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Interfacial Heat and Mass Transfer Effects on Secondary Hydrate Formation under Different Dissociation Conditions
No full textSecondary hydrate formation or hydrate reformation poses a serious threat to the oil and gas transportation safety and natural gas hydrate exploitation efficiency. The hydrate reformation behaviors in porous media have been widely studied in large simulators due to their importance in traditional industries and new energy resources. However, it is difficult to understand the interfacial effects of hydrate reformation on the surface and in micropores of the porous media via a basic experimental apparatus. In this work, in situ X-ray computed tomography (X-CT) technology is used to detect the period, distribution, volume, and morphology characteristics of secondary hydrate formation during hydrate dissociation under depressurization, thermal stimulation, and the combined conditions. It is found that the secondary hydrate formation is inevitable under any conditions of hydrate dissociation. The secondary hydrate morphology varies among porous, grain-enveloping, grain-cementing, granular, and patchy structures, which are closely correlated to the hydrate reformation region and gas/water saturated conditions during hydrate dissociation. Accordingly, we revealed that the interfacial superheating phenomenon before hydrate dissociation could provide a supercooling condition for hydrate reformation. The gas flow along the interface of pores and inside the liquid water, as well as gas accumulation in noninterconnected pores, would exaggerate the hydrate reformation by increasing the local pore pressure. Meanwhile, the hydrate reformation aggravates the nonuniform distribution of gas hydrates in pores. In order to avoid hydrate reformation during dissociation, we further compared hydrate reformation and dissociation behaviors under three hydrate dissociation conditions. It is revealed that the combination of thermal stimulation and depressurization is an effective method for hydrate dissociation by retarding secondary hydrate formation. This study provides visual evidence and an interaction mechanism between interfacial heat and mass transfer, as well as secondary hydrate formation behaviors, which can be favorable for future quantitative research on secondary hydrate formation in different scales under various dissociation conditions
Co-pyrolysis mechanism of waste vehicle seats derived artificial leather and foam
No full textCo-pyrolysis is an important means to realize the clean disposal of organic wastes and generate some value-added chemicals. In the present study, the co-pyrolysis behavior of polyvinyl chloride (PVC) artificial leather (LE) and polyurethane foam (PU), the main components of waste vehicle seats, was systematically investigated to uncover the existing synergistic interaction effects. The pyrolysis experiments and kinetic analysis were carried out using TG/MS and Py-GC/MS, wherein the key parameters such as temperature and LE-to-PU mass ratio were examined. The co-pyrolysis of LE and PU at 650 degrees C remarkably accelerated the formation of aromatic compounds such as styrene. The relative content of aromatics from co-pyrolysis achieved 43.8%, which was much higher than that of 20.4% and 5.2% in the case of individual pyrolysis. The kinetic results further verified that the synergistic effect of LE and PU greatly lowered the reaction energy barriers of key steps in the co-pyrolysis, especially for the cases of LE-to-PU mass ratios of 3:2 and 2:3. The competing reactions such as intermolecular cross-linking of conjugated polyolefin intermediates and C-C cleavage, as well as the thermal conversion of methyl diphenyl diisocyanate in PU, favored the selective production of aromatics. In addition, the plausible pathways and synergistic mechanisms for the co-pyrolysis of LE and PU were discussed in detail. The present research significantly contributes to the selective upgrading of PVC artificial leather and polyurethane foam into highquality pyrolysis oils rich in aromatics, thus achieving the clean disposal and resource utilization of waste vehicle seats
Thermal performance and analysis of high-temperature aquifer thermal energy storage based on a practical project
No full textGeothermal heating technology based on high-temperature aquifer thermal energy storage (HT-ATES) is one of important development directions of geothermal multi-energy complementary and integrated energy system. In present article, thermal performance of HT-ATES based on a practical project is first proposed, and a long-term cycle of HT-ATES is constructed and verified. The heating up storage and isothermal heat storage of HT-ATES are experimentally conducted. The different standing time schemes causing mutation of the heat storage mechanism have been implemented to identify the optimal scheme. And then the outlet water temperature, heat storage efficiency is further calculated and analyzed under the same and different conditions of heat storage capacity. Compared with original heat production, the outlet water temperature is promoted and the single well heat storage efficiency can reach >80 % after 9 years of heat storage. The heat storage flow rate decreases or the heat storage temperature increases can prevent heat dissipation to the surroundings, so that obtaining high outlet water temperature and heat storage efficiency under the persistent annual heat storage capacity. Results also show that the outlet water temperature and heat storage efficiency are promoted when the heat storage temperature increases and heat storage flow rate decreases
Biocompatible organosolv fractionation via a novel alkaline lignin-first strategy towards lignocellulose valorization
