Process for separating glutaric acid from adipic acid byproduct

Abstract

The invention discloses a process for separating glutaric acid from an adipic acid byproduct, and belongs to the technical field of chemical separation. The process comprises the following steps: adsorbing a mixed binary acid solution by resin to remove a catalyst, sequentially carrying out rising-film evaporation and falling-film evaporation concentration, carrying out primary crystallization on a concentrated solution at 20-23 DEG C to separate succinic acid and adipic acid so as to obtain a mother solution rich in glutaric acid, carrying out rising-film evaporation concentration on the mother solution, feeding the mother solution into a multi-chamber series-connected adiabatic evaporation crystallizer, and carrying out vacuum distillation to obtain the glutaric acid. The final crystallization temperature is controlled to be 4-10 DEG C under the gradient vacuum condition, meanwhile, a seed crystal reflux technology is adopted, glutaric acid wet crystals are obtained through separation after crystallization is completed, and glutaric acid products are obtained through drying. The purity of glutaric acid in the glutaric acid product can reach 95% or above, the yield reaches 90% or above, and the method has remarkable industrial application value.

Description

Technical Field

[0001] This invention relates to the field of chemical separation and purification technology, and in particular to a process for separating glutaric acid from adipic acid byproducts. Background Technology

[0002] In the actual production of adipic acid, the byproduct (waste liquid) is a mixed dicarboxylic acid solution mainly composed of succinic acid, glutaric acid, and adipic acid. Glutaric acid is an important organic chemical raw material and intermediate, widely used in the pharmaceutical, food processing, and chemical industries. Due to the similar physicochemical properties of these three dicarboxylic acids, it is difficult to obtain high-purity glutaric acid products using conventional crystallization separation methods.

[0003] In the prior art, CN105130790A discloses a method for separating and purifying succinic acid, glutaric acid and adipic acid from the residual liquid of cyclohexanone oxidized by nitric acid to prepare adipic acid. The method includes preliminary cooling crystallization, solvent separation of succinic acid and adipic acid, chemical purification of glutaric acid and acidification recovery, and finally obtaining glutaric acid product by evaporation and drying. Although this method can effectively remove water-soluble impurities through salt formation and acidification steps and can theoretically obtain high-purity glutaric acid, it has the following obvious defects: (1) The process is complicated, with many operation units and cumbersome process; (2) It requires the consumption of chemical reagents such as magnesium oxide and sulfuric acid, resulting in high raw material costs and the generation of magnesium sulfate wastewater, which increases the cost of waste treatment; (3) It involves strong acid (sulfuric acid) operation, which has higher requirements for equipment and operation safety and poses safety hazards.

[0004] Therefore, there is an urgent need to develop a simple, safe, and environmentally friendly process for separating glutaric acid from adipic acid byproducts in order to solve the aforementioned problems in existing technologies. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides a process for separating glutaric acid from adipic acid byproducts.

[0006] The technical solution of this invention is:

[0007] A process for separating glutaric acid from adipic acid byproducts, characterized by comprising the following steps:

[0008] (1) Catalyst removal

[0009] The mixed dicarboxylic acid solution is first subjected to a resin adsorption reaction, so that the catalyst in the solution is adsorbed and removed by the resin, and the mixed dicarboxylic acid solution after the catalyst is removed is obtained.

[0010] During the production of adipic acid, companies typically add catalysts containing copper and vanadium. After these catalysts react, some metal ions (such as copper and vanadium ions) remain in the final byproduct—the mixed diacid solution. Pre-removing these catalyst metal ions from the mixed diacid solution prevents them from triggering side reactions and affecting product quality during subsequent high-temperature evaporation and crystallization.

[0011] (2) Evaporation and concentration

[0012] The mixed dicarboxylic acid solution after catalyst removal in step (1) is first subjected to rising film evaporation at a temperature of 100℃~120℃, and then subjected to falling film evaporation at a temperature of 140℃~155℃ to obtain a concentrated solution.

[0013] Among them, rising film evaporation uses a rising film evaporator, which is a high-efficiency evaporation device. Its advantages over ordinary evaporators are: high heat transfer efficiency, the material is mainly driven upward by the lift of steam bubbles in the heating tube, the heat transfer coefficient is large, and the evaporation speed is fast. Utilizing the high efficiency of the rising film evaporator at medium and low concentrations and large evaporation volumes, most of the water in the mixed dicarboxylic acid solution is quickly removed. At this time, the material viscosity is low, which is suitable for rising film operation. After the mixed dicarboxylic acid solution is initially concentrated by rising film, the viscosity will increase and the concentration will further increase. At this time, falling film evaporator is used to continue falling film evaporation. The material forms a film at the top of the falling film evaporator through the distributor and mainly relies on gravity to drive downward flow. It is suitable for processing materials with higher viscosity that require deep concentration and can better avoid the risk of thermal decomposition caused by excessive residence time at high temperature (150℃).

