Isobutene dimerization

Silica-alumina-nickel oxide, amorphous to X-rays, with a high ratio of Si02/ AI2O3 was found to be a suitable catalyst for dimerizing isobutene into a- and P-di-isobutene with high selectivity and was also useful for oligomerizing propene to dimers and trimers. ... 

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. 

Some types of reactions involving gases that have been studied in IFs are hydrogenations [16, 25-37 ], oxidations [38, 39], and hydroformylations [25, 40 5]. In addition, some dimerizations and allcylations may involve the dissolution of condensable gases (e.g., ethylene, propylene, isobutene) in the IF solvent [46-50]. 

An alternative method for separating the hutenes is hy extracting isobutene (due to its higher reactivity) in cold sulfuric acid, which polymerizes it to di- and triisohutylene. The dimer and trimer of isobutene have high octane ratings and are added to the gasoline pool. 

The catalytic asymmetric cyclopropanation of an alkene, a reaction which was studied as early as 1966 by Nozaki and Noyori,63 is used in a commercial synthesis of ethyl (+)-(lS)-2,2-dimethylcyclo-propanecarboxylate (18) by the Sumitomo Chemical Company (see Scheme 5).64 In Aratani s Sumitomo Process, ethyl diazoacetate is decomposed in the presence of isobutene (16) and a catalytic amount of the dimeric chiral copper complex 17. Compound 18, produced in 92 % ee, is a key intermediate in Merck s commercial synthesis of cilastatin (19). The latter compound is a reversible... 

Cold Acid A process for polymerizing isobutene, mainly into dimers and trimers, for making high-octane gasoline blending components. It is catalyzed by 60 to 70 percent sulfuric acid at 25 to 35°C. Developed by the Shell Companies. See also Hot Acid. 

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... 

Figure 4 shows the reaction pathway for the isobutene oligomerization. After the dimer formation, the addition of another one butene molecule will depend mainly of Brbnsted acidity to stabilize the formation of the carbocation. The oligomerization to heavier olefins will be favored on catalyst showing a low L/B acids sites ratio [12]. 

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,... 

Isobutylene is more reactive than n-butene and has several industrial uses. It undergoes dimerization and trimerization reactions when heated in the presence of sulfuric acid. Isobutylene dimer and trimers are use for alkylation. Polymerization of isobutene produces polyisobutenes. Polyisobutenes tend to be soft and tacky, and do not set completely when used. This makes polyisobutenes ideal for caulking, sealing, adhesive, and lubricant applications. Butyl rubber is a co-polymer of isobutylene and isoprene containing 98% isobutene and 2% isoprene. 

A combination of the thermal polymerization process and the U.O.P. catalytic process was introduced in 1937 at the Shamrock Oil and Gas Co., Sunray, Tex. (28). In 1934 the Shell Development Co. introduced the cold acid process (18), which selectively polymerizes isobutene, using sulfuric acid as catalyst. The hot acid process was also developed by them and differed from the cold acid process in polymerizing all C4 olefins. Both products are predominantly the dimer. The cold acid process produces a large pro-... 

The absorption step occurs at a temperature of about 68° to 104° F. and whatever pressure is necessary to maintain the hydrocarbon feed in the liquid phase. When using a 65% acid about 90 to 95% of the isobutene is absorbed. Polymerization takes place at a temperature of 200° to 220° F., producing approximately 75 to 80% dimer, the rest trimer. Thus about 67% of the isobutene in the feed is converted to iso-octenes. 

Butadiene is available commercially as a liquefied gas underpressure. The polymerization grade has a minimum purity of 99%, with acetylene as an impurity in the parts-per-million (ppm) range. Isobutene, 1-butene, butane and cis-l- and Zrc//7.s-2-butcnc have been detected in pure-grade butadiene (Miller, 1978). Typical specifications for butadiene are purity, > 99.5% inhibitor (/c/V-butylcatecliol). 50-150 ppm impurities (ppm max.) 1,2-butadiene, 20 propadiene, 10 total acetylenes, 20 dimers, 500 isoprene, 10 other C5 compounds, 500 sulfur, 5 peroxides (as H2O2), 5 ammonia, 5 water, 300 carbonyls, 10 nonvolatile residues, 0.05 wt% max. and oxygen in the gas phase, 0.10 vol% max. (Sun Wristers, 1992). Butadiene has been stabilized with hydroquinone, catechol and aliphatic mercaptans (lARC, 1986, 1992). 

Dimerization and aromatization have been reported for isobutene and n-butenes, analogous to propene, over catalysts like Bi203. Isobutene radicals dimerize more easily than n-butene radicals, which are less stable and rapidly form butadiene. 

The dimerization and aromatization of olefins occurs in consecutive reaction steps. Isobutene, for example, reacts as follows... 

Bismuth phosphate has been investigated as a catalyst for aromatization of the four different butene isomers at 550°C. An optimal catalyst has an atomic ratio Bi/P = 2 (Sakamoto et al. [271]). Isobutene is converted at short contact times (r 0.3 sec) to dimers and to aromatics, with a selectivity of 29% each. n-Butenes give much lower yields. 

The Ti and Hf compounds are monomers, whereas the Zr complex was dimeric. As found by Hrncir and Skiles, the series of M[OSi(OBu-t)3]4 compounds are all moisture-sensitive. TGA studies indicate that the Ti complex decomposes cleanly at temperatures >240 °C and gives a ceramic yield of 25 wt% whereas the theoretical ceramic yield for TiSiC>4 should be 29.07 wt%. The primary gaseous thermolysis products were identified by mass spectroscopy to be isobutene and water. A likely pathway for decomposition appears to involve /1-hydrogen elimination followed by condensation of the resulting Si—OH groups to generate isobutene, water and an oxide network as shown in equations 66 and 67. 

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