Oligomerization of C5 Olefins in Light Catalytic Naphtha - Energy

Refinery gasoline contains C5 alkanes and alkenes that are being displaced due to regulations on maximum seasonal Reid vapor pressure (RVP) limits and...
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Energy & Fuels 2008, 22, 1148–1155

Oligomerization of C5 Olefins in Light Catalytic Naphtha Roland Schmidt,* M. Bruce Welch, and Bruce B. Randolph ConocoPhillips, BartlesVille Technology Center, BartlesVille, Oklahoma 74004 ReceiVed January 3, 2008. ReVised Manuscript ReceiVed January 7, 2008

Refinery gasoline contains C5 alkanes and alkenes that are being displaced due to regulations on maximum seasonal Reid vapor pressure (RVP) limits and increased blending of ethanol. As volumes of displaced C5’s increase, technologies for returning C5’s to the gasoline or diesel pools become increasingly important. Isolation of C5 streams followed by dimerization/oligomerization of the C5 olefins is one route to return displaced C5’s to the gasoline pool. Large pore, acidic zeolite catalysts have been evaluated for this purpose. The process results in an overall volume loss due to volume contraction and a possible loss of research octane number (RON).

Table 1. Effects of Renewable Fuels on C5’s in Gasoline Summer 2012

1. Introduction Much refinery-related research over the past 5–10 years has been directed at converting light naphtha streams1 that are too high in Reid vapor pressure (RVP) for large volume use in gasoline to higher molecular weight gasoline and diesel range compounds with lower RVP values.2 The desire for such capabilities continues to grow with downward pressure on gasoline RVP to reduce fugitive emissions into the atmosphere and increasing the use of ethanol in the gasoline pool. While RVP waivers can reduce this problem, the pressure for removal of high RVP components will increase if waivers are discontinued. The Reid vapor pressure (RVP) is a measure of the vapor pressure of gasoline, volatile crude oils, and other volatile petroleum products determined at approximately 38 °C.3 In past decades, the Environmental Protection Agency (EPA) imposed regulations controlling hydrocarbon emissions from fuel sources2 in order to reduce ground ozone levels. Volatile organic compounds (VOCs) from evaporative sources are a major source for the generation of this urban ozone. Pentenes are among the lightest, highest vapor pressure components in gasoline, and they have a significant ozone formation potential.4,5 Thus, restrictions on light hydrocarbon streams are likely to become more stringent, forcing the lightest components out of the available fuel pool. With increased ethanol blending, this problem will be exacerbated since blending ethanol requires a lower RVP base stock to achieve overall final fuel RVP specifications. Refineries address this issue by applying various strategies.6 Among others, the following existing options have been considered: • Storage of C5 during summer months and blending back into the gasoline pool in the winter (C5’s can and are currently * Corresponding author. Tel.: +1 918 661 3506. Fax: +1 918 662 1097. E-mail address: [email protected]. (1) Meyer, E. Chemistry of Hazardous Materials, Third ed.; Prentice Hall: New York, 1998: p 458. (2) Gary, J. E. Handwerk, G. E. In Petroleum Refining, 4th ed.; Marcel Dekker Inc.: New York, 2001. (3) Standard Test Method for Vapor Pressure of Petroleum Products (Reid Method); Designation D 323-99a, American Society for Testing and Materials (ASTM): Conshohocken, PA, June 1999. (4) Simpson, D. J. Atmosph. Chem. 1995, 20 (2), 163–177. (5) Dunker, A. M.; Morris, R. E.; Pollack, A. K.; Schleyer, C. H.; Yarwood, G. EnViron. Sci. Technol. 1996, 30 (3), 787–801. (6) Hartmann, M. Erdöl, Erdgas, Kohle 2004, 120 (12), 423–424.

scenario

1

2

3

4

RVP, psi oxygenate required renewables, MBPDb displaced C5’s, MBPD

7 no 163 157

6.5 no 163 212

7 yes 326 314

6.5 yes 326 424

RFGa

a

RFG ) reformulated gasoline. b MBPD ) thousand barrels per day.

