Descaling of jackets of glass-lined instruments

A descaling method for the inside of jackets of glass-lined instruments is disclosed, comprising using a hydrochloric acid solution comprising at least one compound selected from the group consisting of laurylamine, lauryldimethylamine and propargyl alcohol, with or without tin(II) chloride.

FIELD OF THE INVENTION 
This invention relates to a descaling method for the inside of jackets of 
glass-lined instruments. More particularly, it relates to a descaling 
method to remove iron oxide base scales generated inside of a jacket by 
dissolving with a hydrochloric acid-based detergent to avoid breaking a 
lining glass due to hydrogen permeation. 
BACKGROUND OF THE INVENTION 
Glass-lined instruments are used with heating media such as stream, water, 
and heat conductive fluids passing through jackets. In a prolonged use of 
such jackets, however, scales based on iron oxides such as Fe.sub.3 
O.sub.4 and Fe.sub.2 O.sub.3 generate due to corrosion, and adheres to the 
inside surface of the jacket. Predominant in the use at relatively low 
temperatures is Fe.sub.2 O.sub.3, whereas Fe.sub.3 O.sub.4 is more 
frequently observed at high temperatures. The scale reduces heat 
conductivity and not only leads to a considerable decrease in productivity 
but also increases the use of stream or cooling water. Thus, periodical 
descaling of the jacket inside is desired. 
Known methods for descaling of the jacket inside of glass-lined instruments 
include physical methods using high-pressure water, and chemical methods 
by dissolution removal using organic acid-based detergents. 
In the case of using chemical detergents such as hydrochloric acid for 
descaling of the jacket inside of glass-lined instruments, hydrogen 
generated by reaction of the acid with the metal transports through the 
inner lattice of the metal structure and reaches the boundary of the 
lining glass and the steel plate where it stays and gradually increases 
the pressure to finally attain a force large enough to break the glass. 
Thus, acid impact is feared. Accordingly, generally preferred is a 
physical method such as high-pressure water cleaning (see Shinko Faudler 
Catalogue, No. 702, "Handling and Maintenance of Glass-Steel 
Instruments"). 
In the case of physical cleaning methods such as high pressure water 
cleaning, a removable area from the open end is limited such that drilling 
of cleaning holes in the instrument is required. Thus, its recovery work 
should be made with the consumption of time and money. In addition, 
complete descaling cannot be expected and is less effective as compared 
with chemical methods. Application of chemical methods is also under way, 
however, those methods under trial are applicable only to scales at their 
initial stages of formation since they use relatively mild detergents 
based on such as organic acids. Generally, no effective results are 
anticipated when applied to practical removal of iron oxide base scale 
deposits. 
The use of powerful detergents based on hydrochloric acid or the like may 
cause acid impact. Repairing of the broken lining glass due to the acid 
impact is difficult and also brings about a considerably large loss of 
opportunity. As a result, though there is needed removal of the scale to 
improve thermal efficiency and to increase productivity, no 
countermeasures are taken in the practical use. 
As a solution to the above problems, the present inventors have made 
extensive investigations on methods to easily remove iron oxide base 
scales generated inside jackets of glass-lined instruments without giving 
any damage to glass linings, and found that a hydrochloric acid solution 
containing specific compounds is effective enough to remove the scales 
free from any acid impact. 
SUMMARY OF THE INVENTION 
The present invention relates to a method for descaling inside of jackets 
of glass-lined instruments by using hydrochloric acid containing at least 
one compound selected from the group consisting of laurylamine, 
lauryldimethylamine and propargyl alcohol, with or without tin(II) 
chloride. 
DETAILED DESCRIPTION OF THE INVENTION 
The glass-lined instruments referred to in the present invention include 
glass-lined, jacket-equipped reaction vessels, polymerization vessels and 
conduits. 
