CN103803691A - Low-concentration formic acid wastewater treatment process - Google Patents

Abstract

A new process for the treatment of low-concentration formic acid wastewater, which sprays low-concentration formic acid wastewater with a mass fraction of 0.1% to 3% into the esterification-extraction tower after atomization and spraying, and the spray density is 8 to 50m ³ / (m ² ·h), the atomized water droplets are evenly distributed in the upper packing in the tower under the action of gravity, and finally settle naturally in the high-carbon alcohol oil phase. After heating, it undergoes esterification reaction with alcohol, converts to the corresponding formic acid ester and then extracts it in the oil phase. The reaction temperature is 85-105°C, and the reaction temperature is maintained by the introduction of water vapor. The water from which formic acid has been removed continues to fall to the water layer at the bottom of the tower, using its heat to preheat the initial formic acid wastewater, and the water layer is taken out for simple biochemical treatment. Extract the organic layer from the lower part of the esterification extraction tower to the rectification tower for vacuum distillation, separate the ester from the alcohol, extract high-purity ester from the top of the tower, and send the high-temperature alcohol at the bottom of the tower to supplement part of the alcohol before sending it to esterification-extraction Tower recycling.

Description

A low-concentration formic acid wastewater treatment process

technical field

The invention relates to a treatment process for low-concentration formic acid wastewater.

Background technique

Formic acid (CH ₂ O ₂ ), also known as formic acid, is colorless, has a pungent odor, and is corrosive, with a boiling point of 100.8°C. Due to the special structure of formic acid, one of its hydrogen atoms is directly connected to the carboxyl group, which can also be regarded as a hydroxy formaldehyde, so formic acid has the properties of both acid and aldehyde. In the chemical industry, formic acid is widely used in the production of textile printing and dyeing, leather processing, rubber processing, silage and medicine.

The boiling point of formic acid is 100.8°C, which is almost the same as water and miscible with water. The intermolecular association is very strong. If the dilute solution of formic acid is simply concentrated by distillation, the effect will be very poor. And when the temperature is high, formic acid is volatile.

Table 1: Relationship between formic acid residual amount and formic acid wastewater temperature

temperature/℃ 70 65 60 55 50 45 40 35 30 20 Residual amount of formic acid/% 3.9 5.1 5.9 6.8 8.2 9.0 9.2 9.2 9.2 9.6

As shown in Table 1, when the temperature is below 40°C, the concentration of formic acid in water is basically stable at about 9.2%, but when the temperature rises, the concentration of formic acid will drop sharply, and when it reaches 70°C, it is only about 4%. At present, the esterification method treats formic acid wastewater, and the temperature is generally above 85°C. Therefore, it is easy to treat when the concentration of formic acid in industrial wastewater is above 3%, but when the concentration of formic acid is higher, it is difficult or costly to treat by ordinary methods.

At present, for the research on the treatment of organic wastewater containing formic acid, the treatment methods of formic acid decomposition are mostly used, such as oxidation method, catalytic decomposition method, biochemical treatment method, adsorption method, and electrolysis method. Although these methods have better treatment effects, they often cost more High, the processing capacity is small, not suitable for industrial applications. In the industry, rectification, esterification distillation or azeotropic-fractionation are often used to recover and treat formic acid wastewater. Among them, the rectification method cannot be used alone because the boiling points of formic acid and water are very close. The basic principle of the esterification method is to make formic acid and alcohols undergo an esterification reaction. The reaction equation is as follows:

HCOOH+ROH→HCOOR+H ₂ O

This type of method usually uses two steps of esterification and rectification to complete the treatment of formic acid wastewater, which can treat formic acid wastewater with higher concentration. For low-concentration (<4%) formic acid wastewater, the proportion of water is high, the energy consumption required for heating wastewater and rectification is large, and the cost of wastewater treatment is high. Moreover, formic acid wastewater is corrosive and will Strengthen corrosion wastewater treatment equipment.

Contents of the invention

The purpose of the present invention is to provide a new process for the treatment of low-concentration formic acid wastewater with low energy consumption. First, in the esterification-extraction tower, formic acid and high-carbon alcohols in the wastewater are esterified into esters, dissolved and extracted in high-carbon The alcohol is separated from the water, and the waste water is discharged after stratification. The oil phase is further rectified to separate the ester and alcohol, and the alcohol is reused in the esterification-extraction process.

