Vanadium transport

It is the purpose of this paper to study which mechanism, particle-to-particle or vapor phase transport, is responsible fa- the mobility of vanadium in the FCC unit The approach used in this work is to measure the rate of vanadium transport to a basic oxide "vanadium trap" in fluid bed experiments. By varying the particle size distribution, the collision frequency can be changed and the rate of transport determined. Also, calculations of the mass transfer of a vapor species in a fluid are performed. 

The results of this work show that even though the vapor pressure of vanadium is low, the transfer velocity of vanadium vapor is high and the rate of mass transfer in a fluidized bed is high. A high rate of vanadium transport to traps and a low rate of vanadium transport by transpiration are consistent with the vapor phase transport model. The vapor pressure of the vanadic acid follows a second order Freundlieh isotherm, which reflects a coverage dependent heat of adsorption. The rate of vanadium transfer from catalyst to trap is only weakly dependent on the number density of the catalyst or trap particles. This lack of dependence suggests that inter-particle collisions are not the dominant mechanism for vanadium transfer. Vanadium mobility in FCCU s is a complex issue dependent on many operating variables. 

Mechanism of Vanadium Transfer. In previous literature two mechanisms of vanadium migration were postulated Uquid or gas phase vanadium transport. The results in this study lead us to propose a third alternative mechanism It appears from our data that a more appropriate mechanism involves interparticle vanadium transport which occurs as a result of a solid state interaction between vanadium containing particles. 

Table 2. Vanadium transport to CPS deactivated metals trap from a commercial FCC catalyst, blended at 75 wt.% catalyst and 25 wt.% trap. The FCC catalyst contains 4900 ppm...

Seefeldt, L. C., Hoffman, B. M., Dean, D. R. (2009). Mechanism of Mo-dependent nitrogenase. The Annual Review ofBiochemistry, 78,701—722. Ueki, T, Furano, N., Michibata, H. (2011). A novel vanadium transporter of the Nramp family expressed at the vacuole of vanadium-accumulating cells of the ascidian Ascidia sydneiensis samea Biochimica et Biophysica Acta, 1810, 457—464. 

Duce RA, Hoffman GL. 1976. Atmospheric vanadium transport to the ocean. Atmospheric Environment 10 989-996. 

K. Kustin, W. E. Robinson Vanadium Transport in Animal Systems In Metal Ions in Biological Systems,... 

Edel J and Sabbioni E (1989) Vanadium transport across placenta and milk of rats to the fetus and newborn. Biol Trace Elem Res 22 265-275. 

Kustin K and Robinson WE (1995) Vanadium transport in animal systems. In Sigel H and Sigel A, eds. Metal Ions in Biological Systems, Vanadium and its Role in Life, pp. 511-542. Marcel Dekker, Inc New New York, Basel, Hong Kong. 

Vanadium Transport in Animal Systems Kenneth Kustin and William E. Robinson... 

Vanadium (IV) Chloride. Vanadium(IV) chloride (vanadium tetrachloride, VCy is a red-brown hquid, is readily hydrolyzed, forms addition compounds with donor solvents such as pyridine, and is reduced by such molecules to trivalent vanadium compounds. Vanadium tetrachloride dissociates slowly at room temperature and rapidly at higher temperatures, yielding VCl and CI2. Decomposition also is induced catalyticahy and photochemically. This instabihty reflects the difficulty in storing and transporting it for industrial use. 

The appHcations of supported metal sulfides are unique with respect to catalyst deactivation phenomena. The catalysts used for processing of petroleum residua accumulate massive amounts of deposits consisting of sulfides formed from the organometaHic constituents of the oil, principally nickel and vanadium (102). These, with coke, cover the catalyst surface and plug the pores. The catalysts are unusual in that they can function with masses of these deposits that are sometimes even more than the mass of the original fresh catalyst. Mass transport is important, as the deposits are typically formed... 

Loop Tests Loop test installations vary widely in size and complexity, but they may be divided into two major categories (c) thermal-convection loops and (b) forced-convection loops. In both types, the liquid medium flows through a continuous loop or harp mounted vertically, one leg being heated whilst the other is cooled to maintain a constant temperature across the system. In the former type, flow is induced by thermal convection, and the flow rate is dependent on the relative heights of the heated and cooled sections, on the temperature gradient and on the physical properties of the liquid. The principle of the thermal convective loop is illustrated in Fig. 19.26. This method was used by De Van and Sessions to study mass transfer of niobium-based alloys in flowing lithium, and by De Van and Jansen to determine the transport rates of nitrogen and carbon between vanadium alloys and stainless steels in liquid sodium. 

A thin layer deposited between the electrode and the charge transport material can be used to modify the injection process. Some of these arc (relatively poor) conductors and should be viewed as electrode materials in their own right, for example the polymers polyaniline (PAni) [81-83] and polyethylenedioxythiophene (PEDT or PEDOT) [83, 841 heavily doped with anions to be intrinsically conducting. They have work functions of approximately 5.0 cV [75] and therefore are used as anode materials, typically on top of 1TO, which is present to provide lateral conductivity. Thin layers of transition metal oxide on ITO have also been shown [74J to have better injection properties than ITO itself. Again these materials (oxides of ruthenium, molybdenum or vanadium) have high work functions, but because of their low conductivity cannot be used alone as the electrode. 

The Industrial Revolution was made possible by iron in the form of steel, an alloy used for construction and transportation. Other d-block metals, both as the elements and in compounds, are transforming our present. Copper, for instance, is an essential component of some superconductors. Vanadium and platinum are used in the development of catalysts to reduce pollution and in the continuing effort to make hydrogen the fuel of our future. 

Another current development in the use of F-T chemistry in a three-phase slurry reactor is Exxon s Advanced Gas Conversion or AGC-21 technology (Eidt et al., 1994 Everett et al., 1995). The slurry reactor is the second stage of a three-step process to convert natural gas into a highly paraffinic water-clear hydrocarbon liquid. The AGC-21 technology, as in the Sasol process, is being developed to utilize the large reserves of natural gas that are too remote for economical transportation via pipelines. The converted liquid from the three-step process, which is free of sulfur, nitrogen, nickel, vanadium, asphaltenes, polycyclic aromatics, and salt, can be shipped in conventional oil tankers and utilized by most refineries or petrochemical facilities. 

Buxbaum, R.E. and T.L. Marker, Hydrogen transport through non-porous membranes of palladium-coated niobium, tantalum and vanadium. /. Membr. Sci., 85, 29-38,1993. 

Nuclear and magneto-hydrodynamic electric power generation systems have been produced on a scale which could lead to industrial production, but to-date technical problems, mainly connected with corrosion of the containing materials, has hampered full-scale development. In the case of nuclear power, the proposed fast reactor, which uses fast neutron fission in a small nuclear fuel element, by comparison with fuel rods in thermal neutron reactors, requires a more rapid heat removal than is possible by water cooling, and a liquid sodium-potassium alloy has been used in the development of a near-industrial generator. The fuel container is a vanadium sheath with a niobium outer cladding, since this has a low fast neutron capture cross-section and a low rate of corrosion by the liquid metal coolant. The liquid metal coolant is transported from the fuel to the turbine generating the electric power in stainless steel... 

A number of studies (9,10) have demonstrated that the valence of coordination of vanadium in typical vanadia catalysts changed with gas composition in contact with the catalyst. As we discuss below, changes at the surface are partially offset by transport of oxygen from interior strata of the catalyst. We believe it is the diffusion of oxygen, as an ion, which is responsible for the relaxation time observed. 

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