Fiat Panda city car now with Euro 5 engines
Chevrolet sets first-half global sales record with 2.35M units; 14% growth

New method of ammonia pretreatment for biomass increases saccharification rates up to 5-fold; prospects for more cost-effective biofuels and chemicals production

The new pretreatment approach uses ammonia (NH3) to reorganize the hydrogen bond network within cellulose, resulting in up to a 5-fold increase in saccharification rates. Credit: ACS, Chundawat et al. Click to enlarge.

Researchers at the US Department of Energy’s Los Alamos National Laboratory (LANL, the Great Lakes Bioenergy Research Center (GLBRC) and Michigan State University (MSU) have developed a new biomass pretreatment method that reorganizes the hydrogen bond network within crystalline cellulose. (Earlier post.)

The new method enhances saccharification rates by up to 5-fold compared to other pretreatment approaches that hydrolyze cellulose to glucose, enabling it to be converted to biofuels (e.g., alcohols, hydrocarbons) via microbial fermentation or chemical catalysis.

Cellulose tends to orient itself into a sheet-like network of highly ordered, densely packed molecules. These sheets stack upon themselves and bond together very tightly due to interactions between hydrogen atoms—somewhat like sheets of chicken wire stacked together and secured by loops of bailing wire. This stacking and bonding arrangement prevents enzymes from directly attacking most of the individual cellulose molecules and isolating the sugar chains within them. The new process reduces the strength of the hydrogen bonds in the network—as if the bailing wire in the bound chicken-wire analogy had been removed and replaced more loosely with thread.

This, in turn, significantly reduces the tightness of the cellulose network and leaves it more vulnerable to conversion into sugar by fungi-derived cellulolytic enzymes. This new approach can thus significantly reduce the enzyme loading necessary to achieve economical conversion of lignocellulosic biomass, the researchers note in a paper published in the Journal of the American Chemical Society. The study also provides fundamental insights into the nature of cellulose recalcitrance.

Several different approaches are being developed to pretreat lignocellulose so that its complex architecture can be disrupted, thereby making its cellulosic component more accessible to water and enzymes for an accelerated conversion to glucose. These approaches can be classified into two major categories of thermochemical pretreatments: the first type facilitates removal of hemicellulose and/or lignin and increases enzyme accessibility to embedded crystalline cellulose fibrils (with little or no major change to cellulose crystallinity), whereas the second type proceeds further to disrupt cellulose crystallinity and hence increase glycosidic bond accessibility.

Most thermochemical pretreatments fall within the first category (e.g., dilute acid, ammonia fiber expansion (AFEX), steam explosion, hot water, organosolv), except the ones that use ionic liquids or concentrated acids (like 85% phosphoric acid). However, complexities associated with both the cost-effective utilization and recycling of these chemicals have so far prevented rapid commercialization of either of these approaches.

...A route to improve cellulose conversion is to engineer enzymes with enhanced specific activities for crystalline cellulose hydrolysis. However, despite significant advances in our understanding of the molecular-scale enzymatic mechanisms driving cellulose deconstruction, engineering highly efficient cellulases remains a major challenge. An alternative approach relies on the use of inexpensive and easily recoverable chemicals to alter the cellulose crystal structure in order to increase its rate of depolymerization.

—Chundawat et al.

The approach taken by the team involves a structural conversion between crystalline forms of cellulose catalyzed by ammonia to enhance the depolymerization kinetics. This ammonia-based pretreatment produces cellulose IIII (without any relevant loss of crystallinity) with enzymatic hydrolysis rates the closest to those of amorphous cellulose among all reported cellulose allomorphs.

Ammonia transformed the naturally occurring crystalline allomorph Iβ to IIII, which led to a decrease in the number of cellulose intrasheet hydrogen bonds and an increase in the number of intersheet hydrogen bonds. This rearrangement of the hydrogen bond network within cellulose IIII, which increased the number of solvent-exposed glucan chain hydrogen bonds with water by ~50%, was accompanied by enhanced saccharification rates by up to 5-fold (closest to amorphous cellulose) and 60–70% lower maximum surface-bound cellulase capacity. The enhancement in apparent cellulase activity was attributed to the “amorphous-like” nature of the cellulose IIII fibril surface that facilitated easier glucan chain extraction.

