John M. Andresen

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.

Fixed-bed pyrolysis and hydropyrolysis of sunflower bagasse: Product yields and compositions

Abstract Pyrolysis and hydropyrolysis experiments at different temperatures, heating rates and pressures have been conducted on a sample of sunflower pressed bagasse to investigate the effect of particle size, sweep gas velocity, and hydrogen pressure on the product yields and characteristics. In contrast to coal and oil shales, char and oil yields from sunflower pressed bagasse were found to be largely independent of particle size and sweep gas velocity in a Heinze retort with the oil yield of ≈ 40% w/w being the same as that from a well-swept fixed-bed reactor in which a much smaller sample size was used. The use of high hydrogen pressure ( > 50 bar) increased the oil yields by up to ≈ 10% w/w but these increases are much greater when expressed on a carbon basis due to the reduced oxygen contents of the oils. Even at low pressure, it has been estimated that ≈ 40% of the carbon aromatized during pyrolysis.

Quantitative solid-state 13C n.m.r. measurements on cokes, chars and coal tar pitch fractions

Bloch decay or single pulse excitation (SPE) 13C n.m.r., generally recognized as the best approach to obtain quantitatively reliable aromaticity values and other skeletal parameters for coals, was applied to partly carbonized coal samples, a biomass char and the toluene-insolubles from a coal tar and a corresponding pitch. As found previously for coals, the aromaticities and non-protonated carbon concentrations were generally higher than those estimated by cross-polarization (CP). Furthermore, in terms of accumulation times, the shorter 13C T1s of low-temperature chars makes SPE a more efficient technique than for coals. The higher concentrations of paramagnetic centres responsible for the shorter 13C T1s still result in observability of 75% of the carbon in the chars by the SPE technique. The HC ratios derived from the SPE measurements agree well with those obtained from elemental analysis.

Quantitative 13C NMR study of structural variations within the vitrinite and inertinite maceral groups for a semifusinite-rich bituminous coal

Abstract To determine the structural variation within vitrinite and inertinite maceral groups, fractions with purities over 90% in vitrinite and semifusinite were obtained by density gradient centrifugation from a medium volatile Australian bituminous coal and the bulk structural compositions of the maceral concentrates were determined by the quantitatively reliable single pulse excitation (SPE) solid state 13C NMR technique. As previously reported for coals and chars, the aromaticities determined by cross polarisation are often lower than those by SPE, due to the unfavourable spin dynamics. As expected, the aromaticities of the vitrinite fractions are significantly lower than those of the semifusinite ones, but the aromaticity, the fraction of non-protonated aromatic carbon and the number of rings per cluster all increase with density within both the maceral groups. The vitrinite and semifusinite fractions contain 3–6 and 9 to over 15 aromatic rings, respectively. Methyl groups account for greater proportions of the aliphatic carbon with increasing density. These structural trends are consistent with the variations evident in random reflectance.

Bio-oil and bio-char from low temperature pyrolysis of spent grains using activated alumina.

The pyrolysis of wheat and barley spent grains resulting from bio-ethanol and beer production respectively was investigated at temperatures between 460 and 540 °C using an activated alumina bed. The results showed that the bio-oil yield and quality depend principally on the applied temperature where pyrolysis at 460 °C leaves a bio-oil with lower nitrogen content in comparison with the original spent grains and low oxygen content. The viscosity profile of the spent grains indicated that activated alumina could promote liquefaction and prevent charring of the structure between 400 and 460 °C. The biochar contains about 10-12% of original carbon and 13-20% of starting nitrogen resulting very attractive as a soil amendment and for carbon sequestration. Overall, value can be added to the spent grains opening a new market in bio-fuel production without the needs of external energy. The bio-oil from spent grains could meet about 9% of the renewable obligation in the UK.

Physical cleaning of high carbon fly ash

An industrial fly ash sample was cleaned by three different processes, which were triboelectrostatic separation, ultrasonic column agglomeration, and column flotation. The unburned carbon concentrates were collected at purities ranging up to 62% at recoveries of 62%. In addition, optical microscopy studies were conducted on the final carbon concentrates to determine the carbon forms (inertinite, isotropic coke and anisotropic coke) collected from these various physical-cleaning processes. The effects of the various cleaning processes on the production of different carbon forms from high carbon fly ashes will be discussed.

