Abstract: 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.

Abstract: 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.

Abstract: The invention relates to the method for producing high purity crystalline carbamide. The method comprises the crystallization and drying of carbamide, wherein an aqueous carbamide solution is preheated from +30° C. to +130° C., and thereafter the solution is purified by electrodialysis at a voltage in the range of 400 V-600 V. The technical result is the production of high-purity crystalline carbamide that can be used as an additive in the food industry and as a reagent in laboratory analyzes.

Abstract: Disclosed is a method for urea finishing. A urea solution is subjected to crystallization and, other than in conventional processes, the urea crystals are shaped by exerting mechanical force onto them. Thus, the conventional prilling or granulation finishing steps can be avoided, and so are the corresponding emissions of ammonia and/or dust. The crystallization comprises a flash crystallization. The invention also pertains to the urea particles obtainable by the process, to a urea plant, and to a method of modifying an existing urea plant.

Abstract: Processes for the treatment of an aqueous mixture comprising a dipolar aprotic compound, comprise: a) an adsorption step, in which the aqueous mixture is brought into contact with a porous adsorbent, whereby the porous adsorbent is chosen such that the dipolar aprotic compound adsorbs to it more readily than water; b) a desorption step, in which the porous adsorbent is brought into contact with a desorbing agent, whereby a recovery solution is formed comprising the desorbing agent and the dipolar aprotic compound.

Abstract: A stripper (SN) for carbamate decomposition and ammonia plus carbon dioxide recovery from a urea solution (U) is realized with a shell-and-tube heat exchanger, where a liquid falling film of urea solution and a counter-current gaseous flow of a stripping medium fed to a bundle of surface-heated tubes (6); the stripping medium such as carbon dioxide is distributed into the tubes (6) by a plurality of gas risers (32); the gas risers are preferably associated to a perforated tray (30) in the bottom chamber (11) of the stripper. Revamping of a conventional CO2 stripper is also disclosed.

Abstract: The invention relates to a process for the treatment of an aqueous mixture comprising a dipolar aprotic compound, comprising: a) an adsorption step, in which the aqueous mixture is brought into contact with a porous adsorbent, whereby the porous adsorbent is chosen such that the dipolar aprotic compound adsorbs to it more readily than water; b) a desorption step, in which the porous adsorbent is brought into contact with a desorbing agent, whereby a recovery solution is formed comprising the desorbing agent and the dipolar aprotic compound.

Abstract: The invention relates to a process for the granulation of a concentrated urea solution whereas the granulation produces a urea granulate and a dust laden air, which is then fed into a dust scrubber which removes the coarser dust with a less concentrated urea solution and which releases a residual air comprising air with ammonia, carbon dioxide water and an aerosol comprising mainly ammonium isocyanate and a part of very fine urea sublimate, whereas the aerosol is then separated off and fed into a isomerisation unit which comprises a stripping where the ammonium isocyanate reacts with steam to form urea which is then redirected into the dust scrubber as a less concentrated urea solution, and the residual air is directed into an acidic scrubber which releases clean air into the atmosphere which finally leads to a recycling of the aerosol of ammonium isocyanate into urea. The invention also relates to a device for carrying out the related process.

Abstract: A method for co-producing electric power and urea from carbonaceous fuels such as coal, by pyrolizing the coal with oxygen to produce a raw rich gas and a hot char which is gasified with air to produce a raw lean gas. Subsequent to the cleaning of the two gases, the cleaned rich gas is made up of CO and 2H2, and the clean lean gas is made up of N2+CO. The CO in the rich gas is separated from the 2H2 and is added to the lean gas to enrich it with CO to become a lean fuel gas which fuels a gas turbine and is part of a combined cycle system which efficiently generates electric power while exhausting an off-gas (flue gas) made up of N2+CO2. The 2H2 separated from the CO, and the N2+CO2 of the exhausted flue gas are together synthesized to produce urea —CO(NH2)2.

