Isothermal tests

E>/m = capacity per unit weight of carbon at the influent concentration W = weight of liquid used in the isotherm test = influent concentration... 

An isotherm test can determine whether or not a particular contaminant can be adsorbed effectively by activated carbon. In very dilute solutions, such as contaminated groundwater, a logarithmic isotherm plot usually yields a straight line represented by the Freundlich equation62 63 ... 

Figure 2.6B shows the heat evolution in isothermal tests of material decomposing in an autocatalytic mode at two temperatures. Typical curves for autocatalytic decomposition are also shown in Figure 2.8 discussed later in Example 3 [30]. 

FIGURE 2.6. Typical Curves Obtained from (A) Constant Heating Rate Tests, (B) Isothermal Tests, ( C) Differential Thermal Analysis and (D) Adiabatic Calorimetry... 

Figure 2.8 illustrates typical autocatalytic decompositions at three temperatures, 80°C, 90°C, and 100°C by isothermal tests. 

The isoconversion points (i.e., points of equal Q), can also be determined by numerical integration of the heat production-time curve of each of the individual isothermal tests performed at different temperatures. 

By plotting the heat production, q, at points of equal Q (as calculated from each isothermal test) as a function of 1 /T, in the form of Figure 2.19, the Ea can be calculated. 

From an isotherm test it can be determined whether a particular organic material can be removed effectively. It will also show the approximate capacity of the carbon for the application and provide a rough estimate of the carbon dosage required. Isotherm tests also afford a convenient means of studying the effects of pH and temperature on adsorption. Isotherms put a large amount of data into concise form for ready evaluation and interpretation. Isotherms obtained under identical conditions using the same contaminated groundwater for two or more carbons can be quickly and conveniently compared to determine the relative merits of the carbons. 

Feldspar, among many natural substances such as termite mount-clay, saw dust, kaolinite, and dolomite, offers significant removal ability for phosphate, sulfate, and color colloids. Optimization laboratory tests of parameters such as solution pH and flow rate, resulted in a maximum efficiency for removal of phosphate (42%), sulfate (52%), and color colloids (73%), x-ray diffraction, adsorption isotherms test, and recovery studies suggest that the removal process of anions occurs via ion exchange in conjunction with surface adsorption. Furthermore, reaction rate studies indicated that the removal of these pollutants by feldspar follows first-order kinetics. Percent removal efficiencies, even under optimized conditions, will be expected to be somewhat less for industrial effluents in actual operations due to the effects of interfering substances [58]. 

Both batch and column tests have been used to estimate the sorption capacity for barrier materials. Batch isotherm tests are easier to perform and are particularly useful for comparing the performance of alternative additives (e.g., Adu-Wusu et al., 1997 Bradl, 1997). However, isotherm tests may overestimate the sorption capacity applicable to a field setting due to kinetic effects and/or artifacts associated with the solids effect in batch experiments. Gullick (1998) provided a thorough review of possible explanations for differences in apparent sorption as a function of liquid /solid (L/S) ratio, and also conducted detailed batch experiments for different L/S conditions. The results indicated that a significant solids effect occurred for some, but not all, of the materials tested. Gullick recommended that batch experiments be performed at a L/S ratio as close to the anticipated field conditions as possible. 

The Kd calibrated from the column studies was approximately 58 percent of the value measured in batch isotherm tests using the same materials. The precise reasons for these differences is a subject of further investigation, but the result suggests that caution should be exercised in using the results of batch sorption tests to extrapolate the performance of amended slurry walls. 

Figure 6. Isothermal test for JCPA-60 aged sample held 19 hr at 212°C. Peak heights are h and h for aged and unaged samples, respectively. % reaction =h X 100/h0.

For microscale testing, accepting the fact that the MAT is nearly an isothermal test, we chose to take the catalyst mix temperature as the operating temperature of our new test. 

Dynamic properties ASTM D4065-90 ASTM D4473-90 Viscoelastic properties Cure effects on viscosity Dynamic properties of supported and unsupported resins Isothermal and non-isothermal tests... 

Spiral die mould with numerical Isothermal tests Advantages... 

The effects of cure on the viscosity of thermoset resins are monitored on the catalysed resin and are associated with the late injection, packing and curing cycles of a thermoset process. There are essentially two types of test methods, namely isothermal and non-isothermal tests, which are usually performed in dynamic or steady shear. 

A standardized procedure was adopted to get reprodudble samples for characterization. The stored catalysts were pretreated in tu in H2 at 400°C and heated under N2 flow to 500, 700 or 900°C. At those temperatures the catalysts were treated under reaction mixture (molar ratio 02/CH4=2/l, N2 balance ) for 3 h and cooled in N2 to 320°C to be isothermally tested for 4 hours consecutively at 320, 340, 350 and 360°C, (standard reaction). After reaction, the system was cooled to room temperature in N2 and the catalysts were stored in a dry box after air exposure. 

For our DTA tests we use equipment from Adolf Kuhner AG ( 1 ) We run two types of DTA tests. One type is a dynamic heating method with a 2.5 C/min. heating rate, and the other is an isothermal heating method. In the isothermal test we preheat the heating block to a specific temperature, insert the sample, and keep the heating block at the specific temperature for at least eight hours. 

Another reason that isothermal heating methods are used in the initial screen is to identify materials that have time dependent thermal stability. These materials have a thermal decomposition that does not follow a simple Arrhenius relationship in which the reaction rate increases exponentially with an increase in temperature. Instead an extended induction period is required before the decomposition becomes detectable. An example of this behavior is shown in Figure 2. The DTA isothermal test recorder traces of methane sulfonic acid, 3,7-dimethyloctyl ester at different test temperatures are shown. The induction time varies from less than 1 hr. at 180 C to 46 hr. at 130 C. As with this compound, it is not unusual that once decomposition is detected it proceeds very rapidly, releasing all of the heat in a short period of time. Dynamic heating methods do not indicate if this type of thermal instability is present if it is, the initial detection temperature from dynamic tests will be grossly misleading as to the thermal stability of the material. 

During our initial screen, we also check the thermal stability of the sample in the presence of stainless steel. Accidents have occurred when processes that were no problem in glass equipment were either scaled-up in, or switched to stainless steel equipment. We perform this check during our isothermal DTA test by running duplicate samples and adding stainless steel powder to one of them. We use the isothermal test because it allows longer contact time between the sample and the stainless steel. 

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