Hydrothermal Stabilization Research Articles

Влияние верхнего граничного условия на гидротермическое поле земляного полотна железных дорог в районах вечной мерзлоты

Purpose: Based on numerical model that takes into account the hydrothermal interrelation of soil humidity and temperature, to carry out numerical modeling of hydrothermal field of railway subgrade in the area of permafrost spread. To study the influence degree of global warming and temperature annual amplitude on hydrothermal field of subgrade. To determine the need for reasonable and economical engineering measures to ensure the stability of subgrade. Method: Calculation of hydrothermal bonding of railroad subgrade has been performed in COMSOL Multiphysics software with the use of partial differential equation (PDE) module with the methods of finite elements. Different values of the parameters of subgrade upper boundary temperature function are specified and the effect of these parameters on subgrade hydrothermal field is studied. Results: Based on measured data temperature function, the influence of global warming effect and temperature annual amplitude on subgrade hydrothermal field was determined. Change law and characteristics of temperature distribution, ice content and unfrozen water in railway subgrade in permafrost areas after hydrothermal field stabilization has been obtained. The periods of maxima and minima onset for temperature as well as for ice content and unfrozen water are given. Practical significance: The use of given numerical model allows to predict effectively the tendency of subgrade hydrothermal field change in permafrost areas under global warming influence. Based on the numerical calculation results, relevant technical recommendations are shown for elimination or reduction of engineering accidents caused by temperature changes in permafrost regions.

Minimizing rare earth content of FCC catalysts: Understanding the fundamentals on combined P-La stabilization

Fluidized Catalytic cracking (FCC) is one of the main conversion processes in conventional refineries and employs a multicomponent catalyst with Y zeolite as the main source of activity and selectivity towards value added products. In order to meet the severe requirements of the FCC unit, the hydrothermal stability of this large pore zeolite is traditionally improved by means of controlled hydrothermal treatments that can be combined with acid washing cycles, with rare earth (RE) ion exchange or with a combination of both. Phosphorus has also been described as a hydrothermal stabilization element. Although most of the studies are based on ZSM-5 zeolites, a new Y zeolite containing FCC catalyst, PhinesseTM, was developed recently. This catalyst, based on the partial substitution of RE by P allowed obtaining the same activity and the same yields to the main products as its conventional RE stabilized counterpart in the catalytic cracking of a vacuum gas oil (VGO). In this work, we present a systematic study where the hydrothermal stability of P- and La-free USYs with different dealumination degrees is compared with that of the corresponding USYs containing P or La alone or a combination of both stabilizing elements. The samples have been thoroughly characterized and their catalytic performance has been tested in a MAT unit. According to the results obtained, when using RE alone, only high contents (> 3.5 wt% RE) are able to stabilize the catalysts towards steaming under severe conditions (100% steam, 750 ºC). However, lower RE ( wt%) can lead to similar hydrothermal stabilization when combined with intermediate phosphorus contents (∼1.0 wt%). The results obtained provide the bases for understanding the reasons behind the benefits of this combined P-La stabilization observed for the commercial Phinesse™ catalyst as compared to a high REO catalyst.

Process and mechanism of hydrothermal stabilization for arsenic sulfide sludge containing elemental sulfur

An optimized hydrothermal treatment was employed to stabilize the arsenic sulfide sludge (ASS). Under the optimal conditions (160 °C, 2 h, liquid-to-solid (L/S) ratio of 1:1, and initial pH of 2), the leaching concentrations of As and Cd decreased from 504.0 and 12.0 mg/L to 1.23 and 0.03 mg/L of the treated ASS, respectively. The results indicate that the stabilization of the ASS was achieved through structure transformation from the particles into a bulk and the speciation transformation of As and Cd. Besides, sulfur in the ASS could significantly improve the stabilization property due to its melting and polymerization.

Transformation behavior of the morphology, structure and toxicity of amorphous As2S3 during hydrothermal process

Arsenic sulfide sludge (ASS) is a typical hazardous waste in the non-ferrous smelting industry. In our previous study, ASS was effectively stabilized by hydrothermal treatment. However, the mechanism of hydrothermal stabilization is still unclear. Amorphous As2S3 is the main component of ASS. Therefore, in this work, the hydrothermal transformation behavior of amorphous As2S3 precipitated with NaAsO2 and Na2S·9H2O under acidic aqueous was investigated for a better understanding of hydrothermal stabilization process of ASS. It was found that under the conditions of 210 °C, initial pH 2 and solid-to-liquid (S/L) ratio 1:5, amorphous As2S3 floc gradually transformed to spherulitic particles and showed aggregation behavior with the extension of hydrothermal duration. The spherulitic particles were identified as orpiment, which was the crystalline arsenic mineral in the nature. Moreover, the As leaching concentration of hydrothermal products decreased remarkably with the transformation from amorphous As2S3 to orpiment. Under certain hydrothermal conditions, the As leaching concentration of amorphous As2S3 can be reduced from 139.4 mg/L to less than 5 mg/L. Hence, the mineralization from amorphous As2S3 to orpiment was the significant reason for the stabilization of arsenic sulfide during hydrothermal treatment. This paper provided a theoretical support for the hydrothermal stabilization of ASS.