The hydrochloric acid solution used in the present invention comprises at 
least a compound selected from the group consisting of laurylamine, 
lauryldimethylamine and propargyl alcohol, with or without tin(II) 
chloride. Preferable among them is a hydrochloric acid solution containing 
laurylamine, propargyl alcohol, and tin(II) chloride because it is the 
lowest in both of the corrosion rate of the matrix and the hydrogen 
permeation rate and is high in dissolution rate of the scale. Laurylamine 
and lauryldimethylamine (referred to as laurylamines hereinafter) readily 
dissolve into hydrochloric acid if their hydrochlorides or like inorganic 
salts are employed. Free amines, on the other hand, are not easily 
dissolved. Therefore, it is desired to before-handedly dissolve the amine 
into a surfactant such as diethylene glycol and then mix with hydrochloric 
acid. 
At least a compound selected from laurylamine, lauryldimethylamine and 
propargyl alcohol should be added to the aqueous hydrochloric acid 
solution in an amount about 50 to 1,000 ppm, preferably 100 to 500 ppm. 
The corrosion rate of the matrix and the hydrogen permeation rate are both 
increased when the concentration is lower than about 50 ppm. Concentration 
exceeding about 1000 ppm is not effective since the effect is not so 
improved with an increase of concentration. Moreover, a large amount of 
the surfactant is necessary to dissolve laurylamines, and also, 
inconveniences such as deposition of laurylamines are encountered. 
It is not necessary to dissolve propargyl alcohol itself or laurylamines 
themselves to hydrochloric acid, but may be incorporated into chemicals 
comprising them as components. 
It is possible to remove the scale while depressing the corrosion of the 
matrix and acid impact without the aid of tin(II) chloride, however, the 
addition of tin(II) chloride further decreases the corrosion and promotes 
the scale dissolution. 
A suitable amount of tin(II) chloride added to the aqueous hydrochloric 
acid solution is about 0.1 to 0.5%, preferably 0.5 to 3%. Addition of less 
than about 0.1% gives a small effect, and addition exceeding about 5% is 
not so effective in that an effect expected from the concentration is not 
attained. 
An appropriate concentration of hydrochloric acid is chosen in the range of 
from about 5 to 15% depending on the adhesion state of the scale. The 
dissolution rate of the scale is approximately proportional to the 
concentration of hydrochloric acid, however, the rate is decreased in 
concentrations lower than about 5%. A concentration exceeding about 15% 
has no problem in the scale removal, however, it is not desired since 
hydrochloric acid fume generation increases and a demand for 
countermeasures newly arises. 
Sulfuric acid has a less descaling ability and is thus undesirable. Nitric 
acid is also undesirable since it increases the corrosion of the matrix. 
Mineral acids such as sulfuric acid and phosphoric acid, or corrosion 
preventives commonly used for descaling may also be incorporated in the 
hydrochloric acid solution. 
The dissolution rate is approximately proportional to the temperature of 
descaling. The descaling temperature is not especially restricted but is 
determined while taking into consideration the amount of the scale and the 
concentration of hydrochloric acid. Normally, it is set at about 
40.degree. to 70.degree. C. The descaling rate is decreased at 
temperatures lower than about 40.degree. C., whereas the corrosion of the 
matrix is increased at temperatures higher than about 70.degree. C. 
Descaling is normally performed by circulating the cleaning solution inside 
the jacket. Generally, the initial solution as it is circulated to the 
end. Hydrochloric acid, propargyl alcohol or laurylamines, or tin(II) 
chloride may be added in case of need, such as when the acid concentration 
is decreased. 
Descaling is normally performed for about 2 to 6 hours, but may be changed 
depending on the adhesion state of the scale. 
No breakage by acid impact occurs under the above-specified conditions, 
however, the detection of hydrogen permeating the matrix to the glass side 
is difficult. Therefore, hydrogen permeated to the outer surface of the 
jacket may be monitored. It is safer to monitor the hydrogen on the jacket 
side since normally, jackets are thinner than the matrix and higher 
hydrogen permeation is obtained on the jacket side. 
