Process and apparatus for decolorizing hydrolate of hyacinth

Abstract

The application discloses a kind of hydantoin hydrolysate decolorization method and special rotary disc decoloring tower, belong to chemical separation technical field.The decolorization method uses activated carbon as decoloring agent, adopts rotary disc decoloring tower as core equipment, by the strong shearing action dispersion material generated by rotary disc rotation, solid-liquid mass transfer is strengthened, and the efficiency of activated carbon adsorption decolorization is improved;After decolorization, material is separated activated carbon by precision filtration, and then the hydrolysate mother liquor entrained by activated carbon is recovered by filter pressing and returned to the system for recycling.The special rotary disc decoloring tower includes apron, tower body, multiple rotary disc, stirring shaft and transmission system, and the continuous decolorization process is adapted by optimizing the aspect ratio, rotary disc layer number and spacing.The application significantly improves the decolorization efficiency and processing capacity of hydantoin hydrolysate, while reducing the entrainment loss of active ingredients, reducing waste residue discharge and production cost, adapting to the continuous production needs of methionine industrialization, and having good economic benefits and industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of chemical separation technology, specifically relating to a decolorization method for hydantoin hydrolysate and a dedicated rotating disc decolorization tower for use with it, which is particularly suitable for the continuous decolorization and purification of alkaline hydrolysate in the hydantoin process for preparing D,L-methionine. Background Technology

[0002] D,L-methionine (2-amino-4-methylthiobutyric acid) is an essential sulfur-containing amino acid for livestock and poultry growth. Animals cannot synthesize it themselves and it is mainly obtained through exogenous supplementation in feed. Currently, the mainstream industrial production process for D,L-methionine is the hydantoin process. The core steps include: ① A condensation reaction of 3-methylthiopropionaldehyde, HCN, CO2, and NH3 to generate the intermediate 5-[(2-methylthio)ethyl]hydantoin (hydantoin); ② Hydrolysis of hydantoin under alkaline conditions to obtain methionine hydrolysate; ③ Decolorization, neutralization, crystallization, and purification of the hydrolysate to obtain the finished product, D,L-methionine.

[0003] According to the GB / T17810-2009 standard for feed-grade DL-methionine, qualified products should be white or light gray powder / flaky crystals, with specific requirements for color and purity. However, hydantoin hydrolysate is usually dark brown. The reasons for this color are mainly twofold: firstly, the natural organic pigments inherent in the raw materials; and secondly, the large molecular colored impurities generated during high-temperature, high-pressure hydrolysis through side reactions such as polymerization and oxidation. If decolorization is incomplete, these colored impurities will precipitate along with the product during subsequent crystallization, leading to a darker finished product color and exceeding color standards, severely reducing product quality and market value.

[0004] Currently, industrial production commonly employs powdered activated carbon adsorption decolorization technology, relying on the large specific surface area and well-developed pore structure of activated carbon to achieve the physical adsorption and removal of pigments. However, existing conventional processes mostly use batch decolorization kettles, which have the following significant drawbacks: First, the mass transfer efficiency is low, resulting in limited decolorization. Traditional stirred tanks have insufficient shear strength, poor mixing uniformity between activated carbon particles and hydrolysate, and a small solid-liquid contact area. This prevents the full utilization of adsorption sites within the activated carbon, leading to low light transmittance of the decolorized hydrolysate. Increasing the amount of activated carbon added to improve the decolorization effect would cause a large amount of methionine to be adsorbed by the activated carbon, significantly reducing the product yield. It is difficult to achieve a balance between decolorization efficiency and product yield.

[0005] Secondly, the intermittent production process limits processing capacity. The decolorization kettle operates in batches, requiring sequential completion of processes such as feeding, heat preservation and adsorption, discharge filtration, and slag discharge. This results in low equipment utilization and a small processing capacity per unit, making it unable to meet the capacity requirements of large-scale continuous production lines.

