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a Over 8,000,000 barrels of crude oil are separated daily by the petroleum industry in the United States. This amount of crude oil is equivalent to nearly 3 billion barrels per year or nearly 500,000,000 tons per year. The crude is separated b y many processes into usual products of gasoline, kerosine, Diesel fuel, lubricating oil, wax, asphalt, specialty products, and chemical raw materials. The most common process is distillation. Solvent extraction, extractive distillation, crystallization, and adsorption are other types of separation employed on this large scale. The exacting requirements for new and modern products from the petroleum industry make it necessary that separation processes not be taken for granted but that extensive research and development, leading to new processes, go on at an accelerated pace. The Symposium on Advances in Separation of Hydrocarbons and Related Compounds presents a small portion of this active field. It gives a representative cross section of the separation work going on in modern petroleum research laboratories. Most of the separations depend upon small differences in physical properties of hydrocarbons and derivatives. Nearly all separation processes involve two phases: vapor-liquid, liquid-liquid, or solidliquid. However, one of the newer processes, thermal diffusion, i s a single-phase separation process in which remarkable separations have been achieved. New solid-liquid phase processes include adsorption, a process in which compounds of the same molecular weight, but of different chemical structure, can be separated quantitatively; and the formation of complexes of hydrocarbons or derivatives with urea or thiourea. Still another solid-liquid separation process i s used in the manufacture of p-xylene, one of the important raw materials used in the manufacture of Dacron. Use of hydrocarbons and related compounds in large scale chemical manufacture requires exacting types of separation, and processes are available or are being developed to meet these needs. Many o f these large scale processes are available because the needs of the petroleum industry itself have been exacting. Large scale purification of materials used in the manufacture of gasolines, waxes, and lubricating oils has resulted in application on a large scale but with the precision usually required for fine chemicals. Separation processes should not be regarded as unchanging but as a growing field with much research and development to meet the rapidly expanding requirements of the chemical industry. The processes described in this symposium are applicable outside the petroleum industry, and i t i s a purpose of the symposium to make available the information of this changing field. If this symposium provides inspiration for further development of new processes, it will have achieved an even greater purpose. W . H. CLAUSSEN AND VANDERVEER VOORHIES, Cochairmen
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The symposium on advances in separations of hydrocarbons and related compounds was Q presentation of the ACS Division of Petroleum Chemistryat the 126th Meeting of the American Chemical Society, New York, N. Y. LIQUID PHASE ADSORPTION STUDIES Alfred E. Hirschler and Thomas S. Mertes
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THERMAL DIFFUSION SEPARATIONS OF ORGANIC LIQUID MIXTURES Charles R. Begeman and Paul 1. Cramer
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ROTARY AND PACKED THERMAL DIFFUSION FRACTIONATING COLUMNS FOR LIQUIDS Lloyd J. Sullivan,Thomas C. Ruppel, and Charles 8. Willinghom
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LUBRICATING OIL FRACTIONS PRODUCED BY THERMAL DIFFUSION A. Letcher Jones
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UREA AND THIOUREA COMPLEXES IN SEPARATING ORGANIC COMPOUNDS Daniel Swern
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SELECTIVE SOLVENTS FOR AROMATIC HYDROCARBONS Davis A. Skinner
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SOLVENT EXTRACTION WITH LIQUID CARBON DIOXIDE Alfred W . Francis
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SULFUR DIOXIDE EXTRACTION OF SULFUR COMPOUNDS AND AROMATICS R. C. Arnold and A. P. Lien
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SULFUR COMPOUNDS IN KEROSINE BOILING RANGE O F MIDDLE EAST CRUDES S. F. Birch, T. V. Cullum, R. A. Dean, and R. L. Denyer
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SEPARATION O F XYLENES Clark J. Egan and Raymond V. Luthy
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ADVANCES IN DISTILLATION SEPARATIONS J. A. Gerster
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Four papers in this symposium will be published in the February issue of Analyfical Chemistry
Liquid-Phase Adsorption Studies Related to the Arosorb Process ALFRED E. HIRSCHLER AND THOMAS S. MERTES, Sun Oil Co., Norwood, P a .
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AY (3)was one of the first to apply an adsorption column to the separation of petroleum hydrocarbons. He allowed oil to diffuse upward through a column of fuller’s earth and showed that unsaturated and aromatic hydrocarbons were preferentially retained in the lower portion of the tube. Mair and coworkers (16)made extensive application of silica gel adsorption to laboratory procedures for the separation and analysis of petroleum fractions. Research on the application of silica gel adsorption to the commercial separation of aromatics from petroleum resulted in development of the Arosorb process. The engineering aspects of the Arosorb process have been discussed previously (11). The purpose of this paper is t o describe some of the fundamental adsorption studies carried out in connection with this development. These studies deal largely with the two principal problems in the design and operation of liquid phase adsorption columns-the adsorption equilibria and the rate processes involved in obtaining these equilibria. An empirical Adsorption Index is described which is an aid in the selection of suitable desorbents for cyclic adsorption processes.
Adsorption Equilibria When an adsorbent is brought into contact with a binary mixture of two liquids having different adsorption affinities, the composition of the liquid phase changes. The change occurs rapidly a t first, but after a definite time interval which depends on the properties of the adsorbent and also on the nature of the liquid, the concentration reaches a constant value. The apparent selective adsorption (per unit weight of adsorbent) may be calculated by a u = - (zll - Z) (1) m
rium concentrations of the preferentially adsorbed component, expressed in volume fraction. This equation ignores the change in total volume of the solution which is caused by removal of the preferentially adsorbed material. By taking into account this change in volume, as was first proposed by Williams (&’I), one can calculate a “corrected” selective adsorption.
Many workers have used Equation 1 to calculate selective adsorption while others (18)have employed the equivalent of Equation 2. Concentrations may be expressed in other units, such as weight fraction, mole fraction, or volume per cent, with either equation. The selective adsorptive capacity of an adsorbent is a function both of temperature and the concentration of the preferentially adsorbed component in the mixture. The selective adsorptive capacity as a function of concentration, at constant temperature, is known as the adsorption isotherm. Pore Volume. Gurwitsch (10)equilibrated samples of a given charcoal with the saturated vapors of a number of different liquids and observed that while the weights of liquid taken up varied considerably, the volumes adsorbed were substantially constant. This relation has been termed the Gurwitsch rule. The volume of liquid adsorbed per gram of adsorbent is termed the specific pore volume, V,. The pore volume may also be determined from the relation (3)
v
where V is the volume of initial mixture contacted with a known weight, m,of adsorbent, and zoand x are the initial and equilib-
February 1955
where Vt and V uare the true and apparent specific volumes of the adsorbent and Dt and D, the corresponding densities. The true density is the density of the adsorbent immersed in a liquid which
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