Catalyst fines

The most obvious way to reduce an aldehyde or a ketone to an alcohol is by hydro genation of the carbon-oxygen double bond Like the hydrogenation of alkenes the reac tion IS exothermic but exceedingly slow m the absence of a catalyst Finely divided metals such as platinum palladium nickel and ruthenium are effective catalysts for the hydrogenation of aldehydes and ketones Aldehydes yield primary alcohols... 

Fluidized-bed reaction systems are not normally shut down for changing catalyst. Fresh catalyst is periodically added to manage catalyst activity and particle size distribution. The ALMA process includes faciUties for adding back both catalyst fines and fresh catalyst to the reactor. 

Process water streams from vinyl chloride manufacture are typically steam-stripped to remove volatile organics, neutralized, and then treated in an activated sludge system to remove any nonvolatile organics. If fluidized-bed oxychlorination is used, the process wastewater may also contain suspended catalyst fines and dissolved metals. The former can easily be removed by sedimentation, and the latter by precipitation. Depending on the specific catalyst formulation and outfall limitations, tertiary treatment may be needed to reduce dissolved metals to acceptable levels. 

To reduce catalyst losses even further, additional separation equipment external to the regenerator can be installed. Such equipment includes third-stage cyclones, electrostatic precipitators, and more recentiy the Shell multitube separator, which is Hcensed by the Shell Oil Co., UOP, and the M. W. Kellogg Co. The Shell separator removes an additional 70—80% of the catalyst fines leaving the first two cyclones. Such a third-stage separator essentially removes from the due gas stream all particles greater than 10 p.m (36). 

Recovered catalyst and blowdown gas (- 3% of the flue gas) exit from the bottom of the separator to an electrostatic precipitator or to a small, fourth-stage cyclone for further concentration of catalyst fines. The flue gas, with 70—90% of the catalyst particles removed, passes from the separator into the power expander. 

In a hot gas expander, the major problems associated with catalyst fines are centered on erosion of components and particulate plugging. Either problem can cause machine vibration and sometimes power train emergency shutdown. Because many failures have resulted from these factors, machinery manufacturers recommend that the maximum permissible solids concentration upstream of an expander not exceed 200 ppm. It is further stipulated that 97% of the particles be smaller than 10 p. Allowing concentrations of 160 ppm with 95% of the particle less than 10 p is considered reasonable. 

Modify the FCCU to allow the use of catalyst fines - Some FCCUs can be modified to recycle some of the catalyst fines generated. 

NICKEL CATALYST, FINELY DIVIDED, ACTIVATED OR SPENT 1378 ... 

Internal Equipment Blockage bv Collapsed Internals - Contingencies such as collapsed reactor bed vessel internals (e.g., fixed-bed reactor grids, coked catalyst beds, accumulation of catalyst fines, plugging of screens and strainers, lines blocked with sediments, etc.) should be considered to identify any overpressure situations that could result. The use of the "1.5 Times Design Pressure Rule" is applicable in such cases, if this is a remote contingency. 

A salient feature of the fluidized bed reactor is that it operates at nearly constant temperature and is, therefore, easy to control. Also, there is no opportunity for hot spots (a condition where a small increase in the wall temperature causes the temperature in a certain region of the reactor to increase rapidly, resulting in uncontrollable reactions) to develop as in the case of the fixed bed reactor. However, the fluidized bed is not as flexible as the fixed bed in adding or removing heat. The loss of catalyst due to carryover with the gas stream from the reactor and regenerator may cause problems. In this case, particle attrition reduces their size to such an extent where they are no longer fluidized, but instead flow with the gas stream. If this occurs, cyclone separators placed in the effluent lines from the reactor and the regenerator can recover the fine particles. These cyclones remove the majority of the entrained equilibrium size catalyst particles and smaller fines. The catalyst fines are attrition products caused by... 