Verification of the linear relationship between carbon aromaticities and H/C ratios for bituminous coals

Carbon aromaticities for a further 15 bituminous coal samples, including vitrinite and semi-fusinite maceral concentrates, have been obtained by solid state 13C NMR using the quantitative single-pulse excitation (SPE) technique, to add to the results for samples reported previously (Fuel, 1994, 73, 1926). A virtually identical linear correlation between the aromaticity (values in the range 0.73–0.91) and atomic HC ratio holds for the new samples investigated, confirming that it is independent of both inertinite content and geological provincialism.

Bio-oil deoxygenation by catalytic pyrolysis: new catalysts for the conversion of biomass into densified and deoxygenated bio-oil.

This work proposes an innovative catalytic pyrolysis process that converts bio-refinery residues, such as spent grains, into intermediate bio-oil with improved properties compared to traditional bio-oils, which allows the use of existing crude-oil refinery settings for bio-oil upgrading into fuels. The integration of bio-oil into a crude-oil refinery would decrease the economic disadvantage of biomass compared to fossil fuels. The catalytic pyrolysis was able to produce bio-oil with a lower O and N content and high levels of aliphatics and H by using activated serpentine and olivine at 430-460 °C. The activated materials seem to be beneficial to the bio-oil energy content by increasing it from less than 20 MJ kg(-1) in the original biomass to 26 MJ kg(-1). Approximately 70-74 % of the starting energy remains in the bio-oil using activated olivine (ACOL) and activated serpentine (ACSE) at 430 °C, whereas only 52 % is retained using alumina (ALU) at the same temperature. There was a strong reduction of the O content in the bio-oils, and the deoxygenation power decreased in the following order: ACOL>ACSE>ALU. In particular, ACOL at 430-460 °C was able to reduce the O content of the bio-oil by 40 %. The oxygenated bio-oil macromolecules interact in the catalysts active sites with the naturally present metallic species and undergo decarboxylation with the formation of C(5)-C(6) O-depleted species.

Structural characterisation of catalytic coke by solid-state 13C-NMR spectroscopy

Abstract After reviewing some recent studies on the characterisation of coke deposits on fluid catalytic cracking (FCC) and hydroprocessing catalysts by solid state 13C-NMR, the quantitative structural information that has been obtained through the use of demineralisation of FCC catalysts to provide coke concentrates for analysis will be described. The deactivated catalysts investigated contain only approx. 1% (w/w) carbon and were obtained both from refinery units operating with heavy feeds and from laboratory fluidised-bed tests with n-hexadecane. As for other carbonaceous materials, the use of a low-field field strength in conjunction with the single pulse excitation (SPE or Bloch decay) technique has enabled most of the carbon to be detected and, therefore, NMR-invisible graphitic layers are not thought to be major structural features of the cokes. Although stripping the catalysts gives rise to highly aromatic cokes (aromaticity>0.95), even for n-hexadecane, differences in feedstock composition are still reflected in the structure of the resultant cokes with those derived from n-hexadecane containing less condensed aromatic nuclei than those from heavy feeds.

In situ 1H NMR study of the fluidity enhancement for a bituminous coal by coal tar pitch and a hydrogen-donor liquefaction residue

Abstract Hydrogen-donor ability has been ascribed as one of the factors responsible for stabilisation of the plastic phase during coal carbonisation. In situ high-temperature 1 H nuclear magnetic resonance spectroscopy (NMR) is used here to compare quantitatively the interactions of a low-volatile, poor coking bituminous coal with a heat-treated coal tar pitch (CTP) and with a hydrogen-donor pitch (HDP) (> 450°C residue) obtained from a two-stage coal liquefaction process. When the CTP was added to the coal (25% w/w, 150–250 μm), the amount of fluid material increased by nearly 20% more than that predicted at maximum fluidity close to 450°C. Indeed, an even larger synergistic effect was observed with the HDP. By 400°C, 90% of the fluid phase concentration observed at 450°C had already been generated, corresponding to an enhancement of 50% over that predicted. However, particle size appears to be a dominant factor under the slow heating regime used, in that no enhancement in fluidity was detected when the coal size was