CN112279220A - Continuous production method of high-purity sulfuric acid - Google Patents
Continuous production method of high-purity sulfuric acid Download PDFInfo
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Abstract
The invention discloses a continuous production method of high-purity sulfuric acid, which comprises a step of analyzing fuming sulfuric acid, a step of refining sulfur trioxide, a step of absorbing sulfur trioxide and a step of removing sulfur dioxide by vacuum plasma, wherein the sulfur trioxide with the sulfur dioxide content of less than 0.4 percent is obtained by analysis, and the content of single metal cations in the sulfur trioxide is less than 5ppt and the sulfur dioxide is less than 20ppm by refining; in the procedure of removing sulfur dioxide, a degassing tower which is provided with a filler and is provided with a plasma excitation device is adopted, sulfuric acid passes through the degassing tower from top to bottom, so that the sulfuric acid forms a falling film on the surface of the filler, and oxygen is introduced from bottom to top and oxygen-sulfur dioxide plasma is formed in the degassing tower, and finally high-purity sulfuric acid is obtained. The invention has the advantages of high production efficiency, low energy consumption, less pollutant discharge, good process stability and safety, stable product quality and good product quality, and can be used for cleaning and etching high-integration chips.
Description
Technical Field
The invention relates to a preparation method of ultra-pure high-purity electronic chemicals, in particular to a purification production method of high-purity sulfuric acid.
Background
With the rapid development of electronic industry in China and the rapid improvement of chip manufacturing level, the international society for semiconductor equipment and materials industry sets up a more rigorous SEMI C12 standard. The technical requirements of ultra-pure and high-purity electronic chemicals, which are key technical materials for chip manufacturing, are gradually increased. The purity of electronic chemicals directly affects the electrical performance, yield and reliability of the chip. Sulfuric acid is used as a strong acid with oxidation property, can remove most metals, metal oxides and organic matters, and is widely used for cleaning and etching chips.
At present, domestic manufacturers adopt the processes of rectification, resin filtration, membrane filtration and the like to reduce the metal content in the sulfuric acid raw material, and the product meets the SEMI C8 standard. By adopting the production process, the operation process is complex, the production quality is difficult to control, and further, a stable product is difficult to obtain. As the IC storage capacity is gradually increased, the oxide film as an insulating layer becomes thinner, and alkali metal impurities in the electronic chemical species dissolve into the oxide film, resulting in a decrease in the insulating voltage; heavy metal impurities adhere to the surface of the silicon wafer and lower the P-N junction withstand voltage. For IC process technologies with different line widths, high-purity electronic chemical reagents with different grades need to be matched.
Sulfuric acid is widely applied in the IC industry, mainly in the cleaning and removing process of photoresist. The existing ultra-high purity sulfuric acid production process mainly comprises two methods, namely an industrial sulfuric acid distillation method and a sulfur trioxide absorption method. The industrial sulfuric acid contains 0.2-0.4% of sulfur dioxide, a so-called potassium permanganate reducing substance. The national standard for sulfur trioxide also contains 0.2 to 0.4 percent of sulfur dioxide. The existence of sulfur dioxide has great influence on the processes of oxidizing and vaporizing photoresist at high temperature by hydrogen sulfate peroxide in the photoresist removing process in the semiconductor industry. The industry generally controls the potassium permanganate reducing substance in the sulfuric acid to be less than 2000 ppb.
The distillation process of small quartz equipment is adopted, and a large amount of potassium permanganate needs to be added into industrial sulfuric acid. The distillation process is easy to scale, and the purification energy consumption of each ton of sulfuric acid is 1000-2000 ℃. Through various processes of energy saving, heat preservation, heat exchange and the like, the unit purification energy cost is 200 plus 300 ℃ of electricity, and the energy consumption is large. Meanwhile, the ultrahigh distillation temperature of 330 ℃ and above not only causes the problem that quartz equipment is easy to crack, but also metal ions in quartz are dissolved out, so that the limit level of the metal ions in the sulfuric acid prepared by the method can only reach the G3 standard (less than 1 ppb) in SEMI.
The main problem with the sulfur trioxide absorption process is the problem of sulfur trioxide purification. The sulfur trioxide evolved by the fuming sulfuric acid desorption method typically contains 2000-4000ppm sulfur dioxide. The performances of sulfur trioxide and sulfur dioxide are similar, and the purification process is difficult. The sulfur trioxide absorption method also has the problem of acid mist, and a common coping method in the industry is to adopt a high-temperature stripping technology. Namely, under the condition of keeping about 100 ℃, a large amount of high-purity nitrogen gas and the like are introduced to blow off and remove sulfur dioxide in sulfuric acid. However, the viscosity of the sulfuric acid is high, the solubility of sulfur dioxide in the sulfuric acid is high, the stripping is greatly fluctuated along with the process temperature, namely the quantity of stripping gas, the product quality is unstable, and the quantity of sulfur dioxide in the sulfuric acid after stripping is still high; and the nitrogen amount for stripping needs to be very large to generate a certain stripping effect, and the stripped gas contains sulfur dioxide, so that a large amount of waste gas is generated, and the treatment cost is high.
