Hexane ammoxidation

Hydrocarbon-rich conditions imply that oxygen is the limiting reactant, due to the high oxygen-to-hydrocarbon stoichiometric ratio in n-hexane ammoxidation. Therefore, the conversion of the hydrocarbon is low this should favour, in principle, the selectivity to products of partial (amm)oxidation instead of that to combustion products. 

Catalysts tested for the reaction of n-hexane ammoxidation are reported in Table 40.1. Samples with composition SnA /Nb/Sb (atomic ratios between components) equal to x/0.2/1/3 were prepared and characterized. The atomic ratio between V, Nb and Sb was fixed becanse it corresponds to the optimal one for the active components when these catalysts are used for propane ammoxidation (10). 

Figure 40.3. Conversion of reactants in n-hexane ammoxidation as a function of the reaction temperature. Symbols conversion of n-hexane ( ), annnonia (A) and oxygen ( ). Catalyst SnA /Nb/Sb 1/0.2/1/3.

The only example reported in the literature concerning n-hexane ammoxidation is, once again. Reference [124]. In this paper, for a conversion of approx 12%, a selectivity to adiponitrile close to 40% and to hexanenitrile of approx 30% are reported, at 425 °C and with a molar feed ratio hexane/air/ammonia of 0.6-1.0/4.2/1.5. To our knowledge, these interesting results have never been confirmed. 

The Gas-Phase Ammoxidation of /i-Hexane to Unsaturated 5 Dinitriles, Intermediates for Hexamethylenediamine Synthesis... 

This chapter reports about an investigation on the catalytic gas-phase armnoxidation of u-hexane aimed at the production of 1,6-Ce dinitriles, precursors for the synthesis of hexamethylenediamine. Catalysts tested were those also active and selective in the ammoxidation of propane to aciylonitrile mtile-type V/Sb and SnA /Nb/Sb mixed oxides. Several A-containing compounds formed however, the selectivity to cyano-containing aliphatic linear Ce compounds was low, due to the relevant contribution of side reactions such as combustion, cracking and formation of heavy compounds. 

These processes are used commercially for many years. However, an interest exists for the development of alternative technologies for HMD A production, that may offer advantages with respect to conventional ones, such as (i) the use of less dangerous reactants, and (ii) a better overall economics, also achieved by the use of highly selective catalytic systems. One possible synthetic pathway is the gas-phase ammoxidation of -hexane to 1,6-Ce dinitriles, the latter containing either a saturated... 

In the present chapter, we report about an inveshgahon of the catalyhc performance of rahle-type V/Sb and Sn/V/Sb/Nb mixed oxides in the gas-phase ammoxidation of n-hexane. These catalysts were chosen because they exhibit intrinsic mulhfunctional properties in fact, they possess sites able to perform both the oxidahve dehydrogenahon of the alkane to yield unsaturated hydrocarbons, and the allylic ammoxidahon of the intermediate olefins to the unsaturated lutriles. These steps are those leading to the formahon of acrylonitrile in propane ammoxidahon. The SnW/Sb/(Nb)/0 system is one of those giving the best performance in propane ammoxidahon under hydrocarbon-rich condihons (8,9). 

In order to make a new catalyst for the ammoxidation of acrylonitrile, we decided to mix these two systems SbA, in order to activate the paraffin, and Sn/Sb, having already been utilized to ammoxidate the relative olefin. In this paper, the effects of the method of preparation and calcination of a Sn-V-Sb mixed oxide on its catalytic performance are analysed. In particular we changed the medium in which the starting material were dissolved, utilizing ethanol, iso-butanol and water, in order to understand the interaction between the solvent and the metallic ions and to enhance the performance of the catalyst. Moreover we made a mixture of oxides and hydroxide in n-hexane to compare the coprecipitation with a simple mixture. The catalyst with the best performance was then calcined at different temperatures and in different atmospheres in order to optimize the thermal treatment. 

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