Alkaline Earth Metallic Species Research Articles

Evolution of Char Structure During In-Situ Biomass Tar Reforming: Importance of the Coupling Effect Among the Physical-Chemical Structure of Char-Based Catalysts

In order to illustrate the importance of a coupling effect in the physical-chemical structure of char-based catalysts on in-situ biomass tar reforming, three typical char-based catalysts (graphite, Zhundong coal char, and sawdust biochar) were studied in the fixed-bed/fluidized-bed reactor. The physical-chemical properties of carbon-based catalysts associated with their catalytic abilities were characterized by inductively coupled plasma-atomic emission spectroscopy (ICP-AES), Raman, X-ray photoelectron spectroscopy (XPS), scanning electron microscope–energy dispersive spectrometer (SEM-EDS) and N2 adsorption. The relationship between the specific reactivity and tar reforming ability of carbon-based catalysts was discussed through a micro fluidized bed reaction analyzer (MFBRA–MR). The results indicate that the char-based catalyst has a certain removal ability for in-situ biomass tar of corn straw in an inert atmosphere, which is as follows: sawdust biochar > Zhundong (ZD) coal char > graphite. During the in-situ tar reforming, the alkali and alkaline earth metal species (AAEMs) act as adsorption/reaction sites, affecting the evolution of the aromatic ring structure and oxygen-containing functional groups of the char-based catalyst, and also its pore structure. AAEM species on the surface of char-based catalysts are the active sites for tar reforming, which promotes the increase of active intermediates (C-O bond and C-O-AAEMs), and enhances the interactions between char-based catalysts and biomass tar. The abundant AAEMs may lead to the conversion of O=C–O and C=O to C–O. For tar reforming, the internal pore structure of char-based catalysts is little changed, mainly with the carbon deposit forming on the surface pore structure. The carbon deposit from the reformation of straw tar on the char surface has better reactivity than the inherent carbon structure of ZD coal char and sawdust biochar. There is a positive relationship between the MFBRA–MR specific reactivity and tar catalytic reforming ability of char-based catalysts (decided by the coupling effect in their physical-chemical structure), which can be used to determine the catalytic ability of char-based catalysts on tar reforming directly.

Proton intercalation into different CoO2 layer matrices

The hexagonal CoO2 layer is an integral part of many important functional materials such as the LixCoO2 battery electrode, the NaxCoO2 and [CoCa2O3]0.62CoO2 thermoelectrics, and the Na0.3CoO2(H2O)1.3 superconductor. However, the CoO2-layer piling is prone to incorporate not only positively-charged metal and metal oxide layers but also protons between successive CoO2 layers. Here we systematically investigate the de-intercalation of the intervening alkali metal and metal oxide layers, and the subsequent intercalation of protons for an extensive series of LiCoO2, NaxCoO2 (x = 0.6–0.9) and [CoCa2O3]0.62CoO2 samples. First, we demonstrate the partial extraction of sodium from NaxCoO2 through immersion in an aqueous solution of either n-butylamine or NH4NO3. Such a treatment results in an appreciably low Na content of x = 0.37 or 0.10, respectively, but a simultaneous incorporation of certain amounts of charge balancing protons into the crystal lattice. Then, using a newly developed hydrothermal route we demonstrate the complete de-intercalation of the alkali and alkaline earth metal species from LiCoO2, NaxCoO2 and [CoCa2O3]0.62CoO2, and the intercalation of protons between the CoO2 layers. Finally we synthesize and characterize a water-containing NaxCoO2(H2O)z sample for comparison. As the protonation is found to be a common tendency of all the studied multilayered functional materials based on the CoO2 layer we believe that our work is not only of fundamental scientific interest but also of more practical relevance.

