CN111548249A

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Info

Publication number: CN111548249A
Application number: CN201911382238.4A
Authority: CN
Inventors: 李子平; 高德喜; 李金元
Original assignee: Andomai Co ltd
Current assignee: Andomai Co ltd
Priority date: 2019-12-27
Filing date: 2019-12-27
Publication date: 2020-08-18

Abstract

The invention discloses a method for recovering chloroform and hydrogen chloride in a methyl isocyanate production process, and belongs to the technical field of fine chemical production. The production of methyl isocyanate comprises the steps of synthesizing methyl carbamoyl chloride by adopting phosgene and monomethylamine, and decomposing the methyl carbamoyl chloride into methyl isocyanate and tail gas containing chloroform and hydrogen chloride, wherein the method comprises the following steps: 1) the tail gas containing chloroform and hydrogen chloride passes through a condenser, most of chloroform gas is condensed into liquid and is captured, and the rest chloroform and hydrogen chloride gas are sprayed into hydrochloric acid mixed solution through water of a falling film absorber; 2) cooling the mixed solution of hydrochloric acid obtained in the step 1) to 20-60 ℃, then sending the mixed solution into a delayer along a tangential liquid inlet arranged on the side part of the delayer, deflecting and rotating in each baffle arranged in the delayer to enable chloroform and hydrochloric acid to settle and delaminate, wherein the hydrochloric acid flows into a hydrochloric acid circulating tank along an overflow port arranged on the top of the delayer, the chloroform flows into a chloroform receiving kettle from a liquid outlet arranged on the bottom of the delayer, and the rest mixed solution in the delayer is sent into the delayer again along the liquid outlet and the tangential liquid inlet.

Description

Method for recovering chloroform and hydrogen chloride in methyl isocyanate production process

Technical Field

The invention relates to recovery of a reaction solvent and byproducts, belongs to the technical field of fine chemical production, and particularly relates to a method for recovering chloroform and hydrogen chloride in a methyl isocyanate production process.

Background

Chloroform (CHCl) as the term₃) The main physicochemical properties are as follows: colorless transparent liquid, special smell, sweet taste, high refraction, low toxicity, incombustibility, heavy weight and easy volatilization. The pure product is sensitive to light and can react with oxygen in the air when being irradiated by light to be gradually decomposed to generate virulent phosgene (carbonyl chloride) and hydrogen chloride. Relative density 1.484, freezing point-63.5 deg.C, boiling point 61.3 deg.C, and refractive index 1.4476.

The production method of domestic methyl isocyanate is characterized by using phosgene and monomethylamine as raw materials to synthesize methyl carbamyl Chloride (CH) at the temperature of 210-230 DEG C₃NHCOCl), then using trichloromethane solvent as carrier, decomposing and rectifying to obtain the invented product. The reaction equation is as follows:

CH₃NH₂+COCl₂→CH₃NHCOCl+HCl↑；

CH₃NHCOCl→CH₃NCO+HCl↑；

for example, Chinese patent application (application publication No. CN 103694190A, application publication date: 2014-04-02) discloses a method and equipment for producing methyl isocyanate, which comprises the following steps:

(1) with CO₂、O₂Producing CO with coke, producing phosgene with CO and chlorine, and synthesizing methylamino formyl chloride with phosgene and monomethylamine;

(2) after being synthesized, the methylamino formyl chloride is sent to a liquid mixing tank to be added with a solvent for mixing, the mixed liquid of the methylamino formyl chloride and the chloroform contains a small amount of solid residue of the methylamine hydrochloride, and the methyl carbamoyl chloride is sent to a decomposer after being continuously filtered and deslagged through a filter which is additionally provided with a wire mesh filler and 350-mesh filter cloth for two-stage filtration;

(3) decomposing the mixed solution of the methyl carbamoyl chloride and the chloroform filtered in the step (2) in a decomposer to obtain methyl isocyanate, dissolving the methyl isocyanate, and then feeding the dissolved methyl isocyanate into a deslagging and purifying production system: carrying out first-stage filtration on solid slag through a slag steaming kettle; carrying out gas-liquid separation and condensation on the decomposed product, collecting a solid-liquid mixture containing the methyl isocyanate and the solid slag, sending the solid-liquid mixture to a crude ester tower for separation, sending the high-boiling-point solid slag in the solid-liquid mixture to a slag steaming kettle through a reflux main pipe for secondary filtration of the solid slag, and further removing solid impurities in the solid-liquid mixture to obtain a methyl isocyanate mixture containing a small amount of impurities;

