Colin E. Snape

Fossil steroids record the appearance of Demospongiae during the Cryogenian period

The Neoproterozoic era (1,000–542 Myr ago) was an era of climatic extremes and biological evolutionary developments culminating in the emergence of animals (Metazoa) and new ecosystems. Here we show that abundant sedimentary 24-isopropylcholestanes, the hydrocarbon remains of C30 sterols produced by marine demosponges, record the presence of Metazoa in the geological record before the end of the Marinoan glaciation (∼635 Myr ago). These sterane biomarkers are abundant in all formations of the Huqf Supergroup, South Oman Salt Basin, and, based on a new high-precision geochronology, constitute a continuous 100-Myr-long chemical fossil record of demosponges through the terminal Neoproterozoic and into the Early Cambrian epoch. The demosponge steranes occur in strata that underlie the Marinoan cap carbonate (>635 Myr ago). They currently represent the oldest evidence for animals in the fossil record, and are evidence for animals pre-dating the termination of the Marinoan glaciation. This suggests that shallow shelf waters in some late Cryogenian ocean basins (>635 Myr ago) contained dissolved oxygen in concentrations sufficient to support basal metazoan life at least 100 Myr before the rapid diversification of bilaterians during the Cambrian explosion. Biomarker analysis has yet to reveal any convincing evidence for ancient sponges pre-dating the first globally extensive Neoproterozoic glacial episode (the Sturtian, ∼713 Myr ago in Oman).

Impact of Water Coadsorption for Carbon Dioxide Capture in Microporous Polymer Sorbents

Alcohol-containing polymer networks synthesized by Friedel-Crafts alkylation have surface areas of up to 1015 m(2)/g. Both racemic and chiral microporous binaphthol (BINOL) networks can be produced by a simple, one-step route. The BINOL networks show higher CO(2) capture capacities than their naphthol counterparts under idealized, dry conditions. In the presence of water vapor, however, these BINOL networks adsorb less CO(2) than more hydrophobic analogues, suggesting that idealized measurements may give a poor indication of performance under more realistic carbon capture conditions.

Materials challenges for the development of solid sorbents for post-combustion carbon capture

In an effort to reduce the energy penalty and cost associated with state-of-the-art carbon capture technologies, a range of 2nd and 3rd generation CO2 capture technologies are being developed. One of these technologies, based on solid sorbents for the gas separation in carbon capture, has the potential to significantly reduce the energy penalty and avoid some of the problems associated with the current technologies. However to realise this potential, two main developments are required: new porous materials and new plant integration processes. This application note describes the performance requirements and challenges associated with the development of functional materials for this application. We describe the key challenges for materials development and the requirements in terms of operating conditions, gas composition, stability, and lifetime to make solid sorbents a viable large scale CO2 capture process. Examples of potential future research and breakthrough materials currently being developed are also discussed.

Structural analysis of supercritical-gas extracts of coals

Abstract The chemical structure of two extracts prepared by supercritical extraction of low-rank coals with toluene, with and without hydrogen, have been determined using solvent and Chromatographic fractionation followed by ultimate analysis, 1 H nuclear magnetic resonance (n.m.r.) spectroscopy, molecular weight and OH measurements. 13 C n.m.r. and i.r. spectroscopy have been used to obtain confirmatory evidence. The extract obtained in the absence of hydrogen, which amounted to 27% of the coal, was found to contain aromatic structures linked by ring-joining methylene or heterocyclic groups. The hydrogen-assisted extract (47.5 wt % coal) was more condensed and contained more smaller molecules, apparently as a result of the cleavage of heterocyclic groups in the coal. It also incorporated more hydroaromatic substituents. 13 C n.m.r. showed that virtually all the non-phenolic oxygen was present as aromatic ether.

Quantitative reliability of aromaticity and related measurements on coals by 13C n.m.r. A debate

While solid state 13C n.m.r. has made a major contribution to the characterization of coal and other insoluble carbonaceous materials over the past decade, there has been considerable uncertainty concerning the quantitative reliability of the technique. This debate addresses this important topic and comprises six contributions from authors who are recognized experts in n.m.r. characterization of solid fuels. The principal issue discussed is the accuracy of aromaticity measurements on coals by cross-polarization — magic-angle spinning (CP/MAS) 13C n.m.r., together with additional problems posed by high field measurements and spectral editing, and with some discussion of emerging techniques. There is a consensus that significant errors can arise in CP/MAS 13C n.m.r. measurements of aromaticity due to the unfortunate spin-dynamics of coals, which typically result in only ≈50% of the carbon being observed for bituminous coals. There is clear discrimination against aromatic carbon, but differences of opinion exist over the magnitude of the errors (from 2 to 15 mole carbon %) and whether high field (⩾ 50 MHz) measurements are as accurate as those of low field (< 25 MHz) because either sideband suppression or extremely high speed MAS has to be employed to eliminate sidebands. From the evidence presented, it is suggested that a combination of low field, single pulse excitation with long relaxation delays and the use of a suitable reagent to quench paramagnetic centres is the most satisfactory, albeit time consuming, recipe for obtaining reasonably reliable results on unknown samples. An inter-laboratory exercise is being organized by Argonne National Laboratory to check the precision and to further investigate quantitative reliability of 13C n.m.r. measurements on coals from their Premium Coal Sample Bank.

