Alkaline Earth Metallic Species Research Articles

Machine learning model with a novel self–adjustment method: A powerful tool for predicting biomass ash fusibility and enhancing its potential applications

Biomass ash has been extensively studied for its potential applications, owing to its high content of alkali and alkaline earth metallic species (AAEMs). These AAEMs can act as catalysts in biomass thermochemical conversion and other industrial processes. However, AAEMs can also cause slagging and agglomeration, which can significantly impact system operations. To better understand these effects, we investigated the relationship between ash melting behavior and the chemical composition of biomass ash using a machine learning (ML) model. To enhance the model's performance, we employed a self-adjustment (SA) method, which significantly improved predictive accuracy. The SA-ETR model achieved an R2 value greater than 0.93, based on a dataset of 268 data points. We provided a detailed explanation of the SA-optimized ML model using Python's Shapley Additive Explanations (SHAP) library, which included global and local feature importance analysis, investigation of simultaneous effects between two features, and individual data point prediction analysis. The contents of K2O, SiO2, CaO, and Al2O3 were considered as the most significant factors affecting biomass ash's initial deformation temperature (IDT). The insights gained from this study can help investors and researchers reduce experimental complexity and improve system operation.

Leaching char with acidic aqueous phase from biomass pyrolysis: Valorization of the leachate via catalytic hydrothermal gasification

Aqueous phase of bio-oil (APB) is a general stream of waste produced from biomass pyrolysis and fractional condensation of pyrolytic volatiles and has very limited applications. We have demonstrated a sequence of leaching of alkali and alkaline earth metallic species (AAEMs) from char and catalytic hydrothermal gasification (CHTG) for valorizing char and APB, respectively. The majority of AAEMs can be removed from the char by leaching with APB and the removal rates were almost equivalent to those leached with HCl (1.0 M). CHTG of an aqueous solution of the spent APB with a total organic carbon of 14,450 ppm was performed in a continuous flow reactor, employing an activated carbon-supported Ru catalyst (Ru loading, 4.6 wt%). The catalyst exhibited a stable activity for carbon conversion of 98.8 % at 350 °C for at least 360 min while gaseous product consisting of H2, CH4, and CO2 was produced with a cold gas efficiency of 101–103 %, on a higher heating value basis. The cold gas efficiency exceeding 100 % is mainly because of the generation of H2 from water through water-gas shift reaction. The CHTG performance of APB was enhanced by char leaching through the uptake of coke-forming precursors of APB onto char and the enrichment of AAEMs in the spent APB. These AAEMs played roles in suppressing coke formation and deposition onto the catalyst and maintaining Ru particle size by providing a less acidic hydrothermal environment.

Effect of Alkali and Alkaline Earth Metallic Species on Gas Evolution and Energy Efficiency Evolution in Pyrolysis and CO2-Assisted Gasification

Abstract In this study, the same moles of alkali and alkaline earth metallic species were introduced into pine wood to investigate their effects on biomass pyrolysis and carbon dioxide-assisted gasification. First, thermogravimetric analysis was conducted to examine the pyrolytic behavior of pine wood loaded with alkali and alkaline earth metallic species. A semi-batch fixed bed platform was used to quantify gaseous product parameters, including gas mass flowrate, gas yield, recovered energy, energy efficiency, and net carbon dioxide consumption. Thermogravimetric results indicated that the loading of alkali and alkaline earth metallic species promoted the thermal decomposition of pine wood at low temperatures, but an inhibitory effect was observed at high temperatures. In terms of pyrolysis, adding alkaline earth metals increased syngas yields, and recovered energy, as well as energy efficiency, whereas alkali metals had the opposite effect. For the gasification, the loading of alkali metals showed a stronger catalytic than the pine wood loaded with alkaline earth metals. Based on the evolution of carbon monoxide, the effects of alkali and alkaline earth metallic species on enhancing the biochar's gasification reactivity were in the sequence of sodium > potassium > calcium > magnesium. In addition, the addition of alkali metals exhibited a stronger capacity for carbon dioxide consumption, which contributed to the management of the greenhouse gas. Considering only energy efficiency, adding alkaline earth metals in biomass pyrolysis is an optimal choice due to the higher overall energy efficiency obtained in less time.

