Uptake of Metal Ions on Humic Acids

The kinetics, the sorption capacities, pH and temperature dependence of sorption of humic acids (HAs) of Turkish brown coals with respect to Zn(II), Cu(II), Ni(II), Co(II) and Pb(II) ions were investigated, and the roles of the carboxylic and phenolic groups in the adsorption of metals ion on HAs were searched in this work. These metal ions are able to form complex compounds with carboxylic and phenolic groups of HAs. Adsorption equilibrium was achieved in between 50 and 60 min for all studied cations. HAs extracted from different brown coals have been characterized by chemical and physical methods. The chemical properties of HAs showed differences depending on the source from which they were obtained. The sorption of metals on the surface of HAs depends strongly on the pH, and sorption decreases with decreasing pH. Maximum removal of metal ions was demonstrated at pH values of 4.1–5.0. The Langmuir adsorption isotherm was used to describe observed sorption phenomena. The Δ G ⁰ became negative as the temperature increased, and so the equilibrium constant decreased slightly. The investigation proved that the HAs are suitable materials for the studied heavy metal ion removal from aqueous solution and could be considered as potential material for purification of effluent polluted with toxic metal ions.     

Hydrogen storage in activated carbons produced from coals of different ranks: Effect of oxygen content

20 activated carbons (ACs) were prepared by activation of four coals of different ranks (bituminous, low-ash bituminous and sub-bituminous coals, and one anthracite) with potassium hydroxide, in order to evaluate their hydrogen storage capacities at −196 °C. The effect of surface area and oxygen content on hydrogen storage was examined. Oxygen content was determined by temperature-programmed desorption. The significance of oxygen content on hydrogen storage capacity was evaluated by Analysis of Variance (ANOVA). Apparent surface areas higher than 3000 m² g⁻¹ and hydrogen adsorption as high as 6.8 wt.% were obtained. The best results were obtained with ACs from bituminous coals. No significant effect of oxygen content on hydrogen adsorption was observed. We concluded that surface area controls hydrogen storage capacity at −196 °C.     

The properties of Chinese typical brown coal water slurries

Eight typical Chinese brown coals were evaluated for their potential as coal water slurries (CWSs). The solid ratios and stability of brown coal water slurries were studied and compared with bituminous coal slurries. Results showed the amounts of oxygen functional groups in brown coals are much higher than that in bituminous. Thus, solid ratios at fixed viscosity for brown coal slurries are about 46–55%wt, much lower than those for the bituminous samples that are about 65%wt. Most slurries of brown coals exhibit good stability. Moreover, additives never universally improve slurry ability and stability simultaneously.     

Hydrogen production via steam gasification of ash free coals

The kinetics of the coal to hydrogen conversion can be significantly enhanced by introducing catalysts. The catalysts are, however, commonly deactivated by irreversible interaction with mineral matters in coal. This work addresses hydrogen production via steam gasification of ash free coals. Following the production of ash free coals (AFCs) derived from various raw coals (brown, bituminous, and coking coal), fixed-bed steam gasification of the AFCs was performed as a function of temperature and which was compared with one another and also with that of the matching raw coals. In the absence of a catalyst, AFCs produced from different parent coals exhibited similarly low gasification reactivity, comparable to a high rank coal (coking coal) at 700 °C. As expected, the reaction became faster with increasing temperature in the range, 700–900 °C. The steam gasification of AFCs was highly activated by K₂CO₃ above 700 °C. It was very likely that water–gas shift reaction associated with the gasification of AFCs was also catalyzed.     

Synthesis and characterization of KOH/boron modified activated carbons from coal and their hydrogen sorption characteristics

Activated carbons from bituminous coal taken from the area of Zonguldak Kilimli region in Turkey were synthesized by chemical activation using a mixed combination of KOH and as a boron source borax decahydrate. The modification process consists of chemical activation of the demineralized coal with KOH (KOH/coal:4/1) and various concentrations of borax decahydrate solutions (0.025–0.1 M). Textural properties such as surface area and pore structure were studied by volumetric methods using N₂ adsorption data at 77.4 K (P/P₀ = 0–1). The samples obtained have high microporosity, in the form of irregular structures. The EDAX spectra indicate that Boron heteroatoms are attached to surface of AC41, and as BDH concentration increases from 0.025 M to 0.1 M, higher atomic percent of boron is accumulated at the surfaces. AC41 exhibits amorphous structures, whereas BDH modified AC41 consists of predominantly amorphous structure and disordered graphitic carbon. Among the synthesized boron modified samples, the highest surface area, total pore volume and average pore diameters were found for the 0.025 M_BDH-AC41 sample. As the BDH concentration increases, the volume of N₂ adsorbed decreases. Surface area of CC and AC41 samples were 52.62 and 2228 m²/g, respectively, whereas surface area of the boron modified samples were found in the range of 2190–2704 m²/g. Hydrogen sorption capacities of the KOH/boron modified samples were found in the range between 2.08 and 3.74% wt. Hydrogen sorption capacity of AC41 obtained was 4.11% wt. Increasing boron concentration resulted in the decrease of hydrogen sorption capacities. Boron modified activated carbons were prepared successfully from coal samples by chemical activation using a mixed combination of KOH and BDH.     

