JPH07112555B2 - Method for treating wastewater containing organic acidic substances - Google Patents

Description

The present invention relates to a method for treating wastewater containing an organic acid or an ester or an aldehyde in addition to an organic acid by alkali treatment, concentration and incineration. The present invention relates to a method for concentrating incineration of acidic wastewater generated from processes such as production of organic acids by gas phase oxidation and esterification of acids, or gasification by partial oxidation of hydrocarbons.

[Conventional technology]

Conventionally, formic acid, oxalic acid, acetic acid, acrylic acid, propionic acid,
In the chemical industry dealing with organic acids of C ₄ or less such as butyric acid, methacrylic acid, succinic acid, and maleic acid, waste water containing about several% of organic acids may be unavoidably discharged in the refining or recovery process. When biological treatment is difficult, these are neutralized with an alkali to suppress the volatility of the organic acid contained and then concentrated to save auxiliary fuel and then incinerated. Is referred to as an alkali carbonate) for recycling for neutralization (see, for example, JP-B-60-7558 or JP-B-57-58564).

However, the wastewater discharged from the production process of organic acids by vapor-phase oxidation of hydrocarbons or lower aldehydes is not limited to organic acids, but aldehydes such as formaldehyde and methacrolein that do not bind hydrogen to α-carbon, or acetaldehyde and acrolein. In addition to such aldehydes, the ester used in the extraction step of the product, or the ester derived from wastewater containing the ester discharged from the esterification step of the organic acid and the like are often contained at the same time.

Further, the wastewater produced in the thermal decomposition process such as partial oxidation of hydrocarbons may contain acidic substances weaker than carbonic acid such as phenol. The organic carboxylic acid is fixed as an alkali salt in the above method in which alkali carbonate is used for the wastewater containing the aldehydes, esters or phenols together with the organic acid.

[Problems to be Solved by the Invention]

However, in the wastewater after neutralization, the ester gradually hydrolyzes during concentration, and the alcohol, which is a decomposition product, distills out as COD. Alternatively, polyformaldehyde existing as an oligomer in wastewater is depolymerized to formaldehyde monomer, or phenols that are not neutralized by alkali carbonate are gradually distilled out together with water.
It tends to be high, which is difficult to concentrate due to difficult biochemical treatment.

That is, the waste water that causes secondary pollution due to concentration in the past was often incinerated using auxiliary fuel without being concentrated. However, due to the rise in energy costs, enrichment using the above-mentioned neutralization method has come to be used for fuel saving. The purpose of concentration is to reduce the water content as much as possible and to avoid the inconvenience of simply heating water to the incineration temperature. However, even if the waste water as described above is fixed with a volatile organic acid by using a carbonate, the organic volatile components such as formaldehyde, lower alcohol, etc., or ester etc. are continuously decomposed and decomposed during the concentration. Also, some wastewater releases phenol, etc., along with evaporated water, so that
Since the COD value becomes extremely high, biochemical treatment was not possible, and it was difficult to reduce fuel cost by highly concentrating wastewater.

The present invention cannot easily be made non-volatile with organic acid substances that are difficult to be efficiently separated from water as described above, as well as esters, formaldehyde and other lower aldehydes, or alkali carbonates such as phenol. When detoxifying waste water containing a compound by incineration, as a pretreatment, in order to be able to contain COD components in the condensate of evaporated water generated in large amounts within the range where biochemical treatment is possible, It also provides means for solving the problems such as reducing the consumption of alkaline substances and energy as much as possible.

[Means for Solving the Problems]

The wastewater that is the subject of the present invention has a relatively small volatility because it is dilute, is azeotropic with water, or is relatively volatile because it is difficult to separate it from water in terms of energy cost.
In addition to organic acids of C ₄ or less, aldehydes, especially formaldehyde, and in some cases, esters and phenols, and in addition to these, sometimes low-volatile water-soluble organic and inorganic substances Is. Its main source is dilute wastewater from a chemical plant that has a gas-phase oxidation process of hydrocarbons and its primary oxides such as aldehydes as its main process, and may produce derivative products thereof.

