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813 *Author to whom all correspondence should be addressed. E-mail: [email protected]. Options for Nitriles Removal from C 4 −C 5 Cuts: 1. Via Adsorption Maria M. Ramírez-Corredores ∗ , Zaida Hernández, Julia Guerra, Jaqueline Medina and Rosa Alvarez PDVSA Intevep, Refinación y Petroquímica, Apdo. 76343, Caracas 1070A, Venezuela. (Received 19 January 2004; revised form accepted 19 August 2005) ABSTRACT: Light cuts from fluid catalyst cracking (FCC) units are commonly used as feedstocks for etherification units in oil refineries. These feedstocks contain nitriles and diolefins that poison the etherification catalyst. PDVSA Intevep has developed several methods for removing these nitriles. An adsorption- based option is discussed in this paper; two other options reported recently were based on catalytic conversions (Ramírez-Corredores et al. 2002, 2003). The oligomerization tendencies of the diolefins dictated the use of a rather inert adsorbent. Some of the critical features of this adsorbent and the adsorption process are discussed. The adsorbent design was based on a geometrical premise and on active non-acid sites to achieve a highly selective adsorbent with a high adsorption capacity for nitriles. Chemical shift was selected for the desorption stage of the removal process to preserve the active lifetime of the adsorbent in the treatment of reactive feedstocks. This was demonstrated to be both effective and beneficial. 1. INTRODUCTION The original motivation of this work was the removal of poisoning components from the C 4 and C 5 streams of FCC units, which are fed into the etherification units for the production of methyl t-butyl ether (MTBE), ethyl t-butyl ether (ETBE) and t-amyl methyl ether (TAME). However, the situation has changed in the USA since the prohibition in California on the use of these additives as gasoline components. The same situation does not apply in other US states or in the rest of the world, where the California concerns are still under consideration. Despite the situation in the USA, such concerns have not led to similar drastic decisions in European countries. In those countries, the removal of nitriles from reactive feedstocks or their conversion into value-added products might be of interest for a wide variety of applications. Catalyst life is one of the major concerns in etherification processes. All commercially avail- able etherification technologies employ the same family of acidic ion-exchange resin catalysts that are susceptible to the same type of poisons. The basic compounds, metal cations and nitriles derived from these poisons neutralize the acidic sites on the catalyst. Diolefins are highly reactive towards polymerization, forming gums that deposit on the catalyst surface. Typically, they may be selectively hydrogenated before or at the etherification reactor. Although nitriles do not directly affect the acidic functions of the etherification catalyst, they react with methanol and water in contact with the strong acid resin to form basic compounds that neutralize the acidic function of the catalyst. Propionitrile (PPN) and acetonitrile (ACN) are the main AST 23(10)-67-P4 2/5/06 1:06 pm Page 813
