The decomposition rates of N2H4 on a palladium surface are studied. Experiments were conducted in a circulating unit at atmosphere pressure. The experimental method is described. The laws found for the reaction kinetics are explained by equations

Apelbaum, L. O.

Khomenko, A. A.

English

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NASA TECHNICAL MEMORANDUM NASA TM-88549 
STUDY OF THE KINETICS OF CATALYTIC DECOMPOSITION OF HYDRAZINE 
VAPORS ON PALLADIUM 
A.A. Khomenko and L.O. Apel'baum 
Translation of: "Issledovaniye kinetiki kataliticheskogo 
razlozheniya parov gidrazina na palladii," pp. 143-52 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON, D.C. 20546 JANUARY 1987 
1 
INASA-Ta-t28549) S T U D Y  OF THiE KIKETICS OF 
C A T A L Y T I C  D E C C H E G S I T I C N  OF HYKLAZIME VAPOBS 
CN P A L L A D I U H  ( S C I Z R A N ,  I n c . )  11 & CSCL 07D 
N% 7- 1 E 2 6 6  
Unclas 
G3/25 40354 
https://ntrs.nasa.gov/search.jsp?R=19870005853 2020-03-20T12:24:04+00:00Z
STUDY OF T H E  K I N E T I C S  OF HYDRAZINE 
DECONPOSITION OF HYDRAZINE VAPORS 
ON PALLADIUM 
A. A .  Khomenko and L. 9. Apel'baum* 
Hydrazine decomposition is described by stoichiometric equations /1 
I_ 
r 1 1 :  
Catalytic decoinposition of hydrazine on the surface of various 
metals has been studied in a number of publications [2 - 1 2 1 .  The 
data obtained in these publicati.ons demonstrated that the ratio 
of deconposition rates of N2H4 from equations (1) and ( 2 )  depends 
on the nature of the metal, and on some metals, it also depends on 
the hydrogen content in the reaction mixture and the reaction 
temperature. Different hypotheses on the mechanism of the reaction 
[ 4 ,  6, 7 - 133 have Seen advanced to interpret the obtained data. 
We studied the decompositio-i of N2Hq on a palladium surface. 
was desirable because of the special features of the Pd - H2 system. 
There are no corresponding datz  in the literature. The experiments 
were conducted in a 
At 120 - 165" the catalyst used was palladim foil (geonetric surface 
S = 1140 cm 1, at 220" it r~zs  a semipermeable palladium membrane [ 1 4 1 .  
This 
ezirculating unit at atnospheric pressure. 
2 
Hydrazine vapors wt i re  fed i n to  the reacticr,  cyc le  by passkg 
He, H2 o r  a mixture of these gases t5rough an evaporator with liquic? 
hydrazine at temperature 80 - 90"  and two temperature-contrclled 
-i .. 
L. Ya. Karpov Scientific ?.esearch Physicoc'7enical Institute,Moscow 
J t A X  
Numbers in right margin indicate pagination in orLgina1 text. 
1 
condensers. 
su r f ace  of a semipermeable mezbrane, t h e  c a t a l y s t  used was a 
palladium t e s t  tube with sur face  1 7  cm2 sea led  i n t o  a quar tz  
r eac t ion  v e s s e l  (50 cm3 in volume) Tqith t h e  he lp  of a Kovar-. 
molybdenum glass - quar tz  junc t ion .  The inne r  volume of t h e  
palladium test  tube w a s  1:ontlected t o  a system 2c;ntainiing a gas 
rnercgry bure t  and manometer t o  supply hydrogen to t h e  reaccion s i d e  
o r  remove hydroger, frcm t h e  r eac t ion  s i d e .  This :art  of t h e  u n i t  
could be f i l l e d  wi th  hydrogen arid pumped out .  
I n  t h e  experiments cn hydrazine decomposition on t h e  -- / 1 4 4  
The gas n i x t u r e  emerging from t h e  r e a c t i o n  cyc le ,  a f t e r  f r e e z i n g  
of t h e  formed NH3 and unreacted N2H4 i n  a l i q u i d  ni t rogen-cooled 
t r i p ,  entered the  gas analyzer  t o  d e t e n i i i e  t h e  hydrogen content  
and ,a foam flow meter.  The gas mixture  i n  t h e  gas analyzer  was 
heated t o  200" a rd  passed above t h e  exccrnal  su r f ace  o f t h e  palladium 
re s t  t i ~ b e  xhese i m e r  voliime WCLS connected t o  a mercury p res su re  gauge. 
