Treatment thermal

In contrast to catalytic treatment, coke formation during thermal treatment leads only to pipe blocking and poor thermal conductivity of the reactor walls. The most important difference between coke formation in catalytic and thermal treatment is that a free radical mechanism in coke formation is not possible in the case of thermal processing. 

The rate or velocity of coke formation is, first of all, a function of the feedstock characteristics. Seidel [1] reported about the tendencies of different components of heavy vacuum residues to coke formation. The following sequence shows a descending tendency to coke formation during thermal treatment  

A comparison between the activation energies for coke formation from light aromatics (52-58 kJ/mol) and from asphaltenes and resins (34— 47 kJ/mol) shows that the reaction velocity of coke formation from light aromatics grows faster with increasing temperature than for coke formation from asphaltenes or resins. 

Marcel Dekker, Inc. 270 Madison Avenue. New York, New York 10016 

It has been shown [21] that, at low concentrations (below the critical micelle formation concentration), asphaltenes in solution are in a molecular state. Above the critical micelle concentration, however, asphaltene micelle formation occurs in a manner similar to that in surfactant systems where surfactant monomers are more uniform in their structure and less polydisperse. Now, it is obvious that coke for- 

The nucleation and crystal growth in the exposed areas is caused by a thermal treatment using two residence steps. The agglomerates of silver atoms created during the UV exposure act as heteroseeds or -nuclei. The nucleation temperature is less above the transformation temperature Tg (see Sect. 1.2.4), whereas the crystal growth occurs above temperatures of 550°C. The crystallisation temperatures should be below 600° C to avoid homogeneous, undesired nucleation in the not exposed areas. 

X-ray diffraction (Fig. 9.5) was used to confirm that the crystal phase in both cases is lithium metasilicate (Li20 Si02). Normally this crystal phase is white, however, because of the presence of agglomerates of silver atoms acting as nuclei, these crystals have brown colour. The intensity of the colour as well as colour shifts from yellow to brown and green depend not only on the number of nuclei but also the size and shape of the LMS crystals. 

Crystallisation at a temperature of 600°C (10 K higher than 590°C ) would also lead only to the formation of the lithium metasilicate crystal phase, 

Calculations and Measurements of the Amount of Crystal Phase in FS21 

Quantitative X-ray diffractometry allows the determination of the real amount of LMS crystals that formed within the glass (128). It requires a calibration of the XRD-curve. This was performed using mixtures of synthetic lithium metasilicate and the exactly composed glass phase as described above [128]. Ehrhardt estimated that only 15mass% lithimn metasUicate crystals form, which is significantly lower than the theoretically possible crystalline phase. This discrepancy is due to the diffusion limitation of the lithium ions in the glass matrix. 

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Thermal reforming Thermal sensitization Thermal stability Thermal transfer Thermal-transfer printing Thermal treatment Thermal wave imaging Thermate Thermate-TH2 Thermate-TH3 Therm-Chek... 

Terephthahc acid (TA) or dimethyl terephthalate [120-61 -6] (DMT) reacts with ethyleae glycol (2G) to form bis(2-hydroxyethyl) terephthalate [959-26-2] (BHET) which is coadeasatioa polymerized to PET with the elimination of 2G. Moltea polymer is extmded through a die (spinneret) forming filaments that are solidified by air cooling. Combinations of stress, strain, and thermal treatments are appHed to the filaments to orient and crystallize the molecular chains. These steps develop the fiber properties required for specific uses. The two general physical forms of PET fibers are continuous filament and cut staple. 

Pretreatment of Suspensions. Another important aspect of soHd—Hquid separation is conditioning or pretreatment of the feed suspension to alter some important property of the suspension and improve the performance of a separator that follows. A conditioning effect is obtained using several processes such as coagulation and docculation, addition of inert filter aids, crystalliza tion, freezing, temperature or pH adjustment, thermal treatment, and aging. The first two operations are considered in more detail due to their importance and wide use. 

Thermal Cracking. In addition to the gases obtained by distillation of cmde petroleum, further highly volatile products result from the subsequent processing of naphtha and middle distillate to produce gasoline, as well as from hydrodesulfurization processes involving treatment of naphthas, distillates, and residual fuels (5,61), and from the coking or similar thermal treatment of vacuum gas oils and residual fuel oils (5). 

Polyquinolines have also been obtained by a post-polymerization thermal treatment of poly(enamino nitriles) (93). The resulting polymers show excellent thermal stabiUty, with initial weight losses occurring between 500 and 600°C in air (tga) under nitrogen, initial weight loss occurs at about 600°C and there is a 20% weight loss up to 800°C. 

Stripping is accompHshed by dehydration using sulfuric acid (38), lithium chloride [7447-41-8] (39), and tertiary amines containing from 14—32 carbon atoms in an organic solvent immiscible with water followed by thermal treatment of the HCl—organic complex (40). 

Fig. 2. Generalized process flow chart for the thermal treatment of soHd wastes. To a certain extent, steps 2, 3, 4, and 5 always proceed in parallel because...

In general, the desorptive behavior of contaminated soils and soHds is so variable that the requited thermal treatment conditions are difficult to specify without experimental measurements. Experiments are most easily performed in bench- and pilot-scale faciUties. Full-scale behavior can then be predicted using mathematical models of heat transfer, mass transfer, and chemical kinetics. 

Mass Transfer and Kinetics in Rotary Kilns. The rates of mass transfer of gases and vapors to and from the sohds iu any thermal treatment process are critical to determining how long the waste must be treated. Oxygen must be transferred to the sohds. However, mass transfer occurs iu the context of a number of other processes as well. The complexity of the processes and the parallel nature of steps 2, 3, 4, and 5 of Figure 2, require that the parameters necessary for modeling the system be determined empirically. In this discussion the focus is on rotary kilns. 

