New bioreactor could pave way for chemical feed stocks from biomass

ARGONNE, Ill. (July 22, 2005) — When Argonne biochemical engineer Seth Snyder drives past a corn field on the outskirts of Chicago, he sees the potential to reduce U.S. dependence on foreign oil while benefiting rural economies. Snyder and his colleagues in Argonne's Energy Systems (ES) Division are partners with agribusiness giant Archer Daniels Midland Co. (ADM), Decatur, Ill., in a cooperative research and development agreement to develop a technology that turns corn sugars into valuable chemicals.

Most chemical building blocks used to make plastics, medicines and other consumer products originate from petroleum refineries, which process crude oil. As oil supplies tighten, a growing movement is pushing to develop biorefineries that turn raw biomass from crops, grasses and trees into electricity, transportation fuels and refined chemicals. This movement is supported by the U.S. Department of Energy Biomass Program in the Office of Energy Efficiency and Renewable Energy, which is funding Argonne's research along with ADM.

To succeed economically, biorefineries must produce chemicals as cheaply as or cheaper than their petroleum counterparts. 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. The plan is to produce these chemicals along with fuel ethanol.

Most of these chemicals are organic acids and polyols, which are building blocks for a host of secondary chemicals used to make consumer products. For example, 3-hydroxypropionic acid is used to make acrylate derivatives for contact lenses and super-absorbent polymer used in diapers. Also, aspartic acid is an intermediate in pharmaceutical and sweetener manufacturing.

Snyder and his colleagues at Argonne are working with ADM to optimize the production of an organic acid called gluconic acid from sugar using Argonne's patented separative bioreactor technology. Eventually, the technology could be applied to a variety of organic acids and polyols.

Engineering a natural process for mass production

Gluconic acid is produced by the biochemical oxidation of glucose, a type of sugar. This 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. ADM and Argonne are very familiar with gluconic acid so it was selected as the logical first organic acid target.

The separative bioreactor, developed by a multidisciplinary team of ES scientists, could overcome technical and economic barriers to the production of gluconic acid, Snyder said.

Inside the separative bioreactor, enzymes turn glucose into gluconic acid, and the gluconic acid is separated immediately from the glucose solution. This separation eliminates a major problem in large-scale fermentation: the enzyme's incompatibility with the product acid.

During simple sugar fermentation, gluconic acid builds up, increasing the broth's acidity and disabling the enzyme. The acid can be chemically neutralized, much like people neutralize stomach acid with an antacid tablet, but the extra treatments raise the process cost and generate waste.

Electrodeionization makes product separation possible

The separative bioreactor is 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.

ES researchers developed and patented an improved EDI resin wafer stack that won a 2002 R&D 100 Award. Research on the stack research – which efficiently removes salt added during a manufacturing process from high fructose corn syrup – was supplied by DOE's Industrial Technology program.

While EDI technology was advancing, other ES researchers were finding ways to chemically attach enzymes to surfaces. Snyder said the major breakthrough for separative bioreactors came in 2001, when the two technology advances were merged into a single package. Researchers attached a glucose-oxidizing enzyme to the EDI resin, and the resin became a platform for two simultaneous processes: the enzymatic conversion of glucose to gluconic acid and the ionization and separation of the gluconic acid from the glucose solution.

Over the past year, Lin and chemical engineer Michael Henry have led research to make substantial improvements in fabricating and using the resin wafer. Argonne has filed five additional patents during the development.

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. The cell uses electricity, but Snyder said the cost of the electricity is “very, very small. It's well within our goals for the overall bioprocessing cost.”

Thinking bigger, thinking $$$

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.

ADM, one of the largest producers of biobased chemicals in the world, understands the economics of large-scale production. Economics – not environmental considerations – will determine the commercial success of any bio-based production process.

Still, Snyder said bio-based production offers substantial environmental benefits including reduced dependence on imported petroleum and reduction in greenhouse gases. He said DOE Biomass Program Manager Douglas Kaempf focuses on projects that offer these benefits, but have real chance for commercial success.

“There is a saying in this field,” Snyder said. “The only green that counts is dollars. If you can't make the product for the same cost or less than your competitor, then it doesn't matter that you say yours is green and theirs is fossil.”

In the petrochemical industry, the production cost of chemicals is split evenly between the feedstock and the refining. In bio-based chemical production, the cost of feedstock, such as corn sugar, makes up 20 percent of the total cost, with processing and separation making up the remaining cost. “We want to get that ratio down to fifty-fifty by reducing the processing costs,” Snyder said. “We think this technology will help do that.”

For now, Argonne researchers are testing and improving the separative bioreactor's efficiency at turning glucose into gluconic acid. “We chose gluconic acid because researchers at Argonne are interested in the enzyme glucose-fructose oxidoreductase,” Snyder said. ES microbiologist Edward St. Martin realized the enzyme's unique biochemical properties, and ES molecular biologist Michelle Arora developed the technology to produce it in large quantities.

“If we prove the technology with this enzyme, and ADM commercializes it, the other applications will come along nicely, but you need that first commercial success before you worry about the third or fourth,” Snyder said.

If the gluconic acid system is a commercial success, and the Argonne technology is extended to the production of other organic acids and polyols, many consumer products could be made from bio-based chemicals. Even liquid crystal displays, like the one you may be reading this story from, could eventually contain bio-based materials produced in a biorefinery with the help of Argonne technology. – David Barry