Mixed Gas System Research Articles

Facile shaping of flexible MIL-53(Al) for effective separation of propylene over propane

A facile granulation approach using polyvinyl butyral (PVB) as a polymer binder was developed to control the textural properties of the flexible metal–organic framework MIL-53(Al). The large pore (LP) structure of MIL-53(Al) contracted after granulation due to a strong interaction between MOF and polymer binder. This contraction enhances propylene's selectivity over propane at saturation pressure (region II), as confirmed by single-component adsorption isotherms. The adsorption kinetics showed faster adsorption of C3H6 compared to C3H8 over time in the case of the granules, while no difference was observed for the powder sample. Breakthrough experiments successfully separated C3H6 over C3H8 using MIL-53(Al)-B10% granules, whereas the pristine MIL-53(Al) powder did not separate the C3H8-C3H6 gas mixture. The breakthrough finding reaffirms that the observed gate-opening effect in MIL-53(Al) within pressure region I is ineffective for separating a mixed gas system containing propane and propylene. The constrained pores of the shaped granules could facilitate strong π-π stacking interactions with C3H6 and decrease the diffusion rate for C3H8 molecules. These findings indicate that the simple granulation approach can modulate the textural properties of flexible MIL-53(Al) and improve its selectivity for C3H6/C3H8 separation resulting from increased MOF-propylene affinity and kinetic factors.

Understanding poly(ethylene terephthalate) degradation using gas-mediated simulated recycling

While mechanical recycling is a key enabler of a plastics circular economy, poly(ethylene terephthalate) (PET) is highly susceptible to degradation during melt processing. Through rheology-simulated and extrusion recycling experiments we demonstrate that the degradation of PET during high temperature processing can be understood and mitigated by control of gaseous environment. Processing under nitrogen induces up-shifts in melt viscosity and molecular weights by up to 20%. By contrast, the presence of oxygen initiates chain scission reactions, decreasing molecular weight and viscosity. Carbon dioxide plasticises the PET melt, offering the potential for improved processing and property retention. Expanding experiments to nitrogen-oxygen mixed-gas systems, we identify the presence of two distinct regimes associated with chain growth and scission which are subsequently tuned by controlling the oxygen concentration of the environment. This research facilitates a simple, additive-free approach to improving PET recyclability, thus enabling improved circularity of an often-challenging plastic material to recycle.

Sensing Characterization of Metal Oxide Semiconductor-Based Sensor Arrays for Gas Mixtures in Air

Micro-electronic gas sensor devices were developed for the detection of carbon monoxide (CO), nitrogen oxides (NOx), ammonia (NH3), and formaldehyde (HCHO), as well as binary mixed-gas systems. Four gas sensing materials for different target gases, Pd-SnO2 for CO, In2O3 for NOx, Ru-WO3 for NH3, and SnO2-ZnO for HCHO, were synthesized using a sol-gel method, and sensor devices were then fabricated using a micro sensor platform. The gas sensing behavior and sensor response to the gas mixture were examined for six mixed gas systems using the experimental data in MEMS gas sensor arrays in sole gases and their mixtures. The gas sensing behavior with the mixed gas system suggests that specific adsorption and selective activation of the adsorption sites might occur in gas mixtures, and allow selectivity for the adsorption of a particular gas. The careful pattern recognition of sensing data obtained by the sensor array made it possible to distinguish a gas species from a gas mixture and to measure its concentration.

