US2873176A - Reaction-regeneration system for hydroforming naphtha with platinumalumina catalyst - Google Patents

Description

Feb. 10, 1959 R. J. HENGSTEBECK REACTION-REGENERATION SYSTEM FOR HYDROFORMING NAPHTHA' WITH PLATINUM-ALUMINA CATALYST File'd March 14, 1955 Met/lane I I2 1% /4 m /8 r Air 2 PPM, Air 39 8a 4/ 42\ Flue Gas a l E1 36 27 iii A; If; 42:5 I0

Air 56' 54 E 55 Flue 60.9 n

BY F lg. 2

28 IN VEN TOR.

Robert J. Hangs/aback United Stats Pate 2,873,176 nnAorroN-nsounnnariou sysriuM son as- DROEORMING NAFH-EIHA WITH PLATINUM- ALUMINA CATALYST Robert J. Hengstebeck, Valparaiso, lush, assignot'. to Standard Oil Company, Chicago, 1th., a corporation. of Indiana ApplicationMarch 14, 1955, Serial No. 493 862 3Ciaims. (Ct. 23--288) This invention relates to a reaction-regeneration sysmm for the hydroforming of naphtha with platinumaluinina catalyst, and it pertains more particularly to a so-called blocked out regeneration system wherein portions of the on-stream equipment are utilized in effecting regeneration.

The first commercial naphtha hydroformin'g system employing platinum-alumina catalyst, the so-called platforming process, was of the so-called continuous or nonregenerative type which required operation at pressures of about 500 p. s. i. g. or higher in order to obtainrun lengths of the desired duration, after which the catalyst was replaced; this avoided the expense of regeneration equipment, but it sacrificed the flexibility and the high yield-octane performance attainable by operations at lower pressures. More recent platinum-alumina hydroforming processes, such as the ultraforming process (Pesolemn Engineer, volume XXVI, April 1954, at page (L35), are operated at low pressures, usually inthejrang'e of abo1tt 2'Q0 to 400 p. s. i. g., and are provided with regeneration facilities which are separate and distinct from the equipment "employed in on-stream operations; these systems ojlfer operating advantages not attainable by the lion-regenerative process, but require much larger capital investment. The object of this invention is to provide a regenerative platinum-alumina hydroforming system which will cornbinethe advantages of both prior systems but which will avoid the large capital investment heretofore required for regeneration equipment. Other objectsywill be apparent as a detailed description of the invention proceeds.

Mysystem does not require an added swing reactor as is heretofore employed in ultraforming 's'ystems,s"o that it effects a substantial saving in required catalyst inventory. It employs the usual on-stream equipment, including a preheater, a first reactor, a reheater, a second reactor, one orniore additional reheater-reactor combinations, an effluent product heat exchanger, a cooler, a gas separator, a recycle gas compressor, and the usual connecting lines therebetween. When regeneration is required, the naphthat flow to the system is stopped but the recycled hydrogen flow isc ntinued until substantially all naphtha has been purged from the system and removed from the separator, at which time the naphtha discharge line from the separator is closed by a suitableblock valve or blinds.

The system is then depressured to approximately atmospheric pressure, i. e., about 1 to p. s. i. g., by venting hydrogen therefrom and flue gas is introduced into the system and circulated therethrough by the recycle gas compressor in order to complete the purging of hydrogen therefrom. Next, the flue gas pressure in the circulating system is increased to at least about 100 p. s. i., but usually not higher than 400 p. s. i., and the temperature of the circulating gases is controlled by the preheater and/or reheaters to bring each catalyst-bed to a temperature in the range of 550 to 750 F. A small amount of air is then introduced intothe tail reactor to effect combustion of carbonaceous deposits from the catalyst bed therein, the amount being controlled to keep combustion front temperatures within the range of about 850 to l050 F. The hot combustion products are preferably ice cooled in the same cooler employed in on-stream operations for condensing water formed in the combustion step and the condensed water is separated from. flue gas in the on-stream separator and removed therefrom by a separate valved line. The dry high-pressure flue gas thus generated by combustion is then circulated by the same compressor employed in on-strearn operations through the same preheater and thence back to the combustion zone, any net line gas production being vented from the system.

it is important that preheaters, transfer lines, and ex-- changers employed in oil-stream operations should not be subjected to an oxidizing atmosphere during regeneration since this may result in scaling, corrosion, er other injury to the furnace coils, etc, particularly when the naphtha charge contains appreciable amounts of sulfur. Therefore, when the combustion 'zone approaches the outlet end of the reactor, the introduction of air should be discontinued in order to prevent any break-through of uncombined oxygen.

