Alumina hydroxide adjuvant with pseudo-boehmite crystal structure and controllable particle size and preparation method thereof

Abstract

The present application relates to the technical field of vaccine adjuvant preparation, and discloses an aluminum hydroxide adjuvant with boehmite crystal structure and controllable particle size and a preparation method thereof. The Z-average hydrodynamic particle size of the adjuvant particles measured by dynamic light scattering is 200-350 nm, the polydispersity index is not greater than 0.20, the particle size intensity distribution is unimodal, and the adjuvant particles do not contain bayerite and gibbsite within the detection limit of X-ray diffraction. In the preparation, an aluminum salt solution and an alkali solution are separately sent into a boehmite seed crystal dispersion liquid through multiple independent rapid mixing units, the pH and its difference at each mixing position are controlled, a front-fast and rear-slow staged feeding mode is adopted, the ripening end point is determined according to the particle size and the polydispersity index, and rapid cooling is performed after the ripening end point is reached. The method can coordinate the processes of precipitation nucleation, crystal phase conversion and grain growth, and is conducive to improving the preparation stability and process amplification consistency of the target particle size product.

Description

Technical Field

[0001] This invention relates to the field of aluminum hydroxide adjuvant technology, specifically to an aluminum hydroxide adjuvant with a pseudo-boehmite crystal structure and controllable particle size, and its preparation method. Background Technology

[0002] Aluminum hydroxide adjuvant is one of the commonly used inorganic adjuvants in vaccine formulations. The aluminum hydroxide used as a vaccine adjuvant is usually not the ideal stoichiometric aluminum hydroxide trihydrate crystal, but rather has a low crystallinity hydrated alumina as its main structure. Among them, boehmite-type aluminum hydroxide has a relatively loose layered structure and more surface hydroxyl groups, which can be used to adsorb protein, peptide or polysaccharide antigens.

[0003] Existing boehmite-type aluminum hydroxide adjuvants are typically prepared by neutralizing and precipitating aluminum salts with alkali, followed by aging, washing, and redispersing. During the neutralization and precipitation process, aluminum ions and hydroxide ions initially form amorphous or low-order aluminum hydroxide precursors upon contact. These precursors gradually transform into a boehmite structure during subsequent aging. In this process, precipitate nucleation, precursor phase transformation, grain growth, and particle aggregation occur simultaneously and are all influenced by aluminum salt concentration, alkali concentration, local pH, mixing time, reaction temperature, and aging time. While shorter aging times help limit further particle growth, the resulting precipitate tends to retain more amorphous aluminum hydroxide, resulting in an unstable boehmite crystal structure. Extending the aging time, while improving the orderliness of the boehmite structure, intensifies the maturation process, leading to the dissolution of small particles and their migration to larger particles. This can cause particle sizes to exceed the predetermined range and result in a wider particle size distribution. Especially for the submicron particle size range of 200-350nm, insufficient aging can easily result in particles smaller than this range, while excessive aging can easily result in particles larger than 350nm. Therefore, it is difficult to stably obtain products with the target particle size by simply fixing the aging time.

[0004] Furthermore, the neutralization reaction between aluminum salts and alkali solutions is relatively rapid. When using single-point addition or direct addition of alkali solution to the aluminum salt solution, instantaneous high concentrations and localized high pH levels are prone to occur near the feed site, causing nucleation of precipitates at different locations under varying degrees of supersaturation. Excessively high local supersaturation leads to the formation of numerous fine particles, while insufficient local mixing easily results in the formation of larger aggregates, resulting in a bimodal distribution of products with both large and small particles. When the local pH deviates from the conditions for boehmite formation, it may also induce the formation of impurities such as Bayerite or gibbsite. Simply detecting and adjusting the macroscopic average pH within the reactor is insufficient to reflect the instantaneous pH differences near each feed site in a timely manner. During process scale-up, changes in reactor size, stirring power, circulation flow rate, and feed site make it difficult to maintain consistency between the mixing timescale of aluminum salts and alkali solutions and laboratory conditions. The concentration and pH gradients formed by single-point feeding intensify with increasing reactor volume, leading to inconsistent nucleation times in different regions, which in turn causes particle size drift and batch-to-batch variations. Summary of the Invention