Hydrogen contained i n  the  analyzed mixture  flowed i n s i d e  of t h e  
t es t  tube u n t i l  t h e  establishment of s ta t . ionary pressure  equal t o  
the  p a r t i a l  p ressure  of H2 i n  the mixture;  hydrogen p res su re  was 
measured by pressure gauge. 
mixture w a s  d e t e m i n e d  by the  method Qf gas  chromatography. I n  
order  t o  determine t h e  quant i ty  of unreacted hydrazine and t h e  
formed ammonia, t h e  hydrazine frozen i n  t h e  t r a p  and t h e  ammonia 
were blown out  by a helium cur ren t  i n t o  a v i a l  with t i t e r e d  s o l u t i o n  
of HC1. T i t r a t i o n  of ind iv idua l  samples o f  hydrochlor ic  a c i d  s o l u t i o n  
by KO and K B r 0 3  s o l u t i o n s  made it  p o s s i b l e  t o  determine t h e  
quan t i ty  of  N2H4 and NH3.  
The N2 content  i n  t h e  uncondensed gas 
Experiments were p re l imina r i ly  conducted on hydrazine decompo- 
s i t i o n  i n  empty r e a c t i o n  vesse l s .  
experimental  condi t ions ,  decomposition of hydrazine on the  w a l l s  
of t h e  v e s s e l  and i n  t h e  gas phase could be ignored. 
They showed t h a t  under our 
The r e s u l t s  o f  t h e  experiments on decomposition of hydrazine 
a r e  presented i n  t a b l e s  1 and 2 .  I n  t h e  t a b l e s ,  Q des igna tes  t h e  
t o t a l  volume of gases emerging f r o m  t h e  r e a c t i o n  cyc le  In l i t e r s  
(0.3- atm. ) /hour;  'N2H4' 'N2' P H2' 'NH3' 'He a r e  the  p a r t i a l  
2 
pressures of hydrazine, nitrogen, hydrogen, ammonia and helium in 
the gas mixture; 
and ammonia expressed by the volume of the corresponding gas reduced 
to 0" and 760 mm Hg formed on this quantity of catalyst in one hour. 
and rNH are linked The rates of nitrogen and ammonia formation, 
to these quantities by the equalities . J ~ ~  *%* S
nates the volatility of hydrogen in palladium measured by s ationary 
pressure of hydrogen on the supply sideofthe semipermeable membrane 
[I41 
and WNH are the output of catalyst for nitrogen 
wN2 3 
3 
and 
rN2 
where s is the surface of the catalyst. fH desig- z '5 - %' 6* 
The dependence of WN and IdNH on the com?osition of the 
2 reactive mixture at 1 4 0 "  is preseAted in table 1. 
it that in the mixtures which do not contain added hydrogen, hydra- 
zine decomposition on palladium at 1 4 0 "  occurs predominantly by 
equation i l l .  Especially set-up experiments demonstrated that at 
temperatures 140 - 220" ammonia is not decomyosed on palladium, 
and consequently, hydrogen is formed directly from hydrazine by 
equation (1). The addition of hydrogen to the initial mixture 
severely inhibits W . The data presented in table 1 regarding 
can be described by the equation: 
It follows from 
N2 
wN2 
0.85 
where KN is a constant. The quantities KN computed from 
equation ( 3 )  are presented in table 1; within each series of 
experiments they preserve satisfactory constancy. Deceleration 
of the reaction by hydrogen to a degree greater than 1 cannot be 
explained by filling the surface with hydrogen. It should be 
nttributed to reversibility of the intermediate stages of the 
2 2 
reaction. The temperature relationship of WN 
Arrhenius equation with activation energy 21. 3 
is described by an 
f 2.5 kcal/mole. 
