Effect of coal soluble constituents on caking property of coal

Three cokemaking bituminous coals were extracted by the CS₂/NMP mixed solvents with different content of NMP, and the effect of the amount and the component of coal soluble constituents on the caking property of the extracted residues of coals were investigated in this study. The CS₂/NMP mixed solvent (1:1 by volume) was found to give the maximal extraction yields for the three coals, and the fat coal gave the highest extraction yield of 78.6% (daf) corresponding to its highest caking index of 101. It was found that for coking coal, when the extraction yield got to the maximum of 25.3% in the 1:1 by volume of CS₂/NMP mixed solvent, the residue extracted still had caking property with the caking index of 19. This means parts of the caking constituents of coal are un-extractible because of covalent bonding or strong associative cross-links. The soluble components extracted by the CS₂/NMP mixed solvent and their effects on the caking indexes of the residues at a similar extraction yield quite differed depending on the NMP content in the mixed solvent. The coal solubles extracted by the CS₂/NMP mixed solvent with NMP less than 50% contained less light constituents with less of oxygen groups. This may lead to the decrease in the caking indexes for the residues obtained at the similar extraction yields compared to those of the CS₂/NMP mixed solvent with NMP more than 50%.     

Comparison of the associative structure of two different types of rich coals and their coking properties

Solvent extractions of two different types of Chinese rich coals i.e. Aiweiergou coal (AG) and Zaozhuang coal (ZZ) using the mixed solvent of carbon disulfide/N-methyl-2-pyrrolidinone (CS₂/NMP) with different mixing ratios were carried out and the caking indexes of the extracted residues were measured. It was found that the extracted residues from the two types of coals showed different changing tendencies of the caking indexes with the extraction yield. When the extraction yield attained about 50% for ZZ coal, the extracted residue had no caking property. However for AG coal, when the extraction yield reached the maximum of 63.5%, the corresponding extracted residue still had considerable caking property with the caking index of 25. This difference indicated the different associative structure of the two coals although they are of the same coalification. Hydro-thermal treatment of the two rich coals gave different extract fractionation distributions for the treated coals compared to those of raw coals respectively. The coking property evaluations of the two coals and their hydro-thermally treated ones were carried out in a crucible coking determination. The results showed that the hydro-thermal treatment could greatly improve the micro-strengths of the resulting coke from the two coals, and the improvement was more significant for the more aggregated AG coal. The reactivities of hydro-thermally treated AG coal blends were almost the same as those of raw coal blends. The higher coke reactivities of AG raw coal and its hydro-thermally treated ones than those of ZZ coal might be attributed to its special ash composition.     

Flash pyrolysis of coals: influence of cations on the devolatilization behaviour of brown coals

The influence of cations on the pyrolysis behaviour of brown coals under flash heating conditions was investigated by means of a small fluidized-bed pyrolyser. A stream of coal particles in nitrogen was injected at rates of 1–3 g coal/h directly into a heated bed of sand fluidized by nitrogen. Yields of tar, C₁–C₃ hydrocarbons and total volatile matter from four Gelliondale brown coals and a Montana lignite were determined as a function of pyrolysis temperature. With all coals the maximum tar yield was obtained at 600 °C. Removal of cations present in the coals markedly increased the yields of tar and total volatile matter, with little effect on the yields of hydrocarbon gases. The converse was also observed in that the addition of Ca²⁺ to a cation-free coal decreased the yields of tar and total volatile matter. The extent of the reduction in tar yield at 600 °C in the presence of cations was found to be similar for all coals. After acid washing, tar yields appear to correlate with the atomic $\text{H}\text{C}$ ratios of the coals in a manner similar to that observed previously with bituminous coals.     