stored in the summer for use in the winter. Storage of C5’s usually requires refrigeration and/or pressurization.) • Increase in alkylation capacity (Alkylation of C5 olefins using existing alkylation technologies is a viable alternative, but there are as many disadvantages as advantages. Advantages frequently cited include reduced olefin content of the FCC gasoline, increased motor octane number of the gasoline pool, and increased alkylate yields. Disadvantages include higher acid soluble oil production rates, loss of alkylate octane (relative to the alkylation of butylenes), and higher isopentane production.)7,8 • C5 disproportionation9. • C5 cracking (C5’s can be cracked to ethene or further to produce hydrogen. To get the produced olefins back into the gasoline pool would require a second process step.) • C5 discounting (selling C5’s at a discount). Proposed future regulations make removing C5’s a growing problem. Table 1 shows our estimates of the potential size of the problem for the United States by 2012. In 2012, it is estimated that 326 MBPD of renewable fuels (ethanol) will be mandated. The use of ethanol in RFG10–12 will not be optional for many refiners as they will need to use it to achieve octane. If by 2012 the entire gasoline pool is mandated to be RFG, then the displaced C5 would further double assuming (7) Abbott, R. G.; Randolph, B. B.; Anderson, R. L. Control of synthetic isopentane production during alkylation of amylenes. U.S. Patent 5,382,744, 1995. (8) Randolph, B. B. Method for removing amylenes from gasoline and alkylating such amylene and other olefins while minimizing synthetic isopentane production. U.S. Patent 5,629,466, 1997. (9) Publications in preparation. (10) http://www.epa.gov/otaq/rfg.htm. (11) Zong, B.; Min, E.; He, M.; Li, D. China Petrol. Proc. Petrochem. Technol. 2000, 4, 28–31. (12) Quintus-Wessels, P. Critical Reports on Applied Chemistry. Motor Gas. 1995, 34, 217–238.

10.1021/ef800005v CCC: $40.75  2008 American Chemical Society Published on Web 02/28/2008

Oligomerization of C5 Olefins

the required volume of renewables remains constant. In addition, these objectives would need be met without negatively impacting other fuel parameters such as octane2,13,14 and distillation points. The Society of Automotive Engineers has reported the permeation rate for a 10% ethanol blend to be roughly 1.5 times greater than that with no ethanol.15 If this fact is taken into consideration, C5’s could be reduced even further. The World Wide Fuels Charter standards16 already include lowering of RVP to 6.5 psi. This change in standards was considered in scenarios 2 and 4 of Table 1. From these scenarios, it is clear that options for returning converted C5 streams with low RVP and high octane values to the gasoline pool will be needed. Various processes have been developed where zeolite catalysts have proven to be a low cost option to upgrade refinery products. Often, they have reasonable cycle times, and lifetimes, and they can be regenerated.17–19 In the present work, we dimerized and oligomerized C5 olefins over zeolite catalyst to branched decene (and higher) oligomer products. In order for such a process to be viable, it must have a relatively low cost since any process improvements in a refinery are strongly tied to commodity product pricing and return on capital investment measures. 2. Background Acid-catalyzed oligomerization of propylene and butylenes was the first commercial catalytic process of the petroleum industry. Ipatieff and Egloff20 developed phosphoric acid on a kieselguhr support in 1935 to convert dilute propene and butenes streams to branched gasoline-range olefins. Subsequently, Paul Hogan and Robert Banks21,22 worked on more selective catalysts (nickel on alumina23) for oligomerization of these lighter olefins. In order to increase catalyst stability, chromium was added. This led to the discovery of crystalline polypropene and subsequently to high density polyethene.24–27 The recent ban on the use of methyl t-butyl ether (MTBE) in the United States in motor fuel has led to numerous articles and patents for converting isobutene (and other butenes) to high octane fuels. Of particular importance are the efforts to make (13) Westbrook, C. K. Chem. Ind. (London, United Kingdom) 1992, 15, 562–566. (14) Textiles, soap, fuels, petroleum, aromatic hydrocarbons, antifreezes, water. In Standards; American Society for Testing Materials: Conshohocken, PA, 1950; Chapter V. (15) Octane Week 2004, XIX (34), 5. (16) World Wide Fuel Charter, 4th ed. In Proceedings of the Asian Petroleum Symposium; Cambodia, Jan 18–19, 2006. (17) Kadyrov, I.; Bekturdiev, G. M.; Molodozhenyuk, T. B.; Salimov, Z. S.; Saidakhmedov, S. M.; Sharafutdinov, U. T. Chem. Technol. Fuels Oils 1999, 35 (3), 172–175. (18) Guisnet, M.; Magnoux, P. Catal. Today 1997, 36 (4), 477–483. (19) Haentsch, W.; Spindler, H.; Wittke, H.; Staudte, B.; Seidel, R. Chem. Techn. (Leipzig, Germany) 1991, 43 (3), 114–16. (20) Schmerling, L.; Ipatieff, V. N. AdV. Catal. 1950, 21, 2. (21) Hogan, J. P. Solid crystalline olefin polymers. Can. Patent CA 956748 19741022, 1974. (22) Hogan, J. P. Solid polymers of olefins and production of such polymers. U.S. Patent 4,376,851 A 19830315, 1983; cont.-in-part of U.S. Ser. No. 333,576, abandoned. (23) Hogan, J. P. Catalytic polymerization of olefins. U.S. Patent 2,794,842 1957. (24) Hogan, J. P. Polymers and production thereof. U.S. Patent 2,825,721 1958. (25) Hogan, J. P. Stabilized catalyst and improved polymerization process. U.S. Patent 2,846,425 1958. (26) Hogan, J. P. Polymerization catalyst and production thereof. U.S. Patent 2,951,816 1960. (27) Hogan, J. P. Solid polymers of olefins and production of such polymers. U.S. Patent 4,376,851 1983; cont.-in-part of U.S. Ser. No. 333,576.