In conclusion, no continuous production process report capable of realizing stable production of high-purity sulfuric acid in large batch exists in the prior art, the reported method has various defects and is difficult to popularize and apply, the produced sulfuric acid cannot meet the standard requirement of SEMI G3 or above, and the production technology of the ultra-high-purity sulfuric acid for production in the IC industry is not localized up to now.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a continuous production method of high-purity sulfuric acid, which can be used for producing high-purity sulfuric acid meeting the SEMI G5 standard and above in a large scale.
In order to achieve the purpose, the invention adopts the following technical scheme:
a continuous production method of high-purity sulfuric acid comprises the following steps of:
(1) a step of desorbing fuming sulfuric acid: analyzing the fuming sulfuric acid to obtain sulfur trioxide, wherein the concentration, the temperature and the analysis air pressure of the fuming sulfuric acid are controlled to obtain sulfur trioxide with the sulfur dioxide mass content lower than 0.4%;
(2) refining procedure of sulfur trioxide: rectifying the sulfur trioxide obtained in the analysis procedure to obtain refined sulfur trioxide, and controlling the mass content of single metal cations in the refined sulfur trioxide to be below 5ppt and the mass content of sulfur dioxide to be below 20 ppm;
(3) a sulfur trioxide absorption process: absorbing sulfur trioxide obtained in the refining procedure to obtain sulfuric acid;
(4) a vacuum plasma sulfur dioxide removal process: adopting a degassing tower which is filled with filler, is provided with a plasma excitation device and is connected with a vacuumizing device, leading the sulfuric acid obtained in the absorption procedure to pass through the degassing tower from top to bottom, wherein sulfuric acid forms a falling film on the surface of a filler, oxygen is introduced from bottom to top while a vacuumizing device is used for pumping gas in a degassing tower, the pressure in the degassing tower is controlled to be negative pressure, oxygen generates oxygen plasma which is positioned on the surface of the sulfuric acid and permeates into the sulfuric acid under the excitation action of a plasma excitation device, sulfur dioxide contained in the sulfuric acid is oxidized into sulfur trioxide, and the high-purity sulfuric acid is obtained through the degassing tower, the mass content of single metal cations in the high-purity sulfuric acid is below 5ppt, the mass content of sulfur dioxide is below 200ppb, and the mass content of single anions except sulfate ions is below 50 ppb.
Furthermore, in the step of analyzing the fuming sulfuric acid, the adopted fuming sulfuric acid meets the GB/T534-2014 standard, wherein the mass content of iron is less than 50ppm, the mass content of lead is less than 50ppm, and the mass content of arsenic is less than 1 ppm.
Preferably, in the step of analyzing the oleum, the mass content of sulfur trioxide in the oleum is 25-35%, the analyzing temperature is 110-135 ℃, the analyzing pressure is 10-90 kPa, and the mass content of sulfur dioxide in the sulfur trioxide obtained by analyzing under the above conditions is controlled to be less than 200ppm, and the mass content of single metal cation is less than 10 ppt. According to some specific and preferred aspects of the invention, the sulfur trioxide content of the oleum is 25% to 30% by mass, and the desorption temperature is 120 to 135 ℃. According to other specific and preferred aspects of the present invention, the sulfur trioxide content in the oleum is 30-35% by mass, and the desorption temperature is 110-120 ℃. In some embodiments, the mass contents of sulfur trioxide in the oleum are 25%, 30% and 35%, and the resolved resolving temperatures are 135 degrees celsius, 120 degrees celsius and 110 degrees celsius, respectively.
Preferably, the refining step employs vacuum rectification.
Further preferably, the rectification pressure is controlled to be 70-90 kPa, the reflux ratio is 1.5-2.0, the temperature at the top of the tower is 45-50 ℃, and the temperature at the bottom of the tower is 65-80 ℃. The mass content of the single metal cation in the sulfur trioxide can be reduced to below 5ppt by rectification, and simultaneously, the sulfur dioxide is partially removed in the rectification process and reduced to below 20 ppm.
Preferably, the refining process further comprises heating and gasifying the sulfur trioxide obtained by rectification, and then sequentially carrying out demisting and precise filtering to obtain sulfur trioxide gas. And the demisting is to remove fog drops in sulfur trioxide by a demisting tower internally provided with a wire mesh and/or a filler. The microfiltration is further preferably performed using a nano-scale filter.
