Bradley Bockrath

Characterization of the surfaces of single-walled carbon nanotubes using alcohols and hydrocarbons: a pulse adsorption technique

A pulse mass analyzer was used to study the vapor phase adsorption of organic compounds on single-walled carbon nanotubes and chemically modified/oxidized SWCNTs. The change in mass of a packed bed of adsorbent held at 200 °C was observed following the injection of a pulse of an organic compound from the series: ethanol, iso-propanol, cyclohexane, cyclohexene, benzene, or n-hexane. The relative strength of adsorption was obtained by the mass increase resulting from injection of the pulse and by the time required for desorption. This time was broken into the transit time to reach the end of the bed and the half-time for return from peak to baseline. Hexane was the most strongly held compound of the organic sequence. Oxidative purification of a raw nanotube sample produced a less hydrophobic surface. The effect of the purification was reversed by thermolysis at 700 °C, which removed oxygenated functional groups and increased the affinity for hydrocarbons. The amorphous carbon associated with the raw nanotube sample is a strong adsorbent for hydrocarbons. By comparison, an activated carbon had a greater affinity for hydrocarbons than any of the nanotube samples.

Effect of sulphur on coal liquefaction in the presence of dispersed iron or molybdenum catalysts

Abstract The effects of dispersed catalysts on coal liquefaction under hydrogen pressure were studied using small autoclaves. The catalysts were generated in situ by addition of elemental sulphur plus an oil-soluble carboxylic salt of either iron or molybdenum. Finely divided catalysts of relatively high activity were generated by this method. Residues isolated after liquefaction with added iron carboxylate and sulphur contained pyrrhotite, which is proposed to be the catalytically active species. The prime role of sulphur is to form pyrrhotite in combination with the iron. Addition of sulphur alone did not increase conversion. This method of catalyst preparation seems useful for further scientific study of the relationship between sulphur, metal sulphide catalysts and liquefaction activity.

Permanent Trapping of CO(2) in Single-Walled Carbon Nanotubes Synthesized by the HiPco Process.

Infrared spectroscopy is used to study trapped and physisorbed CO2 in single-walled carbon nanotube bundles (SWNTs) synthesized by the HiPco process. CO2 is entrapped within the SWNTs by acid oxidation of the unpurified sample followed by vacuum heating to 700 K. The trapped CO2 has a single nu3 mode at 2327 cm-1, is stable during temperature cycling from 77 to 700 K, and remains after venting to room air. CO2 physisorption studies show a nu3 mode at 2330 cm-1 for the as-received HiPco samples, 2340 cm-1 for the acid-oxidized sample, and 2327 and 2340 cm-1 for the oxidized sample after vacuum heating. The sites responsible for the infrared peaks of the physisorbed and trapped species are discussed.

Coal-derived asphaltenes: effect of phenol content and molecular weight on viscosity of solutions

Phenol contents and molecular weights of coal-derived asphaltenes are shown to affect the viscosity of their solutions. Phenol contents were determined by non-aqueous titrimetry. Intermolecular aggregation probably involving hydrogen bonding is a prime factor in the increase in viscosity found with increased asphaltene concentration in a reference solvent system composed of an 8812 (wtwt) mixture of 1-methylnaphthalene and o-cresol. Aggregation effects are greater for those asphaltenes with relatively higher phenol contents. Asphaltenes were separated into fractions of different polarity by adsorption chromatography. The more polar subfraction was found to increase viscosity in the reference solvent to a greater extent than the less polar subfraction. The logarithmic viscosity numbers of solutions of the asphaltenes and their subfractions are correlated by a linear combination of molecular weights and phenol contents. It is concluded that an effective means of reducing the viscosity of coal-derived liquids would be to reduce the phenol content of the asphaltene fraction.

Coal-derived asphaltenes. Relationship between chemical character and process history

Abstract The chemical character of asphaltenes isolated from coal-derived liquids and the relative ease of their catalytic and noncatalytic conversion to oil has been found to depend upon their processing history. To facilitate chemical characterization, a simple analytical method was developed for separation of the asphaltenes into three subfractions according to their relative strength of absorption on silica gel. Using this separation technique, differences in the relative content of polar molecules were found among asphaltenes of various processing histories. In general, the relative content of polar compounds in the asphaltenes decreases with increasing conversion to oil. The relative rate of conversion also declines after the asphaltene content reaches a low level. The asphaltenes remaining after long hydrotreatment are more aromatic, contain fewer polar functional groups and are of somewhat smaller molecular size than those obtained after short hydrotreatment. The initial rates of asphaltene conversion were considerably enhanced by a commercial CoMo hydrodesulfurization catalyst. The catalyst increased the conversion of the nonpolar subfraction to a greater extent than the polar subfraction.

