RU2792667C2 - Systems and methods for production of ammonium carbamate solution containing equilibrium mixture - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to systems and methods for the production of ammonium carbamate and, more particularly, relates to systems and methods for the production of aqueous ammonium carbamate solutions. A method for the production of an ammonium carbamate solution is proposed, the method includes: provision of a reactor containing an ammonia solution; supply of carbon dioxide to the ammonia solution to form a mixture; combination of a sodium hydroxide solution and the mixture to form ammonium carbamate.

EFFECT: proposed method allows for obtainment of an ammonium carbamate mixture.

9 cl, 7 dwg, 4 tbl, 6 ex

Description

RELATED APPLICATIONS

The present application claims advantage over the U.S. non-provisional application. No. 15/947182 filed April 6, 2018

FIELD OF TECHNOLOGY TO WHICH THE INVENTION RELATES

The present invention generally relates to systems and methods for the production of ammonium carbamate and, more specifically, relates to systems and methods for the production of aqueous solutions of ammonium carbamate.

BACKGROUND OF THE INVENTION

Conventional systems and methods for producing ammonium carbamate are based on the reaction of gaseous mixtures of ammonia, water and carbon dioxide to form solid ammonium carbamate. One conventional system and process for producing ammonium carbamate utilizes a synthesis reaction chamber and introduces ammonia gas and carbon dioxide from opposite ends of the reaction chamber. When the gaseous ammonia and carbon dioxide are distributed throughout the reaction chamber, when the gases interact with each other, a reaction occurs to form solid ammonium carbamate. The solid ammonium carbamate is then removed from the synthesis reaction chamber and delivered to consumers as a solid crude material. Solid ammonium carbamate can then be processed into aqueous solutions of ammonium carbamate for use in various industrial, commercial and agricultural products such as biocides and fertilizer.

The use of solid ammonium carbamate leads to several quality and application concerns. During transportation of solid ammonium carbamate, solid ammonium carbamate is in equilibrium with the atmosphere in which it is located, which leads to partial decomposition of ammonium carbamate, depending on the duration of transportation and temperature. The purity of solid ammonium carbamate can vary, which affects the quality of the resulting aqueous solution. Solid ammonium carbamate releases ammonia gas when used to prepare an aqueous solution, so environmental controls are needed to reduce worker exposure.

Therefore, the development of systems and methods for the production of ammonium carbamate is desirable. In addition, other desirable features and characteristics will become apparent from the following summary and detailed description, as well as the appended claims in conjunction with the accompanying drawings and the preceding description of the technical field to which the invention pertains and the prior art.

SUMMARY OF THE INVENTION

The present invention discloses various non-limiting embodiments of ammonium carbamate solutions and various non-limiting embodiments of systems and methods for their preparation.

One non-limiting embodiment is a process for preparing an ammonium carbamate solution containing an equilibrium mixture. The method includes, but is not limited to, providing a reactor containing an ammonia solution. The method further includes, but is not limited to, supplying carbon dioxide to the ammonia solution to form a mixture. The method further includes, but is not limited to, combining the sodium hydroxide solution and the mixture to form ammonium carbamate.

One non-limiting embodiment is a system for producing an ammonium carbamate solution containing an equilibrium mixture. The system includes, but is not limited to, a reactor having an interior. The reactor includes, but is not limited to, a supply conduit located in the interior. The supply conduit includes, but is not limited to, an inlet and an outlet, wherein the inlet is in fluid communication with the outlet. The outlet channel is located in the interior of the reactor. The system further includes, but is not limited to, an ammonia solution in the interior. The system further includes, but is not limited to, a source of carbon dioxide, including but not limited to carbon dioxide, and is in fluid communication with the inlet. The system further includes, but is not limited to, a source of sodium hydroxide, including but not limited to sodium hydroxide, and is in fluid communication with the reactor. The supply line is configured to receive carbon dioxide from the source of carbon dioxide into the inlet and remove carbon dioxide through the outlet. The carbon dioxide exiting through the outlet port is set to be fed into the ammonia solution during the formation of the ammonium carbamate solution.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the disclosed subject matter will be readily understood as it becomes better understood from the following detailed description when considered in conjunction with the accompanying drawings, which are as follows:

