50 results about "Nitrogen rich" patented technology

The invention discloses a preparation method and application of nitrogen-rich biochar, and relates to the technical field of water treatment. The invention aims to solve the problem that antibiotics and heavy metals are difficult to remove at the same time in the existing nitrogen-doped biochar. The method comprises the following steps: 1, cutting soybean straws, mixing the cut soybean straws with urea and distilled water to obtain a mixture, carrying out ultrasonic oscillation on the mixture, then transferring the mixture into a container, and drying the mixture in a drying oven to obtain urea-loaded straws; and 2, putting the obtained urea-loaded straw into a tubular furnace into which nitrogen is introduced for heating, then taking out the straw, grinding, sieving, mixing the sieved material with alkali liquor, activating, cleaning, finally putting the cleaned sample into a drying oven, and drying until the mass is constant, thereby obtaining the nitrogen-rich biochar. The nitrogen-rich biochar prepared by the invention can adsorb oxytetracycline (OTC) and Cu (II) at the same time.

The application relates to the technical field of refrigeration equipment, and discloses a refrigerator which comprises a cabinet, a drawer seat, an air-regulating film assembly and a suction pump, the cabinet is used for forming a low-temperature storage space; the drawer seat is arranged in the low-temperature storage space; the drawer body is internally limited by a storage cavity; the air-regulating film assembly is arranged in a mounting cavity located at the rear side of the drawer seat, the air-regulating film assembly comprises at least one layer of air-regulating film; the air suction port of the suction pump is communicated with the mounting cavity, under the suction of the suction pump, oxygen in air which is allowed to pass through by the air-regulating film is discharged, at least part of nitrogen in the air is blocked in the mounting cavity, the atmosphere of nitrogen-rich and oxygen-poor gas is reserved in the drawer seat, and the purpose of long-term preservation of fruits and vegetables is achieved. The air-regulating film assembly is arranged at the rear end of the drawer body, the oxygen removal effect on the inside of the drawer seat is guaranteed, the mounting space of the drawer seat in the vertical direction is effectively reduced, and the air-regulating preservation system is facilitated to be quickly maintained and replaced.

The application discloses a preparation method of an environment-friendly chitosan-based heavy metal adsorption air-precipitated bead, and comprises the following steps: preparing chitosan water-precipitated beads through acid-base neutralization solidification, loading the ammonia metal organic framework UiO-66-NH2 prepared through hydrothermal reaction on the chitosan water-precipitated beads through Schiff base reaction of a crosslinking agent, and then further loading polyethylene imine on the composite water-precipitated beads through the same loading means. The CS-UiO-GA-PEI-GA air-precipitated bead adsorbent is prepared through freeze-drying of the water-precipitated beads by a freeze dryer. The secondary crosslinking method gives the adsorbent certain mechanical strength, and provides a basis for regeneration and circulation of the adsorbent; the nitrogen-rich polyethylene imine and the high-porosity UiO-66-NH2 greatly enrich the active adsorption sites of the adsorbent, and significantly improve the adsorption capacity of the adsorbent for Cr(VI); and the removal rate of the adsorbent for Cr(VI) is up to 100% in the detection limit range of Cr(VI).

The invention relates to the technical field of grain and oil by-product high-value utilization and food functional ingredient preparation, in particular to a nitrogen-rich mesoporous carbon-based cholesterol adsorption ingredient as well as a preparation method and application thereof. According to the method, soybean meal and rice bran are taken as a carbon source and an endogenous nitrogen source, and urea or melamine is compounded as an exogenous nitrogen-rich precursor, so that an internal-external synergistic nitrogen-rich system is constructed; the method comprises the following steps: compounding a zinc chloride or potassium hydroxide chemical activator with a ferric chloride catalytic graphitizing agent to form a nitrogen-rich-catalytic synergistic conversion system; the method comprises the steps of raw material pretreatment, nitrogen-rich slurry preparation, catalytic activation precursor preparation and the like. The prepared carbon-based ingredient has a developed mesoporous structure and high-content alkaline nitrogen-containing functional groups, and is large in cholesterol adsorption capacity and high in selectivity, and the raw materials are grain and oil processing byproducts, so that the cost is low, and the carbon-based ingredient is green and environment-friendly; the preparation process has the advantages of controllable parameters and good repeatability, is suitable for industrial production, and provides a new technical path for the development of functional food ingredients for reducing blood fat.

