PROCESS FOR PREPARATION OF NITROGEN OXIDES AND NITRIC ACID FROM NITROUS OXIDE

Abstract

Described herein is an improved conversion of nitrous oxide (N.sub.2O) present as a by-product in a chemical process to NO.sub.x which can be further converted to a useful compound or material, such as nitric acid.

Claims

1.-20. (canceled)

21. A process for preparing adipic acid, comprising: reacting at least one of cyclohexanone and cyclohexanol with nitric acid to produce adipic acid and an offgas comprising: nitrous oxide; and optionally nitrogen; converting the nitrous oxide present in the offgas to nitrogen oxide by passing the offgas through a reactor to yield a product composition comprising nitrogen oxide; compressing the product composition; and converting nitrogen oxide in the compressed product composition to nitric acid.

22. The process of claim 21, wherein the compressing comprises: compressing the product composition to a pressure ranging from 15 psig to 150 psig.

23. The process of claim 21, further comprising further comprising: quenching the product composition to form a cooled product composition.

24. The process of claim 23, wherein the cooled product composition has a temperature less than 1600 F.

25. The process of claim 23, wherein the cooled product composition has a temperature ranging from 900 F. to 1400 F.

26. The process of claim 21, further comprising: preheating the offgas prior to the converting.

27. The process of claim 26, wherein the off gas is preheated to a temperature less than 1800 F.

28. The process of claim 21, wherein the reactor operates at a temperature greater than 2200 F.

29. The process of claim 21, wherein the converting step has a yield greater than 15%.

30. The process of claim 21, further comprising: wherein the converting step has a yield greater than 15%.

31. A process for preparing adipic acid, comprising: reacting at least one of cyclohexanone and cyclohexanol with nitric acid to produce adipic acid and an offgas having a temperature less than 800 F. and comprising nitrous oxide; and optionally nitrogen; preheating the offgas in a preheater unit to a temperature less than 1800 F.; converting the nitrous oxide present in the offgas to nitrogen oxide at a yield of greater than 15% by passing the offgas through a reactor operating at a temperature of 2200 F. or greater to yield a product composition comprising nitrogen oxide; and converting the nitrogen oxide to nitric acid.

32. The process of claim 31, wherein the preheater unit is separate from the reactor.

33. The process of claim 31, wherein the off gas leaving the adipic acid production reaction is not treated to remove nitrogen oxide.

34. The process of claim 31, wherein the preheated offgas is directly fed to the reactor.

35. The process of claim 31, wherein the preheating comprises: preheating the offgas in a preheater unit to a temperature ranging from 900 F. to 1800 F.

36. A process for preparing adipic acid, comprising: reacting at least one of cyclohexanone and cyclohexanol with nitric acid to produce adipic acid and an offgas having a temperature less than 800 F. and comprising nitrous oxide; and optionally nitrogen; preheating the offgas in a preheater unit to a temperature less than 1800 F.; converting nitrous oxide present in the offgas to nitrogen oxide at a yield of greater than 15% by passing the offgas through a reactor operating at a temperature of 2200 F. or greater to yield a product composition comprising nitrogen oxide; compressing the product composition; and converting nitrogen oxide present in the compressed product composition to nitric acid; wherein the reactor has a length to diameter ratio (L/D) of greater than 4; and wherein no external heat is added to the reactor after start of reaction.

37. The process of claim 36, wherein the offgas comprises greater than 60 mol % nitrous oxide.

38. The process of claim 36, wherein the residence time of the feedgas from the preheater to the reactor is less than 30 seconds.

39. The process of claim 36, further comprising further comprising: quenching the product composition to form a cooled product composition; and compressing the cooled product composition.

40. The process of claim 36, wherein the cooled product composition has a temperature less than 1600 F.

Description

DETAILED DESCRIPTION OF THE INVENTION

Definitions

[0156] As used herein, the term feedstream gas or feedstock gas or feedstock or feedgas refers to a N.sub.2O-containing gas that reacts under the conditions described herein to generate NO.sub.x, which is then optionally converted to nitric acid.

[0157] As used herein, the term offgas refers to a gas that is produced as a by-product or side effect of a process, such as an industrial-scale process. An offgas can be a feedgas.

[0158] As used herein, the phrase conversion reaction refers to the chemical reaction that occurs in the reactor or reactor zone during which N.sub.2O is converted to NO.sub.x (where x=1 or 2) in a yield of at least 15%. Under the conditions of the conversion reaction, a portion of the N.sub.2O also decomposes to N.sub.2 and O.sub.2.

[0159] As used herein, the phrase reactant composition refers to compositions containing N.sub.2O that have not been passed through the reactori.e., compositions that have not undergone the conversion reaction. The reactant composition may exist in any physical form but is most commonly present as a gas stream and may also be referred to as a feedstream gas or feedstock gas or feedstock or feedgas or offgas.