These wastewaters use too much auxiliary fuel to burn directly as they are, contain high concentrations of COD or TOC that are not suitable for biological treatment, or contain aldehydes or phenols that are biotoxic. In many cases, it is not suitable for biochemical treatment because of the fact that it does. Therefore, in order to treat this wastewater pollution-free, it is best to incinerate it by distilling water by some means and reducing the use of auxiliary fuel.

To this end, it is important to suppress the volatility of organic substances and improve their separation from water. Since the organic acid is usually stronger than carbonic acid, it can be fixed in water by adding an alkali carbonate or bicarbonate to the wastewater to neutralize it, thereby forming an alkali salt of the corresponding organic acid. However, organic acid esters and compounds such as formaldehyde and acetaldehyde,
Alternatively, phenols react slowly with carbonates or do not change easily, so some of them serve as a rich source of COD in the distillate during concentration.

We have found that these compounds have a pH above 12, preferably
An experiment was conducted with the idea that the compound can be converted into a compound that can be easily treated by making it a strong alkaline of 13 or more, and more preferably by heat treatment at the same time, and keeping in mind the amount of expensive caustic alkali used. As a result, the present invention has been reached.

That is, the present inventors, considering the properties of the target wastewater as described above, came to the idea of treating the wastewater with an alkali, and directly added caustic alkali to the wastewater and heated and stirred. The reaction expected from this is RCOOR '＋ MOH → RCOOM ＋ ROH …… (3) RCOOH ＋ MOH → RCOOM ＋ H ₂ O …… (4) ArOH ＋ MOH → ArOM + H ₂ O …… (5) M = K or Na, R = hydrocarbon residue, Ar = aromatic residue Like that.

(1) is a so-called Cannituaro reaction. For example, formaldehyde becomes a non-volatile formate and a low boiling point methanol as the oligomer depolymerizes. (2) becomes an involatile high-boiling substance by aldol condensation. (3) is a saponification reaction of an ester, an organic acid group is fixed, and an alcohol having a relatively low boiling point is liberated. (4) and (5) are neutralization reactions of organic carboxylic acids and phenols, respectively. These reactions proceed faster at higher temperatures, and may be, for example, 80 ° C. for 30 minutes. Also, if phenols are present, they naturally become alkaline salts and become non-volatile. In this way, a considerable amount of volatile organic substances are fixed as non-volatile organic salts by the alkali treatment, and a large amount of generated relatively low boiling point substances are included, so that it is easy to remove as a pretreatment for full-scale concentration. It has been found.

Therefore, the first aspect of the present invention is the first evaporation for preliminarily evaporating the volatile component as necessary in concentrating the wastewater containing both the substance that reacts with the organic acid and the alkaline component to generate the volatile component. A caustic component is added to the residual liquid of the process and the first evaporation process to heat it to pH 12 or more to generate a volatile component, and at the same time, a reaction process of suppressing the volatility of the remaining organic matter and a vaporization of the generated volatile component. It consists of two evaporation steps and a concentration step of concentrating the residual liquid.

The second aspect of the present invention is to neutralize the wastewater first with an alkali carbonate, and then to increase the pH to 12 or more, preferably 13 or more with a caustic alkali to promote the chemical reaction, thereby making the organic matter non-volatile and promoting the volatility. The volatile components are removed at the same time, and it is possible to significantly reduce the degree of mixing of COD components in the concentrated water during the subsequent concentration by evaporation of water.

Further, the amount of heat used in the first evaporation tower heater and the second evaporation tower heater can be reduced by supplying the gas containing the steam and the volatile component generated in the second evaporation step to the first evaporation step. Thus highly concentrated wastewater can be incinerated with the aid of less energy.

[Embodiment] Embodiment 1 An embodiment of the first invention will be described with reference to FIG.