煤燃烧产生的细微粒子中重金属元素富集性的实验研究

本文详细地研究了燃烧温度，燃烧气氛及煤粉细度对几种有毒重金属的燃烧过程中的行为的影响，发现温度，气氛及煤粉细度对各重金属元素在燃烧中的行为有重要的影响，再从各元素的总量角度研究了燃烧工产史对重金属行为的影响，并比较了不同煤种燃烧时重金属行为的差异。     

Understanding hydrogen adsorption performance of lithium-doped MIL-101(Cr) by molecular simulations: Effects of lithium distribution

Metal-organic frameworks (MOFs) have been recognized as one of the most compelling physical adsorption hydrogen storage materials owing to their ultrahigh surface area and excellent hydrogen adsorption performance. In order to further improve their hydrogen adsorption performance, lithium doping is an effective approach to increase the number of hydrogen adsorption sites as well as enhance the interaction strength towards hydrogen molecules according to grand canonical Monte Carlo(GCMC) simulations. However, in previous simulation studies, lithium ions were commonly assumed to be randomly distributed in MOF frameworks. In fact, the lithium-doped MOFs were prepared by immersing MOFs in a lithium salt solution and then drying them under high temperatures, in which the distribution of Li⁺ in MOF frameworks is elusive. In this work, the lithium-doped MIL-101 models (i.e., Immersion model) with varying lithium contents were constructed according to experimental operation and their hydrogen adsorption performance from GCMC simulations was also investigated in comparison with the equivalent models with randomly distributed lithium ions (i.e., Random model). It is found that in contrast to the uniform distribution of lithium ions in Random model, the accumulation of lithium ions was inspected in Immersion models especially at high loadings, leading to the reduced pore size. On the contrary, the hydrogen adsorption capacities of Immersion models are significantly improved owing to the enhanced interaction strength with hydrogen molecules resulting from the reduced pore size and the strengthened charged-induced dipole interaction.     

Recent Studies on Activated Carbons and Fly Ashes from Turkish Resources

This article deals with adsorptive properties of activated carbons (ACs) and fly ashes from Turkish coal and biomass resources. ACs because of their high surface area, microporous character and the chemical nature of their surface have been considered potential adsorbents for the removal of heavy metals from industrial wastewater. Pyrolysis is an established process method for preparation of activated carbon from biomass. The bio-char is can be used as AC. The adsorption properties of ACs were strictly defined by the physicochemical nature of their surface and their texture, i.e., pore volume, pore size distribution, surface area. It is well known that the pH of the solution-adsorbant mixture is an important variable in the adsorption process. Fly ash has the highest adsorption capacity (198.2 mg/g) for Cd(II). Almond shell AC has the lowest adsorption capacity (2.7 mg/g).     

Heterosubstituted sumanene as media for hydrogen storage: A theoretical study

Recently, bowl-shaped π-conjugated compounds, considered as carbon-based materials, have shown noticeable capacities in the hydrogen storage. Doping these compounds with appropriate elements remains the main target to improve the hydrogen adsorption properties. In this regards, we carried out a theoretical study, by means of MP2 method, on a series of mono-, di- and tri-heterosubstituted sumanene compounds, adsorbing hydrogen molecule from concave and from convex side, respectively. Benzylic carbons have been substituted by O, S, NH and NCH₃ groups. The influence of this substitution on the adsorption properties has been reported. Our investigation has involved binding energies corrected to basis set superposition error (BSSE) and structural parameters like equilibrium distances as well as bowl depths. Dipole moment, HOMO-LUMO energy gap and the changes after the adsorption process have also been evaluated. The results show that the binding energy values belong to the range of the intermediate interval of physisorption mechanism. Natural population analysis (NPA) associated to natural bond orbitals (NBO) elucidate the charge transfer occurring between the heterosubstituted compounds and the hydrogen molecule. We classified the substituents upon the binding energy for mono-, di- and trisubstitution and no similarities have been reported between the adsorption sides. These classifications can be of interest to any prospective experimental investigation.     

