WO1997033953A1

WO1997033953A1 - Catalytic distillation and hydrogenation of heavy unsaturates in an olefins plant

Info

Publication number: WO1997033953A1
Application number: PCT/US1997/002354
Authority: WO
Inventors: Stephen J. Stanley; Charles Sumner
Original assignee: Abb Lummus Global Inc.
Priority date: 1996-03-12
Filing date: 1997-02-13
Publication date: 1997-09-18
Also published as: AU2273597A; ID18844A

Abstract

In an olefins plant for the production and recovery of ethylene and propylene, the hydrogenation of the C2 acetylene, the C3 acetylenes and dienes and the C4 and heavier acetylenes, dienes and olefins and the selective separation of the resulting products is carried out by the use of various arrangements of one or more reaction distillation columns. These columns contain a hydrogenation catalyst and concurrently perform a catalytic hydrogenation reaction and a distillation function.

Description

Catalytic Distillation And Hydrogenation Of Heavy Unsaturates In An Olefins Plant

Background of the Invention

The present invention relates to a process system for the production of olefins and particularly to processing the charge gas feed to more effectively recover the product and process the by-products.

Ethylene, propylene and other valuable petrochemicals are produced by the thermal cracking of a variety of hydrocarbon feedstocks ranging from ethane to heavy vacuum gas oils. In the thermal cracking of these feedstocks, a wide variety of products are produced ranging from hydrogen to pyrolysis fuel oil. The effluent from the cracking step, commonly called charge gas or cracked gas, is made up of this full range of materials which must then be separated (fractionated) into various product and by-product streams followed by reaction (hydrogenation) of at least some of the unsaturated by-products.

The typical charge gas stream, in addition to the desired products of ethylene and propylene, contains C₂ acetylenes, C₃ acetylenes and dienes and C₄ and heavier acetylenes, dienes and olefins as well as a significant quantity of hydrogen. In the majority of prior processes, the C₂ acetylenes and C₃ acetylenes and dienes and the C₅ and heavier dienes, acetylenes and olefins are catalytically hydrogenated in fixed bed reactors using a series of commercially available catalysts. In a growing number of applications, the C₄ acetylenes, dienes, and olefins are also catalytically hydrogenated in fixed bed reactors. These separate hydrogenation steps take place in one of two process sequences. In a typical prior art process, the charge gas is compressed to between 2.76 and 4.14 MPa (400 and 600 psia). It is then progressively chilled condensing the C₂ and heavier components. Hydrogen is cryogenically recovered and methane is fractionated out of the stream. The remaining C₂ and heavier stream enters a series of fractionation towers. The first tower, the deethanizer, produces an overhead stream containing the C₂ acetylenes, olefins, and paraffins. This stream is sent to a fixed bed, vapor phase reactor where the C₂ acetylene is selectively hydrogenated using the hydrogen cryogenically separated earlier from the charge gas stream.

The second tower in this sequence, the depropanizer, produces an overhead stream containing the C₃ acetylenes, dienes, olefins and paraffins. This stream is sent to a fixed bed, vapor or liquid phase reactor where the C₃ acetylenes and dienes are selectively hydrogenated using the hydrogen cryogenically separated earlier from the charge gas stream.

The third tower, the debutanizer, produces an overhead stream containing the C₄ acetylenes, dienes, olefins, and paraffins. This stream is then sent either to battery limits as a final product or to a fixed bed, liquid phase reactor where the dienes, acetylenes, and in some instances the olefins are hydrogenated using the hydrogen cryogenically recovered previously from the charge gas. The bottoms of the third tower contains the C₆ and heavier dienes, acetylenes, olefins and paraffins. This stream is sent to a series of two fixed bed, liquid phase reactors. In the first, the acetylenes and dienes are catalytically hydrogenated. The olefins are catalytically hydrogenated in the second reactor. Both reactors utilize the hydrogen cryogenically recovered previously from the charge gas. In some applications, the third tower produces an overhead stream containing both the C₄ and C₅ acetylenes, dienes, olefins, and paraffins. These are hydrogenated as discussed previously for the C₄'s alone, in a single fixed bed, liquid phase reactor. The C_β and heavier dienes, acetylenes, olefins and paraffins exit in the bottoms of the third tower and are hydrogenated as discussed previously in two fixed bed, liquid phase reactors.

