共查询到16条相似文献,搜索用时 140 毫秒
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以CO在铂催化剂上发生的催化氧化反应为例,以L-H机理和E-R机理为基础,建立了该催化反应的5种动力学模型。利用化学反应网络理论,并依据该反应的多定态特性,对5种可能的动力学模型进行了筛选。筛选结果表明:根据L-H机理得到的模型对应的反应网络能够出现多定态现象,根据E-R机理得到的模型对应的反应网络则无法出现反应体系的多定态现象,因此,L-H机理更为接近CO在铂催化剂上催化氧化的真实反应机理,这与文献结论吻合,证明了利用反应的多定态特性筛选催化反应动力学模型的可行性。 相似文献
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对铂催化剂上乙烯和一氧化碳同时氧化反应多定态特性的实验研究结果表明:在实验条件下体系最多存在有两个稳定的定态,随乙烯和/或一氧化碳浓度的增加,系统的点火温度升高,熄火温度下降,存在多定态的操作参数区域增大;在较高的乙烯和/或一氧化碳浓度条件下,系统将出现自持,实验观测不到熄火现象。通过对体系多定态特性的分析可知,同时氧化反应体系的多定态特性并不等于两个单独氧化反应体系多定态特性的简单迭加,在两个反应之间,除了热量的相互作用外,还存在着动力学抑制作用。 相似文献
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以环氧乙烷与水合成乙二醇为模型体系进行了实例分析,得到了该反应精馏系统在一定条件下的多定态解,利用超熵产生判据式对各定态解的稳定性进行了分析,在此基础上进一步讨论了多稳态产生的原因.结果表明:浓度涨落、温度涨落、其他操作负荷的变化以及反应动力学特性都可以成为反应精馏系统出现多稳态的原因.将超熵产生判据用于反应精馏体系定态稳定性的判定,较为可靠.因为超熵产生判据式是由热力学基本原理推导而来,较好地反映了反应精馏过程演化的非线性不可逆的热力学本质,因此本方法对反应精馏系统稳定性的研究,具有普遍的理论指导意义. 相似文献
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为解决现有蓝藻生长动力学模型难以有效描述实际水体中蓝藻生长时变系统的非线性动力学特性,导致水华预测准确性不高的问题,构建蓝藻摄食和营养盐循环模型,并考虑水温、光照等主要影响因素随时间变化对蓝藻生长的影响,进一步建立蓝藻生长时变系统非线性动力学模型,对其常值参数采用遗传算法与数值算法结合的方法进行优化率定,对其时变参数采用多元时序方法进行建模预测,根据分岔理论及时变系统理论分析水华暴发行为的非线性动力学机理,实现对蓝藻生长时变系统的水华预测。通过太湖流域监测实例表明,与现有研究相比,引入时变参数的蓝藻生长动力学模型更能反映蓝藻生长时变系统下水华暴发行为的非线性动力学特性,其水华预测结果更为准确。 相似文献
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化学反应体系的多定态特性 总被引:2,自引:0,他引:2
化学反应体系的多定态特性是化学反应体系存在的固有特性。近年来,对它的研究已成为化学反应工程研究的热门课题。本文对化学反应体系的多定态特性的研究进展,特别是对化学反应器、催化剂题粒的多定态特性及其理论研究模型和实验研究成果进行了评述,指出了今后研究工作的发展方向。 相似文献
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The catalytic oxidation of ethylene to carbon dioxide in excess air has been studied atsteady state.The catalyst temperature was measured for various feed temperature and concentration.The bifurcation diagrams Which describe the dependence of the catalyst temperature on the feed gastemperature were obtained for different ethylene concentrations in the feed gas.The ignition and ex-tinction temperatures were found out and the unique and multiple steady state regions could bedetermined from these diagrams.The experimental results can be satisfactorily explained by thecatastrophe theory and singularity theory.According to the steady state multiplicity features an at-tempt to discriminate the competitive kinetic models was made for the reaction. 相似文献
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A. V. Kulikov N. A. Kuzin A. B. Shigarov V. A. Kirillov A. E. Kronberg K. R. Westerterp 《Catalysis Today》2001,66(2-4):255-262
The impact of the combined evaporation of the liquid phase and reaction on single catalyst pellet performance has been studied experimentally. The exothermic, catalyzed hydrogenation of -methylstyrene (AMS) to cumene has been employed as a model reaction. Steady state and dynamic experiments have been performed in a single catalytic pellet reactor using five catalytic pellets of different porous structures, thermal conductivity, apparent catalytic activity and distribution of catalyst in the pellet. Gas-phase temperature, concentration of AMS in the gas phase and the liquid flow rates have been varied. The measured center and surface temperatures of each pellet reveal the existence of two significantly different steady states in the range of liquid flow rate. The range of the liquid flow rate over which the two steady states were observed, the pellet temperature and the pellet dynamics depend strongly on the amount of AMS vapor in the gas phase and the catalyst properties. The obtained experimental data are helpful to elucidate the mechanism of hot-spot formation and runaway in multiphase fixed-bed reactors. 相似文献
