CA1040215A - Method of controlling water content in urea reactions - Google Patents
Method of controlling water content in urea reactionsInfo
- Publication number
- CA1040215A CA1040215A CA209,047A CA209047A CA1040215A CA 1040215 A CA1040215 A CA 1040215A CA 209047 A CA209047 A CA 209047A CA 1040215 A CA1040215 A CA 1040215A
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- Canada
- Prior art keywords
- urea
- reactor
- gases
- water
- melt
- 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
- C07C273/04—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 from carbon dioxide and ammonia
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
METHOD OF CONTROLLING WATER CONTENT IN UREA REACTIONS
Abstract of the Disclosure A method of preparing urea is disclosed in which extremely high yields of urea are obtained at relatively low pressures. The method comprises, in a continuous urea process in which off-gases are recycled, partially removing water from the urea melt. This is accomplished by feeding to the urea melt a mixture of gases containing recycled gases, which has been rendered low in water content prior to entry into the urea reaction vessel.
Abstract of the Disclosure A method of preparing urea is disclosed in which extremely high yields of urea are obtained at relatively low pressures. The method comprises, in a continuous urea process in which off-gases are recycled, partially removing water from the urea melt. This is accomplished by feeding to the urea melt a mixture of gases containing recycled gases, which has been rendered low in water content prior to entry into the urea reaction vessel.
Description
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The present invention relates to a method of keeping the water content in a urea reaction vessel low and to an apparatus suitable therefor.
Prior art processes for the manufacture of urea by reaction of carbon dioxide and ammonia under increased pressure and high temperatures (e.g. 170 bars and 180C) are character-ized in that in addition to the urea formed, comparable quantities of principally carbamate are produced. If the pressure does not exceed 200 bars, urea yields up to 70% can be obtained.
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The present invention relates to a method of keeping the water content in a urea reaction vessel low and to an apparatus suitable therefor.
Prior art processes for the manufacture of urea by reaction of carbon dioxide and ammonia under increased pressure and high temperatures (e.g. 170 bars and 180C) are character-ized in that in addition to the urea formed, comparable quantities of principally carbamate are produced. If the pressure does not exceed 200 bars, urea yields up to 70% can be obtained.
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~O~OZ15 To separate the carbamate from the urea, the carbamate is decomposed with the aid of heat. Various methods are known for reintroducing into the reactor the resultant gaseous substances. One of the earliest of these known methods dates back to the 1950's and is based on the fact that under suitable conditions, ammonia can be selecti~ely separated from carbon dioxide with the:aid of an ammonium nitrate solution (cf. e.g., Swiss Patent -No. 290,289; French Patent No. 1,085,316). Although this b~ known process proved successful in industrial operations, it was soon replaced by less costly and more efficient processës (cf. e.g. U.S. Patent No. 3,317,601).
. Common to all of these prior art known methods is the separation of the carbamate at pressures lower than the reactor pressure in more or less numerous stages, and - the absorptive return into the pressure autoclave of the unconverted reactants.
Another method which has met with some success is - the stripping process of Netherlands Staatsmijnen (see, i ~o e.g., U.S. Patent No. 3,356,723). This method utilizes the principle of counter-flow (countercurrent). The carbamate i8 decomposed and the resuLting products are returnet isobaricall~ to the reactor.
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_3 -~ ' ' - ' ' All of these prior art processes are disadvantageous in that the melt in the reaction chamber contains a large amount of water and the conversion into urea relative to carbon dioxide at the outlet of the reactor is relatively slight.
Moreover, in all cases the urea must be released from the reaction water at low pressure and at low temperature. During "prilling" the melt must again be brought to a high temperature.
All of these steps increase the energy requirement for the process and large unused quantities of energy are released directly into the environment at low temperatures. U.S.
Patent No. 2,527,315 teaches that through the use of a large excess of ammonia it is possible to obtain a urea-melt having a lower water content. However, ~he use of a large excess of ammonia requires extensive equipment and the input of con-siderable quantities of energy.
The present invention overcomes the aforementioned disadvantages of the known processes. It should be noted that in developing this invention it was found that an NH3 to CO2 mole ratio of 2 or sligntly more could be employed. This is remarkable because it is now possible to dispense with the use of usual excess ammonia while maintaining very high urea yields.