[0014] In step (2), the concentration and viscosity of the mixed dicarboxylic acid solution vary greatly. It is difficult for a single type of evaporator to maintain optimal efficiency throughout the entire concentration range. The combination of rising film evaporation and falling film evaporation ensures that the evaporation process is always carried out under the most suitable conditions, so as to guarantee the final product quality and yield.

[0015] (3) Preliminary crystallization

[0016] The concentrate obtained in step (2) is subjected to preliminary crystallization. The concentrate is cooled to 20-23°C and crystallized at a constant temperature for 2-3 hours. Then, it is centrifuged to obtain a solid phase and a first liquid phase. The first liquid phase is a mother liquor enriched with glutaric acid.

[0017] The purpose of initially cooling to 20–23°C during the preliminary crystallization process is to utilize the fact that succinic acid and adipic acid have significantly lower solubility than glutaric acid within this temperature range. This allows succinic acid and adipic acid to crystallize out preferentially, while glutaric acid, due to its higher solubility, remains in the mother liquor, achieving preliminary separation and enrichment. Temperatures below 20°C will cause glutaric acid eutectic precipitation, reducing the glutaric acid yield; temperatures above 23°C will result in insufficient precipitation of succinic acid and adipic acid, affecting the subsequent purity of glutaric acid.

[0018] The mother liquor contains: 11%–13% succinic acid, 69%–71% glutaric acid, and 7%–9% adipic acid.

[0019] (4) Concentration and crystallization separation of glutaric acid

[0020] The mother liquor obtained in step (3) is sent to a rising film evaporator and heated to 45℃~50℃ for evaporation and concentration. Then it is sent to a multi-chamber series adiabatic evaporation crystallizer. The crystallization temperature is gradually reduced from 45℃~50℃ to 4℃~10℃ by gradient vacuum control. After the adiabatic evaporation crystallization is completed, centrifugation is used to separate glutaric acid wet crystals and the second liquid phase.

[0021] Although succinic acid and adipic acid both tend to crystallize at low temperatures, this invention effectively suppresses impurity crystallization through the following synergistic mechanism, thereby achieving high-purity separation of glutaric acid:

[0022] First, the concentration advantage dominates the crystallization process. After preliminary crystallization and enrichment in step (3), the concentration of glutaric acid in the mother liquor is absolutely dominant (typically 71%), while the concentrations of succinic acid and adipic acid are significantly reduced (usually 13% and 9%).

[0023] Secondly, the mother liquor obtained in step (3) is sent back into the rising film evaporator for evaporation and concentration. The temperature of the mother liquor is first raised to 45℃~50℃ before it enters the adiabatic evaporation crystallizer for crystallization. Its function is:

[0024] (1) In the mother liquor of the preliminary crystallization step (step 3), there may be trace amounts of glutaric acid or impurities such as "fine crystals" or "crystal nuclei" that are invisible to the naked eye. Heating to 45℃~50℃ helps to dissolve these unstable microcrystals and provides a stable starting solution for the subsequent adiabatic evaporation crystallization process. This avoids irregular crystal nuclei from directly entering the subsequent adiabatic evaporation crystallization environment and ensures that the crystallization process is completely guided by the high-quality "seed crystals" added later.

[0025] (2) The core principle of adiabatic evaporation crystallization is to use the solution to boil and evaporate under vacuum to remove heat and achieve cooling. Preheating the mother liquor to 45℃~50℃ before entering the first chamber below means that the crystallization process will start from this relatively high initial temperature and gradually decrease to the final temperature (4℃~10℃). This significant temperature drop of about 40℃ provides the system with ample time and space to reduce the supersaturation of the solution at a gradual and controllable rate. This can effectively suppress explosive spontaneous nucleation and ensure that the crystals mainly grow in an orderly manner on the refluxed seed crystals, thereby obtaining a product with uniform particle size and high purity. If the mother liquor enters directly at room temperature (20℃~25℃), the temperature drop of the entire crystallization process is extremely small (about 10℃~15℃), which can easily lead to a sharp increase in the supersaturation of the solution in a narrow temperature range, triggering uncontrollable nucleation, producing a large number of fine crystals, deteriorating product quality, and reducing process controllability.

[0026] (3) During the process of heating the mother liquor from room temperature to 45℃~50℃, some water will be evaporated. This further increases the concentration of glutaric acid in the solution, making it easier to reach a supersaturated state during the subsequent adiabatic evaporation crystallization cooling process. The crystallization driving force is stronger, which is conducive to improving the final yield of glutaric acid.

[0027] Secondly, the crystallization process is precisely controlled by multi-chamber series connection and gradient vacuum degree control to avoid drastic fluctuations in supersaturation, creating a stable environment for the orderly growth of glutaric acid on the seed crystal, and further preventing impurity eutectic caused by excessive supersaturation.

