Primary drying is one of those subjects where the details matter more than the headlines. This page pulls together the background, the mechanisms, and the practical points readers ask about most.
Updated 2026-04-08. Numbers and descriptions here follow the published literature rather than marketing material.
Secondary drying removes bound water that remains after ice sublimation. Shelf temperature is raised gradually while pressure remains low, reducing water content to a target range. Over-drying can cause brittleness or electrostatic issues, while under-drying affects stability. The endpoint is often judged by pressure rise tests, temperature measurements, or water content analysis. Scale-up depends on matching heat and mass transfer across equipment sizes. Small changes in shelf temperature or pressure can alter cycle length substantially.
Lyophilization, or freeze-drying, removes water from a material by freezing it and then lowering pressure so ice changes directly to vapor. The process relies on sublimation, the phase transition from solid to gas without an intervening liquid state. It is used for heat-sensitive materials that would degrade in conventional drying. The three stages are freezing, primary drying, and secondary drying, each with distinct temperature and pressure requirements. In practice, cycle design balances these variables.
Freezing determines ice crystal structure and pore size, which affect drying speed and product uniformity. Rapid freezing creates small crystals, while slow freezing creates larger crystals and often faster sublimation. During primary drying, chamber pressure is held below the vapor pressure of ice, and shelf temperature supplies heat for sublimation. The ice front recedes, leaving a porous matrix. Thermal limits such as collapse and eutectic temperatures set safe boundaries for formulation. These limits vary with solute composition and concentration.
Industries use lyophilization for pharmaceuticals, biological products, and food preservation. In the pharmaceutical sector, it extends the shelf life of injectable drugs, vaccines, and proteins that are unstable in aqueous solution. Food manufacturers apply freeze-drying to coffee, fruits, and ready meals to retain flavor and texture. The process is energy-intensive and requires specialized equipment, which limits its use to high-value products. Ongoing research examines how formulation and process parameters affect the quality of the final dried product.
Lyophilization, also known as freeze-drying, is a process that removes water from a material by freezing it and then reducing pressure to allow ice to sublimate directly into vapor. The method begins with a freezing step that solidifies the water content. Next, primary drying lowers the pressure below the triple point of water, enabling sublimation without passing through a liquid phase. A final secondary drying step removes bound water through desorption. This sequence produces a dry, porous cake that can be reconstituted later.
The process relies on the phase diagram of water, where the triple point marks the conditions at which ice, liquid water, and vapor coexist. By maintaining pressure below this point, typically around 0.01 to 0.1 millibar, sublimation becomes the dominant mechanism. Formulations often include excipients such as sugars or polymers that act as lyoprotectants and bulking agents. These additives help preserve the structure of the active ingredient and prevent collapse during drying. The choice of excipient and freezing rate influences the final cake morphology and stability.
| Property | Value | Notes |
|---|---|---|
| Process name | Lyophilization or freeze-drying | Both terms appear in technical standards and literature. |
| Phase transition | Sublimation | Solid ice becomes vapor without a liquid step. |
| Typical chamber pressure | 0.05-0.5 mbar | Range depends on product temperature and equipment. |
| Typical product temperature | -40 °C to -10 °C | Measured during primary drying; formulation sets limits. |
| Water content after drying | 0.5-3% w/w | Target varies by material and stability needs. |
The low pressure used during drying allows water vapor to move from the ice surface to a cold condenser. Energy supplied as heat drives sublimation but must stay below the collapse temperature of the frozen matrix. If the product becomes too warm, the frozen structure may soften or melt, reducing pore formation and slowing drying. Formulations often include bulking agents, stabilizers, or buffers to support a rigid cake. The final moisture content depends on formulation, freezing rate, and the length of secondary drying.
Freeze-drying is distinct from simple evaporation and from spray drying. Evaporation removes water at temperatures above freezing, while spray drying rapidly dries droplets in a heated gas stream. Lyophilization avoids high temperatures, which can be useful for heat-sensitive materials such as proteins, vaccines, and some foods. The porous cake produced by sublimation dissolves or rehydrates more quickly than a dense dried mass. Not all materials tolerate freezing or the pH shifts that can occur as solutes concentrate during ice formation.
Lyophilization removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts liquid water into ice and fixes the structure of the sample. After freezing, primary drying lowers pressure so ice changes directly to vapor without passing through a liquid phase. Secondary drying then removes bound water that remains after ice sublimation. The result is a dry, porous solid that often retains its original shape.