[0160] As used herein, the phrase product composition refers to compositions that have undergone the conversion reaction with the result that the N.sub.2O component of the reactant composition has been oxidized to NO.sub.x in a yield of at least 15%. The product composition may exist in any physical form but is most commonly present as a gas stream.

[0161] As used herein, the term reactor refers to the place (e.g., the vessel, tube, chamber, pipe or the like) where nitrous oxide (N.sub.2O) present in a reactant composition is subjected to thermal reaction conditions under which the N.sub.2O is converted to NO.sub.x (wherein x=1 or 2) in a yield of at least 15%.

[0162] As used herein, the terms nitrous oxide and N.sub.2O are used interchangeably.

[0163] As used herein, the terms nitrogen oxide and nitrogen oxides and NO.sub.x are used interchangeably to describe a mixture of nitrogen monoxide (NO) and nitrogen dioxide (NO.sub.2) where x=1 or 2.

[0164] As used herein, the phrase heat of reaction refers to the heat released as a result of a chemical reaction that is exothermic in nature.

[0165] As used herein, the phrase residence time or RT refers to the period of time that the feedstream gas is present in a particular component (e.g., the preheater, the reactor or the quench unit) of the N.sub.2O conversion system described herein.

[0166] As used herein, the phrase mol % refers to the percentage that the moles of a particular component represent compared to the total moles that are present.

[0167] As used herein, the term psig is a commonly used measurement of pressure relative to ambient atmospheric pressure and is quantified in pounds per square inch gauge.

[0168] As used herein, the phrase an adiabatic process is a process that occurs without transfer of heat or matter between a thermodynamic system and its surroundings.

Reactant Composition Containing N.SUB.2.O

[0169] The reactant composition of the present invention is typically in the form of a gas stream, but is not so limited, and is any composition that contains N.sub.2O in an amount of at least 10 mol % up to 100 mol %. Other components may optionally be present in the reactant composition in varying amounts such as, for example, nitrogen monoxide (NO), nitrogen dioxide (NO.sub.2), nitrogen (N.sub.2), oxygen (O.sub.2), water (H.sub.2O), carbon dioxide (CO.sub.2), inorganic compounds (including metal-containing compounds) and organic molecules (of various molecular weights). Some of these components, such as water and NO.sub.x, were observed to have a negative impact on the conversion of N.sub.2O to NO.sub.x. In a particular embodiment, the yield of NO.sub.x was observed to decrease by between approximately 0.10% and 1.0%, such as between 0.10% and 0.50% with each 1% increase of water vapor present in the feedstock gas. In another particular embodiment, the yield of NO.sub.x was observed to decrease by between approximately 0.5% and 3.5%, such as 1.0% and 2.0% with each 1% increase of NO.sub.x present in the feedstock gas. As a result, efforts may be taken to reduce the amounts of one or more of these detrimental components before passage of the reactant composition through the reactor, such as by passing the reactant composition through a scrubbing unit (e.g., a knock-out pot or inlet filter).

[0170] The source of the reactant composition is not particularly limited and may be, for example, any process that generates N.sub.2O as a by-product. In an exemplary embodiment, the reactant composition is in the form of an offgas from the chemical process for preparing adipic acid. In other embodiments, the source of the reactant composition is the offgas from the production of nitrogen-containing fertilizers such as ammonium nitrate. Nitric acid is a primary ingredient in nitrogen-containing fertilizers and is manufactured by oxidizing ammonia with a platinum catalyst which generates nitrous oxide.

[0171] In an exemplary embodiment, the reactant composition comprises greater than 40 mol %, such as greater than 60 mol % N.sub.2O, such as greater than 80 mol % N.sub.2O. The concentration of N.sub.2O in the reactant composition may be the direct result of a chemical process. Alternatively, the concentration of N.sub.2O in the reactant composition is the result after further concentration by conventional means of the initial concentration of N.sub.2O generated by a chemical process to higher levels. Although it was observed that the yield of NO.sub.x from N.sub.2O decreased with increasing N.sub.2O concentrations in the reactant composition, it was also observed that higher reaction temperatures (for converting N.sub.2O to NO.sub.x) were achieved with higher N.sub.2O concentrations. Higher reaction temperatures unexpectedly resulted in higher yields of NO.sub.x which more than offset the loss of yield of NO.sub.x associated with increased N.sub.2O concentration. In a particular embodiment, the yield of NO.sub.x was observed to increase with increasing reactor temperature up to approximately 1830 F. where the yield of NO.sub.x remained constant at temperatures up to approximately 2600 F. and reactor residence times ranging from 0.01 seconds to 12 seconds. In addition, higher concentrations of N.sub.2O in the reactant composition desirably resulted in smaller-sized downstream equipment for further processing of the generated NO.sub.x, such as its conversion to nitric acid. The cost savings for using smaller-sized equipment is significant when operating on an industrial (commercial) scale. Further, the higher reaction temperatures employed for conversion of the N.sub.2O to NO.sub.x provides a more stable and robust reaction system relative to feed flow and composition. Higher N.sub.2O concentrations and higher reaction temperatures are also preferred for operating the reactor in a self-sustaining manner with no burner assistance required (thus eliminating the negative effects on the yield of NO.sub.x associated with such assistance by, e.g., water-contaminated flue gas) to continuously maintain the conversion reaction.

