JPS6022997B2 - How to use wastewater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides wastewater discharged from a process for producing acrylic acid by catalytic gas phase oxidation reaction and a process for producing acrylic acid ester by esterifying nucleic acrylic acid with alcohols. The present invention relates to a method for treating and supplying the obtained water to the above process again for use.

To explain in more detail, the present invention involves adding an alkaline substance to the wastewater containing organic matter discharged from the above two processes to treat it, leading this wastewater to a distillation column, and removing light boiling point substances from the top of the column. , the can liquid is further evaporated and concentrated, and the resulting concentrated wastewater of high-boiling organic matter is led to a waste liquid combustion device together with the previous light-boiling point fraction, where it is combusted and rendered harmless, and the water as the evaporated fraction is directly used in the above two processes. This provides a method for recycling and reusing wastewater. In the process of producing acrylic acid by catalytic gas phase oxidation of propylene or acrolein, a considerable amount of water vapor is mixed with propylene or acrolein in the oxidation reaction, and along with this water vapor, the water produced by the reaction is also produced in the reaction. It is condensed and collected together with the main product, acrylic acid, in the substance collection equipment, and usually 20
Recovered as ~60% by weight aqueous acrylic acid solution. Moreover, the collection operation described above is usually performed by liquid-liquid contact with cooling water. This aqueous solution is then subjected to an extraction separation process to separate acrylic acid, and is then discharged as a large amount of waste water.

In addition to unrecovered acrylic acid, this wastewater usually contains organic acids such as acetic acid, acrolein, acetaldehyde, and their derivatives, as well as organic solvents for extraction, polymerization inhibitors, polymers, etc. in a total of 1 to 5 weight. Contains %. In addition, by directly subjecting the acrylic acid obtained by separation and purification to an esterification reaction with alcohols such as methanol, ethanol, propanol, butanol, and 2-ethylhexanol, contamination from water and raw materials produced by the esterification reaction can be avoided. The resulting water is contained in the esterification reaction products, and these are discharged as wastewater. This wastewater usually contains unreacted acrylic acid and alcohol, as well as acrylic acid ester, propionic acid ester, polymers, polymerization inhibitors, and the like. Furthermore, in the process of producing esters of butyl acrylate and 2-ethylhexyl that use sulfuric acid or organic sulfonic acids (such as para-toluenesulfonic acid) as esterification catalysts, in addition to the above-mentioned Sosei Water, an acid catalyst for neutralization treatment is used. Alkaline aqueous solution and washing water will also be mixed in, resulting in wastewater. The above-mentioned wastewater contains a considerable amount of organic matter and cannot be discharged as is, and in some cases has odor and color, so even the activated sludge method may not be able to completely treat these wastewaters. Therefore, complete treatment of these wastewaters has been considered to require considerable processing costs. The present inventors have found that it is advantageous to adopt a method of concentrating wastewater and incinerating it for treatment of these wastewaters, and that it is economically advantageous to use the water obtained by treating the wastewater again with the acrylic acid. The present invention was researched and completed with the aim of using it in the acrylic acid ester manufacturing process, thereby completing a complete Claude system.

Therefore, one of the objects of the present invention is to recover water from treated wastewater, and to recover water to such an extent that it can be reused in the acrylic acid production process or acrylic acid ester production process. The purpose of the present invention is to provide a method for utilizing wastewater that has been repurified and recovered.

