JPH0254816B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing monosaccharide oxides by oxidizing monosaccharides using a catalyst. More specifically, the present invention relates to a method for producing monosaccharide oxides in which aldose-type monosaccharides are oxidized with an oxygen-containing gas in an alkaline aqueous solution using a catalyst containing selenium and palladium. Monosaccharide oxides are used in many industrial fields, and the most representative example is gluconic acid or its salts. These include chelating agents, cleaning agents for metal and glass surfaces such as iron and aluminum, detergent builders, concrete admixtures,
Widely used in medicines, food additives, etc.
This will be explained below using gluconic acid as an example. Currently, gluconic acid is produced industrially mainly by fermentation. Although this method is easy and economical and has been carried out industrially, it has many drawbacks such as difficulty in separating bacterial cells, controlling by-products, and treating wastewater. Therefore, in order to improve the drawbacks of these fermentation methods, a method for producing gluconic acid was developed, such as the
As disclosed in the above publication, many catalytic oxidation methods have been proposed in which glucose and molecular oxygen are reacted in the presence of a noble metal catalyst such as platinum or palladium while maintaining alkalinity. However, for example, the above publication uses a 2% palladium on carbon catalyst, but it takes 5 to 50 minutes to complete the reaction.
It takes 8 hours and the yield is low at 80-85%. Furthermore, when glucose is oxidized at a reaction temperature of 50 to 55°C and a pH of 10, the product becomes deep red and has a very poor quality. The present inventors also proposed a ``method for oxidizing monosaccharides'' in Japanese Patent Publication No. 53-37333. According to this publication, the yield of sodium gluconate is stated to be over 97%, but as a result of subsequent research, this value was lower because the analysis of sodium gluconate was performed using TMS gas chromatography. It was found that soda and by-products such as saccharic acid and silanized products such as mannose overlapped on the peaks and were measured higher than the actual yield. As a result of quantifying sodium gluconate using an enzyme method reagent that selectively reacts with sodium gluconate, we found that
The yield of sodium gluconate obtained by the method disclosed in the above publication was 85 to 90%. Coupled with this, the reason why the method for producing gluconic acid using the catalytic oxidation method is not currently being adopted industrially is that compared to the method for producing gluconic acid using the fermentation method, (a) there is a large amount of unreacted glucose; This is because there are drawbacks such as a) poor purity of gluconic acid and low yield, and (iii) a requirement for the raw material glucose to be of high purity. That is, due to the oxidation reaction of glucose, glucose is isomerized to fructose in an alkaline aqueous solution, and as the conversion rate of glucose is increased, in addition to the gluconic acid produced, oxidized saccharic acid and side reactions occur. This concurrently caused a decrease in the purity and yield of gluconic acid.
Furthermore, impurities contained in the raw material glucose affect the catalyst used, and the reaction does not proceed at all or the reaction rate becomes extremely slow, making it difficult to obtain gluconic acid at a high rate.
Therefore, the production cost of gluconic acid by the conventional catalytic oxidation method is higher than that by the fermentation method, and cannot compete with the conventional method. Under these circumstances, it is generally desired to develop a production method with excellent production efficiency using a catalyst that does not have these drawbacks, that is, has excellent catalytic activity, selectivity, and durability in the production of monosaccharide oxides. was. The purpose of the present invention is to firstly provide a highly selective catalyst for the production of monosaccharide oxides using a catalytic oxidation method, that is, to quantitatively oxidize glucose, minimize unreacted glucose, and suppress side reactions. Second, to provide a durable catalyst that uses a small amount of catalyst; and third, to produce gluconic acid by the conventional fermentation method.
