Dodecene cracking

An Arrhenius plot of log rate constant vs. reciprocal temperature (Figure 6) indicates an activation energy of 61.9 1.3 kcal/mol for dodecene cracking. This is similar to the activation energies measured for n-paraffin cracking and is somewhat higher than previously measured values for alpha-olefins (6). 

Figure 6. Determination of the activation energy for dodecene cracking in the range 475°-550°C...

Figure 7. Variation in the molar ratio of ethane to ethylene produced from dodecene cracking at 525°C with initial dodecene partial pressure...

The estimated relative contributions of the three paths for dodecene cracking under a variety of conditions are shown in Table V. Two trends are visible in the data. First, at constant temperature and increasing dodecene partial pressure, the relative importance of the retro-ene path decreases while that of the abstraction path increases. The contribution of the addition path remains constant. The average estimated relative contributions of the retro-ene reaction at 525°C taken from Table V correspond to a reaction order of 0.95 0.4 in dodecene this satisfies the requirement that retro-ene reaction be first order. 

Table V. Relative Contributions of Reaction Paths in Dodecene Cracking...

In this case, the endothermicities of Reactions A-3 and A-4 are not equal since Reaction A-3 produces an allyl ladical. Therefore, one would expect Reaction A-3 to be somewhat faster than Reaction A—4. If Radicals I and II are present in equal concentrations, then the yield of nonene from the hydrogen-abstraction path is between one and two times the yield of octene. The nonene in excess of this is formed by the retro-ene reaction. This defines a range of importance for the molecular path and by difference the contribution of the hydrogen abstraction path. This procedure is illustrated for the dodecene cracking yields from column two of Table II. 

Detergents have been manufactured from long-chain alkenes and sulfuhc acid, especially those obtained from shale oil or cracking of petroleum wax. These are sulfated with 90—98 wt % acid at 10—15°C for a 5-min contact time and at an acid—alkene molar ratio of 2 1 (82). Dialkyl sulfate initially forms when 96 wt % acid is added to 1-dodecene at 0°C, but it is subsequently converted to the hydrogen sulfate in 80% yield upon the further addition of sulfuhc acid. The yield can be increased to 90% by using 98 wt % sulfuhc acid and pentane as the solvent at -15°C (83). 

Compounds with 6 to 18 carbons are the most common alpha olefins (a-olefins) and Ziegler catalysts are used in this process. Certain olefins such as nonene (C9) and dodecene (C12) can also be made by cracking and dehydrogenation of n-paraffins, as practiced in the petrochemical section of a refinery. 

The relative contributions of the three proposed reaction paths remain to be determined. The products from both the retro-ene and the addition reactions can be predicted with some quantitative certainty. For dodecene, the former produces only 1-nonene and propylene. The product distributions from the addition paths should be identical to those from the cracking of the corresponding paraffins. These product distributions can be predicted using the method of Rice and Kossiakoff (16). This approach parallels excellently with experiments (16,17). (From available data we estimate its accuracy as d=10%.) For dodecene, the addition of hydrogen atoms, methyl radicals, and ethyl radicals will produce Ci2H25, Ci3H27, and Ci4H29 parent radicals. The product distributions predicted by the Rice-Kossiakoff method for the decomposition of these radicals at 525°C are shown in Table IV. 

The high reactivity of an acidic solid such as the silica-alumina component for the cracking of the high molecular weight olefin has been indicated by previous work 20, 21). It was demonstrated for the particular conditions of our work (19), when dodecene-1 was passed over the silica-alumina... 

Furthermore, the molecular weight distributions of the products from the cracking of dodecene-1 and from the hydrocracking dodecarae are characteristically similar. Figure 12 shows approximate carbon number distributions obtained from a run of dodecene-1 cracking over silica-alumina (left... 

Derivation Benzene is alkylated with dodecene, to which it attaches itself in any secondary position the resulting dodecylbenzene is sulfonated with sulfuric acid and neutralized with caustic soda. For ABS (branched-chain alkyl) the dodecene is usually a propylene tetramer, made by catalytic polymerization of propylene. For LAS (straight-chain alkyl), the dodecene may be removed from kerosene or crudes by molecular sieve, may be formed by Ziegler polymerization of ethylene, or by cracking wax paraffins to a-olefins. 

When 1-dodecene was passed over the catalyst at 300°C the product distribution shown in Fig. 5 was obtained. Within any one carbon number the ratio of branched chain/straight chain molecules was very high, being about 4 1 for C s and 3 1 for Cg s. The lifetime of catalysts was substantially reduced by cracking but as the cracking activity decreased the ability of the catalyst to skeletally isomerize without cracking became apparent. Thus, after 21 hours cracking of 1-dodecene at 300°C the products from the catalyst consisted almost entirely of branched (but unidentified) dodecenes. 

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