US2402875A - Catalytic conversion process - Google Patents

Description

June 25, 1946.

`P. w. CORNELL GATALYTIC CONVERSION PROCESS Fileduuly 5, 1941 2 sheets-sheet 1 All.

a, NQ QN Wm. w Nm dweoou June 25, 1946- P. w. coRNl-:LL

`CA'AJYTIC CONVERSION PRGESS Filed July 5, 1941 2 Sheets-Sheet 2 Ivnuan atented .lune 25, i946 CATALYEIC CONWERSIN PROCESS Paul W. Cornell, Pittsburgh, Pa., assigner, by mesne assignments, to .tasca Incorporated, a corporation of Louisiana Application .luly 5, 19411, Serial No. 401,257

(Cl. Itis-F52) 9 Claims. l

This invention relates to catalytic conversion processes and pertains more particularly to processes wherein the conversion is carried out in successive stages employing a solid catalyst in finelydivided form.

While the invention in its broader aspects has a more general application, it is particularly adapted for hydrocarbon conversion wherein it is desired to carry out the same type of reaction in successive stages with the 'same catalyst operating under different conditions, or to carry out different types of reactions in a successive manner with the same catalyst under diierent conditions of time, temperature, and pressure.

For example, in catalytic cracking it is sometimes desirable to carry out the initial cracking treatment under one set of conditions and the final stages of the cracking operation under a diiierent set of conditions. For example, it may be desirable in some cases to crack the fresh oil during the initial stages with a relatively low catalyst concentration and at a relatively low temperature and then to crack the resulting products at a materially higher catalystconcentration and at a somewhat higher temperature, Another example is in the conversion of paraffin gases into oleiins and dlolens, such as the conversion of butane into butadiene. In the latter case, butane may be iirst dehydrogenated to form butene and then further dehydrogenated under carefully controlled conditions to form butadiene. As another example, gasoline of low octane rating may be first reformed in one stage to improve its anti-knock characteristics and the reformed products may then be rened under a different set of conditions employing the same type of catalyst to polymerize unstable constituents in the gasoline or to remove sulfur-containing compounds therefrom.

One of the principal objects of the present invention is to provide an improved process for carrying out catalytic conversions in successive stages which will require less equipment for a unit of given capacity.

Another object of the invention is to provide an improved process for catalytic conversions in successive stages which will have a lower operating cost for a unit of given capacity.

Another related object of the invention is to provide an improved apparatus for successivestage catalytic conversions.

Other more specific objects and advantages of the invention will be apparent from the detailed description hereinafter.

In accordance with the present invention, the

Z. successive reactions or successive stages of the same general reaction are carried out in a single reaction vessel of particular shape and design to permit one type of reaction tobe carried out under one set of conditions and the total products together with the catalyst are passed to a second zone within the same reactor wherein further reaction is carried out under a diere'nt set of conditions. The change in operating conditions in the two zones within the same reactor may comprise a change in the contact time, partial pressure of reactants, linear velocity of the reaction products, temperature, and catalyst concentrations. c

Having set forth the general nature and objects, the invention will be best understood from the detailed description hereinafter in which reference will be made to the accompanying drawings in which- Fig. I is a diagrammatic illustration of one type of apparatus forming a part of the present invention; and

Fig. II is a similar illustration of a modified form.

Referring now to the drawings, and particularly to Fig. I, the reference character I0 designates a charge line through which the products to be reacted are introduced into the system. For illustrative purposes, the invention will be applied speciiically to the'conversion of butane into butadiene, it being understood that the invention has a more general application as hereinbefore stated.