It i s  d i f f i c u l t  t o  judge the type of dependence of WNH a t  1 4 0 "  
on p a r t i a l  p ressures  of N2H4 and H2 s i n c e  wi th  low content  3 of NH3 
i n  t h e  mixture wi th  hydrazine,  the r e l a t i v e  e r r o r  of determining NK3 
was l a r g e .  This r e l a t i o n s h i p  can be approximately represented  by 
an equat ion of  t h e  type I 
/1 -
where i"NH3 i s  a cons tan t ,  m and n a r e  exponents (m = 0 . 4  - 0.2; 
n = 0.2 - 0 ) .  
Table 2 p resents  the  r e s u l t s  obtained from hvdrazine decomposition 
on t h e  su r face  of a palladium membrane a t  2 2 0 " ;  they can be descr ibed 
by t h e  following k i n e t i c  equations: 
The q u a n t i t i e s  % 
are presented i n  gable 2. 3They a r e  approximately cons tan t  w i t h i n  
each s e r i e s  of experiments. 
and KNH computed from equat ions (5) and ( 6 )  
I t  fol lows from t h e  experimental  d a t a  obtained i n  t h e  work a t  
220" t h a t  with s p e c i f i c  PN 
value  r ega rd le s s  of whethe$ hydrogen i s  passed thraugh t h e  membrane 
and P , WN2 and 167" have the  same 
H2 
o r  i s  added d i r e c t l y  t o  t h e  o r i g i n a l  gas mixture .  This  r e s u l t  does 
not  agree  with t h e  hypothesis  on t h e  chain mechanism f o r  t h e  r e a c t i o n  
with adsorbed atoms of hydrogen as  a c t i v e  c a r r i e r s  of t h e  chain 1143 .  
I n  the  absence of a flow o f  hydrogen through t h e  membrane, 
s t a t i o n a r y  hydrogen pressure  i s  on t h e  supply s i d e  of t h e  membrane 
4 
ORIGINAL PAGE IS 
of#n>R(pr#nv 
TABLE 1 
RATE OF HYDRAZINE DECOXPOSITION WITH DIFFERENT COMPOSITIONS OF 
REACTING I4IXTURE. REACTION TEYPERATURE 1 4 0 " .  CATALYST I S  PALLAD1UE.I 
FOIL: S = 1 1 4 0  cm2 
Pd 
Key : 
a .  
b .  
C .  
L!. 
e .  
f .  
g .  
h. 
liydroyen ~-7as adTicd t o  t he  r e a c t i o n  mixture i n  
the  experinent  
Eefore the ex?eri;nez:t, ?al laeiuA Tias o x i d i z e d  
and reduced 
Series and nunber of experiment 
1 / 1-, 
Pa t i a l  Dressures in  r e a c t i n g  mixture ,  atm. 
fr m equat ion 
2 I L  L-111 , I  - 
cm 9 /h x atrn. 
* . pn 
'2 - .  2 ( see  t a b l e  2 ) .  This observat ion is explained. i f  we assume 
t h a t  t h e  r eac t ion  occurs with intermediate  formation of hydrogen . 
atoms which are adsorbed and dissolved in the metal, and their 
concentration during t he  reaction is more equilibrium in relation to 
TABLE 2 
RATE OF HYDRAZINE D E C O N P O S I T I O N  W I T H  D I F F E R E N T  COMPOSITIONS 
OF R E A C T I N G  M I X T U R E .  REACTION TEMTERATURE 220" .  CATALYST 
I S  PALLADIUI'I  MEMBRANE; S = 17 cm 
Pd 
Key : 
a. Hydrogen was added to the reaction mixture in the 
b. 
c .  l/h 
d. Partial pressures in reacting mixture, a t m .  
experiment 
Series and number of experiment 
e. f at?g cm /h 
g. from equation 
6 
could be explained /lI -
Here Z designates the adsorption center on the palladium surface; the 
area 2 contains two of these centers. In scheme ( 7 1 ,  Z2W2H3 and 
Z2i'J2H2 designate the chemosorbed particles of N2R3, NZH2 and so 
forth; (H) is the hydrogen atom dissolved in palladium. The 
stoichiometric numbers are presented on the right of the equations 
of stages. The columns of stoichiometric numbers determine the base 
routes of the reaction N (1) and N ( 2 ) .  The summary equation of the 
route N coincides with equation (l), while route N (2) coincides 
with equation (2). The presented scheme is similar to the one 
proposed for the reaction of hydrogenization of ethane E161. 
