Hydrocarbon Sorption Behavior

The assessment of the practical usefulness of such systems for oil-spill clean-up is based on the following four main criteria  

Let us start by presenting selected results of absorption and desorption studies [18] with various organic solvents. 

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The sorption behavior of perfluorocarbon polymers is typical for nonpolar partially crystalline polymers (89). The weight gain strongly depends on the solubihty parameter. Litde sorption of substances such as hydrocarbons and polar compounds occurs. 

You work in a research laboratory, and part of your duty is to determine the sorption behavior of a series of polycyclic aromatic hydrocarbons in laboratory columns. In one series of experiments you use a column that is 1 m long and has a diameter of... 

Recently, Bonin and Simpson (2007) showed in their study that polycyclic aromatic hydrocarbons sorptive behavior could not be solely attributed to a specific SOM chemical characteristic (i.e., aliphaticity or aromaticity) and concluded that both structure and OM physical conformation are important in sorption processes. Martin-Neto et al. (1994b) used analysis of microwave power saturation curves (Weil et al., 1994) to obtain information about HA conformation. They observed that at pH > 3.5 a typical curve of homogeneous saturation was obtained for the oxisol HA, whereas at pH 2.3 inhomogeneous saturation occurred. The peat HA showed only homogeneous saturation. However, a similar inhomogeneous trend ... 

Less information exists on the sorption behavior of aromatic hydrocarbons such as benzene, toluene, the three isomeric xylenes, mesitylene, and... 

Karickhoff (1980) and Karickhoff et al. (1979) have studied sorption and desorption kinetics of hydrophobic pollutants on sediments. Sorption kinetics of pyrene, phenanthrene, and naphthalene on sediments showed an initial rapid increase in sorption with time (5-15 min) followed by a slow approach to equilibrium (Fig. 6.7). This same type of behavior was observed for pesticide sorption on soils and soil constituents and suggests rapid sorption on readily available sites followed by tortuous diffusion-controlled reactions. Karickhoff et al. (1979) modeled sorption of the hydrophobic aromatic hydrocarbons on the sediments using a two-stage kinetic process. The chemicals were fractionated into a labile state (equilibrium occurring in 1 h) and a nonlabile state. 

Shallow geochemical environments consist of solid, aqueous, and air reservoirs and their interfaces. Hydrocarbon compounds partition into these various reservoirs in a manner determined by the stmcture and physical properties of the compounds and the media, and the mechanism of hydrocarbon release. The structure and physical properties of the compounds and media understandably impact their sorption, solubility, volatility, and decomposition behavior (e.g., Schwarzenbach et al., 1993). In addition, hydrocarbon partitioning in real systems is holistically a disequilibrium process hence, the distribution of hydrocarbons depends as much on the pathway taken as on the final physical state of the system (e.g., Schwarzenbach et al., 1993 Luthy et al., 1997). Shallow aquatic systems may tend towards some equilibrium distribution (Figure 10), but this is seldom, if ever, truly attained. 

Einally, there is now increasing recognition of a critical need for detailed characterization of the mechanisms of solid phase association of hydrocarbons in sediments or aquifer solid phase. The likelihood that the sorption/desorption behavior, bioavailability, and overall cycling of hydrocarbons depend critically on the nature of solid phase association provides a strong impetus for future work. 

In the third case (H-mordenite), r jD increases considerably within each step as equilibrium is approached. The sorption kinetics can no longer be described by a concentration-dependent diffusion coefficient, but rather as a consecutive process of rapid diffusion and slow relaxation in the solid as discussed above. The same behavior as for CgHs in H-mordenite was also found in our laboratory for a number of other gas-zeolite systems, e.g., W-C5H12 in HY and Cg to C5 hydrocarbons in H-mordenite. 

The sorption isotherms of 7 with various gases such as CO2, N2, O2, Xe, and linear alkanes C1-C4 were measured volumetrically at room temperature [30] (Fig. 39.6c). These host materials show higher affinity for CO2, Xe, and linear alkanes compared to O2, and N2. The sorption isotherms are type-1 in nature, indicating microporous behavior. The isotherms are saturated at pressure of 40 bar where each assembly is occupied by two guest molecules. The sorption of hydrocarbon is more preferred over CO2 at lower pressure region (<5 bar). 

The reason for the self-assembly is the sorption of a certain end on the surface, usually some specific affinity of a molecule group to the surface material. The off-standing rests of the molecules, e.g., some hydrocarbon chain, interact with each other (van-der-Waals-interaction) additional stability of the overall structure may be achieved by corresponding end-heads of the molecules away from the substrate surface. The films are quite compact, but pin-hole imperfections may be deteriorating the surface characteristics. Self-assembling behavior is quite frequently employed for generating sensing surfaces. 

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