CA1136381A - Catalytic process for the production of urea and ammonium cyanate - Google Patents
Catalytic process for the production of urea and ammonium cyanateInfo
- Publication number
- CA1136381A CA1136381A CA000295840A CA295840A CA1136381A CA 1136381 A CA1136381 A CA 1136381A CA 000295840 A CA000295840 A CA 000295840A CA 295840 A CA295840 A CA 295840A CA 1136381 A CA1136381 A CA 1136381A
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- Canada
- Prior art keywords
- degrees
- nox
- urea
- process according
- catalyst
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C273/00—Preparation of urea or its derivatives, i.e. compounds containing any of the groups, the nitrogen atoms not being part of nitro or nitroso groups
- C07C273/02—Preparation of urea or its derivatives, i.e. compounds containing any of the groups, the nitrogen atoms not being part of nitro or nitroso groups of urea, its salts, complexes or addition compounds
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
- C01C3/00—Cyanogen; Compounds thereof
- C01C3/20—Thiocyanic acid; Salts thereof
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Catalysts (AREA)
- Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)
- Treating Waste Gases (AREA)
- Exhaust Gas Treatment By Means Of Catalyst (AREA)
Abstract
Abstract of the Disclosure A catalytic process has been found to produce urea or its equivalent NH4NCO, under relatively mild pressure and temperature conditions. This process entails flowing a gas mixture containing NOx, CO, and a source of hydrogen such as H2 or H2O over a hydrogenation catalyst such as platinum. Yields of urea above 90 percent based on NOx conversion are obtainable.
Description
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Background of the Inven;tion 1. Field of the Invention The invention is related to the production of urea or its equivalent such as ammonium cyanate. More particularly, the invention relates to a catalytic process for the production of these compounds.
Background of the Inven;tion 1. Field of the Invention The invention is related to the production of urea or its equivalent such as ammonium cyanate. More particularly, the invention relates to a catalytic process for the production of these compounds.
2. Description of the Prior Art Urea or its equivalent, i.e., ammonium cyanate, is used for many economically significant applications. For example, urea is used as a main constituent of fertilizers, as a monomer in the production of plastics, and as an ingredient in animal feed. Large quantities of urea, on the order of 4,000,000 tons/year or more in the United States alone, are synthesized commercially by contacting CO2 and NH3 under high pressure, typically 200 to 400 atm., and at temperatures between 140 and 210 degrees C to form ammonium carbamate, which is then decomposed into urea and water.
The high pressures necessitate the use of expensive, sophisticated equipment. Further the low conversion efficiencies usually obtained in this commercial process, e.g., about 50%, require the recycling of unreacted NH3 and CO2. Thus, production of smaller quantities by this high-pressure process is not fiscally acceptable. Even if large quantities are desired, the initial capital investment is an obstacle. Since the commercial production of NH3, a reactant in the process, also involves a high-pressure method which is only economical on a scale of approximately 500,000 tons/year" the monetary and quantity limitations ~L3~i3~
inherent in the commercial urea manufacturing process are further compounded.
Certain situations, however, are most suitable for small-quantity, low-investment techniques. For example, the need for only a relatively small capital investment would facilitate production of urea for fertilizer in a low-technology agrarian country. Similarly, the on-site production of urea from waste by-products of another pro-cess is a desirable process usually involving relatively small scales. Such a recovery process is often econom-ically advantageous iE a sufficiently high-conversion efficiency from reactant by-products to salable products is obtainable. These two specific situations and many analogous ones illustrate two important factors. First, techniques involving relatively mild-pressure conditions are important in reducing the associated initial invest-ment and technical complexities. Second, the possibilities of increased efficiency in the utilization of raw materials offered by a high-yield method of making urea from by-products is significant. Thus a relatively mild-pressure, high-efficiency process of making urea is beneficial in many circumstances.
Summar~ of the Invention According to the invention there is provided a process for producing urea or ammonium cyanate, which comprises reacting in the presence of a hydrogenation catalyst a mixture of gases including a) an oxide of the composition NOX wherein x is 1 or 2, b) carbon monoxide, and c) hydrogen or a source of hydrogen, said carbon monoxide and NOX being included in a ratio of from 0.5:1 to 10:1, and said hydrogen or said source of hydrogen and NOX
. ., ~
, :
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such that the ratio of H2 to NOX i5 from 1:1 to 10:1, conducting the said reacting at a temperature in the range of from 200 to fiO0 degrees C, and collecting a resultant compound.
- 2a -, ~L~a3~3~
~ .~ It has been ~ that when a gaseous mixture oE
NOX where x is 1 or 2, carbon monoxide arld a source of hydrogen, such as H2O or H2, is passed over a hydro-genation catalyst, such as platinum or rhodium, urea is obtained if the product is condensed at temperatures above 60 degrees C and ammonium cyanate, NH40CN, is obtained for condensation below 60 degrees C. Ylelds o up to 100 percent (based on the conversion of the NOX to urea or NH40CN) are possible. Other catalysts such as MONEL
(Trade Mark) give lower yields, e.g., above 30 percent but are still useful. Such yields are obtained at atmospheric pressure and at temperatures between about 200 and 600 degrees C.