In FIG. 1 is a block diagram illustrating one non-limiting embodiment of a system for producing ammonium carbamate;

In FIG. 2 is a perspective view illustrating a comparative ammonium carbamate solution;

In FIG. 3 is a diagram illustrating experimental data for one non-limiting embodiment of the system shown in FIG. 1;

In FIG. 4 is a diagram illustrating additional experimental data for one non-limiting embodiment of the system shown in FIG. 1;

In FIG. 5 is a diagram illustrating additional experimental data for one non-limiting embodiment of the system shown in FIG. 1;

In FIG. 6 is a diagram illustrating additional experimental data for one non-limiting embodiment of the system shown in FIG. 1; And

In FIG. 7 is a perspective view illustrating a non-limiting embodiment of the ammonium carbamate solutions shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is merely exemplary in nature and is not intended to limit the systems and methods described herein. In addition, it is not intended to be limited to any theory given in the prior art or in the following detailed description.

The present invention relates to an ammonium carbamate solution containing an equilibrium mixture. The ammonium carbamate solution containing the equilibrium mixture includes the reaction product of the ammonia solution, carbon dioxide and sodium hydroxide solution. In some embodiments, the ammonia solution and carbon dioxide react to form a mixture. In these embodiments, the mixture can be combined with sodium hydroxide solution to form ammonium carbamate. In these embodiments, the order in which the ammonia solution, carbon dioxide, and sodium hydroxide solution are added can increase the efficiency of the ammonium carbamate reaction. As one example, if carbon dioxide is introduced into water in the absence of ammonia, carbon dioxide does not solubilize in water due to its low water solubility. As another example, if ammonia and sodium hydroxide are first combined to form a solution, then a higher pH and an increase in the temperature of the solution can cause ammonia gas to be released. In addition, carbon dioxide introduced into this ammonia/sodium hydroxide solution will precipitate carbonates.

The present invention also relates to a process for the production of ammonium carbamate. The process may be a semi-continuous or continuous process. In a semi-batch process, a fixed volume of ammonia at a fixed concentration can be combined with carbon dioxide and sodium hydroxide. In a continuous process, ammonia, carbon dioxide and sodium hydroxide are combined at a controlled flow rate. The method below describes in detail the method for semi-continuous technology; however, a person skilled in the art can easily convert this method to one or more continuous methods.

The use of raw materials used for the production of ammonium carbamate as starting materials and the preparation of a solution containing an equilibrium mixture from these substances requires fewer steps than in conventional methods. In addition, the gas-liquid reaction of the present invention is less exothermic than conventional methods, so that the heat of reaction can be more easily removed. In addition, this gas-liquid reaction can be carried out in conventional reactor equipment and eliminate the need for solids handling. The set of equilibrium reactions below describe the characterization of ammonium carbamate solutions with other species such as ammonium bicarbonate so that the use of a solid carbamate as starting material does not give a solution different from a solution made from the appropriate amounts of ammonia and carbon dioxide.

