Low Molecular Weight Aromatics Research Articles

Development of an Effective Au : Pd Bimetallic Heterogeneous Catalyst for Oxidative Lignin Depolymerization to Low Molecular Weight Aromatics

AbstractLignin, a phenolic‐rich biomass component, holds promise for producing value‐added products. However, its complex structure and recalcitrance present challenges for its effective utilization. To overcome this, a AuPd/Li−Al layered double hydroxide (LDH) catalyst was developed to facilitate lignin depolymerization. Various AuPd bimetallic nanoparticle compositions were supported on a basic Li−Al LDH support via a sol‐immobilization method and characterized using N2‐physisorption, X‐ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The catalysts were then evaluated in the oxidation of several benzylic alcohols using O2 as the oxidant, from which Au7Pd3/Li−Al LDH and Au1Pd1/Li−Al LDH were identified as possessing promising catalytic activity. Further investigations focused on the aerobic oxidation of β‐O‐4 linked lignin model dimers under atmospheric pressure. The tested catalysts demonstrated sequential oxidation of the model compounds, leading to cleavage of the β‐O‐4 linkage. Finally, the catalysts were applied to the oxidative deconstruction of γ‐valerolactone (GVL) extracted maple lignin at 120 °C. Au1Pd1/Li−Al LDH emerged as the most effective catalyst, yielding a range of aromatic monomers with a total monomer yield of 27 %. These results highlight the potential of the Au1Pd1/Li−Al LDH catalyst system as an eco‐friendly approach for lignin depolymerization under mild conditions.

Toward a hydrogen-free reductive catalytic fractionation of wheat straw biomass.

The reductive catalytic fractionation (RCF) of lignocellulosic biomass is an attractive method for the conversion of lignin toward valuable low-molecular weight aromatics. A limitation to the upscaling of such technology is represented by the use of pressurized hydrogen gas. Here, the role of hydrogen gas within the RCF of wheat straw biomass is investigated. The use of H2 is shown to enhance lignin depolymerization, by virtue of an improved hydrogenolysis and hydrogenation of lignin fragments, with a yield of phenolic monomers that increased from ~12 wt% of acid-insoluble lignin in the initial biomass under inert atmosphere, up to ~25 wt% under H2 (in methanol, at 250 °C, with Ru/C). The adoption of methanol, ethanol or isopropanol as hydrogen-donor solvents was also investigated in the absence of H2. Ethanol was found to give the highest yield of monophenolics (up to ~20 wt%) owing to a better balance between solvolysis, hydrogenolysis, and hydrogenation of lignin. Nevertheless, a substantial loss of the carbohydrate fraction was observed. The use of a lower temperature (200 °C) in combination with H3PO4 resulted in an improved recovery of cellulose in the pulp and in the solubilization of hemicellulose and lignin, with the formation of monosaccharides (~14 wt% of polysaccharides in the initial biomass) and phenolic monomers (up to 18 wt%, in the absence of H2). Overall, a tradeoff exists between the removal of H2 from the process and the production of low-MW phenolics during RCF.

Ex-situ catalytic fast pyrolysis of wood chips over lamellar MFI zeolite supported nickel catalyst

Lamellar MFI zeolite and lamellar MFI zeolite supported nickel were synthesized and examined for ex-situ catalytic upgrading of the vapors (without using any fluidized gases such as N2 and H2) resulted from fast pyrolysis of wood chips in comparison to its commercial MFI zeolite and its supported nickel counterparts. Pyrolysis tests were carried out using a catalytic augur reactor at atmospheric pressure, while pyrolysis unit was operating at 450 °C and upgrading unit at 420 °C, respectively. The introduction of nickel with a high dispersion over the zeolitic supports caused a significant increase in the products of aromatic compounds. Moreover, the addition of nickel to zeolite supports changed their acidity and decreased the total number of acid sites and the ratio of Brønsted to Lewis acid sites as determined by pyridine-FTIR spectroscopy. The use of lamellar zeolite catalysts increased the efficiency of catalytic cracking of pyrolysis vapors and their modification with nickel helped tuning the Lewis acidity to further increase catalytic cracking which resulted in a higher yield of the low molecular weight aromatics present in the bio-oil.

