(250a) Development of a Cold-Quench Bio-Oil Separation System and Its Effect On Cellulose Bio-Oil Yield and Composition

Renewable energy and sustainable energy production are top priorities for the nation to help provide nation, economic, and environmental security.  Among the renewable energy sources, biomass is most promising for production of liquid fuels that can be utilized in the existing infrastructure, so called “drop-in fuels”.  Biomass offers the advantages that it is renewable in that it grows back every year, it’s chemical energy is derived from solar energy, the only truly renewable source of energy for the planet, and it removes CO2 from the atmosphere as it grows thus resulting in a carbon neutral or carbon negative fuel which helps to mitigate concern of atmospheric carbon dioxide concentration. 

Two main pathways exist for conversion of biomass to liquid fuels; the biochemical pathway commonly utilized in existing ethanol plants using micro-organisms to ferment starches to ethanol, and the thermochemical pathway which is increasingly gaining attention.  Of the many thermochemical pathways, fast pyrolysis, the rapid thermal decomposition of organic compounds in the absence of oxygen to produce liquids fuels and gases, can be used to produce a liquid bio-oil that can be upgraded to fuels.  Monosaccharides resulting from the depolymerization of biomass components cellulose and hemicellulose offer advantages in that they can be directly upgraded to liquid fuels by processes such as aqueous phase upgrading, or fermented similar to starch in existing ethanol plants.  In either case, cellulose must be depolymerized to monosaccharides before it can be utilized by microorganisms in biological conversion or upgraded to hydrocarbons in aqueous phase upgrading.

Achieving high yields of sugar rich bio-oil is dependent on feedstock, operating conditions, and bio-oil collection systems. Previous research by Kuzhiyil et al.[1] has shown that feedstock can be optimized for sugar production by an acid infusion technique.  Operating conditions, such as temperature and sweep gas flow rate, also contribute to the overall sugar yield from biomass.  The third piece of the puzzle, bio-oil collection, has also been explored by several other reasearchers, however has not been optimized for sugar production. 

Bio-oil compounds are known to be intermediates between the original biomass and the end slow pyrolysis products which are char, essentially carbon, and water.  Since these compounds are intermediates they tend to be unstable and continue to react once condensed to form polymers leading to phase separation between the organic and aqueous phases.  Therefore, storage of a whole bio-oil can be problematic where separating the reactive species into specific stage fractions during the collection process can prove to be beneficial and has been subject of several researchers[2].  Temperatures of 400-600C and a continuous flow of inert sweep gas must be employed in order to generate the necessary heat and mass transfer characteristics to devolatilize anhydrosugars from biomass.  Once the volatile anhydrosugars enter the vapor stream, they may continue to react, where polymerization is commonly an issue as well as continued dehydration leading to formation of char and water.  Thus the bio-oil compounds, especially carbohydrates that are easily dehydrated, must be quickly quenched from the reactor temperature to a temperature where they are no longer prone to polymerization or dehydration.  To achieve this, a novel bio-oil separation process was co-invented between Iowa State University and the Phillips 66 Company where liquid nitrogen is used to quickly quench the pyrolysis vapors immediately after solids separation to prevent secondary reactions[3]. Quenching the volatile anhydrosugars cools them below their dew point where they form an aerosol in the vapor stream which is then removed in an electrostatic precipitator.  It was found that the flow rate of liquid nitrogen could be controlled to selectively quench the pyrolysis stream to temperatures critical to separation of the organic and aqueous phases.  In order to quantify changes of bio-oil yields and composition, a 100 gram per hour fluidized bed unit was used to pyrolyze pure cellulose under identical conditions where the bio-oil collection system was then changed between a conventional condenser separation system and this novel cold-quench system.  Yield and composition of the resulting bio-oil were then compared to quantify differences in bio-oil due to effect of cooling rate.

1.            Kuzhiyil, N., et al., Pyrolytic Sugars from Cellulosic Biomass. Submitted.

2.            Pollard, A.J.S., Comparison of bio-oil produced in a fractionated bio-oil collection system, in Mechanical Engineering, Biorenewable Resources and Technology2009, Iowa State University: Ames, Iowa.

3.            Daugaard, D.E.S., OK, US), Jones, Samuel T. (Dewey, OK, US), Dalluge, Dustin L. (Ames, IA, US), Brown, Robert C. (Ames, IA, US), SELECTIVE TEMPERATURE QUENCH AND ELECTROSTATIC RECOVERY OF BIO-OIL FRACTIONS, 2011, IOWA STATE UNIVERSITY RESEARCH FOUNDATION, INC. (Ames, IA, US),CONOCOPHILLIPS COMPANY - IP SERVICES GROUP (Houston, TX, US): United States.