Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C43/00—Ethers; Compounds having groups, groups or groups
  • C07C43/02—Ethers
  • C07C43/03—Ethers having all ether-oxygen atoms bound to acyclic carbon atoms
  • C07C43/04—Saturated ethers
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C41/00—Preparation of ethers; Preparation of compounds having groups, groups or groups
  • C07C41/01—Preparation of ethers
  • C07C41/09—Preparation of ethers by dehydration of compounds containing hydroxy groups
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C41/00—Preparation of ethers; Preparation of compounds having groups, groups or groups
  • C07C41/01—Preparation of ethers
  • C07C41/34—Separation; Purification; Stabilisation; Use of additives
  • C07C41/40—Separation; Purification; Stabilisation; Use of additives by change of physical state, e.g. by crystallisation
  • C07C41/42—Separation; Purification; Stabilisation; Use of additives by change of physical state, e.g. by crystallisation by distillation

Definitions

• This invention relates to processes for the production of dimethyl ether by dehydration of methanol, and the separation and recovery of the produced dimethyl ether from that portion of the feed methanol which remains unconverted, with recycle of the unconverted portion of methanol for further conversion into dimethyl ether.
• Dimethyl ether may be produced by the conversion of two molar quantities of methanol in contact with an acid catalyst into one molar quantity of dimethyl ether (DME) with coproduction of one molar quantity of water.
• DME dimethyl ether
• the dehydration of methanol to DME is not complete and a portion of the feed methanol remains unconverted after catalyst contact and carries into the product gas composition.
• the incomplete conversion of methanol into dimethyl ether has presented no problem since the resulting methanol-dimethyl ether mixtures were produced as but an intermediate methoxy composition for further processing into other final end products.
• the methanol desirably should be relatively free of any water content since the presence of water in the feed methanol reduces the degree of methanol conversion into DME product. Even with a dry methanol, its single pass conversion to DME is equilibrium limited to about 80.8% of methanol converted. The presence of water in the feed methanol reduces this degree of methanol conversion to DME as the quantity of water in the feed methanol increases.
• the product gas resulting from conversion of a dry methanol feed to DME contains 19.16 mole % of the initial methanol feed as unconverted methanol, and the unconverted methanol and water content of the produce gas are present in a relative mole fraction of their molar sum of 0.6784 water and 0.3216 methanol.
• any further increase in water content contributed by water contained in the feed methanol increases the mole percent of the feed methanol that goes unconverted and increases the mole fraction of water relative to unconverted methanol in the product gas.
• the process of this invention utilizes methanol containing significant quantities of water, both as a fresh feed stock and/or as a recycle methanol stream, for the production of dimethyl ether (DME) which is recovered essentially free of any significant content of methanol or water.
• the process further comprises the separation of a quantity of the water recovered in the unconverted methanol separated from the DME product in an amount sufficient to prevent water buildup in the DME process due to the methanol recycle operation.
• the process minimizes the distillation duties in terms of equipment costs and reflux recycle with respect to the optimum for methanol conversion to DME to provide a process that is practical for production of DME as a commodity product.
• Fig. 1 illustrates a process for producing and recovering DME from the dehydration of methanol (MeOH) over an acid catalyst, with the use of a stripper for the recovery and recycle of unconverted MeOH as feed to the DME reactor and the separation and rejection from the DME process of that water contributed to the product gas from the fresh MeOH feed and as a by-product of the DME reaction.
• MeOH methanol
• the process of this invention utilizes methanol for production of a dimethyl ether (DME) containing reaction gas from which the dimethyl ether is recovered separately from that portion of methanol which remains unconverted and water produced as a reaction by-product or passed into the reaction product gas from the fresh methanol feed or contained in the recycled methanol.
• the methanol feed to the DME reactor comprises a fresh methanol feed portion and a portion of methanol recovered from the product gas and recycled back to the DME reactor.
• That portion of the methanol which is the fresh methanol feed may be secured from any source.
• the fresh methanol feed is of a water content less than 18 weight %, more preferably less than 10 weight % water.
• a methanol stream of about 5 weight % water content or less may be directly produced from natural gas without the need for distillation by processes as described in U.S. Patent Nos. 5,177, 1 14 and 5,245, 1 10, the descriptions of which are hereby incorporated by reference.
• commonly owned copending U.S. Patent Application Serial No. 08/336,298 describes an improved process for methanol production whereby methanol of a water content of about 10 weight % or less may be produced without the need for distillation, and the description of that application is hereby incorporated by reference.
• the recycle methanol portion of the methanol feed is recovered by first subjecting the DME process reaction gas to distillation treatment wherein the DME content of the product gas is separated as an overhead stream leaving the unconverted methanol and water content of the product gas to be recovered as a bottom stream.
• the bottom stream comprises methanol containing at least 54 weight % water.
