Difasol™ process

From these results, the Institut Fran ais du Petrole (IFF) has developed a biphasic version of its established monophasic Dimersol process , which is offered for licensing under the name Difasol process [98]. The Difasol process uses slightly acidic chloroaluminate ionic liquids with small amounts of allcylaluminiums as the solvent for the catalytic nickel center. In comparison to the established Dimersol process , the new biphasic ionic liquid process drastically reduces the consumption of Ni-cata-lyst and allcylaluminiums. Additional advantages arise from the good performance obtained with highly diluted feedstodcs and the significantly improved dimer selectivity of the Difasol process (for more detailed information see Section 5.3). 

Diethyl sulfite reaction, 10 530 Diethyltoluenediamine (DETDA), 25 197 Dietzeite, 6 471t Difasol process, 26 899 Difenzoquat, 13 322 Difference spectroscopy, 14 236 23 144 Difference tests, in flavor characterization, 11 512... 

Showing so much promise it is not surprising that ionic liquids are already used within large-scale industrial appUcations and that further industrial processes are in development. The Dimersol/Difasol process developed by the Institut Francais du Petrole uses an ionic Uquid to dissolve the catalyst and to separate the catalyst phase from the product [19]. The products of the reaction—C 8 olefins—are not soluble in the ionic Hquid and form a second phase that can be easily separated. The nickel catalyst dissolved in the ionic liquid can be recycled. In addition, the catalyst shows in the ionic Hquid increased activity and better selectivity to the desired dimers rather than to the undesired higher oUgomers. 

Another example is butene dimerization catalyzed by nickel complexes in acidic chloroaluminates 14). This reaction has been performed on a continuous basis on the pilot scale by IFF (Difasol process). Relative to the industrial process involving homogeneous catalysis (Dimersol process), the overall yield in dimers is increased. Similarly, selective hydrogenation of diene can be performed in ionic liquids, because the solubility of dienes is higher than that of monoene, which is higher than that of paraffins. In the case of the Difasol process, a reduction of the volume of the reaction section by a factor of up to 40 can be achieved. This new Difasol technology enables lower dimer (e.g., octenes) production costs 14). 

As an indication of things to come, a year ago IFF in Paris revealed that it had just launched a commercial process based on ionic liquids that are available for licensing. The Difasol process for dimerizing butenes to isooctenes was developed at Rueil-Malmaison, and pilot-scale trials were carried out at IFP s pilot facilities at the Industrial Research Development Center at Solaize, near Lyon. 

The new Difasol process for manufacturing isooctenes consumes less catalyst. The process dimerizes n-butene in a continuous two-phase operation that uses the industrial Dimersol nickel catalyst dissolved in a chloroaluminate ionic liquid. The n-bu-tenes are introduced continuously into the reactor, and the products are only poorly miscible with ionic liquid, and separate in settler. The process shows 70-80% conversion with 90-95% selectivity (Freemantle, 1998). 

The French Petroleum Institute has developed an ionic liquid based process for the dimerization of alkenes (Dimersol process) and it has been patented as the Difasol process. Interestingly, it can be retrofitted and operated in existing Dimersol plants. However, its biphasic nature offers several advantages over the traditional, homogeneous Dimersol process (Table 10.6). 

The oligomerization of olefins is mostly catalyzed by cationic complexes which are very soluble in ionic liquids. The Pd-catalyzed dimerization of butadiene [36] and the Ni-catalyzed oligomerization of short-chain olefins [5, 37], which is also known as the Difasol process [1 d] if chloroaluminate melts are used, can be mn in imidazolium salts 1 [38, 39]. Here, the use of chloroaluminate melts and toluene as the co-solvent is of advantage in terms of catalyst activity, product selectivity, and product separation. Cp2TiCl2 [6] and TiCU [40] in conjunction with alkylaluminum compounds were used as catalyst precursors for the polymerization of ethylene in chloroaluminate melts. Neither Cp2ZrCl2 nor Cp2HfCl2 was catalytically active under these conditions. The reverse conversion of polyethylene into mixtures of alkanes is possible in acidic chloroaluminate melts without an additional catalyst [41]. 

The range of homogeneous reactions that has been transposed into ILs is probably wider than into SCCO2 or perfluorinated solvents due to the great versatility of ILs. However, most of these reactions are limited to laboratory- or bench-scale with just a few examples of pilot-scale. A relevant industrial example is the Difasol process, which can be seen as an extension of the Dimersol family of processes developed by IFP [94] ... 

This process, using the ionic liquid solvent system, has been commercialized by IFP, as the Difasol process. In this process butene is dimerized in a continuous two-phase procedure with high conversion of olefin and high selectivity to the dimer (Figure 2.9). Catalyst consumption is divided by a factor of about ten and a higher yield of dimers is obtained. Most important, the Difasol system can be retro-fitted into existing Dimersol plants to give improved yields, lower catalyst consumption and associated costs and environmental benefits. 

