Process for purifying and separating n-hexane waste gas in grain oil production

Abstract

The application discloses a process for purifying and separating n-hexane waste gas in grain oil production and belongs to the technical field of waste gas treatment of agricultural and sideline products. Mixed adsorbents are introduced into a solvent absorption tower, n-hexane waste gas is adsorbed by the solvent absorption tower to obtain mixed absorption liquid, and the mixed absorption liquid is treated by a desorption tower to realize separation of n-hexane and the mixed adsorbents. The whole process does not involve catalytic reaction, mainly relies on physical absorption and desorption process to realize separation and recovery of n-hexane, and does not need to suspend grain oil production, realizes synchronous performance of grain oil production and n-hexane tail gas separation, and can effectively improve grain oil processing efficiency.

Description

Technical Field

[0001] This invention belongs to the field of agricultural and sideline product waste gas treatment technology, specifically relating to a process for purifying and separating n-hexane waste gas in grain and oil production. Background Technology

[0002] Grains and oils are essential basic necessities in daily life, widely used in home cooking, food processing, and industrial production. They mainly include cereals, oilseeds, and their processed and semi-finished products, forming a major component of the diet and providing the human body with energy, carbohydrates, fats, and other nutrients. With increasing awareness of food safety and nutritional health, the quality requirements for grain and oil products are becoming increasingly stringent. Oilseeds are a crucial part of agricultural production, containing high levels of oil. These oils, after processing, can be converted into edible oils used in daily life, including soybean oil, peanut oil, and rapeseed oil. Extracting and processing oils from oilseeds is one of the core links in the grain and oil industry. Oil extraction from oilseeds mainly relies on physical or chemical methods. Traditional oil extraction methods include pressing and solvent extraction. Pressing involves physically pressing oilseeds to allow the oil to flow out naturally. This process is simple, involves no chemical reagents, and effectively preserves the nutritional properties and original flavor of the oil, meeting food safety requirements and making it suitable for oilseeds with high oil content. However, this method is costly, yields low oil, and contains many impurities, requiring complex subsequent chemical processes such as filtration, alkali refining, decolorization, and deodorization before the oil is edible. Furthermore, the high-temperature processes such as steaming during the pre-processing of oilseed crops denature nutrients such as proteins, starches, and polyphenols in the oilseeds.

[0003] Solvent extraction utilizes the principle of "like dissolves like," using organic solvents to dissolve the oils in oilseeds, followed by post-processing to separate the organic solvents from the oils. This method is a relatively advanced oil extraction method, simple to operate, with a high oil yield, and the nutrients are less likely to be altered. However, because the organic solvents used are toxic to humans, they can enter the body through various routes such as the respiratory tract, digestive tract, and skin, leading to poisoning. Therefore, the removal of organic solvents during the production and processing of oil crops has become an important research objective in grain and oil production.

[0004] Hexane is a commonly used organic solvent in grain and oil production. During the processing of grains and oils, due to its volatility and low boiling point, hexane is released into the air during extraction and evaporation, which can cause serious harm if not handled properly. Current technologies mostly rely on the physical adsorption of biochar materials to treat hexane waste gas. However, biochar materials easily reach adsorption saturation, and their structure can affect adsorption efficiency. In actual production, it is often necessary to replace the biochar material, which can lead to a halt in grain and oil processing, thus affecting production efficiency.

[0005] Therefore, researching a method for separating n-hexane that does not require frequent replacement of adsorbent materials is of great significance for improving the efficiency of grain and oil processing. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention introduces a mixed adsorbent into a solvent absorption tower. Hexane waste gas is adsorbed in the solvent absorption tower to obtain a mixed absorbent liquid, which is then treated in a desorption tower to separate hexane and the mixed adsorbent, thereby solving the technical problems mentioned in the background art. Specifically, the technical solution of this invention includes the following:

[0007] A process for purifying and separating hexane waste gas from grain and oil production, the process comprising the following steps:

[0008] The mixed adsorbent is pumped into the solvent absorption tower via the absorbent replenishment pump;

[0009] The n-hexane waste gas is introduced into the solvent absorption tower by a centrifugal fan and mixed with the mixed adsorbent to obtain a mixed absorbent liquid. The remaining gas in the solvent absorption tower is discharged through the top of the solvent absorption tower.

