Initial Desorption Rate Research Articles

Structure and activity relationships for CO 2 regeneration from aqueous amine-based absorbents

A study to determine the relationships between structure and activity of various amine-based CO 2 solvents was performed. The desorption of CO 2 from saturated solvents at 80 °C and atmospheric pressure was measured to assess the initial desorption rate and desorption capacities at pseudo-equilibrium. Evaluation of the desorption capacity at lower temperature, 80 °C, will give a better understanding for more energy efficient and lower circulation rate absorbent for CO 2 absorption process. Results showed that an increase in chain length between the amine and different functional groups in the solvent structure up to four carbon, results in an increase in initial desorption rate and also an increase in the desorption capacity at pseudo-equilibrium was observed for most solvents. Steric hindrance effect was noticed when a side chain with an alkyl group was present at α-carbon position to amine group in the structure. Increase in the number of the amine group in solvent structure, results in higher desorption capacity up to 75% of CO 2 is desorbed. Aromatic amines substituted with an amine group by a side chain at the cyclic ring shows an increase in desorption capacity at pseudo-equilibrium compare to other group substitution.

Hydrogen storage behavior of ZrNi 70/30 and ZrNi 30/70 composites

The Zr–Ni compositional alloys, namely (i) ZrNi 70/30 and (ii) ZrNi 30/70 (both by weight) have been investigated for the reversible hydrogenation behavior. These composites show Zr–Ni intermetallic multi-phase formation as explored by X-ray diffraction studies. The sorption kinetics of ZrNi 70/30 seems much faster (∼3–4 times) than that of ZrNi 30/70 alloys. The initial desorption rate increasing with an increase in temperature. A well-defined plateau region was obtained for the ZrNi 70/30 with an equilibrium pressure range from <1 bar (300 °C) to 10 bars (390 °C). For ZrNi 30/70, the sloppy plateau region extends to higher equilibrium pressures. It is estimated that the total effective hydrogen concentration for ZrNi 70/30 (∼1.0 wt.%) is at least 2 times that of ZrNi 30/70 (∼0.5 wt.%) composites. From the PCT isotherms, the enthalpy of reaction (Δ H) has been calculated to be ∼39 kJ/mol H 2 for the ZrNi 70/30. The surface morphologies of the hydrogenated materials exhibit the presence of cracks and particle size pulverization in comparison to the pristine alloys.

Effect of activated alloys on hydrogen discharge kinetics of MgH 2 nanocrystals

Activated alloys synthesized by arc-melting were examined as catalysts for improving the hydrogen sorption characteristics of nanostructured magnesium hydride, proposed as a reversible hydrogen storage material. The MgH 2-catalyst absorbing materials were prepared by ball milling of pure MgH 2 with hydrided Zr 47Ni 53, Zr 9Ni 11, and other investigated alloys. The nanostructured MgH 2-intermetallic systems were tested at 250 °C and catalyst addition of eutectoid Zr 47Ni 53 resulted in the fastest desorption time and highest initial desorption rate. Also, the catalyzed Mg-hydride with activated Zr 9Ni 11 and Zr 7Ni 10 phases showed fast desorption kinetics. Moreover, the results demonstrated that the composition of dispersed Zr x Ni y catalysts has a strong influence on the amount of accumulated hydrogen and desorption rate of Mg-nanocomposite.

