Ether recovery

Abstract: The alcohol, ether and hydrocarbon components of the reaction effluent from various etherifications of C₄ or C₅ isoolefins with an alcohol such as methanol or ethanol which produce MTBE, ETBE, TAME, or TAEE are separated using identical process equipment. The components are recovered by first removing a portion of the alcohol in a first water extraction step, then fractionating the ether, followed by the removal of additional alcohol in a second water extraction step and then fractionating the alcohol. Hydrocarbons are recovered from a extract stream of the second water extraction step.

Description: This invention relates to the recovery of ethers from a reaction mixture. In one aspect it relates a method of separating reactor effluent in the preparation of tertiary alkyl ethers. In another aspect this invention relates to an arrangement of columns designed for extracting alcohol with water. Background of the Invention It is known that tertiary alkyl ethers, which are high octane blending components for motor fuels, can be prepared by reacting a primary alcohol with an olefin having a double bond on a tertiary carbon atom. For example, methanol reacts with isobutylene or isoamylene to form respectively methyl tert-butyl ether (MTBE) and tert-amyl methyl ether (TAME). Similar reactions are known which produce ethyl tert-butyl ether (ETBE) and tert-amyl ethyl ether (TAEE). Reference is made to U.S. Patents Nos. 4,071,567; 3,979 ,461; 3,135,807; 3,846,088; among many others, These ether reactions are so selective for tertiary olefins that they constitute a valid process for the removal from olefinic streams where there are encountered together with linear olefins. When producing such ethers however, it is desirable to remove the unreacted alcohol from the ether in the reaction effluent and recycle it to the ether reactor. A variety of processes is known for the separation of alcohol from tertiary alkyl ether products. All of the known individual processes, however, fail to provide the flexibility of separating alcohol from a number of different ether products such as MTBE, ETBE, TAME and TAEE. DE-A-3 614 726 discloses a process for the production of t-amyl methyl ether, wherein a feed containing hydrocarbons is subjected to an etherification in the presence of an alcohol, the alcohol/hydrocarbon/ether-reaction mixture being formed in the etherification is separated and the alcohol is recycled at least partially to the etherification step, wherein the alcohol is extracted by an extracting agent from the reaction mixture and after separation from the extraction mixture recycled to the etherification step. Accordingly it is an object of this invention to provide a process which will recover alcohol from a reaction mixture containing a tertiary alkyl ether. Another object of this invention is to provide an improved arrangement of columns for extracting alcohol with water. Another object of this invention is to provide a process which uses essentially identical process equipment to separate MTBE, TAME, ETBE or TAEE reaction products. Still another object of this invention is to recover unreacted hydrocarbons from a tert-alkyl ether reaction product. Brief Summary of the Invention In accordance with this invention there is provided a process as defined in claim 1 and an apparatus as defined in claim 10. Thus, there is provided a process for separating alcohol from a reaction effluent stream in the etherification of C 4 or C 5 isoolefins, which process uses essentially the same process equipment to separate a variety of ether compounds such as MTBE, ETBE, TAME or TAEE or mixtures thereof. In this process, which features dual water wash steps plus fractionation, the entire reaction product from a tertiary alkyl ether reaction containing the high octane ether components, along with hydrocarbons which include unreacted C 4 or C 5 isoolefins and inert hydrocarbons such as linear olefins and paraffins and also unreacted alcohol, is separated in a first separation zone to provide a product stream containing the ether component, a stream containing a water/alcohol mixture and a stream primarily containing hydrocarbons but also containing alcohol. This later stream of hydrocarbons containing alcohol is further separated in a second separation zone to provide a hydrocarbon product stream for further utilization as desired, and a water/alcohol mixture stream which is combined with the water/alcohol mixture stream of the first separation zone. The combined water/alcohol mixture stream is separated in a third separation zone to provide an alcohol product stream which is suitable for recycle to the ether reactor and a water stream which is suitable for other uses. In a preferred embodiment the first separation zone includes a water extraction step followed by fractionation of ether in which the water extraction step removes a first portion of alcohol from the reaction effluent. Accordingly, this water extraction yields an extract containing alcohol and a raffinate containing the ether, hydrocarbons and also containing lesser amounts of alcohol carried over with the hydrocarbons. This raffinate is passed to the ether fractionator to yield the ether product in a bottom stream and an overhead stream containing hydrocarbons and alcohol which is passed to the second separation zone. The second separation zone includes a water extraction step followed by a hydrocarbon stripping operation. This extraction step in the second separation zone removes a second portion of alcohol which is essentially all of the remaining alcohol in the reaction effluent, and is employed to further reduce alcohol losses. Accordingly, the water extraction in the second separation zone yields an extract containing alcohol and a raffinate containing hydrocarbons with essentially no alcohol. This raffinate stream is passed to a hydrocarbon stripper column for further purification and produces a stabilized hydrocarbon stream. The third separation