JPS6317767B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for preventing the accumulation of impurities that occurs when caustic soda recovered from soda-containing organic waste liquid via ferric acid soda is repeatedly used for the extraction of organic acidic substances from organic substances or in the treatment process of organic substances. . Waste liquids containing both soda and organic substances, such as the waste liquid from the alkaline pulp cooking process (so-called black liquor) in the pulp industry and the waste liquid produced as a by-product when synthesizing cyclohexanone through the air oxidation reaction of cyclohexanone in the petrochemical industry, are called soda. It is generally called as containing organic waste liquid. Since this waste liquid contains a large amount of soda that can be recovered as caustic soda, the method of recovering caustic soda that combines the recovery of soda carbonate by incineration and causticization with slaked lime, which has been used industrially, is being replaced. A new method for recovering caustic soda has been proposed (Special Publication No. 56-1160). This is done by mixing soda-containing organic waste and ferric oxide in an appropriate ratio and then using a reactor such as a rotary kiln or fluidized bed in an oxidizing atmosphere.
The organic matter in the soda-containing organic waste liquid is combusted at 850 to 1000°C, and sodium ferrate (Na ₂ Fe ₂ O ₄ ) is synthesized, and then the sodium ferrate is hydrolyzed using high-temperature water and oxidized with an aqueous solution of caustic soda. The proposal is to reuse the caustic soda aqueous solution and ferric oxide after conversion to ferric iron and solid-liquid separation for extraction of organic acids, treatment of organic matter, and synthesis of sodium ferrate, respectively. The inventors of the present invention have made a
As a result of various studies on 1160, we found that repeated use of recovered caustic soda causes impurities to accumulate in the circulating fluid (caustic soda aqueous solution), causing undesirable problems in system operation and management during the organic acid extraction process. It became clear that there was room for improvement. That is, caustic soda is a hydrolysis product of sodium ferrate synthesized from soda-containing organic waste liquid and ferric oxide by roasting it in a rotary kiln lined with a refractory or in a fluidized bed. If you repeatedly use
Impurities, especially aluminum and silicium compounds, accumulate in the circulating fluid. When these impurities reach a certain concentration depending on the type of process, for example, in an organic acid extraction process, when the concentration of any one compound reaches approximately 1 wt% as an element,
It was found that problems such as precipitation of gel-like substances occur during the extraction process of organic acids in the product, which deteriorates the quality of the product and prevents stable operation of the equipment, which is undesirable. Therefore, the inventors further conducted intensive research on the sources of impurities and methods for preventing the accumulation of impurities, and found that one of the main sources of impurities is commercially available ferric oxide, and the other is ferric oxide. It turned out to be a refractory lined in a soda synthesis reactor. That is, in the process of synthesizing sodium ferrate at high temperatures, the ferric oxide and the aluminum and silicium compounds contained in the refractory gradually combine with soda compounds such as soda carbonate that have not yet combined with ferric oxide. It reacts with and becomes a compound that is easily soluble in water or aqueous caustic soda solution, and this migrates to the aqueous caustic soda solution side during the hydrolysis of sodium ferrate.
It has been experimentally revealed that in the process of repeatedly using the recovered caustic soda aqueous solution, it gradually accumulates in the circulating fluid, and furthermore, the impurities of aluminum and silicium compounds accumulated in the circulating fluid in this way are carbon dioxide gas or other impurities. It has been found that by aerating the circulating liquid at a pH value of 9.5 to 11 with a gas containing, for example, the combustion gas used when synthesizing sodium ferrate from soda-containing organic waste liquid, it is possible to simultaneously remove it efficiently. The present invention was achieved by discovering that the concentration of monosilicate ions in the mother liquor obtained at this time was approximately one order of magnitude lower than the concentration expected from the above PH value. That is, the present invention provides a system in which a caustic soda aqueous solution obtained by hydrolyzing sodium ferrate synthesized from a soda-containing organic waste liquid and ferric oxide is repeatedly used in the process of extracting organic acids from organic substances or treating organic substances. The aluminum and silicium compounds accumulated in the caustic soda aqueous solution are converted into compounds insoluble in water or alkaline aqueous solution using a carbon dioxide-containing gas, preferably carbon dioxide gas in the combustion gas, and these are removed from the system. The object of the present invention is to provide a method for recovering caustic soda from a soda-containing organic waste