Study of the Dissolution and Diffusion of Propane, Propylene and Nitrogen in Polydimethylsiloxane Membranes with Molecular Dynamics Simulation and Monte Carlo Simulation

Volatile organic compounds (VOCs) are important sources of atmospheric pollutants on account of their high recycling value. The membrane of dense silicone rubber polydimethylsiloxane (PDMS) has wide-ranging prospects for the separation and recovery of VOCs. In this study, PDMS membrane body models were established in BIOVIA Materials Studio (MS) to simulate VOCs with C3/N2 gases, and to study the structure of PDMS membranes and the dissolution and diffusion process of gas in the membranes. The free volume fraction (FFV), cohesive energy density (CED), radial distribution function (RDF), diffusion coefficient and solubility coefficient of C3H8, C3H6 and N2 in PDMS membranes were calculated, and the permeability coefficients were calculated according to these values. At the same time, the effects of temperature and mixed gas on the dissolution and diffusion of C3/N2 in PDMS membranes were investigated. The results show that the mass transfer process of C3 in PDMS membranes is mainly controlled by the dissolution process, while that of N2 is mainly controlled by the diffusion process. In a C3/N2 mixed gas system, there is a synergistic relationship between gases in the diffusion process, while there is competitive adsorption in the dissolution process. With an increase in temperature, the diffusion coefficients of the three gases in PDMS gradually increase, the solubility coefficients gradually decrease, and the overall permeability selectivity coefficients of the gases gradually decrease. Therefore, low-temperature conditions are more conducive to the separation of C3/N2 in PDMS membranes. The simulation results of the permeability selectivity coefficients of pure C3 and N2 in PDMS are similar to the experimental results, and the relationship between the micro- and macro-transport properties of PDMS membranes can be better understood through molecular simulation.

Dual-functional gas hydrate inhibition of tetramethylammonium chloride for carbon dioxide-methane mixed gas systems

The present work deals with evaluating the dual-functional gas hydrate impact of tetramethylammonium chloride (TMACl) in the presence of different CO2-CH4 content mixed gas hydrate systems (30%CO2 + 70%CH4, 50%CO2 + 50%CH4, and 70%CO2 + 30%CH4). A custom-made high-pressure gas hydrate reactor was used to acquire the temperature–pressure loops for the studied systems in the absence/presence of different concentrations of aqueous TMACl solutions via T-Cycle and isochoric constant cooling method for both THI and KHI investigations, respectively. The electrolyte-based thermodynamic model was also applied to validate the obtained HLwVE results for all the studied systems. The obtained results revealed that TMACl acts dual-functional (thermodynamic and kinetic) hydrate inhibitor for high CO2 content gas systems. The increased concentration of TMACl induces more shifts in HLwVE data with maximum variation attained at10 wt% concentration up to 1.46 K for a high CO2 content methane system owing to the increased hydrogen bonding ability of TMACl. Moreover, TMACl delayed the hydrate formation up to 1.4 and1.5 folds for 274.0 and 277.0 K conditions for high CO2 content mixed gas systems. Moreover, the applied electrolyte-based model could predict the HLwVE data of TMACl in the presence of a mixed gas system within the AAE value of 0.1 % for all the studied mixed gas systems. Furthermore, the KHI performance of TMACl was also compared with commercial inhibitor, i.e., polyvinyl pyrrolidone (PVP), and obtained comparable results.Therefore, the acquired dual-functional results (THI = 1.46 K, KHI = 1.5-fold delay) signpost that TMACl can efficiently work as a potential dual-functional hydrate inhibitor for CO2 enriched mixed gas systems.

Implications of Blanc's Law for Use in Trapped Ion Mobility Spectrometry.

Blanc's Law has served as a way to predict the mobilities of ions in mixed drift gases for over 100 years yet has remained largely unexplored using newer ion mobility spectrometry (IMS) configurations, including traveling wave and trapped IMS (TIMS) systems. Here, we evaluate a drift-tube IMS (DTIMS) and compare it to a similar set of experiments performed in TIMS. We found that Blanc's Law can be applied in a DTIMS to determine the mobility of an analyte in the minor gas component of a ternary mixed drift gas system within 2% error. Additionally, the calibration procedure for TIMS to convert elution voltages into a mobility value corrects for significant deviations (>4%) from Blanc's Law in the elution voltage domain. For the range of gas identities probed in this effort, up to an 11% error in calibrated mobilities was observed when using a gas mixture in the TIMS that differed from the gas used for the reference mobility. However, when the gas mixture within the TIMS was the same as the respective calibrant mobilities, calibration errors within the TIMS were as low as 0.01%. Interestingly, when probing the behavior of ions with argon-containing mixtures within the TIMS, the current accepted paradigm of elution voltage being proportional to inverse mobilities in TIMS calibrations procedures was shown to deviate substantially from the trends observed with DTIMS measurements. With this initial effort, foundations for future mixed drift gas measurements in TIMS are set for expanded analyte classes and larger molecules.