[0028] Specifically, the adiabatic evaporator crystallizer is a six-chamber series structure with a stirring structure. The gradient vacuum of the adiabatic evaporator is set as follows: after the mother liquor enters the first chamber of the adiabatic evaporator, the vacuum degree of the first chamber is gradually reduced to -45 kPa to -50 kPa; after the mother liquor enters the second chamber from the first chamber, the vacuum degree of the second chamber is gradually reduced to -55 kPa to -60 kPa; and as the mother liquor subsequently flows into the third to sixth chambers, the vacuum degree of the third chamber is gradually reduced. The vacuum levels in the first to sixth chambers of the adiabatic evaporator gradually decrease from -65 kPa to -70 kPa, from -75 kPa to -80 kPa in the fourth chamber, from -85 kPa to -89 kPa in the fifth chamber, and from -90 kPa to -95 kPa in the sixth chamber. The cooling rate of the first to sixth chambers of the adiabatic evaporator is 0.5 to 1 °C / h. Furthermore, the use of seed crystal reflux to guide the directional growth of crystals provides readily available growth points for glutaric acid molecules, which greatly promotes the homogeneous crystal growth of glutaric acid.

[0029] Meanwhile, in the multi-chamber series-connected adiabatic evaporation crystallizer, seed reflux is used to guide the directional growth of crystals, providing ready-made growth points for glutaric acid molecules, which greatly promotes the homogeneous crystal growth of glutaric acid.

[0030] Furthermore, when the vacuum level in the sixth chamber is insufficient (i.e., the absolute value is below -90 kPa, for example -89 kPa), the corresponding solution equilibrium temperature (boiling point) is high, resulting in a total crystallization temperature above 10°C. At this temperature, the solubility of glutaric acid remains high, and the driving force for crystallization is insufficient, causing a large amount of glutaric acid to fail to precipitate and remain in the mother liquor, resulting in a reduced yield. When the vacuum level in the sixth chamber is too high (i.e., the absolute value is above -98 kPa, for example -98 kPa), the corresponding solution equilibrium temperature is too low, resulting in a final crystallization temperature below 4°C. At this low temperature, although the yield of glutaric acid may increase, the solubility of the impurity succinic acid decreases more drastically, its supersaturation increases significantly, and it is easy for glutaric acid to co-crystallize, thereby contaminating the product and causing a decrease in purity. Moreover, energy consumption increases sharply, and there is a risk of localized freezing of the solution. The vacuum level and final crystallization temperature of the sixth chamber are controlled within the ranges of -90 kPa to -95 kPa and 4℃ to 10℃, respectively. This ensures that glutaric acid is fully extracted to guarantee the yield, while also effectively suppressing impurity eutectic to ensure the purity of glutaric acid.

[0031] Furthermore, the first to sixth chambers of the adiabatic evaporator are each equipped with the stirring structure, and the stirring speed of the stirring structure is 800 to 900 rpm;

[0032] This stirring structure is used to promote mass and heat transfer and maintain solution homogeneity. If the stirring rate is too low (<800 rpm), the crystals precipitated during the crystallization process are prone to agglomeration, settling, or adhering to the container wall, thereby affecting mass and heat transfer or normal crystal growth and the final product yield. If the stirring rate is too high (>900 rpm), strong fluid shear force will be generated, which will easily break the crystals precipitated during the crystallization process, produce fine crystals, and increase the risk of impurity adsorption.

[0033] Compared to ordinary cooling low-temperature crystallization, adiabatic evaporation crystallization utilizes the evaporation of the solution itself to remove heat, eliminating the need for an external coolant. In addition, multi-chamber series connection enables staged control of the crystallization process, with each crystallization chamber maintaining a different supersaturation level, which is conducive to orderly crystal growth. Gradient vacuum control can precisely match the crystallization temperature requirements of each chamber, avoiding abrupt supersaturation changes, reducing the generation of fine crystals, and improving product purity and particle size uniformity.

[0034] (5) Drying

[0035] The wet glutaric acid crystals obtained in step (4) are dried to obtain the glutaric acid product.

[0036] Furthermore, in step (2), the diacid content in the mixed diacid solution accounts for 18% to 23% of the total solution volume; after evaporation and concentration, the diacid content in the concentrate accounts for 55% to 60% of the total solution volume.

[0037] Furthermore, step (2) also includes adding activated carbon to the mixed dicarboxylic acid solution or the concentrated solution for decolorization and adsorption of impurities.

[0038] Furthermore, in step (3), the concentrate is fed into an atmospheric pressure crystallizer, and the final temperature is controlled to be 20-23°C by cooling water.

[0039] Furthermore, step (4) also includes returning a portion of the material discharged from the last chamber to the second chamber as seed crystals, with a seed crystal reflux ratio of 5% to 15%.

