Regenerated deactivated catalyst

Figure 5. XRD spectra of the regenerated deactivated catalyst showing PbO and no Pb° after reaction in the absence of O2 at 820 C, 770 C, and 700 C. Legend same as Figure 1, plus A = a-Al203.

Not only does the decreasing catalyst activity lead to a loss of productivity, it is also often accompanied by a lowering of the selectivity. Therefore, in industrial processes great efforts are made to avoid catalyst deactivation or to regenerate deactivated catalyst. Catalyst regeneration can be carried out batchwise or preferably continuously while the process is running. 

The Snamprogetti fluidized-bed process uses a chromium catalyst in equipment that is similar to a refinery catalytic cracker (1960s cat cracker technology). The dehydrogenation reaction takes place in one vessel with active catalyst deactivated catalyst flows to a second vessel, which is used for regeneration. This process has been commercialized in Russia for over 25 years in the production of butenes, isobutylene, and isopentenes. 

A successful procedure for the formation of 2,5-di-t-butylfuran involves reaction of the parent heterocycle with f-butyl chloride in the presence of iron(III) chloride and iron(III) oxide. Iron(III) oxide acts as a hydrogen chloride scavenger and at the same time regenerates the catalyst. Concurrent polymerization normally deactivates the catalyst (82CI(L)603). 

Carbon monoxide has been found to poison cobalt molybdate catalysts. It causes not only instantaneous deactivation but a cumulative deactivation as well. It should be removed from treat gas entirely or at least reduced to a very low value. Carbon dioxide also must be removed since it is converted to CO in the reducing atmosphere employed in Hydrofining. Liquid water can damage the structural integrity of the catalyst. Water, in the form of steam does not necessarily hurt the catalyst. In fact 30 psig steam/air mixtures are used to regenerate the catalyst. Also, steam appears to enhance the catalyst activity in... 

The process is characterized by high yield (nearly complete hydrogenation of acetylenes) and high selectivity (only a small loss of butadiene by hydrogenation). The process does not lead to polymerization, which might otherwise cause catalyst deactivation, and only infrequent regeneration of catalyst is necessary. 

It should be noted that the catalytic activity falls markedly with an increase in the time-on-stream. Similar falls in catalytic activity were also observed in the cases of the other W-based mixed oxides, such as W-Sn, W-Ti, and W-Mo. It was also found that the deactivated catalysts can easily be regenerated by a heat-treatment at 500°C in air for 1 h. 

The purpose of this review is to integrate the literature on this topic, along with some of the work we have performed, to provide a clearer understanding on the role of carbon as a deactivation mechanism. The minimization of carbon by promotion, regeneration of catalysts, and some selectivity implications will also be briefly discussed. 

Figure 12.4 Some modes of operation of semicontinuous reactors (a) gas-liquid reaction (b) gas-solid (catalyst or reactant) reaction (c) cyclic operation (reaction)-) and regeneration)- -)) for deactivating catalyst...

The previous chapters assumed that the effectiveness of catalysts in promoting reactions remains unchanged with time. Often this is not so, in which case the activity usually decreases as the catalyst is used. Sometimes this drop is very rapid, in the order of seconds sometimes it is so slow that regeneration or replacement is needed only after months of use. In any case, with deactivating catalysts regeneration or replacement is necessary from time to time. 

This moderately endothermic process results in the formation of 2 moles of hydrogen per mole of methane consumed above a certain threshold reaction temperature. A gradual catalyst deactivation is expected due to the accumulation of carbon on the catalyst. The catalyst can be regenerated by removing the carbon on the catalyst in a separate step. Thus, hydrogen production by this approach involves two distinct steps (a) catalytic decomposition of methane and (b) regeneration of catalyst. 

The model provides a performance reference to evaluate commercial reformer operation by taking into account the wide variation in operating conditions, feedstocks, and product octane typically experienced commercially. Such variations in reformate yield have already been discussed in Fig. 29, where the model effectively predicts the yield variations. As a monitoring tool, the model is routinely used to assess reformer yield and activity losses due to catalyst deactivation relative to fresh catalyst model estimates. When commercial yield and/or activity losses relative to the model are uneconomical, a decision to regenerate the catalyst is made. A typical monitoring trend (Fig. 36) illustrates the use of the model as a performance reference. 

THERMOFOR PROCESS. A moving-bed catalytic cracking process in which petroleum vapor is passed up through a reactor countercurrent to a flow of small beads or catalyst. The deactivated catalyst then passes through a regenerator and is recirculated. 

The condensation of methyl N—phenyl carbamate witli IICHO to methylene diphenyl diurethane has been studied in a batch reactor in the presence of cation exchanged resins. Unlike conventional H0SO4 catalyst, fresh resin catalysts did not form a byproduct N—benzyl compound. However, accumulation of water from repeated uses of the catalyst caused a decreased activity and the formation of the byproduct. The deactivated catalyst could be completely regenerated by drying in vacuo. Ethylacetate and toluene were found to be efficient solvents with the resin catalysts. 

If the avoidance of deactivation by poisoning is difficult, could a partially deactivated catalyst be regenerated by chemical or physical means In the oil and chemical industry, catalyst reactivation is a standard procedure, done sometimes in situ or after removal from the reactor. Logistically, it does not seem to be feasible to remove an automotive... 

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