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Title Chemical kinetics in the reaction between NH3 and CO2 underpressure
Author(s) Kiyama, Ryo; Suzuki, Keizo
Citation The Review of Physical Chemistry of Japan (1951), 21: 23-30
Issue Date 1951
URL http://hdl.handle.net/2433/46664
Right
Type Departmental Bulletin Paper
Textversion publisher
Kyoto University
The Review of Physical Chemistry of Japan Vol. 21 No. 1 (1950)
CHEMICAL KINETICS IN THE REACTION BETWEEN
NHa AND COz UNDER PRESSURE.
liy Ryo Ktva~ta and Kcizo Suzu~:~.
The study of the field of kinetics of the reaction behcecn \ I I, and CO_ under
pressure has scarcely been done. Therefore there are many obscure points. In the view of chemical kinetics, this investigation is carried out in order to clear
the mecl'anism of the reaction.
Apparatus and Procedure.
The schematic layout of the equipment is shown in Fig. I. ~\, is the reaction
vessel made of mild steel, the volume of which is 43 cc ; A_ and .4;,, the bombs,
each being filled with liquid Nff, or liquid CO,; r\„ the spiral tube in m~der to
preheat CO, gas ; G, and G.,, the burdon type pressure gauges ; "1'„ the copper-
constantan thermocouple, which is
put into the reaction vessel ; T.;and T„ the mercury thermometers;
the train of points denotes the
electric heater; V„ ......, V,,, the
valves. The samples, N11, and
CO_, arc stored in :\, or A; 6om
each convnerdll bomb and high
pressure is obtained by heating.
The procedure to carry out
the experiment at a given ratio of
pariial pressure of NI [; and CO_
is as (ollotrs; gaseous CO, is charged in
of G, becomes equal as' the partial pre:
and then until the reading of G, comes to
then the reading of G. falls down from
is charged into the vessel in use of the
reaction.
The esperintental procedure is as fo
>I5 As
Va
T~
vq
va
ez
vi
~ ,~ Pig. 1 Schematic layuW of equipment.
1 into the reaction vessel until the reading
pressure of \ H.; in the case of espcriment
to a definite total pressure of esperimen4
m P, to Yo. Tlius a given quantity of CO,
the reading of P, and P_. in performing the
follws; gaseous NH, is charged into the
TM
I
n
II 1 ,A..
i--®
nI
k n:*an
`t91:.,
i
t
I
i i
i
I
I
~,
.i
I
N 6
Y
O
O
m
9
The Review of Physical Chemistry of Japan Vol. 21 No. 1 (1950)
,°,} it. K71':filL1 and I:. SU'LDK7
reaction t•essel under a constant pressure and a definite quantity of gaseous CO,
is led into fhc acsscl in use of G,, as above mentioned. ~~ftenvards the readings
of G, against time arc recorded. `1'hc ratio of packing calculated as NII,C0~1'I-I _, from the pressure is 0.0~~-
0.`21 s/cc in tltc range of the reaction.
Moreover, after the reaction finished, the resultanU are cooled rapidly and
the sravimetric analysis of urea is carried out. The reproducibilih• of the csperimcot is within >°,n of the initial pressure
in the readings of Gr.
Experimental Results.
The experiments are perform=d in the range of pressure, 15210 1:5/cm-,
temperature, GO-•200°C, under various rations of partial pressure. Fig. ?-Fig. fi arc the pressure change curves plotted Crow the data of t;•le readings of pressure
sauce against time. Fig. 7 is the results of the urea Conversion percent curves.
s y PNNS~ PCOt
15 F,~ry3 : Pt03 m 2 1 190°C 6xp.35 t3 1~ t l00°C Exy.3 m B t 1 190°C Sry. PS
° 9 4 1 150°C 6xP-1B 11 4 1 100°C ffi9.5 m 6
9 m E t 100°0 6x9.2 n~ 2 : 1 150°0 6t9. 17 7
n 10 5 ~ t 3 13tl°C 6x9.8
J ~ 30 2 I 60°C 6x91 ~ EO i
10 EO 30 q0 50 ed 30 EO 30 40 50 80 00 lE0 'limo ;r.in.~ T1ae l~n.,
Fig. 9 Pressure change tunes. Fig. 7 Pressure change curres. Initial Preswre lb kgJeni=. Suitial press'are 36 pgja~,=.
Discussions.