2NH _{3 (aq)} + CO _{2 (q)} ← → NH ₂ COONH _{4 (aq)}

2NH ₄ HCO _{3 (aq}} ← → (NH ₄ ) ₂ CO _{3 (aq)} + CO _{2 (q}} + H ₂ O

NH ₄ HCO _3(aq) ← → NH _3{aq) + _(q) + Η ₂ O

(NH ₄ ) ₂ CO _3(aq} ← → 2NH _3(aq} + _(q) +

NH ₂ COONH _{4 (aq)} + ← → NH ₄ HCO _{3 (aq)} + NH _{3 (aq)}

Shown in FIG. 1 (shown as a semi-continuous process using system 10), the process includes the steps of providing a reactor 12 containing an ammonia solution. The ammonia solution may include ammonia and a solvent such as water. The ammonia solution may include ammonia in an amount equal to at least about 5 wt. %, alternatively not less than about 7 wt. % or, alternatively, not less than about 10 wt. % in terms of the total weight of the ammonia solution. The ammonia solution may include ammonia in an amount equal to from about 5 to about 50 wt. %, alternatively from about 7 to about 40 wt. % or, alternatively, from about 10 to about 30 wt. % in terms of the total weight of the ammonia solution. In embodiments, the ammonia solution is an aqueous solution containing water in an amount equal to from about 50 to about 95 wt. %, alternatively from about 60 to about 93 wt. % or, alternatively, from about 70 to about 90 wt. % in terms of the total weight of the ammonia solution.

The method further includes the step of supplying carbon dioxide to the ammonia solution to form a mixture. Ammonia solution means an ammonia solution containing at least about 1 wt. %, alternatively not less than about 5 wt. %, alternatively not less than about 10 wt. %, alternatively not less than about 15 wt. % or, alternatively, not less than about 25 wt. % in terms of the total weight of the ammonia solution. As shown in more detail below, the carbon dioxide fed to the reactor 12 has improved interfacial interaction with the ammonia solution. In embodiments, carbon dioxide is supplied to the ammonia solution in an NH ₃ /CO ₂ molar ratio of from about 1.6 to about 2.1, alternatively from about 1.8 to about 2.1, or alternatively from about 2.0 up to about 2.1. In embodiments, the supply of carbon dioxide to reactor 12 is stopped after the desired molar ratio has been established. In embodiments using a semi-continuous process, the carbon dioxide supply step is carried out as quickly as possible, as far as the limitations on heat and mass transfer in the system allow.

In embodiments, the step of supplying carbon dioxide is defined as supplying a plurality of bubbles of carbon dioxide gas to an ammonia solution to form a mixture. It should be understood that a plurality of carbon dioxide gas bubbles may only pass through a portion of the ammonia solution and still be considered fed into the ammonia solution. The method may further include the step of forming a plurality of bubbles having a sufficiently small diameter through a suitable combination of bubbler opening/pore size and agitation conditions. In one embodiment, sufficiently small bubbles were formed using a porous sparger element, the pore size of which was from 2 to 10 microns. A set of bubbles can have a relation

surface area to volume equal to at least about 8100 m ² /m ³ . The plurality of bubbles may have a surface area to volume ratio of from about 8100 to about 60,000,000 m ² /m ³ , alternatively from about 8100 to about 600,000 m ² /m ³ , or alternatively from about 8100 to about 14,000 m ² /m ³ . In embodiments, smaller diameter pores result in the formation of smaller diameter bubbles with a higher surface area to volume ratio, which enhances the interfacial interaction of the carbon dioxide gas and the ammonia solution. A more significant interfacial interaction of gaseous carbon dioxide and ammonia solution can increase the rate of dissolution of carbon dioxide in the ammonia solution and thereby improve the kinetics of the reaction of carbon dioxide and ammonia. Conversely, bubbles with a reduced surface area to volume ratio can pass through the ammonia solution too quickly and remove ammonia vapor from the ammonia solution, thereby leading to deposits on dry surfaces of the reactor 12 (eg, in the headspace). The plurality of bubbles may include carbon dioxide in an amount equal to at least about 50 vol. %, alternatively not less than about 75 vol. % or alternatively not less than about 90 vol. % based on the total volume of the plurality of bubbles. Many bubbles may include carbon dioxide in an amount equal to about 50 to 100 vol. %, alternatively from about 75 to 100 vol. % or, alternatively, from about 90 to 100 vol. % based on the total volume of the plurality of bubbles. In embodiments, the carbon dioxide is pure carbon dioxide supplied as a liquid and then vaporized to form a gas prior to being used to form ammonium carbamate.

