A method for preparing pyridine hydrobromide using pyridine hydrochloride mother liquor

Abstract

The invention discloses a method for preparing pyridine hydrobromide using pyridine hydrochloride mother liquor, belongs to the technical field of pyridine hydrochloride, and is characterized in that it comprises the following steps: adding purified water to pyridine hydrochloride mother liquor, stirring and standing the mixed solution to be layered, and obtaining a lower layer solution; adding calcium hydroxide solution to the lower layer solution, adjusting the pH to neutral, and adding a phase transfer aid to saturation, stirring and standing the mixed solution to be layered, and obtaining an upper layer of recovered pyridine solution; passing hydrogen bromide gas into the recovered pyridine solution, and collecting the reaction solution; the reaction solution is decolorized, concentrated, cooled, crystallized and dried to obtain pyridine hydrobromide. The beneficial effects of the invention are: the mother liquor produced in the production process of pyridine hydrochloride, creatively introduces a phase transfer aid as calcium chloride, and the overall recovery rate of pyridine is increased from 50% to 90%.

Description

Technical field:

[0001] The invention belongs to the technical field of pyridine hydrochloride, and more specifically relates to a method for preparing pyridine hydrobromide by utilizing pyridine hydrochloride mother liquor. Background technology:

[0002] Pyridine hydrochloride, also known as pyridine hydrochloride, CAS No. 628-13-7, molecular formula C5H5N·HCl, relative molecular mass: 115.56. Pyridine hydrochloride is a white crystal with a melting point of 144-146℃. It is miscible with organic solvents such as water and ethanol, and insoluble in acetone, ether, carbon tetrachloride and aromatic hydrocarbons. The product is very easy to absorb moisture, and the solubility of pyridine hydrochloride in water at room temperature is 560g / 100g water.

[0003] The synthesis of pyridine hydrochloride mainly has the following process routes:

[0004] 1. The liquid-liquid synthesis method of pyridine and hydrochloric acid and the gas-liquid synthesis method of pyridine and hydrogen chloride gas were used respectively. The yield of the liquid-liquid synthesis method was 85%, and that of the gas-liquid synthesis method was 92%. The liquid-liquid synthesis method requires distillation of too much water, which not only fails to obtain anhydrous pyridine hydrochloride, but also has poor product quality.

[0005] 2. Using dichloromethane as solvent, hydrogen chloride and pyridine are reacted to prepare pyridine hydrochloride, with a product content of 98% and a yield of 94%. However, dichloromethane has a low boiling point, a low industrial recovery rate, and a high production cost.

[0006] 3. The product quality and yield are unknown when hydrogen chloride gas is introduced into an anhydrous ether solution of 20-40% pyridine. However, anhydrous ether is difficult to use in industry because it has a low boiling point, is volatile, has a low recovery rate, and is prone to explosions during recovery. This method is limited to preparing a small amount of samples in the laboratory.

[0007] According to our invention patent "A method for cleanly preparing high-purity pyridine hydrochloride" ZL201310714902.7, a method for preparing pyridine hydrochloride is disclosed. The hydrogen chloride gas produced in step (2) is dried with concentrated sulfuric acid, passed through a buffer tank, and introduced into the mixed solution in step (1), and reacted at a temperature of 20-60°C. By controlling the feeding rate of hydrochloric acid, the pressure in the kettle is kept at 0.01-0.05MPa, and the molar ratio of hydrogen chloride to pyridine in the mixed solvent is 1:1.0-1.2. Filtration is performed, and the filter cake is wet pyridine hydrochloride. The filtrate is returned to the production system for repeated use.

[0008] However, the mother liquor (i.e., filtrate) generated during the production of pyridine hydrochloride contains multiple components as the number of uses increases, mainly toluene, pyridine, hydrogen chloride, and impurities. The product quality is affected due to increased viscosity and darker color, and it needs to be scrapped and disposed of as hazardous waste, resulting in a waste of resources and increased production costs. There is currently no method for recycling it.

[0009] At present, our company only treats the mother liquor produced in the production process of pyridine hydrochloride by adding liquid alkali to adjust the pH to neutral and then directly discharging it. This not only increases the difficulty of subsequent water treatment, but also causes waste.

