CA1204693A - Catalyst regeneration process - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A process for regenerating, and reactivating, coked noble metal catalysts, especially platinum-containing polymetallic catalysts in a system which includes separate, interconnected primary and secondary regeneration gas circuits in which gas is circulated from one circuit to the other, (i) a primary regenera-tion gas circuit which contain a preheat gas furnace, a reactor which contains said catalyst from which said coke can be burned by contact with hot gas from said preheat gas furnace, and a steam boiler through which said hot gas can be passed and cooled, and the cool gas injected, or returned to said secondary circuit; and (ii) the secondary circuit is one which contains a regeneration gas scrubber, a gas drier (optional) and fines solids filter. The circuit also includes regen-eration gas means, i.e. a compressor, for circulating the gas in said circuits. A gas, constituted in major part of flue gas, is passed through the preheat gas furnace, preheated, then passed into the coked catalyst-containing reactor wherein the coke is combusted by contact of a combustible mixture of the gas with the catalyst, the gas heated thereby, then cooled by passage through the steam boiler, and the cooled gas then injected into the secondary circuit. The hot flue gas, or gas within the secondary circuit, is conditioned for use as a purge gas within the primary circuit.

Description

6~3 1 ~ACKGROUND OF THE INVENTION AND PRIOR AR~

2 Catalytic reforming, or hydroforming, is a

3 well-established industrial process employed by the

4 petroleum industry for improving the octane quality of naphthas or straight run gasolines. In reforming, a 6 multi-functional catalyst is employed which con~ains a 7 metal hydrogena~ion-dehydrogenation (hydrogen ~ransfer) 8 component, or components, subst3ntially atomically 9 dispersed upon the surface of a porous, inorganic oxide support, notably alumina. Noble metal catalysts, 11 notably of the platinum type, are currently employed in 12 reforming. Platinum has been widely commercially used 13 in recent years in the ~roduction of reforming catalysts, 14 and platinum-on-alumina catalysts have been commercially employed in refineries for the last few decades. In the 16 last decade, additional metallic components have been 17 added to platinum as promotors to further improve the 18 activity or selectivity, or both, of the basic platinum ~9 catalyst, e.g., iridium, rhenium, tin, and the like.
Reforming is defined as the total effect of the molecu-21 lar changes, or hydrocarbon reactions, produced by 22 dehydrogenation of cyclohexanes and dehydroisomerization 23 of alkylcyclopentanes to yield aromatics; dehydrogena-24 tion of paraffins to yield olefins; dehydrocyclization of paraffins and olefins to yield aromatics; isomeriza-26 tion of normal paraffins; isomerization of alkylcyclo-27 paraffins to yield cyclohexanes; isomeri~ation of 28 substituted aromatics; and hydrocracking of paraffins 29 which produces gas, and inevitably coke, the latter being deposited on the catalyst.

31 In a conventional process, a series of reac-32 tors constitute the heart of the reforming unit. Each 33 reforming reactor is generally provided with fixed beds 3~ of the catalyst which receive upflow or downflow feed, and each is provided with a heater, because the reac-, , ~. , r~

6~3 1 tions which take place are endothermic. A naphtha feed,2 with hydrogen, or hydrogen recycle gas, i5 concurrently 3 passed through a preheat furnace and reactor, and then 4 in sequence through subsequent interstage heaters and reactors of the series. The product from the last 6 reactor is separated into a liquid fraction, and a 7 vaporous effluent. The latter is a gas rich in hydrogen, 8 and usually contains small amounts of normally gaseous g hydrocarbons, from which hydrogen is separated from the Cs+ liquid product and recycled to the process to 11 minimize coke production.

12 The activity of the catalyst gradually 13 declines due to the buildup of coke. Coke formation 14 is believed to result from the deposition of coke precursors such as anthracene, coronene, ovalene and 16 other condensed r~ng aromatic molecules on the catalyst, 17 these polymerizing to form coke. During operation, 18 the temperature of the process is gradually raised to 19 compensate for the activity loss caused by the coke deposition. Eventually, however, economics dictates the 21 necessity of reactivating the catalyst. Consequently, 22 in all processes of this type the catalyst must neces-23 sarily be periodically regenerated by burning the coke 24 off the catalyst at controlled conditions, this consti-tuting an initial phase of catalyst reactivation.

