Vanadium catalysts tubular

Although the earlier workers undoubtedly felt that a somewhat milder form of catalyst than liad been used in the oxidation of naphthalene to produce phthalic anhydride would be necessary for the formation of anthraquinone, it was soon shown that vanadium catalysts were applicable. These catalysts consisting of vanadium oxides supported on pumice were used in tubular reaction chamber.28 Such disposition of the catalyst represented ail advance over the early method since it permitted a better control of gas rates and time of contact, a necessity when such active catalysts were used for the small degree of oxidation required in the reaction. A temperature range of 300° to 500° C. was specified and the use of diluent gases to control the reaction intimated. 

The second-step oxidation is normally by means of nitric acid, but catalytic air oxidation results in good yields of adipic acid. In recent practice, the refined first-step product of cyclohexane oxidation freed of unconverted hydrocarbon and a 50-60 per cent nitric acid solution containing copper-vanadium catalyst are separately and continuously fed to a jacketed reaction vessel at a ratio such that weight ratio of 100 per cent nitric acid to organic feed is between 2.5 and 6. The reaction mixture is rapidly recirculated through a tubular reactor at 60-80°C, and fresh feed is admitted to give about 5 min time of contact. Yields are improved by reheating the continuously withdrawn effluent stream to 95-100°C for a... 

BASF Platinized asbestos produced by impregnating asbestos with platinic chloride solution followed by reduction with formaldehyde. Operated up to 10-12 years in several 10 20 cm layers. Contained 8-10% platinum. Tubular reactors were still designed for vanadium catalysts until 1950s. Agreement with Grillo up to 1898. 

The second type of solution polymerization concept uses mixtures of supercritical ethylene and molten PE as the medium for ethylene polymerization. Some reactors previously used for free-radical ethylene polymerization in supercritical ethylene at high pressure (see Olefin POLYMERS,LOW DENSITY polyethylene) were converted for the catalytic synthesis of LLDPE. Both stirred and tubular autoclaves operating at 30—200 MPa (4,500—30,000 psig) and 170—350°C can also be used for this purpose. Residence times in these reactors are short, from 1 to 5 minutes. Three types of catalysts are used in these processes. The first type includes pseudo-homogeneous Ziegler catalysts. In this case, all catalyst components are introduced into a reactor as hquids or solutions but form soHd catalysts when combined in the reactor. Examples of such catalysts include titanium tetrachloride as well as its mixtures with vanadium oxytrichloride and a trialkyl aluminum compound (53,54). The second type of catalysts are soHd Ziegler catalysts (55). Both of these catalysts produce compositionaHy nonuniform LLDPE resins. Exxon Chemical Company uses a third type of catalysts, metallocene catalysts, in a similar solution process to produce uniformly branched ethylene copolymers with 1-butene and 1-hexene called Exact resins (56). 

In the first stage of the investigation the catalyst can be considered in the form of powder in order to derive intrinsic transient kinetics of all the relevant reactive processes. To this purpose, dynamic reactive experiments can be performed in a simple tubular fixed-bed microreactor over small quantities (50-200 mg) of finely powdered catalyst in principle, this guarantees negligible transport limitations and more controlled conditions (e.g. isothermal catalyst bed), hence enabling a direct estimation of intrinsic rate parameters by kinetic fit. Internal diffusion limitations are particularly relevant to the case of bulk (extruded) monolith catalysts, such as vanadium-based systems for NH3/urea SCR however, they... 

Both oxidations are highly exothermic and carried out almost exclusively in tubular reactors cooled by a molten salt.1024 Supported vanadium oxide with additives to improve activity, selectivity, and stability usually serves as the catalyst.970 990 1025 Because of its more favorable stoichiometry (no carbon is lost in oxidation), most new plants use o-xylene as the starting material. 

