JPH0376299B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing calcium gluconate. Calcium gluconate is traditionally used in miso, tofu,
It is used as a calcium fortifier in konnyaku, sweets, etc. Methods for oxidizing glucose to gluconic acid or gluconate include electrolytic oxidation, fermentation, and catalytic oxidation, but the catalytic oxidation method has not been industrialized because the catalyst used is expensive, and gluconic acid Only sodium is produced by fermentation. In addition, due to problems in maintaining enzyme activity during fermentation, calcium gluconate is produced by first producing sodium gluconate, which is then treated with a cation exchange resin, neutralized with calcium carbonate, concentrated, and crystallized. It is manufactured by performing the following steps and is therefore expensive. Various methods for producing sodium gluconate by catalytic oxidation of glucose have been reported.
Platinum catalysts and palladium catalysts are considered to be good because of their high oxidation activity. However, there are few reports on the production of calcium gluconate using this method, and this is because the catalyst is severely poisoned by the calcium salt as a neutralizing agent and the heavy metal salts contained therein during oxidation, resulting in severe catalyst deterioration. This seems to be due to the lack of a suitable catalyst. The present inventors conducted various studies on catalysts suitable for producing calcium gluconate by catalytic oxidation, and as a result, they arrived at the present invention. That is, the gist of the present invention is to use metal borohydride reduced palladium in the production of calcium gluconate by catalytic oxidation of glucose. The metal borohydride-reduced palladium catalyst used in the method of the present invention is partially mentioned in JP-A-53-40713, but the method for producing the catalyst is not specified, and furthermore, it does not have glucose oxidation activity. is listed. The present inventors investigated a method for preparing the above-mentioned palladium catalyst, and found that a palladium salt such as palladium chloride or palladium nitrate was dissolved in a small amount of concentrated hydrochloric acid, activated carbon and water were added, and the pH of the mixture was adjusted to 2 with an alkali. By adjusting the above, adding a metal borohydride aqueous solution at room temperature while stirring, and washing with water,
We succeeded in obtaining a catalyst with high glucose oxidation activity. In the above preparation method, reduction of palladium salt and adsorption onto activated carbon are instantaneously performed when metal borohydride is added, but if the pH at the time of reduction is too low, the reduction will not be sufficient and no activity will be obtained. It is preferable to adjust the pH to 2 or more.
Further, since a portion of the metal borohydride is decomposed when it comes into contact with activated carbon, it is necessary to add the metal borohydride in an amount 2 to 5 times the amount required for reduction of the palladium salt. To explain the method of the present invention in which glucose is catalytically oxidized using the catalyst prepared as described above, the palladium catalyst described above is added to an aqueous glucose solution with a concentration of 5 to 20%, and the solution is maintained at 40 to 60°C while being oxygenated. Alternatively, air is blown into the reactor to cause a reaction, and the gluconic acid produced is neutralized with calcium hydroxide or calcium carbonate to adjust the pH to 8 to 10. Calcium gluconate is obtained by separating the catalyst from the reaction-completed liquid, concentrating the liquid, and crystallizing it. In the method of the present invention, the higher the pH during oxidation, the faster the oxidation rate, but if it is too high, part of the glucose will isomerize to fructose and the yield of calcium gluconate will decrease, so the reaction is carried out at a pH of 8 to 10. is preferable. Calcium hydroxide is a good neutralizing agent, and when calcium carbonate is used, it is preferably mixed with calcium hydroxide. It is preferable to use oxygen as the gas during the reaction because the oxidation rate is the fastest, but since it is expensive, it is economical to use air. The catalyst used in the method of the present invention has many advantages in that it can be prepared easily and inexpensively, has high catalytic activity, and can withstand repeated use. Example 1 Palladium chloride 64 mg (38 mg as palladium)
was dissolved in 1 ml of concentrated hydrochloric acid, 30 ml of water and 3.8 g of activated carbon (manufactured by Takeda Pharmaceutical Co., Ltd., trade name: Shirasagi) were added, and the pH was adjusted to 5 with a 10% aqueous sodium hydroxide solution. While stirring this mixture at room temperature, a solution of 67 mg of sodium borohydride in 2 ml of water was added over about 10 seconds, followed by filtering and washing with water to prepare a 1% palladium-carbon catalyst. Next, put a thermometer and pH in a 1-volume three-necked flask.
300 g of an aqueous glucose solution with a concentration of 8% (w/w) and the above catalyst were placed in a device equipped with electrodes, and air was blown from the bottom at a rate of 3 per minute while maintaining the temperature at 50°C. At the same time, a suspension of calcium hydroxide in water was added to maintain the pH at 9 to 9.5.
The theoretical amount of calcium hydroxide was consumed in 3 hours.
The catalyst was separated from the reaction-completed liquid, and the catalyst was washed with water and the liquid was combined to obtain 310 g of a colorless and transparent liquid.
When a portion of this liquid was sampled and the glucose content was measured using high performance liquid chromatography, it was found to be 1.4%.
(relative to solid content). The above liquid was concentrated to 52 g, left to stand overnight, and the precipitated crystals were separated and dried at 70° C. under reduced pressure to obtain 22.6 g of first crystals of calcium gluconate. The separated liquid of the crystals was concentrated to 12 g and crystallized in the same manner to obtain 5.3 g of second crystals. The combined yield of the first and second crystals is
The yield was 93.3% (versus the theoretical yield). When the purity of the obtained crystals was measured using the sodium ethylenediaminetetraacetate method described in the Japanese Pharmacopoeia Law, the first crystal was
It was 99.8%, and the second crystal was 99.2%. Example 2 41.6 mg of palladium nitrate was dissolved in 1 mg of concentrated hydrochloric acid, 40 ml of water and 7.6 g of activated carbon were added, and the pH was adjusted to 9 with a 10% aqueous sodium hydroxide solution. After stirring this solution at room temperature and adding a solution of 48 mg of potassium borohydride in 2 ml of water for about 10 seconds,
A 0.5% palladium-carbon catalyst was obtained by filtering and washing with water. When an oxidation reaction was carried out in the same manner as in Example 1 using the above palladium-carbon catalyst, 4.5
The theoretical amount of calcium hydroxide was consumed in hours. 23.0g as the first crystal, and 23.0g as the second crystal.
5.2 g was obtained, for a total yield of 94.3% (versus theory). Example 3 The catalyst used in Example 1 was recovered and an oxidation reaction was carried out by repeating the same procedure as in the same example. As a result, the theoretical amount of calcium hydroxide was consumed in 3.5 hours. The catalyst was used repeatedly in the same manner, and the results were as shown in Table 1.