In order to achieve the above object, the technical scheme of the present invention is as follows:

A treatment process for low-concentration formic acid wastewater. Its process is shown in Figure 1, including the following steps:

(1) Preheat the low-concentration formic acid wastewater with a mass fraction of 0.1% to 3% through the formic acid wastewater preheating pipeline 1 and the formic acid wastewater heat exchanger 15, and then spray it through the atomizing nozzle spray device 5 until esterification-extraction Tower 2, the upper part of the esterification-extraction tower is equipped with a packing layer 3, and the steam heating pipe 13 is passed into the middle part to heat the alcohol to speed up the esterification reaction. The spray volume of the device 5 is 10-50m ³ /(m ² ·h), and the droplets move downward under the action of gravity and are evenly distributed inside the packing layer 3 of the esterification-extraction tower 2. The spray volume depends on the treatment of the device. The scale and the amount of high-carbon alcohols are different. The high-carbon alcohols are water-insoluble alcohols, including n-butanol, n-pentanol or isoamyl alcohol. The amount of high-carbon alcohols depends on the diameter of the tower. Occupying between 1/2 and 2/3 of the volume of the tower, it is generally necessary to completely submerge the packing layer (3), the formic acid wastewater mist is evenly dispersed in the packing, and after slowly entering the interior of the high-carbon alcohol liquid, it settles downward under the action of gravity , the water droplet moves from the top of the oil layer to the bottom of the oil layer, and the contact time with high-carbon alcohol is not less than 120s. During this process, the water droplet is rapidly heated by the alcohol, and the formic acid in the water droplet fully contacts with the surrounding alcohol to undergo esterification reaction and then enters the oil phase. Because the amount of formic acid wastewater sprayed is much smaller than the amount of alcohol in the tower, it can be heated rapidly in the tower; at the same time, because the amount of alcohol is much larger than the amount of formic acid, it promotes the balance movement of the positive reaction and accelerates the rate of esterification reaction;

The purpose of the formic acid wastewater preheating described in the process of the present invention is not only to increase the temperature of the formic acid wastewater entering the tower, but also to reduce the temperature of the formic acid wastewater after the treatment at the bottom of the esterification-extraction tower, so that the dissolved organic matter returns to the oil layer and reduces the purification rate. The content of organic matter in formic acid wastewater, the purpose of atomization and spraying of formic acid wastewater is not only to make formic acid fully contact with high-carbon alcohols in the tower, and to be heated quickly to reach the temperature required for esterification reaction; Sufficient contact, so that part of the formic acid can be dissolved in alcohol to achieve the purpose of extraction.

(2) The treated formic acid wastewater is extracted from the bottom water layer 12 of the esterification-extraction tower 2, and the output amount is approximately equal to the spray amount of the atomization device. The formic acid content of the formic acid wastewater extracted from the bottom is less than 0.05%, which can be passed The wastewater extraction pipeline 14 is directly discharged or discharged after simple biochemical treatment;

The purpose of the preheating of the treated waste water in the process of the present invention for the initial formic acid waste water is to make full use of the heat in the formic acid waste water to improve the temperature at which the formic acid initial formic acid waste water enters the esterification-extraction tower, so that it can reach the esterification-extraction tower rapidly. The temperature required for the chemical reaction can reduce the energy consumption of the entire treatment system.

(3) Esterification-The middle layer oil 4 in the extraction tower 2 is extracted to the fractionation tower 7 through the pump 6. The oily substance mainly contains higher carbon alcohols, esters and a very small amount of formic acid. In the tower 7, the oil layer liquid is rectified under reduced pressure , the ester can be separated from the alcohol. After rectification, the ester is extracted through the pipeline 8, and the alcohol at the bottom of the tower is sent to the esterification-extraction tower 2 for recycling through the pipeline 9, and continues to be used in the esterification extraction process. The alcohol lost in the middle passes through the Tonic Alcohol Pipeline 10 Supplement.

