单模微波下褐煤二元催化热解制轻质芳烃

Binary catalytic pyrolysis of lignite for light aromatics under single mode microwave

以苯、甲苯、二甲苯为主的轻质芳烃作为重要的化工原料,在染料、农药、医药领域应用广泛。我国石油资源匮乏但褐煤资源丰富,利用微波加热技术的选择性与高效均匀性,有望通过褐煤的微波热解获得富含轻质芳烃的焦油。以云南褐煤为原料,采用对微波电场分布控制精度更高的单模微波反应器,从微波电场分布的角度探究二元金属氧化物NiFe_(2)O_(4)、NiMoO_(4)与Fe_(2)(MoO_(4))_(3)在微波热解过程中对电场分布、焦油中轻质芳烃含量以及热解行为的影响。通过矢量网络分析仪对煤样的介电参数进行测量,并模拟对应的电场分布。结果表明,二元金属氧化物的加入改变了煤样所处电场分布,使其整体强度降低,有效增加了煤样吸收微波并转化为热的能力,提升了煤样热解的升温速率与最终温度。通过GC-MS、FT-IR等手段对焦油与半焦的化学组成进行分析,可知二元金属氧化物的添加促进大分子烷基以及大分子芳香结构的裂解,增强了热解体系内小分子烷基与·H含量,有效提高了焦油中轻质芳烃含量,在添加NiFe_(2)O_(4)、Fe_(2)(MoO_(4))_(3)与NiMoO_(4)后,轻质芳烃质量分数分别从21.21%增至44.28%、37.46%与43.21%,但因裂解反应增加焦油产率从10.28%降至9.76%、6.51%与9.20%,气体产率增加;另外过渡金属活性中心存在d轨道空穴,通过与含氧基团相结合,形成R_(2)-O X-R_(1)(X为金属活性组分)结构,促进了含氧结构的裂解,对降低焦油中含氧物质含量有积极作用。

Light aromatic hydrocarbons including benzene,toluene and xylene,as important chemical raw materials,have important applications in the fields of dyes,pesticides and medicine.Petroleum resources is scarce but lignite resources is rich in China.Using the selectivity,high efficiency and heating uniformity of microwave heating technology,it is expected that tar rich in light aromatics is obtained by microwave pyrolysis of lignite.In this study,Yunnan lignite was used as raw material,and a single-mode microwave reactor with higher control accuracy of microwave electric field distribution was adopted,to explore the effects of binary catalysis NiFe_(2)O_(4),NiMoO_(4)and Fe_(2)(MoO_(4))_(3)on electric field distribution,light aromatics content in tar and pyrolysis behavior during microwave pyrolysis from the perspective of microwave electric field distribution.The dielectric parameters of the coal samples were measured by vector network analyzer,and the electric field distribution was simulated.The results show that the addition of binary metal oxides changes the electric field distribution,reduces electric field intensity and effectively increases the coal samples′ability of absorbing microwaves energy and converting it into thermal energy,which improves the heating rate and final temperature during pyrolysis.The chemical composition of tar and char was analyzed by GC-MS,FT-IR.The results show that the addition of binary metal oxides increases the content of small molecular alkyl groups and·H in the decomposed system effectively by promoting the cracking of macromolecular alkyl and macromolecular aromatic structures and effectively improves the content of light aromatics in tar.After the adding of NiFe_(2)O_(4),Fe_(2)(MoO_(4))_(3)and NiMoO_(4),the content of light aromatics increases from 21.21%to 44.28%and 37.46%and 43.21%respectively,but the tar yield decreases from 10.28%to 9.76%,6.51%and 9.20%due to the increase of the cracking reaction,and the gas yield increases;in addition,there are d orbital holes in the active center of the transition metal,and by combining with oxygen-containing groups,an R_(2)-O X-R_(1)(X is a metal active component)structure is formed,which promotes the cracking of the oxygen-containing structure and has a positive effect on reducing the content of oxygen-containing substances in tar.