Options for Nitriles Removal from C - American Chemical Society

This option uses a proprietary catalyst9,10 for the simultaneous hydrogenation of nitriles and diolefins with high selec- tivity (>90%) to increase th...
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Ind. Eng. Chem. Res. 2002, 41, 5385-5392

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Options for Nitriles Removal from C4-C5 Cuts: 2. via Catalytic Hydrogenation M. M. Ramı´rez-Corredores,* T. Romero, D. Djaouadi, Z. Herna´ ndez, and J. Guerra PDVSA Intevep, Refinacio´ n y Petroquı´mica, Apartado 76343, Caracas 1070A, Venezuela

C4 and C5 cuts from FCC units can be useful in the preparation of oxygenates such as MTBE, ETBE, and TAME. Removal of the nitriles and diolefins present in these feedstocks is required to avoid poisoning of the etherification catalyst. Technological options include water washing and adsorption for nitriles and selective hydrogenation for the diolefins. PDVSA Intevep has developed several methods to address this problem. One includes nitrile removal by adsorption (part 1 of this work, Ramı´rez-Corredores, M. M.; Herna´ndez, Z.; Guerra, J.; Medina, J.; Alvarez, R. Adsorption, manuscript submitted), and two others are based on catalytic conversion. In this paper, we discuss the critical features of a catalytic system for the simultaneous hydrogenation of nitriles and diolefins. A very high selectivity so as to inhibit saturation of the mono-olefins is also desired in such catalyst. Different metal phases and support materials were evaluated and characterized. Both model and real feedstocks were considered for evaluation at the bench and pilot-plant scales. Characterization methods used include chemical composition analysis, temperature-programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS). A particular oxidation state of the metal phase and the nitrile adsorption capability of the support material were found to be the key properties of the developed catalytic system. 1. Introduction The original motivation of this work was to remove the poisoning components from the C4 and C5 streams of FCC units, which are fed into etherification units for the MTBE and TAME production. However, the situation has changed in the U.S. since the use of such additives as gasoline components was banned in California. That is not the situation in other U.S. states or in the rest of the world, where California’s concerns are still under consideration. On the other hand, nitrile removal (from such reactive cuts) or conversion into more valuable products might be of interest for different applications. Regarding etherification processes, catalyst life is one of the major concerns. All commercially available etherification technologies employ the same family of acidic ion-exchange resin catalysts, which are susceptible to the same type of poisons. Of these poisons, basic compounds, metal cations, and nitriles cause neutralization of the acidic sites on the catalyst. Propionitrile and acetonitrile (ACN) are the main nitrile poisons in the C4-C5 cut. ACN can be effectively removed by means of a water wash. However, goodquality water is not always available to the refinery and might be costly to supply, particularly in dry areas. Furthermore, for propionitrile, its lower solubility in water requires 4-5 times more water for removal to the same low levels as ACN. Hence, water washing is neither effective nor economical for propionitrile removal. Under such situations, an adsorption process could be economically viable,1,2 but in the presence of a high diolefin content, hydrogenation might be an option. Obviously, there are known processes and catalysts for hydrogenating unsaturated compounds in liquid hydrocarbon feedstocks, such as nitriles3 and dienes.4 * Corresponding author. Phone: (58-212) 908 6055. Fax: (58-212) 908 7230. E-mail: [email protected]