Abstract: A method of treating waste matter from animals, the method comprising: a) collecting waste matter from the animals; b) inhibiting urease activity in said collected waste matter; and c) separating said urease-activity inhibited waste matter into a urea-rich fraction and a urea-lean fraction; a system for treating waste matter from animals; a urea-lean biogas fuel product; a urea-rich animal waste-matter product; a method of controlling the content of nitrogen in manure from animals; a method of reducing gaseous ammonia in stables for animals; a stable for animals; a biogas reactor system for producing biogas from waste matter from animals; a method of producing urea from waste matter of animals; a method of producing urea formaldehyde; and a method of producing biogas fuel from waste matter of animals.

Abstract: A process for urea production comprises a first process step in which ammonia (7) and carbon dioxide (6) are obtained, subjecting natural gas (1) to reforming treatments (12, 14), and a second step of urea (8a) production from such ammonia (7) and from carbon dioxide, through a formation of a solution comprising urea and ammonium carbamate in a urea synthesis reactor (20) and a subsequent decomposition of the ammonium carbamate and. urea recovery, the process comprises the steps of:—treating combustion smokes (5) comprising carbon dioxide with an aqueous solution (9a) comprising a part (7b) of such ammonia (7), obtaining an aqueous ammonium carbamate solution (9c);—supplying the solution (9c) thus obtained to the second process step.

Abstract: Apparatus and methods for producing urea are provided. In one or more embodiments, an apparatus for producing urea can include a first zone, which can include a first flow channel in fluid communication with a first tube disposed about a first end of a plurality of trays, a second flow channel in fluid communication with a second tube disposed about the first end of the trays and a second end of the trays, and a third flow channel in fluid communication with a third tube disposed about the first and second ends of the trays. The apparatus can include a second zone, which can include a fixed bed comprising one or more inert packing materials disposed therein to provide additional surface area. The apparatus can include a third zone, which can include a plurality of tubes disposed therein. The second zone can be disposed between the first and third zones.

Abstract: The invention relates to a process for the treatment of an aqueous mixture comprising a dipolar aprotic compound, comprising: a) an adsorption step, in which the aqueous mixture is brought into contact with a porous adsorbent, whereby the porous adsorbent is chosen such that the dipolar aprotic compound adsorbs to it more readily than water; b) a desorption step, in which the porous adsorbent is brought into contact with a desorbing agent, whereby a recovery solution is formed comprising the desorbing agent and the dipolar aprotic compound.

Abstract: The invention relates to a method for contacting molten urea with a gas stream that contains ammonia and/or carbon dioxide, in which use is made of an additional stream the temperature of which differs from the temperature of the molten urea and/or the gas stream. The additional stream preferably contains ammonia. The method is preferably part of a process for the preparation of melamine.

Abstract: The invention relates to a process for the preparation of urea from ammonia and carbon dioxide, which preparation takes places wholy or partly with the application of a synthesis reactor, a condenser, a scrubber and a stripper, wherein an outlet of the stripper, through which a gas stream is discharged during operation, is functionally connected to the inlet of the condenser and to the inlet of the reactor and wherein an outlet of the condenser is functionally connected to an inlet of the scrubber and wherein the obtained reaction mixture is stripped in the stripper in countercurrent with one of the starting materials, wherein the gas stream coming from the top of the submerged condenser is subjected to an extra washing step before this gas stream is supplied to the high-pressure scrubber. The submerged condenser operating as such may be for example a submerged condenser of horizontal or vertical design of a falling-film high-pressure carbamate condenser transformed into a submerged condenser.

Abstract: Process for the preparation of urea from ammonia and carbon dioxide, wherein the waste gases released at virtually atmospheric pressure in a urea plant are compressed by an ejector driven by the waste gas from the high-pressure synthesis and are supplied to a medium-pressure absorber. The pressure of the waste gases is increased by 0.15-1 MPa.

