Butanol 101

This story was initially intended to cover a recent interview that I did with Cobalt Technologies CEO Rick Wilson. However, the introduction and background on butanol became long enough that I felt it was a standalone story. The interview with Rick Wilson will follow this story in a few days.

I have mentioned before that my first job out of college was with Celanese (at that time Hoechst Celanese). For most of my seven years with Celanese, I was a butanol engineer. I first spent two years developing computer models of the process, doing lab work, and providing engineering support to the Celanese plant in Bay City, Texas. I then transferred to Bay City and spent two years working as the process engineer in that plant (we did some major projects in the unit, including a large capacity expansion of the butanol unit and the conversion of our gasifiers from fuel oil to natural gas feed). Finally, I relocated to Germany and spent two years in Oberhausen working in the butanol unit there primarily as a production engineer, but also with a research and development role. (My last year at Celanese before joining ConocoPhillips was spent as a Six Sigma Black Belt working primarily on energy projects).

I received a patent for my work in Germany. The US version of the patent is number 7,087,795 — Method for the production of aldehydes. It was first granted in Germany (DE10160368), followed by the European Patent Office (EP1456162), South Africa (2004/3935), and it has been filed in multiple other countries. As an aside, German law required a German to be listed first on German patents, so even though it was my idea and I supervised all of the lab work to prove the concept, the Germans that were involved were named ahead of me on the patent. I just want to clarify that because sometimes people are named on patents who didn’t have a whole lot to do with the invention; in this case this was my baby.

So what is an aldehyde, and what does that have to do with butanol? While butanol was once produced commercially via the biological process denoted ABE, after the petrochemical process was discovered it put ABE out of business in the Western world. I have heard anecdotes that the ABE process is still practiced in China, but according to this link on the history of the process the last plant there closed in 2004. Small amounts of butanol can be produced via a syngas reaction to produce mixed alcohols, but butanol is a very small component relative to the methanol and ethanol that are produced. Butanol is not commercially produced anywhere directly from syngas; such a process would be a major breakthrough for butanol producers.

The petrochemical process involves three steps. First, synthesis gas is produced (usually from coal or natural gas, but could be produced from biomass) and is reacted with propylene (a product from oil refining and natural gas processing) to form normal-butyraldehyde (BuH) and iso-butyraldehyde in a hydroformylation reaction. Second, the butyraldehydes are hydrogenated to form n-butanol (BuOH) and i-butanol. In the final step n-butanol and i-butanol are separated in a distillation train. Major producers of butanol include BASF, Dow Chemical, Eastman Chemical, Celanese, and Shell — and butanol production in just the U.S. and Western Europe is around 1.4 million metric tons per year (3 billion pounds).

At the time I worked on it, butanol was mostly a boring chemical intermediate. It was used as a paint solvent and as an ingredient of brake fluid, but most of it went into producing higher value products like butyl acrylate or butyl acetate. In the past decade, however, butanol has gotten a lot of attention as a promising biofuel. The reasons are that it is more energy dense than ethanol and doesn’t absorb water to the extent that ethanol does, and is thus easier to use in existing infrastructure. Inventor David Ramey probably did more than anyone to bring awareness to butanol’s potential as a renewable fuel by driving his family car from Ohio to California on 100% butanol. You can hear Ramey tell that story at this YouTube link.

However, biological routes for butanol suffer some problems that must be overcome if biomass-based butanol is to be competitive with petrochemical-derived butanol. As I explained in The Problem with Biobutanol, the petrochemical process generally produces crude product with only 5-10% water. The biological processes, on the other hand, generally produce butanol with 95% or more water. Therefore, the energy requirements for purification are much lower for the petrochemical process. In fact, the energy requirements are so high for separating out a 3% butanol solution from water that in chemical plants this concentration is often considered a waste stream and is disposed of.

If butanol could be produced without having to purify it via such an energy-intensive distillation, the energy return would be much higher and the costs should be lower. If butanol was completely insoluble in water, for instance, it would float to the top as it was produced and it could just be skimmed off. However, n-butanol is about 8% soluble in water, which means it won’t start phasing until that concentration is reached. But for biological processes, butanol poisons the microorganisms that produce it well before the phasing concentration is reached. (The solubility of i-butanol is a bit higher at about 10%; further i-butanol is less toxic to microorganisms).

Some of the work in recent years has been in the development of microbes that are more tolerant to higher butanol concentrations, but the holy grail of tolerance at the phasing concentration has not been reached. One of the companies doing a lot of work in this area is Cobalt Technologies. In the next essay, I will post an interview with Cobalt CEO Rick Wilson about the work they are doing.