In particular, the wastewater treatment process according to the present invention is a process in which acrylic acid is produced by catalytic gas phase oxidation of propylene or acrolein, and an acrylic acid ester production process, in which the concentration of combustible organic matter in the discharged wastewater is relatively high. Advantageously applied to wastewater. That is,
The present invention involves adding an alkaline substance to wastewater discharged in the process of producing acrylic acid by catalytic gas phase oxidation of propylene or acrolein, and in the process of producing acrylic acid ester by esterifying the obtained acrylic acid. 4 while maintaining the wastewater alkaline.
After heat treating the powder for 5 hours at a temperature of 0 to 10 psi, it is supplied to a distillation column to extract 5 to 2% by weight of the waste water, and the resulting bottom liquid is sent to an evaporator where it is heated to 10 % by weight. Concentrate the liquid to ~2% by weight, lead the resulting concentrated liquid together with the distillate from the previous distillation column to a waste liquid combustion device for combustion treatment, and use the crab water obtained from the evaporator to process the above-mentioned acrylic acid production process. The present invention also provides a method for utilizing wastewater by recycling and reusing it in an acrylic acid ester manufacturing process.

The above-mentioned method of the present invention will be explained in more detail below with reference to its embodiments.

The wastewaters from the acrylic acid process and the acrylic acid ester process that are treated by the present invention can, of course, be treated separately, or can be mixed and used for treatment.

This wastewater is subjected to a so-called neutralization treatment, that is, a heat treatment at 40 to 100° C., preferably 50 to 7 pi for 20 minutes to 5 hours, while maintaining the pH at 8 to 13, preferably 9 to 12, with an alkaline substance. The alkaline substances used include alkali metal hydroxides such as potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, and sodium bicarbonate, and alkali metal hydroxides such as carbonates, bicarbonates, and calcium hydroxide. Examples include things. Any of these can be used in the form of an aqueous solution or an aqueous slurry, but when a large number of polymers are present in the target wastewater, the use of alkali metals is not suitable because of the formation and precipitation of precipitates. If the condition for alkaline treatment of wastewater is less than 8, the alkaline treatment will be insufficient, and when it is concentrated in the evaporator later, there will be a lot of organic matter in the water that comes out of the crabs, and if it is left as it is, it will not be recycled. It is impossible to use it, and it is not preferable to discharge it as waste water as it is because it causes problems of environmental pollution. Furthermore, the same results may occur if the processing time is too short or the processing temperature is too low, which is not desirable.
On the other hand, even if the pH is set to 13 or higher, the same effect cannot be obtained, so it is not necessary to set the pH to 13 or higher in terms of economics and process operation.

Although it is possible to carry out alkali treatment at a temperature exceeding 100 qo, that is, under pressure and heat, such conditions are unnecessary and not particularly advantageous within the scope of the present invention. The alkaline treated wastewater is then fed to a distillation column.

As the distillation column, a plate column such as a packed column, a bubble column, a sheep column, etc. is preferably used. The supplied wastewater is distilled in a column having a column with a number of theoretical plates of 5 or more at a reflux ratio of 2 to 10, and 5 to 2% by weight, preferably 5 to 1% by weight of the supplied wastewater is output. The cut crab meat contains flammable organic matter with a low boiling point, and is supplied to a waste liquid combustion device and incinerated together with a liquid containing high-boiling combustible organic matter, which is concentrated in the next step. The distillation column liquid is fed to the evaporator for concentration operation.

One or more evaporators are used in series, and the operating conditions are a temperature of 40 to 80°C and a temperature of 50 to 40°C.
Under reduced pressure of 0Q Hg, a concentration ratio of 5 to 10 is adopted.

The can liquid concentrated here is supplied to a waste liquid combustion device and rendered harmless through incineration treatment.On the other hand, the water obtained by distillation is recovered water that contains almost no organic matter, and is COD (Mn
) can be easily obtained with less than 300 feet of COD (Mh), and especially when COD (Mh) can be obtained as recovered water of about 100 feet as shown in the example below, it can be used directly as water for each process, especially for collecting acrylic acid. It can be used as cooling water supplied to the equipment and as washing water in the acrylic acid ester manufacturing process. Of course, the contamination of organic matter is unavoidable, and the recommended method for removing this as much as possible is to pass it through an adsorption layer such as activated carbon. Note that the waste liquid combustion equipment can also use a normal incineration method, such as simply incinerating it with heavy oil or LPG.
Adoption of a submerged combustion method, particularly an underwater combustion method, is advantageous in the method of the present invention. Next, an example of an embodiment of the method of the present invention will be explained with reference to the attached flow sheet.

