WO2001058839A1

WO2001058839A1 - Process to recover condensable gases from oxygen containing mixtures

Info

Publication number: WO2001058839A1
Application number: PCT/US2000/031117
Authority: WO
Inventors: Timothy Richard Nolen; Steven Edward Briley; Vera Williams Mcgill
Original assignee: Eastman Chemical Company
Priority date: 2000-02-07
Filing date: 2000-11-13
Publication date: 2001-08-16

Abstract

Vaporous hydrocarbonaceous materials in a mixture with oxygen are recovered from an epoxidation reaction system purge stream by condensing the hydrocarbonaceous materials while adding a sufficient amount of a non-condensable gas to the purge stream to avoid formation of flammable gas compositions.

Description

PROCESS TO RECOVER CONDENSABLE GASES FROM OXYGEN CONTAINING MIXTURES BACKGROUND OF THE INVENTION

Field of the Invention:

The present invention relates to the recovery of condensable gases, and particularly C₃ to C₁₂ combustible gases from oxygen containing vaporous mixtures. More Particularly, the present invention relates to the recovery of C₃ to C₁ hydrocarbon constituents from hydrocarbon-oxygen vaporous mixtures.

Background of the Invention

3,4-Epoxy-l-butene (epoxybutene), also known as butadiene monoxide and vinyl- oxirane, is an important compound and generally has uses as an intermediate for preparing materials such as tetrahydrofuran and 1,2-butylene oxide. Methods for preparing epoxybutene are disclosed in U.S. Patent Nos. 5,618,954, 5,362,890 and 4,897,498, the disclosures of which are incorporated herein by reference. One method for the manufacture of epoxybutene so described generally includes the selective epoxidation of 1,3-butadiene (referred to herein as butadiene). The butadiene is contacted with an oxygen-containing gas in the presence of certain silver catalysts.

A problem associated with such reactions is the accumulation of impurities in the reaction system. Such impurities may result from the reaction of oxygen in the oxygen containing stream which can cause the accumulation of trace noble gasses or of nitrogen when air is used as the oxygen source. Another source of impurities are inertly-reactive materials purposefully introduced into the reaction system that, over a period of time, accumulate sufficiently to interfere with the desired reaction.

Typically, concentrations of impurities are controlled by taking a purge stream from the materials recycled back to the reaction zone. However, in industrial operations, the purging of the impurities results in losses of important and expensive hydrocarbon gases to the atmosphere. This venting represents valuable material losses as well as atmospheric contamination. Additionally, when such streams contain sufficient oxygen, an explosive hazard can result. As explained in Lees, F.P., "Loss Prevention in the Process Industries, Volume 1," 485-86 (1980), a flammable gas, e.g., methane, butane, and other alkane hydrocarbons, burns in oxidizing environments only over a limited compositional range. The upper and lower flammability limits are mixtures having concentration extremes of: 1) high oxygen and low combustible concentrations; or 2) low oxygen and high combustible concentrations. Between these flammability limits, a mixture of a flammable gas and an oxidant can continue to burn once the mixture ignites. These flammability extremes are a function of temperature, pressure, and composition. Flammability limits are usually expressed as volume or mole percent flammable gas in a mixture of an oxidant (usually oxygen), inert, and flammable gas. The smaller value is the lower (lean) limit and the larger value is the upper (rich) limit. Typically, the safe operating range for a given flammable gas and oxidant mixture decreases as temperature and pressure increase, and amount of inert gas decreases. Increases in pressure have a larger effect than the increases in temperature. The limits of flammability for gas mixtures , e.g., n-butane and 1,3-butadiene, can be estimated by the well-known LeChatlier's Rule.