[0006] Third, there is significant material entrainment loss and high environmental costs. The decolorized activated carbon filter cake will carry a large amount of mother liquor containing methionine. Directly disposing of it as solid waste not only wastes raw materials and reduces product yield, but also increases the amount of hazardous waste to be disposed of and the wastewater treatment load, thereby increasing production and environmental costs. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a continuous decolorization method for hydantoin hydrolysate, which enhances solid-liquid mass transfer to improve decolorization efficiency, and simultaneously recovers activated carbon entrained with mother liquor to reduce raw material loss; it also provides a matching special rotary decolorization tower equipment to realize continuous feeding and discharging, and adapts to the needs of large-scale industrial production.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is a decolorization method for hydantoin hydrolysate, comprising the following steps: A. Preparing an activated carbon suspension: Mixing activated carbon with a solvent and stirring to prepare a uniform activated carbon suspension; B. Continuous adsorption decolorization: Continuously feeding the hydantoin hydrolysate to be decolorized and the activated carbon suspension into a rotating decolorization tower, dispersing the material through the rotational shearing action of the rotating disc 3 inside the tower, so that the activated carbon and the hydrolysate can fully contact each other and adsorb and remove colored impurities; C. Primary solid-liquid separation: After the decolorized material is discharged from the rotating decolorization tower, it is filtered to obtain a decolorized clear liquid and activated carbon filter residue; D. Filter residue recovery treatment: The activated carbon filter residue obtained in step C is subjected to pressure filtration treatment, the filtrate is recovered and returned to the decolorization system for recycling, and the filter cake is centrally disposed of.

[0009] Further, the activated carbon in step A has a particle size of 1-15 μm. In step B, the total added mass of activated carbon is 2‰ of the total mass of the hydantoin hydrolysate system; the rotation speed of the rotating disc 3 in the rotating disc decolorization tower in step B is 0-50 r / min; the decolorization temperature in step B is 60-100℃, and the decolorization pressure is atmospheric pressure. The residence time of the material in the rotating disc decolorization tower is 100-400 min. In step C, a precision filter is used for filtration separation. The filter element of the precision filter is a polyamide polymer sintered microporous filter element with a filtration accuracy of 1 μm. In step D, a plate and frame filter press is used for pressure filtration, and the recovered filtrate is returned to the activated carbon suspension preparation process for reuse. The decolorization effect is evaluated using a UV-Vis spectrophotometer, scanning the entire wavelength range of 200-500 nm, and selecting 450 nm as the quantitative detection wavelength to determine the transmittance.

[0010] The present invention also provides a rotary decolorizing tower for the decolorization method of claim 1, comprising a skirt 1, a tower body 2, a stirring shaft 4, multi-layer rotary discs 3, end caps 5, and a transmission part 6; the tower body 2 is fixedly disposed above the skirt 1, the end caps 5 are respectively sealed and installed at the top and bottom of the tower body 2, the transmission part 6 is disposed above the top end cap 5, the stirring shaft 4 penetrates the interior of the tower body 2 axially and its upper end is connected to the transmission part 6, the multi-layer rotary discs 3 are fixedly fixed to the stirring shaft 4 at intervals along the axial direction, and the stirring shaft 4 and the end caps 5 are sealed and connected.

[0011] Furthermore, the transmission component includes a drive motor, a frequency converter, a reducer, a coupling, and a frame. The frame is fixed to the top end cap, the reducer is mounted on the frame, the drive motor is connected to the input end of the reducer, and the output end of the reducer is connected to the upper end of the stirring shaft via a coupling. The frequency converter is used to adjust the speed of the drive motor. The length-to-diameter ratio of the tower body 2 is 8-14:1. The number of layers on the turntable 3 is 20-80, the diameter of the turntable is 80-120cm, and the spacing between adjacent turntables 3 is 20-100cm.

[0012] The beneficial effects that this invention can achieve are: 1. Significantly improved decolorization efficiency The strong shear force field generated by the rotating disc disperses and refines the activated carbon particles and hydrolysate, multiplying the solid-liquid contact surface area and significantly improving mass transfer kinetics, thus fully utilizing the adsorption sites of the activated carbon. With the same activated carbon dosage, the transmittance of the decolorized hydrolysate is far higher than that of the traditional batch process, consistently achieving a higher level and completely resolving the issue of excessive color in the finished product.

