Method for preparing naphthalene sulfonic acid formaldehyde condensate with low sodium sulfate content, low chroma and high performance

Abstract

The invention discloses a method for preparing a low-sodium-sulfate-content, low-chroma and high-performance naphthalene sulfonic acid formaldehyde condensate, which comprises the following steps: carrying out sulfonation reaction on naphthalene and concentrated sulfuric acid at 155-165 DEG C, adding benzene, methylbenzene, xylene or a mixture of two or three of benzene, methylbenzene and xylene into a reactor, forming azeotrope steam from water generated by the reaction and benzene or methylbenzene, and reacting to obtain the low-sodium-sulfate-content, low-chroma and high-performance naphthalene sulfonic acid formaldehyde condensate. Steam is condensed and then flows into an oil-water separator to be layered, water is discharged through a piston at the bottom end of the oil-water separator, the sulfonation degree is evaluated according to the quality of the discharged water, when the discharged water amount reaches 5 / 32 of the mass of naphthalene, it is proved that sulfonation reaction is completed, excessive solvent is evaporated out, the temperature is reduced to 110-120 DEG C, water with the mass ratio of naphthalene to water being (0-9): 128 is added for hydrolysis, the temperature is reduced to 100-120 DEG C, and the sulfonation degree is evaluated according to the quality of the discharged water. The mass ratio of the formaldehyde to the naphthalene is 83: 128-87.5: 128, the mass ratio of the formaldehyde to the naphthalene is 83: 128-87.5: 128, the polymerization reaction is carried out for 4-8 hours, the mass ratio of the water to the naphthalene is 9: 32-45: 64, the viscosity of the system is reduced, after full reaction, a sodium hydroxide solution is used for neutralization, and the product is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, and particularly relates to a method for preparing a naphthalenesulfonic acid formaldehyde condensate with low sodium sulfate content, low chroma and high performance. Background Art

[0002] Naphthalenesulfonic acid formaldehyde condensate sodium salt is a kind of widely used high-efficiency dispersant, which has good dispersibility for hydrophobic particles, but the water produced in the sulfonation reaction can cause the concentrated sulfuric acid concentration in the system to continuously decrease, so that the sulfonation reaction cannot proceed. Therefore, excessive concentrated sulfuric acid needs to be added in the reaction to maintain the concentration of sulfuric acid to ensure that the reaction can proceed and reach a higher degree of sulfonation. However, excessive sulfuric acid will react with naphthalene to produce a large amount of darker compounds such as sulfones and polysulfonates, which will darken the color of the final product, and excessive sulfuric acid will also make the sodium sulfate content in the final product too high. The product color is too dark and will affect the product appearance. The sodium sulfate content is too high, which will also cause the cement setting speed to be too fast, the effective ingredients will decrease, the dispersing power will decrease, and a series of problems such as low-temperature crystallization. In the past, in order to obtain low sodium sulfate content products in industry, it is often necessary to add lime water and other precipitations to remove sodium sulfate in the final product, which will also bring additional waste and high waste disposal fees.

[0003] Chinese invention patent application CN201310702394 discloses a high-concentration naphthalene-based water reducer, which uses aqua regia, industrial naphthalene, formaldehyde, and sodium hydroxide as raw materials, and synthesizes a low-concentration naphthalene-based water reducer through four steps of sulfonation, hydrolysis, condensation, and neutralization, and then undergoes a calcium sulfate precipitation and separation process to obtain a high-concentration naphthalene-based water reducer. This method reduces the sodium sulfate content of the product, but still cannot change its color and cannot solve the problem of calcium sulfate production.

[0004] Chinese invention patent application CN201510492527 relates to a production method of a high-concentration naphthalene-based water reducer and a solid-liquid separation device thereof. The method reduces the sodium sulfate content in the product by improving the neutralization method. Although the product purity is improved, a large amount of residue is still generated.

[0005] Chinese invention patent CN201410414873.7 provides a method for producing a naphthalene-based high-concentration water reducer. The method shortens the sulfonation time by adjusting the ratio of industrial naphthalene, concentrated sulfuric acid and formaldehyde and the reaction conditions, but still cannot improve its color and avoid the problem of excessive sodium sulfate in the product, so it is difficult to achieve better results.