A number of methods have been proposed for the separation of the hydrocarbon constituent from such oxygen containing mixtures. For example, U.S. Patent No. ^■ 4,305,734, issued to McGill, discloses a process for separating flammable gases such as methane from flammable gas-air mixtures by passing the gas mixture through a bed of adsorbent which adsorbs the flammable gas in preference to air. The principal purification step comprises passing the feed mixture through the adsorption bed while simultaneously producing non-adsorbed gas from the adsorber. This step is followed by co-currently flushing carrier gas from the adsorber with the desired flammable gas and then recovering flammable gas from the adsorber by depressurization of the adsorber. Although this process may result in increased feed gas throughput, the purity of the desorbed product can be lower than is desired since the inlet region of the adsorber will contain a greater concentration of carrier gas when the flammable gas purge step begins.

U.S. Patent No. 5229089 issued to Rarnachandran et al. discloses a process for separating methane from an oxygen-containing gas mixture which contains methane at a concentration greater than the upper flammable gas mixture limit using pressure swing absorption. The process uses an adsorbent which more strongly adsorbs the desired component, i.e. methane, relative to the absorption of other components present in the gas stream. The process includes the steps of (a) raising the pressure in the adsorber to the desired production pressure by introducing the feed mixture cocurrently into the adsorber, (b) introducing high purity desorbed product gas cocurrently into the adsorber using either a cocurrent purge or a co-purge while simultaneously cocurrently withdrawing nonadsorbed product gas from the adsorber, (c) cocurrently partially depressurizing the adsorber, thereby producing expansion gas, and (d) further counter-currently depressurizing the adsorber, thereby producing high purity desorbed product gas. The high purity desorbed product gas that is cocurrently introduced into the adsorber in step (b) may be gas obtained from step (d) of previous cycles of the process or it may be obtained from an external source.

U.S. Patent No. 5,468,885 issued to Jubin, Jr. discloses a process for the recovery of oxygen formed by hydrogen peroxide decomposition during epoxidation of an olefin. In the process the olefin/oxygen vapor purge stream from the epoxidation reaction is contacted with a liquid absorbent stream, preferably a stream comprised of the secondary alcohol from which the hydrogen peroxide is formed, to absorb the olefm and enable separation of gaseous oxygen from the liquid olefin-containing absorbent. In addition, an inert gas diluent such as methane is added to replace absorbed olefm in order to avoid the formation of oxygen-containing gas mixtures which are in the flammable range Accordingly, there is a need for a process where a combustible gas, and particularly a hydrocarbonaceous combustible gas, in an oxygen containing mixture can be safely and efficiently recovered. There is a further need for a process where the purge gas stream of an epoxidation reaction zone be safely and effectively treated for the recovery of the hydrocarbonaceous materials. SUMMARY OF THE INVENTION

Briefly, the process of the present invention provides a method where a hydrocarbonaceous material from a vaporous oxygen-containing mixture can be recovered. The invention is particularly useful for separating a C₃-C₁₂ hydrocarbonaceous flammable material from an oxygen-containing gaseous mixture in which the hydrocarbonaceous material is present at a concentration greater than the upper flammable limit for the gas mixture. However, the present invention is not so limited and is applicable to the recovery of hydrocarbons in an oxygen-containing gaseous mixture where the hydrocarbonaceous material is present at a concentration less than the lower flammable limit for the gas mixture since it permits the separation to be effected without the formation of a flammable mixture. In accordance with the present invention, the process includes adding an amount of a non-condensable gas to a vaporous hydrocarbon and oxygen-containing stream and condensing at least a portion of the hydrocarbonaceous material. The amount of non-condensable gas added should be sufficient to avoid the formation of oxygen-containing vapor mixtures which are in the flammable range. It is an object of the present invention to provide a process for the recovery of hydrocarbon components from a vaporous hydrocarbon-oxygen mixture.

It is another object of the present invention to provide a safe and economical process for the recovery of hydrocarbon components from a vaporous hydrocarbon- oxygen mixture. These and other objects and advantages of the present invention will become apparent to those skilled in the art from the following description when read in conjunction with drawing and the appended claims.

BRIEF DESCRIPTION OF THE DRAWING

The Figure of drawing illustrates a preferred embodiment of the present invention as it relates to a vaporous purge stream from 3,4-Epoxy-l-butene epoxidation reaction.

