Bulk separation

Bulk separations Bulk sweeteners Bulk viscosity Bulletproof vests Bullet-resistant glass Bullets... 

The enhanced concentration at the surface accounts, in part, for the catalytic activity shown by many solid surfaces, and it is also the basis of the application of adsorbents for low pressure storage of permanent gases such as methane. However, most of the important applications of adsorption depend on the selectivity, ie, the difference in the affinity of the surface for different components. As a result of this selectivity, adsorption offers, at least in principle, a relatively straightforward means of purification (removal of an undesirable trace component from a fluid mixture) and a potentially useflil means of bulk separation. 

Removal of trace impurities from gases or liquid streams Bulk separations (gas or liquid)... 

Gas-phase adsorption is widely employed for the large-scale purification or bulk separation of air, natural gas, chemicals, and petrochemicals (Table 1). In these uses it is often a preferred alternative to the older unit operations of distillation and absorption. 

Bulk Separations. Air separation, methane enrichment, and iso-/normal separations are the principal bulk separations for PSA. Others are the recovery of CO and CO2. 

In contrast to trace impurity removal, the use of adsorption for bulk separation in the liquid phase on a commercial scale is a relatively recent development. The first commercial operation occurred in 1964 with the advent of the UOP Molex process for recovery of high purity / -paraffins (6—8). Since that time, bulk adsorptive separation of liquids has been used to solve a broad range of problems, including individual isomer separations and class separations. The commercial availability of synthetic molecular sieves and ion-exchange resins and the development of novel process concepts have been the two significant factors in the success of these processes. This article is devoted mainly to the theory and operation of these Hquid-phase bulk adsorptive separation processes. 

BulkSepa.ra.tlon, The adsorptive separation of process streams into two or more main components is termed bulk separation (see Fig. 12). The development of processes and products is complex. Consequently, these processes are proprietary and are purchased as a complete package under licensing agreements. High purities and yields can be achieved. 

For bulk separations, more highly adsorbed component should be in minority in feed, generally <10 20%. 

For these various reasons one may ask if it is possible to develop automated or semi-automated methods that will simultaneously measure compositions and other thermodynamic parameters at reservoir pressures and temperatures, without waiting for bulk separation of dispersed phases in the apparatus. 

Isoperibolic calorimetry measurements on the n-butanol/water and n-butoxyethanol/water systems have demonstrated the accuracy and convenience of this technique for measuring consolute phase compositions in amphiphile/water systems. Additional advantages of calorimetry over conventional phase diagram methods are that (1) calorimetry yields other useful thermodynamic parameters, such as excess enthalpies (2) calorimetry can be used for dark and opaque samples and (3) calorimetry does not depend on the bulk separation of conjugate fluids. Together, the present study and studies in the literature encompass all of the classes of compounds of the amphiphile/CO ydrocarbon/water systems that are encountered in... 

Polymeric membranes, which offer bulk separation of hydrogen... 

Some of the polymeric membranes are suitable for bulk separation of hydrogen from impurities to enrich a dilute hydrogen stream. Dense polymers permeate gases by solution diffusion mechanism. The permeation rate of a gas species through a polymer membrane... 

Argon (Ar), 17 343. See also ArF laser bulk quantities of, 17 363 commercial distribution of, 17 362-363 cryogenic shipping, 8 40 doubly ionized, 14 684—685 economic aspects of, 17 365-366 electrostatic properties of, 1 621t in ethylene oxidation, 10 651 gas bulk separation, l 618t high purity, 13 460, 468 in light sources, 17 371-372 liquefaction, 8 40... 

Gas-based muds, 9 3 Gas bulk separation, 1 646-647 commercial processes, l 618t Gas burners, 7 455-460 Gas burner technology, 12 382-383 Gas carburizing... 

Industrial examples of adsorbent separations shown above are examples of bulk separation into two products. The basic principles behind trace impurity removal or purification by liquid phase adsorption are similar to the principles of bulk liquid phase adsorption in that both systems involve the interaction between the adsorbate (removed species) and the adsorbent. However, the interaction for bulk liquid separation involves more physical adsorption, while the trace impurity removal often involves chemical adsorption. The formation and breakages of the bonds between the adsorbate and adsorbent in bulk liquid adsorption is weak and reversible. This is indicated by the heat of adsorption which is <2-3 times the latent heat of evaporahon. This allows desorption or recovery of the adsorbate from the adsorbent after the adsorption step. The adsorbent selectivity between the two adsorbates to be separated can be as low as 1.2 for bulk Uquid adsorptive separation. In contrast, with trace impurity removal, the formation and breakages of the bonds between the adsorbate and the adsorbent is strong and occasionally irreversible because the heat of adsorption is >2-3 times the latent heat of evaporation. The adsorbent selectivity between the impurities to be removed and the bulk components in the feed is usually several times higher than the adsorbent selectivity for bulk Uquid adsorptive separation. 

Chao, C.C. and Sherman,. D. (1985) Bulk separation of inositol and sorbitol by selective adsorption on zeolitic molecular sieves. U.S. Patent 4,482,751. 

Bulk separation of polyhydric alcohols by selective adsorption on... 

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. 

While the Union Carbide organization, which is now in UOP, was the leader in gas phase separations, liquid bulk separations were brought to a high degree of maturity by UOP s Don Broughton and his successors in UOP s liquid phase separations research and development groups. 

The latter relationship is readily derived from a mass balance on the contaminant entering the column. This wave speed is referred to as the stoichiometric wave speed. It applies strictly only to one component. It will be recognized that manipulation of Eq. (9.11) with similar substitutions yields the wave speed result for bulk separations where the derivative of v with respect to the spatial variable does not drop out and where two or more components may adsorb. The result has a very similar form but of course depends on not one isotherm slope but on two or more and very significantly the wave speed depends on the relative mole fractions of the adsorbing species and the initial loadings in the column. 

Another key point of differentiation is the fact that nearly all PSA separations are bulk separations and any investigator interested in a high fidelity description of the problem of adsorption must solve a mass balance equation such as Eq. (9.9), the bulk separation equation, together with the uptake rate model and a set of thermal balance equations of similar form. In addition to the more complicated pde and its attendant boundary and initial conditions the investigator must also solve some approximate form of a momentum balance on the fluid flow as a whole. 

Industrial gas phase separations span a wide variety of apphcations, from ultrapurifications to bulk separations. In the preceding sections I touched upon some of the more widely practiced separations technologies. 

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