A method for recycling by-product magnesium chloride in maltol production

Abstract

This invention relates to the field of magnesium chloride recycling technology, specifically to a method for recycling and reusing magnesium chloride, a byproduct of maltol production. The method includes the following steps: (1) heating a magnesium chloride solution produced by Grignard hydrolysis in a first rotary kiln, and recovering the solvent and water from the magnesium chloride solution by vacuum distillation; (2) under vacuum conditions, using a transport device, sending the magnesium chloride obtained in (1) into a second rotary kiln, heating it to decompose it into magnesium hydroxide; (3) sending the magnesium hydroxide obtained in (2) into a calcination device for high-temperature calcination to obtain magnesium oxide, wherein the calcination temperature is 850℃-900℃. The method provided by this invention offers a new approach for the green and continuous recycling of magnesium chloride, a byproduct of maltol production.

Description

Technical Field

[0001] This invention relates to the field of magnesium chloride recycling technology, specifically to a method for recycling and reusing magnesium chloride, a byproduct of maltol production. Background Technology

[0002] Ethyl maltol, chemically known as 2-ethyl-3-hydroxy-4H-pyrone (C7H8O3), is a white needle-like or white crystalline powder with a fragrant aroma. It is increasingly widely used as a flavor modifier and aroma enhancer. It is widely recognized as a safe, reliable, low-dosage, and highly effective food additive.

[0003] Currently, the mature process for synthesizing ethyl maltol in China is mainly the furfural method. This process involves reacting furfural with a Grignard reagent to prepare ethyl furfuryl alcohol, which then undergoes a series of oxidative rearrangements to synthesize ethyl maltol. This method generates a large amount of magnesium-containing waste and salt-containing waste hydrochloric acid daily; for every ton of ethyl maltol produced, 2-3 tons of magnesium-containing waste residue are generated. Currently, in maltol production, the separation of products and solvents from the Grignard, addition, and hydrolysis reactions from solid magnesium-containing waste is handled through vacuum filtration. However, this method primarily recovers the liquid phase, treating the solid as waste, which also causes significant environmental pollution. Chinese Patent ZL2007100171626 discloses a method for recycling and treating waste from maltol production. This method can fully utilize maltol production waste, maximize solvent recovery, and transform waste into useful products, ultimately reducing costs and pollution. Although this patent can also achieve the recycling of solvents and solid waste, on the one hand, it separates solvent recycling and high-temperature calcination of solids into steps, which makes continuous production impossible and limits the scale of production. On the other hand, its calcination temperature reaches about 1000℃, which affects the service life of the calcination equipment.

[0004] In his 2007 master's thesis, "Preparation of Magnesium Oxide from Ethyl Maltol Waste," He Zhaoping of Xiangtan University described a process where the waste was treated and dissolved in sodium hydroxide by heating, followed by a series of separations to obtain magnesium hydroxide. However, this process resulted in significant environmental pollution due to the presence of organic solvents in the magnesium hydroxide. Patent publication number CN101134584A proposed a method for converting basic magnesium chloride into magnesium oxide, but the resulting magnesium oxide slag is difficult to collect, impacting the production site and resulting in limited market demand.

[0005] As the above analysis shows, how to efficiently and environmentally recycle the solvents and solid wastes in the production waste liquid of ethyl maltol prepared by the furfural method remains a technical problem that needs to be solved in the production process of this field. Summary of the Invention

[0006] In order to solve the above-mentioned problems in the existing technology, the main objective of the present invention is to provide a method for recovering and reusing magnesium chloride, a by-product in maltol production.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] A method for recovering and reusing magnesium chloride, a byproduct of maltol production, includes the following steps:

[0009] (1) The magnesium chloride solution produced by the Grignard hydrolysis reaction is fed into the first rotary kiln, and the solvent and water in the magnesium chloride solution are recovered by vacuum distillation.

[0010] (2) Under real conditions, the magnesium chloride obtained in (1) is fed into the second rotary kiln using a transport device and heated to decompose the magnesium chloride into magnesium hydroxide.

[0011] (3) The magnesium hydroxide obtained in (2) is fed into a calcining device for high-temperature calcination to obtain magnesium oxide product, wherein the calcination temperature is 850℃-900℃.

[0012] In one embodiment of the present invention, step (2) involves using a negative pressure auger to transport the magnesium chloride obtained in step (1) into the second rotary kiln.

[0013] In one embodiment of the present invention, the temperature of the first rotary kiln is controlled to be 70℃-90℃ in step (1).

[0014] As one embodiment of the present invention, the time for vacuum distillation in step (1) is 1-3 hours, for example 1 hour, 2 hours, 3 hours, or 2.5 hours.

