Zeolites hydrocarbon separation

The second part of the book covers zeolite adsorptive separation, adsorption mechanisms, zeolite membranes and mixed matrix membranes in Chapters 5-11. Chapter 5 summarizes the literature and reports adsorptive separation work on specific separation applications organized around the types of molecular species being separated. A series of tables provide groupings for (i) aromatics and derivatives, (ii) non-aromatic hydrocarbons, (iii) carbohydrates and organic acids, (iv) fine chemical and pharmaceuticals, (v) trace impurities removed from bulk materials. Zeolite adsorptive separation mechanisms are theorized in Chapter 6. 

Molecular sieves are used in a variety of fuel processing applications. Uses include drying and water removal from fuel, product purification, hydrocarbon separation and catalysis. Molecular sieves are composed of sodium and calcium aluminosilicate crystals which have been produced from natural or synthetic zeolite compounds. The crystals are dehydrated through heating and are processed to ensure that pore sizes are tightly controlled. 

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. 

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. 

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. 

McCabe-Thiele diagrams for nonlinear and more practical systems with pertinent inequality constraints are illustrated in Figures 11 and 12. The convex isotherms are generally observed for zeolitic adsorbents, particularly in hydrocarbon separation systems, whereas the concave isotherms are observed for ion-exchange resins used in sugar separations. 

Dong J, Lin YS, and Liu W. Multicomponent hydrogen/hydrocarbon separation by MFI-type zeolite membranes. AIChE J 2000 46(10) 1957-1966. 

A brief list of some important separations which are carried out with zeolite adsorbents is given in Table 1.3. A much more comprehensive list has been given by Collins and reprinted by Breck. The large majority of these applications are purification processes in which the zeolite is used as a selective adsorbent to remove an undesirable impurity such as water, HjS, or radioactive Kr. Important examples of true separation processes include the linear/branched chain hydrocarbon separation, carried out with zeolite A and the separation of xylene isomers which utilizes various cationic forms of the X and Y zeolites. Some of these processes are considered in greater detail in Chapters 10-12. 

ENSORB [ExxoN adSORBtion] A process for separating linear from branched hydrocarbons, using a zeolite molecular sieve. The adsorbed gases are desorbed using ammonia. It operates in a cyclic, not a continuous, mode. Developed by Exxon Research Engineering Company, and used by that company on a large scale at the Exxon refinery in Baytown, TX. Asher, W. J., Campbell, M. L., Epperly, W. R., and Robertson, J. LHydrocarbon Process., 1969, 48(1), 134. 

IsoSiv [Isomer separation by molecular sieves] A process for separating linear hydrocarbons from naphtha and kerosene petroleum fractions. It operates in the vapor phase and uses a modified 5A zeolite molecular sieve, which selectively adsorbs linear hydrocarbons, excluding branched ones. Developed by Union Carbide Corporation and widely licensed, now by UOP. The first plant was operated in Texas in 1961. By 1990, more than 30 units had been licensed worldwide. See also Total Isomerization. 

Molex A version of the Sorbex process, for separating linear aliphatic hydrocarbons from branched-chain and cyclic hydrocarbons in naphtha, kerosene, or gas oil. The process operates in the liquid phase and the adsorbent is a modified 5A zeolite the pores in this zeolite will admit only the linear hydrocarbons, so the separation factor is very large. First commercialized in 1964 by 1992, 33 plants had been licensed worldwide. See also Parex (2). 

MS-2 A molecular sieving processes for separating branched-chain aliphatic hydrocarbons from unbranched ones by selective adsorption on a zeolite. Developed by the British Petroleum Company in the 1970s but not commercialized. 

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... 

Parex (2) [Paraffin extraction] A process for separating linear aliphatic hydrocarbons from branched-chain and cyclic hydrocarbons by means of a zeolite 5 A adsorbent. The products are desorbed with a mixture of steam and ammonia. Developed in the mid-1960s by Luena-Werke and Schwedt in East Germany and operated in East Germany, Bulgaria and the USSR. Broadly similar to Molex and not to be confused with Paiex (1). 

TSF [Texaco Selective Finishing] A process for separating linear from branched-chain aliphatic hydrocarbons by PSA, using zeolite 5A as the adsorbent. The desorbent is a hydrocarbon having two to four carbon atoms less than the feed. Developed by Texaco in the late 1950s. Believed to be still in operation in its Trinidad refinery as of 1990. 

Calcium aluminate chloride, phase in Portland cement clinker, 5 472t Calcium aluminate fluoride, phase in Portland cement clinker, 5 472t Calcium aluminoferrite, phase in Portland cement clinker, 5 472t Calcium aluminoferrite hydrate, 5 477t Calcium—aluminum alloys, 4 530 Calcium amalgam, 22 773 Calcium ammonium nitrate, 2 724 Calcium analysis, of water, 26 37 Calcium A zeolite, separation of hydrocarbons by, 16 823 Calcium—barium—silicon alloy, 22 519 Calcium-bearing manganese silicon,... 

Catalytic dewaxing, in which straight-chain paraffin hydrocarbons are selectively cracked on zeolite-type catalysts, and the lower-boiling reaction products are separated from the dewaxed lubricating oil by fractionation. 

In 1962 Mobil Oil introduced the use of synthetic zeolite X as a hydrocarbon cracking catalyst In 1969 Grace described the first modification chemistry based on steaming zeolite Y to form an ultrastable Y. In 1967-1969 Mobil Oil reported the synthesis of the high silica zeolites beta and ZSM-5. In 1974 Henkel introduced zeolite A in detergents as a replacement for the environmentally suspect phosphates. By 2008 industry-wide approximately 367 0001 of zeolite Y were in use in catalytic cracking [22]. In 1977 Union Carbide introduced zeolites for ion-exchange separations. 

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