[0006] Although the above technical solutions have made some progress in reducing the sodium sulfate content of the product and improving the purity of the product, there is currently no method for directly obtaining a qualified low-sodium sulfate product through a single reaction without subsequent treatment and without producing calcium sulfate precipitate. Summary of the invention

[0007] In order to solve the problems in the prior art, the present invention provides a method for preparing a naphthalenesulfonic acid formaldehyde condensate with low sodium sulfate content and low chroma and high performance. The method of the present invention continuously forms an azeotrope with benzene, toluene or a mixture of the two and water generated in a reaction system, thereby increasing the sulfonation rate of naphthalene under the condition of a low ratio of sulfuric acid to naphthalene, and obtaining a final product with low sodium sulfate content and low chroma.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] A method for preparing a naphthalenesulfonic acid formaldehyde condensate with low sodium sulfate content, low chroma and high performance comprises the following steps:

[0010] First, add toluene, benzene or a mixture of the two which is 5% of the mass of naphthalene into a reactor connected with an agitator, a thermometer, an oil-water separator and a condenser, load benzene, toluene, xylene or a mixture of two or three thereof near the overflow port into the oil-water separator, add concentrated sulfuric acid with a mass ratio of 100:128 to 106:128 to naphthalene and a mass concentration of 98% into the reactor at 155-165°C, water produced in the reaction continuously forms azeotropic steam with benzene, toluene or a mixture of the two in the reactor, enters the oil-water separator after condensation through the condenser, and a clear interface is formed after benzene, toluene or a mixture of the two is separated from water in the oil-water separator, wherein benzene, toluene or a mixture of the two is located in the upper layer of water, as the reaction continues, water in the lower layer of the oil-water separator gradually increases, benzene, toluene or a mixture of the two located in the upper layer overflows and re-enters the reactor, and water in the lower layer The water is discharged from the lower end of the oil-water separator, and the sulfonation degree of naphthalene is evaluated by the amount of water separated from the oil-water separator. When the amount of discharged water reaches 5 / 32 of the mass of naphthalene, it is proved that the reaction is complete. During the reaction, the water in the lower layer of the oil-water separator is discharged every half an hour; the oil-water separator and the condenser branch are closed, and a vacuum distillation device is connected, and the vacuum distillation branch is opened to evaporate the benzene, toluene or a mixture of the two remaining in the system under reduced pressure, and the temperature is reduced to 110-120° C., water with a mass ratio of 0 to 9:128 to naphthalene is added to the reactor for hydrolysis, and a formaldehyde solution with a mass ratio of 83:128 to 92:128 to naphthalene is added within 2 hours, and the reaction is continued for 4-8 hours. During the reaction, water with a mass ratio of 9:32 to 45:128 to naphthalene and a mass concentration of 36% is added to reduce the viscosity of the system, and finally a sodium hydroxide solution with a mass concentration of 30% is added for neutralization to obtain the final product.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] (1) The present invention ensures the sulfonation degree of naphthalene under low sulfuric acid ratio and makes the product color lighter;

[0013] (2) The present invention ensures the molecular weight at low acidity;

[0014] (3) The process of the present invention is simple, the conditions are mild, it is easy to operate, it is highly safe, the effect is significant, and it has wide promotion and application value. DETAILED DESCRIPTION

[0015] The present invention will be further described below in conjunction with the embodiments.