DETAILED DESCRIPTION OF THE INVENTION

The process of the present invention is directed to the recovery of valuable hydrocarbonaceous materials from a vaporous mixture of such materials and oxygen. The process will be described as it relates to the recovery of C₃-Cι₂ hydrocarbons, preferably to the recovery of C₃-C₆ hydrocarbons and more preferably to the recovery of 1,3- butadiene and n-butane from an epoxidation reaction system and preferably from a vaporous purge stream from 3,4-epoxy-l-butene epoxidation reaction system.

The hydrocarbon-oxygen mixture typically contains a flammable hydrocarbon at a concentration above the upper flammability limit, but the present invention is not limited to such concentrations. One skilled in the art will understand that the process of the present invention is equally useful in the recovery of valuable hydrocarbons in oxygen containing mixtures where the concentration of the flammable hydrocarbon is at a concentration below the lower flammability limit. As used herein the term "flammable hydrocarbon" means any gas which forms a flammable mixture with a combustion- supporting gas such as oxygen. Examples of such materials include volatile hydrocarbons, such as C₃-C₁₂ lower aliphatic and aromatic hydrocarbons, substituted hydrocarbons, such as alcohols, ketones, and ethers.

An especially preferred embodiment of the present invention is shown in the accompanying drawing which illustrates the recovery of condensable hydrocarbons from a vapor purge stream from an epoxidation reaction system 10. Desirably, the epoxidation reaction system is used for the production of 3,4-epoxy-l -butene. Generally, in the production of epoxybutene, 1,3 -butadiene is contacted with an oxygen-containing gas in the presence of a catalyst to produce an epoxidation effluent comprising epoxybutene, n- butane, butadiene, and oxygen. Silver-catalyzed epoxidation processes are described in greater detail in U.S. Pat. Nos. 4,897,498 and 4,950,773, the disclosures of which are incorporated herein by reference. The gaseous epoxidation effluent typically contains from about 0.5 to about 10 mole percent epoxybutene and preferably from about 1 mole percent to about 7 mole percent epoxybutene, about 4 to 50 mole percent 1,3-butadiene, and about 25 to 85 mole percent n-butane gas, which is used in the process as an inert diluent. The effluent also contains a total of about 0.5 to 10 mole percent of other constituents such as, water, carbon dioxide, acrolein, furan, vinylacetaldehyde, and crotonaldehyde, formed in the epoxidation reactor. Unconsumed organic halide also is present in the epoxidation effluent. Recovery of the epoxybutene and various reaction constituents is known to those skilled in the art. For example, U.S. Pat. Nos. 5,117,012 and 5,312,931 disclose processes for the recovery of EpB. A particularly preferred process for the recovery of epoxybutene is disclosed in a commonly assigned patent application having US Serial No.09/305,679 filed May 5, 1999, the disclosures of which are incorporated herein by reference.

Referring to the accompanying drawing, epoxidation reactants, such as C₃-C₁₂ hydrocarbons and particularly 1,3 -butadiene, diluents, such as n-butane, and inert constituents, such as nitrogen, carbon dioxide, and argon exit the epoxidation system 10 through line 12. A portion of the contents in line 12 is removed via purge stream 14. A control means 16 regulates amount of drawn off or removed from the line 12. Suitable control mechanisms are well known in the art and include such devices as automatic control valves, manual control valves, and orifice plates. In accordance with the present invention, a non-condensable gas is introduced into the purge stream 14 through line 18. The amount of non-condensable gas introduced via line 18 is controlled by a second control means 20, which is similar to that described above. The purge stream 12 and the non-condensable gas stream 18 are combined in line

22 and desirably are mixed using a static in-line mixer 30. The mixed purge / non- condensable gas stream are transferred via line 32 to a condensing means 40 where at least a portion of the desired vaporous hydrocarbons are condensed. The condensed hydrocarbons are recovered for recycling to the epoxidation system and/or purification via line 42. The non-condensable gases exit the condenser via line 44 and may be further processed or burned. As is conventional, the condenser 40 includes a cooling media inlet 46 and outlet 48 so that the cooling media may be circulated through the condenser to chill and condense the vaporous hydrocarbons.