[0040] The purpose of using seed crystal reflux is to provide seed crystals to induce crystallization, suppress spontaneous nucleation, reduce the generation of fine crystals, improve crystal grain size and product purity, and at the same time improve crystallization yield.

[0041] A seed reflux ratio that is too high (>15%) will result in an excessive number of seeds, wasting energy; a seed reflux ratio that is too low (<5%) will result in an insufficient number of seeds, which will not be able to effectively suppress spontaneous nucleation and will easily produce a large number of fine crystals. Because there are many fine crystals, their total surface area is large, which provides favorable conditions for the adsorption and encapsulation of impurities. At the same time, the growth rate of fine crystals is fast, making it easier to encapsulate impurities, thereby leading to a decrease in product purity and an increase in impurity content.

[0042] In addition, the reason for avoiding the backflow of seed crystals into the first chamber is that the first chamber is the feeding chamber, where the material concentration and temperature fluctuate greatly. If the seed crystals flow back into the first chamber, it is easy to cause the seed crystals to dissolve or grow unstably, affecting the control of the crystallization process. The material concentration and temperature in the second chamber are relatively stable, which is more conducive to seed crystallization.

[0043] Furthermore, in step (4), the second liquid phase is returned to the mixed dicarboxylic acid solution after the catalyst is removed, so as to realize the recycling of materials, improve the total yield of glutaric acid, and reduce wastewater discharge.

[0044] Furthermore, in step (5), the drying is carried out by vacuum drying and fluidized bed drying. The drying temperature is 75℃~95℃ and the drying time is 3~5min. The glutaric acid product has a purity of greater than 95% and a yield of greater than 90%.

[0045] Furthermore, in step (3), the solid phase obtained by centrifugation is introduced into a melting tank, heated to 100℃~120℃, and after being slab-formed by a slab-forming machine, it is packaged into mixed dicarboxylic acid; the slab-forming temperature of the slab-forming machine is 5℃~7℃.

[0046] The beneficial technical effects of this invention are:

[0047] (1) Compared with the prior art, this application fundamentally eliminates the source of catalytic side reactions of copper and vanadium metal ions in subsequent high-temperature processes by removing catalysts, thus avoiding product contamination and degradation. Then, by using the synergistic effect of evaporation concentration, preliminary crystallization, and glutaric acid concentration crystallization separation technology, and taking advantage of the difference in solubility of the three dicarboxylic acids in water, a highly selective separation of glutaric acid is achieved. The glutaric acid purity of the final product can reach more than 95%, and the yield can reach more than 90%. Moreover, in the glutaric acid concentration crystallization separation step, a multi-chamber series structure, gradient vacuum degree control of crystallization temperature, and seed reflux technology are adopted, which makes the crystallization process highly controllable, the product particle size uniform, and the quality stable.

[0048] (2) Only physical separation methods are used, without the need for additional chemical reagents, avoiding equipment corrosion, safety risks and wastewater treatment problems caused by chemical methods. The process conditions are mild and suitable for large-scale industrial production.

[0049] (3) The second liquid phase is returned to the system for recycling, resulting in high material utilization and low production cost. Attached Figure Description

[0050] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0051] In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0052] Example 1

[0053] (1) Catalyst removal

[0054] Take 1000 kg of a mixed dicarboxylic acid solution (total dicarboxylic acid concentration of about 23%, of which succinic acid content is about 5%, glutaric acid content is about 14%, adicarboxylic acid content is about 4%, water content is about 76%, and nitrates content is about 1%), a by-product of adipic acid production, and feed it into a resin reactor to allow the catalyst in the solution to be adsorbed and removed by the resin, thus obtaining a mixed dicarboxylic acid solution after catalyst removal.

[0055] The catalyst is a copper- and vanadium-containing catalyst, and the resin reactor is a large-pore acid-resistant resin (Dandong Mingzhu Special Resin Co., Ltd.: DT-010).

[0056] (2) Evaporation and concentration

[0057] The mixed dicarboxylic acid solution after catalyst removal is first fed into a rising film evaporator (Suzhou New District Chemical Titanium Equipment Factory) for one rising film evaporation. The heating temperature of the rising film evaporator is controlled at 120℃. After rising film evaporation and concentration, it continues to be evaporated in a falling film evaporator (Nanjing Debang) at a falling film evaporation temperature of 140℃, thereby obtaining a concentrated solution (the concentration of mixed dicarboxylic acid is about 55%).

[0058] Add activated carbon to the concentrate, decolorize at 140°C for 8 minutes, filter to remove the activated carbon, and obtain the decolorized concentrate.