26 Two major types of reforming are generally 27 practiced in the multi-reactor units, both of which 2~ necessitate periodic reactivation of the catalyst, the 29 initial sequence of which requires regeneration, i.e., burning the coke from the catalyst. Reactivation o~
31 the catalyst is then completed in a sequence of steps 32 wherein the agglomerated metal hydrogenation-dehydro-33 genation components are atomically redispersed. In 34 the semi-regenerative process, a process of the first type, the entire unit is operated by gradually and t 3L2046~313 1 progressively increasing the ~emperature to maintain the 2 activity of the catalyst caused by the coke deposition', 3 until finally the entire unit is shut down for regener-4 ation,, and reactivation', of the catalyst. In the second~, a continuous or cyclic type of process', the 6 reactors are individually isolated, or in effect swung 7 out of line by various manifolding arrangements', motor ~ operated valving and the like. The catalyst is regen-g erated to remove the coke deposits, and reactivated while the other reactors of the series remain on stream.
11 A "swing reactorl' temporarily replaces a reactor which 12 is removed from the series for regeneration and reacti-13 vation of the catalysb, until it is put back in series.

14 There are several steps required for the regeneration', ~nd reactivation of a catalyst. Typically, 16 regeneration of a catalyst is accomplished in a primary 17 a~d secondary coka burnoff. This is accomplished, 18 initially, by burning the coke from the catalyst at a 19 relatively low temperatur~, i.e., at about 800F-950F, by the addition of a ga5, usually nitrogen or flue gas, 21 which contains about 0.6-1 mole percent oxygen. A
22 characteristic of the primary burn is that essentially 23 all of the oxygen is consumed, with essentially no 24 oxygen being contained in the reactor gas outlet.
2S Regeneration is carried out once-through, or by recycle 26 of the gas to the unit. The temperature is gradually 27 raised and maintained at about 950F until essentially 28 all of the coke has been burned from the catalyst, and 29 then the oxygen concentration in the gas is increased;, 30 generally to about 6 mole percent. The main purpose of 31 the secondary burn is to insure thorough removal of coke 32 from the catalyst within all portions of the reactor.
33 The catalyst is then rejuvenated with chlorine and 34 oxygen, reduced', and then sulfided. Thus, the agglom-erated metal, or metals', of the catalyst', is redispersed 36 by contacting the catalyst with a gaseous admixture ~Z0~693 1 containing a sufficient amount of a chloride, e.g., 2 carbon tetrachloride, to decompose in situ and deposit 3 about 0.1 to about 1.5 wt.% chloride on the catalyst;
4 continuing to add a gaseous mixture cont:aining about 6%
oxygen for a period of 2 to 4 hours while maintaining 6 temperature of about 950F; purging with nitrogen to 7 remove essentially all traces of o~ygen irom the reactor;
8 reducing the metals of the catalyst by contact with a g hydrogen-containing gas at about 850F; and then sulfid-ing the catalyst by direct contact with, e.g., a gaseous 11 admixture of n-butyl mercaptan in hydrogen, sufficient 12 to deposit the desired amount of sulfur on the catalyst.

13 In a typical continuous, or cyclic type 1~ process, the regeneration gas is yenerally cooled to relatively low temperatures, i.e., about 100-150F, by 16 passa~e through A cool waterscrubber to remove water by 17 condensation, and the condensate drawn of. In this 18 step, the water produced during combustion, or desorbed 19 from the catalyst during heatup is removed from the process. The water condensate is acidic,- and highly 21 corrosive, since it contains hydrogen chloride stripped 22 fro~ the catalyst. The partially dried flue gas is 23 generally further dried by passage through a dessicant 24 bed, or beds, prior to its return to the reactor con-~aining the catalyst being regenerated. Excessive 26 moisture levels are intolerable since the excessive 27 moisture produces an acidic condensate, further acili-28 tates chloride stripping from the catalyst, and produces 29 high hydrogen chloride levels in the vent gas sent to the atmosphere. Thus, there is a need to prevent the 31 moisture levels in flue gas from exceeding maximum 32 tolerable limits, as dictated by the need to suppress, 33 if not avoid, the amount of condensate that is formed, 34 minimize chloride stripping, and lessen vent gas hydro-gen chloride concentrations~

6g3 1 It is, accordingly, a primary objective of the 2 present invention to meet this need in the operation of 3 cyclic catalyst regeneration units, especially as used 4 in the regeneration of noble metal re~orming catalysts, more particularly platinum containing, or platinum-6 containing polymetallic reforming catalysts.

