Pressure within catalytic reactor

Data obtained from a catalytic hydrogenation which is run at constant temperature, pressure and volume are most easily interpreted. With today s teclmology temperature control is relatively easily attained in most reactors, but maintaining a constant pressure within the reactor while still measuring hydrogen uptake requires special consideration. A common method used to... 

Some others do have this capability but do not operate at constant pressure within the reactor. However, the biggest problem with most of these systems is the small size of the reactors. This may not be a problem with homogeneous catalysts where aliquots of a standard catalyst solution can be used to give identical amounts of the catalytically active species in each reactor. 

All types of catalytic reactors with the catalyst in a fixed bed have some common drawbacks, which are characteristic of stationary beds (Mukhlyonov et al., 1979). First, only comparatively large-grain catalysts, not less that 4 mm in diameter, can be used in a filtering bed, since smaller particles cause increased pressure drop. Second, the area of the inner surface of large particles is utilized poorly and this results in a decrease in the utilization (capacity) of the catalyst. Moreover, the particles of a stationary bed tend to sinter and cake, which results in an increased pressure drop, uneven distribution of the gas, and lower catalyst activity. Finally, porous catalyst pellets exhibit low heat conductivity and as a result the rate of heat transfer from the bed to the heat exchanger surface is very low. Intensive heat removal and a uniform temperature distribution over the cross-section of a stationary bed cannot, therefore, be achieved. The poor conditions of heat transfer within... 

All hydrogenation experiments were carried out at atmospheric pressure in a reactor, consisting of a flask attached to a burette filled with mercury and equipped with stopcocks that permit removal of air before the introduction of hydrogen. The mixed catalyst/solid substrate was placed at the bottom of the flask reactor to form a thin layer (2-3 mm) and then evacuated to approximately 10-3 Torr for 10 min. After introducing hydrogen (760 Torr), the reaction was carried out until complete transformation of the solid had occurred usually the reaction was completed within 18 h. This transformation was accompanied by the formation of thin needles on the surface of the solid catalytic bed, which correspond to the resulting products cA-4-tert-butylcyclohexanol, /ra s-4-/err-butylcyclohexanol and 4-tert-butylcyclohexanone. The reaction mixture was extracted with ethyl ether, and the catalyst separated by simple filtration. Analysis of the products was carried out by gas chromatography and mass spectroscopy. 

A new process that converts propylene and water to diisopropyl ether (DIPE) was developed by Mobil Research Development Corp. DIPE is a high-octane gasoline blending agent which, unlike other ethers, utilizes propylene in its synthesis. The DIPE reaction takes place in a fixed-bed catalytic reactor via a series of reaction steps. Isopropyl alcohol (IPA) is an intermediate which is recycled within the process. A propane/propylene splitter is included in the feed purification section to increase the concentration of propylene in the feed and maximize the DIPE production. DIPE utilizes propylene from the refinery and does not depend on an outside supply of alcohol. DIPE has similar octane blending values of RON and MON as other ethers like MTBE and TAME. DIPE also has a lower Reid vapor pressure than that of MTBE. DIPE is virtually nontoxic and has not caused adverse systemic effects or tissue toxicity [66]. 

Catalytic study of propane oxidation was performed under atmospheric pressure in a stainless tube microreactor (2 cm o.d.) connected with a GC-MS apparatus, either at a temperature in the range 300-400 "C or at 340 C by varying the contact time. To better control the reaction temperature, the thermocouple was installed within the reactor. The gas feed consisted of 40 vol% propane, 20% oxygen and He as balance. Total flow rates were in the range 7.5 to 30 cm min and the mass of the catalyst was... 

The main problem related to SLPC is the loss of solvent because of evaporation in a continuously operated catalytic reactors. This problem can be overcome by using ionic liquids as solvent [17-20]. Ionic liquids are molten salts and their partial pressure is low under conditions commonly used for hydroformylation and hydrogenation reactions. As generally observed for SLPC, the catalytic activity and product selectivity depends on the liquid loading and the nature of the porous support [21]. A detailed discussion can be found in [22]. In order to diminish internal diffusion resistances within the supported liquids by using microstruc-tured supports with high porosity like foams or fibrous materials, are proposed for SLPC [23]. 

Science relies on the development of new techniques in order to make new measurements and gain new insights. While the measurements have always been my priority, rather than the techniques, there was often the need to develop or improve certain methods along the way. The high-pressure-low-pressure apparatus, as described above (3.1, 3.2) enabled catalytic reactions to be carried out at pressures up to a hundred atmospheres, and to be followed by UHV surface characterization, by methods such as XPS, HREELS, LEED and mass spectroscopic measurements, without exposure to the air. This was a significant achievement within the Somorjai group, since it at least partially addressed the pressure gap , between UHV surface science and experiments carried out in catalytic reactors (5.6). 

Pressure Vessels. Refineries have many pressure vessels, e.g., hydrocracker reactors, cokers, and catalytic cracking regenerators, that operate within the creep range, i.e., above 650°F. However, the phenomenon of creep does not become an important factor until temperatures are over 800°F. Below this temperature, the design stresses are usually based on the short-time, elevated temperature, tensile test. 

Compared with laboratory fixed-bed reactors or conventional extruded monoliths, such a microstructured monolith is smaller in characteristic dimensions, lower in pressure loss by optimized fluid guiding and constructed from the catalytic material solely [3]. The latter aspect also leads to enhanced heat distribution within the micro channels, giving more uniform temperature profiles. 

Column reactors can contain a draft tube - possibly filled with a packing characterized by low pressure drop - or be coupled with a loop tube, to make the gas recirculating within the reaction zone (see Fig. 5.4-9). In recent years, the Buss loop reactor has found many applications in two- and three-phase processes About 200 Buss loop systems are now in operation worldwide, also in fine chemicals plants. This is due to the high mass-transfer rate between the gas and the liquid phase. The Buss loop reactor can be operated semibatch-wise or continuously. As a semibach reactor it is mostly used for catalytic hydrogenations. 

An oxidative environment is also an essential element in maintaining catalytic activity. Air is used as the copper(l) reoxidant for safety reasons. Oxygen partial pressure must be held between 2 volume % and 6 volume % during the redox cycle. If the oxygen partial pressure falls below 2 volume %, monoatomic palladium(O) does not reoxidize to palladium(Il) at a sufficient rate, and some catalytic activity is lost due to polymeric palladium metal formation. Under typical oxycarbonylation conditions, copper(ll) cannot reoxidize polymeric palladium metal. An oxygen partial pressure greater than 6 volume % affords a potentially explosive gas mixture with carbon monoxide. Oxygen partial pressure control within these limits was easily achieved in the oxidative-carbonylation pilot plant reactor. 

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