[0010] Therefore, a method for recycling the mother liquor (i.e. filtrate) produced in the pyridine hydrochloride production process is badly needed. Summary of the invention:

[0011] In order to solve the above problems and overcome the shortcomings of the prior art, the present invention provides a method for preparing pyridine hydrobromide from the mother liquor generated in the production process of pyridine hydrochloride, which can effectively solve the problem that the mother liquor generated in the production process of pyridine hydrochloride is difficult to handle.

[0012] The specific technical solution of the present invention to solve the above technical problem is: a method for preparing pyridine hydrobromide using pyridine hydrochloride mother liquor, characterized by comprising the following steps:

[0013] (1) adding purified water to the pyridine hydrochloride mother solution, stirring and standing the mixed solution to separate into layers, thereby obtaining a lower layer solution;

[0014] (2) adding calcium hydroxide solution to the lower solution, adjusting the pH to neutral, and adding a phase transfer agent in an amount of mother liquor: calcium chloride = 10: 2.5-3.5 by mass ratio, stirring and standing the mixed solution to separate layers, and recovering the pyridine solution in the upper layer;

[0015] (3) introducing hydrogen bromide gas into the recovered pyridine solution, controlling the hydrogen bromide gas flow rate to 5-20 L / h, controlling the reaction temperature to 25-70° C., controlling the stirring speed to 63-125 r / min, controlling the free pyridine to less than 1%, stopping the introduction of hydrogen bromide gas, and collecting the reaction solution;

[0016] (4) The reaction solution is decolorized, concentrated, cooled, crystallized and dried to obtain pyridinium hydrobromide.

[0017] Furthermore, the preparation method of the pyridine hydrochloride mother solution is:

[0018] (1.1) dissolving pyridine in an organic solvent to obtain a mixed solution, wherein the volume ratio of pyridine to the organic solvent is 1:5-7;

[0019] (1.2) Add concentrated sulfuric acid into a container and add hydrochloric acid dropwise to generate hydrogen chloride gas. The weight ratio of hydrochloric acid to concentrated sulfuric acid is 1:2.5-3.5;

[0020] (1.3) The generated hydrogen chloride gas is dried and buffered, and then introduced into the mixed solution in step (1.1), wherein the molar ratio of hydrogen chloride to pyridine in the mixed solution is 1:1.0-1.2, and the reaction is carried out at a temperature not higher than 60° C., the pressure in the autoclave is 0.01-0.02 MPa, and the reaction is carried out by filtration to obtain a pyridine hydrochloride mother liquor.

[0021] Furthermore, the phase transfer aid is calcium chloride.

[0022] Furthermore, the decolorization step is to add 0.1-1% activated carbon to the reaction solution and filter to obtain a filtrate.

[0023] Furthermore, the concentration step is to raise the temperature of the filtrate to 80-100° C. under negative pressure, and distill out 40-60% volume of the aqueous solution to obtain a concentrated solution;

[0024] Furthermore, the cooling and crystallization step is to cool the concentrated solution to 5-35°C, wait for crystals to precipitate, and centrifuge to obtain the wet product;

[0025] Furthermore, the drying process is to vacuum dry the wet product for 2-5 hours to obtain pyridinium hydrobromide.

[0026] The beneficial effects of the present invention are:

[0027] The method for preparing pyridine hydrobromide from the mother liquor generated in the production process of pyridine hydrochloride can effectively solve the problem that the mother liquor generated in the production process of pyridine hydrochloride is difficult to handle;

[0028] The mother liquor generated during the production of pyridine hydrochloride was creatively introduced with a phase transfer aid of calcium chloride. Through strong common ion effect and salting-out effect, the pyridine content in the lower solution was reduced to about 10%, and the overall recovery rate of pyridine was increased from 50% to 90%. Toluene and pyridine were recovered, realizing resource utilization and reducing production costs. Specific implementation method:

[0029] In the description of the present invention, specific details are only for a full understanding of the embodiments of the present invention, but those skilled in the art should know that the implementation of the present invention is not limited to these details. In addition, well-known structures and functions are not described or shown in detail to avoid blurring the key points of the embodiments of the present invention. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0030] Specific implementation of the present invention:

[0031] In order to better understand the present invention, a specific embodiment is used for illustration. It is worth emphasizing that the effect of this embodiment is not substantially different from the various embodiments within the protection scope of the present invention, including the respective reagents and the content ratio of the reagents, and all of them can achieve the effects described in the present invention and solve the above-mentioned problems. Other combinations are not described here.