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“iso-octane” (which is 2,2,4-trimethyl pentane with a research octane number (RON) and motor octane number (MON)28 of 100). Universal Oil Products (UOP), Snamprogetti, Fortum, and Lyondell offer process technology to convert isobutene (and n-butenes) to gasoline-range components.29–33 Most employ acidic ion exchange resins commonly used to make MTBE. Frequently, water or light alcohols are added as catalyst moderators, and the olefinic products are hydrogenated after separation from the reactor effluent. UOP does offer technology based on supported phosphoric acid in addition to MTBE unit retrofits. A nonexhaustive review of the patent literature34–50 shows that zeolites have been used since the 1970s to oligomerize light olefins but that the main drawback to these systems was their high deactivation rate. The oligomerization reaction over zeolite catalysts can be rationalized with alkylcarbenium ion chemistry.51 The elementary reaction steps consist of (1) protonation of an alkene with formation of an alkylcarbenium ion, (2) addition of a second alkene to the alkylcarbenium ion, (28) Scherzer, J. Octane-Enhancing Zeolitic Fcc Catalysts: Scientific and Technical Aspects; Marcel Dekker: New York, 1990; pp 7–12. (29) Frame, R. R.; Stine, L. O.; Hammershaimb, H. U.; Muldoon, B. S. Erdöl, Erdgas, Kohle 1998, 114 (7/8), 385–387. (30) Di Girolamo, M.; Sanfilippo, D.; Patrini, R.; Marchionna, M. Oil Gas Eur. Mag. 2005, 2, 70–76. (31) Mariochionna, M.; Di Girolamo, M.; Patrini, R. Catal. Today 2001, 65, 397–403. (32) Refining Processes 2002. Hydrocarbon Process. Mag. 2002, (Nov), 83–150. (33) Petrochemical Processes 2001. Hydrocarbon Process. Mag. 2001, (March), 108. (34) Barrer, R. M. Zeolites and Clay Minerals as Sorbents and Molecular SieVes; Academic Press: New York, 1978. (35) Flannigan, E. M., Union Carbide Corporation. Crystalline MM and process for manufacture thereof. U.S. Patent 3,597,155, 1971. (36) Plank, C. J.; Rosinski, E. J.; Givens, E. N. Converting low molecular weight olefins over zeolites. U.S. Patent 4,021,502, 1977. (37) Garwood, W. E.; Caesar, P. D.; Brenan, J. A. Light olefin processing. U.S. Patent 4,150,062, 1979. (38) Ward, D. J. Process for the production of gasoline from C4 hydrocarbons. U.S. Patent 4,367,356, 1983. (39) Marsh, S. K.; Owen, H.; Wright, B. S. Catalytic conversion system for oligomerizing olefinic feedstock to produce heavier hydrocarbons. U.S. Patent 4,456,781, 1984. (40) Harandi, M. N.; Owen, H.; Tabak, S. A. Production of heavier hydrocarbons from light olefins in multistage catalytic reactors. U.S. Patent 4,788,366, 1988. (41) van den Berg, J. P.; Granndvallet, P.; Kortbeek, A. G. T. G. Process for two-stage catalytic conversion of an olefins-containing feed. U.S. Patent 4,835,335, 1989. (42) Juguin, B.; Raatz, F.; Travers, C.; Martino, G. Method for producing olefin oligomers using a modified mordenite based. U.S. Patent 4,902,847, 1990. (43) Beech, Jr., J. H.; Ragonese, F. P.; Stoos, J. A.; Yurchak, S. Process for upgrading light olefinic streams. U.S. Patent 4,973,790, 1990. (44) Harandi, M. N.; Owen, H. Reactor system for upgrading light olefins in staged reactors. U.S. Patent 5,019,357, 1991. (45) Haddad, J. H.; Harandi, M. N.; Owen, H. Upgrading light olefin fuel gas in a fluidized bed catalyst reactor and regeneration of the catalyst. U.S. Patent 5,043,517, 1991. (46) Mathys, G.; Martins, L.; Baes, M.; Verduijn, J.; Huybrechts, D. Alkene oligomerization. WO Patent 93/16020, 1993. (47) Harandi, M. N.; Hartley, O. Ether production with staged reaction of olefins. WO Patent 93/13043, 1993. (48) Aittamaa, J.; Lindqvist, P.; Koskinen, M.; Linnekoski, J.; Krause, O.; Sourander, M.; Ignatius, J.; Pyhaelahti, A. Process for producing a fuel component. WO Patent 00/23402, 2000. (49) Perego, C.; Flego, C.; Marchionna, M. Process for obtaining a “diesel cut” fuel by the oligomerization of olefins or their mixtures. EP 1 249 486 A1, 2000. (50) Pyhaelahti, A.; Aittamaa, J. Process for dimerizing light olefins to produce a fuel component. U.S. Patent 6,660,898, 2003. (51) Olah, G. A.; Molnar, A. Hydrocarbon Chemistry, 2nd ed.; WileyInterscience: New York, 2003.

