Investigation of spatially patterned catalytic reactors
The theme of this work is to enhance the performance of a primary reaction system by introducing dual-functionality into a packed-bed reactor via a spatial pattern. This paper focuses on a generic system in which the primary reaction is equilibrium-limited and an auxiliary reaction is incorporated to act as a drain-off mechanism alleviating the equilibrium constraint. It is found that patterns in which the two catalysts are spatially layered (and maintained at different temperatures) or well-mixed (and operated at a common temperature) can both offer significant improvements over an unpatterned reactor. Operating the well-mixed pattern at high temperature is generally superior to switching between high- and low-temperature layers in the segmented configuration. The exception to this rule occurs when the mixed bed is punished for being hot as either the equilibrium ceiling on the primary reaction drops sharply or a competitive reaction dominates at high temperature. The extent to which the layered pattern’s improvements are compromised by axial heat dispersion between zones is examined in terms of a backflow mixing cell model.
Numerical Investigation of Resonance Behaviour of a Tubular Packed‐Bed Reactor with Non‐Uniform Activity
The effects of periodic temperature perturbations at the inlet of a packed-bed catalytic reactor were investigated for a system of non-uniform catalyst activity that could arise through catalyst deactivation. A simplified model consisting of zones of active catalyst and inert packing of similar thermal properties was assumed. Simulations showed that large amplification, expressed as gain, can occur. The largest gain is observed at a resonance frequency. Both gain and resonance frequency depend on the number of layers of active catalyst and inert packing, the depth of the inert packing and catalyst layers. 
 
 
 
On a etudie l'effet de perturbations de temperature periodiques a l'entree d'un reacteur catalytique a lit garni pour un systeme d'activite catalytique non uniforme qui peut survenir lors de la desactivation du catalyseur. On suppose un modele simplifie comportant des zones de catalyseur actif et un garnissage inerte aux proprietes thermiques semblables. Les simulations montrent qu'une grande amplification, exprimee comme un gain, peut se produire. Le plus grand gain est observe a une frequence de resonance. Autant le gain que la frequence de resonance dependent du nombre de couches de catalyseur actif et de garnissage inerte, de la profondeur du garnissage inerte et des couches de catalyseurs.
Cytoplsmic uridine phosphorylase of rat liver. Characterization and kinetics.
Abstract Uridine phosphorylase (uridine:orthophosphate ribosyltransferase, EC 2.4.2.3) of rat liver cytoplasm has been purified 1900-fold. Initial velocity patterns of the phosphorolysis of uridine or deoxyuridine and of the synthesis of uridine indicated a sequential mechanism. Product inhibition patterns with uracil or ribose 1-phosphate as inhibitors were consistent with an "ordered Bi Bi" reaction in which inorganic phosphate is the first substrate to bind to the enzyme and ribose 1-phosphate the last product to leave the enzyme. The most highly purified enzyme fractions still retained uridine-, deoxyuridine-, and thymidine-cleaving activities in the ratio of 10:7:1 at pH 7.4. The fractions separated into a major and a minor band of protein on electrophoresis in phosphate buffer. Aging of the enzyme with loss of activity resulted in an increase in the proportion of the minor band. The pH optimum of the enzyme for uridine cleavage was 8.2, for deoxyuridine cleavage, 6.5, and for uridine synthesis, 8.5. Uridine or deoxyuridine synthesis was inhibited 50% in the presence of 1 mm uracil. The enzyme did not catalyze the direct transfer of ribose from uridine to uracil in the absence of phosphate. Uridine protected the enzyme to a greater degree than phosphate against inhibition by o-iodosobenzoate. Thus, at least one sulfhydryl group and possibly three are present at or near the active site. Uridine cleavage, uridine synthesis, and deoxyuridine cleavage were inhibited by deoxyglucosylthymine. The phosphorolysis of deoxyuridine and thymidine by thymidine phosphorylase, also purified from rat liver cytoplasm, was not inhibited by deoxyglucosylthymine. The molecular weights of both uridine and thymidine phosphorylases were estimated to be 110,000.