The butane gas to be reacted is preferably heated prior to introduction into the system to a@ temperature of the order of from 900 F, to 1100 F. The preheated butane may then be admixed with a suitable dehydrogenating catalyst introduced into the feed line l0 through conduit il, This dehydrogenating catalyst is preferably in iinely-divided form, having a particle size ranging, for example, between and 400 mesh or finer. The catalyst employed may be any suitable hydrogenating or dehydrogenating catalyst and may be used alone or carried on suitable inert supports. Catalysts of this type may comprise, for example, the oxides or suldes of the group VI metals, either alone or carried on suitable supports, such as Activated Alumina, magnesia, or the' like. The mixture or suspension of butane gas and catalyst introduced through line I i then passes through line I2'to a reaction chamber I3 which, as illustrated in Fig. I, is in the form ofy a vertical Vtower having an enlarged section i4 adjacent the bottom and a narrow restricted section l5 at the top. The bottom portion of the 3 reaction chamber I3 is preferably of conical shape and may be provided with a perforated plate I6 through which the suspension passes at a relatively high velocity to prevent settling or.

. alyst within the enlarged section I4 of the chamber I3 tends to settle out of the gases and builds up a relatively dense phase which is violently agitated by the passage of gases therethrough.

In lieu of first mixing the catalyst with the butane in the feed line I2, a part or all of the catalyst charged to the bottom section of the reaction chamber I3 may be passed into the reac' tion chamber through line I1. 'I'he temperature of the catalyst introduced may be substantially the same as that of the butane gas charged to the reactor, or it may be at a temperature somewhat higher to supply additional heat to the reaction mixture. In practical operations the temperature of this catalyst is preferably about the maximum temperature employed in regeneration of the catalyst, as will later be described. The temperature, time of contact and partial pressure of the reactants within the lower enlarged section I4 of the reaction chamber I3 are controlled to convert at least a substantial portion of the butane into butenes. The reaction mixture from the enlarged section 'I4 of the reaction chamber I3 passes upwardly to the restricted section I5 in which the velocity of the reaction mixture is increased due to the reduction in the diameter of the chamber. In addition to changing the velocity in` this section of the reaction chamber, additional catalyst may be discharged into the bottom section thereof through line I 3. and diluent gases may be intro duced through lines I9 and 2|. The gas introduced through lines I3 and 2| may be an inert gas from an extraneous source, or it may comprise off gases recovered from the process, as later described. The temperature of the gaseous diluent and catalyst introduced into the restricted section I5 of the chamber I3 may be modified so as to increase or reduce the temperature of the reaction carried out in the restricted section I5. In the conversion of the butenes to butadiene it is normally desirable to heat the reaction products in the restricted section I5. This may be accomplished by introducing catalyst at a higher temperature level or by preheating the diluent gas to a higher temperature level than the reaction mixture introduced therein. For example, the temperature within the restricted section I5 may he of the order of from 1000" F. to 1300 F.

In addition to modifying the temperature and velocity of the products passing through the restricted section, the introduction of a diluent gas reduces the partial pressure of the reactants so that further control of the nature o! the reactants can be effected. The time of contact of the reactants within the restricted section I5 is preferably materially shorter than the time of contact of the reactants with the catalyst within the enlarged section i4. For example, whereas the time of reaction for conversion of butane to butenes may be of the order of from 2 to 20 seconds or more, the time of contact for the conversion of butenes to butadienemay be a fraction of a second, such as one-131th to a hundredth of` a second. This can be readily accomplished according to the present invention by increasing the velocity of the reactants and by the introduction of a diluent gas and catalyst in the second stage of the reaction.

The products from the top of the reaction chamber I3 are removed therefrom through line 22 and may be passed through line 23 to a suitable separator such as a cyclone separator 24 for separation of the catalyst from the reaction products. The catalyst so separated discharges from the bottom section of the cyclone 24 into a conduit 25 from which it may be passed to a regenerating system for the removal of carbonaceous deposits formed during the reaction in a manner later to be described. 'I'he reaction products from the separator 24 are removed through line 26 and may be passed through line 21 and compressor 28 to a fractionating or stabilizing tower 29 in which the products are subjected to fractional condensation to segregate the higher boiling constituents thereof. Condensate formed in the stabilizing tower 29 may be removed through line 3| as a final product of the process.