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(3) skeletal isomerization to more stable intermediates if appropriate, and (4) deprotonation. The reference is made to adsorbed alkyl carbenium ion, but in reality, this reactive species more accurately is described as an alkoxide. Side reactions such as an allylic hydrogen transfer leading to an alkane and allylic cation are undesirable as they can lead to coke formation. Kojima and co-workers reported the use of ion-exchanged mordenite for the oligomerization of a butene feed rich in 1-butene.52 They identified optimum calcination temperatures for the mixed ammonium-sodium form of mordenite and showed that catalytic activity increased nonlinearly with increasing ammonium ion content up to 52%. All the runs showed measurable decay in activity over the course of 10–11 h. Honkela and Krause53 have quantified the effect of linear butenes on olefin conversion and selectivity when codimerized with isobutene using ion exchange resins. Their results were fit to a Langmuir–Hinshelwood-type kinetic model. Catani and coworkers54 described their attempts to make diesel-range material from C4 and C5 olefins using MCM-41 type mesoporous catalysts impregnated with small amounts of nickel, rhodium, and platinum. Catalytic performance was said to be good, and while rhodium and platinum did not significantly alter the catalytic activity, Ni at higher levels (∼3%) tended to reduce activity. Estimates of the cetane numbers of their products ranged from 25 (no metals) to 30 (with 0.3% Rh). It should be mentioned that fuel specifications normally require 40 cetane in the US, and 45 or higher in Europe. Workers at Shell International have recently reported results on the dimerization of n-butenes for high octane gasoline production.55 Their work focused on maximizing the fraction of oligomers with allylic hydrogens based on their work linking these groups to higher octane values. They employed amorphous silica–alumina (ASA) catalysts, and their products (∼50–55% dimer) had blending RON values of ∼130. They also highlight the lower conversions associated with linear butenes relative to isobutene. Under their conditions, the conversion of 1-butene was 0.89 and 2-butene was 0.37, respectively (isobutene ) 1.0). Chiche et al. employed various catalysts for 1-butene oligomerization.56 Their results showed rapid deactivation with microporous catalysts and the ASA, but mesoporous aluminosilicates with uniform pore openings of ∼3 nm had good stability and high selectivity for branched dimer production. Fewer reports in the literature focus on C5 and higher olefins. In addition to the work reported by Snamprogetti and the University of Bologna,54 Martens et al. oligomerized 1-hexene with ultrastable Y zeolite and beidellite57,58 catalysts in the presence of various alkane solvents.59 Their work showed that the length of the alkane chain in the solvent had a strong effect on catalyst deactivation, product selectivity, and cracked products. Hydrogen transfer to produce saturated C6 products (52) Kojima, M.; Rautenbach, M. W.; O’Connor, C. T. Ind. Eng. Chem. Res. 1988, 27, 248–252. (53) Honkela, M. L.; Krause, A. O. I. Ind. Eng. Chem. Res. 2005, 44, 5291–5297. (54) Catani, R.; Mandreoli, M.; Rossini, S.; Vaccari, A. Catal. Today 2002, 75, 125–131. (55) Golombok, M.; de Bruijn, J. Ind. Eng. Chem. Res. 2000, 39, 267– 271. (56) Chiche, B.; Sauvage, E.; Di Renzo, F.; Ivanova, I. I.; Fajula, F. J. Mol. Catal. A: Chem. 1998, 134, 145–157. (57) Kloprogge, J. T.; van der Eerden, A. M. J.; Jansen, J. B. H.; Geus, J. W. Geol. Mijnbouw 1990, 69, 351–357. (58) Kloprogge, J. T.; Jansen, J. B. H.; Geus, J. W. Clays Clay Miner. 1990, 38, 409–414. (59) Pater, J. P. G.; Jacobs, P. A.; Martens, J. A. J. Catal. 1998, 179, 477–482.

