Industrial Gas Phase Adsorptive Separations

Adsorption as a gas phase separation process fills a space in the spectrum of separations processes that encompasses both purification and bulk separations. The market for gas phase adsorptive separations is of the order of several billion US dollars armuaUy when aU sorbent, equipment and related products are included. 

ZeoHte adsorbents play a dominant role in purifications owing to their ability to both adsorb large quantities of material and to achieve extremely low mole fractions of these adsorbed these compounds in product gas. Zeolites are the preferred adsorbent types for dehydration to low levels, purification and in several bulk separations. Zeolites also are employed in a significant portion of the PSA hydrogen purification market segment where they add value to bulk separations by achieving particularly high purity specifications. 

The business that grew out of the Linde Laboratories was the Union Carbide Molecular Sieve business which, since 1988, has been integral to UOP s Catalysts Adsorbents and Specialties business segment. 

This chapter discusses adsorption fundamentals relating to the design and operation of large-scale industrial separations using zeolite molecular sieves. 

Zeolites in Industrial Separation and Catalysis. Edited by Santi Kulprathipanja Copyright 2010 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-32505-4 

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While inert and displacement purge regeneration is widely used in liquid phase separations, there are few industrially relevant inert purge systems employed in gas phase separations. It is sufficient to note that an inert purge regeneration can be done and it will generally be most effective at relatively high adsorption temperatures. 

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... 

Modification of silica gel with volatile or gaseous compounds is performed in the vapour phase. Industrial-scale reactors and laboratory scale gas adsorption apparatus have been used. In the industrial field, fluidized bed and fluid mill reactors are of main importance. In fluidized bed reactors,82 the particles undergo constant agitation due to a turbulent gas stream. Therefore, temperatures are uniform and easy to control. Reagents are introduced in the system as gases. Mass transport in the gas phase is much faster than in solution. Furthermore, gaseous phase separations require fewer procedural steps than solution phase procedures, and may also be more cost-effective, due to independence from the use and disposal of non-aqueous solvents. All these advantages make the fluidized bed reactors preferential for controlled-process industrial modifications. 

Adsorption phenomena can be due to several different molecular mechanisms. These are described and characterized in brief by their respective enthalpies in Sect. 2. Several classes of sorbent materials used for different industrial purposes such as separation of gas mixtures, recovery of volatile solvents or energetic purposes like adsorption-based air conditioning systems, are presented in Sect. 3. This section is complemented by an overview of most often used methods to characterize porous sorbent materials given in Sect. 4. The basic concepts of mass and - to a lesser extent - volume of a sorbed phase are discussed in Sect. 5. In Sect. 6 a short overview of the... 

Activated carbon is a very important industrial adsorbent because it exhibits a well developed porosity (micro, meso and macroporosity) and this is coupled with a great thermal and chemical stability, a relatively large hydrophobicity (thus favouring the adsorption of non-polar substances in the presence of humidity), low production cost, etc. Additionally, the surface of activated carbon can be functionalised with different heteroatoms (but mainly oxygen), thus modifying the chemical nature. A large and accessible surface area is a necessary but not sufficient condition for the preparation of activated carbons to be used in industrial adsorption processes (gas and liquid phase purification, separation, environmental control, etc.), since the last few years has shown that the chemical composition of the carbons surface plays a very important role in the process. 

Although adsorption has been used as a physical-chemical process for many years, it is only over the last four decades that the process has developed to a stage where it is now a major industrial separation technique. In adsorption, molecules distribute themselves between two phases, one of which is a solid whilst the other may be a liquid or a gas. The only exception is in adsorption on to foams, a topic which is not considered in this chapter. 

Butane is extracted from natural gas and is also obtained during petroleum refining. Butane can be obtained from natural gas by compression, adsorption, or absorption. All three processes were used in the early days of the LPG industry, but compression and adsorption were generally phased out during the 20th century. Most butane now is obtained from absorption and separation from oil. Very little butane is obtained from distillation. Gas stream from cracking units in the refining process contain appreciable amounts of... 

Mass transfer plays an important role in many industrial processes. A group of operations for separating the components of mixtures is based on the transfer of material from one homogeneous phase to another. These methods—covered by the term mass-transfer operations—include such techniques as distillation, gas absorption, humidification, liquid extraction, adsorption, membrane separations, and others. The driving force for transfer in these operations is a concentration gradient, much as a temperature gradient provides the driving force for heat transfer. 

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