[0005] The purpose of this invention is to provide an aluminum hydroxide adjuvant with a pseudo-boehmite crystal structure and controllable particle size, and its preparation method, thereby solving the problems existing in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: an aluminum hydroxide adjuvant with a pseudo-boehmite crystal structure and controllable particle size, wherein the aluminum hydroxide adjuvant comprises aluminum hydroxide particles dispersed in an aqueous medium; The aluminum hydroxide particles have a pseudo-boehmite crystal structure and do not contain Bayerite or gibbsite crystal phases within the X-ray diffraction detection limit. The Z-mean hydrodynamic particle size of the aluminum hydroxide particles was measured to be 200–350 nm using dynamic light scattering method. The polydispersity index was not greater than 0.20, and the particle size intensity distribution showed a single peak.

[0007] Specifically, in the particle number distribution measured by the nanoparticle tracking analysis method, the proportion of particles with a diameter of 200-350 nm is not less than 80% of the total number of particles.

[0008] Specifically, the total number of particles with a diameter less than 180 nm and particles with a diameter greater than 400 nm shall not exceed 10% of the total number of particles.

[0009] Specifically, the pH of the aluminum hydroxide adjuvant is 6.0 to 7.2, and the aqueous medium includes at least one of water for injection, sodium chloride aqueous solution, or phosphate buffer.

[0010] On the other hand, the present invention also provides a method for preparing aluminum hydroxide adjuvant, comprising the following steps: S1. Disperse the pseudoboehmite seed crystals in an aqueous medium to obtain a seed crystal dispersion; S2. The aluminum salt solution and the alkaline solution are divided into at least two aluminum salt sub-streams and an alkaline sub-stream, respectively, so that each aluminum salt sub-stream is mixed with the corresponding alkaline sub-stream in an independent rapid mixing unit, and the mixture stream formed by each rapid mixing unit is fed into the seed crystal dispersion from different positions in the reactor. During the addition of the aluminum salt solution and the alkaline solution, the pH at the outlet or corresponding sampling position of each rapid mixing unit is controlled to be 6.4 to 7.6, and the pH difference between any two outlets or corresponding sampling positions is not greater than 0.20. The precipitation reaction temperature is 50 to 70°C. The process of adding the aluminum salt solution includes a first feeding stage and a second feeding stage. In the first feeding stage, the amount of aluminum added is 5-25 mol% of the total aluminum content in the aluminum salt solution, and the aluminum feeding rate per unit effective reactor volume in the first feeding stage is q1. In the second feeding stage, the remaining aluminum salt solution is added, and the aluminum feeding rate q2 per unit effective reactor volume in the second feeding stage is 25-60% of the aluminum feeding rate q1. S3. After the aluminum salt solution is added, the resulting precipitate slurry is aged at 65-85°C, and the hydrodynamic particle size of the aluminum hydroxide particles in the precipitate slurry is monitored during the aging process. When the Z-average hydrodynamic particle size of the aluminum hydroxide particles reaches 230-320 nm and the polydispersity index is not greater than 0.20, the precipitated slurry is cooled to no higher than 40°C within 20 min to terminate the curing process. S4. The cooled precipitated slurry is subjected to solid-liquid separation, washing, and redispersing to obtain the aluminum hydroxide adjuvant.

[0011] Specifically, the Z-average hydrodynamic particle size of the pseudoboehmite seed crystal is 20-100 nm, and the amount of the pseudoboehmite seed crystal added is 0.1-3.0 wt% based on the theoretical mass of alumina in the final product.

[0012] Specifically, the aluminum salt is selected from at least one of aluminum chloride, aluminum nitrate, and aluminum sulfate, and the alkali is selected from at least one of sodium hydroxide, potassium hydroxide, and ammonia water; The concentration of aluminum ions in the aluminum salt solution is 0.10–0.60 mol / L, and the alkali equivalent concentration of the alkali solution is 0.30–2.00 mol / L.

[0013] Specifically, the rapid mixing unit is selected from at least one of a static mixer, an impingement flow mixer, a rotor-stator mixer, and a microchannel mixer, and the effective mixing time of the aluminum salt sub-stream and the alkali sub-stream in the rapid mixing unit is 0.02 to 1.00 s.