The application discloses a kind of microbial compound microbial inoculant and preparation method thereof, the microbial compound microbial inoculant includes microbial inoculum and its fermentation product and carrier;The microbial inoculum includes bacillus subtilis and bacillus licheniformis;The carrier is nitrogen-rich grafted biochar;The nitrogen-rich grafted biochar is prepared after grafting acrylic acid and modified monomer after being modified by nitrogen-rich biochar.The microbial compound microbial inoculant provided in the application can significantly improve the adsorption capacity and flocculation capacity of the microbial inoculant for particles in wastewater by compounding microbial inoculum with excellent flocculation capacity with charge-modified and adsorbed carrier to make microbial inoculant, thereby effectively reducing the content of COD components, ammonia nitrogen and total phosphorus in wastewater, and can be widely applied in the field of wastewater treatment.

This invention discloses a method for preparing high-nitrogen-content nitrogen-doped porous carbon with multiple nitrogen-rich units and its applications, belonging to the field of porous carbon materials. This invention uses a triazine containing a triyne group as the crosslinking center and a pyrazine containing a diazid group as the crosslinking arm. The two react via click chemistry to form a triazole structure, constructing a nitrogen-doped porous polymer with multiple nitrogen-rich units. The nitrogen content is controllable, high, and uniformly distributed, and the nitrogen-containing structure exhibits high stability, resulting in a higher residual nitrogen content after activation and carbonization, thereby improving the CO2 adsorption selectivity of the porous carbon. The nitrogen-doped porous polymer, through activation and carbonization, yields high-nitrogen-content nitrogen-doped porous carbon with multiple nitrogen-rich units, exhibiting high yield, adsorption capacity, selectivity, and reusability, and has broad application prospects in adsorption, catalysis, and membrane separation.

The application discloses a preparation method and application of a multi-level pore biomass activated carbon, and belongs to the technical field of activated carbon preparation. The method uses a mixture of nitrogen-rich agricultural and forestry wastes and industrial by-products as raw materials, optimizes a pretreatment process, innovates a composite activation system, and controls carbonization-activation parameters, so that a biomass-based activated carbon rich in nitrogen elements and having multi-level pores is prepared. The nitrogen elements in the raw materials can be used for nitrogen doping of the activated carbon in the carbonization-activation process. The application effectively solves the problems of low utilization rate of raw materials, single pores and the like in the existing activated carbon preparation process, solves the problem of difficult treatment of industrial by-products, simultaneously simplifies the preparation process of the nitrogen-rich activated carbon, has economic value and environmental protection benefits, and can be widely applied to the fields of water treatment, carbon capture and deep treatment of industrial wastewater and the like.

The application belongs to the field of engine cooling, and particularly relates to a dual-working fluid regenerative cooling system and method. The dual-working fluid regenerative cooling system comprises a dual-working fluid regenerative cooling module, an ammonia cracking product separation module and an energy comprehensive utilization module. The dual-working fluid regenerative cooling module comprises an ammonia supply device, a kerosene supply device and a double-layer regenerative cooling channel. The ammonia cracking product separation module comprises a membrane separator and a pressure swing adsorption unit. The energy comprehensive utilization module comprises a power generation device connected with the nitrogen-rich gas outlet. The application builds a closed-loop system integrating efficient thermal management, stable combustion and energy efficient utilization by means of ammonia and kerosene dual-working fluid cooling, ammonia cracking hydrogen production and nitrogen-rich gas power generation.

The invention discloses nitrogen-doped carbon nanotube array loaded magnetic carbon aerogel and a preparation method thereof.The method comprises the steps that cobalt salt and nickel salt are evenly dissolved in a biomass precursor aqueous solution, and a homogeneous solution is formed; adding a cross-linking aid to construct a three-dimensional network, and wrapping metal ions; performing freeze drying after directional freezing to form a directional porous structure; carrying out heat preservation and carbonization, converting the biomass into a porous carbon matrix, and reducing the cobalt / nickel salt into a uniformly embedded CoNi alloy; through two-stage heat treatment, the nitrogen-rich organic matter is decomposed to release a nitrogen source, and the vertical carbon nanotube array grows in situ. The material integrates CoNi alloy magnetic loss, carbon matrix dielectric loss and multistage structure scattering effect, realizes dielectric-electromagnetic cooperation, optimizes impedance matching, avoids strong surface reflection caused by high conductivity of a single carbon material, introduces polarization loss, widens an absorption frequency band, has excellent broadband efficient electromagnetic wave absorption performance, and is suitable for a complex electromagnetic environment.