No full textSimultaneous valorization of both carbohydrate and lignin fractions in lignocellulose remains a great challenge. Herein, a novel lignin -first strategy using triethylene glycol (TEG) under alkaline conditions for effective biomass fractionation producing highly digestible carbohydrates and reactive lignin was developed. Delignification was over 80% and fermentable sugar yields were close to 90% after pretreatment at 90 celcius. The biocompatibility of TEG allowed direct enzymatic hydrolysis of the solid residue without washing, thus minimizing wastewater generation. Moreover, the obtained lignin (TEGL) had an uncondensed structure with well-preserved beta-O-4 linkage, leading to near -equal aromatic monomer yields compared to cellulolytic enzyme lignin after catalyticfree pyrolysis, demonstrating high valorization potential. Overall, the proposed TEG solvent system is promising for a green and sustainable biorefinery process to achieve the complete utilization of lignocellulose
Investigations into methane hydrate formation, accumulation, and distribution in sediments with different contents of illite clay
No full textFine-grained sediments are widely distributed in naturally occurring hydrate-bearing sediments (HBS). However, the effects of silty and clayey minerals on the kinetics of methane hydrate (MH) formation and distribution are less well understood than in sandy sediments. In this study, a series of experiments were designed, which involves the kinetics and morphological observations to investigate the MH formation in clayey silty sediments with mass fractions of illite ranging from 0 to 50 wt%. The evolution of MH accumulation and distribution were analyzed based on temperature and electrical resistance measurements. The experimental results showed that the mass fraction of illite has a critical effect on MH nucleation, formation rate and distribution within the sandy sediment. The effect of illite on the gas uptake rate is primarily observed in the early MH formation stages, in which the MH formation rate in the system with 10 wt% illite exhibits approximately 1.66 times higher than that of pure sandy sediment. However, as the illite mass fraction increases from 20 wt% to 40 wt%, the MH formation rate decreases, only to increase significantly when the mass fraction reaches 50 wt%, which may be due to changes in the sediment skeletal structure. In the pure sandy system, MH primarily accumulates in the upper layer of the sediment. As the illite mass fraction increases, MH content in the lower layer of the sediment gradually increases. In morphological observations, several new cracks appeared after MH formation in highly silty and clayey sediments, increasing the MH formation rate. The electrical resistance of sediments exhibits a close relationship with hydrate saturation, and it basically increases proportionately with hydrate saturation until certain inflection points. After these points, the electrical resistance shows a significant increase. Moreover, the hydrate saturation at the inflection points tends to increase with higher illite mass fractions due to a more dispersed water distribution
Adsorption experiments and mechanisms of methylene blue on activated carbon from garden waste via deep eutectic solvents coupling KOH activation
No full textCarbon-based adsorbents derived from biomass waste are validly capable of adsorbing and purifying dye wastewater. Herein, a novel adsorbent (p-DES-GHC(KOH)) from garden waste was developed by a two-stage coupling strategy of deep eutectic solvents (DES) modification and KOH activation for methylene blue (MB) adsorption. The properties and adsorption behaviors of p-DES-GHC(KOH) were investigated, and the adsorption mechanisms were thus proposed based on experiments and density functional theory (DFT) calculations. The results indicated that p-DES-GHC(KOH) exhibited superior pore structures with a surface area of 883.95 m(2)/g and substantial oxygenated functional groups. The maximum absorption capacity of MB was 351.72 mg/g at 25 degrees C, with isotherms and kinetics fitting well to the Freundlich model along with the pseudo-second-order kinetic model, respectively. The Elovich fitting results indicated that the adsorption process of MB on the p-DES-GHC(KOH) surface was not mainly dominated by chemisorption, but also regulated by other adsorption processes. The endothermic and spontaneous absorption processes with the stochasticity of MB molecules on the p-DES-GHC(KOH) surface were verified by thermodynamic analysis. DFT calculations revealed that the introduction of hydroxyl and carbonyl groups reduced the adsorption energy and reinforced the adsorption capacity of p-DES-GHC(KOH) for MB through synergistic effects. The adsorption of MB on p-DES-GHC(KOH) might be affected by pore filling, pi-pi interaction, and electrostatic attraction. The potential of p-DES-GHC(KOH) as a promising adsorbent for MB removal from wastewater was confirmed in this study
Holocene Paleoclimate Records in Equatorial West Africa: Insights Based on the Characterization of Glycerol Dialkyl Glycerol Tetraethers
No full textOne gravity core retrieved from the Niger Delta was used to explore the origin of deposited organic matter (OM) and the paleo-climatic and environmental conditions over the Holocene in equatorial West Africa. The geochemical properties of sediments including glycerol dialkyl glycerol tetraethers (GDGTs) and elemental (%OC, %N, C/N) and isotopic (delta 13Corg, delta 15N) signatures were determined. The determination constrained the age of the column and revealed that the sediment OM was mainly derived from a marine source. The isoprenoid (iso)GDGTs were the dominant GDGTs, with a small amount of branched (br)GDGTs, which led to a low-branched and isoprenoid tetraether index (BIT, 0.02-0.21) and represented a low terrestrial input. Most isoGDGTs and OH-GDGTs were produced in situ by Marine Group I (MG-I) Thaumarchaeota, while the brGDGTs were mainly transported from land. A two-endmember model quantified the contribution of terrestrial OM, as 0.9-19.9% by BIT and 1.1-32.6% by delta 13C. Accordingly, the millennium-scale sea surface temperatures (SSTs) were reconstructed based on the cyclopentane ring distribution (TEX86H) and the ring index of OH-GDGTs (RI-OH). The top core SSTs were lower than the modern mean annual SST due to the growth season and habitat depth of Thaumarchaeota. The reconstructed SSTs clearly revealed the four stages of paleoclimate change, in particular, the drought episode of 8.2 kyr and the following humid period. The above research has enhanced our understanding of the paleoclimate change in river outflow during the Holocene at the millennium scale
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