Impact of heavy hydrocarbon impurities on polytetrafluoroethylene (PTFE) membrane stability

Membrane contactor technology has attained considerable attention as a promising technology to reduce CO2 content in natural gas. In this study, the main objective is to investigate the effect of heavy hydrocarbons impurities, often present in natural gas, on polytetrafluoroethylene (PTFE) hollow fibre membrane. The membranes were immersed for months in n-heptane, 1-decene, benzene and toluene, and analysed periodically through its surface morphology, composition, functional groups, hydrophobicity, and thermal stability. The characteristics of PTFE fibres remained unchanged even after long term exposure with heavy hydrocarbons. This study provides a better understanding of the robustness of using PTFE membrane fibre for CO2 removal in membrane contactor system.

Simulation of Biogenic Coalbed Gas from Anthracite in South of Qinshui Basin, China

High rank coal, such as anthracite, has been considered difficult to generate biogas because of the high coalification degree. Selecting anthracite from Sihe coal mine, Qinshui basin, China, as substrate, this study carried out a simulation experiment of biogas generation for 80 days, the purpose of which was to verify whether anthracite could be bio-degraded to produce biogas under laboratory conditions. The results showed that the selected anthracite can be utilized by methanogenic bacteria to produce biogas and the approximate production field was 1.79mL/g, which was less than that of lower rank coal of other published studies. The generation process can be divided into a rapid growth stage (0-30d) and a slow descent stage (30-80d). CO2 and CH4 are the main components of biogas, although some heavy-hydrocarbons were also tested. The CO2 concentrations were low (<30%) and the δ13C-CH4 values were positive (-39.9‰ to -45.8‰), which suggested that the main biogas generation pathway was acetic fermentation. But at the same time, the concentrations of CH4 and CO2 were mutually increasing and decreasing with the passage of experiment time, and δ13C-CH4 tends to be lighten in the later stage(40-80d), suggesting that parts of biogenic CH4 was generated by way of CO2-reduction.

Multiscale Pressure/Volume/Temperature Simulation of Decreasing Condensate/Gas Ratio at Greater than Dewpoint Pressure in Shale Gas-Condensate Reservoirs

Summary In shale gas-condensate reservoirs, when the initial reservoir pressure is greater than the dewpoint pressure, the condensate/gas ratio (CGR) has been observed to decrease continuously as the pressure drops to less than the initial reservoir pressure. This abnormal behavior cannot be explained with conventional pressure/volume/temperature (PVT) models that ignore the presence of nanopores in shale rock. Herein, for the first time, we present a study that provides a physical explanation for the observed CGR trends by including the effect of nanopores on the fluid phase behavior and depletion of shale gas-condensate reservoirs. Our model uses multiscale PVT simulation by means of a pore-size-dependent equation of state (EOS). Two lean gas-condensate cases (shallow and deep reservoirs) are investigated. The simulation results show that hydrocarbons distribute heterogeneously with respect to pore size on the nanoscale. There are more intermediate to heavy hydrocarbons (C3–11+) but fewer light ends (C1–2) distributed in the nanopores than in the bulk region. At the end of depletion, because of confinement effects, large amounts of intermediate hydrocarbons are trapped in the nanopores, causing condensate recovery loss. Multiscale depletion simulations suggest that a decreasing CGR can occur at the beginning of production when the reservoir pressure is higher than the dewpoint pressure. Such behavior is caused by the nanopore depletion in the shale matrix, which is a process of selectively releasing light hydrocarbon components. We also present a novel approach to model the nonequilibrium fluid distribution between the fracture and nanopores using a simple local-equilibrium concept. Our results indicate that the nonequilibrium fluid distribution increases the CGR drop because of the compositional selectivity of the nanopore in favor of intermediate and heavy hydrocarbons.

Combining traditional and geophysical soil investigation for phytoremediation planning in a hydrocarbon polluted area

&lt;p&gt;The spatial variability of hydrocarbon content and the physical and chemical properties of the soil were assessed by combining traditional soil sampling and proximal geophysical survey with the aim of planning a pilot phytoremediation experiment in an agricultural area west of Milan (Lombardy, Italy).&lt;/p&gt;&lt;p&gt;The area, an irrigated arable land of about 1 ha, was affected by a refined oil spillage from an underground pipeline in 2015. Contamination surveys were carried out with a continuous core drilling technique using an hydraulic probe (131 cm diameter core). Heavy (C&gt;12) and light (C&lt;12) alkanes and aromatic compounds (benzene, ethylbenzene, styrene, toluene and xilenes) were measured up to three meters depth. Results showed a predominance of heavy hydrocarbons (C&gt;12) with respect to light hydrocarbons (C&lt;12) and aromatic compounds. A map of heavy hydrocarbons soil concentration was obtained using geostatistical techniques.&lt;/p&gt;&lt;p&gt;In 2019 it was decided to carry out a phytoremediation intervention to reclaim the first meter of contaminated soil where heavy hydrocarbons content ranges from 500 to 5000 mg/kg. The first step of the intervention consists in cultivating a wide variety of vegetal species in experimental plots with different pollution to verify their effectiveness for remediation in the specific environmental condition of that area. For the reclamation of deeper more contaminated layers, enhanced bioremediation have been planned to be used.&lt;/p&gt;&lt;p&gt;Soil properties, which are crucial for planning phytoremediation activities, were investigated using traditional methods and geophysical surveys. Traditional soil survey was performed describing the 23 drilling cores used to monitor pollutants and opening five profiles; the samples were collected from genetic soil horizons and analysed for organic carbon and the main nutrient (nitrogen, phosphorus and potassium) content, total carbonates, texture and pH in water. The distribution of Eutric Luvisols and Cambisols, developed mainly on sandy or sandy skeletal substrate, was represented in a soil map. A proximal geophysical survey was carried out using an electromagnetic induction (EMI) sensor (GSSI Profiler EMP-400) by acquiring multiple frequencies; soil detailed conductivity maps for each frequency (15000, 9000 and 2000 kHz) were obtained. No significant relationships were found between soil electrical conductivity and hydrocarbon concentration, whereas there are relationships with the main soil characteristics: this allowed detailed maps of soil parameters to be obtained.&lt;/p&gt;&lt;p&gt;On the base of both the soil spatial characterization (traditional soil map and detailed soil property maps with geophysical approach) and the contaminant distribution (hydrocarbon map distribution using geostatistical approach), homogeneous areas were identified in which to set up experimental phytoremediation plots to test the most suitable species for reclamation, chosen among the most widespread crops in the region and considering their suitability for biomass and bio-oil production.&lt;/p&gt;