Adsorption of paraffins

The effect of heterogeneity was accounted for by the use of the energy distribution as shown in previous sections. For adsorption of paraffins onto activated carbon, the source of the energy distribution is assumed to be due to the micropore size distribution. This heterogeneity is called the micropore size-induced heterogeneity. The energy of interaction between the micropore and the adsorbate molecules is a strong function of the size of the adsorbate as well as the size of the micropore. The effect of micropore size distribution on adsorption equilibrium has been addressed in Chapter 6. Here we address its role in the adsorption kinetics. 

The available data are meager, and generalizations are very difficult to make. Lowering the pressure will of course reduce the amount of adsorbate upon the adsorbent, as shown in the upper half of Fig, 11.9. In several cases investigated over any appreciable range [24, 62] the relative adsorptivity of paraffin hydrocarbons on carbon decreased at increased pressure, as shown in the lower part... 

Each olefin is more soluble than the paraffin of the same chain length, but the solubiHty of both species declines as chain length increases. Thus, in a broa d-boiling mixture, solubiHties of paraffins and olefins overlap and separation becomes impossible. In contrast, the relative adsorption of olefins and paraffins from the Hquid phase on the adsorbent used commercially for this operation is shown in Figure 2. Not only is there selectivity between an olefin and paraffin of the same chain length, but also chain length has Httie effect on selectivity. Consequentiy, the complete separation of olefins from paraffins becomes possible. 

Olex A version of the Sorbex process for separating olefins from paraffins in wide-boiling mixtures. It can be used for hydrocarbons in the range C6 - C20. Based on the selective adsorption of olefins in a zeolite and their subsequent recovery by displacement with a liquid at a different boiling point. Mainly used for extracting Cn - C14 olefins from the Pacol... 

Lewis, as already mentioned, used a solution of sodium glycocholate and determined the adsorption of the salt by a surface of paraffin oil. The interfacial tension solution—paraffin oil this was measured for a number of concentrations by the drop method just discussed, and the [Pg.42]

In this particular case, the adsorption process can be used to overcome the distillation limitation. This is demonstrated in Figure 6.2, which represents the relative adsorption of C5 and C(, Hnear, branched and cycHc paraffins from the liquid phase of the 5A adsorbent used in the HOP GasoHne Molex process, licensed by HOP. In this process, only Hnear paraffins can enter the pores of 5A zeolite, while branched and cyclic paraffins are completely excluded due to their large kinetic diameters. Also, the selectivity for Hnear paraffins with respect to other types of paraffins is infinite. Consequently, the separation of Hnear paraffins from branched and cyclic paraffins becomes possible. 

Examples of rate-selective adsorption are demonstrated using silicalite adsorbent for separation of Ciq-Cm n-paraffins from non- -paraffins [40, 41] and Ciq-Ch mono-methyl-paraffins from non-n-paraffins [42-45]. Silicalite is a ten-ringed zeolite with a pore opening of 5.4A x 5.7 A [22]. In the case of -paraffins/non-n-paraffins separation [40, 41], n-paraffins enter the pores of silicalite freely, but non-n-paraffins such as aromatics, naphthenes and iso-paraffins diffuse into the pores more slowly. However, the diffusion rates of both normal -paraffins and non-n-paraffins increase with temperature. So, one would expect to see minimal separation of n-paraffins from non-n-paraffins at high temperatures but high separation at lower temperature. 

I Adsorption Adsorption of normal paraffins from the feed with simultaneously displacement of desorbent normals from the adsorhenf s selective volume... 

A recent report describes the radioactive labeled chromium (iii) ion adsorption on stearic acid LB films. The adsorption of chromium (iii) on a stearic acid monolayer on the surface of CrCl3 was described. Stearic acid monomolecular films on I0 3 M CaCl2 subsolutions were deposited in paraffin-coated microscope glass slides by the LB technique (pH range 2-9). 

Heati of Adsorption of Heptyl Alcohol onto Aerosil and HiSil from Paraffin Oil Solutions at SB°... 

