Methanol into hydrocarbons

Svelle, S., Joensen, F., Nervlov, J., Olsbye, U., lillerud, K.-P., Kolboe, S., and Bjorgen, M. (2005) Conversion of methanol into hydrocarbons over the zeolite H-ZSM-5 ethene formation is mechanistically separated from the formation of higher alkenes. /. Am. Chem. Soc., 128,14770-14771. 

The effect of the Si/Al ratio of H-ZSM5 zeolite-based catalysts on surface acidity and on selectivity in the transformation of methanol into hydrocarbons has been studied using adsorption microcalorimetry of ammonia and tert-butylamine. The observed increase in light olefins selectivity and decrease in methanol conversion with increasing Si/Al ratio was explained by a decrease in total acidity [237]. 

Ono et al. (759) reported that heteropolyacids such as H3PW12O40 and H4SiW 2O40 catalyze the conversion of methanol into hydrocarbons, although the activities are less than that of HZSM-5. In contrast to HZSM-5, the main products observed with heteropolyacids are aliphatic C -C6 hydrocarbons, the selectivities for aromatic hydrocarbons being small (Table XIX). 

Product Distribution in Conversion of Methanol into Hydrocarbons (189)... 

Table IV summarizes the results of methanol conversion over the catalyst samples employed in the TPD study 30). The reaction was conducted in a conventional fixed-bed flow reactor under the conditions given in the table. The results are in agreement with those of the TPD measurement. Na - and H -TSMs are inactive for the methanol conversion, whereas Ti -TSM promotes dehydration, converting 50% of the fed methanol into dimethyl ether and a small amount of methane. The negligible activity of Li -Hect is improved slightly by exchanging the Li ion with and dramatically by exchanging Li with Ti. Na -Bent is an acidic clay. All of the three Bent catalysts, even Na -Bent, show higher activity than Ti -TSM, and the hydrocarbon yield reflects this difference in catalytic activity. Na -Bent is sufficiently active to give 60% conversion but has no ability subsequently to dehydrate dimethyl ether into hydrocarbons. The activity of H -Bent is higher than that of Na" -Bent, but the hydrocarbon yield is as low as 9%. As expected from the results of TPD measurement, the activity of Ti -Bent is remarkably high and converts 60% of fed methanol into hydrocarbons that are a mixture of methane, C2-5 olefins, and a small amount of Cs hydrocarbons.

H-ZSM-5 Is an efficient catalyst for converting methanol Into hydrocarbons [1,2]. The reaction may also be carried out over a large number of other protonated zeohtes or other zeo-type materials [3], The reaction mechanism Is still not clarified [2,4]. 

A simulation model for the reaction-regeneration steps in the transformation of methanol into hydrocarbons has been proposed and used for predicting the behaviour of a laboratory fixed bed pseudoadiabatic reactor. Kinetic models for both the main reaction and deactivation have been used, which take into account the attenuating role of water on both the zero time kinetics and the deactivation by coke deposition. The kinetics of coke combustion and the relationship between activity and coke content have been used for the design of the regeneration. The activity-coke content relationship is different in the reaction and regeneration steps. 

The following equation has been proposed in literature [8] for the deactivation of the catalyst in the transformation of aqueous methanol into hydrocarbons ... 

Y. Ono, T. Baba, J. Sakai, T. Keii, J., Conversion of methanol into hydrocarbons catalysed by metal salts of heteropolyacids, Chem. Soc., Chem. Commun., 1981, 400-401. 

The key to the MTG process is the unusual selectivity and activity maintenance of H — ZSM-5 zeolite catalyst. Although many acidic catalysts such as heteropolyacids are known to convert methanol into hydrocarbons, none has ever exhibited the selectivity to aromatics and activity maintenance of ZSM-5 zeolites. To a large extent, these characteristics are due to the unusual pore structure of these zeolites. 

Conversion of Methanol into Hydrocarbons 255 Table 4.12 Yields from methanol for two reactor systems... 

Fuel cells are electrochemical devices transforming the heat of combustion of a fuel (hydrogen, natural gas, methanol, ethanol, hydrocarbons, etc.) directly into electricity. The fuel is electrochemically oxidized at the anode, whereas the oxidant (oxygen from the air) is reduced at the cathode. This process does not follow Carnot s theorem, so that higher energy efficiencies are expected up to 40-50% in electrical energy and 80-85% in total energy (heat production in addition to electricity). 

Onboard reforming for fuel cells depends on catalytic reactions to convert conventional hydrocarbon fuels, such as gasoline or methanol, into hydrogen that fuel cells can then use to produce electricity to power vehicles. 

