Cracking, thermal vapor-phase

Reactions of /l-Butane. The most important industrial reactions of / -butane are vapor-phase oxidation to form maleic anhydride (qv), thermal cracking to produce ethylene (qv), Hquid-phase oxidation to produce acetic acid (qv) and oxygenated by-products, and isomerization to form isobutane. 

Thermal polymerization is not as effective as catalytic polymerization but has the advantage that it can be used to polymerize saturated materials that caimot be induced to react by catalysts. The process consists of the vapor-phase cracking of, for example, propane and butane, followed by prolonged periods at high temperature (510—595°C) for the reactions to proceed to near completion. Olefins can also be conveniendy polymerized by means of an acid catalyst. Thus, the treated olefin-rich feed stream is contacted with a catalyst, such as sulfuric acid, copper pyrophosphate, or phosphoric acid, at 150—220°C and 1035—8275 kPa (150—1200 psi), depending on feedstock and product requirement. 

Thermal Cracking. Thermal chlorination of ethylene yields the two isomers of tetrachloroethane, 1,1,1,2 and 1,1,2,2. Introduction of these tetrachloroethane derivatives into a tubular-type furnace at temperatures of 425—455°C gives good yields of trichloroethylene (33). In the cracking of the tetrachloroethane stream, introduction of ferric chloride into the 460°C vapor-phase reaction zone improves the yield of trichloroethylene product. 

The cracking and the low-temperature oxidation of crude oils have been studied previously in order to simulate the thermal transformations of oil to gas and coke during enhanced oil recovery (1-6). Other authors characterize the thermal modifications of oil in the presence of a vapor phase (7)-... 

Gyro Also called Gyro-cracking. An early vapor-phase thermal cracking process for refining petroleum. 

TVP [True vapor-phase] A thermal cracking process in which vaporized petroleum oil is contacted with a hotter gas such that the temperature of the gas mixture is approximately 500°C. Used in the 1930s, but supplanted by various catalytic cracking processes. 

Gray clay treating a fixed-bed (q.v.), usually fuller s earth (q.v.), vapor-phase treating process to selectively polymerize unsaturated gum-forming constituents (diolefins) in thermally cracked gasoline. 

Cold box and refrigeration system. After the acid gas and water removal, the pyrolysis gas is cooled and condensed to approximately -165°C only hydrogen and some methane remain in the vapor phase. The feed locations are determined via process simulation. Hydrogen and methane are drawn from the lowest temperature stage separator and sent to thermal cracking furnaces as fuel. 

Catalytic cracking is the cracking of heavy hydrocarbons using catalyst. The polyolefins such as PP and PE are recycled through this method. In the laboratory scale setup, these reactions are carried out in a flow reactor. There are two modes of catalytic treatment, liquid phase contact and vapor phase contact. In first case, the catalyst is in contact with molten polymers and here the catalyst reacts mainly with oligomers. In vapor phase contact, the catalyst is in contact with thermally degraded polymer [27]. 

Pyrolysis experiments on silicon and germanium hydrides have led to interesting conclusions about bond stabilities. Thermal decomposition of disilane 3) occurs at temperatures several hundred degrees lower than that required for thermal cracking of simple hydrocarbons (J67). It seems reasonable to suppose, however, that the relative polarities of the Si—H and C—H bonds are important in this connection, and that the pyrolysis pathways will be dissimilar. Indeed, ethylene is a major product of the cracking of ethane 367), while silicon will not form stable double bonds. Decomposition of various hydrides and mixtures of hydrides, followed by vapor-phase chromatographic analysis of the products, showed that Ge—Ge bonds are more readily broken than Si—Ge bonds, while Si—Si links were not broken at all under the conditions employed 368). However, generalities as to the stabilities of M—M bonds are not yet possible. 

Example on Preparation of Cyclopentadiene. Cyclopentadiene is obtained in high-temperature vapor-phase petroleum cracking operations. It is mixed with other hydrocarbons, and its separation is complicated by the fact that it will dimerize and the dimer will depolymerize at about normal distillation conditions. One method of operating is to dimerize the pentadiene and then remove all remaining constituents below C7. The residue is then given a thermal treatment which will depolymerize the dimer, and the mixture is distilled to obtain the cyclopentadiene. A unit is to be designed for this final fractional distillation, and an estimate is to be made of the amount of polymerization that will be obtained. 

Gyro Also called Gyro-cracking. An early vapor-phase Thermal Cracking process for refining petroleum. The Petroleum Handbook, 3rd ed.. Shell Petroleum, London, U.K., 1948,170. 

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