Patent Application
20220009775
Bromine is used in organic chemical synthesis processes, for example, in the production of fire-retardants, polymers such as polyethylene terephthalate (PET), and pharmaceuticals. The hydrogen bromide byproduct of these reactions is usually neutralized with caustic forming a bromide salt solution, which is a waste product. Fresh elemental bromine is supplied to the process.
Cost and waste reductions may result if the hydrogen bromide (HBr) were oxidized with air or oxygen back to elemental bromine (Br2) for reuse within these processes, according to the thermodynamically favorable reaction 4HBr+O2→2Br2+2H2O. However, oxidation of hydrogen bromide to bromine is traditionally not practiced commercially, in part due to the practical difficulties and limited choices of suitable materials for cooling and condensing the very hot gaseous oxidation reactor effluent that contains bromine, water, and trace amounts of hydrogen bromide.
Although nickel alloys are suitable for handling the hot (˜350-500° C.) gaseous reaction mixture as long as the temperature is above the dew point, nickel alloys are rapidly corroded by the presence of an aqueous phase containing Br2 and HBr. Other non-metallic materials such as glass, ceramic, and silicon carbide, while resistant to both hot gaseous and sub-dew point mixtures, may be prone to mechanical or thermal shock. These non-metallic materials may require polymeric pressure seals (such as for silicon carbide heat exchanger tubes) thereby limiting the maximum operating temperature range of these materials to about 260° C., the maximum operating temperature for polytetrafluoroethylene (PTFE) and other fluoropolymers. At or below 260° C., PTFE may be permeated by bromine or hydrogen bromide that may require venting/evacuating the space between the liner and vessel wall and applying a corrosion barrier coating of the internal metal wall. In addition, glass-lined or epoxy-lined carbon steel is suitable for exposure to aqueous bromine and acids, but is limited to use at temperatures below about 260° C. Thus, the transition between the hot superheated vapor and the cooled, condensing mixture in an HBr oxidation and bromine recovery process may be problematic for existing methods. High cost refractory metals such as tantalum, which are resistant to aqueous bromine service at temperatures of about 150° C. or less, are subject to corrosion or embrittlement at temperatures above 300° C. in the presence of oxygen, nitrogen, (present when air is utilized as the lowest-cost oxidant for the HBr oxidation reaction) or bromine.
In an embodiment of the present disclosure, a HBr oxidation/quench system is disclosed. The HBr oxidation/quench system includes a heat exchanger reactor, an adiabatic catalytic reactor in fluid communication with the heat exchanger reactor, and a quench vessel, the quench vessel in fluid communication with the adiabatic catalytic rector. The quench vessel has a flange. The HBr oxidation/quench system also includes a joined three phase separator and absorber column, wherein both the three phase separator and the absorber column are in fluid communication with the quench vessel. In addition, the HBr oxidation/quench system further includes an aqueous stripping column in fluid communication the heat exchanger reactor and the absorber column.
In another embodiment, a method is disclosed. The method includes reacting air and HBr in a heat exchanger reactor to form reactor effluent comprising HBr, water, bromine and air. In addition, the method includes reacting the reactor effluent in an adiabatic reactor to form adiabatic reactor effluent comprising HBr, water, bromine and air. Also, the method includes quenching the adiabatic reactor effluent to form a quench bottoms outlet stream and a quench vessel overhead stream. The method further includes separating the quench bottoms outlet into a bromine product stream and a water recycle stream and using a first portion of the water recycle stream as a quench water feed stream. In addition, the method includes stripping a second portion of the water recycle stream in an aqueous stripper to form a water out stream.
A hot vapor transition assembly is disclosed. The assembly includes a central nickel alloy tube, and an outer annular tube, the outer annular tube annularly enclosing the central nickel alloy tube and forming an inner annular space between the central nickel alloy tube and the outer annular tube. The assembly also includes a lining, the lining annularly enclosing the outer annular tube and forming an outer annular space between the outer annular tube and the lining.
A method is disclosed. The method includes providing a quench vessel, the quench vessel comprising a flange. The method also includes providing a hot vapor transition assembly, the hot vapor transition assembly positioned within the flange. The hot vapor transition assembly includes a central nickel alloy tube and an outer annular tube, the outer annular tube annularly enclosing the central nickel alloy tube and forming an inner annular space between the central nickel alloy tube and the outer annular tube, the outer annular tube having a protruding portion that extends into the quench vessel. The hot vapor transition assembly also includes a lining, the lining annularly enclosing the outer annular tube and forming an outer annular space between the outer annular tube and the lining. The method also includes introducing hot vapor into the central nickel tube, the hot vapor temperature exceeding the dew point temperature of the hot vapor and purging the outer annual space with buffer air. In addition, the method includes cooling the protruding portion with quench water.
The present disclosure is best understood from the detailed description when read with the accompanying figures. In accordance with the standard practice in the industry, various features are not drawn to scale. Schematic drawings are structural or procedural diagrams.
The following disclosure provides many different embodiments and examples. Specific examples of equipment and arrangements are described below to simplify the present disclosure. These are merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.
Various terms are used herein. To the extent a term used in a claim is not defined below, it should be given the broadest definition skilled persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing. Further, unless otherwise specified, all compounds described herein may be substituted or unsubstituted and the listing of compounds includes derivatives thereof.
Further, various ranges and/or numerical limitations may be expressly stated below. It should be recognized that any ranges include iterative ranges of like magnitude falling within the expressly stated ranges or limitations.
