Methanol synthesis problem

A methanol synthesis problem has been used to investigate the model discrimination and the design-of-experiments capabilities of the various software packages. Twenty different, single rate equations were developed of varying complexity and form. A data set, consisting of 27 data points for the reaction rate at different temperatures and partial pressures of the reactants, was given as well. Duplicate experiments were included in the data set in order to allow an estimate of the variability within the data. 

C2. Calculation of Operating conditions and Transport Criteria for the UCKRON Test Problem as a Methanol Synthesis Experiment in the Rotoberty ... 

A.1 Model for Mechanism of Methanol Synthesis Assumed for the Test Problem... 

A.2 Explicit Form of the Rate Equation for Methanol Synthesis by the UCKROH-1 Test Problem... 

Methanol synthesis will be used many times as an example to explain some concepts, largely because the stoichiometry of methanol synthesis is simple. The physical properties of all compounds are well known, details of many competing technologies have been published and methanol is an important industrial chemical. In addition to its relative simplicity, methanol synthesis offers an opportunity to show how to handle reversible reactions, the change in mole numbers, removal of reaction heat, and other engineering problems. 

To facilitate the use of methanol synthesis in examples, the UCKRON and VEKRON test problems (Berty et al 1989, Arva and Szeifert 1989) will be applied. In the development of the test problem, methanol synthesis served as an example. The physical properties, thermodynamic conditions, technology and average rate of reaction were taken from the literature of methanol synthesis. For the kinetics, however, an artificial mechanism was created that had a known and rigorous mathematical solution. It was fundamentally important to create a fixed basis of comparison with various approximate mathematical models for kinetics. These were derived by simulated experiments from the test problems with added random error. See Appendix A and B, Berty et al, 1989. 

The UCKRON AND VEKRON kinetics are not models for methanol synthesis. These test problems represent assumed four and six elementary step mechanisms, which are thermodynamically consistent and for which the rate expression could be expressed by rigorous analytical solution and without the assumption of rate limiting steps. The exact solution was more important for the test problems in engineering, than it was to match the presently preferred theory on mechanism. 

Conclusions from the test problems are not limited by any means to methanol synthesis. These results have more general meaning. Other reactions also will be used to explain certain features of the subjects. Yet the programs for the test problem make it possible to simulate experiments on a computer. In turn, computer simulation of experiments by the reader makes the understanding of the experimental concepts in this book more profound and at the same time easier to grasp. 

A system has been constructed which allows combined studies of reaction kinetics and catalyst surface properties. Key elements of the system are a computer-controlled pilot plant with a plug flow reactor coupled In series to a minireactor which Is connected, via a high vacuum sample transfer system, to a surface analysis Instrument equipped with XFS, AES, SAM, and SIMS. When Interesting kinetic data are observed, the reaction Is stopped and the test sample Is transferred from the mlnlreactor to the surface analysis chamber. Unique features and problem areas of this new approach will be discussed. The power of the system will be Illustrated with a study of surface chemical changes of a Cu0/Zn0/Al203 catalyst during activation and methanol synthesis. Metallic Cu was Identified by XFS as the only Cu surface site during methanol synthesis. 

Because of the pure performance of traditional Cu catalysts in the hydrogenation of C02, efforts have been made to find new, more effective catalysts for direct C02 hydrogenation. The problem is to improve selectivity, specifically, to find catalysts that display high selectivity toward methanol formation and, at the same time, show low selectivity in the reverse water-gas shift reaction, that is, in the formation of CO. It appears that copper is the metal of choice for methanol synthesis from C02 provided suitable promoters may be added. Special synthesis methods have also been described for the preparation of traditional three-component Cu catalysts (Cu-ZnO-A1203 and Cu-Zn0-Cr203) to improve catalytic performance for C02 reduction. 

Spinel oxides with a general formula AB2O4 (i.e. the so-called normal spinels) are important materials in industrial catalysis. They are thermally stable and maintain enhanced and sustained activities for a variety of industrially important reactions including decomposition of nitrous oxide [1], oxidation and dehydrogenation of hydrocarbons [2], low temperature methanol synthesis [3], oxidation of carbon monoxide and hydrocarbon [4], and oxidative dehydrogenation of butanes [5]. A major problem in the applications of this class of compound as catalyst, however, lies in their usually low specific surface area [6]. 

Sulfur poisoning is a key problem in hydrocarbon synthesis from coal-derived synthesis gas. The most important hydrocarbon synthesis reactions include methanation, Fischer-Tropsch synthesis, and methanol synthesis, which occur typically on nickel, iron, or cobalt, and ZnO-Cu catalysts, respectively. Madon and Shaw (2) reviewed much of the early work dealing with effects of sulfur in Fischer-Tropsch synthesis. Only the most important conclusions of their review will be summarized here. 

In this problem, we will determine the degrees of freedom of a process circuit conqjosed of several process units by examining a methanol-synthesis process. Methanol was first synthesized from carbon monoxide and hydrogen on a commercial scale in 1923 by Badische Anilindund Soda-Fabrik (BASF) in Germany [25]. Methanol is an important basic bulk chemical used in the synthesis of formaldehyde and acetic acid [28] and it has been proposed as an automobile fuel and fixel additive [26]. Methanol has also been proposed as a substrate to produce a bacterium suitable as a protein source (single-cell protein). The bacterium would be a soy meal and fishmeal substitute for animal and poultry feeds [27]. If these applications should ever develop, the demand for methanol will increase considerably. 

A typical dual catalyst system studied in our lab consisted of a commercial, Cu-based methanol synthesis catalyst and y-alumina. While all the merits of this process were verified, the study showed that both catalysts suffered rapid deactivation under LPDME conditions. The problem seems common to many other dual catalyst systems containing different dehydration catalysts. This paper focuses on our investigation of the cause and the mechanism of the catalyst deactivation in this dual catalyst system. 

A very common objection to the role of Cu in methanol synthesis was based on the general experience of producers of Cu catalysts for methanol synthesis and water-gas shift, namely, that the activity is proportional to the metallic surface area. However, this problem is only apparent. Cu may have two functions to be an active centre when accessible to the gas phase and to be an anchor for a metallic particle. The role of ions in stabilizing highly dispersed metal is, indeed, a known fact. Cu may also supply H atoms. It is known to be a poor adsorbent for H2 but it does adsorb some at high temperatures and pressures. ... 

Flowsheet analysis and HEN synthesis problem. A material balance has been completed for a process to manufacture styrene and an ethylbenzene byproduct from reactions involving methanol and toluene. See Figure 10.61 for a block flow diagram of the process with the results of material balance calculations. You are to develop an optimal heat exchanger network for this process. Note that ... 

Fewer EXAFS works have been devoted to the study of catalytic systems under reaction conditions due, as already said, to inherent limitations of the technique at high, working temperatures characteristic of catalytic reactions. Among these, a majority include studies of Cu/ZnO (Cu/Si02) in methanol synthesis.The solid state physics of the active copper phase in methanol synthesis is a rather intriguing problem which has not achieved consensus concerning the oxidation state and the hosting of the Cu phase characteristics. The EXAFS works mentioned above elucidated mainly the importance of the metallic state in the reaction. Similarly, the metallic state has been shown to be of importance in the water gas shift reaction (WGS) in Cu, Au, and bimetallic Pd-Cu systems supported on ceria. The importance of ceria vacancies on the activation of water and of the metal (and more precisely, of the metal at support boundaries) for CO activation appear as key elements for this reaction. The bimetallic Pd-Cu work analyses the modulation of Pd behaviour by effect of the alloy with the base... 

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