Experimental study on the influence of aerated gas pressure and confining pressure on low-rank coal gas adsorption process

To deeply study the variation characteristics of the gas content in the process of gas adsorption for coal samples under different gas pressures and confining pressures, low-field nuclear magnetic resonance technology was used to carry out experimental research on the gas adsorption of coal. The relationship between the T2 spectrum amplitude integral and the gas quantity was analyzed. The results show the following: (1) When the samples were inflated for 11 h at each gas pressure point (0.31, 0.74, 1.11, and 1.46 MPa), after ∼5 h of adsorption, the amount of adsorbed gas exceeded 85.0% of the total adsorption capacity; additionally, as the adsorption time increased, the amount of adsorbed gas gradually tended to stabilize. When the gas pressure was >1 MPa, the amount of adsorbed gas exceeded 90.0% of the total adsorption capacity; Higher the pressure of aerated gas, greater the gas pressure gradient or concentration gradient on the surface of the coal sample and the greater the driving force for gas molecules to seep or diffuse into the coal sample. (2) When the samples were inflated for 11 h at each confining pressure point (3, 4, 5, and 7 MPa), the adsorbed gas increased by ∼85.0% of the total adsorbed gas in the first 5 h. When the pressure was <5 MPa, the amount of adsorbed gas exceeded 85.0% of the total amount of adsorption; that is, the increase in adsorbed gas was the largest at ∼5 h in the adsorption process for the columnar coal sample under different confining pressures, and the increase was ∼5.0% from 7–11 h. When the large pores in the coal sample closed, the amount of gas that seeped into the deep part of the coal sample within the same aeration time was reduced.

Different Response to Cd2+ Adsorption by Alkali-modified Biochars Derived From Soybean Straw and Rape Straw

Biochars have been modified by alkali (Ca(OH)2) to enhance Cd sorption capacity in aqueous solution. In this research, the alkali-modified (Ca) biochars were prepared by co-pyrolyzing lime (Ca(OH)2) and soybean straw (SBB) or rape straw (RSB) at 450 °C. The absorption mechanism was investigated by a series of experiments and was provided by quantitative analysis. The maximum adsorption capacities of Cd2+ by Ca-SBB and Ca-RSB were calculated to be 78.49 mg g−1 and 49.96 mg g−1, which were 1.56 and 1.48 times higher than SBB (50.40 mg g−1) and RSB (33.79 mg g−1), respectively. Compared with the original biochar (SBB, RSB), alkali-modified biochars (Ca-SBB and Ca-RSB) were found to have faster adsorption kinetics and lower desorption efficiencies. The mechanism study indicated that Ca(OH)2 modification effectively enhanced the contribution of ion exchange and decreased the contribution of functional groups complexation. After Ca(OH)2 modification, precipitation and ion exchange mechanisms dominated Cd2 + absorption on Ca-SBB, accounting for 49.85% and 34.94% of the total adsorption, respectively. Similarily ion exchange and precipitation were the main adsorption mechanism on Ca-RSB, accounting however for 61.91% and 18.47% of total adsorption, respectively. These results suggested that alkali-modified biochars have great potential in adsorbing cadmium in wastewater.

Quantitative determination of organic adsorption capacity in the Palaeozoic shales from South China

In this study, the methane adsorption capacity of kerogen isolated from the Cambrian, Silurian, and Permian shales and the impact of soluble organic matter (SOM) on the adsorption capacity of these shales were investigated. The results reveal that 1) the adsorption capacity of kerogen varies in a broad range, from 14.48 to 23.22 cm3/g for the Cambrian kerogens, from 15.50 to 36.06 cm3/g for the Silurian kerogens, and from 10.71 to 11.15 cm3/g for the Permian kerogens; 2) the kerogen adsorption accounts for 33.67–70.23% of the total adsorption capacity of these Palaeozoic extracted shales, demonstrating that kerogen is the primary adsorbing substance in shales; 3) the adsorption isotherms of kerogen in highly mature Cambrian and Silurian shales are similar to those of Triassic coal, while the isotherms of kerogen in the relatively immature Permian shales are similar to those of the immature oil shales; and 4) the SOM demonstrates a significant impact on the adsorption capacity of shales as the removal of SOM can cause a maximum increase of 34.29% or a decrease of 23.36% in the total adsorption capacity of shales. However, there is no clear understanding of the impact of SOM on the methane sorption of shales.

Kinetics and Thermodynamic Studies of Cu(II) Ion Adsorption Onto Synthetic Zeolite Synthesized from Coal Fly Ash: Effect of the Co-Ions to the Total Adsorption

Study of kinetics and thermodynamic of Cu(II) ion adsorption onto synthetic zeolite made of coal fly ash have been investigated. The aim of this research was to define the kinetics model and thermodynamic parameters such as Gibbs free energy (DG°), entropy (DS°), and enthalpy (DH°) of adsorption process of Cu(II) ion by synthetic zeolite made of coal fly ash. The effect of the presence of coexisting ion to the efficiency of Cu(II)adsorption had also been investigated. The experimental conditions were 5, 15, 30, 45, 60, 75, 90 minutes for the contact times and 27, 32, 37, 42°C for the temperature. The kinetics data were evaluated using a first-order and a pseudo second-order Lagergren equation. The results revealed that the kinetics data had good correlation with the pseudo second-order kinetics model. Thermodynamic studies indicated that the adsorption process was spontaneous with the increase in entropy and decrease in Gibbs energy. The coexisting Pb(II) or Mn(II) ions decreased the Cu(II) ion adsorption onto synthetic zeolite, but increased the total adsorption capacities.

