Über die Änderung der Zusammensetzung des Rohmontanwachses bei Benzolextraktion von Braunkohlen

Change of Composition of Crude Montana Wax During Benzene Extraction of Lignites Studies were carried out concerning the yield and change in group composition of benzene extracts of different lignites in relation extraction parameters. Special attention was devoted to kinetics of extraction, temperature of extraction and type of lignite used. The group composition of the fractions obtained is highly characteristic, which is mainly dependent upon temperature of extraction and resin content of the lignite bitumen. At a temperature of 20° C and lower mainly resins are extracted with benzene. The studies permit the prediction of several methods for the selective extraction of lignite with benzene for the preparation of crude montana waxes having low content of resins and asphalt. Thus the choice of raw materials in the lignite extraction can be widened.     

Petrographic composition and liquefaction behaviour of North Dakota and Texas lignites

Two US lignites (from Texas and North Dakota) were fractionated by density with appropriately prepared mixtures of liquid halogenated and non-halogenated hydrocarbons. Petrographic analyses confirmed that the procedure resulted in density fractions enriched in specific macerals. Liquid yields obtained upon solubilization at 430 °C and 5.5 MPa hydrogen pressure decreased with increase in the density fraction for both lignites. On plotting the total solubilities of lignites and their density fractions versus their huminite contents a reasonably good linear correlation was obtained (particularly for North Dakota lignite). It is tentatively concluded that in North Dakota lignite, as opposed to Texas lignite, macerals other than huminite did not significantly contribute to generation of liquid products.     

Extractable waxes from Greek lignites

An investigation on the solvent-extraction yields of Greek lignites has shown that the yields are generally low compared with the yields from certain American and German lignites, and similar to the yields from Czechoslovakian lignites. The highest yields were obtained from lignites of the Psachna deposit. The only extract which resembled rather closely in its nature the Riebeck crude montan wax was obtained by benzene extraction from Ptolemais lignite. The most significant differences between benzene extracts from Greek lignites and Riebeck crude montan wax were the differences in melting points and the greater resin content of the Greek waxes. Extraction with benzene/methanol mixture instead of benzene gave higher yields and extracts characterized by higher melting points, and higher acid and ester values. The compatibility of the extracts with paraffin wax was low; only benzene extract from Ptolemais lignite was completely miscible. No relation was found between the wax yield and the ratio volatile matter/fixed carbon of the coal. We also conclude that extraction of waxes from Greek lignites is not commercially attractive.     

Chromatographic separation of alkylated depolymerized Neyveli lignite

The study of macromolecular structure of coal has been subjected to intense research. Neyveli lignite was depolymerized using phenol and phosphotungstic acid and the resultant product was subsequently alkylated. The t-butylated depolymerized lignite exhibited enhanced extractability in organic solvents. The t-butylated depolymerized lignite was fractionated into different components using column chromatography (CC). Three major compounds were isolated and were characterized by FTIR, ¹H NMR and Mass spectral techniques.     

Investigation of parameters affecting atmospheric extraction yields and extract qualities of two Turkish lignites

Four sets of extractions of two Turkish lignites have been performed at atmospheric pressure in Soxhlet-type extractors varying the time of extraction, particle size of the lignite, its moisture, and the solvent. Extractions performed in small-size Soxhlet extractors (capacity 90 g coal) with benzene as the solvent have shown that for the Mengen lignite the most appropriate size range is 20–60 Tyler mesh and the moisture content leading to highest yield is 10–12 per cent. For the Elbistan lignite the corresponding values are 10–60 Tyler mesh and 20 per cent moisture. Extractions carried out with benzene in a larger-size Soxhlet apparatus (capacity 1–1.5 kg coal) have shown that Mengen lignite should be extracted for 30 hours and Elbistan lignite for 24 hours for exhaustion. Most of the extractable material can be obtained in the first five hours in the case of Elbistan lignite and in the first 10 hours in the case of Mengen lignite; the difference is attributed to different porosities.Extractions carried out using various solvents in larger-size Soxhlet extractors under the most appropriate conditions as determined from the first three sets of experiments have indicated that Mengen lignite may be a promising raw material for industrial-scale montan wax production. Yields varying between 10 and 14 per cent on dry basis have been obtained from Mengen lignite with benzene—ethanol, benzene—methanol and tetrahydrofuran as solvents. Elbistan lignite gives a maximum yield of 3.5 per cent with tetrahydrofuran. Solvents characterized by a high substitution ability yield more extract. Montan waxes obtained from Mengen and Elbistan lignites are found to be richer in free acids and esters compared with commercially available ones. Infrared spectra results indicate the raw wax to be predominantly aliphatic. The melting points of the waxes obtained with various solvents are generally found to increase as the asphaltic matter content increases and resinous matter content decreases.     