(4) sequentially feeding the methyl isocyanate mixture subjected to two-stage filter residue treatment in the step (2) into a crude ester tower and a refined ester tower for distillation, and purifying to obtain methyl isocyanate;

(5) and (3) guiding the tail gas generated in the steps (1) to (4) by using a fan, then enabling the tail gas to enter a four-stage tail gas absorption device for serial absorption, and recovering the byproduct hydrogen chloride to reach the standard and discharging.

The tail gas absorption device is complex to operate.

For another example, the chinese patent application (application publication No. CN 104557441a, application publication date: 2015-04-29) discloses a method for recovering chloroform during the production of methyl isocyanate, which comprises the following steps: cooling the decomposed tail gas to 30-40 ℃ through a cooler, then enabling the cooled tail gas to enter a delayer, layering chloroform and hydrochloric acid in the tail gas in the delayer, enabling the chloroform with large specific gravity to flow into a chloroform receiving kettle for receiving and recycling the chloroform for producing methyl isocyanate, and independently recovering the hydrochloric acid with small specific gravity. However, the recovery effect is poor.

Disclosure of Invention

In order to solve the technical problems, the invention provides a method for recovering chloroform and hydrogen chloride in the production process of methyl isocyanate, which can effectively separate chloroform and hydrogen chloride in tail gas generated in the production of the methyl isocyanate, and respectively recover and treat the chloroform and the hydrogen chloride, and then recycle the recovered chloroform solvent after refining and dehydrating, thereby reducing the production cost, reducing the corrosion of the chloroform to glass fiber reinforced plastic equipment, and simultaneously improving the quality of byproduct hydrochloric acid. The consumption of chloroform per ton is reduced from about 100kg of chloroform per ton of methyl isocyanate to 60-65 kg of chloroform per ton of methyl isocyanate.

In order to achieve the purpose, the invention discloses a method for recovering chloroform and hydrogen chloride in the production process of methyl isocyanate, wherein the production of the methyl isocyanate comprises the steps of synthesizing methyl carbamoyl chloride by adopting phosgene and monomethylamine, and decomposing the methyl carbamoyl chloride into the methyl isocyanate and tail gas containing the chloroform and the hydrogen chloride, and the method comprises the following steps:

1) the tail gas containing chloroform and hydrogen chloride passes through a condenser, most of chloroform gas is condensed into liquid and is captured, and the rest chloroform and hydrogen chloride gas are sprayed into hydrochloric acid mixed solution through water of a falling film absorber;

2) cooling the hydrochloric acid mixed solution obtained in the step 1) to 20-60 ℃, then feeding the mixed solution into a delayer along a tangential liquid inlet arranged on the side part of the delayer, deflecting and rotating in each baffle arranged in the delayer to enable chloroform and hydrochloric acid to settle and delaminate, wherein the hydrochloric acid flows into a hydrochloric acid circulating tank along an overflow port arranged on the top of the delayer, the chloroform flows into a chloroform receiving kettle from a liquid outlet arranged on the bottom of the delayer, and the rest mixed solution in the delayer is fed into the delayer again along the liquid outlet and the tangential liquid inlet.

Furthermore, more than one baffle is arranged in the delayer, and the baffles are arranged close to each other to form a spiral line type structure. The mixed liquid can be sufficiently mixed, collided and centrifugally separated in the baffle plate with the spiral structure.

Furthermore, a liquid collecting part is further arranged in the delayer, liquid after baffling and rotation flows into the liquid collecting part again, the overflow port is located at the top end of the liquid collecting part, and the liquid discharging port is located at the bottom end of the liquid collecting part.

Further, the temperature in the delaminator is set to be 20-60 ℃.

Further, in the step 1), the condenser adopts a circulating brine condensing working medium to realize condensation of the chloroform gas.

