Reactive Flash Volatilization - Discovery

Discovery

Reactive flash volatilization was demonstrated in 2006 in the journal Science by the high temperature (700–800 °C) conversion of soybean oil (triglycerides) and sugar (D-(+)-glucose) to synthesis gas (H₂ + CO) and olefins (ethylene and propylene). Complete, continuous catalytic conversion of heavy fuels was surprising, because the initial pyrolytic chemistry has been shown to generate significant amounts of solid residue called "char" which was expected to block the necessary interaction between the reactant compounds and the solid metal catalyst.

The process has been described, "The low volatility of these biofuel feedstocks not only leads to soot production when they are used directly in internal combustion engines but also causes them to coat industrial catalysts with a deactivating layer of carbon, thus hindering their conversion to lighter products. James Richard Salge and colleagues show that if heavy fuels such as soybean oil or biodiesel are sprayed onto hot rhodium-cerium catalysts as fine droplets in the presence of oxygen, the fuels can self-heat and fully react to form hydrogen without carbon formation and catalyst deactivation." RFV: Triglyceride + O₂ + Catalyst → Ethylene + Propylene + CO₂ + H₂O + Catalyst

The process converted 70% of the atomic hydrogen in soy-oil triglycerides to molecular H₂, and 60% of atomic carbon to carbon monoxide on a Rh-based catalyst with Cerium supported on alpha-alumina. Under different operating conditions, the process can produce a significant amount of ethylene and propylene.

The first demonstration of reactive flash volatilization occurred by a series of experimental steps:

1. The researchers start with either pure soybean oil or a thick sugar syrup.
2. The reactor consists of an automotive fuel injector, used to spray the oil or syrup as fine droplets through a tube. Sitting like a plug in the tube is a porous ceramic disk made of a rhodium-cerium catalyst material.
3. As the droplets hit the disk-whose surface temperature is 1,000 °C-the heat and oxygen break apart the molecules of oil or sugar.
4. The catalyst guides the breakdown toward the production of syngas rather than toward water vapor and carbon.
5. The syngas passes through the porous disk and is collected downstream in the tube.
6. No external heating is needed because the chemical reactions release enough heat to break up molecules of oil or sugar following in their wake.

An initial supply of heat is necessary to achieve temperatures of 300 °C, after which the reaction initiates, or "lights off," and quickly rises to temperatures of 700–800 °C. Under steady conditions, the reaction generates sufficient heat to maintain the high temperature, extremely fast chemistry. The total time for conversion of heavy, nonvolatile compounds to volatile or gaseous species occurs in milliseconds (or thousandths of a second).