[0013] 2. Continuous production significantly improves processing capacity. Adopting a continuous tower design, the material is continuously fed from the bottom of the tower and continuously overflowed from the top, realizing the continuous operation of the decolorization process. At the same time, the effective volume of the tower structure is much larger than that of the decolorization kettle with the same floor area, the single tower processing capacity is increased several times, the equipment utilization rate is high, and it can be directly connected to the large-scale continuous methionine production line.

[0014] 3. Reduced raw material loss, resulting in significant environmental and economic benefits. By removing the mother liquor entrained in the activated carbon through plate and frame filtration and recycling the mother liquor back to the preparation system, the loss of methionine products with the waste activated carbon is significantly reduced, and the utilization rate of raw materials is improved. At the same time, the liquid content of the waste carbon filter cake is significantly reduced, which reduces the amount of solid waste disposal and wastewater treatment load, thus achieving both economic benefits and environmental value.

[0015] 4. The process operates stably and is easy to use. The frequency converter can precisely adjust the turntable speed, and with stable control of temperature and feed flow, it can ensure that the process parameters of the whole tower are uniform and stable, and the product quality fluctuations between batches are small. The whole system has a high degree of automation, which reduces the intensity of manual operation and operating costs. Attached Figure Description

[0016] Figure 1 This is a process flow diagram of the hydantoin hydrolysate decolorization method described in this invention; Figure 2 This is a schematic diagram of the rotary decolorizing tower described in this invention.

[0017] The markings in the diagram are as follows: 1-Skirt, 2-Tower body, 3-Rotating disc, 4-Stirring shaft, 5-End cap, 6-Transmission part. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] It should be noted that: in the embodiments of the present invention, the directional indicators (such as "up", "down", "forward", "backward") are only used to explain the relative positional relationship of each component under a specific posture (as shown in the figure). If the posture changes, the directional indicators will be adjusted accordingly; the terms "connection" and "fixed" are understood in the conventional mechanical field and can refer to fixed connection, detachable connection or integral, depending on the assembly requirements; the component numbers in all figures are consistent with the specification to ensure clear correspondence.

[0020] Combination Figure 1 As shown, the decolorization system for hydantoin hydrolysate of the present invention mainly consists of an activated carbon preparation tank, a rotary decolorization tower, a precision filter, a plate and frame filter press, and supporting conveying pipelines. The whole system adopts a continuous operation mode and can be directly connected to the upstream hydrolysis process and the downstream acidification process.

[0021] The activated carbon preparation tank is a sealed tank equipped with a stirrer, used to prepare a uniformly concentrated activated carbon suspension. During operation, powdered activated carbon, fresh water, and mother liquor recovered from plate and frame filtration are added to the tank. The stirrer is turned on and continuously stirred to ensure that the activated carbon is fully dispersed in the liquid phase, preventing sedimentation and stratification, and ensuring a stable suspension concentration. The prepared activated carbon suspension is metered out by a metering pump and continuously fed into the rotary decolorizing tower from the bottom of the tower along with the hydantoin hydrolysate to be decolorized via separate feed lines. The two materials undergo preliminary mixing in the feed area at the bottom of the tower, forming a uniform solid-liquid suspension system, which flows upward along the tower body with the feed.

[0022] The rotary disc decolorization tower is the core reaction equipment in the decolorization process. Multiple rotating discs, synchronized with the stirring shaft, are installed inside the tower. During the rotation of the discs, a continuous shear force is applied to the solid-liquid mixture, dispersing the activated carbon particles and hydrolysate into a fine scale. This significantly increases the contact surface area between the solid and liquid phases, enhancing the mass transfer and diffusion process of pigment molecules into the pores of the activated carbon. As the material flows upward through the multiple rotating discs, it is subjected to shear dispersion at each stage, ensuring full contact and adsorption of the activated carbon and colored impurities, thus completing the decolorization and purification process. A heating jacket is installed on the outside of the tower, allowing steam or hot water to be introduced to maintain the reaction temperature inside the tower, ensuring that the adsorption process takes place at a suitable temperature.