Pyrolysis—gas chromatography of Australian coals. 2. Bituminous coals

Pyrolysis—gas chromatography (Py—g.c.) was used to characterize quantitatively a series of high- to low-volatile bituminous Permian Australian coals. The levels of n-alkanes, n-alkenes and triterpenoids released by pyrolysis all decrease as a function of increasing rank and thus, the coal samples can be classified into three distinct groups. Carbon Preference Indices (CPI's) for alkanes and alkene/alkane ratios also decrease as a function of rank. The triterpenoids have exclusively the hopane skeleton. The hopane isomeric distributions exemplify the geological maturity of bituminous coals relative to brown coal (lignite). A significant correlation has been established between the level of n-alkanes and n-alkenes released under Py-g.c. conditions and the predicted oil yield by pyrolysis of these coals. Further development and application of the techniqueshould enable much to be learnt relating to the quality and yield of flash pyrolysis tars as well as the original coal macromolecular structure.     

Effect of acid treatment on thermal extraction yield in ashless coal production

Coals of different ranks were acid-treated in aqueous methoxyethoxy acetic acid (MEAA), acetic acid (AA), and HCl. The acid-treated coals were extracted with polar N-methyl-2-pyrrolidinone (NMP) and nonpolar 1-methylnaphthalene (1MN) solvents at temperatures from 200 to 360 °C for 10-60 min. The thermal extraction yields with NMP for some acid-treated low-rank coals increased greatly; for example, the extraction yield for Wyodak coal (%C; 75.0%) increased from 58.4% for the raw coal to 82.9% for coal treated in 1.0 M MEAA. Conversely, the extraction yields changed minimally for all the acid-treated coals extracted in 1-MN. The type and concentration of acid affected the extraction yield when NMP was used as the extraction solvent. With increasing MEAA concentration from 0.01 to 0.1 M, the extraction yield for Wyodak coal increased from 66.3 to 81.4%, and subsequently did not change clearly with concentration. Similar changes in the extraction yield with acid concentration were also observed with AA and HCl. The de-ashing ratio for coals acid-treated in MEAA, AA, and HCl also increased greatly with concentration from 0.01 to 0.1 M, which corresponded to the change in the thermal extraction yield in NMP. For the acid-treated coals, high extraction yields were obtained at lower extraction temperatures and shorter extraction times than for the raw coal. The mechanisms for the acid treatment and thermal extraction are discussed.     

The characterization of surface properties and steam reactivities of two Spanish coals of high ash content

Studies were made on two Spanish coals of high as content (a semi-anthracite and a high volatile bituminous coal) and on the coals after heat treatment and on acid demineralisation in HCl and HF. X-ray diffraction revealed that the mineral matter content of the coals included quartz, siderite and aluminosilicate minerals; siderite and the aluminosilicates were decomposed by heat treatment. Mineral matter content was substantially reduced by acid treatment, but the metallic element content, as revealed by EDAX, remained similar to that of the raw coals. N₂ and CO₂ adsorption isotherms and mercury porosimetry show that the coals contain mainly micropores and macropores, the semi-anthracite having the greater microporosity. For bituminous coal, macro- and micro-porosity increase substantially upon heat treatment; for anthracite there is a smaller increase in macroporosity and a decrease in microporosity. Microporosity in both coals is unaffected by acid demineralisation, but macroporosity is increased. The steam reactivity of the bituminous coal char is greater than that of the anthracite coal char, and demineralisation of the coals increases steam reactivity. N₂ surface areas and steam reactivities for both coal chars follow trends with parent coal rank previously established for US coals.     

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.     

Dependence of coal liquefaction behaviour on coal characteristics. 6. Product distributions from coals treated in a continuous-flow reactor

Further experimentation with coals in a continuous-flow reactor system at 440 and 455°C confirms the significance of the previous classification of a set of coals by cluster analysis. The greatest yields of distillable products tend to be given by coals of high sulphur content in the middle of the range of the high-volatile bituminous rank classes. Yet the lowest yields of preasphaltene (toluene-insoluble material) tend to be given by coals of high rank and medium sulphur content. The group of low sulphur, low-rank coals (mostly Rocky Mountain province), in a solvent different from that used for the other groups, showed poor conversion and poor distillate yield at the higher temperature. It is concluded that this coal/solvent combination is particularly prone to retrogressive reactions, including coking.     