The beneficial effects of the invention are mainly embodied in the following aspects:

the recovery method designed by the invention is simple to operate, and can better realize the separation of chloroform and hydrogen chloride, wherein the recovery rate of chloroform is about 95 percent, and the recovery rate of hydrogen chloride is about 99 percent; the recovered chloroform is further refined and dehydrated and can be reused in the production of methyl isocyanate, which is beneficial to reducing the production cost.

Drawings

FIG. 1 is a schematic diagram of the structure of the layering device used in the recycling method of the present invention.

FIG. 2 is a process flow diagram of a recovery process.

Wherein, each part in fig. 1 is numbered as follows:

a delayer 1 (wherein, the tangential liquid inlet 1.1, the baffle 1.2, the liquid collecting part 1.3, the overflow port 1.4 and the liquid outlet 1.5).

Detailed Description

The invention discloses a method for recovering chloroform and hydrogen chloride in the production process of methyl isocyanate, wherein the production of the methyl isocyanate comprises the steps of synthesizing methyl carbamoyl chloride by adopting phosgene and monomethylamine, and decomposing the methyl carbamoyl chloride into methyl isocyanate and tail gas containing the chloroform and the hydrogen chloride, and the method comprises the following steps: as shown in particular in fig. 2;

1) and the tail gas containing chloroform and hydrogen chloride passes through a condenser, wherein the condenser is internally provided with a circulating brine condensing working medium to realize the condensation of the chloroform gas. Most (about 65 percent) chloroform gas is condensed into liquid and is captured, and the rest chloroform and hydrogen chloride gas are sprayed into hydrochloric acid mixed solution through water of a falling film absorber;

2) the hydrochloric acid mixed solution in the step 1) is cooled to 20-60 ℃, and then is sent into a delayer 1 shown in the figure 1 to realize separation, specifically, a tangential liquid inlet 1.1 arranged along the side part of the delayer 1 is sent into the delayer 1, and baffling and rotation are generated in baffles 1.2 arranged in the delayer 1, wherein, in the invention, the baffles 1.2 are preferably arranged close to each other to form a spiral line type structure. The hydrochloric acid mixed liquid continuously generates baffling, rotation and the like in the spiral structure, can realize full mixing and finally flows into the liquid collecting part 1.3 and realizes chloroform and hydrochloric acid sedimentation and layering, wherein the hydrochloric acid flows into the hydrochloric acid circulating tank along an overflow port 1.4 arranged at the top of the layering device 1, the chloroform flows into the chloroform receiving kettle from a liquid discharge port 1.5 arranged at the bottom of the layering device, and the rest mixed liquid in the layering device is sent into the layering device again along the liquid discharge port and the tangential liquid inlet. As can be seen from fig. 1, the delayer 1 designed by the present invention includes an outer shell, and more than one baffle 1.2 located inside the outer shell, wherein the baffles 1.2 are closely arranged and form a spiral structure. The mixed liquid can be sufficiently mixed, collided and centrifugally separated in the baffle plate with the spiral structure. In addition, still be equipped with the liquid collecting part 1.3 in the delayer 1, liquid after baffling and rotation flows into liquid collecting part 1.3 again, overflow mouth 1.4 is located the liquid collecting part 1.3 top, and discharge port 1.5 is located the liquid collecting part 1.3 bottom, and the liquid through baffling and rotation can realize fully separating and layering in liquid collecting part 1.3.

In order to better explain the invention, the following further illustrate the main content of the invention in connection with specific examples, but the content of the invention is not limited to the following examples.

Example 1

The embodiment discloses a method for recovering chloroform and hydrogen chloride in the production process of methyl isocyanate, which comprises the following steps:

1) the tail gas containing chloroform and hydrogen chloride is passed through a condenser to effect condensation of the chloroform gas. Most of chloroform gas is condensed into liquid and captured, and the rest chloroform and hydrogen chloride gas are sprayed into hydrochloric acid mixed solution by water of a falling film absorber; 2) cooling the mixed solution of hydrochloric acid obtained in the step 1) to 30 ℃, then sending the mixed solution of hydrochloric acid into a delayer along a tangential liquid inlet arranged on the side part of the delayer, deflecting and rotating in each baffle arranged in the delayer to enable chloroform and hydrochloric acid to settle and delaminate, wherein the hydrochloric acid flows into a hydrochloric acid circulating tank along an overflow port arranged on the top of the delayer, the chloroform flows into a chloroform receiving kettle from a liquid outlet arranged on the bottom of the delayer, and the rest mixed solution in the delayer is sent into the delayer again along the liquid outlet and the tangential liquid inlet. The yield of hydrochloric acid recovered in this example was 98.5% and the yield of chloroform recovered was 95.6%.

