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Biomass Fractionation

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PureVision’s core technology separates the primary constituents of cellulosic biomass within one pressurized reaction chamber into three streams. This continuous process employs a counter-current extraction technique that removes and recovers the hemicellulose and lignin fractions in two liquid streams, resulting in a solid fraction containing a relatively pure cellulose or fiber. This patented biomass fractionation process occurs within approximately 10 minutes.

In the PureVision process, cellulosic biomass is size-reduced and fed into a pressurized reaction chamber uniquely designed for counter-current processing. The PureVision technology can be accomplished in a single stage or in multi-stages, depending upon the desired products. A distinguishing feature of the PureVision process is the ability to efficiently separate (fractionate) biomass into its three main constituents: hemicelllulose, lignin and cellulose.
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In a two-stage setup, the target within the reaction chamber is to first wash out most of the hemicellulose in the form of hemicellulose sugars while keeping as much of the lignin and cellulose intact in a solid form. After the solids enter the second half of the reaction chamber, the pH, temperature and pressure are adjusted to wash and remove as much lignin as possible. These two washing stages yield (1) the xylose-rich liquor fraction, (2) the lignin-rich liquor fraction and (3) the remaining solid and relatively pure cellulose fraction.

In the first stage most of the solid hemicellulose can be converted into hemicellulose sugars. These sugars can then be fermented to produce products such as ethanol, xylitol or furfural or can be processed into a purified xylose stream. The first wash liquor fraction also contains smaller portions of the lignin, cellulose, protein, and ash components of the biomass, most of which can be recovered.

After the counter-flow washing of the hemicellulose occurs, most of the lignin and possibly the remaining hemicellulose are washed out in a second stage. This second stage wash liquor fraction contains most of the lignin and any targeted amount of the remaining hemicellulose sugars. This lignin-rich fraction is then further processed to produce a high quality, low-molecular weight lignin that can be sold as an industrial raw material to produce hundreds of industrial and consumer products. The lignin can also be used as a bio-fuel to provide energy for making electricity and steam to run the biorefinery.

The remaining cellulose fraction is between 90% to 97% cellulose, as most of the lignin, hemicellulose and extractives have been stripped off in the wash liquor fractions. Because of the high purity of the cellulose fraction, it can be sold as a pulp or enzymatically hydrolyzed into glucose requiring far less enzymes compared to competing technologies.

The PureVision process has enormous versatility and flexibility due to the many processing variables that can be achieved with steady state, counter-current processing. If the primary target is to produce a quality pulp for making paper products, the process targets the pulp specifications required by the pulp and paper industry to make paper products or dissolving pulps to make numerous industrial products. Alternatively, if the objective is to produce ethanol or other industrial chemicals, then the processing parameters will be targeted to maximize sugar production from the cellulose and hemicellulose fractions.

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Written by Casey McConnell

March 8, 2008 at 5:55 pm

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