Liquid adsorption processes

Adsorption may in principle occur at all surfaces its magnitude is particularly noticeable when porous solids, which have a high surface area, such as silica gel or charcoal are contacted with gases or liquids. Adsorption processes may involve either simple uni-molecular adsorbate layers or multilayers the forces which bind the adsorbate to the surface may be physical or chemical in nature. 

Liquid adsorption processes hold a prominent position ia several appHcations for the production of high purity chemicals on a commodity scale. Many of these processes were attractive when they were first iatroduced to the iadustry and continue to iacrease ia value as improvements ia adsorbents, desorbents, and process designs are made. The UOP Parex process alone has seen three generations of adsorbent and four generations of desorbent. Similarly, Hquid adsorption processes can be applied to a much more diverse range of problems than those presented ia Table 3. 

The large demand for benzene is due to its use as a starting material in the production of polystyrene, acrylonitrile styrene butadiene rubber, nylons, polycarbonates and linear alkyl benzene detergent. All of these final chemical products that are suitable to form into consumer goods have multiple chemical transformations in various industrial processes to obtain them from benzene. Because the production of benzene does not involve a liquid adsorptive process on a zeolite, these processes are not described here but can be found in other sources. However, it is important to note that benzene is typically a large byproduct from an aromatics... 

The production ofp-xylene begins with petroleum naphtha, as does the production of the other mixed xylene components, benzene and toluene. Naphtha is chemically transformed to the desired petrochemical components and the individual components are recovered at required purity in what is known in the industry as an aromatics complex [12]. A generic aromatics complex flow scheme is shown in Figure 7.2. It is useful to briefly review the general flow scheme of this complex for subsequent discussion of the liquid adsorptive processes. The process blocks... 

The Parex, Toray Aromax and Axens Eluxyl processes are the three adsorptive liquid technologies for the separation and purification of p-xylene practiced on a large scale today. The MX Sorbex process is the only liquid adsorptive process for the separation and purification of m-xylene practiced on an industrial scale. We now consider a few other liquid adsorptive applications using Sorbex technology for aromatics separation that have commercial promise but have not found wide application. 

Expansion of Sorbex technology to the production of m-xylene shows how the process concept can be used for multiple applications in separations that cannot be performed by other means. One can expect that, as demand for new, difficult to separate aromatics increases, the simulated moving bed liquid adsorption processes can provide a means for production. 

Figure 15.26. Continuous and UOP simulated continuous moving bed liquid adsorption processes [Broughton, Sep. Sci. Technol. 19, 723-736 1984-1985)]. (a) Continuous moving bed liquid adsorption process flows and composition profiles, (b) UOP Sorbex simulated moving bed adsorption process.

Liquid adsorption processes hold a prominent position in several applications for die production of high purity chemicals 00 a commodity scale. 

Activated carbons are the most widely used adsorbents in gas and liquid adsorption processes. They are manufactured from carbonaceous precursors by a chain of chemical and thermal activation processes. The temperature for carbonization and activation reaches up to 1100°C in thermal processes. Activated carbons develop a large surface area, between 500 and 2000m2g 1, and micropores with an average pore diameter <2nm. Mesoporosity and macroporosity is generated by secondary procedures such as agglomeration. The products are shaped as granules, powders and pellets depending on their application. 

Estimation of the Effective Hamaker Constant for Solid-Vapor Interactions for Different Soils. The Hamaker constant represents interactions between macro-objects such as mineral surfaces and liquid due to short-range (< 100A) van der Waals forces (Ackler et al., 1996 Bergstrom, 1997). The presence of van der Waals surfacial interactions in most liquid adsorption processes in nalural porous media renders the proper estimation of the Hamaker constant an important task. The Hamaker constant for liquid-liquid interactions through the intervening vapor is a... 

Activated Carbons Activated carbons are the most widely used adsorbents in gas and liquid-adsorption processes. They are manufactured from... 

As a supplement we add pure and binary mixture data taken for adsorption equilibria in a liquid-solid system. This is to be understood as an example demonstrating that microbalances can also provide information on liquid adsorption processes, a field which in view of protein adsorption phenomena for separation certainly has potential for future development. 

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