Breakthrough experiment

Table 6. COj separation data from our COj and CO2/CH4 breakthrough experiments.

Adsorption/desorption kinetics the time of the adsorption-regeneration cycle greatly depends on the kinetics of the C02 adsorption-desorption profile, which is measured in breakthrough experiments. Sorbents that adsorb and desorb C02 in a shorter time are preferred as these reduce the cycle time as well as the amount of sorbent required, and ultimately the cost of C02 separation. 

Acidic micro- and mesoporous materials, and in particular USY type zeolites, are widely used in petroleum refinery and petrochemical industry. Dealumination treatment of Y type zeolites referred to as ultrastabilisation is carried out to tune acidity, porosity and stability of these materials [1]. Dealumination by high temperature treatment in presence of steam creates a secondary mesoporous network inside individual zeolite crystals. In view of catalytic applications, it is essential to characterize those mesopores and to distinguish mesopores connected to the external surface of the zeolite crystal from mesopores present as cavities accessible via micropores only [2]. Externally accessible mesopores increase catalytic effectiveness by lifting diffusion limitation and facilitating desorption of reaction products [3], The aim of this paper is to characterize those mesopores by means of catalytic test reaction and liquid phase breakthrough experiments. 

Liquid-phase breakthrough experiments were also developed in order to characterize mesopores. The principle of the methodology relied on the analysis of the diffusion and adsorption of molecular probes with various molecular dimensions and adsorption strength. The relative proportion of occluded and accessible mesopores in the studied dealuminated Y zeolite could then be estimated. To allow this estimation, it is necessary to use molecular probes that can or cannot penetrate into the microporosity of the Y zeolite (see Figure 2). 

Table 2 Molecular dimensions (nm) of the solvent and probe molecules used for the breakthrough experiments.

Table 6. C02 separation data from our C02 and CQ2/CH4 breakthrough experiments.

Since the main intent in synthesizing our materials was the development of new versatile adsorbents capable of effectively removing either acidic or basic TICs at ambient conditions, the dynamic breakthrough experiments were carried out at ambient conditions. The details of the homemade experimental setup are presented in [42-44]. Ammonia, hydrogen sulfide and nitrogen dioxide were our target TICs. 

Cu(NH3)2BTC2/3 and finally copper hydroxide in the presence of water. The formation of the BTC salts was supported by the collapse of the structure after interaction of ammonia with unsaturated copper centers. The release of BTC and copper oxide centers provides sites for reactive adsorption of ammonia during the course of the breakthrough experiments. Interestingly, even though the structure collapses, some evidence of the structural breathing of the resulting materials caused by reactions with ammonia was found, based on the ammonia adsorption at equilibrium and the analysis of the heat of interactions [51]. 

Using the local equilibrium analysis, the isotherm of a system can be found from breakthrough experiments using the following equation ... 

It is thus necessary to include a description of the thermodynamics and kinetics of hydrocarbon storage in a model of such a DOC. Typically, we have based this on hydrocarbon breakthrough experiments. In this experiment, hydrocarbon in an inert carrier is passed over an outgassed DOC core sample. 

Another feature of the breakthrough method is that the uniform geometry of the packed column permits fairly straightforward analysis of the thermal waves produced due to heats of adsorption, and of their effect on the shape of the sorption fronts. The most obvious advantage of this method, however, is the fact that the results of the breakthrough experiments can be applied rather directly to the design of commercial adsorbers, with relatively little analysis of the data. 

Since the columns used in the various breakthrough experiments varied from run to run (see experimental section), certain questions needed to be resolved with the help of the above-mentioned computer programs, along with the LRC coefficients for prediction of the multicomponent loadings and heats of sorption. These questions included the following ... 

Pure component loadings for CO2, N2 and O2 on commercial pelleted forms of Linde type 4A, 5A and 13X molecular sieve zeolites were derived from various gravimetric and volumetric measurements. The range of pressures and temperatures over which these measurements were made were at least as broad as those encountered in the breakthrough experiments described here, to permit accurate estimations of heats of adsorption in the manner described by equation (6) above. As mentioned above, the pure component data were correlated to the LRC model, and the CO2 loadings predicted by the multicomponent LRC model compared to actual loadings in the breakthrough runs at bed saturation. 

