Characterisation of Ion Exchange Resins for the Catalytic Conversion of Biorefinery Streams to Fuels

Abstract

This thesis describes the work performed to test and characterise various ion exchange resins as heterogeneous catalysts for the transesterification reaction of tributyrin with methanol to produce methyl butyrate as biodiesel. Depleting reserves of fossil fuel and environmental restrictions on the emission of greenhouses gases have been drawing attention to find a renewable resource such as biodiesel. Biodiesel can be produced via transesterification reaction of oil using an acid or base as a homogenous catalyst. Due to the disposal problem of these catalysts; a more sustainable alternative such as a heterogeneous catalyst is required. Due to the lack of literature on the use of resins as a catalyst, in particular for anionic resins, a preliminary study of the pre-treatment of ion exchange resins was initially carried out to build the foundations for further experiments. Then, a screening test was performed to detect the most promising catalyst. The strong anion exchange resins showed much higher catalytic activity than the strong cation exchange resins. Among the anion exchange resins, Amberlyst 26OH with high density of functional groups and the ability to swell in the reaction mixture gave rise to the conversion of approximately 88 %. The influence of the reaction parameters such as temperature, molar ratio, catalyst loading and stirring rate was investigated by factorial design. The pore size and volume of resins can affect activity for triglyceride transesterification. A proper study of the internal mass transfer on the resins was introduced here. Diffusion Ordered Nuclear Magnetic Resonance Spectroscopy (DOSY NMR) has been utilized for the first time to characterize the internal mass transfer using the motion of the reacting species, confined within their pores. The measurements on the resins failed because of heterogeneity of the samples and the presence of moisture. The results of these resins were compared with mesoporous silica SBA-15, which allowed simple characterisation. Tributyrin and methyl butyrate showed reduced diffusion coefficients within the confined pores. At the same time, glycerol exhibited interesting behaviour; it showed enhancement of its diffusion coefficient due to the ability of the silica support to disrupt the intermolecular H-bonding network of glycerol. Ion exchange resins are high-performance catalysts and catalytically active even at very low temperature. The work reported here enhance the use of ion exchange resins more used in catalysis, and the