Method for separating and recovering hydrogen chloride from tail gas of process for preparing 1, 2-dichloroethane by ethane method and application

Abstract

The invention discloses a method for separating and recovering hydrogen chloride from tail gas of a process for preparing 1, 2-dichloroethane by an ethane method and application of the method, and belongs to the field of chemical production. According to the method, ethylene glycol is used as an absorbent at room temperature to absorb the 1, 2-dichloroethane process tail gas prepared by an ethane method, and ethylene glycol absorbing hydrogen chloride gas and a residual gas phase are respectively obtained. The inventor finds that ethylene glycol is used as an absorbent, and efficient separation of hydrogen chloride gas in the tail gas of the process for preparing 1, 2-dichloroethane through an ethane method can be well achieved. Meanwhile, separation of hydrogen chloride by ethylene glycol is not affected by side reaction, 1, 2-dichloroethane is a byproduct after ethylene glycol is used for a long time, and 1, 2-dichloroethane is a target product and can be fully utilized. Importantly, the price of ethylene glycol is only 30-50% of that of diethylene glycol and is basically equivalent to that of ethane, so that the problem of cost rise caused by side reaction is avoided, and the economical efficiency and environmental protection benefits of the whole process are remarkably improved.

Description

Technical Field

[0001] The invention belongs to the field of chemical production, and specifically relates to a method and application of separating and recovering hydrogen chloride from tail gas in a process of preparing 1,2-dichloroethane by an ethane process. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] 1,2-Dichloroethane is a raw material for synthesizing vinyl chloride and can be produced by the ethylene method. The ethylene method produces 1,2-dichloroethane by an addition reaction between ethylene and chlorine, and then produces vinyl chloride and hydrogen chloride by cracking 1,2-dichloroethane. The ethylene method is the mainstream process abroad, and only a small number of domestic companies use this method. At present, the mainstream process for preparing vinyl chloride in China is the acetylene method, which uses acetylene and hydrogen chloride as raw materials to obtain vinyl chloride through an addition reaction between the two. This process has been eliminated abroad due to its high energy consumption for preparing acetylene and the use of highly toxic Hg-based catalysts. With the rise in the price of fossil resources, using natural gas or shale gas with a high ethane content as raw materials, and producing 1,2-dichloroethane by chlorination reaction of ethane and chlorine, has higher economic efficiency. Especially in areas rich in ethane resources, the price of raw materials is only 25-30% of ethylene and about 50% of acetylene, which has significant cost advantages. Therefore, the ethane method for producing 1,2-dichloroethane is very competitive.

[0004] In order to utilize cheap natural gas resources rich in ethane, foreign companies have conducted extensive research on the preparation of 1,2-dichloroethane by ethane. Although large-scale commercialization has not yet been achieved, great progress has been made. For example: Javier Pérez-Ramírez et al. reported that in the absence of oxygen and catalyst, excess ethane and chlorine (ethane: chlorine = 2:1, molar ratio) can undergo a substitution reaction, chlorine is almost completely converted, and the selectivity of 1,2-dichloroethane is as high as 90%.

[0005] C2H6+2Cl2=C2H4Cl2+2HCl

[0006] As shown in the reaction equation, the ethane method produces 1,2-dichloroethane, and 1 mol of HCl is produced as a by-product for every 1 mol of chlorine used. This process will produce a large amount of HCl gas. Because 1,2-dichloroethane has a high boiling point (83.5°C), it can be separated from the mixed tail gas by cooling and liquefaction, but hydrogen chloride and excess unreacted ethane are discharged in the form of mixed tail gas. At present, domestic companies generally use the "wet method" to remove HCl from the by-product HCl gas, that is, to use water to absorb HCl to generate hydrochloric acid to achieve the purpose of separation. However, the water washing process produces a large amount of waste hydrochloric acid, which causes serious corrosion of subsequent equipment; on the other hand, because the waste acid contains a certain amount of organic impurities, a lot of processing costs are also required. Therefore, how to effectively and reasonably treat HCl has become a difficult problem that restricts the future application of the ethane method.

[0007] Patent CN109603437A reports a method for separating hydrogen chloride from a mixed gas containing hydrogen chloride using diethylene glycol as an absorbent. However, the price of diethylene glycol is comparable to that of acetylene, and long-term use will produce 2-chloroethoxyethanol and dichlorodiethyl ether as byproducts, which are difficult to handle and cause a significant increase in the cost of use. Therefore, it is very urgent to find a more economical and environmentally friendly HCl separation technology. Summary of the invention

[0008] In order to solve the deficiencies of the prior art, the purpose of the present invention is to provide a method and application of separating hydrogen chloride from tail gas in the process of preparing 1,2-dichloroethane by ethane method and separating and recovering hydrogen chloride. The present invention adopts ethylene glycol as an absorbent and takes a mixed gas of hydrogen chloride and ethane as a treatment object, thereby achieving separation of hydrogen chloride from the mixed gas while making it easy to fully utilize the ethylene glycol by-product, thereby significantly reducing the use cost.

