Isobutane/2-butene alkylation

An interesting variation on sulfated metal oxide type catalysts was presented by Sun et al. (198), who impregnated a dealuminated zeolite BEA with titanium and iron salts and subsequently sulfated the material. The samples exhibited a better time-on-stream behavior in the isobutane/1-butene alkylation (the reaction temperature was not given) than H-BEA and a mixture of sulfated zirconia and H-BEA. The product distribution was also better for the sulfated metal oxide-impregnated BEA samples. These results were explained by the higher concentration of strong Brpnsted acid sites of the composite materials than in H-BEA. 

Cesium salts of 12-tungstophosphoric acid have been compared to the pure acid and to a sulfated zirconia sample for isobutane/1-butene alkylation at room temperature. The salt was found to be much more active than either the acid or sulfated zirconia (201). Heteropolyacids have also been supported on sulfated zirconia catalysts. The combination was found to be superior to heteropolyacid supported on pure zirconia and on zirconia and other supports that had been treated with a variety of mineral acids (202). Solutions of heteropolyacids (containing phosphorus or silicon) in acetic acid were tested as alkylation catalysts at 323 K by Zhao et al. (203). The system was sensitive to the heteropoly acid/acetic acid ratio and the amount of crystalline water. As observed in the alkylation with conventional liquid acids, a polymer was formed, which enhanced the catalytic activity. 

Triflic acid has also been supported on a porous silica carrier (220). The authors emphasized the importance of a strong interaction between the acid and the support to prevent leaching of the acid. In pulsed liquid-phase isobutane/ 1-butene alkylation experiments at 298 K, the catalysts produced a very high-quality alkylate, made up almost exclusively of isooctanes. With silanol groups on the silica surface or with added water, triflic acid was found to form a monohydrate that was firmly grafted to the silica surface. 

Silica-supported triflic acid catalysts were prepared by various methods (treatment of silica with triflic acid at 150°C or adsorption of the acid from solutions in trifluoroacetic acid or Freon-113) and tested in the isobutane-1-butene alkylation.161 All catalysts showed high and stable activity (near-complete conversion at room temperature in a continuous flow reactor at 22 bar) and high selectivity to form saturated C8 isomers (up to 99%) and isomeric trimethylpentanes (up to 86%). Selectivities to saturated C8 isomers, however, decreased considerable with time-on-stream (79% and 80% after 24 h). 

The isobutane-1 -butene alkylation was studied in dense CO2 in both fixed-bed and slurry reactors.165-167 Both Nafion SAC-13 and Nation SAC-25 exhibited steady-state conversions and selectivities for 50 h. Enhanced Cg alkylate selectivity could be achieved at near total butene conversion. The maximum value attained, however, was only about 40%. The higher effective alkylation rate constant for SAC-25 compared to SAC-13 indicates improved accessibility of the acid sites. Nafion SAC-13 and SAC-25 applied in a study to test the effect of supercritical fluids on alkylation exhibited only modest activities.168... 

Table 9.3 Kinetic parameters and heat of reaction for isobutane/1 -butene alkylation.

Deactivation of catalysts, LaY, LaP, ASA and SZR, used in isobutane/1-butene alkylation occurs by pore blockage mechanism. The amount and the chemical nature of organic... 

Rorvik et al. studied unsupported Nafion for isobutane/1-butene alkylation in a stirred liquid phase batch reactor [12]. The production of trimethylpentanes (the most desirable alkylate product) was shown to cease within 30 minutes of operation. More recently, silica-supported Nafion was used to catalyze the same reaction [13]. Once again, rapid deactivation with respect to trimethylpentane formation was observed. It was hypothesized that the strongest acid sites—the most active for alkylation—are also the first to be poisoned. 

RON values of various alkanes and the C54. composition of isobutane/butene alkylates produced with various acids in laboratory... 

The use of a polyfunctional catalyst could enhance the life of the catalyst. A clear example is the use of H3PWi2O40-SO4 /ZrO2 mixtures for isobutane/ butenes alkylation (Table 13.4-). However, modifications of the t) pe of reactor could also favor extended catalyst longevity." During the last few years, other alternatives have been proposed that favor a better catalyst regeneration and/or lower catalyst deactivation the use of supercritical isobutene regeneration or dense-C02 enhanced the reaction media. ... 

M.F. Simpson, J. Wei, and S. Sudaresan. Kinetic analysis of isobutane/butene alkylation over ultrastable H-Y zeoUte. Ind. Eng. Chem. Res., 35 3861-3873,... 

