Mongolian Academy of Sciences Mongolian Journal of Chemistry The Institute of Chemistry & Chemical Technology Mongolian Journal of Chemistry 14 (40), 2013, p12-19 INTRODUCTION Coal is the major energy source and feedstock of chemical industry among fossil resources in the coming century because of its abundant reserves and easy availability. Because of instability on world oil market, the diversification of energy carriers is practically implemented in many countries with involvement of various nontraditional types of organic raw materials, primarily, coal, whose reserves are much greater than oil and gas reserves. Mongolia is the country of lack of oil source with relative rich in coal resource. Mongolia has 20 billion tons of proven coal reserves and estimated resources totalling 163 billion tons, mostly of them is low-rank brown coal, but remains undeveloped due to a lack of infrastructure. Such reserves include the huge Tavan tolgoi deposit in the South Gobi, which contains over 6.4 billion tons of high quality stone and coking coal, but lies more than 400 km from the nearest railway. There is a large brown coal basin (Jurassic origin), which contains the Baganuur, Ovdogkhudag, Aduunchuluun, Tevshiin govi, Khoot, Tsaidam nuur and Shivee ovoo deposits and this is located in the central economic region of Mongolia [1]. The most important features of these deposits are accessed by opencast mining and coal can be transported using the nearby railway. In Mongolia coal is currently the main energy carrier for thermal power plants and local boiler houses and there is almost no other form of large-scale coal utilization industry [2]. Now Mongolia exports about 15 million tons raw coal by trucks from the South gobi to China. However, coal samples from the Tavan tolgoi deposit have been assessed for benefication [3] and coke production [4], samples from Baganuur, Bayanteeg and Shivee ovoo deposits as fuel for pyrolysis [5], hydrogenation [6] and gasification [7, 8]. Also samples from Ovdogkhudag and Aduunchuluun deposits have been assessed for their liquefaction potential using facilities in Japan [9]. At present time Mongolian government pays much more attention for the future development of coal processing industries such as coal benefication, coking, semicoking, gasification and liquefaction. There are already established several small scale semicoking factories in Ulaanbaatar and in Darkhan for production of smokeless fuel. The “Energy Resourses” Company built a middle- scale coal washing factory in South gobi. Mongolian government is planning to establish a coking factory in the framework of “Sainshand” industrial park and “MAK” company a coal liquefaction factory on basis of Aduunchuluun coal deposit. How to convert coal into oil and gas is a major issue in the country, which will affect the national safety and the economic sustainable development. Therefore more detailed investigation of above mentioned most important coal deposits by using of modern instrumental analysis such as petrographic and different pyrolysis experimental sets is very important for the future development of coal processing industries in Mongolia. Investigation on characterization and liquefaction of coals from Tavan tolgoi deposit B. Purevsuren 1 , S. Jargalmaa 1 , B. Bat-Ulzii 1 , B. Avid 1 , T. Gerelmaa 1 1 Institute of Chemistry and Chemical Technology, MAS, Peace avenue, Ulaanbaatar 13330, Mongolia ARTICLE INFO: Received 16 October 2013; revised 18 October 2013; accepted 21 October 2013 Abstract: On the basis of proximate, ultimate, petrographic and IR analysis results have been confirmed that the Tavan tolgoi coal is a high-rank G mark stone coal. The results of X-ray fluorescence analysis of coal ash show that the Tavan tolgoi coal is a subbituminous coal. The ash of Tavan tolgoi coal has an acidic character. The results of pyrolysis of Tavan tolgoi coal at different heating temperatures show that a maximum yield - 5.0% of liquid product can be obtained at 700 o C. The results of thermal dissolution of Tavan tolgoi coal in tetralin with constant mass ratio between coal and tetralin (1:1.8) at 450 0 C show that 50.0% of liquid product can be obtained after thermal decomposition of the COM (coal organic matter). Keywords: coal, pyrolysis, petrographic analys, mineral compounds, thermal dissolution * corresponding author: e-mail: bpurevsuren.icct@gmail.com 12 Mongolian Journal of Chemistry 14 (40), 2013, p2-3 EXPERIMENTAL The type, resource and other information of the coals of Tavan tolgoi deposit are given in Table 1. The analytical samples of coals from these 2 deposits were prepared according to Mongolian National Standards (MNS) and main technical specifications including moisture (MNS 656-79), ash (MNS 652-79), volatile matter (MNS 654-79), caloric value (MNS 669-87), sulphur content (MNS 895-79) have been determined. Table 1. Some informations about coal samples of Tavan tolgoi deposit Name