Activación de una sepiolita con disoluciones diluidas de NO₃H y posteriores tratamientos termicos: I. Estudio de la superficie específica

Abstract

ResumenUna sepiolita procedente de Toledo (España) se ha activado por tratamiento con disoluciones 0·25, 0·50 y 0·75 n de NO3H, seguido de calentamiento durante 10 h a 110, 200, 300, 400 y 500°C. Para cualquier concentración ácida, un calentamiento de 110, 200 y, a veces, 300°C, produce un aumento del número de poros mientras que las temperaturas superiores significan un cierre de los mismos tanto mayor cuanto más elevada es la temperatura de tratamiento. El máximo desarrollo de la superficie accesible al N2 tiene lugar con una disolución 0·50 n de NO3Hy 200°C (449 m2/g, método de BET); la superficie específica de la sepiolita natural es de 321 m2/g.

Activation of a sepiolite with dilute solutions of HNO3and subsequent heat treatments: III. Development of porosity

“…It was shown in a previous paper of the series (Lopez-Gonzalez et al, 1981) that for any of the temperatures used in the heat treatments, the BET surface area reached a maximum after treatment with either 0.50 or 0.75 M nitric acid. On the other hand, for a given acid concentration the maximum surface area value was reached after heating at 200~ Based on this information, the following groups of products were selected for further investigation of the dependence of surface texture and porosity on activation conditions: (i) four samples activated with 0.75 M HNO3 and subsequently heated at 110, 200, 300 and 400~ for 10 h; (ii) four samples activated with different concentrations of HNO3 (0.25, 0.50, 0-75 and 1.0 M) and heated thereafter at 200~ for 10 h; (iii) four samples heated at 110, 200, 300 and 400~ for 10 h without previous acid treatment; (iv) one sample heated at 900~ for 100 h. The f-plot method of Gregg (1975) was used to follow the changes in the N2 adsorption isotherms of the sepiolite products.…”

“…Adsorption of nitrogen at 77 K was carried out in a conventional gravimetric system (Jimenez-Lopez et al, 1978); the adsorption isotherms for all the products have been published elsewhere (Jimenez-Lopez et al, 1978;Lopez-Gonzalez et al, 1981).…”

“…Previous studies (Jim6nez-L6pez et al, 1978) have shown that when HNO3 was used as the activating agent the best results, in terms of surface area development, were obtained with concentrations ~< 1 M. In the first two papers of this series (Lopez-Gonzalez et al, 1981;Bonilla et al, 1981) the effects of various combinations of dilute HNO3 and subsequent heat treatments on the surface properties were discussed. The present paper describes the effects of acid and subsequent heat treatment on the porosity (including pore size distribution) of sepiolite, changes in this property being monitored by analysis of N2 adsorption isotherms at 77 K on selected products from the activation experiments mentioned above.…”

Activation of a sepiolite with dilute solutions of HNO3 and subsequent heat treatments: II. Determination of surface acid centres

“…Material used for this and the previous (L6pez- Gonzalez et al, 1981) This formula was derived from the chemical analysis of a carbonate-free sample which had been ignited at 1000~…”

“…Material used for this and the previous (L6pez- Gonzalez et al, 1981) series of experiments was a natural sepiolite from Toledo, Spain. Its exchange capacity was 8 mEq/100 g and its structural formula [Sis.s0 A10.20] This formula was derived from the chemical analysis of a carbonate-free sample which had been ignited at 1000~…”