Low-temperature Thermal Desorption Research Articles

Damage Accumulation and Recovery Involving Vacancy-Type Defects Enhanced by Hydrogen in Tempered Martensitic Steel Showing Quasi-Cleavage Fracture

Hydrogen embrittlement (HE) is increasingly becoming a critical issue for using high-strength steels in the automotive and infrastructure industries. To overcome the risk posed by HE of structural components under a hydrogen uptake environment in long-term service, it is necessary to clarify the mechanism of HE. In the present study, the presence of hydrogen-enhanced strain-induced vacancies (HESIVs)—one type of defect associated with proposed HE mechanisms—was validated by low-strain-rate tensile tests with in-situ electrochemical hydrogen charging for tempered martensitic steel showing quasi-cleavage fracture with a tensile strength. The effect HESIVs on the mechanical properties of tempered martensitic steel was also studied. The combined use of low-temperature thermal desorption spectroscopy and tensile tests led to the following observations: (i) hydrogen enhanced the accumulation of vacancy-type defects under plastic strain, (ii) accumulated vacancy-type defects adversely affected the ductility of the tempered martensitic steel after hydrogen release, and (iii) aging at 150 °C after applying a given plastic strain with hydrogen charging decreased the amount of newly formed vacancy-type defects and resulted in recovery of ductility.

Activated carbon with high mesopore ratio derived from waste Zanthoxylum bungeanum branches by KNO3-assisted H3PO4 staged activation for toluene adsorption.

Waste Zanthoxylum bungeanum branches were used to prepare activated carbon adsorbents with high mesopore ratio by H3PO4 staged activation method with adding KNO3 additive. The prepared activated carbon adsorbents were characterized by SEM, BET, FT-IR, and XRD. The adsorption properties of the prepared activated carbon adsorbents were evaluated by the toluene adsorption/desorption in air. The quasi-first-order, quasi-second-order, and Bangham models were used to fit the obtained toluene adsorption results. The oxidative etching of KNO3 additive improved the pore-forming ability of the H3PO4 activator to enhance the activation pore-forming effects of the selected biomass raw material. The secondary pore-forming effects of K atoms promoted the effective expansion of the pore diameter in the activated carbon preparation process to prepare activated carbon adsorbents with high mesopore proportion. The specific surface area and mesopore proportion of the activated carbon adsorbents prepared by adding KNO3 additive exceeded 1100 m2/g and 71.00%, respectively, and the toluene adsorption capacity exceeded 370.00 mg/g. The rich mesopore structures can effectively reduce the toluene mass transfer resistance, which can promote the corresponding activated carbon adsorbent to be regenerated by low-temperature (40 °C) thermal desorption. The toluene adsorption on the prepared activated carbon adsorbents includes surface adsorption and diffusion in pore structures, and the toluene adsorption mechanism is more consistent with the Bangham kinetic model.

Quantitative hydrogen trap states on high-angle grain boundaries and at dislocations in iron

Low-temperature thermal desorption spectrometry (L-TDS), by which specimens can be heated from -200 °C, was used to quantitatively evaluate the hydrogen desorption peak temperatures (Tp), the hydrogen desorption activation energies (Ea), and the hydrogen occupation ratios (θ) of high-angle grain boundaries and dislocations in iron. Cold-rolled iron was subjected to recrystallization and grain growth to produce three kinds of specimens with different areas of high-angle grain boundaries, in which low-angle grain boundaries were annihilated. L-TDS spectra of specimens containing dislocations and high-angle grain boundaries displayed two hydrogen desorption peaks, denoted as Peak 1 and Peak 2. Peak 1 corresponded to dislocations and displayed Tp, Ea, and θ values of 23 °C, 28.6 kJ·mol−1, and 1.1 to 2.7 atom·nm−1, respectively. In contrast, Peak 2 corresponded to high-angle grain boundaries and displayed Tp, Ea, and θ values of 85 °C, 43.7 kJ·mol−1, and 2.3 to 2.9 atom·nm−2, respectively.