The process gives advantageous conversion to urea or NH~OCN when the NOX concentration is as low as 200 ppm.
or as high as 5%. Thus, the method is adaptable for using the NOX by-products of other manufacturing operations.
This is particularly significant since normally nitrogen oxides in low concen-trations have a negative manufacturing cost, e.g., there is a significant expense in converting NOX into other relatively valueless non-pollutants to meet the requirements of federal environmental statutes.
The inventive process in essence has the potential for transforming a manufacturing expense into a manufacturing asset. This transmogrification is associated with a reasonably small capital investment resulting from the relatively mild reaction conditions. The attractiveness of the process is further enhanced by the high-conversion ~i efficiencies which are achievable.
Brief Descri~tlon of the Drawings FIG. 1 is a schematic diagram of an apparatus suit-able for the practice of the invention;
The high pressures necessitate the use of expensive, sophisticated equipment. Further the low conversion efficiencies usually obtained in this commercial process, e.g., about 50%, require the recycling of unreacted NH3 and CO2. Thus, production of smaller quantities by this high-pressure process is not fiscally acceptable. Even if large quantities are desired, the initial capital investment is an obstacle. Since the commercial production of NH3, a reactant in the process, also involves a high-pressure method which is only economical on a scale of approximately 500,000 tons/year" the monetary and quantity limitations ~L3~i3~
inherent in the commercial urea manufacturing process are further compounded.
Certain situations, however, are most suitable for small-quantity, low-investment techniques. For example, the need for only a relatively small capital investment would facilitate production of urea for fertilizer in a low-technology agrarian country. Similarly, the on-site production of urea from waste by-products of another pro-cess is a desirable process usually involving relatively small scales. Such a recovery process is often econom-ically advantageous iE a sufficiently high-conversion efficiency from reactant by-products to salable products is obtainable. These two specific situations and many analogous ones illustrate two important factors. First, techniques involving relatively mild-pressure conditions are important in reducing the associated initial invest-ment and technical complexities. Second, the possibilities of increased efficiency in the utilization of raw materials offered by a high-yield method of making urea from by-products is significant. Thus a relatively mild-pressure, high-efficiency process of making urea is beneficial in many circumstances.
Summar~ of the Invention According to the invention there is provided a process for producing urea or ammonium cyanate, which comprises reacting in the presence of a hydrogenation catalyst a mixture of gases including a) an oxide of the composition NOX wherein x is 1 or 2, b) carbon monoxide, and c) hydrogen or a source of hydrogen, said carbon monoxide and NOX being included in a ratio of from 0.5:1 to 10:1, and said hydrogen or said source of hydrogen and NOX
. ., ~
, :
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such that the ratio of H2 to NOX i5 from 1:1 to 10:1, conducting the said reacting at a temperature in the range of from 200 to fiO0 degrees C, and collecting a resultant compound.
- 2a -, ~L~a3~3~
~ .~ It has been ~ that when a gaseous mixture oE
NOX where x is 1 or 2, carbon monoxide arld a source of hydrogen, such as H2O or H2, is passed over a hydro-genation catalyst, such as platinum or rhodium, urea is obtained if the product is condensed at temperatures above 60 degrees C and ammonium cyanate, NH40CN, is obtained for condensation below 60 degrees C. Ylelds o up to 100 percent (based on the conversion of the NOX to urea or NH40CN) are possible. Other catalysts such as MONEL
(Trade Mark) give lower yields, e.g., above 30 percent but are still useful. Such yields are obtained at atmospheric pressure and at temperatures between about 200 and 600 degrees C.
The process gives advantageous conversion to urea or NH~OCN when the NOX concentration is as low as 200 ppm.
or as high as 5%. Thus, the method is adaptable for using the NOX by-products of other manufacturing operations.
This is particularly significant since normally nitrogen oxides in low concen-trations have a negative manufacturing cost, e.g., there is a significant expense in converting NOX into other relatively valueless non-pollutants to meet the requirements of federal environmental statutes.
The inventive process in essence has the potential for transforming a manufacturing expense into a manufacturing asset. This transmogrification is associated with a reasonably small capital investment resulting from the relatively mild reaction conditions. The attractiveness of the process is further enhanced by the high-conversion ~i efficiencies which are achievable.
Brief Descri~tlon of the Drawings FIG. 1 is a schematic diagram of an apparatus suit-able for the practice of the invention;
- 3 -3~;3~3~
FIGS. 2-7 show conversion effic;.encies under var.ious reaction conditions.
Detai.led Description The preferred embodiment of the invention can best be described by indivi.dually detailing the steps in the synthesis process by reference to FIG. 1.
