Hydrothermal Conversion Of Biomass Research Articles

H2SO4 assisted hydrothermal conversion of biomass with solid acid catalysis to produce aviation fuel precursors

With hydrothermal reaction, lignocellulosic biomass can be efficiently converted into furfural (FF) and levulinic acid (LA), both of which are key platform compounds that can be used for the subsequent preparation of aviation fuels. In order to reduce the acid concentration in traditional hydrolysis and provide a reaction system with good catalytic activity, we propose a biomass conversion route as dilute acid hydrolysis coupled with solid acid catalysis. Firstly, at different temperatures, the hemicellulose and cellulose in corn stover were step-hydrolyzed by sulfuric acid solution with a concentration of 0.9 wt.% to produce xylose and glucose, with conversion reaching 100% and 97.3%, respectively. Subsequently, a new resin-derived carbon-based solid acid catalyst was used to catalyze the aforementioned saccharide solutions to obtain FF with yield of 68.7 mol% and LA of 70.3 mol%, respectively. This work provides a promising approach for the efficient production of bio-aviation fuel precursors.

Low-temperature synthesized hierarchical porous carbon from waste hydrochar with super capacity for dye adsorption

Hydrochar is a by-product of subcritical hydrothermal conversion of biomass for bio-oil production, which has received more and more attention in environmental remediation, but the low porosity of hydrochar severely limits its effective utilization. Herein, a novel method of low-temperature activation of hydrochar with sodium amide (NaNH2) was proposed to enhance its porosity. The resulting hydrochar-derived porous carbon (PC) possessed a large pore volume (1.147 cm3/g) and a high specific surface area of up to 2185.3 m2/g. Further, NaNH2 also increased the relative oxygen content of PC during activation. 2D-FTIR correlation spectra suggested that the change in the infrared signal intensity of -C-O ordinarily occurred before that of aromatic CC as the NaNH2 dosage changed. More importantly, as-prepared PC exhibited excellent adsorption properties for methylene blue (MB), up to 833.33 mg/g, which is mainly attributed to the pore-filling-effect. And the oxygen-containing functional group was also beneficial to improve the adsorption capacity of PC for MB. The adsorption process of MB on as-prepared PC was well described using the Langmuir adsorption isotherm model, indicating that the adsorption process was single-layer adsorption. Undoubtedly, it is a feasible strategy to prepare PC for MB adsorption by low-temperature activation of waste hydrochar with NaNH2.

Partial oxidation gasification kinetics of indole in supercritical water for hydrogen production

Indole is one of refractory intermediate products in hydrothermal conversion of biomass, and its decomposition significantly restricts the improvement of gasification efficiency and hydrogen production in biomass supercritical water gasification (SCWG). In order to improve gasification efficiency of indole and moderate reaction conditions for hydrogen production in biomass SCWG, indole (0.25 mol/L) was gasified in supercritical water at 540–600 °C, 25 MPa, 0–0.8 of oxidation coefficients (OC) in min-batch reactors. Corresponding pathways and kinetics of partial oxidation of indole in supercritical water for hydrogen production were explored. The results showed that the addition of oxidant (hydrogen peroxide) promoted steam reform and decomposition, especially ring-opening reactions, so increasing the gasification efficiency of indole and the yields of H2 and CO2 in gaseous products. The maximum hydrogen gasification efficiency could reach up to 60.3% at OC = 0.6, which was about twice that of non-oxidant. Moreover, 29 groups of reaction rate constants, activation energies and Arrhenius constants were obtained in the established kinetic model.

A Sustainable Approach on Spruce Bark Waste Valorization through Hydrothermal Conversion

In the context of sustainable use of resources, hydrothermal conversion of biomass has received increased consideration. As well, the hydrochar (the solid C-rich phase that occurs after the process) has caused great interest. In this work, spruce bark (Picea abies) wastes were considered as feedstock and the influence of hydrothermal process parameters (temperature, reaction time, and biomass to water ratio) on the conversion degree has been studied. Using the response surface methodology and MiniTab software, the process parameters were set up and showed that temperature was the significant factor influencing the conversion, while residence time and the solid-to-liquid ratio had a low influence. Furthermore, the chemical (proximate and ultimate analysis), structural (Fourier-transform infrared spectroscopy, scanning electron microscopy) and thermal properties (thermogravimetric analysis) of feedstock and hydrochar were analyzed. Hydrochar obtained at 280 °C, 1 h processing time, and 1/5 solid-to-liquid ratio presented a hydrophobic character, numerous functional groups, a lower O and H content, and an improved C matter, as well as a good thermal stability. Alongside the structural features, these characteristics endorsed this waste-based product for applications other than those already known as a heat source.

