Songgeng Li

A Comparison of Monomeric Phenols Produced from Lignin by Fast Pyrolysis and Hydrothermal Conversions

Abstract Lignin, a by-product in biorefining industries such as lignocellulose-to-ethanol and paper-making processes, is a promising renewable source for value-added phenolic chemicals. Hydrothermal conversion and fast pyrolysis are two main thermo-chemical approaches for depolymerization of lignin. Hydrothermal conversion is a low temperature (250–500°C) and high pressure (5–30 MPa) process particularly suited for high moisture materials, whereas fast pyrolysis takes place at atmospheric pressure and moderate temperatures in the absence of oxygen and requires drying of the feedstock. In this paper, we present experimental results that provide a comparison of distributions of monomeric phenols produced by fast pyrolysis and hydrothermal conversion of lignin. Hydrothermal conversion experiments were performed in a 150 ml autoclave at 300°C for 30 minutes with different alkaline concentrations. Pyrolysis was carried out in a spouted bed reactor at 500°C. Hydrothermal conversion of lignin under 1 M alkaline solutions resulted in lower char yields (12.1%) compared to fast pyrolysis, which resulted in 54.5% solid yields. Monomer phenols obtained from hydrothermal conversion of lignin were found to have a narrower distribution dominated by catechol and its methyl derivative. In contrast, fast pyrolysis produced a wider distribution of monomeric phenols dominated by guaiacol and its derivatives with various chains substituted para to the hydroxyl group. Mechanisms of lignin fast pyrolysis and the methoxy group conversion under hydrothermal conditions were proposed respectively. In conclusion, hydrothermal technology is better suited for production of value added monomer phenols from lignin.

Chemical forms of the fluorine, chlorine, oxygen and carbon in coal fly ash and their correlations with mercury retention

Fly ashes recovered from the particulate control devices at six pulverized coal boiler unites of China, are studied using an X-ray photoelectron spectroscopy (XPS) with a particular focus on the functionalities of fluorine (F), chlorine (Cl), carbon and oxygen on fly ash. It is found that the inorganic forms of F and Cl are predominant on the ash surface in comparison with their organics, and the proportion of organic Cl is relatively higher than that of organic F. Similar results are also obtained in the bulk by correlating the F and Cl contents with those of the unburnt carbon and other compositions in ash. Strong correlations of mercury retention with surface carbon-oxygen functional groups indicate that the C=O, OH/C-O and (O-C=O)-O on surface are of significant importance for mercury retention in fly ash. Their surface concentrations are related to coal type. The presence of Cl in fly ash helps with mercury retention. No obvious effect of F is observed.

Cyclic CO2 capture performance of carbide slag

ABSTRACT The carbonate looping process is a promising technology for CO2 capture. The decay of sorbents reactivity over multiple cycles is an obstacle for realizing the carbonate looping process. In this work, the reactivity and stability of carbide slag for CO2 capture have been examined. The results show that carbide slag exhibits superior CO2 capture performance even at severe calcination temperatures in comparison with limestones, shells, pure CaCO3, and Ca(OH)2. X-ray diffraction analysis shows that there is mayenite (Ca12Al14O33) formed in the calcination step for carbide slag, which is the main reason for its high stability in the carbonate looping process.

Cyclic CO2 Capture Performance of Carbide Slag: Parametric Study

In this work, CO2 capture performance of carbide slag has been investigated in a thermogravimetric analyzer (TGA). Effects of operation parameters including particle size, reaction temperature and reaction duration on CO2 capture capacity were studied. The experimental results indicate that the increase of particle size ranging from 80 to 180 μm has a positive effect on the CO2 capture capacity of carbide slag. The sorbent reactivity decreases with an increase of calcination temperature. The prolonged exposure to carbonation conditions has a beneficial effect on sorbent behavior as a function of the number of calcination/carbonation cycles; however, the duration in the calcination step has little effect. Based on the experimental results, the reaction rate constant of carbonation reaction is obtained from Jander equation. It is found that it decreases with the increasing cycles.

Local slip velocity in a downer

Abstract Based on the EMMS model, the local slip velocity between gas and solid is systematically analyzed and a theoretical correlation of local slip velocity with local voidage for a downer is derived as follows:n u s ( r ) u t = D 8 / 7 ( 1 - ɛ mf ) - 2 / 7 [ 1 - ɛ ( r ) ɛ ( r ) ] 8 / 7 ɛ ( r ) 47 / 14 ɛ ( r ) - ɛ mf ɛ ( r ) . Using this correlation, the local gas-solid slip velocity in a downer is calculated. The calculated results are well consistent with experimental data. In addition, the variation of the local slip velocity with its corresponding solid holdup is also discussed.

Fuel gas production from dusty tar pyrolysis

ABSTRACT Dusty tar is an undesired product obtained from a coal pyrolysis/combustion system. Thermal conversion of dusty tar into fuel gas was studied with a fixed-bed reactor. It is found that C2-C5 hydrocarbons are mainly derived from the cracking of long-chain aliphatics, while CH4 from the decomposition of long-chain aliphatics and alkyl-substituted aromatic chemicals. The yield of the gas product increases monotonously, but the heating value of gas gradually decreases as temperature increases from 400 to 950°C. Decomposition of chemicals with a boiling point over 360°C contributes to 50–90% C1-C5 hydrocarbons and COx when pyrolysis temperature is lower than 600°C.

Radial Hydrodynamics of High Velocity Gas-Solid Down-Flow Fluidized Beds

Experiments have been carried out in a gas-solids co-current down-flow circulating fluidized beds. The radial profiles of particle velocity and solid concentrations were measured by a fiber optical probe. Local solid flux was calculated based on the measured local particle velocity and solid concentration. The influence of gas velocity and solid recirculation rate on the radial flow structure has been examined. The experimental results show that the radial flow structure at high gas velocity has its own prominent characteristics in comparison with that at low gas velocity.Copyright