Carbonaceous Solids Research Articles

Enhanced conversion of heavy feedstock through the circulation of catalytic components in tail oil derived from coal liquefaction

The co-hydroprocessing of lignite and heavy residue generates a substantial amount of tail oil, compromising the technical efficiency and posing significant environmental hazards. We proposed a cascade utilization scheme via the combination of tail-oil cycling and tail-oil co-hydrocracking, to maximize the utilization of catalytic components and enhance the conversion of heavy feedstock. At a cycling ratio of 50 wt%, the conversion efficiency of carbonaceous solids increased from 88 % to over 95 % after 5 cycles. The effluent tail oil also represented a favorable hydrocracking performance when mixed with Merey atmospheric residue. The spent catalysts and iron-containing minerals gradually accumulated in solid residues, which provided additional catalytic components for hydrogenation and coke inhibition in the co-hydroprocessing and co-hydrocracking systems. Moreover, the cycling process improved the colloidal stability and enhanced the hydrogenolysis of heavy components, effectively curbing the degradation tendency within the reaction system and producing more light oils.

Interaction of derivatives of cellulose and lignin in co-HTC, co-pyrolysis and co-activation

Cellulose and lignin co-exist in agroforestry biomasses and their distinct structures lead to the formation of varied derivatives in their thermal conversions. This might induce interaction of these derivatives and shape the properties of resulting products. In this study, potential interaction of the derivatives from cellulose and lignin was investigated in three scenarios: hydrothermal carbonization (HTC) at 250 °C, pyrolysis at 550 °C and activation with CO2 at 800 °C. The results indicated interactions among volatiles and between volatiles and char, influencing properties of varied chars. The co-HTC of cellulose/lignin reduced the yield of hydrochar, due to the enhanced depolymerization of feedstocks and heavy organics with the aid of carboxylic acids derived from cellulose. In converse, cross-polymerization reaction between volatiles and biochar in pyrolysis/activation formed additional carbonaceous solids, increasing the yield of biochar (by 5.5%) and activated carbon (by 12.4%) as well as large π-conjugated organics in the bio-oils. Aromatization reaction was enhanced during the co-pyrolysis of lignin/cellulose, making the biochar thermally more stable, while co-activation of mixture significantly increased the specific surface area of resulting activated carbon (889.0 m2g−1 versus 691.5 m2g−1 in theoretical average), as the volatiles of varied origins involved in activation of the biochar. Additionally, the co-HTC, co-pyrolysis and co-activation also significantly affected evolution of functionalities, hydrophobicity and morphologies of the hydrochar/biochar/activated carbon.

Improved cell performance and sulphur tolerance using A-site substituted Sr2Fe1.4Ni0.1Mo0.5O6–δ anodes for solid-oxide fuel cells

AbstractSolid-oxide fuel cells (SOFCs) offer great promise for producing electricity using a wide variety of fuels such as natural gas, coal gas and gasified carbonaceous solids; however, conventional nickel-based anodes face great challenges due to contaminants in readily available fuels, especially sulphur-containing compounds. Thus, the development of new anode materials that can suppress sulphur poisoning is crucial to the realization of fuel-flexible and cost-effective SOFCs. In this work, La0.1Sr1.9Fe1.4Ni0.1Mo0.5O6–δ (LSFNM) and Pr0.1Sr1.9Fe1.4Ni0.1Mo0.5O6–δ (PSFNM) materials have been synthesized using a sol-gel method in air and investigated as anode materials for SOFCs. Metallic nanoparticle-decorated ceramic anodes were obtained by the reduction of LSFNM and PSFNM in H2 at 850°C, forming a Ruddlesden–Popper oxide with exsolved FeNi3 bimetallic nanoparticles. The electrochemical performance of the Sr2Fe1.4Ni0.1Mo0.5O6–δ ceramic anode was greatly enhanced by La doping of A-sites, resulting in a 44% decrease in the polarization resistance in reducing atmosphere. The maximum power densities of Sr- and Mg-doped LaGaO3 (LSGM) (300 μm) electrolyte-supported single cells with LSFNM as the anode reached 1.371 W cm −2 in H2 and 1.306 W cm–2 in 50 ppm H2S–H2 at 850°C. Meanwhile, PSFNM showed improved sulphur tolerance, which could be fully recovered after six cycles from H2 to 50 ppm H2S–H2 operation. This study indicates that LSFNM and PSFNM are promising high-performance anodes for SOFCs.

