CN113429269A

CN113429269A - Pressurized rectification purification process equipment for methylal

Info

Publication number: CN113429269A
Application number: CN202110866124.8A
Authority: CN
Inventors: 孟长春; 蒋俊; 王建清
Original assignee: Nantong Jiangshan Agrochemical & Chemicals Co ltd
Current assignee: Nantong Jiangshan Agrochemical & Chemicals Co ltd
Priority date: 2021-07-29
Filing date: 2021-07-29
Publication date: 2021-09-24
Anticipated expiration: 2041-07-29
Also published as: CN113429269B

Abstract

The invention discloses a pressurized rectification purification process device for methylal, which is particularly suitable for processing a solution obtained by neutralizing dilute methanol separated from glyphosate production process by a glycine method, wherein a pressurized rectification tower is adopted for fractionation, and methylal and methyl chloride are subjected to rectification fractionation under a pressurized condition, so that the content of the methyl chloride in the methylal is reduced; then feeding the methylal gas or condensed liquid discharged from the top of the tower into a methanol normal-pressure rectifying tower for rectification to obtain the methanol. The invention increases the difference of the boiling points of the methylal and the chloromethane by pressure rectification, can fully separate the two components, and ensures that the methylal product and the methanol product meet the technical index requirements of various application places.

Description

Pressurized rectification purification process equipment for methylal

Technical Field

The invention relates to a rectification technology in the chemical industry.

Background

After being neutralized, the diluted methanol removed in the production process of glyphosate by a glycine method mainly comprises methyl chloride, methylal, methanol, water, sodium chloride and the like, and is firstly put into a methylal rectifying tower to recover the methylal and the methanol, the content of the methylal obtained at the tower top is about 85 percent, the methyl chloride is 8-11 percent, and the balance is the methanol. Then the mixture enters a methanol rectifying tower, relatively pure methanol is obtained at the top of the tower, and the rest is residual liquid.

The methylal obtained by the process contains 8-11% of methyl chloride, the boiling point of the methyl chloride is low (the boiling point of the methyl chloride is-23.76 ℃), and when the temperature rises, the methylal is volatile, so that the problem of barrel expansion (methyl chloride overflow) can occur in the storage and transportation processes, and serious potential safety hazards exist (the methylal and the methyl chloride are inflammable substances). Meanwhile, the methylal quality standard in the glyphosate industry requires that: the mass fraction of methylal is more than 80 percent, and the mass fraction of chloromethane is less than 6 percent.

In the production process, because methylal is rectified into the atmospheric pressure rectifying tower, although the content of methylal is improved by increasing the reflux amount, the effect cannot reach the target, the content of methyl chloride is 7-9%, and meanwhile, the energy consumption of steam is greatly increased.

The reason is that under normal pressure, the boiling points of methylal and chloromethane are lower, the methylal and chloromethane have intersolubility, azeotropic formation is easy to occur, the distillation separation degree under normal pressure is lower, the chloromethane content in the methylal cannot be reduced to a lower range, and the separation effect of the methylal and the chloromethane is poor.

Disclosure of Invention

The purpose of the invention is as follows:

the problems of approximate boiling points of methylal and chloromethane, lower separation degree and large energy consumption of atmospheric distillation under normal pressure are solved, and the methylal pressure distillation purification process equipment which has low equipment investment and can greatly reduce the content of chloromethane in methylal is provided.

The technical scheme is as follows:

the pressurized rectification and purification process equipment for methylal can be used for treating a neutralized solution of dilute methanol obtained in the production process of glyphosate by a glycine method, firstly, a pressurized rectification tower (or a normal-pressure rectification tower for rectification and then a rectification tower for pressurized rectification) is adopted for pressurized rectification, firstly, methyl chloride is fractionated at a lower temperature, then, the temperature is raised, and the methyl chloride is fractionated to obtain the formal, so that the methylal and the methyl chloride are rectified under the pressurized condition, the boiling point difference of the methylal and the methyl chloride is increased, the separation effect is improved, and the content of the methyl chloride in the methylal is reduced; then, the solution in the tower bottom is decompressed and sent into a methanol distillation tower (adopting a conventional rectifying tower) for distillation to obtain the methanol solution.

By referring to the literature and combining the tests of the inventor, the following comparison tables I and II are obtained:

table one: chloromethane boiling point pressure comparison table

。

TABLE II, METHANAL BOILING POINT PRESSURE COMPARATIVE TABLE

。

Since the boiling point of methyl chloride at normal pressure (100 kpa) is-23.7 ℃ and the boiling point at 200kpa is-6.4 ℃.