Preferably, in the absorption process, the sulfur trioxide is absorbed by the absorbent, and then water is added to adjust the concentration, so that the release of heat during absorption can be controlled, and the production safety is ensured. Further, the absorbent is the high-purity sulfuric acid or higher sulfuric acid, and the water used is high-purity water with the mass content of single anions below 10ppb and the mass content of single metal cations below 5 ppt. In the absorption process, the temperature is controlled to be 70-90 ℃, and the temperature is preferably controlled to be 75-85 ℃.
According to one aspect of the invention, the mass fraction of the high-purity sulfuric acid produced by the method is 95.5-97%, and the mass fraction of the high-purity sulfuric acid used as the absorbent in the absorption process is preferably 95.5-97%.
Preferably, in the vacuum plasma sulfur dioxide removal step, the thickness of the falling film formed on the surface of the filler by the sulfuric acid is 0.1 to 2000 μm. More preferably, the thickness of the falling film formed by the sulfuric acid on the surface of the filler is 10 to 1500 micrometers, and still more preferably 50 to 1000 micrometers.
Further, the height of the filler is preferably 2-7 m, and more preferably 3-7 m. The time for the sulfuric acid to pass through the degassing tower is preferably 10 to 2000 seconds, more preferably 100 to 1500 seconds, and even more preferably 200 to 1000 seconds.
Further, in the vacuum plasma sulfur dioxide removing process, the air pressure in the degassing tower is generally 0.01 to 100 kpa, and the air pressure in the degassing tower is preferably 1 to 100 kpa, and more preferably 10 to 50 kpa.
Further, in the vacuum plasma sulfur dioxide removal process, the plasma excitation frequency is preferably controlled within a range of 1Hz to 10GHz, preferably 1kHz to 10GHz, and more preferably 1kHz to 2.45 GHz. In some embodiments, the plasma excitation frequency is between 10kHz and 50 kHz.
Further, in the vacuum plasma sulfur dioxide removing process, the plasma density in the degassing tower is preferably controlled to be 10 per cubic centimeter8-1013More preferably, the plasma density is controlled to 1010-1013And (4) respectively.
Further, in the vacuum plasma sulfur dioxide removal process, the equivalent concentration of ozone generated by the plasma in the degassing tower is preferably controlled to be 1-1000ppm, and more preferably the equivalent concentration of ozone is controlled to be 100-1000 ppm.
According to some specific and preferred aspects of the present invention, in the vacuum plasma sulfur dioxide removing process, the gas pressure in the degassing tower is controlled to be 0.01 to 100 kpa, the plasma excitation frequency is controlled to be 1Hz to 10GHz, and the temperature is controlled to be 70 to 90 ℃, so that the plasma density in the degassing tower is 10 per cubic centimeter8-1013The equivalent concentration of ozone generated by the plasma is 1-1000 ppm.
According to a further preferable aspect of the present invention, in the step of removing sulfur dioxide by vacuum plasma, the air pressure in the degassing tower is controlled to be 10 to 50 kpa, the plasma excitation frequency is controlled to be 1kHz to 2.45GHz, and the equivalent concentration of ozone generated by plasma in the degassing tower is made to be 100-1000 ppm.
Preferably, the degassing tower and the packing material are made of quartz.
Preferably, the plasma excitation device is provided outside the degasser. The excitation source used by the plasma excitation device is not particularly limited, and as a preferred embodiment of the present invention, one or a combination of several of microwave, high-frequency discharge and barrier dielectric discharge can be used. The input power of the plasma excitation device is preferably 10-100 kilowatts, and more preferably 10-50 kilowatts.
Preferably, in the vacuum plasma sulfur dioxide removal process, the purity of the oxygen used is more than 99.99999 wt%. The input amount of the oxygen is 10-100L per ton of high-purity sulfuric acid, wherein the input amount of the oxygen is more preferably 20-80L, and still more preferably 40-60L.
Further, the method adopts a continuous production system, the continuous production system comprises a raw material tank, an analysis tower, a rectifying tower, a reboiling tower, a demisting device, a precision filter, an absorption device, the degassing tower and a finished product tank, the analysis tower, the rectifying tower, the reboiling tower, the demisting device, the precision filter, the absorption device, the degassing tower and the finished product tank are sequentially arranged and communicated, the analysis process is carried out in the analysis tower, and the absorption process is carried out in the absorption device.
