Thermal Decomposition Of Organic Matter Research Articles

Biochar from sugarcane bagasse: Synthesis, characterization, and application in an electrochemical sensor for copper (II) determination

Biochar (BC) is a carbonaceous material obtained from the thermal decomposition of organic matter under limited oxygen supply that plays an attractive role in waste management. In this study, biochar was prepared from sugarcane bagasse, using pyrolysis temperatures from 300 to 700 °C, and chemically activated with HNO3. Structural characterizations showed that degradation increased as pyrolysis temperature increased. Furthermore, a higher number of functional groups were observed for the materials produced under the lowest temperatures. Chemical activation resulted in oxidation and nitration of carbonaceous structure, increasing the number of functional groups on the materials. All materials were evaluated for the construction of electrochemical sensors towards Cu2+ ions voltammetric determination. The material produced at 400 °C pyrolysis temperature and activated (BCA400) provided the most intense response, which can be related to the presence of one of the highest numbers of surface groups, such as oxygen groups, on it. A method for Cu2+ determination was successfully developed based on differential pulse adsorptive stripping voltammetry (DPAdSV). A linear dynamic range (LDR) from 1.0 to 15.0 μmol L−1 was achieved, with limit of detection (LOD) of 0.36 μmol L−1, and limit of quantification (LOQ) of 1.09 μmol L−1. The method was also adequate in terms of accuracy and precision, as well as selective against most cationic species commonly found in tap water. The analyte was determined in tap water samples, in natura and spiked with the maximum concentration allowed by Brazilian legislation, and successful recovery values were obtained. Therefore, biochar from sugarcane bagasse, an environmentally-friendly material, was successfully used to construct an electrochemical sensor and determining an environmental and health interest analyte.

Experimental and modeling study of the effect of confinement on the thermal decomposition of organic materials

Simultaneous Thermal Analysis is widely used to study thermal decomposition of a variety of organic materials, and the choice of experimental conditions is very important to obtain reliable mass loss and heat flow curves. In this work we investigate the effect of confinement on the thermal decomposition of organic materials. As an example, we explore high-density polyethylene (HDPE) and one of its pyrolysis products, namely eicosane (C20H42), through experiments and modeling in open crucibles and crucibles closed with a pierced lid. A new model is developed for evaporation and sublimation from open and pinhole thermal-analysis pans. It considers the kinetic resistance of evaporation at the liquid-vapor interface, inhibition of evaporation by buildup of vapor inside the pan, thermal expansion of vapor inside the pan, and diffusion of vapor from the pan. The model is validated using simultaneous heat-flow and mass-loss measurements of n-eicosane evaporation for various pinhole sizes, down to 50 µm. The importance of product evaporation inhibition for measuring polymer decomposition was demonstrated using HDPE. This study sheds light on the effect of confinement on the mass loss rate of organic materials.

Geochemical evidence for biodegradation in high-rank coals from Qinshui Basin, North China

Understanding the generation of secondary microbial methane (SMM) is important for the evaluation of natural gas resources and instructive for the stimulation of methane production. Coal seams are popular targets for extracting in situ preserved methane and studying microbe-stimulated methane yield. However, few studies have been done on overmature coals. Here we collected gas samples from coals varying from bituminous to meta-anthracite in the Qinshui Basin, North China, and analysed the molecular and stable isotopic compositions to systematically evaluate the influence of biodegradation in high-rank coals in geological settings. The stable isotope signatures (δ13C and δD) of methane are dominated by the thermal decomposition of organic matter in deep coals but inconsistent with the maturity rank of shallow burial coals. The decoupling of coal maturity with C1/C2+ ratios and δ13C-CH4 values, and positive δ13C-CO2 values (−9.2 to +24.4 ‰) suggest biodegradation of light wet gases (C2+ components) and CO2 reduction. Negative trends between δ13C-CO2 and CH4/CO2 in shallow burial coal seams reveal the mutual conversion of CH4 and CO2 and carbon isotope exchange, driven by microorganisms. The calculated isotopic temperatures (33–328 °C) based on the carbon isotope fractionation factors between CH4 and CO2 (1.024–1.069) demonstrate that carbon isotope exchange is prevalent in high-rank coals. It also reveals that the burial depth is an imperative factor in controlling microbial environments and thus the biodegradation process. This study implicates the potential of high-rank coals as the target for microbial-enhanced methane recovery and also implies that microorganisms are widely involved in reservoir carbon cycling.

