JPH01317531A - Improved gypsum resolvent - Google Patents

Abstract

PURPOSE:To permit an efficient removal of gypsum adhered to metals by dissolving the same without causing corrosion thereto by adding alkali hydrogen carbonate to an aqueous diamine derivative solution to thereby use the solution adjusted to a predetermined pH value. CONSTITUTION:Water is added to a compound represented by the formula I (wherein R1-R4 are identical or different groups, each having at least one hydroxyl or carboxyl group or its salt at the end thereof and R5 is phenylene group, alkylene group containing carbon atoms of 1-10 or ether or polyether group containing carbon atoms of 1-5) and slowly heated for dissolution. The resulting solution, cooled for dissolving potassium hydrogen carbonate to thereby adjust its pH value to 7.5, is capable of dissolving gypsum nearly 100 percent. The use of this solution permits an efficient cleaning of the inner walls of combustion furnace, reactor, rectifying tower and pipeline for petroleum and coal without causing corrosion thereto and the addition thereto of a dispersing or surface-active agent leads to the retention of the gypsum dissolving power.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a solvent for dissolving gypsum (calcium sulfate), which is a poorly soluble substance.

BACKGROUND OF THE INVENTION Since gypsum is poorly soluble in water as well as in acids and alkalis, various methods have been tried to clean it.

Particularly, in factories that use fossil fuels such as oil and coal, gypsum adheres as a residue to the inner walls of combustion furnaces, reactors, rectification towers, pipelines, etc., and has an adverse effect. As a method for removing this deposited gypsum, attempts have been made for some time to chemically dissolve it using phosphate-based compounds. However, phosphate-based compounds dissolve gypsum but are less desirable because they corrode metals such as iron, nickel, and chromium used in these furnaces, reactors, rectifiers, and pipelines. isn't it.

In addition to the phosphate system, attempts have also been made to remove gypsum by using various chelates to form calcium chelate complexes, but the extraction of calcium ions against the chelating agents is a typical equilibrium method. It is a reaction and is not very efficient.

Problems to be Solved by the Invention Therefore, various phosphates and various chelating agents used as gypsum dissolving agents are corrosive to metals such as iron, nickel, and chromium, and furthermore, the extraction rate of calcium ions is low. There are problems such as limitations.

Means for Solving the Problems The present inventors have continued to conduct intensive research on these problems, namely the corrosivity of metals and the extraction rate of calcium ions.

As a result, it has been traditionally used as a chelating agent.
An unexpected fact was discovered that diamine derivatives with two nitrogen atoms with lone pairs of electrons not only generate calcium ions and calcium chyronate, but also directly generate calcium salts with calcium ions. .

Therefore, if the pH value of the solution can be adjusted, gypsum can be easily dissolved. However, dissolving the diamine derivative in water is disadvantageous because the pH value of the solution changes due to hydrolysis. Furthermore, since the calcium salt production reaction is essentially an exchange reaction with hydrogen, the pH value of /81& decreases as the gypsum melts, which is undesirable.

Based on the above findings, the present inventors basically added a buffer to the solution of the diamine derivative to keep it neutral, and removed hydrogen ions generated in the calcium salt production reaction with an alkali bicarbonate. succeeded in doing so. by this,
The above problems were solved all at once, and the present invention was completed.

(a) General formula (1): % formula % (wherein R1-R4 are the same or different and have at least one hydroxyl group or carboxyl group, or a salt thereof at the end) (b) This is an improved gypsum dissolving agent, which is a solution mainly composed of two alkali hydrogen carbonate components, and the pH value of the solution is adjusted to 6 or more and 8 or less.

The diamine derivative which is the main component of the gypsum dissolving agent according to the present invention is a compound having two nitrogen atoms having a lone pair of electrons and is represented by the general formula (1). In the general formula (1), R1-R4 represents the general formula ]I X-C)-C-A-(2) (wherein, 1 to 5 alkylene groups) or X-0-A-(3) (wherein, (means a group).

