JPS6121718B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating alkaline waste liquid containing alkali sulfide etc. generated from chemical factories such as petroleum refining, petrochemical, barium salt, cellophane, and rayon manufacturing, and in particular, the present invention relates to a method for treating alkaline waste liquid containing alkali sulfide, etc., generated from chemical factories such as petroleum refining, petrochemical, barium salt, cellophane, and rayon manufacturing. The present invention relates to a method for recovering valuable components in the waste liquid at the same time as treating the waste liquid.

The above alkaline waste liquid is generated or discharged from various alkali cleaning processes for the purpose of desulfurization in chemical factories such as petroleum refining, petrochemicals, and cellophane manufacturing. The waste liquid is difficult to treat because it not only contains alkali or caustic alkaline components, but also alkali-soluble organic substances dissolved in the components to be cleaned (hereinafter, such waste liquid is referred to as alkaline waste liquid). ). Conventionally, in order to treat such alkaline waste liquid for pollution prevention, its alkaline content is neutralized with acid and then dissolved.
An acidic solution (usually pH 3) is used to reduce H ₂ S content.
Excess acid is added until the solution reaches ~4), and further stripping is performed, but since there is a trace amount of H ₂ S dissolved in this acidic solution, oxidation with an oxidizing agent is necessary to completely render it harmless. It is treated by carrying out methods such as treatment, activated carbon treatment, activated sludge treatment, etc. singly or in combination. On the other hand, H ₂ S generated when excessive acid is added can be used for sulfur recovery, sulfuric acid recovery,
Detoxification is being attempted by recovering gypsum, or in some cases by absorbing it into an alkaline solution and recovering it again as sulfide.

In this way, pollution control treatment of alkaline waste liquid is carried out in two ways.
Next, tertiary treatment is required, which complicates the treatment process, resulting in an increase in equipment costs and operating expenses, and those involved are constantly struggling to find countermeasures.
Establishment of an inexpensive and easy treatment method is desired.

In addition, a method for recovering alkaline hydrosulfide solution by absorbing and reacting H ₂ S gas has been developed by industrializing the alkaline waste liquid utilization treatment method previously developed by the present inventors (Patent No. 401527, No. No. 418472, no.
No. 638775, No. 800401, No. 900772) have been effective.

Furthermore, the present inventors have also provided a technique for recovering an alkaline hydrosulfide solution by using the alkaline waste liquid as a cleaning chemical when alkali cleaning gases containing H ₂ S and CO ₂ are used as an effective use of the alkaline waste liquid as described above. (Refer to Special Publication No. 1971-71604).

These methods use H ₂ S as the gas source used to treat alkaline waste liquid, with the aim of recovering solutions whose main component is alkali hydrosulfide.
The present invention was developed as a result of research into a method for promoting the reaction of H ₂ S and suppressing the reaction between acidic gases represented by CO ₂ gas accompanying H ₂ S and alkaline components. is a research project that fundamentally changes that idea and focuses on the use of CO ₂ gas, which was considered an unnecessary or harmful component in the conventional method described above, and pursues the possibility of recovering hydrosulfides and carbonates at the same time. started,
It was completed by discovering the processing conditions.

That is, in the treatment of alkaline waste liquid containing alkali sulfide, alkali carbonate, and alkali hydrosulfide or caustic alkali, the waste liquid is reacted with carbon dioxide gas or a gas containing carbon dioxide gas to form alkali hydrosulfide and alkali carbonate as main components. The present invention relates to a method for treating alkaline waste liquid, which is characterized by recovering a solution.

Hereinafter, the present invention will be explained along with the circumstances that led to its completion.

The present inventors use CO ₂ as an acid gas source for treating alkaline waste liquid, which is cheaper and more easily available than H ₂ S, and treat alkaline waste liquid with CO ₂ gas. As a result of the experiment, as the absorption reaction progresses, the temperature inside the system gradually increases, eventually reaches a peak, and then gradually decreases, and at the same time, in response to this change in phenomenon, the component composition within the reaction system changes to alkali hydrosulfide, It was confirmed that after passing through a state in which the main component is alkali carbonate, there is a gradual transition to a decomposition phenomenon of alkali hydrosulfide that generates H ₂ S.