Experimental investigation on electromagnetic induction thermal desorption for remediation of petroleum hydrocarbons contaminated soil

A novel electromagnetic induction low temperature thermal desorption treatment (EMI LTTD) for petroleum hydrocarbons contaminated soil was introduced in this work. The removal rate of total petroleum hydrocarbons (TPH) under various factors, the morphology changes of soils as well as removal mechanism were investigated. Results suggested that increasing the heating temperature significantly increased the removal rate of TPH. At the beginning of 20 min, most of hydrocarbons (93.44–96.91 wt%) was removed with the temperature ranged from 200 °C to 300 °C. Besides, the initial contaminants concentration, particle size and thickness of soil slightly influenced the removal rate of TPH. Desorption kinetic study demonstrated that first-order model was well-described for desorption behavior. Response surface methodology analysis showed the temperature of 216 °C, the residence time of 21 min and the moisture content of 18% was an optimum condition recommended for potentially practical application. Under this condition, the results for the composition of hydrocarbons based on carbon number fractions indicated that the fractions of C10∼C16, C17∼C22 still existed in soil, while C23∼C28 was not detected after EMI LTTD treatment. Proposed mechanism was both hydrocarbons removed by evaporation at any temperature, while parts of heavy hydrocarbons was cracked within the soil close to induction medium, resulting in re-adsorption of light hydrocarbons. A buckwheat germination and growth test indicated that soil treated by EMI LTTD was potential in reutilization for planting.

Enhancing low-temperature thermal remediation of petroleum sludge by solvent deasphalting.

Thermal treatment is a promising technique for treating petroleum sludge (PS). However, asphaltenes as a recalcitrant fraction of PS induce strong bounding between petroleum and minerals, and therefore lead to the need for high temperature and hence high energy consumption in thermal treatment of PS. In this study, a novel method combining a deasphalting pretreatment of PS with low-temperature thermal desorption (LTTD) was developed. The efficiency of deasphalting was found to be positively correlated to the ability of n-alkanes and asphaltene dispersants in dispersing asphaltenes. In treating six different kinds of PS, the residual oil contents were all below 2.5% after the deasphalting alone. Compared with direct thermal desorption at 600°C for 1h, dodecyl benzene sulfonic acid (DBSA)-assisted heptane deasphalting made thermal desorption at 350°C for 1h sufficient to treat these APS. The residual oil content of sludge after LTTD is lower than 0.45%. FT-IR, Raman spectra and XPS analysis confirmed that the carbon residue in APS after LTTD is primarily graphite state, which is extremely stable and does not migrate to the surrounding environment as compared with the crude oil in the APS. Hence, solvent deasphalting results in effective treatment of PS by LTTD, while the solvent can be recycled by distillation and crude oil recovered as value-added petroleum resource. The LTTD represents therefore a novel green strategy for treating PS and resource utilization.

Preparation of an overall intergranular fracture surface caused by hydrogen and identification of lattice defects present in the local area just below the surface of tempered martensitic steel

An overall intergranular (IG) fracture surface was prepared in a load reduction test and analyzed by low-temperature thermal desorption spectroscopy (L-TDS). The purpose was to clarify on the atomic scale lattice defects present in the local area just below the surface of a hydrogen-induced IG fracture in tempered martensitic steel. The tracer hydrogen peak corresponding to vacancies and vacancy clusters was present just below the IG fracture surface. Local plasticity and nano-voids were observed on and near the prior austenite grain boundaries by the combined use of electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI). These findings clearly indicate that local plastic deformation and associated vacancy formation play an essential role in hydrogen-induced IG fracture in tempered martensitic steel.

Sustainable remediation of dibenzofuran-contaminated soil by low-temperature thermal desorption: Robust decontamination and carbon neutralization.

Thermal desorption (TD) is generally considered to be an effective but unsustainable technology. Decontamination performance, charring behaviors and physicochemical properties during TD of dibenzofuran-contaminated soil (DCS) are explored. After treatment at 300°C for 20min, the dibenzofuran concentration decreases from 3969.37mg/kg to 17.29mg/kg, lower than Chinese risk screening value. More than 99% of dibenzofuran in soil are removed at low temperature of 300°C, meanwhile the organic carbon is partially retained in soil. Removal mechanism of DCS at 300°C is proposed, including desorption, cracking, and charring. Char material of low H:C ratio is produced by the generation, polymerization and dehydrogenation of aromatic intermediates, and then increases carbon stocks and reduces the carbon footprint of contaminated soil. Meanwhile, due to the char generated, pH, cation exchange capacity and specific surface area of DCS heated at 300°C are higher than those of raw DCS, promoting ecological restoration and enhancing carbon sink in soil ecosystems. The aforesaid saving energy, reducing carbon footprint and enhancing carbon sink are exactly the main innovative technologies for achieving carbon neutrality. Hence, it may be a contribution to climate change mitigation, in addition to a robust and sustainable remediation of organic contaminated soil.

