摘要
A series of both unsupported and coal‐supported iron–oxygen compounds with gradual changes in microstructure were synthesized by a precipitation‐oxidation process at 20 to 70°C.The relationship between the microstructures and catalytic activities of these precursors during direct coal liquefaction was studied.The results show that the microstructure could be controlled through adjusting the synthesis temperature during the precipitation‐oxidation procedure,and that compounds synthesized at lower temperatures exhibit higher catalytic activity.As a result of their higher proportions ofγ‐FeOOH orα‐FeOOH crystalline phases,the unsupported iron–oxygen compounds synthesized at 20–30°C,which also had high specific surface areas and moisture levels,generate oil yields 4.5%–4.6%higher than those obtained with precursors synthesized at 70°C.It was also determined that higher oil yields were obtained when the catalytically‐active phase formed by the precursors during liquefaction(pyrrhotite,Fe1-xS)had smaller crystallites.Feed coal added as a carrier was found to efficiently disperse the active precursors,which in turn significantly improved the catalytic activity during coal liquefaction.
煤直接液化生产液体燃料是煤洁净转化和高效利用的一种重要途径,是平衡富煤少油地区资源的有效技术手段.高效煤直接液化催化剂能够促进煤的热解,加速热解大分子的加氢裂化,提高液化产物中油的收率和油的品质.各种含铁物质如赤泥、天然铁矿石、合成型铁硫化物、合成型铁氧化物、以及油溶性和水溶性含铁物质都被用做了煤直接液化催化剂的前驱体,它们在煤液化条件下都能原位转化为磁黄铁矿相(Fe_(1-x)S)从而起到催化作用.由于前驱体组成和性质差异,原位生成的活性相的性质也会有较大差异,导致煤液化结果有很大不同.对前驱体的性质和其原位形成的活性相及其煤液化催化活性的关联研究,对于催化剂前驱体的筛选、设计和生产都具有非常重要的指导意义.但由于影响煤液化结果的因素很多,并且催化剂前驱体的来源、组成或制备条件的差异,很难判定前驱体的某一性质是影响煤液化催化活性的决定性因素,更难以获得前驱体的晶相、晶粒度、比表面积、粒度等因素与煤液化结果的趋势性关联关系.我们采用相同的制备方法和相同的反应原料,仅改变一个容易调变的温度参数,成功制备出同一体系且具有渐变微观结构的铁氧化合物前驱体,并在高压釜内考察了硫化性质和对神华神东煤的催化液化活性,通过SEM,XRD,TG,BET和H2-TPR等表征手段研究了不同温度合成的铁氧化物前驱体的微观结构与性质,进而探索建立与煤液化催化活性之间的关联.结果发现,铁氧化物的微观结构可以通过控制液相合成时的沉淀及氧化反应温度来调变,铁氧化物前驱体晶相是最重要的影响因素.正是得益于包含较多的γ-FeOOH和α-FeOOH晶相,以及较大的比表面积,较高的含水量和更多的活性氧数量,相比高温(70°C)合成的铁氧化物低温(20–30°C)合成的铁氧化物油收率可提高4.5%–4.6
基金
神华集团科技创新项目(MZY-13-12)
国家重点研发计划(2016YFB0600303).
