UPGRADING STREAMS COMPRISING C3 AND C4 HYDROCARBONS

Abstract

A first stream containing 1,3-butadiene, C.sub.4 acetylenes, and optionally C.sub.3 hydrocarbons, is mixed with a portion of the liquid recycle stream from a C.sub.4 acetylene hydrogenation reactor containing hydrogenated C.sub.4 acetylenes and a molecular hydrogen-containing stream, the resulting mixed stream is then fed to a C.sub.4 acetylene hydrogenation reactor to selectively hydrogenate the C.sub.4 acetylenes in the crude butadiene stream without appreciable 1,3-butadiene conversion.

Claims

1. A selective hydrogenation process, comprising: contacting (a) a first stream comprising hydrocarbon compounds with a recycle portion of a liquid stream containing hydrogenated C.sub.4 acetylenes and (b) a molecular hydrogen-containing stream to form a mixed feed stream, wherein the mixed feed stream comprises: (i) one or more C.sub.3 hydrocarbon compounds, and (ii) C.sub.4 hydrocarbon compounds including C.sub.4 acetylenes and 1,3-butadiene; sending the mixed feed stream to a hydrogenation reactor to hydrogenate at least a portion of the C.sub.4 acetylenes to form an effluent stream containing hydrogenated C.sub.4 acetylenes; separating the liquid stream from the effluent stream, and removing the recycle portion from the liquid stream.

2. The selective hydrogenation process of claim 1 where the first stream additionally comprises at least one C.sub.3 hydrocarbon compound.

3. The selective hydrogenation process of claim 1 where the mixed feed stream additionally comprises propylene.

4. The selective hydrogenation process of claim 1 where the hydrogenation of at least a portion of the C.sub.4 acetylenes is conducted at a pressure great enough to keep the hydrocarbons in liquid phase.

5. The selective hydrogenation process of claim 4 where the pressure ranges from about 320 psia (about 2.2 MPa) to about 565 psia (about 3.9 MPa).

6. The selective hydrogenation process of claim 1 where the hydrogenation reactor has an inlet, and where the temperature at the inlet ranges from about 80° F. (27° C.) to about 122° F. (about 50° C.).

7. The selective hydrogenation process of claim 1 where the hydrogenation converts: (1) at least 45 wt % of the first stream's C.sub.4 acetylenes; and (2) an additional conversion selected from the group consisting of: at least 10 wt % of the first stream's 1,3-butadiene, less than or equal to 10 wt % of the first stream's C.sub.3 hydrocarbon, and a combination thereof.

8. The selective hydrogenation process of claim 1 where a recycle ratio of weight of the recycled portion of the separated liquid hydrocarbon to weight of the first stream ranges from about 0.75 to about 1.5.

9. An upgraded hydroprocessed product produced by the selective hydrogenation process of claim 1 comprising: from about 0.5 to about 1.0 wt % hydrogenated C.sub.4 acetylenes; and from about 8 to about 37 wt % hydrogenated 1,3-butadiene.

10. A selective hydrogenation system comprising: a debutanizer overhead reflux drum containing crude butadiene; a pump in fluid communication with crude butadiene in a first stream from the debutanizer overhead reflux drum through a heat exchanger to a hydrogenation reactor; a molecular hydrogen-containing stream in fluid communication with the first stream; an effluent line from the hydrogenation reactor directing an effluent stream through the heat exchanger to a recycle drum; a recycle line in communication with the first stream; and a hydrogenated product stream in fluid communication with the recycle line.

11. The selective hydrogenation system of claim 10 where the first stream additionally comprises at least one C.sub.3 hydrocarbon compound.

12. The selective hydrogenation system of claim 10 where the heat exchanger is a first heat exchanger and where the selective hydrogenation system further comprises a second heat exchanger in the first stream between the first heat exchanger and the hydrogenation reactor.

13. The selective hydrogenation system of claim 12 where the second heat exchanger is configured to receive low pressure steam to heat the first stream.