The raw waste water 12 having the properties shown in Table 1 discharged from the acrylic acid production process by the catalytic air oxidation reaction of propylene is supplied to the first evaporation tower 1 and circulated by the attached first evaporation tower circulation pump 2. Meanwhile, it is heated by steam or the like by the first evaporation tower heater 3. The volatile components come into countercurrent contact with the diffusion air and are separated into a first vaporization column overhead gas 13 and a first vaporization column effluent 15.

The effluent 15 is supplied to the reaction tank 4 and reacts with the caustic soda aqueous solution 16 supplied to the reaction tank 4 under predetermined conditions. Here, in addition to neutralization of free acid at pH 12.5 or higher, reactions such as saponification of ester or cannitaro reaction of formaldehyde, aldol condensation of higher aldehyde, etc. are usually carried out, and both production of volatile components and nonvolatization are performed. Occurs. The reaction liquid 17 exiting the reaction tank 4 is supplied to the second evaporation tower 6 by the reaction tank pump 5. Here again, the reaction liquid is heated by the second evaporation tower heater 8, and the second evaporation tower circulation pump 7
Volatile components (mainly alcohols) are stripped by the air 18 for circulation during circulation. A part of the circulating liquid is taken out and is sent to the vacuum condensing can 9 together with the second evaporating tower effluent 19 for the final concentrating treatment. 11
Is a vacuum generator, and the concentrated water from the condenser 10 is sent to an activated sludge tank as needed. The concentrated wastewater obtained here is incinerated in an incinerator (not shown) using a necessary amount of auxiliary fuel together with air for diffusion. Table 1 shows the flow rate and properties of the substance flowing through the main part of Fig. 1 per unit time. The incineration temperature was 1000 ° C.

Comparative Example 1 When incinerating at 1000 ° C. as it is without condensing the same wastewater as in Example 1, about 10 times as much auxiliary fuel is required, that is, 250 parts are required, and accordingly, the combustion air, the scale of the incinerator, etc. are also 10 times.
You will need twice. In the case of Example 1, when air was not emitted prior to the concentration, the COD value of the condensed water was 9000 ppm or more, the biochemical toxicity was strong, and the activated sludge treatment could not be performed.

Embodiment 2 An embodiment of the second invention will be described with reference to FIG. This method is to save caustic.

In the figure, the wastewater is sent to the neutralization tank 32 by the supply pipe 31, and the organic acid contained therein is neutralized by the carbonate sent from the carbonate circulation line 40. The carbon dioxide gas generated at this time is released from the conduit 47. It is economical to use carbonates produced by incineration of concentrated wastewater as this carbonate,
Of course, it can be supplied separately. The wastewater in which the organic free acid is neutralized is then sent to the strong alkaline treatment tank 33 through the conduit 48. The alkali hydroxide 46 as a strong alkali may be mixed in the conduit 48 as shown in the figure or may be supplied to the treatment tank 33, but the pH in the tank is always 12 or more, preferably 13 or more to promote the reaction. Above all preferred. The treatment tank 33 is preferably heated in order to accelerate the reaction. Although steam is used for heating in the figure, sensible heat of the circulating carbonate aqueous solution may be used. In the figure, this sensible heat is generated by the heat exchanger 53. It is used for preheating, and any method can be used.

The above-mentioned (1), (2), and (3), which are the main reactions that occur here
The volatile components of the substances produced in
Since the temperature can be increased to obtain the concentrated organic vapor in the conduit 51, it is possible to burn directly in the combustion furnace. If necessary, the treatment liquid may be treated separately in a diffusion tower (not shown) to remove low boiling point substances. In this case, air may be diffused as disclosed in Japanese Patent Publication No. 51-35063. Thus, the wastewater, which has a significantly reduced degree of volatilization of organic substances due to evaporation, is guided to the concentrator 34, where a large amount of water is evaporated and concentrated.

