A preparation process and system for caramel coloring

Abstract

This invention discloses a preparation process and method for caramel color, belonging to the field of caramel color preparation technology. The process involves using xylose mother liquor as raw material, heating it at a low temperature to 75-85°C, passing it through a nanofiltration membrane device for nanofiltration, obtaining a filtrate and a retentate; using a double-barrel centrifuge, the retentate is centrifuged, allowed to stand, and then evaporated and concentrated to a refractive index ≥70, and dried to obtain caramel color powder. This invention, on the one hand, recovers and reuses the xylose mother liquor, a byproduct of xylose production, which not only helps improve the sustainability of the xylose preparation process but also significantly reduces COD generation in wastewater; on the other hand, by employing specific control conditions and equipment, this preparation process ensures that it not only works well with the xylose mother liquor byproduct but also guarantees that the prepared caramel color has uniform particle size, high dispersibility, good flowability (low conversion rate), high purity, and good quality, and is free of 4-methylimidazole.

Description

Technical Field

[0001] This invention relates to a preparation process and system for caramel color, belonging to the fields of comprehensive utilization of xylose mother liquor resources and preparation technology of caramel color. Background Technology

[0002] The xylose preparation process includes steps such as alkali removal from hemicellulose raw materials, acid-adjusting hydrolysis, decolorization, electrodialysis, ion exchange, evaporation crystallization, and centrifugation. The main sources of hemicellulose raw materials are: 1. Corn cobs; 2. Waste alkaline solutions containing hemicellulose from chemical fiber plants (e.g., CN102643935A, CN109112233A, CN112195209A, and CN110564898A). Compared to corn cobs, waste alkaline solutions containing hemicellulose have advantages in procurement and transportation costs. However, this process involves dealkalization and desalination, and imposes strict requirements on processes such as decolorization, electrodialysis, ion exchange, evaporation crystallization, and centrifugation. It also generates a specific waste liquid: xylose mother liquor. This xylose mother liquor is formed during evaporation crystallization and centrifugation processes. It contains 40-50% xylose, 15-25% mannose, 8-12% glucose, and 8-12% xylan. Through practice, it has been found that this waste liquid, after specific processing, can form caramel coloring.

[0003] Generally, caramel color is a complex reddish-brown or dark brown mixture formed by the condensation of sugary raw materials (such as maltose, sucrose, molasses, etc.) through heating and dehydration. It is a widely used semi-natural food coloring agent in my country. Currently, the main industrial processes for producing caramel color include:

[0004] I. The conventional method involves caramelizing the sugar at high temperatures, specifically heating the syrup at 200°C. This method has drawbacks including long reaction time, low yield, and high energy consumption.

[0005] II. Ammonium method: Sugar reacts with amino compounds (ammonia, ammonium salts, amino acids, etc.) via the Maillard reaction, i.e., heating the syrup at 140°C. This method has a short reaction time, requires the addition of additional substances, and has a high yield; however, the production process generates a certain amount of 4-methylimidazole (a convulsant; chronic toxicity studies have shown it causes a decrease in white blood cells and slows growth in animals). Currently, this method is rarely used.

[0006] 3. Ammonium sulfite process: In the conventional production process, ammonium sulfite is added as a catalyst, which means that sulfuric acid needs to be added separately.

[0007] Although the prior art CN216614473U discloses "a system for co-producing xylitol and caramel color using xylose mother liquor," in which xylose mother liquor is used as raw material, and after decolorization treatment by a nanofiltration membrane device, a retentate and a permeate are obtained, the retentate is the pigment solution and the permeate is the decolorized solution; then, the decolorized solution undergoes ion exchange, chromatographic separation, purification, and browning reaction to finally obtain caramel color. However, the process involved is complex, especially the high requirements for the ion exchange, chromatographic separation, purification, and browning reaction of the decolorized solution; and the ion exchange treatment of the decolorized solution introduces a large amount of COD into the wastewater, thus significantly increasing the wastewater treatment cost. Summary of the Invention

[0008] To address the problems in existing technologies, a preparation process and system for caramel color is proposed. In this technical solution, xylose mother liquor, a byproduct of xylose production, is used as raw material. It is heated from a low temperature to 75–85°C to obtain a caramel color conversion solution. Subsequently, the caramel color conversion solution is nanofiltered using a nanofiltration membrane, and the resulting filtrate is directly returned to the heating process. The resulting effluent is then purified using a specific centrifuge device for high-efficiency, low-energy processing, transforming the crude caramel color solution into a semi-refined caramel color solution, ensuring the quality and purity of the final caramel color product. After standing, the concentrated solution is evaporated and concentrated to a refractive index ≥70, and then dried to obtain refined caramel color powder.

