Audubon Sugar Institute Helps Meet Demand for Biofuels Research

Linda Benedict  |  3/2/2007 11:02:29 PM

This small vial of pure ethanol was created from bagasse in experiments at the LSU AgCenter’s Audubon Sugar Institute. (Photo by John Wozniak)

Chang-Ho Chung, a post-doctoral researcher at the Audubon Sugar Institute, with the hydrolysis reactor. Enzymatic hydrolysis followed by fermentation is being pursued in the development of ethanol from sugarcane bagasse. A process is being used in a small-scale pilot system to produce sufficient amounts of treated bagasse to conduct pilot-scale hydrolysis/fermentation experiments. The treated bagasse is enzymatically hydrolyzed and the sugars fermented toalcohol. (Photo by Benito Stradi)

Peter Rein

A sugarcane-based biorefinery has been discussed for many years at the Audubon Sugar Institute. In the past few years funding has become available and work has started in earnest.

A sugar mill is in a sense already a biorefinery, producing sugar and molasses as products and generating bagasse used as a fuel in boilers. The true concept of a biorefinery, however, envisages producing from sugarcane biomass a slate of products – particularly fuels and chemicals – which together provide a much-increased revenue stream. This changes a sugar mill into a sugarcane processing plant.

While in most instances cane leaves and tops (also called cane leaf matter or CLM) represent a disposal problem, they are a potential source of fiber and fermentable materials. The extraneous matter left in the fields keeps the temperature of the soil down, delaying germination of the next year’s crop and reducing cane yields. The common practice is to burn this material in the fields or rake it away from the sugarcane roots. In a biorefinery, however, the leaves and tops have value. Combining the CLM with the cane can virtually double the amount of bagasse produced.

Lignocellulosic Alternative
The use of lignocellulosic material (the essential part of plants’ woody cell walls consisting of cellulose and lignin) is an excellent alternative to fossil fuels because it is an abundant, renewable resource that does not generate additional carbon dioxide in the Earth’s atmosphere. In addition, innovative expansion in the field of biofuel production would spur substantial job creation and stimulate the economy.

Using sugarcane to produce liquid fuels and electric power can yield considerable benefits, including:
  • No net increase in the generation of greenhouse gases.
  • Use of renewable resources for energy production.
  • Reduction in the nation’s reliance on imported fuels.
  • Incentive to expand agricultural production in Louisiana.
  • Elimination of burning of CLM.

Because the sugarcane industry is a major contributor to Louisiana’s rural economy, the effect of a new, vibrant production sector would have considerable effect because it also affects the supporting industries of equipment and process plant suppliers and providers of other goods and services. An increase of just 10 percent in cane production would enhance the state’s economy by an estimated $100 million more a year.

Energy Department Funding
More than $4 million in grants from the U.S. Department of Energy over the past three years has enabled Audubon to mount a serious research effort. These grants have been in collaboration with MBI International, a nonprofit spin-off of Michigan State University. Ethanol can be produced from sugarcane biomass in two ways, which are both being investigated at Audubon:

  1. The fibrous bagasse can undergo hydrolysis (the chemical reaction in which one substance reacts with water to produce other compounds) to produce sugars that can be fermented to produce ethanol. Maximum value from bagasse can in theory be obtained by separating bagasse into its three major components – cellulose, lignin and hemicellulose. Cellulose and hemicellulose are hydrolyzed, but lignin is not hydrolyzed and may be the source of other value-added products
  2. Biomass can be subjected to thermochemical treatment, which subjects it to high-temperature pyrolysis (the use of heat to break down complex chemical substances into simpler substances), or gasification, which turns it into a gas. Pyrolysis produces bio-oils, and gasification produces a synthesis gas that can be converted to liquid fuel.

Many claims have been made of how value-added products can be produced from sugarcane biomass. Apart from the production of paper from bagasse and generation of electricity using bagasse as a fuel in boilers, few of these are economically viable. The challenge is to find those processes, which, when incorporated into a biorefinery, will lead to products that justify the capital investment. It is anticipated that the capital required could be large, and economies of scale obtained through highvolume processing would be needed.

Many different schemes have been devised in the laboratory. The approach at Audubon has been to move from the laboratory to pilot-plant scale. This enables us to obtain data that can be used to generate design data, bringing commercial realization one step closer. Active research and recent technological improvements are likely to make commercialization possible.

Thus far, major efforts have been directed toward treating bagasse and CLM, recovering of phenols from the lignin fraction of the biomass, optimizing the enzymatic hydrolysis for different treatments and addressing the challenges of fermenting both glucose and pentose sugars into ethanol and other products. Additional work has been done on producing more cellobiose (a type of sugar that is produced from the partial hydrolysis of cellulose) for the production of added-value chemicals. Gasification research is at an early stage, but progress will be boosted with additional research help. A smaller program for producing biodiesel in a modified process using bio-ethanol rather than methanol is also under way.

What the Future Holds  
A raw sugar mill already has the infrastructure in place for collecting and processing sugarcane biomass. This is a major advantage over other lignocellulosic processing options using corn stover or forest wastes. Selected add-on options, depending on the economics of individual processes, provide the route for converting a sugar mill into a biorefinery.

The economics of a biorefinery are likely to be improved by economies of scale. For instance, combining surplus bagasse and CLM from four mills in the Teche area of Louisiana can supply a plant that can process 2,000 tons of biomass dry matter per day. Augmented with molasses, this will result in a plant capable of producing about 70 million gallons of ethanol per year – a viable size for an ethanol plant. At the present average crop size of 14 million tons of sugarcane per year, the potential for ethanol production from bagasse and CLM in Louisiana is about 250 million gallons per year. This is after allowing for the use of some of the bagasse in the boilers for the generation of steam and power.

Assuming that production of ethanol from biomass becomes a commercial reality, the biorefinery potential can be greatly enhanced by processing high-biomass cane or “energy cane.” Such cane bred for biomass rather than sucrose yield can substantially improve biorefinery output. Further augmentation with sweet sorghum and perhaps the perennial grass miscanthus could make the biorefinery even more attractive and enhance the agricultural opportunities in Louisiana.

Making a sugarcane biorefinery a reality is still a few years away. But the potential rewards to Louisiana and the nation are tremendous.

(This article was published in the winter 2007 issue of Louisiana Agriculture.)

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