(679f) Product Distribution and Kinetics of Hydropyrolysis of Agro Residues Via Py-GC/MS and Py-FT-IR

Approximately 140 billion tons/yr of agricultural waste is generated globally, which is equivalent to 50 billions tons of crude oil. (UNEP Report 2011). In India, a major fraction of the agro residues is unutilized and simply burnt in the farm, while the rest are either used as fodder or co-fired with coal in furnaces. These are large volume, yet low value solutions. Generating liquid bio-crude/biofuel from the agro residues via thermochemical techniques is a promising option to reduce the dependency on fossil-based fuels. Although fast pyrolysis of biomass residues is a promising technique that is being deployed to produce bio-oil/bio-crude, there are inherent difficulties associated with the utilization of bio-oil. These include high oxygen content, low heating value, poor storage and thermal stability, which are attributed to the presence of moisture and organics like carbonyl compounds, carboxylic acids, alcohols and phenols. While this stability issue can be partially addressed by catalytic fast pyrolysis that produces a fairly deoxygenated bio-oil, the bio-oil still requires further upgradation via catalytic hydrodeoxygenation process. Hydropyrolysis is a single step process wherein biomass is fast pyrolyzed at c.a. 500 ^oC in presence of hydrogen gas at moderate pressures (<35 bar). This results in the production of a high quality liquid fuel with very low O/C ratio. It is, therefore, necessary to thoroughly characterize the evolution of pyrolysates from fast hydropyrolysis and compare it with conventional fast pyrolysis process to understand the mechanism of formation of products. In this study, analytical pyrolysis (Py) of rice straw, empty palm fruit bunch (EFB) and pine wood biomass is conducted and the products are characterized using gas chromatograph/mass spectrometer (GC/MS) and Fourier transform infrared spectrometer (FT-IR).

The biomass characteristics such as volatile matter, fixed carbon, ash content, elemental C, H, N, S and O, and heating value were evaluated using standard techniques. It is important o note that the biomasses investigated in this study vary mainly in ash composition, and follow the trend: rice straw (19%) > EFB (7.5%) > pine wood (0.7%). Fast pyrolysis and hydropyrolysis experiments were conducted in a Pyroprobe^® 5200 pyrolyzer in trap mode. Approximately 0.5 mg of the agro residues were pyrolyzed at a heating rate of >10,000 ^oC/s to the preset temperature of 400-700 ^oC and held for 60 seconds in hydrogen atmosphere. The vapors were characterized using Agilent two-dimensional GC/MS. The effect of hydrogen pressure from 1 to 25 bar on pyrolysate composition was investigated, and compared with pyrolysate composition in presence of He environment at atmospheric pressure. Experiments were also conducted wherein the time evolution of key functional groups of the pyrolysates was analyzed using an online FT-IR spectrometer (Agilent Cary 660). A significant reduction in the formation of oxygenated organics, especially carboxylic acids, furan derivatives and phenolics, and a concomitant increase in the production of linear and aromatic hydrocarbons were observed during fast hydropyrolysis compared to normal fast pyrolysis of Indian rice straw, even at medium pressures of hydrogen. High temperatures slightly improved the yield of linear hydrocarbons, but greatly increased the yield of aromatics during hydropyrolysis. Py-FT-IR study revealed the time evolution of the pyrolysates, and the reaction completion time. The time taken for maximum production of oxygenates varied from 10-15 s at 500 ^oC, which was similar for all three biomass varieties. More interesting results on (a) the evolution of individual functional group vibrations, (b) product characterization, and (c) char formation, for different biomass varieties will be discussed during the presentation. The implications of the results on the quality of bio-oil and its properties will also be addressed.