搅拌釜费托铁催化剂反应动力学研究
Studies on the kinetics of Fischer-Tropsch synthesis for iron-based catalyst in CSTR
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摘要: 为获取铁基催化剂在费托合成反应中的CO转化集总动力学模型,为费托反应器设计和工艺优化提供依据,使用自主研发的工业催化剂CNFT-1(主要成分Fe-Cu-K-B-Si,堆密度0.8 g/cm3),基于经典且广泛接受的碳化物机理(Carbide),以次甲基生成基元反应为速率控制步骤,推导了LHHW型CO转化集总动力学模型。在1 L搅拌釜反应器(高径比2.5)中首先排除了内外扩散的影响(搅拌转速>400 r/min,空速>7 000 mL/(g·h)且粒径<150 μm),然后通过正交试验进行了30组反应动力学实验,条件如下:503~553 K,1.0~4.0 MPa,8 000~20 000 mL/(g·h)以及合成气氢碳比1.0~5.0。在此范围内得到的CO转化率20%~70%,基本符合动力学的要求,并且CO转化率和CO2选择性随反应条件的变化趋势符合费托反应基本规律,数据可靠合理。以CO转化率相对残差MARR为目标函数建立模型,通过目标函数最小化(MARR=8.7%,复相关指数R2=0.92)来求解方程并获得最优模型参数,得到动力学模型参数估计值,并根据模型参数所代表的物理意义(合理的活化能Ek=105.0 kJ/mol)和统计意义(Fc=73.3,>10倍F0.05=3.1,F检验显著),对动力学模型进行了考察。结果表明:H2吸附热焓小于CO吸附热焓,说明CO在催化剂表面为强吸附,H2相对为弱吸附,这一结果与诸多文献相符。此外,动力学模型活化能Ek的数值也与文献报道值接近,因此,本研究所得的动力学模型可信度较高,可以较好地解释铁基费托催化剂的反应性能。通过本动力学模型得到的CO消耗计算值和实验值相对误差<15%,可用于费托反应器设计和工艺优化。同时,集总动力学模型不能提供反应产物信息,为解决这一不足,需要进行更复杂的详细产物选择性动力学研究。Abstract: To support the design of commercial scale reactor and process optimization for Fischer-Tropsch synthesis (FTs),a lumped mechanism kinetic model of CO conversion was established over the commercial iron-based catalyst CNFT-1 (Fe-Cu-K-B-Si,bulk density:0. 8 g / cm3 ). Firstly,the LHHW kinetics model of CO conversion was de- rived based on the classical and widely accepted carbide mechanism and the assumption of methylene formation reac- tion as rate determining step. 30 sets of kinetic data were obtained from a 1L continuously stirred tank reactor (CSTR,H / D ratio was 2. 5) experiments,which were conducted under the conditions of eliminating diffusion effect related to intra-particle and external,i. e. agitation speed > 400 r / min,GHSV >7 000 mL / ( g·h) and catalyst particle size