The regular solution model (the Hildebrand–Scatchard equation) has been improved so that it can be applied to polar mixtures by introducing the exponent-type mixing rule and interaction parameters between unlike molecules. The applicability of the proposed regular solution model is examined by correlating vapor–liquid equilibria of several ethanol + hydrocarbon binary systems, and it is found that the proposed model can be adopted for polar mixtures. For calculations, solubility parameters and liquid molar volumes at given temperatures can be estimated from the molecular structures of constituent pure components by using additive methods.
In this paper, a modified solution–diffusion model is proposed to account for the mass transport of penetrants in the polymer membrane. In the model, the group contribution method (the UNIFAC-ZM model) is introduced to calculate the activity of penetrants in the polymer membrane, and a new temperature-dependence diffusion coefficient equation is developed to describe the diffusion behavior of the penetrants. The aim of this work is to establish a predictive solution–diffusion model. By refitting the group interaction parameters based on pervaperation data of penetrants-membrane systems, the model can be applied to predict the fluxes and separation factors of various polymer membrane systems. As an exemplary application of the model, the permeation fluxes and separation factors of benzene/cyclohexane mixtures in a PDMS membrane system have been predicted and shown to be in good agreement with experimental values.
We conduct a numerical study on the formation process of vortex rings that were observed in a previous experimental study. The numerical simulation of the process is challenging since it is a three-dimensional problem involving unstable drop motion. We use a method in which a three-dimensional domain is discretized; the coupled level-set/volume-of-fluid (CLSVOF) method is used to determine the motion of the drop interface and a sharp interface treatment is used for enforcing the boundary conditions at the drop interface. It is numerically shown that there are two different evolution regimes for vortex ring motion, depending on the value of the Eötvös number (Eo). The simulation results show that the transient evolution process of a vortex ring is sensitive to the drop size. Thus, our results agree with those of the previous experimental study. We also explore the effect of the viscosity ratio (=μD/μC) on vortex ring formation resulting from a falling drop.
The void fraction distribution in the vertical direction in a tall, sparged, gas–liquid reactor of 0.48 m diameter is measured at various temperatures with and without glass beads in the suspension. The agitator comprises two up-pumping wide-blade hydrofoils positioned above a hollow-blade dispersing turbine. Operating temperatures range from 24 to 81°C with solid concentrations of up to 21 vol%. Detailed comparisons of the void distributions at 24 and 81°C in the presence of 9 and 15 vol% solids are presented. All the experiments reported here are performed at a constant agitator speed of N = 6 s–1. Temperature affects the overall and integrated local void distributions in a similar manner. At all temperatures, the local gas fraction is the maximum in the region just above the levels of the top and bottom impellers. At fixed agitator speeds and superficial gas flow rates the overall and local gas holdup values are always less at high temperature in the absence of solids. At ambient temperature, the local gas fraction is reduced at high solid concentrations. At 81°C, on the other hand, the effect of solid concentration on the void fraction is almost nil although the local extremes in the void distribution are somewhat high. The measured local void fractions show a less uniform gas distribution in the presence of solids and at high temperatures. The results of this study help improve our understanding of the differences between two- and three-phase reactors operating under cold- and hot-sparged conditions.
The power consumption, gas dispersion, and mass transfer volumetric coefficients are investigated in a gas–liquid agitated vessel with a disk turbine for various geometries, positions of the sparger, and directions of gas discharge. A sparger larger than the impeller is effective for obtaining high aeration power consumption and a high mass transfer volumetric coefficient. When the sparger is used, the flooding phenomenon does not occur easily. The gas is sufficiently dispersed when the large sparger is used, even if the gas is not blown directly into the impeller.
Matrine extraction using reverse micelles of a non-ionic trialkyl phosphine oxide (TRPO) surfactant was studied. Theoretical analysis and experimental results showed that the driving forces for the extraction are the coordination forces between matrines and TRPOs. Oxymatrine and oxysophocarpine cannot form coordination bonds with TRPO, and therefore, they can be separated with matrine from a raw matrine solution. The effect of several important factors such as pH, W0, and co-solvent on the partition coefficient of matrine was studied. The presence of ions in the system did not affect the partition coefficient significantly. Under the optimum operating conditions, determined by orthogonal experiments, the yield of matrine from the raw matrine solution can reach 70%; the purity of the matrine is higher than 90%. The mass transfer coefficient for both forward and back extraction was calculated and compared with that for reverse micellar extraction of proteins reported in the literature. This paper ends with a discussion of the kinetics of the extraction.
An assemble-type multi-stage microreactor with thin film catalyst has been developed. A new thin membrane carbon catalyst loaded with Cu/Zn is prepared through the carbonization of polyamic acid membrane loading Cu and Zn by ion exchange method. Using the microreactor with the catalyst developed, we perform steam reforming of methanol in order to selectively produce hydrogen for fuel cell usage. The methanol conversion and yield of H2 reached 0.74 and 2.2 mol mol-methanol–1, respectively, at the low temperature of 220°C when using a 15-stage microreactor. As compared with the yields by a conventional tubular reactor, the methanol conversion is high and the CO yield is significantly suppressed in the microreactor. The advantage of the microreactor is presumably due to the concentration profile under a gaseous laminar flow in the micro space. Finally, the compact reactor system, which consists of a micro-reformer, micro-combustor and tubular-combustor, has been developed, and high yield of hydrogen and less than 5 ppm of CO has been successfully achieved.
Lactide production and racemization under microwave irradiation are compared with those under conventional heating. The amount of lactide including L,L-, D,D-, and meso-lactides that was produce in the reaction mixtures under microwave irradiation at 25 mmHg and 180°C for 12 h was almost 2.7 times the corresponding amount produced under conventional heating. The ratio of the number of meso-lactide to the total number of lactides was higher under microwave irradiation than under conventional heating by a factor of 8.9. These differences between lactide production under microwave irradiation and that under conventional heating became increasingly noticeable as the reaction time and temperature increased. However, it was observed that at pressures under 15 mmHg, the ratio of the number of meso-lactide to the total number of lactides under microwave irradiation was decreased and became equal to the corresponding value under conventional heating.
In the study, a semianalytic optimization algorithm was used to achieve the suboptimal performance under specific operating constraints of the fed-batch fermentation process. By applying Pontryagin’s minimum principle, the substrate feed rate was taken as the manipulated variable and characterized in a piecewise manner. On the basis of the repetitive optimization algorithm, a varied reference was developed by adjusting the switching times and other parameters. The reference-based model prediction strategy was successfully implemented to ensure the satisfactory output regulation, whereas the amount of product obtained was measured separately. The symbolic software MapleTM was used to implement the complete control structure, and the effectiveness of the proposed methodology was verified by performing closed-loop simulation tests.
A kinetic analysis method using the nonisothermal weight loss technique is proposed to conveniently determine the kinetic parameters of degradation of polycarbonate (PC) in supercritical methanol. Experiments have been carried out for three heating rates of 8, 10.5 and 13°C/min. The slope of a straight line plot for a function of the weight fraction vs. the temperature gives the activation energy of PC degradation in supercritical methanol. In addition, the weight fraction at which the inflection occurs in the weight loss curve determines the reaction order. From this work, it has been found that the activation energies of PC degradation in supercritical methanol are 386.5–501.9 kJ/mol. Further, it has also been found that the reaction orders are 1.79–2.89 and there are variations in the calculated kinetic parameters depending on the heating rate.