Aral Olcay

Supercritical-gas extraction of two lignites☆

Abstract 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.

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

Abstract 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 1 H-decoupled pulse Fourier-transform (PFT) 13 C-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. 13 C-n.m.r. also reveals the presence of aromatic ether-O in polar fractions. Narrow aromatic signals in 100 MHz 1 H-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.

Supercritical-gas extraction of Turkish coking coal

Abstract Treatment of Zonguldak coal with toluene at 360 °C gave yields of extract which increased from 19–32% as the pressure of the extraction was increased from 11.6 to 29 M Pa. These yields were similar to those previously obtained by supercritical-gas extraction of lignites but the composition of the extracts differed. The lignite extracts contained a much higher proportion of petroleum ether-soluble material and only half the proportion of material insoluble in both petroleum ether and benzene than the Zonguldak coal extract. Benzene, biphenyl, naphthalene, phenanthrene, pyrene, benzoanthracene and be-nzophenanthrene nuclei were identified in the coal extract. Comparison of the yields of substituted benzenes with those obtained by low-temperature carbonization suggests that the proportions of different substitution pattern is determined by the structure of the fuel. Less naphthalene nuclei were found than expected but relatively large yields of biphenyls were obtained which were attributed to their formation from toluene in the presence of phenols.

Liquefaction of Turkish coals in tetralin with microwaves

Abstract The effect of the ratio of solvent to coal (S/C) and the period of heating by microwave on the solubilization of Turkish Coals (Beypazari, Bolu-Goynuk, Mugla-Yatagan, Soma-Merkez, Tuncbilek lignites and Zonguldak coal) in tetralin have been investigated. For the investigation of the effect of the S/C ratios with values of 4/1, 5/1, 6/1, 7/1 and 8/1, the coal samples were heated by microwave for 10 min. The results indicated that the optimum S/C ratio depends on the coal type to obtain the highest yields of THF solubles. The effect of microwave heating period was investigated at the values of 4/1 and 8/1 of S/C ratios and the heating period was changed from 2 to 10 min at 2-min intervals. The yield of THF solubles decreased with increasing heating period at the value of S/C ratio of 4/1, they increased with increasing heating period when the value of S/C ratio was 8/1. The yield of THF soluble coal products after 10 min of microwave heating period changed from 13% to 23%, depending on the coal type.

Centrifugal float-sink separation of fine Turkish coals in dense media

Abstract Zonguldak bituminous coal, Tuncbilek and Soma–Merkez lignites were each separated into two sub-fractions, coal rich and mineral matter rich, using a centrifugal float–sink separation technique in heavy media. An isopropyl alcohol (IPA)–carbon tetrachloride (CCl 4 ) mixture and a zinc chloride (ZnCl 2 ) solution, with a specific gravity of 1.40 g cm −3 at 25°C were used as dense medium liquids. The addition of surface active agents (Triton X-100 and Brij-35) to the zinc chloride solution improved the removal of minerals. The recovery and purity of the final product (float) obtained from the heavy media separation depend on such parameters as the density of the medium, rotor speed and centrifugation time. The separation efficiency of each coal differed significantly. Particle size distributions of the coals and their float and sink fractions were analysed using a Laser Particle Size Analyser. A Scanning Electron Microscope (SEM) was used to interpret the liberation of minerals from the coal particles.

Dissolution of two Turkish lignites in tetralin under hydrogen or nitrogen : effects of the extraction parameters on the conversion

Abstract Two Turkish lignites were extracted with tetralin in a batch autoclave under nitrogen or hydrogen atmosphere. The isothermal extraction temperatures ranged from 325 to 425 °C at 25 °C intervals and the isothermal extraction periods were 0, 30, 60 and 120 min. After removal of char and solvent, the remaining products, which were completely soluble in tetrahydrofuran, were separated into three fractions: preasphaltenes (benzene insolubles), asphaltenes (benzene soluble, n-pentane insolubles) and oils (n-pentane solubles) by successive extractions with benzene and n-pentane. The variations in coal conversion and soluble product composition were investigated with respect to the extraction conditions. The conversion was low below 350 °C but high above 375 °C. As the conversion of the lignites increases, transformation of tetralin to naphthalene also increases. An increase in extraction period affects the product composition but not the percentage conversion, at temperatures of 400 °C and above. In general, the effect of type of gaseous atmosphere on the total conversion was minor. Depending on the extraction conditions, however, the gaseous atmosphere affected the soluble product composition.