[0032] As the pretreated pyridine hydrochloride mother liquor of the present invention, our company's invention patent "A method for cleanly preparing high-purity pyridine hydrochloride" ZL201310714902.7 discloses a method for preparing pyridine hydrochloride.

[0033] Specifically, the hydrogen chloride gas generated in step (2) is dried with concentrated sulfuric acid, passed through a buffer tank, and introduced into the mixed solution in step (1), reacting at a temperature of 20-60° C., controlling the feeding rate of hydrochloric acid so that the pressure in the kettle is 0.01-0.05 MPa, the molar ratio of hydrogen chloride to pyridine in the mixed solvent is 1:1.0-1.2, filtering, the filter cake is wet pyridine hydrochloride, and the filtrate is pyridine hydrochloride mother liquor;

[0034] Embodiment 1:

[0035] (1) adding purified water to the pyridine hydrochloride mother solution, stirring and standing the mixed solution to separate into layers, thereby obtaining a lower layer solution;

[0036] (2) adding calcium hydroxide solution to the lower solution, adjusting the pH to neutral, and adding a phase transfer agent in an amount of mother liquor: calcium chloride = 10:2.5 by mass ratio, stirring and standing the mixed solution to separate layers, and obtaining an upper layer of recovered pyridine solution;

[0037] (3) introducing hydrogen bromide gas into the recovered pyridine solution, controlling the hydrogen bromide gas flow rate to 5-20 L / h, controlling the reaction temperature to 25-70° C., controlling the stirring speed to 63-125 r / min, controlling the free pyridine to less than 1%, stopping the introduction of hydrogen bromide gas, and collecting the reaction solution;

[0038] (4) the reaction solution is decolorized, concentrated, cooled, crystallized and dried to obtain pyridinium hydrobromide;

[0039] Specifically, the decolorization process is to add 0.1-1% activated carbon to the reaction solution and filter to obtain a filtrate. The concentration process is to increase the temperature of the filtrate to 80-100°C under negative pressure, distill out 40-60% of the volume of the aqueous solution, and obtain a concentrated solution; the cooling and crystallization process is to cool the concentrated solution to 5-35°C, wait for crystals to precipitate, and centrifuge to obtain a wet product; the drying process is to vacuum dry the wet product for 2-5 hours to obtain pyridinium hydrobromide.

[0040] Embodiment 2:

[0041] (1) adding purified water to the pyridine hydrochloride mother solution, stirring and standing the mixed solution to separate into layers, thereby obtaining a lower layer solution;

[0042] (2) adding calcium hydroxide solution to the lower solution, adjusting the pH to neutral, and adding a phase transfer agent in an amount of mother liquor: calcium chloride = 10:3.5 by mass ratio, stirring and standing the mixed solution to separate layers, and recovering the pyridine solution in the upper layer;

[0043] (3) introducing hydrogen bromide gas into the recovered pyridine solution, controlling the hydrogen bromide gas flow rate to 5-20 L / h, controlling the reaction temperature to 25-70° C., controlling the stirring speed to 63-125 r / min, controlling the free pyridine to less than 1%, stopping the introduction of hydrogen bromide gas, and collecting the reaction solution;

[0044] (4) the reaction solution is decolorized, concentrated, cooled, crystallized and dried to obtain pyridinium hydrobromide;

[0045] Specifically, the decolorization process is to add 0.1-1% activated carbon to the reaction solution and filter to obtain a filtrate. The concentration process is to increase the temperature of the filtrate to 80-100°C under negative pressure, distill out 40-60% of the volume of the aqueous solution, and obtain a concentrated solution; the cooling and crystallization process is to cool the concentrated solution to 5-35°C, wait for crystals to precipitate, and centrifuge to obtain a wet product; the drying process is to vacuum dry the wet product for 2-5 hours to obtain pyridinium hydrobromide.