[0009] In order to achieve the above object, the technical solution of the present invention is:

[0010] The first aspect of the present invention provides a method for separating hydrogen chloride from tail gas of a process for preparing 1,2-dichloroethane by an ethane process, wherein ethylene glycol is used as an absorbent to absorb the tail gas of a process for preparing 1,2-dichloroethane by an ethane process, and ethylene glycol for absorbing hydrogen chloride gas and a residual gas phase are obtained respectively;

[0011] The absorption temperature of the absorption is 0-60°C.

[0012] The present invention successfully separates hydrogen chloride gas by using ethylene glycol as an absorbent for the first time, with simple operation and mild conditions. In addition, after long-term use, ethylene glycol will be dehydrated to produce 1,2-dichloroethane as a by-product, which is the product of the ethane method and can be fully utilized. What is important is that the price of ethylene glycol is only 30-50% of that of diethylene glycol, which is basically equivalent to the price of ethane, thus avoiding the cost increase problem caused by side reactions and significantly improving the economy and environmental benefits of the entire process.

[0013] Preferably, at room temperature, normal pressure and stirring conditions, the tail gas of the ethane method for preparing 1,2-dichloroethane is contacted with ethylene glycol, the hydrogen chloride gas is absorbed into the liquid phase by ethylene glycol, and the remaining gas phase is insoluble in ethylene glycol, that is, ethylene glycol absorbing the hydrogen chloride gas and the remaining gas phase are obtained respectively. When the tail gas is in contact with ethylene glycol, a spray absorption tower, a falling film absorption tower or a static tubular mixer can be used, ethylene glycol is used as an absorbent, the tail gas is passed into the spray absorption tower, the hydrogen chloride gas is absorbed into the liquid phase by ethylene glycol, and the remaining gas phase is discharged from the top of the tower. It is also possible to use an ethylene glycol storage device (such as a liquid storage tank, etc.) and an air bag filled with tail gas, and connect the air bag to the ethylene glycol storage device.

[0014] Preferably, the tail gas from the ethane process for preparing 1,2-dichloroethane can be contacted with ethylene glycol under high pressure and stirring conditions. High pressure conditions are conducive to improving the absorption rate of hydrogen chloride gas.

[0015] Preferably, the tail gas of the ethane method for preparing 1,2-dichloroethane is a mixed gas of hydrogen chloride and ethane. Javier Pérez-Ramírez et al. reported that in the absence of oxygen and catalyst, excess ethane and chlorine (ethane: chlorine = 2:1, molar ratio) can undergo a substitution reaction, and the chlorine is almost completely converted. It can be seen that the molar ratio of ethane to hydrogen chloride gas in the tail gas of the ethane method for preparing 1,2-dichloroethane is about 3:2. It can be seen that the tail gas contains a large amount of ethane and hydrogen chloride gas, so the separation of hydrogen chloride and ethane is of great significance for the reuse of ethane and chlorine resources.

[0016] Preferably, in the mixed gas, the volume ratio of hydrogen chloride to ethane is 1-20:1-50.

[0017] Preferably, ethylene glycol is used as an absorbent to absorb hydrogen chloride in the tail gas of the process for preparing 1,2-dichloroethane by the ethane method until the absorption rate is 5-55%.

[0018] The second aspect of the present invention provides a method for separating and recovering hydrogen chloride from tail gas of a process for preparing 1,2-dichloroethane by an ethane process, comprising the following steps:

[0019] 1) As described above, the method for separating hydrogen chloride from tail gas in the process of preparing 1,2-dichloroethane by ethane method is used to obtain ethylene glycol absorbing hydrogen chloride gas and a residual gas phase;

[0020] 2) heating and desorbing the ethylene glycol absorbed by the hydrogen chloride gas obtained in step 1) to obtain hydrogen chloride gas and ethylene glycol respectively; the heating and desorption temperature is 80-160°C.

[0021] Preferably, in step 2, the ethylene glycol obtained in step 1 that absorbs the hydrogen chloride gas is subjected to stirring, heating and analysis.

[0022] Preferably, the ethylene glycol obtained by heating and decomposing is circulated to step 1) to continue absorbing hydrogen chloride gas.

