Pyrolysis in the presence of hydrogen

Another method for the determination of oxygen in coal involves reduction of the coal by pyrolysis in the presence of hydrogen, whereupon the oxygen is converted catalytically to water. However, the procedure is relatively complex and the catalyst may be poisoned by sulfur and by chlorine. 

It was attempted in this study, therefore, to have a more detailed investigation of propylene pyrolysis in the presence of hydrogen. Furthermore propylene was subjected to pyrolysis in the presence of deuterium. Kinetic isotope effect was measured and deuterium distributions in the pyrolysis products were analyzed. 

An elegant modern method of identification of the basic carbon skeleton consists in pyrolysis in the presence of hydrogen combined with gas chromatography, which is mainly stiitable for aliphatic compounds (56—58). The necessary equipment is conunercially available (59). 

In direct liquefaction, coal is heated in the presence of hydrogen and a catalyst such as cobalt-molybdenum or nickel-molybdenum on alumina to give a greater yield of high-quality hydrocarbons than that produced by pyrolysis. This hydrogenation process has been demonstrated in several 50- to 250-ton-per-day plants. 

Naphthalene is produced from coal tar or petroleum. It is made from petroleum by dealkylation of methylnaphthalenes in the presence of hydrogen at high temperature and pressure. Petroleum was a major source of naphthalene until the 1980s, but now most naphthalene is produced from coal tar. The pyrolysis of bituminous coal produces coke and coke oven gases. Naphthalene is condensed by cooling the coke gas and then separated from the gas. Naphthalene production in the United States is slightly greater than 100,000 tons annually. 

High-temperatnre pyrolysis and cracking of waste thermoplastic polymers, such as polyethylene, polypropylene and polystyrene is an environmentally acceptable method of recycling. These type of processes embrace both thermal pyrolysis and cracking, catalytic cracking and hydrocracking in the presence of hydrogen. Mainly polyethylene, polypropylene and polystyrene are used as the feedstock for pyrolysis since they have no heteroatom content and the liquid products are theoretically free of sulfur. 

TCBTs are relatively persistent and non-flammable (and therefore useful in hydraulic oils). Pyrolysis in a closed system for two days in the presence of hydrogen peroxide at 300 °C produced as main components chlorinated benzo-phenones, fluorenes, fluorenones, xanthenes, and xanthones. Polychlorodiben-zofurans (PCDF) and polychlorodibenzo-p-dioxins (PCDD) were formed in much lower concentrations than from PCB product Pyralene T1 under identical conditions [84]. In pyrolysis at 450-700 °C with excess oxygen TCBTs produce more PCDFs and PCDDs. In parallel with the behavior of PCBs, PCDFs are formed in significantly higher amounts than PCDDs from PCBTs [86],... 

Following the work with pure argon as diluent, Kijewski and Troe [212] have studied the pyrolysis of H2O2 in the presence of hydrogen at... 

Some such studies on the ethane pyrolysis in the presence of nitric oxide have been made by Pratt > who has been particularly concerned with the kinetics of formation of nitrogen, hydrogen, methane and butane. Work has recently been carried out at the University of Ottawa on the pyrolyses of ethane (Esser and Laidler ) and of acetaldehyde (Schuchmann and Laidler ). The technique of gas-liquid chromatography has been used for the most part to analyze the reaction... 

The geminal dicyanovinyl azides (92) also decompose, although rather slowly, at room temperature When the decomposition is carried out in aprotic solvents, only polymeric products are obtained. Pyrolysis in the presence of ethanol or hydrogen chloride, however, led to the isolation of the 2-aminoethylene-l,l-dicarbonitriles (93). This result indicates that iminoketenes are intermediates (equation 12). 

In addition to comonomers, nylons are frequently used in blends. The pyrolysis of blends typically shows little interaction between the compounds generated from the individual blend components. However, a study on the co-pyrolysis of several polyamides in the presence of PVC showed interactions [40]. The study was done on nylon-12, nylon-6,6 and poly(1,4-phenylene terephthalamide) (Kevlar) in the presence of poly(vinyl chloride). Polyamide-PVC mixtures (typical mass ratio 1 1) were pyrolyzed at 700 and 900°C. It was found that the presence of PVC promoted the hydrol ic decomposition routes of amide groups and volatile nitrile formation from all examined polyamides due to the hydrogen chloride eliminated from PVC under pyrolysis. In the presence of PVC, an elevated yield of alkenenitriles was observed from nylon-12. For Kevlar in the presence of PVC, it was noticed the evolution of benzeneamine, benzoic acid, benzenenitrile and benzeneisocyanate. At 900°C in the presence of PVC, an enhanced evolution of HCN from nylon-12 and nylon-6,6 was noticed. 

Mechanism of Surface Carbon Formation During the Pyrolysis of Benzene in the Presence of Hydrogen... 

The mechanism of carbon formation on polycrystalline Cu foils was studied for the pyrolysis of benzene in the presence of hydrogen. The study was carried out on a microbalance tubular flow reactor at temperatures rapging form 800 to 1050°C. The rate of surface carbon deposition was constant after an initial period during which no appreciable deposition was observed. 

Stepanenko and Kolodii [171] used a flamedonization detector for the detection of halogenated hydrocarbons, these compounds are converted to hydrocarbons by pyrolysis at 1000°C in the presence of hydrogen. 

Two hexafluoroacetone-hydrogen cyanide adducts have been characterized previously, viz. the cyanohydrin (58) (from piperidine-catalysed reaction) and the 2 1 adduct 2,2,5,5-tetrakistrifluoromethyl-4-oxazolidinone (59) [from (CFs)aCO-NaCN-MeCN]. It has now been reported that large transparent crystals of the 3 2 adduct (60) separate from a sample of the cyanohydrin (58) when it is stored for more than 1 year this new adduct is more readily prepared from the cyanohydrin by treating it with an excess of hexafluoroacetone in the presence of DABCO at 100 °C for 16 h (or DABCO alone at 25 °C for a prolonged period ). Addition of an excess of the ketone to hydrogen cyanide (KCN catalyst) or to preformed cyanohydrin (58) (piperidine catalyst) gives a new 3 1 adduct (61) (>93%) and not the 3 2 adduct (60). Adduct (61) can be distilled at reduced pressure, but pyrolysis in the presence of cone. H2SO4 (trace) affords a mixture of... 

Pyrolysis (or carbonization Chapters 13 and 16) is perhaps the oldest technique for obtaining liquid products directly from coal and involves heating the coal in the absence of air (or oxygen) to produce heavy and light oils, gases, and char. In the presence of hydrogen, the process is called... 

When the pyrolysis of PCS precursor fibers is carried out in the presence of hydrogen, or when boron or aluminum doped PCS precursor fibers are pyrolyzed, it is possible to obtain quasi-stoichiometric silicon carbide fibers. Alternatively, quasi-stoichiometric fibers are also obtained from precursor fibers consisting of SiC powder reinforced polymers. 

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