[0010] The mixed absorbent is pumped into the desorption tower for desorption treatment to obtain the bottom liquid and desorbed gas of the desorption tower. The bottom liquid of the desorption tower is treated by a cooler and enters the solvent absorption tower from the bottom of the desorption tower. The desorbed gas is treated by a cooler and enters the solvent-water separator from the top of the desorption tower. The oil-water mixture in the solvent-water separator is recovered by a solvent transfer pump to obtain n-hexane liquid.

[0011] Furthermore, the mixed adsorbent is composed of 1-ethyl-3-methylimidazolium diethyl phosphate salt and paraffin oil in a weight ratio of 0.7~0.8:1.

[0012] Furthermore, the flow rate of the mixed adsorbent pumped into the solvent absorption tower via the absorbent replenishment pump is 250 kg / h.

[0013] Furthermore, the concentration of the n-hexane waste gas is 10000 mg / cm³. 3 .

[0014] Furthermore, the conditions under which the n-hexane waste gas is introduced into the solvent absorption tower via a centrifugal fan include an air volume of 1000 m³ / h. 3 / h and temperature 25℃.

[0015] Furthermore, the conditions for the mixed adsorption include an adsorption temperature of 25°C, a liquid-to-gas ratio of 0.25 to 0.3 for the mixed adsorbent and the n-hexane waste gas, and an adsorption time of 50 to 60 minutes.

[0016] Furthermore, the conditions for the residual gas in the solvent absorption tower to be discharged through the top of the solvent absorption tower include an air volume of 1000 m³ / h and a temperature of 25°C.

[0017] Furthermore, the flow rate of the mixed absorbent pumped into the desorption tower is 250 kg / h and the temperature is 35°C.

[0018] Furthermore, the conditions for the desorption treatment include a desorption temperature of 96℃~103℃, a theoretical plate number of 6~7, a reflux ratio of 0.4~0.5, and a desorption time of 30 min.

[0019] Furthermore, the conditions for treating the bottom liquid of the desorption tower by the cooler include a flow rate of 250 kg / h and a cooling temperature of 35°C.

[0020] Furthermore, the conditions under which the desorbed gas is processed by the cooler include a flow rate of 10 kg / h and a cooling temperature of 35°C.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) The present invention uses ionic liquid 1-ethyl-3-methylimidazolium phosphate diethyl ester salt and paraffin oil to form a mixed adsorbent. The hydrophobic alkyl side chain on the cationic structure of 1-ethyl-3-methylimidazolium phosphate salt and the long hydrophobic carbon chain of paraffin oil synergistically enhance the selective adsorption of n-hexane. No chemical reaction occurs between 1-ethyl-3-methylimidazolium phosphate diethyl ester salt, paraffin oil and n-hexane, avoiding the influence of side reactions during the separation process. Moreover, the boiling point of this mixed adsorbent is much different from that of n-hexane, and n-hexane can be easily separated from the mixed adsorbent by subsequent high-temperature desorption. A mixed adsorbent is used as the absorbent for adsorbing n-hexane waste gas. The n-hexane waste gas is passed into a solvent absorption tower containing the mixed adsorbent. Taking advantage of the fact that the solubility of n-hexane in the mixed adsorbent is much greater than its dispersion in air, it is absorbed. The absorbed n-hexane, in a liquid state, mixes with the mixed adsorbent to form a mixed absorbent. This mixed absorbent is then passed into a desorption tower, where it undergoes heating treatment to obtain desorbed gas containing n-hexane and a bottom liquid containing the mixed adsorbent. This achieves the separation of the mixed adsorbent and n-hexane. The separated bottom liquid is recycled back into the solvent absorption tower. Furthermore, the adsorption separation process designed in this invention improves the separation efficiency of n-hexane, enabling better adsorption and capture of n-hexane. The entire process does not involve catalytic reactions; it mainly relies on physical absorption and desorption processes to achieve the separation and recovery of n-hexane. Moreover, it does not require interruption of grain and oil production, achieving simultaneous grain and oil production and n-hexane tail gas separation, effectively improving grain and oil processing efficiency.

[0023] (2) Through the process designed in this invention, the concentration of n-hexane in the residual gas discharged from the top of the solvent absorption tower is reduced to 50 mg / m³. 3 The concentration of n-hexane in the desorbed gas was as high as 99.98%, indicating that the process of the present invention has a good effect on the treatment of n-hexane waste gas and is suitable for industrial application in grain and oil production and processing. Attached Figure Description

[0024] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Unless otherwise stated, all raw materials and reagents used in this invention are commercially available or can be prepared by known methods.