Synergistic effects of peracetic acid and oxalic acid on structural transformation of eucalyptus and its conversion

Biomass pretreatment solvent plays an important role in the utilization of lignocellulosic feedstocks. In this study, the synergistic effects of peracetic acid and oxalic acid (PAO) were investigated as a pretreatment solvent for maximizing cellulose conversion as well as recovering biologically transformable lignin. The PAO pretreatment with 4.5% oxalic acid and 2.0% peracetic acid effectively fractionated lignin (85.4%) under a mild temperature (140 °C) and resulted in a high glucose release (758 mg/g biomass) from the pretreated eucalyptus. Also, the PAO pretreatment could fractionate and deconstruct lignin to low molecular weight (1231 g/mol) aromatics with 5.8% of β-O-4 linkages and a relatively uniform molecular weight distribution (PDI 1.3). The pretreatment using PAA and OA enhanced not only the hydrolysis of cellulose but also the recovery of biologically transformable lignin as a value-added coproduct for a successful biorefinery approach.

Catalytic upcycling paper sludge for the recovery of minerals and production of renewable high-grade biofuels and bio-based chemicals

Paper sludge is a solid waste by-product abundantly produced in the paper industry and contains fine minerals and lignocellulosic biomass. In this contribution, the ex-situ catalytic fast pyrolysis of paper sludge with a high mineral content of ca. 71 wt% is reported for the first time and demonstrated in a pilot-scale unit (feeding rate of 11.3 kg h−1) using a granular Na2CO3/γ-Al2O3 catalyst (loading of 650 g) to produce a high-grade bio-oil at a fast pyrolysis temperature of 475 ± 5 °C (pre-screened using a pyroprobe) and a catalytic upgrading temperature of 500 °C. Besides, > 99 wt% minerals in the paper sludge could be recovered, including paper fillers such as CaCO3 (major) and talc. The bio-oil obtained at a carbon yield of 21 C.% has a low oxygen content of 3.2 wt%, a low total acidity number of 5.2 mg KOH g−1, low H2O content of 0.7 wt%, and a high higher heating value of 40.9 MJ kg−1. It consists of value-added bio-based chemicals such as paraffins, olefins, and low molecular weight aromatics. The results demonstrate that the use of paper sludge to recover minerals and to obtain fuels and chemicals using ex-situ catalytic pyrolysis is technically feasible at a pilot plant scale, which will be of importance for the development of future bio-based economy.

Catalytic hydrocracking of a Mexican heavy oil on a MoS2/al2o3catalyst: II. Study of the transformation of isolated aromatics fraction obtained from SARA analysis

Catalytic hydrocracking of isolated aromatics fraction from a heavy crude oil was studied on a slurry batch reactor at isothermal conditions using 8.27 MPa H2 pressure, different temperatures (380 °C, 390 °C, and 400 °C), different reaction times (1.0 h, 2.5 h, and 4.0 h) and employing a sulfided Mo/γ-Al2O3 catalyst. The ASTM D2007 method had been applied to a Mexican heavy oil to obtain the aromatics fraction. Feedstock and products (gas and liquid) were analyzed by GC-MSD and GC-FID. Additionally, the liquid phase was analyzed by the ASTM D7169 method. A kinetic model was proposed to establish the effect of the processing the heavy cuts (gasoil, atmospheric residue, and vacuum residue) to light distillate cuts production (gas, naphtha and, kerosene). It was determined that the feedstock is composed of aromatics (mono, di, tri, or tetra-cycle) with alkyl tails, oxygenated aromatics, nitrogen aromatics, and sulfur aromatics. The catalytic hydrocracking products were saturate compounds and lower molecular weight aromatics; no coke was detected. The produced gas was composed by saturated compounds. The fitted kinetic parameters and the chromatographic analyses indicate that aromatics in feedstock were transformed following primary reactions in series. The main producers of naphtha were aromatics in kerosene and atmospheric residue, the reactions were dealkylation or hydrogenation; this after the opening of aromatic rings in the high molecular aromatics. The gas producers were substituted aromatics in the kerosene cut that is kept at the liquid phase during reaction, also, at high temperatures the hydrotreatment reactions of aromatic compounds in gasoil produces gas.

