Reactors and Reaction Conditions

Reactions were also conducted in a stirred slurry reactor operating in continuous mode with the solution injected by means of a pump and the catalyst retained by a filter at the liquid outlet [19,21]. A fixed-bed reactor was used by Kimura [71,72,74] for the oxidation of glycerol and derivatives. 

Most liquid-phase oxidation reactions were performed in water, sometimes on highly concentrated solutions, e. g. for glucose up to 1.7 mol L [61]. For water-insoluble alcohols, organic solvent could, in principle, be used, but most should be strictly avoided for safety reasons. Acetic acid was, however, used as solvent for the oxidation of retinol (3,7 dimethyl-9-(2,6,6-trimethyl-l-cyclohexe-nyl)-2,4,6,8-nonatetraen-l-ol) to retinal [84], Oxidation of water-insoluble molecules can be performed in the presence of surfactants [50]. 

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The remainder of this text attempts to establish a rational framework within which many of these questions can be attacked. We will see that there is often considerable freedom of choice available in terms of the type of reactor and reaction conditions that will accomplish a given task. The development of an optimum processing scheme or even of an optimum reactor configuration and mode of operation requires a number of complex calculations that often involve iterative numerical calculations. Consequently machine computation is used extensively in industrial situations to simplify the optimization task. Nonetheless, we have deliberately chosen to present the concepts used in reactor design calculations in a framework that insofar as possible permits analytical solutions in order to divorce the basic concepts from the mass of detail associated with machine computation. 

The practical aspects of heterogeneous catalysis and the application of theory will be introduced in the following chapter. However, it is important to note that in the performed experiments, the applied reactors and reaction conditions depend on the reaction, the catalyst, and the desired information. 

Different types of reactors and reaction conditions are used for PE and PP manufacturing processes. Choice of the reactors and process conditions are determined primarily by the specifications of the desired products. It is important to note that within the broad polymer categories such as HDPE, LLDPE, PP, etc., subcategories differing from each other in terms of a range of polymer properties exist. Different manufacturing processes must meet those product specifications and balance the rate of production with the market demand. 

Before we can proceed with the choice of reactor and operating conditions, some general classifications must be made regarding the types of reaction systems likely to be encountered. We can classify reaction systems into five broad types ... 

Single-reaction-step processes have been studied. However, higher selectivity is possible by optimizing catalyst composition and reaction conditions for each of these two steps (40,41). This more efficient utilization of raw material has led to two separate oxidation stages in all commercial faciUties. A two-step continuous process without isolation of the intermediate acrolein was first described by the Toyo Soda Company (42). A mixture of propylene, air, and steam is converted to acrolein in the first reactor. The effluent from the first reactor is then passed directiy to the second reactor where the acrolein is oxidized to acryUc acid. The products are absorbed in water to give about 30—60% aqueous acryUc acid in about 80—85% yield based on propylene. 

The cmde phthaUc anhydride is subjected to a thermal pretreatment or heat soak at atmospheric pressure to complete dehydration of traces of phthahc acid and to convert color bodies to higher boiling compounds that can be removed by distillation. The addition of chemicals during the heat soak promotes condensation reactions and shortens the time required for them. Use of potassium hydroxide and sodium nitrate, carbonate, bicarbonate, sulfate, or borate has been patented (30). Purification is by continuous vacuum distillation, as shown by two columns in Figure 1. The most troublesome impurity is phthahde (l(3)-isobenzofuranone), which is stmcturaHy similar to phthahc anhydride. Reactor and recovery conditions must be carefully chosen to minimize phthahde contamination (31). Phthahde [87-41-2] is also reduced by adding potassium hydroxide during the heat soak (30). 

Halogenated Butyl Rubber. The halogenation is carried out in hydrocarbon solution using elemental chlorine or bromine in a 1 1 molar ratio with enchained isoprene. The reactions ate fast chlorination is faster. Both chlorinated and brominated butyl mbbers can be produced in the same plant in blocked operation. However, there are some differences in equipment and reaction conditions. A longer reaction time is requited for hromination. Separate faciUties are needed to store and meter individual halogens to the reactor. Additional faciUties are requited because of the complexity of stabilising brominated butyl mbber. 

Three polymer seeds were prepared in a batch reactor. The reactor with styrene and benzene was cooled to 0 C in an ice bath, initiator was injected into the reactor and reaction began with a gradual increase in temperature. Table II presents the initial conditions used in preparing the seed polymer and the molecular weights of the seed polymer. The molecular weight distribution of the pol3nner seeds are shown in Figure 5. 

Film diffusion may influence the overall reaction because of the low gas flow rate. As the bulk concentrations change little with time along the length of the reactor, an assumption of constant difference between bulk and catalyst surface concentrations is used in this study and the rate constants will change with gas flow rates. Nevertheless, the activation energies will remain constant, and the proposed reaction kinetics still provides useful hint for understanding the reaction mechanism and optimizing the reactor and operation conditions. 