The object of the present invention is to provide a method for producing gluconic acid, which completes the reaction in a relatively short time of 1 to 4 hours, although it requires a long time of 12 hours or more. As described above, an object of the present invention is to provide an economical method for producing monosaccharide oxides. As a result of intensive research into a method for producing monosaccharide oxides for this purpose, the present inventors discovered that a palladium-selenium catalyst containing palladium and a selenium compound oxidizes monosaccharides with good selectivity, and completed the present invention. did. That is, the present invention is a method for producing monosaccharide oxides, which is characterized in that a catalyst containing palladium and selenium is used in producing monosaccharide oxides by oxidizing aldose-type monosaccharides with an oxygen-containing gas in an alkaline aqueous solution. It is the law. According to the method of the present invention, unreacted substances and side reaction products can be completely eliminated, and the reaction can be quantitatively promoted. Furthermore, the reaction can be completed in a short time with an even smaller amount of catalyst. Therefore, the method of the present invention has significantly superior reactivity compared to conventional fermentation methods, and is an industrially extremely superior method that solves various problems of conventional catalytic oxidation methods. One embodiment of the present invention will be described in more detail as an example of producing gluconic acid by oxidizing glucose. First, the catalyst used in the present invention is prepared as follows. Activated carbon is suspended in water, an aqueous solution of a selenium compound such as selenium oxide is added thereto, and the selenium compound is adsorbed onto the activated carbon while stirring. Subsequently, into this suspension/or after drying at 100 to 200°C, this activated carbon is suspended in water,
Palladium chloride is completely adsorbed onto the selenium compound-treated activated carbon by adding an aqueous palladium chloride solution. Subsequently, the palladium salt is reduced by formalin reduction, formic acid reduction, etc., and then washed with water to obtain a palladium-selenium carbon catalyst. This material is subjected to an oxidation reaction as it is or after being dried. Next, the above catalyst is added to an aqueous solution of glucose at a concentration of 20 to 40%, and oxygen or oxygen-containing gas is blown into the reaction solution while stirring and maintaining this solution at 30 to 60°C. dropwise aqueous alkaline solution. As the reaction accelerates, gluconic acid is produced, so add enough alkali to neutralize the acid to bring the pH of the solution to 8.
Adjust the amount of alkali to be added dropwise so that the amount is between 9 and 11, preferably between 9 and 10. Check the progress of the reaction from the amount of alkali consumed. The reaction proceeds rapidly and quantitatively, and after the reaction is completed, the catalyst is removed to obtain a colorless to pale yellow aqueous solution of alkali gluconic acid salt. There is no isomerization of glucose to fructose and no production of saccharic acid, and highly pure gluconate can be obtained. For many industrial applications, the catalyst can be used as it is separated from the reaction product, or after being concentrated or crystallized by conventional methods. Furthermore, it has the advantage that gluconic acid and glucono-δ-lactone can be easily produced by the ion exchange method. As the carrier for the catalyst used in the present invention, alumina,
Silica alumina, diatomaceous earth, etc. can be used, but
Activated carbon is the best, and finely powdered activated carbon achieves a faster reaction rate and is effective in suppressing isomerization and improving yield. The following metal compounds are used in preparing the catalyst of the present invention. That is, examples of palladium metal compounds include palladium chloride, palladium nitrate, palladium hydroxide, etc. These metals or compounds are sparingly soluble in water and cannot be mixed with hydrochloric acid,
It is necessary to dissolve it in a mineral acid such as aqua regia and adsorb it on activated carbon in the dissolved state. Examples of selenium compounds include selenium oxide, selenic acid, and sodium selenate. The optimal amount of selenium compound to be adsorbed and supported on activated carbon is 0.01 to 5% by weight as selenium metal. If a selenium compound exceeding this range is adsorbed, the reaction will either not proceed at all, or the reaction rate will be slow and glucose will be isomerized into fructose etc. in an alkaline aqueous solution, causing a decrease in yield. The supported amount of palladium is 1 to 10% by weight, preferably 2% by weight.
Palladium-selenium carbon catalysts are prepared in the range of 6% to 6% by weight. As monosaccharides used in the present invention, pentoses such as arabinose, xylose, and ribose, and aldoses such as hexoses such as glucose, mannose, and galactose are effective, and among these, glucose is particularly effective. Ketoses such as fructose and sorbose are not oxidized in the method of the present invention. These monosaccharides used in the present invention are water-soluble and are subjected to the reaction as an aqueous solution with a concentration of 5 to 50% by weight. Monosaccharides are prone to isomerization in alkaline aqueous solutions, which reduces the yield of the desired oxide, so the reaction must be completed in a lower pH range and within a short time. In this sense, the amount of catalyst used in the present invention is 0.5% by weight or more, preferably 1 to 2% by weight of a palladium carbon catalyst supporting 5% palladium, based on the monosaccharide. In the method of the present invention, the PH value decreases as the reaction progresses, so an alkali such as a caustic soda aqueous solution is added as necessary to maintain the PH value in the range of 8 to 11, preferably 9 to 10. Oxygen, air, etc. can be used as the oxygen-containing gas as the oxidizing agent in the method of the present invention. Oxidation reaction temperature is 20℃~boiling point preferably 30~60℃
Although the reaction can be carried out under normal pressure, the reaction rate can be further improved by carrying out the reaction under increased pressure of up to about 10 atmospheres. By such a method, the reaction is completed in 1 to 4 hours. As described above, the method of the present invention is superior to conventionally known methods for obtaining monosaccharide oxides, such as the method of the present invention using a palladium-carbon catalyst that does not contain a specific metal, and the fermentation method. It has extremely excellent characteristics in that it can achieve high reactivity, minimize the amount of residual raw material glucose, and at the same time suppress side reactions and isomerization, allowing only the desired oxide to be obtained with good selectivity. Hereinafter, it will be explained in detail using examples. Example 1 94 g of commercially available activated carbon was suspended in 1, and 7.0 g of a 20% by weight selenium dioxide aqueous solution (1
g) was added and adsorbed for 6 hours while stirring at room temperature. Subsequently, 33.4 g of palladium solution (5 g as palladium) was dropped into the suspension, and the palladium salt was completely adsorbed on the activated carbon while stirring. Next, 75 g of a 20% by weight aqueous sodium hydroxide solution was added to this suspension to make it alkaline, and 14 ml of formalin was added.