Although Pd is the preferred active phase for the hydrogenation of almost any unsaturation, non-noblemetal catalysts are also employed. However, the severity under which each process is operated differs depending on whether it is used for diolefins or for nitriles. Under conditions where nitriles are hydrogenated, the diolefins will be completely saturated. Clearly, investment costs might be decreased if these two types of compounds could be hydrogenated in the same unit while still maintaining the desired selectivity in diolefins hydrogenation. Accordingly, the object of this work was to develop a catalyst useful for the simultaneous and selective hydrogenation (SSH) of diolefins and nitriles present in a hydrocarbon feedstock and, more particularly, those used in etherification reactions. A great number of catalysts have been developed for the selective conversion of nitriles to amines, with Raney nickel being the most frequently used. Selectivity in nitrile hydrogenation refers to avoiding the hydrogenation of any other unsaturation present in the molecule. The most common use of the Raney nickel catalyst is the preparation of primary alkylamines, unsaturated secondary or tertiary amines and particularly fatty acid amines. Herkes5 developed a chromium-promoted Raney nickel-cobalt catalyst that, in the presence of water, produces diamines from dinitriles. Borninkhof et al.6 used a catalyst containing nickel, copper, and/or cobalt promoters for the preparation of secondary alkylamines from alkylnitriles, where the alkyl branch contains 2-30 carbon atoms, with carbon-carbon unsaturated bonds as well as aromatic rings. Abe et al.7 presented a method for primary or secondary aliphatic amine preparation from the corresponding nitrile without hydrogenation of the unsaturated C-C bonds of the molecule. The process uses a copper catalyst promoted with manganese, iron, cobalt, nickel, or zinc; it can also contain alkaline metals such as lithium, sodium, potassium, or cesium and rare earth metals. It seems that first raw

10.1021/ie0105932 CCC: $22.00 © 2002 American Chemical Society Published on Web 09/25/2002

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Figure 1. SSH process scheme.

transition metals are good candidates for the selective hydrogenation of unsaturated C-N bonds, when other C-C unsaturations are present in the same molecule. Concerning unsaturated hydrocarbons, great emphasis has been placed on the selective hydrogenation of acetilenic and diolefinic compounds using nickel catalysts (with Ni contents between 1 and 20%), nickel oxide supported on alumina, and in some cases sulfiding pretreatment.8 The object of the present work is to describe one of the technologies that PDVSA Intevep has developed for the hydrogenation of both nitriles and diolefins, with such a selectivity that mono-olefins are not hydrogenated. On one hand, the simultaneous hydrogenation of these compounds and, on the other, the possibility of diminishing the needed severity for nitrile hydrogenation were motivating factors of this work. This option uses a proprietary catalyst9,10 for the simultaneous hydrogenation of nitriles and diolefins with high selectivity (>90%) to increase the mono-olefin content in the original feedstock. The catalyst comprises a support material selected from the group consisting of an inorganic oxide-zeolite composite, carbon, or zeolite. The most important particularity of the support material is its capability for nitrile adsorption. Thus, the PDVSA Intevep proprietary adsorbent materials used in the NAP technology, previously described1 in the first part of this work, constitute the preferred support materials for this type of catalyst. The reduction state of the active phase has a determining effect on the catalytic properties and constitutes the main focus of this issue. Of course, support materials also affect the reducibility of the metal phases and the stability of the resulting reduced species, and so, they are considered here as well. The process scheme sketched in Figure 1 shows how the selective and simultaneous hydrogenation (SSH) process can be integrated into an etherification unit. The nitrogen compounds produced upon hydrogenation can be washed downstream or removed by a guard bed. 2. Experimental Section 2.1. Catalyst Characterization. To study the oxidation state of the catalysts, two series of five catalysts each, using Cu and Ni as the active phases, were prepared by incipient impregnation on the powder supports. The supports, namely, Na-Y zeolite (LZY52 from Union Carbide), alumina (CP3 from ALCOA), and their mixtures (25, 50, and 75%), were dried at 120 °C for 4 h and then calcined at 450 °C for 5 h. The supports were impregnated with a solution of the metal nitrate and then dried and calcined at 120 and 450 °C for 2 and 8 h, respectively.