Kinetics of Copper Desorption from Highly Calcareous Soils

Desorption of copper (Cu) is an important factor in determining Cu availability in calcareous soils. Kinetics of native and added Cu desorption by DTPA (diethylene‐triaminepentaacetic‐acid) from 15 highly calcareous soils of southern Iran were studied in a laboratory experiment. Our results showed that two constant‐rate, Elovich, simple Elovich, and parabolic‐diffusion equations were the best‐fitted equations among eight kinetic models used. The copper desorption pattern based on the parabolic‐diffusion equation revealed that the rate of native Cu desorption was higher in the first 2 h followed by a slower release rate, which suggests that two different mechanisms are involved. The trend may describe why the DTPA soil test has been considerably successful in predicting Cu availability in calcareous soils. Stepwise multiple regression equations indicated that CCE (calcium carbonate equivalent), CEC (cation exchange capacity), and clay content are the most important soil characteristics that predict the rate constants of the kinetic models. Mean extractant recovery percentage (ERP) of the soils was only 20%, which indicated that after 20 days, DTPA extracted only one‐fifth of added Cu. Regression equations indicated that as soil OM (organic matter) content increased, the value of ERP decreased. From results reported herein it seems that CCE, CEC, and clay are the most important factors controlling Cu release from highly calcareous soils of southern Iran. However, the initial soil Cu desorption rate is probably controlled by CEC.

Comparison of mineralization of solid-sorbed phenanthrene by polycyclic aromatic hydrocarbon (PAH)-degrading Mycobacterium spp. and Sphingomonas spp.

The mineralization of 14C-phenanthrene, sorbed to porous synthetic amberlite sorbents, i.e., IRC50, XAD7-HP, and XAD2, by three phenanthrene-degrading Mycobacterium soil isolates, i.e., strains VM552, VM531, and VM451 and three phenanthrene-degrading Sphingomonas soil isolates, i.e., strains LH162, EPA505 and LH227, was compared. In P-buffer and in the presence of IRC50, for all strains the maximum rate of mineralization of 14C-phenanthrene was significantly higher (1.1-1.9 ng ml(-1) h(-1)) than the initial abiotic desorption rate (0.2 ng ml(-1) h(-1)), indicating that both Mycobacterium and Sphingomonas utilize sorbed phenanthrene with a higher rate than can be explained by abiotic desorption. Because all Mycobacterium and Sphingomonas strains belonged to different species, it can be suggested that this feature is intrinsic to those genera rather than a specific feature of a particular strain. The final mineralization extent in P-buffer in the presence of IRC50 was about a factor of two higher for the Mycobacterium strains compared to the Sphingomonas strains. Moreover, a significantly higher normalized phenanthrene mineralization ratio in the presence of IRC50 to the control (without IRC50) was found for the Mycobacterium strains compared to the normalized ratio found for the Sphingomonas strains. Addition of minimal nutrients had a more beneficial effect on phenanthrene mineralization by Sphingomonas compared to Mycobacterium, resulting into similar mineralization extents and rates for both types of strains in the presence of IRC50. Our results show that Mycobacterium is better adapted to utilization of sorbed phenanthrene compared to Sphingomonas, especially in nutrient-poor conditions.

Toxicology and fate of Pestanal® and commercial propetamphos formulations in river and estuarine sediment

To quantify the impact of organophosphate pesticides on aquatic ecosystems requires a mechanistic understanding of their behaviour in a range of environmental matrices. The objective of this study was to compare the sorption/desorption, biodegradation and toxic effects of the Pestanal® grade and commercial formulation (Ectomort Centenary) of the organophosphate insecticide propetamphos in river and estuarine sediments. For both formulations, the sorption of propetamphos onto sediment was initially very rapid followed by a slower sorption phase. Similarly, the initial rate of desorption was rapid, followed by a much slower rate. In both sorption and desorption experiments, the level of sorbed propetamphos was considerably higher for the commercial formulation of propetamphos ( K d = 7–11) than for the Pestanal® grade ( K d = 4–10). The rate of propetamphos biodegradation was sediment dependent but was most rapid where microbial activity and nutrients were the highest and sorption was the lowest. Propetamphos was more rapidly degraded in sediments under aerobic ( t 1 / 2 = 15 d) compared to anaerobic conditions ( t 1 / 2 = 19 d). However, no significant difference in the biodegradation rates of the Pestanal® grade and commercial formulations of propetamphos were observed. The toxic effect of propetamphos on sediment microbial communities was significantly greater for the commercial formulation than for the Pestanal® grade of propetamphos based on EC 50 (21 versus 236 μg g − 1) and EC 10 values (0.3 versus 54 μg g − 1). In conclusion, our results highlight the importance of using commercial pesticide formulations when carrying out ecotoxicological testing.