Insight into the desorption behavior and mechanism of tight oil with in-situ low-temperature thermal

A major challenge faced in using enhanced oil recovery techniques in tight sandstone reservoir is the unknown desorption mechanism of adsorbed oil in the reservoirs. In-situ low-temperature thermal desorption (LTTD) was used in this study to detect the desorption behavior and mechanism of tight oil found in tight sandstones. The study provides an insight into the micro-occurrence states, carbon number-based fractions, and functional group changes of adsorbed tight oil. The micro-occurrence states of adsorbed tight oil can be in the form of oil aggregate and oil film. The desorption capacity of tight oil present in tight sandstones at 120 °C, 160 °C, 200 °C, 240 °C and 280 °C were 0.028, 0.171, 0.886, 0.945 and 0.954 mg/g, respectively. The desorption behavior of tight oil reverses at approximately 200 °C. At temperatures below 200 °C, desorption of tight oil is dominated by the oil aggregate in the 20–200 nm reservoir space, while the desorption process itself is controlled by the original physical properties, skeleton minerals and original oil saturation level of the tight sandstone reservoir. However, at temperatures above 200 °C, clay minerals control the desorption of tight oil present in form of an oil film adsorbed on the 2–7 nm sized pores of the mineral surface. During the process of in-situ conversion of tight oil, the amount of aliphatic compounds in it decreases, the amount of aromatic compounds in it increases, and the branching chain degree increases. As the temperature increases, the oxygen-containing functional groups continue to increase in number.

Isotope-selective pore opening in a flexible metal-organic framework.

Flexible metal-organic frameworks that show reversible guest-induced phase transitions between closed and open pore phases have enormous potential for highly selective, energy-efficient gas separations. Here, we present the gate-opening process of DUT-8(Ni) that selectively responds to D2, whereas no response is observed for H2 and HD. In situ neutron diffraction directly reveals this pressure-dependent phase transition. Low-temperature thermal desorption spectroscopy measurements indicate an outstanding D2-over-H2 selectivity of 11.6 at 23.3 K, with high D2 uptake. First-principles calculations coupled with statistical thermodynamics predict the isotope-selective gate opening, rationalized by pronounced nuclear quantum effects. Simulations suggest DUT-8(Ni) to remain closed in the presence of HT, while it also opens for DT and T2, demonstrating gate opening as a highly effective approach for isotopolog separation.

Low-Temperature Thermal Desorption Effectively Mitigates Accumulation of Total Mercury and Methylmercury in Rice (Oryza sativa L.).

For maximally reserving soil fertility, two critical parameters (i.e. time and temperature) of low-temperature thermal desorption (LTTD) were initially optimized to remediate the mercury-contaminated soil from a mercury mining area. The effect of LTTD on soil properties was investigated, and the bioaccumulation of total mercury (THg) and methylmercury (MeHg) in rice (Oryza sativa L.) were researched via a pot experiment. Results indicated that the physicochemical properties and fertility of the soil after LTTD still meet the requirements of rice growth. Moreover, the concentrations of THg and MeHg in the remediated soil were decreased by 94.1% and 98.8%, respectively. Further, the bioavailability of Hg in soil was significantly reduced. More importantly, the concentrations of THg and MeHg in the seed of rice plant cultivated on the remediated soil were decreased by 57.6% and 80.2%, respectively. Overall, LTTD technology could efficiently remediate Hg-contaminated soil and be a promise remediation strategy.

