Equilibrium testing

The microautoclave solvent activity tests measure coal conversion in a small batch reactor under carefully controlled conditions. The tests are described as Kinetic, Equilibrium and SRT. The Kinetic and Equilibrium Tests measure coal conversion to tetrahydrofuran solubles at conditions where conversion should be monotonically related to hydrogen transfer. The Kinetic Test is performed at 399°C for 10 minutes at an 8 to 1 solvent to coal ratio. The combination of high solvent ratio and low time provide a measure of performance at essentially constant solvent composition. The measured conversion is thus related to the rate of hydrogen donation from solvent of roughly a single composition. In contrast, the Equilibrium Test is performed at 399°C for 30 minutes at a 2 to 1 solvent to coal ratio. At these conditions, hydrogen donors can be substantially depleted. Thus performance is related to hydrogen donor... 

Autoclave Results - Solvent Activity Test. The initial microautoclave work was done with tetralin and methylnaphtha-lene, using Indiana V bituminous coal (Table I). Base line data is shown in Figure 4. All three tests, Kinetic, SRT, and Equilibrium, show an increase in coal conversion with an increase in the concentration of tetralin. The Equilibrium Test shows the highest coal conversion of approximately 86 wt% of the MAF coal (based on the solubility in the tetrahydrofuran) at the 50% tetralin concentration. The Kinetic Test shows lower coal conversion. The hydrogen transferred to the coal from the tetralin in the Equilibrium Test at the 50 wt% tetralin feed concentration is approximately 0.5 wt% of the MAF coal. In the Kinetic Test 50 wt% tetralin feed concentration results in a much smaller transfer at the short reaction time of 10 minutes. 

The severe headache accompanied by slight loss of equilibrium in one of several sensitive equilibrium tests after a 6.25-h (rounded down to 6 h) exposure at 0.5 ppm was considered the threshold for inability to escape and was used to derive the AEGL-2 values. A UF of 3 was used to adjust the value as no susceptible populations were identified and the threshold for narcosis for most anesthetics does not differ among individuals by more than a factor of 2 (Kennedy and Longnecker 1996 Marshall and Longnecker 1996). The intraspecies UF of 3 is supported by the steep dose-response curve for the induction of headaches namely, a 2-fold difference in the threshold concentration of PGDN and the concentration that induces headache in the majority of healthy individuals (Stewart et al. 1974). The 6-h 0.5-ppm concentration was... 

Generally, there is no simple and easy theoretical procedure which can provide exact or nearly precise quantitative predictions of what and how much will be adsorbed/desorbed by any solid phase over a period of time [9, 136-139]. Understanding sorption/desorption characteristics of any solid phase materials requires two main laboratory experimental techniques (a) batch equilibrium testing, and (b) continuous solid phase column-leaching testing. These involve... 

Whereas batch equilibrium tests are designed to study equilibrium sorption of solid phase particles with various pollutants, singly or in combination with other pollutants, solid phase column-leaching tests study both sorption and diffusion of organic pollutants through the subsurface environment [10,11,127, 141,142]. 

Batch equilibrium tests are conducted on solid phase suspensions, prepared with previously air-dried solids, ground to uniform powdery texture for mixing with various concentrations of the pollutants of interest in solution. The concentrations of these pollutants or the COMs leachate in the solution are designed to evaluate the capability of the suspended solids to adsorb all the pollutants possible with increasing amounts of available pollutants, consistent with interaction characteristics dictated by the surface properties of the solids and the pollutants [1,16,22-26,66,67,71]. For a successful and proper study of solid particle sorption of pollutants, the requirement for complete dispersion of solid particles in solution is absolute [143 -145]. Common practice is to use a solution to solid ratio of 10 1 [1], together with efficient sample agitation at a constant temperature (e.g.,48 h at 20 °C). 

Batch equilibrium tests used for sorption isotherm determinations involve solid suspensions (i. e., the full surface area of the solid particles is exposed to... 