Can soil conditioners of plant origin be used for pest control?

Bio-oil is a byproduct of the thermal decomposition of organic materials under low concentrations of oxygen at controlled temperatures. This product is commonly used as a potential soil conditioner. However, as it is of plant origin, this product may also have secondary metabolic properties capable of assisting in the alternative management of agricultural pests. Therefore, this work aimed to evaluate the acaricidal effect of bio-oil based on coffee straw and eucalyptus bark, obtained at a temperature of 600 ºC, on adults of the red mite Oligonychus ilicis. The treatments were calculated on a logarithmic scale, and the concentrations of the bio-oil solutions were 1.00; 1.58; 2.51; 3.98; 6.31, and 10.00 % (v v-1). Each solution was applied on mite adults, each treatment consisting of 7 Petri dishes, with 12 red mite individuals per dish. The experimental units consisted of coffee leaf disks (4 cm in diameter), with cotton moistened around these disks to prevent the mites from escaping. The application of bio-oil solutions on the mites was carried out directly, being sprayed with the aid of an Alfa 2 airbrush, connected to a calibrated compressor with a constant pressure of 1.3 psi. 2mL of solution of each concentration was applied. The experimental units were kept in a climate-controlled chamber (25 ºC, 70 % RH, 12h photophase). The acaricidal effect on adults was evaluated 24, 48, and 72 hours after spraying the solutions. Mortality data were submitted to Probit analysis (p≤0.05) using the R statistical program. Coffee bio-oil and eucalyptus bio-oil caused mortality in O. ilicis in a dose-dependent manner, with an estimated LC50 of 1.52 and 2.15 % (v v-1), respectively. The estimated LC90 of these bio-oils was 5.90 % and 8.02 % (v v-1), respectively, indicating that doses lower than the maximum concentrations used caused almost all the mortality of individuals under controlled environment conditions. Thus, it is concluded that the coffee straw bio-oil, as well as the eucalyptus bio-oil, have a high potential for use in the alternative management of adults of the red coffee mite O. ilicis.

Experimental Study of Biochar Production Process Using a Pilot Carbonization Kiln as a Biofuel’s Properties Improvement Module

Pyrolysis is a thermo-chemical process of biomass conversion to a carbon neutral or better fuels and materials from biomass. It is a thermal decomposition of organic material in a controlled (insufficient) oxygen at a high temperature thereby producing solid (biochar), liquid (oil) and gaseous products. Biochar produced during this process is a very valuable material that can be utilized as soil additive and in carbon sequestration, where the carbon can be stored (locked) in the soil. The result is improved soil structure, pH, water and nutrient retention and the mitigation of climate change. Biochar can also be utilized as biofuel in energy generation directly or converted to biomass briquettes thereby, improving its energy and economic value. Therefore, the present study, involved the production of biochar from an improvised 100 litres volume pilot carbonization kiln and experimentally studied the biochar yield. The result showed a yield of 2505g at average charring ratio of 33.9 % from 7396g of composite wastes, comprising of 1844g of mixture of Maize cob and coconut husk, 1030g of mixed vegetable stem and discarded fruits (sundried watermelon and fruits, 3321g of peeled yam, cassava peels, potatoes peels and discarded food materials, and 1201g of plantain bunches and peels. This results is an indication of good performance outcome of the carbonization kiln in biochar production for soil nutrient improvement and (or) for energy supply applications as refuse derived fuels (RDF).

Beneficial effects of biochar application on mitigating the drought and salinity stress implications on plants

Biochar, an amorphous and highly porous carbonaceous substance derived from the thermal decomposition of organic matter, has been empirically proven to enhance soil water retention capacity, mitigate soil salinity, and augment nutrient bioavailability. Consequently, these improvements exert a stimulating influence on the growth and development of medicinal plants. Numerous scientific investigations have corroborated that the incorporation of biochar into the cultivation of medicinal flora can lead to increased plant biomass, heightened photosynthetic efficiency, and augmented accumulation of bioactive compounds. Furthermore, the utilization of biochar exhibits the potential to curtail the necessity for chemical fertilizers, which can otherwise have deleterious effects on soil health and the environment. A comprehensive comprehension of biochar's prospective role as a sustainable, long-term strategy for augmenting the productivity and resilience of medicinal plant cultivation in arid and saline environments holds paramount importance for ensuring a consistent supply of medicinal plants in the forthcoming years. This review aims to delve into the mechanistic foundations underpinning the beneficial impacts of biochar on plant development and the accumulation of bioactive constituents. It also explores the feasibility of biochar as a sustainable instrument for enhancing the cultivation of medicinal plants under adverse environmental conditions.

