Zeolite adsorbate olefins

Rosback, D.H. (1973) Adsorbing olefins wih a copper-exchanged type Y zeolite. U.S. Patent 3,720,604. 

Zeolites have an enormous impact on our daily lives, both directly and indirectly. For example, upstream hydrocarbons such as aromatics and olefins are produced using zeolite catalysts. The aromatics or olefins are then separated from the reaction mixtures using zeolite adsorbents. The purified components produced by these zeolite-based methods are then used in downstream processes to produce products that we use daily, such as clothes, furniture, foods, construchon materials and materials to build roads, automobile parts, fuels, gasoline, etc. In addihon to the indirect impacts mentioned above, zeolites also have a direct impact on our daily lives. For example, zeolites are used as builders in detergent formulations. 

Olefin Separation. U.O.P. s Olex Process. U.O.P. s other hydrocarbon separation process developed recently—i.e., the Olex process—is used to separate olefins from a feedstock containing olefins and paraffins. The zeolite adsorbent used, according to patent literature 29, 30), is a synthetic faujasite with 1-40 wt % of at least one cation selected from groups I A, IIA, IB, and IIB. The Olex process is also believed to use the same simulated moving-bed operation in liquid phase as U.O.P. s other hydrocarbon separation processes—i.e., the Molex and Parex processes. 

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. 

Corma et al. [204] studied the conversion of -heptane over a series of dealuminated Y zeolites. They did not correlate the hydride transfer activity to the presence of adjacent sites, as often done in the literature, but to the more hydrophobic nature of a more severely dealuminated zeolite. The tendency to adsorb a more polar molecifle (i.e., an olefin) decreases compared to the less polar molecule (i.e., a paraffin) and, therefore, the conversion of adsorbed olefins to paraffins will decrease. By a change in adsorption properties hydride transfer, which is a bimolecular mechanism, will be much more influenced than cracking, which proceeds via a monomoleciflar mechanism. This explains the stronger decrease of hydride transfer compared to cracking. 

Sorbex configuration) utilizes a 5A zeolite adsorbent and light naphtha as desorbent for the separation of linear and branched chain paraffins. Olefins may be separated from saturated hydrocarbon isomers by the Olex process using CaX zeolite as adsorbent and heavy naphtha as desorbent. Separation of fructose from glucose is achieved in the Sarex process using CaY zeolite as adsorbent and water as desorbent. All of these processes are summarized in Table 5.1. 

Monitoring the label scrambling in adsorbed olefins on acid forms of zeolites. 

Operando DRIFTS examination of the working zeolite catalysts shows adsorbed hexane but do not support the presence of bound alkoxide/olefin/carbenium ion species. Data substantiate that alkanes may be activated without full transfer of zeolite proton to the alkane, i.e., without generation of any kind of real carbocation as transition state or surface intermediate. 

As documented in Chapter 5, zeolites are very powerful adsorbents used to separate many products from industrial process steams. In many cases, adsorption is the only separation tool when other conventional separation techniques such as distillation, extraction, membranes, crystallization and absorption are not applicable. For example, adsorption is the only process that can separate a mixture of C10-C14 olefins from a mixture of C10-C14 hydrocarbons. It has also been found that in certain processes, adsorption has many technological and economical advantages over conventional processes. This was seen, for example, when the separation of m-xylene from other Cg-aromatics by the HF-BF3 extraction process was replaced by adsorption using the UOP MX Sorbex process. Although zeolite separations have many advantages, there are some disadvantages such as complexity in the separation chemistry and the need to recover and recycle desorbents. 

The coimnerdal liquid adsorptive separation process of Ciq-Ch -olefins from Cio-Ci4 n-paraffins is another unique example of how zeolite adsorption can be applied. As shown in Table 6.1, distillation is not an option to separate C10-C14 olefins from Ciq-Cu paraffins because of their close boiling points. In this case, the UOP Olex process using NaX adsorbent is used to separate Ciq-Cm olefins from Cio-Ci4 paraffins. 

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. 

The conversion of methanol to hydrocarbons (MTHC) on acidic zeolites is of industrial interest for the production of gasoline or light olefins (see also Section X). Upon adsorption and conversion of methanol on calcined zeolites in the H-form, various adsorbate complexes are formed on the catalyst surface. Identification of these surface complexes significantly improves the understanding of the reaction mechanism. As demonstrated in Table 3, methanol, dimethyl ether (DME), and methoxy groups influence in a characteristic manner the quadrupole parameters of the framework Al atoms in the local structure of bridging OH groups. NMR spectroscopy of these framework atoms under reaction conditions, therefore, helps to identify the nature of surface complexes formed. 

