Liliana Giraldo Gutiérrez

A batch-type heat conduction microcalorimeter for immersion heat determinations: design, calibration and applications

Abstract A batch-type heat conduction microcalorimeter is designed and constructed for the determination of immersion heats of microporous solids in polar and non-polar solvents. The apparatus is of the twin type and uses high sensitivity thermopiles for the detection of thermal effects. The calibration constant of the equipment is determined for the constructed aluminum and Pyrex brand glass cells, at different levels of work and electric power (between 0.25 J and 2 J, and 1 mW and 16 mW, respectively). The values of the calibration constant vary between 18 WV−1 and 22 WV−1. Chemical calibrations are also carried out with the standard systems HCl-NaOH, and THAM-HCl (THAM = trishydroxymethylaminomethane). The results, −56.40 ± 0.08 kJ mol−1 for the neutralization heat of aqueous solutions of HCl and NaOH, and −47.40 ± 0.01 kJ mol−1 for the protonation heat of THAM with a dilute aqueous solution of HCl, are in good agreement with those reported in the literature and corroborate the correct functioning of the microcalorimeter. The equipment was employed in the determination of surface areas of activated carbons, between 250 and 1500 m2 g−1, with an imprecision of 0.45%; the results show better sensitivity with respect to previously reported determinations. Also, immersion heats of activated carbons in 0.1 M NaOH and HCl were determined and related to the number of acid or basic groups of the carbon.

Relación entre la entalpía de inmersión de monolitos de carbon activado y parametros texturales

In this study, Disc and honeycomb-shaped activated carbon monoliths were obtained using as a precursor coconut shell, without the use of any binder. Textural characterization was performed by adsorption of N2 at 77 K and immersion calorimetry into benzene. The experimental results showed that the activation with zinc chloride produces a wide development of micropores, yielding micropore volumes between 0,38 and 0,79 cm3 g-1, apparent BET surface area between 725 and 1523 m2 g-1 and immersion enthalpy between 73,5 and 164,2 J g-1.Were made comparisons between textural parameters and energy characteristics.

Study of 2,4-dinitrophenol adsorption from aqueous solution on bovine bone char

A sample of bovine bone, an industrial by-product, was submitted to carbonisation at 800°C for 2 h at a heating rate of 3°C min–1 and a N2 flow of 80 cm3 min–1. The char obtained was characterised by nitrogen adsorption isotherms at 77 K using scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The textural parameters showed a surface area of 171 m2 g–1, pore volume of 0.07 cm3 g–1 and morphological characteristics of meso- and macroporous material. Additionally, adsorption isotherms of 2,4-dinitrophenol (2,4-DNP) were made on the char obtained, and the adsorption behaviour was studied using the models of Langmuir, Freundlich, Redlich-Paterson and Toth. Of these, the one that best describes the adsorption system was the Toth model, which indicates a multilayer adsorption. The adsorption capacity of 2,4-DNP was 41.3 mg L–1, from a model solution of 100 mg L–1. Finally, we evaluated the adsorption kinetics, correlating the experimental data with pseudo-first-order and pseudo-second-order models. It was found that the chemical kinetics of the removal of 2,4-DNP in the bovine char was described by the pseudo-second-order equation, which represented the chemisorption between the adsorbate and adsorbent in a monolayer on the surface.

Activated Carbon for CO2 Adsorption Obtained through the Chemical Activation of African Palm Stone

In this study, activated carbons were prepared and tested as CO2 adsorbents at a temperature of 273 K and at atmospheric pressure. African palm stone was used as the precursor material, which was initially impregnated with CaCl2 solutions at different concentrations. The textural characterization of activated carbons was performed by nitrogen adsorption at 77 K. The energetic parameters were determined by immersion calorimetry in benzene and water. In addition, the total acidity and basicity were estimated using Boehm titrations. A maximum surface area of 1700 m2 g−1 was obtained with a pore volume of 0.64 cm3 g−1. Immersion calorimetry provided results between −17.95 and −95.75 J g−1 in benzene and between −13.63 and −30.24 J g−1 in water. The materials had a maximum CO2 adsorption capacity of 5.75 mmol CO2 g−1. It was found that the adsorption of gas increased with the total basicity and decreased with acidity. Finally, correlations were established between the textural characteristics, determined by gas adsorption and the immersion enthalpy data.