Xu Jiang

Within the carbon capture, utilization and storage (CCUS) chain, buried CO₂ pipelines are an indispensable engineering solution under complex topographic conditions. Experimental investigations show that leakage from buried supercritical CO₂ (sCO₂) pipelines features a two-stage pressure decline: an initial rapid drop driven by high leaking medium mass flow, followed by a linear decrease governed by homogeneous liquid CO₂ vaporization. Notably, the choking flow effect homogenizes linear pressure drop rates across distinct experimental conditions. Leakage orifice diameter is a dominant factor for pipeline temperature distribution: small orifices yield consistent temperature drop rates at different vertical pipeline positions, while larger ones cause faster cooling at the pipeline bottom, forming significant vertical temperature gradients that intensify closer to the leakage orifice. Leakage direction and initial pipeline pressure are key regulators of leakage dynamics: vertical upward leakage (0°) leads to faster pressure drops due to the reduced soil resistance, and elevated initial pressure not only intensifies the pressure drop rate and amplifies CO₂’s endothermic effect but also modulates the phase transition pathway of sCO₂ during leakage.

In order to solve the problems of low calorific value and pipeline corrosion caused by high concentration of CO₂ in oil-associated gas, and promote the resource utilization of associated gas, this study used validated grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulation to investigate the adsorption characteristics of 11 different topological structures (straight-channel MFI/BEA, cage-channel LTA/FAU/CHA) and cation types (Ca²⁺, Na⁺, H⁺) of commercial zeolites for CO₂ and alkanes (CH₄, C₂H₆, C₃H₈) at 0%~90% RH. The results showed that the CO₂ adsorption capacity of all zeolites decreased with increasing humidity, but straight-channel zeolites (ZSM5-300, BETA-25) had excellent moisture resistance, with only a 20.8% and 30.6% decrease in capacity at 90% RH, respectively. The performance of cage-channel zeolite drops sharply under high humidity. Topology structure and cation synergistically regulate separation efficiency, maintaining stable diffusion order in straight channels. Ca²⁺ enhances dry state capacity but is prone to hydrophilic failure. The adsorption heat of CO₂ on straight-channel zeolite is 25–38 kJ/mol, resulting in lower regeneration energy consumption. ZSM5-300 is preferred for PSA (CH₄/CO₂ kinetic separation coefficient of 809.52 at 90% RH), and NaFAU is preferred for TSA (CO₂ adsorption capacity of 3.6 mmol/g and selectivity of 502.6 at 90% RH). This study clarifies the core structure-activity relationship and provides key theoretical support for the decarbonization of oil-associated gas.

In this work, a molecular simulation method was used to study the adsorption of seven combustion products (CO₂, H₂O, SO₂, N₂, O₂, NO and NO₂) on three zeolites with different topological structures (4A, MIF and MOR). Adsorption isotherms of pure components and mixtures at a wide range of temperatures (253–333 K) were calculated using the Monte Carlo method, obtaining equilibrium parameters including the adsorption capacity, adsorption heat and energy distribution. The calculation results indicated that 4A zeolite with more micropores has a stronger adsorption performance for CO₂. The presence of water significantly reduced the CO₂ capture efficiency of the three zeolites, and the CO₂ adsorption amount decreased by more than 80%. Adsorption kinetics was studied using the molecular dynamic (MD) method, MFI and MOR, with channel-type pore structures exhibiting stronger gas diffusion performance, though their separation efficiency was not high. A 4A zeolite has the potential for kinetic separation of CO₂.

The adsorption thermodynamics and kinetics of CO₂ and six combustion products (H₂O, SO₂, N₂, O₂, NO and NO₂) of two most commonly used commercial zeolites (13X and 5A) were studied based on validated molecular simulations. Adsorption isotherms at wide range of temperatures (253–333 K) were fitted by a Langmuir model, obtaining equilibrium parameters including the adsorption capacity, strength, heterogeneity and CO₂ selectivity from the mixture. The diffusion coefficients, isosteric adsorption heats and distributions of potential energy were simulated for further explanation. The comprehensive evaluation results suggest that, in actual combustion product mixtures, the presence of H₂O in combustion products has a significant impact on CO₂ capture efficiency. Under the influence of water, the adsorption capacity of CO₂ was reduced by over 80%.

In thermal cracking and collision-induced dissociation (CID) processes, molecules/ions mainly undergo cleavage reactions. In theory, the cleavage reaction is preferred for weak bonds in both processes. The present study investigates the thermal cracking and CID behavior of polar compounds in vacuum residue. By controlling the thermal reaction temperature and collision energy, different degrees of fragmentation were achieved. The molecular composition before and after the cracking process was analyzed through electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). There was a correlation between the reaction temperature and the collision energy for the average carbon number value. Both desulfurization and decarboxylation were also observed in two processes due to the low C-S bond energy and poor stability of carboxylic acid groups. Nevertheless, the two processes still had some differences in reaction selectivity. Polar species tended to be directly dealkylated down to the C1–C5 substituted aromatic core in the CID process, showing a discontinuity in the carbon number vs. double bond equivalence (DBE) distribution for the CID product. On the contrary, the carbon number distribution in the thermal reaction showed a continuously reduced trend. In summary, the CID process can qualitatively reflect the cracking behavior. However, the product structural distribution of the thermal cracking product cannot be fully predicted, especially for sidechain cracking reactions. In addition, the research results can provide a new method to realize the simulation of the thermal cracking without energy and time consumption, so as to guide the selection of the feedstock and optimization of the reaction condition.

Surfactants and nanoparticles play crucial roles in controlling the oil-water interfacial phenomenon. The natural oil-wet mineral nanoparticles that exist in crude oil could remarkably affect water-oil interfacial characteristics. Most of recent studies focus on the effect of hydrophilic nanoparticles dispersed in water on the oil-water interfacial phenomenon for the nanoparticle enhanced oil recovery. However, studies of the impact of the oil-wet nanoparticles existed in crude oil on interfacial behaviour are rare. In this study, the impacts of Span 80 surfactant and hydrophobic SiO₂ nanoparticles on the crude oil-water interfacial characteristics were studied by measuring the dynamic and equilibrium crude oil-water interfacial tensions. The results show the existence of nanoparticles leading to higher crude oil-water interfacial tensions than those without nanoparticles at low surfactant concentrations below 2000 ppm. At a Span 80 surfactant concentration of 1000 ppm, the increase of interfacial tension caused by nanoparticles is largest, which is around 8.6 mN/m. For high Span 80 surfactant concentrations, the less significant impact of nanoparticles on the crude oil-water interfacial tension is obtained. The effect of nanoparticle concentration on the crude oil-water interfacial tension was also investigated in the existence of surfactant. The data indicates the less significant influence of nanoparticles on the crude oil-water interfacial tension at high nanoparticle concentration in the presence of Span 80 surfactant. This study confirms the influences of nanoparticle-surfactant interaction and competitive surfactant molecule adsorption on the nanoparticles surfaces and the crude oil-water interface.