Continuous process for cleaning process waste air obtained in the production of silicones

{
  "publication_number": "US10583390B2",
  "country": "US",
  "kind": "B2",
  "title": "Continuous process for cleaning process waste air obtained in the production of silicones",
  "abstract": "Organosilicon compounds in a process exhaust stream from silicone production are removed by contacting the exhaust stream with a semipermeable silicone membrane which is selectively permeable to organosilicon compounds and oxygen relative to nitrogen. The pressure on the permeate side of the membrane is preferably less than the pressure on the retentate side.",
  "claims": [
    "1. A continuous process for purifying process exhaust gas containing organosilicon compounds, obtained in a production process for preparing silicones, comprising: separating linear, cyclic and branched siloxanes having from 2 to 18 Si atoms, triorganosilanols, and mixtures thereof from a process exhaust gas stream containing nitrogen and oxygen, by contacting the process exhaust gas stream with one or more membrane separation apparatuses which contain a polyoctylmethylsiloxane composite membrane as a semipermeable membrane, where the semipermeable membrane is selectively permeable to organosilicon compounds and oxygen relative to nitrogen, and the process exhaust gas stream which is to be separated and which contains organosilicon compounds, nitrogen, and oxygen is continuously introduced at an inlet of the membrane separation apparatus in which it is continuously separated by the membrane into a retentate gas substream which is depleted in organosilicon compounds and leaves the membrane separation apparatus, and a permeate gas substream which is enriched in organosilicon compounds and leaves the membrane separation apparatus, wherein the initial total concentration of the organosilicon compounds in the process exhaust gas stream is from 0.3 g/m 3 to 1000 g/m 3, and the burden of the organosilicon compounds in the process exhaust gas stream is from 10 g/h to 10 000 g/h.",
    "2. The process of claim 1, wherein the organosilicon compounds are compounds comprising linear siloxanes of the formula R 3 SiO(R 2 SiO) n SiR 3 (I), where the radicals R are identical or different and are each a monovalent hydrocarbon radical having from 1 to 12 carbon atoms, and n is 0 or an integer from 1 to 16, cyclic siloxanes of the formula (R 2 SiO) x (II), where R is as defined above and x is an integer from 3 to 18, triorganosilanols of the formula R 3 SiOH (III), where R is as defined above, and mixtures thereof.",
    "3. The process of claim 2, wherein in formulae (I), (II), and (III), the R radicals contain from 1 to 6 carbon atoms, and in formula (II), if present, x is an integer from 3 to 6.",
    "4. The process of claim 2, wherein R is methyl or vinyl.",
    "5. The process of claim 1, wherein the pressure in the permeate gas substream is not more than 0.15 bar.",
    "6. The process of claim 1, wherein the pressure ratio of the feed gas stream to permeate gas substream is in the range of from 7 to 50.",
    "7. The process of claim 1, wherein the pressure ratio of the feed gas stream to permeate gas substream is in the range of from 15 to 20.",
    "8. The process of claim 1, wherein the semipermeable membrane comprises a polyoctylmethylsiloxane (POMS) composite membrane on a porous support structure composed of polyacrylonitrile/polyester nonwoven.",
    "9. The process of claim 1, wherein the retentate gas substream is continuously recirculated to the production process for preparing silicones.",
    "10. The process of claim 1, wherein the retentate gas substream is continuously discharged into the environment.",
    "11. The process of claim 1, wherein the organosilicon compounds present in higher concentration in the permeate gas substream are continuously separated from the permeate gas substream by condensation and the resulting purified permeate gas stream is continuously discharged into the environment.",
    "12. The process of claim 1, wherein a plurality of membrane separation apparatuses are connected in series."
  ],
  "description_excerpt": "The process relates to a continuous process for purifying process exhaust air which contains organosilicon compounds and is obtained in the production process for preparing silicones.\n\nU.S. Pat. No. 4,941,893 discloses a process for removal gas in the preparation of semiconductor silicon metal, wherein hydrogen and hydrogen chloride are selectively separated off from chlorosilane in the gas mixture by means of a semipermeable membrane. As a selective membrane, preference is given to using a polysulfone composite membrane coated with sulfonated polysulfone.\n\nM. Alkar, M. Travesset, S. Yüce and T. Melin, “Siloxan removal from landfill and digester gas - A technology overview”, Bioresource Technology 101, 2913-2923 (2010), describes the separation of volatile siloxanes from landfill gas by means of various technologies, including by means of membranes.\n\nIn the thesis entitled “Membran-based Removal of Volatile Methylsiloxanes from Biogas” at the Hochschule Aachen (2011), pages 68-104 Marc Ajhar describes the use of a polydimethylsiloxane (PDMS) membrane for removing volatile methylsiloxanes from biogenic gases, with volatile methylsiloxanes present in small amounts in the region of about 0.15 g/m 3 being separated off from a methane/carbon dioxide gas mixture.\n\nIt was an object of the invention to provide a continuous process for purifying process exhaust air which contains organosilicon compounds and is formed in the production of silicones, in which organosilicon compounds, in particular siloxanes, can be selectively removed even in relatively large amounts from nitrogen/oxygen gas mixtures.",
  "cpc": [
    "B01D 53/226",
    "B01D 2257/553",
    "B01D 2257/556",
    "B01D 53/002",
    "B01D 53/22",
    "B01D 53/228",
    "B01D 53/229",
    "B01D 71/70",
    "B01D 71/701",
    "B01D 71/78",
    "C07F 7/20",
    "C08L 83/04"
  ],
  "ipc": [
    "B01D 53/22",
    "B01D 71/70",
    "B01D 71/78",
    "C07F 7/20",
    "B01D 53/00",
    "C08L 83/04"
  ],
  "assignees": [
    "Wacker Chemie AG"
  ],
  "inventors": [
    "Josef FUERST",
    "Nils Becker",
    "Dieter Duschl",
    "Johann Schuster"
  ],
  "filing_date": "2016-07-11",
  "publication_date": "2020-03-10",
  "grant_date": "2020-03-10",
  "priority_date": "2015-07-15",
  "application_number": "US-201615739960-A",
  "family_id": "56511553",
  "cited_by_count": 1,
  "citations": [
    "US4941893A",
    "US4941893B1",
    "US6221131B1",
    "US20090277326A1",
    "US20140142205A1"
  ]
}