Investigation of structural composition of thermally cracked olefins and of the effect of double bond isomerization by infrared spectroscopy

Abstract

Tins s tudy had two objectives: to develop a quanti tat ive method for the analysis of the structure and composition of narrow olefin hydrocarbon fractions in the Novo-Kuibyshev and Drogobych petroleum refineries by infrared spectroscopy and s tudy the effect of isomerization of the double bond of olefin hydrocarbon fractions during meta]lization. The quantitative distribution of various unsaturated structures in olefin industrial specimens of olefin hydrocarbons is of considerable importance both in thermal cracking technology and in numerous subsequent processes in which these olefins are used. The most important characteristics of olefin metallization (carried out to obtain unsaturated acids) can be derived from the isomer composition of olefins determined before and after the reaction of metallization. The ratio of olefin molecules with a varying configuration before and after the metallization reaction being known, the mechanism of this reaction can be correctly interpreted. Thus, a convenient and reliable quant i tat ive method of analysing the isomeric composition of olcfin fractions is of undoubted value both in a practical and theoretical respect. Characteristic infrared bands corresponding to out-of-plane deformation vibrations of = C H bonds are of the greatest interest for analytical purposes. These intensive bands have been used by many scientists to solve various analytical problems [1-4]. In this s tudy infrared spectroscopy was used for the quanti tat ive analysis of olefin fractions in respect of aand trans-isomers. The following analytical bands were selected for analysis: 910 cm -1 (a-isomers) and 965 cm -1 (trans-isomers). Figure 1 gives the infrared spectra of one of the fractions (Cx3--C14) before and after metallization. The analytical bands selected of aand trans-olefins are marked with arrows. When carrying out the analyses the mutual effect of aand trans-isomers was taken into account as, in addition to the a-isomer, the trans-isomer has some effect on optical density at a wave number of 910 cm -x and the optical