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Method for Purifying a Chlorine Supply Verfahren Zur Reinigung Einer Chloreinspeisung Procédé De Purification D’Une Charge De Chlore

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Method for Purifying a Chlorine Supply Verfahren Zur Reinigung Einer Chloreinspeisung Procédé De Purification D’Une Charge De Chlore (19) TZZ ZZ_T (11) EP 2 499 090 B1 (12) EUROPEAN PATENT SPECIFICATION (45) Date of publication and mention (51) Int Cl.: of the grant of the patent: C01B 7/07 (2006.01) C01B 7/075 (2006.01) 26.10.2016 Bulletin 2016/43 C01B 31/28 (2006.01) B01D 3/14 (2006.01) (21) Application number: 10774238.9 (86) International application number: PCT/EP2010/067233 (22) Date of filing: 10.11.2010 (87) International publication number: WO 2011/058069 (19.05.2011 Gazette 2011/20) (54) METHOD FOR PURIFYING A CHLORINE SUPPLY VERFAHREN ZUR REINIGUNG EINER CHLOREINSPEISUNG PROCÉDÉ DE PURIFICATION D’UNE CHARGE DE CHLORE (84) Designated Contracting States: (56) References cited: AL AT BE BG CH CY CZ DE DK EE ES FI FR GB EP-A1- 1 972 609 WO-A1-2004/018355 GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO DE-A1-102006 008 606 GB-A- 767 792 PL PT RO RS SE SI SK SM TR US-A- 2 199 797 US-A- 3 668 078 US-A- 3 702 234 US-A- 5 437 711 (30) Priority: 13.11.2009 US 261176 P US-A1- 2007 180 855 (43) Date of publication of application: • Schneider, Wolfgang et al.: "Phosgene", 19.09.2012 Bulletin 2012/38 Ullmann’s Encyclopedia of Industrial Chemistry, 15 June 2000 (2000-06-15), page 1-10, (73) Proprietor: BASF SE XP002618922, Internet DOI: 67056 Ludwigshafen am Rhein (DE) 10.1002/14356007.a19_411 [retrieved on 2011-01-26] (72) Inventors: • ULRICH H ET AL: "ISOCYANATES, ORGANIC", 1 • GAGNON, Steven Dallas January 1989 (1989-01-01), ULLMANN’S Prairieville, LA 70769 (US) ENCYCLOPEDIA OF INDUSTRIAL CHEMISTRY. • JACOBS, Johannes IMMOBILIZED BIOCATALYSTS TO ISOPRENE; NL-4641 PE Ossendrecht (NL) [ULLMANN’S ENCYCLOPEDIA OF INDUSTRIAL • DOERR, Robert A. CHEMISTRY], WEINHEIM, VCH VERLAG, DE, Baton Rouge, LA 70817 (US) PAGE(S) 611 - 625, XP002918926, page 616 • BORDELON, Kenneth K. • SEADER, J.D. ET AL.: "Distillation", PERRY’S Geismar, LA 70734 (US) CHEMICAL ENGINEERS’ HANDBOOK, 1 March • GRZANKA, Thomas A. 2001 (2001-03-01), pages 13-1-13-5, Houston, TX 77284 (US) XP002618923, ISBN: 978-0-07-049841-9 (74) Representative: Herzog, Fiesser & Partner Patentanwälte PartG mbB Isartorplatz 1 80331 München (DE) Note: Within nine months of the publication of the mention of the grant of the European patent in the European Patent Bulletin, any person may give notice to the European Patent Office of opposition to that patent, in accordance with the Implementing Regulations. Notice of opposition shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). EP 2 499 090 B1 Printed by Jouve, 75001 PARIS (FR) EP 2 499 090 B1 Description FIELD OF THE INVENTION 5 [0001] The present invention generally relates to a method for purifying a chlorine supply including a chlorine compo- nent, a bromine component, and nitrogen trichloride. More specifically, the method includes utilizing a particular distillation system to form purified chlorine gas and to decompose the nitrogen trichloride. DESCRIPTION OF THE RELATED ART 10 [0002] Chlorine gas is typically commercially produced using one or more well known electrolysis processes such as mercury cell electrolysis, diaphragm cell electrolysis, membrane cell electrolysis, and/or electrolysis of fused chloride salts according to the Downs Process. The electrolysis processes typically produce chlorine through electrochemical reactions in brine solutions (e.g. NaCl and KCl solutions) as follows: 15 Cathode: 2 H+ (aq) + 2 e- → H2 (g) - - Anode: 2 Cl (aq) → Cl2 (g) + 2 e 20 [0003] Overall process: 2 NaCl (or KCl) + 2 H 2O → Cl2 (g) + H2 + 2 NaOH (or KOH) After formation, the chlorine gas can be treated with water and/or steam and then dried by cooling or treatment with sulfuric acid to minimize chlorine hydrate formation. [0004] At various points during the formation of chlorine gas, nitrogen trichloride (NCl3) is also typically formed. It is believed that NCl3 forms from side reactions of chlorine atoms and anhydrous ammonia or ammonium salts (e.g. am- 25 monium hydroxide, ammonium chloride, and ammonium sulfate) that are present at one or more points in the process. These side reactions typically occur as follows: + - NH3 + 3Cl2 → NCl3 + 3H + 3Cl 30 + + - NH4 + 3Cl2 → NCl3 + 4H + 3Cl + - + - NH4 + Cl + 3HClO → NCl3 + H + Cl + 3H2O The formation of nitrogen trichloride typically occurs due to brine contamination, steam contamination, and/or water 35 contamination. Any urea that is present in the brine, steam, or water can hydrolyze to form ammonium which can then be converted into nitrogen trichloride. Alternatively, salts used to form the brine can be contaminated with ammonium nitrate that can be converted into nitrogen trichloride. Sodium hydroxide that is typically used to form the brine can also be contaminated with ammonia depending on purification processes. In some cases, sulfuric acid used to dry the chlorine gas can be contaminated with ammonia. In still other