Alkylation with Solid Acid Catalysts

They are dangerous to handle and to transport as they corrode storage and disposal containers. In addition, because the reaction products are mixed with acids, the separation at the end of the reaction is often a difficult and energy consuming process. Very frequently at the end of the reaction these acids are neutralized and 

however, that liquid acids are still largely used in refinery and petrochemical processes. For example, HF alkylation (for isobutane alkylation with light olefins) is still among the top-ten refining processes licensed by UOP, with over 100 units installed worldwide. However, UOP introduced from 2002 the Alkylene process, which uses a liquid phase riser reactor with a solid acid catalyst for the isobutane alkylation. However, HF alkylation remains the best economic choice [223], notwithstanding environmental and corrosion problems. Also in this case, the conventional process has been improved, for example by HF aerosol vapor suppression. Other aspects of isobutane alkylation have been reviewed by Hommeltoft [224]. 

In aromatic alkylation with olefins, the solid acid catalyst based process has instead largely substituted the homogeneous acid catalysis process. This evidences that the change of substrate (isobutane vs. aromatic) could change completely the applicability of one technology with respect to another. 

The alkylation of benzene with ethylene is an electrophilic substitution on the aromatic ring. Alkylation reactions are commonly considered as proceeding via carbenium-ion-type mechanisms. On a Bronsted acid site ethylene is protonated to form the active species. The latter can follow two major routes  

To a very small extent EB undergoes alkylation to diphenylethane. The DEB and TEB can be easily recovered by transalkylation with benzene to EB, so they can be considered useful products. Conversely, the formation of olefins and other alkylbenzenes heavily affects the efficiency of the process by increasing the specific consumption of ethylene and benzene and reducing the EB quality. 

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The low temperature regeneration procedure using ozone could be an option to be considered for a process of isobutane alkylation with solid acid catalysts. 

This section is a review of alkylation process technology. The processes in which liquid acids are used are all mature technologies and described briefly here. Information about process developments with solid acid catalysts is also presented. 

The industrial alkylation of aromatics with olefins is one of the major examples of development of environmentally friendly processes with solid acid catalysts [221, 222]. The principal products obtained are ethylbenzene (EB), cumene (CUM), p-diethylbenzene, p-diisopropylbenzene, Cio-Ci4linear alkylbenzenes (LAB) and cymene. Figure 2.28 summarizes several aromatic alkylations industrially applied for the preparation of important chemical intermediates [222]. These reactions include the most important aromatic substrates, benzene, toluene and xylene, and different olefins. They also include two different kinds of alkylation electrophilic alkylation on the aromatic ring catalyzed by acids and side-chain alkylation catalyzed by bases. In terms of production volume, add-catalyzed alkylations are by far the most... 

Alltylation of Aromatic Amines and Pyridines. Commercially important aromatic amines are aniline [62-55-5] toluidine [26915-12-8]y phenylenediamines [25265-76-5] and toluenediamines [25576 5-8] (see Amines, aromatic). The ortho alkylation of these aromatic amines with olefins, alcohols, and dienes to produce more valuable derivatives can be achieved with solid acid catalysts. For instance, 5-/ butyl-2,4-toluenediamine (C H gN2), which is used for performance polymer applications, is produced at 85% selectivity and 84% 2,4-toluenediamine [95-80-7] (2,4-TDA)... 

It has been shown in the literature that isobutane (Pc = 36.5 bar, = 408 K)/butene (Pc= 40.2 bar, Tcf= 420 K) alkylation on solid acid catalysts at supercritical temperatures suffers from increased butene oligomerization and cracking reactions at these temperatures, increasing the catalyst deactivation potential [16-18]. Lower temperatures tend to favor the alkylation reaction. Supercritical operation at 95°C can be facilitated by diluting the isopar-affin/olefin feed with suitable amounts of a low inert solvent such as CO2 (Pc = 73.8 bar. Pc = 304 K), and has been shown to give rise to steady alkylation activity on USY and beta zeolites [19]. However, the alkylate yields are very low (< 10%) on these catalysts, attributed to severe pore diffusion limitations on these catalysts. 

In transalkylation, one of the alkyl groups is transferred from one alkylaromatic molecule to another aromatic molecule. The mechanism of transalkylation was studied extensively in Friedel-Crafts chemistry. Though the reaction conditions are quite different from those of Friedel - Crafts catalysts, it seems quite probable that an essentially same mechanism is operative also in transalkylation with solid-acid catalysts. Thus, Kaeding et al. proposed the following mechanism for disproportionation of toluene over zeolites. ... 

As shown in Table 3, after a pretreatment performed at 333 K, the activity of the K3P sample increased with time on stream (TOS), giving rise to a high production of dimethylhexanes (DMH) and of olefins (Cg" ). After a dehydratation performed at 423 K, the conversion of C4= and the selectivities towards TMP were initially high. As generally observed in the aliphatic alkylation reaction with solid acids, the decrease of the catalyst activity was accompanied by a concomitant decrease of the selectivity in TMP and an increase of the selectivities in DMH and olefins (C4 dimerization) indicating... 

