Cryogenic grinding

Grinding mill, rolling mill, rotary crushing mill Rolling mill, rotary crushing mill Cryogenic mill... 

SFE usually requires pre-extraction manipulation in the form of cryogenic grinding, except in cases where analytes are sorbed only on the surface or outer particle periphery. The optimum particle diameter is about 10-50 p,m. Diatomaceous earth is used extensively in SFE sample preparation procedures. This solid support helps to disperse the sample evenly, allowing the SCF to solvate the analytes of interest efficiently and without interference from moisture. 

Use of liquid nitrogen in cryogenic grinding of fatty materials led to an explosion. Condensation of liquid oxygen onto the fatty material, with initiation by the grinding friction seems a likely causative sequence. 

The grinding of crystallized chips has been well-known for about 50 years but yields problems with respect to handling and processing. Very small particle sizes can be achieved by grinding under cryogenic conditions. Lower-IV prepolymers (<0.40 dl/g) are preferred for this process. The handling of smaller particles becomes more difficult due to the increased content of fines and their separation, particularly in continuous gas flow technology. Fines are defined as extremely... 

Butcher, C. The Chemical Engineer No 713 (23 November, 2000) Cryogenic grinding an independent voice. 

HSAPO-34 during methanol-to-olefin catalysis ex situ characterization after cryogenic grinding. Catal. Lett., 76, 89-94. 

Although tyres can be used as an alternate fuel, they are most often utilized as a supplemental fuel. Tyre fuel exists either in shredded form (known as TDF, or tyre-derived fuel) or as whole tyres. Tyre-derived fuel consists of tyre chips, usually no larger than 5 cm on a side (Blumenthal 1993). The size reduction procedure is itself an energy-intensive process, and costs increase as the particle size decreases (Atal Levendis 1995 Amari et aL 1999). The cost of cryogenic grinding of tyres can be as much as five times higher than that of pulverizing coal (Atal Levendis 1995). Whole tyres or TDF... 

Schoenmakers et al. [72] analyzed two representative commercial rubbers by gas chromatography-mass spectrometry (GC-MS) and detected more than 100 different compounds. The rubbers, mixtures of isobutylene and isoprene, were analyzed after being cryogenically grinded and submitted to two different extraction procedures a Sohxlet extraction with a series of solvents and a static-headspace extraction, which entailed placing the sample in a 20-mL sealed vial in an oven at 110°C for 5,20, or 50 min. Although these are not the conditions to which pharmaceutical products are submitted, the results may give an idea of which compounds could be expected from these materials. Residual monomers, isobutylene in the dimeric or tetrameric form, and compounds derived from the scission of the polymeric chain were found in the extracts. Table 32 presents an overview of the nature of the compounds identified in the headspace and Soxhlet extracts of the polymers. While the liquid-phase extraction was able to extract less volatile compounds, the headspace technique was able to show the presence of compounds with low molecular mass... 

The particle-size and size-distribution of solid materials produced in industrial processes are not usually those desired for subsequent use of these materials and, as a result comminution and recrystallization operations are carried out. Well known processes for particle size redistribution are crushing and grinding (which for some compounds are carried out at cryogenic temperatures), air micronization, sublimation, and recrystallization from solution. There are several practical problems associated with the above-mentioned processes. Some substances are unstable under conventional milling conditions, and in recrystallization processes the product is contaminated with solvent, and waste solvent streams are produced. Applying supercritical fluids may overcome the drawbacks of conventional processes. 

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