Dimersol/Difasol process

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. 

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). 

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). 

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 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 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... 

Table 5.4-4 Comparison of performance between homogeneous Dimersol process and [Dimersol + Difasol] arrangement with a feed containing 79 wt.% butenes...

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. 

Rather than a purification section, a Standalone Difasol plant also requires a larger biphasic reactor than a Dimersol + Difasol unit. For instance, a 160 000 tpa C4 cut unit requires a 50 m Difasol reactor when it operates in Standalone mode and only a 30 m reactor when it works as a conversion achiever. Table 6 shows a simplified mass-balance comparison for a Dimersol process, a Dimersol + Difasol arrangement, and a Standalone Difasol unit. 

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...

Figure 5.3-7 Process scheme integrating Dimersol and Difasol.

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. 

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

Standalone Difasol allows both interesting chemical consumption and flexibility in terms of octene production, just by tuning the chemical consumption, when compared with the classical Dimersol process. 

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