In the physical separation process, a molecular sieve adsorbent is used as in the Union Carbide Olefins Siv process (88—90). Linear butenes are selectively adsorbed, and the isobutylene effluent is distilled to obtain a polymer-grade product. The adsorbent is a synthetic zeolite, Type 5A in the calcium cation exchanged form (91). UOP also offers an adsorption process, the Sorbutene process (92). The UOP process utilizes a liquid B—B stream, and uses a proprietary rotary valve containing multiple ports, which direct the flow of liquid to various sections of the adsorber (93,94). The cis- and trans-isomers are... 

In addition to performing acid/base catalysis, zeolite structures can serve as hosts for small metal particles. Transition metal ions, e.g., platinum, rhodium, can be ion exchanged into zeolites and then reduced to their zero valent state to yield zeolite encapsulated metal particles. Inside the zeolite structure, these particles can perform shape selective catalysis. Joh et al. (16) reported the shape selective hydrogenation of olefins by rhodium encapsulated in zeolite Y (specifically, cyclohexene and cyclododecene). Although both molecules can be hydrogenated by rhodium supported on nonmicroporous carbon, only cyclohexene can be hydrogenated by rhodium encapsulated in zeolite Y since cyclododecene is too large to adsorb into the pores of zeolite Y. 

A patent (230) to Atlantic Richfield Co. claims that hydride platinum group metal carbonyl complexes such as ClRh(PPh3)3 supported on zeolites, for example, NaY, are suitable catalysts for the hydroformylation of low molecular weight olefins. However, since the bulky metal complex cannot diffuse into the inner pores of the zeolite it must simply be adsorbed on the external surface of the support. This is consistent with the rather poor catalyst stability which was attributed to leaching of the active species from the support. 

In other cases however, the high concentration of some reactants leads to undesired side reactions. In the alkylation of isobutane with butenes, zeolites are very efficient catalysts but lack stability because olefins are more strongly adsorbed than the paraffin and over a matter of minutes, their oligomerization takes over the alkylation reaction and deactivates the catalyst by pore blocking. 

The molecular sie es employed for this operation are synthetic siflco-alumioas which carry metallic ions, with uniform pore diameters between 3 and 10 A, and whose structure is comparable to that of natural zeolites. They are capable of separating linear carbon chains, which are specifically adsorbed, from those that are branched. Many technologies have been develops particularly by Exxon, BP British Petroleum), Texaco, UQP and 7fubn Carbide, which exploit their capacity for selective adsorption to isolate n-paraflins from their branched isomers as well as linear olefins from their branched homologues. ... 

Loaded Adsorbents. Wliere highly efficient removal of a trace impurity is required it is sometimes effective to use an adsorbent preloaded with a reactant rather than rely on the forces of adsorption. Examples include the use of zeolites preloaded with bromine to trap traces of olefins as their more easily condensible bromides zeolites preloaded with iodine to trap mercury vapor, and activated carbon loaded with cupric chloride for removal of mercaptans. 

Paramagnetic ions are now being used quite extensively to study adsorption phenomena. Mn ions have been used as probes for studying molecular motion in synthetic zeolites, (350) Co and Ni ions have been used for studying the complexation of molecular hydrogen on the surface of zeolites, (351) and these same ions have been used in a variety of studies of adsorption on Aerosil surfaces. (352-358) Adsorbed molecules studied include olefins, saturated hydrocarbons, alcohols, and benzene. From the measured line-shifts the number of active surface sites can be deduced in favourable cases. (357, 358)... 

The adsorption properties of silver- and cupper-loaded zeolites for C2 and C3 hydrocarbons were investigated to explore excellent materials for cold-start hydrocarbon trap. The adsorption property and the stability of the adsorbents depended significantly on the metal species and host zeolites. It has turned out that silver-loaded ferrierite zeolite is the promising material with excellent olefin selectivity, high adsorption capacity, desirable storage ability and hydrothermal stability. 

Two kinds of functional adsorbents are used to which one is for selective adsorption removal of paraffins and the other for C4 olefins. The former is zeolite A and the latter... 

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