不同煤种混煤燃烧时NO_x生成和燃尽特性的试验

在一维沉降炉上对无烟煤、贫煤、烟煤及其混煤的燃烧特性进行了研究,分析了不同因素对NOx排放量的影响,并讨论了不同过量空气系数、掺混比及一、二次风比例对燃尽率的影响,试验结果表明：当烟煤的掺混比例为25％,NOx的排放量较低,混煤燃烧时沿程分析结果表明,煤种特性的不同导致NOx排放时有不同的峰值。     

Distribution and Occurrence of Arsenic in Two Typical Chinese Coals

Abstract

Two complementary methods, float-sink experiment and sequential chemical leaching were used to probe into the occurrence of arsenic in two Chinese coals: Yima (YM) and Datong (DT). Flow injection-hydride generation atomic fluorescence spectrometry was employed to measure the arsenic content in parent coals as well as the size and density-fraction samples. Float-sink experiment indicated that the heavy density fractions were enriched mineral containing arsenic in two bituminous coals studied, as confirmed by the sequential chemical leaching method. Sequential chemical leaching revealed that sulfide arsenic was the primary mode of occurrence (> 50%), stable form also abounded in coal with content between 30 and 40%, and a small amount of arsenic took the occurrence of organic form.     

Effect of high-temperature treatment on the desorption efficiency of gas in coalbed methane reservoirs: Implication for formation heat treatment

Formation heat treatment has been considered as a potential stimulation technology for the enhanced recovery of coalbed methane. However, the influence of heat treatment on the desorption efficiency of coalbed methane has not been clarified. In this study, isothermal adsorption experiments of a cylindrical anthracite coal treated at 25 °C, 200 °C, 400 °C, 600 °C, and 800 °C were conducted to investigate the variation in the methane adsorption potential and desorption efficiency. The pore structure of coal was characterized by nuclear magnetic resonance measurements and scanning electron microscopy. Changes in the organic matter and functional group content of coal were monitored by proximate analysis and Fourier transform infrared spectroscopy. Results reveal that pore structure and composition are the main factors that affect the coal adsorption potential. With the increase in the temperature to 200–600 °C, the maximum adsorption potential of coal increased by 7% due to the increase in the pore volume and the functional group content. At a heat-treatment temperature of 800 °C, the functional group content decreased, which in turn reduced the maximum adsorption potential by 76%. Comparison of isothermal adsorption data of coals with different ranks reveals that the Langmuir parameter of bituminous coals is more easily affected by heat treatment in comparison with that of anthracite coal. Based on the reversible theory of coalbed methane isothermal adsorption and desorption process, weighted pressure was proposed, which could comprehensively evaluate the desorption efficiency of coal after heat treatment at different temperatures, and the heat treatment temperature for the optimal desorption efficiency can be determined by the weighted pressure.     

Adsorption of Co(II) and Hg(II) from Water and Wastewater onto Modified Lignin

Abstract

In this study, adsorptions of heavy metal ions Co(II) and Hg(II) onto modified lignin from Ailanthus altissima woods by alkali glycerol delignification are presented. The Langmuir isotherm model is only applicable to batch adsorber systems where sufficient time is provided to allow equilibrium between toxic metal ion in solution and the toxic metal ion adsorbed on the media to occur. The maximum adsorption capacities are 7.1–7.7 and 4.4–5.3 mg per g of the modified lignin for), Co(II) and Hg(II), respectively. The adsorption of the heavy metal ions increases with pH.     

Impact of heavy metals in Indian fly ashes on its application as soil ameliorant

Coal contains various organic and inorganic substances including trace quantities of the heavy metals. Therefore, the combustion of coals releases some of the ultimately to the environment of some heavy metals elements in the form of their oxides and in a redistribution of these heavy metals in the surface soil and water bodies, particularly in the vicinity of coal-fired power plants. The fly ash and pond ash of different thermal power stations of India were mixed with soil at different doses separately to compare their impact on crop produce and soil. The present study deals with the presence of the heavy metals in the coal ash and its movement through the amendment of coal ash to the soil and crop produce.     

An incremental model for coal evaluation—I. Liquefaction

Because of differences in requirements for specific applications, coal values can vary greatly. We have devised a model to evaluate feedstock coals for hydrogenative liquefaction. In this method, incremental values are assigned to conventionally available quality parameters of coal based on stoichiometry, technology and general process economics. In addition, incremental values for variations in chemical reactivity, mechanical property and transportation cost were derived. These incremental values represent quantitative expressions for premium and discount of the coal with variations in quality. The relative values of coal may be calculated from these incremental values by using a simple procedure. The model provides a guide in technical and marketing studies.As a feedstock to liquefaction, the most desirable qualities of coal decrease in the order: high hydrogen content > low oxygen content > low sulfur content > low nitrogen content > low ash > low moisture. Thus, a W. Virginia bituminous A coal is highly valuable as a feedstock for liquefaction but a New Mexico sub-bituminous coal is not. The model may be updated, but it is relatively insensitive to technology and remains useful even if the technology should advance substantially. The major factors determining these incremental values are stoichiometric requirements which cannot be altered by technology.     