[0059] (3) Preliminary crystallization

[0060] The decolorized concentrate was fed into a stirred atmospheric pressure crystallizer (Cangzhou Mingliang Chemical Machinery Co., Ltd.), cooled to 20°C at a cooling rate of 1.5°C / min, and crystallized at this temperature for 2 hours. A solid phase and a first liquid phase were obtained by centrifugation. The solid phase consisted of 51.7% succinic acid, 18% glutaric acid, and 29.5% adipic acid. The first liquid phase was a mother liquor enriched with glutaric acid, consisting of 13% succinic acid, 71% glutaric acid, and 9% adipic acid. The solid phase was then fed into a melting tank, heated to 100°C, and precipitated into flakes using a flake-forming machine. The resulting product was packaged as a mixed dicarboxylic acid product. The heating temperature of the flake-forming machine was 5°C.

[0061] (4) Concentration and crystallization separation of glutaric acid

[0062] The mother liquor obtained in step (3) is fed into a rising film evaporator, heated to 50°C, and concentrated by evaporation. Then, it is fed into an adiabatic evaporator crystallizer (Shanghai Sensong). This adiabatic evaporator crystallizer has a six-chamber series structure, with each chamber equipped with a stirring structure at a stirring rate of 800 rpm. This stirring structure is used to promote mass and heat transfer and maintain solution homogeneity. The mother liquor is fed into the first chamber of the adiabatic evaporator after passing through the rising film evaporator. The vacuum level of the first chamber is gradually reduced to -45 kPa. When the vacuum level of the first chamber reaches -45 kPa, the material in the first chamber flows into the second chamber of the adiabatic evaporator, and the vacuum level of the second chamber is gradually reduced to -55 kPa. When the vacuum level of the second chamber reaches -55 kPa, the material in the second chamber flows into the third chamber of the adiabatic evaporator, and the vacuum level of the third chamber is gradually reduced to -65 kPa. When the vacuum level of the third chamber reaches -65 kPa, the material in the third chamber flows into the fourth chamber of the adiabatic evaporator, and the vacuum level of the fourth chamber is gradually reduced. The vacuum level is gradually reduced to -75 kPa. When the vacuum level in the fourth chamber drops to -75 kPa, the material in the fourth chamber flows into the fifth chamber of the adiabatic evaporator, and the vacuum level in the fifth chamber is gradually reduced to -85 kPa. When the vacuum level in the fifth chamber drops to -85 kPa, the material in the fifth chamber flows into the sixth chamber of the adiabatic crystallizer, and the vacuum level in the sixth chamber is gradually reduced to -90 kPa. When the vacuum level in the sixth chamber reaches -90 kPa (at which point the temperature of the material in the sixth chamber is 10 °C), wet glutaric acid crystals and a second liquid phase are obtained. During the process of gradually reducing the vacuum level from the first to the sixth chamber, the cooling rate of each chamber is 1 °C / h.

[0063] In addition, a portion of the material discharged from the sixth chamber is returned to the second chamber as seed crystals, with a seed crystal reflux ratio of 15%.

[0064] After crystallization, glutaric acid wet crystals and a second liquid phase are obtained by centrifugation. The second liquid phase is returned to the mixed dicarboxylic acid solution as a raw material for recycling.

[0065] (5) Drying

[0066] The wet glutaric acid crystals obtained in step (4) were dried in a fluidized bed at a temperature of 85°C for 5 minutes, and finally 131.2 kg of glutaric acid product was obtained (yield 93.7%).

[0067] The yield is calculated as follows: (mass of glutaric acid product / theoretical mass of glutaric acid in raw material) × 100%. In Example 1, the theoretical mass of glutaric acid in the raw material is approximately 140 kg (1000 kg × 14% = 140 kg).

[0068] Example 2

[0069] The only difference between Example 2 and Example 1 is that the seed reflux ratio in step (4) is adjusted to 5%. 130 kg of glutaric acid product was finally obtained (yield 92.8%), and all other steps and conditions were the same.

[0070] Example 3

[0071] The difference between Example 3 and Example 1 is that in step (4), the vacuum gradient of the adiabatic evaporation crystallizer is set as follows: the vacuum degree of the first chamber is gradually reduced to -50 kPa, the vacuum degree of the second chamber is gradually reduced to -60 kPa, the vacuum degree of the third chamber is gradually reduced to -70 kPa, the vacuum degree of the fourth chamber is gradually reduced to -80 kPa, the vacuum degree of the fifth chamber is gradually reduced to -89 kPa, and the vacuum degree of the sixth chamber is gradually reduced to -95 kPa. When the vacuum degree of the sixth chamber reaches -95 kPa (at this time the material temperature in the sixth chamber is 4℃), wet glutaric acid crystals and the second liquid phase are obtained. During the process of gradually reducing the vacuum degree from the first chamber to the sixth chamber, the cooling rate of each chamber is 0.5℃ / h.

[0072] Each chamber is equipped with a stirring structure with a stirring rate of 900 rpm.

[0073] The final yield was 133 kg of glutaric acid (95.0% yield). All other steps and conditions were the same as in Example 1.