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.     

Determination of dominant macerals from some Turkish Tertiary lignites by means of heavy-liquid separation: a case study

The effectiveness of density separations on the maceral group composition of lignite and sub-bituminous coal samples taken from five different localities has been investigated. Although mineral rich and organic rich, some mineral poor fractions could be obtained. A technique of van Krevelen, ‘Coal’, Elsevier, 1961, p. 113, was unsuccessful in separating the lignites into their maceral groups.     

Sulfur removal from original and acid treated lignites by pyrolysis

Six original, three hydrochloric acid treated and three demineralized lignite samples were pyrolysed at seven different temperatures between 350 and 950 °C for 7 min under evolved gas atmosphere. All samples and their chars were analysed quantitatively for their total sulfur content and pyritic, sulfate and organic sulfur forms. The alkaline oxide contents of original lignites and their hydrochloric acid treated counterparts were determined. The results clearly indicate that calcium and sulfurous compounds in the parent lignites undergo various chemical changes during pyrolysis. The pyrolysis temperature, types of sulfur and calcium compounds, all affect the behaviour of sulfur during pyrolysis. Higher pyrolysis temperatures favour total sulfur removal for all lignites, reaching 30-54% around 850 and 950 °C. HCl treatment and demineralization decreases calcium contents, hence, increases quantitative sulfur removal from the lignites by pyrolysis. The maximum total sulfur removal from acid treated lignites is observed as 77%. The ratios of the total sulfur to heating value decreases with increases of pyrolysis temperature up to around 600 °C for acid treated lignites and no major changes are observed at higher pyrolysis temperatures; no common behaviour is observed for original lignites.     

Gelation of water–bentonite suspensions at high temperatures and rheological control with lignite addition

The effectiveness of lignite addition to prevent gelation of 6.42% w/w water–bentonite suspensions exposed to high temperatures has been studied, using twenty six lignites from various basins in Greece with variable organic and inorganic contents at concentrations of 0.5% and 3.0%. The lignite-free bentonite suspensions thickened considerably when heated at 177 °C for 16 h, as was indicated by a two-fold increase of the yield stress, when compared to samples hydrated only at room temperature. However plastic viscosity did not change appreciably. Full flow curves showed a Herschel–Bulkley behavior of all suspensions. Addition of lignite maintained the stability of the suspensions exposed to high temperatures (177 °C) by keeping the yield stress low and did not affect plastic viscosity. Some of the Greek lignites performed equally well with a commercial lignite product and improvements of 80 to 100% of the stability of the suspensions, compared to lignite-free suspensions, have been found. Lignite addition also lowered yield stresses for the hydrated samples. No specific trends have been identified between the effectiveness of lignites to stabilize bentonite suspensions and their humic and fulvic acids and humins content. However, those lignites with highest humic and fulvic acid contents have maximum stabilization capacity. Similarly, no specific trends have been observed between the stabilization capacity of lignites and their inorganic components such as oxygen and ash content and also with the cation exchange capacity. The effectiveness of the Greek lignites to stabilize bentonite suspensions is very high and the minor differences in the efficiency of the different lignites cannot be attributed solely to any specific component.     

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.     