Expressed as chloromethane at normal temperature of 20 ℃, normal pressure or low pressure of 1-2atm (100-; this differs not sufficiently from methylal having a boiling point of 42.3 to 58.2 at 1 to 2atm by about 22.3 to 38.2 ℃; the separation degree is low and the proportion of methyl chloride doped in methylal is high when the two components are separated by distillation at normal temperature, normal pressure or low pressure.

Therefore, when distillation is carried out under pressure (4-6 atm), the boiling point of methyl chloride is close to normal temperature, the boiling point of methylal is much higher than normal temperature, and the difference between the two boiling points is 59.4-61 ℃. The methylal and the chloromethane are better separated by controlling the distillation temperature, and the mass fraction of the methylal in the obtained fraction is more than 90 percent, and the mass fraction of the chloromethane is less than 5 percent; when the pressure of the rectifying tower is 450-550 kpa, methylal with the content of more than 93% is obtained at the tower bottom, wherein the content of methyl chloride is less than 3%.

The process is described as follows:

the solution obtained by neutralizing the dilute methanol removed in the production process of glyphosate by a glycine method is firstly sent into a crude methylal (wherein the content of methyl chloride is 8-11%) obtained by rectifying in a conventional rectifying tower, and then is pumped into a rectifying tower (a pressurized rectifying tower) by a pump. Or directly feeding the neutralized solution of the dilute methanol removed in the production process of glyphosate by the glycine method into a second rectifying tower. Controlling the pressure in the tower to be 450-550 kpa, and controlling the tower top temperature of the second rectification tower to be 80-95 ℃ during distillation of methylal; and when methyl chloride is distilled, controlling the temperature at the top of the tower to be 20-30 ℃. And condensing the light components at the top of the tower through a salt water condensing pipeline, then carrying out total reflux, and processing the uncondensed methyl chloride gas and then accessing the treated methyl chloride gas into a methyl chloride system for recycling. The gas or the condensate discharged from the tower top obtains a methylal solution with the content of more than 90 percent (the content of methyl chloride is less than 5 percent), and the separation effect of methylal and methyl chloride is ensured. Then, the solution in the rectifying tower of the conventional rectifying tower or in the tower bottom of the rectifying tower is decompressed and sent into a methanol distilling tower (adopting the conventional rectifying tower) for distillation, and the methanol solution is obtained.

Introduction of equipment:

conventional rectification column (or atmospheric rectification column): and a gas outlet at the top of the rectifying tower is communicated with a condenser through a pipeline, condensate of the condenser enters the reflux tank and is pumped by the reflux pump into the rectifying tower, and uncondensed gas of the condenser is discharged from a discharge port at the top of the condenser as a distillate. A reboiler for circulation is connected below the rectifying tower body or connected with the rectifying tower body, and residual solution is discharged from a tower kettle outlet at the bottom of the tower.

Pressurized rectifying tower (rectifying second tower): the condensing tower is provided with a pressurizing rectifying section and a tower top condensing section, the tower top condensing section is directly arranged above the pressurizing rectifying section (wherein a plurality of condensing reflux pipelines are vertically arranged, and brine with the freezing point of about-10 ℃ is used as cooling liquid, so that the condensation is faster and more efficient, the methylal is fully condensed and refluxed in the initial fraction, the methyl chloride fraction basically has no formal, and the waste of formal components is avoided), and the interval between the condensing reflux pipelines is used for discharging and collecting the fraction from a tower top outlet after the fraction passes through. A pressure gauge for testing the pressure in the tower is arranged between the pressure rectifying section and the tower top condensing section, or a thermometer with a testing temperature is used for measuring the temperature at the position, so that the temperature in the tower can be tested preliminarily, and the temperature and the flow of a refrigerant required by the condensation at the tower top can be controlled; the top of the overhead condenser section is provided with a thermometer to measure the precise temperature of the distillate. The device is also provided with a controller which receives a pressure signal of a pressure gauge and a temperature signal of a thermometer (a tower top thermometer or a tower body thermometer), and when the pressure reaches a designed pressure interval and the respective fractionation temperature, the controller controls a tower top automatic control valve to be opened, and relatively pure methyl chloride fraction and methylal fraction are discharged successively.

In the pressurizing process of the chloromethane and methylal rectification secondary tower, an external tower reflux process of a reflux tank and a reflux pump is not used, so that the arrangement space of external equipment is reduced, and the equipment cost is reduced.

Distilling to discharge and recover methyl chloride fraction, measuring the lowest temperature point of distillation by a thermometer at the top of the tower, wherein the temperature is not lower than the boiling point of methyl chloride under the pressure, and ensuring that the methyl chloride is almost completely distilled out; the body thermometer measures the highest distillation temperature point, which is not higher than the boiling point of methylal at that pressure, ensuring that methylal is not substantially vaporized as methyl chloride is withdrawn.

