R-Squared Energy Blog

Pure Energy

Chemistry: The Future of Cellulose

I am not a big believer in a commercial future for the biochemical conversion of cellulose into fuels. There are many big hurdles in place that are going to have to be overcome before cellulose is commercially converted to ethanol. In a nutshell, one is the logistical problem, which I have covered before. Beyond the logistical problem is the issue that biochemistry often starts to malfunction as the conditions in a reactor change, and with cellulosic ethanol that means that if you get a 4% solution of ethanol in water, you are doing well. But from an energy return point of view, a 4% solution is about like the trillions barrels of oil shale reserves we have. If it takes over a trillion barrels of energy to extract and process them, that largely defeats their usability.

Chemistry is a different matter, which is why I favor gasification processes over fermentation processes. But even beyond gasification, I have wondered about chemically processing cellulose in a refinery. I used to have a guy who e-mailed me all the time and told me he had invented a chemical process for reacting cellulose to hexane, which can then be turned into gasoline. If you look at cellulose (there is a graphic of a segment of cellulose at the previous link), you can envision that it could be done. (Whether he had actually done it is a different story).

But the chemistry pathway isn’t limited to fuels. With that preface, I want to thank a reader for bringing this story to my attention. In a recently published story in Applied Catalysis A: General (available online at Science Direct), scientists at Pacific Northwest National Laboratory have reported on a new process for converting cellulose directly into an important chemical building block (e.g., for plastics and fuel):

Single-step conversion of cellulose to 5-hydroxymethylfurfural (HMF), a versatile platform chemical

Now we all know that you can do lots of neat things in the lab that can’t really be done on a larger scale. But this particular process does not appear to be overly complicated. The abstract from the paper explains what they are doing:

Abstract

The ability to use cellulosic biomass as feedstock for the large-scale production of liquid fuels and chemicals depends critically on the development of effective low temperature processes. One promising biomass-derived platform chemical is 5-hydroxymethylfurfural (HMF), which is suitable for alternative polymers or for liquid biofuels. While HMF can currently be made from fructose and glucose, the ability to synthesize HMF directly from raw natural cellulose would remove a major barrier to the development of a sustainable HMF platform. Here we report a single-step catalytic process where cellulose as the feed is rapidly depolymerized and the resulting glucose is converted to HMF under mild conditions. A pair of metal chlorides (CuCl2 and CrCl2) dissolved in 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl) at temperatures of 80–120 °C collectively catalyze the single-step process of converting cellulose to HMF with an unrefined 96% purity among recoverable products (at 55.4 ± 4.0% HMF yield). After extractive separation of HMF from the solvent, the catalytic performance of recovered [EMIM]Cl and the catalysts was maintained in repeated uses. Cellulose depolymerization occurs at a rate that is about one order of magnitude faster than conventional acid-catalyzed hydrolysis. In contrast, single metal chlorides at the same total loading showed considerably less activity under similar conditions.

So they take cellulose and react it with two metal chlorides at 80–120°C for a direct conversion of cellulose into HMF – which can be easily converted to fuel or plastics. I would think then the important considerations would be 1). What happens to the lignin and hemicellulose in the biomass?; and 2). How much energy does it take? The second item is particularly important if fuel is the objective.

While it is too early to tell whether there is a fatal flaw, this one certainly bears watching. It also strengthens my conviction that in the long-run, the right way to process cellulose is chemically.

May 23, 2009 Posted by | biomass gasification, cellulose, chemistry, refining | 44 Comments

Fire from Water

Based on some of the comments following my post on the “water car”, I think several people misunderstood the point. It was not to debunk the water car. You can in fact run a car with water as one of the reactants. I could even run a car on crushed ice or Jell-O, if I used the right second reactant.

My point was merely to show how a car could be run on water, and to further point out that it requires a second, very reactive substance. In other words, the “water car” is not running solely on water. The other point was that the reactive substance will always take more energy to produce than you will get back from splitting the water. That’s simply pointing out the thermodynamics. It doesn’t mean that there might not be times that it makes economic sense to do this – just that there is much more to the story than a car that runs on water.

Keeping with that theme, here are some videos showing how water can react with various metals/compounds to produce fire – and this should give you an indication of what’s happening in the water car.