The method further includes the step of combining the sodium hydroxide solution and the mixture to form ammonium carbamate. In embodiments, the sodium hydroxide solution is combined with the mixture at a weight ratio of sodium hydroxide to carbon dioxide weight of from about 0.54 to about 0.91, alternatively from about 0.64 to about 0.83, or alternatively from about 0, 64 to about 0.74. In embodiments, the sodium hydroxide solution is an aqueous solution containing water.

The step of combining the sodium hydroxide solution and the mixture is carried out after the ammonia solution has established an NH ₃ /CO ₂ molar ratio of from about 1.6 to about 2.1, alternatively from about 1.8 to about 2.1, or alternatively , from about 2.0 to about 2.1.

The ammonium carbamate solution containing the equilibrium mixture may include ammonium carbamate and a solvent such as water. The solution containing the equilibrium mixture may include ammonium carbamate (formed from ammonia and carbon dioxide) in an amount equal to at least about 15 wt. %, alternatively not less than about 17 wt. % or, alternatively, not less than about 19 wt. % in terms of the total weight of the solution containing the equilibrium mixture. The solution containing the equilibrium mixture may include ammonium carbamate (formed from ammonia and carbon dioxide) in an amount equal to from about 15 to about 50 wt. %, alternatively from about 17 to about 40 wt. % or, alternatively, from about 19 to about 30 wt. % in terms of the total weight of the solution containing the equilibrium mixture. It should be understood that the equilibrated solution is in equilibrium and thus ammonium carbamate is present in an amount of at least about 15% by weight at one point in time, but may be present in a different amount at another point in time.

The ammonium carbamate solution containing the equilibrium mixture may have a pH of at least about 9.2, alternatively at least about 10.4, or alternatively at least about 10.6. The equilibrated solution may have a pH of from about 9.2 to about 11.0, alternatively from about 10.4 to about 11.0, or alternatively from about 10.6 to about 10.8. The pH value of the solution containing the equilibrium mixture can be used to determine the compounds in equilibrium that are in the solution containing the equilibrium mixture. In embodiments, an increase in the amount of sodium hydroxide used to produce ammonium carbamate results in an increase in the pH of the solution containing the equilibrium mixture.

The equilibrated ammonium carbamate solution may have an electrical conductivity at 25°C of at least about 75 mS/cm, alternatively at least about 86 mS/cm, or alternatively at least about 97 mS/cm. The solution containing the equilibrium mixture may have an electrical conductivity at 25°C of from about 75 mS/cm to about 160 mS/cm, alternatively from about 86 mS/cm to about 109 mS/cm, or alternatively from about 97 mS/cm to approximately 100 mS/cm. The electrical conductivity of a solution containing an equilibrium mixture can also be used to determine the compounds in equilibrium contained in an ammonium carbamate solution.

The ammonium carbamate solution containing the equilibrium mixture may have a nitrogen content of at least about 47,200 ppm, alternatively at least about 53,500 ppm, or alternatively at least about 59,700 ppm. The equilibrium mixture containing solution may have a nitrogen content of from about 47,200 ppm to about 184,000 ppm, alternatively from about 53,500 ppm to about 147,000 ppm, or alternatively from about 59,700 ppm. ppm to about 111,000 ppm

In some embodiments, the method further includes the step of monitoring the amount of carbon dioxide supplied to the ammonia solution. In embodiments, data obtained during monitoring of the amount of carbon dioxide supplied to the ammonia solution can be used to improve control of the amount of carbon dioxide supplied to the ammonia solution. The step of monitoring the amount of carbon dioxide includes one or more of the following steps: determining the pH of the mixture, determining the electrical conductivity of the mixture, and determining the temperature of the mixture. In other embodiments, a carbon dioxide mass flow controller can be used to determine the amount of carbon dioxide fed to the ammonia solution.

