Difasol catalyst

The Difasol catalyst is concentrated and operates in the ionic phase, or maybe at the phase boundary. The reaction volume is therefore much lower than in the conventional one-phase Dimersol process, where the catalyst concentration is very low. The Difasol reactor volume can be downscaled 15-fold compared to the classical one-phase Dimersol-X 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. 

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. 

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. 

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]... 

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... 

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... 

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 Dimersol-Difasol arrangement ensures more efficient overall catalyst utilization and an increase in the yield of octenes by about 10 wt.% (Table 5.4-4). Table 5.4-5 shows a simplified mass balance comparison for the Dimersol process and... 

The ionic liquid-based Difasol technology improves further the performance of the classical Dimersol for lightly branched octenes production. Since the catalyst is concentrated and operates in the ionic phase and also probably at the phase boundary, the reaction volume is much lower in the biphasic technology compared... 

From an engineering point of view, ILs offer a huge potential (similar to the aqueous variants as described in Chapter 2) for separating reaction products and recycling the catalyst. New reactors may be smaller than in conventional homogeneous catalysis (e.g., the Difasol or Basil processes), which contributes to making processes environmentally friendlier . 

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]. 

Despite all these advantages, two limitations remain, i.e., the continuous catalyst carry-over by the products that implies disposal, and the conversion level for olefins is highly dependent on their initial concentration in the feed. These commercial limitations have been greatly overcome through Difasol two-phase catalysis technology. 

In the Difasol technology, the catalyst is dissolved in IL reaction products are poorly soluble. The reactants miscibility remains adequate to ensure reaction. Batch laboratory experiments on butene dimerization demonstrated that no reaction occurs in the organic phase. This indicates that the reaction takes place at the interface or in the ionic liquid phase. Experiments also proved that rising the mixing efficiency increases the reaction rate but does not change the octene selectivity. So excellent mixing is necessary to ensure good conversion by rapid mass transfer and efficient interaction of the ionic catalyst with the substrate. 

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. 

The Difasol biphasic system has been evaluated in terms of activity, selectivity, recyclability, and lifetime of the IL by continuous-flow pilot plant operation. During a typical run, feed in its liquid state enters continuously a well-mixed reactor that contains the ionic active phase. The effluent (a mixture of the two liquid phases) leaves the reactor via an overflow into a settler. The separation of the IL and the organic phase occurs rapidly and completely, favored by the difference in density. The IL containing the catalyst is recycled while the product stream is recovered and on line analyzed. 

A continuous test-run engaging an industrially representative rafEnate-2 feed (70% n-butenes, 2% isobutene, and 25% butanes) was then conducted. A productivity of 30 kg butenes converted/g Ni and 12 kg butenes converted/g IL was easily maintained over a period of 5500 h. During the whole test, butene conversion and octene selectivity were steady. The Difasol system achieved more than 70% butene conversion with 95% octene selectivity. This is five selectivity points higher than the classical Dimersol system. Moreover, unlike what is observed with Dimersol, octene selectivity remained higher than 90%, even at 80% butene conversion, which was easily obtained by increasing the catalyst concentration. 

The catalyst injection rate is decreased in the one-phase Dimersol reactor to provide low butene conversion. The effluent from the Dimersol reactor is partly vaporized to separate imconverted C4 cuts from octenes. Products and catalyst are sent to the neutralization section while the vapor phase is condensed and sent to the Difasol reactor. Butene conversion is achieved with less catalyst and more selectivity, thanks to the biphasic system. This [Dimersol -1- Difasol] combination, which uses the same Dimersol catalytic system, improves the yield of octenes by about 10% with a lower consumption of nickel. 

This particular combination of a one-phase and a two-phase technology is possible because of high Difasol efficiency on the diluted feed recovered from the Dimersol reactor. This arrangement is suitable either for grass-roots units or for upgrading of existing Dimersol-X units. It considerably reduces the overall unit volume compared to existing (up to four-reactor) Dimersol-X units. It also induces lower catalyst consumption, i.e., lower catalyst and disposal costs (Table 4). 

The best arrangement, to remove these poisons as deeply as possible, includes a water wash with condensed or feed boiling water, followed by a water removal device. Currently a simple azeotropic and de-isobutanizer is recommended. The dry feed is then treated with the proper molecular sieves in order to remove both oxygenates and sulfur compoimds. It should be noticed that all these feedstock treatments are also recommended to minimize classical Dimersol catalyst consumption, but using Standalone Difasol leads to more severe treatments and therefore higher investment and chemical expense. Table 5 summarises the main acceptable poison contents in the Dimersol + Difasol arrangement and in the Standalone Difasol configuration. 

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. 

Maintained over a wide range of alkene concentrations with the same catalyst consumption. Difasol feed is completely purified from the eventual impurities that could accumulate in the IL. 

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