In the process of the present invention, the material extracted through the extraction pipeline 8 is the ester substance obtained by formic esterification, and the higher alcohol at the bottom of the tower can continue to be used for esterification in the esterification-extraction tower 2, and the purpose is to make Its recycling can save costs and improve economic benefits.

Description of drawings

Fig. 1 is the technological schematic diagram of low-concentration formic acid wastewater treatment of the present invention, wherein: 1-formic acid wastewater preheating pipeline; 2-esterification-extraction tower; 3-packing layer; 4-oil layer; 5-spray device; 6-oil layer Production pump; 7-fractionating tower; 8-ester production pipeline; 9-alcohol circulation pipeline; 10-supplemented alcohol pipeline; 11-formic acid wastewater transportation pipeline; Post-wastewater extraction pipeline; 15-formic acid waste water heat exchanger.

Detailed ways

The present invention is described in detail by the following examples, but it should not be understood as a limitation to the scope of patent protection of the present invention.

Example 1:

(1) Spray the low-concentration formic acid wastewater containing 1% to the esterification-extraction tower 2 through the atomization spray device 5, the tower diameter is 0.8m, the tower height is 6m, and the spray volume is 50m ³ /(m ² ·h ), so that it moves downward under the action of gravity and is evenly distributed inside the packing layer 3. The lower part of the esterification-extraction tower 2 is n-butanol, with a volume of 1.8m ³ , and the pipeline 13 feeds steam to heat the n-butanol, and the n-butanol is normal The temperature of the butanol layer was 85°C. Formic acid wastewater droplets are uniformly dispersed in the filler, slowly enter the lower layer of n-butanol liquid, and settle down under the action of gravity. The full contact time of oil and water two phases is about 150s. During this process, due to the amount of formic acid wastewater sprayed relative to the column The amount of n-butanol in the lower part is very small, and the water droplets are heated rapidly; the amount of n-butanol is greatly excessive relative to the amount of formic acid, which promotes the equilibrium shift of the positive reaction and accelerates the rate of esterification reaction.

(2) After the reaction is stabilized, esterification-the formic acid wastewater treated in the water layer 12 at the bottom of the extraction tower 2 passes through the heat exchanger 15 to preheat the formic acid wastewater in the pipeline 1. After the heat exchange, the water temperature drops by 12°C, and the formic acid content is 0.04%, and then extracted from the pipeline 14, transported to the biochemical pool for treatment. The output of formic acid wastewater after treatment is equal to the spray volume of the atomization device, which is about 6m ³ /h. The water temperature of the formic acid wastewater in pipeline 1 is 52°C after preheating, and then it is transported to the top of the tower for spraying through pipeline 11.

(3) When the reaction is stable, the oil 4 in the middle layer of the esterification-extraction tower 2 is extracted to the fractionation tower 7 through the pump 6. The oily substances mainly contain butanol, esters and a very small amount of formic acid. In the fractionation tower 7, the oil layer The liquid is distilled under reduced pressure to separate the alcohol ester from the formic acid. After the distillation, the ester is extracted through the pipeline 8, and the n-butanol at the bottom of the tower is sent to the esterification-extraction tower 2 through the pipeline 9 for recycling, and continues to be used in the esterification and extraction process. .

Example 2:

(1) Spray the waste water containing 0.1% formic acid to the esterification-extraction tower 2 through the atomization spray device 5, the tower diameter is 0.9m, the tower height is 8m, and the spray volume is 15m ³ /(m ² ·h), Make it move downward under the action of gravity and distribute evenly inside the packing layer 3 of the esterification-extraction tower 2. The middle and lower section of the tower 2 is isoamyl alcohol with a reserve volume of 3.2m ³ , and the pipeline 13 is fed with steam to heat the isoamyl alcohol , The temperature of the isoamyl alcohol phase is 105°C. Formic acid wastewater droplets are uniformly dispersed in the filler, slowly enter the interior of the lower high-carbon alcohol liquid, and settle down under the action of gravity. The full contact time of the oil-water two-phase is about 135s. During this process, due to the amount of formic acid wastewater sprayed relative to the column The remaining amount of alcohol in the lower part is very small, and the water droplets are heated rapidly; the amount of alcohol remaining is greatly excessive relative to the amount of formic acid, which promotes the shift of positive reaction equilibrium and accelerates the rate of esterification reaction.