[0027] Example 1:

[0028] A process for purifying and separating hexane waste gas from grain and oil production specifically includes the following steps:

[0029] Using a centrifugal pump, 1-ethyl-3-methylimidazolium diethyl phosphate salt and paraffin oil were pumped into a mixed adsorbent storage tank at a weight ratio of 0.7:1 and mixed to obtain a mixed adsorbent. Then, at a flow rate of 250 kg / h, the mixed adsorbent in the mixed adsorbent storage tank was pumped from the top of the solvent absorption tower into the solvent absorption tower through an absorbent replenishment pump, while simultaneously adding adsorbent at a concentration of 10000 mg / cm³. 3 The hexane exhaust gas, with a flow rate of 1000... 3 A centrifugal fan with a flow rate of 1000 m³ / h introduces hexane waste gas into the solvent absorption tower from the bottom. The temperature of the introduced hexane waste gas is controlled at 25°C, ensuring thorough mixing and contact between the mixed adsorbent and the hexane waste gas in a counter-current manner. The temperature of the solvent absorption tower is also controlled at 25°C, and the liquid-to-gas ratio of the mixed adsorbent to the hexane waste gas is controlled at 0.25. The mixture is then subjected to adsorption for 50 minutes. The resulting mixed absorbent is then heated to 35°C and pumped into the desorption tower at a flow rate of 250 kg / h using a centrifugal pump. The desorption temperature in the desorption tower is controlled within the range of 96–103°C, the theoretical plate number is controlled at 6, and the reflux ratio is controlled at 0.4. Desorption is then initiated for 30 minutes. The remaining gas in the solvent absorption tower is discharged through the top of the tower at a flow rate of 1000 m³ / h and a temperature of 25°C. The residual concentration of hexane in the discharged gas is then measured, and the concentration is 41.62 mg / m³. 3 The desorption tower bottom liquid and desorbed gas obtained after desorption treatment are processed as follows: The bottom liquid is pumped out from the bottom of the desorption tower and cooled by an absorbent cooler at a flow rate of 250 kg / h and a cooling temperature of 35°C. The resulting mixed adsorbent is then re-entered into the solvent absorption tower via a circulating pump. The desorbed gas is discharged from the top of the desorption tower, and its concentration is measured to be 99.98% hexane. The desorbed gas is then cooled by an absorbent cooler at a flow rate of 10 kg / h and a cooling temperature of 35°C. The resulting oil-water mixture enters a solvent-water separator and is then recovered as liquid hexane via a solvent transfer pump. See the detailed process flow diagram below. Figure 1 .

[0030] Example 2:

[0031] A process for purifying and separating hexane waste gas from grain and oil production specifically includes the following steps:

[0032] Using a centrifugal pump, 1-ethyl-3-methylimidazolium diethyl phosphate salt and paraffin oil were pumped into a mixed adsorbent storage tank at a weight ratio of 0.75:1 and mixed to obtain a mixed adsorbent. Then, at a flow rate of 250 kg / h, the mixed adsorbent in the mixed adsorbent storage tank was pumped from the top of the solvent absorption tower into the solvent absorption tower through an absorbent replenishment pump, while simultaneously adding adsorbent at a concentration of 10000 mg / cm³. 3 The hexane exhaust gas, with a flow rate of 1000... 3 A centrifugal fan with a flow rate of 1000 m³ / h introduces hexane waste gas into the solvent absorption tower from the bottom. The temperature of the introduced hexane waste gas is controlled at 25°C, ensuring thorough mixing and contact between the mixed adsorbent and the hexane waste gas in a counter-current manner. The temperature of the solvent absorption tower is also controlled at 25°C, and the liquid-to-gas ratio of the mixed adsorbent to the hexane waste gas is controlled at 0.27. The mixture is then subjected to adsorption for 55 minutes. The resulting mixed absorbent is then heated to 35°C and pumped into the desorption tower at a flow rate of 250 kg / h using a centrifugal pump. The desorption temperature in the desorption tower is controlled within the range of 96–103°C, the theoretical plate number is controlled at 6, and the reflux ratio is controlled at 0.4. Desorption is then performed for 30 minutes. The remaining gas in the solvent absorption tower is discharged through the top of the tower at a flow rate of 1000 m³ / h and a temperature of 25°C. The residual concentration of hexane in the discharged gas is then measured, and the concentration is 45.15 mg / m³. 3 The desorption tower bottom liquid and desorbed gas obtained after desorption treatment are processed as follows: The bottom liquid is pumped out from the bottom of the desorption tower and cooled by an absorbent cooler at a flow rate of 250 kg / h and a cooling temperature of 35°C. The resulting mixed adsorbent is then re-entered into the solvent absorption tower via a circulating pump. The desorbed gas is discharged from the top of the desorption tower, and its concentration is measured to be 99.47% for n-hexane. The desorbed gas is then cooled by an absorbent cooler at a flow rate of 10 kg / h and a cooling temperature of 35°C. The resulting oil-water mixture enters a solvent-water separator and is then recovered as liquid n-hexane via a solvent transfer pump. See the detailed process flow diagram below. Figure 1 .

