Linear homogeneous catalysts

In the Institut Fransais du Petrc le process (62), ethylene is dimerized into polymer-grade 1-butene (99.5% purity) suitable for the manufacture of linear low density polyethylene. It uses a homogeneous catalyst system that eliminates some of the drawbacks of heterogeneous catalysts. It also inhibits the isomerization of 1-butene to 2-butene, thus eliminating the need for superfractionation of the product (63,64). The process also uses low operating temperatures, 50—60°C, and pressures (65). 

In the early 1970 s, Bayer et al. reported the first use of soluble polymers as supports for the homogeneous catalysts. [52] They used non-crosslinked linear polystyrene (Mw ca. 100 000), which was chloromethylated and converted by treatment with potassium diphenylphosphide into soluble polydiphenyl(styrylmethyl)phosphines. Soluble macromolecular metal complexes were prepared by addition of various metal precursors e.g. [Rh(PPh3)Cl] and [RhH(CO)(PPh3)3]. The first complex was used in the hydrogenation reaction of 1-pentene at 22°C and 1 atm. H2. After 24 h (50% conversion in 3 h) the reaction solution was filtered through a polyamide membrane [53] and the catalysts could be retained quantitatively in the membrane filtration cell. [54] The catalyst was recycled 5 times. Using the second complex, a hydroformylation reaction of 1-pentene was carried out. After 72 h the reaction mixture was filtered through a polyamide membrane and recycled twice. 

The homogeneous nature of the catalysts is confirmed by the linear dependence of the catalytic activity on the concentration of nickel(II). Only in the case of a truly homogeneous catalyst is the activity expected to be directly proportional to the catalyst concentration. In the case of the formation of nanoclusters, larger agglomerates - and, therefore, a comparatively lower number of active sites - will be formed at higher concentrations of the nickel salt Furthermore, a sigmoidal curve for the rate of consumption of substrate has been proposed... 

Another approach is to separate the products from the homogeneous catalyst using a two phase liquid system. For example, this method is used in the oligomerization step of the Shell Higher Olefins Process for the manufacture of linear a-olefins.5,9-11,330 A polar nickel catalyst containing a P- chelate ligand is dissolved in a polar solvent e.g. 1,4-butanediol, which is immiscible with higher oc-olefins, and recovery of the catalyst is easily achieved by simple phase separation. 

Much less severe conditions can be used with the Wilkinson homogeneous catalyst rhodium tricarbonyl triphenyl phosphate, HRh(CO)3(PC6H5)3. Pressures equal to 225 psig and temperatures of 100°C selectively produce the more useful linear form.34 The milder conditions more than compensate for the more expensive Rh (1000 times that of Co). The aldehyde product is distilled leaving the catalyst in the solvent ready for reuse. 

Since the twenties and thirties butanol together with acetone was produced by fermentation of carbohydrates (corn). In the sixties the process was replaced by the hydroformylation of propene. In the OXO process alkenes react with synthesis gas in the presence of a homogeneous catalyst to give a mixture of branched and linear aldehydes ... 

Alpha-Sablin [Alpha Sabic Linde] A process for making linear C4 to C10 -olefins from ethylene. A proprietary homogeneous catalyst is used in a bubble-column reactor. Developed between 1994 and 2001 by Sabic and Linde. One plant was under construction in Al-Jubail, Saudi Arabia, in 2005. 

Homogeneous catalysts have significant advantages compared with heterogenous catalysts concerning both theoretical studies and technological applications. Reports on the application of cyclic and linear poly (aluminoxanes)... 

Although most soluble homogeneous catalysts could be made fluorous-soluble by attaching fluorous ponytails to the catalyst core in appropriate size and number [9], transition metal complexes have mostly been converted to fluorous-soluble through ligand modification [10]. The most effective fluorocarbon moieties are linear or branched perfluoroalkyl chains with high carbon number that may con-... 

The use of CO + HjO as an in situ source of H2 via the shift reaction or as a source of reducing electrons with concomitant oxidation of CO to CO2 has recently been explored with homogeneous catalyst solutions. Equations (a) and (b) are modifications (Reppe) of hydroformylation (see 14.6.3) and olefin hydrogenation, respectively. The most effective catalysts for equation (a) are Ru3(CO),2, Rh fCOlig, Ir4(CO)i2 in alkaline THE or MeOH. The first of these shows great selectivity in the formation of linear vs. branched aldehyde . With Rhg(CO),5, the aldehyde is reduced further to the alcohol. A different catalyst based on Co2(CO)g/diphos in polar ether solvents has also been used to catalyze equation (a) with propylene as substrate. ... 

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