Back-mixed continuous flow reactor,

Y. Lu, J. A. Biesenberger, and D. B. Todd, A Backmix Drag-flow Reactor, SPE. ANTEC, Tech. Papers, 51, 27-29 (1993) also Y. Lu, J. A. Biesenberger, and D. B. Todd, Continuous Polymerization in a back-mixed Drag Flow reactor, SPE. ANTEC Tech. Papers, 52, 113-115 (1994). 

Equation (100) applies also to a continuous-flow reactor in which the contents experience no back-mixing (equiveilent to plug flow) time has been eliminated from the expressions. When complete back-mixing is achieved in a continuous-flow reactor, concentration gradients are absent and we have... 

If the same reactions occur in a continuous-flow reactor with complete back-mixing then, at steady-state conditions... 

More recent process research aimed at anionic PS is that of BASF AG. Unlike the Dow Process, the BASF process utilizes continuous linear-flow reactors (LFR) with no back-mixing to make narrow polydispersity resins. This process consists of a series alternating reactors and heat exchangers (Fig. 22). Inside the reactors, the polymerization exotherm carries the temperature from 30°C at the inlet to 90°C at the outlet. The heat exchangers then take the temperature back down to 30°C. This process, which requires no solvent, results in the formation of narrow polydispersity PS. 

Chen, C.-C., Continuous production of solid polystyrene in back-mixed and linear-flow reactors, Polym. Eng. Sci., 40, 441-464 (2000). 

Because there is no back-mixing of fluid elements along the direction of flow in a tubular reactor, there is a continuous gradient in reactant concentration in this direction. One does not... 

Continuous flow stirred tank reactors are normally just what the name implies—tanks into which reactants flow and from which a product stream is removed on a continuous basis. CFSTR, CSTR, C-star, and back-mix reactor are only a few of the names applied to the idealized stirred tank flow reactor. We will use the letters CSTR as a shorthand notation in this textbook. The virtues of a stirred tank reactor lie in its simplicity of construction and the relative ease with which it may be controlled. These reactors are used primarily for carrying out liquid phase reactions in the organic chemicals... 

Restrictions which may exist for the choice of a commercial reactor need not be imposed at the development stage. In some cases, a reactor of one type may be best for acquiring data in model characterisation, whereas a reactor of another type might be more suitable for full-scale production. (The cautions expressed in Sect. 4 must be taken into account.) Continuous flow back-mixed reactors can be very useful for kinetic studies because the absence of concentration gradients can reduce uncertainties in concentration measurements. When these reactors have attained a steady state, many of the problems associated with stiffness (see above) can be avoided. 

The interaction of chemical and physical rate processes can affect the dynamic behaviour of reactors used for polymerisation or other complex reaction processes. This may lead to variations in the distribution of reaction products. As an example, consider a continuous-flow back-mixed reactor in which an exothermic reaction occurs. A differential material balance may be written for each reaction component... 

In real tubular (or column) reactors there is, usually, a back-mixing effect which influences the performance of the ideal plug-flow reactor. This axial dispersion is higher for fluidized-bed reactors than for packed-bed reactors, although comparatively lower than for continuous-feed stirred-tank reactors, where the mixing is complete. 

The continuous-stirred tank reactor is one of the two primary types of ideal flow reactors. It is also referred to as a mixed-flow reactor, back-mix reactor, or constant-flow stirred-tank reactor. 

To guide the reactor selection process, Walas [7] has classified reactions according to the operating mode (batch or continuous), reactor type (tank, tank battery, tubular), flow type (back mixed, multistage back mixed), and the phases in contact. This reactor classification in Table 7.2 indicates if a particular reactor arrangement is commonly used, rarely used, or not feasible. 

Until recently only a few papers were available on moving beds in cross flow [11-18]. This type of reactor is sometimes a favorable process solution for a selective catalytic process with a moderate catalyst rcsidence time and with a short gas residence time, especially when the process is accompanied by a continuous catalyst regeneration. The use of conventional short-contact-time reactors like fluidized-bed reactors, risers, and fixed-bed reactors does not always yield satisfactory results. This may be explained by problems connected with gas back-mixing, channeling of gas, low catalyst holdup, attrition of the solid catalyst, or difficulties in temperature control. 

If either the batch or the tubular type of reactor is chosen, the reactor size and product distribution can be calculated by using the batch or longitudinal-flow equations. For a stirred-tank continuous reactor, the backmixing equations can be used. If a packed or baffled tower is used, then the calculations must be made for both the longitudinal and back-mixing cases. Proper extrapolation must then be made from empirical data or previous experience. 

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