Regeneration of the next to the last reactor is then effected in the same way that the tail reactor is regenerated,

but in order to avoid water formed by combustion from catalyst in the succeeding reactor, the effluent from each reactor under oing regeneration is preferably by-pas'sed around succeeding reactors and introduced directly into the cooler and separator for removing water of combustion. Each reactor in theseries is thus successively regenerated, care being taken in all instances to avoid any break-through of oxygen in amounts which would lead to scaling or corrosion of furnace tubes, exchangers or transterlines. g

After regeneration, flue gas may be purged from the system by depressuring and turtherpur'ged by introduction of a nonreactive hydrocarbon gas such as methanqwhich is employed to establish circulation and the desired temperature and pressure conditions in the system for subsequent start-up. When it is necessary or desirable to effect rejuvenation in addition to regeneration, each reactor is blocked off from the rest of the system by means of block valves or blinds after the catalyst therein has been brought to a temperature of at least 850, and preferably 950% 1050 F., and air is introduced into the reactors to attain a total pressure in the range of about to 400 p. i., thus providing an oxygen partial pressure therein jinfth'e range of about 1 to 4 atmospheres. After a soaking period of about .5 to 5 hours or more, the air is vented from the reactor by depressuring and the reactor is subsequently purged from oxygen by pressuring and depressuring with flue gas, after which the flue gas is purged from the systern with methane as hereinabove described.

It will thus be seen that I have provided a blockedout regeneration system which requires only a small fraction of added investment cost heretofore deemed necessary. This has been accomplished by utilizing on-stream equipment for eifecting regeneration in such a manner as to avoidcorrosion or other injury to the equipment which could be caused by exposing it to oxidizing gas and at the same time avoiding injury to the catalyst which would be caused bypermitting water and water-soluble materials such as S0 from building up in the recycle gas stream and contacting previously regenerated catalyst. My system is particularly advantageous for converting existing non-regenerative platinum-alumina hydroforming systems into regenerative systems. It is highly advantageous in the design of new installations, particularly those operating in the range of about 300 to 750 p. s. i. and characterized by long on-stream operating periods with relatively infrequentregeneration.

The invention will be-more clearly understoodfrom the following detailed description of specific examples thereof read, in conjunction with the accompanying, drawings which form a part of this specification and "in which:

Pa tented Feb. 10, 1959 Figure .1 is a schematic flow diagram of a reactionregencration system employing downflow in both operations, and

Figure 2 is a schematic flow diagram of such a system wherein the flow during regeneration is in the opposite direction from flow during on-stream operations.

The invention will be described as applied to a system for hydroforming naphtha with platinum-alumina catalyst at a pressure of approximately 400 p. s. i. While a Mid-Continent naphtha boiling in the range of about 150 to 360 F. is employed in this case as a charge, it should be understood that the invention is applicable to any naphtha charging stocks suitable for platinum-on-alumina hydroforming operations. Such charge'may be introduced by line through opened valve 11 to preheater 12 in admixture with about 2,000 to 8,000 cubic feet per barrel, e. g., 4,000 cubic feet per barrel, of a recycled hydrogen stream from line 13. If desired, the hydrogen may be preheated in a separate coil from that in which the naphtha is preheated, the heated mixture then being introduced by transfer line 14 into lead reactor 15 which contains a bed of platinumalumina catalyst in the form of one-eighth inch pills, the amount of catalyst preferably being such as to give a Weight space velocity in the first reactor in the range of about 2 to 12, the reactor being normally operated at a pressure somewhat above 400 p. s. i. with an inlet temperature in the range of about 875 to 975 F. The catalyst in reactor 15 may be any known type of platinurnalumina hydroforrning catalyst'and it may be prepared by combining halogen with alumina prior to depositing platinum thereon as described in Haensel U. S. Patent 2,479,109, or by simply compositing platinum chloride on an alumina support as described in U. S. Patent 2,659,701. A desirable catalyst support may be prepared as described in U. S. Patent 2,636,865. The catalyst preferably contains about .3 10 .6' weightpercent platinum.