Effects of mineral matters on the interactions between lignite and corncob during temperature-programmed co-pyrolysis

A lignite and a corncob were employed to investigate the effects of the inherent minerals on the interactions between lignite and corncob during pyrolysis. Prior to pyrolysis experiments, the selected samples were demineralized by using HCl and HF solution. Pyrolysis experiments for the raw samples, demineralized samples and their various purposeful blends of lignite and corncob were conducted in a lab-scale fixed-bed reactor. The results showed that the inherent minerals can significantly affect the pyrolysis behavior of the individual feedstocks. Particularly, it was observed that the alkali and alkaline earth metal species (AAEMs) in corncob was capable of promoting the decomposition of tar macromolecules and cracking liquid tar to form gas and char, which thus led to an increased gas yields with distinct soot observed. In terms of the blends, it was observed that the blends of the demineralized corncob and the demineralized lignite produced an unexpected higher yield of liquid tar than other blends. This suggested that the AAEMs in corncob or lignite could play a catalytic role in the decomposition of tar macromolecules, and this catalytic ability in corncob became stronger than that in lignite. The experimental results also indicated that the catalytic ability of the AAEMs varied in the blends of lignite and corncob. For the blends of the raw samples of lignite and corncob, this catalytic ability of the AAEMs was weaker for decomposing tar macromolecules compared to that in the blends of raw corncob and demineralized lignite or demineralized corncob and raw lignite. The interaction between catalytically active K and Ca species from corncob and the aluminosilicate species in the coal mineral matter occur, leading to the formation of calcium silicate (Ca2SiO4), which resulted in the formation of inactive compounds. In addition, it was observed that the inherent minerals in the raw samples could promote the reactivity of char with oxygen, which could be particularly observed with the char made from the raw sample of corncob.

Dissolution of Cl in alkaline earth (Ca, Sr, Ba) aluminosilicate glasses

Some particular hazardous and nuclear wastes containing a large amount of chlorine would cause the problematic processing during the waste vitrification, because of the low solubility of Cl in silicate glasses. Although a few works reported the chlorine behavior in aluminosilicate glasses, the results do not always show the consistency and a small variation of glass compositions may cause the significant changes. The present work studied the dissolution of Cl in the range of alkaline earth aluminosilicate glasses with the nominal mole composition of 50SiO2-10Al2O3-40AeO (Ae = Ca, Sr or Ba). The solubility of Cl in the glasses with different alkaline earth species followed the order of Ca (~8.1 wt%) > Sr (~6.0 wt%) > Ba (~3.5 wt%). The glass density and glass transition temperature decreased with the addition of Cl in three types of glasses, and AeCl2 salts, identified with X-ray diffraction, segregated from the glasses, when Cl addition exceeds its solubility. Raman spectra indicate the dissolution of Cl leads to the increase of bridged oxygen bonds in glasses, supposing that Ca2+ ions are attracted by Cl− ions, leaving the non-bridging oxygens that initially associated with Ca2+ ions are bonded to Si4+ (Al3+) to become bridging oxygens.

Effect of volatile–char interactions on PM10 emission during the combustion of biosolid chars under air and oxyfuel conditions

This study reports the significant effect of volatile–char interactions on the emission of particulate matter (PM) during the combustion of biosolid chars in drop-tube furnace at 1300 °C under air and oxyfuel conditions. Slow and fast heating chars were prepared from biosolid pyrolysis and then interacted with the volatiles produced in situ from the pyrolysis of polyethylene (PE) and double acid-washed biosolid (DAWB) in a novel two-stage quartz reactor at 1000 °C (limited by the operating temperature of quartz). The results clearly show that under the experimental conditions, the interactions between chars and small non-oxygenated reactive species in both volatiles substantially decrease the yield of PM with aerodynamic diameter < 1 µm (i.e. PM1), dominantly PM with aerodynamic diameter < 0.1 µm (PM0.1) during char combustion. The interactions between oxygen-free volatiles (produced from PE pyrolysis) and char also reduce char macroporosity, leading to a reduction in the yield of PM with aerodynamic diameter between 1 µm and 10 µm (i.e. PM1-10). However, the interactions between O-containing reactive species (produced from DAWB pyrolysis) and char significantly increase char macroporosity. Higher heating rate with shorter aging process during pyrolysis significantly weakens the effect of volatile–char interactions on PM1 emission but intensifies its effect on PM1-10 emission during char combustion. The combustion atmospheres have little effect on the net yield of PM contributed by volatile–char interactions. Combustion of chars interacted with the oxygen-free volatiles lead to a reduction in the yield of refractory elements (i.e. Mg, Ca, Al, Si, Fe, Ni, Co, Cu, Mn, V and Zn) in PM1-10 but those interacted with the O-containing volatile resulted in an enhanced yield of these elements in PM1-10. Furthermore, the interactions between O-containing reactive species and chars significantly decrease Cr yield in PM0.1 due to formation of volatile chromium oxyhydroxides. In addition, volatile–char interactions have little influence on the forms of alkali and alkaline earth metallic (AAEM) species and P in PM10, i.e. as (Na, K)PO3 in PM1 and (Mg,Ca)3(PO4)2 in PM10.

