Glycerol transformation to value added C₃ diols: reaction mechanism, kinetic, and engineering aspects

Abstract

Glycerol can serve as a starting material for the production of a variety of chemicals currently formed via fossil-based routes. The selective hydro-deoxygenation to C 3 -diols is one of the most attractive methods for glycerol upgrading. 1,2-and 1,3-Propanediols which are the target products of this reaction are high added value chemicals with a wide range of applications. The reaction mechanisms for both routes (1,2-and 1,3-diols) are presented and analyzed including the strategies followed for mechanistic understanding. 1,2-Propanediol is proposed to be formed via two mechanisms namely dehydration-hydrogenation and dehydrogenation-dehydration-hydrogenation. The selective conversion of glycerol to 1,3-propanediol is suggested to proceed through dehydration-hydrogenation and direct hydrogenolysis mechanisms. The reaction mechanism depends on various factors such as the catalyst formulation, acid and basic character of the system and the H 2 origin. A section focusing on engineering issues describes and compares the reaction mode ie batch-continuous and liquid-gas phase operation. The different reaction configurations have an impact mainly on product distribution and catalyst stability, which is greatly improved when continuous operation is applied. In addition, the impact of reaction temperature, hydrogen pressure, glycerol concentration as well as the reaction kinetics are also discussed. The approach of operating under inert conditions with H 2 generated in situ seems to be a very promising concept for process intensification.

Selective Hydrogenolysis of Glycerol and Crude Glycerol (a By-Product or Waste Stream from the Biodiesel Industry) to 1,2-Propanediol over B2O3 Promoted Cu/Al2O3 Catalysts

“…The reaction mechanisms of glycerol hydrogenolysis to 1,2-propanediol has been reported in the literature [49,50]. Based on the products formed in the present study it is believed that the reaction involves a dehydration and hydrogenation mechanism in which dehydration of glycerol forms acetol which undergoes hydrogenation in the next step to form 1,2-propanediol.…”

Hydrodeoxygenation of glycerol with in situH2 formation over Pt catalysts supported on Fe modified Al2O3: effect of Fe loading

“…The substitution of fossil fuels and chemicals by those derived from biomass is under growing interest. Biomass is the only renewable and sustainable organic carbon source . As one of the twelve building block chemicals, glycerol valorization has received great attention.…”

“…The most successful catalytic processes for glycerol conversion include reforming, dehydration to hydroxyacetone and acrolein, oxidation to dihydroxyacetone, etherification and hydrogenolysis/hydrodeoxygenation to propanediols . The most attractive method to remove oxygen from glycerol, a molecule with high O/C ratio, is by the addition of hydrogen (hydrodeoxygenation); this method can produce 1,2‐propanediol if one terminal oxygen atom is removed. 1,2‐propanediol is a value added chemical with a wide range of applications, as it is used as the raw material for the production of unsaturated polyester resins, antifreeze fluids, foods, drugs, liquid detergents etc .…”

Towards selective electrochemical conversion of glycerol to 1,3-propanediol

“…Examples of derivable high value C 3 chemicals from glycerol include: propylene glycols, hydroxyacids, and diacid. [14][15][16] Among the possible glycerol derivable C 3 chemicals, 1,3-propanediol (1,3-PD) is of special interest because it is a bulk chemical that has wide applications in polymers, lubricants, cosmetics, foods and in the synthesis of heterocyclic compounds. 17 The traditional routes of commercial synthesis of 1,3-PD use acrolein (DuPont) and ethylene oxide (Shell) as starting feedstock.…”