Adsorption onto zeolites

Previous studies of our work group demonstrated that isomaltose exhibits a distinct higher affinity towards certain dealuminated p-zeolites as opposed to other carbohydrates like fructose or glucose [94, 109]. Sucrose is not adsorbed at all. As a consequence, a process could be developed which directly removes the isomaltose from the reaction solution by adsorption onto zeolite. For this purpose a fluidized bed reactor has been utilized with a special focus on the separation of the two solid phases (Fig. 14). The biocatalyst containing entrapped dextransucrase is produced by the jet-cutter method [110] the alginate beads have a mean particle size of 0.5 mm. To accomplish an adequate high density of biocatalyst, silica flour (30% w/v) is included. The particle diameter of the second solid phase (zeolite) is adjusted to 10 pm. As a consequence, zeolite is loaded with isomaltose inside the reactor and can then freely exit the reactor together with the product solution, whereas the biocatalyst is retained inside the fluidized bed reactor [92, 94],... 

Kazansky (2003) presented results on interactions of H2 with different zeolites using the FTIR spectroscopy, which could be more interesting if the H NMR spectra were recorded in parallel for the same samples. The same conclusion is for the paper (Prasanth et al. 2008) describing the hydrogen adsorption onto zeolite Z. Ganapathy et al. (2003) studied titanium... 

A static measurement using small doses of water vapour as adsorptive onto zeolite 3A held in an ice bath. The isotherm is shown in Figure 6. 

Sojka, Z. and Witkowski, S. (2002) EPR study of CO adsorption onto CoZSM-5 zeolite Evidence for spin crossover upon coordination and lz2, 2A1) ground state, Top. Catal., 18, 279. 

Liquid phase zeoHtic separation includes two main events adsorption and desorption. Adsorption of an adsorbate (liquid component being adsorbed by solid) onto zeolitic adsorbent is dictated by the characteristics of the adsorbate-adsorbent interaction. A zeolitic adsorbent is a crystalline porous solid having particular characteristics (see Chapter 2). When immersed in a liquid mixture, the porous... 

Until now we have mainly treated adsorption onto non-porous surfaces. In reality, most industrial and many natural materials are porous Textiles, paper, bricks, sand, porous rocks, food products, zeolites etc. We start our discussion with a classification of pores according to their size, which is recommended by IUPAC ... 

Our main focus for this review is to briefly and critically describe some of the defluoridation techniques as a means of getting a basis to support the adsorption technique, to evaluate the defluoridation adsorbents now being utilized and those novel defluoridation adsorbents reported in literature over the last two decades, with special reference to drinking water. Emphasis is laid toward the adsorbents availability, fluoride sorption capacity and where applicable their kinetic adsorption characteristics and column performances are reported. Detailed characteristics of fluoride adsorption onto surface-tailored zeolite are provided. In addition, various adsorber configurations are reexamined and challenges to and prospects for their application to less developed countries (LDCs) are discussed. 

Characteristics of fluoride adsorption onto surface-tailored low-silica zeolite... 

In carrying out material balance over a small control volume of a fixed bed, it is considered that fluoride removal is solely by adsorption onto the zeolite particles. Additionally, the system is assumed to be isothermal, non-equilibrium and non-adiabatic single-component fixed-bed adsorption. For the control volume (Fig. 6), Axdz, for a limiting situation z->0, the material balance is given by... 

So far, only very little attention has been focussed on the use of zeolites in biocatalysis, i.e., as supports for the immobilization of enzymes. Lie and Molin [116] studied the influence of hydrophobicity (dealuminated mordenite) and hydrophilicity (zeolite NaY) of the support on the adsorption of lipase from Candida cylindracea. The adsorption was achieved by precipitation of the enzyme with acetone. Hydrolysis of triacylglycerols and esterification of fatty acids with glycerol were the reactions studied. It was observed that the nature of the zeolite support has a significant influence on enzyme catalysis. Hydrolysis was blocked on the hydrophobic mordenite, but the esterification reaction was mediated. This reaction was, on the other hand, almost completely suppressed on the hydrophilic faujasite. The adsorption of enzymes on supports was also intensively examined with alkaline phosphatase on bentolite-L clay. The pH of the solution turned out to be very important both for the immobilization and for the activity of the enzyme [117]. Acid phosphatase from potato was immobilized onto zeolite NaX [118]. Also in this study, adsorption conditions were important in causing even multilayer formation of the enzyme on the zeolite. The influence of the cations in the zeolite support was scrutinized as well, and zeolite NaX turned out to be a better adsorbent than LiX orKX. 

Upon adsorption of thiophene on NiNaY zeolites (Figure 4) the most intense bands were observed at 3108, 3093, and 1396 cm which resemble similar bands in the spectrum of liquid thiophene [9,11]. The intensity of the (NiOH) band did not change. In agreement with these results, the infrared spectra of silica supported nickel in contact with thiophene did not show any effects which could be attributed to adsorption onto the metal rather than the oxide surface [10]. 

Sensors based on adsorption of species onto or into lattice structures have been reported for molecules besides water. For example, devices based on the detection of carbon dioxide adsorption onto semiconductor materials have been developed [10]. In other cases, dielectric materials that have some degree of chemical specificity have been used for making chemically-sensitive layers. One such application is the use of the highly porous zeolite lattice to detect adsorbed hydrocarbons [11]. The specific dimensions and shape of the zeolite pores allows for size and chemical selectivity in the lattice. As in the case of the humidity devices, the adsorbed molecules dipoles cause a local change in the electric fields that can be detected through a capacitive effect. 

P-15 - Simulation for removal of binary solvent vapor by adsorption onto high silica zeolite... 

A detailed discussion of adsorption onto mesoporous solids is beyond the scope of this text, but certain features relevant to microporous solids should be described. Firstly, microporous solids can themselves contain mesoporosity. The most important example of this is observed in zeolites such as Y or mordenite that have been treated after synthesis to remove aluminium from the framework (Section 6.2.3). The migration of silica leaves mesopores that are evident from nitrogen adsorption isotherms and directly visible by electron microscopy. The presence of secondary mesopores enhances diffusion and catalytic properties. Conversely, mesoporous solids that are well ordered on the mesoscale can contain disordered micropores in their walls. The mesoporous channels of calcined SBA-15, for example, are connected by micropores that result from removal of block copolymer chains that run between the large channels in the as-synthesised material. This is observed from nitrogen... 

Atomistic Simulations of CO2 During Trapdoor Adsorption onto Na-Rho Zeolite... 

Budd et al. (2004) prepared multilayer membranes by altering the adsorption of cationic polyelectrolyte, chitosan, and an anionic polyelectrolyte, poly(4-styrene sulfonate) onto zeolite. The films were formed on porous supports in sheet and tube forms. The multilayer membranes were shown to exhibit high selectivity for water over alcohols associated with zeolite A but to be considerably more stable under acidic conditions than the pure zeolite A membrane. The membranes were successfully applied to the selective removal of water by PV in the esterification of lactic acid with EtOH, catalyzed by p-toluenesulfonic acid. For esterification at 70°C, yields of... 

The second mechanism appears to be adsorption onto porous solids (Urushizaki, 1987 Kader et al., 1989). Examples include sachets containing activated carbon or molecular sieves, and plastic films containing dispersed Ohya stone, crystobalite, coral sand, silica gel and synthetic zeolite (Abe, 1990). 

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