CN107266294B - Method for purifying guaiacol primary product for catalytic synthesis of catechol and methanol - Google Patents
Method for purifying guaiacol primary product for catalytic synthesis of catechol and methanol Download PDFInfo
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- CN107266294B CN107266294B CN201710605654.0A CN201710605654A CN107266294B CN 107266294 B CN107266294 B CN 107266294B CN 201710605654 A CN201710605654 A CN 201710605654A CN 107266294 B CN107266294 B CN 107266294B
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Abstract
The invention discloses a purification method of guaiacol primary product for catalytic synthesis of catechol and methanol; the guaiacol as the primary product is subjected to melt crystallization, temperature rise and sweating to obtain high-purity guaiacol; respectively collecting residual mother liquor in the crystallization process and mother liquor generated in the sweating process, combining the mother liquor with the purity higher than 90% and raw materials for direct crystallization, and carrying out crystallization after the components with the purity lower than 90% are subjected to vacuum rectification so that the guaiacol is enriched to meet the crystallization requirement; and (3) carrying out reduced pressure rectification to obtain a mixture rich in the o-dimethyl ether, and carrying out back extraction treatment to obtain a pure o-dimethyl ether product. The invention has low energy consumption in the purification process, high product quality and low separation cost; the method can obtain a byproduct, namely the o-dimethyl ether while obtaining a high-purity guaiacol main product; the purity of the obtained guaiacol finished product can reach more than 99.5 percent, wherein the content of impurities 6-methyl guaiacol and 3-methyl guaiacol is below 0.05 percent.
Description
Technical Field
The invention belongs to the technical field of synthetic spices, and particularly relates to a method for purifying a guaiacol primary product synthesized by catalyzing catechol and methanol.
Background
Guaiacol is an important fine chemical product and can be used as food additive, perfume and raw material for synthesizing vanillin and guaifenesin. The global annual demand reaches nearly 2 ten thousand tons at present. There are two main synthetic methods for guaiacol, namely, the ortho-nitrochlorobenzene method and the catechol method (see patent publication CN101081805), and the catechol method is relatively cleaner, so that the ortho-nitrochlorobenzene method tends to be replaced comprehensively. The reaction equation for the catechol process to produce guaiacol is shown in FIG. 1.
The reaction of catechol and methanol to synthesize guaiacol is completed in a fixed bed reactor under the action of solid acid catalyst at 270 deg.c. Due to the high reaction temperature, when the target product guaiacol is generated, part of the side products of the o-dimethyl ether, the 6-methyl guaiacol and the 3-methyl guaiacol are generated, and the proportion of the three side products can change along with the change of the type of the catalyst and the reaction temperature, but is generally between 0.2 and 3.0 percent. The 6-methyl guaiacol and the 3-methyl guaiacol in the initial guaiacol product can influence the subsequent synthesis of vanillin, so the initial guaiacol product obtained by the reaction needs to be separated and purified to obtain a product with higher purity, and the content of the 6-methyl guaiacol and the 3-methyl guaiacol in the guaiacol product needs to be controlled to be less than 0.05 percent in the actual production.
The currently known purification method is to use the difference of boiling point between the product and the raw material and by-product, and to purify the product by using the conventional rectification method. The difference between the boiling points of the o-dimethyl ether, the 6-methyl guaiacol and the 3-methyl guaiacol and the boiling point of the guaiacol is small, and the rectification efficiency is low. The small amount of 6-methyl guaiacol contained in the product may have a great influence on the use of the product and may significantly affect the melting point of vanillin. For example, when vanillin is synthesized from guaiacol containing a small amount of 6-methyl guaiacol, 5-methyl vanillin is mixed into vanillin (see FIG. 2). The physical properties of the 5-methyl vanillin are very similar to those of vanillin, and the 5-methyl vanillin is difficult to remove by conventional methods such as rectification or crystallization, so that the yield and purity of the vanillin product can be obviously influenced, and the melting point of the vanillin finished product can be influenced. The effect of 3-methyl guaiacol on vanillin synthesis is similar to that of 6-methyl guaiacol. Therefore, in the guaiacol product for synthesizing vanillin, the content of 6-methyl guaiacol and the content of 3-methyl guaiacol are required to be less than 0.05 percent in actual production. The boiling points of 6-methyl guaiacol, 3-methyl guaiacol and guaiacol are slightly different, and although the separation can be realized by a rectification method, the separation difficulty is high, and the energy consumption is high. In order to separate and remove a small amount of 6-methyl guaiacol in a laboratory, a rectifying tower with theoretical plate number of 50 is needed, and the reaction temperature is increased to 5: in the case of 1, the primary yield was only about 50%. When in factory production, a plurality of towers are often used in series to ensure the product quality, and the steam energy consumption in the separation process of a ton of product reaches more than 10 tons.