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A novel methodology has been developed to design an optimum heterogeneous catalytic reactor, by considering non‐uniform catalyst pellet under shell‐progressive catalyst deactivation. Various types of non‐uniform catalyst pellets are modelled in combination with reactor design. For example, typical non‐uniform catalyst pellets such as egg‐yolk, egg‐shell and middle‐peak distribution are developed as well as step‐type distribution. A progressive poisoning behavior is included to the model to produce correct effectiveness factor from non‐uniform catalyst pellet. As opposed to numerical experiment with limited type of kinetic application to the model in the past, this paper shows a new methodology to include any types of kinetic reactions for the modeling of the reactor with non‐uniform catalyst pellet and shell‐progressive poisoning. For an optimum reactor design, reactor and catalyst variables are considered at the same time. For example, active layer thickness and location inside pellet are optimised together with reactor temperature for the maximisation of the reactor performance. Furthermore, the temperature control strategy over the reactor operation period is added to the optimization, which extends the model to three dimensions. A computational burden has been a major concern for the optimization, and innovative methodology is adopted. Application of profile based synthesis with the combination of SA (Simulated Annealing) and SQP (Successive Quadratic Programming) allows more efficient computation not only at steady state but also in dynamic status over the catalyst lifetime. A Benzene hydrogenation reaction in an industry scale fixed‐bed reactor is used as a case study for illustration. 相似文献
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Effective intraparticle diffusion coefficients in different industrial catalysts were determined with three different measuring methods. On the one hand by steady state counterdiffusion measurements and dynamic pulse response measurements on single pellets in a diffusion cell, on the other hand by the gas chromatographic method employing the “single pellet string reactor” (S.P.S.R.). In general the steady state method and the dynamic pulse response measurements on single pellets yielded similar values for the effective diffusion coefficients. Within limits, the S.P.S.R. gave comparable diffusion coefficients, however, a statistical consideration indicates that with this method experimental uncertainties may lead to significantly broader confidence limits for the diffusion coefficients than with measurements on single pellets in a diffusion cell. Different pore models are employed for the prediction of the intraparticle diffusivities in the commercial catalyst pellets. The diffusivities predicted with the random pore model are about 1.5 times larger than the experimentally determined values. With measurements carried out on single pressed pellets in the diffusion cell no axial anisotropy effects caused by pellet pressing could be observed. 相似文献
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《Chemical engineering science》1986,41(4):1117-1122
Temperature overshoots and undershoots were found for a Pd on alumina catalyst pellet in its course towards a new steady state after a change in concentration of one of the reactants ethylene or hydrogen. When cooling the pellet, after heat-up by reaction, with pure hydrogen a sudden temperature peak appears after a short time.A mathematical model is introduced, which can explain the over- and undershoots by slow ad- or desorption on the active sites of the catalyst of one of the reactants. 相似文献