Lignin Depolymerization by Catalytic Hydrodeoxygenation Performed with Smectitic Clay‐Based Materials

The present investigation aims at exploring the application of low‐cost catalysts based on smectitic clays to the hydrodeoxygenation (HDO) of Cynara cardunculus derived lignin. Two types of clay minerals, montmorillonite and saponite, are pillared and decorated with suitable metals by means of an optimized process and characterized by X‐ray powder diffraction (XRPD), porosity, scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDX), Fourier‐transform infrared spectroscopy (FTIR), UV–vis–NIR, Raman, and thermogravimetric analysis (TGA). Alkaline lignin is obtained from steam‐treated cardoon. Lignin depolymerization is conducted in a bench‐scale apparatus under subcritical conditions, at relatively low temperature (320 °C), for 3 h, under 5‐6 MPa of total pressure. Four catalysts are tested, namely, Fe/Al‐pillared montmorillonite (FAMO) and saponite (FASA), and Ni‐exchanged Ni/Al‐pillared montmorillonite (Ni–Ni/AMO) and saponite (Ni–Ni/ASA). Results indicate that mineral clay–based catalysts result effectively in the hydrogenolysis of lignin, producing several low molecular weight aromatics and other species, with overall conversions in the range 60–70%. Montmorillonite‐based catalysts yield the highest substrate conversion, with a prevalence of phenols and substituted phenols, whereas only Ni–Ni/ASA generates a higher abundance of aliphatic hydrocarbons. Overall, data indicate that smectitic clays are promising catalyst supports for products‐oriented HDO of lignin.

Enzymatic depolymerization of industrial lignins by laccase-mediator systems in 1,4-dioxane/water.

Lignin is the second most abundant polymer after cellulose in lignocellulosic biomass. Its aromatic composition and recalcitrant nature make its valorization a major challenge for obtaining low molecular weight aromatics compounds with high value-added from the enzymatic depolymerization of industrial lignins. The oxidation reaction of lignin polymer using laccases alone remains inefficient. Therefore, researches are focused on the use of a laccase-mediator system (LMS) to facilitate enzymatic depolymerization. Until today, the LMS system was studied using water-soluble lignin only (commercial lignins, modified lignins, or lignin model compounds). This work reports a study of three LMS systems to depolymerize the three major industrial lignins (organosolv lignin, Kraft lignin, and sodium lignosulfonate). We show that an enzymatic depolymerization of these lignins can be achieved by LMS using laccase from Trametes versicolor, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt as mediator and a cosolvent (25% of 1,4-dioxane) to enhance the solubilization of lignins.

Isotope heterogeneity in ethyltoluenes from Australian condensates, and their stable carbon site-specific isotope analysis

Low-molecular-weight (LMW) aromatic compounds from petroleum fluids have not been widely studied for fluid-source correlations due to their volatility and their relatively low abundances in source rocks. However, LMW aromatics are important components in fluids, including condensates which lack biomarkers (molecular fossils typically used for correlation studies). Here, we have investigated the distribution of ethyltoluenes (o-ET, m-ET and p-ET; ortho, meta and para, respectively) in fluvial-deltaic condensates which contain relatively high abundances of the meta-isomer. The meta-selectivity found in these petroleum fluids is consistent with a mineral catalytic effect on the molecular distribution of these compounds, as it occurs during the clay-catalyzed synthesis of ethyltoluenes. Isomers differ up to 6‰ in δ13C values. Condensates from the Northern Carnarvon Basin, North West Shelf of Australia (NWS), have been analyzed by compound specific isotope analysis (CSIA) by GC-ir-MS, and site-specific isotope analysis (SSIA) using a Q-Exactive-GC Orbitrap™-based mass spectrometer. The SSIA revealed a 13C enrichment at the methyl end of the ethyl branch of m-ET, following a normal kinetic isotope effect during thermal maturation (cleavage). Continuous development of this first SSIA application will make possible high resolution analysis of light aromatics to outline the evolution of the organic matter to hydrocarbons in petroleum systems.

