Composite zeolite adsorbent

Fig. 10 Schematic representation showing the formation of a composite zeolite adsorbent and the various resistances to mass transfer. From Ruthven and Post [35]...

The teehnique of desorption by simulated countercurrent flow displacement is also applied to other separation operations the separation of ethylbenzene from a mixture of aromatics and that of olefins from a mixture of olefins and paraffins. The composition of the zeolite adsorbent is adjusted in each case to optimize the effectiveness of the separation Na-Y or KSr-X zeohtes for ethylbenzene and Ca-X or Sr-X for olefins. The nature of the liquid desorbent also depends on the molecule to be separated. 

While the control samples having no zeolites did not adsorb methylene blue, composites having zeolites adsorbed it significantly as shown in Table 1. 

A model of a composite zeolite pellet must thus be represented by a combination of coupled equations for intracrystalline diffusion and macropore diffusion. The diffusion of adsorbate within crystals was discussed in the previous section and intracrystalline diffusion is given by equation (4.17). Macropore diffusion for a spherical pellet of radius Rp, macropore diffusivity Dp and porosity Cp is described by... 

Gas composition is an important processing variable in ion plating. The gas used for an inert plasma should be free of contaminants such as water vapor and oxygen that will become activated in the plasma. Inert gases can be purified using heated reactive svufaces such as copper, titanium, or uranium chip beds. Reactive plasmas should be free of contaminants. In reactive gases or gas mixtures, water vapor can be removed by cold traps utilizing zeolite adsorbers. 

The products of the reaction are the following /-butyl-phenyl-ether (TBPE), p-/-butyl-phenol (p-TBP), o-/-butyl-phenol (o-TBP) and 2,4-di-/-butyl-phenol (2,4-DTBP). Compounds adsorbed on the external surface were recovered in methylene chloride (CH2C12) by a soxhlet treatment for 24 hours of the deactivated zeolite sample. The content of the compounds inside the zeolite (coke) was determined after dissolution, in 40 % HF at room temperature, of the catalyst recoved after 5 min, 45 min, 5h and 7.5 h extraction by CH2C12 then followed. The composition of soluble coke was investigated by analysis GC-MS. The procedure is reported in detail elsewhere [10]. 

Patents assigned to Mobil (217) describe the use of boron trifluoride supported on several porous carriers. BF3 supported on silica was found to exhibit a slightly higher performance with added water in the alkylation of a mixed alkene feed at 273 K. It was also shown that self-alkylation activity was considerably lower than that with HF as catalyst. Another patent (218) describes the use of a pillared layered silicate, MCM-25, promoted with BF3 to give a high-quality alkylate at temperatures of about 273 K. BF3 was also supported on zeolite BEA, with adsorbed water still present (219). This composite catalyst exhibited low butene isomerization activity, which was evident from the inferior results obtained with 1-butene. At low reaction temperatures, the product quality was superior to that of HF alkylate. 

In general, the 2 1 clays are not very simple systems in which to study the interaction of water and surfaces. They have complex and variable compositions and their structures are poorly understood. Water occurs in several different environments zeolitic water in the interlayer regions, water adsorbed on the external surfaces of the crystallites, water coordinating the exchangeable cations, and, often, as pore water filling voids between the crystallites. Thus, there are many variables and the effects of each on the properties of water are difficult to separate. 

Overall the period since the 1980s can be described as a period of explosion in the discovery of new compositions and structures of molecular sieves. This can perhaps be seen most vividly by comparing the numbers of structure types contained in the various editions of the Atlas of Zeolite Structure Types [4]. The first edition (1978) contained 38 structure types, the second edition (1987) 64, the third edition (1992) 85 and the most recent edition (2007) 176. Thus 112 new structure types have been discovered since 1978. However, the reader should be cautioned that a significant number of the structure types included in the Atlas are not truly microporous or molecular sieve materials (i.e., they are not stable for the removal of as-synthesized guest species, typically water or organic templates) and therefore carmot reversibly adsorb molecules or carry out catalytic reactions. Unfortunately, the Atlas gives only limited information on the stability of the structures described. 

