Organic compounds -- part of the class 532-570 series – Organic compounds – Nitriles
Reexamination Certificate
2000-08-07
2001-07-17
Tsang, Cecilia (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Nitriles
Reexamination Certificate
active
06262290
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to the manufacture of acrylonitrile by the direct ammoxidation of a saturated hydrocarbon (e.g., propane), ammonia and oxygen in a reactor containing an ammoxidation catalyst. More specifically, the invention is related to the substantial reduction of unreacted ammonia, ammonium salts and resulting waste products produced from the unreacted ammonia. In particular, the invention relates to the addition of C
2
-C
5
olefin to the reactor to react with the unreacted ammonia thereby reducing and/or eliminating unreacted ammonia from the reactor effluent. This substantial reduction of ammonia in the reactor effluent provides significant environmental and economic advantages.
This invention has particular utility in the conversion of existing propylene based feed acrylonitrile plants to propane based feed acrylonitrile plants.
2. Description of the Prior Art
The production of acrylonitrile from propane is an emerging technology. While there are numerous patents related to catalysts and processing schemes for such technology. Commercialization of this technology has not yet occurred and acrylonitrile continues to be produced throughout the world via the ammoxidation of propylene (a more expensive feedstock than propane).
For both the ammoxidation of propylene and propane to acrylonitrile, ammonia is a required feedstock. Typically, unreacted ammonia remains in the reactor effluent, a condition known as “ammonia breakthrough”. In order to remove unreacted ammonia in commercial propylene based processes, the reactor effluent is contacted with a sulfuric acid quench to form ammonium sulfate which is then removed from the process as an aqueous waste stream which is then deep-welled or subjected to biological treatment.
In processes for the fluid-bed ammoxidation of propylene to acrylonitrile, U.S. Pat. Nos. 5,288,473 and 5,457,223 teach the substantial reduction of ammonia in the reactor effluent by the strategic addition of an oxygenate compound, preferably methanol, to the reactor.
An object of the present invention is a solution to ammonia breakthrough in processes for the ammoxidation of propane or isobutane to acrylonitrile.
A further object of the instant invention is an economical process scheme for the conversion of a propylene feed acrylonitrile plant to a propane or isobutane feed plant.
SUMMARY OF THE INVENTION
The invention is a method for the reduction of ammonia breakthrough in processes for the manufacture of acrylonitrile from propane and/or isobutane. More specifically, the invention is a process for the manufacture of acrylonitrile comprising introducing a hydrocarbon selected from the group consisting of propane and isobutane; ammonia and an oxygen-containing gas into a lower portion of a fluid-bed reactor containing an ammoxidation catalyst, and then reacting the hydrocarbon, ammonia and oxygen in the presence of said catalyst to produce acrylonitrile, wherein the improvement comprising introducing into the reactor at least one C
2
to C
5
olefin which will react with at least a portion of the unreacted ammonia and oxygen present in the reactor to substantially reduce the amount of ammonia present in the reactor effluent exiting the reactor.
The significance of the process in the present invention is that it provides a simple and economic procedure for the substantial elimination of ammonia breakthrough (i.e., unreacted NH
3
) in a fluid-bed reactor along with the additional advantage of eliminating ammonium sulfate as a by-product during the manufacture of acrylonitrile. The elimination of ammonium sulfate from the waste stream during acrylonitrile manufacture means that the waste stream does not contain any or only a minimal amount of ammonium salts. This leads to a significant economic advantage in the production of acrylonitrile, especially if one cannot practice deep-well injection. Without a substantial reduction in ammonia in the reactor effluent, the waste stream emanating from the quench column would contain ammonium sulfate (NH
4
)
2
SO
4
in a fairly high concentration making disposal of this stream in an economic and environmentally acceptable manner more difficult. The minimization or the elimination of the ammonium sulfate from this stream can make these streams acceptable to waste treatment procedures which do not require severe conditions or expensive materials of construction leading to significant economic and environmental advantages.
The present invention thus reduces or eliminates the amount of ammonia that escapes from the reactor and therefore minimizes or eliminates the cost required to quench, recover, dispose of, or recycle the unreacted ammonia. Furthermore, the invention provides an added benefit of producing additional useful products from the olefin.
Another embodiment of the instant invention is a method for the conversion of a propylene based feedstock acrylonitrile manufacturing process, wherein propylene, ammonia and oxygen are reacted in a reactor in the presence of a catalyst to produce acrylonitrile, to a propane based feedstock acrylonitrile manufacturing process, wherein propane, ammonia and oxygen are reacted in the presence of a catalyst to produce acrylonitrile. This method comprises:
(a) substituting a propane based feedstock for the propylene based feedstock,
(b) introducing into the reactor at least one C
2
to C
5
olefin which will react with at least a portion of unreacted ammonia and oxygen present in the reactor to substantially reduce the amount of ammonia present in the reactor effluent exiting the reactor, and
(c) adding to the process a means for the separation, recovery and recycle of unreacted propane.
An advantage of this embodiment is the ability to convert the plant from propylene based feedstocks to lower cost propane based feedstocks at a lower overall capital cost than needed to build a new propane based feedstock plant through the maximum use of existing equipment.
DETAILED DESCRIPTION OF THE INVENTION
The present invention reduces the production of ammonium sulfate generated during the manufacture of acrylonitrile from the reaction of propane and/or isobutane, ammonia and oxygen by adding at least one C
2
-C
5
olefin to the reactor. The addition of the C
2
-C
5
, olefin allows for the substantial or complete reaction of excess ammonia in the reactor with the olefin which in turn leads to substantial or complete elimination of ammonium sulfate from the waste stream emanating from the quench column of an acrylonitrile plant. Moreover, the reaction of the C
2
-C
5
olefin with excess ammonia provides for the additional production of useful products (e.g. the reaction of propylene to acrylonitrile).
In the preferred practice of the present invention, propane, ammonia and air react in the presence of a catalyst in a fluid-bed catalytic reactor to produce acrylonitrile. In such reactors, the propane, ammonia and air are introduced at or near the base of the reactor, the gaseous reactants rise through the catalyst bed while reacting to produce acrylonitrile. The reaction products, by-products and unreacted feeds exit at or near the top of the reactor.
Any catalyst capable of catalyzing the reaction of propane and/or isobutane in contact with ammonia and oxygen to yield acrylonitrile and/or methacrylonitrile is suitable for the instant invention. One such catalyst is described by the following general formula:
V
v
Sb
m
A
a
D
d
O
x
wherein A, when present, is at least one of Sn, Ti, and Fe,
D, when present, is at least one of Li, Mg, Na, Ca, Sr, Ba, Co, Cr, Ga, Ni, Zn, Ge, Nb, Zr, Mo, W, Cu, Te, Ta, Se, Bi, Ce, In, As, B, Al, and Mn.
V is 1
m is 0.5 to 10
a is 0 to 10
d is 0 to 10
x is a value sufficient to satisfy the valence requirements of the other elements present.
These catalysts may be either unsupported or supported on a suitable carrier. Typical suitable carriers, also known as “supports”, include silica, alumina, zirconia, titanium and their combinations. Silica is the preferred support.
In the practice of the insta
Brazdil, Jr. James F.
Padolewski Joseph P.
Murray Joseph
The Standard Oil Company
Tsang Cecilia
Yusko David P.
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