When the present invention is carried out continuously, the melt in the reactor is continually drained and the concentration of water is kept low. -~
Surprisingly, it was discovered that the free, sub-critical water does not stay in the liquid phase, as would be expected, but instead is distributed almost equally between - . ... .. ..
the two phases, liquid and gas. The ammonia, which is above its critical temperature, is surprisingly found to a large extent in the liquid phase; while carbon dioxide at higher temperatures prefers the gaseous phase almost exclusively.
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Accordingly, the present invention concerns a process for the continuous production of urea from the reaction of ammonia and carbon dioxide in a reactor. The process is characterized in that water is continually removed from the urea melt in the reactor. Preferably, the water is removed at a rate such that the mole ratio of water to urea produced in the reactor is always less than 1. This is achieved by con-tinually feeding the urea melt with a mixture of recirculated gases consisting of CO2, NH3 and H20 which has been at least partially dried before entering the urea reactor. The process is further characterized in that a reaction temperature of at least 160C is employed, a temperature of 170-200C being preferred. The preferred mole ratio of ammonia to carbon dioxide is 2 : 1.
Thus the process exhibits the following advantages:
1. The urea conversion in the melt relative to CO2 is large (e.g., 93~ and more).
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2. The content of water in the melt is ver~ low.
. .
.
~O~OZ15 To separate the carbamate from the urea, the carbamate is decomposed with the aid of heat. Various methods are known for reintroducing into the reactor the resultant gaseous substances. One of the earliest of these known methods dates back to the 1950's and is based on the fact that under suitable conditions, ammonia can be selecti~ely separated from carbon dioxide with the:aid of an ammonium nitrate solution (cf. e.g., Swiss Patent -No. 290,289; French Patent No. 1,085,316). Although this b~ known process proved successful in industrial operations, it was soon replaced by less costly and more efficient processës (cf. e.g. U.S. Patent No. 3,317,601).
. Common to all of these prior art known methods is the separation of the carbamate at pressures lower than the reactor pressure in more or less numerous stages, and - the absorptive return into the pressure autoclave of the unconverted reactants.
Another method which has met with some success is - the stripping process of Netherlands Staatsmijnen (see, i ~o e.g., U.S. Patent No. 3,356,723). This method utilizes the principle of counter-flow (countercurrent). The carbamate i8 decomposed and the resuLting products are returnet isobaricall~ to the reactor.
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_3 -~ ' ' - ' ' All of these prior art processes are disadvantageous in that the melt in the reaction chamber contains a large amount of water and the conversion into urea relative to carbon dioxide at the outlet of the reactor is relatively slight.
Moreover, in all cases the urea must be released from the reaction water at low pressure and at low temperature. During "prilling" the melt must again be brought to a high temperature.
All of these steps increase the energy requirement for the process and large unused quantities of energy are released directly into the environment at low temperatures. U.S.
Patent No. 2,527,315 teaches that through the use of a large excess of ammonia it is possible to obtain a urea-melt having a lower water content. However, ~he use of a large excess of ammonia requires extensive equipment and the input of con-siderable quantities of energy.
The present invention overcomes the aforementioned disadvantages of the known processes. It should be noted that in developing this invention it was found that an NH3 to CO2 mole ratio of 2 or sligntly more could be employed. This is remarkable because it is now possible to dispense with the use of usual excess ammonia while maintaining very high urea yields.
When the present invention is carried out continuously, the melt in the reactor is continually drained and the concentration of water is kept low. -~
Surprisingly, it was discovered that the free, sub-critical water does not stay in the liquid phase, as would be expected, but instead is distributed almost equally between - . ... .. ..
the two phases, liquid and gas. The ammonia, which is above its critical temperature, is surprisingly found to a large extent in the liquid phase; while carbon dioxide at higher temperatures prefers the gaseous phase almost exclusively.
-, ., ~ ,. . . .
- .. .. : : .