Abstract: A process for the combined production of ammonia and urea of the type comprising an ammonia synthesis reactor (2), a urea synthesis reactor (5) and a urea recovery section (21) stands out for the fact of submitting at least a part of a flow comprising carbamate in aqueous solution coming from the urea recovery section (21) to a partial decomposition treatment, to obtain a flow comprising ammonia and carbon dioxide in vapor phase and a flow comprising diluted carbamate in aqueous solution, which is fed together with a gas flow comprising hydrogen, nitrogen and carbon dioxide, preferably obtained by hydrocarbons steam reforming, and a flow comprising ammonia coming from the ammonia synthesis reactor (2) to a carbamate synthesis section (3), where ammonia and carbon dioxide are caused to react, to obtain a flow comprising carbamate in aqueous solution and a gas flow comprising hydrogen and nitrogen.

Abstract: The invention relates to compositions for defoaming aqueous media, comprising as defoamers urea derivatives of the formula I where R1—is a hydrocarbon radical, preferably having 4 to 30 carbon atoms or a hydrocarbon radical, preferably having 4 to 24 carbon atoms and one nitrogen atom or a hydrocarbon radical, preferably having 4 to 30 carbon atoms and one carbonyl group, R2—is a hydrogen atom or a hydrocarbon radical, preferably having 1 to 24 carbon atoms, R3—is a hydrogen atom or a hydrocarbon radical, preferably having 1 to 24 carbon atoms, R4—is an organic radical, preferably having 2 to 30 carbon atoms, and n—is from 0 to 5; in the form of solid particles, which are obtained by crystallization from a clear homogeneous melt dispersed in a carrier medium, and a process of preparation thereof.

Abstract: A method for enhancing the purity of a desired compound comprising: Step (a) treating a crude reaction product which contains at least one desired compound, unreacted starting materials and/or byproducts with at least one bifunctional quenching agent that is capable of selective covalent reaction with unwanted byproducts, or excess reagents; Step (b) allowing the quenching agent to covalently react with unreacted starting materials and/or byproducts to afford a derivatized compound of the quenching agent: and Step (c) isolating the desired compound is described as well as novel quenching agents and methods for their use in the rapid purification of synthetic intermediates and products in synthesis, combinatorial chemistry, and automated organic synthesis.

Abstract: The invention relates to a process for the preparation of urea from ammonia and carbon dioxide, the preparation being effected in whole or in part in a vertical combi-reactor. The gas stream leaving the stripper is fed to the condenser section of a vertical combi-reactor in which this gas stream is wholly or partially condensed in the carbamate stream which is transferred from the scrubber section to the condenser section via a downcomer. Ammonia and carbon dioxide are partially converted into urea in this condenser section of the combi-reactor. The urea conversion is completed in the reaction section of the combi-reactor.

Abstract: In a process for urea production, substantially pure ammonia and carbon dioxide are reacted in a main reaction space from which outgoes a reaction mixture subjected to stripping to obtain a partially purified mixture sent to a urea recovery section. From this section, a dilute carbamate solution is obtained which is recycled to an auxiliary reaction space in which the residual carbamate is converted into urea. This process achieves high average conversion yield with reduced energy consumption.

Abstract: A method for the modernization of a plant for urea production of the type comprising a reactor (2) for urea synthesis, a stripping unit (3) with carbon dioxide and at least one vertical condensation unit (4) of the film type, foresees the provision of means (36) for feeding a major portion of a flow comprising ammonia and carbon dioxide in vapor phase leaving the stripping unit (3) to the condensation unit (4) and the provision in said condensation unit (4) of means (37) for subjecting to substantially total condensation such major portion of the flow comprising ammonia and carbon dioxide in vapor phase, obtaining a flow comprising urea and carbamate in aqueous solution, then fed to the reactor (2) for urea synthesis. Thanks to the present method of modernization, the efficiency of the condensation unit (4) is remarkably improved, thus permitting an increase of its capacity.

Abstract: A process for producing an urea preparation of reduced particle-size and narrow particle-size distribution by using an air milling process is provided. Also provided is an urea preparation of reduced particle-size, narrow particle-size distribution, and high purity.

