Adsorption experiments

An interesting example of a large specific surface which is wholly external in nature is provided by a dispersed aerosol composed of fine particles free of cracks and fissures. As soon as the aerosol settles out, of course, its particles come into contact with one another and form aggregates but if the particles are spherical, more particularly if the material is hard, the particle-to-particle contacts will be very small in area the interparticulate junctions will then be so weak that many of them will become broken apart during mechanical handling, or be prized open by the film of adsorbate during an adsorption experiment. In favourable cases the flocculated specimen may have so open a structure that it behaves, as far as its adsorptive properties are concerned, as a completely non-porous material. Solids of this kind are of importance because of their relevance to standard adsorption isotherms (cf. Section 2.12) which play a fundamental role in procedures for the evaluation of specific surface area and pore size distribution by adsorption methods. 

This section reviews static adsorption experiments which were performed by Borchardt [40] to determine the effect of olefinsulfonate chemical structure on... 

From adsorption isotherms and competitive adsorption experiments (ref. 19) the strength of adsorption of the reaction components on zeolite CaY appeared to be HBr > o-dibromo > bromo- > p-dibromobenzene > Br2. 

In addition, the results of adsorption experiment in Fig. 4 revealed that H2O2 promotes the adsorption of 4-NP on the Cr-Ti-MCM-41 surface. From considering above results, it can be said that H2O2 increases the reaction rate by the promotion of adsorption of reactant and the removing of surface-trapped electrons. 

Nitrogen adsorption experiments showed a typical t)q5e I isotherm for activated carbon catalysts. For iron impregnated catalysts the specific surface area decreased fix>m 1088 m /g (0.5 wt% Fe ) to 1020 m /g (5.0 wt% Fe). No agglomerization of metal tin or tin oxide was observed from the SEM image of 5Fe-0.5Sn/AC catalyst (Fig. 1). In Fig. 2 iron oxides on the catalyst surface can be seen from the X-Ray diffractions. The peaks of tin or tin oxide cannot be investigated because the quantity of loaded tin is very small and the dispersion of tin particle is high on the support surface. 

CO2 adsorption capacities with dry sorbents before and after attrition were shown in Fig.3. We found variation of CO2 adsorption capacity during operation by examining effect of attrition on adsorption capacity. So, adsorption experiments for each sorbent fluidized for 30hours were carried out. As a result, percentage losses of adsorption capacity of molecular sieve 5A and molecular 13X were 14.5% and 13.5%, but those of activated carbon and activated alumina were 8.3% and 8.1% respectively. This is because retention time of molecular sieve 5A and molecular 13X decreased due to elutriation of particle generated from attrition. 

The sticking coefficient of H2 on a metal has been determined through an adsorption experiment. The metal surface is assumed to have No = 1.5 x 10 sites m and each adsorption site is assumed to be occupied by one hydrogen atom when the surface is saturated. The experiment was performed by exposing the surface to a known pressure of hydrogen over a well-defined period of time (dosis) and then sequentially determining how much was adsorbed by, for example, TPD. All adsorption experiments where performed at such low temperatures that desorption could be neglected. 

Fourier-transform infrared (IR) spectra (resolution 2 cm- ) were recorded with a Perkin Elmer 1750 instrument in a quartz cell connected to grease-free evacuation and gas manipulation lines. The self-supporting disk technique was used. Before recording the spectra, the samples were treated with O2 at 450°C (Ih), then cooled down to r.t. before evacuating the O2. The sample was then evacuated at 400°C. Evacuation at higher temperatures lead to a drastic cut off of IR trasparency. All reactants were purified prior to the adsorption experiments. Due to the better resolution of the spectra, only results for Sb V=1.0 are reported here, however the IR data for Sb V=3.0 were not significantly different. 

Co-adsorption experiments show a complex role of the nature and concentration of chemisorbed ammonia species. Ammonia is not only one of the reactants for the synthesis of acrylonitrile, but also reaction with Br()>nsted sites inhibits their reactivity. In particular, IR experiments show that two pathways of reaction are possible from chemisorbed propylene (i) to acetone via isopropoxylate intermediate or (ii) to acrolein via allyl alcoholate intermediate. The first reaction occurs preferentially at lower temperatures and in the presence of hydroxyl groups. When their reactivity is blocked by the faster reaction with ammonia, the second pathway of reaction becomes preferential. The first pathway of reaction is responsible for a degradative pathway, because acetone further transform to an acetate species with carbon chain breakage. Ammonia as NH4 reacts faster with acrylate species (formed by transformation of the acrolein intermediate) to give an acrylamide intermediate. At higher temperatures the amide may be transformed to acrylonitrile, but when Brreform ammonia and free, weakly bonded, acrylic acid. The latter easily decarboxylate forming carbon oxides. 

In two recent papers [8,10], we have initiated studies aimed at understanding the catalytic behavior of WZ and PtWZ. Our observations, which motivated the present study, can be summarized as follows, a) Water of reduction results in the formation of Br0nsted acid sites, as monitored by pulsed addition of pyridine to a DRIFTS chamber at room temperature [8,10]. In this paper, we have complemented those results with similar pyridine adsorption experiments at... 

The classical method to study adsorption deals with establishing a correspondence between thermodynamically equilibrium amount of absorbed gas, the temperature and the partial pressure of the gas in space surrounding adsorbent. Usually, a constant temperature is maintained throughout an adsorption experiment. The shape of isotherms obtained gives information on the character of adsorption. 

Notes on Procedure. In partition chromatography as well as adsorption experiments, successful results require a certain amount of skill which is acquired after some practice. 