[0015] As one embodiment of the present invention, in step (1), the vacuum degree of the first rotary kiln is controlled to be no less than -0.09 MPa; preferably, it is controlled to be between -0.08 MPa and -0.09 MPa.

[0016] As one embodiment of the present invention, the first rotary kiln in step (1) includes five zones: zone one, zone two, zone three, zone four, and zone five. The temperature of zones one to five shows an upward trend, and the temperature difference between adjacent zones is 0-10℃; for example, 0℃, 5℃, and 10℃.

[0017] As a preferred embodiment of the present invention, the temperatures of zones one to five in the first rotary kiln in step (1) are 70°C for zone one, 80°C for zone two, 80°C for zone three, 85°C for zone four, and 90°C for zone five, respectively.

[0018] In one embodiment of the present invention, the rotational speed of the rotary kiln in step (1) is 5-20Hz.

[0019] As one embodiment of the present invention, the temperature inside the second rotary kiln in step (2) is 170℃-300℃.

[0020] As one embodiment of the present invention, the temperature in the second rotary kiln in step (2) is raised in stages, first to 170-180°C for 1.5 hours, and then to 250-300°C for 1 hour.

[0021] The magnesium chloride solution produced by Grignard hydrolysis in step (1) of this invention is prepared by conventional processes in the art.

[0022] As one embodiment of the present invention, step (3) further includes a dust removal step before feeding magnesium hydroxide into the calcination device for calcination. The dust removal step can be carried out in a grinding and drying machine, and specifically includes the following operations:

[0023] (1) Before calcination, magnesium hydroxide is first ground into 200-mesh powder using an advanced grinding mill; (2) Start the dust collector bag ventilation device; (3) Use negative pressure to draw the powdered magnesium hydroxide through the cooling pipe and into the dust collector bag; (4) After entering the dust collector, magnesium hydroxide is transported to the calcination kiln using a winch.

[0024] The main beneficial effects of this invention are as follows:

[0025] This invention utilizes the advantages of a rotary kiln with a large temperature control area and controllable discharge speed to perform segmented solvent recovery, calcination into magnesium hydroxide, and high-temperature calcination to obtain magnesium oxide. This enables continuous and closed-loop production of magnesium oxide from magnesium chloride solution, achieving the recovery of solvent and solid waste residue and continuous production of magnesium oxide from waste residue. At the same time, due to the fully controlled closed-loop production conditions, the leakage of smoke and solvent is reduced, achieving green recovery of by-products in maltol production. Detailed Implementation

[0026] Those skilled in the art can refer to the content of this document and appropriately improve the process parameters to achieve the desired results. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be within the scope of protection of this invention. The methods and applications of this invention have been described through preferred embodiments, and those skilled in the art can obviously make modifications or appropriate alterations and combinations to the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0027] Unless otherwise stated, all raw materials or excipients used in this invention are commercially available.

[0028] The present invention will be further illustrated below with reference to the embodiments. Unless otherwise stated, the amount of each component in the following embodiments of the present invention is in parts by weight.

[0029] Example 1

[0030] A method for recovering and reusing magnesium chloride, a byproduct of maltol production, includes the following steps:

[0031] (1) When the vacuum pump is turned on and the vacuum degree inside the first rotary kiln reaches -0.09Mpa, the temperature inside the rotary kiln rises to 70℃. Then, the basic magnesium chloride solution produced by the Grignard hydrolysis reaction is fed into the first rotary kiln using the negative pressure feeding method.

[0032] The rotation speed of the rotary kiln is adjusted to 8 Hz to ensure that the basic magnesium chloride is distilled in the rotary kiln for 2.5 hours. (The temperature of the rotary kiln is controlled in five zones: 70℃ in zone 1, 80℃ in zone 2, 80℃ in zone 3, 85℃ in zone 4, and 90℃ in zone 5). The basic magnesium chloride is distilled in stages in the rotary kiln, and the temperature rise is stable. This effectively allows the solvent in the solid slag of the basic magnesium chloride to be fully distilled, extracted and recovered, which can effectively ensure the quality of the finished magnesium hydroxide product.

[0033] (2) After the solvent is removed from the first rotary kiln, magnesium chloride is fed into the second rotary kiln using a negative pressure unloading device and heated to 170°C again. Basic magnesium chloride is decomposed into magnesium hydroxide at 170°C. After the temperature is maintained for 1.5 hours, the temperature is raised to 250°C-300°C and held for 1 hour. The residual organic matter of magnesium hydroxide is decomposed again at high temperature and discharged by the exhaust fan; thus, high-quality magnesium hydroxide is obtained.