[0046] Embodiment 3:

[0047] (1) adding purified water to the pyridine hydrochloride mother solution, stirring and standing the mixed solution to separate into layers, thereby obtaining a lower layer solution;

[0048] (2) adding calcium hydroxide solution to the lower solution, adjusting the pH to neutral, and adding a phase transfer agent in an amount of mother liquor: calcium chloride = 10:3 by mass ratio, stirring and standing the mixed solution to separate layers, and obtaining an upper layer of recovered pyridine solution;

[0049] (3) introducing hydrogen bromide gas into the recovered pyridine solution, controlling the hydrogen bromide gas flow rate to 5-20 L / h, controlling the reaction temperature to 25-70° C., controlling the stirring speed to 63-125 r / min, controlling the free pyridine to less than 1%, stopping the introduction of hydrogen bromide gas, and collecting the reaction solution;

[0050] (4) the reaction solution is decolorized, concentrated, cooled, crystallized and dried to obtain pyridinium hydrobromide;

[0051] Specifically, the decolorization process is to add 0.1-1% activated carbon to the reaction solution and filter to obtain a filtrate. The concentration process is to increase the temperature of the filtrate to 80-100°C under negative pressure, distill out 40-60% of the volume of the aqueous solution, and obtain a concentrated solution; the cooling and crystallization process is to cool the concentrated solution to 5-35°C, wait for crystals to precipitate, and centrifuge to obtain a wet product; the drying process is to vacuum dry the wet product for 2-5 hours to obtain pyridinium hydrobromide.

[0052] In order to more intuitively demonstrate the process advantages of the present invention, the method of preparing pyridine hydrobromide by using pyridine hydrochloride mother liquor of the present invention is compared with the method of using equivalent replacement in the same process.

[0053] Comparative Example 1:

[0054] Adopt the existing treatment method of our company: the treatment method of the mother liquor generated in the production process of pyridine hydrochloride is to add liquid alkali to adjust the pH to neutral and then discharge it directly;

[0055] Comparative Example 2:

[0056] The preparation method is the same as that of Example 3, except that: in the preparation process of this comparative example, liquid alkali is used to adjust the pH to neutral; and no phase transfer aid calcium chloride is added;

[0057] Specifically:

[0058] Step (2) After the first step of pretreatment, add liquid alkali to the lower solution to adjust the pH to neutral; stir for 1 hour, let stand for 30 minutes, and separate the mixed solution into layers;

[0059] Comparative Example 3:

[0060] The preparation method is the same as that of Example 3, except that: liquid alkali is used to adjust the pH to neutral, and sodium chloride is added as a phase transfer aid;

[0061] Comparative Example 4:

[0062] The preparation method is the same as that of Example 3, except that the pH is adjusted to neutral using liquid alkali, and calcium chloride is added as a phase transfer aid;

[0063] Specifically:

[0064] In the preparation process of this comparative example, after the first step pretreatment in step (2), liquid alkali is added to the lower solution to adjust the pH to neutral, and calcium chloride as a phase transfer aid is added in an amount of mother liquor: calcium chloride = 10:3 by mass ratio, and the mixed solution is stirred and allowed to stand for stratification, and the upper layer of recovered pyridine solution is stirred for 1 hour, allowed to stand for 30 minutes, and the mixed solution is stratified;

[0065] Comparative Example 5:

[0066] The preparation method is the same as that of Example 3, except that no phase transfer aid calcium chloride is added;

[0067] Specifically:

[0068] Step (2) After the first step of pretreatment, calcium hydroxide was added to the lower solution to adjust the pH to neutral, stirred for 1 hour, allowed to stand for 30 minutes, and the mixed solution was separated into layers;

[0069] Comparative Example 6:

[0070] The preparation method is the same as that of Example 3, except that the phase transfer aid calcium chloride is replaced by sodium chloride;

[0071] Specifically:

