Cyclopentane cracking

Catalytic Reforming. Worldwide, approximately 30% of commercial benzene is produced by catalytic reforming, a process ia which aromatic molecules are produced from the dehydrogenation of cycloparaffins, dehydroisomerization of alkyl cyclopentanes, and the cycHzation and subsequent dehydrogenation of paraffins (36). The feed to the catalytic reformer may be a straight-mn, hydrocracked, or thermally cracked naphtha fraction ia the... 

Cyclopentane was cracked over a palladium-alumina catalyst at 200 C in a differential reactor (J Catal 54 397, 1978). Data of time against fractional... 

Several years ago, one of the authors found that nickel, platinum, and some other hydrogenating agents, when deposited on fresh synthetic silica-alumina cracking catalyst, made a new catalyst that would isomerize paraffin and naphthene hydrocarbons in the presence of hydrogen at elevated pressures and nominal temperatures. Table I shows some early typical results calculated from mass spectrometer analyses of the products obtained by passing methyl cyclopentane, cyclohexane, and n-hexane over a catalyst composed of 5% nickel in silica-alumina at the indicated reaction conditions. Isomerization of a number of other hydrocarbons has also been studied and reported elsewhere (2). 

Cycloalkanes may be pyrolized in a manner similar to that for alicyclic alkanes. Cyclopentane, for instance, yields methane, ethane, propane, ethylene, propylene, cyclopentadiene, and hydrogen at 575°C. Analogous to cracking of alicyclic alkanes, the reaction proceeds by abstraction of a hydrogen atom followed by p scission. The cyclopentyl radical may undergo successive hydrogen abstractions to form cyclopentadiene. 

Cracking and disproportionation in the reaction of hexane could be suppressed by the addition of cycloalkanes (cyclohexane, methylcyclopentane, cyclopentane).101 Furthermore, 3-methylpentane and methylcyclopentane also reduced the induction period. These data indicate that reactions are initiated by an oxidative formation of alkene intermediates. These maybe transformed into alkenyl cations, which undergo cracking and disproportionation. When there is intensive contact between the phases ensuring effective hydride transfer, protonated alkenes give isomerization products. 

Reactions of 3-methylhexane were found to occur on the support alone which complicated the above studies. Besides aromatization to toluene (A), isomerization to cyclopentane derivatives (B), isomerization to heptane and other branched hexanes (C) and cracking to Ci to C6 hydrocarbons (D) were all observed as depicted in Eq. 5.23... 

Petrov and Shchekin (297) showed that below the cracking temperature (250-316°C.) cyclohexene undergoes over silica-alumina hydrogen disproportionation and dimerization. Identical results were obtained from 1-methyl-l-cyclopentene. Ring expansion of lower alkylated cyclopentanes occurs simultaneously with polymerization. However, no bicyclic compounds with similar rings were formed. 

Sulfided Mo-Y and Ni-Mo-Y catalysts were tested in thiophene hydrodesulfurization and hydrogenation of pentene-1 and cyclopentene. Catalysts were prepared by thermal decomposition of supported Mo(CO)g encaged in Y and stabilized Y zeolites. Cracking ability in both reactions is related to the surface acidity of catalysts but is not parallel to their HDS activity. H S generates protonic acidity over NaY and KY zeolites. Synergetic effect between Ni and Mo sulfided species in HDS reaction was observed. The presence of extra-lattice aluminum in stabilized forms of Y-zeolites favours selectivity towards formation of isopentane and cyclopentane during hydrogenation. 

C=C—C—C—C—C. Isomerization to a methylpentane would result in localizing the carbonium ion on the tertiary position. This structure can no longer ring close to a cyclopentane but only to a highly strained cyclobutane. Since skeletal isomerization occurs readily at reforming conditions, most of the n-hexane would be converted to isohexane or cracked products rather than to cyclopentane. 

Methylcyclopentane is a primary product from a reaction involving tertiary-to-tertiary cracking while cyclohexane is not. Therefore, the high ratios of methylcyclopentane to cyclohexane shown in Table III are consistent with the proposed mechanism. Statistical considerations similar to those discussed in the preceding paragraph account for the lower ratios of cyclopentanes to cyclohexanes in the C7 and C8 products. 

Fig. 5.1. Chromatograms of products of catalytic cracking (A) without reactor and (B) with reactor. Sorbent, 11% quinoline on refractory brick temperature, 25 C column length, 10.5 m. Peaks 1 = propane 2 = propylene 3 = isobutane 4 = n-butane 5 = isobutene 6 = butene-1 7 = rmns-butene-2 8 = cis-butene-2 9 = isopentane 10 = 3-methylbutene-l 11 = n-pentane 12 = pentene-1 13 = 2,2-dimethylbutene 14 = 2-methylbutene-l 15 = tnms-pentene-2 16 = cfsi)entene-2 17 = 2-methyl-butene-2 18 = 2,3-dimethylbutane 19 = 2-methylpentane 20 = 3-methylpentane 21 = 3-methylpen-tene-1 22 = 4-methylpentene-l 23 = c -4-methylpentene-2 24 = cyclopentane 25 = 2,3-dimethyl-butene-1 26 = fmns-4-methylpentene-2 27 = w-hexane 28 = cyclopentene 29 = 2-methylpentene-l 30 = hexene-1 31 = 2,4-dimethylpentane 32 = cis-hexene-3 33 = tnms-hexene-3 34 = 2-ethylbu-tene-1 35 = trans-hexene-2 36 = methylcyclopentane 37 = cis-methylpentene-2 38 = 2-methylpen-tene-2 39 = pisns-3-methylpentene-2 40 = methylcyclopentene-4 41 = 4-methylcyclopentene 42 = cw-3-methylpentene-2 43 = 2,3-dimethylpentane 44 = 2-methylheptane 45 = 2,3-dimethylbutene-2 46 = methylheptane 47 = cyclohexane 48 = C, olefin. Reprinted with permission from ref. 1.

Cyclopentane is a petroleum product. It is formed from high-temperature catalytic cracking of cyclohexane or by reduction of cyclopentadiene. It occurs in petroleum ether fractions and in many commercial solvents. It is used as a solvent for paint, in extractions of wax and fat, and in the shoe industry. 

The reaction of cyclohexene over differently dealuminated H-Y samples at 370 K (isomerization to methylcyclopentene and hydroisomerization to methyl-cyclopentane, hydrogen transfer resulting in benzene and cyclohexane, cracking and coke formation) was monitored by Joly et al. [904] via in-situ IR spectroscopy in an IR flow-reactor cell coupled with a gas chromatograph. A good correlation was reported between the activity of the Bronsted acid sites and their strength... 

The precise composition of crude petroleum varies widely from one source to another, but the principal components are always hydrocarbon paraffins (40-75%), cycloparaffins or naphthenes (mainly cyclopentane and cyclohexane derivatives) (20—50%) and aromatic hydrocarbons (5-20%). The first step in petroleum refining is distillation into broad fractions, which typically have the boiling ranges and compositions given in Table 2.1. None of these distillates contain significant amounts of olefins. The lower olefins, ethylene, propylene and butenes are produced principally by subsequent cracking operations. 

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