14. The selective hydrogenation system of claim 10 where the debutanizer is upstream of a depropanizer.

15. An ethylene plant comprising: a gas cracker comprising a crude product effluent; a debutanizer in fluid communication with the crude product effluent, the debutanizer comprising a debutanizer overhead reflux drum containing mixed C.sub.3s and Cas with the Cas including undesireable C.sub.4 acetylenes and desireable butadiene; a pump in fluid communication with crude butadiene in a first stream from the debutanizer overhead reflux drum through a heat exchanger to a hydrogenation reactor; a molecular hydrogen-containing stream in fluid communication with the first stream; an effluent line from the hydrogenation reactor directing an effluent stream through the heat exchanger to a recycle drum; a recycle line in communication with the first stream; and a hydrogenated product stream in fluid communication with the recycle line.

16. The ethylene plant of claim 15 where the first stream additionally comprises at least one C.sub.3 hydrocarbon compound.

17. The ethylene plant of claim 15 where the heat exchanger is a first heat exchanger and where the selective hydrogenation system further comprises a second heat exchanger in the first stream between the first heat exchanger and the hydrogenation reactor.

18. The ethylene plant of claim 17 where the second heat exchanger is configured to receive low pressure steam to heat the first stream.

19. The ethylene plant of claim 15 where the debutanizer is upstream of a depropanizer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1 is a schematic illustration of a non-limiting embodiment of a process for hydrogenation of C.sub.4 acetylenes in a crude butadiene stream also containing C.sub.3 hydrocarbons. FIG. 2 is a schematic illustration of the ethane cracker showing the placement of the C.sub.4 acetylenes reactor in the product recovery system.

DETAILED DESCRIPTION

[0025] It has been discovered that mixing a crude butadiene stream containing 1,3-butadiene, propylene, and C4 hydrocarbons, and optionally C.sub.3 hydrocarbons, with a molecular hydrogen-containing stream before feeding the resulting stream to the C.sub.4 acetylene hydrogenation reactor may preserve selectively for the hydrogenation of the C.sub.4 acetylenes in the stream while avoiding an increase in the loss of 1,3-butadiene and propylene in the stream.

[0026] In one embodiment, the C.sub.4 and C.sub.3 hydrocarbons in the stream may be a mixture of saturates, olefins, diolefins, and acetylenes. Example feed conditions of the C.sub.4 acetylenes and hydrogen (H.sub.2) feed are provide in Table Y below along with operating conditions.

TABLE-US-00001 Table-Y Feed conditions Operating conditions Pressure, psia (MPa) 340 (2.3) Temperature (inlet), F 93 Feed, lb/hr (kg/hr) 1 (0.45) H2, lb/hr (g/hr) 0.0007 (0.318) C.sub.4 acetylenes reactor feed H.sub.2 Components wt % wt % Hydrogen 0.01 100 Ethane 0.04 Methyl Acetylene 0.6 Propadiene 0.4 Propylene 41 Propane 7 Vinyl Acetylene 0.7 1-Butyne 0.1 1,3-Butadiene 38 1-Butene 4 Cis-2-Butene 1 Trans-2-Butene 1 Isobutylene 0.2 n-Butane 6 3-Methyl-1-Butene 0.1 Total 100 100

[0027] The hydrogenation catalyst(s) useful for hydrogenating the C.sub.4 acetylenes in the stream may be, without limitation, palladium-on-alumina catalysts with a proprietary component which improves vinyl acetylene conversion and selectivity. The primary reactions and possible but minor reactions are show below. Key process parameters are also provided below.

Primary Reactions

[0028] Vinyl Acetylene (C.sub.4H.sub.4)+H.sub.2.fwdarw.Butadiene (C.sub.4H.sub.6)
Ethyl Acetylene (C.sub.4H.sub.6)+H.sub.2.fwdarw.Butene (C.sub.4H.sub.8)
Butadiene (C.sub.4H.sub.6)+H.sub.2.fwdarw.Butene (C.sub.4H.sub.8)

Possible but Minor Reactions

[0029] Methyl Acetylene (C.sub.3H.sub.4)+H.sub.2.fwdarw.Propylene (C.sub.3H.sub.6)
Propadiene (C.sub.3H.sub.4)+H.sub.2.fwdarw.Propylene (C.sub.3H.sub.6)
Propylene (C.sub.3H.sub.6)+H.sub.2.fwdarw.Propane (C.sub.3H.sub.8)

TABLE-US-00002 Operating Temp. 27~50 Moderate Condition (° C.) LHSV 10~20 High Throughput Pressure (MPag) 2.2~3.9 Avoid vaporization Vinyl Acetylene   50~80% High Activity Conversion Butadiene Loss  −1.0~−0.2% Butadiene Gain Regeneration Depends on VA Period in Feed Regeneration Time 1~2 Day  Air Burning Process

[0030] Certain forms for the selective hydrogenation of C.sub.4 acetylenes contained with a crude butadiene stream comprising a mixture of a plurality of hydrocarbon compounds is shown schematically in in FIG. 1. The process and system are not limited to these forms, and this description should not be interpreted as excluding other forms within the broader scope of the process and/or system.

