Methods and systems for isolating nitrogen from a gaseous mixture

Disclosed herein are methods and systems to isolate nitrogen from a mixture of gases. In an embodiment, a method of isolating nitrogen from a gaseous mixture involves contacting the gaseous mixture with a superparamagnetic catalyst to form a reaction mixture, and exposing the reaction mixture to a fluctuating magnetic field at ambient conditions.

RELATED APPLICATION

This application is a U.S. national stage filing under 35 U.S.C § 371 of International Application No. PCT/US2015/040285 filed on Jul. 14, 2015 entitled “METHODS AND SYSTEMS FOR ISOLATING NITROGEN FROM A GASEOUS MIXTURE,” which claims priority to Indian Patent Application No. 3474/CHE/2014, filed Jul. 14, 2014, entitled, “Methods and Systems for Isolating Nitrogen from a Gaseous Mixture,” the contents of each of which are herein incorporated by reference in their entireties.

BACKGROUND

Nitrogen is frequently prepared by the fractional distillation of liquid air or by pressure swing adsorption (PSA) from atmospheric air. In the synthesis of nitrogen by PSA, the feed air is compressed and/or a vacuum pump is employed for reduction of bed pressure. Nitrogen recovery by PSA is rather low (40-50%) and the mechanical power required is very high. In the air fractionation process, likewise, the feed air needs to be compressed (to about 100 psi) and cooled prior to distillation. Therefore, it is relatively expensive to isolate nitrogen by this method.

SUMMARY

Disclosed herein are methods and systems to purify nitrogen from a mixture of gases. In an embodiment, a method of isolating nitrogen from a gaseous mixture involves contacting the gaseous mixture with a superparamagnetic catalyst to form a reaction mixture, and exposing the reaction mixture to a fluctuating magnetic field.

In an additional embodiment, a method of making a catalyst involves contacting a paramagnetic oxide, cerium (IV) oxide, and a base. In some embodiments, the catalyst may be FeCe2O4nanoparticles.

In a further embodiment, a reactor system for isolating nitrogen from a gaseous mixture includes a closed reaction vessel configured to receive a gaseous mixture and a superparamagnetic catalyst, and at least one current carrying element arranged in proximity to a surface of the reaction vessel to provide a fluctuating magnetic field.

DETAILED DESCRIPTION

Disclosed herein are methods and systems for isolating or purifying nitrogen from a mixture of gases. In some embodiments, a method of isolating nitrogen from a gaseous mixture involves contacting the gaseous mixture with a superparamagnetic catalyst to form a reaction mixture, and exposing the reaction mixture to a fluctuating magnetic field at ambient conditions. The gaseous mixture may be air, flue gas, natural gas, or any combination thereof. In some embodiments, the gaseous mixture includes nitrogen, hydrogen, oxygen, carbon dioxide, or any combination thereof. In other embodiments, the gaseous mixture may be compressed air.

FIG. 1depicts an illustrative diagram of a reactor system100in accordance with an embodiment of the present disclosure. System100may be utilized for a one-step process for isolating nitrogen from air. The reactor system (or apparatus)100generally comprises a reaction vessel101, an inlet valve for gaseous mixture102, an outlet valve for nitrogen103, and a current carrying element104. Further, the catalyst FeCe2O4105may be disposed within the reaction vessel.

In some embodiments, the reactor system100comprises at least one current carrying element104arranged in proximity to a surface of the reaction vessel and configured to provide a fluctuating magnetic field. Current carrying elements may be configured to generate magnetic fields of various strengths. The greater the current flow and coil density, the stronger the magnetic field. For instance, coil density may be high in order to produce a uniform magnetic field. In addition, the quantity of power required to achieve a particular magnetic field may depend on various factors, including the scale, structure, and location of the current carrying element with respect to the reaction vessel.