[0033] Example 3:

[0034] A process for purifying and separating hexane waste gas from grain and oil production specifically includes the following steps:

[0035] Using a centrifugal pump, 1-ethyl-3-methylimidazolium diethyl phosphate salt and paraffin oil were pumped into a mixed adsorbent storage tank at a weight ratio of 0.8:1 and mixed to obtain a mixed adsorbent. Then, at a flow rate of 250 kg / h, the mixed adsorbent in the mixed adsorbent storage tank was pumped from the top of the solvent absorption tower into the solvent absorption tower through an absorbent replenishment pump, while simultaneously adding adsorbent at a concentration of 10000 mg / cm³. 3 The hexane exhaust gas, with a flow rate of 1000... 3 A centrifugal fan with a flow rate of 1000 m³ / h introduces hexane waste gas into the solvent absorption tower from the bottom. The temperature of the introduced hexane waste gas is controlled at 25°C, ensuring thorough mixing and contact between the mixed adsorbent and the hexane waste gas in a counter-current manner. The temperature of the solvent absorption tower is also controlled at 25°C, and the liquid-to-gas ratio of the mixed adsorbent to the hexane waste gas is controlled at 0.3. The mixture is then subjected to adsorption for 60 minutes. The resulting mixed absorbent is then heated to 35°C and pumped into the desorption tower at a flow rate of 250 kg / h using a centrifugal pump. The desorption temperature in the desorption tower is controlled within the range of 96–103°C, the theoretical plate number is controlled at 7, and the reflux ratio is controlled at 0.5. Desorption is then initiated for 30 minutes. The remaining gas in the solvent absorption tower is discharged through the top of the tower at a flow rate of 1000 m³ / h and a temperature of 25°C. The residual concentration of hexane in the discharged gas is then measured, and the concentration is 47.48 mg / m³. 3 The desorption tower bottom liquid and desorbed gas obtained after desorption treatment are processed as follows: The bottom liquid is pumped out from the bottom of the desorption tower and cooled by an absorbent cooler at a flow rate of 250 kg / h and a cooling temperature of 35°C. The resulting mixed adsorbent is then re-entered into the solvent absorption tower via a circulating pump. The desorbed gas is discharged from the top of the desorption tower, and its concentration is measured to be 99.06% for n-hexane. The desorbed gas is then cooled by an absorbent cooler at a flow rate of 10 kg / h and a cooling temperature of 35°C. The resulting oil-water mixture enters a solvent-water separator and is then recovered as liquid n-hexane via a solvent transfer pump. See the detailed process flow diagram below. Figure 1 .

[0036] The test results of Examples 1-3 show that the mixed adsorbent composed of ionic liquid 1-ethyl-3-methylimidazolium phosphate diethyl ester salt and paraffin oil, with its hydrophobic alkyl side chain on the cationic structure of 1-ethyl-3-methylimidazolium phosphate salt and long hydrophobic carbon chain on paraffin oil, synergistically enhances the selective adsorption of n-hexane. No chemical reaction occurs between 1-ethyl-3-methylimidazolium phosphate salt, paraffin oil, and n-hexane, avoiding the influence of side reactions during separation. Furthermore, the large difference in boiling point between this mixed adsorbent and n-hexane facilitates the separation of n-hexane from the mixed adsorbent through subsequent high-temperature desorption. The adsorption separation process designed in this invention improves the separation effect of n-hexane, enabling better adsorption and capture of n-hexane. The highest concentration of n-hexane in the desorbed gas can reach 99.98%, indicating a good separation and treatment effect on n-hexane waste gas. Moreover, the n-hexane content in the residual gas in the solvent absorption tower is reduced to 50 mg / m³. 3 The following significantly reduces the environmental pollution caused by the exhaust gas from the solvent absorption tower. The entire process does not involve catalytic reactions; it mainly relies on physical absorption and desorption to separate and recover n-hexane. Furthermore, it does not require interrupting grain and oil production, enabling simultaneous grain and oil production and n-hexane exhaust gas separation, thus effectively improving grain and oil processing efficiency.