Preparation of platform compounds by hydrothermal conversion of lemon peel under the catalysis of sulfuric acid

Lemon peel, as a typical carbon solid waste in fruit processing industry, of which efficient recycling and resource utilization contribute to the development of renewable liquid fuel and economic benefits. Citric acid contained in lemon peel has been proved to be a weak acid that can effectively promote the hydrothermal conversion of biomass and its derivatives to produce high value-added furan products. Therefore, sulfuric acid is used to catalyze the hydrolysis of lemon peel to produce precursor of important liquid fuel, such as levulinic acid (LA) and furfural (FF). The promotion effect of common metal salt on catalysis of sulfuric acid to the hydrolysis process of lemon peel is explored. The citric acid contained in lemon peel promotes the hydrolysis process. Combined with catalysis of sulfuric acid, the LA yield as 22.6% can be obtained under the mild hydrolysis conditions of 170°C and 90 min, and the addition of the KCl can effectively inhibit the secondary reaction of the decomposition process of the lemon peel and enhance the interaction of the sulfuric acid and the lemon peel. Compared with AlCl3 and FeCl3, the LA yield is increased to 27.9% by the addition of KCl. Preparing conditions of glucose and FF are milder than that of LA. Enhancement of temperature and acidic concentration, and prolonging reaction time all lead to significant decrease in glucose and FF yield.

Biomass hydrothermal conversion under CO2 atmosphere: A way to improve the regulation of hydrothermal products

In this study, batched hydrothermal experiments on corn stalk were conducted at 240–330 °C under CO2 or inert (N2) atmosphere. The distribution and characteristics of gaseous, solid, and liquid products were analyzed in detail to comprehensively investigate the effects of CO2 on the hydrothermal conversion of biomass, especially on the cellulose and lignin in biomass. The results demonstrate that compared with N2, CO2 slightly increased the liquid and gas yields and significantly improved the control effect of temperature on bio-oil components. Under CO2 atmosphere, bio-oil achieved effective enrichment of ketones and phenols at 240 °C and 300 °C, respectively, and their highest relative contents reached 44.8% and 62.0%, respectively. In addition, the hydrochar obtained under CO2 atmosphere showed higher crystallinity, which is conducive to its subsequent utilization. This study explored the feasibility of introducing CO2 into the biomass hydrothermal process to realize the high-value utilization of biomass waste and the reuse of CO2.

Thematic issue: Hydrothermal conversion of biomass

Thematic issue: Hydrothermal conversion of biomass

Mechanism of solvothermal conversion of xylose to furfural in rich-methanol solution: A study based on density functional theory

The hydrothermal conversion of biomass is an important method for furfural (FF) production. The development of methods for converting five-carbon sugars to FF can improve the utilization rate of biomass polysaccharides, which has important research value. FF is a valuable furan organic compound in the decomposition of xylose and can be produced in large quantities under hydrothermal conditions. In this study, density functional theory (DFT) method was used to study the mechanism of xylose forming FF and the effect of methanol-water mixed solution on FF formation. In this paper, through quantitative calculations, the best way to convert xylose to FF is explored, in order to understand the basic conversion way of biomass hydrothermal conversion to high-value molecular FF. It shows that water molecules participate in the catalytic reaction, and the Gibbs free energy is significantly reduced. This is consistent with the experimental results. In the gas phase, the catalytic reaction shows excellent effects. The Gibbs free energy in the solution is significantly lower than the Gibbs free energy in the gas phase. Combining experimental results and theoretical calculations, it is confirmed that the yield of FF produced by hydrothermal liquefaction of xylose is significantly higher than that of gas-phase pyrolysis. It was also confirmed that methanol played a role in protecting active functional groups, while water played a role as a catalyst. At the same time, methanol and water have a synergistic effect on the solvent.

Development of a mathematical model for hydrothermal carbonization of biomass: Comparison of experimental measurements with model predictions

The present study aims to develop a mathematical model for hydrothermal carbonization (HTC) by incorporating heat transfer rate, reaction kinetics, and the porous structure of the biomass for the first time using various modules of COMSOL Multiphysics software. HTC experiments on pine wood particles using a batch reactor were performed to calibrate the model. Operating parameters such as temperature, residence time, biomass to water ratio, and power consumption were recorded, and the obtained products were characterized via ultimate analysis, and bomb calorimetry experiments. Experimental results validate the predictions of the developed model. It is observed that the predicted energy consumption was considerably deflected from the experimental value when the reactions during the processing and porosity of biomass were not considered. Hence, the developed model can potentially be used as a first step in designing an industrial reactor for hydrothermal conversion of biomass, which may attract investors and policy makers for commercialization of this technology.

