Dimerization of isobutene

Other Dimer Olefins. Olefins for plasticizer alcohols are also produced by the dimerization of isobutene [115-11-7] 4 8 codimerization of isobutene and / -butene [25167-67-3]. These highly branched octenes lead to a highly branched isononyl alcohol [68526-84-1] product. BASE, Ruhrchemie, ICl, Nippon Oxocol, and others have used this source. 

Cation-exchange resins are used as catalysts in the produdion of MTBE (methyl tertiary-butyl ether, 2-methoxy-2-methylpropane) and various other oxygenates and, lately, also in the dimerization of isobutene [30]. Other commercial applications of the cation-exchange resins indude dehydration of alcohols, alkylation of phenols, condensation readions, alkene hydration, purification of phenol, ester hydrolysis and other reactions [31]. The major producers of ion-exchange resins are Sybron Chemicals Incorporated [32] (Lewatit resins), Dow Chemical Company [33] (DOWEX resins), Purolite [28] (Purolite resins), and Rohm and Haas Company [27] (Amberlyst resins). 

In the dimerization of isobutene, tertiary-butyl alcohol (TBA, 2-methyl-2-propanol) has a strong role in modifying the selectivity of the reaction to Cg hydrocarbons and limits further oligomerization to C12 and Ci6 hydrocarbons [34]. Also, in the etherification of glycerol with isobutene the addition of TBA has a clear effect on the selectivity and on hydrocarbon distribution. The selectivity to ethers increased and the fraction of the Cu and Ci6 hydrocarbons decreased while the concentration of TBA was increased from 0 to 2.6 mol.%. As a conclusion, the formation of C12 and C16 hydrocarbons can be prevented in two ways either TBA should be added to the reaction mixture or the reaction should be carried out at high temperatures [8]. 

Above we have mentioned several heterogeneous applications such as the OCT process and SHOP. Neohexene (3,3-dimethyl-1-butene), an important intermediate in the synthesis of fine chemicals, is produced from the dimer of isobutene, which consists of a mixture of 2,4,4-trimethyl-2-pentene and 2,4,4-trimethyl- 1-pentene. Cross-metathesis of the former with ethene yields the desired product. The catalyst is a mixture of W03/Si02 for metathesis and MgO for isomerisation at 370 °C and 30 bar. The isobutene is recycled to the isobutene dimerisation unit [48],... 

Hydrogen fluoride also is used as a catalyst in alkylation of aromatic compounds and for dimerization of isobutene. Other catalytic applications are in isomerization, polymerization, and dehydration reactions. Other uses are in... 

Butenes are used extensively in gasoline production to produce high-octane gasoline compounds. In alkylation reactions, butenes combine with isobutane to produce branched gasoline-range compounds (see Butane). Isooctane can be produced by dimerization of isobutene in the presence of sulfuric acid. Dimerization is the combination of a molecule with itself to produce a molecule called a dimer. The dimer has exactly twice the number of atoms in the original molecule. Therefore the dimerization of isobutene produces two dimers with the formula C H,... 

Dimethvihexane Formation. Dimethyl hexane formation Is believed to result largely from reactions of butene-l. This includes (I) codimerization of butene-l and isobutene, (2) dimerization of butene-l, and (3) dimerization of isobutene, and (4) isomerization of dimethylhexyl carbonlum Ions each of these reactions is followed by abstraction of a hydride ion from isobutane. Reactions follow ... 

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-... 

In 2001, a CD process for the production of 2,2,4-trimethylpentane with 100 octane rating from the dimerization of isobutene and hydrogenation of the octenes using a Pd/cation-exchange resin was disclosed, but no data were given in the patentJ ... 

The absorption of isobutene in subazeotropic aqueous ethanol, to give ETBE and tert-butyl alcohol (TBA) was investigated [58]. The experiments were conducted in a stainless steel autoclave of one liter capacity. The catalyst used was Amberlyst-15, which is an acidic, macroporous cation exchange resin, in the form of spherical beads. In the ETBE synthesis reaction using ethanol and isobutene, the side reactions are the dimerization of isobutene to form diisobutene and the formation of diethyl ether. These byproducts show a tendency to increase with an increase in reaction temperature. Hence, the... 

The same kind of product can be obtained by acid-catalyzed dimerization of isobutene, followed by hydrogenation. 

Dimerization of isobutene with a catalyst of Si02/Al203 molar ratio of 102, NiO/Si02 molar ratio 0.021 in autoclave at 60 °C, 15 min and conversion 44% oligomerization of propylene with the above formula for catalyst, space velocity 2.87h , 3.08 MPa, 94 C, conversion 79%... 

Fig. 8.17 Influence of cross-linking of polymer/ceramic ion-exchange catalysts for the dimerization of isobutene during MTBE synthesis at low polymer loading...

Fritsch, Randjelovic, and Keil (2004) studied a forced-flow catalytic membrane reactor for dimerization of isobutene to isooctene. They examined several catalysts, such as sihca-supported Nafionl (Nafionl SAC-13), Nafionl NR50, AmberlystTM... 

Alkyl- and aryl-acetylenes, e.g. (70), but not acetylene itself, co-dimerize with allylic halides (71) in the presence of catalytic amounts of palladium complexes to give halogenated 1,4-dienes (72) in excellent yields. " The most active catalyst appears to be the [PdX2(PhCN)2] complex. The procedure involves very careful addition of the acetylenic compound to the allylic halide solution at 20 °C to prevent polymerization in this exothermic reaction. The co-dimerization of isobutene with trichloroethylene can produce useful quantities of l,l-dichloro-4-methylpenta-1,4-diene in the presence of t-butyl peroxide at 500 °C in a gas-phase reactor. The reaction probably occurs by a radical transfer mechanism. 

Hie neohexene process starts with the acid-catalyzed dimerization of isobutene, followed by metathesis with ediylene, to give neohexene, an intermediate in the manufacture of synthetic musk, and regenerate isobutene. 

The "acidity scale" was tentatively compared with an "activity scale" obtained for the dimerization of isobutene into isooctenes. 

The dimerization of isobutene carried out in a forced-flow polymeric catalytic membrane reactor was reported by D. Fritsch and co-workers. The authors prepared composite porous membranes consisting of a catalytic layer made of solid add catalysts, such as siUca supported Naflon , Nafion NR50, Amberlyst 15 and silica supported tungstophosphoric add dispersed in polymeric binders such as Teflon AF, Hyflon AD, polytrim-ethylsilylpropyne, or polydimethylsiloxane (PDMS), cast on microporous support membranes made of polyacrylonitrile (PAN) or Torlon . The membranes were assembled in the membrane reactor into which isobutene was fed in the retentate side with a build-up pressure of 4 bar. The liquid product was collected on the permeate side. 

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