Origins of sediments and fluids in submarine mud volcanoes off Tanegashima Island, northern Ryukyu Trench, Japan

Mud volcanoes are topographic features through which over-pressurized sediments are intruded upward and erupted, transporting fluids and sediments from the deep subsurface to the surface/seafloor. To understand material and biogeochemical cycling through mud volcanoes, we investigated the origins of sediments and fluids erupted by four submarine mud volcanoes off Tanegashima Island, along the northern Ryukyu Trench: MV#1–3 and MV#14. We estimated the ages of the source sequences of the mud volcano sediments to be middle to late Miocene based on nannofossils and 10Be ages. The sediments were characteristically enriched in illite. The similar mineral compositions and vitrinite reflectance values (0.42%–0.45%) of sediments erupted by the mud volcanoes strongly suggest that each is rooted in the same source sequence. Pore waters had Cl− concentrations ∼40% that of seawater and were proportionally enriched in 18O and depleted in D, indicating the addition of freshwater from the dehydration of clay minerals. However, the smectite and illite contents (<40%) in the clay size fraction ruled out in situ smectite dewatering as the cause of the pore water Cl− dilution. Thus, fluids derived from clay dewatering must have originated from deeper than the source sequence of the mud volcano sediments. Vertical Cl− profiles indicate that the upward fluid advection rate and eruption frequency decrease from MV#3 to MV#2, MV#1, and MV#14 (MV#14 being dormant). At the active mud volcanoes, the C1/C2 ratios (<100) and methane δ13C values (−56‰ to −42‰) indicate that hydrocarbon gases are mostly derived from the thermal decomposition of organic matter in deep sediments where the in situ temperature exceeds 80°C. At the dormant MV#14, high C1/C2 ratios (700–4,000) and low methane δ13C values (ca. −75‰) suggest the limited supply of thermogenic methane and the subsequent shallow methanogenesis. Because vitrinite reflectance values indicate that the source sediments are too immature to produce thermogenic hydrocarbons, the hydrocarbon gases, like the fluids derived from clay dewatering, were probably supplied from deeper than the source strata. The supply of deep fluids into the source sequence might be a universal phenomenon in subduction zones, and may play an important role in mud volcanism and associated biogeochemical cycling.

The Role of Reductive Carbonaceous Surrounding Rocks in the Formation of Porphyry Mo Deposits

Porphyry Mo deposits are the most important type of Mo resource. They result from a high oxygen fugacity of the parent magma, which acts as an effective indicator for evaluating the mineralization. In the ore-forming system of porphyry Mo deposits, sulfur exists mainly as sulfate in highly oxidized magma but as sulfide in ores. What triggers the reduction in the mineralization system that leads to sulfide precipitation has not yet been determined. Most of the previous studies have focused on the origin and evolution of the ore-forming parent magma, and the effects of reductive surrounding rocks on porphyry mineralization have been ignored. In this study, a comprehensive geological–geochemical investigation and review have been performed on the typical porphyry Mo deposits, the Nannihu-Sandaozhuang, Yuchiling, and Shapingou deposits in China, and the Mt. Emmons deposits in America. Black carbonaceous sedimentary layers commonly surround porphyry Mo ores, which are widely altered and discolored during mineralization. CH4 is commonly present in fluid inclusions in the main mineralization stage, and the δ13CV-PDB values of calcite and fluid inclusions from the altered surrounding rocks and ore minerals are generally low and significantly different from those of marine sedimentary carbonate rocks, indicating that the involvement of reductive components from carbonaceous surrounding rocks might be key to the redox state transformation leading to mineral precipitation. On the other hand, the CH4 produced by the thermal decomposition of organic matter or carbonaceous reaction with H2O can diffuse into the ore-forming system along the structural fractures and reduce the SO42− in the ore-forming hydrothermal fluids to form sulfide precipitation without direct contact between the intrusion and the carbonaceous surrounding rocks. Moreover, the CH4 content controls the location of the orebody formation with the high content producing orebodies mainly in the porphyry intrusion, while the low CH4 content results in the orebodies mainly occurring at the contact zone between the porphyry and carbonaceous surrounding rocks. Compared to the magmatic stage of mineralization, the involvement of reductive components in the carbonaceous surrounding rocks during the hydrothermal stage is more favorable for forming giant/large Mo deposits. The highly oxidized porphyry with reductive carbonaceous surrounding rocks or Fe-rich volcanic rocks offers a new indicator for efficiently evaluating porphyry Mo mineralization.