The non-condensable gas 18 utilized can be any gaseous material that has a condensation temperature relatively lower than that of the desired condensable hydrocarbons. The non-condensable gas 18 can be a combustible gas, such as methane, or a non-combustible gas, such as nitrogen, carbon dioxide, helium, and argon, and mixtures thereof. A sufficient amount of non-condensable gas 18 is introduced into the purge stream 14 to avoid formation of flammable vapor-oxygen mixtures. Typically, the amount of non-condensable gas 18 introduced into the purge stream 14 is from about 0.1 mole to about 10 moles per mole of oxygen, more preferably from about 0.3 to about 10 moles per mole of oxygen, and most preferably from about 0.5 moles to about 5 moles per mole of oxygen.

In accordance with the present invention, at least about 2 % of the desired hydrocarbon material present in the purge stream 14 is condensed. Desirably, from about 5 % to about 80 % of the desired hydrocarbon material present in the purge stream 14 is condensed and preferably from about 5 % to about 95 % of the desired hydrocarbon material present in the purge stream 14 is condensed. In an especially preferred embodiment of the present invention, the condensed hydrocarbon material is recovered and recycled to the epoxidation system 10 with or without further purification. The following examples are illustrative of the present invention.

EXAMPLE 1

A purge gas stream comprising 60 mole % n-butane, 20 mole % oxygen and 20 mole % nitrogen is at a pressure of 80 psia (5.5 bar) and a temperature of 50°C. Using LeChatlier's Rule, the oxygen content of this mixture would have to be 25.7 mole % to be in the flammable region. The purge stream is condensed at a pressure of 70 psia (4.8 bar) and 10°C. However, without the addition of a non-condensable gas, the 70 psia and 10°C vapor from the condenser would comprise 30.8 mole % butane, 34.6 mole % oxygen and 34.6 mole % nitrogen, which is in the flammable region.

In accordance with the invention, 0.228 moles of nitrogen per mole of purge added to the purge stream will result in a composition, after condensing, having 30.7 mole % butane, 22.1 mole % oxygen and 47.2 mole % nitrogen. It is calculated that 26.1 mole % oxygen is necessary for the mixture to be flammable. Accordingly, 54 % of the butane present in the purge stream is recovered without forming a flammable mixture.

EXAMPLE 2 A purge gas stream comprising 78 mole % n-butane, and 20 mole % oxygen is at a pressure of 90 psia (6.2 bar) and a temperature of 60°C. The oxygen content of this mixture would have to be 28.4 mole % to be in the flammable region. The purge stream is condensed at a pressure of 85 psia (5.9 bar) and 5°C. Without the addition of a non- condensable gas, the 85 psia, 5°C vapor from the condenser would comprise 21.1 mole % butane and 78.9 mole % oxygen, which is in the flammable region.

In accordance with the invention, 0.468 moles of methane per mole of purge added to the purge stream will result in a composition, after condensing, having 21.2 mole % butane, 25.2 mole % oxygen and 53.6 mole % methane. It is calculated that 29.2 mole % oxygen is necessary for the mixture to be flammable. Accordingly, 76 % of the butane present in the purge stream is recovered without forming a flammable mixture.

EXAMPLE 3

A purge gas stream comprising 10.65 mole % butadiene, 57.25 mole % n-butane, 0.39 mole % methane, 1.61 mole % carbon dioxide, 9.42 mole % nitrogen, 5.27 mole % argon and 15.42 mole % oxygen is at a pressure of 88 psia (6.1 bar) and a temperature of 44°C. To this mixture .31 moles of methane per mole purge added to the purge stream. The stream is condensed at a pressure of 87 psia (6.0 bar) and a temperature of 5°C.

It is calculated that 72 % of the butadiene and 77 % of the n-butane are condensed. The vent gas contains 19.5 mole % oxygen. It is calculated that 24.1 mole % oxygen is necessary for the mixture to be flammable.

From the above description it is apparent that the present invention provides an efficient and safe method for recovering condensable hydrocarbons without costly and elaborate absorbers and subsequent processing equipment.

