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"It's a prediction because right now there are no biorefineries built that handle cellulosic material" like that which switchgrass provides so.. nobody can fer

"It's a prediction because right now there are no biorefineries built that handle cellulosic material" like that which switchgrass provides so.. nobody can ferment it but it gives a higher ethanol yield than corn.. how does that work

Magnap 3y ago
The issue is not so much that it's cellulosic as that it's lignocellulosic; we have a pretty good grasp these days on cellulose (and hemicellulose, but we can handle that too so I'll skip over it). Lignin is (oversimplifying, but not by too much) what makes the difference between soft paper pulp and hard woodchips. The lignin crosslinks the (hemi)cellulose and makes it much harder to access for the enzymes we'd use to break down the cellulose, while itself being very difficult to break down (it's thought that the whole reason we have coal is due to how long it took for fungi to evolve the enzymes needed to break down lignin effectively in order to degrade wood). You need a bunch of equipment and/or biochemical processing to break down lignocellulosic plant matter into something that can be efficiently fermented (keyword: "lignocellulosic biomass pretreatment"), so while thay may be available at a lab scale, it's not necessarily possible on an industrial scale (yet). As one example, there's a method called "steam explosion" where you apply very hot (around 160-260 °C) and high-pressure (tens of atmospheres) steam to the biomass, then release the pressure relatively fast. The hot steam causes chemical reactions like hydrolysis, and the pressure release breaks down the material physically as the steam expands. Imagine the sort of equipment you'd need to do that on an industrial scale. Nowhere out of reach for modern chemical engineering, but someone has to build it. Now, as you might imagine from how relatively non-woody switchgrass is, it doesn't have a ton of lignin compared to trying to ferment woodchips, but it still has enough to be problematic, and in fact there's research being done on how to reduce its lignin content, such as by genetic engineering.
zdragnar 3y ago
Fermenting on a tiny scale in a lab is fundamentally different than fermenting on a commercial production scale. Basic calculations of energy density + small experiments support the assertion, but without a working larger scale production that can consistently yield ethanol (i.e. preventing the bacteria responsible from being displaced by wild strains, yeast or other fungi, ensuring batches run to completion, etc) it's nothing but a prediction.

Magnap 3y ago

The issue is not so much that it's cellulosic as that it's lignocellulosic; we have a pretty good grasp these days on cellulose (and hemicellulose, but we can handle that too so I'll skip over it). Lignin is (oversimplifying, but not by too much) what makes the difference between soft paper pulp and hard woodchips. The lignin crosslinks the (hemi)cellulose and makes it much harder to access for the enzymes we'd use to break down the cellulose, while itself being very difficult to break down (it's thought that the whole reason we have coal is due to how long it took for fungi to evolve the enzymes needed to break down lignin effectively in order to degrade wood). You need a bunch of equipment and/or biochemical processing to break down lignocellulosic plant matter into something that can be efficiently fermented (keyword: "lignocellulosic biomass pretreatment"), so while thay may be available at a lab scale, it's not necessarily possible on an industrial scale (yet). As one example, there's a method called "steam explosion" where you apply very hot (around 160-260 °C) and high-pressure (tens of atmospheres) steam to the biomass, then release the pressure relatively fast. The hot steam causes chemical reactions like hydrolysis, and the pressure release breaks down the material physically as the steam expands. Imagine the sort of equipment you'd need to do that on an industrial scale. Nowhere out of reach for modern chemical engineering, but someone has to build it. Now, as you might imagine from how relatively non-woody switchgrass is, it doesn't have a ton of lignin compared to trying to ferment woodchips, but it still has enough to be problematic, and in fact there's research being done on how to reduce its lignin content, such as by genetic engineering.

zdragnar 3y ago

Fermenting on a tiny scale in a lab is fundamentally different than fermenting on a commercial production scale. Basic calculations of energy density + small experiments support the assertion, but without a working larger scale production that can consistently yield ethanol (i.e. preventing the bacteria responsible from being displaced by wild strains, yeast or other fungi, ensuring batches run to completion, etc) it's nothing but a prediction.