Competitive adsorption of multicomponent volatile organic compounds on biochar

Crude oil contaminated lands are recognised to have significant contributions to airborne volatile organic compounds (VOCs) with adverse effects on human health and tropospheric ozone. Soil capping systems for controlling harmful emissions are critical engineering solutions where advanced soil remediation techniques are neither available nor feasible. Studies on the adsorption of single VOC species in biochar have shown promising results as a potential capping material; however, current understanding of mixed gas system and multi-component adsorption of VOCs on biochar which would represent more realistic in situ conditions is very limited. We present, for the first time, the results of a study on competitive adsorption of mixed VOCs, including aromatic and non-aromatic VOCs commonly emitted from crude oil contaminated sites on two types of biochar pyrolysed at 500°C from wheat straw and bagasse as feedstock. The kinetics of sorption of multicomponent VOCs including acetone, hexane, toluene and p-xylene in biochar are studied based on the results of an extensive experimental investigation using a bespoke laboratory setup. Both biochar types used in this study presented a high sorption capacity for VOC compounds when tested individually (51–110 mg/g). For the multicomponent mixture, the competition for occupying sorption sites on biochar surface resulted in a lower absolute sorption capacity for each species, however, the overall sorption capacity of biochar remained more or less similar to that observed in the single gas experiments (50–109 mg/g). The chemical interactions via hydrogen bonds, electrostatic attraction, and pore-filling were found to be the main mechanisms of adsorption of VOC in the biochar studied. The efficiency of biochar regeneration was assessed through five cycles of adsorption-desorption tests and was found to be between 88% and 96%. The incomplete desorption observed confirm the formation of likely permanent bonds and heel build-ups during the sorption process.

Experimental Measurement of Multiple Hydrate Structure Formation in Binary and Ternary Natural Gas Analogue Systems by Isochoric Equilibrium Methods

Traditionally, it is commonly assumed that a single gas hydrate (or clathrate hydrate) structure/phase is formed in natural gas systems—e.g., “s-II natural gas (NG) hydrates” or “s-I methane hydrates”—based on that which is understood to be the most thermodynamically stable at incipient phase boundary conditions. This applies with respect to both studies of hydrates in natural sediments, and in the case of hydrocarbon production operations, including the testing of low-dosage hydrate inhibitors (LDHIs). Here, we present the results of experimental studies of simple propane (C₃), binary methane–propane (C₁–C₃), and ternary methane–ethane–propane (C₁–C₂–C₃) hydrate systems, aimed at investigating phase behavior at higher subcoolings where significant water conversions to clathrates—and associated gas fractionation—might be expected to result in the formation of more than one hydrate structure. Measurements were made by means of established, reliable, isochoric equilibrium step-heating/cooling approaches. In the single guest propane system, pressure–temperature (PT) conditions follow the gas hydrate phase boundary, in agreement with the univariant hydrate + gas + water (H + G + W) equilibrium. By contrast, binary and ternary mixes clearly show PT behavior consistent with the growth of at least two and four hydrate phases, respectively, with these forming sequentially on cooling, and dissociating in the corresponding reverse order upon heating. In-house hydrate model (HydraFLASH) predictions support experimental observations, pointing to processes being gas fractionation driven; the mixed C₃–C₁ or C₃–C₂–C₁ s-II type hydrates formed first close to the phase boundary preferentially incorporating the most strongly clathrate cage (5¹²6⁴) stabilizing propane, making the remaining gas leaner. Once C₃ is largely consumed, trends agree with less stable C₂–C₁ structures (s-II followed by s-I) then growing (where ethane is present), with this, like C₃ uptake, making remaining free gas increasingly of almost pure C₁. This ultimately drives systems toward the final simple, single guest C₁ s-I clathrate formation as the well-established univariant phase boundary for this structure is reached. As observed phase behavior arises because of gas fractionation, it can be expected to occur during hydrate formation in all mixed gas systems of relatively fixed composition (at constant volume or pressure). The findings highlight that care should be taken in the application of isochoric methods to multicomponent gas systems, given the potential for numerous (rather than just one) clear changes in heating curve slopes as different hydrate structures form/dissociate. In addition, results show that extending equilibrium steps well into the hydrate region can reveal important information on clathrate phase behavior with potentially significant implications for issues such as gas production from hydrates in sediments, hydrate technologies for gas capture/separation/storage in the energy industry, and flow assurance in hydrocarbon production operations.