Alkali and alkaline earth metals catalytic steam gasification of ashless lignin: Influence of the catalyst type and loading amount

This work studies the effects of alkali and alkaline earth metallic species (AAEMs) (Na2CO3, K2CO3, and CaCO3), Na+ impregnation amount (2, 5, and 7 mmol) and sodium salts (NaHCO3, Na2SO4, and NaAlO2) on the gasification characteristics and product distribution of G-type lignin in a fixed-bed system for continuous gasification. The results showed that six catalysts all could improve lignin gasification performance by increasing total gas yields, syngas yields, H2/CO ratios, and carbon conversion rates. Na2CO3 had the strongest catalytic ability, followed by NaHCO3 and K2CO3, while CaCO3, Na2SO4 and NaAlO2 had poor catalytic abilities. Gaseous AAEMs, especially NaOH and KOH, could enhance tar cracking, volatiles reforming, coke gasification, the water-gas shift reaction, and methane steam reforming. The high melting points of CaO and NaAlO2 greatly reduced the catalytic capacities of CaCO3 and NaAlO2. AAEMs could combine with the carbon matrices to form carboxylate structures or phenol/aldehyde structures which might volatilize to catalyze homogeneous reactions. Moderately increasing Na+ impregnation amount to 5 mmol was beneficial to lignin gasification, but excessive impregnation reduced the gasification parameters. In addition, all six catalysts had effects on the tar composition, especially K2CO3 and NaAlO2, which could effectively catalyze tar cracking and reduce heavy compounds.

Valorization of sewage sludge via air/steam gasification using activated carbon and biochar as catalysts

The catalytic gasification of sewage sludge was explored using different catalyst particle sizes, bed temperatures, and gasifying agents. Activated carbon and sawdust biochar were used as catalysts in this study. The effects of the porosity of activated carbon on tar adsorption and cracking, and biochar containing alkali and alkaline earth metallic species (AAEMs), which can enhance gasification reactions, were investigated under different conditions. A catalyst bed temperature of 800 °C and particle size of 0.5–1.7 mm showed optimum conditions for increasing H2 and CO content and decrease CO2 fraction; however, a higher solid residue (∼38 wt%) was also observed due to the high ash content in sewage sludge. Furthermore, the introduction of steam had a positive effect on the H2 increment, owing to the presence of inherent AAEMs in the biochar, promoting water gas shift and hydrocarbon steam reforming reactions. The results of this study provide effective measures for using activated carbon and affordable biochar to enhance H2 production with a parametric effect on the catalyst bed.

Effects of AAEMs on the char heterogeneous structure evolution during Zhundong coal pyrolysis: Insights from micro-Raman spectroscopy

The effects of alkali and alkaline earth metallic species (AAEMs) on the heterogeneous evolution of coal/char structure during pyrolysis are rarely investigated. In this study, micro-Raman mapping technology was developed to characterize the effects of AAEMs on the distribution and heterogeneous evolution of the chemical structure of coal/char particles on micro-scale during pyrolysis. The pyrolysis chars from raw coal, leached coal and loaded coal samples were prepared by using a thermogravimetric analyzer, and more than 300 Raman spectra for each sample were analyzed by micro-Raman mapping technology. The results indicate that the water-soluble AAEMs inhibit the release of volatiles during the whole pyrolysis process. The ion-exchangeable AAEMs promote the release of volatiles at the early stage of pyrolysis and then inhibit the release. For integral char structure evolution, water-soluble and ion-exchangeable AAEMs enhance the average relative amount of small aromatic rings obviously at the devolatilization stage and aromatization polymerization stage, respectively. Besides, both water-soluble and ion-exchangeable AAEMs firstly decrease the average relative amount of active structures obviously and then slightly. For heterogeneous evolution, at the devolatilization stage, the water-soluble AAEMs promote the crack of polyolefin and substitutional groups from active components, and the transformation of these species to small aromatic rings. Meanwhile, water-soluble AAEMs promote the breakdown of the cross-linked structures of the large aromatic ring system from inert components and decrease the heterogeneity of the chemical structure of char particles obviously. Besides, the ion-exchangeable AAEMs promote the breakdown of chemical bonds between aromatic rings and the release of the active components. At the aromatization polymerization stage, the ion-exchangeable AAEMs inhibit the condensation of small aromatic rings and increase the heterogeneity of the chemical structure of char particles. In the later stage of pyrolysis, char chemical structure tends to be stable and AAEMs have little effect on the chemical structure of char particles.

