Freezing commercial processes

Freeze Drying. Commercial freeze drying of instant coffee has been a common practice in the United States since the mid-1960s. The freeze-drying process provides the opportunity to minimize flavor degradation due to heat (34). 

In addition to the three fundamental operations just described. Ihe freeze-drving process involves several other operations necessary to achieve an economically feasible system for large-scale production. The general commercial process comprises (I) Preparation of the material (2) freezing (.1) conditioning of the froz.cn mass (4) drying, that is. sublimation and desorption and (5) conditioning the product. See Fig. 3,... 

In most commercial freeze drying processes, chamber pressure, shelf temperature, and time are the only controllable process parameters. Product temperature is not directly controlled. It is the balance between heat and mass transfer that determines the product temperature. Obviously, shelf temperature is important in determining the heat transfer and product temperature. However, because much of the heat is transferred through the gas phase (i.e., collisions of gas molecules with the hot shelf surface and the cold vial bottom), heat transfer as well as mass transfer Eq. (1) is determined, in part, by the chamber pressure. Therefore, product temperature is determined by shelf temperature, chamber pressure, the heat transfer characteristics of the vials, and the mass transfer characteristics of the product and semistoppered vials. 

Shutts, B., Freezing the Commercial Process—Issues and Challenges, talk contributed at The Third International Conference on Process Development Chemistry, Amelia Island, FA, March 26,1997. 

In some of our own work, we have developed formulations to lyophilize and preserve bacteria for extended periods of time at relatively high temperatures (Conrad et al., 2000 Ekdawi-Sever and de Pablo, 2003). Some of our data are shovm in Figure 9.2, where it can be seen that freeze-dried samples of Lactobacillus acidophilus in trehalose-phosphate mixtures retain more than 60% of their viability after 3 months of storage at relatively high temperatures. In contrast, commercial processes and formulations lead to complete loss of viability after a few days of storage. 

This report discusses practical aspects of the effects of heating, evaporation, freeze concentration and reverse osmosis on certain juice constituents, most notably, the volatile flavor constituents. The commercial processes used to remove water from citrus juices have a requirement for thermal treatment of the feed stream to reduce microbial load and inactivate enzymes. While heating stabilizes juice to chemical changes caused by enzymes and microbes, it results in changes to volatile and non-volatile constituents. 

The first attempt at a commercial freeze drying process was in Florida in the late 50 s to store fruit juices. The process was a failure at that time, because the product became quite gummy. Can you suggest a possible explanation for this, knowing that fruit juices contain sugars ... 

Probably the most well known freeze-dried product is coffee. The commercial process is as follows a coffee extract containing 20 to 25% solids is filtered, then frozen to concentrate the solids to 30 to 40%. This material then is frozen to -25 to -43 C and crushed into small particles. These particles are freeze dried to remove the ice. A vacuum of about 0.2 torr (0.027 kPa) is used, and the final product contains 1 to 3% water. The entire process takes about 7 hours. 

Based on these field tests, practical application of the freeze-thaw process on a large scale is believed to be feasible. To effectively use the infrastructure and impoundment areas necessary for commercial application, freeze-thaw processing of fine tailings requires long time frames,... 

This wet process allows the freeze-dry process to be omitted and the polymerization time to be shortened. Therefore, it has the potential to be used for the mass-production of nylon clay nanocomposites on a commercial basis. 

As T, and, hence, T, are raised to increase the rate of drying, two limits may possibly be reached. First, the outer surface temperature T, cannot go too high because of thermal damage. Second, the temperature Ty must be kept well below the melting point. For the situation where k/AL is small compared to k and D /RT AL, the outer-surface temperature limit will be encountered first as T, is raised. To further increase the drying rate, k must be raised. Hence, the process is considered to be heat-transfer-controlled. Most commercial freeze-drying processes are heat-transfer-controlled (Kl). 

The quahty of naphthalene required for phthaUc anhydride manufacture is generally 95% minimum purity. The fixed plants do not require the high (>98%) purity naphthalene product and low (<50 ppm) sulfur. The typical commercial coal-tar naphthalene having a purity ca 95% (freezing point, 77.5°C), a sulfur content of ca 0.5%, and other miscellaneous impurities, is acceptable feedstock for the fixed-bed catalyst process based on naphthalene. 

Methyl- and dimethylnaphthalenes are contained in coke-oven tar and in certain petroleum fractions in significant amounts. A typical high temperature coke-oven coal tar, for example, contains ca 3 wt % of combined methyl- and dimethylnaphthalenes (6). In the United States, separation of individual isomers is seldom attempted instead a methylnaphtha1 ene-rich fraction is produced for commercial purposes. Such mixtures are used for solvents for pesticides, sulfur, and various aromatic compounds. They also can be used as low freezing, stable heat-transfer fluids. Mixtures that are rich in monomethyinaphthalene content have been used as dye carriers (qv) for color intensification in the dyeing of synthetic fibers, eg, polyester. They also are used as the feedstock to make naphthalene in dealkylation processes. PhthaUc anhydride also can be made from m ethyl n aph th al en e mixtures by an oxidation process that is similar to that used for naphthalene. 

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