Here, a vacuum evaporation can utilizing the waste heat of incineration is preferably used. Although the figure shows a single-can type, a multi-effect can may be used. Alternatively, a slight amount of reflux may be applied to concentrate the volatile components while distilling off the water from the top of the column to distill off the water. This has the advantage that the volatile components can be distilled off and concentrated at the same time. . In this case, it is reasonable to measure the heat recovery by the vapor recompression method. Further, the organic matter in the distilled water has many alcohol components, and even if COD of about 1000 to 300 ppm is present, there is no particular problem in the subsequent biochemical treatment.

The concentrated wastewater is sent to the incinerator 35 through the conduit 50 and is sprayed and incinerated with the help of the auxiliary fuel 36 if necessary. The incineration temperature at this time is usually 900 to 1000 ° C., which is higher than the melting point of carbonate, and the residence time is usually 1 to 2 seconds. Combustion gas can be quenched 37
The water is rapidly cooled with water, and the produced carbonates are sent to the neutralization tank 32 through the conduit 40 as an aqueous solution or slurry. During this period, excess carbonate aqueous solution or slurry is removed from the purge line 39 and separately processed or used. Exhaust gas from incineration contains a large amount of water, but duct 41
The concentrated water is discharged as a drain 42, and the exhaust gas is diffused into the atmosphere through the exhaust duct 43. For incineration, spray incineration as described above may be used, but it is also possible to recover carbonate as a dry solid by fluidized bed incineration or a waste heat boiler method (in this case, there is no bicarbonate). In this case, the neutralization tank 32 may be fed as a solid.

Next, a specific description will be given using numerical values.

The results of neutralization, alkali treatment, concentration, and incineration treatment of 1000 kg / h of dilute wastewater having the following composition by the apparatus shown in Fig. 2 are shown.

Prior to treatment, the neutralization tank 32 is filled with waste water, and Na ₂ CO ₃ is 1.05 times the amount required for neutralizing the free acid, that is, per ton of waste liquid.
30.6 kg was added. This neutralized solution was sent to the decomposition distillation column 33 (strong alkali treatment tank) using a strong alkali. A 47% aqueous solution of NaOH 46 was replenished by a line mixer (not shown) so that the liquid in the middle decomposition distillation column always maintained pH> 12.5. The supply amount of NaOH at this time was 26 kg / h, and the average residence time in the column was 30 minutes, and the temperature was maintained at 100 ° C. with steam for heating. Through the volatile component conduit 51 connected to the top of the tower, a total of about 10.3 kg / h of lower alcohol produced by hydrolysis of methanol and ester produced by the Cannizzaro reaction and a small amount of water were sent to the incinerator 35. . The alkaline wastewater depleted in low boiling point decomposition products is sent to the condenser 34 by a conduit 49,
It was concentrated under reduced pressure at 60 mmHg. Concentrated water obtained here 45 of 80
The COD value of 0 kg / h was 300 ppm or less, and the activated sludge could be sufficiently treated. Wastewater is a concentrated liquid with a solid content of about 55%.
200 kg / h was spray-incinerated together with the auxiliary fuel LPG 8 kg / h in the incinerator 35 through the concentrated liquid supply pipe 50. The air supplied to the furnace including that for spraying was 480 Nm ³ / h, the air ratio was 1.2, the incineration temperature was 950 ° C, and the residence time was 1.5 seconds. Combustion gas containing sodium carbonate is rapidly cooled to about 90 ° C. with water in a quench tank 37 to form a slurry containing sodium carbonate and sodium bicarbonate in a ratio of about 2: 1. A mixture of sodium carbonate and sodium bicarbonate is separated from this slurry at a rate of 0.58 kg mol / h as Na content and sent to the neutralization tank 32. The separation step is not shown in the figure (the figure shows the case where the solution is sent to the neutralization tank after heat exchange). The remaining Na content of 0.64 kg / h is removed as carbonates (in the case of a solution, from the purge line 39). Therefore, this amount and the loss amount of 0.01 kg mol / h in total of 0.65 kg mol / h may be supplied from the NaOH supply pipe 46 in the form of NaOH. According to this example, the amount of caustic soda used is halved.