Study on the hydrothermal treatment of Shenhua coal

In this paper, the hydrothermal treatment of Shenhua coal was carried out under 0.1 MPa (initial pressure) nitrogen and different temperature. Effects of hydrothermal treatment on the structure and the hydro-liquefaction activity of Shenhua coal were investigated by the ultimate and proximate analyses, the FTIR measurements and TG analyses of hydrothermally treated coals, and the characterizations of extraction and swelling properties, and the batch hydro-liquefaction of treated coal were also carried out. The results indicate that hydrothermal treatment above 200 °C can increase the hydrogen content of treated coal and decrease the yield of volatiles and the content of ash, especially a large amount of CO and CH₄ are found in gas products obtained by the hydrothermal treatment above 250 °C. Hydrothermal treatment disrupts the weak covalent bond such as ether, ester and side-chain substituent by hydrolysis and pyrolysis, and changes the distribution of H-bond in coal. The swelling ratio and the Soxhlet extraction yield of treated coal decrease with the increase of hydrothermal treatment temperature. The conversion of liquefaction and the yield of CS₂/NMP mixed solvent extraction at ambient temperature are enhanced by hydrothermal treatment at 300 °C. Therefore hydrogen donation reactions and the rupture of non-covalent bond and weak covalent bonds present in the process of hydrothermal treatment resulting in the changes of structure and reactivity of Shenhua coal. The results show that the hydro-liquefaction activity of Shenhua coal can be improved by hydrothermal pretreatment between 250 °C and 300 °C.     

Ignition characteristics of coal blends in an entrained flow furnace

Ignition tests were carried out on blends of three coals of different rank - subbituminous, high volatile and low volatile bituminous - in two entrained flow reactors. The ignition temperatures were determined from the gas evolution profiles (CO, CO₂, NO, O₂), while the mechanism of ignition was elucidated from these profiles and corroborated by high-speed video recording. Under the experimental conditions of high carbon loading, clear interactive effects were observed for all the blends. Ignition of the lower rank coals (subbituminous, high volatile bituminous) enhanced the ignition of the higher rank coal (low volatile bituminous) in the blends. The ignition temperatures of the blends of the low rank coals (subbituminous-high volatile bituminous) were additive. However, for the rest of the blends the ignition temperatures were always closer to the lower rank coal in the blend.     

The associative nature of lower rank coal

Initial volumetric swelling in tetrahydrofuran of pyridine-unextracted parts from subbituminous coal and lignite showed no dependence of their concentration, and was smaller than that of their pyridine extracts. These results are opposite to those obtained from high volatile bituminous coals and coincide with predictions for the cross-linked network model of coal. However, when ionic forces in these coals were reduced by acid washing or O-alkylation, these coals showed the same associative nature as did high volatile bituminous coals. Swelling kinetics were analysed on the basis of associative equilibria controlled by the ionic forces. It was concluded that solvation of the ionic forces was the rate determining step of volumetric swelling of lower rank coal rather than solvent diffusion into the coal, although diffusion has been proposed to be the most important factor in swelling.     

Examination of the role of CS2 in the CS2/NMP mixed solvents to coal extraction

The roles of CS₂ in the CS₂/NMP mixed solvent to coal extraction and solubilization were investigated in this study. There was little effect of removing of CS₂ from the solutions on the solubilities of UF coal extract and pyridine insoluble (PI) of the extract in the NMP/CS₂ mixed solvent, suggesting that NMP has high enough solubilities to the UF coal extract and PI. Six Argonne different rank coals were extracted with the CS₂/NMP mixed solvent and NMP, respectively. It was found that the extraction yield difference between NMP and CS₂/NMP mixed solvent for UF coal is largely deviated from the curve obtained for the other 5 coals, suggesting that the pre-swelling of CS₂ in the mixed solvent may be one of important roles for high extraction yield of UF coal in the CS₂/NMP mixed solvent. FTIR indicated that there was a strong interaction between CS₂ and NMP in the CS₂/NMP mixed solvent of 1 : 1 volume ratio, which made the strong absorbance at 2156 cm^− 1 in the FTIR spectra, and this interaction may disrupt the dipole based association of NMP thus making the CS₂/NMP mixed solvent lower viscosity, to penetrate more quickly into the network structure of coal, resulting in the larger solvent partner (NMP) to enter and break the stronger coal–coal interactions.     

