JPS60226502A - Preparation of dicarboxyl polysaccharide - Google Patents

Abstract

PURPOSE:To prepare a polysaccharide having improved performance in preventing scale deposition in high-temperature systems, by reacting a slurry of a polysaccharide having 6-membered monosaccharide rings with a hydrochlorite under specific conditions. CONSTITUTION:A >=10wt% slurry is prepared from a polysaccharide having 6- membered monosaccharide rings, e.g. starch or cellulose, or a derivative thereof, and a hypochlorite, e.g. sodium hypochlorite, having >=6wt% available chlorine concentration corresponding to 2-4 equivalents available chlorine based on one equivalent glucose residue in the above-mentioned polysaccharide is added continuously to the above-mentioned slurry for 15min-3hr. The pH is controlled at 8-9 in the reaction, and the reaction temperature is controlled at 25-40 deg.C to give the aimed polysaccharide. The above-mentioned polysaccharide preferably has 30,000-100,000 average molecular weight and contains 40-80wt% dicarboxyl units expressed by the formula [R is H, (CH2)n-COOM (M is H, alkali metal ion or NH4<+>; n is 1-3) or COOM].

Description

Detailed Description of the Invention "Industrial Application Field" The present invention relates to a method for producing dicarboxyl polysaccharide, and more specifically, it has a molecular weight within a specific range and is used to prevent scale deposition in aqueous systems, particularly in high-temperature systems. The present invention relates to a method for producing a dicarboxyl polysaccharide having excellent anti-deposition properties.

"Prior Art and Problems" Conventionally, it is well known that glucose groups in starch, etc., are oxidized with an oxidizing agent such as hypochlorite or periodate to dicarboxylate them. In this well-known method,
Generally, under alkaline conditions at any starch and oxidizing agent concentration,
Oxidized at room temperature, heating or cooling. However, the dicarboxylated products obtained under such general oxidation conditions over a wide range of conditions have large variations in yield and quality, especially in molecular weight, which is extremely wide and has large variations. When used as an agent, especially when used in a high-temperature water system, fully satisfactory results cannot be obtained.

Furthermore, for example, Japanese Patent Publication No. 49-1281 discloses that dicarboxylated starch obtained by oxidatively cleaving the glucose group of starch is useful as a detergent bilge. This publication discloses oxidative cleavage of starch with an alkali hypochlorite. However, when the oxidatively cleaved dicarboxyl starch obtained by the method described in the publication is used as a scale inhibitor in a high temperature system, it exhibits sufficiently satisfactory performance similar to that obtained by the conventional well-known method. As a result of studies conducted by the present inventors, it has been found that this is not possible.

That is, dicarboxyl starch obtained by conventional general oxidation conditions exhibits uniformly good effects in relatively low-temperature aqueous systems, such as aqueous systems at temperatures below 50°C, but dicarboxyl starch obtained under conventional oxidation conditions exhibits uniformly good effects in aqueous systems at relatively low temperatures, such as aqueous systems at temperatures below 50°C; A sufficient effect cannot be obtained under conditions of around 100°C, such as in desalination equipment.

"Means for Solving the Problem" Therefore, in view of the above circumstances, the inventors of the present invention
As a result of intensive studies on the production method of dicarboxyl polysaccharide that exhibits effective scale prevention properties even in high temperature systems around o'C, we found that dicarboxyl starch with a specific molecular weight range produced under specific reaction conditions, It has been found that it exhibits extremely excellent performance, and the present invention has been made based on this.

That is, the present invention provides (a) a slurry of a polysaccharide having a six-membered monosaccharide ring or a derivative thereof at a concentration of at least 10% by weight, and (O) a slurry containing, for each equivalent of glucose residue of the polysaccharide, Hypochlorite having an available chlorine concentration of at least 6% by weight, which corresponds to 2 to 4 equivalents of available chlorine, is added continuously over a period of 15 minutes to 6 hours, and (c) the pH during the reaction is adjusted. 8-9, reaction temperature 25-4
The present invention relates to a method for producing dicarboxyl polysaccharide, which is characterized in that the reaction is controlled at 0°C.

The dicarboxyl polysaccharide obtained by the method of the present invention as described above has an average molecular weight of 30,000-1
00,000 (measured by gel p-filtration method),
Approximately 4096 dicarboxyl units represented by the following general formula
Contains ~80%.

[In the formula, R is H or (CH2)n-C00M, C00
M represents H, an alkali metal ion or an ammonium ion, and n is 1 to 3. ] The molecular weight within the above range obtained by the method of the present invention is particularly effective for preventing scale in high temperature systems, and the dicarboxyl polysaccharide having a molecular weight within such a specific range can be obtained by the method of the present invention, that is, It can be obtained by reacting while simultaneously satisfying the conditions (a) to e (e) above.