Hydrotreatment of pyrolysis liquids derived from second-generation bioethanol production residues over NiMo and CoMo catalysts

Lignin-rich digested stillage from second-generation bioethanol production is a unique biomass-derived feedstock, not only because it contains high amounts of lignin but also due to its residual amounts of cellulose and hemicellulose. In this study, catalytic hydrotreatment experiments were conducted on pyrolysis liquids obtained from the lignin-rich feedstock using sulphided NiMo/Al2O3 and CoMo/Al2O3 catalysts. The aim was to obtain a high conversion of the initial pyrolysis feed into a hydrotreated oil with a high phenolics and aromatics fractions. Experiments were carried out in a stirred batch reactor at 350 °C and 10 MPa of H2 (initial pressure). Product oils were obtained in about 60–65% w/w, the remainder being an aqueous phase (12–14% w/w), solids (7–8% w/w) and gas phase components (all on initial pyrolysis oil feed basis). The product oils were characterised in detail using various techniques (elemental composition, GCxGC-FID, GPC, and 2D HSQC NMR). The oxygen content was reduced from 23% w/w in the pyrolysis oils to 7.5–11.5% in the hydrotreated oils, indicative of the occurrence of hydrodeoxygenation reactions. This was also evident from the chemical composition, showing an increase in the amounts of low molecular weight aromatics, alkylphenolics, alkanes and cycloalkanes in hydrotreated oils. Performance of the two catalysts was compared, and a higher degree of deoxygenation was observed for the NiMo catalyst. The implications of the findings for the valorisation of second-generation bioethanol residues are also discussed.

Catalytic co-liquefaction of lignin and lignite coal for aromatic liquid fuels and chemicals in mixed solvent of ethanol-water in the presence of a hematite ore

In this work, a raw hematite ore (Fe2O3) displayed to be a low-cost but effective catalyst for co-liquefaction of hydrolysis lignin (HL) and Xilinguole lignite (XL) in ethanol-water (50:50, v/v) mixed solvent under initial N2 atmosphere to produce heavy oil (HO) as a potential source of liquid fuel and aromatic chemicals. The liquefaction of HL and XL separately without catalyst resulted in a maximum of approx. 18 and 11 wt% yield of HO, respectively, while the co-liquefaction process resulted in up to approx. 26 wt% of HO, indicating synergy effect in co-liquefaction of lignin and lignite. The addition of the hematite ore in the co-liquefaction operation produced HO at a very high yield of about 40 wt% at 400 °C for a residence time of 2 h, nearly doubling that of the operation without catalyst. The Produced HO products from the co-liquefaction operations at 400 °C for2 h contain significant concentrations of low molecular weight aromatics at ∼14 mg/g-HO in the presence of non-reduced hematite or goethite, and ∼17 mg/g-HO in the presence of reduced hematite or goethite, compared with only <5 mg/g-HO without iron ore catalyst.

Pre-senescence Harvest of Switchgrass Inhibits Xylose Utilization by Engineered Yeast

Proper timing of switchgrass harvest for bioenergy is important to maximize yield and optimize end use conversion. Proposed windows range from peak biomass to the following spring after overwintering in the field. There are various pros and cons associated with harvest timing: earlier harvests maximize yield but can remove nutrients from the field that may require replacement, while later harvests have reduced biomass yields due to weathering but maximize nutrient resorption in belowground tissues. Switchgrass composition changes during the harvest period, with losses of potential fermentation nutrients (amino acids and minerals), and sources of pretreatment-derived inhibitors (soluble sugars), which could affect downstream conversion by microorganisms. For this work we investigated whether switchgrass harvest could be timed to maximize beneficial impacts on fermentation. Switchgrass samples were harvested from five replicate field plots in Wisconsin, roughly every 2-3 weeks from peak biomass (Aug. 20) until after the killing frost (Nov. 7). Cell wall composition showed little consistent variation with harvest date while bulk biomass analysis showed a relative increase in cell wall content (lignin and structural sugars) and loss of extractives (minerals, protein, soluble sugars, and others). Following high or low severity AFEX pretreatment and high solids enzymatic hydrolysis (6% glucan loading), two field replicates were fermented using Saccharomyces cerevisiae 424A, a strain engineered to utilize xylose in addition to glucose. For both pretreatment severities, S. cerevisiae 424A grown in hydrolysates from the three earlier harvests utilized only a small fraction of available xylose, while almost complete utilization occurred within 96 hr for the last three harvest dates. Detailed analysis of the hydrolysate low molecular weight aromatics did not indicate any compounds potentially responsible for the inhibition, with most of the observed variation in their concentration due to pretreatment severity. Amino acid composition also did not appear to be limiting. Current indications point to a plant-generated compound that degrades during senescence, which future work will attempt to identify. Ultimately this work demonstrates that, although an attractive option to maximize yield, harvesting switchgrass before it begins senescing could have a negative effect on downstream conversion processes.

