Catalyst carryover

A major concern in die application of power recovery expanders in die FCC process is catalyst carryover from die diird-stage separator dial enters die expander. 

Carryover of catalyst from the reactor disengager vessel to the main fractionator is always a concern and particularly susceptible during start-up operations. The modification of the riser termination as part of a short contact time riser revamp, depicted in Figure 7.3, has increased the concern for catalyst carryover. 

Indications that catalyst carryover is occurring include ... 

If catalyst carryover starts, the following measures will help avoid a lengthy shutdown ... 

Fluidized bed reactors typrcally are vertical cylindrical vessels equipped with a support grid and feed sparger system for adequate fluidization and feed distribution, internal cooling coils for heat removal, and either external or internal cyclones to minimize catalyst carryover. Fluidizauon of the catalyst assures intimate contact between feed and product vapors, catalyst, and heat-transfer surfaces, and results in a uniform temperature within the reactor. Reaction heat can be removed by generating steam within the cooling coils or by some oilier heat-transfer medium. 

In packed bed reactors the solid catalyst is held stationary by plates at the top and bottom of the bed. In contrast, in fluidized bed reactors, the catalyst bed is relatively loosely packed, and there is no plate at the top. Rapid fluid flow from the bottom raises the bed and ensures good mixing, leading to insignificant temperature or concentration gradients. However, due to high fluid velocity some catalyst carryover is common. 

The biphasic system has been evaluated in terms of activity, selectivity, recyclability and lifetime of the ionic liquid, in a continuous flow pilot operation. A representative industrial feed (Raffinate II), composed of 70 wt.% butenes (27% of which is 1-butene) and 1.5 wt.% isobutene (the remainder being n-butane and isobutane) enters continuously into the well mixed reactor containing the ionic liquid and the nickel catalyst. Injection of fresh catalyst components can be made to compensate for the detrimental effects of random impurities present in the feed and for a slight catalyst carryover by the organic phase. The reactor is operated... 

The oxychlorination reactor is a vertical cylindrical shell made of carbon steel with a support grid/air sparger system and internal cooling coils. Internal or external cyclones are used to minimize catalyst carryover. The reactor internal parts are made from corrosion-resistant alloy. The reactor has many design features depicted in Fig. 1. 

A venturi scrubber is also provided to remove the small quantity of catalyst carryover from the cyclones and to protect downstream switch condensers in the event that the cyclones malfunction. 

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

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... 

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. 

Catalyst flux is defined as catalyst circulation rate divided by the full cross-sectional area of the stripper. For efficient stripping, it is desirable to minimize the catalyst flux to reduce the carryover of hydrogen-rich hydrocarbons into the regenerator. 

Entrainment Separators. In any process in which the product is volatilized, including both Gas Recycle and Liquid Recycle, ppm or ppb levels of metal catalyst may be entrained in the vapors leaving the separation system. Entrainment separators (Figure 2.9) are often included to recover the metal. Vaporous product effluent from a gas recycle reactor may be sent to a separator where it is passed through a demisting pad to return some aldehyde and condensation product and particularly to prevent potential carryover of catalyst. [6]... 

Anyone who is seriously involved in catalytic cracking, whether as an operator, a catalyst manufacturer, or a researcher, soon learns how severely sodium, vanadium, nickel, iron, and copper act as poisons. In the past, FCC feedstock preparation via vacuum distillation was to a considerable extent, determined by metal carryover. Generally, metal carryover to the fluid unit was limited to 0.1 ppm or less of each of these metals. 

An additional problem with the powdered silicate catalyst in the polymer melt is that carryover (i.e. entrainment) of fine catalyst particles into the diesel stream can occur. 

X-Ray. X-ray analysis data, summarized in Table 1, shows that the deposit contains 20.8 % nickel (Ni) plus vanadium(V), and 8.8 % sulfur (S). Interestingly, the data reveals only 2.5% of each of the primary catalyst components aluminum (Al) and molybdenum (Mo) hence, it is unlikely that carryover of the catalyst contributes significantly to the accumulation of V and Ni. Furthermore, it appears unlikely that major amounts of V and Ni derive from the reactor metallurgy, as the deposit contains only 1.7% iron (Fe). The rejection of "vanadium-and nickel-sulfide"[5] from the catalyst surface may account for the high amounts of V, Ni, and S. 

Occluded or Cat/Oil Coke This coke results from carryover of hydrocarbons adsorbed in the catalyst pores and by incomplete stripping in the stripper. It can be reduced by shifting the pore size distribution to higher values by ... 

The Difasol reaction involves a mechanically stirred reactor and settlers. An injection of fresh catalyst components is defined to compensate the detrimental effects of accidental impurities present in the feed and slight carryover of the catalyst. Mixing of the solvent phase with the organic phase ensures advantageous butene conversion. However, importantly, the stirring power combined with a high... 

Inorganic impurities are normally detected and quantified using pharmacopoeia or other appropriate procedures. Carryover of catalysts to a new drug substance should be evaluated during development. The need for inclusion or exclusion of inorganic impurities in a new drug substance specification should be discussed. Acceptance criteria should be based on pharmacopoeial standards or known safety data. 

From a practical standpoint catalyst loss due to carryover with the gas stream from the reactor and regenerator may be an important problem. Attrition of particles decreases their size to a point where they are no longer fluidized, but move with the gas stream. It has been customary to recover most 6f these catalyst fines by cyclone separators and electrical precipitation equipment placed in the effluent lines from reactor and regenerator. 

Rhodium complexes generated from the polyethylene glycol)-functionalized phosphine 9 (n = 1, x = 0, R = Me, Bu), which should behave as a nonionic surfactant and be able to induce micelle formation, have been used as catalysts in the hydroformylation of 1-dodecene in an aqueous/organic two-phase system [31]. The conversion of 1-dodecene was 80% and the n/iso ratio 60 40, with no carryover of the rhodium catalyst into the organic phase. The Rh/9 (n = 1, x = 0, R = Me, Bu) catalyst remained active after one recycle step [31],... 

However, its distribution has not been extensively studied because a suitable quantitative method for low concentrations has not been available. In addition to naturally occurring molybdenum, minute quantities can be introduced into distillate fuels by exposure to some processing catalysts or by carryover from the crude. 

No plugging of the small inlets in the control valve downstream of the reactor was noted, and fines formation and carryover of catalyst were not a problem at the low fluidization velocities used in this test. Bed expansion was not measured directly, but it was calculated to be about 7-10%. 

In the DCDA process, the candle type demister developed by Monsanto (USA) was the major breakthrough. This prevents 99.99% of mist above 1 pm. Any mist carryover would hurt not only the heat exchangers but would also affect the catalyst activity in the converter passes 4 and 5. 

---