A low-consumption and high-efficiency separation method for tail gas containing hydrogen fluoride, hydrogen chloride and nitrogen

Abstract

The present invention relates to a low-cost and high-efficiency separation method for tail gas containing hydrogen fluoride, hydrogen chloride and nitrogen, and belongs to the field of chemical separation. The separation method provided by the present invention first compresses and condenses the tail gas to partially liquefy it, and then performs gas-liquid separation, and the separated gas phase is sent to an absorption tower to recover the hydrogen chloride contained in the gas, and the liquid phase is sent to a distillation tower, and the distillation tower is used for continuous distillation to achieve the separation of light components mainly composed of hydrogen chloride and hydrogen fluoride. The separation method provided by the present invention can effectively separate and recover hydrogen fluoride and hydrogen chloride, realize the resource utilization of tail gas, greatly reduce operating costs, improve the economic benefits of the entire process, and also make the entire process run more smoothly.

Description

Technical Field

[0001] The invention relates to the field of chemical separation, and in particular to a low-consumption and high-efficiency separation method for tail gas containing hydrogen fluoride, hydrogen chloride and nitrogen. Background Art

[0002] Tail gas containing hydrogen fluoride, hydrogen chloride and nitrogen is a very common tail gas in the field of fluorine chemical industry. Especially in the production process of lithium hexafluorophosphate, a large amount of such tail gas will be produced, which is extremely harmful to the environment and human body. Therefore, there are high requirements for the treatment of such tail gas. At the same time, the hydrogen chloride and hydrogen fluoride contained in this type of tail gas have a high recovery value. If this type of tail gas can be economically and reasonably recycled, then while achieving the reasonable treatment of this type of chemical tail gas, it will also increase certain economic benefits. However, for the technical problems of recycling and treating this type of tail gas, a recognized and effective treatment method has not yet been established. Commonly used methods mainly include absorption methods and condensation methods, but both have obvious technical defects. The products obtained after the above-mentioned technical treatment have problems such as incomplete separation of hydrogen fluoride and hydrogen chloride and low application value of the separated products. Patent 202111579824.5 reports a method of pressurized distillation. When the pressure is 0.6-3.0Mpa, hydrogen fluoride and hydrogen chloride can be effectively separated, high-purity hydrogen fluoride is obtained at the bottom of the tower, and a mixed gas of hydrogen chloride and hydrogen fluoride is obtained at the top of the tower. Hydrochloric acid and nitrogen can be obtained by absorption separation. However, this method requires the tail gas to be pressurized to a higher pressure, which consumes a lot of energy. Patent 202111634638.7 improves this process. After the tail gas is initially pressurized, almost all the hydrogen fluoride and most of the hydrogen chloride are condensed by condensation, and sent to the heat exchange tower by a high-pressure pump. The residual gas is pressurized by the compressor and then enters the heat exchange tower. After the two fluids are heat exchanged in the heat exchange tower, they enter the distillation tower for distillation separation, and high-purity hydrogen fluoride is obtained at the bottom of the tower, and a mixed gas of hydrogen chloride and hydrogen fluoride is obtained at the top of the tower. Compared with Patent 202111579824.5, the amount of gas compressed by this method is greatly reduced, so it can save a lot of energy consumption. However, due to the low added value of hydrochloric acid, the hydrochloric acid revenue obtained is difficult to cover the operating costs of the compressor compared to the energy consumed by the compressor. In addition, the presence of a large proportion of nitrogen not only increases the difficulty of commissioning and operating the distillation tower, but also makes it difficult to condense the steam at the top of the tower. Higher pressure and very low temperature are required to meet the condensation requirements of hydrogen chloride, which also increases the operating costs. Therefore, it is very necessary to develop a low-energy and efficient treatment process for chemical tail gas mainly containing hydrogen fluoride, hydrogen chloride and nitrogen. Summary of the invention

[0003] In order to solve the problem of high energy consumption in the prior art, the present invention provides a low-consumption and high-efficiency separation method for tail gas containing hydrogen fluoride, hydrogen chloride and nitrogen. After a series of pretreatments, hydrogen fluoride and hydrogen chloride are separated by distillation to obtain by-products with application value, thereby realizing the reasonable and full utilization of this type of chemical tail gas.