Figure 19 shows the C CP/MAS NMR spectra recorded lOmin to 53 h after adsorption of [ C-l]-l-octene on zeolite HZSM-5. The spectra indicate that the C-labeled terminal olefinic =Cll2 groups evident in the spectra at ca. 113 ppm are transformed into terminal C-labeled paraffinic CH3 groups, evident at 14.3 ppm. Furthermore, the selective label penetrates into internal -CH2- groups of the octene hydrocarbon skeleton, characterized by resonances occurring at 33.0 ppm. 

NorrishJ has sought to connect the catalytic activity of surfaces with their polar nature. By polar nature is meant a certain chemical unsaturation, usually associated with the presence of oxygen in the molecule. His work on the combination of ethylene and bromine has already been mentioned. The combination hardly takes place at all in vessels coated with paraffin wax, but is promoted by surfaces of such oxygen-containing substances as cetyl alcohol and stearic acid. To be quite conclusive such observations would have to be combined with others showing that the actual adsorption on paraffin wax is not very... 

Only a few studies have been reported on the effect of molecular size on the adsorption of normal paraffins in zeolites. For both small- and large-pore low silica/alumina zeolites, in liquid phase... 

It appears that temperatures in the range of 500.to 670 K for the adsorption of n-paraffins in the 560-740 K boiling range on type 5A molecular sieves should be considered for investigating the combination supercritical fluid volatility amplification-vapor phase molecular sieve process. The pressure of operation will be governed by the critical pressures of potential solvents with critical temperatures in this range. The supercritical solvent of choice should not be adsorbable on type 5A molecular sieves and should not be expensive. 

Because of the high molecular weight materials at the upper end of the boiling range for medium lube oil stocks, the desorption technique of choice should probably employ a displacement chemical with a high heat of adsorption, in order to overcome the high heat of adsorption of the in-paraffins. Ammonia at temperatures near 660 K and near atmospheric pressure appears to have good potential. 

This weight includes the adsorption of n-paraffin in the molecular sieve cages, oil raffinate and solvent adsorbed in the voids and macropores, and water adsorbed during molecular sieve transfer to and from autoclave. 

The velocity of deposition of radioiodine, defined as in equations (2.3) and (2.4), is controlled by the rate of adsorption at the surface. When the adsorption or chemisorption at the surface is strong, the rate of deposition of 131I, when expressed in terms of suitable non-dimensional parameters, is similar to the rate of heat transfer to or from the surface (Chamberlain, 1953). In field experiments, artificial leaves of copper or silver foil were attached to vegetation, and it was found that the uptake of 131I to real leaves was typically 0.4 to 0.7 times the uptake to artificial leaves. Since a thin film of paraffin was found to inhibit... 

Probably the same reaction, the dehydrogenation, condensation, and irreversible adsorption of highly condensed aromatic hydrocarbons, causes the loss of activity of the WS2 catalyst when used at pressures well below 200 atm. As an example (20), in experiments with a paraffin-base petroleum-oil fraction boiling between 200° and 325°C. the results in the accompanying tabulation were obtained ... 

The paraffin oxidation by immobilized Por and Pc complexes is strongly influenced by the polarity of the support. This has been studied in detail for the oxidation of cyclohexane with f-BuOOH by immobilized phthalocyanines. Thus, adsorption of the polar reaction products cyclohexanol and r-butyl alcohol competes with sorption of the cyclohexane reagent, particularly when a polar support such as a zeolite Y is used (124,134). Consequently, the activity decreases rapidly, and it can be restored only by extensive solvent extraction. In contrast, FePc on the apolar support carbon black is much less sensitive to this type of deactivation (121). 

We first consider the parameterization of the enthalpy changes of adsorption. It has been established that the heats of adsorption of various paraffins in zeolites vary linearly with carbon number (124-126). Therefore, we define the enthalpy of formation for a surface species as... 

Kazansky VB, Serykh AI, Pidko EA (2004) DRIFT study of molecular and dissociative adsorption of light paraffins by HZSM-5 zeolite modified with zinc ions methane adsorption. Journal of Catalysis 225(2) 369-373... 

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