The catalysts are identified using the metal symbol followed by the nominal concentration (for example, Cu5 stands for 5 wt % Cu) and a slash prior to the support acronym. The supports are identified with a Z for Na-Y zeolite, followed by its content in the support, i.e., Z25, Z50, and Z75 are Na-Y zeolite-alumina mixtures containing 25, 50, and 75 wt % Na-Y zeolite, respectively. The Z0 support represents alumina, of course. The active metal concentration on each catalyst was varied between 1, 5, and 10%, nominally. The elemental chemical composition was determined by atomic absorption. Temperature-programmed reduction (TPR) profiles were recorded as the hydrogen uptake of a calcined (50100 mg) catalyst specimen previously dried at 120 °C under a nitrogen flow rate of 100 cm3/min for 2 h. A quartz microreactor was loaded with a sample, and after the sample had been dried and cooled, the nitrogen flow was replaced by a 5% hydrogen in argon mixture at a flow rate of 30 cm3/min. The reactor was then heated at 7.5 °C/min until it reached a temperature of 800 °C while the TPR profile was recorded using a thermal conductivity detector. X-ray photoelectron spectra (XPS) of the calcined and reduced catalysts were obtained using an aluminum anode (KR ) 1486.6 eV) in an LHS-11 instrument. The signals corresponding to C 1s, Si 2p, Al 2p, O 1s, and Cu or Ni 2p were recorded, and their binding energies (BEs) were calculated taking the C 1s (284.6 eV) line as the reference. The reduced form of the catalyst, used for XPS characterization, was obtained by heating in hydrogen at 250 °C (for Cu) or 450 °C (Ni) for 2 h. The Cu/Si and Cu/Al ratios were determined as an indirect measure of the surface dispersion; the higher the surface ratio, the higher the dispersion. Because Si is the major support metal at the surface of the zeolite-supported catalysts, we considered the Si concentration as indicative of the support concentration, for comparison of the dispersion values. The surface-to-bulk concentration ratios (XPS/CA, where CA is the value of the concentration obtained from chemical analysis) were evaluated as a mean to assess the effect of the reduction treatment. 2.2. Catalyst Evaluation. The conversion of diolefins and nitriles was carried out simultaneously in the same reactor under conditions similar to those used for the selective hydrogenation of diolefins (temperatures between 50 and 250 °C; pressures of 150-650 psi; and at a liquid hourly space velocity, LHSV, between 1 and 4.5 h-1). Several catalyst formulations were considered in this study; the support materials included alumina, clays, carbon, and zeolite Na-Y, together with some mixed supports composed of mixtures of pairs of them. The composite supports denoted zeolite-alumina and zeolite-clay contain 15% Na-Y zeolite. First, monometallic catalysts were considered, in which the active metals consist of group VIII metals, such as Pd, Ni, and Co, and Cu as an example of a group IB metal. Two different reducing treatments were employed. When partial reduction is mentioned, it was accomplished under the following conditions: temperature 150-300 °C, pressure 15-350 psi H2, flow rate 0.1-8.0 L/h. Complete reduction was carried out under the following conditions: temperature 200-600 °C, pressure 15-350 psi H2, flow rate 0.1-8.0 L/h.

Ind. Eng. Chem. Res., Vol. 41, No. 22, 2002 5387 Table 1. Feedstock Characteristics FCC naphtha C3 C4 C4d C5 C5d iC5 C6+ diolefins

synthetic

conversion (%)

composition (wt %) 0.00 2.92 6.98 38.25 25.56 25.96 0.40 3

0.00 0.00 0.00 98.00 1.00 0.00 0.00 0.5

nitriles (ppmv) 0.24 80.17 80.40

0.00 5000 5000

acetonitrile propionitrile total basic nitrogen (ppm) total sulfur (ppm) mercaptans (ppm) water (ppm)