Preferably, during production, all equipment in the continuous production system, which is in contact with the materials, is totally closed and ultra-clean. The ultra-clean refers to that the material of the equipment is dissolved in sulfur dioxide, sulfur trioxide or 98wt% sulfuric acid at the temperature of below 150 ℃, and the dissolved metal in 24 hours is less than 5 ppt. The optional materials comprise high-purity quartz, high-purity fluoroplastic, high-purity silicon carbide materials and other high-purity equipment materials. The totally-enclosed operation means that materials are operated in equipment, all gas balance ports and pipeline valves are in a purification design, namely, the materials are sealed by adopting high-purity nitrogen with the pressure of more than 99.9999 percent and the positive pressure, the pressure is more than 5 kilopascals, and the materials enter a system and need to be filtered by a nanometer-level high-precision air filter element. Finally, the realization of the totally-enclosed ultra-clean process can pass through the cleaning and purifying process of the production process for 10-15 days, and other parts of the total production system except the rectifying still, the resolving tank and the partial area of the tail gas all meet the corresponding production purity requirements.
Preferably, the lower end of the degassing tower is communicated with the finished product tank through a pipeline, a vertical height difference of 8-12 m is formed between the lower end of the degassing tower and the top end of the finished product tank, and the part of the pipeline communicating the lower end of the degassing tower and the top end of the finished product tank is in a U shape with an upward opening. The specific gravity of the sulfuric acid is 1.84kg/L, and according to the liquid pressure theory, the pressure of 1atm can support the sulfuric acid with the height difference of 5.33 meters. By the pressure difference of the sulfuric acid liquid column of the pipeline, the isolation of the vacuum degassing system and other equipment is kept while the continuous and stable production of the whole system is kept, and the totally-closed and high-cleanness production process is realized.
Furthermore, the method also comprises the steps of (circularly) filtering the high-purity sulfuric acid after the vacuum plasma sulfur dioxide removal process, and subpackaging.
Further preferably, the production environment, the material protection and the like are totally closed and ultra-clean besides the requirement of ultra-clean equipment.
Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages:
the method adopts a multi-step grading continuous purification process, sulfur dioxide is removed through analysis, refining, absorption and vacuum plasma, and high-purity sulfuric acid is prepared through continuous purification, in the process, sulfur trioxide is rectified instead of sulfuric acid, the content of metal ions is controlled, and the content of the sulfur dioxide is enabled to be below 20ppm, furthermore, in the process of removing the sulfur dioxide through the vacuum plasma, vacuum degassing and countercurrent falling film are organically combined to form oxygen and sulfur dioxide plasma, one part of the sulfur dioxide is removed through vacuum, the rest part of the sulfur dioxide is permeated into the sulfuric acid, and the oxygen plasma positioned on the surface of the sulfuric acid is oxidized into the sulfur trioxide and is remained in the sulfuric acid, the removal rate of the sulfur dioxide in the sulfuric acid reaches above 99.99 percent, and the content of the sulfur dioxide in the obtained high-purity sulfuric acid is reduced to below 200 ppb; meanwhile, only a small amount of partial sulfur dioxide is removed in vacuum, and most of sulfur dioxide is converted into sulfur trioxide, so that the production amount of acid waste gas (the acid waste gas generated by producing one ton of high-purity sulfuric acid can be reduced to 0.1L) and the treatment cost are remarkably reduced, and the yield of the high-purity sulfuric acid is improved.
The high-purity sulfuric acid prepared by the method has the advantages that the content of each single metal ion is lower than 5ppt, and the content of each single anion except sulfate radicals is lower than 50 ppb. Compared with the prior art, the product obtained by the method has stable quality, meets or even exceeds the requirements of SEMI G5 standard, and can be used for cleaning and etching high-integration chips. And moreover, the production efficiency is high, the energy utilization efficiency is high, the energy consumption is low, the pollutant discharge amount is small, and the process stability and the safety are good.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a schematic structural view of a high-purity sulfuric acid continuous production apparatus according to an embodiment of the present invention;
in the drawings: 1. a raw material tank; 2. a resolution tower; 3. a rectifying tower; 4. a reboiling column; 5. a defogging device; 6. a precision filter; 7. an absorption device; 70. an absorption tower; 71. an absorbent tank; 72. a high-purity water inlet pipe; 8. a degassing tower; 80. the lower end of the degassing tower; 9. a finished product tank; 90. the top end of the finished product tank; 10. a microwave feed-in port; 11. a U-shaped portion; 12. an analysis tank; 13. a sulfur trioxide collection tank.