Oxidative catalytic steam gasification of sugarcane bagasse for hydrogen rich syngas production

Reactive Flash Volatilization (RFV) is an emerging thermochemical method to produce tar free hydrogen rich syngas from waste biomass at relatively lower temperature (<900 °C) in a single stage catalytic reactor within a millisecond residence time. Here, we show catalytic RFV of bagasse using Ru, Rh, Pd, or Re promoted Ni/Al2O3 catalysts under steam rich and oxygen deficient environment. The optimum reaction conditions were found to be 800 °C, steam to carbon ratio = 1.7 and carbon to oxygen ratio = 0.6. Rh–Ni/Al2O3 performed the best, resulting in highest hydrogen concentration in the synthesis gas at 54.8%, with a corresponding yield of 106.4 g-H2/kg bagasse. A carbon conversion efficiency of 99.96% was achieved using Rh–Ni, followed by Ru–Ni, Pd–Ni, Re–Ni and mono metallic Ni catalyst in that order. Alkali and Alkaline Earth Metal species present in the bagasse ash and char, that deposited on the catalyst, was found to enhance its activity and stability. The hydrogen yield from bagasse was higher than previously reported woody biomass and comparable to the microalgae.

Volatile-char interactions during biomass pyrolysis: Effect of biomass acid-washing pretreatment

The purpose of this study is to investigate the effect of acid-washing pretreatment on the poplar wood (PW) pyrolysis under different volatile-char interactions, the experiment was conducted in a self-designed fixed-bed pyrolysis reactor. It was found that acid-washing pretreatment could alter the surface morphology of PW, increase the cellulose crystallinity and reduce the inorganic ash components (mainly Alkali and Alkaline Earth Metal species, AAEMs). AAEMs acted as catalysts for sugar ring fragmentation and charring reactions during both primary pyrolysis of biomass and secondary volatile-char interactions. The removal of AAEMs would increase the bio-oil yield and decrease the biochar and non-condensable gas yields, same trend was also observed with the decreasing volatile-char interactions. The removal of AAEMs and weakened volatile-char interactions both resulted in an increase of C content and a decrease of O content of biochar with more pore structures generated, especially micropores, the content of anhydrosugars in bio-oil was also largely enhanced. In addition, the decrease of volatile-char interactions would significantly reduce the effect of AAEMs in biomass on the pyrolysis process. A highest bio-oil yield of 63.37 wt% with 34.38% of anhydrosugars could be obtained even for a packed fixed-bed reactor by intentionally reducing volatile-char interactions and removing AAEMs from biomass during the process.

Microfabricated strontium atomic vapor cells.

We demonstrate strontium (Sr) atomic vapor cells having a total external volume of 0.63 cm3 that can operate above 300 °C for times exceeding 380 h. The cells are fabricated using micromachined silicon frames anodically bonded to glass windows that have a 20-nm thick protective layer of Al2O3 deposited on the interior surfaces. The presence of Sr vapor in the cell is confirmed through laser absorption spectroscopy for the 1S0 → 1P1 transition in Sr at 461 nm. Measurements of sub-Doppler linewidths indicated negligible (<3 MHz) broadening of this transition from residual background gas collisions. This compact and manufacturable, high-temperature atomic vapor cell can enable narrow-line optical frequency references based on strontium and other alkaline earth species.

