Hydrochar Formation Research Articles

Influence mechanism of aqueous organic components on the hydrochar formation reaction during the biomass hydrothermal carbonization wastewater recycling

Reusing the wastewater byproduct of the hydrothermal carbonization (HTC) process as a water source to prepare biomass slurry feedstock for the next HTC run provides a feasible wastewater disposal method. However, the influence of various organic components contained in the hydrothermal wastewater (HW) on the formation routes and characteristics of hydrochar is yet to be clarified. In this study, five representative organic components, phenol, acetic acid, furfural, 5-hydroxymethylfurfural (5-HMF), and 2,5-hexanedione, were selected to study their effects on the hydrochar fuel characteristics and HW components, based on which the hydrochar formation pathways in an organic wastewater environment were proposed. The phenol, furfural, and 5-HMF contained in the wastewater source could polymerize with the active intermediates from biomass degradation, thereby resulting in an increase in the hydrochar mass yield (HCY) by 1.13%–7.07% and an increase in the higher heating value of hydrochar to 27.36 MJ/kg. In contrast, the acetic acid and 2,5-hexanedione contained in the wastewater source resulted in a decrease in HCY, probably because of the catalytic effects of volatile fatty acids on biomass hydrolysis. Moreover, wastewater sources with all five organic components increased the energy recovery efficiency from biomass to a high level of 97.28% under the two effects of deep polymerization and catalytic carbonization.

Microwave-Assisted Hydrothermal Carbonization of Pomegranate Peels into Hydrochar for Environmental Applications

Several studies have reported that the hydrothermal carbonization method (HTC) of agricultural waste is able to produce a solid residue with interesting properties for the adsorption of organic pollutants from contaminated water. This work represents a facile method to prepare hydrochar (HC) from pomegranate peels’ waste using the microwave-assisted hydrothermal carbonization method (MHTC) at 200 °C for 1 h with a mass ratio of peel to water = 1:10. Activated hydrochar (AHC) was prepared by in situ chemical activation using ZnCl2 and MHTC. Several techniques have been applied to characterize the prepared samples as FTIR, XRD, TEM and SEM. The samples were investigated for their possible use as adsorbents of methylene blue (MB) dye. The results confirm the formation of amorphous hydrochar with a porous structure. The pH of zero point charge (pHzpc) is 4.3 and 4.6 for HC and AHC samples, respectively. The maximum adsorption capacity of HC and AHC samples are 194.9 and 12.55 mg/g (i.e., mg of adsorbate/g of adsorbent), respectively.

Inorganic Salt Catalysed Hydrothermal Carbonisation (HTC) of Cellulose

The presence of inorganic salts either as part of the substrate or added to the reaction medium are known to significantly affect the reaction pathways during hydrothermal carbonisation (HTC) of biomass. This work aims to understand the influence of salts on hydrothermal carbonisation by processing cellulose in the presence of one or more inorganic salts with different valency. Batch experiments and Differential Scanning Calorimetry were used to investigate the change in reaction pathways during hydrothermal conversion. The effect of salts on the rate of HTC of cellulose can be correlated with the Lewis acidity of the cation and the basicity of the anion. The effect of the anion was more pH-dependent than the cation because it can protonate during the HTC process as organic acids are produced. The introduction of salts with Lewis acidity increases the concentration of low molecular weight compounds in the process water. The addition of a second salt can influence the catalytic effect of the first salt resulting in greater levulinic acid yields at the expense of hydrochar formation. Salts also play an important role in cellulose dissolution and can be used to modify the yield and composition of the hydrochars.

Co-hydrothermal carbonization of cellulose, hemicellulose, and protein with aqueous phase recirculation: Insight into the reaction mechanisms on hydrochar formation