Freeze-drying is used for materials whose activity or structure depends on low temperature and low water content. Examples include certain biologics, diagnostic reagents, starter cultures, coffee, and porous inorganic precursors. The dried product forms a cake whose porosity aids rapid wetting and dissolution. Main drawbacks are high energy use, long cycle times, and sensitivity to formulation and equipment variation. Questions remain about how freezing rates and ice morphology affect batch uniformity, especially when moving from laboratory to production scale.
Lyophilization, also called freeze-drying, is a dehydration process in which a solvent, usually water, is frozen and then removed by sublimation under reduced pressure. The method preserves heat-sensitive materials that would degrade in conventional drying. Large-scale use grew during the mid-twentieth century for blood plasma and antibiotics, and it later expanded to vaccines, enzymes, foods, and advanced materials. The process produces a dry, porous solid that usually reconstitutes rapidly. It is distinct from simple evaporation because the solvent bypasses the liquid phase during primary removal.
A freeze-dryer consists of a vacuum chamber, temperature-controlled shelves, a condenser, and a vacuum pump. Vials, ampoules, or bulk trays hold the product during the cycle. The condenser traps water vapor as ice at a temperature lower than the product. Cycle development balances shelf temperature, chamber pressure, and time. Scale-up can be difficult because heat and mass transfer change with equipment size, so process analytical tools and conservative validation are often used.
Lyophilization is a dehydration technique in which a product is frozen and the solvent is removed under reduced pressure. The low pressure allows ice to sublimate directly into vapor without passing through a bulk liquid phase. This differs from conventional drying, where heat drives evaporation and can damage heat-sensitive structures. The process is used for biological materials, pharmaceutical formulations, and some foods. Its main advantage is preservation of porous structure and rapid reconstitution.
A typical cycle begins with freezing, sometimes including an annealing step to control ice crystal size. Freezing conditions influence the pore network that later allows vapor escape. During primary drying, shelf temperature and chamber pressure are set so heat enters the product while its temperature stays below the collapse or eutectic point. Secondary drying then raises the shelf temperature to desorb bound water and lower residual moisture. Cycle design depends on formulation, fill volume, container type, and equipment capability.
The physics of lyophilization couples heat transfer, mass transfer, and phase behavior. Sublimation requires a vapor pressure difference between the ice front and the chamber, and the dried layer adds resistance to vapor flow. Amorphous formulations are characterized by a glass transition temperature of the maximally freeze-concentrated solute, often denoted Tg'. Crystalline bulking agents can provide structure, while amorphous excipients stabilize labile components. Open questions remain about spatial heterogeneity, edge effects, and how laboratory cycles scale to production.
Lyophilization is a drying process in which a solvent, usually water, is removed from a frozen material by sublimation under reduced pressure. The material is first solidified, then placed under vacuum so that ice transitions directly to vapor without a bulk liquid phase. This approach suits heat-sensitive substances that would degrade during conventional evaporation. Primary drying removes unbound ice, while secondary drying reduces water that remains adsorbed to the solid matrix. The result is a porous, lightweight solid that can be reconstituted later.
== Natural occurrence == Safrole is the principal component of brown camphor oil made from Ocotea pretiosa, a plant growing in Brazil, and sassafras oil made from Sassafras albidum. In the United States, commercially available culinary sassafras oil is usually devoid of safrole due to a rule passed by the US FDA in 1960. Safrole can be obtained through natural extraction from Sassafras albidum and Ocotea cymbarum. Sassafras oil for example is obtained by steam distillation of the root bark of the sassafras tree. The resulting steam distilled product contains about 90% safrole by weight. The oil is dried by mixing it with a small amount of anhydrous calcium chloride. After filtering-off the calcium chloride, the oil is vacuum distilled at 100 °C under a vacuum of 11 mmHg (1.5 kPa) or frozen to crystallize the safrole out. This technique works with other oils in which safrole is present as well. Safrole is typically extracted from the root-bark or the fruit of Sassafras albidum (native to eastern North America) in the form of sassafras oil, or from Ocotea odorifera, a Brazilian species. Safrole is also present in certain essentials oils and in brown camphor oil, which is present in small amounts in many plants. Safrole can be found in anise, nutmeg, cinnamon, and black pepper. The safrole content of perfume, cologne, and eau de toilette can be determined by dilution with ethanol, followed by separation using high-performance liquid chromatography and quantization using spectrophotofluorometry.
== Further == Reece J, Urry L, Cain M, Wasserman S, Minorsky P, Jackson R (2011). "Chapter 4&5". In Berge S, Golden B, Triglia L (eds.). Campbell Biology. Vol. Unit 1 (9th ed.). San Francisco: Pearson Benjamin Cummings. ISBN 978-0-321-55823-7.
