Freeze granulation is a granulation technology used in modern industrial production. It offers unique advantages not found in other granulation methods. If you are looking for the right granulation technique for your product, please read this article. This article provides a comprehensive introduction to freeze granulation.
What Is Freeze Granulation?
Freeze granulation(also known as spray freeze granulation or freeze-dry granulation in some literature) is a powder preparation technique in which liquid material is atomized into tiny droplets, rapidly frozen in a low-temperature environment, and then subjected to freeze-drying to remove ice crystals, finally obtaining dry granules.
Unlike traditional granulation techniques, freeze granulation does not rely on heat to evaporate solvents. It removes the liquid medium through the sublimation of ice crystals. So it can maximize the preservation of the granules’ internal structure and component distribution.
Process of Freeze Granulation
Although the designs of different devices vary, the basic process of Freeze Granulation typically consists of four steps.
Feed Preparation
You should first prepare the solution, suspension, slurry, emulsion, or colloid system according to the product requirements. Common feed liquid compositions include active powders, solvents, dispersants, binders, and additives.
Spray Freezing
The feed liquid is atomized into tiny droplets by a nozzle or rotary atomizer. Once the droplets enter the cryogenic environment, they freeze rapidly to form solid particles. The freezing process is usually completed within milliseconds to a few seconds. The exact time depends on droplet size and cooling conditions. In this step, the most commonly used coolant is liquid nitrogen.
Particle Collection
The frozen particles are collected and transferred to the freeze-drying equipment. At this point, the moisture or solvent within the particles still exists in the form of solid ice crystals.
Freeze Drying
Transfer the frozen particles to the freeze dryer. Under vacuum conditions, the ice crystals sublimate directly into water vapor without passing through a liquid phase and are then vented. What remains are dry and porous particles.
2 Types of Freeze Granulation
Depending on the freezing method, freeze granulation can generally be divided into Wet Cooling Freeze Granulation and Dry Cooling Freeze Granulation. The main difference lies in the second step, spray freezing.
Wet Cooling Freeze Granulation
Wet cooling involves directly spraying feed liquid into a liquid nitrogen bath for freezing. This method has the highest freezing efficiency, but it requires a large amount of liquid nitrogen. You need to consider the operating costs and safety protection.
Dry Cooling Freeze Granulation
Dry cooling uses the cold air generated by the evaporation of liquid nitrogen for cooling. It is safer and requires a relatively lower amount of liquid nitrogen.
Advantages of Freeze Granulation
Protecting Heat-Sensitive Materials
This is the key advantage of freeze granulation. Since freeze granulation does not rely on high-temperature evaporation to remove solvents, the thermal stress on the material is significantly lower than that in spray drying. The granules produced by freeze granulation do not shrink due to the thermal effects of the drying process. This is also friendly to heat-sensitive components.
High Homogeneity
Freezing occurs instantly, locking most ingredients in place. This reduces the migration of fine particles and binders within the granules. If your product requires good uniformity, then freeze granulation may be suitable.
Porous Structure
Freeze granulation typically produces spherical or near-spherical granules with a relatively high degree of porosity. This structure provides a larger contact surface area when immersed in water, leading to faster wetting, better dispersion, and lower coagulation.
Nano-Friendly
Freeze granulation can convert a nanoscale suspension into micron-sized particles while preserving the nanostructure. After processing, these particles can be redispersed into a nanoscale powder, effectively preventing agglomeration of the nanoparticles.
Low Oxidation Risk
The entire process of freeze granulation is carried out under low temperatures. The freeze-drying stage is performed under vacuum, which helps you minimize the risk of oxidation of non-oxides and metals.
Batch Flexibility
The freeze granulation equipment can not only handle large-scale production batches, but also easily handle laboratory-scale batches. This feature is of great practical value if your product is in the research and development stage.
Drawbacks of Freeze Granulation
Time-Consuming
Freeze granulation requires freezing followed by freeze drying, resulting in a relatively long production cycle. However, you can achieve semi-continuous production by connecting multiple freeze dryers and freeze granulators in series.