[0014] Specifically, the number of rapid mixing units is 2 to 8, and the mixture inlet corresponding to each rapid mixing unit is arranged at intervals along the circumferential and / or axial direction of the reactor; The actual flow rate of each aluminum salt sub-flow rate deviates from the average flow rate of the aluminum salt sub-flow rate by no more than 10%, and the actual flow rate of each alkali sub-flow rate deviates from the average flow rate of the alkali sub-flow rate by no more than 10%.

[0015] Specifically, the maturation temperature is 70-80℃, and the pH of the precipitated slurry during the maturation process is 6.8-7.5; after the maturation termination condition is reached, the precipitated slurry is cooled to 20-35℃ within 5-15 minutes.

[0016] Specifically, in step S4, the precipitated slurry is subjected to solid-liquid separation and washing using tangential flow filtration or dialysis filtration, and the washed precipitate is redispersed using water for injection or sodium chloride aqueous solution.

[0017] Specifically, the pH at the outlet or sampling position of the corresponding rapid mixing unit is controlled by adjusting the flow rate of each alkaline sub-stream. The pH value at each outlet or sampling position is continuously collected during the first and second feeding stages, and the flow rate of the corresponding alkaline sub-stream is adjusted based on the collected pH value.

[0018] As can be seen from the above technical solution, the present invention has the following beneficial effects: This method for preparing an aluminum hydroxide adjuvant with a pseudoboehmite crystal structure and controllable particle size involves directional precipitation in the presence of pseudoboehmite seed crystals. The aluminum salt solution and alkaline solution are separately diverted and initially mixed in multiple independent rapid mixing units. Simultaneously controlling the pH at each mixing location and their differences reduces localized supersaturation and pH shifts caused by single-point feeding, allowing precursors to preferentially form on the surface of the pseudoboehmite seed crystals. By employing a staged aluminum feed rate that is higher in the initial stage and lower in the later stage, a relatively stable number of growth nuclei can be established in the initial stage, limiting secondary nucleation and subsequent formation. Disordered aggregation between particles; by monitoring the Z-average hydrodynamic particle size and polydispersity index during the aging process, and rapidly cooling after reaching the set particle size window, insufficient aging or excessive growth caused by fixed aging time can be avoided, thus facilitating the acquisition of boehmite-type aluminum hydroxide adjuvants with a particle size of 200-350 nm, a polydispersity index of no more than 0.20, a single-peaked particle size distribution, and no Bayerite or gibbsite within the X-ray diffraction detection limit; by adopting a unit effective volume feed rate and multi-point independent feedback control, reactors of different sizes can also have similar local mixing conditions, improving particle size consistency during process scale-up. Attached Figure Description

[0019] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0020] 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. 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.

[0021] Example 1: like Figure 1 As shown, the present invention provides a technical solution: An aluminum hydroxide adjuvant with a pseudo-boehmite crystal structure and controllable particle size, the aluminum hydroxide adjuvant comprising aluminum hydroxide particles dispersed in an aqueous medium; The aluminum hydroxide particles have a pseudo-boehmite crystal structure and do not contain Bayerite or gibbsite crystal phases within the X-ray diffraction detection limit. The Z-mean hydrodynamic particle size of the aluminum hydroxide particles was measured to be 200–350 nm using dynamic light scattering method. The polydispersity index was not greater than 0.20, and the particle size intensity distribution showed a single peak.

[0022] 1. Terminology Explanation The aluminum hydroxide adjuvant in this invention refers to an aqueous alumina dispersion system that can be used as an antigen adsorption carrier, including an aqueous dispersion with AlOOH·nH2O as the main solid phase with a pseudo-boehmite structure, and does not require it to have an Al(OH)3 composition with an ideal stoichiometric ratio.

[0023] The “pseudo-boehmite crystal structure” referred to in this invention refers to a low-crystallinity hydrated alumina structure that exhibits broadened diffraction peaks characteristic of pseudo-boehmite as detected by X-ray diffraction.

[0024] In this invention, "not detected Bayerite and gibbsite" means that, under the specified sample preparation method, instrument conditions, and quantitative method, the contents of both Bayerite and gibbsite are below the method detection limit. In the following embodiments, a combined content of 2 wt% for Bayerite and gibbsite is used as the suggested detection limit. The actual detection limit should be verified by the instrument and analytical method used.

[0025] The "aluminum feeding rate q per unit effective reactor volume" referred to in this invention is calculated according to the following formula: q = Total feed flow rate of aluminum salt solution / Effective working volume of reactor.