In a variation of the typical process just described, the cracked gas is compressed to between 2.07 and 3.45 MPa (300 and 500 psia) and sent to a fractionation tower. The overhead of the tower is the C₃ and lighter portion of the charge gas. It is sent to a series of fixed bed, vapor phase reactors where the C₂ acetylene and a portion of the C₃ acetylenes and dienes are hydrogenated using a small portion of the hydrogen contained in the C₃ and lighter stream. The unhydrogenated portion of the C₃ acetylenes and dienes as well as the C₄ and heavier acetylenes, dienes, and olefins are hydrogenated in a fashion similar to that described above. In many new olefin plants, butadienes are hydrogenated to olefins or butadienes and butenes are totally hydrogenated to butanes. In some cases, the saturated C₄'s, and in some instances the saturated C₆'s also, are recycled to the cracking heaters.

While widely practiced, the typical processes described above have a number of disadvantages. Where the unsaturated C₃'s (methyl acetylene and propadiene), C₄'s and gasoline (including the C₆'s) are being hydrogenated, at least three separate fixed bed reactors are required. If gasoline is being hydrogenated in two stages, the number of fixed bed reactors is four. This number of fixed bed reactors contributes significantly to the capital cost of the system and to the operational complexity. Even when a system is used which processes the C₄ and C₅ unsaturates together, rather than the C₄'s separately and the C₅'s together with the gasoline, one less fractionating tower is required but the number of hydrogenation reactors remains the same.

Summary of the Invention The present invention involves the recovery of ethylene and propylene in an olefins plant and the hydrogenation and separation of the heavier unsaturates. An object of the present invention is to provide a method for the hydrogenation of the C₂ acetylenes, the C₃ acetylenes and dienes and the C₄ and heavier acetylenes, dienes and olefins and the selective separation of the resulting products in a process scheme which minimizes the required number of reactors and fractionators thereby minimizing capital and operational costs. More specifically, the invention involves the use of combined reaction-fractionation steps known as catalytic distillation to simultaneously carry out the hydrogenation reactions and the desired separations. Brief Description of the Drawings

Figure 1 is a flow sheet for a conventional prior art olefin plant. Figure 2 is a flow sheet for a modified prior art olefin plant. Figure 3 is a flow sheet for an olefin plant according to the present invention.

Figures 4 to 8 are flow sheets similar to the flow sheet of Figure 3 but illustrating alternate embodiments of the present invention.

Description of the Preferred Embodiments

Referring first to Figure 1 which illustrates a conventional prior art olefin plant, the typical pyrolysis and associated heat recovery units, generally designated 4, produce a charge gas 6 and a heavies stream 8 consisting mainly of C_β and heavier components. The charge gas 6 is first compressed at 12 up to a pressure of 2.76 to 4.14 MPa (400 to 600 psia). The majority of the compressed gas then undergoes cryogenic treatment at 14 to separate hydrogen 15 followed by separation of methane at 16. A small portion of the C₃ and heavier material condenses in the compressor train and often bypasses the cryogenic demethanization and deethanization steps going directly to the depropanizer 30 as stream 31. The gas stream 18 is then deethanized at 20 with the C₂ acetylenes in the C₂ gas stream being hydrogenated at 22 with hydrogen 15 and fractionated at 24 to produce essentially ethylene 26 and ethane 28. The bottoms 29 from the deethanizer 20 are depropanized at 30 with the separated C₃ acetylenes and dienes in the C₃ stream 32 being hydrogenated at 34 also with hydrogen 15 and fractionated at 36 to produce essentially propylene 38 and propane 40. Likewise, the bottoms from the depropanizer 30 are debutanized at 42 producing the C₄ stream 44 which is hydrogenated at 46.