[0072] In the preparation process of this comparative example, after the first step pretreatment in step (2), liquid alkali is added to the lower solution to adjust the pH to neutral, and a phase transfer aid sodium chloride is added in an amount of a mass ratio of mother liquor: calcium chloride = 10:3, and the mixed solution is stirred and allowed to stand for stratification, and the upper layer of recovered pyridine solution is stirred for 1 hour, allowed to stand for 30 minutes, and the mixed solution is stratified;

[0073] The above examples and comparative examples are based on the national standard of the People's Republic of China GB / T 24199-2009

[0074] Gas chromatography method for determining the pyridine content in pure pyridine, and testing the pyridine recovery rate and the purity of pyridine hydrobromide;

[0075] Table 1: Pyridine recovery and pyridine hydrobromide purity comparison of different embodiments and comparative examples

[0076] Preprocessing pH Adjuster Phase transfer aid Pyridine recovery Pyridine hydrobromide purity Example 1 + Calcium hydroxide Calcium chloride 92.1％ 99.55％ Example 2 + Calcium hydroxide Calcium chloride 89.7％ 99.46％ Example 3 + Calcium hydroxide Calcium chloride 90.3％ 99.49％ Comparative Example 1 - Liquid caustic soda - - - Comparative Example 2 + Liquid caustic soda - - - Comparative Example 3 + Liquid caustic soda Sodium chloride 45.6％ 99.18％ Comparative Example 4 + Liquid caustic soda Calcium chloride 48.4％ 99.27％ Comparative Example 5 + Calcium hydroxide - 30.7％ 99.22％ Comparative Example 6 + Calcium hydroxide Sodium chloride 51.2％ 99.31％

[0077] From the data analysis in Table 1, we can see that:

[0078] (1) Embodiment 1-3:

[0079] Using calcium hydroxide solution, after adjusting the pH to neutral, calcium chloride was added continuously. The solubility of calcium chloride in 20°C water reached 74.5g. Through the strong salting-out effect, the pyridine content in the lower solution was reduced to about 10%, and the overall recovery rate of pyridine was increased from 50%-60% to 80%-90%, and the purity of pyridine hydrobromide reached 99%;

[0080] (2) Comparative Example 1 is the existing treatment method of our company: that is, the treatment method of the mother liquor generated in the production process of pyridine hydrochloride is to add liquid alkali to adjust the pH to neutral and then directly discharge it; since the liquid alkali destroys the combination of hydrochloric acid and pyridine, the pyridine hydrochloride solution dissolved in water is decomposed into a mixed solution of pyridine, sodium chloride and toluene. Toluene and pyridine are mutually soluble, making it impossible to recover pyridine, so it can only be discharged to sewage treatment, which not only causes waste of resources, but also creates great pressure on sewage treatment.

[0081] (2) In Comparative Example 2: a pretreatment process was adopted, that is, the pyridine hydrochloride mother liquor was split using a certain amount of purified water, the upper layer was toluene and organic impurities, and the lower layer was the pyridine hydrochloride solution;

[0082] Since the pH regulator is liquid alkali, the liquid alkali destroys the combination of hydrochloric acid and pyridine, and decomposes the hydrochloric acid pyridine solution dissolved in water into a mixed solution of pyridine, sodium chloride and toluene. Toluene and pyridine are mutually soluble, making it impossible to recover pyridine. Therefore, although a pretreatment step is adopted, this method cannot recover pyridine.

[0083] (3) Comparative Examples 3 and 4 are further improvements of Comparative Example 2, with the addition of phase transfer aids calcium chloride or sodium chloride.

[0084] Since the pH regulator is liquid alkali, the liquid alkali destroys the combination of hydrochloric acid and pyridine, and the hydrochloric acid pyridine solution dissolved in water is decomposed into a mixed solution of pyridine, sodium chloride and toluene. Although the phase transfer aid calcium chloride or sodium chloride is added later, the pyridine cannot be recovered;

[0085] (4) Comparative Example 5: Compared with the present invention, no phase transfer aid calcium chloride is added; hydrogen chloride cannot be neutralized, and hydrogen chloride affects the production quality of pyridine hydrobromide.

