Scientists harness CO2 to consolidate biofuel production process

Scientists have shown that adding carbon dioxide gas during the deconstruction phase of biofuel production successfully neutralized the toxicity of ionic liquids. The technique, which is reversible, allows the liquid to be recycled, representing a major step forward in streamlining the biofuel production process.


Carbon dioxide has emerged as a secret ingredient in the recipe for making ethanol, and that addition represents a major step forward in streamlining the biofuel production process.

The innovation comes from researchers at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) and Sandia National Laboratories (Sandia) working at the Joint BioEnergy Institute (JBEI). The scientists have demonstrated that adding carbon dioxide (CO2) gas during the deconstruction phase of biofuel production successfully neutralized the toxicity of ionic liquids, the room-temperature molten salt solvent used at JBEI to break down cellulosic plant material. Moreover, the process is easily reversible, allowing the liquid to be recycled for use as a solvent again.

Using carbon dioxide as a reversible method of controlling pH eliminates the need for separation and purification of the liquid after biomass pretreatment and before two other major steps used in biofuel production – saccharification and fermentation.

The study, published online this month in the journal Energy and Environmental Sciences, addresses a significant obstacle to expanding the market for biofuels: lowering the cost of production.

According to a preliminary economic analysis reported in the study, a CO2-enhanced process could lower production costs by 50 to 65 percent compared with conventional ionic liquid-based pretreatment methods. Much of the appeal of using carbon dioxide gas to neutralize the ionic liquid is the ease with which the technique can be integrated into existing industrial operations. This solution is also relatively non-toxic compared to other common industrial gases or pH-adjustment techniques.

The ionic liquids used for pretreatment at JBEI are typically highly alkaline and must be washed away so that they do not interfere with the enzymes and microbes used in the latter stages of biofuels production. The enzymes are needed to release the sugars from the slurry of cellulose and hemicellulose after pretreatment, a step called saccharification. The bacteria's job is to convert that sugar to churn out biofuel, a step called fermentation.

The study authors pointed out that microbes generate carbon dioxide as a byproduct of fermentation, so harnessing that gas for use in the pretreatment phase leads to an even greener source of energy.

For several decades, researchers have been working to reduce the amount of energy and handling needed for each stage of this process. Some focus on engineering enzymes and bacteria so that they can withstand the exposure to ionic liquids, while this study focuses on neutralizing the ionic liquid so it won't harm the enzymes and microbes.

The researchers said that this process could soon be ready for implementation in ethanol production.

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