Catalysts dilution

Reactor dilute phase (dome) pressure Reactor catalyst dilute phase bed level Reactor-stripper catalyst bed level Reactor-stripper catalyst density Spent catalyst standpipe elevation Pressure above the spent catalyst slide valve Spent catalyst slide valve AP ( 55% opening)... 

The cracking of diphenylmethane (DPM) was carried out in a continuous-flow tubular reactor. The liquid feed contained 29.5 wt.% of DPM (Fluka, >99%), 70% of n-dodecane (Aldrich, >99% solvent) and 0.5% of benzothiophene (Aldrich, 95% source of H2S, to keep the catalyst sulfided during the reaction). The temperature was 673 K and the total pressure 50 bar. The liquid feed flow rate was 16.5 ml.h and the H2 flow rate 24 l.h (STP). The catalytic bed consisted of 1.0 g of catalyst diluted with enough carborundum (Prolabo, 0.34 mm) to reach a final volume of 4 cm. The effluent of the reactor was condensed at high pressure. Liquid samples were taken at regular intervals and analyzed by gas chromatography, using an Intersmat IGC 120 FL, equipped with a flame ionization detector and a capillary column (Alltech CP-Sil-SCB). 

Effect of dimer formation on deactivation. Another possible mode of deactivation is formation of inactive Co dimers or oligomers. To test for these species, we examined the ESI-mass spectram of fresh and deactivated Co-salen catalysts in dichloromethane solvent (22). The major peak in the mass spectram occurred at m/z of 603.5 for both Jacobsen s Co(II) and Co(III)-OAc salen catalysts, whereas much smaller peaks were observed in the m/z range of 1207 to 1251. The major feature at 603.5 corresponds to the parent peak of Jacobsen s Co(II) salen catalyst (formula weight = 603.76) and the minor peaks (1207 to 1251) are attributed to dimers in the solution or formed in the ESI-MS. The ESI-MS spectrum of the deactivated Co-salen catalyst, which was recovered after 12 h HKR reaction with epichlorohydrin, was similar to that of Co(II) and Co(III)-OAc salen. Evidently, only a small amount of dimer species was formed during the HKR reaction. However, the mass spectram of a fresh Co(III)-OAc salen catalyst diluted in dichloromethane for 24 h showed substantial formation of dimer. The activity and selectivity of HKR of epichlorohydrin with the dimerized catalyst recovered after 24 h exposure to dichloromethane were similar to those observed with a fresh Co-OAc salen catalyst. Therefore, we concluded that catalyst dimerization cannot account for the observed deactivation. 

Another Hydrogenation with Platinum Oxide. JACS, 55, 2694. This method is used to reduce those hydrox-mandelonitriles in the amphetamine section. It uses low pressure and can be used on about any reducible compound. It can also use palladium oxide as the catalyst. A solution of 35.8 g of phenyl-2-propanol in 250 ml of 80% ethanol containing 7.3 g of HCl is hydrogenated for 3 hours in a Parr hydrogenation bottle at 3,5kg/cm or 50 p.s.i, over 0,5 g of platinum oxide (or palladium oxide Raney nickel may also work) or an equimolar ratio of analog catalyst for about 3 hours. Filter off the catalyst and rinse with a little water to wash all the product from the catalyst. Dilute the filtrate to 1 liter of volume with water and extract twice with ether to remove any acid insoluble material. The ether extracts do not contain product. The aqueous layer is made alkaline with solid NaHCOs to a pH of 8-9 and the basic oil which separates is extracted with two 300 ml portions of ether. This ether solution is dried over MgS04, and filtered, then evaporated to remove the ether. To convert to the oxalate, add ether to the crude product and add to a solution of 9.6 g of oxalic acid dihydrate in a small volume of methanol. Give ample... 

The reduction in concentration of reactants, enzymes, and solute molecules can provide important information about kinetic systems. For example, one can readily differentiate a first-order process from a second-order process by testing whether the period required to reduce a reactant concentration to 50% of its initial value depends on dilution. First-order processes and intramolecular processes should not exhibit any effect on rate by diluting a reactant. In terms of enzyme-catalyzed processes, the Michaelis-Menten equation requires that the initial reaction velocity depends strictly on the concentration of active catalyst. Dilution can also be used to induce dissociation of molecular complexes or to promote depolymerization of certain polymers (such as F-actin and microtubules). 

