Mobilization of hydrocarbons

In general, the standard enthalpy of micellization is large and negative, and an increase in temperature results in an increase in the c.m.c. the positive entropy of micellization relates to the increased mobility of hydrocarbon side chains deep within the micelle as well as the hydrophobic effect. Hoffmann and Ulbricht have provided a detailed account of the thermodynamics of micellization, and the interested reader will find that their tabulated thermodynamic values and treatment of models for micellar aggregation processes are especially worthwhile. 

Fluorination of Alkanes. Fluorination of alkanes is extremely difficult to control. The reaction usually results in substantial C—C bond rupture and can readily lead to explosion.136 However, several methods for controlled direct radical fluorination of hydrocarbons have been developed. The key and obvious observation was that the only reaction sufficiently exothermic to cause fragmentation is the termination step between a carbon radical and a fluorine atom. Consequently, if the atomic fluorine population and the mobility of hydrocarbon radicals are minimized, controlled fluorination becomes feasible. 

In zeolites the mobility of hydrocarbon molecules with double bonds is specifically restricted because of a specific interaction between the 7r-elec-trons and the zeolite (2). As expected, proton spin relaxation of benzene, cyclohexadiene, cyclohexene, and cyclohexane adsorbed on NaY reveals an increasing restriction of mobility with increasing number of -electrons (8, 4, 8). This is shown in Figure 1, where the longitudinal (7 ) and transverse (T2) proton relaxation times are plotted. 

Inclusion of other molecules of irregular shape within membranes also lowers Tm. However, a molecule of cholesterol can pack into a bilayer with a cross-sectional area of 0.39 nm2, just equal to that of two hydrocarbon chains.49 It tends to harden membranes above Tm but increases mobility of hydrocarbon chains below Tm.97 -100 A complex of cholesterol and phosphatidylcholine may form a separate phase within the membrane.101102 The ether-linked plasmalogens may account for over 30% of the phosphoglycerides of the white matter of the brain and of heart and ether linked phospholipids are the major lipids of many anaerobic bacteria.103 Their Tm values are a few degrees higher than those of the corresponding acyl phospholipids.104... 

The most fundamental and obvious observation to be made concerning the thermochemistry in Table I is that no individual step in this reaction sequence is exothermic enough to break carbon—carbon bonds except the termination step 3a of —97.5 kcal mole 1. Consequently procedures or conditions that minimize the atomic fluorine population or decrease the mobility of hydrocarbon radical intermediates, such as keeping them in the solid state during reaction, are desirable. It is necessary to decrease the reaction rate to the extent that these hydrocarbon radical intermediates have finite lifetimes so that the advantages of fluorination in individual steps may be realized experimentally. It has been demonstrated by EPR(8) methods that under reaction conditions with high fluorine dilution, the various radicals do indeed have appreciable lifetimes. 

Figure 1.7. Mobility of hydrocarbon chain. The diagram shows mobility of a polymer chain composed of carbon atoms attached by single bonds with hydrogen side chains. Rotational freedom of the single carbon-to-carbon bonds allows hydrogen atoms to rotate freely about the backbone.

Inclusion of other molecules of irregular shape within membranes also lowers T. However, a molecule of cholesterol can pack into a bilayer with a cross-sectional area of 0.39 nm, just equal to that of two hydrocarbon chains It tends to harden membranes above but increases mobility of hydrocarbon chains below -100 complex of cholesterol and phospha-... 

Electrobioremediation Mobilization of Hydrocarbons and Increase of Bacteria Mobility... 

Translational diffusion and intramolecular mobility of hydrocarbon molecules inside the pores of zeotype materials plays a critical role in the performances of these materials as catalysts and adsorbents. Therefore, it is no wonder that much work has been done to measure and characterize the mobility of molecules in zeotype materials [93]. 

Extensive discussions have focused on the conformation of the alkyl chains in the interior ". It has been has demonstrated that the alkyl chains of micellised surfactant are not fully extended. Starting from the headgroup, the first two or three carbon-carbon bonds are usually trans, whereas gauche conformations are likely to be encountered near the centre of tlie chain ". As a result, the methyl termini of the surfactant molecules can be located near the surface of the micelle, and have even been suggested to be able to protrude into the aqueous phase "". They are definitely not all gathered in the centre of tire micelle as is often suggested in pictorial representations. NMR studies have indicated that the hydrocarbon chains in a micelle are highly mobile, comparable to the mobility of a liquid alkane ... 

Mobil MTG and MTO Process. Methanol from any source can be converted to gasoline range hydrocarbons using the Mobil MTG process. This process takes advantage of the shape selective activity of ZSM-5 zeoHte catalyst to limit the size of hydrocarbons in the product. The pore size and cavity dimensions favor the production of C-5—C-10 hydrocarbons. The first step in the conversion is the acid-catalyzed dehydration of methanol to form dimethyl ether. The ether subsequendy is converted to light olefins, then heavier olefins, paraffins, and aromatics. In practice the ether formation and hydrocarbon formation reactions may be performed in separate stages to faciHtate heat removal. 