The invention discloses a pyrazinyl nitrogen-rich hydrophobic porous organic cage material as well as a preparation method and application thereof, and belongs to the technical field of porous organic cage materials. Resorcinol calix [4] arene, pyrazine-2, 5-diamine, an organic solvent and the like react to obtain the pyrazinyl nitrogen-rich hydrophobic porous organic cage material. A nitrogen-rich pyrazine ring is introduced into the material to enhance the SF6 adsorption capacity; the introduction of isobutyl endows the material with strong hydrophobicity, so that the material keeps stable structure and unchanged adsorption performance under high humidity. The obtained material is good in water and chemical stability, the SF6 adsorption capacity reaches up to 53.6 cm < 3 > g <-1 > under the conditions of normal temperature and normal pressure of 25 DEG C and 1 bar, the adsorption capacity ratio of SF6 to nitrogen (N2) reaches 20.02 in a creative record, and the adsorption capacity ratio reaches the maximum value in all reported porous organic cage materials at present. The pyrazinyl nitrogen-rich hydrophobic porous organic cage material provided by the invention provides a new thought for efficient adsorption and separation of SF6.

The present application relates to the sewage treatment technical field, specifically relates to a kind of preparation and application in water purification bacteriostasis of nitrogen-rich carbide piezoelectric composite material.The present application is coupled by high molecular piezoelectric polymer and nitrogen-rich carbide, and modified piezoelectric composite material with high piezoelectric catalytic activity is formed, and the efficient degradation of various organic pollutants in water is realized by driving force induction piezoelectric effect, and has excellent bacteriostatic performance.The preparation process in the present application is simple, green, low cost, material mechanical strength is high, degradation process is free of secondary pollution, easy to mass production, the method can effectively solve water pollution problem, help ecological environment protection, and escort for human health.

The present application relates to a kind of methods for regulating the morphology of nitrogen-rich metal organic framework material using organic template agent, belong to the technical field of micro-nano material synthesis.The purpose of the present application is to solve the problems of single morphology, uneven particle size distribution and other problems of nitrogen-rich MOFs micro-nano particles obtained by the prior art, and to provide a method for regulating the morphology of nitrogen-rich metal organic framework material using organic template agent;By using organic template agent, the reaction solvent, reaction temperature and reaction time are controlled, the ratio of organic ligand, metal salt and organic template agent is controlled, so that the morphology and size of MOFs micro-nano particles are effectively controlled, and spherical, flower-like, snowflake-like, interpenetrating, cubic or sheet-like morphology can be obtained, with high yield, high repeatability, and morphology transformation of MOFs material is simultaneously controlled.

Title of the invention; Process for separating a mixture of CO2 and nitrogen by adsorption and by partial condensation and / or distillation and / or solidification. In a process for separating a mixture of CO2 and nitrogen by adsorption and by partial condensation and / or distillation and / or solidification, the mixture of CO2 and nitrogen is separated by adsorption forming a nitrogen-enriched and CO2-depleted gas stream (NRI) and a CO2-enriched and nitrogen-depleted gas stream. The nitrogen-enriched stream is heated by sending it to the bottom of a tower (T) fed at an inlet level above the outlet level of the nitrogen-enriched stream by a water stream (CWI). The CO2-enriched stream is separated by partial condensation and / or distillation and / or solidification to form a CO2-enriched stream, and a stream containing nitrogen and water vapor rising in the tower is heated by a heat exchanger (E).The heat exchanger is heated by a fluid flow (F1) which is itself heated by a heat source (I) generated by the separation process. Fig. 3,

The application discloses a preparation method of six-element high-entropy single-atom nitrogen-rich porous photothermal material. In the solvent-free condition, 1h-123-triazole is introduced as one of raw materials, a six-element high-entropy single-atom nitrogen-rich photothermal material precursor is prepared through a mechanical ball milling method, then the six-element high-entropy single-atom nitrogen-rich photothermal material is obtained through washing, centrifugation, high-temperature annealing reaction and cooling at room temperature. The six-element high-entropy single-atom nitrogen-rich photothermal material precursor is obtained through an in-situ mechanical chemical preparation method, and 1h-123-triazole is added, so that nitrogen-nitrogen "explosion" caused by nitrogen-nitrogen double bond is generated in the later annealing process, and then the photothermal material with high porosity and high stability is obtained. The application is an effective method for preparing the porous photothermal material, which is simple and convenient in operation, green and safe, good in repeatability and high in efficiency.

