Modeling of Nitrogen Removal from Natural Gas in Rotating Packed Bed Using Artificial Neural Networks

Novel or unconventional technologies are critical to providing cost-competitive natural gas supplies to meet rising demands and provide more opportunities to develop low-quality gas fields with high contaminants, including high carbon dioxide (CO₂) fields. High nitrogen concentrations that reduce the heating value of gaseous products are typically associated with high CO₂ fields. Consequently, removing nitrogen is essential for meeting customers' requirements. The intensification approach with a rotating packed bed (RPB) demonstrated considerable potential to remove nitrogen from natural gas under cryogenic conditions. Moreover, the process significantly reduces the equipment size compared to the conventional distillation column, thus making it more economical. The prediction model developed in this study employed artificial neural networks (ANN) based on data from in-house experiments due to a lack of available data. The ANN model is preferred as it offers easy processing of large amounts of data, even for more complex processes, compared to developing the first principal mathematical model, which requires numerous assumptions and might be associated with lumped components in the kinetic model. Backpropagation algorithms for ANN Lavenberg-Marquardt (LM), scaled conjugate gradient (SCG), and Bayesian regularisation (BR) were also utilised. Resultantly, the LM produced the best model for predicting nitrogen removal from natural gas compared to other ANN models with a layer size of nine, with a 99.56% regression (R²) and 0.0128 mean standard error (MSE).

Methane and Carbon Dioxide Hydrate Formation in the Presence of Metal-Based Fluid

Hydrate-based technology has yet to find its way to commercial applications due to several issues, including formation conditions and slow kinetics. Several solid particles were introduced to speed up hydrate formation. However, these solid compounds have given contradictory results. This study investigated the effect of high thermal conductive metallic nanofluids of silver (Ag) and copper (Cu) on CH₄ and CO₂ hydrates. The solid particles were suspended in a 0.03 wt% SDS aqueous solution, and the results were compared with the 0.03 wt% SDS and deionized water samples. A stirred tank batch reactor was used to conduct the thermodynamic and kinetic experiments. The thermodynamic study revealed that 0.1 wt% of solid particles do not shift the equilibrium curve significantly. The kinetic evaluation, including induction time, the initial rate of gas consumption, half-completion time, t₅₀ and semi-completion time, t₉₅, gas uptake, and storage capacity, have been studied. The results show that the Ag and Cu promote CH₄ hydrates while they inhibit or do not significantly influence the CO₂ hydrates formation. A predictive correlation was introduced to get the apparent rate constant of hydrate formation in the presence of metal-based fluid at the concentrations range of 0.005-0.1 wt%.

Correction to "Suitable Binary and Ternary Thermodynamic Conditions for Hydrate Mixtures of CH4, CO2, and C3H8 for Gas Hydrate-Based Applications"

[This corrects the article DOI: 10.1021/acsomega.1c06186.].

Suitable Binary and Ternary Thermodynamic Conditions for Hydrate Mixtures of CH4, CO2, and C3H8 for Gas Hydrate-Based Applications

The selection of suitable hydrate formers and their respective gas composition for high hydrate formation, driving force is critical to achieve high water recovery and metal removal efficiency in the hydrate-based desalination process. This study presents a feasibility analysis on the possible driving force and subcooling temperatures for the binary and ternary mixtures of methane, carbon dioxide, and propane for hydrates-based desalination process. The driving force and subcooling for the gas systems was evaluated by predicting their hydrate formation phase boundary conditions in 2 wt % NaCl systems at pressure ranges from 2.0-4.0 MPa and temperatures of 1-4 °C using modified Peng-Robinson equation of state in the PVTSim software package. The results suggest that the driving force of CH₄ + C₃H₈ and CO₂ + C₃H₈ binary systems are similar to their ternary systems. Thus, the use of binary systems is preferable and simpler than the ternary systems. For binary gas composition, CO₂ + C₃H₈ (70:30) exhibited a higher subcooling temperature of 8.07 °C and driving force of 1.49 MPa in the presence of 2 wt % aqueous solution. In the case of the ternary system, CH₄-C₃H₈-CO₂ gas composition of 10:80:10 provided a good subcooling temperature of 12.86 °C and driving force of 1.657 MPa for hydrate formation. The results favor CO₂-C₃H₈ as a preferred hydrate former for hydrate-based desalination. This is attributed to the formation of sII structure and it constitutes 136 water molecules which signifies a huge potential of producing more quantities of treated water.

