Isomerization of 4-Methyl-1-pentene and 1-Hexene Catalysed by Macroporous Ion Exchange Resin: A Kinetic Study
Magdalena Mitkova* and Kurti Kurtev “Professor Assen Zlatarov University”, Department of Organic Chemical Technologies, 1 Prof. Yakimov Str., 8010 Bourgas, Bulgaria
The isomerization of 4-methyl-1-pentene and1-hexene, thermodynamically the most unstable propene dimers, was studied. The isomerization was catalyzed by strongly acidic ion exchange resins in the temperature range of 362-384 K and under atmospheric pressure. The reaction scheme and kinetic equations, which best fit the experimental data are given.
Keywords: Isomerization; Kinetics; 4-Methyl-1-pentene; 1-Hexene; Sulfonic acid resin; Catalyst.INTRODUCTION It is a well known fact that the dimerization of propen, catalyzed by transition metal complexes results in the production of eleven isomers of hexane.1 The isomerization of these C6-alkenes on ion exchange resins leads to their thermodynamically most stable products: 3-hexene, 2-methyl-2pentene and 2,3-dimethyl-2-butene, which are of significant industrial interest. Theisomerization of 4-methyl-1-pentene and 1-hexene yields all possible isomers of the methylpentenes and the linear hexenes, which are also the products of propene dimerization. In our experiment on the isomerization of propene dimers instead of the traditional homogeneous catalysts2 we used acidic ion exchange resins. The investigations of other authors3-8 showed that alkenes isomerization occurs on acidicion exchange resin at moderate temperature and pressure with high selectivity and yield. The rate of isomerization depends in general on the form of the ion exchange resin. Substitution of H+ with different metal ions reduces the catalytic activity of the used resins. This fact was ascertained by several authors.9-12 Polymerization reaction of the alkenes also takes place on the surface of theresin, especially at high pressure.13-15 Slomkievicz13 reported the kinetic characteristics of isomerization of 1-butene, cis- and trans-2-butene on acid resin in a wide pressure and temperature range. A process of 1-alkenes isomerization to olefinic oil with a catalytic quantity of nonmetallic sulfonic or perfluorosulfonic acid resins is also described.16 This paper studies the kinetics and thereaction scheme of 1-hexene and 4-methyl-1-pentene isomerization on ion exchange
resin Wofatit OK-10. The Wofatit ion exchange resins are commercially available under various trade designations. They provide greater surface area for contact and therefore high catalytic efficiency. Wofatit OK-10 is also of great interest because there is no corrosion; it is easily separated from ensuing reactionmixtures that make the process technically advantageous and environmentally benign.
RESULTS AND DISCUSSION All isomerization reactions were carried out in a continuous flow, tubular glass reactor. The reaction mixture was in vapor phase and the temperatures were constant to within better than ±0.3 °C. For a particular W/FAo value the steady state operation of the reactor was usually achieved infour to five space times or less. The conversion degree XA was determined by analyzing the resulting mixture, from the effluent concentration CA. To clarify the mechanism of 4-methyl-1-pentene isomerization on catalyst Wofatit OK-10, we performed a series of experiments with different initial concentrations of the substrate, different values of W/FAo and different temperatures. The kinetic curves ofall products from a reaction carried out at T = 384 K are shown in Fig. 1. The data for the kinetic curves describing the same reaction carried out at other two temperatures, 372 K and 362 K, are similar. The data for the last two temperatures was also used in our calculations. Different hypotheses for the isomerization of the substrates which include a set of 12 reaction steps, 12 rate con-...