Executive Summary : | This project aims to develop a sustainable catalytic process for bio-acrylic acid synthesis via aldol condensation of biomass-derived feedstock (acetic acid and formaldehyde) using novel Sn-beta zeolites. Acrylic acid (AA) is a vital chemical for the Indian polymer industry, with about 260 kiloton demand per annum. But, more than 90% of AA is being imported because of the lack of sustainable production routes in India. In industry, AA is produced by energy-intensive gas-phase oxidation of propylene (crude oil derivative). Long-term sustainability and raw material sourcing strategies forced the researchers to develop biomass-based routes to produce AA. The biomass-derived chemicals used for AA synthesis are glycerol, lactic acid, and 3-hydroxypropionic acid. But, using acetic acid and formaldehyde for AA synthesis is somewhat overlooked. Both reagents can be available from biomass. The shift to acetic acid is due to its efficient production via sugar fermentation. The aldol condensation of acetic acid with formaldehyde can be catalyzed by acid sites (mainly Lewis acid sites). Zeolites are widely used heterogeneous catalysts because of their shape-selectivity, tunable Brønsted/Lewis acidity, and high BET surface area. So, using zeolites for AA synthesis is a promising option. For bimolecular reactions, like acetic acid condensation with formaldehyde, zeolites require sufficient place to enhance reagents' adsorption and product selectivity. For this, this project introduces a novel site space adjusting concept in Lewis acidic Sn4+-beta zeolites. The idea is to take advantage of the redox property of Sn4+/Sn2+, creating more spatially ‘open’ sites that can enhance the reagents’ adsorption and reaction mechanism, thus expecting a higher formation rate of AA. The challenge is to create such openness at the active site without destroying (the stability of) the catalytic activity. For this, Sn loading (0.1-5 wt%) and reduction temperature (500-900 °C in H2 flow) will be optimized. The acetic acid condensation with formaldehyde likely proceeds via basic-site promoted proton-abstraction on the carbon, next to the carboxylic acid. The Brønsted acid sites can induce coke formation and catalyst deactivation by promoting polymerization and side reactions. So, reducing the Brønsted acidity in zeolites is one of the main goals of this project. For this, an ion-exchange method with alkali metal ions (Na+, K+, and Cs+) will be done to remove the protons in zeolites, thus decreased Brønsted acidity with improved basicity will be achieved. To understand/optimize the zeolites’ properties, a thorough study of the acid-base-redox chemistry and Sn-site environment will be done using various analytical techniques. Systematic screening of the zeolites for the gas-phase condensation of acetic acid with formaldehyde in a fixed bed reactor will be done, followed by catalyst’s durability and kinetic/mechanistic studies to achieve improved conversions and high AA selectivity. |