Plasma interactions with the N2O background gas: Enhancing the oxidization of alkaline-earth species for pulsed laser deposition

Using N2O as an alternative background gas to O2 when growing oxide thin films by pulsed laser deposition (PLD) was previously expected to result in larger oxygen contents of as-grown thin films. In this work, we investigate the composition and kinetic energy of the pulsed laser induced plasmas that propagated in N2O and O2 by using mass spectrometry and plasma imaging. Two distinguished features were observed when using N2O instead of O2. (1) In N2O background gas as compared to O2, a larger proportion of negative oxygen ions was detected. (2) The alkaline-earth elements were fully oxidized in the N2O background, which is not achievable in O2. These observations are attributed to the smaller dissociation energy of the N2O molecules as compared to O2. The smaller dissociation energy of the background gas molecule is expected to reduce the interaction strength during their central collisions with the plasma species. As a result, the dissociable or electron detachable plasma species can be formed in larger amounts in N2O background, compared to O2. Comparing the composition of the deposited thin films indicates a larger oxygen content of the film grown in N2O background gas, as compared to O2, at pressures of ∼10−1 mbar, which is the most commonly used deposition pressure in PLD. Nevertheless, this was not achieved when performing PLD at ∼10−2 mbar, since the pressure was not high enough to trigger the formation of the shockwave front during the plasma expansion and thereby the lightest oxygen plasma species were preferentially scattered.

Effects of alkali and alkaline earth metal species on the combustion characteristics of single particles from pine sawdust and bituminous coal

Alkali and alkaline earth metal (AAEM) species are the main components of the ash of biomass, and which would influence the combustion of biomass and coal during the co-firing process. The aim of this paper is to investigate the effects of potassium (K), sodium (Na), calcium (Ca), and magnesium (Mg) on the combustion characteristics of pine sawdust (PS) and bituminous coal (BC) by a single particle combustion method. The raw, ash-free and impregnated samples were prepared, and their combustion processes were recorded by a high speed camera. Based on the recorded flame images, the effects of K, Na, Ca and Mg on the combustion characteristics (ignition, volatiles combustion, char combustion) of PS and BC were analyzed. The results reveal that the demineralization treatment brings negative effects on the combustion of PS, which reflects in longer ignition delay time, volatiles and char burnout time, and lower combustion temperature, while the effects on the combustion of BC are opposite. The impregnated samples exhibit shorter ignition delay time, volatiles and char burnout time, and higher combustion temperature than the ash-free samples. In the entire combustion process of PS and BC, K exhibits the strongest promotion effect. When the concentration of K increases from 0 to 2 wt%, the ignition delay time of PS and BC decreases about 5.5 ms and 16.4 ms respectively, the volatiles combustion temperature increases about 41 °C and 77 °C respectively, and the char combustion temperature increases about 226 °C and 141 °C respectively.

