基于遗传算法的费托合成反应动力学模型参数优化

详细动力学模型是费托合成反应技术从实验室走向工业化过程中最关键的基础研究项目之一。目前对动力学模型的参数估算仍然停留在传统的LM算法上,LM算法属于无约束方法,在计算中容易因参数越界而使计算失败,计算结果强烈依赖于初值,且容易陷于局部最优,运用遗传算法来解决费托合成反应详细动力学模型的参数优化问题,是一种全新的尝试,通过系统的实验我们获得了比较满意的参数估算结果,证明该算法用于解决动力学模型参数优化是非常有效的。     

用于选择性合成清洁液体燃料的钴基F-T合成催化剂*

在传统F-T合成（Fischer-Tropsch synthesis）中,烃类产物受到Anderson-Schulz-Flory (ASF)方程的控制,这使得烃类产物分布宽,不具有选择性。因此,如何突破ASF产物分布控制,实现以合成气为原料,高选择性合成特定碳数范围内的烃类产品是F-T合成研究领域中的前沿和热点之一。本文以钴基负载型催化剂的活性中心和载体孔结构与F-T合成产物分布之间的关联为探讨重点,综述了这一领域的最新研究成果。     

工业固定床Fe-Cu-K催化剂浆态床F-T合成适应性研究

采用连续搅拌釜式反应器,在接近F-T合成实际工况下考察了工业固定床Fe-Cu-K催化剂浆态床F-T合成反应性能,研究反应温度、压力、原料气空速和氢碳摩尔比等操作参数对催化剂反应活性、产物选择性和稳定性的影响,实验总运转时间达2 500 h;同时采用扫描电镜技术（SEM）对催化剂的抗磨损性能进行了研究,结果表明,操作参数对催化剂的活性、选择性和目标产物产率有较大的影响,工业固定床Fe-Cu-K催化剂具有一定的抗磨损性能,F-T合成烃产物分布合理;催化剂具有较高的稳定性,在589 h的稳定条件运行内,催化剂的失活速率为0.23%/d（以CO转化率的降低计）;在整个运行期间CH4选择性维持在较低的水平。     

焙烧温度对Fe-Mn催化剂结构和F-T合成性能影响

研究了焙烧温度对Fischer-Tropsch(F-T)合成Fe-Mn催化剂的织构性质、还原行为以及在还原和反应过程中结构变化的影响；在H2/CO=2.0、260 ℃、2.5 MPa和1 000 h－1条件下在固定床反应器上考察了焙烧温度对Fe-Mn催化剂F-T合成反应活性、烃产物选择性和运行稳定性的影响。XRD和TPR结果表明，随着焙烧温度的升高，催化剂中α-Fe2O3晶粒增大，催化剂比表面积降低，促进Mn3+渗入α-Fe2O3晶格中，形成了铁锰固溶体物相，使得催化剂难于还原，当焙烧温度升高到700 ℃时，催化剂中的α-Mn2O3相完全消失。催化剂F-T合成反应评价表明，在不降低催化剂活性的同时，焙烧温度的升高可显著地提高催化剂的反应运行稳定性，并促使烃产物分布向高碳数方向偏移；600 ℃焙烧的Fe-Mn催化剂运行200 h，总体活性高，失活速率较低，对低碳烯烃和中间馏分油段产物选择性好。     

片状催化剂F-T合成宏观动力学

采用固定床积分反应器,在工业条件下,对压片Ｆｅ－Ｃｕ－Ｋ催化剂进行了Ｆ－Ｔ合成宏观动力学考查。在稳态下,用集总的方法,在保持一定的轴向温度分布及取其平均温度条件下,求得两组宏观动力学方程,两者分别与实验数据吻合较好,同时两者之间也存在较好的一致性。     

