Friendly fuels

Cellulosic ethanol looks to be the next major development in ethanol production. The Verenium Corporation, in conjunction with BP, is building a new plant in the United States to make the development a commercial reality. The first step is a state-of-theart test refinery.

DATUM 2017-07-12 FÖRFATTARE Michael Giusti

A mere six miles away from where W Scott Heywood discovered Louisiana’s oil patch a century ago, scientists and engineers are working to commercialize what could be the next generation of motor fuel — cellulosic ethanol.

Unlike the traditional ethanol being produced across the globe, which is made mostly from sugar-rich food crops, cellulosic ethanol comes from woody, fibrous, inedible parts of plants.

Scientists have long struggled with converting cellulose into ethanol on a commercially viable scale. But that is just the process Verenium Corporation is working towards at its facility in Jennings in the US state of Louisiana.

The 1.4 million-gallon-per-year demonstration refinery is tucked into a landscape dotted with oil wells and surrounded by a sea of sugarcane farmland — an appropriate setting for the task of bridging the agriculture and petroleum worlds.

Working in small-batch “campaigns”, scientists at the facility are using a process that they plan to scale up to a commercial level by the end of 2012. And they have a powerful ally backing them – British oil giant, BP. Verenium has formed a joint venture with BP to build a massive cellulosic ethanol plant in South Florida, with plans to break ground this year.

But first, plenty of work still needs to be done at the Jennings test refinery. The primary goal of the facility, according to Carey Buckles, vice president of operations at Verenium, is to test different enzymes, microbes and pretreatments, with the ultimate goal of converting what are essentially piles of wood chips into motor fuel.

Environmentalists and sustainability fans have long sung the praises of ethanol, largely because it is made with home-grown resources and does not rely on fossil fuels.

Cellulosic ethanol has some other strategic benefits, according to Verenium, because the crops used to make cellulosic ethanol are generally not commodities used in other industries, such as food production. Company officials hope that, since they won’t be competing with other industries that might have driven up commodity prices, their costs will be contained.

Verenium’s three feedstocks of choice so far are energy cane, sugarcane bagasse and sorghum (see facts box on page 27). These feedstocks are ideal, Buckles says, because they have some very attractive traits.

According to Michael E Salassi, professor of agricultural economics for the Louisiana State University department of agricultural economics and agribusiness, crops such as energy cane are grown for their biomass rather than their sugar content. That means they often have lower production costs per acre while offering more biomass yield per acre.

Another benefit is that, with energy cane, farmers don’t have to worry about traditional pests, Salassi says.

“With cane grown for its sugar, you have to contend with sugarcane borers, which would cause damage and affect the juice and sugar production,” he says. “With energy cane, you wouldn’t be worried about that.”

Evaluating feedstocks is one of the primary missions of Verenium’s test facility.

“And that is the race — to find that best product and see who can build a commercial business out of it first,” Buckles says.

So far, energy cane is the winner. Verenium officials estimate that once their process is scaled up to full commercial size, it will yield 1,800 gallons (6,814 litres) of ethanol per acre annually from energy cane, compared with about 650 gallons (2,460 litres) of conventionally produced ethanol from sugarcane in countries such as Brazil.

To strip sugars out of woody plants and grasses to make ethanol Verenium hauls in small mountains of already ground feedstock. From there, the feedstock gets a steam and acid treatment to produce sugars. Verenium has been using an Alfa Laval NX 438 decanter centrifuge to separate the pentose sugars (sugars in solution) from the hexose sugars (sugars in solid form).

The pentose sugars are in a chain containing five carbon atoms; the hexose sugars are in a chain containing six carbon atoms. The different carbon structures call for different “digestion” treatments. To that end, engineers apply a custom mix of microorganisms and enzymes to each sugar stream, freeing those sugars to a more accessible form.

Those streams are then recombined in a tank called a “beer well”. The tank’s name is appropriate, because at that point, in a process very similar to brewing beer, yeast is applied, and the sugars are fermented to make the alcohol
that will be distilled out as ethanol.

Verenium has also been using the Alfa Laval decanter for its original intended use – dewatering the solid lignins and fibres remaining after ethanol distillation. On a commercial scale, the dewatered solids discharged by the decanter could potentially be burned to produce power for the ethanol plant.

If all goes well, Vercipia Biofuels — BP and Verenium’s joint venture — will be churning out 36 million gallons (136 million litres) of cellulosic ethanol a year beginning in 2012. The companies have committed 45 million US dollars to the project and leased 36,000 acres of land in Highlands County, Florida. Verenium intends to use 20,000 acres of this, which is now lying fallow, to grow feedstock such as energy cane.

Construction of the facility is expected to cost nearly USD 300 million.

In February 2009, Verenium and BP submitted an application under the US Department of Energy’s loan guarantee programme. In June, the DOE invited them to the next phase of the process. If awarded, the loan guarantee could provide the companies with up to 80 percent of the debt funding necessary for the construction of the new facility.

Based on the data from the Jennings test facility, Verenium hopes to produce ethanol that will sell at the retail level of USD 2.10 per gallon — a price point that is competitive with traditional ethanol and with today’s petrol prices.