Even with proper operation of the reactor and regenerator cyclones, catalyst particles smaller than 20 microns still escape from both of these vessels. The catalyst fines from the reactor collect in the fractionator bottoms slurry product storage tank. The recoverable catalyst fines exiting the regenerator are removed by the electrostatic precipitator or lost to the environment. Catalyst losses are related to ... 

The bottom section of the main column provides a heat transfer zone. Shed decks, disk/doughnut trays, and grid packing are among some of the contacting devices used to promote vapor/liquid contact. The overhead reactor vapor is desuperheated and cooled by a pumparound stream. The cooled pumparound also serves as a scrubbing medium to wash down catalyst fines entrained in the vapors. Pool quench can be used to maintain the fractionator bottoms temperature below coking temperature, usually at about 700°F (370°C). 

The ash content of the DO is affected by the reactor cyclone s performance and catalyst physical properties. To meet the CBFS ash requirement (maximum of 0.05 wt%), DO product may need to be filtered for the removal of the catalyst fines. 

An increase in the recovery of catalyst fines from the electrostatic precipitator or the tertiary separator... 

Consider switching to a harder catalyst. For a short-term solution, if the losses are from the reactor side, consider recycling slurry to the riser. If the catalyst losses are from the regenerator, consider recycling catalyst fines to the unit. 

The main concerns in the design and operation of a power recovery system are catalyst fines and temperature. Catalyst fines will lead to serious blade wear, deposits, power loss, and rotor vibration. Deposit occurs most frequently where flue gas velocities are at maximum levels, such as blade outer diameter. 

One disadvantage of fluidized beds, as discussed previously, is that attrition of the catalyst can cause the generation of catalyst fines, which are then carried over from the bed and lost from the system. This carryover of catalyst fines sometimes necessitates cooling the reactor effluent through direct contact heat transfer by mixing with a cold fluid, since the fines tend to foul conventional heat exchangers. 

The curves in Fig. 22 were calculated by means of the above equation, the points being experimental values. Figure 24 (Kwauk, Wang, Li, Chen and Shen, 1985) shows empirical correlations for the constants e and ea for FCC catalyst, fine and coarse alumina, pyrite cinder and iron ore concentrate. 

Alkyl chloride Olefins are chlorinated to alkyl chlorides in a single fluidized bed. In this process, HCl reacts with 02 over a copper chloride catalyst to form chlorine. The chlorine reacts with the olefin to form alkyl chloride. The process was developed by Shell Development Co. and uses a recycle of catalyst fines in aqueous HCl to control the temperature [Chem. Proc. 16 42 (1953)]. 

Catalytic cracking Heater stack gas (CO, SOx, NOx, hydrocarbons, and particulates), fugitive emissions (hydrocarbons), and catalyst regeneration (CO, NOx, SOx, and particulates) Spent catalysts (metals from cmde oil and hydrocarbons), spent catalyst fines from electrostatic precipitators (alnminum silicate and metals)... 

Hydrotreating/ Heater stack gas (CO, SOx, NOx, Spent catalyst fines... 

Catalytic processes (finid catalytic cracking, catalytic hydrocracking, hydro-treating, isomerization, ether manufacture) also create some residuals in the form of spent catalysts and catalyst fines or particulates. The latter are sometimes separated from exiting gases by electrostatic precipitators or filters. These are collected and disposed of in landfills or may be recovered by off-site facilities. The potential for waste generation and hence leakage of emissions is discussed below for individual processes. 

Like catalytic cracking, hydrocracking processes generate toxic metal compounds, many of which are present in spent catalyst sludge and catalyst fines generated from catalytic cracking and hydrocracking. These include metals such as nickel, cobalt, and molybdenum. 

Hydrotreating also produces some residuals in the form of spent catalyst fines, usually consisting of aluminum silicate and some metals (e.g., cobalt, molybdenum, nickel, tungsten). Spent hydrotreating catalyst is now listed as a hazardous waste (K171) (except for most support material). Hazardous constituents of this waste include benzene and arsenia (arsenic oxide, AS2O3). The support material for these catalysts is usually an inert ceramic (e.g., alumina, AI2O3). 

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