凝汽式电站锅炉排烟温度偏高对供电煤耗的影响

在合理简化条件下,对国内凝汽式火力发电厂主流炉型亚临界、超临界、超超临界锅炉燃用大同烟煤、开滦烟煤、西山贫煤、阳泉无烟煤、元宝山褐煤的排烟温度升高引起供电煤耗提高的状况进行计算及分析.计算结果表明:当排烟温度升高5℃时,凝汽式电厂的供电煤耗提高约0.567～0.934g/kWh,当煤种相同时,过热蒸汽压力越高,排烟温度...     

Effect of the type of bed material in two-stage fluidized bed gasification reactors on hydrogen gas synthesis and heavy metal distribution

Different bed materials were tested for two-stage fluidized bed gasification, and the hydrogen gas composition and heavy metal distribution in the syngas were investigated. Silica sand, zeolite, calcium oxide, calcined coal, and activated carbon were used. For the results, using activated carbon resulted in the most significant increase in hydrogen after second stage (16.3 mol%) and had highest ratio of hydrogen gas in the syngas (53.1 mol%). For distribution of heavy metals, using activated carbon as bed material in the second stage, the concentration of trapped heavy metals was the highest. Regarding the emission of heavy metals, the use of calcined coal and silica sand resulted in the greatest emission concentration, and activated carbon had the lowest emission concentration. Therefore, to increase the amount of hydrogen gas produced in the gasification process and limit the emission of heavy metals, activated carbon is the best choice of these five bed materials.     

Adsorption of ciprofloxacin pollutants in aqueous solution using modified waste grapefruit peel

ABSTRACT

The feasibility of using discarded solid biomass as modified waste grapefruit peel (MWGP) for the removal of ciprofloxacin (CIP) pollutants from aqueous solution was explored in terms of equilibrium studies, kinetic studies, and adsorption mechanism elucidation. Characterization of MWGP by SEM and FTIR analyses indicate irregular pore structures and carboxylates as the active adsorption sites. Optimum adsorption conditions were determined in terms of pH, Na⁺/Ca²⁺ concentration, adsorbent time, adsorbent dosage, and initial concentration of CIP. Maximum uptake of CIP is 1.71 mmol·g^?1 under optimal experimental conditions. Adsorption data fit the Langmuir isotherm model and the adsorption process follows pseudo-second order kinetics. Mechanistic studies showed that electrostatic, hydrophobic, hydrogen bonding, and π-π interactions are the main driving forces for CIP adsorption on MWGP. These findings suggest that MWGP is a promising adsorbent for the removal of CIP from aqueous solutions.     

Modeling the behavior of selenium in Pulverized-Coal Combustion systems

The behavior of Se during coal combustion is different from other trace metals because of the high degree of vaporization and high vapor pressures of the oxide (SeO₂) in coal flue gas. In a coal-fired boiler, these gaseous oxides are absorbed on the fly ash surface in the convective section by a chemical reaction. The composition of the fly ash (and of the parent coal) as well as the time-temperature history in the boiler therefore influences the formation of selenium compounds on the surface of the fly ash. A model was created for interactions between selenium and fly ash post-combustion. The reaction mechanism assumed that iron reacts with selenium at temperatures above 1200 °C and that calcium reacts with selenium at temperatures less than 800 °C. The model also included competing reactions of SO₂ with calcium and iron in the ash. Predicted selenium distributions in fly ash (concentration versus particle size) were compared against measurements from pilot-scale experiments for combustion of six coals, four bituminous and two low-rank coals. The model predicted the selenium distribution in the fly ash from the pilot-scale experiments reasonably well for six coals of different compositions.     

Influence of functional group structures on combustion behavior of pulverized coal particles

The ignition and combustion behavior of pulverized coal was studied with respect to coal rank in a custom-designed visual drop tube furnace. The results showed that low-rank coals were ignited in a shorter time, mainly due to the presence of larger amounts of functional groups, while the ignition delay time of high-rank coals was longer. With increasing temperature and particle size, the ignition mode of coals shifted from heterogeneous into homogeneous, which was related to the increased yield of volatile matter. The chemical percolation devolatilization analysis results showed a clear relationship between the yield and composition of volatile matter and the amount and type of functional groups in coal. In addition, the tar yield was consistent with the amount of aliphatic hydrocarbons and the length of aliphatic chains, which explained the tailing combustion mode of the bituminous coal. The findings of the study showed that the yield and composition of volatiles in coal had a significant impact on the ignition behavior, which depended on the composition of functional groups, particle size, and the combustion environment.