TitleSynthesis of melamine from urea, II.

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7 Issue Date 9-0- URL http://hdl.handle.

1 TtleSynthess of melamne from urea, II Author(s) Knoshta, Hdeo Ctaton The Revew of Physcal Chemstry of 7 Issue Date 9-0- URL Rght Type Departmental Bulletn Paper Textverson publsher Kyoto Unversty

2 SYNTHESIS OF MELAMINE FROM UREA, III By H~na~> KINtGnt''a Introducton It was reported n the prevous paperst '--> that n the reacton of yeldng melamne rom urea, the frst step s the escape of ammona from urea and the second step s the reacton between ammona and cyanurc acd whch are formed n the frst step. Namely, the hydroxyl radcals of cyanurc and are replaced by amno radcals, and -at the same tme the water s produced. Consequently. melamne s formed accordng to the next process, urea-+cyanurc acd-+ammelde->ammelne--*melamne. The yeld of melamne was on the assumpton tnat the dehydrated water formed n the above second step decomposes urea, ammelde, ammelne and melamne and the water does not reman. The author studed knetcally the successve reacton of ammelde ammelne-*melamne n the reacton of yeldng melamne from urea. Expermentals Mcroautoclaves, the capacty of whch s about cc, are used n measurng the velocty of the formaton of melamne. The. autoclaves are protected from corroson by the slver lnng. At the reacton temperature (the tme necessary to the reacton temperature s about mnutes), the autoclaves aze kept for each reacton tme and cooled rapdly by ce water. Expermental Results The condtons of ths experment aze as follows, packng ratos are 0. and 0. g/cc", temperatures, 7, 90, 00 and YC and tme range, up to hours. The weght percentage of sold formed for the urea used and that of each component n sold aze shown n Fg.. The analyss s all the same as the prevous paper~> but the quanttes of ammelde and ammelne are calculated from the ntrogen content measured by Kjeldahl. After the formaton of cyanurc acd n the reacton of yeldng melamne from wen, as the reacton type s dehydraton, the water formed may decompose urea, ammelde, ammelne and melamne. In Fg., the quanttes of sold products after ~ Sakyo Unversty "* The packng ratos of 0. and 0.g/cc are chosen because of dffculty of packng above OSg/cc and analysng below 0. g/cr. ) H, Knoshta. T~s joeam(,, (9) ) ~I-. I{noshta, bd.., 9 (9)

3 o The Revew of Physcal Chemstry of Japan Vol. No (9) fg H. Knoshta B~ 0 0 o- ~ '. 'C ~~ 0: s!=r B ~o 7"C O.Ss/== a 90 C O.S a~== ~ o f--o-~ ZO a 0 D~ o_ g X_' a' a a G a so C 0. s/r= 7'C 0. sl== 90`C 0:ar== L [J C W u L m.~ so ao fo I ao nl so GO '~ -~ ~. ---~ :~ 00'C 00' C o~ _ c~" ~e 0. sr= ~ 0. er=r O- _.~,~ a z a s e a A 0`C q 0'C O.S srrr > z 0. ar=r,~ o 0 ~,~.~"~ z a Fg. Weght percentage of sold for urea used, and that of each component n sold. > sora Urea Ammelde Ammelne hfelamne 0 O e e ~A o.-'o ~~ 0 ~ a a p ~ - Tme. hr