Disclosure of Invention
In order to solve the problem that the separation and purification of the dimethyl phthalate, the 6-methyl guaiacol and the 3-methyl guaiacol in the guaiacol produced by the synthesis method of catechol and methanol are difficult, the invention aims to provide a purification method of a guaiacol primary product for catalytic synthesis of catechol and methanol. The method has the advantages of simple process, low energy consumption, wide application range and high treatment efficiency, and is suitable for large-scale production, and the by-product of the dimethyl ether is generated.
In the invention, firstly, the guaiacol as a primary product with the content of 95-98% is melted and crystallized, and the mass percent of the guaiacol is more than or equal to 99.5% through melting and crystallization; meanwhile, impurities in the guaiacol as a primary product are enriched in the crystallization mother liquor through melt crystallization. The crystallization mother liquor with higher guaiacol purity is continuously purified by melt crystallization, and is not suitable for melt crystallization when the guaiacol purity is below 90%. Mother liquor which is not suitable for melt crystallization is rectified to improve the content of guaiacol to be more than 90 percent for crystallization, and simultaneously, the dimethyl phthalate, the 6-methyl guaiacol and the 3-methyl guaiacol are enriched in a tower kettle. The components of the o-dimethyl ether, the 6-methyl guaiacol and the 3-methyl guaiacol which are enriched at the bottom of the tower are rectified again, and the o-dimethyl ether with higher purity can be collected from the top of the tower. And (3) carrying out back extraction on the enriched o-dimethyl ether by using alkaline liquor, washing various guaiacols containing phenolic hydroxyl into a water phase, and separating to obtain an organic phase, namely the pure o-dimethyl ether.
The technical scheme of the invention is specifically introduced as follows.
The invention provides a method for purifying a guaiacol primary product for catalytic synthesis of catechol and methanol, wherein the guaiacol content in the guaiacol primary product is 95-98 wt%, the impurities comprise dimethyl phthalate, 6-methyl guaiacol and 3-methyl guaiacol, the content of a single impurity is 0.2-3.0 wt%, and the guaiacol pure product is obtained by separation and purification by adopting a melt crystallization-rectification-back extraction coupling process, and a dimethyl phthalate byproduct is obtained at the same time; the method comprises the following specific steps:
(1) rapidly heating the crystallizer added with the guaiacol primary product to 28-40 ℃ to completely dissolve the guaiacol primary product, then cooling slowly to 5-15 ℃ through a jacket, keeping for 5-20 hours, and filtering out the non-crystallized mother liquor;
(2) after the mother liquor is discharged, slowly raising the temperature of the crystals to 22-26 ℃ by controlling the temperature of a jacket, keeping for 30-60 min to enable the crystals to be partially melted and sweated, filtering out the sweated liquid at different temperature points, and respectively collecting the sweated liquid as the mother liquor according to the purity;
(3) rapidly heating the crystallizer to 28-40 ℃ to completely dissolve the crystals to obtain guaiacol with the purity of more than 99.5 wt%, wherein the content of 6-methyl guaiacol and 3-methyl guaiacol is less than 0.05 wt%;
(4) mother liquor filtered in the crystallization process in the step (1) and the sweating process in the step (2) are combined according to the principle of similar content, and the component with the content of more than 90 wt% is mixed with the guaiacol primary product and then returned to the step (1) to be used as a crystallization raw material for continuous use;
(5) when the guaiacol content in the mother liquor obtained by filtering in the crystallization process and the sweating process is lower than 90 wt% and is not suitable for the components purified by the melt crystallization method, merging and collecting the components, then carrying out vacuum rectification, collecting guaiacol fraction with the purity of more than or equal to 95 wt% from the top of a rectifying tower, and returning the guaiacol fraction to the step (1) to be used as a crystallization raw material for continuous use;
(6) collecting and combining the tower bottom liquid obtained by the vacuum distillation in the step (5), carrying out vacuum distillation again, collecting the front fraction with the guaiacol content of more than 5 wt% from the tower top, returning the front fraction to the step (5) for recovering guaiacol, collecting the fractions with the guaiacol content of less than 5 wt% and the phthalic ether content of more than 5 wt% and combining the fractions as a phthalic ether mixture for recovering the phthalic ether;
(7) and (3) carrying out back extraction on the o-dimethyl ether mixture collected in the step (6) by using an alkali solution with the mass fraction of 5-15 wt%, and layering to obtain a o-dimethyl ether organic phase finished product and an aqueous solution containing 6-methyl guaiacol sodium salt and 3-methyl guaiacol sodium salt.
