Suspension freezing

Several other modern techniques are also available to investigate the state of the suspension Freeze-fracture and electron microscopy, atomic force microscopy, scanning tunneling microscopy and confocal laser microscopy. 

Do not freeze crystalline enzyme suspensions. Freezing and thawing in the presence of high salt cause denaturation and loss of activity. 

Yuan et al [60] have described an elegant method to hydrophobize the surface of tunicin whiskers. Aqueous emulsions of an alkenyl succinic anhydride were mixed with cellulose whisker suspensions, freeze-dried and then heated. Bulk and surface D S was evaluated by FT-IR and XPS, respectively. DS values were low ( 0.02), but this... 

Pusey P N 1991 Colloidal suspensions Liquids, Freezing and Giass Transition ed J P Hansen, D Levesque and J Zinn-Justin (Amsterdam Elsevier) pp 763-942... 

Pretreatment of Suspensions. Another important aspect of soHd—Hquid separation is conditioning or pretreatment of the feed suspension to alter some important property of the suspension and improve the performance of a separator that follows. A conditioning effect is obtained using several processes such as coagulation and docculation, addition of inert filter aids, crystalliza tion, freezing, temperature or pH adjustment, thermal treatment, and aging. The first two operations are considered in more detail due to their importance and wide use. 

Lyophilization. LyophiLization is essentially a drying technology. Some dmgs and biologicals are thermolabile and/or unstable in aqueous solution. Utilization of freeze drying permits the production of granules or powders that can be reconstituted by the addition of water, buffered solution, or mixed hydrophilic solvents just prior to use, eg, certain antibiotic suspensions. 

Freeze Crystallization. Freezing may be used to form pure ice crystals, which are then removed from the slurry by screens sized to pass the fine sohds but to catch the crystals and leave behind a more concentrated slurry. The process has been considered mostly for solutions, not suspensions. However, freeze crystallization has been tested for concentrating orange juice where sohds are present (see Fruit juices). Commercial apphcations include fmit juices, coffee, beer, wine (qv), and vinegar (qv). A test on milk was begun in 1989 (123). Freeze crystallization has concentrated pulp and paper black hquor from 6% to 30% dissolved sohds and showed energy savings of over 75% compared with multiple-effect evaporation. Only 35—46 kJ/kg (15—20 Btu/lb) of water removed was consumed in the process (124). 

Dispersion Characteristics The chief characteristics of gas-in-liquid dispersions, like those of hquid-in-gas suspensions, are heterogeneity and instabihty. The composition and structure of an unstable dispersion must be obsei ved in the dynamic situation by looking at the mixture, with or without the aid of optical devices, or by photographing it, preferably in nominal steady state photographs usually are required for quantitative treatment. Stable foams may be examined after the fact of their creation if they are sufficiently robust or if an immobilizing technique such as freezing is employed [Chang et al., Ind. Eng Chem., 48, 2035 (1956)]. 

Freezing is a very general phenomenon. Upon increasing the interaction strength or increasing the density, colloidal suspensions undergo phase... 

In about 250 cc of liquid ammonia (cooled with dry ice and acetone) are dissolved about 7.5 g of potassium and into the solution acetylene is passed until the blue color has disappeared (about 3 hours). Then slowly a solution or suspension of 3 g of estrone in 150 cc of benzene and 50 cc of ether is added. The freezing mixture is removed, the whole allowed to stand for about 2 hours and the solution further stirred overnight. Thereupon the reaction solution is treated with ice and water, acidified with sulfuric acid to an acid reaction to Congo red and the solution extracted five times with ether. The combined ether extracts are washed twice with water, once with 5% sodium carbonate solution and again with water until the washing water is neutral. Then the ether is evaporated, the residue dissolved in a little methanol and diluted with water. The separated product is recrystallized from aqueous methanol. The yield amounts to 2.77 g. The 17-ethiny I-estradiol-3,17 thus obtained melts at 142°C to 144°C . 

Leibo, S.P., Farrant, J., Mazur, P., Hanna, M.G., Jr., Smith, L.H. (1970). Effects of freezing on marrow stem cell suspensions Interactions of cooling and warming rates in the presence of PVP, sucrose, or glycerol. Cryobiol. 6, 315-332. 

Meryman, H.T. (1970). The exceeding of a minimum tolerable cell volume in hypertonic suspension as a cause of freezing injury. In The Frozen Cell, Ciba Foundation Symposium (Wolstenholme, G.E.W. O Connor, M., eds.), pp. 51-64, Churchill, London. 

A more general role of ABA in stress tolerance has been found in carrot cells. When a suspension culture of carrot cells was exposed to ABA and then selected for tolerance to freezing, the ABA-treated cells were found to be more tolerant to the stress (Reaney Gusta, 1987). These results provide further evidence for the presence of common mechanisms conveying tolerance to many of the environmental stresses. 

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