LS
Accordingly, the present invention concerns a process for the continuous production of urea from the reaction of ammonia and carbon dioxide in a reactor. The process is characterized in that water is continually removed from the urea melt in the reactor. Preferably, the water is removed at a rate such that the mole ratio of water to urea produced in the reactor is always less than 1. This is achieved by con-tinually feeding the urea melt with a mixture of recirculated gases consisting of CO2, NH3 and H20 which has been at least partially dried before entering the urea reactor. The process is further characterized in that a reaction temperature of at least 160C is employed, a temperature of 170-200C being preferred. The preferred mole ratio of ammonia to carbon dioxide is 2 : 1.
Thus the process exhibits the following advantages:
1. The urea conversion in the melt relative to CO2 is large (e.g., 93~ and more).
. . - . . . .
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2. The content of water in the melt is ver~ low.
3. There is a modest equilibrium of reaction - pressure even at high temperatures.
4. Although the operation is effected with or without a very slight excess of NH3, the liquid phase is strongly alkaline.
5. Due-to the high alkalinity, little biuret i8 created despite the low H2O content.
-10 6. All the compounds in the liquid phase can be decomposed into ~ and CO2. Thus it is possible, at a relatively low reaceor pressure and low biuret content, to employ a high temperature. In this manner, a high reaction ~peed is achieved, a small reactor can be utilized and a ~all C2 compressor output is requiret.
The figure illustrates, in schematic representation, typical flow diagram of a preferred embodiment of the present invention. As is apparent from the figure the apparatus consists of horizontally disposed reaction vessel 1, vertical ! 20 partial condenser 2, gas circulating blower 3, urea work-up unlt 12, separsting unit 10 and piping (represented by connecting lines and arrows) belonging to the system.
The mode of operation of this process is as follows:
The water-saturated gas leaves reaction vessel 1 and reaches partial condenser 2 at its lower end via a short pipe 4, which ~8 hydrodjnamically well designed. Together with the constituents flowing in from pipe 5 and hereinafter descri~ed, the mixture of gases is conveyed upwardly through the condenser tubes, being . .. . . . . . . . -:. - . . . .
-1()4U'~i5 partially condensed as the temperature falls in the direction of flow. The ascending saturated vapor is consequently conveyed in counter-current relationship to the film of condensate trickling down the walls, the condensate accumulating at the lower end of the condenser 2 surprisingly showing a very high concentration of water. This condensate also contains carbamate. The water is separated in separating unit 10 and drawn of f via the pipe 11. The gaseous carbamate mixture is conveyed into the condenser 2 via the pipe 6. The uncondensed vapor now low in water is drawn in by the circulating blower 3 and introduced tangentially into the urea melt at a plurality of points at the periphery of the reaction vessel 1 via the pipe 7. By momentum exchange between the gas and the liquid, the latter is kept in rotary movement, in such manner, in fact, that in the interior of the reaction vessel 1 there is formed a ring of liquid from the hollow space of which the saturated vapor mixture is drawn off towards the partial con-denser 2. The gas circuit described is thereby closed. From the reaction vessel 1, the urea is conveyed together with CO2, 20 NH3 and H20 via the pipe 9 into the work-up unit 12 and is separated therein in known manner, the urea being drawn off through the pipe 13 and the other constituents flowing into the gas circuit through pipe 5 into pipe 4.
The reaction vessel 1 is preferably placed in a horizontal position. As is apparent from the foregoing, it is desirable to bring the gas entering the reaction vessel and low in water into intensive contact with the urea melt in order to saturate the gas with as much water as possible.
This operation could be suitably carried out in a vertical bubble column. In order to keep investment costs low, pressure apparatus of small diameter is preferred. For a given : : .
~ ' ~ ' . .
