The Chemical Engineering Journal最新文献

Extraction of penicillin G from the filtrate of fermentation broth indicates that neutral phosphorus esters can be used to substitute butyl acetate as the extractant and that the equilibrium pH can be controlled at 3.0–4.0 because of the higher extraction capability of neutral phosphorus esters. The equilibrium constants of the extraction, the molar ratios of tributyl phosphate to penicillin G in the extract and the bonding structures of the extracted species have been established using chemical analysis and the absorbance shift of Fourier transform IR spectra of the functional groups in penicillin G.

A new type of evaporator is proposed in this paper. The thin film to be evaporated flows over spiral fins wound around a vertical tube made of metal or graphite and heated from the inside. Experimental results show the heat transfer enhancement on these tubes compared with conventional vertical falling film exchangers.

Most pipeline network problems can be solved by the orthogonal transformation approaches — the mesh and nodal methods. However, when the network size becomes too large, the mesh and nodal approaches may not be suitable. Under such circumstances, the mesh diakoptics and nodal diakoptics methods can be used. The diakoptics approaches are nevertheless subjected to a constraint, which is all the flows of the network have to be specified. If a combination of flows and pressures is specified, these methods cannot be used. In the present work, a special technique called the fictitious branch method is employed to complement the diakoptics approaches to solve mixed specification problems. It is found that for an all pressure specified problem, it is better to use the nodal diakoptics approach. Otherwise, the mesh diakoptics approach is always preferred.

Gas hold-up in a bi-dimensional three-phase spouted bed, operated continuously with respect to the gas flow and batchwise with respect to liquid and solid, was investigated using a bed expansion technique. Experiments were performed in a column of 22 mm × 220 mm × 1250 mm. Sand particles 1.0 mm in diameter, solid fractions 0.05, 0.10, 0.15 and 0.20, five different nozzle sizes (4.0 mm, 5.5 mm, 7.0 mm, 10.0 mm and 12.0 mm), four static bed heights (0.17 m, 0.32 m, 0.58 m and 0.69 m) and superficial gas velocities ranging from 0.34 to 3.43 m s⁻¹ were employed. A correlation for the gas hold-up was developed with an average deviation of 2.5% and maximum deviation not exceeding 9%.

Set point weighting (SPW) is a technique for achieving optimum performance of feedback control for both load and set point disturbances. It involves assigning a weighting factor to the set point in the proportional action part of the control algorithm. In this paper, simplified model predictive control (SMPC) is modified to include SPW. The modification consists of first tuning the SMPC controller for load disturbances and then optimizing the weighting factor for set point disturbances. The performance of the resulting feedback control system is studied through simulation and the results compared with those in the absence of SPW. In general, the results demonstrate that SPW offers significant benefits at practically no additional expense to digital control systems experiencing both load and set point variations.

The suitability of input/output models for state estimation of fermentation processes has been investigated. A batch glucoamylase fermentation provides an example and a relatively simple ARMAX model was used to estimate, on-line, both the enzyme activity and the biomass concentration from ammonia addition and carbon dioxide evolution measurements, respectively. The model parameters were estimated by the recursive least-squares method. Model fit and estimator performance were improved by signal conditioning. The estimator was capable of estimating the state of the process starting from the same initial parameter values and off-line measurements could be used readily for updating the estimator parameters thereby further improving the estimator performance.

In the hydration of α-pinene, catalysed by an H₂SO₄ aqueous solution, a solvent such as isobutyl alcohol can be used as a solubility promoter. The consumption of α-pinene shows an apparent deviation from first-order kinetics. However, if the temperature is sufficiently high to avoid terpine formation first-order kinetics are observed. To explain this behaviour, a kinetic model was derived which takes into account the equilibrium between the phases and assumes that the chemical reaction takes place only in the aqueous phase and that the volume of the phases may change during the reaction. The parameters of the model were estimated by non-linear regression analysis. The good fit of the model to the experimental points allows the deviation from first-order kinetics, observed at low temperatures, to be explained by the change in volume of the phases during the reaction and the different solubilities of the species in the two phases.

The activities of two nickel catalysts prepared in our laboratory and of a commercial platinum catalyst were compared for benzene formation by dehydrogenation of cyclohexane and cyclohexene. A 15% nickel on alumina catalyst compares favourably with the commercial platinum catalyst at 300 °C; at lower as well as higher temperatures in the range 200–340 °C, the platinum catalyst is more effective. A 20% nickel catalyst compares unfavourably at all temperatures in the range studied. Results indicate that the orientation of adsorbed benzene depends on the dispersion of metal in the nickel catalyst and also on the temperature. During dehydrogenation of cyclohexene a small fraction was disproportionating, the extent of which was found to depend on the catalyst and the temperature.

The accumulation of small bubbles during the aeration of suspensions of a solid in a highly viscous liquid has been investigated. It was found that bubble size distribution is dependent on aeration time. Displacement of the maxima in the direction of smaller bubble diameters occurs during the aeration time and the maxima becomes higher. The distribution curves do not change after an “establishment time”. After this time, the small bubble hold-up and the total gas hold-up reach their final values. The contribution of small bubbles to the gas volume in the dispersion reaches about 60%, and depends on the liquid viscosity, the gas flow rate and the solid loading. The course of the small bubble accumulation process is described by the first order kinetic equation. The accumulation rate constant was found to be dependent on the superficial gas velocity and the apparent suspension viscosity.