Zeolite adsorbate acetone

The H/D exchange between the methyl groups of adsorbed acetone molecules and the Bronsted acid sites of zeolite HZSM-5 was also observed upon adsorption of C-2-acetone on a deuterated catalyst (D,HZSM-5, nsi/ Ai = 21.5) at room temperature (Figs 20c and d). The " C MAS NMR spectrum of C-2-acetone adsorbed on zeolite D,HZSM-5 (Fig. 20e) consists of the carbonyl signal at 223 ppm with a featured sideband pattern and a methyl signal at 29 ppm. No significant... 

It implies from the above discussion that "neutral" acetone complex previals at room temperature on the surface of H-zeolites if the coverage of OH groups is less than 100%. The domination of the acetone "neutral" species on the H-zeolite surfaces were also confirmed by the results of low temperature (125 K) measurements of MAS NMR of adsorbed acetone [8]. 

The first natural microporous aluminosilicate, i.e., natural zeolite, was discovered more than 200 years ago, and after long-term practical applications, the intrinsic properties of natural zeolites such as reversible water-adsorption capacity were fully recognized.13 41 By the end of the 19th century, during exploitation of ion-exchange capacity of some soils, it was found that natural zeolites exhibited similar properties some cations in natural zeolites could be ion-exchanged by other metal cations. Meanwhile, natural chabazite could adsorb water, methanol, ethanol, and formic acid vapor, but could hardly adsorb acetone, diethyl ether, or benzene. Soon afterwards, scientists began to realize the importance of such features, and use these materials as adsorbents and desiccants. Later, natural zeolites were also used widely in the field of separation and purification of air. 

Citric acid separation from fermentation broth employs the full allotment of Sorbex beds in addition to the four basic Sorbex zones. The process utilizes a resin instead of a zeolite based adsorbent. The resin is a nonionic cross-linked polystyrene polyvinyl benzene formulation. Operating temperatures for this process are sufficient to overcome diffusion limitations with a corresponding operating pressure to maintain liquid-phase operation. The desorbent consists of water blended with acetone. Subsequent processing steps remove the desorbent from the desired extract product citric acid. 

Sepiolite clay (<100 mesh) was heated in air at 120°C in order to remove the zeolitic and surface bound water molecules. The partially dehydrated clay mineral was subsequently exposed to acetone vapor at room temperature for a period of four days. H and 29Si CP MAS-NMR experiments revealed that the acetone molecules penetrated into the microporous channels of the sepiolite structure. Broad line 2H NMR studies using acetone-d6 revealed that, in addition to fast methyl group rotations, the guest acetone-d6 molecules were also undergoing 2-fold re-orientations about the carbonyl bond. The presence of acetone-d6 molecules adsorbed on the exterior surfaces of the sepiolite crystals was also detected at room temperature. 

Finally, the 29Si CP/MAS-NMR spectrum of a partially dehydrated sepiolite that was subsequently exposed to acetone vapor is presented in Fig. 2c, and is strikingly similar to the spectrum of the original, untreated sepiolite (Fig. 2a). Since zeolitic water molecules are not present in this sample, and in light of the discussion of the partially dehydrated sepiolite sample, it appears that the acetone molecules have penetrated inside the microporous channels and reversed the structural changes that were caused by partial dehydration. Thus Fig. 2c confirms that acetone molecules enter the microporous channels of sepiolite, and are not simply adsorbed on the crystallite exterior surfaces. 

The catalytic activity of MePc depends on the nature of the ligand in the apical position and should therefore be solvent dependent.[56] From the chromatographic determination of the respective adsorption coefficients of the reaction partners in pre-catalytic conditions, a very pronounced activity difference is found depending on the nature of the solvent used.[64] However, the sequence of the adsorption coefficients is of zeolitic origin and reflects a sorption effect rather than a coordination effect. The respective values of the adsorption coefficients indicate that for the oxidation of alkanes, cyclohexane, with organic peroxide for example, in acetone the oxidant is enriched in the intracrystalline voids, resulting preferentially in peroxide decomposition. In excess cyclohexane, the substrate is enriched in the pores, so that every adsorbed peroxide molecule results in an efficient oxygenation. 

Thermodielectric experiments were performed using the Na-X zeolite (Si/Al = 1.25 provided by Laporte, London, UK). Within the framework of the cavities of the Na-X zeolite, the following were adsorbed water(withadielectricconstante=78.5at25°C), acetone... 

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. 

Adsorbates were admitted in small successive doses into a vacuum cell with a thin zeolite plate (7 mg cm 2) at room temperature. The fraction of OH groups interacting with adsorbate (OH coverage ) was determined from intensities of the bands of free hydroxyls before and after the adsorption. To accelerate the formation of PyH" , the sample with pyridine was shortly heated to 150 °C (together with the apparature walls). The IR spectra were always measured at room temperature using a Nicolet MX-1E FTIR spectrometer (resolution 2 cm ). The interaction complexes of acetonitrile and acetone were also studied spectroscopically at higher temperatures, but the results of these measurements are notinduded in this paper. 

Acetone. The spectra of acetone surface complexes at low OH coverages of zeolites are given in Fig. 4. For comparison, the spectrum of acetone adsorbed on weak silanol groups of silicagel is also displayed. The spectral features found can be divided into three groups belonging to... 

Figure 4. Difference spectra of acetone-he adsorbed on zeolites (a) and spectra of zeolites (b) before (1) and after (2) acetone-hg adsorption (HX. HY 0.8-1.0, HZSM-5 0 55 mmol AC/g). Spectrum of acetone-dg on HZSM-5 is designated (AC-dg).

Figures 1 and 2 show the self-diffusivities of the various adsorbates in NaX and CsNaX, respectively. Acetone and isopropanol are the largest of the molecules studied and have the lowest mobilities. Specific interactions of the adsorbate oxygen atoms with the cations of the zeolite may also reduce the mobility. The smaller molecules, propene and water, are considerably more mobile. Water is seen to have the highest activation energy for diffusion of the adsorbates investigated.

The shift in > max (Figure 6), after exposure to ammonia vapour, is an indication that the ammonia has interacted with the Co exchanged into the zeolite. To exclude possible interferences from other environmental contaminants, the study included additional adsorbates with similar functional groups (such pyridine), abundant in the ambient atmosphere (such as water), and abundant in organic environments (such as acetone), and the results expressed in cm energy units shown in Table 1. 

When CoX was similarly treated with ammonia vapour a band at 1312 cm, similarly associated to C0-NH3 symmetric vibration, was observed (see Figure 8). When compared to other adsorbates (pyridine, acetone and water vapour) for their ability to shift the Metal-Zeolite bands (at 896 cm for CuX and 918 cm for CoX), the band positions for each of the metal-adsorbate vibrations was distinct (see Table 2). 

The aldol condensation of acetone to form diacetone alcohol is a well known reaction catalyzed by basic catalysts. This is also regarded as one important reason for the deactivation of MBOH reaction over alkali-exchanged X and Y zeolites ° Thus the pure acetone vapour was introduced into the infrared cell which contains fresh zeolite samples. It is found that the spectra after acetone adsorption are nearly completely the same as those obtained after MBOH reactions ° except for the region around 3400 cm where the spectra after MBOH reaction at 180°C still showed some bands belonging to the residual adsorbed MBOH. Figure 2 shows the IR spectra of alkali exchanged X zeolites and other Na exchanged zeolites... 

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