Method for accurately controlling pH of tetrachloroethylene finished product

Abstract

The invention relates to a method for accurately controlling the pH value of a tetrachloroethylene finished product. The method comprises the following steps: carrying out alkali washing on tetrachloroethylene in the production process, and adding a stabilizer into the tetrachloroethylene at the time t after the alkali washing is completed; wherein the alkali washing process is as follows: the mixing time of the tetrachloroethylene and the alkali solution is more than or equal to 3 minutes; the volume ratio of the tetrachloroethylene to the aqueous alkali is 1: (4-9), and the mass concentration of the aqueous alkali is 5-10%; the time t is 2 to 4 hours or 4.5 to 6 hours. According to the method, the pH value of the tetrachloroethylene finished product is effectively controlled in a specific interval and maintained in a corresponding interval for a long time, and the application of the tetrachloroethylene finished product as a cleaning agent and a refrigerant production raw material is met.

Description

Technical Field

[0001] The present invention relates to the technical field of tetrachloroethylene production, and more specifically, to a method for accurately controlling the pH value of a tetrachloroethylene finished product. Background Art

[0002] At present, the production process of finished tetrachloroethylene in China includes synthesis-light removal-distillation-alkali washing-separation-drying, which is as follows: the synthesized tetrachloroethylene first passes through a light removal tower to remove carbon tetrachloride, and then is transported to a distillation tower. After distillation, tetrachloroethylene with qualified purity is obtained. At this time, the tetrachloroethylene often contains a small amount of HCl, which is further sent to the alkali washing system. The alkali washing system adds alkali to the inlet of the alkali washing pump. After the tetrachloroethylene and the alkali are fully stirred to reach a certain pH, phase separation is performed to discharge the waste alkali, and then the tetrachloroethylene is dried. After drying, a stabilizer is usually added to stabilize the pH of the finished tetrachloroethylene product, so that it can be sold as a finished product.

[0003] Tetrachloroethylene is widely used, among which being a cleaning agent and as a raw material for refrigerant production are two of its uses. When tetrachloroethylene is used as a cleaning agent, the domestic industry strictly requires that the pH of tetrachloroethylene be 7-8 and the moisture content be 0-50ppm. Purchasers basically do not accept it if it exceeds this range. When tetrachloroethylene is used as a raw material for refrigerant production, purchasers strictly require that the moisture content of tetrachloroethylene be 0-50ppm, and the pH must be 6-7. Only by accurately controlling the moisture content and pH of the finished tetrachloroethylene product within the required range can its application in the above two scenarios be met. However, since the pH of the finished tetrachloroethylene product will decrease during storage, not only is the initial pH of the finished tetrachloroethylene product required to be in the corresponding range, but the pH is also required to be maintained in the corresponding range for a certain period of time (the time interval from leaving the factory to use may be as long as half a year).

[0004] After the drying step in the production process, stabilizers are added to the finished tetrachloroethylene product. The stabilizers can stabilize the pH of the tetrachloroethylene product within a wide range of 5 to 9 for a certain period of time, but it is difficult to accurately control the pH of the tetrachloroethylene product to stabilize within the ranges of 6 to 7 and 7 to 8. Generally, if the pH of the finished tetrachloroethylene product cannot be controlled within the range of 6 to 7 or 7 to 8 in a single production, it cannot be used as a cleaning agent or as a raw material for refrigerant production. At this time, the finished product may be treated as waste or used for other purposes, and needs to be reproduced to meet customer needs, which greatly increases production costs.

[0005] The Chinese patent entitled A method for purifying and drying tetrachloroethylene proposes that the pH of the finished tetrachloroethylene product be detected within 30 minutes after production. It does not focus on how to obtain a tetrachloroethylene product in two specific pH ranges, nor does it focus on the long-term stability of the pH of the finished tetrachloroethylene product.