[0004] In order to achieve the above-mentioned invention object, the present invention provides the following technical solutions:

[0005] The present invention provides a low-consumption and high-efficiency separation method for tail gas containing hydrogen fluoride, hydrogen chloride and nitrogen, comprising the following steps:

[0006] (1) First, the exhaust gas is compressed and pressurized by a compressor;

[0007] (2) cooling the pressurized tail gas obtained in step (1) through a heat exchanger, and partially condensing the tail gas to obtain a gas-liquid two-phase;

[0008] (3) Using a distillation tower to distill the liquid phase obtained in step (2), producing high-purity hydrogen fluoride liquid at the bottom of the tower, and producing a mixture of high-purity hydrogen chloride and a small amount of nitrogen at the top of the tower.

[0009] Preferably, the tail gas in step (1) is compressed by a compressor and then pressurized from normal pressure to 2.0-8.0 bar.

[0010] Preferably, the condensing temperature of the heat exchanger in step (2) is -25 to -80°C.

[0011] Preferably, in step (3), the number of theoretical plates of the distillation tower is 6-30, and the reflux ratio of the distillation tower is 0.5-5.

[0012] Preferably, the feeding position of the liquid phase in step (3) is the 3rd to 20th theoretical plates from top to bottom in the distillation tower.

[0013] Preferably, in step (3), the top temperature of the distillation tower is -55 to 5°C, and the top pressure of the distillation tower is 5-30 bar.

[0014] Preferably, the tail gas mainly contains hydrogen fluoride, hydrogen chloride and nitrogen, and also contains a small amount of phosphorus pentafluoride. The content of each component is calculated by mass fraction: 20-70% hydrogen fluoride, 10-60% nitrogen, 5-50% hydrogen chloride, and 0.01%-1.5% phosphorus pentafluoride. The separation method provided by the present invention first compresses and condenses the chemical tail gas to obtain gas-liquid two phases, wherein the gas phase is mainly nitrogen and hydrogen chloride, and the hydrogen chloride can be recovered through an absorption tower, and a small amount of hydrogen fluoride can be removed in advance by absorption; the liquid phase is a mixed liquid mainly containing hydrogen chloride, hydrogen fluoride and a small amount of nitrogen and phosphorus pentafluoride, which is pumped into a distillation tower to complete the separation of hydrogen fluoride and hydrogen chloride in the distillation tower. High-purity hydrogen fluoride is produced in the bottom of the tower, and gas mainly composed of hydrogen chloride is produced at the top of the tower, which can be used as a hydrogen chloride product, or prepared as hydrochloric acid through absorption. The present invention has the following significant advantages:

[0015] (1) The gas phase is directly absorbed to prepare hydrochloric acid without going to the distillation tower, which can save the subsequent compression energy consumption of this part of the gas and greatly reduce the operating cost. At the same time, the operating pressure of the distillation tower is reduced and the operating temperature is increased, which also makes the operating conditions more moderate and reduces the operating cost;

[0016] (2) The nitrogen content in the liquid phase entering the distillation is extremely low, which is conducive to the continuous and stable operation of the distillation tower;

[0017] (3) The distillation method has better separation effect and greater processing capacity, and can obtain high-quality hydrogen fluoride and hydrogen chloride. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a low-consumption and high-efficiency separation method of tail gas containing hydrogen fluoride, hydrogen chloride and nitrogen in an embodiment of the present invention; in the figure, 1 is a compressor, 2 is a condensing heat exchanger, 3 is a gas-liquid separation tank, 4 is an HCl absorption tower, 5 is a distillation tower feed pump, 6 is a distillation tower, 7 is a distillation tower condenser, 8 is a distillation tower reflux tank, 9 is a reflux pump, and 10 is a distillation tower reboiler DETAILED DESCRIPTION