[0023] Preferably, the gas released during the heating and parsing process is condensed to obtain a liquid product and hydrogen chloride gas; the liquid product is distilled to obtain 1,2-dichloroethane. As the number of ethylene glycol cycles increases, a dehydration reaction occurs to generate 1,2-dichloroethane. The boiling point of 1,2-dichloroethane is 83.5°C. In the step of heating to release hydrogen chloride gas, it is cooled and collected, and can be fully utilized as the target product for preparing 1,2-dichloroethane by the ethane method.

[0024] Preferably, the heating decomposition is performed until the release rate of hydrogen chloride gas reaches 95% or more.

[0025] The third aspect of the present invention provides the use of ethylene glycol as an absorbent for separating hydrogen chloride from tail gas of the process of preparing 1,2-dichloroethane by ethane method at room temperature. In the prior art, diethylene glycol is used to separate hydrogen chloride from a mixed gas containing hydrogen chloride. The inventors of the present invention have found that diethylene glycol is expensive and will produce 2-chloroethoxyethanol and dichlorodiethyl ether as byproducts after long-term use. The byproducts are difficult to handle, which greatly increases the cost of separating hydrogen chloride. In the actual production process, the inventors found a non-aqueous solvent, ethylene glycol, based on the composition of the tail gas of the process of preparing 1,2-dichloroethane by ethane method. Through a simple absorption process, the separation and recovery of hydrogen chloride in the tail gas can be efficiently completed, which greatly reduces the production cost and improves the utilization rate and added value of ethane and hydrogen chloride.

[0026] At the same time, the inventors found that ethylene glycol is different from diethylene glycol in that the dehydration byproducts of ethylene glycol after long-term use are mainly a mixture of 1,2-dichloroethane, ethylene oxide, and 1,4-dioxane, of which 1,2-dichloroethane accounts for more than 95%. Moreover, 1,2-dichloroethane is the target product of the ethane method for preparing 1,2-dichloroethane, and can be fully utilized after being separated by distillation. While successfully separating hydrogen chloride from ethane, the problem of increased processing costs caused by by-products is avoided.

[0027] The beneficial effects of the present invention are:

[0028] The inventors of the present invention have found that ethylene glycol not only has a large solubility for hydrogen chloride, but also has stable properties. It will not decompose or deteriorate when desorbed at a higher temperature, and has a high desorption efficiency, which well realizes the efficient separation and recovery of hydrogen chloride gas in the tail gas of the ethane method for preparing 1,2-dichloroethane. The absorption rate of hydrogen chloride gas is as high as 55%. At the same time, ethylene glycol has stable properties, does not react or decompose when absorbing and desorbing hydrogen chloride, and has no secondary pollution. It can be recycled after desorption, saving costs.

[0029] The separation of ethylene glycol from hydrogen chloride will not be affected by side reactions. After long-term use of ethylene glycol, 1,2-dichloroethane is produced as a byproduct. It is the target product of the ethane method for preparing 1,2-dichloroethane and can be fully utilized. Importantly, the price of ethylene glycol is only 30-50% of that of diethylene glycol, which is basically equivalent to the price of ethane, avoiding the cost increase caused by side reactions and significantly improving the economic and environmental benefits of the entire process.

[0030] In summary, the method of the present invention achieves efficient separation and recovery of hydrogen chloride gas, while avoiding the problem of handling ethylene glycol side reaction products, achieving two goals at one stroke, and having outstanding economic and environmental advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0032] Figure 1 This is the GC-MS analysis spectrum of the liquid product of Example 2. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0034] Example 1

[0035] A method for separating and recovering hydrogen chloride from tail gas in a process for preparing 1,2-dichloroethane by an ethane process comprises the following steps:

[0036] A gas bag (10L) filled with a mixture of hydrogen chloride HCl and ethane (HCl:ethane = 1:1, v / v) was connected to a flask containing ethylene glycol (5mL) and kept under stirring for 12 hours. After the experiment, the weight of ethylene glycol was weighed and the absorption rate was 38%. (The calculation formula for absorption rate is: absorption rate = mass of hydrogen chloride / mass of adsorbent ethylene glycol before adsorption, mass of hydrogen chloride = mass of adsorbent ethylene glycol after adsorption - mass of adsorbent ethylene glycol before adsorption)

[0037] The above ethylene glycol was heated and stirred at 150° C. for 30 minutes, and the HCl gas release rate was 97%.

[0038] Through the above process, HCl gas can be effectively separated from the HCl and ethane mixed gas.