1.45 40 400 °C. In summary, there seems to be a variety of Cu species distributed on each of the support components. The oxidation state of each of those species depends on the reducing conditions. The binding energy values and oxidation states determined by XPS were evaluated for catalysts containing 5 and 10 wt % of metal (Table 4). The Cu 2p XPS spectrum of the Cu5/Z0 fresh catalyst is centered at a binding energy of 933 eV, which is low compared to the values of 934.4 and 935 eV observed for CuO and CuAl2O4, respectively.15 The satellite line attributed to the presence of Cu2+ was not observed for this catalyst. The Auger parameter was calculated to be 1847.8 eV, which might correspond to the oxidation state of Cu+. After reduction at 250 °C, the binding energy shifted slightly to 932.5 eV and the Auger parameter became 1848.4, reconfirming the presence of Cu+. The Cu+ state of copper should correspond to a very strong interaction with the support. That interaction probably leads to the distribution of the Cu species only at the very top layers of the alumina (thus making it undetectable by XRD), as in the Friedman et al. model of the Cu-alumina catalyst.14 However, one might think also of a reducing effect of the high-vacuum conditions of the XPS spectrometer, as has been already proposed,21 which would preferentially affect the top-layer species. The reducibility of bulk Cu-Al-O spinel has been followed by XPS,22 and only a very small proportion of the Cu2+ species was reduced to Cu0 at 250 °C. In our catalyst, exhibiting such a strong interaction between the CuAl system, the observation of a complete reduction of the Cu surface spinel seems unlikely. The results obtained for the bulk chemical analysis (CA) and surface chemical composition (XPS) of the copper catalysts have been summarized in Table 5. The surface-to-bulk metal ratio (XPS/CA), together with the dispersion values (Cu/Si and Cu/Al ratios) obtained by both techniques, are also included. The Cu/Al XPS intensity ratio of the reduced Cu5/Z0 catalyst decreases nearly 40% compared to the catalyst in its oxide form (Table 5). This might indicate a significant dispersion decrease during the reduction process, which might be due to the sintering of the Cu species, leading to the

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formation of larger Cu particles. Because the particles seem to be growing during reduction by a factor of almost 2 in size (40% decrease in dispersion) and the species are still Cu+, a very strong stabilizing support effect must be inhibiting them from reducing further than Cu+. For the zeolite-supported catalyst, the presence of Cu2+ was evidenced by a satellite line of low intensity observed in the spectra of the fresh catalysts. However, the binding energy (932.9 eV) was too low to be associated with the presence of CuO.14 The binding energy of the Cu2p3/2 signal from ion-exchanged copper in zeolite cages has been reported to be higher than that observed for bulk copper oxides.15,16 Meanwhile, the Auger parameter was found to be 1846.9 eV, which corresponds instead to the Cu+ species. The presence of Cu+ in a Cu/Na-Y zeolite was explained as being due to a selfreduction process,23 in which approximately 25% of the Cu2+ convert to Cu+ by the action of water and framework oxygen ions through the reactions

H2O + Cu2+ + Z-O f [Cu(OH)]+ + Z-OH 2[Cu(OH)]+ f 2Cu+ + H2O + 1/2O2 Although an evaluation of the population distribution of the several copper species present in zeolite-containing catalysts can be pursued by means of characterization techniques, a deeper comparative study is needed to establish their relative reactivities. On the reduced zeolite catalysts, the presence of Cu0 is evidenced by a binding energy value of 932.5 eV, with an Auger parameter of 1851.1 eV. Regardless of the copper content, the behaviors of the dispersion (Cu/Si) values upon reduction are similar for all catalysts. The dispersion value diminished to Cu/Si ) 0.06, when the catalyst is reduced. The value of the CuXPS/CuCA ratio can also be taken as a measure of the particle size of the outermost copper crystallites, i.e., the copper species on the external surface of the zeolite particles. The large value (1.33) observed for Cu5/Z100 is a clear indication that, during impregnation, the metal species were distributed not only within the internal zeolite area but also over the outermost surface. This is consistent with the TPR data showing at least two species. The two locations are evident from the XPS Cu 2p line. The high CuXPS/CuCA value observed in the Cu5/Z100 fresh catalyst indicates a larger particle population on the outermost surface of the zeolite crystals, which directly implies a lower population of Cu species inside the cages. Comparing this value with that obtained for the Cu10/Z100 catalyst (Table 5) with an increased copper content, the outermost particle population does not seem to grow, but the particle size grows instead. Upon reduction, sintering is induced by the original existence of large copper particles in the fresh catalyst. However, the implications derived from the variations in the value of the CuXPS/CuCA ratio on species migration cannot be ignored. The mobility of copper ions in zeolites, mainly Cu2+ in Y-zeolite, has been proposed as the determining factor for the formation of Cu+ species.22 Also, the mobility of Cu+ has been assigned as being responsible for the reversibility of the redox cycle between Cu+ and Cu0. The XPS results of the present work seem to indicate a migration of the copper species from the outermost surface to inside the cages upon reduction. This effect is even higher at higher Cu