Pretreatment of the Reactant Composition Prior to Entry into the Reactor

[0172] In an exemplary embodiment, the reactant composition (such as in the form of an offgas) is subjected to pretreatment in a preheater unit before its passage through the reactor where the N.sub.2O present in the reactant composition is converted to NO.sub.x. The preheater unit performs an important function by heating the reactant composition to a temperature of greater than 800 F., such as greater than 900 F., such as greater than 950 F. to ensure the ability of the conversion reaction occurring in the reactor to continuously sustain itself without the need for an external heat source. In an exemplary embodiment, the heat generated in the reactor by reaction of the N.sub.2O present in the reactant composition is recycled directly or indirectly (such as through one or more cooling quench units) to the preheater unit for the purpose of preheating the reactant composition prior to its passage through the reactor. In an exemplary embodiment, a significant portion of the heat required by the preheater unit for preheating the reactant composition is provided by this heat of reaction generated in the reactor. In another embodiment, substantially all of the heat required by the preheater unit for preheating the reactant composition is provided by the heat of reaction generated in the reactor such that no additional heat source is required.

[0173] The degree to which the reactant composition is preheated and the rate at which it is delivered to the reactor is carefully monitored and controlled by the preheater unit in order to maintain an environment in the reactor where the conversion reaction is self-sustaining while avoiding conditions where the conversion reaction becomes too robust and potentially develops into a runaway reaction. If, for example, the temperature in the preheater becomes too high, a controlled amount of water can be introduced into the preheater to lower the temperature. Therefore, the preheater unit represents a highly cost-effective on-demand feature of the present invention that allows for precision control of reaction conditions in the reactor in order to safely achieve optimal mass flow, volume flow and heat flow on a commercial scale.

[0174] In another embodiment of the present invention, the preheater unit, in addition to controlling the temperature and rate at which the reactant composition enters the reactor, may also control other properties and aspects of the reactant composition such as, for example, the pressure at which the reactant composition enters the reactor.

Reactor and Reactor Conditions

[0175] The reactor, while not limited to a particular design or structure, must be capable of providing the reaction conditions sufficient for conversion of the N.sub.2O present in the reactant composition to NO.sub.x as described herein. In practice, substantially all of the N.sub.2O is consumed when subjected to the reactor conditions and NO.sub.x is obtained in a yield of greater than 15%, such as greater than 17%, such as greater than 18%, such as greater than 20%, such as greater than 21%, such as greater than 23%, such as greater than 25%. In addition to the generation of NO.sub.x, a portion of the N.sub.2O degrades to N.sub.2 and O.sub.2. In an exemplary embodiment, the reactor design is such that the reactor is able to fully operate regardless of whether an external heat source capable of providing on-demand flame assistance is employed to maintain the reactant composition at an optimal temperature range. In a preferred embodiment, the reactor accomplishes this without utilizing moving parts (such as damper valves or retractable devices).

[0176] In terms of pressure, it was observed in a particular embodiment that increasing pressure in the reactor had a negative effect on the yield of NO.sub.x, with the NO.sub.x yield decreasing by between 0.1% and 2.0% (such as 0.5% and 2.0%) with each 10 psig increase in pressure.

[0177] In an exemplary embodiment, the interior surface of the reactor comprises a refractory, such as a ceramic (see, e.g., ASTM C71), that would be suitable for use at reactor temperatures of 3000 F. and higher. Such a ceramic material can be clay-based or non-clay-based. Suitable clay-based refractories include fireclay, high-alumina and mullite ceramics. Suitable non-clay refractories include basic, high alumina, silica, silicon carbide, and zircon materials.

[0178] In an exemplary embodiment, the interior surface of the reactor comprises refractory in a thickness of 10 to 40 inches, which may optionally include multiple layering of ceramic in the form of tiles or bricks or blocks interspersed with high-temperature insulation wool (such as amorphous alkaline earth silicate wool (AES), aluminosilicate wool (ASW) or polycrystalline wool (PCW)).

