Composition and structure characteristics of soluble organic matter from Naomaohu lignite by sequential extraction and thermal conversion performance of the corresponding residue
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摘要: 采用二硫化碳、甲醇、丙酮和二硫化碳/丙酮(等体积混合溶剂)对淖毛湖褐煤(NL)进行逐级超声萃取,得到各级萃取物(E1−E4)和最终萃余物(ER)。采用GC-MS对各级萃取物E1−E4中的化合物组成和结构进行分析,发现E1中主要为烷烃、芳烃、醇类化合物和酯类化合物;E2中以烷烃、醇类化合物和酯类化合物为主。醇类化合物、酚类化合物以及酯类化合物是E3中的主要物质,且酯类化合物主要为邻苯二甲酸二酯类化合物。受到CS2和丙酮这两种溶剂协同作用的影响,E4中的烯烃类化合物的相对含量也比较高。采用FT-IR对NL、E1−E4和ER中所含官能团进行表征分析,结果发现,超声萃取过程只是将淖毛湖褐煤大分子骨架中游离的小分子化合物以及与大分子骨架以弱共价键相连的小分子萃取了出来,并未破坏煤样的大分子骨架结构。此外,NL和ER红外数据的分峰拟合结果显示,经过超声萃取后,ER中红外吸收峰的种类并未增加,只是峰的强度发生了改变。通过NL和ER的TG-DTG曲线可知,超声萃取后,NL的失重量由47.09%增加至51.04%,最大失重速率峰由450 ℃提前至430 ℃。NL和ER基于Coats-Redfern模型的热解动力学分析结果表明,经过超声萃取后,ER在快速热解阶段的活化能比NL更低,热解过程更容易进行。Abstract: Carbon disulfide (CDS), methanol, acetone and isometric carbon disulfide/acetone mixture (IMCDSAM) were used as solvents to sequentially extract Naomaohu lignite (NL) via ultrasonic-assisted extraction to obtain extracts (E1−E4) and final extraction residue (ER). Composition and structure of E1−E4 were analyzed by GC-MS. It is found that the main compounds in E1 are alkanes, aromatics, alcohols and esters. Alkanes, alcohols and esters are the main compounds in E2. Alcohols, phenolics and esters are the main components in E3, and esters are mainly phthalic diester compounds. Affected by synergistic effect of the two solvents CDS and acetone, the relative content of alkenes in E4 is relatively high. FT-IR was used to characterize functional groups in NL, E1−E4 and ER. The results show that the ultrasonic extraction process only extracts free small compounds from macromolecular skeleton of the NL and some other molecules, which connect the macromolecular skeleton by weak covalent bonds, and the process does not destroy the macromolecular skeleton structure. In addition, peak fitting results from FT-IR show that types of infrared absorption peaks in ER do not change after ultrasonic extraction, while intensity of the peaks varies. TG-DTG profiles of NL and ER indicate that after ultrasonic extraction weight loss of NL increases from 47.09% to 51.04%, and peak of the maximum weight loss rate is advanced from 450 to 430 ℃. Pyrolysis kinetic analyses of NL and ER based on Coats-Redfern model show that after ultrasonic extraction activation energy of ER in rapid pyrolysis stage is lower than that of NL, and the pyrolysis process is easier to proceed.