In the invention, in the step (1) and the step (3), the temperature reduction rate in the crystallization process is controlled to be 0.5-3.0 ℃/h, and the temperature rise rate is controlled to be 0-5.0 ℃/h.
In the present invention, in step (5), the conditions for rectification under reduced pressure are as follows: the theoretical plate number is 10-30, the reflux ratio in the rectification process is 1-3, and the vacuum degree is controlled to be 10-30 mmHg.
In the invention, in the step (6), the number of the rectified theoretical plates is 50-60, the reflux ratio in the rectification process is 3-5, and the vacuum degree is controlled to be 10-30 mmHg.
In the invention, in the step (7), sodium hydroxide or sodium carbonate is used as alkali, and the concentration of the alkali liquor is 5-15 wt%.
In the invention, in the step (7), the addition amount of alkali enables the pH value of the back-extracted water phase to be larger than 8, and the back-extracted organic phase is the pure product of the o-phenylether.
Compared with the prior art, the invention has the following advantages:
1. the provided melt crystallization-rectification-back extraction coupling process is used for guaiacol purification, greatly reduces energy consumption compared with a single rectification process, and can also improve the guaiacol separation yield.
2. The purity of guaiacol obtained by separation is more than 99.5 percent, the content of 6-methyl guaiacol and 3-methyl guaiacol is less than 0.05 percent, and the purity meets the production requirement of vanillin; the total separation yield can be over 98 percent after multiple times of separation and purification.
3. Besides guaiacol, a finished product of a by-product of o-dimethyl ether can be obtained, and the purity of the o-dimethyl ether can reach more than 98%.
Drawings
FIG. 1 shows the reaction equation for the synthesis of guaiacol by catechol method.
FIG. 2 shows the reaction equation for synthesizing vanillin from guaiacol and impurities.
Figure 3 is a typical gas chromatogram of the guaiacol as a primary product after catechol recovery.
Figure 4 is a typical gas chromatogram of guaiacol after melt crystallization purification.
Detailed Description
The present invention will be described in further detail with reference to examples, but the present invention is not limited to the following examples.
Example 1: melt crystallization
A certain amount of guaiacol (the mass content of main substances is 97.73%, 6-methyl guaiacol 0.64%, dimethyl phthalate 1.29% and 3-methyl guaiacol 0.29%) as a primary product is put in a crystallizer with a glass jacket. The diameter of the inner pipe of the crystallizer is 50mm, the height is 230mm, the diameter of the outer pipe is 65mm, the height is 200mm, and heating or cooling water can be introduced between the inner pipe and the outer pipe for temperature control. And (3) heating the crystallizer to above 28 ℃ until the crystals are completely dissolved, then cooling to 15 ℃ at a cooling rate of 1.0 ℃/h, and keeping the temperature for 20 h. Opening a valve at the bottom of the crystallizer to discharge the mother liquor which is not crystallized, and taking the mother liquor as the raw material for rectifying and enriching the guaiacol. And slowly heating by a jacket to raise the temperature for sweating at the rate of 1.0 ℃/h to 26 ℃, keeping the temperature for 60min, discharging sweat after sweating is finished, collecting the sweating liquid, and mixing the sweating liquid with the raw materials to be used as a crystallization raw material. The crystallizer is quickly heated to above 28 ℃ to melt the crystals to obtain colorless transparent liquid, and the single-pass crystallization yield is 70.5%. After gas chromatographic analysis, the guaiacol purity in the product is 99.97%, and the content of single impurities is less than 0.05%. Figure 3 is a typical gas chromatogram of the primary guaiacol product after recovery of catechol. Figure 4 is a typical gas chromatogram of guaiacol after melt crystallization purification.