[0009] To achieve the above technical objectives, the following technical solution is proposed:

[0010] The primary objective of this technical solution is to provide a process for preparing caramel coloring, comprising the following steps:

[0011] S1: Using xylose mother liquor as raw material, heat to 75-85℃;

[0012] The xylose mother liquor includes xylose at a concentration of 40-50%, mannose at a concentration of 15-25%, glucose at a concentration of 8-12%, and xylan at a concentration of 8-12%.

[0013] S2: The heated material is passed into the nanofiltration membrane device, and the temperature is controlled at 40-45℃ and the pressure is controlled at 28-32 bar to obtain throttling liquid and filtrate. The throttling liquid is crude caramel coloring liquid.

[0014] The threshing liquid contains 40-50 g / L xylose, has a xylose concentration of 4-5%, and a xylose purity of 25-30%. The threshing liquid has a refractive index of 15-20 and a conductivity of 25000-30000 μs / cm.

[0015] The filtrate contains 50-60 g / L xylose, with a xylose concentration of 5-6% and a xylose purity of 55-60%. The filtrate has a refractive index of 10-13 and a conductivity of 200-300 μS / cm. It can be used as a raw material and directly participates in heating.

[0016] Nanofiltration membrane devices use nanofiltration membranes with a molecular weight of less than 300.

[0017] S3: Using a double-barrel centrifuge device, the obtained threshing liquid is centrifuged to obtain semi-refined caramel coloring liquid; then, it is allowed to stand to obtain refined caramel coloring liquid.

[0018] The centrifugation speed is 60-200 r / min and the settling time is 10-30 min. This setting improves processing efficiency and quality while reducing production costs, thus enhancing economic efficiency.

[0019] Preferably, three-stage continuous centrifugation is performed to improve the yield of caramel color;

[0020] S4: Under the conditions of a temperature of 65-75℃ and a negative pressure of 0.040-0.050MPa, the obtained refined caramel color liquid is evaporated and concentrated to a refractive index ≥70, and then dried to obtain refined caramel color powder.

[0021] The process involves spray drying at 120–150°C, and the residual heat from the spray drying is then reused to heat the xylose mother liquor. This temperature setting effectively prevents air from entering the particles of the caramel color powder, thus resolving quality issues. Furthermore, excessively high temperatures can cause the powder particles to soften and stick to the drying walls, compromising the continuity of subsequent drying processes.

[0022] The obtained caramel color product specifications include: color index (EBC units) ≥33000, refractive index ≥70, ammonia nitrogen (as NH) ≤0.005%, sulfur dioxide (as SO) ≤0.002%, arsenic (as As) ≤0.05 mg / L, lead (as Pb) ≤0.05 mg / L, heavy metals ≤0.1 mg / L, and 4-methylimidazole not detected.

[0023] The second objective of this technical solution is to provide: a caramel color preparation system, the preparation system including a heating tank, a nanofiltration membrane device, a double-barrel centrifuge device, a settling tank and an Mvr evaporation device, wherein the feed inlet of the heating tank is connected to a raw material storage tank, and the raw material storage tank is connected to the xylose mother liquor outlet of the xylose production system.

[0024] The nanofiltration membrane unit is located behind the heating tank, and the heating tank is connected to the nanofiltration membrane unit.

[0025] The dual-barrel centrifuge is located behind the nanofiltration membrane unit, and the throttling liquid outlet on the nanofiltration membrane unit is connected to the dual-barrel centrifuge.

[0026] The settling tank is located at the rear of the station of the double-barrel centrifuge, and the light phase liquid outlet of the double-barrel centrifuge is connected to the settling tank.

[0027] The MVR evaporation unit is located behind the station of the settling tank. The settling tank is connected to the MVR evaporation unit, and the MVR evaporation unit is connected to the caramel color product storage tank.

[0028] A continuous pathway for the preparation and preservation of caramel color is formed between the raw material storage tank, heating tank, nanofiltration membrane device, double-barrel centrifuge device, settling tank, Mvr evaporation device and caramel color product storage tank.

