Methanol into light olefins conversion

Surprinsingly, the hydrocarbon distribution obtained with mixed pillared laponites does not follow a Schulz-Flory law. This selectivity deviation is comparable to the shape selectivity observed with zeolite encapsulated metal clusters in the conversion of syngas or methanol into light olefins as shown by Nazar et al, 1983 (Ref. 4). 

The appetite for natural gas as an industrial fuel continues unabated and is only limited by the supplies available in the major industrialized countries, in particular in the U.S.A., which has led to significant increases in its pricing. Large reserves of natural gas at low cost exist in remote of less industrialized areas. This has led to the increase in the number of LNG facilities and also to the construction of facilities at such locations where natural gas can be advantageously exploited in new ventures for the manufacture of methanol and light olefins and for the conversion of natural gas into liquid fuels for transportation applications. 

Small-pore SAPOs were recently used as catalysts for methanol conversion into light olefins.These molecular sieves have shown a very high selectivity for light olefins at 100% methanol conversion. SAPO-17 and SAPO-34 were the more active and selective for this reaction. The high activity is related to the presence of 3,600 cm Al-OH groups.SAPO-16 and SAPO-44 were also used as... 

SAPO molecular sieves, with their mild acidity, are a very interesting alternative to attain high selectivities for light olefins. The conditions of synthesis, dealumination, and cation exchange seem to be very important for obtaining a catalyst with a good performance for methanol conversion into light olefins. 

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]. 

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. 

The conversion of methanol into olefins is similar to the commercially proven methanol to gasoline (MTG) which was commercialised using natural gas as the feedstock in New Zealand. The variant generally uses similar catalysts to produce light olefins only, rather than the iso-paraffins and aromatics of the MTG process. This leads to the prospect of coal or gas conversion into resins (solids). These high value products may be easier to transport and sell than liquid fuels Figure 11.6 illustrates the basic unit operations for the process. 

Since the beginning of the 20th century, highly efficient and robust catalysts have been developed for the selective conversion of methanol into ethylene and propylene. SAPO-34 is regarded as the most carbon-efficient catalyst today to produce light olefins [11,20]. The ZSM-5 modified samples, on the other hand, provide the highest propylene yield, the most versatile product distribution, and a possibility to recycle back heavier olefins to boost the yield to light olefins [8]. 

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