The C₅+ stream 48 is fed to the gasoline hydrotreater 50 along with the heavies 8 from the front end of the system and hydrogen 15. The C₆+ stream including the heavies from the front end are usually hydrogenated in two stages. In the first stage, the diolefins and acetylenes are hydrogenated. In the second stage, olefins are hydrogenated and sulfur compounds are converted to hydrogen sulfide. The partially hydrogenated product 52 from the first gasoline hydrotreater 50 is then fractionated at 54 which removes the C₆'s to C_β's as overhead 56 leaving the C_β+ as a bottoms product 58. The overheads 56 are then further hydrogenated at 60 followed by fractionation at 62 producing the overhead 64 of saturated C₆'s and a bottoms gasoline product 66 of saturated C_β's to C_β's. The C₅ stream 64 is combined with the saturated C₄ stream from the hydrogenation step 46 and the combined stream 65 of the C₄'s and C_s's is usually recycled to the pyrolysis heaters. The ethane and propane streams 28 and 40 may also be recycled to the pyrolysis heaters.

Figure 2 illustrates a prior art variation of the process shown in Figure 1 wherein the C₄ and C_G unsaturates are processed together rather than processing the C₄'s separate from the C₆'s as in Figure 1 where the C₅'s are processed with the gasoline. In this Figure 2 embodiment, the C₄+ bottoms from the depropanizer 30 together with the heavies 8 from the front end of the system are fed to the fractionator 42 which is now operated as a depentanizer to separate the C₄'s and C_ε's in the overhead 44. Once again, the overhead 44 is hydrogenated at 46 to produce essentially the same C₄ and C₅ stream 65 as in Figure 1. The bottoms stream 48 from the depentanizer 42, which now contains the C_β+ components including those from the heavies stream 8, is again fed to the gasoline hydrotreater 50 for partial hydrogenation, to the fractionator 54 for separation of the C₉+ fraction and to the hydrotreater 60 for final hydrogenation leaving the C_β to C_β gasoline stream 66 just as in Figure 1. As can be seen, this Figure 2 embodiment employs one less fractionator than the Figure 1 embodiment but both of these schemes use five separate hydrogenators or hydrotreaters.

The object in these processes is to separate the desired fractions and to selectively hydrogenate the C₂ and C₃ acetylenes and dienes as well as the C₄ and acetylenes, dienes and olefins without hydrogenating the desired olefins, i.e., the ethylene and propylene. For example, the selective hydrogenation of a propylene cut is not only essential for the production of high purity propylene but the hydrogenation of the methyl acetylene and propadiene in this cut (collectively referred to as MAPD) produces additional propylene resulting in a high yield. In the present invention, these separations and hydrogenation are carried out at least in part by catalytic distillation hydrogenation.

Catalytic distillation is a process which combines conventional distillation with catalytic reactions. In the process of the present invention, the catalytic reaction is hydrogenation. Catalytic distillation employs the catalytic material within the distillation column as both a catalyst for the reaction and as a column packing for the distillation. The catalyst has both a distillation function and a catalytic function. For additional information relating to catalytic distillation in general and catalytic distillation hydrogenation in particular, reference is made to U.S. Patents 4,302,356; 4,443,559 and 4,982,022.

