Etherification of some C8-alkenes to fuel ethers

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Doctoral thesis (article-based)
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47, [53]
Industrial chemistry publication series / Helsinki University of Technology, 12
Tertiary ethers are formed in a reaction between alcohols and alkenes. They are used in gasoline to enhance its burning and to reduce harmful exhaust emissions. They also have high octane rating, which is beneficial for gasoline blending. Regulations in regard to fuel composition and exhaust emissions are tightening and new, cleaner burning high octane gasoline components are of wide interest. This work concerns the etherification of C8-alkenes. Several C8-alkenes were screened for their reactivity. Study of the properties of the resulting ethers showed that some of them are potential for gasoline blending. 2,4,4-Trimethyl pentenes were chosen for more detailed study in view of the availability of the feed stock in industrial scale and the promising properties of the resulting ether. The reactivity of 2,4,4-trimethyl pentenes was tested with various alcohols. The marked effect of the alcohol on the reaction rate was attributed primarily to the polarity of the alcohol, which affects the adsorption of the components and the catalyst. Compared with the ethers currently in commercial production, the C8-alkenes are etherified rather slowly. A new catalyst was sought to enhance the reaction rate. Traditionally, etherification is catalysed by strong cation exchange resin beads, such as Amberlyst resins, but a novel fibrous Smopex-101 catalyst was found to be more active in the etherification of 2,4,4-trimethyl pentenes with methanol, evidently because diffusional limitations were less. A kinetic model was developed for the etherification of 2,4,4-trimethyl pentenes with methanol for purposes of reactor design. Kinetic experiments were performed with Smopex-101 as catalyst. Before the kinetic studies, thermodynamic parameters were derived for the etherification reactions and for the isomerisation reaction between 2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene. The results of the kinetic modelling indicated that the adsorption of the alkenes was minor. The best models to describe the data were the Langmuir-Hinshelwood type model where the adsorption of alkenes is assumed to be negligible compared to other reactive components and the Eley-Rideal type model where alkenes are not adsorbed. Adsorption behaviour was different on the fibrous catalyst than on the ion exchange resins: ether was better adsorbed than alcohol on the fibrous catalyst, whereas alcohol is known to better adsorb than ether on the traditional ion exchange resin catalyst. The better adsorption of ether on the fibrous catalyst was attributed to the greater hydrophobicity of this catalyst.
etherification, 2,4,4-trimethyl pentenes, C8-alkenes, 2-methoxy-2,4,4-trimethyl pentane
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