Alkylation of isobutane with olefins

Alkylation of isobutane with C3 to Cs olefins to form C7 to C9 isoparaffins is a very important industrial reaction for the production of high octane fuels. The reaction is performed in the liquid phase with sulfuric acid or nearly anhydrous hydrogen fluoride as the catalyst. These catalysts have, however, some drawbacks such as the corrosive nature of the catalyst or the disposal of enviromenttilly hazardous products. A clean process using solid catalyst remains highly desirable. 

There are many works on the alkylation of isobutane with olefins by using faujasite-type zeolites, especially rare-earth exchanged varieties. The recent progress in this field is comprehensively summarized by Weitkemp. In general, although zeolites are initially very active, they undergo rapid deactivation. 

Weitkemp studied the time course of alkylation of isobutane with n-butenes over CaX and CaY zeolites. At low times on stream, alkylation is extremely selective no olefins, naphthenes or aromatics are formed. During this initial alkylation stage, the conversion of the feed olefins is 100%. Carbon number distribution of the products at this stage is given in Fig. 4.6. A complex mixture ofCs to C12 isoparaffins is formed. In all cases, isooctanes predominate, though the distribution changes with time on 

Stream. After a certain time, the alkylation stage ends and butenes begin to appear After this point, the Cs fraction mosdy consists of octanes, indicating that butenes ar consumed mainly by dimerization or oligomerization. This change indicates that th strong acid sites required for hydride-transfer are deactivated by carbonaceou deposits. 

Because of the rapid deactivation, the alkylation of isobutane with butenes is eco nomically unattractive at the present time. 

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A. Mantilla-Ramirez, G. Ferrat-Torres, J.M. Dominguez, C. Aldana-Rivero, and M. Bernal. Influence of reaction parameters and comparison of fluorinated alumina and silica supports in the heterogeneous alkylation of isobutane with olefins. Appl. Cat. A, 143 203-214, 1996. 

In the early days, in the late 1930 s and early 1940 s, of the alkylation of isobutane with olefins using a sulfuric acid catalyst, the acid catalyst was low in cost, the production of alkylate was limited, and the discarded or used catalyst could be used in other processes, such as naphtha and lube oil treating... 

A process termed SARP has been developed for the recovery of the used or discarded catalyst from the alkylation of isobutane with olefins using strong sulfuric acid as the catalyst. The process was used commercially for several years by two companies, but currently is not in commercial operation. 

This chapter continues the discussion of the use of solid reagents to minimize exposure to hazardous reagents, to make workups easier, and to minimize waste. Liquid acids are also corrosive, may be difficult to recycle for repeated use, and may show low activity or selectivity in some reactions.1 Large amounts of sulfuric acid and hydrogen fluoride are used in petroleum refining for the alkylation of isobutane with olefins to produce high-octane gasoline.2 A typical reaction of this type (6.1) is shown. 

This is a very active research area. There is a good chance that, with further understanding of just what these catalysts are and how they work, one will be found for the commercial alkylation of isobutane with olefins. At present, the reaction must be run at subambient temperatures to avoid the side reaction of dimerization of the olefin. Perhaps, the catalyst being offered by Hydrocarbon Technologies is of this type and will be suitable. Because sulfated zirconia contains... 

The principal use of the alkylation process is the production of high octane aviation and motor gasoline blending stocks by the chemical addition of C2, C3, C4, or C5 olefins or mixtures of these olefins to an iso-paraffin, usually isobutane. Alkylation of benzene with olefins to produce styrene, cumene, and detergent alkylate are petrochemical processes. The alkylation reaction can be promoted by concentrated sulfuric acid, hydrofluoric acid, aluminum chloride, or boron fluoride at low temperatures. Thermal alkylation is possible at high temperatures and very high pressures. 

Nivarthy, G.S., Feller, A., Seshan, K., Lercher, J.A., Alkylation of isobutane with light olefins catalyzed by zeolite beta, Microporous Mesoporous Mater., 2000, 75, 35-36. 

A clear example of the possible use of acid and/or superacid solids as catalysts is the alkylation of isobutane with butenes. Isobutane alkylation with low-molecular-weight olefins is one of the most important refining process for the production of high-octane number (RON and MON), low red vapor pressure (RVP) gasoline. Currently, the reaction is carried out using H2SO4 or HF (Table 13.1), although several catalytic systems have been studied in the last few years. 

The ability of zeolites to catalyze paraffin-olefin alkylation has been known since 1968. Garwood and Venuto of Mobil described the use of rare-earth hydrogen X faujasite for the alkylation of isobutane with ethylene to give branched Cg-Cg... 