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Key words:
- lignite /
- sequential extraction /
- thermochemical conversion /
- GC/MS
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图 9 (a) NL和ER在3600−3000 cm−1红外分峰谱图;(b) NL和ER在3000−2800 cm−1红外分峰谱图;(c) NL和ER在1800−1000 cm−1红外分峰谱图;(d) NL和ER在900−700 cm−1红外分峰谱图
Figure 9 (a) FT-IR curve-fitting results of NL and ER (3600−3000 cm−1); (b) FT-IR curve-fitting results of NL and ER (3000−2800 cm−1); (c) FT-IR curve-fitting results of NL and ER (1800−1000 cm−1); (d) FT-IR curve-fitting results of NL and ER (900−700 cm−1)
表 1 淖毛湖褐煤的工业分析和元素分析
Table 1 Proximate and ultimate analyses of NL
Proximate analysis w /% Ultimate analysis wdaf /% Mad Ad Vdaf C H N S Oa H/C O/C 7.12 10.49 49.20 71.89 5.17 0.88 0.74 21.32 0.86 0.22 a: by difference 表 2 NL和ER中官能团的相对含量及其变化
Table 2 Contents and changes of functional groups in NL and ER
Band position σ/cm−1 Functional group Area percentage/% Δ = (ER−NL)/NL*100% NL ER 3512 OH−π 11.16 22.48 101.53 3416 self-associated −OH 37.29 30.57 −18.02 3312 OH−ether 21.13 21.17 0.15 3207 cyclic−OH 21.31 16.48 −22.65 3099 OH−N 9.11 9.30 2.05 2956 aliphatic −CH3 11.25 18.92 68.19 2922 asymmetric aliphatic −CH2− 44.93 31.67 −29.52 2892 aliphatic −CH 14.04 20.72 47.53 2853 symmetric aliphatic −CH2− 29.77 28.69 −3.63 1713 conjugated C=O 16.09 22.41 39.24 1615 aromatic C=C 66.13 59.25 −10.40 1443 asymmetric −CH3, −CH2 7.75 8.49 9.49 1385 CH3−Ar, R 2.50 2.12 −14.97 1285 symmetric deformatrion −CH3 1.60 2.05 28.06 1231 symmetric deformatrion −CH3 1.62 0.88 −46.04 1172 C−O phenols 1.52 1.83 20.42 1102 grease C−O 1.66 1.73 4.47 1036 alkyl ethers 1.58 0.86 −45.19 1013 alkyl ethers 0.55 0.38 −30.77 868 one adjacent H deformations 7.03 5.71 −18.88 834 two adjacent H deformations 15.54 15.30 −1.47 815 two adjacent H deformations 15.91 16.80 5.65 797 three adjacent H deformations 18.70 14.90 −20.35 780 three adjacent H deformations 14.58 17.55 20.34 765 three adjacent H deformations 13.43 13.59 1.21 748 four adjacent H deformations 14.81 16.15 9.00 表 3 NL和ER的TG/DTG曲线中的特征温度
Table 3 Characteristic temperatures in TG/DTG curves of NL and ER
Sample tc /℃ ti /℃ tm /℃ tmax /℃ tn /℃ tp /℃ tf /℃ NL 70 190 374 450 550 740 855 ER 57 190 360 430 550 665 850 表 4 NL和ER不同反应级数下的热解动力学参数
Table 4 Calculation results of pyrolysis kinetic parameters under different reaction orders of NL and ER
Pyrolysis stage Sample Reaction
orderRegression
equationCorrelation
coefficient R2Activation energy
E/(kJ·mol−1)Pre-exponential
factor A/min−12RT/E Fast pyrolysis stage ER 1 y = −3003.94x − 9.39 0.9750 24.974 1.259 0.250 2 y = −4875.12x − 6.39 0.9893 40.532 40.839 0.154 3 y = −7154.77x − 2.78 0.9907 59.485 2222.755 0.105 NL 1 y = −2325.23x − 10.19 0.9637 19.332 0.875 0.318 2 y = −4009.08x − 7.40 0.9888 33.332 24.463 0.185 3 y = −6071.70x − 4.03 0.9942 50.480 1080.650 0.122 -