Optical and mass-spectral characterization of mixed-gas flowing atmospheric-pressure afterglow sources

Plasma-based ambient desorption/ionization (ADI) sources for mass spectrometry (MS) often use helium as the primary discharge gas due to the large reaction cross section of excited helium species with atmospheric gases, which ultimately leads to efficient reagent-ion formation. However, some studies have shown that mixed-gas plasmas provide unique advantages. For instance, our group showed that a helium‑oxygen flowing atmospheric-pressure afterglow (He:O2-FAPA) source yielded enhanced ion signals for small polar analytes, but compounds with aromatic rings underwent chemical modification to produce pyrylium species. Here, it is shown that the addition of H2 to the helium FAPA gas significantly decreased the reagent-ion signals, but analyte-ion signal was not affected to the same degree. In addition, mass spectra obtained with He:H2-FAPA were chemically cleaner with fewer ions stemming from analyte species and produced less oxidation of analytes. Addition of nitrogen increased the abundance of negative reagent ions (e.g., NO2− and NO3−) which led to enhanced ion signal for RDX. To better understand these unique advantages of a mixed-gas FAPA, the impact of molecular-gas (O2, N2, or H2) addition on the optical-emission spectra from the discharge was also measured. Spatially resolved emission was obtained from the anode- and negative-glow regions. In general, addition of small fractions (~0.1%) of molecular gases decreased helium and OH emission intensities. Atomic oxygen and hydrogen emission increased with the addition of O2 and H2, respectively. Furthermore, emission characteristics of N2, N2+, and NO with respect to molecular gas composition on He-FAPA were measured. Fundamental plasma parameters, such as OH rotational temperature (Trot), were also calculated for these mixed-gas systems.

Study on Mass Transfer Characteristics of Hydrate-based Gas Absorber

Hydrated-based gas separation is a method capable of selectively separating and recovering greenhouse gases. Although a conventional hydrate-based gas separation apparatus is a batch or a semi-batch system, continuous operation is preferable to increase the throughput of gas without changing the apparatus volume. Recently, we proposed a flow type apparatus to allow continuous operation of hydrate formation (absorption) and subsequent decomposition (desorption). The aim of this study is to investigate the mass transfer characteristics of the continuous apparatus using the HFC134a-N2 mixed gas system. The volumetric mass transfer coefficient was calculated especially during a steady state of gas absorption. Besides, we compared mass transfer performance between the hydrate-based gas absorber and a conventional bubble column. Sodium dodecyl sulfate was used as a hydrate dispersant. In the flow type apparatus, the gas-liquid contact was good and the hydrate slurry state was observed during hydrate formation. In the surfactant solution, the volumetric mass transfer coefficient increased in comparison with that in water. The volumetric mass transfer coefficient with hydrate was higher than that of the bubble column. These results suggest that hydrate formation improves gas absorption performance.

