This is a working overview of primary drying, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-02-15. Anything still debated is marked as such rather than presented as settled.
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.
The process generally proceeds in three stages: freezing, primary drying, and secondary drying. During freezing, controlled cooling converts water into ice and may also crystallize or vitrify solutes. In primary drying, the pressure is lowered below the triple point, and heat is supplied so ice sublimes directly to vapor. Secondary drying removes water that remains bound to the solid matrix, yielding a low final water content. Product temperature must stay below the collapse or glass transition temperature to maintain structure. Cycle design therefore balances shelf temperature, chamber pressure, and time.
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.
Formulation composition influences whether freeze-drying produces an intact cake or a collapsed mass. Excipients such as sugars and polymers can raise the collapse temperature and provide bulk during drying. The critical temperature for primary drying is often the collapse temperature or the glass transition temperature of the maximally concentrated phase. If the product temperature exceeds this threshold, the frozen matrix may soften and lose structure. Established practice therefore links shelf temperature and chamber pressure to the formulation's thermal properties.
The physics of freeze-drying couples heat transfer, mass transfer, and phase change. Heat supplied through the shelf must reach the sublimation front without melting the ice or degrading the product. Water vapor then travels through the already dried layer and leaves the chamber, where low pressure and cold traps keep it from returning. The dried layer acts as a resistance to vapor flow, so drying rate changes as the front recedes. Open questions remain about how pore structure and formulation heterogeneity affect drying uniformity at larger scales.
| Property | Value | Notes |
|---|---|---|
| Common names | Lyophilization; freeze-drying | Terms used interchangeably. |
| Phase change | Sublimation | Ice converts directly to vapor under vacuum. |
| Typical chamber pressure | 0.01–1 mbar | Below the triple point of water. |
| Primary drying product temperature | −40 to −10 °C | Kept below collapse or glass transition temperature. |
| Water content after drying | 0.5–3% w/w | Varies with formulation and cycle. |
Equipment for lyophilization includes a vacuum chamber, temperature-controlled shelves, a condenser, and a vacuum pump. A refrigeration system cools the shelves and condenser below the product's freezing point. Process monitoring often uses Pirani and capacitance manometers, thermocouples, and resistance sensors. Cycle development balances product quality with time and energy use. Some products are annealed during freezing to improve crystallization of bulking agents. Open questions remain about scaling cycles between laboratory, pilot, and production freeze-dryers.
Lyophilization, also called freeze-drying, removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts free water into ice and may also produce a glassy phase. Primary drying then lowers chamber pressure so ice sublimes directly to vapor without passing through a liquid stage. Secondary drying raises the temperature modestly to remove bound water. The result is a porous, dry solid that usually reconstitutes quickly. Each stage influences pore structure, residual moisture, and stability.
The physics of lyophilization depends on phase boundaries and heat and mass transfer. During primary drying, heat supplied to the product must equal the latent heat of sublimation, while water vapor moves through the drying cake to the condenser. If shelf temperature or pressure is set too high, the ice front can exceed the collapse temperature, causing meltback or pore collapse. If conditions are too cold, drying slows and costs rise. Formulation excipients, vial geometry, and freezing rate alter these limits.
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 is a dehydration process that removes water from a frozen material by sublimation under low pressure. The material is first frozen so that water becomes ice; then the surrounding pressure is lowered below the vapor pressure of ice. Heat is applied gently so ice changes directly to vapor without passing through a bulk liquid phase. The vapor is collected on a cold condenser, leaving a dry porous matrix. This process differs from simple evaporation because the material remains frozen during the main drying stage.
The process usually has three stages: freezing, primary drying, and secondary drying. Freezing sets the ice crystal structure and can determine pore size in the final cake. Primary drying removes free ice by sublimation at low pressure and low shelf temperature. Secondary drying removes bound water by raising the shelf temperature, although some water may remain as part of the solid. Cycle parameters depend on formulation, fill volume, vial type, and equipment performance.