Abstract: A method for enhancing the purity of a desired compound comprising:Step (a) treating a crude reaction product which contains at least one desired compound, unreacted starting materials and/or byproducts with at least one bifunctional quenching agent that is capable of selective covalent reaction with unwanted byproducts, or excess reagents;Step (b) allowing the quenching agent to covalently react with unreacted starting materials and/or byproducts to afford a derivatized compound of the quenching agent: andStep (c) isolating the desired compound is described as well as novel quenching agents and methods for their use in the rapid purification of synthetic intermediates and products in synthesis, combinatorial chemistry, and automated organic synthesis.

Abstract: A process for reducing the residual free ammonia emissions from an urea production plant comprises the step of feeding a gas flow comprising carbon dioxide (8) to a melt urea flow (3) coming from the concentration section (13) of the plant.

Abstract: A process for recovery of solid and reusable urea from the urea adduction process. Refinery streams are subjected to a step of urea adduction for removal of unwanted branched products, aromatics and sulphur. The adduct is purified, dried and then subjected to the step of mechanical shearing.

Abstract: An improved urea recovery process is presented. In the improved process, multiple vacuum rated surface condensers used to condense water vapor evolved during urea vacuum evaporation/concentration are replaced by a direct contact cooler/absorber to obtain substantial capital and utility cost savings. Improved heat exchange efficiency of the present process significantly reduces cooling water usage in comparison to the surface condensers.

Abstract: Process for the preparation of urea, wherein in a first step ammonia and carbon dioxide react in suitable conditions so as to form a first mixture containing a quantity of urea, wherein in one or more subsequent steps ammonia and carbon dioxide are removed from the first mixture and the obtained urea is concentrated until a urea concentration has been reached suitable to be granulated in a gas stream, whereby apart from urea granules a second mixture containing air, gaseous ammonia and urea dust is formed which subsequently is washed, and wherein before or during the washing an amount of formaldehyde is added to the second mixture of air, ammonia and urea under circumstances wherein the ammonia can react with the formaldehyde in order to form hexamethylenetetramine (HMTA) whereupon the so formed HMTA is separated from the gas stream and is returned into the process before the granulation step.

Abstract: A composition for thermal energy storage or thermal energy generation comprising a silica based gel or dry powder in the form of silica particles containing a water/urea phase change material for thermal energy storage or an endothermic or exothermic compound for thermal energy generation. The water/urea phase change material stores and releases at least 50 cal/gm of thermal energy in freezing and melting, and has a melting and a freezing point in the range of -11.degree. C. to -15.degree. C. The endothermic compound is preferably ammonium nitrate, urea, or combinations thereof. The exothermic compound is preferably calcium oxide or calcium chloride. The thermal energy storage composition may find use in a variety of applications including medical wraps, food servingware, and "blue ice" for cold packs or food storage.

Abstract: A urea production process combining lower pressure urea concentration and carbamate recovery steps into a single non-vacuum operation. Following high pressure stripping wherein a bulk of unreacted carbamate is recovered from the reaction effluent, remaining carbamate is stripped by heated air at atmospheric pressure wherein urea is concurrently concentrated without the use of vacuum evaporators. Weak carbamate solution subsequently formed is stripped of water (and residual urea is hydrolyzed) using air and steam at a medium pressure single tower hydrolyzer/stripper to obtain a concentrated carbamate stream suitable for recycle to the reactor. The process employs heat integration for enhanced energy efficiency and produces a good quality aqueous condensate suitable for direct use as boiler feed water. Thus the aqueous condensate produced requires no additional cooling and ammonia treatment. The process employs simplified and reduced process unit operation to eliminate equipment for cost reduction.

Abstract: A process for neutralizing the ammonia present in the molten urea originating from the concentration section of a plant for its production, comprising adding to the molten urea a small quantity of an acid.