Cylinders of the reactant gases (1, 2, and 3 in FIG. 1) and a cylinder oE an inert ca:rrier gas 4, is - 3a -, ~
f~ , ~36,;~
attached through individual flow controllers, 5, 6, 7 and ~, to a manifold 9. The reactant gases are a nitrogen oxide, i.e., NO or N02 or a combination of NO and N02, carbon monoxide, and a third material which provides a source of hydrogen. Molecular hydrogen and water are exemplary of the materials suitable as hydrogen sources. In the latter case, since the process involves a gas phase reaction, the water is added by techniques su~h as passing the reactant gaseq through a water bubbler. Indeed, if the other reactants have a sufficiently high water impurity content no further addition is necessary. The particular material used as the inert gas is not critical. Typically, in laboratory preparation, helium is used because of its availability and because it facilitates analysis of reaction products.
However, other inert gases such as N2 are also acceptable.
The catalyst 10 is inserted in the reaction vessel 11, and a thermocouple 12, or other temperature monitoring means placed near the catalyst. The catalyst used is a hydrogenation catalyst. For example, catalysts such as rhodium, platinum and palladium, are suitable.
Other specific hydrogenation catalysts such as monel are also useful. The physical form of the catalyst is not - critical. Conventional forms such as small metal particles or a supported catalyst are useful. The yield of urea or urea equivalent i.e., NH40CN, depends on the reaction conditions and the particular catalyst used. It is desirable for many uses to select the conditions and the catalyst to yield conversions of NOx to urea or NH40CN of greater than 30 percent. Preferably for small-scale commercial applications conversions greater than 70 percent are advantageous.
After the reactants and catalysts are positioned, the apparatus is sealed and the entire system is purged with the inert gas. Then, if desired, the catalyst is cleaned by runnin~ H2 over the catalyst which is heated to between 200 and 600 degrees C, preferably between 300 and 500 degrees C
~or 1 to 24 hours. For this purpose, H2 is introduced in the system either in pure ~orm or diluted with an inert gas in a ratio of inert ~as to H2 of between 0 and 50. This cleaning removes oxygen from the catalyst surface an~
generally makes the catalyst more active.
To start the reaction process, NOx, CO, the hydrogen source e.g., H2, and an inert gas are bled through their respective flow controllers into the manifold 9, and are directed through mixing coil 14 to insure homogeneity.
Exemplary of the concentration of reactants in the gas flow is an NOX partial pressure of 2 x 10 4 atm to .05 atm, preferably 2 x 10 3 a~m to 0.02 atm, a CO/NOX ratio of between 0.5 and 10, preferably between 1 and 4 and a H2/NOX
ratio of between 1 and 10, preferably between 1 and 2. The remainder of the gas flow is composed of inert gas, i.e., gas which does not interfere with the desired reaction.
Suitable pressures for the total gas flow are between about 1/2 and 5 atm, preferably between 3/4 and 1 1/2 atm. Within these limitations of reactant concentration total gas flow and pressure, situations are encompassed where no inert gas is used and the system operates at a partial vacuum. Such situations are within the ambit of the inven~ion. However, it is generally most convenient to work at pressures in the range of 1 atm which usually ~ecessitates the addition of some inert gas. The gas mixture is passed over the catalyst which is heated to a temperature between about 200 and 1~3638~
600 degrees C, preferably between 300 and S00 degrees C.
The gas flow rate is regulated to allow sufficient time for a substantial portion of the reactants to react and yet provide a commerciall~ viable throughout time. Generally, for typical catalysts, flow rates between about 1,000 and 100,000 ml/h per m2 are acceptable. (The M~ refers to the total surface area of the catalyst accessible to the reactant gas flow.) The reacted gas passes out of the reactor into tube 15 and the NH40CN is frozen out of the gas flow by passing through a trap 17, which is kept at a temperature between 0 degree C and 120 degrees C. Ammonium cyanate is stable in the gas phase. Mowever, when condensed, it spontaneously converts to urea at temperatures above 60 degrees C. Urea decomposes in the solid state at 120 degrees C. Therefore if the reacted gases are frozen below 60 degrees C NH40CN is the solid obtained. If the gases are condensed between 60 degrees C and 120 degrees C, urea is obtained. Condensation above 120 degrees C is not recommended. The remaining gases are then vented through tube 25.
The ultimate yield obtained depends on the particular reaction conditions used. In each specific situation a controlled sample is used to fix the desired optimum conditions. The following examples demonstrate the effect of various parameters and the results obtainable by the practice of the invention.
Examples 1 through 4 show the effect of temperature on yield for various catalysts. Each example was done with a total gas pressure of 1 atm. Some of the examples use NOX to CO ratios outside the suggested ranges. These examples 3~L
are taken from experiments which we~e done with a large excess of CO early ~n the evaluation of the invention to insure reaction of the nltrogen oxide. The suggested ranges, however, are those centering around stoichiomet:ric proportions, and thus, are closer to an equivalent of CO to NO in the reaction mixture. In this way, the CO is more efficiently utilized and the uneconomical waste of a reactant gas is prevented.