2 
In order to explain the results which refer to 1 4 0 " ,  we assume 
stages l), 21, 3 )  and 6) to be equilibrium, and stages 4 )  and 7) 
to the irreversible. Considering the surface of the catalyst to 
be uniform and the coatings of the surface with intermediate forms 
of dehydrogenization to be small (the percentage of freeqplaces on 
the surface /Z2/ = I), we obtain from scheme (7) the following 
kinetic equations: 
Equation (8) is close to empirical equation ( 3 ) ,  while equation 
( 9 )  agrees qualitatively with equation ( 4 ) .  
In order to explain the kinetic relationships which were obtained 
at 2 2 0 ° ,  we assume that at this tenperature the equilibrium of 
stages 21, 3) and 6 )  is shifted to the right so that these stages 
becor!e essentially irreversible. In t h F s  case, t h e  rate of 
nitrogen formation rN 
21, while the velocity of ammonia formation is determined by the 
velocity of stage 6). 
will be determined by the velocity of stage 
In addition it was assumed that at temperature 
2 
. 
7 
e 
2 2 0 "  it is impossible to ignore the coating of the surface with 
chemosorbed particles of N2H3,  that is 
where /Z N H / is the percentage of the sites on the surface 
occupied by chemosorbed particles of N2H3. 
kinetic equations from mechanism (7) with these assumptions: 
2 2 3  
We obtain the following 
Kinetic equations (11) and ( 1 2 )  agree satisfactorily with equations 
(5) and ( 6 )  found in experiment if we assume n = 0.7. 
to the conclusion that the scheme proposed above f o r  the mechanism 
makes it possible to explain the kinetic relationships obtained on 
palladium. 
One can come 
/lC -
The published data on decomposition of hydrazine on P e ,  Id, N o ,  
Cu, Cr and Ir show that on these metals, hydrazine even at low 
temperatures (60 - 160") is predominantly decomposed into N2 and 
NH3. 
fact that stage (5) has very low velocity as compared to stages 
6 )  and 7). 
Based on scheme ( 7 ) ,  these data can be explained by the 
BIBLIOGRAPHY 
1. Odrit, L.; Ogg,  E .  Khimiya sidrazina [Chemistry of Hydrazine], 
IL, Ploscow, 1954. 
2. Tanstar, K.; Z. Phys. Chem., 4 1 A ,  2 7 ,  1 9 0 2 .  
3 .  Askey, P. J.; J. h e r .  Chem. SOC., No.. 5 2 ,  970, 1 9 3 0 .  
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Paper N 7 0 ,  6 0 G ,  San Diego, 1370 .  
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1 2 .  Contour, J .  P . ;  Panne t i e r ,  G . ;  J .  C a t a l y s i s ,  2 4 ,  4 3 4 ,  1972. 
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1 4 .  Tenkin, M. I . ;  Apel'baum, L .  0. Problemy k i n e t i k i  i k a t a l i z a ,  
1 0 ,  MOSCOW, Izd.  AN SSSR, 1 9 6 0 ,  p.  392. 
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k a t a l i z a ,  7 ,  671 ,  1966 .  
. 
0 
0 
a 9 
e 
0 
A.A. Khomenko and L.O. Apel'baum 
10. Worb Unit No. 
- 11. Conweel e* Ctont Ho. 
- , Porformang O t ~ m i a ~ t t o a  N.m* .nJ Aldcer r  NASw - 4 0 0 4  
Translation 
13. T7p* * f  Reprtt m d  Pwied Corocrd S C I T W  
Box 5456 
CA qIu3p 
. S r ~ o , , n g  A on Name on4 Ird&*#r 
ritional Aeroaautice and space Adminiatration - 
Wmningtoa, D.C. 20546 14. +r.r(y  AIM^ G& 
8. L ~ l o m o m t w r  Nonr 
Translation of: "Issledovaniye kinetiki kataliticheskogo 
razlozheniya parov gidrazina na palladii," pp. 143-52 
The decomposition rates of N 2 H 4  on a palladium 
surface are studied. ~ 1 Experiments 
were conducted in a circulating unit at 
atmosphere pressure. The experimental method 
is described. The laws found for  the 
reaction kinetics are explained by 


Study of the kinetics of catalytic decomposition of hydrazine vapors on palladium

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