Pyrolysis of hydrogen

A simplest vessel used for experimental investigation of pyrolysis of hydrogen, oxygen, and nitrogen, as well as other molecules is shown in Fig.4.3. The pyrolysis Hlament (below) is separated from the adsorption chamber (above) by a plane shutter driven by a magnet, whidi permits the sensor to be exposed to the established atomic flux during a required... 

Table 1.6 Typical Mass Spectral Data of Characteristic Degradation Products produced on pyrolysis of Hydrogenated NBR ...

Electron-deficient alkenes add stereospecifically to 4-hydroxy-THISs with formation of endo-cycloadducts. Only with methylvinyl-ketone considerable amounts of the exo isomer are produced (Scheme 8) (16). The adducts (6) may extrude hydrogen sulfide on heating with methoxide producing 2-pyridones. The base is unnecessary with fumaronitrile adducts. The alternative elimination of isocyanate Or sulfur may be controlled using 7 as the dipolarenOphile. The cycloaddition produces two products, 8a (R = H, R = COOMe) and 8b (R = COOMe, R =H) (Scheme 9) (17). Pyrolysis of 8b leads to extrusion of furan and isocyanate to give a thiophene. The alternative S-elimi-nation can be effected by oxidation of the adduct and subsequent pyrolysis. 

Pyrolysis of chlorodifluoromethane is a noncatalytic gas-phase reaction carried out in a flow reactor at atmospheric or sub atmospheric pressure yields can be as high as 95% at 590—900°C. The economics of monomer production is highly dependent on the yields of this process. A significant amount of hydrogen chloride waste product is generated during the formation of the carbon—fluorine bonds. 

Vlayl fluoride [75-02-5] (VF) (fluoroethene) is a colorless gas at ambient conditions. It was first prepared by reaction of l,l-difluoro-2-bromoethane [359-07-9] with ziac (1). Most approaches to vinyl fluoride synthesis have employed reactions of acetylene [74-86-2] with hydrogen fluoride (HF) either directly (2—5) or utilizing catalysts (3,6—10). Other routes have iavolved ethylene [74-85-1] and HF (11), pyrolysis of 1,1-difluoroethane [624-72-6] (12,13) and fluorochloroethanes (14—18), reaction of 1,1-difluoroethane with acetylene (19,20), and halogen exchange of vinyl chloride [75-01-4] with HF (21—23). Physical properties of vinyl fluoride are given ia Table 1. 

Acetylene traditionally has been made from coal (coke) via the calcium carbide process. However, laboratory and bench-scale experiments have demonstrated the technical feasibiUty of producing the acetylene by the direct pyrolysis of coal. Researchers in Great Britain (24,28), India (25), and Japan (27) reported appreciable yields of acetylene from the pyrolysis of coal in a hydrogen-enhanced argon plasma. In subsequent work (29), it was shown that the yields could be dramatically increased through the use of a pure hydrogen plasma. 

Utilisa tion of shale oil products for petrochemical production has been studied (47—51). The effects of prerefining on product yields for steam pyrolysis of shale oil feed and the suitabiUty of Green River shale oil as a petrochemical feedstock were investigated. Pyrolysis was carried out on the whole oil, vacuum distillate, and mildly, moderately, and severely hydrogenated vacuum distillates. 

The only commercially important dialkyl sulfates are dimethyl sulfate and diethyl sulfate. Estimated worldwide production in 1996 for dimethyl sulfate was 90,000 metric tons per year. Dimethyl sulfate was initially made by vacuum pyrolysis of methyl hydrogen sulfate ... 

Another important use of a-pinene is the hydrogenation to i j -pinane (21). One use of the i j -pinane is based on oxidation to cis- and /n j -pinane hydroperoxide and their subsequent catalytic reduction to cis- and /n j -pinanol (22 and 23) in about an 80 20 ratio (53,54). Pyrolysis of the i j -pinanol is an important route to linalool overall the yield of linalool (3) from a-pinene is about 30%. Linalool can be readily isomerized to nerol and geraniol using an ortho vanadate catalyst (55). Because the isomerization is an equiUbrium process, use of borate esters in the process improves the yield of nerol and geraniol to as high as 90% (56). 

Dihydromyrcene Manufacture. 2,6-Dimethyl-2,7-octadiene, commonly known as dihydromyrcene (24) or citroneUene, is produced by the pyrolysis of pinane, which can be made by hydrogenation of a- or P-pinene (101). If the pinene starting material is optically active, the product is also optically active (102). The typical temperature for pyrolysis is about 550—600°C and the cmde product contains about 50—60% citroneUene. Efficient fractional distUlation is requited to produce an 87—90% citroneUene product. 

