A method for preparing hydrogen chloride with low energy consumption

Abstract

The present invention discloses a low-energy hydrogen chloride preparation method, belonging to the technical field of by-product hydrochloric acid treatment. The method comprises the following steps: Step 1. Using a sulfuric acid solution or a salt solution as an absorbent to cool and absorb impurity hydrogen chloride gas; Step 2. Transporting the mixed liquid that has absorbed the hydrogen chloride to a desorption (desorption) tower, converting the hydrogen chloride into a gas phase and extracting the liquid phase by increasing the temperature, cooling the hydrogen chloride gas to form a high-concentration hydrogen chloride, and returning the desorbed sulfuric acid or salt solution to the low-temperature absorption stage to circulate and absorb the hydrogen chloride. The present invention no longer uses water to absorb and desorb hydrogen chloride, but instead uses a sulfuric acid solution or a salt solution to directly absorb the hydrogen chloride, eliminating the investment in the water removal process of the existing desorption device and eliminating the need to consume energy for subsequent water evaporation. Steam energy consumption is significantly reduced compared to that of existing process devices, no acidic wastewater is generated, and pollutant emissions are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of by-product hydrochloric acid treatment, and in particular relates to a method for preparing hydrogen chloride with low energy consumption. Background Art

[0002] At present, the national caustic soda production capacity is 38.9 million tons / year, which is equivalent to 34.5 million tons / year of chlorine production capacity. Most of the chlorine (85%) is used to produce hydrogen chloride to produce vinyl chloride. The molar excess in the production process is about 9%, producing nearly 3450*0.85*0.09=2.64 million tons / year of hydrogen chloride. The rest is used in halogenated products, producing nearly 3450*0.15 / 2=2.58 million tons / year, totaling about 5.2 million tons / year of hydrogen chloride. Most of the existing hydrogen chloride post-processing processes in the industry use water absorption to form 31% hydrochloric acid, which is sold externally or the hydrochloric acid is analyzed to recover hydrogen chloride and return the hydrogen chloride to the hydrogen chloride user. Due to the overall overcapacity of hydrochloric acid, some by-product hydrochloric acid companies in the industry have installed hydrochloric acid analysis equipment to recover hydrogen chloride in the hydrochloric acid for use in production equipment. The following hydrochloric acid analysis technologies are currently in operation in the industry, and the energy consumption is calculated based on the treatment of 31% hydrochloric acid:

[0003] ① Conventional hydrochloric acid distillation and desorption technology for producing hydrogen chloride: Hydrogen chloride desorption consumes approximately 1.5 tons of steam per ton of hydrogen chloride. However, the absorption gradient must be maintained during the absorption process, and the absorption device must be replenished with water once, ultimately leading to an imbalance between absorption and desorption (desorption). This increases the amount of concentrated hydrochloric acid by 10%, requiring external sales or the addition of deep desorption technology to achieve water balance.

[0004] ② Hydrogen chloride production technology by pressure swing distillation: Hydrogen chloride decomposition consumes about 9 tons of steam per ton of hydrogen chloride, but the wastewater contains about 0.5% hydrogen chloride, which requires neutralization and recovery treatment, increasing alkali solution consumption;

[0005] ③ Calcium chloride method for hydrogen chloride production by distillation and analysis: The energy consumption of hydrogen chloride analysis is about 3.5 tons of steam per ton of hydrogen chloride, but the wastewater contains about 1.5% hydrogen chloride, which needs to be neutralized and recovered, and the consumption of alkali solution is very high;

[0006] ④ Technology for producing hydrogen chloride by sulfuric acid distillation and analysis: The energy consumption of hydrogen chloride analysis is about 3.5 tons of steam per ton of hydrogen chloride, but the wastewater contains about 0.2% hydrogen chloride, which needs to be neutralized and recovered. Compared with the technology for producing hydrogen chloride by pressure swing distillation and analysis and the technology for producing hydrogen chloride by calcium chloride distillation and analysis, the alkali solution consumption is less.

