Hydrothermal Conversion Process Research Articles

Co-hydrothermal conversion of kitchen waste and agricultural solid waste biomass components by simple mixture: study based on bio-oil yield and composition

The co-hydrothermal conversion of kitchen waste and lignocellulosic biomass solid waste into bio-oil holds the potential to revolutionize the production of multi-source biomass hydrothermal bio-oil. In this study, the interaction between kitchen waste and agricultural solid waste during the hydrothermal conversion process was investigated, focusing on the yield and properties of the resulting bio-oil, the obtained bio-oil was characterized. Results reveal that the Maillard reaction plays a pivotal role in influencing the production of hydrothermal bio-oil during the co-hydrothermal conversion process. Proteins and amino acids, in particular, exhibit a strong promotional effect on the generation of hydrothermal bio-oil. The introduction of kitchen waste did not significantly change the chemical and elemental composition of the bio-oil derived from agricultural solid waste. However, the specific content of compounds within the hydrothermal bio-oil varied widely. When compared to single-component hydrothermal bio-oils derived from lignin, cellulose, and hemicellulose respectively, the addition of kitchen waste resulted in a notable enhancement of the bio-oil's overall calorific value and a reduction in its oxygen content. The findings of this study have the potential to pave the way for sustainable and economically viable processes for multi-source biomass hydrothermal bio-oil preparation.

Fundamental properties and phosphorus transformation mechanism of soybean straw during microwave hydrothermal conversion process

Microwave hydrothermal (MHT) conversion is emerging as a promising technology for the disposal and reutilization of biowastes. This study investigated the fundamental properties and phosphorus transformation mechanism of soybean straw during the MHT conversion process. The oxygen-containing functional groups in soybean straw were stripped, and a trend of dehydration was observed as the temperature increased during the MHT process. Cellulose was identified as the major component of the MHT solid products at high temperature. Glucose and glucuronic acid in the MHT liquid products were gradually converted to formic acid and acetic acid with increasing temperature and holding time. The characteristics of the MHT products directly affected the changes in P speciation and transformation. Most of the P was distributed in liquid products and the impact of holding time was not significant on P distribution at low MHT temperature. With the increase in temperature and holding time, P gradually transferred into the solid products. The proportion of organic phosphorus and soluble inorganic phosphorus in soybean straw was high, and it decreased noticeably after the MHT process. The increase in MHT temperature promoted the conversion of OP and AP into IP and NAIP respectively. P K-edge X-ray absorption near edge structure analysis reveals that Ca5(PO4)3(OH) was the major component of soybean straw and more Ca5(PO4)3(OH) was formed at lower MHT temperature. This study provides fundamental knowledge on the property changes of soybean straw and the transformation of phosphorus during MHT conversion process, which is essential for its disposal and further utilization.

Life cycle assessment of bio-oil prepared from low-temperature hydrothermal oxide-catalyzed cotton stalk

The technological development of preparing bio-oil from low-temperature hydrothermal conversion of agricultural and forestry waste has positive significance for alleviating the shortage of oil energy supply and reducing environmental pollution. This paper selects typical oxides (Al2O3, CeO2, MgO, SiO2, TiO2, and ZnO) as catalysts to set up a low-temperature (220 °C) hydrothermal conversion process of cotton stalk containing pretreatment processes including chopping. For moderate amplification estimation, lab-scale experimental data is used as a benchmark for calculation, and the functional unit for this study is set to be a 1 kg bio-oil product. The results suggest that the cerium dioxide-involved process with the highest bio-oil yield and highest synthetic consumption, and the silica-involved process with the lowest bio-oil yield, caused the highest environmental impact, resulting in greenhouse gas (GHG) emissions of 67.729 kg CO2e/kg and 60.001 kg CO2e/kg, respectively. It indicates that catalysts need to consider the balance between synthetic consumption and catalytic performance. Magnifying lab-scale data to an industrial scale using scale-up frameworks introduces a low model uncertainty, as the practical value had little effect on the overall evaluation results. However, existing equipment data should be used to reduce the uncertainty of the model itself. The environmental sustainability of bio-oil production by low-temperature hydrothermal liquefaction still needs to be improved, especially by catalyst recovery and bio-oil yield improvement.

