EU-SICHERHEITSDATENBLATT Dieselkraftstoff ... - Schmierstoffe

100.0
Half-life predicted (days)
10.0
Freshwater
P criterion
Marine Water
1.0
1.0 10.0 100.0
Half-life observed (days)
Figure 2. BioHCwin (Y-axis) vs. experimental half-lives (X-axis) for n-paraffins
3.2 Iso-paraffins
Degradation of iso-paraffins is influenced negatively by increased branching of the
molecule, because complex branching hinders the initial oxidation and the subsequent
lipid catabolism of the hydrocarbon molecules (Prince and Walters 2007). Accordingly,
the BioHCwin model predicts a half-life above 60 days for 2,2,4,4,6,8,8-
heptamethylnonane, a highly branched C16 structure (Figure 3). For less branched
structures, BioHCwin predicts half-lives above 60 days for structures above C21. The
only experimental half-life above 60 days is the value for the extremely branched C16
structure, 2,2,4,4,6,8,8-heptamethylnonane, confirming the model prediction (Table 2).
Adjacent quaternary carbons (e.g. pentamethylheptane) are not characteristic of
petroleum hydrocarbons (Quann and Jaffe 1992; Sarpal et al. 1997; Quann 1998); results
for this compound may overstate the persistence for this HCB. Experimental half-lives
for iso-paraffins are available for carbon chains up to C20, and are all below the
persistence criterion. The experimental half-life for the C20 structure is 28 days, meaning
that half-life predictions for iso-paraffins above C21 may be over-estimated.
For carbon numbers for which persistence data are available, predicted and experimental
data are consistent. For structures up to C20, half-lives are below the persistence
criterion with the exception of the structure mentioned above (Figure 4). In several cases,
there are data for multiple hydrocarbons with the same number of carbons. It can be
concluded that, based on the available data, iso-paraffins at or above C21 may have halflives
above the persistence criterion.
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