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The Habitable Planet: A Systems Approach to Environmental Science 

Energy Challenges Interview with Andy Aden

Interviewer: Tell me about the National Renewable Energy Laboratory and what you do there.

ANDY: I work at the National Renewable Energy Laboratory as a research engineer. This building that we’re in now is called the AFUF, the Alternative Fuels User Facility, and this is where we do a lot of research on alternative fuels specifically from cellulosic biomass.

Interviewer: Biomass has been a source of energy for a long time. Can you tell us a little bit about the history of biomass?

ANDY: In essence, biomass is plant matter. It’s the fibrous material that’s left over after you’ve harvested say, for example, corn grain or soybeans; it’s just really a plant matter that’s available out there. For a long time, all the way back as far as human existence, people have burned wood in fire stoves, for energy purposes, campfires. Now we’re looking to take all these different biomass resources that are out there, of which there are many, and fully utilize them in better capacities to be more energy efficient with these feedstocks whether it to make fuels, whether it be to make power or whether it be to even make renewable chemicals.

Interviewer: What is renewable energy?

ANDY: There are a lot of different renewable energy technologies out there. Solar cells or what are called photovoltaics, wind power, and even biofuels are considered renewable. The nice thing about biomass and biofuels that makes them renewable is they’re a renewable source of carbon. Carbon is recycled throughout the carbon cycle and used to grow plants using photosynthesis. CO2 is recycled all the way around in the carbon cycle, and that makes this a renewable process so that we can make things like fuels and chemicals on a continuous basis without using up feedstocks like petroleum or gas or finite resources.

Interviewer: What about transportation fuels — what’s the situation now and how does it relate to renewable energy?

ANDY: When you pull up to the gas pump today, you have two choices basically — gasoline or diesel – both of which come from petroleum. What we’re trying to do is make renewable energy technology or biofuels that are a renewable source of fuels for our transportation needs. That means taking biomass that grows naturally and recycles carbon in the whole carbon cycle so that as you’re burning the fuel and producing CO2, that CO2 is not just getting captured in the atmosphere, it’s getting recycled back to the front end of the process. Taken out by plants and used — they use the CO2 in photosynthesis; it’s really a closed system so that you can recycle and continually meet your needs without taking up finite resources of valuable material.

Interviewer: Is there any biomass fuel being produced at this time?

ANDY: Right now, there is a fair amount of biomass fuels that are out there. In the United States, there are over four billion gallons of ethanol currently produced almost entirely from corn. There is about an equivalent amount of ethanol produced from sugarcane down in Brazil. So those two types of biofuels are really plentiful out there right now. There is something called biodiesel that’s largely produced from vegetable oils that are being used as a diesel substitute for petroleum diesel. That’s not nearly as large a market right now, but it’s definitely growing; in fact, it tripled over the past year. So there are certain amounts of biofuels out there. But when you’re comparing things on the order of five billion gallons to the one hundred and forty billion gallons of gasoline we utilize every year, there’s still quite a discrepancy that we have to make up.

Interviewer: When I go to the gas pump, I see that it says “up to 10% ethanol.” Tell us what the ethanol situation is.

ANDY: Ethanol, as you’ve heard of it, is really just alcohol that you can use to burn in your gas tank as a cleaner-burning alternative to a hydrocarbon fuel like gasoline. You’ve probably seen it in your gas tanks at the ten percent blend level; that’s often done to help reduce the emissions from gasoline, specifically in big, urban areas. What we would like to see happen is to have larger volumes of ethanol be used in the fuel source in the United States to be able to really make a larger bang for the buck, further reduce our emissions environmentally, improve our national security so that we don’t have to purchase petroleum from foreign countries in hostile areas, and really have a benefit to rural America as well. Bring some revitalization to these areas that are agriculturally based and can provide more economic benefit to those societies.

Interviewer: How do you make ethanol?

ANDY: We’ve known how to make alcohol and ethanol specifically for quite a number of years, all the way back to fermenting from grapes and producing it in wine and beer and everything else. The same ethanol that you drink potentially is the same ethanol that’s used as a fuel. We’re just using it as a cleaner-burning fuel and an alternative to gasoline. Currently, the United States produces about four billion gallons of ethanol every year, and that number keeps increasing. But it’s still a very small percentage compared to the one hundred and forty billion gallons of gasoline that we consume every year, and that number, too, also keeps increasing. Most of the ethanol in the United States used for fuel is made from corn grain in Brazil and other countries. Sometimes it’s made from sugarcane.

Interviewer: What are some of the issues associated with ethanol?