In other embodiments, the reactor system described herein may further comprise a thermoelectric couple, a pressure gauge, a temperature controller, a cooling system, a mechanical stirrer, or any combination thereof. In some embodiments, the current carrying element may be in close proximity to the reaction vessel. In other embodiments, the current carrying element may form a circular coil around a reaction vessel, as illustrated inFIG. 1. According to some embodiments, the strength of a magnetic field generated by the current carrying element may be about 0.1 millitesla to about 1 tesla, about 0.1 millitesla to about 0.5 tesla, about 0.1 millitesla to about 0.1 tesla, about 0.1 millitesla to about 10 millitesla, about 0.1 millitesla to about 1 millitesla, or any range between any two of these values (including endpoints). The current carrying elements may be energized using various methods, including, without limitation, direct current, alternating current, and high-frequency alternating current. According to embodiments, the high-frequency alternating current may be about 25 hertz (Hz) to about 1 megahertz, about 25 hertz to about 500 kilohertz, or about 25 hertz to about 100 kilohertz. Specific examples include, but are not limited to, about 25 hertz, about 100 hertz, about 500 hertz, about 1 kilohertz, about 300 kilohertz, about 400 kilohertz, about 500 kilohertz, and about 1 megahertz, or any range between any two of these values (including endpoints). In some embodiments, the electric current may be in the range of about 0.1 ampere (A) to about 100 A, about 0.1 ampere to about 50 A, about 0.1 ampere to about 30 A, or about 0.1 ampere to about 1 A. Specific examples include, but are not limited to, about 0.1 A, about 5 A, about 10 A, about 20 A, about 50 A, and about 100 A, or any range between any two of these values (including endpoints).

The reactor system described herein may be a batch reactor system or a continuous flow reactor system. In some embodiments, the reaction vessel may be configured to maintain a constant pressure of gaseous mixture during the reaction process. For example, the gaseous mixture may be present at a pressure of about 0.5 atmosphere to about 1.5 atmospheres, about 0.5 atmosphere to about 1 atmosphere, or about 0.5 atmosphere to about 0.75 atmosphere. Specific examples include about 0.5 atmosphere, about 0.75 atmosphere, about 1 atmosphere, about 1.25 atmospheres, and about 1.5 atmospheres, or any range between any two of these values (including endpoints).

The catalyst105that may be used in the reaction system100may be a superparamagnetic catalyst, such as FeCe2O4, NiCe2O4, or CoCe2O4, or any combination thereof. In some embodiments, the catalyst may be in the form of nanoparticles. The catalyst described in the embodiments herein may be unsupported or may be supported over a surface of a support in a manner that maximizes the surface area of the catalytic reaction. A suitable support may be selected from any conventional support, such as polymer membrane or a porous aerogel. For example, the catalyst may be coated on a polymer membrane and woven into a 3D mesh and introduced in the reactor system100.

In some embodiments, the catalyst described herein may be present in the reaction mixture at about 0.1 mole percent to about 1 mole percent, about 0.1 mole percent to about 0.5 mole percent, or about 0.1 mole percent to about 0.2 mole percent of the total reaction mixture. Specific examples include, but are not limited to, about 0.1 mole percent, about 0.2 mole percent, about 0.3 mole percent, about 0.4 mole percent, about 0.5 mole percent, about 0.6 mole percent, about 0.7 mole percent, about 0.8 mole percent, about 0.9 mole percent and about 1 mole percent, or any range between any two of these values (including endpoints).

In some embodiments, the reaction mixture is exposed to a fluctuating magnetic field for about 30 minutes to about 3 hours. In some embodiments, the reaction mixture is exposed to a fluctuating magnetic field for about 30 minutes to about 2 hours. In some embodiments, the fluctuating magnetic field is applied for about 30 minutes to about 1 hour. In some embodiments, the reaction mixture is exposed to the fluctuating magnetic field for about 30 minutes, about 45 minutes, about 1 hour, about 1.5 hours, or about 3 hours, or any value or range of values between any of these values (including endpoints).

