Researchers Produce Biocrude from Switchgrass with Subcritical Water
27 August 2009
| Major pathways for the conversion of biomass to biofuels. The subcritical pathway in the study is outlined in red. Credit: ACS. Click to enlarge. |
Researchers at Auburn University have shown a subcritical water treatment (hydrothermal liquefaction) that effectively liquefies switchgrass to produce a biocrude at a comparatively low temperature (235 °C) in a flow reactor. The biocrude in this study is an aqueous carbohydrate solution derived from the direct liquefaction of biomass; it can be converted to liquid fuel, hydrogen, or chemicals.
One of the perceived advantages to a hydrothermal liquefaction process is its ability to utilize mixed biomass feedstock without any pretreatment or drying, at a comparatively low temperature. Since water is used both as a reactant and as the reaction medium, the moisture content of biomass is not an issue.
Liquefaction of biomass in subcritical water proceeds through a series of structural and chemical transformations involving:
- Solvolysis of biomass resulting in micellarlike structure;
- Depolymerization of cellulose, hemicelluloses, and lignin; and
- Chemical and thermal decomposition of monomers to smaller molecules.
The focus of the study by Sandeep Kumar and Ram B. Gupta, published online in the ACS journal Energy & Fuels, was to explore the possibility of depolymerizing the entire holocellulose and lignin fraction of switchgrass in subcritical water to produce biocrude and converting them to sugar and lignin derived components in a semicontinuous reactor.
| The apparatus for biocrude production. Credit: ACS. Click to enlarge. |
They pumped subcritical water through a tubular reactor packed with switchgrass particles of 40-60 mesh size. They found that the use of potassium carbonate (K2CO3) as a catalyst significantly enhanced the hydrolysis of macromoleculer components of switchgrass into water-soluble products.
More than 50 wt% of the organic carbon available in switchgrass was converted to biocrude after 20 minutes of steady operation at 235 °C in the presence of 0.15 wt % of K2CO3. At 260 °C, dehydration of biomass was favored over hydrolysis reactions.
The resulting biocrude consists of an aqueous phase and solid precipitates. The aqueous phase contains oligomers and monomers of five and six carbon sugars, degradation products (5-HMF and furfural), organic acids (lactic, formic, and acetic acid), 2-furancarboxaldehyde, and other phenolic products containing five to nine carbon atoms. The residual solid (i.e., biochar) contained mainly lignin fractions and a small amount of cellulose.
Using infrared spectroscopy and electron microscopy, they confirmed that subcritical water treatment leads to a breakdown of lignocellulosic structure.
Resources
Sandeep Kumar and Ram B. Gupta (2009) Biocrude Production from Switchgrass Using Subcritical Water. Energy & Fuels doi: 10.1021/ef900379p
This sounds relatively economical.
Would a chemical engineer comment if it is?
Posted by: kelly | 28 August 2009 at 08:04 AM
Subcritical water hydrolysis can be made highly efficient. Subcritical high pressure water hydrolysis was invented by Denis Papin about 1679. It was modified by Fred T. Zimmermann to make artificial vanilla from wood after 1900 and is still used principally to regenerate charcoal powder in waste water purefication systems in the form of wet-air-oxidation.((TM)ZIMMPRO)
Deep well processes have been used in experiments to make the pumping less costly by using gravity to increase water pressure. Such systems are related to Geysirs. The resultant products can more easily be digested by organisms. It would be a way to make more high valued cattle feed from grass.
Almost any organic material can be substantially modified by Wet-Air-Oxidation at low temperatures, and the rest can be made into CO2 and water by Supercritial water oxidation.
Even minerals, such as fools gold, iron sulphide, can be oxidized.
Modified by subcritical water, coal might make a good synthetic crude. Silverado made dewatered coal powder that way.
Highly supercritital water will produce hydrogen from organic materials as you migh have read in these pages. ..HG..
Posted by: Henry Gibson | 30 August 2009 at 01:51 PM
Hi Im prasad balegedde (from Uni twente). Saw ur poster in TCBiomass 2009. It was really interesting to see the process and especially switch grass. I was wondering about the minerals/metals present in switchgrass whether it will go to char/liquid phase and its catalytic activity. thanks and all d best
Posted by: www.facebook.com/profile.php?id=611292101 | 27 September 2009 at 03:27 AM