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Ind. Eng. Chem. Res. 2005, 44, 1102
Rebuttal to the Comments of Professor Albright on the Paper “Mathematical Description of Isobutane Alkylation with Butenes in the Presence of Trifluoromethanesulfonic Acid” Anatoly S. Berenblyum,*,† Evgeny A. Katsman,‡ and Sven I. Hommeltoft§ Haldor Topsøe A/S (Moscow Representative Office), Bryusov Street 11, 103009 Moscow, Russia, The All Russian Research Institute for Organic Synthesis Company, Radio Street 12, 107005 Moscow, Russia, and Haldor Topsøe A/S, DK-2800 Lyngby, Denmark
Sir: We are pleased that our paper generated interest and that we have the possibility to further discuss this interesting alkylation reaction chemistry. In the following, we endeavor to respond to the comments of Professor Albright. We agree with Professor Albright that our model is empirical in nature. We would like to add that the mathematical model describes a homogeneous system with one or two liquid phases and with varying acidity and phase volume ratio. It is neither presented nor intended as a model for a specific “system tested by Haldor Topsøe A/S”. We assume that Professor Albright refers to the trademarked FBA (fixed-bed alkylation) technology. As anticipated, we do observe a product mixture of C8H18 isomers predominantly trimethylpentanes (∼97%), and the relative ratio of these toward the end of reaction appears to be consistent with the formation of the corresponding equilibrium mixture of C8H17+ carbenium cations. We share the interest of Professor Albright in the chemical nature of ASOs and in their effect on alkylation chemistry. ASOs are a complex mixture of unsaturated cyclic hydrocarbons, which we have found can be represented by the generic formula C20H36 (Table 1, footnote b, p 6989), giving a H/C ratio of 1.8. This and other aspects of ASO chemistry including evidence of the formation of an ASO-acid complex of the general formula [ASO‚2TfOH] are published elsewhere.1,2 The intention of the article “Mathematical Description of Isobutane Alkylation with Butenes in the Presence of Trifluoromethanesulfonic Acid” is to present a mathematical description of this chemistry including the already-published observations on the effect of ASOs. The effect of ASOs on the triflic acid-catalyzed alkylation seems to differ from the observations made by Professor Albright in his work with sulfuric acid. Professor Albright and his associates, for example, reported that small amounts of ASOs had an accelerating effect on the sulfuric acid-catalyzed alkylation. He attributes this effect to ASOs acting as hydride donors. We did not observe this effect in the triflic acid-catalyzed isobutane alkylation. This difference might reflect the different physical natures of triflic acid and sulfuric acid. Triflic acid has a low viscosity and is capable of dissolving significant amounts of isobutane, whereas sulfuric acid has a high viscosity and a much poorer ability to dissolve isobutane. Phase transfer between the * To whom correspondence should be addressed. E-mail:
[email protected]. † Haldor Topsøe A/S (Moscow Representative Office). ‡ The All Russian Research Institute for Organic Synthesis Company. § Haldor Topsøe A/S.
acid phase and the hydrocarbon phase is much easier in the triflic acid system than in the sulfuric acid system, and because ASOs in their protonated forms can act as phase-transfer agents, ASOs are suspected to have a more pronounced effect on mass transfer in sulfuric acid-catalyzed alkylation. Furthermore, the solubility of isobutane in triflic acid means that isobutane is available for direct hydride-transfer reactions, making the need for ASOs as a hydride source less important in triflic acid-catalyzed alkylation than in sulfuric acid-catalyzed alkylation. Concerning the effect of agitation, we stated that the experiments were conducted in a kinetic regime (3000 rpm). Contrary to Professor Albright’s expectations, neither the reaction rate nor the product composition depended on the agitation intensity in the 1500-3000 rpm interval. We agree with Professor Albright that the reaction of sec-butyl ester with isobutane to form alkylate and acid is not a simple second-order reaction. This is reflected in the mechanism, which includes steps 5a and 6a (Table 1, p 6989). More information about the ester chemistry and its importance in triflic acid-catalyzed alkylation is published elsewhere.3,4 With respect to the butyl cations involved in the alkylation, the sec-butyl cations are formed initially from 2-butenes and/or from sec-butyl ester, whereas tertbutyl cations are formed as a result of hydride-ion transfer from isobutane to carbenium cations. Whether the sec-butyl carbenium ion isomerizes to tert-butyl carbenium ion or not does not have any impact on the mathematical model. Literature Cited (1) Berenblyum, A. S.; Ovsyannikova, L. V.; Katsman, E. A.; Zavilla, J.; Hommeltoft, S. I.; Karasev, Yu. Z. Acid soluble oil, byproduct formed in isobutane alkylation with alkene in the presence of trifluoro methane sulfonic acid. Part I. Acid soluble oil composition and its poisoning effect. Appl. Catal. A 2002, 232, 51. (2) Katsman, E. A.; Berenblyum, A. S.; Zavilla, J.; Hommeltoft, S. I. Poisoning Effect of Acid Soluble Oil on Triflic Acid-Catalyzed Isobutane Alkylation. Kinet. Catal. 2004, 45(5), 676. (3) Hommeltoft, S. I.; Ekelund, O. E.; Zavilla, J. Role of Ester Intermediates in Isobutane Alkylation and Its Consequence for the Choice of Catalyst System. Ind. Eng. Chem. Res. 1997, 36, 6(9), 3491. (4) Hommeltoft, S. I.; Berenblyum, A. S.; Zavilla, J.; Katsman, E. A.; Ovsyannikova, L. V. Reaction Steps Involved in the Isobutane Alkylation with Butenes. Div. Pet. Chem. Prepr. 1999, 44, 130.
IE040289J
10.1021/ie040289j CCC: $30.25 © 2005 American Chemical Society Published on Web 01/19/2005