[0016] Example 1

[0017] 128g of industrial naphthalene and 6.4g of toluene were added to a 500ml four-necked flask equipped with a thermometer, a condenser, an oil-water separator, a stirrer and a thermometer. 6g of toluene was added to an oil-water separator with a total volume of 10ml and a bottom piston. The four-necked flask containing the reaction raw materials was heated to 155°C in an oil bath. Within 1 hour, 101g of 98% concentrated sulfuric acid was added through a dropping funnel, and the system temperature was maintained at 155°C. During the reaction, toluene and water in the flask formed azeotropic vapor, which entered the condenser. The vapor was condensed in the condenser and flowed into the oil-water separator through the branch provided by the oil-water separator. The azeotropic mixture of toluene and water was stratified in the oil-water separator to make a clear toluene\water interface appear in the oil-water separator, with water in the lower layer and toluene in the upper layer. As the reaction progressed, The condensed liquid increases, the liquid level in the oil-water separator continues to rise, and the toluene flows back into the reaction bottle to continue to bring out the water produced by the reaction. During this process, the piston is opened every half an hour to release the water in the lower layer. After the cumulative water output in the oil-water separator reaches 20g, the reaction temperature is lowered to 120°C, the oil-water separator and the condenser branch are closed, and the vacuum distillation device is connected to evaporate the toluene in the reaction bottle. After the vacuum distillation is completed, the vacuum distillation branch is closed, the oil-water separator and the condenser branch are opened, and the reaction temperature is lowered to 110°C. Within 2 hours, 83g of formaldehyde with a mass concentration of 36% is slowly added using a dropping funnel. After the product is obviously thickened, 45g of hot water is added, and the reaction is continued for 6 hours. 133g of sodium hydroxide solution with a mass concentration of 30% is added to neutralize to alkalinity to obtain the final product.

[0018] After the sulfonation reaction is completed, the naphthalenesulfonic acid sample is taken for acid-base titration to test its sulfonation degree, the sodium sulfate content of the reaction product is tested according to the GBT-6366-2012 method, and the molecular weight is determined by gel chromatography. The appearance is observed after drying, and the appearance, sodium sulfate content, and naphthalene sulfonation degree of the naphthalenesulfonic acid formaldehyde copolymer sodium salt sulfonated with the same ratio of naphthalene to concentrated sulfuric acid without using the above method are compared after drying. The results are shown in Table 1. As can be seen from Table 1, this type of product has lower sodium sulfate content and chromaticity.

[0019] Table 1 Comparison of properties of naphthalenesulfonic acid formaldehyde copolymers prepared by different methods

[0020]

[0021] Example 2

[0022] 128g of industrial naphthalene and 6.4g of benzene were added to a 500ml four-necked flask equipped with a thermometer, a condenser, an oil-water separator, a stirrer and a thermometer. 8g of benzene was added to an oil-water separator with a total volume of 10ml and a bottom piston. The four-necked flask containing the raw materials was heated to 155°C in an oil bath. Within 1 hour, 103g of concentrated sulfuric acid with a mass concentration of 98% was added through a dropping funnel. The system temperature was maintained at 155°C. During the reaction, the benzene in the flask formed an azeotropic vapor with water and entered the condenser. The vapor condensed in the condenser became liquid and flowed into the oil-water separator through the branch provided by the oil-water separator. Benzene and water were separated into layers in the oil-water separator. A clear benzene / water interface appeared in the oil-water separator. Water was in the lower layer and benzene was in the upper layer. As the amount of liquid increased, Benzene is continuously refluxed back into the reaction flask to continue to bring out the water produced by the reaction. During this process, the piston is opened every half an hour to release the water in the lower layer. The reaction is stopped when the accumulated water output in the oil-water separator reaches 20 g, the reaction temperature is reduced to 120°C, the oil-water separator and the condenser branch are closed, and a vacuum distillation device is connected to remove the benzene in the reaction flask. After the vacuum distillation is completed, the vacuum distillation branch is closed, the oil-water separator and the condenser branch are opened, the reaction temperature is reduced to 110°C, 9 g of water is added, and the reaction is carried out for half an hour. Within 2 hours, 87.5 g of formaldehyde with a mass concentration of 36% is slowly added using a dropping funnel. After the product is obviously thickened, 36 g of hot water is added, and the reaction is continued for 6 hours. 141 g of sodium hydroxide solution with a mass concentration of 30% is added to neutralize to alkalinity to obtain the final product.