The wastewater enters the alkaline neutralization tank 101 through line 2, and the pH is maintained within a certain range by alkaline water added through line 2. The neutralization tank 101 is equipped with a heating device to maintain the temperature within a constant range, and is designed to maintain a constant residence time. The neutralization tank 101 is equipped with a frame expansion machine in order to completely carry out the pretreatment by alkali IJ'. The wastewater that has been pretreated by neutralization with alkali passes through line 3 and is supplied to distillation column 102, and the light boilers are sent to underwater combustion device 103 via lines 4 and 8. In addition, wastewater from the can section is transferred from line 5 to evaporator 105.
The water vapor is supplied to and evaporated under reduced pressure, and the water vapor passes through line 15 and is condensed in condenser 106, and condensed water is obtained from line 17. This water is reused as water for each process. A line 18 is a vacuum line for the evaporator 105, and is used for depressurization by an ejector and a vacuum pump. line 1
6 provides condensed water of steam as a heat source for the evaporator 105, which can also be used as water for each process. The concentrated liquid in the evaporator 105 is supplied to the evaporator 104 through the line 13. Further, the water vapor coming out from the line 12 serves as a heat source for evaporation in the evaporator 105. Condensed water from line 14 is returned to the bottom of underwater combustion device 103. Further, combustion waste gas is discharged from line 19. This is cleaned and then purged as necessary. Concentrated wastewater obtained from line 10 is mixed with wastewater from line 4 and supplied to the upper part of underwater combustion device 103 from line 8, where it is completely combusted with fuel from line 6 and an oxygen source (air) from line 7. The incinerated wastewater is collected in a water tank at the bottom of the underwater combustion furnace, and is discharged through a line 11 as harmless wastewater that does not contain organic matter. Steam and combustion gas are discharged from the line 9 and serve as a heat source for the evaporator 104. Water is then supplied from the line 20 as make-up water to the underwater combustion device 103. This wastewater treatment program. In the process, wastewater 1 is discharged as condensed water 17, condensed water 16, and treated wastewater 11, and the condensed water can be reused in each process individually or after mixing, and the treated wastewater is detoxified and is therefore necessary. Depending on the situation, solid matter can be removed and discharged, and a part of it can be reused for preparing an alkaline aqueous solution. The wastewater that is advantageously applied to the above flow sheet has a more specific treatment method as described in the examples below, but the wastewater shown in the examples below is generated according to the following process. This is what I did. Propylene is passed through two stages of catalyst tanks to produce acrylic acid, the resulting acrylic acid, water vapor,
The reaction product gas, which mainly contains nitrogen gas, oxygen, carbon dioxide, unreacted propylene, etc., is led to the acrylic acid collector.

In the collection device, cooled collection water is supplied together with a polymerization inhibitor,
Acrylic acid from cold soot is collected with condensed water to obtain an acrylic acid aqueous solution. This aqueous solution is then introduced into an extraction device where it is treated with an extraction solvent mainly consisting of ethyl acetate to separate the aqueous layer as yuzu residue. This aqueous layer is subjected to a distillation operation in an extraction solvent recovery column to separate and recover the solvent, and it contains small amounts of unrecovered organic acids such as acrylic acid and acetic acid, acrolein, acetaldehyde, extraction solvent, other polymers, and polymerization inhibitors. Wastewater is extracted from the collection tower. This wastewater is contaminated and contains light to high boiling point substances, and it is undesirable from the viewpoint of product quality and process operation to use this wastewater as it is as process water for an acrylic acid scavenger or the like.
In addition, wastewater from the acrylic acid ester manufacturing process is
It is mainly produced by separating the water produced during the esterification reaction, and contains small amounts of unreacted alcohol, unreacted acrylic acid, acrylic acid ester, propionic acid ester, polymers, and polymerization inhibitors. In addition to this raw water, a small amount of sodium hydroxide aqueous solution for neutralizing the acid catalyst for esterification and a sodium hydroxide aqueous solution for washing are mixed in to form waste water from the esterification process. When the above wastewaters were combined, wastewater containing impurities having the composition shown in Table 1 was obtained. Table 1 Composition (leg) COD (Mh/Cr) 15 700/30,0
00 Alcohols (as CQOH) 200 Esters (as methyl acetate) 800 Acids (as acetic acid) 4,500 Others (as acrylic acid polymer) 500 (Note) COD analysis is based on JISK
According to -0102.