• This methanol-water bottom stream is then subjected to another distillation step to produce as an overhead stream one which is more concentrated in methanol relative to water and as a bottom stream water containing no greater than 0.5 and preferably no greater than 0.05 weight % methanol.
• the overhead stream of this second distillation step contains at least 99% of the unconverted methanol and may be used without further distillative processing as the methanol recycle stream.
• the focus for the most beneficial employment of the process of this invention is upon the operation of the second distillative step wherein the methanol-water bottom stream recovered from the DME distillation step is processed to produce a methanol recycle stream and a bottom water stream which is rejected from the DME process. Since the methanol recycle stream from this step also contains a quantity of water, this introduces water into the methanol feed to the DME reactor. To prevent water buildup from occurring in the DME production process the quantity of water rejected as a bottom stream from this step must equal that quantity of water contributed to the product gas as water from the fresh methanol feed and water by-product from the conversion of methanol to DME.
• the requisite quantity of water rejection can readily be obtained by simply distillation equipment, such as a stripper, without significant loss of methanol in the rejected water.
• a stripper vessel may be employed to obtain the requisite quantity of reject water with a methanol content not exceeding about 0.05 weight % methanol.
• a stripper is an exceedingly simple distillation vessel which is operated without need for reflux of any portion of its overhead distillate.
• a dedicated stripper is a distillation vessel having no external reflux capability. The efficiency at which a dedicated stripper may be operated is essentially a function of its plate equivalency, and its reboiler duties.
• a refluxing distillation vessel can be employed at a low reflux ratio with a small number of theoretical plates to obtain the requisite quantity of reject water having a methanol content not exceeding about 0.05 weight % methanol.
• a simple overhead condenser can be employed to provide the requisite quantity of liquid reflux needed for feed back to the top of the column.
• a refluxing distillation column operated with a zero reflux ratio is, in effect a stripper. So employment of such a simple refluxing distillation column provides a great flexibility of the DME production process to handle fresh feed methanol having a wide range of water content.
• the overhead stream of such processing under the concepts of this invention comprises methanol with a significant content of water.
• This overhead stream may be used without need for further distillative processing as the methanol recycle stream for addition to the fresh methanol feed to form the combined methanol feed to the DME reactor.
• this overhead methanol-water stream as recycle for forming the combined methanol feed contributes water to the methanol feed, this water content of the methanol recycle only reduces the degree of methanol conversion to DME to an extent which is minor in comparison to the advantages realized from the simplified distillation duties attendant to its recovery.
• a simple stripper may be utilized to separate the MeOH-water recovered as the bottom stream from the DME recovery step into a water rejection stream and a MeOH-water recycle stream, while maintaining the single pass conversion rate of MeOH to DME on the order of a 74 to 79 % conversion of methanol (91.5 to 97.7% of the theoretically possible conversion).
• a simple stripper may be used to provide the rejection water and MeOH-water recycle streams while maintaining the MeOH conversion level to DME at about 75% or greater (about 92.8 % of theoretical).
• Raw methanol having a water content in the 3 to 10 weight percent range may be directly produced without any distillate treatment by processes as described in commonly owned U.S. Patent Nos. 5,177,1 14 and 5,245,1 19 and pending U.S. Patent Application Serial No. 08/336,298.
• Use of raw MeOH as produced by these processes as the fresh MeOH feed is preferred since this allows the use of a simple stripper to obtain the rejection H 2 0 and MeOH-H 2 0 recycle streams needed for practice of the DME production process.
• Raw MeOH produced by conventional methanol production processes containing from about 15-18 weight % H 2 0, may also be utilized as the fresh feed MeOH, and the necessary rejection water and MeOH-water recycle streams secured by a simple stripper, albeit the MeOH conversion to DME will be reduced to the 70-75% range (86.6 to 92.8% of theoretical).
• a source of fresh MeOH feed 2 and recycle MeOH-water 3 are combined and pressurized up to from about 10 to about 12 atmospheres absolute (ata) by compressor 4 and fed by line 6 to indirect heat exchanger 8 wherein the combined MeOH feed is heated to a temperature of from about 550 to about 650°F by indirect heat exchange with reaction product gases fed by line 14 to heat exchanger 8.
• the combined MeOH feed is then passed by line 10 into reactor 12 and therein contacts an add catalyst, such as addic alumina, wherdn a portion of the MeOH content of the combined feed is converted to DME and by-product water.
• the reaction product gases comprising DME, unconverted MeOH and water, passes by line 14 through heat exchanger 8 and from there by line 16 to a chill water heat exchanger 18 wherein the product gas is cooled to from about 150 to about 200°F and thereafter passes by line 20 to DME distillation column 22 for the separation of the DME and minor amounts of other ethers, such as methyl ethyl ether, from the unconverted MeOH and water content of the product gas.