An assumption implicit in most adsorption studies is that adsorption is fully reversible. In other words, once the empirical coefficients are measured for a particular substance, Equations 20.6 to 20.10 describe both adsorption and desorption isotherms. This assumption is not always true. Collins and Crocker140 observed apparently irreversible adsorption of phenol in flowthrough adsorption experiments involving phenol interacting on a Frio sandstone core under simulated deep-well... 

Well head pressures increased when injection was stopped at Well No. 1 for more than 24 h, apparently caused by a combination of precipitation reactions and backflow of sand. Injecting a slug of brine after every period of interrupted flow solved this problem. Movement of the main organic constituents (n-hexylamine, butanal, butanol, and phenol) was assumed to be slowed by adsorption. This conclusion was based on laboratory adsorption experiments by involving a different geologic formation (Cottage Grove sandstone) no direct observations were made of the injected waste. For current hazardous waste injection wells in Texas, the reader can refer to Texas Environmental Profiles web site for on-line resources for the State of Texas.185... 

N02 adsorption experiments were also performed over the reference P(—Ba/y-Al203 (1/20/100 w/w) sample and similar results have been obtained (see Figure 6.3). It is worthwhile noting that in this case, the NO outlet concentration can be related to both the N02 disproportionation and the N02 decomposition reactions. In fact, 02 formation was also observed in this case, in line with N02 decomposition to NO and oxygen over Pt sites. FTIR spectra collected over the Pt-Ba/y-Al203 reference catalyst (Figure 6.3b) pointed out also in this case that nitrate species are formed upon N02 adsorption. 

Results of adsorption experiments for butylate, alachlor, and metolachlor in Keeton soil at 10, 19, and 30°C were plotted using the Freundlich equation. A summary of the coefficients obtained from the Freundlich equation for these experiments is presented in TABLE IV. Excellent correlation using the Freundlich equation over the concentration ranges studied (four orders of magnitude) is indicated by the r values of 0.99. The n exponent from the Freundlich equation indicates the extent of linearity of the adsorption isotherm in the concentration range studied. If n = 1 then adsorption is constant at all concentrations studied (the adsorption isotherm is linear) and K is equivalent to the distribution coefficient between the soil and water (Kd), which is the ratio of the soil concentration (mole/kg) to the solution concentration (mole/L). A value of n > 1 indicates that as the solution concentration increases the sorption sites become saturated, resulting in a disproportionate amount of chemical being dissolved. Since n is nearly equal to 1 in these studies, the adsorption isotherms are nearly linear and the values for Kd (shown in TABLE IV) correspond closely to K. These Kd values were used to calculate heats of adsorption (AH). 

Also, other dependent variables associated with CO2-foam mobility measurements, such as surfactant concentrations and C02 foam fractions have been investigated as well. The surfactants incorporated in this experiment were carefully chosen from the information obtained during the surfactant screening test which was developed in the laboratory. In addition to the mobility measurements, the dynamic adsorption experiment was performed with Baker dolomite. The amount of surfactant adsorbed per gram of rock and the chromatographic time delay factor were studied as a function of surfactant concentration at different flow rates. 

Experiment A is a non-adsorption experiment through the core, performed to measure the time for emergence of the peak. A 1.3% (concentration higher than the standard) acidified brine is loaded into the sample loop to be used as a sample medium. This particular experiment is carried out to measure the retention time by recording the time required before the peak is observed. The retention time can also be used to compute the exact porosity of the core, under the assumption of zero adsorption of salts from the brine. 

Experiment B is also a non-adsorption experiment in which flow through the capillary tube is used. The sample medium used is the surfactant solution prepared in the 1% acidified brine. Results will be combined with those from Experiment C to get the information on the permanent or irreversible adsorption on the porous medium by measuring peak areas. 

Results and Discussion on Dynamic Adsorption Measurements. Baker dolomite was used to study the dynamic adsorption experiment. The computed porosity of the rock was 24%. One concentration below the CMC of AEGS, one at CMC, and two concentrations above CMC were chosen to measure the adsorption of this surfactant with Baker dolomite. The mass of surfactant adsorbed per gram of rock is plotted as a function of flow rate in a semi-log plot in Figure 9. 

The slopes of the peaks in the dynamic adsorption experiment is influenced by dispersion. The 1% acidified brine and the surfactant (dissolved in that brine) are miscible. Use of a core sample that is much longer than its diameter is intended to minimize the relative length of the transition zone produced by dispersion because excessive dispersion would make it more difficult to measure peak parameters accurately. Also, the underlying assumption of a simple theory is that adsorption occurs instantly on contact with the rock. The fraction that is classified as "permanent" in the above calculation depends on the flow rate of the experiment. It is the fraction that is not desorbed in the time available. The rest of the adsorption occurs reversibly and equilibrium is effectively maintained with the surfactant in the solution which is in contact with the pore walls. The inlet flow rate is the same as the outlet rate, since the brine and the surfactant are incompressible. Therefore, it can be clearly seen that the dynamic adsorption depends on the concentration, the flow rate, and the rock. The two parameters... 

It is also observed in Fig. 5.3 that Pd(II) ions are partly adsorbed on AI2O3 before ultrasonic irradiation the concentration of Pd(II) just before irradiation becomes ca. 0.8 mM, although 1 mM Pd(II) was added in the sample solution. From a preliminary adsorption experiment, the rate of Pd(II) adsorption on A1203 was found to be slow compared with those of Pd(II) reduction in the presence of alcohols. Therefore, it is suggested that the sonochemical reduction of Pd(II) in the presence of alcohols mainly proceeds in the bulk solution. The mechanism of the Pd/Al203 formation is also described in the section of sonochemical synthesis of supported metal nanoparticles. 

The nitrogen adsorption experiment was carried out with catalysts Pd-15, Pd-45, and Pd-105 only. As shown in Fig. 10, the 2260 cm"-1 band due to adsorbed nitrogen was observed on all of them. 

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