IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
III.B.2. Studies on Thermochemical Aspects of
Sodium-Alcohol Reaction and Characteristics of the Product
In sodium cooled fast
reactors, a thin layer of sodium
gets deposited on the surface of
steel components that are in
physical contact with liquid
sodium. Some of these
components need to be taken
out for periodic maintenance or
replacement. Exposure of these
components to ambient air
poses fire hazard and possible
hydrogen explosion due to
vigorous reaction of sodium
with moisture present in air. To
avoid this, sodium needs to be
removed from the component
surface prior to maintenance
work. Alcohols are generally
employed world wide for
cleaning sodium from small
and delicate components. Ethyl
carbitol used for cleaning
sodium storage tanks which
contains a few kilogram of
sodium has been reported to
cause run-away reactions
leading to accidents in France
and Germany. For clear
understanding of the chemistry
of sodium-alcohol reactions,
data on thermochemical
properties like enthalpies of
reaction, enthalpies of solution,
enthalpies of formation and
heat capacity of the
constituents and reaction
products in sodium-alcohol
system are essential. Owing to
limited or non-availability of
such data, studies have been
taken up in this system.
Enthalpies of solution, reaction
and formation
Molar enthalpies of solution
of sodium in methanol, ethanol
and n-propanol and of sodium
alkoxides in their
corresponding alcohols were
measured at 298.15 K using an
isoperibol solution calorimeter.
The measured molar enthalpies
of solution of sodium in the
above alcohols are
∆ sol H 0 m(Na/ROH)= -204.0±1.1, -
190.4±1.3 and -180.9±0.8
kJ mol -1 , respectively. The
measured molar enthalpies of
solution of sodium alkoxides in
its corresponding alcohols are
∆ sol H 0 m(RONa/ROH) = -76.8±0.3,
-54.8±0.4 and -41.9±0.7 kJ
mol -1 , respectively. The molar
enthalpies of reaction of
sodium with methanol,
ethanol and n propanol
were measured and
found to be ∆ r H 0 m(Na/ROH)=
127.11±1.34, -135.59±1.40
and -138.97±1.07 kJ mol -1 ,
respectively. From these results
and other data, the standard
molar enthalpies of formation,
∆ f H 0 m(RONa) of sodium
methoxide, sodium ethoxide
and sodium n propoxide were
calculated and found to be
366.3±1.3, 413.3 1.4 and
441.6±1.2 kJ mol -1 ,
respectively. Fig. 1 shows the
variation of ∆ f H 0 m(NaOR)) vs
∆ f H 0 m(ROH measured in the
present study and compared
with literature data (Leal and
NBS). A linear correlation has
been found between
∆ f H 0 m(NaOR) and ∆ f H 0 m(ROH) as
given in Eqn. (1), which is
useful to predict the enthalpies
of formation of higher sodium
alkoxides.
∆H (RONa, cr) =
f
( 1.19 ± 0.02) ∆H
(ROH,l) − ( 82.10 ± 6.15)
f
(1)
In a similar fashion,
enthalpies of solution of
sodium and sodium alkoxides
in respective alcohols were
plotted against enthalpies of
formation of corresponding
alcohols and shown in Fig. 2.
The linear correlations
obtained from Fig. 2 are given
in Eqns. (2) and (3),
respectively. These correlations
may be used to estimate the
enthalpy of solutions of higher
n-alkyl derivatives of sodium
alkoxides.
R&D FOR FBRs 41