Zeolites olefinic hydrocarbons

B.2. Olefinic Hydrocarbons Formed in Various Protonic Zeolites... 

Basic zeolites are able to catalyze double bond isomerization of olefins [133]. Although this can also be achieved with acidic zeolites, the lower reactivity of basic zeolites towards hydrocarbons (i.e., the complete absence of skeletal isomerization) leads to higher yields [134]. A good example for this is the double bond isomerization of 1-octene over potassium loaded NaY. It is claimed that high yields can be achieved in that way and that the impregnation of the zeolite with an excess of alkali cations is important to obtain a good catalyst [135]. 

When methanol synthesis catalyst, prepared from CuO, ZnO and CrOj, was mixed with HY zeolite, C2+ hydrocarbons were obtained in a good selectivity(Run 1)[2]. The same catalyst made into granule gave better results (Run 3). The selectivities to ethane, propane and butane were higher and that to methane was lower. No olefin was observed. The hydrocarbons distribution of typical Cu-Zn-Cr/HY is shown in Figure 1. This is a typical distribution of MTG reaction, and quite different from Schultz-Anderson-Flory law. 

Carbenic mechanisms. Venuto and Landis [10] were the first to address the question of mechanism of hydrocarbon formation from methanol over zeolites, in this case zeolite X [11]. These workers proposed a scheme involving a-elimina-tion of water and polymerization of the resultant methylcarbenes to olefins. Swabb and Gates [12], elaborating on Venuto-Landis, proposed that concerted action of acid and basic sites in the zeolite (mordenite) facilitates a-elimina-tion of water from methanol. According to Salvador and Kladnig [13], carbenes are generated through decomposition of surface methoxyls (a-el imination of silanol) formed initially upon chemisorption of methanol on the zeolite (zeolite Y). Hydrocarbons are assumed to form, in the latter two schemes, also by carbene polymerization. 

Alpha A process for making aromatic hydrocarbons and LPG from C3-C7 olefins. The catalyst is a metal-modified ZSM-5 zeolite. Developed by Asahi Chemical Industries and Sanyo Petrochemical and used since 1993 at Sanyo s Mitzushima refinery. 

Isotex A process for isomerizing olefines, catalyzed by a novel zeolite. It is intended for making methyl /-butyl ether from C4 hydrocarbons. 

MOG [Mobil olefins to gasoline] A process for converting dilute streams of C2- to C4-hydrocarbons to gasoline, using a fluidized bed of zeolite ZSM-5 catalyst. Developed by Mobil Research Development Corporation and piloted in 1990. 

Olex A version of the Sorbex process for separating olefins from paraffins in wide-boiling mixtures. It can be used for hydrocarbons in the range C6 - C20. Based on the selective adsorption of olefins in a zeolite and their subsequent recovery by displacement with a liquid at a different boiling point. Mainly used for extracting Cn - C14 olefins from the Pacol... 

Several metal oxides could be used as acid catalysts, although zeolites and zeo-types are mainly preferred as an alternative to liquid acids (Figure 13.1). This is a consequence of the possibility of tuning the acidity of microporous materials as well as the shape selectivity observed with zeolites that have favored their use in new catalytic processes. However, a solid with similar or higher acid strength than 100% sulfuric acid (the so-called superacid materials) could be preferred in some processes. From these solid catalysts, nation, heteropolyoxometalates, or sulfated metal oxides have been extensively studied in the last ten years (Figure 13.2). Their so-called superacid character has favored their use in a large number of acid reactions alkane isomerization, alkylation of isobutene, or aromatic hydrocarbons with olefins, acylation, nitrations, and so forth. 

As documented in Chapter 5, zeolites are very powerful adsorbents used to separate many products from industrial process steams. In many cases, adsorption is the only separation tool when other conventional separation techniques such as distillation, extraction, membranes, crystallization and absorption are not applicable. For example, adsorption is the only process that can separate a mixture of C10-C14 olefins from a mixture of C10-C14 hydrocarbons. It has also been found that in certain processes, adsorption has many technological and economical advantages over conventional processes. This was seen, for example, when the separation of m-xylene from other Cg-aromatics by the HF-BF3 extraction process was replaced by adsorption using the UOP MX Sorbex process. Although zeolite separations have many advantages, there are some disadvantages such as complexity in the separation chemistry and the need to recover and recycle desorbents. 

Conversion of methanol to hydrocarbons over zeolite H-ZSM-5 on the origin of the olefinic species. 

Yao, J., Kimble, J.B., and Drake, C.A. (2000) A method of making such improved zeolite material and the use thereof the conversion of non-aromatic hydrocarbon to aromatics and light olefins. U.S. Patent 6, 048,815. 

Zeolites have an enormous impact on our daily lives, both directly and indirectly. For example, upstream hydrocarbons such as aromatics and olefins are produced using zeolite catalysts. The aromatics or olefins are then separated from the reaction mixtures using zeolite adsorbents. The purified components produced by these zeolite-based methods are then used in downstream processes to produce products that we use daily, such as clothes, furniture, foods, construchon materials and materials to build roads, automobile parts, fuels, gasoline, etc. In addihon to the indirect impacts mentioned above, zeolites also have a direct impact on our daily lives. For example, zeolites are used as builders in detergent formulations. 

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