Example 2: melt crystallization
A certain amount of guaiacol (the mass content of main substances is: 97.93%, 0.54% of 6-methyl guaiacol, 1.02% of o-dimethyl ether and 0.44% of 3-methyl guaiacol) as a primary product is put into a crystallizer with a glass jacket as in example 1, the temperature of the crystallizer is raised to above 28 ℃ until the crystals are completely dissolved, then the temperature is lowered to 15 ℃ at the cooling rate of 2.0 ℃/h, and the temperature is kept for 10 h. Opening a valve at the bottom of the crystallizer to discharge the mother liquor which is not crystallized, wherein the mother liquor can be used as a raw material for rectifying and enriching the guaiacol. And slowly heating by a jacket to raise the temperature for sweating at the rate of 1.0 ℃/h to 26 ℃, keeping the temperature for 60min, discharging sweat after sweating is finished, and collecting the sweating liquid which can be used as a crystallization raw material. The crystallizer is quickly heated to above 28 ℃ to melt the crystals to obtain colorless transparent liquid, and the single-pass crystallization yield is 72.1%. After gas chromatographic analysis, the guaiacol purity in the product is 99.92%, and the content of single impurities is less than 0.05%.
Example 3: melt crystallization
A certain amount of a primary product guaiacol (the mass content of main substances is 95.23 percent of guaiacol, 1.19 percent of 6-methyl guaiacol, 1.36 percent of o-dimethyl ether and 0.69 percent of 3-methyl guaiacol) is placed in a crystallizer with a glass jacket as in the example 1, the temperature of the crystallizer is raised to over 28 ℃ until crystals are completely dissolved, then the temperature is lowered to 5 ℃ at the cooling rate of 3.0 ℃/h, and the temperature is maintained for 10 h. Opening a valve at the bottom of the crystallizer to discharge the mother liquor which is not crystallized, wherein the mother liquor can be used as a raw material for rectifying and enriching the guaiacol. And slowly heating by a jacket to raise the temperature for sweating at a heating rate of 3.0 ℃/h to 24 ℃, keeping the temperature for 30min, discharging sweat after sweating is finished, and collecting the sweating liquid which can be used as a raw material for rectifying and enriching the guaiacol. The crystallizer is quickly heated to above 28 ℃ to melt the crystals to obtain colorless transparent liquid, and the single-pass crystallization yield is 68.8%. After gas chromatographic analysis, the purity of guaiacol in the product is 99.88%, and the content of single impurity is less than 0.05%.
Example 4: rectification under reduced pressure
A reduced pressure rectification experiment is carried out by taking the mother liquor collected in the melt crystallization in the example 1 as a raw material, and the mass content of main substances in the product is as follows: 87.79% of guaiacol, 3.82% of 6-methyl guaiacol, 4.79% of o-dimethyl ether and 1.70% of 3-methyl guaiacol. 1000g of the product is taken in a three-neck flask, and is rectified in a rectifying tower with the theoretical plate number of 10, the pressure in the rectifying process is about 10mmHg, the reflux ratio is 3: 1. 832.4g of overhead fraction were finally collected, and the content of the main substances in the collected fraction was analyzed as follows: 95.87 percent of guaiacol, 0.61 percent of 6-methyl guaiacol, 0.84 percent of o-dimethyl ether and 1.27 percent of 3-methyl guaiacol can be used as crystallization raw materials. Simultaneously, the tower bottom fraction can be obtained, and the contents of main substances are as follows: 49.87 percent of guaiacol, 11.61 percent of 6-methyl guaiacol, 23.22 percent of o-dimethyl ether and 12.02 percent of 3-methyl guaiacol, and can be used as the raw material for re-rectifying and enriching the o-dimethyl ether.
