Isoamylene Oligomerization over Zeolite Catalysts
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Isoamylene Oligomerization over Zeolite Catalysts N. G. Grigor’evaa,*, D. V. Serebrennikova, S. V. Bubennova, and B. I. Kutepova a Institute
of Petroleum Chemistry and Catalysis, Russian Academy of Sciences, Ufa, 450075 Russia *e-mail: [email protected] Received June 5, 2020; revised October 20, 2020; accepted November 5, 2020
Abstract—The study of isoamylene oligomerization over a number of microporous zeolites such as H–Y, H–MOR, H–Beta, H–ZSM-12, and H–ZSM-5 revealed that the isoamylene conversion rate decreases in the following order: H–MOR > H–Y > H–Beta-40 >> H–ZSM-12 > H–ZSM-5. The maximum yields of isoamylene oligomers were achieved by using H–MOR (85.0%), H–Y (80.1%), and H–Beta-40 (79.8%). The predominant isoamylene oligomers are dimers regardless of the zeolite catalyst used. The trimer yield reaches its highest when wide-pore zeolites like H–MOR, H–Y, or H–Beta-40 are employed. An increase in the number of acid sites enhances monomer conversion rate, oligomer yield, and oligomer molecular weight. Conditions for producing isopentene dimers and trimers with the maximum possible yield were determined. Keywords: isoamylene, oligomerization, dimers, trimers, isomerization, cracking, zeolites
DOI: 10.1134/S096554412102002X Oligomerization of light alkenes is a promising solution for producing higher-molecular-weight compounds for use as engine fuel components [1]. Silica-phosphate systems, which are the most common industrial catalysts for oligomerization of lower (C3–C4) olefins [2], have serious disadvantages such as short lifetime, complications in their removal from the reactor and disposal, and equipment corrosion. More state-ofthe-art lower-olefin oligomerization processes employ ZSM-5 based catalysts (Mobil Oil MOGD process) [3]. Isoamylene oligomerization has been the least explored for lower (C3–C5) olefins. Many studies on isoamylene oligomerization utilized cation-exchange resins such as Amberlyst, Pyrolite, or Nafion [3–10]. Some earlier papers [3–7] report attempts at selective production of dimers, driven by the following: (1) isoamylene dimers have a high octane number (specifically, the research octane number is 96, and even reaches 105 after hydrogenation), thus representing an option alternative to isooctane; and (2) amylene dimerization is a method to decrease the light naphtha vapor pressure and thus reduce C5 emissions, because the high reactivity of amylenes enables them to largely contribute to the tropospheric ozone formation [4]. Dimerization of isoamylenes in the presence of cation exchange resins occurs under relatively mild conditions (60–100°C, autoclave pressure up to 2 MPa) with the formation of primarily isodecenes (at least 90%). It was
found that isodecene selectivity can be improved up to 97% by adding low-molecular alcohols, although this gives rise to esterification byproducts. The recently increasing demand for diesel fuel has stimulated Granollers et al. [8] to study isoamylene trimerization in the presence of cation exchange resins. Catalysts with a high degree of polym
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