Prom the pressure chance curves, there are bl•o cases; ate, a rapid pressure
decrease occurs, and the other does not, at the initial step. of the reaction. .\lso,
it is shown in the Urea co~mersion percent c_uves. Pig. 7, that there is some
difference in the forms of the reaction.
(I) The formation of NH,GQ_N~_
From the reason discussed below it can be considered that the rapid pres-
t6
t3
it
5
FHry3
i
P~Oy
I00°C 6xy.s
i
4 toa°C IDro. S
9
9
6
l
~~ O8 ~0
E
2
l taa°c
60°G
6LP.2
Bxy.l
~ J
B
PNNb
2
FCOp
1 1 90°C 8xp.35
L 1 170°C!i
7q
,aI6
~O
40
30
YO
Sry. ?5
150°CO
1 1 ~p.1B
_~6Yy,17
ID[P•B
2
t
i
3
150°C
13tl~C0 0
30 EO 3G 40 50 80 00 1b0
The Review of Physical Chemistry of Japan Vol. 21 No. 1 (1950)
CIIE~1rC AI. 1iINF.T1(.S IN TIIE RF.ACTInN RETNF.EN Nlr} AN17 CO. Sl
d[NH4CONHe] =k,[Lrtennediate product]. (4) dt
As K, is the equilibrium constant, from the step (1)
[Intermediate product]=K,[NH,]'[CO,J. (5)
In such a case as N}hCO.NH_ is not formed, accordingly, from Equations (4) and
(u"") the velocity of urea formation gives
d[NII,CONHo] =K,k,[N[I,]°[COs]=k[N}1~=[CUo], (8) dt
where
k=Krks• (~
Aifferentiating with respect to temperature from the Equation (~,
d LIk d I nK tl hlk ( ) dT dT r+ dT ~• 8
If A is the activation energy corresponping to d•, A„ the activation energ}• of
step (3), and Q„ the heat of reaction in (1), the next relations are given,
d lnk _ A d lnk,= A, d InK,= Q, (9) d T RT' ~ d T RT= ~ d T RT' '
where it is presumed that the endothermic heat of reaction has a positive sign.
From Equations (3) and (9),
The heat of reaction in the case of the formation of NI I,CO,NH~ from NH, and
COY`is about -40 kcal'r. Then, it is permitted that the heat of reaction in the
step (I) tikes the value nearly -40 kcal. The value of A is about -20 kcal as
above described and so A, can take a positive value. From these considerations it can be recognized that the velocity constant, k, of this reaction in which
NH,COpNIie is not produced has the negative temperature coefficient.
The authors express hearty thanks to the Ministry n( Edccation for the Scientific Research Grant.
Tke z~r,~•~~ry of Physitn! Ckeouistry, ICyato University.
4) k. C. Clark and II. Q Iietheringlnn, f. Anr. Chrm. 3oa, 99, 1909 (19:;)
The Review of Physical Chemistry of Japan Vol. 21 No. 1 (1950)
CI [F.V ICe11.
sure ch:mec aC the
K iNE'CI(S IN 'CI{Is Rt:AC'1'1f)N IiE'CWhaiN Ntia ANn Cf)_ 9."t
initial time of the reaction is due to the formation of
grw LJO
le0
~ll0 2100
`a YO
e ~
70 9 2w
enns.
a`---a_ 0^0+
A
L: ~?-
a;
~O=
E:
xos
• aoo°e re.~e
i
i
i
i
i i
lOTt: O[p, 56 O
190°C tip.51
r r may, ya
19WC Zrp. aO 160°C pp,El
~~
180°C isp.>Q
1' __ --
0140 a .
150
i la
110
100
° 00
o ~
m 90
[e1t181 pneaurs
150 t~a~ tiy.50
lE0 tg/~ tip.>e -O
40 tg/mtOtap.B
60 aH/cnE Rp.E9
10 a0 tO 60 1M 10 W 80 10 0 aD Oti- 140 Tla~ (Vy.t 91ma Imf °-1 Pig. ~1 l'n5surc change curvt5. Fig.:i Prtssure change tunes.
hlilial pressure 1501;gfcm=. 1',t•Ha: YCYS_C: 1, 1;0°C.
I) From the dissociation pressure cf NII,CO.NH.,.
In the case of F:xp. 1 at (i0°C in Fig. 2, the rapid pressure decrease and the
heat cvolntion follow at the initial tiute, then pressure decrease, to L kg/cni'.
