Solubilities in the systems melamine-sulfur dioxide-sulfur trioxide

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Ind. Eng. Chem. Prod. Res. Dev. 1982, 21, 464-470

electrophilic reaction at the site of metalation. The lithiated polymer is by far the most reactive, but is not shelf-stable. Additionally, the exact degree of functionalization is difficult to control. The mercurated species can be loaded to the greatest extent and retains quite favorable reaction characteristics. By virtue of its reactivity and loading capabilities, the mercurated resin is nearly always superior to the silylated species, except in those cases where acid sensitivity presents a problem, at which point the silyl compound becomes more appropriate. Literature Cited

Figure 3. IR spectrum of sulfonation of mercurated polymer.

the sulfonic acid moiety, in analogy to previously reported spectra (Zundel, 1969). Substitution for mercury could not be obtained cleanly when electrophiles were used which possess appreciable acidity or which form highly sensitive functions. Thus, reaction with TTFA, CH3SO2C1/BF3,and CSI afforded only unfunctionalized polystyrene resin, the product of protodemercuration.

Conclusion Silylated, mercurated, and lithiated polystyrene comprise a hierarchy of metalated reagents activated toward

Buehler, C. A,: Pearson, D. E. "Survey of Organic Synthesis"; Wiley: New York, 1970; Vol. 1, p 586. Burlitch, J. M.; Winterton, R. C. J. Organomet. Chem. 1978, 759, 299. Chang, Y. H.; Ford, W. T. J. Org. Chem. 1981, 4 6 , 3756. Farrall, M. J.; Frechet, J. M. J. J. Org. Chem. 1976, 4 1 , 3877. Felix, G.; Dunogues, J.; Calas, R. Angew. Chem. Int. Ed. Engl. 1979, 18, 402. Frechet, J. M. J.; Pelle, G. J. Chem. SOC. Chem. Commun. 1975, 225. Grubbs, R. H.; Su, S. H. J. Organomet. Chem. 1976, 122, 151. Letsinger, R. L.; Kornet, M. J.; Mahadevan, V.; Jerina, D. M. J. Am. Chem. SOC. 1964, 8 6 , 5163. Mathur, N. K.; Narang, C. K.; Williams, R. E. "Polymers as Aids in Organic Chemistry"; Academic Press: New York, 1980. Silverstein, R. M.; Bassler, G. C.; Morrell, T. C. "Spectrometric Identification of Organic Compounds", 4th ed.; Wiley: New York, 1981; p 169. Taylor, R. T.; Crawshaw, D. 9.; Paperman, J. B.; Flood, L. A.; Cassell, R. A. Macromolecules 1981, 74, 1134. Traylor, T. G.; Berwin, H. J.; Jerkunica, J.; Hall, M. L. Pure. Appl. Chem. 1972, 30, 599. Warshawsky, A,; Kaler, R.; Patchnornik, A. J. Org. Chem. 1978. 43. 3151. Zundel, G. Angew. Chem. I n t . Ed. Engl. 1989, 8 , 499.

Received for review October 28, 1981 Revised manuscript received December 2, 1981 Accepted January 22, 1982

Part of this work was reported at the 33rd Southeastern Regional Meeting of the American Chemical Society, Lexington, KY, Nov 5,1981; Abstract p 109. Acknowledgement is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for the support of this research. Funds for the purchase of the Perkin-Elmer Model 680 spectrometer were provided in part by the National Science Foundation through Grant TFI-8022902.

Solubilities in the Systems C3H6N6-S02-S03-H20 at 25 and 50 "C and C3H6N6-NH3=SO3-H20at 25 "C Joe Gautney," A. Wllllam Frazler, Yong K. Kim, and John D. Hatfleld Division of Chemical Development, National Fertilizer Development Center, Tennessee Valley Authority, Muscle Shoals. Alabema 35660

Solubilities in the systems C3H,N,-SO2-SO3-H2O at 25 and 50 OC and C3H,N,-NH3-S03-H20 at 25 OC were studied. The two systems include the absorption and chemical regeneration steps, respectively,of the melamine scrubbing process. The system C3H,N,-SO2-SO3-H2O is characterized by saturation fields of C3H6N,, (C3H6N6),.H2S04.4H20, (C3H6Ne)2.H2SO,*2H2O, (C3H,Ne)2.H2SO3.4H2O, (C3H,Ne)5'3H2S03.4H20, and C&&N,*H2SO3. Four invariant POlntS were identlfied in this system at 25 OC: ~3H,N,-(C3H,N,)4~H2~04~4HzO-(C3~,N,),~Hz~~3~4H2~ at pH 5.73, (C3H ~ N ~ ) ~ ~ H ~ S O ~ ~ 4 H ~ O - ( C ~ H e N B )at2 pH ~ H 5.2~1,~(C3H6N,)2.H2S03.4H20-(C3H,N6)2. O ~ * 4 H ~ ~ - ( ~ ~ ~ ~ ~ ~ ) ~ ~ ~ H2SO,.2H20-(C3H~N~)~.3H2so3.4H2o at pH 3.35, and (C3H~N,)2.H2S04.2H2O-(c3H~N~)5.3H2~o3.4H2o-c3H~N~'H2~o3 at pH 2.81. All but the last invariant point were also obtained at 50 OC. The system C3H,N6-NH3-S03-H20 over the pH range 5 to 11 at 25 "C is characterized by saturation fields of C3H,N, (C3H6N,)2.H2S04.2H20, (C3H6N6),-H2S0,.4H20, (NH,),SO, and a melamine sulfuric acid adduct-ammonium sulfate double salt tentatively identified Four invariant points were identified, each forming a corner of the double as (C3H6N6)4.H2S04.(NH,)2S04.2Hz0, salt saturation field.

