A method for high-shear wet granulation processing, a corresponding apparatus and plant

Abstract

A method of high-shear wet granulation, HWSG, processing, the method comprising: providing a set of powder substances (Pi, Po) in a HSWG processing space (12) The HSWG processing space (12) comprises at least one mixing device (14, 16). The method further comprises: exerting at least one torque via at least one motor (MA, MC) coupled to the at least one mixing device (14, 16); sensing (S; S0, S1, S4) a first sensing signal (I, ω) indicative of said torque (T) exerted by the motor (MA, MC) of the at least one mixing device (14, 16) to blend the powders (Pi, Po) having a dry mass; providing at least one adjustable flow (VV) of at least one liquid substance (L1, L2) in the HSWG processing space (12) via a liquid distribution device (L) and wetting the first powder substance (Pi) therewith; sensing (S, S3) a second sensing signal indicative of the liquid flow introduced in the processing space (12) via the liquid distribution device (L); based on the second sensing signal, computing a cumulative amount of liquid introduced in the HSWG processing space (12) and normalizing the computed value by the dry mass, obtaining a liquid- to-solid ratio as a result; adjusting (306) the flow of the at least one liquid substance (L1, L2) based on the computed torque and liquid-to-solid ratio. The method also comprises detecting a second HSWG process transition point, e.g., by computing a third derivative of the computed torque with respect to the computed liquid-to-solid ratio and detecting a zero-crossing therein, and introducing a pre-set amount of at least one second powder substance (Po) in the HSWG processing space (12) and mixing the blended powder with the at least one second powder material (Po).

Description

[0001] A METHOD FOR HIGH-SHEAR WET GRANULATION PROCESSING, A CORRESPONDING APPARATUS AND PLANT

[0002] TEXT OF THE DESCRIPTION

[0003] Field of the invention

[0004] The present disclosure concerns methods and systems for performing wet granulation processing.

[0005] One or more embodiments can be applied to the preparation of solid colorant pigments, such as redispersible pigment granules.

[0006] Technical background

[0007] Pigments are a key component in formulating and tinting coatings and plastics and play a relevant role when it comes to performance.

[0008] As an effective alternative to liquid pigment dispersions, structured solid pigments have to readily achieve a comparable degree of fineness when applied to the medium for which they are intended.

[0009] Producing solid pigments that are easily dispersible presents various difficulties.

[0010] Document EP 3 137 559 A2 discusses a solid colorant comprising a. 30-97 wt% of a pigment b. less than 5 wt% of a solvent c. 3-40 wt% surfactants and wherein: the ratio S / A [Std dev of the particle size distribution / average particle size] of the solid colorant is <25%, preferably <22% and more preferably <20%, wherein wt% is relative to the total weight of the solid colorant, and wherein the particle size distribution is determined with light scattering with fully automated image analysis according to ISO 13322-1 Static image analysis First edition 2004- 12-01 by the use of the OCCHIO ZEPHYR ESR analyzer. Various industries, such as the pharmaceutical one, use a variety of systems for performing granulation of substances.

[0011] High shear wet granulation (HSWG) is one of these methods and it can be used in the pharmaceutical sector for producing oral solid dosage (OSD) forms.

[0012] Literature related to HSWG comprises the following documents:

[0013] [1] S.M. Iveson, J.D. Litster: “Fundamental studies of granule consolidation part 2: Quantifying the effects of particle and binder properties”, Powder Technology, Volume 99, Issue 3, 1998, Pages 243-250, ISSN 0032-5910, doi: 10.1016 / S0032-5910(98)00116-8 discusses glass ballotini of surface mean size 10, 19 and 37 pm granulated in a 30 cm diameter tumbling drum, with water, glycerol and surfactant solutions used to vary the viscosity and surface tension of the binder liquid; the change of porosity with time was found to be well described by a simple, empirical, exponential decay equation; the results show that capillary, viscous and friction forces play a role in granule consolidation.

[0014] [2] Iveson, Simon M. et al.: “Growth regime map for liquid-bound granules: further development and experimental validation”, Powder Technology 117 (2001): 83-97, doi: 10.1016 / 80032-5910(01)00317-5 discusses an attempt to quantify the boundaries and validate the granule growth regime map for liquid-bound granules postulating that the type of granule growth behaviour is a function of only two dimensionless groups: the amount of granule deformation during collision (characterised by a Stokes deformation number, A7dcf) and the maximum granule pore saturation, ■Sma\.

[0015] The output of HSWG systems can largely depend on the rheological properties of the wet mass. Conventional solutions such as the use of dimensionless Stokes deformation number (Stdef) may present limits in predicting the granulation regime, in particular when using water or low-viscosity binders.

[0016] Document Franceschinis, E. et al.: “Prediction of the Growth Kinetics and Agglomeration Mechanisms Using a Mixer Torque Rheometer.” Chemical Engineering Research and Design 159 (July 2020): 328-38. doi: 10.1016 / j.cherd.2020.04.024 discusses the evolution of high-shear wet granulation processes which can be deemed based on strength and plasticity of the wet masses, to develop a rheological method able to predict the granule growth, recording the torque evolution over the time of three different wet powder formulations, where the torque profiles were then analyzed to find a characteristic torque value that could be correlated to the strength and the deformability of the wet granules.

[0017] Document US 2009 / 0135666 Al discusses a kneading and granulating machine comprising: a container containing a material to be kneaded; a kneading member, which moves along the inner wall surface of the container and revolves and spins at the same time within the container; and a crushing blade, which revolves and spins at the same time within the container to shear the material to be kneaded in the container, where the kneading member comprises a blade having a shape corresponding to the inner wall surface of the container, which enables kneading the material to be kneaded between itself and the inner wall surface of the container.

[0018] Conventional solutions present the drawback of, at most, envisaging the possibility to increment the quantity of liquid substance in the working volume by discrete amounts, thereby failing to counter the known phenomenon currently denoted as “induction growth”.

[0019] Further drawbacks that limit the application of conventional HSWG processing comprise: non-linearity in dissolution properties in producing granules, for instance due to their low porosity; large number of entwined variables; and high degree of deviation of size and other parameters among the output granules.

[0020] Object and summary

[0021] The object of this disclosure is to contribute to overcoming the aforementioned drawbacks.

[0022] According to the invention, the above object is achieved thanks to the subject matter recalled specifically in the ensuing claims, which are understood as forming an integral part of this disclosure.

[0023] One or more embodiments relate to a wet granulation apparatus, such as a high shear wet granulation (HSWG) apparatus.

[0024] One or more embodiments relate to a corresponding method for operating a wet granulation apparatus as per the present disclosure.

[0025] A discontinuous high-shear wet granulation process for producing redispersible pigment granules may be exemplary of such a method.

[0026] The present inventors found out that, under specific conditions, wet granulation of pigments performed in batch operated high shear mixers can attain semi-permanent aggregates in which dispergated pigment particles are still distinguished and are easily redispersible in the final medium.

[0027] One or more embodiments exploit Rehbinder’s theory to facilitate promoting dispergation under shear when the liquid quantity is sufficient to lower the surface energy.

[0028] One or more embodiments involve control of how the liquid is adsorbed into the solids, enhancing the dispersion quality of the granules.

[0029] One or more embodiments facilitate reaching a substantially uniform distribution for both nuclei and resultant granules, aiming for enhanced dispersion in the final applications.

[0030] One or more embodiments facilitate reducing the amount of liquid used for granulation, to improve the quality and consistency of the produced granules.

[0031] One or more embodiments facilitate reducing energy consumption, for instance during a drying phase.

[0032] One or more embodiments facilitate producing redispersible granular pigments with pre-determined properties. For instance, one or more embodiments facilitate providing a cheaper high-performance alternative to existing paint and coating solutions.

[0033] One or more embodiments facilitate implementing a torque-based process control method in an industrial setting.

[0034] For instance, the process control involves real-time data acquisition and processing, ensuring accurate torque measurement, dealing with variability in material properties, and adapting the control strategy to different granulation scales.

[0035] One or more embodiments are preferably used for the preparation of solid colorant pigments.

[0036] One or more embodiments exploit a process control approach that hinges on a detailed analysis of the mechanical forces at play during the granulation process.

[0037] One or more embodiments exploit the second derivative of torque with respect to the normalized cumulative volume of liquid sprayed. For instance, this parameter serves as a pivotal indicator for rheological transitions during the formation of wet granules.

[0038] One or more embodiments may encompass various stages, such as: a first phase comprising modulating operational parameters in response to detecting a change of sign in the second derivative (that is, a zero crossing of the function): such a phase involves reducing the mass flow rate of the liquid being sprayed while adjusting the internal pressure to a threshold level (e.g., about 0.85 bar); this phase facilitates maintaining consistency in the early stages of granulation; a second phase involving performing polymeric binder addition in response to detecting that the second derivative reaches a minimum, corresponding to a zerolevel of the third derivative; introducing a pre-determined quantity of solid polymeric binder into the apparatus at this point facilitates ensuring uniformity in the granulation process; a third phase of transition to massing which is triggered when the second derivative exhibits a second zero crossing; during the third phase, the completion of the liquid spraying phase is reached; stopping the liquid at this point correlates with the onset of capillary liquid bridges within the wet granules.

[0039] Subsequently, the impeller velocity can be reduced to a value that corresponds to a Froude number equal to or lower than 0.5, initiating the massing phase.

