CN1757599A

CN1757599A - Method for producing ammonium sulfate

Info

Publication number: CN1757599A
Application number: CN 200510032344
Authority: CN
Inventors: 文捷
Original assignee: HUNAN BAILI ENGINEERING SCI-TECH Co Ltd
Current assignee: HUNAN BAILI ENGINEERING SCI-TECH Co Ltd
Priority date: 2005-11-03
Filing date: 2005-11-03
Publication date: 2006-04-12

Abstract

A process for preparing ammonium sulfate features that the Backmann rearranged liquid in caprolactam equipment is neutralized and crystallized, and the caprolactam is separated to obtain ammonium sulfate.

Description

Method for producing ammonium sulfate

One, the technical field

The invention relates to a method for producing ammonium sulfate, in particular to a method for treating Beckmann heavy liquid discharge in a caprolactam device to produce ammonium sulfate and separate caprolactam in the heavy liquid discharge by adopting a neutralization crystallization technology.

Second, background Art

Caprolactam is prepared by the Beckmann rearrangement reaction of cyclohexanone oxime under the catalysis of oleum, and the reaction product is a mixture of caprolactam and oleum (commonly known as heavy liquor). In order to separate caprolactam from sulfuric acid, ammonia water neutralization is generally used in industry, fuming sulfuric acid reacts with ammonia in an aqueous phase to generate ammonium sulfate, and the ammonium sulfate is separated from the caprolactam by utilizing the characteristic that the ammonium sulfate is difficult to dissolve in water compared with the caprolactam and the difference of densities of the ammonium sulfate and the caprolactam, and the reaction formula is as follows:

the ammonium sulfate formed in the reaction is separated from the liquid phase by crystallization. The traditional method for treating Beckmann heavy liquid discharge comprises the following steps: the heavy liquid and ammonia water enter a neutralization kettle together to carry out neutralization reaction to generate ammonium sulfate, and the reaction heat is removed through an external circulating cooler. The ammonium sulfate solution and the caprolactam solution after the reaction enter a layering tank for layering, the ammonium sulfate solution at the bottom is pumped into an extraction tower, benzene is used as an extracting agent for extracting and recovering caprolactam in the ammonium sulfate solution, and raffinate is obtainedThe ammonium sulfate solution is sent to a stripping tower to recover benzene therein, and then enters an ammonium sulfate crystallization process.

The crystallization of the ammonium sulfate solution adopts a double-effect evaporation crystallization process, the ammonium sulfate solution from the bottom of a stripping tower is pumped to a circulating pipe of one-effect evaporation, and the ammonium sulfate solution enters a one-effect evaporator after being heated by a one-effect heater. The steam at the top of the first-effect evaporator is used as a heat source of the second-effect heater, ammonium sulfate is evaporated and concentrated by the first-effect evaporator and the second-effect evaporator and then enters the crystallizer for crystallization, and when the content of solid ammonium sulfate in the ammonium sulfate meets the requirement, ammonium sulfate crystal slurry is pumped to a thickening and centrifuging process.

Through the process,the main problems in the process operation can be seen that neutralization of ① reliquefied liquid and crystallization of ammonium sulfate are respectively carried out in two working procedures, the flow is long, the equipment is more, the investment is high, ② unreasonable energy utilization is that the reaction heat generated by reaction of sulfuric acid and ammonia water in the reliquefied liquid in the neutralization working procedure is not utilized, but is removed by cooling water in an external circulation cooler, a large amount of circulating water is consumed, and medium-pressure steam is used for providing a heat source in the crystallization working procedure to evaporate moisture in the ammonium sulfate solution to achieve the purpose of crystallization.

Third, the invention

The invention aims to provide a method for producing ammonium sulfate, in particular to a method for producing ammonium sulfate by using a neutralization crystallization technology and using SO as much as possible₃The reaction heat generated by the reaction of sulfuric acid with water and ammonia to generate ammonium sulfate shortens the process and achieves the purposes of reducing investment, saving energy and reducing consumption.

The invention is realized by the following modes, wherein:

the neutralization reaction of the re-draining liquid and the crystallization of ammonium sulfate are both carried out in a neutralization crystallizer. Gas ammonia (or ammonia water) and rearrangement liquid are respectively fed into neutralization crystallizer after being metered, and SO in the heavy discharge liquid₃The reaction of sulfuric acid with ammonia produces ammonium sulfate and produces crystal nucleus. The heat of reaction is carried away by water evaporation. The ammonium sulfate is gradually crystallized alongwith the evaporation of the water, and the ammonium sulfate is neutralized in the crystallizerThe density difference between the oil phase of lactam and the inorganic phase of ammonium sulfate, the vast majority of the ammonium sulfate magma is in the internal circulation channel, while the caprolactam is enriched at the top of the baffling area, thus separating caprolactam and ammonium sulfate. At the bottom of the neutralization crystallizer, ammonium sulfateThe solid content reaches 20-30% (wt), and the part of crystal mush is conveyed to a thickener by a pump for thickening and then is separated by a centrifuge to obtain solid ammonium sulfate.

