Isobutene dimers

Good hydrocarbon dispersion in hydrofluoric acid is an impxjrtant factor In producing alkylate rich in trimethylpentanes and thus favors olefin isomerization (to isobutene), isobutene dimerization, and maximizes hydrogen transfer and primary alkylation reactions. Excess olefin polymerization to form residue is suppressed by good dispersion. 

The following facts are the basis for butene isomerization (I) There is a basic similarity in the composition of alkylates produced from all four butene isomers. (2) Alkylate molecules, once formed, are relatively stable under alkylation conditions and do not isomerize to any appreciable extent alkylate fractions having the same carbon number ore not equilibrated (see Table I). (3) Thermodynamic equilibrium between the butene olefins highly favors isobutene formation at alkylation temperatures. (4) Normal butenes p>roduce only small and variable amounts of normal butane, thus indicating only a small and variable amount of chain initiation from normal butenes. Yet the alkylate composition shows a high concentration of trimethylpentanes and a low concentration of dimethylhexanes. (5) A few of the octane isomers can be explai.ned only by isomerization of the eight-carbon skeletal structure this isomerization occurs while isobutene dimer is in ionic form. For example, 2,3,3- and 2,3,4-trimethylpentanes... 

Artemisinin has been converted in two steps into the stable trioxane isobutene dimer 41. Reactions at the linking unit leave the trioxane fragments intact and allow the synthesis of a variety of dimers that possess desirable pharmacological properties <03JMC1060>. 10-Bromoalkyl and 10-aminoalkyl derivatives of deoxoartemisinin have been prepared and used to form dimers and a trimer in which artemisinin residues are linked through alkylamide and alkylthio functions <03JMC987>. 

Figure 2.37a reports the reaction scheme for isooctane production by isobutene dimerization. Various isooctane processes are commercially available and are different in terms of reaction conditions and type of catalysts ... 

Figure 2.37 (a) Reaction network for isooctane production by isobutene dimerization (b) schematic flow-sheet of the NExOCTANE/NExSAT process of Neste Oil. 

Selectivity to ETBE is usually very high and the main side reactions are isobutene dimerization with formation of 2,4,4-trimethyl-l-pentene and 2,4,4-trimethyl-2-pentene (DIB), ethanol self-condensation to diethyl ether (DEE), water addition to isobutene with formation of tert-butyl alcohol (TBA) and the etherification of linear butenes, if present, to produce ethyl sec-butyl ether (ESBE). 

In the field of fine chemistry, the Phillips neohexene process was an early commercial application of olefin metathesis [20]. Neohexene (3,3-dimethyl-l-butene) is an important intermediate in the synthesis of musk perfume. The Phillips neohexene process is based on ethenolysis of an isobutene dimer consisting of a mixture of 2,4,4-trimethyl-2-pentene and 2,4,4-trimethyl-1-pentene. Ethenolysis of the former yields the desired product (Eq. 6). 

The 2,4,4-trimethyl-l-pentene is not wasted because a dual catalyst can be used to ensure that it is converted into 2,4,4-trimethyl-2-pentene as this gets used up by ethenolysis. With a 1 3 catalyst mixture of a W03/Si02 metathesis catalyst and a MgO isomerization catalyst (at 370 °C and 30 bar ethene pressure), an average of 65-70 % conversion of the diisobutene can be achieved with approximately 85 % selectivity for neohexene. The coproduct isobutene can be recycled to an isobutene dimerization reactor. Neohexene is used to make the class of synthetic... 

A high conversion level of isobutene (99%) can be reached with a double-stage configuration where, in both stages, water-cooled tubular reactors (WCTR), (1,2), are used for the isobutene dimerization to maintain optimal temperature control inside the catalytic bed. 

Due to a joint development agreement between Saipem and Catalytic Distillation Technologies (CDTech) for the isobutene dimerization (Dimer8 process), the plant configuration can be optionally modified... 

The catalytic properties of SAPO-34 in isobutene dimerization have been... 

Fig. 8.12 Influence of polymer load on the formation of isobutene dimer...

Torres, Gutierrez, Mugica, Romero, and Lopez (2011) synthesized P-zeolite membranes with different acidities. They demonstrated that catalytic membrane shows high activity toward isobutene dimers and attributed this to the surface acidity of the membrane and the control of short residence time within the zeolite membrane active pores contributing to the large butane oligomer Cie elimination. 

Recently we examined the possibility of selectively synthesizing the isobutene tetramer (IB4.) and trimer (IB3) by the reaction of two isobutene dimers (IBj) or isobutene dimer with isobutene (IB), respectively ... 

Isooctane synthesis was performed using ZSM-5 and ZSM-23 zeolites in sc-CO via isobutene dimerization in comparison with sc-propane [200]. Except for dimerization, oligomerization and coke formation occur. The ZSM-23 catalyst exhibited the initial isobutene conversion of 80%. The conversions in sc-CO and sc-propane were 56% after 200h and 32% after 120h, respectively. 

By an adequate choice of the IL, selectivity for isobutene dimers can reach 88 wt% (at 70% isobutene conversion) with possible recycling of the catalytic system without loss of activity and selectivity. 

Magna, L. Bilde, J. Olivier-Bourbigou, H. Robert, T. Gilbert, B. (2009). About the Acidity-Catalytic Activity Relationship in Ionic Liquids Application to the Selective Isobutene Dimerization. Oil Gas Technol., 64,669-679, ISSN 1294-4475. 

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