Microsoft Word - A_32_Feher_R.doc HUNGARIAN JOURNAL OF INDUSTRIAL CHEMISTRY VESZPRÉM Vol. 39(1) pp. 63-66 (2011) OLIGOMERIZATION OF IZOBUTENE IN THE PRESENCE OF IONIC LIQUID – BASED CATALYSTS C. FEHÉR1, R. SKODA-FÖLDES1 , E. KRIVÁN2, J. HANCSÓK2 1University of Pannonia, Institute of Chemistry, Department of Organic Chemistry H-8201 Veszprém, P. O. Box 158, HUNGARY E-mail: skodane@almos.uni-pannon.hu 2University of Pannonia, Department of MOL Hydrocarbon and Coal Processing H-8201 Veszprém, P. O. Box 158, HUNGARY In the petrochemical industry, the C4 stream including isobutene is an important raw material that can be upgraded. Oligomerization of isobutene is a very promising reaction, as the hydrogenation products of dimers and trimers, obtained from isobutene, can be used as gasoline and diesel additives, respectively. In the present paper, our results concerning the use of Brønsted acidic ionic liquids as oligomerization catalysts are presented. The ionic liquids were supported on silica. Most of the solid catalysts were reused several times without loss of activity. By the proper choice of the ionic liquid and reaction conditions, good selectivity towards either C8 or C12+ products could be achieved. Keywords: oligomerization, isobutene, ionic liquid Introduction The oligomerization of light olefins is an important alternative for the production of higher molecular weight hydrocarbon mixtures useful as fuels (e.g. gasoline or diesel). Both Brønsted and Lewis acids have been used as oligomerization catalysts in either homogeneous (H2SO4, organometallic complexes, etc.) or heterogeneous (mixed oxides, zeolites, clays, ion exchange resins etc.) phase. [1] The main challenges in the design of catalysts for this reaction are focused to reach high conversion and high selectivity. Consequently, several solid acid catalysts of different types have been developed for the oligomerization of lower alkenes, such as isobutene. [2] At the same time, Ni-based catalysts containing phosphine ligands can be used efficiently in the homogeneous phase in the presence of various additives. [3, 4] However, a great drawback of homogeneous catalytic reactions is the problem of catalyst recovery and recycling. The use of a two-phase solvent system, together with a transition metal complex, is an attractive alternative, as it enables catalyst separation and reuse. This methodology was found to be very efficient in alkene oligomerization by cationic nickel complexes in chloroaluminate [5-8] or hexafluorophosphate [9] ionic liquids as solvents. Chloroaluminate ionic liquids with Lewis acidic character were shown to catalyze oligomerization themselves, without the addition of transition metal complexes or salts. [10] These catalysts were applied in the oligomerization of linear 1-olefins. [11] Imidazolium ionic liquids with SO3H functionalized side chains were also found to be excellent and reusable catalysts in oligomerization of various alkenes. [12] Generally, ionic liquids (ILs) have gained increasing attention with multiple applications in synthesis and catalysis. [13] Despite their advantages, there are also some drawbacks, including the difficulties in product purification or IL recycling and the problems for application in fixed bed reactors. Also, biphasic ionic liquid-organic systems require large amounts of the expensive ILs, which hinders industrial applications. These difficulties can be overcome by the use of supported ionic liquid phases (SILPs) prepared by the immobilization of ionic liquids on solid supports. [14] Based on these findings, we decided to explore the possibility of the use of silica-supported SO3H- functionalised ILs as catalysts in the oligomerization of isobutene. In this paper, we report on our results concerning the effects of the changes in the reaction conditions on the outcome of the oligomerization