铁催化剂对煤热解过程中氮元素迁移的影响

EFFECT OF IRON ADDITION ON TRANSFORMATION OF NITROGEN DURING COAL PYROLYSIS

应用ＸＲＤ和ＥＸＡＦＳ技术表征了热解温度对煤中铁催化剂形态的影响，用ＸＰＳ表面分析方法研究了铁催化剂对煤热解过程中氮元素迁移的影响。结果表明：铁元素在低温制备煤焦中的主要物相是Ｆｅ２Ｏ３和Ｆｅ３Ｏ４，而在高温制备的煤焦中，还原态αＦｅ和铁碳物种（Ｆｅ，Ｃ）是铁元素的主要存在形态。煤或焦中的氮元素以季胺盐、吡啶和吡咯等三种形态存在。铁能催化季胺盐在较低温度下分解。与吡咯类氮相比较而言，铁能优先催化吡啶类氮脱除。说明铁催化剂对不同形态的氮元素，在煤热解过程中的逸出影响是不同的。煤中掺入铁催化剂，能使其中的氮元素较多地留在低温煤焦中，从而减少了煤的低温热解阶段污染性氮化物气体的逸出量。

Lignite with an iron catalyst precipitated using a Fe(NO 3) 3 solution was pyrolyzed at 400℃￣1000℃ in a fixed bed reactor XRD(Xray diffraction) and EXAFS (Extended Xray absorption fine structure) techniques were used to study the change in chemical forms of iron catalysts during the pyrolysis The forms of the iron species in the pyrolyzed char depended strongly on pyrolysis temperature With an increase in pyrolysis temperature, the forms of iron varied according to the following sequence: FeOOH→Fe 2O 3→Fe 3O 4→αFe→Fe 3C and Fe 5C 2 XPS (xray photoelectron spectroscopy) was applied to study the functional forms of nitrogen surface concentration of Fe and N elements in chars The result shows that the presence of iron loading changes the transformation of coal nitrogen during pyrolysis, the nitrogen content of the char produced at lower temperature with iron is higher than that without iron Three types of coal nitrogen (pyrrolic, pyridinic and quaternary functionalities) in coal and chars, were quantified The variation of the decomposed fraction of each nitrogen type during coal pyrolysis as a function of pyrolysis temperature were determined by XPS analysis The addition of iron catalyst promoted quaternary nitrogen to be evolved at lower temperatures Pyridinic nitrogen evolves in larger amount than pyrrolic nitrogen at the same temperature due to iron catalysis