Hard carbon microspheres with bimodal size distribution and hierarchical porosity via hydrothermal carbonization of trehalose.

Hydrothermal carbonization (HTC) is an efficient thermochemical method for the conversion of organic feedstock to carbonaceous solids. HTC of different saccharides is known to produce microspheres (MS) with mostly Gaussian size distribution, which are utilized as functional materials in various applications, both as pristine MS and as a precursor for hard carbon MS. Although the average size of the MS can be influenced by adjusting the process parameters, there is no reliable mechanism to affect their size distribution. Our results demonstrate that HTC of trehalose, in contrast to other saccharides, results in a distinctly bimodal sphere diameter distribution consisting of small spheres with diameters of (2.1 ± 0.2) μm and of large spheres with diameters of (10.4 ± 2.6) μm. Remarkably, after pyrolytic post-carbonization at 1000 °C the MS develop a multimodal pore size distribution with abundant macropores > 100 nm, mesopores > 10 nm and micropores < 2 nm, which were examined by small-angle X-ray scattering and visualized by charge-compensated helium ion microscopy. The bimodal size distribution and hierarchical porosity provide an extraordinary set of properties and potential variables for the tailored synthesis of hierarchical porous carbons, making trehalose-derived hard carbon MS a highly promising material for applications in catalysis, filtration, and energy storage devices.

Deuterated Polycyclic Aromatic Hydrocarbons in the Interstellar Medium: The C–D Band Strengths of Multideuterated Species

Abstract Observationally, the interstellar gas-phase abundance of deuterium (D) is considerably depleted and the missing D atoms are often postulated to have been locked up into carbonaceous solids and polycyclic aromatic hydrocarbon (PAH) molecules. An accurate knowledge of the fractional amount of D (relative to H) tied up in carbon dust and PAHs has important cosmological implications since D originated exclusively from the Big Bang and the present-day D abundance, after accounting for the astration it has experienced during Galactic evolution, provides essential clues to the primordial nucleosynthesis and the cosmological parameters. To quantitatively explore the extent to which PAHs could possibly accommodate the observed D depletion, we have previously quantum-chemically computed the infrared vibrational spectra of monodeuterated PAHs and derived the mean intrinsic band strengths of the 3.3 μm C–H stretch (A 3.3) and the 4.4 μm C–D stretch (A 4.4). Here we extend our previous work to multideuterated PAH species of different deuterations, sizes, and structures. We find that both the intrinsic band strengths A 3.3 and A 4.4 (on a per-unit-bond basis) and their ratios A 4.4/A 3.3 not only show little variation among PAHs of different deuterations, sizes, and structures, they are also closely similar to that of monodeuterated PAHs. Therefore, a PAH deuteration level (i.e., the fraction of peripheral atoms attached to C atoms in the form of D) of ∼2.4% previously estimated from the observed 4.4 to 3.3 μm band ratio based on the A 4.4/A 3.3 ratio of monodeuterated PAHs is robust.

Demineralization of Miscanthus Biocrude Obtained from Catalytic Hydrothermal Liquefaction: Conditioning through Acid Washing

In this contribution, we successfully applied demineralization (i.e., solvent-assisted separation and acid washing) for the removal of carbonaceous solids and inorganics from a biocrude obtained from the catalytic hydrothermal liquefaction (HTL) of Miscanthus. The experimental results of all six employed acids showed that 0.1 M H2SO4 was the most effective and significantly reduced metallic (Fe by 93.9%, &lt;15 µg/g and Mg by 95.6%, 2.1 µg/g) and ash content (by 92.7% to 337 µg/g) from the already filtered biocrude. The utilized demineralizing agents caused a loss of nitrogen and of organic carbon (1% total organic carbon (TOC) and 0.058% total nitrogen (TN) in 0.1 M H2SO4). Gas chromatography-mass spectrometry (GC–MS) results clarified the nature of this loss, showing that 54% of ketones and 39% of alcohols were removed when 0.1 M H2SO4 was employed. Furthermore, FT-IR spectra remained the same before and after acid washing without affecting any functional groups. This work therefore proposes demineralization as a viable route for the removal of high inorganic content from lignocellulosic HTL biocrudes.