7 A specific object is to provide a novel 8 process for the regeneration of such catalysts, at g conditions which favor high cost-effectiveness and energy efficienc~ by recycling as purge gas a portion of 11 the ~lue gas used to remove combustion water, or water 12 desorbed from the catalyst, while suppressing corrosion;
13 and also minimize expensive nitrogen now used as once-14 through purge gas.

These objects and others are achieved in 16 accordance with the present invention, embodying 17 improvements in a process for regenerating, and reacti-1~ vating, said types of coke deactivated noble metal 19 catalysts, in a system which includes separate, inter-connected primary and secondary regeneration gas cir-21 cuits in which gas is circulated from one circuit to 22 the other, (i) the primary regeneration gas circuit 23 containing a preheat gas furnace, a reactor which 24 contains said catalyst from which said coke can be burned by contact with hot gas from said preheat 26 gas furnace, and steam boiler through which said hot 27 gas can be passed and cooled without the occurrence 28 of condensation, and the cool gas returned to said 29 secondary circuit, (ii) the secondary circuit containing a regeneration gas scrubber, a gas drier (optional) 31 and particulate `filter, and including regeneration 32 gas compression means, e.g. a compressor, for circulat-33 ing the gas in said circuits. A gas, constituted in 34 major part o~ flue gas, is withdrawn from ~he secondary circuit and passed through the preheat gas furnace, pre-.~ ~

~Z~4693 1 heated, then passed into the coked catalyst-containing 2 reactor (reaction zone~ wherein the coke is combusted by 3 contact of a combustible mixture of tlle gas with the 4 catalyst, the gas heated thereby, then cooled by passage through the steam boiler, and at least a portion of 6 the cooled gas is then returned into the secondary 7 circuit.

8 The hot flue gas, or gas within the secondary 9 circuit, is countercurrently contacted with cooling water in a regeneration gas scrubber to condense out the 11 combustion water and water desorbed from the catalyst, 12 as well as extract the hydrogen chloride stripped from 13 the catalyst, The temperature of the hot Elue gas is 1~ reduced to within a range of from abo~t 60F to about 120F, preferably from about 80F to about 105E', and 16 the hydrogen chloride to a concentration ranging from 17 about 0 to about 20, preferably from about 0 to about 5, 18 parts per million parts by volume (vppm) of total gas, 19 while the acid condensate is removed from the bottom of the scrubber and sent to disposal. To maintain system 21 pressure gas is purged to the atmosphere. Air and 22 nitrogen are added to the system as purge gas. Although 23 the combustion air carries along a significant quantity 24 of nitrogen, a relatively small quantlty of nitrogen may be needed, and added, to prevent moisture levels from 2~ exceeding maximum tolerable limits as dictated by the 27 need to avoid condensation, minimize chloride stripping, 28 and the amount of hydrogen chloride vented to the 29 atmosphere. Suitably, the gas is then dried if desired, and filtered to effect particulates removal, while the 31 gas, as purge gas, is recycled to the primary circuit 32 for reuse in regeneration of the deactivated catalyst.
33 The moisture level of the gas transferred to the primary 34 circuit is maintained at a level ranging from about 0.1 percent to about 1 percent, preferably from about 0.2 3~2~6~3 1 percent to about 0.6 percent, based on the total volume 2 of gas in the secondary circuit.

3 In i~s essence, the invention is one wherein 4 the gas is conditioned in the secondary circuit for use in the pri~ary circuit, and constitutes a source of 6 regeneration gas, or purge gas for use in the primary 7 circuit. The gas is withdrawn, or transferred, from the 8 primary circuit into the secondary circuit as needed.
g The increasing cost of energy has caused a significant rise in the cost of inert gas and hence, the present 11 invention sharply reduces the need for purge gas from 12 other sources of supply.

13 These features and others will he better 14 understood ~y reference to the followlng more detailed description of t~e invention, and to the drawings to 16 which reference is made.

17 In the drawings:

18 Figure 1 depicts, by means of a simplified 19 flow diagram, a preferred cycllc reforming unit inclu-sive of multiple on-stream reactors, and an alternate or 21 swing reactor inclusive of manifolds for use with 22 catalyst regeneration and reactivation equipment ~not 23 shown).

