Zeolite Separation Processes

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). 

MOLPSA-nitrogen [Molecular sieve pressure swing adsorption] A version of the PSA process for separating nitrogen from air, developed by Kobe Steel. Most PSA processes for nitrogen use molecular sieve carbon as the adsorbent, but this one uses zeolite X. Water and carbon dioxide are first removed in a two-bed PSA system, and then the nitrogen is concentrated and purified in a three-bed system. 

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... 

OXYWELL A process for separating oxygen from air by PSA, using vacuum desorption from a zeolite. Used for medical oxygen generators, hence the name. Developed by Nippon Sanso. 

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). 

Total Isomerization Also called TIP. An integrated process which combines light paraffin isomerization, using a zeolite catalyst, with the IsoSiv process, which separates the unconverted normal paraffins so that they can be returned to the reactor. Developed by Union Carbide Corporation and now licensed by UOP. The first plant was operated in Japan in 1975 by 1992, more than 25 units had been licensed. 

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. 

Industrial applications of zeolitic separation processes fall into the following general appHcation categories ... 

Barthomeuf D.M. (1986) Process for separating ethylbenzene from xylenes by selective adsorption on a Beta zeolite. U.S. Patent 4,584,424. 

Leflaive, P., Dubreuil, A.G., Gaullet, P., Patarin, J., and Paillaud, J.L (2005) Process for separation by selective adsorption on a solid containing a zeolite with a crystalline structure analogous to lM-12. F.R. Patent 2,877,237. 

Guo, G. and Long, Y. (2001) Process for separating p-xylene with hydrophobic silicic zeolite by selective adsorption. C.N. Patent 1,280,977. 

Aspects of Mechanisms, Processes, and Requirements for Zeolite Separation... 

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. 

Recognizing the need for a more economically and environmentally friendly citric acid recovery process, an adsorptive separation process to recover citric acid from fermentation broth was developed by UOP [9-14] using resin adsorbents. No waste gypsum is generated with the adsorption technique. The citric acid product recovered from the Sorbex pilot plant either met or exceeded all specifications, including that for readily carbonizable substances. An analysis of the citric acid product generated from a commercially prepared fermentation broth is shown in Table 6.2, along with typical production specifications. The example sited here is not related to zeolite separation. It is intent to demonstrate the impact of adsorption to other separation processes. 

I 6 Aspects of Mechanisms, Processes, and Requirements for Zeolite Separation Table 6.5 Base strengths of aromatic hydrocarbons relative to HF. 

Shape-selective adsorption, also known as molecular sieving, is a process that separates molecules based on inclusion or exclusion from specific zeolite pores. In contrast, the equilibrium- and rate-selective mechanisms are based on adsorb-... 

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