Role of the lattice-energy from chemical agents in the activation of highly-condensed carbons

Highly condensed carbons from pet-coke were first treated with Na/K hydroxides and carbonates and then with H2SO4. The esterification reaction of palmitic acid reached conversions of up to 97 % on the yielded activated carbons. The results evidence the relationship between the efficacy of Na/K hydroxides and carbonates as treatment agents and their lattice potential energy. Moreover, the analysis of carbonaceous solids confirms that both surface area and acidity are primary factors promoting activity in the esterification reaction. Furthermore, the results do not indicate a direct relationship between the activity and the oxidized species (SOx) arising from the treatment with H2SO4. The relatively low melting and decomposition temperature of Na/K hydroxides can improve their effect on the pet-coke matrix, leading to higher surface areas, acidities, and catalytic activities than treatment with carbonates. This supports an affinity between the carboxyl functions of the fatty acid molecules and the polar and catalytically active centers of the hydroxide-treated solid surface.

Oxidative stability and corrosivity of biodiesel produced from residual cooking oil exposed to copper and carbon steel under simulated storage conditions: Dual effect of antioxidants

This work investigates the oxidative stability and corrosivity of residual cooking oil (RCO) methyl biodiesel exposed to metallic coupons (copper and carbon steel) under simulated storage conditions (static immersion for 90 days within closed vessels) and the effect of antioxidants (tert-butylhydroquinone, curcumin, propylgallate, and butyl-hydroxyanisole) on biodiesel and metallic surfaces. The induction period measured during the experiment showed that all antioxidants retarded biodiesel degradation due to their antioxidant properties. Scanning-electron microscopy and X-ray diffraction of the metallic surfaces revealed the presence of oxides due to the corrosion by biodiesel in absence of antioxidants. Nevertheless, the presence of carbonaceous solids over the metallic surfaces was found which evidences the anticorrosive properties of the antioxidants, confirmed by X-Ray spectroscopy that showed increase in the content of carbon and oxygen on the surfaces. Measurements of corrosion rate also confirmed the anticorrosive action of all antioxidants. Hence, this work shows the dual properties of antioxidants acting as free radical scavengers in the RCO biodiesel as well as corrosive inhibitors, with a special performance of propylgallate, probably due to the presence of more hydroxyl groups in its structure that also may facilitate its interaction with the metallic surface.

Did a Complex Carbon Cycle Operate in the Inner Solar System?

Solids in the interstellar medium consist of an intimate mixture of silicate and carbonaceous grains. Because 99% of silicates in meteorites were reprocessed at high temperatures in the inner regions of the Solar Nebula, we propose that similar levels of heating of carbonaceous materials in the oxygen-rich Solar Nebula would have converted nearly all carbon in dust and grain coatings to CO. We discuss catalytic experiments on a variety of grain surfaces that not only produce gas phase species such as CH4, C2H6, C6H6, C6H5OH, or CH3CN, but also produce carbonaceous solids and fibers that would be much more readily incorporated into growing planetesimals. CH4 and other more volatile products of these surface-mediated reactions were likely transported outwards along with chondrule fragments and small Calcium Aluminum-rich Inclusions (CAIs) to enhance the organic content in the outer regions of the nebula where comets formed. Carbonaceous fibers formed on the surfaces of refractory oxides may have significantly improved the aggregation efficiency of chondrules and CAIs. Carbonaceous fibers incorporated into chondritic parent bodies might have served as the carbon source for the generation of more complex organic species during thermal or hydrous metamorphic processes on the evolving asteroid.