Step 4 of the thermal treatment process (see Fig. 2) involves desorption, pyrolysis, and char formation. Much Hterature exists on the pyrolysis of coal (qv) and on different pyrolysis models for coal. These models are useful starting points for describing pyrolysis in kilns. For example, the devolatilization of coal is frequently modeled as competing chemical reactions (24). Another approach for modeling devolatilization uses a set of independent, first-order parallel reactions represented by a Gaussian distribution of activation energies (25). 

F. S. Larsen, The Thermal Treatment of Contaminated Soils and the Incineration of Waste Fuels, PhD dissertation. University of Utah, Salt Lake City, 1994. 

Isomerization. Maleic acid is isomerized to fumaric acid by thermal treatment and a variety of catalytic species. Isomerization occurs above the 130 to 140°C melting point range for maleic acid but below 230°C, at which point fumaric acid is dehydrated to maleic anhydride. Derivatives of maleic acid can also be isomerized. Kinetic data are available for both the uncatalyzed (73) and thiourea catalyzed (74) isomerizations of the cis to trans diacids. These data suggest that neither carbonium ion nor succinate intermediates are involved in the isomerization. Rather, conjugate addition imparts sufficient single bond character to afford rotation about the central C—C bond of the diacid (75). 

Regulations. In order to decrease the amount of anthropogenic release of mercury in the United States, the EPA has limited both use and disposal of mercury. In 1992, the EPA banned land disposal of high mercury content wastes generated from the electrolytic production of chlorine—caustic soda (14), accompanied by a one-year variance owing to a lack of available waste treatment faciUties in the United States. A thermal treatment process meeting EPA standards for these wastes was developed by 1993. The use of mercury and mercury compounds as biocides in agricultural products and paints has also been banned by the EPA. 

The ammonium perchlorate solution is spray-dried to the desired crystal size at air temperatures below 150°C and crystal temperatures of about 110°C. This procedure provides a pure product having a controlled grain size. Prior mechanical and thermal treatment affects the isothermal... 

Many pyrophosphates can be prepared by thermal treatment of the acid orthophosphates. 

Some phosphides, such as titanium phosphide [12037-65-9] TiP, can be prepared bypassing phosphine over the metal or its haUde. Reaction of phosphine with heavy metal salt solutions often yields phosphines that may contain unsubstituted hydrogens. Phosphides may also be prepared by reducing phosphoms-containing salts with hydrogen, carbon, etc, at high temperatures, the main example of which is the by-product formation of ferrophosphoms in the electric furnace process for elemental phosphoms. Phosphoms-rich phosphides such as vanadium diphosphide [12037-77-3] may be converted to lower phosphides, eg, vanadium phosphide [12066-53-4] by thermal treatment. 

Fe remains ia supersaturated soHd solution. This excess amount can precipitate as Al Fe dispersoids duting subsequent thermal treatment. In more... 

Thermal treatment at 250°C and higher (annealing) converts the metastable precipitates to the equhibrium AI2CU precipitates (9), and the product softens. 

The activated aluminas comprise a senes of nonequilibrium forms of partially hydroxylated aluminum oxide [1344-28-1], AI2O2. The chemical composition can be represented by Al20 2 ranges from about 0 to 0.8. They are porous soHds made by thermal treatment of aluminum hydroxide... 

Selenium purification by zone refining is not feasible. At practical zone-refining speeds, crystallization does not occur and impurities do not segregate. However, a controlled differential thermal treatment of selenium in a long vertical glass tube has been described (45). The treatment time is several weeks to several months. 

Strength. The fracture strength of vitreous sihca depends on its surface quaUty, which can be affected by thermal treatment and handling conditions. Microcracks, surface contamination, and crystallisa tion can reduce the strength from the value of pristine vitreous sihca by several orders of magnitude. 

Soaking a siUca gel in dilute ammonium hydroxide solution at 50—85°C can result in significant coarsening of the gel texture (5). Aging and thermal treatments result in a one-way process, ie, loss of specific surface area and in increase in pore size. The pore size can also be enlarged by dissolution of some of the siUca. Treating a siUca gel with O.S-N KOH or dilute HF can enlarge the pores from 0.7 to 3.7 nm (3). 

The concept and use of food polymer science in describing the behavior of starch during and after thermal treatment has been developed (20,21). In... 

Some of the most common stabilization—soHdification processes are those using cement, lime, and pozzolanic materials. These materials are popular because they are very effective, plentiful, and relatively inexpensive. Other stabilization—soHdification technologies include thermoplastics, thermosetting reactive polymers, polymerization, and vitrification. Vitrification is discussed in the thermal treatment section of this article and the other stabdization—soHdification processes are discussed below. 

Thermal treatment is used to destroy, break down, or aid in the desorption of contaminants in gases, vapors, Hquids, sludges, and soHds. There are a variety of thermal processes that destroy contaminants, most of which are classified as incineration. Incineration HteraHy means to become ash (from Medieval Latin, incinerare in or into ashes). With respect to the incineration of hazardous wastes regulated in the United States, however, there is a strict legal definition of what constitutes an incinerator. The Resource Conservation and Recovery Act (RCRA) definition of incinerator at 40 CFR 260.10 is... 

Factors Affecting Performance. There are many factors that affect both the choice of a particular thermal treatment and its performance. Chief among these are waste characteristics, temperature, residence time, mixing or turbulence, and air supply. 

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