Release of covalently-bound alkane biomarkers in high yields from kerogen via catalytic hydropyrolysis

Fixed-bed pyrolysis of kerogens at high hydrogen pressures (> 10 MPa, hydropyrolysis) in the presence of a dispersed sulphided molybdenum catalyst gives rise to extremely high yields of dichloromethane (DCM)-soluble oil (> 65%). To illustrate the potential of this approach, the yields and conformations of the hopanes, steranes and methyl steranes released from Goynuk oil shale (a type I kerogen) by hydropyrolysis after prior sequential extraction of the shale with DCM and pyridine and batchwise hydrogenation at 300°C (cf 520°C for hydropyrolysis) are reported here. The total yield of aliphatic hydrocarbons from hydropyrolysis represented ca 30% w/w of the kerogens organic matter with yields of the C29–C32 17β(H), 21β(H)-hopanes being between three and ten times greater than those from DCM extraction and the milder hydrogenation treatment. The yields of the C33–C35 17β(H), 21β(H)-hopanes, not found in the DCM extracts and only minor constituents in normal pyrolysis oil, were again typically at least three times higher than from hydrogenation.

Swellable, Water- and Acid-Tolerant Polymer Sponges for Chemoselective Carbon Dioxide Capture

To impact carbon emissions, new materials for carbon capture must be inexpensive, robust, and able to adsorb CO2 specifically from a mixture of other gases. In particular, materials must be tolerant to the water vapor and to the acidic impurities that are present in gas streams produced by using fossil fuels to generate electricity. We show that a porous organic polymer has excellent CO2 capacity and high CO2 selectivity under conditions relevant to precombustion CO2 capture. Unlike polar adsorbents, such as zeolite 13x and the metal-organic framework, HKUST-1, the CO2 adsorption capacity for the hydrophobic polymer is hardly affected by the adsorption of water vapor. The polymer is even stable to boiling in concentrated acid for extended periods, a property that is matched by few microporous adsorbents. The polymer adsorbs CO2 in a different way from rigid materials by physical swelling, much as a sponge adsorbs water. This gives rise to a higher CO2 capacities and much better CO2 selectivity than for other water-tolerant, nonswellable frameworks, such as activated carbon and ZIF-8. The polymer has superior function as a selective gas adsorbent, even though its constituent monomers are very simple organic feedstocks, as would be required for materials preparation on the large industrial scales required for carbon capture.

Molecular mass calibration in size-exclusion chromatography of coal derivatives

A number of procedures have been investigated for the calibration of a size-exclusion chromatography (s.e.c.) column in the determination of molecular mass (MM) distributions of coal derivatives. The behaviour of narrow fractions of coal extracts in the MM range 200–3000 was compared with a variety of the more generally available calibration standards. Calibration with preparative s.e.c. subfractions of materials similar to those under study has been recommended. Polystyrene standards are satisfactory, however, for MM < 1000, but above this range other polymer standards should be sought. Universal and molar volume calibration do not apply to coal-derived materials.

Solid state13C NMR investigation of lipid ligands in V-amylose inclusion complexes

The characteristics of the ligands in inclusion complexes formed from stearic, palmitic, oleic, linoleic, linolenic and docosahexaenoic acids, glycerol monooleate (GMO), glycerol monopalmitate (GMP) and lysophosphatidylcholine (LPC) have been studied by13C NMR in dry and hydrated forms of the complexes, with13C labels being used for the car☐yl and C-1(3) glycerol carbons in stearic acid and GMO, respectively.13C NMR provides definitive proof that V-amylose inclusion complexes have been formed with the mono-car☐ylic fatty acids of varying degrees of unsaturation, GMO, GMP and LPC. The chemical shift of the mid-chain methylenes in stearic acid moves about 1.5 ppm upfield upon complexation with the1H rotating frame relaxation times becoming identical for the lipid and amylose. With the exception of docosahexaenoic acid, the mid-chain methylenes inside the V-helical segments have essentially the same chemical shift for all the other unsaturated fatty acids and lipids investigated. The cross-polarisation dynamics for the car☐yl and glycerol groups in stearic acid and GMO, respectively, have indicated that these bulky polar groups occupy highly mobile conformations in the hydrated complexes which must lie outside the V-helical segments adjacent to the amorphous domains.

Release of bound aromatic hydrocarbons from late Archean and Mesoproterozoic kerogens via hydropyrolysis

Hydrogen-lean kerogens (atomic H/C<0.4) isolated from the 2.5-billion-year-old (Ga) Mt. McRae Shale, Hamersley Group, at Tom Price, Western Australia, were studied via hydropyrolysis, a continuous-flow technique that degrades organic matter in a stream of high-pressure hydrogen assisted by a dispersed Mo catalyst. The hydropyrolysates yielded predominantly phenanthrene and pyrene, and higher polyaromatic hydrocarbons and alkylated homologues were generated in low relative concentrations. Saturated hydrocarbons were not detected. The molecular and carbon isotopic compositions of the hydropyrolysates are very similar to aromatic hydrocarbons obtained by solvent extraction of the host rocks. Because molecular structures covalently attached to kerogen are unaffected by contamination, this indicates that both the bound and extractable aromatic fractions are syngenetic with the host rocks. Therefore, the results of the hydropyrolysis experiments provide compelling evidence for preserved bitumen of Archean age. The very high proportion of nonalkylated polyaromatic hydrocarbons in the hydropyrolysates is consistent with hydrothermal dehydrogenation of the kerogen, and a marked concentration difference of pyrene in rock extracts and hydropyrolysates might be explained by hydrothermal redistribution of the bitumen. The kerogen and bitumen composition is therefore consistent with models suggesting a hydrothermal origin for the giant iron ore deposits at Mt. Tom Price. Comparison of the Archean samples with hydropyrolysates from immature Mesoproterozoic kerogens from the Roper Group, McArthur Basin, Northern Territory, and with pyrolysis experiments on Proterozoic kerogens in the literature suggests that Precambrian kerogens are frequently highly aromatic and lipid-poor regardless of their degree of thermal preservation.