24 Figure 2 depicts, in schematic fashion, for convenience, a simplified regeneration circuit.

26 Referring generally to Figure 1, there is 27 described a cyclic unit comprised of a multi-reactor 28 system, inclusive of on-stream Reactors A, B, C, D and a 29 swing Reactor S, and a manifold useful with a facility for periodic regeneration and reactivation of the 31 catalyst of any given reactor, swing Reac~or S being ~Z~34693 1 manifolded to Reactors A, B, C, D so that it can serve 2 as a substi~ute reactor for purposes of regeneration 3 and reactivation of the catalyst of a reactor taken 4 off-stream. The several reactors of the series A, B, C, D, are arranged so that while one reactor is 6 off-stream for regeneration and reactivation of the 7 catalyst, the swing Reactor S can replace it and 8 provision is also made for regeneration and reactivation 9 of the cat~lyst of the swing reactor.

In particular, the on-stream Reactors A, B, C, 11 D~ each of which is p~ovided with a separate furnace or 12 heater FA, or reheater FB, Fc, FD, respectively, are 13 connected in series via an arrangement of connecting 14 process piping and valves so that feed can be passed in seriatim through FA~, FB~, FCO, FVD, respectively; or 16 generally similar grouping wherein any of Reactors A, ~, 17 C, D are replaced by Reactor S. This arrangement of 18 piping and valves is designated by the numeral 10. Any 19 one of the on-stream Reactors A, B, C, D, respectively, can be substituted by swing Reactor S as when the 21 catalyst of any one of the former requires regeneration 22 and reactivation. This is accomplished in "paralleling"
23 the swing reactor with the reactor to be removed from 24 the circuit for regeneration by opening the valves on each side of a given reactor which connect to the upper 26 and lower lines of swing header 20, and then closing off 27 the valves in line 10 on both sides of said reactor so 28 that fluid enters and exits from said swing Reactor S.
29 Regeneration facilities, not shown, are manifolded to each of the several Reactors A, ~, C, D, S through a 31 parallel circuit o connecting piping and valves which 32 form the upper and lower lines of regeneration header 33 30, and any one of the several reactors can be individ-34 ually isolated from the other reactors of the unit and the catalyst thereof regenerated and reactivated.

1%~46~3 _ 9 _ 1 In conventional practice the reactor regen-2 eration sequence is practiced in the order which will 3 optimize the efficiency of the catalyst based on a 4 consideration of the amount of coke deposited on the catalyst of the different reactors during the operation.
6 Coke deposits much more rapidly on the catalyst of 7 Reactors C, D and S than on the catalyst of Rea~tors A
8 and B and, accordingly, the catalysts of the former g are regenerated and reactivated at greater fre~uency than the latter. The reactor regeneration sequence 11 is characteristically in the order ACDS/BCDS, i.e., 12 Reactors A, C, D, B, etc., respectively, are substituted 13 in order by another reactor, typically swing Reactor S, 14 and the catalyst thereof regenerated and reactivated while the other four reactors are left on-stream~

16 Fi~ure Z presents a simplified schematic 17 diagram of the improved regeneration system o~ this 18 invention, the Reactor S, e.g., representing a deacti-i9 vated catalyst-containing reactor which has been removed from the series of on-stream reactors of the unit 21 (Reactors A, B, C, D) for purposes of regeneration, and 22 reactivation, of the catalyst. The regeneration system 23 includes generally, a first, or primary recycle gas flow 24 circuit which includes, besides the regenerating reactor, Reactor S, a regeneration furnace FS and a steam boiler 26 SB. A secondary circuit includes a regeneration gas 27 scrubber GS, a drier D (optional~, represented by a 28 block diagram representin~ dual vessel driers, inclusive 29 of facilities for air reactivation of the driers, and a particulate filter FF. The system also includes a 31 regeneration gas compressor C, which circulates gas in 32 the total system.~

33 Regeneration gas is circulated via furnace Fs 34 to Reactor S, and the gas is then cooled in steam boiler SB and returned to the suction side of compressor C. A
-~2~46g3 1 quantity of gas for purging, as determined by the target 2 system moisture level, is taken from the discharge of 3 the recycle, or circulation compressor C and sent to 4 packed scrubber GS where it is countercurrently con~act-ed with wate~, the gas scrubbed to remove contaminan~s 6 and water, and the water condensate then sent to dis~
7 posal. The gas, which enters the scrubber GS temper-8 ature at a temperature of from about 350~ to about 9 650F, or more often from about 450F to about 550F, is cooled to a temperature ranging from about 60F to about ll 120F, preferably from about 80F to about 105F, and 12 the hydrogen chloride content of the gas, originally 13 ranging from about 100 to about lO00 parts, more speci-14 fically from about 200 to about 700 parts, per million parts by volume (vppm)!, is reduced to from about 0 to 16 about 20 vppm, or more gen~rally from about 0 to about 17 5 vppm. The gas leaving the scrubber overhead is 18 hydrated, or water saturated. A small amount of the l9 gas is vented to the atmosphere for pressure control.