Fe-Mn催化剂的费托合成产物分布动力学

在固定床反应器上进行了Fe-Mn超细粒子催化剂F -T合成反应动力学研究。以碳化物机理为基础推导出简化的F -T合成产物生成动力学模型 :　RCnH2n 2 =kHC5PH2 (1-α)αn在温度 5 76～ 6 10K ,压力 1 5～ 2 5MPa ,空速 2 5 0 0～ 45 0 0h-1和原料气H2 /CO比为 2 0的条件下进行动力学试验 ,通过模型拟合 ,求得动力学方程参数 :　kHC5=kHC5(5 80K)exp[EaR(1T - 15 80 ) ]其中 ,kHC5(5 80K) =2 82× 10 -6mol/ (mlcat·MPa·s) ,Ea=6 6 0 7kJ/mol结果表明 ,该模型与实验值拟合较好 ,链增长几率α与温度和反应器内H2 /CO比具有简单的关系 :α =1/ (1 ρRHC)。     

C302铜基催化剂上甲醇合成的动力学研究 Ⅰ.动力学模型

采用微型等温积分反应器,在５ＭＰａ,２１０－２７０℃和气体组成（摩尔分数）ＣＯ４．２１％－１４．４８％,ＣＯ２１．５５％－１３．６７％,Ｈ２５８．３４％－８７．００％,Ｎ２４．８１％－２６．５０％,ＣＨ４０－０．１１％条件下,对国产Ｃ３０２低压铜基催化剂上甲醇合成的动力学特征进行了系统的研究,对基于ＣＯ和ＣＯ２竞争加氢双路线合成甲醇的六种动力学模型,以Ｓｉｍｐｌｅｘ－Ｍａｒｑｕａｒｄｔ与Ｍｅｒｓｏｎ复合法估计了相应的模型参数,数理统计检验结果表明,六种动力学模型均是可信的,这说明由等温实验数据和传统的数理统计检验获得的动力学模型具有不确定性。     

工业Fe-Mn催化剂上基于详细反应机理的F-T合成动力学模型Ⅱ.不同校正方法的动力学模型分析

 通过平衡闪蒸模拟催化剂孔道液体组成、烯烃物理吸附和虚拟烯烃分压等方法,考察了化学反应以外的非本征因素对F-T合成动力学模型的校正. 平衡闪蒸模拟催化剂孔道中烯烃组成的校正计算结果表明,在烯烃浓度出现峰值前,溶解度效应对烯烃再吸附及参与二次反应起主导作用,而在烯烃浓度出现峰值后,烯烃的扩散和物理吸附等效应可能起主导作用. 分析烯烃添加的反应器模拟结果发现,考虑烯烃物理吸附作用的动力学模型校正方法不能够正确反映烯烃添加实验的定性规律,而虚拟烯烃分压校正方法能够正确反映烃分布规律并可定量预测烯烃添加对产物分布规律的影响,这对需要尾气循环的F-T合成工业操作具有重要意义.     

催化裂化气体烃生成反应动力学模型的研究

本文经蜡油和渣油催化剂裂化反应实验和参数估计，确定气体烃生成反应动力学模型参数，原料油组成的关联系数和活化能参数，建立了催化裂化气体烃生成反应动力学模型。统计检验结果表明，所建模型具有较高的计算精度。     

Product distributions of Fischer-Tropsch synthesis over Co/AC catalyst

The product distributions of Fischer-Tropsch synthesis over Co/AC catalyst are investigated under different reaction conditions in an integral fixed bed reactor.It is found that the product distributions deviate from the ASF distribution.The deviation from ASF distribution is analyzed by taking the readsorption of alkenes and the following secondary reaction into consideration.It is noted that the contents of alcohol,alkene and alkane decline with the increasing carbon number,showing a slighter declining tendency of alkanes than those of alkenes and alcohols.It is also found that high temperature,space velocity,H2/CO in feed gas and low pressure are preferential for light hydrocarbons and alcohols while against the chain propagation.The effect of space velocity on the product distributions especially on the light products is not obvious.It is noticed that low temperature,space velocity,H2/CO and high pressure lead to high contents of alcohols;high temperature,H2/CO and low space velocity lead to high contents of alkanes.The effect of pressure on the amounts of alkanes is not significant;high space velocity and low temperature,pressure,H2/CO are preferential for alkenes.     