Hydrothermal Carbonization of Digestate Produced in the Biogas Production Process

In agricultural biogas plants, besides biogas, the by-product digestate is also produced. Due to its high moisture content and organic origin, it can successfully be applied in the hydrothermal carbonization process to avoid the fate of landfilling. This paper reviews the properties of agricultural digestate and its hydrothermal conversion (HTC) into hydrochar and process water. The type of feedstock and the parameters of the HTC process, such as temperature, pressure and residence time, affects the physical and chemical characteristics of hydrochar. Therefore, its possible application might be as a biofuel, fertilizer, soil improver, adsorber, or catalyst. In this paper, the properties of hydrochar derived from agricultural digestate are widely discussed.

Strong interaction and confine effect of manganese oxide-cobalt embedded in self-templated nitrogen-doped carbon enable ultra-stable zinc-air batteries

Developing efficient bifunctional oxygen electrocatalysts with high stability is of great significance for the implementation of rechargeable Zn–air batteries. Herein, MOC-NC bifunctional electrocatalyst with active MnO–Co components embedded in the N-doped carbon sphere is prepared by facile hydrothermal conversion and post-pyrolysis process. The strong interaction between MnO and Co, and confine effect induced by the microstructure endow the fabricated MOC-NC composite with modified electronic configuration, improved conductivity, and significantly reinforced stability. Consequently, the MOC-NC electrocatalyst exhibits good activity and ultrahigh stability for oxygen electrocatalysis. Moreover, when the catalyst was applied to the cathode electrode for the zinc-air battery, it shows excellent performance (specific capacity of 718 ​Wh kgZn−1, power density of 152.3 ​mW ​cm−2) and extraordinary long-term stability (after 200 ​h of charge and discharge cycling, the round-trip efficiency still maintains at 44%). The present work demonstrates a strategy for synthesizing ultrastable bifunctional non-precious metal electrocatalysts for oxygen electrocatalysis.

Study on water and heat transport of different types of vegetations and fields in Pengbo alpine irrigation district of Qinghai Tibet Plateau

Many water-saving projects have been initiated in the typical alpine irrigation district in Tibet, which resulted in dramatic changes to the hydrothermal conversion process. There is an urgent need to fully understand the hydrothermal transport process and to clarify the mechanism under which agricultural hydrology evolves in the alpine irrigation district of Tibet. This study selected highland barley field, oat field, wasteland (Natural herbage field without irrigation) in Pengbo irrigation district of Tibet as study objects to study soil water and heat dynamics and soil water balance. Observed water and temperature data were used to calibrate and validate simulations of the HYDRUS_1D model for 2019 and 2020, respectively. Simulations of soil water and temperature were in good agreement with the measured values, with determination coefficient of 0.69–0.91.This study proposes a set of hydrothermal parameters to fill the gap in the hydrothermal research of Tibet. The results showed that the variation of soil temperature was approximately sinusoidal, with a lag effect. The temperatures of the 0–20 cm and 30–50 cm soil layers lagged by about 1–2 h and 3–5 h, respectively. The highest rate of soil temperature increase occurred from the initial growth period to the rapid growth period during which the soil temperature of each layer increased by an average of 2 °C, however, the soil temperature in this period was not the most suitable for crop growth. Soil evaporation of highland barley field, oat field, and wasteland during the growth period accounted for 20 % – 29 %, 20 % – 29 %, 10 % – 18 % of the rainfall and irrigation, whereas transpiration accounted for 33 % – 43 %, 42 % – 50 %, and 36 % – 57 %, and percolation accounted for 42 %, 35–39 %, and 16–45 %, respectively. Implementation of water-saving projects resulted in reductions in irrigation volume and percolation rate. This study can provide a reference for clarifying the hydrothermal transport process and allocating agricultural water resources in the alpine irrigation district of Tibet.