Separate Silicate and Carbonaceous Solids Formed from Mixed Atomic and Molecular Species Diffusing in Neon Ice

Abstract The formation and growth of refractory matter on pre-existing interstellar dust grain surfaces was studied experimentally by annealing neon-ice matrices in which potential precursors of silicate grains (Mg and Fe atoms, SiO and SiO2 molecules) and of solid carbon (C n molecules, n = 2–10) were initially isolated. Other molecules, mainly O3, CO, CO2, C3O, and H2O, were embedded at the same time in the matrices. The annealing procedure caused the cold dopants to diffuse and interact in the neon ice. Monitoring the procedure in situ with infrared spectroscopy revealed the disappearance of the silicon oxide and carbon molecules at temperatures lower than 13 K, and the rise of the Si–O stretching band of silicates. Ex situ electron microscopy confirmed the formation of silicate grains and showed that their structure was amorphous. It also showed that amorphous carbon matter was formed simultaneously next to the silicate grains, the two materials being chemically separated. The results of the experiments support the hypothesis that grains of complex silicates and of carbonaceous materials are reformed in the cold interstellar medium, as suggested by astronomical observations and evolution models of cosmic dust masses. Moreover, they show that the potential precursors of one material do not combine with those of the other at cryogenic temperatures, providing us with a clue as to the separation of silicates and carbon in interstellar grains.

The role of temperature on slow pyrolysis of olive cake for the production of solid fuels and adsorbents

Abstract In this work, slow pyrolysis of olive cake has been carried out under nitrogen atmosphere at different temperatures to obtain carbonaceous materials with possible applications as solid fuels and adsorbents of heavy metals from aqueous solutions. The carbonaceous materials have been completely characterized. The Gain and Loss method has been applied in order to find the best operating temperature in terms of quality of the carbonaceous material for its use as fuel. Also, a basic reaction scheme has been proposed for representing the kinetics of thermal degradation in nitrogen and air atmospheres. Good correlation of calculated and experimental data was observed for different materials. Finally, adsorption experiments were performed to test ability of carbonaceous materials as adsorbents of cadmium, chromium, copper, nickel and lead. In general, the carbonaceous solids obtained by slow pyrolysis improved the adsorption capacities of the raw material. For example, a maximum lead adsorption capacity of 102 mg/g was found for carbonaceous material obtained at 450 °C. Also, for this material, the values of maximum adsorption capacity indicated the higher preference of solid for lead ions.

Making hydrochar suitable for agricultural soil: A thermal treatment to remove organic phytotoxic compounds

Unlike biochars, hydrochars often have initial phytotoxic effects that prevent their being directly applied to soil, an undesirable property thought to be due to the volatile organic compounds they contain. Thermal treatment in the 200–600 °C temperature range was proposed for mitigation purposes and it was shown that at a temperature of 275 °C phytotoxicity is eliminated from the carbonaceous solids. The phytotoxic property was “recovered” or maintained in the separated liquid, which can be used to generate heat in the HTC process, thereby achieving the safe disposal of harmful compounds at no additional cost. The post-treatment unlocks the potential of transforming the organic fraction of municipal solid waste into a soil amendment product in a zero-waste process.The absence of phytotoxicity was confirmed by the Zucconi method on seed germination. A gas-chromatographic method was also developed, based on the quantification of the total amount of substances detected by desorption, for a rough but quick estimation of hydrochar phytotoxicity. It was shown that the absence of these volatile compounds is in line with the absence of phytotoxicity as evaluated by the Zucconi method.

Sustainable N-containing biochars obtained at low temperatures as sorbing materials for environmental application: Municipal biowaste-derived substances and nanosponges case studies

Bio-based substances (BBS) obtained from composted urban biowaste and nanosponges obtained from β-cyclodextrins (βCD) were used as green source to produce biochar via pyrolysis performed under mild conditions. Pyrolysis conditions were optimized by means of TGA analysis, and different temperatures of pyrolysis were investigated. The resulting carbonaceous materials were characterized with several physicochemical techniques (elemental analysis, FTIR spectroscopy, XRD, SEM, surface area analysis, and zeta potential measurements). Additionally, the adsorption capacity of such materials was tested toward the removal of charged dyes from aqueous environment. Isothermal experiments carried out at circumneutral pH indicated an important charge-selectivity, which encourages their use as sustainable alternative materials in wastewater purification treatments. Moreover, the analysis of the adsorption capacity as a function of specific surface area of materials suggests the strategy to obtain carbonaceous solids with enhanced capacity in capture of polar molecules.