zone is an alcohol fractionation yielding products of ether and water separated from water/alcohol mixtures obtained from the first and second separation zones. Other objects, aspects as well as the several advantages of the invention will be apparent particularly in the art upon reading the specification and the appended claims and the drawing in which: Brief Description of the Drawing FIG. 1 is a simplified schematic illustration showing a process flow and arrangement of apparatus according to a preferred embodiment of this invention. Detailed Description of the Invention It will be appreciated by those skilled in the art that since FIG. 1 is schematic only many items of equipment which would be needed in a commercial plant for successful operation have been omitted for the sake of clarity. Such items of equipment would include for example, flow, pressure, and temperature measuring instruments with corresponding process controllers; pumps, heat exchangers, valves, etc. all these items would be provided in accordance with standard chemical engineering practice, however, they play no part in the explanation of the present invention. Referring now to FIG. 1 the entire reaction product of a reaction that selectively reacts a tertiary olefin having 4 or 5 carbon atoms per molecule with an alcohol (e.g. methanol or ethanol) to produce an ether, is feed via conduit 4 to a first separation zone which includes an extraction column 2 and a fractionator 6. This reaction effluent supplied via conduit 4 contains a product tertiary alkyl ether in an excess of unreacted and inert hydrocarbons and also contains unreacted alcohol. The extraction column or so called water washing operation, involves counter currently contacting the feed material with water supplied via conduit 12 at a temperature typically about 40°C and a gauge pressure e.g. 1000 to 1200 kPa, which is sufficient to keep the hydrocarbons in the liquid phase. A first portion of the unreacted alcohol comprising at least about 50 wt.% of the alcohol in the feed is removed in the extraction step in the first separation zone. While not wishing to be limited by theory, it is thought that sufficient alcohol is removed from the feed material by the water extraction step carried out in extraction column 2 such that operation of the ether fractionator 6, which follows, is enhanced either because the separation factors of the remaining components are improved or because the ether fractionator 6 does not operate in an ether/alcohol/hydrocarbon azeotrope. The overhead raffinate from the extraction in column 2 contains principally inert hydrocarbons plus the product ether together with lesser amounts of unreacted isoolefins and alcohol. This raffinate stream is passed to a distillation column 6 via conduit 8 from which is recovered an overhead stream in conduit 10 containing hydrocarbon plus lesser quantities of alcohol. The bottom stream in conduit 14 recovers the product ether for use such as a high octane blending component for motor fuel. The extract bottoms from the water wash operation in extraction column 2 contains a mixture of water and alcohol where the total amount of alcohol comprises a concentration of about 20% by weight of the total stream. This stream is passed via conduits 16 and 32 to an alcohol fractionator 18. A bypass conduit 30 around the extraction column(2), is provided for excluding the water wash column 2 when processing MTBE. The overhead hydrocarbon phase withdrawn from the ether fractionator 6 is passed to the second separation zone where additional alcohol may be recovered while purity of the hydrocarbon stream is improved. The second separation zone includes water extraction column 20 and stripper column 22. The overhead stream withdrawn from fractionator 6 is passed via conduit 10 to extraction column 20 into which water is introduced via conduit 24, A hydrocarbon raffinate stream being substantially free of alcohol is withdrawn from column 20 via conduit 26, and an alcohol/water mixture is withdrawn via conduit 21 and combined with a stream of similar composition in conduit 16. Further purification of the overhead hydrocarbon stream so as to meet certain purity specification is provided in stripper column 22, where the lighter fractions are removed from the hydrocarbons via conduit 27 and a stabilized hydrocarbon product is removed via conduit 28. The water/alcohol mixture supplied to fractionator 18 via conduit 32 is separated in fractionator 18 to provide an alcohol stream in conduit 34 which is suitable for recycle to the ether reactor, and a water stream in conduit 36 which is suitable for recycle to extractors 2 and/or 20. While actual operating conditions for the individual units illustrated in FIG. 1 will depend to some extent on the make-up of the feed, typical operating conditions of the individual units of the ether recovery operation are given In Table I below, where the numbers in parenthesis correspond to the reference numerals in FIG. 1. Typical Operating Conditions Extractor (2) Temp °C 40 Gauge Press. kPa 1100 Fractionator (6) Temperature °C Top 50-60 Bottom 110-160 Gauge Pressures kPa Top 540-740 Bottom 580-770 Extractor (20) Temp °C 38 Press. kPa 827 Stripper (22) Temp °C 50-70 Gauge Press. kPa 540-1360 Fractionator (18) Temperature °C Top 76-103 Bottom 116-130 Gauge Pressures kPa Top 158 Bottom 172 The present invention is applicable to a variety of ether forming units where the above described dual washing steps in combination with fractionations provide the novel elements. In operation the first extractor 2 can remove at least about 50 wt.% and preferably about 75 wt.% of the alcohol contained in the feed, which as previously stated can be sufficient alcohol removal to prevent an ether/alcohol/hydrocarbon azeotrope from forming in fractionator 6 for reaction products comprising ETBE, TAME, and TAEE or mixtures thereof, thus improving separation in fractionator 6. Additional alcohol is then removed in a second water extraction 20.

