METHOD OF MAKING ANILINE FROM BROMOBENZENE

FIELD OF THE INVENTION

[0001] The invention relates generally to methods of synthesizing aniline and, more particularly, to the production of aniline from bromobenzene and ammonia in the presence of a metal oxide. An integrated process of aniline synthesis and metal oxide regeneration is also disclosed.

BACKGROUND OF THE INVENTION

[0002] Aniline is an important industrial chemical used in the production of isocyanates, rubber chemicals, dyes, pigments, hydroquinone, pharmaceuticals, and other chemicals. At least three major processes have been or are used to produce aniline. These processes are listed below, along with their respective disadvantages:

[0003] 1. Reduction of nitrobenzene with hydrogen. Suffers from (a) slow reaction rates (i.e., hours) in the nitration step, and (b) a large excess of hydrogen (9: 1) is required in the hydrogenation step.

[0004] 2. Ammonolysis of chlorobenzene ~ chlorination of benzene and reaction with ammonia (operated by DOW until 1966). Suffers from (a) chlorine is lost as HCl, and (b) the reaction is carried out at high pressures (6-75 bar).

[0005] 3. Ammonolysis of phenol. Suffers from (a) high temperatures (425 ⁰ C) and pressure (200 bar) are required, and (b) a phenol intermediate is required. Given the disadvantages associated with each of the processes, there is a strong need for an improved process of producing aniline. Advantageously, such a process would:

[0006] 1. Utilize lower cost starting materials (ammonia versus nitric acid, and avoidance of phenol);

[0007] 2. Operate at low pressures;

[0008] 3. Allow full recovery of halogen reactant(s); and

[0009] 4. Provide high selectivity.

BRIEF DESCRIPTION OF THE DRAWING

[0010] The Figure is a schematic illustration of an integrated process for making aniline according to one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0011] According to a first aspect of the invention, it has been discovered that aniline can be made in an efficient manner by reacting bromobenzene with ammonia (or an ammonia source) in the presence of a metal oxide. The reaction is carried out in either the gas or liquid phase.

[0012] In a second aspect of the invention, aniline is produced in two steps: First, benzene is brominated to generate bromobenzene. Second, the bromobenzene is reacted with ammonia or an ammonia source, in the presence of a metal oxide, to form aniline and one or more metal bromides.

[0013] In other aspects of the invention, one or more additional steps are utilized.

Nonlimiting examples include the optional separation of any unreacted benzene and/or higher brominated benzene isomers (if any) produced in the bromination step; separation of the metal bromide from aniline; and regeneration of the metal oxide using air or oxygen. Nonlimiting examples of higher brominated benzene isomers include dibromobenzene (C ₆ H ₄ Br ₂ ) and tribromobenzene (C ₆ H ₃ Br ₃ ).

[0014] According to the invention, any of a number of metal oxides are used to facilitate the production of aniline. Preferred oxides include oxides of calcium, vanadium, molybdenum, chromium, manganese, zinc, lanthanum, tungsten, tin, indium, and bismuth, as well as alkali-doped versions of such compounds. Even more preferred are any of the following: (i) binary oxides such as CuO, MgO, Y ₂ O ₃ , NiO, Co ₂ O ₃ , and Fe ₂ O ₃ ; (ii) alkali metal-doped mixed metal oxides, e.g., oxides of copper, magnesium, yttrium, nickel, cobalt, or iron, doped with one or more alkali metals (e.g., Li, Na, K, Rb, Cs) (most preferably with 5-20 mol % alkali content); (iii) alkali metal bromide-doped oxides of copper, magnesium, yttrium, nickel, cobalt, or iron (nonlimiting examples of alkali metal bromide dopants include LiBr, NaBr, KBr, RbBr, and CsBr); and (iv) supported versions of any of the aforementioned oxides and doped oxides. Nonlimiting examples of suitable support materials include zirconia, titania, alumina, and silica. One or more metal oxides (with or without alkali dopants) are used.

[0015] Although bromobenzene can be purchased as a commodity chemical, in some embodiments of the invention it is preferred to generate bromobenzene as part of an integrated process that includes benzene bromination, metal-oxide-facilitated synthesis of aniline, regeneration of metal oxide and recycling of bromine. Such a process is schematically illustrated in Fig. 1 and described below in greater detail.

[0016] In one embodiment of the invention, molecular bromine (Br ₂ ) is used to brominate benzene in the liquid phase, at moderate temperatures (0 to 150 ⁰ C, more preferably 20 to 75 °C) and pressures (0.1 to 200 atm, more preferably 5 to 20 atm), over the course of 1 minute to 10 hours (more preferably 15 min. to 20 hrs), using FeBr ₃ or another suitable catalyst. In an alternate embodiment, bromination is accomplished with FeBr ₃ , in the absence of Br ₂ , generating bromobenzene, hydrogen bromide, and FeBr ₂ . After removing bromobenzene and HBr, the FeBr ₂ can be reacted with Br ₂ to regenerate FeBr ₃ .

