Compositions – Preservative agents – Anti-oxidants or chemical change inhibitants
Patent
1981-02-17
1983-08-16
Konopka, P. E.
Compositions
Preservative agents
Anti-oxidants or chemical change inhibitants
252411S, 252412, 585486, 585489, B01J 2396, B01J 2104, C07C 418, C07C 1506
Patent
active
043990517
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to petrochemical processing, and more particularly, to methods for regeneration of rhodium-containing catalysts. The invention is particularly concerned with methods for regeneration of rhodium-containing catalysts for dealkylating alkyl benzenes.
DESCRIPTION OF THE PRIOR ART
Known in the prior art is a method for dealkylating alkyl benzenes by conversion with steam. The known method seeks to obtain aromatic hydrocarbons with less molecular weight than that of alkyl aromatic hydrocarbons contained in a raw material. Dealkylation of toluene for example proceeds as follows: +3H.sub.2
The process is carried out at a temperature of from 400.degree. to 500.degree. C. and at a pressure up to 30 atm using individual alkyl aromatic hydrocarbons or their mixtures with hydrocarbons of other classes as a raw material. Dealkylation of aromatic hydrocarbons with steam is carried out using catalysts containing noble metals of Group VIII of the Periodic System, preferably rhodium, applied to alumina (Cf. USSR Inventor's Certificate No. 229,477, Int. Cl. CO7c 15/04, published Mar. 22, 1972).
To increase activity, selectivity and stability of the rhodium/alumina catalyst, alkali metals, alkaline-earth metals as well as metals belonging to the group of copper, ferrum, chrome and lanthanum are introduced into the catalyst composition (Cf. British Pat. No. 1,313,941, Int. Cl. CO7c 3/58, patented Apr. 18, 1973; U.S. Pat. Nos. 3,436,433 and 3,436,434, Int. Cl. CO7c 3/58, BO1j 21/04, patented Apr. 1, 1969; U.S. Pat. Nos. 3,649,706 and 3,649,707, Int. Cl. CO7c 3/58, BO1j 21/04, patented Mar. 14, 1972; U.S. Pat. No. 3,848,014, Int. Cl. CO7c 3/58 patented Nov. 12, 1974).
Rhodium-containing catalysts are also used to conduct the reaction of dealkylation with hydrogen (hydrodealkylation).
Under conditions of dealkylation, the activity of the rhodium-containing catalysts drops. Therefore, the process is carried out by alternating reaction cycles with that of regeneration. The processes influencing a decline in activity of the catalyst are still not clearly understood. Some of them are due to carbon deposits on the catalyst surface and a decline in specific surface of rhodium due to agglomeration of its crystals.
Known in the prior art is a method for regeneration of a rhodium-alumina catalyst, residing in purging it with either hydrogen or a mixture of hydrogen with steam at a temperature of from 300.degree. to 550.degree. C. and pressure up to 20 atm (Cf. USSR Inventor's Certificate No. 348,033, Int. Cl. BO1j 11/68, published Mar. 5, 1978). The above method makes it possible to reclaim the catalyst activity provided the length of the reaction period does not exceed 100-120 hours. Moreover, it is not possible to reclaim the catalyst activity if the dealkylation process is carried out under severe conditions (over 480.degree. C.).
Also known in the art is a method for regenerating a rhodium-containing catalyst, residing in treating it with either a nitrogen-oxygen mixture or air-steam mixture in order to burn out coke, followed by chlorination at a temperature between 400.degree. and 600.degree. C. with a nitrogen-oxygen mixture containing 0.1 to 0.2 g/l of chlorine or a chlororganic compound. The catalyst is then reclaimed in a flow of hydrogen at a temperature of from 450.degree. to 550.degree. C. followed by treatment of the catalyst with steam at a temperature of from 400.degree. to 500.degree. C. and further using it in the process of dealkylation (Cf. USSR Inventor's Certificate No. 448,671, Int. Cl. BO1j 11/58, published Mar. 15, 1978).
Activity of the regenerated catalyst increases in case a chlorine-containing gaseous mixture used in the chlorination stage contains, in addition, water vapour in an amount of 0.002 to 0.1 g/l (Cf. USSR Inventor's Certificate No. 627,849, Int. Cl. BO1j 11/68, published Oct. 15, 1978).
However, the rhodium-containing catalyst regeneration by means of carbon-burning-out or chlorination is efficient only in case the latter has not undergone su
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patent: 2225782 (1940-12-01), Ipatieff et al.
patent: 3117076 (1964-01-01), Brennan et al.
patent: 3440007 (1969-04-01), Takevichi et al.
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Lukina Zoya P.
Mozhaiko Viktor N.
Rabinovich Georgy L.
Volkova Kira L.
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