Influence of inherent hierarchical porous char with alkali and alkaline earth metallic species on lignin pyrolysis

This study aimed to explore the influence of inherent hierarchical porous char with alkali and alkaline earth metallic species (AAEMs) during pyrolysis of lignin derived from agricultural crop residues in a laboratory fixed-bed at 550 °C. A catalytic strategy was implemented to investigate volatile-char interactions based on ex situ lignin pyrolysis. The physico-chemical properties of the AAEMs-loaded char were characterized by FTIR, XRD, SEM-EDX and N2 nitrogen adsorption analyses. Results indicated that AAEMs-loaded char had a large specific surface area, hierarchical porosity, amorphous carbon structure, surface-active functional groups and highly dispersed metal species. Specifically, the specific surface area of AAEMs-loaded char was significantly reduced owing to coke deposition after interaction with pyrolysis vapours. Bio-oil composition revealed substantial increases in phenol, o-cresol, p-cresol and catechol. These increases were mainly attributed to demethylation, demethoxylation, or alkyl substitution reaction. The experimental results confirmed the occurrence of significant volatile-char interactions during lignin pyrolysis.

Impacts of char structure evolution and inherent alkali and alkaline earth metallic species catalysis on reactivity during the coal char gasification with CO2 /H2 O

In this work, we studied the effects of char structural evolution and alkali and alkaline earth metallic species (AAEMs) catalysis on the reactivity during the char gasification with CO2, H2O, and their mixture. The gasified chars with different carbon conversion levels were prepared, and their physicochemical structures were characterized via nitrogen adsorption and FT-Raman techniques. The concentrations of AAEMs in different modes were obtained by the sequential chemical extraction method. The reactivities of the raw and gasified chars were analyzed by the thermogravimetric analysis. The gasification atmospheres had varied effects on the physicochemical structure of coal char. The gasified char obtained in the CO2 atmosphere had a lower aromatic condensation degree compared with that obtained in the H2O atmosphere, irrespective of the temperature. The impact of the atmospheres on the specific surface area of the char varied with the temperature because H2O and CO2 have different routes of development of pore structure with coal char. A large specific surface area facilitates the exposure and dispersion of more AAEMs on the surface of the channel, which is conducive to their contact with the gasification agent to play the catalytic role. Thus, the reactivity of the gasified char is well correlated with its specific surface area at different gasification temperatures. In the absence of AAEMs, the chemical structure of coal char becomes the dominant factor affecting the reactivity.

Incorporation and phase separation of Cl in alkaline earth aluminosilicate glasses

Pyrochemical reprocessing of spent nuclear fuels may lead to the generation of chloride containing wastes. 36Cl wastes may also arise from the treatment of irradiated graphite. Such wastes will have limited solubility in the borosilicates currently used for waste vitrification. Despite requiring higher processing temperatures aluminosilicate glasses show promise for this application. In a series of alkaline earth aluminosilicate glasses we demonstrate that chloride solubility is related to the alkaline earth species as follows Sr > Sr + Ba > Ba > Ca > Mg, with the strontium aluminosilicate glass accommodating up to 5.92 at% Cl. Typical chloride retention rates are ∼80% of the batched chloride content at 1400 °C. It has also been observed that, when Cl is present in the glass in excess, phase separation firstly occurs as formation of non-Cl crystals (mainly alkaline earth aluminosilicates, with a minority of aluminates); a segregated chloride layer is only formed at higher chlorine loadings. This indicates that chlorine solubility in glass is not only controlled by the capacity of glass network to accommodate Cl− but also by the stability of glass network after Cl− incorporation. In addition, increased incorporation of Cl− in glass results in steadily decreased glass densities and glass transition temperatures.

The formation of deposits and their evolutionary characteristics during pressurized gasification of Zhundong coal char

