Zeolite, commercial application

The unique properhes of zeolite materials combined with the conhnuous separahon properhes of membranes make zeolite membranes very attrachve for a wide range of separahon and catalysis applications. Zeolite membranes, however, have poor processability, poor mechanical stability and are much more expensive than the commercial polymer membranes with current state-of-the-art membrane manufacturing process. So far, the only large-scale commercial zeolite membrane is the A-type zeolite membrane and it has been used for dehydrahon of alcohols [22]. Further advancement in making thinner zeolite membranes and continuous improvement in membrane produchon techniques and reproducibility will make zeolite membranes more successful in commercial applicahons. 

Chapter 7 gives a review of the technology and applications of zeolites in liquid adsorptive separation of petrochemical aromatic hydrocarbons. The application of zeolites to petrochemical aromatic production may be the area where zeolites have had their largest positive economic impact, accounting for the production of tens of millions of tonnes of high-value aromatic petrochemicals annually. The nonaromatic hydrocarbon liquid phase adsorption review in Chapter 8 contains both general process concepts as well as sufficient individual process details for one to understand both commercially practiced and academic non-aromatic separations. 

The major problem of the application of zeolites in alkane-alkene alkylation is their rapid deactivation by carbonaceous deposits. These either strongly adsorb on acidic sites or block the pores preventing the access of the reactants to the active sites. A further problem is that in addition to activity loss, the selectivity of the zeolite-catalyzed alkylation also decreases severely. Specifically, alkene formation through oligomerization becomes the dominant reaction. This is explained by decreasing ability of the aging catalyst to promote intermolecular hydride transfer. These are the main reasons why the developments of several commercial processes reached only the pilot plant stage.356 New observations with Y zeolites reconfirm the problems found in earlier studies.358,359... 

New applications of zeolite adsorption developed recently for separation and purification processes are reviewed. Major commercial processes are discussed in areas of hydrocarbon separation, drying gases and liquids, separation and purification of industrial streams, pollution control, and nonregenerative applications. Special emphasis is placed on important commercial processes and potentially important applications. Important properties of zeolite adsorbents for these applications are adsorption capacity and selectivity, adsorption and desorption rate, physical strength and attrition resistance, low catalytic activity, thermal-hydrothermal and chemical stabilityy and particle size and shape. Apparent bulk density is important because it is related to adsorptive capacity per unit volume and to the rate of adsorption-desorption. However, more important factors controlling the raJtes are crystal size and macropore size distribution. 

A major application of synthetic and natural zeolites Is in dehydration processes. However, much of the published work has been concentrated on the drying of either gases or liquid paraffinic hydrocarbons, while relatively little published Information exists on commercial application of zeolites for dehydration of other liquid feedstocks. 

Table 3.6 shows that zeolites Na-X and Na-Y have been produced depending on the reaction time. These materials are similar in phase composition to commercial Na-X and Na-Y zeolites, because, are composed of about 80 wt % of the zeolitic phase. In commercial zeolites because part of the phases are binders [124], the amount of zeolite is about 80 wt %. Applications of these type of materials are described elsewhere [11,25,52,125,126],... 

As far as commercial applications of zeolites are concerned, the following list can be made ... 

Sophisticated catalysts, such as ZSM-5 or HZSM-5 [22] and other zeolites are also suggested in numerous papers, e.g. KEY [23], HY and H-mordenite [24], Re-zeolite-based Engelhardt FCC commercial catalyst [25], and steamed commercial zeolite catalyst [26]. These investigations are mainly devoted to fundamental studies and the correlation between feed composition, catalyst properties, process parameters and efficiency connected with prodnct distribution. Iron supported on silica-alumina, mesoporous silica and active carbons serves as the next example of materials applied in the waste plastics cracking [27, 28]. On the other hand, according to some results [29] application of cracking catalysts such as Zn-13X, Fe-5A and CoMo-HY are ineffective in waste plastics cracking. 

N. Y. Chen (Mobil Research Development Corp., Princeton, N. J. 08540) It might be of interest to the audience, particularly to those who are not familiar with the application of zeolites in industrial catalytic processes, to mention that since the discovery of catalysis over shape-selective zeolite first published by Weisz and Frilette in I960, a commercial process based on selective hydrocracking reactions similar to that reported in this paper has been in operation on a large scale in more than four of our refineries since 1967. A technical paper describing this process, known as the Selectoforming process, was published in 1968. 

