Anne M Stark
The thermodynamic and kinetic properties of hydrocarbons at high pressures and temperatures are important for understanding carbon reservoirs and fluxes in Earth.
The work provides a basis for understanding experiments that demonstrated polymerization of methane to form high hydrocarbons and earlier methane forming reactions under pressure.
Hydrocarbons (molecules composed of the elements hydrogen and carbon) are the main building block of crude oil and natural gas. Hydrocarbons contribute to the global carbon cycle (one of the most important cycles of the Earth that allows for carbon to be recycled and reused throughout the biosphere and all of its organisms).
The team includes colleagues at UC Davis, Lawrence Livermore National Laboratory and Shell Projects & Technology. One of the researchers, UC Davis Professor Giulia Galli, is the co-chair of the Deep Carbon Observatory’s Physics and Chemistry of Deep Carbon Directorate and former LLNL researcher.
Geologists and geochemists believe that nearly all (more than 99 percent) of the hydrocarbons in commercially produced crude oil and natural gas are formed by the decomposition of the remains of living organisms, which were buried under layers of sediments in the Earth’s crust, a region approximately 5-10 miles below the Earth’s surface.
But hydrocarbons of purely chemical deep crustal or mantle origin (abiogenic) could occur in some geologic settings, such as rifts or subduction zones said Galli, a senior author on the study.
‘ Our simulation study shows that methane molecules fuse to form larger hydrocarbon molecules when exposed to the very high temperatures and pressures of the Earth’s upper mantle,’ Galli said. ‘ We don’t say that higher hydrocarbons actually occur under the realistic dirty Earth mantle conditions, but we say that the pressures and temperatures alone are right for it to happen.’ “
A snapshot taken from a first-principles molecular dynamics simulation of liquid methane in contact with a hydrogen-terminated diamond surface at high temperature and pressure. The spontaneous formation of longer hydrocarbons are readily found during the simulations.
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