(281b) Millisecond Reactors for Renewable Energy

While autothermal millisecond reactors have been used for over 100 years starting with the Ostwald process for making nitric acid, their capabilities are still being expanded as new feedstocks and applications dictate.  We summarize some of these results to illustrate new and unexpected behaviors.

First, the stability of high temperature catalysts is such that conventional poisons have little effect on performance.  Sulfur, the classic catalyst poison, has little effect because it evaporates, and carbon does not accumulate because it reacts away as CH₄ or CO.  Most catalyst formulations are stable for many hours on either monoliths or pellets with Rh forming near-equilibrium syngas and Pt tending to form olefins.

Bio oil and lignocellulose can also be converted to nearly equilibrium syngas over Rh without catalyst deactivation by “reactive flash volatilization” in which high molecular weight liquid drops and solid particles rapidly decompose on the front surface of the catalyst and form volatile species that react within the catalyst.  High speed microphotography at 1000 frames per second has been used to quantify this process.  We have recently used this technique to decompose solid polystyrene particles into styrene monomer with 80% yield.

Lignocellulose contains 1 to 10% inorganics that can accumulate on the catalyst.  We have recently examined affects of P, K, Na, Si, Ca, and Mg to determine tolerable levels of these impurities in biomass.  One interesting result with P and K is that they cause the catalyst to become acidic and basic respectively, which alters their product selectivities.

Finally, we explore the use of staged catalysts to obtain products that cannot be obtained in a single stage configuration.  Using a Pt or Rh combustion catalyst in front of an acid catalyst, we can obtain selectivities of alcohols to olefin over 80% by feeding a sacrificial fuel such as CH₄ to the combustion stage to generate heat while introducing the alcohol as a side feed to the second acidic stage.