Catalysis of lignite char gasification by exchangeable calcium and magnesium

A Montana lignite was pretreated in either HCI—HF or ammonium acetate. The former treatment replaced cations associated with carboxyl groups by hydrogen, as well as removing essentially all mineral matter. The latter treatment replaced cations by ammonium ions but left the mineral matter intact. The pretreated lignites were then loaded with varying amounts of Ca and Mg, separately or jointly, by ion exchange. Reactivities of chars produced from these exchanged lignites, as well as the raw and pretreated lignites, were determined in air, CO₂ and steam. Gasification of exchanged lignites was strongly catalysed by Ca; its activity was not affected by the presence of Mg on the char. At a comparable Ca loading, gasification rates of the 1273 K raw lignite char in the various atmospheres was higher than that of the acid treated 1273 K char but lower than that of the ammonium acetate treated 1273 K char. The former finding is attributed to chlorine retention in the lignite and char; the latter, to enhanced sulphur release during lignite pyrolysis.     

Effect of precarbonization temperature on liquefaction of lignites

Soya Koishi and North Dakota lignites were precarbonized at 350, 400 and 420 °C to reduce the oxygen content prior to hydrogenation at 400 °C under an initial hydrogen pressure of 10 MPa for 1 h. After hydrogenation, the solubility in tetralin and benzene remained almost constant to the precarbonization temperature of 420 °C for Soya Koishi lignite and 400 °C for North Dakota lignite. The hydrogen consumption decreased by ≈25% for the former and by ≈50% for the latter. The hydrogen content also decreased by precarbonization which increased the tetralin-insoluble fraction.     

Depolymerization of Turkish lignites. 2. Effect of phenol concentration in a closed system

A lignite (C, 66.9 wt%) was depolymerized, using sulphuric acid as a catalyst, in a closed system in which the phenol/coal ratio was varied from 1.5 to 10. The products were separated by solvent extraction and silica gel chromatography. The i.r. and n.m.r. spectra, and the molecular weight of the products were measured. In the experiments with a phenol/coal ration of 10, complete depolymerization of the coal was seen provided the temperature of depolymerization was at least 210 °C. The products generally contained disubstituted aromatic structures connected by methylene bridges, it was found that as the phenol/coal ratio was increased there was a decrease in the number of methylene bridges connecting the aromatic structures. The molecular weights of the straight-chain pentane and benzene-soluble material were lower than the molecular weights of similar fractions in depolymerization experiments carried out in open systems. A method for the structural analysis of straight-chain pentane and benzene-soluble material based on i.r., ¹H n.m.r. and molecular weight measurements is suggested.     

Combustion of lignite carbon under agitation

To get insights into the burning of large coal particles as agitated beds in the recently developed rotary chambers, combustion behaviour of eight Turkish lignites was studied in a laboratory-size rotating wire mesh basket. Single particles from 0.5 to 5 g average weight were loaded in the basket, which was then inserted into a preheated tube furnace. The net effect of removing ash continuously as a result of agitation on the combustion rates and times was searched for all the lignites, whereas the other parameters, such as rotation speed of the basket, particle size, temperature and air velocity, were investigated on only Çan lignite. Because both volatile and char combustion times and their confident prediction have important bearings in the design and capacity of coal combustion systems, experimentally determined char combustion rates and times were compared to those found by using double resistance theory. It was observed that combustion of lignite chars in the agitated beds proceed faster and lasted in shorter times as expected, mainly due to the removal of ash layer by agitation during the period of char combustion. The influence of the agitation on the combustion of chars from lignites with high-volatile matter content was especially noticeable. Combustion rates increased more as the speed of basket was increased. A combined control mechanism could be used to describe combustion rates of lignite chars.     

