Recent Advances of Polymeric Membranes in Tackling Plasticization and Aging for Practical Industrial CO2/CH4 Applications—A Review

Membranes are a promising technology for bulk CO2 separation from natural gas mixtures due to their numerous advantages. Despite the numerous fundamental studies on creating better quality membrane efficiency, scaling up the research work for field testing requires huge efforts. The challenge is to ensure the stability of the membrane throughout the operation while maintaining its high performance. This review addresses the key challenges in the application of polymeric technology for CO2 separation, focusing on plasticization and aging. A brief introduction to the properties and limitations of the current commercial polymeric membrane is first deliberated. The effect of each plasticizer component in natural gas towards membrane performance and the relationship between operating conditions and the membrane efficiency are discussed in this review. The recent technological advancements and techniques to overcome the plasticization and aging issues covering polymer modification, high free-volume polymers, polymer blending and facilitated transport membranes (FTMs) have been highlighted. We also give our perspectives on a few main features of research related to polymeric membranes and the way forwards. Upcoming research must emphasize mixed gas with CO2 including minor condensable contaminants as per real natural gas, to determine the competitive sorption effect on CO2 permeability and membrane selectivity. The effects of pore blocking, plasticization and aging should be given particular attention to cater for large-scale applications.

Research on Organic Nanopore Adsorption Mechanism and Influencing Factors of Shale Oil Reservoirs

The adsorption properties of shale oil are of great significance to the development of shale oil resources. This study is aimed at understanding the microscopic adsorption mechanism of shale oil in organic nanopores. Thus, a molecular model of organic micropore walls and multicomponent fluids of CO2, C4H10, C8H18, and C12H26 is constructed to investigate the adsorption pattern of multicomponent fluids in organic nanopores under different temperature and pore size conditions. The quantity and heat of adsorption are simulated with the Monte Carlo method, which has been used in previous studies for single-or two-component fluids. The results demonstrate that the ability of CO2 to displace various alkanes is different. Specifically, medium-chain n-alkanes are slightly weaker than light alkanes in competitive sorption, and long-chain n-alkanes are less conducive to competitive sorption. The higher the CO2 sorption ratio, the more the sorption sites occupied by CO2. Thus, it is the best replacement for shale oil. The adsorption quantity of carbon dioxide, n-butane, and n-octane in organic nanopores first increases and then decreases as temperature rises. Meanwhile, the adsorption quantity of n-dodecane decreases firstly and then increases. With the increase in the pore size, the adsorption quantity of carbon dioxide, n-butane, and n-octane in organic nanopores increases while the adsorption quantity of n-dodecane first increases and then decreases. Besides, the model with larger pore sizes is more sensitive to pressure changes in the adsorption of carbon dioxide and n-butane than the model with smaller pore sizes. The heat of adsorption is CO2, C12H26, C8H18, and C4H10 in descending order. All are physical adsorption. Moreover, the adsorption quantity of all four components mixed fluid in the organic matter nanopores is positively correlated with the heat of adsorption.

SORPTION OF ERYTHROSINE ONTO SILICA GEL MODIFIED BY CETYLPYRIDINIUM BROMIDE

In the current paper, adsorbent based on silica gel L 40/100 modified with cetylpyridinium bromide was obtained. The presence of cetylpyridinium cations on the silica gel surface was confirmed by the diffuse reflectance infrared fourier transform spectroscopy method. The sorption conditions of erythrosine from dilute aqueous solutions with the proposed sorbent were studied and optimized. It is shown that the use of modified silica gel allows efficient (>95%) extraction of erythrosine from aqueous solutions. Under optimal sorption conditions (pH 7, sorbent dosage 0.1 g and sorption time is 15 min), the sorption capacity of modified erythrosine sorbents was determined. It is shown that, with increasing temperature, a change in the isotherm type from the H‑type to the L‑type is observed. This change can be explained by the aggregation of erythrosin in solution, which is a competitive sorption process. It was shown that adsorption isotherms were well described by the Langmuir equation. Thermodynamic studies have made it possible to establish the spontaneous sorption. The desorption of erythrosine from the surface of silica gel modified with cetylpyridinium bromide was studied. It is shown that when using solutions of sulfuric acid, sodium hydroxide and distilled water, desorption does not occur. It was shown that the most effective eluent is solution of sodium dodecylsulfate in alkaline medium, and desorption of erythrosine occurs due to the destruction of ion pairs of dye anions with cetylpyridinium cations fixed on the surface. The data obtained can then be used to develop a test system for determination of erythrosine via corresponding colorimetric scales or for quantitative solid phase extraction and adsorption-spectroscopic quantification of erythrosine in some real samples.