solution, which is characterized by separating and avoiding operational troubles such as precipitation in the extraction of organic acids or treatment of organic substances. Now, the reaction of synthesizing sodium ferrate using pure sodium carbonate and ferric oxide, and then hydrolyzing this sodium ferrate with water to convert it into caustic soda has long been known as the Lowig reaction. There is. In addition, as mentioned earlier, a method for synthesizing sodium ferrate by burning a soda-containing organic waste liquid in the presence of ferric oxide, and then hydrolyzing the sodium ferrate with high-temperature water to obtain a caustic soda aqueous solution. is already known (Japanese Patent Application Laid-Open No. 54-52697). As described above, the basic chemical principles and techniques for recovering caustic soda from soda carbonate or soda-containing organic waste liquid using ferric oxide are well known. Now, the reaction to synthesize sodium ferrate from soda-containing organic waste liquid and ferric oxide in an oxidizing atmosphere is as follows.
It involves the Lowing reaction (2) and can generally be expressed as the following reaction: 2NaxCyHzOA+1/2(x+4y+Z-2A)O ₂ = xNa ₂ CO ₃ + (2y-x) CO ₂ + ZH ₂ O... …(1) xNa ₂ CO ₃ +xFe ₂ O ₃ =xNa ₂ Fe ₂ O ₄ +xCO ₂ …(2) (1) + (2) 2NaxCyHzO _A +1/2 (x+4y+z−2 _A ) O ₂ +xFe ₂ O ₃ =xNa ₂ Fe ₂ O ₄ +2yCO ₂ +ZH ₂ O...(3) The mechanism of impurity accumulation is not clear, but it is estimated as follows. In the above reaction, reaction (1) is relatively fast, and reaction (2) is slow compared to (1). As a result, before the sodium carbonate produced in the reactor reacts with iron oxide at high temperatures, reaction products such as aluminate and silicate, which were produced by reacting with components such as alumina and silica in the furnace material, It will be mixed into the sodium ferrate, which is the original target, and will be dissolved in the recovered caustic soda during the hydrolysis of sodium ferrate, and will gradually accumulate over a long period of cyclic use. In addition to the above, commercially available iron oxide contains trace amounts of impurities such as alumina and silica, which are generally more reactive than those compounds found in furnace materials, and these are also used in make-up. It is thought that as iron oxide is replenished, it gradually accumulates in the recovered caustic soda. In addition to the above, a direct reaction between sodium ferrate and alumina, silica, etc. is also possible, but under normal reaction conditions, it is a reaction between solids.
Based on the experience of the inventors, this does not seem to be much of a problem. When the sodium ferrate is hydrolyzed, a considerable portion of the aluminum and silicium compound impurities transferred to the sodium ferrate is transferred to the caustic soda side. Already known methods for preventing or removing aluminum and silicium-based impurities are: (1) Part of the liquid circulating in the system (for example, a caustic soda aqueous solution) is extracted from the system, neutralized, and then disposed of. To find use in a method or another use. (2) A method in which the caustic soda aqueous solution extracted from the system is treated with slaked lime. In method (1), effective caustic soda must be neutralized and discarded, or a new use must be found, making on-site treatment difficult. Furthermore, it is necessary to replenish fresh caustic soda corresponding to the extracted amount and to use a neutralizing agent (acid), which is not preferable from the point of view of process economy. In addition, when the treatment method using slaked lime (2) was examined experimentally, it was found that it was somewhat effective in reducing the silicium compounds in the caustic soda aqueous solution, but it was hardly effective in removing the aluminum compounds, and the accumulation of aluminum and silicium compounds. It is not appropriate to adopt it as a prevention method. There are many problems in solving the precipitation problem caused by the accumulation of aluminum and silicium compounds using known methods, and the inventors conducted intensive research to find a new method for preventing the accumulation of aluminum and silicium compounds. invented a new method of treatment using a gas containing carbon dioxide, which is completely different from known methods. In other words, at least a relatively dilute aqueous caustic soda solution, which is the supernatant liquid of the slurry produced when ferric acid soda, which has accumulated impurities due to cyclic use, is wet-pulverized prior to hydrolysis, or at least an aqueous caustic soda solution after hydrolysis. Take a portion, leave it as is, or adjust it to an appropriate concentration, and then treat it with gas containing carbon dioxide (including pure carbon dioxide, of course) to bring the pH to 11.5-9.
Preferably, by setting the value to 11 to 9.5, it became possible to simultaneously precipitate and remove aluminum and silicium compounds as insoluble compounds. Separation and removal of silicium compounds is particularly difficult at pH 11.5 or above.