Turning now to the present invention as depicted in Figure 3, the deethanizer bottoms 29 are fed to the catalytic distillation hydrogenation/depropylenizer 68 usually together with the heavies 8 from the front end and compressor condensates 36. Although various known hydrogenation catalysts can be used, one preferred catalyst is 0.3 wt. % palladium oxide on a spherical aluminum oxide support with a particle size of about 1/8 inch (3.2 mm). The depropylenizer 68 has a catalyst bed 70 above and another catalyst bed 72 below the generally centrally located feed zone 74. The MAPD is hydrogenated mostly in the upper section 70 of the tower while the C₄+components are at least partially hydrogenated in the lower section 72. The depropylenizer is operated under conditions of pressure and temperature such that the overheads 76 are essentially all propylene and the bottoms 78 contain most of the propane and C₄+components. Hydrogen 15 from the cryogenic separation unit 14 may be fed to the feed zone 74 and/or into the bottom of the tower. The depropylenizer bottoms, since they are now significantly hydrogenated, are much less subject to fouling and can be fractionated at relatively higher temperatures than in a normal process thereby decreasing refrigeration requirements. In this Figure 3 embodiment, the bottoms 78 from the depropylenizer 68 are fed to the depentanizer 80 which is a distillation unit functioning to remove the propane and the C₄'s and C₅'s as overhead 82 and the C_β+ components as bottoms 84. The overhead 82, which is for the most part now the saturated C₃, C₄ and C₅'s, is preferably recycled to the pyrolysis heater. The bottoms 84 from the depentanizer 80, which are already at least partially hydrogenated, are fractionated at 86 to remover the C₉+ components as bottoms 88 and then hydrotreated at 90 to complete the hydrogenation. The product 92 is a saturated C_β - C₈ gasoline. As can be seen, this embodiment of the present invention, which achieves the same separations and degree of reaction as the Figures 1 and 2 processes, substitutes the one catalytic distillation hydrogenation unit 68 for the depropanizer 30, the hydrogenation 34, the f ractionation 36, the hydrogenation 46 and the hydrotreater 50 of the prior art Figure 2 arrangement. Figure 4 depicts another embodiment of the present invention which includes a depropylenizer 68 similar to the Figure 3 embodiment. The bottoms 78 from the depropylenizer 68 are fed to a depentanizer 94 which in this Figure 4 embodiment is another catalytic distillation hydrogenation tower containing the catalyst beds 96 and 98. Although this adds an additional catalytic distillation hydrogenation unit in place of the depentanizer distillation unit 80 of Figure 3, it provides more operating flexibility. The hydrogenation beds in the depropylenizer 68 now only need to hydrogenate the acetylenes and dienes leaving the olefin hydrogenation for the depentanizer 94. This will usually result in lower propylene losses (or greater propylene gains) through hydrogenation in the depropylenizer 68. A further variation of the present invention is shown in Figure 5 where the deethanizer bottoms 29 are fed to a catalytic distillation hydrogenation unit 100 which is operated as a depentanizer rather than as a depropylenizer as 68 in Figures 3 and 4. This unit 100 contains a catalyst bed 102 in the upper portion above the feed and a second catalyst bed 104 in the lower portion below the feed. MAPD, C₄'s and C₅'s are mostly hydrogenated in the upper portion while the C₆+ are mostly hydrogenated in the lower portion. The overhead 106 from the depentanizer 100 containing the C₃ - C₆ components is fed to the depropylen izer 108 where the propylene product 110 is separated from the basically saturated C₃ - C₆ components 112 which are recycled to the pyrolysis heater. The C_β+ bottoms 114 from the depentanizer 100 is fractionated at 86 to remove C_fl+ components and hydrotreated at 90 to produce C_β - C₈ gasoline 92. Figure 6 is a variation of the invention shown in Figure 4 and involves the use of catalytic distillation hydrogenation in conjunction with the deethanizer. A hydrogenation catalyst bed 116 is placed in the bottom of the deethanizer column 118. The overhead from the deethanizer, which still contains the C₂ acetylenes, the ethylene and the ethane, is handled the same as in Figure 4. In the catalyst bed 116 in the bottom part of the deethanizer 118, the C₃+ acetylenes and dienes can be totally or at least mostly hydrogenated. This minimizes the chances of fouling caused by unsaturates in the bottom of the deethanizer. In this arrangement, any excess or unreacted hydrogen from deethanizer 118 flows to the hydrogen ator 22 along with the hydrogen 15 for hydrogenation of acetylene. Since hydrogenation is now taking place in the deethanizer, the depropylenizer 120 need not have catalytic distillation and hydrogenation as in the Figure 4 arrangement. The depropylenizer 120 now merely involves fractionation to separate the propylene from the bottoms 78 which are processed the same as in Figure 4. In this scheme, the balance of the hydrogenation which is not completed in the deethanizer 118 is essentially completed in the depentanizer 94. Although not shown in Figure 6, the deethanizer 118 would require a side condenser to remove the heat of the hydrogenation reaction. As a variation, the overhead from the deethanizer 118 could also contain the C₃ components.