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Example 1 The apparatus shown in FIG. 1 including, for the purpose of analysis, a gas chromatograph 20, to measure the concentration of NOX and N2 in the exhaust gas and a Modified Technicon Colorimetric Auto-Analyzer 22, to measure the concentration of NH40CN, was used. The modification of the analyzer was necessary to prevent clogging of the apparatus with urea or NH40CN. The modification consisted of installing an absorber which forced the hot gases through a silver nozzle followed by condensation and dissolution of the cyanate component on a surface which is continually flushed with an alcoholic solution. The solution is heated to between 60 and 90 degrees C to effect total conversion to urea. The urea solution is then analyzed using the carbamido-diacetyl reaction. (See J. Biochemistry 33, 902 (1939).) Approximately 5 grams of platinum sponge with an active surface area of 0.12 m /gm (area available for contact with the reactants) was put into the reaction vessel. A gas mixture of 0.3 percent NO, 0.5 percent H2, 5.0 percent CO and the remainder He was flowed at 115 cç/min over the catalyst (total pressure 1 atm). Measurement of urea (NH40CN) production for various temperatures of the catalyst in the range of 300 to 500 de~rees C was made.
(The catalyst was heated by a fluidized sand bed with a heating coil, 27.) A sample of the reactor effluent was dried and CO2 removed with an ascarite trap 13. Exhaust from the ascarite trap was analyzed on the gas chromatograph for components such as N2, NO, NO2 and C0. Another sample of effluent was analyzed in the auto-analyzer 22, for N~40CN
and/or urea content. The results are shown graphically in FIG. 2.
Example 2 The catalyst of Example 1 was reduced (cleaned) by running a 2 percent H2 in He mixture over the platinum sponge for 8 hours at 480 degrees C and then for 3 hours at 500 degrees C. The data obtained under the same reaction conditions as in Example 1 is shown in FIG. 3.
A comparison of these two FIGS. shows the improved effect generally associated with cleaning the catalyst.
Example 3 Approximately 1.5 grams of rhodium sponge with an active sur~ace area of 1.69 m2/gm was put into the reaction chamber. Pure H2 was flowed over the catalyst at 100 cc/min. The catalyst was heated to 500 degrees C and maintained at this temperature for 1-3/4 hours. The catalyst temperature was then reduced to room temperature and the gas flow was changed from pure H2 to pure He for overnight storage. A mixture of 0.31 percent NO, 0.5 percent H2, S.0 percent CO, and the balance He (total pressure 1 atm) was flowed at a ræte of 230 cc/min. over the rhodium as it was heated to 360 degrees C. Product analysis was then done at various catalyst temperatures and the result is shown in FIG. 4.
Example _ Approximately 4 grams of monel metal filings (active surface area 0.12 m2/gm) was placed in the reactor and heated to 450 degrees C under a 2 percent H2/He flow of 100 cc/min. The cleaning process was continued overnight.
The catalyst temperature was then lowered to 200 degrees C
and the gas flow was changed to pure H2 at 100 cc/min. The temperature was then increased to 450 degrees C for ~3;i3~
FIGS. 2-7 show conversion effic;.encies under var.ious reaction conditions.
Detai.led Description The preferred embodiment of the invention can best be described by indivi.dually detailing the steps in the synthesis process by reference to FIG. 1.
Cylinders of the reactant gases (1, 2, and 3 in FIG. 1) and a cylinder oE an inert ca:rrier gas 4, is - 3a -, ~
f~ , ~36,;~
attached through individual flow controllers, 5, 6, 7 and ~, to a manifold 9. The reactant gases are a nitrogen oxide, i.e., NO or N02 or a combination of NO and N02, carbon monoxide, and a third material which provides a source of hydrogen. Molecular hydrogen and water are exemplary of the materials suitable as hydrogen sources. In the latter case, since the process involves a gas phase reaction, the water is added by techniques su~h as passing the reactant gaseq through a water bubbler. Indeed, if the other reactants have a sufficiently high water impurity content no further addition is necessary. The particular material used as the inert gas is not critical. Typically, in laboratory preparation, helium is used because of its availability and because it facilitates analysis of reaction products.
However, other inert gases such as N2 are also acceptable.
The catalyst 10 is inserted in the reaction vessel 11, and a thermocouple 12, or other temperature monitoring means placed near the catalyst. The catalyst used is a hydrogenation catalyst. For example, catalysts such as rhodium, platinum and palladium, are suitable.
Other specific hydrogenation catalysts such as monel are also useful. The physical form of the catalyst is not - critical. Conventional forms such as small metal particles or a supported catalyst are useful. The yield of urea or urea equivalent i.e., NH40CN, depends on the reaction conditions and the particular catalyst used. It is desirable for many uses to select the conditions and the catalyst to yield conversions of NOx to urea or NH40CN of greater than 30 percent. Preferably for small-scale commercial applications conversions greater than 70 percent are advantageous.
After the reactants and catalysts are positioned, the apparatus is sealed and the entire system is purged with the inert gas. Then, if desired, the catalyst is cleaned by runnin~ H2 over the catalyst which is heated to between 200 and 600 degrees C, preferably between 300 and 500 degrees C
~or 1 to 24 hours. For this purpose, H2 is introduced in the system either in pure ~orm or diluted with an inert gas in a ratio of inert ~as to H2 of between 0 and 50. This cleaning removes oxygen from the catalyst surface an~
generally makes the catalyst more active.