The cleaning solution is drained from the jacket after descaling is 
finished. The jacket is then rinsed, neutralized with alkalis, rinsed 
again, and reused to effect the reaction.

The present invention is now illustrated in greater detail with reference 
to non-limiting Examples. cl REFERENCE EXAMPLE 1 
Dissolution states were investigated for scale components Fe.sub.3 O.sub.4 
and Fe.sub.2 O.sub.3, and for a scale collected from the inside of a 
jacket of a glass-lining-made reaction vessel. 
Two grams of Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4, or the scale was fed into 
50 ml of a 10% HC1 solution in a flask, kept at 60.degree. C., and 
stirred. Solutions were collected at a constant time interval and analyzed 
for the Fe ion concentration. The results are given in Table 1. 
REFERENCE EXAMPLE 2 
The results obtained in Reference Example 1 revealed that Fe.sub.2 O.sub.3 
was slightly soluble in the HC1 solution. Thus, Fe.sub.2 O.sub.3 was 
investigated under various temperatures and HC1 concentrations (the amount 
of Fe.sub.2 O.sub.3 feed was decreased to 1 g for tests under varied HC1 
concentrations), whereas other samples were subjected to tests under the 
same conditions as in Reference Example 1. The results are given in Tables 
2 and 3. 
REFERENCE EXAMPLE 3 
Hydrogen permeation rate and peeling of a glass lining were separately 
measured since their relationship cannot be directly measured. 
One side of a soft steel plate was brought into contact with a 10% 
hydrochloric acid solution at 60.degree. C. to effect corrosion, and the 
amount of hydrogen generated and reached to the other side by permeation 
was measured. The hydrogen permeation rate was measured by the glycerol 
substitution method (Boshoku-Gijutsu, 26, 504 (1977)) at a contact area of 
7.07 cm.sup.2, from the values obtained after 3 and 6 hours. The results 
are given in Table 4. 
A glass-lined steel plate (100.times.100 mm.sup.2) was similarly tested 
with a 10% hydrochloric acid solution (at a contact area of 7.07 
cm.sup.2), and the time elapsed was measured until the peeling off due to 
permeated hydrogen occurred. The results are given in Table 5. 
Though not unequivocal since the hydrogen permeation rate of the 
glass-lined steel plate differs in a strict sense from that of the plate 
having no linings, peeling of glass seemingly occurs at a hydrogen stay of 
about 30 to 40 ml per m.sup.2 of the lined surface area. 
REFERENCE EXAMPLE 4 
Hydrogen permeation rate was measured in the same manner as in Reference 
Example 3 on a 1 mm-thick soft steel plate using cleaning solutions based 
on a 10% hydrochloric acid solution with changing additives. The Fe 
concentration of the solution was simultaneously measured to obtain a 
corrosion rate. The results are given in Table 6. 
REFERENCE EXAMPLE 5 
This example was essentially the same as in Reference Example 4, except 
that the additives were changed in amounts or were used as mixtures 
thereof. The results are given in Table 7. 
REFERENCE EXAMPLE 6 
A glass-lined test piece (a 3 mm-thick steel plate having a 1.5 mm-thick 
glass lining) was brought into contact at 60.degree. C. with cleaning 
solutions shown in Table 7 on the steel side. No glass peeling occurred 
after 100 hours except for Pieces No. 1 and No. 4. 
REFERENCE EXAMPLE 7 
The effect of tin(II) chloride on the dissolution of the scale was 
investigated on a scale collected from the inside of a jacket of a 
glass-lined polymerization vessel. 
The same method as in Reference Example 1 was followed, except that a 10% 
hydrochloric acid solution comprising 200 ppm of propargyl alcohol, 100 
ppm of laurylamine (900 ppm of diethylene glycol), and tin(II) chloride 
was employed. The results are given in Table 8. 
REFERENCE EXAMPLE 8 
The effects of tin(II) chloride on corrosion rate of the matrix and on 
hydrogen permeation rate were investigated. 
