Acrylonitrile propane ammoxidation

Ammonia also reacts with the acrolein intermediate, via the formation of an imine or possibly oxime intermediate which transforms faster to the acrylonitrile than to the acrylamide intermediate. This pathway of reaction occurs at lower temperatures in comparison to that involving an acrylate intermediate, but its relative importance depends on the competitive reaction of the acrolein intermediate with the ammonia species and with catalyst lattice oxygens. NH3 coordinated on Lewis sites also inhibits the activation of propane differently from that absorbed on Brsurface reaction network in propane ammoxidation. 

The catalytic behavior of Fe-MTW zeolites in the direct ammoxidation of propane was investigated. The obtained catalytic results are compared with behavior of Fe-silicalite catalysts whose activity in propane ammoxidation was recently published. It was found that Fe-MTW catalysts exhibit the similar activity as Fe-silicalites but the selectivity to acrylonitrile was substantially lower. On the other hand, Fe-MTW catalysts produce higher amount of propene and have better acrylonitrile-to-acetonitrile ratio. 

The increasing volume of chemical production, insufficient capacity and high price of olefins stimulate the rising trend in the innovation of current processes. High attention has been devoted to the direct ammoxidation of propane to acrylonitrile. A number of mixed oxide catalysts were investigated in propane ammoxidation [1]. However, up to now no catalytic system achieved reaction parameters suitable for commercial application. Nowadays the attention in the field of activation and conversion of paraffins is turned to catalytic systems where atomically dispersed metal ions are responsible for the activity of the catalysts. Ones of appropriate candidates are Fe-zeolites. Very recently, an activity of Fe-silicalite in the ammoxidation of propane was reported [2, 3]. This catalytic system exhibited relatively low yield (maximally 10% for propane to acrylonitrile). Despite the low performance, Fe-silicalites are one of the few zeolitic systems, which reveal some catalytic activity in propane ammoxidation, and therefore, we believe that it has a potential to be improved. Up to this day, investigation of Fe-silicalite and Fe-MFI catalysts in the propane ammoxidation were only reported in the literature. In this study, we compare the catalytic activity of Fe-silicalite and Fe-MTW zeolites in direct ammoxidation of propane to acrylonitrile. 

V-containing silicalite, for example, has been shown to have different catalytic properties than vanadium supported on silica in the conversion of methanol to hydrocarbons, NOx reduction with ammonia and ammoxidation of substituted aromatics, butadiene oxidation to furan and propane ammoxidation to acrylonitrile (7 and references therein). However, limited information is available about the characteristics of vanadium species in V-containing silicalite samples and especially regarding correlations with the catalytic behavior (7- 6). 

Recently, amorphous high surface area vanadium aluminium oxynitrides have been reported as active catalysts for propane ammoxidation to yield acrylonitrile (AC) at atmospheric pressure. Optimal performance was achieved at 500°C using a C3Hg 02 NH3 molar ratio of 1.25 3 1 (see Tables 4 and 5). The space time yields of these catalysts have been reported to be much higher than for other catalysts reported in the literature. 

Processes based on propane ammoxidation to manufacture acrylonitrile have also been developed,915 966 and BP has announced commercialization.966 Dehydrogenation at high reaction temperature (485-520°C), which is about 100°C higher than for propylene ammoxidation, results in the formation of propylene, which subsequently undergoes normal ammoxidation. Despite higher investments and the markedly lower selectivity (30-40%), the process can be economical because of the price difference between propylene and propane.966 Better selectivites can be achieved at lower (40-60%) conversions. 

Figure 9.4 Reaction scheme of propane ammoxidation to acrylonitrile.

Centi, G., Graselli, R. K., Trifiro, F., Propane ammoxidation to acrylonitrile, an overview, Catal. Today, 661-666, 1992... 

FIGURE 16 Raman spectra recorded during propane ammoxidation on alumina-supported nanocrystalline V-Sb-O system and simultaneous activity data determined by online gas chromatography (Guerrero-Perez M.O., and Banares, M.A. Chem. Commun. 1292 (2002), Operando Raman study of alumina-supported Sb-V-O catalyst during propane ammoxidation to acrylonitrile with on line activity measurement, reproduced with permission of the Royal Society of Chemistry) (Guerrero and Banares, 2002). 

