Phosphoms oxide

The catalyst used in the production of maleic anhydride from butane is vanadium—phosphoms—oxide (VPO). Several routes may be used to prepare the catalyst (123), but the route favored by industry involves the reaction of vanadium(V) oxide [1314-62-1] and phosphoric acid [7664-38-2] to form vanadyl hydrogen phosphate, VOHPO O.5H2O. This material is then heated to eliminate water from the stmcture and irreversibly form vanadyl pyrophosphate, (V(123,124). Vanadyl pyrophosphate is befleved to be the catalyticaHy active phase required for the conversion of butane to maleic anhydride (125,126). 

Promoters are sometimes added to the vanadium phosphoms oxide (VPO) catalyst during synthesis (129,130) to increase its overall activity and/or selectivity. Promoters may be added during formation of the catalyst precursor (VOHPO O.5H2O), or impregnated onto the surface of the precursor before transformation into its activated phase. They ate thought to play a twofold stmctural role in the catalyst (130). First, promoters facilitate transformation of the catalyst precursor into the desired vanadium phosphoms oxide active phase, while decreasing the amount of nonselective VPO phases in the catalyst. The second role of promoters is to participate in formation of a soHd solution which controls the activity of the catalyst. 

Vanadium phosphoms oxide-based catalysts ate unstable in that they tend to lose phosphoms over time at reaction temperatures. Hot spots in fixed-bed reactors tend to accelerate this loss of phosphoms. This loss of phosphoms also produces a decrease in selectivity (70,136). Many steps have been taken, however, to aHeviate these problems and create an environment where the catalyst can operate at lower temperatures. For example, volatile organophosphoms compounds are fed to the reactor to mitigate the problem of phosphoms loss by the catalyst (137). The phosphoms feed also has the effect of controlling catalyst activity and thus improving catalyst selectivity in the reactor. The catalyst pack in the reactor may be stratified with an inert material (138,139). Stratification has the effect of reducing the extent of reaction pet unit volume and thus reducing the observed catalyst temperature (hot... 

Fluidized-bed reactor systems put other unique stresses on the VPO catalyst system. The mixing action inside the reactor creates an environment that is too harsh for the mechanical strength of a vanadium phosphoms oxide catalyst, and thus requires that the catalyst be attrition resistant (121,140,141). To achieve this goal, vanadium phosphoms oxide is usually spray dried with coUoidal siUca [7631-86-9] or polysiUcic acid [1343-98-2]. Vanadium phosphoms oxide catalysts made with coUoidal sUica are reported to have a loss of selectivity, while no loss in selectivity is reported for catalysts spray dried with polysUicic acid (140). 

Butane-Based Fixed-Bed Process Technology. Maleic anhydride is produced by reaction of butane with oxygen using the vanadium phosphoms oxide heterogeneous catalyst discussed earlier. The butane oxidation reaction to produce maleic anhydride is very exothermic. The main reaction by-products are carbon monoxide and carbon dioxide. Stoichiometries and heats of reaction for the three principal reactions are as follows ... 

Phosphoric acids and the phosphates maybe defined as derivatives of phosphoms oxides where the phosphoms atom is in the +5 oxidation state. These are compounds formed in the M2O—P20 system, where M represents one cation equivalent, eg, H", Na", 0.5 Ca ", etc. The molecular formula of the phosphoms(V) oxide [1314-56-3] is actually P O q, but this oxide is commonly referred to in terms of its empirical formula, P2O5. StmcturaHy, four phosphoms—oxygen (P—O) linkages are arranged in an approximate tetrahedral configuration about the phosphoms atom in the phosphate anion. Compounds containing discrete, monomeric PO ions are known as orthophosphates or simply as phosphates. 

All phosphoms oxides are obtained by direct oxidation of phosphoms, but only phosphoms(V) oxide is produced commercially. This is in part because of the stabiUty of phosphoms pentoxide and the tendency for the intermediate oxidation states to undergo disproportionation to mixtures. Besides the oxides mentioned above, other lower oxides of phosphoms can be formed but which are poorly understood. These are commonly termed lower oxides of phosphoms (LOOPs) and are mixtures of usually water-insoluble, yeUow-to-orange, and poorly characteri2ed polymers (58). LOOPs are often formed as a disproportionation by-product in a number of reactions, eg, in combustion of phosphoms with an inadequate air supply, in hydrolysis of a phosphoms trihahde with less than a stoichiometric amount of water, and in various reactions of phosphoms haUdes or phosphonic acid. LOOPs appear to have a backbone of phosphoms atoms having —OH, =0, and —H pendent groups and is often represented by an approximate formula, (P OH). LOOPs may either hydroly2e slowly, be pyrophoric, or pyroly2e rapidly and yield diphosphine-contaminated phosphine. LOOP can also decompose explosively in the presence of moisture and air near 150° C. 