Friedel-Crafts alkylations are among the most important reactions in organic synthesis. Solid acid catalysts have advantages in ease of product recovery, reduced waste streams, and reduction in corrosion and toxicity. In the past, people have used (pillared) clays (18), heteropolyacids (19) and zeohtes (20) for Friedel-Craft alkylations, with mixed success. Problems included poor catalyst stabihty and low activity. Benzylation of benzene using benzyl chloride is interesting for the preparation of substitutes of polychlorobenzene in the apphcation of dielectrics. The performance of Si-TUD-1 with different heteroatoms (Fe, Ga, Sn and Ti) was evaluated, and different levels of Fe inside Si-TUD-1 (denoted Fei, Fe2, Fes and Feio) were evaluated (21). The synthesis procedure of these materials was described in detail elsewhere (22). 

Figure 2 also includes a comparative experiment, where the solid acid catalyst is a sample of non-fluorided (but calcined), acidic mordenite. Here we see a) a significant loss of alkylation activity with time on stream and b) a measurably lower... 

This contribution is an in-depth review of chemical and technological aspects of the alkylation of isobutane with lightalkenes, focused on the mechanisms operative with both liquid and solid acid catalysts. The differences in importance of the individual mechanistic steps are discussed in terms of the physical-chemical properties of specific catalysts. The impact of important process parameters on alkylation performance is deduced from the mechanism. The established industrial processes based on the application of liquid acids and recent process developments involving solid acid catalysts are described briefly. 2004 Elsevier Inc. 

The technology and chemistry of isoalkane-alkene alkylation have been thoroughly reviewed for both liquid and solid acid catalysts (15) and for solid acid catalysts alone (16). The intention of this review is to provide an up-to-date overview of the alkylation reaction with both liquid and solid acids as catalysts. The focus is on the similarities and differences between the liquid acid catalysts on one hand and solid acid catalysts, especially zeolites, on the other. Thus, the reaction mechanism, the physical properties of the individual catalysts, and their consequences for successful operation are reviewed. The final section is an overview of existing processes and new process developments utilizing solid acids. 

Table I gives the compositions of alkylates produced with various acidic catalysts. The product distribution is similar for a variety of acidic catalysts, both solid and liquid, and over a wide range of process conditions. Typically, alkylate is a mixture of methyl-branched alkanes with a high content of isooctanes. Almost all the compounds have tertiary carbon atoms only very few have quaternary carbon atoms or are non-branched. Alkylate contains not only the primary products, trimethylpentanes, but also dimethylhexanes, sometimes methylheptanes, and a considerable amount of isopentane, isohexanes, isoheptanes and hydrocarbons with nine or more carbon atoms. The complexity of the product illustrates that no simple and straightforward single-step mechanism is operative rather, the reaction involves a set of parallel and consecutive reaction steps, with the importance of the individual steps differing markedly from one catalyst to another. To arrive at this complex product distribution from two simple molecules such as isobutane and butene, reaction steps such as isomerization, oligomerization, (3-scission, and hydride transfer have to be involved.

The modem gasolines are produced by blending products from cmde oil distillation, that is, fluid catalytic cracking, hydrocraking, reforming, coking, polymerization, isomerization, and alkylation.Two clear examples of the possible use of solid-acid catalysts in refining processes are the isomerization of lineal alkanes and the alkylation of isobutene with butanes. In both these cases, and due to the octane... 

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. 

Concentrated sulfuric acid and hydrogen fluoride are still mainly used in commercial isoalkane-alkene alkylation processes.353 Because of the difficulties associated with these liquid acid catalysts (see Section 5.1.1), considerable research efforts are still devoted to find suitable solid acid catalysts for replacement.354-356 Various large-pore zeolites, mainly X and Y, and more recently zeolite Beta were studied in this reaction. Considering the reaction scheme [(Eqs (5.3)—(5.5) and Scheme 5.1)] it is obvious that the large-pore zeolitic structure is a prerequisite, since many of the reaction steps involve bimolecular bulky intermediates. In addition, the fast and easy desorption of highly branched bulky products, such as trimethylpentanes, also requires sufficient and adequate pore size. Experiments showed that even with large-pore zeolite Y, alkylation is severely diffusion limited under liquid-phase conditions.357... 

Mesitylene was alkylated with propylene or 2-propanol in supercritical CO2 using Deloxane, a polysiloxane-supported solid acid catalyst in a continuous flow reactor.406 Monoisopropylation with 100% selectivity occurred with 2-propanol. 