If any of these conditions is not satisfied, the desired result cannot be obtained. Further, as shown in the Examples and Test Examples described later, only those having a molecular weight within the above-mentioned specific range exhibit extremely excellent performance.

The polysaccharide having a six-membered monosaccharide ring in the present invention is a polysaccharide having adjacent hydroxyl groups, and includes, for example, starch such as corn, potato, rice, wheat, waste, tapioca, dextrin, cellulose, wood flour, Examples include polyuronic acids such as alginic acid, etc.
In addition, partial hydrolysis within the range where the molecular weight does not change significantly,
Chemically modified compounds such as esters, ethers, or carboxylated compounds can also be used. Among these, starch, cellulose, or modified products thereof are preferably used from the viewpoint of availability, cost, reactivity, etc., and starch is particularly preferred.

Further, the hypochlorite used in the present invention is an alkali metal salt of hypochlorite, and sodium hypochlorite is usually used.

The present invention will be described in detail below using starch as an example.

As for the reaction conditions in the method of the present invention, the amount of water in the reaction solution is related to the quality, particularly the molecular weight, of the dicarboxyl starch produced, and when the amount of water is large, the molecular weight tends to increase. Therefore, it is necessary that the starch slurry concentration at the time of reaction preparation be at least 10% by weight or more, preferably 30% by weight or more. Although there is no particular restriction on the upper limit of the slurry concentration, it is usually difficult to form a water-dispersed slurry of starch with a concentration of 50% by weight or more, so the slurry concentration is generally 10-50% by weight. The hypochlorite added to the starch slurry has an effective chlorine concentration of 6% by weight or more, preferably 10% by weight or more. If the available chlorine concentration is low, this also results in an increase in the average molecular weight of the desired product, which is undesirable.

The amount of hypochlorite added to starch is also one of the important factors in obtaining the target product of the present invention.
Hypochlorite is equivalent to 1 equivalent of glucose residue in starch.
It is added in an amount corresponding to 2 to 4 equivalents of available chlorine, and usually 2 equivalents are added.

Next, the method of adding hypochlorite to starch slurry is 1.
Continuous addition is required over a period of 5 minutes to 3 hours.

If starch and hypochlorite are added simultaneously or if hypochlorite is added in less than 15 minutes, it is not only difficult to control the reaction temperature, but also dicarboxyl starch with the required molecular weight cannot be obtained. do not have.

Furthermore, if the addition time of hypochlorite is made longer than 6 hours, not only will the reaction time be unnecessarily extended, but dicarboxylic starch with the required molecular weight cannot be obtained.

In addition, the pH of the solution during the reaction can be adjusted to a specific range, that is, pH
Maintaining the molecular weight within the range of 8 to 9 is an important factor in obtaining the target product of the present invention, and it is not sufficient to simply carry out the reaction under alkaline conditions. In the present invention, it is particularly preferable to maintain the pH between 8.5 and 9.

Further, in the present invention, the reaction is usually accompanied by heat generation, and the reaction temperature is carried out at 25°C to 40°C, but it is particularly necessary to prevent the temperature from rising above 40°C.

If the temperature is higher than 40°C, the molecular weight of the carboxyl starch produced will be low; if the temperature is low, on the other hand, the reaction will be difficult to proceed, not only will the reaction take a long time, but the resulting dicarboxyl starch will have a low molecular weight. The molecular weight becomes high, which is not preferable.

In the present invention, when polysaccharides having other six-membered monosaccharide rings and their derivatives are oxidized, the same as above is applied.

"Examples" and "effects" The present invention will be explained below with reference to Examples and Test Examples.

Example 1 Dicarboxylic starch was produced using corn starch as the starch and sodium hypochlorite as the oxidizing agent, changing the starch slurry concentration and the available chlorine concentration of the sodium hypochlorite.

The equivalent ratio of starch to available chlorine in sodium hypochlorite was approximately 1:2, and the pH was adjusted with 20% sodium hydroxide while stirring.
The temperature was maintained at 8.5 and the reaction was carried out at 30° C. for 6 hours with external cooling.

The reaction was carried out by preparing the entire amount of starch slurry in advance and adding sodium hypochlorite continuously over an initial period of 1 hour.

Methanol was added in an amount three times the amount of the liquid after the reaction to precipitate the target product. After repeating reprecipitation with methanol and confirming that chlorine ions were no longer detected, it was separated and vacuum-dried at 50°C.

The yield was determined, the dicarboxyl unit content in the product was determined by conductometric titration, and the molecular weight was determined by gel filtration.

The results are shown in Table-1. As can be seen from Table 1, when the starch slurry concentration is 5% by weight or the available chlorine of sodium hypochlorite is 4% by weight, it is recognized that the molecular weight becomes higher than necessary.