Table 6. Effect of the Support Material on Percent Conversion for Pd Catalysts conversion (%) run

support

[Pd] (%)

diolefins

mono-olefins

nitriles

9 10 11

γ-alumina C γ-alumina

1 0.3 0.3

100 100 100

88 0 30

18 50 20

content. Shpiro et al. reported similar observations24 for catalysts prepared by impregnation and by ion exchange. They also observed a larger decrease in the Cu/ Si ratio after a reduction compared to that observed upon calcination. Jacobs et al.23 also proposed that the limited reduction of the copper species inside the zeolite cages, producing an unbalance presence of Cu+, might create a driving force for ion migration from the external surface toward the cage. Thus, the outermost surface might be enriched with ionic copper species that migrate there during calcination, but on reduction, only small clusters of metallic copper remain there, and others form within the cage by migration from the external surface. Thus, by controlling the reduction conditions, combining different redox cycles, and regulating the copper content, one can adjust the population distribution of the copper species. In summary, the copper catalysts prepared by impregnation of Na-Y zeolite showed a distribution of copper species, namely, species inside the cages (occupying exchange positions) and others on the outermost surface of the zeolite particles. On alumina-based catalysts, a model can be proposed as formed by a surface copper spinel, CuAl2O4, on which CuO begins to appear at high metal content. The interaction with the support decreases the reduction temperature of the oxide species as compared to that exhibit by bulk CuO. The dispersion of the metal oxide and ion migration strongly affect the reduction of the copper species. The high mobility of the copper species involves not only those ions inside the cages but also migration from the external surface of the zeolite to the cages. During reduction, the migration follows the reverse pattern from that followed upon oxidation. Finally, the roles in the activity and selectivity for the hydrogenation of nitriles and diolefins of completely reduced species of group VIII metals and partially reduced species of group I metal have been confirmed. Effect of the Support Material. In addition to the aspects already discussed for the Cu case on the effect of the metal-support interaction, the chemical nature of the support material also affects the performance of the catalysts. To observe the effect of the catalyst support on activity and selectivity, Pd catalysts supported on carbon and alumina were prepared and evaluated. The results are shown in Table 6. The carbon-supported catalyst (run 10) was effective for the simultaneous hydrogenation of diolefins and nitriles in a selective manner, whereas the γ-aluminasupported catalysts (runs 9 and 11) achieved no selective conversion of diolefins and low conversions of nitriles. Although the alumina catalysts contain the active species to hydrogenate the diolefins and nitriles simultaneously, selectivity cannot be achieved. The results lead one to conclude that the carbon and zeolite present in the inorganic oxide-zeolite composites are effective catalyst supports for this type of catalysts. Both the zeolite and the carbon contain the optimum nitrileadsorbing sites that are believed to be responsible for