The pressure, 1 kgjnv°, is the dissociation pressure of NH.,COe\H.1 at 60°C't and
under such condition file formation oC urea does not occur. Accordingly the
curve can be considered as the one of the formation of \II,CO_\I-1._
The comparison between the pressure at the inlle~ion point*, where the curve
showing the rapid pressure decrease at the initial step crosses the following slow
change curve,:md the dissociation pressure of .\'ILiC(J_\FI_ estralx~lated frrnn the
data of Egan ct al"., at the same temperature, is shua'n in Table I. Moth pres-
Tahle ]
Eep ~~ ~ Temperature t°I } Initi9l press. f~Sfrnl=)
v
~I
30
:LI
101 (lOD)
l3G (130)
15S (150)
16i (100) li5 (li0)
134 (lS0)
!a
UO
1•iU
15U
I:~
X10
Press. al the in0esion Disncial ion press. at pt. (kg/cm-) NII,CD_\IL (kg/cm=)
B
Sri
qti
100
la::
li'
i
'J
,li
4~
1(la
ldl
13~
1) ] I'. 1?gun, f. li. 1'ous and r.. D. I'ous, Jd. h.'qs. C/r~iu., 3d, -4:i4 (19-IG) ~ Lr the graphical e.pr4sinn n( the equntiun cunxrning In the Ihinl order reLrcity constant
, desvibed Inter (Chemical lr inerics in the cenClion ..t um &rtinnliwu), !wn strnigh! lines crcns a! the initial
rirate. 'l'ire trussing point is rtganle<l as the in8esiou Iwiur.
The Review of Physical Chemistry of Japan Vol. 21 No. 1 (1950)
°6
surer in
rz
_ laa
~'ltaa +~lm
~Iro L lao
2 ~
L o ~
° ~o
a
~ ~ eo
the
R. KTl'A~IA
comoarison nearly coincid
to ro x ~o so rm. tm.i
Fig. 6 Pressure cLange carves. lu0°C. Initial pressure
Q l50 kg/cm= Insp. CO ~ 1E01:G(cme Esp. 19
~ 53 k~(cm= Exp. 1'i Yvxy: Yaw_=a.1:1
3) Prom the relation of the dins The relation of 81e dissociation e
N' H,CO,NH: (solid)-- 2NH,+CO:. In next relations are derived from the DI
r 3 ~~ a ~~ ra, where c„ e, are respectively excess in
normal dissociation pressure of NH,C
of NH, and CO, is stoichiomctric,
NH,CO,NHq in the vapor in the case
dingly, the total pressures are c,+^ 1
T
and K. SUZUKI
e. The value shown in the parenthesis in
the temperature cohtmn is the tem-
perature before the reaction begins,
but owing to the heat evolved
at the initial time of the reaction,
the temperature rises, and then at
the inflexion point it becomes the
value shown on the left hand of
the temperature column. Fig. 6 e
shows the rapid pressure decrease
e~ at the initial time in every case of the initial pressure except
v3 kg/an",less than the dissociation
pressure of NH,CO,NII,, has the inflexion point at nearly the same
point. ociation equilibrium of NH.,CO_NH,.
quilibrium of NH,CO VrH., is as follows ; the case of excess of NH;, or of CO_, the
ass Law"'.
T~ 3 ~~ Za/ R~, presure of NH, and of CO._ T~ is the
O;NH_ when the ratio of partial pressure
a is the partial pressure of dissociated
of having exccs§ iu NH, or CO_. Accor-
vhcu NH, is in excess, e,+- in excess of
able 3
Esp. No.Temperature
(eC)Initial prc5s.
(via=m')
3
18
31
los (loo)
loa (look
153 (150J 774 (170J
15
15
150
4:1
1°
~:1
4:1
Press. (kg(cm=)
obs.
11.0
13.8
73.5
140
cilc.
11.0
13.4
73.9
]43
9) T. R. Briggs and V. \ligrdichian, J. P/ry.r. Chnu., 28, 11_1 (194)
The Review of Physical Chemistry of Japan Vol. 21 No.
CIB's?IICAL KINETICS IN THE 1:E:1CT10N BETWEEN NI[a AND CO= 117
CO_. It has been experimentaly proved that this relation holds in the ]ow pres-sure rcgion't. In Table 2 the conaparisoas bchvicen the obaelved pressure at the
inflcsion point and the pressure calculated from the above relation are shown and the consistency in both values is good. The parenthesis in the temperature column denotes the same as in Table 1.