To start the reaction process, NOx, CO, the hydrogen source e.g., H2, and an inert gas are bled through their respective flow controllers into the manifold 9, and are directed through mixing coil 14 to insure homogeneity.
Exemplary of the concentration of reactants in the gas flow is an NOX partial pressure of 2 x 10 4 atm to .05 atm, preferably 2 x 10 3 a~m to 0.02 atm, a CO/NOX ratio of between 0.5 and 10, preferably between 1 and 4 and a H2/NOX
ratio of between 1 and 10, preferably between 1 and 2. The remainder of the gas flow is composed of inert gas, i.e., gas which does not interfere with the desired reaction.
Suitable pressures for the total gas flow are between about 1/2 and 5 atm, preferably between 3/4 and 1 1/2 atm. Within these limitations of reactant concentration total gas flow and pressure, situations are encompassed where no inert gas is used and the system operates at a partial vacuum. Such situations are within the ambit of the inven~ion. However, it is generally most convenient to work at pressures in the range of 1 atm which usually ~ecessitates the addition of some inert gas. The gas mixture is passed over the catalyst which is heated to a temperature between about 200 and 1~3638~
600 degrees C, preferably between 300 and S00 degrees C.
The gas flow rate is regulated to allow sufficient time for a substantial portion of the reactants to react and yet provide a commerciall~ viable throughout time. Generally, for typical catalysts, flow rates between about 1,000 and 100,000 ml/h per m2 are acceptable. (The M~ refers to the total surface area of the catalyst accessible to the reactant gas flow.) The reacted gas passes out of the reactor into tube 15 and the NH40CN is frozen out of the gas flow by passing through a trap 17, which is kept at a temperature between 0 degree C and 120 degrees C. Ammonium cyanate is stable in the gas phase. Mowever, when condensed, it spontaneously converts to urea at temperatures above 60 degrees C. Urea decomposes in the solid state at 120 degrees C. Therefore if the reacted gases are frozen below 60 degrees C NH40CN is the solid obtained. If the gases are condensed between 60 degrees C and 120 degrees C, urea is obtained. Condensation above 120 degrees C is not recommended. The remaining gases are then vented through tube 25.
The ultimate yield obtained depends on the particular reaction conditions used. In each specific situation a controlled sample is used to fix the desired optimum conditions. The following examples demonstrate the effect of various parameters and the results obtainable by the practice of the invention.
Examples 1 through 4 show the effect of temperature on yield for various catalysts. Each example was done with a total gas pressure of 1 atm. Some of the examples use NOX to CO ratios outside the suggested ranges. These examples 3~L
are taken from experiments which we~e done with a large excess of CO early ~n the evaluation of the invention to insure reaction of the nltrogen oxide. The suggested ranges, however, are those centering around stoichiomet:ric proportions, and thus, are closer to an equivalent of CO to NO in the reaction mixture. In this way, the CO is more efficiently utilized and the uneconomical waste of a reactant gas is prevented.
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~ iL36~3~L
Example 1 The apparatus shown in FIG. 1 including, for the purpose of analysis, a gas chromatograph 20, to measure the concentration of NOX and N2 in the exhaust gas and a Modified Technicon Colorimetric Auto-Analyzer 22, to measure the concentration of NH40CN, was used. The modification of the analyzer was necessary to prevent clogging of the apparatus with urea or NH40CN. The modification consisted of installing an absorber which forced the hot gases through a silver nozzle followed by condensation and dissolution of the cyanate component on a surface which is continually flushed with an alcoholic solution. The solution is heated to between 60 and 90 degrees C to effect total conversion to urea. The urea solution is then analyzed using the carbamido-diacetyl reaction. (See J. Biochemistry 33, 902 (1939).) Approximately 5 grams of platinum sponge with an active surface area of 0.12 m /gm (area available for contact with the reactants) was put into the reaction vessel. A gas mixture of 0.3 percent NO, 0.5 percent H2, 5.0 percent CO and the remainder He was flowed at 115 cç/min over the catalyst (total pressure 1 atm). Measurement of urea (NH40CN) production for various temperatures of the catalyst in the range of 300 to 500 de~rees C was made.
(The catalyst was heated by a fluidized sand bed with a heating coil, 27.) A sample of the reactor effluent was dried and CO2 removed with an ascarite trap 13. Exhaust from the ascarite trap was analyzed on the gas chromatograph for components such as N2, NO, NO2 and C0. Another sample of effluent was analyzed in the auto-analyzer 22, for N~40CN
and/or urea content. The results are shown graphically in FIG. 2.
Example 2 The catalyst of Example 1 was reduced (cleaned) by running a 2 percent H2 in He mixture over the platinum sponge for 8 hours at 480 degrees C and then for 3 hours at 500 degrees C. The data obtained under the same reaction conditions as in Example 1 is shown in FIG. 3.
A comparison of these two FIGS. shows the improved effect generally associated with cleaning the catalyst.
