典型烟煤的分子结构及模型模拟的初步研究

	典型烟煤的分子结构及模型模拟的初步研究
	孙溶1,2
学位类型	硕士
导师	陈颖军 ; 田崇国 ; 高彦博
	2017-05-17
学位授予单位	中国科学院大学
学位授予地点	北京
关键词	Pahs可抽提率母体多环芳烃烷基多环芳烃组成特征挥发分含量分子结构模型模拟
摘要	民用燃煤是我国重要的黑碳(BC)和多环芳烃(PAHs)排放源，但其排放因子明显受控于煤的地质成熟度。因此，本研究基于分子水平对不同成熟度原煤中游离态小分子和大分子网络骨架分别进行解析，进而为我国民用燃煤源黑碳(BC)和多环芳烃(PAHs)的排放特征提供理论基础。首先，本研究选择了中国7种不同成熟度的烟煤(干燥无灰基挥发分含量V_daf为19.4%-48.3%)，以正己烷和二氯甲烷有机溶剂进行索氏抽提，通过气相色谱-质谱联用仪(GC-MS)进行分析检测，获得了27种正构烷烃、16种优控母体多环芳烃(pPAHs)以及16种烷基多环芳烃(aPAHs)的含量和组成特征。在此研究基础上，探讨正构烷烃、PAHs的含量和组成及与煤成熟度的关系，为研究民用燃煤BC和PAHs的生成机理提供理论支持。其次，本研究利用傅里叶变换红外光谱仪(FTIR)和超导核磁共振波谱仪对原煤化学结构进行检测以及对光谱分析，通过分峰拟合获得7种不同成熟度煤化学结构参数，并初步构建出其大分子结构模型。研究的主要结论如下：对原煤中游离态小分子的研究结果：本研究定量检测了7种不同成熟度烟煤中游离态从C₁₀到C₃₆的27种正构烷烃的含量。研究结果发现，不同成熟度烟煤中正构烷烃总含量范围为25.12-369.53 mg/kg。随着挥发分含量的增加，正构烷烃的总含量呈现先增加后减少的趋势。不同成熟度烟煤之间正构烷烃总含量差异较大，不同煤种之间相差2-15倍。同时研究发现，挥发分含量最高的烟煤继承了植物体内烷烃的含量特征，且随着挥发分含量的增加，原煤中烷烃C_max值先增加后减小的趋势。本研究发现不同成熟度原煤中最大碳数、碳优势指数(CPI)以及低分子正构烷烃(≤C₂₄)与高分子正构烷烃(>C₂₄)比值都呈现相同的趋势，而这些特征值能够更好的指示煤变质过程中烷烃的行为特征。本研究定量检测了7种不同成熟度烟煤中游离态PAHs含量，包括16种pPAHs和16种aPAHs。研究结果发现，不同成熟度烟煤中两者总含量范围为39.8-289.0 mg/kg，中挥发分烟煤(V_daf为25.6%-35.5%)明显高于高挥发分(V_daf=48.3%)和低挥发分(V_daf=19.4%)烟煤，不同烟煤之间的差异可达7倍，与民用燃煤排放PAHs和BC的情况相似；(2) 不同成熟度烟煤中pPAHs总含量范围为8.3-58.4 mg/kg，在V_daf为25.6%-30.5%时最高；不同成熟度烟煤中aPAHs的含量为31.4-236.5 mg/kg；aPAHs含量平均比pPAHs高4倍，这种差异以及PAHs的含量范围与燃煤烟气成分均较为一致，说明民用燃烧条件下煤烟成分对原煤游离态PAHs有较好的继承；(3)pPAHs和aPAHs的组成特征均表现为：随着煤的挥发分含量降低，即煤的成熟度提升，PAHs的环数分布表现为从以高环为主向以中低环为主过渡的趋势；pPAHs在V_daf为25.6%以下时以低环(2-3环)为主，而在V_daf高于30%时以中高环(4-6环)为主；aPAHs的情况相似，即中高成熟度烟煤以低环为主，而4环aPAHs在30.5%-35.5%最高。PAHs组成上的这种变化趋势很好地反映了煤大分子结构随成熟度演变的规律，也能较好地解释中挥发分烟煤PAHs和BC排放因子最高的现象，但含量比pPAHs更高的aPAHs对燃烧产物的贡献应引起重视。二、对原煤化学结构的研究结果：原煤结构中不同含氧官能团含量特征如下：(1)羟基、共轭C=O和不饱和羧酸C=O含量在高挥发分烟煤LK和低挥发分烟煤LL中，三者比值相近；(2)随着挥发含量的增加，三种含氧官能团含量均有所变化，其中羟基和羰基含量比重增大，不饱和羧酸比例有所下降，当挥发分含量增加至29%时，羟基和羰基含量最高，不饱和羧酸含量最低；(3)当挥发分含量小于25%时，原煤中羰基含量和不饱和羧酸含量相同，同时羟基含量降低。综上所述，研究发现在较高挥发分原煤和较低挥发分原煤中三种含氧官能团含量特征一致，而在中等挥发分原煤中含氧官能团主要是羟基，其次是羰基，而不饱和羧酸相对含量最低。原煤结构中不同脂肪碳含量特征如下：(1)随着挥发分含量的增加，原煤中R₂CH₂/RCH₃含量的比值增大，当挥发分含量超过30%时，RCH₃含量达到最大值，其R₂CH₂/RCH₃含量的比值为7:1；(2)当挥发分含量再次升高且含量小于35%时，原煤中R₂CH₂/RCH₃含量的比值下降至3:1；(3)挥发分含量为48%的LK烟煤中R₂CH₂/RCH₃含量的比值有所增加，比值为4:1。这一变化规律与不同成熟度原煤中游离态aPAHs含量特征一致，说明游离态小分子结构以及含量特征与煤大分子结构具有一定的一致性。 7种不同成熟度烟煤大分子结构模型中芳香结构单元组成特征如下：(1)氮在不同种烟煤中主要存在形式是吡咯和吡啶；(2)苯环主要存在于挥发分含量较高的烟煤LK中，并且是煤大分子主要的结构单元；(3)当挥发分含量低于40%时，原煤分子结构单元主要以2环的形式存在，当挥发分含量为30%时，YCW中2环含量达到最大值；(4)当挥发分含量小于30%时，原煤中芳香结构单元逐渐从以2环为主转变成2环和3环平均分布，并且向更高的环数发生转变。综上所述，在不同煤阶的煤化学结构中，游离态小分子和煤大分子网络结构中芳香单元变化特征一致，表现为从以高环为主向以中低环为主过渡的趋势；原煤中脂肪碳的存在形式主要从甲基碳含量降低，逐渐向其他脂肪碳形式转变；氧元素在原煤中主要是从共轭C=O和不饱和羧酸C=O向羟基过渡的形式存在。研究发现，本文7种烟煤化学结构变化特征如下：(1)低挥发分烟煤，分子尺寸大，芳香度高，芳香单元主要以2-3环分布为主，侧链少；(2)中挥发分以及中高挥发分烟煤主要是以2-3环为主，且支链化和脂肪化高，且中高挥发分烟煤以甲基侧链含量和羰基含量较高，中挥发分烟煤脂肪碳以亚甲基为主；(3)高挥发分烟煤，分子尺寸小，芳香度高。研究结果表明，成熟度是影响煤大分子化学结构的主要因素，其次是与其沉积环境和沉积物种类有关。随着成熟度的增加，烟煤中芳香碳含量呈现先降低后增加的趋势，煤分子化学结构排列规律，热稳定性高；同时，中挥发分烟煤和中高挥发分烟煤大分子结构中，脂肪化增加，表现出甲基、乙基等侧链增多，由于其热稳定性差，导致其特殊性。
其他摘要	Residential coal combustion (RCC) is the most important emission source of black carbon (BC) and polycyclic aromatic hydrocarbons (PAHs) in China.Their emission factors are obviously controlled by coals’ geological maturity, therefore they may be related with the concentration and composition of soluble PAHs in coals.Seven bituminous coals with different maturity were selected in this study to determinate the soluble PAHs by GC/MS after Soxhlet extraction successively with hexane and dichloromethane solvent.Through analyzing normal alkane series, sixteen parent PAHs(pPAHs) and sixteen alkylated PAHs (aPAHs),the paper discussed the relationship between concentration and composition of PAHs and coal’s maturity.Moreover the study may be helpful to explain the formation mechanism of PAHs and BC during RCC. Secondly, through Fourier transform infrared spectrometer (FTIR) and solid superconducting mri (¹³C-NMR) to test the raw coal chemical structure