l~lt~
residence-time, however, the bubble-dolumn reaction vessel and, consequently, the static liquid pressure acting on the bottom of the reaction vessel, becomes high. This static and very important liquid pressure must be supplied, in addition to the other pressure losses occurring in the cir-culating system, by the circulating blower 3, whereby its energy requirements increase markedly. Due to the horizontal reaction vessel with the melt revolving at above-critical speed, a liquid ring is obtained. If this ring is developed, then there is obtained, together with the length of reaction vessel in accordance with the above residence-time, a layer of liquid with a considerable base area and of small height or depth. The area increases with increasing length of the reaction vessel. In accordance with the small layer height (ring thickness), the feed or charging of this layer with gas requires a comparatively small energy consumption. The large reaction vessel surface (base area) may have a large number ~-`
of tangentially drilled holes through which the melt is intensively charged with gas in consequence of the large area of the bubbles formed. This arrangement consequently avoids - high energy requirements by the circulating blower 3 with low investment costs for the reaction vessel 1. At the same time, an equal residence-time and an equally intensive exchange of substances is ensured in comparison with a bubble column. The advantage achieved in this way is decisive for the economy of the method, since the circulating mass of gas for an average 500 tons per day plant, is, for example, 650 tons per hour. Another advantage of the method is that the heat liberated by the partial liquefaction of the gas can be ~
30 used for generating 6-bar steam. ~ ~ -Examples 1-4 hereafter are batchwise experiments in . . - . , .
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which an NH3/CO2 molar ratio of 2:1 was employed. The ratio of water and urea introduced to the autoclave to the volume of the reactor was 530 kg/m3. The mole ratio of H20 : CO2 was varied between 0.5 Example 1 H20/co2 mole ratio = 1 Temperature = 160C.
The H20/CO2 mole ratio refers to the liquid and the gaseous phase. The experiments were carried through isochorically.
~ith these parameters the following results are obtained:
Pressure = 85 bar Composition of liquids (w' = percentage by weight):
w' = 37.8 w' = 25.4 w' = 24.8 w' = 11.3 w' = ~.7 Urea NH3 C02 H2o Biuret Composition of gases (w" = percentage by weight):
w" = 1~.8 w" = 78.7 w" = 2.5 Urea conversion in the melt relative to CO2 = 60.4%.
Example 2 H20/Co2 mole ratio = 1 Temperature = 170C.
Pressure = 120 bar Composition of liquids (w' = percentage by weight):
w' = 40.7 w' = 23.3 w' = 23.1 w' = 11.5 w' = 1.4 Urea NH3 CO2 H2o Biuret Composition of gases (w" = percentage by weight):
w" = 18.1 w" = 77.1 w" = 4.80 Urea conversion in the melt relative to CO2 = 63.8%.
Example 3 H20/CO2 mole ratio = 0.63 Temperature = 170C
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-With these parameters the following results are obtained:
Pressure = 108 bar Composition of liquids (w' = percentage by weight~:
w' = 55.3 w' = 23.7 w' = 16.8 w' = 2.5 w' = 1.7 Urea NH3 C02 H2o Biuret Composition o~ gases (w" = percentage by weight):
w" = 23.1 w" = 72.0 w" = 4.9 Urea conversion in the melt relative to C02 = 76.7%.
Example 4 H20/Co2 mole ratio = 0.63 Temperature = 180C
With these parameters the following results are obtained:
Pressure = 127.5 bar Composition of liquids (w' = percentage by weight):
w' = 64.6 w' = 24.8 w' = 5.0 w' = 3.3 w' = 2.3 Urea NH3 C02 H2o Biuret Composition of gases (w" = percentage by weight):
w" = 21.2 w" = 76.2 w" = 2.6 Urea conversion in the melt relative to CO2 = 92.8%. ~ -,- - - -, : ' , - ', ' - '; ;, ' , : - . . . .
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Example 5 ~ 5 This Example illustrates the continuous operation of the present invention. Reference to the apparatus corresponds to the figure.
For an output of 500 tons of urea per day, reaction vessel 1 i8 fed with 4.24 kg/s CO2 and 3.28 kg/s ~H3.
The pressure in the reaction vessel is 125 bars and the temperature is adjusted to 180C. The gas circulates in the circu~t 1-4-2-3-7. The gas leaving the reaction vessel through pipe 4 consists of 136.4 kg/s C02, 37.95 kg/s NH3 and 4.65 kg/s ~ O.
When this gas stream is combined with the constituents coming from the urea work-up unit by way of pipe 5, 136.83 kg/s C2 J 40.09 kg/s NH3 and 4.93 kg/s H20 enter the lower part of the part~al condenser 2 at a temperature of 180C. This apparatus is operated at the same pressure as the reaction vessel, the heat being carried off in the ~scket by 6-bar steam.