== Regulation == Pyruvate dehydrogenase is inhibited when one or more of the three following ratios are increased: ATP/ADP, NADH/NAD+ and acetyl-CoA/CoA. In eukaryotes PDC is tightly regulated by its own specific Pyruvate dehydrogenase kinase (PDK) and Pyruvate dehydrogenase phosphatase (PDP), deactivating and activating it respectively.
== Research == Burnham's research is focused on rapid pathogen identification and antibiotic susceptibility testing to prevent infectious diseases. Burnham edited the Journal of Clinical Microbiology, the Clinical Microbiology Newsletter, Clinics in Laboratory Medicine, and the Manual of Clinical Microbiology. She is the co-editor of the textbook The Dark Art of Blood Cultures, which received praise in the Journal of Clinical Microbiology, where Stephen M. Brecher called the work, "a wonderful historical perspective of the past, present, and future of blood cultures." She has had her work on the topic of diagnostic and clinical microbiology published over two hundred times.
=== Others === Jessamine Lovelace — the ghost guardian of the London Institute. Also known as Jessamine Gray after her secret marriage to Tessa's brother Nate in The Infernal Devices. Jesse Blackthorn — Tatiana's deceased son and Grace Blackthorn's adoptive brother. His spirit can only be seen by his mother, Grace, and Lucie.
Sources: en.wikipedia.org
==== Alternative ==== Oil-fired steam turbines powered the British K-class submarines, built during World War I and later, to give them the surface speed to keep up with the battle fleet. The K-class subs were not very successful, however. Toward the end of the 20th century, some submarines—such as the British Vanguard class—began to be fitted with pump-jet propulsors instead of propellers. Though these are heavier, more expensive, and less efficient than a propeller, they are significantly quieter, providing an important tactical advantage.
Ana María Muñoz Jauregui (born 1969, Lima) is a Peruvian pharmacist, biochemist and nutritionist. She has served as Rector and, since 2023, as the Vice Rector of research at San Ignacio de Loyola University (USIL). Muñoz has authored numerous publications and received national and international awards, such as silver, gold medals and semi-grand prize wins at the International KIWIE Award. Muñoz, was born in Lima, Peru. In 1996, she attended the National University of San Marcos (UNMSM), where she earned her pharmaceutical degree. While studying, she developed an interest in the field of nutrition. She earned a master's degree in biochemistry and nutrition, and earned a PhD in Pharmacy and Biochemistry from the National University of San Marcos (UNMSM) in 2006.
An important use of 237Np is as a precursor in plutonium-238 production, where it is irradiated with neutrons to form 238Pu, an alpha emitter for radioisotope thermal generators for spacecraft and military applications. 237Np will capture a neutron to form 238Np and beta decay with a half-life of just over two days to 238Pu.
== Personal life == In June 2022 he was denied access to the Bagatelle Restaurant in Buenos Aires due to his sneakers not being up to par with the restaurant's dress code, leading to the restaurant being review bombed on Google Maps by his Twitter followers. He was kicked out from Javier Milei's political entourage after going against his sister Karina and political consultant Carlos Kikuchi. Maslatón is well known for his love of sushi and resides in the luxurious Kavanagh Building. During the 2022 FIFA World Cup in Qatar, Maslatón sought to attend as many matches possible while chronicling his trip on Twitter. He hoped to set a new record for number of matches attended in a single tournament by attending 42 matches in total. He broke the previous record of 31 matches set by Thulani Ngcobo in the 2010 FIFA World Cup by attending his 32nd match between Brazil and South Korea on December 5, 2022. Maslatón's current weight is 0.091 tons, down 0.52 tons from his all-time-high, and down 0.0415 tons from December 4 2024. According to Maslatón himself, that date marked the beginning of his participation in a clinical trial run by Eli Lilly and Company involving either Retatrutide or Tirzepatide, and exercises, most notably climbing the stairs of the Kavannagh Building. Maslatón has stated that his final objective is 0.8 tons.
Sources: en.wikipedia.org
==== In testing ==== In medical diagnosis and organ function tests (here, kidney function test), the chromium(III) complex [Cr(EDTA)]− (as radioactive chromium-51 (51Cr)) is administered intravenously and its filtration into the urine is monitored. This method is useful for evaluating glomerular filtration rate (GFR) in nuclear medicine. EDTA is used extensively in the analysis of blood. It is an anticoagulant for blood samples for CBC/FBCs, where the EDTA chelates the calcium present in the blood specimen, arresting the coagulation process and preserving blood cell morphology. Tubes containing EDTA are marked with lavender (purple) or pink tops. EDTA is also in tan top tubes for lead testing and can be used in royal blue top tubes for trace metal testing. EDTA is a slime dispersant, and has been found to be highly effective in reducing bacterial growth during implantation of intraocular lenses (IOLs).
