WO1992001658A1

WO1992001658A1 - Extraction of selected hydrocarbons from a hydrocarbon stream using a carbon adsorbent

Info

Publication number: WO1992001658A1
Application number: PCT/US1991/004701
Authority: WO
Inventors: John Di-Yi Ou
Original assignee: Exxon Chemical Patents Inc.
Priority date: 1990-07-17
Filing date: 1991-07-02
Publication date: 1992-02-06

Abstract

Poly-isobutylene (PIB) is selectively removed from a hydrocarbon stream by activated carbon. The stream which can exceed 100 ppm PIB is contacted with the activated carbon for a sufficient time to reduce the PIB content of the hydrocarbon stream to less than about 1 ppm.

Description

EXTRACTION OF SELECTED HYDROCARBONS FROM A

HYDROCARBON STREAM USING A CARBON ADSORBENT

BACKGROUND OF THE INVENTION

1. Field of the Invention The present invention relates to extraction of selected hydrocarbons from mixed hydrocarbon and raffinate streams using carbon. More particularly, the present invention is directed to adsorbing polymeric hydrocarbons from hydrocarbon or raffinate streams using activated carbon as the adsorbent. Specifically, the present invention is directed to the extraction of poly-isobutylene from C< and/or C_s raffinate using activated carbon as the adsorbent.

2. Discussion of Background and Material Information Steam cracked naphtha produces several product streams including a C₄ raffinate stream. This C₄ stream is a mixture of four carbon hydrocarbons and can be used in the production of methyl tert-butyl ether (MTBE) or poly-isobutylene (PIB) .

In MTBE production, the process steps include adding methanol to the C₄ raffinate stream to produce MTBE and subsequent recovery of methanol.

In the PIB process, the C₄ stream is contacted to an acidic catalyst to convert isobutylene to poly-isobutylene. At steps during the PIB process a second C₄ raffinate stream is recovered. This C₄ stream typically contains butene-l, butene-2, isobutylene, n-butane, isobutane, and a low level of impurities including a small amount of PIB.

A C₄ stream with a small PIB content, however, is considered unacceptable for MTBE production due in part to the high boiling point of PIB. Related to this, even small quantities, in parts per million, have been observed to plug a methanol recovery column in a processing plant and cause a shut down.

PIB has a molecular weight which ranges from 112 - 2

gram/mole to more than 2,500 gram/mole with a typical weight of 900 gram/mole.

Distillation separation of PIB from the second C₄ stream is impractical because of the relatively low levels of PIB present, the relatively high molecular weight of PIB, and because PIB is relatively viscous and has a high boiling point relative to the C₄ isomers.

U.S. Patent 3,725,377, COTTLE, assigned to Phillips Petroleum Company, is directed to a process for polymerizing monomers which involves contacting the polymerization feedstock stream with an adsorbent material to remove non- polymerizable hydrocarbons separated from the feedstock stream. More specifically, COTTLE discloses the clean-up of butadiene for anionic polymerization, although he also discloses that the process can be used to purify other olefinic, dienic, styrenic streams, and even hydrocarbon solvents. COTTLE begins his process by partially purifying the feed by hydrogenation and fractional distillation, and then contacts the resultant stream with an adsorbent which may be activated carbon. Although isobutylene is a component of the stream used in the example, as indicated in the Table, there is no teaching or suggestion that poly-isobutylene is a contaminant in the stream, or that poly-isobutylene would be adsorbed by the activated carbon. U.S. Patent 2,765,914, SEYFRIED, assigned to Esso Research and Engineering Company, is directed to a method for removing free sulfur from liquified hydrocarbon gas, and more specifically by removing the elemental sulfur by adsorption of the sulfur on adsorbent carbon. SEYFRIED discloses treating a C^C_β, non-aromatic, liguefiable hydrocarbon with activated carbon to remove sulfur. Although C_j-C_β, non- aromic, liguefiable hydrocarbons are broadly disclosed and claimed, liquified petroleum gas is disclosed as being most preferred for purposes of treatment in accordance with the invention disclosed by SEYFRIED. SEYFRIED does not teach or suggest the attraction of branched-chain hydrocarbons, or poly-isobutylene, using activated carbon. U.S. Patent 4,734,273, HASKELL, assigned to Shell Oil Company, is directed to a process for selectively sorbing trace amounts of oxygen from low molecular weight olefins and inert gases by contacting with high surface area particulate coal-derived activated carbon having high ash and moisture contents. 1- and 2-butene and isobutene are disclosed as being suitable for this process; and the oxygen which is removed is originally present in concentrations up to about 10 ppm. There is no teaching or suggestion that the activated carbon adsorbent would be effective to remove branched-chain hydrocarbons or poly-isobutylene from raffinate streams.