[0017] Bromination of benzene can result in the formation of more highly brominated isomers of benzene, such as dibromobenzene, tribromobenzene, etc. However, because the boiling points of benzene (80 ⁰ C), bromobenzene (155 ⁰ C), dibromobenzene (~220°C), and higher brominated isomers differ significantly, bromobenzene can be readily separated from benzene and other brominated isomers via distillation.

[0018] Reaction of bromobenzene with ammonia (or an ammonia source) in the presence of a metal oxide yields aniline, metal bromide, water, and possibly hydrogen bromide. Table 1 identifies the metal bromides that are believed or predicted to be formed as a result of the metal oxide-facilitated synthesis of aniline from bromobenzene and ammonia (or an ammonia source).

[0019] Table 1. Predicted Metal Bromides Generated from Bromobenzene and Selected Metal Oxides and Dopants

[0020] Without being bound by theory, it is believed that the alkali metal in an alkali metal-doped oxide of copper, magnesium, yttrium, nickel, cobalt, or iron (and possibly others) will, upon interaction with bromobenzene, be converted into an alkali metal bromide (LiBr, NaBr, KBr, etc.) and remain as such. It is further believed that such dopants will not provide a sink for bromine, though they will likely influence the chemistry of the metal oxide. Metal oxide supports, such as zirconia, titania, alumina, silica, etc., are not expected to be converted to their respective bromides.

[0021] Advantageously, in some embodiments of the invention, metal bromide formed during the synthesis of aniline is converted back into the metal oxide using air or another source of oxygen. If molecular bromine is used as the brominating agent, it may be regenerated concurrently with the regeneration of the metal oxide. The reaction may be generalized as MBr _2x + O ₂ → MO _x + Br ₂ , where the value of x depends on the oxidation state of the metal.

[0022] Thus, an integrated process of aniline formation is provided. Referring to the Figure, bromobenzene is formed from benzene and bromine. Ammonia and bromobenzene are then allowed to react in the presence of a metal bromide, producing aniline, water, and

metal bromide. The metal bromide is allowed to react with air or oxygen, thereby regenerating the metal oxide cataloreactant and producing bromine, which can then react with additional benzene, starting the cycle anew.

[0023] Gas Phase Production of Aniline

According to one embodiment of the invention, aniline is produced in the gas phase at moderate temperatures (100 to 45O ⁰ C, more preferably 200 to 300°C) and pressures (0.1 to 200 atm, more preferably 5 to 20 atm), in a fixed bed, fluidized bed, or other suitable reactor. Target reaction times are 0.1 to 600 seconds, more preferably 1 to 30 seconds.

[0024] When aniline is produced in the gas phase, either gaseous ammonia (NH ₃ ) or some other source of ammonia is used as a reactant. Optionally, steam (H ₂ O) is also introduced into the reactor.

[0025] Nonlimiting examples of alternate ammonia sources include (a) aqueous ammonium hydroxide (NH ₄ OH), which is vaporized to produce ammonia; (b) ammonium bromide (NH ₄ Br) which, when vaporized, decomposes into water, ammonia, and hydrogen bromide (which will react with the metal oxide and form metal bromide and water); and (c) a co-feed of nitrogen and hydrogen gas which, in the presence of a metal oxide catalyst such as iron oxide and oxides containing a small amount of ruthenium, is converted into ammonia.

[0026] In one embodiment, ammonia or its equivalent is introduced into a single, fixed bed, gas phase reactor charged with spherical or cylindrical metal oxide pellets. Alternatively, multiple reactors are employed, so that, as one is being regenerated, another is producing aniline.

[0027] It is preferred that the metal oxide pellets have, on average, a longest dimension of

0.1 to 3 inches (more preferably 0.25 to 1 inch). Alternatively, the reactor is charged with comparably dimensioned spherical or cylindrical pellets of a suitable support material, such as zirconia, silica, titania, etc., onto which is supported the desired metal oxide(s) in a total amount of 1 to 50 wt.% (more preferably, 10 to 33 wt.%).

[0028] In another embodiment of the invention, aniline is produced in the gas phase in a fluidized bed reactor that contains metal oxide particles having, on average, a grain size of 10 to 500 microns (more preferably 50 to 150 microns).

[0029] For a gas phase reaction, aniline is conveniently separated from metal bromide generated in the reactor by simply exhausting the aniline from the reactor, leaving solid metal bromide behind. Optionally, saturated steam is introduced into the reactor to remove residual metal bromide (a process referred to as "steam stripping"), preferably at temperatures and pressures comparable to those used in the gas phase production of aniline.