ANDY: Ethanol is a great alternative fuel. It burns cleaner than gasoline; it’s produced in our own country. There are a lot of benefits to it. But we’re producing it at a very small scale, and we really need to produce it at a much larger scale in order to make a significant dent in petroleum and gasoline. That’s why we really have to look at the next generation of ethanol, which is coming from plant matter or biomass. Biofuels research is the next generation of where we’re going. There are lots of different types of biomass. There are agricultural residues like corn still or wheat straw — things that are currently left in the field after the grain has been harvested. There are wood types of feedstocks that are biomass; woodchips like poplar, for example, are biomass, all the way to even a prairie grass like switchgrass. President Bush mentioned this in his State of the Union Address as a potential energy crop for cellulosic ethanol. This would be grown specifically for its value as a producer of an ethanol type fuel.

Interviewer: What is one of the big potential benefits of using biomass as opposed to corn?

ANDY: There are a lot of reasons and a lot of additional benefits for using biomass as a source of ethanol as opposed to just corn grain, one of which is there is a lot more of it out there. The second is you avoid the food versus fuel issues. Corn grain is obviously an edible compound that can be eaten by humans and animals and everything else. Plant matter does not have that same food market so you avoid that debate. The third potential benefit is to farmers and rural America because it adds an additional income source and an additional market to sell the material. Here’s some corn stover — the stocks, the husks, the leaves, the cobs — every part of the plant that’s left over after the corn has been harvested. There are probably over one hundred million tons of this material available every year in the United States, most of which is just simply plowed back into the ground to help control erosion and build up the organic soil; there is really no other market for it and nothing else to do with it.

This material, on the other hand, is quite a bit different. This is a hardwood poplar feedstock. The advantage of this type of biomass are that it’s a very fast-growing tree. It can often be grown within five years up to full size; and you can potentially have plantations of this material that can produce large amounts of biomass for fuel. And finally there is switchgrass. President Bush mentioned this in his State of the Union Address as a potential energy crop for cellulosic ethanol. It’s really just a prairie grass that’s grown in the various different locations throughout the United States. The benefit of this material is that it’s very drought tolerant, doesn’t take a lot of water to grow like corn does, for example, and you can get a lot more tonnage of this material off of an acre of land than you can a residue like the corn stover.

Interviewer: Tell me about the process of turning biomass into ethanol.

ANDY: This is one of our vats of milled corn stover. Biomass like this is made up of primarily three things: cellulose, which is primarily long chains of sugars found in the cell wall of a plant; hemicellulose, which is also long chains of sugars, just different sugars; and then a third substance that we call lignan. Lignan is like the glue that holds a plant together, makes it stand up straight in the field instead of falling over in the wind. It provides structural rigidity and natural protection against insects and other things.

Nature has made biomass materials to be resistant to being broken down. As a result, we have to do a little bit of pretreatment to start breaking these materials down. We use dilute acid as a chemical hydrolysis agent to begin doing that. Hydrolysis is really just a fancy chemical term for adding water to the chemical reaction. This part of the process starts to get those sugars that are produced into a solution. This is a sample of pretreated corn stover. This is a sample of pretreated corn stover. Some of the hemicellulosic sugars have been broken down and are going into solution at this point. As I take this off and take a whiff of it, it smells sweet, kind of like raisins and molasses. And those are some of those sugars that are starting to come off. The rest of the material that you see here, then, is the rest of the cellulose and the lignan that’s left and ready to be processed. Once we’ve pretreated the biomass, we bring that pretreated biomass in a slurry or a paste into our fermenters and this is where we add our cellulase enzyme into the process. Cellulase enzyme is simply a natural protein that acts as a catalyst to break down the cellulose into its individual sugar units. It’s a lot harder to do than starch even though cellulose and start are very similar on a chemical level. It’s analogous to graphite and diamond, both resources of carbon, but graphite is very brittle and diamond is the hardest substance on earth. Starch is very easy to break down because of the way it’s chemically bonded. That’s why it’s easy to produce ethanol from corn grain. Cellulose is much more difficult to break down; because it’s bonded differently chemically. That’s why we use the enzymes to do it naturally, do it very specifically, and do it much more efficiently. Each of these tanks is about nine thousand liters or about twenty-five hundred gallons. They’re made of stainless steel and they have agitators inside to keep that slurry and pasty material mixed up with the enzymes and the organisms that we add.

Interviewer: Tell me about the enzymes that you add. What exactly is an enzyme?

ANDY: The cellulase enzymes are actually a mixture of different proteins. They serve specific functions to more efficiently break down the biomass. There are enzymes that act on the ends of the structure, there are enzymes that act in the middle of the structure. and then there are enzymes that work to break down longer chains into shorter chains. They all function very synergistically to make this a very efficient process and do it naturally. A big portion of the research that we do at NREL is on the enzyme systems themselves. Five years ago, the cellulase enzymes were the single largest cost component of this whole entire process. Within the past five years, we’ve done research both here and with the industry to really reduce the cost of those enzymes and make those enzymes much more efficient. We’ve done biotechnology experiments and improved the whole biotechnology area to enhance these enzymes and make them perform much more efficiently and, therefore, more cost-effectively.

