褐煤油煤浆预热过程中溶剂-煤相互作用及其机制

The reserve of lignite or brown coal in China is abundant,however, the efficiency of its utilization is very low because of its high content of moisture and oxygen. Preheating of brown coal-oil slurry before direct liquefaction is important for improving efficiency and lowering hydrogen consumption of the process. As far as we know, there is little information on the coal-solvent interactions during this preheating stage and lack of knowledge about the effects of the preheating on coal phsico-chemical structure and solvent properties. The research of this project is mainly on the the coal-solvent interactions during low temperature (<350oC) pretreatment of brown coal with different solvent and its effects on the structure of brown coal and slvent properties. The dewatering and the transformation of oxygen containing groups in brown coal will be studied. The effects and mechanism of organic solvent treatment on the physical and chemical structures of brown coal will be obtained by analyzing its pore structure, oxygen containing groups and hydrogen bonds, etc, of the lignite after preheating. The properties changes of the solvent after treatment and the dissolution of the low molecular compounds, also the hydrogen transferring during preheating will be studied to further investigate the coal-solvent interactions. Through the above-mentiond studies, we hope to provide theoretical guidance of coal chemistry for the optimization of preheating of coal-oil slurry and hydrogenation of solvent during direct liquefaction of brown coal, and this study will widen the contents of the chemistry of low-rank coal utilization as well.

我国褐煤储量丰富，但褐煤高水高氧含量的特点决定了其热转化过程的能效较低。因此褐煤直接液化过程中油煤浆的预热过程对于提高过程能效、降低氢耗具有重要作用。而针对此阶段循环溶剂与褐煤的相互作用的研究较少，也缺乏对这种相互作用引起的煤结构及溶剂性质的改变的清晰认识。本项目针对低温预热阶段（<350oC）中溶剂与褐煤之间的相互作用及其对褐煤物化结构、溶剂性质的影响展开研究。重点研究有机溶剂存在条件下褐煤中水分的脱除和含氧官能团的变迁规律；通过对不同条件下预热处理后褐煤的孔道结构、含氧官能团、氢键等的分析，获得溶剂预热过程对褐煤物理化学结构的影响规律和机制；研究预热后溶剂结构性质变化及褐煤中小分子的溶出特性，结合此过程中的氢转移机制，进一步研究溶剂-煤相互作用。通过本项目的研究，为优化褐煤直接液化过程中油煤浆预热工艺和溶剂加氢工艺提供煤化学的理论指导，同时也将丰富低阶煤利用化学的内容。

褐煤直接液化过程中油煤浆的预热过程对于提高过程能效、降低氢耗具有重要作用，本项目针对预热阶段循环溶剂与褐煤的相互作用以及由此引起的煤结构及反应性的变化进行深入研究，以期为油煤浆预热及溶剂加工工艺提供理论基础。研究发现油煤浆预热过程中，温度和停留时间对预热过程影响最为显著。预热温度升高可促进气体、油品（正己烷可溶物）、水产率增加。停留时间延长有助于油品收率增加，水、气体产率在15 min基本达到平衡。预热阶段生成的水产率随原煤含氧官能团数量的增加而升高，油煤浆预热处理可以有效脱除褐煤中的氧元素。原煤中过高的羧基含量会导致煤在350oC就发生明显的交联反应，降低固体反应性，不利于后续加氢液化。预热过程中煤生成的自由基首先诱导四氢萘α氢自芳环脱除，并激活β位自由基氢。自由基数量增多可促进氢转移反应的剧烈程度。预热阶段溶剂氢耗与油水收率和转化率呈明显的正线性关系。在无催化剂、同一温度条件下，供氢溶剂的供氢能力远高于氢气，是煤加氢的主要来源，并且气相氢与供氢溶剂在对煤的供氢过程中形成竞争关系。对于高反应性低阶煤，在惰性气氛下提供充足的供氢溶剂即可取得高液化转化率和油收率。烷基芳烃类溶剂中的Cal-Car可由煤基自由基或氢自由基诱发断裂，从外界获取氢生成链烷烃和芳烃，降低煤液化体系中的氢利用效率，并在氢源不足时抑制油品生成。因此液化溶剂中应严格控制烷基芳烃的含量，或者在溶剂加工工艺中使其催化转化生成具有供氢能力的溶剂。理论计算结合实验研究表明，溶剂中较强氢键受体苯的存在一定程度上促进了酚羟基和羧基中C-O共价键的断裂，即预热过程中酚羟基和羧基的分解。在预热阶段停留可以使煤和溶剂充分接触，煤裂解生成的自由基充分加氢，未分解部分在溶剂中充分溶胀，孔体积变大，减小了溶剂的移动阻力，利于高温段煤中化学键断裂后及时获取氢自由基，提高后续液化过程的油收率。