In other words, the reaction between a solution containing alkali sulfide, alkali carbonate, and alkali hydrosulfide and _CO2 gas is
In the initial stage, all CO ₂ mainly reacts only with alkali sulfide to produce alkali hydrosulfide and alkali carbonate, and heavy reactions such as the reaction between alkali hydrosulfide and CO ₂ gas and the reaction between alkali carbonate and CO ₂ gas occur. Although the reaction leading to the formation of carbonate does not proceed or is very suppressed, and the temperature of the reaction system at this stage increases significantly due to the heat of reaction between the alkali sulfide and CO ₂ gas, this reaction does not terminate. In the next reaction stage that begins to proceed later, the temperature rise in the reaction system stops or decreases.

Therefore, the present inventors used _Na2S (15%), NaSH
(24%), Na ₂ CO ₃ (20%) were adjusted to remove CO ₂ while keeping the CO ₂ gas supply constant.
The absorption reaction was attempted.

The reaction in this reaction system can generally be assumed to have the following reaction formula.

2Na ₂ S＋CO ₂ +H ₂ O→2NaSH＋Na ₂ CO ₃ ... NaSH＋CO ₂ +H ₂ O→NaHCO ₃ +H ₂ S ... Nb ₂ CO ₃ +CO ₂ +H ₂ O→2NaHCO ₃ ... At this time, in Na ₂ S solution, the reaction formula is An increase in weight of approximately 4.1%, which is close to the theoretical increase due to the increase in weight, was observed, and the temperature within the system increased by 13°C, indicating a clear peak in temperature rise. In addition, in the NaSH solution and Na ₂ CO ₃ solution, the weight increase was 0.3% and 0.8%, and the temperature increase in the system was 1.3°C and 1.5°C, respectively, with no clear peak state observed.

As described above, there is a significant difference in the reaction conditions of the CO ₂ gas absorption reaction for these solutions between the Na ₂ S solution and the NaSH, Na ₂ CO ₃ solution. Alkaline sulfide and
The reaction with CO ₂ preferentially and selectively proceeds rapidly with significant heat generation, increasing the production of alkali hydrosulfide and alkali carbonate in the reaction system, and decreasing consumption of alkali sulfide. This is clear from the analysis of the composition of the liquid in the reaction system near the highest temperature point, which shows that the main components are alkali hydrosulfide and alkali carbonate (see Example 1). ).

Furthermore, when an alkaline waste liquid containing alkali-soluble organic substances is treated, the behavior of the soluble organic substances is such that the soluble organic substances eventually separate clearly with a clouding phenomenon immediately before the system temperature reaches its maximum point. This phenomenon is the result of a change in the composition of the system due to the absorption and reaction of CO ₂ gas and a change in the composition of the soluble organic matter itself, resulting in insolubilization.
It is presumed that the separation proceeded from within the aqueous solution system. In any case, practically the entire amount separates and floats (see Example 1 below).

Next, the present inventors conducted various experiments to clarify the relationship between the composition of alkaline waste liquid and the amount of _CO2 , which is one of the conditions necessary for implementing the present invention, and found that the amount of CO2 required for the present invention was ₂ is a theoretical amount equivalent to only alkali sulfide and caustic alkali, regardless of other components in the alkaline waste liquid, and when implementing this method, it is necessary to absorb 95 to 105% of the theoretical amount of CO ₂ gas. It was confirmed that the object of the present invention could be achieved by causing the reaction.

Therefore, in order to carry out the treatment of alkaline waste liquid according to the present invention, it is sufficient to absorb and react CO ₂ gas in an amount corresponding to the alkali sulfide and caustic alkali content in the alkaline waste liquid. Particular attention must be paid when carrying out the process continuously.In practice, alkali sulfide,
This can be easily adjusted by supplying CO ₂ corresponding to the amount of caustic alkali, or by supplying alkaline waste liquid containing the amount of alkali sulfide or caustic alkali corresponding to the amount of CO _2. This can be done by using existing plants or known methods. It can be easily carried out by the method described above, and its effects are truly great.

