Reactor choice single reactions

In the preceding section, the choice of reactor type was made on the basis of which gave the most appropriate concentration profile as the reaction progressed in order to minimize volume for single reactions or maximize selectivity for multiple reactions for a given conversion. However, after making the decision to choose one type of reactor or another, there are still important concentration effects to be considered. 

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) ... 

Reactor conversion. In Chap. 2 an initial choice was made of reactor type, operating conditions, and conversion. Only in extreme cases would the reactor be operated close to complete conversion. The initial setting for the conversion varies according to whether there are single reactions or multiple reactions producing byproducts and whether reactions are reversible. 

We have managed to produce a batch profile that achieves a larger maximum toluene concentration than a single batch reactor. This is accomplished with no more than a suitable choice of reaction time, and the careful mixing of product and feed concentrations in the correct ratios. Yet, what further improvements are available by continuing with additional reaction steps Let us define a reaction step as one where... 

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. 

Another possibility to improve selectivity is to reduce the concentration of monoethanolamine in the reactor by using more than one reactor with intermediate separation of the monoethanolamine. Considering the boiling points of the components given in Table 2.3, then separation by distillation is apparently possible. Unfortunately, repeated distillation operations are likely to be very expensive. Also, there is a market to sell both di- and triethanolamine, even though their value is lower than that of monoethanolamine. Thus, in this case, repeated reaction and separation are probably not justified, and the choice is a single plug-flow reactor. 

In this chapter, we describe how experimental rate data, obtained as described in Chapter 3, can be developed into a quantitative rate law for a simple, single-phase system. We first recapitulate the form of the rate law, and, as in Chapter 3, we consider only the effects of concentration and temperature we assume that these effects are separable into reaction order and Arrhenius parameters. We point out the choice of units for concentration in gas-phase reactions and some consequences of this choice for the Arrhenius parameters. We then proceed, mainly by examples, to illustrate various reaction orders and compare the consequences of the use of different types of reactors. Finally, we illustrate the determination of Arrhenius parameters for die effect of temperature on rate. 

We shall develop next a single-channel model that captures the key features of a catalytic combustor. The catalytic materials are deposited on the walls of a monolithic structure comprising a bundle of identical parallel tubes. The combustor includes a fuel distributor providing a uniform fuel/air composition and temperature over the cross section of the combustor. Natural gas, typically >98% methane, is the fuel of choice for gas turbines. Therefore, we will neglect reactions of minor components and treat the system as a methane combustion reactor. The fuel/air mixture is lean, typically 1/25 molar, which corresponds to an adiabatic temperature rise of about 950°C and to a maximum outlet temperature of 1300°C for typical compressor discharge temperatures ( 350°C). Oxygen is present in large stoichiometric excess and thus only methane mass balances are needed to solve this problem. 

Catalytic distillation and other process configurations that combine reaction and separation in a single vessel are relatively new. Currently, only a few commodity chemicals are manufactured using catalytic distillation. This is not due to a lack of versatility of this design concept. Rather it is a reflection of the timing of process selection. The choice between process configurations that are as different as fixed bed reactors and catalytic... 

Let us consider the situation where reactor temperature is a design parameter. We explore the impact of controllability questions on the choice of the best temperature for two kinetic cases a simple reaction case A B, and a consecutive reaction case A B —> C. Only single-CSTR processes are discussed. 

For the combined EDS-batch SCWO, a variety of technical issues must be addressed the choice of materials of construction, the method used to introduce oxidant into the vessel, the durability of seals, the stability of SCWO reactions in a large-diameter vessel, the methods used to heat the vessel, the possibility of scaling and corrosion under batch SCWO conditions (salts are proposed to be captured in apan placed in the vessel, but this has not yet been demonstrated), the method used to fabricate the vessel (e.g., single forging vs. welded sections), the impact of repeated explosions followed by thermal and pressure cycles on the integrity of the EDS vessel and SCWO reactor (e.g., crack propagation), the most appropriate method of cooldown and depressurization following munition destruction, and the disposition of process residuals. 

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