[0026] The aluminum feeding rate per unit effective volume in the first feeding stage is denoted as q1, and the aluminum feeding rate per unit effective volume in the second feeding stage is denoted as q2.

[0027] 2. Detection Method 2.1 Dynamic light scattering detection The aluminum hydroxide adjuvant to be tested was diluted with an aqueous medium of the same composition as its continuous phase to achieve a concentration of 0.10 mg / mL based on aluminum element. After equilibration at 25 °C for 2 min, dynamic light scattering detection was performed. Each sample was measured three times consecutively, and the average of the three measurements was taken. The Z-mean hydrodynamic particle size and polydispersity index were calculated using the cumulative method.

[0028] All examples and comparative examples used the same dilution factor, dispersion medium, equilibration time, and instrument parameters. Samples were only slowly inverted and mixed before testing, without ultrasonic treatment, to avoid any additional impact of ultrasonic treatment on particle aggregation.

[0029] When the particle size intensity distribution shows only one distinguishable main peak, it is determined to be a unimodal distribution; when two separate particle size peaks with identifiable intensities appear, it is determined to be a bimodal distribution.

[0030] 2.2 Nanoparticle Tracking Analysis The sample was diluted with the same continuous phase as in dynamic light scattering detection to ensure the particle concentration was within the instrument's recommended detection range. Five video segments were acquired for each sample, with each segment lasting 60 seconds. The percentage of particles between 200 and 350 nm and the combined percentage of particles smaller than 180 nm and larger than 400 nm were calculated based on the particle number distribution.

[0031] 2.3 Crystal Phase Detection The aluminum hydroxide adjuvant sample was centrifuged, washed twice with water for injection, and then freeze-dried. The resulting dried sample was then ground into a fine powder and analyzed by powder X-ray diffraction.

[0032] The X-ray source used was CuKα radiation, with a scanning range of 5°–70° and a step size of 0.02°. Phase identification was performed based on the standard diffraction patterns of boehmite, bayonet, and gibbsite. For quantitative analysis, a known amount of internal standard was added, and quantification was performed using a full-spectrum fitting method.

[0033] 2.4 Multi-point pH detection Temperature-compensated pH detection units are installed at the outlet pipes of each rapid mixing unit or at the corresponding reactor feed location. The pH value at each detection location is continuously recorded during the feeding process, with data recorded every 10 seconds.

[0034] The difference between the highest and lowest pH values ​​at any given time and location is taken as the multi-point pH difference at that time. The maximum multi-point pH difference that occurs during the feeding process is taken as the maximum pH difference for that batch.

[0035] 3. Preparation of pseudo-boehmite seed crystals The following examples use a pre-prepared and tested qualified boehmite seed crystal dispersion. The Z-mean hydrodynamic particle size of the boehmite particles in the seed crystal dispersion is controlled to be 70-95 nm, the polydispersity index is not greater than 0.20, and no detectable Bayerite and gibbsite characteristic peaks appear in the X-ray diffraction pattern.

[0036] A feasible method for preparing seed crystals is as follows: A 0.10 mol / L aluminum chloride aqueous solution and a 0.30 mol / L sodium hydroxide aqueous solution were heated to 60 °C respectively. The solutions were then introduced into a static mixer at a flow rate that maintained the pH of the mixture at 6.7–7.0. The effective mixing time in the static mixer was controlled to be 0.05–0.20 s. The mixture was collected into a stirred container and stirred at 60 °C for 10 min, followed by heating to 70 °C and maintaining this temperature for 15–25 min.

[0037] After maturation, the slurry was cooled to no higher than 35°C, washed using tangential flow filtration, and redispersed with water for injection. Dynamic light scattering and X-ray diffraction were performed on the seed crystal dispersion. Batches with a Z-average hydrodynamic particle size of 70–95 nm, a polydispersity index of no more than 0.20, and no detectable Bayerite or gibbsite were selected as seed crystals for subsequent reactions.

[0038] The amount of seed crystal added is calculated as a percentage of the equivalent mass of alumina in the seed crystal to the theoretical mass of alumina in the final product.

[0039] 4. Example 1 4.1 Raw materials and equipment A jacketed reactor with an effective working volume of 5.0L is used, and the reactor is equipped with a paddle agitator and two independent static mixing units. The two mixture inlets are arranged opposite each other along the circumference of the reactor.

