Z. P. Xu

Effect of internal diffusion on heterogeneous catalytic esterification of acetic acid

Theoretical analysis has been performed to determine the effect of internal diffusion on a second-order reversible esterification of acetic acid with methanol catalyzed by a solid acid catalyst, Amberlyst 15. The results of the analysis show that the catalyst effectiveness factors are above 0.94 for the beads smaller than 0.6 mm diameter at the reaction temperature lower than 80°C. However, the effectiveness factors were lower than 0.77 for the beads larger than 1.0 mm diameter at reaction temperatures higher than 94°C. For the commercial Amberlyst 15 with an average particle size of 0.7 mm diameter, an overall effectiveness factor of 0.87 was predicted for a reaction temperature of 94°C. The predicted effectiveness factors agree with those obtained from the kinetic measurements.

Predicting Mass Transfer in Packed Columns Containing Structured Packings

A model has been developed for predicting mass transfer in packed columns containing structured packings. The model was verified by experimental results from a 300 mm diameter distillation column installed with three types of structured packings (Gempak 2.5A, AW7 and AW12). Three systems (methanol/isopropanol, water/acetic acid and methanol/water) and two operating pressures (710 and 260 mmHg) were used in the tests. Hence, a large range of physical properties were covered for the modeling. A total of 62 data points was obtained from the distillation tests. The average deviation between the measured values of HOG and the predicted values is ±10.2%. The deviations are within ±20% for 90% of the data points.

Prediction of packed sieve tray efficiency in distillation

The mass transfer efficiencies of a packed sieve tray and a sieve tray have been measured for the distillation of six binary mixtures. These mixtures cover a wide range of physical properties. The efficiency of the sieve tray was found to increase significantly by adding a layer of mesh packing on the tray which can be attributed to a higher interfacial area, longer vapour/liquid contact time (i.e. higher froth height) and a lower liquid backmixing. An efficiency model for the packed sieve tray was developed by combining a fundamental point efficiency model and the correlation of liquid mixing for the packed sieve tray. The point efficiency model is based on the analysis of the dispersion structure and zone contribution on the tray and experimentally measured values of tray efficiency in the distillation of six binary mixtures. The predicted point efficiencies for packed sieve tray agree with measured values with an average error of 3.9%.