Chemistry isobutane alkylation

Slightly over half of the papers deal with the alkylation of isobutane widi light olefins to produce high quality gasoline blending hydrocarbons. New information is presented for isobutane alkylation relative to die chemistry and mechanism, process improvements, recovery of acid catalyst, and status of commercial units. Papers are also presented for die alkylation of aromatics, heterocyclics, coal, and other hydrocarbons. Alkylations using transition metal catalysts, strong acids, free radicals, and bases are also reported. 

The first group of papers (chapters 1-12) covers the more theoretical and fundamental aspects of alkylation, including the chemistry, mechanism, and various techniques and catalysts that can be used besides sulfuric acid and hydrogen fluoride. Most papers of this group deal with isobutane alkylation for production of high quality fuels. 

Cationic reaction steps occur when protonic acids or Friedel-Crafts-type catalysts are used (1,2). The chemistry for isobutane alkylation is discussed next. 

The forty-eighth volume of Advances in Catalysis includes a description of a new and increasingly well understood class of catalysts (titanosilicates), a review of transmission electron microscopy and related methods applied to catalyst characterization, and summaries of the chemistry and processes of isobutane-alkene alkylation and partial oxidation and C02 reforming of methane to synthesis gas. 

Chemistry and Technology of Isobutane/Alkene Alkylation Catalyzed by Liquid and Solid Acids... 

Feller, A. and Lercher, J.A. (2004) Chemistry and technology of isobutane/ alkene alkylation catalyzed by liquid and solid acids. Adv. Catal., 48, 229-295. 

Albright, Lyle K.W. Li, Eckert, Roger E., "Alkylation of Isobutane with Light Olefins Using Sulfuric Acid" Industrial Engineering Chemistry, (1970) Vol. 9, Alkylation. 

In current processes that use either sulfuric acid or HF, isobutane in large excess and olefins are introduced as liquids into the reactor. After completion of the reactions, the liquid-liquid dispersions are separated by decanting. The alkylate product is separated by distillation or stripping from the unreacted isobutane, which is recirculated to the reactor. This entry reviews the chemistry, physicochemical phenomena, current processes, and finally suggests methods to improve significantly the alkylation process. 

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. 

Noteworthy also is the selectivity for higher alkanes. For example the metathesis of propane gives mainly butanes rather than pentanes, and butane rather than isobutane. This is in agreement with stereoelectronic factors that favor the transfer of one carbon on to, preferentially, primary alkyl surface species, leaving tertiary alkyl species unreactive (Scheme 10). The alkane selectivity also depends on the structure of the starting alkane (Figure 1). Overall, this reaction shows the potential of surface organometallic chemistry, and new, unprecedented reactions will be probably discovered in the near future. 

This method of nomenclature is called systematic nomenclature. It is also called lUPAC nomenclature because it was designed by a commission of the International Union of Pure and Applied Chemistry (abbreviated lUPAC and pronounced eye-you-pack ) at a meeting in Geneva, Switzerland, in 1892. The lUPAC mles have been continually revised by the commission since then. Names such as isobutane and neopentane—nonsystematic names—are called common names and are shown in red in this text. The systematic or lUPAC names are shown in blue. Before we can understand how a systematic name for an alkane is constructed, we must learn how to name alkyl substituents. 

Considering alkylation reactions of isobutane with both liquid and solid catalysts, the compositions of the alkylate products are quite similar except fewer heavy isoparaffins are found with the solid catalyst. The lower levels of diffusivity of the heavy isoparaffins out of the pores would explain this observation (41). Heavy isoparaffins are also precursors for CPs. Since alkylate compositions are similar with both types of catalysts, the overall chemistries are probably similar. Temperatures employed, however, vary from about 5-15°C with sulfuric acid to up to 100°C with solid catalysts (42-46). In this range, higher temperatures are used with solid catalysts to minimize the adsorption of olefins on the catalyst surfaces. The higher temperatures result in lower quality (or lower octane number) alkylates plus increased formation of CPs. Super-critical fluids have been tested to promote higher diffusion coefficients. There is no known evidence that such fluids substantially improve the overall alkylation reactions. 

Investigations of both the chemistry and physical phenomena that occur during alkylation reactions have been highly successful in improving commercial processes. Yet, further improvements seem possible. For the alkylation of isobutane, the following objectives are desired higher quality alkylates, increased yields of... 

Albright LP, Kranz KE Alkylation of isobutane withpentenes using sulfuric acid as a catalyst chemistry and reaction mechanisms, Ind Eng Chem Res 31 475—481, 1992. http //dx.doi. org/10.1021/ie00002a004. 

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