Conversion of Methanol to Olefins

Light olefins are intermediates in the MTG reaction, according to Equation (3). By proper selection of reaction conditions and with suitable catalyst design, it is possible to decouple the olefination step from aromatization. This is the basis of the Mobil MTO process, which utilizes fluidized-bed technology. The process has not yet seen commercialization, but has been scaled up [51,52] and demonstrated on a 100 bpd scale. Alternatively, olefin yield can be increased by operating under partial conversion conditions, recovering the intermediate 

The discussion of MTG kinetic effects just presented is generally applicable to MTO. Olefin selectivity is improved by decreasing methanol partial pressure, increasing temperature, and increasing zeoUte Si02/Al203. An additional effect, that of varying zeolite crystallite size, was reported by Howden et al [61], who found that when the crystallite size was reduced from 30 to 3 pm, ethylene selectivity increased. This was attributed to enhanced diffusivity of li t products, which reduces their opportunity for further reaction. 

In principle, the kinetic models developed for MTG should be applicable to MTO. However, imder conditions in which olefination is lar ly decoupled from aromatization, a simple reaction scheme 

Light olefin selectivity as a functbn of ZSM-5 Si02/Al2o3 at 500°C, 1 atm 

First-order plot of oxy nate disappearance in MTO. (From Ref 24.) 

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L.o 18-21 The conversion of methanol to olefins is an intermediate step in the conversion of methanol to... 

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. 

Two variants of the process are available, one maximising ethylene and the other propylene. The performance appears to be similar to that of the conversion of methanol to olefins using small pore zeolites. Such systems suffer from high methane yield (which has to be recycled back to a reformer) and high coke yields. The formation of olefins is promoted by using crude methanol, which can contain up to about 17% water. 

In the subsequent sections, a literature survey of the use of TEOM is presented, followed by detailed examples illustrating the use and characteristics of the TEOM for conversion of methanol to olefins (MTO) catalyzed by SAPO-34 and steam reforming of natural gas on nickel catalysts. 

The Role of Coke Deposition in the Conversion of Methanol to Olefins over SAPO-34... 

Other modifications of zeolites can be achieved with, reagents which react with OH groups. The silanation of various mordenites is the only process to be studied in detail. ZSM-5 treated with dimethyl silane has been described as a catalyst for the conversion of methanol to olefins. The use of various other reagents (P, B, and Sb compounds) with ZSM-5 and related zeolites has also been described. The effects observed in catalysis are broadly similar... 

The conversion of methanol to olefins over ZSM-5 was discovered by Mobil scientists in the 1970 s, together with the similar process of conversion of methanol to gasoline. Initial process development was in small-scale reactors (ref. 15). 

The synthesis of olefins from methanol using aluminophosphate molecular sieve catalysts was studied [76], Process studies were conducted in a fluid-ized-bed bench-scale pilot plant unit utilizing small-pore silicaluminophosph-ate catalyst synthesized at Union Carbide. These catalysts are particularly effective in the catalytic conversion of methanol to olefins, when compared to the performance of conventional aluminosilicate zeolites. The process exhibited excellent selectivities toward ethylene and propylene, which could be varied considerably. Over 50 wt% of ethylene and 50 wt% propylene were synthesized on the same catalyst, using different combinations of temperatures and pressures. These selectivities were obtained at 100% conversion of methanol. Targeting light olefins in general, a selectivity of over 95% C2-C4 olefins was obtained. The catalyst exhibited steady performance and unaltered... 

Principal Characteristics. - Molecular sieves with pore openings of about 0.45 nm show very interesting shape-selectivity properties for the conversion of methanol to olefins (MTO process). The small-pore molecular sieves studied in the MTO process are chabazite, erionite, zeolite T, ZK-5, ZSM-34, zeolite A, SAPO-17, SAPO-34, and SAPO-44. All of them can sorb only straight chain molecules, e.g. primary alcohols and linear paraffins and olefins, but no branched isomers and aromatics the pore opening is smaller than the kinetic diameter of branched and aromatic molecules, but large enough to permit the access of linear molecules. 

Medium-pore zeolites can be generally described as crystalline molecular sieves consisting of linked silica- and alumina-tetrahedra forming 10-membered oxygen ring channels. The dimensions of these medium-size pores are 0.5 to 0.6 lun. With respect to the conversion of methanol to olefins, only ZSM-5 or its isostructural analogs and, to a much less extent, ZSM-11 and ZSM-48 have been studied. 

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... 

Conversion of Methanol to Olefins. The conversion of methanol to C2-C4 olefins using the medium pore ZSM-5 and the small pore ZSM-34 catalysts has been described earlier in the literature. Selectivities for the production of small olefins of above 80% have been reported. 

Maurer, T. (2004) Investigation of Mass Transport Phenomena in the Conversion of Methanol to Olefins over Technical Alumina/ZSM-5 Catalysts. Dissertation, Shaker, Aachen, University of Karlsruhe. 

Bleken F, Bjorgen M, Palumbo L, et al The effect of acid strength on the conversion of methanol to olefins over acidic microporous catalysts with the CHA topology. Top Catal 52 218-228, 2009. 

Hunger M, Seiler M, Buchholz A In situ MAS NMR spectroscopic investigation of the conversion of methanol to olefins on sdicoaluminophosphates SAPO-34 and SAPO-18 under continuous flow conditions, Catal Lett 74 61—68, 2001. 

UOP and Norsk Hydro have jointly developed and piloted a fluid bed process for the conversion of methanol to olefins (Fig. 16.) The process uses Union Carbide s (now part of UOP) SAPO-34 catalyst. A two fluidized bed reactor/regenerator system is used. 

Dewaele O, Greers VL, Froment GA, Marin GB. The conversion of methanol to olefins a transient kinetic study. Chem Eng Sci 1999 54 385. 

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