[0040] In one or more embodiments, the strategic use of the second derivative of torque facilitates producing granules with high consistency in particle size distribution (PSD) and yield.

[0041] One or more embodiments provide a precision-driven approach that facilitates reaching top quality in the formed granules for their intended application in pigment preparation, thereby enhancing their performance in paints and coatings.

[0042] Brief description of the drawings

[0043] One or more embodiments will now be described, by way of non-limiting example only, with reference to the annexed Figures, wherein:

[0044] Figure 1 is a diagram exemplary of an apparatus as per the present disclosure;

[0045] Figure 2 is a diagram exemplary of principles underlying one or more embodiments;

[0046] Figure 3 is a diagram exemplary of a method as per the present disclosure;

[0047] Figure 4 is a diagram exemplary of operations in the method exemplified in Figure 3;

[0048] Figure 5 is a diagram exemplary of identifying a transition point during operation of the apparatus exemplified in Figure 1;

[0049] Figure 6 is a diagram exemplary of a method for operating the apparatus exemplified in Figure 1, and

[0050] Figure 7 is a diagram exemplary of a plant equipped with an apparatus as per the present disclosure.

[0051] Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated.

[0052] The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale.

[0053] The edges of features drawn in the figures do not necessarily indicate the termination of the extent of the feature.

[0054] Detailed description of the invention

[0055] In the following description, numerous specific details are given to provide a thorough understanding of embodiments. The embodiments can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the embodiments.

[0056] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0057] The headings provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.

[0058] The High Shear Wet Granulation (HSWG)is a conventional process largely used in the pharmaceutical sector for the production of oral solid dosage forms. HSWG process is conventionally performed by spraying a liquid (normally referred to as binder) onto the particles as they are agitated in a (high-shear) mixing volume. The liquid forms inter-particle bonds by a combination of capillary and viscous forces until more permanent bonds are formed by subsequent drying.

[0059] Traditional HSWG has its limitations, especially in producing granules with controlled dissolution properties due to inherent low porosity of the granules.

[0060] For the sake of simplicity one or more embodiments are discussed in the following mainly with respect to the exemplary process of producing granular pigments, being otherwise understood that such a type of granulated product is purely exemplary and in no way limiting. One or more embodiments may be applied to the production of notionally any kind of granulated product for any kind of industry, in particular those comprising uniform particles with a low water content.

[0061] Disclosed herein is a way to improve HSWG processing to facilitate the production of redispersible granular pigments (like for example titanium dioxide and iron oxide) optimized for paint and coatings applications. Under the process object of the present disclosure the pigment is converted into a mechanically stable granular form that is easy to handle, store, and transport. Yet, this transformation is reversible as the granules are designed to effortlessly disperse again when introduced into a medium such as water for paints or resin for powder coatings. The redispersibility unlocks the limitations traditionally associated with granular or powdered pigments. Such a product attains the convenience of granules and the performance of a finely dispersed pigment.

[0062] With the term "dispergation" is meant a process of breaking down agglomerates or clusters of solid particles into their primary particles and smaller aggregates. Dispergation consists of two steps: 1. wetting the solid particles to reduce inter-particle forces and facilitate separation, and 2. shearing to physically break down agglomerates and distribute the particles. The outcome of dispergation is a wetted mixture of primary particles and smaller aggregates ready for further processing or incorporation into a medium. Dispergation is different from "dispersion". Dispersion refers to the distribution and stabilization of solid particles within a medium to form a stable system where the particles remain suspended and do not re-agglomerate. The stages of dispersion comprise: 1. wetting; 2. breaking down and distributing particles throughout a medium, and 3. introducing stabilization mechanisms, like adding surfactants or modifying the zeta potential, to prevent particles from settling or re-agglomerating. The outcome of the dispersion is a stable colloidal dispersion where solid particles are evenly distributed and maintained in suspension over time. While dispergation and dispersion relate to the distribution of particles, dispergation in the context of the present invention emphasizes the initial breakdown and the conditions under which particles may spontaneously disperse. On the other hand, dispersion generally refers to the broader process of distributing and stabilizing particles within a medium to ensure they remain suspended. In essence, while dispergation focuses on the initial breaking down of particle clusters, dispersion encompasses the broader process, ensuring not only distribution but also stabilization of particles within a medium.

[0063] With the term "redispersibility" is meant the ability of a dispersion or suspension (in the colloidal physical -chemi cal context) to be redispersed. It refers to how easily or difficult it is to redisperse a sample after it has been at rest for a certain period. Redispersible pigments are pigments that, once dispersed in a medium and then dried or settled, can be redispersed back into the medium upon the addition of a suitable solvent without losing their properties. In the context of redispersibility, the phrase "without losing their properties" signifies that redispersible pigments have the capability to return to their original state with all their inherent characteristics and qualities intact. When redispersing these pigments after they have dried or settled, they should maintain their essential properties, such as color, particle size, stability, and any other relevant attributes that make them suitable for their intended application. Essentially, it means that the pigment can be effectively restored to its initial state without any significant degradation or alteration of its desirable features. The term "dispersible" primarily refers to the pigment's ability to be distributed throughout a medium without necessarily implying that it can be redispersed once settled or dried.

[0064] In one example, the present invention provides a discontinuous high-shear wet granulation process for producing redispersible pigment granules comprising the following steps: a. Providing at least one powder pigment in its natural aggregated and agglomerated form; b. Blending the at least one pigment with at least one (e.g., insoluble) grinding aid and / or disintegrant in powder form obtaining a blend; c. Dispergating the blend with a first liquid mixture comprising at least two non-polymeric surfactants by means of high-shear mixing, obtaining pigment particles with an average particle size lower than the average particle size of the pigment agglomerates and aggregates of step a.; d. Wetting the pigment particles with a second liquid mixture comprising at least one polymeric surfactant and letting the wetted pigment particles to nucleate under high-shear mixing; e. Feeding at least one granulating polymeric binder in solid form to the wetted particles under high-shear mixing, resulting in the formation of a cohesive solid bed of particles; f. Spraying the second liquid mixture onto the solid bed of particles under high-shear mixing, obtaining wetted granules; g. Massing the wetted granules to grow by coalescence, preferably in a cascade flow regime; and h. Drying the wetted granules to obtain redispersible pigment granules, wherein steps a. to f. are carried out in a high-shear wet granulator, step g. either in a high-shear mixer or, preferably, in a tumbler, and step h. in a fluid bed dryer, wherein the granulator is equipped with at least one impeller, at least one side-chopper, some nozzles for liquid spraying (into the granulator) and a vacuum system.

[0065] The pigment powders of step a. consist of aggregates / agglomerates of similar particles.

[0066] In the dispergation phase (step c.) of the process, it is the magnitude of the cohesive forces between the individual particles that determine the extent of deagglomeration before the mechanical action (high shear mixing) is applied. This step comprises two distinct phases, a first one of wetting the pigment powder with a mixture of surfactants, and a second one of high-shear mixing the wetted particles to obtain pigment particles with an average particle size lower than the average particle size of the pigment agglomerates and aggregates of step a.

[0067] Dispergation can be achieved through mechanical methods, such as milling and grinding, and chemical methods, such as the use of surfactants and polymers.

[0068] In the dispergation phase, it is more important to disrupt pigment agglomerates and aggregates than to secure a stable dispersion of primary particles. This means maximizing the speed of wetting and the speed of deagglomeration. Mechanical energy is required to destroy aggregates or break down single crystals into smaller units. The fine breaking down of solids to create new interfaces is facilitated by the adsorption of the non-polymeric surfactants (contained in the first liquid mixture) at structural defects in the surface, which are normally present in the natural state and might also appear as microcracks during the high-shear mixing of step c. The efficiency of deagglomeration is related to the degree of lowering of the free surface energy by surfactant(s) adsorption, which is the dominating effect.

[0069] The weakening of solids by controlled adsorption of surface-active agents (in the present case the at least two non-polymeric surfactants) is known as the Rehbinder effect, also known as Adsorption-Induced Reduction of Strength (AIRS). It is a phenomenon in physics that causes a decrease in strength and specific work of fracture in solids due to the interaction between the solid and the surfaceactive agents of an environment. This effect can be applied to the dispergation phase occurring in the high-shear mixing of powders, where it can facilitate the breakdown of agglomerates and aggregates by weakening the interatomic bonds in the solid. The Rehbinder effect is sensitive to the superatomic structure of the solid, strain rate, and temperature. In this context, the Rehbinder effect can be considered a mechanism of the dispergation process, as it aids in the dispersion of solids by reducing the strength of agglomerates and aggregates and facilitating their breakdown into smaller particles, leading to a more efficient process.

[0070] By leveraging the Rehbinder effect in the context of the claimed process, the inventors found out that surface-active agents with high affinity for pigments surface can be effectively adsorbed in sufficient amounts to lower free surface energy of the solid-liquid system, hence improving the breaking down efficiency as exerted by the mechanical work of the high-speed mixer impeller and the lateral chopper. It was surprisingly noted that enough shear and impact energy can be transferred to the solid particles for an effective dispergation phase. The key to this phase is to avoid the formation of liquid bridges among the solid particles which would have a detrimental effect on the break-up of the agglomerates and aggregates.

[0071] Furthermore, the dispergation phase can be greatly improved, in terms of robustness, by adding to the input pigment a small quantity of (e.g., insoluble) grinding aid(s) and / or disintegrant(s) in powder form (step b.).