(2) After the reaction is stabilized, esterification—the formic acid wastewater treated in the bottom water layer 12 of the extraction tower 2 passes through the heat exchanger 15 to preheat the formic acid wastewater in the pipeline 1. After the heat exchange, the temperature of the treated formic acid wastewater drops by 8°C. The content of formic acid is 0.01%, and then it is extracted from the pipeline 14, transported to the biochemical pool for simple treatment and then discharged. The output of formic acid wastewater after treatment is equal to the spraying volume of the atomization device, about 6m ³ /h. The formic acid wastewater in pipeline 1 is preheated to a temperature of 46°C, and then transported to the top of the tower for spraying through pipeline 11.

(3) When the reaction is stable, the oil 4 in the middle layer of the esterification-extraction tower 2 is extracted to the fractionation tower 7 through the pump 6. The oily substance mainly contains isoamyl alcohol, esters and a very small amount of formic acid. In the fractionation tower 7, the The vacuum rectification of the oil layer liquid can separate the ester from the alcohol. After the rectification, the ester is extracted through the pipeline 8, and the isoamyl alcohol at the bottom of the fractionation tower 7 is sent to the esterification-extraction tower 2 for recycling through the pipeline 9, and continues to be used for the esterification. chemical extraction process.

Example 3:

(1) Spray the low-concentration formic acid wastewater containing 2% to the esterification-extraction tower 2 through the atomization spray device 5, the tower diameter is 1.0m, the tower height is 7m, and the spray volume is 12m ³ /(m ² ·h ), so that it moves downward under the action of gravity and is evenly distributed inside the packing layer 3. The lower part of the esterification-extraction tower 2 is n-pentanol, and the reserve is 6m ³ . The n-pentanol phase is at 105°C. Formic acid wastewater droplets are uniformly dispersed in the filler, slowly enter the interior of the lower high-carbon alcohol liquid, and settle down under the action of gravity. The full contact time of the oil-water two-phase is about 140s. The remaining amount of alcohol in the lower part is very small, and the water droplets are heated rapidly; the amount of alcohol remaining is greatly excessive relative to the amount of formic acid, which promotes the shift of positive reaction equilibrium and accelerates the rate of esterification reaction.

(2) After the reaction is stabilized, the treated formic acid wastewater in the water layer 12 at the bottom of the tower 2 passes through the heat exchanger 15 to preheat the formic acid wastewater in the pipeline 1. After the heat exchange, the temperature of the treated formic acid wastewater drops by 8°C, and the formic acid content is 0.04%, and then extracted from the pipeline 14, transported to the biochemical pool for simple treatment and discharged. The output of formic acid wastewater after treatment is equal to the spraying volume of the atomization device, about 9.5m ³ /h. The formic acid wastewater in pipeline 1 is preheated to a temperature of 45°C, and then transported through pipeline 11 to the top of the tower for spraying.

(3) When the reaction is stable, the oil 4 in the middle layer of the esterification-extraction tower 2 is extracted to the fractionation tower 7 through the pump 6. The oily substance mainly contains n-amyl alcohol, esters and a very small amount of formic acid. In the fractionation tower 7, the The oil layer liquid is distilled under reduced pressure to separate alcohol esters from formic acid. After distillation, the esters are extracted through pipeline 8, and the n-pentanol at the bottom of the fractionation tower is sent to the esterification-extraction tower 2 for recycling through pipeline 9, and continues to be used for esterification and extraction. process.

Example 4:

(1) Spray the low-concentration formic acid wastewater containing 3% to the esterification-extraction tower 2 through the atomization spray device 5, the tower diameter is 0.85m, the tower height is 6.5m, and the spray volume is 12m ³ /(m ² · h), make it move downward under the action of ^gravity and distribute evenly inside the packing layer 3, the middle and lower section of the esterification-extraction tower 2 is n-butanol, and the reserve volume is 2.6m Alcohol, n-butanol phase temperature is 85°C. Formic acid wastewater droplets are uniformly dispersed in the filler, slowly enter the interior of the lower high-carbon alcohol liquid, and settle down under the action of gravity. The full contact time of the oil-water two-phase is about 140s. The remaining amount of alcohol in the lower part is very small, and the water droplets are heated rapidly; the amount of alcohol remaining is greatly excessive relative to the amount of formic acid, which promotes the shift of positive reaction equilibrium and accelerates the rate of esterification reaction.

