Thin-film apparatus evaporator

T iquid films, whether in the form of natural falling films or in the more advanced form of mechanically agitated films in thin-film apparatus, offer convenient conditions for the solution of many difficult processing problems because of the films favorable surface-to-volume ratio and good heat transfer. This is especially so with an agitated film between heating wall and film. The agitated-film principle has previously found its broadest application in thin-film evaporators. 

The favorable working conditions of the thin-film evaporator enabled the equally successful application of the thin-film principle for fractionation (5), absorption, chemical reactions (6), and drying (7, 8). In these processes and applications, the thin-film apparatus is used mainly to treat heat sensitive and lower-viscosity products that flow on the influence of gravity alone. This particular type of apparatus in a special design can also be used to process highly viscous products to... 

The author s thin-film apparatus, as developed further by VEB Glaswerk Stiitzer-bach and illustrated in Fig. 196, was adapted from the early types of molecular stills operating with a falling film. It contains two concentric tubes. The inner tube, which is interchangeable by the provision of a ground joint, can be heated by an element a and functions as a surface for evaporation. The outer tube acts as condensing surface. 

The methods of steam distillation have been summarized by Bernhauer [13] and Thormann [14]. A detailed discussion of practical and theoretical aspects of steam distillation as illustrated by the distillation of essential oils is given by von Weber [15], Rigamonti [16] developed a nomogram which can be used to calculate the steam requirements for various enrichments. Prenosil [16a] compared theoretical and experimental steam distillation data for multicomponent mixtures. He modified the calculating method by introducing a value for evaporation efficiency. Steam distillation can also be carried out in thin-film apparatus. Berkes etal. [16 b] give a description of the material transfer conditions of a steam distillation performed in such apparatus in terms of the balance equations. 

The Matsuura method (57) compares the photolysis result of a solution actinometer with that of a thin crystalline film of equal surface area after exposure. Thus, evaporation of a solution containing the photoreactive substrate results in a thin crystalline film on the glass wall of a test tube, which is subsequently exposed to actinic radiation in a merry-go-round type photolysis apparatus. To test for complete absorption of the incident photons within the crystalline film, the evaporation process is carried out at various concentrations of the substrate, which leads to films of different thickness. If the yield of photoproduct after a certain exposure time is independent of the concentration of the original solution before evaporation, complete absorption of all actinic photons is established. The quantity of the photons absorbed by the crystalline film is then estimated by parallel photolysis of a 0.1 M solution of 2,4,6-triisopropylbenzophenone in methanol solution, which has a well-established quantum yield of 0 = 0.52 (58). The volume of this actinometer solution in the test tube is adjusted so that the crystalline film and the solution exhibit irradiated surfaces of identical size. In summary, this method provides approximate estimates of solid-state quantum yields however, differences in the reflection of the... 

Tlie CVD method is usually used to produce a thin film material which is formed on a heated substrate. However, nanostructured particles of ceria and ceria-yttria have been synthesized by some arrangements of the apparatus. Figure 3.8 shows the schematic CVD reactors for synthesizing ceria-based nanopanicles.Two types of rector has been presented. The nanoparticles are collected either on a cooled quartz susceptor (A) that is in a furnace, or in a cold wall container outside the furnace (B), The precursor cerium chloride set on the container is evaporated and... 

FIG. 7 Rotary evaporator. The rate of evaporation with this apparatus is very fast due to the thin film of liquid over the entire inner surface of the rotating flask, which is heated under a vacuum. Foaming and bumping are also greatly reduced. 

The distilland (sample) is added to the top and allowed to flow by the force of gravity down the surface in a thin film. The still usually consists of two vertical concentric cylinders, one being the evaporator and the other the condenser. Most of the sample is stored at low temperature and only the portion that is in immediate contact with the evaporator is heated and then only for a few seconds (10-50). Most falling films are from 0.1 to 2.0 mm thick. The efficiency is better than that of all but the smallest batch apparatus with f values approaching 1 and having one theoretical plate between the evaporator and the condenser. A value of 5-6 g/secW is reasonable with small units. From 5-10 % of the sample is distilled in one pass. Such a still is shown in Figure 7-3. 

Audiere et al. (122) described a thin-film micro-DTA apparatus that permitted the study in situ of thin-film materials. The samples are deposited by evaporation, cathodic sputtering, and so on, on to a substrate bearing metallic films, which constitute the thermocouples of the DTA. The sample... 

By continuous thin-film distillation fatty acid fractions up to an acid value of 90 could be separated off, so that the distillates were higher than Cjo- The thin-film procedure has also proved to be very suitable for fractionating silicone oils (which are distributed with great uniformity on the heater) and for distilling waxes. Gutwasser and Midler [22] developed a thin-film evaporator which has been successfully used for the distillation of spermaceti-od fatty acids. Fig. 198 shows the whole apparatus. 

The studies of amorphous RAl alloy thin films are recent ones. Two modes of evaporation have been used to obtain such samples. They consist either of utilizing a rf sputtering apparatus, or of evaporating from a tungsten crucible an agglomerate such as RAU. 

Svblimatum. Binitrophenol largely sublimes when heated in high vacuum at 70—80 0 in a special apparatus designed by Mills [169]. Some DNP-methionine and, as observed in our laboratory, also di-D15P-cystine may be lost. If necessary, the sublimation procedure may have to be interrupted, the substance dissolved in a little acetone and redeposited as a thin film on the walls of the vessel by evaporation. 

By distributing the feedstock as a thin film on a heated surface the product holdup in the apparatus and thus the exposure time can be minimised as well. On vertical, heated surfaces the liquid flows downwards due to the gravity whereby the volatile fractions are being evaporated. The produced vapours are condensed on a cold surface installed in a short distance (see Figure 15.3). 

Wilcock, J. D. and Campbell, D. S. (1969), A sensitive bending beam apparatus for measuring the stress and evaporated thin films. Thin Solid Films 3, 3-12. 

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