|
Abstract: The corrosion inhibition of a green scale
inhibitor, polyepoxysuccinic acid (PESA) was studied based on dynamic
tests. It is found that when PESA is used alone, it had good corrosion
inhibition. So, PESA should be included in the category of corrosion
inhibitors. It is not only a kind of green scale inhibitor, but also
a green corrosion inhibitor. The synergistic effect between 2+ 2+ PESA
and Zn or sodium gluconate is poor. However, the synergistic effect
among PESA, Zn and sodium gluconate is excellent, and the corrosion
inhibition efficiency for carbon steel is higher than 99%. Further study
of corrosion inhibition mechanism reveals that corrosion inhibition
of PESA is not affected by carboxyl group, but by the oxygen atom inserted.
The existence of oxygen atom in PESA molecular structure makes it easy
to form stable chelate with pentacyclic structure.
Keywords: Green scale inhibitor, polyepoxysuccinic acid, corrosion
inhibition, synergistic effect.
PESA, which is free of nitrogen and phosphorus, is one of the two
green water treatment 1 agents recognized all over the world . The development
of PESA breakthroughs the traditional way in which different monomer
groups connect together simply. An oxygen atom is inserted into PESA
molecular chain. This makes it superior to 2 polyacrylic series in scale
inhibition . The research has mainly concentrated on scale inhibition
but lacked on the corrosion inhibition and corrosion inhibition synergistic
effect till now. PESA is used as scale inhibitor and phosphor series
compounds as corrosion inhibitors for all the existing developed formulas.
Although these formulas have good performance, they lose the green advantage
of PESA. The present paper breakthroughs the traditional idea from which
PESA is used with phosphor and azoles. Our study is on corrosion inhibition
synergistic effect between PESA and the compounds free of nitrogen and
phosphorus. The best corrosion inhibition formula is obtained and the
corrosion inhibition mechanism is also discussed from the view of molecular
structure.
The experiments were carried out by using standard rotating weight
loss tests on a dynamic corrosion test instrument. Standard carbon steel
specimens were fixed on a rack and put into the bottle filled with standard
corrosion water (CaCl2!2H2O 735 mg/L MgSO4 493 mg/L NaCl 658 mg/L NaHCO3
168 mg/L) plus inhibitor. The bottle was mounted in a constant temperature
bath at 50 °C The specimens were rotated at 90 rps.
Rong Chun XIONG et al.
The water was supplied every 4 hours because of evaporation. After
72 hours, experiment was stopped. Corrosion rate and percentage inhibition
efficiency were calculated with the equations as follows:
X=87600 W-W0 / ADT X2 (%)=10 0 (X0-X1) / X0
Here, X is corrosion rate, mm/a; W is specimen weight before test,
g; W0 is weight 2 3 after test, g; A is specimen surface area, cm ;
D is its density, g/cm ; T is test time, h; X2 is inhibition efficiency,
%; X0 is uninhibited corrosion rate, mm/a; X1 is inhibited corrosion
rate, mm/a.
The results are shown in Figture 1. In all the references about PESA,
PESA is researched as a kind of highly effective scale inhibitor or
chelate. The corrosion inhibition of PESA has never been studied until
now. To obtain good corrosion inhibition effect, the existing formulas
are applied with the aid of other corrosion 2,3 inhibitors such as phosphor
series . However, It is evident from our experimental data (Figure 1)
that when PESA dosage is low, PESA has a certain corrosion inhibition
effect on carbon steel. With the increase of PESA dosage, corrosion
inhibition increases. When dosage is more than 90 mg/L, corrosion inhibition
efficiency is over 60 %. These data show that corrosion inhibition of
PESA is better than the typical corrosion inhibitors, 4 sodium benzoate
and sodium salicylate . For this reason, PESA should be included in
the category of corrosion inhibitor. It is not only a kind of green
scale inhibitor, but also a green corrosion inhibitor.
4 2+ The synergistic effect among PESA (green compound ), Zn (safe
but low effective 4 corrosion inhibitor ) and sodium gluconate was studied.
The result is shown in Figure 2+ 2. It is found that when PESA and Zn
are used together, the inhibition efficiency is worse than that of each
alone. Namely, there is no synergistic effect between PESA and 2+ Zn
. PESA with sodium gluconate shows no synergistic effect either. However,
2+ when PESA, Zn and sodium gluconate are simultaneously used and the
content ratio is inside the loop area of the bold line area in Figure
2, the formulas give corrosion inhibition efficiency more than 96 99
at 50 mg/L of total dosage. However, when their dosage ratio is on the
right side and under the bold line area in Figure 2,
Corrosion
Inhibition of Polyepoxysuccinic Acid
although PESA content is high, corrosion inhibition efficiency is
still poor. Because the best region of corrosion inhibition efficiency
is close tightly to the worse one, it is 2+ implied that there exists
a value effect for the contents of PESA, Zn and sodium gluconate in
this formula.
2+ Figrue 2 The synergistic effect of PESA, Zn and sodium gluconate
for carbon steel
To understand the corrosion inhibition mechanism of PESA, the synergistic
effects of polyacrylic (PAA) and acrylic acid-maleic acid copolymer
(PAA-HPMA), the molecular structures of which are alike, were also studied
under the same condition. Experimental data show that PESA has one more
carboxyl group of PAA, its corrosion inhibition efficiency (99.09 )
is better than that of PAA (27.81 ); PAA/HPMA has one more carboxyl
group than PESA, but its corrosion inhibition efficiency is only 6.27%.
It is inferred that the corrosion inhibition of PESA is not mainly affected
by carboxyl group, but by the oxygen atom inserted. The existence of
oxygen atom in PESA molecular structure makes it easy to form stable
chelate with pentacyclic structure.
Acknowledgment
This work is financially supported by the National Key Technologies
R&D Programme item of China (2002BA313B01).
References
-
1. R. C. Xiong, Environmental Engineer, 2000, 18 (2), 22.
-
2. R. C. Xiong, G. Wei, D. Zhou, Industrial Water Treatment, 1999, 19 (3), 11.
-
3. D. Darling, R. Rakshpal, J. Material Performance, 1998, 37 (12), 42.
-
4. T. L. He, Handbook of Water Treatment Chemicals, Chemical Industry press, Beijing, 2000,
p. 211.
|