Schmidt et al. Table 2. Dimerization of 2-Methyl-2-butene (2MB2) and 1-Pentene with Zeolites and Nickel Impregnated Zeolite Catalystsa experiment catalyst

1

17.6 wt% Ni on beta 25 zeolite temperature, °C 75 2.1 WHSVb feed 2-me-2-butene C3 0.01 C4 0.03 C5 7.09 C6 1.23 C7 0.04 C8 0.20 C9 7.09 C10 69.71 C11 2.11 C12+ 12.47

2

3

4

17.6 wt% Ni on beta 25 zeolite 75 2.2 1-pentene 0.00 0.00 69.69 0.01 0.00 0.00 0.44 24.47 0.10 5.26

control beta 25 zeolite 75 1.8 1-pentene 0.00 0.00 74.41 0.03 0.00 0.00 0.29 15.10 0.00 10.15

Mordenite 40 75 1.8 1-pentene 0.00 0.00 45.13 0.03 0.02 0.00 0.77 44.18 0.05 9.94

a Product concentrations are shown in weight percent excluding isopentane. b WHSV ) weight hourly space velocity.

was the main side reaction and was more abundant with dodecane than with octane as the solvent. The micro- and mesopores of the USY catalysts were blocked with large hydrogen-deficient molecules, whereas the larger pores associated with beidellite were not as sensitive. The USY catalyst was more stable in the presence of octane, whereas the beidellite favored dodecane. However, catalyst decay was apparent over 15 h in all runs. Most recently, Guillaume has rationalized the oligomerization of light olefins using single event theory modified to account for characteristic properties of the reactions and to generate the detailed reaction network.60 As this brief literature review shows, the area of acidcatalyzed olefin oligomerization reactions has been extensively researched for various reasons of which a few are listed above. Apparent problems include catalyst selectivity, activity, and lifetime due to coking and poisoning as well as expensive metals precipitated on the chosen support materials including various zeolitic materials. Our research focused on developing an inexpensive process able to convert C5 olefins more selectively to higher value refinery products suitable for fuel blending in order to meet anticipated, future fuel specifications. 3. Results and Discussion The envisioned process consists of isolating C5 refinery streams, i.e. catalytic naphtha,1 and passing them through guard beds if necessary to reduce potential catalyst poisons before passing over the acid catalyst bed especially nitrogen and sulfur containing organic compounds. The reactions were conducted at fairly mild conditions in order to minimize undesired side reactions. After separating C12+ fractions, the dimerization product is returned to the gasoline pool. The higher fractions may be used in diesel. 3.1. Initial Experiments. Initially, idealized feeds of the respective C5 olefin (∼10 vol %) in isopentane were passed through nickel impregnated zeolite catalysts (see Table 2). Comparison of runs 1 and 2 in Table 2 shows that, at similar conditions, 2-methyl-2-butene (2MB2) dimerizes (93% conversion) more easily than 1-pentene (30% conversion). In run 3, the beta zeolite support was run without nickel impregnation. Conversion was approximately the same as with nickel impregnation, but (60) Guillaume, D. Ind. Eng. Chem. Res. 2006, 45, 4554–4557.

Oligomerization of C5 Olefins

Energy & Fuels, Vol. 22, No. 2, 2008 1151

Table 3. Large and Medium Pore Zeolite Comparisona experiment catalyst temperature, °C WHSV feed C3 C4 C5 C6 C7 C8 C9 C10 C11 C12+ a

5

6

Mordenite 40 75 75 1.8 1-pentene 0.00 0.00 45.13 0.03 0.02 0.00 0.77 44.18 0.05 9.94

7

Pentasil 90 125

1.8 1-pentene 0.00 0.00 92.90 0.06 0.00 0.00 0.10 5.60 0.00 1.36

1.4 1-pentene 0.00 0.01 73.69 0.08 0.05 0.03 0.37 22.74 0.04 2.93

8 75

9

ZSM-5 50 125

1.8 1-pentene 0.00 0.00 83.25 0.08 0.03 0.02 0.21 14.34 0.00 2.08

1.7 1-pentene 0.00 0.02 84.84 0.16 0.10 0.05 0.32 13.33 0.00 1.18

Figure 1. Thirty-four hour continuous dimerization bench run.

