【作者】 李志强；

【导师】 鲍卫仁；

【作者基本信息】 太原理工大学 ， 化学工程与技术， 2014， 硕士

【摘要】 随着一次能源消费的持续增长,优质煤储量大幅下降,低阶煤尤其是褐煤资源的开采和利用将是缓解能源需求压力的合理途径。我国褐煤资源储量丰富,但高含水量、低热值、干燥后易复吸和自燃的特性限制了其大规模利用。褐煤表面具有丰富的极性含氧官能团,这些官能团亲水性强,是褐煤高含水量以及脱水提质煤易复吸的重要原因。因此,表面含氧官能团对褐煤吸水性能的影响是褐煤清洁高效利用的关键,该研究具有重要的理论意义和实用价值。本文选择有代表性的胜利褐煤为研究对象,对其进行碱溶液及热提质处理,采用化学滴定法测定处理前后褐煤中各类含氧官能团的含量,考察提质褐煤的水分复吸行为,并分析探讨煤中各类含氧官能团对水分复吸性能的影响。研究结果主要包括以下几个方面：(1)褐煤中酸性含氧基团较多,主要以酚羟基为主,羧基次之且部分羧基以羧酸盐的形式存在,羰基在煤中占有一定比例；碱溶液可以有效改变褐煤中酸性含氧基团的含量,褐煤经碱溶液处理后,表面酸性含氧基团发生解离,碱溶液的pH值越大,煤中的酸性含氧基团解离程度越大；碱溶液处理后的褐煤中酸性含氧基团减少,表面亲水性下降,褐煤复吸水分的吸附速率降低和吸水量减少。(2)褐煤在不同条件下进行热提质后,化学结构会发生不同程度的变化。褐煤的失重率随温度的升高而增大,不同温度范围内含氧基团的变化趋势有所差别,羧基是对温度最为敏感的含氧官能团,温度达到160℃时有明显的分解；羰基在200℃之前变化缓慢,之后分解加快；温度高于240℃时,酚羟基和羧酸盐开始有较明显的分解。干燥气氛对褐煤热提质过程中含氧官能团有一定影响,褐煤在空气中热提质时,含氧官能团呈现出先增加后降低的趋势；CO2与煤之间存在一定的物理化学作用,导致褐煤在C0：气氛中提质后含氧基团含量比在Ar中提质后偏低。(3)褐煤的表面亲水性主要受孔结构和含氧官能团的控制,提质煤复吸水分的变化量在较低提质温度下主要受比表面积的影响、较高温度时含氧基团变化的贡献显著。褐煤复吸水分时吸水量q(mg/g)与各含氧官能团含量n(mmol/g)之间的关系式可以表示为：q=55.19+15.83n-COOH+9.90nAr-OH +9.65n.c=o,羧基对褐煤吸水性的贡献最大,酚羟基比羰基的吸水能力略强。(4)提质褐煤吸附较少的水分时,表面的极性基团与水分子形成强氢键,导致吸附热较大,当吸附较多的水分时,水分子之间的较弱的氢键造成了平均吸附热的降低；随着提质温度的升高,提质煤表面含氧基团减少,复吸水分时释放的热量也随之减小。更多还原

【Abstract】 With the increasing growth of primary energy consumption, high-quality coal reserves have dropped significantly. Mining and use of low-rank coal, especially for lignite resources, is a reasonable way to relieve stress for energy demand. Lignite reserve in China is relatively abundant, but the high moisture content, low calorific value and easy moisture re-adsorption greatly restrict its utilization fields. The abundant polar oxygen-containing groups in lignite with the great hydrophilia are the main factors leading to its high moisture content and the big adsorbing moisture capacity of dewatered sample. Therefore, researching the influence of oxygen functional groups on the moisture adsorption is very important for the clean and efficient use of lignite.In this paper, SL lignite was selected as a research object. It was treated with alkali solution and thermal upgrading process. Chemical titration method was used to determine the content of oxygen-containing groups in lignite before and after treatment, and the relationship between oxygen-containing groups and moisture re-adsorption of lignite was also investigated. The main findings include the following aspects:(1) There exist many kinds of acidic oxygen-containing groups in lignite. Phenolic hydroxyl accounts for mainly, carboxyl in which some of carboxyl groups is carboxylate, and the carbonyl exists for a certain proportion. Alkaline solution can effectively change the content of acidic oxygen-containing groups in lignite. The acidic oxygen-containing groups dissociates when the lignite is treated with alkaline solution, and it does more greatly with the increased pH value of alkaline solution. The hydrophilicity of lignite weakens after alkaline solution treatment due to the decrease of oxygen-containing groups, which results in a slow adsorption rate and reduction of adsorbing moisture amount.(2) The different thermal upgrading conditions lead to various changes of chemical structure for lignite. The weight loss rate of lignite increases with rising temperature, but along with varied change trends of different containing-oxygen groups in the whole temperature region. Carboxyl is the most susceptive group to temperature, which can be decomposed dramatically at above 160℃. Carbonyl groups start to breakdown at above 200℃, while carboxylate and phenolic hydroxyl groups appear to be stable up to 240℃. Drying medium also greatly affects the removal of oxygen-containing groups, which proceeds more easily in CO2 atmosphere compared with that in Ar. The oxygen-containing groups increase first because of oxidation reaction of lignite exposed to air in the upgrading process and then decrease due to the decomposition.(3) The hydrophilia of lignite is mainly controlled by pore structure and oxygen-containing groups. The adsorbing moisture capacity of dewatered lignite changes mainly with the surface area at low drying temperature and the contributions of oxygen-containing groups are obvious. The relationship between moisture re-adsorption content of q (mg/g) and oxygen-containing groups of n (mmol/g) accords with following formula:q= 55.19+15.83n.cooH +9.90nAr-oH+9.65n_c=o. Carboxyl, as the polar oxygen group, contributes the most to the moisture adsorption content.(4) The isosteric heat of adsorption is relevant to the adsorbing moisture content of upgraded lignite. As the upgraded lignite adsorbs less moisture, the moisture molecule combines with oxygen groups in the form of great hydrogen bond, resulting in higher isosteric heat. When more moisture is adsorbed to lignite, the weak hydrogen bond between moisture molecules leads to the decrease of isosteric heat. As the upgrading temperature rises, the isosteric heat of upgraded coal decreases.更多还原