Difasol

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). 

Figure 5.3-7 Process scheme integrating Dimersol and Difasol.

Since the catalyst is concentrated and operates in the ionic phase, and also probably at the phase boundary, reaction volumes in the biphasic technology are much lower than in the conventional single-phase Dimersol process, in which the catalyst concentration in the reactor is low. As an example, the Difasol reactor volume can be up to 40 times lower than that classically used in the homogeneous process. 

If the ionic liquid can be recycled and if its lifetime is proven to be long enough, then its initial price is probably not the critical point. In Difasol technology, for example, ionic liquid cost, expressed with respect to the octene produced, is lower than that of the catalyst components. 

Chloroaluminate laboratory preparations proved to be easily extrapolated to large scale. These chloroaluminate salts are corrosive liquids in the presence of protons. When exposed to moisture, they produce hydrochloric acid, similarly to aluminium chloride. However, this can be avoided by the addition of some proton scavenger such as alkylaluminium derivatives. In Difasol technology, for example, carbon-steel reactors can be used with no corrosion problem. 

Very few data [47] relating to the disposal of used ionic liquids are available. In Difasol technology, the used ionic liquid is taken out of the production system and the reactor is refilled with fresh catalyst solution. 

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). 

Difasol An improvement on the Dimersol process for dimerizing propene or butenes. The process utilizes an ionic liquid based on imidazoliniumaluminate and a nickel-based Dimersol catalyst. Developed by IFP in 1999, but not commercialized by 2005. 

The above protocol for the dimerisation of butenes has also been tested on a pilot-plant scale and the reaction run continuously for 5,500 hours, after which it was stopped deliberately. By immobilising the catalyst in the chloroaluminate ionic liquid, nickel consumption was lowered by a factor of 10 relative to the process in neat substrate. The process is meanwhile available for licensing from IFP under the name of Difasol but has not yet been commercialised. The technical implications of the process are described in some detail elsewhere.[3 14]... 

Table 10.6 Summary of key advantages of Difasol (ionic liquid) process over the Dimersol (solvent free) process for alkene dimerization. ...

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]. 

Phase separation Immiscibility of ionic liquid with product/ extract, immobilisation of catalyst in ionic liquid phase BASIL [108, 109, 193-195], Difasol [82, 111, 112] Easy removal, low energy requirement Loss of catalyst to product phase if not well immobilised, contamination of product... 

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 Difasol reaction involves a mechanically stirred reactor and settlers. An injection of fresh catalyst components is defined to compensate the detrimental effects of accidental impurities present in the feed and slight carryover of the catalyst. Mixing of the solvent phase with the organic phase ensures advantageous butene conversion. However, importantly, the stirring power combined with a high... 

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