[0029] Furthermore, a filtrate storage tank is provided at the rear of the nanofiltration membrane device. The filtrate outlet of the nanofiltration membrane device is connected to the filtrate storage tank, and the filtrate storage tank is connected to the raw material storage tank and / or the heating tank.

[0030] Furthermore, the preparation system also includes a spray drying tower, which is located between the Mvr evaporator and the caramel color product storage tank.

[0031] Furthermore, the dual-barrel centrifuge device includes an inner barrel and an outer barrel sleeved outside the inner barrel. The inner barrel and the outer barrel are arranged along the same central axis, and a cavity for the flow of crude caramel coloring liquid is formed between the outer wall of the inner barrel and the inner wall of the outer barrel.

[0032] The outer barrel is cylindrical and sealed. The upper part of the outer barrel is equipped with a crude caramel coloring liquid inlet, and the throttling liquid outlet is connected to the crude caramel coloring liquid inlet through a transfer pump.

[0033] The inner barrel is tank-shaped and sealed. Inside the inner barrel is a stirring mechanism with a dispersion plate at the bottom. The lower wall of the inner barrel has through holes that communicate with the cavity. The upper part of the inner barrel has a light phase liquid outlet and a heavy phase liquid outlet. The light phase liquid outlet extends towards the central axis through one end of the light phase liquid outlet pipe, and the other end of the light phase liquid outlet pipe is connected to the settling tank.

[0034] The heavy phase liquid outlet is located above the light phase liquid outlet.

[0035] The stirring mechanism includes a main shaft and detachable stirring blades mounted on the main shaft, with a dispersing plate located below the detachable stirring blades. The main shaft extends outward from the inner barrel and is connected to a motor via a coupling, with a speed reducer provided between the coupling and the motor.

[0036] Furthermore, the height-to-diameter ratio of the inner tub is 5 to 10:1. Here, "height-to-diameter ratio" specifically refers to the proportional relationship between the height and the inner diameter.

[0037] Furthermore, there are three dual-barrel centrifuge devices, with the heavy phase liquid outlet of the upper-level dual-barrel centrifuge device connected to the feed inlet of the lower-level dual-barrel centrifuge device.

[0038] In this technical solution, the raw material storage tanks, heating tanks, nanofiltration membrane devices, intercepting liquid temporary storage tanks, filtrate temporary storage tanks, double-barrel centrifuge devices, settling tanks, MVR evaporation devices, spray drying towers, and caramel color product storage tanks are connected by transfer pumps and pipelines. Furthermore, precise automated control is achieved through the installation of transfer pumps, pipelines, pressure monitoring instruments, temperature detection instruments, etc.

[0039] The positional relationships involved in this technical solution, such as "middle," "upper," "external," "one end," "the other end," "above," "behind the workstation," and "between," are defined based on the actual usage conditions and are common terms in this technical field, as well as common terms used by those skilled in the art in actual use.

[0040] The beneficial technical effects of adopting this technical solution are as follows:

[0041] I. Compared with the traditional caramel color preparation process, the present invention obtains a caramel color conversion solution by heating from a low temperature to 75-85°C, and then separates the formed caramel color using a nanofiltration membrane device. This process has low energy consumption and the caramel color formed at low temperature has excellent fluidity.

[0042] Second, the present invention avoids the possibility of producing 4-methylimidazole by using a low-temperature cycling process without adding additional nitrogen-containing catalysts, thereby improving the food safety of caramel color products.

[0043] Third, in this invention, a double-barrel centrifuge is used to effectively separate the crude caramel color liquid (nanofiltration effluent) into a heavy phase liquid and a light phase liquid, which is a high-efficiency and low-energy purification process to ensure the quality and purity of the final caramel color product. Then, the light phase liquid is allowed to stand and concentrated, which can effectively improve the quality and purity of the caramel color. The heavy phase liquid is continuously centrifuged, which can effectively improve the yield of caramel color.