The gas is prepared for recycle by drying if 21 desired;, and particulate removal. Thus, the final 22 treatment steps for the remainder of the gas are drying 23 via passage of the gas through driers D ~optional), 24 and the removal o~ particulates via passage through the particulate filter FF. The gas driers per se are 26 conventional, and may be dual-vessel alumina driers, 27 generally arranged in parallel for alternate use, with 28 simple reactivation facilities, such as once-through, 29 steam heated air for heatup and cool, dry air (e.g., instrument air) for cooldown. The gas stream is then 31 returned to the suction of the recycle compressor under 32 flow control. Due to the extraordinary cleanliness 33 requirements for the compressor a buffer seal gas is 34 employed, and a separate clean nitrogen makeup and air makeup streams are injected into the secondary circuit.
36 Flue gas, as purge gas, is wi~hdrawn from the secondary lZ~b~6~3 1 circuit and passed into the primary circuit wherein the 2 moisture level is maintained below about 4 percent, 3 preferably about 2 percent, based on the total volume of 4 gas in said primary circuit.

The invention will be more fully understood by 6 reference to the following nonlimiting examplea 7 EXAMPL~

8 In a catalyst regeneration system, such as is g specifically described by reference to Figure 2, a coked, deactivated platinum catalyst is regenerated by 11 burning the coke from the catalyst as described for 12 a typical operation. The secondary circuit in~ludes 13 only a particulates Eilter, in addition to a compressor 14 and regeneration gas scrubber; and the primary circuit includes a regeneration gas furnace, regenerating 16 reactor, and steam boiler. With air and nitrogen added 17 to the system, the system is balanced in terms of flow 1~ rates per thousand SCF/hour as given in the Table.

Flow Rate of Gas SCF/Hr Section of System Referenced 21 5,288 to Regeneration Furnace, FS
22 5,288 to Re~ctor S
23 5,292 to Steam Boiler, SB
24 5,829 to Inlet of Compressor, C
573 to Regeneration Gas Scrubber, GS
26 266 to Purge Gas to Atmosphere 27 299 ~ownstream of Regeneration 28 ~ Gas Scrubber, GS
29 238 Air Makeup 537 to Particulate Filter .
, .

:~oa~3 1 Pursuant to these conditions the moisture 2 level within the primary circuit is maintained below 3 2 vol.% water, and the hydrogen chloride level at about 4 500 ppm.

The catalysts employed in accordance with this 6 invention are constituted of composite particles which 7 contain, besides a carrier or support material, a noble 8 metal hydrogenation-dehydroganation component, or compo-g nents, a halide component and, preferably, the catalyst is sulfided. The catalyst contains a Group VIII noble 11 metal, or platinum group metal (ruthenium, rhodium, 12 palladium, osmium, iridium and platinum); and suitably 13 an additional metal or metals component, e.g., rhenium, 1~ iridium, tin, germanium, tungsten, or the like. The support material is constituted of a porous, refractory 16 inorganic oxide, particularly alumina. The support 17 can contain, e.g., one or more of alumina, bentonite, 18 clay, diatomaceous earth, zeolite, silica, activated 19 carbon, magnesia, zirconia, thoria, and the like;
though the most preferred support is alumina to which, 21 if desired, can be added a suitable amount of other 22 refractory carrier materials such as silica, zirconia, 23 magnesia, titania, etc., usually in a range of about 1 24 to 20 percent, based on the weight of the support. A
preferred support for the practice of th~ present 26 invention is one having a surface area of more than 27 50 m2/9, preferably from about 100 to about 300 m2/g, 28 a bulk density of about 0.3 to 1.0 g/ml, preferably 29 about 0.4 to 0.8 g/ml, an average pore volume of about 0.2 to 1.1 ml/g, preferably about 0.3 to 0.8 ml/g, and 31 an average pore diameter of about 30 to 300A.

32 The metal hydrogenation-dehydrogenation 33 component can be composited with or otherwise intimately 34 associated with the porous inorganic oxide support or 3S carrier by various techniques known to the art such .