[0031] Referring to FIG. 1, a selective dehydrogenation process 10 is schematically shown which comprises a mixed C.sub.3/C.sub.4 product stream 11 containing 1,3-butadiene, propylene, and C.sub.3/C.sub.4 hydrocarbon mixture is pumped via pump 14 from debutanizer overhead reflux drum 12 and heated in first heat exchanger 16 to desired temperature of about 75-100° F. (about 17 to about 38° C.) in one non-limiting embodiment. It is appreciated that in another non-limiting embodiment that the pressure of the system and process should be great enough to keep hydrocarbons in liquid phase through the selective hydrogenation reactor 24, such as in the non-limiting range of about 325-375 psia (about 2.24 to 2.59 MPa). A portion of the liquid recycle stream 21 leaving the recycle drum 18 that is used to separate any vapor from the liquid in the cool reactor effluent stream 19 is combined with the mixed C.sub.3/C.sub.4 product stream 11. Pump 20 withdraws the recycle stream 21 from recycle drum 18. In one non-limiting embodiment, the recycle weight ratio of recycle stream 21 to mixed C.sub.3/C.sub.4 product stream 11 is in the range of about 0.75 to about 1.5, and will vary from the start to the end of the reactor run. This ratio may be optimized for determination of the size of the reactor and pumps, exchangers.

[0032] After the combination of mixed C.sub.3/C.sub.4 product stream 11 and 21 is heated, a molecular hydrogen-containing stream 13 is then added. This mixed reactor feed stream 15 is fed to a selective hydrogenation reactor 24 filled with suitable hydrogenation catalyst to selectively hydrogenate any C.sub.4 acetylenes in the feed. Mixed reactor feed stream 15 may be heated in second heat exchanger 22 by low pressure (LP) steam 25 for startup or end-of-run conditions. A warm reactor effluent stream 17 containing the selectively hydrogenated product is conducted away from the reactor outlet, cooled, and then sent to a recycle drum 18 for vapor/liquid separation. Part of the drum liquid, recycle stream 21, is directed to be combined with mixed C.sub.3/C.sub.4 product stream 11 and the upgraded hydroprocessed mixed C.sub.3/C.sub.4 product 23 containing the upgraded hydroprocessed mixed C.sub.3/C.sub.4 product is conducted away from the process for storage and/or further processing.

[0033] Referring to FIG. 2, a gas cracker is shown featuring ethane feed 30 (or a mix of ethane and propane) to the Pyrolysis System 31. The cracked gas 32 passes to the Quench and Condensate Recovery System 33 where it is cooled. The cooled crack gas 34 feeds the Compression, Acid Gas Removal and Drying Systems 35. The compressed cracked gas 36 feeds the Deethanizer and Acetylene Reactor Systems 37 where the C.sub.2 and lighter components 38 are separated from the C.sub.3 and heavier components 39. The C.sub.3 and heavier components 39 make up three products that have value: a propylene-rich mixed Cas product 40, a crude butadiene product 41, and a pyrolysis gasoline product 42.

[0034] Producing the crude butadiene product normally would have the C.sub.3 and heavier components feed a Depropanizer, with the bottoms then feeding a Debutanizer to produce a mixed C.sub.4s product on the Debutanizer overhead. The Debutanizer overhead can then be treated in a C.sub.4 Acetylene Reactor System provided to upgrade the crude butadiene product as the reduction or elimination of acetylenes can yield higher market value for the product stream or it could result in savings in a butadiene unit that exceed the cost of the C.sub.4 Acetylene Reactor System. However the C.sub.4 Acetylene Reactor System adds light end contaminants that would need to be removed by an additional Stripper System.