Kilometer-scale Δ13CH3D profiles distinguish end-member mixing from methane production in deep marine sediments

Methane stored in marine sediments can form by microbial and thermal decomposition of organic matter. Identifying the source of methane allows us to assess the potential of natural gas reservoirs and the limits of subsurface microbial life. However, such assessments are complicated by the burial and transport of methane, which can produce mixtures from multiple sources. We measured the abundances of stable isotopes (13C/12C and D/H), clumped isotopologue 13CH3D, and n-alkanes (C1/C2+3, methane over ethane plus propane) for gas samples collected by mud-logging to investigate how 13CH3D can be used to constrain sources of methane. Two kilometer-scale depth profiles representing the transition between microbial and thermal methanogenic zones were analyzed from the northeastern Gulf of Mexico and the western Black Sea. We found that Δ13CH3D values of methane do not follow conservative two-component mixing between shallow microbial methane and deep thermogenic methane transported by advection. Rather, methane isotopologues indicate re-equilibration along geothermal gradients following burial, which continues up to apparent temperatures of 100 ± 15 °C. The re-equilibration is likely microbially catalyzed, although this apparent temperature is ca. 20 °C higher than the putative upper-temperature limit of microbial methanogenesis in marine sediments. Above 150 °C, methane isotopologues are expected to equilibrate along geothermal gradients because the rate of abiotic D/H exchange becomes comparable to that of temperature increase with burial. This study provides novel kilometer-scale profiles of clumped methane isotopologues as a means to trace the upper-temperature limits of microbial activity in hydrocarbon-rich marine sedimentary environments.

Direct H2S, HS− and pH Measurements of High‐Temperature Hydrothermal Vent Fluids With In Situ Raman Spectroscopy

AbstractHydrothermal H2S is an important energy source for hydrothermal ecosystems. However, it is difficult to obtain accurate hydrogen sulfide concentrations in high‐temperature hydrothermal fluids because they are highly susceptible to oxidation and compositional variability with mixing. In this study, a new in situ approach for measuring H2S, HS− and pH in hydrothermal fluids was developed and applied to the detections of Okinawa Trough hydrothermal activities. The in situ total H2S concentrations in the Jade and Biwako fluids were determined to be 31.4 and 76.7 mmol/kg, respectively. The in situ measured pH of the Jade fluids was determined to be 6.3, which has exceeded that of a neutral fluid at a specific temperature and pressure, indicating that the pH of Jade fluids is weakly alkaline. The pH transition of hydrothermal fluids from alkaline to acidic may be attributed to the thermal decomposition of organic matter and sulfide precipitation.

Pyrolysis-induced phosphorus transformations for biosolids from diverse sources.

Biosolids have been long used as a soil amendment to promote nutrient recovery. The readily releasable forms of nutrients present in this biowaste, such as phosphorus (P), along with their over application, can be detrimental to the environment, causing eutrophication. Pyrolysis, the thermal decomposition of organic materials at elevated temperature and low oxygen, seems to be a promising strategy to lower P release from biowastes such as biosolids. We pyrolyzed biosolids from various treatments and locations (Florida and Illinois; Galicia, Spain; and São Paulo, Brazil) to convert to biochar. Our objectives were (a) to use solid-state assessments, such as X-ray diffraction and scanning electron microscopy, and chemical assessments, such as water-soluble P (WSP), pH, Mehlich 3-extractable P (M3-P), total P (TP), and total Kjeldahl nitrogen, to evaluate changes caused by the conversion and (b) to compare P leaching potentials of biosolids and their corresponding biochars on two soils with varying P retention capacities. Pairwise comparisons indicated that biochar conversion significantly increased TP in the final material, but the absolute WSP decreased. However, M3-P remained the same after conversion to biochar. Cumulative P leached as a fraction of TP was greater for biosolids than their corresponding biochars. Two soils with contrasting P retention capacities predictably differed in P leaching behaviors as amended with biosolids and biochars. Differences suggest that future research could evaluate the efficacy of using mixtures of biosolids and biochar for a given soil to maintain soil fertility while reducing environmental P loss risk.

