Reaction parameters reactor design

Methane-coupling reaction conversions and yields less than 25 percent initially were—and still are—below those acceptable for commercial fuel and chemical feedstock production. But worldwide research and development in more recent years continue to suggest that variations in process parameters, reactor design, and catalyst composition and structure may bridge this gap. Lower reaction temperatures—in the 300-400°C range may... 

Introduction Mechanisms and Theory Kinetics and Reaction Rate Intermediates and By-products Process Parameters Reactor Design... 

CVD reactions are most often produced at ambient pressure in a freely flowing system. The gas flow, mixing, and stratification in the reactor chamber can be important to the deposition process. CVD can also be performed at low pressures (LPCVD) and in ultrahigh vacuum (UHVCVD) where the gas flow is molecular. The gas flow in a CVD reactor is very sensitive to reactor design, fixturing, substrate geometry, and the number of substrates in the reactor, ie, reactor loading. Flow uniformity is a particulady important deposition parameter in VPE and MOCVD. 

Two complementai y reviews of this subject are by Shah et al. AIChE Journal, 28, 353-379 [1982]) and Deckwer (in de Lasa, ed.. Chemical Reactor Design andTechnology, Martinus Nijhoff, 1985, pp. 411-461). Useful comments are made by Doraiswamy and Sharma (Heterogeneous Reactions, Wiley, 1984). Charpentier (in Gianetto and Silveston, eds.. Multiphase Chemical Reactors, Hemisphere, 1986, pp. 104—151) emphasizes parameters of trickle bed and stirred tank reactors. Recommendations based on the literature are made for several design parameters namely, bubble diameter and velocity of rise, gas holdup, interfacial area, mass-transfer coefficients k a and /cl but not /cg, axial liquid-phase dispersion coefficient, and heat-transfer coefficient to the wall. The effect of vessel diameter on these parameters is insignificant when D > 0.15 m (0.49 ft), except for the dispersion coefficient. Application of these correlations is to (1) chlorination of toluene in the presence of FeCl,3 catalyst, (2) absorption of SO9 in aqueous potassium carbonate with arsenite catalyst, and (3) reaction of butene with sulfuric acid to butanol. 

The kinetics of a complex catalytic reaction can be derived from the results obtained by a separate study of single reactions. This is important in modeling the course of a catalytic process starting from laboratory data and in obtaining parameters for catalytic reactor design. The method of isolation of reactions renders it possible to discover also some other reaction paths which were not originally considered in the reaction network. 

The importance of dilfusion in a tubular reactor is determined by a dimensionless parameter, SiAt/S = QIaLKuB ), which is the molecular diffusivity of component A scaled by the tube size and flow rate. If SiAtlB is small, then the elfects of dilfusion will be small, although the definition of small will depend on the specific reaction mechanism. Merrill and Hamrin studied the elfects of dilfusion on first-order reactions and concluded that molecular diffusion can be ignored in reactor design calculations if... 

Since many reactions of this type involve a series of second-order processes, it is instructive to consider how one analyzes systems of this sort in order to determine the kinetic parameters that are necessary for reactor design purposes. We will follow a procedure described previously by Frost and Pearson (11). Consider the following mechanistic equations. 

Most of the illustrative examples and problems in the text are based on actual data from the kinetics literature. However, in many cases, rate constants, heats of reaction, activation energies, and other parameters have been converted to SI units from various other systems. To be able to utilize the vast literature of kinetics for reactor design purposes, one must develop a facility for making appropriate transformations of parameters from one system of urtits to another. Consequently, I have chosen not to employ SI units exclusively in this text. 

The Anton Paar Synthos 3000 (Fig. 3.16 and Table 3.5) is the most recent multi-mode instrument to come onto the market. It is a microwave reactor dedicated for scaled-up synthesis in quantities of up to approximately 250 g per run and designed for chemistry under high-pressure and high-temperature conditions. The instrument enables direct scaling-up of already elaborated and optimized reaction protocols from single-mode cavities without changing the reaction parameters. 

In this introductory chapter, we first consider what chemical kinetics and chemical reaction engineering (CRE) are about, and how they are interrelated. We then introduce some important aspects of kinetics and CRE, including the involvement of chemical stoichiometry, thermodynamics and equilibrium, and various other rate processes. Since the rate of reaction is of primary importance, we must pay attention to how it is defined, measured, and represented, and to the parameters that affect it. We also introduce some of the main considerations in reactor design, and parameters affecting reactor performance. These considerations lead to a plan of treatment for the following chapters. 

The transfer hydrogenation methods described above are sufficient to carry out laboratory-scale studies, but it is unlikely that a direct scale-up of these processes would result in identical yields and selectivities. This is because the reaction mixtures are biphasic liquid, gas. The gas which is distilled off is acetone from the IPA system, and carbon dioxide from the TEAF system. The rate of gas disengagement is related to the superficial surface area. As the process is scaled-up, or the height of the liquid increases, the ratio of surface area to volume decreases. In order to improve de-gassing, parameters such as stirring rates, reactor design and temperature are important, and these will be discussed along with other factors found important in process scale-up. 

