Recent advances in reaction routes and catalysts for chemical synthesis of1,3-propanediol

1,3-Propanediol (1,3-PDO) is an important chemical raw material with broad commercial applications in the industrial sector including the polymers, pharmaceuticals, daily chemicals, and food industries. Owing to its fast-growing demand as a monomer in the production of biodegradable polyesters such as polytrimethylene terephthalate (PTT), synthesis of 1,3-PDO through more efficient and greener routes has attracted considerable attention in recent years. However, the production of 1,3-PDO still faces the challenge of high costs. Compared to the biological method which can be operated under mild conditions, the chemical synthesis routes are still popularly applied all over the world. The key to achieving low-cost and large-scale production of 1,3-PDO via chemical synthesis methods lies in the development of efficient and environmental-friendly catalytic processes and catalysts. In this review, we provide a comprehensive overview of the chemical synthesis routes for 1,3-PDO production, including hydration-hydrogenation of acrolein, carbonylation of ethylene oxide, hydroesterification of ethylene oxide, hydrogenolysis of glycerol, condensation of formaldehyde and acetaldehyde, as well as hydrogenation of dialkyl malonate. Specifically, the reaction conditions for the hydration-hydrogenation of acrolein are generally mild. However, this route poses a high safety risk due to the nature of its raw materials, and low hydration efficiency which always cause a high energy consumption for the whole process. For carbonylation of ethylene oxide, in addition to the use of toxic ligands, the formation of unstable 3-hydroxypropanal intermediates and their subsequent side reactions significantly impact the yield of 1,3-PDO. By contrast, hydroesterification of ethylene oxide does not generate 3-hydroxypropanal. However, more efforts should be devoted to the improvement in terms of catalyst recycling in homogeneous systems or selectivity in Cu-based heterogeneous catalysts during the hydrogenation of methyl 3-hydroxypropionate. Hydrogenolysis of biomass-derived glycerol is one of the promising green routes for the future production of 1,3-PDO. Reducing the cost of Pt-based catalysts by increasing the utilization of noble metal atoms while maintaining their performance determines the feasibility of this route. Condensation of formaldehyde and acetaldehyde is less studied at present, necessitating the development of efficient catalysts under mild conditions to enhance their competitiveness. Dialkyl malonate can be produced from malic acid, a bio-based platform compound, making the hydrogenation of dialkyl malonate a potential green synthetic route for 1,3-PDO. The currently employed Cu-based catalysts are typically accompanied by using elevated temperatures and high hydrogen pressures, thereby resulting in the occurrence of side reactions such as decarboxylation and hydrolysis, which impose limitations on their industrial applications. The development of catalysts with high catalytic activity and products selectivity under mild conditions is of great significance for the hydrogenation of dialkyl malonate to 1,3-PDO. Among above-mentioned chemical synthesis routes, the use of bio-based feedstocks for the production of 1,3-PDO aligns with the imperative of sustainable development and deserves further investigation that combines the synthesis of new or better catalysts and the design of more efficient process. In summary, in this review article, the factors affecting the activity and selectivity of the catalysts in different chemical synthesis routes along with their underlying causes are discussed in detail, which are projected to provide new insights in developing improved catalytic systems for the production of 1,3-PDO.