炭质吸附剂吸附煤热解废水中有机物机理研究

Study on adsorption mechanism of carbonaceous adsorbent for organic matter in wastewater from coal pyrolysis

低阶煤分质梯级利用是煤化工发展的重要方向,是实现煤炭清洁高效转化的重要途径。但低阶煤热解过程中反应温度较低,会伴随焦油和酚等产生,通常油水分离过程不能将其完全分离,因此部分有害物质被带入水中,增大废水处理难度。吸附法是处理煤热解废水中最简单最直接的方法,处理效果稳定。以此废水为研究对象,采取吸附法,选用商用活性炭、褐煤粉焦、烟煤粉焦、不定形活性焦4种吸附剂,探究炭质吸附剂处理废水的可行性。炭质吸附剂具有相似的表面元素组成和碳元素的结合形式,但比表面积、平均孔径等参数差异性明显。通过序批式试验,证明在一定范围内,吸附剂投加量越大、吸附时间越长、pH越小水样中COD去除效果越好。4种炭质吸附剂对苯和苯的衍生物有较好的吸附作用,去除率均在78%以上,对含氮杂环化合物吸附作用略差,最高仅在47%左右。商用活性炭和褐煤粉焦去除长链烃类的效果远高于不定形活性焦。从理论上分析了吸附剂对有机物的吸附动力学与热力学过程,发现4种吸附剂对污染物的吸附动力学行为均可用准二级动力学模型描述,且吸附速率由颗粒内扩散过程和液膜扩散过程共同控制。Langmuir等温吸附模型可更好地描述有机物在吸附剂上的吸附行为,吸附过程以单分子层吸附为主,该过程是自发、放热、熵减的过程,且以物理吸附为主。

The cascade utilization of low rank coal is an important direction of coal chemical industry development and an important way to achieve clean and efficient transformation of coal.However,tar and phenol will be produced when the reaction temperature is relatively low during the pyrolysis of low rank coal.Usually,the oil-water separation process cannot completely separate them,so some harmful substances will be brought into the water,increasing the difficulty of wastewater treatment.Adsorption is the simplest and most direct method to treat coal pyrolysis wastewater,and the treatment effect is stable.Taking this wastewater as the research object,the feasibility of treating wastewater with carbonaceous adsorbent was explored by adopting adsorption method and selecting four adsorbents,namely commercial activated carbon,lignite fine coke,bituminous coal fine coke and amorphous activated coke.Charcoal adsorbent has similar surface element composition and carbon element combination form,but its specific surface area,average pore diameter and other parameters are obviously different.Through sequencing batch experiment,it is proved that within a certain range,the greater the dosage of adsorbent,the longer the adsorption time,and the smaller the pH,the better the removal effect of COD in the water sample.The removal efficiency of long chain hydrocarbons by commercial activated carbon and lignite fine coke is much higher than that of amorphous activated coke.The adsorption kinetics and thermodynamic process of the adsorbents on organic matters were analyzed theoretically.It is found that the adsorption kinetics of the four adsorbents on pollutants can be described by a quasi second order kinetic model,and the adsorption rate is jointly controlled by the diffusion process in the particles and the diffusion process in the liquid film.Langmuir isotherm adsorption model can better describe the adsorption behavior of organic substances on the adsorbent.The adsorption process is mainly single-layer adsorption,which is a spontaneous,exothermic,entropy reducing process,and mainly physical adsorption.