This invention provides an immersion preservation method and preservation solution that maintain organs for transplantation in good condition for a longer period than conventional methods. [Solution] The present invention relates to a method for preserving organs for transplantation, which involves immersing the organs in a nitrogen-rich UW solution at a temperature suitable for immersion preservation, where the dissolved oxygen content is 1.0 mg / L or less and the nitrogen content is 90 mg / L or more at one atmosphere. As an example, a nitrogen-rich UW solution is prepared in which the dissolved oxygen content is 1.0 mg / L or less and the nitrogen content is 90 mg / L or more at one atmosphere and a temperature suitable for immersion preservation, and the organs for transplantation are immersed in the prepared nitrogen-rich UW solution. As another example, a nitrogen-rich UW solution is prepared in which the dissolved oxygen content is 1.0 mg / L or less and the nitrogen content is 90 mg / L or more at one atmosphere and room temperature, and the prepared nitrogen-rich UW solution is cooled to a temperature suitable for immersion preservation before the organs for transplantation are immersed in it.

The invention belongs to the technical field of crystal porous material preparation and adsorption separation, and relates to a nitrogen-rich porous metal organic framework material, a preparation method and ethylene propylene adsorption separation application. The chemical formula of the nitrogen-rich metal organic framework material is [Ni6 (OH) 6 (APY) 3 (TCTA) 2], the composition and the structure of the nitrogen-rich metal organic framework material are novel, N atoms are densely distributed on the inner surface of the framework, the material has high porosity, the specific surface area of the material is 1975 m < 2 > / g, and the pore size distribution is 4.5-7.5. Due to permanent pore channels and high-density N atom distribution, the material is suitable for ethylene / propylene adsorption separation.

The invention discloses a preparation method and application of nitrogen-rich biomass in-situ nitrogen-doped activated carbon, relates to the technical field of activated carbon, and aims to simplify the technological process and reduce the preparation cost. According to the preparation method, common biomass is used as a main carbon-containing precursor, and nitrogen-rich biomass is used as a nitrogen source and is placed on a bottom layer or a middle layer; in the pre-carbonization stage, cellulose, hemicellulose and the like are decomposed and carbonized preferentially, and a primary carbon layer with rich internal pore channels is constructed; in the subsequent carbonization stage, the protein and the lignin are subjected to synergistic pyrolysis, a large amount of nitrogen-containing volatile components are released, and the volatile components are captured and anchored during cross-linking with a carbon layer and the lignin in the diffusion, especially upward diffusion process, so that in-situ nitrogen doping is realized. According to the preparation method, the nitrogen element is more uniformly distributed in a carbon skeleton, the performance and the stability of the activated carbon are improved, chemical reagents do not need to be additionally added, the technological process is simplified, and the preparation cost is remarkably reduced.

This disclosure relates to a manufacture method of a bushing, a bushing and an excavator to alleviate the problems of insufficient lubricity and wear resistance of the bushing. The bushing includes an inner ring and an outer ring. The manufacture method of the bushing includes the following steps: grinding a first mixed powder containing Fe, Al, Ti, Cr and V, nitriding the ground first mixed powder to form a nitrogen-rich stable compound powder, and then carrying out molding by pressing and sintering the nitrogen-rich stable compound powder to form the outer ring; grinding a second mixed powder containing Fe and Mo, sulfurizing the ground second mixed powder to form a sulfurized powder containing FeS and MoS2, and carrying out molding by pressing the sulfurized powder to form the inner ring; and placing the inner ring in the outer ring and carrying out sintering to obtain the bushing.

The invention belongs to the field of engine cooling, and particularly relates to a double-working-medium regenerative cooling system and method. The double-working-medium regeneration cooling system comprises a double-working-medium regeneration cooling module, an ammonia cracking product separation module and an energy comprehensive utilization module. The double-working-medium regeneration cooling module comprises an ammonia supply device, a kerosene supply device and a double-layer regeneration cooling channel, the ammonia cracking product separation module comprises a membrane separator and a pressure swing adsorption unit, and the energy comprehensive utilization module comprises power generation equipment connected with the nitrogen-rich gas outlet. Through ammonia and kerosene double-working-medium cooling, ammonia cracking hydrogen production and nitrogen-rich gas power generation, a closed-loop system integrating efficient heat management, stable combustion and efficient energy utilization is constructed.