[0072] In one embodiment, the dispergation of step c. comprises (preferably consists of) two phases, wherein:

[0073] - the first phase involves spraying the first liquid mixture on the pigment agglomerates and aggregates under vacuum and under high-shear mixing, and

[0074] - the second phase involves stopping the spraying of the first liquid mixture and high-shear mixing under a mixing condition of a Froude number equal or greater than 20, under vacuum. The Froude number is a dimensionless number used in fluid dynamics to compare inertial forces to gravitational forces. It is defined as: wherein, co is the angular velocity in (rad / s), r is the radius of the rotation in meters (m), and g is the acceleration due to gravity in (m / s2).

[0075] In one example, the spraying of the first liquid mixture is stopped when the amount of liquid sprayed onto the particles is sufficient to cover their surface with a surfactant adsorbed layer lower than 10 monolayers.

[0076] In the first phase of dispergation the solid-air interface is replaced by one between solid and liquid. This means that when the first liquid mixture comprising the mixture of at least two non-polymeric surfactants is sprayed over the mass of powder, air has to escape from the capillaries through the liquid and the voids. This is the reason why proper wetting requires low surface tension of the 1-v interface, contrary to what is normally stipulated in the HSWG process or by the Washburn equation.

[0077] Moreover, the Inventors observed that operating under mild to strong vacuum surprisingly boosts the quality of step c., as better breakdown of the agglomerates and aggregates is achieved. As a result of such observation, the claimed process can start with blending the powder pigments with the at least one (e.g., insoluble) grinding aid(s) and / or disintegrant(s) above described (step b.) while applying vacuum to the system.

[0078] In one example, step b. is carried out under vacuum, preferably at a pressure P equal to or lower than 0.85 bar, more preferably at a pressure P comprised between 0.4 and 0.05 bar. Preferably, the vacuum is then held also for the entire step c. (dispergation phase) up to the completion of step e. (granulating polymeric binder addition).

[0079] From a process operating conditions standpoint, dispergation is carried out at the maximum transferable mechanical momentum, which corresponds to a fully developed roping flow of the powder as defined by Iveson and Litster in their seminal works. In the context of powder dispersion in process engineering, a "roping flow" regime refers to a specific flow pattern observed in the movement of powders, particularly in pneumatic conveying systems or similar environments. This regime is characterized by the formation of a concentrated, rope-like stream of powder particles that moves along the boundaries of the conveying medium, typically air. This state is achieved at a specific flow rate and pressure that results in the formation of this roping flow, where the particles behave almost like a fluid, ensuring effective and uniform dispersion as described by Iveson and Litster.

[0080] In one example, step c. is carried out at a powder flow regime corresponding to a Froude number of at least 20.

[0081] The Inventors also found out that the side-chopper, traditionally used to break large lumps of over-grown granules, is effective during the dispergation phase when high shear is applied to break up agglomerates and aggregates.

[0082] As far as the spraying of the first liquid mixture, such a step is carried out to operate in the drop-penetration regime (see K.P. Hapgood and J.D. Litster): a high- pressure hydraulic multiple fan-shaped type nozzles arrangement is used, to minimize the volumetric flow rate for each nozzle and simultaneously reduce the spray area. Measured in water-like viscosity, nozzles operate at an average drop size of < 100 microns. Such conditions are facilitated by using hydraulic pressure ranging from 6 to 45 barg. Under a water-like viscosity level, the hydraulic pressure of the nozzle is about 25 to 30 barg.

[0083] With the combination of powder flow (incipient roping flow regime) and multiple nozzles arrangement, a spray-flux number target for step c. is lower than 0.15. The dimensionless spray-flux number (see K.P. Hapgood, D.J. Lister) is a critical parameter in the context of granulation processes. It quantifies the coverage of the powder surface by liquid droplets in relation to the movement of powder through the spray zone. The spray-flux number can be expressed analytically as follows:

[0084] Rate of wetted area coverage by droplets

[0085] Spray -flux number= - - - - - - - - - - - — -

[0086] Area flux of powder through the spray zone

[0087] To expand this into a more detailed expression, consider the following parameters:

[0088] - Let QLbe the liquid spray rate (volume per unit time, e.g.,

[0089] - Let d be the average diameter of the droplets (e.g., in meters).

[0090] - Let w be the width of the flat spray nozzle (e.g., in m units).

[0091] - Let vpbe the velocity of the powder through the spray zone (e.g., in m / s).

[0092] It can be estimated by the Froude number as vp« 0.15^ / r - r ■ g

[0093] The rate of wetted area coverage by droplets can be approximated as the product of the number of droplets per unit time and the average area covered by each droplet.

[0094] The area flux of powder through the spray zone can be defined as w x vprepresenting a linear measure of the powder flow through the spray zone

[0095] Putting these together, the dimensionless spray-flux number can be expressed as:

[0096] Spray — flux number=Ratedr°Pletarea

[0097] Substituting the expressions, the result is:

[0098] The given expression quantifies the density of droplets covering the powder surface in the granulation process, enabling the understanding and optimization of wetting and granulation efficiency.

[0099] In one example, in step c. the first liquid mixture (liq) is sprayed at a rate ranging between 0.1 and 3 kgiiq / kgsoi / h, preferably between 0.5 and 1 kgiiq / kgsoi / h with respect to unit mass of the dry pigment (sol).

[0100] In the example considered, in step c. the first liquid mixture is sprayed in an amount ranging between 0.1% and 5%, preferably between 0.5% and 2%, with respect to dry pigment weight.

[0101] Still in the considered example, in step c. the first liquid mixture is sprayed in an amount ranging between 1 and 10 monolayers, preferably between 1 and 3 monolayers, with respect to the total surface area of the particles.

[0102] In the dispergation phase, following the completion of the targeted liquid mixture addition, which consists of non-polymeric surfactants for full adsorption, the spray is discontinued and the chopper mechanism is activated. The termination of Step c. is then contingent upon one of two criteria: it may be considered complete after a predefined period of time, such as 4 minutes, subsequent to the initiation of the chopper; or, as an alternative condition, the completion can be determined when the power consumption (or torque) profile, as a function of time, consistently displays a zero first derivative (f) for a minimum duration of two minutes. This latter criterion is indicative of a stable and optimized state in the breakdown process of the agglomerates and aggregates.

[0103] Once the step c. is complete, step d. is initiated by deactivating the chopper and starting the addition of the second liquid mixture under the drop-penetration flow regime described earlier.

[0104] In step d., granules nuclei (seeds) are formed as pendular liquid bridges are initially established. The wetting phase commences with the spraying of a liquid mixture (liq) onto the particles at a flow rate ranging between 0.5 and 5 kgiiq / kgsoi / h, preferably between 1.0 and 3 kgiiq / kgsoi / h with respect to unit mass of the dry pigment (sol).

[0105] In one example, in step d. the second liquid mixture is sprayed in an amount ranging between 5% and 40%wt, preferably between 10% and 25%wt with respect to the dry pigment weight.

[0106] Still in the considered example, step d. is carried out at a powder flow regime corresponding to a Froude number of at least 20.

[0107] Feeding of at least one granulating (e.g., polymeric) binder in solid form (powder or granules) into the system (step e.) may be carried out while keeping the roping flow regime of the now-formed wetted mass unchanged. By keeping this flow regime unchanged, the binder is effectively mixed with the wetted particles, ensuring uniform granulation and efficient binding. This step facilitates reaching desired properties in the final product, such as consistent particle size, strength, and stability. Such granulating (e.g., polymeric) binders are used to form a more coherent mass at the intragranular level with a high degree of plasticity needed to ensure homogeneous, dense, dry granules with low friability, whilst ensuring adhesion and cohesion in the wet state, as well as, excellent plasticity and redispersibility after the granules are dried. A stable structure of sufficient strength is thus formed in order to withstand the hydrophilic forces arising due to the evaporation of water. A structure-forming 'cement' allows the pigment granules to be soluble in the medium into which it is desired to disperse the pigment in order to regenerate the fine particles.

[0108] A specific advantage offered by the granulating (e.g., polymeric) binder(s) is to contribute to minimizing the total amount of surfactants. This is particularly interesting given the adverse effect of excess surfactants on wet-scrubbing resistance and water permeability of the paint systems. Excess surfactant does not improve dispersion stability and may alter the water sensitivity of the resulting paint.

[0109] In one example, the granulating (e.g., polymeric) binder(s) is(are) either soluble or miscible in the liquid mixtures sprayed in steps c. and d.

[0110] In one example, the granulating (e.g., polymeric) binder(s) has(have) a Tg lower than 60° Celsius.

[0111] In one example, the granulating (e.g., polymeric) binder(s) is(are) added in dry form and in amounts ranging between 0.5% to 2%wt to dry pigment.

[0112] The addition of the second liquid mixture can later be stopped as soon as a pore saturation of min 80% is reached, indicating that the majority of the pores within the granules are filled with the liquid. This level of saturation facilitates granule formation, as it ensures sufficient wetness for granule growth while preventing excess liquid that could lead to over-wetting and undesirable agglomeration. In terms of granulation dynamics, this point corresponds to the formation of full funicular liquid bridges and the onset of capillary state formation in the granules.