A Two-Step Catalytic Depolymerization of Alkali Treated Pennisetum glaucum L. and Melia dubia cav. into Low Molecular Weight (LMW) Aromatics

A Two-Step Catalytic Depolymerization of Alkali Treated Pennisetum glaucum L. and Melia dubia cav. into Low Molecular Weight (LMW) Aromatics

Gold-catalyzed conversion of lignin to low molecular weight aromatics.

A heterogeneous catalyst system, employing Au nanoparticles (NPs) and Li-Al (1 : 2) layered double hydroxide (LDH) as support, showed excellent activity in aerobic oxidation of the benzylic alcohol group in β-O-4 linked lignin model dimers to the corresponding carbonyl products using molecular oxygen under atmospheric pressure. The synergistic effect between Au NPs and the basic Li-Al LDH support induces further reaction of the oxidized model compounds, facilitating facile cleavage of the β-O-4 linkage. Extension to oxidation of γ-valerolactone (GVL) extracted lignin and kraft lignin using Au/Li-Al LDH under similar conditions produced a range of aromatic monomers in high yield. Hydrolysis of the Au/Li-Al LDH oxidized lignin was found to increase the degree of lignin depolymerization, with monomer yields reaching 40% for GVL extracted lignin. Based on these results, the Au/Li-Al LDH + O2 catalyst system shows potential to be an environmentally friendly means of depolymerizing lignin to low molecular weight aromatics under mild conditions.

Microwave-assisted selective cleavage of Cα[sbnd]Cβ bond for lignin depolymerization

Lignin is an alternative renewable feedstock for the production of low molecular weight aromatics. The cleavage of phenyl side-chain CαCβ bond is a valid depolymerization pathway to obtain aromatic monomers. The selective cleavage of the CαCβ bonds in two lignin model dimers and lignin with ferric sulfate as the catalyst was investigated to narrow the distribution of aromatic monomers. The CαCβ bonds in phenolic and non-phenolic dimers were selectively cleaved under microwave irradiation. The acidity promoted the etherification of Cα-hydroxyl groups with methanol solvent. Both the etherification and the decomposition of alkenyl products occurred in fast reaction steps, but the formation of alkenyl products was a decomposition-determining step. Density functional theory (DFT) calculations indicated that the phenolic dimer was more thermodynamically favorable to form alkenyl product than non-phenolic dimer, which resulted in the CαCβ bond cleavage reactivity of phenolic dimer being higher than that of non-phenolic dimer. Microwave heating contributed to 96.3% of CαCβ bond cleavage of organosolv lignin (OL), and a narrow distribution of aromatic monomers which mainly contained vanillin, syringaldehyde, methyl vanillate, and methyl syringate. This work highlights the prospect of microwave-assisted selective cleavage of the CαCβ bond to achieve the selective production of aromatic monomers from lignin.

Biotransformation and Detoxification of Xylidine Orange Dye Using Immobilized Cells of Marine-Derived Lysinibacillus sphaericus D3.