The process conditions of the neutralization crystallization are as follows: the pressure at the top of the neutralization crystallizer is 10-30 kPa (A), the temperature of the neutralization crystallizer is 55-75 ℃, and the pH value is 3.0-4.5, preferably 3.5-4.0.

The invention has the advantages that the hydrolysis reaction of fuming sulfuric acid, the neutralization reaction of sulfuric acid and ammonia and crystallization operation are concentrated in the neutralization crystallizer by adopting a neutralization crystallization technology, the reaction heat is fully utilized, so that evaporation crystallization does not need external steam, and a large amount of energy is saved; meanwhile, the process is shortened, so that the equipment investment is low and the operating cost is low.

In the aspect of product quality, as the novel neutralization crystallizer is adopted, and the neutralization crystallizer is provided with the inner guide cylinder and the high-efficiency stirrer, an inner circulation channel is formed. Besides the internal circulation channel, the crystallizer is also provided with an external circulation channel: in the baffling area of the crystallizer, ammonium sulfate solution containing a large amount of fine crystals atthe middle lower part is sent back to the bottom of the crystallizer through an external circulating pump, and partial condensed water is added at the inlet of the external circulating pump for eliminating excessive fine crystals and elutriating the product granularity, so that the product has large grain size and narrow distribution range. Because the neutralization crystallizer is arranged in the internal circulation channel and the external circulation channel, a high saturation area can be eliminated, the supersaturation degree of each part in the crystallizer is relatively uniform, the particle size of the produced ammonium sulfate particles is more than 85 percent of that of the ammonium sulfate particles with the particle size of more than 0.5mm, and the particle size of the ammonium sulfate particles is greatly improved compared with the ammonium sulfate particles produced by the traditional process; the separated caprolactam is further kept stand for layering, so that the ammonium sulfate entrained in the caprolactam is not higher than 0.8 percent (wt), which is equivalent to the traditional process and can meet the requirements of a caprolactam refining unit.

Description of the drawings

FIG. 1 is a schematic flow chart of the production of ammonium sulfate according to the present invention

In the attached figure 1, 1 is a neutralization crystallizer; hydrolysis reaction of fuming sulfuric acid, neutralization reaction of sulfuric acid and ammonia and crystallization operation are carried out in a neutralization crystallizer;

the 2 is a condenser, the water evaporated after the neutralization reaction is condensed by the condenser 2 and collected in a water condensation tank 15, and the condensed water is sent into a neutralization crystallization system again by awater condensation pump 14 for recycling;

3 is a decanter, the caprolactam oil phase coming out of the baffling area 6 of the neutralization crystallizer is sent to the decanter 3 through a decanter feeding pump 12, and in the decanter 3, the caprolactam oil phase is separated from the ammonium sulfate solution to remove most ammonium sulfate;

4, thickening the ammonium sulfate crystal slurry to 40-60% (wt) in a thickener;

5 is a flow guide cylinder in the neutralization crystallizer;

6 is a baffling area of the neutralization crystallizer;

7, a static mixer is used, when ammonia is fed in a gas ammonia form, the gas ammonia independently passes through the static mixer, when ammonia is fed in an ammonia water form in the production process, a valve on a condensate pipe line in front of the static mixer is opened, condensate water is added, and the ammonia water is mixed by the static mixer to form ammonia water feeding;

8 is a feed nozzle of the neutralization crystallizer;

9 is a neutralizing crystallizer bottom stirrer;

10 is a circulating mother liquor pump, and an external circulating channel of the neutralization crystallizer can be provided by the circulating mother liquor pump;

11, an ammonium sulfate crystal slurry pump, wherein the crystal slurry containing 20-30% (wt) of solid ammonium sulfate at the bottom of the neutralization crystallizer is conveyed to the thickener 4 through the ammonium sulfate crystal slurry pump;

12 is a decanter feeding pump caprolactam oil pump;

13 is a caprolactam oil pump;

14 is a condensate pump;

15 is a condensate tank;

16 is a mother liquid pump;

17 is a circulating mother liquor tank

The filtrate is saturated ammonium sulfate solution, the filtrate is collected in a circulating mother liquor tank 17 and is sent back to the neutralization crystallizer 1 through a mother liquor pump 16 for recrystallization. The filter cake is solid ammonium sulfate;

fifth, detailed description of the invention

In the present invention, ammonia can be added in the same manner as in examples 1 and 2, and the addition manner of example 1 is preferred.