〔The invention's effect〕

INDUSTRIAL APPLICABILITY The present invention effectively utilizes the difference in reactivity of organic compounds contained in a dilute wastewater discharged from a chemical reaction process such as a gas-phase oxidation reaction of hydrocarbons and the like, in which byproducts of various lower organic compounds are inevitable. Then, the pollution of the wastewater can be increased and the auxiliary fuel can be saved, and the incinerator can be made compact.
Furthermore, the amount of expensive chemicals used can be reduced, which is extremely useful in industry.

[Brief description of drawings]

1 and 2 show flow charts illustrating embodiments of the first and second aspects of the present invention, respectively. 1 ... First evaporation tower, 2 ... Circulation pump 3 ... Heater, 4 ... Reaction tank 5 ... Pump, 6 ... Second evaporation tower 7 ... Circulation pump, 8 ... Heater 9 ... Concentrator, 10 …… Concentrator 11 …… Vacuum generator, 12 …… Original wastewater 13 …… Top gas, 14 …… Top gas 15 …… Effluent, 16 …… Caustic soda 17 …… Reaction liquid, 18 ...... Air 19 ...... effluent, 20 ...... conduit 21 ...... concentrated water, 22 …… concentrated liquid 31 …… waste water supply pipe, 32 …… neutralization tank 33 …… strong alkaline treatment tank, 34 …… concentrator 35 …… Incinerator, 36 …… Auxiliary fuel 37 …… Quenching tank, 38 …… Makeup water 39 …… Purge line, 40 …… Circulation line 41 …… Exhaust gas duct, 42 …… Drain 43 …… Exhaust duct, 44 …… Condenser 45 …… Concentrated water, 46 …… Strong alkali 47 …… Vent pipe, 48, 49, 50, 51, 54 …… Conduit 52 …… Vacuum line, 53 …… Heat exchanger S …… Steam

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Rie Tatesen, Rie Tatesen 3-17-1 Motomachi, Urawa-shi, Saitama Prefecture (72) Hiro, Yoshida 992-1 Nishioki, Okihama, Aboshi-ku, Himeji-shi, Hyogo Nihon Catalytic Chemical Co., Ltd. Himeji Manufacturing Co., Ltd. In-house (56) Reference JP-A-54-90868 (JP, A)

Claims (3)

[Claims] Upon 1. A process the waste water containing at least one compound selected from volatile organic acids and C ₄ following a lower alcohol ester and formaldehyde organic acids, as an additive to pH12 or an alkaline substance to the waste water A non-volatile compound and a volatile compound are induced by a reaction, and at least a part of the volatile compound is vaporized and removed, and the waste water is further concentrated and then incinerated, which includes an organic acidic substance. Waste water treatment method. 2. A method wastewater containing at least one compound selected from a lower alcohol ester and C ₄ following aldehydes of volatile organic acids and C ₄ following organic acids, after treatment with an alkaline substance In the method of incineration after concentration, after neutralizing the free organic acid in the wastewater using an alkali carbonate, pH12 or more, preferably heated by adding caustic alkali necessary to maintain pH13 or more, Residual esters and / or aldehydes are converted to high-boiling substances or non-volatile substances and volatile substances, at least a part of the volatile substances formed is vaporized and removed, and then water is evaporated to be incinerated as concentrated waste water. A method for treating wastewater containing an organic acidic substance, characterized in that the required amount of ash produced by incineration or a new alkali carbonate is used for the neutralization treatment. 3. Treatment of wastewater containing an organic acidic substance according to claim 1 or 2, wherein a first evaporation step for preliminarily evaporating the volatile components of the wastewater is added before adding the alkaline substance. Method.