Hydrocarbons, chlorination cracking

Polysulfones are handicapped by light and UV sensitivity requiring an efficient protection for outdoor exposure sensitivity to environmental stress cracking and attacks by chemicals such as aromatic hydrocarbons, chlorinated solvents and ketones the cost (justified by the performances) sometimes an insufficient fire resistance, but special grades are marketed. 

Materials of Construction. GeneraHy, carbon steel is satisfactory as a material of construction when handling propylene, chlorine, HCl, and chlorinated hydrocarbons at low temperatures (below 100°C) in the absence of water. Nickel-based aHoys are chiefly used in the reaction area where resistance to chlorine and HCl at elevated temperatures is required (39). Elastomer-lined equipment, usuaHy PTFE or Kynar, is typicaHy used when water and HCl or chlorine are present together, such as adsorption of HCl in water, since corrosion of most metals is excessive. Stainless steels are to be avoided in locations exposed to inorganic chlorides, as stainless steels can be subject to chloride stress-corrosion cracking. Contact with aluminum should be avoided under aH circumstances because of potential undesirable reactivity problems. 

The most important olefins used for the production of petrochemicals are ethylene, propylene, the butylenes, and isoprene. These olefins are usually coproduced with ethylene by steam cracking ethane, LPG, liquid petroleum fractions, and residues. Olefins are characterized by their higher reactivities compared to paraffinic hydrocarbons. They can easily react with inexpensive reagents such as water, oxygen, hydrochloric acid, and chlorine to form valuable chemicals. Olefins can even add to themselves to produce important polymers such as polyethylene and polypropylene. Ethylene is the most important olefin for producing petrochemicals, and therefore, many sources have been sought for its production. The following discusses briefly, the properties of these olefmic intermediates. 

Nature of the environment This is usually water, an aqueous solution or a two- (or more) component system in which water is one component. Inhibitors are, however, sometimes required for non-aqueous liquid systems. These include pure organic liquids (Al in chlorinated hydrocarbons) various oils and greases and liquid metals (Mg, Zr and Ti have been added to liquid Bi to prevent mild steel corrosion by the latter ). An unusual case of inhibition is the addition of NO to N2O4 to prevent the stress-corrosion cracking of Ti-6A1-4V fuel tanks when the N2O4 is pressurised... 

PPSU alloys have the best hydrolytic stability, thermal stability and oxidation resistance. This resin is resistant to mineral acids and alkalis, while ketones, chlorinated hydrocarbons and aromatic hydrocarbons may cause stress cracking. 

Highly undesired is the formation of carbon deposit. This phenomenon is favored by higher wall temperature, by the presence of heavy chlorinated hydrocarbons, as well as by some heavy impurities, namely trichloroethylene (TRI). Preventing the coke formation is a major problem in operating the furnace for EDC cracking. Keeping the reaction temperature below 500 °C prevents the coke formation but decreases the reaction rate. Therefore, as already mentioned, it is rational to use initiators , such as nitromethane, chloroform or carbon tetrachloride. 

The BP process [7] is based on a sand fluidized-bed pyrolysis reactor. The cracking temperature is kept at 400-600°C. Low-molecular hydrocarbons can be obtained. The process mainly involves converting waste plastics into normal linear hydrocarbons, the average molecular weight of which is 300-500. Most plastics can be treated by this process. Polyolefins are decomposed into small molecules with the same linear structure. PS is converted into styrene monomers and PET into mixture of hydrocarbons, carbon monoxide and carbon dioxide. A maximum of 2% PVC is allowed in this process, and the content of chlorine in the products is lower than 5 ppm. The distribution of alkene products in this process is like that in petroleum pyrolysis. The BP process was industrialized in 1997. 

The unsaturated hydrocarbons are, in contrast with the paraffins, very reactive. They react rapidly with chlorine to form oily liquids hence the name olefin ( oil-forming"). Tinder the proper conditions they react readily with hydrogen which saturates the double bonds and forms the corresponding paraffin. Because of their hi reactivity these unsaturated hydrocarbons are not found in crude oil to any great extent. However, they are formed in large amounts in petroleum-cracking processes and have considerable industrial importance. 

The photochemical oxidation of chlorinated hydrocarbons into phosgene has been the subject of particular concern for the welding workshop [679,2217]. Solvent residues from degreasing procedures may remain on the part to be welded, particularly in cracks and cavities where the solvent may have been drawn by capillary action [627]. Upon exposure to the heat of the welding arc, the residues vaporize and although some thermal oxidation will then... 

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