CATALYTIC PROCESS CONVERTS
SORTED WASTE INTO AROMATIC
COMPOUNDS
By Scott Jenkins | October 1, 2016
3
The rising cost of landfilling trash creates a strong incentive to utilize the waste for saleable products. A recently piloted process is an example: the process can convert municipal solid waste
(MSW) into a narrow range of valuable aromatic compounds. It depends on a two-component catalyst capable of first generating alcohols from synthesis gas (syngas), and then converting those
to aromatic hydrocarbons.
The process was first developed by Mark White, professor emeritus at Mississippi State University (Starkville, Miss.; www.msstate.edu), and has been licensed for commercialization to Epurga
LLC (Baton Rouge, La.;www.epurga.com).
An initial gasification step converts sorted trash or wood construction debris (or both) into syngas. After cleaning, the syngas is fed into a high-pressure (70 bars) reactor, where it passes over a
catalyst consisting of molybdenum oxide (MoO 3) embedded inside a zeolite material (H-ZSM-5). The MoO3 promotes conversion of syngas into alcohols, such as ethanol and propanol. The
zeolite promotes reactions converting them into aromatic compounds, while the pore structure restricts the molecular weight (MW) distribution to ~78–160 g/mol. Major products include
toluene, xylenes and trimethyl benzene — feedstocks for polystyrene, polyurethanes, polyesters and other polymers.
In addition to providing a source of bio-based aromatic species, the process offers lower operating costs than Fischer-Tropsch (F-T) processes, says Michael Harrelson, CEO of Epurga, by
overcoming some of F-T’s main limitations. By keeping the product size range narrow, the Epurga process eliminates the need for subsequent cracking operations to break the high-MW waxes
into lower-MW species, as in F-T.
Also, because F-T synthesis requires H2-rich feed gas, a water-gas shift unit operation is carried out to achieve the desired H2-to-CO ratio (most gasifiers produce equal amounts of the two gases).
In the Epurga process, MoO3 also acts as a water-gas shift catalyst, operating in the same temperature range as the alcohol synthesis and avoiding the need for a separate water-gas shift step.
Epurga is building a plant to convert MSW into 200 ton/d of aromatic products on the banks of the Mississippi River in Port of Cates Landing, Tenn., and is looking for customers to purchase the
MSW-derived aromatics, Harrelson says.