Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
  • B01D61/36—Pervaporation; Membrane distillation; Liquid permeation
  • B01D61/362—Pervaporation
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D323/00—Heterocyclic compounds containing more than two oxygen atoms as the only ring hetero atoms
  • C07D323/04—Six-membered rings
  • C07D323/06—Trioxane
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S159/00—Concentrating evaporators
  • Y10S159/27—Micropores
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S159/00—Concentrating evaporators
  • Y10S159/28—Porous member

Definitions

• the invention relates to a process for separating trioxane from an aqueous mixture which consists essentially of trioxane, formaldehyde and water.
• trioxane creates an azeotropic mixture that consists essentially of trioxane, water and formaldehyde.
• Trioxane is extracted from this mixture with the aid of an entrainer, e.g. chlorine-containing entraining agents such as methylene chloride or benzene are separated off.
• an entrainer e.g. chlorine-containing entraining agents such as methylene chloride or benzene are separated off.
• Other constituents of the mixture in minor amounts are usually formic acid, methylal and dimethoxy dimethyl ester.
• the entrainer is recovered and returned to the extractive distillation.
• large amounts of entraining agents have to be used and recovered with high energy expenditure. Inevitable emissions have to be disposed of, since methylene chloride and benzene are classified as dangerous pollutants.
• EP-A 596 381 discloses a process for the separation of trioxane which removes water from the azeotropic mixture by pervaporation.
• aqueous mixture consisting of 65% by weight of trioxane, 27.5% by weight of water and 7.5% by weight of formaldehyde is in a pervaporation unit 2 which has a membrane 3 made of polyvinyl alcohol from Sulzer Chemtech GmbH -Membrantechnik, D-66540 Neun Wegn / Saar contains, water (line 4) withdrawn.
• the separation takes place at 90 ° C.
• the pressure on the retentate side 5 is 1 bar, on the permeate side 6 50 mbar.
• the permeate obtained is water and the retentate is a mixture of 84% by weight of trioxane, 10% by weight of formaldehyde and 6% by weight of water (line 7).
• the retentate is decomposed in a rectification column 8 under normal pressure into pure trioxane (bottom product, line 9) and an azeotropic mixture of trioxane, formaldehyde and water (top product, line 10).
• This process has the disadvantage that it does not offer complete trioxane workup. A return of the column stream 10, for example before the pervaporation, would not make sense, since formaldehyde would accumulate.
• the object of the present invention was to provide a process for separating trioxane from this azeotropic mixture, which offers the most complete possible possible recovery of the trioxane.
• trioxane is removed from the mixture by pervaporation and the trioxane-enriched mixture (permeate) by rectification in trioxane and an azeotropic mixture of trioxane, water and formaldehyde.
• the process according to the invention offers the advantages of a largely quantitative work-up of the reactor discharge with the most complete possible recovery of the trioxane and formaldehyde. No other feedstocks are required.
• Stream 1 represents the reactor discharge which is produced in the production of trioxane. As a rule, this consists essentially of 35 to 45% by weight of trioxane, 35 to 45% by weight of water and 15 to 30% by weight of formaldehyde. Stream 1 is passed into a 1st rectification column K1, in which there is a separation into 2 fractions, stream 2 containing a mixture of water and formaldehyde and stream 3 containing the azeotropic mixture.
• the distillation is preferably carried out in a rectification column K1, which can have up to 60 trays. As a rule, the distillation is carried out under normal pressure.
• Stream 2 is then returned to the formaldehyde concentration.
• the azeotropic mixture (stream 3) is transferred to a vaporization unit (PV) which contains suitable membranes for organophilic pervaporation.
• the membranes used are usually pore-free polymer membranes, in which the permeating component dissolves and diffuses through the membrane.
• Suitable membranes are, for example, those made from polydimethylsiloxane and polyether amide block copolymers.
• the polydimethylsiloxane membrane preferably contains a hydrophobic zeolite.
• the thickness of the membrane is preferably from 5 to 200 ⁇ m, preferably from 50 to 150 ⁇ m.
• Such membranes are commercially available under the trade names Pervap® 1070 from Sulzer Chemtech GmbH-Membrantechnik and PEBA 40 from GSE (Gesellschaft für Spezialfolienponent).
• the pervaporation is preferably carried out at temperatures from 70 to 120 ° C., preferably from 80 to 90 ° C. and a pressure of 1 to 3, preferably 1 to 1.5 bar on the retentate side and 10 to 150 mbar, preferably 10 to 20 mbar on the permeate side.
• the stream 5 depleted in trioxane (retentate) is returned to the first distillation column K 1, while the stream 6 enriched with trioxane (permeate) is fed into a second distillation column K 2, in which rectification then takes place.
• the trioxane fraction is the product and (stream 7) is fed into a reactor in which polyoxymethylenes are produced from trioxane.
• aqueous mixture consisting of 40% by weight of trioxane, 40% by weight of water and 20% by weight of formaldehyde was in a first distillation column (Kl, 25 stages) under normal pressure in a water / formaldehyde stream (stream 2) and separated into an azeotropic mixture (stream 3).
• Stream 3 was passed into the pervaporation unit, which contained a membrane of polydimethylsiloxane with a hydrophobic zeolite.
• the total thickness was 200 ⁇ m
• the support layer consisted of polyacrylonitrile.
• the thickness of the separating layer was 15-20 ⁇ m. (Membrane Pervap® 1070 from Sulzer Chemtech GmbH-membrane technology). The separation took place at 80 ° C.
• the pressure on the retentate side (5) was 1 bar and on the permeate side (6) 10 mbar.
• the stream depleted in trioxane (stream 5) was fed to the first distillation column (K1).
• the bottom stream from this distillation column was passed on to the formaldehyde concentration.
• trioxane 98.4% by weight of trioxane, based on 3200 kg of trioxane used - 100% by weight of formaldehyde, based on 1600 kg of formaldehyde used

Landscapes

• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Water Supply & Treatment (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Heterocyclic Compounds That Contain Two Or More Ring Oxygen Atoms (AREA)
• Separation Using Semi-Permeable Membranes (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Applications Claiming Priority (3)

Publications (1)

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Family Applications (1)

Country Status (8)

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• 1997
  • 1997-07-26 DE DE19732291A patent/DE19732291A1/de not_active Withdrawn
• 1998
  • 1998-07-02 KR KR1020007000817A patent/KR20010022244A/ko not_active Application Discontinuation
  • 1998-07-02 EP EP98939607A patent/EP1001954A1/de not_active Withdrawn
  • 1998-07-02 WO PCT/EP1998/004094 patent/WO1999005137A1/de not_active Application Discontinuation
  • 1998-07-02 JP JP2000504133A patent/JP2001510839A/ja not_active Withdrawn
  • 1998-07-02 CN CN98807365A patent/CN1264374A/zh active Pending
  • 1998-07-02 PL PL98338381A patent/PL338381A1/xx unknown
  • 1998-07-02 US US09/462,627 patent/US6200429B1/en not_active Expired - Fee Related

Non-Patent Citations (1)

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