Alan W. Scaroni

Preparation and characterization of novel CO2 "molecular basket" adsorbents based on polymer-modified mesoporous molecular sieve MCM-41

Abstract Novel CO2 “molecular basket” adsorbents were prepared by synthesizing and modifying the mesoporous molecular sieve of MCM-41 type with polyethylenimine (PEI). The MCM-41-PEI adsorbents were characterized by X-ray powder diffraction (XRD), N2 adsorption/desorption, thermal gravimetric analysis (TGA) as well as the CO2 adsorption/desorption performance. This paper reports on the effects of preparation conditions (PEI loadings, preparation methods, PEI loading procedures, types of solvents, solvent/MCM-41 ratios, addition of additive, and Si/Al ratios of MCM-41) on the CO2 adsorption/desorption performance of MCM-41-PEI. With the increase in PEI loading, the surface area, pore size and pore volume of the PEI-loaded MCM-41 adsorbent decreased. When the PEI loading was higher than 30 wt.%, the mesoporous pores began to be filled with PEI and the mesoporous molecular sieve MCM-41 showed a synergetic effect on the adsorption of CO2 by PEI. At PEI loading of 50 wt.% in MCM-41-PEI, the highest CO2 adsorption capacity of 246 mg/g-PEI was obtained, which is 30 times higher than that of the MCM-41 and is about 2.3 times that of the pure PEI. Impregnation was found to be a better method for the preparation of MCM-41-PEI adsorbents than mechanical mixing method. The adsorbent prepared by a one-step impregnation method had a higher CO2 adsorption capacity than that of prepared by a two-step impregnation method. The higher the Si/Al ratio of MCM-41 or the solvent/MCM-41 ratio, the higher the CO2 adsorption capacity. Using polyethylene glycol as additive into the MCM-41-PEI adsorbent increased not only the CO2 adsorption capacity, but also the rates of CO2 adsorption/desorption. A simple model was proposed to account for the synergetic effect of MCM-41 on the adsorption of CO2 by PEI.

An experimental and theoretical study of the adsorption of aromatics possessing electron-withdrawing and electron-donating functional groups by chemically modified activated carbons☆

Abstract The adsorption of model aromatic compounds (aniline and nitrobenzene) on chemically tailored activated carbons has been systematically investigated. Adsorption experiments at controlled solution pH conditions confirmed that both electrostatic and dispersive adsorbate/adsorbent interactions can have a significant influence on the equilibrium uptakes of ionic and nonionic adsorbate species. For aniline (a weak electrolyte), maximum uptakes were found on oxidized carbon surfaces at solution pH near the adsorbates point of zero charge (pH PZC ). In contrast, nondissociating nitrobenzene uptakes were enhanced on heat-treated surfaces with graphene layers unperturbed by electron-withdrawing functional groups, particularly at solution pH ~ pH PZC . A theoretical model that can successfully account for the observed trends is hereby proposed as a much needed predictor of the experimental conditions and adsorbent surface chemical properties that will maximize the uptake of aromatic compounds by activated carbons.

13C and 15N NMR spectroscopic investigation on the formation of fossil algal residues

13C and 15N NMR spectroscopy was applied to modern (a mixed algal culture, its algaenan and its compost), ancient (algal derived sediments from Mangrove Lake, Bermuda) and fossilized algal residues (Torbanite, Green River Shale) for the purpose of establishing the forms of nitrogen algal remains and evaluating their long-term stabilities. The results indicate that proteinaceous material can resist microbial degradation in sediments as old as 4000 yr, possibly in refractory biopolymers, by encapsulation into their macromolecular network. The 15N NMR spectra of the Torbanite and the Green River Shale show a relative enrichment of heterocyclic-N, which may derive from selective preservation of biogenic heterocyclic compounds or by rearrangement of peptide chains during diagenesis.

The influence of surface functionality on the activity of carbon-supported catalysts

The aim of this research is to investigate how the presence of surface functional groups can influence the activity of carbon-supported MoS2 catalysts for coal asphaltene hydrogenation. Porous carbons were subjected to various chemical treatments in order to introduce oxygen and nitrogen surface functionalities prior to impregnation with ammonium tetrathiomolybdate. Supports and catalysts were examined by FTIR. Preoxidation of polymer-derived carbons lowered catalyst activity whereas preoxidation of a carbon black composite support increased it. Similar mixed results have been reported in the literature. The modified catalytic activity cannot be unequivocally attributed to surface oxygen. Qualitatively, it is considered that these groups exert some influence, but it is the structure of the carbon which is ultimately the controlling factor. In some cases, oxidation may introduce sites which promote interaction with metal species and, in others, oxidation may modify or destroy favourable sites which are already extant. Prenitriding was found to have a distinct influence in enhancing catalyst activity. The presence of nitrogen-containing surface groups may provide preferential sites for the adsorption of Mo species.

Calcination of Pulverized Limestone Particles under Furnace Injection Conditions

The calcination behaviour of limestone particles (6–90 μm) under furnace injection conditions (1073–1673 K) was determined. Scanning electron microscopic analysis of partially calcined particles revealed that calcination occurred over the total (internal and external) surface area with different calcination rates at different locations. A model consistent with experimental rate data indicated that the calcination rate was influenced by heat transfer, mass transfer and chemical kinetics. Internal temperature and CO2 partial pressure gradients produced a location-dependent calcination rate. For particles >20 μm and gas temperatures >1473 K, external heat transfer and pore diffusion of CO2 offered the major resistances to calcination. For particles <10 μm and gas temperatures <1073 K, chemical kinetics were rate-controlling.