The total effluentfrom lead reactor 15 is introduced by line 16 through reheater 17 and transfer line 13 into second reactor 19, which contains approximately the same amount of the same type of catalyst as is contained in reactor 15 and which may operate at about the same conditions but at a slightly lower pressure and a' slightly higher average temperature. Eflluent from reactor 19 is passed by line 20 through reheater 21 and transfer line 22 into tail reactor 23, which like wise contains approximately the same amount of the same type of catalyst heretofore described, the tail reactor operating at a pressure slightly below that of reactor 19 but in the vicinity of 400 p. s. i. It should be understood that more than three on-stream reheaterreactor combinations may be employed and that the tail reactor may be the fourth, fifth, or sixth reactor instead of the third.

The flow stream from the tail reactor is withdrawn through line 24 through heat exchanger 25, lines 26 and 27, and cooler 28 to separator 29 from which condensed naphtha product is withdrawn through line 30 to aconventional stabilizer and/or product recovery system. The separated hydrogen is withdrawn from the separator through line 31 and recycled by circulating compressor 32 through heat exchanger and line 13 back to preheater 12, any net hydrogen production being withdrawn through line 33.

After a number of months in on-strcarn operation, the activity and/or selectivity of the catalyst in this system may decline to such an extent that, regeneration is necessary or desirable. In accordance wih my invention, such regeneration is effected largely by use of equipment forming a part of the tin-stream reaction system and supplemented only by source 01' flue gas 34, a flue gas compressor 35, a line 36 for introducing compressed flue gas into the system, a valved line 57 for removing aqueous condensate from the separator, lines 38, 39, and 40 for introducing and withdrawing air, and block valves or blinds 14a, 18a, 22a, 16a, 20a, and 24a for blocking out the individual reactors when it is desirable to effect rejuvenation of catalyst therein. Additionally, it is desirable to have crossover lines 41, 42, and 43, each provided with a suitable block valve for discharging effluent from the reactors directly to flue gas inlet line 36. For purging operations, it may be desirable to have a crossover line 44 connecting line 24 to vent line 33.

For etfecting regeneration of catalyst in this system, valve 11 is closed, and the recycle of hydrogen through the system is continued by circulating compressor 32 in order to purge substantially all naphtha from the system. When no further naphtha accumulates in separator 29, this separator is emptied and valve a is closed. The system is then depressured by opening the valve in line 44- and venting hydrogen from the system, flue gas being introduced from source 34 by compressor 35 and line 36 to sweep out all hydrogen from the system While it is depressured. As soon as the system is free from hydrogen, the valve in line 44 is closed, the system is repressured to about 100 to 400 p. s. i with flue gas and the circulation of flue gas is continued with adjustment of preheater and reheater temperatures to bring each catalyst bed to a temperature of approximately 700 F. Next, the introduction of flue gas from source 34 is discontinued and small controlled amounts of air are introduced by line into the circulating flue gas stream in order to burn carbonaceous deposits from the catalyst in reactor 23 while holding combustion zone temperature within the range of about 850 to 1050 F. When the thermocouple near, but spaced from the outlet end of, the catalyst bed indicates that the combustion zone has passed this point,

introduction of air through line 40 is immediately stopped so that there will be no break-through of free oxygen. Instead of relying upon thermocouples, an oxygen analyzer may be employed in line 24 and oxygen introduction through line 40 may be discontinued immediately on the appearance of a detectable amount of uncombined amount of oxygen in the eflluent flue gas. The avoidance of oxygenbreak-through is important because the circula- 1 tion of an oxidizing gas by compressor 32 through the preheater and reheaters and other lines, valves, and exchangers causes scaling, corrosion, and is generally detrimental.