cases, direct contact cooling water or steam can be treated with 40 amines, ammonia based flocculants, or chloramines which can lead to formation of nitrogen trichloride. Even ground water can include ammonia compounds that can be converted into nitrogen trichloride. [0005] As is well known in the art, nitrogen trichloride is sensitive to heat, light, sound, and shock and can quickly degrade at a rate sufficient to cause an explosion. Accordingly, nitrogen trichloride is preferably removed from chlorine gas but is typically done so in a complex, time consuming, and expensive manner. As set forth in Figure 1, which 45 represents the prior art, dried chlorine gas formed from electrolysis is typically washed with liquid chlorine in a washing column to minimize an amount of the nitrogen trichloride and cool the chlorine gas thereby increasing safety. In addition, the washing column also separates chlorinated organic compounds from the chlorine gas thereby increasing the purity of the chlorine gas. The washing column is typically connected to an external condenser and reboiler to increase the efficiency of the washing process, as also set forth in Figure 1. In the washing column, the nitrogen trichloride and the 50 various chlorinated organic compounds typically condense or dissolve in the liquid chlorine and may be recycled through the external condenser and reboiler, as described above. The reboiler is typically operated cold (0°C - 5°C) or hot (45°C - 60°C) and can act as a storage vessel for the nitrogen trichloride or as a point of decomposition. Carbon tetrachloride (CCl4) is typically added to the washing column to extract the nitrogen trichloride and allow for its removal from the washing column and subsequent disposal. Upon addition of the carbon tetrachloride, the nitrogen trichloride is separated 55 from the chlorine, which is vaporized in the reboiler and returned to the washing column. After the chlorine gas is washed and separated from the nitrogen trichloride and the various chlorinated organic compounds, the chlorine gas is typically compressed using liquid ring compression, reciprocating compression, or centrifugal compression, cooled using inter- and after-coolers, and then liquefied into liquid chlorine. The liquid chlorine then can be scrubbed and sold commercially. 2 EP 2 499 090 B1 However, even after drying, washing, compression, cooling, and liquefaction, trace amounts of both the carbon tetra- chloride and the nitrogen trichloride, in addition to trace amounts of scrubbing compounds, typically leach into the liquid chlorine and act as impurities when the liquid chlorine and/or chlorine gas is used in downstream commercial synthetic processes. 5 [0006] In addition to the nitrogen trichloride, commercial production of chlorine gas tends to produce a variety of byproducts including molecular bromine (Br 2), bromine-chloride (Br-Cl), and various organic compounds. These byprod- ucts, in addition to the carbon tetrachloride and the nitrogen trichloride, are also impurities when the chlorine gas is used in commercial processes. As is known in the art, when chlorine gas is used to synthesize phosgene, which in turn is used to synthesize isocyanates, presence of the carbon tetrachloride, nitrogen trichloride, and brominated compounds 10 typically add color to the isocyanates which makes the isocyanates less commercially desirable. Accordingly, these byproducts are typically removed using distillation and other separation techniques because chlorine gas is more volatile than many of the byproducts. However, entire chlorine streams are typically evaporated to achieve such distillations. One example of a distillation process is schematically set forth in Figure 1, as first introduced above. In this distillation process, and in many similar processes, external condensers and reboilers are used and connected via long lengths of 15 pipes to form effective distillation systems. However, use of these types of systems is very expensive, untimely, and complex. In addition, the long lengths of pipes used in these systems only increase a number of points at which the systems can fail, thus increasing safety risks and concerns. Furthermore, many of these systems also fail to effectively reduce amounts of nitrogen trichloride to sufficient levels. [0007] Some distillation systems utilize high pressure steam heated reboilers which have a tendency to lead to film 20 boiling, hot spots, and superheated chlorine gas, all of which are undesirable. Moreover, many distillation systems have a tendency to suffer from chlorine and nitrogen trichloride "holdup," i.e., accumulation of excess amounts of chlorine gas and nitrogen trichloride in the distillation systems, which leads to safety and environmental concerns. [0008] Other distillation systems do not effectively control amounts of incoming chlorine in relation to the efficiency of distillation and separation of desired compounds. This lack of control tends to reduce efficiency of the distillation systems 25 and does not allow for customization of distillation processes to maximize separation of desired compounds.
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