In one embodiment, the pH is used to determine the amount of carbon dioxide fed into the ammonia solution. pH measurement can be done with a calibrated online probe immersed in the reaction mixture, or samples can be taken from the reactor and examined with a calibrated benchtop pH meter. As the molar ratio of NH ₃ /CO ₂ decreases, for example, from about 3:1 to about 1.5:1, the pH of the mixture can decrease, for example, from a pH of about 10.4 at 25°C to a pH of about 9.2 at 25°C, respectively.

In another embodiment, the electrical conductivity is used to determine the amount of carbon dioxide supplied to the ammonia solution. A calibrated online conductivity probe immersed in the reaction mixture can be used to determine the current conductivity value, or a sample can be taken from the reactor and examined using a benchtop conductivity meter. By decreasing the molar ratio of NH ₃ /CO ₂ , for example, from about 3:1 to about 1.5:1, the electrical conductivity of the mixture can increase, for example, from about 115 millisiemens per cm (mS/cm) at 25°C to about 170 mS/cm at 25°C, respectively.

In another embodiment, an energy balance is used to determine the amount of carbon dioxide supplied to the ammonia solution. The reaction of carbon dioxide and ammonia is exothermic; therefore, the heat released during the reaction can be an indicator of the amount of carbon dioxide that has reacted with ammonia, and thus characterize the molar ratio of NH ₃ /CO ₂ . A real-time measurement of the reaction temperature, together with a real-time measurement of the rate of heat removal through the shell and/or external heat exchanger, can be used to determine the amount of carbon dioxide that has reacted with ammonia.

In some embodiments, the process for producing ammonium carbamate may be an isothermal process. This isothermal process can take place in a range of different temperatures, and during the process, the temperature of the mixture is maintained at a predetermined temperature of 15°C to 55°C, at normal or elevated pressure. In other embodiments, the process for producing ammonium carbamate may be a semi-adiabatic process. This semi-adiabatic process can proceed in a mixture starting at a temperature of only 15°C and increasing to about 55°C. The heat released during the process can be removed from the mixture using a jacket or by circulating the mixture through a heat exchanger. Although 55° C. is specified as the maximum operating temperature in the present invention, one skilled in the art can operate at higher temperatures and pressures while minimizing NH ₃ losses to the reactor headspace.

The present invention also relates to a system 10 for the production of ammonium carbamate. As indicated above, in FIG. 1 is a block diagram illustrating one non-limiting embodiment of a system 10 for producing ammonium carbamate. The system 10 includes a reactor 12. The reactor 12 has an internal part 14. The reactor 12 includes a supply line 16 located in the internal part 14. The supply line 16 includes an inlet 18 and an outlet 20, the inlet 18 being in fluid communication with the outlet 20 The outlet 20 is located in the interior 14 of the reactor 12. The system 10 further includes an ammonia solution located in the interior 14. The system 10 further includes a source of carbon dioxide 22 containing carbon dioxide and is in fluid communication with the inlet 18. System 10 further includes a sodium hydroxide source 24 containing sodium hydroxide and is in fluid communication with the reactor 12. Feed conduit 16 is configured to receive carbon dioxide from the carbon dioxide source 22 into inlet 18 and withdraw carbon dioxide through outlet 20. Carbon dioxide , output through the outlet channel 20, is set to feed into p ammonia solution during the formation of ammonium carbamate.

The reactor 12 includes a reaction region 26 and a headspace 28 adjacent to the reaction region 26, where the headspace 28 during formation of ammonium carbamate is substantially free of ammonium carbamate and other ammonium salts. The expression "essentially does not contain" when used in the present invention means that the area of headspace above the product 28 contains less than about 5 wt. %, alternatively less than about 1 wt. % or, alternatively, less than about 0.1 wt. % based on total volume (w/v %) headspace 28. As shown above, bubbles or droplets containing carbon dioxide and having a reduced surface area to volume ratio can pass through the ammonia solution too quickly and remove ammonia vapor from the ammonia solution, thereby leading to the formation of deposits on the dry surfaces of the reactor 12 (for example, in the headspace above the product). Therefore, in embodiments, the formation of ammonium carbamate in the headspace region 28 is minimized or prevented by proper dissolution of carbon dioxide in the ammonia solution.

