Supercritical
CO2 flooding has been considered as a promising enhanced
oil recovery (EOR) method because it can effectively improve the oil
recovery and promote greenhouse gas sequestration. However, the solubility
of different petroleum components in supercritical carbon dioxide
(SC-CO2) has not been well investigated. This paper presents
the molecular selectivity of SC-CO2 extraction on crude
oil under different pressures and temperatures. The crude oils were
loaded on the surface of kieselguhr and extracted by SC-CO2. The extracts and residues from SC-CO2 extraction were
analyzed by gas chromatography–mass spectrometry and Fourier
transform ion cyclotron resonance mass spectrometry. Our results showed
that the operating pressure (20–30 MPa) affected the extraction
yields more than the temperature (50–70 °C). SC-CO2 preferentially extracted small molecules with relatively
low aromaticity and polarity. Compound classes containing multiple
heteroatoms had lower extraction yields than hydrocarbons. The carbon
number distribution ranges of various compound classes in the residues
were largely different. Carboxylic acids and phenolic compounds were
found to have poor solubility in SC-CO2. The risk of asphaltene
precipitation in CO2 EOR is also discussed.
Crayfish, carp, and crab threaten the consumer’s health due to the enrichment of the toxic elements. The concentration of the toxic elements (As, Cr, Cd, and Pb) in these aquatics was less investigated simultaneously in situ. In this study, the toxic elements in these aquatics from the same site of Hanchuan, Hubei Province, China were measured by ICP-MS to assess the enrichment of the four toxic elements in them and the health risk to the consumer. The results showed that the concentrations of these elements in muscle were lower than those in hepatopancreas/ liver, except for Cr in crayfish. Furthermore, the concentrations of Cd in the hepatopancreas of crayfish and crab exceeded the standards of China and the European Union. Accordingly, the hepatopancreas of crayfish and crab are not recommended for consumption. The estimated daily intake of these elements in the muscle of crayfish, carp, and crab did not exceed the provisional tolerable daily intakes, the corresponding target hazard quotient (THQ), and the cancer risk (CR) values for As were lower than 1 and 1 × 10–6, respectively. However, the accumulated consumption of the muscle of the three freshwater catches could result in a significant increase in the total THQ value. The total ingestion of the muscle of these catches should be limited. Collectively, these findings may renew interest in food safety and the health risk to humans owing to the consumption of freshwater catches.
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