Transport limited reactions

In transport limited reactions in gas/liquid systems, mass transfer is usually dimensioned according to P/V = idem and v = q/S = idem, see section 10.4.1. In scaling up, these conditions also speak in favor of decoupling the gas supply and... 

The reversible systems Au or Pt/((PQ2+ 2Br )n]8urf. were shown to be superior electrodes for cyt c(ox) reduction compared to the naked electrodes.(6) Reduction of cyt c(ox) was found to be mass transport limited when the electrode potential was held sufficiently negative to reduce the [(PQ2+)n]8urf. to ((PQf)n]8urf.. Thus, the results accord well with a mechanism where the reduction of cyt C(ox) occurs in a mass transport limited reaction with surface-confined PQ+ centers. 

It is interesting that, despite the high nonuniformity of currents along a CER (Fig. 36), a plot of In versus 6 often yields a Tafel-like behavior from which an apparent transfer coefficient and rate constant can be extracted (60-62). Thus, potential-current density data are not sufficient to indicate multiple reactions. At long retention times in the reactor, however, an unusual maximum and subsequent decrease of the average current density with potential occurs for series reactions (60). This results from fast depletion of species A and B with potential at long space-times, but it is not related to zero concentrations or mass transport-limited reactions. Such maxima or limiting currents have been observed in the stepwise oxidation of unsaturated... 

Gower, R.C., A Determination of the Transport-limited Reaction Rate for a Gas-Solid Reaction Forming a Porous Reaction Product, Lehigh University, 1971. Hills, A.W.D., Chem. Eng. Sci, 23, 297, 1968. 

Liquid phase component transport limited reactions. An industrially inportant reaction of this type is hydrotreating to remove sulfur, nitrogen and metals from gas oils and residual oils. These feeds are commonly liquid under reactor conditions. 

Gas phase component transport limited reactions. There are several studies in the literature representative of reactions limited by transport of the gas phase component. In these studies, the gas phase component must first dissolve in the liquid to be then transported to a catalytic site by diffusion into the catalyst pores. Alternatively, the gas phase reactant can contact the catalyst particle outer surface directly without first dissolving in the moving liquid stream. Because the direct contact... 

The mechanism of oxidation of D-glucose in alkaline media at gold electrodes has been investigated. Experiments using cyclic voltammetry at a rotating disc electrode indicated that the mass-transport-limited reaction proceeds an enediol intermediate hydrogen-bonded to catalytic hydrous gold oxide. The enediol is... 

APPENDIX A MASS-TRANSPORT LIMITED REACTIONS AT ROTATING DISC ELECTRODES. 

If we assume the reaction occurs only at the catalyst layer interface, which is true for high-current-density mass-transport-limited reactions, and we neglect kinetic effects, we are left with the Nernst equation at each electrode ... 

Gas-Phase Limiting Current Density and D usion Resistance In Chapter 4, we derived an expression for concentration polarization based on the concept of a mass-transport-limited reaction rate at a given electrode. Now, we can derive an analytical expression for this value, assuming one-dimensional transport to the catalyst surface. First, we equate the rate of reactant consumption to the diffusive and adjective transport to the reaction surface ... 

Preliminary studies have shown that polyester copolymers can be produced using biomass-derived starting materials. Iron(III) produced more consistent yields than aluminum chloride under mass transport limited reaction conditions and higher yields than tin(II) chloride. These reactions will be scaled-up and steps taken to overcome the mass transport limitations in future work. In addition, more extensive physical and chemical property characterization of the resultant polymers is plaimed. 

---