Reactions of coals of different ranks with CO---H2 mixtures with and without sodium aluminate

Well-characterized coals of different H/C atomic ratio and rank were reacted at 365°C with CO, H₂ and CO---H₂ mixtures in water in the presence and absence of sodium aluminate. The optimum H₂/CO ratio for conversion was found to vary with the type of coal. It was <1 : 1 for low-rank and subbituminous coals, whereas the conversion of bituminous coals either did not vary with H₂/CO ratio or reached a maximum at a higher H₂/CO ratio (2 : 1). Even for a bituminous coal there was no advantage in reducing the water/coal ratio below 2 : 1 in NaAlO₂-catalysed reactions. The conversions increased with increasing H/C atomic ratio of the coal and decreasing rank, with or without NaAlO₂. Asphaltene yields increased with increasing coal rank and increasing proportion of CO in the H₂---CO reacting gases. The mechanistic implications of these results are briefly discussed.     

Hydrogen transferring liquefaction of some bituminous coals with hydrogenated fluoranthene under high temperature-short contact time conditions

Hydrogen transferring liquefaction using hydrogenated fluoranthene at high temperatures was very effective for three Japanese bituminous coals, with a total yield of oil and asphaltene > 85 wt%. The high temperature-short contact time conditions (480 °C for 10 min or 510 °C for 2.5 min) resulted in a total yield of > 90 wt% from the coal of lowest rank, with low consumption of hydrogenated fluoranthene. The oil yields were as high as 75 and 68 wt% at 480 °C and 510 °C, respectively. In contrast, the lower temperature of 450 °C appeared more effective in diminishing preasphaltene formation with the highest rank coal providing oil and asphaltene yields of 47 and 38 wt%, respectively. Longer times or higher temperature increased the oil yield but without reducing the preasphaltene. Higher temperature was found favourable for the formation of asphaltene of lower molecular weight. The reactivity of butiminous coals of different rank is discussed from the viewpoint of their structure.     

Structural analysis of quinoline and pyridine extracts of coals

Various ranks of coals were extracted in an autoclave with quinoline at 350–380°C for 1–4 h. More than 50% of bituminous coals were dissolved, and almost 100% of Japanese bituminous coals in particular were dissolved. These quinoline extracts were further extracted by shaking with pyridine at room temperature for 8 h and the extraction yield attained a maximum of 85%. NMR spectra of these extracts were recorded using deuteroquinoline and deuteropyridine as solvent. The structural indices calculated from the observed spectra showed a good agreement between quinoline extracts and pyridine extracts, which indicates that the coal structure is almost homogeneous. The aromatic ring number in structural units varied from 1–2 in younger coals to 5 in coking coals. f_a increased from 0.7 for younger coals to 0.9 for coking coals. The aliphatic carbon number per structural unit increased from younger to older coals, but foreign coals had smaller values than Japanese coals, which corresponds well with higher values of H/C in Japanese coals.     

Evolution of organic oxygen bonds during pyrolysis of coal

Five Czech coals of different rank (70.2, 71.5, 74.5, 75.0 and 83.3 wt% carbon) were heated at different temperatures in the range 250–850 °C and the contents of oxygen-containing functional groups (OH, COOH, CO, OCH₃) were determined in the coals and carbonization residues. The coals and residues were subjected to pyrolysis chromatography at 740 °C and the yields of phenol produced were measured. The dependence of the oxygen functions and the phenol yield on temperature and coal rank is discussed. In the coals studied, the most resistant oxygen groups appear to be hydroxyl and methoxyl; carboxyl and carbonyl oxygen are eliminated below 550 °C.     

