Butanol Production Process
In my previous job, I worked for a major chemical company for seven years. For six of those years, I worked on various processes to produce butanol. This included roles in R&D, process, and production, and I received a patent while working in Germany for devising a novel process for making butanol. Butanol is an alcohol like ethanol, but whereas ethanol has 2 carbon atoms, butanol has 4.
The most common industrial process to produce butanol involves a few steps. First, synthesis gas is produced. Synthesis gas is a very important raw material. It is composed of hydrogen and carbon monoxide, and is produced by burning a feed at a high temperature while limiting the oxygen available for the reaction. The feed material for producing synthesis gas can be natural gas, fuel oil, coal, or even biomass. Once synthesis gas is produced, it can be used to make a wide variety of chemicals, including diesel (via the Fischer-Tropsch reaction), methanol, ethanol, propanol, or butanol.
If the desired end product is butanol, the synthesis gas is reacted under pressure with propylene to first produce butyraldehyde, and then this is reacted with hydrogen under pressure to produce butanol. The crude product contains butanol, isobutanol, and water, and must be distilled to obtain specification butanol, which has a wide variety of end uses.
The energy return on investment (EROI) for producing butanol in this way is certainly less than 1. I have never bothered to calculate it, but there are a number of energy intensive steps involved in butanol production. However, given the end uses for butanol, the EROI was never a major concern. Sure, saving energy during the production of butanol was always a priority, but since it typically is not used as a fuel, there was no requirement that the EROI be greater than 1 in order to have a viable process.
Bio-Butanol versus Bio-Ethanol
I have made clear in several of my essays on ethanol that my primary objection to using ethanol as fuel is the poor EROI. Ethanol production consumes large quantities of natural gas via fertilizer for corn and then distillation of the ethanol. (If coal is used instead of natural gas, you may have an economic process, but certainly not a green one). The reason so much distillation energy is required is that ethanol is completely soluble in water. The end product of the fermentation results in something like an 8% ethanol/92% water solution. It takes a lot of energy to heat water up, so the distillation of ethanol into a pure form uses up a lot of energy and contributes to the poor EROI.
Butanol, on the other hand, has a more limited solubility in water. According to the Material Safety Data Sheet (MSDS) for butanol, it is only 7.7% soluble in water. What does this mean? There is a much less energy intensive method of separating butanol from water, and that is by letting it phase out (just like oil and water). Therefore, you would expect the EROI for producing butanol from corn would be much better than for producing ethanol from corn.
Until this weekend, I didn’t realize that anyone was producing butanol from corn or biomass. During my graduate school studies, we produced butyric acid as a very smelly byproduct of our biomass process, and this can be converted into butanol. But one of the editors over at Omninerd pointed me to a site this weekend that demonstrates the viability of producing butanol from biomass. I encourage you to check out the claims at http://www.butanol.com, which are based on the work of a chemical engineering professor at Ohio State.
The entire site is worth a read. Here are a few excerpts:
How does butanol compare with ethanol as an alternative fuel?
Butanol has many superior properties as an alternative fuel when compared to ethanol. These include:
· Higher energy content (110,000 Btu’s per gallon for butanol vs. 84,000 Btu per gallon for ethanol). Gasoline contains about 115,000 Btu’s per gallon.
· Butanol is six times less “evaporative” than ethanol and 13.5 times less evaporative than gasoline, making it safer to use as an oxygenate in Arizona, California and other states, thereby eliminating the need for very special blends during the summer and winter months.
· Butanol can be shipped through existing fuel pipelines where ethanol must be transported via rail, barge or truck
· Butanol can be used as a replacement for gasoline gallon for gallon e.g. 100%, or any other percentage. Ethanol can only be used as an additive to gasoline up to about 85% and then only after significant modifications to the engine. Worldwide 10% ethanol blends predominate.
They claim the process is competitive with ethanol on a per gallon basis. Given that butanol has substantially more BTUs than ethanol, the price per BTU would be much lower than for ethanol:
Our preliminary cost estimates suggest that we can produce butanol from corn for about $1.20 per gallon, not including a credit for the hydrogen produced. This compares with ethanol production costs of about $1.28 per gallon. Taking into account the higher Btu content of butanol, this translates to 105,000 Btu per dollar for butanol and 84,000 Btu per dollar for ethanol with corn at $2.50 per bushel. As a further point of reference, butanol produced from petroleum costs about $1.35 per gallon to manufacture.
The economics of the EEI process will be even more attractive when waste material is used as feedstock instead of corn and the price to produce a gallon is $0.85. In such cases the need and cost to grow and prepare the corn for fermentation, by far among the major cost items, are eliminated.
A couple of other claims are worth noting. They say that they can produce 2.5 gallons of butanol for every bushel of corn. On a BTU basis, that is 30% more BTUs than can be produced if ethanol is the end product. Second, they also claim that butanol can be used in biodiesel applications, and can be blended with diesel. If true, that would give butanol a significant advantage over many other alternative fuel options. Finally, they note that the process produces a significant amount of hydrogen as a byproduct.
What’s the Catch?
I need to spend some time going over the patents and linked reports more closely to see if anything suggests a problem that has been glossed over. I can think of one possible issue off the top of my head. One of the knocks on methanol is the toxicity. Ethanol is considered non-toxic for the most part. If trace quantities of ethanol entered the groundwater, it would not be as alarming as methanol getting into our water supplies. Butanol is less toxic than methanol, but more toxic than ethanol, and it is somewhat soluble in water. Therefore, the one thing that should be addressed is the potential for butanol to find its way into our water supplies.
Other than that, this looks worth pursuing. Butanol has a number of clear-cut advantages over ethanol, and it should have a superior EROI. The authors of the site indicate that they need to complete testing on a demonstration plant and a pilot plant. I look forward to the results of their testing.