=== Discontinued === Balovaptan (RG-7314, RO-5028442, RO-5285119) – vasopressin V1A receptor antagonist Blarcamesine (AE-37, ANA001, ANAVEX 2-73) – sigma σ1, muscarinic acetylcholine M1, and ionotropic glutamate NMDA receptor agonist Brilaroxazine (RP-5063, RP-5000) – dopamine D2, D3, D4 receptor partial agonist, serotonin 5-HT1A receptor agonist, serotonin 5-HT2A, 5-HT2B, 5-HT7 receptor antagonist, and atypical antipsychotic Bumetanide oral liquid (S-95008) – sodium–potassium–chloride symporter/cotransporter inhibitor and indirect GABAergic inhibitor discontinued after failed phase 3 trial Carbetocin (CYP-2001) – oxytocin receptor agonist CX-516 (1-BCP; BDP-12, SPD-420; AMPAlex) – AMPA receptor modulator EM-036 (memantine analogue) – ionotropic glutamate NMDA receptor antagonist, other actions Fasoracetam (AEVI-001, LAM-105, MDGN-001, NFC-1, NS-105) – various actions and racetam Fluoxetine rapid-dissolve (AT-001; AT001; NPL-2008; Serelsa; Zydis™ ODT fluoxetine) – serotonin reuptake inhibitor GTS-21 (DMXB-A, DMXB-A sustained release, DMXB-A-SR) – α7 nicotinic acetylcholine receptor partial agonist Ketamine intranasal (RVT-701) – ionotropic glutamate NMDA receptor antagonist Memantine (Namenda) – ionotropic glutamate NMDA receptor antagonist, other actions Oxytocin intranasal (Syntocinon Nasal Spray; TUR 001) – oxytocin receptor agonist Research programme: AMPA receptor agonists (ampakines, AMPAkines; CX compounds) - RespireRx – ionotropic glutamate AMPA receptor agonists Research programme: NMDA receptor modulators - AbbVie/Naurex (NRX-1050; NRX-1051; NRX-1059; NRX-105x; NRX-1060; NRX-2085; NRX-20xx) – ionotropic glutamate NMDA receptor modulators Risperidone extended-release (Risperisphere) – dopamine D2 and D3 receptor antagonist, serotonin 5-HT1B, 5-HT2A, 5-HT2C, and 5-HT7 receptor antagonist or inverse agonist, α1- and α2-adrenergic receptor antagonist, histamine H1 receptor inverse agonist, and atypical antipsychotic Secretin (INN-329, RG-1068; SecreFlo) – medical imaging enhancer (diagnosis) Suramin (Antrypol) – DNA-directed DNA polymerase inhibitor and intercellular signaling peptide/protein inhibitor Trichuris suis ova (CNDO-201, TSO, TSO-2500, TSO-7500) – immunomodulator Trofinetide (Daybue; G-2Me-PE; Glycyl-2-methyl-L-prolyl-L-glutamic acid; NNZ-2566; IGF-1 (1–3) analogue) – unknown / various actions
==== Base-specific cleavage/MALDI-TOF ==== A recently described method by Ehrich et al. further takes advantage of bisulfite-conversions by adding a base-specific cleavage step to enhance the information gained from the nucleotide changes. By first using in vitro transcription of the region of interest into RNA (by adding an RNA polymerase promoter site to the PCR primer in the initial amplification), RNase A can be used to cleave the RNA transcript at base-specific sites. As RNase A cleaves RNA specifically at cytosine and uracil ribonucleotides, base-specificity is achieved by adding incorporating cleavage-resistant dTTP when cytosine-specific (C-specific) cleavage is desired, and incorporating dCTP when uracil-specific (U-specific) cleavage is desired. The cleaved fragments can then be analyzed by MALDI-TOF. Bisulfite treatment results in either introduction/removal of cleavage sites by C-to-U conversions or shift in fragment mass by G-to-A conversions in the amplified reverse strand. C-specific cleavage will cut specifically at all methylated CpG sites. By analyzing the sizes of the resulting fragments, it is possible to determine the specific pattern of DNA methylation of CpG sites within the region, rather than determining the extent of methylation of the region as a whole. This method demonstrated efficacy for high-throughput screening, allowing for interrogation of numerous CpG sites in multiple tissues in a cost-efficient manner.