[1] HE W J, LIU Z Y, LIU Q Y, SHI L, SHI X, WU J F, GUO X J. Behavior of radicals during solvent extraction of three low rank bituminous coals[J]. Fuel Process Technol,2017,156:221−227. doi: 10.1016/j.fuproc.2016.10.029 [2] KONG J, WEI X Y, ZHAO M X, LI Z K, YAN H L, ZHENG Q X, ZONG Z M. Effect of sequential extraction and thermal dissolution on the structure and composition of Buliangou subbituminous coal[J]. Fuel Process Technol,2016,148:324−331. doi: 10.1016/j.fuproc.2016.03.014 [3] 殷甲楠, 张凤桐, 樊丽华, 梁英华, 王蕾. 低阶煤有机溶剂萃取的研究进展[J]. 洁净煤技术,2014,20(6):100−103+51.YIN Jia-nan, ZHANG Feng-tong, FAN Li-hua, LIANG Ying-hua, WANG Lei. Research progress of organic solvent extraction of low rank coal[J]. Clean Coal Technol,2014,20(6):100−103+51. [4] MA Y Y, MA F Y, MO W L. Five-stage sequential extraction of Hefeng coal and direct liquefaction performance of the extraction residue[J]. Fuel,2019,266:117039. [5] 王晓华, 魏贤勇, 宗志敏. 溶剂分级萃取法研究平朔煤的化学组成特征[J]. 煤炭转化,2006,29(2):4−7. doi: 10.3969/j.issn.1004-4248.2006.02.002WANG Xiao-hua, WEI Xian-yong, ZONG Zhi-min. Study on chemical constituent characteristic of fractionated extraction from Pingshuo coal[J]. Coal Convers,2006,29(2):4−7. doi: 10.3969/j.issn.1004-4248.2006.02.002 [6] 戈军, 郭龙德, 郭智慧, 石斌, 张建芳. 溶剂与溶胀促进剂对神华煤溶胀行为的影响[J]. 化工进展,2010,29(10):1885−1889.GE Jun, GUO Long-de, GUO Zhi-hui, SHI Bing, ZHANG Jian-fang. Shenhua coal swelling with solvents and swelling promoters[J]. Chem Ind Eng Prog,2010,29(10):1885−1889. [7] IINO M, TAKANOHASHI T, OHSUGA H, TODA K. Extraction of coals with CS2-N-methyl-2-pyrrolidinone mixed solvent at room temperature: Effect of coal rank and synergism of the mixed solvent[J]. Fuel,1988,67(12):1639−1647. doi: 10.1016/0016-2361(88)90208-6 [8] 吴法鹏, 鲁浩, 闫洁, 王瑞玉, 赵云鹏, 魏贤勇. 两种不同还原性次烟煤可溶有机质分子组成差异[J]. 燃料化学学报,2018,46(7):769−777. doi: 10.3969/j.issn.0253-2409.2018.07.001WU Fa-peng, LU Hao, YAN Jie, WANG Rui-yu, ZHAO Yun-peng, WEI Xian-yong. Differences in molecular composition of soluble organic species in two Chinese subbituminous coals with different reducibility[J]. J Fuel Chem Technol,2018,46(7):769−777. doi: 10.3969/j.issn.0253-2409.2018.07.001 [9] LIU F J, WEI X Y, GUI J, WANG Y G, LI P. Characterization of biomarkers and structural features of condensed aromatics in Xianfeng lignite[J]. Energy Fuels,2013,27(12):7369−7378. doi: 10.1021/ef402027g [10] LIU F J, WEI X Y, GUI J, LI P, WANG Y G, LI W T, ZONG Z M, FAN X, ZHAO Y P. Characterization of organonitrogen species in Xianfeng lignite by sequential extraction and ruthenium ion-catalyzed oxidation[J]. Fuel Process Technol,2014,126:199−206. doi: 10.1016/j.fuproc.2014.05.004 [11] HAS B, GI A, JW A. Pyrolysis characteristics and kinetics of low rank coals by distributed activation energy model[J]. Energy Convers Manage,2016,126:1037−1046. [12] LIU J X, MA J F, LEI L, ZHANG H, JIANG X M. Pyrolysis of superfine pulverized coal. Part 5. Thermogravimetric analysis[J]. Energy Conver Manage,2017,154:491−502. doi: 10.1016/j.enconman.2017.11.041 [13] LIU F J, WEI X Y, FAN M H, ZONG Z M. Separation and structural characterization of the value-added chemicals from mild degradation of lignites: A review[J]. Appl Energy,2016,170:415−436. doi: 10.1016/j.apenergy.2016.02.131 [14] HU R N, WANG Z C, LI L, WANG X L, PAN C X, KANG S G. Effect of solvent extraction pretreatments on the variation of macromolecular structure of low rank coals[J]. J Fuel Chem Technol,2018,46(7):778−786. doi: 10.1016/S1872-5813(18)30034-3 [15] LV J H, WEI X Y, WANG Y H, WANG T M, LIU J, ZHANG D D. Mass spectrometric analyses of biomarkers and oxygen-containing species in petroleum ether-extractable portions from two Chinese coals[J]. Fuel,2016,173:260−267. doi: 10.1016/j.fuel.2016.01.067 [16] SHI D L, WEI X Y, FAN X, ZONG Z M, CHEN B, ZHAO Y P, WANG Y G, CAO J