Flexible ligands-dependent formation of a new column layered MOF possess 1D channel and effective separation performance for CO2

A new column layered MOF with (3,6)-connected nets, namely [Co(pysa)(H2O)]n (YAU-7), was synthesized by using Co(NO3)2·6H2O and organic ligand 2-(pyrid-4′-yl)-benzimidazole-5-carboxylic acid (H2pysa) as flexible linkers. Single-crystal X-ray diffraction evidences the 3D YAU-7 MOF with (3,6)-connected nodes, a binuclear cluster [Co2(COO)2] structure and 1D tunnel feature. The weak interactions of π---π stacking enhances chemical stability of YAU-7 3D structure. Interestingly, the YAU-7 presents high chemical/thermodynamic stability, superior adsorption performance for CO2, CH4, C2H2 and C2H4, and high IAST selectivities for mixed gas systems of C2H2/CO2, C2H4/CO2, and CH4/CO2 (50/50). In contrast, YAU-7 exhibits higher uptake of CO2 (55.70 ​cm3 ​g−1) compared with CH4, C2H2, and C2H4 (27.39, 23.36, and 9.04 ​cm3 ​g−1) at 273 ​K. YAU-7 takes separation values for C2H2/CO2, C2H4/CO2, and CH4/CO2 mixture (37.6, 22.7, and 31.2) significantly higher than the C2H2/C2H4, C2H2/CH4, C2H2/CO2, C2H4/CH4 mixture gas (1.30, 1.83, 1.67). The YAU-7 MOF is a promising material for CO2 separation under ambient conditions.

Key Applications and Potential Limitations of Ionic Liquid Membranes in the Gas Separation Process of CO2, CH4, N2, H2 or Mixtures of These Gases from Various Gas Streams

Heightened levels of carbon dioxide (CO2) and other greenhouse gases (GHGs) have prompted research into techniques for their capture and separation, including membrane separation, chemical looping, and cryogenic distillation. Ionic liquids, due to their negligible vapour pressure, thermal stability, and broad electrochemical stability have expanded their application in gas separations. This work provides an overview of the recent developments and applications of ionic liquid membranes (ILMs) for gas separation by focusing on the separation of carbon dioxide (CO2), methane (CH4), nitrogen (N2), hydrogen (H2), or mixtures of these gases from various gas streams. The three general types of ILMs, such as supported ionic liquid membranes (SILMs), ionic liquid polymeric membranes (ILPMs), and ionic liquid mixed-matrix membranes (ILMMMs) for the separation of various mixed gas systems, are discussed in detail. Furthermore, issues, challenges, computational studies and future perspectives for ILMs are also considered. The results of the analysis show that SILMs, ILPMs, and the ILMMs are very promising membranes that have great potential in gas separation processes. They offer a wide range of permeabilities and selectivities for CO2, CH4, N2, H2 or mixtures of these gases. In addition, a comparison was made based on the selectivity and permeability of SILMs, ILPMs, and ILMMMs for CO2/CH4 separation based on a Robeson’s upper bound curves.