It will be noted that both the initially introduced flue gas and the flue gas formed by combustion of carbonaceous deposits pass through cooler 28 to separator 29 so that any water formed by combustion can be removed from the flue gas before it is circulated by compressor 32. The removal of water from the circulating gas is important from the standpoint of avoiding catalyst deactivation, particularly when the water contains dissolved S0 The aqueous condensate its thus removed by line 37 during the regeneration operation, thus affording protection both to the equipment and to the catalyst in the system. 7

When the catalyst in reactor 23 has thus been regenerated, the catalyst in reactor 19 may be similarly regenerated, but in this case, the hot combustion gases are preferably introduced directly by line 42 and line 36 to cooler 28 so that the combustion products will not contact regenerated catalyst. The catalyst in reactor 15 and in any number of other reactors is likewise regenerated, care being taken in all cases to prevent oxygen break-through.

lf rejuvenation is not required, the system may next be depressured by opening the valve in line 44 and venting flue gas from the system, the flue gas being further purged from the system by methane or other non-rcactive hydrocarbon gas introduced through line 45. It is important that flue gas be purged from the system before again going on stream because the carbon dioxide content of flue gas in the presence of generated ydrogen causes catalyst deactivation and/or removal of the platinum component of the catalyst from the system. The system is then pressured with methane to about 50 to 100 p. s. i. and the catalysts in the reactors are brought to desired start-up temperatures of about 700 to 750 F., at which time preheated naphtha may be again introduced by opening valve 11., the dehydrogenation of the introduced naphtha quickly generating the required amount of hydrogen for onstream operation. When a desired hydrogen purity of about 95% and the desired amount or" recycled hydrogen is available, the inlet temperatures of the reactors may be' raised to normal operatinglevels of about 875 to 975 F.

If rejuvenation is required, it may be necessary to insure removal of substantially all of the carbonaceous deposit by closing the valve in lines 41, 42 and 43, respectively, at the point of oxygen breakthrough and continuing the introduction of air to complete the combustion while venting through lines 41a, 42a and 43a, the flue gas being supplied at this time from source 34. After purging oxygen from the beds through 41a, 41b and 41c, these lines are closed and the catalyst in each of the reactors is reheated by circulating flue gas heated to a temperature of at least 850, and preferably about 950 to 1050 B, after which circulating compressor 32 is stopped, and each reactor is blocked-out by closing the necessary block valves. Air is then introduced into the reactors through lines 38, 39, and 40 until the pressure in the reactors is built up from about atmospheric to about 100 to 400 p. s. i., after which time the catalyst is allowed to soak in the gas of high oxygen partial pressure for a period of about .5 to 5 hours or more. After this soaking period, the vessels may be depressured by opening the valves in lines 41a, 42a, and 43a and oxygen may then be purged from the reactors with flue gas which may be introduced through lines 38, 39, and 40 and removed through lines 41a, 42a, and 43a, after which time the flue gas may be purged with methane and the catalyst beds may be returned on stream in the manner hereinabove described.

The embodiment shown in Figure 2 is similar to that hereinabove described except that provision is made for up-fiow regeneration. In this case, an auxiliary line 46 may be employed during regeneration by closing valve 14a, line 46 being connected to the bottom of reactors 15, 19, and 23 by valved lines 47, 4S, and 49 respectively. The purging of gases from the reactors in this embodiment may be effected by opening valves in lines 50, 51, and 52 which lead to header 53, which in turn leads to vent line 33. Air from source 54 may be introduced by compressor 55 to header 56 from which air may be introduced into reactors 15, 19, and 23 in amounts controlled by valves in lines 57, 58, and 59. The operation of this system is the same as the operation of the previous system up to the point of initiating combustion of car bonaceous deposits from catalyst. At this point, valves 14a, 16a, 18a, 20a, 22a, and 24a are closed and the flue gas is introduced through line 46 into the bottom of any one or all of the reactors through lines 47, 48, and 49, while controlled amounts of air are introduced thereto through lines 57, 58, and 59. That portion of the combustion products required for recirculation is returned by line 60 to line 36, while the remainder of the combustion products are vented through line 33. Here again it is important to prevent substantial break-through of oxygen and the flow of combustion air should be stopped just before the combustion front reaches the upper part of the catalyst bed. When rejuvenation is not required, the valves in lines 46 to 49, 57 to 59, and 50 to 52 may be closed and methane from line 45 may be cycled through the system for start-up in the manner described in Figure 1. For rejuvenation, however, the catalyst beds are more completely regenerated by burning after oxygen break-through while supplying flue gas from source 34,

(instead of by line 60) for final regeneration and purg- 6 ing. The catalyst beds are then heated to a temperature of 8501050 F. by circulation of the flue gas through preheater 12, the reactors are blocked off by closing valves 14a, 16a, 18a, 20a, 22a, and 24a, and air is introduced by compressor 55 into each reactor to build up its presure from about atmospheric to about to 400 p. s. i. to obtain the desired oxygen soaking for a period of .5 to 5 hours or more, after which the air is vented.

from the system by lines 50-53 and vent line 33 and oxygen is purged from the system by flue gas introduced from source 34 and compressor 35. After this flue gas purge, the system may be purged of hue gas with methane and again started up in the manner described in Figure 1.

