James R. Fair

General model for prediction of pressure drop and capacity of countercurrent gas/liquid packed columns

Abstract A generalized model has been developed for the prediction of pressure drop and flooding in packed columns in which gas and liquid flow countercurrently. The model has been validated for a wide variety of packings, both random and structured. A single mathematical expression is used to describe all flow regimes: dry gas, irrigated gas flow below the load point, loading region, and flooding. The approach to the model development is fundamental in character and is an improvement over models published earlier.

Liquid film flow and area generation in structured packed columns

Several correlations are available in the literature for the prediction of wetted area or the effective interfacial area in packed columns. A careful examination shows considerable discrepancies in the calculated areas and conflicting predictions concerning the influence of viscosity on the interfacial areas. In this work, the effect of physical properties of liquids and of surface treatment on wetted area of structured packings was experimentally studied. Several wetting tests were performed on metallic and ceramic plates with flat, smooth or textured surfaces, using a circulation system, specially designed for this purpose. The liquid film width and thickness were measured for solutions with different surface tension and viscosities in a wide range (1 to 200 cP). The experimental results show that the liquid film width, and hence the wetted area, decreased with liquid viscosity, contrary to earlier correlations in the literature. Also the influence of contact angle is not so strong as stated in the literature for random packings. In this study, a new statistical correlation for the estimation of the wetted area and for the liquid film thickness is proposed, reflecting the measured variations with viscosity and advancing contact angles.

Hydraulics and mass transfer efficiency of a commercial-scale membrane extractor

Abstract In recent years there has been significant interest in utilizing microporous hollow fiber membranes for liquid-liquid extraction. The membrane extractor resembles the shell and tube heat exchanger with the tube section composed of 1000–2500 fibers/in2. The diameter of each fiber is approximately 300 microns. In this process, the feed may be passed through the shell side, while the solvent is passed through the fiber side, or vice versa. Mass transfer occurs across the liquid-liquid interface formed in the pores of the fiber wall. The advantages of this technology are high throughput capacities, independence of density difference between the feed and solvent, and potentially high mass transfer areas. The mass transfer performance of an available commercial scale nonbaffled membrane extraction module was determined to be lower than expected from results obtained in smaller scale modules. Mass transfer studies of a commercial-scale membrane extraction module at the Separations Research Program have ...

Scale-up of hollow fiber extractors

Abstract The performance of a commercial-scale hollow fiber extraction system was investigated by the Separations Research Program (SRP) at the University of Texas at Austin. In this work, hexanol was extracted from water into octanol using a large-scale extraction/distillation system. In the membrane extractor studies, the octanol-rich phase was fed on the tube-side while in the packed column studies, the octanol-rich phase was chosen as the dispersed phase. This chemical system was selected because of its high solute distribution coefficient. As a result, the required solvent to feed ratio was low which creates hydraulic problems for conventional dispersive extractors such as the packed column. Under identical operating conditions, the mass transfer performance of the hollow fiber extractor compared favorably with that of a commercial-scale type 2 structured packing. A height equivalent to a theoretical stage (HETS) of 1.5 meters was obtained with the membrane extractor as compared to 15 meters for the ...

Direct-Contact Gas-Liquid Heat Transfer in a Packed Column

Abstract Heat transfer coefficients were measured for the cooling of water or a nonvolatile oil by direct contacting in a packed column. The column contained random packing, and separate measurements were made on a number of different types of packing elements. Volumetric coefficients were correlated by empirical equations as well as by relationships based on a heat transfer/mass transfer analogy. The latter approach proved effective, and it is concluded that the large body of information on packed column mass transfer rates can be directly useful for predicting heat transfer coefficients for direct-contact exchangers.

Evaluation of packings for use in liquid-liquid extraction columns

Experimental investigations of packing performance in extraction service were conducted in a 10.2 cm. diameter column. Both random and structured packing elements were covered in separate studies. Test systems were toluene/acetone/water and n-butanol/succinic acid/water. Measurements were made of dispersed phase holdup and mass transfer rate. A tentative correlation was developed, based on a modification of basic tests using an empty column, involving an effective drop diameter.

Mass Transfer in Countercurrent Supercritical Extraction

Abstract This paper addresses problems and background information associated with the design of sieve-tray extraction col-ums operating in the supercritical solvent region. An appropriate mass transfer model is selected, and the needs and sources of basic data are reviewed. The model is executed for both conventional and supercritical extraction cases. Comparisons for both cases are made against measured data. It is concluded that stage efficiencies for the supercritical case are superior, largely due to favorable transport properties.

LIQUID-LIQUID EXTRACTION: POSSIBLE ALTERNATIVE TO DISTILLATION

Abstract Liquid-liquid extraction can often be a viable alternative to distillation for the separation of liquid mixtures. While it does not enjoy the support of confirmed, reliable methods for scaleup and design, as is the case for distillation, it does offer a potential for energy reduction and also can handle temperature-labile materials. The purpose of this paper is to provide an overview of extraction principles and applications that should be useful for conceptual design of new processes under development.

Distillation: Research Needs

Abstract Distillation will undoubtedly continue to be the most-used method for separating liquid mixtures, at any scale of operation. For this reason, and also because of its recognized energy intensiveness, distillation commands continued scrutiny with respect to cost-effective improvements. In this special report the authors suggest fruitful areas of research that can lead to lower cost distillation separations. The areas of research are classified under the headings of phase equilibrium, material and energy balances, mass transfer efficiencies, equipment design, and system energy consumption. For each of the categories a summary is given of the present status of the technology as well as directions that improvement-type investigations might take.

Low-energy separations for the process industry

Abstract An amount of energy equivalent to 800,000 bpd of crude oil is consumed in distillation processes in the petrochemical and petroleum refining industries in the United States. This paper reviews separation processes, including (1) distillation, (2) adsorption, (3) liquid-liquid and supercritical extraction, and (4) membrane processes. Conclusions are drawn on the merits of each type of separation process.