Hot catalyst

A urea melt is suppHed to a one-stage reactor containing a fluid-bed catalyst. The reactor is heated internally by circulating molten salt. Upon entering the reactor, the urea is converted to melamine by the hot catalyst. 

Fluidized-bed catalytic cracking units (FCCUs) are the most common catalytic cracking units. In the fluidized-bed process, oil and oil vapor preheated to 500 to SOOT is contacted with hot catalyst at about 1,300°F either in the reactor itself or in the feed line (called the riser) to the reactor. The catalyst is in a fine, granular form which, when mixed with the vapor, has many of the properties of a fluid. The fluidized catalyst and the reacted hydrocarbon vapor separate mechanically in the reactor and any oil remaining on the catalyst is removed by steam stripping. 

In its development, it adapted two existing technologies, In the agricultural sector, the mechanics of grain elevators provided a model for how to move solids vertical distances and in closed-loop flow arrangements. Sacony engineers modified the elevator bucket systems traditionally used by the grain industry to carry hot catalyst from the bottom to top of vessels and between vessels. 

In the moving bed processes, the preheated feed meets the hot catalyst, which is in the form of beads that descend by gravity to the regeneration zone. As in fluidized bed cracking, conversion of aromatics is low, and a mixture of saturated and unsaturated light hydrocarbon gases is produced. The gasoline product is also rich in aromatics and branched paraffins. 

During the reaction of the hot catalyst surface with a flammable gas the temperature of the device increases. The Platinum coil itself serves at the same time as a resistance thermometer. The resistance increase of the coil then is a direct measure for the amount of combusted gas. Usually the amount of heat that develops during combustion is small and amounts to 800 kj/mol for methane, for example [8], Therefore the sensor is connected in a bridge circuit to a second resistor which shows the same setup as the pellistor but is catalytically inactive. The bridge voltage is then controlled by the temperature difference of the two sensors (see Fig. 5.34). 

Catasulf A catalytic process for converting hydrogen sulfide in gas streams to elemental sulfur. The gas, to which a stoichiometric quantity of air or oxygen has been added, is passed over the hot catalyst. Invented in 1983 by BASF. One plant had been built as of 1990. 

Deoxy A process for removing small concentrations of oxygen from natural gas. The gas is passed over a hot catalyst, which converts the oxygen to carbon dioxide. 

Figure 13. Oxidation of a-pinene with 30% H2O2 over sol-gel H5PWnTi04o/Si02 composite [149] (a) catalyst recycling and (b) hot catalyst filtration experiment. Reaction conditions a-pinene, 0.1 mmol, H2O2, 0.12 mmol, catalyst, 14 mg, MeCN, 1 mL, 30 °C.

Feed to the FCC unit is mixed with hot catalyst and steam in a reactor line called a riser. The ratio of catalyst oil feed can typically range from 4 1 to 9 1 by weight. Overall, FCC is an endothermic process. Heat provided by the hot, circulating catalyst is the prime source of energy driving the FCC process. In the riser, vaporized oil is cracked catalytically in less than two seconds. The vapors and catalyst flow out of the riser and into the reactor. At this point, most cracking reactions have occurred. 

Riser Cracking—Applied to fluid catalytic cracking units where the mixture of feed oil and hot catalyst is continuously fed into one end of a pipe (riser) and discharges at the other end where catalyst separation is accomplished after the discharge from the pipe. There is no dense phase bed through which the oil must pass because all the cracking occurs in the inlet pipe (riser). 

In the process (Figure 8-10), the preheated feedstock (which may be whole crude, atmospheric residuum, vacuum residuum, or bitumen) is injected into a stream of fluidized, hot catalyst (trade name ArtCat). Complete mixing of the feedstock with the catalyst is achieved in the contactor, which is operated within a pressure-temperature envelope to ensure selective vaporization. The vapor and the contactor effluent are quickly and efficiently separated from each other and entrained hydrocarbons are stripped from the contaminant (containing spent... 

A two-stage stripper is utilized to remove hydrocarbons from the catalyst. Hot catalyst flows at low velocity in dense phase through the catalyst cooler and returns to the regenerator. Regenerated catalyst flows to the bottom of the riser to meet the feed. 

Fluid catalytic cracking (FCC) of heavy oil fractions is a well-known process in oil refineries. Numerous books (e.g., 1—3) and publications about the different aspects of this subject are available. This chapter is concerned with the modeling of the transfer line or riser reactor of an FCC unit (FCCU) or of a pilot plant. The riser reactor in FCCUs is a vertical pipe about 1 m in diameter and 10-30 m in height. The hot catalyst coming from the regenerator at about 710 ° C first comes in contact with steam and is fluidized. Then, at a height of some meters above, the catalyst is mixed with the preheated feedstock at about 300 ° C. 

In catalytic cracking, a large amount of heat needs to be supplied at the reactor inlet to vapourize the feed and provide the heat of reaction. In commercial units, this heat is provided by the hot catalyst recirculated from the regenerator. High heat transfer rates are achieved when the fluidized catalyst is mixed with the feed. In some experimental units, feed and catalyst are injected at reactor temperature. The heat of reaction must then be supplied by an external heating element, at much slower rates of heat transfer. The product selectivity from such laboratory units cannot be expected to simulate that of commercial units... 

In current industrial practice, reactor (or riser) temperature is usually controlled by the flowrate of hot catalyst fed to the reactor from the regenerator. A slide valve in the... 

This plant in Tokuyama, Japan, passes ethane rapidly over a hot catalyst. The products are ethylene and hydrogen. 

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