Oligomerization of isobutene

Several authors suggest the use of the NiY zeolite and Ni/Si-Al as catalysts for the oligomerization of isobutene [7-9]. The aim of this work is to compare the performance of two different green acid catalysts in situ sulfated Ti02 synthesized by the sol-gel method [22] with NiY zeolite, in the gas phase trimerization of isobutene at mild pressure and temperature conditions atmospheric pressure and 40°C, in terms of activity, selectivity and stability. 

The oligomerization of isobutene in function of the time is shown in Figures 1 and 2 for the sultated Ti02 and NiY zeolite catalysts respectively. After a stabilization time of 2 hours on stream, the sulfated Ti02 catalyst showed initial conversion values after 3 h in stream of 100, 70, 65 and 42% at GHSV of 8, 16, 32 and 64 h, respectively (Fig. 1). For the NiY zeolite catalyst the activities were 56, 43, 33 and 17% for the previous GHSV values respectively (Fig. 2). 

An important intermediate for synthetic p-ionone (36) is the C8 building block methyl heptenone (37). In addition to the synthesis shown above, two further processes are known for its industrial production. In the process of Rhodia INC 36), the starting material is isoprene, and methyl heptenone (37) is obtained via prenyl chloride. At BASF, methyl heptenone (37) is produced, for economic reasons, in the form of its double bond isomer (37 a) by thermal condensation of isobutylene, formaldehyde and acetone 37) (see page 13). By suitable choice of the reaction conditions, various side-reactions, such as the Cannizzarro reaction of formaldehyde, the oligomerization of isobutene and aldol condensation between formaldehyde and acetone, can largely be suppressed. 

Two methods are available for the selective oligomerization of isobutene. They are practised by VOP and IFP in particular, and apply to the following situations ... 

The second stage in the process is required because the MTBE formation is an equilibrium reaction. The temperature needed ( 100°C) to achieve a sufficiently high rate of conversion means a decrease in isobutene equilibrium conversion (XiB = 0.9 at 65°C, Xjb = -0.75 at 100°C). The main side reaction in the MTBE process is the dimerization of isobutene towards di-isobutene (two isomers). Side reactions with essentially no significance are the formation of f-butyl alcohol (due to the presence of water as feed impurity), the formation of dimethyl ether from methyl alcohol, and the oligomerization of isobutene towards tri- and tetramers. A (three stage) process is also in operation which tolerates butadiene. The butadiene/ methyl alcohol reaction is faster than that of the n-butenes but consider-... 

Synthetic oils with high viscosity indices were produced in the oligomerization of isobutene using HZSM-5 catalyst, surface-deactivated with 2,6-di-/ert-butyl-pyridine. Chen and Bridger proposed a protonated cyclopropyl intermediate for the isobutene-HZSM-5-system in the formation of linear oligomers. 

Torres M., GutiOTez M., Mugica V., Romero M., Lopez L. 2011. Oligomerization of isobutene with a beta-zeolite membrane Effect of the acid properties of the catalytic membrane. Catalysis Today 166(1) 205-208. 

Cai Tianhi, Selective oligomerization of isobutene in C4 mixture using heteropolyacids as catalysts, Shigou Huagong, 15, 207, 1986 (Chinese). 

Luxton, R. A., The preparation, modification and applications of nonfunctional liquid polybutadienes, Rubb. Chem. Technol, 54, 546, 1981 (a) Minsker, K. S., and Sangalov, lu. A., Isobutylene and their oligomers, Khimija, Moscow, 1986 (Russian). Hsish, H. I., Structure and molecular weight distribution of oligomers resulted in oligomerization of isobutene,/. Polym. Sci., A-1, 7, 449, 1969. 

Bette, C., Oligomerization of isobutene in tubular reactors, Chimie et Industrie, 87, 246, 1962. 

Such a concept may be proposed for some other cationic complexes which react preferentially with branched olefins. Thus Pt(MeCN)4[BF4]2 in nitromethane [19] and Rh(NO)(NCMe)4[BF4]2 [20] induce dimerization and oligomerization of isobutene or 2-methyl-2-butene. This is typical of a cationic mechanism. 

Minachev et al. studied the activities of a variety of zeolites for oligomerization of isobutene at atmospheric pressure and found that L-type zeolite manifests the highest activity oligomer yield greater than 90% was obtained at 373 K. 

Oligomerization of isobutene was carried out using a silica gel having sulfobenzyl groups as catalyst.At 403 K and atmospheric pressure, the conversion of isobutene was quantitative and yielded 52 wt% of di-, 40 wt% of tri- and 3 wt% of tetraisobu-tene besides a maximum of 2 wt% of odd carbon-number products. 

---