Figure 7 depicts still another variation of the invention in which the bottoms from the deethanizer 20 together with the streams 8 and 31 are fed to the catalytic distillation hydrogenation unit 122 which is operated as a depropanizer. The MAPD is hydrogenated in the upper catalyst bed 124 and the C₃+ acetylenes and dienes are hydrogenated in the lower catalyst bed 126. The overhead 128 comprising the C₃'s is fed to the depropylenizer 130 where the propylene 132 is separated from the propane 134. The bottoms 136 from the catalytic distillation hydrogenation unit 122 are fed to the catalytic distillation hydrogenation unit 138 which is operated as a depentanizer and in which all the olefins are converted to saturates. The overhead C₆- stream 140 is combined with the propane stream 134 to form the stream 142 for recycle to the pyrolysis heater. The bottoms stream 144 of C₆+ is then processed the same as in Figures 3 to 6.

Figure 8 is a variation on the Figure 7 embodiment. This involves the same catalytic distillation hydrogenation unit 122 and depropylenizer 130 but the bottoms 136 from the unit 122 are fed to a catalytic distillation unit 146 which is now operated as a debutanizer. Again, the MAPD and the C₄ acetylene and dienes are hydrogenated in the depropanizer 122 while the remaining hydrogenation to saturates occurs in the debutanizer 146. The overhead 148 from the debutanizer 146 now contains the saturated C₄'s and it is joined with the propane stream 134 to form stream 150 for recycle. The bottoms stream 152 containing the C₆+ is fractionated at 154 to produce a C_s product 156. The C₆+ bottoms 158 from the fractionator 154 is then handled in the same manner as the C_β+ streams in the other schemes. As a variation of the flow schemes described and referring to Figure

3, the catalytic distillation tower 68 can be operated at conditions which produce totally or mostly saturated products. In this mode of operation, stream 82 is totally or mostly saturated hydrocarbons and typically would be recycled to the cracking heaters to produce additional desired dehydrogenated products. It is possible to also operate catalytic distillation tower 68 to remove acetylenes and dienes only, preferably with minimum co-current conversion of olefins. In this case, stream 82 has a high olefin content and can then be further processed to produce butane products, methy tertiary butyl ether (MTBE), tertiary amyl methyl ether (TAME), or utilized in gasoline alkylation, or for other suitable processing as well known in the prior art. This same variation can also be applied to the other flow schemes of the present invention.

Claims

Claims:

1. A method of processing a cracked feed stream containing C₂ components including ethylene, C₃ components including propylene, acetylenes and dienes, C₄ and C₆ components including acetylenes, dienes and olefins and C₆+ components including unsaturates to recover said ethylene and propylene therefrom and to hydrogenate said C₃ acetylenes and dienes to produce additional propylene and to hydrogenate at least some of said C₄ and C₆ acetylenes, dienes and olefins to saturates and to hydrogenate said C_β+ unsaturates to a mixture of olefins and saturates without significantly hydrogenating said ethylene and propylene comprising the steps of: a. separating said C₂ components from said feed stream leaving a C₃+ stream; b. separating said ethylene as a product from said separated C₂ components; c. introducing said C₃+ stream and hydrogen into a reaction distillation column containing a hydrogenation catalyst; d. concurrently: (i) contacting said C₃+ stream in said reaction distillation column with said hydrogen and said hydrogenation catalyst whereby said C₃ acetylenes and dienes are hydrogenated producing additional propylene and whereby at least some of said C₄ and C₅ acetylenes, dienes and olefins are hydrogenated to C₄ and C₅ saturates and whereby at least some of said C₆+ unsaturates are hydrogenated to C_β+ olefins and saturates; and (ii) distilling said C₃+ stream and separating essentially all of said propylene as overhead and essentially all of said C_β+ olefins and saturates as bottoms; e. recovering propylene as a product from said overhead.

2. A method as recited in claim 1 wherein essentially all of said C₄ and C₅ components are separated with said bottoms.

3. A method as recited in claim 2 and further including the step of distilling said bottoms and separating a second overhead stream containing essentially all of said C₄ and C₅ components and a second bottoms stream containing essentially all of said C_β+ components.

4. A method as recited in claim 3 wherein said C₃+ stream further contains propane and said bottoms further contains essentially all of said propane and said second overhead stream also contains essentially all of said propane.

5. A method as recited in claim 3 and wherein said C₆+ components include C_β to C_β components and C₉+ components and further including the step of fractionating said second bottoms stream and separating a third overhead stream containing essentially all of said C_β to C₈ components and a third bottoms stream containing essentially all of said C₉+ components and further hydrogenating said third overhead stream.

6. A method as recited in claim 3 wherein said step of distilling said bottoms comprises the step of contacting said bottoms in a second reaction distillation column containing a hydrogenation catalyst whereby said bottoms are further hydrogenated.

7. A method as recited in claim 6 wherein said C₃+ stream further contains propane and said bottoms further contains essentially all of said propane and said second overhead stream also contains essentially all of said propane.

8. A method as recited in claim 6 wherein said C_β+ components include C_β to C_β components and C₉+ components and further including the step of fractionating said second bottoms stream and separating a third overhead stream containing essentially all of said C_β to C_β components and a third bottoms stream containing essentially all of said C₉+ components and further hydrogenating said third overhead stream.

9. A method as recited in claim 3 wherein said C₃+ stream further contains propane and said overhead contains essentially all of said propane and further including the step of fractionating said overhead and recovering propylene.

10. A method as recited in claim 1 wherein said C₃+ stream further contains propane and wherein essentially all of said propane and said C₄ and C₅ components are separated with said propylene as overhead and wherein said step of recovering propylene comprises the step of fractionating said propylene from said propane and said C₄ and C₅ components.

11. A method as recited in claim 10 wherein said C₆+ components include C_β to C_β components and C₉+ components and further including the step of fractionating said second bottoms stream and separating a third overhead stream containing essentially all of said C_β to C_β components and a third bottoms stream containing essentially all of said C₉+ components and further hydrogenating said third overhead stream.

12. A method as recited in claim 2 and further including the step of distilling said bottoms and separating a second overhead stream containing essentially all of said C₄ components and a second bottoms stream containing all of said C_s components and said C_β+ components.

13. A method as recited in claim 12 and wherein said C₃+ stream further contains propane and said overhead contains essentially all of said propane and further including the step of fractionating said overhead and recovering propylene.

14. A method as recited in claim 12 and further including the step of fractionating said second bottoms stream and separating said C₆ components from said C_β+ components.

15. A method as recited in claim 14 wherein said C₆+ components include C₆ to C_β components and C₉+ components and further including the step of fractionating said second bottoms stream and separating a third overhead stream containing essentially all of said C₆ to C₈ components and a third bottoms stream containing essentially all of said C₉+ components and further hydrogenating said third overhead stream.