[0086] (5) Comparative Example 6: Compared with the present invention, the phase transfer aid added was sodium chloride, and the production quality of pyridinium bromate was lower than that of the present invention.

[0087] This may be due to the strong common ion effect and salting-out effect, the pyridine content in the lower solution is reduced to about 10%, and the overall recovery rate of pyridine is increased from 50%-60% to 80%-90%.

[0088] In summary: the method for preparing pyridine hydrobromide from the mother liquor generated in the production process of pyridine hydrochloride can effectively solve the problem that the mother liquor generated in the production process of pyridine hydrochloride is difficult to handle;

[0089] The mother liquor generated during the production of pyridine hydrochloride creatively introduces a phase transfer aid, calcium chloride. Through strong common ion effect and salting-out effect, the pyridine content in the lower solution is reduced to about 10%, and the overall recovery rate of pyridine is increased from 50%-60% to 80%-90%. Toluene and pyridine are recovered, realizing resource utilization and reducing production costs.

Claims

1. A method for preparing pyridine hydrobromide using pyridine hydrochloride mother liquor, characterized in that The steps include: (1) adding purified water to the pyridine hydrochloride mother solution, stirring and standing the mixed solution to separate into layers, thereby obtaining a lower layer solution; (2) adding calcium hydroxide solution to the lower solution, adjusting the pH to neutral, and adding a phase transfer agent in an amount of mother liquor: calcium chloride = 10: 2.5-3.5 by mass ratio, stirring and standing the mixed solution to separate layers, and recovering the pyridine solution in the upper layer; (3) introducing hydrogen bromide gas into the recovered pyridine solution, controlling the hydrogen bromide gas flow rate to 5-20 L / h, controlling the reaction temperature to 25-70° C., controlling the stirring speed to 63-125 r / min, controlling the free pyridine to less than 1%, stopping the introduction of hydrogen bromide gas, and collecting the reaction solution; (4) The reaction solution is decolorized, concentrated, cooled, crystallized and dried to obtain pyridinium hydrobromide.

2. The method for preparing pyridine hydrobromide by utilizing pyridine hydrochloride mother liquor according to claim 1, characterized in that The preparation method of the pyridine hydrochloride mother solution is: (1.1) dissolving pyridine in an organic solvent to obtain a mixed solution, wherein the volume ratio of pyridine to the organic solvent is 1:5-7; (1.2) Add concentrated sulfuric acid into a container and add hydrochloric acid dropwise to generate hydrogen chloride gas. The weight ratio of hydrochloric acid to concentrated sulfuric acid is 1:2.5-3.5; (1.3) The generated hydrogen chloride gas is dried and buffered, and then introduced into the mixed solution in step (1.1), wherein the molar ratio of hydrogen chloride to pyridine in the mixed solution is 1:1.0-1.2, and the reaction is carried out at a temperature not higher than 60° C., the pressure in the autoclave is 0.01-0.02 MPa, and the reaction is carried out by filtration to obtain a pyridine hydrochloride mother liquor.

3. The method for preparing pyridine hydrobromide by utilizing pyridine hydrochloride mother liquor according to claim 1, characterized in that The phase transfer aid is calcium chloride.

4. The method for preparing pyridine hydrobromide by utilizing pyridine hydrochloride mother liquor according to claim 1, characterized in that The decolorization process is to add 0.1-1% activated carbon to the reaction solution and filter to obtain a filtrate.

5. The method for preparing pyridine hydrobromide by utilizing pyridine hydrochloride mother liquor according to claim 4, characterized in that The concentration process is to raise the temperature of the filtrate to 80-100° C. under negative pressure, distill out 40-60% volume of the aqueous solution, and obtain a concentrated solution.

6. The method for preparing pyridine hydrobromide by utilizing pyridine hydrochloride mother liquor according to claim 5, characterized in that The cooling and crystallization process is to cool the concentrated solution to 5-35°C, wait for crystals to precipitate, and centrifuge to obtain the wet product.

7. The method for preparing pyridine hydrobromide by utilizing pyridine hydrochloride mother liquor according to claim 6, characterized in that The drying process is to vacuum dry the wet product for 2-5 hours to obtain pyridinium hydrobromide.