[0113] In one example, in step f. the second liquid mixture is sprayed in an amount ranging between 1% and 20%wt, preferably between 5% and 15%wt with respect to the dry pigment weight.

[0114] In one example, in step f. the second liquid mixture (liq) is sprayed at a rate ranging between 0.1 and 3 kgiiq / kgsoi / h, preferably between 0.5 and 1.5 kgiiq / kgsoi / h with respect to unit mass of the dry pigment (sol).

[0115] Steps a. to f. as discussed in the foregoing can be carried out in an apparatus 10 as exemplified in Figure 1 using a method as per the present disclosure.

[0116] For the sake of simplicity, one or more embodiments are discussed in the following with respect to the granulation apparatus exemplified in Figure 1 which may be deemed to belong to the class of vertical axis granulators.

[0117] Such an exemplary scenario is in no way limiting as one or more embodiments may be applied to notionally any kind of granulation apparatus, such as horizontal axis granulators, conical shape granulators, multifunctional one-pot granulators and so on.

[0118] As exemplified in Figure 1, a high shear wet granulation, HSWG apparatus 10 comprises: a vessel comprising an internal volume (or space) 12 to perform HSWG granulation processing of (powder) materials inserted therein; at least one input duct (or filling spout or hatch 13) configured to couple the internal volume 12 of the vessel to a set of (buffer) tanks or volumes of powder materials Po, Pi, such as a first tank comprising a first subset of powder materials Pi (e.g., at least one pigment powder and / or filler) Pi and at least one second tank comprising a second subset of powder materials (e.g., solid powder materials Po such as glidants or grinding aids, disintegrants, granulating binders, for instance); for instance, in case the first powder material comprises pigment powder, it is possible to timely synchronize, with respect to transition points of the HSWG processing, inserting a granulating (e.g., polymeric) binder in the volume 12 via a control unit CU, as discussed in the following; a mixer device 14, such as an agitator or impeller 14, comprising a rotating body 14 (e.g., comprising at least two blades with elongated side wings) coupled to an actuator MA configured to impart rotation thereto, the first mixer device configured to impart (high) shear to particles for effective processing; a liquid distribution sub-system L configured to spray at least one liquid substance on the solid bed of the internal volume 12 in a controllable manner (e.g., via a metering pump VV) during the operation of the apparatus 10.

[0119] As exemplified in Figure 1, the liquid distribution sub-system L comprises: at least one source of liquid substances LI, L2, and one or more nozzles 15, 17 coupled to the sources LI, L2 and configured to spray the at least one liquid substance on the solid bed of the internal volume 12 after it has been filled with powder materials and after blending thereof.

[0120] As exemplified in Figure 1, the central body of the mixing device 14 is coupled to a set of blades 140, e.g. three helical blades forming a three-blade impeller.

[0121] It is noted that the exemplified number and shape of blades 140 is purely exemplary and in no way limiting as one or more embodiments may employ virtually any number of blades greater than two. As appreciable to those of skill in the art, in order to perform HSWG, the impeller 14 has a diameter substantially equal to the diameter of the internal volume 12.

[0122] In the exemplary scenario considered herein, the actuator MA of the mixing device 14 is equipped with an electric motor integrated with a variable frequency drive (VFD) unit for speed control throughout the granulation process. Additionally, it can include a sensor or transducer SO, such as a current sensor, to monitor the motor parameters.

[0123] For the sake of simplicity one or more embodiments are discussed herein mainly with reference to an electric motor MA, MC as actuating device for the rotating elements 14, 16 of the apparatus 10. This is purely exemplary as in one or more embodiments the actuation may be of the hydraulic kind rather than electromechanical, for instance. In the latter case, while the physical parameters for actuation may be different, a ratio of developed torque over power of the motor may remain independent from the chosen actuation system. For instance, blades 140 can attain tip speeds of up to 15 m / s.

[0124] As exemplified in Figure 1, the apparatus 10 optionally comprises an auxiliary mixing device 16, currently referred to as a chopper. For instance, the chopper 16 is smaller and faster than the main agitator 14 in order to break down lumps during granule growth. As exemplified in Figure 1, the chopper 16 is mounted on the side of the vessel. In alternative scenarios, the chopper can also be mounted on top of the vessel.

[0125] As exemplified in Figure 1, the chopper 16 is coupled to an auxiliary electric motor MC comprising a VFD unit for speed control and / or a (e.g., current) sensor / transducer to detect the motor parameter values.

[0126] As appreciable to those of skill in the art, a tip velocity of the chopper can be calculated based on the chopper's diameter and rotational speed.

[0127] For instance, for an apparatus 10 having an internal volume 12 about 700 liters, the chopper 16 is configured to reach a tip velocity equal or greater than 1500 rpm (rounds per minute), preferably up to 3000 rpm, and has a multi disk knifetype design (with minimum three disks), preferably having an outer diameter equal or greater than 120 mm (1 mm = 1 millimeter = 10'3m).

[0128] As exemplified in Figure 1, the electric motor(s) MA, MC are connected to a control unit CU designed to effectively manage the velocity of the mixing device(s) 14, 16. The CU processes signals not only from the Variable Speed Drive (VSD) but also incorporates inputs from other sensors, including a more specific type of power meter, to precisely regulate the granulation process. This integrated approach ensures accurate control of the mixing speed, contributing to the efficiency and consistency of the granulation outcome.

[0129] As exemplified in Figure 1, the electric motor(s) MA, MC have an encoder SI attached thereto.

[0130] For instance, an encoder SI (preferably, an absolute encoder) as those produced and commercialized by Siemens is suitable for use in one or more embodiments.

[0131] In a manner per se known, an absolute rotary encoder SI is a device configured to measure an absolute angle of a rotating shaft of an electric motor MA, MC.

[0132] Still referring to the exemplary apparatus of Figure 1, a set of sensors S is coupled to the (parts within) the internal volume 12 of the vessel of the apparatus 10, e.g., to sense properties of the material to be or being processed. As exemplified in Figure 1, the set of sensors S is further coupled to the control unit CU of the apparatus 10 to provide sensing signals thereto.

[0133] For instance, the set of sensors S comprises one mass flow meter (MFM) device S3 which, in a manner per se known, exploits the Coriolis effect to provide an indication of a flow rate of a mass through a sensing tube. As exemplified in Figure 1, the MFM device S3 is coupled to the liquid distribution sub-system L. A MFM device as the one produced and sold under the name of Coriolis Micro Motion Series F by the company Emerson with address 8000 West Florissant Avenue, P.O. Box 4100, St. Louis, MO 63136, United States may be suitable for use in one or more embodiments.

[0134] In one or more embodiments, also other known sensor types or alternative sensors (per se known) may be employed for use in the set of sensors S, such as a torque meter sensor S4 coupled to the electric motors MA, MC, for instance.

[0135] There are several types of online torque meters suitable for coupling to a motor shaft driving the impeller 14 (or the chopper 16) for a high shear wet granulator 10. In general, a torque meter sensor S4 may be configured to measure the torque applied to the shaft in real-time. Conventional torque meters S4 suitable for use in one or more embodiments may comprise strain gauge torque sensors, rotary torque transducers, in-line torque sensors, magnetic torque sensors, optical torque sensors, digital torque sensors and so on.

[0136] Advantageously, the control unit CU is configured to control the granulation process dynamically and precisely by operating the apparatus 10, preferably varying the process parameters such as liquid source inputs (e.g., via high-pressure positive displacement pumps with variable speed control) and / or frequency of the electric motor(s) MA, MC based on the sensing signal received from the sensor(s) S.

[0137] As exemplified in Figure 1, the apparatus 10 comprises a conventional vacuum system comprising pressure variation device (such as a vacuum pump, not visible in Figure 1) coupled to the apparatus 10 via the outlet of a bag filter 19 installed thereon or on a sealing lid 18 of the internal space 12 of the apparatus 10. For instance, the vacuum system 19 (known per se) is used for maintaining a lower pressure than the atmospheric one and / or for filtering undesired solid and is configured to vary (e.g., reduce) the pressure within the internal space 12 of the apparatus 10 based on process parameters / phases, as discussed in the following.

[0138] As exemplified in Figure 1, the set of sensors S comprises a pressure transducer S2 coupled to the vacuum system 19 via the control unit CU to adjust the pressure inside the internal space 12 of the apparatus 10 based on process parameters / phases, as discussed in the following.

[0139] As appreciable to those of skill in the art, the granulator 10 may also comprise a jacket for heating or cooling the vessel, in a manner per se known.

[0140] In the exemplary scenario in which the HSWG apparatus 10 is used to produce pigments, one or more powder pigments Pi are blended with additives like (e.g., insoluble) grinding aids and / or disintegrants Po while absolute pressure is dropped (via the vacuum 19) to favor air removal and improve milling efficiency.

[0141] Initial breaking down of particle agglomerates exploits high shear in the presence of surfactants or wetting agents adsorbed on a few monolayers, for instance.

[0142] In one or more embodiments, controlled wetting of particles to form granule nuclei can be facilitated by regulating the addition of liquid via a metering system VV of the liquid distribution sub-system L.

[0143] For instance, such a controlled wetting facilitates providing a substantially uniform particle size distribution for both nuclei and resulting processed granules, facilitating enhanced dispersion in the final applications of the solid pigments. For instance, such a method may facilitate dispersibility and / or fineness of grind of notionally any formulated colorant.

