Chromatographic Catalytic Reactors CCR the Use of Fluid Logic Modules

A GC catalytic reactor deliberately combines the chromatographic separation of components with a catalytic function in the same reactor bed. The technique, first described in 1956, is a variant of the microcatalytic reactor just discussed. The reactor, in conjunction with pulse techniques, can be used for yield enhancement by displacing equilibria and for preserving primary products from secondary reactions with one of the reactants. The yields of primary products from a conventional catalytic reactor are ultimately limited, either thermodynamically through the value of the equilibrium constant, or kinetically by consumption of primary products, which often react more rapidly with one of the reactants, such as oxygen, than does the other reactant, such as an alkene or alkane. Both these limitations can be avoided in a chromatographic catalytic reactor (CCR). The equilibrium limitation arises because the catalyst accelerates the second-order back-reactions as much as it does the forward reaction. The back-reactions may be minimized by chromatographically separating the products from each other. Figure 4 illustrate the case for the simple equilibrium, A = B + C. The back-reaction can only occur in the initial regions of the column where there is overlap between the B and C peaks. If the bed is long enough, then complete conversion of A into B and C is possible. The laws of thermodynamics are not broken because the equilibrium limitation is circumvented by an energy input to maintain the gas flow and peak separation. By CCR it has been possible to achieve virtually complete de-hydrogenation of cylcohexane to benzene at temperatures where the equilibrium constant was 10~3 mol L_1. The yields of useful primary products such as alcohols and epoxides are often low because of their rapid secondary reactions. The secondary reactions can be reduced chromatographically by holding back the primary product on the catalyst surface while the reactant pulse rapidly sweeps down the column because of its lower retention. Figure 5 illustrates the simplified situation for the reaction sequence given below:

The occurrence of reaction [II] can be reduced by rapid separation of the reactant pulse containing oxygen from the ROH formed and retained in the catalytic chromatographic column. By using a silica-supported silver oxide CCR, large quantities of crotonal-dehyde have been preserved in the catalytic oxidation of but-1-ene. The lifting of both the thermodynamic and kinetic limitations is enhanced by using narrow injected pulses. Injectors based on fluid logic modules, which have no moving parts and none of the intrinsic delays of actuating the opening and closing of solenoid valves, are ideal for this task and have previously been used for fast GC analysis. Pulses down to 10 ms have been generated and further reductions are possible.

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Solar Panel Basics

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