[0030] To regenerate the metal oxide in a fixed bed reactor, the bed is heated or cooled to a temperature of approximately 200 to 500°C, and air or oxygen (optionally preheated) at a pressure of 0.1 to 100 atm (more preferably, 0.5 to 10 atm) is introduced into the reactor. Bromine, and possibly nitrogen or unreacted oxygen, will then leave the bed. The bromine can be separated by condensation and/or adsorption and recycled for further use.

[0031] To regenerate the metal oxide in a fluidized bed reactor, solid metal oxide/metal bromide particles are removed from products and any remaining reactants in a first cyclone. The particles are then fed into a second fluidized bed, heated or cooled to a temperature of approximately 200 to 500°C, and mixed with air or oxygen (optionally preheated) at a pressure of 0.1 to 100 atm (more preferably, 0.5 to 10 atm). Solid materials (regenerated metal oxide) are then separated from bromine, and possibly nitrogen or unreacted oxygen, in a second cyclone. The metal oxide particles can then be reintroduced into the first (or another) fluidized bed reactor. The bromine can be separated by condensation and/or adsorption and recycled for further use.

[0032] Liquid Phase Production of Aniline

According to another aspect of the invention, aniline is produced in the liquid phase at moderate temperatures (100 to 450 ⁰ C, preferably 200 to 300°C) and pressure (1 to 200 atm, preferably 10 to 50 atm), in a semi-batch, fluidized bed, or other suitable reactor. Target reaction times are 5 min. to 24 hr. (more preferably 30 min. to 3 hr).

[0033] The ammonia source is either liquid ammonia, aqueous ammonium hydroxide, or aqueous ammonium bromide (which decomposes into ammonia and hydrogen bromide in the presence of a metal oxide) The hydrogen bromide will, in turn, react with the metal oxide to form water and metal bromide).

[0034] In one embodiment, a simple, semi-batch reactor vessel is charged with reactants and fine metal oxide particles; aniline is formed; and the products are removed. Products are separated either by increasing the reactor temperature, decreasing the reactor pressure, and/or via a solvent wash. The residual solid is regenerated in the vessel.

[0035] For a liquid phase reaction carried out in a semi-batch reactor, it is preferred to use fine metal oxide particles having, on average, a grain size of 10 microns to 5mm (more preferably, 100 to 1000 microns).

[0036] In an alternate embodiment, aniline is produced in the liquid phase in a fluidized bed, with liquid reactants, etc., flowing through a bed of fine metal oxide particles. The grain size of such particles is preferably 10 to 1000 microns (more preferably, 50 to 150 microns).

[0037] For a liquid phase reaction, aniline is conveniently separated from metal bromide generated in the reactor according to any suitable separation technique. According to one approach, aniline is vaporized (and then exhausted from the reactor) by heating the metal oxide/metal bromide/reactant/product slurry to a temperature of 200 to 300 ⁰ C (at a pressure of, e.g., 1 to 10 atm),leaving solid metal bromide behind. In a second approach, carried out at 200 to 300 ⁰ C and 5 to 20 atm, aniline is removed by rinsing the metal bromide with an organic solvent, such as benzene. In a third approach, metal bromide is dissolved in water, and the water-immiscible aniline is separated from the aqueous metal bromide solution, which is then dried, and the solid metal bromide is then regenerated. Optionally, drying may be accomplished by a spray drying step in which the metal bromide solution is sprayed into a hot zone, forming metal bromide and steam. The metal bromide particles may be separated from the steam in a cyclone prior to being regenerated with air or oxygen.

[0038] After removal of all liquids from the reactor, the metal oxide can be regenerated in a manner essentially the same as that described above for a fixed bed, gas phase reactor.

[0039] Example

The following nonlimiting example illustrates one embodiment of the invention. 1. A batch reactor having a volume of approximately 0.5ml was half filled with copper oxide. To the reactor were added five drops of a 90 wt.% bromobenzene, 10 wt.% tetradecane (as an internal standard) mixture, and five drops of an aqueous solution of ammonium hydroxide (30 wt.% NH ₃ ). The reactor was sealed and heated to 200 ⁰ C for six hours. Thereafter, the products were removed and analyzed by gas chromatography. The resulting spectrum showed 100% conversion of the bromobenzene and the production of aniline. Utilizing peak area analysis, the yield of aniline was determined to be greater than 50%.

[0040] The present invention offers the advantages of utilizing lower cost starting materials (ammonia versus nitric acid; avoidance of phenol; etc.), operating at low pressure;

providing full recovery of halogen (as compared to the chlorobenzene process) and potentially providing high selectivity.

[0041] The invention has been described and illustrated by various preferred and exemplary embodiments, but is not limited thereto. Other modifications and variations will likely be apparent to the skilled person, upon reading this disclosure. The invention is limited only by the claims and their equivalents.