reaction. Experimental Materials The ionic liquids (IL-1 — IL-4) were synthesized by methods analogous to literature procedures. [15, 16] The supported catalysts (SILP-1 — SILP-4) were obtained by reacting the ionic liquid (IL-1, IL-2, IL-3 or IL-4) (10 mmol) and silica gel (Kieselgel 60 (0.040–0.063 mm), pre-heated at 250 °C for 5 h) (10 g) in 25 ml MeOH at 64 room temperature for 24 h. MeOH was removed in vacuo and the catalyst was dried at 60 °C in vacuo for 1 h. Oligomerization experiments The reactions were carried out in an autoclave under argon. The autoclave was cooled to -15 °C and isobutene (5 ml, 57.5 mmol) was charged into the reactor, which contained the catalyst (10 mmol of IL-1 or IL-2 or 1 g of the supported ionic liquids SILP-1 — SILP-4). The autoclave was pressurised with argon (22 bar, room temperature). In a typical reaction the mixture was stirred at 100 °C for 5 h. The autoclave was cooled to -15 °C, the organic phase was separated and analysed by gas chromatography. The SILP catalysts were washed with pentane (3x5 ml), dried in vacuo and reused. Analytical methods Reaction mixtures were analyzed by gas chromatography using a Hewlett Packard 4890D instrument equipped with a FID detector and a 30 m HP-1 column. GC-MS measurements were carried out with a Hewlett Packard 5971A GC-MSD. Results and discussion Four Brønsted acidic ionic liquids (IL-1 — IL-4) were prepared and were immobilized on silica gel by adsorption to give catalysts SILP-1 — SILP-4 (Scheme 1). N NR SO3 - N NR SO3H CF 3SO3H CF3SO3 -150 oC, 5 h IL-1 R= CH3 IL-2 R= (CH2)3CH3 N NR SO3H HSO4 - IL-3 R= CH3 IL-4 R= (CH2)3CH3 H2SO4 150 oC, 5 h SILP-1 SILP-2 silica M eOH rt, 24 h SILP-3 SILP-4 silica M eOH rt, 24 h Scheme 1: Synthesis of ionic liquids IL-1 and IL-2 and supported ionic liquids SILP-1 — SILP-4 To compare the activity and selectivity of immobilized and non-immobilized ionic liquids, oligomerization was carried out first in IL-1 and IL-2 under the standard conditions (100 °C, 5 h). In these reactions, the isobutene/catalyst ratio was 57.5/10. Almost total conversion was obtained in both cases and the ratio of C12 products was higher in IL-2 than in IL-1 (Table 1, entries 1, 2). This phenomenon can be explained by the higher solubility of C8 in the ionic liquid with the longer side chain. Similar change in the selectivity of oligomerization with increasing alkyl chain length of the ionic liquid catalysts had been observed by Deng et al. before [12]. The supported ionic liquid catalysts (SILP-1 — SILP-4) were also found to be active in the oligomerization (Table 1, entries 3-6). Immobilization of the ionic liquids resulted in a change in the selectivity of the reaction (compare entries 1, 3 and 2, 4). In the presence of IL-1, the dimers were obtained as the main products (entry 1). At the same time, good C12+ selectivity was observed using the immobilized version of the same catalyst (SILP-1, entry 3). On the contrary, immobilization of IL-2 led to an increase in C8 selectivity (entry 4), compared to the results obtained with IL-2 (entry 2). It should be mentioned, that in the case of the reactions carried out with the immobilized catalysts, the substrate/ionic liquid ratio was much lower (57.5/1 instead of 57.5/10). Despite this, the conversion of isobutene was similar, or even a little higher under the same reaction conditions. Table 1: Oligomerization of isobutene in the presence of ionic liquid based catalystsa Entry Catalyst Conv. [%]b Ratio of products [%] b C8 C12 C16 C20 1 IL-1 98 75 24 1 - 2 IL-2 99 33 60 7 - 3 SILP-1 100 16 54 29 1 4 SILP-2 100 54 35 10 1 5 SILP-3 85 83 17 - - 6 SILP-4 92 82 18 - - a Reaction conditions:100 °C, 5 h b Determined by GC The catalysts containing ionic liquids with hydrogensulfate anion showed the best selectivity toward the dimers but their activity was found to be somewhat lower (entries 5, 6) compared to the other two supported catalysts. The possibility of the reuse of the supported catalysts was also investigated. SILP-1 (Fig. 1) and SILP-2 (Fig. 2) 65 were reused several times without loss of activity or considerable change in selectivity. 