Decomposition of propylene

Whereas the electrochemical decomposition of propylene carbonate (PC) on graphite electrodes at potentials between 1 and 0.8 V vs. Li/Li was already reported in 1970 [140], it took about four years to find out that this reaction is accompanied by a partially reversible electrochemical intercalation of solvated lithium ions, Li (solv)y, into the graphite host [64], In general, the intercalation of Li (and other alkali-metal) ions from electrolytes with organic donor solvents into fairly crystalline graphitic carbons quite often yields solvated (ternary) lithiated graphites, Li r(solv)yC 1 (Fig. 8) [7,24,26,65,66,141-146],... 

The pores of the silica template can be filled by carbon from a gas or a liquid phase. One may consider an insertion of pyrolytic carbon from the thermal decomposition of propylene or by an aqueous solution of sucrose, which after elimination of water requires a carbonization step at 900°C. The carbon infiltration is followed by the dissolution of silica by HF. The main attribute of template carbons is their well sized pores defined by the wall thickness of the silica matrix. Application of such highly ordered materials allows an exact screening of pores adapted for efficient charging of the electrical double layer. The electrochemical performance of capacitor electrodes prepared from the various template carbons have been determined and are tentatively correlated with their structural and microtextural characteristics. 

For our experiments, a carbon fiber cloth (Figure 3 a) was prepared by carbonization of viscose under neutral atmosphere for 15 minutes, successively at 400, 700 and 1000°C. The carbon cloth was coated with pyrolytic carbon, using chemical vapor decomposition of propylene (2.5 ml/mn) diluted in nitrogen (100 ml/mn) during 10 minutes at 900°C. The resulting composite carbon material exhibits a very low irreversible capacity and 1.5 times the reversible capacity of graphite9 11. 

The CVI procedure can lead to some very interesting composite materials. Lackey et al. [17] have produced composites of carbon fibers in a laminated SiC/carbon matrix (see Figure 3.37). The alternating SiC/carbon layers were produced by CVI of two different reactions the decomposition of methyltrichlorosilane (MTS) in the presence of hydrogen and the decomposition of propylene in hydrogen, respectively. There is also an excellent opportunity to model these processes with the intent at gaining better control of the CVI process [18]. 

Under ordinary conditions, this may not be a major reaction, but for the problem of acetylene formation it is notable that Cvetanovic and Callear (19), and Mitchell and Le Roy (49), in studies of the photosensitized decomposition of ethylene, found a uni-molecular mechanism. Ingold and Stubbs (33) also found that the decomposition of propylene starts with a molecular rearrangement and decomposition ... 

Using uniform and straight nanochannels of an anodic aluminum oxide (AAO) film as a template, CNTs can be prepared by pyrolytic carbon deposition on the AAO film [109-116]. Briefly, the AAO film was subjected to carbon deposition from the pyrolytic decomposition of propylene at 800°C, which resulted in a uniform pyrolytic carbon coating on the inner wall of the template nanochannels. Then, the AAO template was removed with HF washing, and only carbon was left as an insoluble fraction. The formation process of carbon tubes using this chemical vapor deposition (CVD) technique is illustrated in Figure 3.8. 

The methylvinyl radical (IV) can abstract a hydrogen atom from a feed or product molecule to form propylene or it can lose a hydrogen atom to form allene or propadiene as products. For the 2-butenes, steric factors inhibit methyl radical addition thus C5 products are formed to a far lesser extent than from 1-butene. While ethylene may be formed by a sequential decomposition of propylene, this cannot be the only path for its formation, as the yield of ethylene in the high conversion region increases about twice as rapidly as does the methane yield. An additional source of ethylene is the symmetrical cleavage of butadiene to vinyl radicals. 

The formation of cyclopropane as a minor primary product in the mercury photosensitized decomposition of propylene has been reported/ and the formation of methylcyclopropane from but-l-ene. (This may be evidence for the formation of some triplet propylene.)... 