It is important to differentiate between the two different types of sorption/ desorption tests (i. e.,batch and column-leaching), and the sorption characteristics determined from one should not be confused with the other. Sorption isotherms obtained with batch equilibrium tests are applied mainly to solid suspensions. The physical model, assumed with this situation, is one of a completely dispersed solid particle system, where all solid particle surfaces are exposed and available for interactions with the contaminants of concern. In contrast, column-leaching tests are performed with intact solid samples, and the sorption characteristics obtained from them are the results of contaminant interactions with a structured system where not all-solid particle surfaces are exposed or available for interactions with the contaminants. 

The sorption behavior of 11 PAH compounds (a training set, Table 11) on various solid phases (e.g., three soils and two sediments) with different properties to relevant sorption (e.g., organic carbon content, clay content, pH, cation exchange capacity CEC Table 12), was determined by batch equilibrium studies [1]. Batch equilibrium tests were designed to determine rates of equilibrium sorption under conditions of high mixing and high surface areas of the solid particles (see Chap. 3). 

It is uncertain just how relevant the results for these resin studies are to actual drinking waters because lead in drinking water is likely to be in solution and to have had time to reach equilibrium. Tests on actual drinking waters with background levels of lead will provide more definite answers to these questions. 

A 12 hour rest period is then suggested to allow reversible structure to reform before testing with at least 6 cycles being applied at each test condition before measurements are taken to allow reversible structure to reach near equilibrium. Testing should begin with the least severe conditions... 

If a logarithmic ramp is performed, then the data should not be fit with linear models (unit m.i). These data should be plotted as viscosity versus shear rate on logarithmic axes and the Carreau-Yasuda or Cross models (or subsets) should be used instead. It is unlikely that the zero-shear plateau will be seen in these types of tests. For a complete flow curve, the equilibrium tests described in Basic Protocol 2 should be used. 

The best way to detect problems occurring during the test is to visually inspect the sample rather than to focus on the data appearing on the monitor. One typical problem resulting from time-dependent behavior is irregular changes in rotor speed as the sample breaks down. Switching from a nonequilibrium to an equilibrium test can improve this problem, especially if a controlled-stress device is used. 

Analysis of a sample using Basic Protocol 1 will take 15 to 30 min. Using the equilibrium test in Basic Protocol 2 will take 25 to 60 min per sample, with longer times required as the number of data points increases. 

The experimental work can conveniently be classified into four major categories (a) Static equilibrium Testing (b) Dynamic Equilibrium Testing ... 

Figure 3 shows the results obtained for the benzene-water system and compares these with the results from the benzene-water-hydrochloric acid system. The acid-free system exhibited the almost linear adsorption isotherm expected at low water concentrations, while the data from the acid system, although somewhat scattered, suggest that the adsorption capacity was increased when some HC1 was present. In any case, the feasibility of using Z200H to dehydrate the benzene-hydrochloric acid system was demonstrated, and justified embarking on regeneration and dynamic equilibrium test studies. 

Figure 3. Static adsorption equilibrium tests on Z200H (Q) benzene-water system, ( Z1) benzene-water-HCl system...

Isotherms are normally developed to evaluate the capacity of the carbon for the adsorption of different contaminants. Data are obtained in batch tests, which determine the equilibrium relationship between the compound adsorbed on the carbon and that remaining in solution. The isotherms are used as screening tools to determine which carbon is suitable for a given application. Batch equilibrium tests are often complemented by dynamic column studies to determine system size requirements, contact time, and carbon usage rates [19]. Other parameters that are used to characterize activated carbons for water treatment include phenol number, an index of the ability to remove taste and odor, and molas.ses number, which correlates with the ability to adsorb higher molecular weight substances. However, these parameters still do not reflect performance in service, and they can only be considered as guidelines. 

A number of test methods have been used to determine sink model parameters. The most common test protocol uses a dynamic, flow-through chamber and involves challenging a test sink material with a test gas [20, 31, 35, 36]. Details on this technique are presented later. Other methods include static tests and microbalance measurements. Borrazzo et al. [37 ] took a fundamental physical chemistry approach and used static equilibrium tests to determine partition coefficients for trichloroethylene and ethanol vapors and several types... 

