Olefins methanol conversion

M. G. Block, R. B. Callen and J. H. Stockinger, The analysis of hydrocar bon products obtained from methanol conversion to gasoline using open tubular GC columns and selective olefin absorption , ]. Chromatogr. Sci. 15 504-512 (1977). 

Wu, X. and Anthony, R.G. (2001) Effect of feed composition on methanol conversion to light olefins over SAPO-34. Appl Catal A, 218, 241-250. 

Kaiser, S.W. (1985) Methanol conversion to light olefins over silicoalumino-phosphate molecular sieves. Arab. J. 

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]. 

Fig. 4 (right) Autocatalysis and retardation. Yields of paraffins, olefins, aromatics and "coke" as a function of duration of the experiment. Methanol conversion on HZSM5, 270 °C, Pqi oqu =2.5 bar, WHSV = 1 h. Differential coke yield abtained through internar standard). 

Fig. 6 Schematic drawing of ZSM5 catalyst bed deactivation. View of the fused silica reaction tube at about 40 % of catalyst life time. Black zone (I) of deactivated catalyst particles covered with coke ("methanol coke"). Small dark reaction zone (II) in which methanol conversion to 100 % occurs. Blue/grey zone (III) of active catalyst on which a small amount of "olefin coke" produced by the olefinic hydrocarbon product mixture has been deposited on the crystallite surfaces. The quartz particles before and behind the catalyst bed (zones 0) remain essentially white.

It is necessary, however, to maximize the intermediate olefin product at the expense of the aromatic/paraffin product which makes up the gasoline ( ). The olefin yield increases with increasing temperature and decreasing pressure and contact time. Judicious selection of process conditions result in high olefin selectivity and complete methanol conversion. The detailed effect of temperature, pressure, space velocity and catalyst silica/alumina ratio on conversion and selectivity has been reported earlier ( ). The distribution of products from a typical MTO experiment is compared to MTG in Figure 4. Propylene is the most abundant species produced at MTO conditions and greatly exceeds its equilibrium value as seen in the table below for 482 C. It is apparently the product of autocatalytic reaction (7) between ethylene and methanol (8). 

Catalytic reaction nethod. The methanol-conversion reaction was carried out in a ordinary flow reactor under atmospheric pressure. A 0.5 ml portion of the catalyst was packed into a Pyrex tubular reactor of 6 mm inner diameter. The reaction gas, composed of 20 100% MeOH balanced with N2, was then allowed to flow through the catalyst bed at a temperature in the range 24-0 360°C and a space velocity (SV) in the range 4-00 4-000 liter"liter 1,h 1. The olefin-conversion reaction was carried out in a flow reactor of 8 mm inner diameter. The reaction gas, composed of an olefin (CgH, C3H6 or C,Hg) and N2 mixed at various ratios, was then allowed to flow through the catalyst bed at a temperature in the range 260 360°C and a space velocity in the range 900 4500 h-1. 

The reaction mechanism for the conversion of methanol to hydrocarbons over molecular sieve catalysts has been extensively investigated over the past 25 years. It is widely accepted that methanol conversion initially proceeds through equilibration with DME. Early work with ZSM-5 showed that light olefins are then the initial hydrocarbon products, followed by heavier olefins, paraffins and aromatics (Figure 12.5) (2). 

UOP and Norsk Hydro have jointly developed and demonstrated a new MTO process utilizing a SAPO-34 containing catalyst that provides up to 80% yield of ethylene and propylene at near-complete methanol conversion. Some of the key aspects of the work have included the selection of reactor design for the MTO process and determination of the effects of process conditions on product yield. Evaluation of the suitability of the MTO light olefin product as an olefin polymerization feedstock and demonstration of the stability of the MTO-lOO catalyst have also been determined during the development of this process. 

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. 

The process has been demonstrated on a pilot scale by Lurgi and Statoil. Sufficient propylene has been produced to make polypropylene resin product by Borealis. This process appears to use an oxide doped ZSM-5 zeolite catalyst in fixed bed reactors. The oxide doping promotes the methanol conversion to olefins. All olefins, other than propylene, are recycled to extinction or purged as fuel gas or produced as naphtha. The flow sheet is illustrated in the Figure 11.8. 

V. Methanol Conversion to Light Olefins Catalyzed by SAPO-34 A... 

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.

We also studied the effect of ion exchange with on the catalytic activity of acid-treated Bent (H -Bent ), sometimes called activated clay. The results are given in Table IV. H" -Bent is virtually the same as H -Bent in catalytic activity. However, the catalytic activity of Ti -Bent for methanol conversion to hydrocarbons is much higher than that of Ti -Bent. The hydrocarbon yield reaches 90%, and the products, in addition to methane, are primarily olefins lower than Ce. The selectivity for olefin formation is estimated to be 90% or higher based on C2 and C3 hydrocarbon product distribution. Ti -Bent appears to surpass the phosphorus compound-modified zeolite proposed by Kaeding and Butter (31) in selective activity for olefin formation, and has the potential to exceed H-Fe-silicate (32) and Ni-SAPO-34 (33), proposed recently by Inui et al. 

G. Maria and O. Muntean, Model Reduction and Kinetic Parameters Identification for the Methanol Conversion to Olefins, Chem. Eng. Sci. 42 (1987) 1451-1460. 

The methanol to DME ratio was found to increase with coke formation on the catalysts (Fig. 6b). This ratio was quite far from the ratio at chemical equilibrium, which was calculated at 425°C to be 0.47. The deviation from chemical equilibrium ratio was found to be larger at higher coke contents and on the externally precoked samples. This indicates that the methanol conversion to DME is not fast enough to reach equilibrium, probably due to the moderate external acidity of SAPO-34 and partly also due to the effect of diffusion of DME at the higher coke contents. MTO can be considered a simple sequence reaction Methanols DME- olefins... 

Because the market for olefins currently greatly exceeds that for methanol production, olefin production could become an important new outlet for the potentially vast quantities of low-cost methanol. Methanol conversion produces a mixture of ethylene and propylene of various ratios or primarily propylene depending on the process. Currently, there are two processes for the production of propylene from methanol the first process is methanol to olefin (MTO) process, developed by UOP and Hydro,... 

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