A method for crystallizing glyoxylic acid monohydrate

Abstract

This invention discloses a crystallization method for glyoxylic acid monohydrate, comprising the following steps: Step 1: Adding seed crystals to a drum granulator, the seed crystal mass being 9 times the mass of an 80% glyoxylic acid solution; Step 2: Adding the 80% glyoxylic acid solution to the drum granulator through spray guns located at the feed end of the drum granulator. The maximum flow rate of each spray gun is 2 t / h, and each spray gun is equipped with two solid conical atomizing nozzles with a solid cone angle of 55-60°. The number of spray guns is selected according to the production scale. This invention, by adding seed crystals at a mass of 9 times the mass of an 80% glyoxylic acid solution, allows the atomized 80% glyoxylic acid solution to mix with the seed crystals within the drum granulator, achieving rapid agglomeration and hardening of the mixture within a short time. After crystallization, the mixture is cooled. The product is graded according to particle size, with intermediate grades directly packaged. The implementation scheme is highly operable and economical to operate; it can be operated continuously and is suitable for large-scale industrial continuous production.

Description

Technical Field

[0001] This invention relates to the field of glyoxylic acid technology, and more specifically to a method for crystallizing glyoxylic acid monohydrate. Background Technology

[0002] Glyoxylic acid is an important organic chemical intermediate with wide applications in fragrances, pharmaceuticals, paints, papermaking, and fine chemicals. There are three main methods for producing glyoxylic acid: glyoxal-nitric acid oxidation, oxalic acid electrolysis, and maleic anhydride ozone oxidation. Currently, most domestic glyoxylic acid producers use processes such as glyoxal-nitric acid oxidation, primarily producing 40-50% glyoxylic acid aqueous solutions. Glyoxylic acid monohydrate, as a high-purity product, can be used in high-end markets such as fine chemical products. Glyoxylic acid monohydrate is generally produced using maleic anhydride ozone oxidation or maleic anhydride ozone with catalyst oxidation, which are relatively advanced processes, resulting in high product purity, good quality, and very little environmental pollution.

[0003] Crystalline glyoxylic acid exists in three forms depending on the presence of water of crystallization: anhydrous glyoxylic acid (CHOCOOH), which is a monoclinic crystal with a melting point of 98℃; glyoxylic acid with partial water of crystallization, which is a colorless columnar crystal with a melting point of 70-75℃; and glyoxylic acid with complete water of crystallization, which has a melting point of 50-52℃ and a solution concentration of 80%. An 80% glyoxylic acid solution has a viscosity of 60 cp at 50℃. Upon cooling, the viscosity increases rapidly, but crystallization does not occur quickly. Even with the addition of seed crystals, rapid crystallization is not achieved; in fact, cooling to -20℃ is less efficient than crystallization at around 20℃.

[0004] According to the patent document with authorization announcement number CN105669433B and titled "A method for preparing glyoxylic acid monohydrate crystals", the main process involves heating 40-50% crude glyoxylic acid, adding a precipitant, stirring, cooling, and filtering. Activated carbon is added to the filtrate, which is then cooled and filtered again. The filtrate is concentrated to 55-67 wt%, then cooled again, glyoxylic acid monohydrate crystals are added, and the mixture is kept warm and then cooled to -10 to -5°C to obtain a crystallizing liquid. The crystallizing liquid is filtered to obtain a filter cake, which is then dried to obtain glyoxylic acid monohydrate.

[0005] This technique, because it controls the solution concentration to 55-67 wt%, does not achieve an 80% glyoxylic acid solution with a monohydrate crystal ratio. Even if glyoxylic acid monohydrate crystals are added and the temperature is lowered to -10 to -5℃ and kept warm, the resulting material is still a viscous liquid. Due to its high viscosity, it is difficult to filter the crystallization liquid and obtain a filter cake, making the operation difficult to implement.

[0006] The method described in "A Purification Method for Glyoxylic Acid" (CN201210261106.8) involves using a calcifying agent to remove some oxalic acid from crude glyoxylic acid, followed by direct cooling to precipitate crystals. However, the glyoxylic acid solution precipitated with the calcifying agent will precipitate again after a period of time, negatively impacting the crystallization and appearance quality of the purified solution and hindering the formation of glyoxylic acid crystals. Direct cooling crystallization requires high purity of the glyoxylic acid solution, as impurities such as oxalic acid significantly affect crystallization. The resulting glyoxylic acid crystals are of low purity and rarely achieve a white color. With only one crystallization cycle, the yield of glyoxylic acid is low, making it impractical for industrial applications.