The study of a particular adsorption process requires the knowledge of equilibrium data and adsorption kinetics [4]. Equilibrium data are obtained firom adsorption isotherms and are used to evaluate the capacity of activated carbons to adsorb a particular molecule. They constitute the first experimental information that is generally used as a tool to discriminate among different activated carbons and thereby choose the most appropriate one for a particular application. Statistically, adsorption from dilute solutions is simple because the solvent can be interpreted as primitive, that is to say as a structureless continuum [3]. Therefore, all equations derived firom monolayer gas adsorption remain vafid. Some of these equations, such as the Langmuir and Dubinin—Astakhov, are widely used to determine the adsorption capacity of activated carbons. Batch equilibrium tests are often complemented by kinetics studies, to determine the external mass transfer resistance and the effective diffusion coefficient, and by dynamic column studies. These column studies are used to determine system size requirements, contact time, and carbon usage rates. These parameters can be obtained from the breakthrough curves. In this chapter, I shall deal mainly with equilibrium data in the adsorption of organic solutes. 

Adsorption of surfactant on reservoir rock can be determined by static tests (batch equilibrium tests on crushed core grains) and dynamic tests (core flood) in the laboratory. The units of surfactant adsorption in the laboratory can be mass of surfactant adsorbed per unit mass of rock (mg/g rock), mass per unit pore volume (mg/mL PV), moles per unit surface area (peq/m ), and moles per unit mass of rock (peq/g rock). The units used in field applications could be volume of surfactant adsorbed per unit pore volume (mL/mL PV) or mass per unit pore volume (mg/mL PV). Some unit conversions follow ... 

Equilibrium tests at the local deformation stage of a sample provide adequate changes of external forces to internal efforts of a material to resist with corresponding static development of the main crack. These tests are most appropriate when using bending or tension of the samples, because the fracture process will be defined by development of a unique breakaway type of crack, which allows determination of the actual surface area of the fracture. This means that the tests correctly provide the real physical processes of fracture of a concrete and the principles of nonlinear fracture mechanics with traditional mechanical characteristics of concrete and allows determination of a set of power and energy parameters of the material fracture. 

A schematic diagram of the device for the equilibrium test of concrete samples at a three-dot bend is shown in Figure 3.9. 

FIGURE 3.9 Test machine for equilibrium testing. (1) Test sample with initiated cut, (2) elastic steel ring, (3) punch, (4) distributive patch, (5) base, (6) press. (Reprinted from O. Figovsky, D. Beilin, and Yu. Zemlyanushnov, Fracture and Crack Resistance of Silicate Polymer Concrete, Journal Scientific Israel Technology Advanced 14, no. 4 (2012) 38-48. With Permission.)... 

A block diagram of the control algorithm of equilibrium tests is shown in Figure 3.10. The compositions of test SPC samples are illustrated in Table 3.15. 

The knowledge of the total fracture energy of concrete determined by equilibrium tests is especially important for structures operating in corrosive environments, shock, and cyclic mechanical loads because in this case the material acts, as a rule, beyond ultimate strength (descending branch of the deformation graph, Figure 3.11). 

Nonequilibrium and Equilibrium Tests of a Concrete, http //www.npp-geotek.ru/ employee/articles/concret/newarticlel.php sphrase id = 93290 print = Y... 

To calculate the length of unused bed from the breakthrough curve, the total solute adsorbed up to the break point is determined by integration. The capacity of the solid is obtained by integration of a complete breakthrough curve or from separate equilibrium tests. The ratio of these two quantities is the fraction of the bed capacity utilized at the break point, and 1.0 minus this ratio is the unused fraction. The unused fraction is converted to an equivalent length of bed (LUB), which is assumed to be constant. The break-point time is calculated from the ideal time and the fraction of bed utilized ... 

In another set of static equilibrium tests, one pore volime (PV) of alkaline solution was mixed individually with Aminoil IMZ, THUMS Ranger and Berea sandstone sands. The volume of one PV used was calculated from the porosity of the same sand v en it was packed for sand pack flow study. After standing for a number of days, the mixtures were filtered and the filtrates were analyzed for their alkaline consurtption by titration with standard acid. As depicted in Table II, the consurapticxis were rapid in all cases and the alkaline chemicals were totally or almost totally consumed after 6 to 9 days for the THUMS Ranger and Aminoil IMZ sands. The consumption with Berea sandstone sand was slower by comparison but still quite significant. 

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