[0034] (3) The qualified high-quality magnesium hydroxide produced by the second rotary kiln is transported to the grinding mill by the conveyor and crushed to 200 mesh. The powdered magnesium hydroxide passes through the dust removal system and then enters the third rotary kiln for high-temperature calcination. The temperature is controlled at 850℃-900℃ and calcined for 2.5 hours to obtain qualified magnesium oxide products.

[0035] Example 2

[0036] The difference between this embodiment and Embodiment 1 is that:

[0037] In step (1), the temperature of the first rotary kiln is controlled at 90°C in zones one through five.

[0038] Example 3

[0039] The difference between this embodiment and Embodiment 1 is that:

[0040] In step (1), the temperature of the first rotary kiln is controlled at 70°C in zones one through five.

[0041] Example 4

[0042] The difference between this embodiment and Embodiment 1 is that:

[0043] In step (2), after the solvent is removed from the first rotary kiln, magnesium chloride is fed into the second rotary kiln using a negative pressure unloading device and heated again to 250-300℃. Basic magnesium chloride is decomposed into magnesium hydroxide at 250-300℃. During this stage, the temperature is maintained at 280℃ to obtain high-quality magnesium hydroxide.

[0044] Comparative Example 1

[0045] The steps for this comparative example are as follows:

[0046] In step (1)-(3), the original process (1) magnesium chloride is manually put into a dryer under open conditions for negative pressure distillation for 2 hours to 80°C. Due to the defects of the dryer equipment, the vacuum negative pressure can only reach -0.06Mpa, and the organic solvent is not completely recovered. (2) After the drying negative pressure distillation is completed, the material is discharged into the secondary distillation tank, a certain amount of water is added, and the material is distilled at normal pressure to 110°C and then fed into the filter press. (3) After the filter press is completed, the removed filter cake is put into the stirring tank, washed with water, and then put into the filter press. The entire process will generate a large amount of wastewater that needs to be treated. (4) The magnesium hydroxide filter cake after the filter press is bagged and sent to the calcination device. Due to the defects of the process, the organic matter cannot be completely extracted, resulting in poor quality of magnesium hydroxide (magnesium oxide content is less than 40%, water content is greater than 30%, chloride ion content is greater than 8%), which seriously restricts the quality and yield of magnesium oxide.

[0047] Performance testing

[0048] The quality indicators of magnesium oxide obtained from the above embodiments and comparative examples are statistically summarized as follows:

[0049] Magnesium oxide content % Chloride ion content % Whiteness L* Magnesium oxide product standards ≥93 ≤0.12 ≥95 Example 1 99 0.02 99 Example 2 98.5 0.03 98.5 Example 3 99 0.02 99 Example 4 99 0.02 99 Comparative Example 1 96.5 0.08 96

[0050] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A method for recovering and reusing magnesium chloride, a byproduct of maltol production, comprising the following steps: (1) The magnesium chloride solution produced by the Grignard hydrolysis reaction is put into the first rotary kiln for heating, and the solvent and water in the magnesium chloride solution are recovered by vacuum distillation; (2) Under vacuum conditions, the magnesium chloride obtained in (1) is fed into the second rotary kiln using a transport device, and heated to decompose the magnesium chloride into magnesium hydroxide; (3) The magnesium hydroxide obtained in (2) is fed into a calcining device for high-temperature calcination to obtain magnesium oxide product, wherein the calcination temperature is 850℃-900℃; The first rotary kiln includes five zones: Zone 1, Zone 2, Zone 3, Zone 4, and Zone 5. The temperature in Zones 1 to 5 shows an upward trend. The temperatures in Zones 1 to 5 of the first rotary kiln are 70℃ in Zone 1, 80℃ in Zone 2, 80℃ in Zone 3, 85℃ in Zone 4, and 90℃ in Zone 5, respectively. The temperature inside the second rotary kiln is 170℃-300℃. The temperature inside the second rotary kiln is increased in stages: first, the temperature is increased to 170-180℃ and held for 1.5 hours, and then the temperature is increased to 250-300℃ and held for 1 hour.

2. According to the method of claim 1, the time for vacuum distillation in step (1) is 1-3 hours.

3. According to the method of claim 1, in step (1), the vacuum degree of the first rotary kiln is controlled between -0.08 MPa and -0.09 MPa.

4. According to the method of claim 1, the rotational speed of the first rotary kiln in step (1) is 5-20Hz.

5. The method according to any one of claims 1-4, wherein step (3) further includes a dust removal step before feeding magnesium hydroxide into the calcination apparatus for calcination.