[0019] The present invention provides a low-consumption and high-efficiency separation method for tail gas containing hydrogen fluoride, hydrogen chloride and nitrogen, comprising the following steps:

[0020] (1) First, the exhaust gas is compressed and pressurized by a compressor;

[0021] (2) cooling the pressurized tail gas obtained in step (1) through a heat exchanger, and partially condensing the tail gas to obtain a gas-liquid two-phase;

[0022] (3) Using a distillation tower to distill the liquid phase obtained in step (2), producing high-purity hydrogen fluoride liquid at the bottom of the tower, and producing a mixture of high-purity hydrogen chloride and a small amount of nitrogen at the top of the tower.

[0023] Preferably, the tail gas in step (1) is compressed by a compressor and then pressurized from normal pressure to 2.0-8.0 bar.

[0024] Preferably, the condensing temperature of the heat exchanger in step (2) is -25 to -80°C.

[0025] Preferably, in step (3), the number of theoretical plates of the distillation tower is 6-30, and the reflux ratio of the distillation tower is 0.5-5.

[0026] Preferably, the feeding position of the liquid phase in step (3) is the 3rd to 20th theoretical plates from top to bottom in the distillation tower.

[0027] Preferably, in step (3), the top temperature of the distillation tower is -55 to 5°C, and the top pressure of the distillation tower is 5-30 bar.

[0028] Preferably, the tail gas mainly contains hydrogen fluoride, hydrogen chloride and nitrogen, and also contains a small amount of phosphorus pentafluoride. Calculated by mass fraction, the content of each component is: hydrogen fluoride 20-70%, nitrogen 10-60%, hydrogen chloride 5-50%, phosphorus pentafluoride 0.01%-1.5%.

[0029] In the present invention, it is preferred to compress the chemical tail gas mainly containing hydrogen fluoride, hydrogen chloride and nitrogen and then condense it.

[0030] The present invention has no special limitation on the compression, and any method known in the art may be used.

[0031] The condensate can be cooled directly by using an external cooling source, or the chemical tail gas can be condensed by exchanging heat with the mixed gas mainly composed of hydrogen chloride / nitrogen obtained at the top of the distillation tower.

[0032] In the present invention, it is preferred that the gas-liquid two phases obtained in step (2) are separated in a gas-liquid separation tank and the liquid phase is sent to a distillation tower for further distillation separation; the gas phase is sent to the bottom of the absorption tower and countercurrently contacts with the absorbent in the absorption tower to absorb the hydrogen chloride contained in the gas.

[0033] After the distillation is completed, the present invention preferably extracts the top distillate, and then sequentially undergoes partial condensation and gas-liquid separation to obtain gas-liquid two-phases, wherein the liquid phase is refluxed into the distillation tower and the gas phase is extracted.

[0034] The present invention has no particular limitation on the condensation, and any method known in the art may be used.

[0035] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] Example 1

[0037] Figure 1 The process flow chart of a low-cost and high-efficiency separation method of tail gas containing hydrogen fluoride, hydrogen chloride and nitrogen in the embodiment is as follows: the above-mentioned chemical tail gas is condensed and pressurized to 2.0-8.0 bar by compressor 1 at normal temperature and pressure, and then sent to condensation heat exchanger 2. After being partially condensed to -25-80°C in the condensation heat exchanger, the gas-liquid two-phase is sent to gas-liquid separation tank 3. The gas phase extracted from the top of the gas-liquid separation tank enters the bottom of the hydrogen chloride absorption tower 4, and contacts with the absorbent in the absorption tower in countercurrent to absorb the hydrogen chloride contained in the gas phase. The liquid phase extracted from the bottom of the gas-liquid separation tank enters the distillation tower 6 through the distillation tower feed pump 5. In the distillation tower 6, the light components mainly composed of hydrogen chloride are distilled from the top of the tower, and are partially condensed by the distillation tower condenser 7 and the gas-liquid separation is carried out by the distillation tower reflux tank 8. The liquid phase is completely refluxed into the distillation tower 6, and the gas phase is extracted to obtain a gas mainly composed of hydrogen chloride with extremely low hydrogen fluoride content; the distillation tower reboiler 10 provides rising steam in the tower, and the distillation tower 6 tower kettle extracts high-purity hydrogen fluoride, which enters the hydrogen fluoride product tank for storage after cooling.

