Newswise — Pretreating bulky biomass feedstocks to make them into a denser, more compact form as a first step toward making them into biofuels may require less energy at the front end than scientists had thought.
That’s the good news thus far from a $1.1 million study funded largely by the North Central Sun Grant Center at South Dakota State University.
Scientists already know the biofuels of the future will likely require regional biomass processing centers to pretreat and densify materials such as switchgrass and cornstalks. Pretreating and densifying feedstocks will make it easier to ship biomass to processing facilities as much as 50 to 100 miles away. The new study explores some of the actual methods and technologies that could be used.
“Biomass is very bulky. So there are going to be a lot of logistical hurdles in moving this bulky biomass from the field to the centralized biorefining operation,” said professor Kasiviswanathan Muthukumarappan of South Dakota State University’s Department of Agricultural and Biosystems Engineering.
The current study — a collaboration involving researchers in South Dakota, North Dakota, and Michigan — takes advantage the adhesive-like qualities of one of the chief ingredients of biomass, lignin.
South Dakota State University scientists are collecting three kinds of biomass, switchgrass, prairie cordgrass, and corn stover. They mill the biomass to get particles of specified sizes. They then send the biomass to professor Bruce Dale of Michigan State University, where the samples will be pre-treated by a technique called AFEX processing. AFEX stands for “ammonia fiber expansion.”
The process brings lignin to the surface of the biomass particles so that it can be used as a natural binding agent that is already present in the material.
After pretreatment, the samples are sent to Michael Flaherty of Federal Machine Co. in Fargo, N.D., where engineers have developed a compaction device for compacting pretreated biomass. The biomass is compacted to form paks, which are then sent back to South Dakota State University, where the physical and chemical characteristics of the samples are analyzed.
The good news from the study thus far, Muthukumarappan said, is that pretreatment processing apparently won’t have to spend as much energy slicing and dicing biomass into pieces of very small diameter.
“We found that in terms of compacting these AFEX-treated biomass samples, we don’t have to go to lower particle sizes, we can use the larger particle sizes. What it means is that it’s going to require less energy in pre-processing these biomasses,” Muthukumarappan said.
In other words, instead of chopping biomass into pieces with a diameter of, say, 2 millimeters, the process will work with pieces as large as 8 to 12 millimeters. That is one small step toward lowering the cost of making new biofuels from biomass feedstocks.
Scientists had been afraid that they would have to chop the biomass into particles of smaller size in order to create more surface area so that enough lignin would be available to act as a binding agent. But they found they were able to make a compacted material even with the higher particle size.
The project also includes a storage study to determine how long these packs can be stored without any adverse effects.
The samples will be processed by three different labs. Assistant professor Scott Pryor’s lab at North Dakota State University uses a technology s called “separate hydrolysis and fermentation.”
Professor William Gibbons in SDSU’s Department of Biology and Microbiology at SDSU will use a processing technique called “simultaneous saccharification and fermentation.”
Associate professor Lew Christopher’s lab at the South Dakota School of Mines and Technology will explore whether unique microbes scientists have from the former Homestake Gold Mine in western South Dakota — so-called “extremophiles” that are adapted to the extreme conditions deep underground — might serve as a possible biomass breaker in the process of converting biomass to biofuels.
Instructor Michael Twedt at South Dakota State University and assistant professor Chris Saffron at Michigan State University also are looking at the technical and economic feasibility of whole biomass processing operations.
The wide-ranging study also will consider issues such as flowability, or how well the processed material will flow when it is unloaded at a processing facility, and whether the compacted biomass will produce the same amount of biofuel as uncompacted biomass.
The two-year project runs until June 2012. The North Central Sun Grant Center is funding $700,000 of the $1.1 million project. The remaining $400,000 is a cost-share match from the different partners in the research.
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