Experimental short-time wildfire simulation—Physicochemical changes of forest mucky topsoil

Today, fires constitute one of the most important factors that can affect soil properties, acting at a rapid pace and on a large scale. They often result from climate change. The present study was aimed at examining how water capacity as well as carbon and nitrogen concentration change during a simulated fire of forest mucky soil under laboratory conditions. The combustion was carried out in two short-time variants—for 3 and 9 min. The results presented herewith show that even a short-term fire of the soil cover contributes to visible changes in the physicochemical parameters of the soil. Thermal decomposition of organic matter caused an increase in total carbon and nitrogen concentrations and a slight increase in the Ct/Nt ratio. The burning of soil samples caused a slight upward trend in soil pH and this was associated with soil organic matter (SOM) deprotonation. The experiment showed the effect of mucky soil burning on the change of its water relations. The 3-min combustion significantly increased the maximum water storage capacity (both after 4 and after 24 h of immersion in water), while the 9-min combustion showed significantly worse results.

Carbon Dioxide and its Carbon Isotopic Composition of Natural Gas in the Sichuan Basin, SW China

The Sichuan Basin, covering an area of 180 × 103 km2, has the following advantages in natural gas geology: The sedimentary rocks are 6,000–12,000 m thick with high maturity of source rocks, and nine sets of primary gas source rocks are developed in the basin with a gas–oil ratio of 80:1, and thus it is a gas basin. The remaining recoverable reserves of conventional and unconventional natural gas are up to 13.6404 × 1012 m3. Multiple gas-bearing systems are developed with 25 conventional and tight oil and gas producing layers and 135 discovered gas fields, and the total proved geological reserves and cumulative production of natural gas by the end of 2019 were 5.7966 × 1012 m3 and 648.8 × 109 m3, respectively. The CO2 components and the correlation with relevant parameters for 243 samples from 22 gas fields indicate that CO2 in the Sichuan Basin display the following two characteristics: (1) Relatively low CO2 content of 0.02%–22.90% with an average of 2.96%, which guaranteed the commerciality of natural gas exploration and production; (2) cratonic CO2, which is characterized by low CO2 contents (<5%) and low R/Ra ratios (<0.24). According to the δ13CCO2 values and the relationship with R/Ra, δ13C1, CO2 contents, and wetness coefficient (W) for 263 gas samples, the δ13CCO2 values display three characteristics: (1) The highest δ13CCO2 value (10.4‰) in China is found in the Fuling shale gas field, which extends the interval values from previous −39‰–7‰ to −39‰–10.4‰. (2) The δ13CCO2 values can be applied to identify the CO2 origin of natural gas in the Sichuan Basin: type A, organic origin from thermal decomposition of organic matter, with an average δ13CCO2 value of −12.8‰ and average wetness coefficient of 7.8% for 44 samples; type B, organic origin from thermal cracking of organic matter, with an average δ13CCO2 value of −15.7‰ and average wetness coefficient of 1.30% for 34 samples; type C, inorganic origin from thermal decomposition or organic acid dissolution of carbonate rocks or minerals, with an average δ13CCO2 value of −1.8‰ and average wetness coefficient of 0.85% for 175 samples. (3) δ13CCO2>δ13CCH4. This is a common characteristic shared by all geological age (from Z2dn to J2s) gas reservoirs and various gas types (coal-derived gas, oil-associated gas, and shale gas).

Functional Group Structure of Bamboo and Pine Wood Biochar Due to Differences in Pyrolysis Temperature

The quality of biochar produced through the pyrolysis process depends on the combustion temperature, duration of combustion, and the raw materials used. Biochar is a carbon-rich product resulting from the thermal decomposition of organic matter. Biochar from bamboo and pinewood was produced at 400℃ and 800℃ using a closed chamber where the temperature could be set. Biochar is made through carbonization with pyrolysis. This study aimed to find out the functional group characteristics of two types of raw materials, bamboo and pine wood. This research was conducted at the Environmental Soil Physics Laboratory, Universitas Syiah Kuala. Two types of feedstocks, bamboo, and pinewood, were used as sample experiments. The feedstocks were burned inside a closed chamber with no oxygen present. (Thermo scientific thermolyne F4820-33). The temperature was at 400℃ and 800℃, and a burning time of four hours. Fourier Transform Infra-Red (FTIR) was used to characterize the functional groups of biochar tested. Our research showed biochar from pinewood burned at a temperature of 400℃ gave the characteristics of the functional groups OH, CH, and C=O with strong intensity. It indicates that there was decomposition of organic matter into organic compounds taking place

Preparation and Characterization of Glass-Ceramic Foam from Clay-Rich Waste Diatomaceous Earth.