Fragmentary kinetic models of the mechanism of the Fischer-Tropsch synthesis

Unlike traditional kinetic models describing the dependence of the concentrations of all the products on the number of carbon atoms and widely used for analysis of the mechanism of the Fischer-Tropsch synthesis, fragmentary models establish a relationship between the concentrations of a limited number of products. They can be constructed if it is possible to obtain a dimensionless function of the concentrations that does not change with change in the concentrations themselves. Such models are based on fragments of the kinetic schemes of the process and are designed both for identification and discrimination among the mechanisms with data obtained in both differential and integral reactors. The general principles for the construction of fragmentary models are described. Examples of identification and discrimination among the various mechanisms from the results of fragmentary modelling using previously obtained experimental data for a cobalt catalyst are presented. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 2, pp. 67–81, March–April, 2006.     

Correlation between hydrocarbon distribution and water-hydrocarbon ratio in Fischer-Tropsch synthesis

In order to shorten the evaluation cycle of cobalt catalyst before the optimized catalyst is fixed on, a mathematical method is proposed to calculate weight percentage of C5+ hydrocarbons. Based on the carbide polymerization mechanism and the main hydrocarbons being linear alkanes and α-olefins, the correlation between hydrocarbon distribution and the molecular mass ratio of water to hydrocarbons is discussed. The result shows the ratio was within the range of 1.125-1.286 and the lower the ratio, the more gaseous hydrocarbons were obtained. Moreover, a linear equation between the weight percentage of C5+ hydrocarbons and the weight ratio of C5+ hydrocarbons to the total water is established. These results are validated by corresponding experiments. The weight percentage of C5+ hydrocarbons could be immediately calculated by this linear equation without detailed gas chromatography (GC) analysis of them.     

Pretreatment of Alumina and Its Influence on the Properties of Co/Alumina Catalysts for Fischer-Tropsch Synthesis

16.6%Co/γ-Al_2O_3 catalysts prepared by incipient wetness impregnation method were used for Fischer-Tropsch synthesis.The support was pre-treated with different concentration of NH_4NO_3 aqueous solution.The effect of support pre-treatment on the properties of support and performance of supported- cobalt-based catalysts was investigated.To treat the support with NH_4NO_3 aqueous solution enlarged the pore ofγ-Al_2O_3,decreased the impurity Na_2O content,and weakened the surface acidity ofγ-Al_2O_3. The change in the properties of the support decreased the interaction between cobalt species and support, enhanced the CO hydrogenation rate and the C_(5 )selectivity.For all catalysts,increasing the reaction temperature increased the CO hydrogenation rate or the CO conversion,slightly decreased the total hydrocarbon selectivity,and favored the formation of methane and light hydrocarbons,while the chain growth probability decreased.For 16.6%Co/γ-Al_2O3 catalysts,prepared with the support treated with 100 g/L NH_4NO3 aqueous solution,the CO conversion,the CH_4 selectivity,and the C_(5 )selectivity were 83.13%,6.86% and 82.75% respectively,and the chain growth probability was 0.83 under the condition of 493 K,1.5 MPa,500 h~(-1)and the molar ratio of H_2 to CO being 2.0 in feed.     

Kinetic models of the molecular mass distribution of the products of the Fischer-Tropsch synthesis at cobalt catalysts

Kinetic models were used to investigate the Fischer-Tropsch synthesis at increased pressures. The general mechanism proposed for the process at low and increased pressures was based on quantitative analysis of the products obtained with cobalt catalysts at pressures of 2.5–10 MPa using various kinetic models, the previously developed reference point method, and published data. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 6, pp. 333–348, November–December, 2007.     