Gases remaining uncondensed in the stabilizing tower 29 are removed therefrom through line 32 and may be passed to a cooler 33 for eiecting further condensation of the vapors. Products from the condenser 33 then pass to a receiver 34 in which a liquid condensate formed in the cooler 33 is separated from reaction gases. 'I'his liquid is withdrawn from receiver 34 through line 35 and is removed from the system through line 36. If desired, a portion ofthe liquid so Withdrawn may be returned to the top of the stabilizing tower '29 through line 31 and pump 33. Gases separated in receiver 34 pass overhead through line 39 and may be passed to a suitable absorption system for separation of the higher boiling hydrocarbons from lower boiling gaseous constituents. For example, such gases may be introduced int-o an absorption tower 4I in which they are contacted with a liquid absorption medium such as a light hydrocarbon fraction, e. g. gas oil, kerosene, or the like. This liquid absorption medium tends to selectively absorb the higher boiling constituents of the gases. The unabsorbed gases after passing through the absorber 4I are removed through line 42 and may be rejected from the system through line 43. Ac-

cording to one of the preferred embodiments of I the invention, however, at least a portion of these gases is returned to the top section I5 of the reaction chamber I3 as .a diluent gas. For example, a part of the oi gases removed from the absorber 4I through line 42 may be passed through line 44 to a heat exchanger 45 in which the temperature of-the gases may be modified before being returned to the top section I5 of the reaction chamber I 3.

In the conversion of butane to butadiene, it is desirable in most instances to operate the process at a relatively low pressure, such as subatmospherc or substantiallyA atmospheric pressure. To this end, the product line 21 is. provided with a compressor 28 for applying suction to the reaction chamber. In cases where the reaction chamber is operated at a pressure above atmospheric, this compressor 23 may be omitted or the products by.passed around the compressor through line 46.

For simplicity, only a singlek cyclone separator 24 has been shown on the drawings. understood, however, that additional separating equipment may be provided for effecting fur- It will be' I more.

'ther purification of the reaction products before passing the same to the stabilizing tower 29.

Returning to the cyclone separator 28, the catalyst separated from the reaction products discharges through conduit 25 through which it may pass to either of two repressuring chambers i1 and i9 through lines 49 and 5I, respectively. The purpose of these repressuring hoppers S1 and 48 is to build up the necessary pressure on the catalyst for passing it through the regenerating system. For example, when operating the reaction chamber under subatmospheric pressure and when operating the regenerating system under superatmospheric pressure, it is necessary to build up sulcient pressure on the catalyst passing to the regenerating zone to meet the pressure requirements of the regenerating system. To this end, the catalyst from conduit 25 may discharge for a predetermined interval into repressuring chamber 81. Meanwhile the catalyst in chamber 48 may be repressured andl discharged into the regenerating stream. The

y flow to the pressure chambers is then reversed such as air is passed. The mixture of catalyst and air isl then transferred through line 8| to a regenerating chamber 82 in which the catalyst is retained for a. period sufficient to remove combustible deposits formed thereon during the cracking operation. The velocity of the regenerating gas passing through the regenerating chamber 62 is preferably controlled so that the time of residence of the catalyst within the reaction chamber is materially longer than the time required for the passage of the regenerating gas therethrough. For example, the velocity of the gases within the regenerating chamber may be of the order of from 1 to 5 feet per second. Under these conditions, catalyst may be retained within the regenerating chamber for a period of from 5 minutes to 30 minutes or The regenerated catalyst and spent regenerating gas are removed from the regenerating chamber 62 through line 63 which leads to a suitable separator sucl as a cyclone separator 64 for separation of the spent regenerating gas from the regenerated catalyst. generating gas is vented from the cyclone separator 84 through line 65 and the catalyst discharges into a vertical tube or conduit 66 from which a portion may discharge through line 61 to the conduit I8 leading to the upper section I5 of the reactor I3. In order to modify the temperature of the catalyst passing to the upper section of the reactor, a. heat exchanger 68 may be provided in the conduit 61. Another portion of catalyst from the column 66 may discharge through line 69 into conduit I1 leading directly to the bottom section I4 of the reactor I3 or through conduit II into the feed line I8 leading to the reactor I3.