[0040] Prepare 2.0 L of 0.30 mol / L aluminum chloride solution and 2.0 L of 0.90 mol / L sodium hydroxide solution. Both solutions are prepared with water for injection and filtered.

[0041] The aluminum chloride solution contains 0.60 mol of aluminum, corresponding to a theoretical alumina mass of approximately 30.6 g. 1.0 L of water for injection is added to the reactor, along with 0.306 g of pseudoboehmite seed crystals (equivalent to 1.0 wt% of the theoretical alumina mass). Stirring is started, and the seed crystal dispersion is heated to 60 °C.

[0042] 4.2 Staged sedimentation The aluminum chloride solution and sodium hydroxide solution were each divided into two equal streams, with one aluminum chloride stream and one sodium hydroxide stream entering a static mixing unit. By adjusting the flow rates of the two sodium hydroxide streams, the pH at the outlet of both mixing units was maintained between 6.80 and 7.00.

[0043] In the first feeding stage, 15% of the total aluminum chloride solution, or 300 mL, is added. The total feed flow rate of the aluminum chloride solution in the first feeding stage is 120 mL / min, and the aluminum chloride sub-flow rate corresponding to each static mixing unit is 60 mL / min.

[0044] After the first feeding stage, the total feed flow rate of the aluminum chloride solution is reduced to 50 mL / min, the aluminum chloride sub-flow rate corresponding to each static mixing unit is 25 mL / min, and the remaining 1700 mL of aluminum chloride solution is added. Therefore, the ratio of q2 to q1 is approximately 0.42.

[0045] During the feeding process, maintain the reaction temperature at 60±2℃ and the stirring speed at 350 r / min. The maximum pH difference between the two mixing points should be controlled to be no greater than 0.15.

[0046] 4.3 Maturation and Termination After feeding, the precipitated slurry is heated to 74°C for maturation. Samples are taken every 10 minutes to test the Z-average hydrodynamic particle size and polydispersity index.

[0047] When the average hydrodynamic particle size reaches 260–290 nm and the polydispersity index is not greater than 0.20, heating is stopped and a cooling medium is introduced to reduce the slurry temperature to no higher than 35 °C within 15 minutes.

[0048] 4.4 Washing and redispersion The cooled precipitated slurry was washed using a tangential flow filter with a molecular weight cutoff of 100 kDa. The washing solution was water for injection, and the washing volume was 5 times the initial slurry volume.

[0049] After washing, the adjuvant dispersion was redispersed using an aqueous solution containing 0.85 wt% sodium chloride to adjust the aluminum concentration of the adjuvant dispersion to 2.0 mg / mL and the pH to 6.5–6.8, thus obtaining aluminum hydroxide adjuvant.

[0050] 5. Example 2 The main differences between this embodiment and Embodiment 1 are the amount of seed crystal added, the feeding rate of the second feeding stage, and the maturation endpoint.

[0051] The amount of pseudoboehmite seed crystals added is 2.0 wt% of the theoretical alumina mass, and 10% of the total amount of aluminum chloride solution is added in the first feeding stage. The total feed flow rate of aluminum chloride solution in the first feeding stage is 100 mL / min, and the total feed flow rate of aluminum chloride solution in the second feeding stage is 35 mL / min. The ratio of q2 to q1 is 0.35.

[0052] The precipitation reaction temperature was 58℃, and the pH at each rapid mixing point was controlled at 6.70 to 6.95, with a maximum pH difference of no more than 0.18.

[0053] After feeding, the slurry is heated to 70°C for maturation. When the Z-average hydrodynamic particle size reaches 230–255 nm and the polydispersity index is not greater than 0.20, the slurry is cooled to no higher than 35°C within 15 minutes. The washing and redispersion methods are the same as in Example 1.

[0054] 6. Example 3 The main differences between this embodiment and Embodiment 1 are the amount of seed crystal added, the proportion of aluminum added in the first feeding stage, the feeding rate in the second feeding stage, and the maturation conditions.

[0055] The amount of pseudoboehmite seed crystals added is 0.5 wt% of the theoretical alumina mass, and 20% of the total amount of aluminum chloride solution is added in the first feeding stage. The total feed flow rate of aluminum chloride solution in the first feeding stage is 100 mL / min, and the total feed flow rate of aluminum chloride solution in the second feeding stage is 55 mL / min. The ratio of q2 to q1 is 0.55.