[0179] The presence of the refractory in the reactor is important for storage of the heat of reaction generated by the exothermic degradation of N.sub.2O to N.sub.2 and O.sub.2. This heat is then utilized in the endothermic conversion of N.sub.2O to NO.sub.x which facilitates the self-sustaining aspects of the reactor. The presence of the refractory is also important for storing the heat of the preheated reaction composition.

[0180] In an exemplary embodiment, the reactor is of a substantially vertical or a substantially horizontal tubular design with a length to diameter ratio (L/D) of at least 4, such as at least 6, such as at least 10, such as at least 12, such as at least 14, such as at least 16, such as least 18, such as at least 20. In a particular embodiment, the reactor is structurally designed to operate as an adiabatic plug flow reactor with no back mixing of the reactant/product composition (as a gas stream) as it passes through the reactor. In another particular embodiment, the reactor is structurally designed to act substantially as a plug flow reactor but also to provide a limited amount of back mixing of the passing gas stream to achieve a dispersion coefficient that translates into superior yields in the conversion reaction.

[0181] In an exemplary embodiment, the reactor is insulated to minimize heat loss through the exterior of the reactor surface (i.e., to maintain adiabatic operation of the reactor). In an exemplary embodiment, the exterior surface of the reactor is maintained at a temperature above 200 F., such as above 250 F., to prevent the possible condensation of nitric acid, which results as NO.sub.x generated during the conversion reaction permeates through the interior wall of the reactor and reacts with water (in the form of moisture).

Post-Reactor Conditions

[0182] In an exemplary embodiment, the product composition exiting the reactor is cooled by passage through a quench unit (heat exchanger) to a temperature that is sufficient to heat the reactant composition in the preheater to a temperature of at least 900 F., such as at least 1200 F., but lower than 1400 F. In a particular embodiment, the temperature of the product composition (in the form of a gas stream) exiting the reactor is in the range of 2200 to 2900 F. and is cooled to less than 1600 F. by passage through the quench unit and the removed heat is transferred to the preheater to heat the offgas generated from the preparation of adipic acid to a temperature in a range of 900 to 1400 F. before the heated offgas enters the reactor.

[0183] In another exemplary embodiment, the cooled product composition (in the form of a gas stream) exits the preheater (from the first quench unit) and passes through a second quench unit (heat exchanger) for further cooling before the NO.sub.x present in the product composition gas stream is converted to nitric acid. In a particular embodiment, the temperature of the product composition exiting the preheater is less than 900 F., such as less than 700 F. and is cooled to less 300 F., such as less than 200 F., by passage through the second quench unit.

[0184] Suitable types of quench units include, but are not limited to, direct contact spray quench systems, shell and tube heat exchangers, plate heat exchangers, plate shell heat exchangers and plate fin heat exchangers.

[0185] In an exemplary embodiment, the preheater, the reactor and the quench unit(s) exist in a geometric arrangement that is substantially U-shaped, which conserves space and is conducive for facilitating the preferred mass, heat and volume transfers for converting N.sub.2O to NO.sub.x on a commercial scale.

Production of Nitric Acid

[0186] In an exemplary embodiment, the cooled product composition (in the form of a gas stream) after exiting a first or a second quench unit is at a temperature of less 300 F., such as less than 200 F. The cooled product composition is then optionally compressed to 15 to 150 psig, such as 15 to 100 psig, such as 15 to 50 psig before the NO.sub.x present in the composition is converted to nitric acid by any known means, such as those described, for example, in U.S. Pat. Nos. 5,985,230; 5,360,603; 5,266,291; 4,925,639; 4,263,267; 4,235,858; 4,183,906; 4,064,22; 4,062,928; and 4,036,934.

Recycling of the Nitric Acid

[0187] The nitric acid that is generated from the product composition may be collected for future use or sale or alternatively, may be recycled as a reactant in the same chemical process that originally resulted in the formation of a N.sub.2O-containing composition or in a different chemical process that also employs nitric acid as a reactant where N.sub.2O is generated as a by-product of the reaction.

EXAMPLES

[0188] The following examples represent specific embodiments of the present invention and are not intended to otherwise limit the scope of the invention as described herein.

Example 1

[0189] A 12-inch section of an empty mullite tube with an internal diameter of 1 inch was heated to 2552 F. by external heating. A feed gas containing 60 mol % N.sub.2O, 25 mol % N.sub.2, 9 mol % O.sub.2 and 6 mol % CO.sub.2 was passed through the tube at a pressure of 2.5 psig. The L/D ratio of the reaction zone was equal to 12. The STP residence time was set to 5 seconds. The effluent gas flow was cooled to ambient temperature and the concentrations of NO and NO.sub.2 (collectively, NO.sub.x) were measured using a chemiluminescence NONO.sub.2NO.sub.x analyzer. The calculated yield of NO.sub.x was 20%.