[0144] Inventors have observed that using torque exerted on the impeller 14 as a control variable for operating the apparatus 10 it is possible to gain insights into the wet mass's rheological behavior. Therefore, it is possible to provide an estimate of the optimal amount of liquid to provide for effective granulation and understanding the granules' plastic deformation strength.

[0145] A method to estimate liquid-to-solid ratio (L / S) for the High Shear Wet Granulation (HSWG) process, as carried out by the apparatus 10, includes the following operations: performing discrete increments in the amounts of sprayed liquid, e.g., via the metering system VV of the feeding pump(s), and monitoring, via a set of sensors (S) to detect changes in torque exerted on impeller 14. For instance, this operation includes direct measurement of the shaft’s behavior and analyzing data from the Variable Frequency Drive (VFD) unit. For instance, operations of the method are coordinated and processed by the control unit (CU), which integrates the sensor inputs for effective management and control of the impeller’s rotational dynamics.

[0146] A method of determining the liquid-to-solid ratio (L / S) for the HSWG processing, thereby controlling the apparatus 10 accordingly, comprises: after introducing the first subset of powder materials Pi (such as one or more pigments, for instance) in the internal volume 12, spraying the liquid substance(s) LI, L2 via 15, 17 and computing a second derivative of the torque of the impeller 14 as a function the normalized cumulative liquid volume inside the processing space 12; detecting rheological transition points in the evolution of the torque profile by detecting zero-crossing points and local minima for the second derivative of the torque as a function of the normalized cumulative liquid volume; for instance, a first zero-crossing is indicative of transitions in the granulation process, for instance the shift from pendular to funicular liquid bridges; via the liquid distribution sub-system L, in response to detecting a first transition point (e.g., at a first zero crossing in the second derivative of the torque as a function of the normalized cumulative liquid volume), reducing a flow rate of the liquid substance LI, L2 being sprayed via the nozzles 15, 17; preferably, also varying a pressure inside the internal volume 12 via the vacuum system 19; and / or inserting the second powder material Po, such as a granulating (e.g., polymeric) binder, in response to detecting a second transition point (e.g., at a zerocrossing of the third derivative); and / or stopping spraying the liquid substance(s) LI, L2, via the nozzles 15, 17, in response to detecting a third process transition point, e.g. in response to the second derivative reaching a second zero-crossing after detecting a minimum value.

[0147] Portion a) of Figure 2 is a plot diagram exemplary of an evolution of the torque T (ordinate axis, in Isb / kg units) as a function of the cumulative liquid-to- solid ratio at time t (mass of liquid over mass of dry-solid L / S, abscissa axis, in kg / kg units).

[0148] Portion b) of Figure 2 is a plot diagram exemplary of an evolution of the second derivative f ’(X) (ordinate axis, in Isb / kg units) of the torque T exemplified in portion a) as a function of the cumulative liquid-to-solid ratio at time t (mass of liquid over mass of dry-solid L / S, abscissa axis, in kg / kg units).

[0149] As exemplified in portion b) f Figure 2: a first (e.g., round) marker T1 is indicative of a first transition point in the HSWG process, a second (e.g., square) marker T2 is indicative of a second transition point in the HSWG process, and a third (e.g., triangle) marker T3 is indicative of a third transition point in the HSWG process.

[0150] Specifically: the first marker T1 indicates the first occurrence of a change of sign (or zero crossing) in the second derivative function f ’(X), indicative of an initial transition point in the granulation process (e.g., marking a transition from pendular to funicular liquid bridges among the particles); the second marker T2 identifies the point in which the second derivative f ’(X) reaches a minimum value subsequent to the detected zero-crossing (e.g., at the completion of a phase of formation of funicular liquid bridges among wet pigment particles, just before the onset of capillary states), triggering the addition of the second powder substance (e.g., solid powder binder); the third marker T3 identifies a subsequent change of sign (or zero crossing) in the second derivative function f ’(X), following the local minimum value detected at the second marker T2, indicative of a third transition point in the granulation process (e.g., the onset of capillary liquid bridges, for instance where pore saturation is equal or greater than 80%).

[0151] Inventors have observed that reducing the liquid spraying and the internal pressure in response to detecting the first process transition facilitates maintaining consistency of the particles in the early stages of granulation processing.

[0152] As exemplified in portion a) of Figure 2: a concavity of the torque function is negative between the first and second transition points T2; at the second transition point T2, in response to introducing the binder Po, the torque T reaches a sort of plateau thanks to the effect of absorbance of the liquid provided by a pre-set quantity of (e.g., polymeric) binder Po being introduced at once in the processing volume 12; thereafter, the concavity of the torque profile T changes and becomes positive: stopping spraying the liquid via the nozzles 15, 17 in synch with the change of convexity of the profile (at the third transition point T3) facilitates reaching a step of massing and a flux or cascading regime, thereby improving the process efficiency and the quality of the wet granules.

[0153] For instance, the torque T is reduced again after the third transition point T3, preferably reducing the velocity of the impeller 14 to a value that corresponds to a Froude number equal to or lower than 0.5, initiating the massing phase of the wet granules.

[0154] Inventors have observed that it may be possible to exploit one or more transition points to precisely, finely control the granulation process, facilitating providing consistent and high-quality outcomes in the properties of the granulated products.

[0155] As exemplified in Figure 1, the wet granulated products are provided to user systems A as an output of the apparatus 10, for instance via a dedicated output duct.

[0156] In one or more embodiments as per the present disclosure, the control unit CU of the apparatus 10 is configured to vary 19 a pressure and / or reduce the liquid sprayed (e.g., by the metering system VV of the pumps) in response to detecting, via signals received from the set of sensors S and via drive signals provided to the motor MA one or more transition points Tl, T2, as discussed in the following. As exemplified in Figure 3, a method of operating the apparatus 10, in particular during a first and second process transition points Tl, T2, comprises: block 300: (e.g., continuously) measuring a first signal indicative of a torque T exerted by a motor (e.g., MA) of a mixing device (e.g., 14) for instance based on the driving parameters (e.g., current, frequency, hydraulic pressure) of the motor; block 302: (e.g., continuously) measuring a second signal V indicative of a flow rate of the liquid substance LI, L2 being introduced via a nozzle 15, 17 in the internal volume 12 of the apparatus 10, for instance via the sensor S3 as discussed in the following; block 304: based on the second signal, calculating a cumulative volume V of liquid normalized by the mass M of solids in the volume 12; block 306: analyze the first torque signal T as a function of the second liquid volume signal V to detect at least one transition point Tl, T2 in the granulation process (e.g., transition from pendular to funicular liquid bridges among particles); block 308: in response to detecting the at least one transition point in the granulation process, via the control unit CU, synchronize the introduction of the second powder substance and / or vary process parameters, preferably reducing the pressure in the internal volume 12 via the vacuum system 19 and / or reducing the spraying of liquid via the nozzles 15, 17, as discussed in the following.

[0157] It is noted that the value of mass M used for calculations is known a-priori and it is equal to the (initial) dry mass of the first powder substances Pi inserted in the apparatus 12 via the duct 13. As appreciable to those of skill in the art, in batch processing the total mass M remains constant throughout all the phases of the process. In alternative scenarios, it may be possible to also consider the mass of the second subset of powder substance Po in case such an additional mass is much lower than the mass M of the first subset of powder substances Pi.

[0158] As exemplified in Figure 4, an operation of detecting a first transition point, during the HSWG process performed via the apparatus 10, comprises: block 400: based on the first signal indicative of a torque T and of the second signal V indicative of the total cumulative liquid volume, computing the first derivative dT / dV and second derivative d2T / d2V (or f ’) of the torque exerted by the motor (e.g., MA or MC) with respect to the normalized cumulative liquid volume V; as appreciable to those of skill in the art, such a computation may employ a numerical differentiation method, such as finite differences, to approximate these derivatives from the collected data; block 402: tracking the sign changes and local minima in the computed second derivative function f ’ in order to detect the first process transition at a first zero crossing (ZCD); block 404: in response to detecting the first process transition point Tl, triggering the control unit CU to drive the liquid distribution sub-system L to reduce the flow rate of the liquid substance sprayed via the nozzles 15, 17; optionally, further varying (via the vacuum system 19) the pressure inside the internal volume 12 (e.g., up to P = 0.85 atm = -150 mbar where 1 mbar = 10'3bar) until reaching a target pressure value (detected via the pressure sensor S2, for instance); optionally, either maintaining unaltered or varying the speed of the impeller 14 in response to reaching the first transition point Tl.

[0159] Without being bound to any specific theoretical model, the Inventors have observed that, upon reaching the first transition point Tl, an effective strategy to enhance the drop-penetration regime of the liquid in the wet powder blend — which is otherwise impeded by the increased resistance of the liquid to penetrate the capillaries of the granule nuclei — is to adjust the liquid flow rate while keeping the speed of the impeller 14 constant. This approach facilitates a further reduction in the spray-flux number, thereby optimizing the liquid distribution within the powder blend.

[0160] Inventors have observed that reducing the flow of sprayed liquid at Tl counters the risk of an accumulation of liquid on the surface of the powder particles, which could lead to an uncontrolled growth of their sizes (as per the known phenomenon currently denoted as “induction growth”).

[0161] Without being bound to any specific theoretical models, Inventors have observed that the reduction of pressure inside the volume 12 seems to induce a state akin to fluidization in the powder particles, apparently mitigating the cohesive forces of particle collisions.