The ASA of carbon materials corresponds to the cumulated surface area of the different types of defects present on the carbon surface (stacking faults, single and multiple vacancies, dislocations) [14, 30] these sites are responsible for the interactions with the adsorbed species. A perfect linear relationship between the irreversible capacity and the value of ASA has been documented for different series of carbon samples [22]. While Cj. can be possibly not correlated with the BET area. Fig. 23.4 shows that it is linearly dependent of the ASA [31]. Moreover, all the samples coated with a thin carbon layer by pyrolytic decomposition of propylene demonstrate the lowest values of irreversible capacity and ASA (Fig. 23.4) [22, 31]. Figure 23.5 illustrates the positive effect of such a coating on the charge-discharge characteristics of carbon fibers from viscose. 

The high pressure STM was also used to study the structure of a Pt(lll) model catalyst surface during the thermal decomposition of propylene. Carbonaceous clusters were produced by partial dehydrogenation and polymerization of the hydrocarbon. Finally, SFG revealed new CO species in CO oxidation and provided strong evidence for their active role for oxidation to CO,. 

B.E. Bent, C.M. Mate, J.E. Crowell, B.E. Koch, and G.A. Somoijai. Bonding and Thermal Decomposition of Propylene, Propadiene, and Methyl Acetylene on the Rh(lll) Single-Crystal Surface. J. Phys. Chem. 91 1493 (1987). 

Dousek, F. R Jansta, J. Riha, J. Electrochemical system for galvanic cells in organic aprotic solvents. IV. Decomposition of propylene carbonate on lithium, /. Electroanal. Chem., 1973, 46, 281-287. 

Wang, Y Balbuena, P.B. Theoretical insights into the reductive decompositions of propylene carbonate and vinylene carbonate density functional theory studies, 1. Chem. Phys. B. 2002, 706,4486-4495... 

Mogi R., Inaba M., Myama Y., Abe X, Ogumi Z. Study of the Decomposition of Propylene Carbonate on Lithiirm Metal Sirrfaceby P5rrolysis-Gas Chromatography-Mass Spectroscopy, Langmuir 2002,19, 814-821. 

Wang, Y. Balbuena, P. B. Theoretical Insights into the Reductive Decompositions of Propylene Carbonate and Vinylene Carbonate Density Functional Theory Studies, J. Phys. Chem. B 2002,106,4486-4495. 

Whereas, the investigations on the influence of other compounds on the rate of decomposition of propylene itself are quite scare. Szwarc (10), Kunugi et al (6) and Robinson Weger (8) have only reported that the rate of decomposition of propylene had a tendency to be accelerated by the addition of small amounts of diallyl, 1-butene and propane in the feed, respectively. 

The thermal decomposition of propylene involves a series of primary and secondary reactions leading to a complex mixture of products. Studies showed that the distribution of pyrolysis products varies considerably with the pyrolysis conditions and the type of reactor used. There is agreement among the studies on propylene pyrolysis that the three major products of pyrolysis are methane, ethylene, and hydrogen. However, there is disagreement on the types and amounts of minor or secondary product species. Ethane, butenes, acetylene, methylacetylene, allene, and heavier aromatic components are reported in different studies, Laidler and Wojciechowski (1960), Kallend, et al. (1967), Amano and Uchiyama (1963), Sakakibara (1964), Sims, et al. (1971), Kunugi, et al. (1970), Mellouttee, et al. (1969), conducted at different conversion and temperature levels. Carbon was also reported as a product in the early work of Hurd and Eilers (1943) and in the more recent work of Sims, et al. (1971). 

One feature of the pyrolysis reaction which is not fully understood is the role of reactor surface. Although the thermal decomposition of propylene has been at least implicitly assumed in some cases to be a completely homogeneous gas-phase reaction, the influence of reactor surfaces has been demonstrated frequently. Factors such as the material of construction, surface-volume ratio of the reactor, and chemical treatment of reactor surface often affect the rate of reaction and/or the product distribution. Many previous investigations are of limited value in determining the role of surface in the pyrolysis reaction. The literature on surface effects contains predominantly qualitative information and often contradictions and anomalies. Early studies... 

Wang C, Nakamura H, Komatsu H, Noguchi H, Yoshio M, Yoshitake H (1998) Suppression of electrochemical decomposition of propylene carbonate (PC) on a graphite anode in PC base electrolyte with catechol carbonate. DenM Kagaku oyobi Kogyo Butsuri Kagaku 66 286-292... 

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