Example 2

[0190] A 12-inch section of an empty mullite tube with an internal diameter of 1 inch was heated to 2642 F. by external heating. A feed gas containing 60 mol % N.sub.2O, 25 mol % N.sub.2, 9 mol % O.sub.2 and 6 mol % CO.sub.2 was passed through the tube at a pressure of 2.5 psig. The L/D ratio of the reaction zone was equal to 12. The STP residence time was set to 5 seconds. The effluent gas flow was cooled to the ambient temperature and the concentrations of NO and NO.sub.2 (collectively, NO.sub.x) were measured using a chemiluminescence NONO.sub.2NO.sub.x analyzer. The calculated yield of NO.sub.x was 20%.

Example 3

[0191] In an example reflective of pilot plant scale, an adipic plant off-gas having a composition of 60 mol % N.sub.2O, 25 mol % N.sub.2, 2 mol % O.sub.2, 6 mol % CO.sub.2, 1.2 mol % H.sub.2O and 0.5 mol % NO was passed through a preheater that increased the temperature of the gas to 1200 F. The gas was then passed through a furnace reactor at the rate of 1200 pph. The internal diameter of the reactor was 2 feet and the length of the reaction zone was 24 feet. During the process, natural gas (at a flow of 21 pph) and air (at a flow of 415 pph) was introduced to the front of the reactor as a flue gas from a burner. The temperature in the reactor was 2400 F. The effluent gas flow was cooled to the ambient temperature and the concentrations of NO and NO.sub.2 (collectively, NO.sub.x) were measured using a chemiluminescence NONO.sub.2NO.sub.x analyzer. The calculated yield of NO.sub.x was 16%.

[0192] The examples listed in the table below represent the amount of NO.sub.x product predicted by computer simulation when N.sub.2O-containing compositions are subjected to reaction conditions associated with the process of the present invention as well as reaction conditions reflective of comparative process conditions. The simulated runs were treated as predictive of the relative impact on the amount of NO.sub.x product produced from various N.sub.2O-containing reactant compositions when the identified reaction parameters were varied. The entries in the table represent specific embodiments of the present invention as well as comparative embodiments and are not intended to limit the scope of the present invention as described herein or to limit the influence of any particular reaction parameter (either alone or in combination) on the yield of NO.sub.x product. In the Yield column of the table, A represents NO.sub.x yields of greater than 23%; B represents NO.sub.x yields of 19% up to, but not including, 23%; and C represents NO.sub.x yields of less than 19%, where the NO.sub.x yields are based on the amount of N.sub.2O present in the reactant feed. In an exemplary embodiment of the present invention, the A examples provide NO.sub.x yields of 24 to 35%, such as 25 to 32%, such as 25 to 30% and the C examples provide NO.sub.x yields of less than 17%, such as less than 15%, such as less than 13%, such as less than 10%. In an exemplary embodiment, the C examples may be considered as comparative examples, especially when providing yields of less than 15% or less than 13%.