~L2C~4693 1 as ion-exchanger coprecipitation with the alumina in 2 the sol or gel form, and the like. For example, the 3 catalyst composite can be formed by adding together 4 suitable reagents such as a salt of pla~inum and ammo-nium hydroxide or carbonate, and a salt of aluminum 6 such as aluminum chloride or aluminum sulfate to form 7 alu~inum hydroxide. The aluminum hydroxide containin~
g the salts of platinum can then be heated, dried, formed g into pellets or extruded, and then calcined in nitrogen or other non-agglomerating atmosphere. The metal 11 hydrogenation components can also be added to the 12 catalyst by impregnation, typically via an "incipient 13 wetness" technique which requires a minimum of solution 14 so that the total solution is absorbed, initlally or after some evaporat~on.

16 It is preferred to deposit the platinum and 17 additional metals used as promoters, if any, on a 18 previously pilled, pelleted, beaded, extruded, or sieved 19 particulate support material by the impregnation method.
Pursuant to the impregnation method, porous refractory 21 inorganic oxides in dry or solvated state are contacted, 22 either alone or admixed, or otherwise incorporated with 23 a metal or metals-containing solution, or solutions, and 24 thereby impregnated by either the ~inci~ient wetness"
technique, or a technique embodying absorption from a 26 dilute or concentrated solution, or solutions, with 27 subsequent filtration or evaporation to effect total 28 uptake of the metallic components.

29 Platinum in absolute amount, is usually supported on the carrier within the range of from about 31 0.01 to 3 percent, preferably from about 0.05 to 1 32 percent, based on the weight of the catalyst (dry 33 basis). The absolute concentration of the metal, of 34 course, is preselected to provide the desired catalyst for each respective reactor of the unit. In compositing .

~Z~6g~

1 the metal, or metals, with the carrier, essentially any 2 soluble compound can be used, but a soluble compound 3 which can be easily subjected to thermal decomposition 4 and reduction is preferred, for example, inorganic salts such as halide, nitrate, inorganic complex compounds, or ~ organic salts such as the complex salt of acetylacetone, 7 amine salt, and the like. Where, e.g., platinum is to 8 be deposited on the carrier, platinum chloride, platinum 9 nitrate, chloroplatinic acid, ammonium chloroplatinate, potassium chloroplatinate, platinum polyamine, platinum 11 acetylacetonate, and the like, are preferably used. A
12 promoter metal, when employed, is added in concentration 13 ranging from about 0.01 to 3 percent, preferably from 14 about 0.05 to about 1 percent, based on the weight of the catalyst.

16 To enhance catalyst performance in reorming 17 operations, it is also required to add a halogen compo-18 nent to the catalysts, fluorine and chlorine being 19 preferred halogen componentsO The halogen is contained on the catalyst within the range of 0.1 to 3 percent, 21 preferably within the range of about 1 to about 1.5 22 percent, based on the weight of the catalyst. When 23 using chlorine as a halogen component, it is added to 2~ the catalyst within the range of about 0.2 to 2 percent, preferably within the range of about 1 to 1.5 percent, 26 based on the weight of the catalyst. The introduction 27 of halogen into catalyst can be carried out by any 28 method at any time. It can be added to the catalyst 29 during catalyst preparation, for example, prior to, following or simultaneously with the incorporation of 31 the metal hydrogenation-dehydrogenation component, or 32 components. It can also be introduced by contacting 33 a carrier material in a vapor phase or liquid phase 34 with a halogen compound such as hydrogen fluoride, hydrogen chloride, ammonium chloride, or the like.

~2~693 1 The catalyst is dried by heating at a temper-2 ature above about 80F, preferably between about 150F
3 and 300F, in the presence of nitrogen or oxygen, or 4 both, in an air stream or under vacuum. The catalyst is calcined at a temperature between about 500F to 6 120QF, preferably about 500F to 1000F, either in the 7 presence of oxygen in an air stream or in the presence 8 of an inert gas such as nitrogen.

9 Sulfur is a highly preferred component of the catalysts, the sulfur content of the catalyst 11 generally ranging to about 0.2 percent, preferably from 12 about 0.02 percen~ to about 0.15 percent, based on the 13 weight of the catalyst (dry basis). The sulfur can be 14 added to the catalyst by conventional methods, suitably by breakthrough sulfiding of a bed o~ the catalyst with lh a sulfur-containiinq gaseous stream, e.g., hydrogen 17 sulfide in hydrogen, perormed at temperatures ranging 18 from about 350F to about 1050F ~nd at pressures 19 ranging from about 1 to about 40 atmospheres for the time necessary to achieve breakthrough, or the desired 21 sulfur level.