In addition, when a large amount of caustic alkali exists in the alkaline waste liquid, a large amount of alkali carbonate is generated by CO ₂ gas treatment, and a large amount of alkali carbonate crystals are deposited in the reaction system. In order to make the solid-liquid separation operation or the solid-liquid separation after the completion of the reaction extremely difficult, alkali hydrosulfide which has been treated and recovered from alkaline waste liquid in advance by the method of the present invention, or alkali hydrosulfide produced by other methods. After adding and mixing the caustic alkali in an amount equivalent to or more than the caustic alkali to convert the caustic alkali into alkali sulfide, CO ₂
It is desirable to allow the reaction to proceed while keeping the treatment liquid in a solution state by gas treatment.

In addition, if a slurry of alkali carbonate (including a mixture with alkali bicarbonate) is generated in the system or is expected, it can be easily treated by adding alkali waste liquid or alkali hydrosulfide in advance or each time. Not only can it be handled easily, but it can also be easily handled by common means such as heating and dilution.

In other words, when recovering alkali hydrosulfide and alkali carbonate from alkaline waste liquid containing alkali sulfide, alkali carbonate, and alkali hydrosulfide or caustic alkali, if the absorption reaction of CO ₂ gas is carried out in batches, the temperature in the system will rise. Near the peak, the liquid composition becomes a composition in which alkali hydrosulfide and alkali carbonate are the main components, and there is no or very little alkali sulfide, and the absorption reaction by CO ₂ gas takes precedence over caustic alkali and alkali sulfide. The reaction proceeds selectively and with considerable heat generation until most of the alkali sulfide is consumed.

Furthermore, if the absorption reaction in the system continues even after the temperature rise reaches its peak, the temperature in the system stops rising and then a temperature decrease phenomenon due to heat radiation is observed, while the temperature in the system is compared to the initial reaction described above. A marked change occurs.

A large amount of carbonate was crystallized, and when the residual liquid composition of the slurry was subjected to an analytical test, it was confirmed that the alkaline carbonate content had also decreased.

From these experimental results, in order to obtain a mixed treatment solution of alkali hydrosulfide and alkali carbonate, which is the objective of the present invention (precipitation of carbonate slurry makes operation of the absorption reaction step difficult), the conditions of the reaction system must be adjusted as described above. It is important to take the reaction in the reaction formula as the main reaction and provide a means to suppress the reaction in (batch-type absorption reactions do not require such strict adjustment).

Therefore, depending on the method adopted for the CO ₂ gas absorption reaction for these alkaline waste liquids, for example, in the case of a batch type, it is easy to meet the purpose by preparing simple instrumentation such as continuous temperature measurement within the system. In the case of continuous processing,
Calculate and supply CO ₂ gas corresponding to alkali sulfide and caustic alkali content in alkaline waste liquid, or
A mixed solution containing alkali hydrosulfide and alkali carbonate as the main components (a small _amount of carbonate (which may contain slurry) can be easily recovered.

Next, the CO ₂ gas source used in the method of the present invention includes not only industrial CO ₂ but also gas containing at least 5% or more preferably 10% or more of CO ₂ , such as
It is very easy to secure a gas source because combustion exhaust gas such as LPG, city gas, kerosene, diesel oil, and heavy oil, as well as cracked gas, can be used. In addition, although the influence of coexisting gases such as SO ₂ and SO ₃ that coexist with these CO ₂ -containing gases depends on their content, in the case of general combustion gases, alkali hydrosulfide and carbonate Although there is an impact on the alkali yield,
It has been confirmed that the effect on the absorption reaction is minimal. It has also been confirmed that when using a CO ₂ -containing gas that coexists with H ₂ S, this can be easily achieved by reducing the amount of CO ₂ used corresponding to the amount of H ₂ S.