of deposit Type Location of the coal deposit Approx. resources in million ton Discovered in Tavan tolgoi High rank bituminous and coking coal Tsogttsetsi village of Southgobi aimak,14 km from the Tsogttsetsi soum to the south and 600 km from Ulaanbaatar to the South gobi Geological reserves 6.4 billion tones In 1966 The pyrolysis experiments of coal samples were performed in a laboratory small quarts retort (tube) which could contain air dried and powdered to a particle size < 0.2 mm 1 g- of coal sample. The retort was placed in a horizontal electric tube furnace with a maximum heating temperature of 950 0 C. A chrome- alumel thermocouple was immersed in the tube furnace to measure the actual heating temperature.The pyrolysis experiments have been carried out at different heating temperatures 200 - 800 0 C with constant heating rate 20 0 C/min. First of all the quarts retort with coal sample was heated for example to 600 0 C with heating rate 20 o C/min. and kept at 600 0 C for 80 min. The retort was connected with a thermostable glass tube heated also in a tube furnace at 80 0 C for collecting of tars and this tube is also connected with a air-cooled glass vessel for collecting of pyrolysis water. The glass vessel for pyrolysis water is also connected with a thin glass tube for non-condensable gases [10]. The yields of pyrolysis products including solid residue (coal char), tar (condensed liquid product) and pyrolysis water determined by weighing, and the yield of gases by differences. For petrographic studies samples were embedded in a resin, ground flat and polished. All samples were cuttings which were embedded without any specific orientation. Vitrinite reflectance was measured following the standard procedures [11]. It was attempted to measure 50 particles per sample. In addition, fluorescence microscopy was used for rapid qualitative information on maturity and organofacies. Resedimented vitrinite particles are characterized by higher reflectivity than autochthonous vitrinite. Usually, only the vitrinite population with the lowest reflectance values is measured and reported. For the determination of mineral content in both coals have been obtained completely burned ashes of coals during slowly and continuously burning in furnace at 200 - 850 0 C. The content of mineral elements in both coal samples and their oxides have been determined by using of X-ray fluorescence spectrometry. The thermal dissolution of coal samples have been carried out in a laboratory standard stainless steel autoclave by using tetralin as a hydrogen donor solvent. Air dried for 24 h, and powdered to a particle size < 0.2 mm 1g coal sample mixed with 1.8g tetralin (mass ratio 1:1.8) in autoclave and heated in a laboratory furnace at temperatures of 350, 400, 450 o C for 2 h. After completion of experiment the autoclave with sample cooled at room temperature and removed all uncondensed gas and resulting liquid products were filtered, and the solid residue on filter was subjected to sequential extraction with chloroform in a Soxhlet apparatus. An extract of liquid products of thermal dissolution of coal in tetralin was distilled by a laboratory rotary evaporation apparatus for complete removing of chloroform. The degree of coal conversion was determined from the loss of the organic matter of coal (OMC) after extraction and also change in the ash contents of the initial coal samples and the insoluble residue. RESULTS AND DISCUSSION The results of ultimate and proximate analysis of coal samples of boreholes no.4 and 8 from Tavan tolgoi deposit are shown in Table 2. The technical characteristics of Tavan tolgoi coals in Table 2 show that the content of ash in borehole VIII is higher than in borehole IV. The content of sulfure in Borehole VIII is a little bit higher than in Borehole IV and in generally both are comparatively lower which is good for environmental point of view. Table 2. Proximate and Ultimate analyses of Tavan tolgoi coals Coal samples of Tavan tolgoi Proximate analysis, % Ultimate analysis, % Borehole IV W a А d V daf Q daf Stotal С daf % Н daf % (N+O) daf , % 0.82 14.8 29.9 7524 0.98 84.0 5.42 10.25 Borehole VIII 0.94 18.4 35.7 7283 1.4 76.0 4.40 19.17 13 Mongolian Journal of Chemistry 14 (40), 2013, p2-3 Also the content of volatile matter in Borehole IV is lower and caloric value is higher than in Borehole VIII. It means that the coal of Borehole IV has a characteristic of a higher quality than Borehole VIII. The content of C is higher and O is lower in Borehole IV coal than in Borehole VIII. First time these two coal samples have been characterized with petrographic analysis by microscopic photograph of specially prepared and polished samples and the petrographic photographs (two photographs from each samples) are presented in Figure 1. Fig. 1. The petrographic photographs of polished coal samples of Tavan tolgoi deposit: Photograph of coal from borehole IV; B- photograph of coal