Argonne Bioreactor to Deliver Chemical Feedstocks from Biomass

25 July 2005

A component resin wafer from the separative bioreactor.

Researchers at Argonne National Laboratory are developing, in partnership with Archer Daniels Midland (ADM), a biorefinery technology to optimize the conversion of corn sugars into gluconic acid—a mild organic acid.

A recent report from the DOE Biomass Program listed 12 chemicals produced by biological or chemical conversion of sugars that could be made profitably in biorefineries. Most of these chemicals are organic acids and polyols, which are building blocks for a host of secondary chemicals used to make consumer products. The plan is to produce these chemicals along with fuel ethanol.

Most chemical building blocks currently used to make plastics, medicines and other consumer products originate from petroleum refineries.

ADM and Argonne are very familiar with gluconic acid (and interested in the enzyme glucose-fructose oxidoreductase), and so selected it as the logical first organic acid target—not because it is on the top-12 list, but because the technology developed could be applied to the variety of organic acids and polyols that are.

Gluconic acid is produced by the biochemical oxidation of glucose. The reaction, facilitated by enzymes in fermentation broths, has been known for more than 100 years, said YuPo Lin, a chemical engineer in Argonne’s ES division. He said the challenge is one of engineering—how to process organic acids cheaply and cleanly enough to compete economically with petrochemicals.

The Argonne-ADM researchers are using a separative bioreactor, itself an offshoot of a salt-removal technology called electrodeionization (EDI). EDI is commonly used in biochemical labs, chemical and semiconductor factories to produce ultrapure water. An EDI cell contains ion exchange resins, similar to those found in some commercial water-softening units.

During simple sugar fermentation, gluconic acid builds up, increasing the broth’s acidity and disabling the enzyme. The acid can be chemically neutralized, but the extra treatments raise the process cost and generate waste.

Inside the separative bioreactor, however, the gluconic acid is separated immediately from the glucose solution, eliminating the product incompatibilities.

The separative bioreactor features a flexible, compressible wafer, roughly the thickness of a compact disk, made of ion exchange resin. Enzymes are attached to the resin's surface. The wafer is porous, so water easily flows through it, and it is sandwiched tightly between two special membranes in an EDI cell. The membranes allow ions and water to pass through into a separate compartment of the EDI cell, but neutral molecules, such as sugars, bounce off the membranes like a ball hitting a brick wall.

As the glucose solution flows through the EDI cell, enzymes convert it to gluconic acid. The gluconic acid then ionizes on the resin wafer, and an electrical field pulls the ions through the membranes into a separate compartment, where they recombine into gluconic acid.

The net result of the technology is that a glucose solution flows into the EDI cell and a gluconic acid solution flows out.

Argonne has filed five additional patents during the development of the gluconic acid bioreactor.

In the test-scale systems at Argonne, the process is conducted at speeds of about a gallon a day in a unit that uses resin wafers with footprints of about one tenth of a square meter. The pumping speed depends on the resin wafer size and the accompanying EDI apparatus. A commercial-scale resin wafer would cover an area of one square meter; hundreds of units would be stacked together to achieve industrial-scale output.

Argonne researchers are now testing and improving the separative bioreactor’s efficiency at turning glucose into gluconic acid. If the gluconic acid system is a commercial success, the Argonne technology could be extended to the production of other organic acids and polyols.

Resources:

• Top Value-Added Chemicals from Biomass

• EERE Biomass Program