Supercritical-gas extraction of two lignites

Supercritical-gas extracts of two lignites have been obtained; the yields were similar to those reported for mature coals. The extracts have been fractionated and many of the compounds they contain have been identified by gas chromatography/mass spectrometry. The formation and yields of these compounds are discussed in terms of the structure of the parent fuels and the mechanism of extraction.     

The influence of process parameters on desulfurization of two Turkish lignites by selective oxidation

The chemical desulfurization of two high-sulfur Turkish lignites was investigated using a mixture of hydrogen peroxide in acetic acid. Sulfur removal was measured with respect to particle size, reaction time, reaction temperature and ultrasonic irradiation. In general, all inorganic sulfur and some organic sulfur were removed from these coals under mild conditions. Cayirhan lignite seemed more reactive towards peroxyacedic acid at slightly higher temperatures and longer reaction times, but under these conditions, solubility was high and yields of solid products declined. Reaction time and reaction temperature slightly changed the level of sulfur removal from Gediz lignite. The level of desulfurization was largely independent of the particle size for Gediz lignite, while sulfur removal from Cayirhan lignite seemed dependent of the particle size reaction temperature and reaction time.     

Chlorination kinetics of pyrite mineral in two Turkish lignites

The kinetics of the chlorination of pyrite in two Turkish lignites in water and water-carbon tetrachloride media at ambient pressure ( 610 mm Hg) are investigated. The effects of speed of stirring (5–20 s⁻¹), particle size (74–88, 150–180 and 250–425 μm), temperature (13–70°C) and reaction time (0–18 000 s) were studied. The experimental data were analyzed on the basis of the unreacted shrinking core model. The fine pyrite particles are assumed to be embedded inside the coal particles. The rate-controlling step was found to be diffusion of chlorine through the ash (the coal matrix). The activation energies were calculated as 25.1 kJ mol⁻¹ for Dada i coal in water medium and 25.0 kJ mol⁻¹ for Mengen coal in water-carbon tetrachloride medium.     

Aromatic products of 340 °C supercritical-toluene extraction of two Turkish lignites: an n.m.r. study

Fractions of Elbistan and Seyitomer (Turkish) lignites, extracted with supercritical toluene at 340 °C and 8 MPa, have been separated by solvent extraction and silica-gel chromatography. Analyses by n.m.r. and i.r. spectroscopies and other methods have been combined in structural-analysis schemes to yield information about the average molecule in aromatic extracts. Carbon aromaticities, f_a, derived from 22.63 MHz ¹H-decoupled pulse Fourier-transform (PFT) ¹³C-n.m.r. are more widely spread for Elbistan (0.34–0.56) than for Seyitomer (0.40–0.43), and are lower than for supercritical-gas (SCG) products from bituminous coals. ¹³C-n.m.r. also reveals the presence of aromatic ether-O in polar fractions. Narrow aromatic signals in 100 MHz ¹H-n.m.r. spectra suggest the presence of single-aromatic-ring average structures. In the hexane-soluble aromatics, 27% (Elbistan) and 29% (Seyitomer) of the available sites are substituted by alkyI groups, some of which are at least eight carbon atoms long; the hexane-soluble polar and asphaltene/asphaltol fractions contain fewer such groups.     

Sulphur removal by pyrolysis of Turkish lignites

Modes of distribution of sulphur have been determined in eleven lignite samples from major reserves in Turkey. Total sulphur contents have been found to vary 0.91%–10.32% on dry basis. The lignites contain relatively high amounts of organic sulphur. Distributions of sulphur have been determined in chars from the pyrolysis of lignites at 440 °C. Reductions in combustible sulphur contents have been found to vary 15.7%–72.0%. No correlation has been found between the extent of desulphurization by pyrolysis and the relative amounts of forms of sulphur in the parent lignites.     

The effect of moisture content and air-drying on spontaneous combustion characteristics of two Turkish lignites

The results of an experimental study aimed at evaluating the spontaneous combustion characteristics of two Turkish lignites moistured and air-dried at varying times are discussed. The spontaneous combustion characteristics of the coals were determined using Crossing Point Methods adapted to our laboratories conditions. The content of three predominant oxygen functional groups (carboxyl, hydroxyl, and carbonyl) of untreated, moisten and air-dried coal samples were also determined with wet chemical methods. The content of oxygen functional groups in moisten coal samples do not differ significantly that of untreated coal samples, for realized in vacuum desicator to moistured of coal samples. The liability of spontaneous combustion of the two coals was reduced when moisture content increased with increase in contacted time to water vapour. The moisten coal samples was dried in laboratory during 24 and 48 h time period. The concentration of oxygen contain functional groups of drying coal samples increased with increase of contact time with air and decrease of particle size. The liability of spontaneous combustion of the air-dried coal samples increased with increase of contacted time with air and with decrease of moisture content.     