TABLE-US-00001 Reactant Composition Process Conditions in Reactor Zone N.sub.2O H.sub.2O NO.sub.x Preheater Reactor NO.sub.x (mol (wt (wt Temp Temp Pressure RT Yield Example %) %) %) (F.) (F.) (psig) (sec) L/D (%) 1. 15 0.3 0.3 1000 1700 2 2 6 C 2. 15 0.3 0.3 1000 2500 2 2 6 B 3. 15 0.3 0.3 1000 3200 2 2 6 A 4. 15 0.1 0.1 1000 3200 2 2 6 A 5. 15 0.3 0.3 500 2800 2 2 6 A 6. 15 0.3 0.3 2000 2800 2 2 6 A 7. 15 0.3 0.3 1000 2800 10 2 6 B 8. 15 0.3 0.3 1000 2800 2 0.05 6 A 9. 15 0.3 0.3 1000 2800 2 2 18 A 10. 15 0.3 0.3 1000 2800 10 0.05 18 A 11. 15 0.3 0.3 1000 2800 10 20 18 A 12. 15 0.3 3.0 1000 2800 2 2 6 B 13. 15 3.0 0.3 1000 2800 2 2 6 B 14. 15 3.0 3.0 1000 2800 2 2 6 C 15. 15 0.3 3.0 1000 2800 10 2 6 C 16. 15 3.0 0.3 1000 2800 2 0.05 6 B 17. 15 0.3 3.0 1000 2800 2 2 18 B 18. 15 0.3 3.0 1000 2800 10 0.05 18 B 19. 15 0.3 3.0 1000 2800 10 20 18 B 20. 30 1.0 2.0 1100 2900 10 0.1 4 C 21. 40 0 1.0 900 2700 2 2 8 B 22. 40 0.3 0.3 1000 1700 2 2 6 C 23. 40 0.3 0.3 1000 2500 2 2 6 B 24. 40 0.3 0.3 1000 3200 2 2 6 A 25. 40 0.1 0.1 1000 3200 2 2 6 A 26. 40 0.3 0.3 500 2800 2 2 6 B 27. 40 0.3 0.3 2000 2800 2 2 6 B 28. 40 0.3 0.3 1000 2800 10 2 6 B 29. 40 0.3 0.3 1000 2800 2 0.05 6 B 30. 40 0.3 0.3 1000 2800 2 2 18 B 31. 40 0.3 0.3 1000 2800 10 0.05 18 B 32. 40 0.3 0.3 1000 2800 10 20 18 B 33. 40 0.3 3.0 1000 2800 2 2 6 C 34. 40 3.0 0.3 1000 2800 2 2 6 B 35. 40 3.0 3.0 1000 2800 2 2 6 C 36. 40 0.3 3.0 1000 2800 10 2 6 C 37. 40 3.0 0.3 1000 2800 2 0.05 6 B 38. 40 0.3 3.0 1000 2800 2 2 18 B 39. 40 0.3 3.0 1000 2800 10 0.05 18 C 40. 40 0.3 3.0 1000 2800 10 20 18 C 41. 50 0.3 0.3 1000 1900 2 2 6 C 42. 50 0.3 0.3 1000 2200 2 2 6 C 43. 50 0.3 0.3 1000 2500 2 2 6 C 44. 50 0.3 0.3 1000 2800 2 2 6 B 45. 50 0.3 1.0 1000 2800 2 2 6 B 46. 50 1.0 0.3 1000 2800 2 2 6 B 47. 50 1.0 1.0 1000 2800 2 2 6 C 48. 50 1.0 2.0 1000 2800 2 2 6 C 49. 50 2.0 0.5 1200 2400 4 10 20 C 50. 50 2.0 1.0 1000 2800 2 2 6 C 51. 50 0.3 0.3 1000 3100 2 2 6 B 52. 50 0.3 1.0 1000 3100 2 2 6 B 53. 50 1.0 0.3 1000 3100 2 2 6 B 54. 50 1.0 1.0 1000 3100 2 2 6 B 55. 50 1.0 2.0 1000 3100 2 2 6 B 56. 50 2.0 1.0 1000 3100 2 2 6 B 57. 50 0.3 0.3 1000 3400 2 2 6 A 58. 50 0.3 0.3 1000 2200 5 2 6 C 59. 50 0.3 0.3 1000 2500 5 2 6 C 60. 50 0.3 0.3 1000 2800 5 2 6 B 61. 50 0.3 1.0 1000 2800 5 2 6 B 62. 50 1.0 0.3 1000 2800 5 2 6 B 63. 50 1.0 1.0 1000 2800 5 2 6 B 64. 50 0.3 0.3 1000 3100 5 2 6 A 65. 50 0.3 1.0 1000 3100 5 2 6 B 66. 50 1.0 0.3 1000 3100 5 2 6 B 67. 50 1.0 1.0 1000 3100 5 2 6 B 68. 60 0.5 1.5 1400 2200 1 5 12 C 69. 80 0.3 0.3 1000 1700 2 2 6 C 70. 80 0.3 0.3 1000 2500 2 2 6 C 71. 80 0.3 0.3 1000 3200 2 2 6 B 72. 80 0.1 0.1 1000 3200 2 2 6 B 73. 80 0.3 0.3 500 2800 2 2 6 C 74. 80 0.3 0.3 2000 2800 2 2 6 C 75. 80 0.3 0.3 1000 2800 10 2 6 C 76. 80 0.3 0.3 1000 2800 2 0.05 6 B 77. 80 0.3 0.3 1000 2800 2 2 18 B 78. 80 0.3 0.3 1000 2800 10 0.05 18 C 79. 80 0.3 0.3 1000 2800 10 20 18 C 80. 80 0.3 3.0 1000 2800 2 2 6 C 81. 80 3.0 0.3 1000 2800 2 2 6 C 82. 80 3.0 3.0 1000 2800 2 2 6 C 83. 80 0.3 3.0 1000 2800 10 2 6 C 84. 80 3.0 0.3 1000 2800 2 0.05 6 C 85. 80 0.3 3.0 1000 2800 2 2 18 C 86. 80 0.3 3.0 1000 2800 10 0.05 18 C 87. 80 0.3 3.0 1000 2800 10 20 18 C

