Cost-effective lignin valorization is critical to US DOE BioEnergy Technology Office’s (BETO) Biochemical Conversion Platform. Separations-related work in this research area is critical for the development of scalable lignin upgrading approaches. In the alkaline pretreatment liquor (APL) of waste lignin, most of the low molecular weight hydrocarbon compounds are organic acids. A cascade membrane separations technologies were applied to extract organic acids and reduce the processing volume for downstream upgrading to fuel or chemicals.<br/>In the integrated separation process, a tangential flow filtration (TFF) was applied to the fractionation of high molecule weight (HMW) compounds from APL. This is followed by electrochemical membrane separation to simultaneously capture organic acids and inorganic bases in separate streams from the low molecule weight (LMW) lignin in the TFF permeate. Different pore sizes of filtration membranes were evaluated to reduce the processing volume of permeate while still catching most of the LMW organic compounds. The electrochemical separations technique, resin-wafer electrodeionization (RW-EDI), was used to extract the organic acid and inorganic base from the TFF permeate. Balanced between performance and membrane fouling issues, an optimal operation condition was selected to maximize the capture performance with manageable membrane fouling issues. The first step of TFF was to remove 54% HMW and allow 90% LWM in the permeate stream for acid and base extraction. The second step operation of RW-EDI was able to remove &gt;97% of acids from the permeate of TFF. 95% of the removed organic acids was captured in a stream with a 20-35X concentrated titer compared to untreated permeate of TFF. Over 96% of the total process volume from TFF permeate was reduced, significantly reducing the upgrade reactor size in downstream. Techno-economic analysis and life-cycle analysis were performed to assess processing cost and environmental impacts.

Membrane separations to capture organic acids and valuable co-product from alkaline-pretreated-liquor of lignin

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ACS Fall 2022

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