Vapour losses

A pressure relief valve is attached to the roof. This valve is opened automatically when pumping product to, or withdrawing product from, the tank. The valve shuts when pumping stops so that vapour losses from the tank are contained. A bursting disc on the roof also provides emergency pressure relief for sudden pressure rises. The final tank specification is summarized in Table 12.1. 

Spruits, D., Interference of some substances with water vapour loss from human skin, Am. Perfum. Cosmet., 86, 27, 1971. 

Acharya, C.L. and Prihar, S.S., 1969. Vapour losses through soil muleh at different wind velocities. Agronomy J., 61 666-668. 

Vapour loss of a chemical warfare agent from the skin surface affects percutaneous toxicity by reducing the dose available for skin absorption. For agents of low volatility, such as VX, practically all of the applied dose may potentially be absorbed and so the percutaneous toxicity (LD50) approaches that of an intravenous (IV) LD50. In contrast, more volatile chemicals, such as G-agents, are subject to extensive vapour loss... 

Clearly, factors which reduce or prevent the skin-surface vapour loss of a chemical warfare agent will tend to enhance skin absorption and percutaneous toxicity. Occlusion of contaminated skin (for example, with ointments or impermeable dressings) is an obvious means of impeding vapour loss and has implications for the... 

In vitro studies with human skin have quantified the influence of occlusion on the percutaneous absorption of HD. Under unoccluded conditions, up to 80% of an applied dose of HD evaporates from the skin surface. However, physical occlusion prevents this vapour loss and results in a five-fold increase in the total amount of absorbed HD (Figure 11) and a nine-fold increase in the skin absorption rate (Chilcott et al., 2000). 

Propham and chlorpropham are not photodecomposed by ultraviolet light. The volatilisation of chlorpropham from dry soil is not great below 35°C. In the case of propham below 2S°C there is no vapour loss from dry soil. Dissipation is strongly increased by increased temperature and soil moisture. 

P, G. M. Van Der Walk, J, P. Naier. E. Bleumink. Skin irritancy of surfactants as assessed by water vapour loss measuremems. J. Invest, Demaioi, 82 291-293. 1984... 

The German Degussa process, - operated during the Second World War, was essentially of this type, but Degussa tended to operate their cells simply with a sodium chloride-beryllium chloride melt. This necessitates a higher temperature and vapour losses, or alternatively working between two high beryllium chloride concentration limits, so that even at the end of electrolysis about 30 per cent of beryllium chloride is still present in the melt. 

Goh CL, Chia SE (1988) Skin irritabUity to sodium lauryl sulphate - as measured by skin vapour loss - by sex and race. Clin Exp Dermatol 13 16-19... 

Coenraads PJ, Pinnagoda (1985) J Dermatitis and vapour loss in metal workers. Contact Dermatitis 13 347-348... 

Van der Valk PGM, Nater JP, Bleumink E (1985) Vulnerability of the skin to surfactants in different groups of eczema patients and controls as measured by water vapour loss. Clin Exp Dermatol 10 98-102... 

Malten KE, Den AJ (1978) Topical toxicity of various concentrations of DMSO recorded with impedance measurements and water vapour loss measurements. Contact Dermatitis 4 80-92... 

Blanken R, Van Vilsteren MJZ, Tupker RA, Coenraads PJ (1989) Effect of mineral oil and linoleic-acid-containing emulsions on the skin vapour loss of sodium-lauryl-sulphate-induced irritant skin reactions. Contact Dermatitis 20 93-97... 

Sorbic acid has to be dissolved in boiling water due to slow dissolution in cold water. But because sorbic acid is volatile with water vapour, loss of sorbic acid has to be prevented by immediately closing the vessel after the additimi of the boiling water. When the preparation is processed in a Stephan mixer in vacuum the sorbic acid may evaporate fast as well. An alternative is to use potassium sorbate instead of sorbic acid and to adjust the pH of the preparation subsequently. 

Another option available with rotary vacuum drum filters is full enclosure. This enables operation under nitrogen or other atmospheres, for reasons such as safety, prevention of vapour loss, etc. Enclosure may also be used to prevent contamination of the material being filtered or to confine the spray from washing nozzles. The rotary dmm filter can also be enclosed in a pressure vessel and operated under pressure and this is the idea behind some simple pressure filters introduced in chapter 12. 

The peeler centrifuge of Figure 3.34 can also be sealed against vapour loss, or given a nitrogen blanket to protect the cake (or filtrate) from air oxidation. 

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