[0007] The aforementioned hydrogen chloride desorption technology requires separating hydrogen chloride from water. Each of these processes evaporates the hydrogen chloride and water in different stages, followed by cooling and recovery of the different substances. Therefore, in addition to recovering the hydrogen chloride, the desorption device must also evaporate the water from the hydrochloric acid, using 31% hydrochloric acid for deep desorption (desorption). Approximately 27% of the energy consumption is used to evaporate the hydrogen chloride, while 73% is used to evaporate the water, increasing the energy consumption of the desorption (desorption) device. Furthermore, the aforementioned hydrogen chloride desorption (desorption) method also produces acidic wastewater, increasing pollutant emissions. Summary of the Invention

[0008] The purpose of the present invention is to provide a low-energy consumption method for preparing hydrogen chloride, so as to solve the problems of high energy consumption and acidic wastewater discharge in the existing hydrogen chloride analysis (desorption) technology.

[0009] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0010] The present invention relates to a method for preparing hydrogen chloride with low energy consumption, which comprises the following steps:

[0011] Step 1. Using sulfuric acid solution or salt solution as absorbent to cool and absorb impurity-containing hydrogen chloride gas;

[0012] Step 2. The mixed liquid that absorbs hydrogen chloride is transported to a desorption tower or a stripping tower, and the hydrogen chloride is converted into a gas phase and extracted into a liquid phase by heating. The hydrogen chloride gas is cooled to form a high-concentration hydrogen chloride.

[0013] Preferably, after hydrogen chloride is extracted from the liquid phase in step 2, the liquid phase is cooled and then returned to step 1 for use as an adsorbent.

[0014] Preferably, in step 1, a sulfuric acid solution is used as the adsorbent, the sulfuric acid concentration of the sulfuric acid solution is 40-70%, the temperature during cooling and absorbing the impurity-containing hydrogen chloride gas is 0-25° C., and in step 2, the temperature during converting hydrogen chloride into a gas phase and extracting the liquid phase by heating is 100-180° C.

[0015] Preferably, in step 1, a salt solution is used as the absorbent, and the salt solution is an aqueous solution made from one or more of calcium chloride, potassium chloride, magnesium chloride, ferric chloride, and potassium sulfate.

[0016] Preferably, in step 1, a calcium chloride salt solution is used as the adsorbent, the concentration of the calcium chloride salt solution is 20-45%, the temperature during cooling and absorbing the impurity-containing hydrogen chloride gas is 0-25° C., and in step 2, the temperature during converting hydrogen chloride into a gas phase and extracting the liquid phase by heating is 100-160° C.

[0017] Preferably, in step 1, when cooling and absorbing the impure hydrogen chloride gas, a single-stage or multi-stage absorption method is used to absorb the impure hydrogen chloride gas, so that the adsorbent reaches saturation with hydrogen chloride. Using a single-stage or multi-stage absorption method to absorb the impure hydrogen chloride gas can increase the absorption gradient and completely absorb the hydrogen chloride.

[0018] Preferably, in step 2, when converting hydrogen chloride into a gas phase and extracting a liquid phase by heating, vapor-liquid mass transfer is performed with the high-temperature gas heated in the desorption tower or the desorption tower kettle, so that the mixed liquid is heated and hydrogen chloride is stripped out of the liquid phase.

[0019] Preferably, in step 2, the hydrogen chloride gas is cooled by two-stage cooling to form high-concentration hydrogen chloride.

[0020] Preferably, before the step 1 uses sulfuric acid solution or salt solution as an absorbent to cool and absorb the impure hydrogen chloride gas, the impure hydrogen chloride gas is first cooled to form condensed hydrochloric acid, and then enters the low-temperature absorption stage to absorb hydrogen chloride.

[0021] Preferably, the condensed hydrochloric acid and the mixed liquid that absorbs hydrogen chloride are subjected to absorption in step 1 and desorption or desorption in step 2, and then the liquid phase is evaporated to remove water in the liquid phase.