In various embodiments, when the ammonium carbamate is formed, the outlet 20 is immersed in an ammonia solution. One skilled in the art of multiphase mixing can optimize by using a mixer and/or sparger to ensure that the carbon dioxide is dissolved in the ammonia solution. The outlet 20 may have a plurality of holes and carbon dioxide may be discharged through the plurality of holes. The plurality of holes can be configured to form bubbles of carbon dioxide or droplets of carbon dioxide as the carbon dioxide passes through the plurality of holes. Each of the plurality of holes may have a diameter of no greater than about 60 microns, alternatively no greater than about 30 microns, or alternatively no greater than about 10 microns. Each of the plurality of holes may have a diameter of from about 1 to about 60 microns, alternatively from about 2 to about 30 microns, or alternatively from about 2 to about 10 microns.

In various embodiments, system 10 includes a water source 32 containing water, such as deionized or softened water. System 10 may further include an ammonia source 34 containing ammonia. System 10 may further include a heat exchanger 36 to remove heat from reactor 12. System 10 may further include a gas absorber 38 to minimize the release of gases to the environment.

The ammonium carbamate solution, system for its production or process for its production can be used in various applications, including, but not limited to, the formation of biocides and the synthesis of urea.

While at least one exemplary embodiment has been presented in the foregoing detailed description of the present invention, it should be understood that a large number of variations exist. It should also be understood that the exemplary embodiment or exemplary embodiments are only examples and are not intended to limit the scope, applicability, or configuration of the present invention in any way. Rather, the foregoing detailed description provides those skilled in the art with a convenient roadmap for implementing an exemplary embodiment of the present invention. It should be understood that without departing from the scope of the present invention as set forth in the appended claims, various changes may be made to the function and arrangement of the elements described in the exemplary embodiment.

EXAMPLES

Example 1 Possible Compositions of Typical Equilibrium Mixed Ammonium Carbamate Solutions

Possible compositions of typical ammonium carbamate solutions containing an equilibrium mixture can be prepared as follows. The ammonia solution is diluted to about 12 wt. % in a reaction vessel with cooling devices. Carbon dioxide is fed in for some time and a final NH ₃ /CO ₂ molar ratio of about 2 is obtained. Ammonia and NaOH can be used in different concentrations and the amount of water is adjusted accordingly. When using 25 wt. % ammonia solution and 50 wt. % NaOH solution in a vessel, mix 35.96-39.38 parts of water and 34.03-35.05 parts of ammonia solution at ambient temperature. This can be done with or without refrigeration.

Carbon dioxide is fed into the mixture such that the ratio of moles of ammonia to moles of carbon dioxide is between 2.00 and 2.06 (10.99 parts being a typical feed value). Carbon dioxide reacts with ammonia in solution to form ammonium carbamate. The feed may be carried out outside of the vessel, or may be conducted into the recirculation circuit of the vessel. The vessel can be used at atmospheric pressure or under pressure. When carbon dioxide is added, the mixture is cooled while maintaining the temperature below 60°C, since heat is released during the reaction.

Then 15.60 to 18.00 parts of 50% NaOH solution are slowly added to the mixture to achieve the desired pH and electrical conductivity. While the NaOH solution is being added, the mixture is cooled to keep the temperature below 60° C., since heat is released when the NaOH is dissolved. Possible compositions are shown below in table 1.

