Sulphur transformation during pyrolysis of an Australian lignite

Transformation of various sulphur forms, including inherent and added pyrite, sulphates (CaSO₄ and FeSO₄) and organic sulphur, during pyrolysis of an Australian lignite was studied using TGA, TGA-MS and a fixed bed reactor, supplemented by sulphur form analysis. It was shown that hydrogen sulphide (H₂S) and a small quantity of sulphur dioxide (SO₂) were released during the pyrolysis of the pyrite-lignite blend. However, only SO₂ was detected during the pyrolysis of the lignite with high pyrite content. Inorganic matter was found to help retaining some of the inorganic sulphur, including pyrite, in the char. Inherent sulphates decomposed at much lower temperatures than the added sulphates, releasing SO₂ rather than H₂S. The inherent sulphates in the lignite were dominated by iron sulphates which started to decompose and release SO₂ at around 500 K and all sulphate had been decomposed at 1073 K. The retention of organic sulphur in the high organic sulphur lignite was higher than in its acid washed lignite sample, due to the interaction between inherent inorganic matter with the organic sulphur retaining the organic sulphur in the solid phase. SO₂ was the only sulphur gas produced during pyrolysis of acid washed lignite. A comprehensive mechanism of sulphur transformation during pyrolysis of lignite was proposed.     

Primary release and transformation of inorganic and organic sodium during fast pyrolysis of sodium-loaded lignin

This study employs a wire-mesh reactor (WMR) to understand the primary release and transformation of inorganic and organic sodium during fast pyrolysis of various sodium-loaded lignin samples at 300–800 °C. Due to the minimization of volatile-char interactions in WMR, the overall sodium release during lignin pyrolysis is relatively low, i.e., ∼9–11% and ∼7–14% for the inorganic and inorganic sodium loaded lignin, respectively. The presence of the inorganic sodium in the condensed volatiles (so-called oil) clearly indicates the important role of thermal ejection in the release of the inorganic sodium, since sodium salts are unlikely to evaporate under current conditions. While the release of the organic sodium into oil can be due to both thermal ejection of aerosols and evaporation of low carboxylates. Despite the low sodium release, significant transformation of the inorganic and organic sodium can take place during lignin pyrolysis. For the inorganic sodium loaded lignin, the inorganic sodium decreases continuously from ∼67% at 300 °C to ∼42% at 800 °C, accompanied by a steady increase in the organic sodium (i.e., the ion-exchangeable sodium) from ∼17% at 300 °C to ∼37% at 800 °C. While for the organic sodium loaded lignin, its transformation into the inorganic sodium is faster at higher temperatures, leading to a large increase in the inorganic sodium (i.e., carbonates) from ∼9% at 300 °C to ∼48% at 800 °C, as well as a reduction in the organic sodium from ∼79% at 300 °C to ∼28% at 800 °C. The data generated in this study will be important to understand the catalytic mechanism of sodium during thermochemical processing of alkali lignin for the production of bioenergy and biofuels.     

Characteristics of chars formed during rapid pyrolysis of biomass model components at high temperature

This paper reports char formation and inherent inorganic transformation during rapid pyrolysis of various biomass model components under simulated pulverized fuel (PF) conditions at 1300 °C. A drop-tube furnace with a novel double-tube configuration was deployed to achieve direct determination of char yield. The results show that rapid pyrolysis of xylan and water-washed lignin (W-L) under the conditions results in char yields of 3.4 wt.% and 12.6 wt.%, respectively, while no char was founded during rapid pyrolysis of water-washed cellulose (W-C). After loading K₂CO₃ into the W-C (i.e. KW-C) and W-L (i.e. KW-L), the char yields increase to 2.1 wt.% and 15.6 wt.%, respectively. The retentions of Na and S are low in chars after pyrolysis. After rapid pyrolysis, W-L and KW-L chars have higher retentions of AAEM species than xylan, W-C and KW-C chars. Micromorphology analysis shows char particles formed after rapid pyrolysis of all biomass components have a cenospheric structure and a rough surface with many bubbles and pores, demonstrating strong melting processes. For xylan and KW-L, the abundant inorganics accelerate char formation with swelling and reduce the extent of particle shrinkage, resulting in char particles with apparent sizes bigger than the parent feedstock particles. Oppositely, for KW-C and W-L that have low contents of inorganic species, the pyrolyzing particles experience significant shrinkage, resulting in formed char particles with apparent sizes that are much smaller than feedstock particles.     

