Make butanol from ethanol: the unspoken RFS work-around?

Blender pumps, E15, drop-in fuels, aviation, amending the RFS, outright repeal — seems like everyone has a fix for the fight over the Renewable Fuel Standard.

But why not convert abundant ethanol into higher-blending butanol?

Technologies to do just that are under development.

Of all the items on the “critical” list for the renewable fuels industry, perhaps the one undeservingly receiving the least attention is the opportunity to catalytically convert ethanol to butanol.

The United States is relatively awash in ethanol compared to its ability to distribute it. Accordingly, obligated parties under the Renewable Fuel Standard are screaming hard about the “blend wall” which prevents them from distributing more than 10% ethanol content into the gasoline supply, pointing to the lack of demand for higher ethanol blends, and falling gasoline sales — all of which, their view, create a “perfect storm” that has “broken” the RFS.

On the renewable fuels side — producers point to opportunities to distribute E15 as a standard gasoline blend, and offer blender pumps featuring attractive blends like E30 to owners of flex-fuel vehicles, of which there are more than 10 million nowadays in the US.

So far, the battle between the obligated parties and renewable fuels producers and supporters has resembled the Vietnam War — costly, divisive, and long. One of the ways that the battle manifests itself is through RIN prices — when obligated parties simply refuse to make or blend ethanol and seek to buy credits, RIN prices rise.

Panic at the White House

Which recently panicked the White House — fearing rising gas prices — into waving the white flag on the RFS and proposing, through the EPA to massively scale back on renewable fuel targets.

Something that classical economists didn’t predict — assuming as they did that rising RIN prices would result in more ethanol distribution rather than a expansion in White House panic.

A potential fix? Butanol.

Why butanol?

Primarily, because it safely blends at 16 percent into cars that can only accept 10 percent ethanol content — and because a plant that produces 100 million gallons of ethanol will produce 80 million gallons of butanol from the same inputs.

Most of these plants, as we are finding out from the cellulosic technology providers, could increase their inputs by 25 percent in terms of accepting cellulosic sugars. Why aren’t they? Many shy away from expanding capacity because of concerns overt the “blend wall” and the RFS.

Now, if the US can distribute 13 billion gallons of ethanol into the fuel supply (as it did last year), it could safely distribute 20.8 billion gallons of biobutanol. By expanding capacity to accept cellulosic inputs, US ethanol producers would just about hit that number with the existing ethanol fleet.

And, because biobutanol has a higher energy density than ethanol, for purposes of the Renewable Fuel Standard, a gallon of butanol is counted as 1.3 gallons of ethanol-equivalent fuels. So, 20.8 billion gallons of biobutanol equates to 27.04 billion gallons of ethanol-equivalent fuels.

Toss in 2 billion gallons of renewable diesel, 700 million gallons of renewable gasoline and 3 billion gallons of biodiesel (based on increasing capacity by 2022), and you have a means to meet the 2022 RFS target of 36 billion ethanol-equivalent gallons. Building roughly 2.5 billion gallons of additional “greenfield” capacity, or around 300 million gallons per year.

Now, why isn’t anyone heading in that direction?

Well, most attention in the US has been focused on producing biobutanol directly from corn sugars — which is to say, introducing a new fermentation technology for a one-step system from corn sugars to biobutanol. Gevo and Butamax are working on isobutanol, and Cobalt and Green Biologics are working on n-butanol.

Cobalt, Green Biologics and Gevo are more avowedly working on chemical applications and markets — where the higher margins are — though both Cobalt and Gevo have extensive programs in producing renewable jet fuel. But only Butamax has been relentlessly focused on fuels — and despite much progress — it’s going to be a while before they have their first commercial plant in steady-state operations. Perhaps by 2016.
Which raises the question: why not catalytically convert ethanol to biobutanol? Though the product would cost more — it’s not like other renewable fuels aren’t going through a secondary upgrading process to be fuel market-ready (for example, most pyrolytic technologies produce a fuel intermediate that is then upgraded into a finished fuel).

Now — catalysts don’t achieve 100% conversion of anything to anything — there are limits on selectivity and the catalysts often result in a range of molecules. So, 100 million gallons of bioethanol would probably result in some combination of ethanol, biobutanol and other high-value molecules, depending on the catalyst.

Tell you one thing, I can’t think of anything more valuable technology, right now, than one that breaks the (so-called) “renewable fuel blend wall”, affordably.

Advances in the art

On this subject last year, ACS’s Stephen Ritter reported:

“A solution offered by Duncan F. Wass and his research team at the University of Bristol, in England, is a new family of ruthenium catalysts that readily convert ethanol to butanol…The ruthenium catalysts are very efficient, he added, producing butanol with 95% selectivity and ethanol conversion of better than 40%…The Bristol catalytic process has been patented, and Wass is working with scientists at BP Biofuels to develop the technology.”

The researchers themselves report:

“Unprecedented selectivity of over 94 % at good (20 %+) conversion was observed for the upgrade of ethanol to the advanced biofuel 1-butanol with a ruthenium diphosphine catalyst (see picture; P orange, Ru blue). Preliminary mechanistic studies indicate that control over the notoriously uncontrolled acetaldehyde aldol condensation is critical for the high selectivity, and evidence was found for an on-metal condensation step.”

More on that, here.

Another group of researchers out of the UK and Iran published an interesting paper last year in RSC Advances on a technology in this ballpark. The paper was titled “One-step continuous process for the production of 1-butanol and 1-hexanol by catalytic conversion of bio-ethanol at its sub-/supercritical state.”

Charles Xu of the Institute for Chemicals and Fuels from Alternative Resources (ICFAR), at Canada’s Western University, and Hassan S. Ghaziaskar of the Department of Chemistry at Iran’s Isfahan University of Technology write:

A one-step, easy to scale-up, continuous process was developed to catalytically convert bio-ethanol into 1-butanol and 1-hexanol as chemicals or fuels, as well as some other compounds that are also useful as biogasoline. The process is novel as it employs ethanol at its sub- and supercritical states. The reactions were performed in a continuous-flow fixed-bed tubular reactor with γ-alumina supported Ni catalysts at 135–300 °C at a weight hourly space velocity of 6.4–15.6 h−1 using neat ethanol. The process at 250 °C and 176 bar with an 8% Ni/γ-alumina catalyst led to ethanol conversion of 35%, with the highest selectivity of approximately 62% and 21% towards 1-butanol and 1-hexanol, respectively. In addition to 1-butanol and 1-hexanol, other minor biogasoline components such as butanal, and 2-pentanone, etc. were also synthesized from this process. The catalyst was found active for 18 h on stream in this study, and the regenerated catalysts retained their activities for the reactions.

A step on the right path

Now, a catalyst that produces a mix of n-butanol and 1-hexanol away from making biobutanol fuel at affordable costs – for one, n-butanol is not quite as attractive in terms of fuel markets as its isomer isobutanol.

But it’s a step along the right path — and it would be good to read or hear of others.