[0006] How to control and stabilize the pH of the finished tetrachloroethylene product in the range of 6-7 and 7-8 within a certain period of time in a single production, while controlling the moisture content of the finished tetrachloroethylene product at a low level to reduce the production cost of the manufacturer, is a problem that needs to be solved urgently. Summary of the invention

[0007] The purpose of the present invention is to overcome the problem of insufficient research on controlling and stabilizing the pH of the finished tetrachloroethylene product in the two intervals of 6 to 7 and 7 to 8, and to provide a method for accurately controlling the pH of the finished tetrachloroethylene product. The method controls the time of alkali washing, the amount of alkali solution and the concentration of the alkali solution, and adds a stabilizer at a specific time after alkali washing, so that the initial pH of the obtained tetrachloroethylene product is in the two intervals of 7 to 8 and 6 to 7, and after being placed for 3 months and 6 months, the pH is still in the two intervals of 7 to 8 and 6 to 7, and the initial moisture content is within 50ppm. The method effectively controls the pH of the finished tetrachloroethylene product in a specific interval and maintains it in the corresponding interval for a long time, meeting the use of the finished tetrachloroethylene product as a cleaning agent and as a raw material for refrigerant production.

[0008] Another object of the present invention is to provide the use of the tetrachloroethylene product obtained by the above method as a cleaning agent or as a raw material for refrigerant production.

[0009] The above-mentioned object of the present invention is achieved by the following technical solutions:

[0010] A method for accurately controlling the pH of a finished perchloroethylene product comprises the following steps:

[0011] Performing alkali washing on tetrachloroethylene in the production process, and adding a stabilizer to the tetrachloroethylene at a time t after the alkali washing is completed;

[0012] Wherein, the alkali washing process is as follows: the mixing time of tetrachloroethylene and alkali solution is ≥ 3 minutes;

[0013] The volume ratio of tetrachloroethylene to the alkaline solution is 1:(4-9), and the mass concentration of the alkaline solution is 5-10%;

[0014] The time t is 2 to 4 hours or 4.5 to 6 hours.

[0015] The inventors of the present invention have found through research that the pH of tetrachloroethylene in the production process changes differently at different stages; in order to regulate the pH of the finished tetrachloroethylene product within the two intervals of 6-7 and 7-8 and maintain it within the two intervals for a certain period of time (6 months) and to control the initial moisture content of the finished tetrachloroethylene product at a low level (within 50 ppm), the control of the alkali washing process before adding the stabilizer is critical, and the time of adding the stabilizer is also critical.

[0016] The present invention controls the time of alkali washing, the amount of alkali solution and the concentration of the alkali solution, and adds a stabilizer at a specific time after alkali washing, so that the initial pH value of the obtained tetrachloroethylene product is in the range of 7-8 and 6-7, and after being placed for 3 months and 6 months, the pH value is still in the range of 7-8 and 6-7, and the initial moisture content is within 50ppm. The method effectively controls the pH value of the tetrachloroethylene product within a specific range and maintains it within the corresponding range for a long time, so as to meet the use of the tetrachloroethylene product as a cleaning agent and a raw material for refrigerant production.

[0017] Specifically, when the time t is 2 to 4 hours, the initial pH of the finished perchloroethylene product is in the range of 7 to 8, and after 3 and 6 months of storage, the pH is still in the range of 7 to 8. When the time t is 4.5 to 6 hours, the initial pH of the finished perchloroethylene product is in the range of 6 to 7, and after 3 and 6 months of storage, the pH is still in the range of 6 to 7.

[0018] Even if the same amount of alkali is used, if the volume ratio of tetrachloroethylene to alkali solution is not properly controlled, the initial pH of the obtained tetrachloroethylene product can fall within a specific range, but it cannot be maintained in the specific pH range after being placed for 6 months, and cannot meet the use requirements of the corresponding scene. In addition, if the time t is 4<t<4.5, although the initial pH of the obtained tetrachloroethylene product is within the specific range, it cannot be maintained in the original specific range after being placed for a certain period of time.

