Furfural: Future Feedstock for Fuels and Chemicals

Furfural, a sister chemical to the increasingly popular hydroxymethylfurfural or HMF molecule, is regaining attention as a biobased alternative for the production of everything from antacids and fertilizers to plastics and paints.
By Jessica Ebert
Over the past couple of years, several research groups have described approaches to converting six-carbon sugars such as glucose and fructose into a chemical called hydroxymethylfurfural or HMF. This molecule represents a renewable building block for the synthesis of plastics and industrial and household chemicals. In addition, last October, Avantium, an Amsterdam, the Netherlands-based technology company announced the results of engine tests of its novel furan-based biofuel derived from HMF. The company dubbed its fuel, Furanics, and reported that various blends of Furanics with regular diesel yielded positive results including smooth engine performance for several hours and significant reductions in soot emissions from vehicle exhaust.

Now, a sister chemical to HMF, furfural, is beginning to gain the attention of cellulosic ethanol producers and academic researchers. Furfural is an almond-scented, oily, colorless liquid that turns yellow to dark brown when exposed to air. It is used as a solvent for refining lubricating oils, as a fungicide and weed killer and in the production of tetrahydrofuran, an important industrial solvent. In addition, furfural along with its sister molecule HMF, can serve as a building block for other potential transportation fuels including dimethylfuran and ethyl levulinate.

Furfural is produced by removing water from or dehydrating five-carbon sugars such as xylose and arabinose. These pentose sugars are commonly obtained from the hemicellulose fraction of biomass wastes like cornstalks, corncobs and the husks of peanuts and oats. In fact, in the 1920s several tons of furfural was produced each month from the cereal waste stockpiles at the Quaker Oats Co. in Cedar Rapids, Iowa. But cheap oil prices in the latter part of the 20th century brought domestic production of furfural to a veritable halt.

Today, about 90 percent of furfural production capacity is installed in three countries, China, which houses the most at about 74 percent, South Africa and the Dominican Republic, according to SRI Consulting, an international business research service for the chemical industry. However, in this climate of unprecedented high oil prices, interest in producing furfural in the United States is growing.

"One of the largest applications of furfural was to convert it into tetrahydrofuran," explains Kendall Pye, chief scientific officer at Lignol Innovations Ltd., a Canadian developer of biorefining technologies and a subsidiary of Lignol Energy Corp. But the oil industry found a way to make furans from petroleum-based maleic anhydride. "Now that oil prices have gone sky high, there's a strong interest in producing furfural again because it really looks like it could be cheaper," Pye says.

A Biorefinery Revenue Stream
In the cellulosic ethanol production technology employed by Lignol, furfural represents a "happy coincidence," a potentially lucrative consequence of the process. "We don't deliberately make furfural," Pye explains. "The whole objective of our biorefinery is to cook up wood under pressure and relatively high temperatures to remove lignin." The process produces a highly pure lignin that can exceed the value of the ethanol that is subsequently produced from glucose obtained from the cellulose. In addition, it turns out that as the hemicellulose fraction of the wood continues to cook, the polymer degrades into the xylose sugars, which under those same process conditions, turns into furfural. "We get furfural as a consequence of the conditions that we use in our process," Pye says.

This up-front, delignification process was first developed by the University of Pennsylvania and General Electric in the early 1970s. Later dubbed the Alcell pulping process, it was commercialized and applied to the pulp and paper industry in the '90s. Lignol acquired the technology in 2001 and modified it by recently developing processes for saccharification and fermentation. Earlier this summer, the company announced that it has begun building a 100,000-liter (26,000 gallon) ethanol pilot plant on the campus of the British Columbia Institute of Technology in Burnaby, British Columbia. The company also has plans to build a commercial-scale demonstration plant that will be based in Colorado, which will be partially funded by a $30 million U.S. DOE grant.

"We regard this technology as being the closest thing to a high-quality biorefinery," Pye says. "We take wood and split it up into its various fractions and get the highest value we can for each of those fractions."

Although ethanol and lignin will be the primary products of the process, furfural will provide a third source of revenue. The significance of that money stream, however, will depend on the source of the feedstock. Softwoods like lodgepole pine harbor less xylose than hardwoods or annual crops such as straw and corn stover. But in a demonstration-size plant that processes hundreds of tons of biomass per day, the proportion of furfural that can be extracted from a softwood feedstock would still be significant, Pye says.

For Raven Biofuels International, a New Jersey-based biofuels company, the origin of the feedstock is not a big factor because the company's technology is tunable to the
concentration of sugar in the feedstock. Raven Biofuels uses commercially available technology that's used in the pulping industry to produce ethanol and furfural from a wide variety of cellulosic feedstocks, including construction waste and wood chips, explains John Sams, chief operating officer of Raven Biofuels.

The two-stage process has been tested extensively at the U.S. federal laboratory, Tennessee Valley Authority pilot facility at Muscle Shoals, Ala. Over the past eight years, 32 different feedstocks have been tested and engineering and scale-up data has been generated.

In the first step, the biomass feedstock is treated with steam and weak sulfuric acid in an anaerobic digestor to break down the wood to the point where various sugar streams can be removed. Under these same conditions of heat and acid, the pentose sugars are dehydrated and subsequently converted into furfural, which is further refined through a distillation process. Meanwhile, the hexose sugars are fermented in a second step to ethanol. "The reason our system is more forgiving is that we can adjust the concentration of the acid, the flow of the acid or the steam to get more of the sugar out if there's a lower sugar content in the feedstock," Sams says.

In addition, the process allows for the extraction of any remaining fibers that can be sold or put in a boiler to provide process heat for the plant. "In our case we're removing C-5 sugars in the first stage of the process to make furfural and in the second stage, the C-6 sugars are made into ethanol through a normal fermentation process," he explains. "The Raven patented technology is centered around the production of furfural in combination with ethanol and for the production of high-level derivative chemicals from furfural."

The first project that Raven Biofuels is developing will be located in Washington state. The plant will produce 7 MMgy of cellulosic ethanol and 4 MMgy of furfural from 500 tons of construction waste per day collected by a company based in the state. Sams says the plant is expected to be in operation by the spring of 2010. "We believe we're going to the have the first real commercial plant operating in the United States and certainly the first one in the West," he says. In addition, the company is planning to build a similar plant in British Columbia, which will use wood from pine beetle-infested forestlands.

Along with ethanol, the company can sell the raw furfural or install additional equipment to convert that furfural into derivative chemicals. "The primary thrust of the process is to produce ethanol but furfural is a key part of that because what makes our plant very profitable is that the furfural sells for $4.50 to $5 per gallon," Sams explains.
Although it may be too early to make sweeping predictions about the future of furfural in a biobased economy, it's clear that producers are diversifying and that the production of specialty chemicals and the expansion of those industries will piggyback the growth in cellulosic ethanol production.

Jessica Ebert is a freelance writer for Biomass Magazine. Reach her at [email protected].