ELIMINATION DE L'OXYGENE PAR L'ACIDE ERYTHORBIQUE OU ASCORBIQUE, CATALYSEE PAR LE MANGANESE

MANGANESE CATALYZED ERYTHORBIC ACID OR ASCORBIC ACID FOR OXYGEN REMOVAL

Abrégé anglais

ABSTRACT OF THE DISCLOSURE
An improved method for scavenging dissolved oxygen from
alkaline waters with either erythorbic acid or ascorbic acid is
described. The acid is used combined with either magnesium ion
or copper ion as catalysts, or in the presence of a pH control
agent which maintains the pH above 7. By this means the known
oxygen scavenging properties of these acids are substantially
improved.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for scavenging dissolved oxygen from boiler feed water
with either erythorbic or ascorbic acid which comprises either
(a) adjusting the pH of such waters to a pH greater than 7; or
(b) adjusting the pH of such waters to an alkaline pH and adding,
as catalyst, at least 0.5 ppm of manganese ion; or
(c) adjusting the pH of such waters to an alkaline pH and adding,
as catalyst, at least 0.5 ppm of copper ion,
prior to treatment of the water with either erythorbic acid or ascorbic acid.
2. An improved method for scavenging dissolved oxygen from boiler feed
water with either erythorbic acid or ascorbic acid which comprises adjusting
the pH of such waters to a pH greater than 7 prior to treating such waters
with either erythorbic acid or ascorbic acid.
3. The method of claim 2 where the acid is erythorbic acid.
4. The method of claim 2 where the acid is ascorbic acid.
5. The method of claim 2 where the pH of the water is greater than 9.
6. An improved method for scavenging dissolved oxygen from alkaline
boiler feed waters with either erythorbic acid or ascorbic acid which comprises
using as a catalyst in the water at least 1/2 ppm of manganese ion.
7. The method of claim 6 where the acid is erythorbic acid.
8. The method of claim 6 where the acid is ascorbic acid.
9. An improved method for scavenging dissolved oxygen from alkaline

boiler feed waters with either erythorbic acid or ascorbic acid which comprises
using as a catalyst in the water at least 1/2 ppm of copper.
10. The method of claim 9 where the acid is erythorbic acid.
11. The method of claim 9 where the acid is ascorbic acid.

Description

In the trade brochure o~ Charles P~izer entitled
"Quality Chemicals" r published in 1970, erythorbic acid is
described as an oxygen scavenger as Eollows:
"The pronounced antioxidant properties of
erythorbic acid (C6H8~6) and the erythorbates make them
outstanding candidates for various industrial applica-
tions ~here the presence of dissolved oxygen causes
diffieulties or where speciflc reducing properties are
desired. Erythorbic acid is effective as an anti-
oxidant in the preparation o~ photographic developers.
Sodium erythorbate also shows promlse as agentle reducing agent in the textile industry, as a
deoxidizer in boiler feedwater to prevent corrosion and
scale formation and as an antioxidant in fields where
an inorganic compound cannot be used.i'
It is also known that ascorbic acid can function as an
oxygen scavengerO
The amount of either erythorbic or ascorbic acid that
may be utilized to scavenge oxygen may be expressed in terms of
moles of acid per mole of oxygen (O)~ Generally, amounts as
little as 2:1 may be used although it is preferred to use more
than 2 up to as much as 20:1.
~ t has now been found that the oxygen sca~enging ability
of either ascorbic acid or erythorbic acid can be significantly
increased if the condi-tions under whlch they are used are
carefully controlled. It has been discovered that the presence
of either certain catalysts or o~ a p~ control agent giving a pH
-- 1 --

above 7 provides such an increase.
Thus this invention provides, in its broadest aspect,
an improved method for scavenging dissolved oxygen from water
with either erythorbic or ascorbic acid which comprises elther
(a) adjusting the pH o~ such waters to a pH greater than 7; or
(b) adjusting the pH oE such waters to an alkaline pH and adding,
as catalyst, at least 1/2 ppm of manganese ion; or
(c) adjusting the p~ of such waters to an alkaline pH and adding,
as catalyst, at least 1~2 ppm of copper ion;
prior to treatment of the water with either erythorbic acid or
ascorbic acid.
The efficiency of these aclds is thus shown to be
dependent upon pH. Ad;ustment of the water pH to a value above 7,
and preferably to a value abo~e ~, for example by adding sodium
hydroxide or other alkali, improves the efficiency. The
efficiency can also be improved by adding a water soluble
mangenese (II) salt, such as manganese chloride, or of a water
soluble manganese (III) salt. Any manganese salt capable of
releasing manganese ions in alkaline water may be used. At least
1~2 ppm of manganese ion, and preferably at least 1 ppm of
manganese ion is used. The efficiency can also be improved by
adding a water soluble copper (II) salt, such as cupric chloride,
or of a water soluble copper (I) salt, Any ~ater soluble copper
salt capable of releasing copper ions in alkaline water may be
used.
Test Metho~
A four neck 500 ml reaction flask ~as fitted with a
-- 2 --

small rubber septum, a three~way c~nnecting tube holding a thermo-
meter and a ventlng stopcock, a stopcock connected to a funnel
and an Orion Research oxygen electrode, Model 97 08. This
oxygen electrode is connected to a pH meter in the prescribed
manner for direct reading of the oxygen concentration. The flask
is filled through the funnel w~th air-saturated wa-ter obtained by
bubbling air through water at room temperature for two hours,
making sure that no air 13 trapped ~n the flaskO The stopcocks
are closed. The oxygen con~ent of this water is 8 - 9 ppm. The
solution of the oxygen scavenger candidate is then injected into
the magnetically stirred water with a syringe through the septum
cap and readings of the oxygen concentration are made every 5
seconds, after in~ecting 0.25 ml of 25% NaOH to take pH to 10.7.
Test :Res:ults
These are largely shown in the drawings which each
represent plots of oxygen amount v. time. In Figure 1 a manganese
catalyst i5 present; in Figure 2 the pH is controlled and in
Figure 3 a copper catalyst is present~
Usiny a manganese (II) catalyst, the test m~t.hod gave
the following typical results:
TABLE I
Sca enger, 100 ppm~ Catalyst Catalyst %*
Conc. Oxygen
(ppm) _ Dec:rease**
Isoascorbic acid none - 41
" " Manganese (II) l 90
Manganese (II)
at pH 5 1 x
-- 3 --

"x" indicates no catalytic effect
* b~sed on average initial oxygen concentration: 8.43 ppm
** after one minute.
Figure 1 shows that 1 ppm of manganese dramatically
improves the oxygen scavenging effect of lsoascorbic acid.
For pu~rposes of comparison, it should be noted that
comparative -tests were run using cerium, cobalt, and iron. None
of these metals catalyzed or improved the oxygen scavenging
capability of erythorbic acid or ascorbic acid.
Similarly, using the same test method, isoascrobic acid
was tested under the following condltions of pH with the follow-
ing results being obtained:
Scavenger, 100 ppm pH %*
Oxygen
Decrease**
Isoascroblc acid 5 o
" " 7 10
" " 9 35
* - hased on average initial oxygen concentration: 8.43 ppm
** - after one minute.
Additional results are shown in Figure 2.
Similarly, the improved eEfects obtained using 1 ppm of
copper (II) with isoascorbic acid is shown in Figure 3~
For purposes of comparison, it should be noted that
comparati~e tests were run using soluble salts of cerium, cobalt,
and iron. None of these metals catalyzed or impro~ed the oxygen
scavenging capability of erythorblc or ascorbic acid.