There are a number of differences between thermal and catalytic cracking, but the main ones are the variation in temperature and pressure used in the processes. Both processes are used in the refining of petroleum to break down hydrocarbon molecules. Naphtha Catalytic Cracking in FCC Units Past & Present? Christopher Dean - High Olefins Technology Services LLC. Thermal Cracking • Non-catalytic Free Radical Chain Formation. Microsoft PowerPoint - FRI 845 CATCRACKING.COM Author. Vapor phase thermal cracking process: Low boiling fraction e.g., kerosene is cracked in the vapor phase at a temperature of about 875 K and under a pressure of 3 atmosphere. Catalytic cracking. Higher hydrocarbons can also be cracked at lower temperature (600 - 650 K) and lower pressure (2 atm) in the presence of a suitable catalyst. Thermal and catalytic cracking of both high and low-density polyethylene (HDPE and LDPE, respectively) under mild conditions have been investigated in order to study the properties of the solid waxy product so obtained. In petroleum refining: Catalytic cracking. The use of thermal cracking units to convert gas oils into naphtha dates from before 1920. These units produced small quantities of unstable naphthas and large amounts of by-product coke. The catalyst particle and rapidly lowers its activity. • To maintain the catalyst activity at a useful level, it is necessary to regenerate the catalyst by burning off this coke with air. • As a result, the catalyst is continuously moved from reactor to regenerator and back to reactor. • The cracking reaction is endothermic and the regeneration reaction exothermic. • Some units are designed to use the regeneration heat to supply that needed for the reaction and to heat the feed up to reaction temperature. These are known as ‘‘heat balance’’ units. 1000°F (480– 540°C), with oil feed temperatures from 500 to 800°F (260–425°C) and regenera- tor exit temperatures for catalyst from 1200 to 1500°F (650–815°C). • The catalytic-cracking processes in use today can all be classified as either moving-bed or fluidized-bed units. • There are several modifications under each of the classes depending upon the designer or builder, but within a class the basic operation is very similar. • The Thermafor catalytic cracking process (TCC) is representative of the moving-bed units and the fluid catalytic cracker (FCC) of the fluidized-bed units. • The hot oil feed is contacted with the catalyst in either the feed riser line or the reactor. • As the cracking reaction progresses, the catalyst is progressively deactivated by the formation of coke on the surface of the catalyst. • The catalyst and hydrocarbon vapors are separated mechanically, and oil remaining on the catalyst is removed by steam stripping before the catalyst enters the regenerator. • The oil vapors are taken over head to a fractionation tower for separation into streams having the desired boiling ranges. Reactivated by burning off the coke deposits with air. • Regenerator temperatures are carefully controlled to prevent catalyst deactivation by overheating and to provide the desired amount of carbon burn-off. This is done by controlling the air flow to give a desired CO/CO ratio in the exit flue gases or the desired temperature in the regenerator. • The flue gas and catalyst are separated by cyclone separators and electrostatic precipitators. • The catalyst in some units is steam-stripped as it leaves the regenerator to remove adsorbed oxygen before the catalyst is contacted with the oil feed. • The most important cracking reaction of naphthenes in the presence of silica- alumina is dehydrogenation to aromatics. • There is also carbon–carbon bond scission in both the ring and attached side chains but at temperatures below 1000°F (540°C) the dehydrogenation reaction is considerably greater. • Dehydrogenation is very extensive for C9 and larger naphthenes and a high-octane gasoline results. The return of the king extended edition subtitrari romana.
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