Example 2 Corn starch was used as the starch, sodium hypochlorite was used as the oxidizing agent, and dicarboxylic starch was produced by changing the addition time of the sodium hypochlorite.

The equivalent ratio of starch to available chlorine in sodium hypochlorite was approximately 1:2, and the pH was adjusted with 20% sodium hydroxide while stirring.
was maintained at 8.5, and the reaction was carried out at 30° C. for 6 hours with external cooling.

For the reaction, the total amount of 30% by weight starch slurry was prepared in advance, and sodium hypochlorite containing 12.1% by weight of available chlorine was added for 5 minutes to 24 hours.
It was added continuously over a period of 0 minutes. Analysis, measurement, etc. of the obtained reaction solution were performed in the same manner as in Example 1.

The results are shown in Table-2. As can be seen from Table 2, when the addition time of sodium hypochlorite is set to 5 minutes or 240 minutes, it is recognized that the molecular weight becomes lower or higher than necessary.

Example 3 Dicarboxylic starch was produced using corn starch as the starch and sodium hypochlorite as the oxidizing agent, changing the reaction pH 1 and the addition equivalent ratio of corn starch and sodium hypochlorite. The total amount of 60% by weight starch slurry was prepared in advance, and sodium hypochlorite containing 12.1% by weight of available chlorine was added continuously over 60 minutes, so that the available chlorine was 0.1% by weight or less in the reaction solution. I reacted until.

The reaction pH was set at 7.5-9.5, and the reaction temperature was set at 20°C-5.
The reaction solution obtained under each condition was analyzed and measured in the same manner as in Example 1, with the temperature at 0° C. and the addition equivalent ratio of available chlorine in starch and sodium hypochlorite being 1=1 to 1:5.

The results are shown in Table-3. As seen from Table 3, reaction p
It is recognized that when the H1 reaction temperature and the addition equivalent ratio of starch and sodium hypochlorite are out of the range of the present invention, the molecular weight, yield, and carboxyl unit content decrease.

Test Example Products 111 to (26) obtained in Examples 1 to 6 were tested for scale adhesion prevention effect in a high-temperature system intended for an evaporative seawater desalination plant.

Ca ion 0,809/yu, MF ion 2 as test solution
．． Synthetic seawater equivalent to a 2-fold concentration with a pH of 8.2 and adjusted with a reagent to contain 0.2817 kl of HCOs ions was used.

V of the products (1) to (26) of Examples 1 to 3 were added to the test solution so that the concentration in the solution was 5 ppm.

The test liquid was added to a cylindrical glass cell with an internal volume of 2 liters, and a U-shaped tube made of SUS304 (surface area of the wetted part: 147 cm) was placed inside the cell.
m2) was attached, and steam at 160 to 170°C was passed inside the U-shaped tube. The seawater temperature is adjusted to 110℃ using a pressure regulating valve.
I kept it.

Further, the test liquid was continuously supplied into the cell at a rate of 600 d/hour, and was discharged through a pressure regulating valve.

A condenser was attached to the top of the cell to prevent seawater from evaporating and condensing during the test. After 24 hours, the U-shaped tube was removed from the glass cell, scale adhering to the surface of the U-shaped tube was scraped off, and the sample was dried at 110° C. for 3 hours and then weighed.

In addition, tests were also conducted in the case where no chemicals were added and in the case where a commercially available scale inhibitor was added at an active ingredient concentration of sppm.

The results are shown in Table 4. As can be seen from Table 4, it is recognized that the products of the present invention have extremely excellent scale prevention effects in high-temperature water systems.

As described above, the dicarboxyl polysaccharide having a specific range of molecular shapes obtained by the method of the present invention is
It has particularly excellent performance in preventing scale deposition in high-temperature systems, and can be used as a scale inhibitor for high-temperature systems, such as evaporative seawater desalination systems, industrial cooling water systems with heat exchangers with high heat loads, and high-temperature systems. It is convenient for application to boiler water systems, etc., and exhibits far superior performance compared to conventionally commonly used scale inhibitors.

Patent applicant Mitsubishi Gas Chemical Co., Ltd. Representative Kazuyoshi Nagano

Claims (1)

[Claims] (a) A polysaccharide having a six-membered monosaccharide ring or a derivative thereof is made into a slurry of at least 10% by weight, (cO), the glucose residue of the polysaccharide is
Hypochlorite with an effective chlorine concentration of at least 6% by weight, which corresponds to 2 to 4 equivalents of available chlorine, for 15 minutes to
It took 3 hours to add continuously, and the pH during the reaction was 8.
9. A method for producing dicarboxyl polysaccharide, which comprises controlling the reaction temperature to 25 to 40°C.