It is believed that the catalyst nanoparticles in the reaction mixture adsorb other gases in the mixture, leaving behind nitrogen, which exits the reaction vessel via an outlet. The obtained nitrogen gas is about 90% pure, about 95% pure, about 96% pure, about 97% pure, about 98% pure, about 99% pure, about 99.1% pure, about 99.5% pure, about 99.99% pure, or 100% pure. At the end of the reaction process, the superparamagnetic catalyst may be recovered by applying a magnetic field. For example, a bar magnet may be used to collect FeCe2O4particles at the end of the reaction. The catalyst thus obtained can be reused.

Also disclosed herein are methods to make a catalyst. In some embodiments, the method involves contacting a paramagnetic oxide, cerium (IV) oxide, and a base. Non-limiting examples of paramagnetic oxides that my used include, but are not limited to, iron oxide, nickel oxide, and cobalt oxide, or any combination thereof. In some embodiments, the base may be aqueous ammonia or hydrazine hydroxide, or a combination thereof.

In some embodiments, the catalyst FeCe2O4may be prepared by contacting Fe2O3, CeO2, and aqueous ammonia. Aqueous ammonia (ammonium hydroxide) may have a concentration of about 20 weight percent to about 50 weight percent, about 20 weight percent to about 40 weight percent, or about 20 weight percent to about 30 weight percent. Specific examples include, but are not limited to, about 20 weight percent, about 25 weight percent, about 30 weight percent, and about 50 weight percent, or any range between any two of these values (including their endpoints). In some embodiments, contacting may be accomplished by any suitable means, including mixing, stirring, combining, shaking, agitation, and the like. Fe2O3, CeO2, and aqueous ammonia may be contacted for about 10 minutes to about 1 hour, about 10 minutes to about 45 minutes, about 10 minutes to about 30 minutes, or about 10 minutes to about 20 minutes. Specific examples include, but are not limited to, about 10 minutes, about 20 minutes, about 30 minutes, about 45 minutes, and about 1 hour, or any range between any two of these values (including their endpoints). In some embodiments, Fe2O3and CeO2may be contacted in a molar ratio of about 1:6 to about 1:2, about 1:6 to about 1:3, about 1:6 to about 1:4, or about 1:6 to about 1:5. Specific examples include, but are not limited to, about 1:6, about 1:5, about 1:4, about 1:3, and about 1:2, or any range between any two of these values (including their endpoints). In some embodiments, CeO2, Fe2O3, and ammonia may be contacted in a molar ratio of about 4:1:5, about 4:1:6, about 4:2:5, about 2:1:3, or about 1:1:1.

After the mixing step, the solvent is evaporated. This step may be performed by any known process in the art, such as heating, rotary evaporation, air drying, Soxhlet extraction, refluxing, or evaporating in an oven until the solvent is substantially evaporated. For example, the solvent may be heated to about 80° C., about 100° C., about 120° C., or about 130° C., using a reflux condenser. The reaction process may be outlined as follows:
8CeO2+2Fe2O3+10NH3OH→4FeCe2O3+20H2O+5N2

In some embodiments, the FeCe2O3obtained may further be subjected to the steps of washing, filtering, and drying. Drying may generally be performed in a hot air oven by heating to temperature of about 80-120° C. for 30-60 minutes. After drying, the FeCe2O3powder may be heated in a furnace to a temperature of about 500° C. to about 800° C. The heating may be carried out, for about 5 minutes to about 1 hour, about 5 minutes to about 45 minutes, about 5 minutes to about 30 minutes, or about 5 minutes to about 15 minutes. Specific examples include, but are not limited to, about 5 minutes, about 10 minutes, about 15 minutes, about 30 minutes, about 45 minutes, and about 1 hour, or any ranges between any two of these values (including their endpoints).