Product concentrations are shown in weight percent.

selectivity to C10 dimers was lower. Run 4 shows that other zeolites may be even more active at dimerizing 1-pentene. Modifications of the zeolites with various additives based on nickel and other metals were tried with a variety of C5 olefin feeds. Although some of these catalysts performed well, none exceeded the commercial base zeolites. The product of the reaction of C5 olefins over zeolite catalysts is primarily dimers and trimers. However, the product mixture also contains C6-C20 products, suggesting that there are various parallel reactions such as disproportionation,9 cracking,2,61,62 and aromatization.2,63–65 3.2. Zeolite Pore Size. Table 3 shows the comparison of large-pore Mordenite (6.0–8.0 Å 12 ring structures) with medium-pore Pentasil and ZSM-5 (4.5–6.0 Å 10 ring structures) zeolites.66 The medium-pore zeolites are only about a third as active as the large pore zeolite. Even increasing temperature on the medium-pore zeolites by 50 °C did not increase dimerization activity to that of the Mordenite 40 catalyst at the lower temperature. However, the amount of 1-pentene remaining in the product for the different catalysts was in the range of 5.8–13 wt % for all except run 2 which was at 64.8 wt %. This indicates that all of these catalysts are good double-bond isomerization catalysts and that the Mordenite catalyst is superior at dimerization. The literature (see above) is full of comments about the short cycle times of the zeolite catalysts. Many references indicate that the cycle time is as short as a few hours for butene dimerization. Thus, the relatively stable conversions observed with Mordenite 40 over an extended period of more than 10 h were surprising. To further explore this finding, a 34 h bench scale experiment was conducted with ∼10 vol % 1-pentene in isopentane as the feed. The results are shown in Figure 1. With moderate temperature increases, conversion was held within a relatively narrow range throughout the experiment. This, coupled with the regenerability of the zeolites, suggested that zeolites are good candidates for dimerizing C5 olefins to C10 olefins. (61) Uhl, W. C. World Pet. 1972, 43 (6), 53–56. (62) Le, Q. N.; Owen, H.; Schipper, P. H. Integrated process for production of gasoline and ether. U.S. Patent 4,969,987, 1992. (63) Pickering, J. L., Jr.; Nemet-Mavrodin, M. Increased conversion of C2-C12 aliphatic hydrocarbons to aromatic hydrocarbons using a highly purified recycle stream. U.S. Patent Appl. 4,996,381 A1 9910226, 1991. (64) Aufdembrink, B. A.; Degnan, T. F.; McCullen, S. B. Aromatization process and catalyst utilizing a mixture of shape-selective porous crystalline silicate zeolite and pillared layered metal oxide. U.S. Patent Appl. 4,933,310 A1 9900612, 1990; abandoned. (65) Chu, C. C. Aromatization reactions with zeolite catalysis. Eur. Pat. Appl. EP 205300 A2 19861217, 1986. (66) http://www.iza-structure.org/databases/

Figure 2. Variation in the silica/alumina molar ratio. The data shown was taken after 6 h on stream.

3.3. Zeolite Silica to Alumina Molar Ratio. As the dimerization reaction is acid catalyzed, methods of altering the acidic nature of the acid center on how the zeolites should affect conversion. A convenient method of altering zeolite acidity is to vary the silica to alumina molar ratio.67–70 The results of these experiments are shown in Figure 2. The notation indicates the atomic silicon to aluminum ratio, i.e., for Mord 40, Si:Al ) 40. For conversion of 1-pentene to decene dimers, Mordenite 40 was observed to be marginally better than Mordenite 14 and 130. It should be noted, however, that the binder and concentration of zeolite in the pellets were not carefully controlled. Under more controlled conditions, results could vary. 3.4. Simulated C5 Refinery Feed. Real feed composition as encountered in a refinery would consist of a mixture of C5 compounds. Therefore, a feed consisting of 50 wt % isopentane, 25 wt % 1-pentene, and 25 wt % 2-methyl-2-butene (2M2B) was prepared and tested. In Table 4, data is shown for the mixed feed run over the Mordenite 40 catalyst. Run 10 was made with guard beds containing molecular sieve 3Å and 13X as well as silica gel in use whereas Run 11 was made without. The results indicate that guard beds had little effect on product conversions or distributions for these blended feeds. In run 10, conversion of 2-methyl-2-butene to higher olefins was 96% and conversion of 1-pentene to other olefins was 79%. However, 1-pentene was isomerized to 2-pentene isomers and only 28% was converted to higher olefins. (67) Rabo, J. A. Zeolite Chemistry and Catalysis; ACS Monograph 171; American Chemical Society: Washington, DC, 1976. (68) Bielanski, A.; Datka, J.; Drelinkiewicz, A.; Malecka, A. Wiss. Ztschr.-Friedrich-Schiller-UniVersitaet Jena, Math.-Naturwissenschaftliche Reihe 1978, 27 (5–6), 549–565. (69) Barthomeuf, D. Mater. Chem. Phys. 1987, 17 (1–2), 49–71.