Abstract: A process for the purification of technical-grade N-alkyl urea, particularly mono-ethyl urea, including an alkali metal sulphate, characterised in that it includes the steps of:treating the technical alkyl urea with a C.sub.1 -C.sub.4 alcoholic solvent to cause the selective dissolution of the alkyl urea,separating the soluble fraction from the alkali metal sulphate which is insoluble in the alcoholic solvent, andremoving the alcoholic solvent from the soluble fraction to recover the N-alkyl urea.

Abstract: Process for vacuum-concentrating urea solutions in which the final step of evaporation of the urea solution under vacuum is carried out within the injection of overheated water vapor in the overhead portion of the concentrator, in order to counteract the formation and deposition of high-melting, fouling compounds derived from urea.

Abstract: A new method of preparing a new aminoureaformaldehyde fertilizer composition which exhibits high cold water insoluble nitrogen (CWIN) levels and high Availability Indices (AI). The method utilizes the discoveries that ammonia compounds, usually ammonium salts, inhibit the urea-formaldehyde polymerization reaction and decrease the formation of hot water insoluble nitrogen (HWIN), and that the ammonium compounds take part in the reaction to form controlled release compounds which are both cold water soluble and insoluble. The process is carried out at elevated temperatures between 60 and 125.degree. F., so that it may be completed in an order of magnitude less time than either the dilute or concentrated conventional commercial ureaform processes, requiring between 2 and 20 minutes for completion. In the process, between 3 and 25 percent of the total nitrogen is supplied as ammonia nitrogen with the remainder from urea, respective formaldehyde to urea to ammonia mol ratio is 1.0, between 1.0 and 2.

Abstract: A method is described which enables ammonia plant process condensate contaminated with ammonia, carbon dioxide and methanol and urea plant condensate contaminated with urea, ammonia, carbon dioxide and other combined forms of ammonia and carbon dioxide to be simultaneously converted, in a single treatment vessel, substantially and continuously to a vaporous stream rich in ammonia, carbon dioxide and methanol and an liquid stream poor in ammonia, carbon dioxide, methanol and urea. The vaporous stream thus produced is recycled and employed as a feedstock in the reforming section in the ammonia plant.

Abstract: A process to modernize existing urea plants which use a stripping with carbon dioxide, and to increase urea yields and flexibility under overload conditions while at the same time reducing energy consumption, corrosion phenomena and possible risks of explosive mixtures. The plant includes: a passivation stage with the introduction of an oxidizing agent and reduction of the air fed to the system; a medium pressure distillation stage of the products leaving the stripping section, and a condensation of the products of the distillation, effected in a pre-evaporation phase to concentrate at low pressure the urea solution.The modernized plant, includes at the start at least a reactor, a scrubber, a condenser, a stripper and the evaporators, includes also a passivation section, a medium pressure distillation section, and a distillation section with double-effect technique.

Abstract: Method for obtaining an organic polycrystalline material having in particular electro-optical properties, said material obtained and an electro-optical modulator comprising said material.This method includes a stage (1) for preparing a powder having a size grading of 500 to 800 nm of an organic compound having a delocalized system of electrons .pi. and presenting a non-centrosymmetrical crystalline structure, as well as intramolecular load transfer groupings, a stage (2) for drying the powder under vacuum, a stage (3) for pre-pressing the powder under vacuum, and a hot stage (5) for the uniaxial compression of the dried powder under vacuum.This method enables polycrystalline materials to be obtained, said materials comprising elongated monocrystalline grains orientated according to a given direction.

Abstract: A method for processing exposed and developed photographic silver dye-bleach materials, in which the exposed and developed material is treated with aqueous bleaching preparations which contain (a) an acid component, (b) a silver complexing agent, (c) one or more bleach catalysts, (d) optionally an antioxidant, (e) optionally a water-soluble oxidizing agent and (f) optionally a bleaching accelerator.A water-soluble and as a rule solid adduct of an acid amide or a lactam and a strong mineral acid is used as acid component (a).