Liquid-phase adsorption and desorption of phenol onto activated carbons with ultrasound

The effect of 48-kHz ultrasound on the adsorption and desorption of phenol from aqueous solutions onto coconut shell-based granular activated carbons was studied at 25 °C. Experiments were performed at different carbon particle sizes (1.15, 2.5, 4.0 mm), initial phenol concentrations (1.06–10.6 mol/m 3), and ultrasonic powers (46–133 W). Regardless of the absence and presence of ultrasound, the adsorption isotherms were well obeyed by the Langmuir equation. When ultrasound was applied in the whole adsorption process, the adsorption capacity decreased but the Langmuir constant increased with increasing ultrasonic power. According to the analysis of kinetic data by the Elovich equation, it was shown that the initial rate of adsorption was enhanced after sonication and the number of sites available for adsorption was reduced. The effect of ultrasonic intensity on the initial rate and final amount of desorption of phenol from the loaded carbons using 0.1 mol/dm 3 of NaOH were also evaluated and compared.

Characterisation of Mg–x wt.% FeTi (x = 5–30) and Mg–40 wt.% FeTiMn hydrogen absorbing materials prepared by mechanical alloying

Composites based on Mg with intermetallic FeTi (up to 30wt.%) and FeTiMn (40wt.%) were prepared by mechanical alloying for evaluation of their hydrogen storage characteristics. In the first case FeTi was prepared by mechanical alloying and subsequently milled with Mg under argon in different proportions. Powders milled under argon had to be activated by remilling under hydrogen. In the second case FeTiMn prepared by melting was milled together with MgH2 under hydrogen. Hydrogen storage characteristics, pressure-composition isotherms and kinetics were investigated under different parameters. Among the FeTi composites, Mg–5wt.% FeTi had the maximum absorption capacity of 5.80wt.% at 300°C and 5.12wt.% at 200°C. At 300°C the initial desorption rate was the highest for Mg–10wt.% FeTi, but its final desorption capacity was less than that of Mg–5wt.% FeTi. None of the compositions showed any desorption at 200°C. In the case of composites with FeTiMn, absorption and desorption temperatures decreased by ball milling and higher storage capacities were achieved. In Mg–40wt.% FeTiMn, the lowest absorption and desorption temperatures were 80 and 240°C, respectively, with the material absorbing 4wt.% hydrogen even at 80°C. The kinetics improved with increasing milling time.

Pb (II) Sorption with Calcite: A Radiotracer Study

A 210Pb radiotracer was used to monitor Pb solid-aqueousphase partitioning in sorption experiments at ambient temperature, pH = 8.2, and atmospheric PCO2 in 0.15 M NaNO3 solutions. A 24 h isotherm is linear up to Pb concentrations of 4 × 10-6 M, above which an increase in slope suggests precipitation. The effect of Pb concentration, calcite loading, and ionic strength on Pb sorption with time was monitored. Sorption kinetics are rapid, followed by a slower sorption step.At a constant calcite loading500 mg L-1,fractional sorptiondecreases with increasing initialPb concentration. The reverse isobserved for surface coverage, with0.6, 5.6 and 40.2% of availableCa2+sites occupied at10-8,10-7 and10-6 MPb after 96 h. At a constant Pb concentration of10-6 M,fractional sorption increases with increasing particleloading, however surface coverage decrease with72.5 and 22.1%Ca2+sites occupied at 100 and200 mg L-1calcite after 96 h.The adsorption coefficient (Kd) is approximately 103,increases with initial Pb concentration, but remains unaffected by variable calcite loading. Absence of an ionic strength effect on Pb sorption is interpreted as the dominance of inner-sphere complexation. For desorption experiments conducted over a range of initial sorption times, an average desorption index > 0.8 but < 1 indicates that sorption is largely reversible, but is accompanied by slight incorporation. Solid-solution formation increases with time, as observed by slower initial desorption rates for samples with longer sorption times. These findings indicate that Pb may be effectively sequestered by calcite; however re-release via desorption is likely as Pb does not become significantly incorporated into the mineral structure.