In this study, the potential use of waste diatomaceous earth from the production of diatomaceous earth for filtration purposes, as an alternative raw material for foam glass production, was explored. The chemical and mineralogical composition and the high temperature behavior of waste diatomite were studied to assess its suitability for foam glass production. Glass-ceramic foams were prepared using NaOH solution as a foaming agent, via a hydrate mechanism. The influence of different pretreatments and firing temperatures on the foam’s structure, bulk density and compressive strength was investigated. High temperature behavior was studied using TG/DTA analysis and high temperature microscopy. Phase composition was studied using X-ray diffraction analysis. Glass-ceramic foam samples of a high porosity comparable to conventional foam glass products were fabricated. The pretreatment temperature, foaming temperature and sintering holding time were found to have a significant influence on foam properties. With increased pretreatment temperature, pyrogenic carbon from the thermal decomposition of organic matter contained in the raw material acted as an additional foaming agent and remained partially unoxidized in prepared foams. The bulk densities of prepared samples ranged from 150 kg/m3 to 510 kg/m3 and their compressive strengths were between 140 and 1270 kPa.

The effect of plastic type on the yield and quality of lignite and plastic waste pyrolysis products

Lignite is a low rank coal which has great potential in South Kalimantan. However, it has not been used optimally due to its low quality. One of the ways to improve it is pyrolysis. Pyrolysis is the thermal decomposition of organic material in the absence of oxygen which will produce three products (char, tar and gas). Pyrolysis can make lignite into liquid fuel (pyrolysis liquid), but it still requires improvement due to the need for pure hydrogen donors. Plastic waste has a higher hydrogen/carbon ratio than coal. This material can be used as an additive in the pyrolysis process because it is rich in hydrogen. The samples of plastic waste used were ppolyethylene (PE), ppolypropylene (PP), and polystyrene (PS). Samples of lignite and plastic (plastic composition was 25 wt%) were used for every experiment, and pyrolysis was carried out with a holding time of 60 minutes at 500°C. The pyrolysis liquid obtained is then analyzed for its yields and properties (density, kinematic viscosity, heating value). The most feasible result for fuel alternative was obtained with the addition of PE.

Chemical speciation and risk assessment of heavy metals in biochars derived from sewage sludge and anaerobically digested sludge.

Dewatered sewage sludge (DSS) and anaerobically digested sludge (ADS) were pyrolyzed at 550 °C to investigate the characteristics of derived biochar and evaluate the risk of heavy metals (Cr, Ni, Cu, As, Cd, and Pb). The results showed that the pH value of the biochar derived from DSS (DSS-C) was slightly lower than that of the biochar derived from ADS (ADS-C), while DSS-C presented relatively higher specific surface area and total pore volume. DSS-C also showed higher H/C and lower O/C ratios than ADS-C, indicating a higher aromatic condensation and a lower polarity. Total concentrations of Cr, Ni, Cu, As, Cd, and Pb in DSS and ADS increased significantly after pyrolysis owing to the thermal decomposition of organic matter in the sludge, with corresponding rise of the Nemerow pollution index (NPI) of the biochars compared with the raw sludge. In addition, the sequential extraction procedure (BCR) analysis revealed that the pyrolysis process promoted the transformation of heavy metals from bio-available fractions to stable fractions. The potential environmental risk of heavy metals decreased from moderate and extremely high levels in the DSS and ADS to low risk and moderate levels in DSS-C and ADS-C after pyrolysis, respectively.

