Wyniki wyszukiwania - Biblioteka Nauki

1

Badanie procesu nieodwracalnej dezaktywacji stopowych katalizatorów żelazowych do syntezy amoniaku

100%

Narkiewicz U.

Prace Naukowe Politechniki Szczecińskiej. Instytut Technologii Nieorganicznej

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2000

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tom Nr 554(6)

9-148

EN

The process of irreversible (chemical and thermal) deactivation of fused iron catalyst has been studied. Laboratory simulation of the poisoning process under industrial conditions has been carried out. The process may take place either during manufacture, transport, manipulation and storage (catalyst precursor - oxidised form), or during ammonia synthesis (active catalyst reduced form). In the latter case, the deactivating effect can be observed directly after the introduction of poison, while the same effect for the oxidised catalyst requires a long work period. This difference is because the catalyst in its active form adsorbs the poison from the gas phase directly on its active surface. In the case of the catalyst precursor, the poison may form compounds with promoters, sometimes of exceptional stability (e.g. calcium sulphate), which remain in the intergranular space and decompose only to a minor degree during reduction of the catalyst. As a result, the diffusion of poison to the active surface is very slow. It may thus be concluded that traces of poisons in raw materials used for preparation of the catalyst, or contamination during improper transport or charging of the catalyst, may lead to gradual loss of catalytic activity, albeit at a much slower pace than in the case of poisoning of the active catalyst from the gas phase. The effect of three poisons: sulphur, chlorine and phosphorus, on the activity of the catalyst has been compared. It was found that these non-metals are very strong poisons of the iron catalyst, with even minor quantities causing a marked and irreversible loss of activity. The deactivating effects of sulphur and chlorine are similar, and phosphorus is less potent. The process of poisoning continues with two phases: during the first (low poison concentration) significant loss of catalytic activity occurs with increasing poison concentration; during the second (high poison concentration) increasing poison concentrations have little effect on activity and even at very high concentrations some catalytic activity is still observed. Measurements of catalytic activity of the poisoned catalyst have been interpreted using data from a model system (modified surface of monocrystalline iron sample) under ultra-high vacuum conditions. A method for estimating the number of adsorption sites in defects of the monocrystalline sample based on measurements of segregation kinetics has been developed. A mechanism of permanent deactivation of the iron catalyst for ammonia synthesis has been proposed, explaining chemical deactivation at low poison concentrations by simple blocking of active sites, and at higher poison concentrations by reconstruction of the catalyst surface. In the latter case, segregation of poison atoms from the bulk grains or from the intergranular space to the active surface becomes more prominent. Interactions between poison atoms and oxygen atoms (occupying part of the adsorption sites and responsible for thermal stability of the catalyst), as well as between poison atoms and potassium atoms become increasingly important. leading to reconstruction of the surface and loss of catalytic activity. Deactivation is greater for higher poison concentrations and for more negative Gibbs free energy of poison segregation. Thermal deactivation of the iron catalyst is caused by sintering of iron crystallites and elimination of potassium from the active surface. A method for partial regeneration of the iron catalyst has been proposed, based on the addition of potassium into the catalyst bed. Regeneration may be effected through impregnation of the passivated catalyst in the ammonia synthesis reactor using a solution of potassium hydroxide. Before impregnation it is necessary to remove the most poisoned part of the catalyst bed (near the gas inlet where the majority of poisons is adsorbed) and to sieve the catalyst before recharging, in order to avoid excessive pressure drop on the catalyst bed.

2

Wpływ temperatury redukcji na powierzchnię właściwą i aktywną preredukowanego katalizatora żelazowego do syntezy amoniaku

75%

Jasińska I. , Lubkowski K. , Arabczyk W.

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tom T. 82, nr 3

230-233

3

Badanie procesu azotowania katalizatora żelazowego

75%

Kiełbasa K. , Wilk B. , Arabczyk W.

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2013

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tom T. 92, nr 5

859-861

4

Studies of the kinetics of CH4 decomposition to Fe3C on the promoted iron catalysts

75%

Arabczyk W. , Narkiewicz U. , Konicki W. , Grzmil B.

