PREFACE
Downloaded by 80.82.78.170 on January 15, 2017 | http://pubs.acs.org Publication Date: June 16, 1983 | doi: 10.1021/bk-1983-0223.pr001
I^ÎEW
SÉPARATION TECHNIQUES, particularly for improving gas technologies, have increased dramatically in recent years. These advances have stemmed not only from the obvious needs to reduce process costs and environmental pollution, but also from the synthesis and identification of novel materials. Such materials include unique membranes and zeolites. The use of membranes to separate gases commercially is a relatively new application. Both Du Pont and Union Carbide had ventures in the early 1970s for recovering H 2 and He from industrial processes, but these projects were never fully commercialized. Recently, however, a combination of improved economics and better technology has resulted in membrane products that signal a new era in the commercial use of membranes for large-scale gas separation. Diffusion processes in polymers have been studied since the 1860s, and gas diffusion in polymers was studied intensively in the 1950s and 1960s by such notables as Weller, Steiner, Kammermeyer, Stannett, Michaels, Rogers, and Stern. Although these studies generated a large amount of permeability data for gas diffusion through polymers, industrial applications were not implemented until nearly 15 years later. Clearly, the use of membranes to separate gases commercially is not a simple task. Companies currently trying to commercialize such processes are well aware of the need to combine basic understanding with sophisticated fabrication technology. Both the understanding of gas transport and the number of engineering ventures that are using membranes have been growing rapidly. This symposium explores gas-transport mechanisms and models and presents several industrial applications of gas membranes. Although agreement on the transfer mechanism has not yet been reached for either mixed- or single-gas permeation, the understanding is sufficient to develop both energyand cost-effective purification and bulk separation processes for industrial use. Adsorption separation—an important unit operation in the separation of industrial gases—is achieved by adsorbing one or more component(s) onto the active sites of a solid adsorbent. For cyclic processes, the solid is regenerated by shifting the equilibrium toward the gas phase by increasing the adsorbent temperature or by decreasing the partial pressure of the adsorbate in the gas. Some of the more important commercial combinations
ix Whyte et al.; Industrial Gas Separations ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
Downloaded by 80.82.78.170 on January 15, 2017 | http://pubs.acs.org Publication Date: June 16, 1983 | doi: 10.1021/bk-1983-0223.pr001
of adsorbents and regeneration techniques are discussed in a paper in this symposium. As the understanding of cyclic adsorption processes has developed, more and more of the assumptions used in designing systems have been reexamined and discarded for more rigorous treatments. Many more sophisticated models of the adsorption phenomenon are being postulated, such as that offered for pressure swing separation of light gases. In other separations, the molecular size dimensions of the microporous solids are used to control kinetic selectivity as well as or in place of adsorptive selectivity. For example, the natural zeolite clinoptilolite is used for the separation of methane and nitrogen. In some adsorptive processes, the bonding energy associated with adsorption is similar in magnitude to that of a chemical reaction. For such cases, the regeneration may be achieved more effectively by shifting a chemical reaction equilib rium. Such an approach has been used for an iron oxide sorbent. The papers presented cover the spectrum of applications, adsorbents, and types of cycles. Absorption is another unit operation that has many parallels to adsorption. Although the sorption media is liquid rather than solid, many of the underlying principles are the same. Most commercial applications for purification and bulk separation involve weak physical bonding of absorbate to absorbent. Again, regeneration of sorbent is accomplished by increasing the liquid temperature and/or by decreasing absorbate partial pressure. This volume contains a discussion of a process for recovering methane from hydrogen and carbon monoxide using liquid propane—a separation that might also have been attempted with a suitable solid adsorbent. Another state-of-the-art approach—the removal of acid gases (sulfur compounds and carbon dioxide)—is detailed; in this process the con taminant carbon dioxide becomes both an active adsorbent and a com ponent of an absorptive fluid. THADDEUS E . WHYTE, JR.
Catalytica Associates, Inc. Santa Clara, CA CARMEN M. YON
Union Carbide Corporation Tarrytown, NY EARL H . WAGENER
Dow Chemical Company Walnut Creek, CA February 28, 1983 χ Whyte et al.; Industrial Gas Separations ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