Rapid pyrolysis of biochar prepared from slow and fast pyrolysis: The effects of particle residence time on char properties

This paper investigates the evolution of char properties with particle residence time during rapid pyrolysis of biochar under conditions pertinent to pulverized fuel (PF) applications. Two biochar samples were considered, prepared via slow (S-BC) and fast (F-BC) pyrolysis of mallee wood (150–250 µm) at 500 °C and two different heating rates (10 °C/s and ∼400 °C/s), respectively. The biochar samples were then subjected to rapid pyrolysis at 1300 °C using a novel drop-tube furnace (DTF), which enables direct determination of char yield experimentally. The evolution of char yield, the release of alkali and alkaline earth metallic (AAEM) species, and particle size and shape during rapid pyrolysis are investigated as a function of particle residence time (0.45 s to 1.4 s). The results show that char yields decrease from ∼77% to 75% when particle residence time increases from 0.45 s to 1.4 s. Rapid pyrolysis of F-BC has slightly higher char yields, due to the higher ash content of F-BC. More Cl in F-BC facilitates the release of Na during rapid pyrolysis, leading to the lower retention of Na in FC than in SC. Nevertheless, the retentions of K (∼90%), Mg (∼85%), and Ca (∼90%) are higher in FC, which can be ascribed to its higher contents of oxygen after rapid pyrolysis. The investigation of particle size and shape shows that biochar particles exhibit little changes after rapid pyrolysis, indicating their strong resistance to shrinkage and deformation even at high temperature.

Effect of acid washing and K/Ca loading on corn straw with the characteristics of gas-solid products during its pyrolysis

Alkali and alkaline earth metallic species (AAEMs) significantly affect the thermal conversion and utilization of biomass. However, the bonding mechanism between AAEMs and biomass carbon substrates is still unclear. In this paper, corn straw with different AAEMs contents were prepared by acid washing and K/Ca loading with impregnation method. A horizontal furnace was used to conduct the fast pyrolysis experiment at 800 °C. The Fourier transform infrared spectroscopy (FTIR) was used to analyse the chemical structural characteristics of corn straw and biochar. The production of pyrolysis gases was online monitored by a synthetic gas analyzer. The main conclusions are as follows: the K/Ca loading promotes the conversion of C–O–C and CO to COO- and C–O in corn straw. K is linked to corn straw mainly through COO- group, and Ca is linked to corn straw mainly through C–O group. Both K/Ca elements are effective in inhibiting the consumption of C–O–C group during corn straw pyrolysis. Besides, K element can catalyze the depletion and decomposition of C–O group during pyrolysis. The K element inhibits the decomposition of the unstable carbon matrix and CO group during pyrolysis, thereby reducing the emission levels of CH4 and CO. K can promote the release of CO2 during pyrolysis, while Ca has no obvious effect. The pyrolysis reactivity of K-loaded corn straw is extremely low, while that of H-form corn straw and Ca-loaded corn straw is at a high level. AAEMs promote the release of H/O elements during corn straw pyrolysis, and the role of K is significantly stronger than that of Ca.

Torrefaction of woody biomass and in-situ pyrolytic reforming of volatile matter: Analyses of products and process heat demand

Torrefaction of Japanese cedar (TR) and in-situ vapor-phase pyrolytic reforming of volatile matter from TR (PYR) were investigated with three main objectives; quantification of the heats required for TR and PYR (QTR and QPYR, respectively), demonstration of high conversion of bio-oil into syngas by PYR without either catalyst or oxidizing agent, and clarification of effects of water washing of the cedar prior to TR on QTR and QPYR as well as the product distribution. The cedar was subjected to TR and PYR at temperatures of TTR = 250–350 °C and TPYR = 500–800 °C, respectively. QTR was defined as the difference in enthalpy between the TR products at TTR and dry cedar at 25 °C, and determined from compound or elemental composition of char, bio-oil, water, and non-condensable gases. QTR increased with TTR in a range of 1.0–4.0% of the cedar HHV, which could be covered by burning the gas and a small portion (0.5–13.0%) of bio-oil from TR at TTR ≥ 280 °C. The water washing removed substantial portions of the inherent alkali and alkaline earth metallic species. This resulted in slight increase in QTR, 0.2–0.8%-HHV and decrease in the gas yield, in particular, those of CO and CO2. PYR converted substantial portions of the bio-oil from TR at TTR = 300 °C. The bio-oil conversion into CO/H2–rich gas was 85–90% at TPYR = 800 °C. QPYR, which was defined as the enthalpy difference between the volatile matter from TR at 300 °C and that from PYR at TPYR, increased with TPYR but as small as 1.4–5.8% of the cedar HHV. The water washing slightly decreased QPYR, and this was quantitatively explained by slightly smaller bio-oil yield from TR of the water-washed cedar at TTR = 300 °C than that of the cedar. QPYR was a function of decrease in the bio-oil yield by PYR, which was not influenced by the water washing.