A 10% hydrochloric acid solution comprising 200 ppm of propargyl alcohol, 
100 ppm of laurylamine (900 ppm of diethylene glycol), and tin(II) 
chloride was prepared and allowed to react with a 1.5 mm-thick soft steel 
plate to measure the corrosion rate of the matrix and the hydrogen 
permeation rate in the same method as in Reference Example 4. The results 
are given in Table 9. 
EXAMPLE 1 
An iron oxide base scale (with an estimated adhesion of about 20 kg and 
average scale thickness of 2 mm) generated on a glass lined reaction 
vessel (a soft steel thickness of the glass-lined side being 9 mm) having 
a body internal volume of 500 l and a jacket internal volume of about 160 
l was removed by steps as follows. 
Laurylamine was dissolved into diethylene glycol, and the solution was 
added to hydrochloric acid to give 250 l of a 10% aqueous hydrochloric 
acid solution comprising 200 ppm of laurylamine (with 0.5% of diethylene 
glycol). The solution maintained at 60.degree. C. was fed to the jacket 
side and circulated for 5 hours to effect the cleaning. 
The hydrogen permeation rate measured with a measuring apparatus attached 
to a part of the outer wall (having a plate thickness of 5 mm) of the 
jacket was 1 m1/m.sup.2 .multidot.hr or less. 
Cleaning was stopped after 5 hours, followed by thoroughly rinsing (an 
alkali neutralization treatment included). A sound glass surface was 
obtained after the cleaning and megascopic observation revealed that about 
100% of the scale was removed from the inside wall of the jacket. 
The total thermal conductivity of 152.6 kcal/m.sup.2 
.multidot.hr.multidot..degree. C. before cleaning was 29.5% improved to 
give 197.7 kcal/m.sup.2 .multidot.hr.multidot..degree. C. after cleaning. 
EXAMPLE 2 
A scale (with an estimated adhesion of about 140 to 150 kg) containing 
approximately equal amounts of Fe.sub.3 O.sub.4 and Fe.sub.2 O.sub.3 
generated on a jacket of a glass-lined reaction vessel having a body 
internal volume of 6 m.sup.3 and a jacket internal volume of about 1 
m.sup.3 was cleaned by a method as follows. 
1.5 m.sup.3 of a 10% aqueous hydrochloric acid solution comprising 100 ppm 
of laurylamine and 100 ppm of propargyl alcohol (with 0.5% of diethylene 
glycol) was prepared and circulated over the jacket for 5 hours with the 
solution temperature maintained at 60.degree. C. 
The hydrogen permeation rate was measured 1 m1/m.sup.2 .multidot.hr or less 
with an apparatus being attached to a part of the outside wall of the 
jacket. 
After cleaning for 5 hours was finished, thorough rinsing (an alkali 
neutralization treatment included) was performed. A sound glass surface 
was obtained and megascopic observation revealed that about 100% of the 
scale was removed from the inside wall of the jacket. 
The total thermal conductivity of 132.2 kcal/m.sup.2 
.multidot.hr.multidot..degree. C. before cleaning was 28.3% improved to 
give 69.6 kcal/m.sup.2 .multidot.hr.multidot..degree. C. after cleaning. 
EXAMPLE 3 
A scale (with an estimated adhesion of about 90 kg) based on iron oxides 
generated on a jacket of a glass-lined reaction vessel (a soft steel 
thickness of the glass-lined side being 12 mm) having a body internal 
volume of 14 m.sup.3 and a jacket internal volume of about 1.7 m.sup.3 was 
removed by steps as follows. 
Laurylamine was dissolved in diethylene glycol, and the solution was added 
to hydrochloric acid to give 2.8 m.sup.3 of an aqueous 10% hydrochloric 
acid solution comprising 100 ppm of laurylamine (with 900 ppm of 
diethylene glycol), 200 ppm of propargyl alcohol, and 0.5% of tin(II) 
chloride. The resulting solution maintained at 60.degree. C. was fed to 
the jacket side to effect cleaning by circulating for 3.5 hours. 
