Loop reactor design

The process, set up with a loop reactor part and a gas phase reactor part, is similar to corresponding single reactor processes. The catalyst is mixed with propane diluent and fed into a pre-polymerisation reactor. Cocatalyst, ethylene, comonomer and hydrogen are also fed into this reactor. The pre-polymerised slurry, together with the main feeds, is then fed into the slurry loop reactor, designed for supercritical conditions and typically operated at 85 - 100 C and 5.5 - 6.5 MPa. This reactor produces a low molecular weight, high density product. The reactor content is sent to a flash tank where diluent and unreacted components are separated from the polymer produced in the loop reactor. The diluent is condensed and recycled back into the loop reactor. 

Phillips Pilot PlantVertical Pipe-Loop Reactor Design... 

An improved loop reactor design with cone-shaped zones that transition the loop to a wider diameter section was recently patented by Basell Polyolefine GmbH [29]. This design is illustrated in Figure 5.15. 

The proposed commercial unit for this process operates with about 2 wt% catalyst in a "loop reactor," designed to have efficient heat transfer and gas-liquid dispersion [93]. The CO and methanol conversions are 95 and 30%, respectively, with MF production of approximately 800 gdi/L [87]. The process has been proven on the pilot scale [93]. 

Table I provides an overview of general reactor designs used with PS and HIPS processes on the basis of reactor function. The polymer concentrations characterizing the mass polymerizations are approximate there could be some overlapping of agitator types with solids level beyond that shown in the tcd>le. Polymer concentration limits on HIPS will be lower because of increased viscosity. There are also additional applications. Tubular reactors, for example, in effect, often exist as the transfer lines between reactors and in external circulating loops associated with continuous reactors.

Reaction occurs in the loop as well as in the stirred tank, and it is possible to eliminate the stirred tank so that the reactor volume consists of the heat exchanger and piping. This approach is used for very large reactors. In the limiting case where the loop becomes the CSTR without a separate agitated vessel, Equation (5.35) becomes q/Q > 10. This is similar to the rule-of-thumb discussed in Section 4.5.3 that a recycle loop reactor approximates a CSTR. The reader may wonder why the rule-of-thumb proposed a minimum recycle ratio of 8 in Chapter 4 but 10 here. Thumbs vary in size. More conservative designers have... 

The aim of this report is to examine the principles of shear stress on particles that would allow the design of bioreactors for technical use, mainly stirred tanks, bubble columns and loop reactors. 

Airlift loop reactor (ALR), basically a specially structured bubble column, has been widely used in chemical industry, biotechnology and environmental protection, due to its high efficiency in mixing, mass transfer, heat transfer etc [1]. In these processes, multiple reactions are commonly involved, in addition to their complicated aspects of mixing, mass transfer, and heat transfer. The interaction of all these obviously affects selectivity of the desired products [2]. It is, therefore, essential to develop efficient computational flow models to reveal more about such a complicated process and to facilitate design and scale up tasks of the reactor. However, in the past decades, most involved studies were usually carried out in air-water system and the assumed reactor constructions were oversimplified which kept itself far away from the real industrial conditions [3] [4]. 

Eulerian two-fluid model coupled with dispersed itequations was applied to predict gas-liquid two-phase flow in cyclohexane oxidation airlift loop reactor. Simulation results have presented typical hydrodynamic characteristics, distribution of liquid velocity and gas hold-up in the riser and downcomer were presented. The draft-tube geometry not only affects the magnitude of liquid superficial velocity and gas hold-up, but also the detailed liquid velocity and gas hold-up distribution in the reactor, the final construction of the reactor lies on the industrial technical requirement. The investigation indicates that CFD of airlift reactors can be used to model, design and scale up airlift loop reactors efficiently. 

A gas-inducing agitator system is an alternative to a multistirrer system. It contains a hollow shaft with orifices above the liquid level and a hollow impeller. A typical hollow impeller consists of a tube that is, at the centre, connected to the hollow shaft. Both ends of the impeller are cut at 45 so that, at rotation, the open portions of the tube are at the near side of the stirrer. There are several modifications of this design. Obviously, there is a minimum impeller speed at which the onset of gas induction occurs. Loop reactors are also successfully used. 

Schoutens, G. EL, Guit, R. P., Zieleman, G. J., Luyben, K. C. A. M., and Kossen, N. W. F., A Comparative Study of a Fluidised Bed Reactor and a Gas Lift Loop Reactor for the IBE Process Part I. Reactor Design and Scale Down Approach, J. Chem. Tech. Biotechnol., 36 335 (1986a)... 

Abstract This chapter embodies two sections. In the first section a survey of the state of the art of azo-dye conversion by means of bacteria is presented, with a focus on reactor design and operational issues. The relevance of thorough characterization of reaction kinetics and yields is discussed. The second section is focused on recent results regarding the conversion of an azo-dye by means of bacterial biofilm in an internal loop airlift reactor. Experimental results are analyzed in the light of a comprehensive reactor model. Key issues, research needs and priorities regarding bioprocess development for azo-dye conversion are discussed. 

Table 26.1 shows the effects of the two main design variables. Specifically, the results of the batch simulations for the same system as described above are given for different in-loop reactor (catalyst) volumes, recirculation rates. As would be expected increasing the catalyst volume decreases the hypochlorite concentration at all points and times through the process. Increasing the recirculation rate also appears to have a... 

Economic analysis of designs at lower natural hypochlorite strengths equally show potential investment benefits. They are, however, much less significant than the batch and high concentration cases described above. While an economic case can be made for retrofitting an in-loop reactor to a system that already has an end-of-pipe treatment system based on payback, it is not always clear that this is a better option than an end-of-pipe hybrid system as described earlier in the chapter. For a particular system the optimum solution is often as much a function of the required expenditure on the heat exchangers as it is the relative cost of the reactor options. 

As the next step in multiphasic hydrogenation, the design and implementation of a continuously driven loop reactor as a laboratory-scale plant model led to comparable selectivity applying the same water soluble ruthenium-based catalyst system. 

The air-lift consists of two pipes, intercoimected at top and bottom. In one of the pipes (the riser) air is sparged at the bottom. The air rises and escapes at the top. Therefore, nnder most circnmstances there is no air present in the other pipe (the downcomer). The density difference between riser and downcomer canses an intensive liquid circulation. Two designs can be used, i.e., the internal (Figure 11.8A) and the external loop reactor (Figure 11.8B). 

In the literature many examples of more or less exotic bioreactors can be found. Few actually are applied, outside the laboratory. Here two novel designs, the membrane and the liquid-impelled loop reactor, are discussed briefly. These two reactors are simple to use and, to a certain extent, liable to scale-up and both integrate the actual biocatalysis with part of the down-stream processing. 

A novel bioreactor, especially designed to work with two liquid phases, is the liquid-impelled loop reactor (Figme 11.10), in which the advantages of air lifts and... 

---