as well as to analysis the spectral, the study obtained seven kinds of different maturity of China coals chemical structure information. The main conclusions are as follows: The results showed that the different bituminous coal is alkanes content ranged from 25.12 mg/kg to 369.53 mg/kg.With the increase of the content of volatile matter content , the corresponding normal alkanes was presented to increase and then decreased. At the same time, compared with other bituminous coals, the total corresponding normal alkanes was two to fifteen times.Volatile and at the same time, the study found the highest levels of bituminous coal inherited the alkane content characteristics of plant, and with the increase of the content of volatile matter of raw coal alkane Cmax value decreases after increasing first.This study found that the characteristics of the biggest carbon number, carbon advantages index (CPI) and low/high molecular polymer (≤C₂₄)/(>C₂₄) ratio of different maturity raw coals were in the same trends.These characteristic values can better instruction behavior characteristics of paraffin in the process of coal metamorphism. The results showed that:(1) the total PAH concentrations in the six tested coals ranged from 39.8 mg/kg to 289.0 mg/kg, which the coals with middle volatile material content in dry and ash-free basis (V_daf) were higher PAHs than high and low V_daf bituminous coals. Seven times of difference occurred among various coals, which is similar with the trend of emission factors of PAHs and BC of RCC;(2) pPAHs concentrations ranged from 8.3 mg/kg to 58.4 mg/kg in the seven coals, which the highest value occurred in coals with V_daf from 25.6 mg/kg to 30.5 mg/kg.The content of aPAHs ranged from 31.4 mg/kg to 236.5 mg/kg; aPAHs concentration was higher than pPAHs by four times in average. The similar ranges of PAHs concentration in both raw coals and RCC smoke as well as higher alkylated PAHs than pPAHs may illustrate the succession of PAHs in coal smoke from soluble compounds;(3) as for the composition, low-ringed compounds (2-3 ringed) dominated pPAHs in coal with V_daf less than 25.6%, while middle to high-ringed PAHs (4-6 ringed) dominated the concentration at V_daf over 30%; aPAHs had this similarity, in which 2-3 ringed compounds is the main part in the bituminous coals with middle to high maturity while 4-ringed compounds is highest at V_daf from 30.5% to 35.5%. This compositional trend of soluble PAHs reflected the evolution rule of geological maturity of coal chemistry, and to some extent also explains the phenomenon of highest emission factors of PAHs and BC for middle volatile bituminous coals during RCC. Secondly, The research results of raw coal chemical structure： Different content of oxygen functional groups the structure features of coal as follows:(1) the content of oxygen functional groups (hydroxy, conjugated C=O skeleton vibration, unsaturated carboxylic acid C=O skeleton)in the high volatile coal LK and low volatile coal LL were consistent;(2) with the increase of volatile content, three kinds of content of oxygen containing functional groups are changed, the hydroxyl and carbonyl content proportions increase, unsaturated carboxylic acid ratio decreased, when the volatile content increased to 29%, the hydroxyl and carbonyl content is the highest, unsaturated carboxylic acid content is the lowest;(3) with the increase of maturity again, carbonyl content and unsaturated carboxylic acid content in raw coal showed a similar trend, at the same time the hydroxyl content is lower. Above findings shows that the characteristics of three kinds of content of oxygen functional groups in coal with a high volatile and low volatile showed a similar trend, and