Methanol conversion to olefins

2 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. 

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 

Tsitsishvili et al. have carried out experiments of methanol conversion on H-offretite and TMA-offretite. TMA-offretite zeolites were calcined at 200 and 450 °C. H-offretite zeolites were prepared by ammonium ion-exchange and then calcined at 300 and 450 C. TMA-offretite calcined at 200 C was inactive, probably because the channels are blocked by the large Me N ions so that the acid sites become inaccessible for methanol molecules. A hydrocarbon fraction containing principally propylene, propane, n-butane, and n-butene was obtained in the cases of TMA-offretite and H-offretite calcined at 450 C. At reaction temperatures lower than 210 C only dimethyl ether was detected. H-offretite zeolites are active in the isomerization of xylenes, indicating that the removal of TMA-cations enlarged the pore opening. 

Ceckiewicz studied the methanol conversion between 25 and 400 C on zeolite H-T (SiOj/AljOj molar ratio of 7.4) with different degrees of decationization and dealumination. By Fourier transform infrared spectroscopy (FT-IR) he found that CH3OH molecules interact principally with the most active 3,600 cm OH groups corresponding to Al-OH bonds. No transformation of methanol occurred at 25 C. The dehydration of methanol to dimethyl ether was the most important reaction between 200 and 300 C. The conversion of methanol to hydrocarbons was evident at temperatures higher than 300 C. The conversion of methanol was less than 100% in all the cases. After 

18% led to a methanol conversion of 84.5% at 400 C and 0.11 g methanol/g catalyst min. The products were ethylene (13.1%), ethane (1.1%), propylene (29.8%), propane (7.6%), C4-C5 hydrocarbons (18.3%), and dimethyl ether (14.6%). The hydrocarbon yields and methanol conversion decreased markedly with time on streeun. The conversion of methanol dropped from 85 to 30% after only 30 min on streeun. 

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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. 

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

FURTHER STUDIES ON THE PROCESS OF METHANOL CONVERSION TO OLEFINS... 

Methanol Conversion to Olefins on Modified ZSM-5. - To increase the selectivity toward light olefins in the conversion of methanol, several modifications of the Mobil ZSM-5 catalyst were proposed. A distinction can be made between the attempts to increase the shape-selective properties and/or to reduce the acid strength by ion-exchange or impregnation of cations or chemical compounds and the attempts dealing with the isomorphous substitution of lattice aluminum atoms to reduce the acidity. 

On the basis of the carbene mechanism, Mihail et al. developed a kinetic model for the methanol conversion to olefins up... 

Yasuda, Y. and Nomura, K., Frequency response method for study of kinetic details of a heterogeneous catalytic reaction of gases. 2. A methanol conversion to olefins, J. Phys. Chem., 97, 3319-3323, 1993. 

Table 7 Methanol Conversion to Olefins over SAPO-34a...

Chang CD, Chu CTW, Socha RF. Methanol conversion to olefins over ZSM-5 1. Effect of temperature and zeolite SiOjAl Oj. J Catal 1984 86 289-96. 

Wu W, Guo W, Xiao W, Luo M. Methanol conversion to olefins (MTO) over H-ZSM-5 evidence of product distribution governed by methanol conversion. Fuel Process Technol 2013 108 19-24. 

Li J, Xiong G, Feng Z, Liu Z, Xin Q, Li C. Coke formation during the methanol conversion to olefins in zeolites studied by UV Raman spectroscopy. Microporous Mesoporous Mater 2000 39 275-80. 

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