Advanced Biomass-to-value Chains by Integrating Hydrothermal Carbonization Into Complex Conversion Process Schemes

Advanced Biomass-to-value Chains by Integrating Hydrothermal Carbonization Into Complex Conversion Process Schemes

Utilization of the Coffee Ground-Derived Hard Carbon and Enhancement of Its Electrochemical Performance Via Sulfur Doping

Waste reduction and recycling performance in global economic and ecologic spheres are beginning to take shape every year. Undoubtedly, a particular attention is being devoted to the utilization of biomass-derived products for battery fabrication. It is significant to note that a selection of relevant biomass material, possessing a high and stable capacity (~300 mAh/g) within 200 cycles is a challenging part, becoming the main objective of the research project.In this context, coffee ground derived anode material for Sodium-ion battery (SIB) preserved a semi-stable structure with intergranular and microcracks due to the successive thermal treatments. Hydrothermal conversion processes acts as a significant part of the thermal conversion from coffee ground to hard carbon due to the continuous re-condensation reactions, allowing fabricating low surface area and blocked pores. Doping hard carbon with S improved electrochemical performance by achieving higher capacity than undoped material. The sulfur doped carbonized material has a unique porous structure that increased specific surface area and provided additional active site for sodium ion adsorption. Subsequently, further investigation will be focused on enhancement of hard carbon’s pores. Acknowledgments This work was supported by the Ministry of Education and Science of the Republic of Kazakhstan Grant (AP09259165), “Utilization of the biowaste-derived carbon and enhancement of its electrochemical performance via doping”.

Hydrochar: A Review on Its Production Technologies and Applications

Recently, due to the escalating usage of non-renewable fossil fuels such as coal, natural gas and petroleum coke in electricity and power generation, and associated issues with pollution and global warming, more attention is being paid to finding alternative renewable fuel sources. Thermochemical and hydrothermal conversion processes have been used to produce biochar and hydrochar, respectively, from waste renewable biomass. Char produced from the thermochemical and hydrothermal decomposition of biomass is considered an environmentally friendly replacement for solid hydrocarbon materials such as coal and petroleum coke. Unlike thermochemically derived biochar, hydrochar has received little attention due to the lack of literature on its production technologies, physicochemical characterization, and applications. This review paper aims to fulfill these objectives and fill the knowledge gaps in the literature relating to hydrochar. Therefore, this review discusses the most recent studies on hydrochar characteristics, reaction mechanisms for char production technology such as hydrothermal carbonization, as well as hydrochar activation and functionalization. In addition, the applications of hydrochar, mainly in the fields of agriculture, pollutant adsorption, catalyst support, bioenergy, carbon sequestration, and electrochemistry are reviewed. With advancements in hydrothermal technologies and other environmentally friendly conversion technologies, hydrochar appears to be an appealing bioresource for a wide variety of energy, environmental, industrial, and commercial applications.

Biobased bitumen analogue formation during hydrothermal treatment of microalgae residues, part 1: Influence of reaction enthalpy on the process

The hydrothermal conversion process of industrial Spirulina sp. residues into bitumen analogue is studied with an instrumented reactor heated at 260 °C under autogenous pressure. During hydrothermal conversion experiments, an exothermic reaction starts during the heating ramp above 200 °C and perturbs the thermal regulation of the process. The end of the reaction is detected from recorded pressure and temperature signals. Thermal insulation of the reactor and monitoring of the electrical energy input for thermal regulation allows estimating a total reaction enthalpy ΔHr ≈ - 1.7 MJ/kg of dry biomass by performing two successive heating-isotherm experiments: First with biomass until complete reaction and again with reaction products after cooling. This second run is used as a reference for energy balance calculations.