Hydrogen desorption from polycrystalline platinum chemically modified by sulfur pre-coverage

Hydrogen desorption energetics from clean polycrystalline platinum (Pt(Poly)) and (Pt(Poly)) with sulfur (S) pre-coverage (S/Pt(Poly)) have been studied using temperature programmed desorption (TPD) over a wide range of hydrogen and S coverages. Hydrogen desorption energies have been calculated and tabulated. At saturation, hydrogen desorbs from clean Pt(Poly) in three states (384, 320, and 282 K). The 384 K state is attributed to hydrogen from defect sites. The 320 and 282 K states are both attributed to hydrogen from (1 1 1) sites, the latter state induced by repulsive lateral interaction between hydrogen in neighboring sites. On clean Pt(Poly), the desorption energy for hydrogen from defect sites is essentially fixed over the entire coverage range, dilute to saturation. In contrast, the desorption energy for hydrogen from (1 1 1) sites begins to decrease when about 50% of the surface is saturated. The decrease onset is attributed to significant accumulation of hydrogen in fcc three-fold hollows relative to hcp hollows. With increasing hydrogen and S coverages, the energies of desorption converge to 4.5 kcal/mol, the barrier height to hydrogen diffusion on (1 1 1) terraces of d-band transition metal surfaces via classical over-the-barrier hopping. Therefore, increasing S coverage has the same effect on the binding strength of Pt( Poly) for hydrogen as increasing hydrogen coverage (site blocking). But more interestingly, at high surface coverage, atomic hydrogen recombination immediately after hopping out of the adsorption well without surface diffusion is indicated. Though, S site blocking has been found as the primary cause of decreased hydrogen desorption temperatures, several trends in the data cannot be rationalized using a pure site blocking argument alone. Sulfur induced additional repulsive lateral interaction at high coverage is strongly suggested, through-space, short range electronic effects. Further, long range S effects (through space) are also clearly supported. The uniform percent decrease in hydrogen adsorption independent of exposure is not consistent with pure site blocking but can be readily explained by a decreased sticking coefficient on S/Pt(Poly) surfaces due to long range S effects. In particular, the strong inhibition of hydrogen adsorption on S/Pt(Poly) surfaces (the long range effect) is attributed mostly to electrostatic repulsion of approaching hydrogen caused by non-bonding electron pairs in hybrid valence sulfur orbitals normal to the surface. Insight has also been gained into the dynamics of hydrogen adsorption. The study of fixed hydrogen exposures as a function of S coverage shows zero order kinetics for the initial rate of desorption of the 320 K state, i.e. the leading edges are `pinned'. Thus, hydrogen adsorption on Pt(Poly) in patches nucleated at defects that attain similar density independent of coverage is implied. Key steps in the adsorption and desorption trajectories as indicated by this TPD work are illustrated in a schematic.

Kinetics of Water Sorption in NafionThin Films − Quartz Crystal Microbalance Study

Quartz crystal microbalance measurements are used to investigate the water sorption in the cast Nafion films exposed to water vapor. Equilibrium and kinetic sorption data are reported for H- and Na-form Nafion films of a thickness ca. 0.02 μm. Water sorption isotherms obtained agree well with the literature data for Nafion117. However, the water diffusion coefficients evaluated from the initial sorption and desorption rates by using the theory of diffusion in a plane sheet are ca. 7 orders of magnitude lower than those obtained from sorption measurements in ca. 200 μm thick Nafion117 membranes. It is concluded that the kinetics of water sorption (desorption) in the partially hydrated Nafion exposed to water vapor is controlled by the first-order process of water transfer in and out of the nanoscopic hydrophilic regions (ion clusters) for membranes thinner than 10 μm. On the other hand, the linear diffusion is the rate-determining step of water transport in thick Nafion membranes and in fully hydrated thin Nafion films.

Influence of the nonionic surfactant Brij 35 on the bioavailability of solid and sorbed dibenzofuran.