In the above general formula (2) or (3), it is basically desirable that X be a hydrogen atom, but in order to increase the solubility in water, You can. In addition,
In general formula (2) or (3), X is basically an atom or molecule with an oxidation number of +1, but substantially X may be a metal with an oxidation number of +2. In this case,
) means a group from which X is removed. ). The alkylene group is a linear or branched divalent aliphatic hydrocarbon group having 1 to 5 carbon atoms.

Further, in the diamine derivative represented by the general formula RI R2-N-R5-N-R3R4, R5 is a phenylene group,
An alkylene group having 1 to 10 carbon atoms or an ether group or polyether group having 1 to 5 oxygen atoms is used, but if a highly hydrophilic one is required, the general formula: % formula % (5 ) (In the formula, B means an alkylene group having 1 to 5 carbon atoms, and n is an integer from 1 to 5.) A linear divalent ether group or polyether group represented by is desirable.

On the other hand, if organic substances such as alcohols and carboxylic acids coexist in the solution and a certain degree of hydrophobicity is required, a phenylene group or a carbon atom number of 1 to 1 is used.
A linear or branched divalent aliphatic hydrocarbon group up to O is desirable.

These diamine derivatives include, for example, phenylenediaminetetraacetic acid, phenylenediaminetetraacetic acid; sodium salt, ethylenediaminetetraacetic acid, ethylenediaminetetraacetic acid; sodium salt, ethylenedisiminetetraacetic acid; potassium salt, ethylenediaminetetraacetic acid; ammonium salt, ethylenediamine Tetraacetic acid; magnesium salt, ethylene glycol-bis-(β-aminoethyl ether')-N,N'
-Tetraacetic acid, ethylene glycol-bis-(β-aminoethyl ether)-N,N'-tetraacetic acid; sodium salt, ethylene glycol-bis-(β-aminoethyl ether)-N,N'-tetraacetic acid; potassium salt, phenylenediaminetetraethanol, ethylenediaminetetraethanol, etc.; however, if the purpose is to react selectively with calcium ions, ethylene brecol-bis-(β-aminoethyl ether) can be used.
-N.

N”-tetraacetic acid; the sodium salt is particularly preferred.

Incidentally, the gypsum dissolving agent of the present invention has a major feature in that it generates the diamine derivative, calcium ion, and calcium salt, but this reaction is greatly influenced by the pH value of the solution. That is, in an acidic range with a pH value of 6 or less, this reaction hardly occurs, and in an alkaline range with a pH value of 8 or more, calcium ions and hydroxide ions in the solution associate to produce calcium hydroxide. As a result, the reaction is inhibited, which is not preferable. Therefore, the solution has a pH value in the neutral range of 6 to 8 (preferably 7 to 8).
). In this case, in order to bring the solution into a neutral range, an appropriate buffer may be dissolved therein.

Buffers used in the gypsum dissolving agent according to the present invention include:
Preference is given to mixtures with acids, bases or their salts. These buffers include potassium hydrogen phthalate-sodium hydroxide, boric acid-hydrium chloride-sodium hydroxide, disodium phosphate-sodium hydroxide, veronal sodium-hydrochloric acid, 2.4.6-collidine- Hydrochloric acid, Tris-
(Hydroxymethyl)-aminomethane-hydrochloric acid may be mentioned. In the gypsum dissolving agent according to the present invention, considering that it does not have an adverse effect on the diamine derivative represented by the general formula (1) and the alkali hydrogen carbonate, which are the main components, the kW iE agent is, for example, dihydrogen phosphate. Mixtures of weak acids, weak bases, or salts thereof such as potassium-disodium hydrogen phosphate, disodium hydrogen phosphate-citric acid, acetic acid-sodium acetate are preferred. It is not necessarily necessary to use two or more types of these slowing induction agents, and even one type of chemical species can be used as long as it exhibits a buffering effect. Examples of these include disodium citrate, ammonium citrate, ammonium acetate, sodium tetraborate, and sodium carbonate.

