Descaling of jackets of glasslined vessels

Abstract: To descale the inside of the jacket of a glass-lined vessel (e.g., reaction vessel) or conduit, especially of glass-and-metal, there is used a descaling solution of hydrochloric acid, preferably 5 to 15% by wt., containing 50 to 1,000 ppm of laurylamine, lauryldimethylamine or propargyl alcohol, at a temperature of 40 to 70°C., and optionally containing 0.1 to 5% by wt., of tin (II) chloride. The cleaning solution is circulated normally for 2 to 6 hours and drained and the jacket rinsed and neutralised with alkali. Iron oxide scale is thus totally removed, without damage by generation of hydrogen gas and without corrosion.

Description: This invention relates to a descaling method for the inside of jackets of glass-lined vessels. More particularly, it relates to a descaling method to remove iron oxide scale generated inside a jacket, by dissolving with a hydrochloric acid-based detergent to avoid breaking the lining glass. Glass-lined instruments on vessels such as reaction vessels or conduits are used with heating media, such as steam, water and heat-conductive fluids, passing through jackets. After prolonged use of such jackets, however, scale containing iron oxide such as Fe₃O₄ and Fe₂O₃ is generated due to corrosion, and adheres to the inside surface of the jacket. Predominant after use at relatively low temperatures is Fe₂O₃, whereas Fe₃O₄ 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 steam or cooling water. Thus, periodical descaling of the inside of the jacket is desired. Known methods for descaling of such jackets include physical methods using high-pressure water, and chemical methods of dissolution removal using detergents based on organic acids. In the case of using strong acids such as hydrochloric acid for descaling of the jacket inside glass-lined vessels, hydrogen generated by reaction of the acid with a metal part of the instrument passes through the inner lattice of the metal structure and reaches the boundary of the lining glass and the metal plate where it stays and gradually increases the pressure to finally exert a force large enough to break the glass. Thus, the use of acid is dangerous. Accordingly, generally preferred is a physical method such as high-pressure water cleaning (see Shinko Faudler Catalogue , Japan, No.702, 'Handling and Maintenance of Glass-Steel Instruments'). For physical cleaning such as high pressure water, the extent of a portion of the instrument removable from the open end is limited, so that drilling of cleaning holes in the instrument is required. Thus,this recovery work involves 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 the initial stages of formation of scale since they use relatively mild detergents, e.g. based on organic acids. Generally, no effective results are obtained in the 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 a broken lining glass due to the acid impact is difficult and there is a considerable loss of use of the instrument. Thus, as a result, although removal of scale is needed to improve thermal efficiency in glass-lined vessels and to increase productivity, no satisfactory method has hitherto been found. We have therefore investigated methods to easily remove iron oxide scale generated inside jackets of glass-lined vessels without causing any damage to the glass linings, and found that a hydrochloric acid solution containing specific compounds is effective to remove the scales without any acid damage. The present invention relates to a method of descaling the inside of the jacket of a glass-lined vessel, comprising contacting said inside with a 5 to 15 wt% hydrochloric solution at a temperature of 40 to 70°C until the scale is removed; characterized in that said solution also contains 50 to 1,000 parts per million of an additive compound selected from laurylamine, lauryldimethylamine and propargyl alcohol and tin(II) chloride. The glass-lined vessels 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 contains at least one compound selected from laurylamine, lauryldimethylamine and propargyl alcohol, with or without tin(II) chloride. Preferred among them is a hydrochloric acid solution containing laurylamine, propargyl alcohol and tin(II) chloride, because it causes the lowest corrosion rate of the substitute hydrogen permeation rate and it has a high 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 preferred to previously dissolve the amine into a surfactant such as diethylene glycol and then mix with hydrochloric acid. At least one compound selected from laurylamine, lauryldimethylamine and propargyl alcohol should be added to the aqueous hydrochloric acid solution in amount of 50 to 1,000 ppm, preferably 100 to 500 ppm. The corrosion rate of the substrate 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 much 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. We may use not only propargyl alcohol itself or laurylamines themselves but also chemicals comprising them as components. A suitable amount of tin(II) chloride added to the aqueous hydrochloric acid solution is 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% gives no problem in the scale removal, however, it is not desired since there is increased production of hydrochloric acid fumes, which requires means to deal with the fumes. Sulfuric acid has less descaling ability and is thus undesirable. Nitric acid is also undesirable since it increases the corrosion of the substrate. 