Benzene, adsorption isotherms

An all-glass apparatus was used for gravimetric sorption measurement with benzene as adsorbate. Prior to the measurement, the sample was heated to 360 C at a rate of 5 C/ min with simultaneous evacuation to 1.3 10 Pa, and further degassed at that temperature for 3 h. Then the sample was cooled down to 32X3, at which the benzene adsorption isotherm was measured. 

Fig. 1 shows the benzene adsorption isotherms of samples before and after the boronation. Compared with the parent sample, the isotherms of boronated samples are so slanting at medium and high relative pressure that they deviate greatly from Brunauer Type I curve characteristic of microporous solid. At the same relative pressure, the adsorption capacities of boronated samples are significantly larger than that of parent sample, suggesting that the void volumes in the boronated samples increase and more spaces inside pores are accessible to benzene molecules. N, adsorption isotherms in Fig.2 further show that the hysteresis... 

Figure 3. Benzene adsorption isotherm (310 K) for mesoporous silica.

Additionally, according to the method elaborated by Carrot, Roberts and Sing [13], based on the concept of primary and secondary adsorption processes [14], the carbon dioxide and benzene adsorption isotherms were used - as described earlier for other adsorptives [15,16] - to determine the volumes corresponding to pore widths below 0.4 nm (approximate dimension of one carbon dioxide molecule), between 0.4 and 0.8 nm (one to two benzene molecules) and between 0.8 to 2 nm (two to five benzene molecules). 

Bokhoven and van der Meijden17 express a preference for the use of the benzene adsorption isotherm, obtained at 20° or 30° C, for the evaluation of their activated carbons. The use of HzO serves... 

Activated carbons have hydrophobic smfaces with the properly that nonpolar molecules or organic compotmds with a very poor solubility in water such as benzene or toluene are preferably adsorbed. However, small amormts of oxides or functional groups present in the smface can change the hydrophobic character of the adsorbent surface. The capacity of carbonic adsorbents is evaluated by means of benzene adsorption isotherms. 

Swiatkowski, A, Trznadel, B.J., and Zietek, S., Description of active carbon micropore size distribution based on the Horvath-Kawazoe equation adapted to benzene adsorption isotherms, Adsorpt. Sci. Technol., 14(1), 59-68(1996). 

Fig. 11. Benzene adsorption isotherm for MCM-41 having a pore size of 40 A (from [7])...

Active carbons and the core samples were investigated by densimetry, mercury porosimetry and adsorption. This made it possible to obtain a synthetic image of their texture within the micro- and macropores. Pore volume, accessible to helium was determined from measurements of true and apparent densities. Mercury porosimetry was used to analyse pores between 100-7500 nm. Benzene adsorption isotherm and the Kelvin equation were used to determine pore radii 1.5-100 nm. 

Fig. XI-11. Relation of adsorption from binary liquid mixtures to the separate vapor pressure adsorption isotherms, system ethanol-benzene-charcoal (n) separate mixed-vapor isotherms (b) calculated and observed adsorption from liquid mixtures. (From Ref. 143.)...

Fig. 2.19 Adsorption isotherm of benzene on (I) hydrated, and (II) dehydrated siliea gel. (After Kiselev .)...

Fig. 4.2 Adsorption isotherms of benzene at 25°C on (1) a charcoal from anthracite coal, activated to 56% yield (2) an activated coconut charcoal. (After Cadenhead and Everett.)...

Fig. 5.8 Adsorption isotherms at 25°C of benzene and cyclohexane on a mesoporous silica gel. Curve (A), benzene curve (B), cyclohexane. Solid symbols denote desorption.

Fig. 5.14 Adsorption isotherms of water on carbon in (a) to f) with corresponding isotherms of nitrogen in (a), (c) and (J), and of benzene in (f>). (a) Charcoal (b) active carbon AY8 (c) charcoal A (J) charcoal (e) a coal tar pitch kilned at 1200°C (/) a charcoal (S600H). (Redrawn from the diagrams in the original papers.)...