The effects of interstitial hydrogen and carbon atoms and aging temperature on annihilation behavior of hydrogen-enhanced strain-induced vacancies in iron

The effects of interstitial hydrogen and carbon atoms and aging temperature on the annihilation behavior of hydrogen-enhanced strain-induced vacancies (HESIVs) in iron were examined using low-temperature thermal desorption spectroscopy (L-TDS) that can raise the temperature from −200 °C. Specimens containing HESIVs were aged under various conditions and charged with tracer hydrogen for detecting lattice defects. Atmospheric aging at 30 °C reduced small vacancies such as single vacancies and divacancies, which were thermally unstable, with increasing aging time, however, clustered vacancies remained after 7 days. In contrast, aging at −196 °C hardly caused any vacancy diffusion, aggregation, or annihilation. Aging in the presence of hydrogen and carbon at 30 °C reduced the rate of vacancy annihilation and left more vacancies, respectively. These findings indicate that interstitial hydrogen and carbon atoms in iron suppress the diffusion and annihilation of vacancies, resulting in vacancy stabilization.

Quantities and distribution of strain-induced vacancies and dislocations enhanced by hydrogen in iron

The role of hydrogen in the formation behavior of various lattice defects induced by plastic strain in pure iron specimens has been investigated using low-temperature thermal desorption spectroscopy (L-TDS), which can start measurement from −200 °C. Specimens were subjected to various plastic strains within a uniform elongation range in the absence and presence of hydrogen. Strain-induced lattice defects were quantitatively evaluated using L-TDS for specimens saturated with hydrogen as a probe for detecting lattice defects, not only vacancies but also dislocation cores. The L-TDS spectra contained two hydrogen desorption peaks: a low-temperature peak associated with dislocations and a high-temperature peak associated with vacancies. The tracer hydrogen content corresponding to each peak increased with plastic strain. However, when compared at the same plastic strain of 25%, the low-temperature peak, i.e., dislocations, was not enhanced by hydrogen, whereas the high-temperature peak, i.e., vacancies, was enhanced by hydrogen, increasing by about six times at 25% plastic strain and by seven times at 40% plastic strain. Analyses conducted by electron channeling contrast imaging (ECCI) and electron backscattered diffraction (EBSD) revealed that strain was localized along the vicinity of the ferrite grain boundaries at 25% plastic strain in the presence of hydrogen. Hence, the role of hydrogen in the formation behavior of plastic strain-induced lattice defects is presumably to enhance vacancy formation and the localization of the dislocation configuration near the grain boundaries without affecting the amount of dislocations formed.

Changes in Soil Health with Remediation of Petroleum Hydrocarbon Contaminated Soils Using Two Different Remediation Technologies

For sustainable soil management, there is an increasing demand for soil quality, resilience, and health assessment. After remediation of petroleum hydrocarbon (PHC)-contaminated soils, changes in the physicochemical and ecological characteristics of the soil were investigated. Two kinds of remediation technologies were applied to contaminated soils: land farming (LF) and high temperature thermal desorption (HTTD). As a result of total petroleum hydrocarbons (TPH), PHC-contaminated soils were efficiently remediated by LF and HTTD. The soil health could not be completely recovered after the removal of pollutants due to adverse changes in the soil properties, especially in soil enzyme activities. Therefore, monitoring is necessary for accurate estimation of soil ecotoxicity and effective remediation, and additional soil management, such as fertilizer application or organic amendments, is needed to restore soil heath. In the case of HTTD, soil ecological properties are severely changed during the remediation process. The decision to reuse or recycle remediated soils should reflect changes in soil quality. HTTD is a harsh remediation method that results in deterioration of soil fertility and ecological functions. Alternatives, such as low-temperature thermal desorption or additional soil management using fertilizer or organic amendments, for example, are needed.

Low-temperature thermal desorption and secure landfill for oil-based drill cuttings management: Pollution control, human health risk, and probabilistic cost assessment

Oil-based drill cuttings (OBDCs) were managed in two scenarios including low-temperature thermal desorption (LTTD) and secure landfill through a case study. The removal of polycyclic aromatic hydrocarbons (PAHs) and heavy metals in OBDCs by LTTD under different conditions was investigated. Probabilistic human health risk assessment was performed to quantify the health risk posed to waste management workers under the two scenarios, while the associated costs were also analyzed. The results show that LTTD at 300 °C for >20 min could remove 96.27% of PAHs in OBDCs but its removal effect on heavy metals was not significant. It was found that cancer risks posed by PAHs in both securely landfilled and LTTD-treated OBDCs were not significant (<1e-06); however, significant cancer risks (7.95e-05–9.45e-05) were identified for exposure to toxic heavy metals. Increased health risk was observed as a result of exposure to LTTD treatment residues compared to securely landfilled OBDCs. Inhalation of chromium(VI) and oral ingestion of arsenic in OBDCs were critical exposure routes. Both cancer and non-cancer risks in the secure landfill scenario were negligible. The cost analysis results suggest that LTTD combined with stabilization/solidification could be more economically attractive than secure landfill for the handling of OBDCs.

