Sorption measurements

In our work, sorption by PA-6 of CO2 saturated with succinic anhydride (SA, around 5 wt% in CO2) and of both supercritical and subcritical CO2/IO mol% 1,4-dioxane mixtures saturated with SA was investigated in order to achieve a better idea of the amount of supercritical fluid absorbed in the amorphous region of the polymer. A magnetic suspension balance was used to determine the amount of fluid absorbed by the polymer. The mass increase of the polymer samples due to sorption of the fluid and the density of the fluid were simultaneously recorded. 

The sorption of a fluid into a polymer is dependent on the crystallinity of the polymer. The diffusion of a supercritical fluid and therewith the diffusion of small molecules dissolved in this fluid into an amorphous polymer is much more pronounced than it is into a crystalline polymer because of better swelling of the amorphous polymer. As a consequence, the sorption by the PA-6 granules is not expected to be large, since PA-6 is a semi-crystalline polymer. Also, the fact that PA-6 has a polar character, due to the amide bonds in the polymer chain, does not have a positive effect on the amount of CO2 absorbed by the polymer. 

In Fig. 13.3 the sorption of the CO2 saturated with SA as well as the sorption of C02/l,4-dioxane saturated with SA by the PA-6 granules at 50 and 140°C is plotted against time. 

In Fig. 13.4, the concentration of the amine end groups (determined by po-tentiometric end-group titrations) after blocking with succinic anhydride in CO2/IO mol% 1,4-dioxane is given vs time. 

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A typical sorption experiment involves exposing a polymer sample, initially at an equilibrium penetrant concentration of c to a bathing penetrant concentration of Ci. The weight gain or loss is then measured as a function of time. The term sorption used in this context includes both absorption and desorption. The sorption is of the integral type if c° = 0 in the case of absorption or if cf = 0 in the case of desorption. Details of the experimental setup for the sorption measurement are discussed elsewhere [4],... 

As discussed above, hysteresis loops can appear in sorption isotherms as result of different adsorption and desorption mechanisms arising in single pores. A porous material is usually built up of interconnected pores of irregular size and geometry. Even if the adsorption mechanism is reversible, hysteresis can still occur because of network effects which are now widely accepted as being a percolation problem [21, 81] associated with specific pore connectivities. Percolation theory for the description of connectivity-related phenomena was first introduced by Broad-bent et al. [88]. Following this approach, Seaton [89] has proposed a method for the determination of connectivity parameters from nitrogen sorption measurements. 

The sorbates used were Ar (spectroscopically pure), Kr (between 99 and 100% pure balance Xe), and Xe (between 99 and 100% pure, balance Kr). Sorption measurements were made volumetrically. The sorbents were partially outgassed at room temperature to about 10 5 mm Hg and the temperature was then increased during outgassing to 350° C at a rate not more than 70°C/hr. Outgassing was continued at 350° C for 24 hr and finally the temperature was decreased to room temperature over an interval of at least 3 hr. Between runs involving rare gases outgassing was effected at 200° C for 5 hr. 

The differential thermal analysis, thermogravimetric analysis, and x-ray results establish that the cationic modifications are stable under the outgassing conditions used in the sorption measurements. 

Nitrogen sorption measurements were performed on a Quantachrome Autosorb 6B (Quantachrome Corporation, Boynton Beach, FL, USA). All samples were degassed at 423 K before measurement for at least 12 hours at 1 O 5 Pa. Mercury-porosimetrie has been measured on a Porosimeter 2000 (Carlo Erba Instruments) Scanning electron micrographs were recorded using a Zeiss DSM 962 (Zeiss, Oberkochen, Germany). The samples were deposited on a sample holder with an adhesive carbon foil and sputtered with gold. 

Zeolites (3 were treated with a NaBO, solution, and the porous properties of boronated samples were investigated by sorption measurements with benzene and nitrogen as adsorbate, TEM, SEM and composition analysis. It is shown that the micropores are converted into the mesopores and the mesopores are developed into larger mesopores due to the extraction of framework silicon by base. The small atom size of boron and the poor stability of boron in framework should be responsible for the silicon removal in a large amount. The dissolution of silicon also causes the corrosion of outer surface of particles and the decrease of particle size. 