16. A method as recited in claim 1 wherein said cracked feed stream further includes heavy cracked gasoline and wherein said at least a portion of said heavy cracked gasoline is separated from said cracked feed stream prior to said step (a) of separating said C₂ components and further including the step of feeding said separated heavy cracked gasoline into said reaction distillation column together with said C₃+ stream and hydrogen.

17. A method as recited in claim 16 and further including the step of distilling said bottoms and separating a second overhead stream containing essentially all of said C₄ and C_s components and a second bottoms stream containing essentially all of said C₆+ components.

18. A method as recited in claim 17 wherein said C₃+ stream further contains propane and said bottoms further contains essentially all of said propane and said second overhead stream also contains essentially all of said propane.

19. A method as recited in claim 17 and wherein said C_β+ components include C_β to C_β components and C₉+ components and further including the step of fractionating said second bottoms stream and separating a third overhead stream containing essentially all of said C_β to C_β components and a third bottoms stream containing essentially all of said C₉+ components and further hydrogenating said third overhead stream.

20. A method as recited in claim 17 wherein said step of distilling said bottoms comprises the step of contacting said bottoms in a second reaction distillation column containing a hydrogenation catalyst whereby said bottoms are further hydrogenated.

21. A method as recited in claim 20 wherein said C₃+ stream further contains propane and said bottoms further contains essentially all of said propane and said second overhead stream also contains essentially all of said propane.

22. A method as recited in claim 20 wherein said C₆+ components include C_β to C_β components and C₉+ components and further including the step of fractionating said second bottoms stream and separating a third overhead stream containing essentially all of said C₆ to C„ components and a third bottoms stream containing essentially all of said C₉+ components and further hydrogenating said third overhead stream.

23. A method as recited in claim 17 wherein said C₃+ stream further contains propane and said overhead contains essentially all of said propane and further including the step of fractionating said overhead and recovering propylene.

24. A method as recited in claim 16 wherein said C₃+ stream further contains propane and wherein essentially all of said propane and said C₄ and C₅ components are separated with said propylene as overhead and wherein said step of recovering propylene comprises the step of fractionating said propylene from said propane and said C₄ and C₅ components.

25. A method as recited in claim 24 wherein said C„+ components include C_β to C_β components and C_β+ components and further including the step of fractionating said second bottoms stream and separating a third overhead stream containing essentially all of said C_β to C„ components and a third bottoms stream containing essentially all of said C₉+ components and further hydrogenating said third overhead stream.

26. A method as recited in claim 16 and further including the step of distilling said bottoms and separating a second overhead stream containing essentially all of said C₄ components and a second bottoms stream containing all of said C_s components and said C_β+ components.

27. A method as recited in claim 26 and wherein said C₃+ stream further contains propane and said overhead contains essentially all of said propane and further including the step of fractionating said overhead and recovering propylene. 17

28. A method as recited in claim 26 and further including the step of fractionating said second bottoms stream and separating said C₆ components from said C_β+ components.

29. A method as recited in claim 28 wherein said C₆+ components include C_β to C₈ components and C₉+ components and further including the step of fractionating said second botto s stream and separating a third overhead stream containing essentially all of said C_β to C₈ components and a third bottoms stream containing essentially all of said C₉+ components and further hydrogenating said third overhead stream.

30. A method as recited in claim 1 wherein said separating step (a) and said step (d) of contacting said C₃+ stream with said hydrogen and said hydrogenation catalyst and distilling said C₃+ stream are combined in said reaction distillation column and wherein essentially all of said C₃+ components are separated as bottoms.

31. A method as recited in claim 30 wherein said propylene is distilled from said bottoms.

32. A method as recited in claim 1 wherein said separating step (a) and said step (d) of contacting said C₃+ stream with said hydrogen and said hydrogenation catalyst and distilling said C₃+ stream are combined in said reaction distillation column of step (c) and wherein essentially all of said C₂ and C₃ components are separated as overhead and said C₄+ components are separated as bottoms.

