Zeolites ADSORPTION,LIQUID SEPARATION

Zeolite Y, 2 345t, 5 238-239, 11 678, 679 coke formation on, 5 270 for liquid separation adsorption, 1 674 manufacture, 2 359 structure, 1 675 Zeolite ZSM-5, 11 678 Zeolitic cracking catalysts, 16 835 Zeolitic deposits, 16 813 Zeonex, 10 180 Zeotypes... 

Palkhiwala, A.G., lin, Y.H., Perlmutter, D.D., and Olson, D.H. (1999) Liquid phase separation of polar hydrocarbons from light aromatics using zeolites. Adsorption, 5, 399 07. 

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. 

Ba-Modenite s selectivity to MX is higher than OX, but the opposite is true for BaY. This reversal in selectivity is a result of differences in adsorbent framework characteristics mordenite has higher acid strength compared to Y zeolite. Adsorption and desorption rates of xylenes are expected to be faster in BaY compared to Ba-Mordenite because Mordenite is a one-dimensional channel system while Y zeoUte is a three-dimensional channel. With the reason stated, a three-dimensional channel ZeoUte is the preferred mass separating agent of choice compared to one-or two-dimensional channels for the liquid adsorption separation. 

Chapter 7 gives a review of the technology and applications of zeolites in liquid adsorptive separation of petrochemical aromatic hydrocarbons. The application of zeolites to petrochemical aromatic production may be the area where zeolites have had their largest positive economic impact, accounting for the production of tens of millions of tonnes of high-value aromatic petrochemicals annually. The nonaromatic hydrocarbon liquid phase adsorption review in Chapter 8 contains both general process concepts as well as sufficient individual process details for one to understand both commercially practiced and academic non-aromatic separations. 

New applications of zeolite adsorption developed recently for separation and purification processes are reviewed. Major commercial processes are discussed in areas of hydrocarbon separation, drying gases and liquids, separation and purification of industrial streams, pollution control, and nonregenerative applications. Special emphasis is placed on important commercial processes and potentially important applications. Important properties of zeolite adsorbents for these applications are adsorption capacity and selectivity, adsorption and desorption rate, physical strength and attrition resistance, low catalytic activity, thermal-hydrothermal and chemical stabilityy and particle size and shape. Apparent bulk density is important because it is related to adsorptive capacity per unit volume and to the rate of adsorption-desorption. However, more important factors controlling the raJtes are crystal size and macropore size distribution. 

Olex A version of the Sorbex process for separating olefins from paraffins in wide-boiling mixtures. It can be used for hydrocarbons in the range C6 - C20. Based on the selective adsorption of olefins in a zeolite and their subsequent recovery by displacement with a liquid at a different boiling point. Mainly used for extracting Cn - C14 olefins from the Pacol... 

Fructose separation adsorbents, 7 587t liquid adsorption, 7 665, 674 with zeolite KX, 7 610 Fructosyloligosaccharides (FOS), 23 480 Fruit(s)... 

The most commonly employed crystalline materials for liquid adsorptive separations are zeolite-based structured materials. Depending on the specific components and their structural framework, crystalline materials can be zeoUtes (silica, alumina), silicalite (silica) or AlPO-based molecular sieves (alumina, phosphoms oxide). Faujasites (X, Y) and other zeolites (A, ZSM-5, beta, mordenite, etc.) are the most popular materials. This is due to their narrow pore size distribution and the ability to tune or adjust their physicochemical properties, particularly their acidic-basic properties, by the ion exchange of cations, changing the Si02/Al203 ratio and varying the water content. These techniques are described and discussed in Chapter 2. By adjusting the properties almost an infinite number of zeolite materials and desorbent combinations can be studied. 

This chapter addresses the fundamentals of zeolite separation, starting with (i) impacts of adsorptive separation, a description of liquid phase adsorption, (ii) tools for adsorption development such as isotherms, pulse and breakthrough tests and (iii) requirements for appropriate zeolite characteristics in adsorption. Finally, speculative adsorption mechanisms are discussed. It is the author s intention that this chapter functions as a bridge to connect the readers to Chapters 7 and 8, Liquid Industrial Aromatics Adsorptive Separation and Liquid Industrial Non-Aromatics Adsorptive Separation, respectively. The industrial mode of operation, the UOP Sorbex technology, is described in Chapters 7 and 8. 

In this particular case, the adsorption process can be used to overcome the distillation limitation. This is demonstrated in Figure 6.2, which represents the relative adsorption of C5 and C(, Hnear, branched and cycHc paraffins from the liquid phase of the 5A adsorbent used in the HOP GasoHne Molex process, licensed by HOP. In this process, only Hnear paraffins can enter the pores of 5A zeolite, while branched and cyclic paraffins are completely excluded due to their large kinetic diameters. Also, the selectivity for Hnear paraffins with respect to other types of paraffins is infinite. Consequently, the separation of Hnear paraffins from branched and cyclic paraffins becomes possible. 

Liquid phase zeoHtic separation includes two main events adsorption and desorption. Adsorption of an adsorbate (liquid component being adsorbed by solid) onto zeolitic adsorbent is dictated by the characteristics of the adsorbate-adsorbent interaction. A zeolitic adsorbent is a crystalline porous solid having particular characteristics (see Chapter 2). When immersed in a liquid mixture, the porous... 

When developing a liquid phase adsorptive separation process, a laboratory pulse test is typically used as a tool to search for a suitable adsorbent and desorbent combination for a particular separation. The properties of the suitable adsorbent, such as type of zeolite, exchange cation and adsorbent water content, are a critical part of the study. The desorbent, temperature and liquid flow circulation are also critical parameters that can be obtained from the pulse test. The pulse test is not only a critical tool for developing the equilibrium-selective adsorption process it is also an essential tool for other separation process developments such as rate-selective adsorption, shape-selective adsorption, ion exchange and reactive adsorption. 

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. 

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... 

Major industrial adsorption processes using zeolite adsorbents may be classified as follows (I) hydrocarbon separation processes, (II) drying gases and liquids, (III) separation and purification of industrial streams, (IV) pollution control applications, and (V) nonregenerative applications. Some important commercial processes in each of these areas are discussed briefly. 

Adsorption. Although several types of microporous solids are useful as adsorbents for the separation of vapor or liquid mixtures, the distribution of pore diameters does not enable separations based on the molecular-sieve effect. The most important molecular-sieve effects are shown by crystalline zeolites. The sieve effect ntay be total or partial. 

Very often the liquids to be processed may be contaminated with substances detrimental to some types of zeolites consequently a complete knowledge of the process stream composition and physical properties must be available before preliminary sieve selection can be made. In the absence of prior knowledge of separation factors, competitive co-adsorption, environmental stability, regeneration techniques, or irreversible zeolite contamination, zeoli te contamination, zeolite specification must be proceded by time-con-... 

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