4 Synthess of Melamne from Urea, III 9 dryng are consdered as constant rrespectve of the slght decrease wth the lapse of rme. Moreover, the quanttes of urea n sold are also consdered as constant regardless of the slght ncrease at hgh temperature. It s antcpated that the decomposton of each component by dehydrated water s smaller except n the ntal perod of reacton as there s small pressure ncrease or pressure constant at 7`C or above 00 C~I. So the composton of gas phase and the concentratons of ammona n lqud phase may be almost constant. The concentratons of ammona n lqud phase at each tme n 'fables are nearly constant. The concentraton of ammona s calculated as follows :frst of all, the total ammona n autoclave s calculated from the quantty of each sold component by usng the followng equatons. In each of the below equatons, the same equatons are ntroduced n the cases of urea, atmnelde, ammelne and melamne whch are decomposed by dehydrated water. NH,CONH,=(NH,CN), +NH,+C0: () SNH,CONH_ =(CN),(NH,),(OH) + NH, + C0. ( ) NH,CONH. _ (CNh(NH,)(OH), + NH~ - CO_ ( ) Next, the quantty of ammona n gas phase and the concentraton of t n lqud phase are calculated on the assumpton that the composton of gas phase s NI,: CO.=: I. The pressures at, 90 and D'C are nterpolated n the curves of pressures and temperatures at 0, 7, 0D and `C, and the specfc gravty of lqud phase s assumed as constant (lglcc)", regardless of the varaton of each component. Knekcal Consderatons At the temperature and tme ranges of ths experment, the reacton product conssts of ammelde, ammelne and melamne, and at hgher temperature ammelde does not exst except n the ntal perod of reacton. In the calculaton of reacton velocty, t s assumed that the sold product, urea and the concentraton of ammona n lqud phase are all constant at each temperature and packng rato. Moreover, t s assumed that ammelde and ammelne are dssolved n melted urea because that ammelde or ammelne does not melt at expermental temperature, and that the ammelne s formed n urea by the reacton between ammelde and ammona and suc cessvely melamne s formed by the reacton between ammelne and ammona. And the reacton velocty of the above two steps of successve reacton are calculated as homogeneous and bmoleculaz reacton n urea. The ntal concentraton of ammelde (at lower temperature) or ammelne (at hgher temperature) s obtaned by extrapolatng the quantty of sold from whch s excepted the quantty of urea to the startng tme of reacton. k and ks are calculated at the temperatures of, 7 and 90 C, and " The specfc gravty of lqud phase n expermental condton s consdered as about lg/cc, from~thestuaton. of the surface of lqud phase n.autoclave.

5 I 70 H. I{noshta k: only at 00 and 0 C. x, r, ammelde-~ ammelne-~ melamne a=ntal concentraton of ammelde or ammelne Ce, Ca and C =concentratons of ammelde, ammelne and melamne. Rate constant of the reacton of ammelde-'ammelne When the concentratons of ammelde and ammona n lqud phase are [C~] and [NH,], the decreasng velocty of ammelde s as follows: _ at dca = k,jnh,7lc ]. ( ) The equaton () s so]ved as follows on the assumpton that [NH,] s constant. k = INH].0 log a.,,t C,. C ) The rate constants of the frst step, k;, at the temperatures of, 7 and 90 C obtaned by usng the above equaton are shown n Table. Table Temp. C '~ Packng Q rato,~ Q/cc ' f Urea \I mole/ 0A..9 0.f Tme hr z a S J 7 Ce k /mole, lss Ss o.oso mean mean hr I kp /mole, o.o~~ ht r~ 0. a oe. s.7 ~ 7s o.oss z ss loa mean r LL mean ~ z /9 / 'C A mean O.D99 mean 0.79 In Table P, the value of k, at the packng rato of O.Sg/cc s ~ tmes of that of 0.g/cc: The effect of pressure may be consdered as the pressure becomes hgher when the packng rato becomes larger On the otherhand, the rato of the quanttes of urea as a solvent n the cases of tmo packng ratos s.:. Namely, the rate constant s proportonal to the. concentraton of urea, and so the larger the packng rato-the hgher the concentraton of urea, the larger the rate constant.

