Sustainable processes using heterogeneous acid catalysts. Some examples of industrial interest.

In recent years the need for the design of more sustainable processes and the development of alternative reaction routes to reduce the environmental impact of the chemical industry has gained vital importance. Main objectives especially regard the use of renewable raw materials, the exploitation of alternative energy sources, the design of inherently safe processes and of integrated reaction/separation technologies (e.g. microreactors and membranes), the process intensification, the reduction of waste and the development of new catalytic pathways. The present PhD thesis reports results derived during a three years research period at the School of Chemical Sciences of Alma Mater Studiorum-University of Bologna, Dept. of Industrial Chemistry and Materials (now Dept. of Industrial Chemistry “Toso Montanari”), under the supervision of Prof. Fabrizio Cavani (Catalytic Processes Development Group). Three research projects in the field of heterogeneous acid catalysis focused on potential industrial applications were carried out. The main project, regarding the conversion of lignocellulosic materials to produce monosaccharides (important intermediates for production of biofuels and bioplatform molecules) was financed and carried out in collaboration with the Italian oil company eni S.p.A. (Istituto eni Donegani-Research Center for non-Conventional Energies, Novara, Italy) The second and third academic projects dealt with the development of green chemical processes for fine chemicals manufacturing. In particular, (a) the condensation reaction between acetone and ammonia to give triacetoneamine (TAA), and (b) the Friedel-Crafts acylation of phenol with benzoic acid were investigated

Zeolite catalysts for phenol benzoylation with benzoic acid: Exploring the synthesis of hydroxybenzophenones

In this paper, we report on the reaction of phenol benzoylation with benzoic acid, which was carried out in the absence of solvent. The aim of this reaction is the synthesis of hydroxybenzophenones, which are important intermediates for the chemical industry. H-beta zeolites offered superior performance compared to H-Y, with a remarkably high conversion of phenol and high yields to the desired compounds, when using a stoichiometric amount of benzoic acid. It was found that the reaction mechanism did not include the intramolecular Fries rearrangement of the primary product phenyl benzoate, but indeed, the bimolecular reaction between phenyl benzoate and phenol mainly contributed to the formation of hydroxybenzophenones. The product distribution was greatly affected by the presence of Lewis-type acid sites in H-beta; it was suggested that the interaction between the aromatic ring and the electrophilic Al3+ species led to the preferred formation of o-hydroxybenzophenone, because of the decreased charge density on the C atom at the para position of the phenolic ring. H-Y zeolites were efficient than H-beta in phenyl benzoate transformation into hydroxybenzophenones

Zeolite Catalysts for Phenol Benzoylation with Benzoic Acid: Exploring the Synthesis of Hydroxybenzophenones

In this paper, we report on the reaction of phenol benzoylation with benzoic acid, which was carried out in the absence of solvent. The aim of this reaction is the synthesis of hydroxybenzophenones, which are important intermediates for the chemical industry. H-beta zeolites offered superior performance compared to H-Y, with a remarkably high conversion of phenol and high yields to the desired compounds, when using a stoichiometric amount of benzoic acid. It was found that the reaction mechanism did not include the intramolecular Fries rearrangement of the primary product phenyl benzoate, but indeed, the bimolecular reaction between phenyl benzoate and phenol mainly contributed to the formation of hydroxybenzophenones. The product distribution was greatly affected by the presence of Lewis-type acid sites in H-beta; it was suggested that the interaction between the aromatic ring and the electrophilic Al3+ species led to the preferred formation of o-hydroxybenzophenone, because of the decreased charge density on the C atom at the para position of the phenolic ring. H-Y zeolites were efficient than H-beta in phenyl benzoate transformation into hydroxybenzophenones

Idrolisi acida diretta di biomasse lignocellulosiche e cellulosiche: confronto tra catalizzatori a base di Zr/P/O e Nb/P/O

La trasformazione di biomasse lignocellulosiche in sostanze chimiche utili è strategica nello sviluppo del concetto di bio-raffineria. Il punto di partenza di questa trasformazione è la destrutturazione della lignocellulosa, con conseguente depolimerizzazione delle frazioni cellulosiche ed emicellulosiche in monosaccaridi, o la successiva trasformazione di questi zuccheri in bio-molecole piattaforma. Le difficoltà principali in questo processo sono rappresentate dalla resistenza della guaina esterna di lignina e dall’elevato impaccamento delle catene cellulosiche. Per questo motivo, vi è un grande interesse nello sviluppo di sistemi catalitici acidi eterogenei efficaci nell’idrolisi di biomassa lignocellulosa. Nel nostro lavoro sono state confrontate le prestazioni catalitiche di diversi sistemi acidi eterogenei, zirconio e niobio fosfato, impiegati nell’idrolisi diretta di farina di conifera grezza e di cellulosa pretrattata. Dalle prove di reattività condotte sia sulla farina di conifera grezza che sulla cellulosa pretrattata in mulino a sfere, è possibile osservare che entrambi i sistemi catalitici presentano conversioni simili della matrice lignocellulosica. Il sistema niobio fosfato risulta però maggiormente attivo nella conversione della parte emicellulosica, mentre il sistema zirconio fosfato è attivo nella trasformazione sia della frazione cellulosica che emicellulosica. Diverse sono invece le prestazioni dei due sistemi in termini di prodotti ottenuti: mentre il sistema zirconio fosfato presenta rese molto più alte in monosaccaridi (specialmente in glucosio), il sistema niobio fosfato è maggiormente attivo nella formazione dei successivi prodotti di idratazione/condensazione (in particolare 5-idrossimetilfurfurale, furfurale e acido levulinico). Quando si utilizza l’irraggiamento microonde anziché quello tradizionale, si ottiene una significativa diminuzione del tempo di reazione, a parità di selettività; questo conferma perciò i benefici dell’irraggiamento microonde nell’idrolisi delle biomasse. Le diverse prestazioni catalitiche ottenute sono state correlate alle proprietà acide dei due sistemi a base di metallo-fosfato

Direct acid hydrolysis of lignocellulosic and cellulosic biomasses: Zr/P/O system vs. Nb/P/O system

The conversion of lignocellulosic biomass into valuable chemicals is a strategic issue within the framework of the biorefinery concept. The starting point of the transformation chain is the deconstruction of the lignocellulose and depolymerization of the hemicellulose and cellulose to give monosaccharides, or even transform sugars into other valuable bio-based building blocks. Difficulties derive from both the resistant lignin sheath and the tight packing of cellulose chains Tthe catalytic performances of different metallic phosphate systems (Zr/P/O and Nb/P/O) in the heterogeneous catalytic process of direct acid hydrolysis of untreated softwood dust and ball-milled microcrystalline cellulose were investigated. From the tests conducted on both lignocellulose and ball-milled microcrystalline cellulose, it is possible to observe that the two systems allow similar conversion of the lignocellulosic biomass: however, while the ZrPO system is active both in the conversion of cellulosic and hemicellulosic fractions, the NbPO system is active mainly in the conversion of latter fraction. When microwave irradiation was adopted instead of the traditional heating, a significant shortening of the reaction time was reached with similar selectivity results, thus confirming the beneficial role of MW irradiation on biomass hydrothermal conversion. The differences of catalytic performances between the two metal phosphate catalysts can be explained by invoking both the different total concentration and type of acid sites