Ka-Yiu San, Ph.D.

Plant waste has long been seen as a possible source of sustainable biofuels, and new research out of Rice University could unlock some of the energy that scientists say lies waiting in organic material.

According to materials provided by Rice, bioengineer Ka-Yiu San and his lab have developed a way to turn plant waste into fatty acid, which can then be further converted into fuel. The key is a genetically modified strain of the E. coli bacteria which they created by combining traits from several other strains. The scientists fed inedible cellulose from sorghum to the bacteria, which converts the sugar-heavy hydrolysate from the plants into fatty acids. These fatty acids could somedaybe converted into synthetic diesel fuel or oil-like lubricants, say the researchers.

“Green” chemistry developed at Rice University is at the center of a new government effort to turn plant waste into fatty acids, and then into fuel.

The Rice lab of bioengineer Ka-Yiu San is part of a recently announced $25 million United States Department of Agriculture project to develop a new generation of renewable energy and bio-based products from switchgrass and forestry residues and from a new hybrid of sorghum being developed at Texas A&M University.

Patent-pending fermentation processes created by San and his colleagues use genetically modified E. coli bacteria to produce fatty acids from hydrolysates. The sugary, carbon-rich hydrolysate is extracted from cellulose, the tough, inedible part of plants that is usually thrown away. San said his lab already gets an 80-to-90 percent yield of fatty acids from model sugars and hopes to improve that over the next few years.

“Adding another 1 or 2 percent doesn’t seem like much,” said San, based at Rice’s BioScience Research Collaborative. “But when you’re talking about making several million tons per year, it’s huge.”

For most environmentalists, the biggest focus in recent years has been the effort to switch from fossil fuels to renewable energy sources, but hydrocarbons like oil and gas go to more than just energy. One engineering research team at Rice University believes that it has found a way to replace petroleum with a renewable crop, soybeans, for the production of a crucial industrial chemical.

Succinic acid is commonly used in everything from plastic and polyester to many types of processed foods. Once known as spirit of amber, the substance was historically produced by crushing amber, but was eventually extracted as a by-product from refining crude oil.

But, like many petroleum products, researchers are finding increasingly efficient ways of replicating succinic acid from biomass. In 2004, the U.S. Department of Energy included the chemical among a list of products that could be produced from biological feedstock and should be targeted for further engineering research and development.

Rice scientists George Bennett and Ka-Yiu San first developed a process several years ago using the common research bacterium E. coli to convert basic sugars into succinic acid. That initial process proved reasonably cost-effective, but the pair soon decided to specifically target a major low-cost feedstock – soybean waste.

Rice University scientists turn low-value soy mash into high-value succinic acid

The humble soybean could become an inexpensive new source of a widely used chemical for plastics, textiles, drugs, solvents and as a food additive.

Indigestible byproducts of soybeans can be turned into valuable succinic acid through a process developed at Rice University.
Succinic acid, traditionally drawn from petroleum, is one focus of research by Rice chemists George Bennett and Ka-Yiu San. In 2004, the Department of Energy named succinic acid one of 12 “platform” chemicals that could be produced from sugars by biological means and turned into high-value materials.

Several years ago, Rice patented a process by Bennett and San for the bio-based production of succinic acid that employed genetically modified E. coli bacteria to convert glucose into succinic acid in a way that would be competitive with petroleum-based production.

The new succinate process developed by Bennett, San and Chandresh Thakker and reported recently in Bioresource Technology promises to make even better use of a cheap and plentiful feedstock, primarily the indigestible parts of the soybean.