Methanol conversion into hydrocarbons

Finally, the presence of the 3,600 cm OH groups, which correspond to Al-OH bonds, were found to be the most active for methanol conversion into hydrocarbons.Consequently, it is very important that the access to these acid sites is not blocked. Molecular sieves with very low concentration of these acid sites were found to be inactive for MTO. 

Figure 4 Methanol conversion into hydrocarbons on SAPO-34. ...

SAPO-5, MAPO-5, and MeAPO-5 molecular sieves are also active catalysts for methanol conversion into hydrocarbons. However, high concentrations of aromatics can also be obtained on these molecular sieves. In SAPO-5, the selectivity toward olefins can be improved by decreasing the Si/Al ratio, therefore, the concentration of strong acid sites. Incorporating bivalent elements to the aluminophosphate freunework also modifies the acid properties. Cations like and Co " " lead to active catalysts for methanol conversion, but the production of aromatics is high so that the olefin selectivity is lower. 

T=480 C Si/Al=80 feed 30/70 wt% methanol-water. Figure 10 Methanol conversion into hydrocarbons on mordenite. 

Ono Y, Mori T. Mechanism of methanol conversion into hydrocarbons over ZSM-5 zeohte. J Chem Soc, Faraday Trans 11981 77 2209 21. 

Hierarchical (or mesoporous) zeolites became the focus of the review by Christensen et al. [7]. The main reason behind the development of hierarchical zeolites is to achieve heterogeneous catalysts with an improved porous structure and thereby enhanced performance in alkylation of benzene with alkenes, alkylation, and acylation of other compounds, methanol conversion into hydrocarbons, aromatization processes, isomerization of paraffins, cracking of diverse substrates and raw materials (naphtha, aromatic compounds, hexadecane, vacuum gas oil, and some polymers), and hydrotreating. The reactions that are of interest from the point of view of fine chemicals synthesis occurring on hierarchical zeohtes include aldol condensation, esterification, acetalization, olefin epoxidation, and Beckmarm rearrangement. 

Catalytic hydrogenation of CO2 to hydrocarbons is classified into two categories. The one is direct hydrogenation fix)m H2/CO2 to hydrocarbons. The other is indirect process which includes methanol sjmthesis fix>m H2/CO2, followed by in situ methanol conversion to hydrocarbons using sohd acid catalyst in H2/CO2 feed. Study on indirect hydrocarbon synthesis is now popular. 

Reaction steps of methanol (MeOH) conversion into hydrocarbons. Adapted from ChangCD,... 

Reaction steps of MeOH conversion into hydrocarbons. Adapted from Chang CD. Hydrocarbons from methanol. Catal Rev Sci Eng 1983 25 1—118 Ceckiewicz S. Methanol conversion to hydrocarbons and dimethyl ether on decationized zeolite-T. Kinet Catal Lett React 1981 16 11. 

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

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)... 

Complete Methanol Conversion - The major products of the MTG conversion are hydrocarbons and water. Consequently, any unconverted methanol will dissolve into the water phase and be lost unless a distillation step to process the very dilute water phase is added to the process. Thus, essentially complete conversion of methanol is highly preferred. 

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. 

Methanol conversion was adopted as a probe reaction to explore the catalytic activity of M" -TSM, because methanol is a simple molecule that transforms into easily assignable compounds and is converted into different products through different routes employing different catalysts. Methanol is decomposed into carbon monoxide and hydrogen over metal catalysts [including Ni (77)], is dehydrogenated into formaldehyde or methyl formate over Zn- or Cu-containing catalysts (78), and is dehydrated into dimethyl ether and successively into hydrocarbons over acid catalysts (79). 

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.

Under mild reaction conditions and particularly over zeolite of low aluminiun content at high temperature, the products of methanol conversion are olefins. Subsequent, less facile reactions convert the sorbed olefins into cycloalkanes, and to benzenoid hydrocarbons and alkanes. These subsequent reactions involve hydride anion transfer reactions and cyclization reactions of larger sorbed olefins (ref. 27). Figure A shows the product sequence. 

Since it was first reported in 1976 that protonated ZSM-5 zeolites are excellent catalysts for conversion of methanol (and many other oxygenated compounds ) into hydrocarbons in the C - C q range the catalyst and the reactions have been intensely studied. Several aspects of the reactions leading to hydrocarbon formation from methanol or dimethyl ether over H-ZSM-5 or other protonated zeolites still remain unclear. In particular the first OC bond formation has been debated, and several mechanisms proposed (ref. 1). 

Methanol is a key compound in Cl chemistry because it allows the conversion of raw materials, from which it is produced, into more valuable organic chemicals. However, the main application of heterogeneous catalysts for the activation of CH3OH is related to their transformation into hydrocarbons. For these technologies, the catalytic reactions are based on the acid-base properties of surfaces, and the catalytic materials consist of zeolites (such... 

Methanol Conversion to Olefins. - Chabazite, erionite, zeolite T, and ZK-5 have been used by Chang et al. for the conversion of methanol into olefins. The C2-C4 olefin concentration in the hydrocarbon fraction was always less than 60 wt% at 100% methanol conversion. It follows from Table 3 that the hydrocarbon fraction becomes richer in Cj-C olefins as the conversion of methanol decreases. That is because the conversion of olefins to paraffins is lower. Hydrocarbon fractions with more than 80 wt% of Cj-C olefins were attained with a dealuminated H-erionite, but the conversion of methanol was very low. 

Ono et al. ° observed an abrupt jump in the conversion of methanol on HZSM-5 at constant space time when the temperature was increased from 280 to 300 C. Because the apparent activation energy associated with it is too high for ordinary chemical reactions and because this "jump" was also observed when feeding dimethylether, autocatalytic effects in the transformation of dimethylether into hydrocarbons were invoked. The temperature at which the "jump" occurred depended on the Si/Al-ratio. Such a sudden... 

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 first of these new cobalt catalysts were made in 1986 by coprecipitation techniques using aqueous solutions with ammonium bicarbonate as the precipitant in a similar way to the methods used for methanol synthesis catalysts. The new catalysts were immediately found to be very active and selective catalysts for the conversion of syngas into hydrocarbons. A particularly attractive feature was their low methane make and tolerance of CO2 The CO2 tolerance was ascribed to the interplay between the support and the cobalt phase both in the oxidized and reduced forms. The general belief is that the support stabilizes the cobalt phase such that the catalyst can be operated at the higher temperatures, required to maintain activity despite competitive adsorption by CO2, without any loss in stability. Other investigators e.g. Shell have used similar strategies [2]. 

As indicated, the process can be directed towards ethylene production and hence chemical synthesis. The use of ZSM-5 catalysts for direct conversion of syngas into hydrocarbons (i.e., without the need to produce methanol first) and selective preparation of benzene, toluene, and xylene aromatics only are already being actively investigated. 

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