[0038] (1) First, the exhaust gas is compressed and pressurized by a compressor;

[0039] (2) cooling the pressurized tail gas obtained in step (1) through a heat exchanger, and partially condensing the tail gas to obtain a gas-liquid two-phase;

[0040] (3) Using a distillation tower to distill the liquid phase obtained in step (2), producing high-purity hydrogen fluoride liquid at the bottom of the tower, and producing a mixture of high-purity hydrogen chloride and a small amount of nitrogen at the top of the tower.

[0041] According to mass fraction, the chemical tail gas includes 42.7% hydrogen fluoride, 28.1% hydrogen chloride, 28.9% nitrogen, and 0.3% phosphorus pentafluoride;

[0042] The chemical tail gas in step (1) is pressurized to 2.1 bar;

[0043] The gas phase of step (2) is partially condensed to -25°C via a condensing heat exchanger;

[0044] The number of theoretical plates of the distillation tower is 30, and the reflux ratio is 2.0;

[0045] The feeding position of the liquid phase is the 11th theoretical plate from the top to the bottom of the distillation tower;

[0046] The top temperature of the distillation tower is -51°C and the top pressure is 5.0 bar;

[0047] The mixed gas mainly composed of nitrogen and hydrogen chloride obtained from the tower top contains, by mass fraction, 98.51% hydrogen chloride, 1.01% nitrogen, 0.47% phosphorus pentafluoride, and hydrogen fluoride <100ppm;

[0048] The tower bottom produces high-purity hydrogen fluoride, with a purity of >99.99% and a purity of <50 ppm of hydrogen chloride in terms of mass fraction.

[0049] Example 2

[0050] A low-consumption and high-efficiency separation method for tail gas containing hydrogen fluoride, hydrogen chloride and nitrogen:

[0051] (1) First, the exhaust gas is compressed and pressurized by a compressor;

[0052] (2) cooling the pressurized tail gas obtained in step (1) through a heat exchanger, and partially condensing the tail gas to obtain a gas-liquid two-phase;

[0053] (3) Using a distillation tower to distill the liquid phase obtained in step (2), producing high-purity hydrogen fluoride liquid at the bottom of the tower, and producing a mixture of high-purity hydrogen chloride and a small amount of nitrogen at the top of the tower.

[0054] According to mass fraction, the chemical tail gas includes 48.7% hydrogen fluoride, 28.6% hydrogen chloride, 22.5% nitrogen, and 0.2% phosphorus pentafluoride;

[0055] The chemical tail gas in step (1) is pressurized to 5.0 bar;

[0056] The gas phase in step (2) is partially condensed to -50°C via a condensing heat exchanger;

[0057] The number of theoretical plates of the distillation tower is 21, and the reflux ratio is 3.2;

[0058] The feeding position of the liquid phase is the 15th theoretical plate from the top to the bottom of the distillation tower;

[0059] The top temperature of the distillation tower is -27°C and the top pressure is 12 bar;

[0060] The mixed gas mainly composed of nitrogen and hydrogen chloride obtained from the tower top contains, by mass fraction, 99.29% hydrogen chloride, 0.49% nitrogen, 0.21% phosphorus pentafluoride, and hydrogen fluoride <100ppm;

[0061] The tower bottom produces high-purity hydrogen fluoride, with a purity of >99.99% and a purity of <50 ppm of hydrogen chloride in terms of mass fraction.

