High-pressure pyrolysis and gasification of biomass

With the limited reserves of fossil fuels and the environmental problems associated with their use, the world is moving towards cleaner, renewable, and sustainable sources of energy. Biomass is a promising feedstock towards attaining this goal because it is abundant, renewable, and can be considered as a carbon neutral source of energy. Syngas can be further processed to produce liquid fuels, hydrogen, high value chemicals, or it can be converted to heat and power using turbines. Most of the downstream processing of syngas occurs at high pressures, which requires cost intensive gas compression. It has been considered to be techno-economically advantageous to generate pressurized syngas by performing high-pressure gasification. Gasification utilizes high temperatures and an oxidizing gas to convert biomass to synthesis gas (syngas, a mixture of CO and H2). Most of the past studies on gasification used process conditions that did not simulate an industrial gasification operation. This work aims at understanding the chemical and physical transformations taking place during high-pressure biomass gasification at heating rates of practical significance. We have adopted an approach of breaking down the gasification process into two steps: 1) Pyrolysis or devolatalization (fast step), and 2) Char gasification (slow step). This approach allows us to understand pyrolysis and char gasification separately and also to study the effect of pyrolysis conditions on the char gasification kinetics. Alkali and alkaline earth metals in biomass are known to catalyze the gasification reaction. This potentially makes biomass feedstock a cheap source of catalyst during coal gasification. This work also explores catalytic interactions in biomass-coal blends during co-gasification of the mixed feeds. The results of this study can be divided into four parts: (a) pyrolysis of loblolly pine; (b) gasification of pine chars; (c) pyrolysis and gasification of switchgrass; (d) co-gasification of pine/switchgrass with lignite and bituminous coals.Ph.D

Effect of Temperature, Pressure, and Residence Time on Pyrolysis of Pine in an Entrained Flow Reactor

High-pressure biomass gasification is poorly understood at heating rates of practical significance. This paper addresses this knowledge gap by performing pyrolysis of pine at high temperatures (600–1000 °C) and high pressures (5–20 bar) in an entrained flow reactor. Heating rates of 10³–10⁴ °C/s are achieved with solids residence time ranging from 4 to 28 s. The pyrolysis chars, gases, and tars are characterized using several techniques: N₂ and CO₂ physisorption, elemental analyses, SEM, XRD, micro-GC, FTIR-MS, and GCxGC-TOF-MS. The evolution of gases at high pressure is studied by pyrolyzing pine in PTGA at 800 °C between 5 and 30 bar. Pyrolysis pressure, temperature, heating rate, and residence time dramatically influence the physical and chemical properties of char, mainly through differences in the release of volatiles, evolution of char morphology, and carbonization of the char skeleton. The surface area and pore properties of chars correlate with the development of graphite-like structures in the carbon matrix. The gas composition from both the PTGA and PEFR shows that CO, CO₂, H₂, and CH₄ are the major light gases evolved, whereas C₂–C₄ hydrocarbons, oxygenates, and benzene are the minor light gas species observed. The formation of polynuclear aromatic tars at the longest residence times appears to occur via gas phase molecular weight growth reactions. The knowledge of char structure evolution developed in this paper will help us better understand char gasification kinetics which is important for the design of gasifiers

Structure Analysis of Pine Bark‑, Residue‑, and Stem-Derived Light Oil and Its Hydrodeoxygenation Products

Three constituents of loblolly pine (stem, residue, and bark) were independently pyrolyzed to produce light oil. The chemical structures of the light oils were analyzed using GC-MS, ¹H NMR, ¹³C NMR, and HSQC-NMR. The experimental results indicate that levoglucosan observed in the light oil is the major product from cellulose pyrolysis. Furanic and phenolic monomers are derived from hemicellulose and lignin, respectively. The light oil hydrodeoxygenation reaction study was carried out using carbon-supported ruthenium as a catalyst. Light oils from all three constituents were independently upgraded under 8 MPa hydrogen gas at 300 °C for 2 h. After the upgrading process, the aromatic rings were hydrogenated and the oxygen-containing functional groups were extensively removed. According to ¹H NMR, the percentage of the CH_<i>n</i>O peak area for stem, residue, and bark decreases by 90.03%, 77.84%, and 94.98%, respectively, compared to that for the pre-HDO light oil After upgrading, the carbon yields are 83.31% for the bark and approximately 100% for both the stem and the residue. The results indicate that ruthenium can hydrogenate carbonyl (CO) bonds, furan ring, and aromatic ring as well as cleave the aliphatic C–O and C–C bonds by hydrogenolysis. However, it cannot cleave the ether and ester type bonds