Claims: A process for separating an etherification reaction effluent stream containing a tertiary alkyl ether, hydrocarbons comprising unreacted isoolefins and other inert hydrocarbons, and unreacted alcohol, said process comprising: (a) passing said etherification reaction effluent stream to a first separation zone including a water extraction step (2) followed by fractionation (6); (b) separating said reaction effluent stream in said first separation zone under conditions which provide a first stream comprising a mixture of said hydrocarbons and said alcohol, a second stream comprising said tertiary alkyl ether substantially free from alcohol, and a third stream comprising a water/alcohol mixture; (c) passing said first stream to a second separation zone including a water extraction step (20) followed by stripping (22); (d) separating said first stream in said second separation zone under conditions which provide a fourth stream comprising said hydrocarbons substantially free of alcohol and a fifth stream comprising a water/alcohol mixture; and (e) combining said fifth stream and said third stream to form a sixth stream and passing said sixth stream to a third separation zone comprising a fractionation (18) which yields a seventh stream substantially comprising alcohol. A process in accordance with claim 1 wherein said third stream is formed by extracting a first portion of alcohol contained in said reaction effluent stream in said water extraction step (2) of said first separation zone. A process in accordance with claim 2 wherein said third stream is formed by counter currently contacting the alcohol contained in said reaction effluent stream with water. A process in accordance with claim 2 wherein said first portion of alcohol comprises the major part of unreacted alcohol contained in said etherification reaction effluent stream. A process in accordance with claim 1 wherein said fifth stream is formed by extracting a second portion of alcohol comprising alcohol contained in said first stream in a water extraction step (20) in said second separation zone. A process in accordance with claim 5 wherein said fifth stream is formed by counter currently contacting the alcohol contained in said first stream with water. A process in accordance with claim 2 wherein said alcohol is selected from the group comprising methanol and ethanol. A process in accordance with claim 2 wherein said tertiary alkyl ether is selected from the group comprising MTBE, TAME, ETBE and TAEE or mixtures thereof. A process in accordance with claim 1 wherein said unreacted hydrocarbons comprise C 4 or C 5 isoolefins and said inert hydrocarbons comprise paraffins and linear olefins. Apparatus for separating an etherification reaction effluent stream as defined in any of claims 1 and 7 to 9 said apparatus comprising: a first water extraction means (2); means (12) for introducing water into said first water extraction means (2); means (4) for introducing said reaction effluent stream into said first water extraction means (2) for producing a third stream comprising an extract mixture of alcohol and a stream comprising a raffinate mixture of said ether, hydrocarbons and alcohol; a first fractionator means (6); means (8) for introducing said stream as a feed stream to said first fractionator means (6) wherein said stream is fractionated under conditions sufficient to produce a third stream comprising said ether substantially free of alcohol, and a first stream comprising a mixture of said hydrocarbons and alcohol; a second water extraction means (20); means (24) for introducing water into said second extraction means (20); means (10) for introducing said first stream into said second water extraction means (20) for producing a fifth stream comprising an extract mixture of alcohol and a fourth stream comprising a raffinate of said hydrocarbons substantially free of alcohol; a second fractionation means (18); means (32) for combining said third stream and said fifth stream to form a sixth stream, and for introducing said sixth stream as a feed stream to said second fractionator (18), wherein said sixth stream is fractionated under conditions sufficient to producing an overhead stream essentially comprising alcohol and a bottom stream essentially comprising water; and a stripping column (22). Apparatus in accordance with claim 10, said apparatus additionally comprising: means (26) for introducing said fourth stream as a feed stream near the top of said stripping column wherein said fourth stream is stripped of light ends to provide a stabilized hydrocarbon stream. Apparatus in accordance with claim 10 additionally comprising: a bypass means (30) around said first water extraction means.

Inventors: EASON JOHN H, KLEPAC JOSEPH, EASON, JOHN H., KLEPAC, JOSEPH
Applicants: PHILLIPS PETROLEUM CO, PHILLIPS PETROLEUM COMPANY
Application year: 1993
Main classification: C07C41
IPC codes: C07C43, C07C41