Cd(II) sorption onto chemically modified Australian coals

Cadmium (II) adsorption onto chemically modified Australian coals has been studied as a function of p[H⁺] at 25 °C. The low rank Collie and Loy Yang coals and the bituminous Norwich Park and Mount Arthur coals were modified with hydrogen peroxide. While both treated bituminous coals showed little affinity for Cd(II) the adsorption properties of the two low rank coals were drastically modified by treatment with hydrogen peroxide. NICA-Donnan model calculations for the treated Collie coal indicated an increase in functionality (ca. 5-fold) which was reflected in the important increase in Cd(II) adsorption obtained from batch adsorption experiments. On the other hand, the modified Loy Yang coal underwent a ca. 6.25 decrease in surface functionality and decomposition of the coal structure itself. These changes were reflected in the DRIFT spectra in bands characteristic of the oxygen-containing functional groups. The Cd(II) adsorption capacity of this modified coal was consequently substantially decreased. The two low rank coals were also treated with ammonia at p[H⁺] 7.5 and 9.5. This treatment did not, however, induce any substantial change in the adsorption of Cd(II). DRIFT spectra showed that the predominant functional groups present in both Collie and Loy Yang coal remained essentially unchanged after treatment with aqueous ammonia.     

煤快速热解固相和气相产物生成规律

利用能有效避免二次转化反应的高频炉热解装置对3种不同变质程度的煤进行了600～1200℃条件下的快速热解,考察了在煤热解最初阶段焦产率、焦-C产率、热解气产率、热解气4种主要组分H₂、CO、CH₄和CO₂的比例以及热解气热值随煤阶和热解温度的变化规律。结果表明,焦的产率和焦-C的产率均随煤阶的升高而升高,热解气的产率随煤阶的升高而降低;热解温度的提高能显著降低煤焦和焦-C的产率并提高热解气的产率。热解气组分以H₂相似文献   

Determination of specific heats of coal powders by differential scanning calorimetry

Specific heats (C_p) of bituminous and subbituminous coals were investigated in the temperature range 300–360K by differential scanning calorimetry (DSC). To establish the validity of the procedure, specific heats of glass beads and graphites in powdered and bulk form were determined. Good agreement was obtained with the values for the specific heats of glass and graphites in the literature, and it was established that the specific heats were not dependent on the degree of diminution of these materials. Specific heats of coal samples were found to depend upon mesh size, temperature, rank, moisture content and whether the coal powder was wet- or dry-screened. However, there were only minor differences in C_p between bituminous and subbituminous coals.     

Differences in the behaviour of US bituminous and subbituminous coals during short contact time liquefaction

The short contact time (SCT) liquefaction of Belle Ayr subbituminous coal has been compared with that of Illinois No. 6 and Pittsburgh seam bituminous coals. Each bituminous coal was highly solubilized (90 wt%, daf coal) in 3–4 min at 450 °C and 13–16 MPa hydrogen pressure. More than 80 wt% of each coal was converted to solvent-refined coal (SRC, pyridine-soluble residuum), with only small quantities of distillate oil and C₁–C₄ gas being formed. A longer reaction (up to 30 min) gave only a small increase in total conversion, but gas and distillate yields increased significantly. Iron sulphides did not appear to catalyse coal solubilization. By contrast, only 65 wt% of the Belle Ayr coal dissolved rapidly in SCT liquefaction and pyrite addition catalysed the conversion of the remaining insoluble organic matter (IOM). With an equivalent amount of pyrite present the Belle Ayr coal also gave more C₁–C₄ gas and substantially more distillate in SCT liquefaction than the bituminous coals. These differences in product distributions obtained from bituminous and subbituminous coals in SCT liquefaction can be rationalized on the basis of differences in the structures of the starting coals. However, the origin of high IOM yields with the Belle Ayr coal remains unclear.