Hydrothermal conversion of biomass to higher alcohol fuels for compression ignition engine

Abstract Higher alcohol (C5/C6 alcohol) blended with diesel or bio-diesel is a promising alternative clean fuel for the compression ignition engine. The most important puzzle is the technology development of biomass to higher alcohol fuels. In this paper, a novel approach of hydrothermal conversion of biomass into C5/C6 higher alcohol fuels was proposed. High yield of higher alcohol fuels was obtained from the real biomass with the C5/C6 alcohol selectivity of 77% under the mild hydrothermal conditions. The properties of the produced higher alcohol fuels are similar to that of 0# diesel. The exhaust emission of compression ignition engine decreased vigorously by blending the higher alcohol fuels with diesel at weight ratio of 20/80.

Cellulose conversion into lactic acid over supported HPA catalysts

One-pot hydrothermal conversion of biomass into lactic acid over a green heterogeneous bifunctional catalyst.

Characterization and utilization of aqueous products from hydrothermal conversion of biomass for bio-oil and hydro-char production: a review

Hydrothermal conversion (HTC), including hydrothermal liquefaction and hydrothermal carbonization, is a promising thermochemical technology for biomass utilization.

Hydrothermal conversion of biomass (Xanthium strumarium) to energetic materials and comparison with other thermochemical methods

In the present study, the biomass was converted into liquid and solid residues by using hydrothermal liquefaction method at 250, 300 and 350 °C with (FeCl3, NaOH) and without catalyst. The resultant products were examined using GC–MS, FT-IR, 1H NMR, SEM, and elemental analysis methods. According to the performed analyses, the highest liquid product yield (total bio-oil) was found to be 38.08% at 300 °C by using FeCl3 as catalyst. In the experiments carried out at 350 °C, the highest HHV value was found to be 32.35 MJ kg−1 by using NaOH catalyst. The energy values of products obtained at the end of experiments were compared to the values obtained from pyrolysis and supercritical liquefaction method, and it was determined that the liquid products having higher level of energy value were achieved by using hydrothermal liquefaction method.

Factors controlling the formation of persistent free radicals in hydrochar during hydrothermal conversion of rice straw

In the environment, persistent free radicals (PFR) have adverse effects on human health. PFR are generated by thermal conversion of biomass, such as hydrothermal carbonization to produce hydrochar. So far, the mechanism and control factors of PFR production in hydrochar are poorly known. Therefore, we investigated here the impacts of hydrothermal temperature, residence time and solid load on the formation of PFR in hydrochar from hydrothermal carbonization of rice straw, by electron paramagnetic resonance (EPR) coupled with Fourier transform infrared spectrometers. Results show that the EPR signal intensity increased with increasing hydrothermal temperature from 180 to 240 °C and then decreased at 260 °C. A shorter residence time and a higher solid load led to formation of more PFR in hydrochar. The types of PFR also depended on hydrothermal temperature, residence time and solid load. This is the first report on the formation of PFR and relevant influencing factors during hydrothermal conversion of biomass. Based on these results, hydrochar from hydrothermal conversion of biomass at relatively higher temperature, i.e., 260 °C, longer residence time, i.e., 4 h, and lower solid load, i.e., 1:10, is suggested for safer application.

Hydrothermal conversions of waste biomass: Assessment of kinetic models using liquid-phase electrical conductivity measurements

This experimental study proposes the systematic monitoring of liquid phase electrical conductivity as a new technique for evaluating kinetic models for hydrothermal conversion of biomass. The application to the hydrothermal carbonization of three different wooden materials is validated by batch experiments at 200 °C, up to 120 min of reaction time, and at a 7:1 water to solid ratio. Whatever the biomass, the time course of electrical conductivity follows a unique law, unquestionably corresponding to the evolution of solid-phase carbon content. The model tested comes from literature, and is a simple first-order pattern. The network of elementary steps satisfactorily explains the experimental data. The evidence reported demonstrates that the electrical conductivity should become a standard measurement. In fact, this lumped parameter is for the first time used for predicting the time variation of furfural, an important compound ubiquitously found in the HTC liquid phases. Ordered trends also appear from experiments at higher temperatures, up to 440 °C, but the method highlights a different behavior. The observed discrepancies give useful feedback for steering the upgrading of kinetic equations toward a more structured model, which necessarily should account for the bio-crude. Additional runs with potato peels, an entirely different kind of biomass were used here as a stress test for the method, and as expected gave different results. This new response correctly signals that another model is required for describing the process applied to starchy materials, and confirms the power of the proposed technique as a tool for build-up suitable kinetic models.

Combined Hydrothermal Conversion of Biomass (Algae and Aquatic Vegetation) from Lake Baikal Littoral Zone and Heavy-Oil Resids to Produce Biofuel

The prodigious growth of filamentous algae that has been occurring since 2011 in the littoral zone of Lake Baikal poses an acute ecological problem. Samples of algal biomass and aqueous vegetation were collected from the littoral zone of Lake Baikal and converted by hydrothermal treatment into biofuel in the presence of ammonium heptamolybdate. It was demonstrated that algal biomass from the Baikal littoral zone could be a potential source of feedstock for producing biofuel by thermocatalytic treatment. The addition of heavy-oil resids to algal and aquatic vegetation biomass increased the motor-fuel yield and modified its composition.