A system and method for removing nitrogen from a natural gas or liquefied natural gas stream. More specifically, a system and method for removing nitrogen from a natural gas feed stream using a twin column system in which the first column is operated at a pressure lower than the operating pressure of the second column. A first nitrogen-rich vapor stream from the first column is compressed and cooled, and then the resulting stream is directed to a second column that produces a second nitrogen-rich vapor stream and a second methane-rich liquid stream. Cooling in the system is provided in a heat exchanger that warms a first methane-rich liquid stream from the first column and a second methane-rich liquid stream from the second column.

This method for producing an organic material comprises: a step (A) in which a first gas containing nitrogen and oxygen is converted into arc plasma by arc discharge to obtain a second gas containing nitrogen oxides; and a step (B) in which the second gas is supplied to a solid organic material. In the step (A), the first gas may be converted into arc plasma and ejected in a plasma jet flow state, and in the step (B), the second gas after ejection thereof may be cooled to a temperature of 50°C or less and supplied to the organic material.

The invention provides a preparation method of a hydrophilic nitrogen-rich carbon nitride nanosheet, which comprises the following steps: grinding and uniformly mixing 5-aminotetrazole and potassium chloride, heating to 550 DEG C in an air atmosphere, calcining at a constant temperature, naturally cooling to room temperature to obtain calcined powder, adding water, stirring and dispersing, and removing salt through dialysis to obtain the hydrophilic nitrogen-rich carbon nitride nanosheet. And freeze-drying the aqueous solution of the sample to obtain the hydrophilic nitrogen-rich carbon nitride nanosheet. The invention also provides application of the hydrophilic nitrogen-rich carbon nitride nanosheet for photocatalytic hydrogen production. The hydrophilic nitrogen-rich carbon nitride nanosheet is synthesized in one step, the synthesis period is short, the yield is high, the hydrophilicity of nitrogen-rich carbon nitride can be adjusted by adjusting the input amount of potassium chloride, and the hydrophilic nitrogen-rich carbon nitride nanosheet is used for photocatalytic hydrogen production.

The application belongs to the field of activated carbon preparation, and discloses a kind of nitrogen-rich hydrolysate reinforced hydrothermal nitrogen-doped preparation activated carbon and its room temperature desulfurization application, and the preparation method comprises the following steps: (1) high water content nitrogen-rich organic solid waste is mixed with liquid water, and heat hydrolysis reaction is carried out to obtain nitrogen-rich hydrolysate;(2) the nitrogen-rich hydrolysate is mixed with high water content organic solid waste, and then hydrothermal reaction is carried out to obtain nitrogen-containing hydrothermal coke;(3) nitrogen-containing hydrothermal coke is activated to obtain nitrogen-doped activated carbon.The application uses high water content nitrogen-rich organic solid waste as raw material, first obtains nitrogen-rich hydrolysate through heat hydrolysis reaction, then uses nitrogen-rich hydrolysate and other high water content organic solid waste to carry out hydrothermal reaction to obtain nitrogen-containing hydrothermal coke, and finally carries out activation treatment, which not only realizes harmless, reduction and resource utilization of solid waste, but also solves the problem of high preparation cost of current carbon-based catalyst, and the method can prepare carbon-based catalyst with high specific surface area, and has high practical value.

The invention discloses a normal-temperature bionic reductive dehalogenation suspension system and a preparation method and application thereof.The normal-temperature bionic reductive dehalogenation suspension system is formed by mixing nitrogen-rich biochar, patina and cobalt hydroxide according to the mass ratio of 1: (1-5): (0.8-3.8) in a water phase at the normal temperature, nitrogen functional groups in the nitrogen-rich biochar and cobalt hydroxide are utilized to synergistically construct a cobalamin-like structure, active hydrogen is generated and stabilized in situ, and the suspension system is obtained. The patina provides reducing iron species, participates in electron transfer, can form heterojunctions with cobalt hydroxide, and can also be directly adsorbed in a nitrogen structure of bone black, so that the reaction is efficiently carried out, the patina has enzyme-like catalysis characteristics, efficient reduction and dehalogenation of halogenated organic pollutants such as trichloroethylene are realized, the reaction conditions are mild, and the method is suitable for industrial production. Meanwhile, acetylene can be directionally converted into ethylene and ethane.