Enhanced devolatilization during torrefaction of blended biomass streams results in additive heating values and synergistic oxidation behavior of solid fuels

Torrefaction improves energy density, grindability, and hydrophobicity of raw biomass for gasification and combustion. While literature focuses on single biomass torrefaction, industrial production is likely to be from biomass mixtures. To address this knowledge gap, we torrefied three raw biomasses (pistachio nutshells, feed corn stover, cherry pits) at 250 °C, as “pure” biomasses and in multiple component mixtures to understand if synergistic interactions during torrefaction impact oxidation behavior of resulting solid fuels. The combustion enthalpies of blended biomasses were well predicted by an additive function, whereby a blend's property was the mass-weighted average of each biomass' torrefied property. However, synergistic effects that enhanced devolatilization when biomasses were comingled during torrefaction led to systemically lower volatile matter contents and higher surface areas of resulting solid fuels. This synergistic behavior continues in terms of activation energy of oxidation of the torrefied samples. Co-torrefaction of biomass may lead to a solid fuel with predictable heat content, but synergistic effects lead to oxidation of blended streams at different rates and activation energies, with blends often having lower reactivities and higher activation energies than an “additive” prediction of pure fuel components. This is attributed to enhanced devolatilization among biomasses, leading to more condensed carbonaceous solids.

Validation and application of a kinetic model for biomass gasification simulation and optimization in updraft gasifiers

Biomass gasification has attracted great interest recently for its great potential as a thermal degradation method that converts biomass or carbonaceous solids into combustible gases with a usable heating value. However, accurate simulation of biomass gasification faces significant challenges as it has a complicated dependence on reaction kinetics, reactor geometry, processing methodology and operating condition. In this paper, a reaction model (RXN model) based on comprehensive biomass gasification kinetics is introduced and validated to predict the syngas and tar compositions. By comparing the simulating predictions with data from two updraft gasification experiment findings available in the literature, it is demonstrated that the RXN model is able to provide a more accurate description for updraft biomass gasification than the minimizing Gibbs free energy model (MGFE model), which can substitute for the widely used yet not accurate MGFE model. Parametric optimization studies were conducted to investigate the impacts of equivalence ratio (ER), gasifier temperature, biomass feed types on syngas and unreacted tar compositions. The results of this work provide vital information for large-scale gasifier design, operating decisions, and optimization.

A method to assess downward flame spread and dripping characteristics of fire‐retardant polymer composites

SummaryA method is described to assess the flame retardancy of polyethylene composites by measuring both their downward flame spread rates as well as their combined melting and dripping rates on rectangular rods, ignited at their top. The composite materials were produced by mixing pulverized polymer with organic additives of differing particle sizes, shapes, and mass fractions. The resulting mix was melted in a mold, and then it was solidified into rods. The additives were carbonaceous solids with particle sizes spanning from tens of nanometers to tens of micrometers. The mass fraction of the additives in the polymer matrix varied from 1 to 5 wt%. Upon ignition of the upper tips of the polymer composite rods, the downward flame spread rate and the melting and dripping rate were separately assessed by measuring their mass loss and their heights. The addition to polyethylene of finely sized carbonaceous additives at mass fractions of 4 to 5 wt% proved effective at significantly slowing down its downward flame spread by drastically hindering its dripping tendency. The effectiveness of the additives increased with increasing their mass fraction and decreasing their particle size. High mass fractions of carbon additives resulted in wicking, which can enhance radiatively the heat transfer.

Contrasting behavior of covalent and molecular carbon allotropes exposed to extreme ultraviolet and soft x-ray free-electron laser radiation

All carbon materials, e.g., amorphous carbon (a-C) coatings and C60 fullerene thin films, play an important role in short-wavelength free-electron laser (FEL) research motivated by FEL optics development and prospective nanotechnology applications. Responses of a-C and C60 layers to the extreme ultraviolet (SPring-8 Compact SASE Source in Japan) and soft x-ray (free-electron laser in Hamburg) free-electron laser radiation are investigated by Raman spectroscopy, differential interference contrast, and atomic force microscopy. A remarkable difference in the behavior of covalent (a-C) and molecular (C60) carbonaceous solids is demonstrated under these irradiation conditions. Low thresholds for ablation of a fullerene crystal (estimated to be around 0.15 eV/atom for C60 vs 0.9 eV/atom for a-C in terms of the absorbed dose) are caused by a low cohesive energy of fullerene crystals. An efficient mechanism of the removal of intact C60 molecules from the irradiated crystal due to Coulomb repulsion of fullerene-cage cation radicals formed by the ionizing radiation is revealed by a detailed modeling.

