Polymerization during cracking

Propene is used as a starting material for numerous other compounds. Chief among these are isopropyl alcohol, acrylonitrile, and propylene oxide. Isopropyl alcohol results from the hydration of propylene during cracking and is the primary chemical derived from propylene. Isopropyl alcohol is used as a solvent, antifreeze, and as rubbing alcohol, but its major use is for the production of acetone. Acrylonitrile is used primarily as a monomer in the production of acrylic fibers. Polymerized acrylonitrile fibers are produced under the trade names such as Orion (DuPont) and Acrilan (Monsanto). Acrylonitrile is also a reactant in the synthesis of dyes, pharmaceuticals, synthetic rubber, and resins. Acrylonitrile production occurs primarily through ammoxidation of propylene CH3- CH = CH2 + NH3 + 1.5 02—> CH2 = CH - C = N + 3 H20. 

The ratio of the ester to paraformaldehyde governs the degree of polymerization during this condensation, which in turn affects the viscosity of the reaction mixture and also the efficiency and temperature of the cracking step. ... 

Two distinct types of material are found in cracked fuel oil (1) scarcely decomposed straight-run asphaltic material derived from residual feedstocks, and (2) condensation or polymerization materials derived from reactive fragments produced during cracking. In addition, the straight-run asphaltic material is frequently exposed to the mild operation known as viscosity breaking (either in a separate coil or as part of the recirculation in a black-oil coil). The viscosities and gravities of these com-... 

Combining processes. Two processes, alkylation and polymerization, are used to produce gasoUne-blending stocks from the gaseous hydrocarbons formed during cracking processes. 

Elastomers. Ethylene—propylene terpolymer (diene monomer) elastomers (EPDM) use a variety of third monomers during polymerization (see Elastomers, ethyiene-propylene-diene rubber). Ethyhdenenorbomene (ENB) is the most important of these monomers and requires dicyclopentadiene as a precursor. ENB is synthesized in a two step preparation, ie, a Diels-Alder reaction of CPD (via cracking of DCPD) with butadiene to yield 5-vinylbicyclo[2.2.1]-hept-2-ene [3048-64-4] (7) where the external double bond is then isomerized catalyticaHy toward the ring yielding 5-ethyhdenebicyclo[2.2.1]-hept-2-ene [16219-75-3] (ENB) (8) (60). 

During fatigue the stress amplitude usually remains constant and brittle failure occurs as a result of crack growth from a sub-critical to a critical size. Clearly the rate at which these cracks grow is the determining factor in the life of the component. It has been shown quite conclusively for many polymeric materials that the rate at which cracks grow is related to the stress intensity factor by a relation of the form... 

One of the drawbacks of thermal cracking in an FCC is that a high percentage of the olefins formed during intermediate reactions polymerize and condense directly to coke. 

Due to the retractive forces in stretched mbber, the aldehyde and zwitterion fragments are separated at the molecular-relaxation rate. Therefore, the ozonides and peroxides form at sites remote from the initial cleavage, and underlying mbber chains are exposed to ozone. These unstable ozonides and polymeric peroxides cleave to a variety of oxygenated products, such as acids, esters, ketones, and aldehydes, and also expose new mbber chains to the effects of ozone. The net result is that when mbber chains are cleaved, they retract in the direction of the stress and expose underlying unsaturation. Continuation of this process results in the formation of the characteristic ozone cracks. It should be noted that in the case of butadiene mbbers a small amount of cross-linking occurs during ozonation. This is considered to be due to the reaction between the biradical of the carbonyl oxide and the double bonds of the butadiene mbber [47]. 

It occurs during the chain cracking and radiolysis of hydrocarbons [38], radical polymerization and oligomerization of monomers [39], thermal and thermooxidative destruction of polymers (see Chapter 19) and hydrocarbon oxidation at low dioxygen pressure. 

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