Catalysts catalyst losses

Heterogeneous hydrogenation catalysts can be used in either a supported or an unsupported form. The most common supports are based on alurnina, carbon, and siUca. Supports are usually used with the more expensive metals and serve several purposes. Most importandy, they increase the efficiency of the catalyst based on the weight of metal used and they aid in the recovery of the catalyst, both of which help to keep costs low. When supported catalysts are employed, they can be used as a fixed bed or as a slurry (Uquid phase) or a fluidized bed (vapor phase). In a fixed-bed process, the amine or amine solution flows over the immobile catalyst. This eliminates the need for an elaborate catalyst recovery system and minimizes catalyst loss. When a slurry or fluidized bed is used, the catalyst must be separated from the amine by gravity (settling), filtration, or other means. 

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). 

Much effort has been made by catalyst manufacturers to improve catalyst atttition resistance and thus reduce the formation of fines (see Catalysts, supported). In the 10-year petiod from 1980 to 1990, most catalyst manufacturers improved the atttition resistance of their catalyst by a factor of at least 3—4. This improvement was achieved even though the catalyst zeoHte content duting this petiod was continually increasing, a factor that makes achieving catalyst hardness more difficult. As an example of the type of atttition improvement that has been achieved, the catalyst atttition index, which is directiy related to catalyst loss rate in a laboratory attrition test, decreased from 1.0 to 0.35 for one constant catalyst grade during 1989—1990 (37). 

The distance above the catalyst bed in which the flue gas velocity has stabilized is refened to as the transport disengaging height (TDH). At this distance, there is no further gravitation of catalyst. The center-line of the first-stage cyclone inlets should be at TDH or higher otherwise, excessive catalyst entrainment will cause extreme catalyst losses. 

While there are hydroformers still operating, reforming today is generally carried out in fixed bed units using platinum catalysts, because of their superior product yield and distribution. Fluid platinum catalyst processes are not feasible because catalyst losses would be too great. 

Perhaps the most important concern in cyclone selection is that they have the required collection efficiency. In a large cat cracker, two stages of cyclones in series must have a combined efficiency of 99.99% to keep catalyst losses to an acceptable... 

In cases in which product solubility in the ionic liquid and the product s boiling point are high, the extraction of the product from the ionic liquid with an additional organic solvent is frequently proposed. This approach often suffers from some catalyst losses (due to some mutual solubility) and causes additional steps in the workup. Moreover, the use of an additional, volatile extraction solvent may nullify the green solvent motivation to use ionic liquids as nonvolatile solvents. 

The hydration reaction is carried out in a reactor at approximately 300°C and 70 atmospheres. The reaction is favored at relatively lower temperatures and higher pressures. Phosphoric acid on diatomaceous earth is the catalyst. To avoid catalyst losses, a water/ethylene mole ratio less than one is used. Conversion of ethylene is limited to 4-5% under these conditions, and unreacted ethylene is recycled. A high selectivity to ethanol is obtained (95-97%). 

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 ... 

Early FCC units had soft catalyst and inefficient cyclones with substantial carryover of catalyst to the main column where it was absorbed in the bottoms. Those FCC units controlled catalyst losses two ways. First, they used high recycle rates to return slurry to the reactor. Second, the slurry product was routed through slurry settlers. 

The PSD is an indicator of the fluidization properties of the catalyst. In general, fluidization improves as the fraction of the 0-40 micron particles is increased however, a higher percentage of 0-40 micron particles will also result in greater catalyst losses. 

Bulk density can be used to troubleshoot catalyst flow problems. A too-high ABD can restrict fluidization, and a too-low ABD can result in excessive catalyst loss. Normally, the ABD of the equilibrium catalyst is higher than the fresh catalyst ABD due to thermal and hydrothermal changes in pore structure that occur in the unit. 

Catalyst Circulation Catalyst Loss Coking/Fouling Flow Reversal... 

Catalyst losses will have adverse effects on the unit operation, the environment, and operating cost. Catalyst losses appear as excessive... 

Changes in the fresh catalyst s physical properties may contribute to catalyst losses. The losses could be due to the fresh catalyst s being soft. Softness is evidenced by the quality of the catalyst binder and the large amount of 0-40 microns. It will increase the attrition tendency of the catalyst and thus its losses. 

Changes in operating parameters also affect catalyst losses. Examples are ... 

To stop excessive catalyst losses, it should be identified whether the loss is from the reactor or the regenerator. In either case, the following general guidelines should be helpful in troubleshooting catalyst losses ... 

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. 

Excessive Catalyst loss can cause Unit Shutdown and possible State or Federel Environmental fines... 

Severe damage to the Unit causing Product loss, revenue loss. Catalyst loss, etc. 

The catalyst losses in either system are moderate and not excessively costly when inexpensive iron catalyst is used (as for production of liquid hydrocarbons). It is questionable, however, whether comparable losses of expensive nickel catalysts (for methanation) could be tolerated. For this reason, it is quite likely that the fluidized catalyst system will be used for methanation only after a cheap methanation catalyst is developed. 

The direction of gas flow through the pellet bed could be important. A pulsating high speed flow of exhaust gases can cause rapid attrition of catalysts, especially if the converter has empty spaces due to catalyst loss or shrinkage, which would promote the internal circulation of catalysts in the converter. The design of a sideflow or an upflow bed must include provisions to avoid empty spaces. A downflow design would minimize these attrition losses. 

Because of their potential for easy recycle and low catalyst losses, Pd-... 

The loss of sulfate during the reaction steps or during regeneration may become a critical issue when analyzing the potential of these materials as commercial catalysts. Sulfate losses during the butene TPD, made evident by the evolution of SO2 (m/e=64), started to occur at about 500°C. We have previously demonstrated the evolution of SO2 in the presence of adsorbates such as ammonia, benzene, or pyridine at temperatures much lower than those required to produce SO2 from clean sulfated zirconia [14]. For instance, A treatment in He at 600°C causes drastic losses which result in a significant drop in activity (see Fig. 3) It is... 

In addition to the general improvement of transfer in micro reactors, there is evidence that the voltage of electroosmotic flow (for EOF see [14]) in combination with the large internal surface area in glass chips can induce hydroxide ion formation [6]. Concerning catalyst loss, there is no obvious direct correlation rather, micro reactors can act as mini fixed beds fixing heterogeneous catalyst particles. 

In addition, it was assumed that too high reactivation temperatures were used, as a comparison with literature protocols reveals [60, 62]. Cracks in the plate and void areas with catalyst loss seem to corroborate this assumption. 

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