An increasingly important use of urea is in reducing air pollution from diesel engines in cars, buses and lorries. Containing 46% N, it is the most concentrated nitrogen fertilizer, and is readily available as free-flowing prills (granules). Urea is the world's most commonly used nitrogen fertilizer and indeed more urea is manufactured by mass than any other organic chemical. At normal atmospheric temperatures, approximately 1 pound of urea can be dissolved in 1 pound of water. 1. Urea-Water-Solution Properties: Density, Viscosity, and Surface Tension in an Under-Saturated Solution. The diesel engine is combined with an electric motor which allows for purely electric driving even at high speeds which reduces the amount of pollutants significantly compared to a pure diesel engine. Methanal plastics (Formaldehyde plastics), Poly(methyl 2-methylpropenoate) (Polymethyl methacrylate), Poly(tetrafluoroethene) (Polytetrafluoroethylene). Ammonia and carbon dioxide are heated together at 450 K and 200 atm pressure. Instead a solution of urea in water is injected into the hot gases emerging from the engine in the exhaust. Urea itself also forms important resins. It is the cheapest form of nitrogen fertilizer to transport and it is also the least likely to 'cake'. The urea is added to the exhaust gases as a 32% aqueous solution often known as BlueTEC. Figure 5 An aerial view of a large plant in Alberta, Canada, in which ammonia is synthesized. Ammonia reacts with carbon dioxide to produce urea. Another series is based on zeolites, in which some of the cations have been exchanged with a metal such copper. Figure 2 Urea tanks are now standard equipment for most new diesel lorries, buses and cars in many countries. It is therefore favoured in developing countries. First ammonium carbamate is formed, which rapidly decomposes to form urea: Figure 5 An aerial view of a large plant in Alberta, Canada, in which ammonia is synthesizedand then converted to urea.By kind permission of Agrium Inc. Much of the urea is prilled (Figure 6) and sold in that form. It is therefore favoured in developing countries. Research indicates that urea should contain no more than 0.25 percent biuret for use in foliar sprays. The products, ammonia and carbon dioxide, together with the exhaust gases, are passed immediately over a catalyst in the exhaust system. Figure 3 A Mercedes-Benz E-Class E300 BlueTEC Hybrid car. In this photo, a Mercedes bus is being filled with BlueTEC solution (with the blue nozzle to the lower tank) and diesel (the upper tank). The process is complex but the overall reaction can be represented thus: The system is known as Urea SCR (urea-based selective catalytic reduction) and can reduce pollution by nitrogen oxides to almost zero. Figure 4 A line diagram of the car above illustrating five key elements in the design of the exhaust system. Urea is highly water soluble. Several catalysts have been used. Urea, the diamide of carbonic acid. One way to remove this pollutant is to allow it to react with ammonia to form nitrogen. Potash Corporation, 20132. International Fertilizer Industry Association, 2014. When applying urea fertilizer, make sure the outside temperature is between 32 degrees and 60 degrees Fahrenheit. Ammonia reduces the oxides of nitrogen (mainly nitric oxide), formed in the combustion processes, to nitrogen. Figure 1 This rice paddy field in Thailand has been treated with urea, the nitrogen-containing fertilizer that is most used in developing countries. Urea is always manufactured close to an ammonia plant (Figure 5). For many crops, the quantity of nitrogen applied at one time shouldn’t exceed 20 pounds of nitrogen per acre. One series is based on transition metal oxides (for example those of vanadium and tungsten) on a carrier, titanium dioxide.
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