Example 5: rectification under reduced pressure
A reduced pressure rectification experiment is carried out by taking the mother liquor collected in the melt crystallization in the example 2 as a raw material, and the mass content of main substances in the product is as follows: 86.42% of guaiacol, 3.62% of 6-methyl guaiacol, 5.95% of o-dimethyl ether and 2.50% of 3-methyl guaiacol. 1000g of the product is taken in a three-neck flask, and is rectified in a rectifying tower with the theoretical plate number of 30, the pressure in the rectifying process is about 20mmHg, the reflux ratio is 1: 1. 824.4g of overhead fraction were finally collected, and the content of the main substances in the collected fraction was analyzed as follows: 97.01% of guaiacol, 0.58% of 6-methyl guaiacol, 0.92% of o-dimethyl ether and 0.87% of 3-methyl guaiacol, which can be used as crystallization raw materials. Simultaneously, the tower bottom fraction can be obtained, and the contents of main substances are as follows: 34.03 percent of guaiacol, 20.11 percent of 6-methyl guaiacol, 32.72 percent of o-dimethyl ether and 12.98 percent of 3-methyl guaiacol, and can be used as the raw material for re-rectifying and enriching the o-dimethyl ether.
Example 6: rectification under reduced pressure
A reduced pressure rectification experiment is carried out by taking the mother liquor collected in the melt crystallization in the example 3 as a raw material, and the mass content of main substances in the product is as follows: 89.17 percent of guaiacol, 2.38 percent of 6-methyl guaiacol, 5.12 percent of o-dimethyl ether and 2.34 percent of 3-methyl guaiacol. 1000g of the product is taken in a three-neck flask, and is rectified in a rectifying tower with the theoretical plate number of 30, the pressure in the rectifying process is about 30mmHg, the reflux ratio is 2: 1. 846.9g of overhead fraction were finally collected, and the content of the main substances in the collected fraction was analyzed as follows: 97.23 percent of guaiacol, 1.75 percent of 6-methyl guaiacol, 1.04 percent of o-dimethyl ether and 0.73 percent of 3-methyl guaiacol can be used as crystallization raw materials. Simultaneously, the tower bottom fraction can be obtained, and the contents of main substances are as follows: 36.42 percent of guaiacol, 19.24 percent of 6-methyl guaiacol, 31.52 percent of o-dimethyl ether and 11.65 percent of 3-methyl guaiacol, and can be used as the raw material of o-dimethyl ether enriched by rectification again.
Example 7: rectification under reduced pressure
A vacuum rectification experiment is carried out by taking 1000g of the enriched bottom mother liquor of the examples 4-6 as a raw material, and the mass contents of main substances in the product are 42.43% of guaiacol, 17.56% of 6-methyl guaiacol, 27.43% of o-dimethyl ether and 13.23% of 3-methyl guaiacol: 1000g of the product is taken in a three-neck flask and rectified in a rectifying tower with the theoretical plate number of 50, the pressure in the rectifying process is 20mmHg, and the reflux ratio is 5: 1. Firstly, collecting and recovering a fraction with the guaiacol content of more than 5 percent, combining the fraction with a molten crystallization mother liquor to be used as a raw material for enriching and recovering guaiacol, then collecting an intermediate fraction containing o-dimethyl ether, stopping collecting the intermediate fraction until the o-dimethyl ether content is less than 5 percent, and finally collecting 285g of the intermediate fraction, wherein the content of main substances in the collected fraction is analyzed as follows: 2.05 percent of guaiacol, 9.55 percent of 6-methyl guaiacol, 81.46 percent of o-dimethyl ether and 5.91 percent of 3-methyl guaiacol.
Example 8: stripping treatment
100 g of the o-dimethyl ether mixture obtained by rectification in example 7 was taken and added into a 500 ml three-necked flask, and 5% sodium hydroxide solution was added dropwise with stirring until the pH value of the aqueous phase reached 8.5. The mixed solution was transferred to a 500 ml separatory funnel for stratification, and the organic phase was collected as 81.2 g of finished o-dimethyl ether product, which was 98.49% pure by gas phase analysis.
Example 9: stripping treatment
100 g of the o-dimethyl ether mixture obtained by rectification in example 7 was taken and added into a 500 ml three-necked flask, and 10% sodium hydroxide solution was added dropwise with stirring until the pH value of the aqueous phase reached 8.0. The mixed solution was transferred to a 500 ml separatory funnel for stratification, and the organic phase was collected as 81.3 g of finished o-dimethyl ether product, which was 98.01% pure by gas phase analysis.