Example 1 gaseous ammonia and heavy liquid (101) enter the guide shell (5) through a plurality of nozzles (8) on the ring-shaped distributor in the neutralization crystallizer 1, and ammonia and sulfuric acid in the heavy liquid (101) are subjected to neutralization reaction in the guide shell (5) to generate ammonium sulfate and generate crystal nuclei. Under the stirring of a stirrer (9) arranged at the bottom of the neutralization crystallizer 1, the ammonium sulfate solution is quickly lifted to the upper part of the guide cylinder (5), and when the rising solution reaches the free surface of the liquid, the water begins to evaporate. The evaporated moisture is condensed by the condenser 2 and then added to the circulating pipe at the bottom of the crystallizer again, and the addition of the condensed water in the process can dissolve fine crystals and balance the influence of reaction heat on moisture evaporation; in the lower region outside the guide shell (5), the flow rate decreases due to the change in the shape of the crystallizer, a part of the suspension is returned to the guide shell (5) by the action of the stirrer, and another part flows upwards to the deflectionzone (6), where caprolactam is separated from the mother liquor due to the difference in density, floating on top of the mother liquor as an organic layer, which is drawn off together with a certain amount of mother liquor and sent to the decanter 3 for separation. Sending the separated organic phase which is caprolactam to a caprolactam refining unit; the inorganic phase is saturated ammonium sulfate solution, returns to the circulating mother liquor tank, and enters the neutralization crystallizer 1 through a mother liquor pump 16 for recrystallization. When the solid content of the ammonium sulfate in the neutralization crystallizer 1 reaches 25 percent (wt), the ammonium sulfate crystal slurry pump 11 at the bottom of the neutralization crystallizer 1 is sent to the thickener 4, the ammonium sulfate crystal slurry is thickened by the thickener 4, the crystal slurry containing 40 to 60 percent of the solid ammonium sulfate is sent to the centrifugal machine 18, the solid ammonium sulfate is obtained by the separation of the centrifugal machine 18, and the filtrate returns to the ammonium sulfate mother liquor circulating tank 17 and is sent back to the neutralization crystallizer 1 by a pump for recrystallization.

Example 2 gaseous ammonia and a part of condensed water from the outlet of the condensate pump 14 are mixed together by the static mixer 7 to prepare ammonia water, and the concentration of the prepared ammonia water can be adjusted by an adjusting valve on a condensed water pipeline according to the production requirement. The other portions are the same as in example 1.

Claims

1. A method of producing ammonium sulfate, wherein: the heavy discharge liquid and ammonia directly enter a neutralization crystallizer for reaction, and SO in the heavy discharge liquid₃Reacting with water to generate sulfuric acid, reacting the sulfuric acid with ammonia to generate ammonium sulfate, evaporating water to obtain ammonium sulfate crystals by utilizing reaction heat under the conditions that the absolute pressure is 10-30 kPa, the temperature is 55-75 ℃ and the pH value is 3.0-4.5, and separating caprolactam from a baffling area of a neutralization crystallizer.

2. The process according to claim 1, wherein the rearrangement solution is subjected to the hydrolysis step and directly fed into the neutralization crystallizer for neutralization.

3. A process according to claim 1 or 2, characterized in that the ammonia required for the reaction is either gaseous or aqueous ammonia, preferably gaseous ammonia.

4. Process according to any of claims 1-3, characterized in that the difference in density between the oil phase of caprolactam and the inorganic phase of ammonium sulfate in the neutralisation crystallizer is used, an enlarged baffling zone is provided in the neutralisation crystallizer, so that caprolactam is enriched at the top of the baffling zone, and that after removal of this caprolactam, a further separation by settling is achieved, so that the caprolactam has no more than 0.8% (wt) entrained ammonium sulfate.

5. A method according to any one of claims 1-3, characterized in that the density difference between the caprolactam oil phase and the ammonium sulphate inorganic phase in the neutralisation crystallizer is such that the major part of the ammonium sulphate magma is in the internal circulation channel, the ammonium sulphate solids content in the bottom of the neutralisation crystallizer amounts to 20-30% (wt), this part of the magma is pumped to the thickener where it is thickened to 40-60% (wt) by back flushing of the ammonium sulphate mother liquor, and the thickened magma is separated by means of a centrifuge to obtain solid ammonium sulphate.

6. A method according to any one of claims 1-3, characterized in that the water evaporated from the top of the neutralising crystalliser, after condensation, is re-introduced into the neutralising crystalliser, to maintain the water balance of the system and to eliminate some of the fines.

7. The process according to any of claims 1 to 6, characterized in that the saturated ammonium sulphate solution after separation in the centrifuge is re-introduced into the neutralisation crystalliser to recover the ammonium sulphate therein.

8. The process according to claim 1, wherein the pH is 3.5 to 4.0.