[0074] Example 4

[0075] The difference between Example 4 and Example 1 is that the crystallization temperature in step (3) is 23°C, and the crystallization is carried out at a constant temperature for 3 hours, and 132.3 kg of glutaric acid product is finally obtained (yield 94.5%). Other steps and conditions are the same as in Example 1.

[0076] In step (3) of Example 4, the mother liquor obtained contains 12.5% ​​succinic acid, 71% glutaric acid, and 9% adipic acid.

[0077] Example 5

[0078] The difference between Example 5 and Example 1 is that in step (2), the rising film evaporation temperature is 100°C and the falling film evaporation temperature is 150°C, thereby obtaining a concentrated solution (diacid concentration of approximately 60%). Finally, 128 kg of glutaric acid product was obtained (yield 91.4%), and other steps and conditions were the same as in Example 1.

[0079] Comparative Example 1

[0080] The difference between Comparative Example 1 and Example 1 is that, in step (4), the seed reflux ratio is 16%.

[0081] All other steps and conditions are the same as in Example 1.

[0082] Comparative Example 2

[0083] The difference between Comparative Example 2 and Example 1 is that, in step (4), the seed reflux ratio is 4%.

[0084] All other steps and conditions are the same as in Example 1.

[0085] Comparative Example 3

[0086] Compared with Example 1, Comparative Example 3 differs in that the initial crystallization separation temperature in step (3) is changed to 25°C, while the other steps and condition parameters are the same as in Example 1.

[0087] In step (3) of Comparative Example 3, the mother liquor obtained contained 14% succinic acid, 69% glutaric acid, and 10% adipic acid.

[0088] Comparative Example 4

[0089] Compared with Example 1, Comparative Example 4 differs in that the initial crystallization separation temperature in step (3) is changed to 18°C, while the other steps and condition parameters are the same as in Example 1.

[0090] In step (3) of Comparative Example 4, the mother liquor obtained contained 14% succinic acid, 67% glutaric acid, and 9.5% adipic acid.

[0091] Comparative Example 5

[0092] Compared with Example 1, Comparative Example 5 differs in that, in step (4), the first to sixth chambers are equipped with a stirring structure with a stirring rate of 700 rpm.

[0093] All other steps and conditions are the same as in Example 1.

[0094] Comparative Example 6

[0095] Compared with Example 1, Comparative Example 6 differs in that, in step (4), the first to sixth chambers are equipped with a stirring structure with a stirring rate of 1000 rpm.

[0096] All other steps and conditions are the same as in Example 1.

[0097] Comparative Example 7

[0098] Compared with Example 1, Comparative Example 7 differs in that the vacuum gradient and final crystallization temperature of the adiabatic evaporation crystallizer are set differently in step (4). Specifically, the vacuum degree of the first chamber is gradually reduced to -35 kPa, the vacuum degree of the second chamber is gradually reduced to -50 kPa, the vacuum degree of the third chamber is gradually reduced to -60 kPa, the vacuum degree of the fourth chamber is gradually reduced to -70 kPa, the vacuum degree of the fifth chamber is gradually reduced to -80 kPa, and the vacuum degree of the sixth chamber is gradually reduced to -85 kPa (at this time, the temperature of the sixth chamber is 12°C). Other steps and conditions are the same as in Example 1.

[0099] Comparative Example 8

[0100] Compared with Example 1, Comparative Example 8 differs in that the vacuum gradient and final crystallization temperature of the adiabatic evaporation crystallizer are set differently in step (4). Specifically, the vacuum degree of the first chamber is gradually reduced to -55 kPa, the vacuum degree of the second chamber is gradually reduced to -65 kPa, the vacuum degree of the third chamber is gradually reduced to -75 kPa, the vacuum degree of the fourth chamber is gradually reduced to -85 kPa, the vacuum degree of the fifth chamber is gradually reduced to -90 kPa, and the vacuum degree of the sixth chamber is gradually reduced to -98 kPa (at this time, the temperature of the sixth chamber is 3°C). Other steps and conditions are the same as in Example 1.

[0101] Comparative Example 9

[0102] The difference between Comparative Example 9 and Example 1 is that in step (4), the mother liquor obtained in step 3 is not concentrated by rising film evaporation and heating. Instead, the mother liquor is directly introduced into the adiabatic evaporator crystallizer at a temperature of 20-23°C for crystallization. Other steps and conditions are the same as in Example 1.

[0103] The analytical results of the glutaric acid products obtained in Examples 1-5 and Comparative Examples 1-9 are shown in Table 1.

[0104] Table 1

[0105]

[0106] As shown in Table 1, the process conditions described in this invention can stably yield high-purity, high-yield glutaric acid products from adipic acid byproducts. Specifically, the purity of glutaric acid in the glutaric acid products is all above 95.0%, and the yield is all above 90%.

