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About this report: Thin stillage from corn ethanol plants is currently utilized by adding it to DDG and subsequently drying the blended streams to yield DDGS. This is convenient since it avoids treating the thin stillage as a waste stream. Generating new value-added products from the thin stillage stream offers an opportunity to add more positive cash flow to the equation independent of corn prices. Thin stillage is a potential source for several value-added biobased products that include phosphorous, fatty acids, and hydrochar that are produced by a process called Hydrothermal Carbonization (HTC). Hydrochar porosity and structure can be modified by post chemical and thermal treatment for applications such as activated carbons, polymer strengthening additives and electric double layer capacitors.

The HTC processing unit would be inserted in the process flow to receive the condensed distillers solubles (CDS). CDS can be converted to new products such as activated hydrochars with utility as adsorbents for a variety of organic chemicals, phosphate as a fertilizer component, and fatty acids that can be converted to biodiesel.

HTC will remove about a portion of the solids present in the concentrated thin stillage in the form of a hydrochar to which phosphorous that was dissolved in the thin stillage and the remaining corn oil (in form of fatty acids) are sorbed by the hydrochar. The hydrochar with sorbed components is recovered by conventional filtration. The filtrate from the HTC unit that still contains 70%+ of the original solids is then could be combined with the wet DDG’s and dried to a stable moisture content in the normal manner or alternately utilized a fertilizer for corn.

Conclusions:

  • HTC hydrochars can be effective adsorbents for HMF as well as furfural
  • Sorption of HMF appears to be a non-linear function of BET area and pore volume.
  • The batch post treatment oven should be converted to a flow through configuration to eliminate loading and gas flow issues. The batch crucible configuration is not scale able whereas the flow through design would be.
  • Hydrochars need to be characterized before and after post treatment for carbon content and number of carboxyl groups present.
  • Starting materials need to be characterized for variation in composition and subsequently processed under HTC conditions that will yield a chemically consistent hydrochar from one source to another.

Project outcomes: This research opens up new avenues of cash flow generation for corn ethanol plants.

Partners: Minnesota Corn Research & Promotion Council, Institute for Energy & the Environment