Co-hydrothermal carbonization (Co-HTC) coupled with aqueous phase (AP) recirculation has huge potential to improve hydrochar production. In this study, three model compounds, namely wheat straw cellulose (cellulose, Ce), xylan (hemicellulose, He), and soya-protein (protein, Pr), were processed by HTC individually or Co-HTC in combination, with or without AP recirculation. Hydrochar formation behavior was investigated through analysis of hydrochar and AP by elemental analysis, X-ray photoelectron spectroscopy (XPS), Pyrolyzer-gas chromatography-mass spectrometry (Py-GC-MS), GC-MS, and a series of other characterizations. Elemental compositions reveal that both Co-HTC and AP recirculation promoted hydrochar formation and reduction of oxygen in hydrochar, and the combination promoted these effects. Furthermore, XPS and Py-GC-MS results show that the building blocks of hydrochar were oxygenated compounds from Ce and He such as furans and furfurals, and nitrogen-containing compounds from Pr such as amino acids and N-heterocycles. Subsequently, hydrochar formation mechanisms were proposed by results from GC-MS analysis of AP and the above observations. The major mechanisms account for enhanced hydrochar formation during Co-HTC with AP recirculation were Maillard reaction occurred between amino acids and saccharides, catalytical effects (mainly on Maillard reaction) from acids in the recycling AP, and the repolymerization or condensation of accumulated compounds in AP.

Activated carbon induced hydrothermal carbonization for the treatment of cotton pulp black liquor

Powdered activated carbon (PAC) was introduced into hydrothermal carbonization (HTC) as a catalyst for treatment of cotton pulp black liquor (CPBL) in the present work. The influence of main operating parameters on treatment efficiency in hydrothermal carbonization catalyzed by PAC (PAC-HTC) and changes of PAC due to hydrochar formation on PAC surfaces were studied. Experimental results showed that high temperature and sufficient carbonization time were crucial for HTC of CPBL. The presence of PAC in HTC resulted in significant improvement for CPBL decontamination for 6 h of reaction at 300 °C. Removals of chemical oxygen demand (COD), UV254 and lignin reached 89.59%, 99.71% and 99.79%, respectively. PAC can not only adsorb small molecule organics, but also promote the decomposition and carbonation of biomass macromolecules such as lignin. PAC showed outstanding reusability in the PAC-HTC process, as organics adsorbed on the surface of PAC participated in HTC reactions to realize in-situ regeneration. The PAC-HTC process developed in this work may provide a new alternative for CPBL treatment.

Co-Hydrothermal Carbonization of Cellulose, Hemicellulose, and Protein with Aqueous Phase Recirculation: Insight into the Reaction Mechanisms on Hydrochar Formation

Co-Hydrothermal Carbonization of Cellulose, Hemicellulose, and Protein with Aqueous Phase Recirculation: Insight into the Reaction Mechanisms on Hydrochar Formation

Recovery, separation and production of fuel, plastic and aluminum from the Tetra PAK waste to hydrothermal and pyrolysis processes.

The establishment of a method of separation of materials from Tetra Pak waste to obtain products for use as raw material, fuel or other purposes was investigated in this study. First, the feasibility of hydrothermal treatment for the production of a solid fuel (hydrochar) and solid fraction formed by polyethylene and aluminum, called composite was analyzed. The results indicated that hydrothermal treatment performed at 240°C yield the formation of hydrochar with good properties for its use as fuel and a composite of polyethylene and aluminum. The best conversion and separation of the cardboard and polyethylene/aluminum were obtained using 120min as operating time. Then, the recovery of the aluminum fraction from the composite by using spent olive oil waste was studied. A partial separation of the composite layers (polyethylene and aluminum) was accomplished with improved aluminum purity for higher operating temperatures. Finally, the operating conditions of the pyrolysis process for the production of a solid (char) and high purity composite (aluminum) were optimized. The characterization results indicated that both char and aluminum resulting from the pyrolysis of the Tetra Pak at 400°C still have a significant amount of polyethylene while higher purity levels of aluminum can be obtained at temperatures equal of higher than 500°C.

Influence Mechanism of Aqueous Organic Components on the Hydrochar Formation Reaction During the Biomass Hydrothermal Carbonization Wastewater Recycling

Influence Mechanism of Aqueous Organic Components on the Hydrochar Formation Reaction During the Biomass Hydrothermal Carbonization Wastewater Recycling

Chemical Reaction: Understanding the Key to the Formation of Carbonaceous Materials from Sucralose