[0044] Fourth, unlike traditional processes, this invention does not add a catalyst and operates at low temperatures, resulting in a low single-pass conversion rate. This avoids the traditional carbonization and precipitation / caking phenomena. Most importantly, it solves the problem of 4-methylimidazole production that can occur with catalysts. Since it does not use nitrogen-containing catalysts or high temperatures, it essentially eliminates the food safety risk associated with 4-methylimidazole. Furthermore, because the xylose mother liquor is purified by an ion exchange resin (this technical solution uses xylose mother liquor as raw material, and the xylose mother liquor is formed in a xylose preparation process purified by an ion exchange resin), the heavy metal ions in the xylose mother liquor are extremely low. No additional catalyst is needed in the subsequent preparation of caramel color, and the final product contains almost no residual xylose mother liquor. All xylose mother liquor is recycled, resulting in a caramel color conversion rate of over 95%, significantly improving raw material utilization and reducing wastewater generation and treatment.

[0045] V. In this invention, the caramel color preparation process is designed within the process of preparing xylose using hemicellulose from a viscose fiber production line. According to this process design, nanofiltration membranes are used to replace the activated carbon decolorization step, which not only significantly reduces the amount of activated carbon used in the traditional process, but also optimizes the sugar solution and produces high-quality low-temperature caramel color.

[0046] VI. Xylose mother liquor, as a byproduct of xylose production, has low value, thus significantly reducing the raw material cost for caramel color preparation in this invention. Furthermore, since the xylose mother liquor can be obtained through centrifugation, its preparation efficiency is improved compared to traditional methods; and the use of nanofiltration membranes for separation, coupled with controlled specific conditions, effectively enhances the purity and quality of the caramel color. Attached Figure Description

[0047] Figure 1 This is a process flow diagram related to the present invention;

[0048] Figure 2 This is a diagram of the equipment layout involved in the present invention;

[0049] Figure 3 This is a structural diagram of the dual-barrel centrifuge device involved in the present invention;

[0050] Figure 4 This is a top view of the dual-barrel centrifuge device involved in the present invention;

[0051] In the diagram, 1. Raw material storage tank, 2. Heating tank, 3. Nanofiltration membrane device, 4. Interceptor liquid temporary storage tank, 5. MVR evaporator, 6. Caramel color product storage tank, 7. Filtrate temporary storage tank, 8. Double-barrel centrifuge device, 80. Inner barrel, 81. Outer barrel, 82. Cavity, 83. Crude caramel color liquid inlet, 84. Stirring mechanism, 840. Main shaft, 841. Detachable stirring blades, 85. Dispersion plate, 86. Through hole, 87. Light phase liquid outlet, 88. Heavy phase liquid outlet, 9. Settling tank, 10. Spray drying tower, 11. Coupling, 12. Motor, 13. Reducer, 14. Light phase liquid outlet pipe. Detailed Implementation

[0052] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0053] Regarding the preparation of caramel color, existing technologies mostly involve the dehydration, decomposition, and polymerization of sugars (such as maltose, sucrose, molasses, invert sugar, lactose, malt syrup, and starch hydrolysis products) at high temperatures to form a complex reddish-brown or dark brown mixture. Some of these mixtures are colloidal aggregates, which are widely used semi-natural food coloring agents. However, these technologies involve several problems: the high-temperature dehydration caramelization reaction results in a long reaction time and low yield; and the addition of ammonium sulfite as a catalyst requires the addition of sulfuric acid. Alternatively, the Maillard reaction is carried out between sugars and amino compounds (ammonia, ammonium salts, amino acids, etc.), and the syrup is heated at 140°C. This production process generates harmful substances such as 4-methylimidazole.

[0054] Therefore, this invention is based on the characteristics of the xylose preparation process using hemicellulose from a viscose fiber production line as raw material: A xylose mother liquor is formed, comprising 40-50% xylose, 15-25% mannose, 8-12% glucose, and 8-12% xylan. Then, the xylose mother liquor is heated to 75-85°C at a low temperature to convert the sugar components into caramel color. The caramel color conversion solution is then nanofiltered using a nanofiltration membrane with a molecular weight below 300. The resulting filtrate is directly returned to the heating process. The resulting effluent is then purified efficiently and with low energy using a specific centrifuge device, transforming the crude caramel color solution into a semi-refined caramel color solution, ensuring the quality and purity of the final caramel color product. After standing, the concentrate is evaporated and concentrated to a refractive index ≥70, and then dried to obtain refined caramel color powder.

