Global distillation effect

Figure 6. The global distillation effect. Semi-volatile chemicals tend to move toward cold climates as a result of their lower vapor pressures at colder temperatures. is the temperature of conden.salion ( C) defined as the temperature at which half the total air concentration of that compound is in the vapor phase, and half is in the aerosol phase assuming that constant aerosol concentrations and other standard conditions prevail. We expect chemicals with higher volatilities and lower Tc values to be transported the furthest. Based on Wania Mackay (1993, 1996),...

Considerable attention has been given to the investigation of organochlorine residues in the marine polar ecosystems where the two effects of global distillation and bioaccumulation combine to produce high residues in predatory species such as marine mammals, fish and sea birds. As these compounds preferentially reside in fatty tissues, the high fat content of many of the northern marine species, and the inherited contamination through lactation, indicate that such ecosystems may be some of the most vulnerable. 

The Global Distillation Model, also called the Grasshopper Effect and the Cold-Condensation Effect, predicts a global fractionation of these chemicals will occur whereby more... 

This distillation effect has been shown to influence global distributions of many semivolatile organic contaminants. Simonich Hites (1995) showed that concentrations of the most volatile POPs in tree bark (HCH, HCB, PCA) increased significantly at higher latitudes whereas less volatile compounds (DDT, endosulfan) were not correlated with latitude, consistent with the predictions of the global distillation model (Fig. 6). 

The effects of climate change on the speciation and fate of mercury in Polar ecosystems is particularly important. Not only is mercury increasing in the atmosphere but atmospheric deposition will be favored in colder climates due to changes in atmospheric redox chemistry. This means that mercury released in equatorial areas will undergo a global distillation via a process similar to the grasshopper effect observed with semi-volatUe organic pollutants. 

This sensitivity of conclusion to a single reaction coupled with the needed to distill a vast number of reactions into tractable subsets, the effect of which can be interpreted and tested by observations, restricts the strategy used to test models with field observations. We seek, therefore, to distill the orchestra of reactions into a few rate limiting steps to highlight which measurements must be made to test the mechanisms central to theories of global ozone depletion. 

As the supply and demand of global crude changes, heavier crudes become more attractive to process. However, many existing columns cannot produce cuts that meet distillation product specifications. There are many process changes that could improve the distillation curve of a given product However, it may be unclear what the side effects of a given change could be. In this case study, we look at how we can improve the distillation curve (5%) of the heavy naphtha and kerosene cut One option is to draw more or less of a particular cut to force the distillation curve to shift However, this will affect other product draws as well. 

FIGURE 14.1 Global market share of the technologies applied for desalination. MSF, multistage flash MED, multiple effect distillation ED, electrodialysis RO, reverse osmosis. (Data from T. Mezher et al.. Desalination, 266, 263, 2011.)... 

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