Zeolite-based processes

As with many zeolite-based processes, the zeolite is not used alone since it is highly active, resulting in rapid coke deactivation and poisoning... 

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. 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. 

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. 

Over the past seven years, cumene producers have begun to convert to the more environmentally friendly and more efficient zeolite-based processes. Principal among these are processes licensed by Dow, CDTech, Mobil-Badger, Enichem, and UOP. The zeolite based processes produce higher cumene yields than the conventional SPA process because most of the diisopropylbenzene byproduct is converted to cumene in separate transalkylation processes. Operating and maintenance costs are reduced because there is no corrosion associated with the zeolite catalysts. Finally, environmental concerns associated with the disposal of... 

The availability of pure water will certainly be one of the major environmental issues of the 21s1 Century. Water contamination can originate from domestic, agricultural, agroindustrial or industrial activities, and accidental damages. The major pollutants are heavy metals, radionuclides, ammonia, nitrates and organic compounds. Health problems are associated with each of them, such as leukaemia, saturnism..., as well as modifications of the eco-system, e.g. entrophication of lakes and rivers. The nature of water treatments obviously depends on the kind of contaminants, and zeolite-based processes are of great concern in this field. 

Zeolite-based processes have gradually displaced conventional ones, involving supported H3P04 or A1C13 as catalysts, in the manufacture of cumene, the raw material for phenol production [1, 6, 39]. A three-dimensional dealuminated mordenite (3-DDM) catalyst was developed by Dow Chemical for this purpose [39]. Dealumination, using a combination of acid and thermal treatments, increases the Si/Al ratio from 10-30 up to 100-1000 and, at the same time, changes the total pore volume and pore-size distribution of the mordenite. The... 

The early use and success of molecular sieve catalysis was spurred by the dramatic improvement in activity selectivity for catalytic cracking of vacuum gas oil achieved by using the faujasite based catalysts in comparison to the previously used amorphous SiOj/AUOj. These catalysts had a factor of about 10 -10 higher catalytic activity than the amorphous SiOj/AfrOj catalysts [42]. Paraffin, C4 to C8 isomerization [43] was one of the first successful non-petroleum processing applications using zeolite catalysts. The complexity of tailoring zeolite catalysts, however, is well illustrated by the fact that is only four years back that Shell has developed the first zeolite based process for isomerization of n-butene to isobutene [44]. 

This process is a good example of how a new procedure can at the same time be cost-efficient and environmentally friendly. The principles of this process have been extended, and Rhodia is also manufacturing acetoveratrole at the same plant by use of a zeolite-based process. 

Recently, selective synthesis of / -cymene from toluene and propane or isopropanol over zeolite catalysts has been thoroughly investigated. Zeolite-based processes avoid the disposal of spent catalyst, product contamination by the catalyst, separation of the catalyst from the product and corrosion of the reactor and tubes. The results using various zeolite types were promising. However, the formation of undesired -propyl toluene is observed particularly in the presence of MFI type zeolites, whereas large pore zeolites yield significant amounts of m-and o-cymene besides the desired / -cymene. However, low conversion and relatively low selectivity are the drawbacks of these investigations. 

Impact of Micropore Diffusion in Zeolite-Based Processes... 

The separation of linear and branched alkanes is also of importance in the process known as dewaxing, in which the removal of normal alkanes makes the product hydrocarbon less viscous and reduces the so-called pour point temperature. Such processes can be combined with catalytic isomerisations to optimise the value of oil fractions (Chapter 8). Linear paraffins are also separated using a zeolite-based process from kerosene fractions to give reactants for the synthesis of linear alkylbenzene sulfonate anionic surfactants, which are both cost effective and biodegradable. 

Dow Chemical has developed a two-step zeolite-based process to produce styrene from butadiene contained in crude C4 streams. As shown in the following scheme, 1,3-butadiene (in the mixed C4 stream) undergoes a liquid-phase cyclodimerization (Diels-Alder reaction) over a proprietary copper-loaded zeolite catalyst at moderate temperature and pressure, to give 4-vinyl-l-cyclohexene (4-VCH) with 99% selectivity. In the second step, the 4-VCH is catalytically oxidized (in the presence of steam) to styrene over one of Dow s proprietary oxide catalysts. The overall yield of styrene is greater than 90%. This process was originally tested in a 40-lb-per-hour pilot plant, and is now in commercialization. 

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