In some embodiments, the FeCe2O3obtained after heating is subjected to ethanol washing in the presence of oxygen. This step converts FeCe2O3to FeCe2O4. This process may further impart a superparamagnetic property to the catalyst.

The FeCe2O4catalyst obtained by the methods disclosed herein may be a nanoparticle having an average diameter of about 1 nanometer to about 50 nanometers, about 1 nanometer to about 40 nanometers, about 1 nanometer to about 25 nanometers, or about 1 nanometer to about 10 nanometers. Specific examples include, but are not limited to, about 1 nanometer, about 5 nanometers, about 15 nanometers, about 25 nanometers, and about 50 nanometers, or any range between any two of these values (including their endpoints). A putative structure of FeCe2O4catalyst is shown inFIG. 2.

EXAMPLES

Preparation of FeCe2O4Catalyst

About 1 gram of Fe2O3and 5 grams of CeO2were mixed and about 50 mL of ammonia solution was added drop by drop to the mixture of oxides at room temperature for about 30 minutes to form a solution. The solution was transferred to a reflux condenser and maintained at 120° C. until all the solvent was evaporated. The FeCe2O3powder obtained was washed with distilled water until a pH of 7 was reached. The FeCe2O3powder was dried in an hot air oven at 100° C. for 30 minutes. After drying, the FeCe2O3powder was heated in a furnace for 10-15 minutes at 700° C. The powdered material was removed and about 10 mL of ethanol was added immediately in the presence of atmospheric oxygen. Addition of ethanol to the hot powdered material instantly vaporized ethanol, thus imparting superparamagnetism to the catalyst. The FeCe2O4catalyst prepared was characterized by X-ray diffraction and shows a polycrystalline structure (FIG. 3).

Isolating Nitrogen Gas from Compressed Air

About 500 milligrams of FeCe2O4catalyst prepared in Example 1 was introduced in a closed reaction vessel, connected to an air compressor and an outlet connected to a gas collection chamber. Air was introduced into the reaction vessel and was exposed to a fluctuating magnetic field by supplying an electric current of 230V, 50 Hz, 240 mA for 60 minutes (magnetic field about 1000 μtesla). During the reaction process, the outlet valve was opened to collect nitrogen that was released. The nitrogen gas that was obtained was 99% pure. The FeCe2O4catalyst was recovered using simple magnets (0.03T) for reuse.

Isolating Nitrogen from Flue Gas

About 500 milligrams of FeCe2O4catalyst prepared in Example 1 is introduced in a closed reaction vessel, connected to a flue gas source and an outlet connected to a gas collection chamber. Flue gas is introduced into the reaction vessel and is exposed to a fluctuating magnetic field by supplying an electric current of 230V, 50 Hz, 240 mA for 75 minutes (magnetic field about 1000 μtesla). During the reaction process, the outlet valve is opened to collect nitrogen that is released. The nitrogen gas that is obtained is 98% pure. The FeCe2O4catalyst is recovered using simple magnets (0.03T) for reuse.

Measurement of Adsorption-Desorption Rates of Oxygen to FeCe2O4Catalyst

About 100 milligrams of FeCe2O4catalyst was placed in an enclosed chamber (250 mL vol) and exposed to various amounts of compressed air for 5 minutes. The initial pressure of compressed air was measured at the start of the experiment (A, Table 1). The chamber pressure after 5 minute exposure to 100 milligrams of FeCe2O4was measured (B, Table 1), which indicated adsorption rate. To measure desorption, FeCe2O4particles were kept in vacuum and subsequently exposed to hyperthermia for 5 minutes and the chamber pressure was measured (C, Table 1). The release of the adsorbed gas indicated the desorption rate.

While various compositions, methods, and devices are described in terms of “comprising” various components or steps (interpreted as meaning “including, but not limited to”), the compositions, methods, and devices can also “consist essentially of” or “consist of” the various components and steps, and such terminology should be interpreted as defining essentially closed-member groups.