煤结构松弛与小分子相分离过程的调控及加氢液化性能研究

Direct coal liquefaction (DCL) is a multiphase reaction process, especially in the initial stage of DCL, the hydro-liquefaction of coal is obviously controlled by the mass-transfer process. To accelerate the diffusion of hydrogen-donor solvent into coal matrix can improve the liquefaction property of coal by suppressing the regressive condensation of pyrolyzed free radical. By the thermal extraction of coal below the pyrolysis temperature and the hydro-liquefaction of extracted coal, this project will focus on the influences of the structural relaxation of macro-molecule network and the separation of mobile phase from coal through heat treatment in solvent on the diffusion behavior of hydrogen-donor solvent and the liquefaction property of treated coal. The relationship of the structure and liquefaction reactivity of treated coal will be further clarified. Finally, the regulation mechanisms on the controllable separation of the mobile phase and the structure of treated coal used to hydro-liquefaction will be formed. In detail, based on the research on the relaxation behavior of coal macro-molecule and its influences on the microstructure, the diffusion effects of solvent and the liquefaction performances of treated coal, the mechanism of structural relaxation of coal and the diffusive control on the hydro-liquefaction of coal will be revealed. Meanwhile, the liquefaction behavior and mechanism of the mobile phase in DCL process, and interaction between the structural relaxation and the separation of the mobile phase will also be clarified by the research on the thermal extraction rule of the mobile phase and the hydro-liquefaction property of extracted coal. Therefore, the obtained results in this project will not only offer the essential theoretical and technical support for the solution of relevant problems in DCL technology, such as the coking in the preheater, lower yield of oil, etc., but also can promote the step-wise conversion and utilization of coal.

煤直接液化属于多相反应过程，尤其在初始液化阶段煤的加氢液化主要由传质过程控制，促进供氢溶剂扩散，可以抑制煤热解自由基逆向缩合，改善液化性能。本项目提出通过煤非热解条件下的热抽提和抽余煤加氢液化，重点研究溶剂和热场作用下煤大分子结构松弛和小分子相分离对溶剂扩散行为和液化性能的影响规律，揭示处理煤的结构与液化性能的构效关系，形成煤中小分子相可控分离及适合于加氢液化的抽余煤结构调控机制。拟通过煤大分子结构松弛行为及其对煤微观结构、溶剂扩散效应和液化性能的影响规律研究，阐明溶剂热处理过程中煤的结构松弛机理及液化过程中溶剂扩散的控制作用；通过小分子相热抽提规律以及小分子相分离后抽余煤的液化性能研究，揭示小分子相在煤液化过程中的作用行为以及大分子结构松弛与小分子相分离的交互作用。本项目的研究将为解决煤直接液化工艺中预热器结焦、油收率偏低等相关问题提供必要的理论和技术支撑，并有助于煤的分级转化与利用。

为了研究煤结构松弛和小分子相分离对煤液化性能的影响规律，促进煤高效液化和分级利用。以神府次烟煤（SF）、锡林郭勒褐煤（XL）、先锋褐煤（XF）等为研究对象，通过THF和CS2/NMP溶剂抽提及热溶等方法考察了煤中小分子相分离性能，结合抽余煤分子结构和溶胀与扩散动力学表征，研究了煤分子结构松弛行为与溶剂扩散规律。然后，通过抽余煤煤加氢液化，研究了煤结构松弛和小分子相分离对加氢液化性能的影响规律。. 研究结果表明：中低价煤以共价键交联的大分子结构存在，非共价键交联密度高，小分子相含量低。甲苯/甲醇等常规溶剂热溶可以有效分离煤中小分子相，调变溶剂组成和热溶温度是实现小分子相可控分离的有效途径。甲苯和甲醇间存在明显的协同作用，甲苯/甲醇（T/M=3）混合溶剂效果最佳。溶剂中小分子相分离能够引起抽余煤分子间非共价键作用重排。其中，XL抽余煤孔径和孔隙率较原煤明显提高；SF抽余煤孔径增大，孔隙率变化不明显。热溶抽提能够不同程度松弛了煤大分子结构，溶胀过程遵循Fickian扩散机理，活化能低。抽余煤中溶剂扩散呈现一级扩散动力学特征，有效扩散系数都处于4.2-7.4×10-8m2/h范围内。溶剂抽提和热溶能够改善煤的液化性能，提高煤液化转化率和油气收率。提高热溶温度、添加适量甲醇有利于热溶煤加氢液化。虽然溶剂抽提能够松弛煤结构，有利于供氢溶剂传质，但是小分子相分离不利于煤分子热解自由基的原位供氢。同时，XL煤具有良好的高温热解液化性能，可以在氮气和THN供氢溶剂中进行非催化热解液化，形成以油气为主的轻质产物，其液化过程主要是活泼氢诱导下的加氢裂解过程，添加氢转移剂可以促进XL煤热解液化。此外，研究也发现乙醇胺水溶液对XL煤具有良好的溶胀能力，其溶胀机理与断裂离子键有关。. 上述研究，完成了计划书研究内容，达到了相应研究目标。相关研究成果可以为解决煤直接液化相关工艺问题，促进煤的分级利用供理论和技术支撑。