Numerical Simulation and Modeling on CO2 Sequestration Coupled with Enhanced Gas Recovery in Shale Gas Reservoirs

CO2 geological sequestration in shale is a promising method to mitigate global warming caused by greenhouse gas emissions as well as to enhance the gas recovery to some degree, which effectively addresses the problems related to energy demand and climate change. With the data from the New Albany Shale in the Illinois Basin in the United States, the CMG-GEM simulator is applied to establish a numerical model to evaluate the feasibility of CO2 sequestration in shale gas reservoirs with potential enhanced gas recovery (EGR). To represent the matrix, natural fractures, and hydraulic fractures in shale gas reservoirs, a multicontinua porous medium model will be developed. Darcy’s and Forchheimer’s models and desorption-adsorption models with a mixing rule will be incorporated into the multicontinua numerical model to depict the three-stage flow mechanism, including convective gas flow mainly in fractures, dispersive gas transport in macropores, and CH4-CO2 competitive sorption phenomenon in micropores. With the established shale reservoir model, different CO2 injection schemes (continuous injection vs. pulse injection) for CO2 sequestration in shale gas reservoirs are investigated. Meanwhile, a sensitivity analysis of the reservoir permeability between the hydraulic fractures of production and injection wells is conducted to quantify its influence on reservoir performance. The permeability multipliers are 10, 100, and 1,000 for the sensitivity study. The results indicate that CO2 can be effectively sequestered in shale reservoirs. But the EGR of both injection schemes does not perform well as expected. In the field application, it is necessary to take the efficiency of supplemental energy utilization, the CO2 sequestration ratio, and the effect of injected CO2 on the purity of produced methane into consideration to design an optimal execution plan. The case with a permeability multiplier of 1,000 meets the demand for both CO2 sequestration and EGR, which indicates that a moderate secondary stimulation zone needs to be formed between the primary hydraulic fractures of injection and production wells to facilitate the efficient energy transfer between interwell as well as to prevent CO2 from channeling. To meet the demand for CO2 sequestration in shale gas reservoirs with EGR, advanced and effective fracking is essential.

Modeling of sorption kinetics of U(VI) micro-quantities nanostructured materials with anatase mesoporous structures

The sorption kinetics of uranyl ions micro-quantities from fluoride solutions by nanostructured materials with anatase mesoporous structures has been studied. Using the model of competitive sorption of ions and positively charged complexes of uranyl ion on deprotonated hydroxyl groups of an anatase, kinetic curves of changes in the ratio of ionic forms of uranium in solution were calculated. Modeling was carried out under the assumption of a two-stage mechanism of uranium complex ions sorption. The modeling considered the influence of the uranyl ion carbonate complexes formation. The shift in equilibrium among ionic forms of uranyl correlates with the stability of the complexes in solution.

Competing Sorption of Se(IV) and Se(VI) on Schwertmannite

Schwertmannite (SHM) is a naturally occurring mineral that has been shown to effectively scavenge oxyanions from contaminated water. In this study, Fourier-transform infrared spectroscopy and X-ray absorption spectroscopy techniques in combination with wet-chemical techniques were used to study the competitive sorption of Se(IV) and Se(VI) at pH 3. The experiments were conducted with three types of schwertmannite obtained from oxidative synthesis, biogenic synthesis and high-pressure compaction at different initial Se concentrations and mixing ratios for 48 h and 56 days, respectively. A threshold value for the uptake mechanisms was identified, which reflects the amount of easily exchangeable sulphate (~0.5 mmol/g). At adsorbate concentrations below this threshold, an inner-sphere corner-sharing bidentate binuclear complex forms upon exchange with sulphate. At higher concentrations, both oxyanions become bound to SHM through co-occurrence of mainly inner-sphere and partly outer-sphere corner-sharing bidentate binuclear complexes with Fe(III) containing surface sites. Single species experiments clearly indicate a higher affinity of SHM for Se(IV). However, in mixed species experiments, competitive sorption occurs with equal or even preferential uptake of Se(VI) at concentrations much lower than the threshold value, presumably due to geometrical similarity between selenate and sulphate, and increasing preference for Se(IV) at high Se concentrations.

Challenges in Membrane Process for Gas Separation from Natural Gas

Membrane technology is cost effective solution for CO2 removal from natural gas. However, there is challenges during its application depending on the polymer material characteristic. Understanding on the polymer fundamental and transport properties, will enable proper design of pre-treatment and operating conditions that suits its capability envelope. Diffusivity selective membrane favors high pressure and high temperature conditions and vice versa for solubility selective polymer. On top of that, the robustness and durability of the resultant membrane, need to be evaluated with multicomponent mixture to understand the effect of competitive sorption, plasticization and aging phenomena that will seriously impacting the membrane performance during its application.

Preparation of Chitosan/Calcium Alginate/Bentonite Composite Hydrogel and Its Heavy Metal Ions Adsorption Properties

In order to avoid the secondary pollution of the toxic residue of chemical crosslinking agent accompanied by chemical hydrogel adsorbent and enhance the adsorption performance of physical hydrogel, chitosan/calcium alginate/bentonite (CTS/CA/BT) composite physical hydrogel was constructed. The formation mechanism and structure of the composite hydrogel were determined by FTIR, XRD and SEM. Adsorption performances of the hydrogel toward Pb2+, Cu2+ and Cd2+ in water under different condition as well as multi-ion competitive sorption were investigated. The adsorption processes were described with the canonical adsorption kinetics and isotherms models. With the utilization of XPS analysis and adsorption thermodynamics analysis, it was found that the adsorptions were spontaneous physico-chemical adsorptions. The results showed that the maximum adsorption capacity of the hydrogel for Pb2+, Cu2+ and Cd2+ reached up to 434.89, 115.30 and 102.38 mg·g−1, respectively, better than those of other physical hydrogels or chitosan/bentonite composite. Moreover, the composite hydrogel improved the collectability of bentonite and showed a good reusability. The modification of bentonite and the formation of hydrogel were completed simultaneously, which greatly simplifies the operation process compared with the prior similar works. These suggest that the CTS/CA/BT composite hydrogel has promising application prospects for removal of heavy metal ions from water.