[0007] Through repeated experiments, the inventors discovered that an 80% glyoxylic acid solution, when sealed, can crystallize naturally at room temperature, but the process is extremely time-consuming. The viscosity of an 80% glyoxylic acid solution at 50°C is approximately 60 cp. Even rapid cooling only increases the viscosity, not the crystallization itself; in fact, at very low ambient temperatures, the crystallization time is even longer. Only by appropriately cooling the solution and adding a certain proportion of seed crystals can the solution crystallize naturally at room temperature in approximately 3-5 days. Lowering the solution temperature and ambient temperature has little effect on the crystallization time; applying vibration or tapping during crystallization shortens the time; increasing the proportion of seed crystals shortens the crystallization time, and when the amount of seed crystals added is several times that of the 80% glyoxylic acid solution, the crystallization time is significantly shortened. A certain amount of heat is released during crystallization, and the material temperature rises noticeably.

[0008] This invention seeks a method for crystallizing glyoxylic acid monohydrate, which can rapidly crystallize 80% glyoxylic acid solution within a normal temperature range, enabling continuous industrial production. Summary of the Invention

[0009] The purpose of this invention is to provide a method for crystallizing glyoxylic acid monohydrate to solve the problems mentioned in the background art.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] A method for crystallizing glyoxylic acid monohydrate includes the following steps:

[0012] Step 1: Add seed crystals into the drum granulator. The mass of the seed crystals is 9 times the mass of the 80% glyoxylic acid solution.

[0013] Step 2: Add 80% glyoxylic acid solution into the drum granulator through the spray guns set at the feed end of the drum granulator. The maximum flow rate of each spray gun is 2t / h. Each spray gun is equipped with 2 solid cone atomizing nozzles with a solid cone angle of 55-60°. The number of spray guns is selected according to the production scale.

[0014] Step 3: During the rotation of the drum in the drum granulator, the 80% glyoxylic acid solution atomized particles are either wrapped by the solid powder particles of the seed crystals or adhered to the large seed crystals, quickly forming 0.5-10mm spherical or blocky objects. These particles gradually harden during the rotation of the drum in the drum granulator, and then crystallize after 10-20 minutes. The rotation of the drum in the drum granulator then discharges the crystallized granular glyoxylic acid monohydrate from the discharge port.

[0015] Step 4: The granular glyoxylic acid monohydrate extracted in Step 3 is fed into a cooling machine. The crystallized granular glyoxylic acid monohydrate continues to cool in the cooling machine until all the heat released during crystallization is removed, and the granular glyoxylic acid monohydrate becomes hardened crystals.

[0016] Step 5: The fully crystallized granular glyoxylic acid monohydrate from Step 4 is fed to a screening machine. The output is screened into three size grades: less than 2.5mm in diameter, 2.5-4mm in diameter, and more than 4mm in diameter. The 2.5-4mm particles are product grade and enter the packaging stage. Depending on the total amount of particles less than 2.5mm and larger than 4mm in diameter, a portion can be separated and returned to the drum granulator as seed crystals. Fine particles less than 2.5mm are returned to the drum granulator as seed crystals via the buffer hopper. Large particles larger than 4mm are crushed into particles less than 2.5mm by the crusher and returned to the drum granulator via the buffer hopper as seed crystals. This cycle continues the crystallization process.

[0017] Preferably, in step one, the seed crystals are glyoxylic acid monohydrate powder or particles smaller than 4 mm.

[0018] Preferably, in step one, the mass of the 80% glyoxylic acid solution is measured by a flow meter, and the mass of the induced crystal seed is controlled by the rotation speed of the screw conveyor, so that the mass of the induced crystal seed is 9 times the mass of the 80% glyoxylic acid solution.

[0019] Preferably, in step two, the droplet diameter after the nozzle disperses the 80% glyoxylic acid solution is 80-100 μm, the spray gun and nozzle are made of S31608 stainless steel or other materials resistant to glyoxylic acid corrosion, and the air pressure during atomization is 0.6 MPa.

