热解预处理对昭通褐煤润湿性的影响机制

Influential mechanism of pyrolysis pretreatment on wettability of Zhaotong lignite

褐煤的强亲水性为其加工和利用造成了许多不利影响,热解预处理是调控褐煤润湿性的有效方法之一。采用工业分析、傅立叶变换红外光谱(FTIR)、X射线衍射(XRD)和接触角测量探究了热解预处理对褐煤润湿性的影响机制。热解预处理的温度分别为200℃,300℃,400℃和500℃,时间分别为30 min,60 min,90 min和120 min。结果表明:热解预处理改变了褐煤的化学结构和组成,显著影响了褐煤的润湿性。褐煤的羧基在200℃时开始裂解逸出,并在300℃时基本消失;褐煤的酯基在300℃时开始裂解逸出,并在400℃时基本消失;而褐煤的C—O(醚键、酚和醇)的热稳定性较好,热解预处理后其相对含量略微增加;褐煤的芳碳率随着热解温度和时间的增加而增大,且芳香核尺寸在300℃时开始增大。如果使用热解预处理来减弱褐煤的亲水性,则应确保在较低温度下有足够的热解时间来去除褐煤的含氧官能团,而在较高温度下应使用较短的时间来防止褐煤的有机质过度损失。在300℃(120 min)或400℃(30 min)热解条件下,褐煤的亲水性含氧官能团(羧基或酯基)裂解逸出,且疏水性芳香核尺寸增大,从而使其亲水性显著减弱,接触角由原煤的44.00°分别增大为87.50°和85.75°。然而,在400℃(热解时间大于30 min)和500℃条件下,褐煤的有机质过度损失,导致矿物质或无机质的相对含量增加,使其亲水性仍然较强。

The significant hydrophilicity of lignite has caused many adverse effects on its processing and utilization.Pyrolysis pretreatment is one of the effective methods to regulate the wettability of lignite.The influential mechanism of pyrolysis pretreatment on the wettability of lignite was investigated using proximate analysis,Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),and contact angle measurement.The temperatures of pyrolysis pretreatment were set as 200℃,300℃,400℃,and 500℃,and the times were 30 min,60 min,90 min,and 120 min,respectively.The results show that pyrolysis pretreatment alters the chemical structure and composition of the lignite,significantly affecting its wettability.The carboxyl group of lignite starts to decompose and volatilize at 200℃,and basically disappears at 300℃.The ester group starts to break down and volatilize at 300℃,and basically disappears at 400℃.C—O(ether bonds,phenols,and alcohols)exhibits high thermal stability,with a slight increase in relative content.The aromatic-carbon ratio of lignite increases with temperature and time,and the size of aromatic core begins to expand at 300℃.If pyrolysis pretreatment is adopted to attenuate the hydrophilicity of lignite,it is essential to ensure sufficient pyrolysis time to remove oxygen-containing functional groups effectively at lower temperatures.Conversely,a shorter pyrolysis time should be available to prevent excessive loss of organic matter at higher temperatures.At the pyrolysis conditions of 300℃(120 min)or 400℃(30 min),hydrophilic oxygen-containing functional groups(carboxyl or ester groups)are decomposed and volatilized,and the size of hydrophobic aromatic core increases,resulting in a significant decrease in hydrophilicity.The contact angle increases from 44.00°of raw coal to 87.50°and 85.75°,respectively.However,at 400℃(pyrolysis time greater than 30 min)and 500℃,excessive loss of organic matter leads to an increase in the relative content of minerals or inorganic matter,resulting in still strong hydrophilicity.