煤的可溶性与溶剂结构、性质间的定量关系

Thermal extraction is an effective way for obtaining value-added organic compounds and liquid fuel from coals under mild conditions. However, the coal dissolubility is the main reason for restricting industrial use of the thermal extraction processes. Therefor, revealing the relationship between the structures and properties of solvents, the chemical composition of coals and coal dissolubility is crucially important for the dissolution of organic matter in coals. In this project, coal dissolution behavior is investigated in various solvents, which are selected according to the structural and property parameters. Depending on the liquid yields, the quantitative relationship between coal dissolubility and structure-property of solvents is analyzed using various statistical methods. The liquid products are finely separated into several fractions by high-speed countercurrent chromatography and spinning band distillation column. All of the liquid fractions and extraction residues are then analyzed with multiple advanced analytical instruments for investigating the existing form of organic matter, including functional group, the degree of condensation of the aromatic ring, substituted type and structural features of aliphatic chain, and their clustering distribution behavior at the molecular level. To investigate the detailed mechanisms for coal dissolution and the association characteristics of coal molecules, we use ReaxFF reactive force field to perform a series of molecular dynamics simulations on model compounds. Furthermore, the mathematical model for illustrating the quantitative relationship between coal dissolubility and structure-property of solvent is optimized according to the results from ReaxFF simulations. These investigations will provide scientific evidences and technical supports for the efficient coal directional conversions.

煤的溶剂热萃取是能够在温和条件下获取高附加值有机化学品和液体燃料的有效途径。而煤的可溶性是制约煤溶剂热萃取的主要内在因素，因此揭示溶剂的结构和性质、煤的组成结构以及煤的可溶性之间的关系对于实现煤中有机质的可溶萃取至关重要。本项目拟根据化合物结构和性质参数选取适宜的溶剂，运用多种统计方法系统考察煤的可溶性与溶剂结构和性质间的定量关系；利用高速逆流色谱和旋转带蒸馏仪对液体有机产物进行精细分离，并采用多种先进的分析手段详细分析液体有机产物和萃余物，重点从分子水平上了解煤中可溶有机质的存在形态（包括官能团、芳环缩合度和取代类型以及脂肪链烃结构特征）及其在不同性质溶剂中的聚类分布规律；借助模型化合物和ReaxFF反应动力学模拟，考察煤中典型有机分子的缔合特征及溶解机理，根据ReaxFF模拟结果优化煤的可溶性与溶剂结构、性质间定量关系数学模型。基于上述研究为开发煤的高效液化工艺提供科学依据和技术支撑。

煤的热溶是一种反应条件温和，煤中有机质能够充分利用且操作过程简单的高效直接液化工艺。目前，尚无一种能够有效关联煤的可溶性与溶剂性质的数学关系，更缺少有效筛选具有特殊溶解性能的溶剂的理论方法。.本项目首先选取合适的煤分子模型，利用分子动力学计算其溶解度参数；采用Marcus状态方程对多种常见溶剂的热力学性质进行了计算。结果显示，当溶剂的溶解度参数为20-26 MPa1/2时，煤中有机质能够有效地溶解其中。预测通过合理的温度调控能实现甲醇、乙醇及丁内酯对煤的溶解。模拟结果还显示，煤中氢含量、含氧官能团和桥键类型、芳香缩合度及煤的密度对煤的溶解性有很大的影响，而通过减少煤中氢含量和桥键数量能够促进煤的可溶。.在250 oC乙醇溶剂中对多种煤样进行了热溶反应性考察，同时采用相关和通经分析对实验结果进行了深入的剖析。结果显示，氢含量和氮含量皆与煤热溶产率呈显著正相关关系。而煤中水含量、硫含量及氧含量与煤热溶收率成明显负相关。通经分析进一步说明，煤中氮含量和碳含量分别对煤热溶产率具有显著的直接和间接作用；煤中碳含量、氢含量，尤其是氮含量的升高明显有利于煤热溶收率的增加。并且构建了热溶收率与煤性质参数的回归模型。.基于单一溶剂的研究结果，考察了水/乙醇混合溶剂对榆家梁次烟煤的可溶性反应，发现当温度为270 oC时，采用体积比为7：3的乙醇/水混合溶剂能够实现煤中48.27%有机质的可溶。该结果与亚临界水（350 oC）水对煤的溶解效果相当，但反应条件更加温和。通过对溶解过程的调控和产物分析，发现可溶有机质主要来源于热溶升温过程。.采用scaffold tree方法对煤中可溶有机质进行了聚类分析。分析结果显示，煤中可溶有机质可分为线性分子和环型分子两大类。其中线性分子主要包括烷烃、酸、烯烃、烷醇、酯、酮、醛、含氮有机物及含硫有机物。环型分子结构较为复杂，但通过对其进行深入分析能够获得煤中丰富的碳骨架和桥键等信息。.采用ReaxFF动力学方法对几种常见的煤相关模型化合物进行了加氢反应模拟。结果表明，加氢引发反应的活性位不仅与超离域能有关，还与空间位阻效应有关。由于所需活化能较小，加氢引发反应主要发生于芳环取代位的邻位，虽然H•附加于取代位形成的加氢自由基在热力学上更加稳定，说明加氢引发反应主要受动力学控制。ReaxFF模拟结果与无硫体系的加氢实验结果一致。