Sunday, July 19, 2015

Making Clean, High-Quality Fuels from Low-Quality Oil

What happens when hexyl sulfide is processed in a reactor vessel by raising the temperature without adding water (left) and by mixing it with supercritical water (SCW, right). In each experiment, samples were removed at regular intervals up to 30 minutes. All samples taken at or after 10 minutes include smaller hydrocarbons, some with bound sulfur. But only the SCW samples include pentane, carbon monoxide (CO), and carbon dioxide (CO2). The presence of the last two products indicates that water (H2O) — the only source of oxygen — must be reacting and providing the hydrogen atoms needed to remove the sulfur as hydrogen sulfide (H2S). (Credit: Click to Enlarge.
Findings by MIT researchers could help advance the commercialization of supercritical water technology for the desulfurization and upgrading of high-sulfur crude oil into high-value, cleaner fuels such as gasoline without using hydrogen—a major change in refining technology that would reduce costs, energy use, and CO2 emissions.

Supercritical water upgrading (SCWU) of heavy oils has been of interest for years in industry and academia;  SCWU reduces sulfur content and decreases average molecular weight or crude without rejecting carbon as coke products.
More than a third of the world’s energy needs are met using oil;  reliance on oil will likely continue for decades to come, especially in the transportation sector.  Increasingly, however, crude oil tends to be heavier, and higher in sulfur, than the lightweight, clean, and easily refined crudes produced in the past.  When refined, these heavier, more sour crudes yield a higher fraction of lower-value, heavier products such as asphalt along with residual coke.

Processes now used to upgrade and desulfurize heavy crude oil are expensive, energy-intensive, and require hydrogen, which companies typically produce from natural gas—a high-cost process that consumes valuable gas resources and releases high levels of CO2.
So there’s a lot of interest in finding alternative processes for converting low-quality crude oil into valuable fuels with less residual coke and for removing the sulfur efficiently and economically without using hydrogen.

—Ahmed Ghoniem, the Ronald C. Crane ('72) Professor of Mechanical Engineering at MIT}
SCWU uses water rather than natural gas as the source of the hydrogen molecules needed for the key chemical reactions in the refining process.  Although oil and water don’t normally mix, using supercritical water solves that problem.

Read more at Making Clean, High-Quality Fuels from Low-Quality Oil

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