Propylene dimerization

Blends of piperylenes and amylenes (mixed 2-methyl-1-butene and 2-methyl-2-butene) or UOP propylene dimers can be adjusted to produce softening points of 0—100°C and weight average molecular weights of <1200 (32,33). Careful control of the diolefin/branched olefin ratio is the key to consistent resin properties (34). 

Propylene Dimer. The synthesis of isoprene from propjiene (109,110) is a three-step process. The propjiene is dimeri2ed to 2-methyl-1-pentene, which is then isomeri2ed to 2-methyl-2-pentene in the vapor phase over siUca alumina catalyst. The last step is the pyrolysis of 2-methyi-2-pentene in a cracking furnace in the presence of (NH 2 (111,112). Isoprene is recovered from the resulting mixture by conventional distillation. 

As shown, ia the case of chlotination of aEyl chloride, the resonance states of the chloroaEyl radical iatermediates are not symmetrical and their propagation reactions lead to the two different dichloropropene isomers ia an approximate 10 90 ratio (26). In addition, similar reactions result ia further substitution and addition with products such as trichloropropanes, trichloropropenes, tetrachloropropanes, etc ia diminisbing amounts. Propylene dimerization products such as 1,5-hexadiene, benzene, 1-chloropropane, 2-chloropropane, high boiling tars, and coke are also produced ia smaE amounts. 

Until the mid-1970s metal-catalyzed propylene dimerization had practical significance in isoprene manufacture. Goodyear developed a process to dimerize propylene in the presence of tri-n-propylaluminum to yield 2-methyl-1-pentene.16,95,96 This was then isomerized to 2-methyl-2-pentene followed by cracking into isoprene and methane. This and other synthetic pocesses, however, are no longer practiced since they are not competitive with isoprene manufactured by cracking of naphtha or gas oil. 

It is also known that mildly anionic trialkylaluminums do not produce isotactic polypropylene. Only propylene dimers have been reported from this catalyst and there have been no indications of any steric control in this reaction. 

Steam cracking of various petroleum fractions is gaining widespread use for the production of olefins. These olefins are produced essentially for use as feed stock for numerous petrochemical processes, but the by-product butylenes and propylenes are sometimes used as feed stock for aviation and motor alkylation units. Ethylene is the most important of the olefins produced from this type of cracking, and propylene is second in importance. These two olefins are normally charged to either alkylation or polymerization units for the production of petrochemicals or petrochemical intermediates. Polyethylene and propylene dimers, trimers, tetramers, and penta-mers are some of the more important polymers produced, while ethybenzene, dodecylbenzene, cumene, diisopropylbenzene, and alkylated... 

Commercial polymerization was once used only for converting the olefins from cracked gases into motor fuel. However, it is rapidly becoming very important in the production of such petrochemicals as heptene, propylene dimer, trimer, tetramer and pentamer and the alkylated aromatics such as ethylbenzene, isopropylbenzene, cymene, and butyl-benzenes. This list may be expected to grow as new uses are found for the heavier olefins. 

Similarly to nonyltrichlorosilane, one can obtain other alkylchlorosi-lanes and other higher radicals at the silicon atom. For example, methyl-nonyldichlorosilane can be obtained from methyldichlorosilane and propylene trimer, hexyltrichlorosilane can be obtained from trichlorosilane and propylene dimer, isobutyltrichlorosilane can be produced from trichlo-... 

NiX, however, showed a high selectivity resulting in 95.5% dimers under the reaction conditions. The product composition of propylene dimers was studied as a function of contact time in order to distinguish between primary and secondary products. 3-Methylpentenes were shown to be primary prod-... 

One of the industrially important dimerization reactions that involves the use of homogeneous catalysts is the dimerization of propylene. Dimerization of propylene produces mixtures of the isomers of methyl pentenes, hexenes, and 2,3-dimethyl butene and is practiced by the Institut Francis du Petrole (IFP), Sumitomo, and British Petroleum (BP). The methyl pentenes and hexenes are used as gasoline additives. Dimethylbutene is used in the fragrance and the agrochemical industries. 

Figure 7.6 Industrial use of (from the top) propylene dimerization, butadiene dimerization, butadiene trimer-ization, and butadiene plus ethylene codimerization. In EPDM rubber, the terminal double bond of 1,4-hexadiene takes part in polymer formation. The internal double bond is used during curing.