Sulfonates for Enhanced Oil Recovery. The use of hydrocarbon sulfonates for reducing the capillary forces in porous media containing cmde oil and water phases was known as far back as 1927—1931 (164,165). Interfacial tensions between 10 and 10 N/m or less were estabUshed as necessary for the mobilization and recovery of cmde oil (166—169). 

The dense fluid that exists above the critical temperature and pressure of a substance is called a supercritical fluid. It may be so dense that, although it is formally a gas, it is as dense as a liquid phase and can act as a solvent for liquids and solids. Supercritical carbon dioxide, for instance, can dissolve organic compounds. It is used to remove caffeine from coffee beans, to separate drugs from biological fluids for later analysis, and to extract perfumes from flowers and phytochemicals from herbs. The use of supercritical carbon dioxide avoids contamination with potentially harmful solvents and allows rapid extraction on account of the high mobility of the molecules through the fluid. Supercritical hydrocarbons are used to dissolve coal and separate it from ash, and they have been proposed for extracting oil from oil-rich tar sands. 

One notes in Table 1.2 a uniform increase in the adsorption energies of the alkanes when the microspore size decreases (compare 12-ring-channel zeohte MOR with 10-ring-channel TON). However, at the temperature of hydroisomerization the equilibrium constant for adsorption is less in the narrow-pore zeohte than in the wide-pore system. This difference is due to the more limited mobility of the hydrocarbon in the narrow-pore material. This can be used to compute Eq. (1.22b) with the result that the overall hydroisomerization rate in the narrow-pore material is lower than that in the wide-pore material. This entropy-difference-dominated effect is reflected in a substantially decreased hydrocarbon concentration in the narrow-pore material. 

Gygax R, Wirz J, Sprague JT, Allinger NL. Electronic structure and photophysical properties of planar conjugated hydrocarbons with a 4n-membered ring. Part III. Conjugative stabilization in an antiaromatic system The conformational mobility of l,5-bisdehydro[12]annulene. Helv Chim Acta 1977 60 2522-9. 

Zeolites are used in various applications such as household detergents, desiccants and as catalysts. In the mid-1960s, Rabo and coworkers at Union Carbide and Plank and coworkers at Mobil demonstrated that faujasitic zeolites were very interesting solid acid catalysts. Since then, a wealth of zeolite-catalyzed reactions of hydrocarbons has been discovered. Eor fundamental catalysis they offer the advantage that the crystal structure is known, and that the catalytically active sites are thus well defined. The fact that zeolites posses well-defined pore systems in which the catalytically active sites are embedded in a defined way gives them some similarity to enzymes. 

The presence of impurities is an important issue in mobile applications where the hydrogen at least initially will be supplied by the decomposition of hydrocarbons or methanol in on-board reformer systems as long as no appropriate hydrogen storage media are available. In such systems CO is an unavoidable by-product, and since CO binds more strongly to Pt than hydrogen, the low operating temperature... 

Waste gas from produced hydrocarbons can be safely disposed by reinjecting into a formation. The waste gas is mixed with a surfactant to form a foam that, in turn, is placed within a disposal zone of a subterranean formation. The waste gas is trapped within the foam, thereby reducing the mobility of the gas in the formation, which, in turn, restricts the ability of the waste gas to readily flow out of the disposal zone and into the producing zone of the formation. The waste gas foam can be placed into the formation by coinjecting the surfactant and the waste gas, or it can be formed in situ by first injecting the surfactant and then injecting the waste gas [1356]. 

In steam injection, the mobility of the hydrocarbons is greater if a Ci to C25 hydrocarbon is added than if steam is used alone under substantially similar formation conditions [647,1321,1322]. 

The displacing fluid may be steam, supercritical carbon dioxide, hydrocarbon miscible gases, nitrogen or solutions of surfactants or polymers instead of water. The VSE increases with lower mobility ratio values (253). A mobility ratio of 1.0 is considered optimum. The mobility of water is usually high relative to that of oil. Steam and oil-miscible gases such as supercritical carbon dioxide also exhibit even higher mobility ratios and consequent low volumetric sweep efficiencies. 

Lande, S.S., Hagen, D.F., Seaver, A.E. (1985) Computation of total molecular surface area from gas phase ion mobility data and its correlation with aqueous solubilities of hydrocarbons. Environ. Toxicol. Chem. 4, 325-334. 

A recent development, which could lead to a reassessment of the Fischer-Tropsch reaction as a route to gasoline range product, is the announcement by Mobil of a direct route from methanol to hydrocarbons and water (101) ... 

Since hydrocarbon and water are immiscible fluids, free-phase recoverable LNAPL can simplistically be viewed as being perched on the capillary fringe above the actual water table with the understanding that what is being referred to as actual NAPL thickness is what one could perceive as being equivalent to the approximate thickness of that portion of the zone of hydrocarbon saturation that is considered mobile. The physical relationships that exist are illustrated in Figure 6.5. This discrepancy can be a result of one or a combination of factors or phenomena. Some of the more common factors or phenomena are schematically shown in Figure 6.6 and include ... 

Actual formation thickness of the mobile free hydrocarbon ... 

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