The liquid leaving the tubes ~through pipe 8) consists of 2.7 kg/s C02, 2.08 kg/s NH3 and 1.86 kg/s H20.
The mixture of gases drawn in by the blower (composed of gas from pipe 6 and gas not condensed in condenser 2) has a temperature of 165C and contains 136.83 kg/s C02, 40.09 kg/s and 3.2 kg/s H2O, this being returned to reaction vessel 1 through pipe 7. The melt leaving the reaction vessel through pipe 9 consists of the following mixtures:
5.78 kg/s urea, 0.43 kg-~s- C02, 2.14 kg/s NH3 and 0.28 kg/s ~ O.
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.
This mixture is split up by a work-up unit 12, known in the art, the urea being drawn off through pipe 13, while the other constituents are introduced into the gas circuit (through pipe 5~ into pipe 4~
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-10 6. All the compounds in the liquid phase can be decomposed into ~ and CO2. Thus it is possible, at a relatively low reaceor pressure and low biuret content, to employ a high temperature. In this manner, a high reaction ~peed is achieved, a small reactor can be utilized and a ~all C2 compressor output is requiret.
The figure illustrates, in schematic representation, typical flow diagram of a preferred embodiment of the present invention. As is apparent from the figure the apparatus consists of horizontally disposed reaction vessel 1, vertical ! 20 partial condenser 2, gas circulating blower 3, urea work-up unlt 12, separsting unit 10 and piping (represented by connecting lines and arrows) belonging to the system.
The mode of operation of this process is as follows:
The water-saturated gas leaves reaction vessel 1 and reaches partial condenser 2 at its lower end via a short pipe 4, which ~8 hydrodjnamically well designed. Together with the constituents flowing in from pipe 5 and hereinafter descri~ed, the mixture of gases is conveyed upwardly through the condenser tubes, being . .. . . . . . . . -:. - . . . .
-1()4U'~i5 partially condensed as the temperature falls in the direction of flow. The ascending saturated vapor is consequently conveyed in counter-current relationship to the film of condensate trickling down the walls, the condensate accumulating at the lower end of the condenser 2 surprisingly showing a very high concentration of water. This condensate also contains carbamate. The water is separated in separating unit 10 and drawn of f via the pipe 11. The gaseous carbamate mixture is conveyed into the condenser 2 via the pipe 6. The uncondensed vapor now low in water is drawn in by the circulating blower 3 and introduced tangentially into the urea melt at a plurality of points at the periphery of the reaction vessel 1 via the pipe 7. By momentum exchange between the gas and the liquid, the latter is kept in rotary movement, in such manner, in fact, that in the interior of the reaction vessel 1 there is formed a ring of liquid from the hollow space of which the saturated vapor mixture is drawn off towards the partial con-denser 2. The gas circuit described is thereby closed. From the reaction vessel 1, the urea is conveyed together with CO2, 20 NH3 and H20 via the pipe 9 into the work-up unit 12 and is separated therein in known manner, the urea being drawn off through the pipe 13 and the other constituents flowing into the gas circuit through pipe 5 into pipe 4.
The reaction vessel 1 is preferably placed in a horizontal position. As is apparent from the foregoing, it is desirable to bring the gas entering the reaction vessel and low in water into intensive contact with the urea melt in order to saturate the gas with as much water as possible.
This operation could be suitably carried out in a vertical bubble column. In order to keep investment costs low, pressure apparatus of small diameter is preferred. For a given : : .
~ ' ~ ' . .
l~lt~
residence-time, however, the bubble-dolumn reaction vessel and, consequently, the static liquid pressure acting on the bottom of the reaction vessel, becomes high. This static and very important liquid pressure must be supplied, in addition to the other pressure losses occurring in the cir-culating system, by the circulating blower 3, whereby its energy requirements increase markedly. Due to the horizontal reaction vessel with the melt revolving at above-critical speed, a liquid ring is obtained. If this ring is developed, then there is obtained, together with the length of reaction vessel in accordance with the above residence-time, a layer of liquid with a considerable base area and of small height or depth. The area increases with increasing length of the reaction vessel. In accordance with the small layer height (ring thickness), the feed or charging of this layer with gas requires a comparatively small energy consumption. The large reaction vessel surface (base area) may have a large number ~-`
of tangentially drilled holes through which the melt is intensively charged with gas in consequence of the large area of the bubbles formed. This arrangement consequently avoids - high energy requirements by the circulating blower 3 with low investment costs for the reaction vessel 1. At the same time, an equal residence-time and an equally intensive exchange of substances is ensured in comparison with a bubble column. The advantage achieved in this way is decisive for the economy of the method, since the circulating mass of gas for an average 500 tons per day plant, is, for example, 650 tons per hour. Another advantage of the method is that the heat liberated by the partial liquefaction of the gas can be ~
30 used for generating 6-bar steam. ~ ~ -Examples 1-4 hereafter are batchwise experiments in . . - . , .
