Stills wiped-film still

Wiped film stills in place of continuous still pots —Centrifugal extractors in place of extraction columns —Flash dryers in place of tray dryers —Continuous reactors in place of batch —Plug flow reactors in place of CFSTRs —Continuous in-line mixers in place of mixing vessels... 

Wiped film stills in place of continuous still pots... 

Figure 7-5. Schematic of the process of a wiped-film still.

Figure 7-7 is a photograph of a 2" laboratory size wiped film still and is shown as a diagram in Figure 7-8. 

What is the purpose of brushes or scrapers in a wiped film still ... 

To form crosslinked coatings, the polymer must be free of unreacted functional monomer that would act as a chain terminator in the crosslinking reaction. The unreacted VEC could be easily removed from the acrylic copolymer by passing the resin solution through a wiped film still under vacuum, then redissolving the polymer in solvent. GC analysis indicated that the unreacted VEC had been totally removed. 

Attempted isolation of diethyl hydroxymethyl phosphonate by standard vacuum distillation technique is accompanied by extensive decomposition. The use of Kugelrohr apparatus allows the isolation to be accomplished at a lower temperature, and therefore the product is obtained in higher yield. Alternately, the checkers found that distillation using a 2 wiped-film molecular still (Pope Scientific, Inc.) significantly raised product yields, especially when the reaction was performed on a larger scale (Notes 3 and 6). 

The still bottoms are drawn off and sent to a second distillation step to remove as much of the remaining glycerine as possible. This system can be a small still, similar to a foot s still, or a wiped film evaporator. The foots still bottoms, or pitch, from this step is comprised mostly of sodium soaps, polyglycerols, salts, and minor quantities of organic compounds formed in the treatment and distillation steps. 

As a residual solid or viscous liquid is concentrated to dryness, stirring becomes difficult, especially in an immobile vessel. Due to the small surface area-to-volume ratio of large equipment, heat transfer and distillation take longer than similar operations in the laboratory. Decomposition may occur with extended heating, especially if there is uneven heat distribution. Complete removal of residual solids and viscous liquids is difficult from vessels with access limited through manways. Residual solvents may be removed ( stripped ) from liquids using specialized stills, e.g., wiped film evaporators, in which the mobile liquid flows over a heated zone. Only rarely are extracts concentrated to dryness. 

The Eastman process has operated in Texas (USA) with three continuous, stirred-tank reactors, a wiped-film evaporator, a distillation train and a continuous, counter-current, liquid-liquid extractor for recovery of the catalysts since 1996 (1400 metric tons per year capacity, e.g., semiworks facility), but full commercial capacity has not yet been reached. The main problem is still the formation of oligomers. Another answer to the problem of IL loss to the organic phase consists in the extraction of the products from the IL using a supercritical fluid [101], but operational costs are high. 

Operating conditions. Instead, the wall (film) temperature, pressure, and feed rate that will produce a fraction with a given end point are determined from in-house correlations developed by matching yields between the wiped-waU distillation and the conventional distillation (ASTM D-1160, ASTM D-5236). And wiped-wall stills are often used because they allow higher end points and can easily provide sufficient quantities of the fractions for characterization purposes. 

The main thrust of a commercial still is to provide a large evaporating surface and a continuous process. Batch stills first were rotated to increase the surface area, but several developments since then have occurred. The falling film method, the centrifugal method, the wiped film method, and the fractionating method are all now common. 

The damage that a runaway reaction may cause is due to the energy that is released and the inability of the equipment to remove it as fast as it is produced. It is obvious therefore that the likely damage will be reduced if the inventory of the material in the plant is minimized. Large batch stills are not a good choice for processing unstable materials. The very low hold-up of thin film or wiped film evaporators (1 min or less in the highest temperature zone) make them specially suitable for this function. 

Fourlfa, the i ent may dissolve into die aTSP during exposure and not be completely removed by die cleaning procedure. The cleaning procedure following HD vt r eiqposure involves wiping each site with two dry foam-covered cotton swabs. This process removes most of die aTSP but a small film still remains on die skin surface (2d). If HD dissolved into die aTSP and was not completely neutralized, a small amount could have been in contact with the skin surfiice until the postexposure readings were made (24 hr). 

The purification of amides as many other products are performed in a typical two-step operation removal of light impurities in a wiped film evaporator and overhead distillation of the product in a short path still. Heavy impurities remain in the residue. 

The retro Diels-Alder reaction sets in 165 , and recommended cracking procedures involve heating with P2 Og at this temperature [106] or at 390-400 in a wiped film molecular still [105]. Yields of 80-90% are claimed. 

Falling-film stills are constructed of two vertical concentric tubes. The inner tube is heated internally, and the liquid to be distilled flows down the outer wall of the inner tube in a thin film. The outer tube is the condenser, and the annular space is under vacuum. Some thin-film arrangements involve continuous wiping of the film by a rotating blade. 

Cream cleansers were created to address some of the shortcomings of powder cleaners, being easier to apply and eliminating dust. However, they still suffer from one of the difhculties of powder cleaners, which is difficulty of rinsing. The abrasive in both products tend not to be easy to rinse down the drain and builders, being powder ingredients, can be left behind as a film when dry. Both of these can contribute to a dulling residue if they are not ultimately rinsed or wiped away. 

As shown in Table 5, in the mode I test, the thicknesses of the residual adhesive layer on the failure surfaces were about 250 xm for all the specimens with different surface preparations, which indicated that the failures all occurred in the middle of the adhesive layer in the test regardless of the surface preparation method since the total thickness of the adhesive of the specimens was 0.5 mm. When the phase angle increased as in the asymmetric DCB test with h/H = 0.75, which contains 3% of mode II fracture component, a layer of epoxy film with a thickness of around SO xm was detected on the failure surfaces of all the specimens. Although the failure was still cohesive, the decrease in the film thickness on the metal side of the failure surfaces indicated that the locus of failure shifted toward the interface due to the increase in the mode mixity. On the other hand, because the failure was still cohesive, no significant effect of interface properties on the locus of failure was observed. When the mode mixity increased to 14% as in the asymmetric DCB test with h/H = 0.5, where the mode mixity strongly forced the crack toward the interface, the effect of interface properties on the locus of failure became pronounced. In the specimen with adherends prepared with acetone wipe, a 4-nm-thick epoxy film was detected on the failure surfaces in the specimen with adherends treated with base/acid etch, the film thickness was 12 nm and in the P2 etched specimen, a visible layer of film, which was estimated to be about 100 nm, was observed on the failure surfaces. This increasing trend in the measured film thickness from the failure surfaces suggested that the advanced surface preparation methods enhance adhesion and displace failure from the interface, which also confirmed the indications obtained from the XPS analyses. In the ENF test, a similar trend in the variation of film thickness was observed. 

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