Nfi.~CO,NII, is not formed under the lolver pressure than the pressure of
dissociated NI-I,CO.,NII_. ~Yhen the dissociation pressure is 750 kg/cm', the tem-
perature is 176'C*. Prom the pressure dlange curves in Fig. 4, the rapid pressure decrease at the initial time occurs at the Ycmerature below 770°C, while this rapid drange does not above 180'C. From Che correlation between the condition of
the NI-I,CO,NH_ formation and these pressure change cnrves, NH,CO.~I-L, is
formed not above 1.80°C, bat below I70°C. .11so, in Pig. >, NIIaCO_NlI_ having the dissociation pressure of L6l:y/uii= at 170°C, in the case of the initial pres-
sure 1c70 kg/au=, the pressure decreases rapidly at the initial time, while in the case of the initial pressure below L'261cg/cm=, the rapid change does not occur.
In other cases, the elperimental results are satisfactory in consideration. According to the above consideration, the rapid pressure decrease at the
initial time of the reaction is due to the formation of NH,CO,NH. and the for-mation of NH,CO~NH, is dependent upo~1 t11c initial pressure which is higher
than the dissociation pressure of NH,CO.NH...
(II) The formation of urea. 1) General consideration.
From the results of the quantitative analysis of urea it may be found that
it is always possible to produce urea whether NH,CO,NH_ is Im'c
formed or not. The urea conver-
sion percent curves, Fig. 7, are
the results in the same condition
as the pressure change carves in
Fig° 4. At 150°C and 1.60°C NH,-
CO.,NH° is fornted and at 180°C
and 190°C is not, as described
before. However, the formation
of urea occurs in both cases.
accordingly the view that NH,-
w a 0
:~
G,a
O
1 (1950)
O lso°c
IYO°c
30 JO 00 pp T1ma (m1n.l
Pig. 7 Urea convereien °6 Nn•es. Initial pressure 150 kg~cm~. Ps~~; : Pcvi.=::1
* ct. 1J
L10
i
The Review of Physical Chemistry of Japan Vol. 21 No. 1 (1950)
i:8 P.. K11'A\tA and li. 5UZUK1
CO,NH., is the direct iutermediatc substance in the reaction mechanism is not
generally admitted. In the pressure change cun•es at the condition that iVII,CO_NH, is not
formed (i. c. above ISO°C in Fig. 4), the pressure, in any case, decreases below
the equilibrium pressure" in the formation of urea. From this result it may be
considered that the reaction oP urea at this conditiat goes on in the gaseous
state.
In the urea conversion percent curves, Fig. !, the temperature effect on the
urea conversion is reverse between 160730°C, namely the limiting temperature
of the existence of VH,CO.NH_,.
The effects of pressure and the ratio of partial pressure on the urea con-
version percent from the results of analysis are shown in 'T'able 3. Excess of
'1'xble 3
F..p..iu.
t', n~
3i,
3f,,
3V
31
°:~
^G
i
i
'temperature (`r)
15U
lu0
7.90
]9l1
liU
liU
770
7iU
Tiive of rcactiov (mint
Initial press. (~Sicm=)
I',w?a : I'cn,
:.o
:.a
ca
ca
is
i~
i:;o
1 ~~
~o
tso
so
~so
iso
i~o
su
90
~:,
~:,
,~:1
3:1
~:1
d:l
~:I
11
is rea cnm'ersion lip)
1.. 0
O.:i
0.0
10.8
Sri. 0
$li.
i. i
11. fi
• The case , $I[,CO:NIi_ is formed.
NH, and the pressure effect upon
CO~,ATI-h_ is formed or rot.
?) Chemical kinetics in the
The order of the reaction is
lion velocities in the rivo cases 7
the yield of
reaction
obtiined
and 3.
urea are recognized o~hether Nl-I,-
of urea formation.
from the folllvina relations of the reac-
lvhen [Peon]
dt
i-[hCOz]er
[Pco,]
~u=
~r
rtx log
dt~
~~
_)o~~r~, qtr
IOSLhYH.;~~-IOgLY\H~~e~
3) ~f. 1'nkunka, f. Agr. C~kvu. Snt. Jrspmq IQ 1333 (19.`34) C. )falignon and )L Frejacques, Cumis[. rwd., 174, lib (10"_2)
R. KiYanu and II. Kinoshita, ThIS,JJId'n,1(, 21, 0 (1051)
• The Review of Physical Chemistry of Japan Vol. 21 No.
