煤萃取方法研究综述

近几年全球的环境污染日益严重,煤炭作为一次能源,在中国能源消费中煤炭的消耗仍然超过半数,因此对煤炭的高附加值开发受到广泛重视,目前利用溶剂萃取技术对煤炭进行高附加值开发是洁净煤技术发展的一个方向,本文主要是通过对无灰煤的制备研究进展进行综述,初步展望了无灰煤的发展趋势。

基于煤萃取物的类石墨状多孔炭的制备及其电容性能研究

以褐煤萃取物为炭前驱体,MgO为阻隔剂,KOH为活化剂,在800℃惰性气氛下制备出类石墨状多孔炭材料。对该多孔炭材料进行了红外(FTIR)、X射线衍射(XRD)、透射电镜(TEM)和拉曼(Raman)表征。以活化前和活化后多孔炭为电极材料,利用循环伏安、恒电流充放电、交流阻抗对其进行了电化学电容性能评价和比较。结果表明:活化后炭材料呈现多孔的薄膜状,比表面积高达1396 m^2/g,而活化前炭材料比表面积仅为138.4 m^2/g。当电流密度为1 A/g和4 A/g时,活化后炭材料比电容分别为533 F/g和390 F/g;而活化前炭材料对应的比电容为366 F/g和198 F/g。在电流密度为5 A/g下循环8000圈后,活化前后炭材料的电容保持率分别为72.5%和89.6%。可见,经过KOH活化后的炭材料比电容和电化学稳定性有了显著提高。该研究证明阻隔剂和活化剂的使用,能够获得高度柔性的高电容性能的类石墨状多孔炭。

平朔气煤DF_5的组成特性及煤液体统计平均结构参数的相似性

Two kinds of coal liquid, the distilled fraction (270～340℃) (DF 5) of low temperature carbonization tar and the extracts by heptane (P M1 ) and THF/MET (P M7 ) from Chinese Pingshuo bituminous coal were studied using GC-MS and 13 C-NMR, and were compared with each other The results show that the compounds in DF 5 can be classified as paraffinic compounds and non-paraffinic compounds The average molecular weight of the paraffinic compounds (M PC =303 03) is as same as that of the extract PM 1 (M PM 1 =298 16), as well as their molecular weight distributions The statistical average molecular structural parameters of the non-paraffinic compounds, such as aromatic carbon f a and the structure unit number M SP , were similar to that of the extract PM

Heavy metals leaching in bottom ash and fly ash fractions from industrial-scale BFB-boiler for environmental risks assessment

The bottom ash and fly ash from the co-combustion of wood residues and peat at a bubbling fluidised bed boiler（296 MW） contained only quartz（SiO_2）, microcline（KAl Si_3O_8） and albite（NaAlSi_3O_8）. Thus, X-ray powder diffraction（XRD） was not useful for clarifying the difference in the release of associated heavy metals from ash matrices. In order to assess the release of heavy metals from ashes under changing environmental conditions, they were sequentially extracted and fractionated by the BCR-procedure into acid soluble/exchangeable（CH_3COOH）, reducible（NH_2OH-HCl） and oxidizable（H_2O_2/CH_3COONH_4） phases. The CH_3 COOH extractable fraction in conjunction with the total heavy metals concentrations were used to calculate the risk assessment code values for heavy metals leaching from the ash matrix. The leaching studies indicate that the heavy metals in the bottom ash and fly ash are bound to different fractions with different strengths. From the environmental and utilization perspectives, heavy metals in ashes posed different levels of environmental contamination risk. Only As in the bottom ash posed a very high risk. High risk metals were Cd in the bottom ash as well as As, Cd and Se in the fly ash.

Non-covalent associative structure of coal

The recent progress of non-covalent associative structure of coal, and the mechanisms of the CS2/NMP (1:1 by volume) mixed solvent and the additive addition enhancing the extraction yield of coals were reviewed, and the aggregation behavior of coal in solid and solution states were presented, and the aggregation behavior of coal in solid and solution states were introduced in this paper. Coal extraction and swelling in organic solvents at room temperature were the most useful methods to understand the associative structure of coal. CS2/NMP (1:1 by volume) is a unique solvent to give high extraction yields for some bituminous coals. Some additives can dissociate the stronger interactions among coal molecules and enhance the extraction yields of coal in the mixed solvent.

Study on microwave-assisted extraction of coal

The effect of different factors on coal extraction yield-temperature, solvent, coal type and irradiation time were investigated for different China coals under microwave-assisted extraction（MAE）. The results show that the optimum temperature for ethanol, acetone and THF are 393,373 and 373 K respectively and the extraction yield of THF is higher than that of other two solvents under MAE. Extraction with several single organic solvents were conducted for the 5 typical China coals-Shenfu, Tongchuan, Panzhihua, Yitai and Huating coal under microwave-assisted extraction and Soxhlet extraction. Results indicat that extraction yield of ethylenediamine, ethanol, acetone, tetrahydrofuran under MAE are all higher than that of Soxhlet extraction and MAE required less time. Tongchuan coal extracts of ethanol and acetone which were extracted by MAE and Soxhlet extraction were analyzed by GC/MS.

Solubilization of small molecules from coal and the resulting effects on the pore structure distribution

The solubilization of small molecules from coal by solvent extraction and the resulting effects on the pore distribution of a low rank coal were studied. Samples were extracted, in succession, with petroleum ether and with CS2. Extract and residue fractions collected during the solubilization process were analyzed by FTIR and by surface area and porosimetry. The results show that an obvious inflection point exists that allows separating the dissolution sequence into stages. Small molecules are first extracted from the free state, then molecules trapped in micropores are extracted and, finally, molecules trapped in the coal-matrix network are extracted. This is indicated from the extraction yield curves. Chain-like carbonyl compounds, -OH (or -NH) containing compounds that are hydrogen bonded and phenolics dominate the petroleum ether extracts. Chain-like carbonyl components and ether compounds (aliphatic ethers and aromatic ethers) dominate the CS2 extracts. A solvent dissolution mechanism and the effect of small molecule extraction on the pore structure are put forward. Diffusion, dissolution, pore opening, pore shrinking or even collapsing caused by swelling, creating of new micropores, pore opening and, finally, colloidallization of some micropores occurs. In the later stages of the extraction the internal structure of the coal is colloidallized due to swelling and the pore number or volume is greatly reduced.