Thermal decomposition of long-chain fatty acids and its derivative in the presence of montmorilloniteA thermogravimetric (TG/DTG) investigation

In sedimentary environments or clay-rich rocks, clay minerals are usually combined with organic matter; however, little research has focused on the effects of combinations of organic matter and clay minerals on the thermal degradation of organics and on subsequent hydrocarbon generation. In this study, the long-chain fatty acid octadecanoic acid (OA) and its derivative octadecy trimethyl ammonium bromide (OTAB) were selected as model organics. The organics were prepared for clay–organic associations with Na-based montmorillonite (Mt(Na)). The thermal decomposition behaviors of these associations were studied via thermogravimetric (TG/DTG) analysis. In the presence of Mt(Na), OA decomposed at 275.2 °C, decomposing sooner than pure OA. The thermal decomposition behavior of OTAB is nearly consistent with that of pure OTAB, but for interlayer OTAB, the decomposition temperature increased to higher than 300 °C. The results indicate that Mt(Na) plays a dual role in the thermal decomposition of fatty acid. Mt(Na) may accelerate the thermal decomposition of OA, and inherent solid acidity levels may be the key factor. In addition, the interlayer structure of Mt(Na) can increase the thermal stability of OA and OTAB. The above results further demonstrate that the thermal decomposition behavior of a given organic material may also depend on its structure and composition. In the presence of Mt(Na), organics with amino and amine structures are more stable than those with carboxyl groups.