In order to control the temperature of regeneration, it may be desirable in some cases to cool a portion of the regenerated catalyst and to return The spent reseparates from the carrier gas.

the same to the regenerating chamber to reduce the temperature therein. To this end, a portion of the regenerated catalyst from the tube 88 may be passed through a heat exchanger 1I where the temperature of the catalyst is reduced. The cooled catalyst then discharges through conduit 12 into the regenerating gas stream in line 8 I.

As a further alternative, a portion of the catalyst withdrawn from the reaction chamber may be recycled thereto without regeneration. To this end, a portion of the products removed from the top of reaction chamber i3 may pass through line 13 to a cyclone separator 14 wherein the catalyst is separated from the reaction products. The catalyst so separated may then discharge through conduit 15 leading to conduit 81 -and heat exchanger 68 from whence the catalyst may be returned to the top section of the reactor through conduit I8.

In lieu of separating catalyst from reaction products in the cyclone separator 1d, a portion of the catalyst separated in thecyclone separator 28 may be injected into a stream of diluent gas and the mixtureof diluent gas and catalyst then passed to the separator 14. A portion of the recycled gas or other diluent gas employed in the process from line lili and heat exchanger 45 may be passed through line 16 to line 11 into which a yportion of the catalyst separated in the cyclone separator may be discharged through conduit 18. The dispersion of diluent gas and catalyst may then pass through lines 18 and 13 to the cyclone separator 14 wherein the catalyst separates from the diluent gas. The catalyst so separated may then discharge through conduit 15, heat exchanger 68 and line I8 into the top section of the reaction chamber I3. In this case the diluent gas separated from the catalyst in the cyclone separator 14 may be passed through line 8| and line I9 to the reactor I3.

As a further alternative, the catalyst from the conduit 18 receiving catalyst from the cyclone separator 24 may be discharged into a carrier gas operating in a closed system. For example, gas from a. gas accumulator tank 82 may be passed through line 83 and compressor 84 to conduit 11 into which catalyst from line 18 discharges. This mixture then passes through lines 19 and 13 to the cyclone separatorv 14 wherein the catalyst The carrier gas removed from the cyclone separator 14 may then discharge through lines 8l and 85 back to the gas storage tank 82 from whence it may be recycled, as just described.

In cases where a portion of the reaction products and catalyst withdrawn from the top of reaction chamber I3 through line 22 is discharged through line 13 tothe separator 14, the reaction products separated in the cyclone separator 14, as previously described, may discharge through lines 8| and 88. This latter line merges with line 21 receiving reaction products from the cyclone separator 24 and discharges the same into the rectifying column 29. Referring again to the absorber tower 4I employed for absorbing the higher boiling constituents of the reaction gases, the enriched absorber oil after passing through the absorber 4I is withdrawn from the bottom thereof through line 81 and may be passed to a 'distilling column 88 from which the absorbed gases are liberated. To this end, the distilling column 88 may be heated by any suitable means, such as by means of a heating coil 89 located at the bottom thereof. The gases liberated in the distillation of the absorber oil are remo"ed from aecaers 7 the distilling tower 8B through line 9| as a nal product of the process. The lean absorber oil is withdrawn from the bottom of the distilling tower 88 through line 92 from whence it may pass to a cooler 93 and back to the top of the tower 4| through line 94.

Fig. II represents a modication wherein the second stage of the reaction is carried out at low velocities, whereas the first stage is carried out at higher velocities and at lower catalyst concentrations. In other respects, the apparatus illustrated in Fig. II is similar to that in Fig. I and for simplicity corresponding parts in Fig. l1 have been indicated by the same numbers. This type -of equipment nds particular application in the catalytic cracking of oils and in the combined reforming and refining of gasolines.