Detailed Description
The process of the invention takes fuming sulfuric acid and high-purity water as raw materials to prepare the high-purity sulfuric acid. The process is mainly characterized by high-precision control step by step. The ultra-high purity sulfur trioxide gas is obtained by refining the precisely resolved fuming sulfuric acid and the sulfur trioxide, the ultra-high purity sulfur trioxide is further absorbed by the ultra-high purity water to prepare the high-purity sulfuric acid, and the high-purity sulfuric acid is subjected to a vacuum oxygen plasma sulfur dioxide removing process, so that the sulfur dioxide in the high-purity sulfuric acid is efficiently and environmentally removed. In order to avoid the influence of the vacuum plasma treatment process on the continuous production and equipment safety, a vacuum liquid seal technology is adopted to seal the degassing tower. Compared with the prior art, the technical progress is mainly shown in the following aspects:
firstly, the quality of high-purity sulfuric acid is greatly improved, the content of single metal cations is reduced to below 5ppt from 1ppb, the daily yield of the high-purity sulfuric acid reaches 50-135 tons, and the product quality is stable;
secondly, the production energy consumption of the high-purity sulfuric acid is reduced from 200 and 400 kilowatt hour/ton to 0.1 to 10 kilowatt hour/ton;
thirdly, the waste gas treatment capacity of the high-purity sulfuric acid is greatly reduced, and the consumption of the high-purity gas is reduced to 0.1-100L/ton from the ordinary 180000L/ton;
fourthly, the production safety of the high-purity sulfuric acid is greatly improved, the production temperature is changed from high corrosivity of 330 ℃ and above and high oxidizing sulfuric acid steam to the limit temperature of about 100 ℃. The safety risk to sulfuric acid production equipment and production personnel is reduced by two orders of magnitude;
the method mainly comprises an analysis process, a refining process, an absorption process and a vacuum plasma sulfur dioxide removal process. As shown in FIG. 1, the process of the present invention can be carried out in a continuous production system as shown in the figure.
As shown in figure 1, all the equipment of the production system of high-purity sulfuric acid adopts a fully-closed ultra-clean design. The production system mainly comprises a raw material tank 1, an analytical tower 2, a rectifying tower 3, a reboiling tower 4, a demisting device 5, a precision filter 6, an absorption device 7, a degassing tower 8, a finished product tank 9, a connecting pipeline, a pump, a control valve and other necessary equipment which are arranged in sequence. A quartz packing (not shown) is provided inside the degassing tower 8, a plasma excitation device is provided outside the degassing tower 8, and a vacuum-pumping device (not shown) is connected to the top of the degassing tower 8. During production, sulfuric acid obtained in the absorption process passes through a degassing tower from top to bottom, wherein the sulfuric acid forms a falling film on the surface of a filler, oxygen is introduced from bottom to top, a vacuumizing device is used for pumping gas in the degassing tower, the pressure in the degassing tower is controlled to be negative, oxygen plasma which is positioned on the surface of the sulfuric acid and permeates into the sulfuric acid is generated by the oxygen under the excitation action of a plasma excitation device, and sulfur dioxide contained in the sulfuric acid is oxidized into sulfur trioxide. In one embodiment, the plasma excitation device is a microwave plasma device, microwave energy is output through the microwave feed port 10 and passes through the degassing tower 8 to enter the tower, oxygen and sulfur dioxide plasma is generated in the degassing tower 8, the electronegativity of the oxygen plasma is far greater than 2.07V of ozone, and sulfur dioxide is fully oxidized into sulfur trioxide through the continuous reaction of counter-current falling film and is retained in sulfuric acid. The pipe between the degassing column 8 and the finished product tank 9 is provided with a U-shaped section 11 and there is a height difference of about 10 meters between the lower end 80 of the degassing column 8 and the top end 90 of the finished product tank 9. The design has the effect of vacuum liquid seal, the degassing tower 8 is sealed, the influence of a vacuum plasma treatment process on continuous production and equipment safety is avoided, and the whole production system is kept to be fully closed, highly clean and continuously and stably produce high-purity sulfuric acid.
In addition, as shown in fig. 1, after the refined liquid sulfur trioxide is obtained from the rectifying tower, the subsequent absorption process is not directly performed, but the liquid sulfur trioxide is heated and gasified by a reboiler 4, and then is sequentially subjected to a defogging device 5 to remove fog drops and a precise filter 6 (such as a 3nm precise air filter) to filter, and then enters the next absorption link, and the step can ensure that possible micro particulate matters in the sulfur trioxide can be stably and effectively removed. The demisting device 5 may in particular employ a wire mesh demisting device and/or a packing demisting.
In some embodiments, the absorption apparatus 7 includes an absorption tower 70, an absorbent tank 71 located at the bottom of the absorption tower 70, the absorbent tank 71 is connected to the top of the absorption tower 70 and the degassing tower 8 through pipes, and a pump is provided, before the production starts, an absorbent such as 96.5wt% high purity sulfuric acid is pre-stored in the absorbent tank 71, when the system starts, the material in the absorbent tank 71 is conveyed to the top of the absorption tower 70 through the pump and sprayed, sulfur trioxide gas introduced into the absorption tower 70 is absorbed, meanwhile, a high purity water inlet pipe 72 is connected to the absorbent tank 71, high purity water is synchronously added, the sulfuric acid generated in the absorbent tank 71 is subsequently circulated into the absorption tower 70 according to a set proportion, and the rest enters the degassing tower 8.