Cellulose hydrolysis catalyzed by highly acidic lignin-derived carbonaceous catalyst synthesized via hydrothermal carbonization

Acidic carbonaceous solids were synthesized from mass pine alkali lignin via hydrothermal carbonization followed by sulfonation. Hydrothermal carbonization of lignin in the presence of acrylic acid (LAHC-SO3H) provided many more carboxylic groups than that in the absence of acrylic acid, allowing subsequent sulfonation to produce a highly active and stable catalyst for cellulose hydrolysis in the [BMIM]Cl-H2O solvent system. The hydrochar and catalyst were characterized using field emission scanning electron microscopy, X-ray diffractometer, X-ray photoelectron spectroscopy, thermal gravimetric analysis, Fourier transform infrared spectrometer, Brunauer–Emmett–Teller and acid–base titration. Results showed that a high acid content of 5.48 mmol/g, including carboxylic group (2.85 mmol/g), phenolic hydroxyl group (1.05 mmol/g) and sulfonic acid group (1.58 mmol/g), contributed significantly to the highly efficient hydrolysis of cellulose. Further, it was found that addition of trace water in [BMIM]Cl was favorable to cellulose hydrolysis. The highest yield (75.4%) of total reducing sugar (TRS) obtained in [BMIM]Cl-H2O at a mass ratio of 100:1 was more than twice that (36.1%) achieved in [BMIM]Cl without water; the corresponding reaction conditions were 50 mg of microcrystalline cellulose, 30 mg of catalyst, 1.0 g of [BMIM]Cl, 10 mg of H2O, reaction temperature of 130 °C and reaction time of 2 h. Furthermore, the TRS yield with 5 cycles for LAHC-SO3H was higher than 68.1%, and the catalytic activity of catalyst could be fully recovered (74.0% of TRS yield) easily by regeneration.

Faecal sludge treatment and utilization by hydrothermal carbonization

Hydrothermal carbonization (HTC) is a thermal conversion process that can be applied to convert faecal sludge into carbonaceous solids, called hydrochar. In this study, the technical feasibility of hydrochar production by HTC of faecal sludge was investigated. Experimental results showed energy contents of the produced hydrochar to be about 19–20 MJ/kg, comparable to natural coals and therefore usable as a solid fuel. The produced hydrochar contained a carbon content of approximately 40%wt, which could be processed further to make it suitable as an anode in batteries. The produced hydrochar also had adsorption characteristics for removing heavy metals and micropollutants in wastewater. Liquid by-products obtained from the HTC process were found to contain high concentrations of organic matter, while the amount of gas produced was 10 L-gas/kg-FS with CO2 is the main component. The bio-methane potential tests of this liquid product suggested the methane production of about 2.0 L-CH4 per kg-faecal sludge could be obtained.

Improving the production of hydrogen from the gasification of carbonaceous solids using supercritical water until 1000 bar

In this work, the advantages provided by supercritical water (SCW) to one of the most extended methods to produce H2, the gasification of carbonaceous materials, are investigated. The broad range of experimental conditions assayed (1–1000bar) allows not only the comparison of the use of steam and SCW but also the investigation of how H2 production varies within the supercritical region. The results obtained reveal important advantages when the supercritical fluid is used. In the gasification with SCW, H2 production is greater, and in general, the consumption of the raw material is optimized since more H2 is obtained when the same amount of solid is consumed. Furthermore, the gaseous streams are very rich in H2 and CO2 and poor in CO and CH4. On the other hand, the use of two carbonized materials of different natures (a phenolic textile fiber and holm oak wood) allows us to highlight that H2 production depends strongly on the surface irregularities and surface chemistry of the solid. The material of vegetal origin is more suitable because more H2 is produced and mixtures of gases that are more easily purified are obtained from it. However, higher amounts of CO2 than those registered for the solid of synthetic origin are released during its gasification.