6 The Revew of Physcal Chemstry of Japan Vol. No. (9) Synthess of Mrlamnc from Urea. ]II 7 boreocer, n the Prevous paper'>, the reacton between water nsohble (N=9. d) and ammona proceeds slghtly at 00`C, and the reacton between ammelne and ammona does not proceed at 00 C, t s capable to consder that the reacton between ammelde or ammelne and ammona does not proceed when the urea does not exst. Consequent ly, t s assumed fnat the rate constant k, when the mole fracton of solvent s N., s equal to the product of k~* whch s the rate constant at nfmte dluton, and N;. I, The value of k,* and n (constant pecular to the reacton) are obtaned by solvng the two equatons for k, and N. The value of tt to the reacton of ammelde-.ammelne are -.. Ry usng k,* n Table, u; the relaton between log k~* and /T s obtaned as n Fg.. As ammelde exsts n shorter tme at ntal perod of reacton above 90 C, the value of k*, above 90`C may be naccurate. And so the straght lne of log k,* and / T s drawn for two ponts of and 7`C, and from the nclnaton of ths straght lne, the ac~vaton energy of the reacton of ammelde-.ammelne s evaluated as l. Kcal. hate constant of the reacton of ammelne -* melamne a) Relow 7-C. In the successve reacton as ammelde-+ammelne-~melamnc, ammelne s shown when the rate constant of the and that of the formaton of mel~ melamne s k:, tlws: dcn dca d =k, [NHsI[< NH,I[Cal-k;INH,I[C l. - () a [ The equaton (S) s solved as folk follows> on the assumpton that [NH,] s constant as n the equaton (). CA-aḳ k (e C.=a-C c -La _~ _a L~ the k CA=ate-(C lcsfl]lt-c-l9(sii,$),-k, -CA O k: velocty of the formaton of decrease of ammel de s k,, = a ~ - k=e_k ;.e,,:-k,e-xacx,r,y (9) ~ h~-k, ~' The value of k_ s obtaned graphcally by usng the value of k whch s shown n Table. The value of k_ at the temperatures of and 7`C are shown n Tabte. There exsts the same tendency n the value of k_ at each packng rato ) S. Glasstone; Fdenrents of Physcal Cken~stry, y 0 (900).a --> I/TxCs Fg. k. Ls

7 7 -T-I. Knoshta Table Temp, C ~ Packng rato ; a 9,! Urea g/cc I THa I mole/ /mole, Tme ~ C~ hr ~ hr ~ k, /male, hr ~- /mole, hr G 0.9. ~ A I n , I 0.0 mean D.007 mean 0.0 L 0 O.O~A mean mean 0.0 o.oa n Table as n the value of k,. The value of k', whch s the rate constant of nfnte dlute soluton, s obtaned approxmately by usng the same equaton as that of (7). b) Above 90 C. As ammelde exsts n shorter tme at the ntal perod of reacton, the fast step of the successve reacton s neglected and the rate constant of the second step ke s calculated. The values of k. n Table are obtaned by usng the followng equaton whch s led as n the case of the reacton of ammelde-+ ammelne. k.=.0 log a [NH,]t C~ [NH,]t a-g In ths case also, k,' s obtaned by usng the same equaton as (7) because the value of k, s dfferent wth packng rato. The values of n n ths case are.-.. By usng k,` n Tables and, the relaton between log k,' and (T s obtaned n Fg.. From the nclnaton of the straght lne, the actvaton energy of the reacton of ammelne-+melamne s evaluated as 9. Kcal. Conclusons I) In the reacton of yeldng melamne from urea, the rate constants of the successve reacton as ammelde-+ammelne-.melamne, are calculated under the assumptons that the reacton s homogeneous and bmolecular n lqud phase, urea exsts as a solvent. and the concentraton of ammona s unchangeable at each

8 Synthess of Melamne from Urea, III 7 Table Temp. C Packng j n rato g/cc I 0. 7 S Urea...9 I~H mole/ 9 0. Tme hr /9 C~ k, k,~ /mole, hr /mole, lu 9.. 'LL , L mean 0.00 ' T mean o.o7s 00 os 0 sa ff sa.a f.9 s.a 7.9 z/ / 'L : mean mean I/ /.. 0. mean 0 S. 7.0 / f 9.f mean temperature and packng rato except n the ntal perod of rcactor.. ) It s consdered that the dfference of rate constant by packng rato s du_ to the mole-fracton of the solvent (urea), and the.rate constant at nfnte dluton s~decded as that of the temperature. ) Actvaton energes of the successve reacton as ammelde-.ammelne-.melamne.are. obtaned as. and -9. Kcal. respectvely. The author wshes to express hs hearty thanks to Prof. R. Kyama for hs encouragement and revson.. The author s partly ndebted to the Department of Educaton for the Grant n Ad for Fundamental Scentfc Research. The L bor tory of Physcal Chemstry,.Kyoto Unversty

Title solubility of compressed acetylene.

Title solubility of compressed acetylene. Ttle The solubltes of compressed acet solublty of compressed acetylene Author(s) Hraoka, Hroyuk Ctaton The Revew of Physcal Chemstry of 18 ssue Date 1954-09-10 URL http://hdl.handle.net/2433/46704 Rght