The characteristics of deposits formed on stainlesssteel substrate (boiler tube) during pressurized gasification of Zhundong coal char with excessively high Na content were investigated in this work. The occurrences of alkali and alkaline earth metallic species in raw coal and its derived chars were determined by a sequential extraction method. The morphology, mineralogy and chemical compositions of deposits and bottom ash produced during the gasification of Zhundong coal char at 800, 1000 and 1200 °C were analyzed by X-ray diffraction and scanning electron microscopy combining energy dispersive X-ray spectrometer. Results show that water-soluble and ammonium acetate solution soluble sodium and potassium in raw coal tended to be converted to hydrochloric acid solution soluble form during Zhundong coal pyrolysis. Rising pyrolysis temperature increased the content of water-soluble calcium by enhancing the decomposition of CaCO3 and organically bonded calcium. During the gasification of Zhundong coal char, the released inorganic species, especially Na, Ca, Cl and S, could condense and/or agglomerate as sticky fine particles, resulting in fouling and slagging on the probes. Specifically, after Zhundong char gasification at 800 °C, alkali and alkaline earth metallic species-bearing minerals loosely clung on the probes as silicate or aluminosilicate. During char gasification at 1000 °C, a Na-S-O and/or Na-S deposit layer with a thickness of ca. 2 μm was formed on the probe No. 1 at 514 °C, while abundant Ca-Mg-Si-O and few Na2SO4 crystals were accumulated on the probe No. 2 at 771 °C. During Zhundong char gasification at 1200 °C, the minerals deposited at low temperature region (599 °C) were mainly composed of agglomerated and sintered alkali and alkaline earth metallic species-bearing compounds (mainly NaCl, KCl and Ca-Mg-Si-O). However, only few isolated particles were observed on the probe with temperature higher than 924 °C. Residual alkali and alkaline earth metallic species in bottom ash could form low-melting eutectics, such as NaAlSiO4 and Ca2Al2SiO7.

Steam Gasification of Sawdust Biochar Influenced by Chemical Speciation of Alkali and Alkaline Earth Metallic Species

The effect of chemical speciation (H2O/NH4Ac/HCl-soluble and insoluble) of alkali and alkaline earth metallic species on the steam gasification of sawdust biochar was investigated in a lab-scale, fixed-bed reactor, with the method of chemical fractionation analysis. The changes in biochar structures and the evolution of biochar reactivity are discussed, with a focus on the contributions of the chemical speciation of alkali and alkaline earth metallic species (AAEMs) on the steam gasification of biochar. The results indicate that H2O/NH4Ac/HCl-soluble AAEMs have a significant effect on biochar gasification rates. The release of K occurs mainly in the form of inorganic salts and hydrated ions, while that of Ca occurs mainly as organic ones. The sp3-rich or sp2-sp3 structures and different chemical-speciation AAEMs function together as the preferred active sites during steam gasification. H2O/HCl-soluble AAEMs could promote the transformation of biochar surface functional groups, from ether/alkene C-O-C to carboxylate COO− in biochar, while they may both be improved by NH4Ac-soluble AAEMs. H2O-soluble AAEMs play a crucial catalytic role in biochar reactivity. The effect of NH4Ac-soluble AAEMs is mainly concentrated in the high-conversion stage (biochar conversion &gt;30%), while that of HCl-soluble AAEMs is reflected in the whole activity-testing stage.

Theoretical study on the binding selectivity of 18-membered azacrown ethers with alkaline earth metal species

The binding selectivity of 18-membered azacrown ethers (monoaza- N1, diaza- N2, triaza- N3, tetraaza- N4, pentaaza- N5, and hexaaza-18-crown-6 N6) with Ca2+, Sr2+, Ba2+ have been studied by density functional theory (DFT) calculations. The complex binding selectivity was analyzed in term of interaction energies, thermodynamic properties, second order interaction energies, and charge transfer effects. The geometrical study shows that Ca2+ and azacrown complexes acquire envelope like structure, leading to shorter bond lengths. As a result, these complex systems have the highest interaction energies. Theoretical study also showed that N6 complex with alkaline earth metal ion were shown to be more stable complex than those ligand with lower nitrogen number. The interaction energy order is N0 &lt; N1 &lt; N2 &lt; N3 &lt; N4 &lt; N5 &lt; N6. This trend shows that the presence of more nitrogen on the crown ether cavity increases the interaction energies by approx. 7.3 % in going from N0 to N6. It is clearly showed that the contribution of the number of nitrogen play a dominant role in the binding selectivity of these systems.