An all-glass apparatus was used for gravimetric sorption measurement with benzene as adsorbate. Prior to the measurement, the sample was heated to 360 C at a rate of 5 C/ min with simultaneous evacuation to 1.3 10 Pa, and further degassed at that temperature for 3 h. Then the sample was cooled down to 32X3, at which the benzene adsorption isotherm was measured. 

Vapour and gas sorption measurements can be performed with static or dynamic methods, either of which can provide information on equilibrium behaviour. Furthermore, the measurements can be performed using gravimetric or volumetric based instrumentation. The most common flow methods are inverse gas chromatography (IGC) [1] for volumetric studies and dynamic gravimetric instrumentation [2]. 

This example shows that, for modelling purposes, the in-situ structure of the polymer formed is to be taken into account and, for example, sorption measurements using recrystallized polymers can be misleading if one wants to model heat- and mass- transfer of the polymerizing particle. 

It is noteworthy that the effective coefficients Pe, De and Sc are obtainable in this way without recourse to equilibrium sorption measurements. This amounts to a kinetic method of measuring Se, exactly analogous to that applicable to ideal systems (where measurement of La(l) suffices for this purpose). This method is also applicable... 

Notes (a) Se obtained from equilibrium sorption measurements ... 

J. S. Mackie and P. Meares (86) could largely avoid these, however, by introducing an empirical formula of the activity coefficients. For the purpose they carried out sorption measurements at ion-exchange membranes. 

Sorption measurements were made in conventional McBain quartz-helix balances mounted in a water bath with a Plexiglass face the temperature of the bath was constant to within ... 

Prior to sorption measurements, zeolite samples were activated by evacuation at elevated temperatures. There is frequently some question as to how precisely one can establish the mass of a zeolite sample from which all zeolitic water, but no water arising from collapse of structural hydroxyl groups, has been removed (l f ). In order to establish that the (zeolitic-water-free) masses of the activated zeolite samples used here are well defined, the following stepwise activation procedure was used. Each sample was first heated in vacuo at 300°C. When the pressure had dropped to below about 10 torr, the balance was isolated from the pumps, the rate of pressure increase measured, and evacuation resumed. This process was repeated until the rate of pressure increase fell to below 5 X 10 torr min l, a duration of time which was from 15 to 30 minutes. This is a rate such that were the increase due to water vapor alone, and were the rate to remain constant, the weight loss would still be undetectable after 2h hrs., a duration seldom exceeded in activating zeolites. 

The isosteric heats of sorption reported in Table VI are also in acceptable agreement with values based on sorption measurements made near ambient temperature by other investigators, as the comparisons in Table VIII show. 

Both the matrix-model and the dual-model represent the experimental data satisfactory (Fig. 1). After modeling sorption measurements in several gas-polymer systems we have observed no systematic differences between the mathematical descriptions of the two models. 

Compaction of SMZ under the loading conditions of a permeable barrier is a potential problem. Since the hydraulic conductivity of SMZ can be tailored by varying the particle size, SMZ with a laboratory conductivity significantly greater than that of the aquifer material should be used in permeable barriers. Based upon the pilot-test data collected, it appears that contaminant retention by SMZ in a permeable barrier can be well-predicted from laboratory sorption measurements. 

Permeability should be demonstrated (e.g. by gas sorption measurements, spectroscopic evidence of guest exchange or crystallography). 

The isoreticular MOFs based on the Zn40(C0i)6 SBU also possesses favorable sorption properties for the storage of molecular hydrogen. At 77 K, microgravimetric sorption measurements gave H2 (mg/g) values of 13.2,15.0, 16.0, and 12.5 for IRMOF-1, IRMOF-8, IRMOF-11, and MOF-177, respectively. At the highest pressures attained in the measurements, the maximum uptake values for these frameworks are 5.0, 6.9, 9.3, and 7.1 molecules of H2 per Zn4OI unit where L stands for a linear dicarboxylate. 

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