The choice of appropriate reaction conditions is crucial for optimized performance in alkylation. The most important parameters are the reaction temperature, the feed alkane/alkene ratio, the alkene space velocity, the alkene feed composition, and the reactor design. Changing these parameters will induce similar effects for any alkylation catalyst, but the sensitivity to changes varies from catalyst to catalyst. Table II is a summary of the most important parameters employed in industrial operations for different acids. The values given for zeolites represent best estimates of data available from laboratory and pilot-scale experiments. 

The viability of one particular use of a membrane reactor for partial oxidation reactions has been studied through mathematical modeling. The partial oxidation of methane has been used as a model selective oxidation reaction, where the intermediate product is much more reactive than the reactant. Kinetic data for V205/Si02 catalysts for methane partial oxidation are available in the literature and have been used in the modeling. Values have been selected for the other key parameters which appear in the dimensionless form of the reactor design equations based upon the physical properties of commercially available membrane materials. This parametric study has identified which parameters are most important, and what the values of these parameters must be to realize a performance enhancement over a plug-flow reactor. 

Amination of i-butanol to diisobutylamine was investigated on vanadium modified granulated Raney nickel catalyst in a fixed bed reactor. The addition of 0.5 wt.% V to Raney nickel improved the yield of amines and the stability of catalyst. Factorial experimental design was used to describe the conversion of alcohol, the yield and the selectivity of secondary amine as a function of strong parameters, i.e. the reaction temperature, space velocity and NHs/i-butanol molar ratio. Diisobutylamine was obtained with 72% yield at 92% conversion and reaction parameters P=13 bar, T=240°C, WHSV=1 g/g h, and molar ratios NH3/iBuOH= 1.7, H2/NH3= 1.9. 

The highest (iBu)2NH yield (72 %) was obtained a conversion level of 92% and at reaction parameters P=13 bar, T=240°C, WHSV=1.0 g/g h, NH3/iBuOH= 1.7, H2/NH3= 1.9. In conclusion, a secondary amine yield above 70 % can be was obtained in fixed bed reactor using vanadium promoted Raney nickel catalyst without recycling unconverted alcohol. In order to describe the conversion of alcohol, as well as the yield and selectivity of diisobutylamine in the function process parameters, experiments were carried out and results were evaluated according to orthogonal factorial design (6,7). 

The kinetic parameters chosen for comparison are rate constants and t1/2. Radiation influences and the effect of reactor design are usually identical when these kinetic data are compared between the various AOPs tested. The values for pseudo first-order kinetics and half-lives for various processes are given in Table 14.3. In most cases, the values of f3/4 are equal to two times those of t1/2 therefore, the reactions obey a first-order kinetics. Figure 14.5. shows that Fenton s reagent has the largest rate constant, e.g., approximately 40 times higher than UV alone, followed by UV/F C and Os in terms of the pseudo first-order kinetic constants. Clearly, UV alone has the lowest kinetic rate constant of 0.528 hr1. 

In this chapter we study the steady-state design of perfectly mixed, continuously operating, liquid-phase reactors. The effects of a wide variety of reaction types, kinetics, design parameters, and heat removal schemes are explored. The important elfects of design conversion and design temperature on heat transfer area and other process parameters are quantitatively studied. 

Initially, the reactor was charged with 400 g of rapeseed oil and heated to the set temperature with agitation. Catalyst was dissolved in the required amount of methanol and heated to the set temperature. After reaching the set temperature of reactant and catalyst, methanolic catalyst was added to the base of the reactor to prevent evaporation of methanol. The reaction was timed immediately after the addition of catalyst and methanol. Reaction experiment parameters were designed to determine the conversion yield of rapeseed oil (Table 2). 

Many methods have been used to size relief systems area/volume scaling, mathematical modeling using reaction parameters and flow theory, and empirical methods by the Factory Insurance Association (FIA). The Design Institute for Emergency Relief Systems (DIERS) of the AIChE has performed studies of sizing reactors undergoing runaway reactions. Intricate laboratory instruments as described earlier have resulted in better vent sizes. 

A number of flow regime maps are available for packed bubble columns [see, e.g., Fukushima and Lusaka, J. Chem. Eng. Japan, 12 296 (1979)]. Correlations for the various hydrodynamic parameters can be found in Shah (Gas-Liquid-Solid Reactor Design, McGraw-Hill, 1979), Ramachandran and Chaudhari (Three-Phase Catalytic Reactors, Gordon and Breach, 1983), and Shah and Sharma [Gas-Liquid-Solid Reactors in Carberry and Varma (eds.), Chemical Reaction and Reactor Engineering, Marcel Dekker, 1987]. 

In general, a reaction kinetics following a LHHW model is suitable, but the identification of parameters remains demanding. For some catalysts power-law models may be appropriate, for others not. For example, reaction orders identical with stoichiometric coefficients were suitable for Pd/Al203 doped with different metals. On the contrary, for Pd/MgO reaction orders with respect to phenol ranging from -0.5 to 0.5 were observed [17]. However, the bibliographic search was not able to find a quantitative kinetic model for Pd-type catalysts suitable for reactor design. 

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