[0193] In the process of the present invention, increasing the amount of water (H.sub.2O) and/or the amount of nitrogen oxide (NO.sub.x) present in the reactant composition was observed to adversely impact the yield of NO.sub.x product. Increasing the internal temperature of the reactor (particularly to 2500 F. and above, such as to 2800 F. and above) was observed to improve the yield of NO.sub.x product, even in the presence of increasing amounts of yield-decreasing components (such as H.sub.2O and NO.sub.x) in the reactant composition. Increasing the reactor pressure was generally observed to have a negative impact on the yield of NO.sub.x product. Increasing L/D was generally observed to have a positive impact on the yield of NO.sub.x product. Changes in the residence time (RT) of the reactant composition in the reactor (i.e., the length of time that the reactant composition is exposed to the process conditions in the reactor) were generally observed not to have a significant impact on NO.sub.x yield. Regression equations can be generated from collected data and/or from predictive computer simulation results to identify the contributed impact of each of the various reaction parameters for which data was collected, thereby allowing for optimization of NO.sub.x product. When the processes are carried out on an industrial scale, even seemingly modest improvements in NO.sub.x yields can prove to be cost-effective in terms of increasing the amount of nitric acid product produced (recycled) from the N.sub.2O initially present in an offgas generated from an industrial process and also in terms of reducing or eliminating the cost associated with conventional (destructive) techniques for disposal of the highly regulated N.sub.2O present in the offgas.

[0194] The following exemplary combinations of reactant compositions and process conditions, which represent preferred embodiments of the present invention, are not intended to otherwise limit the full scope of the invention as described herein.

[0195] Combination 1: Reactant composition containing 10 to 95 mol % N.sub.2O/between 0 to 2.0 mol % H.sub.2O/between 0 to 2.0 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 2000 F./feed rate of greater than 3000 pph/internal reactor temperature of 2400 to 3500 F./external surface temperature of reactor greater than 100 F./residence time of less than 30 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0196] Combination 2: Reactant composition containing 10 to 95 mol % N.sub.2O/between 0 to 1.0 mol % H.sub.2O/between 0 to 2.0 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2400 to 3500 F./external surface temperature of reactor greater than 100 F./residence time of less than 30 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0197] Combination 3: Reactant composition containing 20 to 80 mol % N.sub.2O/between 0 to 2.0 mol % H.sub.2O/between 0 to 1.0 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2400 to 3200 F./external surface temperature of reactor greater than 100 F./residence time of less than 30 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0198] Combination 4: Reactant composition containing 20 to 80 mol % N.sub.2O/between 0 to 1.5 mol % H.sub.2O/between 0 to 1.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2400 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0199] Combination 5: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 1.0 mol % H.sub.2O/between 0 to 1.0 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2400 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0200] Combination 6: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 1.5 mol % H.sub.2O/between 0 to 1.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2600 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0201] Combination 7: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 1.0 mol % H.sub.2O/between 0 to 1.0 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2600 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0202] Combination 8: Reactant composition containing 60 to 80 mol % N.sub.2O/between 0 to 1.5 mol % H.sub.2O/between 0 to 1.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2600 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0203] Combination 9: Reactant composition containing 60 to 80 mol % N.sub.2O/between 0 to 1.0 mol % H.sub.2O/between 0 to 1.0 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2600 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0204] Combination 10: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 1.5 mol % H.sub.2O/between 0 to 1.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2800 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0205] Combination 11: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 1.0 mol % H.sub.2O/between 0 to 1.0 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2800 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0206] Combination 12: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 1.5 mol % H.sub.2O/between 0 to 1.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2800 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0207] Combination 13: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 1.0 mol % H.sub.2O/between 0 to 1.0 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2800 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0208] Combination 14: Reactant composition containing 60 to 80 mol % N.sub.2O/between 0 to 1.5 mol % H.sub.2O/between 0 to 1.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2600 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0209] Combination 15: Reactant composition containing 60 to 80 mol % N.sub.2O/between 0 to 1.0 mol % H.sub.2O/between 0 to 1.0 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2600 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0210] Combination 16: Reactant composition containing 60 to 80 mol % N.sub.2O/between 0 to 1.5 mol % H.sub.2O/between 0 to 1.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2800 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0211] Combination 17: Reactant composition containing 60 to 80 mol % N.sub.2O/between 0 to 1.0 mol % H.sub.2O/between 0 to 1.0 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2800 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0212] Combination 18: Reactant composition containing 20 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2400 to 3200 F./external surface temperature of reactor greater than 100 F./residence time of less than 30 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0213] Combination 19: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2400 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0214] Combination 20: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2400 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0215] Combination 21: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2600 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0216] Combination 22: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2600 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0217] Combination 23: Reactant composition containing 60 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2600 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0218] Combination 24: Reactant composition containing 60 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2600 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0219] Combination 25: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2800 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0220] Combination 26: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2800 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0221] Combination 27: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2800 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0222] Combination 28: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2800 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0223] Combination 29: Reactant composition containing 60 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2600 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0224] Combination 30: Reactant composition containing 60 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2600 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0225] Combination 31: Reactant composition containing 60 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2800 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0226] Combination 32: Reactant composition containing 60 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 3000 pph/internal reactor temperature of 2800 to 3200 F./external surface temperature of reactor greater than 150 F./residence time of less than 15 seconds/reactor pressure of less than 10 psig/reactor L/D of less than 40.

