Olefin from methanol

Direct fuel appHcations of methanol have not grown as anticipated (see Alcohol fuels). It is used in small quantities in California and other locations, primarily for fleet vehicle operation. Large-scale use of methanol as a direct fuel is not anticipated until after the year 2000. Methanol continues to be utilised in the production of gasoline by the Mobil methanol-to-gasoline (MTG) process in New Zealand. A variant of this process has also been proposed to produce olefins from methanol. 

In the propagation centers of chromium oxide catalysts as well as in other catalysts of olefin polymerization the growth of a polymer chain proceeds as olefin insertion into the transition metal-carbon tr-bond. Krauss (70) stated that he succeeded in isolating, in methanol solution from the... 

Although the mechanism proposed for the ZSM-5/methanol system adequately explains the production of the primary C2-C5 products, it is not clear how these are converted into the final gasoline product or indeed why this product should be so rich in aromatics. Production of olefins from methanol over zeolite catalysts has previously been described (110, 112) however, the ZSM-5 system appears to be unique with respect to both product selectivity and catalyst stability. Mobil now has some 140 patents relating to the preparation and use of ZSM-5 zeolites and has stated that "given a favorable economic and political climate a commercial unit could be in operation by the early 1980 s (101). 

The wild card that ethylene producers must watch for is the emergence of new technologies that could tap other low-cost feeds, particularly if crude oil-linked feedstock prices stay high. Foremost is conversion of methanol into olefins (MTO), using low-cost methanol sourced from the world s abundant supplies of stranded natural gas. While this technology is as yet unproven on a large scale, in theory the world s huge volumes of untapped stranded gas could be used to produce methanol which could be converted to olefins and polymers in situ, or shipped to end markets such as China and converted to olefins and polymers there. 

Diphenyl carbonate from dimethyl carbonate and phenol Dibutyl phthalate from butanol and phthalic acid Ethyl acetate from ethanol and butyl acetate Recovery of acetic acid and methanol from methyl acetate by-product of vinyl acetate production Nylon 6,6 prepolymer from adipic acid and hexamethylenediamine MTBE from isobutene and methanol TAME from pentenes and methanol Separation of close boiling 3- and 4-picoline by complexation with organic acids Separation of close-boiling meta and para xylenes by formation of tert-butyl meta-xyxlene Cumene from propylene and benzene General process for the alkylation of aromatics with olefins Production of specific higher and lower alkenes from butenes... 

The fact that the methanol is stored as an intermediate brings strength to this route as it de-couples the methanol synthesis from the subsequent conversion of methanol into olefins. 

When the catalyst was exposed to i-butanol at 500°C, the coke formation was relatively fast. 1.5 wt% coke was deposited during 10 minutes. The formation of olefins from methanol was lower for this precoked sample. This is probably due to n-butene formation, originating from i-butene isomerization at 500°C. n-Butene probably forms inactive coke in the pores or at the pore openings, which results in significant deactivation. 

The effect of coke deposition on the MTO reaction is rather complex. Coke was found to influence not only the external DME formation, but also the DME conversion taking place internally during MTO. However, the effect of coke deposition on the DTO reaction is much more simple and allows us to focus on the effect of intracrystalline coke on the DME conversion. The amount of methanol formed from DME at DTO reaction conditions is quite small since methanol formation requires water produced from olefin formation. Thus, the DTO reaction model appears to be straightforward DME diffuses into the pores and is converted to olefins on the acidic sites in the cavities of SAPO-34. 

Although DME and methanol are the primary feedstocks for the ZSM-5 catalyzed MTG or MTO process (ref. 7)r higher alcohols that can be produced over methanol catalysts by reactions (5), or esters by reactions (6), have been demonstrated to be suitable feedstocks for conversion to aromatic gasoline or olefins over the ZSM class of acid catalysts (ref. 8). Hence, crude methanol containing from < IX to a large fraction of higher oxygenates may be used in the MTG and MTO processes. 

However, equilibrium between olefins of 3+ carbon atoms is almost certainly established under conditions of methanol conversion (ref. 11). Thus the olefins observed are products of the quasi-equilibrium, and their relative amounts are determined by the position of equilibrium and rates of diffusion. One expects increase in partial pressure to favour higher olefins and increase in temperature to favour lower olefins. It is clearly not possible for methanol conversion to give propylene selectively or butenes selectively. Equally clearly, it is difficult to obtain evidence on the mechanism of methanol conversion from labelling experiments if carbon and hydrogen are scrambled rapidly in the olefinic products. 