[0022] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0023] 1. The low-energy hydrogen chloride production method of the present invention uses a sulfuric acid solution or a salt solution as an absorbent to absorb impurity hydrogen chloride gas at a reduced temperature. The hydrogen chloride is converted into a gas phase and then withdrawn into a liquid phase by heating. The hydrogen chloride gas is cooled to form high-concentration hydrogen chloride. The present invention eliminates the use of water to absorb and desorb (desorb) hydrogen chloride. Instead, the hydrogen chloride is directly absorbed using a sulfuric acid solution or a salt solution. This eliminates the investment in the water removal step of the existing desorption (desorption) device and eliminates the need for subsequent energy consumption for water evaporation. Steam energy consumption is significantly reduced compared to that of prior art process devices.

[0024] 2. The low-energy hydrogen chloride production method of the present invention uses sulfuric acid solution or salt solution as an absorbent to absorb impurity hydrogen chloride gas at a reduced temperature, without using water to absorb and desorb (desorb) hydrogen chloride. Therefore, no acidic wastewater is generated, pollutant emissions are reduced, and environmental protection is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The present invention provides a flow chart of a method for preparing hydrogen chloride with low energy consumption.

[0026] Reference numerals: 1-low temperature absorption stage, 2-high temperature desorption (desorption) stage. DETAILED DESCRIPTION

[0027] The present invention is described in detail below, clearly and completely describing the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0028] Example 1

[0029] The low-energy consumption hydrogen chloride preparation method involved in this embodiment comprises the following steps:

[0030] Step 1. The impure hydrogen chloride gas is passed into one or more absorption towers. The absorption towers use a sulfuric acid solution as an absorbent to absorb the impure hydrogen chloride gas at low temperature, i.e., entering the low-temperature absorption stage 1. Different concentrations of sulfuric acid have different absorption rates for hydrogen chloride. Considering the recovery of hydrogen chloride, it is recommended to use a sulfuric acid solution with a concentration of 40-70%. However, it should be noted that sulfuric acid solutions of other concentrations can also absorb hydrogen chloride, but will affect the conditions for absorption and desorption (desorption) of hydrogen chloride and affect steam consumption. The temperature during absorption of the impure hydrogen chloride gas is 0-25°C. During the absorption process, a multi-stage absorption method is preferably used to absorb the impure hydrogen chloride gas, which can increase the absorption gradient and achieve saturation of the adsorbent with hydrogen chloride. The absorption process is a continuous operation.

[0031] Step 2. The mixed liquid that absorbs hydrogen chloride is transported to a desorption tower or a stripping tower to enter the high-temperature desorption (desorption) stage 2. After acid-acid heat exchange, sulfuric acid enters the top of the desorption (desorption) tower. The mixed liquid that absorbs hydrogen chloride and the gas phase generated by heating the tower bottom section (by steam heating or electric heating) are subjected to vapor-liquid mass transfer in the sulfuric acid desorption (desorption) tower, so that the mixed liquid is heated to 100-180°C, hydrogen chloride is converted into a gas phase and a liquid phase is extracted. The hydrogen chloride gas is cooled by two stages to form a high-concentration hydrogen chloride, which is transported to the hydrogen chloride use station. The high-temperature sulfuric acid in the desorption (desorption) tower bottom is cooled by acid-acid heat exchange and cooled by a cooling medium, and then returned to the absorption tower by a delivery pump to be used as an adsorbent for subsequent hydrogen chloride purification operations.

[0032] If the impure hydrogen chloride gas contains water, the impure hydrogen chloride gas is first condensed to produce hydrochloric acid before being passed into the absorption tower (or the gas phase is directly entered into the low-temperature absorption stage after cooling), and then mixed with the mixed solution in which the sulfuric acid solution absorbs hydrogen chloride in step 1. In step 2, the mixed solution that absorbs hydrogen chloride is passed into a desorption (desorption) tower for desorption (desorption). After the desorption (desorption) is completed, the water absorbed during the absorption process is removed by evaporating the absorbent.

