Coked regeneration

The original performance of the fresh catalyst can be successhiUy restored by proper regeneration to remove this coke. Regeneration allows continued use of the same catalyst for many years. Thus even expensive and sophisticated catalysts can become economical for commercial use in petroleum refining. 

The catalyst remained active and did not start to deactivate for about 50 h on stream without any regeneration. After that, the catalyst activity started to drop slowly but steadily.The deactivation could be caused either by sintering of Pt nanoparticles or by coke deposited on the Pt atoms. If the catalyst deactivation was caused by coking, regeneration may reestablish catalyst activity. However, regeneration in air did not improve catalyst activity, which suggests that the cause of deactivation was not coke. 

Coking - regeneration cycle was examined. Surface area diminished while Pt-Sn alloy increased. Sn2+ and A1203 interaction important in catalyst stability. Ce02 addition enahnced stability.68 ... 

At the end of a given number of coking/regeneration cycles, catalyst pellets were sampled at selected reactor locations. The sampling points were always in the vicinity of a thermocouple, in order to know the thermal history of the particles sampled. These particles were then subjected to kinetic tests in order to determine their activity, and to XPS measurements, from which the catalyst surface area and the atomic ratios of the different elements on the catalyst surface were obtained. 

Figjre 3. Temperature-time history of particles sampled at different positions in the bed. 7 coking/regeneration cycles. The regenerations were carried out with 6% oxygen concentration in th gas and a total gas flow rate of 2 l/min. 

The notation i-it-iii Indicates i) the type of coking/regeneration series perfomed (A 6% oxygen concentration, 2 l/min B 10% oxygen concentration, 3 l/min). ii) the number of coking/regeneration cycles and iii) the reactor position (1-reactor entrance, 7- reactor exit )... 

It should be noted that the CTO regime can start before the maximum delta coke (regenerator temperature) constraint is reached (Figure 5). What we have then is no longer regenerator-temperature-limited RFCC, but CTO-limited RFCC. 

Cu-Cr oxides furfuryl alcohol ex furfural 150-200 coke regenerate with oxidation... 

It is of note that except for ZnO, the principal reduction reactions of metal oxides with CO are exothermic at operating temperature. However, the reaction of CO2 with coke regenerating CO for reduction is highly endothermic, as well as the decomposition of lead snlfate (Equation 5.10) and the roast reaction as given by Equation 5.11. 

Cracking reactions are endothermic the energy balance is obtained by the production of coke that deposits on the catalyst and that is burned in the regenerator. 

Coke (deposited on the catalyst) which is burned in the regenerator producing energy (electricity, steam) and the necessary heat for the reaction. Produced gases are cleansed when necessary of SOj and NO as well as particles of entrained catalyst. 

This was a Hquid-phase process which used what was described as siUceous zeoUtic catalysts. Hydrogen was not required in the process. Reactor pressure was 4.5 MPa and WHSV of 0.68 kg oil/h kg catalyst. The initial reactor temperature was 127°C and was raised as the catalyst deactivated to maintain toluene conversion. The catalyst was regenerated after the temperature reached about 315°C. Regeneration consisted of conventional controlled burning of the coke deposit. The catalyst life was reported to be at least 1.5 yr. 

SO2 absorbed from gas with Mg(OH)2 slurry, giving MgSO —MgSO sohds which are calcined with coke or other reducing agent, regenerating MgO and releasing SO2. 

The MTO process employs a turbulent fluid-bed reactor system and typical conversions exceed 99.9%. The coked catalyst is continuously withdrawn from the reactor and burned in a regenerator. Coke yield and catalyst circulation are an order of magnitude lower than in fluid catalytic cracking (FCC). The MTO process was first scaled up in a 0.64 m /d (4 bbl/d) pilot plant and a successfiil 15.9 m /d (100 bbl/d) demonstration plant was operated in Germany with U.S. and German government support. 

The catalyst is employed in bead, pellet, or microspherical form and can be used as a fixed bed, moving bed, or fluid bed. The fixed-bed process was the first process used commercially and employs a static bed of catalyst in several reactors, which allows a continuous flow of feedstock to be maintained. The cycle of operations consists of (/) the flow of feedstock through the catalyst bed (2) the discontinuance of feedstock flow and removal of coke from the catalyst by burning and (J) the insertion of the reactor back on-stream. The moving-bed process uses a reaction vessel, in which cracking takes place, and a kiln, in which the spent catalyst is regenerated and catalyst movement between the vessels is provided by various means. 

During regeneration the coke is burned off the catalyst. The techniques employed are fairly sophisticated so as to maintain the platinum and any other active metals ia a well dispersed form and to restore the original catalyst activity. Regeneration usually takes several days. 

Dehydrogenation of /i-Butane. Dehydrogenation of / -butane [106-97-8] via the Houdry process is carried out under partial vacuum, 35—75 kPa (5—11 psi), at about 535—650°C with a fixed-bed catalyst. The catalyst consists of aluminum oxide and chromium oxide as the principal components. The reaction is endothermic and the cycle life of the catalyst is about 10 minutes because of coke buildup. Several parallel reactors are needed in the plant to allow for continuous operation with catalyst regeneration. Thermodynamics limits the conversion to about 30—40% and the ultimate yield is 60—65 wt % (233). 

The most dominant catalytic process in the United States is the fluid catalytic cracking process. In this process, partially vaporized medium-cut petroleum fractions called gas oils are brought in contact with a hot, moving, freshly regenerated catalyst stream for a short period of time at process conditions noted above. Spent catalyst moves continuously into a regenerator where deposited coke on the catalyst is burnt off. The hot, freshly regenerated catalyst moves back to the reactor to contact the hot gas oil (see Catalysts, regeneration). 

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