Simulated binary isothermal adsorption on activated carbon in periodic countercurrent column operation

Abstract

Simulation studies are presented of single-and two-component adsorption in periodic, countercurrent, multicolumn systems. It is demonstrated that long adsorption profiles are likely to occur in the adsorption of organic contaminants from wastewater onto activated carbon, thus favoring the use of multicolumn rather than single-column systems. For two-component adsorption in a multicolumn system, it is shown that more switching periods are needed than in the single-column case before the profiles stabilize, that the stabilized profiles can differ substantially from those found in a single-column system, and that their shape is strongly influenced by the relative concentrations of the components in the feed. ROLAND KLAUS SCOPEThe adsorption of contaminants from fluid streams onto activated carbon is becoming an increasingly important separation method. The use of a single column often gives relatively poor carbon utilization so that, in practice, two or more columns are normally used in series. Although many studies have appeared in the literature on the modeling and simulation of single-column operation, very little has been reported on periodic countercurrent systems. Continuous countercurrent systems have been modeled for film and film plus pore resistance with linear and irreversible isotherms (Kasten and Amundson, 1952; Neretnieks, 1974a, b, and c). Svedberg (1976) reports results for the simulation of periodic countercurrent operation with film plus pore diffusion and a linear isotherm.When more than one component is adsorbed, the shape of the concentration profiles in the adsorber will change radically, giving peaks and plateaus which result from interactions between the adsorbed solutes and cannot be modeled by the assumption of linear or irreversible isotherms.The purpose of the work described here was to simulate multicomponent adsorption on activated carbon in multicolumn periodic operation, since this is the case most commonly found in practice. CONCLUSIONS AND SIGNIFICANCEIt is demonstrated from approximate calculations that for conditions similar to those commonly found in practice, the adsorption profile is so long that the use of a single-column system is likely to be uneconomic. Multicolumn periodic operation is, thus, the natural choice for carbon adsorption systems.Results for single-component adsorption with film and pore diffusion in a two-column system show that for the conditions examined, the concentration profiles in a twocolumn system stabilize rapidly. There is little change in profile shape after the first switch, although there are indications that at lower feed concentrations, the transient phase would be longer.For the two-component system that is simulated with film resistance, the concentration profiles take much longer to stabilize and can change profoundly with changes in the relative concentration of the components in the feed. The simulations show that as a result of the displacement phenomenon occurring in a multicomponent adsorption, the relative concentrations of components i...

Numerical solution of liquid‐phase multicomponent adsorption in fixed beds

“…Also it can be noticed that the breakthough curves were delayed by 1.5, 2 and 5.5 hours for component 1, 2 and 3 respectively. Similar observations have been reported by Zwiebel et al (1974), Klaus et al (1977), Halzli et al (1978 and Sung et al (1979). It is believed that the height of the peak is a function of the length of the column; because, the longer the bed the larger the total amount of the nonkey component displaced.…”

“…Similar observations were reported by Helfferich and Klein (1970) and have been found by others including Zwiebel et al (1974), Hsieh et a]. (1977), Klaus et al (1977), Balzli et al (1978), and Sung et al (1979). In order to explain this phenomena let us define the components in a multicomponent system according to the degree of adsorption affinity or the degree of nonlinearity in their equilibrium isotherms.…”

“…Adsorption is one of the most important processes used in industry for the separation of solutes from a fluid stream onto a solid surface and especially important in advanced wastewater treatment Rosen (1952,1954) Tien and Thodos (1960 Colwell and Dranoff (1966) Liaw et al (1979) Tien and Thodos (1959,1965) Cooney and Lightfoot (1966) Hall et al (1966 Kostecki et al (1967) Morton and Murrill(l967) Chen et al (1968) Colwell and Dranoff (1969, 1971) Cooney and Strusi (1972) Usinowics (( 1972) Gariepy and Zwiebel(l975) Tien et al (1976) Klaus et al (1977) Hsieh et al (1977 von ) Balzh et al (1978) Sung et al (1979 Reis et al (1979) Only asymptotic solution was obtained. ** Pseudwbinary isotherms were used.…”

Optimal design of multistage adsorption‐bed systems

“…IR recent years, a few research groups (Chen et al, 1972;Svedberg, 1976;Klaus et al, 1977) carried out analyses, simulating the periodic countercurrent operation of multistage adsorption-bed systems. In view of the practical importance of multicomponent, liquid phase ad-…”

Numerical Methods for the Solution of Adsorption Models

“…This is the case when we use Ficks law for particle mass transfer insted of the linear driving force model. If finite differences or collocation are applied to the spatial derivatives in the parabolic PDE's then the problem is transformed into a form that allows the use of the numerical method of characteristics; equation (7) becames now a set of equations k= 2, ... ,N+l (12) Several authors used this approach with fmite differences [43] or collocation [44, 45,46]. If due to the complexity of the equations it is difficult to determine analytically the characteristic directions the problem can be solved by means of the so-called pseudocharacteristics method proposed by Carver [47] …”