Solid acid catalysts for biorefinery processes

The present work regards the study of alternative synthetic routes for biofuels and biochemicals. Biofuels and biochemicals constitute the two main classes of biorefinery products. Biofuels are obtained from biomass and have many environmental advantages over the traditional fuels. In this work particular attention has been given to biodiesel, one of the most widely used biofuels. Biodiesel is a safe, non-toxic, and biodegradable alternative diesel fuel. The development of active acid catalysts for biodiesel synthesis could reduce the production costs, in particular because the acid catalysts permit the use of low value feedstocks such as waste and non-edible oils. Biodiesel production occurs with co-production of glycerol, which is co-product also in other industrial productions such as the production of fatty acids and soaps. Because of its large production the market demand is largely less than the supply. For this reason glycerol is considered a problematic product. Possible solution to its disposal is the use as platform chemical in the production of high value bioproducts. Among them are particularly interesting the trioses dihydroxyacetone and glyceraldehyde. They could be feedstocks for an alternative synthetic way for lactic acid and its esters. Lactic acid and lactates are, nowadays, considerably important because they are used as building blocks in the production of biodegradable polymers (the polylactic acids), which are potential substitute for petroleum derived polymers. Lactic acid is also one of the most promising bio-based platform molecules. The high costs of the conventional production process hinder the use of lactic acid and lactates in many applications. So it is essential to develop cheaper and greener synthetic routes. In this work catalysts synthesis, characterization of the materials, and catalytic testing have been carried out mainly at the Laboratory of Industrial Chemistry in the Department of Chemical and Geological Sciences of the University of Cagliari. The study involved the use of several techniques for the characterization of the materials. All the catalytic results have been related to the acid properties of the tested materials. For this reason the measurements of adsorption microcalorimetry and adsorption FTIR using basic probe molecules have been the most important used techniques in this work. The measurements of adsorption microcalorimetry were carried out at the Laboratory of Industrial Chemistry in Cagliari while the measurements of adsorption FTIR were carried out under the supervision of Prof. Konstantin Hadjiivanov at the Institute of General and Inorganic Chemistry of the Bulgarian Academy of Sciences. This work is divided in five chapters. The first chapter is an introduction of the fundamentals of sustainable chemistry, biorefinery and acid-base heterogeneous catalysis. The second chapter is a description of the most important techniques for the characterization of acid-base properties of solid materials. In the third chapter are listed the used materials, the experimental procedures and apparatus. The chapter four is the study of the acid catalyzed transesterification of tryglicerides for the production of biodiesel and glycerol. In chapter five is described the work on the conversion of dihydroxyacetone to methyl lactat

Remarkable acid strength of ammonium ions in zeolites: FTIR study of low-temperature CO adsorption on NH4FER

FTIR spectra of CO adsorbed at 100 K reveal remarkable acid strength of the free NH groups of tridentate ammonium ions in NH4FER zeolite.</p

Adsorption microcalorimetry characterization of microporous and mesoporous zeolites for soybean oil transesterification

The combined influence of the catalyst acidity and porosity features on the transesterification of soybean oil with methanol was investigated over micro/mesoporous hierarchical Beta (Si/Al = 18 and 30), conventional microporous Beta (Si/Al = 23 and 43) and MCM-22 (Si/Al = 40) zeolites. All the catalysts were characterized as to their structure and texture by X-ray diffraction and N2 physisorption, respectively. Their acid features were assessed by adsorption microcalorimetry, using NH3 as probe molecule. Catalytic testing was carried out in batch at 453 K and 4 MPa. The nature of the organic material adsorbed/trapped in the catalyst during reaction ("coke") was determined by GC/MS after solvent extraction. Fatty acid methyl esters (FAMEs) yields of 22-40 mol% were attained with a reaction time of 24 h over the conventional Beta and MCM-22 samples, whereas remarkably higher values (50-70 mol%) were observed over the hierarchical Beta zeolites. For both the hierarchical and conventional zeolites, the initial FAMEs yield was found to increase with the concentration of the acid sites able to adsorb ammonia with strength higher than ca. 100 kJ mol-1. In comparison with the conventional zeolites of similar acidity, the methyl esters yield over the hierarchical zeolites was twice to three times higher, as a consequence of the enhanced reactants diffusion in their secondary mesoporous system. The presence of free fatty acids in the reaction mixture and the nature of the coke revealed that several acid-catalyzed reactions and thermal degradation processes can occur simultaneously with transesterification. A general scheme for the different reaction pathways for the oil transformation was outlined