[0037] Comparative Example 1:

[0038] A process for purifying and separating hexane waste gas from grain and oil production specifically includes the following steps:

[0039] Using a centrifugal pump, 1-ethyl-3-methylimidazolium diethyl phosphate salt and paraffin oil were pumped into a mixed adsorbent storage tank at a weight ratio of 0.8:1 and mixed to obtain a mixed adsorbent. Then, at a flow rate of 250 kg / h, the mixed adsorbent in the mixed adsorbent storage tank was pumped from the top of the solvent absorption tower into the solvent absorption tower through an absorbent replenishment pump, while simultaneously adding adsorbent at a concentration of 10000 mg / cm³. 3 The hexane exhaust gas, with a flow rate of 1000... 3A centrifugal fan with a flow rate of 1000 m³ / h introduces hexane waste gas into the solvent absorption tower from the bottom. The temperature of the introduced hexane waste gas is controlled at 25°C, ensuring thorough mixing and contact between the mixed adsorbent and the hexane waste gas in a counter-current manner. The temperature of the solvent absorption tower is maintained at 25°C, and the liquid-to-gas ratio of the mixed adsorbent to the hexane waste gas is controlled at 0.2. The mixture is then subjected to adsorption for 60 minutes. The resulting mixed absorbent is then heated to 35°C and pumped into the desorption tower at a flow rate of 250 kg / h using a centrifugal pump. The desorption temperature in the desorption tower is controlled within the range of 96–103°C, the theoretical plate number is controlled at 7, and the reflux ratio is controlled at 0.5. Desorption is then initiated for 30 minutes. The remaining gas in the solvent absorption tower is discharged through the top of the tower at a flow rate of 1000 m³ / h and a temperature of 25°C. The residual concentration of hexane in the discharged gas is then measured, and the concentration is 108.14 mg / m³. 3 The desorption tower bottom liquid and desorbed gas obtained after desorption treatment are processed as follows: The bottom liquid is pumped out from the bottom of the desorption tower and cooled by an absorbent cooler at a flow rate of 250 kg / h and a cooling temperature of 35°C. The resulting mixed adsorbent is then re-entered into the solvent absorption tower via a circulating pump. The desorbed gas is discharged from the top of the desorption tower, and its concentration is measured to be 98.68% hexane. The desorbed gas is then cooled by an absorbent cooler at a flow rate of 10 kg / h and a cooling temperature of 35°C. The resulting oil-water mixture enters a solvent-water separator and is then recovered as liquid hexane via a solvent transfer pump. See the detailed process flow diagram below. Figure 1 As can be seen from Comparative Example 1, when the liquid-to-gas ratio is too low, the mixed adsorbent may not be able to effectively capture the target components in the n-hexane waste gas, resulting in insufficient mass transfer area, poor adsorption driving force, and decreased separation efficiency.

[0040] Comparative Example 2:

[0041] A process for purifying and separating hexane waste gas from grain and oil production specifically includes the following steps:

[0042] Using a centrifugal pump, 1-ethyl-3-methylimidazolium diethyl phosphate salt and paraffin oil were pumped into a mixed adsorbent storage tank at a weight ratio of 0.8:1 and mixed to obtain a mixed adsorbent. Then, at a flow rate of 250 kg / h, the mixed adsorbent in the mixed adsorbent storage tank was pumped from the top of the solvent absorption tower into the solvent absorption tower through an absorbent replenishment pump, while simultaneously adding adsorbent at a concentration of 10000 mg / cm³. 3 The hexane exhaust gas, with a flow rate of 1000... 3A centrifugal fan with a flow rate of 1000 m³ / h introduces hexane waste gas into the solvent absorption tower from the bottom. The temperature of the introduced hexane waste gas is controlled at 25°C, ensuring thorough mixing and contact between the mixed adsorbent and the hexane waste gas in a counter-current manner. The temperature of the solvent absorption tower is maintained at 25°C, and the liquid-to-gas ratio of the mixed adsorbent to the hexane waste gas is controlled at 0.4. The mixture is then subjected to adsorption for 60 minutes. The resulting mixed adsorbate is then heated to 35°C and pumped into the desorption tower at a flow rate of 250 kg / h using a centrifugal pump. The desorption temperature in the desorption tower is controlled within the range of 96–103°C, the theoretical plate number is controlled at 7, and the reflux ratio is controlled at 0.5. Desorption is then initiated for 30 minutes. The remaining gas in the solvent absorption tower is discharged through the top of the tower at a flow rate of 1000 m³ / h and a temperature of 25°C. The residual concentration of hexane in the discharged gas is then measured, and the concentration is 95.76 mg / m³. 3 The desorption tower bottom liquid and desorbed gas obtained after desorption treatment are processed as follows: The bottom liquid is pumped out from the bottom of the desorption tower and cooled by an absorbent cooler at a flow rate of 250 kg / h and a cooling temperature of 35°C. The resulting mixed adsorbent is then re-entered into the solvent absorption tower via a circulating pump. The desorbed gas is discharged from the top of the desorption tower, and its concentration is measured to be 98.91% for n-hexane. The desorbed gas is then cooled by an absorbent cooler at a flow rate of 10 kg / h and a cooling temperature of 35°C. The resulting oil-water mixture enters a solvent-water separator and is then recovered as liquid n-hexane via a solvent transfer pump. See the detailed process flow diagram below. Figure 1 As can be seen from Comparative Example 2, when the liquid-to-gas ratio is too high, the liquid flow rate is much greater than the gas flow rate. The gas may not be able to fully contact the liquid, which reduces the mass transfer efficiency and decreases the separation efficiency.

[0043] Comparative Example 3:

[0044] A process for purifying and separating hexane waste gas from grain and oil production specifically includes the following steps:

[0045] Using a centrifugal pump, 1-ethyl-3-methylimidazolium diethyl phosphate salt and paraffin oil were pumped into a mixed adsorbent storage tank at a weight ratio of 0.8:1 and mixed to obtain a mixed adsorbent. Then, at a flow rate of 250 kg / h, the mixed adsorbent in the mixed adsorbent storage tank was pumped from the top of the solvent absorption tower into the solvent absorption tower through an absorbent replenishment pump, while simultaneously adding adsorbent at a concentration of 10000 mg / cm³. 3 The hexane exhaust gas, with a flow rate of 1000... 3A centrifugal fan with a flow rate of 1000 m³ / h introduces hexane waste gas into the solvent absorption tower from the bottom. The temperature of the introduced hexane waste gas is controlled at 25°C, ensuring thorough mixing and contact between the mixed adsorbent and the hexane waste gas in a counter-current manner. The temperature of the solvent absorption tower is also controlled at 25°C, and the liquid-to-gas ratio of the mixed adsorbent to the hexane waste gas is controlled at 0.3. The mixture is then subjected to adsorption for 60 minutes. The resulting mixed absorbent is then heated to 35°C and pumped into the desorption tower at a flow rate of 250 kg / h using a centrifugal pump. The desorption temperature in the desorption tower is controlled within the range of 96–103°C, the theoretical plate number is controlled at 8, and the reflux ratio is controlled at 0.5. Desorption is then initiated for 30 minutes. The remaining gas in the solvent absorption tower is discharged through the top of the tower at a flow rate of 1000 m³ / h and a temperature of 25°C. The residual concentration of hexane in the discharged gas is then measured, and the concentration is 112.09 mg / m³. 3 The mixed adsorbent bottom liquid obtained after desorption treatment and the desorbed gas are pumped out from the bottom of the desorption tower and cooled by an absorbent cooler. The flow rate pumped into the absorbent cooler is 250 kg / h, and the cooling temperature is controlled at 35°C. The cooled mixed adsorbent is then re-entered into the solvent absorption tower via a circulating pump. The desorbed gas is discharged from the top of the desorption tower, and its concentration is measured to be 99.21% for n-hexane. The desorbed gas is also cooled by an absorbent cooler. The flow rate discharged into the absorbent cooler is controlled at 10 kg / h, and the cooling temperature is controlled at 35°C. The resulting oil-water mixture enters a solvent-water separator, and is then recovered as liquid n-hexane by a solvent transfer pump. See the detailed process flow diagram below. Figure 1 As can be seen from Comparative Example 3, when the number of theoretical plates is too large, it may increase the flow resistance of the gas and liquid phases, preventing effective contact between the gas and liquid, reducing mass transfer efficiency, and decreasing separation efficiency.

