Solid acids alkylations

Since the discovery of alkylation, the elucidation of its mechanism has attracted great interest. The early findings are associated with Schmerling (17-19), who successfully applied a carbenium ion mechanism with a set of consecutive and simultaneous reaction steps to describe the observed reaction kinetics. Later, most of the mechanistic information about sulfuric acid-catalyzed processes was provided by Albright. Much less information is available about hydrofluoric acid as catalyst. In the following, a consolidated view of the alkylation mechanism is presented. Similarities and dissimilarities between zeolites as representatives of solid acid alkylation catalysts and HF and H2S04 as liquid catalysts are highlighted. Experimental results are compared with quantum-chemical calculations of the individual reaction steps in various media. 

Scale-up strategy applied to solid-acid alkylation process. Oil Gas J., 48-54. 

Environmental and safety concerns regarding acid-based processes are promoting research and development efforts on solid-acid alkylation processes. Liquid catalysts pose possible risks to the environment, employees, and the general public from accidental atmospheric releases. Also, these acid... 

A second indirect alkylation process, InAlk, is also a solid catalyst process (Fig. 18.25).12 29 InAlk combines two commercially proven technologies polymerization and olefin saturation. Isobutylene is reacted with light olefins (C3-C5) in a polymerization reactor. The resulting mixture of iso-olefins is saturated in the hydrogenation reactor. Excess hydrogen is recycled and the product is stabilized to produce a paraffinic gasoline blending stream. Yet, new solid-acid alkylation processes face tech-... 

According to the open literature, other solid acid alkylation catalysts are generally susceptible to poisoning/deactivation by water and other common feed impurities (e.g., oxygenates, sulfur compounds, dienes, etc.), thus necessitating (potentially costly) feedstock pretreatment for their removal. In some cases, this requirement is further mandated by the potential corrosion problems associated with the use of halogens in the catalyst system. 

D Amico, V.J. et al. (2004) AlkyClean solid acid alkylation will it finally become a reality Akzo Nobel Catalysts Scope Symposium, Florence, Italy, June 21-23. 

Besides, it is worth mentioning that despite ionic liquids having the appropriate composition might be an alternative to the less environment friendly H2SO4 and HF acids, it would be much more interesting from the practical viewpoint to immobilize these ionic liquids on solid supports so as the resulting catalyst contains ionic complexes in which either anion or cation is covalently bonded to the porous carrier (70,71). In this respect, it has been shown that the imidazolium-type ionic liquid immobilized on a high surface area (946 m /g) ordered mesoporous silica (Si-MCM-41) performed relatively well for the alkylation reaction at temperatures around 80° C, with a selectivity to isooctanes of about 60 wt% (72). Nevertheless, as usually occurs in solid acid alkylation, the activity of immobilized IL catalyst starts to fall at a certain time on stream after which butenes dimerization instead of alkylation becomes the predominant reaction (72). 

Fixed bed and liquid riser type reactors are found in the majority of the proposed commercial solid acid alkylation processes, as will be detailed hereinafter. Nevertheless, other reactor configurations have been proposed for alkylation processes employing solid catalysts. For instance, a spouted bed reactor is constituted by a gas flow propelled riser, an annular downcomer where part of the solid and liquid are recycled to the reactor inlet and a hydrocyclon in which the solid catalyst is collected to be regenerated in continuous at a neighboring unit. Recently, a spouted bed reactor equipped with a fluidized-bed catalyst regenerator has been designed to be used in solid alkylation processes, employing a Pt/S0x(Zr-Ti)02... 

Several applications of the in situ decoking concept have appeared in the literature. One such application involves stabilizing the activity of solid acid catalysts such as in alkylation reactions. As reviewed elsewhere (55), numerous efforts aimed at developing solid acid alkylation catalysts and solid acid-based isobutane-olefin alkylation processes have been reported for more than three decades. However, to date, none of the solid alkylation catalysts has gained acceptance in industry for one or more of the following drawbacks rapid catalyst... 

Example 2. Solid Acid Alkylation—Solids Flow Pattern in a Riser 20... 

EXAMPLE 2. SOLID ACID ALKYLATION—SOLIDS FLOW PATTERN IN A RISER... 

For solid acid alkylation, the phenomenological model for the riser consists of plug-flow of hquid, fuUy developed sohds velocity and sohds holdup profile with superimposed axial and radial sohds diffusivities (Ramaswamy et al., 2005). These eddy diffusivities can be computed from the 3D CFD model. This model can now be coupled with appropriate reaction and deactivation kinetics. CFD can now provide ah the required model parameters. In summary, a direct measurement of the sohds RTD is also obtained from CARPT data. As evident from Fig. 1.8 (Roy, 2000), the flow pattern is not ideal plug-flow as assumed by many, and the RTD of sohds depends on the conditions used and varies from two to six tanks-in-series. 

There is one very recent example of application of the rigorous approach outlined here. It deals with the deactivation in the solid acid alkylation process for the production of high octane gasoline [Martinis and Froment, 2006]. The kinetic modeling of the reaction between 1-butene and i-butane on a Y-zeolite catalyst was expressed in terms of elementary steps and the kinetics were written in terms of single events, discussed in Chapters 1 and 2. It was found that the... 

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