The cationic nickel complex [ /3-allylNi(PR3)]+, already described by Wilke etal. [21], as an efficient catalyst precursor for alkene dimerization when dissolved in chlorinated organic solvents. It proved to be very active in acidic chloroaluminate ionic liquids. In spite of the strong potential Lewis acidity of the medium, a similar phosphine effect is observed. Biphasic regioselective dimerization of propylene into 2,3-dimethylbutenes can then be achieved in chloroaluminates. However, there is a competition for the phosphine between the soft nickel complex and the hard aluminum chloride coming from the dissociation of polynuclear chloroaluminate anions. Aromatic hydrocarbons, when added to the system, can act as competitive bases thus preventing the de-coordination of phosphine ligand from the nickel complex [22 b]. Performed in a continuous way, in IFP pilot plant facilities, dimerization of propene and/or butenes with this biphasic system (Difasol process) compares... 

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]. 

Although not yet studied, this could happen in the presence of ionic liquids too. Thus such a reaction could be responsible for the slow deactivation of the catalyst in the dimerization of olefins, as a small proportion of the Ni is found in the hydrocarbon phase (Difasol process see Section 5.5.1) [14]. 

Cost. The cost of ionic liquids has to be taken into consideration. If completely insoluble in the reaction products and/or stable enough during separation, they can be considered as a simple investment Thus, in the Difasol process [14] it has been demonstrated that l-butyl-3-methyHmidazolium chloride/AlClj liquid has been used in a pilot plant for more than six months (more than 5000 hours) without any loss. In this case the solvent has practically no impact on the operating costs but this could be not a general case, and experiments have to be conducted for each set of circumstances. 

The main advantage of the biphasic Difasol process remains the ease of product separation that can be performed in a subsequent step. There is no co-miscibiHty between the products and the IL thus, product separation by settling does not require heating and results in energy saving plus reduced loss of catalyst by thermal decomposition. 

During 2003 we saw the first published process based on ILs [6], In its BASIL process (see Section 5.3.2), BASF has disclosed the involvement of an imidazolium-based ionic-liquid in the production of alkoxyphenylphosphines. This constitutes an impressive demonstration that IL technology can result in significant financial savings. Another process said to be poised for licensing is the French Petroleum Institute s butene dimerization process, the Difasol process (see Section 5.3.1). Besides these, some more promising applications are currently under investigation, and are hoped to be disclosed in the near future. Notable examples of research areas are in electrochemistry (batteries), biocatalysis, and the application of ILs in extraction processes, e.g., the deep desulfurization of diesel oil. 

The processes are ordered within the Tables according to their industrial relevance, starting with the two commercial processes — Ruhrchemie/Rhone-Poulenc s oxo process and the SHOP process of Shell [5]. As has been described in the preceding chapters, all other developments are more or less proposals rather than processes they are on the way from laboratory scale to first pilot plant apphcations and finally to industrial scale — some are in an advanced stage of realization, such as the Difasol process of IFP, BASIL of BASF, or Swan s TMCH process. For both tables, the degree of reahzatiorf depends on a few criteria, but decisive ones, which will be discussed below. 

An industrial example of the use of chloroaluminate ionic liquids in aUcene catalysts is the recent development of the IFF Difasol process which is widely used industrially for aUcene dimerization (typically propene and butanes). It was observed by Chauvin and coworkers that chloroaluminate(III) ionic liquids would be good solvents for the nickel catalyst used in the reaction, and discovered that by using a ternary ionic liquid system ([C4-mim]Cl-AlCl3-EtAlCl2) it was possible to form the active catalyst Irom aNiCl2L2 precursor and that, the ionic liquid solvent stabilized the active nickel species. 

Similarly, the Institut Fran(jais du Petrole s Difasol process for the dimerization of propene to hexenes with nickel(ll) catalysts in acidic chloroaluminate(lll) ionic liquids, which was one of the earhest announced uses of ionic hquids [133, 134], appears to not yet have been apphed on a commercial scale. 

Fig. 20.19 Integrated Dimersol and Difasol processes. Image adapted from [Ic] with permissi

The advantages of the biphasic Difasol process in comparison to the homogeneous Dimersol process, are summarized in Table 20.8. 

Table 20.8 Advantages of Difasol process in comparison to Dimersol process Process Difasol...

Olivier-Bourbigou Lecocq, 2003) Chloroaluminate ILs and Ni(COD)(2) with a Bronsted acid ILs Biphasic ethylene oligomerization or butene and higher olefins dimerization (Difasol process). These solvents stabilize and activate nickel catalysts, even without ligand, and greatly enhance the reaction activity. The presence of a diimine ligand allows the production of C4-C6 linear olefins with improved alpha-selectivities. 

The Difasol process produces mixtures of low branched octenes which are good starting materials for isononanol pa-oduction (intermediates in the plasticizer industry). The reaction takes place with nickel catalyst precursor using chloroaluminate ILs, acting as both solvent and co-catalyst. The best results were obtained from [BMlM][Cl]/AlCb/EtAlCl2 (1 1.2 0.11) mixtures. ... 

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