Catalytic tests of n-pentane oxidation were carried out in a laboratory glass flow-reactor, operating at atmospheric pressure, and loading 3 g of catalyst diluted with inert material. Feed composition was 1 mol% n-pentane in air residence time was 2 g s/ml. The temperature of reaction was varied from 340 to 420°C. The products were collected and analyzed by means of gas chromatography. A FlP-l column (FID) was used for the separation of C5 hydrocarbons, MA and PA. A Carbosieve Sll column (TCD) was used for the separation of oxygen, carbon monoxide and carbon dioxide. 

The catalyst pretreatment process for both the clay-supported and the reference catalysts consists of loading into the HDS reactor under N2, purging in N2 at 20°C for 30 min at 1000 cmVmin., drying in N2 at 150°C for 60 min and at 400°C for 60 min, and finally sulfiding in a 5% H2S/H2 mixture at 400°C for two hr prior to use as catalysts. The laboratory scale liquid-phase continuous-flow HDS reactor consists of a thick-walled 0.375" ID 316 SS tube, with 1 g catalyst diluted with 5 g tabular alumina (LaRoche T-1061, 10 m2/g) sitting between plugs of quartz wool. Beneath the lower plug is a 0.125" ID, 0.375" OD deadman used to minimize volume between the reactor and the liquid receiver. The liquid test feed consisted of 0.75 wt % sulfur as dibenzothiophene (DBT), dissolved in hexadecane and is representative of a middle distillate oil. All liquid-filled lines were heated to 50°C. The reaction was carried out at 400°C LHSV = 10-40/hr. 

Fig. 20. Dependence of exit conversion on inlet temperature. Platinum catalyst diluted with inert particles (homogeneous mixing) linear velocity w = 5.3 cm, bed length L = 6 cm.

Fig. 21. Three steady states in a catalyst bed. Pt catalyst diluted with inert particles (heterogeneous mixing).

The reactor wells are pre-loaded with catalyst (diluted with silicon carbide if desired) and inserted into the module. Two graphite seals are used per well, one to pressure seal each vial and one to prevent bypass flow around the vial. A single central bolt in tension supplies the sealing force onto these seals (Fig. 3.12b). 

Figure 5 Hot spot reduction using spatially structured catalyst dilution. Selectivity profiles for base case with constant coolant temperature, cocurrent coolant strategy and axially profiled catalyst activity strategy. The base case chosen in the calculations is the one in which the coolant temperature is constant and the activity profile along the length of the reactor is at the level unity. (From Ref. 5.)...

As mentioned, from the reaction kinetics viewpoint the behavior of zeolite catalysts shows large variability. In addition, the apparent kinetics can be affected by pore diffusion. The compilation of literature revealed some kinetic equations, but their applicability in a realistic design was questionable. In this section we illustrate an approach that combines purely chemical reaction data with the evaluation of mass-transfer resistances. The source of kinetic data is a paper published by Corma et al. [7] dealing with MCM-22 and beta-zeolites. The alkylation takes place in a down-flow liquid-phase microreactor charged with catalyst diluted with carborundum. The particles are small (0.25-0.40 mm) and as a result there are no diffusion and mass-transfer limitations. 

The catalyst diluted with inert quartz was placed in a tubular stainless steel reactor and the temperature in the bed was measured by a movable thermocouple inserted in a thermowell at the center of the reactor... 

Home, P. A. and Williams, P. T., Upgrading of biomass-derived pyrolytic vapours over zeolite ZSM-5 catalyst Effect of catalyst dilution on product yields. Fuel 1996, 75, (9) 1043-1050. 

Thus, in the often used TiCh-based catalysts diluted TiCl4 is first reduced by reacting with, for instance, AlEt.s to a solid brown, black, or sometimes purple reaction product which is subsequently activated with the same or sometimes another alkylaluminum compound. Cooper and Rose (10) showed that the composition of the reaction product formed in the reducing step may... 