In the past, therefore, the PIB contaminated streams normally have been discarded because of the associated processing difficulties. However, a substantially PIB-free C₄ stream can be utilized in further processing; and the present invention is directed to a process for treating a raffinate stream to remove objectionable amounts of PIB from the raffinate, as well as a resultant substantially PIB-free raffinate stream.

SUMMARY OF THE INVENTION The present invention is based on the discovery that the adsorption characteristics of carbon are particularly suitable for removing selected hydrocarbons from mixed hydrocarbon streams.

In this regard, it has been discovered that carbon unexpectedly adsorbs polymeric hydrocarbons, for example, poly-isobutylene, preferentially over nonpolymeric hydrocarbons, for example, butene, which are often present in mixed hydrocarbon streams.

The discovery of the present invention is particularly effective for removing, extracting, adsorbing or otherwise separating selected hydrocarbons, i.e., polymeric hydrocarbons, e.g., poly-isobutylene, from C₄ and/or C₅ hydrocarbon streams.

The present invention advantageously uses the discovery that the carbon adsorbent has more affinity for a higher molecular weight hydrocarbons, such as branched-chain hydrocarbons, i.e., polyisobutylene, which have a higher molecular weight distribution, e.g. , within the range of about 112 gram/mole to about 2,500+ gram/mole, with a majority in the 900 gram/mole region, than lower molecular weight C₄ isomers, e.g., less than 58 gram/mole.

In accordance with a preferred embodiment of the present invention, the process of this invention involves removing PIB from a C₄ and/or C₆ hydrocarbon stream, such as a raffinate stream, by contacting the stream with activated carbon for adsorption of the PIB.

In accordance with the present invention, therefore, mixed hydrocarbon streams which contain PIB, including C₄ streams, C₅ streams or a mixture of both C₄ and C₅ streams, are exposed to or otherwise contacted with carbon for a sufficient time to permit selected adsorption of the PIB. Activated carbon adsorbs PIB with a greater affinity than the other components and isomers of the C₄ or C₅ stream.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a flow chart for the adsorption process of the present invention.

Fig. 2 is a flow chart for a process for the production of MTBE, for example, as depicted in Fig. 1. DETAILED DESCRIPTION OF THE INVENTION In general, the present invention is directed to a process for treating a mixed hydrocarbon or raffinate stream by the selective separation of hydrocarbons having certain characteristics from the mixed hydrocarbon and raffinate streams wherein the process involves contacting the stream which includes an amount of selected hydrocarbons having certain characteristics which are to be removed from the stream, also referred to herein as undesirable hydrocarbons, with carbon under adsorption conditions and for a time effective for adsorption of such undesirable hydrocarbons from the stream to produce a resultant stream having a reduced amount of the undesirable hydrocarbons.

The carbon preferred for purposes of the present invention has at least one characteristic selected from the group consisting of a surface area within the range of about 50 m^J/g to about 2000 τs?/q and a pore volume within the range of about 0.2 cc/g to about 1 cc/g; with a surface area within the range of about 500 m2/g to about 1200 m'/g, and with a pore volume within the range of about 0.6 cc/g to about 1 cc/g being preferred; and a surface area within the range of about 1000-1100 m²/g and a pore volume of about 0.88 m'/g being most preferred. The carbon may be in a form selected from the group consisting of granular activated carbon and powdered activated carbon, although granular activated carbon is preferred. Also, the carbon adsorbent may be placed in a fixed bed, column, canister, or any other suitable configuration, which permits the passage of the hydrocarbon or raffinate stream therethrough so as to permit exposure and contact of the hydrocarbon or raffinate stream with the carbon adsorbent for effective adsorption of the undesirable hydrocarbons from the hydrocarbon or raffinate stream. The amount of carbon used depends on the surface area and pore - 6 -

size of the carbon selected and the amount of PIB in the stream. For purposes of the present invention, it is preferable to use an activated carbon having characteristics as described above as the absorbent. Representative examples of activated carbon preferred for purposes of the present invention are commercially available as CAL, OL, SGL from Calgon Carbon Corp. ; as PETRODARCO from American Norit Co. ; and as NUCHAR from Westvaco. The activated carbon absorbent more preferred for purposes of the present invention has a pore volume within the range of about 0.6 to lcc/g. Typically 0.09 Kg to 0.45 Kg of the preferred activated carbon is used per 450 Kgs of C₄ stream containing 50 ppm of PIB. The amount of activated carbon can be adjusted based on the PIB content of the stream. The carbon adsorbent is preferably maintained at a temperature within the range of about 10^*C to about 100*C and more preferably within the range of about 25*C to about 65^*C during processing in accordance with the present invention.

