Olefin conversion aromatization

Crude oil processing is mainly aimed towards the production of fuels, so only a small fraction of the products is used for the synthesis of olefins and aromatics. In Chapter 3, the different crude oil processes are reviewed with special emphasis on those conversion techniques employed for the dual purpose of obtaining fuels as well as olefmic and aromatic base stocks. Included also in this chapter, are the steam cracking processes geared specially for producing olefins and diolefms. 

The fit of these equations to the data is very good, as seen in Fig. 18. These equations are valid to very small values of CO concentrations, where the reaction becomes first order with respect to CO. In a mixture of CO with oxygen, there should be a maximum in reaction rate when the CO concentration is at 0.2%, as shown in Fig. 19. When the oxidation of olefins and aromatics over a platinum loaded monolith is over 99% complete, the conversion of higher paraffins may be around 90% and the conversion of the intractable methane is only 10%. 

Another well-known transformation of carbonyl derivatives is their conversion to pinacols (1,2-diols) via an initial one-electron reduction with highly active metals (such as sodium, magnesium, aluminum, samarium iodide, cerium(III)/ I2, yttrium, low-valent titanium reagents (McMurry coupling), etc.), amines, and electron-rich olefins and aromatics as one-electron donors (D).43 Ketyl formation is rapidly followed by dimerization44 (equation 22). 

Light hydrocarbons (Ci to C4) and aromatics (mainly Ce to Ce) were produced by ZSM-5 due to the the conversion of olefins and paraffins. Thus,these results provide evidence for cracking of olefins, paraffins and cyclization of olefins by ZSM-5 at 500 C. The steam deactivated ZSM-5 catalyst exhibited reduced olefin conversion and negligible paraffin conversion activity. 

Products = (H2 -t- (Cl to C4) -I- (C5 and Cg olefine) -1- aromatics) in product. All of the catalysts demonstrated 100% conversion at very initial stage of the reaction under the condition employed. They showed, however, great differences in the stability of the activity. While H-ZSM-5 showed rapid decline of conversion, on the other hand, Zn-Al-silicate (A), showed more stable activity. Accordingly, metallosilicate exhibited better stability. 

For MTO, where the object is to optimize the olefins, we raise the temperature to about 500°C, which favors olefin formation. We also modify the catalyst to slow down the conversion of olefins to aromatics and paraffins. These changes produce a dramatic change in the reaction path. As Figure 17 shows, we have now decoupled the aromatics + paraffins plot from the olefins plot. 

These processes also largely fall into the category of hydrocarbon conversion or conversion of nonhydrocarbons to hydrocarbons over acid catalysts. They include the reactions of olefins, paraffins, aromatics and their mixtures in the production of high octane gasoline, high quality diesel, jet fuel, distillate fuels and lubricants. Table 1 shows a partial list of these processes. 

Methanol Conversion. Methanol conversion reactions based on borosilicate catalysts have been studied extensively (10.15,24,28.33.52-54). During the conversion of methanol, the reaction proceeds through a number of steps, to yield dimethylether, then olefins, followed by paraffins and aromatics. The weaker acid sites of borosilicate molecular sieves relative to those of aluminosilicates require higher reaction temperatures to yield aromatics. The use of less forceful process conditions leads to the formation of olefins selectively, instead of a mixture of paraffins, olefins, and aromatics (10.28.53.54). 

It may also be noted that hydrogen transfer reactions of olefins to aromatics lead to the formation of three moles of paraffins for every mole of aromatics formed (Kaa) over HZSM-5,. The alternative dehydrogenation pathway (Km2) provided by zinc for the conversion of C6-Cg oligomers to aromatics suppresses the hydrogen transfer reactions hence more olefinic molecules are available for the aromatization reaction. Thus, the pathways Kmi and Km2 provided by zinc results in the significant increase in aromatics yield... 

The principal technical problems associated with converting crude oil into ethylene and other light olefins and aromatics stem from conversion of the heavier fractions and in particular the heavy residues which contain asphaltenes, metalloorganic compounds, etc. Several approaches can be taken to solve this problem. 

Klyueva et al. have investigated the acidic properties of erionite modified by isomorphous substitution of B , Ga , and Fe " " by Si and Al . The incorporation of these elements in the aluminosilicate framework led to the generation of new acid centers. These acid centers have a lower concentration of aluminum cations than aluminosilicates, leading to s unples with lower acidity. Consequently, the rate of reactions involving hydrogen transfer, like olefin conversion into paraffins, was lower on isomorphous-substituted erionite samples. Table 5 shows that this enhanced the selectivity toward light olefins. The production of aromatics may... 

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