Adsorbed mass

On-line GC analysis (Shimadzu GC 14A) was used to measure product selectivity and methane conversion. Details on the analysis procedure used for batch and continuous-flow operation are given elsewhere [12]. The molecular sieve trap was found to trap practically all ethylene, COj and HjO produced a significant, and controllable via the adsorbent mass, percentage of ethane and practically no methane, oxygen or CO, for temperatures 50-70 C. The trap was heated to -300°C in order to release all trapped products into the recirculating gas phase (in the case of batch operation), or in a slow He stream (in the case of continuous flow operation). 

The ethylene selectivity (Fig. 5) and thus the ethylene yield depend strongly on the adsorbent mass (Fig. 5). For fixed catalyst mass, oxygen supply I/2F and methane conversion there is an optimal amount of adsorbent for maximizing ethylene selectivity and yield (Fig. 5). Excessive amounts of adsorbent cause quantitative trapping of ethane and thus a decrease in ethylene yield according to the above reaction network. This shows the important synergy between the catalytic and adsorbent units which significantly affects the product distribution and yield. 

Figure 5. Effect of adsorbent mass in the molecular sieve trap on the ethylene, ethane and total C2 selectivity at a fixed methane conversion of 15%. Recirculation flowrate 220 cm3 STP/min...

This means that representing the equilibrium adsorbate mass (or volume) adsorbed versus concentration (or partial pressure) should be a straight line if plotted on logarithmic scales. Other theoretically based correlating equations are available for the adsorption of gases and vapors9, but all equations have their limitations. 

Engine runs normally on a lean mixture. During this stage, the nitrogen oxides (after being oxidized to N02) are stored in nitrate form on an adsorbant mass. 

Fig. 2. Schematics of adsorption isotherms for polymers, where the adsorbed mass r per unit area of the sorbent surface is plotted against the polymer concentration cp in solution. The steep initial slope of the isotherms indicates...

Fig. 9. Adsorption isotherms where the adsorbed mass f/rngm 2, of various sorbent surfaces is plotted against the protein concentration cl g dm 3, in solution. Sorbents Teflon (o), polystyrene (x),... 

When chloroform was added, the equilibrium response of the sensor progressively decreased. This is probably related to the combination of the nonlinear behavior of the effective refractive index of the coupled cladding mode on the overlay refractive index with the nonlinear relationship between adsorbed mass of... 

Hence, water molecules enhance the acidic properties of the zeolite s Bronsted acids. Adsorbate-adsorbent interactions and, therefore, adsorbent selectivity and adsorbate mass transfer rates are altered due to water polarization. When developing an adsorbent to be used in a commercial adsorptive separation process, the water content of the adsorbent is adjusted to balance adsorbent selectivity and component mass transfer rate. 

The two adsorbent chambers contain the zeolitic adsorbent, the liquid xylenes and p-diethylbenzene desorbent. Proper loading of the adsorbent into the large diameter vessels in industrial production plants is of critical importance to maximize adsorbent mass in the fixed vessel volume and not generate low and high density areas within the adsorbent bed. Density inconsistencies could adversely affect liquid flow distribution and thereby have a detrimental effect on the performance of the process. Adsorbent loading methods are a matter of proprietary know how of the technology licensors. However, Seko has published a paper on the practical matters involved in an actual problem case [20]. 

The sensible heat required to heat the dry adsorbent mass from the adsorption temperature to the regeneration temperature. This is generally a function of temperature and can be readily evaluated. 

These piezoelectric crystal oscillators are very accurate mass sensors because their resonant frequencies can be measured precisely with relatively simple electronic circuitry. For certain quartz crystals, the resonant frequency is inversely related to the crystal thickness. A crystal resonating at 5 megahertz is typically 300 micrometers thick. If material is coated or adsorbed on the crystal surface, the resonant frequency will change (decrease) in proportion to the amount of material added. The effect of adsorbed mass on the oscillator frequency varies according to the operational mode of the device. In any case, interpretation of mass via changes in frequency or amplitude assumes that the coated films are rigidly elastic and infinitesimally thin (that is, an extension of the crystal). 

Most of the early theories of polymer adsorption were not concerned with the interaction between adsorbed polymers so that they have little relevance for a comparison with experimental results. In actuality, the adsorbed mass per unit area is very large even when adsorption of polymers occurs from a very dilute solution. In this section, some typical theories allowing for the interaction between adsorbed polymers are reviewed. 

Analytical equations for adsorbate uptake and radial adsorbent temperature profiles during a differential kinetic test are derived. The model assumes that the mass transfer into the adsorbent can be described by a linear driving force model or the surface barrier model. Heat transfer by Fourier conduction inside the adsorbent mass in conjunction with external film resistance is considered. 

Experimental uptake data for sorption0of i-octane on 13X zeolite and n-pentane on 5A zeolite were quantitatively described by the model. The results show that internal thermal resistance of the adsorbent mass plays a significant role during the uptake for these systems even though the adsorbent temperature changes are small. 

The model shows that the non-isothermal uptake curve for an adsorbent mass which has low effective thermal conductivity (k ) is identical in form to that of the isothermal Fickian diffusion model for mass transport. 

We assume that the adsorbent mass used in the kinetic test consists of a sphere of radius R. It may be composed of several microsize particles (such as zeolite crystals) bonded together as in a commercial zeolite bead or simply an assemblage of the microparticles. It may also be composed of a noncrystalline material such as gels or aluminas or activated carbons. The resistance to mass transfer may occur at the surface of the sphere or at the surface of each microparticle. The heat transfer inside the adsorbent mass is controlled by its effective thermal conductivity. Each microparticle is at a uniform temperature dependent on time and its position in the sphere. 

We assume that the adsorbent mass is initially in equilibrium with the adsorbate at pressure P and temperature T, and a differential step change in the gas phase pressure to is applied at time t = 0. The pressure inside the adsorbent mass (or the microparticles), P(t), increases with time, which is given by ... 

Where T is the temperature of the adsorbent mass at radius r and time t. n is the adsorbate loading per unit weight of the adsorbent at radius r and time t. q is the isosteric heat of adsorption, p, c and k are, respectively, the density, the heat capacity and the effective thermal conductivity of the adsorbent mass. 

The last boundary condition accounts for the external heat transfer from the adsorbent mass, h is the effective external heat transfer coefficient, a, b, c, p, q, kfi, kg and h can be assumed to be constants for a differential test. 

The average adsorbate loading in the adsorbent mass, n(t), can be obtained by ... 

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