Deactivation regeneration

Water quality and components present in the solution matrix affect the catalytic reaction. Acids dissolve the Pd metal, while bases promote some reactions. Batch tests showed that oxygen, sulfate, nitrate, and nitrite slowed reaction somewhat sulfite slowed it significantly, and bisulfide deactivated the catalyst completely. Column tests of TCE reaction on a Pd/alumina catalyst with DI water caused no observable deactivation, but deactivation was seen with the reaction of TCA on Pd/C. In the Pd/alumina column, the addition of nitrate to DI water did slow the reaction phosphate, carbonate, and carbon dioxide caused some deactivation. Regeneration through evacuation and oxidation of the catalyst improved the activity. 

Figure 6. n-Hexane adsorption capacity as a function of the number of deactivation-regeneration cycles. S1Q is the initial zeolite material before Ga ion-exchange. 

Related work includes investigations of carbon formation during hydrogenation of C5 hydrocarbons catalyzed by nickel and palladium (5P) interactions of N2O with a hydrotalcite-derived multimetallic mixed oxide catalysts (60,61) changes in mass of solid oxides (62) methanol sorption in Nafion-117 (proton-exchange) membranes (63) vanadyl pyrophosphate catalysts for butane oxidation (64-66) and deactivation/regeneration of a Rb0 c/Si02 catalyst for methylene valerolactone synthesis (67). 

The overall objective of the project was to develop catalytic wood fired boilers with low emissions of unbumed components. In this specific work the objective was to evaluate the possibility to use net-based catalysts instead of the more commonly applied monolithic catalysts. The conversion over the catalyst when integrated in the wood fired boiler is measured and compared with calculated values and the deactivation, regeneration and possibilities to prolong the lifetime of the catalyst are shown. 

Coke formation is a common cause of catalyst deactivation. Regeneration of coked catalyst can generally be achieved by gasification of the coke deposits with oxygen, carbon dioxide, steam or hydrogen. The first of these methods gives rise to oxidative regeneration processes with which this work is concerned. 

Albemarle and ABB Lummus Global began collaboration in 1996 to develop a catalyst/process combination that addresses the aforementioned product selectivity and deactivation/regeneration issues. The following targets were the focal points of our efforts ... 

Next, reactors may be designed to accommodate rapid deactivation-regeneration cycles. The best example is catalytic cracking where coke deposition is so fast that decay takes only minutes. Since, in this case, the feed is the precursor to coke, treatment or guard chambers are not practical. The only solution is to use fluidized beds, which provide reaction and regeneration in a continuous cycle. Other cases are slurry and moving bed reactors, w hen deactivation is not so rapid. 

The following questions can in principle be addressed with spectroscopy (1) Zeolite synthesis what are the mechanisms of ZSM-5 synthesis and how do they influence the quality of the catalyst synthesized (2) Catalyst characterization what are the structure and composition of the zeolite, and what is the configuration of the active site for methanol conversion (3) How do methanol and dimethylether interact with the active sites i.e. what species are present in the catalyst in the initial stages of methanol conversion (4) What are the subsequent reaction pathways leading to the final alkane, alkene and aromatic products (5) What causes catalyst deactivation This question concerns both the temporary deactivation associated with coke formation, which can be reversed by oxidative regeneration, and the permanent deactivation which occurs after repeated deactivation-regeneration cycles. 

Processes Occurring during Deactivation/Regeneration of a Vanadia/AIumina Catalyst under Propane Dehydrogenation Conditions... 

Catalysts were submitted to a series of deactivation-regeneration cycles (DRC). Coke deposit on fresh samples was carried out by means of an 4.5 h isobutane dehydrogenation reaction run, under the conditions stated below. Then, the hydrocarbon feeding was replaced by an inert steam (Ar), simultaneously cooling the reactor up to 250°C. Once this temperature has been reached, Ar was replaced by an air flow and the temperature was raised up to 550°C, with a heating rate of 5°Cmin. After one hour under this condition, the samples were cooled to room temperature, and kept that way overnight. In this way, samples are ready to be use in a new cycle. 

In order to evaluate the catalyst resistance in successive deactivation-regeneration cycles (DRC), they were tested under more severe conditions in the dehydrogenation reaction. Pure isobutane at 550°C was used as feed. Under these conditions, the deactivation is accelerated and besides, the work is carried out imder conditions nearer the ones of the industrial operation. 

The activation-regeneration study performed with sample c comprises three steps 1) toluene oxidation at 440 °C, 2) toluene flow interruption followed by heating of the reactor bed in air flow up to 490 °C 3) cooling of the reactor bed down to 440 °C followed by toluene oxidation. In figure 3 the temperature profile and the evolution of toluene conversion during these three steps deactivation - regeneration - deactivation, is shown. The comparison... 

Figure3. Toluene conversion during deactivation-regeneration-deactivation process.

The averaged activity of a fluidized bed can be maintained even though each catalyst particle undergoes rapid deactivation-regeneration. However, this process does not apply to situations in which the product and selectivity are sensitive to catalyst activity, as deactivated catalysts may lead to undesirable products. 

Deactivation/Regeneration for Methylene Valerolactone Synthesis, Appl Catal A. 2004,272,241-248. 

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