[0033] Example 2

[0034] The low-energy consumption hydrogen chloride preparation involved in this embodiment is the same as that in Example 1 and will not be elaborated in detail in this embodiment.

[0035] The low-energy consumption hydrogen chloride preparation method involved in this embodiment comprises the following steps:

[0036] Step 1. Passing the impure hydrogen chloride gas into one or more absorption towers, the absorption towers use calcium chloride salt solution as an absorbent to absorb the impure hydrogen chloride gas at low temperature, i.e., entering the low-temperature absorption stage 1. Different concentrations of calcium chloride salt solution have different absorption rates of hydrogen chloride. Considering the recovery of hydrogen chloride, it is recommended to use a calcium chloride salt solution concentration of 20-45%. However, it should be noted that other different concentrations of calcium chloride salt solution can also absorb hydrogen chloride, and the maximum solubility of calcium chloride solution at 0°C is about 37.8%. Too low a temperature of the device will cause system crystallization, affecting the stable operation of the device. Different concentrations of calcium chloride solution will affect the conditions for absorbing and desorbing (desorbing) hydrogen chloride and affect steam consumption. The temperature during absorption of the impure hydrogen chloride gas is 0-25°C. During the absorption process, a multi-stage absorption method is preferably used to absorb the impure hydrogen chloride gas, which can increase the absorption gradient and make the adsorbent reach saturation with hydrogen chloride. The absorption process adopts a continuous operation.

[0037] Step 2: The mixed liquid that absorbed hydrogen chloride is transported to a desorption tower and enters the high-temperature desorption stage 2. In the tower bottom section, the mixed liquid that absorbed hydrogen chloride is heated by steam or electric heating to 100-160°C, converting the hydrogen chloride into a gas phase and removing the liquid phase. The hydrogen chloride gas is cooled through two stages to form a high-concentration hydrogen chloride, which is then transported to the hydrogen chloride user. The high-temperature calcium chloride salt solution in the desorption tower bottom is cooled by a cooling medium and then returned to the absorption tower via a transfer pump to be used as an adsorbent for subsequent hydrogen chloride purification operations.

[0038] If the impure hydrogen chloride gas contains water, the impure hydrogen chloride gas is first condensed to produce hydrochloric acid before being passed into the absorption tower (or the gas phase is directly entered into the low-temperature absorption stage after cooling), and then mixed with the mixed solution of the sulfuric acid solution absorbing hydrogen chloride in step 1. In step 2, the mixed solution absorbing hydrogen chloride is passed into the desorption tower for desorption. After the desorption is completed, the water absorbed during the absorption process is removed by evaporating the absorbent.

[0039] It should be noted that the salt solution used in this embodiment can be other salt solutions besides calcium chloride solution, such as an aqueous solution made of one or more of potassium chloride, magnesium chloride, ferric chloride, and potassium sulfate. However, the absorption rate of hydrogen chloride by other salt solutions of different concentrations is different. Since salt has a certain solubility in water, excessively high concentrations will crystallize at low temperatures, causing the device to fail and affecting the stable operation of the device. Salt solutions of different concentrations will affect the conditions for absorbing and decomposing hydrogen chloride and affect steam consumption. Therefore, for different salt solutions, their concentrations should be controlled so that they do not crystallize at low temperatures.

[0040] Effect example:

[0041] Compared with the existing hydrogen chloride desorption (desorption) technology, the low-energy hydrogen chloride production method of the present invention eliminates the investment in the water removal process of the existing desorption (desorption) device, greatly reducing the company's initial investment. Compared with the technology that uses water to absorb and desorb hydrogen chloride, the steam energy consumption is greatly reduced compared with the energy consumption of the existing process device. This example compares Example 1 with the traditional hydrogen chloride desorption method, and the comparison is as follows:

[0042] The energy consumption of using sulfuric acid solution as an absorbent to absorb hydrogen chloride and producing hydrogen chloride by temperature rise analysis (desorption) is 1.1 tons of steam per ton of hydrogen chloride, which is equivalent to 148.5 kg of standard coal per ton of hydrogen chloride.

