The present invention discloses a method for recycling urea in the process of separating and purifying unsaturated substances through a urea adduction method. The method comprises the following steps: liposoluble substances containing target unsaturated components are used as raw materials, and subjected to urea adduction, crystallization and filtration to produce a filtrate, from which the specific unsaturated components are obtained; the urea adduct is dissolved in a polar solvent, and after the adducted adducts are layered and released, adding a certain solvent to the urea solution to adjust the polarity, then cooling for crystallization, and recycling the urea. The method can realize complete release of the adducted components and recycling and reuse of urea, and the process is simple, the recovery rate is high, and the adduction effect is not influenced when recycling urea for reuse, and the production cost of the urea adduct is reduced, thus alleviating the adverse impact of urea discharges on the environment.

The present invention discloses a method for recycling urea in the process of separating and purifying unsaturated substances through a urea adduction method. The method comprises the following steps: liposoluble substances containing target unsaturated components are used as raw materials, and subjected to urea adduction, crystallization and filtration to produce a filtrate, from which the specific unsaturated components are obtained; the urea adduct is dissolved in a polar solvent, and after the adducted adducts are layered and released, adding a certain solvent to the urea solution to adjust the polarity, then cooling for crystallization, and recycling the urea. The method can realize complete release of the adducted components and recycling and reuse of urea, and the process is simple, the recovery rate is high, and the adduction effect is not influenced when recycling urea for reuse, and the production cost of the urea adduct is reduced, thus alleviating the adverse impact of urea discharges on the environment.

Disclosed are methods of recovering urea from a urea/oil complex by drying the complex, combining the complex with water to form a urea solution, and removing water from the urea solution. Methods for recycling the urea in urea complexation processes are also disclosed. Also disclosed are methods of recovering polyunsaturated fatty acids or derivatives thereof from the urea/oil complexes.

Disclosed are methods of recovering urea from a urea/oil complex by drying the complex, combining the complex with water to form a urea solution, and removing water from the urea solution. Methods for recycling the urea in urea complexation processes are also disclosed. Also disclosed are methods of recovering polyunsaturated fatty acids or derivatives thereof from the urea/oil complexes.

Disclosed are methods and systems for removing submicron particles from a gas stream, in particular from urea prilling off-gas, wherein a Venturi ejector is used. A method comprises contacting a gas stream containing submicron particles in a Venturi ejector with an injected high velocity scrubbing liquid to provide a pumping action, wherein the scrubbing liquid has an initial velocity of at least 25 m/s and wherein the ratio of scrubbing liquid and gas flow is between 0.0005 and 0.0015 (m.sup.3/h)/(m.sup.3/h).

Disclosed are methods and systems for removing submicron particles from a gas stream, in particular from urea prilling off-gas, wherein a Venturi ejector is used. A method comprises contacting a gas stream containing submicron particles in a Venturi ejector with an injected high velocity scrubbing liquid to provide a pumping action, wherein the scrubbing liquid has an initial velocity of at least 25 m/s and wherein the ratio of scrubbing liquid and gas flow is between 0.0005 and 0.0015 (m.sup.3/h)/(m.sup.3/h).

In an integrated process for urea and melamine production, urea is produced in a urea plant (10) comprising a high pressure urea synthesis section (11) from which an aqueous solution comprising urea, ammonium carbamate and ammonia is obtained and a urea recovery section (21) operating at low pressure, and melamine is produced in a melamine plant (40) wherein off-gases resulting as by-products of the melamine synthesis are discharged from said plant at a medium pressure and recycled to the high-pressure urea synthesis section (11).

In an integrated process for urea and melamine production, urea is produced in a urea plant (10) comprising a high pressure urea synthesis section (11) from which an aqueous solution comprising urea, ammonium carbamate and ammonia is obtained and a urea recovery section (21) operating at low pressure, and melamine is produced in a melamine plant (40) wherein off-gases resulting as by-products of the melamine synthesis are discharged from said plant at a medium pressure and recycled to the high-pressure urea synthesis section (11).

This invention provides for synthesis of citrulline from a transition metal complex of ornithine using cyanate to derivatize the terminal amino group of ornithine. The invention also provides improved methods for purification of citrulline produced by reaction of cyanate with ornithine via the steps of reprecipitation of copper complex of citrulline, removal of the complexing metal by sulfide precipitation, activated carbon adsorption and antisolvent crystallization.

This invention provides for synthesis of citrulline from a transition metal complex of ornithine using cyanate to derivatize the terminal amino group of ornithine. The invention also provides improved methods for purification of citrulline produced by reaction of cyanate with ornithine via the steps of reprecipitation of copper complex of citrulline, removal of the complexing metal by sulfide precipitation, activated carbon adsorption and antisolvent crystallization.