Figure 5. Langmuir Adsorption Isotherms for Benzene, Butyl Chloride and Chloroform...

A countercurrent moving-bed adsorption column is used to remove benzene from a gaseous emission. Activated carbon is employed as the adsorbent. The flowrate of the gas is 1.2 kg/s and it contains 0.027 wt/wt% of benzene. It is desired to recover 99% of this pollutant. The activated carbon entering the column has 2 X 10 wt/wt% of benzene. Over the operating range, the adsorption isotherm (Yaws et al., 1995) is linearized to... 

The reason for enhancement of adsorption performance of PA/AC was considered to be due to combination effect of increase of BET surface area and chemical modification by the treatment with PA. Consequently, lwt%-PA/AC was determined to be a best candidate as an adsorbent for removing benzene, toluene, p-xylene, methanol, ethanol, and iso-propanol. Therefore, lwt%-PA/AC was used as the adsorbent to investigate the adsorption isotherm, adsorption and desorption performance. 

Example 10.4 A gas mixture with a flowrate of 0.1 m3 s-1 contains 0.203 kg m-3 of benzene. The temperature is 10°C and the pressure 1 atm (1.013 bar). Benzene needs to be separated to give a gas stream with a benzene concentration of less than 5 mg m-3. It is proposed to achieve this by adsorption using activated carbon in a fixed bed. The activated carbon is to be regenerated using superheated steam. The experimental adsorption isotherms cannot be adequately represented by Freundlich isotherms and, instead, can be correlated at 10°C by the empirical relationship ... 

NaY yields a compietely reversible type I isotherm, characteristic of micropore filling common in many zeolites. However, USY-B and DAY yield an isotherm close to type IV. Similar differences in adsorption isotherms were observed for n-hexane, cyclohexane, n-pentane and benzene. Furthermore, many of the isotherms measured on DAY zeolites showed hysteresis loops (Figure 6). 

Beyer and Belenykaia (27) have investigated the sorption properties of DAY zeolites prepared from Y zeolite and SiCl vapors. They reported a very low adsorption capacity for water and ammonia, similar to that of the almost aluminum-free silicalite (49). The low adsorption capacity for water is indicative of a hydrophobic zeolite surface. The adsorption isotherms for n-butane, benzene and n-hexane obtained on the aluminum-deficient zeolite have a shape similar to those obtained on NaY zeolite and are characteristic for micropore structures. They show the absence of secondary pores in this DAY zeolite. 

Comparison of these adsorption isotherms with those obtained for the linear alkyl aryl sulfonates (Figure 6) reveals the behavior of the 2 ( ) HDBS to be close to that which would be expected for a 1 (t> HDBS and that of the 8 ( ) HDBS to be equivalent to that of a tridecyl benzene sulfonate. Development of a cguantitative model that can account for the effect of the position of the benzene group on the chain warrants additional data for a variety of surfactants with branched chains. 

Equation 10.27 is generally known as Freundlich equation. Equation 10.27 with concentration replaced by pressure was also used to describe the adsorption isotherms of gases on solids, suggesting the incorrect idea that adsorption from solution by a solid could be paralleled with gas or vapor adsorption on the same adsorbents. Whereas in some cases the restriction to dilute solutions was imposed by the solubility of solids (e.g., benzoic acid in water or stearic acid in benzene) it was not imposed on the investigation of mixtures of completely miscible liquids, e.g., acetic acid in water. 

The sorption of butanol isomers (303 K) enables us to further investigate the sorption characteristics of the phenyl-modified silica.. The adsorption isotherms presented here were measured using a gravimetric technique and are compared with previously reported nitrogen, water and benzene sorption data.3... 

Figure 1. Adsorption isotherms of n- and /erf-butyl alcohol (303 K) and benzene (293 K) measured on a microporous phenyl-modified silica.

Figure 4. Adsorption isotherm for dodecyl benzene sulfonate (O) experimental data, (--------------------------) 3-parameter equation...