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Table 4. Isopentane, 1-Pentene, 2-Methyl-2-Butene Mixed Feeda experiment catalyst temperature, °C WHSV feed guard beds 3MB1b iC5c 1-pentene 2MB1 t-2-pentenee c-2-pentenef 2MB2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12+

10 40

11 40

12

Mordenite 40 120

13

Table 5. C5 Fraction of Desulfurized, Refinery Feed Passed over Different Mordenitesa experiment

150

1.8 2.0 3.3 5.0 47.8% iC5, 24.8% 1C5), 1.7% 2MB1d, and 25.2% 2MB2 yes no no no 0.00 0.01 0.02 0.01 49.77 50.22 51.33 51.66 5.19 11.30 1.32 0.79 0.06 0.14 0.25 0.15 8.91 6.42 13.00 9.80 3.66 2.98 4.34 3.44 0.87 1.95 2.22 1.20 0.03 0.02 0.05 0.10 0.14 0.14 0.20 0.21 66.62 73.19 72.66 67.30 0.19 0.14 1.03 1.38 0.00 0.00 0.07 0.26 0.05 0.02 0.20 0.75 1.79 1.59 2.46 4.72 28.65 22.85 20.44 18.69 0.25 0.05 0.72 1.86 2.27 2.01 2.28 4.43

a Product concentrations are shown in weight percent. b 3MB1 ) 3-methylbutene-1. c iC5 ) isopentane. d 2MB1 ) 2-methylbutene-1. e t ) trans. f c ) cis.

Run 1 in Table 2 shows similar conversions for 2MB2, but Run 4 in Table 2 indicates that conversion of 1-pentene should be about 55%. As the earlier runs were made at 75 °C versus the 40 °C runs in Table 4, one can argue that temperature differences account for the difference in conversion of the pentenes. Run 12 shows that at 120 °C conversion of pentenes is still only 25%. Only when a run temperature of 200 °C is reached does the conversion of pentenes (45%) approach that of neat pentenes. This suggests that pentenes react preferentially with other pentenes and that the drop in conversion is due to the dilution effect of the other components. It is interesting to note that the C10 product fraction changes little with temperature. The biggest change is to the C9 and C12+ fractions indicating an increase in trimerization and side reactions. 3.5. Experiments with the C5 Fraction of Refinery Desulfurized Feed. The performance of the catalysts with simulated feeds encouraged us to take the next step and try real feeds. Results using a fractionated, desulfurized C5 refinery stream are shown in Table 5. The feed contained 1.38 ppm sulfur, 0.66 ppm nitrogen (determined by ANTEK analysis), and 600 ppm cyclopentadiene which, as a diolefin, can also poison catalysts71,72. The feed was tested with three different Mordenite catalysts as shown in experiments 14-16. Although differences are small, the Mordenite 90 catalyst yielded higher conversions. In experiment 15, the conversion of the branched C5 olefins was 70%, conversion of the linear pentenes was 2%, and conversion of the cyclopentene was 53%, respectively. Figure 3 shows the effect of run time on conversion for the Mordenite 90 run at 3.3 WHSV, 160 °C, and 34 bar. The rate of activity loss is about 2.9% per day. Conversions of under 50% at 8–10 h intervals were caused by shutdown and startup of the reactor system to continue the experiments. (70) Lunsford, J. H. Prepr. Pap.sAm. Chem. Soc., DiV. Pet. Chem. 1990, 35 (4), 654–60. (71) Remirez-Corredores, M. M.; Romero, T.; Djaouadi, D.; Hernandez, Z.; Guerra, J. Ind. Eng. Chem. Res. 2002, 41 (22), 5385–5392. (72) Kaminsky, M. P. U.S. Pat. Appl. Publ. U.S. 2003225305 A1 20031204, 2003.