Ind. Eng. Chem. Res., Vol. 41, No. 22, 2002 5391 Table 8. Effect of Complete Reduction of Metal Phase conversion (%) catalyst

metal ratio

support

diolefins

nitriles

Ni Ni/Cu Ni/Co Ni/Fe

2:1 2:1 2:1

zeolite-clay zeolite-clay zeolite-clay zeolite-clay

100 77 100 100

97 79 100 95

Table 9. Effect of Appropriate Reduction of Group IB Metal Phase conversion (%)

Figure 4. Pilot-plant test results (Ni catalyst). Table 7. Catalytic Performance of Bimetallic Catalysts conversion (%) catalyst

metal ratio

support

diolefins

nitriles

Ni Ni/Cu Ni/Cu Ni/Cu Ni/Cu Ni/Cu Ni/Cu Ni/Co Ni/Fe Ni/Fe Ni/Fe

1:1 1:2 2:1 2:1 7:1 40:1 1:1 1:1 1:2 2:1

zeolite-clay zeolite-clay zeolite-clay zeolite-clay zeolite-alumina zeolite-alumina zeolite-alumina zeolite-clay zeolite-clay zeolite-clay zeolite-clay

75 96 83 92 100 95 91 88 80 80 89

73 79 77 74 95 97 89 93 94 42 82

the superior activity characteristics of the catalysts of the present work. We have found that, to address activity, selectivity, and simultaneity, the catalytically active phase deposited on the support material must consist of a partially reduced group IB metals or completely reduced group VIII metals. Moreover, the support material must exhibit the capability for adsorbing nitriles. This proposed model of the catalyst led us to speculate inon possible ways to decrease the severity needed for nitrile hydrogenation. The nitrile-adsorbing sites might be located close to metal sites capable of activating hydrogen. That proximity might allow nitrile hydrogenation to proceed, even though activated hydrogen could also be spilled over onto adsorbed nitrile molecules. Once the bench-scale testing was completed, a pilotplant evaluation was carried out using a Ni catalyst. The results obtained with the FCC feedstock whose characteristics are collected in Table 1 initially indicated total conversion of diolefins and nitriles (Figure 4). However, whereas diolefin hydrogenation was complete and stable, the nitrile hydrogenation activity deactivated after 24 h on stream. Two alternatives were proposed to address the deactivation problem. On one hand, catalyst improvements were considered, as described in the next section, and on the other, a process scheme modification was developed that will be the subject of another paper comprising part 3 of this work.25 3.2. Bimetallic Catalysts. The first approach tested for improving catalyst stability was the incorporation of a second metal into the formulation. The second metal was selected from among those already described as exhibiting the desired functionality (simultaneity and selectivity). The results collected in Table 7 show the performance of bimetallic catalysts prepared and activated as previously detailed. The metal phase consists of 12 wt % total metal content of two different metals in the specific atomic ratio shown in Table 7 for each catalyst. The support materials were already described in the Experimental Section.

catalyst

metal ratio

support

diolefins

nitriles

Ni Ni/Cu Ni/Co

2:1 2:1

zeolite-clay zeolite-alumina zeolite-clay

100 100 100

73 100 100

Table 10. Performance of Bimetallic Catalyst conversion (%)

catalyst

metal ratio

Ni Ni/Fe Ni/Co

2:1 2:1

original FCC feedstock partial/complete reduction diolefins nitriles 75/100 89/100 88/100