After combining all these equations, the overall conversion of biomass into hydrocarbon or methanol adopts the stoichiometry of Reactions (6) and (7) ... 

Bjorgen, M., Olsbye, U., Petersen, D., and Kolboe, S. (2004) The methanol-to-hydrocarbons reaction insight into the reaction mechanism from [12C] and [13C] methanol co-reactions over zeolite H-beta. /. Catal, 221, 1-10. 

In additional experiments, HZSM-5 was precoked by converting methanol alone (into hydrocarbons) at 400 °C. Afterwards the zeolite was exposed to the 2-methylnaphtha-lene/methanol mixture, under the usual reaction conditions. The initial yield of 1-methylnaphthalene was significantly reduced (1.5 % compared to 4 % for the fresh catalyst, cf. Fig. 4). Furthermore, the initial content of 2,6- + 2,7-dimethylnaphthalene in the dimethyl-naphthalene fraction was 84 % instead of 70 % for the fresh catalyst. In another run, HZSM-5 was loaded with 0.5 wt.-% of Pt, and H2 was used as carrier gas instead of N2. Under these conditions, the formation of coke was avoided or at least drastically diminished. In-line with our model, no changes in the product yields and in the distribution of the dimethylnaphthalene isomers were observed with time on stream. 

MN always decreased with time on stream, whereas the methylation of the DMN isomers either remained nearly constant or only slightly increased. After 10 h, 50% of the DMN isomers were composed of 2,6-DMN, with all three of these narrow DMN products accounting for more than 90% of the product. These results clearly indicate that shape-selectivity becomes more pronounced with time on stream. Over an HZSM-5 catalyst precoked at 400 °C by converting methanol alone (into hydrocarbons), the initial yield of 1-MN was significantly reduced (to 1.5% vs. 4% for a fresh catalyst), with the initial content of 2,6- and... 

Elements such as B, Ga, P and Ge can substitute for Si and A1 in zeolitic frameworks. In naturally-occurring borosilicates B is usually present in trigonal coordination, but four-coordinated (tetrahedral) B is found in some minerals and in synthetic boro- and boroaluminosilicates. Boron can be incorporated into zeolitic frameworks during synthesis, provided that the concentration of aluminium species, favoured by the solid, is very low. (B,Si)-zeolites cannot be prepared from synthesis mixtures which are rich in aluminium. Protonic forms of borosilicate zeolites are less acidic than their aluminosilicate counterparts (1-4). but are active in catalyzing a variety of organic reactions, such as cracking, isomerization of xylene, dealkylation of arylbenzenes, alkylation and disproportionation of toluene and the conversion of methanol to hydrocarbons (5-11). It is now clear that the catalytic activity of borosilicates is actually due to traces of aluminium in the framework (6). However, controlled substitution of boron allows fine tuning of channel apertures and is useful for shape-selective sorption and catalysis. 

Afterwards, the synthesis of various new zeolites, especially ZSM5 (MFI, 1967), the discovery of new shape selective transformations such as the (accidental) discovery of the remarkably stable and selective conversion of methanol into gasoline range hydrocarbons over HZSM5 (7), the development of post-synthesis treatments of zeolites,. .. combined to make them the single most important family of catalysts used all other the world. 

Molecular sieve catalysts that have been used for the conversion of methanol to hydrocarbons fall into two general classifications. Most of the initial research was done using ZSM-5 (MFI), a medium-pore size zeolite with a three dimensional pore system consisting of straight (5.6 x 5.3 A) and sinusoidal channels (5.5 x 5.1 A). While most of this work was directed at the conversion of methanol to liquid hydrocarbons for addition to gasoline, it was found that the product slate could be shifted toward light olefins by the use of low pressure and short contact times. 

Early attempts to convert methanol into olefins were based on the zeolite ZSM-5. The Mobil MTO process was based on the fluidised bed version of the MTG technology. Conversion took place at about 500°C allegedly producing almost complete methanol conversion. However, careful reading of the patent Uterature indicates that complete methanol conversion may not have been achieved by this means. Because of incomplete conversion, there would be a necessity to strip methanol and dimethyl ether from water and hydrocarbon products in order to recycle unconverted methanol. In this variant, the total olefin yield is less than 20% of the products of which ethylene is a minor but not insignificant product. The major product is gasoUne. Ethylene is difficult to process and has to be treated specially. Claims that it is possible that ethylene can be recycled to extinction conflict with the known behaviour of ethylene in zeolite catalyst systems and have to be viewed with some suspicion. 

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