Methanol to olefin reaction

Engineers at Mobil Oil Corporation are satisfied that a one-dimensional analysis is suitable for treating reaction kinetics in these beds, simply using an appropriate Peclet number to represent the effective axial gas diffusivity (Avidan, 1982 Krambeck et al, 1987). Inputs for Mobil s analysis are two (1) the Peclet number expected for a commercial fluid bed in question—they estimate this to be 7 for beds they contemplate for carrying out Mobil s methanol-to-gasoline or methanol-to-olefin reactions—and (2) kinetic data from a pilot fluid bed, which can be expected to reflect, reasonably well, whatever top-to-bottom mixing of powder will occur in the commercial bed. 

J. Marchi at Ryksuniversiteit Gent (Belgium) provide a comprehensive review of zeolite catalysis for the methanol-to-olefin reaction. He examines small, medium, and large-pore zeolites, the important role of acidity and shape selectivity on product distribution, and, like several of the other Reporters, the importance of understanding the coke-forming deactivation processes. 

Wei YX, Yuan CY, LiJZ, et al Coke formation and carbon atom economy of methanol-to-olefins reaction, ChemSusChem 5 906—912, 2012b. 

Xu S, Zheng A, Wei Y, et ah Direct observation of cyclic carbenium ions and their role in the catalytic cycle of the methanol-to-olefin reaction over chabazite zeolites, Angew Chem Int Ed 52 11564-11568, 2013. 

Nishiyama N, Kawaguchi M, Hirota Y, Van Vu D, Egashira Y, Ueyama K. Size control of SAPO-34 crystals and their catalyst lifetime in the methanol-to-olefin reaction. Appl Catal A 2009 362 193-9. 

S. B., and Seo, G. (2008) Effects of cage shape and size of 8-membered ring molecular sieves on their deactivation in methanol-to-olefin (MTO) reactions. Appl. Catal. A, 339, 36-44. 

J. F., Nicholas, J.B., Heneghan, C., Methybenzenes Are the Organic Reaction Centers for Methanol-to-Olefin Catalysis on HSAPO-34, p. 10725-10727, Copyright 2000 American Chemical Society... 

Chen and co-workers have studied the role of coke deposition in the conversion of methanol to olefins over SAPO-34 [111]. They found that the coke formed from oxygenates promoted olefin formation while the coke formed from olefins had only a deactivating effect The yield of olefins during the MTO reaction was found to go through a maximum as a function of both time and amount of coke. Coke was found to reduce the DME dilfusivity, which enhances the formation of olefins, particularly ethylene. The ethylene to propylene ratio increased with intracrystal-line coke content, regardless of the nature of the coke. 

One of the most important considerations in designing a process for converting methanol to olefins was to find the best way to remove the considerable heat of reaction. Despite the fact that we are stopping the reaction at the intermediate olefin product, the reactions leading to these intermediates give off almost 90% of the heat released in the overall MTG reaction scheme (49 vs. 56 kJ/mole of methanol converted for MTO vs. MTG). Efficient removal of the heat of reaction is one of the main reasons a fluid-bed reactor was selected for scale-up demonstration. A second advantage of the fluid-bed is that product composition can be kept constant, since optimum catalyst activity can be maintained by continuous make-up and regeneration. 

Fig. 5. Methanol-to-hydrocarbons reaction path at 371°C, where (A ) is methanol ( ), dimethyl ether (0 ), water ( ), paraffins (and C6 + olefins) (O),...

This is an important industrial reaction, alone or in combination with others. The CH3OH production is often coupled to oxidation to formaldehyde, methanol to gasoline (Mobil) process, methanol to olefins process, carbonylation, etc. Due to this, a large volume of information already exists on catalyst preparation, kinetics, reactors and all other aspects of the related chemical technology [53]. However, let us concentrate our attention here on just one selected problem the role of the promoter and the nature of the active site on the metal on oxides catalysts. Let us mention in passing that pure metals (promoter free) most likely do not catalyze the synthesis. 

The methanol, which need not be the highest grade chemical methanol, is produced and stored prior to feeding to the methanol to olefins (MTO) plant. The conversion of methanol into olefins is highly exothermic and in order to help control heat evolution some processes use a primary reactor to convert some of the methanol into dimethyl ether (DME) by the reaction ... 

But if we adjust the reaction conditions and modify the catalyst, we can virtually double the olefin yield. This discovery has led to the development of another ZSM-5 process — called methanol-to-olefins, or MTO (Refs. 18, 19). 

The mechanisms of acid-catalyzed DME formation from methanol and aromatiza-tion of olefins were widely investigated in the years before the discovery of the methanol-to-gasoline reaction. There is a consensus that the intermediate in DME formation from methan.ol over solid acid catalysts is a protonated surface methoxyl, which is subject to nucleophilic attack by methanol [2]. Aroma-tization of olefins is believed to proceed along classical carbenium pathways, with concurrent hydrogen transfer [3]. The mechanism of the crucial step of initial C-C bond formation from MeOH/DME is an unsolved problem, however, and is the subject of ongoing controversy. At last tally, there were some two dozen mechanistic proposals in the literature. It is not possible here to present a comprehensive review of the entire field. However, a number of common themes can be identified. This commonality is discussed and the concepts currently in vogue are critically reviewed. Another issue, whether ethylene is the "first" olefin, has been widely debated [2], but is beyond the scope of this survey. 

For this process, there are gaps in the literature in aspects such as the establishment of a kinetic model for the main reaction and for deactivation, in order to quantify the product distribution and the effect of operating conditions on this distribution. A kinetic model for deactivation by coke deposition is proposed in this paper, which pays special attention to the role of water on the attenuation of coke deposition, and takes as a reference the recent results in the kinetic modelling of deactivation by coke in the MTG process (methanol to gasoline) on a HZSM-5 zeolite [8] and in the MTO process (methanol to olefins) on a SAPO-34 [9]. 

In the context of the zeolite-catalyzed reactions of methanol-to-gasoline (MTG process) and methanol-to-olefins (MTO process), the activation of CH3OH on acid zeolite surfaces was particularly interesting. It was, for instance, studied in detail through the picosecond infrared technique (cf., e.g., [821]). 

The first step in the catalytic conversion of methanol to olefins or gasoline, for example, has been extensively studied by both cluster and plane wave methods. The first reaction is the formation of dimethylether by the apparent... 

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