Referring specifically to Fig. II, the reactor I3 has a restricted lower section Il and an enlarged upper section I5, whereas in Fig. I the lower section I4 is enlarged and the upper section i5 is restricted. Furthermore, the upper section I5 of the reaction chamber I3 may be provided with heating or cooling tubes Si located at the top portion thereof.

When employing the type of equipment illustrated in4 Fig. 11,. the fresh feed introduced through line I0, which in this case may be a gas oil vapor to be cracked or a gasoline to bereformed, is admixed with the reforming or cracking catalyst introduced through line H and the resulting mixture is then passed to the reduced section of the reaction chamber |13 through which the mixture passes at a relatively high velocity. Additional catalyst may be introduced directly into the bottom section of the reaction chamber I3 through line I1. Products from the initial zone of the reaction chamber pass through a perforated grid I6' into the enlarged section I5 where they meet withadditional catalyst introduced through line I8, as described in connection with Fig. I. Also additional diluent gas may be discharged into the top section of the reactor through line 2 I. The velocity of the vapors passing through-the enlarged section I5 in reactor Il is preferably controlled so as to build up a relatively high density mixture of catalyst and oil vapors therein and the temperature in this portion of the reactor may be controlled by modifying the temperature oi.' the catalyst introduced through line Il or the temperature of the diluent gas introduced through line 2l.

The presence of a perforated grid I6' prevents intimate mixing of the catalyst powder in the different sections of the reactors and permits maintaining a sharp temperature differential between the vdifferent reaction zones.

The remaining portion of the equipment operates as described in Fig. I. For simplicity, apparatus for recycling unregenerated catalyst back to the top section of the reaction chamber has been omitted from this gure. It will be understood that such equipment may be added if so desired.

Also, repressuring chambers I1 and 48 have been omitted since in catalytic cracking and reforming operations both the regenerating chamber and the cracking chamber may operate at substantially the same pressure. However, when omitting the repressuring chambers l1 and I8, the height of the tube discharging Spent catalyst into the regenerating stream should be sufiicient to develop sulcient static pressure at the bottom thereof to overcome the pressure drop through the circuit. Additional static pressure may also be developed in the conduit GS employed for charging the regenerated catalyst into the reaction chamber. In either case, it is important to maintain the catalyst passing through the pipes 25 or 66 in suilciently huid condition to transmit the pressure from the top to the bottom of the tubes. To this end, a fiuidizing gas may be introduced at spaced points along the tubes, if necessary.

Having described the preferred embodiment of the invention, it will be understood that it embraces such other variations and modications as come within the spirit and scope thereof.

- What is desired to be protected by Letters Patent is:

l. A process for the catalytic conversion of hydrocarbons which comprises forming a mixture of hydrocarbons to be converted and solid conversion catalyst in finely-divided state, passing said mixture upwardly through a reaction zone of predetermined cross-sectional area, thereafter passing the resulting mixture upwardly through a second zone having a cross-sectional -area different than said first-named zone, re-

moving the reaction products and catalyst from the last-named zone, separating the catalyst from the reaction products, regenerating a portion of the catalyst so separated, thereafter mixing a portion of the regenerated catalyst with the remaining unregenerated catalyst and returning said mixture to the second-named reaction zone.

2. A process for the catalytic conversion of hydrocarbons which comprises forming a mixture of hydhocarbons to be converted and solid conversion catalyst in finely-divided state, passing said mixture upwardly through a reaction zone of predetermined cross-sectional area, thereafter mixing additional catalyst with said reaction mixture, the temperature of said additional catalyst being diii'erent than the reaction mixture to thereby modify the temperature thereof. passing the resulting stream upwardy through a second reaction zone immediately above the first-named reaction zone, said second reaction zone having a cross-sectional area different than said firstnamed zone, preventing catalyst from said second-named zone fromrdischarging downwardly into said iirst-named zone and thereafter separating the reaction products from the conversion catalyst.