In addition, other components were measured by gas chromatography.

Same below. Example 1 80 ml of waste water from each production process of acrylic acid and acrylic acid ester having the above composition was placed in one flask.
Add 2% by weight aqueous NaOH solution to pH=12,
Yokoazusa pretreatment was carried out at 80qo for 3 hours.

This was distilled at normal pressure at a reflux ratio of 4 in a Yamayasu Older Show with one actual plate, yielding 6 distillates and 75 bottles. The respective liquid compositions are shown in Table 2. Table 2 Composition (ppm) Distillation column treatment Distillation column treatment fraction Bottle liquid Distillation Bottle liquid COD (Mn/Cr) 5,300/9,000 15,
500/33,40o loo/130 92,700
/173,700 Alcohol 4,500
trace lot
race esters 100 trace
lo trace acids 1
0 trace trace trac
e other trace trace
trace trace This bottom liquid was continuously evaporated in an evaporator with an empty column attached to the flask at a top pressure of 15 m Hg, a top temperature of 60 qo, and a bottom temperature of 65°C, resulting in 600 g of distillate and 14 g of bottom liquid. I was relieved.

The distillate from the evaporator contained almost no organic matter, and was used as absorption water for scavenging acrylic acid.
There were no problems with the process or the quality of acrylic acid. Furthermore, when the can liquid obtained from the evaporator and the crab matter obtained by distillation were incinerated in a small underwater combustion furnace, it was found that the organic matter was completely combusted and rendered harmless. Next, when the same wastewater was distilled and concentrated by evaporation, excluding the neutralization pretreatment,
As shown in Table 3, the organic matter content in the crab exudate from the evaporator increased.

Furthermore, when distillation and evaporation concentration were performed without the neutralization pretreatment and distillation operations, the organic matter content in the distillate was even higher, as shown in Table 3. Table 3 Composition (ppm) Neutralization pretreatment Evaporator distillate water after neutralization distillation operation Evaporator distillate water COD (Mn-Cr) 4,280/5,8005,36
0/6,67o Alcohols 50 350 Esters 60 810 Acids 3,000 4,200
Others 50 100

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing an example of an embodiment of the present invention. 101... Alkali neutralization tank, 102... Distillation column, 1
03... Underwater combustion device, 104 and 105... Evaporator. figure*

Claims (1)

[Claims] 1. In the process of producing acrylic acid by catalytic gas-phase oxidation of propylene or acrolein, and in the process of producing acrylic acid ester by esterifying the obtained acrylic acid with alcohols, (a) an alkaline substance is added to the discharged wastewater; The pH of the wastewater is adjusted to 8 to 1 by adding
20 minutes at 40-100℃ while maintaining the alkalinity level 3.
After heat-treating for 5 hours, this is supplied to a distillation column to distill out 5 to 20% by weight of the waste water; (b) the distillation column bottom liquid is supplied to an evaporator, where 10 to 20% of the supplied bottom liquid is distilled out; (c) Concentrating the resulting concentrate to (20% by weight);
a) Conducting the distillate together with the distillate obtained in step 2 to a waste liquid combustion device for combustion treatment, and (d) recycling and reusing the distillate water obtained from the evaporator in the acrylic acid production process and acrylic acid ester production process. More ways to use wastewater.