RU2554583C1 - Scale removal composition - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: composition contains 20.0-35.0 wt % hydrochloric acid, 4.0-6.0 wt % sodium or potassium or ammonium pyrosulphate or sodium or potassium or ammonium persulphate, 1.0-1.5 wt % non-ionic surfactant, 3.5-5.0 wt % thiourea, 10.0-15.0 wt % dimethylsulphoxide (DMSO) and water - the balance.

EFFECT: high effectiveness of removing scales from metal surfaces of pipes and different processing units and apparatus by increasing the rate of dissolution of scales.

2 dwg, 3 tbl

Description

The invention relates to the petrochemical, chemical industry, power system, water supply and other sectors of the national economy, and in particular to compositions for descaling from the inner surface of pipes, heat exchangers and process apparatuses.

A known composition for descaling according to the patent of the Russian Federation No. 2085517, containing in wt. %: potassium or sodium bisulfate or pyrosulfate 5-12, hydrochloric 4-8, acetic acid 4-6, water - the rest. The disadvantage of the composition is the low efficiency in removing scale from the inner surfaces of the pipes.

A known composition for descaling according to the patent of the Russian Federation No. 2257354, taken as a prototype, containing in wt. %: sodium pyrosulfate, or potassium, or ammonium or sodium sulphate, or potassium, or ammonium - 0.09-10.0, polyphenolic compounds of coniferous bark - 0.003-2.0, urotropin - 0.01-4.0, nonionic surfactant - 0.0015-0.009, polyhexamethylene guanidine chloride - 0.1-1.5, hydrochloric acid - 2.0-15.0, water - the rest. The composition is not effective enough to clean the inner surfaces of pipes from scale due to the low content of the main working substance - hydrochloric acid and the lack of components that can dissolve organic impurities, the content of which varies widely and is the main inhibiting agent in the operation of the descaling agent. During the cleaning process, the descaling compound enters into a chemical reaction with deposits, and as a result, its concentration decreases, which reduces the cleaning efficiency.

EFFECT: increased efficiency of descaling from metal surfaces of pipes and various technological units and apparatuses.

The technical result is achieved due to the fact that the composition for removing scale containing hydrochloric acid, sodium pyrosulfate, or potassium, or ammonium or sodium sulphate, or potassium, or ammonium and a nonionic surfactant, additionally contains thiourea and dimethyl sulfoxide ( DMSO) in the following components, wt. %:

Hydrochloric acid 20.0-35.0 Sodium pyrosulfate, or potassium, or ammonium or sodium sulfate, or potassium, or ammonium 4.0-6.0 Nonionic surfactants 1.0-1.5 Thiourea 3,5-5,0 Dimethyl sulfoxide 10.0-15.0 Water Rest

It is proposed to use DMSO, which has a higher boiling point compared to the acetone used in the prototype, and well dissolves organic deposits of various compositions, which is experimentally confirmed using quantitative nuclear magnetic resonance spectroscopy on hydrogen and carbon nuclei.

The selected optimal concentration of hydrochloric acid allows more intensive dissolution of iron-acid deposits by converting them to soluble salts, which are removed mechanically, by passing an aqueous solution under high pressure. However, the use of a strong acid with a high concentration leads to thinning of the metal and the failure of metal pipes, due to the inability to use high pressure in existing devices. Therefore, there is a need for the use of corrosion inhibitors, which accelerates with the introduction of acid. It is proposed to use thiourea as an inhibitor. Nonionic surface-active substances (surfactants) and DMSO are good agents in the fight against oil and fat deposits, which impede the effective operation of the main component - hydrochloric acid.

The use of DMSO and thiourea in combination with a significantly higher content of hydrochloric acid allowed us to increase the rate of dissolution of scale and increase the efficiency of descaling.

To assess the quality of the work of the proposed composition, samples were prepared simulating various deposits. Their main qualitative composition, imitating the composition of deposits on the inner surfaces of pipes:

1. bicarbonates, sulfates and chlorides of calcium and magnesium;

2. iron (III) hydroxide, as well as its decomposition products FeO (OH);

3. oil and oil fractions of various compositions;

4. sparingly soluble salts of metal carbonates, sulfides and silicates are used as mechanical components.

For testing, 1000 ml of the descaling composition was taken, heated to a temperature of 60-70 ° C, and using high pressure pumps, the solution was circulated along the inner surfaces of the pipes with various deposits, created artificially, but simulating the real scale composition of various enterprises. The determination of the composition of contaminants was studied using various physicochemical methods: photocalorimetry, atomic adsorption, chromatography and mass spectrometry, nuclear magnetic resonance spectroscopy, IR and UV spectrometry. All samples were investigated according to three main parameters characterizing the quality and efficiency of mixtures with different ratios of components:

1. the rate of dissolution of scale;

2. the completeness of the conversion of iron-acid deposits in soluble substances;

3. completeness of removal of organic components of scale.

The rate of dissolution of the scale was estimated by the change in mass (weighed on an analytical balance accurate to the fourth decimal place) in time of artificially created samples, the composition of which is presented above.