Here we report the synthesis and catalytic application of a new porous clay heterostructure material derived from synthetic saponite as the layered host. Saponite is a tetrahedrally charged smectite clay wherein the aluminum substitutes for silicon in the tetrahedral sheet of the 2 1 layer lattice structure. In alumina - pillared form saponite is an effective solid acid catalyst [8-10], but its catalytic utility is limited in part by a pore structure in the micropore domain. The PCH form of saponite should be much more accessible for large molecule catalysis. Accordingly, Friedel-Crafts alkylation of bulky 2, 4-di-tert-butylphenol (DBP) (molecular size (A) 9.5x6.1x4.4) with cinnamyl alcohol to produce 6,8-di-tert-butyl-2, 3-dihydro[4H] benzopyran (molecular size (A) 13.5x7.9x 4.9) was used as a probe reaction for SAP-PCH. This large substrate reaction also was selected in part because only mesoporous molecular sieves are known to provide the accessible acid sites for catalysis [11]. Conventional zeolites and pillared clays are poor catalysts for this reaction because the reagents cannot readily access the small micropores. 

The conventional resinsulfonic acids such as sulfonated polystyrenes (Dowex-50, Amberlite IR-112, and Permutit Q) are of moderate acidity with limited thermal stability. Therefore, they can be used only to catalyze alkylation of relatively reactive aromatic compounds (like phenol) with alkenes, alcohols, and alkyl halides. Nafion-H, however, has been found to be a suitable superacid catalyst in the 110-190°C temperature range to alkylate benzene with ethylene (vide infra) 16 Furthermore, various solid acid catalysts (ZSM-5, zeolite /3, MCM-22) are applied in industrial ethylbenzene technologies in the vapor phase.177... 

Friedel Crafts alkylation has been studied by Poliakoff in a continuous-flow reactor (Hitzler et al., 1998a). The reaction of mesitylene and anisole with propene or 2-propanol over a solid acid catalyst (based on a Deloxan support) in sc C02 provided exclusive formation of the monoalkylated products at 50% conversion. Use of the continuous-flow reactor prevents catalyst deactivation, and permits use of comparatively small reactors. The... 

Styrene. Styrene is the largest benzene derivative with annual consumption about 11.5 billion lb in the United States. It is produced mainly by catalytic dehydrogenation of high-purity ethylbenzene (EB) in the vapor phase. The manufacture process for EB is based on ethylene alkylation with excess benzene. This can be done in a homogeneous system with aluminum chloride catalyst or a heterogeneous solid acid catalyst in either gas or liquid-phase reaction. In the past decade, the liquid-phase alkylation with zeolite catalyst has won acceptance. Those processes have advantages of easier product separation, reducing waste stream, and less corrosion. In addition, it produces less xylene due to lower... 

Cumene (Phenol). Cumene has become the second largest chemical use for benzene. It is produced by alkylating benzene with propylene at elevated temperature and pressure in the presence of a solid acid catalyst. The U.S. production was more than 6.9 billion lb in 1999. Of this, about 96 percent then was converted to phenol. 

Sulfated zirconia is a good example of a structural Lewis acid which has been chemically treated to enhance acidity. It has been extensively studied as a solid acid catalyst for vapour phase reactions and we1112 and others14 have found that a mesoporous version of this material is a particularly effective catalyst for liquid phase Friedel-Crafts alkylation reactions and to a lesser extent Friedel-Crafts benzoylations. The commercial (MEL Chemicals Ltd) material SZ999/1 shows a nitrogen isotherm characteristic of a mesoporous solid (surface area 162 m2g, pore volume 0.22 cm3g )- Whereas microporous and mesoporous materials are capable of rapidly catalysing the alkylation of benzene with various alkenes (Table 1), on reuse only the mesoporous... 

HPAs, however, is their solubility in polar solvents or reactants, such as water or ethanol, which severely limits their application as recyclable solid acid catalysts in the liquid phase. Nonetheless, they exhibit high thermal stability and have been applied in a variety of vapor phase processes for the production of petrochemicals, e.g. olefin hydration and reaction of acetic acid with ethylene [100, 101]. In order to overcome the problem of solubility in polar media, HPAs have been immobilized by occlusion in a silica matrix using the sol-gel technique [101]. For example, silica-occluded H3PW1204o was used as an insoluble solid acid catalyst in several liquid phase reactions such as ester hydrolysis, esterification, hydration and Friedel-Crafts alkylations [101]. HPAs have also been widely applied as catalysts in organic synthesis [102]. 

AlkylClean A process for making alkylate (see previous entry) which uses a solid acid catalyst in place of the usual HF or H2S04. Developed by ABB in conjunction with Akzo Nobel and Forum Oil Gas, and first demonstrated in 1995. 

Alkylene A process for making alkylate (see previous two entries) by reacting olefins with isobutene, using a proprietary solid acid catalyst called HAL-100. The major constituents of this alkylate are branched trimethylpentanes. Developed by UOP from 1995. 

OATS [Olefinic Alkylation of Thiophenic Sulfur] A gasoline desulfurization process. Thiophenes and mercaptans are catalytically reacted with olefins to produce higher-boiling compounds that can more easily be removed by distillation prior to hydrodesulfurization. This minimizes hydrogen usage. The process uses a solid acid catalyst in a liquid-phase, fixed bed reactor. Developed by BPAmoco in 2000 and tested in Bavaria and Texas. First used commercially at the Bayernoil refinery, Neustadt, in 2001. The process won a European Environment Award in 2002. 

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