Zeolite catalysts and adsorbents have also been incorporated into monolithic contactors by several routes, including extruded zeoHte/binder composites [70], wash-coated ceramic monoliths [71] and corrugated thin-sheet monoliths [72]. 

In liquid phase adsorption, some particular components of the feed steam are selectively adsorbed or extracted by a solid zeoUtic adsorbent. At the same time, other components of the feed stream are rejected by the adsorbent. At equilibrium, the liquid composition within the zeolite pores differs from that of the liquid surrounding the zeolite. In the process, a second liquid component, the desorbent, is also introduced into the system. The function of the desorbent is to desorb and recover the extracted feed components from the adsorbent In order for the desorbent to perform well in the process, a suitable interactive force between the desorbent and the extracted components to the adsorbent is required. If the selectivity is too high, it requires high desorbent volume to desorb the extracted components from the adsorbent. If the selectivity is too low, the desorbent tends to compete with extracted components for capacity of adsorbent. 

Adsorptive separation is a powerful technology in industrial separations. In many cases, adsorption is the only technology available to separate products from industrial process streams when other conventional separation tools fail, such as distillation, absorption, membrane, crystallization and extraction. Itis also demonstrated that zeolites are unique as an adsorbent in adsorptive separation processes. This is because zeolites are crystalline soUds that are composed of many framework structures. Zeolites also have uniform pore openings, ion exchange abiUty and a variety of chemical compositions and crystal particle sizes. With the features mentioned, the degree of zeoUte adsorption is almost infinite. It is also noted that because of the unique characteristics of zeoHtes, such as various pore openings, chemical compositions and structures, many adsorption mechanisms are in existence and are practiced commercially. 

There are three liquid-phase adsorption Sorbex technology-based separation processes for the production of olefins. The first two are the UOP C4 Olex and UOP Sorbutene processes and the third is the detergent Olex process(Cio i,5) [25, 26]. The three olefin separation processes share many similarities. The first similarity between the three olefin separation processes is that each one utilizes a proprietary adsorbent whose empirical formula is represented by Cation,([(A102)),(Si02)2] [27]. The cation type imparts the desired selectivity for the particular separation. This zeolite has a three-dimensional pore structure with pores running perpendicular to each other in the x, y and z planes [28]. The second similarity between the three olefin separation processes is the use of a mixed olefin/paraffin desorbent. The specifics of each desorbent composition are discussed in their corresponding sections. The third similarity is the fact that all three utilize the standard Sorbex bed allotment that enables them to achieve product purities in excess of 98%. The following sechons review each process in detail. 

Analytical Procedures. The chemical compositions of both liquid and gas products were determined by gas chromatography (GC). The normal paraffinic concentration in the liquid products and their carbon number distribution were determined by a GC method (5). The sample was analyzed first with a 2-ft silicone gum rubber (SE-30) column and then analyzed again with the same column attached behind a 3-inch Ca/A zeolite column which adsorbed all n-paraffins. 

Zeolites (3 were treated with a NaBO, solution, and the porous properties of boronated samples were investigated by sorption measurements with benzene and nitrogen as adsorbate, TEM, SEM and composition analysis. It is shown that the micropores are converted into the mesopores and the mesopores are developed into larger mesopores due to the extraction of framework silicon by base. The small atom size of boron and the poor stability of boron in framework should be responsible for the silicon removal in a large amount. The dissolution of silicon also causes the corrosion of outer surface of particles and the decrease of particle size. 

The two species in the binary solution are designated as B and A. B is the adsorbate molecule and A is the absence of an adsorbed molecule at a particular adsorption site on the zeolite surface, called a "vacancy". Because of its definition, A is equal in size to the B species molecule. As the gas pressure above the zeolite (i.e., Pg) goes to larger values (Pg" Pg0) the solution composition within the cavity goes toward a pure solution of adsorbed gas (X--+1). As the gas pressure above the zeolite goes to smaller values (i.e., VpJ V Q)> the amount of adsorption becomes less (Xg-K)) and the solution composition within the cavity goes toward a pure solution of vacancies (X -+l). This choice of solution species has the proper asymptotic nature. 

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