Effects of alkali and alkaline earth metal species on the combustion characteristics and synergistic effects: Sewage sludge and its blend with coal

A large amount of alkali and alkaline earth metal species (AAEMs) are contained in sewage sludge (SS) ash, which will affect the combustion characteristics and synergistic effects of the co-combustion of SS and coal. The main objective of this paper is to investigate the effects of K, Ca, Na and Mg on combustion characteristics and synergistic effects of the blend of SS and coal by TGA and single particle combustion methods. The ash-free sludge (AS), impregnated AS and the blends of AS and bituminous coal (BC) were prepared. A high speed camera was used to record the combustion process, which were processed to calculate the ignition delay time, burnout time and combustion temperature. The synergistic effect of co-combustion process was studied by comparing the experimental results with the theoretical calculation results. The synergistic effects main occur at 350–530 °C and the blends of AS and BC with 2 wt% Na has the strongest strength of synergistic effects. The K, Ca and Na are conducive to the shorter ignition delay time, burnout time, higher combustion temperature and stronger synergistic effects of the blends. However, Mg will increase the delay time and reduce the combustion temperature of char of the blends. There are optimal concentrations of AAEMs on the promotion of combustion and synergistic effects, and too high concentrations of AAEMs will have negative impacts. K and Na (alkali metals) have stronger promotion effects than Ca and Mg (alkaline earth metals) on combustion of volatiles and synergistic effects.

Investigation into the interaction of biomass waste with industrial solid waste during co-pyrolysis and the synergetic effect of its char gasification

In this work, the interaction between waste cypress sawdust (WCS) and coal liquefaction residue (CLR), a type of industrial solid waste, during co-pyrolysis was studied by thermogravimetry-mass spectrometry (TG-MS) and pyrolysis-gas chromatography mass spectrometry (Py-GC/MS). The gasification reaction characteristics of co-pyrolysis char were also evaluated. The results showed that both promoting and inhibiting effects existed in the co-pyrolysis process of WCS and CLR. When the pyrolysis temperature was less than 420 °C, the catalysis of minerals was conducive to the pyrolysis reaction. At higher temperatures, the polycondensation and carbonization produced by the interaction between the components inhibited the release of volatiles. The gasification reactivity of co-pyrolysis char was better than that of individual WCS and CLR chars. The synergistic effect was most obvious when the blending ratio of WCS to CLR was 3:1. In the gasification process of co-pyrolysis char, the WCS component with better reactivity preferentially reacted to form an abundant pore structure, which exposed more reactive sites and promoted the diffusion and mass transfer of gasification agent. Moreover, alkali and alkaline earth metal species in WCS and iron bearing minerals in CLR can catalyze the gasification reaction, contributing to the synergistic effect. Therefore, the addition of a suitable solid waste to biomass waste can improve the energy efficiency and simultaneously achieve solid waste utilization.

Impact of alkaline-earth doping on electronic properties of the photovoltaic perovskite CsSnI3: insights from a DFT perspective.

