JPS6341895B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing an aqueous solution of an anthraquinone reduction product by reducing anthraquinone.
More specifically, the present invention relates to a method for producing an aqueous solution of an anthrahydroquinone salt by reducing anthraquinone with hydrogen. Recently, anthraquinones have begun to be used as cooking aids in the pulp cooking of lignocellulosic materials. However, anthraquinone has low solubility in ordinary organic solvents including water, and cannot be used substantially in liquid form. In contrast, anthrahydroquinone, a reduction product of anthraquinone,

Derivatives with phenolic hydroxyl groups such as [Formula] are soluble in alkaline aqueous solutions and can be handled as solutions, and their reduction products are more effective than anthraquinones as pulp cooking aids (Japanese Patent Application Laid-open No. 54-50602)
It is known. Methods for reducing anthraquinone, especially for use as a pulp cooking aid, include dithionite acetic acid, sodium borohydride, inorganic reducing agents such as zinc powder and sodium hydroxide, monosaccharides such as glucose, ethylenediamine, etc. A method using organic reducing agents such as amines and aldehydes (e.g., JP-A-52-1999)
No. 155202, Japanese Unexamined Patent Publication No. 54-50602) have been proposed. These reduction methods have drawbacks such as using expensive reducing agents, generally using excessive amounts, and contaminating the products with the reducing agents. The present inventors reduced anthraquinone in an alkaline aqueous solution using inexpensive hydrogen instead of an expensive reducing agent as in the conventional method. They have discovered that this is the case and have completed the present invention. The method of the present invention is firstly a method for reducing anthraquinone with hydrogen in the presence of a hydrogenation catalyst in an alkaline aqueous solution containing an alkali metal hydroxide in an amount of at least about 2 times the mole of anthraquinone. A method for producing an aqueous anthrahydroquinone alkali metal salt solution, which is characterized by reducing anthraquinone, and the second method is to substantially dissolve the anthraquinone in the first method and to substantially dissolve the anthrahydroquinone in water. The method is characterized in that it is carried out in the presence of no organic solvent. In the method of the present invention, anthraquinone is
Industrial products with a particle size of about 100μ are used. Of course, relatively small particle sizes are preferable, but
The present invention can be carried out without any particular complication if the amount is limited. In the method of the invention, the reduction product of anthraquinone is primarily anthrahydroquinone,
In alkaline solution, it appears deep red and dissolves easily. As the alkali used in the method of the present invention, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide are used, and sodium hydroxide is industrially suitable in terms of price. The amount of alkali metal hydroxide used should be sufficient to dissolve the alkali metal salt of anthrahydroquinone produced by the reaction, and is generally selected to be at least about 2 times the mole of anthraquinone, but it is economical at most. Instead, the amount used is usually 10 times or less, preferably about 2 to 5 times the amount. If the amount of alkali metal hydroxide used is small, the reaction will not proceed smoothly. The concentration of alkali metal hydroxide is selected from a concentration at which anthrahydroquinone alkali metal salt can be completely dissolved. Generally, it is selected from 25% or less, usually from 5 to 20%. The hydrogenation (abbreviated as hydrogenation) catalyst used in the method of the present invention is selected from common hydrogenation catalysts. In particular, metals belonging to Group 8 of the periodic table are preferred. For example, nickel, palladium, ruthenium,
Examples include catalysts such as rhodium, platinum, gold, or Pd-C supported on activated carbon, silica-alumina, diatomaceous earth, and the like. The amount of catalyst is usually based on the weight of anthraquinone.
It is used in an amount of 0.05 to 10%, but it can be selected appropriately depending on the reaction pressure, reaction temperature, concentration, etc. Strictly speaking, the reaction temperature and reaction pressure vary depending on the catalyst used, but generally they are between room temperature and 100℃.
Preferably, a temperature of 30 to 90°C and a normal pressure to 10 Kg/cm ² are economical. The progress of the reaction can be determined by the amount of hydrogen absorbed. That is, if hydrogen is absorbed in an amount equivalent to approximately equimolar times the amount of raw material anthraquinone, anthraquinone is chemically changed into anthrahydroquinone, and the entire amount can be dissolved in the alkali.