oxygen containing functional groups in the volatile medium coal mainly hydroxyl, followed by carbonyl group, but the content of unsaturated carboxylic acid is low. The characteristics of different fat carbon content in the raw coal structure are as follows:(1) with the reduction of volatile content, the ratio of RCH₃ content in raw coal decrease, but when the volatile content more than 30%, the RCH₃ content reached the maximum, with the ratio of 7:1 RCH₃ content;(2) With the increase of volatile matter content and the content is less than 35%, the ratio of RCH₃ content in raw coal reduce to 3:1;(3) when the content of the volatile reached 48%, the ratio of RCH₃ content increased, with the ratio of 4:1. The above transformation law and is consistent with the content of the free PAHs in the raw coal ratio, that free small molecular structure and the characteristics of content to a certain extent were on behalf of the coal chemical structure information. Raw coal structure of aromatic structure units characteristics as follows:(1) the nitrogen in the coal is the main form of pyrrole and pyridine;(2) 1-ringed mainly exist in the higher coal volatile content in LK, and also was the major of coal macromolecular structure unit;(3) with the reduction of volatile matter of coal molecular structure unit was mainly in the form of 2 rings, and 30.0% of the volatile content in the raw coal YCW reached the maximum;(4) when the volatile content is less than 30%, the aromatic structure in the raw coal unit gradually from two rings into three rings and four rings. To sum up, the chemical structure of different coal rank, free of small molecules and coal macromolecular network structure characteristics are consistent, aromatic unit changes in performance for the transition from epipodium primarily to give priority to the trend of low ring; Raw coal in the form of fat carbon mainly from methyl carbon content is reduced, to other forms of fat carbon gradually; Oxygen in raw coal mainly from conjugated C=O and unsaturated carboxylic acid to the transition of the hydroxyl. The study has found that the models characteristics of seven kinds of bituminous coals chemical structure are as follows:(1) the models characteristics of low volatile bituminous coals had big molecular size, high aromaticity, less side chains, and the aromatic unit were mainly composed of 2-3 ringed;(2) the models characteristics of the medium volatile and the medium-high volatile bituminous coals were mainly based on 2-3 ringed, and more branched chains and fat, and the medium-high volatile bituminous coals with more methyl side chain and carbonyl content, in the medium volatile bituminous coals carbon mainly dominated by methylene fat;(3) the models characteristics of the high volatile bituminous coal were small molecular size and high aromaticity. The research result shows that maturity are the main factors influencing the coal macromolecular structure, the second is related to its sedimentary environment and the sediment types. With the increase of maturity, aromatic carbon content in the bituminous coals presents increasing trend after lower first, coal molecular chemical structure arranged regularity and had high thermal stability. At the same time, the midterm volatile bituminous coals and high volatile bituminous coals macromolecular structure consisted of more fat and side chains, such as the methyl, ethyl.Its thermal stability were poor, which lead to its particularity.
文献类型	学位论文
条目标识符	http://ir.yic.ac.cn/handle/133337/22446
专题	中国科学院烟台海岸带研究所知识产出_学位论文
作者单位	1.中国科学院烟台海岸带研究所 2.中国科学院大学
第一作者单位	中国科学院烟台海岸带研究所
推荐引用方式 GB/T 7714	孙溶. 典型烟煤的分子结构及模型模拟的初步研究[D]. 北京. 中国科学院大学,2017.

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