Pentane conversion

As a practical method, designers have employed other methods such as / -pentane conversion as a key component, kinetic severity factor (31), or molecular collision parameter (32) to represent severity. Alternatively, molecular weight of the complete product distribution has been used to define conversion (A) for Hquid feeds. 

Figure 5 summarizes the results obtained for fresh and spent samples the selectivity to MA and that to PA at approximately 43-50% n-pentane conversion are plotted as a function of the average oxidation state of V. The most oxidized the catalyst was, the most preferred was the formation of MA with respect to that of PA, with a MA/PA selectivity ratio equal to 7 at 50% n-pentane conversion for sample 0x3. The opposite was true for most reduced samples, with a MA/PA selectivity ratio... 

Figure 5. Selectivity to MA and to PA at 43-50% n-pentane conversion as functions of the average oxidation state of V in fresh and spent samples.

Data reported in the present work demonstrate that the degree of crystallinity and the acid properties are related the amount of present at the surface of VPP. When the VPP is not fully equilibrated, and hence may contain discrete amounts of it is more selective to MA and less to PA. The reason is that in oxidized catalysts, the olefmic intermediate is preferentially oxidized to MA, rather then being subjected to the acid-catalyzed condensation with a second unsaturated molecule, to yield the precursor of PA. When instead the catalyst is more crystalline, and hence it does contain less oxidized V sites, its surface acid properties predominate over O-insertion properties, and the catalyst becomes more effective in PA formation. In this case, the selectivity to PA at 50% n-pentane conversion becomes comparable to that one of MA. 

In sill C MAS NMR spectroscopy has also been applied to characterize the scrambling in n-butene conversion on zeolite H-ferrierite (97), n-butane conversion on SZA (98), -butane isomerization on Cs2,5Ho.5PWi204o (99), n-pentane conversion on SZA (100), isopropylation of benzene by propene on HZSM-11 (101,102), and propane activation on HZSM-5 (103-105) and on Al2O3-promoted SZA (106,107). The existence of carbenium ions was proposed to rationalize the experimental scrambling results observed by in situ MAS NMR spectroscopy. 

S. Kuba, P. Lukinskas, R. Ahmad, F. C. Jentoft, R. K. Grasselli, B. C. Gates, and H. Knozinger, Reaction pathways in n - pentane conversion catalyzed by tungstated zirconia effects of platinum in the catalyst and hydrogen in the feed, J. Catal. 219, 376-388 (2003). 

In Table 1 the results are shown for the reaction over a variety of catalysts under a hydrogen atmosphere. It is clear that platinum-supported H-ZSM-5 (Pt-ZS.M-5) or hybrid catalyst containing Pt/Si02 (Pt/Si02 + H-ZSM-5) shows high n-pentane conversion and iso-pentane selectivity while both H-ZSM-5 or Pt/Si02 shows quite low activity and low iso-pentane selectivity. 

Catalyst sample Carbon content (%) Chloride content after regeneration (%) n-pentane conversion (%) Toluene conversion (%)... 

Pd-NiSMM contains 15 times as many strong Bronsted sites (defined as sites which adsorb pyridine above 250 C) as Pd-beidellite. We have measured the activity of Pd-beidellite, too. At 250 and 30 bar pressure (H2/HC 1.25 WHSV = 2 g.l l.h" ) we obtained a n-pentane conversion of 1.8 Z 0.9 % was converted to iso-pentane. This corresponds to a kigom about 1 g.g". h". Thus the measured isomerization activities qualitatively in agreement with the number of Bronsted sites which adsorb pyridine above 250 C. 

Homogeneous oxidation of n-pentane presented as conversion vs. reaction temperature under various n-pentane/oxygen ratios displayed tjrpical bell-shape curves over the temperature region of 300 - 500 °C [3], as illustrated in Fig. 2. The n-pentane conversion is near to zero at 5 % of oxygen and increases with oxygen content. 

For a given n-pentane/oxygen ratio, the n-pentane conversion varies in a regular manner (see Fig. 3), increasing with temperature and residence time of the reaction mixture in the empty space of the reactor. 

Addition of MTBE substantially suppressed the n-pentane oxidation, with the onset of n-pentane conversion shifting by about 50 °C to a higher temperature. The typical result of such experiment is depicted in Fig. 

The homogeneous reaction occurred in the void section of the reactor and then the reaction mixture passed through the frit and the catalyst layer. Resulting n-pentane conversion (Ctoti % void section + catalyst), homogeneous conversion (Chom. void section without catalyst), and selectivities to MA and PA (void section + catalyst) are shown in Table I. 

By increasing the void volume of the reactor, the homogeneous reaction diminishes the selectivity to partially oxidised products and, at the same time, increases the n-pentane conversion and significantly modifies the maleic to phthalic anhydride selectivity (see also Fig. 5). 

Such behaviour has been shown to be reversible and, after stopping the MTBE injection, the n-pentane conversion and selectivity to MA and PA return to their former values. Nevertheless, the analysis of the response curves indicates a substantial difference between the transient changes of MA or PA formation. Results characterising the transition behaviour of the system after starting and stopping the MTBE injection are depicted in Fig. 6. 

Precursor B preparation (U route Sbet m /g n-pentane conversion % structural defects evaluation SPA.%... 

Reported in Fig. 4 are the TAP results in multipulse mode with monitoring of the maleic anhydride (MA) formation from n-pemane and feeding a 1 5 mixture of n-pcntane/02 (A) or of only pentane (B). It is shown that MA formation decreases considerably with the number of pulses in both aerobic or anaerobic conditions. The decrease is more dramatic in the absence of O. Parallelely, n-pentane conversion also decreases. If after these experiments, pulses of only C>2 are fed to the catalyst and CO formation is monitored (Fig. 5), it is found that a large fraction of strongly adsorbed intermediates remain on the catalyst surface after interaction with feedstocks with or without O2 together writh alkane. When O2 is fed to the catalyst later, CO2 forms by reaction of O2 with surface C-coniaining molecules. The only other product detected, besides CO, is furan. 

Also the much smaller reduction of pentane conversion when mixed with hexane in Mordenite compared to Faujasite is a strong indication of the non-equilibrium situation in the medium pore zeolite. 

The method is illustrated for the adsorption rate controlling model for n-pentane isomerization. This rate equation contains two independent variables p, and or the n-pentane conversion and the ratio hydrogen/n-pentane. In reality these experiments were not planned according to this criterion. Thirteen experiments were carried out, shown in Fig. 1. This figure shows the limits on the experimental settings, that is, it shows the so-called operability region. 

The basic product of the reaction is 2-methyl-butane-3-one (methylisopropyl ketone) in the absence of water, whereas pivalic acid represents the basic product in the presence of water at 70°C and 8 atm partial CO pressure. Conversion of alkane (36%) was reached at 1 h of the reaction time vmder conditions of batch reactor (81). Under similar conditions n-pentane converts into a mixture of Ce-aldehydes [2-ethyl-butyraldehyde (5%), 2-methyl-pentanaldehyde (3%)] and ketones [2-methyl-pentane-3-one (11%) and 3-methyl-pentane-2-one (5%)] at 24% total conversion of n-pentane (82). In the presence of water n-pentane gives a mixture of three acids 2-ethyl-butjrric acid, 2-methyl-pentanoic acid, and 2,2-dimethyl-butyric acid at 150-200°C, 10 atm CO pressure, and 20% total n-pentane conversion. Carbonylation of propane gives rise to a mixture of isobutyric acid and isobutyraldehyde at 150°C, 10 atm CO pressure, and 22% propane conversion, isobutyric acid being the main product. 

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