- . - - . : : , . ~ ................................. .
- . : ~ ' .
lS
which an NH3/CO2 molar ratio of 2:1 was employed. The ratio of water and urea introduced to the autoclave to the volume of the reactor was 530 kg/m3. The mole ratio of H20 : CO2 was varied between 0.5 Example 1 H20/co2 mole ratio = 1 Temperature = 160C.
The H20/CO2 mole ratio refers to the liquid and the gaseous phase. The experiments were carried through isochorically.
~ith these parameters the following results are obtained:
Pressure = 85 bar Composition of liquids (w' = percentage by weight):
w' = 37.8 w' = 25.4 w' = 24.8 w' = 11.3 w' = ~.7 Urea NH3 C02 H2o Biuret Composition of gases (w" = percentage by weight):
w" = 1~.8 w" = 78.7 w" = 2.5 Urea conversion in the melt relative to CO2 = 60.4%.
Example 2 H20/Co2 mole ratio = 1 Temperature = 170C.
Pressure = 120 bar Composition of liquids (w' = percentage by weight):
w' = 40.7 w' = 23.3 w' = 23.1 w' = 11.5 w' = 1.4 Urea NH3 CO2 H2o Biuret Composition of gases (w" = percentage by weight):
w" = 18.1 w" = 77.1 w" = 4.80 Urea conversion in the melt relative to CO2 = 63.8%.
Example 3 H20/CO2 mole ratio = 0.63 Temperature = 170C
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- - ~ : - -. .
-With these parameters the following results are obtained:
Pressure = 108 bar Composition of liquids (w' = percentage by weight~:
w' = 55.3 w' = 23.7 w' = 16.8 w' = 2.5 w' = 1.7 Urea NH3 C02 H2o Biuret Composition o~ gases (w" = percentage by weight):
w" = 23.1 w" = 72.0 w" = 4.9 Urea conversion in the melt relative to C02 = 76.7%.
Example 4 H20/Co2 mole ratio = 0.63 Temperature = 180C
With these parameters the following results are obtained:
Pressure = 127.5 bar Composition of liquids (w' = percentage by weight):
w' = 64.6 w' = 24.8 w' = 5.0 w' = 3.3 w' = 2.3 Urea NH3 C02 H2o Biuret Composition of gases (w" = percentage by weight):
w" = 21.2 w" = 76.2 w" = 2.6 Urea conversion in the melt relative to CO2 = 92.8%. ~ -,- - - -, : ' , - ', ' - '; ;, ' , : - . . . .
:~ -~ _i . :
Example 5 ~ 5 This Example illustrates the continuous operation of the present invention. Reference to the apparatus corresponds to the figure.
For an output of 500 tons of urea per day, reaction vessel 1 i8 fed with 4.24 kg/s CO2 and 3.28 kg/s ~H3.
The pressure in the reaction vessel is 125 bars and the temperature is adjusted to 180C. The gas circulates in the circu~t 1-4-2-3-7. The gas leaving the reaction vessel through pipe 4 consists of 136.4 kg/s C02, 37.95 kg/s NH3 and 4.65 kg/s ~ O.
When this gas stream is combined with the constituents coming from the urea work-up unit by way of pipe 5, 136.83 kg/s C2 J 40.09 kg/s NH3 and 4.93 kg/s H20 enter the lower part of the part~al condenser 2 at a temperature of 180C. This apparatus is operated at the same pressure as the reaction vessel, the heat being carried off in the ~scket by 6-bar steam.