[0046] Comparative Example 4:

[0047] A process for purifying and separating hexane waste gas from grain and oil production specifically includes the following steps:

[0048] Using a centrifugal pump, 1-ethyl-3-methylimidazolium diethyl phosphate salt and paraffin oil were pumped into a mixed adsorbent storage tank at a weight ratio of 0.8:1 and mixed to obtain a mixed adsorbent. Then, at a flow rate of 250 kg / h, the mixed adsorbent in the mixed adsorbent storage tank was pumped from the top of the solvent absorption tower into the solvent absorption tower through an absorbent replenishment pump, while simultaneously adding adsorbent at a concentration of 10000 mg / cm³. 3 The hexane exhaust gas, with a flow rate of 1000... 3A centrifugal fan with a flow rate of 1000 m³ / h introduces hexane waste gas into the solvent absorption tower from the bottom. The temperature of the introduced hexane waste gas is controlled at 25°C, ensuring thorough mixing and contact between the mixed adsorbent and the hexane waste gas in a counter-current manner. The temperature of the solvent absorption tower is also controlled at 25°C, and the liquid-to-gas ratio of the mixed adsorbent to the hexane waste gas is controlled at 0.3. The mixture is then subjected to adsorption for 60 minutes. The resulting mixed adsorbate is then heated to 35°C and pumped into the desorption tower at a flow rate of 250 kg / h using a centrifugal pump. The desorption temperature in the desorption tower is controlled within the range of 96–103°C, the theoretical plate number is controlled at 5, and the reflux ratio is controlled at 0.5. Desorption is then initiated for 30 minutes. The remaining gas in the solvent absorption tower is discharged through the top of the tower at a flow rate of 1000 m³ / h and a temperature of 25°C. The residual concentration of hexane in the discharged gas is then measured, and the concentration is 87.85 mg / m³. 3 The desorption tower bottom liquid and desorbed gas obtained after desorption treatment are processed as follows: The bottom liquid is pumped out from the bottom of the desorption tower and cooled by an absorbent cooler at a flow rate of 250 kg / h and a cooling temperature of 35°C. The resulting mixed adsorbent is then re-entered into the solvent absorption tower via a circulating pump. The desorbed gas is discharged from the top of the desorption tower, and its concentration is measured to be 98.95% for n-hexane. The desorbed gas is then cooled by an absorbent cooler at a flow rate of 10 kg / h and a cooling temperature of 35°C. The resulting oil-water mixture enters a solvent-water separator and is then recovered as liquid n-hexane via a solvent transfer pump. See the detailed process flow diagram below. Figure 1 As can be seen from Comparative Example 4, when the number of theoretical plates is too small, it may disrupt the dynamic distribution of the gas and liquid phases, resulting in the inability to effectively adsorb n-hexane under the separation process of this system, thus reducing the separation efficiency.

[0049] Comparative Example 5:

[0050] A process for purifying and separating hexane waste gas from grain and oil production specifically includes the following steps:

[0051] Using a centrifugal pump, 1-ethyl-3-methylimidazolium phosphate diethyl ester salt and paraffin oil were pumped into a mixed adsorbent storage tank at a weight ratio of 0.9:1 and mixed to obtain a mixed adsorbent. Then, at a flow rate of 250 kg / h, the mixed adsorbent in the mixed adsorbent storage tank was pumped from the top of the solvent absorption tower into the solvent absorption tower through an absorbent replenishment pump. The remaining process was consistent with Example 3. The residual concentration of n-hexane in the exhaust gas was measured to be 109.63 mg / m³. 3 The concentration of n-hexane in the desorbed gas was 98.75%.

[0052] Comparative Example 6:

[0053] A process for purifying and separating hexane waste gas from grain and oil production specifically includes the following steps:

[0054] Using a centrifugal pump, 1-ethyl-3-methylimidazolium diethyl phosphate salt and paraffin oil were pumped into a mixed adsorbent storage tank at a weight ratio of 0.6:1 and mixed to obtain a mixed adsorbent. Then, at a flow rate of 250 kg / h, the mixed adsorbent in the mixed adsorbent storage tank was pumped from the top of the solvent absorption tower into the solvent absorption tower through an absorbent replenishment pump. The remaining process was consistent with Example 3. The residual concentration of n-hexane in the exhaust gas was measured to be 121.74 mg / m³. 3 The concentration of n-hexane in the desorbed gas was 98.97%.