The methylal fraction is discharged by the subsequent distillation, the overhead thermometer metering at the lowest temperature point of the distillation, which is not lower than the boiling point of methylal at that pressure; the thermometer on the tower body measures the highest temperature point of distillation, which is slightly higher than the boiling point of methylal under the pressure, thereby ensuring that other heavy components are not evaporated and saving energy consumption. The methylal fraction was condensed and collected for further use.

Has the advantages that:

the methylal rectification secondary tower adopts an internal total reflux process, simplifies the production flow, is convenient to operate, cancels the use of a movable device (reflux pump), eliminates the maximum risk point of a system, and saves the investment and risk of electricity and instruments. The running cost is reduced, and the power consumption of the pump is reduced. The use of special equipment such as pressure vessel and pressure pipeline is reduced, the on-the-spot safety risk of device is reduced.

Due to the operation under pressure, the air tightness of the equipment can be detected as soon as possible, and the leakage points of the equipment are reduced.

The control is simpler and more accurate through the simplification of the process flow.

The boiling point difference of the methylal and the chloromethane is increased through the pressurized rectification, and the two components can be fully separated, so that the methylal product and the methanol product meet various application requirements in quality.

Drawings

FIG. 1 is a schematic flow diagram of a rectification process of the present invention;

FIG. 2 is a schematic diagram of the structure of an atmospheric distillation column;

FIG. 3 is a schematic view of the structure of a pressurized rectifying column.

In the figure, 1-a feed pump; 2-a barometer; 3-overhead thermometer; 4-tower top automatic control valve; 5-overhead condenser; 6-a controller; 7-a body thermometer; 8-rectifying the tower body; 9-a reboiler; 10-discharge hole at bottom of tower.

Detailed Description

Adopting the process flow shown in figure 1, firstly adopting the atmospheric distillation equipment shown in figure 2 for fractionation, then adopting the pressurized distillation tower (second distillation tower) shown in figure 3 for secondary distillation of the methylal fraction obtained by the atmospheric distillation tower, firstly distilling out the methyl chloride fraction again, and then distilling out the methylal fraction; finally, the methanol rectifying tower adopts an atmospheric rectifying tower similar to the figure 2. And distilling the tower bottom solution of the atmospheric distillation tower to obtain a methanol solution.

The product obtained was analyzed by pilot test.

The first embodiment is as follows: the pressure in the tower is 450kpa, the temperature at the top of the tower is 80-85 ℃, and the content of a methylal fraction product at the top of the tower is determined by analysis: methylal: 94.1%, methyl chloride: 1.1 percent.

Example two: the pressure in the tower is 550kpa, the temperature at the top of the tower is 90-95 ℃, and the content of a methylal fraction product at the top of the tower is determined by analysis: methylal: 95.01%, methyl chloride: 0.8 percent; the content of the methanol solution obtained by distillation in the methanol distillation tower is 99 percent.

Claims

1. A pressurized rectification and purification process device for methylal is used for treating a neutralized solution of dilute methanol obtained in the production process of glyphosate by a glycine method, and is characterized in that: the method comprises the following steps of (1) increasing the boiling points of methyl chloride and methylal by adopting a pressure rectification technology, fractionating methyl chloride fractions at a lower temperature, and then heating to fractionate methylal fractions; and then feeding the tower bottom solution of the pressure rectification into a methanol distillation tower for distillation to obtain a methanol solution.

2. The methylal pressure distillation purification process equipment as claimed in claim 1, wherein: before the pressure rectification, the primary normal pressure rectification is carried out in a normal pressure rectification tower, and the obtained top gas or the condensate thereof is subjected to pressure rectification.

3. The methylal pressure distillation purification process equipment as claimed in claim 1 or 2, wherein: the pressure in the tower during the pressure rectification is 450-550 kpa; when methyl chloride is distilled, controlling the temperature at the top of the tower to be 20-30 ℃; and then, when the methylal fraction is distilled, controlling the tower top temperature of the second rectifying tower to be 80-95 ℃.

4. The methylal pressure distillation purification process equipment as claimed in claim 1 or 2, wherein: the pressurized rectifying tower used for pressurized rectification is provided with a pressurized rectifying section and a tower top condensing section, and the tower top condensing section is directly arranged above the pressurized rectifying section; a pressure gauge for testing the pressure in the tower is arranged between the pressure rectifying section and the condensing section at the top of the tower, and a thermometer is arranged at the top of the condenser; the controller is additionally arranged and can receive a temperature signal of the tower top thermometer and a pressure signal of the pressure gauge; when the designed pressure interval and the designed fractionation temperature are respectively reached, the controller controls the automatic control valve at the top of the tower to be opened, and relatively pure methyl chloride fraction and methylal fraction are discharged in sequence.