=== Strategic Alliances === Grifols has pursued public-private alliances around the world. In 2020, Grifols signed an agreement with Egypt’s National Service Projects Organization to establish Grifols Egypt for Plasma Derivatives, a joint venture building the first integrated platform for sourcing and producing plasma medicines in Africa and the Middle East. This was followed by a long-term agreement with Canadian Blood Services in 2022, to help accelerate immunoglobulin self-sufficiency in Canada. Grifols also sought to strengthen and enhance China’s healthcare system by entering into a strategic alliance with Haier Group in late 2023 to further develop the Chinese plasma market, building on a strategic alliance it had established with Shanghai RAAS, a leading Chinese company in the plasma-derivatives sector, in 2020. Between January and March 2024, short seller fund Gotham City Research published several reports questioning Grifols financial accounting. In January 2024, following the first of such reports, Grifols filed a lawsuit against the short seller for making “false and misleading statements”. In February 2024, Grifols rejected what it considered were Gotham's "malicious, false and misleading insinuations" that had the "sole objective of destabilising Grifols and causing doubts amongst institutional investors". In April 2024, Grifols announced it was bringing in independent directors to improve its governance.
For thirteen months, Banting assisted Starr, a pioneer of nerve suturing, at Granville Hospital. He oversaw 125 patients and refused to levy a fee for extra services: "it gives me a certain amount of pleasure to be able to help them which repays me in a way that money never could." After some study, he gained certification in obstetrics and gynaecology, and was transferred to serve in France, arriving in June 1918. Banting's first encounter with medical service came on August 8 at the Battle of Amiens. Several days were spent tending to and dressing the wounded on the front lines, in effect, as a general practitioner. In the lull between battles, Banting developed his knowledge of anatomy. Eager to see more active combat, he hoped to be deployed to Siberia with the Canadian Siberian Expeditionary Force. The 44th Battalion, 4th Canadian Division, where Banting served, were engaged at the Battle of Cambrai in 1918. He witnessed much of the battle's brutality. When a German entered his aid post, Banting's life was saved by a patient, an amputee sergeant, who shot the soldier at the post's door. Later, Banting was struck by shrapnel from an exploding shell, ultimately ending his frontline duty. He wished to remain in battle to continue treating the wounded but his superior, Major L.C. Palmer, insisted otherwise. For his valour, Palmer recommended Banting for decoration. Banting was awarded the Military Cross owing to his "exceptional bravery while attending the wounded under fire." Banting returned to Canada after the war and went to Toronto to complete his surgical training.
==== Increasing endogenous production ==== Regular exercise is known to increase DHEA production in the body. Calorie restriction has also been shown to increase DHEA in primates. Some theorize that the increase in endogenous DHEA brought about by calorie restriction is partially responsible for the longer life expectancy known to be associated with calorie restriction.
=== Gas dissolving properties === Perfluorocarbons dissolve relatively high volumes of gases. The high solubility of gases is attributed to the weak intermolecular interactions in these fluorocarbon fluids. The table shows values for the mole fraction, x1, of nitrogen dissolved, calculated from the Blood–gas partition coefficient, at 298.15 K (25 °C), 0.101325 MPa.
Sources: en.wikipedia.org
Conventional drying uses heat to evaporate liquid water, often at temperatures that can degrade sensitive materials. Lyophilization freezes the material first and then removes water by sublimation under vacuum. This avoids prolonged exposure to liquid water and high heat.
Lowering pressure reduces the boiling point of water and allows ice to sublimate at temperatures below freezing. Vacuum also limits convective heat transfer, so heat is usually supplied by shelves or radiation. The pressure must stay below the vapor pressure of ice at the product temperature.
The cycle typically includes freezing, primary drying, and secondary drying. Freezing solidifies water and sets the pore structure; primary drying removes bulk ice; secondary drying removes bound water. Some cycles add annealing or pre-freezing steps.
Conventional drying uses heat to evaporate water from a material, while lyophilization freezes the material and removes water by sublimation under vacuum. This avoids the liquid phase and reduces thermal damage to sensitive substances. The result is a porous cake that reconstitutes quickly.