[0056] The precipitation reaction temperature was 63℃, and the pH at each rapid mixing point was controlled at 6.95 to 7.15, with a maximum pH difference of no more than 0.18.

[0057] After feeding, the slurry is heated to 78°C for maturation. When the Z-average hydrodynamic particle size reaches 300–320 nm and the polydispersity index is not greater than 0.20, the slurry is cooled to no higher than 35°C within 20 minutes. The washing and redispersion methods are the same as in Example 1.

[0058] 7. Example 4: Scaled-up implementation A jacketed reactor with an effective working volume of 50L is used, and four independent static mixing units are set in the reactor. The four mixture inlets are evenly distributed along the circumference of the reactor, with two inlets located at the lower part of the effective liquid level and the other two inlets located at the middle part of the effective liquid level.

[0059] Prepare 20 L of 0.30 mol / L aluminum chloride solution and 20 L of 0.90 mol / L sodium hydroxide solution. Add 10 L of water for injection to the reactor, and add 3.06 g of boehmite seed crystals based on the mass of alumina, which is 1.0 wt% of the theoretical alumina mass.

[0060] In the first feeding stage, 15% of the total amount of aluminum chloride solution is added, the total feed flow rate of aluminum chloride solution is 1.20 L / min, and the aluminum chloride sub-flow rate corresponding to each static mixing unit is 0.30 L / min.

[0061] In the second feeding stage, the remaining aluminum chloride solution is added, reducing the total feed flow rate of the aluminum chloride solution to 0.50 L / min. The aluminum chloride sub-flow rate corresponding to each static mixing unit is 0.125 L / min. The ratio of q2 to q1 is approximately 0.42.

[0062] The aluminum feeding rate per unit effective volume in the first and second feeding stages remained consistent with that in Example 1. The flow rates of the corresponding sodium hydroxide sub-streams were adjusted using four independent feedback loops to maintain the pH at the four mixing locations between 6.80 and 7.00, with a maximum pH difference not exceeding 0.20.

[0063] The precipitation reaction temperature is 60±2℃. After feeding, the slurry is heated to 74℃ for maturation. When the Z-average hydrodynamic particle size reaches 260~300nm and the polydispersity index is not greater than 0.20, the slurry is cooled to no higher than 35℃ within 20min.

[0064] Three batches were run consecutively under the above conditions to verify the batch-to-batch particle size consistency under scale-up conditions.

[0065] 8. Verification results of the examples Table 1 Validation Results of Examples

[0066] Based on the above exemplary expected values, the average Z-mean hydrodynamic particle size of the three batches in Example 4 was approximately 284 nm, and the relative standard deviation between batches was approximately 3.1%.

[0067] 9. Comparative Example 1: No addition of pseudo-boehmite seed crystals Except for not adding pseudo-boehmite seed crystals to the initial aqueous medium, the other operating conditions are the same as in Example 1.

[0068] After feeding, the material was still aged at 74°C, and samples were taken at the same time as in Example 1. This comparative example was used to investigate the effect of precipitate nucleation on crystal phase formation and particle size distribution in the absence of directional seed crystals.

[0069] The product contains a large number of small-diameter particles and some larger aggregated particles, with an increased polydispersity index; the characteristic peaks of pseudoboehmite in the X-ray diffraction pattern are relatively broad, and it may retain a relatively obvious amorphous diffuse background.

[0070] 10. Comparative Example 2: Single-point feed and control of only the macroscopic pH of the reactor The same raw material composition and seed crystal addition amount as in Example 1 were used, but only one feed point was set up. Aluminum chloride solution and sodium hydroxide solution entered the reactor through a static mixing unit.

[0071] During the feeding process, the flow rate of the sodium hydroxide solution was adjusted only based on a pH reading at the center of the reactor to maintain the macroscopic pH of the reactor between 6.8 and 7.0. No independent detection or feedback control of the pH near the feed point was performed. All other operating conditions were the same as in Example 1.

[0072] This comparative example is used to investigate the effect of local pH fluctuations on particle size distribution and impurity crystal formation under single-point feed conditions. It is recommended to install temporary pH probes at the outlet of the static mixing unit and at a location far from the feed point, solely for recording local pH differences and not for feedback regulation.