In our previous paper [6], the authors have demonstrated that production of fine silica powder is possible by phase hydrolpis of tetramethoxysilane fTEMS). In this communication, we report the effect of the shape of reactor and operational condition, especially mixing condition on conversion of the reaction and properties especially diameter of produced silica fines. 

The possibility of a species reacting by parallel paths to yield geometric isomers or entirely different products is often responsible for low yields of a desired product. If circumstances are such that the orders of the desired and unwanted reactions are different with respect to one or more species, it is possible to promote the desired reaction by an appropriate choice of reactor type and reaction conditions. 

Mechanistic details of the microwave-induced oligomerization of methane on a microporous Mn02 catalyst were studied by Suib et al. [67], with emphasis on fundamental aspects such as reactor configuration, additives (chain propagators, dielectrics), temperature measurements, magnetic field effect, and reaction conditions. 

Another advantage of Liquid Recycle is that multiple reactors may be arranged in series with the effluent from one passing on to the next. The alkene concentration is less in the downstream reactors, but reaction conditions can be adjusted to optimize each reactor s performance. In back mixed reactors in continuous operation, the effluent from the reactor is the same as the catalyst solution throughout the reactor. By placing reactors in series, the first reactor can be optimized for high rates and later reactors for high conversion. 

In this chapter, we develop some guidelines regarding choice of reactor and operating conditions for reaction networks of the types introduced in Chapter 5. These involve features of reversible, parallel, and series reactions. We first consider these features separately in turn, and then in some combinations. The necessary aspects of reaction kinetics for these systems are developed in Chapter 5, together with stoichiometric analysis and variables, such as yield and fractional yield or selectivity, describing product distribution. We continue to consider only ideal reactor models and homogeneous or pseudohomogeneous systems. 

Figure 11.1 Illustration of the interplay of reactor design, reaction conditions, and catalyst.

Two approaches are common in modelling the SSP process. For the first approach, an overall reaction rate is used which describes the polycondensation rate in terms of the increase of intrinsic viscosity with time. Depending on the size and shape of the granules, the reaction temperature, the pressure, and the amount and type of co-monomers, the overall polycondensation rate lies between 0.01 and 0.03 dL/g/h. The reaction rate has to be determined experimentally and can be used for reactor scale-up, but cannot be extrapolated to differing particle geometry and reaction conditions. 

These aspects were carefully studied [29,46-48] and analyzed in several macrokinetic models. They are essential for choosing the methods indicated in Fig. 9.3 and constructing the suitable combination of reactor and operation conditions. In Fig. 9.3 the CVD/CVI methods are designated according to the methodology for how a gradient in the chemical potential of the reaction is applied. 

When more than one reactant is involved, the relative yields of reaction products will depend on a greater number of variables. Then it is not usually possible to deduce the best operating strategy by simple inspection of the reaction scheme. Under these circumstances, it is worthwhile developing a formalised procedure for choosing the best reactor and operating conditions. Reaction selectivity is discussed in more detail below. 

The use of a monolithic stirred reactor for carrying out enzyme-catalyzed reactions is presented. Enzyme-loaded monoliths were employed as stirrer blades. The ceramic monoliths were functionalized with conventional carrier materials carbon, chitosan, and polyethylenimine (PEI). The different nature of the carriers with respect to porosity and surface chemistry allows tuning of the support for different enzymes and for use under specific conditions. The model reactions performed in this study demonstrate the benefits of tuning the carrier material to both enzyme and reaction conditions. This is a must to successfully intensify biocatalytic processes. The results show that the monolithic stirrer reactor can be effectively employed in both mass transfer limited and kinetically limited regimes. 

A detailed treatment of the kinetics of groups of catalysts, and comparison between them is hardly possible due to the widely different experimental conditions (e.g. catalyst preparation and pretreatment, reactor type, reaction conditions and experimental methods). Results of kinetic studies will be individually reported in the section on catalysts [Sect. 2.2.2.(d)]. 

B. Flow Reactors. Laboratory-scale catalytic reactors and reactors for the reaction of solids with gases arc often constructed from metal. One of the principal objectives in the use of laboratory-scale catalytic reactors is the determination of rate data which can be associated with specific physical and chemical processes in a catalytic reaction. Descriptions are available for these kinetic analyses as they relate to reactor designs and reaction conditions. ... 

In the chapters devoted to reactors, it was considered that a situation is thermally stable due to the relatively high heat removal capacity of reactors compensating for the high heat release rate of the reaction. We considered that in the case of a cooling failure, adiabatic conditions were a good approximation for the prediction of the temperature course of a reacting mass. This is true, in the sense that it represents the worst case scenario. Between these two extremes, the actively cooled reactor and adiabatic conditions, there are situations where a small heat removal rate may control the situation, when a slow reaction produces a small heat release rate. These situations with reduced heat removal, compared to active cooling, are called heat accumulation conditions or thermal confinement. 

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