Los Alamos lab tests confirm cellulose ammonia pretreatment

| July 28, 2011

A liquid ammonia pretreatment process of cellulosic biomass under development at Michigan State University and the Great Lakes Bioenergy Research Center has been tested, and confirmed, at the Los Alamos National Laboratory. “Our modeling showed, and the experimental evidence confirmed, that the pretreatment reduced the strength of hydrogen bonds in the cellulosic network,” said Los Alamos researcher Sandrasegaram Gnanakaran on the testing.  

The liquid ammonia pretreatment process helps to break down the biomass when used at the right temperatures, allowing the enzymes used in the cellulosic ethanol process to be up to five times more effective, according to a recent paper published by Gnanakaran and others, including Bruce Dale, professor of chemical engineering and material sciences at MSU, who’s been instrumental in developing and researching ammonia-based pretreatment processes.

As LANL describes the makeup of plant matter, “The cellulose tends to orient itself into a sheet-like network of highly ordered, densely packed molecules,” adding that 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.” That arrangement hinders most enzymes’ ability to directly attack some of the individual cellulose molecules.

The ammonia pretreatment process, however, helps “as if the bailing wire in the bound chicken-wire analogy had been removed and replaced more loosely with the thread,” helping to reduce the “tightness” of the cellulose network, Gnanakaran said.

Shishir Chundawat, a researcher on the team, also said that the ammonia pretreatment process acts as a “cost-effective switch or lever.” By using an ammonia-based solvent, he said, the entire cellulose crystal can be switched from one structure to another—“one that’s much easier to break down.” The process can also use high moisture biomass, up to 50 percent, and operates at roughly 150 degrees to 200 degrees Fahrenheit for 15 minutes at 200 pounds per square inch of pressure.

A Michigan-based company, MBI International, is working to further develop and commercialize an ammonia pretreatment called AFEX, ammonia fiber expansion, the same process Dale and his research team developed at MSU.