Properties and potential of formed cokes derived from two Turkish lignites by carbonization of binderless briquettes

Two high-sulphur Turkish lignites were briquetted at room temperature under pressures of 113 or 212 MPa and the briquettes were carbonized to 1158–1173 K over special heating cycles. The lower-rank lignite gave a formed coke of superior mechanical strength, lower porosity and higher sulphur content than typical blast furnace cokes. The formed coke produced from the higher-rank lignite briquettes had slightly poorer mechanical strength, lower porosity and much higher ash yield and sulphur content than conventional cokes. The products were considered attractive for use in non-ferrous metallurgy.     

Depolymerization of Turkish lignites. I. Effect of substituted phenols

A lignite (C, 67.4 wt%) was depolymerized with phenol, p-nitrophenol and o-chlorophenol using sulphuric acid as catalyst. The solubility of the lignite was enhanced by these treatments, with phenol being the most reactive reagent whereas p-nitrophenol was the least reactive. The distribution of nitro- and chloro-groups in the solubilized products was investigated by infrared spectrometry and it was found that these groups were redistributed among the pyridine- and methanol-soluble materials. It is suggested that benzene-soluble material is produced by self-depolymerization of coal or by degradation of pyridine- and methanol-soluble material.     

Chemical cleaning of Turkish lignites by leaching with aqueous hydrogen peroxide

Two Turkish lignites (Beypazari and Tunçbilek) were leached with the solutions of hydrogen peroxide in water or in 0.1 N H₂SO₄. The effects of some process parameters, such as concentration, time and temperature, on the removal of ash and sulphur have been investigated. The rate of ash and sulphur removal are relatively high in the first 30 min, but slow after 60 min of the reaction time. Depending on the type of lignite, the maximum reductions ranged from 30 to 70% in ash, from 70 to 95% in pyritic sulphur, and from 42 to 58% in total sulphur. A relatively small reduction (a maximum of 25%) was estimated for organic sulphur. The optimum process conditions were established as a hydrogen peroxide concentration of 15 wt.%, a temperature of 30 °C and a leaching time of 60 min. High peroxide concentration or high temperature did not result in an appreciable further reduction in ash and sulphur. Due to partial dissolution or oxidation of the lignites, some organic material losses occurred but no heating value loss was estimated. An overall kinetic approach was also applied for pyritic sulphur removal, and the conversion data were analyzed by using both homogenous and heterogeneous reaction models.     

Depolymerization of Turkish lignites: 3. Effect of ultraviolet radiation

The effect of u.v. radiation on the product distribution of the acid-catalysed depolymerization reaction of a lignite (C, 66.9wt%) has been investigated. The products are separated by solvent extraction and silica gel chromatography and their ¹H n.m.r. spectra and molecular weights are also measured. Larger amounts of solubilized material are formed in the u.v.-irradiated depolymerization experiments due to a greater amount of phenol incorporation in the reactions. The relative molar masses of products are lower than those obtained from thermal depolymerization experiments and they contain less hydroaromatic structures connected by fewer methylene bridges. It is suggested that u.v. radiation is making the coal more accessible for phenol in the depolymerization reactions.     

石脑油芳烃抽提工艺改造与参数优化

大庆联谊石化股份有限公司50kt·a~(-1)芳烃抽提装置以常压石脑油为原料,在开工及生产过程中出现了芳烃混浊发泡、颜色发黄、抽余油芳烃含量不合格等问题,通过技术改造,解决了这些问题,优化了常压石脑油芳烃抽提工艺操作参数,取得了很好的经济效益。     

The effects of demineralization and swelling in producing active carbon from Turkish lignites

In this study, active carbon was obtained through chemical activation methods using some pretreatment to Gölbaşı (Adıyaman) and Kangal (Sivas) lignites. For both lignites, pretreatment was carried out in three steps. In the first step, demineralization was achieved by applying HCl–HF pretreatment to raw lignites. In the second one, raw and demineralized lignites were swollen not only with benzene but also with THF (tetrahydrofurane). Later, these two samples at 85 °C were exposed to chemical activation by impregnation with ZnCl₂. Chemical activation processes were carried out in a situation where samples on quartz board in a quartz tube in a cylindrical furnace were kept for 1 h at 500 °C, 100 ml/min N₂ flow speed and 30 °C/min heating rate. The active carbons produced were washed with 10% HCl and later with demineralized water. BET surface area of the active carbon samples was generally higher than 1000 m²/g. The surface area value of the Gölbaşı lignite was relatively higher than that of Kangal lignites. Similarly, the surface area value of the active carbons produced at the end of pretreatment with THF was higher than that of active carbon produced through pre-swelling using benzene. For all active carbon samples, ash, total sulfur and iodine adsorption values were different.     

