The Chemical Engineering Journal最新文献

Combined bioreaction and separation has been carried out successfully on a simulated moving column continuous countercurrent chromatographic reactor-separator (SCCR-S) system. The continuous inversion of sucrose to glucose and fructose using invertase and the biosynthesis of dextran from sucrose in the presence of the enzyme dextransucrase have been studied.

100% sucrose conversions were achieved and product purities of up to 95% w/v were obtained in the inversion studies. The operation was carried out on a preparative scale with throughputs in excess of 16 kg of dry sugar solids per cubic metre of resin per hour used. The simultaneous inversion and product separation was found to overcome problems associated with substrate inhibition. Complete reaction and separation was obtained at feed concentrations as high as 55% w/v.

Previous studies on the biosynthesis of dextran on batch chromatographic systems showed significant improvements in product yields. The simultaneous removal of the acceptor by product fructose from the reaction mixture led to the formation of greater amounts of high molecular weight dextran (over 80% more than the conventional process at 20% w/v sucrose concentration). To carry out dextran biosynthesis on the SCCR-S system, it was necessary to repack it with larger-size resin to allow for the high pressures caused by the more viscous dextran. Complete conversions have been achieved at sucrose concentrations of 5% w/v with dextran and fructose product purities of up to 100% and 97% respectively obtained under certain conditions. Some levan formation occurred after about 50 h of operation, which is readily removed from the dextran in the normal dextran processing procedures.

Many heat and mass transfer problems in a heterogeneous system can be unified and treated in a simple way. Every problem belonging to this class addresses either the transfer of heat-mass in a heterogeneous medium consisting of several phases or the transfer of heat-mass in a multicomponent system. The problem formulation involves a self- adjoint operator consisting of three coefficient matrices and a Sturm-Liouville differential operator resulting from heat-mass diffusion. A solution method based on linear operator theory is proposed to gain solutions to this class of heat and mass transfer problems. The properties of the self-adjoint operator are analysed and applied to obtain theoretical insight to the influence of the parameters on the solution.

The behaviour of fluidized beds of monosized sodium perborate crystals in saturated aqueous solutions has been investigated experimentally. The crystals, 300–700 μm in size, are irregular in shape and have a dendritic surface.

The main aim of the work was to predict the fluidization characteristics (velocities and bed voidages) taking into account the deviation of particle shape from spherical. The terminal velocity, in the range 2–5 cm s⁻¹, has been accurately estimated by means of Clift's correlations, by assuming as a particle a sphere of equal volume. The values of the expansion index n, which are 20%–25% higher than those estimated by the Richardson-Zaki relationship for spherical particles, have been satisfactorily predicted by characterizing crystal dimensions by means of the sphericity factor and by adopting Riba's equation to predict the minimum fluidization velocity.

The calculation procedure adopted permits estimation of expansion bed voidages with an average error of 1.58%.

In polymer reaction engineering, mathematical models of varying complexity are employed to describe reactor behaviour and predict process performance under a variety of operating conditions. When process control is the final aim, it is very important to develop and use models that are simple in mathematical structure, yet capable of adequately describing the essential process characteristics.

In this paper we first derive a detailed mechanistic model for a batch solution polymerization of methyl methacrylate. Subsequently, we show how this complex model can be simplified using various assumptions and approximations. Five models of different levels of complexity are presented and examined for their suitability for process optimization and control applications. Model responses are discussed and compared in order to check whether the simplifications degrade the predictive capabilities of the original model.

The feasibildty was explored of employing biofluidized bed (BFB) technology based on immobilized Saccharomyces cerevisiae for continuous ethanol production from glucose. Long-term, steady and effective performance of ethanol production and glucose utilization is achievable in the BFB reactor when porous microcarriers are used to immobilize and retain yeast cells. More than two- thirds of the total reactor yeast cell mass was immobilized. Zero-order kinetics for ethanol production and glucose utilization existed at bulk liquid glucose concentrations greater than 1 g L⁻¹. Ethanol inhibition of yeast cells was absent at bulk liquid ethanol concentrations as high as 78 g L⁻¹.

We present a theoretical and experimental investigation of the kinetics of the displacement of liquids from filter cakes. The theory, derived from that used in secondary recovery of petroleum, is developed and demonstrates that the forced drainage process occurs in two stages: an initial stage with efficient piston displacement followed by a second stage with inefficient two-phase flow displacement. The effects of the packing structure of the cake, the viscosity of the two phases and the surface tension on the process are taken into account. Experimental results are presented for the air blow displacement of liquids from beds formed from a variety of different types of particle and with different saturating liquids having a range of viscosities and surface tensions. A reasonable agreement is found with the predictions from the theory.

The stability of a magnetized fluidized bed is considered in the context of multiphase composite systems. The structural transition of the composite phase is shown to depend on the composite energy density per unit mass of bed. A criterion of composite phase transition is established using the principle that along the transition line from one structure of the composite phase to another, the change in the composite energy density vanishes.

The criterion is also formulated for the general case of composite systems consisting of statistically dependent phases. Finally, data of transition velocity vs. field intensity are analysed showing that theory and experiment are in good agreement.

The effect of the imposed cell voltage policy on reactant-to-product conversion and the optimal number of elements in a CSTER cascade was analysed in terms of various costs associated with its operation. Optimal operation may be feasible with a single tank or with several tanks in series, according to the relative magnitude of governing costs. Operation with the same voltage imposition on each element is also compared with operation with a non-uniform voltage distribution.

A correlation has been proposed for estimating saturated liquid viscosity based on its relationship with vapour pressure. The viscosity at the normal b

A new model has been developed for the gas hold-up in bubble column reactors. The model is based on two different expressions for the energy dissipation rate used to derive the correlations for the heat transfer rate in bubble column reactors. The present model is applicable to non-newtonian fluids characterized by a power-law model as well as to newtonian fluids.

Predictions were compared with a wide range of available experimental data and correlations. Good agreement with the available results suggests that the proposed model should be useful for the rational prediction of gas hold-up in bubble column reactors.