[0107] In Comparative Example 1, the seed reflux ratio was too high. Excessive seed crystals led to too many growth points, limiting crystal growth space and easily resulting in small, irregularly structured crystals. These crystals have a large specific surface area, making them more prone to encapsulating mother liquor and impurities during growth and subsequent processing. This ultimately resulted in a significant decrease in product purity, and the yield was reduced due to crystal quality issues (such as losses from centrifugation). In Comparative Example 2, the seed reflux ratio was too low, resulting in a severe shortage of seed crystals. This made it impossible to effectively guide and control the crystallization process. After the solution reached supersaturation, crystals precipitated mainly through spontaneous nucleation. Spontaneous nucleation is explosive and disordered, producing a large number of microcrystals and increasing the possibility of impurity molecules being trapped, leading to a decrease in the final product purity and yield.

[0108] The initial crystallization temperature in Comparative Example 3 was too high. At this temperature, the solubility of succinic acid and adipic acid is relatively high, resulting in insufficient separation and removal during the initial crystallization step. A large amount of impurities entered the subsequent glutaric acid concentration and crystallization process, directly contaminating the glutaric acid crystallization system and causing low purity of the final product.

[0109] In Comparative Example 4, the initial crystallization temperature was too low. This low temperature significantly reduced the solubility of glutaric acid, causing it to co-crystallize with succinic acid and adipic acid during the initial crystallization step. This not only resulted in the premature loss of glutaric acid, but also deprived the glutaric acid entrained in the solid phase of the opportunity for further purification. Furthermore, it introduced complex mixed crystals, increasing the difficulty of subsequent processing.

[0110] The results of Comparative Examples 5 and 6 indicate that the stirring speed needs to be controlled within a suitable range. Too low a speed leads to uneven mixing and poor heat transfer, easily creating localized supersaturated zones, causing unexpected precipitation of impurities, or resulting in crystal agglomeration, settling, or adhesion to the container walls, affecting mass transfer. Too high a stirring speed generates strong fluid shear forces on the already formed crystals, causing crystal breakage and the formation of fine crystals. Both of these factors contribute to decreased product purity and yield by increasing impurity adsorption, inclusion, or product loss.

[0111] In Comparative Example 7, the vacuum levels in chambers one through six were outside the gradient vacuum range defined by this invention, and the final temperature of chamber six was too high. At this temperature, the solubility of glutaric acid remained high, resulting in insufficient driving force for crystallization. Consequently, a large amount of glutaric acid failed to precipitate and remained in the mother liquor, directly leading to a low yield. Simultaneously, the overall supersaturation of the system was low, resulting in a slow crystallization process and reducing the selective precipitation advantage of glutaric acid relative to impurities, leading to poor purity. In Comparative Example 8, the vacuum levels in chambers one through six were outside the gradient vacuum range defined by this invention, and the final temperature of chamber six was too low. The solubility of succinic acid decreased more drastically at low temperatures, and its supersaturation increased significantly, leading to severe co-crystallization of succinic acid and glutaric acid. This significantly increased the succinic acid impurity content in the product.

[0112] In Comparative Example 9, the mother liquor was directly introduced into the adiabatic evaporator crystallizer at 20–23°C. This change resulted in a significant decrease in both product purity and yield. The main reason is that gentle preheating (45–50°C) helps dissolve unstable microcrystals, providing a homogeneous (without obvious crystal nuclei) and stable starting solution. This provides a stable starting solution for the subsequent adiabatic evaporation crystallization process, preventing irregular crystal nuclei from directly entering the subsequent adiabatic evaporation crystallization environment and ensuring that the crystallization process is entirely guided by the subsequently added high-quality "seed crystals." Furthermore, the increased temperature during evaporation... Heating alone is also a pre-concentration process. Comparative Example 9 omitting this step means that the concentration of glutaric acid in the mother liquor entering the adiabatic evaporator crystallizer is lower, and it takes longer for the solution to reach supersaturation. The crystallization driving force is relatively weak, which is not conducive to improving the final yield of glutaric acid. Finally, the mother liquor is preheated to 45℃~50℃ and then enters the first chamber described below. This means that the crystallization process will start from this higher starting temperature and gradually decrease to the final temperature (4℃~10℃). This significant temperature drop of about 40℃ provides the system with ample time and space to reduce the supersaturation of the solution at a gradual and controllable rate. This effectively suppresses explosive spontaneous nucleation, ensuring that crystals grow orderly mainly on the refluxing seed crystals, thereby obtaining products with uniform particle size and high purity. If the mother liquor is directly introduced at room temperature (20℃~25℃), the temperature drop range of the entire crystallization process is extremely small (about 10℃~15℃), which can easily lead to a sharp increase in the supersaturation of the solution within a narrow temperature range, triggering uncontrollable nucleation, producing a large number of fine crystals, deteriorating product quality, and reducing process controllability.

