JPS595038B2 - How to prevent calcium phosphate scale - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing calcium phosphate scale.

To date, calcium carbonate scale has been regarded as a problem in various industrial water systems, and various effective agents have been developed and used.

Among the drugs for this purpose, polymerized phosphoric acids have been frequently used, but their use also generates calcium phosphate scale, which has limited the scope of their use.

In particular, as a recent trend, in order to conserve industrial water, it is desirable to use it in a circular manner rather than in a one-time system.As a result, the components in the water are concentrated, the residence time becomes longer, and polymerized phosphoric acids are When used, it hydrolyzes to produce orthophosphoric acid, which inevitably leads to the formation of calcium phosphate scale.

However, to the best of the knowledge of the inventors of the present invention, no drug has been reported that exhibits significant effects on calcium phosphate scale.

As countermeasures, it has been necessary to adjust the pH in systems where there is a risk of calcium phosphate scale generation, or to limit the use of polymerized phosphoric acids themselves, which are the source of scale generation, as mentioned above.

The inventors of this invention previously discovered that using polymerized phosphoric acids and acrylic acid-based polymers in specific proportions in industrial water systems with high salt concentrations, especially yarns where calcium carbonate-based scales occur, can reduce scale formation. I found a way to prevent Kokichi (
This invention was discovered as a result of further development and research.

Incidentally, we investigated whether various agents effective against calcium carbonate scale, such as phosphonic acid and polyacrylic acid, could be used in the yarn of this invention, but we found that they were hardly effective when added in normal amounts. It wasn't done.

The present invention is directed to a specific polymer among acrylic acid polymers, namely, an acrylic acid-methacrylic acid copolymer having a molecular weight of about 500 to 15,000 and a copolymerization ratio of about 1:4 to 4.
:1 compound uses polymerized phosphoric acids as a scale inhibitor or anticorrosion agent and contains about 5 pp of orthophosphoric acid radicals! It has been found that it is highly effective in preventing the occurrence of calcium phosphate scale in industrial water systems containing 11 or more scales.

According to this invention, it is possible to use threads in which it has been virtually impossible to use polymerized phosphoric acids, which are inexpensive and have an excellent effect on calcium carbonate scale prevention, that is, industrial water circulation concentration systems, and even in so-called closed systems. This shows the smoothing effect.

The industrial water to which this invention applies refers to boilers, heat exchangers, cooling system equipment, etc., in which polymerized phosphoric acids (usually meaning salts) are added to prevent calcium carbonate scale from occurring or to prevent corrosion of equipment. should be understood to mean industrial water.

When such industrial water is used in a closed system where it is partially blown rather than temporarily, or in a so-called closed system where it is circulated for a long period of time, the polymerized phosphoric acids contained therein are hydrolyzed. If a calcium source (including one with properties similar to tazoshi calcium) is present, calcium phosphate scale will precipitate.

According to the research results of these inventors, the orthophosphoric acid group produced by hydrolysis of polymerized phosphoric acids has a pH of about 5ppH1.
It was confirmed that when the above conditions were exceeded, the precipitation of the calcium phosphate scale became significant.

Of course, when orthophosphoric acid is produced and reacts with a calcium source, orthophosphoric acid is consumed by it, so the concentration of orthophosphoric acid temporarily decreases, but in this invention, 11 orthophosphoric acid -IJ was defined as being used for yarn 11 in which about 5 or more phosphoric acid radicals are present.In short, when analyzing the target industrial water and measuring orthophosphoric acid radicals, if the concentration is about 51111111 or more, calcium phosphate scale This was done based on the fact that the formation of

The acrylic acid-methacrylic acid copolymer used in this invention has a copolymerization ratio of about 1:4 to 4:1.

When the copolymerization ratio is outside this range, the so-called scale inhibition rate (defined as described below) decreases.

From a practical point of view, those within the above range are preferable, but
More preferably, the ratio is in the range of 2:1 to 1:2, especially about 1
:1 is most preferred.

Note that this copolymerization ratio is indicated by the molar ratio of polymerized monomers.

Further, the molecular weight of this acrylic acid/methacrylic acid copolymer is preferably about 500 to 15,000, and particularly preferably 3,000 to 7,000.

For example, even if the copolymerization ratio is 1:2, the scale suppression rate will be low if the molecular weight is large, for example, 50,000.

Moreover, even if the molecular weight is smaller than 500, the scale inhibition rate is low.

The amount of the copolymer added depends on the properties of the industrial water to which it is applied, such as the amount of polymerized phosphoric acids added, the content of calcium, etc., pH, flow rate, etc., but usually the agent of this invention is used. In this case, a concentration of 2 to 2 ops is sufficient.

However, under severe conditions, the amount added may be increased to a maximum of about 200 mg, but this is extremely rare.

The addition method may be carried out by a conventional method.

In addition, the acrylic acid-methacrylic acid copolymer in this invention includes cases where both acrylic acid and methacrylic acid are free acids, and cases where part or all of them are in the form of salts such as sodium, potassium, lithium, ammonium, etc. It will be done.