The hydrogen permeation rate was measured 1 m1/m.sup.2 .multidot.hr or less 
with an apparatus attached to a part of the outside jacket wall having a 
plate thickness of 5 mm. 
After cleaning for 3.5 hours was finished, through rinsing (an alkali 
neutralization treatment included) was performed. A sound glass surface 
was obtained and megascopic observation revealed that about 100% of the 
scale was removed without any corrosion of the matrix. 
The total thermal conductivity of 244 kcal/m.sup.2 
.multidot.hr.multidot..degree. C. was 53% improved to give 375 
kcal/m1.sup.2 .multidot.hr.multidot..degree. C. after cleaning. 
EXAMPLE 4 
An iron oxide base scale (with an estimated adhesion of about 30 kg) 
generated on a glass-lined reaction vessel having a body internal volume 
of 2.6 m.sup.3 and a jacket internal volume of 0.5 m.sup.3 was removed by 
steps as follows. 
Laurylamine was dissolved into diethylene glycol, and the solution was 
added to hydrochloric acid to give 3 m.sup.3 of a 10% aqueous hydrochloric 
acid solution comprising 120 ppm of laurylamine (with 1000 ppm of 
diethylene glycol), 230 ppm of propargyl alcohol, and 0.8% of tin(II) 
chloride. The resulting solution maintained at 60.degree. C. was fed to 
the jacket side and circulated for 3 hours to effect the cleaning. 
After cleaning for 3 hours was finished, thorough rinsing (an alkali 
neutralization treatment included) was performed. A sound glass surface 
was obtained and megascopic observation revealed that approximately 100% 
of the scale was removed without any corrosion of the matrix. 
The total thermal conductivity of 250 kcal/m.sup.2 
.multidot.hr.multidot..degree. C. before cleaning was 30% improved to give 
327 kcal/m.sup.2 .multidot.hr.multidot..degree. C. after cleaning. 
TABLE 1 
__________________________________________________________________________ 
Fe.sub.3 O.sub.4 
Fe.sub.2 O.sub.3 
Actual scale 
Fe Dissolu- 
Fe Dissolu- 
Fe Dissolu- 
concen- 
tion concen- 
tion concen- 
tion 
Duration 
tration 
ratio 
tration 
ratio 
tration 
ratio 
(hr) (%) (%) (%) (%) (%) (%) 
__________________________________________________________________________ 
0.5 1.5 52 0.6 21 0.6 24 
2.0 2.6 90 1.4 50 1.4 56 
4.0 2.9 100 1.7 61 1.8 72 
__________________________________________________________________________ 
TABLE 2 
__________________________________________________________________________ 
40.degree. C. 50.degree. C. 
60.degree. C. 
Fe Dissolu- 
Fe Dissolu- 
Fe Dissolu- 
concen- 
tion concen- 
tion concen- 
tion 
Duration 
tration 
ratio 
tration 
ratio 
tration 
ratio 
(hr) (%) (%) (%) (%) (%) (%) 
__________________________________________________________________________ 
1.0 0.2 7 0.5 21 1.0 34 
2.0 0.4 14 0.9 30 1.4 48 
4.0 0.8 28 1.5 51 2.0 69 
__________________________________________________________________________ 
TABLE 3 
__________________________________________________________________________ 
HCl; 2.5% HCl; 5% HCl; 10% 
Fe Dissolu- 
Fe Dissolu- 
Fe Dissolu- 
concen- 
tion concen- 
tion concen- 
tion 
Duration 
tration 
ratio 
tration 
ratio 
tration 
ratio 
(hr) (%) (%) (%) (%) (%) (%) 
__________________________________________________________________________ 
1.0 0.12 9 0.25 18 0.62 44 
2.0 0.17 12 0.39 28 0.80 57 
4.0 0.23 16 0.58 41 1.02 73 
__________________________________________________________________________ 
TABLE 4 
______________________________________ 
Soft steel plate thickness 
(mm) 
1 2 3 4 5 
______________________________________ 
Hydrogen 244 42 15 7 3 
permeation 
rate 
(ml/m.sup.2 .multidot. hr) 
______________________________________ 
TABLE 5 
______________________________________ 
Test piece Elapse 
Steel of time 
plate Glass before glass 
thickness thickness 
peeling 
No. (mm) (mm) (hr) 
______________________________________ 
1 3 1.5 4 to 5 
2 8 1.5 12 to 15 
______________________________________ 
TABLE 6 
__________________________________________________________________________ 
Additive Hydrogen 
Concent- 
Diethylene 
Corrosion 
permeation 
ration 
glycol 
rate rate 
No. 