[0113] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A process for separating glutaric acid from adipic acid byproducts, characterized in that, Includes the following steps: (1) Catalyst removal The mixed dicarboxylic acid solution is first subjected to a resin adsorption reaction, so that the catalyst in the mixed dicarboxylic acid solution is adsorbed and removed by the resin, and the mixed dicarboxylic acid solution after the catalyst is removed is obtained. (2) Evaporation and concentration The mixed dicarboxylic acid solution after catalyst removal in step (1) is evaporated and concentrated to obtain a concentrated solution; (3) Preliminary crystallization The concentrate obtained in step (2) is subjected to preliminary crystallization. The concentrate is cooled to 20-23°C and crystallized at a constant temperature for 2-3 hours. Then, it is centrifuged to obtain a solid phase and a first liquid phase. The first liquid phase is a mother liquor enriched with glutaric acid. (4) Concentration and crystallization separation of glutaric acid The mother liquor obtained in step (3) is sent to a rising film evaporator, heated and concentrated, and then enters a multi-chamber series adiabatic evaporation crystallizer. The crystallization temperature is gradually reduced to 4℃~10℃ by gradient vacuum control. After the adiabatic evaporation crystallization is completed, centrifugation is used to separate glutaric acid wet crystals and the second liquid phase. (5) Drying The wet glutaric acid crystals obtained in step (4) are dried to obtain the glutaric acid product.

2. The process for separating glutaric acid from adipic acid byproducts according to claim 1, characterized in that, In step (2), the dicarboxylic acid content in the mixed dicarboxylic acid solution is 18% to 23% of the total solution volume. After evaporation and concentration, the dicarboxylic acid content in the concentrated solution is 55% to 60% of the total solution volume.

3. The process for separating glutaric acid from adipic acid byproducts according to claim 1, characterized in that, In step (2), the mixed dicarboxylic acid solution after catalyst removal in step (1) is first subjected to rising film evaporation at a heating temperature of 100℃~120℃, and then subjected to falling film evaporation at a heating temperature of 140℃~155℃ to obtain the concentrated solution.

4. The process for separating glutaric acid from adipic acid byproducts according to claim 1, characterized in that, In step (3), the mother liquor includes: 11%–13% succinic acid, 69%–71% glutaric acid, and 7%–9% adipic acid.

5. The process for separating glutaric acid from adipic acid byproducts according to claim 1, characterized in that, In step (4), the mother liquor obtained in step (3) is sent to a rising film evaporator, heated to 45℃~50℃ for evaporation and concentration, and then enters a multi-chamber series adiabatic evaporation crystallizer. The crystallization temperature is gradually reduced from 45℃~50℃ to 4℃~10℃ by gradient vacuum control. The adiabatic evaporator is a six-chamber series structure with a stirring structure. The gradient vacuum of the adiabatic evaporator is set as follows: after the mother liquor enters the first chamber of the adiabatic evaporator, the vacuum of the first chamber is controlled to gradually decrease to -45 kPa to -50 kPa. After the mother liquor enters the second chamber from the first chamber, the vacuum of the second chamber is controlled to gradually decrease to -55 kPa to -60 kPa. As the mother liquor subsequently flows into the third to sixth chambers, the vacuum of the third chamber is controlled to gradually decrease to -65 kPa to -70 kPa, the vacuum of the fourth chamber to -75 kPa to -80 kPa, the vacuum of the fifth chamber to -85 kPa to -89 kPa, and the vacuum of the sixth chamber to -90 kPa to -95 kPa, respectively. The cooling rate of the first to sixth chambers of the adiabatic evaporator is 0.5 to 1 °C / h.

6. The process for separating glutaric acid from adipic acid byproducts according to claim 5, characterized in that, In step (4), the first to sixth chambers of the adiabatic evaporator are equipped with the stirring structure, and the stirring speed of the stirring structure is 800 to 900 rpm.

7. A process for separating glutaric acid from adipic acid byproducts according to claim 5 or 6, characterized in that, In step (4), a portion of the material discharged from the last chamber of the adiabatic evaporator is returned to the second chamber of the adiabatic evaporator as seed crystals, with a seed crystal reflux ratio of 5% to 15%.

8. The process for separating glutaric acid from adipic acid byproducts according to claim 1, characterized in that, In step (4), the second liquid phase is returned to the mixed dicarboxylic acid solution after the catalyst has been removed.

9. The process for separating glutaric acid from adipic acid byproducts according to claim 1, characterized in that, In step (5), the drying is carried out by fluidized bed drying, the drying temperature is 75℃~95℃, the drying time is 3~5min, and the glutaric acid product has a purity of greater than 95% and a yield of greater than 90%.

10. The process for separating glutaric acid from adipic acid byproducts according to claim 1, characterized in that, In step (2), the solid phase obtained by centrifugation is heated and then fed into a sheet-forming machine for sheet formation, and then directly packaged into mixed dicarboxylic acid.

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