[0023] After the sulfonation reaction is completed, the naphthalenesulfonic acid sample is taken for acid-base titration to test its sulfonation degree, the sodium sulfate content of the final reaction product is tested according to the GBT-6366-2012 method, and its molecular weight is determined by gel chromatography. The appearance is observed after drying, and the appearance, sodium sulfate content, and naphthalene sulfonation degree of the naphthalenesulfonic acid formaldehyde copolymer sodium salt sulfonated with the same naphthalene and concentrated sulfuric acid ratio without using the above method are compared after drying. The results are shown in Table 2. As can be seen from Table 2, this type of product has lower sodium sulfate content and chromaticity.

[0024] Table 2 Comparison of properties of naphthalenesulfonic acid formaldehyde copolymers prepared by different methods

[0025]

[0026] Example 3

[0027] In a 500ml four-necked flask equipped with a thermometer, a condenser, an oil-water separator, a stirrer and a thermometer, 128g of industrial naphthalene and a mixture of 6.4g of toluene and benzene were added; in an oil-water separator with a total volume of 10ml and a bottom piston, a mixture of 6g of toluene and benzene (2:8) was added; the mixture was heated to 160°C in an oil bath; within 1 hour, 106g of concentrated sulfuric acid with a mass concentration of 98% was added through a dropping funnel; the system temperature was maintained at 160°C; during the reaction, toluene / benzene in the flask formed an azeotrope with water and entered the condenser with the steam; the steam condensed in the condenser and became liquid, and flowed into the oil-water separator through the branch provided by the oil-water separator; toluene / benzene and water were separated into layers in the oil-water separator; a clear toluene, benzene\water interface appeared in the oil-water separator, with water in the lower layer and toluene in the upper layer. As the amount of liquid increases, toluene continuously flows back into the reaction flask to continue to take out the water produced by the reaction. During this process, the piston is opened every half an hour to release the water in the lower layer. The reaction is stopped when the accumulated water output in the oil-water separator reaches 20g, the reaction temperature is reduced to 120°C, the oil-water separator and the condenser branch are closed, and a vacuum distillation device is connected to remove the toluene and benzene in the reaction flask. After the vacuum distillation is completed, the vacuum distillation branch is closed, the oil-water separator and the condenser branch are opened, the reaction temperature is reduced to 110°C, 36g of water is added, and the reaction is carried out for half an hour. Within 2 hours, 85g of formaldehyde with a mass concentration of 36% is slowly added using a dropping funnel. After the product is obviously thickened, 45g of hot water is added, and the reaction is continued for 6 hours. 146g of sodium hydroxide solution with a mass concentration of 30% is added to neutralize to alkalinity to obtain the final product. The sodium sulfate content of the reaction product was tested according to the GBT-6366-2012 method, and its molecular weight was determined by gel chromatography. The appearance was compared with that of commonly used naphthalene additives. The results are shown in Table 3. It can be seen from Table 3 that this type of product has a lower sodium sulfate content and chromaticity.

[0028] Table 3 Comparison of properties of naphthalenesulfonic acid formaldehyde copolymers prepared by different methods

[0029]

[0030] It can be seen from Examples 1, 2 and 3 that the method of the present invention continuously forms an azeotrope with water produced in the reaction system with benzene, toluene or a mixture of the two, thereby increasing the sulfonation rate of naphthalene under a low ratio of sulfuric acid to naphthalene, and obtaining a final product with low sodium sulfate content and low chroma.