Few reports have discussed the structures of Mo V Te Nb oxide catalysts in relation to propane oxidation and ammoxidation. Some reports indicate that not only the elemental composition but also preparative variables greatly affect the structure and performance of Mo-V-Te Nb oxide catalysts. Among the preparative variables, methods for precursor preparation appear to be critical. One example is Mo V Te-Nb oxide, which when prepared by a sohd-state method from corresponding oxides of each element is a mixture of M0O3 and (Mo-X)50i4 (X is other cations) and is inactive for the propane ammoxidation. However, Mo-V-Te-Nb oxide prepared by a hydrothermal reaction method from the same oxide by the solid-state method is a mono-phasic oxide with an orthorhombic layered structure, which selectively catalyzes propane to acrylonitrile. ... 

Active and selective in propane oxidation to acrylic acid propane ammoxid. to acrylonitrile ethane oxidation to ethylene/acetic acid... 

Propane Ammoxidation to Acrylonitrile 789 Table 20.2 Performance of some V/Sb/O-based catalysts described in the literature. 

The literature on ammoxidation is very wide. The majority of papers and patents published in this field deal with propene and propane ammoxidation to acrylonitrile, of isobutane and isobutene ammoxidation to methacrylonitrile and methyl-aromatics and methylpyridines (picoUne) ammoxidation to the corresponding cyano-containing compounds, as discussed in the previous sections. A small amount of literature deals with the ammoxidation of the following molecules ... 

Important classes of reactions not included in the above list, because they are not yet used on a commercial scale, are (i) the oxidative dehydrogenation of C2-C5 alkanes, (ii) the selective oxidation of alkanes, such as the synthesis of maleic and phthalic anhydride from n-pentane and methacrolein or methacrylic acid from isobutene, and (iii) propane ammoxidation to acrylonitrile [317-319]. 

By increasing the temperature of the calcination in nitrogen atmosphere (from 700 to 800°C), the sample becomes more active and selective in acrylonitrile, but still less with respect to the catalyst calcined in air at 700°C. The presence of different phases and of a non-homogenously distributed mixed oxide leads to a less selective sample for propane ammoxidation. 

In the propane ammoxidation a lower selectivity for acrolein plus acrylonitrile is observed. The formation of partial (amm)oxidation products from propane requires more elemental steps than their formation from propene. All these intermediates can undergo a side reaction with electrophilic oxygen species yielding degradation products. 

In this paper, a new computer-aided technique was presented, with which the experimental procedure of developing catalysts is scheduled sequentially. In each sequential step the neural networks model and multi-objective optimization are used to determine optimal design for the next experiment. The sequential method proved very efficient in developing catalysts for propane ammoxidation to acrylonitrile. And the yield of acrylonitrile corresponding to the best catalyst was up to 58.9%. 

The process for direct acrylonitrile (ACN) synthesis from propane ammoxidation ... 

In the paper, we presented a new conq>uter-aided technique, which takes the catalyst development as an iterative procedure, and each iteration includes fom steps, i.e. distributing experimental points, carrying out experiments, modeling the catalytic relationship and forecasting the optimal design. The technique was applied to developing catalysts for propane ammoxidation to acrylonitrile. 

Depending on the sequential method mentioned above, in our work of developing catalysts for propane ammoxidation to acrylonitrile, we also focused efforts on the catalytic active system of V-Sb-Al mixed oxides. The work was divided into three parts, i.e., optimizations of the composition of promoters and supporters, the conq)osition of main conq)onents as well as reaction conditions. 

This work shows the acquired experience in the preparation at pilot-scale of a novel propane ammoxidation catalyst based on a partially nitrided V-Al mixed oxide obtained hy co-precipitation. A systematic investigation of the different parameters controlling the preparation of the catalyst via a co-precipitation route at different scales was carried out. At lab-scale (50 to 100 g), the preparation parameters optimized were precipitation pH, V/Al atomic ratio, V concentration in solution and nitridation conditions, while at pilot-scale (1 kg), the optimized parameters were precipitation and ageing time, solution/solid ratio during the washing step, drying and calcination conditions, and extrusion parameters. Our results show that the optimum preparation conditions for the VAION system are pH = 5.5, V/Al atomic ratio = 0.25, concentration of V species in solution = 30.10 M. This catalyst shows the highest selectivity and yield in acrylonitrile. The samples prepared at different scales show the same activity profile in the propane ammoxidation reaction. 

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