Quick contact reactor

Fig. 4. Quick contact reactor, concurrent downflow cracker. Modified from P. K. Niccum and D. P. Bunn, U. S. Pat. 4,514,284 (1985). 1, catalyst storage 2, recirculating pipe 3, quick contact reactor 4, steam stripper 5, riser regenerator.

Fixed bed plants. In this type of plant, the process flow for all three feeds looks like the plant in Figure 20—3. The feed and compressed air are mixed, vaporized in a heater, and then charged to the fixed-bed reactor, a bundle of rubes packed with the catalyst. The ratio of air to hydrocarbon is generally about 75 1 to keep the mixture outside the explosive range, always a good idea. The feed temperature is 800-900°F, depending on the feed. The reaction time is extremely quick, so the feed is in contact with the catalyst for only 0.1 to 1.0 second. 

The example above shows the severity of the problem that arises from the presence of mercury in natural gas. Not only is it necessary to determine the levels of mercury present, but also to remove the majority of the mercury prior to any contact with aluminium reactors. The latter of course, further compounds the problem, because if 90% or more of the mercury has been removed, then to determine the remaining mercury is even more difficult. An effective analysis system will he able to measure mercury in its organic and inorganic forms and to do so very quickly. If a mercury removal bed is losing its efficiency then it is imperative to stop the process as soon as possible. In addition, these systems are expensive to operate and it is uneconomic to switch to a new unit if the original still has some life left in it. 

The Phillips catalyst contains hexavalent chromium after calcining, but the early discoverers quickly realized that reduction takes place in the reactor on contact with ethylene, leaving chromium in a lower oxidation state as the active species. A worldwide debate has continued to this day about the valence of this reduced species. Chromium in every valence state from Cr(II) to Cr(VI) has been proposed as the active site, either alone or in combination with another valence. The question has received far more attention than it probably deserves, undoubtedly at the expense of more fundamental issues, like the polymerization mechanism. 

Since reaction does not occur until one reactant is jetted into the other, the actual jet does not become involved in the kinetics, it is strictly a method for contacting reactants quickly. The actual reactor performance is based on CSTR assumptions. 

As mentioned earlier, the basic objective of liquid-liquid reactors is to create a fairly high specific area of contact, and at the same time ensure that the phase separation is conveniently achieved. A liquid-liquid system gives high values of specific interfacial area because of low intcrfacial tension. While small density differences in a liquid-liquid system give a large interfacial area, too small a density difference is detrimental to the quick separation of the two phases, and this may lead to operational difficulties. 

The short contact time is accomplished by using a transfer line between the regenerator and the reactor vessels. Most of the reaction occurs within the riser section.912,14 A termination device can be used to separate the catalyst from the products that are taken quickly as overhead. The main reactor vessels contain cyclone separators to remove the catalyst from the products and provide additional space for cracking the heavier fraction of the feed. 

FDP hydrogasification behavior at these relatively low temperatures. This is difficult to do in the present 3-inch id FDP reactor because the coal quickly heats to the reactor wall temperature and, if the wall temperature is below 725°-800°C, the coal adheres to the reactor walls and eventually plugs the reactor. However, the coal that did not contact the walls passed through the reactor and was collected, and its conversion and caking properties were determined. Results of these lower reactor wall-temperature experiments are shown in Figures 3 and 4. The effects of temperature on both the volatile matter and the carbon conversion of the FDP reactor char are shown at the reduced wall temperatures. 

For initial screening, we have operated our micro-catalytic reactor in a pulsed mode. As is shown below (Results Discussion, Figure 2), the catalyst appears to rather quickly achieve steady-state response, after the first few samples of wood (e.g., <100 mg wood per gram of catalyst). This is confirmed by the approximate mass closures (>80 % typically) from summation of all gaseous species evolving from each wood-vapor pulse, plus measured char yields for each pulse, and overall coke yields of 5-10 weight percent (See Table II under Results Discussion). There is some evidence of absorption of water and light aromatics when vapor first contacts the catalyst, so that the reported yields of liquid products are probably conservative. We plan to insert wood dowels in a continuous manner to verify the behavior under steady state of wood addition. 

Similar considerations are important in Py-MS cold spots and wall contact in the Py-MS vacuum systems can also affect transmission of pyrolysates." Py-MS produces a pyrogram of all compounds in the pyrolysis product mixture superimposed in a single mass spectrum. For that reason, interpretation of Py-MS results from a complex sample can be more difficult than interpretation of a Py-GC/MS pyrogram, in which pyrolysis products are chromatographically separated before MS detection. As pointed out by Snyder et al., Py-MS with relatively cold pyrolysis interface walls or with expansion chambers tends to provide only low mass range analysis (under m/z = 2(X)). When direct Py-MS is performed with the pyrolysis reactor close to the ion source, so as to detect larger mass pyrolysis products (m/z = 200 to 1000), the ion source tends to contaminate rather quickly, jeopardizing reproducibility. 

However, this behavior is not true because the residence time of molecules in these reactors is not uniform, with an RTD different of space time, r. The contact time of the molecules in the reactor is proper for each set or element of fluid passing through the reactor. So there are some molecules that leave the reactor quickly and others that stay longer, and consequently affecting the kinetic and, especially, the concentration or distribution of products at the outlet of the reactor. 

Some have argued that the clarifier itself acts as a reactor with a contact time measured in hours. This is a fallacy when applied to the clarified brine portion. Most of the separation between sludge and supernatant brine takes place quickly. The solids population in the clear brine is very low, and there is little opportunity for particle growth. Any further reaction in the clarified brine therefore tends to give particles that are too small to settle. 

Second, isoparaffins containing tertiary C—H bonds can react, or in a sense be alkylated, when mixed with olefins in the presence of acid catalysts. TMPs can react forming first C12—C20 cations. Mechanism 2- and 3-type reactions then occur. The quality of alkylate is often significantly reduced, and some CPs are also produced. To minimize these undesired reactions of especially TMPs, two procedures should be employed. Reactors are needed that minimize contact between TMPs and olefins. In addition, acid/hydrocarbon dispersions should be separated quickly as soon as the alkylation reactions are completed. Less information is available on undesired reactions when HF is used as the catalyst. 

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