Isoprene Synthesis from Formaldehyde and Isobutylene in the Presence of Aluminum- and Niobium-Containing BEA Catalysts
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oprene Synthesis from Formaldehyde and Isobutylene in the Presence of Aluminumand Niobium-Containing BEA Catalysts O. A. Ponomarevaa, b, *, D. L. Chistova, P. A. Kotsa, V. R. Drozhzhina, L. I. Rodionovaa, and I. I. Ivanovaa, b aFaculty
of Chemistry, Moscow State University, Moscow, 119991 Russia Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, 119991 Russia *e-mail: [email protected]
b
Received March 15, 2020; revised April 1, 2020; accepted April 10, 2020
Abstract—A single-stage gas-phase synthesis of isoprene from formaldehyde and isobutylene in the presence of Al–BEA and Nb–BEA zeolite catalysts containing different amounts of aluminum and niobium has been studied. The physicochemical properties of the catalysts have been studied by low-temperature nitrogen adsorption, infrared spectroscopy of adsorbed CO, X-ray fluorescence analysis, and ammonia TPD methods. Catalytic tests have shown that, at similar formaldehyde conversion values, the isoprene selectivity is higher in the presence of the Al-containing BEA catalysts. It has been found that Al–BEA with Si/Al = 12 exhibits the highest activity in isoprene synthesis. Keywords: Prins reaction, isoprene, isobutylene, formaldehyde, Nb–BEA, Al–BEA DOI: 10.1134/S0965544120080125
INTRODUCTION Isoprene is a strategically important monomer of large-scale syntheses of isoprene rubbers, which exhibit properties and structure similar to those of natural rubber and are commonly used in the manufacture of car tires; in addition, isoprene is used in the synthesis of thermoplastic polymers and pressure-sensitive adhesives and in the production of medicines and fragrances. The demand for isoprene exceeds supply; the request for isoprene production is constantly increasing. Currently, the following commercial isoprene synthesis methods are used in most countries of the world: (1) the condensation of isobutylene and formaldehyde, (2) two-stage isopentane dehydrogenation, (3) isoamylene dehydrogenation, (4) propylene dimerization, and (5) isoprene extraction from the C5 fraction of straight-run gasoline pyrolysis. The first method based on isobutylene condensation with formaldehyde is most commonly used; it is the main method for isoprene synthesis in Russia. This common use is apparently attributed to the fact that the two reactants are based on the primary products of refining of petroleum and associated gas, which are used as a fuel in many countries. This method has the following disadvantages: a two-stage nature, which is not efficient from technical and economic points of view; a low isoprene selectivity, which does not exceed
50%; the formation of a large amount of byproducts; and the use of phosphoric acid as a catalyst at the first stage of the process, which leads to equipment corrosion and environmental problems. In this context, the development of a single-stage isoprene synthesis process using heterogeneous catalysts is an urgent task. Unlike the homogeneous condensation of olefins with aldehydes (Prins reaction), whic
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