The oxidation of Sn(II) to the more stable Sn(IV) degrades the photovoltaic perovskite material CsSnI3; however, this problem can be counteracted via alkaline-earth (AE) doping. In this work, the electronic properties of CsSn1-xAExI3, with x = 0 and 0.25, and AE = Mg and Ca, were investigated via Density Functional Theory. It is proven that the synthetic reactions of all these perovskites are thermodynamically viable. Besides, a slight strengthening in the metal-halide bonds is found in the Mg-doped perovskite; consequently, it exhibits the greatest bulk modulus. Nevertheless, the opposite occurrs with the Ca-doped perovskite, which has the smallest bulk modulus due to the weakening of its metal-halide bonds. The calculated bandgaps for CsSnI3, Mg-doped and Ca-doped perovskites are 1.11, 1.32 and 1.55 eV, respectively, remaining remarkably close to the best photovoltaic-performing value for single-junction solar cells of 1.34 eV. Nevertheless, an indirect bandgap was predicted under Mg-doping. These results support the possibility of implementing AE-doped perovskites as absorber materials in single-junction solar cells, which can deliver higher output voltages than that using CsSnI3. Finally, it was found that Sr or Ba doping could result in semiconductors with bandgaps close to 2.0 eV.

Investigation into the catalytic gasification of coal gasification fine slag residual carbon by the leachate of biomass waste: Gasification reactivity, structural evolution and kinetics analysis

In this study, the applicability of chicken manure leachate (CML) to catalytic gasification of coal gasification fine slag residue carbon (RC) was investigated in order to guide the large-scale application of RC as a potential gasification feedstock. Firstly, the effects of different CML loading amount and gasification temperature on RC reactivity were investigated. The structural evolution of RC loaded with CML in gasification was deeply analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and in-situ high temperature stage coupled with optical microscope system (HSOM). The results showed that CML is rich in water-soluble alkali and alkaline earth metallic species, especially potassium, which can significantly improve the gasification reactivity of RC. The gasification activity increased with the increase loading amount of CML, but higher gasification temperature will weaken the catalytic ability of CML. The model free method can well predict the kinetics of RC gasification reaction. The existence of CML reduced the activation energy of gasification obviously. The activation energy of RC20CML was 100.96 kJ/mol, which was 37.81 kJ/mol lower than that of RC. Furthermore, the surface complexes produced during RC gasification were determined by temperature programmed desorption (TPD) technique. The results showed that CML loaded RC released more CO during TPD process, which indicated that CML promoted the formation of more active sites on the RC surface, thus accelerating the gasification reaction. This work will contribute to the classification and resource utilization of coal gasification fine slag.

Steam co-gasification of Japanese cedarwood and its commercial biochar for hydrogen-rich gas production

In this study, steam gasification and co-gasification of Japanese cedarwood and its commercial biochar were performed in a lab-scale fixed-bed reactor to investigate the feasibility for producing H2-rich syngas. Ultimate analysis, proximate analysis, Brunauer-Emmett-Teller (BET) surface area analysis, and scanning electron microscopy (SEM) were conducted to understand the changes caused by the carbonization process. The effects of gasification temperature and steam flow rate on gas production yield from the steam gasification of the individual samples were investigated at first, which showed larger gas production yield and less tar yield for the steam gasification of the commercial biochar than that of raw cedarwood, indicating that the commercial biochar obtained from the carbonization process was more beneficial for the gasification. The co-gasification of raw Japanese cedarwood and its commercial biochar with different mixing ratios was conducted at different reaction temperatures. The synergistic effect was obviously observed. Especially, the commercial biochar with the highly porous structure and high content of alkali and alkaline earth metal (AAEM) species might provide the catalytic effect on cracking and reforming of tar derived from the raw cedarwood, resulting in a larger H2 yield. However, the catalytic effect and gasification reactivity of biochar would decrease by increasing the amount of raw-cedarwood in the blends due to the coke deposition on the surface of biochar.

Leaching Char with Acidic Aqueous Phase from Biomass Pyrolysis: Removal of Alkali and Alkaline-Earth Metallic Species and Uptakes of Water-Soluble Organics

