Thermal desorption solids treatment

Thermal desorption heats the contaminated soil to desorb and volatilize the contaminants, which are then either recovered or destroyed. This entry discusses the specifics of thermal desorption, including desorption kinetics, soil pretreatment requirements, types of thermal desorption units (TDUs), off-gas treatment, solids treatment, as well as system cost and performance. 

Chances for successful identification and quantification are considerably enhanced when analytes are separated. For solutions, chromatography is the supreme tool, whereas for solids some form of thermal treatment may achieve fractionation of matter according to volatility. Vapour evolution from polymers may be controlled and studied by various means, such as sublimation, thermal distillation, vacuum TG-MS, thermal evolution analysis (TEA) including TVA, headspace techniques or thermal desorption. It is obviously desirable that evaporation of the additives takes place below the decomposition temperature of the polymer. In principle, this can also be realised in thermal-programmed pyrolysis (dry distillation in vacuum). Desorption processes are controlled by diffusion. 

Fig. 7.10 Ni Mossbauer spectra of LaNi5 samples after various treatments (a) no hydrogen exposure, (b) activated in hydrogen, (c) after 1,584 thermally induced absorption-desorption cycles, as described in the text. The solid lines are least-squares fits to a single Lorentzian in (a) and (b). (c) was fitted with a single Lorentzian (representing nonmagnetic nickel atoms) and a 12-line hyperfine spectrum (from [20])...

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

Mesoporous zirconia (zirconium oxide) materials containing mainly mesopores have been synthesized via sol-gel reactions from zirconinm propoxide nsing urea as a template. The solid was dried, extracted with water to remove urea, calcined at different temperatures and impregnated with trifluoromethanesulfonic acid. The samples thus obtained were extracted with a tnixmre of dichloromethane and diethyl ether using a Soxhlet apparatus in order to remove the loosely adsorbed acid. The solids were characterized by FT-IR, XRD, DTA-TGA, and N2 adsorption-desorption measnrements. The mean pore diameter of the support was higher than 3.7 mn, which increased with the increment of the thermal treatment temperature. At the same time, the specific surface area and the amount of triflic acid attached on the support decreased. The potentiometric titration with n-butylamine indicated that the catalysts present very strong acid sites. The catalytic activity of the prepared catalysts in the esterification of 4-hydroxybenzoic acid w ith propyl alcohol was evaluated. 

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