22 An isolated reactor which contains a bed of 23 such catalyst, the latter having reached an objection-24 able degree of deactivation due to coke deposition thereon, is first purged of hydrocarbon vapors with a 26 non-reactive or inert gas, e.g., helium, nitrogen, or 27 flue gas. The coke or carbonaceous deposits are then 28 burned ~rom the catalyst in a primary burn by contact 29 with an oxygen-containing gas, particularly one rich in both oxygen and CO2, at controlled temperature below 31 about 1100F, and preferably below about 1000F. Since 32 a major amount of the CO2 formed during combustion 33 will not be removed in the purge, or vent gas cleanup 34 system at the sc~ubber, its concentration will be increased to advantage; since CO2 has a higher heat , :~L2~

1 capacity (on a weight basis) than nitrogen, this per-2 mitting greater air injection rates and faster burns.
3 The temperature of the burn is controlled by controlling 4 the oxygen concentration and inlet gas temperature, this taking into consideration, of course, the amount of coke 6 to be burned and the time desired in order to complete 7 the burn. Typically, the catalyst is initially treated 8 with an oxygen/nitrogen gas having an oxygen partial g pressure of at least abou~ 0.1 p5i (pounds per square inch), and preferably in the range of about 0.2 psi to 11 about 5 psi to provide a temperature of no more than 12 about 950F to about 1000F, for a time sufficient to 13 remove the coke deposits. Coke burn-of is thus accom-14 plished by first introducing only enough oxygen to initiate the burn while maintaining a relatively low 16 temperature, and then gradually increasing the temper-17 ature as the flane front is advanced by additional 18 oxygen injection until the temperature has reached 19 optimum. 5uitably, the oxygen is increased within the mixture to about 6 volume percent and the temperature 21 gradually elevated to about 950F.

22 Typically in reactivating multimetallic 23 catalysts, sequential halogenation and hydrogen reduc-24 tion treatments are required to reactivate the reforming catalysts to their original state of activity, or 26 activity approaching that of fresh catalyst after coke 27 or carbonaceous deposits have been removed from the 28 catalyst. The agglomerated metals of the catalyst are 29 first redispersed and the catalyst reactivated by contact of the catalyst with halogen, suitably a halogen 31 gas or a substance which will decompose in situ to 32 generate halogen~. Various procedures are available 33 dependent to a large extent on the nature of the cata-34 lyst employed. Typically, e.g., in the reactivation of a platinum-rhenium catalyst, the halogenation step is ~zc~4~93 1 carried out by injecting halogen, e.g~, chlorine, 2 bromine, flourine or iodine, or a halogen co~ponent 3 which will decompose in situ and liberate halogen, 4 e.g., carbon tetrachloride, in the desired quantities, into the reaction zone. The gas is generally introduced 6 as halogen, or halogen-containing gaseous mixture, into 7 the reforming zone and into contact with the catalyst at 8 temperature ranging from about 550F to about 1150F, g and preferably from about 700F to about 1000F. The introduction may be continued up to the point of halogen 11 breakthrough, or point in time when halogen is emitted 12 from the bed downstream of the location of entry where 13 the halogen gas is introduced. The concentration of 1~ halo~en is not critical, and can range, e.g., from a few parts per million ~ppm) to essentially pure halogen gas.
16 Suitably, th~ halogen, e.g., chlorine, is introduced in 17 a gaseo~s mixture wherein the halogen is contained in 18 concentration ranging from about 0.01 mole percent to 19 about 10 mole percent, and preferably from about 0.1 mole percent to about 3 mole percent.

21 After redispersing the metals with the halogen 22 treatment, the catalyst may then be rejuvenated by 23 soaking in an admixture of air which contains about 6 to 24 20 volume percent oxygen, at temperatures ranging from about 850F to about g50F.

26 Oxyqen is then purged from the reaction zone 27 by introduction of a nonreactive or inert gas, e.g., 22 nitrogen, helium or flue gas, to eliminate the hazard of 29 a chance explosive combination of hydrogen and oxygen.
A reducing gas, preferably hydrogen or a hydrogen-31 containing gas generated in situ or ex situl is then 32 introduced into the reaction zone and contacted with 33 the catalyst at temperatures ranging from about ~00F to 34 about 1100F, and preferably from about 650F to about 950~F, to effect reduction of the metal hydrogenation-~2~4693 1 dehydrogenation components, contained on the catalysts.
2 Pressures are not critical, but typically range between 3 about 5 psig to about 300 psig. Suitably, the gas 4 employed comprises from about 0.5 to about 50 percent hydrogen, with the balance of the gas being substan-6 tially nonreactive or inert. Pure, or essentially pure, 7 hydrogen is, of course, suitable but is quite expensive 8 and therefore need not be used. The concentration of g the hydrogen in the treating gas and ~he necessary duration of such treatment, and temperature of treatment, 11 are interrelated, but generally the time of treating the 12 catalyst with a gaseous mixture such as described ranges 13 from about 0.1 hour to about 48 hours, and preferably 14 from about 0.5 hour to about 24 hours, at the more preferred te~peratures.

