Solid Urea

2 Urea as Ammonia Precursor Compound 16.2.1 Solid Urea 

The easy release of NH3 from the precursor compound clearly becomes a disadvantage for the application of AdBlue in Mediterranean up to tropical areas. 

Since the commercial introduction of AdBlue in 2004 [24], it has been adopted worldwide for heavy-duty applications of Diesel engines equipped with SCR systems, and is considered the most promising system for the Diesel engine passenger car market [25]. 

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The estimation. Label two 250 ml. conical flasks A and B, and into each measure 5 ml. of urine solution (or about o i g. of solid urea, accurately weighed). Add to each about 20 ml. of water and bring the temperature to about 60°. To A add 3 drops of phenolphthalein solution and to B add i ml. of 0-5% mercuric chloride solution. Now to each solution, add 10 ml. of the urease solution and mix well. The mixture A soon turns red. 

Amino acids are the building blocks of proteins, which have long chainlike molecules. They are oxidized in the body to urea, carbon dioxide, and liquid water. Is this reaction a source of heat for the body Use the information in Appendix 2A to predict the standard enthalpy of reaction for the oxidation of the simplest amino acid, glycine (NH2CH2COOH), a solid, to solid urea (H2NCONH2), carbon dioxide gas, and liquid water ... 

C06-0093. Solid urea, (NH2)2 CO, bums to give CO2, N2, and liquid H2 O. Its heat of combustion is -632.2 kJ/mol. (a) Write the balanced combustion equation, (b) Calculate the heat generated per mole of H2 O formed, (c) Using this heat of combustion and the appropriate thermod3uamic data, determine the heat of formation of urea. 

The baking process, particularly the batch variety, presents a number of serious disadvantages. Not only does the reaction produce solid urea decomposition products, but it also releases large amounts of ammonia and ammonium salts which escape by sublimation. The foam which is thus formed makes for a porous reaction mixture, which in turn even prevents heat conduction. Moreover, the reaction mixture tends to adhere to the surface of the reaction vessel and the stirring unit a phenomenon which adds to the complexity of the problem. 

A 3 1 molar ratio of ammonia and carbon dioxide (excess ammonia) are heated in the autoclave for 2 hr at 190°C, and 1500-3000 psi. The mixture formed is approximately 35% urea, 8% ammonium carbamate, 10% water, and 47% ammonia. It is cooled and the ammonia is distilled at 60 °C. The residue from the ammonia still enters a crystallizer at 15°C. More ammonia is removed by vacuum. The resulting slurry is centrifuged to get solid urea. All excess nitrogenous materials from the liquid are combined and processed into liquid fertilizer, which contains a mixture of all these materials. 

Norma and branched Aliphatic Hydrocarbons. The urea-adduction method for separating normal and branched aliphatic hydrocarbons can be carried out in sulfolane (38,39). The process obviates the necessity of handling and washing the solid urea—normal paraffin adduct formed when a solution of urea in sulfolane is contacted with the hydrocarbon mixture. Overall recovery by this process is typically 85% normal paraffin purity is 98%. 

The urea-product solution, leaving the first decomposition stage and still containing some unreacted carbamate and excess NH3, is let down in pressure and steam heated in the second-staged decomposition section, which operates at about 2 atm and 120°C. Practically all of the residual carbamate is decomposed and stripped from the urea-product solution together with the residual excess ammonia. The 74—75 wt % urea solution thus obtained is further processed to solid urea... 

The combustion of 1 mol of solid urea to liquid water and gaseous carbon dioxide and nitrogen (N2) in a bomb colorimeter at 25°C (constant volume) liberated 666 kj of heat energy. Calculate AH, the change in heat content (enthalpy), for this reaction. 

Urea processes provide an aqueous solution containing 70—87% urea. This solution can be used direcdy for nitrogen-fertilizer suspensions or solutions such as urea—ammonium nitrate solution, which has grown in popularity recently (18). Urea solution can be concentrated by evaporation or crystallization for the preparation of granular compound fertilizers and other products. Concentrated urea is solidified in essentially pure form as prills, granules, flakes, or crystals. Solid urea can be shipped, stored, distributed, and used more economically than in solution. Furthermore, in the solid form, urea is more stable... 

Solid urea containing 0.8—2.0 wt% biuret is primarily used for direct application to the soil as a nitrogen-release fertilizer. Weak aqueous solutions of low biuret urea (0.3 wt% biuret max) are used as plant food applied to foliage spray. 

Suspend 20 g yeast RNA (free acid) in 88 ml H20. Chill in ice and add, with stirring, 12 ml 5 N KOH until the RNA has dissolved. Incubate at 37°C for 24 hours with intermittent stirring or shaking. Add 100 ml H20 and titrate to pH 7.0-7.4 with 1N HO. Add 420 g solid urea and make the volume up to 11 with distilled water. Filter and store frozen. 