Kind (ppm) 
(%) (g/m.sup.2 .multidot. hr) 
(ml/m.sup.2 .multidot. hr) 
__________________________________________________________________________ 
1 Laurylamine 100 0.5 5.9 
2.2 
2 Lauryldimethylamine 
100 0.5 30.9 
11.9 
3 Propargyl alcohol 
200 -- 5.2 
2.5 
4 Butylamine 100 1.0 242 193 
5 Hexylamine 100 1.0 228 189 
6 Octylamine 100 1.0 218 180 
7 Decylamine 200 1.0 203 181 
8 Hexamethylenediamine 
200 2.0 186 172 
9 Hexamethylenetetramine 
200 2.0 39.3 
32 
10 Benzyl chloride 
200 2.0 218 178 
11 Dichloroethane 
200 -- 232 188 
12 -- -- -- 351 252 
__________________________________________________________________________ 
TABLE 7 
__________________________________________________________________________ 
Additive Hydrogen 
Concen- 
Diethylene 
Corrosion 
permeation 
tration 
glycol 
rate rate 
No. 
Kind (ppm) 
(%) (g/m.sup.2 .multidot. hr) 
(ml/m.sup.2 .multidot. hr) 
__________________________________________________________________________ 
1 Laurylamine 
50 0.25 39.9 12.7 
2 Laurylamine 
200 1.0 3.2 2.3 
3 Laurylamine 
400 2.0 3.3 2.5 
4 Lauryldimethylamine 
50 0.25 51.6 16.3 
5 Lauryldimethylamine 
200 1.0 19.6 5.8 
6 Lauryldimethylamine 
400 2.0 9.5 3.2 
7 Laurylamine 
50 0.75 9.6 3.9 
Lauryldimethylamine 
100 
8 Laurylamine 
50 1.0 3.2 2.3 
Propargyl alcohol 
100 
9 Laurylamine 
100 1.0 1.9 1.5 
Propargyl alcohol 
50 
10 Laurylamine 
100 1.0 1.2 1.1 
Propargyl alcohol 
100 
__________________________________________________________________________ 
TABLE 8 
______________________________________ 
Duration Fe concentration (%) 
(hr) SnCl.sub.2 0.5% 
SnCl.sub.2 0.0% 
______________________________________ 
1 1.11 0.89 
2 1.50 1.19 
3 1.90 1.24 
4 1.95 1.30 
______________________________________ 
TABLE 9 
______________________________________ 
Corrosion rate: g/m.sup.2 .multidot. hr 
Fe.sup.3+ Fe.sup.3+ 
SnCl.sub.2 
concentration 
concentration 
Hydrogen 
Concent- in in permeation 
ration hydrochloric hydrochloric 
rate 
(%) acid (0%) acid (0.18%) 
(ml/m.sup.2 .multidot. hr) 
______________________________________ 
0.5 1.0 1.2 0.0 
0.0 1.2 7.5 0.5 
______________________________________ 
While the invention has been described in detail and with reference to 
specific embodiments thereof, it will be apparent to one skilled in the 
art that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.