[0055] Comparative Examples 5 and 6 show that when the amount of ionic liquid used in the mixed adsorbent is too high or too low, it is not conducive to the adsorption of n-hexane.

[0056] Comparative Example 7:

[0057] A process for purifying and separating hexane waste gas from grain and oil production specifically includes the following steps:

[0058] The mixed adsorbent in Example 3 was directly replaced with 1-ethyl-3-methylimidazolium diethyl phosphate salt, and the rest of the process remained the same as in Example 3. The residual concentration of n-hexane in the exhaust gas was measured to be 147.03 mg / m³. 3 The concentration of n-hexane in the desorbed gas was 98.54%.

[0059] Comparative Example 8:

[0060] A process for purifying and separating hexane waste gas from grain and oil production specifically includes the following steps:

[0061] The mixed adsorbent in Example 3 was directly replaced with paraffin oil, while the rest of the process remained the same as in Example 3. The residual concentration of n-hexane in the exhaust gas was measured to be 131.28 mg / m³. 3 The concentration of n-hexane in the desorbed gas was 98.71%.

[0062] Comparative Examples 7 and 8 show that using any one adsorbent from the mixed adsorbents alone results in a poorer adsorption effect on n-hexane compared to using the mixed adsorbents, which is not conducive to the adsorption treatment of n-hexane.

[0063] The following conclusions can be drawn from the test results of the above comparative examples 1 to 8:

[0064] The separation process parameters and the composition ratio of the mixed adsorbent used in this invention have a significant impact on the treatment of n-hexane waste gas.

[0065] The embodiments and accompanying drawings described above have provided a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A process for purifying and separating n-hexane waste gas in grain and oil production, characterized in that, The process Includes the following steps: The mixed adsorbent is pumped into the solvent absorption tower via the absorbent replenishment pump; The n-hexane waste gas is introduced into the solvent absorption tower by a centrifugal fan and mixed with the mixed adsorbent to obtain a mixed absorbent liquid. The remaining gas in the solvent absorption tower is discharged through the top of the solvent absorption tower. The mixed absorbent is pumped into the desorption tower for desorption treatment to obtain the bottom liquid and desorbed gas of the desorption tower. The bottom liquid of the desorption tower is treated by a cooler and enters the solvent absorption tower from the bottom of the desorption tower. The desorbed gas is treated by a cooler and enters the solvent-water separator from the top of the desorption tower. The oil-water mixture in the solvent-water separator is recovered by a solvent transfer pump to obtain n-hexane liquid. The mixed adsorbent is composed of 1-ethyl-3-methylimidazolium diethyl phosphate salt and paraffin oil in a weight ratio of 0.7~0.8:1; The conditions for the mixed adsorption include an adsorption temperature of 25°C, a liquid-to-gas ratio of 0.25 to 0.3 for the mixed adsorbent and n-hexane waste gas, and an adsorption time of 50 to 60 minutes. The conditions for the desorption treatment include a desorption temperature of 96℃~103℃, a theoretical plate number of 6~7, a reflux ratio of 0.4~0.5, and a desorption time of 30 min.

2. The process for purifying and separating n-hexane waste gas in grain and oil production according to claim 1, characterized in that, The mixed adsorbent is pumped into the solvent absorption tower at a flow rate of 250 kg / h via the absorbent replenishment pump.

3. The process for purifying and separating n-hexane waste gas in grain and oil production according to claim 1, characterized in that, The concentration of the n-hexane exhaust gas is 10000 mg / cm³. 3 .

4. The process for purifying and separating n-hexane waste gas in grain and oil production according to claim 1, characterized in that, The conditions under which the n-hexane waste gas is introduced into the solvent absorption tower via a centrifugal fan include an air volume of 1000 m³ / h. 3 / h and temperature 25℃.

5. The process for purifying and separating n-hexane waste gas in grain and oil production according to claim 1, characterized in that, The flow rate of the mixed absorbent pumped into the desorption tower is 250 kg / h and the temperature is 35°C.

6. The process for purifying and separating n-hexane waste gas in grain and oil production according to claim 1, characterized in that, The conditions for the desorption tower bottom liquid to be treated by the cooler include a flow rate of 250 kg / h and a cooling temperature of 35°C.

7. The process for purifying and separating n-hexane waste gas in grain and oil production according to claim 1, characterized in that, The conditions under which the desorbed gas is processed by the cooler include a flow rate of 10 kg / h and a cooling temperature of 35°C.

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