Weitkamp, J. and Traa, Y. (1999) Isobutane/butene alkylation on solid catalysts. Where do we stand. Catal. Today, 49,193-199. 

Sarsani, V.R. and Subramaniam, B. (2009) Isobutane/butene alkylation on microporous and mesoporous solid acid catalysts probing the pore transport effeds with liquid and near critical reaction media. Green Chem., 11, 102-108. 

Petkovic, L.M. and Ginosar, D.M. (2004) The efiect of supercritical isobutane regeneration on the nature of hydrocarbons deposited on a USY zeolite catalyst utilized for isobutane/butene alkylation. Appl. Catal. A, 275, 235-245. 

Feller, A., Barth, J.-O., Guzman, A., Zuazo, I., and Lercher, J.A. (2003) Deactivation pathways in zeolite-catalyzed isobutane/butene alkylation. 

In industrial practice, two liquid acids are employed as catalysts for isobutane/ butene alkylation, namely sulfuric acid and hydrofluoric acid [3, 19, 20]. Both processes deliver a high-quality gasoline component. The catalyst consumption in the H2S04 process is high, typically 70-100kg/t The spent sulfuric acid contains tarry hydrocarbons and water and has to be processed externally. On the other hand, corrosiveness and toxicity of HF are reasons of concern that require use of additives that lower the HF vapor pressure and minimize the amount of HF released in the case of an accident. However, in many industrialized countries, new HF alkylation processes are no longer approved by authorities. 

Chapter 9 Isobutane/Butene Alkylation illustrates in detail the integration of design and plantwide control. Special attention is paid to the reaction/separation/... 

Zeolite Beta has also been studied for isobutane/butene alkylation (65, 66), but it was less selective to the desired TMP than USY, suggesting some diffusional limitations for these highly branched products at the relatively low reaction temperatures used. In fact, an increase of activity was observed when decreasing the crystal size of the Beta zeolite (66). As for USY zeolites, the activity, selectivity and deactivation rate of Beta zeolite were influenced by the presence of EFAL species (67). Medium pore zeolites, such as ZSM-5 and ZSM-11 were also found active for alkylation, but at temperatures above 100°C (68, 69). Moreover, the product obtained on ZSM-5 and ZSM-11 contained more light compounds (C5-C7), and the Os fraction was almost free of trimethylpentanes, indicating serious pore restrictions for the formation of the desired alkylation products. 

Reaction sequence I, 4, and 4-A, and sequence 6 and 6-A shown above are believed to represent the predominant ones involved in isobutane-butene alkylation, since the greater portion (80 to 90 percent) of Cs fractions from all four butenes is made up of trimethylpientanes which are predominantly 2,2,4-trimethylpentane. Hofmann and Schriesheim... 

In summary, the research work performed at the INL demonstrated that the introduction of supercritical cosolvents during the alkylation reaction did not result in improved or sustained catalytic performance. However, supercritical fluids in general and isobutane in particular were shown to be promising regenerants of some solid acid zeolite catalysts that may be utilized in isobutane/butene alkylation reaction. 

Simpson, M.F., J. Wei, and S. Sundaresan, Kinetic Analysis of Isobutane/Butene Alkylation over Ultrastable H-Y Zeolite. Industrial Engineering and Chemistry Research, 1996.35 p. 3861-3873. 

Weitkamp, J., 1980a, Isobutane/butene alkylation on cerium exchanged X and Y Zeolites, in Catalysis by Zeolites, eds B. Imelik, C. Naccache, Y. Ben Taarit, J.C. Vedrine, G. Coudurier and H. Praliaud, Vol. 5 of Studies in Surface Science and Catalysis (Elsevier, Amsterdam) pp. 65-75. 

The goal of this work is to investigate temporal alkylation activity on unsupported and supported Nafion catalysts, both macroporous in nature, for isobutane/butene alkylation in supercritical reaction mixtures in the 358-378 K range, and to examine how the product... 

Table 4. Catalytic Performance of BFs-Supported Catalysts for the Isobutane/Butene Alkylation in a Semibatch Reactor-...

Alkylation Mechanism with Zeolite Catalysts. The fact that the alkylate produced over a zeolite solid acid is quite similar in terms of product distribution to that obtained with sulfuric acid (Table 8) strongly points toward an alike general reaction mechanism occurring in both types of catalysts. The main catalytic cycles involved in the isobutane/butene alkylation mechanism are illustrated in Figure 6. 

Fig. 8. Experimental reaction system for performing isobutane/ -butene alkylation comprising a fixed bed reactor and online differential analysis of reaction products.

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