Reaction system reactors

SCFs [14,18-21]. Figure 4.9-3 shows how kinetic parameters can be obtained from a Lineweaver-Burk plot. The example is from the esterification of ibu-profen with propanol in SCCO2 using Mucor miehei lipase (Scheme 4.9-1) [22]. In this case the Michaelis constant was = 2.8 mmol ester per mole of mixture and the maximum reaction velocity V ax = 360 g ester per kg enzyme per hour. The kinetic parameters are specific to the reaction system, reactor type, enzyme and substrate concentrations as well as to reaction conditions. 

In this chapter, the basic concepts needed for prediction of reactor performance are reviewed. Multiple reaction systems, reactor models, and heat transfer considerations are enphasized. Case studies are presented based on reactors found in the processes used as exanples throughout the text and in the appendixes. 

Most processes are catalyzed where catalysts for the reaction are known. The strategy will be to choose the catalyst, if one is to be used, and the ideal characteristics and operating conditions needed for the reaction system. Decisions must be made in terms of reactor... 

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 ... 

The equilibrium conversion can be increased by employing one reactant in excess (or removing the water formed, or both). b. Inerts concentration. Sometimes, an inert material is present in the reactor. This might be a solvent in a liquid-phase reaction or an inert gas in a gas-phase reaction. Consider the reaction system... 

Multiple reactions in parallel producing byproducts. Once the reactor type is chosen to maximize selectivity, we are in a position to alter selectivity further in parallel reaction systems. Consider the parallel reaction system from Eq. (2.20). To maximize selectivity for this system, we minimize the ratio given by Eq. (2.21) ... 

An alternative way to improve selectivity for the reaction system in Eq. (2.27) is again to deliberately feed BYPRODUCT to the reactor to shift the equilibrium of the secondary reaction away from BYPRODUCT formation. 

The choice of reactor temperature depends on many factors. Generally, the higher the rate of reaction, the smaller the reactor volume. Practical upper limits are set by safety considerations, materials-of-construction limitations, or maximum operating temperature for the catalyst. Whether the reaction system involves single or multiple reactions, and whether the reactions are reversible, also affects the choice of reactor temperature, as we shall now discuss. 

Having considered reactor temperature and pressure, we are now in a position to judge whether the reactor phase will be gas, liquid, or multiphase. Given a free choice between gas- and liquid-phase reactions, operation in the liquid phase is usually preferred. Consider the single reaction system from Eq. (2.19) ... 

However, a note of caution should be added. In many multiphase reaction systems, rates of mass transfer between different phases can be just as important or more important than reaction kinetics in determining the reactor volume. Mass transfer rates are generally higher in gas-phase than liquid-phase systems. In such situations, it is not so easy to judge whether gas or liquid phase is preferred. 

In fact, it is often possible with stirred-tank reactors to come close to the idealized well-stirred model in practice, providing the fluid phase is not too viscous. Such reactors should be avoided for some types of parallel reaction systems (see Fig. 2.2) and for all systems in which byproduct formation is via series reactions. 

In Fig. 8.3, the only cost forcing the optimal conversion hack from high values is that of the reactor. Hence, for such simple reaction systems, a high optimal conversion would he expected. This was the reason in Chap. 2 that an initial value of reactor conversion of 0.95 was chosen for simple reaction systems. 

Staged reactions, where only part of the initial reactants are added, either to consecutive reactors or with a time lag to the same reactor, maybe used to reduce dipentaerythritol content. This technique increases the effective formaldehyde-to-acetaldehyde mole ratio, maintaining the original stoichiometric one. It also permits easier thermal control of the reaction (66,67). Both batch and continuous reaction systems are used. The former have greater flexibiHty whereas the product of the latter has improved consistency (55,68). 

In early reaction systems (9,10,31,32) the vaporized hydrocarbon was combined with nitrogen in a reactor and mixed with a nitrogen—fluorine mixture from a preheated source. The jet reactor (11) for low molecular weight fluorocarbons was an important improvement. The process takes place at around 200—300°C, and fluorination is carried out in the vapor state. 

Fluidized-bed reaction systems are not normally shut down for changing catalyst. Fresh catalyst is periodically added to manage catalyst activity and particle size distribution. The ALMA process includes faciUties for adding back both catalyst fines and fresh catalyst to the reactor. 