Hydrothermal Conversion of Russian Olive Seeds into Crude Bio-oil Using a CaO Catalyst Derived from Waste Mussel Shells

Hydrothermal conversion studies were performed (bio-oil obtained under hydrothermal conditions) using Russian olive (Elaeagnus angustifolia L.) seeds as a waste biomass at different temperatures and different residence times. After the conditions where the highest yield of bio-oil was found, a mussel shell catalyst (which is a source of calcium oxide when calcined at T > 950 °C) was applied for the first time for the hydrothermal conversion of biomass. To compare and evaluate the catalytic performance of the catalyst, the effects of the catalyst on product distributions, elemental contents, and high heating values of products and bio-oil compositions were investigated. The use of the catalyst significantly increased the bio-oil and conversion yields. The bio-oils were analyzed by a gas chromatograph–mass spectrometer (GC–MS). Characterization studies of the catalyst were completed by scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area analysis, and X-ray diffraction (XRD) analysi...

Hydrothermal conversion of woody biomass with disodium octaborate tetrahydrate and boric acid

In this study, Scotch pine (Pinus sylvestris L.) was used as a woody biomass in the form of sawdust. Hydrothermal conversion of the biomass was carried out in the absence and presence of disodium octaborate tetrahydrate and boric acid at the temperatures of 250, 300 and 350°C. The effects of temperature and catalysts on the product distributions and bio-oil compositions were investigated. The highest total bio-oil yield obtained at 300°C with disodium octaborate tetrahydrate was 34.9wt%, whereas the total bio-oil yields from the non-catalytic run and the run with H3BO3 at 300°C were 24.6wt% and 19.1wt%, respectively. Although the composition of bio-oils was similar in all runs, some compounds such as furfural and furfural derivatives were not observed in the light and heavy bio-oils produced from the non-catalytic run and the run with disodium octaborate tetrahydrate at 300°C. The light bio-oils from all runs contained mainly oxygenated hydrocarbons. The major compounds in HBOs were the following: 4-methyl-3-penten-2-one and 4-hydroxy-4-methyl-2-pentanone for disodium octaborate tetrahydrate, 4-hydroxy-4-methyl-2-pentanone and (Z,Z)-9,12-octadecadienoic acid for the non-catalytic run and (Z,Z)-9,12-octadecadienoic acid for the run with boric acid. The maximum heating values for the LBO and HBO were estimated to be about 25 and 28MJ/kg, respectively, and they were obtained with disodium octaborate tetrahydrate. SEM analysis of the bio-char obtained from the non-catalytic run at 250°C showed a semi-char formation. An increase in temperature from 250 to 300°C led to the formation of regular channels on the surface of the bio-char. These open channels closed when the temperature was increased from 300 to 350°C.

Hydrothermal conversion of biomass to fuels and energetic materials

Available biomass, preferentially residues, can be divided in two groups: biomass with a high or natural water content ('wet' or 'green' biomass) and biomass with low water content such as wood and straw. In 'dry' biomass gasification processes, originating in most coal processing technologies, biomass of low water content is necessary to avoid the energy loss by water evaporation. In contrast, hydrothermal processes need water as reaction medium; therefore, these processes are preferentially used for wet or 'green' biomass. In this review paper we will describe the main research directions in the hydrothermal conversion of biomass into fuels and carbon throughout gasification to produce H2 or CH4, liquefaction to produce crude oils and phenols from lignin as well as carbonization to produce carbonaceous materials which can be either used as fuels (carbon negative chars) or interesting energetic materials (hydrothermal carbons).

Hydrothermal conversion of biomass and different model compounds

In this study, a comparison of the hydrothermal behavior of various biomasses such as phyto mass, zoo mass, phyto mass/K2CO3 and glucose K2CO3 (model system for the phyto mass) is given. The experiments have been carried out in a batch reactor at 500°C, 30MPa with a reaction time of 1h. The phenol content of the aqueous phase obtained by biomass conversion was remarkably high. Actually, phenols and furfurals are the most important intermediates formed during the hydrothermal conversion of biomass. No furfural and its derivatives were observed in this study. In order to investigate the hydrothermal biomass conversion in detail, the behavior of the phenols and furfurals, under the same experimental conditions was also studied. The differences between the feedstocks have been discussed. Likely variations of the products and intermediates formed are a consequence of differences in the composition of the feedstock, namely, salts and proteins which seem to influence the chemistry of hydrothermal conversions.