[0073] 11. Comparative Example 3: The same high feeding rate was used throughout the entire feeding process. The same raw material composition, seed crystal addition amount, two static mixing units and multi-point pH feedback method as in Example 1 were used, but a second feeding stage was not set.

[0074] All aluminum chloride solutions were added at a total flow rate of 120 mL / min, meaning the entire feeding process followed the aluminum feeding rate of the first feeding stage in Example 1. The aging, cooling, washing, and redispersion conditions after feeding were the same as in Example 1.

[0075] This comparative example is used to examine the effect of continuous secondary nucleation on the final particle size when a high feeding rate is maintained in the subsequent growth stage.

[0076] 12. Comparative Example 4: Using a fixed long-term aging process The sedimentation process was the same as in Example 1, but the maturation endpoint was not determined based on particle size and polydispersity index. After feeding, the slurry was fixed and matured at 74°C for 110 min, and then cooled, washed and redispersed as in Example 1.

[0077] This comparative example is used to examine the effect of prolonged ripening on the continued growth of particles when no particle size-triggered ripening endpoint is set.

[0078] Table 2. Validation results of the comparative examples

[0079] In the above comparative examples, Comparative Example 1 was used to verify the effect of seed crystals on synchronous nucleation and crystal phase transformation; Comparative Example 2 was used to verify the effect of multi-point mixing and local pH feedback on suppressing impurity crystals and bimodal particle size distribution; Comparative Example 3 was used to verify the effect of reducing the feeding rate in stages on reducing secondary nucleation in the later stage; Comparative Example 4 was used to verify the effect of terminating ripening according to particle size on limiting excessive particle growth compared to fixed long-term ripening.

[0080] In the above embodiments, the aluminum salt can be aluminum chloride, aluminum nitrate, or aluminum sulfate. Considering that different anions will affect the ionic strength and particle surface state of the system, when changing the aluminum salt, the alkali concentration, feed flow rate, and washing volume should be re-determined, and it is not advisable to directly use all the parameters of the aluminum chloride system.

[0081] The alkali can be sodium hydroxide, potassium hydroxide, or ammonia. When using ammonia, because its alkalinity and volatility differ from strong alkalis, the ammonia flow rate should be determined through actual titration, and the residual ammonia content should be tested after washing.

[0082] The rapid mixing unit can be a static mixer, an impingement flow mixer, a rotor-stator mixer, or a microchannel mixer. When selecting a rapid mixing unit, the aluminum salt sub-stream and the alkali sub-stream should be initially mixed before entering the main reactor body, and the effective mixing time should be between 0.02 and 1.00 s. When the reactor size changes, the aluminum feed rates q1 and q2 per unit effective volume should preferably be kept consistent with the example, while increasing the number of rapid mixing units according to the reactor diameter and effective liquid level. The deviation of the actual flow rate of each feed branch from the average flow rate of each branch is preferably no more than 10%.

[0083] The maturation endpoint is not determined solely by a fixed time. The required maturation time may vary depending on the equipment, raw material batch, and seed crystal batch. However, under the same testing conditions, the primary criterion for terminating maturation should be achieving the specified range for the Z-mean hydrodynamic particle size and polydispersity index. To avoid irreversible aggregation caused by drying, the aluminum hydroxide adjuvant of this invention is preferably stored in aqueous dispersion form. Before validation, high-pressure steam sterilization is not considered a necessary step for obtaining the target particle size product in this invention. When used in vaccine formulation production, sterile raw materials, closed-system aseptic preparation, or sterilization processes validated to not cause particle size to exceed the specified range can be used.

[0084] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An aluminum hydroxide adjuvant with a pseudo-boehmite crystal structure and controllable particle size, characterized in that, The aluminum hydroxide adjuvant comprises aluminum hydroxide particles dispersed in an aqueous medium; The aluminum hydroxide particles have a pseudo-boehmite crystal structure and do not contain Bayerite or gibbsite crystal phases within the X-ray diffraction detection limit. The Z-mean hydrodynamic particle size of the aluminum hydroxide particles was measured to be 200–350 nm using dynamic light scattering method. The polydispersity index was not greater than 0.20, and the particle size intensity distribution showed a single peak.