[0055] On the one hand, recycling and reusing the xylose mother liquor, a byproduct of xylose production, not only helps improve the sustainability of the xylose preparation process but also significantly reduces COD generation in wastewater. On the other hand, by adopting specific control conditions and equipment, this preparation process can not only work well with the xylose mother liquor, a byproduct of xylose production, but also ensure that the prepared caramel coloring has uniform particle size, high dispersibility, good flowability (low conversion rate), high purity, and good quality, and is free of 4-methylimidazole.

[0056] The following examples illustrate this:

[0057] Example 1

[0058] This embodiment provides a process for preparing caramel color, such as... Figure 1 As shown, it includes the following steps:

[0059] S1: Using xylose mother liquor as raw material, heat to 75-85℃;

[0060] The xylose mother liquor comprises 40-50% xylose, 15-25% mannose, 8-12% glucose, and 8-12% xylan. Heating to 75-85°C at a low temperature prevents carbonization, precipitation, and clumping, thus effectively improving the quality of the caramel color and the stability of subsequent preparation processes. Preferably, the heating temperature is 80°C.

[0061] S2: The heated material is passed into the nanofiltration membrane device, and the temperature is controlled at 40-45℃ and the pressure is controlled at 28-32 bar to obtain throttling liquid and filtrate. The throttling liquid is crude caramel coloring liquid.

[0062] The intercepted liquid includes caramel color molecules, macromolecular colloids and miscellaneous sugars, with a xylose content of 40-50 g / L, a xylose concentration of 4-5%, and a xylose purity of 25-30%; the refractive index of the intercepted liquid is 15-20, and the conductivity of the intercepted liquid is 25000-30000 μs / cm.

[0063] The filtrate contains 50–60 g / L xylose, has a xylose concentration of 5–6%, and a xylose purity of 55–60%. The filtrate has a refractive index of 10–13 and a conductivity of 200–300 μS / cm.

[0064] In nanofiltration membrane devices, using nanofiltration membranes with a molecular weight below 300 allows most components not belonging to caramel coloring (such as xylose and glucose) to be filtered out, improving the purity of the caramel coloring. If the molecular weight is greater than this, the caramel coloring cannot be effectively intercepted, causing some caramel coloring to undergo excessive reactions, affecting the quality of the caramel coloring. Similarly, using the aforementioned temperature and pressure can effectively ensure the interception effect of the nanofiltration membrane and extend its service life. For example, if the temperature is too low, the processing capacity of the nanofiltration membrane decreases, resulting in poor operating efficiency; if the temperature is too high, it will greatly reduce the service life of the nanofiltration membrane. Likewise, if the pressure is too low, it will affect the processing capacity of the nanofiltration membrane; if the pressure is too high, it will affect the service life of the nanofiltration membrane or even directly damage it. Among these, the preferred nanofiltration conditions are: a temperature of 42°C and a pressure of 30 bar.

[0065] S3: Using a double-barrel centrifuge device, the obtained threshing liquid is centrifuged to obtain semi-refined caramel coloring liquid; then, it is allowed to stand to obtain refined caramel coloring liquid.

[0066] The centrifugation speed is 60-200 r / min and the settling time is 10-30 min. This setting improves processing efficiency and quality while reducing production costs, thus enhancing economic efficiency.

[0067] Preferably, three-stage continuous centrifugation is performed to improve the yield of caramel color;

[0068] S4: Under conditions of 65–75℃ and 0.040–0.050 MPa negative pressure, the obtained refined caramel color solution is evaporated and concentrated to a refractive index ≥70; then, it is spray-dried at 120–150℃ to obtain refined caramel color powder. Preferably, the evaporation and concentration conditions are 70℃ and 0.045 MPa negative pressure.

[0069] The caramel color powder obtained above was tested, and the results are shown in Table 1 below.

[0070]

[0071] Example 2

[0072] Based on Example 1, this example reuses the filtrate obtained in step S2 as a raw material, directly participating in the heating process. This further reduces waste liquid discharge and improves the utilization rate of xylose mother liquor and the yield of caramel coloring.