[0039] Example 2

[0040] A method for separating and recovering hydrogen chloride from tail gas in a process for preparing 1,2-dichloroethane by an ethane process comprises the following steps:

[0041] The experiment in Example 1 was repeated 10 times. During the process of heating ethylene glycol to release HCl, the released gas was treated by a condenser (-30°C-0°C) and the liquid product was collected.

[0042] According to the test, the HCl absorption rate was maintained at 33-39%, the mass of ethylene glycol was reduced by 3.5-5.0%, and the liquid product was mainly a mixture of ethylene oxide, 1,4-dioxane, and 1,2-dichloroethane, of which 1,2-dichloroethane accounted for ≥95%.

[0043] Specifically, GC-MS detection was performed (GC-MS model: Agilent 7890A-5975C, HP-5 gas chromatography column (15m×0.25mm, 1.0μm), vaporization chamber temperature: 290°C, column temperature 220°C maintained for 13min). The detection results are as follows Figure 1 , and as shown in Table 1.

[0044] Table 1 GC-MS test results of liquid products

[0045] Components Retention time content(%) Ethylene oxide 2.52 0.1 1,2-Dichloroethane 2.26 96 1,4-Dioxane 5.22 3.9

[0046] Example 3

[0047] A method for separating and recovering hydrogen chloride from tail gas in a process for preparing 1,2-dichloroethane by an ethane process comprises the following steps:

[0048] A corresponding mass of ethylene glycol (i.e., the reduced mass, 3.5%-5.0%) was added to the flask in Example 2, and the above experiment was repeated 40 times.

[0049] After testing, the HCl absorption rate remained at 34-37%, the mass of ethylene glycol decreased by 3.0-5.5%, and the liquid product was still a mixture of ethylene oxide, 1,4-dioxane, and 1,2-dichloroethane, of which 1,2-dichloroethane accounted for ≥94%.

[0050] The experimental results confirmed that the separation effect of ethylene glycol on HCl was not affected by the side reaction, and the main by-product was 1,2-dichloroethane, which could be fully utilized. A small amount of 1,4-dioxane (boiling point 101°C) and 1,2-dichloroethane (boiling point: 83.5°C) could be sold separately after distillation separation, or they could be added to ethylene glycol for recycling.

[0051] Example 4

[0052] A method for separating and recovering hydrogen chloride from tail gas of a process for preparing 1,2-dichloroethane by an ethane process, which differs from Example 1 in that the HCl and ethane mixed gas (HCl:ethane=1:1, v / v) in Example 1 is replaced with a HCl and ethane mixed gas (HCl:ethane=2:3, v / v), and the other steps are the same.

[0053] After the experiment, the weight of ethylene glycol was weighed and the absorption rate was 36%.

[0054] Example 5

[0055] A method for separating and recovering hydrogen chloride from tail gas of a process for preparing 1,2-dichloroethane by an ethane process, which differs from that of Example 1 in that the HCl and ethane mixed gas (HCl:ethane=1:1, v / v) in Example 1 is replaced with a HCl and ethane mixed gas (HCl:ethane=20:1, v / v), and the other steps are the same.

[0056] After the experiment, the weight of ethylene glycol was weighed and the absorption rate was 45%.

[0057] Example 6

[0058] A method for separating and recovering hydrogen chloride from tail gas of a process for preparing 1,2-dichloroethane by an ethane process, which differs from that of Example 1 in that the HCl and ethane mixed gas (HCl:ethane=1:1, v / v) in Example 1 is replaced with a HCl and ethane mixed gas (HCl:ethane=1:50, v / v), and the other steps are the same.

[0059] After the experiment, the weight of ethylene glycol was weighed and the absorption rate was 9%.

[0060] Example 7

[0061] A method for separating and recovering hydrogen chloride from tail gas of a process for preparing 1,2-dichloroethane by an ethane process, which is different from Example 1 in that the mixed gas of HCl and ethane (HCl:ethane=1:1, v / v) in Example 1 is pressurized to 5-6 atmospheres by a Hastelloy gas compression pump, and the gas outlet is connected to a Hastelloy stirring kettle (100ml) by a Hastelloy pipe, and the kettle contains ethylene glycol (5mL), and the mixture is kept under stirring conditions for 12 hours. After the experiment, the excess gas is discharged into an air bag for receiving, the kettle is opened to take out and the weight of ethylene glycol is weighed, and the absorption rate is 55%.

[0062] Comparative Example 1

[0063] The difference from Example 1 is that the mixed gas of HCl and ethane (HCl:ethane=1:1, v / v) in Example 1 is replaced with HCl gas, and the other steps are the same.