Heterogeneous fixation of N2: Investigation of a novel mechanism for formation of NO

Formation of NO initiated by heterogeneous fixation of N₂ during pyrolysis is investigated experimentally and theoretically. The experiments were conducted with beech wood as well as with the pure biomass components cellulose, xylan, and lignin. The NO formation during char oxidation was recorded as function of pyrolysis atmosphere (N₂ or Ar), pyrolysis temperature (700–1050 °C), and oxidizing atmosphere (O₂ in N₂ or Ar). The results confirm earlier reports that biomass char may be enriched in N during pyrolysis at 900 °C and above. The N-uptake involves re-capture of N-volatiles as well as uptake of N₂. During char oxidation, the captured N is partly oxidized to NO, resulting in increased NO formation. The NO yield from oxidation of beech wood char made in N₂ increases with pyrolysis temperature, and is about a factor of two higher at 1050 °C than the corresponding yield from chars made in Ar. The experiments with pure materials show that the lignin char has the strongest ability to form NO from uptake of N₂, while xylan char forms only small amounts of NO from N₂. Density Functional Theory (DFT) calculations on model chars have revealed a number of chemisorption sites for N₂, many of which are weakly bound and therefore expected to have a short half-life at the higher pyrolysis temperatures. However, the chemisorption of N₂ across a single ring of the armchair surface was found to have an activation energy of 344 ± 30 kJ mol⁻¹ and form a stable, exothermic product with cyano groups. This demonstrates that at least one channel exists for the high-temperature incorporation of N₂ into a char which could give rise to the observed increase in NO release in subsequent char oxidation.     

The transformation and fate of sulphur during CO2 gasification of a spent tyre pyrolysis char

The transformation and fate of sulphur (S) in a spent tyre pyrolysis char during CO₂ gasification were studied by following the S species and contents using X-ray photoelectron spectroscopy (XPS). The spent tyre pyrolysis char (particle size fraction ≤150 µm), without and with 1 M HCl acid washing to remove inorganic S, were gasified in a fixed bed reactor. The effect of temperature (850, 950, 1050 °C), reaction time (1, 2, 3, 6 h) and CO₂ concentration (33.3, 50.0, 66.7 vol% in N₂) on the S species in the char samples were investigated. The main S species in the spent tyre pyrolysis char were ZnS and aliphatic sulphide. After CO₂ gasification, aliphatic sulphide, thiophene, sulphoxide and sulphone became the dominant organic S while ZnS and CaSO₄ were the main inorganic S. The percentage of total S increased with increasing gasification temperature, time and CO₂ concentration. The content of organic S increased with increasing gasification temperature and time, while, the content of inorganic S decreased. Increasing CO₂ concentration had negligible effect on the content of organic S but led to significant reduction in the content of inorganic S since ZnS reacted with CO₂ to produce ZnO and SO₂. Aliphatic sulphide, sulphoxide and sulphone were shown to have transformed to more stable thiophene. ZnS decomposed to release S_X at > 900 °C while CaSO₄ reacted with CO and carbon to produce COS. Both S_X and COS reacted with the organic matrix in the char to form sulphoxide and sulphone.     

Characterization of hybrid organic and inorganic functionalised membranes for proton conduction

Titanium zirconium phosphate and organic polymer hybrid (poly-vinyl alcohol, (3-glycidoxypropyl)-trimethoxysilane and ethylene glycol) based membranes were investigated for their potential application as proton conductors. The hybrid materials were characterized by XRD, FTIR, SEM, TGA and impedance spectroscopy analysis. It was found that embedding of functionalised inorganic particles (TiZrP) into composite polymer matrix allowed for some crystallinity formation, and cross-linking of hydroxyl groups during annealing or reactions within the organic and inorganic phases during synthesis. A complex structure was formed, as many FTIR peaks were masked by more defined peaks assigned to P–O–R bonds. The high concentration of phosphorus in the TiZrP (1:1:9 molar ratio) samples resulted in more hydrophilic particles. This was further reflected in the hybrid membranes as the water losses increased from 13 to 25 wt.% as a function of the TiZrP content changing from 10 to 50 wt.% in the final hybrid membrane, respectively. As a result, proton conductivity increased by two to three orders of magnitude from blank (organic phase only) membranes (2.61 × 10^− 5 S cm^− 1) to TiZrP hybrid membrane (2.41 × 10^− 2 S cm^− 1) at 20 °C. Proton conduction changed as a function of temperature and the Ti1Zr1P9 particles content, mainly attributed to the membrane ability to retain water, thus complying with the Grotthus mechanism.     