Another important process for linalool manufacture is the pyrolysis of i j -pinanol, which is produced from a-pinene. The a-pinene is hydrogenated to (73 -pinane, which is then oxidized to cis- and /n j -pinane hydroperoxide. Catalytic reduction of the hydroperoxides gives cis- and /n j -pinanol, which are then fractionally distilled subsequendy the i j -pinanol is thermally isomerized to linalool. Overall, the yield of linalool from a-pinene is estimated to be about 30%. 

Titanium disulfide can also be made by pyrolysis of titanium trisulfide at 550°C. A continuous process based on the reaction between titanium tetrachloride vapor and dry, oxygen-free hydrogen sulfide has been developed at pilot scale (173). The preheated reactants ate fed iato a tubular reactor at approximately 500°C. The product particles comprise orthogonally intersecting hexagonal plates or plate segments and have a relatively high surface area (>4 /g), quite different from the flat platelets produced from the reaction between titanium metal and sulfur vapor. The powder, reported to be stable to... 

Outside the realm of typical hydrocarbon pyrolysis is the high temperature pyrolysis of methane. In one variant of this process, which has only been commercialized to produce acetylene (with some BTX), methane reacts in an electric arc at about 1500°C (17) with very short contact times. At higher temperatures or with a catalyst and added hydrogen, BTX is produced with fairly high selectivity (18). 

Pyrolysis. Pyrolysis of 1,2-dichloroethane in the temperature range of 340—515°C gives vinyl chloride, hydrogen chloride, and traces of acetylene (1,18) and 2-chlorobutadiene. Reaction rate is accelerated by chlorine (19), bromine, bromotrichloromethane, carbon tetrachloride (20), and other free-radical generators. Catalytic dehydrochlorination of 1,2-dichloroethane on activated alumina (3), metal carbonate, and sulfate salts (5) has been reported, and lasers have been used to initiate the cracking reaction, although not at a low enough temperature to show economic benefits. 

Physical properties of pentachloroethane are Hsted in Table 10. The kinetics and mechanism of the pyrolysis of pentachloroethane in the temperature ranges of 407—430°C and 547—592°C have been studied (133—135). Tetrachloroethylene and hydrogen chloride are the two primary pyrolysis products, showing that dehydrochlorination is the primary reaction. 

Process development of the use of hydrogen as a radical quenching agent for the primary pyrolysis was conducted (37). This process was carried out in a fluidized-bed reactor at pressures from 3.7 to 6.9 MPa (540—1000 psi), and a temperature of 566°C. The pyrolysis reactor was designed to minimize vapor residence time in order to prevent cracking of coal volatiles, thus maximizing yield of tars. Average residence times for gas and soHds were quoted as 25 seconds and 5—10 rninutes. A typical yield stmcture for hydropyrolysis of a subbiturninous coal at 6.9 MPa (1000 psi) total pressure was char 38.4, oil... 

Flash Pyrolysis Coal is rapidly heated to elevated temperatures for a brief period of time to produce oil, gas, and char. The increase in hydrogen content in the gases and hquids is the result of removing carbon from the process as a char containing a significantly reduced amount of hydrogen. Several processes have been tested on a rela-... 

Methylsuccinic acid has been prepared by the pyrolysis of tartaric acid from 1,2-dibromopropane or allyl halides by the action of potassium cyanide followed by hydrolysis by reduction of itaconic, citraconic, and mesaconic acids by hydrolysis of ketovalerolactonecarboxylic acid by decarboxylation of 1,1,2-propane tricarboxylic acid by oxidation of /3-methylcyclo-hexanone by fusion of gamboge with alkali by hydrog. nation and condensation of sodium lactate over nickel oxide from acetoacetic ester by successive alkylation with a methyl halide and a monohaloacetic ester by hydrolysis of oi-methyl-o -oxalosuccinic ester or a-methyl-a -acetosuccinic ester by action of hot, concentrated potassium hydroxide upon methyl-succinaldehyde dioxime from the ammonium salt of a-methyl-butyric acid by oxidation with. hydrogen peroxide from /9-methyllevulinic acid by oxidation with dilute nitric acid or hypobromite from /J-methyladipic acid and from the decomposition products of glyceric acid and pyruvic acid. The method described above is a modification of that of Higginbotham and Lapworth. ... 

The procedure described is a modification of the directions of Prelog, Frenkiel, Kobelt, and Barman. Cyclodecanone has been prepared by the dehydration of sebacoin followed by catalytic hydrogenation, by the pyrolysis of the thorium or yttrium salt of nonane-1,9-dicarboxylie acid, and by the ring enlargement of cyclononanone, as well as by the reduction of sebacoin. ... 

Pyrolysis of alkanes is referred to as eraeking. Alkanes from the paraffins (kerosene) fraetion in the vapor state are passed through a metal ehamher heated to 400-700°C. Metallie oxides are used as a eatalyst. The starting alkanes are broken down into a mixture of smaller alkanes, alkenes, and some hydrogen. 

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