[0073] Example 3

[0074] This embodiment provides a caramel color preparation system, such as... Figure 2As shown, the preparation system includes a heating tank 2, a nanofiltration membrane device 3, a double-barrel centrifuge device 8, a settling tank 9, and an MVR evaporator 5. The inlet of the heating tank 2 is connected to the raw material storage tank 1, and the raw material storage tank 1 is connected to the xylose mother liquor outlet in the xylose production system. The nanofiltration membrane device 3 is located behind the heating tank 2, and the heating tank 2 is connected to the nanofiltration membrane device 3. The double-barrel centrifuge device 8 is located behind the nanofiltration membrane device 3, and the throttling liquid outlet on the nanofiltration membrane device 3 is connected to the double-barrel centrifuge device 8. The settling tank 9 is located behind the double-barrel centrifuge device 8, and the light phase liquid outlet 87 of the double-barrel centrifuge device 8 is connected to the settling tank 9. The MVR evaporator 5 is located behind the settling tank 9, and the settling tank 9 is connected to the MVR evaporator 5. The MVR evaporator 5 is connected to the caramel color product storage tank 6.

[0075] A continuous pathway for the preparation and preservation of caramel color is formed between the raw material storage tank 1, heating tank 2, nanofiltration membrane device 3, double-barrel centrifuge device 8, settling tank 9, Mvr evaporation device 5, and caramel color product storage tank 6.

[0076] The nanofiltration membrane device 3 is also provided with a filtrate storage tank 7 at the rear of the work station. The filtrate outlet on the nanofiltration membrane device 3 is connected to the filtrate storage tank, and the filtrate storage tank is connected to the raw material storage tank 1 and / or the heating tank 2.

[0077] In addition, the preparation system also includes a spray drying tower 10, which is located between the Mvr evaporation unit 5 and the caramel color product storage tank 6.

[0078] Example 4

[0079] Based on Example 3, this example further defines the dual-barrel centrifuge device 8 to further illustrate the technical solution.

[0080] like Figure 3-4 As shown, the double-barrel centrifuge device 8 includes an inner barrel 80 and an outer barrel 81 sleeved outside the inner barrel 80. The inner barrel 80 and the outer barrel 81 are arranged on the same central axis, and a cavity 82 for the flow of crude caramel coloring liquid is formed between the outer wall of the inner barrel 80 and the inner wall of the outer barrel 81.

[0081] The outer barrel 81 is cylindrical and sealed. The upper part of the outer barrel 81 is provided with a crude caramel coloring liquid inlet 83. The throttling liquid outlet is connected to the crude caramel coloring liquid inlet 83 through a transfer pump. Preferably, there are two crude caramel coloring liquid inlets 83.

[0082] The inner tank 80 is tank-shaped and sealed. Inside the inner tank 80, there is a stirring mechanism 84, and below the stirring mechanism 84, there is a dispersing plate 85. There are multiple through holes 86 on the lower wall of the inner tank 80 that communicate with the cavity 82. The inner tank 80 has a light phase liquid outlet 87 and a heavy phase liquid outlet 88 at the upper part. One end of the light phase liquid outlet 87 extends towards the central axis (specifically, a light phase outlet pipe can be connected to the light phase liquid outlet 87), and the other end of the light phase liquid outlet 87 is connected to the settling tank 9.

[0083] The heavy phase liquid outlet 88 is located above the light phase liquid outlet 87.

[0084] The stirring mechanism 84 includes a main shaft 840 and detachable stirring blades 841 mounted on the main shaft 840. A dispersing plate 85 is located below the detachable stirring blades. The main shaft 840 extends outward from the inner barrel 80. The main shaft 840 is connected to the motor 12 via a coupling 11, and a reducer 13 is provided between the coupling 11 and the motor 12.

[0085] The height-to-diameter ratio of the inner tub is 5 to 10:1.

[0086] Preferably, there are three dual-barrel centrifuge units 8, with the heavy phase liquid outlet 88 of the upper-level dual-barrel centrifuge unit 8 connected to the feed inlet of the lower-level dual-barrel centrifuge unit 8. Furthermore, a threshing liquid storage tank 4 and a filtrate storage tank 7 are also provided at the rear of the nanofiltration membrane unit 3. The threshing liquid outlet of the nanofiltration membrane unit 3 is connected to the threshing liquid storage tank 4, which is connected to the dual-barrel centrifuge unit 8. The filtrate outlet of the nanofiltration membrane unit 3 is connected to the filtrate storage tank, which is connected to the raw material storage tank 1 and / or the heating tank 2. The raw material storage tank 1, heating tank 2, nanofiltration membrane unit 3, threshing liquid storage tank 4, filtrate storage tank 7, MVR evaporator 5, and caramel color product storage tank 6 are connected via transfer pumps and pipelines. Precise automated control is achieved through transfer pumps, pipelines, pressure monitoring instruments, and temperature detection instruments.

