反应条件对哈密煤温和液化沥青质结构和热反应性的影响

Effect of reaction conditions on structure and thermal reactivity of asphaltenes from mild liquefaction of Hami coal

沥青质(包括沥青烯和前沥青烯,PAA)作为煤液化的重要产物,其结构和性质对煤的高效液化及其后续利用至关重要。沥青质的结构和性质与液化反应条件密切相关,因此,本研究以四氢萘为溶剂,考察了反应温度、停留时间、反应压力、溶煤比等条件对哈密煤温和液化沥青质(HMPAA)结构和性质的影响。利用元素分析、红外光谱、固体C-NMR等分析了不同温和液化反应条件下所得HMPAA的结构特征;利用TG-MS考察了HMPAA的热解反应性和热解过程中的气体逸出规律。结果表明,HMPAA的收率随反应温度降低、压力升高、停留时间缩短及溶煤比增加而升高。在温度为340℃、停留时间为1 h、压力为3 MPa、溶煤比为2∶1的条件下,HMPAA收率最高,达到35.0%。HMPAA碳结构由脂肪碳和芳香碳组成,其中,芳香碳占80%左右。升高温度有利于哈密煤液化反应向生成芳香化程度更高的HMPAA组分的方向进行;延长停留时间,HMPAA的芳环缩合程度增大;增大溶煤比,HMPAA芳香度和芳环缩合程度均减小;在本研究考察的范围内改变压力对HMPAA结构性质影响不大。HMPAA在250℃左右开始发生热解反应,最大失重峰温为400-500℃,最终失重率基本达40%以上。HMPAA热反应性随反应温度降低、溶煤比增加而增大,改变压力对HMPAA热反应性影响较小。

Asphaltenes including asphaltene and preasphaltene(PAA)are the important products of the direct coal liquefaction process,whose structure and property are essential for the high-efficiency liquefaction and the subsequent utilization.The structure and property of PAA are closely related to the liquefaction conditions.Therefore,in this work,the effects of liquefaction temperature,residence time,pressure,and the ratio of solvent to coal on the structure and property of PAA obtained from mild liquefaction of Hami coal(named as HMPAA),were investigated in a batch autoclave with tetrahydronaphthalene as solvent.The structure features of HMPAA obtained under different conditions were characterized by elemental analysis,infrared spectroscopy and solid-stateC-NMR.Thermal reactivity of HMPAA and the evolution curves of gas product during pyrolysis were analyzed by TG-MS.The results showed that the yield of HMPAA increased with decreasing reaction temperature,increasing pressure,decreasing residence time and increasing the ratio of solvent to coal.The highest HMPAA yield was 35.0%at 340℃,3 MPa,residence time of 1 h,and the ratio of solvent to coal of 2∶1.The carbon structure of HMPAA consisted of aliphatic carbon and aromatic carbon,while the latter accounted for about 80%.Increasing liquefaction temperature was favorable to the formation of HMPAA with higher aromaticity.The aromatic condensation degree of HMPAA increased with extended residence time.The aromaticity and aromatic condensation degree of HMPAA decreased with the increase of the ratio of solvent to coal.The liquefaction pressures examined in this work had little effect on the structure and property of HMPAA.The pyrolysis of HMPAA started at about 250℃and the peak temperature of maximum weight loss was between 400℃and 500℃,and the final weight loss was over 40%.The thermal reactivity of HMPAA increased with decreasing liquefaction temperature and increasing the ratio of solvent to coal,and the change of pressure had little effect on the thermal reactivity of HMPAA.