Lysinibacillus sphaericus D3 cell-immobilized beads in natural gel sodium alginate decolorized the xylidine orange dye 1-(dimethylphenylazo)-2-naphthol-6-sulfonic acid sodium salt in the laboratory. Optimal conditions were selected for decolorization and the products formed were evaluated for toxicity by disc diffusion assay against common marine bacteria which revealed the non-toxic nature of the dye-degraded products. Decolorization of the brightly colored dye to colorless products was measured on an Ultra Violet-Vis spectrophotometer and its biodegradation products monitored on Thin Layer Chromatographic plate and High Performance Liquid Chromatography (HPLC). Finally, the metabolites formed in the decolorized medium were characterized by mass spectrometry. This analysis confirms the conversion of the parent molecule into lower molecular weight aromatic phenols and sulfonic acids as the final products of biotransformation. Based on the results, the probable degradation products of xylidine orange were naphthol, naphthylamine-6-sulfonic acid, 2-6-dihydroxynaphthalene, and bis-dinaphthylether. Thus, it may be concluded that the degradation pathway of the dye involved (a) reduction of its azo group by azoreductase enzyme (b) dimerization of the hydrazo compound followed by (c) degradation of monohydrazo as well as dimeric metabolites into low molecular weight aromatics. Finally, it may be worth exploring the possibility of commercially utilizing L. sphaericus D3 for industrial applications for treating large-scale dye waste water.

Effect of functional groups on hydrogenolysis of lignin model compounds

Lignin is a future feedstock for the production of low molecular weight aromatics, and hydrogenolysis is probably the most promising process for lignin depolymerization. Effect of the benzylic alcohol group, aromatic methoxyl and phenolic hydroxyl groups on the hydrogenolysis of β-O-4 bonds in lignin model compounds was investigated in Pd/C hydrogenolysis system. It was found that the β-O-4 bonds in compounds with no a benzylic alcohol group were cleaved directly and quickly to form two aromatic monomers in near-quantitative yield. However, both dehydrogenation and dehydroxylation occurred for the model compounds containing a benzylic alcohol group, and resulted in more complicated products distribution. The dehydrogenation of a benzylic alcohol group hindered the cleavage of β-O-4 bonds to form aromatic monomer products. The results also indicated that both the aromatic methoxyl and phenolic hydroxyl groups had no impact on products distribution. The aromatic methoxyl group in non-phenolic and phenolic compounds promoted the cleavage of β-O-4 bonds, while the phenolic hydroxyl group had a slightly negative impact on cleavage of β-O-4 bonds.

Base-Catalyzed Depolymerization of Biorefinery Lignins

Lignocellulosic biorefineries will produce a substantial pool of lignin-enriched residues, which are currently slated to be burned for heat and power. Going forward, however, valorization strategies for residual solid lignin will be essential to the economic viability of modern biorefineries. To achieve these strategies, effective lignin depolymerization processes will be required that can convert specific lignin-enriched biorefinery substrates into products of sufficient value and market size. Base-catalyzed depolymerization (BCD) of lignin using sodium hydroxide and other basic media has been shown to be an effective depolymerization approach when using technical and isolated lignins relevant to the pulp and paper industry. To gain insights in the application of BCD to lignin-rich, biofuels-relevant residues, here we apply BCD with sodium hydroxide at two catalyst loadings and temperatures of 270, 300, and 330 °C for 40 min to residual biomass from typical and emerging biochemical conversion processes. We obtained mass balances for each fraction from BCD, and characterized the resulting aqueous and solid residues using gel permeation chromatography, NMR, and GC–MS. When taken together, these results indicate that a significant fraction (45–78%) of the starting lignin-rich material can be depolymerized to low molecular weight, water-soluble species. The yield of the aqueous soluble fraction depends significantly on biomass processing method used prior to BCD. Namely, dilute acid pretreatment results in lower water-soluble yields compared to biomass processing that involves no acid pretreatment. Also, we find that the BCD product selectivity can be tuned with temperature to give higher yields of methoxyphenols at lower temperature, and a higher relative content of benzenediols with a greater extent of alkylation on the aromatic rings at higher temperature. Overall, this study shows that residual, lignin-rich biomass produced from conventional and emerging biochemical conversion processes can be depolymerized with sodium hydroxide to produce significant yields of low molecular weight aromatics that potentially can be upgraded to fuels or chemicals.