(2) After the reaction is stabilized, the treated formic acid wastewater in the water layer 12 at the bottom of the tower 2 passes through the heat exchanger 15 to preheat the formic acid wastewater in the pipeline 1. After the heat exchange, the temperature of the treated formic acid wastewater drops by 8°C, and the formic acid content is 0.05%, and then extracted from the pipeline 14, transported to the biochemical pool for simple treatment and discharged. The output of formic acid wastewater after treatment is equal to the spraying volume of the atomization device, about 6.7m ³ /h. The formic acid wastewater in pipeline 1 is preheated to a temperature of 48°C, and then transported through pipeline 11 to the top of the tower for spraying.

(3) When the reaction is stable, the middle layer oil 4 in the esterification-extraction tower 2 is extracted to the fractionation tower 7 through the pump 6. The oily substance mainly contains n-butanol, esters and a very small amount of formic acid. In the fractionation tower 7, the The oil layer liquid is distilled under reduced pressure to separate alcohol, ester and formic acid. After distillation, the ester is extracted through pipeline 8, and the bottom alcohol of the fractionation tower is sent to the esterification-extraction tower 2 through pipeline 9 for recycling, and continues to be used in the esterification and extraction process .

Claims (2)

1. a treatment process for lower concentration formic acid wastewater, comprises the following steps:

(1) be that 0.1%～3% lower concentration formic acid wastewater sprays to esterification-extraction tower (2) through atomizer spray equipment (5) after by preheating pipe (1) and formic acid wastewater interchanger (15) preheating by containing massfraction, the epimere of esterification-extraction tower arranges packing layer (3), middle part passes into raw steam heating alcohol by steam-heated pipe line (13), enhance esterification speed, after heating, alcohol temperature remains on 85～110 ℃, and the spray flux of atomizer spray equipment (5) is 10～50m ³/ (m ²h), droplet moves downward and is uniformly distributed in packing layer (3) inside of esterification-extraction tower (2) under action of gravity, spray flux is different according to device treatment scale and higher alcohols recoverable amount, higher alcohols are selected water-fast alcohol, the add-on of higher alcohols is determined according to tower diameter size, should account for tower body long-pending 1/2～2/3 between, need complete submergence packing layer (3), formic acid wastewater droplet is dispersed in filler, slowly enter after higher alcohols liquid internal, sedimentation downwards under action of gravity, water droplet moves to oil reservoir bottom from entering top of oil horizon, be not less than 120s duration of contact with higher alcohols, in this process, water droplet is heated rapidly by alcohol, formic acid in water droplet fully contacts and occurs to enter oil phase after esterification with alcohol around, because formic acid wastewater spray flux is much smaller than the alcohol amount in tower, so can be heated rapidly in tower, simultaneously, because the amount of alcohol is much larger than amount of formic acid, promote positive reaction balance to move, accelerated esterification reaction rate,

(2) formic acid wastewater after treatment is from water layer (12) extraction of esterification-extraction tower (2) bottom, produced quantity equals atomisation unit spray flux, the formic acid wastewater of bottom extraction wherein formic acid content, lower than 0.05%, is directly discharged or is discharged after simple biochemical treatment by waste water extraction pipeline (14);

(3) esterification-extraction tower (2) mesonexine oil (4) passes through pump (6) extraction to separation column (7), in oily mater, mainly contain higher alcohols, ester class and minute quantity formic acid, in separation column (7) by the rectifying of oil reservoir liquid pressure-reducing, ester is separated with alcohol, after rectifying, ester class is through piping (8) extraction, alcohol at the bottom of separation column tower is delivered to esterification-extraction tower (2) by pipeline (9) and is recycled, continue on for esterification extraction process, in the middle of process, the alcohol of loss supplements by mending alcohol pipeline (10).

2. the treatment process of lower concentration formic acid wastewater according to claim 1, is characterized in that: described higher alcohols comprise propyl carbinol, Pentyl alcohol or primary isoamyl alcohol.

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