Polish Journal of Chemical Technology

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2002

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tom Vol. 4, nr 3

1-4

EN

The decomposition of methane on the doubly- (A1,O,, CaO) and triply- (K,O, A1,O,, CaO) promoted iron catalyst has been investigated using the thermobalance (considered as an differential reactor). The process of decomposition results in the formation of iron carbide and carbon deposit subsequently. The process was carried out under atmospheric pressure in the temperature range of 500 - 600°C. The rate of Fe3C formation in the kinetic region of the reaction was written using the following expression: r = k-pCH . The apparent activation energy of methane decomposition to Fe,C is equal to 158 kJ/mol for both doubly and triply promoted iron catalysts. The pre-exponential factor k() equals to 1.77-10* and 5.71 105 for doubly and triply promoted catalyst, respectively.

5

Segregacja nanokrystalitów jako sposób na zwiększenie wydajności żelazowego katalizatora w reakcji rozkładu amoniaku

75%

Nowosielecka U.

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2017

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nr 494

189-199

PL

Badano szybkość reakcji katalitycznego rozkładu amoniaku na stosowanym w przemyśle stopowym katalizatorze żelazowym dotowanym trudno redukowalnymi tlenkami promotorów (Al2O3, CaO, K2O) oraz na próbkach tego katalizatora o zmodyfikowanej morfologii. Do modyfikacji katalizatora użyto chemicznej metody do wyodrębnienia z materiału o szerokim rozkładzie wielkości krystalitów frakcji o zawężonym rozkładzie i określonej średniej wielkości krystalitów. Pomiary szybkości reakcji chemicznych przeprowadzono w różniczkowym reaktorze rurowym wyposażonym w układ pomiaru masy oraz miernik stężenia wodoru w fazie gazowej. W wyniku modyfikacji otrzymano nanokrystaliczny materiał, który charakteryzował się ok. 1,6-krotnie większą wydajnością w reakcji katalitycznego rozkładu amoniaku w odniesieniu do próbki referencyjnej, w przeliczeniu na masę użytego katalizatora.

6

Pasywowany katalizator żelazowy do syntezy amoniaku

75%

Hajduk J. , Hajduk M.

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tom Nr 12

318-320

7

The state of studies on iron catalyst for the ammonia synthesis

63%

Arabczyk W.

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tom Vol. 7, nr 3

8-17

EN

The past and present research of the iron catalyst for ammonia synthesis carried out in the Institute of Chemical and Environment Engineering of Szczecin University of Technology has been described. The role of promoters, especially alkali metals, has been explained. The structure of the surface of active iron catalyst has been proposed. The behavior of iron catalyst during the reaction of nitriding has also been shown.

8

Obecny stan wiedzy o katalizatorze żelazowym do syntezy amoniaku

63%

Arabczyk W. , Jasińska I.

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tom T. 85, nr 2

130-137

PL

Na podstawie doniesień literaturowych oraz wyników prac własnych opisano obecny stan wiedzy o katalizatorze żelazowym do syntezy amoniaku. Przedstawiono model powierzchni aktywnej katalizatora żelazowego, w którym założono, że powierzchnia żelaza jest zwilżona tlenkami promotorów oraz, że katalizator w warunkach syntezy amoniaku znajduje się w stanie równowagi. W oparciu o zaproponowany model wyjaśniono mechanizm redukcji oraz dezaktywacji katalizatora.

EN

A review with 78 refs. covering the mechanism of redn. and deactivation of iron catalysts in terms of a catalyst model with the active iron atom surface assumed to be wetted by promoters oxides. Promoters join with the Fe atom via O atom. At >350°C, chem. equil. is rapidly attained in the nanocryst. systems.

9

Ocena aktywności żelazowych katalizatorów syntezy amoniaku w przemysłowych reaktorach typu TVA

63%

Mordecka Z. , Woźniak S.