A six-sectional tubular turbulent device of optimal construction dj = 150 mm, = 75 mm, and = 500 mm) is used in the production of the ethylene propylene copolymer. It is installed at the stage of catalyst decomposition and washing, after the ethylene and propylene copolymerisation, as well as at the introduction of the stabiliser into the ethylene propylene rubber solution. This intensifies the vanadium salt washing from the polymer and guarantees the production of rubber with a content of vanadium and ash, in the end products, which is within the required limits. 

Tubular microreactors , which are in reality mini- or millimeter-scale reactors, have been used to study these reactions. Tubular microreactors take the form of a fixed-bed reactor with various materials of construction. Chao et al. used a quartz tubular microreactor (Sqm i.d.) to compare oxidative dehydrogenation of ethane over vanadium- and magnesium-based catalysts of different preparations [15]. The catalysts were introduced in the middle of the reactor tube with quartz granules used to fill the space above the catalysts and quartz wool used to retain the packing. This quartz microreactor was placed in a tubular furnace with the catalyst bed held in a constant-temperature zone. After performing experiments to study selectivity and conversion on the catalysts, surface analysis of the catalyst materials was used to identify the best catalyst preparation method. 

The latest updates in the production from benzene include the Polynt s high load technology, which consists of the retrofitting of the existing multi-tubular reactors, introducing an improved heat exchange capacity, a new benzene evaporator and an air mixing unit and the use of a specific catalyst based on Vanadium and Molybdenum Oxides. 

Solution processes use autoclave, tubular, or loop reactors. As compared to slurry and gas-phase polymerization, solution processes are commonly operated at a much higher temperature to keep the polymer dissolved in the reaction medium, and at much lower average residence times (5-20 min, as opposed to 1-4 h). Since polymerization conditions are more uniform in solutions reactors - there are no inter- and intraparticle heat- and mass-transfer resistances, for instance - this configuration is commonly used for the production of EPDM rubbers with soluble Ziegler-Natta vanadium-based catalysts. Composition homogeneity is a require-... 

In spite of the numerous publications showing the potential of such periodic operations especially in the field of complex reactions, experimental studies are virtually non-existent. Of the few experimental works, Renken et al. ( ) compared the performance of a tubular reactor in which a single reaction, the hydrogenation of ethylene, took place, under periodic operation and at steady-state. He reported an improvement of 60% in conversion. In another publication, Renken et al. (3) showed experimentally that periodic operation can be used to eliminate the temperature problems associated with highly exothermic reactions, e.g. the oxidation of ethylene over a silver catalyst. In other experimental work Unni et al. W) showed that periodic variation of reactant composition improved the rate of oxidation of SO2 over a vanadium oxide by as much as 30%. Denis and Kabel ( 5) studied the cyclic operation of a heterogeneous reactor for the vapour phase dehydration of ethanol and observed that adsorption/desorption played a predominant role in the transients of the system. 

In this process,an air-benzene mixture (3-wt. % benzene) is fed to a tubular reactor (see Fig. 2-4). The tubes are loaded with a vanadium complex catalyst on extruded cylinders or spheres of alumina. Molten salt bath is used to maintain the temperature of 355-375°C. The recovery system is quite similar to the SD process. Very high yields and long catalyst life have been claimed. 

This process (see Fig. 2-6) utilizes Az-butenes and butadiene mixtures as raw material in a fixed bed tubular reactor, containing 10 000 tubes. The catalyst is vanadium based. The effluent gases from the reactor are cooled and then scrubbed with aqueous maleic acid solution. Film evaporators are used for the concentration of maleic acid solution and dehydration to MA. The latter is purified by continuous rectification. The yield of MA of 72 kg/100 kg of convertible hydrocarbons is claimed (42.6 mole %). 

It is conunon practice to use two reactors. The first reactor contains a conventional bismuth phosphomolybdate catalyst and is used to convert propylene to acrolein. The second reactor contains a selective vanadium molybdate catalyst promoted with tungsten, nickel, manganese or copper, " to convert acrolein to acrylic acid. Fixed bed tubular reactors ate used in both stages. Typical operating conditions ate shown in Table 4.15. 

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