Further, if the pH is below 9, the separation of aluminum compounds is good, but the separation effect of silicium compounds decreases, making it a bad idea overall. We have also found that within this pH range, it is possible to reduce the silicium compound to a level below the solubility of monosilicic acid, which is a commonly thought impurity of silicium. At this time, the amount of caustic soda aqueous solution to be treated does not need to be the entire amount, and it is of course only necessary to extract and treat the minimum amount appropriate to prevent the accumulation of impurities exceeding the limit. The aqueous solution containing soda carbonate and bicarbonate and having a reduced concentration of aluminum and silicium compounds treated in this way can be used as is or after being concentrated, mixed with an organic waste solution containing soda and subjected to the usual ferric acid soda treatment. It's fine.
Note that this process can naturally be applied to cases where there are similar impurities that accumulate in the recovered alkali due to inorganic substances contained in organic substances that require treatment with caustic soda. One embodiment of the present invention will be described below with reference to the drawings. The soda-containing organic waste liquid 1 from the organic matter organic acid extractor 11 is fresh ferric oxide or recovered ferric oxide.
It is charged into the mixing tank 2 together with the iron sludge 13 and mixed to form a homogeneous slurry. The resulting slurry mixture is fed into a combustion reactor 3 lined with refractory material. The combustion reactor 3 has a temperature of 800-1050℃, preferably 900-1000℃ due to combustion of auxiliary fuel.
Furthermore, the air ratio is maintained at 1.2 to 2.0, preferably 1.3 to 2.0.
Maintained in an oxidizing atmosphere of 1.8. Under these conditions,
The soda content in the waste liquid reacts with ferric oxide and is almost quantitatively converted to sodium ferrate. When the combustion reactor is of the rotary kiln type, the solid reaction product containing sodium ferrate as a main component enters the solid-gas separator 4 while moving in parallel with the combustion gas in the reactor. Here, the solid reaction product 14 and the combustion gas 15
are separated. The combustion gas 15 is sent to a waste heat recovery boiler 8 for waste heat recovery. The granular solid reaction product 14 from the solid-gas separator 4 is charged into a wet pulverizer 5 and pulverized to 100 mesh to 200 mesh (Tyler sieve) at a temperature of 60° C. or lower while being indirectly cooled with water. During this wet milling process with water, at least a portion of the aluminum and silicium compounds contained in the solid reaction product 14 is extracted and transferred to the supernatant liquid 16. A portion of the supernatant liquid 16 is transferred to the aeration tank 9.
I will be sent to The proportion of supernatant liquid sent to the aeration tank 9 varies depending on the refractory material of the combustion reactor 3, the quality of the ferric oxide used, and the permissible concentration of impurities in the circulating caustic soda solution, but usually the total number of supernatant liquids is That's about it. In the aeration tank 9, the supernatant liquid 16 is aerated with part of the combustion gas that has passed through the waste heat boiler 8, and the liquid 1
The pH value of 6 becomes 9.5-11. By this aeration treatment, the aluminum and silicium compounds dissolved in the liquid 16 are simultaneously efficiently converted into insoluble compounds. The supernatant liquid containing the insoluble compounds from the aeration tank 9 flows down to the solid-liquid separator 10, where the insoluble separated substances 22 are discharged out of the system. The separated liquid 12 from the solid-liquid separator 10 contains soda, which is a raw material for the synthesis of sodium ferrate.
will be returned to. Solid reaction product 1 pulverized by wet pulverizer 5
4' is fed into the hydrolysis tank 6 in slurry form,
Here, while being supplied with heat by steam 19 from the waste heat recovery boiler 8, it is hydrolyzed at 150 to 220°C for 30 minutes to 1 hour to become a 20 to 25 wt% caustic soda aqueous solution and ferric oxide. The amount of water required to obtain a 20-25wt% caustic soda aqueous solution is
controlled by the amount of water 20 charged. The reaction product after hydrolysis is stored in a cooler 23 as necessary.
After being cooled, it is sent to a solid-liquid separator 7 where it is separated into a caustic soda aqueous solution and ferric oxide. The separated caustic soda aqueous solution 21 is passed through a precision filter 24 if necessary, and then supplied to an organic acid extractor 11 and used for extracting organic acids from organic substances 27. As described above, according to the present invention, when caustic soda is recovered from a soda-containing organic waste liquid and repeatedly used for extracting organic acids from organic substances, soluble aluminum and silicium compounds accumulated in the caustic soda aqueous solution can be efficiently removed at the same time. The problem of precipitation in the organic acid extraction step, which was a problem with the conventional method, can now be resolved, and it is also effective in treating organic waste liquid containing soda. EXAMPLE Cyclohexane was air oxidized by a known method to obtain a mixture consisting of cyclohexanone, cyclohexanol and an organic acid. This mixture is 23wt%
The organic acid was extracted with an aqueous caustic soda solution to produce a soda-containing organic soda waste liquid having the composition shown in Table 1.

