Catalysts carbon removal

Catalysts that do not contain potassium lose activity very quickly because of coke deposition on the surface of the catalyst. Chemical changes that occur when the catalyst is removed from the operating environment make it very difficult to determine the nature of most of the promoter elements during the reaction, but potassium is always found to be present as potassium carbonate in the used catalyst. The other promoters are claimed to increase selectivity and the operating stabiUty of the catalyst. 

Regeneration of noble metal catalysts to remove coke deposits can successfully restore the activity, selectivity, and stabiUty performance of the original fresh catalyst (6—17). The basic steps of regeneration are carbon bum, oxidation, and reduction. Controlling each step of the regeneration procedure is important if permanent catalyst damage is to be avoided. 

Oxidation and chlorination of the catalyst are then performed to ensure complete carbon removal, restore the catalyst chloride to its proper level, and maintain full platinum dispersion on the catalyst surface. Typically, the catalyst is oxidized in sufficient oxygen at about 510°C for a period of six hours or more. Sufficient chloride is added, usually as an organic chloride, to restore the chloride content and acid function of the catalyst and to provide redispersion of any platinum agglomeration that may have occurred. The catalyst is then reduced to return the metal components to their active form. This reduction is accompHshed by using a flow of electrolytic hydrogen or recycle gas from another Platforming unit at 400 to 480°C for a period of one to two hours. 

Process parameters are set to obtain the required octane level ( 90). In the process, minute amounts of carbon are deposited on the catalyst which reduces the product yield, but can be removed by batch burning. Continuous regeneration avoids periodic shutdowns and maximizes the high-octane yield. This employs a moving bed of catalyst particles that is circulated ihrnugli a regenerator vessel, for carbon removal, and returned to the reactor. 

It was dissolved in ethyl acetate (700 ml) and hydrogenated at ambient conditions over a palladium (5%) on carbon catalyst (18 g). The catalyst was removed by filtration and washed with ethyl acetate. The combined filtrates were extracted with water at pH 2.5 by addition of dilute hydrochloric acid. Lyophilization of the aqueous phase gave the hydrochloride of r-ethoxycarbonyloxyethyl 6-(D-a-aminophenylacetamido)penioillinate (94 g), MP... 

To the reduction mixture was then added 3.5 g of 5% palladium on carbon catalyst and the mixture was hydrogenated under a hydrogen pressure of 50 psi at room temperature for 12 hours. The catalyst was removed by filtration and the filtrate was evaporated to a small volume. The concentrated filtrate was dissolved in diethyl ether and the ethereal solution was saturated with anhydrous hydrogen chloride. The reduction product, 3,4-dimethoxy-N-[3-4-methoxyphenyl)-1 -methyl-n-propy 11 phenethylamine was precipitated as the hydrochloride salt. The salt was filtered and recrystallized from ethanol melting at about 147°C to 149°C. 

A solution containing 741 g (5.0 mols) of 1-phenyl-2-propylidenylhydrazine, 300 g (5.0 mols) of glacial acetic acid and 900 cc of absolute ethanol was subjected to hydrogenation at 1,875 psi of hydrogen in the presence of 10 gof platinum oxide catalyst and at a temperature of 30°C to 50°C (variation due to exothermic reaction). The catalyst was removed by filtration and the solvent and acetic acid were distilled. The residue was taken up In water and made strongly alkaline by the addition of solid potassium hydroxide. The alkaline mixture was extracted with ether and the ether extracts dried with potassium carbonate. The product was collected by fractional distillation, BP B5°C (0.30 mm) yield 512 g (68%). 

The carbon removal reaction supposedly takes place at two-phase boundary of a solid catalyst, a solid reactantfcarbon particulate) and gaseous reactants(02, NO). Because of the experimental difficulty to supply a solid carbon continuously to reaction system, the reaction have been exclusively investigated by the temperature programmed reaction(TPR) technique in which the mixture of a catalyst and a soot is heated in gaseous reactants. 

This latter point was stressed by some of us in a recent report studying NO storage and reduction on commercial LSR (lean storage-reduction) catalysts, in order to catch valuable information about the behaviour of typical NO storage materials in real application conditions. Nature, thermal stability and relative amounts of the surface species formed on a commercial catalyst upon NO and 02 adsorption in the presence and in the absence of water were analysed using a novel system consisting of a quartz infrared reactor. Operando IR plus MS measurements showed that carbonates present in the fresh catalyst are removed by replacement with barium nitrate species after the first nitration of the material. Nitrate species coordinated to different barium sites are the predominant surface species under dry and wet conditions. The difference in the species stabilities suggested that barium sites possess different basicity and, therefore, that they are able to stabilize nitrates at different temperatures. At temperatures below 523 K, nitrite species were observed. The presence of water at mild temperatures in the reactant flow makes unavailable for NO adsorption the alumina sites [181]. 

