The DOE’s specific challenge was to demonstrate at least 1,000 hours of bio-oil hydrotreatment on a single catalyst charge, while producing a fuel product suitable as a transportation fuel-blend stock at commercially realistic yield. Longevity of hydrotreatment catalysts has long been one of the challenges to the commercialization of the conversion of biomass pyrolysis oils to biofuels. (Earlier post.)

A pyrolysis process takes biomass, and heats it to about 500 ˚C in the absence of oxygen. This produces a vapor, which is then condensed to form bio-oil. Because raw fast pyrolysis oil is corrosive and thermally unstable, blending or direct insertion into refinery operations at levels greater than 5% is challenging. Therefore, raw fast pyrolysis bio-oil typically is considered to be an intermediate product that can be upgraded via processes such as catalytic hydrogenation, hydrotreating, and hydrocracking. (Earlier post.)

Although numerous researchers have been working at the problem for a long time, said Dr. Abdullah, the problem is that the hydrotreating catalysts used with bio-oil deactivate and die after about 100-150 hours; in addition, rapid coking of the hydrotreatment catalyst and catalyst bed plugging during operation are barriers to a long-lived process. DOE issued its 1,000-hour challenge in 2010, looking for a 10x improvement in catalyst life. Battelle, in partnership with PNNL, began working on the project in 2011.

The approach the partners developed entailed:

• PNNL set out to develop non-carbon-supported catalysts, while Battelle developed a catalyst regeneration process. The novel non-carbon supported metal catalysts with low coke formation rates can be regenerated to remove coke and recover activity.

  The catalyst regeneration approach entails removing loosely bound carbon via rinsing with solvent; removing bound carbon (coke) via chemical reaction; and reactivating the catalyst via reduction with hydrogen.

• Battelle also conducted detailed root cause analyses of catalyst deactivation, and determined that heteroatom poisoning as the root cause for catalyst deactivation. Heteroatoms are non-carbon atoms that have replaced carbon in a molecular structure normally built of carbon atoms. The Battelle team determined that small concentrations of metals from the feedstock were coming in with the bio-oil. )

• Battelle and PNNL developed a filtration and ion exchange process to clean-up bio-oil.

We originally thought that the catalyst deactivated with coking. We developed a procedure in which we can carefully burn the coke off the catalyst. We found that yes, if we burned the carbon off, the catalyst reactivated. But then we found that after we repeated this for four or five times, every time we regenerated the catalyst it died sooner. There was something else going on. Then we did a detailed root cause analysis. We looked at half a dozen mechanisms, including sintering and the deterioration of the catalyst support. In the end we concluded that it was caused by poisoning by very small concentrations of metals coming in with bio-oil.

If look at biomass, it’s from a plant growing in soil. As a plant grows in soil, it picks up minerals and metals from the soil. If you look at the oil, it has a few parts per million of iron and chromium and nickel. By themselves these concentrations are very low. But when the bio-oil was processed through the hydrotreatment catalyst, these very low concentrations were in fact over time poisoning the catalyst.

—Dr. Abdullah

Battelle, in a parallel program, has a great deal of experience and knowledge in waste water treatment—i.e., people who understand how to clean liquids. Collaborating with those colleagues, Abdullah and his team came up with a methodology and an ion exchange method to remove very small concentration of poisoning metals in a process before the bio-oil enters the catalytic reactor.

The result was a two-zone catalytic process with bio-oil clean-up on the front end. The team was able to regenerate the catalyst at least 5 times while retaining 50% activity, while also demonstrating aceptable end product quality.

Battelle/PNNL bio-oil hydrotreatment process. Click to enlarge.

The end product was essentially a completely deoxygenated saturated hydrocarbon product, with generally about one-third of the slate in the range of kerosene and diesel in terms of carbon length and about two-thirds in the gasoline range.

With the specific DOE project ended, Battelle is continuing its work on the process and catalyst, with an eye toward commercialization.

When one develops business models for technology, one says, OK, I have a process, I have to change out catalysts. In the chemicals industry, we want to change out catalysts once a year, maybe every two years. If we can push [our process and catalyst] for 4,000 hours, then we can say, OK, we have something that we can envision commercializing. From a technology development perspective, the next logical step is to take this technology and push it towards commercialization.

—Dr. Abdullah

Marathon Petroleum Corporation provided Battelle with some support in the DOE and helped in assessing the biofuel product. Scientists at PNNL developed bio-oil stabilization catalysts for Battelle’s process.

Battelle has also made progress towards commercializing its modular pyrolysis systems. (Earlier post.) It already has scaled up its proprietary technology from concept to a pilot system that processes more than one ton of biomass per day.

It was Battelle’s ton-per-day pilot system that supplied the bio-oil for its DOE-funded hydrotreating project. Adding to the achievements and near-term commercial focus, late last year Battelle entered into a strategic partnership with Equinox Chemicals, a specialty chemical manufacturer. Together, they seek to use the platform pyrolysis technology for the production of bio-polyols and biochemicals with applications in multiple, rapidly growing, high-value markets.

Resources

• Zia Abdullah (2015) “Upgrading of Biomass Fast Pyrolysis Oil (Bio-oil)” DOE Bioenergy Technologies Office (BETO) 2015 Project Peer Review