The production system also includes some necessary storage/intermediate tanks, such as a resolution tank 12, a sulfur trioxide collection tank 13 as shown in FIG. 1. The analyzing tank 12 is used for collecting sulfuric acid left after the analysis of oleum, the sulfur trioxide collecting tank 13 is used for collecting purer sulfur trioxide obtained by the analysis of oleum, and the sulfur trioxide is conveyed to the next process under the action of the pump.
In some embodiments, when the production system is put into production for the first time, common industrial-grade sulfuric acid can be used as an absorbent in an absorption process, high-purity sulfuric acid produced in a period of time just before operation can be used as common high-purity sulfuric acid, after the system continuously produces the high-purity sulfuric acid for a period of time, the cleanliness of the whole system is higher and higher, the produced sulfuric acid is the high-purity sulfuric acid to be prepared by the invention, and the high-purity sulfuric acid can be used as the absorbent subsequently.
The content of the high-purity sulfuric acid is analyzed by a sodium hydroxide titration method, and the content of metal ions is detected by an inductively coupled plasma mass spectrometer (ICP-MS, Thermo X-7 series).
The above-described scheme is further illustrated below with reference to specific examples; it is to be understood that these embodiments are provided to illustrate the general principles, essential features and advantages of the present invention, and the present invention is not limited in scope by the following embodiments; the implementation conditions used in the examples can be further adjusted according to specific requirements, and the implementation conditions not indicated are generally the conditions in routine experiments. Not specifically illustrated in the following examples, all starting materials are commercially available or prepared by methods conventional in the art.
The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Example 1
This example provides a process for producing high-purity sulfuric acid using a production system as shown in FIG. 1, and the respective steps are as follows.
(1) An analysis step: industrial fuming sulfuric acid with 35% of sulfur trioxide in mass is pumped into an analytical tower through a raw material tank, the temperature is controlled to be 110 ℃, the analytical pressure is 85 kilopascals, continuous analysis is carried out, condensate liquid is collected to be sulfur trioxide, the sulfur dioxide and metal ions in the sulfur trioxide are detected, and the result is shown in table 1. The content of the corresponding substances in the starting oleum is also given in table 1.
Table 1 analysis of results of sulfur trioxide measurements obtained in the procedure
As can be seen from Table 1, the maximum content of single metal ions in the fuming sulfuric acid after being resolved is not more than 10ppt, and the content of sulfur dioxide is not more than 200 ppm.
(2) A refining step: the refining comprises the steps of reduced pressure rectification, heating gasification, demisting and precise filtration which are sequentially carried out, wherein the rectification pressure is 85 kilopascals, the reflux ratio is 1.6, the temperature at the top of the tower is 48 ℃, the temperature at the bottom of the tower is 70 ℃, the precise filtration is 3nm precise filtration, the refined sulfur trioxide gas is finally obtained, the sulfur dioxide and metal ions in the sulfur trioxide gas are detected, and the result is shown in table 2. As can be seen from table 2. The cation concentration in the gas is lower than 5ppt, and the sulfur dioxide concentration is lower than 20 ppm.
TABLE 2 detection results of refined Sulfur trioxide gas
(3) An absorption process: 96.5wt% of high-purity sulfuric acid is used as an absorbent, the temperature is controlled to be about 80 ℃, the adopted high-purity water has the technical indexes that the anions are less than 10ppb, and all the cations are less than 5 ppt. The sulfuric acid output from the absorbent tank was detected, in which the metal ions did not undergo a large change.
(4) A vacuum plasma sulfur dioxide removal process: in the degassing tower, sulfuric acid flows through the filler layer from top to bottom, oxygen is introduced from bottom to top while air is extracted outwards, and plasma excitation energy is applied to generate required oxygen plasmas in the degassing tower, wherein the specific conditions are as follows: the air pressure in the degassing tower is 8.5 kilopascals, the temperature is 80 ℃, the height of the packing layer is 5.7m, the falling film thickness formed by the sulfuric acid flowing through the packing layer is controlled to be about 75 micrometers, and the degassing time is controlled to be 600 s; the purity of the oxygen is more than 99.9999wt%, and the input amount of the high-purity oxygen is 53L/ton (high-purity sulfuric acid yield); the plasma excitation source is microwave plasma discharge with input power of 15 kilowatts and plasma excitation frequency of 2.45GHz, and the density of the plasma in the degassing tower is about 7.5 × 10 per cubic centimeter12Ozone equivalent concentration was about 563 ppm. The content of sulfur dioxide and metal ions in the sulfuric acid after the process is shown in table 3. The waste gas yield is 53L/ton (high-purity sulfuric acid yield), and the energy consumption is 9.5 kW.h/ton. The obtained high-purity sulfuric acid is subjected to circulating filtration and subpackaging to obtain a finished product which is sold and used.
