Nickel-molybdenum pressure effect

It was found that a nickel-activated carbon catalyst was effective for vapor phase carbonylation of dimethyl ether and methyl acetate under pressurized conditions in the presence of an iodide promoter. Methyl acetate was formed from dimethyl ether with a yield of 34% and a selectivity of 80% at 250 C and 40 atm, while acetic anhydride was synthesized from methyl acetate with a yield of 12% and a selectivity of 64% at 250 C and 51 atm. In both reactions, high pressure and high CO partial pressure favored the formation of the desired product. In spite of the reaction occurring under water-free conditions, a fairly large amount of acetic acid was formed in the carbonylation of methyl acetate. The route of acetic acid formation is discussed. A molybdenum-activated carbon catalyst was found to catalyze the carbonylation of dimethyl ether and methyl acetate. 

Catalysts based on transition metal molybdates, typically bismuth, cobalt and nickel molybdates [2-6], have received recent attention. Of the transition metal molybdates, those based on nickel, and in particular the stoichiometric NiMo04, have attracted the greatest interest. NiMo04 presents two polymorphic phases at atmospheric pressure a low temperature a phase, and a high temperature P phase [2,7]. Both phases are monoclinic with space group dim. These phases differ primarily in the coordination of molybdenum which is distorted octahedral in the a phase and distorted tetrahedral in the P phase. The P phase has been shown to be almost twice more selective in propene formation than the a phase for comparable conversion at the same temp>erature [2]. A similar effect has been noted for oxidative dehydrogenation of butane, with the P phase being approximately three times more selective in butene formation than the a phase [8]. The reason for the difference in selectivities is unknown, but the properties of the phases are known to be dependent on the precursors from which they are derived. Typically, nickel molybdates are prepared by calcination of precipitated precursors. 

Hydrogenation experiments with simultaneous acoustic irradiation were carried out by using iso-propanol (2-propanol) as solvent in an automatic laboratory-scale autoclave (Parr 4560) with an effective liquid volume of 250 ml. The operating conditions were as follows 50 bar hydrogen pressure and 70°C (343 K) as the reaction temperature. The catalyst-to-citral ratio was 1 25 (wt wt) in the beginning of the reaction. A commercial molybdenum promoted Raney nickel catalyst with a mean particle size of approx. 22 pm and the specific surface area in the range of 80 m /g was used in the experiments. The reactor contents were analyzed oiF-line with gas chromatography (GC). 

Due to the high chromium contents, duplex alloys are sensitive to 885 (475°C) embrittlement. This generally limits their usage to 600°F (SIS C) maximum for pressure vessels. Due to the presence of nickel, chromium, and molybdenum they are also susceptible to the formation of affect mechanical properties and corrosion resistance due to alloy depletion. The temperature range of 1100°F (593 C)-1600°F (882°C) and most rapidly at about 1450°F (788°C). The deleterious effects of phase formation are not obvious at the elevated temperature but can become a factor at room temperature. The formation of a phase in these alloys is sufficiently rapid to have an effect on properties due to slow cooling (air) after anneal. A measurable effect as a result of exposure in this temperature range due to welding has been demonstrated. 

A low O2 condition is produced at a corrosion interface in the presence of protective scales, and complex corrosion reactions such as chlorination, sulfidation and oxidation occur below the corrosive deposit layer. Thick scales have pores and cracks due to temperature fluctuations and the vaporization of chlorides. As the thickness increases, the scales easily peel off from the surface. In particular, severe thermal cycles or increased gas velocities due to soot blowing accelerate the breakdown and spalling of the scale. Also, as a result of continuously repeated variations of gas conditions on the scales, the balance of chlorination, sulfidation and oxidation reactions at the corrosion interface and in the scales is forced to be changed by the penetration of O2. An increase of the partial pressure of O2 ( /qj ) temporarily halts the chlorination and sulfidation reactions. Therefore, a multi-layered scale stracture is produced. The presence of multi-layered oxides formed by corrosion resistant elements such as chromium, nickel, aluminum, silicon and molybdenum increases the protective effect of the scales against the... 

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