Insights on Cryogenic Distillation Technology for Simultaneous CO2 and H2S Removal for Sour Gas Fields

Natural gas demand has dramatically increased due to the emerging growth of the world economy and industry. Presently, CO2 and H2S content in gas fields accounts for up to 90% and 15%, respectively. Apart from fulfilling the market demand, CO2 and H2S removal from natural gas is critical due to their corrosive natures, the low heating value of natural gas and the greenhouse gas effect. To date, several gas fields have remained unexplored due to limited technologies to monetize the highly sour natural gas. A variety of conventional technologies have been implemented to purify natural gas such as absorption, adsorption and membrane and cryogenic separation. The application of these technologies in natural gas upgrading are also presented. Among these commercial technologies, cryogenic technology has advanced rapidly in gas separation and proven ideally suitable for bulk CO2 removal due to its independence from absorbents or adsorbents, which require a larger footprint, weight and energy. Present work comprehensively reviews the mechanisms and potential of the advanced nonconventional cryogenic separation technologies for processing of natural gas streams with high CO2 and H2S content. Moreover, the prospects of emerging cryogenic technologies for future commercialization exploitation are highlighted.

Physical property and gas transport studies of ultrathin polysulfone membrane from 298.15 to 328.15 K and 2 to 50 bar: atomistic molecular simulation and empirical modelling

Elucidation of ultrathin polymeric membrane at the laboratory scale is complicated at different operating conditions due to limitation of instruments to obtain in situ measurement data of membrane physical properties. This is essential since their effects are reversible. In addition, tedious experimental work is required to collect gas transport data at varying operating conditions. Recently, we have proposed a validated Soft Confining Methodology for Ultrathin Films that can be used to simulate ultrathin polysulfone (PSF) membranes upon confinement limited to 308.15 K and 2 bars. In industry application, these ultrathin membranes are operated within 298.15–328.15 K and up to 50 bars. Therefore, our proposed methodology using computational chemistry has been adapted to circumvent limitation in experimental study by simulating ultrathin PSF membranes upon confinement at different operating temperatures (298.15 to 328.15 K) and pressures (2 to 50 bar). The effect of operating parameters towards non-bonded and potential energy, free volume, specific volume and gas transport data (e.g. solubility and diffusivity) for oxygen and nitrogen of the ultrathin films has been simulated and collected using molecular simulation. Our previous empirical equations that have been confined to thickness dependent gas transport properties have been modified to accommodate the effect of operating parameters. The empirical equations are able to provide a good quantitative characterization with R² ≥ 0.99 consistently, and are able to be interpolated to predict gas transport properties within the range of operating conditions. The modified empirical model can be utilized in process optimization studies to determine optimal membrane design for typical membrane specifications and operating parameters used in industrial applications.

Pioneering work to elucidate and model the effect of operating conditions on physical and transport properties of ultrathin membranes.

Rheology Impact of Various Hydrophilic-Hydrophobic Balance (HLB) Index Non-Ionic Surfactants on Cyclopentane Hydrates

In this study, series of non-ionic surfactants from Span and Tween are evaluated for their ability to affect the viscosity profile of cyclopentane hydrate slurry. The surfactants; Span 20, Span 40, Span 80, Tween 20, Tween 40 and Tween 80 were selected and tested to provide different hydrophilic–hydrophobic balance values and allow evaluation their solubility impact on hydrate formation and growth time. The study was performed by using a HAAKE ViscotesterTM 500 at 2 °C and a surfactant concentration ranging from 0.1 wt%–1 wt%. The solubility characteristic of the non-ionic surfactants changed the hydrate slurry in different ways with surfactants type and varying concentration. The rheological measurement suggested that oil-soluble Span surfactants was generally inhibitive to hydrate formation by extending the hydrate induction time. However, an opposite effect was observed for the Tween surfactants. On the other hand, both Span and Tween demonstrated promoting effect to accelerate hydrate growth time of cyclopentane hydrate formation. The average hydrate crystallization growth time of the blank sample was reduced by 86% and 68% by Tween and Span surfactants at 1 wt%, respectively. The findings in this study are useful to understand the rheological behavior of surfactants in hydrate slurry.

