Chapter 17
Product Analysis from Direct Liquefaction of Several High-Moisture Biomass Feedstocks Douglas C. Elliott, L. John Sealock, Jr., and R. Scott Butner 1
Pacific NorthwestLaboratory ,P. O. Box 999, Richland,WA99352 Experimental results are reported for high-pressure liquefaction of high-moisture biomass. The feedstocks included macrocystis kelp, water hyacinths, spent grain from a brewery, grain sorghum field residue and napier grass. The biomass was processed in a batch autoclave as a ten weight percent slurry in water with sodium carbonate catalyst and carbon monoxide gas. Thirty-minute experiments were performed at 350°C with operating pressures ranging from 270 to 340 atmospheres. The o i l products were collected by methylene chloride and acetone extractions. Oil yields ranged from 19 to 35 mass percent on a moisture and ash-free basis. The o i l products contained from 9.9 to 16.7 percent oxygen with hydrogen to carbon atomic ratios from 1.36 to 1.61. Significant nitrogen content was noted in the o i l product from those feedstocks containing nitrogen (kelp, hyacinth, spent grain). Chemical composition analysis by gas chromatography/mass spectrometry demonstrated many similarities between these products and wood-derived oils. The nitrogen components were found to be mainly saturated heterocyclics.
Significant progress has been made over the past f i f t e e n years toward the development of processes for direct production of l i q u i d fuels from biomass. Process research has generally progressed along two lines — f l a s h pyrolysis and high-pressure processing. Extensive analysis of the l i q u i d products from these two types of processes has demonstrated the s i g n i f i c a n t process-related differences i n product composition. However, the effect of feedstock has received a lesser degree of attention. 1
Operated by Battelle Memorial Institute for the U.S. Department of Energy under Contract DE-AC06-76RLO-1830.
0097-6156/88/0376-0179$06.00/0 * 1988 American Chemical Society
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PYROLYSIS OILS FROM BIOMASS
Process Research i n Direct Liquefaction of Biomass Two generalized categories of direct liquefaction processes can be i d e n t i f i e d (1_). The f i r s t , f l a s h pyrolysis, i s characterized by a short residence time i n the reactor (~1 second) at r e l a t i v e l y high temperature (450-500°C) i n order to obtain maximum y i e l d of l i q u i d product. The second, high-pressure processing, i s usually performed at lower temperature (300-400°C) and longer residence time (0.21.0 h r ) . A t y p i c a l operating pressure i s 200 atm and often reducing gas and/or a catalyst i s included i n the process. The differences i n processing conditions result i n s i g n i f i c a n t differences i n product y i e l d and product composition. Product Analyses. Product analysis i n support of the process development research i n biomass direct liquefaction began at the rudimentary l e v e l of determining solvent-soluble portions of the product. Analysis was soon extended to elemental analyses and proximate analyses, such as ash and moisture. Later, spectrometric analyses were performed followed by detailed chemical analyses used i n conjunction with chromatographic separation techniques. At a l l stages of development, the s i g n i f i c a n t differences i n composition between the products of f l a s h pyrolysis and highpressure processing have been evident. While polar solvents are most e f f e c t i v e for both products, less polar solvents such as methylene chloride and even benzene and toluene have been used as extractants for high-pressure product o i l s . Comparative analysis has demonstrated the higher oxygen content and higher dissolved water content i n the f l a s h pyrolysis o i l s . Detailed analyses with spectrometric and chromatographic methods have added supporting evidence to these findings. Variations i n Product Due to Feedstock. While process-related d i f ferences i n product composition have been evident, extensive study of the effect of feedstock on product composition has never been undertaken. Some limited comparative tests can be gleaned from the l i t e r a t u r e ; however, most process research i n direct l i q u e f a c t i o n of biomass has been performed with woods of various species. Table I provides some of the results available i n the l i t e r a t u r e for nonwoody feedstocks. Significant differences i n heteroatom content are evident, but only limited chemical analysis i s available i n most cases. The researchers at the Pittsburgh Energy Research Center (2-4) steadfastly maintained i n their pioneering work on high-pressure l i q u e f a c t i o n that their o i l products obtained from c e l l u l o s i c wastes were p a r a f f i n i e and c y c l o p a r a f f i n i e i n nature. These products were formed i n the presence of sodium carbonate catalyst with an i n i t i a l overpressure of carbon monoxide at temperatures from 250 to 380°C and pressures from 10.4 to 34.6 MPa with batch residence times of 20 to 60 minutes. They reported the presence of carbonyl and carboxyl functional groups but maintained that there was e s s e n t i a l l y no aromatic material produced except at higher temperature (then only i n very small amounts). These conclusions were based on infrared and mass spectral analysis (_2). Later analysis of the sucrosederived o i l (3_) included proton nuclear magnetic resonance spectral evaluation but resulted i n the same conclusion. Most of the hydrogen was i n methylene or methyl groups and about 4 percent
17. ELLIOTT ET AL.
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Product AnalysisfromDirect Liquefaction
Table I. Product Analyses from Liquefaction Tests with Various Biomasses Feedstock
Temp. (°C)
Pressure (MPa)
C
H
Ν (percent)
0
S
H/C