The removal of alkali and alkaline-earth metallic (AAEM) species from biomass and/or its pyrolysis-derived char is often required to mitigate ash-related issues during their combustion. Leaching of biomass with an acidic aqueous phase (AP) produced from its pyrolysis is a promising strategy but encounters several issues, including high moisture content in wet biomass after dewatering and loss of organic carbon from biomass. Here, we propose a new process that leaches char with pyrolytic AP for the removal of AAEM species from and the uptakes of water-soluble organics by char. The char and pyrolytic AP produced from the pyrolysis of wheat straw at 450 °C in an auger reactor were subjected to time-dependent leaching at a liquid-to-solid mass ratio of 20. The results demonstrate that the majority of K, Mg, and Ca are leached within the first hour. Nonacidic compounds in the pyrolytic AP slightly hinder the leaching of K but have no impacts on that of Mg and Ca. Except for acetol, the uptakes of other organic compounds (e.g., furfural and phenolic compounds) by char are rapid in the first hour, become slower in 1–2 h, and then reach equilibrium. The results from density functional theory (DFT) calculations suggest the presence of chemisorption for the interactions between these organic compounds and char. Repeated leaching runs at the optimized leaching time (1 h) suggest that the pyrolytic AP is sufficient for leaching the char from the same run, achieving removal rates of ∼63.7 wt % for K, ∼43.7 wt % for Mg, and ∼60.7 wt % for Ca. After repeated leaching, there are only four organic compounds, including 2,3-butanedione, acetol, 2(5H)-furanone, and the remaining acetic acid, left in the leachate, simplifying the compositions of the pyrolytic AP. Leaching the char, instead of wheat straw, with the pyrolytic AP offers significant advantages, including the reduced moisture content in the wet solid after dewatering, negligible loss of organic carbon, and enhanced capture of phenolic compounds.

Influence of the nature and amount of carbonate additions on the thermal behaviour of geopolymers: A model for prediction of shrinkage

In order to develop fire resistant geopolymer materials, it is necessary to understand the parameters controlling their thermal behavior such as the content of alkali or rare earth cations. This study highlights the effect of carbonate nature and amount on the thermal behavior of geopolymers in order to propose a model of thermal behaviour and predict shrinkage. For this, various mixtures of kaolin and calcite and/or dolomite with different percentages were calcined at 600 and 750 °C. The feasibility of consolidated materials based on these mixtures were evaluated and the thermal behavior of the obtained materials was investigated. The characterization of the mixtures revealed the persistence of carbonates after calcination at 600 °C and their partial decomposition after calcination at 750 °C. This fact was explained in the case of high dolomite content by the existence of kaolinite gangue hindering its decomposition. Consolidated materials were obtained from the different mixtures. After thermal treatment at 1000 °C, it was evidenced that the amorphous phase crystallizes to form in a major part leucite. At lower available alkaline earth species (Ca2+ and Mg2+) content, only wollastonite is formed and the shrinkage varies between 15 and 12%. However, at higher content, different calcium and magnesium silicates can be formed such calico-olivine and larnite in the case of calcite based materials and akermanite and merwinite for dolomite based materials. This fact leads to lower shrinkage value (from 6 to 8%). Thus, it is possible to control the thermal behavior and predict the shrinkage of geopolymer materials by controlling the available alkaline earth cations.

Hydrogen-rich gas production from steam co-gasification of banana peel with agricultural residues and woody biomass

Steam co-gasification of banana peel with other biomass, i.e., Japanese cedar wood, rice husk and their mixture, was carried out for the hydrogen-rich gas production in a fixed-bed reactor. For the co-gasification process, the banana peels were physically mixed with rice husk, Japanese cedarwood and their mixture respectively by different mixing weight ratios. The effects of reaction temperature and the addition amount of banana peel on the gas production yield were investigated by comparing the experimental data with the calculated ones based on the individual biomass gasification at the same condition. It was found that the banana peel with a high content of alkali and alkaline earth metal (AAEM) species exhibited not only high gasification reactivity but also a significant enhancing catalytic effect on the co-gasification process at the low temperature, especially with the biomass containing no silica species. The high content of silica species in the rice husk had a negative effect on the gasification reactivity of banana peel during the co-gasification since it could hinder the release of AAEM from the biomass and/or lead to the possible formation of inactive alkaline silicates. However, the combination of these three samples with the suitable weight ratio could improve the gasification performance at the low temperature due to the synergetic effect provided by high contents of potassium and calcium from banana peel and cedarwood respectively. Moreover, the addition of calcined seashells as the CaO source could further improve the gas production yield, especially the hydrogen gas yield at a relatively low gasification temperature of 750 ℃.