[0020] Preferably, in step three, the slope between the axial center line of the drum and the horizontal line of the drum granulator is 1.5° or 3%, with the feed end higher and the discharge end lower, which facilitates the control of the residence time of 15 to 30 minutes during the drum rotation process of the drum granulator.

[0021] Preferably, in step four, the cooling machine is a horizontal drum structure, with the drum shell cooled by a water bath, continuing to cool the hardened glyoxylic acid monohydrate crystals inside the drum for 10-20 minutes, removing the residual heat released during the crystallization of glyoxylic acid monohydrate, and controlling the temperature of the finished glyoxylic acid monohydrate to be stable and consistent.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This invention involves adding seed crystals at a mass nine times that of an 80% glyoxylic acid solution. The 80% glyoxylic acid solution is atomized and mixed with the seed crystals in a drum granulator. This process quickly achieves agglomeration and hardening of the mixture, followed by crystallization and cooling. The product is graded according to particle size, with intermediate grades directly packaged. The implementation scheme is highly operable and economical; it can be operated continuously and is suitable for large-scale industrial continuous production. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to specific examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all 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.

[0025] This embodiment describes a method for crystallizing glyoxylic acid monohydrate, comprising the following steps:

[0026] Step 1: Add seed crystals into the drum granulator. The mass of the seed crystals is 9 times the mass of the 80% glyoxylic acid solution.

[0027] Step 2: Add 80% glyoxylic acid solution into the drum granulator through the spray guns set at the feed end of the drum granulator. The maximum flow rate of each spray gun is 2t / h. Each spray gun is equipped with 2 solid cone atomizing nozzles with a solid cone angle of 55-60°. The number of spray guns is selected according to the production scale.

[0028] Step 3: During the rotation of the drum in the drum granulator, the 80% glyoxylic acid solution atomized particles are either wrapped by the solid powder particles of the seed crystals or adhered to the large seed crystals, quickly forming 0.5-10mm spherical or blocky objects. These particles gradually harden during the rotation of the drum in the drum granulator, and then crystallize after 10-20 minutes. The rotation of the drum in the drum granulator then discharges the crystallized granular glyoxylic acid monohydrate from the discharge port.

[0029] Step 4: The granular glyoxylic acid monohydrate extracted in Step 3 is fed into a cooling machine. The crystallized granular glyoxylic acid monohydrate continues to cool in the cooling machine until all the heat released during crystallization is removed, and the granular glyoxylic acid monohydrate becomes hardened crystals.

[0030] Step 5: The fully crystallized granular glyoxylic acid monohydrate from Step 4 is fed to a screening machine. The output is screened into three size grades: less than 2.5mm in diameter, 2.5-4mm in diameter, and more than 4mm in diameter. The 2.5-4mm particles are product grade and enter the packaging stage. Depending on the total amount of particles less than 2.5mm and larger than 4mm in diameter, a portion can be separated and returned to the drum granulator as seed crystals. Fine particles less than 2.5mm are returned to the drum granulator as seed crystals via the buffer hopper. Large particles larger than 4mm are crushed into particles less than 2.5mm by the crusher and returned to the drum granulator via the buffer hopper as seed crystals. This cycle continues the crystallization process.

[0031] In step one of this embodiment, the seed crystals are glyoxylic acid monohydrate powder or particles smaller than 4 mm.

[0032] In step one of this embodiment, the mass of the 80% glyoxylic acid solution is measured by a flow meter, and the mass of the induced crystal seed is controlled by the rotation speed of the screw conveyor, so that the mass of the induced crystal seed is 9 times the mass of the 80% glyoxylic acid solution.

[0033] In step two of this embodiment, the droplet diameter of the 80% glyoxylic acid solution dispersed by the nozzle is 80-100 μm. The spray gun and nozzle are made of S31608 stainless steel or other materials resistant to glyoxylic acid corrosion. The air pressure during spray gun atomization is 0.6 MPa.

[0034] In step three of this embodiment, the drum granulator has a slope of 1.5° or 3% between the axial center line of the drum and the horizontal line, with the feed end higher and the discharge end lower, which facilitates the control of the drum rotation process of the drum granulator to a residence time of 15 to 30 minutes.

