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/cm^3),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>7000 mL/(g·h)且粒径<150μm),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,8000~20000 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R^2=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。
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/cm^3).Firstly,the LHHW kinetics model of CO conversion was derived based on the classical and widely accepted carbide mechanism and the assumption of methylene formation reaction 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>7000 mL/(g·h)and catalyst particle size<150μm.For the orthogonal design kinetic experiments,the conditions were:503-553 K,1.0-4.0 MPa,n(H2)/n(CO)=1.0-5.0 and 8000-20000 mL/(g·h).The kinetic data were collected at steady activity as well as reasonable relations between FTs reaction parameters and CO conversion,CO2 selectivity etc.The CO conversion was in a range of 20%-70%that basically meets the kinetics requirements with respect to the reliability and accuracy.The kinetic parameters of LHHW model was estimated using the nonlinear least squares fitting method by minimizing the objective function(MARR of CO conversion was 8.7%).Model discrimination was performed on the basis of statistical significance values measured by F values(Fc=73.3,much greater than the critical value of F0.05=3.1),R squared values(R^2=0.92)and physical meaning of the parameters(Ek=105.0 kJ/mol).The results show that the adsorption enthalpy of H2(ΔHb)is less than that of CO(ΔHa),indicating that CO adsorption on the iron catalyst surface rather stronger than H2,which is consistent with many literatures results.The activation energy(Ek)of iron catalyst calculated from the kinetics model is close to the published data,indicating its high reliability and fine expression of CNFT-1 catalyst performance.The relative errors between the calculated values and the experimental data of CO consumption rate is less than 15%,hence the kinetics model is accountable for FTs reactor design and process optimization.It is suggested to study the complete FTs product kinetic model besides the lumped kinetic model to provide integrated information.
作者
王涛
张雪冰
张琪
杨如意
孟祥堃
胡云剑
门卓武
WANG Tao;ZHANG Xuebing;ZHANG Qi;YANG Ruyi;MENG Xiangkun;HU Yunjian;MEN Zhuowu(National Institute of Clean-and-Low-Carbon Energy,Beijing 102209,China)
出处
《煤炭学报》
EI
CAS
CSCD
北大核心
2020年第4期1297-1303,共7页
Journal of China Coal Society
基金
国家重点研发计划资助项目(2017YFB0602500)。