A review of carbon-supported hydrodesulfurization catalysts

The purpose of this paper is to provide a comprehensive review of carbon-supported hydrodesulfurization (HDS) catalysts and to serve as a guide to investigators exploring the potential of these catalysts. The preparative techniques and physical properties of the commonly used carbon supports are discussed, as is the influence of the surface functional groups on the carbon surface charge and metal species adsorption. The various techniques which have been applied to the characterization of the active metal sulfide species in HDS catalysts are also described. Where necessary, the properties and performance of conventional γ-Al2O3-supported hydrodesulfurization catalysts are provided and compared to those of the carbon-based counterparts. The results of several investigations indicate that carbon-supported catalysts have a potential advantage over HDS catalysts in current use, both with respect to high desulfurization activity and low coking propensity.

Effect of pressure on the devolatilization and swelling behaviour of a softening coal during rapid heating

Pyrolysis of an Illinois no. 6 bituminous coal was studied under rapid heating conditions in two entrained-flow furnaces at pressures from 0.1 to 3.8 MPa N2. Increasing the pyrolysis pressure slowed the global release rates of volatiles, lowered the asymptotic volatiles yields and promoted secondary reactions of the volatiles which reduced the tar yield and changed the gas yield. The extent of swelling and the volatiles transport mechanism were found to be sensitive to the applied N2 pressure. At 0.1 MPa N2, insignificant swelling occurred and the particle morphologies indicated that bubble transport had not occurred. The coal swelled most extensively with large blow holes observed on the particle surfaces when pyrolysed at 0.8 MPa, an indication that volatiles transport occurred by bubble movement. Further increase in pressure reduced the swelling and the number and size of the holes formed on the particle surfaces. The observed swelling behaviour was attributed to the combined effect of fluidity development and swelling resistance which was a function of the applied pressure. The swelling behaviour at elevated pressure could not be predicted from data taken at atmospheric pressure.

Hydrodesulphurization activity and coking propensity of carbon and alumina supported catalysts

Co—Mo, Fe and Mo catalysts were prepared on alumina and carbon supports. The reactivity of sulphided catalysts for thiophene hydrodesulphurization and the propensity for coke deposition of nonsulphided catalysts during propylene cracking and anthracene carbonization were measured. The hydrodesulphurization activity of Co—Mo and Fe catalysts increased in the order γ-Al2O3 < C-black composite < active carbon. For a given metal, considerable differences in activity were found both between the carbons and alumina and between the carbons themselves. Possible reasons for the different activities include the influence of the supports on metal dispersion and the presence of impurities in the carbons. For alumina supported catalysts there is a correspondence between hydrodesulphurization activity and coking propensity. On carbon supported catalysts, the rates of carbon deposition appear insensitive to the nature of the metal component(s) whereas hydrodesulphurization activity is not. Thus it is possible to enhance the latter without attendant increases in the susceptibility to coke-forming reactions. Increasing Mo loading from 0–12 wt% was found to substantially increase the rate of carbon deposition on alumina, whereas the effect on a carbon support was comparatively small. This behaviour appears to relate to the inherent support acidity and its modification on metal addition.

Kinetics of lignite pyrolysis in an entrained-flow, isothermal furnace

An entrained-flow, isothermal furnace was used to study rapid pyrolysis in nitrogen of a Texas lignite. Weight losses for fixed residence times up to 0.4 s were independent of particle size over the range of mean diameter from 41 to 201 μm and increased with temperature elevation over the range 700 to 1000 °C. The maximum yield of volatiles, 66.7 wt% of the dry-ash-free coal, was particle size independent and relatively temperature independent over the range of operating conditions. The maximum yield represented a fractional increase of 1.30 over the ASTM volatile matter. This yield enhancement was associated with a reduction in the preponderence of secondary char-forming reactions of the volatiles and not directly with the increase in heating rate from 20 °C s−1 in the ASTM test to >104 °C s−1 in the isothermal furnace. Pyrolysis was multi-stage; initial rapid devolatilization to 50% weight loss was followed by slower latter-stage devolatilization. First stage pyrolysis could be fitted by a single, first-order kinetic expression whether total weight loss was taken as just that for the first stage or for complete devolatilization. Rate constants for the two cases were 0.6 × 103 exp(− 45 kJ/mol/RT) and 0.9 × 102 exp(− 32 kJ/mol/RT) s−1, respectively. One or more additional equations would be necessary to describe the completion of pyrolysis. It is argued that the relatively low activation energy is not necessarily indicative of physical rate control and therefore not necessarily in contradiction with the absence of particle size effects.

The structural changes of bituminous coal particles during the initial stages of pulverized-coal combustion

Abstract The effect of the chemical composition of pulverized bituminous coal particles on their physical transformation during the initial stages of combustion has been investigated. The results suggested that cenosphere formation does not require extensive thermal decomposition of the coal particles. The vitrinites in the bituminous coal softened earlier and developed larger cenospheres than the other macerals. The coal particles swelled to a higher extend during combustion than in pyrolysis; however, the cenospheres formed in the former process experienced a higher extent of fragmentation. The formation of micropores in char particles appeared to be related to the thermoplasticity and secondary devolatilization. The increase in microporosity occurred predominantly during the shrinkage of the cenospheres. Inertinite-rich samples developed higher microporosity than liptinite-rich particles during both pyrolysis and combustion for a given extent of weight loss.