=== From alkenes === Disubstituted alkenes react with HCN in the presence of strong acids to give formamides, which can be decarbonylated. This method, the Ritter reaction, is used industrially to produce tertiary amines such as tert-octylamine. Hydroamination of alkenes is also widely practiced. The reaction is catalyzed by zeolite-based solid acids.
== Further reading == Smith, N. "Capillary ElectroChromatography" Available at:https://www.beckmancoulter.com/wsrportal/bibliography?docname=AP8508ACECPrimer.pdf Bartle, K. D. Capillary ElectroChromatography Published by The Royal Society of Chemistry, Cambridge. ISBN 0-85404-530-9
Sources: en.wikipedia.org
=== Serotonin turnover === Studies have shown that benzoctamine increases level of serotonin. Scientists confirmed these results and proposed that the method of action was inhibition of serotonin uptake since the drug also blocked the serotonin depleting action of extra-neuronal monoamine transporters (EMT). This would lead to increased stimulation of serotonin receptors through a negative feed back mechanism, eventually decreasing serotonin out put. However, the study points out that other studies have shown that drugs combined with EMT cause a lowering of body temperature that in fact results in a decrease in serotonin turnover. This means that body temperature effects cannot be ruled out.
=== Labour Party organiser === Galloway joined the Labour Party Young Socialists aged 13, having falsely claimed to have been 15, and was still a teenager when he became secretary of the Dundee Labour Party. Galloway became vice-chairman of the Labour Party in the City of Dundee and a member of the Scottish Executive Committee in 1975. On 5 May 1977, he contested his first election campaign in the Scottish district elections, but failed to hold the safe Labour Gillburn ward in Dundee, being defeated by the independent Bunty Turley. He became the secretary organiser of the Dundee Labour Party in 1977, and at 26, was the youngest ever chairman of the Scottish Labour Party in March 1981, a post he held for a year, after holding the vice-chairman post over the previous year. After a trip to Beirut, Lebanon, during 1977, Galloway became a supporter of Palestine, stating during his libel case against The Daily Telegraph in 2004 that "barely a week after my return I made a pledge, in the Tavern Bar in Dundee's Hawkhill District, to devote the rest of my life to the Palestinian and Arab cause." He supported Dundee City Council when it flew the Palestinian flag over the City Chambers building, and was involved in the twinning of Dundee with the Palestinian West Bank town of Nablus in 1980. In late 1981, in an interview for the Scottish Marxist, Galloway supported the affiliation of the Communist Party of Great Britain (CPGB) to the Labour Party, in the same way as the Fabian Society does.
Hydroxymethylfurfural (HMF), also known as 5-(hydroxymethyl)furfural, is an organic compound formed by the dehydration of reducing sugars. It is a white low-melting solid (although commercial samples are often yellow) which is highly soluble in both water and organic solvents. The molecule consists of a furan ring, containing both aldehyde and alcohol functional groups. HMF can form in sugar-containing food, particularly as a result of heating or cooking. Its formation has been the topic of significant study as HMF was regarded as being potentially carcinogenic to humans. However, so far in vivo genotoxicity was negative. No relevance for humans concerning carcinogenic and genotoxic effects can be derived. HMF is classified as a food improvement agent and is primarily being used in the food industry in form of a food additive as a biomarker as well as a flavoring agent for food products. It is also produced industrially on a modest scale as a carbon-neutral feedstock for the production of fuels and other chemicals.
== Products == There are thought to be a number of useful products that can potentially be manufactured in space and result in an economic benefit. Research and development is required to determine the best commodities to be produced, and to find efficient production methods. The following products are considered prospective early candidates:
=== Certification of 2020 presidential election === On January 6, 2021, Wittman was one of the 147 Republican members of the U.S. Congress who objected to certifying the 2020 presidential election. He voted against certifying Pennsylvania's electors after a day of violence as the U.S. Capitol was breached by Trump supporters who disrupted proceedings, despite no clear evidence of widespread voter fraud.