Urea may be supplied as a solid or in a solution, and solid urea is classified as granular or prilled products. Prilled products have less desirable qualities than granules and are usually marginally cheaper than granulated product.109... 

DANSET MUF is a 64% solids urea formaladehyde condensate in clear liquid form, modified for maximum storage stability. The resin will remain completely water soluble for over a year at room temperature. Its minimum degree of polymerization makes it ideal for shrinkage control and wash and wear properties on rayon and rayon blend fabrics and other cellulosics. 

Many phenols are best prepared by boiling aryldiazonium compounds with water. Excess nitrous acid from the diazotization is first destroyed by addition of solid urea, Some substituted diazonium compounds are hydrolyzed with difficulty. Refluxing with aqueous sulfuric acid, copper sulfate, or sodium sulfatesolutions is usually recommended. 

Changes in the hydrophilicity of UF resins are not uncommon. During an acid advance of a UF cook, solid urea is commonly added. This both adjusts the mole ratio of the cook to the desired level, and has the added advantage of reducing the viscosity. A surprisingly small amount of water will have the same effect on viscosity. 

The infinite-dilution heat of solution for solid urea (CH4N2O) in water at 25°C is reported in T/ie Chemical Engineer s Handbook to be —3609 cal/g. In the same book the heat of formation is reported to be —77.55 kcal/mol for liquid urea and —79.634 kcal/mol for crystalline urea. Compare the heat of melting of urea with its heat of solution. 

Calculate the standard entropies of formation of (1) liquid methanol, and (2) solid urea, making use of the absolute entropies listed in Table 5,2. 

Problem 7.26. When urea dissolves in water, the solution becomes cold. What would you expect to happen to an aqueous solution of urea with additional solid urea in the beaker if it were heated ... 

Urea CO(NH2)z when a solution of a nitrite is treated with solid urea and the mixture acidified with dilute hydrochloric acid, the nitrite is decomposed, and nitrogen and carbon dioxide are evolved. 

Bell and Liu prepared newly designed heterocyclic receptors via the Friedlander condensation and used them in the complexation of urea. For example, urea complex 376 (88JA3673) is at least 10 times more stable than the best crown ether receptor that also solubilizes solid urea in chloroform (Scheme 83) (90AGE931). 

Disperses Solid Urea Partic. in the Pblymer AAotrix... 

The main disadvantage of these liquids is that they corrode mild steel and stainless steel. It is recommended that th be stored and handled in tanks, pipes, and equipment made of plastic (PVC, polyolefins, etc). In the production of NPK add liquid mixtures probably the best combination of ingredients is UAN, solid urea, merchant-grade phosphoric add, and potash. Typical formulations usir these ii iedients are given in Table 10.12. 

Urea is a special amide, a diamide of carbonic acid. A colorless, water-soluble, crystalline solid, urea is the normal end product of protein metabolism. An average adult excretes approximately 30 g of urea in his or her urine daily. Urea is produced commercially from carbon dioxide and ammonia, mainly for use as a fertilizer. 

Urea has gained popularity as the source of ammonia due to reduced handling concern. The urea solution is produced at the site by blending deionized water and solid urea, and the systems are designed to produce gaseous mixture of ammonia, carbon dioxide and water by the hydrolysis of the urea-in-water solution ... 

Typical procedure. Bis-4-(2,2-dimethyl-l,3-dioxolyl)rr)ethyl carbodiimide (BDDC) 1034 [758] Triphenylphosphine (131 g, 110 mol%) was dissolved in dry dichloro-raethane (1.1 L), and the resulting solution was cooled to 0 °C. Bromine (25.7 mL, 80 g, 110 mol%) was added dropwise over a period of 15 min, and then triethyl-amine (157 mL, 114 g, 250 mol%) was added in one portion. Solid urea 1033 (131 g, 0.45 mol) (for the preparation of 1033, see Section 4.3.4.1) was added to the yellow suspension in small portions over a period of 50 min. The resulting brown slurry was stirred at room temperature for an additional 3 h, then diluted with hexane (500 mL), and the solids were filtered off and washed with diethyl ether. The solvents were evaporated from the combined filtrate and washings to leave a brown slurry, which was resuspended in fresh diethyl ether and again diluted with hexane. The solids were filtered off and washed with diethyl ether as before. This procedure of evaporation, suspension, and filtration was repeated until no further solids precipitated (usually four cycles). The final viscous, clear brown oil, crude 1034, was bulb-to-bulb distilled at reduced pressure to give pure BDDC 1034 (107 g, 89%) as a pale-yellow oil. It could be stored indefinitely at 0 °C under argon bp 115-125 °C, 0.3 mmHg IR = 2130 cm . ... 

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