褐煤中有机氧的赋存形态及其在热解过程中的迁移规律

High organic oxygen and water contents and the resulting low calorific value, make lignite difficulty in industrial use, especially for thermoelectricity generation. It is therefore necessary to develop efficient conversion processes to minimize such disadvantages. Pyrolysis was widely used for lignite upgrading as it can convert lignite into useful products of combustible gases, tar, and solid char. However, high oxygen content in lignite represents a drawback of pyrolysis use due to the formation of oxygen containing species, reducing the quality during utilization as fuel.It is of great importance for the clean and highly efficient utilization of lignite to realize the forms and transformation mechanism of organic oxygen during pyrolysis process and the relationship with water evolution. In this project, we mainly use three typical chinese lignites. Main investigations include: (1) supercritical alcoholysis of lignite with methanol, ethanol and n-butanol and charaterization of the resulting soluble reaction mixtures with GC/MS, HPLC/ITMSn and RRLC/TOF-MS/FTIR, understanding of the forms of organic oxygen of lignite in detail association with in situ analysis (including FTIR, XPS, SEM, TEM and DARTMSMS) of the lignite. (2) pyrolysis of lignite at different conditions (including pyrolysis temperature, heating rate, residence time and carrier gas), understanding of the distribution of organic oxygen in pyrolysis products, with the emphases to relatively comprehensively understand structures and compositions of the organic oxygen in resulting tar with multiple advanced analytical instruments and subsequently reveal the organic oxygen transformation behavior during pyrolysis of lignite through the comparison of results of pyrolysis of oxygen-containing model compounds; (3) physico-chemical charaterization of lignite char with in situ analysis and its correlation with water evolution; (4) reveal the relationship between the organic oxygen transformation and water evolution during pyrolysis process.

水分和有机氧含量高是导致褐煤热值低的主要因素。热解是褐煤提质利用的有效手段之一，深入了解褐煤中有机氧的赋存形态及其在热解过程中的迁移规律对于优化褐煤高效提质利用的工艺具有十分重要的指导意义。本项目通过超临界醇解切断褐煤中的含氧桥键进而运用气相色谱/质谱联用仪、高效液相色谱/多级离子阱质谱联用仪和快速高分离液相色谱/飞行时间质谱/红外光谱联用仪分析等先进的分析手段表征所得可溶物中有机氧的分子结构，从分子水平上揭示褐煤中有机氧的赋存形态；在不同条件下热解褐煤及其含氧模型化合物，通过后续的分离和分析研究热解产物的组成分布，特别是所得焦油中有机氧的组成结构，运用直接分析质谱、红外光谱和X射线光电子能谱等先进原位分析手段了解褐煤及所得半焦的含氧官能团的表面物理化学属性，揭示褐煤热解过程中有机氧的迁移规律和水的析出机理，为优化褐煤的热解提质工艺提供理论依据。

水分和有机氧含量高是导致褐煤热值低的主要因素。热解是褐煤提质利用的有效手段之一，深入了解褐煤中有机氧的赋存形态及其在热解过程中的迁移规律，对于优化褐煤高效提质利用的工艺具有十分重要的指导意义。.本文选取白音华（BYH）和锡林郭勒（XLGL）两种褐煤为研究煤样。通过X射线光电子能谱（XPS）、傅里叶变换红外光谱（FTIR）和元素分析等研究褐煤中有机含氧官能团（OFGs）的赋存形态。结果表明：褐煤中的OFGs可以分为羧基、羟基（酚羟基和醇羟基）、羰基、活性醚键和非活性醚键。由于褐煤中水的吸附形态主要与羟基的存在形态有关。通过对红外光谱中羟基官能团的分峰拟合得出褐煤中的羟基主要为自由羟基（FHG）、羟基氢键（PHB）、自由缔合的羟基氢键（SHB）、羟基醚氢键（EHB）、呈环状紧密缔合的羟基（RHB）和羟基N氢键（NHB），其中主要以PHB和EHB的形态存在。.利用固定床石英管反应器对BYH和XLGL两种褐煤进行快速热解，研究了热解温度和气体停留时间（GRT）对热解产物的产率及氧分布的影响，并用多种先进分析手段研究了热解产物中含氧化合物（OOSs）的组分和含量。结果表明，BYH褐煤在500 oC，GRT为2.5 s时焦油产率达到最大值为15.3%（daf）。XLGL褐煤在600 oC，GRT为1.5 s时焦油产率最大为12.9%（daf）。低于600 oC时，CO2为主要的热解气体，并且在低于400 oC下主要来源于羧基的热解。CO的含量随热解温度的升高而显著增加。700 oC时，BYH和XLGL中CO的生成量达最大值分别为46.4和44.0 mL/g（daf）。热解水中氧的产率在200 oC时小于20%，温度增加至700 oC时，由于OFGs的脱除率增加和挥发分的裂解加剧，热解水中的氧的产率显著增加至30%左右。高于400 oC时，OFGs主要分解为热解水和热解气。焦油中可检测到的OOSs为酚类、酮类、酯类、醇类和呋喃类物质，其中酚类物质（苯酚、甲酚和二甲酚）为主要含氧物质。反应条件为500 oC，GRT为10 s时，BYH和XLGL焦油中酚类的最大产率分别为27.1%和26.3%（以焦油含量为基准）。本文探究了褐煤中的氧在热解过程中的迁移规律，为提高褐煤的高效利用提供了理论依据。