Robert L. Laurence

Inactivation of immobilized glucose oxidase by hydrogen peroxide

Abstract In the presence of hydrogen peroxide, the stability of immobilized glucose oxidase was found to be inferior in continuous operation to that in storage tests. Analysis confirmed that the reduced form of the enzyme, which is a product of the glucose-oxidation reaction, is much more readily inactivated by hydrogen peroxide than is the oxidized form. It was found that if the hydrogen peroxide could be removed in the microenvironment of the enzyme, this inactivation could be reduced. Descriptions of the hydrogen peroxide concentration in the microenvironment are presented as an aid to understanding and overcoming the problem. The problem has important implications when the continuous use of immobilized glucose oxidase is being considered, particularly in the analytical field.

Influence of slip velocity at a membrane surface on ultrafiltration performance—I. Channel flow system

Abstract The effect of slip velocity at a membrane surface is studied in detail for a tubular membrane system. A second-order perturbation solution of the equations of motion is found to be very satisfactory. The results are compared with those of the channel flow system reported earlier. As in the case of channel flow system, the effect of slip coefficient on concentration polarization is identical to that of Peclet number—it augments diffusive transport of solute molecules from the membrane surface to the bulk solution.

Linear stability of modulated circular Couette flow

The stability of circular Couette flow when the outer cylinder is at rest and the inner is modulated both with and without a mean shear is examined in the narrow-gap limit. Disturbances are assumed to be axisymmetric. Two criteria are used to determine conditions for stability; the first requires that the motion be strongly stable, the second only that disturbances of arbitrary initial energy decay from cycle to cycle. The behaviour of critical parameters as a function of frequency is similar for the linear and the energy analysis. The range of Reynolds numbers bounded above by certain instability and below by conditional nonlinear stability is enlarged by modulation.

Multiple solutions and hysteresis in steady parallel viscous flows

A study is made of flows of viscous fluids when viscosity varies with temperature according to an Arrhenius law, and when viscous dissipation is taken into account. It is shown that for fluids with highly temperature‐sensitive viscosity the graph of shear rate against shear stress is an S‐shaped curve, with either one or three values of shear rate for given shear stress. In this situation hysteresis can occur if steady unidirectional flow is maintained. The velocity and temperature profiles are calculated, and the manner in which the temperature‐sensitivity parameter affects the conclusions is discussed. The calculations serve as criteria for evaluating the importance of viscous‐heating effects in applications.

The effect of microwave energy on three-way automotive catalysts poisoned by SO2

Recent studies suggest that microwave energy can be employed in catalysis and that the results differ from “conventional” heating. The influence of microwave energy on automotive exhaust catalysis in the presence and absence of a catalyst poison (SO2) was studied. The conclusion is that microwave energy can induce carbon monoxide (CO) lightoff (the temperature where 50% of final conversion is achieved) more efficiently than conventional heating and can reverse the poisoning by SO2 for a commercial three-way catalyst.

An experimental approach to test sorption mechanisms in MCM-41

In order to evaluate the current theories employed to explain hysteresis in mesoporous solids, scanning sorption behavior was determined for several different MCM-41 silicates. Both nitrogen and argon sorption scans at 77 K were studied. Several different scanning behaviors were observed. No single current theory predicts the behavior observed.

THE MINIMUM TIME PROBLEM IN BATCH RADICAL POLYMERIZATION: A COMPARISON OF TWO POLICIES

The minimum time problem for the batch radical polymerization of styrene is formulated with a realistic kinetic model. A policy that minimizes the time to reach a desired conversion is compared with another policy including a number average molecular weight as an additional requirement. The performance of solution methods is discussed.

The design and construction of a frequency response apparatus to investigate diffusion in zeolites

A frequency response device has been designed and built based on previous efforts by Y. Yasuda, L. C. V. Rees, F. Meunier, and Ph. Grenier. This design uses the best attributes of the three previous devices and is improved in five specific ways. First, the device makes use of the fast response capacitance manometer. Second, the device uses a servomotor to push and pull a metal bellows pump, which drives the sinusoidal input function, removing the chance of “floating” the bellows. Third, both sinusoidal and step-change volume perturbations can be studied. Fourth, the overall cost of the device was kept below

The mixing effect on the free radical MMA solution polymerization

30 000. Finally, the pressure transducer is mounted only 8 cm from the sample, instead of ∼30 cm, thus removing any averaging of the pressure signal at higher frequencies. The device is currently capable of measuring frequencies between 0.005 and 5 Hz, a range of three full orders of magnitude. The system can operate at temperatures between room temperature and 473 K and pressures between 0.3 and 300 ...

Mathematical model and analysis of PMMA solution processes

Mathematical models of reactors for the polymerization of methylmethacrylate (MMA) have been developed and analyzed to elucidate reactor dynamics and to determine conditions for improved operation. The effects of mixing and heat transfer in an MMA polymerization reactor system have been explored by the development of an imperfect mixing model. To model imperfect mixing in polymerization, a reactor configuration using two tanks in parallel was used. Bifurcation diagrams developed using numerical analysis of the model have been drawn with two variable parameters, an exchange ratio, σ, and a volume ratio, κ. We use feed and coolant temperatures as bifurcation parameters. If variable parameters are small, the lower solution branch of the steady state solutions is quite different from that of a simple model that assumes perfect macro-mixing as bifurcation parameters change. If σ increases (κ=0.1, σ=1.0), the shape of a steady state solution curve differs significantly from that of a simple model as the feed temperature decreases.