Thermal analysis of pyridine-treated sepiolite and palygorskite

Abstract

A B S T R A C T:The thermal behaviour of sepiolite and palygorskite treated with pyridine (Py) was investigated by DTA, TG, DTG and EGA (by MS) under a flow of air and inert gases (N 2 or Ar). The thermal analysis showed that the organic base was adsorbed by the clays, penetrating into the clay pores and replacing zeolitic and bound water. Its presence in the pores shifted the dehydroxylation peak to temperatures higher than the corresponding peak in the untreated clays. Under N2 and Ar, thermal desorption of Py from sepiolite was observed at 260 and 650~ whereas for palygorskite only traces of Py were detected in the evolved gases. In addition to desorption, reactions of pyrolysis and condensation to coke were detected by the evolution of ammonia, methane and hydrogen, respectively. In air, oxidation of the organic matter led to the appearance of exothermic peaks. The profile of the DTA curve and the temperatures of the most intense exothermic peaks were determined by the rate of the carbon oxidation.In a previous publication (Shuali etal., 1990) we described the thermal behaviour, under air or N2 flow, of the porous clays sepiolite and palygorskite treated with n-butylamine (BA). Under N 2 flow, in addition to thermal desorption of the aliphatic base, reactions of pyrolysis and condensation to coke were detected. In air, oxidation of the sorbed organic matter led to the appearance of exothermic peaks. The temperatures of the most intense exothermic peaks are governed by the rate of carbon oxidation, but the shape of the DTA curves and the temperatures of exothermic shoulders are governed by the rate at which the hydrogen from the organic molecules combine with oxygen from the air.In the present investigation, the thermal behaviour of sepiolite and palygorskite treated with pyridine (Py), both in air and inert atmosphere (N2 or Ar) was studied. There are several publications on the sorption of Py by sepiolite and palygorskite. According to RuizHitzky et al. (1985), the sorption of Py on the external surfaces of these clays takes place in two well-defined steps. In the first step a monolayer is formed with the Py molecules lying with their planes parallel to the (001) plane of the clay crystal; in the second step a bilayer coverage is formed. Blanco et al. (1988) studied the surface acidity of palygorskite by infrared (IR) spectroscopy. After evacuating for 2 h at 150~ the thermally treated clay was saturated with Py. The IR spectra showed the formation of weak hydrogen bonds between Py and Bronsted acid sites which were developed as a result of the thermal treatment. Shuali et al. (1989) identified, by IR spectroscopy, several associations which are formed between palygorskite or sepiolite and Py. During the adsorption process, the base penetrates into the channels replacing part of the zeolitic water and forming hydrogen 9 1991 The Mineralogical Society

Influence of the clay modification and compatibilizer on the structure and mechanical properties of ethylene–propylene–diene rubber/montmorillonite composites

“…For the three OMMTs, the weight loss in the temperature range is about 5.8% because of the organophilic properties of OMMTs containing alkyl ammonium ions. Shulai et al19 observed similar behavior in pyridine‐treated sepiolite and palygorskite.…”

Interaction of Pyridine Derivatives with Sepiolite

“…4 show that the 2-aminopyridine molecules replace the coordination water through the nitrogen of the amino group. During this process, amines, which are very strong electron donors, undergo ion exchange with the weak electron donor, coordinated water molecules, as depicted below: This is apparent from the decrease and eventually disappearance of the Mg 3 OH peaks at 3680 cm −1 and that of the bound water at 530 cm −1 (16). The reappearance of asymmetric and symmetric NH 2 bands at 3325 and ve 3278 cm −1 upon treatment of sepiolite with 2-aminopyridine is another proof for the adsorption of this compound.…”

Thermogravimetric, Infrared and Mass Spectroscopic Analysis of the Desorption of Tetrahydropyran, Tetrahydrofuran and 1,4-Dioxan from Montmorillonite

“…However, the diffusion coefficients for the cyclic ethers did not exhibit the increase with temperature expected of a thermally activated process nor did they conform to the 1/~ dependence for limiting Knudsen diffusion. Consequently, this study was initiated to ascertain whether the cyclic ethers underwent any transformation in the temperature region (18-105~ of the diffusion experiment and was extended up to 800~ to conform with similar studies on alcohols (Breen et al, 1993), acetic acid (AI-Oswais et al, 1987) and nitrogen-containing bases such as cyclohexylamine , pyridine and n-butylamine (Breen et al, Shuali et al 1990, 1991 …”