Example 2 Typical Equilibrium Mixed Ammonium Carbamate Solutions Showing Minimal Performance Differences Between Multiple Batches

Typical equilibrated ammonium carbamate solutions (E1-E5) were prepared as follows. For each solution, a jacketed 12 L glass jar was fitted with a Mott Series 850 Porous (part number 850-3/4-06) porous tube assembly to supply carbon dioxide. The porous pipe block had 10 µm pores. Carbon dioxide was supplied from a gas bottle and the flow rate was controlled by a mass flow controller. 3.54 kg of 28.4 wt. % aqueous ammonia solution and 4.673 kg of deionized water. The reactor was sealed with the exception of one pipe, which was connected to the block of porous tube and the outlet pipe, which went to the bubbler. Carbon dioxide was supplied for 3 hours through the porous tube block and the temperature was maintained at about 36°C during the run. After 3 hours, the reactor was cooled to 25°C and 1.846 kg of 50.1 wt. % sodium hydroxide solution when cooled to maintain a temperature of 25°C. The similarity of characteristics of typical batches of ammonium carbamate solutions containing an equilibrium mixture (E1-E5) was investigated and the results are shown in Table 2 below.

After 24 hours, E1 had a pH of 10.7, an electrical conductivity of 99.7 mS/cm and a measured total nitrogen content of 69,000 ppm. The characteristics of similar batches (E2-E5) were very close and gave a similar product. The closeness of the measured values of the total nitrogen content, electrical conductivity and pH shows that there is a liquid-vapor equilibrium in which ammonia is not removed from the solution and carbon dioxide is completely absorbed by the ammonia solution.

Example 3 Comparative Ammonium Carbamate Solution Leads to Formation of Solids in the Headspace Region of the Reactor Product Due to Large Carbon Dioxide Bubbles

A comparative ammonium carbamate solution (C1) was prepared in a 1 L reactor according to the ammonium carbamate solution prepared in Example 1, with the difference that the pore size of the bubbler element was larger and therefore bubbles were formed having a lower surface area to volume ratio (t .e. bubbles were larger).

Larger bubbles passed through the ammonia solution and fell into the free space above the product until complete dissolution. As shown in FIG. 2, solids, including ammonium carbamate, formed on the walls of the reactor in the headspace above the product. The electrical conductivity of the comparative solution of ammonium carbamate (C1) after 24 hours was only 94.7 mS/cm at 25°C.

Example 4 Comparative Ammonium Carbamate Solution Leads to Formation of Solids in the Headspace Region of the Reactor Due to Ingress of Carbon Dioxide into the Headspace Region of the Reactor

A reference solution of ammonium carbamate (C2) was prepared in a 1 L reactor according to the ammonium carbamate solution prepared in Example 1, with the difference that carbon dioxide was supplied to the headspace region of the reactor product and not to the ammonia solution (i.e. . purged). Then the sodium hydroxide solution was fed into the reactor.

Headspace carbon dioxide readily dissolves in aqueous ammonia as measured by pressure and calorimetry (not shown). However, solids were formed on the reactor walls in the headspace region, including ammonium carbamate and other ammonium salts. The electrical conductivity of the comparative solution of ammonium carbamate (C2) after 24 hours was only 88.5 mS/cm at 25°C.

Example 5 Characteristics of Typical Mixtures Formed from Ammonia and Carbon Dioxide Solutions

Representative mixtures (E6-E25) formed from solutions of ammonia and carbon dioxide were prepared as follows. A series of isothermal reactions were carried out in which carbon dioxide was gradually introduced through a porous tube block into an ammonia solution containing 12.15 wt. % ammonia. The measured pH and electrical conductivity values for the reaction mixtures at four NH ₃ /CO ₂ molar ratios are shown in Table 3 and shown in FIG. 3 and FIG. 4. The values of electrical conductivity and pH are given in table 3 for solutions after adding carbon dioxide to the ammonia solution, but before adding the sodium hydroxide solution to obtain the final product.

As shown in Table 3, the electrical conductivity of typical mixtures increases with decreasing NH ₃ /CO ₂ molar ratio and the pH values of typical mixtures decrease with decreasing NH ₃ /CO ₂ molar ratio. The data show that measurements of temperature, pH and electrical conductivity can be used to check the amount of carbon dioxide fed into the reactor. Such predictable measurement data is provided by supplying CO ₂ to the reactor in the form of fine bubbles and preventing CO ₂ and NH ₃ vapors from escaping from the mixture.