[0019] In the present invention, the time t can specifically be 2, 2.3, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.5, 4.8, 5., 5.2, 5.5, 5.8 or 6 hours.

[0020] Preferably, the tetrachloroethylene and the alkaline solution are mixed for 3 to 10 minutes.

[0021] Preferably, before the alkali washing, the steps of light removal and distillation are also included.

[0022] Preferably, the alkali in the alkaline solution is at least one of sodium hydroxide, potassium hydroxide or calcium hydroxide.

[0023] Preferably, the amount of the stabilizer is: 0.01-0.02 g of stabilizer is added per 1 kg of tetrachloroethylene.

[0024] Preferably, the stabilizer is at least one of phenol, morpholine or diisopropylamine.

[0025] Preferably, the method is carried out at 15-25°C.

[0026] The stabilizer of the present invention refers to a stabilizer that can keep tetrachloroethylene stable and prevent it from being decomposed into acidic substances.

[0027] Preferably, before adding the stabilizer, the method further includes a step of separating tetrachloroethylene and the alkaline solution.

[0028] Preferably, the stabilizer is added to the tetrachloroethylene under stirring conditions.

[0029] More preferably, the stirring speed is 10 to 20 rpm.

[0030] Preferably, after adding the stabilizer, a drying step is also included.

[0031] The use of the tetrachloroethylene product obtained by the above method as a cleaning agent or as a raw material for refrigerant production is also within the protection scope of the present invention.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The present invention controls the time of alkali washing, the amount of alkali solution and the concentration of the alkali solution, and adds a stabilizer at a specific time after alkali washing, so that the initial pH value of the obtained tetrachloroethylene finished product is in the range of 7-8 and 6-7, and after being placed for 3 months and 6 months, the pH value is still in the range of 7-8 and 6-7, and the initial moisture content is within 50ppm. The method effectively controls the pH value of the tetrachloroethylene finished product within the specific range and maintains it within the corresponding range for a long time, so as to meet the use of the tetrachloroethylene finished product as a cleaning agent and a raw material for refrigerant production. DETAILED DESCRIPTION

[0034] In order to more clearly and completely describe the technical solution of the present invention, the present invention is further described in detail through specific embodiments below. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention. Various changes can be made within the scope of the rights of the present invention.

[0035] The words "preferred", "preferably", "more preferred" and the like in the present invention refer to embodiments of the present invention that may provide certain beneficial effects in certain circumstances. However, other embodiments may also be preferred under the same circumstances or other circumstances. In addition, the description of one or more preferred embodiments does not imply that other embodiments are not applicable, nor is it intended to exclude other embodiments from the scope of the present invention.

[0036] In the present invention, when it comes to a numerical interval (i.e., a numerical range), unless otherwise specified, the distribution of the optional numerical values ​​in the numerical interval is considered to be continuous, and includes the two numerical endpoints (i.e., the minimum value and the maximum value) of the numerical interval, and each numerical value between the two numerical endpoints. Unless otherwise specified, when the numerical interval only refers to the integers in the numerical interval, including the two endpoint integers of the numerical range, and each integer between the two endpoints, is equivalent to directly listing each integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be merged. In other words, unless otherwise specified, the numerical range disclosed herein should be understood to include any and all sub-ranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, a percentage, a ratio, etc. "Numerical interval" allows broadly including numerical interval types such as percentage intervals, ratio intervals, and ratio intervals.

[0037] It should be understood that, except in any operating examples, or where otherwise indicated, all numbers indicating, for example, the amounts of ingredients used in the specification and claims should be understood to be modified in all cases by the term "about". Therefore, unless indicated to the contrary, the numerical parameters set forth in the following specification and the appended claims are approximate values ​​that vary depending on the desired properties to be obtained by the present invention.