If an appropriate hydrogenation catalyst such as Pd-C is selected and the reaction is carried out under appropriate temperature conditions such as 50 to 80°C and normal pressure to 1 atm, hydrogen will absorb about equimolar amounts of the anthraquinone starting material and the reaction will almost stop. . Furthermore, if the temperature and pressure are increased, a partial nuclear hydrogenation reaction will occur, which is not industrially preferable due to the equipment, operation, and cost increase due to the increase in hydrogen. The reaction time is determined as appropriate depending on the catalyst, reaction conditions, and purpose of use, such as the point at which hydrogen is absorbed in approximately equal moles as the starting material anthraquinone, the point at which the hydrogen absorption rate becomes extremely low, or the point at which the starting material anthraquinone is almost dissolved in the alkali. You can choose. In the method of the present invention, the presence of an organic solvent that substantially dissolves the anthraquinone and is substantially insoluble in water when the anthraquinone is reduced by hydrogen in the presence of a hydrogenation catalyst in an alkaline aqueous solution. The reaction rate can be increased by performing the above reduction reaction below. The organic solvent has a solubility of anthraquinone at room temperature (g/
100g of solvent) is preferably about 0.05 or more, preferably about 0.1 or more. Organic solvents corresponding to these include aromatic hydrocarbon solvents such as toluene, xylene, cumene, and methylnaphthalene; halogenated benzenes such as trichlorobenzene; halogenated aliphatic hydrocarbons such as trichlene; or mixtures containing the above solvents. Examples include solvent naphtha and gasoline. hexane, which has low solubility of anthraquinone;
Aliphatic hydrocarbons such as heptane are not preferred because they actually reduce the reaction rate. The amount of organic solvent used may be about 5 to 20 times, preferably 10 to 15 times the weight of the anthraquinone. The method of the invention is generally carried out as follows.
That is, a predetermined amount of anthraquinone and a hydrogenation catalyst are added to an alkaline aqueous solution of alkali metal hydroxide at a predetermined concentration, and hydrogen is introduced with or without addition of an organic solvent while stirring. When the amount of hydrogen absorbed is about the same molar amount as that of anthraquinone, or when the rate of hydrogen absorption is extremely reduced, or when most of the anthraquinone is dissolved in the alkaline solution, the reaction is stopped and the organic solvent is separated from the aqueous phase. Afterwards, the catalyst remaining in the aqueous solution or, in some cases, unreacted anthraquinone is separated by excess to obtain an aqueous solution of anthraquinone reduction products (mostly dialkali metal salts of anthrahydroquinone). I can do it. If no organic solvent is present, an organic solvent separation step is not necessary. The separated organic solvent and catalyst can be recycled to the hydrogenation reaction step, which is very convenient. The recovered catalyst can be used in the next reaction, usually in a wet state. Further, unreacted anthraquinone may remain together with the catalyst, and the raw material is not lost by recycling. In the method of the present invention, the hydrogenation reaction step and the solvent or catalyst separation step can be carried out either batchwise or continuously. When the obtained anthraquinone reduction product is analyzed by infrared absorption spectrum, it is found that most of the product is anthrahydroquinone salt. or,
These aqueous solutions were used as a cooking aid for pulp cooking, such as kraft pulp, soda pulp, or sulfite pulp, but the cooking effect was greater than when anthraquinone was used in powder form.