[0162] Inventors have further observed that the combination of reducing the sprayed liquid flow rate and reducing the pressure together in a synchronized way produces an amplified improvement in the granulation process.

[0163] In one or more embodiments, one or more feedback loops facilitate ensuring the robustness of the control method. For instance, such feedback loops comprise recalibrating the transition points Tl, T2, T3 in response to detecting changes during the granulation process.

[0164] One or more embodiments facilitate an online, real-time control of the HSWG apparatus 10 and the granulation process inside the internal volume 12 thereof.

[0165] As exemplified herein Figures 2 and 5, the control unit CU is configured to compute the torque signal T and its derivatives with respect to the normalized cumulative liquid volume V.

[0166] In order to perform such a computation, the control unit CU starts from initializing boundary conditions data, which may be provided by a user from a user interface (not visible in Figure 1) or may be loaded from a data storage portion of the control unit CU, in a manner per se known.

[0167] For instance: a first initial condition signal M provided to the control unit CU is indicative of a total mass of dry solids in the granulator's bowl 12, and a second initialization signal U provided to the control unit CU is indicative of an electrical parameter (e.g., voltage, current or power) of the motor MA.

[0168] In the following, it is provided an analytical framework for expressing relation relations among current / power of the motor MA of the impeller 14 (and / or the auxiliary motor MC of the chopper 16), angular velocity of the shaft coupled to the respective motor and the proxy for torque in a High Shear Wet Granulation (HSWG) apparatus 10.

[0169] The electrical power consumed by an AC motor MA can be expressed as: P=UIcos((|)) where:

[0170] P indicates the power in Watt units (W);

[0171] U indicates the electric voltage in Volt units (V);

[0172] I indicates electric current intensity in Ampere units (A); and cos((|)) is a dimensionless power factor of the motor.

[0173] To arrive at an expression for controlling the torque T of a motor MA, MC using a Variable Frequency Drive (VFD), it is noted that the motor's speed (and consequently its torque) can be adjusted by varying the frequency of the electrical power supplied to the motor MA, MC.

[0174] For instance, in an exemplary case in which U= 400 V, motor frequency f = 50 Hz, and power factor=l, the current I is left as the variable to compute power P.

[0175] As exemplified in Figure 1, an angular velocity m (rad / s) can be directly measured using a sensor SI coupled to the shaft of the impeller 14 In industrial scale applications, a shaft of the motor of the impeller 14 has a speed in a range about 0 to 250 rpm. For instance, the AC motor MA has a speed of 1500 rpm for four poles and decreasing as the number of poles increases. In order to exert the desired torque for the range of speed values indicated above, it is possible to use a mechanical gearbox interposed the motor and the shaft. In such an exemplary scenario, the electric motor controlled by VFD is coupled to a mechanical reducer via pulleys and directly feeds the impeller 14 via a secondary shaft of a reducer. In such an exemplary scenario, in order to reduce signal losses, it is advisable to mount the angular encoder SI directly on the secondary shaft, producing a signal indicating the angular position over time.

[0176] In a manner per se known, the torque T exerted by the motor MA can be calculated from the power and angular velocity using the expression:

[0177] P T= — co

[0178] Expressing the power P as a function of the electric current I and rearranging the members, the expression above becomes:

[0179] T_UIcos(( co

[0180] The speed N (in revolution per minute, RPM units) of an AC motor as a function of the frequency f (in Hertz units, Hz) of the AC power supply can be expressed as: where P is the number of poles of the motor.

[0181] Under the approximation of considering the VFD unit to be configured to maintain a constant voltage-to-frequency ratio (U / f), it follows that, at least at at lower frequencies, the torque T can be expressed as a function of the square of the frequency as:

[0182] T=kx(f)2where k is a constant value that can be determined (e.g., empirically or provided by the manufacturer) based on motor characteristics and the voltage-to- frequency ratio.

[0183] Controlling the torque T therefore involves adjusting the frequency setpoint f determined by the VFD.

[0184] For instance, a desired torque value Tdesiredcan be obtained for a target frequency value f* which can be expressed as As mentioned, this approach assumes a linear or known relationship between torque and frequency, which is generally valid for AC motors under constant V / Hz control, particularly at lower frequencies. At higher frequencies or under varying load conditions, the relationship may become more complex, so that feedback mechanisms may be put in place to maintain the desired torque setpoint.

[0185] In one or more embodiments, setting a baseline for calibrating the torque T of the impeller 14 (and / or chopper 16) comprises: initializing driving the motor MA, MC via the control unit CU, setting an initial frequency value f for the motor MA, MC; via the VFD control system CU of the motor MA, MC, obtaining the measure the current torque (either directly or via detecting the motor current I); performing a comparison among the detected torque T and the desired torque value Tdesired; based on the result of the comparison, adjusting the frequency f according to the expression for the target frequency f* in order to produce the desired torque value Tdesired.

[0186] Still under the considered assumption, a cumulative volume of liquid introduced via discrete increments (sprayed via nozzles 15, 17) into the internal volume 12 of the apparatus 10 from initial time instant tO up to a subsequent time instant t, normalized by the total solid mass introduced (via input channel 13) in the apparatus 10 can be expressed as the integral of a liquid flow rate over time divided by the mass of the solid, namely: t

[0187] Q(r)dr where

[0188] Q(t) is a flow rate of the liquid at time t in liters per minute (L / min) or similar units;

[0189] M is the total mass of the solid in the granulator's bowl 12 in kilogram (kg) or similar units;

[0190] Therefore, the first derivative dT / dV of the torque T over the cumulative volume of liquid V can be expressed as: dT dT dT> dt > dt dV dV Q(t) dt M

[0191] Therefore, the second derivative d2T / dV2of the torque T over the cumulative volume of liquid V can be expressed as: where AV represents a small change in the cumulative volume V(t).

[0192] During the operation of the apparatus 10, a sensor SO in the set of sensors S collects signals as a set of (e.g., digitally) sampled signal values. For instance, at constant time intervals At the control unit CU collects, e.g., via current sensor SO, the values of electric current signal I flowing through the motor, of angular velocity co of the motor and of the flux rate QL(t) of the liquid. Therefore, it may be possible to replace analytical formulae with the corresponding discrete numerical equivalents, in a manner per se known to those of skill in the art.

[0193] For instance, the normalized cumulative liquid volume V may be computed as at each time step t as where At is the time interval between adjacent time steps.

[0194] For each time step, the torque T can be computed based on the current signal I and angular velocity co of the motor MA, MC.

[0195] The first derivative — and the second derivative ^-7 of the torque T can be dV dV2computed using numerical differentiation methods.

[0196] As explained in the foregoing, the possibility to detect the rate of change of the torque T as a function of normalized liquid content V(t) provides insights in understanding and controlling the granulation process.

[0197] Inventors have observed that the first derivative dT / dV is indicative of how sensitive the torque is to changes in the liquid-to-solid ratio.

[0198] Inventors have further observed that the second derivative d2T / dV2facilitates identifying inflection points or changes in the granulation regime as a result of reaching or exceeding a threshold liquid level.

[0199] As exemplified in Figure 6, a method of varying the process parameters during operation of the apparatus 10 comprises: block 600: via the control unit CU, monitoring an evolution of the values of the computed second derivative of torque over mass volume d2T / dV2; block 602: performing a comparison among the signs of adjacent sample values of the computed second derivative d2T / dV2in order to detect a zero crossing (ZCD) of the function; block 604: in response to detecting a first zero crossing in the computed second derivative d2T / dV2(e.g., as a result of the comparison of the signs yielding a change of sign along the second derivative function), identifying the first process transition and varying VV, via the liquid distribution sub-system L, the liquid flow rate and, via the vacuum system 19, of the apparatus 10 (as discussed also with reference to block 404 in Figure 4); block 606: after detecting the first phase transition Tl, analyzing the detecting the next local minimum point in the computed second derivative d2T / dV2(see for instance the square-shaped marker in portion b of Figure 2); in response to detecting the local minimum after the zero crossing in the computed second derivative d2T / dV2, identifying a second process transition point T2 and triggering a control action by the control unit CU to insert the binder powder Po; block 608: keeping analyzing the evolution the computed second derivative d2T / dV2and, in response to detecting a second zero crossing in the computed second derivative d2T / dV2(e.g., as a result of the comparison of the signs yielding a change of sign along the second derivative function), identifying the third process transition T3 and stopping, via the metering system VV driven by the CU, the liquid sprayed via the nozzles; it may also be possible to store the value of a total volume of liquid sprayed until the time instant at which the control action CU has been triggered as a target value for the granulation process 10.

[0200] After block 608, the method comprises providing the wet granulates to user system(s) A.

[0201] For instance, the operation in block 606 comprises further computing the third derivative f ’ ’ (X) (or d3T / dV3) and detecting the value at which it reaches zero.

[0202] Figure 5 is a plot diagram exemplary of an evolution of the third derivative f ”(X) (ordinate axis, in Isb / kg units) as a function of the cumulative liquid-to-solid ratio at time t (mass of liquid over mass of dry-solid L / S, abscissa axis, in kg / kg units) that shows the second transition point T2 at the zero crossing of the function f ”(X).

