Zeolites alkylation process

The numbers for the liquid acids are taken from Refs. (12,23,221). As zeolites are not used in industrial alkylation process, the given values represent the judgment of the authors extracted from laboratory and pilot scale data obtained in a slurry reactor. 

As in FCC, the hydrocarbons can be burned off the catalyst surface. This requires a catalyst with extreme temperature stability, which only ultrastable zeolites achieve. Moreover, as the alkylation process is exothermic and conducted at low to moderate temperatures, large amounts of process heat have to be removed. 

Most of the commercial zeolite catalyzed processes occur either through acid catalysis fluid catalytic cracking (FCC), aromatic alkylation, methanol to olefins (MTO),... 

The large demand for benzene is due to its use as a starting material in the production of polystyrene, acrylonitrile styrene butadiene rubber, nylons, polycarbonates and linear alkyl benzene detergent. All of these final chemical products that are suitable to form into consumer goods have multiple chemical transformations in various industrial processes to obtain them from benzene. Because the production of benzene does not involve a liquid adsorptive process on a zeolite, these processes are not described here but can be found in other sources. However, it is important to note that benzene is typically a large byproduct from an aromatics... 

The reaction mechanism including the formation and decomposition of quaternary cations may be a general pathway in amine alkylation processes on acidic zeolites. Pouilloux et al. (247), for example, synthesized dimethylethylamine from ethylamine and methanol on an acidic catalyst. At the reaction temperature of 503 K, trimethylamine was determined by gas chromatographic analysis, which can be explained by the formation and decomposition of trimethylethylammonium ions, (CIl3)3N CH2CH3. 

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... 

Solid Acid Catalysts. There have been commercial alkylation processes in operation that apply solid acids (viz., zeolites) in the manufacture of ethylbenzene... 

ABB Lummus Crest Inc. and Unocal Corp. have licensed a benzene alkylation process using a proprietary zeolite catalyst. Unlike the Mobil-Badger process, the Unocal-Lummus process is suitable for either ethylbenzene or cumene manufacture (27,28). 

Zeolite-Based Alkylation. Zeolites have the advantage of being noncot-rosive and environmentally benign. The Mobil-Badger vapor-phase ethylbenzene process was ihe lirsl zeolite-based process to achieve commercial success. It is based on a synthetic zeolite catalyst. ZSM-5. and has the desirable characteristics of high activity, low oligomerization, and low coke formation. See also Molecular Sieves. 

Alkylation. Ethylbenzene [100-41-4], the precursor of styrene, is produced from benzene and ethylene. The ethylation of benzene is conducted either in the liquid phase in the presence of a Friedel-Crafts catalyst (A1C13, BF3, FeCl3) or in the vapor phase with a suitable catalyst. The Monsanto/Lummus process uses an aluminum chloride catalyst that yields more than 99% ethylbenzene (13). More recently, Lummus and Union Oil commercialized a zeolite catalyst process for liquid-phase alkylation (14). Badger and Mobil also have a vapor-phase alkylation process using zeolite catalysts (15). Almost all ethylbenzene produced is used for the manufacture of styrene [100-42-3], which is obtained by dehydrogenation in the presence of a suitable catalyst at 550—640°C and relatively low pressure, <0.1 MPa (<1 atm). 

Beside isopropyl benzene (IPB) a substantial amount of polyalkylates is formed by consecutive reactions, mostly as C6H5-(C3H7)2 (DIPB) with some C6H5-(C3H7)3 (TPB). The main reaction has a large exothermal effect, of-113kJ/mol in standard conditions. The alkylation reaction is promoted by acid-type catalysts. The synthesis can be performed in gas or liquid phase. Before 1990 gas-phase alkylation processes dominated, but today liquid-phase processes with zeolite catalysts prevail. Recent developments make use of reactive distillation. 

Over 90 percent of all ethylbenzene is produced by alkylation of benzene with ethylene in the presence of an acidic catalyst such as aluminum chloride or an acidic zeolite. Figure 10.13 shows a liquid phase alkylation process with zeolite catalyst. 