The reactor used was a 10 mm diameter stainless sted tube filled with 0.1 g or 0.25 g catalyst diluted with 1.0 mm glass beads. The reactions considcied were the consecutive reaction 2-ethyl-hexenal (A) —> 2-Etbyl-hexanal (B) —> 2-ethyI-hexanol (C) dimerization of the aldehydes, and the fomiation of heptane by decarbonylization. AU experiments were performed at atmospheric pressure and at a reaction temperature of 120°C. The hydrogen pressure was 1250 Pa (1.23% H ) and 300 Pa. The space velocity was adjusted to get similar conversion... 

Catalytic tests were carried out using 5 grams of catalyst diluted with an equal volume of SiC particles in a fixed-bed down-flow gas phase reactor. The off-gas composition was determined by gas chromatography (GC). For butene isomerization experiments 1-butene (99.5% pure) was used as feedstock without dilution at a total pressure of 1.2 bar. The results reported here have been obtained at 350°C and a weight hourly space velocity of 2 kg(butenes)/(kg of catalyst/hr). 

The performance of the catalysts was studied in a fixed bed reactor testing unit. A 50 ml sample of the catalyst diluted with an equal volume of carborundum was used in the test. In a typical test run in which the catalyst is presulfided, the diluted catalyst is loaded in the reactor and the unit is pressurized with H2 to a pressure of 30 bar. The reactor is heated to 200°C and the presulfiding feed, which consists of gas oil spiked with 5% DMDS, is introduced at a rate of 100 ml/h. The reactor temperature is then raised to 250°C gradually in 2 hours. These conditions are maintained for 8 hours, then the temperature is raised again to 350°C gradually in 8 hours, and maintained under these conditions for an additional 8 hours. The residue feed is then introduced and the unit is brought to the operating conditions of the test, namely, P = 120 bar LHSV = 2.0 T = 425°C Hj/Oil = 1000 VN. 

For an initial catalyst coverage of 0.88, the deposition rate is predicted to be effectively saturated near the start of metal deposition with geometrically driven changes in catalyst coverage on the concave surfaces being minimal (Figure 2.36e). Deposition within the trench proceeds conformally, although motion of the top convex comers of the trench is still inhibited due to the catalyst dilution effects described earlier. 

In the above process, usually 2 mol of isobutylene react with each mole of cresol in the presence of acidic catalyst. Dilute H2SO4 is the most popular catalyst for both alkylation and dealkylation process. Some of the plants use p-toluene sulfonic acid or even a mixture of sulfuric acid and p-toluene sulfonic acid. It is reliably learnt that at least one plant has been using some quantities of a very strong Friedel Crafts alkylation catalyst—Triflic acid or trifluoromethane... 

The catalyst, diluted in cordierite, is placed in a straight Pyrex reactor and pretreated under pure helium at 450°C (ramp rate = 2°C.min ) for 15 minutes. Reactions are carried out at 450°C. Experiments consist in 5 different steps, as presented on Fig. 7.9. 

This time, the addition of a solvent hardly improves the performance of the non embedded catalyst. Dilution of the reaction medium and a more imporant blank reaction are the only consequences. This confirms that a membrane resident catalyst under solvent free conditions can actually be used to reduce interferences from the blank reaction. 

Catalytic measurements were made using 100 mg catalyst diluted with 400 mg of inactive aAl203 in a fixed-bed flow reactor. The typical gas nuxture consisted of 2000 vpm NO, 2000 vpm CsHg, 10 vol. % O2, balance He, without or with 10 vol. % water (total flow rate 10 1 h ). In the absence of water in the reactant nrixture, the temperature was increased from 300 to 773 K (or 873 K) (heating rate 2 K min ) and then decreased to 423 K. Water was then added at 423 K and the temperature increased and decreased again as above. The analysis was performed by gas chromatography with two columns (porapak and molecular sieve) and a TCD detector for CO2, N2O, O2, N2 and CO, and with a porapak column and a flame ionisation detector for hydrocarbons. Moreover, on-line IR and UV analyzers were used for NO, NO2, CO2, and N2O analysis. The NO conversion was calculated from the N2 production and the nitrogen balance was checked. 

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