Abstract: An improved process and apparatus for the concentration of an aqueous urea solution by evaporation of water in a single pass shell and tube heat exchanger having a substantially vertical tube bundle within the shell. The aqueous urea solution is introduced into the top of the vertical tube bundle and caused to fall as a film down the inside of said tubes whereby it is heated and water evaporated therefrom to form a concentrated urea solution. The heat for this evaporation is provided by condensing at least a part of a gas mixture containing NH.sub.3, CO.sub.2 and H.sub.2 O in the shell side of the heat exchanger. This gas mixture is introduced into a lower portion of the shell wherein it is caused to flow upwardly in shell in contact with said tube bundle, counter-current to the flow of the aqueous urea solution within the tubes whereby heat from said condensation is transferred to said aqueous urea solution flowing down the inside of the tubes.

Abstract: An improved process for the preparation of urea from carbon dioxide and excess ammonia at an elevated temperature and pressure to form a urea synthesis solution containing uncoverted ammonium carbamate and free ammonia. A portion of the ammonium carbamate contained in the urea synthesis solution is decomposed in a first decomposition zone by the supply of heat, and the first gas mixture thus obtained is separated and at least partially condensed in a first condensation zone. The residual area solution is heated in a second decomposition zone maintained at a pressure of between about 4 and 40 bar thereby decomposing a further portion of ammonium carbamate and the second gas mixture thus obtained is separated from the second residual urea containing stream. This second residual area stream is introduced into a further decomposition zone wherein remaining ammonium carbamate is substantially removed, and a third gas mixture thereby formed is processed to form a dilute aqueous ammonium carbamate solution.

Abstract: A method for passivating the surface of the strippers of the urea plants, where the temperatures are very high, where the pressures range from 120 to 240 Kg/cm.sup.2 and where the effluent process flow from the synthesis reactor undergoes one or more falling-film evaporations, preferably in countercurrent with a driving gas consisting of NH.sub.3 or CO.sub.2, characterized by the fact that the passivation is carried out by means of a sinergistic combination of oxygen, preferably injected into the bottom of at least one stripper, and of a second passivating agent, preferably injected into the process flow entering the head of at least one stripper, wherein said second passivating agent is injected in the liquid state or as a liquid solution, before or contemporaneously to the start of the evaporation.

Abstract: A falling-film process and apparatus for the cocurrent evaporation of a solution is disclosed. The process utilizes a tube-bundle heat exchanger in which the upper ends of the individual tubes of the tube-bundle are closed. Apertures, preferably in the form of slots, are formed adjacent the closed-end of the individual tubes. A liquid heel is maintained above the highest of said apertures and flows into the interior of the tubes through said apertures. Upon entering the tubes the liquid and any vapor released therefrom flows cocurrently in a downward direction. The vapors released from the liquid are recycled to a point above the liquid heel through conduit means separate from the individual tubes.

Abstract: The biuret content of biuret-containing urea is reduced by contacting a solution or melt of biuret-containing urea with a polar adsorbent under conditions sufficient to remove at least a portion of biuret from the urea. The resulting biuret-containing adsorbent can be regenerated for further use by contact with a polar desorbent under conditions sufficient to desorb at least a portion of the biuret contained on the adsorbent. Optionally, biuret can be recovered by recovering the biuret-containing desorbent, and biuret concentration in the desorbent can be increased by recycling the biuret-containing desorbent into contact with biuret-containing adsorbents, and biuret can be recovered from the desorbent by low temperature crystallization.

Abstract: Purified biuret is recovered from mixtures containing biuret and higher molecular weight urea condensation products by contacting melts or solutions of such mixtures with a polar adsorbent and extracting biuret from the adsorbent with a polar desorbent. The useful biuret-containing mixtures also may contain urea. These methods are capable of recovering biuret of 99.9 percent plus purity from mixture containing higher molecular weight urea condensations products such as triuret, melamine, ammelide, and others. The biuret-containing desorbent can be recycled into contact with biuret-containing adsorbents to increase its biuret concentration, concentrated by evaporation of otherwise, and/or treated to crystallize biuret. An integrated process is provided which involves pyrolyzing urea to form biuret and higher molecular weight condensation products and selectively recovering biuret from the resulting pyrolyzed urea as described.