Interviewer: What is the final result of the enzyme process?

ANDY: Once you’ve used those enzymes, you have a mixture of sugars and that mixture of sugars, can be fermented by either yeast or a bacteria – different organisms — into fuel ethanol. The organisms that utilize those sugars to make ethanol in the current corn ethanol industry only utilize glucose but they do it very well. In this process, we have a mixture of sugars, glucose, xylose, mannose and several other sugars that we need to ferment into ethanol. We have organisms that have been engineering to do glucose and xylose, but we’re trying to get them to function more efficiently on those sugars as well as do additional sugars with more effect — to produce more ethanol from every pound of biomass that we bring in here.

Interviewer: Describe some of the equipment that is involved in the process.

ANDY: The centrifuge is a very important part of the whole process. The lignan residue that is part of the biomass can be separated using this piece of equipment. That lignan plays a very important part of the energy picture of this process. One of the potential downfalls of corn ethanol is the fact that it’s fairly energy-intensive and you don’t get a whole lot more energy out in your field than you put into it. Because cellulosic biomass has this lignan component that can be used for fuel, you don’t have to buy coal, you don’t have to buy natural gas. You can be a self-sustaining energy plant like this by burning this lignan residue. Therefore being able to separate it efficiency is important.

Interviewer: Have you calculated the amount of energy you can get from the lignan?

ANDY: A lot of our engineering calculations show that there is quite a bit of energy in the lignan, so much so that you could not only provide all the energy needs for a processing plant such as this, you could also potentially sell a green energy byproduct to the local power grid.

Interviewer: If you had a standard corn ethanol plant married to a biomass plant, what would be the benefits of that?

ANDY: This is a bucket of corn fiber, also known as DDG, or distillers’ dried grains. It’s the byproduct from today’s corn ethanol plants currently used as an animal feed. But we can use it as a feedstock for a process such as this. Some people have the misconception that we’re actually competing with corn ethanol, and that’s not at all the case. What we’re doing is adding benefit to today’s existing ethanol technology. We can take the current byproduct, which is animal feed, and produce more ethanol out of it, thereby enhancing today’s technology.

Interviewer: What would be the benefit of putting two plants side by side, a biomass plant and corn plant?

ANDY: We’ve done quite a bit of feasibility work to see what would be the best way to operate a process like that, how much better this biomass material would be than, say, corn stover. The nice thing about this material is it’s already been preprocessed. There is not a lot of lignan to it so there’s already a lot of natural sugar present already. There are definite synergies that you can get by taking this material and producing it onsite of an existing ethanol plant as opposed to building a whole new plant from scratch. Not only that, this is new technology we’re doing. By implementing it piecewise at a time, we’re reducing the risk as opposed to building it all up from scratch at once.

Interviewer: What will the first plant that makes ethanol from biomass on a production scale look like?

ANDY: Where we’re really going with this technology is to what’s called the buyer refinery vision. And it’s analogous to today’s petroleum refinery where you bring in petroleum and you produce a slate of products, including fuels, chemicals, and lots of other things. We’re looking to do the same thing from biomass where you bring in biomass sources, you produce fuels, you produce chemicals, and you produce a big slate of things all from one renewable feedstock.

Interviewer: How close to ready are you?

ANDY: The nice thing is this technology is all technically feasible; it’s just a matter of making it cost effective. And that’s really where our research is focused now. Hopefully within the next six to ten years, industry will work with us and take this technology and begin implementing it on a commercial scale.

Interviewer: Where are the places where it’s not cost effective?

ANDY: The primary areas where we’re hoping to reduce the cost of this process are in the pretreatment step and in the fermentation step. The pretreatment step uses chemicals. It uses exotic metals — anything we could do to reduce the cost of the pretreatment and make it more effective is going to reduce the whole overall cost. With the fermentation, if we can make bugs that ferment more sugars and can utilize biotechnology to more efficiently utilize the sugars it already does ferment, then we’re going to get more bang for our buck as well.

Interviewer: What are some of the breaking points? How much more does it cost to generate a gallon of ethanol with this process?

ANDY: Our estimates of taking today’s technology and scaling up to the commercial scale would put production of ethanol at around two twenty-five per gallon. That’s still more expensive than we’d like it to be, especially compared to corn ethanol. We’d like to bring that cost down to something more like a dollar or a dollar twenty-five per gallon to make it more cost effective. Doing the research in these particular areas of pretreatment and fermentation will help to bring those costs down.

Series Directory

The Habitable Planet: A Systems Approach to Environmental Science 


Harvard Smithsonian Center for Astrophysics in association with the Harvard University Center for the Environment. 2007.
  • ISBN: 1-57680-883-1