First up, if you put lithium (or any of several other alkali metals) in water, it reacts explosively. Hydrogen is evolved, and so much heat is produced that the hydrogen ignites:

Lithium + Water = Fire

Second is a reaction I have known of for over 30 years. When I was growing up in Oklahoma, we often went hunting at night. I had a carbide lamp that I used to produce light. The way it worked is that I would put solid calcium carbide pellets (CaC2) in a bottom compartment, and water in the top compartment. The water dripped on the calcium carbide and formed acetylene (C2H2) according to the following reaction:

CaC2 + 2 H2O → C2H2 + Ca(OH)2

Of course acetylene is quite flammable, and this was burned to produce the light for our hunts. Much like the “water car”, I had a “water lamp.” (In fact, one time the lamp caught on fire on top of my head; so there are some safety considerations). One thing to point out is that it takes a lot of energy to make calcium carbide. This is the energy you get back when you burn the acetylene, but it is never as much energy as it took to make the calcium carbide in the first place. Here is a demonstration of someone lighting a carbide lamp.

Water + Calcium Carbide = Fire

The moral? The water car isn’t such a mystery, if you understand a little bit about the chemistry. The question is whether a water car can be cost competitive, given the need for the second reactant. My suspicion is that it will usually be more cost effective to use energy to run a PHEV than to use energy to produce a metal compound that will react with water to run a water car. The reason I say that is that you can’t escape the energy inputs for making the metal compound, and that energy is most efficiently used directly in the car, rather than via the water intermediate.

Note: Following this post, my Internet access is going to be disconnected, and then I will be on the road until Friday night. Responses will be infrequent.

June 18, 2008 Posted by | chemistry, water car | 32 Comments

Fire from Water

Based on some of the comments following my post on the “water car”, I think several people misunderstood the point. It was not to debunk the water car. You can in fact run a car with water as one of the reactants. I could even run a car on crushed ice or Jell-O, if I used the right second reactant.

My point was merely to show how a car could be run on water, and to further point out that it requires a second, very reactive substance. In other words, the “water car” is not running solely on water. The other point was that the reactive substance will always take more energy to produce than you will get back from splitting the water. That’s simply pointing out the thermodynamics. It doesn’t mean that there might not be times that it makes economic sense to do this – just that there is much more to the story than a car that runs on water.

Keeping with that theme, here are some videos showing how water can react with various metals/compounds to produce fire – and this should give you an indication of what’s happening in the water car.

First up, if you put lithium (or any of several other alkali metals) in water, it reacts explosively. Hydrogen is evolved, and so much heat is produced that the hydrogen ignites:

Lithium + Water = Fire

Second is a reaction I have known of for over 30 years. When I was growing up in Oklahoma, we often went hunting at night. I had a carbide lamp that I used to produce light. The way it worked is that I would put solid calcium carbide pellets (CaC2) in a bottom compartment, and water in the top compartment. The water dripped on the calcium carbide and formed acetylene (C2H2) according to the following reaction:

CaC2 + 2 H2O → C2H2 + Ca(OH)2

Of course acetylene is quite flammable, and this was burned to produce the light for our hunts. Much like the “water car”, I had a “water lamp.” (In fact, one time the lamp caught on fire on top of my head; so there are some safety considerations). One thing to point out is that it takes a lot of energy to make calcium carbide. This is the energy you get back when you burn the acetylene, but it is never as much energy as it took to make the calcium carbide in the first place. Here is a demonstration of someone lighting a carbide lamp.

Water + Calcium Carbide = Fire

The moral? The water car isn’t such a mystery, if you understand a little bit about the chemistry. The question is whether a water car can be cost competitive, given the need for the second reactant. My suspicion is that it will usually be more cost effective to use energy to run a PHEV than to use energy to produce a metal compound that will react with water to run a water car. The reason I say that is that you can’t escape the energy inputs for making the metal compound, and that energy is most efficiently used directly in the car, rather than via the water intermediate.

Note: Following this post, my Internet access is going to be disconnected, and then I will be on the road until Friday night. Responses will be infrequent.

June 18, 2008 Posted by | chemistry, water car | 31 Comments