Effect of alkali and alkaline earth metal species on the combustion characteristics of cattle manures.

This study investigates the effects of alkali and alkaline earth metal (AAEM) species on the combustion characteristics of cattle manures (CM). Different AAEM species (K, Na, Ca, and Mg) were mixed with CM and deashing CM (D-CM) samples. The combustion characteristics of raw and char samples were compared. The effects of AAEM species on CM char were analyzed based on the structural characteristics of the char sample. Results show that K and Na exert a positive effect, and this effect varies depending on the addition amount. Ca and Mg also exhibit a positive effect, but this effect does not change with the addition amount. The positive effect of K, Na, and Ca is related to the decrease in graphitization degree and increase in specific surface area. However, the positive effect of Mg is negligible. In conclusion, CM can be mixed with fuels containing K or Na in an appropriate ratio. The amount of Ca to be mixed with fuels has no specific requirement, whereas that of Mg to be mixed with fuels should be controlled.

Transformation of alkali and alkaline earth metallic species during pyrolysis and CO2 gasification of rice straw char

The release of alkali and alkaline earth metallic species (AAEMs) can cause serious technical problems during biomass thermal utilization. The release characteristics of AAEMs from rice straw char during pyrolysis in N2 and CO2 gasification at 900°C were investigated using a fixed-bed reactor. The release and transformation results of AAEMs under both atmospheres were obtained based on analysis of solid residues sampled after different residence time, and effect of CO2 atmosphere on AAEMs migration was discussed. Under both pyrolysis and gasification conditions, K release ratio initially increased rapidly and the growth rate reduced with time. At early stage of gasification, K release ratio is higher than that after pyrolysis for the same time, while the K release ratio is almost same at late stage of gasification and pyrolysis. Little amounts of Ca and Mg were released during both pyrolysis and gasification. During pyrolysis, fractions of acid-soluble K and Ca first decreased and then remained nearly constant, while the fraction of acid-soluble Mg always remained constant. During gasification, the fraction of acid-soluble K first decreased slowly and then decreased rapidly, while that of Ca and Mg increased first and then reduced with time. At early stage of gasification, the fractions of acid-soluble AAEMs were higher than that after pyrolysis. At last stage of gasification, significant higher fractions of insoluble AAEMs were formed. CO2 atmosphere facilitated release of K by enhancing decomposition and release of char-K. Insoluble char-associated AAEMs are transformed to be acid-soluble due to consumption of char matrix. At the end of gasification, significant insoluble AAEM-silicates compounds were formed.

Solar-Thermal Pyrolysis of Mallee Wood at High Temperatures

This study reports solar-thermal pyrolysis of mallee wood powders driven by direct concentrated solar radiations at different temperatures (1540, 1740, and 1930 °C), heating rates (320, 800, and 3200 °C/min), and holding times (0 and 5 min). Under such severe pyrolysis conditions, solar-thermal pyrolysis of mallee wood produces predominantly volatiles (≥90 wt %), with very low char yields (≤10 wt %), as reported on a dry basis. Majorities of inherent alkali and alkaline earth metallic (AAEM) species are also released into the gaseous phase. The severe pyrolysis conditions also lead to the low reactivity of char products as a result of not only the char carbon structure becoming ordered and graphitized (as evidenced by the Raman data) but also significant losses of catalytic AAEM species in the char. For example, during the solar-thermal pyrolysis of mallee wood at 1930 °C, 800 °C min–1, and 5 min holding time, the char yield is only ∼5 wt %, the retentions of Na and Mg are ∼1%, the retentions of K and Ca ...