AbstractAn interesting way to understand carbonaceous materials structure and their properties is to evaluate the chemical reactions involved in their production. However, there are only a few published works describing the main reactions. Here, we report how chemical reactions can help understand the degradation of sucralose in hydrothermal carbonization (HTC), and the formation of hydrochar. To this end, sucralose is treated for 3.0 h, and Raman and mass spectrum data of hydrochar and liquid samples are analyzed, as well quantum chemistry calculations (QCC). The results show that ionization of sucralose is the most important step in the degradation process, and the use of FeCl2 can speed up the degradation process. However, pH leads to ionization, dehydration and dechlorination, but glycosidic bond cleavage is a common subsequent reaction. Raman analysis present hydrochar samples with oxygen‐containing groups and aromatic/heterocyclic ring bands which are important in functionalized materials. Morphologically, the samples generated at initial pH=10.00, and in the presence of MnCl2 presented the smallest microspheres and this phenomenon may be related to the amount of degradation products. Finally, the evaluation of Raman spectroscopy and mass spectrometry data using principal components analysis is useful to suggest the degradation pathways and hydrochar formation processes.

Reaction kinetics for the hydrothermal carbonisation of cellulose in a two-phase pathway

Hydrothermal carbonisation (HTC) of biomass has gained attention in recent years due to its potential applications in functional sustainable materials. Cellulose as the most abundant organic polymer on earth and a key component of multiple biomass sources has been extensively studied, and it is widely accepted that glucose is the major product of the polysaccharide’s hydrolysis above 200 °C. However, differences observed in the hydrochar produced from the HTC of cellulose and glucose have suggested that a direct reaction takes place in the polysaccharide's conversion. In the present study, a solid-state reaction pathway for the HTC of cellulose is elucidated using reaction kinetics modelling and optimisation in a progressive reaction mechanistic and the effect of temperature on reaction selectivity is analysed. The experiments were conducted with glucose and cellulose in a batch reactor with 20% mass feedstock at 220 °C, 240 °C and 260 °C, over a residence time distribution. And the kinetic parameters were established by fitting the experimental data with a series of reaction mechanism and kinetic models via multivariable optimisation. Whilst the activation energy for the hydrochar formation reaction from glucose was 46.6 kJ/mol, the same reaction from cellulose, assuming complete hydrolysis, produced a value three times bigger. Therefore, a composite cellulose model, in which hydrochar through soluble intermediates, is restricted to the glucose reaction constant and balanced with a direct solid-state reaction pathway, produced activation energies of 210.8 kJ/mol for hydrolysis of cellulose and 207.3 kJ/mol for the solid-state reaction.

Microwave-assisted catalytic hydrothermal carbonization of Laminaria japonica for hydrochars catalyzed and activated by potassium compounds

There are limited investigations describing preparation and application of alga-based hydrochars via microwave–assisted catalytic hydrothermal carbonization (MA-CHTC). Therefore, hydrochars were successfully prepared from macroalgae biomass Laminaria japonica impregnated with KH2PO4, KCl, K2CO3, and KOH as acidic, neutral salt, and alkaline catalysts, respectively, via the MA-CHTC. Comprehensive characterization of physicochemical properties of the hydrochars, including yields, elemental and phase composition, specific surface areas, functional groups, and morphology, confirmed different catalytic effects of these catalysts on hydrochar formation. Adsorption kinetics and isotherms of Pb(II) revealed significant improvement of adsorption capacities for Pb(II) due to synergetic chemical activation of the spiked catalysts. Therefore, the synergetic catalytic effects and chemical activation is benefic for tailored design of engineered hydrochars with different properties for special application through selection of catalysts during the MA-CHTC process.

Montmorillonite-Hydrochar Nanocomposites as Examples of Clay–Organic Interactions Delivering Ecosystem Services

AbstractClay–organic interaction is an important natural process that underpins soil ecosystem services. This process can also be tailored to produce clay–organic nanocomposites for industrial and environmental applications. The organic moiety of the nanocomposites, typically represented by a toxic surfactant, could be replaced by hydrochar formed from biomolecules (e.g. glucose) via hydrothermal carbonization. The effect of montmorillonite (Mnt) and glucose dosage on hydrochar formation, however, has not been clarified. In addition, the mechanisms by which Mnt-hydrochar nanocomposites (CMnt) can detoxify and remove carcinogenic Cr(VI) from aqueous solution are not well understood. In the current study, research milestones in terms of clay–organic interactions are summarized, following which the synthesis and characterization of CMnt for Cr(VI) adsorption are outlined. Briefly, 1 g of Mnt was reacted with 75 mL of glucose solution (0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 mol L−1) by hydrothermal carbonization at 200°C for 16 h. The resultant CMnt samples were analyzed for chemical composition, functional groups, morphological features, and Cr(VI) adsorptive properties. Mnt promoted the conversion of glucose to hydrochars, the particle size of which (~80 nm) was appreciably smaller than that formed in the absence of Mnt (control). Furthermore, the hydrochars in CMnt had an aromatic structure with low hydrogen substitution and high stability (C/H atomic ratio 0.34–0.99). The weakened OH (from hydrochar) and Si–O–Si stretching peaks in the Fourier-transform infrared (FTIR) spectra of CMnt are indicative of chemical bonding between Mnt and hydrochar. The CMnt samples were effective at removing toxic Cr(VI) from acidic aqueous solutions. Several processes were involved, including direct reduction of Cr(VI) to Cr(III), complexation of Cr(III) with carboxyl and phenolic groups of hydrochar, electrostatic attraction between Cr(VI) and positively charged CMnt at pH 2 followed by indirect reduction of Cr(VI) to Cr(III), and Cr(III) precipitation.