[0035] FIG. 3 shows resequencing operations to feed the C.sub.3 and heavier components to a Debutanizer 43 first, with the overhead mixed C.sub.3s and Cos crude butadiene 11 then feeding the C.sub.4 Acetylene Reactor System 44. The mixed C.sub.3/C.sub.4 product stream 11 then react with molecular hydrogen-containing stream 13 to achieve the targeted reactions. The upgraded hydroprocessed mixed C.sub.3/C.sub.4 liquid 23 containing light end contaminants can then feed the Depropanizer 45 which will separate out the Crude Butadiene 41 as the Depropanizer bottoms. This eliminates the Stripper System required in the conventional configuration.

[0036] An additional benefit of the reconfigured system is that C.sub.4 Acetylene Reactor System 44 operates at milder conditions which improve selectivity of the hydrogenation reactions as discussed above.

[0037] It is appreciated that conversion of C.sub.4 acetylenes can be targeted to meet the specifications for C.sub.4 acetylenes in the product crude butadiene stream. This is accomplished by controlled injection of hydrogen to hydrogenate C.sub.4 acetylenes selectively. The reactor size, recycle rate, pressure, and temperature of reactor inlet may be designed to achieve or exceed the desired conversion of C.sub.4 acetylenes and to decease or even minimize conversion of the 1,3-butadiene and propylene present in the crude butadiene stream. In one exemplary embodiment, the desired run length may be in the range of about 2 months independently to about 12 months; alternatively from about 6 independently to about 9 months; and the range of space velocity (LHSV) may be in the range of 4 independently to about 20; alternatively from about 8 independently to about 16.

[0038] It will also be appreciated that any hydrogenation of C.sub.3 acetylenes, such as methyl acetylene and propadiene, in this process, though not intended, is beneficial.

[0039] The processes and systems described herein may accomplish a variety of goals including, but not necessarily limited to: hydrogenating C.sub.4 acetylenes in mixed hydrocarbon streams in a manner that substantially maintains selectively and conversion for hydrogenating the C.sub.4 acetylenes; hydrogenating C.sub.4 acetylenes in mixed hydrocarbon streams in a manner that gives increased selectivity and/or conversion; and hydrogenating C.sub.4 acetylenes in mixed hydrocarbon streams with decreased hydrogenation of valuable hydrocarbons such as 1,3-butadiene and propylene. The processes and systems described herein are considered effective and successful even if only one of these goals is accomplished, such as achieving substantially the selectivity and conversion of C.sub.4 acetylenes in a mixed C.sub.3/C.sub.4 stream with a C.sub.4 stream. The processes and systems may be considered even more effective if one or more of the other goals is/are also achieved.

[0040] In the foregoing specification, the invention has been described with reference to specific embodiments thereof. However, the specification is to be regarded in an illustrative rather than a restrictive sense. For example, hydrocarbons, catalysts, hydrogenation reaction conditions and equipment, and composition and conditions of various streams falling within the claimed or disclosed parameters, but not specifically identified or tried in a particular example, are within the scope of this invention.

[0041] The present invention may be practiced in the absence of a feature not disclosed. In addition, the present invention may suitably comprise, consist or consist essentially of the elements disclosed. For instance, the process may comprise, consist of, or consist essentially of contacting a crude butadiene stream comprising 1,3-butadiene, propylene, and other C.sub.4 and C.sub.3 hydrocarbons with a portion of a liquid recycle stream containing hydrogenated C.sub.4 acetylenes and with a molecular hydrogen-containing stream to form a mixed feed stream, sending the mixed feed stream to a hydrogenation reactor to hydrogenate the C.sub.4 acetylene in the mixed feed stream to form an effluent stream containing hydrogenated C.sub.4 acetylenes, sending the effluent stream to a drum for vapor-liquid separation to separate any vapor from the liquid stream containing hydrogenated C.sub.4 acetylenes.

[0042] The words “comprising” and “comprises” as used throughout the claims, are to be interpreted to mean “including but not limited to” and “includes but not limited to”, respectively.

[0043] To the extent used herein, the word “substantially” shall mean “being largely but not wholly that which is specified.”

[0044] As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0045] To the extent used herein, the term “about” in reference to a given parameter is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the given parameter).

[0046] To the extent used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.