Investigation of dissolution mechanism of six Turkish coals in tetralin with microwave energy

Abstract Rates of formation of oil, asphaltenes, and preasphaltenes during liquefaction of six Turkish coals in tetralin with microwave heating have been experimentally determined. Five reaction mechanisms have been proposed and tested to estimate the rates of formation of products. Proposed mechanisms are based on assumptions that the reactions are irreversible and pseudo-first order with respect to the reacting species. Pseudo-first order rate constants for each of the indicated mechanistic steps have been calculated by multivariable non-linear regression analysis. The best fit between experimental data and models suggested was obtained from model 3 (this model suggests that oils, asphaltenes and preasphaltenes formed directly from coal) with Tuncbilek and Zonguldak, from model 4 (this model assumes oils to be produced directly from preasphaltenes in addition to being formed from coal according to model 3) with Mugla–Yatagan and Soma–Merkez, and from model 5 (this model describes conversion of coal to solvent fractionation products incorporating both series and parallel reactions) with Bolu–Goynuk and Beypazari coals. The results indicated that the reaction mechanism of coal liquefaction depends on the coal type.

Supercritical Dioxane Extraction of Spruce Wood and of Dioxane-Lignin and Comparison of the Extracts with the Pyrolysis Products

Abstract Samples of spruce wood and of dioxane-lignin prepared from spruce wood were subjected to supercritical dioxane extraction at 330 C. To compare the yield and the nature of the compounds present in distillate obtained upon pyrolysis to those of supercritical gas extract, the same samples were pyrolysed at 340°C. The extracts and distillates were separated into three fractions by solvent fractionation using hexane and benzene successively. The simpler compounds were identified by GC/MS and the yields of phenols were compared. More complex compounds insoluble both in hexane and benzene have been characterized by 1H NMR spectrometry. It was found that the supercritical extracts and the pyrolysis distillates contained similar compounds; however, demethoxylation during pyrolysis was extensive compared to supercritical gas extraction which occurred under rather mild conditions.

Mild oxidation of reductively ethylated solid fuels

Abstract A reductively ethylated lignite and a reductively ethylated coking coal have been oxidized by alkaline nitrobenzene. The products of the oxidation were separated into fractions by extraction with organic solvents, and the compounds present in the resulting solutions were characterized by a combination of gas chromatography and mass spectrometry. These compounds had molecular weights less than 300 and the oxidation, though mild, had fragmented the reductively ethylated fuels. Many problems remain, but the method appears to lead to an understanding of the structures of reductively ethylated solid fuels. The structures of the oxidation products are listed and discussed; in general they confirm the interpretation of the n.m.r. spectra of reductively ethylated solid fuels 2 .

Dissolution of lignites in tetralin at ambient temperature: effects of ultraviolet irradiation

Abstract The effects of ultraviolet (UV) irradiation, acid treatment and sunlight on the dissolution of Turkish lignites in tetralin have been investigated. Original and 0.01 N HCl washed lignite samples were exposed to UV irradiation for 24, 48, 72, 96 and 120 h and two samples were also exposed to sunlight for 1, 2, 3 and 4 weeks. Tetrahydrofuran (THF) soluble products were separated into three fractions: hexane solubles (oils), toluene solubles (asphaltenes) and toluene insolubles (preasphaltenes). As the irradiation period increased from 24 to 120 h, the yield of THF solubles increased. Sunlight had similar effects. Solubilization of 50% of the organic structure can be achieved, however, the yield of THF solubles depends on the lignite samples. Removal of exchangeable cations resulted in a decrease in the THF solubles at longer reaction times.