The effect of the nonionic surfactant Brij 35 on the bioavailability of solid and Teflon-sorbed dibenzofuran for Sphingomonas sp. strain HH19k was studied in simple model systems. Growth with dibenzofuran and dibenzofuran-specific oxygen uptake in surfactant-free media and with Brij 35 above the critical micelle concentration (cmc) were compared with dissolution and desorption in the absence of bacteria. Brij 35 accelerated dissolution and biodegradation of solid dibenzofuran by a factor of 2. It also enhanced the initial desorption rate of dibenzofuran from Teflon by this factor. Continuously decreasing desorption rates were attributed to slow diffusion of dibenzofuran inside Teflon, leading to depletion of dibenzofuran in the exterior of the Teflon particles. Surprisingly, Brij 35 slowed the initial biodegradation of desorbing dibenzofuran. We propose two processes that led to low bioavailability of sorbed dibenzofuran in the presence of surfactant. First, desorbing dibenzofuran rapidly accumulated in surfactant micelles, leading to reduced truly water-dissolved dibenzofuran concentration as the factor controlling the biodegradation rate. Second, Brij 35 suppressed the contact between bacteria and Teflon. This increased the average diffusion distance of dibenzofuran to the bacteria, which in turn flattened the gradient of the dissolved dibenzofuran concentration between the sorbent and the cells as the driving force for desorption.

Peculiarities of polyacrylic acid adsorption on copper oxide powder

The adsorption of polyacrylic acid on copper(II) oxide powder from aqueous solutions was studied. The amount of the adsorbed polymer was shown to increase with time reaching its maximum over 6–7 min. The desorption kinetics of copper polyacrylates was studied by measuring variations in copper ion concentration in the solution. The rate of desorption was found to be independent of the initial concentration of polyacrylic acid. A decrease in the dispersed phase concentration did not actually affect the initial rate of the polymer desorption. However, it caused a drastic fall in the rate of desorption after 1–1.5 min. A mathematical model was proposed for describing the experimental data.

Conformation of adsorbed bovine serum albumin governing its desorption behavior at alumina-water interfaces

The mode of initial adsorption of bovine serum albumin (BSA) onto positively charged Al 2O 3 particles was studied as a function of surface coverage (θ). The adsorption isotherm of BSA exhibited saturation ( θ= 1) and the existence of an inflection point at θ of 0.82. The relative numbers of ionic groups on a BSA molecule interacting with the Al 2O 3 surface at various θ were monitored by measuring the relative adsorption density of H + and OH −, ([Γ H + − Γ OH − ]), for BSA-adsorbed Al 2O 3 using potentiometric titration. The [Γ H + − Γ OH − ] curves for Al 2O 3, BSA, and BSA-adsorbed Al 2O 3 at various KNO 3 concentrations showed a common intersection point (cip) which was the pH giving the acid-base equivalence point, respectively. Compared with the cip's of Al 2O 3 (5.6) and BSA (5.2), the cip's of BSA-adsorbed Al 2O 3 were situated at points corresponding to more alkaline pH values over the θ range of 0.13 to 1.0. These results suggested that negatively charged groups, mainly carboxyl groups, on the BSA molecule electrostatically interacted with the Al 2O 3 surface. The degree of shift in the cip increased gradually with increasing θ from 0.13 to 0.70, while it decreased markedly over the θ range of 0.82 to 1.0. The variation in the cip reflected the change in the total number of ion pairs formed between BSA molecules and Al 2O 3. The initial rates of BSA desorption during alkali cleaning were low and almost constant over the θ range of 0.13 to 0.70, but increased markedly at θ higher than 0.82. It is suggested that the conformational changes of BSA adsorbed on Al 2O 3, involving changes in the relative magnitude of electrostatic interaction forces, occur discretely at θ of approximately 0.8.