Temperature plays an important role in determining the amount and type of the carbon deposit. Generally during FTS at higher temperatures the amount of carbon deposited will tend to increase,30-31 but the case is often not so straightforward. An example of temperature dependence on the rate of carbon deposition and deactivation is the case of nickel CO hydrogenation catalysts, as studied by Bartholomew.56 At temperatures below 325°C the rate of surface carbidic carbon removal by hydrogenation exceeds that of its formation, so no carbon is deposited. However, above 325°C, surface carbidic carbon accumulates on the surface... 

D. 2,3-Diamino pyridine (Note 12). In an apparatus for catalytic hydrogenation (Note 13) 56.4 g. (0.3 mole) of 2,3-diamino-5-bromopyridine suspended in 300 ml. of 4% sodium hydroxide solution is shaken with hydrogen in the presence of 1.0 g. of 5% palladized strontium carbonate (Note 14). When absorption of hydrogen is completed, the catalyst is removed by filtration, and, after saturation with potassium carbonate (about 330 g. is required), the resulting slushy mixture is extracted continuously with ether until all the precipitate completely disappears (usually about 18 hours, but this depends on the efficiency of the extraction apparatus). The ether is removed by distillation, and the residue of crude 2,3-diaminopyridine is recrystallized from benzene (about 600 ml. is required) using 3 g. of activated charcoal and filtering rapidly through a preheated Buchner funnel. The yield of 2,3-diaminopyridine, obtained as colorless needles, m.p. 115-116°, pKa 6.84, is 25.5-28.0 g. (78-86%) (Note 15). 

The function of the electrolyte membrane is to facilitate transport of protons from anode to cathode and to serve as an effective barrier to reactant crossover. The electrodes host the electrochemical reactions within the catalyst layer and provide electronic conductivity, and pathways for reactant supply to the catalyst and removal of products from the catalyst [96], The GDL is a carbon paper of 0.2 0.5 mm thickness that provides rigidity and support to the membrane electrode assembly (MEA). It incorporates hydrophobic material that facilitates the product water drainage and prevents... 

Pure decarbonylation typically employs noble metal catalysts. Carbon supported palladium, in particular, is highly elfective for furan and CO formation.Typically, alkali carbonates are added as promoters for the palladium catalyst.The decarbonylation reaction can be carried out at reflux conditions in pure furfural (165 °C), which achieves continuous removal of CO and furan from the reactor. However, a continuous flow system at 159-162 °C gave the highest activity of 36 kg furan per gram of palladium with potassium carbonate added as promoter. In oxidative decarbonylation, gaseous furfural and steam is passed over a catalyst at high temperatures (300 00 °C). Typical catalysts are zinc-iron chromite or zinc-manganese chromite catalyst and furfural can be obtained in yields of... 

Recently, UV laser stimulation of catalyst samples has been developed to overcome the problem of interference by coke (carbon deposition) on catalysts.Fig. 9 shows a typical Raman data set that was obtained for carbon deposition as a function of temperature. To explore different coke formation behavior, the reaction of propene on a zeolite was performed. The spectra obtained were (A) C3H6/He flow at 773 K for 3 h (B) O2 flow at 773 K for 1 h and (C) O2 flow at 873 K for 1 h. This data shows that most of the carbon, identified as polyaromatic and pregraphite, can be removed at 773 K with oxygen. However there is still carbon present as identified by the broad band at 1610 cm suggesting that carbon is in a more inert form such as coke. Not until the temperate is taken to 873 K with oxygen is that carbon removed. 

The formation of carbon is in some cases reversible. The catalyst can be taken of stream and the carbon removed by oxidation. 

To a 0.02 M soln of 2-alkyl-2,5-dihydro-l //-pyrrole (85-90% pure) in methanol is added with stirring 5% rhodium on carbon (catalyst/substrate 1 20). The mixture is pressurized (4.6 x 107 Torr) with hydrogen and is stirred at 25 °C for a minimum of 5 h. The catalyst is removed by vacuum filtration, the solution is concentrated under reduced pressure and the residue is purified by bulb-to-bulb distillation to give the product in 95% purity. 

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