Parr Instrument Series 3900 - Manual (Page 7)

Hydrogenation Apparatus
w w w . p a r r i n s t . c o m 7
Operating Procedure
Samples to be treated in a Parr hydrogenator are
placed in a reaction bottle with a catalyst and
clamped in a shaking mechanism. A gas connection
is made to the bottle from a multiple valve and all
air is removed either by evacuation or by fl ushing
with hydrogen. Hydrogen is then introduced from
a 4-liter reservoir while the bottle is shaken vigor-
ously to initiate the reaction. Heating or cooling can
be applied, if necessary. After the reaction reaches
the desired point the shaker is stopped, the bottle
vented and the product and catalyst are recovered.
The individual steps in this operating procedure are
listed below. These can be varied to suit each indi-
vidual application.
1. Place the catalyst, solvent and sample in the
reaction bottle, adding the catalyst fi rst to avoid
possible vapor ignition by the dry catalyst. The
total volume of solution should not exceed two-
thirds the capacity of the bottle.
2. Attach the stopper with connecting tube and
slide the bottle into the guard screen, then set
the assembly in the bottle holder and tighten the
knurled clamping nuts.
3. If air is removed from the bottle by evacua-
tion, attach a vacuum hose to the nipple on the
3A93CA valve; close the bottle valve: open the
gas release valve and evacuate until the solvent
starts to boil. If a low boiling solvent is not used,
evacuate to a negative pressure suffi cient to
remove most of the air. Air can also be removed
by alternately fi lling the bottle with hydrogen to
20 or 30 psig. and venting it at least three times.
After purging the bottle, close the gas release
valve and leave it closed throughout the run.
4. Starting with the hydrogen tank fi lled to 30
psig. open the bottle valve and read the bottle
pressure gage after equilibrium has been estab-
lished.
5. Start the shaker and follow the progress of the
reaction by observing the bottle pressure gage.
If complete hydrogenation is desired, continue
shaking until there is no further pressure drop.
For partial or quantitative hydrogenation, contin-
ue shaking until the pressure drops to a calculat-
ed value as determined by prior standardization
runs.
6. At the end of the run, stop the shaker; close
the bottle valve and allow the catalyst to settle.
Any residual pressure in the bottle and connect-
ing tube can be discharged by opening the gas
release valve.
7. Open the bottle clamp and remove the bottle.
Decant the solution leaving the catalyst in the
bottle for a second reduction, or remove the
catalyst on a fi lter.
Standardization
The apparatus can be standardized by making a
preliminary run with a known amount of any com-
pound that can be completely and quantitatively
reduced. The pressure drop per mole of hydrogen
consumed in such tests is then used as a basis for
estimating the progress of a reaction with unfamil-
iar materials. A procedure is described in reference
(3) for standardizing the apparatus by reducing 11.6
grams (0. 1 mole) of pure maleic acid dissolved in
150 mL of 95% ethanol using 0.1 gram of catalyst.
The reaction is carried out as previously described
with shaking continued until no more hydrogen is
consumed. This usually takes twenty to thirty min-
utes, after which the pressure drop in the tank is
recorded. Since exactly 0.1 mole of hydrogen has
been consumed in this run, this decrease in tank
pressure can be used as a basis for measuring or
regulating the amount of hydrogen consumed when
treating other compounds.
Standardization tests are not limited to runs with
maleic acid. Fumaric acid is equally suitable for
this purpose, or any other pure compound can be
used provided that it is completely or quantitatively
reduced. If the intended usage for the apparatus
involves the consumption of only a small amount
of hydrogen, the apparatus can be standardized
with the tank valve closed. The gage will then give a
more signifi cant reading as gas is consumed from
the connecting tube and bottle alone while these
parts are isolated from the tank.