Mobil, zeolite catalyst

At the low-molecular-weight end of the spectrum, a process newly commercialized by Mobil for converting methanol into gasoline has significantly expanded opportunities in C-1 chemistry— the upgrading of one-carbon molectrles to mrrlticarbon products. The process involves the use of ZSM-5, a shape-selective zeolite catalyst. (See "Zeolite and Shape-Selective Catalysts" in Chapter 9.)... 

FIGURE 9.2 This high-resolution electron micrograph shows the unique pore structure of the ZSM-5 zeolite catalyst. Molecules such as methanol and hydrocarbons can he catalytically converted within the pores to valuable fuels and lubricant products. Courtesy, Mobil Research and Development Corporation. 

Although the mechanism proposed for the ZSM-5/methanol system adequately explains the production of the primary C2-C5 products, it is not clear how these are converted into the final gasoline product or indeed why this product should be so rich in aromatics. Production of olefins from methanol over zeolite catalysts has previously been described (110, 112) however, the ZSM-5 system appears to be unique with respect to both product selectivity and catalyst stability. Mobil now has some 140 patents relating to the preparation and use of ZSM-5 zeolites and has stated that "given a favorable economic and political climate a commercial unit could be in operation by the early 1980 s (101). 

EBMax A continuous, liquid-phase process for making ethylbenzene from ethylene and benzene, using a zeolite catalyst. Developed by Raytheon Engineers and Constructors and Mobil Oil Corporation and first installed at Chiba Styrene Monomer in Japan in 1995. Generally similar to the Mobil/Badger process, but the improved catalyst permits the reactor size to be reduced by two thirds. 

MLPI [Mobil low pressure isomerization] One of a family of processes developed by Mobil Corporation for isomerizing xylene mixtures, using a zeolite catalyst. This one was developed in 1977. See also LTI, MHTI, MVPI. 

Mobil The Mobil Corporation has developed many processes, but in the 1990s the one most associated with its name was the Methanol to Gasoline process, using a zeolite catalyst. See MTG. 

Octgain A hydrofinishing process which reduces the sulfur and olefin content of gasoline without reducing its octane number. A zeolite catalyst is used. Developed by Mobil in 1994. Chem. Eng. (N.Y.), 1994,101(7), 25. 

Alkylation over the MWW Zeolite. The MWW (or MCM-22) zeolite developed by Mobil as catalyst for ethylbenzene and cumene production deserves particular attention. Indeed, this zeolite presents unique structural features (Figure 12.5). Its structure is constituted of three independent pore systems " large supercages (inner diameter of 7.1 A dehned by a 12-member-ring [12-MR], height 18.2 A) each connected to six others through 10-MR apertures... 

Note that ethylbenzene is a derivative of two basic organic chemicals, ethylene and benzene. A vapor-phase method with boron trifluoride, phosphoric acid, or alumina-silica as catalysts has given away to a liquid-phase reaction with aluminum chloride at 90°C and atmospheric pressure. A new Mobil-Badger zeolite catalyst at 420°C and 175-300 psi in the gas phase may be the method of choice for future plants to avoid corrosion problems. The mechanism of the reaction involves complexation of the... 

One shortcoming of the Fischer-Tropsch synthesis is its lack of selectivity in giving complex product mixtures. In an attempt to improve the selectivity of syngas-based hydrocarbon synthesis, Mobil researchers developed a process consisting of converting methyl alcohol (itself, however, produced from syngas) to gasoline (or other hydrocarbons) over a shape-selective intermediate-pore-size zeolite catalyst (H-ZSM-5) 22 78... 

C, 10-50 atm). Xylene benzene ratios of 1-10 may be obtained. Metal catalysts were later replaced by zeolites.210,211,326-328 The most recent development is the Mobil selective toluene disproportionation process,329 which takes advantage of the high para shape selectivity of a zeolite catalyst.210 The catalyst activated by a novel procedure ensures a p-xylene content of up to 95%. After the successful com-mercialization at an Enichem refinery in Italy, the process is now licensed. The catalysts and technologies applied in toluene disproportionation may be also used for transalkylation324,325,331 [Eq. (5.74)] ... 