Example 3 Approximately 1.5 grams of rhodium sponge with an active sur~ace area of 1.69 m2/gm was put into the reaction chamber. Pure H2 was flowed over the catalyst at 100 cc/min. The catalyst was heated to 500 degrees C and maintained at this temperature for 1-3/4 hours. The catalyst temperature was then reduced to room temperature and the gas flow was changed from pure H2 to pure He for overnight storage. A mixture of 0.31 percent NO, 0.5 percent H2, S.0 percent CO, and the balance He (total pressure 1 atm) was flowed at a ræte of 230 cc/min. over the rhodium as it was heated to 360 degrees C. Product analysis was then done at various catalyst temperatures and the result is shown in FIG. 4.
Example _ Approximately 4 grams of monel metal filings (active surface area 0.12 m2/gm) was placed in the reactor and heated to 450 degrees C under a 2 percent H2/He flow of 100 cc/min. The cleaning process was continued overnight.
The catalyst temperature was then lowered to 200 degrees C
and the gas flow was changed to pure H2 at 100 cc/min. The temperature was then increased to 450 degrees C for ~3;i3~
4-1/4 hours. Various runs were made and the system was kept under He for a number of days. Then a gas flow of 0.3 percent N0, 0.5 percent H2, 5.0 percent C0 and the remainder He was introduced at a flow rate of 125 cc/min (total pressure 1 atm). Yields were measured at various catalyst temperatures over an extencled period. The catalyst was kept under pure He when measurements were not beirlg taken. The results are shown in FIG~ 5.
As can be seen from FIGS~ 2 to 5 conversions of N0 to NH40CN closely approaching 100% were possible.
The following example demonstrates a -typical effect of flow rate on yield at various temperatures.
Example 5 The catalyst used in Example 1 was again reduced at 500 degrees C under 2 percent H2 in He (2 hours). Yields at 360 and 410 degrees C for various flow rates of a 0.3 percent N0, 0.5 percent H2, 5.0 percent C0, and the remainder He (total gas pressure 1 atm) mixture was measured. Line 30 of FIGo 6 indicates the results at the lower temperature and line 31 at the higher.
A different sample of approximately 5 grams of platinum sponge (active surface area 0.12 m /gm) was reduced overnight at 500 degrees C under a 2 percent H2/He flow.
The catalyst temperature was adjusted to 430 degrees C and a gas mixture of 0.33 percent N0, 0.5 percent H2, 5.0 percent C0 and the remainder He (total pressure 1 atm) was introduced at a flow rate of 700 ml/min. This flow rate was varied by partial venting the gas flow before the gas mixture reached the reactor. The yields of NH40CN for the different flow rates at 430 degrees C are indicated by line 32 in FIG. 6. (Flow rates are shown as F/S where F is g _ i3~
gas volume in ml per hour and S is the surface area of the catalyst sample accessible to the reactant gas flow.) The following example illustrates the effect of reactant proportions on the reaction yield.
Example 6 Approximately 5 grams of platinum sponge (active surface area 0.12 m /gm) was loaded in the reactor. The catalyst temperature was raised to 450 degrees C and 2 percent H2/He was flowed at a rate of 60 cc/min. through the system overnight. The temperature was then lowered to 404 degrees C and a gas mixture containing 0.3 percent NO,
As can be seen from FIGS~ 2 to 5 conversions of N0 to NH40CN closely approaching 100% were possible.
The following example demonstrates a -typical effect of flow rate on yield at various temperatures.
Example 5 The catalyst used in Example 1 was again reduced at 500 degrees C under 2 percent H2 in He (2 hours). Yields at 360 and 410 degrees C for various flow rates of a 0.3 percent N0, 0.5 percent H2, 5.0 percent C0, and the remainder He (total gas pressure 1 atm) mixture was measured. Line 30 of FIGo 6 indicates the results at the lower temperature and line 31 at the higher.
A different sample of approximately 5 grams of platinum sponge (active surface area 0.12 m /gm) was reduced overnight at 500 degrees C under a 2 percent H2/He flow.
The catalyst temperature was adjusted to 430 degrees C and a gas mixture of 0.33 percent N0, 0.5 percent H2, 5.0 percent C0 and the remainder He (total pressure 1 atm) was introduced at a flow rate of 700 ml/min. This flow rate was varied by partial venting the gas flow before the gas mixture reached the reactor. The yields of NH40CN for the different flow rates at 430 degrees C are indicated by line 32 in FIG. 6. (Flow rates are shown as F/S where F is g _ i3~
gas volume in ml per hour and S is the surface area of the catalyst sample accessible to the reactant gas flow.) The following example illustrates the effect of reactant proportions on the reaction yield.
Example 6 Approximately 5 grams of platinum sponge (active surface area 0.12 m /gm) was loaded in the reactor. The catalyst temperature was raised to 450 degrees C and 2 percent H2/He was flowed at a rate of 60 cc/min. through the system overnight. The temperature was then lowered to 404 degrees C and a gas mixture containing 0.3 percent NO,
5.0 percent CO, 0.3 percent H2 and the balance He (total gas pressure 1 atm) was flowed at the rate of 400 cc/min.
through the system. The CO concentration was varied (He concentration was also varied to compensate) and the yield of NH40CN measured. The following results were o~tained.