Enhancing hydrothermal stability of framework Al in ZSM-5: From the view on the transformation between P and Al species by solid-state NMR spectroscopy

HZSM-5, with good surface acidity and shape selectivity, was reported as hydrocarbon cracking catalyst for multiple decades, however the hydrothermal stability, especially dealumination of tetrahedrally coordinated framework aluminum (TFAl), has been proved extensively as one of the major challenges during reaction-regeneration process. Phosphorus was proposed to stabilize TFAl and indeed it enhanced the hydrothermal stability. Unfortunately, most of the phosphorus species would remain outside of the zeolite pore, mainly as polyphosphate species, and block the micropore severely, with only a limited portion introduced into the channel being able to interact with TFAl. Enlarging the pore size by alkali treatment (desilication) is one of the most convinced methods, but the details about specific P species during alkali treatment and its transformation upon hydrothermal activation is not acquired, thus the mechanism has not been fully understood. Herein, the P-containing species and its transformation during direct P modification and acid/alkali treatment followed by P modification have been studied, and the mechanism on the interaction between P and Al species has been investigated, using several analytical methods, especially Solid-state nuclear magnetic resonance (SSNMR) spectroscopy. It was found that the combination of desilication and subsequent phosphorus modification can enhance the activity of the ZSM-5 for the cracking of ethylcyclohexane, due to the better hydrothermal stabilization of acid sites by the enhanced interaction between phosphorus and TFAl, resulting from the improved accessibility of TFAl because of the successful generation of mesoporosity. Whereas the acid treatment followed by phosphorus modification, with declined retention of crystallinity and P/Al ratio, monoclinic/orthorhombic transition during steam activation, and the failed generation of mesopores, would cause obvious aggregation of the phosphorus species and could not improve the hydrothermal stability of the ZSM-5effectively, and the direct phosphatation turned out much worse. Finally, a specific index that the intensity of the signal at 39 in 27Al MAS NMR spectra before steam activation was proposed as the indicator for determining the efficiency of phosphorus modification. And the proposed mechanism on the interaction between phosphorus and TFAl during the phosphorus modification could also be applicable in other zeolites.

Tailoring in-situ N, O, P, S-doped soybean-derived porous carbon with ultrahigh capacitance in both acidic and alkaline media

In order to improve electrochemical capacitance properties of biomass-derived porous carbon materials, this work develops a low temperature pre-carbonization, hydrothermal stabilization and KOH activation method to derive N, O, P, S co-doped porous carbon materials from protein-rich soybeans and effectively enhances specific capacitances in both acidic and alkaline aqueous electrolytes. Specially, the derived porous carbon demonstrates an ultra-high specific capacitance of 685.1 F g−1 at 0.5 A g−1 in 2 M KOH and 439.5 F g−1 at 1 A g−1 in 1 M H2SO4, respectively. Moreover, a superior cycling stability is achieved with a capacitance retention of 80% after 13,000 cycles at a current density of 20 A g−1 in 2 M KOH. An asymmetric supercapacitor consisting of soybean-derived carbon and NiCo-sulfide delivers a high energy density of 41.8 Wh kg−1 at a power density of 750 W kg−1. The findings above indicate hydrothermal process can effectively stabilize heteroatoms (N and P), improve graphitization and thereby enhance capacitive properties of biomass-derived carbon materials.

Removal of arsenic from acid wastewater via sulfide precipitation and its hydrothermal mineralization stabilization

Abstract To achieve a safe treatment of arsenic-containing acid wastewater, a new process was proposed, including arsenic removal via sulfide precipitation and hydrothermal mineralization stabilization. Under optimal conditions of sulfide precipitation, 99.65% of arsenic from wastewater was precipitated in the form of amorphous As2S3. The As leaching concentration of amorphous As2S3 in TCLP (toxicity characteristic leaching procedure) test was up to 212.97 mg/L, therefore, hydrothermal mineralization was adopted to improve the stability of amorphous As2S3. The results showed that the As leaching concentration of mineralized As2S3 was only 4.82 mg/L. Furthermore, the amorphous As2S3 could be transformed into crystallized As2S3 (orpiment) in the presence of mineralizer Na2SO4. Simultaneously, the As leaching concentration of crystallized As2S3 was further reduced to 3.86 mg/L. Hydrothermal mineralization was an effective method for the stabilization of As2S3. Therefore, this process has a greater application in the treatment of arsenic-containing wastewater.