Study Explores Effects of H2S Scavenger Byproducts on Carbon Steel

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper NACE 2019-13401, “Effects of Triazine-Based H2S Scavenger Byproducts on the Film Composition and Cracking of Carbon Steel in Oilfield Applications,” by Leonardo Caseres, James Dante, and Florent Bocher, Southwest Research Institute, et al., prepared for the 2019 NACE International Corrosion Conference and Exposition, Nashville, Tennessee, USA, 24-28 March. This paper has not been peer reviewed. Triazines are commonly used as hydrogen sulfide (H2S) scavengers. However, stress corrosion cracking (SCC) has been reported recently when using certain triazines, making it necessary to understand the failure mechanism to control this phenomenon. In the complete paper, the authors seek to understand the effect of triazine on the electrochemical response of a carbon-steel surface in a mixed-gas system. Introduction One of the more frequently used H2S scavenger triazines is hexahydro-1,3,5-tris(hydroxyethyl)-s-triazine, or monoethanol amine (MEA)-triazine. It is a yellow, viscous liquid that can be injected into gas streams or used in a contactor tower. It removes H2S from the gas stream. It is relatively inexpensive, easy to use, and effective. The MEA byproducts that form during the scavenging process, however, may cause SCC of steel pipes, as reflected in the literature. On the basis of these findings, it is suggested that SCC is governed by corrosion processes and specifically by the transition from a passive to an active surface. This transition is a complicated function of acid gas concentration [carbon dioxide (CO2) and H2S] and amine adsorption, which are likely different for different systems. Several possible mechanisms exist by which cracking can be induced. First, a reduction in H2S content can reduce the semiprotective iron-sulfide film, thus changing the nature of the active/passive transition and making cracking more likely. Second, specific adsorption of amines onto the surface of the steel will result in a change in the active/passive transition. Therefore, characterization of the MEA/H2S reaction process, the adsorption of amines onto steel, and the electrochemical behavior of the steel under these circumstances are important factors that require study. In this paper, the electrochemistry of API X601 steel is assessed under a variety of test solutions containing H2S, CO2, and MEA triazine. Environmental Conditions The specimens were 0.25 in. in diameter and 4 in. long. Approximately 3 in. of the specimen length was exposed to the solution. All electrochemical tests were conducted at room temperature and atmospheric pressure. Three gas mixtures were employed: 20-ppm H2S balanced with dinitrogen (N2), 20-ppm H2S/2 mol% CO2, and 100% N2. In addition, three triazine-inhibitor (35% triazine concentration solution) volumetric additions were used. The actual inhibitor concentrations in solution were not determined; instead, the H2S concentration in the gas phase was measured with a sensor after the addition of the inhibitor. The supporting electrolyte [0.1-M potassium chloride (KCl)] solution was deaerated N2 gas.

Application of tubular silicone (PDMS) membranes for gas monitoring in CO2–CH4 hydrate exchange experiments

The exchange of hydrate-bond CH4 with CO2 is one possible method for the production of CH4 from hydrate-bearing sediment which was investigated on different scales in the SUGAR project. Tubular polydimethylsiloxane (PDMS) membranes were utilized to monitor the spatial and temporal gas distribution in a large-scale experimental simulation on CO2–CH4 gas hydrate exchange.The suitability of PDMS membranes for the measurement of gaseous and dissolved CO2 and CH4 concentrations in pure and mixed gas systems was evaluated in lab-scale experiments. The results reveal a strong interacting mutual influence of CO2 and CH4 in CO2–CH4 mixed feed composition and in the presence of water. The competitive absorption between CO2 and H2O as well as membrane plasticization, which increases CH4 permeability and reduces CO2 permeability, makes a direct correlation of mixed systems to pure systems and a quantification of the gas concentration in the feed reservoir impossible.The successful run of five tubular PDMS membranes, employed in a large test reservoir during an experimental simulation of CO2-driven CH4 hydrate decomposition, demonstrates the high stability of the material in harsh conditions. Also, a time-resolved observation of the progressing CO2 front is possible and makes membrane incorporation a valuable addition to conventional ex situ gas measurements in reservoir tests of various dimensions. The monitoring technique can significantly contribute to a comprehensive process understanding with respect to the spatial distribution of hydrate formation, dissociation and reformation in the presence of CO2 and CH4.