[0023] The clarified liquid after decolorization is continuously collected from the top of the tower via an overflow weir and transported to a precision filter for primary solid-liquid separation. The precision filter uses a polyamide polymer sintered microporous filter element with a filtration accuracy of 1μm, which can trap most of the fine activated carbon particles, ensuring the clarity of the effluent. The filtered decolorized liquid is then sent to the subsequent acidification process for further treatment via pipeline.

[0024] The waste activated carbon slurry periodically discharged from the bottom of the tower, as well as the activated carbon filter residue intercepted by the precision filter during backwashing, are uniformly sent to a plate and frame filter press for deep filtration and dewatering. High-pressure extrusion fully squeezes out the methionine-containing mother liquor trapped between the activated carbon particles and within their internal pores. The filtrate obtained from the filtration is transported back to the activated carbon preparation tank via pipeline for reuse as preparation water, recovering its effective components. The dry filter cake after filtration is collected as solid waste and entrusted to a qualified professional organization for harmless disposal or recycling.

[0025] (II) Structural Description of Rotary Decolorizing Tower Combination Figure 2 As shown, the rotary decolorizing tower of the present invention mainly consists of a skirt 1, a tower body 2, a rotary table 3, a stirring shaft 4, a head 5, and a transmission part 6.

[0026] Skirt 1 serves as the supporting foundation for the tower body. It is a welded steel structure, fixedly installed on the ground foundation, and is used to bear the entire weight of the tower body and internal materials to ensure the stability of equipment operation. The side wall of the skirt is equipped with a maintenance manhole to facilitate maintenance operations of the bottom pipelines and slag discharge port.

[0027] The tower body 2 is vertically fixed above the skirt 1. It is a cylindrical closed cavity and is the main space for the material decolorization reaction. A heating jacket is set on the outside of the tower body 2 to introduce heating medium to regulate the temperature inside the tower. The jacket is equipped with medium inlet and outlet and temperature detection interface.

[0028] The end caps 5 are respectively sealed and installed at the top and bottom of the tower body 2, forming a complete sealed cavity together with the tower body 2; the bottom end cap is provided with a feed port and a slag discharge port, which are used to introduce the material to be treated and to periodically discharge the deposited waste activated carbon slurry; the top end cap is provided with an overflow discharge port, a shaft through port and an exhaust port.

[0029] The transmission unit 6 is installed entirely above the top head 5 and mainly consists of a drive motor, frequency converter, reducer, coupling, and frame. The frame is fixedly connected to the upper surface of the top head 5, the reducer is fixedly installed on the frame, the drive motor is connected to the input end of the reducer, and the output shaft of the reducer is connected to the upper end of the stirring shaft 4 via a coupling. The frequency converter is located in an independent control cabinet at the top of the tower and can steplessly adjust the speed of the turntable by adjusting the output speed of the drive motor to adapt to the decolorization requirements of different material systems and processing volumes.

[0030] The stirring shaft 4 is vertically arranged along the central axis of the tower body 2, running through the entire tower cavity from top to bottom. A mechanical seal is installed at the insertion point of the stirring shaft 4 and the top end cap 5 to ensure the airtightness of the cavity and prevent material leakage and the entry of external impurities. Multi-layer turntables 3 are fixedly installed at equal intervals along the axial direction of the stirring shaft 4 and rotate synchronously with it. The turntables 3 have a disc-shaped structure, with their edges maintaining a suitable gap from the inner wall of the tower body 2, ensuring smooth rotation while avoiding flow dead zones around the tower wall.

[0031] The length-to-diameter ratio of the tower body 2 is set to 8-14:1. A larger length-to-diameter ratio allows the material to form an approximately plug flow state within the tower, extending the effective residence time and preventing material short-circuiting. The number of rotating discs 3 is set to 20-80 layers, which can form multi-level shear zones within the tower, ensuring that the material is continuously subjected to shear dispersion during its ascent. The diameter of the rotating discs 3 is 80-120cm, and the spacing between adjacent rotating discs 3 is 20-100cm. By matching the diameter of the rotating discs with the spacing between them, a uniform shear force field can be formed throughout the entire tower, ensuring the consistency of the decolorization effect.