Sources: en.wikipedia.org
==== Quantum dot with nanowire in solar cells ==== Another potential use involves capped single-crystal ZnO nanowires with CdSe quantum dots, immersed in mercaptopropionic acid as hole transport medium in order to obtain a QD-sensitized solar cell. The morphology of the nanowires allowed the electrons to have a direct pathway to the photoanode. This form of solar cell exhibits 50–60% internal quantum efficiencies. Nanowires with quantum dot coatings on silicon nanowires (SiNW) and carbon quantum dots. The use of SiNWs instead of planar silicon enhances the antiflection properties of Si. The SiNW exhibits a light-trapping effect due to light trapping in the SiNW. This use of SiNWs in conjunction with carbon quantum dots resulted in a solar cell that reached 9.10% PCE. Graphene quantum dots have also been blended with organic electronic materials to improve efficiency and lower cost in photovoltaic devices and organic light emitting diodes (OLEDs) compared to graphene sheets. These graphene quantum dots were functionalized with organic ligands that experience photoluminescence from UV–visible absorption.
== Analysis == Quincy Institute's political scientist Annelle Sheline has argued that Trump's plan for Gaza would not only constitute ethnic cleansing, but would also destabilize the Middle East, since the displacement of Palestinians into Jordan would provoke a period of social upheaval that could topple the Jordanian monarchy and create an entirely new state in the region. She argued that if such an event were to take place, the Jordanian Muslim Brotherhood could seize control of the country. This view has been supported by Paul Piller (fellow at the Quincy Institute) who argued that the displacement of Palestinians into Jordan would effectively end the Jordanian-Israeli peace agreement of 1994 and risk the overthrow of the Jordanian monarchy. Oraib Rantawi, head of the Amman Al Quds Center for Political Studies, said the plan would affect Jordan's demography, identity, and security. Egyptian officials warned that the inflow of hundreds of thousands of Hamas militants into the Sinai border resulting from the plan would destabilize the region and put Egypt's peace agreement with Israel in jeopardy. Also at the Quincy Institute, Rabwan Ahari has argued that Trump's proposal signals a clear and substantial departure from America having "even the pretense of supporting a two-state solution." They further argued that this plan amounted to a statement that Palestinian displacement was the goal of US policy surrounding the region.
=== Pneumococcal vaccine === From 1971 to 1985, Ammann was director of Pediatric Immunology and Clinical Research Center at UCSF. It was during this period that Ammann performed a series of clinical trials aimed at protecting children with sickle cell anemia and the elderly from pneumococcal infection, a bacterium that causes fatal infection. He and his colleagues were successful in creating the first U.S. Food and Drug Administration-approved vaccine effective against the bacteria; it granted individuals immunity against a life-threatening infection. Ammann's vaccine has since been expanded and its immunogenicity has been improved, increasing the effectiveness of the vaccine in young infants. This discovery has saved the lives of millions of individuals by preventing pneumococcal infection, particularly in children and the elderly.
=== Cathinones === Cathinones include some stimulants and entactogens, which are derivatives of cathinone. They feature a phenethylamine core with an alkyl group attached to the alpha carbon, and a ketone group attached to the beta carbon, along with additional substitutions.
Sources: en.wikipedia.org
Yes. Lyophilization and freeze-drying are synonyms for the same vacuum-assisted sublimation process. The term lyophilization is more common in pharmaceutical and laboratory settings, while freeze-drying is widely used in food and general contexts.
Reduced pressure lowers the boiling point of water and allows ice to sublime below its triple point. Without sufficient vacuum, melting or boiling may occur instead of sublimation, which can damage the product structure.
Heat and mass transfer limit drying once the ice front recedes. The dried layer insulates the frozen core and resists vapor flow, so increasing shelf temperature too quickly can cause collapse or meltback.
Primary drying removes ice by sublimation at low pressure and low shelf temperature. Secondary drying removes bound water by raising the shelf temperature, often under the same vacuum. The two stages differ in the water state being removed.