The gypsum dissolving agent according to the present invention is different from the conventional reaction in which a diamine derivative and a calcium ion coordinate to form a calcium chyronate. to melt. The reaction in this case is essentially 20
10Ca +Z-H2→ Z-C
a+2H(6) (wherein Z means a group obtained by removing two terminal active hydrogen atoms from the organic compound represented by general formula (1)). Therefore, as the reaction represented by formula (6) progresses, the hydrogen ion concentration in the solution increases. This undesirably reduces the pH value of the solution. Therefore, researchers discovered that in order to remove the 0 hydrogen ions produced by the reaction expressed by equation (6) without significantly changing the pH value, it is sufficient to use alkali hydrogen carbonate. . The alkali hydrogen carbonate used in the solution may directly dissolve the salt thereof. Examples of the hydrogen carbonate include sodium hydrogen carbonate, potassium hydrogen carbonate, rubidium hydrogen carbonate, cesium hydrogen carbonate, and ammonium hydrogen carbonate. If these hydrogen carbonates are dissolved in the solution, hydrogen ions can be efficiently removed through the reaction represented by H+ HC03 → H20+ C02 (7), so the pH value of the solution will decrease. It is possible to prevent this. Note that a solution of alkali hydrogen carbonate alone will inevitably have a pH
Since the value is 7 to 8, it is desirable to adjust the OpH value of the solution using a buffer to the same level, that is, to adjust the pH value to 7 to 8.

The gypsum dissolving agent according to the present invention further includes sodium hexametaphosphate, potassium hexametaphosphate, sodium 1.3.6-naphthalenesulfonate, 1-amino-2-naphthol, within a range that does not significantly impair the physical properties obtained. Various dispersants or surfactants such as sodium sulfonate, sodium alkylbenzene sulfonate, magnesium alkylbenzene sulfonate, sodium α-olefin sulfonate, and sodium alkyl ester sulfonate can be added as necessary.

By adding these dispersants and surfactants, the produced calcium salt is dispersed, so that the gypsum dissolving ability can be maintained.

Effects of the Invention The gypsum dissolving agent of the present invention was developed to efficiently dissolve gypsum, which is poorly soluble in water, acids, and alkalis, without corroding metals. That is, the gypsum dissolving agent of the present invention utilizes a reaction that directly produces calcium salts, unlike the conventional metal chelonate producing reaction, and therefore has high efficiency in dissolving gypsum.Furthermore, the gypsum dissolving agent solution Since the pH value is in the neutral range of 6 to 8, it has the advantage of not corroding metals such as iron, nickel, and chromium.

This gypsum dissolving agent, which has the above-mentioned characteristics, can be used to dissolve gypsum that has adhered to the inner walls of combustion furnaces, reactors, rectification towers, pipelines, etc. that are installed in factories that use fossil fuels such as oil and coal. extremely useful for removing. It is also effective for removing gypsum adhering to the inner walls of combustion furnaces and exhaust ports in thermal power plants, and for removing gypsum adhering to the inner walls of automobile engine cylinders and exhaust pipes.

The gypsum dissolving agent of the present invention was developed for the above-mentioned purpose, and its large dissolving ability can be used to dissolve gypsum adhered to various tools used in the fields of arts and crafts and dentistry. It can also be applied to remove equipment without damaging it.

The present invention will be explained in detail with reference to Examples and Comparative Examples shown below.

Example 1 Ethylene glycol bis(β) was added to a 500cc beaker.
-Aminoethyl ether)-N,N'-Add 67.3g (0.2mol) of disodium tetraacetate, and add 300g of water.
cc and was gradually heated to dissolve. At this point, the solution OpH value was approximately 6.9. Thereafter, the solution was cooled to room temperature, and 40 g of potassium hydrogen carbonate was dissolved therein. The pH value of the solution at this time was about 7.5. Add 40g of gypsum to the resulting solution and add 1 lb. of plaster while stirring.
It was left for 20 minutes. Thereafter, the residual liquid was filtered, and the sulfate ions contained in the filtrate were precipitated as barium sulfate and measured by gravimetric method. The amount of dissolved gypsum is (8)
It was calculated according to the formula.

Weight of barium sulfate (gl Dissolved amount of gypsum (g) = x172.
17 (8)233.36 As a result of performing the above operation 5 times and measuring the amount of gypsum dissolved,
Table 1 was obtained. The theoretical amount in the table is ethyl glycol-bis-(β-aminoethyl ether)- in the solution.
This is the amount of gypsum melted when disodium N,N'-tetraacetate and calcium ions produce 100% calcium salt at a binding ratio of 1:1. Furthermore, the melting efficiency was calculated using equation (9).