Life cycle assessment of low-temperature thermal desorption-based technologies for drill cuttings treatment

The life cycle impacts of treatment of typical oil-based drill cuttings (OBDCs) using three low-temperature thermal desorption (LTTD)-based systems, including thermomechanical cuttings cleaner (TCC), screw-type dryer (STD), and rotary drum dryer (RDD), were explored with a case study in British Columbia, Canada. Two energy supply scenarios, including diesel generator-based onsite (scenario i) and hydropower-based offsite (scenario ii) treatments, were considered in the assessment. The results show that RDD generated the lowest life cycle impacts in terms of damages to human health, ecosystems, and resources in scenario i. TCC-scenario ii generated the lowest impacts among all assessed cases, suggesting that using renewable energy can greatly reduce the impacts of LTTD-based OBDCs treatment. Also, net environmental benefits could be achieved considering the reuse of recovered oil, and the highest net environmental benefits were obtained in TCC-scenario ii. The process contribution analysis found that thermal desorption process accounted for 80–95 % of impacts in almost all impact categories. Energy consumption contours and linear regression models were also developed to help drilling waste managers estimate the life cycle impacts of using hydropower-driven TCC to treat OBDCs with different water and oil contents.

Comparing performances, costs and energy balance of ex situ remediation processes for PAH-contaminated marine sediments.

This study proposes a comparison of different ex situ technologies aimed at the removal of polycyclic aromatic hydrocarbons from marine sediments in terms of performances, costs and energy balance. In accordance with the principles of water-energy nexus, anaerobic bioremediation, soil washing and thermal desorption were investigated under low liquid phase and temperature conditions using phenanthrene (PHE) as model compound. After 42days of anaerobic bioremediation, the highest PHE biodegradation of 68 and 64% was observed under denitrifying and methanogenic conditions, respectively, accompanied by N2 and CH4 production and volatile fatty acid accumulation. During soil washing, more than 97% of PHE was removed after 60min using a solid-to-liquid ratio of 1:3. Along the same treatment time, low-temperature thermal desorption (LTTD) allowed a PHE removal of 88% at 200°C. The economic analysis indicated that LTTD resulted in a higher cost (i.e. 1782 €m-3) than bioremediation and soil washing (228 and 371 €m-3, respectively). The energy balance also suggested that bioremediation and soil washing are more sustainable technologies as a lower required energy (i.e. 16 and 14kWhm-3, respectively) than LTTD (i.e. 417kWhm-3) is needed.

Direct detection of chemical warfare agent simulants in soil by thermal desorption-low temperature plasma-mass spectrometry

For rapid, accurate and real-time detection of trace chemical warfare agents in soil, direct detection of chemical warfare agent simulants in soil by thermal desorption-low temperature plasma ionization-mass spectrometry was developed. Multi-factor analysis of variance was used to quantitatively analyze the factors affecting the ionization efficiency of low temperature plasma based on the emission spectra of the plasma flame. The experimental parameters including the distance between low temperature plasma outlet and thermal desorption device, the flow rate of discharge gas, the temperature of ion source, the thermal desorption temperature and different solvents were optimized. Dimethyl methylphosphonate (DMMP, G-series nerve agent simulant), tributyl phosphate (TBP, V-series nerve agent simulant) and 2-Chloroethyl ethylsulfide (CEES, H-series blister agent simulant) were desorbed and ionized, forming the typical positive ions of [DMMP + H]+, [DMMP-HOCH3+H]+, [TBP + H]+, [TBP-3(C4H8)+H]+ and [CEES-Cl]+, [CEES- C2H4Cl]+. The ions were analyzed using the multiple reaction monitoring (MRM) of triple quadrupole mass spectrometer. Detection limit of the method was 5 pg for DMMP (m/z 125→93, S/N＞3:1), 5 pg for TBP (m/z 267→99, S/N＞3:1) and 5 ng for CEES (m/z 89→61, S/N＞3:1). Trace level of CWA simulants can be directly detected with simple sample pretreatment, suggesting that the thermal desorption-low temperature plasma-mass spectrometry method is useful for quick and direct detection of chemical warfare agents in soil.