Migration and transformation mechanism of phosphorus in waste activated sludge during anaerobic fermentation and hydrothermal conversion

This study investigated migration and transformation mechanism of P in waste activated sludge (WAS) during anaerobic fermentation (AF) process and the subsequent hydrothermal conversion (HTC) process. Control of pH during the AF processes was found to be significant, whereby the use of acidic (pH = 5.5) or alkaline conditions (pH = 9.5) facilitated the release of either apatite phosphorus (AP) or non-apatite inorganic phosphorus (NAIP) and organic phosphorus, respectively. At the same pH of 9.5, NaOH promoted the transfer of P into liquid phase, and P in the solid phase was mainly in the form of NAIP. In contrast, Ca(OH)2 enhanced the incorporation of P into the solid products, with the P mainly in the form of AP. The subsequent HTC process promoted the NAIP transferred to AP, and the bioavailability of P in the HTC solid products was decreased. The P K-edge X-ray absorption near edge structure analysis provided detailed information about the phosphates. It demonstrated that the conversion of Ca8H2PO4·6.5H2O to Ca5(PO4)3·OH was facilitated by HTC under the alkaline condition. This study sheds lights on transformation mechanism of P speciations during AF and HTC processes, which would provide fundamental information for effective utilization of P in bio-wastes.

Facile synthesis and luminescence properties of lanthanide ions doped gadolinium phosphate hierarchical hollow spheres

The well-defined GdPO4 hierarchical hollow spheres with uniform size and good dispersity have been fabricated by a facile synthesis strategy. The monodisperse precursor colloidal spheres were firstly obtained by a precipitation route with EG and H2O as mixing solvent. Subsequently, the GdPO4·H2O hollow spheres were synthesized via a hydrothermal conversion process at the expense of the precursor spheres. During the synthesis process, the uniform and well-dispersed precursor spheres not only provide the gadolinium source for the hexagonal GdPO4·H2O but also act as the spherical template for the formation of the hollow spheres. Finally, the monoclinic GdPO4 hollow spheres with enhanced crystallinity were prepared after annealing process in air, which inherit the hollow spherical morphology and good dispersity of the hydrothermal product. Both the down-conversion (DC) and up-conversion (UC) luminescence can be realized by doping appropriate lanthanide activator ions (Ln3+) into the GdPO4host upon ultraviolet (UV) or near-infrared (NIR) excitation. Moreover, the calcined phosphors exhibit stronger emission intensity due to the improved crystallinity. This adopted synthesis strategy may be of significance for the design and preparation of other hollow spherical lanthanide functional materials.

A flexible CNT@nickel silicate composite film for high-performance sodium storage

Abstract Due to the sufficient ion diffusion channels provided by the large interlayer spacing, layered silicates are widely considered as potential anode materials for lithium ion and sodium ion batteries. However, due to the poor electronic conductivity, the application of layered silicates for electrochemical energy storage has been greatly limited. Carbon nanotube (CNT) film has excellent electrical conductivity and a unique interconnected network, making it an ideal matrix for composite electrochemical material. We herein report a CNT@nickel silicate composite film (CNT@NiSiO) fabricated by a SiO2-mediated hydrothermal conversion process, for sodium storage with excellent electrochemical properties. The obtained composite possesses a cladding structure with homogeneous nanosheets as the outermost and CNT film as the inner network matrix, providing abundant ion diffusion channels, high electronic conductivity, and good mechanical flexibility. Due to these merits, this material possesses an excellent electrochemical performance for sodium storage, including a high specific capacity up to 390 mAh g−1 at 50 mA g−1, good rate performance up to 205 mAh g−1 at 500 mA g−1, and excellent cycling stability. On this basis, this work would bring a promising material for various energy storage devices and other emerging applications.