[0038] Example 1

[0039] This embodiment provides a method for accurately controlling the pH of a tetrachloroethylene product, comprising the following steps:

[0040] The tetrachloroethylene in the production process is subjected to alkali washing (before alkali washing, the tetrachloroethylene has been subjected to light removal and distillation treatment), and the alkali washing process is as follows: the tetrachloroethylene and alkali are mixed for 3 minutes, the volume ratio of the tetrachloroethylene to the alkali solution is 1:9, and the alkali solution is a NaOH solution with a concentration of 5wt%. Two hours after the alkali washing is completed (recorded as time t), a stabilizer is added to the tetrachloroethylene under stirring, wherein the stirring speed is 15 rpm, the stabilizer is phenol, and the amount of the stabilizer is 0.01g of stabilizer per 1Kg of tetrachloroethylene. The alkali washing and the process of adding the stabilizer are carried out in a container with a stainless steel inner wall.

[0041] After the addition of the stabilizer is completed, the tetrachloroethylene is dried by a dryer to obtain the finished tetrachloroethylene product.

[0042] Example 2

[0043] This embodiment provides a method for accurately controlling the pH of a finished tetrachloroethylene product, which is basically the same as that of Embodiment 1, except that the time t is 4 hours.

[0044] Example 3

[0045] This embodiment provides a method for accurately controlling the pH of a finished tetrachloroethylene product, which is basically the same as that of Embodiment 1, except that the time t is 5 hours.

[0046] Example 4

[0047] This embodiment provides a method for accurately controlling the pH of a finished tetrachloroethylene product, which is basically the same as that of Embodiment 1, except that the time t is 6 hours.

[0048] Example 5

[0049] This embodiment provides a method for accurately controlling the pH of a finished tetrachloroethylene product, which is basically the same as Embodiment 1, except that: the alkali washing process is as follows: the mixing time of tetrachloroethylene and the alkali solution is 10 minutes, the volume ratio of tetrachloroethylene to the alkali solution is 1:4, and the alkali is a NaOH solution with a concentration of 10wt%.

[0050] Example 6

[0051] This embodiment provides a method for accurately controlling the pH of a finished tetrachloroethylene product, which is basically the same as Embodiment 3, except that: the alkali washing process is as follows: the mixing time of tetrachloroethylene and the alkali solution is 10 minutes, the volume ratio of tetrachloroethylene to the alkali solution is 1:4, and the alkali is a NaOH solution with a concentration of 10wt%.

[0052] Example 7

[0053] This embodiment provides a method for accurately controlling the pH of a finished tetrachloroethylene product, which is basically the same as that of Embodiment 1, except that the stabilizer is morpholine.

[0054] Comparative Example 1

[0055] This comparative example provides a method for controlling the pH of a finished tetrachloroethylene product, which is substantially the same as that of Example 1, except that the time t is 1 hour.

[0056] Comparative Example 2

[0057] This comparative example provides a method for controlling the pH of a finished tetrachloroethylene product, which is substantially the same as that of Example 1, except that the time t is 7 hours.

[0058] Comparative Example 3

[0059] This comparative example provides a method for controlling the pH of a finished tetrachloroethylene product, which is substantially the same as that of Example 1, except that the mixing time of the tetrachloroethylene and the alkali is 1 minute.

[0060] Comparative Example 4

[0061] This comparative example provides a method for controlling the pH of a tetrachloroethylene product, which is basically the same as Example 1, except that the volume ratio of tetrachloroethylene to the alkaline solution is 1:3, and the alkaline solution is a NaOH solution with a concentration of 15 wt%.

[0062] Comparative Example 5

[0063] This comparative example provides a method for controlling the pH of a finished tetrachloroethylene product, which is substantially the same as that of Example 1, except that the alkaline solution is a NaOH solution with a concentration of 2 wt%.