As is clear from the above explanation, the absorption reaction conditions (processing conditions) according to the present invention can be achieved by using general gas-liquid contact equipment and gas absorption reaction equipment, except for the setting and adjustment of reaction conditions in the absorption stage of the reaction system. It is possible to carry out the process under simple operating conditions, such as at room temperature and pressure, or under heating and pressurization.

Furthermore, when implementing the present invention, it is necessary to take into account the changes in system temperature and/or the alkali sulfide content and caustic alkali content in the alkaline waste liquid as described above.
It can be easily adjusted by adjusting the supply amount of CO ₂ gas or the supply amount of alkaline waste liquid (alkali sulfide and/or caustic alkali content) based on the CO ₂ gas content, and can be adjusted depending on the implementation. The existing equipment and instrumentation can be simplified.

The alkaline waste liquid treated by the method of the present invention is a solution mainly composed of alkali hydrosulfide or alkali carbonate, or a slurry of alkali carbonate or alkali bicarbonate alone or in combination. In the latter case, if necessary, the slurry is separated by a conventional method, and each solution is concentrated by a conventional method. If alkali carbonate is precipitated during concentration, the precipitate (mainly carbonate) is separated in a timely manner and recovered as an alkali hydrosulfide solution with a low alkali carbonate content. On the other hand, since the separated alkali carbonate has a small amount of alkali hydrosulfide attached thereto, it is recovered as an alkali carbonate by a conventional method such as washing with warm water and drying.

Therefore, the present invention deals with alkaline waste liquid generated from chemical factories such as petroleum refining, petrochemical, barium salt, cellophane, and rayon manufacturing, that is, alkali sulfide,
Waste liquid containing alkali carbonate, alkali hydrosulfide or caustic alkali is converted into CO ₂ gas or LPG, kerosene, diesel oil,
Such as combustion exhaust gas such as heavy oil, cracked gas, etc.
To recover a solution mainly composed of alkali hydrosulfide or alkali carbonate, or a solution mainly composed of alkali hydrosulfide or alkali carbonate with a slurry mainly composed of alkali carbonate, by processing using _CO2- containing gas. It can be said that this is a new and economical method for treating alkaline waste liquid that has made it possible. Furthermore, depending on the treatment method of the recovered solution, it is possible to recover alkali hydrosulfide as a high-purity alkali hydrosulfide solution or flake-like (including solids) high-purity industrial chemicals, and to simultaneously recover carbonates. This can be said to be a method for treating alkaline waste liquid that can be expected to have multiple effects in terms of pollution control, economy, and resource utilization.

Next, the present invention will be specifically explained using examples.

Example 1 2.0 kg of alkaline waste liquid generated from an oil refinery as shown in Table 1 was collected, and subjected to batch processing at a pressure of 0.5 kg/cm ² G and at room temperature to high-purity carbon dioxide gas (commercially available liquefied carbon dioxide gas). When the temperature rise in the system reached its maximum (see the change in system temperature in the figure), the supply of carbon dioxide gas was stopped, and the organic matter was separated by the standing method, as shown in Table 2. Processing liquids mainly composed of alkali hydrosulfide and alkali carbonate, such as
2.1Kg was recovered.

Table 1 Alkaline waste liquid composition NaSH 7.66% Na ₂ S 12.79% Na ₂ CO ₃ 1.45% Na ₂ SO ₃ 0.35% Na ₂ S ₂ O ₃ 0.20% Organic matter 0.06% Table 2 Treated liquid composition NaSH 14.90% Nba ₂ S 1.32% Na ₂ CO ₃ 8.62% Na ₂ SO ₃ 0.55% Na ₂ S ₂ O ₃ 0.48% Organic matter Trace This treated solution is intermediately concentrated by a conventional method, the precipitated alkali carbonate is filtered out, and the hydrosulfurization is performed as shown in Table 3. An alkaline solution was obtained. This alkali hydrosulfide was further concentrated and solidified, and the composition was as shown in Table 4. These alkaline hydrosulfide liquids and solid substances are commercially available alkaline hydrosulfide liquids as industrial chemicals.
Compared to solid products (the compositions of which are shown in Tables 5 and 6), there was no color loss.