Laboratory preparation and quality control of medicinal composition based on nanosilica and polymethylsiloxane

The prepared ex tempore adsorption composition which consists of nanosilica, polymethylsiloxane, metronidazole and decamethoxin serves as an effective mean for the topical treatment of wounds. The aim of the study was the development of an optimal pathway for laboratory manufacturing and quality control of this drug. We used the method of mechanochemical treatment in a ball mill, chemical methods of identification, absorption spectrophotometry in the IR, UV and visible regions, and the method of sowing on plates to determine microbiological purity. To obtain a uniform powder composition capable wettable in aqueous medium, there is provided a three-step process comprising mechanosorption of metronidazole on nanosilica and, accordingly, of decametoxin – at polymethylsiloxane. The conditions of identification tests and assay of the ingredients of the composition were сlarified and optimized. It was found that microbiological purity of the composition does not yield to known drugs which intended for topical application. Total adsorption activity of the nanocomposition is stated on the absorption of methylene blue, special protein adsorption activity – on the binding of gelatin. The obtained results may be useful for the organization of the recent pharmacy and the future factory production of proposed nanocomposition.

Density Functional Theory Investigation into the B and Ga Doped Clean and Water Covered γ-Alumina Surfaces

The structures and energies of the B and Ga incorporated γ-alumina surface as well as the adsorption of water are investigated using dispersion corrected density functional theory. The results show that the substitution of surface Al atom by B atom is not so favored as Ga atom. The substitution reaction prefers to occur at the tricoordinated A(4) sites. However, the substitution reaction becomes less thermodynamically favored when more Al atoms are substituted by B and Ga atoms on the surface. Moreover, the substitution of bulk Al atoms is not so favored as the Al atoms by B and Ga on the surface. The γ-alumina surface is found to have stronger adsorption ability for water than the B and Ga incorporated surface. The total adsorption energy increases as water coverage increases, while the stepwise adsorption energy decreases. The studies show the coverage of water at 7.5 H2O/nm2 (five H2O molecules per unit cell) can fully cover the active sites and the further water molecule could only be physically adsorbed on the surface.

Effects of Air Humidity on Properties of JO-9159 Explosive by Molecular Dynamics Simulation

To explore effects of air humidity on properties of JO-9159 explosive, the amorphous model of six components was constructed by Materials Studio software, periodic molecular dynamics simulation was conducted at seven kinds of relative humidity ranging from 10% to 70% for (001), (010), (100) crystal planes of JO-9159 explosive in COMPASS force field and NVT ensemble. Mechanical properties, sensitivity and detonation properties of JO-9159 explosive were researched basing on equilibrium trajectory of model. The results show that with the increasing of relative humidity, the total adsorption energy increases. The adsorption capacity of JO-9159 explosive for H2O is much stronger than O2 and N2; The breaking strength has a decreasing trend with the humidity increases and the stiffness and hardness of JO-9159 explosive are smaller at 30% and 40% relative humidity; At 30% relative humidity, the sensitivity of JO-9159 explosive is highest and detonation properties are weakest, while the detonation properties are strongest at 20% relative humidity.

Brønsted activity of two-dimensional zeolites compared to bulk materials

Different reactivity parameters yield different results for the relative acidity of zeolitic Brønsted sites in thin films and in bulk materials. Whereas the adsorption energies of ammonia and pyridine are about the same, the energy of deprotonation is much lower for two-dimensional systems than for three-dimensional systems. It is shown that this is due to the smaller effective dielectric constant of two-dimensional systems, which leads to much lower deprotonation energies, but also to much lower interaction energies between the protonated molecule and the negatively charged surface site. In the total adsorption energies, both effects nearly compensate each other.

Understanding how porosity gradients can make a better filter using homogenization theory

Filters whose porosity decreases with depth are often more efficient at removing solute from a fluid than filters with a uniform porosity. We investigate this phenomenon via an extension of homogenization theory that accounts for a macroscale variation in microstructure. In the first stage of the paper, we homogenize the problems of flow through a filter with a near-periodic microstructure and of solute transport owing to advection, diffusion and filter adsorption. In the second stage, we use the computationally efficient homogenized equations to investigate and quantify why porosity gradients can improve filter efficiency. We find that a porosity gradient has a much larger effect on the uniformity of adsorption than it does on the total adsorption. This allows us to understand how a decreasing porosity can lead to a greater filter efficiency, by lowering the risk of localized blocking while maintaining the rate of total contaminant removal.