Multizone Reactors

Autoclave reactors differ from tubular reactors in two respects. Autoclave reactors have much smaller length-to-diameter ratios (2-4 for single-zone and up to 15-18 for multizone reactors) and operate at a much narrower reaction temperature range. 

In the 1970s, fluorination of volatile ethers, esters and acid fluorides was accomplished in reasonable yield using the same copper filing packed surface multizone reactor for such fluo-rinations (Table 3).18... 

Table 3. Copper Filing Packed Surface Multizone Reactor Fluorination (F, —78 C) of Ethers, Esters and Acid Fluorides18...

The arenediazonium solution can also be manufactured in a continuous way either in two consecutive loop reactors76 or in a multizone reactor, run by the arylamine solution, and where a part of the nitrite solution is fed into the upstream portion of each reaction zone.77,78... 

If this trend is extrapolated to lower temperatures it is clear that at temperatures varying between -78 and -150°C for carbon—hydrogen bonds on various types of hydrocarbons, AF becomes zero and then endothermic. Under these conditions (AG < 0) the reaction with elemental fluorine will not and should not proceed at all Wfe have observed this in many cases experimentally. At temperatures as low as -150°C the reaction of fluorine with all studied organic compounds either does not occur or is extremely slow. We have occasionally reported reactions in the cryogenic reactor as low as -120°C. It should be explained that the — 120°C reported is the temperature of a single trap in a multizone reactor rather than that for the entire reactor. It is possible that fluorination occurs during the volatilization process at such low temperatures. 

After primary compression (1), ethylene, with recycled gas and VAM, enters the secondary compressor (2) to reach the required polymerization pressure. The gas is split into several streams, and injected in selected zones of the multizone reactor (3) where the polymerization occurs. 

Figure 6.2b displays the temperature profile for a 100-zone case that is a tour de force for the optimization routine. The results took less than 20 min of computing time, but the difference in bout between the 10- and 100-zone cases is negligible. These multizone designs give bout = 3.61 compared to 3.59 for the best adiabatic reactor with t = 0.8 h, but multizone reactors would be very expensive to build. Problems 6.11-6.13 suggest practical approaches to achieving a desirable temperature profile. 

Spheripol process, liquid monomer as continuous medium Multizone reactor... 

Since the same will happen in Reactor 2, in the end the ratio of polypropylene to ethylene-propylene copolymer per particle exiting Reactor 2 will also vary widely, which may be undesirable in some applications. Some of the reactor configurations shown in Figure 8.35 can reduce this phenomenon, particularly the configuration adopted for the gas-phase horizontal reactor, because the residence time distribution of this reactor is the equivalent to about three to four CSTRs in series. (Remember that the residence time of an infinite series of ideal CSTRs is that of a plug-flow reactor.) A more recent solution for this problem, in fact a completely new alternative to tandem reactor technology, is the multizone reactor that will be described in more detail below (see Section 8.6.4). 

The current maximum size of autoclave reactors is about 25001 for a capacity of approximately 200kiloton/year of LDPE. The length to diameter ratio L/D can be as low as 2 for a single zone and up to 20 for multizone reactors. Residence time ranges between 8 and 60 s. 

Figure 3 Multizone reactors for high-pressure ethylene polymerization.

---