[0227] Combination 33: Reactant composition containing 20 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 10,000 pph/internal reactor temperature of 2400 to 3200 F./external surface temperature of reactor greater than 200 F./residence time of less than 30 seconds/reactor pressure of less than 5 psig/reactor L/D of less than 20.

[0228] Combination 34: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 10,000 pph/internal reactor temperature of 2400 to 3200 F./external surface temperature of reactor greater than 200 F./residence time of less than 15 seconds/reactor pressure of less than 5 psig/reactor L/D of less than 20.

[0229] Combination 35: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 10,000 pph/internal reactor temperature of 2400 to 3200 F./external surface temperature of reactor greater than 200 F./residence time of less than 15 seconds/reactor pressure of less than 5 psig/reactor L/D of less than 20.

[0230] Combination 36: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 10,000 pph/internal reactor temperature of 2600 to 3200 F./external surface temperature of reactor greater than 200 F./residence time of less than 15 seconds/reactor pressure of less than 5 psig/reactor L/D of less than 20.

[0231] Combination 37: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 10,000 pph/internal reactor temperature of 2600 to 3200 F./external surface temperature of reactor greater than 200 F./residence time of less than 15 seconds/reactor pressure of less than 5 psig/reactor L/D of less than 20.

[0232] Combination 38: Reactant composition containing 60 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 10,000 pph/internal reactor temperature of 2600 to 3200 F./external surface temperature of reactor greater than 200 F./residence time of less than 15 seconds/reactor pressure of less than 5 psig/reactor L/D of less than 20.

[0233] Combination 39: Reactant composition containing 60 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 10,000 pph/internal reactor temperature of 2600 to 3200 F./external surface temperature of reactor greater than 200 F./residence time of less than 15 seconds/reactor pressure of less than 5 psig/reactor L/D of less than 20.

[0234] Combination 40: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 10,000 pph/internal reactor temperature of 2800 to 3200 F./external surface temperature of reactor greater than 200 F./residence time of less than 15 seconds/reactor pressure of less than 5 psig/reactor L/D of less than 20.

[0235] Combination 41: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 10,000 pph/internal reactor temperature of 2800 to 3200 F./external surface temperature of reactor greater than 200 F./residence time of less than 15 seconds/reactor pressure of less than 5 psig/reactor L/D of less than 20.

[0236] Combination 42: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 10,000 pph/internal reactor temperature of 2800 to 3200 F./external surface temperature of reactor greater than 200 F./residence time of less than 15 seconds/reactor pressure of less than 5 psig/reactor L/D of less than 20.

[0237] Combination 43: Reactant composition containing 40 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 10,000 pph/internal reactor temperature of 2800 to 3200 F./external surface temperature of reactor greater than 200 F./residence time of less than 15 seconds/reactor pressure of less than 5 psig/reactor L/D of less than 20.

[0238] Combination 44: Reactant composition containing 60 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 10,000 pph/internal reactor temperature of 2600 to 3200 F./external surface temperature of reactor greater than 200 F./residence time of less than 15 seconds/reactor pressure of less than 5 psig/reactor L/D of less than 20.

[0239] Combination 45: Reactant composition containing 60 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 10,000 pph/internal reactor temperature of 2600 to 3200 F./external surface temperature of reactor greater than 200 F./residence time of less than 15 seconds/reactor pressure of less than 5 psig/reactor L/D of less than 20.

[0240] Combination 46: Reactant composition containing 60 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 10,000 pph/internal reactor temperature of 2800 to 3200 F./external surface temperature of reactor greater than 200 F./residence time of less than 15 seconds/reactor pressure of less than 5 psig/reactor L/D of less than 20.

[0241] Combination 47: Reactant composition containing 60 to 80 mol % N.sub.2O/between 0 to 0.5 mol % H.sub.2O/between 0 to 0.5 mol % NO.sub.x. Process conditions of preheating the reactant composition to less than 1800 F./feed rate of greater than 10,000 pph/internal reactor temperature of 2800 to 3200 F./external surface temperature of reactor greater than 200 F./residence time of less than 15 seconds/reactor pressure of less than 5 psig/reactor L/D of less than 20.

[0242] All publications and patents cited herein are incorporated by reference in their entireties.