Optimization of Washing Processes in Solvothermal Synthesis of Nickel-Based MOF-74

Solvothermal synthesis is the most preferable preparation technique of metal–organic frameworks (MOFs) that consists of reactants mixing, ultrasonication, solvothermal reaction, product washing, and solvent evacuation. Owing to fast reaction kinetics in solvothermal reaction, this technique allows for production of uniform MOF particles with high crystallinity, high phase purity, and small particle sizes. However, it exhibits some difficulties of washing processes that may involve the blockage of pores due to incomplete removal of reactive medium from MOF products. The present study proposes an improvement of washing processes by introducing centrifugal separations with optimized parameters at two different stages: after reaction and after product washing. Nickel-based MOF-74 was synthesized as the experimental material for this purpose. The quality of the produced sample was evaluated by gas adsorption performance using CO₂ at 1 bar and 25 °C. The final sample of the optimized synthesis routes was able to adsorb 5.80 mmol/g of CO₂ uptake, which was competitive with literature data and significantly higher than the sample of the basic synthesis. Fourier-transform infrared spectroscopy (FTIR) and powder X-ray diffraction (PXRD) analysis revealed that the sample displayed much higher crystallinity structure and was clean from impurities after centrifugations. The outcome indicated the success of separation between MOF products and reactive medium during washing processes, leading to the effective pore activation of MOFs.

High frequency ultrasonic-assisted CO2 absorption in a high pressure water batch system

Physical absorption process is always nullified by the presence of cavitation under low frequency ultrasonic irradiation. In the present study, high frequency ultrasonic of 1.7MHz was used for the physical absorption of CO2 in a water batch system under elevated pressure. The parameters including ultrasonic power and initial feed pressure for the system have been varied from 0 to 18W and 6 to 41bar, respectively. The mass transfer coefficient has been determined via the dynamic pressure-step method. Besides, the actual ultrasonic power that transmitted to the liquid was measured based on calorimetric method prior to the absorption study. Subsequently, desorption study was conducted as a comparison with the absorption process. The mechanism for the ultrasonic assisted absorption has also been discussed. Based on the results, the mass transfer coefficient has increased with the increasing of ultrasonic power. It means that, the presence of streaming effect and the formation of liquid fountain is more favorable under high frequency ultrasonic irradiation for the absorption process. Therefore, high frequency ultrasonic irradiation is suggested to be one of the potential alternatives for the gas separation process with its promising absorption enhancement and compact design.

An investigation of blended polymeric membranes and their gas separation performance

Novel blend glassy/rubbery polymeric membranes were produced, and, by adding 20% PVA_c to PES, good selectivity results were obtained.

CO2 and CH4 permeation through zeolitic imidazolate framework (ZIF)-8 membrane synthesized via in situ layer-by-layer growth: an experimental and modeling study

In this work, a general model representing the permeation of CO₂ and CH₄ through Zeolitic Imidazole Framework-8 (ZIF-8) membrane synthesized via in situ layer-by-layer growth under microwave irradiation is developed.

Toxic release consequence analysis tool (TORCAT) for inherently safer design plant

Many major accidents due to toxic release in the past have caused many fatalities such as the tragedy of MIC release in Bhopal, India (1984). One of the approaches is to use inherently safer design technique that utilizes inherent safety principle to eliminate or minimize accidents rather than to control the hazard. This technique is best implemented in preliminary design stage where the consequence of toxic release can be evaluated and necessary design improvements can be implemented to eliminate or minimize the accidents to as low as reasonably practicable (ALARP) without resorting to costly protective system. However, currently there is no commercial tool available that has such capability. This paper reports on the preliminary findings on the development of a prototype tool for consequence analysis and design improvement via inherent safety principle by utilizing an integrated process design simulator with toxic release consequence analysis model. The consequence analysis based on the worst-case scenarios during process flowsheeting stage were conducted as case studies. The preliminary finding shows that toxic release consequences analysis tool (TORCAT) has capability to eliminate or minimize the potential toxic release accidents by adopting the inherent safety principle early in preliminary design stage.