[0087] In addition, the inner tub 80 is equipped with an inspection and observation hole at the top, allowing staff to observe the internal condition of the inner tub 80 for timely maintenance and cleaning. The bottom of the outer tub 81 is connected to a drain valve, facilitating the timely discharge of waste liquid from the outer tub 81, thus ensuring the orderly and stable operation of the centrifugation process. A mounting base is located below the outer tub 81, on which the inner tub 80 is fixed.

[0088] For the dual-barrel centrifuge device 8, the working principle involved includes:

[0089] 1) The residue and filtrate are obtained by nanofiltration through nanofiltration membrane device 3. The residue is a crude caramel coloring solution with a xylose content of 40-50 g / L, a xylose concentration of 4-5%, and a xylose purity of 25-30%.

[0090] 2) The crude caramel coloring liquid enters the outer barrel 81 of the double-barrel centrifuge device 8 in a tangential direction. Through the transfer pump, the crude caramel coloring liquid obtains an initial centrifugal rotation speed.

[0091] 3) The crude caramel coloring liquid enters the bottom of the outer barrel 81 through the cavity 82, and then enters the inner barrel 80 through the through hole 86 on the inner barrel 80; the stirring mechanism 84 and the dispersing plate 85 inside the inner barrel 80 rotate to help the crude caramel coloring liquid rotate in the inner barrel 80 and form a heavy phase zone, a mixing zone and a light phase zone.

[0092] 4) A light phase liquid outlet pipe 14 and a heavy phase impurity outlet are provided at the upper part of the inner barrel 80. Since the height-to-diameter ratio of the inner barrel 80 is 5-10:1, during the residence of the crude caramel coloring liquid in the inner barrel 80, the light phase of the semi-refined caramel coloring liquid tends to be distributed within the inner diameter of the inner barrel 80, while the heavy phase impurities tend to be distributed on the inner wall of the inner barrel 80. Therefore, the light phase liquid outlet pipe 14 is used to ultimately achieve the purpose of extracting the caramel coloring liquid. Since the inner and outer barrels 81 are designed as sealed tanks, the centrifugal force added to the outer barrel 81 will push the crude caramel coloring liquid to continuously and automatically discharge the liquids corresponding to the light and heavy phase zones, ultimately achieving the refining of the crude caramel coloring liquid. Preferably, there are three double-barrel centrifuge devices 8. The heavy phase liquid outlet 88 of the upper-stage double-barrel centrifuge device 8 is connected to the feed inlet of the lower-stage double-barrel centrifuge device 8, ultimately achieving the recovery of caramel coloring in the heavy phase impurities, thereby improving the yield of caramel coloring.

[0093] Example 5

[0094] Based on Example 1, this example selects four batches of xylose mother liquor, heats them at 80°C, and then passes them through a nanofiltration membrane device to obtain a retentate (a crude caramel coloring solution - a low-concentration caramel coloring solution, which, after concentration, forms a high-concentration caramel coloring solution) and a filtrate. The amount of water added and the test results are shown in Table 2 and... Figure 3 As shown.

[0095]

