Dimerization of butene

Although the preceding discussion of the sulfuric and hydrofluoric acid processes has been confined to butene alkylation, isobutane has also been alkylated commercially with other olefins. Ethylene, propylene, pentenes, and dimers of butenes have been used for this purpose. It is also possible to use these olefins for the alkylation of isopentane. Such an operation, however, has not achieved commercial acceptance because it produces an inferior alkylate with a high catalyst consumption, and because isopentane is a satisfactory aviation gasoline component in its own right. 

The dimerization of butenes is very similar to that of propene. Bismuth oxide and several other oxides have a capacity to catalyze this reaction. The combination Bi—Sn—O (Bi/Sn = 1/1), investigated by Seiyama et al. [284], appears to be particularly active. 

An analogous technology commercialized by IFP, Paris, is their continuous, chloroaluminate ionic liquid dimerization of //-butene to isooctane, promoted by a Ziegler-Natta-type homogeneous catalyst. The poorly miscible isooctane product is readily separated. 

BASF s BASIL process [15] and the Dimersol process [16] have both been commercialized. The former uses the ionic liquid as a phase transfer catalyst to produce alkoxyphenylphosphines which are precursors for the synthesis of photoinitiators used in printing inks and wood coatings. The imidazole acts as a proton scavenger in the reaction of phenyl-chlorophosphines with alcohols to produce phosphines. The Dimersol process uses a Lewis acid catalyst for the dimerization of butenes to produce Cs olefins which are usually further hydroformylated giving C9 alcohols used in the manufacture of plasticizers. Several other processes are also at the pilot plant scale and some ionic liquids are used commercially as additive e.g. binders in paints. 

For these studies the NiX precursor catalyst has been impregnated with molten lithium acetate. The catalyst displayed remarkably good selectivity to octenes. A typical set of results is shown in Fig. 18, where the reactant and product concentrations are given as a function of contact time, t. The results indicate that isomerization of 1-butene to an equilibrium mixture with 2-butenes (cis and trans) occurs rapidly, followed by the slower dimerization of butenes to octenes. The reaction was carried out under mixed phase conditions with the 1-butene reactant in the gas phase and the octene products in the liquid phase (trickle-bed reactor). Under the conditions the reaction rate was found to be mass-transfer controlled. 

It is noted that there have been a few, largely unsuccessful attempts to produce solid nickel catalysts for the dimerization of butene to linear octenes.11,12... 

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 ... 

As our first illustration we consider the co-dimerization of propene and butene to produce heptenes (Reaction 1). This reaction is accompanied by two competing, undesirable, reactions dimerization of propene to hexene (Reaction 2), and dimerization of butene to octene (Reaction 3). The second reaction proceeds extremely rapidly and in order to suppress the formation of hexenes we should have progressive injection of propene into the reactor with all the butenes at the beginning of the operation, as is shown in Fig. 22 (Trambouze et al., 1988). 

The dimerization of butene is expected to be a second order process while alkylation would be a pseudo-first order rate process. By this rationale, a CSTR should provide enhanced alkylation activity compared to a PER. As seen in Figure 6, CSTR operation gives a steady alkylate selectivity, as already described, whereas the PFR shows a different steady state with lower alkylate selectivity, favoring higher molecular weight compounds in the product. 

The potential of ILs in liquid-liquid biphasic catalysis for the generation of clean technology has became a reality with the announcement of a commercial process for the dimerization of butenes to isooctenes (Difasol process) by IFF (France) based on nickel complexes immobilized in organo-aluminate imidazolium ILs [138]. 

Table 1 Dimerization of butenes in homogeneous and biphasic systems comparison of dimer selectivity.

The alcohol part comes from variorrs synthetic sources. One source described in ht-erature is Cg alcohol mixture that is obtained by the hydroformylation and Itydrogenation of Cg olefin mixture obtained by dimerization of butene fraction. Two processes of purification are used by this technology. First corrsisterrt octene fraction obtained by the butene dimerization is purified by distillatiort. This is followed by rectification of reaction mixture obtained from alcohol productiorr. After the plasticizer is produced it is still purified by usual methods used in plastieizer syrrthesis. ... 

Dimerization of butenes into octenes First industrial unit in 1980 0.4 Mt products / year... 

This process is used by Nan Ya Plastics Corporation to produce, starting from an isomer mixture of octene the alcohol, INA and has a capacity >100 000 mt/a. After 2-EH, INA is the most important plasticizer alcohol, which is a complex mixture of linear and branched Cg alcohols. The most important plasticizer produced from it is diisononyl phthalate (DINP). The raw material sources can be, for example, a Cg fraction from the extraction of Fluid Catalytic Cracking (FCC) C -based polygas, the product of dimerization of butene from a raffinate-2 fraction using the octol or dimersol process, or diisobutylene from the dimerization of isobutylene from raffinate-1. 

Similar effects were observed in the dimerization of -butenes (Table rV). Due to the high rate of isomerization the same distribution of dimers is obtained starting from either 1-butene or 2-butene (thermodynamic equilibrium is attained soon after the dimerization starts). 

---