Reactant flow rate, effect

In the case of dense membranes, where only hydrogen can permeate (permselectivity for H2 is infinite), the permeation rate is generally much lower than the reaction rate (especially when a fixed bed is added to the membrane). Experimental conditions and/or a reactor design which diminishes this gap will have positive effects on the yield. An increase of the sweep gas flow rate (increase of the driving force for H2 permeation) leads to an increase in conversion and, if low reactant flow rates are used (to limit the H2 production), conversions of up to 100% can be predicted [55]. These models of dense membrane reactors explain why large membrane surfaces are needed and why research is directed towards decreasing the thickness of Pd membranes (subsection 9.3.2.2.A.a). 

Exercise 8.7J. Show that for sufficiently small catalyst particles no problem with multiple steady states can occur. What would be the effect of increasing the reactant flow rate on the probability of multiple steady states Put teeth into your answer by using Exercise 7.3.3. 

In a similar vein. Figure 22 shows the effect of reactant flow rate on the amount of PAT formed over time in the CSTR hydrogenation of PNT described above. At the fastest flow rate the substrate is going through the reactor too fast so less nitrobenzene is being hydrogenated and the amount of hydrogenated product accumulated decreases with time. 

The alternative method is continuous-flow , in which the reactants flow through the detection coil during data acquisition. Continuous-flow NMR techniques have been used for the direct observation of short-lived species in chemical reactions [4—6]. The main difference between stopped- and continuous-flow NMR is that in the latter the sample remains inside the detection coil only for a short time period, termed the residence time, x [7], which is determined by the volume of the detection cell and the flow rate. The residence time alters the effective relaxation times according to the relationship in Eq. (2.5.1) ... 

The value of E - y is called the open-circuit voltage of the cell, which is related to the composition of the product. Note that the steam conversion ratio, X, depends on the open-circuit voltage, and is not affected by the pressure or flow rate of the reactant. Also, the open-circuit voltage decreases with increasing temperature because of the endothermic nature of the reaction. However, due to the temperature dependence of the logarithmic term in Equation 4.5, this effect decreases with the value of X. 

The situation at the upper stable point, when reaction proceeds smoothly to completion at a high temperature without an external source of heat, is described as autothermal or autothermic operation. If the volumetric flow rate of reactants, F, is increased, then the slope of the Ql line is increased and the position of the Qq is also slightly changed the principal effect, however, is that, eventually, an upper intersection of the heat generation and heat loss lines is no longer possible and the autothermic reaction is blown out . 

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