Mobilization of some trace elements from ashes of Turkish lignites in rain water

Short-term water solubility characteristics of bottom ashes and fly ashes from two important Turkish lignites were investigated in association with the concentrations of some heavy metals. For this, the alkaline ashes were interacted with acidic rain water and dilute acidic solutions for leaching times changing from 10 min to 2 days to assess the mobilization potential during ash–water interactions. The concentrations of leachable trace elements such as chromium, lead, cadmium, zinc, and nickel were determined in leachate using Atomic Absorption (AA) Spectrometry. Iron concentrations were also investigated since it plays a critical role on trace element enrichment mechanism. The mineralogical and structural identification of the parent ash samples were carried out by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) techniques. The extent of the mobility of the ashes was identified regarding the physical and chemical properties of the ashes. Concentrations of the trace elements in leachates were compared to the several guideline values regulating the maximum contaminant levels in drinking water and irrigation water as well as the regulatory threshold concentrations in leachate.     

Catalysis of carbon-steam gasification by ash components from two lignites

Ash transfer from a reactive to a less reactive coal is an interesting possibility for improving and equalizing gasification characteristics of coals. To assess the catalytic action of coal impurities in the steam gasification of carbon, three approaches were used. In the first series, the effects of different coal ashes on the gasification kinetics of graphite were compared. A parallel study was made by adding lignite ash to a coal of low reactivity. Finally, gasification rates of chars prepared from demineralized coals were measured. While it was found that ash from reactive coals can significantly enhance the gasification rates of chars derived from coals of lesser reactivity, it was not possible to distinguish clearly between a catalytic lowering of the activation energy and an increase in the number of gasification sites. The gasification enhancement by lignite ash may open practical possibilities for blending coals of different reactivity, and warrants further study to identify the constituents associated with this effect.     

Investigation of polymerization parameters affecting dopamine selectivity of a polymeric membrane

Summary By means of electrochemical oxidative polymerization, poly (1,3-phenylenediamine) films on a gold electrode were prepared at a potential of 0.8 V. The permeation properties of polymeric films at the different thickness were investigated by cyclic and differential pulse voltammetry techniques. Voltammetric studies showed that polymeric film at the 1.2 mC thickness exhibited selective permeation for dopamine while rejecting ascorbic acid. Then, all the polymerization parameters affecting the permselective characteristics were systematically investigated and the optimal values were determined. Moreover, stability of polymeric membrane was examined. The results showed that polymeric membrane, owing to permselective character, could be used as a dopamine selective membrane. Received: 10 December 1999/Revised version: 12 March 2000/Accepted: 27 March 2000     

Investigation of affecting parameters on slip casting of yttria-magnesia IR-transparent bodies

Slip casting of MgOY₂O₃ suspensions has been investigated in this research. For this purpose relatively pure commercial raw materials were used. The Taguchi experiment method was used for design of experiments and selection of suitable solvents and dispersants and theirs optimum values. Preparation of suspensions was done in two stages, according to particle size distributions of powders after different milling time and Taguchi results. The best suspensions were selected based on viscosity and solid load of suspensions. Green bodies were slip casted using the optimized suspensions in order to obtain the green bodies with maximum density and a homogeneous structure in term of porosity size distribution. Results showed that using from ethanol as solvent, an optimum dispersant level of 3%wt. TEA +1%wt. DEA with a constant TEA/DEA ratio of 3/1 and mean particle size of 155 nm (milling time of 48 h) was the best choice for preparing of optimum suspensions. The highest relative green density of 65.91% was obtained for a suspension containing 35 vol % of solid particles casted under 3MPa. The dense Y₂O₃MgO submicron composite samples were sintered by SPS technique at 1250?°C under 70MPa for 6?min with a density about 99.5%.     

Steam extraction of essential oils: Investigation of process parameters

The steam extraction was used to investigate the process parameters important in the extraction of essential oils from the leaves of the Eucalyptus tree. The diffusion process and the application of Fick's law, as well as the temperature dependence of the diffusion coefficient were exhibited. This has enabled the setting up of a model that takes account of the initial amount of oil in the leaves and the effect of temperature. From the literature, it can be seen that the oil collected after an extended time represents all the oil that is present in the material initially. The research conducted indicates that the extraction temperature has a significant effect on the percentage of the initial oil that is eventually extracted, with the amount of oil extracted apparently decreasing for lower temperature. This effect could, however, be modelled accurately by simply considering the temperature dependence of the diffusion coefficient. This model can lead to the design of an optimum steam extraction plant.     

Gas formation regularities at the consecutive and simultaneous impact of ionizing radiations and heat on Turkish lignites

The regularities of formation of gases H₂, CO and hydrocarbons C₁-C₄ at the consecutive and simultaneous influence of ionizing radiations and heat on Turkish lignites of Karaman-Ermenek deposit was researched. It is shown that at the consecutive influence of radiation and heat the gas yield depends extremely on the preliminary irradiation dose. The simultaneous influence of these factors on lignite leads to the gas yield increase which is connected with acceleration of the active radiolytic particles’ diffusion and breaking off reactions with their participation. Under the influence of the accelerated electron beam lignite decomposes with the relatively high radiation-chemical yields than under the influence of gamma radiation which is connected with acceleration of the diffusion processes due to the irradiated sample’s heating.