Claims (5)
1. A method for purifying a guaiacol primary product for catalytic synthesis of catechol and methanol, wherein the guaiacol content in the guaiacol primary product is 95-98 wt%; the impurity comprises o-dimethyl ether, 6-methyl guaiacol and 3-methyl guaiacol, wherein the content of a single impurity is 0.2-3.0 wt%, and the method is characterized in that a melt crystallization-rectification-back extraction coupling process is adopted for separation and purification to obtain a guaiacol pure product, and a o-dimethyl ether byproduct is obtained at the same time; the method comprises the following specific steps:
(1) rapidly heating the crystallizer added with the guaiacol primary product to 28-40 ℃ to completely dissolve the guaiacol primary product, then cooling slowly to 5-15 ℃ through a jacket, keeping for 5-20 hours, and filtering out the non-crystallized mother liquor;
(2) after the mother liquor is discharged, slowly raising the temperature of the crystals to 22-26 ℃ by controlling the temperature of a jacket, keeping for 30-60 min to enable the crystals to be partially melted and sweated, filtering out the sweated liquid at different temperature points, and respectively collecting the sweated liquid as the mother liquor according to the purity;
(3) rapidly heating the crystallizer to 28-40 ℃ to completely dissolve the crystals to obtain guaiacol with the purity of more than 99.5 wt%, wherein the content of 6-methyl guaiacol and 3-methyl guaiacol is less than 0.05 wt%;
(4) mother liquor filtered in the crystallization process in the step (1) and the sweating process in the step (2) are combined according to the principle of similar content, and the component with the content of more than 90 wt% is mixed with the guaiacol primary product and then returned to the step (1) to be used as a crystallization raw material for continuous use;
(5) when the guaiacol content in the mother liquor obtained by filtering in the crystallization process and the sweating process is lower than 90 wt% and is not suitable for the components purified by the melt crystallization method, merging and collecting the components, then carrying out vacuum rectification, collecting guaiacol fraction with the purity of more than or equal to 95 wt% from the top of a rectifying tower, and returning the guaiacol fraction to the step (1) to be used as a crystallization raw material for continuous use;
(6) collecting and combining the tower bottom liquid obtained by the vacuum distillation in the step (5), carrying out vacuum distillation again, collecting the front fraction with the guaiacol content of more than 5 wt% from the tower top, returning the front fraction to the step (5) for recovering guaiacol, collecting the fractions with the guaiacol content of less than 5 wt% and the phthalic ether content of more than 5 wt% and combining the fractions as a phthalic ether mixture for recovering the phthalic ether;
(7) carrying out back extraction on the o-dimethyl ether mixture collected in the step (6) by using an alkali solution with the mass fraction of 5-15 wt%, and layering to obtain a o-dimethyl ether organic phase finished product and an aqueous solution containing 6-methyl guaiacol sodium salt and 3-methyl guaiacol sodium salt;
in the steps (1) to (3), the cooling rate in the crystallization process is controlled to be 0.5-3.0 ℃/h, and the heating rate is controlled to be 1.0-5.0 ℃/h.
2. The purification process according to claim 1, characterized in that: in the step (5), the conditions of the reduced pressure distillation are as follows: the theoretical plate number is 10-30, the reflux ratio in the rectification process is 1-3, and the vacuum degree is controlled to be 10-30 mmHg.
3. The purification process according to claim 1, characterized in that: in the step (6), the number of the rectified theoretical plates is 50-60, the reflux ratio in the rectification process is 3-5, and the vacuum degree is controlled to be 10-30 mmHg.
4. The purification process according to claim 1, characterized in that: in the step (7), sodium hydroxide or sodium carbonate is used as alkali, and the concentration of the alkali liquor is 5-15 wt%.
5. The purification process according to claim 1, characterized in that: in the step (7), the addition amount of alkali enables the pH value of the back-extracted water phase to be larger than 8, and the back-extracted organic phase is the pure o-dimethyl ether product.
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| 熔融结晶及其耦合技术研究的进展;刘海岛 等;《化学工业与工程》;20040930;第21卷(第5期);第367-371页 * |
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