16 The cataly5t o~ A reactor may be presulfided, 17 prior to return or the reactor to service. Suitably a 18 carrier gas, e.g., nitrogen, hydrogen, or admixture 19 thereof, containing from about 500 to about 2000 ppm of hydrogen sulfide, or compound, e.g., a mercaptan, 21 which will decompose in situ to form hydrogen sulfide, 22 at from about 700F to about 950F, is contacted with 23 the catalyst for a time sufficient to incorporate the 24 desired amount of sulfur upon the catalyst.

It is apparent that various modifications and 26 changes can be made without departing from the spirit 27 and scope o F the present invention.

Claims (13)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a process for reforming, with hydrogen, a naphtha feed which is contacted at reforming condi-tions in a reforming unit constituted a plurality of on-stream reactors connected in series, each of which contains a noble metal catalyst which is deactivated by coke which is deposited on the catalyst such that each reactor must be periodically isolated from the other on-stream reactors of the series and the catalyst thereof regenerated by burning the coke from the cata-lyst at controlled conditions, this constituting an initial phase of catalyst reactivation, the improvement comprising establishing a gas regeneration system which includes separate, interconnected primary and secondary regeneration gas circuits in which gas is circulated from one circuit to another, (i) the primary regeneration gas circuit containing, in series, a preheat gas furnace, the isolated reactor which contains said deactivated, coked catalyst, and a steam boiler, (ii) the secondary circuit containing a regeneration gas scrubber, and regeneration gas compression means for circu-lating the gas in the circuits, withdrawing gas from said secondary circuit and passing said gas through the preheat gas furnace to preheat the gas, passing the preheated gas to the isolated reactor and contacting said preheated gas with said catalyst to burn the coke from the catalyst, passing the flue gas from the coke burn through the steam boiler, cooling the flue gas without the occur-rence of condensation, and then passing cooled flue gas into the secondary circuit, countercurrently contacting the flue gas within the secondary circuit with cooling water to condense out the combustion water, and water desorbed from the catalyst, and scrub out the hydrogen chloride, while reducing the temperature of the flue gas, drawing off the condensate from the scrubber, and injecting makeup gas into said gas regenera-tion system to prevent moisture levels from exceeding an amount which would produce corrosion within the system.

2. The process of Claim 1 wherein the temper-ature of the flue gas countercurrently contacted with water in the secondary circuit is reduced to within a range of from about 60°F to about 120°F.

3. The process of Claim 2 wherein the temper-ature of the flue gas is reduced to within a range of from about 80°F to about 105°F.

4. The process of Claim 1 wherein the hydro-gen chloride concentration of the flue gas countercur-rently contacted with water in the secondary circuit is reduced to within a range of from 0 vppm to about 20 vppm.

5. The process of Claim 4 wherein the hydro-gen chloride concentration is reduced to within a range of from 0 vppm to about 5 vppm.

6. The process of Claim 1 wherein the makeup gas injected into the system is added to the secondary circuit as a purge gas.

7. The process of Claim 1 wherein the makeup gas injected into the system comprises air or nitrogen or mixtures thereof.

8. The process of Claim 1 wherein the second-ary circuit also contains a drier downstream of the water contacting and scrubbing step.

9. The process of Claim 1 wherein a particu-late filter is located in secondary circuit downstream of the water contacting and scrubbing step.

10. The process of Claim 1 wherein the mois-ture level of the gas transferred to the primary circuit ranges from about 0.1 to about 1 percent, based on the total volume of gas in the secondary circuit.

11. The process of Claim 10 wherein the moisture level ranges from about 0.2 to about 0.6 percent.

12. The process of Claim 1 wherein the mois-ture level within the primary circuit does not exceed about 4 percent, based on the total volume of gas in the primary circuit.

13. The process of Claim 12 wherein the moisture level does not exceed about 2 percent.