[Table] Commercially available iron oxide was mixed with this waste liquid so that the molar ratio of Fe/Na was 1.3, and a small rotary kiln lined with chamomile castable was used at a temperature of about 950℃ and an average residence time of 2 hours. It was roasted. Obtained sodium ferrate (Na standard yield
97%) was ground in a vibration mill, and then hydrolyzed at 180°C for 60 minutes. The quality of the obtained caustic soda aqueous solution is shown in Table 2 below.

[Table] The PH was adjusted by blowing carbon dioxide gas into the caustic soda aqueous solution obtained, and the concentration of impurities in the supernatant liquid after removing the precipitate was measured, and the results shown in Table 3 were obtained. These liquids were a mixture of sodium carbonate, sodium bicarbonate, and a small amount of impurities, and could be used to regenerate caustic soda without causing any inconvenience.

[Table] Note: * Stock solution The solubility of soluble monosilicate ion in water is approximately
1500, 110, and 80 (ppm), and it is recognized that the present invention has an unexpectedly remarkable effect on removing silicium compounds as well as aluminum compounds. In the above example, the test was conducted on recovered caustic soda with a relatively low impurity concentration, but even if it contains a higher concentration of impurities, as long as it does not cause any inconvenience when recycled.
It is clear that the present invention can be applied. In such a case, the amount of impurities removed per treatment will naturally increase by applying the present invention, so the amount to be extracted for treatment can be further reduced compared to the circulating amount. Of course, this is even more advantageous. As described above, according to the present invention, harmful impurities that accumulate in caustic soda used for recovery and circulation can be efficiently removed by relatively simple operations, and organic acid substances can be extracted and organic substances can be removed. Since the soda-containing organic waste liquid produced by alkali treatment can be treated in a closed loop, it is extremely advantageous in terms of pollution prevention and industry.

[Brief explanation of the drawing]

The figure is a flowchart showing one embodiment of the present invention,
The numbers in the figure correspond to the following. 1...Soda-containing organic waste liquid, 2...Mixing tank, 3
... Combustion reactor, 4 ... Solid-gas separator, 5 ... Wet sand mill, 6 ... Hydrolysis tank, 7, 10 ... Solid-liquid separator, 8 ... Waste heat recovery boiler, 9 ... aeration tank,
11... Organic acid extractor, 12... Separation liquid, 13
... Recovered iron oxide sludge, 14 ... Solid reaction product, 15 ... Combustion gas, 16 ... Supernatant liquid, 17 ...
...Recovered steam, 18... Combustion exhaust gas, 19...
Steam, 20...Demineralized water, 21...Recovered caustic soda aqueous solution, 22...Separated material, 23...Cooler,
24... Precision machine, 25... Exhaust gas, 26...
Combustion air, 27...organic matter.

Claims (1)

[Claims] 1. Iron oxide is mixed with organic wastewater containing sodium discharged from the process of treating organic matter with caustic soda, and the mixture is heated at 800°C in an oxidizing atmosphere.
By roasting at the above-mentioned high temperature, organic matter is burnt and removed, and the sodium content is converted to sodium ferrate, which is then hydrolyzed to regenerate and separate the caustic soda aqueous solution and iron oxide. In the method of repeated use, at least a part of the regenerated caustic soda aqueous solution is treated as it is or after being diluted, and then treated with a gas containing carbon dioxide gas to remove the resulting impurity precipitate.
A method for recovering caustic soda, which comprises treating it as is or by concentrating it in the same manner as the above-mentioned organic waste liquid containing sodium.