Structural consequences of the fluorides using in the synthesis of SBA-15 mesostructured silica

The effect of fluoride presence in a synthesis mixture on the parameters of the fine structure of SBA-15 has been studied. The amount of fluorides, the addition stage and the duration of the hydrothermal stabilization of the structure have been varied. Fluoride addition during SBA-15 synthesis increases the material formation rate and decreases the ordering duration of the highly organized mesostructure. During hydrothermal treatment under conventional conditions, fluorides cause a restructuring of the micropore system. There is micropore merging into relatively large coalesced micropores inside the silicate wall, that are practically undetected by t-plot or α-S methods due to the high ratio of the pore diameter to its length. The addition of fluoride results in a decrease in the thickness of the silica wall and an increase in the mesopores diameter as well as the cell parameter of the final product.

Hydrothermal Stabilization of Rich Al–BEA Zeolite by Post-Synthesis Addition of Zr for Steam Catalytic Cracking of n-Dodecane

The steam cracking of n-dodecane was performed over Zr-modified BEA zeolite. The parent H–BEA zeolite was modified via Zr introduction following earlier treatment (desilication and dealumination). The procedure allowed for achievement of a Si/Zr molar ratio of 100. The changes in BEA crystallinity were observed by X-ray diffraction. The energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance studies were used to confirm the quantity and position of Zr particles in the framework. Changes in the catalyst acidity were also monitored using pyridine FTIR. The addition of zirconium to the BEA framework prevents dealumination as a result of presence of steam as well as improved the catalyst lifetime from 30 min to 4 h. Dodecane cracking results showed that the introduction of Zr to the BEA framework after desilication is more efficient to protect framework Al in the presence of steam compared to dealumination post-treatment.

Alkaline hydrothermal stabilization of Cr(VI) in soil using glass and aluminum from recycled municipal solid wastes

Hexavalent chromium was stabilized in soil by using a mixture of glass and aluminum recovered from municipal solid wastes under alkaline hydrothermal conditions. Cr(VI) concentration was reduced by 94–98% already after 7days of treatment. After the same period, more than 90% of total Cr was stabilized in highly recalcitrant and scarcely mobile chemical forms, with 50% in the residual fraction (when the samples were treated at 1/10w/w mixture/soil ratio). Longer treatments increased Cr stabilization. X-ray microanalyses revealed that Cr was stabilized in geopolymeric structures within large aluminosilicate mineral aggregates (containing both amorphous and crystalline phases). 3D microstructural analyses showed a limited compaction of the soil with still a 20% internal porosity in the neoformed aggregates. Increased pH and salinity after the treatment can be restored by simple soil amendments and washing.

Supramolecular Host-Guest Inclusion for Distinguishing Cucurbit[7]uril-Based Pseudorotaxanes from Small-Molecule Ligands in Coordination Assembly with a Uranyl Center.

Although the capability of supramolecular pseudorotaxane/rotaxane systems as ligands for coordination with actinides has been identified by the on-going emerging of uranyl-organic polyrotaxane compounds, it is, however, still unknown how supramolecular inclusion affects the coordination assembly of the simple "axle" ligand with uranyl species. Herein, a semi-rigid organic dicarboxylate compound [BzBPCEt]Br2 (L1 ) is selected as a small-molecule "axle" ligand and the corresponding cucurbit[7]uril (CB7)-based [2]pseudorotaxane ligand, [BzBPCEt]Br2 @CB7 (L1 @CB7) has been also synthesized through CB7-based inclusion in this work. A detailed comparison between uranyl complexes from the "axle" ligand L1 and those from pseudorotaxane L1 @CB7 has been conducted, demonstrating the significant role of CB7-based inclusion in distinguishing supramolecular pseudorotaxane ligands from small-molecule dicarboxylates in uranyl coordination assembly. Notably, the impact of supramolecular inclusion on the "axle" linker in the system with cucurbituril macrocycles involved is established for the first time. Detailed structure decipherment suggests that the significant effect of CB7 is attributed to hydrothermal stabilization of the "axle" ligand or increased steric hindrance to the groups nearby originated from the bulky size of macrocyclic CB7.