0 10 20 30 40 50 60 70 80 90 100 Run 1 Run 2 Run 3 Run 4 Run 5 Run 6 Run 7 Run 8 % Conv. C8 C12 C16 C20 Figure 1: Oligomerization of isobutene in the presence of SILP-1 (100 °C, 5 h) 0 10 20 30 40 50 60 70 80 90 100 Run 1 Run 2 Run 3 Run 4 Run 5 Run 6 Run 7 Run 8 % Conv. C8 C12 C16 C20 Figure 2: Oligomerization of isobutene in the presence of SILP-2 (100 °C, 5 h) SILP-1 showed good selectivity toward C12+C16 products, resulting in oligomeric mixtures with C12 as the main components (Fig. 1). On the contrary, in the presence of SILP-2, dimers were obtained in yields higher than 50 % and the ratio of C16 products was only around 10 % (Fig. 2). The supported catalysts obtained with ILs with hydrogensulfate anion (SILP-3 and SILP-4) showed lower activity than SILP-1 or SILP-2, similarly to the non-immobilized versions of these catalysts (see Table 1). Besides, a great drop of activity was observed even in the second run when SILP-3 or SILP-4 was recycled (Fig. 3). That means that in spite of the excellent selectivity that can be achieved with these catalysts, their use is unfavourable from an economic point of view. The effect of the change in the temperature on the outcome of oligomerization was explored with supported catalysts SILP-1 (Fig. 4) and SILP-2 (Fig. 5). 0 10 20 30 40 50 60 70 80 90 100 Run 1 Run 2 Run 1 Run 2 Run 3 % Conv. C8 C12 C16 (a) (b) Figure 3: Oligomerization of isobutene in the presence of (a) SILP-3 and (b) SILP-4 (100 °C, 5 h) As it was expected, an increase in the temperature led to an increase in the conversion. With SILP-1, total conversion of isobutene (in 5 h) was observed only at 100 °C or above, but in the presence of SILP-2, the conversion was higher than 90 % even at 60 °C. An increase in the temperature led to a decrease in the C8 selectivity of the reaction with both of the catalysts. The best selectivity for C8 and C12 products can be reached by using SILP-2 at 60 °C and SILP-1 at 100 °C, respectively. 0 10 20 30 40 50 60 70 80 90 100 60°C 80°C 100°C 120°C R. temp. % Conv . C8 C12 C16 C20 Figure 4: Oligomerization of isobutene in the presence of SILP-1 at different temperatures 0 10 20 30 40 50 60 70 80 90 100 60°C 80°C 100°C 120°C R. temp. % Conv. C8 C12 C16 C20 Figure 5: Oligomerization of isobutene in the presence of SILP-2 at different temperatures 66 Conclusions Supported Brønsted acidic ionic liquids were proved to be efficient catalysts in isobutene oligomerizaton. The solid catalysts are easier to handle than the ionic liquids themselves, so separation and recovery of even small amounts of catalysts are simple. Although immobilization of ionic liquids affects slightly the selectivity of oligomerization, the catalysts with the trifluoromethanesulfonate anion can efficiently be used and recycled. By the proper choice of the ionic liquid and reaction temperature, either C8 or C12+ products can be obtained with good selectivity. These results clearly show that this type of supported catalysts can be applied flexibly to follow the changing demands of fuel production. ACKNOWLEDGMENT The authors thank TAMOP-4.2.1/B-09/1/KONV-2010- 0003 ( Mobility and Environment: Research in the fields of motor vehicle industry, energetics and environment in the Central- and Western-Transdanubian Regions of Hungary.) for the financial support. The Project is supported by the European Union and co-financed by the European Social Fund. REFERENCES 1. G. A. OLAH, A. MOLNÁR: Hydrocarbon Chemistry (2nd edition). John Wiley & Sons, Inc., Hoboken, New Jersey, 2003, 723 2. S. H. JHUNG, J. S. CHANG: Trimerization of isobutene over solid acid catalysts, Catal. Surv. Asia, 13, (2009), 229 3. G. A. FOULDS, A. M. A. BENNET, M. L. NIVEN, D. A. THORNTON, K. J. CAVELL, S. DESJARDINS, E. J. 