Figure 3 shows the results obtained for the benzene-water system and compares these with the results from the benzene-water-hydrochloric acid system. The acid-free system exhibited the almost linear adsorption isotherm expected at low water concentrations, while the data from the acid system, although somewhat scattered, suggest that the adsorption capacity was increased when some HC1 was present. In any case, the feasibility of using Z200H to dehydrate the benzene-hydrochloric acid system was demonstrated, and justified embarking on regeneration and dynamic equilibrium test studies. 

With different methods one can recognize different hydrates of phospholipids with different properties. Solved in different organic solvents like benzene, xylene etc. egg yolk phosphatidylcholine adsorbed water in an amount of 13.6 water/mol lipid, independently of the used organic solvent165. Studying adsorption isotherms of water vapor on lipids Elworthy166 has found saturation values at 25 °C ... 

Monolayer coverage is reached at a pressure of P/Po 0.1. At this point the steep slope of the adsorption isotherm levels off. For the first monolayer, a roughly constant heat of adsorption of 43 kJ/mol is observed. This is about 9 kJ/mol higher than the heat of condensation of benzene. 

Figure 9.4 Left Adsorption isotherm for benzene (CeLL) adsorbing to graphitized thermal blacks at 20° C. The insert shows the adsorption isotherm for low coverages in more detail. Dotted lines indicate mono- or multilayer coverages at multiples of 4.12 //mol/m2. The equilibrium vapor pressure of benzene at 20°C is Po = 10.2 kPa. Right Differential heat of adsorption versus adsorbed amount. The dashed line corresponds to the heat of condensation of bulk benzene. Redrawn after Ref. [369].

Following the pioneering works of Ito and Fraissard (57) and Ripme-ester (58), 129Xe NMR of xenon adsorbed on zeolite has proven sensitive probe of its local environment due to its chemical inertness and excellent sensitivity (59). In this work, we used 11 and 13C NMR measurements of the adsorbed benzene in conjunction with 129Xe NMR and adsorption isotherm measurements of the co-adsorbed xenon to study the homogeneous adsorption behavior of benzene on faujasite-type zeolites with various Si/Al ratios. Detailed macroscopic and microscopic adsorption states of the benzene in various NaX and NaY zeolites are discussed in terms of NMR linewidths and chemical shifts and are compared with results obtained from other studies. 

Xenon Adsorption Isotherms and 129Xe NMR Measurements. Figure 1 displays the room temperature (22 °C) xenon adsorption isotherms of the coadsorbed xenon for the three different zeolite samples loaded with various amounts of benzene. A consistent decrease of adsorption with increasing 6 was found for each benzene/zeolite system. By comparing the slope at low xenon pressures, i.e. in the Henry s Law region, we obtained for the adsorption strength NaX(1.23) > NaY(2.49) > NaY(2.70). Moreover, the saturation benzene concentration in faujasite-type zeolites with different Si/Al ratios follows the relation NaX(1.23) < NaY(2.49) < NaY(2.70). 

Figure 1. Room temperature (22 °C) adsorption isotherms of xenon coadsorbed with various amount of benzene in various zeolites (a) NaX, Si/Al = 1.23, (b) NaY, Si/Al = 2.49, (c) NaY, Si/Al = 2.70.

Through the analysis of adsorption isotherms and 129Xe NMR results of the co-adsorbed xenon, we have shown that the dispersal of benzene molecules depends on not only the cation distribution but also the amount of benzene adsorbate within the supercage of zeolite adsorbents. We have also demonstrated for the first time that this well known indirect technique has the capability not only to probe the macroscopic distribution of adsorbate molecule in zeolite cavities but also to provide dynamic information about the adsorbate at the microscopic level. Conventional H and 13C NMR which directly detect the adsorbate species, although providing complimentary results, are relatively less sensitive. 

Figure 5. Adsorption isotherms of benzene on ferric oxide gel...

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