2. The aluminum hydroxide adjuvant according to claim 1, characterized in that, In the particle number distribution measured by nanoparticle tracking analysis, the proportion of particles with a diameter of 200-350 nm is not less than 80% of the total number of particles.

3. The aluminum hydroxide adjuvant according to claim 2, characterized in that, The total number of particles with a diameter less than 180 nm and particles with a diameter greater than 400 nm shall not exceed 10% of the total number of particles.

4. The aluminum hydroxide adjuvant according to claim 1, characterized in that, The pH of the aluminum hydroxide adjuvant is 6.0 to 7.2, and the aqueous medium includes at least one of water for injection, sodium chloride aqueous solution, or phosphate buffer.

5. A method for preparing the aluminum hydroxide adjuvant according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Disperse the pseudoboehmite seed crystals in an aqueous medium to obtain a seed crystal dispersion; S2. The aluminum salt solution and the alkaline solution are divided into at least two aluminum salt sub-streams and an alkaline sub-stream, respectively, so that each aluminum salt sub-stream is mixed with the corresponding alkaline sub-stream in an independent rapid mixing unit, and the mixture stream formed by each rapid mixing unit is fed into the seed crystal dispersion from different positions in the reactor. During the addition of the aluminum salt solution and the alkaline solution, the pH at the outlet or corresponding sampling position of each rapid mixing unit is controlled to be 6.4 to 7.6, and the pH difference between any two outlets or corresponding sampling positions is not greater than 0.

20. The precipitation reaction temperature is 50 to 70°C. The process of adding the aluminum salt solution includes a first feeding stage and a second feeding stage. In the first feeding stage, the amount of aluminum added is 5-25 mol% of the total aluminum content in the aluminum salt solution, and the aluminum feeding rate per unit effective reactor volume in the first feeding stage is q1. In the second feeding stage, the remaining aluminum salt solution is added, and the aluminum feeding rate q2 per unit effective reactor volume in the second feeding stage is 25-60% of the aluminum feeding rate q1. S3. After the aluminum salt solution is added, the resulting precipitate slurry is aged at 65-85°C, and the hydrodynamic particle size of the aluminum hydroxide particles in the precipitate slurry is monitored during the aging process. When the Z-average hydrodynamic particle size of the aluminum hydroxide particles reaches 230-320 nm and the polydispersity index is not greater than 0.20, the precipitated slurry is cooled to no higher than 40°C within 20 min to terminate the curing process. S4. The cooled precipitated slurry is subjected to solid-liquid separation, washing, and redispersing to obtain the aluminum hydroxide adjuvant.

6. The preparation method according to claim 5, characterized in that, The Z-average hydrodynamic particle size of the pseudoboehmite seed crystal is 20-100 nm, and the amount of the pseudoboehmite seed crystal added is 0.1-3.0 wt% based on the theoretical mass of alumina in the final product.

7. The preparation method according to claim 5, characterized in that, The aluminum salt is selected from at least one of aluminum chloride, aluminum nitrate and aluminum sulfate, and the alkali is selected from at least one of sodium hydroxide, potassium hydroxide and ammonia water; The concentration of aluminum ions in the aluminum salt solution is 0.10–0.60 mol / L, and the alkali equivalent concentration of the alkali solution is 0.30–2.00 mol / L.

8. The preparation method according to claim 5, characterized in that, The rapid mixing unit is selected from at least one of a static mixer, an impingement flow mixer, a rotor-stator mixer, and a microchannel mixer. The effective mixing time of the aluminum salt sub-stream and the alkali sub-stream in the rapid mixing unit is 0.02 to 1.00 s.

9. The preparation method according to claim 5, characterized in that, The number of rapid mixing units is 2 to 8, and the mixture inlet corresponding to each rapid mixing unit is arranged at intervals along the circumferential and / or axial direction of the reactor; The actual flow rate of each aluminum salt sub-flow rate deviates from the average flow rate of the aluminum salt sub-flow rate by no more than 10%, and the actual flow rate of each alkali sub-flow rate deviates from the average flow rate of the alkali sub-flow rate by no more than 10%.

10. The preparation method according to claim 5, characterized in that, In step S3, the maturation temperature is 70-80℃, and the pH of the precipitated slurry during maturation is 6.8-7.5; after the maturation termination condition is reached, the precipitated slurry is cooled to 20-35℃ within 5-15 minutes.

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