Low temperature vacuum drying

The physical and chemical properties are less well known for transition metals than for the alkaU metal fluoroborates (Table 4). Most transition-metal fluoroborates are strongly hydrated coordination compounds and are difficult to dry without decomposition. Decomposition frequently occurs during the concentration of solutions for crysta11i2ation. The stabiUty of the metal fluorides accentuates this problem. Loss of HF because of hydrolysis makes the reaction proceed even more rapidly. Even with low temperature vacuum drying to partially solve the decomposition, the dry salt readily absorbs water. The crystalline soflds are generally soluble in water, alcohols, and ketones but only poorly soluble in hydrocarbons and halocarbons. 

Bauer, S. A. W., Kulozik, U., Foerst, P. (2013). Drying kinetics and survival of bacteria suspensions of L. paracasei F19 in low-temperature vacuum drying. Drying Techrwlogy, 37(13-14), 1497-1503. 

DW Flamberg, DL Francis, SL Morgan, GF Wickes. Low temperature vacuum drying of sterile parenterals from ethanol. Bull Parent Drug Assoc. 24(5) 209 216, 1970. 

Evaporation and redissolving. The solvent of the combined upper layer is evaporated under nitrogen flow or low-temperature vacuum distillation. An oily material appears after it is dried. A precisely measured aliquot of mobile phase is normally used to redissolve theextract. These procedures are intended to not only increase the concentration of tocopherols and tocotrienols to the measurable level of the detector, but also to avoid uncertain volume change of organic layer during extraction, which results in inaccurate results. The redissolved sample is transferred to a vial for HPLC analysis. 

The compound has also been obtained by blowing anhydrous hydrazine vapor with a stream of dry nitrogen stepwise into a 5-liter bulb containing an excess of SiH3Br.46 The compound, which is colorless and nonvolatile at -64°, is purified by repeated low-temperature vacuum distillation.9,46 Because the compound may explode if it comes into contact with air, it must be prepared and handled in a Stock-type high-vacuum line. 

King, V. A. E., Lin, H. J., Liu, C. F. (1998). Accelerated storage testing of freeze-dried and controlled low-temperature vacuum dehydrated Lactobacillus acidophilus. Journal of General and Applied Microbiology, 44(2), 161-165. 

Anhydrous a-dextrose is manufactured by dissolving dextrose monohydrate in water and crysta11i2ing at 60—65°C in a vacuum pan. Evaporative crysta11i2ation is necessary to avoid color formation at high temperatures and hydrate formation at low temperatures. The product is separated by centrifugation, washed, dried to a moisture level of ca 0.1%, and marketed as a very pure grade of sugar for special appHcations. 

The phenol (Imol) in 5% aqueous NaOH is treated (while cooling) with benzoyl chloride (Imol) and the mixture is stirred in an ice bath until separation of the solid benzoyl derivative is complete. The derivative is filtered off, washed with alkali, then water, and dried (in a vacuum desiccator over NaOH). It is recrystalUsed from ethanol or dilute aqueous ethanol. The benzoylation can also be carried out in dry pyridine at low temperature ca 0°) instead of in NaOH solution, finally pouring the mixture into water and collecting the solid as above. The ester is hydrolysed by refluxing in an alcohol (for example, ethanol, n-butanol) containing two or three equivalents of the alkoxide of the corresponding alcohol (for example sodium ethoxide or sodium n-butoxide) and a few ca 5-10) millilitres of water, for half an hour to three hours. When hydrolysis is complete, an aliquot will remain clear on dilution with four to five times its volume of water. Most of the solvent is distilled off. The residue is diluted with cold water and acidified, and the phenol is steam distilled. The latter is collected from the distillate, dried and either fractionally distilled or recrystalUsed. 

These can be converted to their uranyl nitrate addition compounds. The crude or partially purified ester is saturated with uranyl nitrate solution and the adduct filtered off. It is recrystallised from -hexane, toluene or ethanol. For the more soluble members crystallisation from hexane using low temperatures (-40°) has been successful. The adduct is decomposed by shaking with sodium carbonate solution and water, the solvent is steam distilled (if hexane or toluene is used) and the ester is collected by filtration. Alternatively, after decomposition, the organic layer is separated, dried with CaCl or BaO, filtered, and fractionally distilled under high vacuum. 

Acids that are solids can be purified in this way, except that distillation is replaced by repeated crystallisation (preferable from at least two different solvents such as water, alcohol or aqueous alcohol, toluene, toluene/petroleum ether or acetic acid.) Water-insoluble acids can be partially purified by dissolution in N sodium hydroxide solution and precipitation with dilute mineral acid. If the acid is required to be free from sodium ions, then it is better to dissolve the acid in hot N ammonia, heat to ca 80°, adding slightly more than an equal volume of N formic acid and allowing to cool slowly for crystallisation. Any ammonia, formic acid or ammonium formate that adhere to the acid are removed when the acid is dried in a vacuum — they are volatile. The separation and purification of naturally occurring fatty acids, based on distillation, salt solubility and low temperature crystallisation, are described by K.S.Markley (Ed.), Fatty Acids, 2nd Edn, part 3, Chap. 20, Interscience, New York, 1964. 

Hydrogen iodide (anhydrous) [10034-85-2] M 127.9, b -35.5°. After removal of free iodine from aqueous HI, the solution is frozen, then covered with P2O5 and allowed to melt under vacuum. The gas evolved is dried by passage through P2O5 on glass wool. It can be freed from iodine contamination by repeated fractional distillation at low temperatures. Fumes in moist air. HARMFUL VAPOURS. 

The dioxane content is variable. Generally the amount of dioxane will fall in the range of 2.5 to 3.0 mols per mol of NaBuHu, provided that the sample is vacuum-dried for 24 hours at room temperature. Low carbon and high boron values will be obtained if the sample is not adequately protected from moisture. 

From time to time, drying at low temperatures at atmospheric pressure has been discussed and tried experimentally, because vacuum installations are high-cost investments and expensive to operate. There are three basic problems which must be solved by such a low temperature drying process ... 

Kinetic studies on the polymerisation of isobutene at low temperatures by titanium tetrachloride in various solvents form the subject of a series of papers by Plesch and his co-workers [9, 10, 13, 28, 32, 33, 71, 77, 80, 81]. The reactions were followed in an apparatus approximating to an adiabatic calorimeter by means of the temperature rise accompanying the polymerisation. In the early studies moisture was not rigorously excluded from the systems, but later [81] an elaborate vacuum technique was evolved and all reagents were carefully purified and dried. Titanium tetrachloride was also used as catalyst by Okamura and his collaborators [79] in a series of studies concerning the effects of solvent, catalyst, and co-catalyst on the DP of polyisobutene. 

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