[0203] As exemplified in portion a) of Figure 2, the second derivative of the torque d2T provides information about the concavity of the torque profile T with respect to the normalized cumulative liquid volume V. A minimum point on this curve T is d.3T identified where the rate of change of the second derivative corresponding to the third derivative of the torque T, crosses zero and changes sign from negative to positive, as exemplified in Figure 5.

[0204] Such a computation and calculation may advantageously reuse concepts already expressed with respect to zero crossing detection (ZCD) operations in block 604 of Figure 6 and blocks 402-404 of Figure 4. In one or more exemplary scenarios, a set of data points and decisions made by the algorithm are stored in a data log for further analysis and feedback.

[0205] One or more embodiments may be equipped with optional data processing routines comprising at least one of:

[0206] - error handling to manage potential issues with data quality or sensor errors;

[0207] - verifying the calculated torque and derivative values against expected trends or historical data thereof.

[0208] The method as per the present disclosure advantageously facilitates to dynamically determine a threshold for an amount of liquid to use for the granulation process, thereby enhancing the efficiency and quality of the product.

[0209] In one or more embodiments, accuracy and resolution of the input data and the robustness of the numerical differentiation and optimization methods can be considered as figures of merit.

[0210] As already mentioned, a transition of the torque function T from concave down to concave up, indicating a minimum T2 in the second derivative, identifies a transition among different wetting stages during the granulation process in the HSWG apparatus 10.

[0211] Therefore, leveraging real-time data collection and analytical expressions, the method as per the present disclosure facilitates precise control over the granulation process in the apparatus 10.

[0212] For instance, the method facilitates ensuring that a threshold amount of liquid is not exceeded, enhancing the quality of the granules produced and optimizing the efficiency of the HSWG apparatus 10.

[0213] As exemplified in Figure 7, the HSWG apparatus 10 may be used as a standalone process or as a member of a plant with a variety of processing stages.

[0214] For instance, a plant 100 for the production of pigments further comprises: a tumbler 20, per se known, coupled to the HSWG apparatus 10 to receive the wet granules WG therefrom, the wet granules WG having a substantial uniform size and a reduced water content as a result of the fine tuning of the HSWG process parameters via the method as per the present disclosure; in particular, the synchronization of the spraying of liquid LI, L2 from the nozzles 15, 17 and the phases of the wetting process thanks to monitoring of the second derivative of the torque of the impeller 14 facilitates providing such an improved output WG from the apparatus 10; a dryer 30, such as a fluid bed dryer per se known, where fines can be separated and collected, further improving the particle size distribution.

[0215] As exemplified herein, the use of the methos as per the present disclosure to operate the apparatus 10 facilitates reducing energy consumption, for instance thanks to the reduced liquid content of the granulated particles produced via the apparatus 10 which are then provided to the dryer 20.

[0216] As exemplified in Figure 7, the fine powders 40 can either be recycled back to the tumbler 20 or the granulator 10. Optionally, the plant 100 comprises further filtering stages 50 to separate exhaust air and fine powders.

[0217] As exemplified herein, a method of high-shear wet granulation, HWSG, processing comprises: providing a set of powder substances Pi, Po in a HSWG processing space 12 (which comprises at least one mixing device 14 for mixing powder substances in the set of powder substances); inserting in the HSWG processing space a first subset of powder substance Pi (having dry mass M) among powder substances in the set of powder substances and exerting at least one torque T via at least one motor MA coupled to the at least one mixing device to blend the substances in the HSWG processing space, obtaining a powder blend having a (dry) mass M (equal to the dry mass of the first subset of powder substances); sensing S; SO, SI, S4 a first sensing signal I, co indicative of the torque exerted by the motor of the at least one mixing device; providing at least one adjustable flow VV of at least one liquid substance LI, L2 in the HSWG processing space via a liquid distribution device L and wetting therewith the powder blend in the HSWG processing space; sensing S; S3 a second sensing signal V indicative of the liquid flow introduced in the processing space via the liquid distribution device; based on the second sensing signal, computing 304 a cumulative amount of liquid introduced in the HSWG processing space and normalizing the computed value by the (dry) mass, obtaining a liquid-to-solid ratio L / S as a result; and adjusting 306 the flow of the at least one liquid substance based on the sensed torque T and liquid-to-solid ratio L / S.

[0218] As exemplified in Figures 1 to 7, the method can further comprise: based on the first sensing signal, computing the torque T exerted by the motor of the at least one mixing device, and computing 400; 602 a second derivative d2T / dV2, f ’(X) of the computed torque with respect to the computed liquid-to-solid ratio; identifying 402, 404; 604 a first transition point T1 of the HSWG processing at a first zero-crossing detected in the computed second derivative, and in response to identifying the first transition point, reducing 606 the flow of the at least one liquid substance introduced in the HSWG processing space.

[0219] For instance, the method further comprises, in response to identifying the first transition point Tl, varying the pressure inside the HSWG processing space via a vacuum system 19 coupled thereto, preferably until the pressure reaches S2 a value about 0.85 atm.

[0220] As exemplified in Figures 1 to 7, the method can comprise detecting a second HSWG process transition point T2 based on the computed torque and liquid- to-solid ratio; and in response to detecting the second HSWG process transition point, introducing 606 a pre-set amount of at least one second powder substance Po in the HSWG processing space and mixing the blended powder with the at least one second powder material Po.

[0221] For instance, the first powder substance comprises a pigment whereas the at least one second subset of powder substances Po comprises at least one substance among a polymeric binder, a (e.g., insoluble) grinding aid and a disintegrant.

[0222] As exemplified in Figures 4 and 6, detecting a second HSWG process transition point T2 based on the computed torque and liquid-to-solid ratio comprises: computing 604 a third derivative f ”(X) of the computed torque T with respect to the computed liquid-to-solid ratio L / S and detecting a zero-crossing in the computed third derivative, or computing 404 a second derivative d2T / dV2of the computed torque T with respect to the computed liquid-to-solid ratio L / S and detecting a minimum value T2 following a first zero-crossing Tl.

[0223] As exemplified in Figures 1 to 7, the method can comprise: based on the first sensing signal, computing the torque exerted by the motor of the at least one mixing device, and computing 400 a second derivative d2T / dV2of the computed torque T with respect to the computed liquid-to-solid ratio L / S; identifying 608 a third transition point T3 in the HSWG processing at a second zero-crossing T3 following a first zero-crossing Tl in the computed second derivative, and in response to identifying the third transition point T3, stopping 608 the flow of at least one liquid substance introduced in the HSWG processing space.

[0224] As exemplified in Figure 1, the method comprises coupling a mass flow meter, MFM device S3 to the HSWG processing space and sensing a flow rate of a mass through the MFM device as the second sensing signal V indicative of the liquid flow introduced in the HSWG processing space via the liquid distribution device.

[0225] As exemplified in Figure 1, sensing the first sensing signal I, co comprises at least one of: coupling an absolute encoder SI to the at least one mixing device and sensing 302, SI an angular velocity co of said at least one mixing device as the first sensing signal indicative of said torque exerted by the motor; coupling a VFD control unit CU to the motor of the at least one mixing device, wherein the motor of the at least one mixing device comprises an electric motor and wherein the method further comprises detecting the electric current driving said motor as the first sensing signal; and coupling a hydraulic transmission control unit to the motor of the at least one mixing device, wherein the motor of said at least one mixing device comprises an hydraulic motor and wherein the method further comprises detecting the pressure of said hydraulic fluid driving the motor as the first sensing signal.

[0226] As exemplified in Figures 1 to 7, a high-shear wet granulation, HWSG processing apparatus 10 comprises: an input duct 13 coupled to a set of tanks of a set of powder substances Pi, Po and configured to insert one or more powder substances among substances in the set of powder substances in a (closed, 18) HSWG processing space (inside the HSWG apparatus); at least one mixing device 14 coupled to the HSWG processing space and configured to exert MA at least one torque T in the HSWG processing space to blend the substances therein, obtaining a powder blend (e.g., a blend of colored powder pigments in the first subset of powder substances Pi having dry mass M); a liquid distribution device L coupled to the HSWG processing space and configured to provide at least one adjustable flow VV of at least one liquid substance LI, L2 to the HSWG processing space to wet the substances therein; a set of sensors S coupled to the liquid distribution device and to the at least one mixing device 14, the set of sensors S comprising sensors SO, SI, S4 configured to sense 302, S a first sensing signal I, co indicative of the torque T exerted by the motor of the at least one mixing device, the set of sensors S further comprising sensors S3 configured to sense 304 a second sensing signal V indicative of the liquid flow introduced in the HSWG processing space via the liquid distribution device; a pressure variation or vacuum system 19 coupled to the HSWG processing space 12 to vary a pressure therein; a processing device CU coupled to the liquid distribution device, to the at least one mixing device, to the set of sensors, to the vacuum system and to the at least one second tank of powder substance.

[0227] As exemplified herein, the apparatus 10 is configured to perform high-shear wet granulation, HWSG, processing according to the method as per the present disclosure.

[0228] As exemplified in Figure 7, a plant 100 comprises: a HSWG apparatus 10 as per the present disclosure; a tumbler 20 coupled to the HSWG apparatus 10 to receive wet granules therefrom and configured to apply tumbler processing thereto, and a drying system 30, preferably a fluid bed dryer, coupled to the tumbler to receive the tumbled wet granules therefrom and configured to apply drying processing thereto.