In-depth comparison of morphology, microstructure, and pathway of char derived from sewage sludge and relevant model compounds

Hydrothermal conversion (HTC) of sewage sludge (SS) and its relevant model compounds such as cellulose, glucose, lignin and soybean protein (substitute for protein) was experimentally conducted at moderate reaction temperature of 260 °C for 60 min. The structural properties, carbon-containing groups, and microstructure of the char were characterised by several techniques. The results revealed that more benzene rings were formed by small clusters and the CO bond on Aryl-alkyl ether decomposed on the surface particles during the HTC process. In addition, the catalyst Zeolite Socony Mobil-5 (ZSM-5, Si/Al: 300) showed an excellent performance on the high graphite degree of the char under moderate reaction temperature of 260 °C. In particular, cellulose has the most dramatic influence on the depolymerisation of C(C,H). As evidenced with SEM, the size of the char derived from SS with ZSM-5 catalyst is 10–15 μm, which is smaller than the char without catalyst. A mechanism for derivation of char from individual model compounds is proposed. The end products of lignin are composed of polyaromatic char, while the composition of the char derived from protein suggests that polymerisation may occur during hydrothermal reaction leading to formation of structures with N-containing compounds.

A New Approach to Kinetic Modeling of Biomass Hydrothermal Carbonization

This study proposes to model hydrothermal carbonization describing the reactions stochastically. A procedure is set up for handling batch reaction data and deducing the probability distributions required for analyzing the process statistically. The progressive formation of the hydrochar and the evolution over time of its composition are connected to the dynamics of Markov processes. The transition probability functions, which rule the solid/liquid reactions, are obtained. The matrix algebra required to evaluate the dynamics of the reacting system is developed. The method furnishes valuable information for the optimization of the industrial reactors. The technique is tested with data concerning batch reactions of both lignocellulosic and agro-food residual biomass carried out at 200 °C, up to 120 min, and at fixed 7:1 water to solid ratio. The model testing also used additional data from the literature. In any case, the accordance between stochastic calculations and experimental data is good. The proposed modeling approach could help to steer the selection of the optimal kinetic pattern among those debated in the literature. The method, fruitful of developments and potentially applicable to the other hydrothermal conversion processes, represents an additional tool for modeling the hydrothermal carbonization.

Condensation of α-Carbonyl Aldehydes Leads to the Formation of Solid Humins during the Hydrothermal Degradation of Carbohydrates.

Catalytic hydrothermal conversion of carbohydrates could provide a series of versatile valuable platform chemicals, but the formation of solid humins greatly decreased the efficiency of the process. Herein, by studying the hydrothermal degradation behavior and analyzing the degradation paths of kinds of model compounds including carbohydrates, furan compounds, cyclic ketone derivatives, and some simple short carbon-chain oxy-organics, we demonstrate that α-carbonyl aldehydes and α-carbonyl acids are the key primary precursors for humin formation during the hydrothermal conversion process. Then, we analyzed the hydrothermal degradation paths of two simple α-carbonyl aldehydes including glyoxal and pyruvaldehyde and found that the α-carbonyl aldehydes could undergo aldol condensation followed by acetal cyclization and dehydration to form solid humins rich of furan ring structure or undergo Cannizaro route (hydration followed by 1,2-hydride shift) to form corresponding α-hydroxy acids. On the basis of the hydrothermal behavior of the α-carbonyl aldehydes, we mapped the hydrothermal degradation routes of carbohydrates (glucose, fructose, and xylose) and illuminated the formation details of α-carbonyl aldehydes, α-hydroxy acids, γ-lactones, furfural derivatives, and humins. Finally, we deduced the typical structure fragments of humins from three α-carbonyl aldehydes of pyruvaldehyde, 2,5-dioxo-6-hydroxy-hexanal, and 3-deoxyglucosone, all of which could be formed during the hydrothermal degradation of hexose.