Natural gas sweetening polymeric membrane: Established optimum operating condition at 70% of CO2 concentration feed gas stream

PETRONAS embarks on breakthrough technology for natural gas sweetening in high CO2 gas fields. Membrane technology is found to be one with high potential and a promising technology for bulk CO2 removal from natural gas. It can be suited to wide operating conditions to process varied natural gas composition, pressure and temperature. This paper focuses on the extensive development of PETRONAS in-house membrane and its evaluation for gas separation performance for high CO2 feed gas at different operating conditions; eg. feed gas flowrate, temperature, pressure, CO2 concentration in mixed gas system, and permeate pressure. For all the cases in this study, samples were tested at optimum gas flowrate of 1000 standard cm3/min (sccm) to obtain representative membrane performance. Feed gas pressure and CO2 concentration have shown significantly affect membrane permeation properties; whereas feed gas temperature and permeate pressure showed negligible impact. There is a trade-off between permeance and selectivity when CO2 concentration is increased from 40% to 70%; where the CO2 permeance increased by 12% which consequently reduces CO2/CH4 selectivity by 15%. In summary, the membrane developed in this study demonstrates high pressure durability up to 50 bar and temperature up to 55oC with satisfactory gas separation performance in the presence of high CO2 concentration in feed gas (up to 70% CO2). This work is breakthrough in establishing the operational boundary of PETRONAS Membrane for technology development and deployment in monetizing high CO2 gas field.

A Micromachined Metal Oxide Composite Dual Gas Sensor System for Principal Component Analysis-Based Multi-Monitoring of Noxious Gas Mixtures.

Microelectronic gas-sensor devices were developed for the detection of carbon monoxide (CO), nitrogen dioxides (NO2), ammonia (NH3) and formaldehyde (HCHO), and their gas-sensing characteristics in six different binary gas systems were examined using pattern-recognition methods. Four nanosized gas-sensing materials for these target gases, i.e., Pd-SnO2 for CO, In2O3 for NOX, Ru-WO3 for NH3, and SnO2-ZnO for HCHO, were synthesized using a sol-gel method, and sensor devices were fabricated using a microsensor platform. Principal component analysis of the experimental data from the microelectromechanical systems gas-sensor arrays under exposure to single gases and their mixtures indicated that identification of each individual gas in the mixture was successful. Additionally, the gas-sensing behavior toward the mixed gas indicated that the traditional adsorption and desorption mechanism of the n-type metal oxide semiconductor (MOS) governs the sensing mechanism of the mixed gas systems.

Selection and Optimization of Composting Packing Media for Biofiltration of Mixed Waste Odors

Biological filtration is an effective biological treatment method for odorous pollutants. The aim of this study was to determine the relationship between the humification degrees of the media and the removal efficiency of the odors. The biological treatment of a mixed waste gas system in four biofilters packed with COM1, COM2, COM3, and COM4 media (media with different humification degrees) was studied. The pilot experiment showed that with the mixed waste gases, the removal rate of methyl mercaptan was 100% via all four different packing media. The finished product composting (COM4) had the best removal efficiency on ammonia, hydrogen sulfide, toluene, and methyl mercaptan, with values of 97.38%, 97.03%, 98.31%, and 100%, respectively. Therefore, the media of COM4 was applied in the compost plant for treating odors and its practical application value was verified. And results of field experiment showed that before replacing the filter, the least removal efficiency of methyl mercaptan of the biofilter was 17.22%. After changing the filter, the value was up to 100%. Besides that, the removal efficiencies of ammonia increased from 38.10% to 89.84% and hydrogen sulfide increased from 24.05% to 87.95%, and the removal rate of carbon disulfide increased by 51%. The higher humification degrees of the media is proved to be beneficial to the removal of odors.

Numerical simulations of the SF6-N2 mixed gas streamer discharge development process

In recent years, as environmental protection requirements have expanded, SF6/N2 mixed gases have been selected as an insulating medium for high-voltage equipment such as GIL (gas insulated transmission line) without undertaking breaking tasks, which is superior in terms of insulation, economy and environmental protection. The development of streamers and the two-dimensional distribution of positive and negative ions over time in an SF6/N2 mixed gas system are shown in this research. The SF6/N2 mixed gas is adopted as the research object, and the discharge model for a needle-plate electrode under mixed gas conditions is built. COMSOL Multiphysics is used to develop a fluid dynamics model for the SF6/N2 mixed gas discharge in a non-uniform field. The spatio-temporal evolution processes for the electron, positive ion and negative ion densities and the electric field strength during discharge are obtained through numerical simulations. At the same time, the influence of the voltage amplitude and mixed gas ratio on the development process of streamers is studied. The presented simulation results can provide a certain microscopic interpretation for the needle-plate discharge defects that appear in power equipment using SF6/N2 mixed gas.