Thus it is possible to represent the formation of olefins from methanol as in Figure 1. Most observers would agree this is the main route to olefins. 

Figure 3.35 shows a process flow diagram of Phillips MTBE/ETBE/TAME process. This process is often called the Phillips Etherification Process. The reaction section (1,2) which receives methanol and isobutene concentrate, contains an ion exchange resin. The isobutene concentrate may be mixed olefins from a Fluid Catalytic Cracking Unit (FCCU) or steam cracker or from the on-purpose dehydration of isobutene (Phillips STAR process). High purity MTBE (99 wt%) is removed as a bottoms product from the MTBE fractionator (3). AH of the unreacted methanol is taken overhead, sent to a methanol... 

In contrast to lower olefins from diminishing resources like naphtha or associated gas, the lower olefins from methanol or dimethyl ether produced from abundant coal or natural gas are attracting attention. Of particular interest is the synthesis of ethylene and propylene from dimethyl ether because of their growing demand as raw materials for polyethylene and polypropylene. The usage of these polymers in everyday life is diverse (e.g., molded plastic items, plastic packaging films, etc.). Increasing demand for isobutene is inevitable since isobutene is used as the raw material for MTBE, MMA (methyl... 

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... 

Gould, R. M., Avidan, A. A., Soto, J. L., Chang, C. D. and Socha, R. F., "Scale-up of a Fluid-bed Process for Production of Light Olefins from Methanol", paper presented at the AIChE National Mtg., New Orleans, LA, April 6-10, 1986. 

Methanol is first dehydrated to dimethylether (DME). The equilibrium mixture thereof is then converted to light olefins. In the final steps of the reaction path, the Cj-Cg olefins are converted to paraffins, aromatics, naphthenes and higher olefins by polycondensation and alkylation reactions. The importance of light olefins as intermediates in the conversion of methanol to gasoline was soon recognized. As a result, several attempts were made to selectively produce light olefins from methanol on zeolite catalysts, not only on medium-pore zeolites but also on small-pore... 

C and the selectivity toward aromatics increased from 4.9% to 16.4% at 380 C and from 3.6% to 18.9% at 500 C as the SiOj/AljOj ratio was raised. GAPO-5 and FeAPO-5 yielded mainly dimethylether. Carbon monoxide and methane were the principal products on VAPO-5. The highest selectivity to hydrocarbons was obtained on BeAPO-5. Hydrocarbon fractions containing 69.8% to 73.6% of olefins were obtained between 380 and 500 C with a BeO/AljOj ratio of 0.25. The conversion of methanol varied from 93.3% to 98.9% for the seune range of temperature. 

Application The UOP/HYDRO Methanol-to-Olefins (MTO) Process produces ethylene and propylene from methanol derived from raw materials such as natural gas, coal, petroleum coke or biomass. 

The elimination of lead in gasoline initiated the development of methyl-/er/-butylether (MTBE) production from isobutene and methanol. Nowadays, MTBE is an integral component of the gasoline pool, and still rapidly increasing demand will result in a more or less quantitative consumption of the isobutene contained in C4-cuts. Further, sometimes there is insufficient isobutene available in a refinery to permit all olefins from the different cuts to be catalytically alkylated to MTBE. 

Inui. T. Highly Selective Synthesis of Light Olefins from Methanol Using Metal-Incorporated Silicoaluminophos-phate Catalysts. In Shape Selective Catalysis, Chemicals Synthesis and Hydrocarbon Processing Song, C.. Garces. J.M., Sugi, Y., Eds. ACS Symp. Series. 1999 Vol. 738. 115-127. Chap. 8. 

When B is introduced in the zeolite framework instead of Al, the acid strength decreases and the resultant materials are selective catalysts to produce olefins from methanol. Using a borosilicate of the MFI structure, propylene is selectively prepared from methanol (221). Modification of the borosilicate by HF, HCl, or extrusion with amorphous silica-alumina, changes the product distribution giving more Q-Q olefins. In the case of mordenite and erionite, the introduction of B in the framework improves the formation of olefins from methanol (222). 

Alkyl transfers from O to C (Stevens rearrangement), carbenes and methyl carbonium ions have all been postulated to explain the formation of lower olefins from methanol and dimethyl ether over heterogeneous acid catalysts the reaction is autocatalytic, e.g. 

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