73/90 82/100 95/100

doped feedstock diolefins nitriles 100 100 100

73 32 100

This first screening was oriented toward the selection of active catalysts that simultaneously hydrogenate diolefins and nitriles. As can be seen in Table 7, with the exception of one of the Ni-Fe catalysts, all of the others showed improved activities compared to the corresponding monometallic systems. A subsequent test (see Table 8) in which the catalysts were completely reduced before testing showed the negative effect of complete reduction for the group IB catalysts. Although the performance of the group VIII metals catalysts was excellent, that of the group-IBcontaining catalyst was rather poor. However, it was found that alumina present in composite supports stabilizes the partially reduced group IB metal species. Thus, we examined the possibility of keeping the partially reduced group IB species through the complete reduction of the group VIII metal(s) when both metals are present in the same catalyst. To this end, a zeolitealumina support was first impregnated with the group IB metal and then calcined and activated through the partial reduction of the group IB metal. This step was followed by impregnation with group VIII metal(s) and calcination and activation through the complete reduction of the group VIII metal(s). The results are shown in Table 9. In summary, achieving a suitable metal combination is the result of careful selection of the preparation method, impregnation sequence, and activation procedure. After confirming the suitability of some of the catalyst for simultaneous hydrogenation of diolefins and nitriles, a test was carried out to examine their stability. Because deactivation is thought to be caused by a nitrile reaction product, the original feedstock was doped with an additional amount of propionitrile (200 ppm), and the initial activity values were compared for the two feedstocks (original and doped). The results can be seen in Table 10, where the effect of reduction state is included to verify the findings for monometallic catalysts in the bimetallic systems. The results show not only how complete reduction for group VIII metals favors the activity, but also how the enhancing effect of Co possibly increases the stability.

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In the case of Fe as the promoter, although the initial activity was improved at low nitrile concentration compared to that of the monometallic Ni catalyst, it is most likely that neither stability nor a good performance at high nitrile concentrations would be attained. Although a long-term run is required to confirm stability, one might expect that these bimetallic catalysts would be particularly useful and stable for the simultaneous and selective hydrogenation of diolefins and nitriles. 4. Conclusions Conceptually, at the molecular level, we considered that, if a catalytic support exhibited an adsorbing capacity for nitriles and the active phase were conceived as a metallic phase that is able to generate active hydrogen (“spilled over hydrogen”), the outlined objective of simultaneity could be achieved. We found that, to address activity, selectivity, and simultaneity, the catalytically active phase deposited on the support material must consist of a partially reduced group IB metal or a completely reduced group VIII metal. The activation process conditions have to be perfectly controlled, so as to achieve the proper reduction state of the active metals. Changes in the catalyst preparation method and incorporation of a second metal were shown to improve the nitrile hydrogenation activity. The combination of the active metals already mentioned did not show any decrease in either the activity or the selectivity, allowing for better overall performance. The hydrogenation option presented might be useful for nitrile removal either when the diolefins concentration is too high, so that it causes premature adsorbent deactivation (adsorption is not an option) or when the process has to be applied in stand-alone mode (in the absence of an etherification unit). Literature Cited (1) Ramı´rez-Corredores, M. M.; Herna´ndez, Z.; Guerra, J.; Medina, J.; Alvarez, R. Adsorption, manuscript submitted. (2) Polzer, M. E.; Glasgow, B. Presented at the CDTech Technology Conference, Los Angeles, CA, Sep 20-23, 1998. (3) Volf, J.; Pasek, J. Catalytic Hydrogenation. Stud. Surf. Sci. Catal. 1986, 27, 105. (4) Eleazar, A. E.; Heck, R. M.; Witt, M. P. Hydroc. Proc. 1979, May, 112. (5) Herkes, F. E. U.S. Patent 4,885,391, 1989. (6) Borninkhof, F. European Patent 0384542 A1, 1990. (7) Abe, H. European Patent 0372544 A2, 1990. (8) (a) Langhout, W. C. U.S. Patent 3,234,298, 1966. (b) Cosyn, J. U.S. Patent 3,472,763, 1969. (c) Gattuso, M. J. U.S. Patent 4,695,560, 1987. (d) Gattuso, M. J. U.S. Patent 4,734,540, 1988.