[0032] Comparative Example 1: Beaker-level intermittent decolorization control test Accurately weigh 200.0 g of the hydantoin hydrolysate to be decolorized into a beaker, place it in a 70℃ constant temperature water bath with a magnetic stir bar, and start stirring at 400 rpm. After the system temperature stabilizes, add 1.0 g of powdered activated carbon (0.5% of the hydrolysate mass), and decolorize at a constant temperature and speed for 30 min. Immediately after the reaction is complete, perform vacuum filtration while hot to separate the activated carbon and collect the clear filtrate.

[0033] Using deionized water as a reference, the transmittance was measured at a wavelength of 450 nm using a UV-Vis spectrophotometer. The results showed that the transmittance of the decolorized hydantoin hydrolysate was 56.98%.

[0034] Comparative Example 2: Intermittent Decolorization Test in a Traditional Decolorization Kettle Accurately weigh 5.0 kg of the hydantoin hydrolysate to be decolorized and place it in a 10 L stainless steel decolorization vessel. The vessel is equipped with an anchor-type stirrer, an electric heating jacket, and a bottom discharge port. Turn on the stirrer and set the speed to 250 rpm. Turn on the electric heating system and wait for the temperature of the material inside the vessel to rise to 70℃ and stabilize. Then add 10.0 g of powdered activated carbon (the dosage is 2‰ of the mass of the hydrolysate). The decolorization reaction is carried out at a constant temperature and rate for 120 min. After the reaction is completed, immediately discharge the decolorized suspension through the bottom discharge port of the vessel. While the solution is still hot, use vacuum filtration to separate the activated carbon and collect the clear filtrate.

[0035] The transmittance was measured at a wavelength of 450 nm using the same method, and the results showed that the transmittance of the decolorized hydantoin hydrolysate was 92.62%.

[0036] This example: Continuous decolorization test of a rotary decolorizing tower This embodiment uses the rotary decolorizing tower described in this invention to conduct a continuous decolorization experiment. The rotary decolorizing tower has a length-to-diameter ratio of 10:1, 40 rotary layers, a rotary diameter of 95cm, and a rotary spacing of 30cm. The rotary speed is infinitely adjustable by a frequency converter, and the tower is equipped with a steam jacket for heating.

[0037] The specific steps are as follows: 1. In the activated carbon preparation tank, mix powdered activated carbon (particle size 3-7μm) with fresh water and recycled mother liquor to prepare an activated carbon suspension with a mass fraction of 5wt%, and continuously stir to keep it uniform.

[0038] 2. The hydrolysate of hydantoin to be decolorized is continuously introduced into the rotary decolorizing tower from the bottom through independent feed pipelines at a flow rate of 6804 kg / h and 5 wt% activated carbon suspension at a flow rate of 284 kg / h. After mixing, the activated carbon content in the system is about 2‰.

[0039] 3. Turn on the steam jacket heating of the tower body to maintain the temperature of the material inside the tower at 70℃ and the system pressure at atmospheric pressure; start the transmission device at the top of the tower and set the turntable speed to 20 rpm to keep the material inside the tower in a uniform suspension state.

[0040] 4. The material flows continuously upward in the tower and is gradually sheared and dispersed by multiple rotating discs to complete the pigment adsorption and decolorization. The average residence time is 240 minutes.

[0041] 5. The clear liquid after decolorization is continuously collected from the overflow weir at the top of the tower and transported to a precision filter (polyamide sintered filter element, precision 1μm) to remove activated carbon. The filtrate is then sent to the subsequent acidification process.

[0042] 6. The waste activated carbon slurry periodically discharged from the bottom of the tower and the filter residue retained by the filter are sent together to a plate and frame filter press for filtration. The recovered filtrate is returned to the activated carbon preparation tank for reuse, and the dry filter cake is centrally disposed of.