The most commonly employed crystalline materials for liquid adsorptive separations are zeolite-based structured materials. Depending on the specific components and their structural framework, crystalline materials can be zeoUtes (silica, alumina), silicalite (silica) or AlPO-based molecular sieves (alumina, phosphoms oxide). Faujasites (X, Y) and other zeolites (A, ZSM-5, beta, mordenite, etc.) are the most popular materials. This is due to their narrow pore size distribution and the ability to tune or adjust their physicochemical properties, particularly their acidic-basic properties, by the ion exchange of cations, changing the Si02/Al203 ratio and varying the water content. These techniques are described and discussed in Chapter 2. By adjusting the properties almost an infinite number of zeolite materials and desorbent combinations can be studied. 

DIPHOSPHORIC ACID, TETRAETHYL ESTER (107-49-3) CgHjcO Pj Reacts with water, forming phosphoric acid and flammable ethylene gas. Alkalis or elevated temperatures above 300°F/149°C can cause deconqjosition, forming flammable ethylene gas and toxic phosphoms oxides. Reaction... 

METHYL AZINPHOS (86-50-0) (86-50-0) CioHjiNjOjPS, Combustible solid or liquid in an organic carrier solvent (see also entry for that specific carrier solvent). Hydrolyzes in water the process accelerates under alkaline conditions. Inconq)atible with perchloric acid. Contact with strong oxidizers may cause fire and explosions. Unstable at temperatures above 392°F/200°C when exposed to elevated temperatures, the containers may explode. On small fires, use dry chemical powder (such as Purple-K-Powder), foam, water spray, or CO2 extinguishers. Thermal decomposition releases toxic nitrogen oxides, phosphoms oxides, and sulfur oxides. 

On small fires, use dry chemical powder (such as Purple-K-Powder), alcohol-resistant foam, or COj extinguishers. PHOSPHORIC ACID, O.O-DIETHYL-O-6-METHYL-2-(l-METHYLETHYL)-4-PYRIMIDINYL ESTER (333-41-5) C.jHj.NjOjPS Commercial products containing hydrocarbon carriers acetone, ethanol, xylene can form explosive mixture with air [flashpoint 82 to 105°F/28 to 41°C]. A weak base. Hydrolyzes slowly in water and dilute acid ll With excess water this conqjound produces diethylthiophosphoric acid and 2-isopropyl-4-methyl-6-pyrimidol. With insufficient water or contact with strong alkalis or acids, this compound produces highly toxic tetraethyl monothiopyrophosphate. Contact with oxidizers may cause the release of toxic phosphoms oxides. Contact with strong... 

TRIS (2,3-DIBROMOPROPYL)-PHOSPHATE (126-72-7) CjAisBr O P Combustible solid (flash point >230°F/>110°C). Incompatible with strong oxidizers. Hydrolyzed on contact with acids or bases, amines, amides, and inorganic hydroxides. Deconqioses in tenperatures above 490°F/254°C, releasing toxic hydrogen bromide and phosphoms oxides. On small fires, use dry chemical powder (such as Piuple-K-Powder), Halon , or COj extinguishers. 

Calculations have revealed that the proazaphosphatrane bases are approximately equal in thermodynamic basicity to the Schwesinger P2 phosphazene bases (Table 2.14). The RHF/ 6-3IG calculations of proton affinities indicate that phosphazene (Z = NH) and phosphorus ylide (phosphorane, Z = CH2) counterparts (146 and 145) are stronger than the parent Verkade superbase 139. Higher basicity is associated with the higher degree of delocalization of the positive charge in the protonated iminophosphoranes and phosphorus ylides as a result of the more electropositive character of phosphorus atom [67]. On the other hand, phosphoms oxides 147 and 150 are weaker than 139, but still above the superbasicity borderline. The strained polycycles 138, 149 and 148, as representatives of superbases... 

B. Yellow/white phosphorus spontaneously combusts in air at room temperature to yield phosphoms oxide, a highly irritating fume. 

Tereshchenko GF, Orekhova NV, Ermilova MM, Malygin AA, Orlova AI (2006) Nanostmctured phosphoms-oxide-containing composite membrane catalysts. Catal Today... 

Emits toxic fumes of nitrogen and phosphoms oxides when heated to decomposition (Lewis, 1990). Products reported from the combustion of malathion at 900°C include carbon monoxide, carbon dioxide, chlorine, sulfur oxides, nitrogen oxides, hydrogen sulfide and oxygen (Kennedy et al., 1972a). 

Emits very toxic fumes of chlorides, sulfur and phosphoms oxides when heated to decomposition (Lewis, 1990). 

Discuss key features of Group 5A(15), especially patterns in oxidation state, oxide acidity, and hydride and halide structures and describe the nitrogen and phosphoms oxides, oxoacids, and oxoanions ( 14.6) (EPs 14.46-14.56)... 

Phosphoms burns in tiir to produce a phosphoms oxide in the following reaction ... 

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