Chemistry of Hydrogen Donor Solvents

Publisher Summary This chapter describes hydrogen donor solvents as important constituents of the feed streams for many proposed or operating direct liquefaction processes. One of the major functions of these liquids is to act as a vehicle for powdered feed coal, thus making a manageable and pumpable feed slurry. In addition to this vital role, donor solvents have several other important roles that relate directly to the chemistry of coal liquefaction. In the initial stage of coal liquefaction, the solvent plays a role in two principal processes: (1) the stabilization of reactive molecular fragments formed during the degradation of coals macromolecular structure by scission of cross-linking bonds, and (2) the dissolution of the resulting fragments in the liquefaction medium. The solvent also plays a vital role in the subsequent stages of liquefaction during which the initial products are upgraded by hydrogenation, removal of heteroatoms, and reduction of their average molecular weight.

Coal conversion and hydrogen utilization in catalytic liquefaction at low temperatures

Abstract The initial stages of coal liquefaction have been investigated in small batch autoclaves at moderate to low liquefaction temperatures. Conventional liquefaction in an organic recycle solvent was compared with liquefaction of coal in water. In conventional liquefaction, the majority of the tetrahydrofuran conversion ultimately obtained at long reaction times had already appeared before 15 minutes or less had elapsed at the set temperature. Addition of ammonium molybdate had a beneficial effect on conversion at lower temperatures as revealed by a decrease in the demands placed on the liquefaction solvent. The use of a catalyst under hydrogen pressure may compensate for the suppression of conversion values normally associated with using substantially smaller amounts of liquefaction solvent. The utilization of hydrogen was determined by elemental and NMR analyses of the organic portion of the entire charge fed to and taken from the autoclave. The net change in hydrogen per 100 carbons was calculated for four categories: hydrogen gas make, heteroatom removal, change in aromaticity (hydrogenation/dehydrogenation), and matrix bond cleavage/condensation. Hydrogen consumption is observed below 400°C in the hydrogenation of aromatic carbon. However, above 400°C, dehydrogenation reactions predominate and hydrogen is released in this category rather than consumed. These results show that the choice of liquefaction temperature, catalyst, solvent, and pressure of reducing gas may be used to control the pattern of hydrogen utilization.

Exfoliated MoS2 catalysts in coal liquefaction

A technique is described for the application of MoS2 to coal particles. The method was used to determine the importance of several parameters to the performance of this direct coal liquefaction catalyst. Improved performance was obtained when MoS2 was intercalated with lithium, then exfoliated in a mixture of tetrahydrofuran and water in the presence of coal. Performance was compared by subjecting dried coal/catalyst mixtures to uniform microautoclave liquefaction tests. Measurements of coal conversion and hydrogen consumption show that a combination of reduction of the MoS2 stacking and improved coal/catalyst dispersion is beneficial.

A pulse-flow microreactor study of coal-catalyst interactions

Abstract The reactions of hydrogen with mixtures of coal and a solid, dispersed liquefaction catalyst have been investigated using a pulse-flow microreactor. The reactor was principally designed to study hydrogen/deuterium exchange reactions. Pulses of deuterium were carried through a heated bed of coal and catalyst and the exit stream was monitored with a mass spectrometer. Exchange reactions were observed after physical mixtures of coal and MoS3 were heated above the temperature required to convert the catalyst precursor to MoS2. After the precursor had been activated, exchange reactions were observed at much lower temperatures, even at 225 °C. The only source of hydrogen was the coal. The results demonstrate that in these simple physical mixtures of coal and catalyst, a large pool of hydrogen on coal is available for transport to the catalyst surface where it may exchange with adsorbed deuterium gas.

Effect of cresol as a co-solvent in coal liquefaction and product analysis

The influence of o-cresol on conversions of Bruceton coal to tetrahydrofuran (THF) extract was determined over the full range of composition for mixtures of o-cresol with either tetralin, phenanthrene, anthracene or pyrene. A maximum was found in both of the plots of coal conversion versus cresol content for mixtures with phenanthrene or pyrene. By comparison, the conversion found in pure tetralin was significantly higher than those found in the polynuclear aromatics and was not increased by addition of o-cresol. The enhancement of conversion by addition of cresol to the polynuclear aromatics was determined to be due to its action during the liquefaction itself, and not due to any influence exerted on post-liquefaction product separation. The relationship of these results to other studies showing the effect of cresol on both liquefaction chemistry and on post-liquefaction product work-up is discussed.