catalyst temperature, °C WHSV guard beds 3MB1 iC5 1-pentene 2MB1 pentane t-2-pentene c-2-pentene 2MB2 cyclopentene cyclopentane C3 C4 C5 C6 C7 C8 C9 C10 C11 C12+ a

feed

0.63 31.11 2.47 6.17 19.37 10.03 5.36 18.48 2.53 2.47

14

15

16

Mord 40 100 2.8 yes 0.24 32.22 1.04 1.06 19.26 12.22 4.47 8.83 1.50 2.42 0.01 0.62 79.44 4.76 0.00 0.02 1.25 12.46 0.72 0.69

Mord 90 100 2.8 yes 0.15 31.99 0.80 0.68 20.00 12.50 4.18 6.67 1.07 2.53 0.01 0.61 76.97 4.64 0.00 0.04 1.69 14.15 1.21 0.67

Mord 130 100 2.8 yes 0.55 31.36 2.19 1.32 19.80 10.36 5.18 11.31 1.82 2.45 0.01 0.59 82.07 4.89 0.00 0.01 1.08 10.06 0.68 0.61

Product concentrations are shown in weight percent.

Figure 3. Effect of run length on conversion over Mordenite 90 catalyst: (experimental conditions) 3.3 WHSV, 160 °C, 34 bar.

Figure 4. Effect of run length on conversion over Mordenite 90 catalyst without guard beds: (experimental conditions) 3.3 WHSV, 160 °C, 34 bar.

With the mixed, simulated feed, the effect of guard beds was minimal. While Figure 3 shows results running with guard beds, Figure 4 shows the effects of running without guard beds with the refinery-derived feed. Run conditions were 3.3 WHSV, 160 °C, and 34 bar over Mordenite 90 catalyst. The first 9 h of the run were made with guard beds, and the remainder of the run was made with the guard beds bypassed. The loss of conversion was 5.5% per day compared to 2.9% per day with guard beds in use. The stair step data suggests that a significant loss in

Oligomerization of C5 Olefins

Energy & Fuels, Vol. 22, No. 2, 2008 1153 Table 6. Comparison of Different Feedstocks Used feed 1 sourcea dienes, ppmw sulfur,b ppmw nitrogen,c ppmw conversion, wt %, 4 days w/o guard beds conversion, wt %, 4 days w guard beds

Figure 5. Increased nitrogen and sulfur levels in feedstock: (experimental conditions) 3.3 WHSV, 160 °C, 34 bar, high sulfur and nitrogen refinery feed.

Figure 6. Effect of sulfur and nitrogen levels in feedstock on conversion: (experimental conditions) 3.3 WHSV, 160 °C, 34 bar.

conversion resulted from shutting the reaction down and restarting and not just from a gradual decay in the number of active sites. 3.6. Bench Sulfur and Nitrogen Sensitivity. To explore the effects of sulfur and nitrogen, a depentanized overhead gasoline feed with higher sulfur and nitrogen (8.5 ppm S and 1.7 ppm N) was used. Results are shown in Figure 5. The loss of conversion was 13.6% per day. This suggests that either sulfur,73–75 nitrogen,76 or a combination of the two is poisoning the catalyst. The linear correlations between sulfur and/or nitrogen feed content and percent relative loss in conversion are shown in Figure 6. 3.7. Continuous Operations Results. The encouraging results prompted us to conduct further experiments on a continuous operation basis which would avoid the stair-step deactivation observed. Such an operational mode could also help establish and explore methods of maintaining conversion at constant levels over extended cycle-times. Mordenite 90 catalyst was chosen, and the overhead fraction of a depentanized C5 gasoline feed was used with guard beds at 160 °C, 34 bar, and 3.6 WHSV. Results are shown in Table 6 (see below). Conversion of the olefins reached 58% at 48 h into the experiment. The activity then began to slowly decay (see Figure 7), reaching 49% conversion at about 140 h into the experiment. At this point, the temperature was increased and activity returned to 55%. Activity was then maintained at this level over the remainder of the experiment of 442 h total (73) Lee, D.; Lee, H.; Kim, S.; Lim, O.; Ko, E.-Y.; Eun, D. Abstracts of the 231st ACS National Meeting, Atlanta, GA, March 26–30, 2006. (74) Yang, H.; Chen, H.; Chen, J.; Omotoso, O.; Ring, Z. J. Catal. 2006, 243 (1), 36–42. (75) Glunt, J. World Refining 2005, 7–8; Suppl. Catalyst. (76) Matsui, T.; Harada, M.; Toba, M.; Yoshimura, Y. Appl. Catal. A: Gen. 2005, 293, 137–144.

feed 2

feed 3

feed product feed product

feed

0.2 2.3 1.0