HBr oxidation/quench system 100 is depicted in
In some embodiments, waste heat may be recovered from the adiabatic reactor effluent 162 in waste heat recovery exchanger HEX-6 170 in forming quench vessel feed 172. Waste heat recovery exchanger HEX-6 170 may be maintained above the dew point of water and bromine condensation such that metallic Nickel or Nickel alloy material may be used in contact with the process-side adiabatic reactor effluent 162.
In certain embodiment, HBr oxidation/quench system 100 may include quench vessel 180 to which quench vessel feed 172 is fed. In certain embodiments, quench vessel 180 may be glass-lined, epoxy-lined or fluoropolymer-lined. In some embodiments, quench vessel 180 may include hot vapor feed transition assembly 300, described below. Quenched bromine and water in quench vessel bottoms stream 182 may be cooled in quench recycle cooler HEX-4 184, forming cooled 3-phase separator feed 186. In certain embodiments, quench recycle cooler HEX-4 184 has tubes made of silicon carbide, alumina, other ceramic material, or a refractory metal or refractory metal cladding such as Tantalum. Quench vessel overhead stream 188, which is fed to absorber column 200, may include hydrogen bromide, bromine, water, nitrogen and unreacted oxygen. In the embodiment shown in
In 3-phase separator 190, a first aqueous liquid phase (containing water, some bromine and ionized HBr) a second liquid bromine phase and vapor phase are separated. The aqueous liquid phase and liquid bromine phase are separated by weir 192 forming bromine product stream 194 and water recycle stream 196. Without being bound by theory, when Br— concentration in the aqueous phase is less than about 5 mol % (corresponding to an HBr conversion of about 95% or higher), a second distinct liquid phase may be formed that is primarily elemental bromine. This second distinct liquid phase, being significantly denser than the first aqueous liquid phase allows the bromine product to efficiently separated from the aqueous phase using simple gravity settling and decanting. When the HBr conversion is greater than 99.9% the bromine phase may contain only about 0.3 wt % water, and furthermore very little unconverted HBr will be lost to the aqueous phase.
Water recycle stream 196 may include dissolved bromine. Bromine may be absorbed in absorber column 200 by absorber column water feed 202. Absorber column overhead 204 may include partially oxygen-depleted air and bromine vapor. Absorber column overhead 204 may be sent to a final scrubbing system to remove any residual hydrogen bromide and bromine.
A portion of water recycle stream 196 may be used for quench water feed 174, while the remainder stream 176 of water recycle stream 196 is fed to aqueous stripping column 220. In certain embodiments, aqueous stripping column 220 is glass-lined, epoxy-lined or fluoropolymer-lined. Aqueous stripping column 220 may include compressed air inlet stream 222 from air compressor 230. Aqueous stripping column 220 uses a compressed air stream to strip bromine from water recycle stream 176 and return the bromine to heat exchanger reactor 140 through aqueous stripping column overhead stream 224 along with compressed air. Aqueous stripping column overhead stream 224, which may include air and bromine, may be heated by heat exchanger HEX-2. Heat exchanger HEX-2 may heat aqueous stripping column overhead stream 224 to a temperature in the range of about 225° C. to 325° C. A portion of water produced in heat exchanger reactor 140 and adiabatic catalytic reactor 160 may be produced as water out stream 226. A second portion of water produced in heat exchanger reactor 140 and adiabatic catalytic reactor 160 may be cooled in refrigerated liquid cooler HEX-5 240 and fed to absorber column 200 through absorber column water feed 202. Refrigerated liquid cooler HEX-5 may use corrosion-resistant tubes composed of silicon carbide, alumina, other ceramic material, or a refractory metal or refractory metal cladding such as Tantalum.
The aqueous phase in the top stages of the absorber column 200 may contain less than about 3.0 or less than 2.0, or less than 1 wt % bromine. The downward flowing chilled water absorbs bromine vapor in the top stages of absorber column 200 and also condenses liquid bromine from the rising residual oxidant vapor further down in the lower stages of absorber column 200.
In the embodiment depicted in
Inner annular space 330 and outer annular space 340 may be purged with buffer air to restrict corrosive gases from entering annular spaces 330, 340. Annular spaces 330, 340 may also form a thermal break, thermally isolating central nickel alloy tube 310, thus protecting lining 350 from melting or damage due to excessive temperature. The flow of buffer air is controlled at a very small rate relative to the high rate of flow of hot gases within the central nickel alloy tube 310 so that central nickel alloy tube wall 360 operates at a temperature well above the dewpoint temperature of the hot reaction mixture, thus retarding corrosion attack of the nickel alloy.
Protruding portion 322 of outer annular tube 320 that protrudes into quench vessel 180 may be maintained at a cooler temperature below the dewpoint of the hot gas mixture by the flowing cooled quench water 370 on outer surface 324 of outer annular tube 320. Because protruding portion 322 is cooled and maintained below the dewpoint of the hot gas mixture, aqueous condensation continuously occurs on inner surface 326 of outer annular tube 320. Titanium may maintain a passivating oxide film in the presence of liquid water, which protects the Titanium metal from corrosion from bromine and trace amounts of HBr acid. Tantalum or other refractory metal are resistant to corrosion attack by aqueous acids or bromine at temperatures below 150 C. Alternatively, Niobium, Molybdenum or Tungsten are similarly resistant to corrosion at the lower temperatures below 150 C.
The foregoing outlines features of several embodiments so that a person of ordinary skill in the art may better understand the aspects of the present disclosure. Such features may be replaced by any one of numerous equivalent alternatives, only some of which are disclosed herein. One of ordinary skill in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. One of ordinary skill in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure.
This application is a nonprovisional application which claims priority from U.S. provisional application No. 63/050,624, filed Jul. 10, 2020, which is incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63050624 | Jul 2020 | US |
