Evaluation of Pressure Drop and Mass-Transfer Characteristics of a Structured Packing for Production and Separation of Food Flavours: Part II: Mass-transfer Characteristics

In Part I of these series, flooding and pressure drop characteristics of a typical structured packing were presented. Here, we present the results of mass-transfer characterisation, and application to the real food flavours.Mass-transfer characteristics were evaluated for the gas and liquid-phases separately by humidification of air, and by oxygen desorption from water. The gas-phase height of transfer unit, HTU, varied from 0.22 m to 0.45 m, and the liquid-phase HTU varied from 0.23 m to 0.40 m, with the former largely a function of gas rate, and the latter of liquid rate. Liquid-side mass-transfer coefficients were compared with the correlation of Bravo et al. (1985), which showed agreement within ± 30%. The gas-phase mass-transfer results were influenced by a change of liquid hold-up with gas flow. Such separate phase data allow, in principle, prediction of overall transfer coefficients and efficiencies for wide ranges of conditions: including very high liquid to vapour flow ratios (strip rates) and very low concentrations of the recovered components. This expectation was tested by distilling fusel oil and orange oil, as representative of food materials, over the packing. HETPs of 0.36−0.48 m and 0.21−0.34 m were found in fusel oil and orange oil distillations, dependent on vapour rate, corresponding to values predicted from separate phase mass-transfer characteristics, to within ± 10% and ± 35%, respectively. The results of fusel oil trials were compared with random packings of similar specific surface area, which showed that structured packing had 15% lower HETPs at high vapour loads.