Although the mixed hydrocarbon and raffinate streams may be process in accordance with the present invention in their liquid phase or in their vapor phase, it is preferable to treat liquid hydrocarbon or raffinate streams with activated carbon in order to remove selected undesirable hydrocarbons from the mixed hydrocarbon or raffinate stream in accordance with the present invention. For purposes of the present invention, a C₄ and/or C₅ raffinate stream is preferred with a C4 raffinate stream being most preferred.

The process of the present invention is preferably performed under a pressure within the range of about 50 psi to about 500 psi, and most preferably at about 300 psi.

In accordance with the present invention, the hydrocarbon or raffinate streams are preferably passed through a bed or other configuration of the activated carbon at a flow rate within the range of about 0.1 LHSV to about 2.0 LHSV, and preferably at a flow rate of about 0.2 LHSV to about 1.0 LHSV. It has been discovered that selected or undesirable hydrocarbons can be separated from a mixed hydrocarbon stream when the amount of activated carbon is in a volume ratio with respect to the hydrocarbon stream within the range of about 1:1 to about 1:4000, and preferably wherein the volume ratio is about 1:500 to 1:1000.

Although the present invention is most preferred for use in separating poly-isobutylene from C₄ and/or C₅ raffinate streams, the invention may also be used to separate polymeric hydrocarbons having a molecular weight within the range of about 100 gram/mole to 2000 gram/mole^', or more, from mixed hydrocarbon streams. The process of the present invention has been discovered to be particularly effective in separating selected or undesirable hydrocarbons which are present within the mixed hydrocarbon or raffinate stream in an amount within the range of up to about 2% but preferably within the range of about 50 ppm to about 600 ppm, and most preferably within the range of about 50 ppm to about 100 ppm, so as to result with a resultant stream containing less than about 5 ppm and preferably less than about 1 ppm of the selected or undesirable hydrocarbon. The process of the present invention is most effective for removing up to about 100 ppm poly- isobutylene from a hydrocarbon stream including C₄ and C, hydrocarbons.

The present invention has been discovered to be most effective in a fixed bed operation. In accordance with the present invention, as described above, a hydrocarbon stream contaminated with poly-isobutylene is pumped through a column packed with activated carbon adsorbent at a temperature ranging from about ambient to about 65*C, a pressure of about 300 psig, and a flow rate of about 0.2 to about 1 LHSV to produce a resultant stream typically containing less than about 1 ppm of poly-isobutylene.

Fig. 1 of the accompanying drawing, which is presented as a representative example of the present invention for illustrative purposes, and is not meant to limit the present invention to the details shown and described, is a flowsheet of the process for the removal of selected hydrocarbons in accordance with the present invention. As shown, the charge stock (containing normal butenes, isobutylene, butanes, and low level of butyl chlorides and poly-isobutylene) to be treated for poly-isobutylene removal is the raffinate stream from the fractionation tower 2 of a poly-isobutylene unit 1. The stream containing 50 ppm to 2% poly-isobutylene is introduced into the adsorption column 3, where it is contacted with the activated carbon adsorbent for purposes of removing the poly-isobutylene from the raffinate stream. The effluent from the adsorption column, which contains less than about 1 to 5 ppm poly-isobutylene, can then be used as a feedstock for a down-stream methyl tertiary butyl ether (MTBE) unit 4.

In this regard, the present invention finds utility in removing poly-isobutylene from a raffinate stream to be used in any conventional process for the production of MTBE, for example, as disclosed in U.S.Patent 4,307,254, the disclosure of which is hereby incorporated in its entirety by reference hereto. Referring, however, now to Fig. 2, a schematic system is shown which can be used to produce MTBE.