CO conc. Percent Percent Conversion NO to NH OCN
5.0 100 (82*) 2.0 100 (72*) 1.75 69.5*
1.25 63.0*
0.89 45.0*
0.45 37.5 (34.5*) * Reading taken on second day of experiment after catalyst was kept in He atmosphere over a 3 day period at room temperature.
The flow was then changed to a 2 percent H2/He mixture (flow rate 60 cc/min.) and the catalyst was reduced overnight at 450 clegrees C. The catalyst temperature was lowered to 420 degrees C and various reaction mixtures were flowed (400 cc./min.) through the system (total pressure of any given mixture was 1 atm). The composition of the reactant gas mixture (remainder not shown was He) and the NH40CN yield is shown in the following tables.
. . .
~3L3~i3~
Effect of NO and H2 Conc.
~NO%CO 2 % Conversion NO to NH OCN
0.6 5.00.662.0 1.2 5.01.~63.0 1.2 5.03.230.5 2.0 5.02.053.5 2.0 5.03.053.5 EffeCt of H2O
%NO ~CO%H2 %H2O~ Converslon 0.6 5.00.6 0.0 62.0 0.6 5.00.6 4.3 77.5 0.6 5.00.0 4.3 69.0 0.6 2,00.6 4.3 72.5 0.3 2.00.5 0.0 62.0 0.3 2.00.5 4.3 60.5 2.0 5.02.0 4.5 61.0 The above tables show that conversion efficiency was insensitive to H2/NO ratio near stoichiometric proportions but that efficiency was reduced significantly when the H2/
NO ratio was increased above approximately 1.5. The table further shows that H2O was effectively used as a source of hydrogen.
The following example illustrates the effect of 2 on the reaction yield. It should be noted that when 2 was introduced NO was converted to NO2.
Example 7 Approximately 5 grams of sponge platinum in a reduced state was raised to 500 degrees C and a gas flow of 0.33 percent NO, 0.5 percent H2, 5.0 percent CO, (remainder He, total gas pressure 1 atm) was flowed through the system at a rate of 14 l/h. ~arious percentages of 2 were introduced and conversion efficiencies measured. The results are shown in FIG. 7.
~ .
, . - - - :.-. . - , ,:,: :. :
through the system. The CO concentration was varied (He concentration was also varied to compensate) and the yield of NH40CN measured. The following results were o~tained.
CO conc. Percent Percent Conversion NO to NH OCN
5.0 100 (82*) 2.0 100 (72*) 1.75 69.5*
1.25 63.0*
0.89 45.0*
0.45 37.5 (34.5*) * Reading taken on second day of experiment after catalyst was kept in He atmosphere over a 3 day period at room temperature.
The flow was then changed to a 2 percent H2/He mixture (flow rate 60 cc/min.) and the catalyst was reduced overnight at 450 clegrees C. The catalyst temperature was lowered to 420 degrees C and various reaction mixtures were flowed (400 cc./min.) through the system (total pressure of any given mixture was 1 atm). The composition of the reactant gas mixture (remainder not shown was He) and the NH40CN yield is shown in the following tables.
. . .
~3L3~i3~
Effect of NO and H2 Conc.
~NO%CO 2 % Conversion NO to NH OCN
0.6 5.00.662.0 1.2 5.01.~63.0 1.2 5.03.230.5 2.0 5.02.053.5 2.0 5.03.053.5 EffeCt of H2O
%NO ~CO%H2 %H2O~ Converslon 0.6 5.00.6 0.0 62.0 0.6 5.00.6 4.3 77.5 0.6 5.00.0 4.3 69.0 0.6 2,00.6 4.3 72.5 0.3 2.00.5 0.0 62.0 0.3 2.00.5 4.3 60.5 2.0 5.02.0 4.5 61.0 The above tables show that conversion efficiency was insensitive to H2/NO ratio near stoichiometric proportions but that efficiency was reduced significantly when the H2/
NO ratio was increased above approximately 1.5. The table further shows that H2O was effectively used as a source of hydrogen.
The following example illustrates the effect of 2 on the reaction yield. It should be noted that when 2 was introduced NO was converted to NO2.
Example 7 Approximately 5 grams of sponge platinum in a reduced state was raised to 500 degrees C and a gas flow of 0.33 percent NO, 0.5 percent H2, 5.0 percent CO, (remainder He, total gas pressure 1 atm) was flowed through the system at a rate of 14 l/h. ~arious percentages of 2 were introduced and conversion efficiencies measured. The results are shown in FIG. 7.
~ .