From the foregoing description of preferred examples, it will be seen that the objects of the invention have been accomplished. The only parts of the described systems which are subjected to strongly oxidizing conditions are the reactors per se and that portion of the lines between the reactors and the block valves. The reactors and said portions of the lines are coated or lined with aluminum metal, but it would not be feasible to so coat or line the entire system.

The drying of the circulating flue gas may be augmented by employing an after cooler and water trap-out following the circulating compressor. The avoidance of free oxygen in preheater and reheater tubes may be further insured by passing the recycled flue gas stream at about 300 F. through a bed of granular copper or reduced copper oxide or a bed of adsorbent alumina coated with reduced copper oxide. These expedients add to the expense of the system, however, and they are usually not necessary if the described operations are carefully controlled. While two examples of the invention have been described in considerable detail, it will be understood of course that alternative arrangements and operating conditions will be apparent from the above description to those skilled in the art.

I claim:

1. A platinum catalyst hydroforming system which comprises a first heater, a first reactor, a second heater, a second reactor, a third heater, a third reactor, a heat exchanger, a cooler, a separator, a recycle gas compressor and connecting lines for passing a gaseous stream in series through the named elements and thence through the heat exchanger back to the inlet of the first heater, each of said reactors containing a bed of platinum hydroforming catalyst, separate lines, each containing a valve, for introducing air in controlled amounts to connecting lines leading to the respective reactors, a line for introducing flue gas to the connecting line which enters the cooler, separate lines connecting the outlet side of each reactor directly to the line for introducing flue gas, a gas vent line containing a valve on the downstream side of the compressor and at least one liquid draw-oif line from the bottom of the separator.

2. The system of claim 1 which includes a line for introducing methane at the inlet side of the compressor.

3. The apparatus of claim 1 which includes cut-ofi valves in the inlet and outlet connecting lines leading to and from each reactor for isolating the reactors from the remainder of the system and connections for passing hot air through the catalyst beds in the reactors while they are in isolated condition.

References Cited in the file of this patent UNlTED STATES PATENTS 2,357,531 Mather et a1. Sept. 5, 1944 2,364,453 Layng et a1. Dec. 5, 1944 2,474,014 Seebold .a June 21, 1949 2,578,704 Houdry Dec. 18, 1951 2,587,425 Adams et al. Feb. 26, 1952 2,746,909 I-lemminger May 22, 1956 2,773,013 Wolf et al Dec. 4, 1956 2,773,014 Snuggs et a1. Dec. 4, 1956

Claims (1)

1. A PLATINUM CATALYST HYDROFORMING SYSTEM WHICH COMPRISES A FIRST HEATER, FIRST REACTOR, A SECOND HEATER, A SECOND REACTOR, A THIRD HEATER, A THIRD REACTOR, A HEAT EXCHANGE, A COOLER, A SEPARATOR, A RECYCLE GAS COMPRESSOR AND CONNECTING LINES FOR PASSING A GASEOUS STREAM IN SERIES THROUGH THE NAMED ELEMENTS AND THENCE THROUGH THE HEAT EXCHANGE BACK TO THE INLET OF THE FIRST HEATER, EACH OF SAID REACTORS CONTAINING A BED OF PLATINUM HYDROFORMING CATALYST, SEPARATE LINES, EACH CONTAINING A VALVE, FOR INTRODUCING AIR IN CONTROLLED AMOUNTA TO CONNECTING LINES LEADING TO THE RESPECTIVE REACTORS, A LINE FOR INTRODUCING FLUE GAS TO THE CONNECTING LINE WHICHENTERS THE COOLER, SEPARATE LINES CONNECTING THE OUTLET SIDE OF EACH REACTOR DIRECTLY TO THE LINE FOR INTRODUCING FLUE GAS, A GAS VENT LINE CONTAINING A VALVE ON THE DOWNSTREAM SIDE OF THE COMPRESSOR AND AT LEAST ONE LIQUID DRAW-OFF LINE FROM THE BOTTOM OF THE SEPARATOR.

Images