Phase Behavior and Raman Spectroscopic Analysis for CH4 and CH4/C3H8 Hydrates Formed from NaCl Brine and Monoethylene Glycol Mixtures

We present pure CH4 and CH4/C3H8 mixed hydrate phase equilibria formed from a mixture of NaCl (10 wt %) and monoethylene glycol (MEG, 10 and 30 wt %) solutions. As expected for thermodynamic inhibitors, the mixture of salt and glycol causes the hydrate phase equilibrium boundary to shift to lower temperatures and higher pressures, and on increasing the MEG concentration, the hydrate stable region shifted more. The measured experimental data are also compared with a thermodynamic model recently developed, named the Hu–Lee–Sum correlation, showing that the data match well with the predictions. The experimental data were used to calculate the enthalpy of hydrate dissociation. The enthalpies of CH4 hydrates in the mixture of 10 wt % NaCl brine and 10 or 30 wt % MEG were found to be ∼58.7 and 54.63 kJ/mol, respectively, corresponding to structure I hydrates, whereas for the CH4/C3H8 (91.98:8.02 mol %) mixed gas system, the enthalpies of dissociation were found to be ∼101.10 kJ/mol (10 wt % NaCl + 10 wt % MEG) ...

Impacts of ammonium based ionic liquids alkyl chain on thermodynamic hydrate inhibition for carbon dioxide rich binary gas

In this work, the thermodynamic inhibition impact of four ammonium-based ionic liquids (AILs) on CO2 rich mixed gas hydrate system (70–30mol% CO2+CH4) is experimentally studied, and the observed behaviour is modelled. The studied AILs are; tetramethylammonium hydroxide (TMAOH), tetraethylammonium hydroxide (TEAOH), tetrapropylammonium hydroxide (TPrAOH) and tetrabutylammonium hydroxide (TBAOH). Initially, the impact of 10wt% AILs in an aqueous solution on the CO2 enriched binary gas phase boundary is evaluated by measuring the dissociation temperature in the pressure range of 1.90–5.10MPa. The thermodynamic inhibition influence of AILs is quantitatively analyzed by calculating the hydrate suppression temperatures for all studied systems. Further, the Clausius–Clapeyron equation is used to determine the molar hydrate enthalpy of dissociation (∆Hdiss) for the studied systems. The results revealed that the inhibition influence of AILs is observed to be decreasing with the increasing alkyl chain length of AILs. Excluding TBAOH, all the other studied AILs act as thermodynamic inhibitors due to the relatively shorter alkyl chain. The ∆Hdiss results of the binary mixed gas system in the presence and absence of AILs revealed that the presence of TMAOH, TEAOH and TPrAOH has negligible effect in hydrate cages formation. However, TBAOH exhibited a significant change in ∆Hdiss which indicates the semi-clathratic nature of it. Among the considered AILs, TMAOH shown better thermodynamic impact attributed to its shortest alkyl chain length. Therefore it is further investigated for various concentrations (1, 5 and10wt%). Moreover, the measured, mixed gas hydrate phase boundaries of various aqueous AILs solutions are also predicted via electrolyte model proposed by Dickens and Quinby-Hunt and are found to be in good agreement with the experimental data apart from TBAOH. Therefore, this study is relevant for the understanding of structural variations (alkyl chain elongation) of AILs on the hydrate phase stability of the high CO2 content mixed gas system.