was added and maintained at 80±5° C. for 1 hour to reduce the palladium salt, followed by filtering, washing with water, and drying to obtain a 5% palladium carbon catalyst containing 1% selenium compound. Glucose (manufactured by Aito Co., Ltd.) 360g (2 moles)
and 5.4 g of the above catalyst (1.5% by weight relative to glucose) were added into a 2.5 reaction vessel equipped with a stirrer, thermometer, alkaline addition funnel, PH electrode and oxygen inlet. While stirring this aqueous solution, it was kept at 50±1° C. and oxygen gas was introduced. As the reaction progresses, gluconic acid is produced, so in order to neutralize this gluconic acid, 40%
Gradually drop a wt% sodium hydroxide aqueous solution,
The pH of the aqueous solution was always maintained at 9.5±0.2. One hour after the start of the reaction, the theoretical amount (2 mol) of alkali was consumed (no more than the theoretical amount of alkali was consumed, and the reaction did not proceed any further). The catalyst was separated from the reaction solution to obtain a colorless and transparent solution. A portion of this reaction solution was subjected to high performance liquid chromatography to quantify unreacted glucose and isomerized sugar (fructose), and enzymatic analysis (enzyme reagent; manufactured by Boehringer Mannheim)
Sodium gluconate was quantitatively determined. the result,
I got the following values. Glucose conversion rate 99.8% Sodium gluconate selectivity 98.7% Sodium gluconate yield 98.5% Example 2 A catalyst was prepared by changing the selenium content by the same method as in Example 1, and the same as in Example 1. The oxidation reaction of glucose was carried out under the following conditions. The results are shown in Table-1.

【table】

[Table] As shown in Table 1, there is clearly an optimum content for the selenium content and glucose oxidation activity of activated carbon, and those containing no selenium or more than 5% by weight have poor selectivity for gluconic acid. Selenium content is 5
As the oxidation activity of glucose increases beyond the weight percent, the oxidation activity of glucose rapidly decreases, and the reaction hardly progresses. Comparative Example 1 A 5% palladium carbon catalyst was prepared without treating activated carbon with a selenium compound. That is, 95 g of commercially available activated carbon was suspended and stirred in 1 part of water, and palladium metal was added into the suspension.
33.3 g of palladium chloride solution containing 15% by weight was added dropwise to completely adsorb the palladium salt onto the activated carbon. Next, 75g of 20% by weight sodium hydroxide aqueous solution
to make this suspension alkaline and formalin.
After adding 12ml and keeping at 80±5℃ for 1 hour for reduction,
The mixture was filtered, washed with water, and dried to obtain a 5% palladium carbon catalyst. When glucose was oxidized using 5.4 g of this catalyst according to Example 1, it took 1.0 hour to complete the reaction. As a result, the glucose conversion rate was 93.8% and the sodium gluconate yield was 84.7%. Furthermore, high performance liquid chromatography analysis confirmed the formation of saccharic acid.

Claims (1)

[Claims] 1. A method characterized by carrying out the reaction in the presence of a catalyst containing palladium and selenium when producing a monosaccharide oxide by oxidizing an aldose type monosaccharide with an oxygen-containing gas in an alkaline aqueous solution. A method for producing a monosaccharide oxide. 2. The method according to claim 1, wherein the catalyst containing palladium and selenium is a palladium-selenium carbon catalyst containing a selenium compound corresponding to 0.01 to 5% by weight of selenium metal. 3. The method according to claim 2, wherein the palladium-selenium carbon catalyst is a palladium-selenium carbon catalyst produced by subsequently adsorbing a palladium compound onto activated carbon that has been pretreated with a selenium compound.