Process synthesis homogeneous models

Schoenmakers and Bessling (Chapter 2) give an overview of the tools that are available today and the methods that are now introduced in the industrial practice of chemical companies. A process synthesis procedure gives good qualitative reference points. Simulation tools have been developed that are mainly based on equilibrium models. But there are further steps to go on the way to the realization of an industrial plant. The scale-up from the miniplant scale used for the experimental validation of a new process is well known for conventional distillation, but complicated by several facts for RD especially in the case of heterogeneous catalysis. To overcome these problems either reference plant experience on an industrial scale or (if not available) further research is required. Other options both for homogeneous and heterogeneous catalysis are possible and are discussed... 

The potential importance of homogeneous catalytic reactions in synthesis gas transformations (i.e., hydrogenation of carbon monoxide) has been widely recognized in recent years. In the first place, such systems could provide structural and mechanistic models for the currently more important, but more difficult to study, heterogeneous catalysts. Secondly, product selectivity is generally more readily achievable with homogeneous catalysts, and this would be an obviously desirable feature in an efficient process converting synthesis gas to useful chemicals and fuels. 

The two-film model representation can serve as a basis for more complicated models used to describe heterogeneously catalyzed RSPs or systems containing suspended solids. In these processes a third solid phase is present, and thus the two-film model is combined with the description of this third phase. This can be done using different levels of model complexity, from quasi-homogeneous description up to the four-film presentations that provide a very detailed description of both vapor/gas/liquid-liquid and solid/liquid interfaces (see, e.g., Refs. 62, 68 and 91). A comparative study of the modeling complexity is given in Ref. 64 for fuel ether synthesis of MTBE and TAME by CD. 

The full pseudo-homogeneous 2D axi-symmetric model, consisting of (11.19) to (11.23), was used to simulate the synthesis gas process. The model was simulated with a grid 17x257 for 3 seconds until the steady state solution was obtained. The time increment in the simulations was At = 10 s. To ensure mass conservation the convergence criteria was set to an error limit of 10 of the residual error. 

The majority of catalysts are subject to deactivation, e.g. to changes (deterioration) of activity with operation time. The time scale of deactivation depends on the type of process and can vary from a few seconds, as in fluid catalytic cracking (FCC), to several years, as in, for instance, ammonia synthesis. Due to the industrial importance, the modelling of deactivation was mainly developed for heterogeneous catalysis. Although the reasons for deactivation (inactivation) of homogeneous and enzymes could differ from solid catalysts, the mathematical approach can sometimes be very similar. 

The synthesis, structure, and reaction chemistry of metal clusters has received intensive study, the primary motivation being their importance as models for chemisorption during homogeneous and heterogeneous catalytic processes occurring at metal surfaces. ... 

Much of the justification for the extensive study of transition metal cluster chemistry is embedded in the assumption that reactions of metal clusters are realistic structural models for reactions at metal surfaces in such processes as heterogeneous catalysis (9,10,11). For example, the metal carbonyl clusters, Ir4(CO)i2 and Os3(CO)i2, were demonstrated to be effective homogeneous catalysts for methanation (12). Additionally, Demitras and Muetterties (13) have found Ir4(CO)i2 to be a homogeneous catalyst in the Fischer-Tropsch synthesis of aliphatic hydrocarbons. Homogeneous catalysis of the water gas shift reaction by metal carbonyl clusters (e.g., Ru3(CO)i2) in alkaline solution has been reported by Laine, Rinker, and Ford (14), and more recently by Pettit s group (15). Nevertheless, mononuclear metal carbonyls (e.g., Fe(CO)s and the group VIb metal hexacarbonyls) have been demonstrated to have considerable activity above 120°C as soluble catalysts for Reaction 2 (16),... 

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