The energy moguls expect switchgrass to be a major replacement for petroleum. Why do you suppose it hasn't happened yet? They have the biggest research laboratories in the world working on it, from Oakridge to Stanford. And this is why it isn't happening. Anything that needs that much research is not going to be competitive with something which is piped out of the ground like oil.

The problem is economics. Brazil virtually replaced gasoline with ethanol by using sugar as the raw material. Sugar only requires one step of processing, which is fermentation. Americans start with corn as the raw material for ethanol, and it requires two processing steps. First, the starch must be broken down into sugar, and then the sugar must be fermented. Switchgrass requires many steps of processing. There is no way to eliminate those steps, and there is no way to make them cheap enough to compete with petroleum.

Here's what the task is: Only the cellulose in switchgrass can be converted into ethanol. It breaks down into sugar, just like the starch in corn does. But the difference is that corn starch is nearly pure, while the cellulose in switch grass is embedded in large amounts of biological material including proteins, lignin, genetic material, chlorophyll, lipids and small molecules. That debris must be separated from the cellulose, before the cellulose can be broken down. Normally, enzymes would be used to break down the cellulose, and they cannot function effectively in the presence of such debris. This problem is what is holding up the process. Separating the debris is too expensive, and enzymes are not efficient in the presence of debris.

The researchers would be looking for substitutes for enzymes which could function in the presence of the debris. This would allow fermentation without separating the debris. But there are not good substitutes for enzymes. The substitutes will be inefficient compared to enzymes, and this will increase the cost.

So the whole question is this: Will researchers find a magical way to break down the cellulose in switchgrass? It won't happen. Biological molecules are too complex for substitutes for enzymes.

Another problem is that the enzymes for breaking down cellulose are not produced by bacteria or yeasts, which are extremely easy to grow in large quantities of liquids. Cellulose is normally broken down by molds, which are not easy to grow in liquids. Therefore, there would probably be a problem of expense in using massive quantities of enzymes to overwhelm the debris in the biomass.

The Latest Twist

The most recent procedure, a supposed breakthrough, is the use of a catalytic procedure to convert cellulose into a gasoline-like product containing aromatic compounds. The problem is that the nitrogen containing debris still has to be removed. Removing it is expensive, and disposing of it creates an environmental problem.

It was stated on television that industrialists who looked into the processing of agricultural cellulose including corn refuse or switchgrass determined that trucking the material more than 20 miles would be impractical, and such a short radius does not justify setting up a plant. This problem eliminates the whole concept of using agricultural sources of cellulose regardless of the method of processing.

So why is the research even continuing? Because scientists do a lot of pretending to justify expensive research. And propagandists do a lot of pretending to justify ulterior motives. They are still exploiting the pretense that alternative sources of energy, or green energy, are just around the corner.

Update

Researchers genetically engineered a bacterium to produce enzymes for breaking down hemicellulose. Hemicellulose is a glue between cells. Being something less than a solid like cellulose, it can be attacked in solution, unlike cellulose which cannot be broken down in water.

Fungi breakdown cellulose under non-aqueous (but damp) conditions. Water is like a preservative, when there is too much of it, because enzymes cannot function while floating in a liquid. Enzymes need to be pinned down, just like an astronaut doing repairs in space. Enzymes cannot make proper physical contact when floating freely.

So conversion of cellulose into fuels is up against the contradiction that a liquid solution is needed, while liquids disrupt the activity of enzymes which are free-floating outside of cells. Researchers get partial and limited results for hemicellulose, but how effective and efficient can it be, particularly with large amounts of debris in the way? Efficiency is always the design killer for converting waste into fuel.

If you want more specific information, searching Google will yield more than I can reproduce here. I describe the underlying knowledge, so you know how to proceed in exploring the subject.