[0062] Example 3

[0063] A low-consumption and high-efficiency separation method for tail gas containing hydrogen fluoride, hydrogen chloride and nitrogen:

[0064] (1) First, the exhaust gas is compressed and pressurized by a compressor;

[0065] (2) cooling the pressurized tail gas obtained in step (1) through a heat exchanger, and partially condensing the tail gas to obtain a gas-liquid two-phase;

[0066] (3) Using a distillation tower to distill the liquid phase obtained in step (2), producing high-purity hydrogen fluoride liquid at the bottom of the tower, and producing a mixture of high-purity hydrogen chloride and a small amount of nitrogen at the top of the tower.

[0067] According to mass fraction, the chemical tail gas includes 55.9% hydrogen fluoride, 30.4% hydrogen chloride, 13.6% nitrogen, and 0.1% phosphorus pentafluoride;

[0068] The chemical tail gas in step (1) is pressurized to 6.0 bar;

[0069] The gas phase of step (2) is partially condensed to -65°C via a condensing heat exchanger;

[0070] The number of theoretical plates of the distillation tower is 10, and the reflux ratio is 4.8;

[0071] The feeding position of the liquid phase is the seventh theoretical plate from the top to the bottom of the distillation tower;

[0072] The top temperature of the distillation tower is -2°C and the top pressure is 25 bar;

[0073] The mixed gas mainly composed of nitrogen and hydrogen chloride obtained from the tower top contains, by mass fraction, 98.28% hydrogen chloride, 1.43% nitrogen, 0.28% phosphorus pentafluoride, and hydrogen fluoride <100ppm;

[0074] The tower bottom produces high-purity hydrogen fluoride, with a purity of >99.99% and a purity of <50 ppm of hydrogen chloride in terms of mass fraction.

[0075] According to the results of the examples, the separation method provided by the present invention can obtain hydrogen fluoride liquid with a mass fraction higher than 99.99%. At the same time, the mixed gas obtained at the top of the tower can be processed in subsequent stages to obtain high-purity hydrogen chloride. Both substances can be used or sold as by-products, which not only reduces the emission of waste gas, but also creates economic value for the enterprise.

[0076] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A low-consumption and high-efficiency separation method for tail gas containing hydrogen fluoride, hydrogen chloride and nitrogen, comprising the following steps: (1) First, the exhaust gas is compressed and pressurized by a compressor; (2) cooling the pressurized tail gas obtained in step (1) through a heat exchanger, and partially condensing the tail gas to obtain a gas-liquid two-phase; (3) using a distillation tower to distill the liquid phase obtained in step (2), producing high-purity hydrogen fluoride liquid at the bottom of the tower, and producing a mixture of high-purity hydrogen chloride and a small amount of nitrogen at the top of the tower; The tail gas in step (1) is compressed by a compressor and then pressurized from normal pressure to 2.0 to 8.0 bar. The condensing temperature of the heat exchanger in step (2) is -25 to -80°C. The number of theoretical plates of the distillation tower in step (3) is 6 to 30, the reflux ratio of the distillation tower is 0.5 to 5, the feed position of the liquid phase is the 3rd to 20th theoretical plates from the top to the bottom of the distillation tower, the top temperature of the distillation tower is -55 to 5°C, and the top pressure of the distillation tower is 5 to 30 bar.

2. The separation method according to claim 1, characterized in that The tail gas mainly contains hydrogen fluoride, hydrogen chloride and nitrogen, and also contains a small amount of phosphorus pentafluoride. Calculated by mass fraction, the content of each component is: hydrogen fluoride 20-70%, nitrogen 10-60%, hydrogen chloride 5-50%, phosphorus pentafluoride 0.01%-1.5%.

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