Correlation between biological and physical availabilities of phenanthrene in soils and soil humin in aging experiments

AbstractThe bioavailability of an organic compound in a soil or sediment commonly declines with the soil‐chemical contact time (aging). A series of parallel desorption and bioavailability experiments was carried out on phenanthrene previously aged up to ∼100 d in Mount Pleasant silt loam (Mt. Pleasant, NY, USA) or Pahokee peat soil to determine as a function of the aging period the degree of correlation between the reduction in bioavailability and the rate and extent of desorption and the influence of soil organic matter composition on availability. The mineralization of phenanthrene by two bacteria and the uptake of phenanthrene by earthworms showed expected declines with aging. Likewise, the rate of phenanthrene desorption in the absence of organisms decreased with aging. The decline in initial rate of mineralization or desorption was nearly an order of magnitude after 50 to 60 d of aging. Plots of normalized rates of mineralization or desorption practically coincided. Similarly, plots of normalized fraction mineralized or fraction desorbed during an arbitrary period gave comparable slopes. The partial removal of organic matter from the peat by extraction with dilute NaOH to leave the humin fraction reduced the biodegradation of phenanthrene aged for 38 and 63 d as compared to the nonextracted peat, but the effect disappeared at longer incubation times. The rate of desorption from samples of peat previously extracted with NaOH or Na4P2O7 declined with aging and, for a given aging period, was significantly slower than from nonextracted peat. This work shows that the reduction in bioavailability of phenanthrene over time in soil is directly correlated with reduction of its physical availability due to desorption limitations. In addition, this study shows that removal of extractable humic substances leads to a decline in the rate of desorption and in the bioavailability of the substrate.

Kinetics and Mechanism of Cationic Surfactant Adsorption and Coadsorption with Cationic Polyelectrolytes at the Silica−Water Interface

We used scanning angle reflectometry to measure the adsorption isotherm, adsorption kinetics, and desorption kinetics for cetyltrimethylammonium bromide (CTAB) surfactants on negatively charged silica surfaces. The initial adsorption rate increased with increasing CTAB concentrations between approximately 0.2 × cmc and 10 × cmc, displaying a discontinuous increase at the critical micelle concentration. The initial desorption rate was a monotonically increasing function of the bulk concentration of the surfactant solution from which the adsorbed layer was formed, both above and below the cmc. Combining equilibrium and kinetic information, we conclude that the adsorption mechanism and the structure of the adsorbed layer both change abruptly at the cmc. Below the cmc, monomeric surfactants adsorb to an extent that is consistent with a defective bilayer structure. Above the cmc, micelles adsorb directly to the surface, to an extent that is consistent with a close-packed monolayer of micelles. The adsorption rate was apparently limited by slow rearrangements within the adsorbed layer. CTAB adsorption was significantly hindered by coadsorption with polylysine, in terms of both the rate and extent of adsorption. The effect of polylysine on CTAB adsorption was very sensitive to the ionic strength and the order in which the surfactant and the polyelectrolyte were exposed to the surface. Different pathways to the same final bulk solution composition produced much different adsorption results. This demonstrates that coadsorption of CTAB and polylysine is inherently a nonequilibrium process dominated by kinetic traps. Although it had an overall hindering effect, coadsorption with polylysine did not alter the basic difference in CTAB adsorption mechanisms above and below the cmc.

Kinetics and Potential Significance of Polycyclic Aromatic Hydrocarbon Desorption from Creosote-Treated Wood

PAHs are major constituents of creosote, and it has been suggested that their volatilization from treated wood could make a major contribution to the U.K. atmospheric emission inventories. This paper reports a study to elucidate the volatilization characteristics of selected PAHs from creosote-treated wood and to estimate the potential significance of this source to the U.K. atmospheric source inventory. Desorption kinetics from untreated and treated wood were measured at 4 and 30 °C for five PAHs (acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene) using chambers in the laboratory. Rates of desorption followed first-order kinetics for all compounds and were higher at 30 than 4 °C. Mean ∑PAH fluxes varied from 2.57 ± 1.52 to 29.5 ± 6.1 mg/m2 treated wood/day at 4 and 30 °C, respectively. A prolonged study of the kinetics at 4 °C showed that the volatilization rate remained constant over about 7 weeks, after which >85% of the compounds still remained sorbed on the wood. Initial desorption rates...