For example, an acrylic acid/methacrylic acid copolymer (free acid type) with a molecular weight of 5,000 and a copolymerization ratio of 1:1 is a powder, and it can be used as it is, but it is usually used with an alkali hydroxide (such as caustic soda). It can be dissolved in an aqueous solution of carbonate (sodium carbonate, etc.) or ammonia and added as a solution.

Also, a suitable organic amine may be used.

That is, the drug of this invention can be added as a powder, but it can also be used as a salt compound or in the form of a salt in an aqueous solution.

In carrying out the method of the present invention, if the pH of the industrial water system to which it is applied is 9 or higher, it is preferably adjusted to 9 or lower.

Hereinafter, the present invention will be explained in detail with reference to Examples and Examples.

Experimental Example A calcium phosphate scale prevention performance test was conducted using Osaka city water and Osaka city water with a concentration of 3 times.

Table 1 shows the quality of the water used. The test method is as follows.

1. To the above two types of water, add 20 pIn of sodium hexametaphosphate as PO43- and 20 pIn of primary sodium phosphate as PO:"-, add a predetermined amount of the drug, and use a mantle heater and thermostat. The mixture was stirred with a stirrer at 1100 rpm for 20 hours while maintaining the temperature at 50°C.

Thereafter, the calcium ion and total phosphoric acid concentrations in the test solution are measured, and the amount of scale precipitation per 1 ta of solution (
That is, m9/L) was calculated.

Thus, the results shown in Table 2 were obtained.

219- Select data for acrylic acid-methacrylic acid copolymers and homopolymers with molecular weights of 4,800 to 6,200 from the results in Table 2, and show the relationship between copolymer copolymerization ratio (a) and scale suppression rate (@). A graph was created and shown in Figure 1.

Curve 1 in FIG. 1 shows the case where 44% of the copolymer was added to Osaka city water, and curve 2 shows the case when 6 ppHl of the copolymer was added to Osaka city water with a concentration of 3.

Note that the copolymerization ratio and scale suppression rate of the copolymer are shown by the following formula.

From the above results, the copolymer of the present invention can be added in a small amount,
It is clear that when polymerized phosphoric acids are used as scale inhibitors or anticorrosive agents, calcium phosphate scale is prevented, and copolymers with a copolymerization ratio of 1:1 are particularly effective.

Comparative Examples Tests similar to those in Examples were conducted by varying the copolymerization ratio and molecular weight of the acrylic acid meccrylic acid copolymer.

The results are shown in Table 3.

As described above, it can be seen that copolymers having molecular weights outside the molecular weight range of the present invention, such as 300 and 20,000, have insufficient scale suppressing effects.

It is also confirmed that the effect is reduced when the copolymerization ratio is 1:9 or 9:1.

Example In the cooling system of a certain factory, lignin and polymerized phosphoric acid were used as anticorrosive agents, and sulfuric acid was used to maintain the pH at 7.0 in order to suppress the scale of the water.

This treatment reduced scale development compared to when pH was not adjusted.

However, calcium phosphate scale gradually forms even at this pH, and the amount of scale deposited per cd per day is 0.50 m11, that is, m, c,
d, (mliperc# day) was recorded at 0.50.

In addition, the corrosivity of water increases due to the increase in sulfate ions, and in the same hot water water pipe, the conventional corrosion loss is 1.2 Ni per 1 dm2, that is, 1.2 as m, d, d, perdm2・day). were kept with mild steel, m, d, d,
It was recorded as 18.5.

Therefore, the addition of sulfuric acid was stopped, and acrylic acid methacrylic acid copolymer (copolymerization ratio 1:1, molecular weight 5000) was added to
After one month of operation with continuous addition, periodic inspections were carried out and the same water pipe section was examined and found that the degree of corrosion had decreased to m, d, d, 1.5, and the amount of scale adhesion was also m, c, d.

was 0.05 or less, and a remarkable effect was recognized.

In addition, lignin and polymerized phosphoric acid were used at 20 ppl each, and the orthophosphoric acid radical concentration during the test period was 7 to 15 ppl.
It was pIII.

In addition, a branched test pipe was always attached to the hot water pipe, and the above test records were made.

The test pipes are commercially available S, G, and P tubes (inner diameter 3/
8 inches, pipe length 1.50vts).

Table 3 shows the quality of the cooling water when using the acrylic acid methacrylic acid copolymer.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the scale inhibition rate of acrylic acid methacrylic acid copolymers having various copolymerization ratios. 1...4 ppl of copolymer in Osaka city water with concentration level 1
Graph when Il is added, 2...Concentration level 3
Graph when copolymer 6pI)In is added to Osaka city water.

Claims (1)

[Claims] 1 Using polymerized phosphoric acids as a scale inhibitor or anticorrosion agent, an acrylic acid-methacrylic acid copolymer (copolymerization ratio of about 1:4 to 4 :1, molecular weight about 500-15.0
00) to prevent calcium phosphate scale.