Furthermore, the over-recovered alkali carbonate was washed with warm water and dried at about 120°C, yielding an alkali carbonate powder with a purity of about 97%.

This alkali carbonate is an alkali source for flue gas desulfurization.
It was found to be fully usable as a neutralizing agent for acidic wastewater and as a raw material for high-purity alkali carbonate.

Table 3 Hydrosulfide alkaline liquid composition NaSH 34.13% Na ₂ S 1.92% Na ₂ CO ₃ 0.37% Na ₂ SO ₃ 0.46% Na ₂ S ₂ O ₃ 0.31% Table 4 Solid matter composition NaSH 67.72% Na ₂ S 3.89% Na ₂ CO ₃ 0.67% Na ₂ SO ₃ 0.54% Na ₂ S ₂ O ₃ 0.51% Table 5 Composition of commercially available alkaline hydrosulfide solution NaSH 28.77% Na ₂ S 1.58% Na ₂ CO ₃ 0.78% Na ₂ SO ₃ 0.48% Na ₂ S ₂ O ₃ 0.29% Table 6 Composition of commercial solids NaSH 67.42% Na ₂ S 4.29% Na ₂ CO ₃ 0.85% Na ₂ SO ₃ 0.63% Na ₂ S ₂ O ₃ 0.49% Example 2 Petroleum as shown in Table 7 2.0 kg of alkaline waste liquid generated from a chemical factory was collected and treated in a batch process at room temperature and pressure using CO ₂ -containing gas, which was obtained by cooling the heavy oil boiler combustion exhaust gas shown in Table 8 to room temperature, condensing water, and removing dust. After the temperature inside the system reached its maximum, the absorption reaction was carried out until a decrease was observed, and the organic matter was separated by the same standing method as in Example 1, and the alkali carbonate and alkali hydrosulfide components as shown in Table 9 were obtained. Approximately 2.1 kg of the main component solution was recovered.

Table 7 Alkaline waste liquid composition Na ₂ S 15.78% NaOH 1.15% Na ₂ CO ₃ 1.25% Na ₂ SO ₃ 0.41% Na ₂ S ₂ O ₃ 0.20% Table 8 Combustion exhaust gas composition CO ₂ 9.9Vol% O ₂ 4.7Vol% Moisture 10.5 Vol% SOX 840ppm NOx 130ppm Organic matter 0.06% N ₂ remaining Table 9 Treatment solution composition NaSH 10.13% Na ₂ S 0.95% Na ₂ CO ₃ 11.04% Na ₂ SO ₃ 0.49% Na ₂ S ₂ O ₃ 0.35% Organic matter Trace This treatment solution The liquid concentrated and filtered by the same treatment method as in Example 1 is an alkali hydrosulfide solution of the same quality as in Example 1, and the over-recovered alkali carbonate is also concentrated by the same treatment method as in Example 1. We were able to recover quality alkali carbonate.

Example 3 The alkaline waste liquid shown in Table 10 was treated with commercially available carbon dioxide gas in the following manner.

A glass tube with an inner diameter of 70 to 71 mm and a length of 1500 mm is filled with a Lutschig ring made from a glass tube with an inner diameter of 5 mm and a length of 10 to 15 mm in the center of the approximately 700 mm tube, and a gas inlet at the bottom, liquid reservoir, and circulation. Using a carbon dioxide absorption reaction tower equipped with a pump, a liquid discharge port, a circulating liquid inlet at the top, a cleaning gas outlet, and a cleaning liquid inlet to the circulation line, carbon dioxide is supplied from the bottom gas inlet at a rate of 500 Nml/min. Then, while supplying an amount of alkaline waste liquid equivalent to carbon dioxide gas to the operating circulation system, an absorption reaction between the alkaline waste liquid and carbon dioxide gas is carried out in the gas-liquid contact part, and the liquid is discharged from the lower liquid outlet as shown in Table 11. Approximately 1.5/hr of treatment solution was collected.

