The Sweating Step

A brief reference should be made to the high-pressure crystallization presented in many papers by Moritoki et al. (1984b) (Kobe Steel Company). The pressure applied is up to 300 MPa under adiabatic conditions. The high-pressure equipment works batch-wise in eycles of about 20 min. The pressure is increased in steps of 20Mpa. At a specific time, about 10 out of a total of 20 min, the pressure is slightly released. 

The period of released pressure is used as sweating time (see the following section). After discharge of the created crystals the remaining highly conterminated melt must be separated before receiving the pure product. The equipment is used industrially, e.g., for the purification of p-cresol from p-/w-cresol mixtures. Successfully executed experiments on the laboratory level are described by Moritoki et al. (1989) for the purification of benzene from benzene-cyclohexane mixtures. 

A process step of this kind is used with the knowledge that it leads to less product. However, the liquid film sticking on the crystal surface or crystal layer surface on the one hand and the liquid inclusions on the other hand are highly contaminated and 

According to Jancic (1989), the product lost in a sweating step is about 10%. The sweating times are also rather different with respect to the processes. Between 10 min in the dynamic Sulzer falling film process (see Jancic 1989) and 30 h in case of the static Hoechst process (see Rittner and Steiner 1985) are example sweating times for the purification of monochlorous acetic acid. 

An additional purification in the same range as a crystallization step. 

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The importance of the sweating step is discussed in detail by Jancic (1989) and Saxer (1993), the former of which also gives examples of overall product recovery and temperature curves for a multicompound mixture of impurities for the purification of benzoic acid. 

Efficiency of the sweating step as a function of its dimensionless number... 

Following the sweating step is "diying", which reduces the moisture content fi om 60-70% to 20-30%. Ilie reduced moisture coutenl b tyjiical for a good quality cured bean and helps to eliminate any microbial activity and to secure a long shelf life. The amount of moisture also affects appearance, flexibility, and quality of the beans. 

This shows the possibilities to save energy and time by a good introduction of the sweating procedure and the co-ordination of the two steps crystallization and sweating. 

The main idea of the presented work is to improve this sweating-step by the application of gases under high pressure. 

The final purity after the pressure sweating step is limited by the melt which adheres at the porous crystal layer. Therefore there is no significant difference between the experiments under 15 bar C02, 50 bar N2 and 175 bar N2 atmosphere which means that there is already enough gas solved at 15 bar CO2 respectively 50 bar N2 in the liquid impurities to transport them with the escaping gas to the crystal layer surface. 

Several strains of LAB isolated from wine were tested for their abilities to metabolize ferulic and p-coumaric acids. Cavin et al. (1993) showed that these acids were strongly decarboxylated by growing cultures of Lactobacillus brevis, Lactobacillus plantarum, and Pediococcus when decarboxylation was observed, volatile phenols (4-ethylguaiacol and 4-ethylphenol) were detected, indicating the possibility of reduction of the side chain before or after decarboxylation. Couto et al. (2006) reported L. collinoides as a producer of volatile phenols, although strain specificity concerning this capacity was observed. L. mali, L. sake, L. viridescens, and P. acidi-lactici were also found to be able to produce volatile compounds but they only perform the decarboxylation step. Volatile phenols cause animal taints such as horse sweat, wet animal and urine that are usually attributed to Brettanomyces spoilage. 

The sweating due to the pressure decrease causes a small temperature decrease due to the latent heat. This temperature decrease prevents an excess amount of partial melt from occurring. This step is also schematically shown by the broken lines in Figure 1. 

The postcrystallization treatment sweating is a temperature-induced purification step. After the crystallization process, the temperature of the cooled surface is raised close to the melting point of the pure component (about 1-2 K below). As a consequence, the impurities adhering to the crystal coat and those contained in pores of the crystalline material remelt (partially diluted with pure material). The remolten impure material flows out of the pores and finally drains under the influence of gravity. During the sweating process, a product loss of about 10% is accompanied. 

As rule of thumb, it can be stated that the purification step sweating is more suitable for the static mode compared to the dynamic mode, because the achieved improvements in distribution coefficient are less than those for static mode. This rule depends, of course, on the mixture (the substances) used. In summary, the possible advantages of sweating are [7,9]... 

The next step up in ERD happened with the invention of agriculture, when farmers controlled calorie production with irrigated, plowed rows of plants and ordered pens of animals, 11,000 to 7,000 years ago. Agricultural society directed energy with controlled burns and powerful oxen to break up soil and grind grains, both of which increased ERD. Overall, more energy was released as heat and sweat. 

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