Actual value of gypsum dissolution amount (g) Dissolution efficiency = (9) Ideal amount (a Table-1 As is clear from the above table, the dissolution efficiency of this melt is 100
%, it can be confirmed that the melting ability is large.

Example 2 Put 76 g (0.2 mo A') of disodium ethylenediaminetetraacetate into a 500 cc beaker and add 3QQ of water.
cc was added and dissolved. The pH value of the solution at this time was about 10.5. In the same manner, three more solutions were prepared from the same solution, and hydrochloric acid was added to these four solutions to adjust the pH values to approximately 9.5, 8, 5, 7, 5, and 6.5, respectively. Furthermore, acetic acid-sodium acetate was added to each solution to reach a predetermined pH value. Add 4 potassium hydrogen carbonate to the resulting solution.
0 g was melted, 40 g of gypsum lumps were added to each, and the mixture was left to stand for 120 minutes while stirring. At this time, the amount of melted gypsum was measured in the same manner as in Example 1, and the results were shown in Table 2.
I got it.

Table 2 * Theoretical amount is the amount of gypsum dissolved when 100% calcium salt is produced at a binding ratio of 1:1 between tetrasodium ethylenediaminetetraacetic acid and calcium ions in the solution according to Example 1.

**Dissolution efficiency was calculated according to equation (9) according to 1.

As is clear from the table above, it can be seen that the gypsum dissolving ability of this solution varies greatly depending on the pH value. Ultimately, the ability to dissolve gypsum is greatest when the pH value is around 7.5.

Comparative Example ■ Melted solution used in Example 1 ■ Sodium hexametaphosphate 0.2 mol/l solution ■ Sodium hexametaphosphate Q, 2 mol/IV solution adjusted to pH 7.5 with acetic acid-sodium acetate ■ Ethylenediamine 0.2mo! ! //! ■~ of melting night
Table 3 was obtained as a result of measuring the dissolution amount of gypsum, iron, nickel, and chromium for each of 300 m6 of (2). The amount of gypsum dissolved was determined according to Example 1. Further, to determine the amount of dissolved iron, nickel, and chromium, 0.1 g of these powders were mixed into each solution and left to stand for 24 hours while stirring. Thereafter, the solution was filtered, and the metal contained in the filtrate was measured by atomic absorption spectrometry to determine the amount of dissolved metal.

Table 3 *Real 11 Gffl is 6 beaks η&? when 100% calcium salt is produced at a binding ratio of 1:3 between sodium hexametaphosphate and calcium ions in the solution. It is.

**The theoretical amount is the amount that is sufficient to produce calcium chyronate having a wax-like structure at a bonding ratio of ethylenediamine and calcium ions in the solution of 1:1.

As is clear from the above table, it can be seen that the phosphate solution dissolves metals such as iron, nickel, and chromium to an order of magnitude better than the gypsum solution of the present invention. Therefore, it can be concluded that phosphate-based solutions are corrosive to metals such as iron, nickel, and chromium. Furthermore, when using a reaction that uses ethylenediamine to produce calcium kylonate, it is found that the efficiency is about 1/4 compared to the gypsum dissolving agent of the present invention.

Claims (4)

[Claims] (1) (a) General formula: ▲ Numerical formulas, chemical formulas, tables, etc. R5 means a phenylene group, an alkylene group having 1 to 10 carbon atoms, or an ether group or polyether group having 1 to 5 oxygen atoms.) A diamine derivative represented by ( b) An improved gypsum dissolving agent comprising a solution characterized by containing two components of alkali hydrogen carbonate, the solution having a pH value of 6 to 8. (2) An improved gypsum dissolving agent characterized by adding a buffer to the gypsum dissolving agent according to claim (1). (3) An improved gypsum dissolving agent according to claim (1) or (2), characterized in that the pH value of the gypsum dissolving agent is 7 to 8. (4) An improved gypsum dissolving agent according to claim (2), characterized in that the buffer added to the gypsum dissolving agent is a weak acid, a weak base, or a salt thereof.