[0229] References

[0230] Iveson, Simon M., James D. Litster, Karen Hapgood, and Bryan J. Ennis. "Nucleation, Growth and Breakage Phenomena in Agitated Wet Granulation Processes: A Review" Powder Technology 117, no. 1-2 (June 2001): 3-39. doi: 10.1016 / 80032-5910(01)00313-8.

[0231] Iveson, S. M., and J. D. Litster. “Growth Regime Map for Liquid-Bound Granules.” AIChE Journal 44, no. 7 (July 1998): 1510-18. doi: 10.1002 / aic.690440705.

[0232] Hapgood, Karen P., James D. Litster, Edward T. White, Paul R. Mort, and Damian G. Jones. "Dimensionless Spray Flux in Wet Granulation: Monte-Carlo Simulations and Experimental Validation" Powder Technology 141, no. 1-2 (March 2004): 20-30. doi: 10.1016 / j.powtec.2004.02.005.

[0233] Knight, P.C, J.P.K Seville, A.B Wellm, and T Instone. "Prediction of Impeller Torque in High Shear Powder Mixers" Chemical Engineering Science 56, no. 15 (August 2001): 4457-71. doi: 10.1016 / S0009-2509(01)00114-2.

[0234] Malkin, A. I. "Regularities and Mechanisms of the Rehbinder’s Effect" Colloid Journal 74, no. 2 (April 2012): 223-38. doi: 10.1134 / S1061933X12020068.

[0235] Rehbinder, P. A. "Formation of Structures in Disperse Systems" Pure and Applied Chemistry 10, no. 4 (January 1, 1965): 337-58. doi:

[0236] 10.1351 / pacl96510040337.

[0237] G.R. Feat and S. Levine “The Double-layer Interaction of Two Charged Colloidal Spherical Particles of a Concentrated Dispersion eina Medium of Low Dielectric Constant”, Journal of Colloid and Interface Science, Vol. 54, No. 1 January 1976.

[0238] Franceschinis, E., F. Schmid, R. Baggio, M. Dal Zotto, N. Realdon, and A.C. Santomaso. “Prediction of the Growth Kinetics and Agglomeration Mechanisms Using a Mixer Torque Rheometer.” Chemical Engineering Research and Design 159 (July 2020): 328-38. doi: 10.1016 / j.cherd.2020.04.024.

Claims

CLAIMS1. A method of high-shear wet granulation, HWSG, processing, the method comprising: providing a set of powder substances (Pi, Po) in a HSWG processing space (12), wherein the HSWG processing space (12) comprises at least one mixing device (14, 16) for mixing powder substances in the set of powder substances (Pi, Po); inserting (13) in the HSWG processing space (12) a first subset of powder substances (Pi) having a mass (M) in the set of powder substances (Pi, Po), and exerting at least one torque (T) via at least one motor (MA, MC) coupled to the at least one mixing device (14, 16) to blend substances in the HSWG processing space (12), obtaining a powder blend; sensing (S; SO, SI, S4) a first sensing signal (I, co) indicative of said torque (T) exerted by the at least one motor (MA, MC) of the at least one mixing device (14, 16); providing at least one adjustable flow (L, VV) of at least one liquid substance (LI, L2) via a liquid distribution device (L) and wetting therewith the powder blend in the HSWG processing space (12); sensing (S, S3) a second sensing signal (V) indicative of the liquid flow introduced in the processing space (12) via the liquid distribution device (L); based on the second sensing signal (V), computing (304) a cumulative amount of liquid introduced in the HSWG processing space (12) and normalizing the computed value by the value of said mass (M), obtaining a liquid-to-solid ratio (L / S) as a result; and adjusting (306, VV) the flow of the at least one liquid substance (LI, L2) based on the computed torque (T) and liquid-to-solid ratio (L / S).

2. The method of claim 1, comprising: based on the first sensing signal (I, co), computing the torque (T) exerted by the motor (MA) of the at least one mixing device (14, 16), and computing (400; 602) a second derivative (d2T / dV2, f ’(X)) of the computed torque (T) with respect to the computed liquid-to-solid ratio (L / S); identifying (402, 404; 602, 604) a first transition point (Tl) of the HSWG processing at a first zero-crossing detected in the computed second derivative(d2T / dV2, f ’(X)), and in response to identifying the first transition point (Tl), reducing (606) the flow of the at least one liquid substance (LI, L2) introduced in the HSWG processing space (12).

3. The method of claim 1 or claim 2, comprising varying (604, 19) the pressure inside the HSWG processing space (12) based on the computed torque (T) and liquid-to-solid ratio (L / S), preferably via a vacuum system (19) coupled thereto until the pressure reaches (S2) about 0.85 atm.

4. The method of any one of the previous claims, comprising identifying (404; 604, 606) a second HSWG process transition point (T2) based on the computed torque (T) and liquid-to-solid ratio (L / S); and in response to identifying (404; 604) the second HSWG process transition point (T2), introducing (606) a pre-set amount of at least one second subset of powder substances (Po) in the HSWG processing space (12) and mixing the blended powder with the at least one second powder material (Po).

5. The method according to claim 4, wherein identifying the second HSWG process transition point (T2) based on the computed torque (T) and liquid-to-solid ratio (L / S) comprises: computing (604, 606) a third derivative (f ”(X)) of the computed torque (T) with respect to the computed liquid-to-solid ratio (L / S) and detecting a zerocrossing in the computed third derivative (f ”(X)), or computing (404) a second derivative (d2T / dV2) of the computed torque (T) with respect to the computed liquid-to-solid ratio (L / S) and detecting a minimum value (T2) following a first zero-crossing (Tl).

6. The method of any one of the previous claims, comprising: based on the first sensing signal (I, co), computing the torque (T) exerted by the at least one motor (MA, MC) of the at least one mixing device (14, 16), and computing (400) a second derivative (d2T / dV2) of the computed torque (T) with respect to the computed liquid-to-solid ratio (L / S); identifying (606, 608) a third transition point (T3) in the HSWG processing at a second zero-crossing (T3) following a first zero-crossing (Tl) in the computed second derivative (d2T / dV2), and in response to identifying the third transition point (T3), stopping (608) the flow of at least one liquid substance (LI, L2) introduced in the HSWG processing space (12).

7. The method of any one of the previous claims, comprising coupling a mass flow meter, MFM device (S3) to the HSWG processing space (12) and sensing (304, S3) a flow rate of a mass through the MFM device as said second sensing signal (V) indicative of the liquid flow introduced in the HSWG processing space (12) via the liquid distribution device (L).

8. The method of any one of the previous claims, wherein sensing said first sensing signal (I, co) comprises at least one of: coupling an absolute encoder (SI) to said at least one mixing device (14, 16) and sensing (302, S) an angular velocity (co) of said at least one mixing device (14, 16) as the first sensing signal indicative of said torque (T) exerted by the at least one motor (MA, MC); coupling a VFD control unit (CU) to the at least one motor (MA, MC) of said at least one mixing device (14, 16), wherein the at least one motor (MA, MC) of said at least one mixing device (14, 16) comprises an electric motor and wherein the method further comprises detecting the electric current driving said motor as the first sensing signal; and coupling a hydraulic transmission control unit to the at least one motor (MA, MC) of said at least one mixing device (14, 16), wherein the at least one motor (MA, MC) of said at least one mixing device (14, 16) comprises a hydraulic motor and wherein the method further comprises detecting the pressure driving said hydraulic fluid driving the motor (MA, MC) as the first sensing signal.

9. A high-shear wet granulation, HWSG processing apparatus (10), comprising: an input duct (13) configured to be coupled to a set of tanks of a set of powder substances (Pi, Po) and configured to insert in a HSWG processing space (12)a first subset of powder substances (Pi) and at least one second subset of powder substances (Po) of set of powder substances (Pi, Po), at least one mixing device (14, 16) configured to exert (MA, MC) at least one torque (T) in the HSWG processing space (12) to blend the substances therein, obtaining a powder blend as a result; a liquid distribution device (L) coupled to the HSWG processing space (12) and configured to provide at least one adjustable flow (VV) of at least one liquid substance (LI, L2) to the HSWG processing space (12) to wet the powder blend; a set of sensors (S) coupled to the liquid distribution device (L) and to the at least one mixing device (14, 16), the set of sensors (S) comprising sensors (S; SO,SI, S4) configured to sense (302, S) a first sensing signal (I, co) indicative of said torque (T) exerted by the at least one motor (MA, MC) of the at least one mixing device (14, 16), the set of sensors (S) further comprising sensors (S3) configured to sense (304, S) a second sensing signal (V) indicative of the liquid flow introduced in the processing space (12) via the liquid distribution device (L); a vacuum system (19) coupled to the HSWG processing space (12) to vary a pressure therein; a processing device (CU) coupled to the liquid distribution device (L), to the at least one mixing device (14, 16), to the set of sensors (S), to the vacuum system (19) and to the at least one second subset of powder substances (Po), wherein the apparatus (10) is configured to perform high-shear wet granulation, HWSG, processing according to the method of any one of claims 1 to 8.

10. A plant (100), comprising: a HSWG apparatus (10) according to claim 9, a tumbler (20) coupled to the HSWG apparatus (10) to receive wet granules therefrom and configured to apply tumbler processing thereto, and a drying apparatus (30), preferably a fluid bed dryer, coupled to the tumbler to receive the tumbled wet granules therefrom and configured to apply drying processing thereto.

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