Remediation of oil-based drill cuttings using low-temperature thermal desorption: Performance and kinetics modeling

A bench-scale apparatus was used for the low-temperature thermal desorption (LTTD) treatment of oil-based drill cuttings (OBDCs). The effects of treatment temperature, treatment duration, sand/OBDCs mixing ratio, and initial oil content on the LTTD treatment performance were investigated. It was found that the petroleum hydrocarbons (PHCs) were barely left in the high-oil-content drill cuttings after LTTD (at 300 °C for 20 min), and thus the overall soil health was improved. The desorption kinetics models of PHCs under various conditions were established, and it was found that the LTTD of OBDCs followed nonlinear least-squares exponential kinetics (adjusted R2 > 0.9). The energy consumption models of LTTD treatment under different temperatures were also developed. The modeling results are of practical guiding significance and useful for designing effective LTTD treatment systems of OBDCs.

Static decontamination of oil-based drill cuttings with pressurized hot water using response surface methodology

Separating organic pollutants from oil-based drill cuttings (OBDC) is the current trend for its safe disposal. In this study, pressurized hot water extraction (PHWE) was adapted to decontaminate OBDC for the first time. Two typical OBDC samples, i.e., diesel-based drill cuttings (OBDC-A) and white oil-based drill cuttings (OBDC-B), were statically extracted in a homemade batch autoclave. Response surface methodology (RSM) with a central composite design (CCD) was applied to investigate the effects and interactive effects of three independent operating parameters (temperature, extraction time, and water volume) and to ultimately optimize the PHWE process. The results suggested that temperature is the dominant parameter, followed by water volume and extraction time. Interactive effects among the three parameters are present in the PHWE of OBDC-A but absent in the PHWE of OBDC-B. The suitable conditions for the effective PHWE of OBDC-A were found to be a temperature of 284-300°C, water volume of 15-35ml, and extraction time of 20-60min. The corresponding conditions were 237-300°C, 15-35ml, and 20-60min for the PHWE of OBDC-B. These different phenomena are caused by the different characteristics of the two OBDC samples. All of the polynomial models obtained from the RSM experiments are very valid and can adequately describe the relationship among the three independent operating parameters and responses. The experimental results also confirmed that PHWE is a more efficient separation technique for decontaminating OBDC than single organic solvent extraction or low-temperature thermal desorption because PHWE integrates the advantages of both these processes.

Changes in the substructure of tempered martensitic steel during the application of cyclic elastic stress in the presence of hydrogen

Changes in the substructure of tempered martensitic steel during the application of cyclic elastic stress in the presence of hydrogen have been investigated. Three types of specimens were prepared. The first type was subjected to cyclic elastic stress (strain rate: 3.0×10-4 s−1, number of cycles: 70000, and stress level: 0.8±0.1 σB) without hydrogen. The second type was subjected to cyclic elastic stress with hydrogen. The third type was prepared by annealing the second type at 200 °C for 2 h. These specimens are denoted here as [(n)-cycled], [H+(n)-cycled] and [H+(n)-cycled+annealed] specimens, respectively. Tracer hydrogen was used as a probe for clarifying changes in the specimen substructure. After tracer hydrogen charging, hydrogen states present in the specimens were examined using low-temperature thermal desorption spectrometry (L-TDS). Tracer hydrogen desorption in the high-temperature range from the [H+(n)-cycled] specimen increased compared with that from the [(n)-cycled] specimen. In addition, tracer hydrogen desorption in the high-temperature range from the [H+(n)-cycled+annealed] specimen was reduced by annealing at 200 °Cto the level of the [(n)-cycled] specimen. As a result, it is inferred that the formation of vacancy type defects was enhanced under the application of cyclic elastic stress in the presence of hydrogen.