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JESS: Alkylation of isobutene with 2-butene using ionic liquids as catalyst, Green Chem. 11, (2009), 1961 << /ASCII85EncodePages false /AllowTransparency false /AutoPositionEPSFiles true /AutoRotatePages /None /Binding /Left /CalGrayProfile (Dot Gain 20%) /CalRGBProfile (sRGB IEC61966-2.1) /CalCMYKProfile (U.S. Web Coated \050SWOP\051 v2) /sRGBProfile (sRGB IEC61966-2.1) /CannotEmbedFontPolicy /Error /CompatibilityLevel 1.4 /CompressObjects /Tags /CompressPages true /ConvertImagesToIndexed true /PassThroughJPEGImages true /CreateJobTicket false /DefaultRenderingIntent /Default /DetectBlends true /DetectCurves 0.0000 /ColorConversionStrategy /CMYK /DoThumbnails false /EmbedAllFonts true /EmbedOpenType false /ParseICCProfilesInComments true /EmbedJobOptions true /DSCReportingLevel 0 /EmitDSCWarnings false /EndPage -1 /ImageMemory 1048576 /LockDistillerParams false /MaxSubsetPct 100 /Optimize true /OPM 1 /ParseDSCComments true /ParseDSCCommentsForDocInfo true /PreserveCopyPage true /PreserveDICMYKValues true /PreserveEPSInfo true /PreserveFlatness true /PreserveHalftoneInfo false /PreserveOPIComments true /PreserveOverprintSettings true /StartPage 1 /SubsetFonts true /TransferFunctionInfo /Apply /UCRandBGInfo /Preserve /UsePrologue false /ColorSettingsFile () /AlwaysEmbed [ true ] /NeverEmbed [ true ] /AntiAliasColorImages false /CropColorImages true /ColorImageMinResolution 300 /ColorImageMinResolutionPolicy /OK /DownsampleColorImages true /ColorImageDownsampleType /Bicubic /ColorImageResolution 300 /ColorImageDepth -1 /ColorImageMinDownsampleDepth 1 /ColorImageDownsampleThreshold 1.50000 /EncodeColorImages true /ColorImageFilter /DCTEncode /AutoFilterColorImages true /ColorImageAutoFilterStrategy /JPEG /ColorACSImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /ColorImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /JPEG2000ColorACSImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /JPEG2000ColorImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /AntiAliasGrayImages false /CropGrayImages true /GrayImageMinResolution 300 /GrayImageMinResolutionPolicy /OK /DownsampleGrayImages true /GrayImageDownsampleType /Bicubic /GrayImageResolution 300 /GrayImageDepth -1 /GrayImageMinDownsampleDepth 2 /GrayImageDownsampleThreshold 1.50000 /EncodeGrayImages true /GrayImageFilter /DCTEncode /AutoFilterGrayImages true /GrayImageAutoFilterStrategy /JPEG /GrayACSImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /GrayImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /JPEG2000GrayACSImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /JPEG2000GrayImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /AntiAliasMonoImages false /CropMonoImages true /MonoImageMinResolution 1200 /MonoImageMinResolutionPolicy /OK /DownsampleMonoImages true /MonoImageDownsampleType /Bicubic /MonoImageResolution 1200 /MonoImageDepth -1 /MonoImageDownsampleThreshold 1.50000 /EncodeMonoImages true /MonoImageFilter /CCITTFaxEncode /MonoImageDict << /K -1 >> /AllowPSXObjects false /CheckCompliance [ /None ] /PDFX1aCheck false /PDFX3Check false /PDFXCompliantPDFOnly false /PDFXNoTrimBoxError true /PDFXTrimBoxToMediaBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXSetBleedBoxToMediaBox true /PDFXBleedBoxToTrimBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXOutputIntentProfile () /PDFXOutputConditionIdentifier () /PDFXOutputCondition () /PDFXRegistryName () /PDFXTrapped /False /CreateJDFFile false /Description << /ARA /BGR /CHS /CHT /CZE /DAN /DEU /ESP /ETI /FRA /GRE /HEB /HRV (Za stvaranje Adobe PDF dokumenata najpogodnijih za visokokvalitetni ispis prije tiskanja koristite ove postavke. 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