Abstract: Methods are provided for removing biuret from biuret-containing aqueous urea solutions which methods involve contacting a quantity of a biuret-containing aqueous urea feed solution with the hydroxide ion form of an anion exchanger under conditions sufficient to remove at least a portion of the biuret from the feed solution, and regenerating the resulting biuret-containing anion exchanger, at least in part, by contact with a substantially non-alkaline aqueous regenerant under conditions sufficient to remove at least a portion of the biuret from the anion exchanger. After completion of the described contacting with the substantially non-alkaline aqueous regenerant, the anion exchanger can optionally be further regenerated by contact with an aqueous solution of a strong base to remove additional quantities of biuret and/or other anion exchanger contaminants such as alkaline earth metal and carbonate ions and/or compounds.

Abstract: Biuret is removed from biuret-containing aqueous urea solutions in a multi-cycle process which involves sequential (A) removal of biuret by contact with an anion exchanger and (B) regeneration of the anion exchanger, in which method, in one or more cycles, the anion exchanger regenerant comprises an aqueous solution of a strong base which has been employed to regenerate the anion exchanger in a previous cycle. This procedure allows for recycling, and thus reuse, of the strong base regenerant which results in significant economy.

Abstract: An improved process for recovering usable components from waste streams containing urea, including a dilute aqueous urea solution, which result from the preparation of particulate urea products. The dilute aqueous urea solution is used to wash a urea containing waste gas stream whereby urea contained in the gas stream is dissolved in the aqueous urea solution. The aqueous urea solution thus obtained is then subjected to a hydrolysis treatment whereby the urea contained therein is hydrolyzed, and the ammonia and carbon dioxide thus formed are separated from the residual liquid stream.

Abstract: Methods are provided for removing biuret from biuret-containing aqueous urea solutions by contacting the biuret-containing urea solutions with the hydroxide ion form of an anion exchanger under anion exchange conditions in which methods one or more aqueous process streams are either formed from materials which are substantially or completely free of alkaline earth metal and/or carbonate impurities or which process streams are treated either before or during their use in the anion exchange process to reduce their content of contaminant alkaline earth metal and/or carbonate compounds. The anion exchanger can be washed and regenerated with one or more aqueous media including water, aqueous solutions of strong base, acidic chloride solutions, and/or other aqueous solutions, and either batch or continuous (fixed bed) contacting can be employed.

Abstract: Methods are provided for recovering biuret from aqueous urea solutions and for producing relatively concentrated biuret-containing extracts which involve contacting a biuret-containing aqueous urea solution with the hydroxide ion form of an anion exchanger to retain at least a portion of the biuret on the exchanger, contacting the resulting biuret-containing ion exchanger with an aqueous extractant under conditions sufficient to form a biuret-containing extract, and contacting the resulting biuret-containing extract with the same or other biuret-containing anion exchanger in the same or subsequent cycles under conditions sufficient to increase the biuret concentration of the extract. The biuret-containing urea feed solution may also contain higher molecular weight urea condensation products, and the biuret can be selectively separated from such condensation products by the disclosed methods.

Abstract: Methods are provided for recovering purified biuret from aqueous solutions containing biuret and higher molecular weight urea condensation products by contacting such solutions with the hydroxide ion form of an anion exchanger and extracting biuret from the ion exchanger with an aqueous extractant. The useful biuret-containing solutions also may contain urea. These methods are capable of recovering biuret of 99.9 percent plus purity from solutions containing higher molecular weight urea condensations products such as triuret, melamine, ammelide, and others. Elevated temperatures increase biuret recovery rate and concentration, and the extractant can be recycled into contact with additional biuret-containing anion exchangers to increase biuret concentration even further. The biuret-containing extract can be employed as is, concentrated by evaporation or otherwise, or treated to crystallize biuret.