from borehole VIII. There are clearly indicated bright segments (parts) in the petrographic photographs of two coal samples (Figure 1, A, B) which is the specific petrographic characteristic of vitrinite maceral groups in the organic maturity of the high-rank coal. The next step of petrographic analysis is to measure the value of so called vitrinite reflectance (%RVt) of points as much as possible on these bright segments (parts) in the petrographic photographs. We have chosen about 50 points on more bright pattern of these photographs and the measured results of %RVt are given in Table 3 and 4. Table 3. The measured results of %RVt from the petrographic patterns of borehole IV coal samples. № Ref, % Time № Ref, % Time 1 0.872 28.9 26 1.004 285.6 2 0.891 32.8 27 1.007 287.8 3 0.838 127.8 28 0.998 289.8 4 0.659 130.5 29 0.875 292.0 5 0.755 133.5 30 0.870 338.7 6 0.876 146.2 31 0.834 342.9 7 0.931 148.7 32 0.801 348.9 8 0.831 151.5 33 0.822 350.5 9 0.856 157.5 34 0.890 353.9 10 0.943 179.5 35 0.951 355.9 11 0.848 181.1 36 0.948 357.8 12 0.761 183.2 37 0.957 359.3 13 0.847 186.5 38 0.904 361.8 14 0.953 210.6 39 0.890 422.0 15 0.941 213.7 40 0.897 425.1 16 0.965 216.4 41 0.883 426.3 17 1.022 221.0 42 0.828 428.0 18 1.016 223.9 43 0.835 430.5 19 0.988 226.4 44 0.880 433.2 20 0.958 228.7 45 0.902 449.0 21 0.890 230.5 46 0.809 451.7 22 0.971 232.7 47 0.873 453.5 23 0.886 235.9 48 0.849 454.2 24 0.910 240.9 49 0.773 455.0 25 1.047 283.7 50 0.899 457.5 14 Mongolian Journal of Chemistry 14 (40), 2013, p2-3 The measured results of %RVt from the petrographic patterns of 2 coal samples in Table 3 and 4 are summarized and shown as a diagrams (Figure 2) for determination of averaged value of %RVt for each coal samples. Table 4. The measured results of %RVt from the petrographic patterns of borehole VIII coal samples. № Ref, % Time № Ref,% Time 1 0.843 74.7 26 0.731 295.3 2 0.680 77.6 27 0.932 320.1 3 0.749 80.0 28 0.969 322.2 4 0.724 83.6 29 1.005 323.3 5 0.904 120.9 30 0.990 325.3 6 0.917 123.2 31 1.006 329.4 7 0.855 125.0 32 0.917 339.9 8 0.851 127.4 33 0.891 377.8 9 0.836 128.7 34 0.927 379.8 10 0.863 129.6 35 0.936 383.7 11 0.814 131.1 36 1.030 399.1 12 0.875 132.6 37 0.740 428.8 13 0.821 143.2 38 0.735 446.6 14 0.813 145.6 39 0.670 448.4 15 0.812 149.8 40 0.830 462.6 16 0.773 152.5 41 0.875 464.6 17 0.791 163.9 42 0.815 465.6 18 0.822 278.1 43 0.835 467.4 19 0.751 280.0 44 0.814 468.1 20 0.772 280.9 45 0.853 510.5 21 0.782 283.2 46 0.847 512.4 22 0.746 285.1 47 0.792 519.7 23 0.792 287.2 48 1.009 527.8 24 0.809 289.7 49 0.985 537.2 25 0.677 292.7 50 0.974 537.8 A B Fig. 2. The diagrams for determination of averaged value of %RVt for coal of Tavan tolgoi deposit: A – for borehole IV; B - for borehole VIII. From the Fig. 2 have been determined the averaged value of %R Vt for coal of borehole IV(A) is 0.893% and for coal of borehole VIII (B) is 0.844%. The determined averaged vitrinte reflectance (%RVt) of each coal samples confirm that the Tavan tolgoi coal has a characteristic (%RVt = 0.893% - 0.844%) of high-rank G mark coking coal [10 P.157]. For the characterization of two coals from Tavan tolgoi deposit have been carried out IR analysis of each coal samples (IR spectra of borehole IV coal in Figure 3 and IR spectra of borehole VIII coal in Figure 4). 15 In the IR spectra of coal from borehole IV and VIII can be recognized following absorption frequency regions: 700 - 900 cm -1 for Car-H; 1000-1300 cm -1 for vibration of bonds in various oxygen-containing groups; 1350 - 1470 cm -1 for vibrations of –CH, - CH2 and – CH3 groups; 1500 - 1630cm -1 for skeletal vibrations of aromatic rings, >C=O bonds in ketones, aldehydes and quinines; 2800 - 2950 cm -1 for stretching vibrations of –CH. -CH2 and – CH3 groups in saturated aliphatic structures; and 3030 -3350 cm -1 for stretching associated vibrations of – OH groups in aromatic rings and aliphatic structures. The both IR spectra are similar. In the case of Tsaidamnuur coal IR spectra have very week and continous absorption bands (the absorption bands are not sharp). The content of mineral elements in both coal samples and their oxides has been determined by using of X-ray fluorescence spectrometry and the results are shown in Figure 5 and 6 and Table 5. Mongolian Journal of Chemistry 14 (40), 2013, p2-3 Fig. 3. The IR spectra of coal from borehole IV Fig. 4. The IR spectrum of coal from borehole VIII Fig. 5. The X-ray fluorescence spectrogram of coal Fig. 6. The X-ray fluorescence spectrogram of coal ash of VIII from Tavan tolgoi deposit ash of IV from Tavan tolgoi deposit The dates in Figure 5 - 6 and Table 4 show that highest content of elements have Si, O and SiO2 in coal ash of both samples of Tavan tolgoi deposit. In the case of Al, Fe, Ca, S and Al2O3, Fe2O3, CaO, SO3 their contents are in a middle position in both samples. Lowest contents have K, P, Ti, Mn, Zn, Sr and their oxides in both coal ashes. The sum of CaO and MgO (CaO+MgO