Example 2

1) the tail gas containing chloroform and hydrogen chloride is passed through a condenser, wherein the condenser is used for condensing the chloroform gas. Most of chloroform gas is condensed into liquid and captured, and the rest chloroform and hydrogen chloride gas are sprayed into hydrochloric acid mixed solution by water of a falling film absorber;

2) cooling the mixed solution of hydrochloric acid obtained in the step 1) to 50 ℃, then sending the mixed solution of hydrochloric acid into a first delayer along a tangential liquid inlet arranged on the side part of the delayer, deflecting and rotating each baffle arranged in the first delayer to enable chloroform and hydrochloric acid to settle and separate layers, wherein the hydrochloric acid flows into a hydrochloric acid circulation tank along an overflow port arranged on the top of the delayer, the chloroform flows into a chloroform receiving kettle from a liquid outlet arranged on the bottom of the first delayer, the rest mixed solution in the first delayer flows into a second delayer again along the liquid outlet, further plays the same role as the first delayer, and the rest mixed solution in the second delayer is sent into the second delayer again along the liquid outlet and the tangential liquid inlet of the second delayer. The yield of hydrochloric acid recovered in this example was 99.2%, and the yield of chloroform recovered was 95.6%.

Example 3

1) the tail gas containing chloroform and hydrogen chloride is passed through a condenser, wherein the condenser is used for condensing the chloroform gas. Most of chloroform gas is condensed into liquid and captured, and the rest chloroform and hydrogen chloride gas are sprayed into hydrochloric acid mixed solution by water of a falling film absorber; 2) the temperature of the hydrochloric acid mixed liquor in the step 1) is reduced to 50 ℃, and then the hydrochloric acid mixed liquor is sent into the delaminators along the tangential liquid inlets arranged on the side parts of the delaminators, preferably 3 delaminators are arranged in series in the embodiment, namely the tangential liquid inlets of the adjacent delaminators are connected with a liquid outlet. The other arrangement is the same as in example 2.

The yield of hydrochloric acid recovered in this example was 99.5% and the yield of chloroform recovered was 95.8%.

In addition, this example also explores the recovery mode of 4 laminators in series and 5 laminators in series, and as a result, it is found that the recovery rate is increased with the increase of the devices, but the effect is not obvious. Therefore, 3 laminators are finally selected and the recycling process is schematically shown in fig. 2. The recovered trichloromethane can be reused in the solvent for producing methyl isocyanate through further refining and dehydration treatment. The recovery method designed by the invention can effectively separate the chloroform and the hydrogen chloride in the tail gas generated in the production of the methyl isocyanate, and researches show that the consumption of chloroform per ton is reduced from about 100kg of chloroform per ton of original methyl isocyanate to 60-65 kg of chloroform per ton of methyl isocyanate.

The above examples are merely preferred examples and are not intended to limit the embodiments of the present invention. In addition to the above embodiments, the present invention has other embodiments. All technical solutions formed by adopting equivalent substitutions or equivalent transformations fall within the protection scope of the claims of the present invention.

Claims

1. A method for recovering chloroform and hydrogen chloride in the production process of methyl isocyanate comprises the steps of synthesizing methyl carbamoyl chloride by adopting phosgene and monomethylamine, and decomposing the methyl carbamoyl chloride into methyl isocyanate and tail gas containing chloroform and hydrogen chloride, and is characterized by comprising the following steps:

2. The method for recovering chloroform and hydrogen chloride in the production process of methyl isocyanate according to claim 1, wherein more than one baffle is arranged inside the delaminator, and each baffle is arranged close to each other and forms a spiral structure.

3. The method for recovering chloroform and hydrogen chloride in the production process of methyl isocyanate according to claim 1, wherein a liquid collecting part is further arranged in the delaminator, the liquid after baffling and rotation flows into the liquid collecting part again, the overflow port is positioned at the top end of the liquid collecting part, and the liquid discharge port is positioned at the bottom end of the liquid collecting part.