, . - - - :.-. . - , ,:,: :. :
Claims (10)
1. A process for producing urea or ammonium cyanate, which comprises reacting in the presence of a hydro-genation catalyst a mixture of gases including a) an oxide of the composition NOx wherein x is 1 or 2, b) carbon monoxide, and c) hydrogen or a source of hydrogen, said carbon monoxide and NOx being included in a ratio of from 0.5:1 to 10:1, and said hydrogen or said source of hydrogen and NOX such that the ratio of H2 to NOx is from 1:1 to 10:1, conducting the said reacting at a temperature in the range of from 200 to 600 degrees C, and collecting a resultant compound.
2. The process according to claim 1, which comprises selecting said hydrogenation catalyst from platinum, rhodium, palladium and Monel?.
3. The process according to claim 1, which comprises conducting the said reacting at a temperature in the range of from 300 to 500 degrees C.
4. The process according to claim 1, wherein said source of hydrogen is water.
5. The process according to claim 1, which comprises selecting said ratio of carbon monoxide to NOx to be from 1:1 to 4:1.
6. The process according to claim 1, which comprises selecting said ratio of H2 to NOX to be from 1:1 to 2:1.
7. The process according to claim 1, which comprises collecting the resultant compound by condensation at a temperature of less than 120 degrees C.
8. The process according to claim 7, which comprises collecting the said compound as solid NH4OCN by conden-sation at a temperature of 60 degrees C or less.
9. The process according to claim 7, which comprises collecting the said compound as solid urea by conden-sation at a temperature of between 60 and 120 degrees C.
10. The process according to claim 1 or claim 2 or claim 3, Which comprises additionally including oxygen into the said mixture of gases.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US77678777A | 1977-03-11 | 1977-03-11 | |
| US776,787 | 1977-03-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1136381A true CA1136381A (en) | 1982-11-30 |
Family
ID=25108363
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000295840A Expired CA1136381A (en) | 1977-03-11 | 1978-01-27 | Catalytic process for the production of urea and ammonium cyanate |
Country Status (12)
| Country | Link |
|---|---|
| JP (1) | JPS5814364B2 (en) |
| AT (1) | AT360036B (en) |
| AU (1) | AU520029B2 (en) |
| BE (1) | BE864762A (en) |
| CA (1) | CA1136381A (en) |
| CH (1) | CH633496A5 (en) |
| DE (1) | DE2809858C2 (en) |
| FR (1) | FR2383168B1 (en) |
| GB (1) | GB1593561A (en) |
| IL (1) | IL54196A (en) |
| IT (1) | IT7867534A0 (en) |
| NL (1) | NL7802410A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4174377A (en) * | 1978-05-25 | 1979-11-13 | Bell Telephone Laboratories, Incorporated | Formation of cyanate compounds |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR540543A (en) * | 1921-08-19 | 1922-07-12 | Process for the production of alcohols, aldehydes and acids from gas mixtures maintained under pressure and subjected to the action of catalytic agents or electricity | |
| JPS5014238A (en) * | 1973-06-06 | 1975-02-14 | ||
| JPS6029464B2 (en) * | 1978-06-07 | 1985-07-10 | ゼネラル・フ−ヅ・コ−ポレ−シヨン | Stable powdered fruit juice with low hygroscopicity and method for producing the same |
-
1978
- 1978-01-13 GB GB1485/78A patent/GB1593561A/en not_active Expired
- 1978-01-27 CA CA000295840A patent/CA1136381A/en not_active Expired
- 1978-03-03 NL NL7802410A patent/NL7802410A/en not_active Application Discontinuation
- 1978-03-06 FR FR7806312A patent/FR2383168B1/fr not_active Expired
- 1978-03-06 IL IL54196A patent/IL54196A/en unknown
- 1978-03-07 DE DE2809858A patent/DE2809858C2/en not_active Expired
- 1978-03-07 AU AU33903/78A patent/AU520029B2/en not_active Expired
- 1978-03-10 CH CH266678A patent/CH633496A5/en not_active IP Right Cessation
- 1978-03-10 JP JP53026759A patent/JPS5814364B2/en not_active Expired
- 1978-03-10 BE BE185821A patent/BE864762A/en not_active IP Right Cessation
- 1978-03-10 AT AT173978A patent/AT360036B/en not_active IP Right Cessation
- 1978-03-10 IT IT7867534A patent/IT7867534A0/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| BE864762A (en) | 1978-07-03 |
| AU520029B2 (en) | 1982-01-14 |
| DE2809858A1 (en) | 1978-09-14 |
| CH633496A5 (en) | 1982-12-15 |
| AT360036B (en) | 1980-12-10 |
| IL54196A (en) | 1982-03-31 |
| IT7867534A0 (en) | 1978-03-10 |
| IL54196A0 (en) | 1978-06-15 |
| GB1593561A (en) | 1981-07-22 |
| AU3390378A (en) | 1979-09-13 |
| JPS5814364B2 (en) | 1983-03-18 |
| JPS53137916A (en) | 1978-12-01 |
| FR2383168B1 (en) | 1981-07-17 |
| ATA173978A (en) | 1980-05-15 |
| DE2809858C2 (en) | 1982-09-30 |
| FR2383168A1 (en) | 1978-10-06 |
| NL7802410A (en) | 1978-09-13 |
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