An intercalation agent for rapid graphite exfoliation in mass production of high-quality graphene is provided, including a transition metal halide salt, a nitrogen source substance and an organic solvent, and the mass ratio of the transition metal halide salt, the nitrogen source substance and the organic solvent is (1-10):1:(2-10). The transition metal halide salt can form a eutectic with the nitrogen source substance or the organic solvent, and the melting point thereof is lower than that of each component, thereby lowering the reaction temperature, and the preparation cost and difficulty; and a hydrogen bond can also be formed between the nitrogen source substance and the organic solvent, thereby avoiding interlayer stacking of the prepared graphene, thus improving the exfoliation efficiency and the product quality.

Provided is a method for preparing graphene by liquid-phase ball milling exfoliation, including following steps: mixing a transition metal halide salt, a nitrogen source substance and an organic solvent to prepare an intercalation agent; mixing the intercalation agent with graphite, carrying out ball milling, and then performing centrifugation to obtain a graphite intercalation compound; washing and filtering the graphite intercalation compound obtained, adding an expansion agent, and carrying out ultrasonic agitation to obtain a graphene dispersion; and washing, filtering and drying the graphene dispersion to obtain graphene powder.

Disclosed is a novel method of controlling the formation of biuret in urea production, and particularly reducing, preventing or reversing such formation. This is accomplished by adding liquid ammonia to a urea aqueous stream. This addition is done at one or more positions downstream of a recovery section in a urea plant. The addition of liquid ammonia serves to shift the equilibrium of biuret formation from urea, to the side of the formation of urea from biuret and ammonia. The invention can be accomplished also in pre-existing urea plant, by the simple measure of providing an appropriate inlet for liquid ammonia, in fluid communication with a source of such liquid ammonia.

Disclosed is a novel method of controlling the formation of biuret in urea production, and particularly reducing, preventing or reversing such formation. This is accomplished by adding liquid ammonia to a urea aqueous stream. This addition is done at one or more positions downstream of a recovery section in a urea plant. The addition of liquid ammonia serves to shift the equilibrium of biuret formation from urea, to the side of the formation of urea from biuret and ammonia. The invention can be accomplished also in pre-existing urea plant, by the simple measure of providing an appropriate inlet for liquid ammonia, in fluid communication with a source of such liquid ammonia.

Integrated process for the production of urea and urea-ammonium nitrate, comprising: reacting ammonia and carbon dioxide to form a reaction mixture (4) containing urea and unconverted materials, and also comprising the recovery of unconverted materials in a first recovery stage at a first pressure and in a second recovery stage at a second pressure, wherein ammonia-containing offgas (19) released by said second recovery stage are condensed at said second pressure, and said condensed offgas (20) are recycled to said first recovery stage.

The present disclosure relates to a preparation method for removing triuret causing turbidity in a urea solution and to a urea solution prepared using the method, and more particularly, to a preparation method, in which urea is introduced to ultrapure water at 15 C. to 24 C. in a magnetic tank with a size of 1 m.sup.3 to 20 m.sup.3, and the mixture is stirred by using a magnetic mixer and filtered through a hollow-fiber type ultrafiltration membrane (having a pore size in a range of 0.01 m to 0.3 m) such that a 32.5% automotive urea solution has a turbidity of 0.02 NTU to 0.2 NTU, and the triuret causing turbidity in a urea solution and reducing conversion efficiency to NH.sub.3 in selective catalytic reduction (SCR) is removed. To achieve the purpose of the present disclosure, there is provided a method of preparing a urea solution by dissolving urea in ultrapure water, wherein the 32.5% automotive urea solution is provided by a preparation method including the steps of: a step of preparing ultrapure water at 15 C. to 24 C.; a step of moving the ultrapure water into a magnetic mixer tank; a step of introducing urea to the ultrapure water contained in the magnetic mixer tank; a step of operating a magnetic mixer to induce vortex effect for mixing and stirring the ultrapure water with urea to prepare a urea solution; and a step of filtering by passing the urea solution including triuret through a hollow-fiber type ultrafiltration filter (U/F) to filtrate 20 L of triuret and impurities per 1,000 L of the urea solution, while maintaining a low temperature of the urea solution resulting from the stirring (S5).

The present disclosure relates to a preparation method for removing triuret causing turbidity in a urea solution and to a urea solution prepared using the method, and more particularly, to a preparation method, in which urea is introduced to ultrapure water at 15 C. to 24 C. in a magnetic tank with a size of 1 m.sup.3 to 20 m.sup.3, and the mixture is stirred by using a magnetic mixer and filtered through a hollow-fiber type ultrafiltration membrane (having a pore size in a range of 0.01 m to 0.3 m) such that a 32.5% automotive urea solution has a turbidity of 0.02 NTU to 0.2 NTU, and the triuret causing turbidity in a urea solution and reducing conversion efficiency to NH.sub.3 in selective catalytic reduction (SCR) is removed. To achieve the purpose of the present disclosure, there is provided a method of preparing a urea solution by dissolving urea in ultrapure water, wherein the 32.5% automotive urea solution is provided by a preparation method including the steps of: a step of preparing ultrapure water at 15 C. to 24 C.; a step of moving the ultrapure water into a magnetic mixer tank; a step of introducing urea to the ultrapure water contained in the magnetic mixer tank; a step of operating a magnetic mixer to induce vortex effect for mixing and stirring the ultrapure water with urea to prepare a urea solution; and a step of filtering by passing the urea solution including triuret through a hollow-fiber type ultrafiltration filter (U/F) to filtrate 20 L of triuret and impurities per 1,000 L of the urea solution, while maintaining a low temperature of the urea solution resulting from the stirring (S5).

A method for the production of a urea ammonium sulphate (UAS) composition in a pipe reactor comprising at least a reactor section, the method comprising: combining in the reactor continuous feeds of at least one of sulphuric acid and ammonium bisulphate, at least one of ammonia and ammonium carbamate, and urea; and including a viscosity-reducing agent selected from water soluble aluminum salts in at least one of the continuous feeds, thereby forming the urea ammonium sulphate (UAS composition, wherein the UAS composition comprises 1 to 40 weight % of ammonium sulphate (AS) relative to the total weight of the UAS composition.

A method for the production of a urea ammonium sulphate (UAS) composition in a pipe reactor comprising at least a reactor section, the method comprising: combining in the reactor continuous feeds of at least one of sulphuric acid and ammonium bisulphate, at least one of ammonia and ammonium carbamate, and urea; and including a viscosity-reducing agent selected from water soluble aluminum salts in at least one of the continuous feeds, thereby forming the urea ammonium sulphate (UAS composition, wherein the UAS composition comprises 1 to 40 weight % of ammonium sulphate (AS) relative to the total weight of the UAS composition.

The invention is directed to a urea plant with a high pressure synthesis section and a recovery section. The high pressure synthesis section comprises a reactor, a stripper and a condenser, wherein the reactor operates at a higher pressure than the stripper and the condenser. The plant further includes a compression unit between the condenser and the reactor. The compression unit utilizes mechanical energy recovered from a decompression unit positioned downstream of the stripper and upstream of the recovery section.