Mobil ZSM-5 zeolite catalysts can be modified to reduce the effective pore and channel dimensions. These modified zeolites allow discrimination between molecules of slightly different dimensions. Because of this shape-selective action, p-ethyltoluene is able to diffuse out of the catalyst pores at a rate about three orders of magnitude greater than the two regioisomers. As a result, p-ethyltoluene is formed with very high (97%) selectivity.333... 

In recent years alkylations have been accomplished with acidic zeolite catalysts, most nobably ZSM-5. A ZSM-5 ethylbenzene process was commercialized jointly by Mobil Co. and Badger America in 1976 (24). The vapor-phase reaction occurs at temperatures above 370°C over a fixed bed of catalyst at 1.4—2.8 MPa (200—400 psi) with high ethylene space velocities. A typical molar ethylene to benzene ratio is about 1—1.2. The conversion to ethylbenzene is quantitative. The principal advantages of zeolite-based routes are easy recovery of products, elimination of corrosive or environmentally unacceptable by-products, high product yields and selectivities, and high process heat recovery (25,26). 

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. 

Mobil s High Temperature Isomerization (MHTI) process, which was introduced in 1981, uses Pt on an acidic ZSM-5 zeolite catalyst to isomerize the xylenes and hydrodealkylate EB to benzene and ethane (126). This process is particularly suited for unextracted feeds containing Cg+ aliphatics, because this catalyst is capable of cracking them to light paraffins. Reaction occurs in the vapor phase to produce a PX concentration slightly higher than equilibrium, ie, 102—104% of equilibrium. EB conversion is about 40—65%, with xylene losses of about 2%. Reaction conditions are temperature of 427—460°C, pressure of 1480—1825 kPa, WHSV of 10—12, and a H2/hydrocarbon molar ratio of 1.5—2 1. Compared to the MVPI process, the MHTI process has lower xylene losses and lower formation of heavy aromatics. 

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). 

The key to the process was the development by Mobil of a size-selective zeolite catalyst, whose geometry and pore dimensions have been tailored so that it selectively produces hydrocarbon molecules within a desired size range. This is a highly exothermic reaction and the major problem in any plant design is the reactor system to effect the necessary heat removal. A plant completed in 1985 in New Zealand uses about 4 million m3/day of natural gas as the feedstock to produce the methanol by the ICI procedure described above. In 1990 the plant produced about 16,000 bbl/day of gasoline, which is somewhat above its design output. 

The transport and adsorption properties of hydrocarbons on microporous zeolites have been of practical interest due to the important properties of zeolites as shape-selective adsorbents and catalysts. The system of benzene adsorbed on synthetic faujasite-type zeolites has been thoroughly studied because benzene is an ideal probe molecule and the related role of aromatics in zeolitic catalysts for alkylation and cracking reactions. For instance, its mobility and thermodynamic properties have been studied by conventional diffusion 1-6) and adsorption 7-9) techniques. Moreover, the adsorbate-zeolite interactions and related motion and location of the adsorbate molecules within the zeolite cavities have been investigated by theoretical calculations 10-15) and by various spectroscopic methods such as UV (16, 17), IR 17-23), neutron 24-27), Raman 28), and NMR 29-39). 

Fig. 19.25. Schematic of Mobil s fluid-bed MTG process, which uses a unique zeolite catalyst to convert methanol to high octane, unleaded gasoline. (CourtesyThe Pace Company, Denver, CO.)...

Another key step was the demonstration by P.B. Weisz and coworkers (3-5) of the shape selectivity of zeolite catalysts related to molecular sieving (1960). This initiated further research in the synthesis of new zeolites as well as industrial applications based on this property. The first commercial shape-selective process, Selectoforming, was developed by Mobil (1968) and allowed the selective cracking of the low octane (n-alkane) components of light gasoline over a natural zeolite (erionite) (6). 

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