N-nonane pre-adsorption

Rodriguez-Reinoso F, Martin-Martinez JM, Molina Sabio M, Torregrosa R, Garrido-Segovia I. Evaluation of the microporosity in activated carbons by n-nonane pre-adsorption. J Coll InterfSci... 

Figure 10.5. Nitrogen isotherms (left, with open circles for adsorption and closed circles for desorption) and as plots (right) for precipitated silica VN3 out gassed at (a) 25°C, (b) 110°C, (c) 200°C and (d) 300°C, with ordinate shifted upwards of 1 mmol g 1, for clarity) Run (e) after outgassing at 200°C and n nonane pre-adsotpbon (Carrott and Sing, 1984)...

The molecular sieving behaviour of Silicalite-I, as illustrated in Table 11.5 by the low saturation uptakes of neopentane and o-xylene, is primarily dependent on size exclusion. It is of interest that n-nonane has been found to give an isotherm of essentially Type I character at 296 K (Grillet et al., 1993). The initial part of this isotherm was completely reversible, but a small sub-step at p/p0 0.2 was followed by a long plateau and associated narrow, Type H4, hysteresis loop. The plateau was located at N° = 4 molec uc"1. This level of pre-adsorption was sufficient to block the whole of the intracrystalline pore structure. The accessibility to nitrogen was gradually restored by the progressive removal of the nonane. These results confirm the complexity of the nonane pre-adsorption and entrapment in relation to the pore network and indicate that there is no simple relation between the thermal desorption of n-nonane and the adsorbent pore structure. 

Another procedure proposed for micropore evaluation is by nonane pre-adsorption, which is dependent on the strong retention of n-nonane molecules in the ultramicropores. However, it is now apparent that the extent of the pore blocking is determined by the network connectivity as well as by the micropore size distribution. 

Adsorption of nitrogen at 77 K on a microptorous carbon after pre-adsorption of n-nonane (cf. Fig. 4.13)... 

Fig. 4J0 Adsorption isotherms on ammonium silicomolybdate powder. (I), (4). nitrogen at 77 K (2), (3), /t-hexane at 298 K. Isotherms I and 2 were measured before, and 3 and 4 after, pre-adsorption of n-nonane. Open symbols, adsorption solid symbols, desorption. (Adsorption is expressed in mm (liquid.)...

As discussed in Chapter 8, the pre-adsorption of n-nonane can be used as a means of blocking narrow micropore entrances (see Section 8.2.3). Thus, in the case of an ultramicroporous adsorbent such as Carbosieve, the pre-adsorption of nonane leads to complete blockage of the pore structure. The effect of progressively removing the pre-adsorbed nonane from a supermicroporous carbon is shown in Figure 9.13. The adsorbent used in this work was a well-characterized carbon cloth with the following properties a(BET), 1330 m2g-1 a(ext), 25m2g 1 fp(mic), 0.44 cm3 g-1 wp, 0.6-2.0 nm (Carrott et al., 1989). 

A novel method for determining the location of the primary water adsorbing sites has been developed by Bailey et al., (1995). This approach involves the pre-adsorption of naphthalene, which was chosen because of its planar molecular shape and immiscibility with water. With some activated carbons it was found that the growth of the H-bonded water clusters was inhibited by the presence of naphthalene, while in other cases there was very little effect. It was thought that sites in larger micro-pores were prone to obstruction by the pre-adsorbed naphthalene. It is too early to judge the success of this interesting approach, which may turn out to be a useful alternative to pre-adsorption by n-nonane. 

For mono-methyl paraffm separation, two pulse test techniques, one with and one without iso-octane pre-pulse, were developed (2,3). In each test the feed was a mixture containing equal volumes of 3,3,S-trimethyl heptane, 2,6-dimethyl octane, 2-methyl nonane, n-decane, and I,3,S-trimethyl benzene. The pulse test column had a volume of 70 cc and was held at a temperature of 120 C in the experiments shown. The flow rate through the column was 1.2 ml/min. The adsorbent was silicalite and the desorbent was a 30/30 volume % mixture of n-hexane/cyclohexane. Test I was run without a pre-pulse and test 2 was run with a pre-pulse of 40 ml of iso-octane injected into the test loop immediately before the feed mixture was injected. Iso-octane pre-pulse diluted the n-hexane concentration at the adsorption zone and increased the adsorbent selectivity for mono-methyl paraffin. 

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