The invention discloses a hydrogen and nitrogen separation and recovery device which comprises a gas separation bin, a membrane assembly is arranged on the inner side of the gas separation bin, a nitrogen enrichment mechanism is arranged above the gas separation bin in a communicating mode, and the top of the nitrogen enrichment mechanism is connected with the output end of a compressor; the nitrogen enrichment mechanism comprises a third pipe body and a separation frame arranged on the inner side of the third pipe body, the third pipe body is divided into three independent spaces by the separation frame, the three independent spaces are all communicated with the bottom of the gas inlet pipe, and through holes communicated with the gas separation bin are formed in the bottoms of the independent spaces; the gas separation bin is arranged, the membrane assembly is arranged on the inner side of the gas separation bin, the mixed gas of the hydrogen and the nitrogen is controlled to be conveyed into the gas separation bin under the action of the compressor, and the nitrogen is intercepted by utilizing the permeation rate difference of the hydrogen and the nitrogen, so that separation of the nitrogen and the hydrogen is realized.

The present application relates to the technical fields of flame retardant and flame retardant composite material, and particularly relates to a nitrogen-rich DOPO-based flame retardant and synthesis and application thereof. The conventional phosphorus-based flame retardant and the epoxy resin have poor polarity matching degree, and are prone to phase separation or migration and precipitation, resulting in unstable flame retardancy of the flame-retardant epoxy resin, and the flame-retardant effect needs to be further improved. In view of the above technical problems, the present application provides a nitrogen-rich DOPO-based flame retardant, which belongs to the reaction-type phosphorus-nitrogen flame retardant. The secondary amine group in the molecular structure of the nitrogen-rich DOPO-based flame retardant can form a chemical bond with the epoxy group in the structure of the epoxy resin. Compared with the conventional phosphorus-based flame retardant, the nitrogen-rich DOPO-based flame retardant has better compatibility with the epoxy resin, is not prone to falling off, has less influence on the mechanical properties and transparency of the epoxy resin, and has a good application prospect.

The invention discloses a method for relieving an ammonia inhibition effect in a nitrogen-rich organic waste anaerobic digestion process and increasing methane yield based on microbial stress regulation. The method comprises the following steps that an active oxygen scavenger solution is added into an anaerobic reactor for producing methane, the ammonia inhibition effect is recovered, the methane yield is increased, and the active oxygen scavenger is selected from one or more of superoxide dismutase, catalase and vitamin C. According to the method, the active oxygen scavenger solution is precisely added into the fermentation system, so that the active oxygen scavenger solution plays a role in the intracellular or extracellular environment of the microorganisms, the microorganisms can still keep high metabolic activity in the high-ammonia-nitrogen environment, finally, the ammonia inhibition phenomenon is substantially recovered, and the methane yield of the system is remarkably recovered and increased.

The invention provides an integrated air separation device. The integrated air separation device comprises an inlet end cover, an outlet end cover and a barrel, wherein the two ends of the cylinder body are respectively fixed with the inlet end cover and the outlet end cover through screws; a gas inlet is formed in the side wall of the inlet end cover; an oxygen-enriched outlet is formed in the side wall of the barrel; a nitrogen-rich outlet is formed in the side wall of the outlet end cover; hollow fiber membranes are arranged in the cylinder body in parallel. According to the integrated air separation device provided by the invention, the two hollow fiber membranes are mounted in the end cover with a specific shape in parallel, so that the two hollow fiber membranes share the same air entraining space, oxygen-enriched space and nitrogen-enriched space, the layout is compact, the occupied space is smaller, the product weight is greatly reduced, and the assembly is simpler and more convenient.

A system and method for removing nitrogen from a natural gas or liquid natural gas flow. More specifically, a system and method for removing nitrogen from a natural gas feedflow using a two-column system in which the first column operates at a pressure lower than the operating pressure of the second column. A first nitrogen-enriched vapor flow from the first column is compressed and cooled, and the resulting flow is then led to a second column, which generates a second nitrogen-enriched vapor flow and a second methane-enriched liquid flow. Cooling in the system is provided in a heat exchanger, which heats the first methane-enriched liquid flow from the first column and the second methane-enriched liquid flow from the second column.