[0064] Performance Testing

[0065] The initial pH, pH after 3 months, pH after 6 months, and initial moisture content of the finished tetrachloroethylene products obtained in each embodiment and comparative example were measured. The results are shown in Table 1:

[0066] Table 1 Index test results of the tetrachloroethylene finished products obtained in each embodiment and comparative example

[0067]

[0068]

[0069] From Table 1, we can see that:

[0070] The initial pH of the tetrachloroethylene products obtained by the methods of Examples 1 to 7 are all in the ranges of 7 to 8 and 6 to 7, and after being placed for 3 months and 6 months, the pH is still in the ranges of 7 to 8 and 6 to 7, and the initial moisture content is within 50 ppm, indicating that the present invention controls the time of alkali washing, the amount of alkali solution and the concentration of the alkali solution, and adds the stabilizer at a specific time after alkali washing, so that the initial pH of the tetrachloroethylene products obtained are all in the ranges of 7 to 8 and 6 to 7, and after being placed for 3 months and 6 months, the pH is still in the ranges of 7 to 8 and 6 to 7, and the initial moisture content is within 50 ppm. This method effectively controls the pH of the tetrachloroethylene products within a specific range and maintains it within the corresponding range for a long time, meeting the use of the tetrachloroethylene products as cleaning agents and as raw materials for refrigerant production.

[0071] In Comparative Example 1, the stabilizer was added too early, and the finished tetrachloroethylene product with an initial pH in the range of 7 to 8 or 6 to 7 could not be obtained, and the initial moisture content of the finished tetrachloroethylene product did not meet the requirements. In Comparative Example 1, the stabilizer was added too late, and the finished tetrachloroethylene product with an initial pH in the range of 7 to 8 or 6 to 7 could not be obtained. The alkali washing time of Comparative Example 3 was too short, and the pH of the obtained finished tetrachloroethylene product was too low. In Comparative Example 4, the same amount of alkali as in Example 1 was used during the alkali washing process, but the volume of the alkali solution was too small, resulting in insufficient alkali washing. The initial pH of the obtained finished tetrachloroethylene product was 6.2, but it dropped to 5.9 after being placed for 6 months. It could not be maintained in a specific pH range within a certain period of time (6 months), and could not meet the use requirements as a raw material for refrigerant production. In Comparative Example 5, the concentration of the alkali solution used during alkali washing was too low, and the finished tetrachloroethylene product with an initial pH in the range of 7 to 8 or 6 to 7 could not be obtained.

[0072] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for accurately controlling the pH of a finished perchloroethylene product, characterized in that: The steps include: Performing alkali washing on tetrachloroethylene in the production process, and adding a stabilizer to the tetrachloroethylene at a time t after the alkali washing is completed; Wherein, the alkali washing process is as follows: the mixing time of tetrachloroethylene and alkali solution is ≥ 3 minutes; The volume ratio of tetrachloroethylene to the alkaline solution is 1:(4-9), and the mass concentration of the alkaline solution is 5-10%; The time t is 2 to 4 hours or 4.5 to 6 hours.

2. The method according to claim 1, characterized in that: Before the alkaline washing, the steps of light removal and distillation are also included.

3. The method according to claim 1, characterized in that: The alkali in the alkaline solution is at least one of sodium hydroxide, potassium hydroxide or calcium hydroxide.

4. The method according to claim 1, characterized in that: The dosage of the stabilizer is: 0.01-0.02 g of the stabilizer is added per 1 kg of tetrachloroethylene.

5. The method according to claim 1, characterized in that: The stabilizer is at least one of phenol, morpholine or diisopropylamine.

6. The method according to claim 1, characterized in that: The method is carried out at 15-25°C.

7. The method according to claim 1, characterized in that: Add the stabilizer to the tetrachloroethylene under stirring.

8. The method according to claim 7, characterized in that: The stirring speed is 10 to 20 rpm.

9. The method according to claim 1, characterized in that: After adding the stabilizer, the method further comprises a drying step.

10. Use of the finished tetrachloroethylene product obtained by the method according to any one of claims 1 to 9 as a cleaning agent or as a raw material for refrigerant production.

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