[0031] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

[0032] Example 4

[0033] In a 500ml four-necked flask equipped with a thermometer, a condenser, an oil-water separator, a stirrer and a thermometer, 128g of industrial naphthalene and a mixture of 6.4g of toluene and xylene (2:8) were added; in an oil-water separator with a total volume of 10ml and a bottom piston, 6g of a mixture of toluene and xylene (mixing ratio of 1:1) was added; the mixture was heated to 160°C in an oil bath; within 1 hour, 106g of concentrated sulfuric acid with a mass concentration of 98% was added through a dropping funnel; the system temperature was maintained at 160°C; during the reaction, toluene / xylene in the flask formed an azeotrope with water, which entered the condenser with the steam; the steam condensed in the condenser and became liquid, which flowed into the oil-water separator through the branch provided by the oil-water separator; toluene and water were separated into layers in the oil-water separator; a clear toluene and xylene / water interface appeared in the oil-water separator, and water was in the lower layer. , toluene and xylene are in the upper layer. As the amount of liquid increases, toluene and xylene continuously flow back into the reaction bottle to continue to bring out the water produced by the reaction. During this process, the piston is opened every half an hour to release the water in the lower layer. The reaction is stopped when the cumulative water output in the oil-water separator reaches 20g, and the reaction temperature is reduced to 120°C. The oil-water separator and the condenser branch are closed, and a vacuum distillation device is connected to remove the toluene and benzene in the reaction bottle. After the vacuum distillation is completed, the vacuum distillation branch is closed, the oil-water separator and the condenser branch are opened, and the reaction temperature is reduced to 110°C. The reaction is carried out for half an hour, and 85g of formaldehyde with a mass concentration of 36% is slowly added using a dropping funnel within 2 hours. After the product is obviously thickened, 45g of hot water is added, and the reaction is continued for 6 hours. 146g of sodium hydroxide solution with a mass concentration of 30% is added to neutralize it to alkalinity to obtain the final product. The sodium sulfate content of the reaction product was tested according to the GBT-6366-2012 method, and its molecular weight was determined by gel chromatography. The appearance was compared with that of commonly used naphthalene additives. The results are shown in Table 5. It can be seen from Table 5 that this type of product has a lower sodium sulfate content and chromaticity.

[0034] Table 4 Comparison of properties of naphthalenesulfonic acid formaldehyde copolymers prepared by different methods

[0035]

[0036] Example 5

[0037] 128g of industrial naphthalene and 5g of xylene were added to a 500ml four-necked flask equipped with a thermometer, a condenser, an oil-water separator, an agitator and a thermometer. 8g of xylene was added to an oil-water separator with a total volume of 10ml and a bottom piston. The four-necked flask containing the reactants was heated to 160°C in an oil bath. Within 1 hour, 108g of concentrated sulfuric acid with a mass concentration of 98% was added through a dropping funnel. The system temperature was maintained at 160°C. During the reaction, toluene / xylene in the flask formed an azeotrope with water and entered the condenser with the steam. The steam condensed in the condenser and became liquid, and flowed into the oil-water separator through the branch provided by the oil-water separator. Toluene and water were separated into layers in the oil-water separator, and a clear toluene and xylene / water interface appeared in the oil-water separator, with water in the lower layer and toluene and xylene in the upper layer. As the amount of liquid increases, toluene and xylene continuously flow back into the reaction flask to continue to take out the water produced by the reaction. During this process, the piston is opened every half an hour to release the water in the lower layer. The reaction is stopped when the accumulated water output in the oil-water separator reaches 20 g, the reaction temperature is reduced to 120°C, the oil-water separator and the condenser branch are closed, and a vacuum distillation device is connected to remove the toluene and benzene in the reaction flask. After the vacuum distillation is completed, the vacuum distillation branch is closed, the oil-water separator and the condenser branch are opened, the reaction temperature is reduced to 110°C, 10 g of water is added, the reaction is continued for half an hour, and 85 g of formaldehyde with a mass concentration of 36% is slowly added using a dropping funnel within 2 hours. After the product is obviously thickened, 45 g of hot water is added, the reaction is continued for 6 hours, and 146 g of sodium hydroxide solution with a mass concentration of 30% is added to neutralize to alkalinity to obtain the final product. The sodium sulfate content of the reaction product was tested according to the GBT-6366-2012 method, and its molecular weight was determined by gel chromatography. The appearance was compared with that of commonly used naphthalene additives. The results are shown in Table 5. It can be seen from Table 5 that this type of product has a lower sodium sulfate content and chromaticity.

