Adsorption is an important separation process, e.g. for the oxygen-nitrogen-separation, the separation of alkanes and iso-alkanes, the separation of p-xylene from C8 -streams and for the purification of waste water and waste gases. For the calculation of such processes and for the development of models, which can be used for the prediction of multicomponent adsorption equilibria a large number of data is required. For the measurement of these data two apparatuses are available. For the measurement of pure component adsorption equilibria a Sartorius Micro Balance is used (Fig. 1).
Fig. 1: Adsorption Balance
With this apparatus the increase of weight during the adsorption of the solvent is measured.
For the measurement of pure component, binary and ternary adsorption equilibria a flow type apparatus is available (Fig. 2).
Fig. 2: Flow-type apparatus for vapor adsorption experiments
A gaseous feed mixture is generated by passing a carrier gas (nitrogen or hydrogen) through the parallel saturators. The saturators are thermostated at the required low temperature to obtain the desired partial pressures of the adsorptives in the gas stream. After mixing, the gas stream pass the glass made adsorption chamber. The concentration in the outlet gas stream is measured with the help of a gas chromatograph, which is connected with a six-way-valve. The content of the six-way-valve sample loop is periodically injected into the gas chromatograph and analyzed by a FID or WLD. The signals of the components are recorded with the help of an integrator to obtain the desired adsorptive breakthrough curves. A typical breakthrough curve is shown in figure 3. With the help of these breakthrough curves and a simple mass balance equation the total adsorbed amount and the adsorbate mole fractions this means the adsorption equilibrium can be calculated.
Fig. 3: Typical breakthrough curve for a ternary adsorption equilibrium
A typical result with the flow-type apparatus is shown in figure 4.
Fig 4: Binary adsorption equilibrium of toluene / tetrahydrofuran on zeolite DAY-55 at 318.15 K and a pressure of 1.0 kPa (Correlation with the model RAST)