High Energy Consumption
Because it requires maintaining an ultra-low-temperature environment and involves a lengthy vacuum sublimation process, the freeze-drying stage consumes amount of electricity. The overall energy consumption is typically higher than that of spray drying.
Limited Large-scale Production
Compared with spray drying, large-scale industrial deployment of freeze granulation remains relatively limited, and production throughput is generally lower. If your production capacity requirement is extremely high, freeze granulation might not be the most mature solution at present.
Solvent Limitations
The freezing point of the solvent is an important limiting factor. The solvent must be compatible with both the freezing and freeze-drying stages. Water and cyclohexane are common choices. If your material requires a different solvent system, you may need to evaluate its feasibility separately.
High Equipment Investment
It is necessary to be equipped with a freeze dryer, a vacuum system， and a refrigeration system. The initial investment is relatively high.
Applications of Freeze Granulation
Ceramics and Powder Metallurgy
Advanced ceramics represent one of the most established application areas of freeze granulation. Freeze granulation helps ceramic manufacturers achieve powder formulations with excellent uniformity, compressibility, and dispersibility.
Nanomaterials
Freeze granulation can assemble nanoparticles into micron-sized particles, reducing agglomeration and maintaining uniform dispersion.
Battery Materials
Freeze granulation is suitable for the preparation of positive and negative electrode materials. And it helps to improve the uniformity of composition and electrochemical performance.
Pharmaceuticals and Biotechnology
Freeze granulation can produce flowable powders suitable for different routes, such as the nasal cavity and lungs. Low-temperature processing can protect the active ingredients and is suitable for heat-sensitive drugs and biological products.
Food Industry
Freeze granulation can produce porous particles with a fast dissolution rate. It is suitable for drying and granulation of food and biological products such as instant food powders, dry spices, and probiotics.
FAQ
What Is the Difference between Freeze Granulation and Freeze Drying?
Freeze drying is a type of drying technology. Its main objective is to remove moisture. The products are usually in the form of bulk, flakes, or fragments. They usually require additional grinding to obtain powder, and the resulting particles have an irregular shape and poor flowability.
Freeze Granulation adds a spray atomization step before freeze-drying. By atomizing the liquid into tiny droplets and then conducting freeze drying, you can directly obtain spherical particles without the need for subsequent grinding.
What Is the Typical Particle Size Range of Freeze Granulation? Can It Be Adjusted according to the Requirements?
The typical particle size range of freeze granulation particles is between 10 μm and 700 μm. The particle size is mainly controlled by adjusting the atomization pressure, feed rate, nozzle structure, and feed liquid viscosity. By changing the process parameters, freeze granulation can produce products of different particle sizes to meet various industrial requirements.
Is the Cleaning Process for the Freeze Granulation Equipment Convenient? How Efficient Is the Production Changeover?
Cleaning requirements depend on the formulation and equipment design. Most Freeze granulation systems adopt a modular design, which is easy to disassemble and clean. This feature also helps you shorten the production changeover time.
What Are the Requirements for the Viscosity of the Feed Liquid in Freeze Granulation?
The acceptable viscosity range depends on the atomization system and formulation. Generally, suspensions with viscosities within the range of 7-208 mPa·s can be processed by freeze granulation. However, excessively high feed liquid viscosity may lead to granulation failure. So you need to carefully select the appropriate combination of binder molecular weight and concentration.
What Is the Amount of Liquid Nitrogen Used for Freeze Granulation?
The consumption of liquid nitrogen is usually related to the processing volume of the feed liquid, the solid content, and the design of the equipment. Take laboratory-scale equipment as an example. When using freeze granulation to process 1 liter of slurry, the consumption of liquid nitrogen is approximately 4-5 liters. However, the exact amount may vary depending on the specific circumstances.
Final Thoughts
If you are looking for spray freeze granulation equipment, Pilotech will offer you customized solutions. Pilotech is a spray dryer manufacturer in China. We have over 20 years of experience in drying and granulation technologies. We are looking forward to cooperating with you. Click to contact us.