3. A process for the conversion of butanes to butadiene which comprises mixing a butanecontaining gas with a solid dehydrogenatlng catalyst in nely-divided state, passing the resulting mixture through a dehydrogenatlng zone of predetermined cross-sectional area, maintaining said zone at a temperature between about 900 F. and 1100 F., controlling the time within said zone to form a substantial amount of butenes, thereafter passing the reaction mixture and catalyst through a second zone of reduced cross-sectional area, maintaining said second zone at a temperature materially higher than said first-named zone, keeping the reaction gases in said secondnamed reaction zone for a period materially shorterthan the time during which the gases are maintained within theilrst-named reaction zone to convert a substantial portion oi' said butenes formed in said first-named zone into 'butadiene and thereafter separating the catalyst from the reaction mixture.

4. In the process defined by claim 3, the further improvement which comprises adding additional catalyst to the stream passing to the secondnamed zone, the temperature of said catalyst being materially higher than the reaction mixture to supply heat thereto.

5. A process for cracking hydrocarbon oils which comprises mixing with the oil to be cracked a solid cracking catalyst in finely-divided state,

passing the resulting mixture upwardly through preventing catalyst from said second-named cracking zone from discharging downwardly into said first-named cracking zone maintaining the oil vapors within said last-named cracking zone for a period suiicient to obtain additional cracking of said oil, and thereafter separating the cracked products from the catalyst.

6. A reaction chamber for the catalytic conversion of hydrocarbon oils which comprises a vertical tower forming an enclosed chamber, means for introducing hydrocarbons to be converted into the bottom section of said tower, a section of enlarged cross-sectional area at one end of said tower, a section of reduced cross-sectional area at the opposite end of said tower, means for introducing finely-divided catalyst into said section of enlarged cross-sectional area, and means for introducing iinely-divided catalyst into said section of reduced cross-sectional area.

7. A reaction chamber for the conversion of hydrocarbon oils comprising a vertical towerforming an enclosed chamber, a section of enlarged cross-sectional area at one end of said tower and a section of reduced cross-sectional area at the other end of said tower, means for introducing products .to b e converted into the lower end of said tower, means for withdrawing tower, means for introducing catalyst in finely- 1G and means for adding additional diluent gas into said tower at a point removed from the means for introducing the products to be reacted.

8. A process for the conversion of butanes to butadiene which comprises mixing a. butane-containing gas with a solid dehydrogenating catalyst in nely divided state, passing the resulting mixturev upwardly thrugh adehydrogenating zone maintained at a temperature between 900 and 1100 F., controlling the time of contact of said gas with said catalyst within said zone to convert a substantial portion of said butane into butenes, thereafter passing the reaction mixture and catalyst directly upward into a second dehydrogenating zone, introducing into the reaction mixture passing to said second zone a stream of finely divided solids at a temperature materially above the temperature of said reaction mixture to thereby rapidly heat said reaction mixture to a temperature materially above the temperature maintained in said first-named reaction zone, keeping the reaction gases in the s econd-named reaction zone for a period materially shorter than the time which the gases are maintained within the first-named reaction zone to convert a substantial portion of said butenes formed in said. first-named reaction zone into butadiene and thereafter separating gaseous re action products from the nely divided catalyst.

9. A process for the catalytic conversion of hydrocarbons which comprises forming a mixture of hydrocarbons to be converted and solid conversion catalyst in finely-divided state, passing the resulting mixture upwardly through a reaction zone of predetermined cross-sectional arca, thereafter adding diluent gas to the reaction mixture, 4the temperature of said diluent gas being different than said reaction mixture to thereby modify the temperature thereof, passing the divided state into said section of enlarged crosssectional area, means for introducing catalyst into said section of reduced cross-sectional area.

resulting stream upwardly through a second reaction zone immediately above the rst-named reaction zone, said second reaction zone having a cross=sectional area different than said firstnamed reaction zone, adding additional catalyst reaction products from the upper end of said 5 to the stream passing to said second reaction zone.

and thereafter separating the reaction products from the conversion catalyst.

PAUL W. CORNELL.

Images