The effect of the calcium in lignite on its effectiveness as a reburn fuel

The effect of the calcium present in lignite on the effectiveness of NO reduction in the reburning method has been studied in the 900-1100 °C temperature range. Lignites from three Polish mines were used. The experiments were carried out in a laboratory scale drop-tube furnace reactor. The demineralised lignites were loaded with Ca using: calcium acetate Ca(CH₃COO)₂, calcium hydroxide Ca(OH)₂ and calcium carbonate CaCO₃. For the reburning process the catalytic effect of the presence of calcium in lignite was found to be rather modest (approx. ±20%) in the temperature range studied. It was shown that up to 1000 °C the calcium added to the demineralised lignites improved their effectiveness as reburn fuels. The effect was almost reversed when the reburn temperature was raised to 1100 °C. With the impregnated lignites the extent of NO reduction appeared to be practically independent of the calcium compound used. Mineral matter in raw lignite exerts a similar catalytic effect to calcium introduced by impregnation.     

Effectiveness of Polish lignites as reburn fuels

The effectiveness of four Polish lignites as reburn fuels was studied in the laboratory-scale drop-tube furnace. The established rank of the lignites and chars used correlates with concentration of calcium in lignite. A comparison of the reburning effectiveness of partially devolatilized chars with that of the parent lignites showed that the parent lignites achieved a higher NO reduction than the chars.     

Characteristics and composition of lignites and boiler ashes and their relation to slagging: The case of Mae Moh PCC boilers

In order to examine the cause of occasional slagging problems, a dedicated 7-day sampling and data collection were carried out on two 300-MWe units of Mae Moh power plant owned by the Electricity Generating Authority of Thailand. The properties of feed lignite varied from low (∼11% in ash) to medium (∼18% in ash) CaO content during the sampling period. The elemental content was measured for collected fly ashes, bottom ashes and slags, and compared with those of the feed lignite. The analysis and operational data obtained during the 7-day sampling period were compared with those obtained from the additional laboratory-scale investigation of high Ca lignites and those obtained from one of the units during another period when slagging problem was experienced. The study found that, apart from Ca, the concentration of three other elements and their compounds - Fe, Al and Si, plays a very important role in slag formation and its control while these lignites are used in large utility units. The flue exit gas temperatures (FEGT) of the unit experiencing slagging were also found to approach the initial deformation temperatures (IT) of the lignite ash. The solution appears to be the monitoring of the concentration of four elements, i.e. oxides of Ca, Fe, Al and Si in the feed lignite, and in ensuring through proper mining or blending that concentration of CaO, Fe₂O₃ and Al₂O₃ is kept <20%, ∼15% and >15%, respectively, at all times. Also, it is important that the FEGT during operation is kept sufficiently below the IT of the ash of feed lignite at all times.     

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

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.     

Reaction of coals in hot acidic phenol at constant acid concentration

Previous work showed that the efficient ‘depolymerization’ of bituminous coals in hot phenol containing p-toluenesulphonic acid failed to occur and that the acid was destroyed during the reaction. Four coals varying in rank from lignite to low volatile bituminous were treated with refluxing phenol containing p-toluenesulphonic acid with the acid concentration held constant. The amount of colloidal material, of pyridine-soluble material, of benzene—ethanol solubles, and the number average molecular weight of the pyridine extractables were measured as a function of time. Although the reaction proceeds better with the lower rank coals, a large portion of the products is colloidal material. Treatment of coals with hot acidic phenol does not lead to their complete depolymerization. Treatment of Bruceton coal with refluxing phenol saturated with BF₃ also failed to give complete depolymerization. The formation of colloidal suspensions during investigations employing spectral and other physical measurements may lead to results that are susceptible to misinterpretation.     

Retention of metallic cations by lignites and humic acids

Adsorption of strontium, lead, uranium and thorium ions from their solutions by several Spanish lignites have been studied. Adsorption isotherms are adequately described by means of the Langmuir equation and can be characterized by two numerical constants: the sorption capacity of lignite, and the geochemical enrichment factor (GEF). Very high values of this GEF have been found for heavy metals. Humic acids were extracted from the lignites and their metal binding ability was determined as a function of pH. Higher pH favours metal retention, also higher atomic weight and valency. A role of humic substances in the retention and accumulation of metals in coals is suggested.