Rapid conversion of red mud into soil matrix by co-hydrothermal carbonization with biomass wastes

Red mud is the alkaline and high-volume residue produced from alumina extraction from bauxite ores. Its disposal in purpose-built areas occupies a large amount of land and poses serious threats to surrounding environment. This study proposes an innovative strategy for rapid conversion of red mud into soil matrix by co-hydrothermal carbonization (c-HTC) with biomass wastes. Effective neutralization of the alkalinity is obtained by c-HTC process, lowering the pH from 10.0 to approximate 7.0. Experiments of employing wet biomass wastes, reusing water for c-HTC and long-term pH stability verify the feasibility and practicality of c-HTC process. Change of alkaline components in red mud, formation of hydrochar, and creation of aggregates are revealed by multiple characterizations. As to soil properties, the cation exchange capacity, electrical conductivity, organic carbon, and particle size of c-HTC product is remarkably improved. Perennial ryegrass is well grown in the soil matrix. The c-HTC strategy promotes future application of phytoremediation of red mud at full field scale.

Quantification and kinetic study of the main compounds in biocrude produced by hydrothermal carbonization of lignocellulosic biomass

The biomass hydrothermal carbonization (HTC) reaction pathway to the formation of primary and secondary hydrochar is proposed in this study. Total sugars were the main product in biocrude at low temperature; their concentration decreased as the temperature increased, producing organic acids and furans. Kinetic study reveals that the hydrolysis activation energy increased as hemicellulose content decreased. Indeed, a value of 63.08 kJ/mol was found for biomass rich in hemicellulose (avocado stone) while for biomass composed of a hemicellulose-cellulose mixture (agave bagasse) the value was 85.02 kJ/mol, and for α-cellulose it was 136.24 kJ/mol. Contrastively, the activation energy for furans formation was higher than that for organic acids in any case. A proposed14-reactions mechanism adequately describes the HTC process considering intermediate to final products (R2 > 0.98). The higher heating value (HHV) of hydrochars was between 22 and 26 MJ/kg, with an energy densification of 34 to 49% compared to the corresponding feedstock.

The formation of 5-hydroxymethylfurfural and hydrochar during the valorization of biomass using a microwave hydrothermal method

5-Hydroxymethylfurfural (HMF) and levulinic acid (LA) are regarded as value-added platform chemicals that can be derived from biomass waste. However, humins are inevitably produced during valorization processes, reducing the product yields. Previous studies indicated that microwave heating combined with acidic seawater as a reaction medium promotes HMF formation. The present work therefore investigated the relationship between the production of HMF and LA in the liquid phase and that of insoluble humins (that is, hydrochar) under microwave heating in acidic seawater. The selectivities for HMF and LA were found to decrease as the reaction time was increased, as a result of hydrochar formation, and both dehydration and decarboxylation evidently dominated the production of hydrochar in succession. HMF evidently played the most important role in hydrochar formation, and was consumed approximately seven times more rapidly than either fructose or LA. The hydrochar formation mechanism reported herein may be applicable to other similar hydrothermal processes.

Nitrogen-Containing Hydrochar: The Influence of Nitrogen-Containing Compounds on the Hydrochar Formation.