A feedstream 7 containing a stoichio etric amount of methanol, based on isobutylene, is introduced together with an isobutylene containing feedstream 10 to a lead synthesis reactor 14. The lead synthesis reactor 14 is provided with an acidic resin catalyst, such as Amberlyst-15 (trademark) , Dowex DR-2040, Lewatit SPC 18 BG, or Dowex M-31, and is heated to an appropriate temperature. The effluent or product stream 16 leaving the reactor is composed of MTBE, unreacted hydrocarbons and methanol (MeOH) . The resultant product stream is the feedstream 18 which is then fed to a distillation column 20. The vaporized overhead 22 is composed of raffinate depleted in olefins branched at the point of unsaturation (sometimes referred to as tertiary olefins which is passed through methanol removal and final clean-up procedures) . As disclosed in commonly owned co-pending application U.S.S.N. 274,557, a stream 12 of methanol is introduced into the catalytic distillation reaction zone. The effluent is then passed to a product topping tower 26 wherein C_s hydrocarbons are removed for separate processing. The resultant effluent stream 30 is then passed to product tailing tower wherein MTBE is removed as product. The effluent 36 from tailing tower contains various components including oxygenates, such as TAME, which may be recycled to a conduit 38 to supply oxygenate to the catalyst reaction zone. Other catalytic distillation processes, such as those disclosed in U.S. Patent Nos. 4,232,177, 4,307,254, and 4,336,407, SMITH, Jr., have been developed to improve the recovery of MTBE, and are suitable processes for modification by the process in accordance with the present invention. The disclosures of U.S. Patent Nos. 4,232,177, 4,307,254, and 4,336,407, also are, therefore, hereby incorporated in their entirety herein by reference thereto.

A C₄ stream typically c^*. -ains up to or exceed 100 ppm PIB. However, a PIB content of less than about 1 ppm in a C₄ feedstock is desirable for downstream processing, such as MTBE production. In accordance with the present invention, the activated carbon effectively reduces the PIB content of such raffinate streams to less than 1 ppm.

EXAMPLE 1 A C₄ raffinate stream of 40% butene-l, 23% butene-2, 35% n-butane and isobutane, 2% isobutylene with 50 ppm PIB was contacted to Calgon Type OL granular carbon (20/50 mesh) . The Calgon Type OL granular carbon has a total surface area of 1000-1100 m^: and pore volume of Q.88 cc/g. The C₄ stream and activated carbon were allowed to equilibrate at a 13:1 volume ratio, respectively, at room temperature of 22^*C at 300 psi pressure. At 18 hours of equilibration the amount of PIB in the C₄ raffinate was less than 5 ppm.

EXAMPLE 2 A C₄ raffinate stream containing 12.9% butene-l 9.5% butene-2, 3.9% isobutylene, 70.6% n-butane, 1.2% isobutane and 1.9% PIB was contacted to Calgon Type OL carbon. The contaminated C₄ stream was pumped through five, 200 cc columns of activated carbon connected in series at an overall flow rate of 0.2 LHSV (Liquid Hourly Space Velocity) at room temperature of about 26*C and 300 psi. The product collected at the outlet of the last column contained less than 1 ppm before the amount of PIB adsorbed on the activated carbon reached 8.1% wt. of the carbon.

Although the invention has been described with reference to particular means, materials, and embodiments, from the foregoing description, one skilled in the art can easily ascertain the essential characteristics of the present invention, and various changes and modifications may be made to various usages and conditions, without departing from the spirit and scope of the invention as described in the claims that follows.

Claims

CLAIMS :

1. A process for treating mixed hydrocarbon streams involving the selective separation of hydrocarbon having certain characteristics from the stream, said process comprising: contacting a mixed hydrocarbon stream comprising an amount of selected hydrocarbons having certain characteristics, with carbon under adsorption conditions and time effective for adsorption of said selected hydrocarbons from said mixed hydrocarbon stream to produce a resultant stream having a reduced amount of said selected hydrocarbons.

2. The process for treating mixed hydrocarbon streams of claim 1, wherein said carbon comprises at least one characteristic selected from the group consisting of a surface area within the range of about 50 m'/*? to about 2000 m^J/g and a pore volume within the range of about 0.2 cc/g to about 1 cc/g.

3. The process for treating mixed hydrocarbon streams of claim 2, wherein said at least one characteristic is a surface area within the range of about 500 m^l/g to about 1200 m²/g.

4. The process for treating mixed hydrocarbon streams of claim 2, wherein said at least one characteristic is a pore volume within the range of about 0.6 cc/g to about 1 cc/g.

5. The process for treating mixed hydrocarbon streams of claim 2, wherein said at least one characteristic comprises a surface area within the range of about 1000-1100 m'/g, and a pore volume of about 0.88 cc/g.

6. The process for treating mixed hydrocarbon streams of claim 2, wherein said carbon is in the form selected from the group consisting of granular carbon and powdered carbon.

7. The process for treating mixed hydrocarbon streams 12 -

of claim 6, wherein said carbon is granular carbon.