Example 2
This example provides a process for producing high-purity sulfuric acid, which comprises the steps (1) to (3) similar to those of example 1, wherein the conditions used in the step (4) are as follows: the air pressure in the degassing tower is 1 kPa,the temperature is 70 ℃, the height of the filler layer is 7m, the falling film thickness formed by the sulfuric acid flowing through the filler layer is controlled to be about 200 microns, and the degassing time is controlled to be 1000 s; the purity of the oxygen is more than 99.9999wt%, and the input amount of the high-purity oxygen is 40L/ton (high-purity sulfuric acid yield); the plasma excitation source is microwave plasma discharge with input power of 10 kilowatts and plasma excitation frequency of 40kHz, and the density of the plasma in the degassing tower is 10.0 × 10 per cubic centimeter12Ozone equivalent concentration 129 ppm. The content of sulfur dioxide and metal ions in the sulfuric acid after the process is shown in table 3. The waste gas yield is 40L/ton (high-purity sulfuric acid yield), and the energy consumption is 8.0 kW.h/ton. The obtained high-purity sulfuric acid is subjected to circulating filtration and subpackaging to obtain a finished product which is sold and used.
Comparative example 1
This example provides a method for producing sulfuric acid, which is substantially the same as in example 1, except that after sulfur trioxide is obtained by analysis, the subsequent steps are directly performed without rectification under reduced pressure, and the results of detection of the produced sulfuric acid are shown in table 3.
Comparative example 2
This example provides a method for producing sulfuric acid, which is substantially the same as example 1, except that the plasma excitation device is not turned on in the sulfur dioxide removal step. The results of the detection of the prepared sulfuric acid are shown in Table 3. The waste gas yield is 53L/ton (sulfuric acid yield), and the energy consumption is 7.0 kW.h/ton.
Comparative example 3
This example provides a process for producing sulfuric acid, which is substantially the same as in example 1, except that in the analysis step, the analysis temperature was 140 degrees centigrade, and that 2530ppm of sulfur dioxide was contained in the sulfur trioxide thus obtained. Correspondingly, the sulfur dioxide content in the sulfur trioxide after the subsequent rectification under reduced pressure is about 873 ppm. The sulfur dioxide and metal ion contents of the finally prepared sulfuric acid are shown in table 3.
TABLE 3 examination results of sulfuric acids prepared in examples 1 to 2 and comparative examples 1 to 3
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
Claims (15)
1. A continuous production method of high-purity sulfuric acid is characterized by comprising the following steps of:
(1) a step of desorbing fuming sulfuric acid: analyzing the fuming sulfuric acid to obtain sulfur trioxide, wherein the concentration, the temperature and the analysis air pressure of the fuming sulfuric acid are controlled to obtain sulfur trioxide with the sulfur dioxide mass content lower than 0.4%;
(2) refining procedure of sulfur trioxide: rectifying the sulfur trioxide obtained in the analysis procedure to obtain refined sulfur trioxide, and controlling the mass content of single metal cations in the refined sulfur trioxide to be below 5ppt and the mass content of sulfur dioxide to be below 20 ppm;
(3) a sulfur trioxide absorption process: absorbing sulfur trioxide obtained in the refining procedure to obtain sulfuric acid;
(4) a vacuum plasma sulfur dioxide removal process: adopting a degassing tower which is filled with filler, is provided with a plasma excitation device and is connected with a vacuumizing device, leading the sulfuric acid obtained in the absorption procedure to pass through the degassing tower from top to bottom, wherein sulfuric acid forms a falling film on the surface of a filler, oxygen is introduced from bottom to top while a vacuumizing device is used for pumping gas in a degassing tower, the pressure in the degassing tower is controlled to be negative pressure, oxygen generates oxygen plasma which is positioned on the surface of the sulfuric acid and permeates into the sulfuric acid under the excitation action of a plasma excitation device, sulfur dioxide contained in the sulfuric acid is oxidized into sulfur trioxide, and the high-purity sulfuric acid is obtained through the degassing tower, the mass content of single metal cations in the high-purity sulfuric acid is below 5ppt, the mass content of sulfur dioxide is below 200ppb, and the mass content of single anions except sulfate ions is below 50 ppb.
2. The continuous production method of high-purity sulfuric acid as claimed in claim 1, wherein in the step of analyzing oleum, the oleum adopted meets GB/T534-2014 standard, wherein the mass content of iron is below 50ppm, the mass content of lead is below 50ppm, and the mass content of arsenic is below 1 ppm.
3. The continuous production method of high-purity sulfuric acid according to claim 1, wherein in the step of desorbing oleum, the mass content of sulfur trioxide in the oleum is 25-35%, the desorption temperature is 110-135 ℃, the desorption pressure is 10-90 kPa, and the mass content of sulfur dioxide in the sulfur trioxide obtained by desorption is less than 200 ppm.