Comparison of Pore Size Distributions Determined by Mercury Injection and Gas Breakthrough Experiments... 

Table 2. Comparison between data from Mercury Injection (Hg) and gas breakthrough experiments (TV.) "N." denotes the N. displacement pressure converted from mercury data to the system N. -water.

Hildenbrand, A., Schlomer, S. and Krooss, B.M. (2002) Gas breakthrough experiments on fine-grained sedimentary rocks. Geofluids 2, 3-23... 

Tert-butylbenzene (BDH Chemicals Ltd Poole, England) and cyclohexane (POCH, Poland) were used as probe organic compounds in the breakthrough experiments. 

The linear flow rate vL for TBB breakthrough experiments was about three times larger than for CHX. The differences in the TBB and CHX breakthrough behaviour for M and S activated carbons/molecular sieve beds could be connected with the magnitude of this linear rate, and the nature of these organics. CHX is not aromatic with a 3D-structure, in contrast to the aromatic TBB with only a 3D-tail (Figure 5). These molecules can interact differently not only with the carbon adsorbent, but also with the sieve. This interaction depends on the presence and distribution of water in the beds. Additionally, a decrease in the Vl value can cause penetration of smaller water molecules deeper into long and narrow pores which can affect the capacity of pores with respect to CHX. 

Comparing the log-scaled TBB breakthrough plots vs time for mixed M and separated S beds of activated carbon and molecular sieve without or with water vapour, it can be affirmed that separated activated carbon/molecular sieve bed ( S ) is more effective than mixed ( M ). In the case of cyclohexane breakthrough a negative effect caused by mixing of activated carbon with molecular sieve is observed. This effect is probably caused by the different linear flow rates for TBB and CHX on the breakthrough experiments. 

Breakthrough Experiments. For the breakthrough experiments the sorbents were packed in 100-mg beds, 4 mm in diameter, and inserted into the six ports in the manifold. The effluent ends of the tubes were connected to a common line leading to the flame ionization detector. While the flame ionization detector, calibrated with the challenge atmosphere, monitored the concentration of vinyl acetate in the combined bed effluents, the pump in the detector drew the challenge atmosphere through each bed at approximately 0.2 L/min. The output from the detector, the breakthrough curve, was recorded with a strip-chart recorder. Most of the porous polymer sorbents tested were first washed with acetone and dried. 

Example 8.8 A wastewater containing 25 mg/L of phenol and having the characteristic breakthrough of the previous example is to be treated by adsorption onto an activated carbon bed. The flow rate during the breakthrough experiment is 0.11 mVs this is equivalent to a surficial velocity of 0.0088 m/s. The XIM ratio of the bed for the desired effluent of 0.06 mg/L is 0.02 kg solute per kg carbon. If the flow rate for design is also 0.11 mVs, design the absorption column. Assume the influent is introduced at the top of the bed. The packed density of the carbon bed is 721.58 kg/ml... 

As mentioned before, the unit operation of bed adsorption may be carried out in a moving-bed mode, either co-currently or countercurrently. When the breakthrough experiment is carried out, the superficial velocity should also be recorded. The reason is that adsorption is a function of the time of contact between the liquid phase containing the solute to be adsorbed and solid-phase carbon bed. Thus, for the breakthrough data to be applicable to an actual prototype adsorption column, the relative velocities that transpired during the test must be maintained in the actual column. When the relative velocities between the flowing water and the carbon bed are maintained, it is immaterial whether or not the bed is moving. 

In a breakthrough experiment, the superficial velocity may be obtained by dividing the volume V of water collected in t time by the superficial area of the experimental column. Breakthrough experiments are invariably conducted in stationary beds. Thus, from the previous equations this superficial velocity is actually the relative velocity of the flowing water with respect to the bed, with Vj equal to zero. This relative velocity must be maintained in the actual column design, if the data collected in the breakthrough experiment are to be applicable. 

A breakthrough experiment is conducted for phenol producing the results shown in Problem 8.7. The length of the active zone is calculated to be... 

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