Hydrothermal carbonization (HTC) of fructose and urea containing solutions was conducted at 180 °C to study the influence of nitrogen‐containing compounds on the conversion process and HTC products properties. The concentration of fructose was fixed, while the concentration of urea was gradually increased to study its influence on the formation of nitrogen‐containing hydrochar (N−HC). The degradation of urea has an important influence on the HTC of fructose. The Maillard reaction (MR) promotes the formation of N−HC in acidic conditions. However, in alkaline conditions, MR promotes the formation of bio‐oil at the expense of N−HC. Alkaline conditions reduce N−HC yield by catalyzing fragmentation reactions of fructose and by promoting the isomerization of fructose to glucose. The results showed that adjusting the concentration of nitrogen‐containing compounds or the pH value of the reaction environment is important to force the reaction toward the formation of N−HC or N‐bio‐oil.

Identification of the Soluble Byproducts Formed during the Hydrothermal Conversion of Cellulose Catalyzed by Solid Tungstated Alumina.

The soluble byproducts formed during the hydrothermal conversion of cellulose catalyzed by solid tungstated alumina (AlW) were analyzed by LC–MS and LC–MS2 to determine their formulas and possible structures. These identified soluble compounds could be roughly divided into four species of carboxylic acids, α-carbonyl aldehydes, carbocyclic compounds, and furanic compounds with molecular mass in the range of 90–220 Da. Compared with the noncatalytic condition, the addition of AlW could increase the selectivity of carboxylic acids (especially α-hydroxy acid) from cellulose and suppress the formation of furanic compounds, carbocyclic compounds, and hydrochar. Based on the product distribution, the hydrothermal conversion route of glucose was proposed by regarding the formed α-carbonyl aldehydes as the key intermediates for formation of carboxylic acids, carbocyclic compounds, and furanic compounds.

Hydrothermal synthesis and applications of advanced carbonaceous materials from biomass: a review

Hydrothermal carbonization (HTC) is a novel method to produce carbonaceous materials, which has been extensively concerned because of its environmentally benign and simple process. This review aims to introduce the approaches and mechanisms of carbonaceous materials prepared by hydrothermal carbonization from biomass in recent years, and discuss the applications of the functional materials transformed from carbonaceous materials. Specifically, the utilizations of various biomass raw materials, including carbohydrates, lignocellulose, and other biomass waste for the production of biochar are discussed. The significant parameter influence and mechanistic aspects of the hydrochar are critically analyzed to better understand the hydrochar formation process. More importantly, recent advances in hydrochar utilization techniques are summarized. Finally, we envision that the ideal designs of the biomass-based functional carbonaceous materials will open up a novel family of functional carbon materials with various applications towards a green and sustainable future.

Insights in mechanisms of carbonaceous microparticles formation from black liquor hydrothermal conversion

The study addresses the formation of secondary hydrochar and the morphology of secondary microparticles from black liquor. The black liquor solution was hydrothermally converted at 350 °C and 16.5 MPa in batch reactors running from 15 min to 24 h at different heating and cooling rates. Spherical carbon microparticles were obtained at a short reaction time (< 90 min) and then coalesced to form aggregates. At a very long reaction time (24 h), spherical carbon microparticles were obtained once again. The carbonaceous solid was enriched in carbon during the first 4 h of reaction. In parallel, the concentrations of total organic carbon and total phenols in the solution decreased drastically. The formation of solids was mainly due to chemical reactions occurring during the first 4 h. Subsequent changes in the solids were mainly due to physical reorganization since the chemical compositions of solutions were almost stable.

Formation of Soluble Furanic and Carbocyclic Oxy-Organics during the Hydrothermal Carbonization of Glucose

In this study, the water-soluble products formed during the hydrothermal carbonization of glucose were analyzed by liquid chromatography (LC)–mass spectrometry (MS) and LC–MS2 to determine the formulas and the possible structures of the main compounds. In addition to the well-known compounds of 3-deoxyglucosone, 5-hydroxymethylfurfural, and levulinic acid, the furanic compounds and the carbocyclic oxy-organics containing hydroxy group and carbonyl group with a molecular mass range between 170 and 260 Da were also identified. Both C–C coupling reaction and C–C cleavage reaction were proved to be involved during the formation of these carbocyclic oxy-organics, so they were proposed to be released via C–C cleavage of the primary polymers, which were formed by aldol condensation of the primary precursors formed during the degradation of glucose. The identification of these carbocyclic oxy-organics was indirect evidence that aldol condensation played a crucial role during the formation of hydrochar from carbonization of glucose.