[0035] In step four of this embodiment, the cooling machine is a horizontal drum structure. The outer shell of the drum is cooled by a water bath to continue cooling the hardened glyoxylic acid monohydrate crystals inside the drum. The cooling time is 10 to 20 minutes. The residual heat released during the crystallization of glyoxylic acid monohydrate is removed, and the temperature of the finished glyoxylic acid monohydrate is controlled to be stable and consistent.

[0036] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0037] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for crystallizing glyoxylic acid monohydrate, characterized in that, Includes the following steps: Step 1: Add seed crystals into the drum granulator. The mass of the seed crystals is 9 times the mass of the 80% glyoxylic acid solution. Step 2: Add 80% glyoxylic acid solution into the drum granulator through the spray guns set at the feed end of the drum granulator. The maximum flow rate of each spray gun is 2t / h. Each spray gun is equipped with 2 solid cone atomizing nozzles with a solid cone angle of 55-60°. The number of spray guns is selected according to the production scale. Step 3: During the rotation of the drum in the drum granulator, the 80% glyoxylic acid solution atomized particles are either wrapped by the solid powder particles of the seed crystals or adhered to the large seed crystals, quickly forming 0.5-10mm spherical or blocky objects. These particles gradually harden during the rotation of the drum in the drum granulator, and then crystallize after 10-20 minutes. The rotation of the drum in the drum granulator then discharges the crystallized granular glyoxylic acid monohydrate from the discharge port. Step 4: The granular glyoxylic acid monohydrate extracted in Step 3 is fed into a cooling machine. The crystallized granular glyoxylic acid monohydrate continues to cool in the cooling machine until all the heat released during crystallization is removed, and the granular glyoxylic acid monohydrate becomes hardened crystals. Step 5: The fully crystallized granular glyoxylic acid monohydrate from Step 4 is fed to a screening machine. The output is screened into three size grades: less than 2.5mm in diameter, 2.5-4mm in diameter, and more than 4mm in diameter. The 2.5-4mm particles are the product grade and enter the packaging stage. Depending on the total amount of particles less than 2.5mm and larger than 4mm in diameter, a portion can be selected and returned to the drum granulator via a buffer hopper as seed crystals. Fine particles less than 2.5mm are returned to the drum granulator via a buffer hopper as seed crystals, while large particles larger than 4mm are crushed into particles less than 2.5mm by a crusher and returned to the drum granulator via a buffer hopper as seed crystals. This cycle continues the crystallization process.

2. The crystallization method of glyoxylic acid monohydrate according to claim 1, characterized in that: In step one, the seed crystals are glyoxylic acid monohydrate powder or particles smaller than 4 mm.

3. The crystallization method of glyoxylic acid monohydrate according to claim 1, characterized in that: In step one, the mass of the 80% glyoxylic acid solution is measured by a flow meter, and the mass of the induced crystal seed is controlled by the rotation speed of the screw conveyor, so that the mass of the induced crystal seed is 9 times the mass of the 80% glyoxylic acid solution.

4. The crystallization method of glyoxylic acid monohydrate according to claim 1, characterized in that: In step two, the nozzle disperses the 80% glyoxylic acid solution into droplets with a diameter of 80-100 μm. The spray gun and nozzle are made of S31608 stainless steel or other materials resistant to glyoxylic acid corrosion. The air pressure during atomization is 0.6 MPa.

5. The crystallization method of glyoxylic acid monohydrate according to claim 1, characterized in that: The drum granulator in step three has a slope of 1.5° or 3% between the axial center line of the drum and the horizontal line, with the feed end higher and the discharge end lower, which facilitates the control of the residence time of 15 to 30 minutes during the drum rotation process of the drum granulator.

6. The crystallization method of glyoxylic acid monohydrate according to claim 1, characterized in that: In step four, the cooler is a horizontal drum structure. The outer shell of the drum is cooled by a water bath, which continues to cool the hardened glyoxylic acid monohydrate crystals inside the drum. The cooling time is 10 to 20 minutes. The residual heat released during the crystallization of glyoxylic acid monohydrate is removed, and the temperature of the finished glyoxylic acid monohydrate is controlled to be stable and consistent.