recently, promising research has shown that digestates can be used in hydroponic systems and potentially replace the use of synthetic fertilisers. The integration of anaerobic digestion with emerging uses, such as extraction of value-added products, algae cultivation, biochar and hydrochar production, can further reduce inhibitory sources of digestate and provide additional economic opportunities for businesses. Moreover, the end-product digestate from these technologies can also be more suitable for use in soil application and hydroponic use.