[0043] Compared with conventional desorption (desorption), steam consumption is reduced by 0.4 tons of steam per ton of hydrogen chloride, saving about 54 kg of standard coal per ton of hydrogen chloride; compared with pressure swing distillation desorption (desorption), steam consumption is reduced by 6.9 tons of steam per ton of hydrogen chloride, saving about 931.5 kg of standard coal per ton of hydrogen chloride; compared with calcium chloride desorption (desorption), steam consumption is reduced by 2.4 tons of steam per ton of hydrogen chloride, saving about 324 kg of standard coal per ton of hydrogen chloride; compared with sulfuric acid desorption (desorption), steam consumption is reduced by 2.4 tons of steam per ton of hydrogen chloride, saving about 324 kg of standard coal per ton of hydrogen chloride.

[0044] Furthermore, compared with the technology of absorbing and analyzing (desorbing) hydrogen chloride using water, the method of the present invention does not produce acidic wastewater and meets environmental protection requirements.

[0045] The present invention has been described in detail above with reference to the embodiments. However, the contents described are only preferred embodiments of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A method for preparing hydrogen chloride with low energy consumption, characterized in that: It includes the following steps: Step 1. Using sulfuric acid solution or salt solution as absorbent to cool and absorb impurity-containing hydrogen chloride gas; Step 2. The mixed liquid that absorbs hydrogen chloride is transported to a desorption tower or a stripping tower, where the hydrogen chloride is converted into a gas phase and extracted into a liquid phase by heating. The hydrogen chloride gas is cooled to form a high-concentration hydrogen chloride; When a sulfuric acid solution is used as the adsorbent, the sulfuric acid concentration of the sulfuric acid solution is 40-70%, the temperature during cooling and absorbing the impurity-containing hydrogen chloride gas is 0-25°C, and the temperature during step 2 of converting hydrogen chloride into a gas phase and extracting the liquid phase by heating is 100-180°C; When a salt solution is used as the absorbent, the salt solution is a calcium chloride solution, the concentration of the calcium chloride solution is controlled at 20-45%, the temperature during cooling and absorbing the impurity hydrogen chloride gas is 0-25°C, and the temperature during step 2 of converting hydrogen chloride into a gas phase and extracting the liquid phase by heating is 100-160°C.

2. The low-energy consumption hydrogen chloride preparation method according to claim 1, characterized in that: After hydrogen chloride is extracted from the liquid phase in step 2, the liquid phase is cooled and returned to step 1 for use as an adsorbent.

3. The low-energy consumption hydrogen chloride preparation method according to claim 1, characterized in that: In the step 1 of cooling and absorbing the impure hydrogen chloride gas, one or more stages of cooling and absorption are used to absorb the hydrogen chloride gas in the impurity gas, so that the adsorbent is saturated with hydrogen chloride.

4. The low-energy consumption hydrogen chloride preparation method according to claim 1, characterized in that: In step 2, when hydrogen chloride is converted into a gas phase and extracted from a liquid phase by heating, vapor-liquid mass transfer is performed with the high-temperature gas heated in the desorption tower or the desorption tower kettle, so that the temperature of the mixed liquid is increased and hydrogen chloride is extracted from the mixed liquid.

5. The low-energy consumption hydrogen chloride preparation method according to claim 1, characterized in that: In step 2, the hydrogen chloride gas is cooled by two-stage cooling to form high-concentration hydrogen chloride.

6. The low-energy consumption hydrogen chloride production method according to claim 1, characterized in that: In step 1, before the sulfuric acid solution or salt solution is used as an absorbent to cool and absorb the impure hydrogen chloride gas, the impure hydrogen chloride gas is first cooled to form condensed hydrochloric acid.

7. The low-energy consumption method for preparing hydrogen chloride according to claim 6, characterized in that: The condensed hydrochloric acid and the mixed liquid that absorbs hydrogen chloride are absorbed in step 1 and analyzed or desorbed in step 2, and then the liquid phase is evaporated to remove water in the liquid phase.

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