[Table] Comparative Example 1 An oxidation reaction was carried out in the same manner as in Example 1 using 1.5 g of a commercially available 5% palladium catalyst (76 mg as palladium). As a result, 50% of the prescribed amount
of calcium hydroxide took 22 hours to consume. Comparative Example 2 A catalyst was prepared with reference to the description in JP-A-53-40713. That is, 1.65 g of palladium chloride (1 g as palladium) was dissolved in an aqueous solution containing 3 ml of concentrated hydrochloric acid to make a total volume of 250 ml. Activated carbon (Shirasagi) 99
g suspended in 1 water, add sodium carbonate
15 g was added to the solution, stirred at room temperature for 1 hour, and then brought to 40° C. The palladium aqueous solution was added and adsorbed while stirring for 4 hours. Next, 3ml of 38% formalin solution
After reducing by adding and keeping at 85±5℃ for 11 hours,
A 1% formalin reducing agent palladium-carbon catalyst was prepared by filtering, washing with water, and drying. An oxidation reaction was carried out in the same manner as in Example 1 using 3.8 g of the above palladium catalyst.
It took 12 hours to consume the specified amount of calcium hydroxide. Furthermore, when the catalyst used in this oxidation reaction was recovered and used repeatedly, it took 16 hours to consume the predetermined amount of calcium hydroxide the second time.

Claims (1)

[Claims] 1. In producing calcium gluconate by oxidizing glucose with an oxygen-containing gas in the presence of a noble metal catalyst and neutralizing the produced gluconic acid with calcium hydroxide, calcium carbonate, or a mixture thereof. A method for producing calcium gluconate, which comprises using, as a noble metal catalyst, a palladium carbon catalyst prepared by adding sodium borohydride or potassium borohydride to a mixture of a palladium salt aqueous solution and activated carbon. 2. The method according to claim 1, wherein the amount of palladium supported on the activated carbon is 0.1 to 5% (by weight) as metal palladium.