The influence of thermal annealing on oxygen uptake and combustion rates of a bituminous coal char

The effect of thermal annealing on the combustion reactivity of a bituminous coal char has been investigated with a focus on the role of the formation of surface oxides by oxygen chemisorption. The combined use of thermogravimetric analysis and of analysis of the off-gas during isothermal combustion of char samples enabled the determination of the rate and extent of oxygen uptake along burn-off. Combustion was carried out at temperatures between 350 and 510 °C. Char samples were prepared by controlled isothermal heat treatment of coal for different times (in the range between 1 s and 30 min) at different temperatures (in the range 900–2000 °C). Results indicate that oxygen uptake is extensive along burn off of chars prepared under mild heat treatment conditions. The maximum oxygen uptake is barely affected by the combustion temperature within the range of combustion conditions investigated. The severity of heat treatment has a pronounced effect on char combustion rate as well as on the extent and rate at which surface oxides are built up by oxygen chemisorption. Chars prepared under severe heat treatment conditions show negligible oxygen uptake and strongly reduced combustion rates. Altogether it appears that a close correlation can be established between the extent and the accessibility of active sites on the carbon surface and the combustion rate. Despite the investigation has been carried out at temperatures well below those of practical interest, results provide useful insight into the relationship existing between thermal annealing, formation of surface oxide and combustion reactivity which is relevant to the proper formulation of detailed kinetic models of char combustion.     

不同变质程度煤燃烧反应性及FTIR分析其热解过程结构变化

利用TG/DTA 6300的热重分析仪对胜利褐煤(SL)、神华烟煤(SH)与塔旺陶勒盖无烟煤(TT)三种不同变质程度的原煤进行空气气氛下燃烧反应;通过FTIR(傅里叶变换红外光谱)分析了三种煤样及不同终温下固定床热解半焦的官能团组成;运用数学高斯函数对FTIR曲线重叠吸收峰进行分峰拟合,利用拟合峰面积计算FTIR的芳香度指数(R)、芳香结构稠合指数(D)及有机成熟度指数(C)结构参数。结果表明： SL,SH与TT煤着火温度分别为299.3,408.2及441.0℃;最大失重速率峰温度分别为348.6,480.5及507.0 ℃,即随煤样变质程度的不同,着火点和最大失重速率温度都不同程度提高。煤中官能团结构较复杂,不同变质程度的煤样的红外光谱曲线中均可以观察到羟基(—OH);脂肪烃(—CH₂,—CH₃);芳环(CC); 含氧官能团(CO, C—O)等主要官能团的振动吸收峰。随着热解炼焦温度的升高,三种煤样中脂肪烃类(—CH₂—,—CH₃)红外振动吸收峰均逐渐减小;炼焦后CO在1 700 cm-1伸缩振动峰在炼焦温度到达550 ℃时基本消失;SL原煤样在1 000～1 800 cm-1 含氧官能团吸收峰区域红外曲线更为复杂,随炼焦温度升高较之其他煤样变化最为显著;而SH及TT煤芳环CC吸收峰在温变过程中峰位及峰强度均无显著变化。通过R,D及C值随热解终温的变化曲线,三种变质程度煤在热解反应过程中主体官能团变化趋势存在差异。     

TG–FTIR analysis on pyrolysis and combustion of marine sediment

In this paper, the pyrolysis and combustion of sediment have been compared using thermogravimetric analysis (TG) coupled with Fourier transform infrared spectrometry (TG-FTIR) analysis. The TG results showed that both the pyrolysis and combustion of sediment presented four weight loss stages, each. The evolving gaseous products during pyrolysis were H₂O, CO₂ and hydrocarbons, while combustion yielded considerable amounts of CO₂, in addition to H₂O, CO, CC, CO and NH₃. Comparing the pyrolysis and combustion TG-FTIR curves, it is possible to evaluate the effect of oxygen presence in the temperature range of 200–600 °C, which increases the volatilisation rate of organic matter in sediment. For the better detection of organic and inorganic matter in sediment by TG-FTIR analysis it is recommended to work in combustion mode of sediment.     