Alkylation. In the field of alkylation of benzene with ethene zeolite-based catalysts are used for the past 20 years, replacing the conventional A1C13- and BF3-on-alumina based processes. Here the question in case of a new plant is not whether a zeolite-based process will be selected but rather which one to choose. The Mobil-Badger process uses ZSM-5 as the catalyst and is the most widely applied though recently other zeolites (Y, Beta and MCM-22) have come to the fore. 

To obtain the coking mechanism of zeolite catalyst for SCFP alkylation of benzene, two kinds of the zeolite used in LP and SCFP alkylation processes were analyzed by using the conventional catalyst analysis methods. Fresh zeolite is also analyzed for comparison. 

Here we will describe the main aspects of the chemistry involved in selected zeolite-catalyzed processes in the field of oil refining and petrochemistry, such as short paraffin aromatization, skeletal isomerization of n-paraffins and n-olefins, isoparaffin/olefin alkylation, and catalytic cracking. 

The mechanism of ethylbenzene disproportionation depends on the zeolite pore structure (3). With large pore zeolites, this reaction occurs mainly through the carbocation chain mechanism proposed for xylene disproportionation (Figure 9.4) which involves benzylic carbocations and diarylmethane intermediates. With MFI zeolites in the pores of which steric constraints limit the formation of the bulky diarylmethane intermediates, ethylbenzene disproportionation occurs mainly through a successive dealkylation-alkylation process ... 

Cumene capacity topped 9.5 million metric tons in 1998 and is projected to reach 10.4 million metric tons by the end of 2003 (19). Like ethylbenzene, cumene is used almost exclusively as a chemical intermediate. Its primary use is in the coproduction of phenol and acetone through cumene peroxidation. Phenolic resins and bisphenol A are the main end uses for phenol. Bisphenol A, which is produced from phenol and acetone, has been the main driver behind increased phenol demand. Its end use applications are in polycarbonate and epoxy resins. The growth rate of cumene is closely related to that of phenol and is expected to be approximately 5.1% per year worldwide over the next five years. Process technologies for both chemicals have been moving away from conventional aluminum chloride and phosphoric acid catalyzed Friedel-Crafts alkylation of benzene, toward zeolite-based processes. 

Application Advanced technology to produce high-purity cumene from propylene and benzene using patented catalytic distillation (CD) technology. The CDCumene process uses a specially formulated zeolite alkylation catalyst packaged in a proprietary CD structure and another specially formulated zeolite transalkylation catalyst in loose form. 

Friedel-Crafts alkylation processes were traditionally operated at 65-70°C with AICI3 and at 40-60°C with HF. A variety of solid acid catalysts have been developed at the laboratory level, mainly based on zeolites, heteropolyacids or sulfated zirconia (zirconia treated with sulfuric acid). The most recent industrial achievement is the Detal process (UOP-CEPSA) which is based on silica-alumina impregnated with HF. The selectivity towards linear alkylbenzenes exceeds 95%. The cymene processes use AICI3 in the liquid phase or supported phosphoric acid as catalysts. 

Conventional sulfuric acid and HF alkylation processes ( >2, ) employ liquid-liquid catalytic systems which are expensive and troublesome because of such problems as maintaining an acid/hydrocarbon emulsion, product separation and waste disposal (H2SO4 process only). A solid catalyst should eliminate many of these problems. In view of their high activity, zeolites have been used by a number of workers (4,5,6,2) cata-... 

Acidic zeolites are known for their excellent catalytic activity in cracking and isomerization of hydrocarbons (75). In the absence of metal, however, these catalysts rapidly deactivate due to the formation of carbonaceous products, usually referred to as coke. The carbonaceous residues are mainly formed via alkylaromatics and polyaromatics, which are the result of dehydrogenation, cyclization, and further alkylation processes. The coke deposits lower the catalytic activity by site poisoning and eventually also by pore blocking, which inhibits access of hydrocarbon molecules to the acid sites (286). 

While the structure of beta was being investigated, new uses for this zeolite were being discovered. A major breakthrough came in late 1988 when workers at Chevron invented a liquid phase alkylation process using beta zeolite catalyst. Chevron patented the process in 1990. While Chevron had significant commercial experience with the use of Y (FAU) zeolite in liquid phase aromatic alkylation. Chevron quickly recognized the benefits of beta over Y as well and other... 

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