In the alkylation of isobutane with butenes, several variables have an important bearing on the quality of the alkylate produced. The most important is the concentration of isobutane in the reactor. Although theoretically only equimolecular ratios of isobutane and butene are required for the reaction, a large excess of isobutane in the reaction zone has been found necessary to suppress undesirable side reactions which result in loss of yield and octane number. Over-all isobutane-olefin ratios of 5 to 1 or higher are necessary for the production of high quality aviation alkylate. 

For purposes of plant design and for optimum operation consistent with feed stock availability, it is necessary to be able to predict accurately the octanes of the alkylate produced under varying operating conditions. Such a correlation developed from several hundred pilot plant and commercial plant tests is presented in Figures 7, 8, and 9. This correlation is applicable to sulfuric acid alkylation of isobutane with the indicated olefins, and was developed specifically for the impeller-type reaction system, although it also appears to be satisfactory for use with some other types of reactors. 

Although aviation gasoline can be made by the alkylation of isobutane with propylene, butylenes, and amylenes, the butylenes are by far the predominant feed. In a few cases a mixture of di- and triisobutylene polymers, which is a byproduct of butadiene manufacture, is used as part of the olefinic charge. Either sulfuric acid or hydrofluoric acid can be used as a catalyst when aviation gasoline is produced by the alkylation reaction. 

Albright, L., 2002, Alkylation of Isobutane with C3-C5 Olefins Feedstock Consumption, Acid Usage, and Alkylate Quality for Different Processes, Ind. Eng. Chem. Res., 41, 5627-5631... 

In other cases however, the high concentration of some reactants leads to undesired side reactions. In the alkylation of isobutane with butenes, zeolites are very efficient catalysts but lack stability because olefins are more strongly adsorbed than the paraffin and over a matter of minutes, their oligomerization takes over the alkylation reaction and deactivates the catalyst by pore blocking. 

Isobutane-to-Olefin Ratio with Propylene Feed. The isobutane-to-olefin ratio has long been recognized as an important process variable in the alkylation of isobutane with either butenes or pxopylene (Phillips Petroleum Company, 1946). By maintaining a sufficiently high concentration of isobutane in the reaction zone, the abstraction of hydride ions from isobutane is favored over abstraction from product isoparaffins. 

In the present paper, catalytic activity of a number of zeolltic catalysts In alkylation of Isobutane with various olefins have been Investigated and some considerations of ethylene alkylation have been made. 

Two-Step Alkylation of Isobutane with C4 Olefins Reactions of C4 Olefins with Sulfuric Acid... 

Albright, L. F., "Mechanism for Alkylation of Isobutane with Light Olefin", This book. Chapter 8, 1977. 

Two-step alkylation of isobutane with C. olefins not only helps clarify the mechanism of alkylation, but may be of commercial importance. Some of the advantages of the now process as compared to the conventional processes are as follows ... 

Albright, L. F., Doshi, B. M., Ferman. M. A., and Ewo, A., "Two-Step Alkylation of Isobutane with C4 Olefins Reactions of C4 Olefins with Sulfuric Acid", This book. Chapter 6 (1977)... 

Mechanism for Alkylation of Isobutane with Light Olefins... 

The basic principles of sulfuric and hydrofluoric acid catalyzed alkylation reactions have been described in many different articles and books, some of which are tabulated in the bibliography (13-23). The complexity of the reaction is such that many details could not be isolated until the advent of sophisticated analytical equipment and techniques. The fact that commercial refinery allqrlation units almost always receive feeds of varying rate and/or composition makes the analysis of such plants performance very difficult. Even with a constant feed, the number of olefinic compounds usually present in the feed promotes different reactions and side-reactions, the products of which generally end up in the alkylate product. Laboratory studies of alkylation of isobutane with individual pure olefins have provided significant data on reaction rates and yields as influenced by the common reaction variables (24). 

Li, K. W., Eckert, R. E., Albright, L. F., "Alkylation of Isobutane with Light Olefins Using Sulfuric Acid", I, II and III, presented at the American Chemical Society Meeting, (Sept. 7-12, 1969). 

The alkylation of isobutane with C4 olefins using solid acid catalysts has become a growing research field during recent years. The main reason is that the currently used processes in industry have the HF or H2SO4 acids as catalysts, both of them being very difficult of being handled or disposed of they also present severe problems for the environment. However, in spite of an important research effort carried out both by industrial (1-4) and academic (5) laboratories, it has been very difficult to solve the major problem that the solid acid catalysts present, which is the fast deactivation due to the coke deposition. 

Albright, L.F. Spalding, M.A. Faunce, J. Eckert, R.E. Alkylation of isobutane with C4 olefins. III. Two-step process using sulfuric acid as catalyst. Ind. Eng. Chem. Res. 1988,27, 391-397. 

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