The liquid leaving the tubes ~through pipe 8) consists of 2.7 kg/s C02, 2.08 kg/s NH3 and 1.86 kg/s H20.
The mixture of gases drawn in by the blower (composed of gas from pipe 6 and gas not condensed in condenser 2) has a temperature of 165C and contains 136.83 kg/s C02, 40.09 kg/s and 3.2 kg/s H2O, this being returned to reaction vessel 1 through pipe 7. The melt leaving the reaction vessel through pipe 9 consists of the following mixtures:
5.78 kg/s urea, 0.43 kg-~s- C02, 2.14 kg/s NH3 and 0.28 kg/s ~ O.
i~ .
.
.
This mixture is split up by a work-up unit 12, known in the art, the urea being drawn off through pipe 13, while the other constituents are introduced into the gas circuit (through pipe 5~ into pipe 4~
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Claims (10)
- The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
l. In a process for preparing urea in which ammonia and carbon dioxide are reacted in a reactor at a temperature of at least 160°C. and an elevated pressure to produce a urea melt, the improvement which comprises withdrawing at least part of the gases present in the reactor, removing water from the gases, and recycling the dried gases to the reactor, thereby maintaining a low concentration of water in the reactor. - 2. The process of claim l in which the concentration of water in the reactor is such that the mole ratio of water in the melt to urea in the melt is less than l.
- 3. The process of claim 2 in which the temperature is 170-200°C.
- 4. The process of claim 2 in which the mole ratio of new ammonia to new carbon dioxide is about 2:1.
- 5. The process of claim 3 in which the mole ratio of new ammonia to new carbon dioxide is about 2:1.
- 6. The process of claim 1 in which the gases withdrawn from the reactor are passed into a partial condenser, the least part of the water contained in the gases is removed in the condenser, thereby producing a partially dried gas stream, and the dried gas stream is returned to the reactor.
- 7. The process of claim 6 in which the gases pass through the condenser in counter-current relationship to the water removed from the gases.
- 8. The process of claim 6 in which the gases in the condenser are at about the same pressure as the pressure in the reactor.
- 9. The process of claim 6 in which the reactor has its length in a horizontal position.
- 10. The process of claim 6 in which the dried gas stream is introduced tangentially into the reactor so as to set the urea melt in rotary motion by means of momentum exchange.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CH1317473A CH581612A5 (en) | 1973-09-13 | 1973-09-13 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1040215A true CA1040215A (en) | 1978-10-10 |
Family
ID=4389996
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA209,047A Expired CA1040215A (en) | 1973-09-13 | 1974-09-12 | Method of controlling water content in urea reactions |
Country Status (5)
| Country | Link |
|---|---|
| AT (1) | AT344721B (en) |
| BR (1) | BR7407575D0 (en) |
| CA (1) | CA1040215A (en) |
| CH (1) | CH581612A5 (en) |
| NL (1) | NL7412073A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1989001468A1 (en) * | 1987-08-13 | 1989-02-23 | Austral-Pacific Fertilizers Ltd. | Process for enhanced urea production |
-
1973
- 1973-09-13 CH CH1317473A patent/CH581612A5/xx not_active IP Right Cessation
-
1974
- 1974-04-02 AT AT273774A patent/AT344721B/en not_active IP Right Cessation
- 1974-09-11 BR BR7575/74A patent/BR7407575D0/en unknown
- 1974-09-11 NL NL7412073A patent/NL7412073A/en not_active Application Discontinuation
- 1974-09-12 CA CA209,047A patent/CA1040215A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1989001468A1 (en) * | 1987-08-13 | 1989-02-23 | Austral-Pacific Fertilizers Ltd. | Process for enhanced urea production |
Also Published As
| Publication number | Publication date |
|---|---|
| NL7412073A (en) | 1975-03-17 |
| DE2438685B2 (en) | 1975-12-04 |
| AT344721B (en) | 1978-08-10 |
| BR7407575D0 (en) | 1975-07-08 |
| AU7063474A (en) | 1976-01-08 |
| CH581612A5 (en) | 1976-11-15 |
| DE2438685A1 (en) | 1975-04-10 |
| ATA273774A (en) | 1977-12-15 |
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