In addition, it can also be used as a catalyst for oxidizing black liquor discharged during pulp cooking (Japanese Patent Application Laid-Open No. 53-81702). Example 1 An aqueous alkali solution was prepared by adding 2 parts of sodium hydroxide (2.5 mole times the anthraquinone used) and 20 parts of water to a reactor equipped with a stirrer and a hydrogen inlet tube that was shut off from the outside air. To this alkaline aqueous solution, 4 parts of anthraquinone powder and 0.2 parts of Pd-C (palladium-carbon) were added, and several drops of a surfactant were further added and stirred to prepare an anthraquinone slurry. Hydrogen was introduced into the reactor while the contents were kept at 65°C and stirred, and the reduction reaction of anthraquinone started. After 1.5 hours, when approximately equimolar amounts of hydrogen were absorbed compared to anthraquinone, the rate of hydrogen absorption decreased rapidly. Since a small amount of hydrogen had been absorbed, the reaction was continued as a precaution, and the reaction was stopped 4 hours after the start of the reaction. There was no anthraquinone powder and the aqueous phase had a clear dark red color. The inside of the reactor was replaced with nitrogen, Pd-C was separated under a nitrogen atmosphere, and the obtained aqueous solution of the reduction product of anthraquinone (substantially an aqueous solution of sodium salt of anthrahydroquinone) was taken into a container, and 50 parts of toluene was added. to cut off contact between the outside air and the oxygen inside. The separated Pd-C was washed with water and acetone,
Stored under hydrogen atmosphere. Anthraquinone was similarly cyclized using the catalyst recovered in the above example, but the hydrogen absorption rate hardly changed, and the process could be carried out in the same manner as in the above example. Example 2 The same procedure as in Example 1 was carried out, except that Pt-C, Ni-C, or Rh-C was used instead of Pd-C as the hydrogenation catalyst, and the same results were obtained. Example 3 Into a reactor similar to Example 1, 4 parts of anthraquinone powder and Pd-C0.2 were added to an alkaline aqueous solution containing 2 parts of sodium hydroxide (2.5 moles relative to the anthraquinone used) and 20 parts of water. A slurry containing anthraquinone was prepared by adding a small amount of surfactant and stirring. To this slurry, 50 parts of toluene or n-heptane (solubility (g/100g solvent); toluene 0.2 (at 15°C), n-heptane 0.1 or less, almost none) was added, and the mixture was kept at 65°C and stirred. At the same time, hydrogen was introduced into the reactor to carry out the reduction reaction of anthraquinone. The amount of hydrogen absorbed, which indicates the progress of the reaction, is shown in Table 1. Addition of toluene increases the reaction rate, but n-heptane, in which anthraquinone has almost no solubility, decreases the reaction rate.

[Table] Comparative Examples 1 and 2 Examples except that in Example 1 and Example 3 (toluene addition), 0.38 g of sodium hydroxide (0.5 mole times the anthraquinone used) was used instead of 2 parts of sodium hydroxide. When carried out in the same manner as in Example 1 and Example 3, the reaction rate was as follows, corresponding to Example 1 and Example 3 (addition of toluene), respectively.
It decreased to about 0.1 times in Comparative Example 1 (no toluene added) and about 0.4 times in Comparative Example 2 (toluene added).

Claims (1)

[Claims] 1. A method for reducing anthraquinone with hydrogen in the presence of a hydrogenation catalyst in an alkaline aqueous solution containing an alkali metal hydroxide in an amount of 2 to 5 times the mole of anthraquinone. A method for producing an aqueous anthrahydroquinone alkali metal salt solution, which is characterized by reduction. 2. The method according to claim 1, wherein the hydrogenation catalyst is a Group 8 metal catalyst such as platinum, nickel, iron, tungsten, palladium, rhodium, ruthenium, or gold, or a supported catalyst thereof. 3. The method according to claim 1, wherein the temperature of the reduction reaction is 30 to 90°C. 4. In a method of reducing anthraquinone with hydrogen, anthraquinone is substantially dissolved in an alkaline aqueous solution containing an alkali metal hydroxide in an amount of about 2 to 5 times the mole of anthraquinone, and is substantially soluble in water. 1. A method for producing an aqueous anthrahydroquinone alkali metal salt solution, which comprises reducing anthraquinone with hydrogen in the presence of a hydrogenation catalyst and a free organic solvent. 5 Solubility of anthraquinone at room temperature (g/
5. The method of claim 4, wherein the organic solvent is about 0.1 or more (100 g solvent). 6. The method according to claim 5, wherein the organic solvent is an aromatic hydrocarbon or its halide, ethers, solvent naphtha, or gasoline.