Solubilities in the systems C3H6N6-S02-S03-H20 and C3H6N6-NH3-S03-H20 are of interest because these two systems include the absorption and chemical regeneration This article not subject to

U S . Copyright.

steps, respectively, of the melamine scrubbing process (Kohler et al., 1979). In the absorption step of the melamine scrubbing process, a gas stream containing sulfur

Published 1982 by the American Chemical Society

Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 3, 1982 465

(Dickerman et al., 1981) indicates that energy costs for the melamine process are slightly less than for the MgO scrubbing process. The solubility data for the systems C3H6N6-SO2-So3-H20and C3H6N6-NH3-SO3-H20 will provide data that will be extremely useful for maximizing FILTRATION Y the efficiency of the new process and for explaining and I solving problems which may be encountered when the process is tested on a larger scale. The solubilities of melamine (Chapman et al., 1943; MELAMINE lNH,12SQ McClellan, 1940; Zagranichnyi and Polyakova, 1963) and FILTRATION CRYSTALLIZATION I many of its acid adducts (Bann and Miller, 1958; Smolin lNH412S4 and Rapoport, 1959) have been reported in the literature; however, very few data are available for the solubility of Figure 1. Flowsheet of melamine process for purification of SOzmelamine in multicomponent systems. The system C3bearing stack gas. H6N6-H3P04-H20 has been studied (Kohler et al., 1981), but to the best of our knowledge, no previous data exist dioxide is contacted with an aqueous melamine slurry. for the Systems C3H6N6-S02-S03-H20 and C3H6N6This forms a hydrated melamine sulfurous acid adduct, NH3-SO3-H20 which are reported here. which precipitates from the solution. Experimental Section C&6N.&Olid) H20 -P C3H6N6(SOlUtiOn) (1) Equilibrium mixtures for the system C3H6N6-SO2-SS02(gas) + H 2 0 H2S03(solution) 0,-H20 were prepared and adjusted as necessary by (2) adding SO2 gas and solid (C3H6N6)2.HzS04.2H20to 2C3H&(SOlUtiOn) + HzS03(solution) + 4H20 aqueous melamine slurries. The (C3H6N6)2.H2S04.2H20 (C3H6N6)2.H2S03.4H20(solid) (3) was prepared in the laboratory and the melamine was reagent grade. A small amount of antioxidant (0.001 w t If SO2 is oxidized or SO3 is present in the gas, then hy9% p-phenylenediamine) (Zil'berman and Ivanov, 1940) was drated melamine sulfuric acid adduct also is precipitated. added to the 50 "C samples. No antioxidant was added to the 25 "C samples. Equilibrium mixtures for the system HzS03(solution) + 0.502 H2S04(solution) (4) C3H6N6-NH3-S03-H20were prepared and adjusted using H 2 0 S03(gas) H2S04 (5) reagent grade (NH4)$04, C3H6N6,NH40H, and H2SO4. The samples in Teflon-lined, screw-capped glass bottles 2C3H6N6(SOlUtiOn) + H2S04(solution)+ 2H20 were allowed to equilibrate in either a 25 f 0.5 "C or 50 (C3H6N6)2.H2S04~2H20(solid) (6) f 0.5 "C water bath equipped with a rotating sample holder for at least one month after petrographic analysis In the regeneration step, the spent slurry which contains (Frazier et al., 1981) showed that two or three solid phases both the melamine sulfurous and sulfuric acid adducts is were present. The samples were chosen so that all of the filtered, and the melamine sulfurous acid adduct is deinvariant point compositions and at least one composition composed thermally at 100-200 "C to yield melamine, SO2, lying on each of the phase boundaries connecting the inand water vapor. variant points would be obtained. After the initial equilibration period, the solid phases were checked again and, if still present, the equilibrium liquid phases were analyzed. Equilibrium liquid phases in the system C3H6N6-So2-So3-H2O were analyzed at approximately 2The sulfur dioxide is used to produce sulfuric acid or elweek intervals for totalnitrogen (NT),total sulfur (h), and emental sulfur. The melamine sulfuric acid adduct, unlike sulfur dioxide by iodine titration, but constant values could the sulfurous acid adduct, cannot be thermally decomposed not be obtained for compositions lying on the phase without first decomposing the melamine. Therefore, the boundaries between the invariant points because of oxithermally regenerated melamine, which contains the dation-related reactions which will be discussed later. The melamine sulfuric acid adduct, is split into two portions. equilibrium liquid phases in the system C3H6N6-So2-SOne portion is returned to the absorption step and the 03-H20 also were analyzed for ammonia nitrogen by other is sent to a chemical decomposer where it is treated NaOH distillation because a preliminary study of this with an aqueous solution of a base stronger than melamine. system at 50 "C indicated that some hydrolysis of melThis regeneratea melamine from the melamine sulfuric acid amine was occurring, especially in the more acidic samples adduct and produces a sulfate salt as a byproduct. Any base stronger then melamine can be used, but we chose (PH