Reservoir capacity

Perhaps the first concern is the volume of the selected reservoir. Does it have the capacity to store the acid gas for the life of the project The size of the potential disposal zone must be such to ensure that it will hold the injected gas over the life of the project. 

In order to estimate the capacity of a selected reservoir, one needs to know the thickness and extent of the formation and its porosity. From the physical dimensions of the reservoir, one can calculate the volume of the rock, and multiplying this by the porosity gives the pore space, which is where the acid gas will be stored. 

The gas is stored not only in the pore volume. Much of the gas will dissolve in the formation fluids, both hydrocarbon and water. Some of the C02 and H2S will react with components in the reservoir and form new minerals - the so-called mineralization. 

The most common cation in reservoir water is sodium (Na+). Both sodium sulfide and sodium carbonate are soluble in water and thus do not provide a mechanism for sequestering the acid gas. Perhaps the next most common cation in the reservoir is calcium (Ca2+). Carbon dioxide can react with the calcium ion and form one of many calcium carbonate minerals including calcite (CaC03). Calcium sulfide is not a very stable compound and readily decomposes and thus is not common on the earth. However, H2S can react with other cations in the reservoir water and produce several sulfide minerals including pyrite. 

In addition, the C02 and H2S can react with minerals in the formation and transform them into different minerals. 

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After an extensive review of possible new materials, the team found a material that had a surface-to-volume ratio closer to 1000 M /M and a void volume up to 98%. A hydrophilic coating could be grafted to its surface to provide a reservoir capacity to release nutrients in a controlled manner. Lastly, the hydrophilic coating could be copolymerized with certain bioactive polymers and ligands that improve cell adhesion dramatically. 

Reservoir capacity is the ability of a polymer to hold solutes within its matrix. BiocompatibiUty is the relationship of a polymer surface with biological materials, specifically living cells. Ligand attachment is the technique of attaching active side chains to the backbone of a polymer. The most interesting example is the covalent immobilization of enzymes without deactivation. 

Reservoir capacity is, in our view, an attempt by a polymer to dissolve. Because of cross-linking and molecular weight, the system does not fully dissociate into a true solution. Rather than dissolving in the normal sense, the polymer is said to swell in the solvent. Absorption of a solvent, water or organic, is a volumetric phenomenon controlled by the relative polarities of polymer and solvent. A nonpolar backbone is preferred for absorbing nonpolar solvents. The molecule we call polyurethane, however, is not entirely nonpolar but is close enough for use as an absorbing matrix. 

When a solvent is polar, a reservoir that reflects that must be developed. Hydrophilic polyurethanes were specifically designed to serve as reservoirs for polar solvents, although the inventors did not express their ideas in that manner. In many commercial cases, reservoir capacity ( the bottle ) is too large. The container swells as it absorbs. The nature of the material is to lose most of its physical strength as it swells. While we need the polarity, we also want to optimize the size of the bottle and strength of the material. The current library of hydrophilic prepolymers does not provide that flexibility, but we now know that we can build our own prepolymers with copolymers of propylene oxide (PO) and ethylene oxide (EO). 

The polarity of the polyurethane can be used to extract components from the environment. Thus, reservoir capacity (more than simply the size of a device) is controlled by the polarity of the polyurethane and the proper choice of polyol. 

The last chemical characteristic is the attachment of ligands. Unlike the other properties (reservoir capacity and biocompatibility) that could be incorporated into a one-shot process, this aspect is most conveniently practiced at the prepolymer level. The philosophy is to use some of the isocyanate functionality of the prepolymer to attach active side chains. This is illustrated in two examples that we will discuss again. 

We described reservoir capacity as the ability to contain an active ingredient within a matrix. In this sense, we give the term active ingredient the broadest possible meaning. We will show how polyurethanes are used to absorb exudates from deep tissue wounds. The exudates are considered active ingredients. We likened reservoir capacity to a bottle and controlled release to a bottle with a leak. A polyurethane can serve as a controlled release device, and we will illustrate this in a number of applications. 

A special class of reservoir capacity known as extraction was introduced in Chapter 4. Thermodynamically, the process is no different from the features described above, but from a use point of view, the process represents a special kind of bottle. Instead of leakage via diffusion caused by a potential energy difference, the leak arises from a shift in the partition coefficient from a change in temperature or in the solvent environment. 

While our focus for this chapter will be on the colonization and the attachment of ligands, we will never entirely leave the topic of reservoir capacity. We discussed earlier the use of polyurethane as a scaffold for the development of colonies of microorganisms. We will use the capacity of polyurethane to hold solutes, both as a reservoir for nutrients and as a buffer, moderating swings in biological load, for example. 

In addition to continued emphasis on reservoir capacity, we will shift our attention to other important specialty characteristics of polyurethane the abilities to be colonized by living cells and to attach active ligands. More specifically, this chapter will illustrate how polyurethanes are used to address environmental problems. The problems we will discuss are different in nature from the problems discussed in the last chapter. This chapter focuses on the treatment of waterborne human waste. 

One more factor must be considered before we summarize this foundation and discuss case histories the factor concept that could explain why hydrophilic polyurethane has shown an improved efficiency in development of biofllms. In a reconsideration of the biofilm model (Figure 5.4), let us consider a model in which the substratum has reservoir capacity (Figure 5.5). 

As we described in Chapter 6, a possible advantage of the system is the ease of attachment of ligands to the hydrophilic polynrethanc. (Copolymerization with attachment ligands or antigens is also conveniently accomplished. Also, the reservoir capacity of the hydrophilic polyurethane is useful for storing nutrients and acting as a buffer as noted in the discussion of biofllters in Chapter 5. 

We discussed the four primary attributes of a polyurethane (architecture, reservoir, biocompatibility, and attachment of ligands) in earlier chapters. Biocompatibility and hgand attachment were discussed in detail, as was architecture in relation to the other attributes. This section covers reservoir capacity and cosmetic delivery applications. Fragrance, soap, pharmaceutical, and other delivery applications are other practical uses for polyurethanes. 

For abbreviation of analyte names see Sect. Abbreviations . ACN acetonitrile, CBA carboxylic acid, FA formic acid, HLB hydrophilic-lipophilic balance, hum human, IS internal standard, LRC large reservoir capacity, MCX mixed-mode cation exchange, metab. metabolites (biotransformation products produced in vivo), MeOH methanol, n.s. not specified, OAc acetate, PB phosphate buffer, PBS phosphate-buffered saline, SCX strong cation exchange Ratio given as v/v... 

Saxena R. K. (1986) Estimation of canopy reservoir capacity and oxygen-18 fractionation in throughfaU in a pine forest. Nordic Hydrol. 17, 251 -260. 

Case Thickness of rock salt seal (m) Methane column held (std. m /m ) Structural height (m) Porosity Max. of reservoir capacity (%) of reservoir (std. m /m ) ... 

Jacobi U, Taube H, Schafer UF, Sterry W, Lademann J (2005) Comparison of four different in vitro systems to study the reservoir capacity of the stratum corneum. J Control Release 103 61-71... 

There should be no warm surface path connected to the cold area. The trap should maintain a low coolant consumption rate and adequate reservoir capacity. 

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