Recovering Valuable Bio-Based Products from Thin Stillage ... Valuable BioBased... · How does HTC fit into the broader spectrum of Thermochemical Processing ? The general objective

Recovering Valuable Bio-Based Products

from Thin Stillage in Corn Ethanol PlantsK.J. Valentas, S. Heilmann and Joseph Molde, University of Minnesota,

ACE Conference August 5, 2014

Cost of corn ethanol operations varies directly with corn prices.

The Problem

Source: Ag. Marketing

Resource Center, March

2013, Iowa State Univ.

extension ethanol model

Sometimes profits are negative

The Opportunity

• Thin stillage can potentially be converted to higher

value products than DDGS to improve cash flow and

stabilize profitability

• A “drop-in” Hydrothermal carbonization (HTC) process

unit can convert condensed distillers solubles (CDS) to

such products

• These products include phosphorous, fatty acids,

fertilizers and functional hydrochars of various types

What is HTC and how does it work in a corn ethanol plant??

How does HTC fit into the broader spectrum of Thermochemical Processing ?

The general objective of thermochemical processing is to increase the carbon:

oxygen ratio of the biomass to improve its fuel properties. There are three

regimes with the product mix determined by the thermal intensity.

(1) Hydrothermal Gasification: Temp. range of 400-8000C, w/wo

catalyst, Products are; Hydrogen, methane, carbon dioxide.

Carbon is consumed and converted to CO2. High concentration

of CO2 prevents distribution in natural gas infrastructure.

(2) Hydrothermal Liquefaction: Temp. range of 250-4500C,

products are Bio-oils (phenols), hydrogen, methane, carbon

dioxide and some char. Bio-oils are particularly problematic

since they are inherently unstable, highly corrosive and toxic.

They also are not oils and are primarily phenols.

(3) Hydrothermal Carbonization (HTC): Temp. range 170-2500C,

Products are Char, fatty acids (if lipids are in biomass), water,

Maillard reaction products, N, K, and P.

How does HTC work?

•Aqueous biomass is heated to about 4000F at

pressure of 260 psia in a confined vessel.

•Biomass solids are dehydrated by elimination

of oxygen and hydrogen in the form of water

with almost no carbon dioxide generated.

•Fatty acids in the biomass are sorbed by the

char.

•Addition of a precipitant would cause the

phosphate in the biomass to also be sorbed by

the char.

•By cooling and simple filtration the hydro- char

and filtrate are easily recovered and separated.

Hydrothermal Carbonization (HTC)

Whole Stillage Thin Stillage

Wet distillers

grain

Drier

Eva

po

rato

r

Condensed

Distillers Solubles

Corn Oil

30% of totalDDGS

Centrifuge

Centrifuge

HTC

Phosphorous

Fatty Acids

Hydrochar

Proposed “drop-in” HTC unit in the

thin stillage process flow.

Filtrate to DDGS

drier or fertilizer

Primary products from HTC processing of CDS

• HTC recovers 32% of the solids in the

concentrated thin stillage as hydrochar

to which about 70 % of the

phosphorous and residual corn oil (in

the form of fatty acids) are sorbed.

• The hydrochar with sorbed

components is readily separated

from the remaining concentrated

thin stillage (68% of the original) by

simple mechanical filtration.

• The filtrate with 68% of the

original solids is combined with wet

distillers grains and dried in the

normal manner or alternatively

converted to a liquid fertilizer

• The fatty acids are recovered

by solvent extraction and the

phosphorous by acid wash from

the hydrochar.

Secondary and higher value-added products from CDS

�

�

�

�

Hydrochar

Surface area =

2m2/gram

+ Metal Salts

Heat to 8000C in

Inert atmosphere

Chemical adsorbents

Polymer additives

Supercapacitor

electrodes

�

Surface area

= 100m2/gram

• Adsorbents are used in many applications including water purification and chemical

processing or as a phosphorous filter to reduce runoff. At the low end these are at least

$1.00/lb. Work in this area is a collaboration with colleagues in the chemical engineering

department

• The high surface area of the modified chars are thought to provide strengthening in

some polymer systems such as polylactides. A collaborative effort with colleagues in the

chemistry department is ongoing

• Micro porosity imparted to the char during post heat treatment could result in

materials suitable for use in supercapacitors. There is an ongoing collaboration with

colleagues at the University of California, Berkeley.

What about the filtrate from the HTC process?

There are at least two viable options

• The filtrate can be added back to the DG’s and dried as is done

now with the CDS

• Filtrate can be concentrated utilizing the energy that would

have been used to dry it and subsequently applied as a liquid

fertilizer for corn and other row crops.

The fertilizer option is attractive since it recycles a part of the

corn crop to the land and reduces the requirement for

conventional fertilizer. This would be viewed as

environmentally sound as it would further reduce the carbon

footprint for corn ethanol

What are the questions that need to be answered to be able to use the

HTC filtrate from CDS as a plant fertilizer?

HTC processing of CDS retains most of the nitrogen and phosphorous in

the filtrate if no steps are taken to cause phosphorous to be purposely

sorbed by the char. At the same time maillard reaction products and other

chemicals are produced that could exhibit phytotoxicity or be detrimental

to soil bacteria.

The major questions are:

• Does the addition of HTC filtrate to soil have any negative

or positive effects on soil microorganisms?

• Does HTC filtrate have any phytotoxic effect on

either seed germination or plant growth

• What is the effect of aging the filtrate prior to application?

• What is effect of concentration of the filtrate on soil

microorganisms and possible phytotoxicity

These questions are currently being addressed on a lab scale for the system

of CDS filtrate and corn. The results will be published in a Masters thesis and

peer reviewed technical papers in the near future..

Cash flow example for 100M gallon/year ethanol plant operating at 30% backset

Mass balance based on preliminary experimental results

• Phosphorous as phosphoric acid = 2700 tons/yr at net value of $540/ton

•Fatty acids = 12.8M lbs/yr. with assumed value of $0.30/lb. ( Corn oil =$0.54

and white grease =$0.34).

• Hydrochar = 20.4 M lbs/yr Value depends on application from low of $1/lb

as activated carbon to high of $7/lb as polymer additive or supercapacitor.

• Thin stillage consumed = 21,400 tons/yr @$240/ton = $ 5.14 M

Incremental Yearly Cash Flow from HTC

$1.5M phosphoric acid + $3.84M fatty acids + $20.4M hydrochar (@ $1/lb) –

< $5.14M > thin stillage = $20.6M

The installed capital cost for an HTC unit for a 100M gallon plant is about $1.5M

What is the financial benefit of adding HTC??

Financial support for this research is

provided by Minnesota Corn Growers, AURI,

and the Institute for Renewable Energy and

the Environment (IREE).

Questions ???