Effects of Alkali and Alkaline Earth Metallic Species and Chemical Structure on Nascent Char–O2 Reactivity

Factors influencing the nascent char–O2 reactivity was investigated in this study from the aspects of alkali and alkaline earth metallic species and char chemical structure. Char samples were prepared from the fast pyrolysis of two low-rank coals (Loy Yang brown coal and Collie sub-bituminous coal) in a wire-mesh reactor at temperature ranging from 600 to 1200 °C with holding time up to 5 s. The concentrations of alkali and alkaline earth metallic species in char were determined by inductively coupled plasma-optical emission spectroscopy. The char chemical structure was characterized by Fourier transform-Raman spectroscopy. Our results show that the char–O2 reactivity is greatly related to the Raman sensitive O-containing functional groups at the initial stage of char formation (short residence time at 600 °C during pyrolysis). As char pyrolysis proceeded to higher temperature, the loss of O-containing functional groups and the condensation of aromatic ring systems play a key role in the decreasing magnitude of char–O2 reactivity. The chemical structure of 1200 °C pyrolysis char is relatively stable, thereby posing limited effect on the changes in char–O2 reactivity. For Loy Yang brown coal, the volatilization of alkali and alkaline earth metallic species during pyrolysis at 1200 °C became the dominant reason for the observed decreases in char–O2 reactivity.

Mixed-modifier effect in alkaline earth metaphosphate glasses

Modifier-mixing provides a useful tool for tailoring the structural dynamics of oxide glasses. Its physical basis, however, remains subject to intense discussion. Here, we extend our previous consideration of Ca-Mg mixing in alkaline earth metaphosphate glasses [J. Non-Cryst. Solids 468, 74–81 (2017)] across the broader range of alkaline earth species. We report on the effects of divalent modifier mixing for pairs selected from the group of Mg, Ca, Sr and Ba. For this, short-range structural features as obtained from nuclear magnetic resonance, Raman and far-infrared spectroscopy are related to various physical properties, including ionic mobility. Depending primarily on the difference in ion size and bond localization among the modifier cation species, we find different extents of the mixed-modifier effect. This agrees with the dynamic structure model in which the mismatch of cation sites governs non-linear mixing effects.

Catalytic mechanism of ion-exchanging alkali and alkaline earth metallic species on biochar reactivity during CO2/H2O gasification

To understand the detailed catalytic mechanism of ion-exchanging AAEM species on biochar structure and its specific reactivity during CO2/H2O gasification, the experiments were carried out in a laboratory fixed-bed reactor at 800 °C, with two kinds of AAEM-loading methods. The migration and precipitation characteristics of AAEM species was evaluated by ICP-AES, while the transformation of biochar structures were analyzed by FTIR and Raman. The specific reactivity of H2O/CO2 gasification biochar was determined by TGA analysis in Air at 370 °C. The results show that the stronger catalytic properties of K and Ca species in H2O atmosphere are obtained than that in CO2. The effect of K is mainly on the formation of O-containing functional groups (e.g. alcohol/phenolic-OH, aldehyde/ester CO and carboxylic COO groups) and the transformation from small ring systems to larger ones, while the catalytic effect of Ca is only to increase the proportion of large aromatic ring structures (≥6 fused benzene rings). The biochar-CO2 reaction took place mainly at the gas-solid interface of biochar, while biochar-H2O one existed throughout the biochar particle. A better distribution of active sites (i.e. surface K/Ca species and O-containing groups) on biochar surface would result in the high specific reactivity of biochar during gasification.

Adsorption Characteristics of Bio-oil on Biochar in Bioslurry Fuels

This study reports the adsorption characteristics of bio-oil on biochar in biochar/bio-oil slurry (i.e., bioslurry) systems at three biochar loading levels (2.4, 4.8, and 16.7%, respectively). At low biochar loading levels (2.4 or 4.8%), heavy organic compounds (particularly those containing fused aromatic systems) in bio-oil was selectively adsorbed onto the biochar. Such selective adsorption also resulted in reduced concentrations of alkali and alkaline earth metallic (AAEM) species in the adsorbed bio-oil phase compared to that in the bio-oil blank. A comparison between the experimental and calculated distributions of AAEM species in bio-oil indicates that at least part of the AAEM species adsorbed on biochar is associated with heavy organic compounds. Consequently, such selective adsorption results in changes in the unadsorbed bio-oil phase that has decreased viscosity and aromaticity and increased polarity. It is interesting to note that the selective adsorption was weakened with an increasing biocha...