Adsorption/desorption cycling

Abstract. A model of the conformational transitions of the nucleic acid molecule during the water adsorption-desorption cycle is proposed. The nucleic acid-water system is considered as an open system. The model describes the transitions between three main conformations of wet nucleic acid samples A-, B- and unordered forms. The analysis of kinetic equations shows the non-trivial bifurcation behaviour of the system which leads to the multistability. This fact allows one to explain the hysteresis phenomena observed experimentally in the nucleic acid-water system. The problem of self-organization in the nucleic acid-water system is of great importance for revealing physical mechanisms of the functioning of nucleic acids and for many specific practical fields. 

Rapid Adsorption-Desorption Cycles For rapid cycles with particle diffusion controlling, when the cycle time is much smaller than the time constant for intraparticle transport, the LDF approximation becomes inaccurate. The generalized expression... 

Laboratory experiments have shown that reaction 15 occurs on ice in the absence of HCl (11-13) furthermore, the product HOCl appears on a time scale of minutes, in contrast to CI2 in reaction 13, which is produced on at most a millisecond time scale (11). Thus, in this mechanism HOCl serves as an intermediate if there is enough HQ on the ice, HOCl will react with HCl while still on the ice surface otherwise the HOCl will desorb, eventually finding an HCl molecule in the ice, perhaps after several adsorption-desorption cycles. 

Figure 5. Top Adsorption isotherms of C02 for 1-en at the indicated temperatures. Bottom Adsorption-desorption cycling of C02 for 1-en showing reversible uptake from (a) simulated air (0.39 mbar C02 and 21% 02 balanced with N2) and from (b) simulated flue gas (0.15 bar C02 balanced with N2). (c) time-dependent C02 adsorption for porous materials (A = 1-en, B = mmen-Mg2(dobpdc), C = 1, D = Mg-MOF-74, E = Zeolite 13X, F = MOF-5). (d) C02 adsorption ratio of 1-en in flue gas (after 6 min exposure to 100% RH at 21 °C) to 1-en in flue gas (Adapted from [192]).

Figures. (A)VoltammogramsofPt(lI0)cooledinH2 + Arand0.1Af HCIO4. (B) Voltammogram of Pt( 110) cooled in H2 + Ar and 0.5M H2SO4, where the dotted curve was observed after the first oxygen adsorption-desorption cycle. The sweep rate was 50 mV s. (From Ref. 26.)...

Details of the trap heater are also shown in Figure 2. The adsorption-desorption cycle may be accomplished conveniently with the use of a six port valve and a plumbing system constructed of materials that neither adsorb volatile organics nor outgas... 

In IR experiments it was confirmed that NO could adsorb as NO, NO and (NO)2- species on the Cu-zeolite, and the anionic species decreased with adsorption time to yield N2 and N2O in the gas phase whereas NO" " increased. After adsorption of NO for about 1 h, anionic species had almost disappeared and the intensity of NO species became approximately constant. These results indicate that all the Cu ions generated through pretieatment at elevated temperature were oxidized to Cu2 ions by oxygen produced in the NO decomposition at ambient temperature and the resulting CU2+ ions acted as adsorption sites for NO" " (Cu2+ + NO = Cu -NO ). This NO species could not be desorbed by evacuation at room temp ature. The IR spectra indicated the presoice of a large amount of NO and small amounts of NO2 and NO3 after the evacuation, i.e., weakly adsorbed or physisorbed NO molecules were absent from the zeolite under these condititHis. These phenomena were further confirmed by ESR experiments the adsorption-desorption cycles of NO resulted in a decrease-increase in the intensity of Cu2+ ESR signals. 

In adsorption/desorption cycles, the amounts of the first and later desorption and the amounts of the second and later adsorption were almost the same as shown in Fig. 1. Therefore, we defined them as a reversible amount adsorbed. On the other hand, the amount of the first adsorption was always larger than the reversible amount adsorbed and, therefore, we defined it as a total amount adsorbed. Moreover, we defined the difference between total and reversible amount adsorbed as an irreversible amount adsorbed. 

Adsorption-desorption cycle in SbF5 was repeated four times. 

Giacomelli CE, Norde W (2001) The adsorption-desorption cycle. Reversibility of the BSA-silica system. J Colloids Interf Sci 233(2) 234-240... 

The analysis of isotherms of gas at the temperature interval 233 - 293 K and pressure interval 0.1-6 MPa was realized by the gravimetric control of the sample (200-400 g) during adsorption/desorption cycle. The experimental set-up is shown in Fig. 5. 

A set of 10 solenoid valves (Atkomatic Inc.) were used for switching the adsorption-desorption cycle. The solenoid valves were controlled by a programmable controller... 

For absolute surfaces ranging from 50 to 5 m the measuring gas to be used is nitrogen. For absolute surface of 5-0.5 m the measuring gas is argon. For absolute surfaces below this level we use krypton. In the latter case, the only possible determination is that of the specific area since, with krypton being solid at liquid N2 temperature, it is not feasible to perform a complete adsorption-desorption cycle for the evaluation of pore distribution and sizes. For obvious reasons, krypton measurement is bound to become the routine one for most freeze-dried pharmaceuticals. 

In processes of solvent recycling activated carbon is usually used as adsorbent. In the following investigation this adsorbent is replaced by a high-silica zeolite. A model plant is supposed with two or more columns working in adsorption-desorption cycles. Only in the desorption steps the zeolitic molecular sieve will be seriously damaged because of the high process temperature. 

The whole adsorption-desorption cycle takes about four hours whereas the heating time of the desorption step is about one hour with a desorption temperature of 473 K. Furthermore, we suppose that the maximal humidity of the waste air or the cleaned air is 20g H20/kg of molecular sieve. The results obtained for such scenario are given in Fig. 4. 

The technical application of high-silica molecular sieves without any non-framework aluminium as protective layer restricts the water loading of the stream in sorption processes. The use of supersaturated steam for the regeneration of the adsorbent is impossible since already after a few adsorption/desorption cycles the molecular sieve is totally damaged. However, adsorbents which are modified by surface alumination are remarkably more resistant against water. 

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