Conversion of methanol to olefins: Stabilization of nanosized SAPO-34 by hydrothermal treatment

Nano-SAPO-34 zeolite catalyst (20nm crystal size) has been stabilized by hydrothermal treatment. After steamed at high temperatures (T⩾550°C), its textural properties and high lifetime during the reaction of methanol to olefins (MTO) are preserved, despite the decrease in acidity, even after months of contact with moisture. The stabilization effect is attributed to the migration of silicon to larger silicon islands in which the contribution of silicon on the edge is lower after steaming. Stabilization is not successful by a thermal treatment in air in the absence of water. Steaming at temperature >400°C is required for achieving hydrothermal stabilization. A stability test for SAPO-34 in MTO reaction is proposed.

Modifying the Hierarchical Porosity of SBA-15 via Mild-Detemplation Followed by Secondary Treatments

Fenton-chemistry-based detemplation combined with secondary treatments offers options to tune the hierarchical porosity of SBA-15. This approach has been studied on a series of SBA-15 mesophases and has been compared to the conventional calcination. The as-synthesized and detemplated materials were studied with regard to their template content (TGA, CHN), structure (SAXS, TEM), surface hydroxylation (Blin–Carteret’s approach), and texture (high-resolution argon physisorption). Fenton detemplation achieves 99% of template removal, leading to highly hydroxylated materials. The structure is better preserved when a secondary treatment is applied after the Fenton oxidation, due to the intense capillary forces during drying in water. Two successful approaches are presented: drying in a low-surface-tension solvent (such as n-BuOH) and a hydrothermal stabilization to further condense the structure and make it structurally more robust. Both approaches give rise to remarkably low structural shrinkage, lower than calcination and the direct water-dried Fenton. Interestingly, the derived textural features are remarkably different. The n-BuOH exchange route gives rise to highly hierarchical structures with enhanced interconnecting pores and the highest surface areas. The hydrothermal stabilization produces large-pore SBA-15 structures with high pore volume, intermediate interconnectivity, and minimal micropores. Therefore, the hierarchical texture can be fine-tuned in these two fashions while the template is removed under mild conditions.

Preparation of an active and regenerable catalyst for liquid-phase alkylation of toluene with 1-decene

Zeolite Y was tested as an alternative solid acid catalyst for the production of linear alkyl aromatics with the emphasis on its activity and stability towards regeneration. Liquid-phase alkylation of toluene with 1-decene at 100°C was used as the model reaction. Deactivated catalyst samples were regenerated by the temperature programmed calcination (TPC) in air flow at 550°C. The activity of the unmodified HY zeolite during alkylation was significant but decreased to a minimum after regeneration, as a result of a partial structure collapse during regeneration using TPC. To avoid the structure collapse hydrothermal stabilization of zeolite Y at 560, 670 and 780°C was performed. Subsequent chemical dealumination using 0.5M HCl or ion-exchange with the 2M NH4NO3 solution, in order to improve the catalyst activity, were carried out. All the samples were then tested in alkylation. The main monitored parameters were the conversion of 1-decene, selectivity to 2-phenyldecane isomer and the amount of side-products. The sample stabilized at 560°C and ion-exchanged subsequently showed the highest activity with the lowest amount of by-products. This sample was also regenerated and reused four times in the cycle alkylation–regeneration with no loss of structure or activity. In fact there was a slight activity increase of this sample after regeneration.

Effects of Hydrothermal Treatment on the Major Heavy Metals in Fly Ash from Municipal Solid Waste Incineration

Circulating fluidized bed (CFB) and stoker grate are the two major municipal solid waste incineration (MSWI) technologies currently being used in China. In this work, the hydrothermal stabilization...

Heavy metals stabilization in medical waste incinerator fly ash using alkaline assisted supercritical water technology

This study investigated the process of aluminosilicate formation in medical waste incinerator fly ash containing large amounts of heavy metals and treated with alkaline compounds at 375 degrees C and examined how this process affected the mobility and availability of the metals. As a consequence of the treatments, the amount of dissolved heavy metals, and thus their mobility, was greatly reduced, and the metal leaching concentration was below the legislative regulations for metal leachability. Moreover, this process did not produce a high concentration of heavy metals in the effluent. The addition of alkaline compounds such as sodium hydroxide and sodium carbonate can prevent certain heavy metal ions dissolving in water. In comparison with the alkaline-free condition, the extracted concentrations of As, Mn, Pb, Sr and Zn were decreased by about 51.08, 97.22, 58.33, 96.77 and 86.89% by the addition of sodium hydroxide and 66.18, 86.11, 58.33, 83.87 and 81.91% by the addition of sodium carbonate. A mechanism for how the formation of aluminosilicate occurred in supercritical water and affected the mobility and availability of the heavy metals is discussed. The reported results could be useful as basic knowledge for planning new technologies for the hydrothermal stabilization of heavy metals in fly ash.

