Petroleum from biogenic hydrocarbons

Interpretation of Hydrocarbon Analyses. Although obtaining accurate hydrocarbon measurements in samples is often a difficult task, it is equally as difficult to determine the sources of hydrocarbons from the data. The following criteria for differentiating petroleum hydrocarbons from biogenic hydrocarbons that have been suggested and applied over the past several years were outlined in (1) and are taken from there. 

Differentiation of Petroleum Hydrocarbons from Biogenic Hydrocarbons. Petroleum and biogenic hydrocarbons can be distinguished as follows, thus providing useful means for detecting petroleum. Note that not all differences apply to all organisms, nor to all crude oils and refined products. 

T his paper addresses three major analytical problems in the determina-tion of aromatic petroleum hydrocarbons in marine organisms, namely, interference from biogenic hydrocarbons, inadequate detection limits using small samples, and losses of volatile aromatic hydrocarbons. 

On the other hand, gas chromatographic methods may overestimate the concentration of total petroleum hydrocarbons in a sample due to the detection of nonpetroleum compounds. In addition, cleanup steps do not separate petroleum hydrocarbons perfectly from biogenic material such as plant oils and waxes, which are sometimes extracted from vegetation-rich soil. Silica gel cleanup may help to remove this interference but may also remove some polar hydrocarbons. 

The hydrocarbons released into the water and in the sediments by biosynthesis from various life forms or issued from non-marine sources are subjected to physical, chemical and biological transformations, some of these affecting the molecular structure of the more labile compounds. There have been several studies of the modification of hydrocarbons in the ocean, initiated mainly by an attempt to evaluate the persistence of crude oil in the sea. The mechanisms affecting petroleum products are closely related to those for natural hydrocarbons with one important exception many biogenic hydrocarbons are unsaturated compounds and probably disappear rapidly in the water column. This is an important consideration in evaluating the persistent contribution of biogenic hydrocarbons to dissolved and particulate lipids of sea water and sediments. 

Thermodynamics. The role of chemical thermodynamics in the origin of petroleum is concerned largely with demonstrating an almost self-evident drive from unstable biogenic molecules to stable hydrocarbons... 

Advances in petroleum characterization at the molecular structure level by GC-MS methods renewed interest in OSC. Within the past few years, at least one-thousand new and novel OSC that previously were not known to be present in petroleum and bitumens have been reported. Tentative molecular structures inferred from GC-MS and other techniques have been confirmed in many cases by synthesis of authentic reference-compounds. The difficult and time-consuming synthetic work has been crucial in validating many of the novel structures. Another key finding has been that immature bitumens and crude oils (samples that have not received significant thermal stress) differ markedly from the previously known OSC in that they have carbon-skeletons resembling ubiquitous biomarker hydrocarbons (e.g., n-alkanes, isoprenoid alkanes, steranes, and hopanes). This similarity, of course, suggests that the hydrocarbons and OSC have common biogenic precursors. 

For comparison, GC-FID chromatograms of representative petroleum contaminants are shown in Figure 2 and chromatograms of hydrocarbons from various marine plants (biogenic) are given in Figure 3. Key pareimeters used for hydrocarbon characterization are listed in Table I. 

Characterization of petroleum contamination from certain land use activities and frcxn biogenic sources has provided information for assessing impact from continued coastal development activities and to assess the duration and extent of impact in the event of a major oil spill in the areas studied. However, time series samples are needed to establish rates of hydrocarbon input and degradation. 

For the removal of biogenic olefins from the aromatic fraction of a macrofauna or zooplankton extract, we discarded the GPC fraction that eluted prior to n-dodecane. The later eluting fraction, which would contain any aromatic hydrocarbons present (including any of the alkyl homologues commonly found in petroleum), was collected and analyzed by gas chromatography. A gas chromatogram of the aromatic fraction... 

In recent years, the production of simple hydrocarbrnis from biomass has attracted strong interest in the renewables community, due to the fact that the products are considered drop-in substitutes for petroleum-derived alkanes, with evident applications to fuels and chemical production. HMF has received much attention in this regard as a platform for extended carbon chain products, the hydrodeoxygenation (HDO) of which gives products which are essentially diesel or aviation fuels, depending on their hydrocarbon distribution. Aldol-type condensation reactions can take place in aqueous solution between HMF (or its derivatives) and biogenic ketones... 

Figure 1.4 Thin-layer chromatography-flame ionization detection chromatogram showing the separation of biogenic lipids from hydrocarbons in an extract of a petroleum-contaminated soil. Solvent systems hexane (40 min), toluene (15 min) and dichloromethane/methanol (95 5 vol./ vol.) (5 min), followed by a single full scan.

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