CHE31h1AI. R]N]iTICS 1N 'CI[li P.fiAC1'fON ]1GT1\'EEN NI1~ AND Cp._ _9
logdr,-lood..t"e
11= ~~ (fR
\vhere Psea and Yco_ are the initial partial pressure of ATH, and CO_ respectively.
Table 4 Substituting the experimental results in
the above relations, the values of In and
F`I'• Ine~l P. n, P~.,. ,,, a arc obtained, which are shown in Nn. III '6lcm=)
_ Table 4. Prom the sum of fra and ra the
s, so co ~ ,au ~, 0 1• o ' order of the reaction is regarded as the .„ too cn :1o third order. Assuming that r: and h
s~ oo 40 ^o t.s 1•o are respectively the initial partial pres-
:ta oo ;ro i °o sure of NH, and CO_ and OP is the
('Cempemtnre, 1:(VC) quantity of pressure change, the third I'.vui, 4=. 40 of Fsp. No. 1LR, ̀̂ ~ are
rcgardea as o,e same presure, order velocity earstant is given as
.follows ;
1 ~ 3 P(2G-a) h~n-~~ ;1 ~•- }?. 3q3 IoQ c~) {rr~n-~.; ~ n~L 3
but when a=?b,
Accordingly. the valves n( the bracket in the former equation or (3b-OP)-= in
the latter against time arc plotted as linear relations and also the tangents arc
proportional to the velocity constants. The time range satisfied with linearit}' in the case of Psn,:Pco.=2:1, is sho+ter than in the case of Yxu,:Pco_=4: 1.
Table 5
i i ~.~~; so i co ~ ao s. o
~Y! ~~ ~ ~~~ i~~
An f0 ;Q n~ ~ ~.5 ~.
.W ~U id ~~
1 (1950)
Esy. \aTemperaturc
(`~ )Initial press.
(kgl«n%) Puts:It~q Vclncih' mnsl.'mt 10~ (cndfkgs . min)
'-
~~
_~
ss
s^
sc
1S
170
170
170
1~0
190
°00
so
90
loo
l00
160
160
~:,
~:~
~:,
~:,
,, :,
~:,
~.~~ ,.~
,. o
~.:;
~,.
- The Review of Physical Chemistry of Japan Vol. 21 No. 1 (1950)
3o K. Kll'ADfA and R. S[17.UK1
It may 6e considered that the continuation of linearity is due to the opposite
reaction that is prevented by c~cess of \I-i,. The veloeity constants obtained
from the above relation, are shown in Table 5. That is, the velocity constants
have the negative temperature coefficient and the activation energy calculated from
the relation of logk- ,1-r is about -30 kcal.
The velocity constants shown in Table G are the values obtained when
NH,CO,NH_ is not formed. The yields of urea calctdated from the velocity
constants and the observed yields in the case of the formation of NHaC0~1\TH.
are shown in Table C. The calculation is as follows;
Table ~
E <p, Nn.
_-4R~ ...
80.
=1i
"A.
Tempentum (°<7
_ 1HO 170
1f0
];.n
Velocity constant 10+
1.0
l.G
3.1
a.
Weight of urea (g)
talc. ~ nhs.
O.S
0.7
o. a
0. A3.4
0.7"_0
0. &03
0. fi.^.4
(Grilinl pressuc, 1fi0 kg~cm=; Pn up: PcM=~:1; lime n( reaction, 130 min.) • extrapolated vaL~e.
field of urea m wci ht =nk ~ Iu I'co_ =uk ~ 2P :( P
where P is the reading n( pre>sure gauge, a is the pn,pottional constant deter-
mined by substituting the 1;•thles at 130'C (NH,C(~ \H, is not formed) in Table G. The calculated weight of urea and the observed arc the values at 30 minutes.
Accordingly, it can be crnysidered that the reaction of urea formation almost
proceeds in the gaseoas state, even in such a case as NIf,CO\II4is formed; at least in the initial state of the reaction.
3) The reaction mechanism. From the reason above described the following mechanism is proposed.
2NH,+CO, ~ Intermediate product. (1) Intel mediate product F NH,CO,NH4, (?)
Intermediate product -~ ATH.CONFI_+fLO. (3)
The step (°_) is )tossible only when the initial pressure is higher than the
dissociation pressure of NH,CO,NhI,. Assuming the equilibrium relation is always CgtalJll$hMI in the steps of (I) :cod (3) and ka is the velocity constant of (3), the Velo:ity of urea formation redeces to