(9) Ramı´rez de Agudelo, M. M.; Romero, T.; Guerra, J.; Medina, M. U.S. Patent 5,523,271, 1996. (10) Ramı´rez de Agudelo, M. M.; Romero, T.; Guerra, J.; Medina, M. U.S. Patent 5,663,446, 1997. (11) Ramı´rez de Agudelo, M. M.; Dajauadi, D.; Guerra, J. U.S. Patent 5,948,942, 1999. (12) Ramı´rez de Agudelo, M. M.; Djaouadi, D.; Guerra, J. El Niquel Soportado en Mezclas de Zeolita-Alumina y su Rol en Hidrogenacion. In Proceedings of the Symposium on Iberoamerican Catalysis; Cordoba, Argentina, 1996; Vol. 2, pp 1191-1196. (13) Gentry, E. D.; Hurst, N. W.; Jones, A. Study of the Promoting Influence of Transition Metals on the Reduction of Cupric Oxide by Temperature Programmed Reduction. J. Chem. Soc., Faraday Trans. 1 1981, 77, 603. (14) Friedman, R. M.; Freeman, J. J.; Lytle, F. W. Characterization of Cu/Al2O3. J. Catal. 1978, 55, 10. (15) Strohmeier, B. R.; Leyden, D. E.; Field, R. S.; Hercules, D. M. Surface Spectroscopic Characterization of Cu/Al2O3 Catalysts. J. Catal. 1985, 94, 514. (16) Dumas, J. M.; Geron, C.; Kribii, A.; Barbier, J. Preparation of Supported Copper Catalysts. Appl. Catal. 1989, 47, L9. (17) Jalowiecki, L.; Wrobel, G.; Daage, M.; Bonnelle, J. P. Structure of Catalytic Sites on Hydrogen-Treated Copper-Containing Spinel Catalysts. J. Catal. 1987, 107, 375. (18) Dow, W. P.; Wang, Y. P.; Huang, T. J. Yttria-Stabilized Zirconia-Supported Copper Oxide Catalyst. J. Catal. 1996, 160, 155. (19) Jacobs, P. A.; Tielen, M.; Linart, J. P.; Nijs, H.; Uytterhoeven, J. B.; Beyer, H. Redox Behaviour of Transition Metal Ions. J. Chem. Soc., Faraday Trans. 1 1976, 72, 2793. (20) Jacobs, P. A.; Linart, J. P.; Nijs, H.; J. Uytterhoeven, B.; Beyer, H. Redox Behaviour of Transition Metal Ions in Zeolite. J. Chem. Soc., Faraday Trans. 1 1977, 73, 1745. (21) Liu, W.; Flytzani-Stephanopoulos, M. Total Oxidation of Carbon Monoxide and Methane over Transition Metal-Fluorite Oxide Composite Catalysts. J. Catal. 1995, 153, 317. (22) Bechara, R.; Aboukais, A.; Bonnelle, J. P. X-Ray Photoelectron Spectroscopic Study of a Cu-Al-O catalyst under H2 or CO Atmosphere. J. Chem. Soc., Faraday Trans. 1 1993, 89 (8), 1257. (23) Jacobs, P. A.; De Wilde, W.; Schoonheyt, R.; J. Uytterhoeven, B.; Beyer, H. Redox Behaviour of Transition Metal Ions in Zeolites. J. Chem. Soc., Faraday Trans. 1 1976, 72, 1221. (24) Shpiro, E. S.; Gru¨nert, W.; Joyner, R. W.; Baeva, G. N. Nature, Distribution and Reactivity of Copper Species in overexchanged Cu-ZSM-5 Catalysts: An XPS/XAES Study. Catal. Lett. 1994, 24, 159. (25) Ramı´rez-Corredores, M. M.; Herna´ndez, Z.; Guerra, J.; Alvarez, R.; Medina, J. Options for Nitriles Removal from C4-C5 Cuts: 3. Catalytic hydrogenation using the Swing Reactive Removal (SRR) Process. Fuel Technol. Process., manuscript submitted.

Received for review July 12, 2001 Revised manuscript received July 1, 2002 Accepted July 29, 2002 IE0105932