Although the present invention has been described in terms of the presently preferred embodiment, it is to be understood that such disclosure is not to be interpreted as limiting to the invention described herein. No doubt that after reading the disclosure, various alterations and modifications will become apparent to those skilled in the art to which the invention pertains. It is intended that the appended claims be interpreted as covering all such alterations and modifications as fall within the spirit and scope of the invention.

Claims

CLAIMS We claim:

1. A process for recovering a hydrocarbonaceous material from a vaporous oxygen- containing mixture comprising adding a sufficient amount of a non-condensable gas to said oxygen-containing mixture to suppress flammability; and condensing said hydrocarbonaceous material.

2. The process of claim 1 wherein said non-condensable gas is a combustible gas having a condensation temperature relatively lower than said hydrocarbonaceous material in said mixture. 3. The process of claim 2 wherein said combustible gas is methane.

4. The process of claim 1 wherein said non-condensable gas is a non-combustible gas having a condensation temperature relatively lower than said hydrocarbonaceous material in said mixture.

5. The process of claim 4 wherein said non-combustible gas is selected from the group consisting of nitrogen, carbon dioxide, helium, argon and mixtures thereof.

6. The process of claim 1 wherein said amount of non-condensable gas added to said oxygen-containing mixture is from about 0.1 moles to about 10 moles per mole of oxygen in said mixture.

7. The process of claim 1 wherein said amount of non-condensable gas added to said oxygen-containing mixture is from about 0.3 moles to about 10 moles per mole of oxygen in said mixture.

8. The process of claim 1 wherein said amount of non-condensable gas added to said oxygen-containing mixture is from about 0.5 moles to about 5 moles per mole of oxygen in said mixture. 9. The process of claim 1 wherein at least about 2 % of said hydrocarbonaceous material in said mixture is condensed.

10. The process of claim 1 further comprising recovering said condensed hydrocarbonaceous material. -lO- l l. A process for recovering a hydrocarbonaceous material from a vaporous oxygen- containing mixture, said process comprising adding a sufficient amount of a non- condensable gas to said oxygen containing mixture to suppress flammability; and condensing at least 2 % of said hydrocarbonaceous material in said mixture. 12. The process of claim 11 wherein said hydrocarbonaceous material contains from 3 to 12 carbon atoms.

13. The process of claim 12 wherein said non-condensable gas is methane.

14. The process of claim 11 wherein said non-condensable gas is selected from the group consisting of nitrogen, carbon dioxide, helium, argon and mixtures thereof. 15. The process of claim 11 wherein said amount of non-condensable gas added to said oxygen-containing mixture is from about 0.1 moles to about 10 moles per mole of oxygen in said mixture.

16. The process of claim 11 wherein said amount of non-condensable gas added to said oxygen-containing mixture is from about 0.3 moles to about 10 moles per mole of oxygen in said mixture.

17. The process of claim 11 wherein from about 5 % to about 80 % of said hydrocarbonaceous material in said mixture is condensed.

18. The process of claim 11 wherein from about 5 % to about 95 % of said hydrocarbonaceous material in said mixture is condensed. 19. A process for recovering a Cz-Cβ hydrocarbonaceous material from an oxygen- containing mixture, said process comprising adding a sufficient amount of a non- condensable gas to said oxygen-containing mixture to suppress flammability; condensing said C₃-C₆ hydrocarbonaceous material; and recovering said condensed Cz-C(, hydrocarbonaceous material. 20. The process of claim 19 wherein said non-condensable gas is selected from the group consisting of methane, nitrogen, carbon dioxide, helium, argon and mixtures thereof.

21. The process of claim 19 wherein said amount of non-condensable gas added to said oxygen-containing mixture is from about 0.5 moles to about 5 moles per mole of oxygen in said mixture and wherein at least about 2 % of said hydrocarbonaceous material in said mixture is condensed.

22. The process of claim 19 wherein said hydrocarbonaceous material is selected from the group consisting of 1,3-butadiene and n-butane.