P. Characterizations of the extracts from geting bituminous coal by spectrometries[J]. Energy Fuels,2013,27:3709−3717. doi: 10.1021/ef4004686 [17] LI Z K, WEI X Y, YAN H L. Advances in lignite extraction and conversion under mild conditions[J]. Energy Fuels,2015,29:6869−6886. [18] LI F, ZHAO G Y, ZHAO Y G, ZHAO M S, TANG J W. Construction of the molecular structure model of the Shengli lignite using TG-GC/MS and FTIR spectrometry data[J]. Fuel,2017,203:924−931. doi: 10.1016/j.fuel.2017.04.112 [19] LIAO J J, FEI Y, MARSHALL M, L. CHAFFEE A, CHANG L P. Hydrothermal dewatering of a Chinese lignite and properties of the solid products[J]. Fuel,2016,180:473−480. doi: 10.1016/j.fuel.2016.04.027 [20] TIAN B, QIAO Y Y, TIAN Y Y, XIE K C, LIU Q, ZHOU H F. FTIR study on structural changes of different-rank coals caused by single/multiple extraction with cyclohexanone and NMP/CS2 mixed solvent[J]. Fuel Process Technol,2016,154:210−218. doi: 10.1016/j.fuproc.2016.08.035 [21] WANG S, TANG Y, SCHOBERT H H, GUO Y, SU Y. FTIR and 13C NMR investigation of coal component of late permian coals from southern China[J]. Energy Fuels,2011,25(12):5672−5677. doi: 10.1021/ef201196v [22] ZHANG W Q, JIANG S G, WANG K, WU Z Y, SHAO H. An experimental study of the effect of ionic liquids on the low temperature oxidation of coal[J]. Int J Min Sci Technol,2012,22(5):687−691. doi: 10.1016/j.ijmst.2012.08.016 [23] SONG H J, LIU G R, ZHANG J Z, WU J H. Pyrolysis characteristics and kinetics of low rank coals by TG-FTIR method[J]. Fuel Process Technol,2017,156:454−460. doi: 10.1016/j.fuproc.2016.10.008 [24] WU D, LIU G J, SUN R Y. Investigation on structural and thermodynamic characteristics of perhydrous bituminous coal by fourier transform infrared spectroscopy and thermogravimetry/Mass spectrometry[J]. Energy Fuels,2014,28:3024−3035. doi: 10.1021/ef5003183 [25] LIN X C, WANG C H, IDETA K, MIYAWAKI J, NISHIYAMA Y, WANG Y G, YOON S, MOCHIDA I. Insights into the functional group transformation of a Chinese brown coal during slow pyrolysis by combining various experiments[J]. Fuel,2014,118:257−264. doi: 10.1016/j.fuel.2013.10.081 [26] KOTYCZKA-MORAŃSKA M, TOMASZEWICZ M. Comparison of the first stage of the thermal decomposition of polish coals by diffuse reflectance infrared spectroscopy[J]. J Energy Inst,2018,91(2):240−250. doi: 10.1016/j.joei.2016.11.011 [27] HE X Q, LIU X F, NIE B S, SONG D Z. FTIR and Raman spectroscopy characterization of functional groups in various rank coals[J]. Fuel,2017,206:555−563. doi: 10.1016/j.fuel.2017.05.101 [28] ARENILLAS A, RUBIERA F, PEVIDA C, PIS J J. A comparison of different methods for predicting coal devolatilisation kinetics[J]. J Anal Appl Pyrolysis,2001,58:685−701. [29] SAIKIA B K, BORUAH R K, GOGOI P K. FT-IR and XRD analysis of coal from makum coalfield of assam[J]. J Earth Syst Sci,2007,116(6):575−579. doi: 10.1007/s12040-007-0052-0 [30] 于文浩, 雷智平, 潘春秀, 任世彪. 预处理对褐煤热解行为的影响研究进展[J]. 燃料与化工,2018,49(2):1−3+11.YU Wen-hao, LEI Zhi-ping, PAN Chun-xiu, REN Shi-biao. Study on the influence of pre-treatment to lignite pyrolysis[J]. Fuel Chem Process,2018,49(2):1−3+11. [31] 刘耀鑫, 伯灵, 冯兆兴, 李晓鹤. 溶胀预处理煤热解特性研究[J]. 煤炭技术,2018,37(4):304−306.LIU Yao-xin, BO Ling, FENG Zhao-xing, LI Xiao-he. Study on behavior of solvent swelling coal pyrolysis[J]. Coal Technol,2018,37(4):304−306.