The completeness of the conversion of iron-acid deposits into soluble substances was evaluated by measuring the content of Fe ⁺³ ions in the solution by the photometric method based on the formation of colored complex compounds with sulfosalicylic acid or its sodium salt with iron salts, and in a weakly acidic medium sulfosalicylic acid reacts only with iron salts ^{( 3+)} (red staining), and in a slightly alkaline medium - with iron salts ⁽²⁺⁾ and ⁽³⁺⁾ (yellow staining). The solution is filtered through a white ribbon filter, ammonium chloride, sulfosalicylic acid, ammonia are added, the pH of the solution should be 7-8 (for litmus indicator paper). Adjust to the mark with distilled water. Mix thoroughly and leave for 5 minutes until color develops. The optical density of the resulting solution was measured at a wavelength of λ = 425 nm in a cuvette with an absorbing layer length of 50 or 10 mm with respect to a blank solution conducted with distilled water through the entire course of the analysis. According to the calibration graph find the iron content.

Contaminants containing organic matter are determined and studied by quantitative NMR spectroscopy on various nuclei. ¹³ C NMR spectra were recorded for carbon nuclei on a Varian VXR 500 S spectrometer (USA) with an operating frequency of 67.7 MHz at 25 ° C in standard ampoules with a diameter of 5 and 10 mm. The content of organic molecules and chemical shifts (δ ¹³ C) were measured relative to the signal of the external standard (measurement accuracy ± 0.1 ppm). The integration error leaves no more than ± 3%.

Prepared and studied samples of mixtures, different in chemical composition. The ratio of components is presented in table 1.

The results of the experiments to study the effectiveness of solutions with different component ratios are presented in table 2.

As can be seen from a comparison of the data (Tables 1 and 2), the dissolution time of the scale and the removal of mechanical impurities decreases during the transition from mixture 1 to mixture 15, which is possibly due to an increase in the content of hydrochloric acid in the solution. It is advisable to use a solution containing at least 25 wt. % of hydrochloric acid. The use of other acids is not recommended due to clogging of the inner surface of the pipes with products of chemical reactions (sparingly soluble salts). The completeness of the conversion of iron oxide deposits into soluble substances also increases with a change in the HCl content in the solution, which is due to the chemical properties of hydrochloric acid. Optimal is the concentration of acid in the solution, which is in the range: 28-35 mass. % of the total mass of the solution.

The completeness of the removal of organic constituent deposits varies widely. Mixtures of 13-15 show good results, which is due to an increase in the content of DMSO and hydrochloric acid in solution.

The degree of corrosion protection for the presented samples varies within rather narrow limits. However, the best results are observed for mixtures numbered 9-15.

Thus, the most optimal are given in examples 13-15, the concentration of the components of the composition in wt. %: hydrochloric acid 20-35, sodium pyrosulfate, or potassium, or ammonium, or sodium sulfate, or potassium, or ammonium 4-6; thiourea 3.5-5; nonionic surfactant 1.0-1.5; DMSO 10.0-15.0 and water - the rest.

Table 3 presents the results of studies of the efficiency of descaling depending on the temperature of the composition for descaling. The most acceptable results were shown by experiments at a temperature of 50-60 ° C, a further increase in temperature does not lead to changes in the results of the studied parameters.

The decrease in the completeness of removal of organic constituent deposits when the temperature reaches above 60 ° C is probably due to the accelerated evaporation of dimethyl sulfoxide as the main component for the removal of organic pollutants. Thus, the optimal temperature for the cleaning process is 60 ° C, with a four-hour circulation of the solution.

Depending on the level of contamination with various deposits, the indicator for the need to update the solution to remove scale is the pH of the solution. During washing, the pH of the solution changes due to the acid reaction and deposits and as a result of a decrease in the concentration of hydrochloric acid in the solution. The efficiency of the mixture decreases. In FIG. 1 shows the dependence of the efficiency of the solution on the pH value.

Thus, when flushing the system, it is necessary to control the pH of the solution, which should not rise above the pH of 4, and if necessary, update the solution for the effective operation of the solution to remove scale and dirt from the inner surfaces of the pipes.

Next, we prepared solutions with various representatives of nonionic surfactants. One of the most numerous groups of nonionic surfactants are polyoxyethylene ethers of alkyl phenols. In FIG. 2 presents the results of assessing the possibility of using various representatives of nonionic surfactants. The best result of descaling was shown by the nonionic surfactant TWEEN 60.

Claims (1)

A descaling composition containing hydrochloric acid, sodium pyrosulfate, or potassium, or ammonium or sodium sulfate, or potassium, or ammonium, a nonionic surfactant, characterized in that it further contains thiourea and dimethyl sulfoxide in the following components, wt. %:
Hydrochloric acid 20.0-35.0 Sodium pyrosulfate, or potassium, or ammonium or sodium sulfate, or potassium, or ammonium 4.0-6.0 Nonionic surfactant 1.0-1.5 Thiourea 3,5-5,0 Dimethyl sulfoxide (DMSO) 10.0-15.0 Water Rest

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