Stability and hydrogenation of polycyclic aromatic hydrocarbons during hydropyrolysis (HyPy) – Relevance for high maturity organic matter

A series of hydropyrolysis (HyPy) experiments have been conducted on a small suite of authentic polycyclic aromatic hydrocarbons (PAHs: coronene, pyrene and perylene) to investigate the HyPy behaviour of these PAHs. This information may help in the interpretation of the structural significance of aromatic HyPy products, often detected in high abundance, from high maturity kerogens. The PAHs were separately treated by HyPy and were all susceptible to some extent of hydrogenation. Perylene also decomposed into low molecular weight aromatics (e.g. methylbiphenyls). Structurally, perylene is much less stable than the more condensed PAHs coronene and pyrene. The total product concentrations (wt% of starting PAH) from all HyPy experiments were consistently less than 100wt%, probably due to either the condensation of semi-volatile products on walls of the transfer line prior to reaching the HyPy trap or the inefficient cold trapping of highly volatile products. Hydrogenation of PAHs was prevalent and was found to be significantly influenced by the addition of a Mo-S based catalyst and potentially the C/Mo ratio, but largely independent of the two final temperatures used (520°C and 550°C). The fully aromatised and hydrogenated products for any stable ring system may provide a general indication of the size distribution of aromatic units within the kerogen structure.

Evidence for a palaeo-oil column and alteration of residual oil in a gas-condensate field: Integrated oil inclusion and experimental results

In the Phuong Dong gas condensate field, Cuu Long Basin, Vietnam, hydrocarbon inclusions in quartz trapped a variety of petroleum fluids in the gas zone. Based on the attributes of the oil inclusion assemblages (fluorescence colour of the oil, bubble size, presence of bitumen), the presence of a palaeo-oil column is inferred prior to migration of gas into the reservoir. When a palaeo-oil column is displaced by gas, a residual volume fraction of oil remains in pores. If the gas does not completely mix with the oil, molecular partitioning between the residual oil and the new gas charge may change the composition and properties of the residual oil (gas stripping or gas washing). To simulate this phenomenon in the laboratory, we sealed small amounts of crude oil (42 and 30°API) and excess pure gas (methane, ethane, or propane) in fused silica capillary capsules (FSCCs), with and without water. These mixtures were characterized with the same methods used to characterize the fluid inclusions, heating and cooling stage microscopy, fluorescence spectroscopy, synchrotron FT-IR, and Raman spectroscopy. At room temperature, mixtures of ethane and propane with the 30°API oil formed a new immiscible fluorescent liquid phase with colour that is visually more blue than the initial oil. The fluorescence of the original oil phase shifted to yellow or disappeared with formation of semi-solid residues. The blue-shift of the fluorescence of the immiscible phases and strong CH stretching bands in FT-IR spectra are consistent with stripping of hydrocarbon molecules from the oil. In experiments in FSCCs with water solid residues are common. At elevated temperature, reproducing geologic reservoir conditions, the fluorescence changes and therefore the molecular fractionation are enhanced. However, the precipitation of solid residues is responsible of more complex changes. Mixing experiments with the 42°API oil do not form a new immiscible hydrocarbon liquid although the fluorescence displays a similar yellow shift when gas is added. Solid residues rarely form in mixtures with 42°API oil. FT-IR spectra suggest that the decrease of fluorescence intensity of the original oil at short wavelengths to be due to the partitioning of low molecular weight aromatic molecules into the vapour phase and/or the new immiscible liquid phase. The decrease of fluorescence intensity at long wavelengths appears to be due to loss of high molecular weight aromatics during precipitation of solid residues by desorption of aromatics and resins from asphaltenes. Desorption of low molecular weight aromatics and resins from asphaltenes during precipitation can also increase the fluorescence intensity at short wavelengths of the residual oil. Water clearly affects the precipitation of semi-solid residues from the oil phase of the lowest API gravity oil.The change of hydrocarbon phase(s) in UV–visible fluorescence and FT-IR enclosed within the FSCCs were compared with the fluorescence patterns of natural fluid inclusions at Phuong Dong gas condensate field. The experimental results support the concept of gas-washing of residual oil and are consistent with the oil inclusion attributes from the current gas zone at Phuong Dong field. The hydrocarbon charge history of the fractured granite reservoir is interpreted to result from the trapping of residual oil after drainage of a palaeo-oil column by gas.