Urea fertilizers

When completed in 1996, the Weihe plant will gasify 1500 t/day of coal to produce 300,000 t/yr of ammonia, which will be used to manufacture 520,000 t/yr of urea fertilizer. This project is the eighth Texaco oil or coal gasification plant Hcensed by Chinese industry. 

For most crops, other than rice, urea in the soil must first undergo hydrolysis to ammonia and then nitrification to nitrate before it can be absorbed by plant roots. One problem is that in relatively cool climates these processes are slow thus plants may be slow to respond to urea fertilization. Another problem, more likely in warmer climates, is that ammonia formed in the soil hydrolysis step may be lost as vapor. This problem is particularly likely when surface appHcation is used, but can be avoided by incorporation of the urea under the soil surface. Another problem that has been encountered with urea is phytotoxicity, the poisoning of seed by contact with the ammonia released during urea hydrolysis in the soil. Placement of urea away from the seed is a solution to this problem. In view of the growing popularity of urea, it appears that its favorable characteristics outweigh the extra care requited in its use. 

The removal of fertilizer N in the crop as NH4+ does not lead to acidification. Hydrolysis of urea fertilizer—by far the main form of N fertilizer used in wetland rice, together with ammonium bicarbonate in some countries—consumes 1 mol of H+ per mol of NH4+ formed (Table 7.1, Process 1). So although absorption of N as NH4+ leads to a net export of H+ from the roots to balance the resulting excess intake of cations over anions (Table 7.1, Process 5), this acidity is matched by the H+ consumed in urea hydrolysis. Likewise there is no net generation of acidity as a result of NH3 volatilization, although 1 mol of H+ is left behind per mol of NH4+ converted to NH3 (Table 7.1, Process 3). 

Cai GX, Zhu ZL, Trevitt ACF, Freney JR, Simpson JR. 1986. Nitrogen loss from ammonium bicarbonate and urea fertilizers applied to flooded rice. Fertiliser Research 10 203-215. 

Synthesis Fischer-Tropsch synthesis 100-700 ammonia propionic and acetic acid urea (fertilizers) butanediol methanol hydrocarbons... 

There are several different processes for making urea fertilizer. One process designed for energy savings is shown in Figs. 1 and 2. 

Brock, B. R. and D. E. Kissel, Eds. 1988. Ammonia Volatilization from Urea Fertilizers. Tennessee Valley Authority, Muscle Shoals, AL. 

Liuzhou Chemical Industry Corporation, Siuzhou, Guangxi, PRC — This gasifier uses a Shell design based on coal feedstock and converts 1,200 t/d of coal into 2.1 x 10 NmVd of syngas. The syngas is used to manufacture ammonia-based fertilizer and oxo-alcohols. Some process CO2 is recovered and used to make urea fertilizer. 

Important for urea fertilizers biuret concentration must be low due to possible plant damage... 

Exposure to urea may occur through inhalation and dermal contact with this compound at workplaces where urea is produced or used, especially to workers applying urea fertilizers. General population may be exposed to urea via ingestion of food, drinking water, and dermal contact with products containing urea. 

Kucey RMN. 1988. Ammonia loss following surface application of urea fertilizers to a calcareous soil. Commun Soil Sci Plant Anal 19(4) 431-445. 

Marshall, V. G., and D. S. Debell (1980). Comparison of four methods of measuring volatilization losses of nitrogen following urea fertilization of forest soils. Can. J. Soil Sci. 60, 549-563. 

Urea Fertilizer Bronchial problems/kidtrey damage... 

Pneumatic Sulfur-Spraying System. Sulfur-Coated Urea with Sealant. Figure 3 is a flow diagram of the pneumatic sulfur-spraying system. This system provides better atomization than the hydraulic system, which is discussed later. With the pneumatic system less sulfur is required, producing a higher analysis sulfur-coated urea fertilizer. 

The manifold designs are usually simple and straightforward when on-line columns are used to enhance sensitivity by retaining the interferents this procedure is often termed on-line clean-up" of the sample. Columns which selectively retain the interferent. but allow the analyte to pass freely, are connected in the sample introduction line either before of behind the injection valve (Fig. 4.3 a. b). Szpunar-Lobinska et al.[39] compared the two approaches in the determination of biuret in urea fertilizers by spectrophotometry, and strongly recommended the second one (Fig. 4.3 b) because ... 

Liang, R., and Liu, M. Z. (2006). Preparation and properties of a double-coated slow-release and water-retention urea fertilizer, J gric ood Chem.. 54,1392-1398. 

Note that in several cases, the plants produce combined products. Both ethylene and propylene are produced from a naphtha cut obtained from the fractionation of crude oil. A combined ammonia-urea fertilizer plant is common. The electrolysis of a brine solution produces both chlorine and sodium hydroxide. Recent literature data are usually given for plant capacities in tonnes per year (1 tonne = 1,000 kg) or tons per day (1 ton = 2,000 lb) of product, but the capacity data in Table 16.8 are given in pounds of product per year. Also included in the table is the value of Q for use in the following modification of Eq. (16.3) ... 

The reaction is written to illustrate the formation of the ionic species most prevalent at soil pHs. While urea is extremely stable at ambient conditions, soil urease converts urea rapidly often urea fertilizer additions are completely hydrolyzed in 2 to 3 days, a very rapid reaction in soil terms. The rate of hydrolysis depends on the soil temperature, moisture, how dispersed the urea is, and the amount of urease present. Very cold or dry soils hydrolyze urea more slowly than warmer or moist soils. The enzyme activity can be significantly different in different zones of a particular soil. High enzyme activities can develop on a moist soil surface because of algal and other microbial growth on the soil surface. 

I CO2 (emissions by Land Converted to Cropland) I CO2 (emissions by Urea Fertilization)... 

Another byproduct of the gas industry, carbon dioxide, was separated from the hydrocarbons and was used to make urea fertilizer. The hydrogen byproduct of this reaction was combined with atmospheric nitrogen to produce ammonia. 

Smirnoff, W. A. and Bernier, B. (1973) Increased mortality of the Swain jackpine sawfly, and foliar nitrogen concentrations after urea fertilization. Can. J. For. Res., 3, 112-15. 

---