Subtle alterations within the cellulose hydrogen bond network provide an attractive way to enhance its deconstruction and offer unique insight into the nature of cellulose recalcitrance. This approach can lead to unconventional pathways for development of novel pretreatments and engineered cellulases for cost-effective biofuels production.

—Chundawat et al.

In addition to LANL, the GLBRC, and Michigan State University, the paper included collaborators from American University and the US Department of Agriculture’s Forest Products Laboratory in Madison, Wisconsin.


  • Shishir P. S. Chundawat, Giovanni Bellesia, Nirmal Uppugundla, Leonardo da Costa Sousa, Dahai Gao, Albert M. Cheh, Umesh P. Agarwal, Christopher M. Bianchetti, George N. Phillips Jr., Paul Langan, Venkatesh Balan, S. Gnanakaran, Bruce E. Dale (2011) Restructuring the Crystalline Cellulose Hydrogen Bond Network Enhances Its Depolymerization Rate. Journal of the American Chemical Society 133 (29), 11163-11174 doi: 10.1021/ja2011115



This could be a simple method. I would just gasify the biomass, but if you want to do pre processing front ends to existing fermentation plants, it might work.


Front ends are the easy route. There are hundreds of corn-ethanol plants running; a bolt-on plant which lets them use corn stalks (or sawdust, or waste paper) instead of corn grain gives them a cheaper feedstock which does not compete with food.

Ammonia is already a widely-used chemical in the farm belt, so it is both readily available and people are accustomed to working with it.

Account Deleted

The key reason that enzymatic conversion of biomass to fuels is more economic than catalytic conversion is that it is more energy efficient and that you don’t destroy high-value substances in the conversion process.

With catalytic conversion you first need to spend energy drying the wet biomass. Then you need to spend energy heating the dried biomass to very high temperatures to get syngas. That process is complicated by the fact that biomass contains non-combustible substances (ashes) that will need to be removed from the oven that produces the syngas. Moreover, syngas is not the only substance that is produced. Other harsh chemicals are produced that will break down the catalysts used to convert the syngas to fuels. The problem is that the catalytic BTL process is energy intensive, capital intensive and catalyst intensive. So far no one has been able to do it economically. Rangefuels was the latest company to bankrupt who tried the catalytic process.

Enzymatic BTL stand a better chance of becoming an economic way of producing fuels. Firstly, it is already producing about one million barrels per day of ethanol from corn in the USA. In itself that is not economical but the enzymatic conversion leaves valuable byproduct like corn oil and protein rich distiller grains unharmed and selling off these byproducts make this type of enzymatic BTL profitable. Another, benefit from enzymatic conversion of biomass is that you don’t need to spend energy on drying wet biomass and enzymatic processes happens at low temperatures unlike syngas production so more energy is saved there.

Poet energy is probably the company that will be first to economically produce ethanol from cellulosic biomass. First large scale production or 25 million gallons per year is planned for 2013 and two more years may be needed before the processes have been optimized enough to be rolled out on all the other ethanol refineries at Poet and elsewhere.

It is essential for the long-term viability of the ethanol industry that it develops economic BTL processes for non-starch and non-sugar based biomass as food prices are likely to rise faster than fuel prices in the future. Food prices will raise faster because humans in the developing world especially China are changing their diets from one based on grain to one based on meat. That will multiply the demand for grain and thereby the food prices. In fact, in about 15 years I doubt ethanol can be produced economically from grain but I am also sure that most ethanol refineries by that time have been converted to using cellulosic biomass and other kinds of non-edible biomass.


I hope the plants convert, there is capital invested and they got hurt by corn price speculation. I think BTL, GTL and CTL can make fuels, it depends on the investment climate.


This does not seem terribly new. This form of treatment has been around since the 80's.


Correction 60's


Using 4 to 5 billion bushels/year of corn and almost as much sugar cane/year to produce fuel for our gas guzzlers while many millions are starving will not make USA and Brazil more acceptable worldwide.

It is a real shame.


If there was no ethanol plants demanding corn, the farmers would not plant it.. the starving masses would not get the corn anyways.

Can this pretreatment be used to enhance feed for cattle?

The comments to this entry are closed.