The Chemical Engineering Journal最新文献

β-Galactosidase from Aspergillus niger was immobilized effectively on a porous ceramic monolith by adsorption and intermolecular cross-linking. The binding efficiency reached 80% and no enzyme leaching was observed even under vigorous mechanical agitation. Immobilization did not change the pH optimum of lactose hydrolysis. The enzyme decay followed first-order kinetics and the thermal stability of the immobilized lactase was considerably enhanced. At 50 °C and pH 3.6 the half-life of the immobilized lactase was 180 days and that of the free enzyme 24 days. The kinetics of lactose hydrolysis by both free and immobilized lactase were studied in a batch reactor system in the absence of any mass transfer limitations. In both cases the totally competitive galactose inhibition kinetic model predicted the experimental data. Simulation of the performance of a laboratory continuous flow immobilized lactase reactor system showed that experimental results could be predicted by the ideal plug flow model when an apparent effectiveness factor n_f=0.65 is used to take into account the external mass transfer limitations.

Catalytic afterburners using short monoliths take advantage of the enhancement of the transfer coefficients in not fully developed flow. The correlations for Nu and Sh in laminar flow in the entrance region of a monolith available from the literature are evaluated and compared with experimental data. A one-dimensional model is proposed and solved using the orthogonal collocation method under stationary and transient conditions.

The calculated results were compared with experimental data for the combustion of lean benzene—air mixtures in a short monolith.

The model is able to describe the behaviour of the afterburner satisfactorily if local Nu and Sh values for simultaneously developing velocity, temperature and concentration profiles are employed. If the light-off occurs part way along the monolith channels, a new thermal entrance should be considered.

A brief presentation and discussion of laboratory work and technical aspects are given. A flow diagram is included. Inherent operational difficulties are mentioned and methods given to eliminate them. The particularly promising aspects of the process are high yields and simplicity.

An invasive plate and frame capacitance probe was designed for dielectric constant measurements over a wide frequency range (10–5000 kHz) in a 5 l stirred tank reactor. Preliminary measurements with polyethylene beads showed a linear variation of the effective permittivity with the volume fraction of the beads, in accordance with the Maxwell-Wagner theory. Results obtained by bubbling air under various agitation and aeration rates at 500 kHz in deionized water, and the effect of a non-ionic antifoam on permittivity variations, are shown and discussed; the technique is thought to allow precise local holdup measurements. Existing limitations and possible further improvements of the technique are discussed, especially in view of the information that can be gained from the standard deviation of the measurements.

Power consumption measurement of screw and helical ribbon agitators of efficient geometry which mixed pseudoplastic fluids in the creeping-flow regime, was performed. The values of the Metzner—Otto coefficient k and relations for its calculation were suggested on the basis of experimental results.

The results of anaerobic digestion in a fluidized bed reactor fed with municipal waste waters enriched with glucose are presented. Several process conditions have been tested by varying the influent chemical oxygen demand (COD) from 4 to 13 kg m⁻³ and the residence time from 5.0 to 68.2 h. The degradation efficiency and methane production rate are substantially affected by an increase in organic loading rate from 4 to 24 kgCOD_i m⁻³ day⁻¹, suggesting a maximum operational value for this parameter. Using a Monod-type kinetic model, a maximum theoretical specific degradation rate of 1.76 kgCOD_r kgVSS⁻¹ day⁻¹ has been calculated, which is very similar to values calculated for other effluents from food industry activities.

The bed height and pressure drop of a tapered fluidized bed were well predicted by a model based on measurements for slugging fluidized beds in the fast bubble regime. Tapered vessels of large apex angle were effective in suppressing the development of square-nosed slugs.