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AssigneeE. I. Du Pont de Nemours and Company
InventorsJohn Anton Thorpe, Harold Felton Porter
Estimating the term…
Process for recovering reactants and products e.g., acrylonitrile and hydrogen cyanide from an aqueous stream obtained in the ammoxidation of propylene which comprises heating an aqueous stream containing the afore-said compounds in a heat exchanger by circulating the stream at a velocity of at least 6 ft/sec through the exchanger while maintaining the stream in the liquid state to increase the temperature of the stream to at least 105.degree. C and thereafter rapidly reducing the pressure of the heated stream sufficiently to vaporize 0.2-5% thereof and thereafter returning the vapor to the acrylonitrile process for recovery of energy used to heat the aqueous waste; usable materials e.g., acrylonitrile and hydrogen cyanide and compounds such as ammonia which can be used to neutralize acid streams and subsequently either incinerating the unvaporized material directly or using the unvaporized material as fertilizer after appropriate treatment.
A process for the recovery of reactants and products contained in dilute aqueous stream from the waste water column of a process for the production of acrylonitrile by ammoxidation of propylene while concentrating said stream which reactants and products comprise hydrogen cyanide, acrylonitrile, ammonia, ammonium sulfate, and high boiling nitrogen containing impurities said process comprising mixing said dilute stream with a stream from the same source as said dilute stream partially concentrated by having a portion of the water removed therefrom passing the mixture obtained through a heat exchanger at a velocity of at least 6 ft/sec while maintaining said mixture in the liquid state to thereby heat the mixture to at least 105.degree. C and thereafter rapidly reducing the pressure of the heated mixture sufficiently to vaporize a portion of said mixture and thereafter returning said vapor to said acrylonitrile process while withdrawing a portion of the unvaporized stream.
A process for concentrating a dilute aqueous waste stream comprising in percent by weight based upon the total weight of the stream hydrogen cyanide 0.1-0.7% (as cyanohydrins), 0.01-0.1% acrylonitrile, 2-6% ammonium sulfate 2.0-5.0% high boiling nitrogen containing impurities, 0.01-0.5% acetonitrile, and 0.001-0.05% acetaldehyde which process comprises introducing said stream into a circulating loop consisting essentially of a heat exchanger, a flasher and a circulating means wherein said loop contains a partially concentrated waste stream, obtained by passing said dilute stream through said heat exchanger and flasher thereby removing a portion of the water therefrom to form a mixture of said dilute and said partially concentrated waste stream, passing said mixture in the liquid state through a heat exchanger at a velocity of at least 6 ft/sec to thereby heat the mixture to at least 105.degree. C and thereafter rapidly reducing the pressure of the heated mixture to vaporize at least 30% of the dilute aqueous waste introduced into said loop, recovering the vapor thus produced and withdrawing a portion of the partially concentrated waste stream while maintaining circulation through said loop.
Dependencies are inferred from the claim text.
No related US applications are recorded in the indexed filing history.
1. Field of the Invention
The present invention is directed to a process for treating the aqueous waste from a process for the production of acrylonitrile by ammoxidation of propylene.
2. Description of the Prior Art
A schematic representation of a typical apparatus for practicing the process of the present invention is shown in the drawing.
The process of the present invention is practiced using the apparatus set forth in the FIGURE attached hereto and made a part of the specification. Steam is introduced via line 1 into heat exchanger 2 and condensate is removed from the heat exchanger via line 3. The aqueous waste stream is introduced into the apparatus via line 4 and thereafter directed via line 5 to pump 6 where it is pressurized and forced via line 7 through heat exchanger 2 and thence via line 8 through orifice 9. The hot stream under pressure is then introduced into flasher 10 which is equipped with an internal separating means comprising a column and hat portion identified as item 11. The vapor is withdrawn from the flasher via line 12 where it is subsequently treated to recover desirable products contained therein. The liquid bottoms are circulated through lines 13, 5 and 7 at a rate of at least 6 ft/sec through the heat exchanger 2. The circulation rate is maintained at a volume which is high relative to the amount of waste water introduced via line 4. The concentrated solution containing ammonium sulfate is removed continuously via line 15 so that a liquid level is maintained in flasher 10 at approximately location 14.
The temperature of the waste water exiting heat exchanger 2 via line 8 must be maintained at least 105.degree. C to provide sufficient energy for vaporization and to prevent undesired precipitation of ammonium sulfate and/or high boilers and polymers contained in the aqueous solution. Usually the temperature of the stream exit the heat exchanger 2 is maintained in the range 120.degree.-150.degree. C and preferably in the range 130.degree.-135.degree. C.
In order to minimize fouling of heat exchanger it has been discovered that it is necessary to maintain a minimal velocity of liquid through the exchanger of at least 6 ft/sec and usually a velocity in the range 6-15 ft/sec. It is preferred to maintain a velocity through the heat exchanger in the range 8-10 ft/sec.
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Preparation of carboxylic acid nitriles: separation; Purification; Stabilisation; Use of additives
Separation; Purification; Stabilisation; Use of additives: separation; Purification
Technologies relating to chemical industry: process efficiency
Technologies relating to chemical industry: improvements relating to the production of bulk chemicals
Term ended 27 Dec 1994 (estimated)
USPTO file history isn’t available for this patent, so only indexed dates are shown.