Cellulosics Conversion Gets a Boost

Control system enhances operation of demonstration plant.

By Rich Chmielewski, Marketing Manager, Siemens Industry

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More and more attention is focusing on developing processes to make biofuels and biochemicals from non-food crops and cellulosic wastes. A leader in such efforts is Biofine Renewables, Waltham, Mass.

Since 2007, the company has operated a demonstration plant in Gorham, Maine, that's successfully converted cellulosic biomass feedstock into levulinic acid intermediates used in a variety of chemicals, plastics and fuels.

"Our product is data and our goal is to prove to our investors and potential clients that second-generation biofuels are worthwhile and profitable," says Steve Fitzpatrick, Biofine Renewables' president.

Many of these clients have immediate access to a low-cost feedstock that's high in cellulose, such as waste wood pulp. Today, though, such a material generally poses burdens not benefits.

The company's technology promises to change that. "Instead of having to pay to haul the waste away or just burning it in a boiler, they can convert it into chemical intermediates that have high values," Fitzpatrick notes. "The process also generates a byproduct called lignin that can be burned to provide energy to the plant or nearby consumers." (Academic and commercial research underway may lead to use of lignin as a biochemicals feedstock or as non-biodegradable soil amender.)

The Technology
The Biofine Renewables process involves high-temperature dilute-acid-catalyzed hydrolytic breakdown of cellulose to form levulinic acid. The company has developed a novel reactor configuration that promotes production of levulinic acid while reducing char formation.

The configuration consists of a plug-flow reactor followed by a lower-temperature continuously stirred tank reactor. Table 1 summarizes conditions in the two reactors. Conditions in the first stage favor the dominant fast first-order high-temperature acid-catalyzed hydrolysis of cellulosic and hemi-cellulose to soluble intermediates. Completely mixed conditions in the second-stage backmix reactor favor a first-order reaction sequence leading to levulinic acid. Calculations show the rate constant for glucose degradation at conditions in the second-stage reactor is at least an order-of-magnitude lower than that of cellulose degradation in the first stage. Additionally, reaction conditions in the first stage followed by vapor separation in the lower-pressure second stage favor high yields of furfural from the hemi-cellulose fraction of the feed.

The overall process leading to commercial-grade levulinic acid consists of five steps carried out continuously:

1. Feedstock preparation and mixing. Raw feedstock is ground to a particle size of around 0.5 cm and mixed with recycle dilute mineral acid.
2. Hydrolysis. The main conversion reactions occur and ligneous char is separated from the reaction mixture.

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