Modeling of heat and mass transfer in the hydrothermal system of the Akademii Nauk caldera

Supposing a leading role of free heat convection in the hydrothermal system above the magma chamber, a model of the hydrothermal system of the Akademii Nauk caldera in Kamchatka is suggested. The model is based on available geological, hydrogeological and geothermal data for the area. Three possible variants of the model are discussed. Based on temperature distribution data, the variant best corresponding to the natural conditions has been chosen. The period of hydrothermal system stabilization for all the variants is close to 7000–8000 years.

Hydrothermal stabilization of ZSM-5 catalytic-cracking additives by phosphorus addition

ZSM-5 zeolites with different Si/Al ratios (15, 25, 40) were impregnated with phosphorus (0.5–3 wt%) in form of H 3PO 4 or NH 4H 2PO 4. The samples were characterized before and after severe hydrothermal treatment by XRD, IR, 27Al, 29Si, 31P MAS NMR, and their activity for the cracking of n-decane was measured. It was found that phosphorus impregnation increases the hydrothermal stability of framework aluminum whatever the source of phosphorus used. The acidity and cracking activity of steamed samples reached an optimum for a P/Al molar ratio of ca. 0.5–0.7. A chemical model for the phosphorus–zeolite interaction is proposed in which the framework aluminum pairs are stabilized by extra-framework cationic species formed by protonation of orthophosphoric acid. The influence of isolated versus pairs of aluminum on activity and selectivity after steaming is discussed. When P-impregnated ZSM-5 sample is used as an additive for cracking industrial feeds, selectivity to propylene and butenes increases.

Hydrothermal phase stabilization of 2-line ferrihydrite by bacteria

Poorly ordered 2-line ferrihydrite deposits from the caldera of Axial Volcano, a site of hydrothermal vent activity along the Juan de Fuca Ridge, are characterized by an abundance of bacterial structures resembling Gallionella ferruginea, Leptothrix ochracea and PV-1 filaments encrusted with nanoparticulate ferrihydrite. Ferrihydrite formed in the absence of bacteria can be metastable and will subsequently react to form more structurally ordered iron oxide phases such as hematite or goethite. Inspection of samples from 2-day 80 °C aqueous heating experiments by electron microscopy and X-ray diffraction revealed that a natural sample of bacteriogenic ferrihydrite from Axial Volcano did not undergo a phase transition, whereas synthetic ferrihydrite, absent of bacteria, transformed to hematite after 2 days. A series of bacterial-ferrihydrite composites exhibited decreasing amounts of transformation to hematite with increased amounts of Fe(III) bound to bacteria. Complete inhibition was observed when 50% of the total Fe was bound as ferric iron and 50% was present as ferrihydrite. For the synthetic ferrihydrite samples containing bacteria, the inhibition of ferrihydrite transformation is attributed to microbial surface functional groups (i.e. carboxyl, phosphoryl, amine) constraining the Brownian motion of surface bound ferrihydrite nanoparticles, thereby eliminating the aggregation and rotation of particles required for crystal growth. The stabilization of ferrihydrite will prolong the longevity of a highly reactive mineral phase, which may have implications for marine geochemistry and environmental remediation. Preservation of bacteria encrusted with transformation resistant ferrihydrite may enhance the potential usefulness of bacteriogenic ferrihydrite to harbour bacterial microfossils, imparting these types of samples with potential use for paleontology and astrobiology.

Direct hydrothermal synthesis and stabilization of high-silica mordenite (Si∶Al = 25) using tetraethylammonium and fluoride ions

The direct crystallization of high-silica mordenite (MOR) zeolite using both tetraethylammonium and fluoride ions was investigated by varying the primary variables of the hydrothermal synthesis such as Si∶Al and H2O∶SiO2 ratios in the starting synthesis mixture. Under well-optimized conditions, highly crystalline MOR zeolites with a Si∶Al ratio of approximately 25 were successfully prepared. From evaluation of the thermal stabilities of the MOR zeolites obtained, it was also found that there is a good relationship between the thermal stability and the bulk Si∶Al ratio of MOR zeolites and that any NaF remaining in the zeolite crystals considerably reduces the thermal stability.