[0038] Table 5 Comparison of properties of naphthalenesulfonic acid formaldehyde copolymers prepared by different methods

[0039]

[0040] Example 5

[0041] 128g of industrial naphthalene and 5g of xylene were added to a 500ml four-necked flask equipped with a thermometer, a condenser, an oil-water separator, an agitator and a thermometer. 8g of xylene was added to an oil-water separator with a total volume of 10ml and a bottom piston. The four-necked flask containing the reactants was heated to 160°C in an oil bath. Within 1 hour, 108g of concentrated sulfuric acid with a mass concentration of 98% was added through a dropping funnel. The system temperature was maintained at 160°C. During the reaction, toluene / xylene in the flask formed an azeotrope with water and entered the condenser with the steam. The steam condensed in the condenser and became liquid, and flowed into the oil-water separator through the branch provided by the oil-water separator. Toluene and water were separated into layers in the oil-water separator, and a clear toluene and xylene / water interface appeared in the oil-water separator, with water in the lower layer and toluene and xylene in the upper layer. As the amount of liquid increases, toluene and xylene continuously flow back into the reaction flask to continue to take out the water produced by the reaction. During this process, the piston is opened every half an hour to release the water in the lower layer. The reaction is stopped when the accumulated water output in the oil-water separator reaches 20 g, the reaction temperature is reduced to 120°C, the oil-water separator and the condenser branch are closed, and a vacuum distillation device is connected to remove the toluene and benzene in the reaction flask. After the vacuum distillation is completed, the vacuum distillation branch is closed, the oil-water separator and the condenser branch are opened, the reaction temperature is reduced to 110°C, 10 g of water is added, the reaction is continued for half an hour, and 85 g of formaldehyde with a mass concentration of 36% is slowly added using a dropping funnel within 2 hours. After the product is obviously thickened, 45 g of hot water is added, the reaction is continued for 6 hours, and 146 g of sodium hydroxide solution with a mass concentration of 30% is added to neutralize to alkalinity to obtain the final product. The sodium sulfate content of the reaction product was tested according to the GBT-6366-2012 method, and its molecular weight was determined by gel chromatography. The appearance was compared with that of commonly used naphthalene additives. The results are shown in Table 5. It can be seen from Table 5 that this type of product has a lower sodium sulfate content and chromaticity.

[0042] Table 5 Comparison of properties of naphthalenesulfonic acid formaldehyde copolymers prepared by different methods

[0043]

[0044] Example 6

[0045] 128g of industrial naphthalene and 5g of benzene were added to a 500ml four-necked flask equipped with a thermometer, a condenser, an oil-water separator, a stirrer and a thermometer. A mixture of 10g of benzene, toluene and xylene (1:6:3) was added to an oil-water separator with a total volume of 10ml and a bottom piston. The four-necked flask containing the reactants was heated to 160°C in an oil bath. Within 1 hour, 108g of concentrated sulfuric acid with a mass concentration of 98% was added through a dropping funnel. The system temperature was maintained at 160°C. During the reaction, toluene / xylene in the flask formed an azeotrope with water and entered the condenser with the steam. The steam condensed in the condenser and became liquid, and flowed into the oil-water separator through the branch provided by the oil-water separator. Toluene and water were separated into layers in the oil-water separator, and a clear toluene and xylene / water interface appeared in the oil-water separator. Water was in the lower layer, and toluene and xylene / water were in the lower layer. Benzene is in the upper layer. As the amount of liquid increases, toluene and xylene continuously flow back into the reaction bottle to continue to take out the water produced by the reaction. During this process, the piston is opened every half an hour to release the water in the lower layer. The reaction is stopped after the accumulated water output in the oil-water separator reaches 20g. The reaction temperature is reduced to 120°C, the oil-water separator and the condenser branch are closed, and a vacuum distillation device is connected to remove the toluene and benzene in the reaction bottle. After the vacuum distillation is completed, the vacuum distillation branch is closed, the oil-water separator and the condenser branch are opened, the reaction temperature is reduced to 110°C, 10g of water is added, and the reaction is carried out for half an hour. Within 2 hours, 85g of formaldehyde with a mass concentration of 36% is slowly added using a dropping funnel. After the product is obviously thickened, 45g of hot water is added, and the reaction is continued for 6 hours. 146g of sodium hydroxide solution with a mass concentration of 30% is added to neutralize to alkalinity to obtain the final product. The sodium sulfate content of the reaction product was tested according to the GBT-6366-2012 method, and its molecular weight was determined by gel chromatography. The appearance was compared with that of commonly used naphthalene additives. The results are shown in Table 5. It can be seen from Table 5 that this type of product has a lower sodium sulfate content and chromaticity.