[0043] After the system is in steady-state operation, a sample is taken from the overflow port at the top of the tower for testing. The transmittance of the decolorized hydrolysate is 99.38% at a wavelength of 450nm, which is significantly better than the traditional batch decolorization process. At the same time, the mother liquor recovery process can recover more than 85% of the entrained mother liquor in the activated carbon, effectively reducing product loss.

[0044] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Those skilled in the art should understand that various changes can be made to them in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A method for decolorizing hydantoin hydrolysate, characterized in that, Includes the following steps: A. Preparation of activated carbon suspension: Mix activated carbon with solvent and stir to prepare a uniform activated carbon suspension; B. Continuous adsorption decolorization: The hydrolysate of hydantoin to be decolorized and the activated carbon suspension are continuously fed into a rotating decolorization tower. The material is dispersed by the rotational shearing action of the rotating disc (3) in the tower, so that the activated carbon and the hydrolysate can be fully contacted and the colored impurities are adsorbed and removed. C. Primary solid-liquid separation: After the decolorized material is discharged from the rotary decolorization tower, it is filtered and separated to obtain decolorized clear liquid and activated carbon filter residue; D. Filter residue recovery and treatment: The activated carbon filter residue obtained in step C is subjected to pressure filtration treatment, the filtrate is recovered and returned to the decolorization system for recycling, and the filter cake is centrally disposed of.

2. The decolorization method for hydantoin hydrolysate according to claim 1, characterized in that, The activated carbon in step A has a particle size of 1-15 μm.

3. The decolorization method for hydantoin hydrolysate according to claim 1, characterized in that, In step B, the total mass of activated carbon added is 2‰ of the total mass of the hydantoin hydrolysate system; the rotation speed of the disc (3) in the disc decolorization tower in step B is 0-50 r / min; the decolorization temperature in step B is 60-100℃ and the decolorization pressure is atmospheric pressure.

4. The decolorization method for hydantoin hydrolysate according to claim 1, characterized in that, The residence time of the material in the rotary decolorization tower is 100-400 minutes.

5. The decolorization method for hydantoin hydrolysate according to claim 1, characterized in that, Step C uses a precision filter for filtration and separation. The filter element of the precision filter is a polyamide polymer sintered microporous filter element with a filtration accuracy of 1μm.

6. The decolorization method for hydantoin hydrolysate according to claim 1, characterized in that, Step C involves using a plate and frame filter press for filtration, and the recovered filtrate is returned to the activated carbon suspension preparation process for reuse.

7. The decolorization method for hydantoin hydrolysate according to claim 1, characterized in that, The decolorization effect was evaluated using a UV-Vis spectrophotometer. The entire wavelength range of 200-500 nm was scanned, and 450 nm was selected as the quantitative detection wavelength to determine the transmittance.

8. A rotary decolorizing tower for use in the decolorization method of claim 1, characterized in that, It includes a skirt base (1), a tower body (2), a stirring shaft (4), a multi-layer turntable (3), a head (5), and a transmission part (6); the tower body (2) is fixedly installed above the skirt base (1), the head (5) is sealed and installed at the top and bottom of the tower body (2) respectively, the transmission part (6) is set above the top head (5), the stirring shaft (4) passes through the interior of the tower body (2) along the axial direction and its upper end is connected to the transmission part (6) for transmission, the multi-layer turntable (3) is fixedly fixed on the stirring shaft (4) along the axial direction at intervals, and the stirring shaft (4) and the head (5) are sealed and connected.

9. The rotary decolorizing tower according to claim 8, characterized in that, The transmission component includes a drive motor, a frequency converter, a reducer, a coupling, and a frame. The frame is fixed to the top end cap, the reducer is mounted on the frame, the drive motor is connected to the input end of the reducer, and the output end of the reducer is connected to the upper end of the stirring shaft via a coupling. The frequency converter is used to adjust the speed of the drive motor.

10. The rotary decolorizing tower according to claim 8, characterized in that, The length-to-diameter ratio of the tower body (2) is 8-14:1, the number of layers of the turntable (3) is 20-80, the diameter of the turntable is 80-120cm, and the distance between adjacent turntables (3) is 20-100cm.

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