Surface modification and characterization of Jordanian kaolinite: Application for lead removal from aqueous solutions

Kaolinite clay was tested for removal of lead ions from aqueous solution. This clay was washed with sulfuric acid solution followed by chemical surface modification using 3-chloropropyltriethoxysilane and sodium hydroxide. XRF results showed that silica to alumina ratio was 2.8:1 for the treated sample compared to 1.6:1 for the raw one.XRD analysis displayed different distinct kaolinite and quartz peaks before treatment while kaolinite peaks were diminished after the treatment. SEM morphology indicated that the raw kaolinite appears as plate structure with no local pores on the plates. However, after treatment the surface was found to have micropores.Different adsorption isotherm models were applied to the experimental data and found that Shawabkeh-Tutunji equation best fit these data adequately. It was also found that chemisorption took place at the surface of the modified kaolinite with maximum adsorption capacity of 54.35 mg/g.     

Laser pyrolysis of coal

A laser pyrolysis study was performed on No. 6 high volatile bituminous Illinois (USA) coal. Possible relationships between the elemental surface composition of solid samples and the variable output power and wavelength of the argon ion laser were observed. For wavelengths of 5017 Å and 5145 Å and incident powers of 0·24 and 0·54 watts, scanning electron microscopy coupled with X-ray energy spectral analysis indicated the highest content reduction in both organic and mineral sulfur.Mass spectroscopy was employed to analyze the composition of the evolved gases from laser pyrolysis of pulverized coal. Coal pyrolysis utilizing a 2·5 watt argon ion laser produced hydrogen sulfide through decomposition of pyritic sulfur FeS₂, or organic sulfur upon irradiation of the coal. Other gases such as methane and ethane were created with solid residues (tars and ash). Pulsed CO₂ laser irradiation of coal samples produced a solid residue having a different elemental composition than that of the original coal sample.     

Effect of phosphorus (P) on the structure and reactivity of biochars produced from the pyrolysis of acid-washed biomass loaded with P of various forms

This paper investigates the effect of phosphorus (P) on char structure and reactivity of char prepared from the fast pyrolysis of purposely-prepared P-loaded biomass samples at 1000 °C in absence of other inorganic species. Biomass was first acid-washed then loaded with P of three different occurrence forms (one organic P i.e. phytic acid, and two inorganic P i.e. orthophosphoric acid and polyphosphoric acid) at the same P content of 0.8 wt%. Experimental results show that both organic and inorganic P substantially increase char yields during pyrolysis from 6.2% for the biomass sample without P to 23.0–26.0% for P-loaded samples due to the enhanced crosslinking by P-containing structures in char, leading to increases in the char C and H contents and decrease in O content. The presence of P in biochars from fast pyrolysis of various P-loaded biomass samples plays important role in the evolution of char structure and intrinsic reactivity measured during low-temperature oxidation at 500 °C in air under chemical-reaction-controlled regime. After pyrolysis and subsequent char oxidation, all P in biomass either as organic or inorganic P are found to be present in forms of acid-insoluble organic structures. For char prepared from acid-washed wood, char reactivity increases with char conversion due to the increasing pore surface area at higher conversion. Comparatively, for char prepared from acid-washed wood loaded with various P at char conversion below 60%, the presence of P increases char intrinsic reactivity due to the enhanced crosslinking of reactive carbon structures and reduced condensation of char structures. However, at conversions above 60%, P-containing species in char lead to a significant decrease in char reactivity, due to the formation of abundant CO-P bonds, that is highly resistant to the oxidation in air, in the reacting chars.     

On-line delta(18)O measurement of organic and inorganic substances

A method for the automated sample conversion and on-line oxygen isotope ratio (delta(18)O) determination for organic and inorganic substances is presented. The samples are pyrolytically decomposed at 1400 degrees C in the presence of nickelized graphite. With the system presented organic as well as inorganic samples such as nitrates, sulphates and phosphates of 50-100 &mgr;g O can be analyzed for their delta(18)O values with a standard deviation usually better than 0.5 per thousand. Additionally, carbon isotope ratios of organic substances and nitrogen isotope ratios of inorganic nitrogenous compounds are available in the same sample run. Data for international and some inter-laboratory reference materials are presented to show the accuracy and reliability of the method. The effect of some additives on the CO yield was checked for substances which do not pyrolyze completely. Copyright 1999 John Wiley & Sons, Ltd.     