[0064] After the experiment, the weight of ethylene glycol was weighed and the absorption rate was 48%.

[0065] The above ethylene glycol was heated and stirred at 150° C. for 30 minutes, and the HCl gas release rate was 98%.

[0066] Through the above process, the absorption, storage and heating release of HCl gas can be achieved.

[0067] Comparative Example 2

[0068] The difference from Example 1 is that the mixed gas of HCl and ethane (HCl:ethane=1:1, v / v) in Example 1 is replaced with ethane, and the other steps are the same.

[0069] After the experiment, the weight of ethylene glycol was weighed and the mass of ethylene glycol did not change, and it had no absorption effect on ethane.

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for separating hydrogen chloride from tail gas of a process for preparing 1,2-dichloroethane by an ethane process, characterized in that: Using ethylene glycol as absorbent to absorb the tail gas of ethane process for preparing 1,2-dichloroethane, ethylene glycol for absorbing hydrogen chloride gas and residual gas phase are obtained respectively; The absorption temperature of the absorption is 0-60°C.

2. The method for separating hydrogen chloride from tail gas of a process for preparing 1,2-dichloroethane by an ethane process as claimed in claim 1, characterized in that: At room temperature, normal pressure and stirring conditions, the tail gas of the ethane process for preparing 1,2-dichloroethane is contacted with ethylene glycol, the hydrogen chloride gas is absorbed into the liquid phase by the ethylene glycol, and the remaining gas phase is difficult to dissolve in the ethylene glycol, that is, the ethylene glycol absorbing the hydrogen chloride gas and the remaining gas phase are obtained respectively; Alternatively, under high pressure and stirring conditions, the tail gas from the ethane process for preparing 1,2-dichloroethane is contacted with ethylene glycol.

3. The method for separating hydrogen chloride from tail gas of a process for preparing 1,2-dichloroethane by an ethane process according to claim 1 or 2, characterized in that: The tail gas of the process for preparing 1,2-dichloroethane by the ethane method is a mixed gas of hydrogen chloride and ethane.

4. The method for separating hydrogen chloride from tail gas of a process for preparing 1,2-dichloroethane by an ethane process as claimed in claim 3, characterized in that: The volume ratio of hydrogen chloride to ethane is 1-20:1-50.

5. The method for separating hydrogen chloride from tail gas of a process for preparing 1,2-dichloroethane by an ethane process according to claim 1 or 2, characterized in that: Ethylene glycol is used as an absorbent to absorb hydrogen chloride in the tail gas of the process for preparing 1,2-dichloroethane by the ethane method until the absorption rate is 5%-55%.

6. A method for separating and recovering hydrogen chloride from tail gas of a process for preparing 1,2-dichloroethane by an ethane process, characterized in that: The following steps are involved: 1) A method for separating hydrogen chloride from tail gas in a process for preparing 1,2-dichloroethane by an ethane process according to any one of claims 1 to 5, wherein ethylene glycol absorbing hydrogen chloride gas and a residual gas phase are obtained respectively; 2) heating and desorbing the ethylene glycol absorbed by the hydrogen chloride gas obtained in step 1) to obtain hydrogen chloride gas and ethylene glycol respectively; the heating and desorption temperature is 80-160°C.

7. The method for separating and recovering hydrogen chloride from tail gas of a process for preparing 1,2-dichloroethane by an ethane process as claimed in claim 5, characterized in that: In step 2, the ethylene glycol absorbed by the hydrogen chloride gas obtained in step 1 is stirred and heated for analysis.

8. The method for separating and recovering hydrogen chloride from tail gas of a process for preparing 1,2-dichloroethane by an ethane process as claimed in claim 5, characterized in that: The ethylene glycol obtained by heating and decomposition is circulated to step 1) to continue absorbing hydrogen chloride gas.

9. The method for separating and recovering hydrogen chloride from tail gas of a process for preparing 1,2-dichloroethane by an ethane process as claimed in claim 5, characterized in that: The gas released during the heating and decomposition process is condensed to obtain a liquid product and hydrogen chloride gas; the liquid product is separated by distillation to obtain 1,2-dichloroethane.

10. The method for separating and recovering hydrogen chloride from tail gas of a process for preparing 1,2-dichloroethane by an ethane process as claimed in claim 5, characterized in that: Heat and decompose until the release rate of hydrogen chloride gas reaches more than 95%.

11. The application of ethylene glycol as an absorbent for hydrogen chloride in the tail gas of the process of preparing 1,2-dichloroethane by separating ethane at room temperature.

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