4. The continuous production method of high-purity sulfuric acid according to claim 1, wherein the refining process adopts reduced pressure rectification, the rectification pressure is controlled to be 70-90 kilopascals, the reflux ratio is 1.5-2.0, the temperature at the top of the tower is 45-50 ℃, and the temperature at the bottom of the tower is 65-80 ℃.
5. The continuous production method of high-purity sulfuric acid according to claim 1 or 4, characterized in that the refining process further comprises heating and gasifying the rectified sulfur trioxide, and then sequentially demisting and fine filtering to obtain sulfur trioxide gas.
6. The continuous production method of high-purity sulfuric acid according to claim 1, wherein in the absorption step, sulfur trioxide is absorbed by an absorbent, and then water is added to adjust the concentration, wherein the absorbent is the high-purity sulfuric acid, and the water used is high-purity water having a mass content of single anions of less than 10ppb and a mass content of single metal cations of less than 5 ppt.
7. The continuous production method of high-purity sulfuric acid according to claim 1 or 6, wherein the mass fraction of high-purity sulfuric acid as the absorbent in the absorption step is 95.5% to 97%.
8. The method for continuously producing high-purity sulfuric acid according to claim 1, wherein the falling film of sulfuric acid formed on the surface of the filler in the vacuum plasma sulfur dioxide removal step has a thickness of 0.1 to 2000 μm.
9. The method for continuously producing high-purity sulfuric acid according to claim 1, wherein the height of the filler in the vacuum plasma sulfur dioxide removal process is 2 to 7m, and the time for the sulfuric acid to pass through the degassing tower is 10 to 2000 seconds.
10. The method for continuously producing high-purity sulfuric acid according to claim 1, wherein in the step of removing sulfur dioxide by vacuum plasma, the gas pressure in the degassing tower is controlled to be 0.01 to 100 kPa, the plasma excitation frequency is controlled to be 1Hz to 10GHz, and the temperature is controlled to be 70 to 90 ℃, so that the plasma density in the degassing tower is 10 per cubic centimeter8-1013The equivalent concentration of ozone generated by the plasma is 1-1000 ppm.
11. The continuous production method of high-purity sulfuric acid as claimed in claim 10, wherein in the step of removing sulfur dioxide by vacuum plasma, the air pressure in the degassing tower is controlled to be 10-50 kPa, the plasma excitation frequency is controlled to be 1kHz-2.45GHz, and the equivalent concentration of ozone generated by plasma in the degassing tower is controlled to be 100-1000 ppm.
12. The continuous production method of high-purity sulfuric acid according to claim 1, 10 or 11, wherein the degassing tower and the filler are made of quartz, the plasma excitation device is arranged outside the degassing tower, the excitation source adopted by the plasma excitation device is one or a combination of microwave, high-frequency discharge and barrier dielectric discharge, and the input power of the plasma excitation device is 10-100 kw.
13. The continuous production method of high-purity sulfuric acid according to claim 1, wherein the purity of the oxygen used in the vacuum plasma sulfur dioxide removal process is more than 99.99999wt%, and the input amount of the oxygen is 10-100L per ton of the high-purity sulfuric acid produced.
14. The continuous production method of high-purity sulfuric acid according to claim 1, wherein a continuous production system is used, the continuous production system comprises a raw material tank, a desorption tower, a rectification tower, a reboiling tower, a defogging device, a precision filter, an absorption device, the degassing tower and a finished product tank, the desorption tower, the rectification tower, the reboiling tower, the defogging device, the precision filter, the absorption device, the degassing tower and the finished product tank are arranged and communicated in this order, the lower end of the degassing tower is communicated with the finished product tank through a pipeline, a vertical height difference of 8-12 m is provided between the lower end of the degassing tower and the top end of the finished product tank, and a part of the pipeline communicating the degassing tower and the finished product tank is in a U shape with an upward opening, the desorption process is performed in the desorption tower, and the absorption process is performed in the absorption device, the daily yield of the high-purity sulfuric acid is 50-135 tons.
15. The continuous production method of high-purity sulfuric acid according to claim 14, wherein each equipment in the continuous production system, which is in contact with the material, is totally closed and ultra-clean, wherein the ultra-clean means that the material of the equipment is dissolved in sulfur dioxide, sulfur trioxide or 98wt% sulfuric acid at a temperature of below 150 ℃ for 24 hours, and the dissolved metal is less than 5 ppt; the totally-enclosed operation means that materials are operated in equipment, all gas balance ports and pipeline valves are in a purification design, namely, the materials are sealed by adopting high-purity nitrogen with the pressure of more than 99.9999 percent and the positive pressure, the pressure is more than 5 kilopascals, and the materials enter the equipment and need to be filtered by a nanometer-level high-precision air filter element.
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