Effects of high pressure and temperature on carbon isotope compositions of some acyclic alkanes and preservation of organic matter

The effects of high pressure and temperature on carbon isotopic compositions of acyclic alkanes and the stability of the acyclic alkanes were experimentally investigated. The pyrolysis of lignite with water in a closed system was conducted at 400–700°C and 1–3 GPa. The carbon isotope data, variations of peak carbon and evident odd–even predominance of acyclic alkanes indicated that: (1) the high pressure retarded the maturation of organic matter and destruction of hydrocarbons, (2) n-C₁₂₊ hydrocarbons from biogenic sources could be preserved in the cool slab subducted into the upper mantle, and (3) some organic compounds might preserve the carbon isotope signals inherited from biogenic sources. The results favor tracing the origins of organic matter in mantle rocks and extraterrestrial organic matter in meteorites and the process of deep carbon cycle.     

Effects of deposition temperature on the surface roughness and the nonlinear optical susceptibility of sprayed deposited ZnO:Zr thin films

Zirconium doped zinc oxide thin films were deposited by reactive chemical pulverization spray pyrolysis technique on heated glass substrates at 400 °C, 450 °C and 500 °C using zinc and zirconium chlorides as precursors. The effect of zirconium dopant and surface roughness on the nonlinear optical properties was investigated using atomic force microscopy (AFM) and third harmonic generation (THG). The best value of susceptibility χ⁽³⁾ was obtained from the doped films with less roughness. A strong third order nonlinear optical susceptibility χ⁽³⁾ = 20.49 × 10⁻¹² (esu) of the studied films was found for the 5% doped sample at 450 °C.     

Swelling properties and intrinsic reactivities of coal chars produced at elevated pressures and high heating rates

A high-temperature, high-pressure flat-flame burner reactor was developed to prepare char at different pressures. This system achieves particle heating rates of 10⁵ K/s, which better mimics industrial conditions than conventional drop tube or radiative flow reactors. Previous data at atmospheric pressure demonstrated a significant decrease in particle swelling during devolatilization as heating rates increased from 10⁴ K/s (the typical drop tube heating rate) to 10⁵ K/s. Pyrolysis experiments were performed at pressures from 1 to 15 atm at 1300 °C for two bituminous coals and a lignite. Average swelling was determined from a combination of the mass release and the average density. The results indicate significantly lower swelling ratios at elevated pressures than reported in the literature. Scanning electron micrographs show that the bubbles in the bituminous coal particles popped before significant swelling at these elevated heating rates. Lignite particles exhibited shrinkage rather than swelling, but still showed a small effect of pressure. TGA oxidation reactivities were determined for the Pitt #8 and Knife River lignite char samples at their respective char preparation pressures. The oxidation reactivities of both the bituminous and lignite chars decreased with increasing pressure.     

Synthesis and characterization of titanium nitride, niobium nitride, and tantalum nitride nanocrystals via the RAPET (reaction under autogenic pressure at elevated temperature) technique

TiN, NbN, and TaN nanocrystals have been selectively prepared through a simple, solvent-free, and convenient reaction under autogenic pressure at moderate temperature (RAPET) process at 350 °C for 12 h, reacting transition metal chlorides and sodium azide. The nanostructures obtained are characterized by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). A reaction mechanism is suggested based on the experimental results. These rapid reactions produce nanocrystals of TiN, NbN, and TaN with average sizes of approximately 30, 28, and 27 nm, respectively (as calculated from X-ray line broadening). An octahedral inorganic fullerene was detected among the various structures of the TiN.     