33. A method as recited in claim 1 wherein said step (a) of separating said C₂ components from said feed stream leaving a C₃+ stream and said step (c) of introducing said C₃+ stream and hydrogen into a reaction distillation column containing a hydrogenation catalyst comprise the step of introducing said feed stream into a reaction distillation column containing a distillation section in the upper portion thereof for the separation of C₂ components and a reaction distillation section containing said catalyst in the lower portion thereof for the combined separation of C₂ components and hydrogenation of C₃+ components.

34. A method as recited in claim 1 wherein said cracked gas feed stream is obtained by the step of cracking a hydrocarbon feedstock and wherein said C₃+ stream further contains propane and wherein said steps of distilling said C₃+ stream includes the step of separating said propane and said C₄ and C₆ saturates and recycling said separated propane and C₄ and C₆ saturates to said step of cracking.

35. A method of processing a cracked gas feed stream containing C₂ components, C₃ acetylenes and dienes, C₄ and C₆ acetylenes, dienes and olefins and C_β+ gasoline range unsaturates comprising the steps of: a. separating said C₂ components from said cracked gas feed stream thereby producing a remaining cracked gas feed stream; b. hydrogenating said remaining cracked gas feed stream in a series of distillation columns at least one of which is a reaction distillation column containing a hydrogenation catalyst whereby said C₃ acetylenes and dienes are hydrogenated primarily to propylene, said C₄ and C_β acetylenes, dienes and olefins are hydrogenated primarily to saturates and said C_β+ gasoline range unsaturates are hydrogenated to a C_β+ mixture of olefins and saturates; and c. separating said propylene, said C₄ and C₅ saturates and said C₆+ mixture by fractionation at least partially in said at least one reaction distillation column.

36. A process as recited in claim 35 wherein said process includes two reaction distillation columns in series.

37. A process as recited in claim 35 wherein said cracked gas feed stream further includes a heavy cracked gasoline fraction and further including the steps of separating said heavy cracked gasoline fraction from said cracked gas feed stream prior to the separation of said C₂ components and feeding said separated heavy cracked gasoline fraction to said reaction distillation column.

38. A method as recited in claim 35 wherein said cracked gas feed stream is obtained by the step of cracking a hydrocarbon feedstock and wherein said hydrogenated remaining cracked gas feed stream further contains propane and wherein said step of separating said C₄ and C₅ saturates further includes the step of separating said propane and recycling said separated propane and C₄ and C₅ saturates to said step of cracking.

39. A method of processing a cracked feed stream containing C₂ components including ethylene, C₃ components including propylene, acetylenes and dienes, C₄ and C₆ components including acetylenes, dienes and olefins and C₆+ components including unsaturates to recover said ethylene and propylene therefrom and to hydrogenate said C₃ acetylenes and dienes to produce additional propylene and to hydrogenate at least some of said C₄ and C₆ acetylenes, dienes and olefins to saturates and to hydrogenate said C„+ unsaturates to a mixture of olefins and saturates without significantly hydrogenating said ethylene and propylene comprising the steps of: a. separating said C₂ and C₃ components from said feed stream leaving a C₄+ stream; b. hydrogenating said separated C₂ and C₃ components and separating said ethylene and propylene as products therefrom; c. introducing said C₄+ stream and hydrogen into a reaction distillation column containing a hydrogenation catalyst; d. concurrently: (i) contacting said C₄+ stream in said reaction distillation column with said hydrogen and said hydrogenation catalyst whereby at least some of said C₄ and C₆ acetylenes, dienes and olefins are hydrogenated to C₄ and C₆ saturates and whereby at least some of said C_β+ unsaturates are hydrogenated to C₆+ olefins and saturates; and (ii) distilling said C₄+ stream and separating essentially all of said C₄ and C_s components as overhead and essentially all of said C_β+ olefins and saturates as bottoms.