Biofuels and biomass have, over the past few years, been a highly researched area as a way to replace petroleum-based fuel sources. The expansion of biofuel production over the previous decades has not been without its own problems and hitches. A main issue with current biofuel production is that it is largely done by using an excess amount of food crops as a fuel source, such as ethanol made from corn.
But this isn’t a very productive process, as plants of this nature thus need to be made to remain edible as a food source, either for human consumers or for farm animal consumption. This limits the capability of scientists and farmers to use the plants for biofuel production in an efficient manner.
Instead, studies have focused on creating more directly focused biofuels, such as with switchgrass. An improvement in the conversion of nonedible parts of existing crops, called the lignocellulosic biomass, has also been of high intent. For corn, this would mean improving the sugar conversion of the stalks, leaves, and other parts of the plant other than the removed corn cob itself. This leftover mass is referred to as the corn stover.
A Double Feature
Today, we’ll be looking at two studies recently released on the topic of biofuels, both funded by the Department of Energy’s (DOE) Great Lakes Bioenergy Research Center, who worked with scientists from the University of Wisconsin–Madison and Michigan State University on the studies.
The first DOE study deals with the problem of efficiency and how biofuel refineries currently lack the capability to keep up with the energy output of petroleum-based refineries. The way that was devised to get around this was to manufacture an integrated refinery that creates multiple output products while properly breaking down the inserted biofuel sources individually.
This has proven to be more difficult than with petroleum because biofuel sources are made up of very disparate kinds of cellulosic materials, such as cellulose, hemicellulose, and lignin. These each require their own individual method of breaking them down into their constituent parts for processing.
Combine this with the risk of investment in a new technical design that may come to nothing and it is easy to see why no new integrated refineries have really come onboard. The researchers in this study propose a biomass fractionation process that would be capable of converting all three of those sources into known market fuel products and even other items.
A Product Extravaganza
These products would include, as a first example, dissolving pulp, a form of cellulose with a greater than 90% concentration that can be placed into a chemically accessible solution good for processing into textile fibers, a form of heat-resistant plastic, or a thickening agent. The second product would be furfural from the hemicellulose, which is used as a polymer for resins and other coatings, as a chemical solvent, and as an adjuvant in herbicides. The last products are made from lignin, which can be turned into fireproof insulating carbon foams or into a high quality battery anode for electrical current.
All of these initial creations are meant to be a method to directly produce cost-effective products that can be sold and recoup the investment on making an integrated refinery. After the risk of cost is reduced, the refinery can be expanded to make the more usual fermentable sugars that biofuels are made from. The cellulose conversion efficiency from their fractionation process would be around 80%, including the efficiency from the other products being made.
Moving up to intermediate scale products like sugars would also open up more ambitious items to be made out of the furfural and lignin processing. As a whole, the entire purpose is to make an integrated refinery capable of making such a wide variety of products that it would remain marketable no matter the prices in any particular field.
Combined with its enhanced efficiency, a wide-scale construction of these integrated biorefineries may prove to be a major competitive source of fuel against the petroleum industry, in addition to providing goods for pulp mills and other industries.
A Climate Hitch
The second DOE study focused more on the growing end of things and how biofuel crops, like the aforementioned switchgrass and corn stover, fare in drought conditions. The answer is not very well and not because of the reasons you might think.
Other than the expected decrease in photosynthetic capabilities and growth inhibition, which both contribute to reduced biofuel yield in their own way, drought conditions also appear to create a conformational change in the sugar structures within the plant cells. Water-stressed plants not only have a reduction in structural carbohydrates, but also the production of certain amino acids and soluble sugars.
When the pretreatment methods involving ammonia-based chemicals were used to break open the plant cells to extract the sugars for bacterial processing, they underwent a chemical makeup change. This resulted in the production of highly toxic compounds like imidazoles and pyrazines. Normally, these components have biologically useful activities, like how imidazole is a primary component in making the amino acid histidine.
But in biofuel processing, it is nothing short of disastrous. When the final step of biofuel processing, conversion, was started, the bacteria and fungi like Saccharomyces cerevisiae used to ferment the sugars into biofuel products were inhibited and unable to properly do the conversion. Since many of the compounds made by the sugars’ chemical conversion were anti-fungal azoles, this heavily impacted the ability of the microorganisms to function.
Though it’s not all bad. The higher accumulation of amino acids and proteins under drought stress provided far higher nutrients for the microorganisms during processing, increasing overall output (ignoring the effects of inhibition noted previously). The researchers suggest several methods for avoiding the downsides from this process.
The first is to look for pretreatment methods that limit the amount of negative chemical formations, though the ability to find and use such a method may not be feasible. The second option would be to remove the soluble sugars before pretreatment, leaving the fermentable sugars and the amino acids and proteins. This might lower the overall amount of available fermentable product, but it is a possibility. The final choice would be to develop bacterial and fungal strains directly resistant to the chemicals in question, making them not a problem.
Out of all of the alternatives, the latter appears to be the best to retain biofuel yields. Though it may also be the most time-complicated, depending on just how difficult it would be to develop such strains of microorganisms.
New Advancements and New Discussionss
Thus, in order to improve lignocellulosic crop production in the future, especially since such agriculture will likely be suffering from higher than average periods of drought conditions due to climate change, some changes will have to be made. There is still a lot of research and experimentation to be done.
Hopefully, with time, we can solve both issues discussed in this article, improving both the efficiency of growing and harvesting of high bioenergy crops and the efficiency of the refining and fermenting of them into usable biofuels and other products. Now that we have our problems and our options laid out in front of us, scientists can focus on making those workarounds a reality.
Photo CCs: Panicum virgatum Parc floral from Wikimedia Commons