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CaBr 2 HYDROLYSIS FOR HBr PRODUCTION USING A DIRECT SPARGING CONTACTOR
Capture/neutralisation of product HBr
The product gases containing unreacted steam and HBr leave the reactor through a port in the SS
(or Pyrex glass) flange assembly. The product gases then pass through a heat-traced line, a glass trap,
and a glass condenser (chilled to 12°C) and are collected into a tank containing (10 N) sodium hydroxide
solution for HBr capture. The system is designed so that all gases introduced to it must pass through
the condensate/neutralisation tank, where liquid or gaseous hydrogen bromide is neutralised by the
following reaction:
HBr + NaOH → NaBr + H 2 O (5)
The use of a concentrated sodium hydroxide solution (10 N) in sufficient volume to neutralise all
hydrogen bromide product formed during the reaction time ensures that even trace levels of HBr will
not be released from the receiver to the vent.
Experimental procedures
Reagent grade anhydrous CaBr 2 (199.888 M.W.) was poured into the melt bath. For start-up and
shutdown, argon, an inert gas, is used to purge the test apparatus. On start-up, argon gas flows at a
rate of 1 L/min to remove residual air in the reactor and the rest of the system before the temperature
is raised. The presence of air (oxygen) in the reactor alters the reaction path and produces bromine
gas. Minor amounts of bromine could be detected with potassium iodide-starch test paper from the
opening of the gas outlet; this testing showed that no release of Br 2 gas was taking place. Argon is also
sparged as fine bubbles in the deionised water for deaerating the feedwater to the steam generator.
At the end of the experiment, the steam is shut off and a flow of argon gas is started to purge HBr
from the reactor and the rest of the system.
Reagent steam is produced at 423 K, 0.525 MPa (5.25 bar). Superheating of 50 K takes place in the
feed lines so that the steam enters the Lindberg furnace at about 473 K. The reagent steam is metered
into the reactor by means of a metering valve. Significantly, COMSOL TM modelling showed that the
steam would quickly reach the temperature of the bath with only a small draw on the heat reservoir.
Success in adopting the approach of feeding low temperature steam considerably simplified the
steam feed arrangement, which employed 316 SS up to the connection with the alumina sparger feed
near the top of the furnace.
Produced HBr is scrubbed by the use of 10 N sodium hydroxide solution to form sodium bromide.
For all the runs, the initial inventory is 1.25 L of sodium hydroxide solution. The NaOH solution was
sampled at regular intervals and sent to Argonne’s Analytical Chemistry Laboratory for analysis. Volume
aliquots of solution samples were diluted with reagent water and analysed by ion chromatography to
determine bromide. Separate aliquots were diluted with acid addition and analysed by inductively
coupled plasma-atomic emission spectrometry (ICP-AES) to determine calcium. During the data analysis,
adjustments are made for the addition of condensed unreacted steam to the neutralisation solution.
Samples of molten salts (calcium bromide-calcium oxide melts; ~2 10 –3 L) were collected on a
graphite rod thrust to the bottom of the molten salt bath. Melt samples are taken at the beginning of
the test run before steam is on and at the end of test run after steam is shut off and the system is
purged with argon for at least 15 minutes. The melt samples were also collected for analysis. The salt
samples are ground to powder with an agate mortar and pestle under dry nitrogen in a glove-bag
enclosure. To determine the amounts of bromide and oxide present in each salt, a portion of powder
(50 10 –6 kg) is treated with methanol (3 10 –3 L), which dissolves the CaBr 2 fraction but does not dissolve
CaO. The methanol solvent was filtered using suction through a 2.5 cm diameter, 5-μm pore-size,
Teflon filter (Millipore), and the solids on the filter are washed with additional methanol. The
methanol filtrate is subsequently transferred to a beaker with water and the volume is reduced by
heating to expel the methanol. The remaining water solution is transferred to a volumetric flask and
diluted for analysis by ion chromatography to determine Br in the salt sample. The solids collected on
the filter are dissolved in dilute nitric acid solution, brought to volume in a volumetric flask, and
analysed by ICP-AES to determine calcium, which is assigned as calcium oxide.
NUCLEAR PRODUCTION OF HYDROGEN – © OECD/NEA 2010 273