油页岩热解过程中的光谱学研究

光谱学分析方法对分析物质结构及组成具有独特的优势。为了分析和认识油页岩及其干酪根的矿物结构特点,以及在不同热解温度下油页岩热解过程中矿物结构变化,分别采用偏光显微镜(POM)、傅里叶变换红外光谱(FTIR)、X射线衍射光谱(XRD)和扫描电镜(SEM)等光学和光谱学手段,研究了甘肃窑街油页岩和酸洗脱灰干酪根的矿物形态结构和组成以及在不同热解温度下(温度300～1 000 ℃,升温速率10 ℃·min-1)矿物质和干酪根的形态结构演化特性及其机理。结果表明,甘肃窑街油页岩富含石英、粘土矿和黄铁矿等无机矿物,干酪根呈条块状不规则地镶嵌于无机矿物中;干酪根的变质程度高,富含芳香族和脂肪族结构;在实验温度范围内,随热解温度的升高,油页岩中矿物质开始分解,300 ℃时高岭石因脱水转变成偏高岭石,在650 ℃时高岭石、蒙脱石等完全分解生成偏高岭石,当温度升高至1 000 ℃时偏高岭石分解生成Si—Al尖晶石和无定型SiO₂,SiO₂与含铁矿物在半焦表面析出了(FeO—Al₂O₃—SiO₂)低熔点共融物;干酪根随温度升高分解,半焦的芳香族和脂肪族C—H基团的强度降低,芳香碳的强度升高,分解后在半焦中形成“沟壑”状残炭印记。研究结果对油页岩热解过程矿物结构演化研究和油页岩矿物的资源综合利用具有重要的现实意义。     

Experimental and modeling study on centimeter pine char combustion in fast-heating Macro TGA

Biomass energy is an important renewable resource, and thermochemical conversion, including pyrolysis and combustion, is one of the main methods of biomass energy utilization. In industrial reactors, the biomass particles will experience a fast heating (∼1000 °C/min) process during pyrolysis. The particle size of biomass applied in industry has a wide range (from millimeter to centimeter scale). The study of the reaction characteristics of biomass pyrolysis and combustion is helpful for optimizing furnace design and working condition selection. In this research, the combustion of centimeter-scale pine char was studied with a newly built fast-heating Macro Thermal Gravimetric Analyzer (Macro TGA). This Macro TGA is able to conduct the pyrolysis and combustion of large biomass samples (up to 40 mm) with a fast heating rate (∼1000 °C/min), which is able to reflect the working conditions in industrial-scale reactors such as grate furnaces and dual fluidized beds. This Macro TGA can measure the online sample weight, temperature and sample size simultaneously during pyrolysis and combustion experiments. The combustion characteristics of different sizes of pine chars were investigated at various temperatures and oxygen concentrations. A zero-dimensional model was established to predict the sample weight loss, temperature change and sample shrinkage during the pine char combustion process. Three kinetic parameters α, A and E were applied in the model, and the values of the kinetic parameters were optimized by a genetic algorithm. The model prediction and experimental results are consistent with each other. Compared with previous studies, this study developed a new experimental method to measure the reaction characteristics (including sample weight, temperature and size) of centimeter-scale biomass under similar pyrolysis and combustion reaction conditions compared to industrial reactors, and a zero-dimensional model was established to describe the pine char combustion process.     

Effect of pyrolysis conditions on gasification reactivity of woody biomass-derived char

The effect of pyrolysis conditions on char reactivity has been studied using Raman spectroscopy. This paper reports on the relationship between the properties of biomass char and the gasification rate. The gasification kinetics of biomass char have been revealed by measuring the rate of weight loss during its reaction with CO₂ as a function of temperature. First-order kinetic rate constants are determined by fitting the weight loss data using a random pore model. The relationship between the char structure and CO₂ gasification reactivity was investigated in the range of 15–600 °C/min at a constant pyrolysis pressure (0.1 MPa), and 0.1–3.0 MPa at a constant heating rate (15 °C/min). The experimental results reveal that the reactivity of biomass char is determined by the pyrolysis condition. The CO₂ gasification rates in char generated at 0.1 MPa exhibited approximately twice the values as compared to those obtained at 3 MPa. This is because the uniformity of the carbonaceous structure increases with the pyrolysis pressure. The uniformity of carbonaceous structures would affect the CO₂ gasification reactivity, and the decreasing uniformity would lead to the progression of cavities on the char surface during the CO₂ gasification process. The gasification rate of biomass char increases with the heating rate at pyrolysis. This is due to the coarseness (surface morphology) of biomass char and rough texture, which increases with the heating rate.