The Sugar Producers
by Susanne Retka Schill (Ethanol Producer Magazine) Sweetwater Energy and Proterro, two companies using widely different approaches, aim for low-cost sugar that may give today’s corn ethanol plants a glide path into advanced ethanol production. They’re in different stages, but share similar promise.
Fundamentally, ethanol production is about feeding the insatiable sweet tooth of the actual ethanol producer—yeast. Two companies using widely different approaches, Sweetwater Energy Inc. and Proterro Inc., are pursuing business models to supplement fermentation broths with sugar water. Sweetwater promises to soon deliver C5 and C6 sugars derived from cellulosic feedstocks while Proterro intends to bring ethanol producers sucrose produced by its patented cyanobacteria.
Sweetwater is reaching the commercialization stage, with a demonstration plant in place at its Rochester, N.Y., headquarters. The company has teamed up with Naturally Scientific Technologies Ltd. to build a commercial facility in the Eastman Business Park in Rochester. The details of the project are close to finalization and construction could begin soon.
Simultaneously, Sweetwater expects to break ground this spring on a commercial-scale facility in Wisconsin, followed by two others.
… Sweetwater is using cellulosic pretreatment technology from Denmark-based BioGasol ApS that uses a dilute acid, he (CEO Arunas Chesonis) explains. … That is followed by enzymatic hydrolysis, using enzymes developed by others. Sweetwater’s proprietary technology lies in the separation of C5 and C6 sugars. “We squeeze out the C5s right in the first hour of the process, and then spend the next two or three days breaking out the C6s from the fiber and the lignin,” Chesonis says.
… Sweetwater will be supplying its cellulosic sugars to Naturally Scientific to convert into higher-value oils for use as feedstocks for diesel or jet fuel production or in biochemical facilities.
The company’s goal is to be able to produce its sugars for 10 to 12 cents per pound and, including the return to investors, sell them for 17 to 18 cents per pound, Chesonis says. That will be competitive with the price of dextrose, which is in the low 20-cent range, although he adds his company is currently paying 25 to 30 cents per pound for dextrose to supplement its cellulosic sugars for Naturally Scientific’s development work.
Proterro’s ambition is to provide an even lower-cost sugar. Its unique sugar platform harnesses the power of the sun in a photobioreactor where microbes convert carbon dioxide and nutrients into easily fermentable sucrose. CEO Kef Kasdin says the company’s economic projections indicate a production cost around 5 cents per pound. A pilot facility with four full-size reactors has been in operation since fall in Orlando, Fla., collecting data to confirm those projections.
The Proterro bioreactor mimics a leaf by growing cyanobacteria microorganisms on a fabric surface, providing maximum exposure to sunlight while a thin layer of water and nutrients flows across the surface. The fabric is enclosed in a polyethylene balloon filled with air and carbon dioxide. At ambient temperatures, the cyanobacteria secrete sugars which are carried away in the flowing water. “That sugar water could go directly into ethanol production or we may need to further concentrate it,” Kasdin explains.
While the modular system is relatively simple, what will contribute to the cost is the number of photobioreactors needed and the land area to support them. Current estimates are that a system of photobioreactors would produce the same amount of sugar as sugarcane on one-thirtieth of the land.
With a minimum temperature of 50 degrees Fahrenheit needed for the microbes to be productive, the outdoor systems are not meant for winter climates. Power or chemical plants would be able to utilize waste CO2 in the systems.
The use of a genetically modified organism requires preparing a Microbial Commercial Activity Notice for review by the EPA.
“Ethanol’s the big existing market for turning sugar into an industrial product,” Kasdin explains. Others would include a number of second-generation fuels, biochemicals or even the production of amino acids for the feed market.