I n d . Eng. Chem. Res. 1989, 28, 638-641
638
should decrease, which agrees with experimental results. The observed steady release rate of urea in water a t all temperatures is due to the sterile media, where the only important factor is urea diffusion through pinholes in the coating film. Finally, a comparison between urea release from PCU and SCU as a function of temperature and incubation time is shown in Figure 9. On the basis of these curves, one can conclude the following. (1)Urea release from PCU shows a steady release pattern throughout the incubation period in all media. (2) The coating film for PCU is quite stable and is not affected by temperature or microbial activity. (3) Urea release from SCU shows a sharp rise in release after a certain incubation period. This period decreases with increasing temperature. (4) The coating film for SCU is susceptible to microbial attack that results in film degradation as evidenced by the sudden change in release rate. This process is enhanced by high temperatures. Acknowledgment This work has been supported in part by the Kuwait Foundation for the Advancement of Sciences. R e g i s t r y No. Polyethylene, 9002-88-4; sulfur, 7704-34-9.
Literature Cited Asokan, P. K.; Vikraman Nair, R.; Sudhakara, K. Dissolution rate of urea and muriate of potash packed in perforated polybags. Agric. Res. J . Kerala 1985, 23(1), 117-120. Brady, N. C. The Nature and Properties of Soils; New York: Macmillan Publishing Co.: 1984. Hashimoto, I.; Mullins, R. C. Dissolution of sulfur-coated urea in soil: I. Wax-sealed sulfur-coated urea. Soil Sci. Soc. Am. J. 1979, 43, 1165-1 168. Hattori, T. Microbial Life in the Soil: A n Introduction; Marcel Dekker: New York, 1973. Hignett, T. P. Controlled release fertilizer. Fert. News, 1971, 16, 42-48.
Jarrell, W. M.; Boersma, C. Model for the release of urea by granules of sulfur-coated urea applied to soil. Soil Sci. Soc. Am. J . 1979, 43, 1044-1050. Jarrell, W. M.; Pettgrove, G. S.; Boersma, L. Characterization of the thickness and uniformity of the coatings of sulfur coated urea. Soil Sci. SOC.Am. J . 1979, 43, 602-605. Johnson, F. H.; Eyring, H.; Polissar, M. T. The Kinetic Basis of Molecular Biology; Wiley: New York, 1954. Orteli, J. J. The effect of coating properties on the nitrogen release from sulfur-encapsulated urea. Agrochimica 1974,18(1-2), 3-9. Phongpan, S. Volatilization losses of ammonia from flooded soils: I. Effects of nitrogen source, method of placement and soil type. Thal. J . Agric. Sci. 1985, 18, 109-122. Prasad, M. The release of nitrogen from sulfur-coated urea as affected by soil moisture, coating weight, and method of placement. Soil Sei. SOC.Am. J . 1976, 40, 134-136. Reynolds, C. M.; Wolf, D. C.; Armbruster, J. A. Factors related to urea hydrolysis in soils. Soil Sci. SOC. Am. J . 1985,49, 104-108. Salman, 0.; Marafi, A.; Khraishi, N.; El-Mowafy, A.; Turk, U. Coating of urea for slow release of nitrogen. Kuwait Institute for Scientific Research, Report KISR1615, Safat, Kuwait, 1985. Savant, N. K.; Clemmons, J. R.; James, A. F. A technique for predicting urea release from coated urea in wetland soil. Commun. Soil Sci. Plant Anal. 1982, 13(9), 793-802. Singh, M.; Yadav, D. S.; Kumar, V. Leaching and transformation of urea in dry and wet soils as affected by irrigation water. Plant Soil 1984, 81, 411-420. Subbarao, M.; Ahmed, N.; Effect of soil acidity and saturating cation on adsorption of urea in soil. Plant Soil 1985, 79, 437-439. Synder, G. H.; Augustin, B. J.; Davidson, J. M. Moisture sensorcontrolled irrigatin for reducing N-leaching in Bermuda grass turf. Agronomy J . 1984, 76, 964-969. Tisdale, S. L.; Nelson, W. L. Soil Fertility and Fertilizers; Macmillan: New York, 1975. TVA Release mechanisms of sulfur-coated urea. New developments in fertilizer technology. National Fertilizer Development Center, Tennessee Valley Authority, Muscle Shoals, AL, 1976. Vyas, B. N.; Mistry, K. B. Hydrolysis of prilled urea, sulphur-coated urea and urea supergranules in an oxisol, vertisol and inceptisol. Indian J . Agric. Sci. 1985, 55(1), 35-40. Received for review August 26, 1988 Revised manuscript received January 23, 1989 Accepted February 15, 1989
COMMUNICATIONS Prediction of Critical Temperature and Pressure of Organic Compounds by Group Contribution T h e model using second-order group contributions developed by Jalowka and Daubert to predict critical temperature and critical pressure of hydrocarbons was extended to organic compounds containing oxygen, nitrogen, sulfur, and halogens. The molecular groups and normal boiling point are inputs to the critical temperature model with either experimental or predicted critical temperature as an added parameter for critical pressure prediction. Average errors of 1.0% and 3.9% result for critical temperature and critical pressure, respectively. The procedure compares favorably in accuracy with other established models and is additionally consistent with prediction methods for other physical and thermodynamic properties using second-order groups. Critical properties are important in most calculations for estimation of thermal properties and vapor-liquid equilibria. Since experimental determination of the critical point is difficult, a reliable and accurate prediction method is essential. All successful generalized methods for prediction of 0888-5885/89/2628-0638$01.50/0
critical temperature and pressure are of the group contribution type. The most accepted and accurate methods currently available for non-hydrocarbon compounds are the first-order methods of Lydersen (1955) and Ambrose (1978, 1979), which neglect next-nearest-neighbor effects and certain types of isomerization. Jalowka and Daubert 0 1989 American Chemical Society
Ind. Eng. Chem. Res., Vol. 28, No. 5 , 1989 639 Table I. Group Increments for the Prediction of the Critical TemDerature of Organic Compounds
O-(H)(C) O-(H)(Cb)
Oxygen Containing Increments 93.051 C-(H)3(0) 25.083 C-(H)z(O)(C) 73.708 C-(H),(O)(C,)
Table 11. Group Increments for the Prediction of the Critical Pressure of Organic ComDounds
-11.130 -11.167 -5.793 -9.546 -24.308 -15.344 -7.109 -2.599 -3.811 28.401 26.049 29.161
62.355 34.763 14.619 22.561 -5.491 -15.215 -41.098 -55.201 28.478
-3.789 -6.375 96.290 28.995 62.930 175.804 128.600
4.218 49.046 74.614 17.491 14.103 58.398 17.816 90.123 72.611
107.651 112.477 84.524 73.299 72.221 206.927 38.622 106.706 105.790 48.369 64.412 126.345 141.419
32.864 35.403 38.690 19.841 24.703 46.143 68.988 24.421 15.265 34.464 20.695 34.599 38.164 47.690
25.371 25.965 9.309 11.733 7.350
(1986) in the hydrocarbon portion of this work review these methods. Using second-order groups that take into account next-nearest neighbors should improve the accuracy of the group contribution approach. The groups utilized in this study were formulated by Benson and Buss (1958) and Benson (1976) for the prediction of ideal gas heat capacity, heat of formation, and ideal gas entropy. The carbon atoms are categorized as follows: C = any single-bonded carbon, Cd = any double-bonded carbon, C, = any triplebonded carbon, Cb = a benzene carbon (any carbon atom that is a member of an aromatic ring), and C, = an allenic carbon (a carbon atom with two double bonds,