Dimensional Analysis. Dimensional analysis can be helpful in analyzing reactor performance and developing scale-up criteria. Seven dimensionless groups used in generalized rate equations for continuous flow reaction systems are Hsted in Table 4. Other dimensionless groups apply in specific situations (58—61). Compromising assumptions are often necessary, and their vaHdation must be estabHshed experimentally or by analogy to previously studied systems. 

The principal advance ia technology for SASOL I relative to the German Fischer-Tropsch plants was the development of a fluidized-bed reactor/regenerator system designed by M. W. Kellogg for the synthesis reaction. The reactor consists of an entrained-flow reactor ia series with a fluidized-bed regenerator (Fig. 14). Each fluidized-bed reactor processes 80,000 m /h of feed at a temperature of 320 to 330°C and 2.2 MPa (22 atm), and produces approximately 300 m (2000 barrels) per day of Hquid hydrocarbon product with a catalyst circulation rate of over 6000 t/h (49). 

Figure 3 shows a simple schematic diagram of an oxygen-based process. Ethylene, oxygen, and the recycle gas stream are combined before entering the tubular reactors. The basic equipment for the reaction system is identical to that described for the air-based process, with one exception the purge reactor system is absent and a carbon dioxide removal unit is incorporated. The CO2 removal scheme illustrated is based on a patent by Shell Oil Co. (127), and minimises the loss of valuable ethylene in the process. 

Use continuous reactors if possible. It is usually easier to control continuous reactors than batch reactors. If a batch reaction system is required, minimize the amount of unreacted hazardous materials in the reactor. Figures 12-40 and 12-41 show typical examples. 

In many cases, two identical reaction systems (e.g., a pilot plant scale and a full-scale commercial plant) exhibit different performances. This difference in performance may result from different flow patterns in the reactors, kinetics of the process, catalyst performance, and other extraneous factors. 

Each stage of particle formation is controlled variously by the type of reactor, i.e. gas-liquid contacting apparatus. Gas-liquid mass transfer phenomena determine the level of solute supersaturation and its spatial distribution in the liquid phase the counterpart role in liquid-liquid reaction systems may be played by micromixing phenomena. The agglomeration and subsequent ageing processes are likely to be affected by the flow dynamics such as motion of the suspension of solids and the fluid shear stress distribution. Thus, the choice of reactor is of substantial importance for the tailoring of product quality as well as for production efficiency. 

Figure 3-6 shows a batch reaction system. A batch of glycerol was placed in the reactor and circulated through a heat exchanger, which... 

To accelerate the polymerization process, some water-soluble salts of heavy metals (Fe, Co, Ni, Pb) are added to the reaction system (0.01-1% with respect to the monomer mass). These additions facilitate the reaction heat removal and allow the reaction to be carried out at lower temperatures. To reduce the coagulate formation and deposits of polymers on the reactor walls, the additions of water-soluble salts (borates, phosphates, and silicates of alkali metals) are introduced into the reaction mixture. The residual monomer content in the emulsion can be decreased by hydrogenizing the double bond in the presence of catalysts (Raney Ni, and salts of Ru, Co, Fe, Pd, Pt, Ir, Ro, and Co on alumina). The same purpose can be achieved by adding amidase to the emulsion. 

The scheme of commercial methane synthesis includes a multistage reaction system and recycle of product gas. Adiabatic reactors connected with waste heat boilers are used to remove the heat in the form of high pressure steam. In designing the pilot plants, major emphasis was placed on the design of the catalytic reactor system. Thermodynamic parameters (composition of feed gas, temperature, temperature rise, pressure, etc.) as well as hydrodynamic parameters (bed depth, linear velocity, catalyst pellet size, etc.) are identical to those in a commercial methana-tion plant. This permits direct upscaling of test results to commercial size reactors because radial gradients are not present in an adiabatic shift reactor. 

Dr. Moeller I think to answer this question now is a bit difficult. It s just a mechanical problem of the maximum temperature the recycle compressor can handle. So, in the end, we will go to the inlet temperature to the compressor in the range of the inlet temperature to the reactor. So what we are endeavoring to attain is a simple reaction system consisting of an adiabatic reactor in series with waste heat boilers and nothing more than one recycle compressor. These compressors are used in the chemical industry with no problem in operation. So, in the end, you can go to hot recycle with an inlet compressor temperature the same as the inlet reactor temperature. All the heat from... 

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