Figure 7.7 Catalytic cycles for propylene dimerization. For the first propylene molecule the left and right cycles represent the anti-Markovnikov and Markovnikov pathways, respectively. Note that for 7.22(A) and 7.23(A) there are two /3-hydride positions.

Thus, propylene dimerization could result in the formation of both isohexanes and isooctanes. However, little propylene dimerization is thought to take place since It should result in the formation of mainly 2,3-dlmethyl-butane a small amount of this isohexane is found in propylene alkylate. 

Raimbault, C. Bonnifay, P. Cha, B. Andrews, J. "Propylene Dimer Fuel or Chemical" Hydrocarbon Processing, (April, 1976)... 

To obtain the HMC as an active component zero-valent nickel complexes of the general formula - Ni[PRj] (n=2-4), where R was Ph or EtjN, characterized by high activity in oligomerization of lower olefins in homogeneous conditions were taken. Heterogenization of these complexes was conducted by method of ligand exchange. In the Literature there are examples of carbonyl complexes of palladium prepared by this method, which show activity in propylene dimerization [8], However, we have failed to find data on such nickel catalysts in the literature. 

An excellent review on soluble systems, including also the more recent progresses in ethylene polymerization, is that of Sinn and Kaminsky who even developed soluble catalytic systems with extremely high activities by using alumoxane and biscyclopentadienyl-titanium or-zirconium compounds. Interesting results have also been obtained in ethylene oligomerization and in propylene dimerization... 

Ethylene and Propylene Dimerization u/ith wAllylnickel Halide Catalysts... 

Even as a toluene emulsion, these complexes show catalytic activity towards ethylene and propylene which is several orders higher than that of TT-allylnickel halides. Paralleling the increase in catalytic activity, the selectivity of this catalyst is also increased—i.e., the products are mainly ethylene or propylene dimers. The most active catalytic systems for dimerizing ethylene and propylene are obtained by replacing toluene with halogenated hydrocarbons such as chlorobenzene since in these more polar solvents, the complexes XIII are soluble. 

Of prime importance for utilizing the new catalyst was the observation that the products of propylene dimerization with phosphine-modified catalyst system, XVI, are strongly influenced by the nature of the phosphine PR3 (24, 25). To understand the phosphine effect, it is necessary to examine the dimerization of ethylene and of propylene in some detail. The dimerization of ethylene formally involves the addition of the C-H bond of one olefin molecule across the double bond of a second one ... 

For propylene dimerization, four products can be written (Table II) if only vinylic C—H bonds are considered. In Paths 1 and 2 the C—H bond of the terminal carbon atom is added giving rise to two products. If the addition proceeds in the manner of metal hydrides, the product is 2-hexene (Path 1) for acidic-type addition (Markovnikov rule), the product is 4-methyl-2-pentene (Path 2). In Paths 3 and 4, the C—H bond of the middle carbon atom is added," giving rise to 2-methyl-l-pentene (hydridic-type addition) and to 2,3-dimethyl-l-butene (acidic-... 

In the course of propylene dimerization, to a first approximation, it is only one propylene molecule which is strongly influenced by the nature of the catalyst (and correspondingly of the phosphine). 

The dimerization reaction has been carried out under two different conditions. In laboratory experiments, the reaction is conveniently carried out under 1 or less than 1 atmosphere and at a temperature of —20° to — 10°C. These relatively low temperatures are necessary to obtain a sufficient concentration of ethylene or propylene in the catalyst solution. The dimerization catalyst for laboratory experiments is usually prepared by mixing, for example, chlorobenzene solutions of a 7r-allylnickel halide and an aluminum halide (or alkylhalide) in molar ratio of at least 1 1. The phosphine-modified catalyst is obtained by simply adding 1 mole of a phosphine per mole of nickel to the solution of the catalyst. When ethylene or propylene is introduced into the catalyst solution, reaction starts immediately, as evidenced by a sudden rise in temperature. Dimerization is exothermic to the extent of about 28 kcal./mole propylene dimer. Hence, the mixture must be stirred and cooled intensively during the reaction. Under these conditions (Table V), reaction rates of about 6 kg. 

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