Claims

1. A process for preparing caramel color, characterized in that, Includes the following steps: S1: Using xylose mother liquor as raw material, heat to 75-85℃; S2: The heated material is passed into a nanofiltration membrane device and nanofiltration is performed using a nanofiltration membrane with a molecular weight of less than 300 to obtain filtrate and filtrate. The filtrate is crude caramel coloring liquid. The threshing liquid contains 40–50 g / L xylose, has a xylose concentration of 4–5%, and a xylose purity of 25–30%. The threshing liquid has a refractive index of 15–20 and a conductivity of 25,000–30,000 μS / cm. S3: Using a double-barrel centrifuge device, the obtained threshing liquid is centrifuged and then allowed to stand to obtain refined caramel coloring liquid. The double-barrel centrifuge device (8) includes an inner barrel (80) and an outer barrel (81) sleeved outside the inner barrel (80). The inner barrel (80) and the outer barrel (81) are arranged on the same central axis. A cavity (82) for the flow of crude caramel coloring liquid is formed between the outer wall of the inner barrel (80) and the inner wall of the outer barrel (81). The upper part of the outer barrel (81) is provided with a crude caramel coloring liquid inlet (83), and the intercepting liquid outlet is connected to the crude caramel coloring liquid inlet (83) through a transfer pump; The inner barrel (80) is equipped with a stirring mechanism (84), and a dispersing plate (85) is provided at the bottom of the stirring mechanism (84); through holes (86) communicating with the cavity (82) are distributed on the lower wall of the inner barrel (80); a light phase liquid outlet (87) and a heavy phase liquid outlet (88) are provided at the upper part of the inner barrel (80); the light phase liquid outlet (87) extends towards the central axis through one end of the light phase liquid outlet pipe (14), and the other end of the light phase liquid outlet pipe (14) is connected to the settling barrel (9); The heavy phase liquid outlet (88) is located above the light phase liquid outlet (87); S4: Evaporate and concentrate the obtained refined caramel color solution to a refractive index ≥70, and dry it to obtain refined caramel color powder; The product specifications for the caramel color include: color index ≥33000, refractive index ≥70, ammonia nitrogen ≤0.005%, sulfur dioxide ≤0.002%, arsenic ≤0.05mg / L, lead ≤0.05mg / L, other heavy metals ≤0.1mg / L, and 4-methylimidazole not detected.

2. The preparation process of caramel color according to claim 1, characterized in that, The xylose mother liquor comprises xylose at a concentration of 40-50%, mannose at a concentration of 15-25%, glucose at a concentration of 8-12%, and xylan at a concentration of 8-12%.

3. The preparation process of caramel color according to claim 1, characterized in that, In the nanofiltration membrane device in step S2, the temperature is controlled at 40–45°C and the pressure at 28–32 bar.

4. The preparation process of caramel color according to claim 3, characterized in that, In step S2, the filtrate contains xylose at a concentration of 50-60 g / L, has a refractive index of 10-13, and a conductivity of 200-300 μs / cm; the filtrate is then directly reused in step S1.

5. The preparation process of caramel color according to claim 1, characterized in that, In step S3, the centrifugation speed is 60-200 r / min, and the settling time is 10-30 min.

6. The preparation process of caramel color according to claim 1, characterized in that, In step S4, an Mvr evaporator is used for evaporation and concentration, and the temperature inside the Mvr evaporator is controlled at 65-75℃ and the negative pressure is 0.040-0.050MPa.

7. A system for preparing caramel color, characterized in that, In the preparation process described in any one of claims 1-6, the preparation system includes a heating tank (2), a nanofiltration membrane device (3), a double-barrel centrifuge device (8), a settling tank (9), and an Mvr evaporation device (5). The feed inlet of the heating tank (2) is connected to the raw material storage tank (1), and the raw material storage tank (1) is connected to the xylose mother liquor outlet in the xylose production system. The nanofiltration membrane device (3) is located behind the work station of the heating tank (2), and the heating tank (2) is connected to the nanofiltration membrane device (3); The double-barrel centrifuge (8) is located behind the station of the nanofiltration membrane device (3), and the throttling liquid outlet on the nanofiltration membrane device (3) is connected to the double-barrel centrifuge (8). The settling tank (9) is located at the rear of the station of the double-barrel centrifuge (8), and the light phase liquid outlet (87) of the double-barrel centrifuge (8) is connected to the settling tank (9). The Mvr evaporation device (5) is located behind the station of the settling tank (9). The settling tank (9) is connected to the Mvr evaporation device (5), and the Mvr evaporation device (5) is connected to the caramel color product storage tank (6). A continuous pathway for the preparation and preservation of caramel color is formed between the raw material storage tank (1), heating tank (2), nanofiltration membrane device (3), double-barrel centrifuge device (8), settling tank (9), Mvr evaporation device (5) and caramel color product storage tank (6).

8. The caramel color preparation system according to claim 7, characterized in that, The nanofiltration membrane device (3) is also provided with a filtrate storage tank (7) at the rear of the station. The filtrate outlet on the nanofiltration membrane device (3) is connected to the filtrate storage tank (7), and the filtrate storage tank (7) is connected to the raw material storage tank (1) and / or the heating tank (2).

9. The caramel color preparation system according to claim 7, characterized in that, The height-to-diameter ratio of the inner barrel (80) is 5 to 10:1.

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