Esterification of crude tall oil catalyzed by Beta zeolite

Abstract

In softwood Kraft pulping process, fatty/resin acids (extractives) react with the white liquor and are saponified, producing Tall Oil Soap (TOS). TOS can be converted back to the respective fatty/resin acids, generating Crude Tall Oil (CTO). In this work, TOS was converted into CTO according to standard methods, producing residual lignin and an aqueous phase as co-products. Then, CTO was esterified in the presence of Beta zeolites with different Si/Al ratios and particle sizes in rotary Teflon-lined stainless-steel autoclave. Compared to esterification of oleic and palmitic acids, esterification of CTO is a slow process, with conversions limited to no more than 83 % after 6 h at 393 K. Smaller particles (0.26 μm) and lower Si/Al ratio (15) showed greater conversion. This may be associated with a higher strength of Brønsted acid sites (due to lower Si/Al ratio) but also with an improved diffusion of reactants/products within zeolite micro- and mesopores (due to the relatively smaller particle size). The esterification product was mainly composed of esters of fatty acids, such as dimethyl 4-isopropyloctanedioate, methyl elaidate and methyl palmitate. Esters of resin acids (methyl abietate and dehydroabietate), phthalic acids, as well as paraffins are also present, but probably in lower concentrations.