Hydrothermal conversion of dewatered sewage sludge: Focusing on the transformation mechanism and recovery of phosphorus

The recovery of phosphorus from sewage sludge was critical due to the depletion of phosphate ore. The present research aims to identify the phosphorus speciation and reveal the phosphorus transformation mechanism of dewatered sewage sludge during hydrothermal conversion (HTC) process, as well as to achieve the high efficiency recovery of phosphorus. Multiple analysis of SMT method, VK diagram, XANES and NMR showed that most phosphorus (>80%) was transferred to the hydrochar and presented as inorganic phosphorus (IP) after the HTC process. A dehydration trend was observed of the HTC process with the increase of sub-critical temperature. Ca-associated phosphorus increased significantly as the temperature increased. The Pyro-P gradually transformed to Ortho-P with the increase of HTC temperature and disappeared at 320 °C. The addition of HCl (6.13 and 12.3 mmol/g) in the HTC process resulted in a high percentage (>80%) of phosphorus transferred to the aqueous phase, and the bioavailability of the residual phosphorus increased significantly. The recovery rate of phosphorus could achieve 98.37% at the pH of 7.52, with the struvite purity of 90.41%. The results of this study provide new insights into the selective transfer of phosphorus in dewatered sludge by HTC process, in addition to some efficient ways for the utilisation of the HTC products.

High-performance hybrid supercapacitors based on novel Co3O4/Co(OH)2 hybrids synthesized with various-sized metal-organic framework templates

In this study, a novel hybrid structure of homogeneously distributed Co3O4 nanograins on a hexagonal Co(OH)2 plate is synthesized using a one-pot hydrothermal reaction of ZIF-67. Particularly, because Co-containing ZIF-67 serves as a self-template during the hydrothermal conversion process, various-sized hybrid structures can be prepared using different sizes of ZIF-67 as the precursor material. Owing to their unique structural features, the obtained hybrids effectively boost the electrochemical activation of Co3O4 and Co(OH)2 by preventing aggregation issues. Among the various-sized architectures, large-sized structure exhibits the highest capacity of 184.9 mAh g−1 (at 1 A g−1) in aqueous 1 M KOH electrolyte, indicating that the electrochemical performance is improved as the size of hybrid increases. Furthermore, multifarious all-solid-state hybrid supercapacitors are successfully fabricated with various-sized Co3O4/Co(OH)2 hybrids as the positive electrode and mesoporous plasma-reduced graphene oxide as the negative electrode. Notably, the as-prepared hybrid supercapacitors deliver a maximum energy density of 37.6 Wh kg−1 and peak power density of 47 kW kg−1 with excellent cycling stability (91% capacity retention after 5000 cycles).

Hydrothermal Carbonization of Seaweed For Advanced Biochar Production

Seaweed such as Eucheuma Cottonii is a potential source of biomaterialIts high moisture content makes it suitable for hydrothermal conversion process since it doesn’t need to utilize dry feedstock. The aim of this study is to convert the biomass of red seaweed Eucheuma Cottonii into alternative fuels and high value biomaterials using hydrothermal process. The hydrothermal process seaweed Eucheuma Cottonii produce two types of products, liquid product and char (solid). This research focus on the char product. The char from hydrothermal process was then activated using the tubular furnace. The yield for activated char is 7.5 % and results of SEM analysis of activated char showed the formation of allotropes carbon include carbon micro spheres, carbon micro fibres and graphene. These structures have encountered application in a wide range of technological fields, such as adsorption, catalysis, hydrogen storage or electronics.

Producing Hydrochar from Cotton Linter Black Liquor and Performing Alkali Recovery

Holistic utilization of cotton linter black liquor is crucial from both economic and environmental standpoints. For this purpose, the hydrothermal conversion process was selected to produce hydrochar from organic materials dissolved in black liquor. Fourier transform infrared spectroscopy (FT-IR) analysis showed that there were no significant functional changes in the hydrochar compared with black liquor solid (BLS) at different preserving temperatures. However, a C-O bond was ruptured by the hydrothermal carbonization. Thermogravimetric analysis also showed that the thermal stability of the hydrochar was increased. The higher heating value (HHV) of hydrochar at the different preserving temperature from 200 °C to 280 °C was higher than BLS, reaching a maximum at 200 °C. On the other hand, the alkali from the liquor production of hydrothermal carbonization was recovered by causticization; the highest causticizing efficiency (CE) was 45.2%. The recovered liquor alkali can be used in pulping or pretreatment strategies.