Przemysł Chemiczny

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2005

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tom T. 84, nr 12

946-948

PL

Analizowano proces dezaktywacji żelazowych katalizatorów syntezy amoniaku w przemysłowych reaktorach typu TVA. Rozpatrzono kilka różnych modeli dezaktywacji katalizatora wzdłuż wysokości złoża, wykorzystując wyniki badania aktywności próbek katalizatora pobranych w czasie wyładunku starannie spasywowanego wsadu. Modele te zastosowano następnie do oceny pracy reaktora. Za pomocą wybranego modelu oceniono szybkość dezaktywacji katalizatora PS3-INS, na podstawie parametrów technologicznych z okresu jego 12-letniej eksploatacji w reaktorze TVA, w jednostce syntezy amoniaku o zdolności produkcyjnej 500 t/d, w ZA „Puławy”.

EN

In an 8–12 mm PS-3-INS catalyst thoroughly passivated and discharged from the reactor, structural promoters (Al, Ca, Mg, Si) were unaffected, S was present in the top layer, and K losses were 26% in the top and up to 10% in other layers. In mid-layers, Fe crystallite size growth was max. Reactor’s operating lines were calcd. by assuming various catalyst activity variation models, plug flow of the gas through the bed, and the exptl. kinetic characteristics of the catalyst. Most affected were temp. profiles; ammonia production only in 2%. The catalyst activity drop, only 30% in a 12-year-long operation of a 500-t NH3/day plant, was attributed to catalyst’s thermal stability and high purity of the synthesis gas.

10

Utilization of spent iron catalyst for ammonia synthesis

63%

Arabczyk W. , Narkiewicz U. , Lendzion-Bieluń Z. , Moszyński D. , Pełech I. , Ekiert E. , Podsiadły M. , Pelka R. , Jędrzejewski R. , Moszyñska I. , Sibera D.

Polish Journal of Chemical Technology

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2007

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tom Vol. 9, nr 3

108-113

EN

Several methods of the utilization of spent iron catalyst for ammonia synthesis have been presented. The formation of iron nitrides of different stoichiometry by direct nitriding in ammonia in the range of temperatures between 350°C and 450°C has been shown. The preparation methods of carbon nanotubes and nanofibers where iron catalyst catalyse the decomposition of hydrocarbons have been described. The formation of magnetite embedded in a carbon material by direct oxidation of carburized iron catalyst has been also presented.

11

Application of XRF and XRD methods for fast analysis of fused iron catalyst for ammonia synthesis

63%

Szczuko D. , Arabczyk W.

Chemia Analityczna

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2000

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tom Vol. 45, No. 2

273-280

EN

A fast method for the determination of chemical composition of fused iron catalyst for ammonia synthesis was developed. The catalysts with different amount of promoters and with different oxidation state of iron were examined. The chemical composition of catalysts was determined using XRF, XRD, ICP spectroscopy, flame photometry and man-ganometric titration. Calibration curves for CaO, Al(2)O(3) and K(2)O were plotted. Using XRD method the dependence of the relative Fe(200) and Fe(3)O(4)(400) peak intensity ratio on iron oxidation state was plotted. This dependence, however was different for magnetite and for wustite catalysts. Using this method for catalysts containing cobalt the total amount of cobalt and iron with second oxidation state was determined.

PL

Opracowano szybką metodę określania składu chemicznego stopowego katalizatora żelazowego do syntezy amoniaku. Zbadano katalizatory o różnym składzie i stopniu utlenienia. Przy użyciu metod takich jak XRF, XRD, spektroskopia ICP, fotometria płomieniowa i manganometria określono ich skład chemiczny. Wykreślono krzywe kalibracji dla CaO, Al(2)O(3) i K(2)O. Stosując dyfrakcję promieni rentgenowskich wykreślono zależność stosunku intensywności pików Fe(200) i Fe(3)O(4)(400) od stopnia utlenienia żelaza. Stwierdzono, że ta sama zależność nie może być zastosowana jednocześnie dla katalizatorów konwencjonalnych i wustytowych. Stosując tą metodę dla katalizatorów zawierających kobalt określono ilość kobaltu i żelaza na drugim stopniu utlenienia.