Methanol sorption

In recent years the Coal Research Laboratory has been investigating the kinetics and isotherm behavior of methanol sorption on coal (6, 7, 10) along with the sorption of other vapors on coal (6) and of polar vapors on swelling gels (9, 10). Methanol sorption was shown to be reversible on coal, and its sorption behavior supports the model of coal as a gel or mixture of gels in its physical structure. All indications (I, 6, 7) are that its interaction is with specific and a fixed number of sites for a particular coal sample. Although the sorption of methanol is reversible, coal exhibits sorption behavior which is interpreted in terms of an irreversible swelling of the coal gel upon initial exposure to methanol vapor. As a result of these studies, an isotherm and experimental rate equation for the sorption and desorption were derived that fit the observed data. The isotherm derived for methanol sorption on coal was ... 

This paper deals with a series of studies on coals of ranks indicated by their carbon contents of between 65 and 81%. It was believed that a detailed study of methanol sorption on these coals, including an investigation of the... 

Reactions 1. 2, and 3 represent surface sorption of methanol, G, on surface sites, S. These reactions are in rapidly established equilibrium. Reactions of type 4a, 4b, and 4c are the slow, rate-determining steps of the sorption of methanol on internal sites, D. The generalized Reaction 5 is the reverse of reactions of type 4 and accounts for the reversibility of the methanol sorption. Reaction 6 is a rapidly established equilibrium whose inclusion in the postulated mechanism is necessary because of the isotherm prediction of one molecule of methanol per site at equilibrium. 

It was the simplified integrated Equations 7 and 8 that were found sufficient for handling the experimental data. However, the (act that B is independent o( S explains the qualitative observation that for slower sorptions —e.g., on acetylated coals—deviations (rom the simplified equations occurred at lower (ractions o( reaction than for (aster reactions. This observation is consistent with the conclusion that acetylation merely reduces the concentration o( all surface sites, and the acetate group itseK is rather inert to methanol sorption. 

If ordered structures involving aromatic polycyclic skeletons of the type studied here were present in coal, it would indicate that such structures would be permeated by methanol, and that surface area measurements based on methanol sorption would give values greater than the true surface area as that area is normally defined. 

Parrott and co-workers (P30,P32,P35,P33) described a more sophisticated method for modelling the hydration process. The fraction of the total water porosity that was below 4nm was calculated by multiplying the volume fraction of C-S- H by an appropriate factor, which depended on whether the C-S-H was formed from alite or belite, the temperature and the amount of space available. The constants assumed were based on experimental data obtained using a procedure based on methanol sorption (Section 8.3.4). The effect of drying was allowed for (P35) by introducing a factor of 0.7 - -1.2(RH — 0.5) for 0.5 < RH < 1, or of 0.7 for RH 0.5. These refinements allow some deviation from the Powers-Brownyard postulate of a fixed volume ratio of gel porosity to product. Typical results for the volume fractions of pores larger than 4 nm in mature pastes of a cement with an alite content of 56% were approximately 0.26, 0.16 and 0.07 for w/c ratios of 0.65, 0.50 and 0.35, respectively (P32). For the two higher w/c ratios, these results are near the capillary porosities of Powers and Brownyard, but for w/c 0.35 the latter value is zero. 

Patel ct at. (P5I) moist-cured blocks of cement pastes of w/c ratio 0.59 for 7 days and then sealed the prism surfaces of each and exposed the ends to air at 20 C and 65% RH. Methanol sorption data obtained using porous glass as a reference standard (Section 8.3.5) showed that, near to the exposed surfaces, the pore structure was markedly coarser and the diffusion time lower. TG evidence showed that less hydration had occurred and that carbonation was increased. These effects were detectable even at a distance of 50 mm from the exposed surface. Further work conlirmed the marked effect of RH on hydration rates (P28) (Section 7.7.1). 

Related work includes investigations of carbon formation during hydrogenation of C5 hydrocarbons catalyzed by nickel and palladium (5P) interactions of N2O with a hydrotalcite-derived multimetallic mixed oxide catalysts (60,61) changes in mass of solid oxides (62) methanol sorption in Nafion-117 (proton-exchange) membranes (63) vanadyl pyrophosphate catalysts for butane oxidation (64-66) and deactivation/regeneration of a Rb0 c/Si02 catalyst for methylene valerolactone synthesis (67). 

Fig. 2 a System for surface temperature infrared (STIR) measurements, b Transient temperature response upon methanol sorption into Na-X zeolite as a function of the square root of time [17]... 

Table 6.2 Pure methanol sorption by Nafion membranes...

The vapor methanol sorption in expanded membranes range between K w 11-13 at temperatures in the range 20-30 °C. The case of very-thin cast membrane [280] will be discussed later. 

Fig. 6.17 Water-methanol sorption of ultra-thin Nation membranes as a function of the methanol mole fraction (Adapted from Ref. [280])...

The behavior observed in Fig. 6.32 is different from that observed Nafion in Fig. 6.17. In the case of PBI, and also for the modified ABPBI membrane, the pme water sorption almost doubles pure methanol sorption, that is, these membranes have a clear preference for water uptake over methanol, while no differences in the uptake of water and methanol was observed in Nafion. The water-methanol uptake from the liquid phase (methanol 20 wt%) of a thick PBI membrane (50-100 pm) shows the same behavior, that is water uptake (A = 3.48) is much higher than methanol uptake (2 = 0.63), which is desirable behaviour for a membrane which intend to be a good barrier for methanol crossover. 

Jalani NH, Choi P, Datta R (2004) Phenomenological methanol sorption model for Nafion 117. Solid State Ion 175 815-817... 

Diaz LA, Aburn GC, Corti HR (2012) Methanol sorption and permeability in Nafion and acid-doped PBl and ABPBI membranes. J Membr Sci 411-412 35-44... 

Figure 10.4 Methanol sorption isotherm for 4000 A thick PPy-TOS and PPy-TFB films. The mass sensitivity of the QMB is 17.7 ng Hz" cm". (Reprinted from Ref [17].)...

For methanol sorption, the excess enthalpy H can be evaluated from the data in Figure 5. Its values range from -3 to -5 kJ/mol over most of the concentration interval inspected. It is negligible for very low methanol concentrations, in close analogy with the ethanol case. 

Ceckiewicz, in Fourier transform infrared spectroscopy (FTIR) studies of methanol sorption on zeolite at 25 50°C, observed the propylene band pattern but failed to detect ethylene [96]. Upon temperature-programmed desorption, however, C -C olefins were identified. In the suggested MTO scheme (Fig. 16), the propylene was nominated as a primary product (ie, obtained directly from MeOH or DME), and the formation of the other products occurs via two parallel routes. 

---