• the DME distillation column is operated at a pressure of from about 9.5 to about 1 1.5 ata.
• DME is recovered as the overhead stream 23 and passed through a chill water heat exchanger 24 and from there through line 26 to DME condenser 28.
• Liquid condensate 30 from condenser 28 comprises DME and other higher boiling ethers.
• This DME condensate passes from the condenser and is split into two streams; one portion thereof is returned by line 32 as reflux to the DME distillation column 22, the second portion is recovered as DME product and passes by the line 34 to product storage or other subsequent processing.
• this DME may be further distilled to separate the minor amounts of higher boiling ethers, such as methyl ethyl ether.
• the bottom stream 36 from DME column 22 comprises MeOH and H 2 0.
• This bottom stream is split, with one portion passing by line 38 through reboiler 40 wherein it is heated to from about 320 to about 480° then passes by line 42 back to the bottom section of the DME column 22.
• the second portion of the bottom stream passes by line 44 through valve 46 then by line 48 as feed to the top of stripper column 50 operated at about 1 ata.
• the bottom stream 52 from stripper 50 comprises H z O with less than 0.05 weight % MeOH.
• This bottom stream is split and one portion of this H 2 0 stream is rejected from the process by line 54.
• the second portion of this H 2 0 passes by line 56 to reboiler 58 where it is heated to from about 215 to about 230°F and then returned by line 60 to the bottom section of stripper 50.
• the overhead stream 62 comprises MeOH and H 2 0.
• This overhead stream passes to a chill water heat exchanger 64 and from there to MeOH condenser 66.
• the liquid MeOH condensate 68 passes from this condenser 66 by line 3 into combination with a fresh portion of MeOH feed stock supplied by line 2.
• the overhead gases 29 from the DME condenser 28 may be washed with a portion of the fresh MeOH feed stock to recover any residual DME vapor from this overhead gas.
• the overhead gases 29 are passed into scrubber 70 and a portion of the fresh MeOH feed stock supplied by line 72 is passed to scrubber 70 and after countercurrent contact with the gases, the gases are vented by line 74 and this portion of the MeOH feed is recovered by line 76 and then combined with the recyde MeOH-water stream in line 3 as illustrated (or added to the fresh MeOH feed in line 2, not illustrated).
• an actual overhead enrichment factor for the overhead gas of at least about 96% of the theoretical enrichment factor was used for determining the overhead gas composition from the stripper.
• An enrichment factor is the value of the mole ratio of H 2 0:MeOH in the feed to the stripper divided by the mole ratio of H 2 0:MeOH in the distillate from the stripper. The results are reported in Tables LA and IB as Examples 1-1 1.
• Example 7 As may be seen by a comparison of Example 7 with Examples 12- 13 as more water is accepted in the stripper overhead relative to the quantity of MeOH recovered for recyde, the requirements for the stripper in terms of its theoretical plate equivalency becomes less - meaning the cost of the stripper becomes less ⁇ although the reboiler duties of the stripper increase due to the increasing amounts of water in the top product of the stripper.
• the optimum operation using a stripper lies within a mole ratio of H 2 O.MeOH in the overhead thereof of from about 0.6 to about 2.0, preferably from about 0.7 to about 1.2 and more preferably from about 0.8 to about 1.0.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Crystallography & Structural Chemistry (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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• 1995
  • 1995-03-15 US US08/404,256 patent/US5750799A/en not_active Expired - Fee Related
• 1996
  • 1996-03-11 AU AU53049/96A patent/AU706437B2/en not_active Ceased
  • 1996-03-11 EP EP96909618A patent/EP0815068A4/en not_active Withdrawn
  • 1996-03-11 CA CA002214141A patent/CA2214141A1/en not_active Abandoned
  • 1996-03-11 WO PCT/US1996/003207 patent/WO1996028408A1/en not_active Application Discontinuation
  • 1996-03-11 BR BR9607149A patent/BR9607149A/pt not_active Application Discontinuation
  • 1996-03-11 TR TR97/00944T patent/TR199700944T1/xx unknown
  • 1996-03-11 IN IN434CA1996 patent/IN187496B/en unknown
  • 1996-03-11 KR KR1019970706340A patent/KR19980702932A/ko not_active Ceased
  • 1996-03-11 CN CN96192554A patent/CN1073979C/zh not_active Expired - Fee Related
  • 1996-03-11 JP JP8527745A patent/JPH11502522A/ja active Pending
  • 1996-03-11 EA EA199700240A patent/EA000693B1/ru not_active IP Right Cessation
  • 1996-03-13 MY MYPI96000918A patent/MY112961A/en unknown
• 1997
  • 1997-09-12 NO NO974232A patent/NO309522B1/no not_active IP Right Cessation

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