Organic compounds in vent fluids from Yellowstone Lake, Wyoming

Hydrothermal fluids were collected over a three-year interval (2016–2018) from two sublacustrine vent fields in Yellowstone Lake, Wyoming: Stevenson Island Deep Hole (YL16 and YL17 series in 2016 and 2017, respectively) and West Thumb (YL18 series in 2018). The TOC content in SI Deep Hole vent fluids varies from 2.7 mg/L to 6.3 mg/L in YL16 and 5.0 mg/L to 16.2 mg/L in YL17. Compared to YL16, the average TOC value of YL17 has more than doubled. The range of TOC is from 7.3 mg/L to 13.7 mg/L in the West Thumb samples. A positive correlation between TOC and dissolved CO2 concentration is observed in most samples, suggesting their close relationship with sublacustrine heat and mass transfer processes. The organic compounds detected at both vent fields are diverse in molecular structure. In the SI Deep Hole, complex cyclic and unsaturated organic compounds are dominant, with cyclic hydrocarbons having the highest abundance, followed by carboxylic acids, PAHs, and alcohols. At West Thumb vents, propanol is most abundant, followed by alcohols, PAHs, alkanes, and carboxylic acids. This difference in structural complexity and relative quantity of organic compounds may be attributed to the involvement of hydrothermal processes. The vapor-dominated hydrothermal system and extensive fluid-rock interactions in SI Deep Hole facilitate alteration/decomposition of organic precursors. While CO2(aq) is predominant in vent fluids, dissolved CH4 is much less abundant. In SI Deep Hole, the carbon isotopic composition of CH4 in most samples ranges from −20.4‰ to −38.0‰, with values of less than −60‰ in three samples, while CO2 ranges from −4.4‰ to −10.5‰. A temporal variation of δ13C values was obtained for CO2, with the average increasing from −9.2‰ (YL16) to −5.2‰ (YL17). In West Thumb, the δ13C value of CO2 and CH4 fall in a similar range, with an average of −10.5‰ and −19.0‰, respectively. There are multiple sources for observed carbon species: the interaction of vent fluids with subsurface rocks and lake sediments is the predominant process, followed by thermal decomposition of organic matter. Microbial activity on the lake floor may contribute to methane formation, while magmatic degassing is the major process that produces CO2. The connection between vapor-dominated hydrothermal alteration, elevated TOC contents and dissolved CO2 in vent fluids, and enrichment of 13C in CO2 in YL17 in SI Deep Hole suggests an interplay of geological, chemical, and biological processes and their imprints on vent fluids, all of which make significant contribution to the carbon cycle in the Yellowstone Lake ecosystem.

Thermal Behavior of Oil Shale Pyrolysis under Low-Temperature Co-Current Oxidizing Conditions.

The thermal behavior of the Huadian oil shale during low-temperature co-current oxidizing pyrolysis was studied by lab-scale experiments under different basic pyrolysis temperatures and input gas flow rates. The results showed that, in the process of oil shale co-current oxidizing pyrolysis, the increasing input gas flow rates under the same basic pyrolysis temperatures can significantly enhance the heat generation of oil shale. Meanwhile, it can be seen from the temperature variation characteristics of oil shale that the heat released by the oxidation reaction of semicoke and oxygen is enough to support the thermal decomposition of organic matter without supplemental heating. Moreover, it can be concluded from the 92.06% effective recovery of shale oil that a high yield of oil without a significant loss can be achieved. Finally, compared with increasing basic pyrolysis temperatures, the increased input gas flow rates have a more obvious effect on improving the effective recovery of shale oil.

Study on pyrolysis kinetics and reaction mechanism of Beizao oil shale

The evaluation of pyrolysis kinetics and the reaction mechanism of organic matter and mineral matrix for oil shale is a rather difficult work due to the concomitant structure and complicated reactions. The pyrolysis process of Beizao oil shale was studied in a thermogravimetric analyzer at various heating rates with obvious existence of two stages. The kinetic parameters were estimated via a model-free method known as Friedman method and a multistep model-fitting method called Coats-Redfern method. A two-stage reaction model is proposed based on thermogravimetric analysis and the obtained kinetic parameters. The results indicated that the reaction model g(α) = −[ln(1 − α)]2 might be in charge of Stage I, and reaction mechanism for Stage II could be interpreted by g(α) = −[ln(1 − α)]3. Furthermore, the curve of conversion rate α was predicted based on the obtained kinetic parameters, and the reaction parameters and models were validated by an extra heating rates beyond those used to generate them. It was speculated that the two-stage reactions could be attributed to the thermal decomposition of organic matter with bitumen as intermediate in Stage I, and the devolatilization of inorganic components, mainly clay aluminosilicates and calcite, in Stage II.