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, the temperature is 40 to 70°C. The descaling rate is decreased at temperatures lower than about 40°C, whereas the corrosion of the matrix is increased at temperatures higher than about 70°C. Descaling is normally performed by circulating the cleaning solution inside the jacket. Generally, the initial solution as it is circulated until the end. Further, 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 alkali, rinsed again and reused for its intended purpose. The present invention is now illustrated in greater detail with reference to non-limiting Examples. TEST 1 Dissolution states were investigated for scale components Fe₃O₄ and Fe₂O₃, and for a scale collected from the inside of a jacket of a glass-lined reaction vessel. Two grams of Fe₂O₃, Fe₃O₄, or the scale was fed into 50 ml of a 10% HCl solution in a flask, kept at 60°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. TEST 2 The results obtained in Reference Example 1 revealed that Fe₂O₃ was slightly soluble in the HCl solution. Thus, Fe₂O₃ was investigated under various temperatures and HCl concentrations (the amount of Fe₂O₃ feed was decreased to 1 g for tests under varied HCl concentrations), whereas other samples were subjected to tests under the same conditions as in TEST 1. The results are given in Tables 2 and 3. TEST 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°C to effect corrosion, and the amount of hydrogen generated and reaching 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 cm², from the values obtained after 3 and 6 hours. The results are given in Table 4. A glass-lined steel plate (100×100 mm²) was similarly tested with a 10% hydrochloric acid solution (at a contact area of 7.07 cm²), 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 m² of the lined surface area. TEST 4 Hydrogen permeation rate was measured in the same manner as in TEST 3 on a 1 mm-thick soft steel plate using cleaning solutions based on a 10% hydrochloric acid solution with various additives. The Fe concentration of the solution was simultaneously measured to obtain a corrosion rate. The results are given in Table 6. TEST 5 This example was essentially the same as in TEST 4, except that the additives were changed in amounts or were used as mixtures thereof. The results are given in Table 7. TEST 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°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. TEST 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. TEST 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 TEST 4. The results are given in Table 9. EXAMPLE 1 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 m³ and a jacket internal volume of about 1.7 m³ was removed by steps as follows. Laurylamine was dissolved in diethylene glycol, and the solution was added to hydrochloric acid to give 2.8 m³ 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°C was fed to the jacket side to effect cleaning by circulating for 3.5 hours. The hydrogen permeation rate was measured 1 ml/m²·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 1021 kJ/m²·hr·°C (244 kcal/m²·hr·°C) was 53% improved to give 1570 kJ/m²·hr·°C (375 kcal/m²·hr·°C) after cleaning. EXAMPLE 2 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 m³ and a jacket internal volume of 0.5 m³ was removed by steps as follows. Laurylamine was dissolved into diethylene glycol, and the solution was added to hydrochloric acid to give 3 m³ 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°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 1046 kJ/m²·hr·°C (250 kcal/m²·hr·°C) before cleaning was 30% improved to give 1369 kJ/m²·hr·°C (327 kcal/m²·hr·°C) after cleaning. Duration (hr) Fe₃O₄ Fe₂O₃ Actual scale Fe concent ratio (%) issolution ratio (%) Fe concent ration (%) Dissolution ratio (%) Fe concent ratio (%) Dissolution ratio (%) 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 Duration (hr) 40°C 50°C 60°C Fe concent ratio (%) Dissolution ratio (%) Fe concent ration (%) Dissolution ratio (%) Fe concent ratio (%) Dissolution ratio (%) 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 Duration (hr) HCl; 2.5% HCl; 5% HCl; 10% Fe concent ratio (%) Dissolution ratio (%) Fe concent ration (%) Dissolution ratio (%) Fe concent ratio (%) Dissolution ratio (%) 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 Soft steel plate thickness (mm) 1 2 3 4 5 Hydrogen permeation rate (ml/m²·hr) 244 42 15 7 3 No. Test piece Elapse of time before glass peeling (hr) Steel plate thickness (mm) Glass thickness (mm) 1 3 1.5 4 to 5 2 8 1.5 12 to 15 Duration (hr) Fe concentration (%) SnCl₂ 0.5% SnCl₂ 0.0% 1 1.11 0.89 2 1.50 1.19 3 1.90 1.24 4 1.95 1.30 SnCl₂ Concentration (%) Corrosion rate: g/m²·hr Hydrogen permeation rate (ml/m²·hr) Fe³+ concentration in hydrochloric acid (0%) Fe³+ concentration in hydrochloric acid (1.8%) 0.5 1.0 1.2 0.0 0.0 1.2 7.5 0.5

Claims: A method of descaling the inside of the jacket of a glass-lined vessel, comprising contacting said inside with a 5 to 15 wt% hydrochloric acid solution at a temperature of 40 to 70°C until the scale is removed; characterized in that said solution also contains 50 to 1,000 parts per million of an additive compound selected from laurylamine, lauryldimethylamine and propargyl alcohol, and tin(II) chloride. A descaling method as claimed in claim 1, wherein the concentration in the hydrochloric acid solution of said at least one additive is from 100 to 500 parts per million. A descaling method as claimed in claim 1, wherein the concentration of tin(II) chloride in the hydrochloric acid solution is from 0.1 to 5% by weight. A glass-lined reaction vessel or conduit which has been descaled by the method of any preceding claim.

Inventors: MATSUDA TERUO, MIKI MASAYOSHI, OCHI HIROMU, MATSUDA, TERUO, MIKI, MASAYOSHI, OCHI, HIROMU
Applicants: SUMITOMO CHEMICAL CO, SUMITOMO CHEMICAL COMPANY, LIMITED
Application year: 1988
Main classification: C23G1
IPC codes: C23G1, C03C23