Making Isobutanol and Ethanol in Luverne, Minnesota

Gevo’s plant in Luverne, Minnesota, is situated among the cornfields. After all, it’s an ethanol plant that was built to capitalize on the government regulations that encourage the use of ethanol blendstock in gasoline. We’ve modified this plant to produce isobutanol.

At an existing dry-mill corn ethanol plant, the corn mash stream coming out of the front end of the process that feeds the ethanol fermentation is the same stream used for isobutanol fermentation. This stream is prepared for isobutanol fermentation, added to large non-sterile fermentation tanks, and where proprietary yeast is added to convert the sugars to isobutanol.

As with any alcohol fermentation, isobutanol has a stress effect on yeast as the fermentation proceeds and the concentration increases, which typically would result in reduced fermentation rate and/or reduced batch size. As one biofuel producer, Gevo has solved for this issue by using its GIFT® (Gevo Integrated Fermentation Technology) process for continuously removing the product during fermentation. Despite the fact that isobutanol’s boiling point is eight degrees Celsius higher than water, the GIFT process is able to remove isobutanol continuously during fermentation to maintain its concentration in the fermenter at target levels to optimize process rates and cost. This is accomplished because isobutanol-water is azeotropic, meaning the vapor has the same composition as the liquid. The fermentation broth is circulated through the GIFT process where it is subject to low-pressure evaporation and isobutanol flashes off the broth resulting in a vapor concentration nearly twenty times greater than what was in the fermenter. When the vapor is condensed, the concentration of isobutanol is now above its solubility limit in water and phase separation occurs, leaving a relatively pure isobutanol-rich phase and a water-rich phase. The isobutanol-rich phase is sent to a purification step and the water-rich phase goes to stripping distillation step where residual isobutanol is removed and the water returned to the fermenter. All of the biomass remains in the fermenter-GIFT system, thereby greatly simplifying purification of the isobutanol.

Using Wind Power to Reduce Our Carbon Intensity

To offset the energy-intensity of the biofuel plant in Luverne, Minnesota, Gevo has secured a partnership with wind turbine company zero6, formerly Juhl Energy, to provide renewable electricity through wind power.

Gevo To Use Wind Turbines to Further Reduce the Carbon Footprint of Isobutanol Production

By Dr. Pat Gruber, CEO, Gevo, Inc.

I’m the first to admit that one of the issues that we’ve been challenged with is that a lot of Gevo’s carbon footprint comes from the electrical power we use in production, which is coal fired electricity from the grid. We’ve always known that we need to replace this with a renewable energy solution. And one thing we have a lot of in Luverne, Minnesota, is wind. So Gevo secured a partnership with wind turbine company zero6, formerly known as Juhl Energy, to provide renewable electricity through wind power at our Luverne facility. At that facility, we manufacture isobutanol and ethanol, and, while more energy efficient than other biofuel production methods, it’s still an energy-intensive process.

We have a straightforward strategy to remove carbon emissions from every step of our biofuel production process. We are all about decarbonization of fuels, which means making hydrocarbon fuels like jet fuel and gasoline with a really small carbon footprint. It’s all about renewability, and we also help the farmers who are our feedstock supply partners to implement growing methods and resource management that improve the carbon sequestration of their soil.

By the same thought process, it doesn’t do any good to invest in the research and science of taking the fossil fuels out of aviation fuel, isooctane gasoline, and isobutanol if we’re just going to draw electricity off the coal-burning electrical grid to run our processes. When you’re re-charging those electrical cars, where do you think that electricity is coming from? Nobody likes a hypocrite and that’s where this latest investment comes in.

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Watch Pat Gruber discuss the Gevo-zero6 windpower initiative here:

zero6 is an expert at wind-development projects, putting up wind towers, and also other energy-development solutions.

We invested in an energy assets company set up by zero6. They’re the developers, so for that we get a return on our preferred stock investment. We buy the electricity from the City of Luverne, Minnesota, and it’s about the same price we were paying before, but all the renewable benefits accrue to Gevo. The transmission wire from the wind turbines will go directly to our plant, so it meets all the requirements for counting toward sustainability.

All sides are cooperating here to make it work. zero6 will sell power to Missouri River Energy Services (MRES), which is the area utility that supplies Luverne. We buy the power from Luverne, but the actual electricity comes directly to us, and we buy the renewable energy credits from zero6 directly.

With the foundation poured and the first pieces of the turbines beginning to be placed, we realistically look to having the wind turbines online the end of Q1 and should begin to see the benefit in a lower carbon intensity score around the second quarter of 2020. With that and some of the other improvements, it can make a pretty big difference.

This all works with our overall strategy of decarbonization and defossilization. Our fossil footprint of our process to produce renewable-resource-based fuels comes from the energy we use: electricity and natural gas. The next step will be work on the natural gas and we’ve got some pretty interesting ideas.