Computational Study on Thermodynamic Properties of Fischer-Tropsch Synthesis Process

Using the highly accurate G4 method, we computed the thermodynamic data of 1287 possible reaction products under a wide range of reaction conditions in the Fischer-Tropcsh synthesis (FTS) process. These accurate thermodynamic data provide basic thermodynamic quantities for the actual chemical engineering process and are useful in analyzing product distribution because FTS demonstrates many features of an equilibrium-controlled system. Our results show that the number of thermodynamically allowed products to increase when lowering temperature, raising pressure, and raising H₂/CO ratio. At low temperature, high pressure and high H₂/CO ratio, many products are thermodynamically allowed and the selectivity of product has to be controlled by kinetic factors. On the other hand, high selectivity of lighter products can be realized in thermodynamics by raising temperature and lowering pressure. We found that the equilibrium product yield will reach a maximum and remain unchanged when lowering temperature, raising pressure, and raising H₂/CO ratio to some limits, implying that optimizing reaction conditions has no effect on equilibrium product yields beyond these limits. The thermodynamic analysis is also useful in designing and evaluating FTS reaction mechanisms. We found that reaction pathways through formaldehyde should be discarded because of its extremely low equilibrium yield. Recently, in the FTS process using metal-oxide-zeolite catalysts for the highly selective production of C₂-C₄ olefins and aromatic hydrocarbons, there are several guesses on the possible reaction intermediates entering the zeolite channel. Our results show that ketene, methanol, and dimethyl ether are three possible reaction intermediates.     

Mo 和 Cu 助剂对 FeK/SiO2 催化剂费托合成性能的影响

 研究了 Mo 和 Cu 助剂对 FeK/SiO₂ 催化剂的性质及费托 (F-T) 合成性能的影响. 采用 N₂ 物理吸附、H₂ 程序升温还原、X 射线衍射、穆斯堡尔谱和 X 射线光电子能谱技术对催化剂进行了表征. 结果表明, Mo 加入后与 Fe 产生了较强的相互作用, 抑制了催化剂的还原和碳化; Cu 助剂的加入促进了催化剂的还原和碳化; 当 Mo 和 Cu 共同加入后, 催化剂的还原和碳化行为与单独加入 Cu 助剂时相似. 催化剂 F-T 合成性能在固定床上于 280 ^oC, 1.5 MPa, 2 000 h^-1, H₂/CO = 2.0 的合成气中测试. 结果表明, Mo 的加入降低了催化剂活性, 但提高了重质烃 (C₅₊) 的选择性; Cu 的添加提高了催化剂的活性, 但对稳定 C₅₊选择性作用不明显. Mo 和 Cu 共同加入后, 催化剂既表现出较为稳定的 C₅₊选择性, 同时其活性也没有降低.     

用UBI-QEP方法分析钴系Fischer-Tropsch合成催化反应机理

采用unity bond index-quadratic exponential potential(UBI-QEP)方法, 以Co(0001) 单晶为模型催化剂, 对Fischer-Tropsch(F-T)合成的三种可能反应机理(表面碳化物机理、烯醇机理和CO插入机理)进行了全面的能学分析. 计算结果表明, 通过表面碳化物机理生成烃类产物从能学角度看较为合理, 其中CO_ads表面解离和C_ads加氢具有较高的活化能垒, 可能是整个F-T反应序列中的慢步骤; 通过CH_2,ads插入金属-烷基键实现链增长的活化能垒最低, 是能量上有利的链增长方式; 在Co(0001)晶面上烷基经β-H消除生成烯烃的活化能垒低于加氢生成烷烃, 而通过CO插入机理生成的有机含氧化合物的二次反应能垒较低, 从而导致其在Co催化剂上的低选择性. 此外, 与Fe/W(110)相比, Co金属上的CH_x,ads加氢以及CH_2,ads插入的活化能垒较低, 从而解释了Co催化剂上甲烷选择性较高和倾向于生成重质烃类产物的特性.