Example 6 Characteristics of Typical Equilibrium Mixed Ammonium Carbamate Solutions

Typical equilibrated ammonium carbamate solutions (E26-E45) were prepared as follows. Spent a series of four reactions at 35°C, in which carbon dioxide was gradually filed through a porous tube block in an ammonia solution containing 12.15 wt. % ammonia. The reactions were carried out at different molar ratios of NH ₃ /CO ₂ . After the addition of carbon dioxide, the batch was divided into four portions and various amounts of sodium hydroxide were added to the portions along with an appropriate amount of water to ensure the same solids content in the sample. The electrical conductivity and pH were determined as a function of the NH ₃ /CO ₂ molar ratio and the amount of sodium hydroxide added, the data are shown in Table 4 and presented in FIG. 5 and 6. Frost resistance was determined from the results of storage of selected representative solutions containing an equilibrium mixture of ammonium carbamate solutions (E26, E30, E34, E38 and E42) at -10°C for 3 days. In FIG. 7 shows an image of an ammonium carbamate solution containing an equilibrium mixture after 3 days. Vessels were inverted before imaging.

As shown in Table 4, the electrical conductivities of typical ammonium carbamate solutions containing an equilibrium mixture increase with decreasing NH ₃ /CO ₂ molar ratio and decrease with increasing NaOH content. The pH values of typical ammonium carbamate solutions containing an equilibrium mixture decrease with decreasing NH ₃ /CO ₂ molar ratio and increase with increasing NaOH content. In other words, the electrical conductivities of typical ammonium carbamate solutions containing an equilibrium mixture increase with decreasing NH ₃ /CO ₂ molar ratio and with decreasing NaOH content.

Shown in FIG. 7 typical solutions containing an equilibrium mixture of ammonium carbamate containing 7 wt. % NaOH, have improved frost resistance compared to typical solutions containing an equilibrium mixture of ammonium carbamate containing 9 wt. % NaOH.

Claims (16)

1. A method for obtaining an ammonium carbamate solution, the method includes: providing a reactor containing an ammonia solution; feeding carbon dioxide into the ammonia solution to form a mixture; And combining the sodium hydroxide solution and the mixture to form ammonium carbamate. 2. The method of claim 1, wherein the step of supplying carbon dioxide is further defined as supplying a plurality of bubbles containing carbon dioxide gas to an ammonia solution to form a mixture with a plurality of bubbles containing carbon dioxide in an amount of at least 50% by volume. in terms of the total volume of a plurality of bubbles. 3. The method of claim 2, further comprising the step of forming a plurality of bubbles having a surface area to volume ratio of at least 8100 m ² /m ³ . 4. The method according to any one of paragraphs. 1-3, further comprising the step of monitoring the amount of carbon dioxide supplied to the ammonia solution. 5. The method according to any one of paragraphs. 1-4, in which the ammonium carbamate solution contains ammonium carbamate in an amount equal to at least 15 wt.% in terms of the total weight of the ammonium carbamate solution. 6. The method according to any one of paragraphs. 1-5, in which the ammonia solution contains ammonia in an amount equal to at least 5 wt.%. 7. The method according to any one of paragraphs. 1-6, further comprising the step of combining water and ammonia solution to the step of supplying carbon dioxide. 8. The method according to paragraphs. 1-6, in which the step of combining the sodium hydroxide solution and the mixture is carried out after carbon dioxide is supplied to the ammonia solution. 9. The method according to any one of paragraphs. 1-8, in which: the ammonium carbamate solution has a pH value of at least 9.2; ammonium carbamate solution has an electrical conductivity of at least 75 mS/cm; the ammonium carbamate solution has a nitrogen content of at least 47,200 ppm; or their combinations.

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