Table 10 Alkaline waste liquid composition NaSH 6.04% Na ₂ S 12.44% Na ₂ CO ₃ 1.63% Na ₂ SO ₃ 0.32% Na ₂ S ₂ O ₃ 0.26% Table 11 Treated liquid composition NaSH 14.05% Na ₂ S 0.12% Na ₂ CO ₃ 9.04% Na ₂ SO ₃ 0.54% Nba ₂ S ₂ O ₃ 0.35% These examples are merely examples for specifically explaining the present invention, and the technical idea of the present invention can be modified and improved within the limits. Of course, this does not restrict the technical scope of the present invention in any way.

As explained above, the present invention is applicable to alkaline waste liquids generated from petroleum refining, petrochemical, chemical factories producing barium salt, cellophane, rayon, etc., that is, waste liquids containing alkali sulfide, alkali carbonate, alkali hydrosulfide, or caustic alkali. Treatment is carried out in a batch or continuous manner using carbon dioxide gas or combustion gas such as LPG, city gas, kerosene, diesel oil, heavy oil, etc., or carbon dioxide-containing gas such as cracked gas, and if necessary, the organic matter is left standing. This is a method for treating alkaline waste liquid, in which a solution containing alkali hydrosulfide and alkali carbonate as the main components is recovered by separating the liquid by filtration, and then recovering a solution containing alkali hydrosulfide and alkali carbonate as the main components.

When the method of the present invention is implemented, the following effects can be expected.

Since the equipment structure for implementation is simple, the construction cost of the equipment is not only low, but also because the operation of the equipment can be easily adjusted, the operation process is simple and the operating cost is low, resulting in great economic synergy.

Alkali hydrosulfide and alkali carbonate can be recovered and reused, preventing the loss of valuable alkali resources, and the economic effects are significant, along with the effects of pollution prevention measures.

[Brief explanation of the drawing]

The attached drawing shows an example of the change in system temperature during CO ₂ gas treatment of alkaline waste liquid.

Claims (1)

[Scope of Claims] 1. When alkaline waste liquid containing alkali sulfide, alkali carbonate, and alkali hydrosulfide or caustic alkali is treated in a batch manner, carbon dioxide gas or carbon dioxide gas-containing gas is added to the waste liquid so that the temperature inside the system increases. The method is characterized by recovering a solution containing alkali hydrosulfide and alkali carbonate as main components by reacting until the mixture becomes constant or until a small amount of alkali carbonate or a small amount of mixed crystals of alkali carbonate and alkali bicarbonate are precipitated. A method for treating alkaline waste liquid. 2. The method according to claim 1, wherein the alkaline waste liquid dissolves alkali-soluble organic substances. 3. During the absorption reaction between alkaline waste liquid containing caustic alkali and carbon dioxide gas or gas containing carbon dioxide, the caustic alkali is converted into alkali sulfide by adding an amount of alkali hydrosulfide equivalent to or more than the caustic alkali. 3. The method according to claim 1 or 2, characterized in that the method comprises converting. 4 When continuously treating alkaline waste liquid containing alkali sulfide, alkali carbonate, and alkali hydrosulfide or caustic alkali, carbon dioxide or carbon dioxide-containing gas is added to the waste liquid to remove the alkali sulfide and/or caustic alkali content in the waste liquid. is adjusted to 95% to 105% of the amount required for carbonate production, and the waste liquid is reacted with carbon dioxide gas or carbon dioxide-containing gas to create a solution whose main components are alkali hydrosulfide and alkali carbonate. A method for treating alkaline waste liquid, characterized by recovering. 5. The method according to claim 4, wherein the alkaline waste liquid dissolves alkali-soluble organic substances. 6. During the absorption reaction between alkaline waste liquid containing caustic alkali and carbon dioxide gas or gas containing carbon dioxide, the caustic alkali is converted into alkali sulfide by adding alkali hydrosulfide in an amount equivalent to or more than the caustic alkali. The method according to claim 4 or 5, characterized in that the method comprises converting.