8. The process for treating mixed hydrocarbon streams of claim 6, wherein said carbon is powdered carbon.

9. The process for treating mixed hydrocarbon streams of claim 6, wherein said carbon is activated carbon.

10. The process for treating mixed hydrocarbons streams of claim 9, wherein said mixed hydrocarbon stream is in the liquid phase.

11. The process for treating mixed hydrocarbon streams of claim 6, wherein said adsorption conditions comprise a pressure within the range of about 50 psi to about 500 psi.

12. The process for treating mixed hydrocarbon streams of claim 11, wherein said pressure is about 300 psi.

13. The process for treating mixed hydrocarbon streams of claim 6, wherein said contacting comprises passing said stream through a bed of said carbon at a flow rate within the range of about 0.1 LHSV to about 2.0 LHSV.

14. The process for treating mixed hydrocarbon streams of claim 13, whereiiv said flow rate is about 0.2 LHSV to about 1 LHSV.

15. The process for treating mixed hydrocarbon streams of claim 6, wherein said carbon is used in an amount relative to said stream at a volume ratio within the range of 1:1 to about 1:4000.

16. The process for treating mixed hydrocarbon streams of claim 15, wherein said volume ratio is about 1:500 to 1:1000.

17. The process for treating mixed hydrocarbon streams of claim 2, wherein said carbon is maintained at a temperature within the range of about 10^*C to about 100*C.

18. The process for treating mixed hydrocarbon streams of claim 5, wherein said temperature is within the range of about 25*C to about 65*C.

19. The process for treating mixed hydrocarbon streams of claim 2, wherein said characteristics of said selected hydrocarbons comprise a molecular weight distribution within the range of about 112 gram/mole to about 2500 gram/mole.

20. The process for treating mixed hydrocarbon streams of claim 19, wherein a majority of said hydrocarbons have a molecular weight distribution of about 900 gram/mole.

21. The process for treating mixed hydrocarbon streams of claim 2, wherein said selected hydrocarbons are present in said stream in an amount within the range of up to about 2%.

22. The process for treating mixed hydrocarbon streams of claim 21, wherein said amount of said selected hydrocarbons is within the range of about 50 ppm to about 600 ppm.

23. The process for treating mixed hydrocarbon streams of claim 22, wherein said amount of said hydrocarbons is within the range of about 50 ppm to about 100 ppm.

24. The process for treating mixed hydrocarbon streams of claim 2, wherein said selected hydrocarbons are polymeric hydrocarbons.

25. The process for treating mixed hydrocarbon streams of claim 24, wherein said polymeric hydrocarbons are selected from the group consisting of poly-propylene, poly-butene, and poly-isobutylenes.

26. The process for treating mixed hydrocarbon streams of claim 24, wherein said polymeric hydrocarbons are poly- isobutylenes.

27. The process for treating mixed hydrocarbon streams of claim 26, wherein said reduced amount of poly-isobutylenes in said resultant stream is less than about 5 ppm.

28. The process for treating mixed hydrocarbon streams of claim 27, wherein said reduced amount of poly-isobutylenes in said stream is less than about 1 ppm.

29. The process for treating mixed hydrocarbon streams

of claim 26, wherein said amount of poly-isobutylenes in said stream is within the range of about 1 ppm to about 600 ppm.

30. The process for treating mixed hydrocarbon streams of claim 28, wherein said mixed hydrocarbon stream is in the liquid phase and said carbon has a surface area within the range of about 50 m'/g to about 2000 m'/g and a pore volume within the range of about 0.2 cc/g to about 1.0 cc/g.

31. The process for treating mixed hydrocarbon streams of claim 24, wherein said stream comprises at least one member selected form the group consisting of C₄ hydrocarbons, C_s hydrocarbons, and mixtures of C₄ hydrocarbons and C_s hydrocarbons.

32. The process for treating mixed hydrocarbon streams of claim 31, wherein said stream comprises C₄ hydrocarbons.

33. The process for treating mixed hydrocarbon streams of claim 31, further comprising adding methanol to said resultant stream under conditions and for a time sufficient to produce a product stream comprising methyl-tert-butyl ether and methanol.

34. The process for treating mixed hydrocarbon streams of claim 30, further comprising recovering at least a portion of said methanol from said product stream.

35. A hydrocarbon stream comprising less than about 5 ppm poly-isobutylene produced by the process of claim 1.

36. The product produced by the process of claim 2.

37. The product produced by the process of claim 5.

38. The product produced by the process of claim 8.

39. The product produced by the process of claim 9.

40. A raffinate stream from a polyisobutylene reactor comprising less than about 1 ppm poly-isobutylene.