The chemical behaviour of aluminosilicates in the presence of water or steam at elevated temperatures determines the technical conditions when considering commercial applications of zeolites as molecular sieves in adsorption or catalytic processes. Under hydrothermal conditions zeolites may be transformed into the amorphous state or into new crystalline structures. In both cases the sorption capacity or catalytic activity of the zeolites may be influenced. 

Besides the commercial zeolites that are widely used as acid or bifunctiona> catalysts in the industrial applications, there is a need for obtaining new specific products. This implies, together with the improvement of already utilized zeolites, the study of other types previously synthesized and characterized that ara potentially applicable as catalysts for specific organic reactions. 

Industrial interest in these materials has been driven by their excellent ion-exchange properties in the hydrated state, and by the exciting adsorption and catalytic properties exhibited by their dehydrated forms. Indeed, it is for this reason that many of the most eye-catching synthetic discoveries have been made in industrial laboratories, such as those of Mobil, Union Carbide (now UOP), British Petroleum and Exxon. Table 18.2 summarizes some of the most important actual and prospective applications. Commercial production of zeolites was approximately one million tons in 1999, most of which was accounted for by the applications in catalytic cracking, xylene isomerization, and detergency. This pattern is gradually changing, however, as new applications are developed. 

Although still the most important applications of zeolite catalysts are in the field of refining, as described in the previous section, the use zeolites in petrochemistry is expected to grow in the near future and several petrochemical processes based on zeolite catalysts have been already developed and commercialized. Moreover, zeolites can offer new opportunities for the development of new petrochemical processes replacing harmful and corrosive mineral acids which are still used in several processes and thus would lead to more efficient, selective, and cleaner processes [200,201,202]. In this section, we will describe the application of zeolites in some relevant petrochemical processes, with especial emphasis in aromatics transformation processes, including well established technologies as well as potential applications in new processes. 

Thermal stability results are significant in a commercial application of zeolites as catalysts. Since the zeolite must be able to withstand treatment with water vapor at quite high temperatures, it is also probable that... 

Measurements by interference microscopy are, under favorable conditions, capable of yielding both internal diffusivities and apparent diffusivities based on overall sorption rates. The former tend to approach the values obtained from microscopic measurements while the latter yield values similar to those obtained by other macroscopic methods. Of necessity these studies have been carried out in large zeolite crystals. One may expect that smaller crystals may be less defective, although the influence of surface resistance may be expected to be greater. The extent to which these conclusions are applicable to the small zeolite crystals generally used in commercial zeolite catalysts and adsorbents remains an open question. 

In the application of the chromatographic method to the measurement of intracrystalline diffusivity it is preferable to pack the column directly with unaggregated crystals rather than with composite (pelleted) material since this eliminates the possible intrusion of macropore resistance. The small crystal size of commercial zeolite samples presents a significant practical problem. Early attempts to utilize a column packed directly with such crys-... 

Rabo has shown that ALPO s and SAPO s may be used in many chemical and petrochemical processes. They give unique opportunities to be tailored to specific requirements. On the other hand, they have only mild acidity (which could be an Advantage in some cases), they are difficult to synthetize, and they may be more expensive than present commercial zeolites. Therefore they rely on their superior performance to compete with their aluminosilicate cousins. Applications include the removal of nitrogen oxides, cracking of heavy petroleum fractions, octane increase in hydrocracking, various reactions of olefins and aromatics such as oligomerization and xylene isomerization, syngas conversions, and methane activations. Co- and Co-Si-aluminophosphates have been active for this last reaction. 

The current commercial zeolite membranes, developed for pervaporation, are not yet useful in gas separations (H2/CO2 selectivity for NaA membranes of Mitsui and Inocermic are 6 and 5.6, respectively) because of the presence of large inter-crystalline defects. They, furthermore, participate in the separation process. During pervaporation the water fills the intra-crystalline and intercrystalline pathways. However, much effort is in progress to produce defect free zeolitic membrane also for gas separations. In this chapter the application of zeolite membranes in gas separations is reported and deeply discussed. The main strategic methods used for the membrane preparation and mass transport through zeolite membranes are also dealt with. 

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