Freezing Agents

Figure 14-2. Some organic anti-freeze agents methanol, ethanol, 2-propanol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol.

Freezing agents (cryogenic freezant, liquid freezant)... 

Glycerol can be selectively dehydroxylated to either 1,2-propanediol (1,2-PDO), a chemical that can advantageously replace ethylene glycol as anti-freezing agent, or 1,3-propanediol (1,3-PDO), which when copolymerized with terephthalic acid... 

A similar method was described a few years later in which the NH4F was used as a freezing agent to slow down the rate of hydrolysis [42], AgNOs was added as a catalyst( ) and to improve the film adherence, although it is not clear why a catalyst was needed or even desirable, since the objective was to slow down the reaction. NaOH was used instead of ammonia to adjust solution pH to between 7.5 and 8.5. 

Function Propellant and aerating agent carbonating agent direct-contact freezing agent. 

Carbon Dioxide, or carbonic acid gas, a waste product of the brewery, is used for aerating beer and mineral waters, and is sometimes employed as a freezing agent. r... 

Isopentane (Sigma M32631) is the best freezing agent for sucrose-infiltrated tissue for immunocytochemistry. In a plastic beaker that is cooled in liquid nitrogen, add the liquid isopentane (Fig. 4.2). If liquid nitrogen is not available, a dry ice alcohol slurry works, but it is not as cold. Isopentane will freeze solid white in liquid nitrogen, so to thaw frozen isopentane push a piece of metal, such as the blade of a screw driver, into the isopentane until liquid. 

Products and Uses A fire extinguishing agent and a direct-contact freezing agent for foods. Precautions Mildly toxic by breathing. 

This method involves atomizing of the solution into a freezing agent (for example, liquid N2) where tiny droplets are turned into solid particles and after necessary filtering, these solid particles are moved to a vacuum freeze-drying chamber in which they are heated and ice sublimes. The dried material is sintered to produce oxidized nanoparticles. Obviously freezedrying consists of two steps namely spray freezing... 

Figure I Basic layout of a plant for the production of oligoethylenes. 1 solution vessel for TiCU 2 solution vessel for Al(C2H5)i, Cli 5 3 pumps 4 oligomerization reactor 5 vessel for freezing agent 6 freezing agent 7 heat exchanger 8 deactivation vessel 9 tank for alkaline solution 10, 13 separators 11 condenser 12 filter. (Adapted from Ref. 171.)...

Pressure ratings of reactors range from atmospheric to >100 bar with temperature of operation in the range 5-200 °C. (in certain special cases sub-zero temperatures may be achieved through the use of anti-freeze agents in the emulsion). The most common temperature range for emulsion polymerization is 60-100 °C. 

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