[0046] Table 5 Comparison of properties of naphthalenesulfonic acid formaldehyde copolymers prepared by different methods

[0047]

[0048] It can be seen from Examples 1 to 5 that the method of the present invention continuously forms an azeotrope with water produced in the reaction system using benzene, toluene and xylene or a mixture of two or three of them, thereby increasing the sulfonation rate of naphthalene under a low ratio of sulfuric acid to naphthalene, and obtaining a final product with low sodium sulfate content and low chroma.

[0049] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a naphthalenesulfonic acid formaldehyde condensate with low sodium sulfate content, low chroma and high performance, characterized in that: The following steps are involved: First, toluene, benzene or a mixture of the two of 5% of the mass of naphthalene is added to a reactor connected to an oil-water separator and a condenser, and benzene, toluene, xylene or a mixture of two or three of them is placed near the overflow port in the oil-water separator. At 155-165° C., concentrated sulfuric acid is added to a reactor in a mass ratio of 100:128 to 106:128 to naphthalene. Water generated in the reaction continuously forms azeotropic steam with benzene, toluene, xylene or a mixture of two or three thereof in the reactor, and enters an oil-water separator after being condensed by a condenser. Benzene, toluene, xylene or a mixture of two or three thereof and water form a clear interface after separation in the oil-water separator, wherein benzene, toluene, xylene or a mixture of two or three thereof are located in the upper layer of water. As the reaction continues, the lower layer of water in the oil-water separator gradually increases, and the benzene, toluene or a mixture of the two located in the upper layer overflows and re-enters the reactor. The lower layer of water is discharged from the lower end of the oil-water separator. The sulfonation degree of naphthalene is evaluated by the amount of water separated in the oil-water separator. When the discharged water amount reaches 5 / 32 of the mass of naphthalene, it is proved that the reaction is complete. Close the oil-water separator and condenser branch, connect to the vacuum distillation device, open the vacuum distillation branch, evaporate the benzene, toluene or the mixture of the two remaining in the system under reduced pressure, and cool down to 100-120℃. Add water in a mass ratio of 0 to 9:128 to naphthalene into the reactor for hydrolysis. Add formaldehyde solution with a mass ratio of 83:128 to 92:128 to naphthalene within 2 hours, and continue the reaction for 4-8 hours. During the reaction, water with a mass ratio of 9:32 to 45:128 to naphthalene is added to reduce the viscosity of the system. Finally, sodium hydroxide solution is added to neutralize and the final product is obtained.

2. A method for preparing a naphthalenesulfonic acid formaldehyde condensate with low sodium sulfate content and low chroma and high performance according to claim 1, characterized in that: During the reaction process, the water in the lower layer of the oil-water separator is discharged every half an hour.

3. A method for preparing a naphthalenesulfonic acid formaldehyde condensate with low sodium sulfate content and low chroma and high performance according to claim 1, characterized in that: The reactor is also connected with a stirrer and a thermometer.

4. A method for preparing a naphthalenesulfonic acid formaldehyde condensate with low sodium sulfate content and low chroma and high performance according to claim 1, characterized in that: The mass concentration of the concentrated sulfuric acid is 98%.

5. A method for preparing a naphthalenesulfonic acid formaldehyde condensate with low sodium sulfate content and low chroma and high performance according to claim 1, characterized in that: The mass concentration of the formaldehyde aqueous solution is 36%.

6. A method for preparing a naphthalenesulfonic acid formaldehyde condensate with low sodium sulfate content and low chroma and high performance according to claim 1, characterized in that: The mass concentration of the sodium hydroxide solution is 30%.

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