Performance of protease as a cleaning agent for stainless steel surfaces fouled with protein

Cleaning experiments were performed by feeding protease solutions as cleaning agents into a packed column of stainless steel particles fouled with β-lactoglobulin or gelatin. By evaluating the initial desorption rate constants (first-order rate constants) and residual amounts of protein, the cleaning efficiencies of the proteases were compared. The initial desorption rate constant depended on the kind of protease used and also on the type of protein to be removed. It increased with protease concentration and reached a constant value at a limit concentration. Kinetic analysis of the proteolytic reactions catalyzed by the proteases revealed that protease with a large V max EK m value for the proteolytic reaction resulted in a large value of the initial desorption rate constant in the enzymatic cleaning at a low protease concentration. The K m value affected the limit concentration of protease yielding a saturation of initial desorption rate constant.

Fouling and Cleaning of Stainless Steel Surface: Adsorption and Desorption Behavior of Bovine Serum Albumin and Gelatin.

Adsorption and desorption behavior of bovine serum albumin (BSA) and gelatin on the surface of stainless steel particles are studied. The amount of BSA adsorbed increases significantly with temperature above 60°C whereas that of gelatin decreases slightly with increasing temperature. Results of adsorption experiments with S-carboxymethylated BSA show that the thermal aggregation of BSA molecules at the surface through intermolecular thiol-disulfide interchange reactions plays an important role in the adsorption of BSA at elevated temperatures. Furthermore, the initial desorption rate constants and residual amounts of the two proteins during caustic and enzymatic cleanings of the fouled particles are compared under various conditions. As a result, a large difference is found in the temperature dependence of the initial desorption rate constant in caustic cleaning, suggesting different modes of adsorption of the proteins.

Extraction of oil shales with sub- and near-critical water

Desorption is routinely employed for assessing the recoverability of coalbed gas resources. However, desorption behavior is strongly affected by coal structure. Canister desorption experiments on undeformed and mylonitic coals collected from drill holes in the Zhina Coalfield (Southwest China) were conducted to study temporal desorption rates and gas compositional shifts. Low-pressure N2 and CO2 adsorption tests revealed that the micropores, mesopores, and macropores in mylonitic coal have larger pore volumes and greater specific surface areas compared to those of undeformed coal. The “ink-bottle-shaped” pore is the main type of pore structure in mylonitic coal, whereas undeformed coal shows well-developed slit-shaped pores with good interconnectivity. The detailed desorption experiments in this study lasted 61 d and 110 h for undeformed and mylonitic coal, respectively. For undeformed coal, CH4 and C2H6 concentrations steadily increased with desorption time, whereas N2 and CO2 concentrations progressively decreased. The gas compositional shift of mylonitic coal during the entire desorption process could be divided into two stages: an initial stage, when CH4 and C2H6 concentrations in the desorbed gas increased (within the first 12 h), and a later stage, when they decreased rapidly; N2 and CO2 concentrations exhibited the opposite trend. The two-stage gas compositional shifts in mylonitic coal are likely linked to its pore structure. Gases in the “parallel-plate-shaped” pores of undeformed coal are mobile, whereas those in ink-bottle-shaped pores of mylonitic coal have restricted mobility. This is because CO2 and N2 can enter the narrow throats (with diameters of 3.3–3.8 Å) of ink-bottle-shaped pores, which are inaccessible to CH4 and C2H6 because of their larger diameter, causing the late-desorbed gas of mylonitic coal to be relatively enriched in CO2 and N2. The initial desorption rate of mylonitic coal is much greater than that of undeformed coal, which is closely related to developed microfractures in mylonitic coal. The desorption rate of undeformed coal is a power function of time, whereas that of mylonitic coal can be divided into two stages in which the relationship between desorption rate and time is a power function. The results suggest that the two-stage desorption rate is attributable to the molecular sieve effect due to the presence of massive ink-bottle-shaped pores in mylonitic coal.